Nickel-based metal organic framework material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of metal organic framework materials and lithium air batteries, and particularly relates to a nickel-based metal organic framework material and a preparation method and application thereof. According to the invention, the nano sheet-shaped porous material is prepared through coordination of the fluoro terephthalic acid ligand and the nickel salt in combination with an ultrasonic-assisted synthesis technology, and the nano sheet-shaped porous material is low in nickel oxidation state and stable in C-F bond. When the material is used as a lithium air battery positive electrode catalyst, the specific discharge capacity (10081mAhg <-1 >) is remarkably improved, the cycle life (1350 times) is remarkably prolonged, and the material has high efficiency, low cost and industrial potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal organic framework materials and lithium-air batteries, and in particular relates to a nickel-based metal organic framework material and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Currently, 80% of global energy demand is met by fossil fuels. Excessive use of fossil fuels releases large amounts of CO2, contributing to global warming and the greenhouse effect. Developing clean, renewable energy sources such as solar, wind, and tidal energy is key to addressing the energy crisis and environmental pollution caused by the depletion of traditional fossil fuels. Developing new energy storage systems is an effective means of addressing the intermittent nature of green energy and achieving efficient storage and distribution.

[0004] With ultra-high theoretical energy density (~3505Wh kg -1 Lithium-air batteries (LIABs) have become potential candidates for sustainable energy storage and energy conversion technologies, showing great value and promise for large-scale applications. However, limited by the efficiency of the oxygen reduction and oxygen evolution reactions at the cathode, LABs still suffer from poor cycling performance, high overvoltage, and poor rate capability, which are the major bottlenecks hindering their practical application. Therefore, developing a suitable cathode material to reduce charge and discharge overvoltage, improve charge and discharge efficiency, and improve reversibility has far-reaching significance for the development and large-scale application of LABs.

[0005] Existing noble metal catalysts (such as Pt, Ir, RuO2, etc.) have outstanding performance in single ORR or OER catalysis, but their bifunctional oxygen electrocatalytic performance is unsatisfactory, and they are scarce and expensive. Metal-organic framework (MOF) materials have become potential candidate materials to replace noble metals due to their high specific surface area, adjustable pore structure and abundant active sites. However, traditional MOF materials have defects such as high oxidation state, insufficient exposure of active sites and poor stability, which limit their catalytic performance. Therefore, the development of an efficient and stable nickel-based MOF material and its preparation method is of great significance to promoting the development of lithium-air batteries. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention provides a nickel-based metal-organic framework material and its preparation method and application. The present invention is based on transition metal nickel salt and fluoroterephthalic acid ligand, and obtains a high-performance fluoronickel-based metal-organic framework catalyst material through ultrasonic-assisted exfoliation. The composite material has a porous nanosheet structure, a low nickel oxidation state and fluorinated functional groups, which provides a large number of effective active sites for ORR and OER, thereby improving the specific capacity and cycle stability of lithium-air batteries.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention provides a nickel-based metal-organic framework (MOF) material comprising a transition metal nickel salt and a coordinated fluoroterephthalic acid. The MOF material, formed by the coordination, comprises a porous nanosheet structure with nanosheets ranging in size from 100 to 2000 nm. The porous nanosheet structure forms three-dimensional through-hole channels, facilitating the diffusion of electrolytes and oxygen within the material. The small size of the nanosheets provides more surface active sites and shortens the transport pathways for ions and gases.

[0009] Preferably, the molar ratio of the transition metal nickel salt to fluoroterephthalic acid is 10:1 to 1:10; further preferably, the molar ratio of the transition metal nickel salt to fluoroterephthalic acid is 1:1 to 1:2. The nickel and ligands are fully coordinated to form a regular porous nanosheet structure, ensuring a high specific surface area and through-pore channels. An excessive amount of nickel salt can result in residual uncoordinated metal ions, forming impurity phases (such as NiO or unreacted salts), which block the pores and reduce the specific surface area. An excessive amount of ligands can cause excess organic ligands to occupy active sites, resulting in a loose structure and reduced stability.

[0010] Preferably, the nickel-based metal organic framework material is lower than ordinary Ni 2+ The reduction of nickel oxidation state is beneficial to maintaining high catalytic activity and optimizing the adsorption energy of nickel sites for oxygen-containing species (O2, LiO2).

[0011] The second aspect of the present invention provides a method for preparing the above-mentioned nickel-based metal-organic framework material, specifically: mixing a transition metal nickel salt and fluoroterephthalic acid in a mixed solvent, adding triethylamine to the obtained mixture for ultrasonic reaction, and post-treating the reaction solution to obtain the nickel-based metal-organic framework material.

[0012] Preferably, the transition metal nickel salt is selected from one or more of nickel chloride, nickel sulfate, nickel nitrate and nickel acetate; the fluoroterephthalic acid is 2,5-difluoroterephthalic acid or 2,3,5,6-tetrafluoroterephthalic acid. The high fluorine density forms a "protective layer" to resist the intermediate products of charge and discharge (such as O2 -, LiO2) erosion, reducing structural collapse, and the rigid skeleton inhibits volume expansion during circulation, maintaining pore connectivity and mechanical stability.

[0013] Preferably, the mixed solvent comprises a mixture of a first organic solvent, a second organic solvent and deionized water, and the volume ratio of the first organic solvent, the second organic solvent and the deionized water is 16 to 64:1:1.

[0014] Further preferably, the first organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and formamide; and the second organic solvent is selected from at least one of ethanol, methanol, and propanol. The high proportion of the first organic solvent is used to provide strong dissolving power, ensuring that the nickel salt and fluorinated ligand are fully dissolved, forming a homogeneous reaction system, and facilitating the regulation of the MOF nucleation rate; the second organic solvent is used to adjust the polarity, promote directional coordination between the ligand and the metal ion, and avoid disordered aggregation; deionized water is used to participate in the formation of coordination bonds and stabilize the crystal structure. Excessive use will destroy the organic solvent system, leading to hydrolysis side reactions, triggering ligand hydrolysis or nickel salt hydrolysis, generating impurities, blocking the pores, and accelerating capacity decay.

[0015] Preferably, the mass volume ratio of the transition metal nickel salt to the first organic solvent in the mixed solvent is (1.29-12.9):1; the mass volume ratio of the fluoroterephthalic acid to triethylamine is (47.6-2380):1.

[0016] By balancing the dissolution and nucleation rates, uniform porous nanosheets are formed, maximizing the specific surface area. Excessive dilution of the reactants (<1.29) results in sparse nucleation sites, leading to uneven growth, oversized nanosheets, and poor pore connectivity. High concentrations (>12.9) can cause local oversaturation and agglomeration, resulting in thick or blocky structures with insufficient exposure of active sites.

[0017] Triethylamine acts as a base to promote ligand deprotonation, ensuring that nickel and fluorinated ligands are fully coordinated to form regular porous nanosheets; when the ratio is too low (<47.6), triethylamine is insufficient, resulting in incomplete coordination reaction, increased defects in the MOF framework (such as residual uncoordinated metal), and reduced specific surface area, which in turn causes insufficient exposure of active sites and decreased catalytic efficiency; when the ratio is too high (>2380), excessive triethylamine destroys the coordination balance, which will cause some ligands to be competed with free base, making the structure loose and the pores collapsed. At the same time, the free base covers the active sites, hindering the diffusion of reactants.

[0018] Preferably, the ultrasonic reaction frequency is 100-1000W, and the duration is 1-24 hours. Insufficient power or too short a duration will result in incomplete exfoliation, forming thick flakes or blocky structures, hindering diffusion, and reducing capacity; excessive power or too long a duration will cause structural damage, reduced performance, and increased energy consumption.

[0019] The third aspect of the present invention provides a use of the nickel-based metal organic framework material described in the first aspect in a lithium-air battery.

[0020] Preferably, the nickel-based metal organic framework material is used as a positive electrode material in a lithium-air battery.

[0021] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0022] (1) The present invention solves the key problems of insufficient activity and poor stability of cathode catalysts for lithium-air batteries by organically combining fluorinated ligand design, ultrasonic synthesis process optimization, structural regulation and performance improvement. The prepared nanosheet porous material has a low nickel oxidation state and a stable CF bond. This material, as a cathode catalyst for lithium-air batteries, significantly improves the discharge specific capacity (10081mAhg -1 ) and cycle life (1350 times), with high efficiency, low cost and industrialization potential.

[0023] (2) The present invention introduces fluoroterephthalic acid as a ligand, which optimizes the electronic structure of the material by stabilizing the C-F bond and enhances the stability of the MOF to discharge products. The introduction of fluorine groups not only reduces the oxidation state of nickel (as shown by the X-ray absorption spectrum), but also forms a nanosheet-like porous structure (500-2000nm) through size control, which facilitates the diffusion of electrolyte and oxygen, improves reaction kinetics, and significantly increases the exposure of active sites.

[0024] (3) The present invention uses an ultrasonic environment (100-1000W) combined with argon protection to achieve uniform nucleation and rapid reaction (1-24 hours) of the material. Compared with the traditional solvent thermal method, this method simplifies the process flow, avoids high temperature and high pressure conditions, and at the same time increases the specific surface area of ​​the material through the controlled growth of the nanosheet structure. Among them, ultrasound is an important energy source for the exfoliation of two-dimensional nanosheets during the MOF generation process. Without this step, a thicker or even blocky MOF structure will be generated. Argon protection can prevent the thermal effect caused by ultrasound from causing oxidation of the transition metal.

[0025] (4) The present invention proposes the application of nickel-based metal-organic framework materials as positive electrode catalysts in lithium-air batteries. Thanks to the introduction of fluorine-based functional groups, the size of the obtained metal-organic framework materials is greatly reduced, fully exposing the active nickel sites; at the same time, the oxidation state of the nickel metal sites is improved, optimizing the adsorption of oxygen; the stability of the metal-organic framework is increased, and the service life of the catalyst is improved.

[0026] Related Mechanism: The present invention introduces fluorine-based functional groups. On the one hand, due to their large electronegativity (4.0), they can optimize the electronic structure of the central metal and the adsorption and desorption of oxygen-containing species during the discharge and charge processes. On the other hand, the presence of C-F bonds makes the MOF organic skeleton more resistant to attack by active species such as superoxide and lithium superoxide, which are intermediate products of charge and discharge, maintaining structural stability. However, substitution with other elements, such as borate, bromine, iodine, chlorine, and nitro groups, does not significantly affect the electronic structure of the central metal site due to their low electronegativity. On the other hand, these substituents and carbon can be attacked by the active components of superoxide and lithium superoxide, causing side reactions, deteriorating the battery reaction, and significantly shortening the battery life.

[0027] (5) The preparation process of the nickel-based organic metal framework of the present invention is short and the method is simple, which is conducive to directly forming a process production line for efficient production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0029] Figure 1 Scanning electron microscope photos of nickel-based metal-organic framework materials prepared in Example 1 of the present invention and Comparative Example 1;

[0030] Figure 2 The infrared spectra of the nickel-based metal-organic framework materials prepared in Example 1 of the present invention and Comparative Example 1 at different size magnifications are shown;

[0031] Figure 3 X-ray absorption spectra of nickel-based metal organic framework materials prepared in Example 1 and Comparative Example 1 of the present invention;

[0032] Figure 4 Graph showing the specific discharge capacity of lithium-air batteries of nickel-based metal-organic framework materials prepared in Example 1 of the present invention and Comparative Example 1;

[0033] Figure 5 This is a graph of the lithium-air battery cycle stability of the nickel-based metal organic framework materials prepared in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0035] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0036] Example 1 :This embodiment provides a nickel-based metal organic framework material and its preparation method

[0037] (1) Dissolve 0.75 mmol of nickel chloride and 0.75 mmol of 2,3,5,6-tetrafluoroterephthalic acid in a mixture of 32 mL of N,N-dimethylformamide, 2 mL of water, and 2 mL of ethanol, and stir to dissolve.

[0038] (2) The mixture was placed in a 600W ultrasonic environment and 0.8 mL of triethylamine was slowly added dropwise. High-purity argon was then introduced into the mixed solution to remove oxygen. The ultrasonic reaction was maintained at room temperature for 8 hours. The solid was separated by filtration and washed several times with deionized water and ethanol to remove the adsorbed N,N-dimethylformamide.

[0039] (3) The obtained solid was added with a small amount of deionized water, ultrasonicated to form a uniform dispersion, quenched with liquid nitrogen, and then freeze-dried to obtain Ni-F-MOF-1.

[0040] Example 2 :This embodiment provides a nickel-based metal organic framework material and its preparation method

[0041] (1) Dissolve 0.75 mmol of nickel chloride and 0.75 mmol of 2,3,5,6-tetrafluoroterephthalic acid in a mixture of 32 mL of N,N-dimethylformamide, 2 mL of water, and 2 mL of ethanol, and stir to dissolve.

[0042] (2) The mixture was placed in a 600W ultrasonic environment and 2 mL of triethylamine was slowly added dropwise. High-purity argon was then introduced into the mixed solution to remove oxygen. The ultrasonic reaction was maintained at room temperature for 4 hours. The solid was separated by filtration and washed several times with deionized water and ethanol to remove the adsorbed N,N-dimethylformamide.

[0043] (3) The obtained solid was added with a small amount of deionized water, ultrasonicated to form a uniform dispersion, quenched with liquid nitrogen, and then freeze-dried to obtain Ni-F-MOF-2.

[0044] Example 3 :This embodiment provides a nickel-based metal organic framework material and its preparation method

[0045] (1) Dissolve 0.75 mmol of nickel nitrate and 0.75 mmol of 2,3,5,6-tetrafluoroterephthalic acid in a mixture of 64 mL of N,N-dimethylacetamide, 2 mL of water, and 2 mL of ethanol, and stir to dissolve.

[0046] (2) The mixture was placed in a 600W ultrasonic environment and 0.8 mL of triethylamine was slowly added dropwise. Then, high-purity argon gas was introduced into the mixed solution to remove oxygen. The ultrasonic reaction was maintained at room temperature for 8 hours.

[0047] The solid was separated by filtration and washed with deionized water and ethanol several times to remove the adsorbed N,N-dimethylformamide;

[0048] (3) The obtained solid was added with a small amount of deionized water, ultrasonicated to form a uniform dispersion, quenched with liquid nitrogen and freeze-dried to obtain Ni-F-MOF-3.

[0049] Example 4 :This embodiment provides a nickel-based metal organic framework material and its preparation method

[0050] (1) Dissolve 0.75 mmol of nickel sulfate and 1.50 mmol of 2,3,5,6-tetrafluoroterephthalic acid in a mixture of 32 mL of N,N-dimethylformamide, 2 mL of water, and 2 mL of methanol, and stir to dissolve.

[0051] (2) The mixture was placed in a 200W ultrasonic environment and 0.8 mL of triethylamine was slowly added dropwise. High-purity argon was then introduced into the mixed solution to remove oxygen. The ultrasonic reaction was maintained at room temperature for 8 hours. The solid was separated by filtration and washed several times with deionized water and ethanol to remove the adsorbed N,N-dimethylformamide.

[0052] (3) The obtained solid was added with a small amount of deionized water, ultrasonicated to form a uniform dispersion, quenched with liquid nitrogen and freeze-dried to obtain Ni-F-MOF-4.

[0053] Example 5 :This embodiment provides a nickel-based metal organic framework material and its preparation method

[0054] (1) Dissolve 0.75 mmol of nickel chloride and 0.75 mmol of 2,5-difluoroterephthalic acid in a mixture of 32 mL of N,N-dimethylformamide, 2 mL of water, and 2 mL of methanol, and stir to dissolve.

[0055] (2) The mixture was placed in a 200W ultrasonic environment and 0.8 mL of triethylamine was slowly added dropwise. High-purity argon was then introduced into the mixed solution to remove oxygen. The ultrasonic reaction was maintained at room temperature for 8 hours. The solid was separated by filtration and washed several times with deionized water and ethanol to remove the adsorbed N,N-dimethylformamide.

[0056] (3) The obtained solid was added with a small amount of deionized water, ultrasonicated to form a uniform dispersion, quenched with liquid nitrogen, and then freeze-dried to obtain Ni-F-MOF-5.

[0057] Example 6 :This embodiment provides a nickel-based metal organic framework material and its preparation method

[0058] (1) Dissolve 0.75 mmol of nickel chloride and 0.75 mmol of 2,5-difluoroterephthalic acid in a mixture of 32 mL of N,N-dimethylformamide, 2 mL of water, and 2 mL of methanol, and stir to dissolve.

[0059] (2) The mixture was placed in a 600W ultrasonic environment and 0.8 mL of triethylamine was slowly added dropwise. Then, high-purity argon gas was introduced into the mixed solution to remove oxygen. The ultrasonic reaction was maintained at room temperature for 1 hour. The solid was separated by filtration and washed several times with deionized water and ethanol to remove the adsorbed N,N-dimethylformamide.

[0060] (3) The obtained solid was added with a small amount of deionized water, ultrasonicated to form a uniform dispersion, quenched with liquid nitrogen and freeze-dried to obtain Ni-F-MOF-6.

[0061] Comparative Example 1 :This comparative example provides a metal organic framework material Ni-H-MOF material and its preparation method

[0062] (1) Dissolve 0.75 mmol of nickel chloride and 0.75 mmol of terephthalic acid in a mixture of 32 mL of N,N-dimethylformamide, 2 mL of water, and 2 mL of ethanol, and stir to dissolve.

[0063] (2) The mixture was placed in a 600W ultrasonic environment and 0.8 mL of triethylamine was slowly added dropwise. Then, high-purity argon gas was introduced into the mixed solution to remove oxygen. The ultrasonic reaction was maintained at room temperature for 1 hour. The solid was separated by filtration and washed several times with deionized water and ethanol to remove the adsorbed N,N-dimethylformamide.

[0064] (3) The obtained solid was added with a small amount of deionized water, ultrasonicated to form a uniform dispersion, quenched with liquid nitrogen, and then freeze-dried to obtain Ni-H-MOF.

[0065] Experimental Example 1 :This example performs structural characterization tests on the nickel-based metal organic framework material prepared in Example 1 and the metal organic framework material prepared in Comparative Example 1

[0066] (1) Infrared spectroscopy characterization

[0067] like Figure 1 As shown, the wave numbers are about 1320, about 1380 and about 1690 cm -1 The absorption peaks at 1320 and 1690 cm-1 correspond to the specific absorption of O=CO. -1 The absorption peak at 1380 cm is attributed to the stretching vibration of CO, while the absorption peak at 1380 cm-1 The absorption peak at is the bending vibration of C=O.

[0068] 1500cm -1 and 1580cm -1 The absorption peak at is attributed to the symmetrical stretching of the C=C in the benzene ring skeleton. The presence of these specific functional groups indicates the presence of benzene rings, CO, and C=O in the synthesized solid catalyst, which is consistent with the functional groups contained in the ligand terephthalic acid. This further confirms that the ligand in the synthesized metal-organic framework is terephthalic acid.

[0069] 1350-1000cm -1 It is the stretching vibration of the CF bond, indicating that in addition to the terephthalic acid structure, there are also a large number of F functional groups in the structure. Combined with the raw materials used, it can be determined that the synthesized metal-organic framework material corresponds to the corresponding ligand group.

[0070] (2) Scanning electron microscopy characterization

[0071] like Figure 2 As shown, Figure 2 (a) and (b) are scanning electron micrographs of the tetrafluoro-substituted nickel-based metal-organic framework material prepared in Example 1 at different magnifications. The morphology is a nanosheet structure with sizes ranging from 100 nm to 2000 nm. The nanosheets also contain a large number of nanoscale pores, which facilitates material transport during the battery reaction process.

[0072] Figure 2 (c) and (d) are scanning electron microscope photos of the fluorine-free nickel-based metal organic framework material prepared in Comparative Example 1 at different magnifications. It is a typical nanosheet structure with a larger size than the tetrafluoroethylene structure, basically above 5 μm, but no obvious nanoscale pore structure was found.

[0073] (3) X-ray absorption spectroscopy characterization

[0074] The fine structure and valence information of Ni sites in two nickel-based metal-organic frameworks were further studied using X-ray absorption near-edge structure spectroscopy. Figure 3 As shown in (a), it can be found that the two materials prepared in Example 1 and Comparative Example 1 have similar X-ray absorption spectra, and the shapes of the near-edge peak and the post-edge oscillation region are basically the same, indicating that the two have similar coordination structures;

[0075] The energy at 0.325 of the maximum absorption of the NiK edge is used to evaluate the valence state, such as Figure 3 As shown in (b), compared with the fluorine-free nickel-based metal organic framework material prepared in comparative example 1, the NiK edge in the tetrafluoro-substituted nickel-based metal organic framework material prepared in example 1 moves toward the direction of low absorption energy, indicating that Ni 2+The oxidation state was slightly reduced. Application Example 1 :This test example is to test the electrochemical performance of the nickel-based metal organic framework materials prepared in Examples 1 to 6 and the metal organic framework material prepared in Comparative Example 1.

[0076] Experimental process:

[0077] Electrode 1: The fluorinated nickel-based metal organic framework material prepared in Examples 1 to 6 was respectively mixed with Ketjen black, carbon nanotubes and a binder with a mass fraction of 1% in a mass ratio of 9:8:1:222.2, and 2 mL of N-methylpyrrolidone was added to form a slurry. The slurry was applied to one side of carbon paper and dried in a vacuum oven at 110°C. It was then cut into circular pole pieces to obtain the positive electrode 1 of the lithium-air battery.

[0078] Electrode 2: The fluorine-free substituted nickel-based metal organic framework material prepared in Comparative Example 1, Ketjen black, carbon nanotubes and a binder with a mass fraction of 1% were mixed in a mass ratio of 9:8:1:222.2, and 2 mL of N-methylpyrrolidone solvent was added to form a slurry. The slurry was applied to one side of the carbon paper and dried in a vacuum oven at 110°C. It was then cut into circular pole pieces to obtain the positive electrode 2 of the lithium-air battery.

[0079] The binder with a mass fraction of 1% refers to a solution containing polyvinylidene fluoride as a solute and N-methylpyrrolidone as a solvent, wherein the mass fraction of the polyvinylidene fluoride is 1%.

[0080] The two electrodes were used as positive electrodes, lithium sheets were used as negative electrodes, and a 1 mol / L LiTFSI-TEGDME (lithium bis(trifluoromethylsulfonyl)imide-tetraethylene glycol dimethyl ether) solution was used as the electrolyte to assemble two lithium-air batteries. The battery assembled with electrode 1 as the positive electrode was labeled as a Ni-F-MOF battery, and the battery assembled with electrode 2 as the positive electrode was labeled as a Ni-H-MOF battery. The battery performance of the two batteries was tested. The test system was a high-purity oxygen atmosphere with a pressure of 1 atmosphere and a temperature of room temperature. The test system was a Xinwei multi-channel battery tester with a constant current charge and discharge voltage range of 2.0V to 4.8V.

[0081] like Figure 4 As shown, Ni-F-MOF-1 prepared in Example 1 and Ni-H-MOF prepared in Comparative Example 1 were used as positive electrode materials at a current density of 500 mAg -1 The constant current discharge curves below show that the capacities of Ni-H-MOF and Ni-F-MOF batteries are 6947 and 10081 mAh g, respectively. -1The discharge capacity of the Ni-F-MOF-1 cathode is one of the highest reported for Ni-based MOF cathode materials, and a stable, high discharge plateau (around 2.65V) is present. These results demonstrate that the fluorinated nickel-based metal-organic framework material prepared by this invention exhibits excellent material properties and a high specific discharge capacity.

[0082] like Figure 5 As shown, the Ni-F-MOF-1 prepared in Example 1 and the Ni-H-MOF battery prepared in Comparative Example 1 have a current density of 500 mAg -1 The cycling performance graph shows that the Ni-F-MOF battery can cycle approximately 1,350 times under the above conditions, while the Ni-H-MOF material can cycle approximately 350 times under the above conditions. This indicates that the Ni-F-MOF battery plays a good catalytic role (oxygen reduction and oxygen evolution reactions), and the material still maintains a high capacity after multiple cycles.

[0083] At a current density of 500 mAg -1 Under these conditions, the specific test data are shown in Table 1:

[0084] Table 1

[0085] sample <![CDATA[Positive electrode discharge capacity (mAh g -1 )]]> Number of cycles Example 1 10081 1350 Example 2 9000 1000 Example 3 9500 1200 Example 4 8500 800 Example 5 8350 550 Example 6 7500 460 Comparative Example 1 6497 350

[0086] The main reasons for the above performance differences may be as follows:

[0087] Compared with Example 1, the ultrasonic time in Example 2 is too short, the sample thickness is large, the number of active sites is limited, and the specific capacity and cycle life are both reduced; in Example 3, the sample concentration is low during the synthesis process, there are many defects in the synthetic structure, and the long-term structural stability is slightly reduced; in Example 4, the type of metal salt and the organic solvent are different, which affects the size structure of the product, and the capacity and cycle number are both reduced; in Example 5, the fluorine substituent content of the difluoroterephthalic acid ligand is small, the optimization ability of the active site is weak, and at the same time, partial F substitution is easy to produce side reactions in the reaction, resulting in a reduction in cycle life; in Example 6, the ultrasonic time is too short, the sample thickness is large, the number of active sites is limited, the diffusion of oxygen and electrolyte during the reaction is hindered, and the specific capacity and cycle life are greatly reduced; in Comparative Example 1, fluorine-free substituted terephthalic acid is used, and the electronic structure of the material cannot be optimized through the stability of the CF bond. The number of active sites is limited, the diffusion of oxygen and electrolyte during the reaction is hindered, and the specific capacity and cycle life are greatly reduced.

[0088] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A nickel-based metal-organic framework material, characterized in that: The nickel-based metal organic framework material comprises a transition metal nickel salt and fluoroterephthalic acid coordinated therewith. The nickel-based metal organic framework material formed by coordination is a porous nanosheet structure, and the size of the nanosheet is 100-2000nm.

2. The nickel-based metal organic framework material according to claim 1, characterized in that The molar ratio of the transition metal nickel salt to fluoroterephthalic acid is 10:1 to 1:10; preferably, the molar ratio of the transition metal nickel salt to fluoroterephthalic acid is 1:1 to 1:

2.

3. The nickel-based metal-organic framework material according to claim 1, characterized in that The nickel-based metal organic framework material is lower than the ordinary Ni 2+ oxidation state.

4. A method for preparing the nickel-based metal organic framework material according to any one of claims 1 to 3, characterized in that: Specifically, transition metal nickel salt and fluoroterephthalic acid are mixed in a mixed solvent, triethylamine is added to the obtained mixture for ultrasonic reaction, and the reaction solution is post-treated to obtain a nickel-based metal organic framework material.

5. The preparation method according to claim 4, wherein The transition metal nickel salt is selected from one or more of nickel chloride, nickel sulfate, nickel nitrate and nickel acetate; and the fluoroterephthalic acid is 2,5-difluoroterephthalic acid or 2,3,5,6-tetrafluoroterephthalic acid.

6. The preparation method according to claim 4, wherein The mixed solvent comprises a mixture of a first organic solvent, a second organic solvent and deionized water, wherein the volume ratio of the first organic solvent, the second organic solvent and the deionized water is 16 to 64:1:1; The first organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and formamide; the second organic solvent is selected from at least one of ethanol, methanol, and propanol.

7. The preparation method according to claim 4, wherein The mass volume ratio of the transition metal nickel salt to the first organic solvent in the mixed solvent is (1.29-12.9):1; the mass volume ratio of the fluoroterephthalic acid to triethylamine is (47.6-2380):

1.

8. The preparation method according to claim 4, wherein The frequency of the ultrasonic reaction is 100-1000W, and the time is 1-24 hours.

9. Use of the nickel-based metal organic framework material according to any one of claims 1 to 3 in a lithium-air battery.

10. The use according to claim 9, characterized in that The nickel-based metal organic framework material is used as a positive electrode material in a lithium-air battery.

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