A phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, its preparation method and application

Abstract

This invention discloses a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, its preparation method, and its application, belonging to the field of new energy technology. Utilizing the interaction between iron ions, fluorine-containing organic compounds, and organophosphoric acid, as well as the three-dimensional network porous structure of zeolite imidazole-8, the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material is obtained through pyrolysis. This invention employs the aforementioned phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, its preparation method, and its application. By adjusting the electronic structure of the catalyst's active sites through phosphorus / fluorine co-doping, the catalytic activity of single-atom iron is improved. Through the coordination between the porous carbon substrate and the single atom, the physical adsorption of porous carbon, the chemical adsorption of single-atom iron, and the highly efficient catalytic effect are synergistically utilized, greatly mitigating polysulfide shuttle, improving electrode conversion reaction kinetics, and realizing high-performance lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, its preparation method, and its application. Background Technology

[0002] Lithium-sulfur batteries also have high energy density (2600Wh / kg) -1 The lithium-sulfur battery has attracted widespread attention due to its advantages such as low cost and environmental friendliness. However, the polysulfide shuttle effect and slow reaction kinetics result in low discharge specific capacity and low coulombic efficiency, severely hindering the commercialization of lithium-sulfur batteries. Therefore, suppressing polysulfide shuttle and improving battery conversion kinetics are key factors in improving the performance of lithium-sulfur batteries.

[0003] Single-atom catalysts (SACs) possess excellent adsorption and catalytic activity, making them a new frontier in lithium-sulfur battery cathode research. Generally, the central metal atom is concentrated on the d-block metal and exists in the form of a nonpolar metal-N4 coordination, but its adsorption and catalytic activity has not yet reached the expected levels. Recent studies have shown that the unsaturated coordination of the central metal atom can form bonds with multiple adjacent coordinating atoms (typically phosphorus, fluorine, sulfur, etc.) on the substrate material, influencing the electronic structure and geometry of the central metal atom. This, in turn, modulates the adsorption capacity and catalytic activity of SACs for polysulfides, thereby affecting battery performance. Summary of the Invention

[0004] The purpose of this invention is to provide a phosphorus / fluorine co-doped single-atom iron supported porous carbon composite material, its preparation method and application. By utilizing phosphorus / fluorine co-doping to adjust the electronic structure of single-atom active sites, the ability of single-atom iron to adsorb polysulfides and its catalytic activity are improved. Then, the porous carbon substrate works synergistically to exert the physical adsorption and confinement of porous carbon and the chemical adsorption and high catalytic activity of single-atom iron, thereby achieving excellent battery performance.

[0005] To achieve the above objectives, the present invention provides a phosphorus / fluorine co-doped monoatomic iron-supported porous carbon composite material, wherein the percentage of each element by mass fraction is as follows: carbon 60%-95% by mass; monoatomic iron 0.1%-10% by mass; nitrogen 4.7%-40% by mass; phosphorus 0.1%-10% by mass; and fluorine 0.1%-10% by mass.

[0006] Preferably, the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material exhibits a dodecahedral structure with a particle size of 100-1000 nm and a specific surface area of ​​500-1500 m². 2 g -1 The pore volume is 0.1-1 cm³. 3 g -1 .

[0007] This invention provides a method for preparing a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, comprising the following steps:

[0008] S1. Dissolve zinc nitrate in methanol to obtain a zinc nitrate solution;

[0009] S2. Dissolve 2-methylimidazole in methanol to obtain a 2-methylimidazole solution;

[0010] S3. Dissolve ferric nitrate, fluorine-containing organic matter, and organophosphorus compounds in methanol to obtain a ferric nitrate solution;

[0011] S4. Mix zinc nitrate solution, 2-methylimidazole solution and ferric nitrate solution, stir in an oil bath, and centrifuge after stirring to obtain precursor powder;

[0012] S5. The precursor powder obtained in S4 is calcined under an argon protective atmosphere, and then the calcined powder is ground to obtain a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material.

[0013] Preferably, the mass ratio of ferric nitrate, fluorine-containing organic matter and organic phosphoric acid in S3 is 1:(0.2-1):(1-4).

[0014] Preferably, the fluorinated organic compound in S3 is one of perfluorooctanoic acid, perfluorododecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, and polytetrafluoroethylene.

[0015] Preferably, the organophosphorus in S3 is one of butyl phosphoric acid, diphenylmethyl phosphoric acid, p-toluenephosphoric acid, and phytic acid.

[0016] Preferably, the mass ratio of zinc nitrate, ferric nitrate and 2-methylimidazole in S4 is 1:(0.03-0.4):(1-4), the stirring temperature is 50-100℃, the stirring rate is 50-100r / min, and the stirring time is 12-24h.

[0017] Preferably, the calcination temperature in S5 is 900-1200℃, and the calcination time is 1-4h.

[0018] This invention also provides an application of a phosphorus / fluorine co-doped single-atom iron supported porous carbon composite material, which is used as a sulfur cathode support in lithium-sulfur batteries.

[0019] Preferably, the preparation of a lithium-sulfur battery includes the following steps:

[0020] Step 1: Weigh sublimed sulfur and phosphorus / fluorine co-doped single-atom iron supported porous carbon composite material at a mass ratio of 3:1. After ball milling the mixed powder for 1-3 hours, pack it into an ampoule and seal it. Heat it at 150-160℃ for 10-12 hours in an argon atmosphere to obtain phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite material. Weigh the phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite material, acetylene black and polyvinylidene fluoride material at a mass ratio of 7:2:1 and mix them. After grinding thoroughly, add N-methyl-2-pyrrolidone solution and stir for 5-7 hours to form a uniform slurry. Coat the above slurry on the surface of aluminum foil and dry it in a vacuum oven at 40-60℃ for 12-24 hours to prepare phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite positive electrode. Cut it into circular positive electrode sheets with a diameter of 10-15 mm for later use.

[0021] Step 2: Assemble the prepared phosphorus / fluorine co-doped single-atom iron-supported porous carbon / sulfur composite cathode, polypropylene separator, and lithium metal sheet anode into a lithium-sulfur battery. The electrolyte drop volume on both sides of the separator is 10-30 μL on the cathode side and 10-30 μL on the anode side, respectively. The electrolyte is a mixed ether electrolyte, in which the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether is 1:1, the concentration of lithium bis(trifluoromethanesulfonate)imide is 1.0 mol / L, and the mass percentage of lithium nitrate is 1 wt%. After the assembled battery is allowed to stand for 5-7 hours, electrochemical tests are performed.

[0022] Therefore, the present invention employs the above-mentioned phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, its preparation method, and its application, which have the following beneficial effects:

[0023] 1) This invention utilizes the three-dimensional porous network structure of zeolite imidazole-8 to confine iron ions and organic groups within the pores of zeolite imidazole-8. After pyrolysis, a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material is obtained. The preparation method is scientific, reasonable, easy to implement, and low in cost, enabling large-scale production.

[0024] 2) This invention utilizes phosphorus / fluorine co-doping to adjust the electronic structure of single-atom active sites, thereby improving the ability of single-atom iron to adsorb polysulfides and its catalytic activity. In addition, it works synergistically with a porous carbon substrate to leverage the physical adsorption and confinement of porous carbon and the chemical adsorption and high catalytic activity of single-atom iron. This effectively suppresses the polysulfide shuttle effect, improves battery reaction kinetics, and thus improves the utilization rate of active materials in lithium-sulfur batteries, achieving excellent battery performance and showing potential application prospects.

[0025] 3) The phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material prepared in this invention has excellent chemical stability as a positive electrode carrier material for lithium-sulfur batteries. The lithium-sulfur battery prepared using this material has a maximum discharge specific capacity of 1215 mAh / g at a discharge rate of 0.2C, and the capacity can still be maintained at 1018 mAh / g after 100 cycles.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a transmission electron microscope (TEM) image of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material prepared in Example 1 of the present invention, which describes the preparation method of the composite material and its application.

[0028] Figure 2 These are high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images and elemental distribution (EDS) diagrams of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material prepared in Example 1 of the present invention, along with its preparation method and application.

[0029] Figure 3 This is an aberration-corrected scanning transmission electron microscope (AC-STEM) image of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material prepared in Example 1 of the present invention, along with its preparation method and application.

[0030] Figure 4 This is an X-ray crystal diffraction (XRD) pattern of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material prepared in Example 1 of the present invention, which is a method for preparing the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material and its application.

[0031] Figure 5 This is a graph showing the cycle performance of a battery prepared using a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, its preparation method, and application example 1, under a discharge rate of 0.2C.

[0032] Figure 6 This invention relates to a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, its preparation method, and the cycle performance of a battery prepared in Comparative Example 1 under a discharge rate of 0.2C.

[0033] Figure 7This is a graph showing the cycle performance of a battery prepared by a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, its preparation method, and its application in Comparative Example 2, under a discharge rate of 0.2C. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0036] This invention provides a phosphorus / fluorine co-doped monoatomic iron-supported porous carbon composite material, wherein the percentage of each element by mass fraction is as follows: carbon 60%-95% by mass; monoatomic iron 0.1%-10% by mass; nitrogen 4.7%-40% by mass; phosphorus 0.1%-10% by mass; and fluorine 0.1%-10% by mass.

[0037] Phosphorus / fluorine co-doped single-atom iron-supported porous carbon composites exhibit dodecahedral structures with particle sizes ranging from 100 to 1000 nm and specific surface areas of 500 to 1500 m². 2 g -1 The pore volume is 0.1-1 cm³. 3 g -1 .

[0038] This invention provides a method for preparing a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, comprising the following steps:

[0039] S1. Dissolve zinc nitrate in methanol to obtain a zinc nitrate solution;

[0040] S2. Dissolve 2-methylimidazole in methanol to obtain a 2-methylimidazole solution;

[0041] S3. Dissolve ferric nitrate, fluorinated organic matter, and organophosphorus compounds in methanol at a mass ratio of 1:(0.2-1):(1-4) to obtain a ferric nitrate solution; the fluorinated organic matter is one of perfluorooctanoic acid, perfluorododecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, and polytetrafluoroethylene; the organophosphorus compounds are one of butylphosphonic acid, diphenylmethylphosphonic acid, p-toluenephosphonic acid, and phytic acid.

[0042] S4. Mix zinc nitrate solution, 2-methylimidazole solution and ferric nitrate solution according to the mass ratio, and stir in an oil bath at 50-100℃ for 12-24h at a stirring rate of 50-100r / min. After stirring, centrifuge to obtain precursor powder. The mass ratio of zinc nitrate, ferric nitrate and 2-methylimidazole in the mixed solution is 1:(0.03-0.4):(1-4).

[0043] S5. The precursor powder obtained in S4 is calcined at 900-1200℃ for 1-4 hours under an argon protective atmosphere. The calcined powder is then ground to obtain a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material.

[0044] This invention also provides an application of a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, which is used as a sulfur cathode support in a lithium-sulfur battery. The preparation of the lithium-sulfur battery includes the following steps:

[0045] Step 1: Weigh sublimed sulfur and phosphorus / fluorine co-doped single-atom iron supported porous carbon composite material at a mass ratio of 3:1. After ball milling the mixed powder for 1-3 hours, pack it into an ampoule and seal it. Heat it at 150-160℃ for 10-12 hours in an argon atmosphere to obtain phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite material. Weigh the phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite material, acetylene black and polyvinylidene fluoride material at a mass ratio of 7:2:1 and mix them. After thorough grinding, add N-methyl-2-pyrrolidone solution and stir for 5-7 hours to form a uniform slurry. Coat the slurry onto the surface of aluminum foil and dry it in a vacuum oven at 40-60℃ for 12-24 hours to obtain the phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite cathode. Cut it into circular cathode electrode sheets with a diameter of 10-15 mm for later use.

[0046] Step 2: Assemble the prepared phosphorus / fluorine co-doped single-atom iron-supported porous carbon / sulfur composite cathode, polypropylene separator, and lithium metal sheet anode into a lithium-sulfur battery. The electrolyte drop volume on both sides of the separator is 10-30 μL on the cathode side and 10-30 μL on the anode side, respectively. The electrolyte is a mixed ether electrolyte, in which the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether is 1:1, the concentration of lithium bis(trifluoromethanesulfonate)imide is 1.0 mol / L, and the mass percentage of lithium nitrate is 1 wt%. After the assembled battery is allowed to stand for 5-7 hours, electrochemical tests are performed.

[0047] Example 1

[0048] A method for preparing a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material includes the following steps:

[0049] S1. Add 3.6g of zinc nitrate and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a zinc nitrate solution.

[0050] S2. Add 3.6g of 2-methylimidazole and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a 2-methylimidazole solution.

[0051] S3. Add 0.12g ferric nitrate, 0.12g perfluorooctanoic acid and 0.19g phytic acid aqueous solution (70%) to a 100mL beaker, add 48mL methanol to the beaker, place it on a stirrer and stir at 100r / min for 0.5h to obtain ferric nitrate solution.

[0052] S4. Quickly pour the solutions prepared in S1, S2 and S3 into a 200 mL beaker, place it in an oil bath and heat and stir at 60 °C, stirring rate of 100 r / min for 24 h. Centrifuge and dry in a vacuum oven at 60 °C for 12 h to obtain precursor powder.

[0053] S5. The precursor powder prepared in S4 was calcined at 1100℃ for 2 hours under an argon-protected atmosphere. The resulting powder was then ground to obtain a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material. Its morphology and structure were analyzed and characterized, such as... Figure 1-4 As shown.

[0054] Figure 1 The image shows a TEM image of a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material. As can be seen from the image, the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material exhibits a dodecahedral shape with a particle size of approximately 150 nm.

[0055] Figure 2 The images show the HAADF-STEM and EDS images of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material. From the images, we can see that no iron aggregates were found in the porous carbon, and other elements were also uniformly distributed in the sample, indicating that the composite material does not contain elemental iron or its compounds.

[0056] Figure 3 The image shows an AC-STEM image of a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material. The image shows many bright spots with a diameter of about 0.1 nm distributed on the carbon substrate, indicating that the iron element is supported on the porous carbon substrate in the form of single atoms.

[0057] Figure 4 The image shows the XRD pattern of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material. Two distinct diffraction peaks are observed, located at approximately 21° and 43°, respectively. These peaks correspond to the (002) and (100) crystal planes of graphite. The broad peak shapes indicate a high degree of disorder. The absence of diffraction peaks for elemental iron and its compounds further confirms the successful preparation of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material.

[0058] The application of phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite materials in lithium-sulfur batteries includes the following steps:

[0059] Step 1: Weigh 3g of sublimed sulfur and 1g of phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, ball mill for 2 hours, and then place the mixture into an ampoule and seal it. Heat at 155℃ for 12 hours in an argon atmosphere to obtain the phosphorus / fluorine co-doped single-atom iron-supported porous carbon / sulfur composite material. Place 0.07g of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon / sulfur composite material, 0.02g of acetylene black, and 0.01g of PVDF in a mortar and grind thoroughly. Pour the mixture into a 2mL volumetric flask, add approximately 1mL of NMP, and stir for 6 hours to form a uniform slurry. Coat the slurry onto the surface of aluminum foil, dry it in a vacuum oven at 50℃ for 24 hours, and then cut it into circular positive electrode sheets with a diameter of 12mm for later use.

[0060] Step 2: Under the anhydrous and oxygen-free atmosphere of a glove box, place the prepared phosphorus / fluorine co-doped single-atom iron-supported porous carbon / sulfur electrode in the center of the positive electrode shell, and add 20 μL of electrolyte. The electrolyte is a mixed ether electrolyte, in which the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether is 1:1, the concentration of lithium bis(trifluoromethanesulfonate)imide is 1.0 mol / L, and the mass percentage of lithium nitrate is 1 wt%. After placing a 19 mm diameter polypropylene separator, add another 10 μL of the above electrolyte, then place a 15 mm diameter lithium metal sheet, add a gasket and spring, cover with the negative electrode shell, and assemble into a lithium-sulfur battery under hydraulic pressure. After the assembled battery has been left to stand for 6 hours, electrochemical tests are performed. The test results are as follows: Figure 5 As shown.

[0061] Figure 5 The graph shows the cycle performance of the battery prepared in Example 1 at a discharge rate of 0.2C. As can be seen from the graph, the battery has an initial discharge specific capacity of 1215 mAh / g at a discharge rate of 0.2C, and retains a discharge specific capacity of 1018 mAh / g after 100 cycles, with a capacity retention rate of 83.8%. This excellent discharge performance is closely related to the fact that phosphorus / fluorine co-doping enhances the catalytic activity of single-atom iron and its ability to adsorb polysulfides, effectively suppressing the polysulfide shuttle effect, improving battery reaction kinetics, and thus improving the utilization rate of active materials in lithium-sulfur batteries.

[0062] Example 2

[0063] A method for preparing a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material includes the following steps:

[0064] S1. Add 3.6g of zinc nitrate and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a zinc nitrate solution.

[0065] S2. Add 3.6g of 2-methylimidazole and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a 2-methylimidazole solution.

[0066] S3. Add 0.16g ferric nitrate, 0.16g perfluorooctanoic acid and 0.25g phytic acid aqueous solution (70%) to a 100mL beaker, add 48mL methanol to the beaker, place it on a stirrer and stir at 100r / min for 0.5h to obtain ferric nitrate solution.

[0067] S4. Quickly pour the solutions prepared in S1, S2 and S3 into a 200 mL beaker, place it in an oil bath and heat and stir at 60 °C, stirring rate of 100 r / min for 24 h. Centrifuge and dry in a vacuum oven at 60 °C for 12 h to obtain precursor powder.

[0068] S5. The precursor powder prepared in S4 was calcined at 1100℃ for 2 hours under an argon-protected atmosphere. The resulting powder was then ground to obtain a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material.

[0069] The steps for applying phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite materials in lithium-sulfur batteries are the same as in Example 1.

[0070] Example 3

[0071] A method for preparing a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material includes the following steps:

[0072] S1. Add 3.6g of zinc nitrate and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a zinc nitrate solution.

[0073] S2. Add 7.2g of 2-methylimidazole and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a 2-methylimidazole solution.

[0074] S3. Add 0.12g ferric nitrate, 0.12g polytetrafluoroethylene dispersion (66% solid content) and 0.19g phytic acid aqueous solution (70%) to a 100mL beaker, add 48mL methanol to the beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain ferric nitrate solution.

[0075] S4. Quickly pour the solutions prepared in S1, S2, and S3 into a 200 mL beaker, place it in an oil bath and heat and stir at 60 °C, 100 r / min, for 24 h. Centrifuge and dry in a vacuum oven at 60 °C for 12 h to obtain precursor powder.

[0076] S5. The precursor powder prepared in S4 was calcined at 1100℃ for 2 hours under an argon-protected atmosphere. The resulting powder was then ground to obtain a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material.

[0077] The steps for applying phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite materials in lithium-sulfur batteries are the same as in Example 1.

[0078] Example 4

[0079] A method for preparing a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material includes the following steps:

[0080] S1. Add 3.6g of zinc nitrate and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a zinc nitrate solution.

[0081] S2. Add 3.6g of 2-methylimidazole and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a 2-methylimidazole solution.

[0082] S3. Add 0.12g ferric nitrate, 0.12g perfluorooctanoic acid and 0.19g butylphosphonic acid to a 100mL beaker, add 48mL methanol to the beaker, place it on a stirrer and stir at 100r / min for 0.5h to obtain ferric nitrate solution.

[0083] S4. Quickly pour the solutions prepared in S1, S2, and S3 into a 200 mL beaker, place it in an oil bath and heat and stir at 60 °C, 100 r / min, for 24 h. Centrifuge and dry in a vacuum oven at 60 °C for 12 h to obtain precursor powder.

[0084] S5. The precursor powder prepared in S4 is calcined at 1000℃ for 2h under argon protection. The resulting powder is then ground to obtain a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material.

[0085] The steps for applying phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite materials in lithium-sulfur batteries are the same as in Example 1.

[0086] Comparative Example 1

[0087] The other conditions are the same as in Example 1, except that no fluorinated organic compounds are added, and the following steps are included:

[0088] S1. Add 3.6g of zinc nitrate and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a zinc nitrate solution.

[0089] S2. Add 3.6g of 2-methylimidazole and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a 2-methylimidazole solution.

[0090] S3. Add 0.12g of ferric nitrate and 0.19g of phytic acid aqueous solution (70%) to a 100mL beaker, add 48mL of methanol to the beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain ferric nitrate solution.

[0091] S4. Quickly pour the solutions prepared in S1, S2, and S3 into a 200 mL beaker, place it in an oil bath and heat and stir at 60 °C, 100 r / min, for 24 h. Centrifuge and dry in a vacuum oven at 60 °C for 12 h to obtain precursor powder.

[0092] S5. The precursor powder prepared in S4 was calcined at 1100℃ for 2 hours under an argon-protected atmosphere. The resulting powder was then ground to obtain a phosphorus-doped single-atom iron-supported porous carbon composite material.

[0093] The steps for applying phosphorus-doped single-atom iron-supported porous carbon composite materials in lithium-sulfur batteries are the same as in Example 1. The battery performance at a discharge rate of 0.2C is as follows: Figure 6 As shown.

[0094] Figure 6 To compare the cycling performance of the battery prepared in Example 1 at a discharge rate of 0.2C, it can be seen from the figure that the battery prepared with phosphorus-doped single-atom iron-supported porous carbon composite material as sulfur carrier has an initial discharge specific capacity of 956 mAh / g at a discharge rate of 0.2C, and still has a discharge specific capacity of 802 mAh / g after 100 cycles, with a capacity retention rate of 83.9%. The discharge specific capacity of this battery is much lower than that of Example 1, indicating that phosphorus doping alone has limited effect on improving the single-atom catalytic activity and the ability to adsorb polysulfides.

[0095] Comparative Example 2

[0096] Other conditions are the same as in Example 1, except that organic phosphoric acid is not added: Specifically, the following steps are included:

[0097] S1. Add 3.6g of zinc nitrate and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a zinc nitrate solution.

[0098] S2. Add 3.6g of 2-methylimidazole and 48mL of methanol to a 100mL beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a 2-methylimidazole solution.

[0099] S3. Add 0.12g of ferric nitrate and 0.12g of perfluorooctanoic acid to a 100mL beaker, add 48mL of methanol to the beaker, place it on a stirrer, and stir at 100r / min for 0.5h to obtain a ferric nitrate solution.

[0100] S4. Quickly pour the solutions prepared in S1, S2, and S3 into a 200 mL beaker, place it in an oil bath and heat and stir at 60 °C, 100 r / min, for 24 h. Centrifuge and dry in a vacuum oven at 60 °C for 12 h to obtain precursor powder.

[0101] S5. The precursor powder prepared in S4 was calcined at 1100℃ for 2 hours under an argon-protected atmosphere. The resulting powder was then ground to obtain a fluorine-doped single-atom iron-supported porous carbon composite material.

[0102] The steps for applying fluorine-doped single-atom iron-supported porous carbon composite materials in lithium-sulfur batteries are the same as in Example 1. The battery performance at a discharge rate of 0.2C is as follows: Figure 7 As shown.

[0103] Figure 7 The graph shows the cycling performance of the battery prepared in Comparative Example 2 at a discharge rate of 0.2C. The battery prepared using fluorine-doped single-atom iron-supported porous carbon composite material as a sulfur carrier has an initial discharge specific capacity of 883 mAh / g at a discharge rate of 0.2C. After 100 cycles, it still has a discharge specific capacity of 764 mAh / g, with a capacity retention rate of 86.5%. Its discharge specific capacity is significantly lower than that of Example 1, indicating that fluorine doping does not improve the battery discharge specific capacity, but only has an effect on the battery cycle stability. This further illustrates the necessity of the fluorine / phosphorus co-doping proposed in this invention.

[0104] Therefore, this invention employs the aforementioned phosphorus / fluorine co-doped single-atom iron supported porous carbon composite material, its preparation method, and its application. By adjusting the electronic structure of the catalyst's active sites through phosphorus / fluorine co-doping, the catalytic activity of single-atom iron is improved. Through the coordination between the porous carbon substrate and the single atom, the physical adsorption of porous carbon, the chemical adsorption of single-atom iron, and the efficient catalytic effect are synergistically utilized, greatly alleviating polysulfide shuttle, improving the electrode conversion reaction kinetics, and realizing a high-performance lithium-sulfur battery.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material for use as a sulfur cathode support in lithium-sulfur batteries, characterized in that: Based on mass fraction, the percentages of each element are as follows: carbon 60%-95%; monatomic iron 0.1%-10%; nitrogen 4.7%-40%; phosphorus 0.1%-10%; fluorine 0.1%-10%. The preparation method of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material includes the following steps: S1. Dissolve zinc nitrate in methanol to obtain a zinc nitrate solution; S2. Dissolve 2-methylimidazole in methanol to obtain a 2-methylimidazole solution; S3. Dissolve ferric nitrate, fluorine-containing organic matter, and organophosphorus compounds in methanol to obtain a ferric nitrate solution; S4. Mix zinc nitrate solution, 2-methylimidazole solution and ferric nitrate solution, stir in an oil bath, and centrifuge after stirring to obtain precursor powder; S5. The precursor powder obtained in S4 is calcined under an argon protective atmosphere, and then the calcined powder is ground to obtain a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material. The fluorinated organic compound in S3 is one of perfluorooctanoic acid, perfluorododecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, and polytetrafluoroethylene; The organophosphorus compounds in S3 are one of butyl phosphoric acid, diphenylmethyl phosphoric acid, p-toluenephosphoric acid, and phytic acid. The calcination temperature in S5 is 900-1200℃, and the calcination time is 1-4h.

2. The phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material according to claim 1, characterized in that: Phosphorus / fluorine co-doped single-atom iron-supported porous carbon composites exhibit dodecahedral structures with particle sizes ranging from 100 to 1000 nm and specific surface areas of 500 to 1500 m². 2 g -1 The pore volume is 0.1-1 cm³. 3 g -1 .

3. The phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material according to claim 1, characterized in that: The mass ratio of ferric nitrate, fluorine-containing organic matter, and organic phosphorus in S3 is 1:(0.2-1):(1-4).

4. The phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material according to claim 1, characterized in that: The mass ratio of zinc nitrate, ferric nitrate and 2-methylimidazole in S4 is 1:(0.03-0.4):(1-4), the stirring temperature is 50-100℃, the stirring rate is 50-100r / min, and the stirring time is 12-24h.

5. An application of a phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material, characterized in that: The phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material described in claim 1 is used as a sulfur cathode carrier in lithium-sulfur batteries.

6. The application of the phosphorus / fluorine co-doped single-atom iron-supported porous carbon composite material according to claim 5, characterized in that: The preparation of lithium-sulfur batteries includes the following steps: Step 1: Weigh sublimed sulfur and phosphorus / fluorine co-doped single-atom iron supported porous carbon composite material at a mass ratio of 3:

1. After ball milling the mixed powder for 1-3 hours, pack it into an ampoule and seal it. Heat it at 150-160℃ for 10-12 hours in an argon atmosphere to obtain phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite material. Weigh the phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite material, acetylene black and polyvinylidene fluoride material at a mass ratio of 7:2:1 and mix them. After grinding thoroughly, add N-methyl-2-pyrrolidone solution and stir for 5-7 hours to form a uniform slurry. Coat the above slurry on the surface of aluminum foil and dry it in a vacuum oven at 40-60℃ for 12-24 hours to prepare phosphorus / fluorine co-doped single-atom iron supported porous carbon / sulfur composite positive electrode. Cut it into circular positive electrode sheets with a diameter of 10-15 mm for later use. Step 2: Assemble the prepared phosphorus / fluorine co-doped single-atom iron-supported porous carbon / sulfur composite cathode, polypropylene separator, and lithium metal sheet anode into a lithium-sulfur battery. The electrolyte drop volume on both sides of the separator is 10-30 μL on the cathode side and 10-30 μL on the anode side, respectively. The electrolyte is a mixed ether electrolyte, in which the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether is 1:1, the concentration of lithium bis(trifluoromethanesulfonate)imide is 1.0 mol / L, and the mass percentage of lithium nitrate is 1 wt%. After the assembled battery is allowed to stand for 5-7 hours, electrochemical tests are performed.

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