Method for preparing sulfur-based polymer material with high nitrogen content

Abstract

The invention relates to a method for preparing a sulfur-based polymer material with high nitrogen content. According to the method, elemental sulfur, hexamethylenetetramine and a polymer are uniformly mixed and heated together, and the high-nitrogen-content sulfur-based polymer material can be obtained. The atomic radius of nitrogen atoms is close to the atomic radius of carbon atoms, so that the carbon atoms in atomic lattices of the carbon material are more easily replaced to form a nitrogen-doped carbon material, the sulfur-based polymer obtained by adding hexamethylenetetramine has high nitrogen content, extranuclear electrons of the nitrogen atoms are more than those of the carbon atoms, and the sulfur-based polymer has higher electron affinity; therefore, the carbon atoms adjacent to the N heteroatoms in the nitrogen-doped carbon material have high charge density, so that the nitrogen-doped carbon material has excellent electrochemical performance. According to the method, the conductivity can be improved by increasing the nitrogen content in the sulfur-based polymer, and the cycle performance and the rate capability of the battery are improved.

Description

Technical Field

[0001] The invention discloses a method for preparing a sulfur-based polymer material with a high nitrogen content, and relates to the field of chemical power sources. Background Art

[0002] Lithium-sulfur (Li-S) batteries have broad application space and commercial prospects in the secondary battery market (electric vehicles, unmanned aerial vehicles and other energy storage fields) due to their high energy density (2600Wh kg-1). Ideal cathode active materials need to have both good capacity performance and cycle stability. At the same time, in order to better meet practical needs, the materials should also meet the requirements of simple preparation process and low raw material cost. Sulfur is abundant in the earth's crust and its low price makes it worry-free after large-scale commercial applications. The conductivity of elemental sulfur materials is low, and the volume expands during cyclic charge and discharge, and the shuttle effect is serious. Due to their high molecular weight and rich functional groups, polymers have the advantages of intrinsic insolubility, structural stability, and functional diversity. In recent years, they have played a great role in promoting the development of sulfur cathodes.

[0003] Polymers can achieve sulfur fixation through physical and chemical adsorption or by forming covalent bonds with sulfur. In practical applications, polymers can be directly compounded with elemental sulfur to obtain active materials, or sulfur-containing polymers can be generated as active materials by reacting sulfur with organic matter. However, sulfur-based polymers have low electrical conductivity and poor cycle performance, and need further improvement. The atomic radius of nitrogen atoms is close to that of carbon atoms, making it easier to replace carbon atoms in the atomic lattice of carbon materials, thereby forming nitrogen-doped carbon materials. After adding hexamethylenetetramine, the nitrogen content can be increased. Compared with carbon atoms, nitrogen atoms have one more extranuclear electron and have a higher electron affinity, so that the carbon atoms adjacent to nitrogen atoms in nitrogen-doped carbon materials have a high charge density, and there is a conjugated effect between the lone pair of electrons of nitrogen atoms and the large π bonds of the carbon atom lattice. In addition, it can also provide excess electrons or form electron holes, thereby improving the electrical conductivity of the material and the utilization rate of sulfur, and effectively inhibiting the shuttle effect. Summary of the invention

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a method for preparing a sulfur-based polymer material with a high nitrogen content, characterized in that the method is carried out according to the following steps:

[0006] S1: uniformly mixing elemental sulfur, hexamethylenetetramine and polymer and heating them together, and cooling them to room temperature after the heat treatment is completed to obtain a sulfur-based polymer with a high nitrogen content;

[0007] S2: The obtained high nitrogen content sulfur-based polymer is mixed with conductive carbon and a binder in an appropriate proportion to form a pole piece and complete the assembly of the battery.

[0008] Preferably, in step S1, the ratio of elemental sulfur, hexamethylenetetramine and polymer is 10:(0.01-5):(0.01-5).

[0009] Preferably, in step S1, the elemental sulfur, hexamethylenetetramine and polymer are mixed by low-speed ball milling, high-speed ball milling and manual grinding.

[0010] Preferably, the heating rate in step S1 is 1-20° C. / min; the heat treatment temperature is 100-600° C.; and the insulation time is 1-40 h.

[0011] Preferably, the polymer in step S1 is polyacrylonitrile, polyaniline, polyethylenedioxythiophene, poly(nitromethylpyrrole), polydopamine, polyethylene oxide, poly(m-aminothiophene), polyimide, polytetravinylpyridine, polyacrylic acid, 1,3-diisopropenylbenzene, poly(3-hexylthiophene-2,5-diyl), 1,3-diethynylbenzene, aminophenol-formaldehyde resin, poly(1,2,4,5-4-amino)benzene; the polymer is a homopolymer and a copolymer.

[0012] Preferably, in step S2, the optional conductive carbon includes acetylene black, multi-walled and single-walled carbon nanotubes, Super P and Ketjen black; and the binder can be selected from PAA, CMC, SBR, guar gum, PVDF and LA133.

[0013] In a second aspect, the present invention provides a high nitrogen-containing sulfur-based polymer material prepared by the preparation method described in any one of claims 1 to 7.

[0014] In a third aspect, the present invention provides a use of the high nitrogen-containing sulfur-based polymer material described in the second aspect, characterized in that it is applied to lithium metal batteries, lithium ion batteries, sodium ion batteries, sodium metal batteries, potassium ion batteries, and potassium metal batteries.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) Increasing the nitrogen content is an effective means to construct high-performance sulfur-based polymer materials. By adding hexamethylenetetramine, the nitrogen content in the sulfur-based polymer can be increased, thereby improving the conductivity of the material and the utilization rate of sulfur and effectively inhibiting the shuttle effect.

[0017] (2) The present invention is easy to prepare and can be prepared on a large scale, and plays an important role in promoting the practical application of lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the charge and discharge curve diagram. DETAILED DESCRIPTION

[0019] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner below in conjunction with the accompanying drawings and preferred experimental examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0020] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0021] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0022] Implementation Case 1

[0023] 8g of elemental sulfur, 2.0g of hexamethylenetetramine, and 2g of 15w molecular weight polyacrylonitrile (homopolymer) were ground in a mortar for 30 minutes, and then placed in a tube furnace at 350°C for 6 hours to obtain a sulfur-based polymer material with a high nitrogen content. The element content was determined, and the results are shown in Table 1.

[0024] Table 1: Comparison of element contents

[0025]

[0026] The obtained high nitrogen content sulfur-based polymer material was used as the positive electrode and metal lithium was used as the negative electrode to assemble a button battery. The electrochemical performance was tested in the voltage range of 1-3V. At a current density of 0.2C, the first discharge specific capacity reached 926.9mAh / g. Figure 1 shown.

[0027] Implementation Case 2

[0028] 10g of elemental sulfur, 3g of hexamethylenetetramine, and 4g of polyaniline (homopolymer) were ground in a mortar for 30 minutes, and then placed in a tube furnace at 300°C for 8h to obtain a sulfur-based polymer material with high conductivity and high nitrogen content. The obtained sulfur-based polymer material with high nitrogen content was used as the positive electrode and metal lithium was used as the negative electrode to assemble a button battery for rate testing in the voltage range of 1-3V. The Li-S battery can be cycled at a rate of 3C, and the discharge capacity of the material is 567mAh / g. When it returns to the initial condition at a rate of 0.5C, the discharge capacity is 906mAh / g. The high nitrogen content gives the sulfur-based polymer good rate performance.

[0029] Comparative Example

[0030] 8g of elemental sulfur and 2g of 15w molecular weight polyacrylonitrile (homopolymer) were ground in a mortar for 20 minutes, and then placed in a tube furnace at 350°C for 6 hours to obtain a sulfur-based polymer material. The element content was determined, and the results are shown in Table 1. The obtained sulfur-based polymer material was used as the positive electrode and metal lithium was used as the negative electrode to assemble a button battery. The electrochemical performance was tested in the voltage range of 1-3V. At a current density of 0.2C, the first discharge specific capacity reached 742.9mAh / g, as shown in Table 1. Figure 1 shown.

Claims

1. A method for preparing a sulfur-based polymer material with a high nitrogen content, characterized in that: Follow these steps: S1: uniformly mixing elemental sulfur, hexamethylenetetramine and polymer and heating them together, and cooling them to room temperature after the heat treatment is completed to obtain a sulfur-based polymer with a high nitrogen content; S2: The obtained high nitrogen content sulfur-based polymer is mixed with conductive carbon and a binder in an appropriate proportion to form a pole piece and complete the assembly of the battery.

2. A method for preparing a sulfur-based polymer material with a high nitrogen content according to claim 1, characterized in that: In the step S1, the ratio of elemental sulfur, hexamethylenetetramine and polymer is 10:(0.01-5):(0.01-5).

3. The method for preparing a sulfur-based polymer material with a high nitrogen content according to claim 1, characterized in that: In the step S1, the elemental sulfur, hexamethylenetetramine and the polymer are mixed by low-speed ball milling, high-speed ball milling and manual grinding.

4. The method for preparing a sulfur-based polymer material with a high nitrogen content according to claim 1, characterized in that: The polymer in step S1 is polyacrylonitrile, polyaniline, polyethylenedioxythiophene, poly(nitromethylpyrrole), polydopamine, polyethylene oxide, poly(m-aminothiophene), polyimide, polytetravinylpyridine, polyacrylic acid, 1,3-diisopropenylbenzene, poly(3-hexylthiophene-2,5-diyl), 1,3-diethynylbenzene, aminophenol-formaldehyde resin, poly(1,2,4,5-4-amino)benzene; the polymer is a homopolymer and a copolymer.

5. The method for preparing a sulfur-based polymer material with a high nitrogen content according to claim 1, characterized in that: The heating temperature in step S1 is 100-600° C.; the heat preservation time is 1-40 hours; and the heating rate is 1-20° C. / min.

6. A method for preparing a sulfur-based polymer material with a high nitrogen content according to claim 1, characterized in that: In step S2, the optional conductive carbon includes acetylene black, multi-walled and single-walled carbon nanotubes, Super P and Ketjen black; the binder can be selected from PAA, CMC, SBR, guar gum, PVDF and LA133.

7. A method for preparing a sulfur-based polymer material with a high nitrogen content, characterized in that: The material is prepared by the method for preparing a sulfur-based polymer material with a high nitrogen content as described in any one of claims 1 to 6.

8. Use of the sulfur-based polymer material with a high nitrogen content according to claim 7, characterized in that: It is prepared as positive electrode material and applied to lithium metal batteries, lithium ion batteries, sodium ion batteries, sodium metal batteries, potassium ion batteries and potassium metal batteries.

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