Preparation method and system of carbon-coated three-phase metal organic framework derived heterojunction nano composite material

Abstract

The invention belongs to the field of nano composite materials, and discloses a preparation method and system of a carbon-coated three-phase metal organic framework derived heterojunction nano composite material. Aiming at the problem of poor conductivity of the copper selenide with a non-ideal ratio at present, the copper selenide with the non-ideal ratio is modified to construct a precursor with a heterojunction structure and a metal organic framework structure; and performing high-temperature pyrolysis on the precursor in an inert atmosphere to prepare the carbon-coated three-phase metal organic framework selenide heterojunction nano composite material. According to the method, the problems of complex and harsh conditions, high cost and difficulty in large-scale production in preparation of the carbon-coated three-phase metal organic framework derived heterojunction nano composite material at present are solved. The preparation method provided by the invention has the advantages of simple preparation process, short synthesis period, good repeatability, high yield, easy realization of industrial production and the like, and also has the characteristic of excellent electrochemical performance, thereby having very wide application prospects in the field of battery energy storage.

Description

Technical Field

[0001] The present invention belongs to, but is not limited to, the technical field of nanocomposites, and particularly relates to a preparation method and system of a carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material. Background Art

[0002] In the context of the rapidly developing world, to meet the huge human demand for energy, reduce the consumption of fossil energy and the environmental problems caused by it, the development of new energy is particularly urgent. Non-ideal stoichiometry copper selenide (Cu 2-x Se), as a typical metal selenide, shows great development potential in the electrochemical field due to its diverse crystal structures, high theoretical capacity and rich reserves. However, Cu 2-x Se negative electrode materials face many problems during charge and discharge processes, such as low utilization rate of active sites, lagging surface / interface ion transport, volume expansion, and polyselenide "shuttle" effect. These problems lead to a low actual specific capacity and poor rate performance, thereby reducing the overall energy density and power density of the battery, seriously restricting its practical application.

[0003] Metal-organic frameworks are complexes formed by the coordination bond between metal ions and organic ligands, which have highly regular infinite network structures. They have the advantages of diverse structure types, adjustable pore sizes, large specific surface areas, and high porosities. MOFs have potential application prospects in the fields of electrochemical energy storage and conversion. Among them, the large surface area and adjustable pore size are proven to be precursors and templates for preparing a class of new porous materials.

[0004] A heterojunction is formed by the contact of two different materials. It integrates the advantages of each component material and exhibits excellent performance that cannot be compared with single materials. Through multi-component electron conversion and synergy, the heterojunction can significantly improve its specific capacity. In addition, at the heterophase interface of the heterostructure composite material, a large number of holes, vacancies and free electrons can be generated, thereby forming excess charges. These charges can serve as additional energy storage sites to further improve the specific capacity of the composite material. In addition, the built-in electric field induced by "electron-hole" at the heterojunction interface of different bandgap materials can provide an additional driving force to accelerate charge transport and improve the ion / electron transfer rate, thus effectively improving the cycle performance and rate performance of the material.

[0005] A large number of research results clearly show that heterojunctions and carbon coating layers are two effective strategies to improve the electrochemical performance of conversion-type anode materials. The built-in electric field induced by electron-hole pairs on the non-uniform interface of materials with different bandgaps can provide additional driving force for accelerating charge transport and improving the ion / electron transfer rate, thereby enhancing the cycling stability and rate performance of the materials. Coating a carbon layer on the material surface can not only effectively reduce the internal resistance and improve the electron transport efficiency in the material, but also buffer the volume change during the charge and discharge process of the material, thus improving energy storage. Therefore, developing an effective strategy that can simultaneously achieve heterojunctions and carbon coating layers is of great significance for improving the 2-x electrochemical performance of Cu

[0006] Therefore, by selecting a trimetallic organic framework as the precursor and performing controllable high-temperature pyrolysis treatment, a carbon-coated trimetallic organic framework-derived heterojunction nanocomposite can be well obtained. This is very difficult to achieve in other types of materials at this point, thus developing a new method for preparing novel-structured and functionalized materials.

[0007] In view of the above analysis, the technical problems urgently to be solved in the prior art are as follows:

[0008] The existing preparation methods for carbon-coated trimetallic organic framework-derived heterojunction nanocomposites have complex and harsh conditions, high costs, and are difficult to mass-produce. Summary of the Invention

[0009] Aiming at the problems existing in the prior art, the present invention provides a preparation method and system for a carbon-coated trimetallic organic framework-derived heterojunction nanocomposite.

[0010] The present invention is implemented as follows. A preparation method for a carbon-coated trimetallic organic framework-derived heterojunction nanocomposite, characterized in that the preparation method for the carbon-coated trimetallic organic framework-derived heterojunction nanocomposite specifically includes:

[0011] S1: Dissolve transition metal salts in 20 - 30 mL of methanol at a certain molar ratio, and under the condition that the stirring speed is 100 - 1000 r / min, stir well for 5 - 15 min to prepare a mixed solution;

[0012] S2: Under the above stirring state, sequentially add an organic ligand and a surfactant to the above mixed solution, so that the molar ratio of the transition metal salt to the organic ligand is 1:0.9 - 1, and the molar ratio of the transition metal salt to the surfactant is 1:4.5 - 5;

[0013] S3: After continuously stirring at room temperature for 3 h, transfer the mixed solution into a high-pressure reactor, react at 100-150 °C for 3 h, collect the obtained blue precipitate, remove impurities by washing multiple times, and dry overnight at 60-80 °C to obtain a trimetallic organic framework precursor;

[0014] S4: Under the protection of an inert gas, place the precursor prepared in S3 in a tubular furnace, heat it up to 600-800 °C at a heating rate of 1-5 °C / min, calcine for 1-2 h, and naturally cool to room temperature to obtain a carbon-coated trimetallic organic framework-derived nanocomposite.

[0015] Further, the transition metal salts in S1 are copper salts, manganese salts, and zinc salts, the copper salts are copper nitrate or copper chloride or copper acetylacetonate; the manganese salts are manganese nitrate or manganese chloride; the zinc salts are zinc nitrate or zinc chloride.

[0016] Further, the molar ratio of copper salt, manganese salt, and zinc salt in S1 is 2:1:1, and the volume of the methanol solvent used is 25 mL.

[0017] Further, the organic ligand in S2 is 1,3,5-benzenetricarboxylic acid or 5-tert-butyl-1,3-isophthalic acid; the surfactant is lauric acid.

[0018] Further, the molar ratio of metal salt to organic ligand in S2 is 1:0.99, and the molar ratio of metal salt to surfactant is 1:4.67.

[0019] Further, in S3, transfer the mixed solution to a high-pressure reactor and react at 125 °C for 3 h, collect the obtained green precipitate by centrifugation, wash it with ethanol and water multiple times to remove impurities, and vacuum dry overnight at 60 °C to obtain a precursor of the trimetallic organic framework.

[0020] Further, the inert mixed gas in S4 is an argon / hydrogen mixed gas with a volume ratio of 9:1. The selenium powder and the carbonized product during the seleniumization process are respectively placed at the upper and lower ends of the porcelain boat, and the mass ratio of selenium powder to precursor is 2:1.

[0021] Further, in S4, under the argon / hydrogen mixed atmosphere, heat it up at a heating rate of 5 °C / min to 700 °C and calcine for 2 h.

[0022] Another object of the present invention is to provide a preparation system for a carbon-coated trimetallic organic framework-derived heterojunction nanocomposite, and this system specifically includes:

[0023] A mixed solution preparation module for dissolving transition metal salts in methanol to prepare a mixed solution;

[0024] A high-pressure reactor is used for reacting at 100 - 150 °C to obtain a trimetallic organic framework precursor;

[0025] A tubular furnace is used to obtain a carbon-coated trimetallic organic framework-derived nanocomposite.

[0026] Combined with the above technical solutions and the solved technical problems, the advantages and positive effects of the technical solution to be protected by the present invention are as follows:

[0027] First, in the preparation method of the present invention, copper salt, manganese salt, and zinc salt are dissolved in methanol, and under the condition of a stirring speed of 300 r / min, they are fully stirred to form a mixed solution. Subsequently, under the condition of continuous stirring, an organic ligand and a surfactant are successively added to the above mixed solution, and after continuously stirring at room temperature for 3 h, then through a one-step solvothermal method at 120 °C for 3 h, washing and drying are carried out to collect a blue precipitate as the trimetallic organic framework precursor, and then a carbon-coated trimetallic organic framework-derived heterojunction nanocomposite is obtained by selenization roasting under an argon / hydrogen mixed atmosphere. The process of the present invention is simple, operable, has good repeatability, high yield, and low cost, and can achieve mass production.

[0028] The present invention retains the structural characteristics of the metal-organic framework precursor, such as large specific surface area, controllable morphology, and adjustable pore size of the material, to enhance the conductivity of the composite material, buffer volume changes, and promote the rapid transmission of ions and electrons, etc. By regulating the temperature, a carbon-coated trimetallic organic framework-derived heterojunction nanocomposite is obtained by "selenization" pyrolysis. Moreover, the TMOFs pyrolysis strategy can obtain a core-shell structure of the carbon-coated layer, which is beneficial to buffering the volume change during the charge and discharge process of the electrode material and improving the cycle stability performance.

[0029] The composite material prepared by the present invention has the advantages of a unique multiphase structure, high specific surface area, mesoporous characteristics, and a carbon-coated layer, and has excellent storage performance, including high specific capacity, superior rate performance, and cycle stability. By making full use of the structural and compositional advantages, the organic ligand in the MOFs is transformed into a carbon-coated layer, and the metal ions are in-situ transformed into a metal selenide heterostructure under a reducing atmosphere. In addition, when this material is assembled in combination with a commercial cathode material, it shows excellent all-cell performance, making it have broad application prospects in the field of electrochemistry.

[0030] The preparation method of the present invention can be extended to the preparation of metal-organic frameworks of other transition metals.

[0031] Second, the existing preparation methods for carbon-coated ternary metal-organic framework-derived heterojunction nanocomposites have complex and demanding conditions, high costs, and are difficult to mass-produce. In contrast, for the present invention, only the molar ratio of the experimental raw materials needs to be confirmed. After mixing, through a simple one-step solvothermal reaction and then a one-step selenization pyrolysis operation, the target product can be obtained. The solvothermal method has mild reaction conditions, the resulting product has high crystallinity, good porosity, and can control the crystal morphology and size, as well as the selectivity of metal ions and ligands. The overall process is simple and convenient, with good repeatability, high yield, and low cost, making it suitable for industrial production. Meanwhile, this preparation method can provide a model for the preparation of composite materials based on multiphase heterostructures.

[0032] It overcomes the defects of structural collapse and poor conductivity caused by volume expansion of the single-metal-source synthesized single-metal organic framework material. By introducing multiple metal sources to construct a multiphase metal-organic framework and form multiple heterojunction interfaces, the prepared composite material has a rich pore structure, abundant active sites, and a relatively stable structure, which helps to improve the conductivity of the material and shows broad development and application prospects in electrochemical energy storage. The ternary metal heterojunction organic framework nanomaterial is prepared by a simple one-step solvothermal method, with simple operation and good repeatability, overcoming the technical problem of interference in the preparation process of metal-organic framework materials; through controllable high-temperature pyrolysis, the original structure is retained and the performance is improved, overcoming the technical problems of low stability and poor environmental stability of metal-organic framework materials.

[0033] Third, by precisely regulating the parameters of each reaction step, such as the molar ratio of metal salts to organic ligands and surfactants, stirring rate, reaction temperature, heating rate, and calcination time, etc., the present invention effectively solves the problems of uneven morphology, inconsistent particle size distribution, and unstable pore structure in the synthesis process of metal-organic frameworks in the prior art.

[0034] Using nitrates or chlorides as metal sources and strictly matching them according to a molar ratio of 2:1:1 ensures the full reaction of each component in the mixed solution, thereby preparing a trimetallic organic framework precursor with good homogeneity. This significantly improves the stability and controllability of subsequent carbon coating and heterojunction formation, overcoming the defect of performance fluctuations caused by uneven component dispersion in traditional methods.

[0035] During the high-temperature calcination and selenization processes, by heating to 700 °C at a heating rate of 5 °C / min in an inert argon / hydrogen mixed atmosphere and strictly controlling the calcination time to 2 h, the uniform formation of the carbon coating layer and the full progress of the selenization process are ensured, thereby obtaining a nanocomposite material with uniform particle size, controllable morphology, rich pore diameters, and large specific surface area. These parameter optimizations directly enhance the application performance of the material in the field of electrochemical energy storage.

[0036] Overall, the parameter settings and reaction process of the present invention have significantly overcome the defects existing in the synthesis of multiphase metal-organic frameworks in the prior art. It not only realizes the stable and controllable preparation process, but also greatly improves the structural uniformity and electrochemical performance of the nanocomposite material, demonstrating remarkable technological progress and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flowchart of the preparation method of the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material provided by the embodiment of the present invention;

[0038] Figure 2 is a module diagram of the preparation system of the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material provided by the embodiment of the present invention;

[0039] Figure 3 is a scanning electron microscope image of the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material provided by the embodiment of the present invention;

[0040] Figure 4 is a high-magnification transmission electron microscope image of the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material provided by the embodiment of the present invention;

[0041] Figure 5 is an X-ray diffraction pattern of the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material provided by the embodiment of the present invention;

[0042] Figure 6 is a cyclic voltammogram of the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material provided by the embodiment of the present invention;

[0043] Figure 7 is a charge-discharge cycle diagram of the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material provided by the embodiment of the present invention;

[0044] Figure 8 is a test result diagram of the electrochemical performance of the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] Example 1: In step S1, copper nitrate, manganese nitrate and zinc nitrate were weighed in a molar ratio of 2:1:1 and dissolved in 25 mL of methanol. The mixture was stirred vigorously for 10 min at a stirring speed of 500 r / min to obtain a homogeneous mixed solution. Subsequently, in step S2, 1,3,5-benzenetricarboxylic acid and lauric acid were successively added to the mixed solution, such that the molar ratio of metal salts to organic ligands was controlled at 1:0.99 and the molar ratio of metal salts to surfactants was controlled at 1:4.67. Stirring was continued at room temperature for 3 h.

[0047] Then, in step S3, the above mixed solution was transferred to a high-pressure reactor and reacted at 125 °C for 3 h. The green precipitate was collected by centrifugation, washed repeatedly with ethanol and water to remove impurities, and vacuum-dried overnight at 60 °C to obtain a precursor of the trimetallic organic framework. Finally, in step S4, the precursor was placed in a tube furnace and heated to 700 °C at a heating rate of 5 °C / min under the protection of an argon / hydrogen mixed gas (volume ratio 9:1) and calcined for 2 h. Subsequently, it was naturally cooled to room temperature to obtain a carbon-coated ternary metal-organic framework-derived heterojunction nanocomposite.

[0048] Example 2: In step S1, copper chloride, manganese chloride and zinc chloride were dissolved in 25 mL of methanol in a molar ratio of 2:1:1, and the stirring rate was controlled at 600 r / min and stirred for 12 min to prepare a mixed solution; in step S2, 5-tert-butyl-1,3-benzenedicarboxylic acid was added as an organic ligand and lauric acid was added as a surfactant, and the molar ratio of metal salts to organic ligands was adjusted to 1:0.99 and the molar ratio of metal salts to surfactants was adjusted to 1:4.67, and stirring was continued for 3 h to ensure uniform reaction.

[0049] In step S3, the mixed solution was transferred to a high-pressure reactor and reacted at 125 °C for 3 h. The green precipitate was obtained by centrifugation, washed repeatedly with ethanol and water, and vacuum-dried overnight at 60 °C to prepare a precursor of the trimetallic organic framework. Subsequently, in step S4, under the protection of an inert gas argon / hydrogen mixed gas (volume ratio 9:1), the precursor and selenium powder were configured in a porcelain boat at a mass ratio of 2:1, with selenium powder placed at the upper end of the porcelain boat and the precursor placed at the lower end. It was heated to 700 °C at a heating rate of 5 °C / min and calcined for 2 h, and then naturally cooled to room temperature to prepare a carbon-coated ternary metal-organic framework-derived heterojunction nanocomposite with selenium modification.

[0050] As Figure 1 shown, the embodiments of the present invention provide a method for preparing a carbon-coated ternary metal-organic framework-derived heterojunction nanocomposite, which specifically includes:

[0051] S1: Dissolve the transition metal salt in 20 - 30 mL of methanol at a certain molar ratio. Under the condition that the stirring speed is 100 - 1000 r / min, stir thoroughly for 5 - 15 min to prepare a mixed solution;

[0052] S2: Under the above stirring state, sequentially add an organic ligand and a surfactant to the above mixed solution, such that the molar ratio of the transition metal salt to the organic ligand is 1:0.9 - 1, and the molar ratio of the transition metal salt to the surfactant is 1:4.5 - 5;

[0053] S3: After continuously stirring at room temperature for 3 h, transfer the mixed solution into a high - pressure reaction kettle, react at 100 - 150 °C for 3 h, collect the obtained blue precipitate, wash it multiple times to remove impurities, and dry it overnight at 60 - 80 °C to obtain a trimetallic organic framework precursor;

[0054] S4: Under the protection of an inert gas, place the precursor prepared in S3 in a tubular furnace, heat it at a heating rate of 1 - 5 °C / min to 600 - 800 °C, calcine for 1 - 2 h, and naturally cool to room temperature to obtain a carbon - coated trimetallic organic framework - derived nanocomposite material.

[0055] In the preparation method of the carbon - coated trimetallic organic framework (MOF) - derived heterojunction nanocomposite material described in the embodiments of the present invention, first, in step S1, the transition metal salt is dissolved in methanol to form a uniform metal ion solution. The solubility and reactivity of the transition metal salt in methanol are the basis for forming a high - quality MOF precursor. During the stirring process, the metal salt is in full contact with the solvent, ensuring the uniform dispersion of metal ions and avoiding non - uniform crystallization caused by local supersaturation. In addition, controlling the stirring speed and time helps to promote the uniformity of the solution and the controllability of the reaction, providing a stable precursor solution for the subsequent reaction steps.

[0056] In step S2, an organic ligand and a surfactant are sequentially added to the above mixed solution to adjust the molar ratios of the transition metal salt to the organic ligand and the surfactant. The purpose of this step is to form coordination bonds between the organic ligand and metal ions to construct the basic structure of the trimetallic organic framework. The addition of the surfactant plays a role in adjusting the interfacial tension, controlling the particle morphology and size, and helps to form a uniform and stable nanostructure. The reasonable design of the molar ratio ensures an appropriate ratio of metal ions to organic ligands in the MOF precursor, thereby optimizing the structure and properties of the final material.

[0057] In step S3, the mixed solution is stirred at room temperature for 3 h and then transferred into a high-pressure reactor, where it reacts at 100 - 150 °C for 3 h to form a blue precipitate. The high-pressure reaction conditions promote the crystallization of the MOF precursor and the formation of an ordered structure. The blue precipitate indicates the presence of transition metals and their successful coordination with organic ligands. Multiple washing and drying steps are used to remove unreacted impurities and by-products, ensuring the purity and quality of the precursor and laying the foundation for the subsequent heat treatment step.

[0058] In step S4, the precursor is subjected to high-temperature calcination in a tubular furnace under the protection of an inert gas. It is heated at a heating rate of 1 - 5 °C / min to 600 - 800 °C and maintained at this temperature for 1 - 2 h to promote the carbonization of the organic ligand and the reduction of metal ions, forming a carbon-coated heterojunction nanocomposite derived from a three-phase metal-organic framework. The carbon coating not only improves the conductivity and stability of the material but also helps to form a heterojunction structure, enhancing its performance in applications such as catalysis, batteries, or sensors. Finally, it is naturally cooled to room temperature to obtain the desired nanocomposite, completing the entire preparation process.

[0059] The transition metal salts described in S1 are copper salts, manganese salts, and zinc salts. The copper salts are copper nitrate, copper chloride, or copper acetylacetonate; the manganese salts are manganese nitrate or manganese chloride; the zinc salts are zinc nitrate or zinc chloride.

[0060] The organic ligands described in S2 are 1,3,5-benzenetricarboxylic acid or 5-tert-butyl-1,3-isophthalic acid; the surfactant is lauric acid.

[0061] The inert mixed gas described in S4 is an argon / hydrogen mixed gas with a volume ratio of 9:1. The selenium powder and the carbonization product during the seleniumization process are placed at the upper and lower ends of the porcelain boat respectively, and the mass ratio of the selenium powder to the precursor is 2:1.

[0062] As Figure 2 shown, a preparation system for a carbon-coated heterojunction nanocomposite derived from a three-phase metal-organic framework provided by an embodiment of the present invention specifically includes:

[0063] A mixed solution preparation module for dissolving transition metal salts in methanol to prepare a mixed solution;

[0064] A high-pressure reactor for reacting at 100 - 150 °C to obtain a three-metal-organic framework precursor;

[0065] A tubular furnace for obtaining a carbon-coated heterojunction nanocomposite derived from a three-phase metal-organic framework.

[0066] Example 3

[0067] Transition metal salt: Iron(III) nitrate (Fe(NO3)3·9H2O)

[0068] Organic ligand: 1,3,5-benzenetricarboxylic acid (H3BTC)

[0069] Surfactant: Cetyltrimethylammonium bromide (CTAB)

[0070] Solvent: Methanol

[0071] Dissolve 0.1 mole of iron(III) nitrate in 25 mL of methanol, set the stirring speed to 500 r / min, and stir thoroughly for 10 min to prepare a homogeneous mixed solution.

[0072] Under continuous stirring, add 0.09 mole of H3BTC and 0.5 mole of CTAB in sequence, so that the molar ratio of the transition metal salt to the organic ligand is 1:0.9, and the molar ratio of the transition metal salt to the surfactant is 1:5. Continue stirring for 3 h to allow the components to react fully and form a precursor solution.

[0073] Transfer the reaction mixture solution to a high-pressure reaction kettle and react at 120 °C for 3 h. After the reaction is completed, collect the generated blue precipitate and wash it multiple times with methanol and deionized water to remove impurities. Dry the washed precipitate at 70 °C overnight to obtain an iron-based trimetallic organic framework precursor.

[0074] Under a nitrogen atmosphere, place the precursor in a tube furnace and heat it to 700 °C at a heating rate of 3 °C / min, and calcine it at this temperature for 1.5 h. After natural cooling to room temperature, a carbon-coated heterojunction nanocomposite derived from a trimetallic organic framework is obtained.

[0075] Example 4

[0076] Transition metal salts: Cobalt(II) nitrate hexahydrate (Co(NO3)2·6H2O), Nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O), Zinc(II) nitrate hexahydrate (Zn(NO3)2·6H2O)

[0077] Organic ligand: 2-methylimidazole (2-MIM)

[0078] Surfactant: Polyvinylpyrrolidone (PVP)

[0079] Solvent: Methanol

[0080] Dissolve 0.05 mol of Co(NO3)2·6H2O, 0.05 mol of Ni(NO3)2·6H2O, and 0.05 mol of Zn(NO3)2·6H2O in 30 mL of methanol. Set the stirring speed to 800 r / min and stir thoroughly for 15 min to prepare a homogeneous triple-metal mixed solution.

[0081] Under continuous stirring, sequentially add 0.045 mol of 2-MIM and 0.25 mol of PVP so that the molar ratio of transition metal salt to organic ligand is 1:0.9, and the molar ratio of transition metal salt to surfactant is 1:5. Continue to stir at room temperature for 3 h to promote the coordination reaction between the organic ligand and metal ions, forming a stable precursor solution.

[0082] Transfer the reacted mixed solution to a high-pressure reactor and react at 130 °C for 3 h. After the reaction is completed, collect the generated blue precipitate and wash it repeatedly with methanol and ethanol to remove unreacted substances and by-products. Dry the washed precipitate at 75 °C overnight to obtain a cobalt-nickel-zinc-based triple-metal organic framework precursor.

[0083] Under argon protection, place the precursor in a tubular furnace, heat it to 800 °C at a heating rate of 4 °C / min, and calcine it at this temperature for 2 h. After the calcination is completed, cool it naturally to room temperature to obtain a carbon-coated cobalt-nickel-zinc triple-metal organic framework-derived heterojunction nanocomposite.

[0084] Evidence related to the technical effects obtained in the embodiments of the present invention.

[0085] Example: A preparation method of a carbon-coated triple-metal organic framework-derived heterojunction octahedron composite material is specifically completed according to the following steps:

[0086] I. Dissolve copper nitrate trihydrate (Cu(NO3)2·3H2O, 0.058 g, 0.24 mmol), manganese nitrate tetrahydrate (Mn(NO3)2·4H2O, 0.030 g, 0.12 mmol), and zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 0.035 g, 0.12 mmol) in 25 mL of methanol. Under the condition of a stirring speed of 300 r / min, stir thoroughly for 10 min to prepare a mixed solution. Subsequently, under the above stirring state, sequentially add an organic ligand and a surfactant to the above mixed solution so that the molar ratio of transition metal salt to organic ligand is 1:0.99, and the molar ratio of transition metal salt to surfactant is 1:4.67. After continuously stirring at room temperature for 3 h, transfer the mixed solution to a high-pressure reactor and react at 125 °C for 3 h. Collect the obtained blue precipitate, wash it repeatedly to remove impurities, and dry it overnight at 60 °C to obtain a CuMnZn-MOF precursor.

[0087] II. Subsequently, under the protection of inert gas, the precursor prepared in Step I was placed in a tube furnace and heated to 700 °C at a heating rate of 5 °C / min for selenization for 2 h, and then naturally cooled to room temperature, thus obtaining a carbon-coated ternary metal-organic framework-derived nanocomposite. In addition, the selenium powder and the carbonized product during the selenization process were respectively placed at the upper and lower ends of the porcelain boat, and the mass ratio of the selenium powder to the precursor was 2:1. Finally, the finally obtained samples were respectively denoted as Cu 2-x Se / MnSe / ZnSe@C.

[0088] The morphology of the carbon-coated ternary metal-organic framework-derived heterojunction octahedral composite Cu 2-x Se / MnSe / ZnSe@C obtained in Step II of this example was tested. Figure 3 This is the scanning electron microscope image of the Cu 2-x Se / MnSe / ZnSe@C sample, Figure 4 This is the high-magnification transmission electron microscope image of the Cu 2-x Se / MnSe / ZnSe@C sample. As can be seen from Figure 3 and Figure 4 , the sample retains the octahedral structure of the precursor, and the nanoparticles on the surface are evenly distributed with basically the same size, and there is no agglomeration of large nanoparticles. It can be further seen from Figure 4 that Cu 2-x Se / MnSe / ZnSe@C is a carbon-coated octahedral structure with a core-shell structure; heterostructures are formed at the intersecting parts of the three metal selenides of Cu 2-x Se, MnSe and ZnSe, and this heterostructure helps to improve the conductivity and reaction kinetics of the electrode material.

[0089] The X-ray diffraction spectrum analysis of the Cu 2-x Se / MnSe / ZnSe@C sample obtained in this example was carried out. As shown in Figure 5 , the X-ray diffraction peaks of the sample prepared in Step II coincide with the diffraction peaks of non-ideally proportioned copper selenide, manganese selenide and zinc selenide respectively. Among them, the characteristic diffraction peaks at 2θ = 26.749°, 31.026°, 44.599° and 52.911° belong to Cu 2-xThe (111), (200), (220), and (311) crystal planes of Se. The diffraction peaks at 2θ = 26.506° and 43.692° belong to the (111) and (220) crystal planes of MnSe. The characteristic diffraction peaks at 2θ = 27.224°, 31.532°, 45.195°, and 53.568° belong to the (111), (200), (220), and (311) crystal planes of ZnSe. The diffraction peaks at 2θ = 13.039°, 25.376°, 26.188°, and 39.763 belong to the (030), (211), (060), and (090) crystal planes of Cu2Se.

[0090] Furthermore, the heat-treated Cu 2-x Se / MnSe / ZnSe@C sample in Step 2 of this experimental procedure was subjected to electrochemical testing. Figure 6 This is the cyclic voltammetry curve. As can be seen from the figure, the curves coincide well after the second week, proving the consistency of the electrochemical reaction and also indicating good cycle stability. Figure 7 This is the charge-discharge cycle performance graph of using the Cu 2-x Se / MnSe / ZnSe@C sample directly as the negative electrode of sodium-ion batteries (SIBs). At a charge-discharge current density of 5 A / g and after 400 cycles, the performance is still very stable and shows a high specific capacity, indicating that the Cu 2-x Se / MnSe / ZnSe@C composite material has good electrochemical performance. In addition, for the Cu 2-x Se / MnSe / ZnSe@C electrode material prepared in this experiment, a full battery was assembled and its electrochemical performance was tested. The test results are Figure 8 . Among them, the commercial electrode material sodium vanadium phosphate (Na2V2(PO4)3) for SIBs was used as the positive electrode material of the full battery. After cycling 100 times at a current density of 0.1 A / g, the discharge specific capacity remained at 132.8 mAh / g. These results prove that the Cu 2-x Se / MnSe / ZnSe@C composite material has good development prospects and application potential as the negative electrode material for SIBs.

[0091] As described above, this is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material, characterized in that: The method includes: S1: dissolving the transition metal salt in 20-30 mL of methanol at a certain molar ratio, stirring at a speed of 100-1000 r / min, and fully stirring for 5-15 min to prepare a mixed solution; S2: under the above stirring state, adding an organic ligand and a surfactant to the above mixed solution in sequence, so that the molar ratio of the transition metal salt to the organic ligand is 1:0.9-1, and the molar ratio of the transition metal salt to the surfactant is 1:4.5-5; S3: After continuous stirring at room temperature for 3 hours, the mixed solution was transferred into a high-pressure reactor and reacted at 100-150°C for 3 hours. A blue precipitate was collected, impurities were removed by multiple washings, and the mixture was dried at 60-80°C overnight to obtain a trimetallic organic framework precursor. S4: Under the protection of inert gas, the precursor prepared in S3 is placed in a tube furnace, heated to 600-800°C at a heating rate of 1-5°C / min, and calcined for 1-2h, and naturally cooled to room temperature to obtain a carbon-coated three-phase metal-organic framework-derived nanocomposite material; S5: The synthesis method of the three-phase metal-organic framework material is relatively stable. This preparation method can be used to obtain a multiphase metal-organic framework heterojunction nanocomposite material with uniform particle size, controllable morphology, rich pore size, and large specific surface area by regulating the type of metal source and the ratio of organic ligand added before the reaction, so as to be used in the development of the field of electrochemical energy storage.

2. The method for preparing the carbon-coated three-phase metal organic framework-derived heterojunction nanocomposite material according to claim 1, characterized in that: The transition metal salt described in S1 is a copper salt, a manganese salt, or a zinc salt. The copper salt is copper nitrate, copper chloride, or copper acetylacetonate; the manganese salt is manganese nitrate or manganese chloride; and the zinc salt is zinc nitrate or zinc chloride.

3. The method for preparing the carbon-coated three-phase metal organic framework-derived heterojunction nanocomposite material according to claim 1, characterized in that: The molar ratio of the copper salt, the manganese salt and the zinc salt in the S1 is 2:1:1, and the volume of the methanol solvent is 25 mL.

4. The method for preparing the carbon-coated three-phase metal organic framework-derived heterojunction nanocomposite material according to claim 1, characterized in that: The organic ligand described in S2 is 1,3,5-benzenetricarboxylic acid or 5-tert-butyl-1,3-isophthalic acid; and the surfactant is lauric acid.

5. The method for preparing the carbon-coated three-phase metal organic framework-derived heterojunction nanocomposite material according to claim 1, characterized in that: The molar ratio of the metal salt to the organic ligand in S2 is 1:0.99, and the molar ratio of the metal salt to the surfactant is 1:4.

67.

6. The method for preparing the carbon-coated three-phase metal organic framework-derived heterojunction nanocomposite material according to claim 1, characterized in that: In S3, the mixed solution is transferred to a high-pressure reactor and reacted at 125° C. for 3 h. A green precipitate is collected by centrifugation, washed with ethanol and water for multiple times to remove impurities, and vacuum dried at 60° C. overnight to obtain a precursor of the trimetallic organic framework.

7. The method for preparing the carbon-coated three-phase metal-organic framework-derived heterojunction nanocomposite material according to claim 1, characterized in that: The inert mixed gas described in S4 is an argon / hydrogen mixed gas with a volume ratio of 9:

1. The selenium powder and carbonization product in the selenization process are placed at the upper and lower ends of the porcelain boat respectively, and the mass ratio of selenium powder to precursor is 2:

1.

8. The method for preparing the carbon-coated three-phase metal organic framework-derived heterojunction nanocomposite material according to claim 1, characterized in that: The temperature is raised to 700° C. and calcined for 2 h at a heating rate of 5° C. / min in the argon / hydrogen mixed atmosphere described in S4.

9. A system for preparing a carbon-coated three-phase metal organic framework-derived heterojunction nanocomposite material according to claims 1-8, characterized in that: The system specifically includes: A mixed solution preparation module, used for dissolving a transition metal salt in methanol to prepare a mixed solution; A high-pressure reactor, used for reacting at 100-150°C to obtain a trimetallic organic framework precursor; Tube furnace for obtaining carbon-coated three-phase metal-organic framework-derived nanocomposites.

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