An MXene composite material, its preparation method and application

Abstract

The application discloses a kind of MXene composite material and its preparation method and application, belong to composite material technical field.The MXene composite material provided by the application includes anthraquinone-based covalent organic framework and aminated MXene;The anthraquinone-based covalent organic framework is covalently connected to the surface of the aminated MXene.By the covalent connection of anthraquinone-based covalent organic framework and aminated MXene, a kind of MXene composite material is obtained, on the one hand, the covalent connection of covalent organic framework and MXene can reduce electron transfer energy barrier, thereby improving the utilization rate of redox active group in covalent organic framework;On the other hand, MXene can not only improve the conductivity of the whole material, and anthraquinone group in anthraquinone-based covalent organic framework can be combined by lithium bond and converted into lithium polysulfide, which is conducive to the preparation of lithium-sulfur battery with excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and particularly relates to an MXene composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-sulfur batteries (Li-S) are considered to be one of the next-generation new high-energy-density battery systems with the greatest development potential due to their high theoretical energy density (2600 Wh·kg -1 ) and the high natural abundance of sulfur elements. However, their commercial progress is still restricted in many aspects. On the one hand, there are complex multiphase reactions in the positive electrode of lithium-sulfur batteries, and there is a large reaction energy barrier in the liquid-solid conversion, resulting in a slow sulfur redox kinetic process. At present, the wide pore size distribution of commercial polyolefin separators cannot inhibit the shuttle effect of soluble polysulfides (LiPSs) (Li2S x , 2 < x ≤ 8) during charge and discharge, leading to a rapid attenuation of the battery capacity. On the other hand, metallic lithium as the negative electrode material is an inevitable choice to match the high discharge capacity of sulfur, but there are still serious safety problems such as dendrite growth piercing the separator in the lithium negative electrode, resulting in battery short circuit or even combustion and explosion.

[0003] Based on the above background, introducing a functional coating that can inhibit the shuttle effect on the positive electrode side of the lithium-sulfur battery separator is considered an effective strategy. However, the initially introduced materials such as carbon nanotubes, graphene, and porous aerogels as functional coatings, although having good electrical conductivity and high specific surface area, cannot further accelerate the sulfur redox kinetics. Researchers further introduced electrocatalytically active transition metal-based compounds into the functional coating. These catalysts are usually compounded with high-specific-surface-area materials and have abundant active sites, which anchor and catalytically convert polysulfides through strong interactions to accelerate the sulfur redox kinetic process. However, the transition metal-based compound hybrid materials lack lithiophilic sites and are difficult to achieve uniform lithium ion transport to inhibit the growth of lithium dendrites. Covalent organic frameworks (COFs) have the advantages of light weight, adjustable structure, high specific surface area, excellent chemical and thermodynamic stability, etc. In the research work of functional modified coatings for lithium-sulfur batteries, it has been proven to be one of the effective strategies to inhibit the polysulfide shuttle effect by electrostatically adsorbing or repelling polysulfides through the unique porous properties of COFs and specific functional groups. In addition, due to the ordered pores and adjustable structural units, the COF functional modified coating can provide a lithium ion transport channel with a large number of lithiophilic groups. However, the intrinsic conductivity of COFs is poor and the utilization rate of polysulfide active components is low, which limits the improvement of the specific capacity of lithium-sulfur batteries. Summary of the Invention

[0004] In order to overcome at least one of the problems existing in the prior art, one of the objectives of the present invention is to provide an MXene composite material that combines MXene with covalent organic framework (COF) materials, so that the two can synergistically perform adsorption-catalysis functions, thereby solving the technical problem of poor cycle stability and poor rate performance of lithium-sulfur batteries due to the poor intrinsic conductivity of COF materials.

[0005] The second objective of this invention is to provide a method for preparing the above-mentioned MXene composite material.

[0006] The third objective of this invention is to provide a modified diaphragm.

[0007] The fourth objective of this invention is to provide a lithium-sulfur battery.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A first aspect of the present invention provides an MXene composite material comprising an anthraquinone-based covalent organic framework and an amino-modified MXene; wherein the anthraquinone-based covalent organic framework is covalently attached to the surface of the amino-modified MXene.

[0010] Furthermore, the anthraquinone-based covalent organic framework is covalently linked to the amino group of the amino-modified MXene.

[0011] In this invention, MXene is a two-dimensional inorganic compound mainly composed of transition metal carbides.

[0012] Preferably, the raw materials for preparing the anthraquinone-based covalent organic framework include diaminoanthraquinone (DAAQ) and trialdehyde phloroglucinol (TFP).

[0013] Preferably, the diaminoanthraquinone comprises 2,6-diaminoanthraquinone. 2,7-Diaminoanthraquinone Or 1,5-diaminoanthraquinone At least one of the following; more preferably, the diaminoanthraquinone is selected from 2,6-diaminoanthraquinone.

[0014] Preferably, the mass ratio of the diaminoanthraquinone to the trialdehyde phloroglucinol is 1:(0.3-1.5); more preferably 1:(0.4-1.2); and even more preferably 1:(0.5-1).

[0015] Preferably, the raw materials for preparing the aminated MXene include diazonium salt and MXene.

[0016] Preferably, the aminated MXene is prepared by a method comprising the following steps: subjecting a diazonium salt and MXene to an amination reaction to obtain the aminated MXene.

[0017] Preferably, the temperature of the amination reaction is -5 to 5°C; more preferably -2 to 2°C; and even more preferably 0°C.

[0018] Preferably, the amination reaction is carried out in water.

[0019] Preferably, the diazonium salt is selected from 4-aminophenyl diazonium salt.

[0020] A second aspect of the present invention provides a method for preparing an MXene composite material, comprising the following steps: mixing aminated MXene, diaminoanthraquinone (DAAQ), trialdehyde phloroglucinol (TFP) and a solvent, and performing a solvothermal reaction to obtain the MXene composite material as described in the first aspect of the present invention.

[0021] Preferably, the temperature of the solvothermal reaction is 100–140°C; more preferably 105–135°C; and even more preferably 110–130°C.

[0022] Preferably, the solvothermal reaction time is 48–96 h; more preferably 54–90 h; and even more preferably 60–84 h.

[0023] Preferably, the solvent includes at least one of glacial acetic acid, N,N-dimethylacetamide (DMAC), or mesitylene; more preferably, the solvent includes glacial acetic acid, N,N-dimethylacetamide, and mesitylene.

[0024] Preferably, the volume ratio of glacial acetic acid, N,N-dimethylacetamide and mesitylene in the solvent is 1:(5-10):(1-5); more preferably 1:(7-8):(2-3).

[0025] Preferably, the ratio of the total mass of the diaminoanthraquinone and the trialdehyde phloroglucinol to the mass of the amino-modified MXene is 1:(0.3-3); more preferably 1:(0.4-2); and even more preferably 1:(0.5-1).

[0026] Preferably, the ratio of the aminoated MXene to the solvent is 1 mg:(0.1-1) mL; more preferably, 1 mg:(0.2-0.8) mL; and even more preferably, 1 mg:(0.3-0.5) mL.

[0027] A third aspect of the present invention provides a modified membrane comprising a substrate layer and a functional coating disposed on the substrate layer; the raw material for preparing the functional coating comprises the MXene composite material described in the first aspect of the present invention.

[0028] Preferably, the raw materials for preparing the functional coating also include binders, conductive agents, and organic solvents.

[0029] Preferably, the adhesive comprises at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, carboxymethyl cellulose, polymethyl methacrylate, styrene-butadiene rubber, or polyvinyl alcohol; more preferably, the adhesive comprises at least one of polyvinylidene fluoride, polyacrylic acid, or polyacrylonitrile; even more preferably, the adhesive is selected from polyvinylidene fluoride (PVDF).

[0030] Preferably, the conductive agent includes at least one of conductive carbon black, acetylene black, carbon nanotubes, or graphene; more preferably, the conductive agent is selected from conductive carbon black (Super P).

[0031] Preferably, the organic solvent includes at least one of N,N-dimethylformamide, N-methylpyrrolidone, acetone, or tetrahydrofuran; more preferably, the organic solvent is selected from N,N-dimethylformamide (NMP).

[0032] Preferably, the mass ratio of the MXene composite material to the adhesive is 1:(0.05-1); more preferably 1:(0.08-0.8); and even more preferably 1:(0.1-0.6).

[0033] Preferably, the mass ratio of the MXene composite material to the conductive agent is 1:(0.05-0.5); more preferably 1:(0.08-0.4); and even more preferably 1:(0.1-0.3).

[0034] Preferably, the thickness of the functional coating is 1–10 μm; more preferably 2–8 μm; even more preferably 3–5 μm.

[0035] Preferably, the material of the substrate layer includes at least one of metal, carbon material or polymer material; more preferably, the material of the substrate layer includes at least one of aluminum, copper, carbon cloth or polyolefin; even more preferably, the material of the substrate layer is selected from polyolefin.

[0036] Preferably, the polyolefin includes at least one of polypropylene, polyethylene, or a polypropylene-polyethylene composite material; more preferably, the polyolefin is selected from polypropylene (PP).

[0037] A fourth aspect of the present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, and a battery separator disposed between the positive electrode and the negative electrode; the battery separator is prepared from MXene composite material as described in the first aspect of the present invention, or the battery separator is a modified separator as described in the third aspect of the present invention.

[0038] The beneficial effects of this invention are as follows: This invention obtains an MXene composite material through the covalent connection of anthraquinone-based covalent organic framework and amino-modified MXene. On the one hand, the covalent connection between the covalent organic framework and MXene can lower the electron transfer energy barrier, thereby improving the utilization rate of redox active groups in the covalent organic framework. On the other hand, MXene can not only improve the overall conductivity of the material, but also anchor and catalyze the conversion of polysulfides through active metal sites. Furthermore, the anthraquinone groups in the anthraquinone-based covalent organic framework can bind to and convert lithium polysulfides through lithium bonds. Therefore, the MXene composite material provided by this invention can achieve synergistic catalysis at both ends of the binding site, effectively solving the problem of poor intrinsic conductivity of the covalent organic framework. This MXene composite material is beneficial for preparing lithium-sulfur batteries with excellent electrochemical performance.

[0039] Specifically, compared with the prior art, the present invention has the following advantages:

[0040] 1. Anthraquinone-based covalent organic frameworks have a microporous structure, which is conducive to the adsorption of polysulfides, restricts the shuttle effect, and achieves synergistic adsorption-catalysis performance. In addition, the ordered pore structure of anthraquinone-based covalent organic frameworks and the abundance of lithium-loving sites (such as carbonyl, ketone-amine bonds and anthraquinone groups) are conducive to promoting efficient and uniform lithium-ion transport.

[0041] 2. This invention achieves a good composite effect by aminated MXene, enabling anthraquinone-based covalent organic frameworks to be covalently linked to the surface of aminated MXene. The resulting MXene composite material can be used to make lithium-sulfur batteries, which can achieve excellent electrochemical cycle performance and rate performance. Attached Figure Description

[0042] Figure 1 SEM images of MXene and DAAQ-TFP / MXene-1.

[0043] Figure 2 The nitrogen adsorption-desorption curves and pore size distribution diagrams for DAAQ-TFP / MXene-1 and DAAQ-TFP are shown.

[0044] Figure 3 The UV-Vis absorption curves are for MXene, DAAQ-TFP / MXene-1, DAAQ-TFP, and the blank group solutions.

[0045] Figure 4 The images are physical photos and SEM images of the DAAQ-TFP / MXene-1@PP.

[0046] Figure 5 Cyclic voltammetry and electrochemical impedance spectroscopy of DAAQ-TFP / MXene-1@PP, DAAQ-TFP@PP, MXene@PP, and PP membrane.

[0047] Figure 6 Comparison chart of rate performance tests for DAAQ-TFP / MXene-1@PP, DAAQ-TFP@PP, MXene@PP and PP separator.

[0048] Figure 7 This is a comparison chart of the long-cycle performance of DAAQ-TFP / MXene-1@PP, DAAQ-TFP@PP, MXene@PP and PP membranes. Detailed Implementation

[0049] The following specific embodiments further illustrate the content of the present invention in detail. It should also be understood that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the principles described herein are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make selections within a suitable range based on the description herein, and are not intended to be limited to the specific data in the examples below. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments and comparative examples can be obtained from conventional commercial sources or by existing known methods.

[0050] Example of preparation of covalent organic framework

[0051] A DAAQ-TFP material, the specific preparation method is as follows:

[0052] DAAQ (13.5 mg), TFP (7.9 mg), DMAC (4.5 mL), mesitylene (1.5 mL), and glacial acetic acid solution (6 M, 0.6 mL) were added to a custom-made glass tube. After sonication for approximately 15 minutes, the glass tube was rapidly frozen at 77 K, followed by three freeze-degassing-thawing cycles, and then the tube was flame-sealed. After the temperature returned to room temperature, the reaction was carried out at 120 °C for 72 hours. After removing the solvent by vacuum filtration, the product was washed three times with DMF and then three times with acetone. After washing, the remaining product was dried in a vacuum oven at 60 °C to completely remove the solvent, yielding the DAAQ-TFPCOF material.

[0053] Composite Material Example 1

[0054] This embodiment provides an MXene composite material, denoted as DAAQ-TFP / MXene-1, and the specific preparation method is as follows:

[0055] S1: 1,4-Phenylenediamine (542 mg, 5.0 mmol) was added to a round-bottom flask along with 40 mL of deionized water, and the minimum amount of hydrochloric acid solution required for dissolution was added dropwise. The resulting solution was maintained at 0°C in a cryogenic reaction vessel. Subsequently, 10 mL of an aqueous solution containing 335 mg NaNO2 (5.0 mmol) was rapidly added dropwise over 20 minutes with stirring. The prepared 4-aminophenyl diazonium salt aqueous solution was slowly added dropwise to 100 mL of an aqueous dispersion containing 300 mg MXene with stirring at 0°C. After reacting the mixture overnight, the solvent was removed by centrifugation, followed by washing with anhydrous ethanol and water sequentially, and the product was separated by centrifugation. After freeze-drying overnight, aminated MXene nanosheets (MXene-NH2) were obtained.

[0056] S2: Aminated MXene nanosheets (21 mg), DAAQ (13.5 mg), TFP (7.9 mg), DMAC (4.5 mL), mesitylene (1.5 mL), and glacial acetic acid (6 M, 0.6 mL) were added to a custom-made glass tube. After sonication for approximately 15 minutes, the glass tube was rapidly frozen at 77 K, followed by three freeze-degassing-thawing cycles, and then flame-sealed. After the temperature returned to room temperature, the reaction was heated at 120 °C for 72 hours. After removing the solvent by vacuum filtration, the product was washed three times with DMF and then three times with acetone. After washing, the remaining product was dried in a vacuum oven at 60 °C to completely remove the solvent, yielding DAAQ-TFP / MXene-1.

[0057] Composite Material Example 2

[0058] This embodiment provides an MXene composite material, denoted as DAAQ-TFP / MXene-2, and the specific preparation method is as follows:

[0059] S1: 1,4-Phenylenediamine (542 mg, 5.0 mmol) was added to a round-bottom flask along with 40 mL of deionized water, and the minimum amount of hydrochloric acid solution required for dissolution was added dropwise. The resulting solution was maintained at 0°C in a cryogenic reaction vessel. Subsequently, 10 mL of an aqueous solution containing 335 mg NaNO2 (5.0 mmol) was rapidly added dropwise over 20 minutes with stirring. The prepared 4-aminophenyl diazonium salt aqueous solution was slowly added dropwise to 100 mL of an aqueous dispersion containing 300 mg MXene with stirring at 0°C. After reacting the mixture overnight, the solvent was removed by centrifugation, followed by washing with anhydrous ethanol and water sequentially, and the product was separated by centrifugation. After freeze-drying overnight, aminated MXene nanosheets (MXene-NH2) were obtained.

[0060] S2: Aminated MXene nanosheets (21 mg), DAAQ (27 mg), TFP (15.8 mg), DMAC (4.5 mL), mesitylene (1.5 mL), and glacial acetic acid (6 M, 0.6 mL) were added to a custom-made glass tube. After sonication for approximately 15 minutes, the glass tube was rapidly frozen at 77 K, followed by three freeze-degassing-thawing cycles, and then flame-sealed. After the temperature returned to room temperature, the reaction was heated at 120 °C for 72 hours. After removing the solvent by vacuum filtration, the product was washed three times with DMF and then three times with acetone. After washing, the remaining product was dried in a vacuum oven at 60 °C to completely remove the solvent, yielding DAAQ-TFP / MXene-2.

[0061] Modified diaphragm Example 1

[0062] This embodiment provides a modified membrane, denoted as DAAQ-TFP / MXene-1@PP, and the specific preparation method is as follows:

[0063] 24 mg DAAQ-TFP / MXene-1 (prepared in Composite Material Example 1), 3 mg PVDF, and 3 mg SuperP were mixed and thoroughly ground. NMP was slowly added dropwise, and grinding continued until the slurry had a metallic luster. The slurry was then coated onto a diaphragm (Celgard 2325) using a 50 μm doctor blade and dried under vacuum at 60 °C to obtain the DAAQ-TFP / MXene-1@PP modified diaphragm.

[0064] Modified diaphragm Example 2

[0065] This embodiment provides a modified membrane, denoted as DAAQ-TFP / MXene-2@PP, and the specific preparation method is as follows:

[0066] 24 mg DAAQ-TFP / MXene-2 ​​(prepared in Composite Material Example 2), 3 mg PVDF, and 3 mg SuperP were mixed and thoroughly ground. NMP was slowly added dropwise, and grinding continued until the slurry had a metallic luster. The slurry was then coated onto a diaphragm (Celgard 2325) using a 50 μm doctor blade and dried under vacuum at 60 °C to obtain the DAAQ-TFP / MXene-2@PP modified diaphragm.

[0067] Modified diaphragm Example 3

[0068] This embodiment provides a modified membrane, denoted as DAAQ-TFP / MXene-3@PP, and the specific preparation method is as follows:

[0069] 24 mg DAAQ-TFP / MXene-1 (prepared in Composite Material Example 1), 12 mg PVDF, and 4 mg SuperP were mixed and thoroughly ground. NMP was slowly added dropwise, and grinding continued until the slurry had a metallic luster. The slurry was then coated onto a diaphragm (Celgard 2325) using a 50 μm doctor blade and dried under vacuum at 60 °C to obtain the DAAQ-TFP / MXene-3@PP modified diaphragm.

[0070] Modified diaphragm comparative example 1

[0071] This comparative example provides a modified membrane, denoted as DAAQ-TFP@PP, and the specific preparation method is as follows:

[0072] 24 mg DAAQ-TFP, 3 mg PVDF, and 3 mg SuperP were mixed and ground thoroughly. NMP was slowly added dropwise, and grinding continued until the slurry had a metallic luster. The slurry was then coated onto a diaphragm (Celgard2325) using a 50 μm doctor blade and dried under vacuum at 60 °C to obtain DAAQ-TFP@PP modified diaphragms.

[0073] Comparative Example 2 of Modified Diaphragm

[0074] This comparative example provides a modified membrane, denoted as MXene@PP, and the specific preparation method is as follows:

[0075] 24 mg MXene, 3 mg PVDF and 3 mg SuperP were mixed and ground thoroughly. NMP was slowly added dropwise and grinding continued until the slurry had a metallic luster. The slurry was then coated onto a diaphragm (Celgard2325) using a 50 μm doctor blade and dried under vacuum at 60 °C to obtain MXene@PP modified diaphragms.

[0076] Performance Characterization

[0077] 1) Morphological characterization of MXene composite materials

[0078] The morphology of DAAQ-TFP / MXene-1 prepared in Example 1 of the composite material was characterized, and the results were as follows: Figure 1 As shown. Figure 1 The images are SEM images of MXene and DAAQ-TFP / MXene-1, where a is the SEM image of MXene and b is the SEM image of DAAQ-TFP / MXene-1.

[0079] according to Figure 1 As can be seen from a, MXene material exhibits a typical two-dimensional sheet-like morphology with a relatively smooth surface; according to Figure 1As can be seen from b, in the DAAQ-TFP / MXene-1 material, there are obvious COF nanoparticles on the surface of the MXene nanosheets.

[0080] 2) Nitrogen desorption experiment and pore size distribution test of MXene composite material

[0081] Nitrogen desorption experiments and pore size distribution tests were conducted on DAAQ-TFP / MXene-1 prepared in Example 1 of composite material and DAAQ-TFP prepared in the covalent organic framework preparation example. Figure 2 The figures show the nitrogen desorption curves and pore size distributions of DAAQ-TFP / MXene-1 and DAAQ-TFP, where a is the nitrogen desorption curve and b is the pore size distribution.

[0082] according to Figure 2 Based on the data of gas adsorption in a, the specific surface areas of DAAQ-TFP / MXene-1 and DAAQ-TFP were calculated using the BET model to be 761.4 m². 2 g -1 and 1154.3m 2 g -1 ;according to Figure 2 As can be seen from b, DAAQ-TFP / MXene-1 and DAAQ-TFP have similar pore structures, with the main pore sizes concentrated at 1.9 nm and 4.8 nm. The numerous micropores can rapidly adsorb lithium polysulfides, and the abundant mesopores are conducive to the rapid transport of lithium ions.

[0083] 3) Lithium polysulfide adsorption test of MXene composite material

[0084] Li₂S₆ adsorption experiments were conducted to visually compare the adsorption-catalytic performance of the materials. Lithium polysulfide adsorption tests were performed on MXene, DAAQ-TFP / MXene-1 prepared in Example 1 (composite material), and DAAQ-TFP prepared in the covalent organic framework preparation example. The results are as follows: Figure 3 As shown, Li2S6 represents the blank solution.

[0085] Figure 3 The UV-Vis absorption curves are for MXene, DAAQ-TFP / MXene-1, DAAQ-TFP, and the blank group solutions.

[0086] from Figure 3 As can be seen, compared with the absorbance of the Li2S6 characteristic peak at 400 nm in the blank solution, the peak intensity of the solution with added DAAQ-TFP / MXene-1 almost disappeared, which proves the great advantage of DAAQ-TFP / MXene-1 in adsorption-catalysis performance.

[0087] 4) Morphological characterization of the modified diaphragm

[0088] The morphology of the DAAQ-TFP / MXene-1@PP membrane prepared in Example 1 was characterized, and the results were as follows: Figure 4 As shown. Figure 4 The images shown are physical photos and SEM images of the DAAQ-TFP / MXene-1@PP. Specifically, a is a physical photo of the DAAQ-TFP / MXene-1@PP; b is a cross-sectional SEM image of the DAAQ-TFP / MXene-1@PP; c is a SEM image of the top surface of the DAAQ-TFP / MXene-1@PP; and d is a SEM image of the bottom surface of the DAAQ-TFP / MXene-1@PP.

[0089] according to Figure 4 As can be seen, DAAQ-TFP / MXene-1 is uniformly distributed on the PP membrane; according to Figure 4 As can be seen from b to d, in DAAQ-TFP / MXene-1@PP, on the top surface with the modified coating, DAAQ-TFP / MXene-1 forms a macroscopically dense modified coating with a thickness of approximately 3 μm; while the bottom surface without the coating material retains the original morphology of the PP membrane.

[0090] 2) Cyclic voltammetry and electrochemical impedance spectroscopy of the modified membrane

[0091] Lithium-sulfur batteries were assembled using DAAQ-TFP / MXene-1@PP prepared in Example 1 (modified separator), DAAQ-TFP@PP prepared in Comparative Example 1 (modified separator), MXene@PP prepared in Comparative Example 2 (modified separator), and PP separators, with the side having the modified coating facing the sulfur cathode. The scanning rate was 0.1 mV·s. -1 Under a voltage window of 1.7–2.8 V, the cyclic voltammetry (CV) curves and electrochemical impedance spectroscopy of the above-mentioned Li-S batteries based on four different separators were tested.

[0092] Figure 5 The cyclic voltammetry and electrochemical impedance spectroscopy (EIS) spectra of DAAQ-TFP / MXene-1@PP, DAAQ-TFP@PP, MXene@PP, and the PP separator are shown, where a is the cyclic voltammetry and b is the electrochemical impedance spectroscopy. Based on... Figure 5As shown in section a, the lithium-sulfur battery assembled with DAAQ-TFP / MXene-1@PP exhibits the highest peak current, and simultaneously shows a significant positive shift in reduction peak potential and a negative shift in oxidation peak potential, indicating that the lithium-sulfur battery assembled with DAAQ-TFP / MXene-1@PP has a faster redox kinetic process. These results fully demonstrate that DAAQ-TFP / MXene-1@PP can reduce battery polarization and catalyze the redox reaction of polysulfides. Based on... Figure 5 As can be seen from b, the lithium-sulfur battery assembled by DAAQ-TFP / MXene-1@PP has the lowest charge transfer impedance, indicating that it significantly enhances the charge transfer and ion diffusion processes.

[0093] 3) Rate performance test of modified diaphragm

[0094] Lithium-sulfur batteries were assembled using DAAQ-TFP / MXene-1@PP prepared in Example 1 (modified separator), DAAQ-TFP@PP prepared in Comparative Example 1 (modified separator), MXene@PP prepared in Comparative Example 2 (modified separator), and PP separators, with the side having the modified coating facing the sulfur cathode. Rate performance tests were conducted at different current densities.

[0095] Figure 6 This is a comparison chart of the rate performance tests of DAAQ-TFP / MXene-1@PP, DAAQ-TFP@PP, MXene@PP, and PP separators. Based on... Figure 6 It can be seen that the Li-S cells assembled by DAAQ-TFP / MXene-1@PP have the highest average specific capacity at C rates of 0.1, 0.2, 0.5, 1, 2, 3, and 5.

[0096] 4) Long-cycle testing of the modified diaphragm

[0097] Lithium-sulfur batteries were assembled using DAAQ-TFP / MXene-1@PP prepared in Example 1 (modified separator), DAAQ-TFP@PP prepared in Comparative Example 1 (modified separator), MXene@PP prepared in Comparative Example 2 (modified separator), and PP separators, with the side having the modified coating facing the sulfur cathode. Long-cycle testing was conducted at a 1C current density.

[0098] Figure 7 This is a comparison chart of the long-cycle performance of DAAQ-TFP / MXene-1@PP, DAAQ-TFP@PP, MXene@PP, and PP membranes. Based on... Figure 7 It can be seen that DAAQ-TFP / MXene-1@PP exhibits the highest initial discharge specific capacity and the lowest average capacity decay rate per cycle. The results demonstrate that DAAQ-TFP / MXene-1@PP possesses excellent cycling performance.

[0099] The anthraquinone-based covalent organic framework prepared in this embodiment of the invention possesses a microporous structure, which is beneficial for the adsorption of polysulfides, restricts the shuttle effect, and achieves synergistic adsorption-catalysis performance. Furthermore, the ordered pore structure and abundant lithiophilic sites (such as carbonyl, ketone-amine, and anthraquinone groups) of the anthraquinone-based covalent organic framework are conducive to promoting efficient and uniform lithium-ion transport. In addition, by amylating MXene in this embodiment of the invention, the anthraquinone-based covalent organic framework can be covalently linked to the surface of the aminated MXene, achieving a good composite effect. The resulting MXene composite material, when used to construct a lithium-sulfur battery, can achieve excellent electrochemical cycling performance and rate performance.

[0100] In summary, this invention provides an MXene composite material through the covalent connection of anthraquinone-based covalent organic framework and amino-modified MXene. On one hand, the covalent connection between the covalent organic framework and MXene lowers the electron transfer energy barrier, thereby improving the utilization rate of redox active groups within the covalent organic framework. On the other hand, MXene not only enhances the overall conductivity of the material but also anchors and catalyzes the conversion of polysulfides through active metal sites. Furthermore, the anthraquinone groups in the anthraquinone-based covalent organic framework can bind to and convert lithium polysulfides via lithium bonds. Therefore, the MXene composite material provided by this invention achieves synergistic catalysis at both ends of the binding site, effectively solving the problem of poor intrinsic conductivity of covalent organic frameworks. This MXene composite material is beneficial for preparing lithium-sulfur batteries with excellent electrochemical performance.

Claims

1. A modified separator, characterized by, The functional coating layer is prepared from a raw material comprising a MXene composite material; The MXene composite material comprises an anthraquinone-based covalent organic framework and an aminated MXene; the anthraquinone-based covalent organic framework is covalently connected to the surface of the aminated MXene; the raw material for preparing the anthraquinone-based covalent organic framework comprises a diaminanthraquinone and a triformylphloroglucinol; The raw material for preparing the aminated MXene comprises a diazonium salt and a MXene; the diazonium salt is a 4-aminobenzene diazonium salt.

2. The modified separator according to claim 1, wherein The diaminanthraquinone comprises at least one of 2,6-diaminanthraquinone, 2,7-diaminanthraquinone or 1,5-diaminanthraquinone; and / or, the mass ratio of the diaminanthraquinone to the triformylphloroglucinol is 1:(0.3-1.5).

3. The modified separator of claim 1, wherein, The MXene composite material is prepared by a preparation method comprising the following steps: mixing the aminated MXene, the diaminanthraquinone, the triformylphloroglucinol and a solvent, and performing a solvothermal reaction to obtain the MXene composite material.

4. The modified separator of claim 3, wherein, The temperature of the solvothermal reaction is 100-140℃; And / or, the time of the solvothermal reaction is 48-96h.

5. The modified separator of claim 3, wherein The solvent comprises at least one of glacial acetic acid, N,N-dimethylacetamide or mesitylene; And / or, the ratio of the total mass of the diaminanthraquinone and the triformylphloroglucinol to the mass of the aminated MXene is 1:(0.3-3).

6. The modified separator of claim 1, wherein The raw material for preparing the functional coating layer further comprises a binder, a conductive agent and an organic solvent.

7. The modified separator of claim 6, wherein, The binder comprises at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, carboxymethyl cellulose, polymethyl methacrylate, butadiene styrene rubber or polyvinyl alcohol; And / or, the conductive agent comprises at least one of conductive carbon black, acetylene black, carbon nanotube or graphene; And / or, the organic solvent comprises at least one of N,N-dimethylformamide, N-methylpyrrolidone, acetone or tetrahydrofuran; And / or, the mass ratio of the MXene composite material to the binder is 1:(0.05-1); And / or, the mass ratio of the MXene composite material to the conductive agent is 1:(0.05-0.5).

8. The modified separator of claim 1, wherein The material of the substrate layer comprises at least one of metal, carbon material or polymer material.

9. A lithium-sulfur battery, characterized by, The battery separator is selected from the modified separator of any one of claims 1-8.

Images