Preparation method of high-rate polyanion sodium-ion battery cathode material

Abstract

The application discloses a preparation method of a high-rate polyanionic sodium ion battery positive electrode material, and comprises the following steps: S1, preparation of an electrostatic spinning precursor solution: dissolving a sodium source, a mixed iron source and a phosphorus source by a wet method, adding a spinning polymer, a carbon source and an active agent, and stirring to form an electrostatic spinning precursor solution; S2, electrostatic spinning: electrostatic spinning is performed on the electrostatic spinning precursor solution obtained in the step S1, and a precursor fiber membrane is collected; S3, pre-oxidation treatment: performing calcination treatment on the fiber membrane precursor obtained in the step S2 to obtain a pre-oxidized precursor; and S4, high-temperature calcination: performing high-temperature calcination on the pre-oxidized precursor obtained in the step S3 to obtain the final polyanionic sodium ion battery positive electrode material. The preparation method of the high-rate polyanionic sodium ion battery positive electrode material has the characteristics of high electronic conductivity, fast ion transmission speed, small polarization effect influence and good structural stability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a method for preparing a high-rate polyanion sodium-ion battery cathode material. Background Technology

[0002] With the rising global demand for clean energy, sodium-ion batteries have become a powerful complement to lithium-ion batteries due to their abundant raw material sources, low cost, and environmental friendliness. There are three main technological routes for sodium-ion battery cathode materials: polyanionic systems, layered oxide systems, and Prussian blue systems. Among them, polyanionic systems have become highly promising cathode materials due to their stable three-dimensional framework structure, good thermal stability, excellent cycle life, abundant natural resources with large reserves, and simple, low-cost, and inexpensive main material preparation processes. As a rising force in the new energy industry, sodium-ion batteries are rapidly entering incremental markets such as special transportation vehicles and large-scale energy storage, thanks to their advantages of high safety, long lifespan, wide temperature range performance, and cost potential.

[0003] Polyanionic sodium-ion battery cathode materials have broad prospects in energy storage and transportation due to their stable framework structure and safety. However, their poor charging rate performance is related to the special characteristics of the materials themselves, mainly due to the following drawbacks:

[0004] If the intrinsic electronic conductivity is low, the strong covalent bonds in the polyanionic framework will produce an "inductive effect," localizing electrons on the transition metal ions and severely hindering electron hopping conduction. Its low intrinsic conductivity results in slow electrode reaction kinetics.

[0005] Sodium ion diffusion kinetics are slow. Sodium ions (Na⁺) have a larger radius than lithium ions (Li⁺), resulting in a higher energy barrier during migration within the crystal lattice and a slower inherent diffusion rate. Furthermore, intrinsic anti-occupancy defects can form during material synthesis, blocking the diffusion channels of sodium ions. This leads to severe polarization in sodium-ion batteries during repeated charging, resulting in a low constant-current charge-to-weight ratio and excessively long constant-voltage charging time, ultimately causing a continuous decrease in battery capacity. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a high-rate polyanionic sodium-ion battery cathode material, which has the characteristics of high electronic conductivity, fast ion transport speed, small influence of polarization, and good structural stability.

[0007] This invention can be achieved through the following technical solutions:

[0008] The present invention discloses a method for preparing a high-rate polyanionic sodium-ion battery cathode material, comprising the following steps:

[0009] S1. Preparation of electrospinning precursor solution: Sodium source, mixed iron source and phosphorus source are wet-dissolved and added to spinning polymer, carbon source and activator, and stirred to form electrospinning precursor solution;

[0010] S2. Electrospinning: The electrospinning precursor solution obtained in step S1 is electrospinned, and the precursor fiber membrane is collected.

[0011] S3. Pre-oxidation treatment: The fiber film precursor obtained in S2 is calcined to obtain the pre-oxidized precursor.

[0012] S4. High-temperature calcination: The pre-oxidized precursor obtained in S3 is calcined at high temperature to obtain the final polyanionic sodium-ion battery cathode material.

[0013] Further, in step S1, the mixed iron source includes an inorganic iron source and an organic iron source, wherein the molar ratio of iron ions in the inorganic iron source to the molar ratio of iron ions in the organic iron source is 1:1. The inorganic iron source is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous bromide, ferric chloride, ferric nitrate, ferric sulfate, ferric perchlorate, and ferric bromide, and the organic iron source is one or more of ferrous acetate, ferric acetate, and ferric oxalate.

[0014] In this invention, both the inorganic and organic iron sources are soluble iron sources. The advantage of using a dual iron source is that the organic iron source typically begins to decompose at lower temperatures (200-400℃). This decomposition process generates reducing gases (such as carbon monoxide and hydrogen) and abundant small organic molecule fragments, which help form a more ordered carbon structure within the material. Simultaneously, the release of these gases leaves abundant micropores and mesopores within the fiber. Furthermore, its decomposition products are an important source for forming the internal carbon skeleton or nano-carbon dots, which can be used as the first step in carbon coating to construct rapid ion transport channels. The inorganic iron source, with its higher decomposition temperature, acts as a "sacrificial template" and "pore-forming agent," promoting porosity within the fiber and synergistically forming a continuous open-pore structure with the gases generated by the organic iron source. This also avoids the impurity problems that may arise from excessive carbon residue or incomplete reaction at the organic iron source. The combination of these two sources achieves a relay of "low-temperature pre-reduction / pore-forming and high-temperature precise reaction." The organic iron source first creates a favorable internal conductive network and porous structure for the material, while the inorganic iron source ensures the high chemical purity and crystallinity of the final product. This is equivalent to simultaneously completing the material's structural modification (carbon coating and pore formation) and phase synthesis in one step. If the proportion of inorganic iron source is too high, it will not provide a carbon source itself, meaning that the total amount of organic ligands (carbon precursors) from the organic iron source in the system will be insufficient. Organic iron salts decompose at high temperatures and the process is complex. If the proportion is too high, even higher temperatures or longer times may be required to ensure that all iron ions participate in the phase-forming reaction of NFPP. The sodium, iron, and phosphorus sources are used in a Na:Fe:P molar ratio of 4:3:4.

[0015] Further, in step S1, the spinning polymer is polyvinylpyrrolidone and / or polyacrylonitrile, and its mass concentration in the spinning solution is 5-15%.

[0016] Further, in step S1, the activator is polymethyl methacrylate, and its addition amount is 0.3-0.5% of the iron source mass. The activator can be uniformly dispersed in the spinning solution, but it will be completely removed after high-temperature calcination, thus leaving mesopores or macropores of controllable size in the composite fiber. This greatly increases the electrolyte wetting area and ion transport channels. Too little addition will result in poor pore-forming effect, while too much will lead to excessive pore formation during high-temperature calcination, damaging the overall structure of the material.

[0017] Furthermore, in step S1, the solvent for wet dissolution is a mixture of ethanol, water, and DMF, wherein the mass ratio of DMF:ethanol:water is 8:1:1. The higher the proportion of DMF, the stronger the dissolution ability of polymers and organic additives, and the more stable the solution.

[0018] Furthermore, in step S2, the conditions for electrospinning are: spinning voltage 10-25 kV, receiving distance 10-20 cm, spinning solution propulsion speed 0.5-2 mL / h, and ambient humidity controlled at 30-50%.

[0019] Furthermore, in step S3, the calcination conditions are as follows: the temperature is increased to 200-300°C in air at a rate of 1-5°C / min, and held for 1-3 hours to set the fiber shape and prevent melting during subsequent high-temperature treatment. If the temperature is too low or the time is too short, the fiber shape will be incomplete, affecting subsequent processing. If the temperature is too high or the time is too long, the fiber will become over-hardened, affecting its internal structure.

[0020] Further, in step S4, the high-temperature calcination conditions are as follows: the protective gas is nitrogen or argon, the heating rate of the plastic is 4-7℃ / min, the calcination temperature is 600-800℃, the holding time is 3-6 hours, and the cooling method is natural cooling to room temperature, thus obtaining a black, self-supporting one-dimensional carbon-coated Na4Fe3(PO4)2(P2O7) / C composite nanofiber cathode material. Too slow a heating rate will result in excessively long reaction time, severe grain coarsening; polymer decomposition products may be completely eliminated, weakening the pore-forming effect; and high energy consumption. Too fast a heating rate will result in high thermal stress, making the fibers prone to cracking or collapse; excessively rapid decomposition of organic matter will lead to violent gas release, damaging the fiber morphology; and insufficient graphitization of the carbon layer. A holding temperature of 600-800℃ ensures thermodynamically pure phase formation. A holding time of 3-6 hours allows the reaction to proceed fully while avoiding excessive grain growth.

[0021] Furthermore, in step S1, the stirring conditions for the electrospinning precursor solution are: magnetic stirring at 60-80°C for more than 12 hours to form a uniform, transparent, and viscous electrospinning precursor solution.

[0022] Further, in step S1, the sodium source is one or more of sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, sodium silicate, sodium acetate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, sodium oxalate, sodium benzoate, sodium citrate, sodium thiosulfate, sodium borohydride, sodium methoxide, sodium ethoxide, sodium stearate, monosodium glutamate, sodium perchlorate, and sodium valproate; the phosphorus source is one or more of triethylphosphine, aminotrimethylphosphonic acid, hydroxyethylidene diphosphate, phosphoric acid, triphenylphosphine, triethyl phosphate, triphenyl phosphate, adenosine triphosphate, glyphosate, triphenylphosphine oxide, tri(chloroisopropyl) phosphate, tetraethyl pyrophosphate, phospholipid, hexamethylphosphoric acid triamine, phosphorous acid, hypophosphite, pyrophosphate, and metaphosphoric acid; the carbon source is citric acid, glucose, or polyethylene glycol, and the molar ratio of the carbon source to the iron source is (0.5-2):1.

[0023] This invention provides a method for preparing a high-rate polyanionic sodium-ion battery cathode material, which has the following beneficial effects:

[0024] First, it boasts high electronic conductivity. The carbon fibers prepared by electrospinning technology can uniformly and densely encapsulate NFPP nanocrystals within their three-dimensional network structure, forming a unique core-shell composite configuration. This creates a continuous and stable conductive carbon layer on the surface of the active material particles, providing a low-resistance pathway for electron transport and constructing a three-dimensionally interconnected "high-speed electron channel" throughout the entire electrode. This structure effectively overcomes the inherent defect of poor electronic conductivity in NFPP materials, significantly reducing contact impedance and charge transfer resistance within the electrode, thereby greatly improving the overall electronic conductivity of the composite material. This lays a crucial foundation for the high-rate performance and long-cycle stability of the battery.

[0025] Secondly, the ion transport speed is fast. In the composite cathode material prepared by electrospinning, the one-dimensional nanofiber structure provides a directional and rapid channel along the fiber axis for the bulk diffusion of sodium ions. This unique continuous one-dimensional topology effectively avoids the tortuous and circuitous path that ions must take in traditional particulate electrodes, shortening the migration distance of sodium ions in the solid phase from the micrometer scale to the nanometer scale. At the same time, the interconnected pores between fibers form a continuous electrolyte wetting network, further promoting the synergistic optimization of interfacial ion transport dynamics. This synergistic effect of axial ion channels and radially shortened diffusion distance significantly reduces concentration polarization and activation polarization, thereby systematically improving the material's rapid charge-discharge capability and high-rate performance.

[0026] Third, the polarization effect is minimal. In this composite electrode material, the carbon fiber network and one-dimensional ion channels together form a dual-continuous, interpenetrating three-dimensional transport system. The highly conductive carbon skeleton provides a low-resistance pathway for electrons, while the oriented nanofibers and their inter-channel mesoporous structures construct a rapid diffusion corridor for sodium ions. This synergistic design of the "electron-ion dual high-speed network" achieves efficient matching of charge transport processes on both spatial and temporal scales: rapid electron injection provides sufficient charge for the electrochemical reaction, while rapid ion replenishment maintains the continuity of the interfacial reaction, thus significantly reducing electrochemical and concentration polarization caused by mass transfer limitations and charge accumulation. This synergistic depolarization effect ensures that the electrode maintains high utilization of active materials and reversibility of reactions during high-rate charge and discharge, enabling the battery to exhibit excellent capacity retention and energy output efficiency even under high-speed operating conditions.

[0027] Fourth, it exhibits high structural stability. The three-dimensional fiber network constructed by electrospinning technology forms a flexible, self-supporting structure with abundant hierarchical pores on a macroscopic scale through the entanglement and overlap of fibers. This open, porous framework provides ample elastic buffer space for the periodic lattice expansion and contraction of NFPP during charging and discharging, effectively absorbing and dispersing mechanical stress through the microscopic deformation of fibers and the volume adjustment of pores. Simultaneously, the continuous carbon coating firmly anchors the active material particles within the fiber matrix, not only suppressing particle displacement and detachment caused by repeated volume changes but also effectively preventing the initiation of microcracks and pulverization of the electrode material. This synergistic protection mechanism of "macroscopic pore buffering" and "microscopic interface constraint" significantly enhances the structural integrity of the electrode during long-term cycling, thereby greatly improving the battery's capacity retention and cycle life. For example, polymethyl methacrylate (PMMA) completely decomposes when heated to approximately 300°C or higher in a protective atmosphere, leaving abundant, size-tunable nanopores within the composite fibers. These pores provide additional, low-resistance radial diffusion channels for electrolyte wetting and sodium ion transport, complementing the axial ion channels of the fiber itself to form a three-dimensional ion conduction network. This reduces local current density, alleviates electrode polarization, and significantly improves the rate performance of the material, enabling it to maintain high capacity even at high current densities.

[0028] Fifth, the preparation process is simple and easy. The carbon composite fiber membrane, directly prepared by electrospinning, exhibits excellent self-supporting strength and structural flexibility due to the three-dimensional mechanical interlocking structure formed by the entanglement of its internal fibers. It can be independently formed into an electrode without the need for traditional metal current collectors. At the same time, the continuous conductive network formed by in-situ carbonization endows it with excellent intrinsic electronic conductivity, enabling the electrode to achieve efficient charge transport with little or no conductive additives. This dual characteristic of self-support and high conductivity realizes the three-in-one functional integration of "active material, conductive agent, and current collector," which not only simplifies the traditional electrode slurry coating process but, more importantly, significantly reduces the mass proportion of inactive materials (such as insulating binders, non-load-bearing current collectors, and excess conductive agents) in the electrode. As a result, the active material loading rate and volumetric energy density of the battery electrode are effectively improved, providing an innovative electrode engineering solution for constructing high-energy-density sodium-ion battery systems. Attached Figure Description

[0029] Figure 1 SEM images of the material obtained in Example 1;

[0030] Figure 2 The curve showing the capacity retention of the material obtained in Example 1 at 10°C during cycling.

[0031] Figure 3 The rate-charge capacity retention rate of the material obtained in Example 1;

[0032] Figure 4 The rate discharge capacity retention rate of the material obtained in Example 1. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0034] The present invention discloses a method for preparing a high-rate polyanionic sodium-ion battery cathode material, comprising the following steps:

[0035] S1. Preparation of electrospinning precursor solution: Sodium source, mixed iron source and phosphorus source are wet-dissolved and added to spinning polymer, carbon source and activator, and stirred to form electrospinning precursor solution;

[0036] S2. Electrospinning: The electrospinning precursor solution obtained in step S1 is electrospinned, and the precursor fiber membrane is collected.

[0037] S3. Pre-oxidation treatment: The fiber film precursor obtained in S2 is calcined to obtain the pre-oxidized precursor.

[0038] S4. High-temperature calcination: The pre-oxidized precursor obtained in S3 is calcined at high temperature to obtain the final polyanionic sodium-ion battery cathode material.

[0039] Further, in step S1, the mixed iron source includes an inorganic iron source and an organic iron source, wherein the molar ratio of iron ions in the inorganic iron source to the molar ratio of iron ions in the organic iron source is 1:1. The inorganic iron source is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous bromide, ferric chloride, ferric nitrate, ferric sulfate, ferric perchlorate, and ferric bromide, and the organic iron source is one or more of ferrous acetate, ferric acetate, and ferric oxalate.

[0040] Further, in step S1, the spinning polymer is polyvinylpyrrolidone and / or polyacrylonitrile, and its mass concentration in the spinning solution is 5-15%.

[0041] Further, in step S1, the activator is polymethyl methacrylate, and its addition amount is 0.3-0.5% of the iron source mass.

[0042] Furthermore, in step S1, the solvent for wet dissolution is a mixture of ethanol, water, and DMF, wherein the mass ratio of DMF:ethanol:water is 8:1:1.

[0043] Furthermore, in step S2, the conditions for electrospinning are: spinning voltage 10-25 kV, receiving distance 10-20 cm, spinning solution propulsion speed 0.5-2 mL / h, and ambient humidity controlled at 30-50%.

[0044] Furthermore, in step S3, the calcination conditions are as follows: heating to 200-300°C at a heating rate of 1-5°C / min in an air atmosphere, and holding at that temperature for 1-3 hours.

[0045] Furthermore, in step S4, the conditions for high-temperature calcination are as follows: the protective gas is nitrogen or argon, the temperature of the plastic is increased by 4-7℃ / min, the calcination temperature is 600-800℃, the holding time is 3-6 hours, and the cooling method is natural cooling to room temperature.

[0046] Furthermore, in step S1, the stirring conditions for the electrospinning precursor solution are: magnetic stirring at 60-80°C for more than 12 hours.

[0047] Further, in step S1, the sodium source is one or more of sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, sodium silicate, sodium acetate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, sodium oxalate, sodium benzoate, sodium citrate, sodium thiosulfate, sodium borohydride, sodium methoxide, sodium ethoxide, sodium stearate, monosodium glutamate, sodium perchlorate, and sodium valproate; the phosphorus source is one or more of triethylphosphine, aminotrimethylphosphonic acid, hydroxyethylidene diphosphate, phosphoric acid, triphenylphosphine, triethyl phosphate, triphenyl phosphate, adenosine triphosphate, glyphosate, triphenylphosphine oxide, tri(chloroisopropyl) phosphate, tetraethyl pyrophosphate, phospholipid, hexamethylphosphoric acid triamine, phosphorous acid, hypophosphite, pyrophosphate, and metaphosphoric acid; the carbon source is citric acid, glucose, or polyethylene glycol, and the molar ratio of the carbon source to the iron source is (0.5-2):1.

[0048] Example 1

[0049] This embodiment relates to a high-rate polyanionic sodium-ion battery cathode material, the preparation method of which includes the following steps:

[0050] S1. Preparation of electrospinning precursor solution: Sodium source, mixed iron source and phosphorus source are wet-dissolved and added to spinning polymer, carbon source and activator, and stirred to form electrospinning precursor solution. Specifically, the mixed iron source includes inorganic and organic iron sources, with a 1:1 ratio of iron ion molar amounts in the inorganic iron source to those in the organic iron source. The inorganic iron source consists of ferrous sulfate, ferrous chloride, and ferrous nitrate, while the organic iron source is ferrous acetate. The spinning polymer is polyvinylpyrrolidone, with a mass concentration of 15% in the spinning solution. The electrospinning precursor solution is stirred magnetically at 70°C for 14 hours. The activator is polymethyl methacrylate, added at 0.3% of the iron source mass. The wet-dissolving solvent is a mixture of ethanol, water, and DMF, with a mass ratio of DMF:ethanol:water = 8:1:1. The sodium source consists of sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, and sodium silicate. The phosphorus source consists of triethylphosphine, aminotrimethylphosphonic acid, hydroxyethylidene diphosphate, phosphoric acid, triphenylphosphine, and triethyl phosphate. The carbon source consists of citric acid and glucose, with a molar ratio of 2:1 to the iron source.

[0051] S2. Electrospinning: The electrospinning precursor solution obtained in step S1 is electrospinned to collect the precursor fiber membrane. Specifically, the electrospinning conditions are: spinning voltage 25 kV, receiving distance 15 cm, spinning solution propulsion speed 0.5 mL / h, and ambient humidity controlled at 30-50%.

[0052] S3. Pre-oxidation treatment: The fiber film precursor obtained in S2 is calcined to obtain a pre-oxidized precursor; specifically, the calcination conditions are: heating to 300°C at a heating rate of 5°C / min in air atmosphere and holding at that temperature for 1 hour.

[0053] S4. High-temperature calcination: The pre-oxidized precursor obtained in S3 is subjected to high-temperature calcination to obtain the final polyanionic sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are: nitrogen as the protective gas, heating rate of the plastic is 7℃ / min, calcination temperature is 700℃, holding time is 3 hours, and cooling method is natural cooling to room temperature.

[0054] Example 2

[0055] This embodiment relates to a high-rate polyanionic sodium-ion battery cathode material, the preparation method of which includes the following steps:

[0056] S1. Preparation of electrospinning precursor solution: Sodium source, mixed iron source and phosphorus source are wet-dissolved and added to spinning polymer, carbon source and activator, and stirred to form electrospinning precursor solution. Specifically, the mixed iron source includes inorganic and organic iron sources. The molar ratio of iron ions in the inorganic iron source to that in the organic iron source is 1:1. The inorganic iron sources are ferric sulfate, ferric perchlorate, and ferric bromide, while the organic iron sources are ferric acetate and ferric oxalate. The spinning polymer is polyacrylonitrile, with a mass concentration of 10% in the spinning solution. The stirring conditions for the electrospinning precursor solution are: magnetic stirring at 60°C for 12 hours. The activator is polymethyl methacrylate, with an addition amount of 0.5% of the iron source mass. The solvent for wet dissolution is a mixture of ethanol, water, and DMF, with a mass ratio of DMF:ethanol:water = 8:1:1. The sodium sources are sodium borohydride, sodium methoxide, sodium ethoxide, sodium stearate, sodium glutamate, sodium perchlorate, and sodium valproate. The phosphorus sources are hexamethylphosphoric acid triamine, phosphorous acid, hypophosphoric acid, pyrophosphoric acid, and metaphosphoric acid. The carbon sources are glucose and polyethylene glycol, with a molar ratio of 1 / 2:1 to the iron source.

[0057] S2. Electrospinning: The electrospinning precursor solution obtained in step S1 is electrospinned to collect the precursor fiber membrane. Specifically, the electrospinning conditions are: spinning voltage 16 kV, receiving distance 10 cm, spinning solution propulsion speed 2 mL / h, and ambient humidity controlled at 30-50%.

[0058] S3. Pre-oxidation treatment: The fiber film precursor obtained in S2 is calcined to obtain a pre-oxidized precursor; specifically, the calcination conditions are: heating to 200°C at a heating rate of 3°C / min in air atmosphere and holding at that temperature for 3 hours.

[0059] S4. High-temperature calcination: The pre-oxidized precursor obtained in S3 is subjected to high-temperature calcination to obtain the final polyanionic sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are: argon as the protective gas, heating rate of the plastic is 6℃ / min, calcination temperature is 600℃, holding time is 6 hours, and cooling method is natural cooling to room temperature.

[0060] Example 3

[0061] This embodiment relates to a high-rate polyanionic sodium-ion battery cathode material, the preparation method of which includes the following steps:

[0062] S1. Preparation of the electrospinning precursor solution: Sodium source, mixed iron source, and phosphorus source are wet-dissolved and added to the spinning polymer, carbon source, and activator, then stirred to form the electrospinning precursor solution. Specifically, the mixed iron source includes inorganic and organic iron sources, with a 1:1 molar ratio of iron ions in the inorganic iron source to that in the organic iron source. The inorganic iron source is ferrous sulfate, ferrous chloride, or ferric bromide, while the organic iron source is ferrous acetate or ferric acetate. The spinning polymer is polyvinylpyrrolidone or polyacrylonitrile, with a mass concentration of 5% in the spinning solution. The stirring conditions for the electrospinning precursor solution are: magnetic stirring at 70°C for 13 hours. The activator is polymethyl methacrylate. The amount added is 0.5% of the iron source mass; the solvent for wet dissolution is a mixture of ethanol, water and DMF, wherein the mass ratio of DMF:ethanol:water is 8:1:1; the sodium source is sodium sulfate, sodium nitrate, sodium silicate, sodium acetate, sodium monohydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate; the phosphorus source is triethyl phosphate, triphenyl phosphate, adenosine triphosphate, glyphosate, pyrophosphate and metaphosphate; the carbon source is citric acid, glucose and polyethylene glycol, and the molar ratio of the carbon source to the iron source is 0.6:1.

[0063] S2. Electrospinning: The electrospinning precursor solution obtained in step S1 is electrospinned to collect the precursor fiber membrane. Specifically, the electrospinning conditions are: spinning voltage 10kV, receiving distance 20 cm, spinning solution propulsion speed 1.3 mL / h, and ambient humidity controlled at 30-50%.

[0064] S3. Pre-oxidation treatment: The fiber film precursor obtained in S2 is calcined to obtain a pre-oxidized precursor; specifically, the calcination conditions are: heating to 250°C at a heating rate of 1°C / min in air atmosphere and holding at that temperature for 2 hours.

[0065] S4. High-temperature calcination: The pre-oxidized precursor obtained in S3 is subjected to high-temperature calcination to obtain the final polyanionic sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are: argon as the protective gas, heating rate of the plastic is 4℃ / min, calcination temperature is 800℃, holding time is 5 hours, and cooling method is natural cooling to room temperature.

[0066] Example 4

[0067] This embodiment relates to a high-rate polyanionic sodium-ion battery cathode material, the preparation method of which includes the following steps:

[0068] S1. Preparation of electrospinning precursor solution: Sodium source, mixed iron source and phosphorus source are wet-dissolved and added to spinning polymer, carbon source and activator, and stirred to form electrospinning precursor solution. Specifically, the mixed iron source includes inorganic and organic iron sources. The molar ratio of iron ions in the inorganic iron source to that in the organic iron source is 1:1. The inorganic iron sources are ferrous nitrate, ferrous bromide, ferric chloride, ferric nitrate, and ferric sulfate, while the organic iron sources are ferrous acetate, ferric acetate, and ferric oxalate. The spinning polymer is polyacrylonitrile, with a mass concentration of 8% in the spinning solution. The stirring conditions for the electrospinning precursor solution are magnetic stirring at 70°C for 12 hours. The activator is polymethyl methacrylate, with an addition amount of 0.4% of the iron source mass. The solvent for wet dissolution is a mixture of ethanol, water, and DMF, with a mass ratio of DMF:ethanol:water = 8:1:1. The sodium sources are sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, and sodium silicate. The phosphorus sources are phosphorous acid, hypophosphoric acid, pyrophosphoric acid, and metaphosphoric acid. The carbon sources are citric acid and glucose, with a molar ratio of 0.8:1 to the iron source.

[0069] S2. Electrospinning: The electrospinning precursor solution obtained in step S1 is electrospinned to collect the precursor fiber membrane. Specifically, the electrospinning conditions are: spinning voltage 15 kV, receiving distance 15 cm, spinning solution propulsion speed 1.5 mL / h, and ambient humidity controlled at 30-50%.

[0070] S3. Pre-oxidation treatment: The fiber film precursor obtained in S2 is calcined to obtain a pre-oxidized precursor; specifically, the calcination conditions are: heating to 250°C at a heating rate of 3°C / min in air atmosphere and holding at that temperature for 2 hours.

[0071] S4. High-Temperature Calcination: The pre-oxidized precursor obtained in S3 is subjected to high-temperature calcination to obtain the final polyanionic sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are: nitrogen or argon as the protective gas, heating rate of the plastic is 6℃ / min, calcination temperature is 750℃, holding time is 5 hours, and cooling method is natural cooling to room temperature.

[0072] Application Example 1

[0073] This embodiment relates to a high-rate polyanionic sodium-ion battery cathode material, the preparation method of which includes the following steps:

[0074] S1. Preparation of electrospinning precursor solution: Sodium benzoate, ferric chloride, ferrous acetate, and aminotrimethylphosphonic acid were dissolved in an ethanol / water / DMF solvent at a Na:Fe:P molar ratio of 4:3:4. 0.4% (by weight of the iron source) of polymethyl methacrylate was added, and the mixture was stirred until completely dissolved. Then, a carbon source and polyvinylpyrrolidone powder were added to achieve a polyvinylpyrrolidone concentration of 10 wt%. The mixture was magnetically stirred in a water bath at 60-80℃ for 15 hours to obtain a uniform and transparent spinning solution.

[0075] S2. Electrospinning: The spinning voltage is 10-25 kV, the receiving distance is 10-20 cm, the spinning solution propulsion speed is 0.5-2 mL / h, and the ambient humidity is controlled at 30%-50%.

[0076] S3. Pre-oxidation treatment: Heat to 250°C in air at a rate of 3°C / min and hold for 2 hours. This sets the fiber and prevents it from melting during subsequent high-temperature treatment.

[0077] S4. High-temperature sintering: The pre-oxidized fiber membrane is transferred to a tube furnace and heated to 350°C at a rate of 5°C / min under argon protection and held for 2 hours. Then, the temperature is increased to 700°C at a rate of 2°C / min and held for 5 hours. The composite nanofiber material is obtained by natural cooling.

[0078] S. Full Cell Test: Using N-methylpyrrolidone (NMP) as the solvent, the conductive agents include SP and MWCNT; the active material is NFPP, and the binder is PVDF. A slurry was prepared according to the mass ratio of active material, binder, and conductive agent: NFPP:PVDF:SP:MWCNT = 94.5:3:1.5:1. The active material NFPP was added to the conductive adhesive in two batches (half each time), stirred until completely dispersed, and an appropriate amount of NMP was added to adjust the viscosity. The discharge viscosity was 5000CP-6000CP, and the slurry solid content was 54%-56%. The slurry was sieved and then coated onto a carbon-coated aluminum foil current collector, with a single-sided surface density of 100 g / m². 2 A sodium-ion battery positive electrode was obtained, and a negative electrode was prepared using hard carbon. 1 mol / L NaPF4 in DME was used as the electrolyte, and a PP / PE / PP three-layer separator was used. The above full cell was subjected to constant current and constant voltage charge-discharge tests, with a current density of 10C and a voltage range of 3.4-1.5 V.

[0079] Comparative Example 1 uses only inorganic iron source

[0080] This embodiment relates to anion-type sodium-ion battery cathode material, and its preparation method includes the following steps:

[0081] S1. Preparation of spinning solution: Sodium benzoate, ferric chloride, and aminotrimethylphosphonic acid were dissolved in an ethanol / water / DMF solvent at a Na:Fe:P molar ratio of 4:3:4. 0.4% (by weight of the iron source) of polymethyl methacrylate was added, and the mixture was stirred until completely dissolved. Then, a carbon source and polyvinylpyrrolidone powder were added to achieve a polyvinylpyrrolidone concentration of 10 wt%. The mixture was magnetically stirred in a water bath at 60-80℃ for 15 hours to obtain a uniform and transparent spinning solution.

[0082] S2. Electrospinning: The spinning voltage is 10-25 kV, the receiving distance is 10-20 cm, the spinning solution propulsion speed is 0.5-2 mL / h, and the ambient humidity is controlled at 30%-50%.

[0083] S3. Pre-oxidation treatment: Heat to 250°C in air at a rate of 3°C / min and hold for 2 hours. This sets the fiber and prevents it from melting during subsequent high-temperature treatment.

[0084] S4 High-Temperature Sintering: The pre-oxidized fiber membrane was transferred to a tube furnace and heated to 350°C at a rate of 5°C / min under argon protection and held for 2 hours. Subsequently, the temperature was increased to 700°C at a rate of 2°C / min and held for 5 hours. The composite nanofiber material was obtained by natural cooling.

[0085] S5. Full Cell Test: Using N-methylpyrrolidone (hereinafter referred to as NMP) as solvent, the conductive agents include SP and MWCNT; the active material is NFPP, and the binder is PVDF. A slurry is prepared according to the mass ratio of active material, binder, and conductive agent: NFPP:PVDF:SP:MWCNT = 94.5:3:1.5:1. The active material NFPP is added to the conductive adhesive in two batches (half each time), stirred until completely dispersed, and an appropriate amount of NMP is added to adjust the viscosity. The discharge viscosity is 5000CP-6000CP, and the slurry solid content is 54%-56%. The slurry is sieved and then coated onto a carbon-coated aluminum foil current collector with a single-sided surface density of 100 g / m². 2 A sodium-ion battery positive electrode was obtained, and a negative electrode was prepared using hard carbon. 1 mol / L NaPF4 in DME was used as the electrolyte, and a PP / PE / PP three-layer separator was used. The above full cell was subjected to constant current and constant voltage charge-discharge tests, with a current density of 10C and a voltage range of 3.4-1.5 V.

[0086] Comparative Example 2: Using only organic iron sources

[0087] This embodiment relates to anion-type sodium-ion battery cathode material, and its preparation method includes the following steps:

[0088] S1. Preparation of spinning solution: Sodium benzoate, ferrous acetate, and aminotrimethylphosphonic acid were dissolved in an ethanol / water / DMF solvent at a Na:Fe:P molar ratio of 4:3:4. 0.4% (by weight of the iron source) of polymethyl methacrylate was added, and the mixture was stirred until completely dissolved. Then, a carbon source and polyvinylpyrrolidone powder were added to achieve a polyvinylpyrrolidone concentration of 10 wt%. The mixture was magnetically stirred in a water bath at 60-80℃ for 15 hours to obtain a uniform and transparent spinning solution.

[0089] S2. Electrospinning: The spinning voltage is 10-25 kV, the receiving distance is 10-20 cm, the spinning solution propulsion speed is 0.5-2 mL / h, and the ambient humidity is controlled at 30%-50%.

[0090] S3. Pre-oxidation treatment: Heat to 250°C in air at a rate of 3°C / min and hold for 2 hours. This sets the fiber and prevents it from melting during subsequent high-temperature treatment.

[0091] S4. High-temperature sintering: The pre-oxidized fiber membrane is transferred to a tube furnace and heated to 350°C at a rate of 5°C / min under argon protection and held for 2 hours. Then, the temperature is increased to 700°C at a rate of 2°C / min and held for 5 hours. The composite nanofiber material is obtained by natural cooling.

[0092] S5. Full Cell Test: Using N-methylpyrrolidone (hereinafter referred to as NMP) as solvent, the conductive agents include SP and MWCNT; the active material is NFPP, and the binder is PVDF. A slurry is prepared according to the mass ratio of active material, binder, and conductive agent: NFPP:PVDF:SP:MWCNT = 94.5:3:1.5:1. The active material NFPP is added to the conductive adhesive in two batches (half each time), stirred until completely dispersed, and an appropriate amount of NMP is added to adjust the viscosity. The discharge viscosity is 5000CP-6000CP, and the slurry solid content is 54%-56%. The slurry is sieved and then coated onto a carbon-coated aluminum foil current collector with a single-sided surface density of 100 g / m². 2 A sodium-ion battery positive electrode was obtained, and a negative electrode was prepared using hard carbon. 1 mol / L NaPF4 in DME was used as the electrolyte, and a PP / PE / PP three-layer separator was used. The above full cell was subjected to constant current and constant voltage charge-discharge tests, with a current density of 10C and a voltage range of 3.4-1.5 V.

[0093] Comparative Example 3: Reducing the Amount of Surfactant Added

[0094] This embodiment relates to anion-type sodium-ion battery cathode material, and its preparation method includes the following steps:

[0095] S1. Preparation of spinning solution: Sodium benzoate, ferric chloride, ferrous acetate, and aminotrimethylphosphonic acid were dissolved in an ethanol / water / DMF solvent at a Na:Fe:P molar ratio of 4:3:4. 0.2% (by weight of the iron source) of polymethyl methacrylate was added, and the mixture was stirred until completely dissolved. Then, a carbon source and polyvinylpyrrolidone powder were added to achieve a polyvinylpyrrolidone concentration of 10 wt%. The mixture was magnetically stirred in a water bath at 60-80℃ for 15 hours to obtain a uniform and transparent spinning solution.

[0096] S2. Electrospinning: The spinning voltage is 10-25 kV, the receiving distance is 10-20 cm, the spinning solution propulsion speed is 0.5-2 mL / h, and the ambient humidity is controlled at 30%-50%.

[0097] S3. Pre-oxidation treatment: Heat to 250°C in air at a rate of 3°C / min and hold for 2 hours. This sets the fiber and prevents it from melting during subsequent high-temperature treatment.

[0098] S4. High-temperature sintering: The pre-oxidized fiber membrane is transferred to a tube furnace and heated to 350°C at a rate of 5°C / min under argon protection and held for 2 hours. Then, the temperature is increased to 700°C at a rate of 2°C / min and held for 5 hours. The composite nanofiber material is obtained by natural cooling.

[0099] S5. Full Cell Test: Using N-methylpyrrolidone (hereinafter referred to as NMP) as solvent, the conductive agents include SP and MWCNT; the active material is NFPP, and the binder is PVDF. A slurry is prepared according to the mass ratio of active material, binder, and conductive agent: NFPP:PVDF:SP:MWCNT = 94.5:3:1.5:1. The active material NFPP is added to the conductive adhesive in two batches (half each time), stirred until completely dispersed, and an appropriate amount of NMP is added to adjust the viscosity. The discharge viscosity is 5000CP-6000CP, and the slurry solid content is 54%-56%. The slurry is sieved and then coated onto a carbon-coated aluminum foil current collector with a single-sided surface density of 100 g / m². 2 A sodium-ion battery positive electrode was obtained, and a negative electrode was prepared using hard carbon. 1 mol / L NaPF4 in DME was used as the electrolyte, and a PP / PE / PP three-layer separator was used. The above full cell was subjected to constant current and constant voltage charge-discharge tests, with a current density of 10C and a voltage range of 3.4-1.5 V.

[0100] Comparative Example 4: Increase the amount of surfactant added

[0101] This embodiment relates to anion-type sodium-ion battery cathode material, and its preparation method includes the following steps:

[0102] S1. Preparation of spinning solution: Sodium benzoate, ferric chloride, ferrous acetate, and aminotrimethylphosphonic acid were dissolved in an ethanol / water / DMF solvent at a Na:Fe:P molar ratio of 4:3:4. 0.6% (by weight of the iron source) of polymethyl methacrylate was added, and the mixture was stirred until completely dissolved. Then, a carbon source and polyvinylpyrrolidone powder were added to achieve a polyvinylpyrrolidone concentration of 10 wt%. The mixture was magnetically stirred in a water bath at 60-80℃ for 15 hours to obtain a uniform and transparent spinning solution.

[0103] S2. Electrospinning: The spinning voltage is 10-25 kV, the receiving distance is 10-20 cm, the spinning solution propulsion speed is 0.5-2 mL / h, and the ambient humidity is controlled at 30%-50%.

[0104] S3. Pre-oxidation treatment: Heat to 250°C in air at a rate of 3°C / min and hold for 2 hours. This sets the fiber and prevents it from melting during subsequent high-temperature treatment.

[0105] S4. High-temperature sintering: The pre-oxidized fiber membrane is transferred to a tube furnace and heated to 350°C at a rate of 5°C / min under argon protection and held for 2 hours. Then, the temperature is increased to 700°C at a rate of 2°C / min and held for 5 hours. The composite nanofiber material is obtained by natural cooling.

[0106] S5. Full Cell Test: Using N-methylpyrrolidone (hereinafter referred to as NMP) as solvent, the conductive agents include SP and MWCNT; the active material is NFPP, and the binder is PVDF. A slurry is prepared according to the mass ratio of active material, binder, and conductive agent: NFPP:PVDF:SP:MWCNT = 94.5:3:1.5:1. The active material NFPP is added to the conductive adhesive in two batches (half each time), stirred until completely dispersed, and an appropriate amount of NMP is added to adjust the viscosity. The discharge viscosity is 5000CP-6000CP, and the slurry solid content is 54%-56%. The slurry is sieved and then coated onto a carbon-coated aluminum foil current collector with a single-sided surface density of 100 g / m². 2 A sodium-ion battery positive electrode was obtained, and a negative electrode was prepared using hard carbon. 1 mol / L NaPF4 in DME was used as the electrolyte, and a PP / PE / PP three-layer separator was used. The above full cell was subjected to constant current and constant voltage charge-discharge tests, with a current density of 10C and a voltage range of 3.4-1.5 V.

[0107] Comparative Example 5: No spinning polymer added.

[0108] This embodiment relates to anion-type sodium-ion battery cathode material, and its preparation method includes the following steps:

[0109] S1. Preparation of the first precursor: Sodium benzoate, ferric chloride, ferrous acetate, and aminotrimethylphosphonic acid were dissolved in an ethanol / water / DMF solvent at a Na:Fe:P molar ratio of 4:3:4. 0.4% (by weight of the iron source) of polymethyl methacrylate was added, and the mixture was stirred until completely dissolved. Then, a carbon source was added. The mixture was stirred in a water bath at 60-80°C for 15 hours to obtain a homogeneous and transparent solution.

[0110] S2. Spray drying: The first precursor is spray-dried using an airflow spray dryer with an inlet air temperature of 180℃ and an outlet air temperature of 110℃. This yields the second precursor.

[0111] S3. Sintering: Using a tube furnace under argon protection, the temperature was increased to 350℃ at a rate of 5℃ / min and held for 2 hours, then increased to 700℃ at a rate of 2℃ / min and held for 5 hours. Natural cooling was then performed to obtain NFPP.

[0112] S4. Full Cell Test: Using N-methylpyrrolidone (hereinafter referred to as NMP) as solvent, the conductive agents include SP and MWCNT; the active material is NFPP, and the binder is PVDF. A slurry is prepared according to the mass ratio of active material, binder, and conductive agent: NFPP:PVDF:SP:MWCNT = 94.5:3:1.5:1. The active material NFPP is added to the conductive adhesive in two batches (half each time), stirred until completely dispersed, and an appropriate amount of NMP is added to adjust the viscosity. The discharge viscosity is 5000CP-6000CP, and the slurry solid content is 54%-56%. The slurry is sieved and then coated onto a carbon-coated aluminum foil current collector with a single-sided surface density of 100 g / m². 2 A sodium-ion battery positive electrode was obtained, and a negative electrode was prepared using hard carbon. 1 mol / L NaPF4 in DME was used as the electrolyte, and a PP / PE / PP three-layer separator was used. The above full cell was subjected to constant current and constant voltage charge-discharge tests, with a current density of 10C and a voltage range of 3.4-1.5 V.

[0113] The performance test results of Application Example 1 and Comparative Examples 1-5 are shown in the table below:

[0114] Table 1. Reversible capacity retention after 200 cycles at 10C

[0115] Example number 10C cycle 200 cycle capacity retention rate (%) Example 1 93.82 Comparative Example 1 86.48 Comparative Example 2 87.69 Comparative Example 3 88.56 Comparative Example 4 90.32 Comparative Example 5 75.21

[0116] This invention proposes a method for preparing NFPP, a high-rate sodium-ion battery cathode material. Through process innovation and material design, its microstructure is optimized, improving the problem of low reversible capacity of NFPP at high rates. Its core advantage lies in the carbon fibers prepared by electrospinning technology, which can uniformly and densely encapsulate NFPP nanocrystals within its three-dimensional network structure (e.g., ...).Figure 1 (As shown). This unique core-shell composite configuration forms a continuous and stable conductive carbon layer on the surface of the active material particles, providing a low-resistance pathway for electron transport and constructing a three-dimensional interconnected "high-speed electron channel" throughout the electrode. Furthermore, the addition of polymethyl methacrylate leaves abundant, tunable-size nanopores within the composite fibers. These pores provide additional, low-resistance radial diffusion channels for electrolyte wetting and sodium ion transport, complementing the axial ion channels of the fibers themselves and constructing a three-dimensional ion conduction network. This reduces local current density, alleviates electrode polarization, and significantly improves the rate performance of the material, allowing it to maintain a high capacity even at high current densities (e.g., ...). Figure 2 (As shown). This provides a high-rate performance solution for sodium-ion batteries in large-scale start-stop systems and new energy vehicles.

[0117] Combined with Table 1 and Figures 1-4 As can be seen, comparing Application Example 1, Comparative Example 1, and Comparative Example 2, Application Example 1 exhibits the highest rate performance, followed by Comparative Example 2, while Comparative Example 1 shows the worst rate performance. This is due to the synergistic effect in Application Example 1, achieving a golden balance in electron-ion transport. At low temperatures, the organic iron source decomposes first, creating a reducing atmosphere and abundant organic fragments, laying the foundation for the formation of a porous, highly conductive carbon framework. At high temperatures, the inorganic iron source reacts precisely, providing a pure iron source that reacts precisely with phosphorus and sodium sources to generate pure-phase NFPP. Simultaneously, the gas generated from the decomposition of inorganic salts synergizes with the pores created by the organic source, further optimizing the hierarchical pore structure. At high rates, electrons and ions can reach the reaction interface synchronously and rapidly, greatly reducing electrochemical polarization and concentration polarization, thus resulting in the highest capacity retention. In Comparative Example 1, the thermal decomposition of inorganic iron salts (such as ferric nitrate) generates an oxidizing atmosphere (releasing NO). x This process is unfavorable for the formation of high-quality, highly graphitized carbon from carbon sources (such as PVP and citric acid). Carbonization mainly relies on externally added polymers (such as PVP), and the resulting carbon layer often lacks a tight bond with the inorganic oxide precursor, easily leading to discontinuous and uneven carbon coating. Therefore, the electron transport network is fragile, and at high rates (high currents), the charge transfer impedance is enormous, resulting in severe polarization and a sharp decrease in capacity. In Comparative Example 2, the decomposition of organic iron salts generates a strongly reducing atmosphere (CO, H2, etc.), which effectively catalyzes the graphitization of the carbon source, forming a carbon layer with good electronic conductivity, and the carbon is tightly bound to the active material. However, excessive, highly graphitized carbon may form an overly dense outer shell. While this shell has good conductivity, it severely hinders electrolyte wetting and the insertion / extraction of sodium ions (i.e., ion transport).

[0118] As shown in Table 1, the addition of 0.2% polymethyl methacrylate (PMMA) in Comparative Example 3 resulted in insufficient number of voids after thermal decomposition, leading to poor connectivity. Ion transport within the fiber still relied on limited inherent voids and interfiber gaps, resulting in high ion diffusion resistance. During high-rate discharge, the ion replenishment rate was lower than the electron injection rate, leading to concentration polarization, a drop in voltage plateau, and incomplete capacity release. Comparative Example 4, using 0.6% PMMA, showed a decreased ability to buffer volume changes during charge and discharge, making the fiber more prone to breakage or pulverization under long-term cycling. Furthermore, excessive PMMA could cause excessively large pores or the formation of closed pores, preventing some pores from being effectively filled by the electrolyte.

[0119] Combined with Table 1 and Figures 1-4 As can be seen, comparing Application Example 1 and Comparative Example 5, the fundamental reason why Application Example 1's rate performance is far superior to Comparative Example 5 is that electrospinning directly constructs a macroscopically ordered microstructure with rapid mass and charge transfer channels. One-dimensional nanofibers and three-dimensional interconnected networks are fundamental solutions to the transport problem from a physical perspective. Drying spray aims to prepare smaller, more uniform particles and improve surface coating. However, its zero-dimensional nature determines the inherent bottleneck of electron and ion transport.

[0120] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-rate polyanionic sodium-ion battery cathode material, characterized in that... Includes the following steps: S1. Preparation of electrospinning precursor solution: Sodium source, mixed iron source and phosphorus source are wet-dissolved and added to spinning polymer, carbon source and activator, and stirred to form electrospinning precursor solution; S2. Electrospinning: The electrospinning precursor solution obtained in step S1 is electrospinned, and the precursor fiber membrane is collected. S3. Pre-oxidation treatment: The fiber film precursor obtained in S2 is calcined to obtain the pre-oxidized precursor. S4. High-temperature calcination: The pre-oxidized precursor obtained in S3 is calcined at high temperature to obtain the final polyanionic sodium-ion battery cathode material.

2. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S1, the mixed iron source includes an inorganic iron source and an organic iron source. The molar ratio of iron ions in the inorganic iron source to the molar ratio of iron ions in the organic iron source is 1:

1. The inorganic iron source is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous bromide, ferric chloride, ferric nitrate, ferric sulfate, ferric perchlorate, and ferric bromide. The organic iron source is one or more of ferrous acetate, ferric acetate, and ferric oxalate.

3. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 2, characterized in that: In step S1, the spinning polymer is polyvinylpyrrolidone and / or polyacrylonitrile, and its mass concentration in the spinning solution is 5-15%.

4. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 3, characterized in that: In step S1, the activator is polymethyl methacrylate, and its addition amount is 0.3-0.5% of the iron source mass.

5. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S1, the solvent for wet dissolution is a mixture of ethanol, water, and DMF, wherein the mass ratio of DMF:ethanol:water is 8:1:

1.

6. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S2, the conditions for electrospinning are: spinning voltage 10-25 kV, receiving distance 10-20 cm, spinning solution propulsion speed 0.5-2 mL / h, and ambient humidity controlled at 30-50%.

7. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S3, the calcination conditions are as follows: the temperature is increased to 200-300℃ at a heating rate of 1-5℃ / min in an air atmosphere, and held for 1-3 hours.

8. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S4, the conditions for high-temperature calcination are as follows: the protective gas is nitrogen or argon, the temperature of the plastic is increased by 4-7℃ / min, the calcination temperature is 600-800℃, the holding time is 3-6 hours, and the cooling method is natural cooling to room temperature.

9. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S1, the stirring conditions for the electrospinning precursor solution are: magnetic stirring at 60-80℃ for more than 12 hours.

10. The method for preparing high-rate polyanionic sodium-ion battery cathode material according to claim 1, characterized in that: In step S1, the sodium source is one or more of sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, sodium silicate, sodium acetate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, sodium oxalate, sodium benzoate, sodium citrate, sodium thiosulfate, sodium borohydride, sodium methoxide, sodium ethoxide, sodium stearate, monosodium glutamate, sodium perchlorate, and sodium valproate; the phosphorus source is one or more of triethylphosphine, aminotrimethylphosphonic acid, hydroxyethylidene diphosphate, phosphoric acid, triphenylphosphine, triethyl phosphate, triphenyl phosphate, adenosine triphosphate, glyphosate, triphenylphosphine oxide, tri(chloroisopropyl) phosphate, tetraethyl pyrophosphate, phospholipid, hexamethylphosphoric acid triamine, phosphorous acid, hypophosphite, pyrophosphate, and metaphosphoric acid; the carbon source is citric acid, glucose, or polyethylene glycol, and the molar ratio of the carbon source to the iron source is (0.5-2):1.

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