Method for preparing lithium-sulfur battery based on hydroxyl aminated covalent organic framework separator

Abstract

The application discloses a lithium-sulfur battery preparation method based on a hydroxyl aminated covalent organic framework diaphragm. First, a hydroxyl aminated covalent organic framework material is synthesized by using an in-situ method, and then the material is prepared into a slurry with conductive carbon black at a certain proportion. Then, a vacuum filtration method is used to form an in-situ covalent organic framework material lithium-sulfur battery modified diaphragm on a commercial diaphragm. After the modified diaphragm is dried, the diaphragm is cut and assembled with a sulfur composite positive electrode material, a negative electrode material and a lithium sheet to form a lithium-sulfur battery. As a result, a lithium-sulfur battery with good thermodynamic stability, small impedance and good cycle performance is obtained. In the above material, the intermolecular force and chemical bond can inhibit the shuttle of polysulfides, relieve the volume expansion and accelerate the lithium ion transmission. Therefore, the battery assembled by the hydroxyl aminated covalent organic framework material has a rated capacity of 1059 mAh g ‑1 at 0.5 C, a coulombic efficiency close to 100% and good cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery material technology, specifically relating to a method for preparing lithium-sulfur batteries based on hydroxyl-amined covalent organic framework membranes. Background Technology

[0002] Lithium-sulfur batteries, as next-generation rechargeable batteries, consist of three parts: a sulfur cathode, a separator, and a lithium anode. The sulfur cathode boasts a theoretical specific capacity 8-10 times higher than currently commercially available cathode materials. Despite this high energy density and theoretical capacity, experiments have revealed poor cycle stability in lithium-sulfur batteries, failing to reach an ideal capacity state. This is likely due to the inherent insulating properties of sulfur, leading to slow reaction kinetics and low actual capacity utilization. Secondly, the generation of intermediate products (polysulfides) results in a significant "shuttle effect" within the battery, with soluble sulfur shuttling between the positive and negative electrodes, severely deteriorating the reaction interface. Furthermore, severe volume changes (80%) cause a decline in the mechanical properties of the sulfur cathode. Currently, numerous modification schemes have been developed for cathode materials, significantly improving the performance of lithium-sulfur battery cathodes.

[0003] However, the separator layer in lithium-sulfur batteries also plays a crucial role, ensuring electrical isolation between the positive and negative electrodes, preventing short circuits, and enabling ion transport within its internal channels. Existing commercial separators, due to their large pores, hydrophobic surfaces, and extremely poor conductivity, are unsuitable for long-cycle lithium-sulfur batteries, severely degrading battery performance. Therefore, extensive research and experimentation are needed on modifying separators for lithium-sulfur batteries to improve cycle stability, ion conduction, and polysulfide suppression. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing lithium-sulfur batteries based on hydroxyl-amined covalent organic framework membranes, which solves the problem of poor conductivity of existing lithium-sulfur battery membranes.

[0005] The technical solution adopted in this invention is a method for preparing lithium-sulfur batteries based on hydroxyl-amined covalent organic framework membranes. This method includes synthesizing hydroxyl-amined covalent organic framework materials, blending them with conductive carbon black to prepare a slurry, vacuum filtering the slurry onto a membrane to obtain a modified membrane, and finally assembling the modified membrane with a composite sulfur cathode and a lithium anode to create a lithium-sulfur battery. The specific operation steps are as follows:

[0006] Step 1: Add 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tricarboxymethylresorcinol, and polyvinylidene fluoride sequentially to a Piezx tube, followed by a mixed solution of o-dichlorobenzene, n-butanol, and acetic acid. After sonication, repeatedly freeze and thaw the tube in liquid nitrogen, then degas and seal it. After cooling to room temperature, filter to separate the solids and wash with acetone to obtain a filter cake. After drying the filter cake, wash it with tetrahydrofuran, acetone, and methanol respectively, and then dry it to obtain covalent organic framework material A.

[0007] Step 2: Grind the covalent organic framework material A obtained in Step 1 and conductive carbon black in a mortar, then add N-methylpyrrolidone and stir until a homogeneous slurry B is formed;

[0008] Step 3: After cutting the diaphragm, fix it on the vacuum filtration device. Use a pipette to drop the slurry B obtained in step 2 onto the surface of the diaphragm. Then, draw a vacuum and transfer the modified diaphragm to a vacuum drying oven to dry. After drying, a uniform modified diaphragm C is obtained.

[0009] Step 4: Take out the modified separator C obtained in Step 3, and cut the separator C into round pieces using a tablet press to obtain the modified battery separator D;

[0010] Step 5: Separate the modified battery separator D obtained in step 4 into sealed bags, put them into a vacuum drying oven, and dry them to obtain the covalent organic framework material lithium-sulfur battery separator E.

[0011] Step 6: Assemble the battery separator E obtained in Step 5, the sulfur positive electrode sheet, and the lithium negative electrode material into a lithium-sulfur battery, and test its performance.

[0012] The invention is further characterized by:

[0013] In step 1, the mass ratio of 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tricarboxymethyl phloroglucinol and polyvinylidene fluoride is 20-22:10-13:8-35.

[0014] In step 1, the volume ratio of o-dichlorobenzene, n-butanol, and acetic acid is 5.5:5.5:1.

[0015] In step 1, the ultrasonic time shall be no less than 10 minutes; the liquid nitrogen freezing and thawing shall be repeated no less than 3 times.

[0016] Step 2: The mass ratio of covalent organic framework material A to conductive carbon black is 4:1. The grinding time is at least 30 minutes and the stirring time is at least 24 hours.

[0017] In step 3, the temperature of the vacuum drying oven is 50℃~70℃, and the drying time is 2h~5h.

[0018] The diaphragm model in step 3 is Celgard 2400 diaphragm.

[0019] In step 4, the diameter of the disc is 17mm-19mm.

[0020] In step 5, the temperature range of the vacuum drying oven is 50℃~70℃, and the drying time is 9h~12h.

[0021] The preparation method of the sulfur positive electrode sheet in step 6 is as follows: sulfur and carbon nanotubes are mixed at a mass ratio of 3:1, ground in a mortar for at least 3 hours, and then placed in a reaction vessel. The mixture is then placed in an oven at 155°C for 12 hours. After the reaction vessel is completely cooled to room temperature, the sulfur composite positive electrode material loaded with carbon nanotubes is obtained. The sulfur composite positive electrode material, conductive carbon black and binder are ground for at least 30 minutes, and then 2-methylpyrrolidone is added and stirred for more than 2 days to obtain the sulfur positive electrode sheet.

[0022] The mass ratio of sulfur composite cathode material, conductive carbon black, and binder is any one of 7:2:1, 15:3:2, and 8:1:1.

[0023] The beneficial effects of this invention are:

[0024] (1) By introducing 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tricarboxymethyl phloroglucinol and polyvinylidene fluoride (PVDF), a covalent organic framework material A was synthesized in situ. Due to the intermolecular forces and chemical bonds, lithium ions are rapidly transported within the covalent organic framework channels, and the shuttle of polysulfides is suppressed, thereby improving the cycle stability of lithium-sulfur batteries.

[0025] (2) The slurry prepared by covalent organic framework material A was filtered onto the surface of Celgard2400 membrane by vacuum filtration to construct a modified membrane for lithium-sulfur batteries using covalent organic framework material. The modified membrane with adhesive properties was prepared by a simple method, so the modified membrane has a certain elastic modulus and can greatly alleviate the change in volume. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the method for preparing a covalent organic framework membrane based on hydroxyl-amined hydrogel in this invention;

[0027] Figure 2 This is an X-ray diffraction pattern of the covalent organic framework material and the in-situ covalent organic framework material and PVDF of the present invention;

[0028] Figure 3 This is a graph showing the relationship between current density and potential (CV) of the lithium-sulfur battery (COF-LSBs) of the present invention;

[0029] Figure 4This is the electrochemical impedance spectroscopy (EIS) diagram of the lithium-sulfur battery of the present invention;

[0030] Figure 5 This is a rate performance diagram of the lithium-sulfur battery of the present invention at different currents.

[0031] Figure 6 This is a graph showing the relationship between efficiency and specific capacity of the lithium-sulfur battery of the present invention after 200 cycles at a rated capacitance of 2C. Detailed Implementation

[0032] The present invention provides a method for preparing a lithium-sulfur battery based on a hydroxyl-aminated covalent organic framework membrane, which includes the synthesis of an in-situ polymer of hydroxyl-aminated covalent organic framework PVDF, followed by blending with conductive carbon black (Super P) to prepare a slurry, which is then filtered onto a Celgard 2400 membrane to obtain a modified membrane. Finally, the modified membrane is assembled with a composite sulfur cathode and a lithium anode to form a lithium-sulfur battery.

[0033] The present invention will be further described below with reference to specific embodiments.

[0034] Example 1:

[0035] This invention relates to a method for preparing lithium-sulfur batteries based on hydroxylated amino-covalent organic framework membranes, the process of which is as follows: Figure 1 As shown, the specific operation steps are as follows:

[0036] In step 1, 1,3,5-tris(4-aminophenyl)benzene (22 mg, 0.15 mmol), 2,4,6-tricarboxymethyl phloroglucinol (13 mg, 0.05 mmol), and PVDF (35 mg) were added to a Pyrex tube. Then, a mixed solution of o-dichlorobenzene (5.5 mL), n-butanol (5.5 mL), and acetic acid (1 mL) was added. After sonication for 10 min, the mixture was thawed by three cycles of liquid nitrogen freezing. After degassing and sealing, the mixture was reacted at 100 °C for 72 h. After cooling to room temperature, the solid was separated by filtration and washed three times with acetone. The filter cake was dried to obtain a grayish-purple powder compound, which was then washed with tetrahydrofuran, acetone, and methanol, respectively, and dried at 80 °C for one day to obtain grayish-purple powder A.

[0037] Step 2: Mix the grayish-purple powder A obtained in Step 1 with conductive carbon black (mass ratio of 4:1) in a mortar and grind vigorously. After grinding for a period of time, put it into a small bottle, add 20 ml of N-methylpyrrolidone to the small bottle and stir. Stir for at least one day until a uniform black slurry B is formed.

[0038] Step 3: After cutting the PP diaphragm into a certain size, fix it on the vacuum filtration device, use a pipette to transfer 2ml of the black slurry B obtained in step 2 onto the diaphragm surface and draw a vacuum, transfer the filtered modified diaphragm to a vacuum drying oven to dry, and obtain a uniform modified diaphragm C.

[0039] Step 4: Take out the modified separator C obtained in Step 3, and cut the separator C into round pieces with a size of 19mm using a tablet press to obtain the modified battery separator D.

[0040] Step 5: Separate the modified battery separator D obtained in step 4 into sealed bags, and place them in a vacuum drying oven at 60°C for 12 hours to obtain the covalent organic framework material lithium-sulfur battery separator E.

[0041] In step 6, the sulfur composite cathode material is prepared by mixing sulfur and carbon nanotubes at a mass ratio of 3:1 and grinding them in a mortar for at least 3 hours. Then, the mixture is placed in a reaction vessel and reacted in an oven at 155°C for 12 hours. After the reaction vessel has completely cooled, the obtained sulfur composite cathode material is ground with conductive carbon black and binder (PVDF) at a mass ratio of 7:2:1 for 30 minutes. Then, 2-methylpyrrolidone is added and the mixture is stirred for more than 3 days to obtain a sulfur cathode sheet. This sheet is then assembled with a modified separator and a lithium anode sheet to form a lithium-sulfur battery, and the performance of the lithium-sulfur battery is tested.

[0042] Example 2:

[0043] Step 1: Add benzidine (22 mg, 0.15 mmol), 2,4,6-tricarboxymethyl phloroglucinol (13 mg, 0.05 mmol), and PVDF (35 mg) to a Piezx tube. Then add a mixed solution of o-dichlorobenzene (5.5 mL), n-butanol (5.5 mL), and acetic acid (1 mL). After sonication for 20 min, thaw the mixture three times by liquid nitrogen freezing. After degassing and sealing, react at 100 °C for 72 h. After cooling to room temperature, separate the solid by filtration and wash it three times with acetone. Dry the filter cake to obtain a grayish-purple powder compound. Wash it with tetrahydrofuran, acetone, and methanol respectively, and dry it at 80 °C for one day to obtain grayish-purple powder A.

[0044] Step 2: Mix the grayish-purple powder A obtained in Step 1 with Ketjen black (mass ratio of 4:1) in a mortar and grind vigorously. After grinding for a period of time, put it into a small bottle, add 20 mL of N-methylpyrrolidone to the small bottle and stir. Stir for at least one day until a uniform black slurry B is formed.

[0045] Step 3: After cutting the PP diaphragm into a certain size, fix it on the vacuum filtration device, use a pipette to transfer 2.5 mL of the black slurry B obtained in step 2 onto the diaphragm surface and draw a vacuum, transfer the filtered modified diaphragm to a vacuum drying oven to dry, and obtain a uniform modified diaphragm C.

[0046] Step 4: Take out the modified separator C obtained in Step 3, and cut the separator C into round pieces with a size of 17mm using a tablet press to obtain the modified battery separator D.

[0047] Step 5: Separate the modified battery separator D obtained in step 4 into sealed bags, and place them in a vacuum drying oven at 60°C for 10 hours to obtain the in-situ covalent organic framework material lithium-sulfur battery separator E.

[0048] Step 6: Assemble the battery separator E, sulfur positive electrode sheet and lithium negative electrode material obtained in Step 5 into a lithium-sulfur battery and test its performance.

[0049] The preparation method of the sulfur positive electrode sheet in step 6 is as follows: sulfur and carbon nanotubes are mixed at a mass ratio of 3:1 and ground in a mortar for at least 3 hours. Then, the mixture is placed in a reaction vessel and placed in an oven at 155°C for 12 hours. After the reaction vessel has completely cooled down, the obtained sulfur composite positive electrode material is ground with conductive carbon black and binder (PVDF) at a mass ratio of 7:2:1 for 30 minutes. Then, 2-methylpyrrolidone is added and stirred for more than 3 days to obtain the sulfur positive electrode sheet. The sulfur positive electrode sheet is then assembled with a modified separator and a negative lithium sheet to form a lithium-sulfur battery, and the performance of the lithium-sulfur battery is tested.

[0050] Example 3:

[0051] In step 1, 1,3,5-tris(4-aminophenyl)benzene (20 mg, 0.15 mmol), 2,4,6-tricarboxymethyl phloroglucinol (10 mg, 0.05 mmol), and PVDF (20 mg) were added to a Pyrex tube. Then, a mixed solution of o-dichlorobenzene (5.5 mL), n-butanol (5.5 mL), and acetic acid (1 mL) was added. After sonication for 30 min, the mixture was thawed by three cycles of liquid nitrogen freezing. After degassing and sealing, the mixture was reacted at 100 °C for 84 h. After cooling to room temperature, the solid was separated by filtration and washed three times with acetone. The filter cake was dried to obtain a grayish-purple powder compound, which was then washed with tetrahydrofuran, acetone, and methanol, respectively, and dried at 90 °C for one day to obtain grayish-purple powder A.

[0052] Step 2: Mix the grayish-purple powder A obtained in Step 1 with conductive carbon black (mass ratio of 7:1) in a mortar and grind vigorously. After grinding for a period of time, put it into a small bottle, add 15 mL of N-methylpyrrolidone to the small bottle and stir. Stir for at least one day until a uniform black slurry B is formed.

[0053] Step 3: After cutting the PP diaphragm into a certain size, fix it on the vacuum filtration device, use a pipette to transfer 1.5 mL of the black slurry B obtained in step 2 onto the diaphragm surface and draw a vacuum, transfer the filtered modified diaphragm to a vacuum drying oven to dry, and obtain a uniform modified diaphragm C.

[0054] Step 4: Take out the modified separator C obtained in Step 3, and cut the separator C into round pieces with a size of 19mm using a tablet press to obtain the modified battery separator D.

[0055] Step 5: Separate the modified battery separator D obtained in Step 4 into sealed bags, and place them in a vacuum drying oven at 65°C for 12 hours to obtain the covalent organic framework material lithium-sulfur battery separator E.

[0056] Step 6: Assemble the battery separator E, sulfur positive electrode sheet and lithium negative electrode material obtained in Step 5 into a lithium-sulfur battery and test its performance.

[0057] The preparation method of the sulfur positive electrode sheet in step 6 is as follows: sulfur and carbon nanotubes are mixed at a mass ratio of 3:1 and ground in a mortar for at least 3 hours. Then, the mixture is placed in a reaction vessel and placed in an oven at 155°C for 12 hours. After the reaction vessel has completely cooled down, the obtained sulfur composite positive electrode material is ground with conductive carbon black and binder (PVDF) at a mass ratio of 15:3:2 for 30 minutes. Then, 2-methylpyrrolidone is added and stirred for more than 3 days to obtain the sulfur positive electrode sheet. The sulfur positive electrode sheet is then assembled with a modified separator and a negative lithium sheet to form a lithium-sulfur battery, and the performance of the lithium-sulfur battery is tested.

[0058] Example 4:

[0059] In step 1, 2,5-diaminobenzene (22 mg, 0.15 mmol), 2,4,6-tricarboxymethyl phloroglucinol (13 mg, 0.05 mmol), and PVDF (8 mg) were added to a Pyrex tube. Then, a mixed solution of o-dichlorobenzene (5 mL), n-butanol (5 mL), and acetic acid (1 mL) was added. After sonication for 20 min, the mixture was thawed by three cycles of liquid nitrogen freezing. After degassing and sealing, the mixture was reacted at 100 °C for 60 h. After cooling to room temperature, the solid was separated by filtration and washed three times with acetone. The filter cake was dried to obtain a grayish-purple powder compound, which was then washed with tetrahydrofuran, acetone, and methanol, respectively, and dried at 80 °C for one day to obtain grayish-purple powder A.

[0060] Step 2: Mix the grayish-purple powder A obtained in Step 1 with conductive carbon black (mass ratio of 9:1) in a mortar and grind vigorously. After grinding for a period of time, put it into a small bottle, add 30 mL of N-methylpyrrolidone to the small bottle and stir. Stir for at least one day until a uniform black slurry B is formed.

[0061] Step 3: After cutting the PP diaphragm into a certain size, fix it on the vacuum filtration device, use a pipette to transfer 2.5 mL of the black slurry B obtained in step 2 onto the diaphragm surface and draw a vacuum, transfer the filtered modified diaphragm to a vacuum drying oven to dry, and obtain a uniform modified diaphragm C.

[0062] Step 4: Take out the modified separator C obtained in Step 3, and cut the separator C into round pieces with a size of 19mm using a tablet press to obtain the modified battery separator D.

[0063] Step 5: Separate the modified battery separator D obtained in step 4 into sealed bags, and place them in a vacuum drying oven at 50°C for 12 hours to obtain the covalent organic framework material lithium-sulfur battery separator E.

[0064] Step 6: Assemble the battery separator E, sulfur positive electrode sheet and lithium negative electrode material obtained in Step 5 into a lithium-sulfur battery and test its performance.

[0065] The preparation method of the sulfur positive electrode sheet in step 6 is as follows: sulfur and carbon nanotubes are mixed at a mass ratio of 3:1 and ground in a mortar for at least 3 hours. Then, the mixture is placed in a reaction vessel and placed in an oven at 155°C for 12 hours. After the reaction vessel has completely cooled down, the obtained sulfur composite positive electrode material is ground with conductive carbon black and binder (PVDF) at a mass ratio of 8:1:1 for 30 minutes. Then, 2-methylpyrrolidone is added and stirred for more than 3 days to obtain the sulfur positive electrode sheet. The sulfur positive electrode sheet is then assembled with a modified separator and a negative lithium sheet to form a lithium-sulfur battery, and the performance of the lithium-sulfur battery is tested.

[0066] Example 5:

[0067] In step 1, 1,3,5-tris(4-aminophenyl)benzene (22 mg, 0.15 mmol), 2,4,6-tricarboxymethyl phloroglucinol (13 mg, 0.05 mmol), and PVDF (11 mg) were added to a Pyrex tube. Then, a mixed solution of o-dichlorobenzene (5 mL), n-butanol (5 mL), and acetic acid (1 mL) was added. After sonication for 10 min, the mixture was thawed by three cycles of liquid nitrogen freezing. After degassing and sealing, the mixture was reacted at 100 °C for 60 h. After cooling to room temperature, the solid was separated by filtration and washed three times with acetone. The filter cake was dried to obtain a grayish-purple powder compound, which was then washed with tetrahydrofuran, acetone, and methanol, respectively, and dried at 80 °C for one day to obtain grayish-purple powder A.

[0068] Step 2: Mix the grayish-purple powder A obtained in Step 1 with conductive carbon black (mass ratio of 3:1) in a mortar and grind vigorously. After grinding for a period of time, put it into a small bottle, add 30 mL of N-methylpyrrolidone to the small bottle and stir. Stir for at least one day until a uniform black slurry B is formed.

[0069] Step 3: After cutting the PP diaphragm into a certain size, fix it on the vacuum filtration device, use a pipette to transfer 2.5 mL of the black slurry B obtained in step 2 onto the diaphragm surface and draw a vacuum, transfer the filtered modified diaphragm to a vacuum drying oven to dry, and obtain a uniform modified diaphragm C.

[0070] Step 4: Take out the modified separator C obtained in Step 3, and cut the separator C into round pieces with a size of 18mm using a tablet press to obtain the modified battery separator D.

[0071] Step 5: Separate the modified battery separator D obtained in step 4 into sealed bags, and place them in a vacuum drying oven at 60°C for 12 hours to obtain the covalent organic framework material lithium-sulfur battery separator E.

[0072] Step 6: Assemble the battery separator E, sulfur positive electrode sheet and lithium negative electrode material obtained in Step 5 into a lithium-sulfur battery and test its performance.

[0073] Step 6: Cut the sulfur positive electrode sheet into square sheets of 2.5cm×2.5cm, and assemble them with the modified separator cut into sheets of 2.7cm×2.7cm and the negative lithium sheet cut into sheets of 2.5cm×2.5cm in an argon-filled glove box to form a lithium-sulfur pouch battery. The sulfur positive electrode is connected to an Al electrode, the negative electrode is connected to a Ni electrode, and the modified separator is in the middle. The electrolyte volume is 200 microliters. The performance of the lithium-sulfur pouch battery is tested on the blue electric channel.

[0074] like Figure 2 The image shows the X-ray diffraction patterns of a covalent organic framework (COF), an in-situ covalent organic framework (COF@PVDF), and PVDF. Crystal peaks of the three materials are clearly visible in the XRD patterns, confirming the successful preparation of the in-situ covalent organic framework (COF@PVDF).

[0075] like Figure 3 As shown, a lithium-sulfur battery (COF-LSB) is assembled using an in-situ covalent organic framework material (COF@PVDF) lithium-sulfur battery separator at a scan rate of 0.5 mV / s. S The current density versus potential (CV curve) curve shows an oxidation peak at the top and two reduction peaks at the bottom, indicating a reaction process from S8 to Li2S. This reveals the rapid redox reaction of sulfur during the charging and discharging process, demonstrating the material's good electrochemical activity.

[0076] like Figure 4 The image shows a lithium-sulfur battery (COF-LSB) assembled using the in-situ covalent organic framework material (COF@PVDF) lithium-sulfur battery separator of this invention. SThe electrochemical impedance spectroscopy (EIS) of a material is used to measure its charge transfer resistance and impedance. The arcs in the high-frequency region and the sloping lines in the low-frequency region of the EIS curve illustrate this. EIS curves are commonly used to evaluate the electrochemical resistance and capacitance performance. The radius of the arc in the impedance spectrum represents the interfacial resistance between the electrolyte and the electrode. Visually, a larger arc in the impedance graph indicates a greater impedance and poorer electrochemical performance of the battery. Figure 4 The small radius of curvature indicates that the battery has low electrochemical impedance.

[0077] like Figure 5 The image shows a lithium-sulfur battery (COF-LSB) assembled using the in-situ covalent organic framework material (COF@PVDF) lithium-sulfur battery separator of this invention. S The rate of change is used to determine the specific capacity of the lithium-sulfur battery at different currents. A rate curve can be used to obtain the specific capacity of the lithium-sulfur battery at different currents. For current lithium-sulfur batteries, this lithium-sulfur battery (COF-LSB)... S It exhibits higher specific capacity at rate performances of 0.5C, 1C, 2C, 3C, and 5C, with specific capacities of 1060 mAh·g. -1 936.5mAh·g -1 797.7mAh·g -1 728mAh·g -1 628.9mAh·g -1 .

[0078] like Figure 6 The image shows a lithium-sulfur battery (COF-LSB) assembled using the in-situ covalent organic framework material (COF@PVDF) lithium-sulfur battery separator of this invention. S The specific capacity long-cycle plot evaluates the change in specific capacity and the retention of coulombic efficiency of a battery after multiple charge-discharge cycles. Coulombic efficiency refers to the ratio of charge-discharge capacity to total capacity in the same cycle. Theoretically, the closer the charge-discharge capacity is to 100%, the better the electrochemical performance of the battery. The figure shows that this battery maintained a specific capacity of 660 mAh / g after 200 cycles at a 2C capacitor, and the coulombic efficiency remained close to 100% throughout the cycle.

[0079] The synthesis principle of the key steps in this invention:

[0080] (I) Covalent Organic Framework Material A: A type of covalent organic framework material A formed by covalent bonds, characterized by high orientation, high density, variable pore size, and high thermodynamic stability. Because covalent organic framework material A contains hydroxyl and amino groups, while polyvinylidene fluoride (PVDF) contains CF bonds, intermolecular forces and chemical bonds are formed between the hydroxyl and amino groups in covalent organic framework material A, enabling rapid lithium-ion conduction within the covalent organic framework channels.

[0081] (ii) Since polyvinylidene fluoride acts as a binder, the use of vacuum filtration will allow the covalent organic framework material A to be uniformly and firmly distributed on the modified separator. This will have a good inhibitory effect on the polysulfides generated in the battery, and will also inhibit the formation of lithium dendrites.

[0082] (III) Celgard 2400 membrane was chosen as the substrate for lithium-sulfur battery membrane because of its porosity, which allows the modified material to be uniformly attached to the membrane surface. In addition, Celgard 2400 membrane is easy to process and has a high cost performance.

Claims

1. A method for the preparation of lithium-sulphur batteries based on hydroxyl aminated covalent organic framework separator membranes, characterized in that, The process includes the synthesis of hydroxylated amino-covalent organic framework materials, their blending with conductive carbon black to prepare a slurry, the vacuum filtration of the slurry onto a separator to obtain a modified separator, and finally the assembly of the modified separator with a composite sulfur cathode and a lithium anode to create a lithium-sulfur battery. The specific steps are as follows: Step 1: Add 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tricarboxymethylresorcinol, and polyvinylidene fluoride sequentially to a Piez tube; then add a mixed solution of o-dichlorobenzene, n-butanol, and acetic acid sequentially. After sonication, repeatedly freeze and thaw in liquid nitrogen, then degas, seal, cool to room temperature, filter to separate the solid, and wash with acetone to obtain a filter cake; after drying the filter cake, wash it with tetrahydrofuran, acetone, and methanol respectively, and dry it to obtain covalent organic framework material A; Step 2: Grind the covalent organic framework material A obtained in Step 1 and conductive carbon black in a mortar, then add N-methylpyrrolidone and stir until a homogeneous slurry B is formed; Step 3: After cutting the diaphragm, fix it on the vacuum filtration device. Use a pipette to drop the slurry B obtained in step 2 onto the surface of the diaphragm. Then, draw a vacuum and transfer the modified diaphragm to a vacuum drying oven to dry. After drying, a uniform modified diaphragm C is obtained. Step 4: Take out the modified separator C obtained in Step 3, and cut the separator C into round pieces using a tablet press to obtain the modified battery separator D; Step 5: Separate the modified battery separator D obtained in step 4 into sealed bags, put them into a vacuum drying oven, and dry them to obtain the covalent organic framework material lithium-sulfur battery separator E. Step 6: Assemble the battery separator E, sulfur positive electrode sheet and lithium negative electrode material obtained in Step 5 into a lithium-sulfur battery and test its performance.

2. The method for preparing a lithium-sulfur battery based on a hydroxylated amination covalent organic framework membrane according to claim 1, characterized in that, In step 1, the mass ratio of 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tricarboxymethyl phloroglucinol, and polyvinylidene fluoride is 20~22:10~13:8~35; the volume ratio of o-dichlorobenzene, n-butanol, and acetic acid in the mixed solution is 5.5:5.5:1; the ultrasonic time is not less than 10 min; and the liquid nitrogen freezing and thawing is not less than 3 times.

3. The method for preparing a lithium-sulfur battery based on a hydroxyl-amined covalent organic framework membrane according to claim 1, characterized in that, The mass ratio of covalent organic framework material A to conductive carbon black in step 2 is 4:1, the grinding time is at least 30 minutes, and the stirring time is at least 24 hours.

4. The method for preparing a lithium-sulfur battery based on a hydroxylated amination covalent organic framework membrane according to claim 1, characterized in that, In step 3, the vacuum drying temperature is 50℃~70℃, and the drying time does not exceed 3 hours.

5. The method for preparing a lithium-sulfur battery based on a hydroxyl-amined covalent organic framework membrane according to claim 1, characterized in that, The diaphragm mentioned in step 3 is a Celgard 2400 diaphragm.

6. The method for preparing a lithium-sulfur battery based on a hydroxyl-amined covalent organic framework membrane according to claim 1, characterized in that, In step 4, the diameter of the disc is 17 mm - 19 mm.

7. The method for preparing a lithium-sulfur battery based on a hydroxyl-amined covalent organic framework membrane according to claim 1, characterized in that, The vacuum drying temperature in step 5 is 50℃~70℃, and the drying time is 9 h~12 h.

8. The method for preparing a lithium-sulfur battery based on a hydroxylated amination covalent organic framework membrane according to claim 1, characterized in that, The preparation method of the sulfur positive electrode sheet in step 6 is as follows: sulfur and carbon nanotubes are mixed at a mass ratio of 3:1, ground in a mortar for at least 3 hours, and then placed in a reaction vessel. The mixture is then placed in an oven at 155°C for 12 hours. After the reaction vessel is completely cooled to room temperature, the sulfur composite positive electrode material loaded with carbon nanotubes is obtained. The sulfur composite positive electrode material, conductive carbon black and binder are ground for at least 30 minutes, and then 2-methylpyrrolidone is added and stirred for more than 2 days to obtain the sulfur positive electrode sheet.

9. The method for preparing a lithium-sulfur battery based on a hydroxylated amination covalent organic framework membrane according to claim 8, characterized in that, The mass ratio of the sulfur composite cathode material, conductive carbon black, and binder is any one of 7:2:1, 15:3:2, and 8:1:1.

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