Preparation of hydrogen-bonded organic framework-sulfur composites and their application in lithium-sulfur batteries

Abstract

The invention discloses a preparation method of a hydrogen-bonded organic framework-sulfur composite material and its application in a lithium-sulfur battery, which is prepared by reacting and compounding a hydrogen-bonded organic framework material (HOFs), sublimated sulfur powder and a conductive material under certain temperature conditions. The preparation method of the invention has the characteristics of low equipment requirements and low cost consumption. The obtained composite material contains abundant hydrogen bonds, and there is a bonding effect between the hydrogen-bonded organic framework material and sulfur. These hydrogen bonds and sulfur-containing chemical bonds can effectively absorb and desorb lithium polysulfide, improve the lithium storage activity and capacity stability of the electrode, so when it is used as a positive electrode material for a lithium-sulfur battery, the initial capacity can be as high as 1000mAh / g, and it shows good cycle life and capacity retention rate, and has good application potential.

Description

Technical Field

[0001] The invention belongs to the field of battery preparation, and specifically relates to a preparation method of a hydrogen bond organic framework-sulfur composite material and application of the hydrogen bond organic framework-sulfur composite material in a lithium-sulfur battery. Background Art

[0002] As society's demand for energy consumption grows, it is urgent to develop new renewable energy sources to solve the energy crisis. Solar and wind energy can effectively avoid environmental pollution, but their uncontrolled and intermittent characteristics greatly limit their practical application. In recent years, common commercial lithium-ion batteries, such as lithium iron phosphate, have been widely used, but due to their limited energy density, their development space is increasingly limited and it is difficult to meet the growing energy demand. Therefore, there is an urgent need to develop a new battery system with higher energy density.

[0003] Lithium-sulfur battery is a new type of high-energy-density secondary battery system that is very popular at present. It has attracted extensive attention and research due to its extremely high energy density, abundant raw material sources, low cost and environmental friendliness. However, the lithium-sulfur battery system still encounters many troubling problems. One of the most important problems is that the sulfur positive electrode will produce a large amount of soluble lithium polysulfide during the cycle. The resulting polysulfide shuttle effect greatly affects the capacity, cycle life and capacity retention rate of the lithium-sulfur battery, restricting the further development of the sulfur positive electrode.

[0004] At present, the main research is to absorb polysulfides through physical or chemical polar effects to inhibit polysulfide shuttle and improve capacity stability. The adsorption force of physical and chemical adsorption is weak, and the number of adsorption sites of chemical adsorption is still difficult to significantly increase. In addition, lithium polysulfide is always chemically transformed during the cycle, so dynamic adsorption and desorption are required at the adsorption point, and the reversible adsorption of the adsorption point is required to be high. Hydrogen-bonded organic framework materials (HOFs) contain abundant polar functional groups and hydrogen bonds. These hydrogen bonds have properties similar to lithium bonds, which can effectively absorb and desorb polysulfides and have good reversibility, inhibiting the polysulfide shuttle effect. It is suitable for targeted solutions to the problems of sulfur positive electrodes in lithium-sulfur batteries. However, there is no technology in this area at present. Summary of the invention

[0005] In view of the problems existing in the art, the present invention proposes a method for preparing a hydrogen-bonded organic framework-sulfur composite material and its application in a lithium-sulfur battery.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing a hydrogen-bonded organic framework-sulfur composite material comprises the steps of mixing sublimated sulfur powder, hydrogen-bonded organic framework material (HOFs), and conductive material in a certain proportion by ball milling, stirring and reacting at a certain temperature for a period of time, and then mechanically crushing to obtain the hydrogen-bonded organic framework-sulfur composite material.

[0008] Furthermore, the mass percentage ratio of the sublimated sulfur powder to the hydrogen-bonded organic framework material and the conductive material is (6-9):(1-3):(0-3).

[0009] Furthermore, the hydrogen-bonded organic framework material is prepared by dissolving 3,5-diamino-1H-1,2,4-triazole and / or 4,4',4",4"'-(9H-carbazole-1,3,6,8-tetrayl)tetrabenzaldehyde in N,N-dimethylacetamide, adding 1,4,5,8-naphthalenetetracarboxylic acid dianhydride and / or tetraphenylethylene, stirring to form a clear solution, and then transferring the solution to a high-pressure reactor, heating the reaction at 120-180°C for 8-12 hours, and cooling naturally to room temperature, centrifuging, washing, and freeze-drying; wherein the molar ratio of the 3,5-diamino-1H-1,2,4-triazole and / or 4,4',4",4"'-(9H-carbazole-1,3,6,8-tetrayl)tetrabenzaldehyde to 1,4,5,8-naphthalenetetracarboxylic acid dianhydride and / or tetraphenylethylene is 1:(1-4).

[0010] Furthermore, the conductive material is one or more of MXene, carbon nanotubes, graphene, porous carbon, carbon black, etc.

[0011] Furthermore, the rotation speed of the ball mill is 100-400 r / min, and the processing time is 10-120 min.

[0012] Furthermore, the stirring reaction is carried out at a temperature of 30-110° C. and for a time of 1-12 h.

[0013] The hydrogen-bonded organic framework-sulfur composite material prepared by the above method can be used to prepare lithium-sulfur batteries. Specifically, the hydrogen-bonded organic framework-sulfur composite material is mixed with an adhesive and a conductive agent, the obtained mixed powder is added to a solvent and mixed evenly, and then coated on a current collector, and dried at 50-80°C for 12-24 hours, and then used as a positive electrode for battery assembly.

[0014] Furthermore, the amount of the conductive agent is 0.1 to 0.4 times the mass of the hydrogen-bonded organic framework-sulfur composite material, and the amount of the adhesive is 0.05 to 0.2 times the mass of the hydrogen-bonded organic framework-sulfur composite material.

[0015] Furthermore, the conductive agent is one or more of carbon black, porous carbon, graphene, and carbon nanotubes; the adhesive is one or more of polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, and polyacrylate.

[0016] Furthermore, the solvent is one or more of N-methylpyrrolidone and water; the mass ratio of the solvent to the mixed powder is 7:5.

[0017] The sulfur powder, hydrogen-bonded organic framework material and conductive material used in the hydrogen-bonded organic framework-sulfur composite material of the present invention have good contact and can produce a certain bonding effect. Among them, the abundant strong reversible hydrogen-bonded functional groups and lithium bonds in the hydrogen-bonded organic framework material have similar characteristics and can effectively absorb and desorb lithium polysulfide. Therefore, the lithium flow battery prepared by the composite material has a high initial capacity and cycle stability. At the same time, the method is simple to operate and is suitable for large-scale promotion.

[0018] The beneficial effects of the present invention are:

[0019] (1) The pores in the hydrogen-bonded organic framework material used in the present invention can conduct lithium ions and enhance the lithium storage rate of the sulfur positive electrode. At the same time, the sulfur-containing chemical bonds between the hydrogen-bonded organic framework material and sulfur can promote the lithium storage activity of the sulfur positive electrode.

[0020] (2) The composite material of the present invention contains abundant hydrogen bonds and polar functional groups, which can effectively adsorb and desorb polysulfides, inhibit the polysulfide shuttle effect, thereby promoting the conversion of polysulfides and improving the battery capacity.

[0021] (3) In the present invention, good contact between sulfur and conductive material can improve the conductivity of the sulfur positive electrode and increase the battery capacity.

[0022] (4) The method adopted by the present invention is simple, requires common equipment, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the molecular structure of the hydrogen-bonded organic framework material prepared in Example 1.

[0024] Figure 2 This is a scanning electron microscope image of the hydrogen-bonded organic framework material prepared in Example 1.

[0025] Figure 3 This is the Fourier infrared spectrum of the hydrogen-bonded organic framework material prepared in Example 1.

[0026] Figure 4 This is the XRD pattern of the hydrogen-bonded organic framework material prepared in Example 1.

[0027] Figure 5This is a long cycle performance test diagram of the lithium-sulfur battery assembled in Example 1.

[0028] Figure 6 This is a long cycle performance test diagram of the lithium-sulfur battery assembled in Example 2.

[0029] Figure 7 This is a long cycle performance test diagram of lithium-sulfur batteries assembled with different material ratios in Example 3. DETAILED DESCRIPTION

[0030] A method for preparing a hydrogen-bonded organic framework-sulfur composite material comprises the following steps: mixing sublimated sulfur powder, a hydrogen-bonded organic framework material, and a conductive material in a mass percentage ratio of (6-9):(1-3):(0-3) by ball milling, transferring the mixture to a sealed container, reacting the mixture at 30-110° C. with continuous stirring for 1-12 hours, and then mechanically pulverizing the mixture to obtain the hydrogen-bonded organic framework-sulfur composite material.

[0031] The hydrogen-bonded organic framework material is prepared by dissolving 3,5-diamino-1H-1,2,4-triazole and / or 4,4',4",4"'-(9H-carbazole-1,3,6,8-tetrayl)tetrabenzaldehyde in N,N-dimethylacetamide, adding 1,4,5,8-naphthalenetetracarboxylic acid dianhydride and / or tetraphenylethylene, stirring to form a clear solution, then transferring the solution to a high-pressure reactor, heating the solution at 120-180°C for reaction for 8-12 hours, cooling the solution naturally to room temperature, centrifuging, washing, and freeze-drying; wherein the molar ratio of the used 3,5-diamino-1H-1,2,4-triazole and / or 4,4',4",4"'-(9H-carbazole-1,3,6,8-tetrayl)tetrabenzaldehyde to 1,4,5,8-naphthalenetetracarboxylic acid dianhydride and / or tetraphenylethylene is 1:(1-4).

[0032] The rotation speed of the ball mill is 100-400 r / min, and the processing time is 10-120 min.

[0033] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0034] Example 1

[0035] 1. Preparation of Hydrogen Bonding Organic Frameworks (HOFs) Materials

[0036] 495.5 mg of 3,5-diamino-1H-1,2,4-triazole (DAT) powder was completely dissolved in 50 ml of N,N-dimethylacetamide in an ice bath and nitrogen atmosphere, and then 670 mg of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) powder was added and magnetically stirred for 1 hour to form a clear solution. 125 ml of N,N-dimethylacetamide was added to the clear solution for dilution, and then the diluted solution was transferred to a high-pressure reactor and placed in an oven at 180°C for 12 hours. After cooling naturally to room temperature, the product was collected by centrifugation and washed 5 times with N,N-dimethylformamide, methanol and distilled water respectively, and finally freeze-dried to obtain a hydrogen-bonded organic framework material (HOFs) powder, the molecular structure of which is shown in the following diagram: Figure 1 .

[0037] Figure 2 This is a scanning electron microscope image of the HOFs powder prepared in this example. It can be seen from the image that the prepared hydrogen bond organic framework material is a two-dimensional material.

[0038] Figure 3 This is the Fourier infrared spectrum of the hydrogen-bonded organic framework material prepared in this example. As can be seen from the figure, there are nitrogen-hydrogen-nitrogen bonds and nitrogen-hydrogen-oxygen bonds in the infrared spectrum of the hydrogen-bonded organic framework material, indicating that the oxygen in the raw material NTCDA and the nitrogen in DAT have a bonding reaction through the action of hydrogen, generating abundant hydrogen bonds.

[0039] Figure 4 This is the XRD diagram of the hydrogen-bonded organic framework material prepared in this example. The characteristic peaks of the hydrogen-bonded organic framework material can be seen from the figure, which further illustrates that the hydrogen-bonded organic framework material was successfully prepared.

[0040] 2. Preparation of Hydrogen-bonded Organic Framework-Sulfur Composites

[0041] Sublimated sulfur powder, HOFs powder and carbon nanotube powder were weighed separately in a mass ratio of 8:1:1. The sublimated sulfur powder and HOFs powder were first ground thoroughly, and then the carbon nanotube powder was added and ground thoroughly. The powder was heated at 50°C for 1h, and then taken out and ground after being cooled to room temperature.

[0042] 3. Battery Assembly

[0043] The prepared hydrogen-bonded organic framework-sulfur composite material, acetylene black and polyvinylidene fluoride (PVDF) were weighed in a mass percentage ratio of 7:2:1, and then an appropriate amount of N-methylpyrrolidone was added in a mass ratio of powder to solvent of 5:7 and stirred to form a uniform slurry, which was then ball-milled in a ball mill at a speed of 200 r / min for 2 hours. The ball-milled slurry was evenly scraped on an aluminum foil by a blade coating method and placed in a vacuum drying oven to dry at 60°C for 12 hours. It was then taken out and cut into discs as the positive electrode, and the pole piece was assembled into a lithium-sulfur battery together with the negative electrode metal lithium, a polyethylene separator (PP separator) and an electrolyte (LiTFSI was dissolved at 1 mol / L in a 1,3-dioxolane / ethylene glycol dimethyl ether mixed solvent with a volume ratio of 1:1, and lithium nitrate of 1% by mass of the solvent was added). The assembled lithium-sulfur battery and the battery with pure sublimated sulfur as the positive electrode were subjected to constant current (0.5C) charge and discharge tests, where the working current of the positive electrode was calculated based on 1C=1675mAh / g (for example, 0.5C=1675×0.5×the mass of the active material of the electrode).

[0044] Figure 5 This is a long cycle performance test diagram of the lithium-sulfur battery assembled in this embodiment. It can be seen from the figure that the initial discharge specific capacity of the positive electrode prepared using the hydrogen-bonded organic framework-sulfur composite material at 0.5C is as high as 1100mAh / g, which is much higher than the capacity of the pure sulfur positive electrode, which shows that the hydrogen-bonded organic framework-sulfur composite material has good lithium storage activity. At the same time, after 200 cycles, its capacity is still higher than that of the pure sulfur positive electrode, indicating that it can effectively inhibit the generation of polysulfides and improve the capacity stability.

[0045] Example 2

[0046] 1. The preparation of HOFs material is the same as that in Example 1.

[0047] 2. Preparation of Hydrogen-bonded Organic Framework-Sulfur Composites

[0048] Sublimated sulfur powder, HOFs powder and MXene powder were weighed separately in a mass percentage ratio of 8:1:1. The sublimated sulfur powder and HOFs powder were first ground thoroughly, and then the MXene powder was added and ground thoroughly. Two portions were heated at 50°C and 150°C for 1 h respectively. After cooling to room temperature, they were taken out and ground into powder.

[0049] The battery assembly is the same as in Example 1.

[0050] Figure 6This is a long cycle performance test diagram of the lithium-sulfur battery assembled in this embodiment. It can be seen from the figure that the initial discharge capacity of the sample prepared by 50°C treatment reaches 1000mAh / g, which is much higher than the sublimated sulfur positive electrode and the sample prepared by 150°C treatment. At the same time, after 200 cycles, the capacity of the sample prepared by 50°C treatment is still much higher than that of the pure sulfur electrode and the sample prepared by 150°C treatment, showing good cycle stability. This may be because at 150°C, sulfur will melt and enter the pores of the hydrogen-bonded organic framework, blocking its pores, and will polymerize with the hydrogen-bonded organic framework material, destroying its functional group structure, thereby reducing its conductivity; while under the heating condition of 50°C, sulfur is still in a solid state, and it mainly reacts with the outside of the hydrogen-bonded organic framework, and due to the low temperature, there is no polymerization with the hydrogen-bonded organic framework material, thereby maintaining the molecular structure stability of the hydrogen-bonded organic framework material, resulting in better performance. In addition, compared with the lithium-sulfur battery assembled in Example 1, its initial capacity is slightly lower and the capacity after cycling is higher, which is mainly due to the stronger conductivity of carbon nanotubes, but the larger specific surface area of ​​Men is conducive to promoting the stability of the battery.

[0051] Example 3

[0052] 1. The preparation of HOFs material is the same as that in Example 1.

[0053] 2. Preparation of hydrogen bonded organic framework-sulfur composite materials:

[0054] The mass percentage ratios of sublimated sulfur powder, HOFs powder and MXene powder were adjusted to 9:1:0, 6:3:1 and 6:1:3 respectively. The sublimated sulfur powder and HOFs powder were first ground thoroughly, and then the MXene powder was added and ground thoroughly, and heated at 50°C for 1h. After cooling to room temperature, it was taken out and ground into powder.

[0055] 3. The battery assembly is the same as in Example 1.

[0056] Figure 7 This is a long cycle performance test diagram of the lithium-sulfur battery assembled in this embodiment. It can be seen from the figure that the capacity of the lithium-sulfur battery prepared by sublimated sulfur powder, HOFs powder and Mxene powder in different proportions is much higher than that of the sublimated sulfur electrode, but it is lower than that of Example 2 (50°C). This is mainly because the mass ratio of the hydrogen-bonded organic framework material and the conductive material will affect the conductivity of the composite material and the inhibition of the shuttle effect of lithium polysulfide, which will lead to changes in the performance of the sulfur composite electrode.

[0057] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a hydrogen-bonded organic framework-sulfur composite material, characterized in that: Sublimated sulfur powder, hydrogen-bonded organic framework material, and conductive material are mixed uniformly by ball milling in a certain proportion, stirred and reacted for a period of time at a certain temperature, and then crushed to obtain the hydrogen-bonded organic framework-sulfur composite material; The hydrogen-bonded organic framework material is prepared by dissolving 3,5-diamino-1H-1,2,4-triazole and / or 4,4',4",4"'-(9H-carbazole-1,3,6,8-tetrayl)tetrabenzaldehyde in N,N-dimethylacetamide, adding 1,4,5,8-naphthalenetetracarboxylic acid dianhydride and / or tetraphenylethylene, stirring to form a clear solution, then transferring the solution to a high-pressure reactor, heating the reaction at 120-180° C. for 8-12 hours, cooling naturally to room temperature, centrifuging, washing, and freeze-drying; wherein the molar ratio of the used 3,5-diamino-1H-1,2,4-triazole and / or 4,4',4",4"'-(9H-carbazole-1,3,6,8-tetrayl)tetrabenzaldehyde to 1,4,5,8-naphthalenetetracarboxylic acid dianhydride and / or tetraphenylethylene is 1:(1-4); The mass percentage ratio of the sublimated sulfur powder to the hydrogen-bonded organic framework material and the conductive material is (6-9):(1-3):(0-3).

2. The method for preparing the hydrogen-bonded organic framework-sulfur composite material according to claim 1, characterized in that: The conductive material is one or more of MXene, carbon nanotubes, graphene, porous carbon, and carbon black.

3. The method for preparing the hydrogen-bonded organic framework-sulfur composite material according to claim 1, characterized in that: The rotation speed of the ball mill is 100-400 r / min, and the processing time is 10-120 min.

4. The method for preparing the hydrogen-bonded organic framework-sulfur composite material according to claim 1, characterized in that: The stirring reaction is carried out at a temperature of 30-110° C. and for a time of 1-12 hours.

5. An application of the hydrogen-bonded organic framework-sulfur composite material prepared by the method of claim 1 in preparing a lithium-sulfur battery, characterized in that: The hydrogen bond organic framework-sulfur composite material is prepared together with an adhesive and a conductive agent into a positive electrode, and then further prepared into a lithium-sulfur battery.

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