Cobalt molybdenum nitride / cobalt modified nitrogen-doped hollow carbon microspheres and preparation and application thereof

Abstract

The invention discloses cobalt molybdenum nitride / cobalt modified nitrogen-doped hollow carbon microspheres as well as preparation and application thereof, and relates to the technical field of electrochemical energy storage devices. Carboxylated polystyrene microspheres, soluble zinc salt and cobalt salt, phosphomolybdic acid and 2-methylimidazole are dispersed in methanol, a PMA (at) ZnCo-ZIFs / PS precursor of a spherical structure is obtained, then the PMA (at) ZnCo-ZIFs / PS precursor is placed in an inert atmosphere for carbonization treatment, and the cobalt molybdenum nitride / cobalt modified nitrogen-doped hollow carbon microsphere material is obtained. According to the structure and the preparation method, the nitride / metal cobalt component and the nitrogen-doped sodium affinity sites are introduced at the same time, uniform transportation and nucleation of sodium ions are effectively induced, sodium metal is guided to deposit in a specific three-dimensional structure, growth of sodium dendrites is effectively inhibited, volume expansion of metal sodium in the reaction process is relieved, the preparation method is simple and convenient, and the preparation method is suitable for industrial production. The cost is low, the electrochemical performance of the sodium metal battery assembled by using the composite material can be remarkably improved, and the composite material has a good large-scale application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage devices, and in particular to cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres and their preparation and application. Background Art

[0002] With the rapid development of electric vehicles, existing energy storage systems are unable to meet the growing demand, and there is an urgent need to develop new energy storage technologies that combine high energy density and stability. Lithium-ion batteries are widely used in fields such as electric vehicles due to their high safety, high energy density, and strong output power. However, the scarcity and uneven distribution of lithium resources limit their application and development in large-scale energy storage systems. In contrast, sodium resources are more abundant, and sodium and lithium belong to the same main group elements, with similar energy storage mechanisms. Therefore, sodium-ion batteries are considered the most competitive candidate for lithium-ion batteries and are gradually becoming an important direction of scientific research.

[0003] Among the numerous sodium-ion battery anode materials, sodium metal is considered the most promising anode material for next-generation sodium-ion batteries due to its high theoretical specific capacity, low redox potential, and abundant reserves. However, the high reactivity and slow ion transport kinetics of sodium metal lead to problems such as SEI membrane instability, volume expansion, and sodium dendrite growth, resulting in low Coulombic efficiency, short cycle life, and safety risks for sodium metal batteries.

[0004] Therefore, it is of great significance to develop a sodium metal negative electrode host material that can effectively inhibit the uncontrollable growth of sodium dendrites and alleviate the volume change of sodium metal. Summary of the Invention

[0005] The present invention aims to provide cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres and their preparation method and application, addressing the aforementioned issues. By simultaneously introducing cobalt-molybdenum bimetallic nitride and metallic cobalt and nitrogen-doped sodium-philic sites onto the nitrogen-doped hollow carbon microspheres, the material effectively induces uniform transport and nucleation of sodium ions, guiding the deposition of sodium metal within a specific three-dimensional structure, achieving more stable sodium metal deposition / stripping, effectively inhibiting the growth of sodium dendrites, and mitigating the volume expansion of metallic sodium during the reaction. This material is simple to prepare and inexpensive. Using it as the negative electrode host material to assemble a sodium metal battery can significantly improve the battery's cycle stability and has good prospects for large-scale application.

[0006] The present invention discloses a method for preparing cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres, comprising the following steps: (1) Carboxylated polystyrene microspheres, soluble zinc salt, soluble cobalt salt, phosphomolybdic acid and 2-methylimidazole are dispersed in methanol to form a methanol solution, and reacted to obtain a spherical structure of PMA@ZnCo-ZIFs / PS precursor; (2) The PMA@ZnCo-ZIFs / PS precursor is placed in an inert atmosphere for carbonization to obtain cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres.

[0007] Preferably, in step (1), the soluble zinc salt is one or more of zinc nitrate, zinc chloride, and zinc sulfate; the soluble cobalt salt is one or more of cobalt nitrate, cobalt sulfate, and cobalt chloride; and the molar ratio of the soluble zinc salt to the soluble cobalt salt is 1:(6-9).

[0008] Preferably, in the methanol solution of step (1), the mass concentration of carboxylated polystyrene microspheres is 1-5 g / L, and the mass concentration of phosphomolybdic acid is 0.38-1.52 g / L.

[0009] Preferably, in the methanol solution of step (1), the molar concentration of 2-methylimidazole is 0.4 mol / L, and the molar ratio of the soluble zinc salt to 2-methylimidazole is 1:(8-10).

[0010] Preferably, the reaction temperature of step (1) is room temperature, and the reaction time is 12h-18h.

[0011] Preferably, the inert atmosphere of step (2) is argon or nitrogen, and the specific operation of carbonization is: heating rate of 3°C / min-5°C / min, calcination temperature of 850°C-950°C, and holding time of 1h-3h.

[0012] The present invention also provides cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres with a hollow porous spherical structure prepared by the above-mentioned preparation method, which are used as the host material of the sodium metal negative electrode, mixed with sodium hydroxymethyl cellulose and carbon black to obtain a negative electrode material slurry, which is then coated on a copper foil current collector to prepare a sodium metal battery negative electrode material. The sodium metal battery negative electrode material is used as a negative electrode in a sodium metal battery.

[0013] Therefore, the present invention adopts the above-mentioned cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres and their preparation and application, which have the following beneficial effects: 1. The cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres prepared in this invention have a unique hollow spherical structure, inherited from a polystyrene template, which provides an effective buffer space for the significant volume expansion of sodium metal during cycling. At the same time, the internal cavity can serve as a reservoir for sodium metal deposition, greatly alleviating the volume change stress of the electrode and improving structural stability. The excellent specific surface area and abundant micro / mesopores effectively reduce the local current density and inhibit the growth of sodium dendrites during cycling. In addition, the in-situ generated cobalt-molybdenum bimetallic nitride (Co3Mo3N) particles with excellent conductivity synergize with metallic cobalt (Co), further significantly enhancing the conductivity and graphitization degree of the overall material. At the same time, the intrinsic sodium-philic sites provided by the nitrogen-doped carbon, together with the strong sodium adsorption energy of Co3Mo3N and metallic Co components, can effectively induce the uniform transport and nucleation of sodium ions, guiding the preferential and uniform deposition of sodium metal within the specific three-dimensional hollow carbon framework, thereby achieving a highly reversible and dendrite-free sodium metal deposition / stripping process, thereby improving the cycle life of sodium metal batteries.

[0014] 2. This invention utilizes carboxylated polystyrene (PS) microspheres as a multifunctional template. In a single methanol solvent system, a single-step reaction achieves in situ encapsulation of phosphomolybdic acid during the growth of ZnCo-ZIFs, forming a composite precursor with a core-shell structure (PMA@ZnCo-ZIFs / PS). This process avoids complex surface pre-modification, additional template removal, or active component loading steps, making raw material mixing and reaction operations extremely simple. The composite precursor is then directly carbonized in an inert atmosphere in a single step. At high temperature, this step simultaneously completes the thermal decomposition and volatilization of the PS template, the conversion of the ZIFs carbon skeleton to nitrogen-doped carbon, the volatilization of the zinc component to form pores, and the reduction and nitridation reactions of the PMA and cobalt components in a confined carbon environment. This strategy completely eliminates cumbersome steps such as template dissolution, acid washing, or post-nitridation, significantly shortening the process flow and significantly reducing energy consumption, equipment requirements, and production costs. Its environmentally friendly nature lays a solid foundation for large-scale industrial production.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The morphology characterization diagrams obtained in Example 1, wherein a and b are SEM images with scales of 200 nm and 100 nm, respectively; c and d are TEM images with scales of 200 nm and 2 nm, respectively; Figure 2 This is the nitrogen adsorption-desorption curve of Co / Co3Mo3N-NHC-6-3 in Example 1; Figure 3is the pore size distribution curve of Co / Co3Mo3N-NHC-6-3 in Example 1; Figure 4 Schematic diagram of the preparation process of Co / Co3Mo3N-NHC-6-3 in Example 1; Figure 5 1 is a coulombic efficiency performance diagram of the sodium metal battery obtained in Example 1; Figure 6 1 is a SEM image of Co-NHC in Comparative Example 1, wherein a is a SEM image with a scale of 500 nm, and b is a SEM image with a scale of 100 nm; Figure 7 1 is a coulombic efficiency performance diagram of the sodium metal battery obtained in Comparative Example 1; Figure 8 2 are SEM images of NHC in Comparative Example 2, wherein a is a SEM image with a scale of 500 nm, and b is a SEM image with a scale of 100 nm; Figure 9 This is the coulombic efficiency performance diagram of the sodium metal battery obtained in Comparative Example 2. DETAILED DESCRIPTION

[0017] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0018] Furthermore, it should be understood that although this specification describes the embodiments, not every embodiment includes only one independent technical solution. This description is for clarity only. Those skilled in the art should consider the specification as a whole. The technical solutions in the various embodiments may also be appropriately combined to form other embodiments that are understandable to those skilled in the art. These other embodiments are also encompassed within the scope of protection of the present invention.

[0019] Example 1 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation process of which is as follows: Figure 4 As shown, the specific steps include: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a 100 mL methanol mixed solution containing 1.3090 g of zinc nitrate, 0.1746 g of cobalt nitrate, and 0.076 g of phosphomolybdic acid was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-6-3 precursor; (2) The PMA@ZnCo-ZIFs / PS-6-3 precursor was placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-6-3).

[0020] The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Co / Co3Mo3N-NHC-6-3 prepared in this example are shown in Figure 2. Figure 1 (a and b are scanning electron microscopy images, c and d are transmission electron microscopy images), the nitrogen adsorption-desorption curve is as shown in Figure 2 As shown, the pore size distribution is Figure 3 shown.

[0021] Depend on Figure 1 The Co / Co3Mo3N-NHC-6-3 in this example exhibits a hollow, porous spherical structure, with carbon nanotubes forming on the surface of the carbon spheres. This hollow structure not only provides a buffer for the volume expansion of metallic sodium but also provides storage space for its deposition. TEM images revealed lattice fringes corresponding to Co3Mo3N and metallic Co. These sodium-loving sites effectively induce uniform and dense deposition of metallic sodium during the reaction.

[0022] Depend on Figure 2 as well as Figure 3 It can be seen that the Co / Co3Mo3N-NHC-6-3 in this example has a large specific surface area and rich micropore / mesoporous structure, and its nitrogen adsorption-desorption curve shows typical mesoporous material characteristics, indicating that the Co / Co3Mo3N-NHC-6-3 prepared in this example helps to reduce the local current density during the cycle and inhibit the formation of dendrites.

[0023] A sodium metal battery, a method for preparing a negative electrode material and testing its performance comprises the following steps: (1) Assembly of half-cell: 0.1 g of the cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material Co / Co3Mo3N-NHC-6-3 in Example 1 was mixed uniformly with sodium hydroxymethyl cellulose (CMC) and carbon black (Super P) at a mass ratio of 8:1:1 by ball milling. Appropriate amounts of anhydrous ethanol and deionized water were added and mixed uniformly to obtain a negative electrode material slurry. The negative electrode material slurry was then coated on a copper foil current collector and dried in a vacuum oven at 60°C for 12 h. After drying, it was cut into circular pole pieces with a diameter of 12 mm and used as the negative electrode host material for electrochemical performance testing of sodium metal batteries.

[0024] In the half-cell, the Co / Co3Mo3N-NHC-6-3 electrode serves as the negative electrode. The counter electrode is a 16mm diameter sodium metal disc. The electrolyte is a 1.0 mol / L sodium hexafluorophosphate dissolved in a diethylene glycol dimethyl ether mixed solvent (52 μL). The separator is a commercial polypropylene porous membrane. The cells were assembled into a CR2032 button cell (i.e., a sodium metal negative electrode battery) in an argon-filled glove box with water and oxygen concentrations below 0.01 ppm.

[0025] (2) Electrochemical test: Coulombic efficiency (CE) is an important indicator of the reversibility of sodium deposition / stripping, reflecting the utilization rate of active sodium. First, the assembled half-cell was tested at 0.05 mA cm -2 The current was cycled between 0.01 and 0.6 V for 5 times, and then at 1 mA cm -2 Repeated deposition / stripping at a current of 1 mAh cm -2 The cut-off voltage of metallic sodium is 0.1V.

[0026] The electrochemical performance of the CR2032 button cell in this embodiment, i.e., the coulombic efficiency, is shown in the figure below: Figure 5 shown.

[0027] Depend on Figure 5 It can be seen that the Co / Co3Mo3N-NHC-6-3 composite material as a sodium metal anode has a high conductivity at 1 mA cm -2 The current density and 1 mAh cm -2 The Coulombic efficiency is relatively stable (maintained at around 100%) at a high capacity and can be cycled stably for more than 600 cycles. This proves that the Co / Co3Mo3N-NHC-6-3 electrode can achieve uniform deposition of metallic sodium and has excellent reversibility.

[0028] Example 2 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.1 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a 100 mL methanol mixed solution containing 1.3090 g of zinc nitrate, 0.1746 g of cobalt nitrate, and 0.076 g of phosphomolybdic acid was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-6-1 precursor; (2) The PMA@ZnCo-ZIFs / PS-6-1 precursor was placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-6-1).

[0029] The Co / Co3Mo3N-NHC-6-1 in this example presents a hollow porous carbon sphere structure.

[0030] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0031] After testing (testing method is the same as that of Example 1), the performance of the CR2032 button battery assembled in this example is close to that of the CR2032 button battery assembled in Example 1.

[0032] Example 3 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.5 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a 100 mL methanol mixed solution containing 1.3090 g of zinc nitrate, 0.1746 g of cobalt nitrate, and 0.076 g of phosphomolybdic acid was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-6-5 precursor; (2) The PMA@ZnCo-ZIFs / PS-6-5 precursor was placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-6-5).

[0033] The Co / Co3Mo3N-NHC-6-5 in this example presents a hollow porous carbon sphere structure.

[0034] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0035] After testing (testing method is the same as that of Example 1), the performance of the CR2032 button battery assembled in this example is close to that of the CR2032 button battery assembled in Example 1.

[0036] Example 4 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a mixed solution containing 1.3387 g of zinc nitrate, 0.1455 g of cobalt nitrate, and 0.076 g of phosphomolybdic acid dissolved in 100 mL of methanol was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-5-3 precursor; (2) The PMA@ZnCo-ZIFs / PS-5-3 precursor was placed in a tube furnace and heated to 900 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-5-3).

[0037] The Co / Co3Mo3N-NHC-5-3 in this example presents a hollow carbon sphere structure. The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0038] After testing (testing method is the same as that of Example 1), the performance of the CR2032 button battery assembled in this example is close to that of the CR2032 button battery assembled in Example 1.

[0039] Example 5 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a mixed solution containing 1.2792 g of zinc nitrate, 0.2037 g of cobalt nitrate, and 0.076 g of phosphomolybdic acid dissolved in 100 mL of methanol was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-7-3 precursor; (2) The PMA@ZnCo-ZIFs / PS-7-3 precursor was placed in a tube furnace and heated to 900 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-7-3).

[0040] The Co / Co3Mo3N-NHC-7-3 in this example presents a hollow porous carbon sphere structure.

[0041] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0042] After testing (testing method is the same as that of Example 1), the performance of the CR2032 button battery assembled in this example is close to that of the CR2032 button battery assembled in Example 1.

[0043] Example 6 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a mixed solution containing 0.5997 g of zinc chloride, 0.0779 g of cobalt chloride, and 0.076 g of phosphomolybdic acid dissolved in 100 mL of methanol was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-6-3-1 precursor; (3) The PMA@ZnCo-ZIFs / PS-6-3-1 precursor was placed in a tube furnace and heated to 900 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-6-3-1).

[0044] The Co / Co3Mo3N-NHC-6-3-1 in this example presents a hollow porous carbon sphere structure.

[0045] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0046] After testing (testing method is the same as that of Example 1), the performance of the CR2032 button battery assembled in this example is close to that of the CR2032 button battery assembled in Example 1.

[0047] Example 7 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a mixed solution containing 0.7897 g of zinc sulfate, 0.093 g of cobalt sulfate, and 0.076 g of phosphomolybdic acid dissolved in 100 mL of methanol was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-6-3-2 precursor; (2) The PMA@ZnCo-ZIFs / PS-6-3-2 precursor was placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-6-3-2).

[0048] The Co / Co3Mo3N-NHC-6-3-2 in this example presents a hollow porous carbon sphere structure.

[0049] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0050] After testing (testing method is the same as that of Example 1), the performance of the CR2032 button battery assembled in this example is close to that of the CR2032 button battery assembled in Example 1.

[0051] Example 8 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a 100 mL methanol mixed solution containing 1.3090 g of zinc nitrate, 0.1746 g of cobalt nitrate, and 0.038 g of phosphomolybdic acid was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-6-3 precursor; (2) The PMA@ZnCo-ZIFs / PS-6-3 precursor was placed in a tube furnace and heated to 900°C at a heating rate of 5°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-6-3).

[0052] The Co / Co3Mo3N-NHC-6-3 in this example presents a hollow porous carbon sphere structure.

[0053] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0054] After testing (testing method is the same as that of Example 1), the performance of the CR2032 button battery assembled in this example is close to that of the CR2032 button battery assembled in Example 1.

[0055] Example 9 This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a 100 mL methanol mixed solution containing 1.3090 g of zinc nitrate, 0.1746 g of cobalt nitrate, and 0.152 g of phosphomolybdic acid was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-6-3 precursor; (2) The PMA@ZnCo-ZIFs / PS-6-3 precursor was placed in a tube furnace and heated to 850°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-6-3).

[0056] The Co / Co3Mo3N-NHC-6-3 in this example presents a hollow porous carbon sphere structure.

[0057] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Experimental Example 1.

[0058] After testing (testing method is the same as that of Experimental Example 1), the performance of the CR2032 button battery assembled in this embodiment is close to that of the CR2032 button battery assembled in Experimental Example 1.

[0059] Example 10: This embodiment provides a cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a 100 mL methanol mixed solution containing 1.3090 g of zinc nitrate, 0.1746 g of cobalt nitrate, and 0.076 g of phosphomolybdic acid was added dropwise to the above solution, and then stirred at room temperature for 16 h. After centrifugation and washing, the product was collected to obtain a spherical structure of PMA@ZnCo-ZIFs / PS-6-3 precursor; (2) The PMA@ZnCo-ZIFs / PS-6-3 precursor was placed in a tube furnace and heated to 950°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain cobalt-molybdenum bimetallic nitride / metallic cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co / Co3Mo3N-NHC-6-3).

[0060] The Co / Co3Mo3N-NHC-6-3 in this example presents a hollow porous carbon sphere structure.

[0061] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0062] After testing (testing method is the same as that of Example 1), the performance of the CR2032 button battery assembled in this example is close to that of the CR2032 button battery assembled in Example 1.

[0063] Comparative Example 1 This comparative example provides a metal cobalt-modified nitrogen-doped hollow carbon microsphere material, the preparation method of which comprises the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a mixed solution containing 1.3090 g of zinc nitrate and 0.1746 g of cobalt nitrate dissolved in 100 mL of methanol was added dropwise to the above solution. The mixture was stirred at room temperature for 16 h. The product was collected after centrifugation and washing to obtain a spherical ZnCo-ZIFs / PS precursor.

[0064] (2) The ZnCo-ZIFs / PS precursor was placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain metal cobalt-modified nitrogen-doped hollow carbon microspheres (denoted as Co-NHC).

[0065] The SEM image of Co-NHC in this comparative example is as follows: Figure 6 shown.

[0066] Depend on Figure 6It can be seen that the Co-NHC in this comparative example presents a hollow carbon sphere structure.

[0067] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0068] The electrochemical performance of the CR2032 button cell in this comparative example, i.e., the coulombic efficiency, is shown in the figure below: Figure 7 As shown. Figure 7 It can be seen that Co-NHC material as sodium metal anode is -2 The current density and 1 mAh cm -2 It can circulate more than 200 times at the capacity of the battery.

[0069] Comparative Example 2: This embodiment provides a nitrogen-doped hollow carbon microsphere material, the preparation method of which includes the following steps: (1) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. Subsequently, a mixed solution containing 1.487 g of zinc nitrate dissolved in 100 mL of methanol was added dropwise to the above solution, and the mixture was stirred at room temperature for 16 h. The product was collected after centrifugation and washing to obtain a spherical Zn-ZIFs / PS precursor.

[0070] (2) The Zn-ZIFs / PS precursor was placed in a tube furnace and heated to 900 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain nitrogen-doped hollow carbon microspheres (NHC).

[0071] The SEM image of NHC in this comparative example is as follows: Figure 8 shown.

[0072] Depend on Figure 8 It can be seen that the NHC in this comparative example presents a hollow porous carbon sphere structure.

[0073] The sodium metal battery negative electrode material was prepared and CR2032 button cells (ie, sodium metal negative electrode batteries) were assembled according to the method of Example 1.

[0074] The electrochemical performance of the CR2032 button cell in this comparative example, i.e., the coulombic efficiency, is shown in the figure below: Figure 9 As shown. Figure 9 It can be seen that NHC material as sodium metal anode is 1 mA cm -2 The current density and 1 mAh cm -2 The battery only cycles for more than 140 cycles at a capacity of 100 nm. This is because the nitrogen-doped carbon substrate has poor affinity with sodium metal, making it difficult to achieve uniform nucleation.

[0075] Therefore, the present invention provides cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres and their preparation and application. Cobalt-molybdenum bimetallic nitrides and metallic cobalt and nitrogen-doped sodium-philic sites are simultaneously introduced into the nitrogen-doped hollow carbon microspheres, effectively inducing the uniform transport and nucleation of sodium ions, guiding the deposition of sodium metal within a specific three-dimensional structure, achieving more stable sodium metal deposition / stripping, effectively inhibiting the growth of sodium dendrites, and alleviating the volume expansion of metallic sodium during the reaction. Furthermore, the material preparation method is simple and low-cost. The sodium metal battery assembled with the obtained negative electrode material can significantly improve the battery's cycle stability and has good prospects for large-scale application.

[0076] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and does not limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres, characterized in that: The following steps are involved: (1) Carboxylated polystyrene microspheres, soluble zinc salt, soluble cobalt salt, phosphomolybdic acid and 2-methylimidazole are dispersed in methanol to form a methanol solution, and reacted to obtain a spherical structure of PMA@ZnCo-ZIFs / PS precursor; (2) The PMA@ZnCo-ZIFs / PS precursor is placed in an inert atmosphere for carbonization to obtain cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres.

2. The method for preparing cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres according to claim 1, characterized in that: In step (1), the soluble zinc salt is one or more of zinc nitrate, zinc chloride, and zinc sulfate; the soluble cobalt salt is one or more of cobalt nitrate, cobalt sulfate, and cobalt chloride; and the molar ratio of the soluble zinc salt to the soluble cobalt salt is 1:(6-9).

3. The method for preparing cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres according to claim 1, characterized in that: In the methanol solution of step (1), the mass concentration of carboxylated polystyrene microspheres is 1-5 g / L, and the mass concentration of phosphomolybdic acid is 0.38-1.52 g / L.

4. The method for preparing cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres according to claim 1, characterized in that: In the methanol solution of step (1), the molar concentration of 2-methylimidazole is 0.4 mol / L, and the molar ratio of the soluble zinc salt to the 2-methylimidazole is 1:(8-10).

5. The method for preparing cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres according to claim 1, characterized in that: The reaction temperature of step (1) is room temperature, and the reaction time is 12h-18h.

6. The method for preparing cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres according to claim 1, characterized in that: The inert atmosphere of step (2) is argon or nitrogen, and the specific operation of carbonization is: heating rate of 3°C / min-5°C / min, calcination temperature of 850°C-950°C, and holding time of 1h-3h.

7. A cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microsphere, characterized in that: The cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres are prepared by the preparation method according to any one of claims 1 to 6, and have a hollow porous sphere structure.

8. A use of the cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres as claimed in claim 7, characterized in that: The cobalt-molybdenum nitride / cobalt-modified nitrogen-doped hollow carbon microspheres are used as the host material of the sodium metal negative electrode, and the negative electrode material slurry obtained by mixing with sodium hydroxymethyl cellulose and carbon black is coated on a copper foil current collector to prepare a sodium metal battery negative electrode material.

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