Carbon nano tube loaded transition metal atom composite material as well as preparation method and application thereof

Abstract

The invention relates to a carbon nano tube loaded transition metal atom composite material and a preparation method and application thereof, the composite material comprises a non-metallic element doped carbon nano tube and transition metal atoms loaded on the carbon nano tube, and the transition metal atoms form an AN4-B five-coordination structure on the carbon nano tube; wherein the transition metal is at least one of Fe, Co, Ni and Cu, the non-metallic element is at least one of N, O, F and S, A is the transition metal, and B is the non-metallic element; after being compounded with sulfur, the composite material is applied to a room-temperature sodium-sulfur battery as a positive electrode material, so that the conversion kinetics of sodium polysulfide is remarkably accelerated, and migration and agglomeration of iron monatomic in the cyclic process are effectively inhibited, thereby realizing high sulfur utilization rate, high rate capability and super-long cycle life. The invention provides an effective catalyst design strategy for solving the problems of shuttle effect and slow reaction kinetics of the room-temperature sodium-sulfur battery.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and electrochemical energy storage technology, specifically relating to a composite material of transition metal atoms supported by carbon nanotubes, its preparation method and application. Background Technology

[0002] The global energy system is undergoing an unprecedented and profound transformation. On the one hand, the increasingly severe climate change problem and the proposed goals of "carbon peaking and carbon neutrality" are driving human society to accelerate its shift away from dependence on fossil fuels and towards clean and renewable energy sources, such as wind and solar power. On the other hand, energy security has become a core strategic concern for countries worldwide, making the construction of an independent, controllable, and diversified energy supply system crucial. However, the inherent intermittency, volatility, and regionality of renewable energy sources such as wind and solar power make them difficult to directly integrate with the power grid, severely limiting their large-scale development and utilization. Therefore, developing efficient, large-scale, and long-term energy storage technologies has become a key necessitation for solving the grid integration challenges of renewable energy and achieving a successful energy structure transformation.

[0003] Secondary battery technology holds a core position due to its flexible deployment, rapid response, and high energy conversion efficiency. Currently, lithium-ion batteries (LIBs) dominate the global electric vehicle and portable electronic device markets. However, the extremely uneven global distribution of lithium resources, coupled with geopolitical factors leading to a fragile supply chain and volatile prices, restricts the further application of lithium-ion batteries in large-scale energy storage. Against this backdrop, abundant and inexpensive sodium-ion battery technology has emerged and is considered one of the most promising candidates to replace or supplement lithium-ion batteries in large-scale energy storage. Sodium is more than 400 times more abundant in the Earth's crust than lithium, and its distribution is widespread, resulting in extremely low raw material costs. Among numerous sodium-ion battery systems, room-temperature sodium-sulfur (RT Na-S) batteries stand out due to their extremely high theoretical specific capacity (1675 mAh g / g). - 1) and energy density (~1274Wh kg) - 1), and the abundant reserves, environmental friendliness, and complete non-toxicity of sulfur as a positive electrode active material, demonstrate enormous application potential and have become the research frontier and hot topic of the next generation of electrochemical energy storage systems.

[0004] However, the transition of RT Na-S batteries from the laboratory to industrialization still faces two long-standing and interconnected core scientific challenges and technological bottlenecks: First, the "shuttle effect," which leads to irreversible loss of active material and rapid capacity decay, and also reacts with the sodium anode, resulting in low coulombic efficiency and battery failure. Second, the slow reaction kinetics: the complex multi-electron reaction pathways in the polysulfide conversion process result in extremely slow sulfur oxidation reaction kinetics, leading to high polarization voltage, poor rate performance, and low sulfur utilization.

[0005] To overcome these challenges, researchers have explored various strategies. Among them, single-atom catalyst technology provides an atomic-level solution for precisely controlling polysulfide conversions, as single atoms can maximize the exposure of active sites and significantly improve catalytic efficiency. However, existing research techniques lack the precise construction of atomically efficient and stable catalytic centers. Currently, most single-atom active sites are traditional M-N4 structures, exhibiting poor catalytic activity. Moreover, under harsh electrochemical cycling conditions, such structures are prone to migration, aggregation, and leaching, leading to irreversible deactivation of active sites and structural collapse. Their long-term stability falls far short of the requirements for practical applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an axially nonmetallic coordinated transition metal single-atom catalyst that possesses both high catalytic activity and excellent structural stability. This catalyst breaks the planar symmetry of the traditional AN4 (A is a transition metal) structure by introducing axially coordinated fluorine atoms to construct a unique AN4-B (A is a transition metal, B is a nonmetal) active center, precisely controlling the electronic structure microenvironment of the transition metal active center. Its application in room-temperature sodium-sulfur batteries can effectively solve problems such as severe polysulfide shuttle effects, slow sulfur reduction reaction kinetics, and poor catalyst stability in existing technologies.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A carbon nanotube-supported transition metal atom composite material, the composite material comprising non-metallic element-doped carbon nanotubes and transition metal atoms supported on the carbon nanotubes, wherein the transition metal atoms form an AN4-B five-coordinate structure on the carbon nanotubes; wherein the transition metal is at least one of Fe, Co, Ni, and Cu, and the non-metallic element is at least one of N, O, F, and S, A is the transition metal, and B is the non-metallic element.

[0009] In some embodiments, the transition metal atoms form an AN4 planar structure on the carbon nanotube, and the non-metallic elements doped in the carbon nanotube form axial AB coordination bonds with the AN4 planar structure where the transition metal atoms are located.

[0010] In some embodiments, the transition metal atoms in the composite material are 0.5-5 wt% of the composite material, in order to ensure a high number of active sites while avoiding the aggregation of non-metallic atoms to form nanoparticles, which would reduce the reaction efficiency of its application process.

[0011] The present invention also provides a method for preparing a carbon nanotube-supported transition metal atom composite material according to any of the above embodiments, the method comprising the following steps:

[0012] Carbon nanotubes doped with non-metallic elements are dissolved in a solvent to prepare a carbon nanotube dispersion; the carbon nanotube dispersion is added to a complex solution formed by a transition metal and an organic ligand to react and obtain a precursor solution; the precursor solution is freeze-dried and then calcined at 700-1000℃ under an inert atmosphere to obtain the carbon nanotube-loaded transition metal atom composite material.

[0013] The organic ligand is one of o-phenanthroline, phenanthroline, 2,2'-bipyridine, and 2,9-dimethyl-4,7-biphenyl-1,10-o-phenanthroline.

[0014] In some embodiments, the preparation of the complex solution formed by the transition metal atom and the organic ligand includes the following steps:

[0015] The transition metal salt and the organic ligand are mixed and added to an organic solvent, and mixed evenly to obtain the complex solution; wherein the molar ratio of the transition metal to the organic ligand in the transition metal salt is 1:1.5-3.

[0016] In some embodiments, the mass ratio of transition metal atoms to carbon nanotubes in the transition metal salt is 0.5-10%.

[0017] In some embodiments, the carbon nanotube dispersion is added to the complex solution at a rate of 5-50 mL / min.

[0018] In some embodiments, the solvent is deionized water.

[0019] In some embodiments, the organic solvent is an alcohol-based organic solvent; preferably, it is ethanol.

[0020] In some embodiments, the freeze-drying specifically involves: first freezing under liquid nitrogen conditions, and then freezing at a temperature below -4°C; preferably, freezing in liquid nitrogen followed by freezing at a temperature of -30 to -4°C.

[0021] In some embodiments, the transition metal salt is at least one of the chloride, nitrate, sulfate, and acetate salts of Fe, Co, Ni, and Cu.

[0022] In some embodiments, the inert atmosphere is either an argon atmosphere or a helium atmosphere.

[0023] In some embodiments, the preparation method of the non-metal-doped carbon nanotubes is as follows: using manganese dioxide nanorods as templates, co-condensing them with non-metallic carbon quantum dots and phenolic resin, followed by high-temperature carbonization and template removal to obtain non-metallic-doped carbon nanotubes. Using specific carbon quantum dots as raw materials, which serve as the core and carrier, atomically dispersed transition metal single atoms are anchored on their surface and interior through strong axial AB bonds. Each transition metal atom is coordinated with four N atoms and one axial non-metal element atom, forming a stable AN4-B five-coordinate structure. This structure is a highly efficient active center for catalyzing polysulfide conversion. The aforementioned BCDs units carrying AN4-B sites are interconnected and cross-linked through their surface functional groups under the action of the template during the preparation process, and after carbonization, ultimately form a hollow carbon nanotube structure. This structure serves as a channel for rapid electron conduction, provides space for sulfur loading and volume expansion, and physically confines polysulfides.

[0024] In some embodiments, the high-temperature carbonization temperature is 800-1000°C; the carbonization time is 2-24 hours.

[0025] In some embodiments, the template removal method is as follows: the precursor material containing the template is immersed in a 0.2-2.0M oxalic acid solution, the reaction temperature is controlled at 60-90℃, and the mixture is stirred continuously for 24-60 hours to finally remove the template.

[0026] In some embodiments, the manganese dioxide nanorods are prepared by dissolving potassium permanganate and polyvinylpyrrolidone in deionized water, mixing them thoroughly, and then heating the mixture to 150-200°C for a hydrothermal reaction to obtain the manganese dioxide nanorods. MnO2 nanorods, acting as templates, not only facilitate the formation of tubular structures, but their decomposition at high temperatures also generates gas, further promoting the pore development of carbon materials and improving specific surface area and mass transfer efficiency.

[0027] The present invention also provides a sulfur composite material, which includes a carbon nanotube-supported transition metal atom composite material of any of the above embodiments or a carbon nanotube-supported transition metal atom composite material obtained by any of the above preparation methods, as well as elemental sulfur attached to the inner and outer surfaces of the carbon nanotube matrix and the three-dimensional porous network of the composite material.

[0028] The present invention also provides a method for preparing the above-mentioned sulfur composite material, the method comprising the following steps:

[0029] A sulfur composite material was obtained by mixing carbon nanotube-loaded transition metal atom composite material with elemental sulfur and reacting it with a gradient temperature increase.

[0030] Specifically, the gradient heating reaction involves first heating to 100-200℃ for the reaction, and then heating to 280-400℃ for the reaction.

[0031] In some embodiments, the mass ratio of the elemental sulfur to the composite material is (1-3):1.

[0032] In some implementations, the gradient temperature reaction specifically involves first heating to 100-200°C for 6-48 hours, and then heating to 280-400°C for 1-10 hours.

[0033] In some implementations, the gradient heating rate is 1-10 °C / min.

[0034] The present invention also provides an electrode active material, wherein the electrode active material comprises the above-mentioned sulfur composite material.

[0035] The present invention also provides an electrode comprising the electrode active material described above.

[0036] The present invention also provides an electrochemical energy storage device, which includes the electrodes described above. Further, the electrochemical energy storage device includes a sodium-sulfur battery.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] The carbon nanotube-supported transition metal composite material provided by this invention is characterized by its unique axial coordination structure, which breaks the planar symmetry of traditional structures. By introducing axially coordinating atoms, a unique AN4-B active center (A = Fe, Co, Ni, Cu, B = N, O, F, S) is constructed, precisely controlling the electronic structure microenvironment of the transition metal active center. When applied to room-temperature sodium-sulfur batteries, this invention effectively solves problems such as severe polysulfide shuttle effect, slow sulfur reduction reaction kinetics, and poor catalyst stability in existing technologies. Furthermore, this invention significantly enhances the catalyst's adsorption capacity and catalytic activity for polysulfides by controlling the electronic structure of the single-atom iron active sites through axial fluorine coordination engineering, thereby effectively improving the cycle stability and rate performance of room-temperature sodium-sulfur batteries.

[0039] This invention is the first to propose and realize the design of axially coordinated single-atom iron AN4-B active sites. Utilizing the extremely strong electronegativity of element B, the central electronic structure of element A is effectively modulated, significantly enhancing the chemisorption capacity and catalytic activity for polysulfides, effectively suppressing the shuttle effect, and accelerating the sulfur reduction reaction kinetics. The composite material prepared by this invention, when applied to room-temperature sodium-sulfur batteries, exhibits extremely high specific capacity, excellent cycle stability, and outstanding rate performance.

[0040] This invention employs a template method combined with a wet impregnation-high-temperature pyrolysis process. The steps are simple, the conditions are mild, and it is easy to scale up, exhibiting good versatility and industrialization prospects. Fluorine-doped carbon nanotubes prepared via the sacrificial template method possess high specific surface area and abundant pore structure, which is beneficial for uniform sulfur loading and rapid ion / electron transport. Attached Figure Description

[0041] Figure 1 TEM images of FCNTs prepared in Example 1 and CNT carbon nanotubes prepared in Comparative Example 1 of the present invention.

[0042] Figure 2 Fe prepared in Example 2 of this invention SACS -FCNT and Fe prepared by Comparative Example 2 SACS -TEM image of CNT composite material;

[0043] Figure 3 Fe prepared in Example 2 of this invention SACS -FCNT and Fe prepared by Comparative Example 2 SACS HAADF-STEM image of -CNT composite material;

[0044] Figure 4 Fe prepared in Example 2 of this invention SACS -FCNT and Fe prepared by Comparative Example 2 SACS XANES diagram of CNT composite material;

[0045] Figure 5 Fe prepared in Example 2 of this invention SACS -FCNT and Fe prepared by Comparative Example 2 SACS - Raman diagram of CNT composite material;

[0046] Figure 6 Fe prepared in Example 3 of this invention SACS -FCNT@S and Fe prepared in Comparative Example 3 SACS TEM image of -CNT@S composite cathode material;

[0047] Figure 7 Fe prepared in Example 3 of this invention SACS -FCNT@S and Fe prepared in Comparative Example 3 SACS Cycling curves of the CNT@S composite cathode material at a current density of 200 mA / g;

[0048] Figure 8 Fe prepared in Example 3 of this invention SACS -FCNT@S and Fe prepared in Comparative Example 3 SACS Cycle rate curve of CNT@S composite cathode material;

[0049] Figure 9 Fe prepared in Example 3 of this invention SACS -FCNT@S and Fe prepared in Comparative Example 3 SACS HAADF-STEM image of -CNT@S composite cathode material after 150 cycles at a current density of 200 mA / g;

[0050] Figure 10 Fe prepared in Example 3 of this invention SACS -FCNT@S and Fe prepared in Comparative Example 3 SACS XANES images of the CNT@S composite cathode material after 150 cycles at a current density of 200 mA / g; where, image a shows the Fe... SACS - XANES diagram of CNT@S composite cathode material; Figure b shows Fe SACS XANES diagram of FCNT@S composite cathode material. Detailed Implementation

[0051] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0053] Preparation of fluorine-doped carbon dots: At room temperature, 10 mL of 2,4,5-trifluorobenzaldehyde was mixed with 20 mL of acetaldehyde solution (40% aqueous solution) and stirred. Then, it was added to a sodium hydroxide aqueous solution with a concentration of 1.2 g / L at a dropping rate of 5 mL / min. After stirring and reacting for 5 days, the fluorine-doped carbon dot FCD powder was obtained by dialysis and lyophilization.

[0054] The fluorine-doped carbon dots obtained above were applied in the following examples.

[0055] In addition, unless otherwise specified, all reagents and raw materials used in the specific embodiments of this invention are commercially available.

[0056] Example 1

[0057] The preparation method of fluorine-doped carbon nanotubes includes the following steps:

[0058] S1. Dissolve 190 mg potassium permanganate and 100 mg polyvinylpyrrolidone in 80 mL of deionized water, stir at 550 rpm for 30 min at room temperature, then transfer to a hydrothermal reactor and react at 160 °C for 9 h; separate solid and liquid, wash the solid product repeatedly with deionized water and ethanol alternately, and then vacuum dry at 60 °C overnight to obtain MnO2 nanorods;

[0059] S2. Mix 32 mL of ethanol, 80 mL of deionized water and 0.4 mL of NH3·H2O to obtain a mixed solution. Then add 160 mg of MnO2 nanorods and 100 mg of FCDs to the mixed solution and disperse by ultrasonication for 10 min. Then add 0.4 mL of formaldehyde and stir at 550 rpm for 30 min at room temperature. Then add 0.4 g of resorcinol and keep stirring at 550 rpm for 24 h. After the reaction is complete, the precipitate obtained by centrifugation is washed several times with deionized water and ethanol alternately and dried under vacuum at 50 °C.

[0060] S3. Transfer the vacuum-dried product obtained in step S2 to a ceramic boat and calcine it at 700°C for 2 hours under a flowing nitrogen atmosphere to obtain the MnO2@FCNT precursor.

[0061] S4. The MnO2@FCNT precursor was immersed in a 0.5M oxalic acid solution for 48 hours to etch the precursor and remove the MnO2 nanorod template, thus obtaining a fluorine-doped carbon nanotube FCNT sample.

[0062] Comparative Example 1

[0063] This comparative example prepares a carbon nanotube (CNT). The preparation method of this carbon nanotube is the same as that of the fluorine-doped carbon nanotube in Example 1. The difference is that in step S2, fluorine-doped carbon dots (FCDs) are not added.

[0064] The carbon nanotube materials FCNT and CNT obtained in Example 1 and Comparative Example 1 were subjected to TEM tests, and the detection results are as follows: Figure 1 As shown. Figure 1 Both groups of carbon nanotube samples had uniform hollow tubular structures with a diameter of about 200 nm.

[0065] Example 2

[0066] Carbon nanotube-supported iron single-atom composite material (Fe SACS The preparation method of FCNT includes the following steps:

[0067] 1) Preparation of FCNT dispersion solution: The FCNT (100 mg) obtained in Example 1 was dispersed in 20 mL of deionized water and sonicated for 30 min;

[0068] 2) Preparation of FeCl3-o-phenanthroline complex solution: Weigh 47.8 mg of FeCl2·4H2O and 142.8 mg of 1,10-phenanthroline respectively, place them in a 10 mL centrifuge tube, then add 5 mL of ethanol and mix. Disperse by ultrasonication to obtain a uniform and transparent red liquid.

[0069] 3) During the ultrasonic dispersion of the FeCl3-o-phenanthroline complex solution, the solution was added to the FCNT dispersion solution at a drop rate of 5 mL / min using a pipette. The solution was ultrasonically dispersed for 90 min and then transferred to a magnetic stirrer for continuous stirring at room temperature for 6 h to obtain the precursor solution.

[0070] 4) The above precursor solution was rapidly cryogenically frozen with liquid nitrogen, and then transferred to a freeze dryer for freeze drying at -10°C to obtain the freeze-dried product;

[0071] 5) The obtained freeze-dried product was transferred to a ceramic boat and heated to 900℃ at a heating rate of 3℃ / min under a flowing argon atmosphere, and held for 3 hours to finally obtain the carbon nanotube-supported iron single-atom composite material Fe. SACS -FCNT.

[0072] Comparative Example 2

[0073] This comparative example prepared a carbon nanotube-supported iron single-atom composite material (Fe). SACS -CNT), its preparation method is the same as Fe in Example 2. SACS The preparation methods for -FCNT are the same, except that in step 1), a CNT dispersion solution is prepared; and in step 3), a CNT dispersion solution is added dropwise to the FeCl3-o-phenanthroline complex solution.

[0074] The Fe obtained from Example 2 and Comparative Example 2 SACS -FCNT and Fe SACS -CNT composite materials were subjected to TEM, HAADF-STEM, XANES, and Raman spectroscopy tests. The test results are as follows: Figures 2-5 As shown.

[0075] in, Figure 2 It is Fe SACS -FCNT and Fe SACS -TEM image of CNT. For example... Figure 2 The composite material obtained after liquid nitrogen freezing and high-temperature calcination retains a good hollow carbon nanotube structure, and no obvious iron metal nanoparticles were observed.

[0076] Figure 3 For Fe SACS -FCNT(a) and FeSACS HAADF-STEM plot of -CNT(b). (See figure) Figure 3 Fe SACS HAADF-STEM images of -CNTs show partially isolated bright spots (Fe single atoms) and a small number of brighter clusters (Fe nanoparticles), indicating a certain degree of Fe atom aggregation; while Fe SACS -FCNTs, on the other hand, show a large number of uniform, isolated bright spots with no obvious clusters, proving that Fe atoms are highly dispersed on the fluorine-doped carbon substrate.

[0077] like Figure 4 As shown, the K-edge XANES spectrum of Fe ( Figure 4 Figure a shows that the absorption edges of both samples are located between the Fe foil and Fe₂O₃, indicating that Fe is in a positive valence state. R-space analysis shows the absence of Fe-Fe bonds (e.g., ...). Figure 4 (See Figure b). It is worth noting that further fitting of the XANES data to determine the coordination number, such as... Figure 4 The c and d graphs, Fe SACS -CNT has a specific coordination number of 4, corresponding to the traditional FeN4 planar coordination, while Fe SACS The specific coordination number of -FCNT is 5, indicating that F doping forms Fe-F bonds and the coordination is axial coordination perpendicular to the plane.

[0078] like Figure 5 As shown, Fe SACS -FCNT and Fe SACS Both CNTs and their Raman spectra are in the range of ~1350 cm⁻¹. - 1 (D belt) and ~1580cm - A characteristic peak appears at 1 (G band), which is attributed to the characteristic peak of carbon materials. No characteristic peaks belonging to other compounds were observed here.

[0079] Example 3

[0080] Sulfur composite cathode material Fe SACS The preparation method of -FCNT@S includes the following steps:

[0081] 200 mg of Fe prepared in Example 2 SACS FCNT and 240 mg of sulfur powder were added to a mortar at a mass ratio of 1:1.2 and thoroughly ground to obtain a mixture. The mixture was then sealed in a quartz ampoule and placed in a temperature-controlled furnace. First, the temperature was increased to 155 °C at a rate of 1 °C / min and held for 12 hours. Then, the temperature was increased to 300 °C at a rate of 5 °C / min and held for 2 hours. After the reaction was complete, the mixture was allowed to cool naturally. The ampoule was then opened to obtain a black sulfur composite cathode material, Fe. SACS -FCNT@S.

[0082] Comparative Example 3

[0083] This comparative example prepares a sulfur-based composite cathode material, Fe. SACS -CNT@S, its preparation method and Fe in Example 3 SACS The preparation method of -FCNT@S is the same, the difference being that in this comparative example, the sulfur powder is mixed with Fe. SACS -CNT.

[0084] The Fe obtained from Example 3 and Comparative Example 3 SACS -FCNT@S and Fe SACS -CNT@S material was subjected to TEM testing, and the test results are as follows: Figure 6 As shown.

[0085] like Figure 6 Fe SACS -FCNT@S and Fe SACS -CNT@S maintained the original morphology of carbon nanotubes, and sulfur was evenly distributed on the inner and outer surfaces of the carbon nanotubes, confirming the successful loading of sulfur and the good structural stability of the composite material.

[0086] Example 4

[0087] Assembly and testing of room temperature sodium-sulfur batteries

[0088] The Fe prepared in Example 3 above SACS Fe prepared by -FCNT@S and Comparative Example 3 SACS -CNT@S composite cathode material is used as the active material in room temperature sodium-sulfur batteries and is made into cathode plates. The specific method is as follows: Fe is separately... SACS -FCNT@S and Fe SACS -CNT@S composite cathode material is mixed with Super P (conductive agent) and polyvinylidene fluoride (PVDF, binder) in a mass ratio of 70:20:10. Then, an appropriate volume of N-methylpyrrolidone solvent is added to prepare a slurry. The slurry is then coated onto current collector aluminum foil. After the N-methylpyrrolidone evaporates, the slurry is vacuum dried at 60°C for 12 hours. The slurry is then removed, cut into discs with a diameter of 14 mm, and pressed under 10 MPa pressure to obtain the cathode sheet.

[0089] In an Ar atmosphere glove box, using metallic sodium as the counter electrode, 1M NaClO4 in EC / PC (1:1) containing 5% FEC as the electrolyte, and a glass fiber membrane as the separator, a CR2032 coin cell was assembled with the prepared positive electrode. Electrochemical performance was then tested, and the results are as follows: Figure 7 and Figure 8 As shown.

[0090] like Figure 7 As shown, the voltage range is 0.8-2.8V and the current density is 200mAg. -1 The next cycle is 150 revolutions, Fe SACS The capacity of the FCNT@S remains at 589.5mAh. -1 And Fe SACS -CNT@S has a capacity of only 409.4 g. -1 The capacity.

[0091] like Figure 8 As shown, the voltage range is 0.8-2.8V, with values ​​of 0.2, 0.5, 1.0, 2.0, and 5Ag. -1 At current density, Fe SACS The reversible specific capacities of the -FCNT@S electrode were 875.5, 795.6, 709.1, 626.8, and 493.2 mAh g, respectively. -1 After charging and discharging at different current densities, when the current density returns to 1.0 Ag... -1 At that time, the reversible specific capacity recovered to 885.6 mAh g. -1 And Fe SACS The reversible specific capacities of the -CNT@S electrode were 872.54, 694.2, 578.8, 459.1, and 302.2 mAh g, respectively. -1 After charging and discharging at different current densities, when the current density returns to 1.0 Ag... -1 At that time, the reversible specific capacity recovered to 640.5 mAh g. -1 This indicates that Fe SACS -FCNT@S electrodes exhibit superior rate performance and reversibility.

[0092] Fe SACS -FCNT@S and Fe SACS -CNT@S electrode at a current density of 200 mAg -1 After 150 cycles, the battery was disassembled in a glove box, and the electrode samples from the two cycled sets were subjected to HAADF-STEM and XANES tests. The test results are as follows: Figure 9 and Figure 10 As shown.

[0093] in, Figure 9 Figure a shows the Fe after cycling. SACS The HAADF-STEM image of -CNT@S shows a large number of obvious metal clusters and particles, indicating that Fe atoms have been severely aggregated during long-term cycling. Figure 9 Figure b shows the Fe after cycling. SACSThe HAADF-STEM image of the -FCNT@S shows that most of the bright spots remain isolated, with only a few small clusters appearing, demonstrating the structural stability of the catalyst during electrochemical cycling and effectively suppressing the migration and aggregation of metal atoms.

[0094] Figure 10 For the corresponding XANES plot, after cycling, Fe SACS The absorption edge of -CNT@S shifts towards lower energies, approaching the metallic Fe foil, indicating that the Fe center is reduced to a zero-valence state, and the catalytic active site is deactivated; while Fe SACS The absorption edge position of -FCNT@S only showed a slight shift, indicating that the valence state and coordination environment of its Fe center remained stable during cycling, thus maintaining high catalytic activity.

[0095] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0096] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A carbon nanotube-supported transition metal atom composite material, characterized in that, The composite material comprises non-metallic element-doped carbon nanotubes and transition metal atoms loaded on the carbon nanotubes, wherein the transition metal atoms form an AN4-B five-coordinate structure on the carbon nanotubes; wherein the transition metal is at least one of Fe, Co, Ni, and Cu, and the non-metallic element is at least one of N, O, F, and S, A is the transition metal, and B is the non-metallic element.

2. The carbon nanotube-supported transition metal atom composite material according to claim 1, characterized in that, The transition metal atoms form an AN4 planar structure on the carbon nanotube, and the non-metallic elements doped in the carbon nanotube form axial AB coordination bonds with the AN4 planar structure where the transition metal atoms are located.

3. The method for preparing the carbon nanotube-supported transition metal atom composite material according to claim 1 or 2, characterized in that, Includes the following steps: Carbon nanotubes doped with non-metallic elements are dissolved in a solvent to prepare a carbon nanotube dispersion; the carbon nanotube dispersion is added to a complex solution formed by a transition metal and an organic ligand to react and obtain a precursor solution; the precursor solution is freeze-dried and then calcined at 700-1000℃ under an inert atmosphere to obtain the carbon nanotube-loaded transition metal atom composite material. The organic ligand is one of o-phenanthroline, phenanthroline, 2,2'-bipyridine, and 2,9-dimethyl-4,7-biphenyl-1,10-o-phenanthroline.

4. The method for preparing the carbon nanotube-supported transition metal atom composite material according to claim 3, characterized in that, The preparation of the complex solution formed by the transition metal atom and the organic ligand includes the following steps: The transition metal salt and the organic ligand are mixed and added to an organic solvent, and mixed evenly to obtain the complex solution; wherein the molar ratio of the transition metal to the organic ligand in the transition metal salt is 1:1.5-3.

5. The method for preparing the carbon nanotube-supported transition metal atom composite material according to claim 3, characterized in that, The mass ratio of transition metal atoms to carbon nanotubes in the transition metal salt is 0.5-10%.

6. A sulfur composite material, characterized in that, It includes the composite material as described in claim 1 or 2 and elemental sulfur attached to the inner and outer surfaces of the carbon nanotube matrix of the composite material and in the three-dimensional porous network.

7. The method for preparing the sulfur composite material according to claim 6, characterized in that, Includes the following steps: The composite material described in claim 1 or 2 is mixed with elemental sulfur, and the reaction is carried out by gradient heating to obtain the sulfur composite material. Specifically, the gradient heating reaction involves first heating to 100-200℃ for the reaction, and then heating to 280-400℃ for the reaction.

8. An electrode active material, characterized in that, Including the sulfur composite material as described in claim 6.

9. An electrode, characterized in that, Includes the electrode active material as described in claim 8.

10. An electrochemical energy storage device, characterized in that, Includes the electrode as described in claim 9.

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