Carbon nanotube-coated high-entropy metal oxide composite material and preparation method thereof

Abstract

The application belongs to the technical field of nanocomposite preparation, and discloses a carbon nanotube-coated high-entropy metal oxide composite material and a preparation method thereof. The method comprises the following steps: dissolving iron precursors, cobalt precursors, nickel precursors, manganese precursors and copper precursors in ethanol to obtain a precursor solution; under a low pressure of 40-50 kPa, methane and air containing a small amount of hydrogen sulfide are introduced into a combustion zone to form a low-pressure premixed combustion flame after ignition, and the temperature of the combustion flame zone is controlled to be 800-900 DEG C; the precursor solution is introduced into the combustion zone to convert the five metal elements in situ to form high-entropy metal oxides, and simultaneously make the methane crack and grow into carbon nanotubes, and the carbon nanotubes are coated on the surface of the high-entropy metal oxides, thereby obtaining the carbon nanotube-coated high-entropy metal oxide composite material. The application simultaneously realizes the formation of high-entropy metal oxides and the in-situ growth of carbon nanotubes in a single low-pressure combustion field, does not need post-calcination, and has a compact interface.

Description

Technical Field

[0001] This invention belongs to the field of nanocomposite material preparation technology, specifically relating to a method for one-step in-situ preparation of carbon nanotube-coated high-entropy metal oxide composite materials using a low-pressure premixed combustion flame, and the composite material prepared by this method. Background Technology

[0002] Carbon nanotubes, due to their excellent electrical conductivity, mechanical strength, chemical stability, and unique one-dimensional tubular structure, have broad application prospects in lithium-ion batteries, supercapacitors, electrocatalysis, and composite functional materials. However, standalone carbon nanotubes still face challenges in practical applications, such as limited active sites and insufficient functional phase carrying capacity. On the other hand, multi-metal oxide materials, especially high-entropy metal oxides, typically exhibit better structural stability, abundant surface active sites, and tunable electronic structures due to their high-entropy effect, lattice distortion effect, hysteresis diffusion effect, and cocktail effect, showing significant application value in energy storage and catalysis.

[0003] In existing technologies, carbon nanotubes and high-entropy metal oxides are typically prepared in steps before being composited. While this method can yield composite materials, it often suffers from the following problems: First, the preparation process is lengthy and involves numerous steps; second, the interfacial bonding formed after composite formation is weak, with the carbon nanotubes and metal oxides usually only in physical contact, making it difficult to construct a tight and stable conductive network; third, the preparation of traditional high-entropy metal oxides generally employs sol-gel methods, co-precipitation methods, solid-state methods, or ordinary solution combustion methods, which typically require subsequent high-temperature calcination, resulting in high energy consumption, easy grain growth, and long process cycles.

[0004] In the preparation of carbon nanotubes, combustion methods offer advantages such as eliminating the need for an external high-temperature furnace, rapid reaction rates, and suitability for continuous preparation. Existing literature reports on low-pressure combustion methods for preparing carbon nanotubes (e.g., patent application number CN2022105245315), but this method is only used for preparing single carbon nanotube products and is insufficient for simultaneously achieving the formation of multi-principal metal oxides and in-situ coating and composite formation of carbon nanotubes within the same combustion field. Furthermore, while flame spray pyrolysis technology can prepare high-entropy oxides (e.g., patent application number CN2024104957646), it does not involve the simultaneous generation of carbon nanotubes.

[0005] Therefore, it is of great significance to develop a simple process that does not require post-calcination, can simultaneously achieve the formation of high-entropy metal oxides and the in-situ growth of carbon nanotubes during low-pressure combustion, and further obtain a carbon nanotube-coated high-entropy metal oxide composite material with tight interfacial bonding. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a carbon nanotube-coated high-entropy metal oxide composite material and its preparation method, so as to solve the problems in the prior art that carbon nanotubes and high-entropy metal oxides are usually prepared in steps, the composite interface is weak, the process is complicated, and the preparation of high-entropy metal oxides usually depends on post-calcination.

[0007] To achieve the aforementioned objectives, the technical solution adopted is as follows: A method for preparing a carbon nanotube-coated high-entropy metal oxide composite material includes the following steps: (1) Iron precursor, cobalt precursor, nickel precursor, manganese precursor and copper precursor are dissolved in ethanol to prepare precursor solution; the total concentration of the five metal elements iron, cobalt, nickel, manganese and copper in the precursor solution is 0.005 to 0.20 mol / L; (2) Under low pressure conditions of 40-50 kPa, methane and air containing trace amounts of hydrogen sulfide are introduced into the combustion zone. After ignition, a low-pressure premixed combustion flame is formed, and the temperature of the combustion flame zone is controlled at 800-900℃. (3) Under the condition of maintaining the stability of the low-pressure premixed combustion flame, the precursor solution obtained in step (1) is introduced into the combustion zone at a rate of 2 mL / min, so that the five metal elements are converted in situ to form high-entropy metal oxides, and methane is cracked and grown into carbon nanotubes at the same time. The carbon nanotubes are grown in situ and coated on the surface of the high-entropy metal oxide particles. The product is collected to obtain the carbon nanotube-coated high-entropy metal oxide composite material. The method does not include post-calcination treatment of the obtained composite material.

[0008] In this invention, "in-situ synchronization" refers to the simultaneous formation of high-entropy metal oxides and the growth of carbon nanotubes in the same low-pressure combustion field, with carbon nanotubes growing directly on the surface of the high-entropy metal oxide particles. This process differs from the "stepwise in-situ" process where oxides are formed first and then carbon nanotubes are grown. Its advantages are: oxide particles are exposed to a carbon-containing atmosphere from the early stages of formation, resulting in abundant surface active sites, which is conducive to the nucleation of carbon nanotubes; carbon nanotubes and oxide particles form a tight interfacial bond during growth, rather than simple physical contact; and the growth of carbon nanotubes can inhibit the aggregation of oxide particles, maintaining the nanoscale.

[0009] This invention controls the system pressure at 40–50 kPa. Within this pressure range, the adiabatic flame temperature of the methane / air premixed flame is approximately 1800–2200 K (the actual flame temperature is lower than the adiabatic temperature due to heat loss). After temperature control, the flame zone temperature can be stabilized at 800–900 °C. This temperature range satisfies both the thermal decomposition and oxidation requirements of the organometallic precursor and is suitable for the catalytic growth of carbon nanotubes. Under low pressure, the gas density decreases, and the gas phase residence time is extended by about 2–3 times (relative to atmospheric pressure) at the same volume flow rate, which is beneficial for the full decomposition of the precursor and the uniform mixing of the five metal elements. The low-pressure environment inhibits Brownian collisions and agglomeration between particles, which is beneficial for obtaining well-dispersed nanoparticles. Under low pressure, the solubility of carbon in the metal catalyst decreases, which is beneficial for controlling the diameter and wall number of carbon nanotubes.

[0010] As a further improvement of the present invention, in step (1), the iron precursor, cobalt precursor, nickel precursor, manganese precursor, and copper precursor are each independently selected from one or more of ferrocene, cobalt dicene, nickel dicene, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, manganese acetylacetonate, and copper acetylacetonate. These organometallic compounds have good solubility in ethanol and can form a homogeneous solution, ensuring that the five metal elements are uniformly mixed at the molecular level; metallocene and acetylacetonate compounds can rapidly decompose at 800-900℃, releasing metal atoms and oxidizing them in situ to form oxides; the organic ligands (cyclopentadiene rings, acetylacetonate) produced by decomposition can serve as auxiliary carbon sources to promote the growth of carbon nanotubes; Fe, Co, and Ni are effective catalysts for the growth of traditional carbon nanotubes, and their metallocene and acetylacetonate compounds can form highly dispersed metal / oxide nanoparticles after decomposition, providing active sites for methane cracking.

[0011] As a further improvement of the present invention, in step (1), the mole fraction of each of the five metal elements is 5 at% to 35 at%.

[0012] As a further improvement of the present invention, in step (1), the molar ratio of iron, cobalt, nickel, manganese and copper is (0.8~1.2):(0.8~1.2):(0.8~1.2):(0.8~1.2):(0.8~1.2).

[0013] As a further improvement of the present invention, in step (2), the flow ratio of methane to air containing trace amounts of hydrogen sulfide is 1:1 to 1:4. By adjusting the flow ratio of methane / air and the flame zone temperature, a local oxidation-reduction zone is formed in the combustion zone: the outer flame region (oxygen-rich zone) is conducive to the oxidation of metal elements to form high-entropy oxides; the inner flame and rear flame regions (fuel-rich zone) are in a reducing atmosphere, which is conducive to methane cracking and carbon nanotube growth. After formation, the metal oxide particles can migrate to the reducing region, serving as a carrier and catalyst for carbon nanotube growth, thereby achieving in-situ coating of carbon nanotubes on the oxide surface.

[0014] As a further improvement of the present invention, the volume fraction of hydrogen sulfide in the air containing trace amounts of hydrogen sulfide is 0.001% to 1%. By introducing trace amounts of hydrogen sulfide (0.001% to 1%) as a growth promoter for carbon nanotubes, H2S decomposes at high temperatures to produce HS· and S· free radicals. These active sulfur species can be adsorbed on the surface of the metal catalyst, reducing the activation energy of carbon nanotube nucleation. Sulfur atoms preferentially adsorb onto the high-energy crystal faces of the metal catalyst, inducing carbon nanotubes to grow along a specific direction. The adsorption of sulfur can inhibit the excessive growth of the metal catalyst, maintain the nanoscale of the catalyst particles, and thus control the diameter of the carbon nanotubes. Compared with sulfur-containing organic compounds such as thiophene, H2S, as a gas, can be directly mixed into the air, dispersed more uniformly, and has simple decomposition products (only H2 and S), without introducing additional carbonaceous impurities.

[0015] As a further improvement of the present invention, in step (3), the precursor solution is not atomized before being introduced into the combustion zone, but is dispersed and enters the combustion zone under the action of the airflow formed by the methane and air containing trace amounts of hydrogen sulfide. The precursor solution of the present invention is not pretreated by ultrasonic atomization, pressure atomization or pneumatic atomization before being introduced into the combustion zone, but is directly injected in the form of liquid flow, and dispersion is achieved by the airflow shear of the combustion gas. The advantages of this liquid supply method are: it simplifies the equipment structure, eliminating the need for atomizing nozzles and a matching gas / liquid source control system; it avoids incomplete reaction or inconsistent product morphology caused by uneven atomized droplet size; the ethanol in the liquid flow evaporates and burns in the flame, which can help maintain flame stability and serve as a supplementary carbon source to promote carbon nanotube growth.

[0016] As a further improvement of the present invention, methane and air containing trace amounts of hydrogen sulfide are first introduced to form a low-pressure premixed combustion flame, and then the precursor solution is introduced into the combustion zone in a continuous feeding manner at a feeding rate of 2 mL / min.

[0017] A carbon nanotube-coated high-entropy metal oxide composite material, comprising carbon nanotubes and high-entropy metal oxide, wherein the high-entropy metal oxide contains five metal elements: iron, cobalt, nickel, manganese, and copper, and the high-entropy metal oxide is a single main phase or a quasi-single main phase, and the carbon nanotubes are grown in situ on the surface of the high-entropy metal oxide and coated on the surface of the high-entropy metal oxide.

[0018] The beneficial effects of this invention are: 1. One-step in-situ simultaneous formation: This invention is the first to achieve the simultaneous formation of high-entropy metal oxides and in-situ growth of carbon nanotubes in a single low-pressure premixed combustion flame. It eliminates the need for step-by-step preparation and post-calcination treatment, resulting in a short process flow, low energy consumption, and suitability for continuous production.

[0019] 2. Tight interface bonding: Carbon nanotubes are not added later or mechanically mixed, but grow directly on the surface of high-entropy metal oxide particles during combustion to form a coating structure. The two are chemically bonded or epitaxially grown at the interface, with high bonding strength, which is conducive to building a stable conductive network and exerting synergistic effects.

[0020] 3. Multifunctional Synergistic Effect of Metal Components: This invention uses a five-element system of Fe, Co, Ni, Mn and Cu as the high-entropy metal oxide components. These transition metal elements not only serve as constituent elements of high-entropy oxides in the combustion flame, but also provide catalytic active sites for methane cracking and carbon nanotube growth, achieving "two uses in one".

[0021] 4. The key regulatory role of trace amounts of H2S: This invention introduces trace amounts of hydrogen sulfide into the combustion-supporting gas, which can regulate the redox state of the metal precursor (avoiding excessive oxidation and catalyst deactivation) and also act as a growth promoter for carbon nanotubes (by etching the catalyst surface or adjusting the chemical atmosphere of the flame). This is one of the key technical means to successfully achieve in-situ coating of carbon nanotubes by low-pressure combustion.

[0022] 5. Controllable Product Structure: By adjusting parameters such as precursor concentration, metal ratio, flame temperature, pressure, methane / air ratio, and H2S concentration, the phase composition and particle size of high-entropy metal oxides, as well as the diameter, graphitization degree, and coating density of carbon nanotubes, can be controlled to meet different application requirements. In this invention, the precursor liquid is not atomized but dispersed and introduced into the combustion zone under the action of airflow, which avoids the dependence on droplet size and nozzle structure of traditional atomization liquid supply mode, making the process implementation simpler. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1The XRD pattern of the composite material prepared in Example 1 of this invention; Figure 2 This is a TEM image of the composite material prepared in Example 1 of the present invention; Figure 3 This is a TEM image of the composite material prepared in Example 2 of the present invention; Figure 4 This is a TEM image of the composite material prepared in Example 3 of the present invention; Figure 5 This is a TEM image of the composite material prepared in Example 4 of the present invention; Figure 6 This is a TEM image of the composite material prepared in Example 5 of the present invention; Figure 7 This is a TEM image of the composite material prepared in Example 6 of the present invention; Figure 8 The image shows a TEM image of the composite material prepared in Comparative Example 1 of this invention. Figure 9 This is a TEM image of the composite material prepared in Comparative Example 2 of this invention; Figure 10 The image shows the XRD pattern of the composite material prepared in Comparative Example 4 of this invention. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0026] In the following embodiments, "high-entropy metal oxide" refers to a multi-principal metal oxide containing five metallic elements: iron, cobalt, nickel, manganese, and copper, with each element having a molar fraction in the total metal content ranging from 5 at% to 45 at%. Preferably, the high-entropy metal oxide exhibits a single main phase or a quasi-single main phase in X-ray diffraction testing. The term "in-situ growth and coating on the surface of high-entropy metal oxide" in this invention refers to the formation of a composite structure containing carbon nanotubes and high-entropy metal oxides in the same low-pressure combustion field without independent subsequent calcination or secondary deposition steps; and under an electron microscope, direct contact and coating between the carbon nanotubes and the surface of the high-entropy metal oxide particles can be observed, rather than a simple physical contact obtained through subsequent mechanical mixing. The above descriptions are used to illustrate the process characteristics and final structural characteristics of this invention and are not intended to limit the specific formation mechanism or strict temporal order.

[0027] Example 1

[0028] A method for preparing a carbon nanotube-coated high-entropy metal oxide composite material includes the following steps: (1) Weigh out ferrocene, cobalt acetylacetonate, nickel acetylacetonate, manganese acetylacetonate, and copper acetylacetonate respectively, mix them in a Fe:Co:Ni:Mn:Cu molar ratio of 1:1:1:1:1, add them to ethanol and stir to dissolve, thus obtaining a precursor solution. Control the total concentration of the five metal elements to be 0.05 mol / L.

[0029] (2) Adjust the pressure of the reaction system to 45 kPa, and introduce methane and air containing trace amounts of hydrogen sulfide into the combustion zone. The flow ratio of methane to air containing trace amounts of hydrogen sulfide is 1:2, the total air flow rate is 10 L / min, and the volume fraction of hydrogen sulfide is 0.05%. After ignition, a stable low-pressure premixed combustion flame is formed, and the flame zone temperature is controlled at 850 °C.

[0030] (3) Under the condition of maintaining a stable low-pressure premixed combustion flame, the above-mentioned precursor solution is continuously introduced into the combustion zone. The precursor solution is not atomized before entering the combustion zone, but is dispersed and introduced into the combustion zone under the action of the airflow formed by methane and air containing trace amounts of hydrogen sulfide. Under the action of the flame, the five metal elements are transformed in situ to form high-entropy metal oxides, while methane is cracked to generate carbon nanotubes. The carbon nanotubes coat the surface of the high-entropy metal oxides. The products are collected to obtain the carbon nanotube-coated high-entropy metal oxide composite material.

[0031] Figure 1 The image shows the XRD pattern of the carbon nanotube-coated high-entropy metal oxide composite material prepared in this embodiment. The diffraction peak positions of the product correspond to the characteristic diffraction peaks of spinel-type oxides. No obvious single metal oxide impurity phase diffraction peaks were observed, indicating that the obtained high-entropy metal oxide exhibits a single main phase.Figure 2 This is a TEM image of the carbon nanotube-coated high-entropy metal oxide composite material prepared in this embodiment. The product contains a large number of one-dimensional tubular structures with a diameter of approximately 20–40 nm, which are typical multi-walled carbon nanotubes. The carbon nanotubes are tightly coated on the surface of particulate high-entropy metal oxide with a particle size of approximately 50–100 nm, forming a core-shell type composite structure. HRTEM shows that the carbon nanotubes have approximately 10–20 wall layers with an interlayer spacing of approximately 0.34 nm, indicating a good degree of graphitization.

[0032] Example 2

[0033] A method for preparing carbon nanotube-coated high-entropy metal oxide composite materials by low-pressure combustion includes the following steps: (1) Weigh out ferrocene, cobalt acetylacetonate, nickel acetylacetonate, manganese acetylacetonate, and copper acetylacetonate respectively, mix them in a Fe:Co:Ni:Mn:Cu molar ratio of 1:1:1:1:1, add them to ethanol and stir to dissolve, thus obtaining a precursor solution. Control the total concentration of the five metal elements to be 0.1 mol / L.

[0034] (2) Adjust the pressure of the reaction system to 45 kPa, and introduce methane and air containing trace amounts of hydrogen sulfide into the combustion zone. The flow ratio of methane to air containing trace amounts of hydrogen sulfide is 1:3, the total air flow rate is 10 L / min, and the volume fraction of hydrogen sulfide is 0.01%. After ignition, a stable low-pressure premixed combustion flame is formed, and the flame zone temperature is controlled at 800 °C.

[0035] (3) Under the condition of maintaining a stable low-pressure premixed combustion flame, the above-mentioned precursor solution is continuously introduced into the combustion zone. The precursor solution is not atomized before entering the combustion zone, but is dispersed and introduced into the combustion zone under the action of the airflow formed by methane and air containing trace amounts of hydrogen sulfide. Under the action of the flame, the five metal elements are transformed in situ to form high-entropy metal oxides, while methane is cracked to generate carbon nanotubes. The carbon nanotubes coat the surface of the high-entropy metal oxides. The products are collected to obtain the carbon nanotube-coated high-entropy metal oxide composite material.

[0036] Figure 3 This is a TEM image of the carbon nanotube-coated high-entropy metal oxide composite material prepared in this embodiment. Figure 3 It can be seen that carbon nanotube-coated high-entropy metal oxide composite materials can also be obtained under the above conditions.

[0037] Example 3

[0038] A method for preparing carbon nanotube-coated high-entropy metal oxide composite materials by low-pressure combustion includes the following steps: 1) Weigh out ferrocene, cobalt acetylacetonate, nickel acetylacetonate, manganese acetylacetonate, and copper acetylacetonate separately, and mix them in a Fe:Co:Ni:Mn:Cu molar ratio of 1:1:1:1:1. Add them to ethanol and stir to dissolve, obtaining a precursor solution. Control the total concentration of the five metal elements to 0.05 mol / L.

[0039] 2) Adjust the pressure of the reaction system to 40 kPa, and introduce methane and air containing trace amounts of hydrogen sulfide into the combustion zone. The flow ratio of methane to air containing trace amounts of hydrogen sulfide is 1:2, the total air flow rate is 10 L / min, and the volume fraction of hydrogen sulfide is 0.05%. After ignition, a stable low-pressure premixed combustion flame is formed, and the flame zone temperature is controlled at 900℃.

[0040] 3) Under conditions of maintaining a stable low-pressure premixed combustion flame, the aforementioned precursor solution is continuously introduced into the combustion zone. The precursor solution is not atomized before entering the combustion zone; instead, it is dispersed and introduced into the combustion zone by an airflow consisting of methane and air containing trace amounts of hydrogen sulfide. Under the influence of the flame, the five metal elements undergo in-situ transformation to form high-entropy metal oxides, while methane is simultaneously decomposed to generate carbon nanotubes. These carbon nanotubes coat the surface of the high-entropy metal oxides. The products are collected to obtain the carbon nanotube-coated high-entropy metal oxide composite material.

[0041] Figure 4 The image shows a TEM image of the carbon nanotube-coated high-entropy metal oxide composite material prepared in this embodiment. The results show that the target composite material can still be formed under low pressure conditions of 40 kPa.

[0042] Example 4

[0043] A method for preparing carbon nanotube-coated high-entropy metal oxide composite materials by low-pressure combustion includes the following steps: 1) Weigh out ferrocene, cobalt acetylacetonate, nickel acetylacetonate, manganese acetylacetonate, and copper acetylacetonate separately, and mix them in a Fe:Co:Ni:Mn:Cu molar ratio of 0.9:0.9:0.9:0.9. Dissolve them in ethanol to obtain a precursor solution. Control the total concentration of the five metal elements to 0.05 mol / L.

[0044] 2) Adjust the pressure of the reaction system to 45 kPa, and introduce methane and air containing trace amounts of hydrogen sulfide into the combustion zone. The flow ratio of methane to air containing trace amounts of hydrogen sulfide is 1:2, the total air flow rate is 10 L / min, and the volume fraction of hydrogen sulfide is 0.05%. After ignition, a stable low-pressure premixed combustion flame is formed, and the flame zone temperature is controlled at 850℃.

[0045] 3) Under conditions of maintaining a stable low-pressure premixed combustion flame, the aforementioned precursor solution is continuously introduced into the combustion zone. The precursor solution is not atomized before entering the combustion zone; instead, it is dispersed and introduced into the combustion zone by an airflow consisting of methane and air containing trace amounts of hydrogen sulfide. Under the influence of the flame, the five metal elements undergo in-situ transformation to form high-entropy metal oxides, while methane is simultaneously decomposed to generate carbon nanotubes. These carbon nanotubes coat the surface of the high-entropy metal oxides. The products are collected to obtain the carbon nanotube-coated high-entropy metal oxide composite material.

[0046] Figure 5 The image shows a TEM image of the carbon nanotube-coated high-entropy metal oxide composite material prepared in this embodiment. The results show that, under the condition of maintaining the equimolar ratio of the five metal elements, by appropriately adjusting the feeding level of each precursor, the high-entropy metal oxide main phase and its carbon nanotube-coated composite structure can still be obtained, indicating that the method of the present invention has good repeatability and process stability.

[0047] Example 5

[0048] A method for preparing carbon nanotube-coated high-entropy metal oxide composite materials by low-pressure combustion includes the following steps: 1) Weigh out ferrocene, cobalt acetylacetonate, nickel acetylacetonate, manganese acetylacetonate, and copper acetylacetonate separately, and mix them in a Fe:Co:Ni:Mn:Cu molar ratio of 1:1:1:1:1. Add them to ethanol and stir to dissolve, obtaining a precursor solution. Control the total concentration of the five metal elements to 0.005 mol / L.

[0049] 2) Adjust the pressure of the reaction system to 45 kPa, and introduce methane and air containing trace amounts of hydrogen sulfide into the combustion zone. The flow ratio of methane to air containing trace amounts of hydrogen sulfide is 1:2, the total air flow rate is 10 L / min, and the volume fraction of hydrogen sulfide is 0.05%. After ignition, a stable low-pressure premixed combustion flame is formed, and the flame zone temperature is controlled at 850℃.

[0050] 3) Under conditions of maintaining a stable low-pressure premixed combustion flame, the aforementioned precursor solution is continuously introduced into the combustion zone. The precursor solution is not atomized before entering the combustion zone; instead, it is dispersed and introduced into the combustion zone by an airflow consisting of methane and air containing trace amounts of hydrogen sulfide. Under the influence of the flame, the five metal elements undergo in-situ transformation to form high-entropy metal oxides, while methane is simultaneously decomposed to generate carbon nanotubes. These carbon nanotubes coat the surface of the high-entropy metal oxides. The products are collected to obtain the carbon nanotube-coated high-entropy metal oxide composite material.

[0051] Figure 6The image shown is a TEM image of the carbon nanotube-coated high-entropy metal oxide composite material prepared in this embodiment. The results show that when the total concentration of the five metal elements is reduced to 0.005 mol / L, the carbon nanotube-coated high-entropy metal oxide composite structure can still be formed, indicating that the method of the present invention still has good applicability at low precursor concentrations.

[0052] Example 6

[0053] A method for preparing carbon nanotube-coated high-entropy metal oxide composite materials by low-pressure combustion includes the following steps: 1) Weigh out ferrocene, cobalt acetylacetonate, nickel acetylacetonate, manganese acetylacetonate, and copper acetylacetonate separately, and mix them in a Fe:Co:Ni:Mn:Cu molar ratio of 1:1:1:1:1. Add them to ethanol and stir to dissolve, obtaining a precursor solution. Control the total concentration of the five metal elements to 0.2 mol / L.

[0054] 2) Adjust the pressure of the reaction system to 45 kPa, and introduce methane and air containing trace amounts of hydrogen sulfide into the combustion zone. The flow ratio of methane to air containing trace amounts of hydrogen sulfide is 1:2, the total air flow rate is 10 L / min, and the volume fraction of hydrogen sulfide is 0.05%. After ignition, a stable low-pressure premixed combustion flame is formed, and the flame zone temperature is controlled at 850℃.

[0055] 3) Under conditions of maintaining a stable low-pressure premixed combustion flame, the aforementioned precursor solution is continuously introduced into the combustion zone. The precursor solution is not atomized before entering the combustion zone; instead, it is dispersed and introduced into the combustion zone by an airflow consisting of methane and air containing trace amounts of hydrogen sulfide. Under the influence of the flame, the five metal elements undergo in-situ transformation to form high-entropy metal oxides, while methane is simultaneously decomposed to generate carbon nanotubes. These carbon nanotubes coat the surface of the high-entropy metal oxides. The products are collected to obtain the carbon nanotube-coated high-entropy metal oxide composite material.

[0056] Figure 7 The image shows a TEM image of the carbon nanotube-coated high-entropy metal oxide composite material prepared in this embodiment. The results show that when the total concentration of the five metal elements is increased to 0.20 mol / L, a carbon nanotube-coated high-entropy metal oxide composite structure can still be formed, indicating that the method of the present invention still has good applicability at higher precursor concentrations.

[0057] Element content test data To verify the compositional uniformity of the high-entropy metal oxides in the obtained composite materials, the carbon nanotube-coated high-entropy metal oxide composite materials prepared in Examples 1-4 were subjected to elemental quantitative analysis. The test results are shown in Table 1. The results show that the contents of the five metal elements Fe, Co, Ni, Mn and Cu in each example are relatively small, indicating that the metal elements in the obtained high-entropy metal oxides are approximately equimolarly distributed.

[0058] Table 1 Results of elemental content determination Comparative Example 1 Except for changing the system pressure to atmospheric pressure, the other conditions are the same as in Example 1.

[0059] Figure 8 The image shows a TEM image of the product prepared in this comparative example. The results indicate that under normal pressure conditions, the carbon nanotube coating structure in the obtained sample is significantly reduced.

[0060] Comparative Example 2 Except for the absence of hydrogen sulfide, the other conditions are the same as in Example 1.

[0061] Figure 9 The image shows a TEM image of the product prepared in this comparative example. The results indicate that no carbon nanotubes were formed without the addition of trace amounts of hydrogen sulfide; only coarse nanoparticles existed. This suggests that trace amounts of hydrogen sulfide are beneficial for carbon nanotube growth.

[0062] Comparative Example 3 Except for not introducing methane, the other conditions are the same as in Example 1.

[0063] No products were collected, indicating that methane is an essential carbon-donating component for the formation of carbon nanotubes.

[0064] Comparative Example 4 Except for adjusting the molar ratio of the five metal precursors in step (1) to Fe:Co:Ni:Mn:Cu = 1.0:0.3:1.8:0.4:1.5, which is significantly deviated from the near equimolar range, the other conditions are the same as in Example 1.

[0065] Figure 10 The XRD pattern of the product prepared in this comparative example shows no obvious single-metal oxide diffraction peaks, indicating that high-entropy metal oxides were not prepared. This demonstrates that high-entropy metal oxides only form when the five metal elements are in a near equimolar ratio.

[0066] The composite materials prepared in each embodiment were directly used as negative electrode active materials to assemble lithium-ion batteries. The reversible specific capacity at a current density of 5000 mA / g based on the total mass of the composite materials is shown in Table 2.

[0067] Table 2 Performance Test Results The above examples and comparative examples demonstrate that under low-pressure conditions of 40–50 kPa, methane and air containing trace amounts of hydrogen sulfide form a stable low-pressure premixed combustion flame, providing a high-temperature environment suitable for the decomposition of pentagonal metal-organic precursors and the in-situ formation of multi-principal metal oxides. Simultaneously, methane undergoes cracking under the influence of the active metal components, and hydrogen sulfide acts as a growth promoter, facilitating the formation and growth of carbon nanotubes, enabling them to form in-situ coated structures on the surface of high-entropy metal oxide particles. Low-pressure conditions (40–50 kPa) play a crucial role in the in-situ coated growth of carbon nanotubes and the uniform dispersion of high-entropy metal oxides; ideal composite structures cannot be obtained under ambient pressure.

[0068] This invention provides a method for preparing carbon nanotube-coated high-entropy metal oxide composite materials using a low-pressure combustion method. By introducing a precursor solution containing five metal elements—Fe, Co, Ni, Mn, and Cu—into a low-pressure premixed combustion flame, the formation of high-entropy metal oxides and the growth of carbon nanotubes are simultaneously achieved, eliminating the need for post-calcination to obtain the carbon nanotube-coated high-entropy metal oxide composite material. This method is simple, produces a tight composite interface, and has promising application prospects.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, component splitting or combination, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a carbon nanotube-coated high-entropy metal oxide composite material, characterized in that, Includes the following steps: (1) Dissolve the iron precursor, cobalt precursor, nickel precursor, manganese precursor and copper precursor in ethanol to prepare a precursor solution; The total concentration of the five metallic elements iron, cobalt, nickel, manganese and copper in the precursor solution is 0.005 to 0.20 mol / L; (2) Under low pressure conditions of 40-50 kPa, methane and air containing trace amounts of hydrogen sulfide are introduced into the combustion zone. After ignition, a low-pressure premixed combustion flame is formed, and the temperature of the combustion flame zone is controlled at 800-900℃. (3) Under the condition of maintaining the stability of the low-pressure premixed combustion flame, the precursor solution obtained in step (1) is introduced into the combustion zone to convert the five metal elements in situ into high-entropy metal oxides, and at the same time, methane is cracked and grown into carbon nanotubes. The carbon nanotubes are grown in situ and coated on the surface of the high-entropy metal oxide particles. The product is collected to obtain the carbon nanotube-coated high-entropy metal oxide composite material.

2. The method for preparing a carbon nanotube-coated high-entropy metal oxide composite material according to claim 1, characterized in that: In step (1), the iron precursor, cobalt precursor, nickel precursor, manganese precursor and copper precursor are each independently selected from one or more of ferrocene, cobalt dicene, nickel dicene, iron acetylacetone, cobalt acetylacetone, nickel acetylacetone, manganese acetylacetone and copper acetylacetone.

3. The method for preparing a carbon nanotube-coated high-entropy metal oxide composite material according to claim 1, characterized in that: In step (1), the mole fraction of each of the five metal elements is 5 at% to 35 at%.

4. The method for preparing a carbon nanotube-coated high-entropy metal oxide composite material according to claim 1, characterized in that: In step (1), the molar ratio of iron, cobalt, nickel, manganese and copper is (0.8~1.2):(0.8~1.2):(0.8~1.2):(0.8~1.2):(0.8~1.2).

5. The method for preparing a carbon nanotube-coated high-entropy metal oxide composite material according to claim 1, characterized in that: In step (2), the flow rate ratio of methane to air containing trace amounts of hydrogen sulfide is 1:1 to 1:

4.

6. The method for preparing a carbon nanotube-coated high-entropy metal oxide composite material according to claim 1, characterized in that: The volume fraction of hydrogen sulfide in the air containing trace amounts of hydrogen sulfide is 0.001% to 1%.

7. The method for preparing a carbon nanotube-coated high-entropy metal oxide composite material according to claim 1, characterized in that: In step (3), the precursor solution is not atomized before being introduced into the combustion zone. Instead, it is dispersed and enters the combustion zone under the action of the airflow formed by the methane and air containing trace amounts of hydrogen sulfide.

8. The method for preparing a carbon nanotube-coated high-entropy metal oxide composite material according to claim 1, characterized in that: First, methane and air containing trace amounts of hydrogen sulfide are introduced to form a low-pressure premixed combustion flame. Then, the precursor solution is continuously fed into the combustion zone at a feed rate of 2 ml / min.

9. A carbon nanotube-coated high-entropy metal oxide composite material, characterized in that: The composite material includes carbon nanotubes and high-entropy metal oxides. The high-entropy metal oxides contain five metal elements: iron, cobalt, nickel, manganese, and copper. The carbon nanotubes are grown in situ on the surface of the high-entropy metal oxides and are coated on the surface of the high-entropy metal oxides.

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