Preparation method of nitrogen-doped zinc carbon material and application of nitrogen-doped zinc carbon material in lithium-sulfur battery

Abstract

The invention belongs to the technical field of materials, and particularly discloses a preparation method of a zinc nitrogen-doped carbon modified diaphragm and application of the zinc nitrogen-doped carbon modified diaphragm in a lithium-sulfur battery, and the zinc nitrogen-doped carbon modified diaphragm is prepared through the following steps: (1) firing a high-nitrogen-content precursor in a muffle furnace to obtain graphite-phase carbon nitride; (2) mixing graphite-phase carbon nitride and zinc powder according to a certain proportion, and firing to obtain a zinc nitrogen-doped carbon material; and (3) mixing the obtained nitrogen-doped zinc carbon material, a conductive carbon material and a binder, adding a solvent, mixing to form uniform slurry, coating the slurry on a common diaphragm, and drying to obtain the nitrogen-doped zinc carbon modified diaphragm. The zinc nitrogen-doped carbon material disclosed by the invention has strong chemical adsorption and efficient catalytic conversion capability of polysulfide. The process is simple, and the electrochemical performance of the lithium-sulfur battery can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of material technology and relates to the preparation of a modified material for a lithium-sulfur battery diaphragm, and specifically to a method for preparing a zinc-nitrogen-doped carbon material and its application in the preparation of a lithium-sulfur battery. Background Art

[0002] Lithium-sulfur batteries have a high theoretical specific capacity (1675 mAh g -1 ) and high energy density (2600Wh kg -1 ) and is considered one of the most promising energy storage devices. Among the many issues with lithium-sulfur batteries, the shuttle effect is the most prominent. Severe shuttle effects can lead to loss of active sulfur, reduced coulombic efficiency, and decreased specific capacity.

[0003] Various research methods have been reported to address the shuttle effect of polysulfides. Sulfur is fixed in carbon materials, such as porous carbon spheres, carbon nanotubes, and graphene, to increase conductivity and improve battery capacity. A physical or chemical "barrier" is constructed by coating the positive electrode side of the separator to block the shuttle diffusion of polysulfide ions. Although these two methods can alleviate the shuttle effect to a certain extent, simple physical and chemical adsorption cannot completely inhibit the migration of polysulfides. The redox reaction kinetics between soluble long-chain lithium polysulfides and insoluble lithium sulfide in polysulfides are slow. Therefore, in order to fundamentally suppress the shuttle effect and improve the utilization rate of sulfur, it is necessary to accelerate the conversion kinetics through a catalytic effect. Therefore, developing a modified material that can both physically and chemically adsorb polysulfides and catalyze the conversion reaction kinetics is of great significance for improving the shuttle effect and promoting the practical application of lithium-sulfur batteries. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing a zinc-doped nitrogen-carbon material. The present invention uses graphite-phase carbon nitride and zinc powder as precursors, and mixes and fires them to obtain a zinc-doped nitrogen-carbon material; the prepared zinc-doped nitrogen-carbon material is then applied to the modification of a lithium-sulfur battery separator to obtain a zinc-doped nitrogen-carbon modified separator. The modified separator can effectively adsorb polysulfides and catalyze the reaction kinetics therein, thereby effectively improving the shuttle effect problem. When applied to a lithium-sulfur battery, it can effectively improve the electrochemical performance of the lithium-sulfur battery.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing a zinc-nitrogen-doped carbon modified diaphragm comprises the following steps:

[0007] (1) sintering a high nitrogen content precursor in a muffle furnace to obtain graphite phase carbon nitride;

[0008] (2) mixing graphite phase carbon nitride and zinc powder in a certain proportion and then firing to obtain zinc-doped nitrogen carbon material;

[0009] (3) After mixing the obtained zinc-doped nitrogen carbon material, conductive carbon material, and binder, adding a solvent to mix into a uniform slurry, and then coating it on a common diaphragm, and obtaining a zinc-doped nitrogen carbon modified diaphragm after drying.

[0010] A further improvement of the present invention is:

[0011] The high nitrogen content precursor is selected from one or a mixture of two or more of urea, melamine, cyanamide, dicyandiamide or thiourea.

[0012] Furthermore, the firing atmosphere in step (1) is air or an inert gas atmosphere, the firing temperature is 400-700° C., and the firing time is 2-8 hours; the inert gas is nitrogen or argon or a mixture of the two.

[0013] Furthermore, in step (2), the mass ratio of graphite phase carbon nitride to zinc powder is 1:0.1-1.5.

[0014] Furthermore, the firing atmosphere in step (2) is air or an inert gas atmosphere, the firing temperature is 500-900° C., and the firing time is 2 h to 8 h; the inert gas is nitrogen or argon or a mixture of the two.

[0015] Furthermore, the mass ratio of the zinc-nitrogen-doped carbon material, the conductive carbon material and the binder in step (3) is 5-8:4-1:1.

[0016] Furthermore, the conductive carbon material in step (3) is one or a mixture of two or more of Super P, Ketjen black or acetylene black.

[0017] And / or, the binder is one or a mixture of two or more of PVDF, PEO, PAA, PVA or chitosan.

[0018] And / or, the solvent is one or a mixture of two or more of N-methylpyrrolidone, acetonitrile, dimethyl sulfoxide or dimethylacetamide.

[0019] And / or, the common membrane is selected from polypropylene membrane, polyethylene membrane, ceramic membrane or cellulose membrane.

[0020] Furthermore, the drying temperature in step (3) is 20° C. to 60° C., and the drying time is 5 h to 60 h.

[0021] A further improvement of the present invention is:

[0022] Application of the zinc-doped nitrogen-carbon modified diaphragm prepared by the above preparation method in the preparation of lithium-sulfur batteries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention uses graphite-phase carbon nitride and zinc powder as precursors, which are mixed and fired to produce a zinc-nitrogen-doped carbon material. This composite material has multiple active sites that can form strong chemical bonds with polysulfide ions, thereby adsorbing polysulfides. Furthermore, the zinc-based compound contained therein can effectively catalyze the reaction kinetics of polysulfide conversion. The synergistic effect of the two can effectively inhibit and improve the shuttling effect of polysulfides. Therefore, the present invention develops a simple, low-cost, and multifunctional new type of membrane modification material. This is of great significance for achieving efficient adsorption and rapid conversion of polysulfides and promoting the practical application of lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope image of the zinc-nitrogen-doped carbon material prepared in Example 1 with a scale bar of 1 μm;

[0026] Figure 2 This is the XRD pattern of the zinc-doped nitrogen-carbon material prepared in Example 1;

[0027] Figure 3 FTIR image of the zinc-doped nitrogen-carbon material prepared in Example 1;

[0028] Figure 4 FTIR graph of the aluminum-doped nitrogen-carbon material prepared in Comparative Example 1;

[0029] Figure 5 Comparison of 100 charge-discharge cycles of a lithium-sulfur battery assembled with a zinc-nitrogen-doped carbon diaphragm prepared in Example 1 and a lithium-sulfur battery assembled with a conventional diaphragm at 0.2C;

[0030] Figure 6 This is a comparison chart of the EIS of the lithium-sulfur battery assembled with the zinc-doped nitrogen-carbon diaphragm prepared in Example 3 and the lithium-sulfur battery with a common diaphragm. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to specific embodiments.

[0032] Example 1

[0033] (1) Graphite carbon nitride was prepared by calcining urea as a precursor at 550 °C for 4 h in air atmosphere;

[0034] (2) The graphite phase carbon nitride obtained in step (1) is mixed with zinc powder in a mass ratio of 1:1, and sintered at 600° C. for 2 h in a nitrogen atmosphere to obtain a zinc-doped nitrogen carbon material.

[0035] (3) Zinc-doped nitrogen-carbon material, Super P, and PVDF were mixed in a mass ratio of 7:2:1, slurried with N-methylpyrrolidone as solvent, coated on a polypropylene membrane, and vacuum-dried at 40°C for 30 h to obtain a zinc-doped nitrogen-carbon membrane.

[0036] The zinc-doped nitrogen-carbon material prepared in this embodiment was characterized, and the results are shown in FIG. Figures 1 to 3 ; Figure 1 The scanning electron microscope image of the zinc-doped nitrogen-carbon material prepared in this embodiment is shown at a scale of 1 μm. Figure 1 It can be seen that the morphology of zinc-doped nitrogen carbon is characterized by a smooth block with an obvious layered stacking structure. Figure 2 is the XRD pattern of the zinc-doped nitrogen-carbon material prepared in this embodiment, Figure 3 This is the FTIR graph of the zinc-doped nitrogen-carbon material prepared in this example. In the graph, diffraction peaks of Zn and ZnO can be clearly observed, which represents the successful incorporation of zinc species. Figure 3 NH, CN, and C=N bonds belonging to the carbon nitride structure can be observed. The carbon nitride structure can chemically adsorb with polysulfides, and the zinc species can promote the redox kinetics between the polysulfides. Material characterization confirms that the present invention can simultaneously produce a material containing Zn, ZnO, and carbon nitride structures through a one-pot process, achieving the dual effects of polysulfide adsorption and catalysis.

[0037] Example 2

[0038] (1) Using triphenylphosphine as a precursor, graphite carbon nitride was prepared by calcining at 550°C for 3 h in an air atmosphere;

[0039] (2) The graphite phase carbon nitride obtained in step (1) is mixed with zinc powder in a mass ratio of 1:0.5, and sintered at 650° C. for 3 h in a nitrogen atmosphere to obtain a zinc-doped nitrogen carbon material.

[0040] (3) Zinc-doped nitrogen-carbon material, Super P, and PVDF were mixed in a mass ratio of 6:3:1, slurried with N-methylpyrrolidone as solvent, coated on a polypropylene membrane, and vacuum-dried at 40°C for 30 h to obtain a zinc-doped nitrogen-carbon membrane.

[0041] Example 3

[0042] (1) Graphite carbon nitride was prepared by calcining urea as a precursor at 550 °C for 4 h in air atmosphere;

[0043] (2) The graphite phase carbon nitride obtained in step (1) was mixed with zinc powder in a mass ratio of 1:0.25, and sintered at 600° C. for 2 h in an argon atmosphere to obtain a zinc-doped nitrogen carbon material.

[0044] (3) Zinc-doped nitrogen carbon material, Super P, and PVDF were mixed in a mass ratio of 6:3:1, slurried with N-methylpyrrolidone as solvent, coated on a polypropylene membrane, and vacuum dried at 35°C for 50 h to obtain a zinc-doped nitrogen carbon membrane.

[0045] Example 4

[0046] (1) Graphite carbon nitride was prepared by calcining urea as a precursor at 550 °C for 4 h in air atmosphere;

[0047] (2) The graphite phase carbon nitride obtained in step (1) is mixed with zinc powder in a mass ratio of 1:1.5, and sintered at 550° C. for 2 h in a nitrogen atmosphere to obtain a zinc-doped nitrogen carbon material.

[0048] (3) Zinc-doped nitrogen-carbon material, Super P, and PVDF were mixed in a mass ratio of 6:3:1, slurried with N-methylpyrrolidone as solvent, coated on a ceramic diaphragm, and vacuum-dried at 40°C for 30 h to obtain a zinc-doped nitrogen-carbon diaphragm.

[0049] Comparative Example 1

[0050] In this comparative example, aluminum powder is used instead of zinc powder, the firing temperature of step (2) is 700°C, and the other operations are roughly the same as those in Example 1, which will not be repeated here. The aluminum-doped nitrogen-carbon material obtained in this comparative example was characterized, and the results are shown in FIG. Figure 4 ,Depend on Figure 4 It can be seen that since the melting point of aluminum is 660°C, the firing temperature in step (2) must be higher than the melting point of the metal. However, at a high temperature of 700°C, the FTIR image shows that the strength of the NH, CN, and C=N bonds in the carbon nitride structure is significantly weakened, which will reduce the material's ability to adsorb polysulfides.

[0051] Example 5: Application of modified diaphragm to lithium-sulfur battery

[0052] The modified diaphragms prepared in Examples 1 to 4 were applied to a lithium-sulfur battery system. In a glove box under a high-purity argon atmosphere, they were used to assemble CR2016 button batteries to investigate the charge and discharge performance of the batteries. Figure 5 It can be seen that the battery assembled with the zinc-doped nitrogen-modified carbon diaphragm prepared in Example 1 has an initial discharge capacity of 1220 mAh g at 0.2C. -1 After 100 cycles, there is still 729.2 mAh g -1 The initial discharge capacity of ordinary diaphragm is 818.7 mAh g -1 After 100 cycles, only 358.9 mAh g remains. -1 .Depend on Figure 6As can be seen, the semicircular diameter of the battery assembled with the zinc-nitrogen-doped carbon-modified separator prepared in Example 3 is smaller in the high-frequency region than that of the battery assembled with a conventional separator, indicating that the battery assembled with the zinc-nitrogen-doped carbon-modified separator has a lower charge transfer resistance. This demonstrates that the zinc-nitrogen-doped carbon separator modified material prepared in this invention can effectively alleviate the shuttle effect of polysulfides, thereby improving the electrochemical performance of lithium-sulfur batteries.

[0053] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a zinc-nitrogen-doped carbon modified diaphragm, characterized in that: The following steps are involved: (1) sintering the high nitrogen content precursor in a muffle furnace to obtain graphite phase carbon nitride; (2) Graphite phase carbon nitride and zinc powder are mixed in a certain proportion and then fired to obtain zinc-doped nitrogen carbon material; (3) The obtained zinc-doped nitrogen carbon material, conductive carbon material and binder are mixed, a solvent is added to mix into a uniform slurry, and then coated on a common diaphragm, and dried to obtain a zinc-doped nitrogen carbon modified diaphragm.

2. The method for preparing a zinc-nitrogen-doped carbon modified diaphragm according to claim 1, characterized in that: The high nitrogen content precursor is selected from one or a mixture of two or more of urea, melamine, cyanamide, dicyandiamide or thiourea.

3. The method for preparing a zinc-nitrogen-doped carbon modified diaphragm according to claim 1, characterized in that: The firing atmosphere in step (1) is air or an inert gas atmosphere, the firing temperature is 400-700°C, and the firing time is 2-8 hours; the inert gas is nitrogen or argon or a mixture of the two.

4. The method for preparing a zinc-doped nitrogen-carbon modified diaphragm according to claim 1, characterized in that: In step (2), the mass ratio of graphite phase carbon nitride to zinc powder is 1:0.1~1.

5.

5. The method for preparing a zinc-nitrogen-doped carbon modified diaphragm according to claim 1, characterized in that: The firing atmosphere in step (2) is air or an inert gas atmosphere, the firing temperature is 500-900°C, and the firing time is 2 h-8 h; the inert gas is nitrogen or argon or a mixture of the two.

6. The method for preparing a zinc-nitrogen-doped carbon modified diaphragm according to claim 1, characterized in that: The mass ratio of the zinc-nitrogen-doped carbon material, the conductive carbon material and the binder in step (3) is 5-8:4-1:

1.

7. The method for preparing a zinc-nitrogen-doped carbon modified diaphragm according to claim 1, characterized in that: The conductive carbon material in step (3) is one or a mixture of two or more of Super P, Ketjen black or acetylene black; And / or, the binder is one or a mixture of two or more of PVDF, PEO, PAA, PVA or chitosan; And / or, the solvent is one or a mixture of two or more of N-methylpyrrolidone, acetonitrile, dimethyl sulfoxide or dimethylacetamide; And / or, the common membrane is selected from polypropylene membrane, polyethylene membrane, ceramic membrane or cellulose membrane.

8. The method for preparing a zinc-nitrogen-doped carbon modified diaphragm according to claim 1, characterized in that: The drying temperature in step (3) is 20°C to 60°C, and the drying time is 5 h to 60 h.

9. A zinc-doped nitrogen-carbon modified diaphragm prepared by the method according to any one of claims 1 to 8.

10. Use of the zinc-doped nitrogen-carbon modified diaphragm according to claim 9 in the preparation of a lithium-sulfur battery.

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