A molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, its preparation method and application

Abstract

The present invention belongs to the technical field of lithium-oxygen batteries, relates to the positive electrode of a lithium-oxygen battery, and particularly relates to a molybdenum disulfide-modified cobalt particle-embedded nitrogen-doped polyhedral carbon composite material, a preparation method thereof, and an application thereof. ZIF-67 is provided and pyrolytically carbonized to obtain a cobalt particle-embedded nitrogen-doped polyhedral carbon material; the carbon material is uniformly mixed with a molybdenum source and a surfactant to obtain a mixture; a mixed gas of an inert gas and hydrogen is introduced into the reaction system and the mixed gas is made to flow from upstream to downstream, a sulfur source is arranged upstream, and the mixture is arranged downstream, and the reaction system is heated to 650-850 °C for a sulfidation reaction to obtain the product. The composite material provided by the present invention is used as a positive electrode catalyst material for a lithium-oxygen battery, can accelerate reaction kinetics, reduce the charging overpotential, and improve the cycle stability of the lithium-oxygen battery. The preparation process of the composite material is simple, the cost is low, and it has broad industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-oxygen batteries, relates to the positive electrode of a lithium-oxygen battery, and particularly relates to a molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention and is not necessarily to be regarded as an admission or any form of implication that this information constitutes prior art already known to those of ordinary skill in the art.

[0003] Due to advantages such as a theoretical energy density as high as 3500 Wh / kg, low cost, and environmental friendliness, lithium-oxygen batteries have become one of the high specific energy energy storage systems with broad application prospects and are expected to promote the iterative upgrade of electrochemical energy storage technology. However, the practical application of lithium-oxygen batteries still faces intractable challenges and problems: low actual charge-discharge capacity of the battery, serious polarization, and poor stability, etc. To address the above problems, the key to the development of lithium-oxygen batteries lies in the development of a bifunctional catalyst with excellent oxygen reduction (ORR) and oxygen evolution (OER) reaction activities to improve the redox reaction kinetics, thereby enhancing the energy utilization efficiency and long cycle stability of lithium-oxygen batteries.

[0004] Metal-organic framework materials (MOFs) and their pyrolysis derivatives are considered excellent lithium-oxygen battery catalysts. Among them, the pyrolysis derivative of Co-MOF has a hierarchical pore structure and a high specific surface area. In addition, cobalt ions in Co-MOF are reduced to metallic Co during pyrolysis and are wrapped by a carbon matrix to form nanoparticles, effectively preventing agglomeration. The organic ligand generates nitrogen-doped carbon after pyrolysis, which can adjust the electronic structure of the carbon matrix, improve the conductivity and catalytic activity. The synergistic effect of cobalt-based active sites and nitrogen-doped carbon can enhance the catalytic activity and can exhibit Pt-like characteristics in ORR. Modifying and protecting the carbon material obtained by calcining Co-MOF is an important method to improve its OER catalytic activity. However, the inventors have found that the pyrolysis derivative of Co-MOF still has problems such as low catalytic performance as a positive electrode catalyst for lithium-oxygen batteries, and poor electrochemical performance such as a high charging overpotential and poor cycle stability of lithium-oxygen batteries. Summary of the Invention

[0005] To solve the deficiencies of the prior art, the object of the present invention is to provide a molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, its preparation method and application. In the present invention, molybdenum disulfide nanosheets are coated on cobalt particle embedded nitrogen-doped polyhedral carbon to form an ORR / OER bifunctional catalyst for use as a cathode catalyst material for lithium-oxygen batteries, which can accelerate reaction kinetics, reduce the charging overpotential, and improve the cycle stability of lithium-oxygen batteries. The preparation process of this composite material is simple and the cost is low, having broad industrial application prospects.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] In the first aspect, a preparation method of a molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material includes the following steps:

[0008] Provide ZIF-67 and pyrolyze and carbonize ZIF-67 to obtain;

[0009] Mix the carbon material evenly with a molybdenum source and a surfactant to obtain a mixture;

[0010] Introduce a mixed gas of an inert gas and hydrogen into the reaction system, and make the mixed gas flow from upstream to downstream. Set the sulfur source upstream and the mixture downstream. Heat the reaction system to 650-850 °C for a sulfidation reaction. Under the premise of not destroying the structure of the cobalt particle embedded nitrogen-doped polyhedral carbon material, coat a layer of MoS2 nanosheets on the surface to obtain the product.

[0011] Through the above preparation process, the present invention can embed cobalt particles into nitrogen-doped polyhedral carbon and molybdenum disulfide materials to generate a large number of active sites. Among them, first, the cobalt particles obtained by pyrolyzing and carbonizing ZIF-67 are embedded into the structure of the nitrogen-doped polyhedral carbon material, which has a dodecahedral porous structure, providing more exposed Co-Nx active sites; then the carbon material is uniformly mixed with a molybdenum source and a surfactant. The purpose of adding the surfactant is to prevent agglomeration. The surfactant adsorbs on the surface of the carbon material, preventing the aggregation of the carbon matrix and improving the dispersibility, facilitating the uniform coating of MoS2 on the surface of the carbon material in the later stage; finally, under the atmosphere of a mixed gas, it is calcined and sulfided. Without destroying the structure of the cobalt particles embedded in the nitrogen-doped polyhedral carbon material, a layer of MoS2 nanosheets is coated on the surface to adjust its microstructure, forming a Mo-N coupling center. At the interface, electrons are transferred from the internal structure to molybdenum disulfide, regulating the charge density of the Co center and enhancing the electron and ion transport kinetics; and the cobalt particles embedded in the nitrogen-doped polyhedral carbon are completely coated by the MoS2 nanosheets, effectively preventing the carbon matrix from contacting the electrolyte and discharge products and inhibiting the formation of by-products. The combination of the two can provide a channel for the diffusion of oxygen and the transmission of the electrolyte, and at the same time can accelerate the electron migration rate, improving the ORR / OER catalytic activity. Therefore, it has excellent catalytic performance when used as the positive electrode catalyst of a lithium-oxygen battery.

[0012] In a second aspect, a composite material of molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon is obtained by the above preparation method.

[0013] In a third aspect, there is provided an application of the above composite material of molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon in the positive electrode of a lithium-oxygen battery.

[0014] In a fourth aspect, a lithium-oxygen battery includes a negative electrode, a positive electrode, a separator, and an electrolyte. The active material of the positive electrode is the above composite material of molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon.

[0015] The beneficial effects of the present invention are as follows:

[0016] (1) The molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material provided by the present invention is composed of cobalt particles embedded in nitrogen-doped polyhedral carbon and molybdenum disulfide nanosheets. The nitrogen-doped carbon dodecahedron material with cobalt nanoparticles embedded in it obtained by directly carbonizing the metal-organic framework Co-MOF generates a large number of active sites. At the same time, molybdenum disulfide has excellent lithium storage performance and rich active sites at the edges to accelerate the sluggish reaction kinetics. The cobalt particles embedded in nitrogen-doped polyhedral carbon are completely coated by molybdenum disulfide nanosheets, effectively preventing the carbon matrix from contacting with the electrolyte and discharge products and inhibiting the formation of by-products. The combination of the two can provide channels for the diffusion of oxygen and the transport of electrolyte. At the same time, at the interface, the cobalt particles embedded in nitrogen-doped polyhedral carbon transfer electrons, which can accelerate the electron migration rate. Therefore, it has excellent catalytic performance when used as a positive electrode catalyst for lithium-oxygen batteries.

[0017] (2) The composite material provided by the present invention is used as a positive electrode catalyst for lithium-oxygen batteries. The results show that under the synergistic effect of cobalt particles embedded in nitrogen-doped polyhedral carbon and molybdenum disulfide, it can accelerate the reaction kinetics, reduce the charging overpotential, improve the cycle stability of lithium-oxygen batteries, and achieve a high discharge capacity of 11516 mAh / g at a current density of 200 mA / g; when the limited capacity is 1000 mAh / g and the current density is 200 mA / g, the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon exhibit a lower discharge overpotential (0.23V) and charging overpotential (0.64V); at a current density of 500 mA / g with a cut-off capacity of 500 mA h / g, it can stably cycle 206 times.

[0018] (3) The preparation process of the present invention is simple and the cost is low, and it has broad industrial application prospects. Description of the Drawings

[0019] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0020] Figure 1 It is the X-ray diffraction pattern (XRD) of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1.

[0021] Figure 2 It is the transmission electron microscope image (TEM) of the cobalt particle embedded nitrogen-doped polyhedral carbon material prepared in Example 1 of the present invention.

[0022] Figure 3 It is the transmission electron microscope image (TEM) of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention.

[0023] Figure 4 It is the adsorption / desorption curve (BET) of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention, and the inset is its pore size distribution diagram.

[0024] Figure 5 It is the thermogravimetric (TG) analysis diagram of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention.

[0025] Figure 6 It is the Raman diagram of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1.

[0026] Figure 7 It is the X-ray photoelectron spectroscopy (XPS) test diagram of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1; A is the total spectrum, B is N 1s, C is Mo 3d, and D is S 2p.

[0027] Figure 8 It is the first charge-discharge curve of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1.

[0028] Figure 9 It is the first charge-discharge curve of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention at different current densities.

[0029] Figure 10 It is the rate performance comparison curve of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1.

[0030] Figure 11 It is the cycle performance curve of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1.

[0031] Figure 12 It is the rate performance curve of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Examples 1-4 of the present invention.

[0032] Figure 13It is the cyclic performance curve of the cobalt particle-embedded nitrogen-doped polyhedral carbon and molybdenum disulfide-modified cobalt particle-embedded nitrogen-doped polyhedral carbon composite prepared in Embodiments 1-4 of the present invention. Detailed Description of the Invention

[0033] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0034] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] In view of the fact that the Co-MOF pyrolysis derivative still has relatively low catalytic performance as the positive electrode catalyst of the lithium-oxygen battery, and the lithium-oxygen battery has problems such as relatively high charging overpotential and poor cycle stability in electrochemical performance. To solve the above technical problems, the present invention proposes a molybdenum disulfide-modified cobalt particle-embedded nitrogen-doped polyhedral carbon composite material, its preparation method and application.

[0036] A typical embodiment of the present invention provides a preparation method of a molybdenum disulfide-modified cobalt particle-embedded nitrogen-doped polyhedral carbon composite material, including the following steps:

[0037] Provide ZIF-67, and pyrolyze and carbonize ZIF-67 to obtain a cobalt particle-embedded nitrogen-doped polyhedral carbon material;

[0038] Mix the carbon material evenly with a molybdenum source and a surfactant to obtain a mixture;

[0039] Introduce a mixed gas of inert gas and hydrogen into the reaction system, and make the mixed gas flow from upstream to downstream. Set the sulfur source upstream and the mixture downstream, and heat the reaction system to 650-850 °C for sulfidation reaction to obtain the product.

[0040] In some embodiments, the mass ratio of the carbon material to the molybdenum source is 1.4-3.0:1.

[0041] In some embodiments, the molybdenum source is ammonium molybdate tetrahydrate, molybdenum trioxide, calcium molybdate or molybdenum hexafluoride.

[0042] In some embodiments, the sulfur source is thiourea, sulfur, thiol, sulfur powder or thioacetamide.

[0043] In some embodiments, the surfactant is cetyltrimethylammonium bromide (CTAB), cetyltrimethylammonium chloride (CTAC), polyvinylpyrrolidone (PVP), or octadecyltrimethylammonium bromide (OTAB).

[0044] In some embodiments, the molar ratio of the molybdenum source to the sulfur source is 1:6.0 - 14.0.

[0045] In some embodiments, the mass of the surfactant accounts for 0.5 - 2% of the total mass of the carbon material and the molybdenum source.

[0046] In some embodiments, the inert gas is helium, neon, argon, or xenon.

[0047] In some embodiments, in the mixed gas, the volume fraction of hydrogen is 4.5 - 5.5%.

[0048] In some embodiments, the heating rate of the sulfidation reaction is 4 - 6 °C / min.

[0049] In some embodiments, a programmed temperature reduction is carried out after the sulfidation reaction. Specifically, the rate of the programmed temperature reduction is 4 - 6 °C / min.

[0050] In some embodiments, in the ZIF-67 pyrolytic carbon, it is calcined at 500 - 1000 °C for 2 - 5 h under an inert atmosphere condition.

[0051] In some embodiments, the preparation method of ZIF-67 is as follows: a methanol solution of a cobalt salt is added to a methanol solution of 2-methylimidazole, stirred evenly at room temperature and left standing for 12 - 48 h, then centrifuged, washed, and dried in a vacuum oven at 50 - 70 °C for 10 - 15 h to obtain it.

[0052] Specifically, the cobalt salt is cobalt chloride, cobalt bromide, cobalt carbonate, cobalt acetate, or cobalt nitrate hexahydrate.

[0053] Specifically, the concentration of the methanol solution of the cobalt salt is 0.1 - 0.2 mol / L; the concentration of the methanol solution of 2-methylimidazole is 0.4 - 0.6 mol / L.

[0054] Specifically, the molar ratio of the cobalt salt to 2-methylimidazole is 1:4 - 10.

[0055] Specifically, the washing is carried out with methanol at least 2 times.

[0056] Another embodiment of the present invention provides a molybdenum disulfide-modified cobalt particle-embedded nitrogen-doped polyhedral carbon composite material obtained by the above preparation method.

[0057] The third embodiment of the present invention provides an application of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material in the positive electrode of a lithium-oxygen battery.

[0058] In some embodiments, in the positive electrode of the lithium-oxygen battery, it includes the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, a conductive agent, a binder, and a current collector. Specifically, the conductive agent is hydroxylated multi-walled carbon nanotubes. Specifically, the binder is polyvinylidene fluoride. Its specific preparation method is as follows: The molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, hydroxylated multi-walled carbon nanotubes, and polyvinylidene fluoride are dissolved in N-methyl-2-pyrrolidone, stirred and mixed into a uniform slurry, coated on a carbon paper current collector, and dried under vacuum to obtain the positive electrode of the lithium-oxygen battery. More specifically, the mass ratio of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, hydroxylated multi-walled carbon nanotubes, and polyvinylidene fluoride is 7:2:1. More specifically, the mass of N-methyl-2-pyrrolidone is 2 to 3 times the total mass of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, hydroxylated multi-walled carbon nanotubes, and polyvinylidene fluoride.

[0059] The fourth embodiment of the present invention provides a lithium-oxygen battery, including a negative electrode, a positive electrode, a separator, and an electrolyte. The active material of the positive electrode is the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material described above.

[0060] In some embodiments, the negative electrode is a lithium sheet.

[0061] In some embodiments, the separator is a glass fiber membrane.

[0062] In some embodiments, the electrolyte is a solution of lithium bis(trifluoromethanesulfonyl)imide in tetraethylene glycol dimethyl ether. Specifically, the concentration of lithium bis(trifluoromethanesulfonyl)imide is 0.8 to 1.2 mol / L. Specifically, the amount of the electrolyte used is 120 to 180 mL.

[0063] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in combination with specific examples and comparative examples.

[0064] Example 1

[0065] (1) Dissolve 3.02 g of cobalt nitrate hexahydrate in 180 mL of methanol, dissolve 5.25 g of 2-methylimidazole in 200 mL of methanol, then quickly pour the methanol solution of cobalt nitrate hexahydrate into the methanol solution of 2-methylimidazole, stir evenly, let stand for 24 h, then centrifuge, wash, and dry in vacuum at 60 °C for 12 h to obtain Co-MOF. Calcinate Co-MOF at 700 °C for 2 h under nitrogen protection to obtain cobalt particles embedded in nitrogen-doped polyhedral carbon materials;

[0066] (2) Grind 1 g of the carbon material obtained in step (1), 0.5 g of molybdenum trioxide, and 0.01 g of CTAB until they are fully and evenly mixed. Place the mixture and 1 g of sulfur powder at the downstream and upstream of the tube furnace respectively, introduce a mixed gas of Ar / H2 (H2 content 5%), heat up at a rate of 5 °C / min to 700 °C, keep the temperature for 2 h, and cool down at a rate of 5 °C / min to obtain a composite material of molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon.

[0067] Figure 1 This is the X-ray diffraction pattern (XRD) of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon prepared in Example 1 of the present invention, and the molybdenum disulfide prepared in Comparative Example 1. It can be seen from Figure 1 that all the spectral peaks of the composite material coincide with the characteristic peaks of cobalt particles embedded in nitrogen-doped polyhedral carbon and molybdenum disulfide, indicating that the obtained material has successfully synthesized molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon.

[0068] Figure 2 This is the transmission electron microscopy image (TEM) of the cobalt particles embedded in nitrogen-doped polyhedral carbon materials prepared in Example 1 of the present invention. It can be seen from Figure 2 that after carbonization at 700 °C for 2 h in an inert atmosphere, the cobalt particles embedded in nitrogen-doped polyhedral carbon maintained the initial rhombic dodecahedron structure of Co-MOF. However, wrinkles appeared on the surface of the cobalt particles embedded in nitrogen-doped polyhedral carbon, and the cobalt particles were evenly dispersed throughout the carbon matrix without agglomeration.

[0069] Figure 3 This is the transmission electron microscopy image (TEM) of the molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite materials prepared in Example 1 of the present invention. It can be seen from Figure 2 that molybdenum disulfide nanosheets grew vertically on the surface of cobalt particles embedded in nitrogen-doped polyhedral carbon and did not significantly damage its original three-dimensional dodecahedron structure, and the thickness of the molybdenum disulfide nanosheets was relatively low. The EDS energy spectrum showed the presence and distribution of Co, N, C, Mo, and S elements, and the presence of cobalt particles and molybdenum disulfide at the edges could be clearly found. The above results indicated the successful synthesis of molybdenum disulfide-modified cobalt nanoparticles embedded in nitrogen-doped polyhedral carbon materials.

[0070] Figure 4 is the adsorption / desorption curve (BET) of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention, where the inset is the pore size distribution diagram. From Figure 4 it can be seen that the specific surface area of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite is 78.1294 m 2 / g, and the pore size distribution is between 2 - 5 nm.

[0071] Figure 5 is the thermogravimetric analysis diagram of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention. From Figure 5 it can be seen that the exact mass percentage of MoS2 in the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon is 71.56 %.

[0072] Figure 6 is the Raman diagram of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. From Figure 6 it can be seen that the two peaks at 470 and 674 cm -1 of the cobalt particle embedded nitrogen-doped polyhedral carbon sample belong to the stretching vibration characteristic peaks of Co (E g , A 1g ). After introducing molybdenum disulfide, the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon sample shows a characteristic peak of molybdenum disulfide at ~400 cm -1 . It is worth noting that the three peaks at 815, 886, and 939 cm -1 belong to the Mo3S 13 characteristic peaks. The material after molybdenum disulfide coating has a higher ID / IG.

[0073] Figure 7 is the X-ray photoelectron spectroscopy test diagram of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. From Figure 7 it can be seen that compared with pure molybdenum disulfide, the Mo3d and S 2p of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon shift towards lower binding energy, while the Co 2p shifts towards higher binding energy, suggesting that there is a transfer of electrons at the interface.

[0074] Figure 8 is the first charge-discharge curve of the cobalt particle embedded nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. FromFigure 8 It can be seen that at a discharge current of 200 mA / g, compared with the battery prepared with cobalt particles embedded in nitrogen-doped polyhedral carbon material and molybdenum disulfide as the positive electrode material, the first discharge capacity of the battery prepared with cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified with molybdenum disulfide as the positive electrode material reaches 11516 mAh / g, with higher specific capacity and lower overpotential, indicating that the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified with molybdenum disulfide have excellent ORR / OER catalytic activity.

[0075] Figure 9 Figure 5 shows the first charge-discharge curves of the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified with molybdenum disulfide prepared in Example 1 of the present invention at different current densities. From Figure 9 it can be seen that as the current density increases, the overpotential of the cobalt particles embedded in nitrogen-doped polyhedral carbon electrode modified with molybdenum disulfide increases and the specific capacity attenuation is not obvious.

[0076] Figure 10 Figure 6 shows the rate performance comparison curves of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified with molybdenum disulfide prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. From Figure 10 it can be seen that when the current density increases to 1000 mA / g, the charging voltage of the cobalt particles embedded in nitrogen-doped polyhedral carbon modified with molybdenum disulfide can be maintained at 4V, and when the current density is restored to 200 mA / g, the ORR / OER voltage has excellent reversibility, while the rate performance of the battery prepared with cobalt particles embedded in nitrogen-doped polyhedral carbon and molybdenum disulfide materials as the positive electrode material is poor.

[0077] Figure 11 Figure 7 shows the cycle performance curves of the cobalt particles embedded in nitrogen-doped polyhedral carbon and Co-NC@MoS2 composite material prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. From Figure 11 it can be seen that for the battery prepared with the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified with molybdenum disulfide as the positive electrode material, it can be stably cycled 206 times at a limited charge-discharge capacity of 500 mAh / g and a current density of 500 mA / g; while the cycle stability of the battery prepared with cobalt particles embedded in nitrogen-doped polyhedral carbon and molybdenum disulfide materials as the positive electrode material is poor.

[0078] Example 2

[0079] (1) Dissolve 3.02 g of cobalt nitrate hexahydrate in 180 mL of methanol. Dissolve 5.25 g of 2-methylimidazole in 200 mL of methanol. Then quickly pour the methanol solution of cobalt nitrate hexahydrate into the methanol solution of 2-methylimidazole, stir evenly, let it stand for 24 h, then centrifuge, wash, and dry in vacuum at 60 °C for 12 h to obtain Co-MOF. Calcinate Co-MOF at 700 °C for 2 h under nitrogen protection to obtain cobalt particles embedded in nitrogen-doped polyhedral carbon material;

[0080] (2) Grind 1 g of the carbon material obtained in step (1), 0.34 g of molybdenum trioxide, and 0.01 g of CTAB until they are fully and evenly mixed. Place the mixture and 1 g of sulfur powder at the downstream and upstream of the tube furnace respectively, introduce an Ar / H2 (H2 content 5%) mixed gas, heat up at a rate of 6 °C / min to 850 °C, keep the temperature for 2 h, and cool down at a rate of 4 °C / min to obtain a molybdenum disulfide-modified cobalt particle embedded in nitrogen-doped polyhedral carbon composite material.

[0081] Example 3

[0082] (1) Dissolve 3.02 g of cobalt nitrate hexahydrate in 180 mL of methanol. Dissolve 5.25 g of 2-methylimidazole in 200 mL of methanol. Then quickly pour the methanol solution of cobalt nitrate hexahydrate into the methanol solution of 2-methylimidazole, stir evenly, let it stand for 24 h, then centrifuge, wash, and dry in vacuum at 60 °C for 12 h to obtain Co-MOF. Calcinate Co-MOF at 1000 °C for 2 h under nitrogen protection to obtain cobalt particles embedded in nitrogen-doped polyhedral carbon material;

[0083] (2) Grind 1 g of the carbon material obtained in step (1), 0.68 g of molybdenum trioxide, and 0.01 g of CTAB until they are fully and evenly mixed. Place the mixture and 1 g of sulfur powder at the downstream and upstream of the tube furnace respectively, introduce an Ar / H2 (H2 content 5%) mixed gas, heat up at a rate of 4 °C / min to 650 °C, keep the temperature for 2 h, and cool down at a rate of 6 °C / min to obtain a molybdenum disulfide-modified cobalt particle embedded in nitrogen-doped polyhedral carbon composite material.

[0084] Example 4

[0085] (1) Dissolve 3.02 g of cobalt nitrate hexahydrate in 180 mL of methanol. Dissolve 5.25 g of 2-methylimidazole in 200 mL of methanol. Then quickly pour the methanol solution of cobalt nitrate hexahydrate into the methanol solution of 2-methylimidazole, stir evenly, let it stand for 24 h, then centrifuge, wash, and dry in vacuum at 60 °C for 12 h to obtain Co-MOF. Calcinate Co-MOF at 500 °C for 10 h under nitrogen protection to obtain cobalt particles embedded in nitrogen-doped polyhedral carbon material;

[0086] (2) Grind 1 g of the carbon material, 0.5 g of molybdenum trioxide, and 0.03 g of CTAB obtained in step (1) until they are fully and evenly mixed. Place the mixture and 1 g of sulfur powder at the downstream and upstream of a tubular furnace respectively. Introduce a mixed gas of Ar / H2 (H2 content is 5%), heat at a rate of 5 °C / min to 700 °C, hold for 2 h, and cool at a rate of 5 °C / min to obtain a molybdenum disulfide-modified cobalt particle-embedded nitrogen-doped polyhedral carbon composite material.

[0087] Figure 12 are the rate performance curves of the cobalt particle-embedded nitrogen-doped polyhedral carbon and molybdenum disulfide-modified cobalt particle-embedded nitrogen-doped polyhedral carbon composite materials prepared in Examples 1-4 of the present invention. From Figure 12 it can be seen that when the current density increases to 1000 mA g -1 -1, Example 1 has excellent reversibility, while the rate performance of the batteries prepared with Examples 2-4 as the positive electrode materials is poor.

[0088] Figure 13 are the cycling performance curves of the cobalt particle-embedded nitrogen-doped polyhedral carbon and molybdenum disulfide-modified cobalt particle-embedded nitrogen-doped polyhedral carbon composite materials prepared in Examples 1-4 of the present invention. From Figure 13 it can be seen that for the battery prepared with Example 1 as the positive electrode material, it can stably cycle 206 times under a limited charge-discharge capacity of 500 mAh / g and a current density of 500 mA / g, showing good cycling stability; while the cycling stability of the batteries of Examples 2-4 is poor, and the capacity decays after 95, 64, and 60 cycles respectively.

[0089] Comparative Example 1

[0090] Place molybdenum trioxide and sulfur powder at the downstream and upstream of a tubular furnace respectively at a molar ratio of 1:4. Introduce a mixed gas of Ar / H2 (H2 content is 5%), heat to 700 °C at a rate of 5 °C / min, and cool at a rate of 5 °C / min to obtain a molybdenum disulfide material.

[0091] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Application of molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material in the positive electrode of a lithium-oxygen battery, and a preparation method of the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, comprising the following steps: Provide ZIF-67, and pyrolyze and carbonize ZIF-67 to obtain a cobalt particle embedded nitrogen-doped polyhedral carbon material; Mix the carbon material evenly with a molybdenum source and a surfactant to obtain a mixture; Introduce a mixed gas of an inert gas and hydrogen into the reaction system, and make the mixed gas flow from upstream to downstream. Set the sulfur source upstream and the mixture downstream. Heat the reaction system to 650-850 °C for a sulfidation reaction. Without destroying the structure of the cobalt particle embedded nitrogen-doped polyhedral carbon material, a layer of MoS2 nanosheets is coated on the surface to obtain the product; The surfactant is cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, polyvinylpyrrolidone or octadecyltrimethylammonium bromide; In the mixed gas, the volume fraction of hydrogen is 4.5-5.5%; The mass ratio of the carbon material to the molybdenum source is 1.4-3:1; The molar ratio of the molybdenum source to the sulfur source is 1:6.0-14.0; The mass of the surfactant accounts for 0.5-2% of the total mass of the carbon material and the molybdenum source; The heating rate of the sulfidation reaction is 4-6 °C / min; The cooling rate after the sulfidation reaction is 4-6 °C / min.

2. The application according to claim 1, characterized in that, The molybdenum source is ammonium molybdate tetrahydrate, molybdenum trioxide, calcium molybdate or molybdenum hexafluoride; Or, the sulfur source is thiourea, sulfur, mercaptan, sulfur powder or thioacetamide.

3. The application according to claim 1, characterized in that, In the ZIF-67 pyrolytic carbon, calcine at 500-1000 °C for 2-5 h under an inert atmosphere condition.

4. The application according to claim 1, characterized in that, The preparation method of ZIF-67 is: add a methanol solution of a cobalt salt to a methanol solution of 2-methylimidazole, stir evenly at room temperature and let stand for 12-48 h, then centrifuge, wash, and dry in a vacuum oven at 50-70 °C for 10-15 h to obtain the product.

5. The application according to claim 1, characterized in that, In the positive electrode of the lithium-oxygen battery, it includes the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, a conductive agent, a binder and a current collector.

6. A lithium-oxygen battery, characterized in that, It includes a negative electrode, a positive electrode, a separator and an electrolyte. The active material of the positive electrode is the molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material used in any one of claims 1-4.

Images