A copper-based MOF with an out-of-plane coordination structure, and a preparation method and application thereof

Abstract

The application discloses a copper-based MOF with an out-of-plane coordination structure and a preparation method and application thereof, and belongs to the technical field of nanomaterials and electrochemical energy storage. The copper-based MOF (P-Cu-DBC) takes 8OH-DBC as a ligand, copper ions as nodes, and pyrrole molecules are coordinated in the axial direction of the copper ions. The preparation method is to first synthesize a Cu-DBC precursor through a solvothermal method, and then make pyrrole molecules axially coordinate at the copper sites. The application introduces pyrrole molecules out of the plane of copper ions, breaks the symmetrical electron distribution of traditional M-N4 sites, forms a polarized active center, and significantly enhances the adsorption and catalytic conversion capacity of polysulfides. Meanwhile, the material is in the form of nanorods and has stable structure. When used as a lithium-sulfur battery positive electrode catalyst, the shuttle effect can be effectively inhibited, the redox kinetics can be accelerated, the specific capacity, rate performance and cycle life of the battery can be greatly improved, and the preparation process is simple, so the application has great application prospect.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and electrochemical energy storage technology, and more specifically to a copper-based MOF with an out-of-plane coordination structure, its preparation method, and its applications. Background Technology

[0002] Lithium-sulfur batteries are based on a reversible sulfur redox chemical process (2Li + S). Li₂S, with a theoretical energy density as high as 2600 Wh / kg, is considered a promising next-generation energy storage technology. However, this technology still faces many severe challenges in practical applications, mainly including: the inherent electronic insulation properties of elemental sulfur and its discharge end products, the slow redox kinetics during electrochemical reactions, and the "shuttle effect" caused by soluble lithium polysulfides shuttling between the positive and negative electrodes. These problems directly lead to rapid capacity decay, reduced coulombic efficiency, and shortened cycle life, thus hindering the commercialization of lithium-sulfur batteries.

[0003] To address these issues, recent research strategies have primarily focused on developing structurally optimized host materials, such as transition metal oxides, nitrides, phosphides, and alloys, to anchor lithium polysulfides and accelerate their conversion kinetics through physical confinement or chemisorption. However, these inorganic metal compounds generally suffer from two major drawbacks: first, their poor conductivity hinders rapid electron transport, thus limiting the rate of electrochemical reactions; second, their limited specific surface area and predominantly surface-based active adsorption sites result in low bulk atomic utilization, leading to insufficient capture and catalytic conversion efficiency of lithium polysulfides. These problems ultimately result in low sulfur utilization and poor cycle stability in lithium-sulfur batteries. Therefore, designing and preparing a novel host catalyst that combines highly exposed active adsorption sites with highly efficient catalytic conversion capabilities for lithium polysulfides is a significant challenge currently facing this field.

[0004] Metal-organic frameworks (MOFs), as novel multifunctional crystalline materials formed by the self-assembly of organic ligands and metal nodes through coordination bonds, have proven to be promising host catalysts for lithium-sulfur batteries due to their ultra-high specific surface area, tunable pore structure, and highly dispersed metal sites. However, most reported MOF catalytic centers follow an in-planar coordinated M-N4 configuration. The symmetrical electron distribution of these centers results in a high adsorption barrier for lithium polysulfides and hinders effective electron transfer with reaction intermediates during catalytic conversion, thus limiting further improvements in their catalytic activity. Therefore, breaking the electronic symmetry of the M-N4 sites and constructing novel MOF catalysts with unique electronic structures and coordination environments is crucial for improving the cycle stability of lithium-sulfur batteries. Summary of the Invention

[0005] In view of this, the present invention provides a copper-based MOF with an out-of-plane coordination structure, its preparation method and application. The method first synthesizes a Cu-DBC precursor with in-plane coordination by a solvothermal method, and then introduces pyrrole molecules into the axial coordination vacancies of copper ions under mild conditions to successfully prepare P-Cu-DBC.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a copper-based MOF with an out-of-planar coordination structure includes the following steps: (1) Copper salt and 8OH-DBC ligand were dissolved in a mixed solvent of deionized water and N,N-dimethylformamide. After ultrasonic dispersion, a solvothermal reaction was carried out in a closed container. After the reaction was completed, the precursor Cu-DBC was obtained by solid-liquid separation, washing and drying. (2) Disperse the Cu-DBC obtained in step (1) in an organic solvent, sonicate to form a uniform suspension, then add pyrrole, stir to allow pyrrole molecules to adsorb and coordinate at the copper sites of Cu-DBC, after the reaction is completed, separate solid and liquid, wash and dry to obtain the copper-based MOF with out-of-plane coordination structure.

[0007] Preferably, the copper salt in step (1) is Cu(OAc)2·H2O; the mass ratio of Cu(OAc)2·H2O to 8OH-DBC ligand is 18:25.8.

[0008] Preferably, the volume ratio of deionized water to N,N-dimethylformamide in the mixed solvent in step (1) is 4:1.

[0009] Preferably, the temperature of the solvothermal reaction in step (1) is 85 °C and the time is 72 h.

[0010] Preferably, the organic solvent in step (2) is acetone; the ratio of Cu-DBC to pyrrole is 40 mg: 20 μL.

[0011] Preferably, the stirring process in step (2) takes 16 hours.

[0012] The present invention also provides a copper-based MOF with an out-of-plane coordination structure prepared by the method described above.

[0013] This invention also provides an application of a copper-based MOF with an out-of-plane coordination structure prepared by the method described above, namely, its application as a cathode catalyst in lithium-sulfur batteries.

[0014] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a copper-based MOF with an out-of-planar coordination structure, its preparation method and application, which has the following beneficial effects: This invention successfully synthesized a copper-based MOF (P-Cu-DBC) with an out-of-planar coordination structure using a solvothermal method. SEM images of P-Cu-DBC show its rod-like morphology, with an average diameter of approximately 50 nanometers and a length between 2 and 3 micrometers. P-Cu-DBC possesses advantages such as structural stability, strong adsorption capacity, and high catalytic activity, solving problems such as slow cathode reaction kinetics and rapid capacity decay, low rate performance, and poor cycle life caused by the lithium polysulfide shuttle effect. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0016] Figure 1 A scanning electron microscope image of the P-Cu-DBC prepared in Example 1; Figure 2 The image shows the performance of P-Cu-DBC prepared in Example 1. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1 A method for preparing a copper-based MOF (P-Cu-DBC) with an out-of-planar coordination structure, comprising the following steps: (1) Dissolve 18 mg Cu(OAc)2·H2O and 25.8 mg 8OH-DBC ligand in a mixed solvent of 6 mL deionized water and 1.5 mL N,N-dimethylformamide (DMF), place the solution in a 20 mL container, and sonicate for 30 minutes to ensure complete dissolution and homogeneity. Then seal the container and place it in an oven at 85 °C for 72 hours. After the reaction, perform solid-liquid separation by centrifugation. Wash the obtained solid product thoroughly with deionized water and acetone several times, and finally vacuum dry overnight at room temperature to obtain the precursor Cu-DBC.

[0019] (2) Take 40 mg of Cu-DBC synthesized in step (1) and disperse it in 20 mL of acetone. Sonicate the solution for 20 minutes to form a uniform suspension. Then, add 20 μL of pyrrole to the suspension and sonicate it again for 10 minutes. Stir the solution magnetically for 16 hours at room temperature to ensure that the pyrrole molecules in the solution can be fully adsorbed and aligned with the copper sites of the Cu-DBC framework. After the reaction is complete, collect the solid product by centrifugation, wash it three times with acetone, and then dry it under vacuum at room temperature to obtain a copper-based MOF with an out-of-plane coordination structure, denoted as P-Cu-DBC.

[0020] The scanning electron microscope (SEM) image of the P-Cu-DBC prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 The results show that it exhibits a regular rod-like shape with an average diameter of about 50 nanometers and a length between 2 and 3 micrometers, indicating that a high aspect ratio nanoscale MOF material has been successfully synthesized.

[0021] P-Cu-DBC and sulfur powder were compounded at a ratio of 3:1 (by mass). Then, a sulfur-containing composite material (active material), Super P, and polyvinylidene fluoride (PVDF) at a mass ratio of 7:2:1 were uniformly ground for 20 min. N-methylpyrrolidone (NMP) was then added in appropriate amounts while rapidly stirring until a uniform slurry was formed. The slurry was uniformly coated onto 12 mm diameter circular carbon paper and quickly dried in a vacuum oven at 60 ℃ for 12 h. Electrode sheets with different sulfur loadings were prepared by controlling the viscosity of the slurry or the coating thickness.

[0022] Full cell: Assemble in the following order: negative electrode shell, lithium sheet, separator, positive electrode sheet, gasket, spring sheet and positive electrode shell (battery shell model: CR2032), and add 15 μL of electrolyte (1.0 M LITFSI in DME:DOL=1:1 Vol% with 2.0% LiNO3) to both sides of the separator. Finally, seal the battery with a button cell packaging machine.

[0023] Galvanostatic charge-discharge (GCD) testing involves charging and discharging the battery at different current densities, recording various electrochemical performance parameters, and using these parameters as a standard to evaluate the battery's cycle and rate performance. The LAND CT2001A battery testing system was used to perform GCD tests within a voltage window of 1.6–2.8 V. All GCD tests were conducted at 25 °C.

[0024] Figure 2It can be shown that using P-Cu-DBC as the positive electrode catalyst for lithium-sulfur batteries can enable lithium-sulfur batteries to have excellent rate performance and cycle stability.

[0025] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a copper-based MOF with an out-of-planar coordination structure, characterized in that, Includes the following steps: (1) Copper salt and 8OH-DBC ligand were dissolved in a mixed solvent of deionized water and N,N-dimethylformamide. After ultrasonic dispersion, a solvothermal reaction was carried out in a closed container. After the reaction was completed, the precursor Cu-DBC was obtained by solid-liquid separation, washing and drying. (2) Disperse the Cu-DBC obtained in step (1) in an organic solvent, sonicate to form a uniform suspension, then add pyrrole, stir to allow pyrrole molecules to adsorb and coordinate at the copper sites of Cu-DBC, after the reaction is completed, separate solid and liquid, wash and dry to obtain the copper-based MOF with out-of-plane coordination structure.

2. The method for preparing a copper-based MOF with an out-of-planar coordination structure according to claim 1, characterized in that, The copper salt mentioned in step (1) is Cu(OAc)2·H2O; the mass ratio of Cu(OAc)2·H2O to 8OH-DBC ligand is 18:25.

8.

3. The method for preparing a copper-based MOF with an out-of-planar coordination structure according to claim 1, characterized in that, The volume ratio of deionized water to N,N-dimethylformamide in the mixed solvent in step (1) is 4:

1.

4. The method for preparing a copper-based MOF with an out-of-planar coordination structure according to claim 1, characterized in that, The temperature of the solvothermal reaction in step (1) is 85 °C and the time is 72 h.

5. The method for preparing a copper-based MOF with an out-of-plane coordination structure according to claim 1, characterized in that, The organic solvent mentioned in step (2) is acetone; the ratio of Cu-DBC to pyrrole is 40 mg: 20 μL.

6. The method for preparing a copper-based MOF with an out-of-planar coordination structure according to claim 1, characterized in that, The stirring process in step (2) takes 16 hours.

7. A copper-based MOF with an out-of-plane coordination structure prepared by the method according to any one of claims 1-6.

8. The application of a copper-based MOF with an out-of-planar coordination structure prepared by the method of any one of claims 1-6 in a cathode catalyst of a lithium-sulfur battery.

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