CN115232326A - Metal organic framework material, preparation thereof and application thereof in electrode material - Google Patents

Abstract

A metal organic framework material, a preparation method thereof and an application thereof in an electrode material. The invention belongs to the field of lithium-sulfur battery cathode materials. The invention aims to solve the technical problems that the existing metal organic framework material applied to the lithium-sulfur battery is weak in charge transfer capacity, low in specific capacity and poor in cycling stability. The metal organic framework material is MOF-ET8 with a chemical formula of [ Zr ] ₂ (L) ₃ ]Wherein L is an organic ligand C ₂₂ H ₂₀ N ₂ O ₆ . The metal organic framework material is used for preparing an electrode material applied to a lithium-sulfur battery.

Description

A metal-organic framework material, its preparation and its application in electrode materials

technical field

The invention belongs to the field of positive electrode materials for lithium-sulfur batteries, in particular to a metal-organic framework material and its preparation and application in electrode materials.

Background technique

In recent years, traditional fuel vehicles are being "replaced" by new energy vehicles step by step. As the power source of new energy vehicles, the quality of battery performance is directly related to the mileage and endurance of the car, and it is also the key to determining whether new energy vehicles can replace traditional fuel vehicles in the future. However, the energy density of ternary lithium batteries, which are widely used in new energy vehicles, is close to the theoretical limit, and the battery life of the lithium iron phosphate battery system is relatively poor, so a new battery system is urgently needed. As an important part of the new generation of battery technology, lithium-sulfur batteries have higher energy density, stronger endurance and more abundant resources, and have received extensive attention from the scientific research community and the industry.

Lithium-sulfur batteries use sulfur as the positive electrode of the battery and metal lithium as the negative electrode of the battery, which is a kind of battery system that effectively realizes the mutual conversion of electrical energy and chemical energy. Lithium-sulfur batteries using sulfur as a positive electrode material are light in weight and can improve the overall energy density of the battery; in addition, the elemental sulfur reserves are abundant, which is environmentally friendly and can be mass-produced. Therefore, lithium-sulfur batteries are considered to be the most powerful batteries for new energy vehicles Competitive candidates. However, lithium-sulfur batteries still face some unsolved problems, such as low capacity utilization and shuttle effect. Therefore, focusing on solving the shuttle effect of polysulfides in lithium-sulfur batteries and improving the utilization rate of capacity are important topics in this research field.

Metal-organic frameworks (MOFs) are porous materials composed of metal ions and organic ligands connected in a highly orderly manner, and have broad application prospects in the fields of gas storage, biomedicine, and catalysis. Its tunable pore size, designable chemically active sites, and high porosity make it a great potential for confining the shuttle of polysulfides. However, the existing metal organic frameworks (MOFs) used in lithium-sulfur batteries still have technical problems such as weak charge transfer ability, low specific capacity and poor cycle stability, which need to be solved urgently.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the technical problems of weak charge transfer ability, low specific capacity and poor cycle stability of the existing metal-organic framework materials used in lithium-sulfur batteries, and provide a metal-organic framework material and the same. Preparation and its application in electrode materials.

One of the objectives of the present invention is to provide a metal organic framework material, the metal organic framework material is MOF-ET8, the chemical formula is [Zr ₂ (L) ₃ ], wherein L is an organic ligand C ₂₂ H ₂₀ N ₂ O ₆ .

。Further defined, the structure of the organic ligand is:

.

The second object of the present invention is to provide a preparation method of an organic ligand, and the preparation method is carried out according to the following steps:

S1: Add n-butyllithium, 1,5-dibromo-2,4-dimethoxybenzene and tetrahydrofuran to n-hexane in sequence at -78°C, heat to 0°C, and stir at 0°C for 12h , then cooled to -78°C, added trimethyl borate, heated to 25°C, stirred at 25°C for 18h, then added hydrochloric acid, stirred at 25°C for 0.5h, washed and dried to obtain Intermediate 1;

S2: Add intermediate 1, 2-amino-4-bromobenzoic acid methyl ester, cesium fluoride, palladium dichloride to the mixed solution of water/dioxane successively, and heat and stir to reflux for 24h under argon protection, Cool to 25°C, add dichloromethane, let stand for stratification, wash, dry, spin dry the organic phase, and finally perform silica gel column chromatography with dichloromethane/ethyl acetate as the eluent to obtain Intermediate 2;

S3: Mix intermediate 2, tetrahydrofuran, methanol and sodium hydroxide solution, heat under reflux and stir for 24h, cool to 25°C, spin dry the organic phase, then adjust the pH value to 5, wash the precipitate after centrifugation, and finally vacuum dry, to obtain organic ligands.

To further limit, the molar ratio of n-butyllithium, 1,5-dibromo-2,4-dimethoxybenzene, and trimethyl borate in S1 is (90-100):30:(30-32).

To be further limited, in S1, water, diethyl ether and chloroform are used for washing in sequence.

To further limit, the molar ratio of intermediate 1, 2-amino-4-bromobenzoic acid methyl ester, cesium fluoride and palladium dichloride in S2 is 2:(4-6):(11-12):(0.1 -0.2).

To further limit, the volume ratio of water and dioxane in the mixed solution of water/dioxane in S2 is 1:1.

To be further limited, in S2, water and saturated sodium chloride solution are sequentially used for washing.

To further limit, the molar ratio of intermediate 2 in S3 to the volume of tetrahydrofuran, methanol, and sodium hydroxide solution is 1 mmol: (15-25) mL: (35-45) mL: (25-35) mL.

To be further limited, the concentration of the sodium hydroxide solution in S3 is 0.3-0.35 mol/L.

The third object of the present invention is to provide a preparation method of a metal organic framework material, and the preparation method is carried out according to the following steps:

Zirconium tetrachloride and organic ligands are dissolved in a mixed solution of N, N-dimethylformamide and hydrochloric acid, first ultrasonically treated, then heated for reaction, centrifuged, washed and dried after the reaction to obtain MOF-ET8, which is metal organic frame material.

Further defined, the molar ratio of zirconium tetrachloride and organic ligand is 0.27:(0.35-0.4).

To further define, the mass ratio of zirconium tetrachloride to the volume of the mixed solution is 63 mg: (7-9) mL.

Further limited, the concentration of hydrochloric acid is 1 mol/L.

Further limited, the heating reaction temperature is 70-90°C, and the time is 10-14h.

The fourth object of the present invention is to provide an application of the above metal organic framework material in electrode materials.

Further defined, the electrode material is CNT@MOF-ET8-S.

The fifth object of the present invention is to provide a preparation method of electrode material CNT@MOF-ET8-S, and the preparation method is carried out according to the following steps:

Step 1: Acid-treated carbon nanotubes (CNTs), then washed with water and freeze-dried;

Step 2: Add MOF-ET8, CNT, and hydrochloric acid solution into N,N-dimethylformamide, first sonicate, then heat for reaction, then centrifuge, wash, and vacuum dry to obtain CNT@MOF-ET8;

Step 3: The CNT@MOF-ET8 and sulfur were mixed, then transferred to an autoclave under argon protection, heated at 150-170 °C for 8-12 h, and then heated at 150-250 °C under nitrogen atmosphere for 1- 3h, the cathode material CNT@MOF-ET8-S was obtained.

To further define, the acid treatment process in step 1: CNTs are added to the mixed acid of sulfuric acid/nitric acid and soaked for 5-7 hours.

Further limited, the volume ratio of sulfuric acid and nitric acid is 7:3, the mass fraction of sulfuric acid is 98%, and the mass fraction of nitric acid is 68%.

To further define, the mass ratio of CNT to the volume of mixed acid is 200 mg: (8-12) mL.

To further define, the mass ratio of MOF-ET8 and CNT in step 2 is 2:3.

To further define, in step 2, the mass ratio of CNT to the volume of hydrochloric acid is 35 mg: (0.45-0.55) mL, and the concentration of hydrochloric acid is 1 mol/L.

To further define, the volume ratio of hydrochloric acid to N,N-dimethylformamide in step 2 is (0.45-0.55): 7.5.

Further limited, in step 2, the heating reaction temperature is 70-90°C, and the time is 10-14h, and the vacuum drying temperature is 110-130°C, and the time is 10-14h.

To further define, the mass ratio of CNT@MOF-ET8 and sulfur in step 3 is 1:(2-4).

The sixth objective of the present invention is to provide an application of an electrode material CNT@MOF-ET8-S in a lithium-sulfur battery.

Compared with the prior art, the present invention has the advantages:

The invention provides a novel metal-organic framework material, which is applied to the preparation of a copolymerized sulfur positive electrode. The positive electrode material can promote the conversion of polysulfides, inhibit the shuttle effect of lithium-sulfur batteries, and promote the uniformity of Li ₂ S in the positive electrode. Deposition and conversion, thereby greatly improving the specific capacity and cycle stability of lithium-sulfur batteries, and has outstanding market potential in the field of new energy vehicle batteries. The specific advantages are as follows:

1) From the single crystal X-ray diffraction test results, it can be seen that the MOF-ET8 of the present invention is a hexagonal crystal system, and the space group is P42 (68). It is an infinite chain-like structure that is connected to each other, which is conducive to the efficient transport of electrons and improves the conductivity of the electrode material.

2) The lithium-sulfur battery based on the positive electrode material CNT@MOF-ET8-S of the porous metal-organic framework material MOF-ET8 of the present invention has a charge transfer impedance of 27.6 Ω and excellent charge transfer capability. In addition, the cycle performance test shows that the initial discharge specific capacity is 1425.8 mA·hg ⁻¹ , and after cycling, the specific capacity of the lithium-sulfur battery can still be maintained at 1325.7 mA·hg ⁻¹ , and the Coulomb efficiency is 99.8%. Good cycling stability and high specific capacity.

Description of drawings

Fig. 1 is the synthetic route diagram of organic ligand in the metal organic framework material of embodiment 1;

2 is a schematic diagram of the structural composition of a lithium-sulfur battery in Application Example 1;

3 is an AC impedance test diagram of the lithium-sulfur battery of Application Example 1 before the undischarged cycle;

FIG. 4 is an AC impedance test diagram of the lithium-sulfur battery of Application Example 1 after charging and discharging cycles;

5 is a cycle performance test chart of the lithium-sulfur battery of Application Example 1.

Detailed ways

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, but not to limit the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified. The used materials, reagents, methods and instruments, unless otherwise specified, are conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels.

The terms "comprising," "including," "having," "containing," or any other variation thereof, as used in the following examples, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or device comprising the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article or device elements.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or a range bounded by a series of upper preferred values and lower preferred values, this should be understood as specifically disclosing any upper range limit or preferred value and any lower range limit or all ranges formed by any pairing of preferred values, whether or not the ranges are individually disclosed. For example, when a range of "1 to 5" is disclosed, the described range should be construed to include the ranges "1 to 4," "1 to 3," "1 to 2," "1 to 2, and 4 to 5." , "1 to 3 and 5", etc. When numerical ranges are described herein, unless stated otherwise, the ranges are intended to include the endpoints and all integers and fractions within the range. In the present specification and claims, range definitions may be combined and/or interchanged, and unless otherwise stated, these ranges include all subranges subsumed therebetween.

Embodiment 1: As shown in FIG. 1 , the preparation method of a metal-organic framework material of this embodiment is carried out according to the following steps:

1,4-Dibromo-2,5-dimethoxybenzene (raw material 1, CAS: 2674-34-2) and methyl 2-amino-4-bromobenzoate (raw material 2, CAS: 2674-34-2) described in the following steps : 135484-83-2) were purchased directly from Sigma-Aldrich.

Synthesis of Intermediate 1:

To 50 mL of n-hexane were added n-butyllithium (60 mL, 96 mmol) followed by 1,5-dibromo-2,4-dimethoxybenzene (8.88 g, 30 mmol) at -78°C ), 10 mL of tetrahydrofuran, the mixed solution was heated to 0 °C, stirred at 0 °C for 12 hours, cooled to -78 °C, then trimethyl borate (3.5 mL, 31 mmol) was added, and heated to 25 ℃, and stirred at 25 ℃ for 18 hours, then added 10 ml of hydrochloric acid solution with a concentration of 2 mol/L, stirred at 25 ℃ for 0.5 hours, and finally washed the precipitate with water, ether and chloroform successively, and dried to obtain a solid 0.59 g, which is intermediate 1, and the yield is 85%.

Identification results of NMR characterization of intermediate 1:

Hydrogen Spectrum: ¹ H NMR (400 MHz, DMSO): δ 3.86 (6 H, s), 6.54 (1 H, s), 7.41 (4 H, s), 7.90 (1 H, s).

Carbon spectrum: ¹³ C NMR (100 MHz, DMSO): δ 55.3, 93.8, 111.9, 144.4, 167.7.

Mass spectrometry characterization results: ESI (m/z): [M+H] ⁺ Calcd. for C ₈ H ₁₂ B ₂ O ₆ , 225.8; Found, 226.6.

Elemental analysis test results: Calcd. for C ₈ H ₁₂ B ₂ O ₆ , C, 42.55, H, 5.36, O, 42.51; Found, C, 43.28, H, 6.02, O, 43.29.

Synthesis of Intermediate 2:

Add 80 ml of water/dioxane mixed solution (water/dioxane v:v=1:1) into a 500 ml three-necked flask, then add intermediate 1 (0.45 g, 2 mmol), 2 -amino-4-bromobenzoic acid methyl ester (1.15 g, 5 mmol), cesium fluoride (1.8 g, 11.8 mmol) and palladium dichloride (0.1 g, 0.14 mmol), and the mixture was heated under argon The reaction system was cooled to 25° C. under protection, stirred and refluxed for 24 hours, 200 ml of dichloromethane was added, and the layers were left to stand, then washed with 500 ml of water and 200 ml of saturated sodium chloride solution in turn, and then dried with sodium sulfate. The organic phase was spin-dried, and finally, silica gel column chromatography was performed with dichloromethane/ethyl acetate as the eluent to obtain 0.69 g of a yellow solid with a yield of 80%.

NMR characterization and identification results of intermediate 2:

Hydrogen Spectrum: ¹ H NMR (400 MHz, DMSO): δ 7.99 (d, 2 H), 7.52 (d, 2 H), 7.36 (s, 4 H), 7.24 (d, 2 H), 7.05 (d, 2 H) 2H), 3.983 (s, 6H), 3.854 (s, 6H).

Carbon Spectrum: ¹³ C NMR (100 MHz, DMSO): δ 166.79, 151.14, 148.97, 139.97, 133.32, 130.90, 116.79, 112.90, 112.38, 110.13, 55.99, 51.52.

Mass spectrometry characterization results: ESI (m/z): [M+H] ⁺ Calcd. for C ₂₄ H ₂₄ N ₂ O ₆ , 436.46; Found, 437.21.

Elemental analysis test results: Calcd. for C ₂₄ H ₂₄ N ₂ O ₆ , C, 66.05, H, 5.54, O, 21.99; Found, C, 66.75, H, 5.91, O, 20.89.

_{Synthesis of} organic ligand _{C22H20N2O6 :}

Add Intermediate 2 (0.33 g, 1 mmol), 20 ml of tetrahydrofuran, 40 ml of methanol, 30 ml of sodium hydroxide (0.41 g, 10 mmol) aqueous solution to the three-necked flask, and the reaction system was heated and refluxed for 24 hours after stirring. Cool to 25°C, spin dry the organic phase, and then add 1 mol/L hydrochloric acid solution to adjust the pH to 5 to obtain a pale yellow paste. Drying under vacuum gave 0.38 g of a yellow solid in 92% yield.

Identification results of NMR characterization of organic ligand C ₂₂ H ₂₀ N ₂ O ₆ :

Hydrogen Spectrum: ¹ H NMR (400 MHz, DMSO): δ 8.16 (d, 2 H), 7.52 (d, 2 H), 7.31 (d, 2 H), 7.15 (d, 2 H), 7.03 (s, 4H), 3.86 (s, 6H).

Carbon spectrum: ¹³ C NMR (100 MHz, DMSO): δ 168.77, 151.14, 149.64, 139.83,

132.57, 130.90, 116.08, 113.69, 112.36, 110.13, 55.99.

Mass spectrometry characterization results: ESI (m/z): [M+H] ⁺ Calcd. for C ₂₂ H ₂₀ N ₂ O ₆ , 408.41; Found, 409.21.

Elemental analysis test results: Calcd. for C ₂₂ H ₂₀ N ₂ O ₆ , C, 64.7, H, 4.94, O, 23.50; Found, C, 65.45, H, 5.42, O, 22.49.

Preparation of metal organic framework material MOF-ET8[Zr ₂ (C ₂₂ H ₂₀ N ₂ O ₆ ) ₃ ]:

Zirconium tetrachloride (63 mg, 0.27 mmol) and organic ligand C ₂₂ H ₂₀ N ₂ O ₆ (155 mg, 0.38 mmol) were dissolved in 500 μl of 1 mol/L hydrochloric acid solution and 7.5 ml of N , N-dimethylformamide, then sonicated for 5 minutes, then heated at 80°C for 12 hours, then centrifuged at 10,000 rpm for 20 minutes using a centrifuge, and washed the precipitate with methanol Three times, 10 ml each time, and finally vacuum-dried at 120 °C for 12 hours to obtain porous MOF-ET8.

Characterization of porous metal-organic framework material MOF-ET8:

The synthesized MOF-ET8 crystal was stored in a glass capillary, and the crystal structure was tested by single crystal X-ray. The instrument was a Bruker-Apex II CCD detector, and the Cu Kα (λ=1.54178Å ) X-ray source was used to collect the data. SADABS The program corrects for absorption, but does not correct for extinction or decay. It is solved directly by the SHELXTL software package. The test results are shown in Table 1.

Table 1 Crystal structure parameters of MOF-ET8

sample MOF-ET8 chemical formula C₆₆H₆₀N₆O₁₈Zr₂ molecular weight 1407.68 crystal system Hexagonal crystal system space group P 42 (68) a/Å 19.9686(6) b/Å 19.9686(6) c/Å 7.2437(3) α/° 90 β/° 90 γ/° 120 volume 2931.71(8) The number of molecules contained in a unit cell 6 unit cell density 0.509 absorption coefficient 1.948 The number of electrons in a unit cell 2578.0 crystal size 0.06 × 0.04 × 0.03 radiation CuKα (λ = 1.54178) Diffraction collection angle 11.59 to 99.58 Diffraction index range -34 ≤ h ≤ 35, -38 ≤ k ≤ 32, -16 ≤ l ≤ 15 Diffraction spot collection 52289 Independent Diffraction Spots 4275 [Rint = 0.0619, Rsigma = 0.0288] Data Restrictive Parameters 4275/175/168 GOF value based on F2 1.085 The residual factor R value of the observed diffraction point R₁= 0.0575, wR₂= 0.1123 Residual factor R value of all diffraction points R₁= 0.0584, wR₂ = 0.1350 Peaks and valleys of residual electron density 1.00/-0.93 CCDC 1989619

Example 2: Application of the metal-organic framework material MOF-ET8 prepared in Example 1 in the electrode material of CNT@MOF-ET8-S.

The preparation method of the cathode material CNT@MOF-ET8-S:

Step 1: Add 200 mg of carbon nanotubes (CNTs) to a mixture of 7 ml of 98% sulfuric acid and 3 ml of 68% nitric acid, soak for 6 hours, rinse the CNTs with deionized water, and then freeze-drying the acid-treated CNTs;

Step 2: Add MOF-ET8, 35 mg of CNTs, and 500 μl of hydrochloric acid solution with a concentration of 1 mol/L obtained in step 1 to 7.5 ml of N,N-dimethylformamide, first ultrasonically treat for 5 minutes, and then put Heating at 80°C for 12 hours, after centrifugation, the precipitate was washed with methanol three times, 10 ml each time, and finally the sample was vacuum-dried at 120°C for 12 hours to obtain CNT@MOF-ET8;

Step 3: The CNT@MOF-ET8 obtained in step 2 and sulfur were mixed in a mass ratio of 1:3, then transferred to an autoclave under argon protection, heated at 160 °C for 10 hours, and then heated at 160 °C in a nitrogen atmosphere. Heating at 200 °C for 2 hours, the cathode material CNT@MOF-ET8-S with high charge transfer performance was obtained.

Application Example 1: The positive electrode material CNT@MOF-ET8-S prepared in Example 2 was used in the preparation of lithium-sulfur batteries, and the specific steps were as follows:

(1) Preparation of positive electrode sheet: The positive electrode material CNT@MOF-ET8-S of Example 2 was mixed with a conductive agent and polyvinylidene fluoride in a mass ratio of 7:2:1, and N-methylpyrrolidone was added. The reaction was stirred at 25°C for 24 hours, then the mixture was evenly coated on aluminum foil, and then placed in a 60°C vacuum oven to dry for 12 hours, and then a 12-mm diameter electrode sheet was fabricated with a hole punch.

(2) Preparation of negative electrode: Mix polyvinylpyrrolidone and polyethyleneimine in a volume ratio of 2:1 as a binder, and then mix propylene carbonate, methyl ethyl carbonate and polyethersulfone in a volume ratio of 3:2 : 1 mix as a solvent, first dissolve the binder in the solvent to obtain a mixed solution, then pour the lithium powder and the carbon material into the above-mentioned mixed solution, after mixing evenly, smear in the foam nickel current collector to obtain a negative electrode sheet; The negative electrode sheet is heated at 70°C, and then the negative electrode sheet is flattened to obtain the negative electrode sheet of the battery.

(3) Battery assembly: The prepared positive electrode sheet and negative electrode sheet were assembled into a lithium-sulfur battery as shown in FIG. 2 .

Characterization of lithium-sulfur battery performance:

(1) AC impedance spectrum test: The above-mentioned battery was left for 24 hours, and the AC impedance spectrum of the lithium-sulfur battery was tested by an electrochemical workstation. The frequency range of the AC impedance test was 100 KHz~10 mHz, and the AC disturbance signal was 5 mV.

The test results are shown in Figure 3. It can be seen from Figure 3 that the charge transfer impedance of the lithium-sulfur battery with the positive electrode material CNT@MOF-ET8-S is 27.6 Ω, indicating that the lithium-sulfur battery with the positive electrode material CNT@MOF-ET8-S Has excellent charge transfer ability.

In addition, after 100 cycles of cycling at a rate of 1 C, the test results are shown in Figure 4. From Figure 4, it can be seen that the impedance after 100 cycles can be clearly seen from the impedance spectra before and after charging and discharging The impedance is significantly smaller than the undischarged impedance, which is due to the mutual conversion between Li ₂ S/Li ₂ S ₂ and S ₈ during the charging and discharging process.

(2) Cycle performance test: The cycle performance test is carried out through the Xinwei battery test system. The charge and discharge voltage range is 1.7 V - 2.8 V, and the discharge rate is 0.2 C.

The results are shown in Fig. 5. It can be seen from Fig. 5 that the lithium-sulfur battery whose cathode material is CNT@MOF-ET8-S has a high specific capacity, and the initial discharge specific capacity is 1425.8 mA hg ⁻¹ . After 100 After the second cycle, the specific capacity can still be maintained at 1325.7 mA hg ⁻¹ with a decay rate of 0.012%, showing good battery performance.

At the same time, it can be seen from Figure 5 in the description that the coulombic efficiency of the CNT@MOF-ET8-S lithium-sulfur battery as the positive electrode material is 99.8%, which indicates that the lithium-sulfur battery with the positive electrode material of CNT@MOF-ET8-S has good performance. Cycling stability, the material contains metal ions that can react with polysulfides, thereby inhibiting the shuttle effect of polysulfides.

The above are only preferred specific embodiments of the present invention, and these specific embodiments are based on different implementations under the overall concept of the present invention, and the protection scope of the present invention is not limited to this. Anyone familiar with the technical field Changes or substitutions that can be easily conceived by a skilled person within the technical scope disclosed by the present invention shall be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (10)

1. The metal organic framework material is characterized in that the metal organic framework material is MOF-ET8 with the chemical formula of [ Zr ] ₂ (L) ₃ ]Wherein L is an organic ligand C ₂₂ H ₂₀ N ₂ O ₆ 。

2. The metal-organic framework material of claim 1, wherein the organic ligand has the structure:

。

3. a process for the preparation of an organic ligand according to claim 2, characterised in that the process comprises the steps of:

s1: sequentially adding n-butyllithium, 1, 5-dibromo-2, 4-dimethoxybenzene and tetrahydrofuran into n-hexane at the temperature of-78 ℃, heating to 0 ℃, stirring for 12 hours at the temperature of 0 ℃, cooling to-78 ℃, adding trimethyl borate, heating to 25 ℃, stirring for 18 hours at the temperature of 25 ℃, adding hydrochloric acid, stirring for 0.5 hour at the temperature of 25 ℃, washing and drying to obtain an intermediate 1;

s2: sequentially adding an intermediate 1, 2-amino-4-methyl bromobenzoate, cesium fluoride and palladium dichloride into a water/dioxane mixed solution, heating, stirring and refluxing for 24 hours under the protection of argon, cooling to 25 ℃, adding dichloromethane, standing for layering, washing, drying, spin-drying an organic phase, and finally performing silica gel column chromatography by using dichloromethane/ethyl acetate as an eluent to obtain an intermediate 2;

s3: and mixing the intermediate 2, tetrahydrofuran, methanol and a sodium hydroxide solution, heating, refluxing and stirring for 24 hours, cooling to 25 ℃, then spin-drying an organic phase, then adjusting the pH value to 5, centrifuging, washing with water, precipitating, and finally drying in vacuum to obtain the organic ligand.

4. A method for preparing a metal-organic framework material according to claim 1 or 2, characterized in that the method is carried out as follows:

dissolving zirconium tetrachloride and an organic ligand in a mixed solution of N, N-dimethylformamide and hydrochloric acid, firstly performing ultrasonic treatment, then heating for reaction, centrifuging after reaction, washing and drying to obtain MOF-ET8, namely the metal organic framework material.

5. The process according to claim 4, wherein the molar ratio between zirconium tetrachloride and organic ligand is 0.27: (0.35-0.4), heating to react at 70-90 ℃ for 10-14h.

6. Use of a metal-organic framework material according to claim 1 or 2 in an electrode material.

7. Use according to claim 6, wherein the electrode material is CNT @ MOF-ET8-S.

8. A process for the preparation of CNT @ MOF-ET8-S as claimed in claim 7, wherein said process is carried out by the following steps:

step 1: performing acid treatment on CNT, then washing with water and freeze-drying;

and 2, step: adding the MOF-ET8, the CNT and a hydrochloric acid solution into N, N-dimethylformamide, performing ultrasound treatment, performing a heating reaction, centrifuging, washing and drying in vacuum to obtain CNT @ MOF-ET8;

and step 3: mixing CNT @ MOF-ET8 and sulfur, transferring the mixture into an autoclave under the protection of argon, heating the mixture for 8 to 12 hours at the temperature of between 150 and 170 ℃, and then heating the mixture for 1 to 3 hours at the temperature of between 150 and 250 ℃ in a nitrogen atmosphere to obtain the positive electrode material CNT @ MOF-ET8-S.

9. The method according to claim 8, wherein the acid treatment process in step 1: adding CNT into mixed acid of sulfuric acid/nitric acid, and soaking for 5-7h; heating in the step 2 at 70-90 ℃ for 10-14h; the mass ratio of CNT @ MOF-ET8 to sulfur in step 3 is 1: (2-4).

10. Use of the electrode material CNT @ MOF-ET8-S of claim 7 in a lithium sulfur battery.

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