Molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium-oxygen batteries, and relates to a positive electrode of a lithium-oxygen battery, in particular to a molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material as well as a preparation method and application thereof. ZIF-67 is provided, and the ZIF-67 is pyrolyzed and carbonized, so that the cobalt particle embedded nitrogen-doped polyhedral carbon material is obtained; uniformly mixing the carbon material with a molybdenum source and a surfactant to obtain a mixture; introducing mixed gas of inert gas and hydrogen into the reaction system, enabling the mixed gas to flow from the upstream to the downstream, arranging a sulfur source at the upstream, arranging the mixture at the downstream, heating the reaction system to 650-850 DEG C, and carrying out vulcanization reaction, so as to obtain the product. The composite material provided by the invention is used for a positive electrode catalyst material of a lithium-oxygen battery, and can accelerate reaction kinetics, reduce charging overpotential and improve the cycling stability of the lithium-oxygen battery. The composite material is simple in preparation process and low in cost, and has a wide industrial application prospect.

Description

Technical Field

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

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Lithium-oxygen batteries have become one of the high-energy storage systems with broad application prospects due to their theoretical energy density of up to 3500 Wh / kg, low cost and environmental protection, and are expected to promote the iterative upgrading of electrochemical energy storage technology. However, the practical application of lithium-oxygen batteries still faces thorny challenges and problems: low actual charge and discharge capacity of the battery, severe polarization and poor stability. In response to the above problems, the key to the development of lithium-oxygen batteries lies in the development of bifunctional catalysts with excellent oxygen reduction (ORR) and oxygen evolution (OER) reaction activity to improve the redox reaction kinetics, thereby improving the energy utilization efficiency and long-cycle stability of lithium-oxygen batteries.

[0004] Metal-organic framework materials (MOFs) and their pyrolysis derivatives are considered to be excellent catalysts for lithium-oxygen batteries. Among them, the pyrolysis derivatives of Co-MOF have a multi-level pore structure and a high specific surface area. In addition, the cobalt ions in Co-MOF are reduced to metal Co during the pyrolysis process and are wrapped by the carbon matrix to form nanoparticles, which effectively prevent agglomeration. The nitrogen-doped carbon generated after the pyrolysis of the organic ligand can adjust the electronic structure of the carbon matrix and 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 properties 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 found that the pyrolysis derivatives of Co-MOF still have low catalytic performance as cathode catalysts for lithium-oxygen batteries, and lithium-oxygen batteries have poor electrochemical performance such as high charge overpotential and poor cycle stability. Summary of the invention

[0005] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a composite material of cobalt particles embedded in nitrogen-doped polyhedral carbon modified by molybdenum disulfide and its preparation method and application. The present invention coats molybdenum disulfide nanosheets on cobalt particles embedded in nitrogen-doped polyhedral carbon to form an ORR / OER bifunctional catalyst, which is used as a positive electrode catalyst material for lithium-oxygen batteries, and can accelerate reaction kinetics, reduce charging overpotential, and improve the cycle stability of lithium-oxygen batteries. The composite material has a simple preparation process, low cost, and has broad prospects for industrial application.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions: In a first aspect, a method for preparing a molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material comprises the following steps: Providing ZIF-67, and pyrolyzing and carbonizing the ZIF-67 to obtain; uniformly mixing the carbon material, the molybdenum source and the surfactant to obtain a mixture; A mixed gas of 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 sulfurization reaction, and a layer of MoS is coated on the surface without destroying the structure of the cobalt particles embedded in the nitrogen-doped polyhedral carbon material. 2 Nanosheets are available.

[0007] The present invention can embed cobalt particles into nitrogen-doped polyhedral carbon and molybdenum disulfide materials through the above-mentioned preparation process to generate a large number of active sites, wherein the cobalt particles obtained by pyrolysis and carbonization of ZIF-67 are firstly embedded into the nitrogen-doped polyhedral carbon material structure with a porous structure of dodecahedron, providing more exposed Co-Nx active sites; then the carbon material is evenly mixed with a molybdenum source and a surfactant, and the purpose of adding a surfactant is to prevent agglomeration. The surfactant is adsorbed on the surface of the carbon material to prevent the aggregation of the carbon matrix, improve the dispersibility, and facilitate the later uniform coating of the carbon material surface with MoS 2 Finally, in a mixed gas atmosphere, calcination and sulfidation are performed to coat the surface with a layer of MoS without destroying the structure of the cobalt particles embedded in the nitrogen-doped polyhedral carbon material. 2 The nanosheets adjust their microstructure to form a Mo-N coupling center, and an internal structure appears at the interface to transfer electrons to MoS2, which regulates the charge density of the Co center and enhances the transmission dynamics of electrons and ions. The cobalt particles embedded in nitrogen-doped polyhedral carbon are completely coated by MoS2 nanosheets, thereby 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, while accelerating the electron migration rate and improving the ORR / OER catalytic activity. Therefore, it has excellent catalytic performance when used as a positive electrode catalyst for lithium-oxygen batteries.

[0008] In a second aspect, a molybdenum disulfide-modified cobalt particle embedded in a nitrogen-doped polyhedral carbon composite material is obtained by the above-mentioned preparation method.

[0009] In the third aspect, an application of the above-mentioned molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material in the positive electrode of a lithium oxygen battery.

[0010] In a fourth aspect, a lithium oxygen battery comprises a negative electrode, a positive electrode, a separator and an electrolyte, wherein the active material of the positive electrode is the above-mentioned molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material.

[0011] The beneficial effects of the present invention are: (1) The molybdenum disulfide modified cobalt particles embedded in 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 dodecahedral material embedded with cobalt nanoparticles obtained by direct carbonization of the metal organic framework Co-MOF produces a large number of active sites. At the same time, molybdenum disulfide has excellent lithium storage performance and has abundant active sites at the edges to accelerate the hysteresis reaction kinetics. The cobalt particles embedded in nitrogen-doped polyhedral carbon are completely coated by molybdenum disulfide nanosheets, which effectively prevents the carbon matrix from contacting the electrolyte and discharge products, 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. At the same time, the cobalt particles embedded in nitrogen-doped polyhedral carbon appear at the interface to 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.

[0012] (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, the reaction kinetics can be accelerated, the charge overpotential can be reduced, and the cycle stability of the lithium-oxygen battery can be improved, achieving a high discharge capacity of 11516 mAh / g at a current density of 200 mA / g; when the limiting capacity is 1000 mAh / g and the current density is 200 mA / g, the cobalt particles modified with molybdenum sulfide embedded in nitrogen-doped polyhedral carbon show lower discharge overpotential (0.23V) and charge overpotential (0.64V); at a cutoff capacity of 500 mA h / g and a current density of 500 mA / g, it can stably cycle for 206 cycles.

[0013] (3) The preparation process of the present invention is simple, low-cost, and has broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0014] Figure 1 X-ray diffraction patterns (XRD) 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.

[0015] Figure 2 This is a transmission electron microscopy (TEM) image of the cobalt particles embedded in the nitrogen-doped polyhedral carbon material prepared in Example 1 of the present invention.

[0016] Figure 3 This is a transmission electron microscope (TEM) image of the molybdenum disulfide modified cobalt particles embedded in the nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention.

[0017] Figure 4 It is an adsorption / desorption curve (BET) diagram of the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention, wherein the inset diagram is its pore size distribution diagram.

[0018] Figure 5 This is a thermogravimetric (TG) analysis graph of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention.

[0019] Figure 6 It is a Raman graph of the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1.

[0020] Figure 7 These are X-ray photoelectron spectroscopy test (XPS) graphs of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention, and the molybdenum disulfide prepared in Comparative Example 1; A is the overall spectrum, B is N 1s, C is Mo 3d, and D is S 2p.

[0021] Figure 8 These are the first charge and discharge curves of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified by molybdenum disulfide prepared in Example 1 of the present invention, and the molybdenum disulfide prepared in Comparative Example 1.

[0022] Fig. 9 This is the first charge and discharge curve of the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention at different current densities.

[0023] Fig.10It is a rate performance comparison curve of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified by molybdenum disulfide prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1.

[0024] Fig.11 These are the cycle performance curves of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified by molybdenum disulfide prepared in Example 1 of the present invention, and the molybdenum disulfide prepared in Comparative Example 1.

[0025] Fig.12 It is the rate performance curve of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Examples 1-4 of the present invention.

[0026] Fig.13 These are the cycle performance curves of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite materials prepared in Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit 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 "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] In view of the fact that Co-MOF pyrolysis derivatives still have low catalytic performance as positive electrode catalysts of lithium-oxygen batteries, and lithium-oxygen batteries have poor electrochemical performance such as high charging overpotential and poor cycle stability, in order to solve the above technical problems, the present invention proposes a molybdenum disulfide-modified cobalt particle embedded in a nitrogen-doped polyhedral carbon composite material, and a preparation method and application thereof.

[0030] A typical embodiment of the present invention provides a method for preparing a molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, comprising the following steps: Providing ZIF-67, and pyrolyzing and carbonizing the ZIF-67 to obtain a cobalt particle embedded nitrogen-doped polyhedral carbon material; uniformly mixing the carbon material, the molybdenum source and the surfactant to obtain a mixture; A mixed gas of 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 sulfurization reaction to obtain the product.

[0031] In some embodiments, the mass ratio of carbon material to molybdenum source is 1.4-3.0:1.

[0032] In some embodiments, the molybdenum source is ammonium molybdate tetrahydrate, molybdenum trioxide, calcium molybdate, or molybdenum hexafluoride.

[0033] In some embodiments, the sulfur source is thiourea, sulfur, mercaptan, sulfur powder or thioacetamide.

[0034] In some embodiments, the surfactant is cetyltrimethylammonium bromide (CTAB), cetyltrimethylammonium chloride (CTAC), polyvinylpyrrolidone (PVP), or octadecyltrimethylammonium bromide (OTAB).

[0035] In some embodiments, the molar ratio of the molybdenum source to the sulfur source is 1:6.0-14.0.

[0036] 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.

[0037] In some embodiments, the inert gas is helium, neon, argon, or xenon.

[0038] In some embodiments, the volume fraction of hydrogen in the mixed gas is 4.5-5.5%.

[0039] In some embodiments, the temperature rise rate of the sulfurization reaction is 4-6 °C / min.

[0040] In some embodiments, the sulfurization reaction is followed by programmed cooling, and specifically, the rate of programmed cooling is 4-6°C / min.

[0041] In some embodiments, ZIF-67 pyrolysis carbon is heated to 500-1000° C. and calcined for 2-5 h under inert atmosphere.

[0042] In some embodiments, the preparation method of ZIF-67 is: adding a methanol solution of a cobalt salt to a methanol solution of 2-methylimidazole, stirring evenly at room temperature and standing for 12 to 48 hours, then centrifuging, washing, and drying in a vacuum oven at 50 to 70° C. for 10 to 15 hours to obtain ZIF-67.

[0043] Specifically, the cobalt salt is cobalt chloride, cobalt bromide, cobalt carbonate, cobalt acetate or cobalt nitrate hexahydrate.

[0044] 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.

[0045] Specifically, the molar ratio of the cobalt salt to the 2-methylimidazole is 1:4-10.

[0046] Specifically, the washing is performed with methanol at least twice.

[0047] Another embodiment of the present invention provides a molybdenum disulfide-modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material obtained by the above-mentioned preparation method.

[0048] A third embodiment of the present invention provides an application of the above-mentioned molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material in the positive electrode of a lithium oxygen battery.

[0049] In some embodiments, the lithium oxygen battery positive electrode includes the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite materials, conductive agents, binders and current collectors. Specifically, the conductive agent is hydroxylated multi-walled carbon nanotubes. Specifically, the binder is polyvinylidene fluoride. The specific preparation method is: the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite materials, 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 vacuum dried to obtain a lithium oxygen battery positive electrode. More specifically, the molybdenum disulfide modified cobalt particles are embedded in nitrogen-doped polyhedral carbon composite materials, and the mass ratio of hydroxylated multi-walled carbon nanotubes to 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 particles embedded in nitrogen-doped polyhedral carbon composite materials, hydroxylated multi-walled carbon nanotubes and polyvinylidene fluoride.

[0050] A fourth embodiment of the present invention provides a lithium oxygen battery, comprising a negative electrode, a positive electrode, a separator and an electrolyte, wherein the active material of the positive electrode is the above-mentioned molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material.

[0051] In some embodiments, the negative electrode is a lithium sheet.

[0052] In some embodiments, the membrane is a glass fiber membrane.

[0053] 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 0.8-1.2 mol / L. Specifically, the amount of the electrolyte is 120-180 mL.

[0054] 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 embodiments and comparative examples.

[0055] Example 1 (1) Dissolve 3.02 g of cobalt nitrate hexahydrate in 180 mL of methanol, and 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, and let stand for 24 h. Then centrifuge, wash, and vacuum dry at 60°C for 12 h to obtain Co-MOF. Calcine Co-MOF at 700°C for 2 h under nitrogen protection to obtain cobalt particles embedded in nitrogen-doped polyhedral carbon materials; (2) 1 g of the carbon material obtained in step (1), 0.5 g of molybdenum trioxide and 0.01 g of CTAB were ground until fully mixed, and the mixture and 1 g of sulfur powder were placed in the downstream and upstream of the tube furnace respectively, and Ar / H 2 (H 2 The mixture was heated at a rate of 5°C / min to 700°C, kept at that temperature for 2 h, and then cooled at a rate of 5°C / min to obtain a MoS2-modified cobalt particle embedded in nitrogen-doped polyhedral carbon composite material.

[0056] Figure 1 X-ray diffraction patterns (XRD) of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified by molybdenum disulfide prepared in Example 1 of the present invention and molybdenum disulfide prepared in Comparative Example 1. Figure 1 It can be seen that all the spectral peaks of the composite material are consistent with the characteristic peaks of cobalt particles embedded in nitrogen-doped polyhedral carbon and molybdenum disulfide. It can be seen that the obtained material successfully composites molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon.

[0057] Figure 2 This is a transmission electron microscopy (TEM) image of the cobalt particles embedded in the nitrogen-doped polyhedral carbon material prepared in Example 1 of the present invention. Figure 2 It can be seen that after carbonization at 700 °C for 2 h in an inert atmosphere, the cobalt particles embedded in the nitrogen-doped polyhedral carbon maintained the initial rhombic dodecahedral structure of Co-MOF. However, wrinkles appeared on the surface of the cobalt particles embedded in the nitrogen-doped polyhedral carbon, and the cobalt particles were evenly dispersed throughout the carbon matrix without agglomeration.

[0058] Figure 3 This is a transmission electron microscopy (TEM) image of the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention. Figure 2It can be seen that MoS2 nanosheets grow vertically on the surface of cobalt particles embedded in nitrogen-doped polyhedral carbon without obvious damage to its original three-dimensional dodecahedral structure, and the thickness of MoS2 nanosheets is relatively low. EDS energy spectrum shows the presence and distribution of Co, N, C, Mo and S elements, and the presence of cobalt particles and MoS2 on the edges can be clearly found. The above results indicate the successful synthesis of MoS2-modified cobalt nanoparticles embedded in nitrogen-doped polyhedral carbon materials.

[0059] Figure 4 : is the adsorption / desorption curve (BET) of the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention, wherein the inset is its pore size distribution diagram. Figure 4 It can be seen that the specific surface area of ​​the MoS2-modified cobalt particles embedded in the nitrogen-doped polyhedral carbon composite is 78.1294 m 2 / g, and the pore size distribution is between 2-5 nm.

[0060] Figure 5 : is a thermogravimetric analysis graph of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles modified with molybdenum disulfide embedded in nitrogen-doped polyhedral carbon composite prepared in Example 1 of the present invention. Figure 5 As can be seen in the figure, the cobalt particles modified with MoS2 are embedded in the nitrogen-doped polyhedral carbon MoS 2 The exact mass percentage is 71.56 %.

[0061] Figure 6 : is a Raman image of the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. Figure 6 It can be seen that the cobalt particles embedded in the nitrogen-doped polyhedral carbon sample have a peak at 470 and 674 cm -1 The two peaks at 100° are attributed to the characteristic peaks of Co stretching vibration (E g , A 1g ). After the introduction of MoS2, the MoS2-modified Co particles are embedded in the N-doped polyhedral carbon sample at ~400 cm -1 The characteristic peaks of MoS2 appear at 815, 886 and 939 cm -1 The three peaks belong to Mo 3 S 13 Characteristic peaks. The material coated with MoS2 has a higher ID / IG.

[0062] Figure 7 The X-ray photoelectron spectrum test diagram of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified by molybdenum disulfide prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. Figure 7It can be seen that compared with pure MoS2, the Mo3d and S 2p of the MoS2-modified cobalt particles embedded in the nitrogen-doped polyhedral carbon shift toward low binding energy, while the Co 2p shifts toward high binding energy, which is speculated to be the case that transfer electrons occur at the interface.

[0063] Figure 8 The first charge and discharge curves of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified by molybdenum disulfide prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. Figure 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 battery prepared with molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material as the positive electrode material has an initial discharge capacity of 11516 mAh / g, which has a higher specific capacity and a lower overpotential, indicating that molybdenum disulfide-modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material has excellent ORR / OER catalytic activity.

[0064] Fig. 9 This is the first charge and discharge curve of the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material prepared in Example 1 of the present invention at different current densities. Fig. 9 It can be seen that with the increase of current density, the number of pass points of cobalt particles modified with molybdenum disulfide embedded in nitrogen-doped polyhedral carbon electrode increases and the specific capacity decay is not obvious.

[0065] Fig.10 The figure is a rate performance comparison curve of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles embedded in nitrogen-doped polyhedral carbon composite material modified by molybdenum disulfide prepared in Example 1 of the present invention and the molybdenum disulfide prepared in Comparative Example 1. Fig.10 It can be seen that when the current density increases to 1000 mA / g, the charging voltage of MoS2-modified cobalt particles embedded in nitrogen-doped polyhedral carbon can be maintained at 4 V, 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 MoS2 materials as the positive electrode materials is poor.

[0066] Fig.11 The cobalt particles prepared in Example 1 of the present invention are embedded in nitrogen-doped polyhedral carbon and Co-NC@MoS 2 The cycle performance curves of the composite material and the molybdenum disulfide prepared in Comparative Example 1. Fig.11It can be seen that the battery prepared with molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite materials as the positive electrode material can stably cycle 206 times at a limited charge and discharge capacity of 500 mAh / g and a current density of 500 mA / g; while the battery prepared with cobalt particles embedded in nitrogen-doped polyhedral carbon and molybdenum disulfide materials as the positive electrode material has poor cycle stability.

[0067] Example 2 (1) Dissolve 3.02 g of cobalt nitrate hexahydrate in 180 mL of methanol, and 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, and let stand for 24 h. Then centrifuge, wash, and vacuum dry at 60°C for 12 h to obtain Co-MOF. Calcine Co-MOF at 700°C for 2 h under nitrogen protection to obtain cobalt particles embedded in nitrogen-doped polyhedral carbon materials; (2) 1 g of the carbon material obtained in step (1), 0.34 g of molybdenum trioxide and 0.01 g of CTAB were ground until fully mixed, and the mixture and 1 g of sulfur powder were placed in the downstream and upstream of the tube furnace respectively, and Ar / H 2 (H 2 The mixture was heated at a rate of 6 °C / min to 850 °C, kept at that temperature for 2 h, and cooled at a rate of 4 °C / min to obtain a MoS2-modified cobalt particle embedded in nitrogen-doped polyhedral carbon composite material.

[0068] Example 3 (1) Dissolve 3.02 g of cobalt nitrate hexahydrate in 180 mL of methanol, and 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, and let stand for 24 h. Then centrifuge, wash, and vacuum dry at 60°C for 12 h to obtain Co-MOF. Calcine Co-MOF at 1000°C for 2 h under nitrogen protection to obtain cobalt particles embedded in nitrogen-doped polyhedral carbon materials; (2) 1 g of the carbon material obtained in step (1), 0.68 g of molybdenum trioxide and 0.01 g of CTAB were ground until fully mixed, and the mixture and 1 g of sulfur powder were placed in the downstream and upstream of the tube furnace respectively, and Ar / H 2 (H 2 The mixture was heated at a rate of 4°C / min to 650°C, kept at this temperature for 2 h, and cooled at a rate of 6°C / min to obtain a MoS2-modified cobalt particle embedded in nitrogen-doped polyhedral carbon composite material.

[0069] Example 4 (1) Dissolve 3.02 g of cobalt nitrate hexahydrate in 180 mL of methanol, and 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, and let stand for 24 h. Then centrifuge, wash, and vacuum dry at 60°C for 12 h to obtain Co-MOF. Calcine Co-MOF at 500°C for 10 h under nitrogen protection to obtain cobalt particles embedded in nitrogen-doped polyhedral carbon materials; (2) 1 g of the carbon material obtained in step (1), 0.5 g of molybdenum trioxide and 0.03 g of CTAB were ground until fully mixed, and the mixture and 1 g of sulfur powder were placed in the downstream and upstream of the tube furnace respectively, and Ar / H 2 (H 2 The mixture was heated at a rate of 5°C / min to 700°C, kept at that temperature for 2 h, and then cooled at a rate of 5°C / min to obtain a MoS2-modified cobalt particle embedded in nitrogen-doped polyhedral carbon composite material.

[0070] Fig.12 1 is the rate performance curve of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles modified with molybdenum disulfide embedded in nitrogen-doped polyhedral carbon composite material prepared in Examples 1-4 of the present invention. Fig.12 As can be seen from the figure, when the current density increases to 1000mAg -1 When the positive electrode material is used as the positive electrode material, Example 1 has excellent reversibility, while the rate performance of the battery prepared by Examples 2-4 is poor.

[0071] Fig.13 1 is the cycle performance curve of the cobalt particles embedded in nitrogen-doped polyhedral carbon and the cobalt particles modified with molybdenum disulfide embedded in nitrogen-doped polyhedral carbon composite material prepared in Examples 1-4 of the present invention. Fig.13 It can be seen that the battery prepared with the positive electrode material in Example 1 can stably cycle 206 times at a limited charge and discharge capacity of 500 mAh / g and a current density of 500 mA / g, and has good cycle stability; while the cycle stability of the batteries in Examples 2-4 is poor, and the capacity decays after 95, 64, and 60 cycles, respectively.

[0072] Comparative Example 1 Molybdenum trioxide and sulfur powder were placed in the downstream and upstream of the tube furnace at a molar ratio of 1:4, and Ar / H 2 Mixed gas (H 2 Content 5%), the temperature was raised to 700℃ at 5℃ / min, and the cooling rate was 5℃ / min to obtain molybdenum disulfide material.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a molybdenum disulfide modified cobalt particle embedded nitrogen-doped polyhedral carbon composite material, characterized in that: The following steps are involved: Providing ZIF-67, and pyrolyzing and carbonizing the ZIF-67 to obtain a cobalt particle embedded nitrogen-doped polyhedral carbon material; uniformly mixing the carbon material, the molybdenum source and the surfactant to obtain a mixture; A mixed gas of 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 sulfurization reaction to obtain the product.

2. The preparation method according to claim 1, characterized in that: The mass ratio of carbon material to molybdenum source is 1.4~3:1; Or, the molar ratio of the molybdenum source to the sulfur source is 1:6.0-14.0; Alternatively, the mass of the surfactant accounts for 0.5-2% of the total mass of the carbon material and the molybdenum source.

3. The preparation method 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; Alternatively, the surfactant is cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, polyvinylpyrrolidone or octadecyltrimethylammonium bromide.

4. The preparation method according to claim 1, characterized in that: The heating rate of the vulcanization reaction is 4~6 ℃ / min; Or, the cooling rate after the vulcanization reaction is 4~6 ℃ / min.

5. The preparation method according to claim 1, characterized in that: The ZIF-67 pyrolytic carbon was heated to 500~1000℃ and calcined for 2~5 h under inert atmosphere.

6. The preparation method according to claim 1, characterized in that: The preparation method of ZIF-67 is as follows: adding a methanol solution of cobalt salt to a methanol solution of 2-methylimidazole, stirring evenly at room temperature and standing for 12 to 48 hours, then centrifuging, washing, and drying in a vacuum oven at 50 to 70°C for 10 to 15 hours to obtain ZIF-67.

7. A molybdenum disulfide modified cobalt particle embedded nitrogen doped polyhedral carbon composite material, characterized in that: Obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material according to claim 7 in the positive electrode of a lithium oxygen battery.

9. The use according to claim 8, characterized in that: The lithium oxygen battery positive electrode comprises the molybdenum disulfide modified cobalt particles embedded in nitrogen-doped polyhedral carbon composite material, a conductive agent, a binder and a current collector.

10. A lithium oxygen battery, characterized in that: The invention comprises a negative electrode, a positive electrode, a separator and an electrolyte, wherein the active material of the positive electrode is the molybdenum disulfide modified cobalt particle embedded nitrogen doped polyhedral carbon composite material as claimed in claim 7.

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