Nitrogen-doped porous carbon nanofiber composites supported by different transition metal tellurides and their preparation methods

Abstract

This invention discloses nitrogen-doped porous carbon nanofiber composites supported on different transition metal tellurides and their preparation method. The method includes the following steps: dissolving ZnCo-ZIF NCs and Te NWs in an ethanol solution, then mixing and stirring the two solutions until homogeneous, adding polyvinylpyrrolidone, and stirring to obtain a spinning solution; spinning to obtain ZnCo-ZIF / Te@PVP nanofibers; pre-oxidizing the ZnCo-ZIF / Te@PVP nanofibers in air, then placing the oxidized fibers and tellurium powder in the downstream and upstream sections of a tube furnace, respectively, and calcining under H2 / Ar conditions by controlling the temperature to obtain nitrogen-doped porous carbon nanofiber composites supported on different transition metal tellurides. This invention can improve redox reaction kinetics, reduce volume expansion, and exhibit better electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage and functional nanomaterials, specifically to nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides and their preparation methods. Background Technology

[0002] Currently, energy storage devices are one solution to the serious environmental problems caused by the excessive consumption of traditional fossil fuels. Meanwhile, lithium-ion batteries and lithium-sulfur batteries, due to their high energy density, abundant active materials, and environmental friendliness, have become the most widely studied rechargeable batteries in next-generation energy storage. However, researchers have discovered several problems hindering sustainable development when studying lithium-ion battery anode materials and lithium-sulfur battery cathode materials. First, during cycling, volume stress changes and electrode fragmentation in lithium-ion batteries lead to thickening of the solid electrolyte interphase (SEI), ultimately resulting in capacity decay. Second, lithium-sulfur batteries suffer from volume expansion during charge and discharge, the insulating properties of sulfur and lithium sulfide affecting charge transport capacity, and the shuttle effect caused by the dissolution of intermediate polysulfides leading to irreversible loss of active materials. Therefore, it is urgent to rationally design a conductive nanocomposite material in terms of structure and composition to improve battery cycle stability and coulombic efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides and their preparation methods. When used as electrode materials, these materials can improve redox reaction kinetics, reduce volume expansion, and exhibit good electrochemical performance during cycling.

[0004] In one aspect of the present invention, a method for preparing nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides is provided. According to an embodiment of the present invention, the method includes the following steps:

[0005] (1) Dissolve ZnCo-ZIF NCs (ZnCo-ZIF nanoparticles) in ethanol solution and Te NWs (tellurium nanowire materials) in ethanol. Then mix the two solutions evenly and add polyvinylpyrrolidone. Stir to obtain a spinning solution and spin to obtain ZnCo-ZIF / Te@PVP nanofibers.

[0006] (2) ZnCo-ZIF / Te@PVP nanofibers were first pre-oxidized in air, and then the oxidized fibers and tellurium powder were placed in the downstream and upstream of a tube furnace, respectively. Under H2 / Ar conditions, the temperature was controlled to calcine the fibers to obtain nitrogen-doped porous carbon nanofiber composite materials supported by different transition metal tellurides.

[0007] Furthermore, the preparation method of nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides according to the above embodiments of the present invention may also have the following additional technical features:

[0008] In some embodiments of the present invention, the preparation method of ZnCo-ZIF NCs in step (1) is as follows: 2-methylimidazole is dissolved in deionized water and stirred evenly to obtain dispersion A; cobalt nitrate hexahydrate and zinc nitrate hexahydrate are dissolved in deionized water, hexadecyltrimethylammonium bromide is added, and ultrasonically homogenized to obtain dispersion B; dispersion B is quickly poured into dispersion A and stirred to precipitate; the precipitated solution is centrifuged to obtain ZnCo-ZIF NCs.

[0009] In some embodiments of the present invention, the mass ratio of cobalt nitrate hexahydrate, zinc nitrate hexahydrate, and 2-methylimidazole is 20-50:20-50:1; the mass of hexadecyltrimethylammonium bromide (CTAB) is 30-35 mg; and the precipitation time is 2-3 h.

[0010] In some embodiments of the present invention, the preparation method of Te NWs in step (1) is as follows: sodium tellurite is dissolved in deionized water, ultrasonically dispersed evenly, and then polyvinylpyrrolidone K30 is added and stirred to form a transparent liquid. Then ammonia water and hydrazine hydrate are added and stirred evenly. The solution is transferred to a reaction vessel and sealed. After being kept at 180°C for 2-4 hours, the solution is cooled to obtain Te NWs stock solution. The Te NWs stock solution is centrifuged and washed to obtain Te NWs.

[0011] In some embodiments of the present invention, the mass ratio of sodium tellurite to polyvinylpyrrolidone K30 is 1-2:1; the volume ratio of sodium tellurite to ammonia and hydrazine hydrate is 1-2g:5-7mL:3-5mL; the centrifugal washing is performed using acetone and ethanol at a centrifugation speed of 7000-12000rpm.

[0012] In some embodiments of the present invention, in step (1), the spinning is carried out using electrospinning technology, with a temperature of 20-25°C, a relative humidity of 40%-60%, a flow rate of 0.2-0.5 mL / h, and a voltage of 6-9 kV; the mass ratio of ZnCo-ZIF NCs, TeNWs, and polyvinylpyrrolidone is 0.3-0.35:0.6-0.8:0.45.

[0013] In some embodiments of the present invention, in step (2), the temperature of pre-oxidation in air is 200-280°C, the heating rate is 2°C / min, and the oxidation time is 1-3h; the mass ratio of fiber to tellurium powder after oxidation is 1:0.8-1.6; and the volume ratio of H2 to Ar is 1:9.

[0014] In some embodiments of the present invention, in step (2), when the calcination temperature is 500-550°C, a ZnTe / CoTe2@NC nanofiber composite material is obtained; when the calcination temperature is 600-650°C, a ZnTe / CoTe@NC nanofiber composite material is obtained; and when the calcination temperature is 700-800°C, a CoTe@NC nanofiber composite material is obtained.

[0015] In another aspect of the present invention, the present invention proposes a nitrogen-doped porous carbon nanofiber composite material for transition metal telluride supported by nitrogen according to the preparation method of the aforementioned composite material for different transition metal telluride supported by nitrogen.

[0016] In another aspect of the invention, an application of the aforementioned transition metal telluride-supported nitrogen-doped porous carbon nanofiber composite material is proposed. According to embodiments of the invention, the transition metal telluride-supported nitrogen-doped porous carbon nanofiber composite material is used as a lithium-ion battery anode material and a lithium-sulfur battery cathode sulfur host material.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] (1) This invention uses bimetallic zeolite imidazole framework ZnCo-ZIF and Te NWs as precursors to obtain one-dimensional nanofibers through electrospinning. Subsequently, nitrogen-doped porous carbon nanofiber composite materials with different transition metal tellurides are obtained under different temperature control conditions, namely ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC. This method is low in cost, simple in preparation process, and has high production efficiency, meeting the requirements of industrial production and showing promising application prospects.

[0019] (2) When applied to electrode materials for lithium-ion batteries and lithium-sulfur batteries, this invention exhibits good cycle performance. When ZnTe / CoTe2@NC is used as a lithium-ion anode material, the specific capacity remains at 1298.9 mAh / g after 300 cycles at a current density of 1 A / g. When used as a sulfur host for lithium-sulfur battery cathode materials, the capacity is 1147 mAh / g in the first cycle at a current density of 0.2 C, and 811.2 mAh / g after cycling, with a retention rate as high as 70.7%.

[0020] (3) This invention obtains carbon nanofiber composite materials supported by different transition metal tellurides by controlling the temperature, which have high conductivity and abundant active sites. Due to the low electronegativity, large atomic size and high conductivity of Te, its compounds have a strong ability to attract electrons. At the same time, nitrogen doping further improves conductivity, the heterostructure improves the electronic coordination environment and promotes ion diffusion, and the one-dimensional carbon skeleton reduces the ion transport path, so as to maintain the structural integrity of the electrode material during cycling.

[0021] (4) The ZnTe / CoTe2@NC heterostructure modifies the electronic structure at the interface, reducing the ion diffusion barrier; Te has a higher electronic conductivity (2×10⁻⁶). 2 S / m), compared to S(6×10 -16 S / m) and Se(1×10 -4 With a particle size of (S / m), it can enhance the conductivity of the material and accelerate charge transfer; the one-dimensional structure can maintain the integrity of the electrode material and shorten the ion diffusion path; compared with ZnTe / CoTe@NC and CoTe@NC, the particles are smaller, which is more conducive to the exposure of active sites. Combining the advantages of composition and structure, ZnTe / CoTe2@NC exhibits high specific capacity, high rate performance and long-term stability when applied to lithium-ion anode materials and lithium-sulfur battery cathode materials.

[0022] (5) When ZnTe / CoTe2@NC is used as the sulfur host in lithium-sulfur cathode material, during cycling, on the one hand, its heterostructure modifies the electronic structure at the interface, accelerating charge transport during the sulfur conversion and reduction reaction; the bimetallic transition metal telluride ZnTe / CoTe2 particles improve the adsorption capacity for polysulfides, thereby reducing the shuttle effect. On the other hand, due to the one-dimensional porous structure of ZnTe / CoTe2@NC, the stability of the electrode material is maintained during cycling. Based on the above advantages, the lithium-sulfur battery based on the ZnTe / CoTe2@NC / S electrode exhibits a high initial capacity of 1147 mAh·g at 0.2C. -1 Furthermore, the capacity retention rate is as high as 70.7% after 100 cycles. Attached Figure Description

[0023] Figure 1 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of ZnCo-ZIF / Te@PVP nanofibers in Example 1 of this invention. The left image is a scanning electron microscope (SEM) image, and the right image is a transmission electron microscope (TEM) image.

[0024] Figure 2 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the ZnTe / CoTe2@NC composite material in Example 1 of this invention, with the left image being the SEM image and the right image being the TEM image.

[0025] Figure 3 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the ZnTe / CoTe@NC composite material in Example 2 of this invention. The left image is a scanning electron microscope (SEM) image, and the right image is a transmission electron microscope (TEM) image.

[0026] Figure 4 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the CoTe@NC composite material in Example 3 of the present invention, wherein the left image is a scanning electron microscope (SEM) image and the right image is a transmission electron microscope (TEM) image.

[0027] Figure 5 The XRD patterns of the ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC composite materials obtained in Examples 1-3 of this invention are shown below.

[0028] Figure 6 The above are the total XPS spectrum and high-resolution XPS spectra of each element of the ZnTe / CoTe2@NC composite material obtained in Example 1 of this invention, where a is the total spectrum, b is the XPS spectrum of C element, c is the XPS spectrum of N element, d is the XPS spectrum of Co element, e is the XPS spectrum of Zn element, and f is the XPS spectrum of Te element.

[0029] Figure 7 This is a cyclic voltammetry curve of a lithium-ion half-cell assembled using ZnTe / CoTe2@NC as the negative electrode material in Example 4 of the present invention.

[0030] Figure 8 This is a cyclic voltammetry curve of a lithium-ion half-cell assembled using ZnTe / CoTe@NC as the negative electrode material in Example 4 of the present invention.

[0031] Figure 9 This is a cyclic voltammetry curve of a lithium-ion half-cell assembled using CoTe@NC as the negative electrode material in Example 4 of the present invention.

[0032] Figure 10 The graph shows the cycling performance of a lithium-ion half-cell assembled using three different transition metal tellurides, ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC, as lithium-ion battery anode materials in Example 4 of this invention, at a current density of 1 A / g.

[0033] Figure 11 The rate performance of lithium-ion half-cells assembled using three different transition metal tellurides, ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC, as lithium-ion battery anode materials in Example 4 of this invention, is shown at different current densities.

[0034] Figure 12 This is the electrochemical impedance spectroscopy of a lithium-ion half-cell assembled using three different transition metal tellurides, ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC, as the negative electrode materials of a lithium-ion battery in Example 4 of the present invention.

[0035] Figure 13 The graph shows the cycling performance of a lithium-sulfur battery assembled using three different transition metal tellurides, ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC, as sulfur hosts in Example 5 of this invention, at a current density of 0.2C.

[0036] Figure 14 This is a graph showing the cycling performance of a lithium-sulfur battery at 1C current density when three different transition metal tellurides, ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC, are used as sulfur hosts and assembled into a battery in Example 5 of the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, all pharmaceuticals / reagents used in the following examples are commercially available. The centrifuge used in the following examples is an Anke TGL-10B manufactured by Shanghai Anting Scientific Instrument Factory, the electrospinning machine is a PHD-2000 manufactured in Japan, the high-temperature tube furnace is an OTF-1200X manufactured by Hefei Kejing Materials Technology Co., Ltd., the scanning electron microscope is a Zeiss Supra40 manufactured in Germany, the transmission electron microscope is a JEOL-F2010 manufactured in Japan, and the battery performance was tested using the LAND testing system and the Donghua Electrochemical Workstation.

[0039] Example 1

[0040] A method for preparing nitrogen-doped porous carbon nanofiber composites supported on different transition metal tellurides includes the following steps:

[0041] (1) Synthesis of ZnCo-ZIF NCs materials

[0042] 10 g of 2-methylimidazole was weighed and dissolved in 100 mL of deionized water, and stirred until homogeneous to form solution A. 0.198 g of zinc nitrate hexahydrate and 0.388 g of cobalt nitrate hexahydrate were weighed and dissolved in 50 mL of deionized water, and stirred until homogeneous. Then, 32 mg of hexadecyltrimethylammonium bromide (CTAB) was added and ultrasonically dispersed until homogeneous to form solution B. Solution B was quickly poured into solution A and stirred for 20 min, then allowed to stand for 2 h to precipitate. The precipitate was washed twice, once with methanol and once with ethanol, by centrifugation at 12000 rpm. After separation, ZnCo-ZIF nanocube particles, i.e., ZnCo-ZIF NCs, were obtained.

[0043] (2) Synthesis of TeNWs materials

[0044] 0.1844 g of sodium tellurite was dissolved in 66 mL of deionized water and ultrasonically dispersed until homogeneous. Then, 1 g of polyvinylpyrrolidone K30 (PVP K30) was added, and the mixture was stirred until a clear solution was obtained. Next, 6.66 mL of ammonia and 3.34 mL of hydrazine hydrate were added, and stirring was continued for 5 min. The resulting solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 180 °C for 3 h. After cooling, the solution was washed once with acetone by centrifugation and twice with ethanol by centrifugation to obtain TeNWs.

[0045] (3) Synthesis of ZnCo-ZIF / Te@PVP nanofibers

[0046] 0.3 g of ZnCo-ZIF NCs and 0.8 g of Te NWs were dissolved in 3 mL of anhydrous ethanol and ultrasonically dispersed for 1 h. After mixing the two solutions thoroughly, 0.45 g of polyvinylpyrrolidone was added and stirred for 4 h to obtain a spinning solution. The spinning solution was loaded into a 10 mL syringe and spun into ZnCo-ZIF / Te@PVP nanofibers using electrospinning technology at a temperature of 25 °C, a relative humidity of 50%, a flow rate of 0.3 mL / h, and a voltage of 8 kV.

[0047] like Figure 1 As shown, ZnCo-ZIF particles are densely distributed within the fiber, while TeNWs are arranged in a complex and interwoven manner within the fiber, with a fiber diameter of approximately 500 nm.

[0048] (4) Synthesis of ZnTe / CoTe2@NC, ZnTe / CoTe@NC and CoTe@NC composite materials

[0049] The fiber film obtained in step 3 was pre-oxidized in air at 250℃ for 2 hours at a heating rate of 2℃ / min. The oxidized fiber film and tellurium powder were placed downstream and upstream of a ceramic boat at a mass ratio of 1:1.5, respectively, and placed in a tube furnace under 10 vol% H2 / Ar conditions at a heating rate of 1℃ / min. Calcination was carried out at 550℃ for 4 hours to obtain ZnTe / CoTe2@NC composite material. Changing the temperature to 650℃ and 750℃ yielded ZnTe / CoTe@NC and CoTe@NC composite materials, respectively.

[0050] like Figure 2 As shown, after calcination in H2 / Ar gas, ZnTe / CoTe2@NC still maintains its nanofiber structure. The ZnTe / CoTe2 particles are uniformly dispersed and small in size, with a particle size between 20 and 40 nm.

[0051] like Figure 6As shown, ZnTe / CoTe2@NC contains C, N, O, Zn, Co, and Te, with the O element originating from the formation of C=O bonds. The N1s high-resolution fine spectrum (c) yielded three peaks at binding energies of 397.9 V, 399.8 V, and 402.6 V, corresponding to pyridine N, pyrrole N, and graphite N, respectively. Pyridine N and pyrrole N effectively increase the electron density and interaction with sulfur / polysulfides, while graphite N improves the material's electrical conductivity.

[0052] Example 2

[0053] The preparation method of nitrogen-doped porous carbon nanofiber composite materials supported by different transition metal tellurides differs from that in Example 1 only in that: in step (4), the calcination temperature is 650℃ to obtain ZnTe / CoTe@NC composite material.

[0054] Example 3

[0055] The preparation method of nitrogen-doped porous carbon nanofiber composite materials supported by different transition metal tellurides differs from that in Example 1 only in that: in step (4), the calcination temperature is 750℃ to obtain the CoTe@NC composite material.

[0056] like Figure 3 , 4 As shown, it can be seen that as the temperature increases, the particle diameter inside the fiber gradually increases. The ZnTe / CoTe particles obtained by calcination at 650℃ are about 60nm in size, while the CoTe particles obtained by calcination at 750℃ are about 80nm in size, but the particles do not agglomerate.

[0057] like Figure 5 As shown, the characteristic peaks of ZnTe / CoTe2@NC and ZnTe / CoTe@NC at 25.2°, 41.9°, and 49.5° correspond to the (111), (220), and (311) crystal planes of ZnTe (PDF#89-3054), while the characteristic peaks at 31.9°, 33.1°, 43.7°, 46.8°, 49.3°, and 58.5° can be attributed to the (111), (220), and (311) crystal planes of CoTe2 (PDF#74-0245). 12), (121), (200), (103), (212) crystal planes, while the characteristic peaks of CoTe (PDF#70-2887) are located at 31.3°, 43.0°, and 46.7°, which correspond exactly to the characteristic peaks of CoTe in ZnTe / CoTe@NC and CoTe@NC. The results prove the formation of the heterostructures of ZnTe / CoTe2@NC and ZnTe / CoTe@NC, as well as the formation of CoTe@NC elemental.

[0058] Example 4

[0059] A method for preparing a lithium-ion half-cell includes the following steps:

[0060] (1) Preparation of negative electrode sheet.

[0061] The ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC composite materials prepared in Examples 1-3 were used as working electrode materials. The electrode materials, acetylene black, and polyvinylidene fluoride (PVDF) were mixed uniformly at a mass ratio of 7:2:1, and then an appropriate amount of N-methylpyrrolidone (NMP) was added and ground into a uniform slurry. The slurry was then coated onto copper foil and dried in a vacuum oven at 80°C for 12 hours. Finally, the dried electrode sheets were cut into 12 mm diameter electrode discs, and the active mass of each electrode disc was recorded.

[0062] (2) Assembly and testing of lithium-ion half-cells.

[0063] The electrode plates were placed in a glove box filled with Ar gas and assembled into a coin cell in the following order: negative electrode shell, lithium plate, separator, electrolyte, electrode, gasket, spring plate, and positive electrode shell. The cell was then sealed using a pressing machine. The separator was made of glass fiber filter paper (GF / D), and the electrolyte was a 1M LiPF6 solution. Finally, the cell was allowed to stand for 12 hours to allow the electrolyte to fully wet the electrodes.

[0064] Cyclic performance and rate performance were tested using the LAND test system, while cyclic voltammetry and electrochemical impedance spectroscopy were performed using the Donghua electrochemical workstation.

[0065] Figure 7-9 As shown, during the first cathode scan, peak values ​​appeared at 0.73V for the ZnTe / CoTe2@NC electrode, 0.74V for the ZnTe / CoTe@NC electrode, and 0.74V and 0.99V for the CoTe@NC electrode. These peak values ​​disappeared in the subsequent two scans. This is attributed to the formation of a stable solid electrolyte interphase (SEI) film on the electrode surface and the formation of irreversible reactions. Figure 7 Taking ZnTe / CoTe2@NC as an example, two reduction peaks appear at 1.28V and 0.75V respectively. These are attributed to the reaction between CoTe2 particles and Li in ZnTe / CoTe2@NC. + Reduction produces Li₂Te and Co, as well as ZnTe and Li. + Reduction to Li₂Te and Zn yields oxidation peaks at 1.86 V and 1.30 V, respectively. Similarly, ZnTe / CoTe@NC shows similar results, although CoTe@NC, lacking a heterostructure, exhibits only one set of redox peaks.

[0066] like Figure 10As shown, the initial specific capacities of ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC in the first cycle were 1735.7, 1667.7, and 1000.8 mAh / g, respectively. After 300 cycles, the specific capacities remained at 1209.2, 787.9, and 637.9 mAh / g, respectively. This result demonstrates that ZnTe / CoTe2@NC has significant long-cycle performance.

[0067] Figure 11 The rate performance curves for the three electrodes are shown at current densities of 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, and 5 A / g, finally returning to 0.2 A / g. The specific capacities of the ZnTe / CoTe2@NC electrode are 1039.8 mAh / g, 867.6 mAh / g, 755.6 mAh / g, 679.8 mAh / g, 562.1 mAh / g, and finally returning to 966.6 mAh / g, respectively. Its specific capacity is consistently higher than that of the ZnTe / CoTe@NC and CoTe@NC electrodes, demonstrating the excellent rate performance of the ZnTe / CoTe2@NC anode material.

[0068] like Figure 12 As shown, the semicircle in the high-frequency region corresponds to the interfacial charge transfer impedance (Rct), and the slanted line in the low-frequency region represents the Warburg impedance (Z). w ), with Li + The diffusion resistance is related to the results, which show that the ZnTe / CoTe2@NC electrode has the smallest semicircle, and therefore the smallest Rct value. This confirms that its heterostructure and the presence of CoTe2 significantly improve electronic conductivity and Li. + The diffusion rate may be due to the modification of the electronic structure between the interfaces by the heterostructure. Compared with CoTe, CoTe2 has a lower antibonding state occupancy rate, and its Co atoms interact more strongly with lithium.

[0069] Example 5

[0070] The ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC composite materials obtained in this embodiment are used as sulfur hosts to become positive electrode materials for lithium-sulfur batteries. The assembly of these materials into lithium-sulfur batteries and performance testing include the following steps:

[0071] A method for preparing a lithium-sulfur battery includes the following steps:

[0072] (1) Preparation of ZnTe / CoTe2@NC / S, ZnTe / CoTe@NC / S, and CoTe@NC / S cathode materials

[0073] First, sublimed sulfur was thoroughly ground with the ZnTe / CoTe2@NC, ZnTe / CoTe@NC, and CoTe@NC prepared in Examples 1-3 at a mass ratio of 7:3. The mixture was then placed in a polytetrafluoroethylene-lined reactor filled with inert gas and sealed. The reactor was heated to 155°C in an oven for 12 hours, and then cooled to obtain ZnTe / CoTe2@NC / S, ZnTe / CoTe@NC / S, and CoTe@NC / S composite materials. Next, the obtained material was ground with acetylene black and polyvinylidene fluoride (PVDF) at a mass ratio of 7:2:1, with an appropriate amount of NMP added. After grinding into a slurry, the slurry was coated onto aluminum foil and heated in a 50°C vacuum oven for 12 hours. The resulting material was then cut into electrode discs with a diameter of 12 mm and a sulfur loading of 1 mg / cm³. 2 about.

[0074] (2) Assembly of lithium-sulfur batteries

[0075] The assembly steps are the same as step (2) of the lithium-ion half-cell in Example 4, wherein the separator is Celgard 2400 and the electrolyte is 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) containing 2wt% LiNO3 and diluted with a mixed solvent of DOL / DEM (volume ratio 1:1), i.e., 1M LiTFSI-DOL / DME (1:1v / v)-2wt% LiNO3.

[0076] The resulting batteries were left to stand for 12 hours before undergoing cycle performance testing on the LAND testing system.

[0077] The cycle performance curves of lithium-sulfur batteries with three different electrode assemblies at a current density of 0.2C (1C = 1675 mA / g) are shown below. Figure 13 As shown, the ZnTe / CoTe2@NC / S electrode exhibited a specific capacity of 1147 mAh / g in the first cycle and maintained 811.2 mAh / g after 100 cycles, demonstrating a capacity retention of 70.7%, which is higher than that of the ZnTe / CoTe@NC / S electrode (58.7%) and the CoTe@NC / S electrode (58.5%). Further evaluation of the long-term cycling performance of the three electrodes at high current densities was conducted, such as... Figure 14As shown, even at a 1C current density, the ZnTe / CoTe2@NC / S electrode achieved a capacity of 575.6 mAh / g after 440 cycles, with a capacity retention of 71.8%. In contrast, the specific capacities of the ZnTe / CoTe@NC / S and CoTe@NC / S electrodes after 440 cycles were 480 mAh / g and 334.3 mAh / g, respectively, both lower than those of the ZnTe / CoTe2@NC / S electrode. This result further verifies that ZnTe / CoTe2@NC exhibits strong adsorption capacity with sulfur / polysulfides when acting as a sulfur host in lithium-sulfur batteries, thereby improving the sulfur conversion rate. Whether used as a negative electrode material for lithium-ion batteries or a sulfur host for positive electrode materials in lithium-sulfur batteries, ZnTe / CoTe2@NC exhibits excellent electrochemical performance. This remarkable performance is attributed to the presence of a heterojunction in ZnTe / CoTe2@NC, which modifies the interfacial electronic structure, promotes ion / electron transport rates, and enhances the adsorption capacity of the material with polysulfides and lithium. In addition, compared with CoTe, CoTe2 has a lower occupancy of antibonded Co atoms, thus its Co interacts more strongly with sulfides and lithium.

[0078] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides, characterized in that, Includes the following steps: (1) Dissolve ZnCo-ZIF nanoparticles in ethanol solution and Te nanowire material in ethanol. Then mix the two solutions evenly and add polyvinylpyrrolidone. Stir to obtain spinning solution and spin to obtain ZnCo-ZIF / Te@PVP nanofibers. (2) ZnCo-ZIF / Te@PVP nanofibers were first pre-oxidized in air, and then the oxidized fibers and tellurium powder were placed in the downstream and upstream of a tube furnace, respectively. Under H2 / Ar conditions, the temperature was controlled to calcine the fibers to obtain nitrogen-doped porous carbon nanofiber composites supported by different transition metal tellurides. Among them, when the calcination temperature was 500~550℃, ZnTe / CoTe2@NC nanofiber composites were obtained. When the calcination temperature is 600~650℃, ZnTe / CoTe@NC nanofiber composite material is obtained; when the calcination temperature is 700~800℃, CoTe@NC nanofiber composite material is obtained.

2. The method for preparing nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides according to claim 1, characterized in that, In step (1), the ZnCo-ZIF nanoparticles are prepared as follows: 2-methylimidazole is dissolved in deionized water and stirred evenly to obtain dispersion A; cobalt nitrate hexahydrate and zinc nitrate hexahydrate are dissolved in deionized water, hexadecyltrimethylammonium bromide is added, and ultrasonically homogenized to obtain dispersion B; dispersion B is quickly poured into dispersion A and stirred to precipitate; the precipitated solution is centrifuged to obtain ZnCo-ZIF nanoparticles.

3. The method for preparing nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides according to claim 2, characterized in that: The mass ratio of cobalt nitrate hexahydrate, zinc nitrate hexahydrate, and 2-methylimidazole is 20~50:20~50:1; the mass of hexadecyltrimethylammonium bromide is 30~35 mg; and the precipitation time is 2~3 h.

4. The method for preparing nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides according to claim 1, characterized in that, In step (1), the preparation method of Te nanowire material is as follows: Sodium tellurite is dissolved in deionized water, ultrasonically dispersed evenly, and then polyvinylpyrrolidone K30 is added and stirred to form a transparent liquid. Then ammonia water and hydrazine hydrate are added and stirred evenly. The solution is transferred to a reaction vessel and sealed. After being kept at 180℃ for 2-4 h, the Te nanowire material stock solution is obtained after cooling. The Te nanowire material stock solution is centrifuged and washed to obtain Te nanowire material.

5. The method for preparing nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides according to claim 4, characterized in that: The mass ratio of sodium tellurite to polyvinylpyrrolidone K30 is 1~2:1; the ratio of sodium tellurite to ammonia and hydrazine hydrate is 1~2 g:5~7 mL:3~5 mL; the centrifugal washing is performed with acetone and ethanol at a centrifugation speed of 7000~12000 rpm.

6. The method for preparing nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides according to claim 1, characterized in that: In step (1), electrospinning is carried out at a temperature of 20~25℃, a relative humidity of 40%~60%, a flow rate of 0.2~0.5 mL / h, and a voltage of 6~9 kV; the mass ratio of ZnCo-ZIF nanoparticles, Te nanowire materials, and polyvinylpyrrolidone is 0.3~0.35:0.6~0.8:0.

45.

7. The method for preparing nitrogen-doped porous carbon nanofiber composite materials supported on different transition metal tellurides according to claim 1, characterized in that: In step (2), the pre-oxidation temperature in air is 200~280℃, the heating rate is 2℃ / min, and the oxidation time is 1-3h; the mass ratio of fiber to tellurium powder after oxidation is 1:0.8~1.6; and the volume ratio of H2 to Ar is 1:

9.

8. A method for preparing nitrogen-doped porous carbon nanofiber composite materials supported by different transition metal tellurides as described in any one of claims 1-7.

9. The application of the transition metal telluride-supported nitrogen-doped porous carbon nanofiber composite material according to claim 8, characterized in that: The transition metal telluride-loaded nitrogen-doped porous carbon nanofiber composite material is used as a negative electrode material for lithium-ion batteries and a sulfur host material for positive electrodes in lithium-sulfur batteries.

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