Preparation method of nitrogen-doped carbon nanotube composite loaded multi-transition metal monatomic electrocatalyst, and obtained product and application

Abstract

The application discloses a preparation method of a nitrogen-doped carbon nanotube composite material loaded multi-transition metal single-atom electrocatalyst, the obtained product and application, at least three transition metal salts, benzimidazole, aniline and a carbon nanotube composite material are added into an acid solution and stirred uniformly, then ammonium persulfate is added, and stirring is continued, then through drying and calcination, a multi-transition metal precursor is self-assembled, then mixed with an organic nitrogen source, and through two-stage calcination, the final catalyst is obtained. The catalyst has excellent conductivity and metal dispersity by introducing the carbon nanotube composite material, in addition, the self-assembly method makes the prepared multi-transition metal single-atom electrocatalyst have uniform dispersion of metal elements, and the active sites are all in single-atom state. The electrocatalyst can be used as a sulfur host material in a lithium-sulfur battery, the assembled lithium-sulfur battery has high discharge specific capacity and excellent cycle stability, and has a wide application prospect in lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to a method for preparing a nitrogen-doped carbon nanotube composite supported multi-element transition metal single-atom electrocatalyst, the resulting product, and its applications, belonging to the field of battery materials technology. Background Technology

[0002] With the continuous development of portable electronic devices and electric vehicles, lithium-ion batteries, due to their limited theoretical capacity and high cost, are unable to meet the ever-increasing energy storage demands. Therefore, the search for lithium-ion rechargeable batteries with good cycle performance, high energy density, and low cost has become a research hotspot. Among them, lithium-sulfur (Li-S) batteries, due to their high theoretical specific capacity (1675 mAh g⁻¹), are particularly promising. -1 The lithium-sulfur battery has attracted widespread attention due to its abundant sulfur resources and environmental friendliness. However, the practical application of lithium-sulfur batteries is still hindered by several challenges: (1) the insulation properties of S and Li2S; (2) the "shuttle effect" in the charge and discharge process of soluble polysulfides; (3) the large energy barrier in the two-phase conversion from solid (S8) to solution (polysulfides) to solid (Li2S2 / Li2S), resulting in poor electrochemical kinetics of sulfur in lithium-sulfur batteries.

[0003] Currently, one of the most effective strategies to address the aforementioned issues is to introduce electrocatalysts into lithium-sulfur batteries. These catalysts can effectively adsorb lithium polysulfides and lower the activation energy of the reaction, thereby suppressing the shuttle effect and accelerating reaction kinetics, thus improving the capacity and cycle stability of lithium-sulfur batteries. Single-atom catalysts, due to their unique coordination chemistry and near-100% atom utilization, have opened up broad prospects for high-efficiency electrocatalyst systems in lithium-sulfur batteries. However, they suffer from difficulties in single-atom preparation, low loading, and a relatively limited variety of active sites, thus limiting their impact on the performance improvement of lithium-sulfur batteries. To further improve the catalytic efficiency of single-atom catalysts, more types of metal elements can be introduced into the single-atom system to obtain multi-element single-atom electrocatalysts. The literature (Nat. Sustain. 2023, 6, 816–826) prepared a high-entropy single-atom catalyst using Ketjen black as a carbon substrate and applied it to ORR and OER catalytic reactions. However, Ketjen black has poor conductivity, limiting its ability to improve electron conduction speed. Patent CN113258088A discloses a carbon-supported multi-element single-atom metal catalyst for use in ORR (Organic Reduction). The active components of the catalyst all contain noble metals, and the carbon support is carbon nanospheres. However, the preparation method is a transient Joule heating process, resulting in extremely high production costs and making it unsuitable for practical applications. Patent CN114433166A discloses a high-entropy single-atom catalyst and its preparation method. This catalyst can be used in ORR reactions, but the carbon support is derived from an organic carbon source, resulting in limited electron transport speed. Patent CN117335094 discloses a method for preparing a membrane modified with a high-entropy single-atom catalyst. This catalyst is used to modify the membrane of lithium-sulfur batteries. The carbon support is derived from an organic carbon source, and the active components contain noble metals, leading to high product costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a multi-element transition metal single-atom electrocatalyst supported on a nitrogen-doped carbon nanotube composite material. This method, through the precise control of the carbon nanotube composite material and the active components, results in a multi-element transition metal single-atom electrocatalyst with uniform element distribution and each metal element exhibiting a single-atom state, thus exhibiting good electrical conductivity.

[0005] This invention prepares a multi-element transition metal single-atom electrocatalyst supported on a nitrogen-doped carbon nanotube composite substrate via a self-assembly method. The carbon nanotube composite substrate improves the conductivity and metal atom dispersion of the catalyst. This method has advantages such as simple preparation, low cost, stable catalyst structure, and excellent catalytic performance. The catalyst obtained by this invention can be used as a sulfur host material in lithium-sulfur batteries, and the assembled lithium-sulfur batteries exhibit excellent electrochemical performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a multi-element transition metal single-atom electrocatalyst supported on a nitrogen-doped carbon nanotube composite material, the method comprising the following steps:

[0008] (1) Dissolve at least three transition metal salts, benzimidazole, aniline, and carbon nanotube composite material in an acid solution, stir and mix, then add ammonium persulfate, stir and react, collect the product after reaction, and then dry and calcine to obtain a nitrogen-doped carbon nanotube composite material loaded with a multi-component transition metal precursor.

[0009] (2) The nitrogen-doped carbon nanotube composite material loaded with multi-element transition metal precursors is acid-washed, dried, and then mixed with an organic nitrogen source. After mixing, it is calcined in two stages to obtain a nitrogen-doped carbon nanotube composite material loaded with multi-element transition metal single-atom electrocatalyst.

[0010] Furthermore, in step (1), carbon nanotube composite material is selected as carbon substrate, which gives the catalyst excellent conductivity and atomic dispersion. In addition, benzimidazole is used as a ligand linker to form a complex with transition metal salt through self-assembly to capture transition metal, effectively preventing metal clusters and forming single atoms.

[0011] Furthermore, in step (1), the transition metal is selected from transition metals such as Fe, Co, Ni, V, Zn, Cu, and Mn. The salt of the transition metal is a soluble salt of the transition metal, such as chloride or nitrate. For example, Fe salt can be ferric nitrate, Co salt can be cobalt nitrate, Ni salt can be nickel nitrate, V salt can be vanadium chloride, and Zn salt can be zinc nitrate.

[0012] Furthermore, in step (1), the transition metal salts are at least three types, thereby forming multi-element transition metal single atoms. The transition metal salts can be three, four, five, six, seven, eight, nine, ten, etc., preferably three to seven types, and more preferably five types.

[0013] Furthermore, in step (1), the transition metal salt can be one of the following combinations, for example, a combination of Fe salt, Co salt, Ni salt, V salt, and Zn salt; a combination of Fe salt, Co salt, Ni salt, and Zn salt; a combination of Fe salt, Co salt, and Ni salt; a combination of Fe salt, Co salt, Ni salt, V salt, Zn salt, and Cu salt; or a combination of Fe salt, Co salt, Ni salt, V salt, Zn salt, Cu salt, and Mn salt.

[0014] Furthermore, in step (1), the molar ratio between each transition metal salt is between 1:1 and 1:1.3, and preferably, each transition metal salt is added in equal molar amounts.

[0015] Preferably, in step (1), the transition metal salt is a combination of Fe salt, Co salt, Ni salt, V salt and Zn salt in a molar ratio of 1:1:1:1:1.

[0016] Furthermore, in step (1), the carbon nanotube composite material is composed of carbon nanotubes and graphene oxide. It is sheet-like, exhibiting better conductivity, better dispersibility, and a larger specific surface area, which is more conducive to improving the performance of the catalyst. The preparation method of the carbon nanotube composite material is as follows: carbon nanotubes and graphene oxide are dispersed in water, and hydrothermal treatment is performed by heating. After hydrothermal treatment, the mixture is freeze-dried, and the freeze-dried product is calcined to obtain the carbon nanotube composite material. The mass ratio of carbon nanotubes to graphene oxide is 3-6:16. The hydrothermal treatment is carried out in a reactor at a temperature of 160-200℃ for 12-13 hours. Calcination is performed under inert gas protection at a temperature of 800-900℃ for 3-4 hours. The inert gas can be nitrogen, argon, etc.

[0017] Furthermore, in step (1), the total amount of transition metal salt: benzimidazole: aniline: ammonium persulfate: carbon nanotube composite material has a molar ratio of 300-700: 250: 330: 77: 400, preferably 500: 250: 330: 77: 400.

[0018] Further, in step (1), the transition metal salt, benzimidazole, aniline, and carbon nanotube composite material are dissolved in an acid solution, wherein the acid solution is a hydrochloric acid solution with a concentration of 1-2 mol / L, for example, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.8 mol / L, or 2 mol / L. After dissolving in hydrochloric acid, the mixture is stirred at room temperature for 25-35 min, for example, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min, or 35 min. The acid is used as a medium, and its amount can be selected as needed.

[0019] Furthermore, in step (1), after adding ammonium persulfate, the reaction is continued by stirring for 3 to 5 hours, for example, 3 hours, 4 hours, or 5 hours.

[0020] Furthermore, in step (1), the drying temperature is 70–90°C, for example, 70°C, 80°C, or 90°C. The drying time is 9–13 hours, for example, 9 hours, 10 hours, 11 hours, 12 hours, or 13 hours.

[0021] Furthermore, in step (1), calcination is carried out under an inert atmosphere, provided by inert gases such as nitrogen and argon. The calcination temperature is 850-950℃, for example, 850℃, 900℃, or 950℃, preferably 900℃. The calcination time is 1-1.5 hours. Preferably, the temperature is increased to the calcination temperature at a heating rate of 5-10℃ / min, for example, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min.

[0022] Furthermore, in step (2), the acid used for pickling is a sulfuric acid solution with a concentration of 0.5–0.9 mol / L, such as 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, or 0.9 mol / L, preferably 0.5 mol / L. The pickling temperature is 76–80℃, such as 76℃, 77℃, 78℃, 79℃, or 80℃. The pickling time is generally 9–13 hours, such as 9 hours, 10 hours, 11 hours, 12 hours, or 13 hours, preferably 12 hours.

[0023] Furthermore, in step (2), the organic nitrogen source is one of melamine, dicyandiamide, or urea.

[0024] Furthermore, in step (2), the mass ratio of the multi-element transition metal precursor to the organic nitrogen source supported on the acid-washed and dried nitrogen-doped carbon nanotube composite material is 1:1.5-2.5, for example, 1:1.5, 1:2.0, 1:2.5.

[0025] Furthermore, in step (2), the multi-transition metal precursor and organic nitrogen source loaded on the nitrogen-doped carbon nanotube composite material after acid washing and drying can be mixed in any mixing method reported in the prior art, such as grinding and mixing, ultrasonic mixing, etc., as long as the two are mixed evenly.

[0026] Furthermore, in step (2), the two-stage roasting is carried out under an inert atmosphere, provided by inert gases such as nitrogen and argon. The roasting temperature of the first stage is 500-600℃, for example, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃, preferably 550℃. The roasting time of the first stage is 1-3 hours, for example, 1 hour, 2 hours, or 3 hours. The roasting temperature of the second stage is 850-950℃, for example, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃, preferably 900℃. The roasting time of the second stage is 2-4 hours, for example, 2 hours, 3 hours, or 4 hours. Preferably, both the first and second stages of roasting are heated to the roasting temperature at a rate of 5 to 10°C / min, for example, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, or 10°C / min.

[0027] The nitrogen-doped carbon nanotube composite material supported by the method of the present invention has uniformly dispersed metal elements and all active sites are in a single-atom state, exhibiting excellent conductivity and metal dispersion. This electrocatalyst can be used as a host material for sulfur in lithium-sulfur batteries to prepare the positive electrode of lithium-sulfur batteries.

[0028] This invention uses various transition metal salts, benzimidazole, aniline, and carbon nanotube composite materials as raw materials. Benzimidazole, acting as a ligand linker, forms a complex with the transition metal salts through self-assembly. Ammonium persulfate is then added, and the mixture is stirred for a certain period. After filtration, drying, and calcination, a multi-component transition metal precursor is obtained. This precursor is then mixed with an organic nitrogen source and subjected to a two-stage calcination to obtain the final nitrogen-doped carbon nanotube composite-supported multi-component transition metal single-atom electrocatalyst. Compared with existing technologies, this invention has the following advantages:

[0029] 1. This invention uses carbon nanotube composite material as carbon substrate. The introduction of carbon nanotube composite material can give the catalyst excellent conductivity and metal dispersion.

[0030] 2. This invention selects a specific combination of transition metal elements and prepares a multi-element transition metal single-atom electrocatalyst through a self-assembly method. Each metal element is uniformly dispersed, and the active sites are all in a single-atom state, which enhances the anchoring of polysulfides, suppresses the shuttle effect, and accelerates the redox reaction kinetics of sulfur. Furthermore, by introducing a nitrogen source a second time, the carbon nanotube composite material is transformed into a nitrogen-doped carbon nanotube composite material, which enhances the polarity and conductivity of the catalyst, facilitates the dispersion of atoms, and greatly improves the electrochemical performance and cycle stability of lithium-sulfur batteries.

[0031] 3. The preparation process of this invention is simple, the active components are all transition metal elements, the required raw materials are widely available, and the content of each metal component is easy to control, which greatly reduces the production cost.

[0032] 4. The electrocatalyst prepared by this invention can be used as a host material for sulfur in lithium-sulfur batteries, and the assembled lithium-sulfur batteries have high discharge specific capacity and excellent cycle stability. Attached Figure Description

[0033] Figure 1 This is a high-angle annular dark-field image with spherical aberration correction scanning transmission electron microscope image of the FeCoNiVZn / N-CNT pentaneous single-atom catalyst prepared in Example 1 of this invention;

[0034] Figure 2 The X-ray diffraction pattern of the FeCoNiVZn / N-CNT five-component single-atom catalyst prepared in Example 1 of this invention;

[0035] Figure 3 Nitrogen isothermal adsorption-desorption curves and pore size distribution (BET) of the FeCoNiVZn / N-CNT pentaneous single-atom catalyst prepared in Example 1 of this invention. Detailed Implementation

[0036] The method of the present invention will be further described below through specific embodiments. However, it should be understood that the following description is merely exemplary and does not limit the scope of protection of the present invention.

[0037] In the following examples and comparative examples, the carbon nanotube composite material was prepared as follows: 20 mg of carbon nanotubes and 64 mg of graphene oxide were added to a 250 ml glass container, then 128 ml of water was added, the mixture was mixed evenly and sealed, and the mixture was heated to 180 °C for hydrothermal treatment for 12 h. The mixture was then freeze-dried for 18 h. The freeze-dried sample was heated to 850 °C at a heating rate of 5 °C / min under N2 atmosphere and calcined for 12 h to obtain the carbon nanotube composite material.

[0038] Example 1

[0039] Preparation method of FeCoNiVZn / N-CNT materials:

[0040] 3g of benzimidazole, 4.04g of Fe(NO3)3 9H2O, 2.91g of Co(NO3)2 6H2O, 2.90g of Ni(NO3)2 6H2O, 2.97g of Zn(NO3)2 6H2O, 1.57g of VCl3, 3ml of aniline, and 480mg of carbon nanotube composite material were dissolved in 200ml of hydrochloric acid aqueous solution (concentration 1.5M). The solution was stirred for 30 minutes, then 1.76g of ammonium persulfate was added, and stirring was continued for 4 hours. The solution was then filtered and dried in a vacuum oven at 80℃ for 12 hours. The dried material was placed in a tube furnace and calcined at 900℃ for 1 hour in an argon atmosphere at a heating rate of 5℃ / min to obtain a pentagonal metal precursor material. The pentagonal metal precursor material was then placed in 0.5M H2SO4 and acid-washed in a water bath at 80℃ for 12 hours, and then dried. 1g of dried material was ground and mixed with 2g of melamine until homogeneous. The mixture was then placed in a tube furnace and calcined at 550℃ for 2 hours in an argon atmosphere at a heating rate of 5℃ / min. The mixture was then calcined at 900℃ for 3 hours at a heating rate of 5℃ / min to obtain a pentagonal single-atom electrocatalyst (FeCoNiVZn / N-CNT) supported on a nitrogen-doped carbon nanotube composite material.

[0041] HADDF-STEM of FeCoNiVZn / N-CNT Figure 1 As shown in the figure, each metal exists in single-atom form and is uniformly distributed on the nitrogen-doped carbon nanotube composite matrix. The XRD pattern of FeCoNiVZn / N-CNT is shown below. Figure 2 As shown, from Figure 2 It can be seen that the catalyst contains only two distinct characteristic peaks corresponding to the (002) and (100) crystal planes of graphitized carbon, and there are no other impurity peaks, indicating that the metal is uniformly distributed in the nitrogen-doped carbon material. The nitrogen isothermal adsorption-desorption curves and pore size distribution of FeCoNiVZn / N-CNT are shown in the figure. Figure 3 As shown, from Figure 3 It can be seen that the catalyst has a large specific surface area (227 cm²). 2 / g).

[0042] Example 2

[0043] Preparation method of FeCoNiZn / N-CNT catalyst:

[0044] 3g benzimidazole, 4.04g Fe(NO3)3 9H2O, 3.63g Co(NO3)2 6H2O, 3.625g Ni(NO3)2 6H2O, 3.71g Zn(NO3)2 6H2O, 3ml aniline, and 480mg carbon nanotube composite material were dissolved in 200ml of hydrochloric acid aqueous solution (concentration 1.6M) and stirred for 25 minutes. Then, 1.76g ammonium persulfate was added, and stirring was continued for 3 hours. The mixture was then filtered and dried in a vacuum oven at 70℃ for 9 hours. The dried material was placed in a tube furnace and calcined at 850℃ for 1.3 hours under an argon atmosphere at a heating rate of 7℃ / min to obtain a quaternary metal precursor material. The quaternary metal precursor material was then placed in 0.7M H2SO4 and acid-washed in a water bath at 76℃ for 10 hours, and then dried. 1g of dried material was ground and mixed evenly with 1.5g of urea, then placed in a tube furnace and calcined at 520℃ for 1 hour in an argon atmosphere at a heating rate of 7℃ / min, followed by calcination at 860℃ for 2 hours at a heating rate of 7℃ / min, to obtain a quaternary single-atom electrocatalyst (FeCoNiZn / N-CNT) supported on nitrogen-doped carbon nanotube composite material. Verification using high-angle annular dark-field imaging-spherical aberration-corrected scanning transmission electron microscopy confirmed that all metals in the catalyst existed in single-atom form and were uniformly distributed on the nitrogen-doped carbon nanotube composite matrix.

[0045] Example 3

[0046] Preparation method of FeCoNi / N-CNT catalyst:

[0047] 3g benzimidazole, 6.73g Fe(NO3)3 9H2O, 4.85g Co(NO3)2 6H2O, 4.83g Ni(NO3)2 6H2O, 3ml aniline, and 480mg carbon nanotube composite material were dissolved in 200ml of hydrochloric acid aqueous solution (concentration 1.8M) and stirred for 27 minutes. Then, 1.76g ammonium persulfate was added, and stirring continued for 5 hours. The mixture was then filtered and dried in a vacuum oven at 80℃ for 10 hours. The dried material was placed in a tube furnace and calcined at 950℃ for 1.2 hours under an argon atmosphere at a heating rate of 6℃ / min to obtain a ternary metal precursor material. Subsequently, the ternary metal precursor material was placed in 0.6M H2SO4 and acid-washed in a water bath at 77℃ for 11 hours, and then dried. 1g of dried material was ground and mixed evenly with 2.5g of melamine, then placed in a tube furnace and calcined at 530℃ for 1 hour at a heating rate of 6℃ / min under an argon atmosphere. The mixture was then further calcined at 950℃ for 4 hours at a heating rate of 6℃ / min to obtain a ternary single-atom electrocatalyst (FeCoNi / N-CNT) supported on a nitrogen-doped carbon nanotube composite material. Verification using high-angle annular dark-field imaging-spherical aberration-corrected scanning transmission electron microscopy confirmed that all metals in the catalyst existed in single-atom form and were uniformly distributed on the nitrogen-doped carbon nanotube composite matrix.

[0048] Example 4

[0049] Preparation method of FeCoNiVZnCu / N-CNT catalyst:

[0050] 3g benzimidazole, 3.36g Fe(NO3)3 9H2O, 2.425g Co(NO3)2 6H2O, 2.41g Ni(NO3)2 6H2O, 2.47g Zn(NO3)2 6H2O, 1.31g VCl3, 2.01g Cu(NO3)2 3H2O, 3ml aniline, and 480mg carbon nanotube composite material were dissolved in 200ml of hydrochloric acid aqueous solution (concentration of 1.2M), stirred for 32 minutes, then 1.76g ammonium persulfate was added, and stirring was continued for 4 hours. The solution was then filtered and dried in a vacuum oven at 90℃ for 11 hours. The dried material was placed in a tube furnace and calcined at 900℃ for 1.5 hours in an argon atmosphere at a heating rate of 8℃ / min to obtain a hexa-metal precursor material. This precursor material was then acid-washed in 0.8M H₂SO₄ in a 78℃ water bath for 9 hours, followed by drying. 1g of the dried material was ground and mixed evenly with 2g of melamine, then placed in a tube furnace and calcined at 580℃ for 2 hours in an argon atmosphere at a heating rate of 8℃ / min, followed by calcination at 920℃ for 3 hours at a heating rate of 8℃ / min to obtain a hexa-metal single-atom electrocatalyst (FeCoNiVZnCu / N-CNT) supported on a nitrogen-doped carbon nanotube composite material. High-angle annular dark-field imaging with spherical aberration correction scanning transmission electron microscopy confirmed that all metals in the catalyst existed in single-atom form and were uniformly distributed on the nitrogen-doped carbon nanotube composite matrix.

[0051] Example 5

[0052] Preparation method of FeCoNiVZnCuMn / N-CNT catalyst:

[0053] 3g benzimidazole, 2.88g Fe(NO3)3 9H2O, 2.07g Co(NO3)2 6H2O, 2.07g Ni(NO3)2 6H2O, 2.12g Zn(NO3)2 6H2O, 1.12g VCl3, 1.72g Cu(NO3)2 3H2O, 1.79g Mn(NO3)2 4H2O, 3ml aniline, and 480mg carbon nanotube composite material were dissolved in 200ml of hydrochloric acid aqueous solution (concentration of 2M), stirred for 35 minutes, then 1.76g ammonium persulfate was added, and stirring was continued for 5 hours. The solution was then filtered and dried in a vacuum oven at 70℃ for 13 hours. The dried material was placed in a tube furnace and calcined at 900℃ for 1.4 hours in an argon atmosphere at a heating rate of 10℃ / min to obtain a seven-membered metal precursor material. This precursor material was then acid-washed in 0.9M H₂SO₄ in a 79℃ water bath for 13 hours, followed by drying. 1g of the dried material was ground and mixed uniformly with 2g of dicyandiamide, and then calcined at 590℃ for 3 hours in an argon atmosphere at a heating rate of 10℃ / min, followed by calcination at 910℃ for 3 hours to obtain a seven-membered single-atom electrocatalyst (FeCoNiVZnCuMn / N-CNT) supported on a nitrogen-doped carbon nanotube composite material. High-angle annular dark-field imaging with spherical aberration correction scanning transmission electron microscopy confirmed that all metals in the catalyst existed in single-atom form and were uniformly distributed on the nitrogen-doped carbon nanotube composite matrix.

[0054] Comparative Example 1

[0055] The preparation method of the FeCoNiVZn / NC catalyst is the same as in Example 1, except that the carbon nanotube composite material is replaced with Ketjen black. The obtained nitrogen-doped carbon-supported pentaneous single-atom electrocatalyst (FeCoNiVZn / NC) was verified by high-angle annular dark-field imaging-spherical aberration corrected scanning transmission electron microscopy. It was found that each metal in the catalyst exists in the form of a single atom and is uniformly distributed on the nitrogen-doped carbon matrix.

[0056] Comparative Example 2

[0057] The preparation method of the FeCoNiZnMg / N-CNT catalyst is the same as in Example 1, except that 1.57g VCl3 is replaced with 2.03g MgCl2·6H2O. The resulting nitrogen-doped carbon nanotube composite supported pentaneous single-atom electrocatalyst (FeCoNiZnMg / N-CNT) was verified by high-angle annular dark-field image-spherical aberration corrected scanning transmission electron microscopy. The results showed that all metals in the catalyst existed in single-atom form and were uniformly distributed on the nitrogen-doped carbon matrix.

[0058] Comparative Example 3

[0059] Preparation method of FeCoNiVZn / CNT catalyst:

[0060] 3g of benzimidazole, 4.04g of Fe(NO3)3 9H2O, 2.91g of Co(NO3)2 6H2O, 2.90g of Ni(NO3)2 6H2O, 2.97g of Zn(NO3)2 6H2O, 1.57g of VCl3, 3ml of aniline, and 480mg of carbon nanotube composite material were dissolved in 200ml of hydrochloric acid aqueous solution (concentration of 1.5M). The solution was stirred for 30 minutes, then 1.76g of ammonium persulfate was added, and the stirring was continued for 4 hours. The solution was then filtered and dried in a vacuum oven at 80℃ for 12 hours. The dried material was placed in a tube furnace and calcined at 900℃ for 1 hour in an argon atmosphere at a heating rate of 5℃ / min to obtain a pentagonal metal precursor material. This precursor material was then placed in 0.5M H₂SO₄ and acid-washed in an 80℃ water bath for 12 hours, followed by drying to obtain a carbon nanotube-supported pentagonal single-atom electrocatalyst (FeCoNiVZn / CNT). High-angle annular dark-field imaging with spherical aberration correction scanning transmission electron microscopy confirmed that all metals in the catalyst existed in single-atom form and were uniformly distributed on the carbon nanotube matrix.

[0061] Comparative Example 4

[0062] Preparation method of FeCo / N-CNT containing catalyst:

[0063] 3g benzimidazole, 10.1g Fe(NO3)3 9H2O, 7.27g Co(NO3)2 6H2O, 3ml aniline, and 480mg carbon nanotube composite material were dissolved in 200ml of hydrochloric acid aqueous solution (concentration 1.5M), stirred for 30 minutes, then 1.76g ammonium persulfate was added, and stirring continued for 4 hours. The mixture was then filtered and dried in a vacuum oven at 80℃ for 12 hours. The dried material was placed in a tube furnace and calcined at 900℃ for 1 hour in an argon atmosphere at a heating rate of 5℃ / min to obtain a binary metal precursor material. This binary metal precursor material was then acid-washed in 0.5M H2SO4 in an 80℃ water bath for 12 hours, and then dried. 1g of dried material was ground and mixed evenly with 2g of melamine, then placed in a tube furnace and calcined at 550℃ for 2 hours under an argon atmosphere at a heating rate of 5℃ / min, followed by calcination at 900℃ for 3 hours at a heating rate of 5℃ / min, to obtain a binary single-atom electrocatalyst (FeCo / N-CNT) supported on nitrogen-doped carbon nanotube composite material. Verification using high-angle annular dark-field imaging-spherical aberration-corrected scanning transmission electron microscopy showed that all metals in the catalyst existed in single-atom form and were uniformly distributed on the nitrogen-doped carbon nanotube composite matrix.

[0064] Comparative Example 5

[0065] Preparation method of Fe / N-CNT containing catalyst:

[0066] 3g benzimidazole, 20.2g Fe(NO3)3 9H2O, 3ml aniline, and 480mg carbon nanotube composite material were dissolved in 200ml of hydrochloric acid aqueous solution (concentration 1.5M), stirred for 30 minutes, then 1.76g ammonium persulfate was added and stirring continued for 4 hours. The mixture was then filtered and dried in a vacuum oven at 80℃ for 12 hours. The dried material was placed in a tube furnace and calcined at 900℃ for 1 hour in an argon atmosphere at a heating rate of 5℃ / min to obtain a monometallic precursor material. This monometallic precursor material was then placed in 0.5M H2SO4 and acid-washed in an 80℃ water bath for 12 hours, followed by drying. 1g of dried material was ground and mixed evenly with 2g of melamine, then placed in a tube furnace and calcined at 550℃ for 2 hours under an argon atmosphere at a heating rate of 5℃ / min, followed by calcination at 900℃ for 3 hours at a heating rate of 5℃ / min, to obtain a monoary single-atom electrocatalyst (Fe / N-CNT) supported on a nitrogen-doped carbon nanotube composite material. Verification using high-angle annular dark-field imaging-spherical aberration-corrected scanning transmission electron microscopy showed that all metals in the catalyst existed in single-atom form and were uniformly distributed on the nitrogen-doped carbon nanotube composite matrix.

[0067] Performance testing

[0068] 1. Sample preparation

[0069] Using the materials obtained in the examples and comparative examples as catalysts, button-type lithium-sulfur batteries were assembled. The preparation process is as follows:

[0070] 1.1 Sulfur loading of catalyst: Sublimed sulfur powder with a mass ratio of 7:3 and the catalyst prepared above are ground and mixed. The mixture is placed in a reaction vessel and then heated in an oven at 155°C for 12 hours. After cooling, sulfur / catalyst composite cathode material is obtained.

[0071] 1.2 Preparation of the positive electrode sheet: The obtained sulfur / catalyst composite positive electrode material, conductive agent (conductive carbon black, SuperP), and binder (LA33) were mixed in a mass ratio of 7:2:1 to obtain a uniformly mixed slurry. The slurry was then coated onto an aluminum foil current collector using a doctor blade with a blade height of 30 μm. The coated sample was placed in a vacuum oven and baked at 70°C for 8 hours. After drying, the positive electrode sheet for the lithium-sulfur battery was prepared, with a sulfur loading of approximately 1.1 mg / cm². -2 Cut the positive electrode into a circular piece with a diameter of 8mm to serve as the working electrode (positive electrode) of the button cell, for later use.

[0072] 1.3 Assembly of Button Cells: 2032 button cells are assembled in the following order: positive electrode shell, positive electrode plate, separator, electrolyte, negative electrode plate (lithium metal electrode), nickel foam, and negative electrode shell. The separator is a polypropylene separator (Celgard 2500). The electrolyte composition is: 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1% lithium nitrate (by mass), and the remainder being solvent. The solvent in the electrolyte is a mixture of 3-dioxolane (DOL) and ethylene glycol dimethyl ether (OME) in a volume ratio of 1:11.

[0073] 2. Performance testing of the packaged button cells.

[0074] 2.1 The electrochemical performance of different lithium-sulfur batteries was evaluated by constant current charge-discharge tests (test voltage range 1.7-2.8V, current density 0.1C) on the Blue Electric system, and the cycle stability of the lithium-sulfur batteries was assessed and compared. The test results are shown in Table 1. As can be seen from Table 1, the first-cycle discharge specific capacity of each embodiment is greater than that of each comparative embodiment. The use of the catalyst in this invention enhances the utilization rate of sulfur, resulting in a higher discharge specific capacity of the battery. Among them, Example 1 has the highest first-cycle discharge specific capacity.

[0075] Table 1. Discharge specific capacity (mAh / g) of different batteries at 0.1C

[0076]

[0077] 2.2 Rate performance was studied by applying different current densities. The test results are shown in Table 2. Table 2 shows that the discharge specific capacities of the batteries assembled with FeCoNiVZn / N-CNT from Example 1 at current densities of 0.2C, 0.4C, 0.6C, 1C, 0.6C, and 0.4C were 1318.2 mAh / g, 1124.2 mAh / g, 1068.4 mAh / g, 991.1 mAh / g, 1055.6 mAh / g, and 1092.7 mAh / g, respectively, demonstrating extremely high ion transport capabilities and exhibiting the best rate performance compared to other samples. When the current density decreased from 1C to 0.4C, it still recovered to a discharge capacity of 1092.7 mAh / g, indicating that the FeCoNiVZn / N-CNT electrode has excellent capacity reversibility and stability, which can effectively improve the electrochemical performance of the battery. Examples 2-5 also exhibit good capacity reversibility and stability, but their performance is inferior to that of Example 1. The capacity reversibility and stability of each comparative example are significantly different from those of each example.

[0078] Table 2 Rate performance of different batteries at different current densities

[0079]

[0080] 2.3. The cycle performance of different lithium-sulfur batteries at 0.1C rate was tested, and the results are shown in Table 3. As can be seen from Table 3, the discharge specific capacity and cycle stability of Examples 1-5 are much higher than those of the comparative examples, with Example 1 showing the highest discharge specific capacity and cycle stability.

[0081] Table 3 Cycle performance of different batteries at 0.1C

[0082]

[0083] The above experiments clearly demonstrate that the multi-element transition metal single-atom electrocatalyst supported on the nitrogen-doped carbon nanotube composite material of this invention can enhance the catalytic conversion of polysulfides, improve sulfur utilization, and enhance the cycle stability of lithium-sulfur batteries.

[0084] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a multi-element transition metal single-atom electrocatalyst supported on a nitrogen-doped carbon nanotube composite material, characterized in that... Includes the following steps: (1) Dissolve at least three transition metal salts, benzimidazole, aniline, and carbon nanotube composite material in an acid solution, stir and mix, then add ammonium persulfate, stir and react, collect the product after reaction, and then dry and calcine to obtain a nitrogen-doped carbon nanotube composite material loaded with a multi-component transition metal precursor. (2) The nitrogen-doped carbon nanotube composite material supported by the multi-element transition metal precursor was acid-washed and dried, and then mixed evenly with an organic nitrogen source. After mixing, it was calcined in two stages to obtain the nitrogen-doped carbon nanotube composite material supported by the multi-element transition metal single-atom electrocatalyst. In step (1), the transition metal of the transition metal salt is selected from Fe, Co, Ni, V, Zn, Cu, and Mn; the carbon nanotube composite material is composed of carbon nanotubes and graphene oxide.

2. The preparation method according to claim 1, characterized in that: In step (1), the transition metal salt is a soluble salt of a transition metal.

3. The preparation method according to claim 2, characterized in that: In step (1), the transition metal salt is a chloride or nitrate of a transition metal.

4. The preparation method according to claim 1, 2 or 3, characterized in that: In step (1), there are 3-7 types of transition metal salts.

5. The preparation method according to claim 4, characterized in that: In step (1), there are 5 types of transition metal salts.

6. The preparation method according to claim 1 or 2, characterized in that: In step (1), the transition metal is one of the following combinations: FeCoNiVZn, FeCoNiZn, FeCoNi, FeCoNiVZnCu, FeCoNiVZnCuMn.

7. The preparation method according to claim 6, characterized in that: The molar amounts of the transition metal are equal in each transition metal salt.

8. The preparation method according to claim 1, characterized in that: In step (1), the preparation method of the carbon nanotube composite material is as follows: carbon nanotubes and graphene oxide are dispersed in water at a mass ratio of 3-6:16, and hydrothermal treatment is performed by heating. After hydrothermal treatment, the mixture is freeze-dried, and the freeze-dried product is calcined to obtain the carbon nanotube composite material.

9. The preparation method according to claim 8, characterized in that: In step (1), during the preparation of carbon nanotube composite materials, the hydrothermal treatment temperature is 160-200℃ and the hydrothermal treatment time is 12-13h.

10. The preparation method according to claim 8, characterized in that: In step (1), during the preparation of carbon nanotube composite materials, calcination is carried out under inert gas protection at a temperature of 800-900℃ for 3-4 hours.

11. The preparation method according to claim 1, characterized in that: In step (1), the total amount of transition metal salts: the molar ratio of benzimidazole: aniline: ammonium persulfate: carbon nanotube composite material is 300-700: 250: 330: 77:

400.

12. The preparation method according to claim 11, characterized in that: In step (1), the total amount of transition metal salts: the molar ratio of benzimidazole: aniline: ammonium persulfate: carbon nanotube composite material is 500: 250: 330: 77:

400.

13. The preparation method according to claim 1, characterized in that: Step (1) includes at least one of the following conditions: a. Dissolve all raw materials in hydrochloric acid solution and stir at room temperature for 25-35 minutes; b. After adding ammonium persulfate, stir and react for 3–5 hours; c. The drying temperature is 70–90℃; the drying time is 9–13 hours; d. The calcination conditions are as follows: calcination is carried out under an inert atmosphere at a temperature of 850-950℃ for 1-1.5 hours, with a heating rate of 5-10℃ / min.

14. The preparation method according to claim 13, characterized in that: In step (1), the concentration of hydrochloric acid solution is 1-2 mol / L.

15. The preparation method according to claim 1, characterized in that: Step (2) includes at least one of the following conditions: a. The acid used for pickling is a sulfuric acid solution with a concentration of 0.5–0.9 mol / L; b. The pickling temperature is 76-80℃, and the pickling time is 9-13 hours; c. The organic nitrogen source is melamine, dicyandiamide, or urea; d. The mass ratio of the multi-component transition metal precursor to the organic nitrogen source supported on the nitrogen-doped carbon nanotube composite material after pickling and drying is 1:1.5-2.

5.

16. The preparation method according to claim 15, characterized in that: In step (2), the acid used for pickling is a sulfuric acid solution with a concentration of 0.5 mol / L.

17. The preparation method according to claim 1, characterized in that: In step (2), the two-stage roasting process is as follows: the two-stage roasting is carried out under an inert atmosphere. The first stage roasting temperature is 500-600℃, the roasting time is 1-3 hours, and the heating rate is 5-10℃ / min. The second stage roasting temperature is 850-950℃, the roasting time is 2-4 hours, and the heating rate is 5-10℃ / min.

18. A nitrogen-doped carbon nanotube composite supported multi-component transition metal single-atom electrocatalyst prepared by the method of any one of claims 1-17.

19. The application of the multi-component transition metal single-atom electrocatalyst supported on the nitrogen-doped carbon nanotube composite material according to claim 18 in lithium-sulfur batteries, characterized in that: The catalyst, as a host material for sulfur, is used to prepare the positive electrode of a lithium-sulfur battery.

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