CN111313111A - A metal-organic framework-derived heteroatom-doped carbon/CoS functional material and its applications - Google Patents

Abstract

The invention discloses a metal-organic framework-derived heteroatom- _doped carbon/CoS2 functional material and an application thereof, wherein the heteroatom- _doped carbon/CoS2 functional material is a metal-organic framework composite structure synthesized by design and is subjected to high temperature Porous CoS ₂ /C functional material obtained after carbonization and gas-phase vulcanization. The heteroatom-doped carbon/CoS ₂ functional material of the present invention has excellent chemical adsorption to polysulfides, that is, the Keesom force effect of the heteroatom-doped carbon and the Lewis acid-base effect of CoS ₂ ; in addition, the porous carbon structure also has Physical barrier and adsorption, conductive carbon can also promote the reaction kinetics, activate "dead sulfur" and "dead lithium", reduce the loss of active materials, and improve battery performance.

Description

A metal-organic framework-derived heteroatom-doped carbon/CoS functional material and its application

technical field

The present invention relates to a metal-organic framework-derived heteroatom-doped carbon/CoS ₂ functional material and its application.

Background technique

The rapid progress of modern technology has led to a great increase in people's dependence on energy. Traditional fossil energy sources are increasingly depleted and cause serious environmental pollution. Therefore, the development and utilization of new and environmentally friendly energy sources is imminent. However, due to the uneven distribution of clean energy such as wind energy, hydro energy, and geothermal energy in time and space, the power resources produced cannot be directly connected to the grid for use. In order to realize the full utilization and popularization of such clean energy, it is very important to adopt an effective electric energy storage method. Electrochemical energy storage systems have the characteristics of light weight, portability and high energy density. They are very suitable for long-term energy storage and instant temporary storage, so they play an important role in electrical energy storage systems.

Lithium-sulfur battery is a kind of battery system with metal lithium as the negative electrode and elemental sulfur as the positive electrode. The system has extremely high theoretical specific capacity and mass specific energy, reaching 1675mAh g ^-1 and 2600Wh kg ^-1 respectively. Lithium-sulfur batteries realize the conversion of chemical energy and electrical energy through the redox reaction between metallic lithium and elemental sulfur, through the cleavage/generation of SS bonds and electron transfer. The separator is an important component in lithium-sulfur batteries, usually polypropylene (PP), polyethylene (PE), or a composite membrane of the two, which acts as a separator between the cathode and anode in the battery, preventing short circuits. The study found that the sulfur cathode will form long-chain polysulfides (Li _{2 Sn} , 4≤n≤8) that are easily soluble in the electrolyte during the discharge process. Long-chain polysulfides pass through the separator under the concentration gradient, and it is difficult to completely migrate back to the cathode in subsequent reactions, resulting in the loss of active species. Second, long-chain polysulfides react with metallic lithium to generate insoluble Li ₂ S ₂ or Li ₂ S, which are deposited on the surface of the negative electrode, hindering lithium ion conduction. Furthermore, this reaction will corrode the surface of metal lithium, which is not conducive to the stable formation of solid electrolyte (SEI) film, and will worsen the growth of lithium dendrites, increasing the possibility of piercing the separator, threatening the safety of the battery. These problems hinder the wide application of lithium-sulfur batteries.

SUMMARY OF THE INVENTION

In view of the above problems, the purpose of the present invention is to provide a kind of structure design based on metal organic frameworks as precursors, and then to derive heteroatom-doped carbon/CoS ₂ functional materials (CoS ₂ /C) with different structures and the same. Application in the modification of lithium-sulfur battery separator. The heteroatom-doped carbon/CoS ₂ functional material of the present invention has excellent chemical adsorption to polysulfides, that is, the Keesom force effect of the heteroatom-doped carbon and the Lewis acid-base effect of CoS ₂ ; in addition, the porous carbon structure also has Physical barrier and adsorption, conductive carbon can also promote the reaction kinetics, activate "dead sulfur" and "dead lithium", reduce the loss of active materials, and improve battery performance.

Based on the metal-organic framework-derived heteroatom-doped carbon/CoS ₂ functional material, the invention first designs and synthesizes the metal-organic framework compound structure, and then obtains the porous CoS ₂ /C functional material through high-temperature carbonization and gas-phase vulcanization.

The metal-organic framework composite structure includes ZIF8/ZIF67 composite structure, LDH/ZIF67 composite structure, Polymer/ZIF67 composite structure and the like.

The present invention is based on a metal-organic framework-derived heteroatom-doped carbon/CoS ₂ functional material, which is prepared by a method comprising the following steps:

Step 1: Preparation of metal-organic framework composite structures

1a. Using ZIF8 (zinc-based metal-organic framework) as a precursor, coating a layer of ZIF67 (cobalt-based metal-organic framework) on its surface to obtain a ZIF8/ZIF67 composite structure;

1b. Using double hydroxide (LDH) as a precursor, using the unsaturated coordination state of metal ions on its surface, anchor and grow ZIF67 on its surface to obtain an LDH/ZIF67 composite structure;

1c. Cobalt salts are coated inside the polymer fibers by electrospinning technology, and then ZIF67 is grown in situ through the reaction of cobalt ions with organic ligands to obtain a Polymer/ZIF67 composite structure.

Step 2: Preparation of CoS ₂ /C Structure

Put the metal-organic framework composite structure obtained in step 1 into a crucible, and then place it in a tube furnace, heat it to 700-900 ° C for 2-6 hours, and naturally cool down and cool to obtain a carbonized product; weigh an appropriate amount of carbonized product and sublimation. Sulfur was placed in two porcelain boats, the porcelain boats were placed in a tube furnace with a distance of 1 cm, the temperature was raised to 400-600 °C for 2-6 hours, and the CoS ₂ /C structure was obtained after natural cooling and cooling.

The metal-organic framework composite structure includes ZIF8/ZIF67 composite structure, LDH/ZIF67 composite structure, Polymer/ZIF67 composite structure and the like. The structure derived from ZIF8/ZIF67 was named CoS ₂ /C-1, the structure derived from LDH/ZIF67 was named CoS ₂ /C-2, and the structure derived from Polymer/ZIF67 was named CoS ₂ / C-3.

In step 2, the mass ratio of the sublimated sulfur to the carbonized product is 1-10:1, and the heating rate is 2-10°C/min.

Further, step 1a includes the following steps:

1a-1: Dissolve an appropriate amount of zinc nitrate hexahydrate and dimethylimidazole in 100 mL methanol solution respectively to prepare solutions A and B; slowly add solution B to solution A, keep stirring for 10-36 hours, and the reaction product Vacuum drying at 50-80° C. for 6-12 hours to obtain ZIF8; wherein, the mass ratio of dimethylimidazole to zinc nitrate hexahydrate is 1-5:1.

1a-2: Disperse a certain amount of ZIF8 in 100 mL of methanol, add an appropriate amount of cobalt nitrate hexahydrate and dimethylimidazole, keep stirring at room temperature for 10-36 hours, and vacuum dry the reaction product at 50-80 °C for 6-12 hours to obtain ZIF8 /ZIF67 composite structure; wherein, the mass ratio of dimethylimidazole and hexahydrate cobalt nitrate is 1-5:1; the mass ratio of ZIF8 and hexahydrate cobalt nitrate is 1:7-20.

Further, step 1b includes the following steps:

1b-1: Dissolve cobalt chloride hexahydrate, aluminum chloride hexahydrate and urea in deionized water, heat up to 70-100°C, keep stirring for 12-48h, collect the product by centrifugation, and then vacuum dry at 50-80°C for 6 -12h, LDH is obtained; wherein, the mass ratio of cobalt chloride hexahydrate, aluminum chloride hexahydrate and urea is 2-6:1:1.5-4.5.

1b-2: Disperse a certain amount of LDH in methanol, add an appropriate amount of cobalt nitrate hexahydrate and dimethylimidazole, keep stirring at room temperature for 0.5-4h, and dry the reaction product at 60-80°C for 8-24h to obtain LDH/ ZIF67 composite structure; wherein, the mass ratio of dimethylimidazole to cobalt nitrate hexahydrate is 1 to 6:1, and the mass ratio of LDH to cobalt nitrate hexahydrate is 1:6 to 18.

Further, step 1c includes the following steps:

1c-1: Dissolve a certain amount of polymer and cobalt nitrate hexahydrate in DMF, stir evenly at room temperature, put the mixture into a 10ml syringe, fix it on a syringe pump, and perform pressure spinning to obtain a polymer / Cobalt salt film, placed in a vacuum oven at 50-80°C for 6-12 hours;

The polymer includes that the polymer is polyacrylonitrile, polyurethane or polyvinylidene fluoride, etc., and the mass ratio of the polymer to cobalt nitrate hexahydrate is 1:1-4.

The applied voltage and flow rate during pressure spinning were 13-20 kV and 0.02-0.5 mm min ^-1 , respectively; the distance between the injector nozzle and the collector was 10-18 cm.

1c-2: The obtained polymer/cobalt salt film is immersed in a methanol solution of dimethylimidazole, and after standing for 10-24 hours, a Polymer/ZIF67 composite structure is obtained; the concentration of the methanol solution of dimethylimidazole is 2-10g/L.

The present invention is based on the application of the metal-organic framework-derived heteroatom-doped carbon/CoS ₂ functional material, which is based on the heteroatom-doped carbon/CoS ₂ functional material (referred to as CoS ₂ /C) for the diaphragm material of lithium-sulfur batteries. Modified to improve battery performance.

Further, the CoS ₂ /C and the binder (polyvinylidene fluoride, PVDF) are mixed and loaded onto the surface of the lithium-sulfur battery separator. Specifically include the following steps:

The CoS ₂ /C and the binder are ball-milled and mixed uniformly in N-methylpyrrolidone (NMP) solution according to a certain proportion, and the mixed solution is passed through a vacuum filtration device, and it is drained on the lithium-sulfur battery diaphragm, and dried in vacuum. After that, the modified separator was obtained.

The diaphragm material is preferably a commercial Celgard 2325 diaphragm (the composition of the commercial diaphragm is polypropylene/polyethylene/polypropylene, sandwich structure, abbreviated as PP/PE/PP).

Among them, the mass ratio CoS ₂ /C:PVDF=1～10:1, the mass ratio NMP:CoS ₂ /C=20～80:1, the ball milling speed is 200-600 rpm, and the binder is PVDF.

The raw materials involved in the modification of the above-mentioned heteroatom-doped carbon/CoS ₂ structure (CoS ₂ /C) for the separator of lithium-sulfur batteries are all commercially available.

Compared with the prior art, the beneficial effects of the present invention are embodied in:

1) The prepared CoS ₂ /C structure has a porous structure, which provides enough space to accommodate the electrolyte and hinder the diffusion of polysulfides, which is beneficial to the performance improvement. Heteroatom doping and active CoS have chemisorption effects _on polysulfides. The presence of conductive carbon promotes the reaction kinetics;

2) The preparation method of the diaphragm is simple and the operation is simple. The prepared CoS ₂ /C@Celgard can effectively inhibit the shuttle effect of polysulfides and avoid the loss of active materials, thereby improving the cycling and rate performance of the battery.

Description of drawings

Figure 1: SEM image of CoS ₂ /C-1@Celgard. It can be seen from Fig. 1 that the CoS ₂ /C-1 modified layer uniformly covers the surface of the commercial separator.

Figure 2: Cycling performance of batteries using CoS ₂ /C-1@Celgard separator. It can be seen from Figure 2 that the battery with CoS ₂ /C-1@Celgard separator still has a discharge specific capacity of about 560mAhg ^-1 after 100 cycles at a current density of 0.5C.

Figure 3: SEM image of CoS ₂ /C-2@Celgard. It can be seen from Fig. 3 that the CoS ₂ /C-2 modified layer uniformly covers the surface of the commercial separator.

Figure 4: Cycling performance of batteries using CoS ₂ /C-2@Celgard separator. It can be seen from Fig. 4 that the battery with CoS ₂ /C-2@Celgard separator still has a discharge specific capacity of about 670 mAhg ^-1 after 100 cycles at a current density of 0.5 C.

Figure 5: SEM image of CoS ₂ /C-3@Celgard. It can be seen from Fig. 5 that the CoS ₂ /C-3 modified layer uniformly covers the surface of the commercial separator.

Figure 6: Cycling performance of batteries using CoS ₂ /C-3@Celgard separator. It can be seen from Figure 6 that the battery with CoS ₂ /C-3@Celgard separator still has a discharge specific capacity of about 563 mAhg ^-1 after 100 cycles at a current density of 0.5 C.

Figure 7: SEM image of a commercial Celgard separator. As can be seen from Figure 7, there are many small pores on the surface of the commercial separator.

Figure 8: Cycling performance of batteries using commercial Celgard separators. It can be seen from Figure 8 that the battery with Celgard separator only has a discharge specific capacity of about 270mAhg ^-1 after 100 cycles at 0.5C.

Detailed ways

Example 1:

1. Preparation of ZIF8/ZIF67 composite structure

Take zinc nitrate hexahydrate and dimethylimidazole with a mass ratio of 1:1 and dissolve them in 100 ml of methanol solution respectively to form A and B solutions, slowly drop B solution into A solution, keep stirring for 24h, and then 60 ℃ vacuum drying for 12h to obtain ZIF8; take a certain amount of ZIF8 and disperse it in 100 ml of methanol, add a mass ratio of 1:1 to cobalt nitrate hexahydrate and dimethylimidazole, and the mass ratio of ZIF8 to cobalt nitrate hexahydrate is 1:7, The reaction was kept stirring at room temperature for 24 h, and then vacuum-dried at 60 °C for 12 h to obtain the ZIF8/ZIF67 composite structure.

2. Preparation of CoS ₂ /C-1 structure

The product ZIF8/ZIF67 was placed in a crucible, then placed in a tube furnace, heated to 700 °C for 4 h, the heating rate was 4 °C/min, and the carbonized product was obtained after natural cooling and cooling; weigh the mass ratio of 1:5. The carbonized product and the sublimated sulfur were placed in two porcelain boats, respectively. The porcelain boats were placed in a tube furnace with a distance of 1 cm, and the temperature was raised to 400 °C for 2 h. The heating rate was 2 °C/min, and the product was obtained after natural cooling.

3. Preparation of CoS ₂ /C-1@Celgard modified separator

Take CoS ₂ /C-1 with a mass ratio of 4:1 and PVDF in a certain mass of NMP solution (mass ratio NMP: CoS ₂ /NSCNHF=20:1) in a low-speed ball mill and mix for 0.5h, and the ball mill rotates at 400 rpm , the above mixture was passed through a vacuum filtration device, dried on a Celgard 2325 membrane, and dried at 80°C for 12 h to obtain a modified membrane CoS ₂ /C-1@Celgard. The SEM images of the commercial separator and the separator and its element distribution results are shown in Figure 1.

4. Assemble the lithium-sulfur battery

Mix elemental sulfur with SuperP and binder PVDF in a mass ratio of 6:3:1. Use NMP as a dispersant to make the mixture into a uniform black slurry, coat it on aluminum foil, and put it in a vacuum oven at 60 °C. After drying for 12h, a positive electrode piece was obtained. Lithium sheet was used as negative electrode, CoS ₂ /C-1@Celgard obtained in step 3 was used as separator, lithium bistrifluoromethanesulfonimide (LiTFSI), 1,3-dioxolane (DOL), The mixed solution of dimethyl ether (DME) was the electrolyte, and the button cell was assembled in a glove box under an argon atmosphere. The button cell was tested by Wuhan Blue Electric Test System. The cycling of lithium-sulfur batteries using the CoS ₂ /C-1@Celgard separator is given in Fig. 2.

Example 2:

1. Preparation of ZIF8/ZIF67 structure

Take zinc nitrate hexahydrate and dimethylimidazole with a mass ratio of 1:1 and dissolve them in 100 ml of methanol solution respectively to form A and B solutions, slowly drop B solution into A solution, keep stirring for 24h, and then 60 ℃ vacuum drying for 12h to obtain ZIF8; take a certain amount of ZIF8 and disperse it in 100 ml of methanol, add a mass ratio of 1:1 to cobalt nitrate hexahydrate and dimethylimidazole, and the mass ratio of ZIF8 to cobalt nitrate hexahydrate is 1:10, The reaction was kept stirring at room temperature for 24 h, and then vacuum-dried at 60 °C for 12 h to obtain ZIF8/ZIF67.

2. Preparation of CoS ₂ /C-1 structure

The product ZIF8/ZIF67 was placed in a crucible, then placed in a tube furnace, heated to 900 °C for 2 h, and cooled naturally to obtain a carbonized product; the carbonized product with a mass ratio of 1:10 was weighed and sublimated sulfur were weighed in two parts. In a porcelain boat, the porcelain boat was placed in a tube furnace with a distance of 1 cm, the temperature was raised to 400 °C for 4 h, and the heating rate was 4 °C/min, and the product was obtained after natural cooling.

3. Preparation of CoS ₂ /C-1@Celgard modified separator

Take CoS ₂ /C-1 and PVDF with a mass ratio of 4:1 in a certain mass of NMP solution (mass ratio NMP: CoS ₂ /C-1 = 20:1) in a low-speed ball mill and mix for 1 h, and the ball mill rotates at 200 rpm/ minutes; the above mixture was passed through a vacuum filtration device, dried on a Celgard 2325 membrane, and dried at 60°C for 12 h to obtain a modified membrane CoS ₂ /C-1@Celgard.

4. Assemble the lithium-sulfur battery

Mix elemental sulfur with SuperP and binder PVDF in a mass ratio of 6:3:1. Use NMP as a dispersant to make the mixture into a uniform black slurry, coat it on aluminum foil, and put it in a vacuum oven at 60 °C. After drying for 12h, a positive electrode piece was obtained. Lithium sheet was used as negative electrode, CoS ₂ /C-1@Celgard obtained in step 3 was used as separator, lithium bistrifluoromethanesulfonimide (LiTFSI), 1,3-dioxolane (DOL), The mixed solution of dimethyl ether (DME) is the electrolyte. Button cell assembly was performed in a glove box under an argon atmosphere. The button cell was tested by Wuhan Blue Electric Test System.

Example 3:

1. Preparation of LDH/ZIF67

Dissolve cobalt chloride hexahydrate, aluminum chloride hexahydrate and urea with a mass ratio of 2:1:1.5 in 500 mL of deionized water, raise the temperature to 90 degrees, and keep stirring for 12 hours. Obtain LDH; take a certain amount of LDH (mass ratio LDH: cobalt nitrate hexahydrate = 1:6) and disperse it in 100 mL of methanol, add cobalt nitrate hexahydrate and dimethylimidazole with a mass ratio of 2:1, and keep stirring at room temperature for reaction 0.5-4h, the reaction product was dried at 80°C for 8h to obtain LDH/ZIF67.

2. Preparation of CoS ₂ /C-2

The product LDH/ZIF67 obtained in step 1 was placed in a porcelain boat, then placed in a tube furnace, and the temperature was programmed to 900 °C for 2 h, the heating rate was 5 °C/min, and the carbonized product was obtained after natural cooling; the mass ratio was weighed as The sublimation sulfur and carbonized products of 6:1 were placed in two porcelain boats, respectively, and the porcelain boats were placed in a tube furnace, heated to 400 °C for 2 hours, and the heating rate was 2 °C/min, and CoS ₂ /C was obtained after natural cooling. -2.

3. Preparation of CoS ₂ /C-2@Celgard modified separator

Take CoS ₂ /C-2 with a mass ratio of 9:1 and PVDF in a certain mass of NMP (mass ratio NMP: NSPCF@CoS ₂ =15:1), and mix them in a low-speed ball mill for 1 hour, and the ball mill rotates at 200 rpm. The above mixed solution was passed through a vacuum filtration device, loaded on a Celgard 2325 membrane, and dried at 60 °C for 8 h to obtain a modified membrane CoS ₂ /C-2@Celgard. Figure 3 presents the SEM images of the commercial separator and the CoS ₂ /C-2@Celgard modified separator.

4. Assemble the lithium-sulfur battery

Mix elemental sulfur with SuperP and binder PVDF in a mass ratio of 6:3:1, and use NMP as a dispersant to make the mixture into a uniform black slurry, coat it on aluminum foil with a film puller, and then put it at 60°C Dry in a vacuum oven for 12 h to obtain the positive electrode plate; use the lithium plate as the negative electrode, use the CoS ₂ /C-2@Celgard obtained in the third step as the separator, and use lithium bistrifluoromethanesulfonimide (LiTFSI), 1 , 3-dioxolane (DOL), ethylene glycol dimethyl ether (DME) mixed solution as electrolyte, button cell assembly was carried out in a glove box under argon atmosphere. The button cell was tested by Wuhan Blue Electric Test System. The cycling of Li-S batteries using CoS ₂ /C-2@Celgard separator is given in Fig. 4.

Example 4:

1. Preparation of LDH/ZIF67

Dissolve cobalt chloride hexahydrate, aluminum chloride hexahydrate and urea with a mass ratio of 4:1:3.5 in 500 mL of deionized water, raise the temperature to 95 degrees, keep stirring for 12 hours, collect the product by centrifugation, and then vacuum dry at 80 °C for 6 hours. Obtain LDH; take a certain amount of CoAlLDH (mass ratio LDH: cobalt nitrate hexahydrate = 1:10) and disperse it in 100 mL of methanol, add cobalt nitrate hexahydrate and dimethylimidazole in a mass ratio of 4:1, and keep stirring at room temperature for the reaction 2h, the reaction product was dried at 80°C for 8h to obtain LDH/ZIF67.

2. Preparation of CoS ₂ /C-2

The product LDH/ZIF67 obtained in step 1 was placed in a porcelain boat, and then placed in a tube furnace, and the temperature was programmed to 800 °C for 3 h, the heating rate was 4 °C/min, and the carbonized product was obtained after natural cooling; the mass ratio was weighed as 10:1 sublimation sulfur and carbonized products were placed in two porcelain boats, respectively, the porcelain boats were placed in a tube furnace, heated to 600 °C for 3 hours, and the heating rate was 3 °C/min, and CoS ₂ /C was obtained after natural cooling. -2.

3. Preparation of CoS ₂ /C-2@Celgard modified separator

Take CoS ₂ /C-2 with a mass ratio of 7:1 and PVDF in a certain mass of NMP (mass ratio NMP: CoS ₂ /C-2 = 25:1) in a low-speed ball mill and mix for 1.5h, and the ball mill rotates at 250 rpm/ minute. The above mixed solution was passed through a vacuum filtration device, loaded on a Celgard 2325 membrane, and dried at 60 °C for 8 h to obtain a modified membrane CoS ₂ /C-2@Celgard.

4. Assemble the lithium-sulfur battery

Mix elemental sulfur with SuperP and binder PVDF in a mass ratio of 6:3:1, and use NMP as a dispersant to make the mixture into a uniform black slurry, coat it on aluminum foil with a film puller, and then put it at 60°C Dry in a vacuum oven for 12 h to obtain the positive electrode plate; use the lithium plate as the negative electrode, use the CoS ₂ /C-2@Celgard obtained in the third step as the separator, and use lithium bistrifluoromethanesulfonimide (LiTFSI), 1 , The mixed solution of 3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) is the electrolyte. Button cell assembly was performed in a glove box under an argon atmosphere. The button cell was tested by Wuhan Blue Electric Test System.

Example 5:

1. Preparation of PAN/ZIF67

Polyacrylonitrile (PAN) and cobalt nitrate hexahydrate (mass ratio 1:1) were dissolved in 10 mL of DMF. After stirring evenly at room temperature, the mixture was put into a 10ml syringe, fixed on a syringe pump, the applied voltage and flow were 15kV and 0.2mm min ^-1 , respectively, and the distance between the syringe nozzle and the collector was 16cm, and spinning was carried out. silk, and the obtained polymer/cobalt salt film was placed in a vacuum oven at 80°C for 6 hours; the polymer/cobalt salt film obtained above was immersed in a methanol solution with a concentration of 2 g/L dimethylimidazole, and allowed to stand for reaction After 10 h, the PAN/ZIF67 composite structure was obtained.

2. Preparation of CoS ₂ /C-3

The product PAN/ZIF67 was placed in a crucible, then placed in a tube furnace, heated to 700 °C for 2 hours, and cooled naturally to obtain a carbonized product. Weigh the carbonized product and sublimed sulfur with a mass ratio of 1:5 into two porcelain boats, place the porcelain boats in a tube furnace, keep the distance 1 cm, heat up to 400 °C for 4 h, and heat up at a rate of 3 °C/min . The product is obtained after natural cooling and cooling.

3. Preparation of CoS ₂ /C-3@Celgard modified separator

Take CoS ₂ /C-3 with a mass ratio of 4:1 and PVDF in a certain mass of NMP solution (mass ratio NMP: CoS ₂ /C-3 = 20:1) in a low-speed ball mill and mix for 1 h, and the ball mill rotates at 200 rpm/ minutes; the above mixed solution was passed through a vacuum filtration device, dried on a Celgard 2325 membrane, and dried at 60 °C for 12 h to obtain a modified membrane CoS ₂ /C-3@Celgard. The morphology of the separator is shown in Figure 5.

4. Assemble the lithium-sulfur battery

Mix elemental sulfur with SuperP and binder PVDF in a mass ratio of 6:3:1. Use NMP as a dispersant to make the mixture into a uniform black slurry, coat it on aluminum foil, and put it in a vacuum oven at 60 °C. After drying for 12h, a positive electrode piece was obtained. Lithium sheet was used as negative electrode, CoS ₂ /C-3@Celgard obtained in step 3 was used as separator, lithium bistrifluoromethanesulfonimide (LiTFSI), 1,3-dioxolane (DOL), The mixed solution of dimethyl ether (DME) is the electrolyte. Button cell assembly was performed in a glove box under an argon atmosphere. The button cell was tested by Wuhan Blue Electric Test System. The cycling performance of the lithium-sulfur battery assembled with CoS ₂ /C-3@Celgard separator is presented in Fig. 6.

Example 6:

1. Preparation of PAN/ZIF67

Polyacrylonitrile (PAN) and cobalt nitrate hexahydrate (mass ratio 1:2) were dissolved in 10 mL DMF, and after stirring evenly at room temperature, the mixture was put into a 10 mL syringe, fixed on the syringe pump, and the applied voltage and The flow rates were 18kV and 0.1mm min ^-1 , respectively, and the distance between the injector nozzle and the collector was 17cm. Spinning was performed, and the obtained polymer/cobalt salt film was placed in a vacuum oven at 80 °C for 6 hours; the above obtained The polymer/cobalt salt film was immersed in a methanol solution with a concentration of 5 g/L dimethylimidazole, and after standing for 12 h, the PAN/ZIF67 composite structure was obtained.

2. Preparation of CoS ₂ /C-3

The product PAN/ZIF67 was placed in a crucible, then placed in a tube furnace, heated to 800 °C for 3 hours, and cooled naturally to obtain a carbonized product; the carbonized product with a mass ratio of 1:8 was weighed and sublimated sulfur were weighed in two parts. In a porcelain boat, the porcelain boat was placed in a tube furnace with a distance of 1 cm, the temperature was raised to 400 °C for 4 h, and the heating rate was 2 °C/min, and the product was obtained after natural cooling.

3. Preparation of CoS ₂ /C-3@Celgard modified separator

Take CoS ₂ /C-3 and PVDF with a mass ratio of 7:1 in a certain mass of NMP solution (mass ratio NMP: CoS ₂ /C-3 = 25:1) and mix them in a low-speed ball mill for 1.5h, and the ball mill rotates at 250 rpm /min; the above mixture was passed through a vacuum filtration device, dried on a Celgard 2325 membrane, and dried at 60°C for 12 h to obtain a modified membrane CoS ₂ /C-3@Celgard.

4. Assemble the lithium-sulfur battery

Mix elemental sulfur with SuperP and binder PVDF in a mass ratio of 6:3:1. Use NMP as a dispersant to make the mixture into a uniform black slurry, coat it on aluminum foil, and put it in a vacuum oven at 60 °C. After drying for 12h, a positive electrode piece was obtained. Lithium sheet was used as negative electrode, CoS ₂ /C-3@Celgard obtained in step 3 was used as separator, lithium bistrifluoromethanesulfonimide (LiTFSI), 1,3-dioxolane (DOL), The mixed solution of dimethyl ether (DME) is the electrolyte. Button cell assembly was performed in a glove box under an argon atmosphere. The button cell was tested by Wuhan Blue Electric Test System.

Comparative ratio:

Mix elemental sulfur with SuperP and binder PVDF in a mass ratio of 7:2:1. Use NMP as a dispersant to make the mixture into a uniform black slurry and coat it on aluminum foil. Then, it was put into a vacuum oven at 60° C. to dry for 12 hours to obtain a positive electrode piece. Lithium sheet is used as negative electrode, commercial Celgard separator is used as separator, and lithium bistrifluoromethanesulfonimide (LiTFSI), 1,3-dioxolane (DOL), and ethylene glycol dimethyl ether (DME) are mixed The liquid is an electrolyte. Button cell assembly was performed in a glove box under an argon atmosphere. The button cell was tested by Wuhan Blue Electric Test System. SEM images of commercial Celgard separators are shown in Figure 7. Cycling of lithium-sulfur batteries using commercial Celgard separators is given in Figure 8.

Claims (10)

1. a heteroatom- _doped carbon/CoS functional material based on metal organic framework derivation, is characterized in that: The heteroatom-doped carbon/CoS ₂ functional material is a porous CoS ₂ /C functional material obtained after the designed and synthesized metal-organic framework composite structure is subjected to high-temperature carbonization and gas-phase vulcanization; The metal-organic framework composite structure includes a ZIF8/ZIF67 composite structure, an LDH/ZIF67 composite structure or a Polymer/ZIF67 composite structure. _2. The heteroatom-doped carbon/CoS functional material according to claim 1, characterized in that it is prepared by a method comprising the following steps: Step 1: Preparation of metal-organic framework composite structures 1a. Using ZIF8 as a precursor, a layer of ZIF67 is coated on its surface to obtain a ZIF8/ZIF67 composite structure; 1b. Using double hydroxide LDH as a precursor, using the unsaturated coordination state of metal ions on its surface, anchor and grow ZIF67 on its surface to obtain an LDH/ZIF67 composite structure; 1c. Cobalt salt is coated inside the polymer fiber by electrospinning technology, and then ZIF67 is grown in situ through the reaction of cobalt ion and organic ligand to obtain a Polymer/ZIF67 composite structure; Step 2: Preparation of CoS ₂ /C Structure Put the metal-organic framework composite structure obtained in step 1 into a crucible, and then place it in a tube furnace, heat it to 700-900 ° C for 2-6 hours, and naturally cool down and cool to obtain a carbonized product; weigh an appropriate amount of carbonized product and sublimation. Sulfur was placed in two porcelain boats, the porcelain boats were placed in a tube furnace with a distance of 1 cm, the temperature was raised to 400-600 °C for 2-6 hours, and the CoS ₂ /C structure was obtained after natural cooling and cooling. 3. The heteroatom-doped carbon/CoS functional material according to claim ₂ , wherein step 1a comprises the following steps: 1a-1: Dissolve an appropriate amount of zinc nitrate hexahydrate and dimethylimidazole in methanol solution respectively to prepare solutions A and B; slowly add solution B to solution A, keep stirring for 10-36 hours, and the reaction product is in Vacuum drying at 50-80℃ for 6-12h to obtain ZIF8; 1a-2: Disperse a certain amount of ZIF8 in methanol, add an appropriate amount of cobalt nitrate hexahydrate and dimethylimidazole, keep stirring at room temperature for 10-36h, and vacuum dry the reaction product at 50-80°C for 6-12h to obtain ZIF8/ ZIF67 complex structure. 4. The heteroatom-doped carbon/CoS functional material according to claim ₂ , wherein step 1b comprises the following steps: 1b-1: Dissolve cobalt chloride hexahydrate, aluminum chloride hexahydrate and urea in deionized water, heat up to 70-100°C, keep stirring for 12-48h, collect the product by centrifugation, and then vacuum dry at 50-80°C for 6 -12h, get LDH; 1b-2: Disperse a certain amount of LDH in methanol, add an appropriate amount of cobalt nitrate hexahydrate and dimethylimidazole, keep stirring at room temperature for 0.5-4h, and dry the reaction product at 60-80°C for 8-24h to obtain LDH/ ZIF67 complex structure. 5. The heteroatom-doped carbon/CoS functional material according to claim ₂ , wherein step 1c comprises the following steps: 1c-1: Dissolve a certain amount of polymer and cobalt nitrate hexahydrate in DMF, stir evenly at room temperature, put the mixture into a 10ml syringe, fix it on a syringe pump, and perform pressure spinning to obtain a polymer / Cobalt salt film, placed in a vacuum oven at 50-80°C for 6-12 hours; 1c-2: The obtained polymer/cobalt salt film is immersed in a methanol solution of dimethylimidazole, and after standing for 10-24 hours, a Polymer/ZIF67 composite structure is obtained. 6. The heteroatom-doped carbon/CoS functional material according to claim ₂ , wherein: In step 2, the mass ratio of the sublimated sulfur to the carbonized product is 1-10:1, and the heating rate is 2-10°C/min. 7. The application of any one of claims 1-6 in metal-organic framework-derived heteroatom- _doped carbon/CoS functional materials, characterized in that: The separator material of the lithium-sulfur battery is modified with the heteroatom-doped carbon/CoS ₂ functional material, so as to improve the performance of the battery. 8. application according to claim 7, is characterized in that: The CoS ₂ /C and the binder were mixed and loaded onto the surface of the lithium-sulfur battery separator. 9. application according to claim 7 or 8 is characterized in that comprising the steps: The CoS ₂ /C and the binder are ball-milled and mixed uniformly in the N-methylpyrrolidone solution according to a certain proportion, the above mixed solution is passed through a vacuum suction filtration device, and it is drained on the lithium-sulfur battery diaphragm, and after vacuum drying, the obtained Modified diaphragm. 10. The application according to claim 9, wherein: Mass ratio CoS ₂ /C:PVDF=1～10:1, mass ratio NMP:CoS ₂ /C=20～80:1, and the binder is PVDF.

Images