A sodium ferric pyrophosphate phosphate positive electrode composite material and a preparation method thereof

Abstract

The application discloses a sodium iron phosphate pyrophosphate positive electrode composite material and a preparation method thereof, and relates to the technical field of sodium ion battery electrode material preparation. The initial discharge specific capacity of the prepared sodium iron phosphate pyrophosphate positive electrode composite material reaches 98 mAh.g ‑1 The capacity retention rate after 100 cycles is higher than 92%, and the sodium iron phosphate pyrophosphate positive electrode composite material has small charge transfer impedance and excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery electrode material preparation technology, specifically to a sodium iron pyrophosphate cathode composite material and its preparation method. Background Technology

[0002] With the development of large-scale energy storage and low-cost electrochemical energy storage technologies, sodium iron pyrophosphate cathode composites have become an important research direction for sodium-ion batteries due to their combination of structural stability, good ion diffusion capabilities, and safety. Sodium-ion batteries have attracted widespread attention due to the abundance of sodium resources, low cost, and high safety, while polyanionic cathode materials are more suitable for large-capacity energy storage applications due to their high thermal stability and long cycle life. Among them, sodium iron phosphate has a stable olivine structure, which can ensure the long-term structural integrity of the cathode material, while sodium iron pyrophosphate has open three-dimensional ion diffusion channels, which is beneficial to improving the migration rate of sodium ions and the rate performance of the material. By combining the two, the synergistic optimization of structural stability and ion dynamics can be achieved, thereby constructing a high-performance multiphase polyanionic cathode system. However, single phosphate or pyrophosphate cathode materials still have problems such as low electronic conductivity, limited sodium ion diffusion dynamics, insufficient particle interface stability, and insufficient structural synergy. To address these issues, existing technologies primarily employ methods such as carbon coating, elemental doping, particle size reduction, and conductive agent compositing to improve conductivity and ion transport capabilities. However, these methods still have shortcomings: firstly, traditional carbon coatings are mostly physical coatings with limited interfacial bonding, making them prone to localized detachment during cycling; secondly, conventional conductive additives only provide electronic conduction pathways, failing to simultaneously address interfacial stability, structural buffering, and ion transport regulation; furthermore, single-phase sodium iron phosphate or sodium iron pyrophosphate materials lack synergy in structural and interfacial regulation, making it difficult to achieve a balance between high-rate and long-cycle performance. Therefore, combining the structural stability of sodium iron phosphate with the excellent ion diffusion characteristics of sodium iron pyrophosphate to construct a multiphase synergistic polyanion cathode system has become an important direction for improving overall electrochemical performance.

[0003] Chinese invention patent CN118572106A discloses a cathode composite material with a double coating layer, its preparation method, and its application. The double-coated cathode composite material includes a sodium iron manganese pyrophosphate / carbon composite core, and an inorganic coating layer and an organic coating layer sequentially disposed on the surface of the sodium iron manganese pyrophosphate / carbon composite core from the inside out. The inorganic coating layer is made of sodium iron manganese pyrophosphate, and the organic coating layer is made of a conductive polymer. This invention, through the design of the organic / inorganic double coating layer, not only enhances the ionic and electronic conductivity of the cathode material but also inhibits the dissolution of manganese ions from the sodium iron manganese pyrophosphate, thereby effectively improving the cycle and rate performance of the cathode material. However, its charge transfer impedance performance is still insufficient.

[0004] Therefore, developing a sodium iron pyrophosphate cathode composite material with stable structure, low interfacial charge transfer impedance, and synergistic electron / ion conduction is of great significance for improving the overall electrochemical performance of sodium-ion batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a sodium iron pyrophosphate cathode composite material and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a sodium iron pyrophosphate cathode composite material includes the following steps: (1) Mix phosphoric acid solution and high-purity iron powder, heat and react to produce Fe. 2+ Phosphoric acid complex solution; cooling, adding hydrogen peroxide solution to react, yielding Fe. 3+ Phosphoric acid complex solution; (2) Mix anhydrous ethanol, deionized water, and functional additives thoroughly to obtain a functional additive solution; add Fe... 3+ Phosphoric acid complex solution, Na2CO3, glucose, and functional additive solution are stirred and mixed to obtain a slurry, which is then ground and spray-dried to obtain a powder. (3) The powder is placed in a sintering furnace for segmented heating and sintering, and then cooled to obtain the final product; The chemical structural formula of the functional additive is as follows: .

[0007] The functional additive is prepared by the following method: S1: 3,4-Dibromo-1H-pyrrole-2,5-dione reacts with (2-mercaptoethyl)phosphonic acid to form an intermediate; the reaction equation is shown below:

[0008] S2: The intermediate reacts with 2,7-bis(bromomethyl)pyrene to generate a functional additive. The reaction equation is shown below:

[0009] In step S1, the molar ratio of 3,4-dibromo-1H-pyrrole-2,5-dione to (2-mercaptoethyl)phosphonic acid is 1:(2.01-2.03).

[0010] In step S2, the molar ratio of the intermediate to 2,7-bis(bromomethyl)pyrene is (2.03-2.05):1.

[0011] The reaction solvent in step S1 is anhydrous ethanol, and the reaction solvent in step S2 is acetone.

[0012] In step (1), the concentration of the phosphoric acid solution is 25wt%-35wt%.

[0013] In step (1), the volume fraction of the phosphoric acid solution is 10-15 parts, the weight fraction of the high-purity iron powder is 2-3 parts, and the volume fraction of the hydrogen peroxide solution is 5-10 parts.

[0014] In step (2), the mass ratio of the functional additive, Na2CO3, and glucose is (0.16-0.56):(10-17):(1-5).

[0015] In step (2), the inlet air temperature of the spray dryer is 180-220℃ and the outlet air temperature is 90-110℃.

[0016] A sodium iron pyrophosphate cathode composite material is prepared by the above method.

[0017] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include: The sodium iron pyrophosphate cathode composite material prepared by this invention achieves an initial discharge specific capacity of 98 mAh·g at a 5C rate. -1 The above results show that the capacity retention rate is over 92% after 100 cycles, and it has a small charge transfer impedance, demonstrating excellent electrochemical performance. Attached Figure Description

[0018] Figure 1 The hydrogen nuclear magnetic resonance spectrum of the functional additive prepared in Example 1.

[0019] Figure 2 The high-resolution mass spectrum of the functional additive prepared in Example 1. Detailed Implementation

[0020] The following description, in conjunction with specific embodiments, provides further details, but the present invention is not limited to these embodiments.

[0021] Example 1: Preparation of Functional Additives S1: Under nitrogen protection, 300 ml of anhydrous ethanol, 0.1 mol of 3,4-dibromo-1H-pyrrole-2,5-dione, and 0.201 mol of (2-mercaptoethyl)phosphonic acid were stirred and mixed. 0.21 mol of triethylamine was added, and the mixture was heated to 45 °C and reacted for 12 h. After filtration, the mixture was distilled under reduced pressure at 50 °C for 1 h. The crude product was purified by silica gel column chromatography (V... 二氯甲烷 :V 甲醇 The ratio of the distillation solution to that of the intermediate was 10:1. The intermediate was obtained by vacuum distillation at 30°C for 1 hour. Its 1H NMR data are as follows: 1 H NMR (400 MHz, DMSO- d6 ) δ 11.45 (s, 1H), 8.82 (s, 4H), 3.17-3.08 (m, 4H), 2.34-2.20 (m, 4H); HRMS (m / z): 377.9562[M+H] + ; S2: Under nitrogen protection, 600 ml of acetone, 0.1 mol of 2,7-bis(bromomethyl)pyrene, and 0.203 mol of the intermediate were stirred and mixed. 0.21 mol of potassium carbonate was added, and the mixture was heated to reflux and reacted for 10 h. The mixture was then filtered, and the solution was distilled under reduced pressure at 35 °C for 1 h. The crude product was purified by silica gel column chromatography (V... 二氯甲烷 :V 甲醇 =10:1→5:1), distilled under reduced pressure at 30℃ for 1 h to obtain the functional additive; its proton NMR spectrum is as follows. Figure 1 As shown, the proton NMR data are as follows: 1 H NMR (400 MHz, DMSO- d 6 δ 8.82 (s, 8H), 7.92 (d, J = 6.6 Hz, 2H), 7.70–7.63 (m, 6H), 4.98–4.85 (m, 4H), 3.20–3.09 (m, 8H), 2.32–2.21 (m, 8H); its high-resolution mass spectrum is shown below. Figure 2 The mass spectrometry data are as follows: HRMS (m / z): 980.9903 [M+H] + .

[0022] Example 2 Preparation of functional additives S1: Under nitrogen protection, 300 ml of anhydrous ethanol, 0.1 mol of 3,4-dibromo-1H-pyrrole-2,5-dione, and 0.202 mol of (2-mercaptoethyl)phosphonic acid were stirred and mixed. 0.21 mol of triethylamine was added, and the mixture was heated to 50 °C and reacted for 11 h. The mixture was then filtered, and the solution was distilled under reduced pressure at 50 °C for 1 h. The crude product was purified by silica gel column chromatography (V... 二氯甲烷 :V 甲醇 =10:1), distilled under reduced pressure at 30℃ for 1 h to obtain the intermediate; S2: Under nitrogen protection, 600 ml of acetone, 0.1 mol of 2,7-bis(bromomethyl)pyrene, and 0.204 mol of the intermediate were stirred and mixed. 0.21 mol of potassium carbonate was added, and the mixture was heated to reflux and reacted for 10.5 h. The mixture was then filtered, and distilled under reduced pressure at 35 °C for 1 h. The crude product was purified by silica gel column chromatography (V... 二氯甲烷 :V 甲醇 =10:1→5:1), and the functional additive was obtained by vacuum distillation at 30℃ for 1 hour.

[0023] Example 3 Preparation of functional additives S1: Under nitrogen protection, 300 ml of anhydrous ethanol, 0.1 mol of 3,4-dibromo-1H-pyrrole-2,5-dione, and 0.203 mol of (2-mercaptoethyl)phosphonic acid were stirred and mixed. 0.21 mol of triethylamine was added, and the mixture was heated to 55 °C and reacted for 10 h. The mixture was then filtered, and distilled under reduced pressure at 50 °C for 1 h. The crude product was purified by silica gel column chromatography (V... 二氯甲烷 :V 甲醇 =10:1), distilled under reduced pressure at 30℃ for 1 h to obtain the intermediate; S2: Under nitrogen protection, 600 ml of acetone, 0.1 mol of 2,7-bis(bromomethyl)pyrene, and 0.205 mol of the intermediate were stirred and mixed. 0.21 mol of potassium carbonate was added, and the mixture was heated to reflux and reacted for 11 h. The mixture was then filtered, and the solution was distilled under reduced pressure at 35 °C for 1 h. The crude product was purified by silica gel column chromatography (V... 二氯甲烷 :V 甲醇 =10:1→5:1), and the functional additive was obtained by vacuum distillation at 30℃ for 1 hour.

[0024] Example 4: Preparation of sodium iron pyrophosphate cathode composite material (1) Add 100 ml of 25 wt% phosphoric acid solution and 20 g of high-purity iron powder (purity 99.99%) to a reaction flask, heat to 60 °C and stir for 4 h to generate Fe. 2+ Phosphoric acid complex solution; cool to 30℃, slowly add 50 ml of 30 wt% hydrogen peroxide solution dropwise, completing the addition over 40 min, and react for 1 h to obtain Fe. 3+ Phosphoric acid complex solution; (2) Mix 6 ml of anhydrous ethanol, 6 ml of deionized water, and 0.8 g of functional additive (prepared in Example 1), and stir at 200 rpm for 10 min to obtain a functional additive solution; add the Fe obtained in step (1) to the mixing tank in sequence. 3+ A slurry was prepared by mixing a phosphate complex solution, 50g Na2CO3, 5g glucose, and a functional additive solution at 300rpm for 1 hour. The slurry was then fed into a sand mill and ground at 2000rpm for 2 hours, resulting in a particle size D50 of 0.3μm. Finally, the slurry was fed into a spray dryer for spray drying (atomization pressure of 0.5MPa, feed rate of 10ml / min, inlet air temperature of 180℃, and outlet air temperature of 90℃) to obtain the dried powder. (3) The powder obtained in step (2) is placed in a sintering furnace under nitrogen atmosphere protection, heated to 350°C at a rate of 0.5°C / min, held for 2 hours, heated to 550°C at a rate of 2°C / min, held for 8 hours, and cooled to room temperature with the furnace to obtain sodium iron pyrophosphate cathode composite material.

[0025] Example 5: Preparation of sodium iron pyrophosphate cathode composite material (1) Add 125 ml of 30 wt% phosphoric acid solution and 25 g of high-purity iron powder (purity 99.99%) to a reaction flask, heat to 70 °C and stir for 3 h to generate Fe. 2+ Phosphoric acid complex solution; cool to 30℃, slowly add 75 ml of 30 wt% hydrogen peroxide solution dropwise, completing the addition over 50 min, and react for 1 h to obtain Fe. 3+ Phosphoric acid complex solution; (2) Mix 15 ml of anhydrous ethanol, 15 ml of deionized water, and 1.8 g of functional additive (prepared in Example 2), and stir at 200 rpm for 10 min to obtain a functional additive solution; add the Fe obtained in step (1) to the mixing tank in sequence. 3+ A slurry was prepared by stirring a phosphate complex solution, 65g Na2CO3, 15g glucose, and a functional additive solution at 300rpm for 1 hour. The slurry was then fed into a sand mill and ground at 2000rpm for 2 hours, resulting in a particle size D50 of 0.3μm. Finally, the slurry was fed into a spray dryer for spray drying (atomization pressure of 0.8MPa, feed rate of 15ml / min, inlet air temperature of 200℃, and outlet air temperature of 100℃) to obtain the dried powder. (3) The powder obtained in step (2) is placed in a sintering furnace under nitrogen atmosphere protection, heated to 350°C at a rate of 0.5°C / min, held for 2 hours, heated to 550°C at a rate of 2°C / min, held for 8 hours, and cooled to room temperature with the furnace to obtain sodium iron pyrophosphate cathode composite material.

[0026] Example 6 Preparation of sodium iron pyrophosphate cathode composite material (1) Add 150 ml of 35 wt% phosphoric acid solution and 30 g of high-purity iron powder (purity 99.99%) to a reaction flask, heat to 80 °C and stir for 2 h to generate Fe. 2+ Phosphoric acid complex solution; cool to 30℃, slowly add 100 ml of 30 wt% hydrogen peroxide solution dropwise, completing the addition in 60 min, react for 1 h to obtain Fe. 3+ Phosphoric acid complex solution; (2) Mix 20 ml of anhydrous ethanol, 20 ml of deionized water, and 2.8 g of functional additive (prepared in Example 3), and stir at 200 rpm for 10 min to obtain a functional additive solution; add the Fe obtained in step (1) to the mixing tank in sequence. 3+A slurry was prepared by stirring a phosphate complex solution, 85g Na2CO3, 25g glucose, and a functional additive solution at 300rpm for 1h. The slurry was then fed into a sand mill and ground at 2000rpm for 2h, resulting in a particle size D50 of 0.3μm. Finally, the slurry was fed into a spray dryer for spray drying (atomization pressure of 1MPa, feed rate of 20ml / min, inlet air temperature of 220℃, and outlet air temperature of 110℃) to obtain the dried powder. (3) The powder obtained in step (2) is placed in a sintering furnace under nitrogen atmosphere protection, heated to 350°C at a rate of 0.5°C / min, held for 2 hours, heated to 550°C at a rate of 2°C / min, held for 8 hours, and cooled to room temperature with the furnace to obtain sodium iron pyrophosphate cathode composite material.

[0027] Comparative Example 1 The preparation method of the sodium iron pyrophosphate cathode composite material is basically the same as that in Example 5, except that the functional additive is replaced with an equal weight of the functional additive prepared by the following method: The preparation method of the functional additive is basically the same as that in Example 2, except that the 3,4-dibromo-1H-pyrrole-2,5-dione in step S1 is replaced with 0.2 mol of 3-bromo-1H-pyrrole-2,5-dione.

[0028] Comparative Example 2 The preparation method of the sodium iron pyrophosphate cathode composite material is basically the same as that in Example 5, except that the functional additive is replaced with an equal weight of the functional additive prepared by the following method: The preparation method of the functional additive is basically the same as that in Example 2, except that the (2-mercaptoethyl)phosphonic acid in step S1 is replaced with an equimolar amount of diethyl(2-mercaptoethyl)phosphonate (CAS No. 51851-63-9).

[0029] Comparative Example 3 The preparation method of the sodium iron pyrophosphate cathode composite material is basically the same as that in Example 5, except that the functional additive is replaced with an equal weight of the functional additive prepared by the following method: The preparation method of the functional additive is basically the same as that in Example 2, except that 2,7-bis(bromomethyl)pyrene in step S2 is replaced with an equimolar amount of 2,7-bis(bromomethyl)-4,5,9,10-tetrahydro-pyrene.

[0030] Comparative Example 4 The preparation method of the sodium iron pyrophosphate cathode composite material is basically the same as that in Example 5, except that the functional additive is replaced with an equal weight of the functional additive prepared by the following method: The preparation method of the functional additive is basically the same as that in Example 2, except that 2,7-bis(bromomethyl)pyrene in step S2 is replaced with an equimolar amount of 2,6-bis(bromomethyl)anthracene.

[0031] Comparative Example 5 The preparation method of the sodium iron pyrophosphate cathode composite material is basically the same as that in Example 5, except that the functional additive is replaced with an equal weight of the functional additive prepared by the following method: The preparation method of the functional additive is basically the same as that in Example 2, except that the amount of intermediate in step S2 is replaced with 0.102 mol and the amount of potassium carbonate is replaced with 0.105 mol.

[0032] Comparative Example 6 The preparation method of the sodium iron pyrophosphate cathode composite material is basically the same as that in Example 5, except that the functional additive is replaced with a mixture of 1.2g intermediate (prepared in step S1 of Example 2) and 0.6g 2,7-bis(bromomethyl)pyrene.

[0033] The high-purity iron powder used in the embodiments and comparative examples of this application has a particle size distribution of 5-20 μm; the CAS number of (2-mercaptoethyl)phosphonic acid is 43064-23-9. The volume parts and weight parts mentioned in this application are converted to equivalent values ​​when feeding materials, for example, 1 mL corresponds to 1 g, and 1 L corresponds to 1 kg.

[0034] Positive electrode preparation: The composite materials prepared in Examples 4-6 and Comparative Examples 1-6, Super P conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1. 100 ml of N-methylpyrrolidone solution was added, and the mixture was stirred at 300 rpm for 10 min to obtain a mixed slurry. The mixed slurry was uniformly coated on the surface of aluminum foil (12 mm in diameter and 15 μm in thickness) using an automatic coating machine. The coating thickness was 100 μm. The foil was placed in a vacuum drying oven and dried at 80 °C for 2 h at 0.1 MPa. Then, the temperature was raised to 110 °C and held for 10 h to obtain the positive electrode.

[0035] Battery Assembly: Using the prepared positive electrode sheet as the positive electrode of the sodium-ion battery, a metallic sodium sheet as the negative electrode, a 1 mol / L NaClO4 solution as the electrolyte, and Whatman glass fiber (GF / D) as the separator, coin cells were assembled in a glove box under a high-purity argon atmosphere. After the assembled batteries were allowed to stand for 10 hours, their electrochemical performance was tested. The test results are shown in Table 1.

[0036] Charge / discharge performance testing: The battery was subjected to constant current charge / discharge and cycle performance testing using a Shenzhen Xinwei BTS4000 instrument (CT-4008T-5V10mA-164). The current rate was 5C, the voltage range was 2-4V, and the temperature was kept constant at 25℃ during the test. The initial discharge specific capacity and the discharge specific capacity after 100 cycles were recorded, and the capacity retention rate was calculated: Capacity retention rate = Discharge specific capacity after 100 cycles at 5C / Initial discharge specific capacity at 5C.

[0037] Electrochemical impedance spectroscopy (EIS) test: The battery was tested using a Wuhan KOST CS300M electrochemical workstation. The frequency was set to 100kHz-10mHz and the amplitude was adjusted to 5mV. The test results were fitted using Zview software.

[0038]

[0039] As shown in Table 1, the sodium iron pyrophosphate cathode composite materials prepared in Examples 4-6 of this application have an initial discharge specific capacity of 98 mAh·g at a 5C rate. -1 The above results show that the capacity retention rate is over 92% after 100 cycles, and it has a small charge transfer impedance, demonstrating excellent electrochemical performance.

[0040] In the preparation of sodium iron pyrophosphate cathode composite materials in Examples 4-6 of this application, the functional additives used pyrene rings as π-conjugated electron cores, along with maleimide structures, thioether bonds, and phosphonic acid groups, constitute a multi-component synergistic system with interface anchoring and electron / ion synergistic conduction. During material preparation, the phosphonic acid groups can form stable Fe-OP coordination bonds with the Fe-O active sites on the surface of sodium iron pyrophosphate particles, allowing the molecule to be firmly adsorbed and directionally distributed at the particle interface. The pyrene ring has a large-size, planar π-conjugated structure, which maintains a high degree of conjugation orientation and undergoes stable π-π stacking during sintering on the particle surface and in the contact area between adjacent particles, forming a π-π stacked structure. This π-π stacked structure is further transformed into a locally ordered conjugated carbon structure during the sintering-induced carbonization and rearrangement process, forming a continuous... The surface-contact conductive channels create an electron delocalization transport network between particles, effectively shortening the electron transport path across particles and reducing the contact resistance between particles. During sintering, the maleimide structure undergoes thermal decomposition and rearrangement reactions, and its nitrogen-containing functional structure participates in the carbonization and conjugated network construction of the interfacial carbon layer, allowing some nitrogen to be doped into the carbon framework, thereby improving the graphitization degree and conductivity of the interfacial carbon layer. The introduction of sulfur doping through thioether bonds after sintering and carbonization helps to regulate the distribution of the interfacial electron cloud and increase the polarity of the carbon layer, thus improving electrolyte wettability and reducing Na+. +Desolvation of the energy barrier. Through the synergistic effect of "anchoring-conductivity-doping-interfacial polarity regulation", the structural units in the functional additive molecules form a continuous, stable, and heteroatom-rich conductive interface layer on the particle surface, effectively reducing the interfacial charge transfer impedance and enhancing the electron / ion co-transmission capability, thereby significantly improving the electrochemical performance of sodium iron pyrophosphate cathode composite material.

[0041] The functional additive used in Comparative Example 4 has a smaller π-conjugated planar structure than the example, which weakens the electron delocalization transport capability and fails to effectively reduce the contact resistance between particles. This results in the electrochemical performance of the prepared sodium iron pyrophosphate cathode composite material being worse than that of the example. The functional additive used in Comparative Example 5 contains only one molecule of maleimide structure, two molecules of thioether bond, and phosphonic acid group. On the one hand, its ability to improve the graphitization degree and conductivity of the interfacial carbon layer during sintering is weakened. On the other hand, the reduced sulfur doping weakens the ability to regulate the interfacial electron cloud distribution, leading to a decrease in the overall electrochemical performance of the prepared sodium iron pyrophosphate cathode composite material.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a sodium iron pyrophosphate cathode composite material, characterized in that, Includes the following steps: (1) Mix phosphoric acid solution and high-purity iron powder, heat and react to produce Fe. 2+ Phosphoric acid complex solution; cooling, adding hydrogen peroxide solution to react, yielding Fe. 3+ Phosphoric acid complex solution; (2) Mix anhydrous ethanol, deionized water, and functional additives thoroughly to obtain a functional additive solution; add Fe... 3+ Phosphoric acid complex solution, Na2CO3, glucose, and functional additive solution are stirred and mixed to obtain a slurry, which is then ground and spray-dried to obtain a powder. (3) The powder is placed in a sintering furnace for segmented heating and sintering, and then cooled to obtain the final product; The chemical structural formula of the functional additive is as follows: .

2. The method for preparing a sodium iron pyrophosphate cathode composite material according to claim 1, characterized in that, The functional additive is prepared by the following method: S1: 3,4-Dibromo-1H-pyrrole-2,5-dione reacts with (2-mercaptoethyl)phosphonic acid to form an intermediate; S2: The intermediate reacts with 2,7-bis(bromomethyl)pyrene to generate a functional additive.

3. The method for preparing a sodium iron pyrophosphate cathode composite material according to claim 2, characterized in that, In step S1, the molar ratio of 3,4-dibromo-1H-pyrrole-2,5-dione to (2-mercaptoethyl)phosphonic acid is 1:(2.01-2.03).

4. The method for preparing a sodium iron pyrophosphate cathode composite material according to claim 2, characterized in that, In step S2, the molar ratio of the intermediate to 2,7-bis(bromomethyl)pyrene is (2.03-2.05):

1.

5. The method for preparing a sodium iron pyrophosphate cathode composite material according to claim 2, characterized in that, The reaction solvent in step S1 is anhydrous ethanol, and the reaction solvent in step S2 is acetone.

6. The method for preparing a sodium iron pyrophosphate cathode composite material according to claim 1, characterized in that, In step (1), the concentration of the phosphoric acid solution is 25wt%-35wt%.

7. The method for preparing a sodium iron pyrophosphate cathode composite material according to claim 1, characterized in that, In step (1), the volume fraction of the phosphoric acid solution is 10-15 parts, the weight fraction of the high-purity iron powder is 2-3 parts, and the volume fraction of the hydrogen peroxide solution is 5-10 parts.

8. The method for preparing a sodium iron pyrophosphate cathode composite material according to claim 1, characterized in that, In step (2), the mass ratio of the functional additive, Na2CO3, and glucose is (0.16-0.56):(10-17):(1-5).

9. The method for preparing a sodium iron pyrophosphate cathode composite material according to claim 1, characterized in that, In step (2), the inlet air temperature of the spray dryer is 180-220℃ and the outlet air temperature is 90-110℃.

10. A sodium iron pyrophosphate cathode composite material, characterized in that, It is prepared by the method described in any one of claims 1-9.

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