Single-atom catalytic conductive carbon network enhanced sodium ferric sulfate positive electrode material and preparation method thereof

Abstract

The application discloses a single-atom catalytic conductive carbon network reinforced sodium ferric sulfate positive electrode material and a preparation method thereof. The material is composed of sodium ferric sulfate active material particles and single-atom catalyst doped conductive carbon network embedded therein. The conductive carbon network is a carbon nanotube co-doped with non-metallic elements. The non-metallic elements are at least two of nitrogen, sulfur and phosphorus. The single-atom catalyst is one or more metal atoms selected from iron, copper, nickel, cobalt and manganese. The metal atoms are coordinated with the non-metallic elements and anchored on the doped carbon nanotube in the form of single atoms. The multi-element doping significantly improves the electronic conductivity of the carbon nanotube, the single-atom catalytic site accelerates the ion migration rate, and the interface impedance is significantly reduced. The composite positive electrode material prepared by the application has high reversible capacity, super-long cycle life (0.5C, capacity retention rate > 88% after 500 cycles), and significantly improved electrochemical performance, and has a high commercial application prospect.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials, and in particular to a sodium iron sulfate cathode material reinforced with a single-atom catalytic conductive carbon network and its preparation method. Background Technology

[0002] With the rapid growth of global demand for renewable energy and large-scale energy storage systems, sodium-ion batteries have become an important alternative to lithium-ion batteries due to their advantages such as abundant sodium resources, low cost, and environmental friendliness. Among the many sodium-ion battery cathode material systems, polyanionic materials, especially sodium iron sulfate (Na2Fe2(SO4)3, NFS), have a relatively high theoretical capacity (approximately 100-120 mAh / g) and a suitable operating voltage (approximately 3.6 V vs. Na2Fe2(SO4)3). + It has attracted widespread attention due to its good thermal stability (Na) and other properties.

[0003] However, the practical application of NFS materials faces two major technical bottlenecks: First, their intrinsic electronic conductivity is extremely low (<10). -10 The first issue is the slow electrode reaction kinetics due to the reduced efficiency (S / cm). Secondly, the large phase transition impedance caused by changes in material structure during sodium ion insertion / extraction limits its rate performance and cycle stability. While traditional carbon coating modification methods can improve electronic conductivity to some extent, simple physical mixing makes it difficult to establish an efficient three-dimensional conductive network, and the interfacial impedance between the carbon layer and the active material remains relatively high.

[0004] Single-atom catalysts (SACs) exhibit exceptional activity in catalysis due to their high atomic utilization and unique electronic structure. Introducing the concept of single-atom catalysis into battery electrode materials aims to utilize single-atom sites to modulate the interfacial electronic structure of the electrode material, catalyzing the electrode reaction process, lowering the reaction energy barrier, and thus significantly enhancing reaction kinetics. However, how to precisely introduce single-atom catalytic sites into the NFS cathode material system and achieve a strong coupling synergistic effect with the conductive network and active material remains a crucial technical challenge to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a single-atom catalytically enhanced NFS composite cathode material with high capacity, excellent rate performance and long cycle life, thereby solving the problems of low electronic conductivity and slow reaction kinetics of existing NFS materials.

[0006] The technical solution adopted in this invention is: A single-atom catalytic conductive carbon network enhanced sodium ferric sulfate cathode material, the material being composed of sodium ferric sulfate active material particles and a conductive carbon network doped with a single-atom catalyst embedded therein; The conductive carbon network is a carbon nanotube co-doped with at least two non-metallic elements, namely nitrogen, sulfur, and phosphorus. The single-atom catalyst is one or more metal atoms selected from iron, copper, nickel, cobalt, and manganese.

[0007] Furthermore, the total content of the non-metallic elements in the carbon nanotubes is 1-10 at%, preferably 3-7 at%.

[0008] Furthermore, the loading of metal atoms on the carbon nanotubes is 0.5-5 wt%, preferably 1-3 wt%.

[0009] The mass fraction of conductive carbon network in single-atom catalytic conductive carbon network-reinforced sodium ferric sulfate cathode material is 1-5%.

[0010] Furthermore, the metal atoms coordinate with the doped non-metallic elements and are anchored on the doped carbon nanotubes in single-atom form. Specifically, the metal atoms and the doped non-metallic elements form MN x MS x or MP x Coordination structure, where x = 2-4, and M represents a metal atom.

[0011] The carbon nanotubes have 1 to 20 layers, a diameter of 1 to 100 nm, and an aspect ratio of 50 to 10000.

[0012] In this invention, the conductive carbon network doped with a single-atom catalyst not only serves as an electron conduction channel in the composite material, but its surface metal single-atom sites also serve as catalytic centers, effectively catalyzing the sodium ion insertion / extraction reaction on the surface of the NFS material and accelerating the reaction kinetics.

[0013] The single-atom catalytic conductive carbon network-reinforced sodium ferric sulfate cathode material of the present invention can be prepared by the following method: (1) Carbon nanotubes are mixed with organic compounds containing nitrogen, sulfur and phosphorus as doping sources and subjected to high-temperature heat treatment under an inert atmosphere to obtain non-metallic element-doped carbon nanotubes. (2) Non-metallic element-doped carbon nanotubes are mixed with a metal salt solution, and then subjected to adsorption, solid-liquid separation, drying and secondary heat treatment to obtain single-atom catalyst-doped carbon nanotubes; the metal salt is one or more of the soluble metal salts of iron, copper, nickel, cobalt and manganese. (3) The carbon nanotubes doped with single-atom catalysts are mixed with ferrous sulfate and sodium sulfate in stoichiometric ratio, and then dry ball milled and calcined to obtain a single-atom catalytic conductive carbon network reinforced sodium ferric sulfate cathode material.

[0014] In step (1), the organic compound doping source containing nitrogen, sulfur, and phosphorus is one or more of melamine (nitrogen source), thiourea (nitrogen-sulfur source), cysteine ​​(nitrogen-sulfur source), phytic acid (phosphorus source), and phenylphosphonic acid (phosphorus source), and the organic compound doping source containing nitrogen, sulfur, and phosphorus includes at least two non-metallic elements among nitrogen, sulfur, and phosphorus.

[0015] In step (1), the mass ratio of carbon nanotubes to organic compound dopant sources containing nitrogen, sulfur, and phosphorus is 1:0.1~1.0, and the total content of non-metallic elements in carbon nanotubes after doping is 1-10 at.

[0016] The mass ratio of nitrogen-, sulfur-, and phosphorus-containing organic compound dopant sources to carbon nanotubes was determined after extensive experimental optimization, and is an effective ratio that can achieve the doping level described in this invention (i.e., total doping amount of 1-10 at%, preferably 3-7 at%). Due to factors such as precursor decomposition, element incorporation efficiency, and high-temperature volatility, the percentage of doped atoms (at%) in the final product is not simply calculated directly from the mass ratio.

[0017] Furthermore, in step (1), the heat treatment temperature is 600-1000℃, and the holding time is 1-5 hours. The heating rate is preferably 1-10℃ / min.

[0018] The inert atmosphere is generally nitrogen, argon, or a mixture thereof.

[0019] In step (2), the metal salt includes one or more nitrates, chlorides or acetylacetone salts of iron, copper, nickel, cobalt and manganese; preferably ferric nitrate, copper nitrate or nickel nitrate.

[0020] In step (2), the mass ratio of metal elements to non-metal element-doped carbon nanotubes in the metal salt is 0.01-0.2:1. In step (2), non-metal element-doped carbon nanotubes are mixed with the metal salt solution. However, metal ions in the metal salt solution generally cannot be completely adsorbed onto the non-metal element-doped carbon nanotubes, leaving some metal ions in the solution. Therefore, the amount of material added was determined after multiple experimental verifications, so that after the second heat treatment, the loading of metal atoms on the carbon nanotubes in the final single-atom catalyst-doped carbon nanotubes is 0.5-5 wt%.

[0021] The concentration of the metal salt solution is 0.001~0.1 mol / L, preferably 0.01~0.02 mol / L.

[0022] Non-metallic element-doped carbon nanotubes are generally first dispersed in a solvent and then mixed with a metal salt solution. The solvent is generally one or more of water, ethanol, and isopropanol. A uniform dispersion of non-metallic element-doped carbon nanotubes is generally obtained by ultrasonic treatment.

[0023] The concentration of non-metallic element-doped carbon nanotube dispersions is generally 0.1-5 mg / mL.

[0024] In step (2), the adsorption temperature is 20-80℃ and the adsorption time is 2-24 hours.

[0025] After adsorption, solid-liquid separation is generally performed by centrifugation or filtration to separate the solid, washing with solvent, and vacuum drying at 60-100℃ for 6-24 hours.

[0026] The secondary heat treatment temperature is 500-900℃, and the holding time is 1-4 hours. The heating rate is 1-5℃ / min.

[0027] The secondary heat treatment is carried out in an inert atmosphere or a reducing atmosphere, wherein the reducing atmosphere is a mixture of argon and hydrogen, and the volume fraction of hydrogen is 1-10%, preferably 5-10%.

[0028] In step (2), metal ions are reduced and anchored to the carbon nanotubes in the form of single atoms in the single-atom catalyst-doped carbon nanotubes.

[0029] Generally, under an inert atmosphere, the reducing properties of non-metallic element-doped carbon nanotubes and precursor metal salts are sufficient to reduce metal ions and coordinate with heteroatoms on the carbon support to form stable single-atom sites. Those skilled in the art can also choose to perform a secondary heat treatment in a reducing atmosphere containing a small amount of hydrogen, depending on the chemical properties of the selected precursor metal salt; this also falls within the scope of protection of this invention.

[0030] In step (3), sodium sulfate and ferrous sulfate are added according to the chemical formula Na 2+2x Fe 2-x The (SO4)3 feed ratio is (2+2x):(2-x), 0≤x≤1.

[0031] In step (3), the carbon nanotubes doped with single-atom catalyst account for 1-5% of the total mass of all raw materials, preferably 3-5%.

[0032] In step (3), the ball milling speed is 200-500 r / min and the ball milling time is 6-24 hours.

[0033] The calcination is carried out under an inert atmosphere at a temperature of 300-500℃ for 4-12 hours. The heating rate is 1-5℃ / min.

[0034] After calcination, the material is ground and sieved (300-500 mesh) to obtain a sodium ferric sulfate cathode material with a single-atom catalytic conductive carbon network.

[0035] This invention also provides a method for preparing a single-atom catalytic conductive carbon network-enhanced sodium ferric sulfate cathode material, the method comprising the following steps: (1) Carbon nanotubes are mixed with organic compounds containing nitrogen, sulfur and phosphorus as dopants and heat-treated at high temperature under an inert atmosphere to obtain non-metallic element-doped carbon nanotubes (denoted as NSP-CNT). (2) Non-metallic element-doped carbon nanotubes are mixed with a metal salt solution, and then subjected to adsorption, solid-liquid separation, drying and secondary heat treatment to obtain single-atom catalyst-doped carbon nanotubes; the metal salt is one or more of the soluble salts of iron, copper, nickel, cobalt and manganese (denoted as M-NSP-CNT). (3) The carbon nanotubes doped with single-atom catalysts are mixed with ferrous sulfate and sodium sulfate in stoichiometric ratio, and then dry ball milled and calcined to obtain a single-atom catalytic conductive carbon network reinforced sodium ferric sulfate cathode material.

[0036] This invention also provides the application of single-atom catalytic conductive carbon network-enhanced sodium iron sulfate cathode materials in the preparation of sodium-ion batteries. It is particularly suitable for preparing high-power, long-life sodium-ion batteries.

[0037] The present invention also provides a sodium-ion battery comprising the aforementioned single-atom catalytically enhanced sodium iron sulfate composite cathode material.

[0038] Furthermore, the sodium-ion battery has an initial discharge specific capacity of ≥90 mAh / g at 0.1C, a capacity retention rate of ≥95% after 100 cycles at 0.5C, and a capacity retention rate of ≥88% after 500 cycles.

[0039] This invention provides a novel single-atom catalytic conductive carbon network-enhanced NFS cathode material. It involves multi-element doping of carbon nanotubes (N, S, P, etc.) and anchoring single metal atoms such as Fe, Cu, and Ni to form a catalytically active conductive network, which is then composited with the NFS active material. This invention significantly improves the conductivity and electrochemical performance of the NFS cathode material through multi-element doping of carbon nanotubes and the construction of single-atom catalytic sites.

[0040] The mechanism by which the single-atom catalytic conductive carbon network enhances the electrical performance of the NFS cathode material of the present invention is as follows: 1. Enhanced electronic conduction: Multi-element doping significantly improves the electronic conductivity of carbon nanotubes, forming a highly efficient three-dimensional electronic conduction network.

[0041] 2. Accelerated ion diffusion: Single-atom catalytic sites can polarize SO4. 2- Polyanionic groups weaken Na + The binding energy between the crystal lattice and Na is reduced. + The diffusion barrier accelerates ion migration rates.

[0042] 3. Improved interfacial kinetics: Single-atom sites, acting as catalytic centers, effectively promote the charge transfer process at the electrode / electrolyte interface, significantly reducing interfacial impedance.

[0043] 4. Improved structural stability: The strong coupling between the robust carbon network and NFS particles suppresses particle pulverization and phase separation during cycling, ensuring the structural integrity of the electrode.

[0044] The beneficial effects of this invention are as follows: 1. Dual Functions of Conductivity and Catalysis: Doping with multiple elements such as N, S, and P not only improves the electronic conductivity of carbon nanotubes (reaching 100-500 S / m), but also creates numerous defect sites for anchoring metal single atoms. These single-atom sites (such as Fe-N4 and Cu-N4) can effectively regulate the charge distribution on the surface of NFSF particles, significantly reducing Na+ as catalytic centers. + The energy barrier of the insertion / extraction process (which can be reduced by 0.1-0.3 eV) accelerates the electrode reaction kinetics.

[0045] 2. Enhanced interfacial coupling: Through optimized dry ball milling and calcination processes, M-NSP-CNTs are brought into full contact with NFS precursors and participate in the reaction process. While NFS particles are generated in situ, they form a tight interfacial coupling and a stable three-dimensional conductive network. The interfacial impedance is reduced by 50-70% compared to traditional carbon coating.

[0046] 3. Improved electrochemical performance: The composite cathode material prepared in this invention exhibits high reversible capacity (up to 100-105 mAh / g at 0.1C, of ​​which Na...) 2.5 Fe 1.75 (SO4)3 material has a theoretical specific capacity of 106 mAh / g and an ultra-long cycle life (capacity retention rate >88% after 500 cycles at 0.5C), and its overall performance far exceeds that of traditional carbon-coated NFS materials.

[0047] 4. Simple preparation process: The raw materials used in the method of this invention are readily available, the process is simple, the parameters are controllable, no complex equipment is required, it is easy to achieve large-scale production, and it has a high prospect for commercial application. Attached Figure Description

[0048] Figure 1 The charge-discharge cycle diagram shows the Fe-SAC@NFS assembled sodium-ion battery prepared in Example 1.

[0049] Figure 2 Charge-discharge cycle diagram of the sodium-ion battery assembled by CNT@NFS prepared for Comparative Example 1.

[0050] Figure 3Charge-discharge cycle diagram of the sodium-ion battery assembled from pure-phase NFS prepared for Comparative Example 2.

[0051] Figure 4 Charge-discharge cycle diagram of the NTP-CNT@NFS assembled sodium-ion battery prepared for Comparative Example 3.

[0052] Figure 5 The charge-discharge cycle diagram is shown for the Cu-SAC@NFS assembled sodium-ion battery prepared in Example 2.

[0053] Figure 6 The charge-discharge cycle diagram shows the Ni-SAC@NFS assembled sodium-ion battery prepared in Example 3. Detailed Implementation

[0054] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0055] Example 1: Iron Single-Atom Catalyst Composite NaFeSO4 Cathode Material Step 1: Preparation of N, S, P multi-element doped carbon nanotubes (NSP-CNTs) Weigh 2g of multi-walled carbon nanotubes (outer diameter 10-20nm, length 10-30μm), 400mg of thiourea (providing N and S), and 200mg of phytic acid (providing P) and grind them thoroughly in an agate mortar for 60 min. Place the ground mixture in a tube furnace and heat it to 800℃ at a heating rate of 5℃ / min under an argon atmosphere (flow rate 100 sccm), hold it at that temperature for 2 hours, and then allow it to cool naturally to room temperature. The resulting black powder is N, S, P co-doped carbon nanotubes (NSP-CNTs). X-ray photoelectron spectroscopy (XPS) analysis showed that the atomic percentages of the doping elements in the obtained NSP-CNTs were: N 3.2 at%, S 1.8 at%, P 0.9 at%, and the total doping element content was 5.9 at%.

[0056] Step 2: Preparation of iron single-atom anchored NSP-CNT (Fe-NSP-CNT) 1 g of the NSP-CNT prepared in step one was dispersed in 1000 ml of ethanol and sonicated for 1 hour to form a uniform dispersion. 200 ml of a 0.01 mol / L ferric nitrate ethanol solution was added (the theoretical maximum iron loading is 11.2 wt% based on the precursor), and the mixture was stirred in a 40°C water bath for 12 hours to allow for sufficient iron ion adsorption. The mixture was centrifuged (8000 rpm, 10 min), washed three times with ethanol, and vacuum dried at 60°C for 12 hours. The dried sample was placed in a tube furnace and heated to 700°C at a rate of 5°C / min under an argon atmosphere (containing 5% hydrogen) and held for 2 hours. After natural cooling, iron-anchored NSP-CNTs (Fe-NSP-CNTs) were obtained. Inductively coupled plasma optical emission spectroscopy (ICP-OES) determined the actual iron loading in the material to be 2.1 wt%. AC-STEM characterization showed that iron was dispersed in single-atom form, with no nanoparticle formation.

[0057] Step 3: Synthesis of composite cathode materials Weigh out the following materials according to stoichiometric ratio: Na₂SO₄ (3.55 g), FeSO₄·H₂O (5.95 g), and Fe-NSP-CNT prepared in step two (0.5 g, accounting for 5 wt% of the total mass). Place the above materials into a planetary ball mill (500 ml tank volume, zirconium oxide grinding balls, ball-to-material ratio 30:1) and dry ball mill at 300 r / min for 12 hours. Transfer the ball-milled mixture to an alumina crucible and heat it to 370 °C at 5 °C / min under an argon atmosphere and hold for 12 hours. After natural cooling, remove the product. Grind the calcined product and pass it through a 400-mesh sieve to obtain the final Fe-SAC@NFS composite cathode material.

[0058] Comparative Example 1: Traditional carbon composite NFS materials No non-metallic element doping or single-atom anchoring was performed. Steps one and two were omitted, and Fe-NSP-CNT in step three was replaced with ordinary CNT (0.5g), which was directly ball-milled and mixed with NFS precursor (Na2SO4 (3.55g), FeSO4·H2O (5.95g, according to the proportion of Example 1) and then calcined. The carbon content was kept the same as in Example 1 (5wt%), and the process parameters were the same as in Example 1 to obtain CNT@NFS composite material.

[0059] Comparative Example 2: Pure NFS material without carbon additives Na2SO4 and FeSO4·H2O were weighed according to the stoichiometric ratio in step three of Example 1. Without adding any carbon materials, they were directly ball-milled and mixed, and then calcined to obtain pure NFS material.

[0060] Comparative Example 3 No single-atom anchoring is performed.

[0061] The same steps as in Example 1 were followed to obtain NSP-CNT. Step 2 was omitted, and Fe-NSP-CNT in Step 3 was replaced with NSP-CNT. The feeding ratio and process parameters were the same as in Example 1 to obtain NSP-CNT@NFS composite material.

[0062] Example 2: Copper Single-Atom Catalyst Composite NaFeSO4 Cathode Material The preparation steps are the same as in Example 1, except that in step two, copper nitrate solution of equal molar concentration is used instead of iron nitrate solution to finally obtain Cu-NSP-CNT and Cu-SAC@NFS composite cathode materials.

[0063] Example 3: Nickel single-atom catalytic composite NaFeSO4 cathode material The preparation steps are the same as in Example 1, except that in step two, nickel nitrate solution of equal molar concentration is used instead of iron nitrate solution to finally obtain Ni-NSP-CNT and Ni-SAC@NFS composite cathode materials.

[0064] Performance testing: The materials prepared in Examples 1-3 and Comparative Examples 1-3 were used as the positive electrode active material (80%), supplemented with Super P conductive carbon black (10%) and PVDF binder (10%) to form an electrode sheet. A sodium metal sheet was used as the counter electrode, and a glass fiber membrane was used as the separator. A CR2032 coin cell sodium-ion battery was assembled for testing. The electrolyte was a 1M NaClO4 EC / PC (1:1 v / v) solution with 5% FEC additive. All batteries were tested at 25°C. The charge-discharge cycle diagram is shown below. Figures 1-5 As shown in Table 1, the statistical results are presented.

[0065] Table 1: Electrochemical properties of NFS cathode materials

[0066] The results show that the Fe-SAC@NFS prepared in Examples 1, 2 and 3 of the present invention has an initial discharge specific capacity of ≥90mAh / g at 0.1C and excellent cycling performance, maintaining more than 89% of the capacity after 500 cycles.

[0067] Comparative Example 2, made of pure NFS, exhibited poor electrical properties. Comparative Example 1, a traditional carbon nanotube composite modification, showed improved electrical properties compared to Comparative Example 2. However, due to the lack of doping and single-atom anchoring of the carbon nanotubes, its initial discharge specific capacity and cycle performance at 0.1C were significantly inferior to those of the Example 1. Comparative Example 3 underwent multi-element doping with N, S, and P, but without single-atom anchoring. While its electrical properties were improved compared to Comparative Example 1, they were still inferior to those of Example 1, which featured single-atom anchoring.

Claims

1. A single-atom catalytic conductive carbon network-enhanced sodium ferric sulfate cathode material, characterized in that... The material is composed of sodium ferric sulfate active material particles and a conductive carbon network doped with a single-atom catalyst embedded therein. The conductive carbon network is a carbon nanotube co-doped with non-metallic elements; the non-metallic elements are at least two of nitrogen, sulfur, and phosphorus. The single-atom catalyst is one or more metal atoms selected from iron, copper, nickel, cobalt, and manganese.

2. The single-atom catalytic conductive carbon network-enhanced sodium ferric sulfate cathode material as described in claim 1, characterized in that... The total content of non-metallic elements in carbon nanotubes is 1-10 at, and the loading of metal atoms on carbon nanotubes is 0.5-5 wt%; the mass fraction of conductive carbon network in single-atom catalytic conductive carbon network reinforced sodium iron sulfate cathode material is 1-5%.

3. The single-atom catalytic conductive carbon network-enhanced sodium ferric sulfate cathode material as described in claim 1, characterized in that... Metal atoms coordinate with doped non-metallic elements and are anchored on doped carbon nanotubes in the form of single atoms.

4. The single-atom catalytic conductive carbon network-reinforced sodium ferric sulfate cathode material as described in any one of claims 1 to 3 is prepared by the following method: (1) Carbon nanotubes are mixed with organic compounds containing nitrogen, sulfur and phosphorus as doping sources and subjected to high-temperature heat treatment under an inert atmosphere to obtain non-metallic element-doped carbon nanotubes. (2) Non-metallic element-doped carbon nanotubes are mixed with a metal salt solution, and then subjected to adsorption, solid-liquid separation, drying and secondary heat treatment to obtain single-atom catalyst-doped carbon nanotubes; the metal salt is one or more of the soluble metal salts of iron, copper, nickel, cobalt and manganese. (3) The carbon nanotubes doped with single-atom catalysts are mixed with ferrous sulfate and sodium sulfate in stoichiometric ratio, and then dry ball milled and calcined to obtain a single-atom catalytic conductive carbon network reinforced sodium ferric sulfate cathode material.

5. The method for preparing the single-atom catalytic conductive carbon network enhanced sodium ferric sulfate cathode material according to any one of claims 1 to 3, characterized in that... The method is as follows: (1) Carbon nanotubes are mixed with organic compounds containing nitrogen, sulfur and phosphorus as doping sources and subjected to high-temperature heat treatment under an inert atmosphere to obtain non-metallic element-doped carbon nanotubes. (2) Non-metallic element-doped carbon nanotubes are mixed with a metal salt solution, and then subjected to adsorption, solid-liquid separation, drying and secondary heat treatment to obtain single-atom catalyst-doped carbon nanotubes; the metal salt is one or more of the soluble metal salts of iron, copper, nickel, cobalt and manganese. (3) The carbon nanotubes doped with single-atom catalysts are mixed with ferrous sulfate and sodium sulfate in stoichiometric ratio, and then dry ball milled and calcined to obtain a single-atom catalytic conductive carbon network reinforced sodium ferric sulfate cathode material.

6. The method as described in claim 5, characterized in that... In step (1), the organic compound doping source containing nitrogen, sulfur, and phosphorus is one or more of melamine, thiourea, cysteine, phytic acid, and phenylphosphonic acid, and the organic compound doping source containing nitrogen, sulfur, and phosphorus includes at least two non-metallic elements among nitrogen, sulfur, and phosphorus. In step (2), the metal salt includes one or more nitrates, chlorides or acetylacetone salts of iron, copper, nickel, cobalt and manganese.

7. The method as described in claim 5, characterized in that... In step (1), the heat treatment temperature is 600-1000℃ and the holding time is 1-5 hours; In step (2), the secondary heat treatment temperature is 500-900℃ and the holding time is 1-4 hours; The secondary heat treatment is carried out under an inert atmosphere or a reducing atmosphere, wherein the reducing atmosphere is a mixture of argon and hydrogen, and the volume fraction of hydrogen is 1-10%.

8. The method as described in claim 5, characterized in that... In step (3), sodium sulfate and ferrous sulfate are added according to the chemical formula Na 2+2x Fe 2-x The proportion of (SO4)3 is as follows: the molar ratio of Na to Fe is (2+2x):(2-x), 0≤x≤1; the carbon nanotubes doped with single-atom catalyst account for 1-5% of the total mass of all raw materials; in step (3), calcination is carried out under an inert atmosphere, the calcination temperature is 300-500℃, and the holding time is 4-12 hours.

9. The application of the single-atom catalytic conductive carbon network enhanced sodium iron sulfate cathode material as described in any one of claims 1 to 4 in the preparation of sodium-ion batteries.

10. A sodium-ion battery comprising the single-atom catalytically enhanced sodium iron sulfate composite cathode material as described in any one of claims 1 to 4, having an initial discharge specific capacity ≥90 mAh / g at 0.1C, a capacity retention rate ≥95% after 100 cycles at 0.5C rate, and a capacity retention rate ≥88% after 500 cycles.

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