Preparation method of high-compaction-density ferric sodium pyrophosphate positive electrode material

Abstract

The invention relates to the technical field of battery materials, and discloses a preparation method of a high-compaction-density ferric sodium phosphate pyrophosphate positive electrode material, and the core of the method is that a specifically synthesized modified gemini quaternary ammonium salt grinding aid is adopted and a two-stage gradient sanding process is combined. The grinding aid has a double-layer hydrophobic structure (short-chain fluoroaryl and long-chain alkyl) and a disulfonic acid / biquaternary ammonium salt gemini structure, can be strongly adsorbed on the surfaces of negatively charged iron phosphate particles through electrostatic interaction, provides an excellent dispersion effect and forms a compact coating layer on the surfaces of the particles. Part of iron phosphate, the grinding aid and water are subjected to superfine grinding, then the remaining iron phosphate is added for common sand grinding, and a finished product with the compaction density reaching up to 2.10-2.20 g / cm < 2 > is obtained after mixing of a sodium source and a phosphorus source, spray drying, sintering and air jet pulverization. The method effectively solves the problems of low compaction density and poor grinding efficiency of sodium ferric phosphate pyrophosphate, realizes in-situ heteroatom doping, and is suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery materials, in particular to a preparation method of a high-compactness-density sodium iron phosphate pyrophosphate positive electrode material. BACKGROUND

[0002] As a sodium-ion battery positive electrode material, sodium iron phosphate pyrophosphate (NFPP) is highly concerned due to its abundant raw materials, high safety and environmental friendliness. However, its industrial application faces severe challenges. First, the existing process for preparing the NFPP material generally has the problem of low compactness density (usually less than 2.0 g / cm3), which leads to insufficient battery volume energy density, and the root cause lies in the single particle size distribution of the material, which forms a large number of voids when stacked. Second, although the traditional sand milling technology attempts to refine the precursor iron phosphate particles, due to the high hardness and great toughness of the material, it is still difficult to stably obtain submicron fine powder (D 50 <0.3 mu m) in a single sand milling process lasting more than 10 hours, which is high in energy consumption and difficult to accurately control the particle size distribution. Third, in order to optimize the particle size distribution, some technologies use a two-burning process, but this process needs to rely on an additional secondary treatment step, which increases the production cost and may introduce impurities. In addition, the intrinsic electronic conductivity of NFPP is low, and the improvement effect of the conventional carbon coating method is limited, and there is a lack of effective grinding aids that are highly matched with the surface properties of the material during the grinding process, which restricts the full play of the electrochemical performance of the material.

[0003] Under the driving of the multiple demands of high compactness density, high gram capacity, high initial efficiency and low cost preparation in the energy storage and low-cost electric vehicle markets, developing an innovative process that can solve the problems of particle size control, sand milling efficiency, interface conductivity and cost control has become a key breakthrough for promoting the large-scale commercial application of NFPP. The grinding aids used in the prior art mainly emphasize their acidity and dispersibility, but the structure is ordinary, the function is single, the interaction with the surface of the iron phosphate is weak and has no specificity, which leads to unsatisfactory dispersing effect, coating uniformity and subsequent doping effect. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the application is to provide a preparation method of a NFPP positive electrode material with high compactness density, high electrochemical performance and low cost. The application cooperates with a two-stage gradient sand milling process and a functionalized gemini quaternary ammonium salt grinding aid with a specific structure. The grinding aid not only significantly improves the grinding efficiency and dispersion stability through its unique structure, but also forms a uniform and dense heteroatom-doped carbon coating layer in situ during the sintering process, thereby solving the above industrialization problems.

[0005] To achieve the above-mentioned purpose, the application adopts the following technical solutions: The application discloses a preparation method of a high-compaction-density sodium iron phosphate pyrophosphate positive electrode material. Step (1), superfine grinding: part of iron phosphate raw materials and modified gemini quaternary ammonium salt grinding aids are added into deionized water, and superfine grinding is carried out for 2-4 hours to form D 50 The primary slurry has a particle size of 0.1-0.3 microns. Step (2), graded grinding: the remaining iron phosphate raw materials are added into the primary slurry, and common grinding is carried out for 1-2 hours to grind the particle size to D 50 The slurry has an ideal grading of 'fine particle filling coarse particle gap', and the particle size is 0.3-0.5 microns. Step (3), mixing: the graded slurry is added with a soluble sodium source, a phosphorus source and a carbon source, and stirring is carried out for 30 minutes to form a homogeneous mixed slurry with a solid content of 30%-40%; Step (4), drying and sintering: the mixed slurry is dried by spraying, the inlet air temperature is 200-280 DEG C, the outlet air temperature is 80-120 DEG C, the obtained precursor powder is heated to 500-600 DEG C at a rate of 3 DEG C / min under a nitrogen atmosphere, and sintering is carried out for 8-12 hours; Step (5), crushing: the sintered powder is treated by a jet mill, and the particle size of the finished product is controlled to be D 10 0.1-0.3 microns, D 50 less than 5 microns, D 99 less than 15 microns, and a high-compaction-density sodium iron phosphate pyrophosphate positive electrode material is obtained.

[0006] As a preferred scheme, in the step (1), the modified gemini quaternary ammonium salt grinding aid is added in an amount of 0.5%-2.0% of the mass of the part of the iron phosphate.

[0007] As a preferred scheme, in the step (2), the mass ratio of the superfine ground iron phosphate to the common ground iron phosphate is 1:1-5.

[0008] As a preferred scheme, in the step (3), the molar ratio of iron in the iron phosphate raw materials to sodium in the sodium source is 0.72-0.75:1.

[0009] As a preferred scheme, in the step (1), the preparation method of the modified gemini quaternary ammonium salt grinding aid comprises the following steps: S1, long chain alkyl amine (tetradecylamine, hexadecylamine, octadecylamine) is added to isopropyl alcohol, stirred and dissolved, 3,5-bis (trifluoromethyl) styrene is added thereto, and stirred and reacted at 65-70 DEG C for 3-5h, after the reaction is completed, rotary evaporation, ethyl acetate recrystallization, to obtain intermediate 1, wherein the molar ratio of long chain alkyl amine and 3,5-bis (trifluoromethyl) styrene is 1:1-1.2, and the amino group contained in the long chain alkyl amine and the alkenyl group contained in the 3,5-bis (trifluoromethyl) styrene are subjected to Michael addition to obtain intermediate 1.

[0010] S2, intermediate 1 is added to isopropyl alcohol, and 1,3-propane sulfonic acid lactone is added thereto, and stirred and reacted at 65-70 DEG C for 4-5h, after the reaction is completed, rotary evaporation, ethyl acetate recrystallization, to obtain intermediate 2, wherein the molar ratio of intermediate 1 and 1,3-propane sulfonic acid lactone is 1:1-1.2, and in this reaction, intermediate 1 and 1,3-propane sulfonic acid lactone are subjected to ring opening reaction to obtain intermediate 2.

[0011] S3, under nitrogen atmosphere, intermediate 2 and 1,4-dibromobutane are added to isopropyl alcohol, stirred and dispersed, and refluxed at elevated temperature for 12-14h, that is, after the quaternary ammonium reaction is completed, rotary evaporation, drying, to obtain modified Gemini quaternary ammonium salt grinding aid, wherein the molar ratio of intermediate 2 and 1,4-dibromobutane is 2.2-2.5:1.

[0012] Compared with the prior art, the beneficial effects of the present application are: (1) Process innovation and breakthrough of compaction density: "two-stage gradient sand grinding" process, first prepare superfine particles (D 50 =0.1-0.3μm) as a filling phase, then add the remaining raw materials to grind to a relatively coarse particle size (D 50 =0.3-0.5μm) as a skeleton phase, to accurately and controllably prepare coarse and fine graded iron phosphate slurry, and to fundamentally solve the accumulation problem of single particle size distribution, and to significantly improve the compaction density of NFPP to more than 2.10 g / cm³.

[0013] (2) Innovation and multifunctional synergy of grinding aid molecular structure: the core of the present application is to design and synthesize a multifunctional grinding aid with a unique "Gemini structure" and "double hydrophobic structure", and the effect is far more than the simple superposition of each functional group, but a significant synergistic effect is produced, specifically: Double-layer hydrophobic structure realizes spatial stability and strong anchoring: One end of the grinding aid molecule is a short-chain 3,5-bis(trifluoromethyl)phenyl structure with extremely strong hydrophobicity and steric hindrance effect; the other end is a long-chain alkyl (C14-C18) which also provides excellent hydrophobic segments. This "double hydrophobic structure" can strongly insert and anchor on the surface of iron phosphate particles, and prevent particle agglomeration through strong steric hindrance effect, so that ultrafine particles can be stably dispersed, and the dispersion effect is much better than that of traditional single-chain structure grinding aids, realizing the effect of spatial stability.

[0014] Grinding aid double structure realizes dense coating and multi-mechanism adsorption: The final product is a double quaternary ammonium salt and double sulfonate structure. This "double structure" has two positively charged quaternary ammonium salt centers and two negatively charged sulfonate centers, bringing multiple adsorption mechanisms. Mechanism 1, electrostatic adsorption: The quaternary ammonium salt cation head is strongly adsorbed on the negatively charged iron phosphate particle surface (environmental pH (7) > IEP (~ 4)). Mechanism 2, coordination bonding: The oxygen atom in the sulfonate (-SO3⁻) has a lone pair of electrons, which can act as an electron donor and form a firm Fe-O-S coordination bond with the iron ion (Fe³⁺) on the surface of iron phosphate. This chemical bonding greatly enhances the adsorption strength and stability of the grinding aid on the particle surface, achieving the effect of strong anchoring, and through multiple adsorption mechanisms, a dense organic monolayer film is formed on the surface of iron phosphate, laying a foundation for subsequent functional performance.

[0015] (3) Synergistic improvement mechanism of in-situ pyrolysis and multi-element doped carbon layer: The above dense organic monolayer film is pyrolyzed in-situ during the sintering process, converting into a layer of uniform heteroatom (N, S, F) doped carbon layer, significantly improving material performance from both physical and chemical aspects, specifically: N, S co-doping optimizes carbon layer electronic structure: N and S atoms derived from quaternary ammonium salt and sulfonic acid group are doped into amorphous carbon matrix. The co-doping effect of N atoms (providing n-type doping) and S atoms (expanding carbon layer spacing) can introduce a large number of defects and active sites near the Fermi level of the carbon layer, significantly change its electron cloud distribution, greatly improve the intrinsic electronic conductivity of the carbon coating layer, and promote the rapid transmission of electrons during charging and discharging.

[0016] F doping constructs a stable interface layer: F element derived from trifluoromethyl will generate a thermodynamically stable metal fluoride (such as NaF) interface layer or C-F bond during pyrolysis. This interface layer can effectively isolate the direct contact between the electrode material and the electrolyte, greatly inhibiting the irreversible interface side reactions and transition metal ion dissolution during the first charge and discharge process, thereby greatly improving the first coulombic efficiency. At the same time, the introduction of F can further optimize the interface ion transport kinetics.

[0017] N / S / F doping produces synergistic effect: N / S doping mainly improves electronic conductivity, while F doping mainly improves interface stability. The three work together to solve the core pain points of low electronic conductivity and poor first efficiency of NFPP materials.

[0018] (4) Precise dispersion mechanism based on scientific principles: The isoelectric point (IEP) of ferric phosphate is very low (pH ~ 4). In the neutral water medium (pH ~ 7) used in the present application, the particle surface has a net negative charge. The active ingredient of the grinding aid of the present application, cationic quaternary ammonium salt, can be precisely and firmly adsorbed on the particle surface through the strong electrostatic attraction and coordination bonding described above. This design based on the intrinsic characteristics of the material makes its dispersion efficiency much higher than that of traditional non-ionic or anionic dispersants.

[0019] (5) Process and cost optimization: The present method can simultaneously achieve particle size grading, carbon coating and multi-element doping through one-step sintering, eliminating the complex steps of traditional secondary sintering, secondary grinding and additional doping sources, significantly reducing production costs and impurity introduction risks, greatly shortening the total sanding time, and being suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the reaction route of the modified gemini quaternary ammonium salt grinding aid.

[0021] Figure 2 is the scanning electron microscope image of the grinding particles prepared in Example 1 of the present application.

[0022] Figure 3 is the XRD pattern of sodium ferric pyrophosphate prepared in Example 1 of the present application.

[0023] Figure 4 is the 0.1C charge-discharge curve of the sodium ion battery prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0025] It should be noted that the raw materials used in the following examples are commercially available.

[0026] The performance test of the button cell was carried out according to the following steps: The prepared positive electrode active material is mixed with a conductive agent and a binder in a mass ratio of 90:5:5, N-methylpyrrolidone is added as a dispersant, and the mixture is uniformly mixed by stirring to prepare a stable positive electrode slurry. The slurry is uniformly coated on the surface of a carbon-coated aluminum foil current collector, and after drying and tabletting, the positive electrode is obtained; a metal sodium sheet is used as the counter electrode, a glass fiber separator is selected, and a sodium ion battery special electrolyte with sodium hexafluorophosphate as the solute is used as the electrolyte. After the battery is assembled, constant current charge and discharge tests are performed at a rate of 0.1C in the voltage range of 2.0-4.0 V (vs. Na⁺ / Na) to evaluate its electrochemical performance.

[0027] Preparation of modified gemini quaternary ammonium salt grinding aid: Preparation Example 1 S1, in a 500 mL three-necked flask equipped with a condenser and a stirrer, 0.25 mol of tetradecylamine and 200 mL of isopropyl alcohol were added, stirred and dissolved, then 0.3 mol of 3,5-bis(trifluoromethyl)styrene was slowly added dropwise, the temperature was raised to 68°C, and the reaction was stirred for 4 hours. After the reaction was completed, most of the solvent was removed by rotary evaporation, and recrystallization was performed with ethyl acetate to obtain intermediate 1-A.

[0028] S2, 0.25 mol of intermediate 1-A was added to 200 mL of isopropyl alcohol, stirred and dissolved, 0.28 mol of 1,3-propane sultone was added, and the reaction was carried out at 68°C for 4.5 hours. After the reaction was completed, rotary evaporation was performed, and recrystallization was performed with ethyl acetate to obtain intermediate 2-A.

[0029] S3, under nitrogen protection, 0.22 mol of intermediate 2-A and 0.1 mol of 1,4-dibromobutane were added to 250 mL of isopropyl alcohol, stirred and heated to reflux for 13 hours. After the reaction was completed, the solvent was removed by distillation under reduced pressure, and the product was dried in a vacuum drying oven at 60°C for 24 hours to obtain grinding aid A.

[0030] Preparation Example 2 The difference between this preparation example and Preparation Example 1 is that the tetradecylamine in S1 is replaced with hexadecylamine, and the remaining steps are the same as those of Preparation Example 1. The product prepared is denoted as grinding aid B.

[0031] Preparation Example 3 The difference between this preparation example and Preparation Example 1 is that the tetradecylamine in S1 is replaced with octadecylamine, and the remaining steps are the same as those of Preparation Example 1. The product prepared is denoted as grinding aid C.

[0032] Preparation of NFPP positive electrode material Example 1

[0033] The preparation method of the positive electrode material in this example includes the following steps: (1) Ultrafine sand grinding: 1 mol of iron phosphate, deionized water and grinding aid B (0.5% of the total mass of iron phosphate) were mixed, zirconia beads with a diameter of 0.3 mm were used, and sand grinding was carried out at a rotation speed of 1200 rpm for 3 hours to obtain a primary slurry D 50 = 0.14 μm.

[0034] (2) Graded sand grinding: 5 mol of iron phosphate was added to the above primary slurry, and the same sand grinding condition was continued for 1.5 hours to obtain a graded slurry D 50 = 0.38 μm.

[0035] (3) Mixing: 2 mol of sodium dihydrogen phosphate, 3 mol of sodium carbonate and 0.4 mol of glucose were added to the graded slurry, and stirred for 30 min to form a homogeneous mixed slurry with a solid content of 30%.

[0036] (4) Drying and sintering: the slurry was spray dried at an inlet temperature of 250°C and an outlet temperature of 100°C to obtain a precursor powder, and the precursor powder was sintered at 550°C for 10 hours under a nitrogen atmosphere with a temperature rise of 3°C / min.

[0037] (5) Crushing: the sintered material was crushed by an air flow crusher to obtain a sodium iron pyrophosphate positive electrode material.

[0038] Test results: the compaction density was 2.19 g / cm³; the 0.1C discharge gram capacity was 110.8 mAh / g, and the initial efficiency was 94.1%. Example Two

[0039] The steps for preparing the sodium iron pyrophosphate positive electrode material in this example and example 1 are basically the same, except that grinding aid A is used instead of grinding aid B.

[0040] The primary slurry D 50 = 0.16 μm after ultrafine grinding; and the slurry D 50 = 0.42 μm after grading.

[0041] Test results: the compaction density was 2.16 g / cm³; the 0.1C discharge gram capacity was 109.2 mAh / g, and the initial efficiency was 93.9%. Example Three

[0042] The steps for preparing the sodium iron pyrophosphate positive electrode material in this example and example 1 are basically the same, except that grinding aid C is used instead of grinding aid B.

[0043] The primary slurry D 50 = 0.19 μm after ultrafine grinding; and the slurry D 50 = 0.45 μm after grading.

[0044] Test results: the tap density is 2.14 g / cm3; the 0.1C discharge gram capacity is 108.6 mAh / g, and the initial efficiency is 91.9%.

[0045] Comparative Example 1 6 mol of iron phosphate and deionized water (adjusting the total slurry solid content to 30%) were weighed and mixed, zirconium oxide beads with a diameter of 0.3 mm were used for sand milling at a speed of 1200 rpm for 2 hours to obtain a slurry D 50 =0.78 μm, 2 mol of sodium dihydrogen phosphate, 3 mol of sodium carbonate and 0.4 mol of glucose were subsequently added, and the stirring, drying, sintering and crushing steps were completely the same as in Example 1.

[0046] Test results: the tap density is only 1.95 g / cm3; the 0.1C discharge gram capacity is 102.9 mAh / g, and the initial efficiency is 83.5%.

[0047] Comparative Example 2 This comparative example is roughly the same as the steps of preparing the sodium iron pyrophosphate phosphate positive electrode material in Example 1, the difference is that cetyltrimethylammonium bromide is used instead of grinding aid B.

[0048] Test results: The once slurry D 50 =0.28 μm after superfine grinding; the graded slurry D 50 =0.50 μm.

[0049] The tap density of the finished product is 2.06 g / cm3; the 0.1C discharge gram capacity is 105.2 mAh / g, and the initial efficiency is 84.5%.

[0050] Comparative Example 3 This comparative example is roughly the same as the steps of preparing the sodium iron pyrophosphate phosphate positive electrode material in Example 1, the difference is that sodium dodecyl benzene sulfonate is used instead of grinding aid B.

[0051] Test results: The once slurry D 50 =0.52 μm after superfine grinding; the graded slurry D 50 =0.68 μm.

[0052] The tap density of the finished product is 2.03 g / cm3; the 0.1C discharge gram capacity is 105.4 mAh / g, and the initial efficiency is 89.2%.

[0053] Through the comparison of the above examples and comparative examples, the following conclusions can be clearly drawn: The invention significantly improves performance: all samples using the Gemini structure grinding aid (Examples 1-3) have significantly better grinding efficiency, final density, tap density and first effect than all the comparative examples. This shows that the synergistic effect of N, S, F and the Gemini molecular structure are essential for improving the comprehensive performance of NFPP. Chain length effect: within the scope of the invention, hexadecylamine (C16) based grinding aid (Example 1) shows the best comprehensive performance, indicating that the alkyl chain length needs to be optimized to achieve the best steric hindrance and dispersion effect. Limited effect of single element: Comparative Examples 2 (containing only nitrogen) and 3 (containing only sulfur) may approach the invention in one parameter (such as first effect of Comparative Example 3), but cannot achieve high levels in all four key indicators of grinding efficiency, compaction density, tap density and first effect, demonstrating the necessity of multifunctional synergy. Mechanism verification: the compaction density and tap density of Comparative Example 2 are higher than those of Comparative Examples 1 and 3, confirming the essential adsorption and grinding aid advantage of cationic grinding aid for negatively charged iron phosphate. The Gemini structure of the invention is a further leap on this basis, achieving a comprehensive breakthrough in performance.

[0054] In summary, the invention effectively solves the industry problems of low grinding efficiency, insufficient compaction density and poor electrochemical performance of NFPP materials through specific grinding aid molecular design, synthesis and application process.

[0055] The preferred embodiments of the invention disclosed above are only used to help explain the invention. The preferred embodiments do not describe all the details and do not limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the specification. The specification selects and describes these embodiments in order to better explain the principles and practical applications of the invention, so that those skilled in the art can well understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a high-density sodium iron pyrophosphate cathode material, characterized in that, The preparation method includes the following steps: Step (1), Ultrafine Grinding: Add some iron phosphate raw material and modified gemini quaternary ammonium salt grinding aid to deionized water and perform ultrafine grinding for 2-4 hours to form D 50 A primary slurry with a particle size of 0.1-0.3 μm; Step (2), gradation grinding: Add the remaining ferric phosphate raw material to the primary slurry and perform ordinary grinding for 1-2 hours until the particle size D is reached. 50 The particle size is 0.3-0.5μm, forming a slurry with an ideal gradation of "fine particles filling the voids between coarse particles"; Step (3), mixing: Add soluble sodium source, phosphorus source and carbon source to the graded slurry, stir for 30 min to form a homogeneous mixed slurry with a solid content of 30%-40%; Step (4), Drying and sintering: The mixed slurry is spray-dried with an inlet air temperature of 200-280℃ and an outlet air temperature of 80-120℃. The resulting precursor powder is heated to 500-600℃ at 3℃ / min under a nitrogen atmosphere and sintered for 8-12 hours. Step (5), Crushing: The sintered powder is processed by an air jet mill to control the particle size D of the finished product. 10 The thickness is 0.1-0.3 μm, D 50 Less than 5μm, D 99 With a thickness of less than 15 μm, a high-density sodium iron pyrophosphate cathode material was obtained.

2. The method for preparing the high-density sodium iron pyrophosphate cathode material according to claim 1, characterized in that, In step (1), the amount of modified gemini quaternary ammonium salt grinding aid added is 0.5%-2.0% of the mass of the iron phosphate.

3. The method for preparing the high-density sodium iron pyrophosphate cathode material according to claim 1, characterized in that, In step (2), the mass ratio of ultrafine ground ferric phosphate to ferric phosphate that has undergone ordinary sand milling is 1:1-5.

4. The method for preparing the high-density sodium iron pyrophosphate cathode material according to claim 1, characterized in that, In step (3), the molar ratio of iron in the iron phosphate raw material to sodium in the sodium source is 0.72-0.75:

1.

5. The method for preparing the high-density sodium iron pyrophosphate cathode material according to claim 1, characterized in that, In step (1), the preparation method of the modified Gemini quaternary ammonium salt grinding aid includes the following steps: S1. Add long-chain alkylamine to isopropanol, stir to dissolve, add 3,5-bis(trifluoromethyl)styrene, stir at 65-70℃ for 3-5 h, after the reaction is completed, rotary evaporate, recrystallize from ethyl acetate to obtain intermediate 1. S2. Add intermediate 1 to isopropanol, then add 1,3-propanesulfonate lactone, and stir the reaction at 65-70℃ for 4-5 hours. After the reaction is complete, evaporate by rotary evaporation and recrystallize from ethyl acetate to obtain intermediate 2. S3. Under a nitrogen atmosphere, intermediates 2 and 1,4-dibromobutane were added to isopropanol, stirred and dispersed, and refluxed for 12-14 hours. After the reaction was completed, the mixture was distilled under reduced pressure and dried to obtain the modified gemini quaternary ammonium salt grinding aid.

6. The method for preparing the high-density sodium iron pyrophosphate cathode material according to claim 5, characterized in that, In S1, the molar ratio of long-chain alkylamine and 3,5-bis(trifluoromethyl)styrene is 1:1-1.

2.

7. The method for preparing the high-density sodium iron pyrophosphate cathode material according to claim 5, characterized in that, In S1, the long-chain alkylamine is one of tetradecylamine, hexadecylamine, and octadecylamine.

8. The method for preparing the high-density sodium iron pyrophosphate cathode material according to claim 5, characterized in that, In S2, the molar ratio of intermediate 1 and 1,3-propanesulfonate lactone is 1:1-1.

2.

9. The method for preparing the high-density sodium iron pyrophosphate cathode material according to claim 5, characterized in that, In S3, the molar ratio of intermediate 2 to 1,4-dibromobutane is 2.2-2.5:1.

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