A method for preparing cobalt telluride-rich carbon nanocages for lithium-sulfur battery positive electrode carrier materials

Abstract

This invention discloses a method for preparing cobalt telluride-rich carbon nanocages for use as cathode supports in lithium-sulfur batteries. The method involves growing ZIF-67 on Te nanowires, followed by a simple water etching and one-step annealing process to obtain the cobalt telluride-rich carbon nanocages. This cathode material has a simple preparation process, excellent cycle stability, and high specific capacity, providing a novel design and preparation strategy for sulfur supports in lithium-sulfur batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode carrier materials for lithium-sulfur batteries, and in particular to a method for preparing a cobalt telluride-rich carbon nanocage for use as a positive electrode carrier material for lithium-sulfur batteries. Background Art

[0002] In order to cope with the energy crisis and environmental pollution, it is imperative to optimize the existing energy structure and seek new energy sources that are renewable, clean, and efficient. Secondary batteries, as the mainstream form of electrochemical energy storage, are considered one of the most promising candidates due to their high efficiency and stability. Among them, lithium-ion batteries are the most widely used, having a profound impact on people's production and life and triggering multiple industrial changes. However, commercial lithium-ion batteries are approaching the upper limit of their theoretical energy density, and there is limited room for improvement. Lithium-sulfur batteries have high theoretical specific capacity and energy density, and their practical energy density is still 2 to 3 times that of today's commercial lithium-ion batteries. In addition, sulfur, the active material of the positive electrode, is naturally abundant and low-cost. Compared with the heavy metal elements in lithium-ion batteries, sulfur is less toxic, which meets the needs of large-scale power storage.

[0003] Currently, the strategy for lithium-sulfur battery cathode carriers is to reduce the loss of electrochemically active substances and accelerate the conversion efficiency of intermediate products. Carbon materials have become one of the most common choices for carrier materials composited with sulfur due to their high conductivity, porous structural characteristics and low cost. At the same time, carbon materials are also excellent substrates for catalytic sites. Therefore, in recent years, various transition metal compounds have been composited with carbon materials to confine soluble polysulfides through physical adsorption and chemical anchoring, while simultaneously combining with catalytic sites to accelerate the reaction kinetics of electrochemically active substances. However, due to the limitations of low electronic conductivity and low durability of materials such as transition metal oxides and sulfides, their electrocatalytic performance towards polysulfides is greatly restricted. Transition metal tellurides have advantages such as high conductivity and high electrocatalytic activity, but due to their low natural abundance and high density, they are rarely used as electrode materials for lithium-sulfur batteries. Summary of the Invention

[0004] In response to the above-mentioned problems currently existing in lithium-sulfur batteries, the present invention provides a method for preparing cobalt telluride-rich carbon nanocages for use as positive electrode carrier materials for lithium-sulfur batteries. The carrier material prepared by this method, due to its reasonable design, minimizes the content of transition metal tellurides and achieves excellent electrocatalytic performance, enabling efficient conversion of polysulfides during battery charging and discharging. It has excellent structural stability and long cycle life, and is suitable for large-scale electrochemical energy storage systems.

[0005] To achieve the purpose, the present invention adopts the following technical solutions:

[0006] A method for preparing cobalt telluride-rich carbon nanocages for use as cathode carrier materials in lithium-sulfur batteries is characterized by first preparing tellurium nanowires, then growing ZIF-67 on the tellurium nanowires, then forming a nanocage structure through water etching, and finally performing a carbonization heat treatment to obtain cobalt telluride-rich carbon nanocages. The method specifically comprises the following steps:

[0007] Step 1, dissolving 0.500-0.700 g of polyvinyl pyrrolidone in 19-23 mL of deionized water, adding 50.0-60.0 mg of sodium tellurite, 1-3 mL of 24-26 wt% ammonia water, and 0.5-1.5 mL of 84-86 wt% hydrazine hydrate and stirring evenly, then transferring to a reactor for hydrothermal reaction to obtain a tellurium nanowire mother liquor; adding acetone to the tellurium nanowire mother liquor, centrifuging, and dispersing the obtained tellurium nanowires in 22-26 mL of anhydrous methanol to obtain a tellurium nanowire dispersion;

[0008] Step 2: dissolving 0.690-0.710 g of cobalt nitrate hexahydrate in 22-26 mL of anhydrous methanol to obtain a cobalt nitrate solution; dissolving 1.500-1.650 g of 2-methylimidazole in 22-26 mL of anhydrous methanol to obtain a 2-methylimidazole solution; adding the cobalt nitrate solution and the 2-methylimidazole solution to the tellurium nanowire dispersion obtained in step 1 and stirring at room temperature to react; washing the obtained product with anhydrous methanol and centrifuging to obtain ZIF-67 grown on the tellurium nanowires;

[0009] Step 3: dispersing the ZIF-67 grown on the tellurium nanowires obtained in Step 2 in a mixed solution of water and anhydrous methanol, performing etching treatment by stirring, and centrifuging and freeze-drying the obtained product;

[0010] Step 4: The freeze-dried product obtained in step 3 is subjected to carbonization heat treatment in an argon atmosphere, and after naturally cooling to room temperature, a cobalt telluride-rich carbon nanocage for a positive electrode carrier material of a lithium-sulfur battery is obtained.

[0011] Preferably, in step 1, the temperature of the hydrothermal reaction is 160-200° C., and the reaction time is 2-4 h.

[0012] Preferably, in step 2, the time of the stirring reaction at room temperature is 2 to 6 hours.

[0013] Preferably, in step 3, the volume ratio of water to anhydrous methanol is 0.25 to 2:1, and the amount of the mixed solution is 65 to 80 mL.

[0014] Preferably, in step 3, the etching treatment time is 0.5 to 2 hours.

[0015] Preferably, in step 4, the carbonization heat treatment temperature is 500-700°C, the heat treatment time is 1-3h, and the heating rate is 2-8°C min -1 .

[0016] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0017] The present invention utilizes ZIF-67 grown on tellurium wire as a precursor, and synthesizes nitrogen-doped hierarchical pore structure carbon nanocage materials loaded with cobalt telluride nanoparticles through water etching and one-step annealing treatment. The ZIF-67-derived carbon substrate exhibits structural characteristics of hierarchical pores. The mesopores increase the sulfur loading capacity and mass transfer capacity during charging and discharging, and the micropores limit the shuttle effect of soluble polysulfides. The large number of cobalt telluride nanoparticles carried therein enhance the chemical adsorption and catalytic conversion capabilities of polysulfides. The positive electrode material of the present invention has a simple preparation process, excellent cycle stability, and high specific capacity, providing a new design and preparation strategy for sulfur carrier materials for lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a flow chart of the preparation method of the cobalt telluride-rich carbon nanocage.

[0019] Figure 2 This is a scanning electron microscope image of the e-CoTe@NC prepared in Example 1 of the present invention.

[0020] Figure 3 This is a transmission electron microscope image of e-CoTe@NC prepared in Example 1 of the present invention.

[0021] Figure 4 This is a high-angle annular dark field scanning transmission image and element distribution map of the e-CoTe@NC prepared in Example 1 of the present invention.

[0022] Figure 5 This is a transmission electron microscope image of CoTe@NC prepared in Comparative Example 1 of the present invention.

[0023] Figure 6 3. It is the X-ray diffraction pattern of e-CoTe@NC prepared in Example 1 of the present invention and CoTe@NC prepared in Comparative Example 1.

[0024] Figure 7 3. High-resolution X-ray photoelectron spectra of Co 2p of e-CoTe@NC prepared in Example 1 of the present invention and CoTe@NC prepared in Comparative Example 1.

[0025] Figure 8 This is the high-resolution X-ray photoelectron spectrum of Te 3d of e-CoTe@NC prepared in Example 1 of the present invention and CoTe@NC prepared in Comparative Example 1.

[0026] Figure 9 2 are the N2 adsorption / desorption isotherm and pore size distribution curve of e-CoTe@NC prepared in Example 1 of the present invention.

[0027] Figure 10 2 are the N2 adsorption / desorption isotherm curves and pore size distribution curves of CoTe@NC prepared in Comparative Example 1 of the present invention.

[0028] Figure 11 2 are cyclic voltammetry curves of Li2S6 symmetric batteries assembled with e-CoTe@NC prepared in Example 1 of the present invention and CoTe@NC prepared in Comparative Example 1.

[0029] Figure 12 Graph showing the Li2S nucleation and deposition performance of lithium-sulfur batteries assembled with e-CoTe@NC prepared in Example 1 of the present invention and CoTe@NC prepared in Comparative Example 1.

[0030] Figure 13 3 is a charge and discharge curve diagram of a lithium-sulfur battery assembled with the e-CoTe@NC prepared in Example 1 of the present invention and the CoTe@NC prepared in Comparative Example 1.

[0031] Figure 14 Graphs showing the cycling performance of lithium-sulfur batteries assembled from e-CoTe@NC prepared in Example 1 of the present invention and CoTe@NC prepared in Comparative Example 1.

[0032] Figure 15 3 is a rate performance diagram of lithium-sulfur batteries assembled with e-CoTe@NC prepared in Example 1 of the present invention and CoTe@NC prepared in Comparative Example 1.

[0033] Figure 16 3 are electrochemical impedance spectroscopy graphs of lithium-sulfur batteries assembled with e-CoTe@NC prepared in Example 1 of the present invention and CoTe@NC prepared in Comparative Example 1. DETAILED DESCRIPTION

[0034] To further illustrate the present invention, the following detailed description of a method for preparing a novel high-performance cobalt telluride-rich carbon nanocage structure positive electrode carrier material for lithium-sulfur batteries provided by the present invention is provided in conjunction with the examples and illustrated in conjunction with the accompanying drawings. However, these descriptions are not to be construed as limiting the scope of protection of the present invention.

[0035] Example 1

[0036] In this embodiment, carbon nanocages rich in cobalt telluride are prepared according to the following steps:

[0037] Step 1. Dissolve 0.6 g of polyvinyl pyrrolidone in 21 mL of deionized water, add 0.0553 g of sodium tellurite, 2 mL of ammonia water and 1 mL of hydrazine hydrate and stir evenly, then transfer to a reactor for hydrothermal reaction at a hydrothermal temperature of 180 ° C and a time of 3 hours to obtain a tellurium nanowire mother liquor; add acetone to the tellurium nanowire mother liquor, then centrifuge it, and disperse the tellurium nanowires with 24 mL of anhydrous methanol to obtain a tellurium nanowire dispersion.

[0038] Step 2: Dissolve 0.699 g of cobalt nitrate hexahydrate in 24 mL of anhydrous methanol to obtain a cobalt nitrate solution; dissolve 1.575 g of 2-methylimidazole in 24 mL of anhydrous methanol to obtain a 2-methylimidazole solution; add the cobalt nitrate solution and the 2-methylimidazole solution to the tellurium nanowire dispersion obtained in step 1 and stir at room temperature for 4 hours; wash the resulting product with anhydrous methanol and centrifuge to obtain ZIF-67 grown on the tellurium nanowires.

[0039] Step 3: The ZIF-67 grown on the tellurium nanowires obtained in step 2 was dispersed in 72 mL of a 1:1 mixed solution of water and methanol, stirred for 1 hour for etching, and the obtained product was centrifuged and freeze-dried.

[0040] Step 4: Place the freeze-dried product obtained in step 3 in a tube furnace in an argon atmosphere at 600°C for 2 hours at a heating rate of 5°C min -1 After cooling naturally to room temperature, a cobalt telluride-rich carbon nanocage, designated e-CoTe@NC, was obtained as a cathode support material for lithium-sulfur batteries.

[0041] Depend on Figure 1 It can be seen that carbon nanocages loaded with cobalt telluride nanoparticles are synthesized by using ZIF-67 grown on tellurium wire as a precursor through simple water etching and one-step annealing treatment.

[0042] Figure 2 This is a scanning electron microscope image of the e-CoTe@NC obtained in this example. It can be observed that the sample can still maintain the basic rhombic dodecahedron structure after etching and annealing, and there are certain channels on the surface.

[0043] Figure 3 This is a transmission electron microscope image of the e-CoTe@NC obtained in this example. In the image, the channels left after the tellurium lines disappear, as well as the channel structure formed by etching, can be seen. The areas with darker contrast are evenly distributed cobalt telluride nanoparticles.

[0044] Figure 4The high-angle annular dark field scanning transmission image and element distribution map of the e-CoTe@NC obtained in this example. The left image shows the uniform distribution of cobalt telluride nanoparticles, and the right image clearly shows that the C, N, Co, and Te elements are evenly distributed on the carbon nanocage.

[0045] Comparative Example 1

[0046] This comparative example prepares a carbon nanomaterial without a nanocage structure according to the following steps:

[0047] Step 1. Dissolve 0.6 g of polyvinyl pyrrolidone in 21 mL of deionized water, add 0.0553 g of sodium tellurite, 2 mL of ammonia water and 1 mL of hydrazine hydrate and stir evenly, then transfer to a reactor for hydrothermal reaction at a hydrothermal temperature of 180 ° C and a time of 3 hours to obtain a tellurium nanowire mother liquor; add acetone to the tellurium nanowire mother liquor, then centrifuge it, and disperse the tellurium nanowires with 24 mL of anhydrous methanol to obtain a tellurium nanowire dispersion.

[0048] Step 2: Dissolve 0.699 g of cobalt nitrate hexahydrate in 24 mL of anhydrous methanol to obtain a cobalt nitrate solution; dissolve 1.575 g of 2-methylimidazole in 24 mL of anhydrous methanol to obtain a 2-methylimidazole solution; add the cobalt nitrate solution and the 2-methylimidazole solution to the tellurium nanowire dispersion obtained in step 1 and stir at room temperature for 4 hours; wash the obtained product with anhydrous methanol, centrifuge, and freeze-dry.

[0049] Step 3: Place the freeze-dried product obtained in step 2 in a tube furnace in an argon atmosphere at 600°C for 2 h. The heating rate of the tube furnace is 5°C min -1 After cooling naturally to room temperature, a carbon nanomaterial without a nanocage structure was obtained, which was recorded as CoTe@NC.

[0050] Figure 5 This is a transmission electron microscope image of CoTe@NC obtained in this comparative example. The contrast is relatively uniform and no carbon nanocage structure exists.

[0051] Figure 6 2 are X-ray diffraction patterns of the samples obtained in Example 1 and Comparative Example 1. The diffraction peaks of the two samples correspond to the standard diffraction pattern of CoTe (PDF#34-0420), indicating the presence of cobalt telluride.

[0052] Figure 7 The Co 2p high-resolution X-ray photoelectron spectra of the samples obtained in Example 1 and Comparative Example 1 are fitted to obtain the Co 2p 1 / 2 and 2p 3 / 2 The positions and intensities of the two characteristic peaks are basically consistent, indicating that the etching process only changes the geometric structure of the material and does not affect its chemical state.

[0053] Figure 8 The Te 3d high-resolution X-ray photoelectron spectra of the samples obtained in Example 1 and Comparative Example 1 are fitted to obtain the Te 3d 3 / 2 and 3D 5 / 2 The positions and intensities of the spin-orbit peaks are basically the same.

[0054] Figure 9 The N2 adsorption / desorption isotherm and pore size distribution curve of e-CoTe@NC obtained in Example 1 show a hierarchical pore structure with abundant micropores and mesopores.

[0055] Figure 10 The N2 adsorption / desorption isotherm and pore size distribution curve of CoTe@NC obtained in Comparative Example 1 show the presence of microporous structure and fewer mesopores, indicating that the etching treatment produces more mesopores.

[0056] The e-CoTe@NC obtained in Example 1 was used as the working electrode and the counter electrode material, and 0.5 mol L -1 The Li2S6 was dissolved in DME / DOL solution as the electrolyte to assemble a symmetrical battery. e-CoTe@NC was used as the positive electrode, lithium foil as the negative electrode, Celgard2400 PP membrane as the separator, and 0.5 mol L -1 Li2S8 and 1 mol L -1 LiTFSI was dissolved in a DME and DOL solution with a volume ratio of 1:1 as the cathode solution, 1 mol L -1 LiTFSI was dissolved in a DME and DOL solution with a volume ratio of 1:1 and 0.1 mol L -1 LiNO3 solution was used as the anolyte, the catholyte was added to the positive electrode side, and the anolyte was added to the negative electrode side. The lithium-sulfur battery was assembled to test the Li2S nucleation and deposition performance. The sulfur-loaded e-CoTe@NC was used as the positive electrode, lithium foil was used as the negative electrode, Celgard 2400 PP membrane was used as the separator, and 1 mol L -1 LiTFSI was dissolved in a DME and DOL solution with a volume ratio of 1:1 and 0.1 mol L -1 LiNO3 solution is used as the electrolyte to assemble lithium sulfur batteries. The above batteries are all button batteries.

[0057] The CoTe@NC prepared in Comparative Example 1 was assembled into various types of batteries using the same method as above.

[0058] The cyclic voltammetry curves of the symmetrical battery were tested on a CHI 760E electrochemical workstation. Figure 11The cyclic voltammetry curves of the Li2S6 symmetric battery of the samples obtained in Example 1 and Comparative Example 1 show that e-CoTe@NC exhibits a more obvious peak shape and a larger redox response current, indicating that the electrochemical reaction kinetics are enhanced.

[0059] Figure 12 Figure 2 is the Li2S nucleation and deposition performance diagram of the lithium-sulfur battery of the samples obtained in Example 1 and Comparative Example 1. e-CoTe@NC exhibits the highest nucleation contribution capacity and the shortest time to reach the peak current, indicating that the reaction kinetics of Li2S nucleation is improved.

[0060] Figure 13 Figure 3 is the charge and discharge curve of the lithium-sulfur battery of the samples obtained in Example 1 and Comparative Example 1. Compared with CoTe@NC, e-CoTe@NC exhibits a smaller polarization potential (ΔE) and a higher degree of discharge completion (Q2 / Q1), indicating that the catalytic conversion ability during the discharge process is effectively improved.

[0061] Figure 14 The cycling performance of the samples obtained in Example 1 and Comparative Example 1 at 0.2C is shown. The e-CoTe@NC still maintains 1027 mAh g after 100 cycles. -1 However, the discharge capacity of CoTe@NC decayed significantly after 100 cycles, reaching only 870 mAh g -1 .

[0062] Figure 15 This is a rate performance diagram of the lithium-sulfur batteries of the samples obtained in Example 1 and Comparative Example 1. The cycle performance of the e-CoTe@NC and CoTe@NC batteries at 0.1C, 0.2C, 0.5C, 1.0C and 2.0C were tested respectively. As the current density increases, the e-CoTe@NC exhibits less capacity decay. When the current density gradually decreases to 0.1C, the specific capacity can recover to a higher value. In contrast, the capacity decay of the CoTe@NC battery is more severe, and it exhibits extremely low specific capacity at high currents.

[0063] Figure 16 1 is the electrochemical impedance spectroscopy of the samples obtained in Example 1 and Comparative Example 1. Compared with CoTe@NC, e-CoTe@NC exhibits a smaller charge transfer resistance, thereby significantly improving the charge transfer at the electrode interface and the redox reaction kinetics.

[0064] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements 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 telluride-rich carbon nanocages for lithium-sulfur battery cathode support materials, characterized in that: The following steps are involved: Step 1, dissolving 0.500-0.700 g of polyvinylpyrrolidone in 19-23 mL of deionized water, adding 50.0-60.0 mg of sodium tellurite, 1-3 mL of 24-26 wt% ammonia water, and 0.5-1.5 mL of 84-86 wt% hydrazine hydrate and stirring evenly, then transferring to a reactor for hydrothermal reaction to obtain a tellurium nanowire mother liquor; adding acetone to the tellurium nanowire mother liquor, centrifuging, and dispersing the obtained tellurium nanowires in 22-26 mL of anhydrous methanol to obtain a tellurium nanowire dispersion; Step 2: Dissolve 0.690-0.710 g of cobalt nitrate hexahydrate in 22-26 mL of anhydrous methanol to obtain a cobalt nitrate solution; dissolve 1.500-1.650 g of 2-methylimidazole in 22-26 mL of anhydrous methanol to obtain a 2-methylimidazole solution; add the cobalt nitrate solution and the 2-methylimidazole solution to the tellurium nanowire dispersion obtained in step 1 and stir at room temperature to react; wash the resulting product with anhydrous methanol and centrifuge to obtain ZIF-67 grown on the tellurium nanowires; Step 3: dispersing the ZIF-67 grown on the tellurium nanowires obtained in Step 2 in a mixed solution of water and anhydrous methanol, performing etching treatment by stirring, and centrifuging and freeze-drying the obtained product; Step 4: The freeze-dried product obtained in step 3 is subjected to carbonization heat treatment in an argon atmosphere, and after naturally cooling to room temperature, a cobalt telluride-rich carbon nanocage for a positive electrode carrier material of a lithium-sulfur battery is obtained.

2. The preparation method according to claim 1, wherein: In step 1, the temperature of the hydrothermal reaction is 160-200°C, and the reaction time is 2-4 h.

3. The preparation method according to claim 1, wherein: In step 2, the stirring reaction time at room temperature is 2 to 6 hours.

4. The preparation method according to claim 1, wherein: In step 3, the volume ratio of water to anhydrous methanol is 0.25-2:1, and the amount of the mixed solution is 65-80 mL.

5. The preparation method according to claim 1, wherein: In step 3, the etching treatment time is 0.5 to 2 hours.

6. The preparation method according to claim 1, wherein: In step 4, the carbonization heat treatment temperature is 500-700 °C, the heat treatment time is 1-3 h, and the heating rate is 2-8 °C min −1 .

7. A cobalt telluride-rich carbon nanocage prepared by the preparation method according to any one of claims 1 to 6.

8. The cobalt telluride-rich carbon nanocage according to claim 7, wherein: The cobalt telluride-rich carbon nanocage is a nitrogen-doped hierarchical pore structure carbon nanocage material on which cobalt telluride nanoparticles are loaded.

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