Bimetallic-atom-loaded porous carbon framework material, and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a bimetallic-atom-loaded porous carbon framework material, and a preparation method therefor and the use thereof. The preparation method comprises: by taking a metal organic framework as a precursor raw material, and by using the self-polymerization of a high-molecular polymer on the surface of the metal organic framework, forming a polymer-coated metal-based organic framework material (PM@MOF) having a core-shell structure; and then capturing the metal of a metal chloride salt solution by using surface functional groups of the PM@MOF dispersed in n-hexane, so as to obtain a bimetallic element-doped polymer-coated metal-based organic framework material, and subjecting same to a high-temperature treatment in an argon gas atmosphere so as to obtain a bimetallic-atom-loaded porous carbon-based material (MD@PC). In the present invention, by loading bimetallic atoms on a nitrogen-doped porous carbon matrix to form MD-NX coordination sites, which have the dual functions of sulfur fixation and catalysis, the agglomeration degree of intermediate phase lithium sulfide can be reduced, thereby guaranteeing that the lithiation reaction of sulfur is more sufficient, rapid and efficient.

Description

Bimetallic atom-loaded porous carbon framework material and its preparation method and application Technical Field

[0001] The present invention belongs to the field of battery technology, and in particular relates to a bimetallic atom-loaded porous carbon skeleton material and a preparation method and application thereof. Background Art

[0002] Lithium-sulfur batteries (Li-S batteries) offer inherent advantages such as high theoretical specific capacity, abundant resources, and convenient recycling, making them a promising electrochemical energy storage technology. However, the sulfur cathode, a key component of Li-S batteries' high energy density, currently suffers from poor intrinsic conductivity and low utilization, significantly impairing their electrochemical performance. Therefore, developing advanced sulfur cathode carriers is crucial for improving Li-S battery performance.

[0003] Porous carbon-based materials are cheap and easy to obtain, have fast electron transfer and good mechanical toughness, and have strong coupling with elemental sulfur. They show excellent potential as sulfur positive electrode support materials. However, the three-dimensional space of porous carbon-based materials is open, the polarity is weak, and the number of functionalized sites is small, which will cause the dissolution and agglomeration of the intermediate phase lithium polysulfide, resulting in irreversible loss of sulfur and insufficient lithiation reaction. Based on this, nitrogen-doped mesoporous carbon coating is an effective strategy to close the open space of porous carbon-based materials (PC) and enhance the polarity. On the one hand, the spatial confinement effect of mesoporous carbon is utilized to encapsulate the elemental sulfur inside it, acting as a physical barrier to prevent the loss of the intermediate phase. On the other hand, nitrogen doping as an active site can enhance the polarity of porous carbon, so that the binding energy between porous carbon and intermediate phase lithium polysulfide is improved, thereby improving the dissolution of the intermediate phase.

[0004] However, in the face of multi-phase / multi-state / multi-electron reactions in lithium-sulfur electrochemical reactions, how to comprehensively improve the comprehensive performance of lithium-sulfur batteries based on the structural design of porous carbon-based materials and carrier modification remains a difficult problem.

[0005] Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a bimetallic atom-loaded porous carbon skeleton material and its preparation method and application. The present invention utilizes bimetallic atoms loaded on a nitrogen-doped porous carbon matrix to form M D -N X The coordination sites have the dual functions of sulfur fixation and catalysis, which can reduce the degree of agglomeration of the intermediate phase lithium sulfide and ensure that the sulfur lithiation reaction is more complete, rapid and efficient.

[0007] The technical solution of the present invention is:

[0008] The present invention relates to a method for preparing a bimetallic atom-loaded porous carbon-based framework material, comprising the following steps:

[0009] (1) A metal-organic framework material as a precursor raw material is dispersed in an aqueous solution of tris(hydroxymethyl)aminomethane, dopamine hydrochloride is added, and the mixture is stirred at room temperature at a speed of ≤350 rpm / min for 1 to 8 hours. After centrifugal washing and drying, a polymer-coated metal-based organic framework material is obtained, which is recorded as PM@MOF.

[0010] (2) PM@MOF was dispersed in n-hexane, and then a metal chloride aqueous solution was added dropwise to the PM@MOF n-hexane dispersion, ultrasonicated in an ice-water bath for 1 to 6 hours, stirred at room temperature for 2 to 10 hours, filtered, and dried to obtain a bimetallic element-doped polymer-coated metal-based organic framework material;

[0011] (3) The metal-based organic framework material doped with a polymer and coated with a bimetallic element is heat-treated at 500-1000°C for 1-10 h in an argon atmosphere and cooled to room temperature. The heat-treated product is first immersed in a hydrochloric acid solution and then immersed in a sodium hydroxide solution at 50-80°C. It is centrifuged, washed, and dried to obtain a porous carbon-based material with uniform bimetallic atoms loaded thereon, which is denoted as MD@PC, where MD represents the metal element and PC represents porous carbon.

[0012] Preferably, in step (1), the precursor raw material is a metal organic framework material of any one of ZIF-67, ZIF-8, ZIF-7, MIL-101 and MIL-88A, and the metal contained in the metal organic framework material is any one of cobalt (Co), zinc (Zn), copper (Cu), and iron (Fe).

[0013] Preferably, in step (1), the concentration of the aqueous solution of tris(hydroxymethyl)aminomethane is 0.2-10 g / L; the mass ratio of the metal organic framework material to tris(hydroxymethyl)aminomethane is in the range of 1:1-1:12, and the mass ratio of the metal organic framework material to dopamine hydrochloride is in the range of 5:1-1:5.

[0014] Preferably, in step (2), the metal chloride is any 1 to 2 of MgCl2, CoCl2, NiCl2, CuCl2, ZnCl2, FeCl3, WCl4 and MoCl5. When it is any one of them, the metal in the metal chloride is different from the metal type contained in the metal-organic framework material. When it is any two of them, the metal of one of them is the same as the metal type contained in the metal-organic framework material, and the metal of the other is different.

[0015] Preferably, the concentration of the metal chloride salt aqueous solution is 5 to 500 g / L. The salt used to prepare the metal chloride salt aqueous solution is an aqueous chloride salt, and the purity is required to be ≥98%.

[0016] Preferably, in step (2), the temperature during the ice-water bath is required to be less than T, which is 3-6°C.

[0017] Preferably, in step (3), the concentration of the hydrochloric acid solution is 0.1 to 5 mol / L, and the soaking time is 1 to 10 h; the concentration of the sodium hydroxide solution is 0.1 to 5 mol / L, and the soaking time is 0.5 to 5 h.

[0018] Preferably, in step (3), the heating rate during the heat treatment is 1 to 20°C / min.

[0019] The present invention also relates to a bimetallic atom-loaded porous carbon-based framework material, prepared using the aforementioned preparation method. The method uses a metal-organic framework (MOF) as a precursor and utilizes the self-polymerization of a high molecular weight polymer on the MOF surface to form a polymer-coated metal-based organic framework (PM@MOF) with a core-shell structure. The surface functional groups of the PM@MOF, dispersed in an n-hexane solution, are then used to capture metals in an aqueous solution of metal chloride salts, thereby obtaining a bimetallic element-doped polymer-coated MOF material. This material is then treated at high temperature under an argon atmosphere to obtain a bimetallic atom-loaded porous carbon-based material (MD@PC).

[0020] Preferably, MD is any two metal elements selected from Mg, Co, Ni, Cu, Zn, Fe, W and Mo, and the percentage of the total molar number of the MD metal elements to the total molar number of all elements in MD@PC is 0.05% to 15%.

[0021] The present invention also relates to the use of the above-mentioned bimetallic atom-loaded porous carbon-based skeleton material in the preparation of lithium-sulfur batteries.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention utilizes bimetallic atoms loaded on a nitrogen-doped porous carbon matrix to form M D -N X The coordination sites have dual functions of sulfur fixation and catalysis, which can reduce the agglomeration degree of the intermediate phase lithium sulfide and ensure that the sulfur lithiation reaction is more complete, rapid and efficient;

[0024] (2) The present invention regulates the conductivity / polarity / site activity of bimetallic atom-loaded porous carbon-based materials, comprehensively grasps the rules of enhancing the electrochemical performance of sulfur cathodes through optimization of composition, structure, and morphology, and obtains theoretical support and technical breakthroughs for the practical application of MD@PC, thereby accelerating the practical application of lithium-sulfur batteries.

[0025] (3) The bimetallic atom-loaded porous carbon-based material prepared by the present invention contains a variety of different bimetallic single atoms, and its catalytic activity significantly improves the reaction kinetics of the lithium-sulfur battery, which is expected to give full play to the ultra-stable cycle and high-rate characteristics of the battery; the bimetallic atom-loaded porous carbon material used in the lithium-sulfur battery as a sulfur storage positive electrode material can stably cycle for at least 3,000 cycles under a high-rate charge and discharge of 5 to 15 minutes, greatly improving the service life of the battery;

[0026] (4) The preparation method of the present invention has the advantages of low cost, simplicity and wide application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0028] FIG1 is an XRD pattern of a bimetallic atom-loaded porous carbon-based framework material prepared in Example 1;

[0029] FIG2 is the SEM morphology of the bimetallic atom-loaded porous carbon-based framework material prepared in Example 2;

[0030] FIG3 is the SEM morphology of the bimetallic atom-loaded porous carbon-based framework material prepared in Example 3;

[0031] FIG4 is a TEM image of a bimetallic atom-loaded porous carbon-based framework material prepared in Example 4;

[0032] FIG5 is the TEM morphology and EDS spectrum of the bimetallic atom-loaded porous carbon-based framework material prepared in Example 5;

[0033] FIG6 is a cyclic voltammetry curve of a bimetallic atom-loaded porous carbon-based sulfur storage cathode material and a pure carbon matrix sulfur storage cathode prepared in Example 6;

[0034] FIG7 is a performance curve of the bimetallic atom-loaded porous carbon-based sulfur storage cathode material prepared in Example 7 in a high current long cycle;

[0035] FIG8 is a TEM morphology of the porous carbon-based composite material prepared in Comparative Example 1;

[0036] FIG9 is the SEM morphology of the composite material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0038] The salt used in the pre-prepared metal chloride aqueous solution in the following examples and comparative examples is an aqueous chloride salt purchased from Aladdin Reagent, and the purity is required to be ≥98%.

[0039] The preparation methods of the metal skeleton materials used in the following examples are as follows, wherein the salts used (zinc nitrate hexahydrate, cobalt nitrate hexahydrate and ferric chloride hexahydrate) are also purchased from Aladdin Reagent, and the purity is required to be ≥98%.

[0040] Preparation of the zinc-based metal-organic framework of ZIF-8: Dissolve 0.725 g of zinc nitrate hexahydrate in 20 mL of deionized water and stir at room temperature until completely dissolved. Add 20 mg of hexadecyltrimethylammonium bromide, sonicate for 5 minutes, and stir for 0.5 hours. This is labeled Solution A. Dissolve 2.8 g of 2-methylimidazole in 80 mL of deionized water and stir until the powder is completely dissolved. This is labeled Solution B. Quickly pour Solution A into Solution B, stir at room temperature for 6 hours, wash by centrifugation three times, and dry at 60°C to obtain a powder sample.

[0041] Preparation of the cobalt-based metal-organic framework of ZIF-67: Dissolve 0.725 g of cobalt nitrate hexahydrate in 20 mL of deionized water and stir at room temperature until completely dissolved. Add 20 mg of hexadecyltrimethylammonium bromide, sonicate for 5 minutes, and stir for 0.5 hours. This is labeled Solution A. Dissolve 2.8 g of 2-methylimidazole in 80 mL of deionized water and stir until the powder is completely dissolved. This is labeled Solution B. Quickly pour Solution A into Solution B, stir at room temperature for 6 hours, wash by centrifugation three times, and dry at 60°C to obtain a powder sample.

[0042] Preparation of the iron-based metal-organic framework of MIL-101: 0.675 g of ferric chloride hexahydrate and 0.205 g of terephthalic acid were dissolved in 30 mL of dimethylformamide. The resulting suspension was sonicated for 0.5 h, then transferred to a hydrothermal reactor and heated at 110°C for 16 h. After cooling the reactor to room temperature, the sample was washed three times with dimethylformamide and then with methanol, then dried at 60°C to obtain a powder.

[0043] Preparation of the iron-based metal-organic framework of MIL-88A: Take 1.2g of ferric chloride hexahydrate and 0.6g of fumaric acid and dissolve them in 15mL of deionized water respectively. Then, the two solutions are fully mixed and transferred to a hydrothermal reactor. The reaction is carried out at 100℃ for 6h. After the reactor is cooled to room temperature, it is washed three times with ethanol and dried at 60℃ to obtain a powder sample.

[0044] Example 1

[0045] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0046] (1) 0.1 g of ZIF-8 zinc-based metal organic framework was dispersed as a precursor in 200 mL of a 2.2 g / L tris(hydroxymethylaminomethane) aqueous solution. After adding dopamine hydrochloride in an amount equal to the mass of the metal organic framework precursor, the mixture was stirred at 150 rpm / min at room temperature for 8 h. The mixture was then centrifuged and washed three times with methanol at 9500 rpm / min and dried in a vacuum oven at 70 °C for 15 h to obtain a polymer-coated metal organic framework material (PM@ZIF-8).

[0047] (2) Weigh 0.1 g of PM@ZIF-8 and redisperse it in 26 mL of n-hexane. Pipette 50 μL of the pre-prepared 100 g / L FeCl3 aqueous solution and add it dropwise to the PM@ZIF-8 n-hexane dispersion. Ultrasonicate in an ice-water bath for 2 h, control the ice-water bath temperature to <5 °C, and stir magnetically at room temperature for 2 h. Filter the clarified solution to obtain a precipitate, which was then dried in a vacuum oven at 60 °C for 10 h.

[0048] (3) The powder obtained in step (2) was placed in an agate mortar and ground for 20 minutes, loaded into a corundum crucible, and then placed in a tube furnace. In an argon atmosphere, the temperature was increased at a rate of 2°C / min and kept at 750°C for 3 hours. After it was cooled to room temperature, the heat-treated product was first dispersed in 25 mL of a 0.2 mol / L hydrochloric acid solution and soaked for 2.5 hours. Then, the oil bath was heated to 65°C and placed in 25 mL of a 2 mol / L sodium hydroxide solution and soaked for 2 hours. After thorough centrifugal washing, it was dried to prepare a bimetallic atom Fe and Zn loaded porous carbon material.

[0049] After analysis: the XRD pattern of the prepared bimetallic atom-loaded porous carbon is shown in Figure 1. It can be seen that the prepared powder is a pure carbon matrix without any metal compound impurities.

[0050] Example 2

[0051] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0052] (1) 0.1 g of ZIF-8 zinc-based metal organic framework was dispersed as a precursor in 200 mL of a 3 g / L aqueous solution of tris(hydroxymethylaminomethane). After adding dopamine hydrochloride in an amount equal to the mass of the metal organic framework precursor, the mixture was stirred at 175 rpm / min at room temperature for 8 h. The mixture was then centrifuged and washed three times with methanol at 9500 rpm / min and dried in a vacuum oven at 70 °C for 15 h to obtain a polymer-coated metal organic framework material (PM@ZIF-8).

[0053] (2) Weigh 0.12 g of PM@ZIF-8 and redisperse it in 28 mL of n-hexane. Pipette 60 μL of the pre-prepared 120 g / L NiCl2 aqueous solution and add it dropwise to the PM@ZIF-8 n-hexane dispersion. Ultrasonicate in an ice-water bath for 1.5 h while controlling the ice-water bath temperature to <6 °C. Stir magnetically at room temperature for 2.5 h. Filter the clarified solution to obtain a precipitate, which was dried in a vacuum oven at 60 °C for 12 h.

[0054] (3) The powder obtained in step (2) was ground in an agate mortar for 15 minutes, placed in a corundum crucible, and then placed in a tube furnace. In an argon atmosphere, the temperature was increased at a rate of 3°C / min and kept at 780°C for 6 hours. After cooling to room temperature, the heat-treated product was first dispersed in 25 mL of a 0.5 mol / L hydrochloric acid solution and soaked for 3 hours. Then, the oil bath was heated to 75°C and placed in 25 mL of a 1 mol / L sodium hydroxide solution and soaked for 1 hour. After thorough centrifugal washing and drying, a bimetallic Ni and Zn atom-loaded porous carbon material was prepared.

[0055] After analysis: The scanning electron microscope image of the prepared bimetallic atom-loaded porous carbon is shown in Figure 2. It can be seen that the prepared powder particles have a regular octahedral morphology under SEM observation, and the original regular skeleton of ZIF-8 is retained after high-temperature carbonization.

[0056] Example 3

[0057] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0058] (1) 0.1 g of the cobalt-based metal organic framework of ZIF-67 was dispersed as a precursor raw material in 200 mL of a 4.5 g / L aqueous solution of tris(hydroxymethylaminomethane). After adding dopamine hydrochloride in an amount equal to the mass of the metal organic framework precursor raw material, the mixture was stirred at 190 rpm / min at room temperature for 6 h. Then, the mixture was centrifuged and washed three times with methanol at 7500 rpm / min, and dried in a vacuum oven at 65 °C for 8 h to obtain a polymer-coated metal organic framework material (PM@ZIF-67).

[0059] (2) Weigh 0.15 g of PM@ZIF-67 and redisperse it in 23 mL of n-hexane. Pipette 85 μL of the pre-prepared 90 g / L FeCl3 aqueous solution and add it dropwise to the n-hexane dispersion of PM@ZIF-67. Ultrasonicate in an ice-water bath for 1 h, control the ice-water bath temperature to <3 °C, and stir magnetically at room temperature for 2 h. Filter the clarified solution to obtain a precipitate, which was dried in a vacuum oven at 60 °C for 12 h.

[0060] (3) The powder obtained in step (2) was ground in an agate mortar for 15 minutes, placed in a corundum crucible, and then placed in a tube furnace. In an argon atmosphere, the temperature was increased at a rate of 8°C / min and kept at 850°C for 2 hours. After cooling to room temperature, the heat-treated product was first dispersed in 25 mL of a 1.5 mol / L hydrochloric acid solution and soaked for 3 hours. Then, the oil bath was heated to 60°C and placed in 25 mL of a 2.5 mol / L sodium hydroxide solution and soaked for 2 hours. After thorough centrifugal washing and drying, a bimetallic atom Fe and Co loaded porous carbon material was prepared.

[0061] After analysis: The scanning electron microscope image of the prepared bimetallic atom-loaded porous carbon is shown in Figure 3. It can be seen that the prepared powder particles have a regular dodecahedral morphology under SEM observation, and the original regular skeleton of ZIF-67 is retained after high-temperature carbonization.

[0062] Example 4

[0063] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0064] (1) 0.1 g of the cobalt-based metal organic framework of ZIF-67 was dispersed as a precursor raw material in 200 mL of a 3.6 g / L aqueous solution of tris(hydroxymethylaminomethane). After adding dopamine hydrochloride in an amount equal to the mass of the metal organic framework precursor raw material, the mixture was stirred at 230 rpm / min at room temperature for 7 h. The mixture was then centrifuged and washed three times with methanol at 8050 rpm / min, and dried in a vacuum oven at 65 °C for 10 h to obtain a polymer-coated metal organic framework material (PM@ZIF-67).

[0065] (2) Weigh 0.16 g of PM@ZIF-67 and redisperse it in 36 mL of n-hexane. Pipette 65 μL of the pre-prepared 180 g / L WCl4 aqueous solution and add it dropwise to the PM@ZIF-67 n-hexane dispersion. Ultrasonicate in an ice-water bath for 2 h, control the ice-water bath temperature to <3 °C, and stir magnetically at room temperature for 2.5 h. Filter the clarified solution to obtain a precipitate, which was dried in a vacuum oven at 60 °C for 12 h.

[0066] (3) The powder obtained in step (2) was ground in an agate mortar for 15 minutes, placed in a corundum crucible, and then placed in a tube furnace. In an argon atmosphere, the temperature was increased at a rate of 5°C / min and kept at 880°C for 6 hours. After cooling to room temperature, the heat-treated product was first dispersed in 25 mL of a 1 mol / L hydrochloric acid solution and soaked for 2.5 hours. Then, the oil bath was heated to 55°C and placed in 25 mL of a 2 mol / L sodium hydroxide solution and soaked for 2 hours. After thorough centrifugal washing and drying, a bimetallic atom W and Co loaded porous carbon material was prepared.

[0067] After analysis: The transmission electron micrograph of the prepared bimetallic atom-loaded porous carbon is shown in Figure 4. It can be seen that the original regular skeleton of ZIF-67 is retained after high-temperature carbonization, and it has a core-shell structure with two layers inside and outside.

[0068] Example 5

[0069] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0070] (1) 0.1 g of the cobalt-based metal organic framework of ZIF-67 was dispersed as a precursor raw material in 200 mL of a 3.6 g / L aqueous solution of tris(hydroxymethylaminomethane). After adding dopamine hydrochloride in an amount equal to the mass of the metal organic framework precursor raw material, the mixture was stirred at 230 rpm / min at room temperature for 7 h. The mixture was then centrifuged and washed three times with methanol at 8050 rpm / min, and dried in a vacuum oven at 65 °C for 10 h to obtain a polymer-coated metal organic framework material (PM@ZIF-67).

[0071] (2) Weigh 0.16 g of PM@ZIF-67 and redisperse it in 36 mL of n-hexane. Pipette 65 μL of the pre-prepared 180 g / L ZnCl2 aqueous solution and add it dropwise to the n-hexane dispersion of PM@ZIF-67. Ultrasonicate in an ice-water bath for 2 h, control the ice-water bath temperature to <3 °C, and stir magnetically at room temperature for 2.5 h. Filter the clarified solution to obtain a precipitate, which was dried in a vacuum oven at 60 °C for 12 h.

[0072] (3) The powder obtained in step (2) was ground in an agate mortar for 15 minutes, placed in a corundum crucible, and then placed in a tube furnace. In an argon atmosphere, the temperature was increased at a rate of 5°C / min and kept at 880°C for 6 hours. After cooling to room temperature, the heat-treated product was first dispersed in 25 mL of a 3 mol / L hydrochloric acid solution and soaked for 2.5 hours. Then, the oil bath was heated to 50°C and placed in 25 mL of a 1 mol / L sodium hydroxide solution and soaked for 2.5 hours. After thorough centrifugal washing and drying, a bimetallic atom Zn and Co loaded porous carbon material was prepared.

[0073] After analysis: The transmission electron micrograph of the prepared bimetallic atom-loaded porous carbon is shown in Figure 5. It can be seen that the four elements Zn / Co / N / C are evenly distributed in the framework of the core-shell structure under the energy spectrum of the prepared powder particles under TEM.

[0074] Example 6

[0075] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0076] (1) 0.2 g of the iron-based metal organic framework of MIL-101 was dispersed as a precursor in 450 mL of a 3.4 g / L aqueous solution of tris(hydroxymethylaminomethane). After adding dopamine hydrochloride in an amount equal to the mass of the metal organic framework precursor, the mixture was stirred at 260 rpm / min at room temperature for 5.5 h. The mixture was then centrifuged and washed three times with methanol at 8350 rpm / min. The mixture was then dried in a vacuum oven at 65°C for 11 h to obtain a polymer-coated metal organic framework material (PM@MIL-101).

[0077] (2) Weigh 0.21 g of PM@MIL-101 and redisperse it in 43 mL of n-hexane. Pipette 85 μL of the pre-prepared 205 g / L MoCl5 aqueous solution and add it dropwise to the n-hexane dispersion of PM@MIL-101. Ultrasonicate in an ice-water bath for 2.5 h while controlling the ice-water bath temperature to <4 °C. Stir magnetically at room temperature for 2.5 h. Filter the clarified solution to obtain a precipitate, which was then dried in a vacuum oven at 60 °C for 12 h.

[0078] (3) The powder obtained in step (2) was ground in an agate mortar for 15 minutes, placed in a corundum crucible, and then placed in a tube furnace. In an argon atmosphere, the temperature was increased at a rate of 6°C / min and kept at 900°C for 5 hours. After cooling to room temperature, the heat-treated product was first dispersed in 36 mL of a 0.2 mol / L hydrochloric acid solution and soaked for 5 hours. Then, the oil bath was heated to 60°C and placed in 36 mL of a 2 mol / L sodium hydroxide solution and soaked for 2.5 hours. After thorough centrifugal washing and drying, a bimetallic atom Mo and Fe loaded porous carbon material was prepared.

[0079] Analysis revealed that the prepared bimetallic Mo and Fe-loaded porous carbon was subjected to melt sulfurization at 155°C to yield a sulfur storage cathode material. The cyclic voltammetry curve of the assembled button cell is shown in Figure 6, comparing this with the porous carbon sulfur storage material. Two distinct reduction peaks appeared on the discharge platform, reaching maximum peak currents at 2.20V and 1.98V, respectively. This corresponds to the stepwise lithiation reaction of the sulfur cathode, where elemental sulfur is converted into long-chain lithium polysulfides: S8→Li2S x (4≤x≤8) and long-chain lithium polysulfides are transformed into short-chain lithium polysulfides: Li2S x (4≤x≤8)→Li2S x (1≤x≤3). Correspondingly, two obvious oxidation peaks appeared on the charging platform, reaching the maximum peak current at 2.40V and 2.48V respectively, corresponding to the delithiation of solid-phase lithium sulfide into sulfur element and the transformation of short-chain lithium polysulfide into long-chain lithium polysulfide: Li2S x (1≤x≤3)→Li2S x(4≤x≤8), and the long-chain lithium polysulfide is converted into sulfur: Li2S x (4≤x≤8)→S8.

[0080] Example 7

[0081] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0082] (1) 0.2 g of the iron-based metal organic framework of MIL-88A was dispersed as a precursor raw material in 450 mL of a 4.6 g / L aqueous solution of tris(hydroxymethylaminomethane). After adding dopamine hydrochloride in an amount equal to the mass of the metal organic framework precursor raw material, the mixture was stirred at 320 rpm / min at room temperature for 6 h. Then, the mixture was centrifuged and washed three times with methanol at 8800 rpm / min, and dried in a vacuum oven at 60°C for 15 h to obtain a polymer-coated metal organic framework material (PM@MIL-88A).

[0083] (2) Weigh 0.18 g of PM@MIL-88A and redisperse it in 39 mL of n-hexane. Pipette 75 μL of the pre-prepared 22.5 g / L NiCl2 aqueous solution and add it dropwise to the n-hexane dispersion of PM@MIL-88A. Ultrasonicate in an ice-water bath for 4 h while controlling the ice-water bath temperature to <3 °C. Stir magnetically at room temperature for 3.5 h. Filter the clarified solution to obtain a precipitate, which was then dried in a vacuum oven at 55 °C for 10 h.

[0084] (3) The obtained powder was placed in an agate mortar and ground for 15 minutes, loaded into a corundum crucible, and then placed in a tube furnace. In an argon atmosphere, the temperature was increased at a rate of 8°C / min and kept at 950°C for 4.5 hours. After it was cooled to room temperature, the heat-treated product was first dispersed in 36 mL of a 0.5 mol / L hydrochloric acid solution and soaked for 4.5 hours. Then, the oil bath was heated to 80°C and placed in 36 mL of a 1 mol / L sodium hydroxide solution and soaked for 1.5 hours. After thorough centrifugal washing and drying, a bimetallic atom Ni and Fe loaded porous carbon material was prepared.

[0085] Analysis revealed that the prepared bimetallic Ni and Fe loaded porous carbon was subjected to melt sulfurization at 155°C to obtain the sulfur storage cathode material Ni-Fe@N-PC-S. The long-cycle performance of the assembled button cell is shown in Figure 7. When the current was increased and the cycle period was extended, the Ni-Fe@N-PC-S composite electrode exhibited more stable high-rate performance. When the test current density was increased to 5C, the Ni-Fe@N-PC-S composite cathode was still able to release an initial discharge capacity of 1141 mAh g-1. After 2000 cycles, the reversible capacity was 809 mAh g-1. Over 2000 cycles, the capacity retention rate was as high as 71%, while the average capacity decay rate per cycle was only 0.015%.

[0086] Comparative Example 1

[0087] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0088] (1) 0.1 g of ZIF-8 zinc-based metal organic framework was dispersed as a precursor in 200 mL of a 3.6 g / L tris(hydroxymethylaminomethane) aqueous solution. After adding dopamine hydrochloride in an amount equal to the mass of the metal organic framework precursor, the mixture was stirred at 300 rpm / min at room temperature for 6 h. The mixture was then centrifuged and washed three times with methanol at 8500 rpm / min and dried in a vacuum oven at 60 °C for 10 h to obtain a polymer-coated metal organic framework material (PM@ZIF-8).

[0089] (2) Weigh 0.16 g of PM@ZIF-8 and redisperse it in 32 mL of n-hexane liquid. Pipette 85 μL of the pre-prepared 195 g / L CuCl2 aqueous solution and add it dropwise to the n-hexane dispersion of PM@ZIF-8. Ultrasonicate for 3 h and magnetically stir at room temperature for 4 h. Filter the clarified solution to obtain the precipitate, which is then dried in a vacuum oven at 55 °C for 10 h.

[0090] (3) The powder obtained in step (2) was placed in an agate mortar and ground for 15 minutes, loaded into a corundum crucible, and then placed in a tubular furnace. In an argon atmosphere, the temperature was increased at a rate of 8°C / min and kept at 800°C for 6 hours to prepare the corresponding porous carbon-based composite material.

[0091] After analysis, the TEM image of the prepared porous carbon-based composite material is shown in Figure 8. It was found that a large number of metal particles were embedded in the porous carbon matrix, not a single bimetallic single atom. It can be seen that during the preparation process, the etching and washing with hydrochloric acid solution and sodium hydroxide solution were not carried out. The prepared powder is not a bimetallic atom-loaded porous carbon material, but a porous carbon-based material loaded with metal particles.

[0092] Comparative Example 2

[0093] A method for preparing a bimetallic atom-loaded porous carbon framework material for lithium-sulfur batteries:

[0094] (1) 0.1 g of the cobalt-based metal-organic framework of ZIF-67 was dispersed as a precursor in 200 mL of a 0.1 g / L aqueous solution of tris(hydroxymethylaminomethane). After adding dopamine hydrochloride in an amount equal to the mass of the metal-organic framework precursor, the mixture was stirred at 800 rpm / min at room temperature for 6 h. The mixture was then centrifuged and washed three times with methanol at 8800 rpm / min and dried in a vacuum oven at 60 °C for 15 h to obtain a polymer-coated metal-organic framework material (PM@ZIF-67).

[0095] (2) Weigh 0.1 g of PM@ZIF-67 and redisperse it in 39 mL of n-hexane. Pipette 75 μL of the pre-prepared 200 g / L ZnCl2 aqueous solution and add it dropwise to the n-hexane dispersion of PM@ZIF-67. Ultrasonicate in an ice-water bath for 4 h while controlling the ice-water bath temperature to <3 °C. Stir magnetically at room temperature for 3.5 h. Filter the clarified solution to obtain a precipitate, which was then dried in a vacuum oven at 55 °C for 10 h.

[0096] (3) The powder obtained in step (2) was ground in an agate mortar for 15 minutes, placed in a corundum crucible, and then placed in a tube furnace. In an argon atmosphere, the temperature was increased at a rate of 8°C / min, and kept at 950°C for 4.5 hours. After cooling to room temperature, the heat-treated product was first dispersed in 25mL of a 0.5mol / L hydrochloric acid solution and soaked for 4.5 hours. Then, the oil bath was heated to 80°C, and the product was placed in 25mL of a 1mol / L sodium hydroxide solution and soaked for 1.5 hours. After thorough centrifugal washing, the product was dried to prepare a porous carbon-based composite material.

[0097] Analysis shows an SEM image of the prepared porous carbon-based composite material, as shown in Figure 9. The metal-organic framework has collapsed overall, indicating that during the preparation process, the concentration of the aqueous solution of tris(hydroxymethyl)aminomethane was below the range of 0.2-10 g / L and the stirring speed was above 350 rpm / min, indicating that the prepared powder was not a bimetallic atom-loaded porous carbon framework material.

[0098] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A method for preparing a bimetallic atom-loaded porous carbon-based framework material, characterized in that: The following steps are involved: (1) dispersing a metal organic framework material as a precursor raw material in an aqueous solution of tris(hydroxymethyl)aminomethane, adding dopamine hydrochloride, stirring at a speed of ≤350 rpm / min for 1 to 8 hours, centrifugally washing, and drying to obtain a polymer-coated metal-based organic framework material, which is denoted as PM@MOF; (2) dispersing PM@MOF in n-hexane, then adding a metal chloride aqueous solution dropwise into the n-hexane dispersion of PM@MOF, ultrasonicating in an ice-water bath for 1 to 6 hours, stirring at room temperature for 2 to 10 hours, filtering and drying to obtain a bimetallic element-doped polymer-coated metal-based organic framework material; (3) The bimetallic element-doped polymer-coated metal-based organic framework material is heat treated at 500-1000°C for 1-10 h in an argon atmosphere and cooled to room temperature. The heat-treated product is first immersed in a hydrochloric acid solution and then immersed in a sodium hydroxide solution at 50-80°C. The product is centrifugally washed and dried to obtain a porous carbon-based material with uniform bimetallic atoms loading.

2. The preparation method according to claim 1, characterized in that: In step (1), the precursor raw material is a metal organic framework material of any one of ZIF-67, ZIF-8, ZIF-7, MIL-101 and MIL-88A, and the metal contained in the metal organic framework material is any one of cobalt, zinc, copper and iron.

3. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the aqueous solution of tris(hydroxymethyl)aminomethane is 0.2-10 g / L; the mass ratio of the metal organic framework material to tris(hydroxymethyl)aminomethane is in the range of 1:1-1:12, and the mass ratio of the metal organic framework material to dopamine hydrochloride is in the range of 5:1-1:

5.

4. The preparation method according to claim 1, characterized in that: In step (2), the metal chloride is any one or two of MgCl2, CoCl2, NiCl2, CuCl2, ZnCl2, FeCl3, WCl4 and MoCl5; and the concentration of the metal chloride aqueous solution is 5 to 500 g / L.

5. The preparation method according to claim 1, characterized in that: In step (2), the temperature during the ice water bath is required to be less than T, which is 3-6°C.

6. The preparation method according to claim 1, characterized in that: In step (3), the concentration of the hydrochloric acid solution is 0.1 to 5 mol / L, and the immersion time is 1 to 10 h; the concentration of the sodium hydroxide solution is 0.1 to 5 mol / L, and the immersion time is 0.5 to 5 h.

7. The preparation method according to claim 1, characterized in that: In step (3), the heating rate during the heat treatment process is 1 to 20°C / min.

8. A bimetallic atom-loaded porous carbon-based framework material, characterized in that: The material is prepared by the preparation method according to any one of claims 1 to 7 and is denoted as MD@PC.

9. The bimetallic atom-loaded porous carbon-based framework material according to claim 8, characterized in that: MD is any two metal elements among Mg, Co, Ni, Cu, Zn, Fe, W and Mo, and the percentage of the total molar number of the MD metal elements to the total molar number of all elements in MD@PC is 0.05% to 15%.

10. Use of the bimetallic atom-loaded porous carbon-based framework material according to claim 8 in the preparation of lithium-sulfur batteries.

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