CN116715862B - Covalent organic framework/alumina composite material containing sulfonic acid group and preparation method and application thereof - Google Patents

Abstract

The invention relates to a covalent organic framework/aluminum oxide composite material containing sulfonic acid groups, and a preparation method and application thereof, and belongs to the technical field of lithium-sulfur batteries. S1, calcining aluminum oxide, and then modifying the aluminum oxide by an amination reagent and an hydroformylation reagent to obtain theta-Al ₂O₃ -CHO; s2, dissolving 2, 5-diaminobenzenesulfonic acid, trialdehyde phloroglucinol, acetic acid and theta-Al ₂O₃ -CHO in a solvent, and heating to react after repeated freezing-thawing-freezing circulation degassing treatment to obtain the covalent organic framework/alumina composite material containing sulfonic acid groups. The alumina doped COF material not only can provide a stable electron transfer channel, but also can absorb polysulfide through synergistic effect, so that the shuttle effect of polysulfide is inhibited.

Description

A covalent organic framework/alumina composite material containing sulfonic acid groups and its preparation method and application

Technical Field

The present invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a covalent organic framework/aluminum oxide composite material containing sulfonic acid groups, and a preparation method and application thereof.

Background Art

Energy is the basic guarantee for the stable development of modern society. The reserves of traditional fossil energy are insufficient to support the rapid development of human society. At the same time, the problems such as global warming and environmental pollution caused by the excessive use of fossil energy have also brought huge challenges to human survival and development. Renewable energy has the advantages of abundant sources, clean and pollution-free, and recyclable, which can better meet the needs of human energy demand development. However, the generation of renewable energy is intermittent in nature, and it is difficult to use it directly. Therefore, the energy storage system assumes the important responsibility of converting renewable energy into storable electrical energy. Secondary batteries are the best choice for large-scale energy storage systems and are also an important component of the rapidly developing electric vehicles and portable electronic devices. Therefore, high-energy-density and high-safety energy storage power system equipment plays an important role in portable electronic products and electric vehicles. Among them, Li-S batteries have been widely studied by researchers because of their ultra-high theoretical specific capacity of 1675mAh g ^-1 and high theoretical energy density of 2600Wh kg ^-1 . At present, the actual energy density of soft-pack Li-S batteries can reach 400Wh kg ^- 1-600Wh kg ^-1 , which is expected to meet the requirements of battery energy density in aerospace fields such as long-flight drones, pure electric aircraft and spacecraft. In addition, elemental sulfur has the advantages of abundant earth reserves, low cost and no pollution, which makes Li-S batteries more economical and environmentally friendly, and also makes them more suitable for the economic and environmental requirements of the electric aerospace field.

However, lithium-sulfur batteries still face many problems. First, during the charge and discharge process, due to the low utilization of active materials and the poor conductivity of S/ _Li2S , the energy density of Li-S batteries will decrease while improving the electrode conductivity. Second, the soluble lithium polysulfide ( _Li2Sn , 4≤n≤8) produced during the electrochemical reaction is easily dissolved in ether electrolytes, forming a "shuttle effect", resulting in the loss of active materials and low coulombic efficiency. These problems have greatly affected the development of Li-S batteries. Therefore, it is still a challenge to produce Li-S batteries with high coulombic efficiency, stable cycle and long service life.

In recent years, research on lithium-sulfur batteries has mainly focused on the design of positive electrode structure, the inhibition of shuttle effect by functional diaphragms, and the solution to negative electrode lithium dendrites. Among them, the inhibition of shuttle effect and lithium dendrites by composite diaphragms modified with functional materials is the most widely studied. However, the carbon materials in the functional coating are stacked together, and lithium polysulfide can still pass through the diaphragm to reach the negative electrode between the gaps of its particles, resulting in capacity decay. In addition, the carbon material coating that plays an adsorption role must reach a certain thickness to work, and the thickness increases, the better the effect of blocking lithium polysulfide. When the positive electrode load increases, the effect will be greatly reduced, and a thicker coating is needed to work, but its shortcomings seriously limit its application in industrialization.

Covalent organic frameworks (COFs) are a class of stable porous organic materials composed of covalent bonds. In recent years, COFs have set off a new wave of research due to their controllable structure and high polysulfide adsorption rate, which have excellent effects on the cycle stability and rate performance of Li-S batteries. However, for advanced separator coatings for Li-S batteries, more precise porosity control and improved electronic/ionic conductivity of COFs should be considered. Therefore, it is still challenging to develop a COF material with appropriate thickness, considerable surface coverage, and a defect-free coating without reducing the overall energy density of Li-S batteries.

Summary of the invention

In order to solve the above technical problems, the present invention provides a sulfonic acid group covalent organic framework/alumina composite material and its preparation method and application. The covalent organic framework containing sulfonic acid groups based on alumina as a multifunctional separator of Li-S battery can significantly improve the electrochemical performance of Li-S battery.

The first object of the present invention is to provide a method for preparing a covalent organic framework/alumina composite material containing sulfonic acid groups, comprising the following steps:

S1, calcining alumina, and then modifying it with an amination agent and a formaldehyde agent to obtain θ-Al ₂ O ₃ -CHO;

S2, dissolving 2,5-diaminobenzenesulfonic acid, trialdehyde phloroglucinol, acetic acid and the θ-Al ₂ O ₃ -CHO described in S1 in a solvent, degassing the mixture through multiple freeze-thaw-freeze cycles, and heating the mixture for reaction to obtain the covalent organic framework/alumina composite material containing sulfonic acid groups.

In one embodiment of the present invention, in S1, the calcination is carried out under a protective atmosphere at 1100° C.-1200° C. for 2 h-3 h to obtain θ-Al ₂ O ₃ .

In one embodiment of the present invention, the protective atmosphere is a nitrogen atmosphere.

In one embodiment of the present invention, in S1, the amination agent is selected from (3-aminopropyl)triethoxysilane.

In one embodiment of the present invention, in S1, the formaldehyde reagent is selected from trimesaldehyde.

In one embodiment of the present invention, in S2, the molar ratio of the 2,5-diaminobenzenesulfonic acid, trialdehyde phloroglucinol and θ-Al ₂ O ₃ -CHO is 15-17:10-12:6.

In one embodiment of the present invention, in S2, the solvent is selected from one or more of ethanol, o-dichlorobenzene, n-butanol and dioxane.

In one embodiment of the present invention, in S2, the temperature of the heating reaction is 115°C-120°C, and the time of the heating reaction is 72h-120h.

The second object of the present invention is to provide a covalent organic framework/aluminum oxide composite material containing sulfonic acid groups prepared by the method.

The third object of the present invention is to provide an application of the covalent organic framework/alumina composite material containing sulfonic acid groups in a lithium-sulfur battery.

The technical solution of the present invention has the following advantages over the prior art:

(1) The preparation method of the present invention uses alumina material as a substrate to obtain a COF-based composite material for Li-S batteries. First, the surface of θ-Al ₂ O ₃ is modified, and then the surface-modified alumina material is used as a matrix to graft a highly conjugated two-dimensional SO ₃ -COF material. Since the alumina-doped COF material can not only provide a stable electron transfer channel, but also can adsorb polysulfides through synergistic effects, thereby inhibiting the shuttling effect of polysulfides.

(2) The alumina used in the covalent organic framework/alumina composite material containing sulfonic acid groups described in the present invention is a porous ceramic carrier with important practical application value, and has the advantages of high strength, high porosity, high mechanical strength, good conductivity, low cost, and easy availability. At present, alumina materials have been widely used in the fields of reaction catalysis, purification and separation. Although the conductivity of alumina is lower than that of some other metal oxides, alumina has higher stability and larger specific surface area. The conductivity of alumina is much higher than that of the covalent organic framework. The composite of alumina and the covalent organic framework can effectively promote the conduction of lithium ions due to its regularly arranged nanochannels and continuous negative charge sites. It can not only prevent the collapse of the covalent organic framework in the electrolyte, but also significantly inhibit the diffusion of polysulfides through electrostatic interactions, improve the cycle stability of the composite material, and retain the high specific surface area of the raw materials, and expand the contact area with the electrolyte.

(3) The covalent organic framework/alumina composite material (Al ₂ O ₃ @SO ₃ -COF) containing sulfonic acid groups described in the present invention is synthesized in one step by solvothermal synthesis method with θ-Al ₂ O ₃ as the matrix. The separator of Al ₂ O ₃ @SO ₃ -COF provides higher initial discharge specific capacity and good cycle performance in Li-S batteries. On the one hand, the negatively charged sulfonate can inhibit the polysulfide anions with the same charge through electrostatic repulsion, thereby improving the cycle stability of the battery. On the other hand, due to the synergistic adsorption effect between θ-Al ₂ O ₃ and COF, polysulfides can be adsorbed and the shuttling of polysulfides can be inhibited. Due to the above structural characteristics, at a current density of 1C, the Li-S battery shows a high capacity of 998.9mAh g ^-1 , and after 500 cycles, the battery retains a discharge specific capacity of 672.14mAh g ^-1 , with excellent electrochemical performance. This is the first time that a composite material of alumina and COF has been used in Li-S battery separators to improve the electrochemical performance of Li-S batteries, and it has broad development prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

FIG1 is a flow chart of the preparation of a covalent organic framework/alumina composite material containing sulfonic acid groups according to Example 1 of the present invention;

FIG2 is a scanning electron microscope image of the material of Test Example 1 of the present invention; wherein (a) is a scanning electron microscope image of SO ₃ -COF, and (b) is a scanning electron microscope image of 60% Al ₂ O ₃ @SO ₃ -COF;

FIG3 is a nitrogen adsorption-desorption analysis and pore size distribution analysis diagram of the material of Test Example 2 of the present invention; wherein (a) is a nitrogen adsorption-desorption analysis diagram, and (b) is a pore size distribution analysis diagram;

Figure 4 is a CV graph and an EIS graph of the Li-S battery of Test Example 3 of the present invention; wherein, (a) is a CV curve of a 60% Al ₂ O ₃ @SO ₃ -COF/PP battery, (b) a CV curve of a SO ₃ -COF/PP battery, (c) CV curves of different separators, and (d) EIS graphs of 60% Al ₂ O ₃ @SO ₃ -COF/PP and SO ₃ -COF/PP batteries;

Figure 5 is an electrochemical performance diagram of the Li-S battery of Test Example 3 of the present invention; wherein, (a) is the rate performance of 60% Al ₂ O ₃ @SO ₃ -COF/PP and SO ₃ -COF/PP, (b) is the cycle performance of 60% Al ₂ O ₃ @SO ₃ -COF/PP and SO ₃ -COF/PP batteries at 1C, (c) is the discharge/charge curve of 60% Al ₂ O ₃ @SO ₃ -COF/PP at various current densities of 0.1, 0.2, 0.5, 1.0 and 2.0C, and (d) is the discharge/charge curve of SO ₃ -COF/PP at various current densities of 0.1, 0.2, 0.5, 1.0 and 2.0C;

FIG6 is a schematic diagram of 500 cycles of the 60% Al ₂ O ₃ @SO ₃ -COF/PP battery of Test Example 3 of the present invention at 1C.

DETAILED DESCRIPTION

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

In the present invention, unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs.

In the present invention, unless otherwise stated, the term "and/or" used in the present invention includes any and all combinations of one or more of the relevant listed items.

In the present invention, unless otherwise stated, the experimental methods used in the embodiments of the present invention are conventional methods unless otherwise stated, and the materials, reagents, etc. used are all commercially available unless otherwise stated.

In the present invention, unless otherwise specified, the instruments and equipment used in the embodiments of the present invention and their models are Shanghai Chenhua electrochemical workstation (Chenhua CHI660E) and Blue Electric Battery Testing System (CT2001A).

Example 1

1 , the covalent organic framework/alumina composite material containing sulfonic acid groups and the preparation method thereof of the present invention specifically comprises the following steps:

Synthesis of S1, θ-Al ₂ O ₃ -CHO:

S11. Synthesis of θ-Al ₂ O ₃ : Weigh nano-Al ₂ O ₃ (8.5 g) and put it into a corundum container, then place the container in a tube furnace and heat it at 1200° C. for 2 h in a nitrogen environment. After cooling to room temperature, white solid powder θ-Al ₂ O ₃ was obtained (yield: 36%).

S12, Synthesis of θ-Al ₂ O ₃ -NH ₂ : First, θ-Al ₂ O ₃ (2 g, 19.62 mmol) was added to a flask, and then a hydrochloric acid solution was added to the flask. Gently stirred and soaked for 5 h, then filtered, the filter cake was washed three times with water, and freeze-dried to obtain active θ-Al ₂ O ₃ powder. Then, APTES (0.9829 g, 0.444 mmol) and activated θ-Al ₂ O ₃ (0.4612 g, 4.52 mmol) were weighed and put into a flask, and anhydrous toluene was used as the solvent, and heated at 100 ° C for 3 h under a nitrogen environment. After cooling to room temperature, the obtained solid was filtered, and washed three times with methanol, water and acetone, respectively, to obtain θ-Al ₂ O ₃ -NH ₂ (yield: 82%).

S13. Synthesis of θ-Al ₂ O ₃ -CHO: θ-Al ₂ O ₃ -NH ₂ (0.015 g) and 1,3,5-benzaldehyde (0.015 g, 0.0925 mmol) were weighed and placed in a polytetrafluoroethylene reactor, followed by the addition of 1,4-dioxane (15 mL), and the mixture was heated at 150° C. in a thermostat for 1 h. After cooling to room temperature, the obtained solid was washed three times with methanol, water and acetone, respectively, to obtain θ-Al ₂ O ₃ -CHO (yield: 85%).

S2. Synthesis of 60% Al ₂ O ₃ @SO ₃ -COF: 2,5-diaminobenzenesulfonic acid (Pa-SO ₃ H, 28 mg, 0.15 mmol), trialdehyde phloroglucinol (TFP, 21 mg, 0.1 mmol), θ-Al ₂ O ₃ -CHO (12.6 mg, 0.06 mmol) and acetic acid (6 M, 0.2 mL) were added to 1 mL (4:1, v/v) of a mixed solvent of mesitylene and 1,4-dioxane. After ultrasonic treatment for 10 min, the tube was quickly frozen at 77 K using a liquid nitrogen bath, degassed by three freeze-thaw-freeze cycles, vacuum sealed, and then heated at 120 °C for 72 h, separated by filtration, washed three times with anhydrous acetone, and dried at 80 °C in vacuum to obtain 60% Al ₂ O ₃ @SO ₃ -COF. The yield of the isolated red powder was 79%.

Comparative Example 1

SO ₃ -COF was synthesized by solvothermal synthesis: 2,5-diaminobenzenesulfonic acid (Pa-SO ₃ H, 28 mg, 0.15 mmol), trialdehyde phloroglucinol (TFP, 21 mg, 0.1 mmol), acetic acid (6 M, 0.2 mL) were added to 1 mL (4:1, v/v) of a mixed solvent of mesitylene and 1,4-dioxane. After ultrasonic treatment for 10 min, the mixture was rapidly frozen at 77 K using a liquid nitrogen bath, degassed by three freeze-thaw-freeze cycles, vacuum sealed, and then heated at 120 ° C for 72 h, filtered, washed with anhydrous acetone for 3 times, and dried at 80 ° C in vacuum to obtain SO ₃ -COF with a red powder isolation rate of 86%.

Test Example 1

The materials prepared in Comparative Example 1 and Example 1 were characterized, and the scanning electron microscope images are shown in Figure 2. As can be seen from Figure 2, the prepared polymer material has an irregular strip structure, which can provide a channel for the transmission of lithium ions.

Test Example 2

The materials prepared in Comparative Example 1 and Example 1 were subjected to nitrogen adsorption/desorption experiments at 77K, and their specific surface areas and porous properties were experimentally analyzed, and the results are shown in Figure 3. As can be seen from Figure 3, SO ₃ -COF and 60% Al ₂ O ₃ @SO ₃ -COF exhibit the characteristics of type IV adsorption isotherms, indicating the presence of a mesoporous structure. The BET surface areas of SO ₃ -COF and 60% Al ₂ O ₃ @SO ₃ -COF are 35 and 24.5 m ² g ^{-1 ,} respectively. The pore volumes are 0.083 and 0.044 cm ³ g ^{-1 ,} respectively. The pore size distribution (PSD) of SO ₃ -COF and 60% Al ₂ O ₃ @SO ₃ -COF was calculated using the non-local density functional theory (NLDFT) method, and was 10.38 and 6.56 nm, respectively. By comparing the above data, it is shown that SO ₃ -COF is successfully grafted onto the alumina material, and the doped alumina material may be stacked with the polymer SO ₃ -COF, thereby covering some of the original pores. Therefore, by limiting the shuttling of polysulfides, the shuttling effect of polysulfides can be better suppressed.

Test Example 3

(1) Synthesis of lithium-sulfur battery separator and assembly of CR2032 button-type half-cell:

The materials prepared in Comparative Example 1 and Example 1 were mixed with polyvinylidene fluoride (PVDF) and Super-P at a weight ratio of 7:1:2, and then the mixture was ground in a mortar for 30 minutes. An appropriate amount of N-methylpyrrolidone (NMP) was added to grind into slurry, and the ground slurry was scraped onto the Celgard-2400 film using a four-sided sample preparation device. Drying was carried out in a vacuum drying oven at 60°C for 12 hours to obtain a 60% Al ₂ O ₃ @SO ₃ -COF composite modified membrane.

Assembly of CR2032 button cell: The battery was assembled in a Lab2000 glove box, the atmosphere in the glove box was high-purity argon, and the assembly order from bottom to top was the negative electrode shell, shrapnel, gasket, metal lithium sheet (negative electrode), diaphragm, positive electrode sheet and positive electrode shell. 40 μL of 1 mol L ^-1 LiTFSI and 1 wt% LiNO ₃ additive dimethyl ether and DOL (1:1, v:v) were used as electrolytes, 40 μL was added each time to fully wet the diaphragm, and finally the button cell was sealed with a special sealing machine under insulator conditions, and the sealed button cell was left to stand for 12 hours.

(2) The cyclic voltammetry and electrochemical impedance of the Li-S battery were measured at 0.1 mV s ^-1 in the voltage range of 1.7 V-2.8 V on a Shanghai Chenhua electrochemical workstation (Chenhua CHI660E ₎ . The results are shown in Figure 4. As can be seen from Figure 4, the CV curve of 60% _Al2O3 @ _SO3 -COF/PP exhibits two obvious reduction peaks and two oxidation peaks. In the cathodic scan, the two reduction peaks are at about 2.02 V and 2.31 V, respectively, corresponding to the conversion of elemental sulfur to _Li2Sn (n=4-8) and the further reduction of long-chain lithium _polysulfides to solid _Li2S2 / _Li2S . In the subsequent _cathodic scan, the two oxidation peaks near 2.35 and 2.43 V are related to the conversion of solid _Li2S2 / _Li2S to long-chain lithium polysulfides and finally to elemental sulfur. The good overlap of these CV curves demonstrates the stability and good reversibility of the battery (Figure 4(a)). Compared with the SO _{3 -COF} / PP battery, the CV curve of _the 60% Al ₂ O ₃ @SO ₃ -COF / PP battery shows a trend of rightward shift of the reduction peak and leftward shift of the oxidation peak (Figure 4 (b)). In addition, the polarization voltage of the 60% Al ₂ O _{3 @SO 3} -COF / PP battery is 0.289V, which is lower than the polarization voltage of the SO ₃ -COF / PP battery of 0.416V (Figure 4 (c)). From the electrochemical impedance spectroscopy (EIS) of the two batteries, it can be seen that compared with the AC impedance of the SO ₃ -COF / PP battery, the semicircle corresponding to the charge transfer resistance Rct (~37Ω) of the 60% Al ₂ O ₃ @SO ₃ -COF / P battery is significantly smaller (Figure 4 (d)). This indicates that the separator using 60% Al ₂ O ₃ @SO ₃ -COF has a lower charge transfer resistance, indicating that the alumina substrate is conductive and can reduce the resistance of the battery.

(3) The cycle stability at 1C and the rate performance of Li-S batteries at different current densities were measured using the Blue Power Battery Test System (CT2001A). The results are shown in Figures 5-6.

As can be seen from Figure 5, the initial discharge capacity of the separator with 60% Al ₂ O ₃ @SO ₃ -COF at 0.05C is 1403.4 mAh g ^-1 , while the initial capacity of the separator with SO ₃ -COF at 0.05C is 1201.7 mAh g ^-1 . At different current densities, the discharge capacity of the 60% Al ₂ O ₃ @SO ₃ -COF/PP battery is 1254.4 (0.1C), 1140.6 (0.2C), 1041.4 (0.5C), 985.8 (1C) and 807 mAh g ^-1 (2C). When it returns to 0.1C, the discharge capacity of 926.1 mAh g ^-1 is restored, indicating fast reaction kinetics and high reversibility. Moreover, the discharge capacity of the Li-S battery with 60% Al ₂ O ₃ @SO ₃ -COF/PP is significantly greater than that of the Li-S battery with SO ₃ -COF/PP, by 1171.7 (0.1C), 998.9 (0.2C), 929.5 (0.5C), 795.8 (1C) and 702.9 mAh g ^-1 (2C). This result indicates that the battery equipped with 60% Al ₂ O ₃ @SO ₃ -COF separator has a strong ability to resist large current shock (Figure 5 (a)). The cycling performance of the two batteries at a current density of 1C for 200 cycles, after the electrodes were pre-activated for 2 cycles at a current density of 0.05C. The 60% Al ₂ O ₃ @SO ₃ -COF/PP battery provided an initial discharge capacity of 998.9 mAh g ^-1 in the first cycle at 1C, and after 200 cycles, the battery provided a capacity of 899.34 mAh g ^-1 , with excellent stability. However, the initial discharge capacity of SO ₃ -COF/PP battery at 1C is 777.2 mAh g ^-1 , showing a lower initial discharge capacity. This difference indicates that the sulfonated covalent organic framework containing θ-Al ₂ O ₃ -CHO can adsorb polysulfides through synergistic effects and inhibit the shuttle effect of polysulfides, thereby improving the electrochemical performance of lithium-sulfur batteries (Figure 5(b)). The constant current charge and discharge curves of 60% Al ₂ O ₃ @SO ₃ -COF/PP and SO ₃ -COF/PP batteries show that as the current density increases from 0.1C to 2C, although the polarization rate gradually increases with the current gradient, the two typical charge and discharge platforms of the sulfur positive electrode can still be clearly seen (Figures 5(c), 5(d)).

As can be seen from Figure 6, after 500 cycles at 1C, the 60% _Al2O3 @ _SO3 -COF/PP battery exhibits a high capacity of _672.14mAh g ^-1 and good cycle stability, with a capacity decay of 0.072% per cycle. The improvement in cycle performance is mainly attributed to the presence of θ- _Al2O3 - _CHO . Since alumina has good conductivity, it can provide strong chemical adsorption and good conductivity for lithium polysulfide, thereby effectively inhibiting the shuttle effect of lithium polysulfide and improving the cycle performance of the battery.

Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims (5)

1. A method for preparing a covalent organic framework/alumina composite material containing sulfonic acid groups, characterized in that it comprises the following steps: S1. After calcining alumina, modifying it with an aminating agent and a hydroformylating agent to obtain θ -Al ₂ O ₃ -CHO; the calcination is carried out under a protective atmosphere at 1100°C-1200°C for 2 h-3 h to obtain θ -Al ₂ O ₃ ; the aminating agent is selected from (3-aminopropyl)triethoxysilane; the hydroformylating agent is selected from trimesaldehyde; S2. Dissolve 2,5-diaminobenzenesulfonic acid, trialdehyde phloroglucinol, acetic acid and the θ -Al ₂ O ₃ -CHO described in S1 in a solvent, degas the solution by multiple freeze-thaw-freeze cycles, and then heat the solution to obtain the covalent organic framework/alumina composite material containing sulfonic acid groups; the molar ratio of the 2,5-diaminobenzenesulfonic acid, trialdehyde phloroglucinol and θ -Al ₂ O ₃ -CHO is 15-17:10-12:6; the temperature of the heating reaction is 115°C-120°C, and the heating reaction time is 72 h-120 h. 2. The method for preparing a covalent organic framework/alumina composite material containing sulfonic acid groups according to claim 1, characterized in that the protective atmosphere is a nitrogen atmosphere. 3. The method for preparing a covalent organic framework/alumina composite material containing sulfonic acid groups according to claim 1, characterized in that in S2, the solvent is selected from one or more of ethanol, o-dichlorobenzene, n-butanol and dioxane. 4. A covalent organic framework/alumina composite material containing sulfonic acid groups prepared by the method according to any one of claims 1 to 3. 5. Use of the covalent organic framework/alumina composite material containing sulfonic acid groups as claimed in claim 4 in a lithium-sulfur battery.