Preparation method and application of copper-iron sulfide nitrogen-doped porous carbon composite material

Abstract

The application relates to the technical field of sodium ion battery negative electrode materials, and discloses a preparation method and application of a copper-iron sulfide / nitrogen-doped porous carbon composite material, which comprises the following steps: (1) mixing copper salt, potassium ferricyanide, a nitrogen source and polyethylene glycol, and obtaining a copper-iron Prussian blue precursor after ball milling; (2) pyrolyzing the copper-iron Prussian blue precursor under an inert atmosphere, washing and removing impurities, and drying to obtain an intermediate product; and (3) heat-treating the intermediate product and a sulfur source under an inert atmosphere to obtain a copper-iron sulfide / nitrogen-doped porous carbon composite material. Through the synergistic effect of the double-metal sulfide and the nitrogen-doped porous carbon composite, sodium ions with a larger ion radius can be more easily embedded and de-embedded in the interlayer spacing, meanwhile, abundant active sites are provided to enhance ion storage, so that the sodium ion battery has outstanding rate performance and stable cycle performance.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, and more specifically relates to a method for preparing and applying a copper-iron sulfide nitrogen-doped porous carbon composite material. Background Technology

[0002] With the accelerating pace of global energy transition, limited lithium reserves constrain the large-scale energy storage applications of lithium-ion batteries (LIBs) in the future, making the exploration of alternatives to LIBs crucial. Sodium-ion batteries (SIBs) have attracted widespread attention due to their similar working mechanism to lithium-ion batteries, low cost, and abundant resources. However, due to the large Na+ radius, traditional graphite anode materials cannot meet the requirements for high sodium storage capacity. Research based on LIB anode materials is not suitable for SIBs. Therefore, exploring and developing novel anode materials that match cathode materials and possess excellent performance has significant research and application value. Currently, electrode materials are developing towards a combination of high reversible specific capacity and high cycle stability, thereby improving the energy density, cycle life, and fast-charging capabilities of SIBs.

[0003] Transition metal sulfides have become a hot research topic in SIB (Sodium-ion Battery) anode materials due to their excellent theoretical specific capacity and abundant active sites. Compared with single metal sulfides, bimetallic sulfides can generate synergistic effects between heterojunctions, while also possessing lower band gaps and higher electronic / ionic conductivity, attracting widespread attention in the energy storage field. However, in sodium-ion batteries, the volume changes of transition metal sulfide electrode materials are relatively significant due to the continuous conversion / alloying reaction mechanism of sodium storage and release. To address these issues, constructing heterojunctions based on bimetallic sulfides can not only effectively improve the structural and electrochemical stability of transition metal sulfides, but also facilitate the acceleration of electron / ion transport in the electrode material.

[0004] However, to date, traditional preparation methods, such as Chinese patent CN110289416A, have yielded a bismuth-molybdenum oxide precursor via a solvothermal process, followed by annealing to obtain Mo7S8 / Bi2S3 nanomaterials. The bismuth-molybdenum bimetallic sulfide prepared in this patent, when used as an electrode in a sodium-ion battery, exhibits high cycle stability and superior long-cycle performance. However, its synthesis conditions are typically quite demanding, requiring high temperature, high pressure, and long reaction times. This not only increases the energy consumption and cost of material preparation but also poses certain safety risks, limiting its practical application. Summary of the Invention

[0005] The main objective of this invention is to address the aforementioned problems by providing a method for preparing and applying a copper-iron sulfide nitrogen-doped porous carbon composite material. The method involves preparing a copper-iron Prussian blue precursor via mechanical ball milling, followed by high-temperature pyrolysis and gas-phase sulfidation to obtain the copper-iron sulfide / nitrogen-doped porous carbon composite material. This method offers advantages such as simple operation, environmental friendliness, and high yield. The resulting copper-iron sulfide nitrogen-doped porous carbon composite material can be used as a sodium-ion anode material with excellent rate performance and a long cycle life.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] One of the technical solutions of the present invention: a method for preparing a copper-iron sulfide nitrogen-doped porous carbon composite material, comprising the following steps:

[0008] (1) A copper salt, potassium ferricyanide, nitrogen source and polyethylene glycol were mixed and ball-milled to obtain a copper-iron Prussian blue precursor.

[0009] (2) The copper-iron Prussian blue precursor was pyrolyzed under an inert atmosphere, impurities were washed away, and the intermediate product was obtained after drying.

[0010] (3) The intermediate product and the sulfur source were heat-treated in an inert atmosphere to obtain a copper-iron sulfide / nitrogen-doped porous carbon composite material.

[0011] In the preparation method of this invention, the reaction principle is as follows: the energy and mechanical force generated during ball milling induce a coordination chemical reaction between metallic copper ions and ferricyanide ions to generate a copper-iron Prussian blue precursor. Subsequently, the ball-milled precursor is heat-treated under an inert atmosphere. At high temperature, the organic components pyrolyze to form a nitrogen-doped carbon framework. Polyethylene glycol can not only serve as a carbon source but also as a template to induce the growth of a two-dimensional lamellar structure, promoting the formation of a porous structure and decomposing to form a carbon framework. Simultaneously, some copper ions are carbothermally reduced to metallic copper, and some iron ions react with carbon to generate iron-carbon compounds, resulting in a black powdered copper / iron-carbon compound / nitrogen-doped carbon composite material with a mixed phase. Finally, a gas-phase sulfidation treatment is performed, where the sulfur source sublimates into sulfur vapor at high temperature, metallic copper and iron-carbon compounds react to generate copper sulfide / iron disulfide, and excess sulfur is removed in gaseous form, yielding a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0012] To address the issues of poor conductivity, significant volume change, and slow ion diffusion kinetics associated with transition metal sulfides during operation, this invention utilizes a simple and efficient mechanical ball milling method to provide a copper-iron sulfide nitrogen-doped porous carbon composite material. The designed composite structure forms a heterojunction between CuS / FeS2, which facilitates the formation of an internal electric field, significantly accelerating electron and ion transport, enhancing sodium ion adsorption, and thus improving the rate performance of the battery material. The porous structure, both on the surface and inside the material, with the CuS / FeS2 heterojunction creating more defects, increases the number of active sites in both the bulk and surface phases, resulting in higher electrochemical activity. The internal and external porous structure helps eliminate the volume effect of the electrode material, while nitrogen doping increases the adsorption sites for sodium ions and improves conductivity, effectively enhancing the sodium storage performance of the electrode material. This invention uses inexpensive and widely available raw materials, employs a simple process, achieves high yield, and produces materials with excellent charge-discharge performance, facilitating industrial production.

[0013] Preferably, the copper salt is any one of copper chloride, copper acetate, and copper nitrate; and the nitrogen source is any one of melamine, nitrotriacetic acid, and glycine.

[0014] Preferably, in step (1), the mass ratio of the copper salt, potassium ferricyanide and nitrogen source is (1-5):(1-3):1.

[0015] Preferably, in step (1), the total mass ratio of the copper salt, potassium ferricyanide and nitrogen source to the mass ratio of polyethylene glycol is (1-4):1.

[0016] Preferably, in step (1), the total mass ratio of the copper salt, potassium ferricyanide, nitrogen source and polyethylene glycol to the mass of the grinding beads is 1:(5-40).

[0017] Preferably, in step (1), the ball milling time is 1 to 12 hours and the rotation speed is 200 to 600 rpm.

[0018] Preferably, in step (2), the pyrolysis temperature is 400–1000°C, and the heating rate is 2–10°C·min. -1 The heat preservation time is 1 to 5 hours; the inert atmosphere is nitrogen or argon.

[0019] Preferably, in step (3), the mass ratio of the intermediate product to the sulfur source is 1:(3-5); the sulfur source is any one of sulfur powder, thiourea and thioacetamide.

[0020] Preferably, in step (3), the heat treatment temperature is 300-600℃ and the holding time is 1-3h; the inert atmosphere is nitrogen or argon.

[0021] The second technical solution of the present invention: the application of a copper-iron sulfide nitrogen-doped porous carbon composite material obtained by the above preparation method as a negative electrode material for sodium-ion batteries.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The present invention uses a mechanochemical method to prepare copper-iron Prussian blue precursors and provides a method for preparing copper-iron sulfide nitrogen-doped porous carbon composite materials. Unlike the traditional solvothermal method, it does not require organic solvents and a high-temperature and high-pressure reaction environment. The preparation method is simple and easy to operate, safe and pollution-free, and low in cost, and can achieve large-scale preparation.

[0024] (2) The copper-iron sulfide nitrogen-doped porous carbon composite material prepared by the present invention has the synergistic effect of bimetallic sulfide and nitrogen-doped porous carbon composite. The carbon matrix obtained by polyethylene glycol carbonization is embedded with metal nanoparticles, which improves the electronic conductivity of the electrode material. Nitrogen doping expands the carbon interlayer spacing, making it easier for sodium ions with larger ionic radii to be inserted and extracted in the interlayer spacing, while providing abundant active sites to enhance ion storage.

[0025] (3) The copper-iron sulfide nitrogen-doped porous carbon composite material prepared by the present invention has a porous structure, which not only facilitates full contact with the electrolyte, but also shortens the electron / ion transport distance, accelerates the reaction kinetics, effectively adapts to the volume expansion during sodium ion insertion / extraction, and has outstanding rate performance and stable cycle performance. Attached Figure Description

[0026] Figure 1 The X-ray diffraction pattern of the final product prepared in Example 3;

[0027] Figure 2 This is a scanning electron microscope image of the final product prepared in Example 2;

[0028] Figure 3 The image shows a scanning electron microscope (SEM) image of the final product prepared in Comparative Example 1.

[0029] Figure 4 The battery rate performance graphs are for the final products prepared in Comparative Example 1 and Example 2. Detailed Implementation

[0030] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0031] Example 1

[0032] (1) Take 0.4g of copper acetate, 0.3g of potassium ferricyanide, 0.1g of glycine and 0.8g of polyethylene glycol (average molecular weight 4200~4800g / mol, the same below) and add them to the agate ball milling jar in sequence; add 40g of agate grinding beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 8h at a speed of 400rpm to obtain copper-iron Prussian blue precursor;

[0033] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and the temperature was 3℃·min -1 The temperature was increased to 800℃ and then pyrolyzed at high temperature for 3 hours to obtain pyrolysis products. The pyrolysis products were soaked in deionized water for 1 hour and the intermediate products were collected by centrifugation.

[0034] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:3 and heat-treated at 500°C for 2 hours under an argon atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0035] Example 2

[0036] (1) Take 0.4g of copper nitrate, 0.3g of potassium ferricyanide, 0.1g of melamine and 0.5g of polyethylene glycol and add them to the agate ball milling jar in sequence; add 20g of agate grinding beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 6 hours at a speed of 500 rpm to obtain copper-iron Prussian blue precursor;

[0037] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and at 5℃·min -1 The temperature was increased to 700℃ and then pyrolyzed at high temperature for 2 hours to obtain pyrolysis products. The pyrolysis products were soaked in deionized water for 1 hour and the intermediate products were collected by centrifugation.

[0038] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:5 and heat-treated at 300°C for 2 hours under an argon atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0039] Example 3

[0040] (1) Take 0.6g of copper acetate, 0.4g of potassium ferricyanide, 0.2g of melamine and 0.6g of polyethylene glycol and add them to the agate ball milling jar in sequence; add 30g of agate grinding beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 6 hours at a speed of 400 rpm to obtain copper-iron Prussian blue precursor;

[0041] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and the temperature was 3℃·min-1 The temperature was increased to 800℃ and then pyrolyzed at high temperature for 2 hours to obtain pyrolysis products. The pyrolysis products were soaked in deionized water for 1 hour and the intermediate products were collected by centrifugation.

[0042] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:3 and heat-treated at 400°C for 2 hours under a nitrogen atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0043] Example 4

[0044] (1) Take 0.5g of copper chloride, 0.6g of potassium ferricyanide, 0.2g of glycine and 0.8g of polyethylene glycol and add them to the agate ball mill jar in sequence; add 40g of agate grinding beads to the agate ball mill jar; transfer the ball mill jar to the planetary ball mill and complete the assembly, and then perform ball milling for a total time of 3h at a speed of 500rpm to obtain copper-iron Prussian blue precursor; (2) Prussian blue precursor is pyrolyzed at high temperature under argon atmosphere protection and at 2℃·min -1 The temperature was increased to 500℃ and then pyrolyzed at high temperature for 2 hours to obtain the pyrolysis product. The pyrolysis product was soaked in deionized water for 1 hour and the intermediate product was collected by centrifugation.

[0045] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:4 and heat-treated at 500°C for 2 hours under a nitrogen atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0046] Example 5

[0047] (1) Take 0.5g of copper acetate, 0.7g of potassium ferricyanide, 0.5g of glycine and 1g of polyethylene glycol and add them to the agate ball mill jar in sequence; add 20g of agate grinding beads to the agate ball mill jar; transfer the ball mill jar to the planetary ball mill and complete the assembly, and then perform ball milling for a total time of 5h at a speed of 500rpm to obtain copper-iron Prussian blue precursor; (2) Prussian blue precursor is pyrolyzed at high temperature under argon atmosphere protection and at 2℃·min -1 The temperature was increased to 500℃ and then pyrolyzed at high temperature for 2 hours to obtain the pyrolysis product. The pyrolysis product was soaked in deionized water for 1 hour and the intermediate product was collected by centrifugation.

[0048] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:3 and heat-treated at 600°C for 3 hours under a nitrogen atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0049] Example 6

[0050] (1) Take 0.6g of copper chloride, 0.5g of potassium ferricyanide, 0.2g of melamine and 0.5g of polyethylene glycol and add them to the agate ball milling jar in sequence; add 40g of agate grinding beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 4 hours at a speed of 400 rpm to obtain copper-iron Prussian blue precursor;

[0051] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and the temperature was 3℃·min -1 The temperature was increased to 600℃ and then pyrolyzed at high temperature for 3 hours to obtain pyrolysis products. The pyrolysis products were soaked in deionized water for 1 hour and the intermediate products were collected by centrifugation.

[0052] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:3 and heat-treated at 400°C for 1 hour under an argon atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0053] Example 7

[0054] (1) Take 0.6g of copper chloride, 0.8g of potassium ferricyanide, 0.5g of glycine and 0.7g of polyethylene glycol and add them to the agate ball mill jar in sequence; add 40g of agate grinding beads to the agate ball mill jar; transfer the ball mill jar to the planetary ball mill and complete the assembly, and then perform ball milling for a total time of 7h at a speed of 500rpm to obtain copper-iron Prussian blue precursor; (2) pyrolyze the copper-iron Prussian blue precursor at high temperature under argon atmosphere protection and at 3℃·min -1 The temperature was increased to 500℃ and then pyrolyzed at high temperature for 2 hours to obtain the pyrolysis product. The pyrolysis product was soaked in deionized water for 1 hour and the intermediate product was collected by centrifugation.

[0055] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:4 and heat-treated at 350°C for 2 hours under a nitrogen atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0056] Comparative Example 1 (without the addition of melamine and polyethylene glycol compared to Example 2)

[0057] (1) Take 0.4g of copper nitrate and 0.3g of potassium ferricyanide and add them to the agate ball milling jar in sequence; add 20g of agate ball milling beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 6 hours at a speed of 500 rpm to obtain copper-iron Prussian blue precursor;

[0058] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and at 5℃·min -1The temperature was increased to 700℃ and then pyrolyzed at high temperature for 2 hours to obtain pyrolysis products. The pyrolysis products were soaked in deionized water for 1 hour and the intermediate products were collected by centrifugation.

[0059] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:5 and heat-treated at 300°C for 2 hours under an argon atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0060] Comparative Example 2 (without polyethylene glycol compared to Example 6)

[0061] (1) Take 0.6g of copper chloride, 0.5g of potassium ferricyanide and 0.2g of melamine and add them to the agate ball milling jar in sequence; add 40g of agate ball milling beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 4h at a speed of 400rpm to obtain copper-iron Prussian blue precursor;

[0062] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and the temperature was 3℃·min -1 The temperature was increased to 600℃ and then pyrolyzed at high temperature for 3 hours to obtain pyrolysis products. The pyrolysis products were soaked in deionized water for 1 hour and the intermediate products were collected by centrifugation.

[0063] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:3 and heat-treated at 400°C for 1 hour under an argon atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0064] Comparative Example 3 (without melamine added compared to Example 4)

[0065] (1) Take 0.6g of copper chloride, 0.5g of potassium ferricyanide and 0.5g of polyethylene glycol and add them to the agate ball milling jar in sequence; add 40g of agate ball milling beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 4 hours at a speed of 400 rpm to obtain copper-iron Prussian blue precursor;

[0066] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and the temperature was 3℃·min -1 The temperature was increased to 600℃ and then pyrolyzed at high temperature for 3 hours to obtain pyrolysis products. The pyrolysis products were soaked in deionized water for 1 hour and the intermediate products were collected by centrifugation.

[0067] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:3 and heat-treated at 400°C for 1 hour under an argon atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0068] Comparative Example 4 (excessive amount of polyethylene glycol compared to Example 6)

[0069] (1) Take 0.6g of copper chloride, 0.5g of potassium ferricyanide, 0.2g of melamine and 1.5g of polyethylene glycol and add them to the agate ball milling jar in sequence; add 40g of agate grinding beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 4 hours at a speed of 400 rpm to obtain copper-iron Prussian blue precursor;

[0070] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and the temperature was 3℃·min -1 The temperature was increased to 600℃ and then pyrolyzed at high temperature for 3 hours to obtain pyrolysis products. The pyrolysis products were soaked in deionized water for 1 hour and the intermediate products were collected by centrifugation.

[0071] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:3 and heat-treated at 400°C for 1 hour under an argon atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0072] Comparative Example 5 (the pyrolysis temperature was too low and the pyrolysis time was too short compared to Example 6)

[0073] (1) Take 0.6g of copper chloride, 0.5g of potassium ferricyanide, 0.2g of melamine and 0.5g of polyethylene glycol and add them to the agate ball milling jar in sequence; add 40g of agate grinding beads to the agate ball milling jar; transfer the ball milling jar into a planetary ball mill and complete the assembly, and then perform ball milling for a total time of 4 hours at a speed of 400 rpm to obtain copper-iron Prussian blue precursor;

[0074] (2) The copper-iron Prussian blue precursor was subjected to high-temperature pyrolysis under an argon atmosphere and the temperature was 3℃·min -1 The temperature was increased to 300℃ and then pyrolyzed at high temperature for 1 hour to obtain the pyrolysis product; the pyrolysis product was soaked in deionized water for 1 hour and the intermediate product was collected by centrifugation.

[0075] (3) The intermediate product and sulfur powder were mixed in a mass ratio of 1:3 and heat-treated at 400°C for 1 hour under an argon atmosphere to obtain a copper-iron sulfide nitrogen-doped porous carbon composite material.

[0076] Performance testing

[0077] The composite materials obtained in Examples 1-7 and Comparative Examples 1-5 were ground and stirred with conductive agent SuperP and binder polyvinylidene fluoride in a ratio of 7:2:1 until uniformly mixed. The mixture was then coated onto copper foil and cut into 12 mm diameter discs as negative electrodes. Sodium metal was used as the counter electrode. 1 M sodium hexafluorophosphate (NaPF6) dissolved in dimethyl ether was used as the electrolyte. Glass fiber was used as the separator. The CR2025 button cell was assembled in a glove box filled with argon atmosphere and with water and oxygen values ​​of less than 0.01 ppm. After being left to stand for 24 hours, a constant current charge-discharge test was performed in the range of 0.01-3V using a Newway tester.

[0078] Table 1. Capacity retention rates of Examples 1-7 and Comparative Examples 1-4 after 200 cycles.

[0079] Case Capacity retention after 200 laps Example 1 78.3％ Example 2 87.1％ Example 3 82.3％ Example 4 77.4％ Example 5 79.5％ Example 6 85.9％ Example 7 79.3％ Comparative Example 1 69.8％ Comparative Example 2 73.5％ Comparative Example 3 74.7％ Comparative Example 4 76.2％ Comparative Example 5 79.3％

[0080] As shown in Table 1, combining Examples 1-7 and Comparative Examples 1-5, it can be seen that the capacity retention rate of Comparative Examples 2-5 is lower than that of Example 6. This is because the synergistic effect of the bimetallic sulfide and nitrogen-doped porous carbon composite in this invention effectively adapts to the volume expansion during sodium ion insertion / extraction, while providing abundant active sites to enhance ion storage, resulting in outstanding rate performance and stable cycling performance. However, an excessively high ratio of nitrogen source to polyethylene glycol affects the exposure of active sites and conductivity; a low pyrolysis temperature leads to incomplete carbonization, resulting in poor conductivity and structural stability of the material; and a short ball milling time and insufficient ball-to-material ratio result in insufficient mixing of the precursor. Therefore, rationally controlling the ball milling parameters, the ratio of nitrogen source and polyethylene glycol, and the pyrolysis temperature can significantly improve the performance of the composite material, while also significantly enhancing its structural cycling stability and extending its cycle life.

[0081] like Figure 1 The X-ray diffraction pattern of Example 3 is shown. As can be seen from the figure, the diffraction peaks of CuS and FeS2 match the standard cards well, and the peaks are strong and sharp. The broad diffraction peak that appears near 26° belongs to amorphous carbon, indicating that the CuS / FeS2 and carbon nanocomposite material was successfully prepared.

[0082] like Figure 2 The image shown is a scanning electron microscope (SEM) image of the composite material in Example 2. The image reveals that the material exhibits a wrinkled, lamellar, porous structure. The CuS / FeS2 nanoparticles are uniformly grown on the surface and inside the porous carbon matrix. This porous structure of the carbon matrix originates from the decomposition of organic components during high-temperature pyrolysis, which not only facilitates electrode / electrolyte contact but also plays a crucial role in accommodating the volume expansion of the electrode material and ensuring rapid electron / ion transport.

[0083] like Figure 3 The image shown is a scanning electron microscope (SEM) image of the composite material in Comparative Example 1. Figure 2 They differ greatly in appearance, being composed of many aggregated particles of varying sizes.

[0084] like Figure 4 The figure shows the battery rate performance of the final product prepared in Example 2. The sodium-ion battery rate performance is shown at 0.2, 0.5, 1, 2, 5 and recovery rate of 0.2 A·g. -1 The reversible specific capacities at current densities were 732, 725, 713, 669, 602, and 781 mAh·g, respectively. -1 It exhibits excellent rate performance.

[0085] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a copper-iron-sulfide-nitrogen-doped porous carbon composite material, characterized in that, The method comprises the following steps: (1) mixing copper salt, potassium ferricyanide, nitrogen source and polyethylene glycol, the nitrogen source being any one of melamine, nitrilotriacetic acid and glycine, the mass ratio of the copper salt, potassium ferricyanide and nitrogen source being (1-5):(1-3):1, the total mass of the copper salt, potassium ferricyanide and nitrogen source to the mass ratio of polyethylene glycol being (1-4):1, and obtaining copper-iron Prussian blue precursor after ball milling; (2) pyrolyzing the copper-iron Prussian blue precursor under an inert atmosphere, the pyrolysis temperature being 400-1000 ℃, the heating rate being 2-10 ℃·min -1 , the holding time being 1-5 h, removing impurities by washing, and obtaining an intermediate product after drying; (3) adding a reducing agent to the intermediate product, and reducing the intermediate product to obtain a copper-iron Prussian blue product. (3) heat treating the intermediate product and a sulfur source in an inert atmosphere, the mass ratio of the intermediate product to the sulfur source being 1:(3-5), and obtaining copper-iron sulfide / nitrogen-doped porous carbon composite material.

2. The preparation method of the copper-iron sulfide nitrogen-doped porous carbon composite material as described in claim 1, characterized in that, The copper salt is any one of copper chloride, copper acetate and copper nitrate.

3. The method for preparing the copper-iron sulfide nitrogen-doped porous carbon composite material as described in claim 1, characterized in that, In step (1), the total mass of the copper salt, potassium ferricyanide, nitrogen source and polyethylene glycol to the mass of the ball milling beads is 1:(5-40).

4. The method for preparing the copper-iron sulfide / nitrogen-doped porous carbon composite material according to any one of claims 1-3, characterized in that, In step (1), the ball milling time is 1-12 h, and the rotating speed is 200-600 rpm.

5. The method for preparing copper-iron sulfide / nitrogen-doped porous carbon composite material according to any one of claims 1-3, characterized in that, In step (2), the inert atmosphere is nitrogen or argon.

6. The method for preparing the copper-iron sulfide nitrogen-doped porous carbon composite material as described in claim 1, characterized in that, In step (3), the sulfur source is any one of sulfur powder, thiourea and thioacetamide.

7. The method for preparing copper-iron sulfide nitrogen-doped porous carbon composite material according to claim 1 or 6, characterized in that, In step (3), the heat treatment temperature is 300-600 ℃, the holding time is 1-3 h, and the inert atmosphere is nitrogen or argon.

8. Application of copper-iron sulfide / nitrogen-doped porous carbon composite material prepared by the preparation method in any one of claims 1-7 as negative electrode material of sodium ion battery.

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