CoTe2 / C@MXene composite material, and preparation method and application thereof

Abstract

The application discloses a CoTe2 / C@MXene composite material and a preparation method and application thereof, and belongs to the field of electrochemical energy storage. The preparation of the composite material comprises the following steps: mixing MXene, a cobalt salt and a melamine mixed solution, and obtaining a precursor through freeze-drying; and then performing a high-temperature tellurization reaction on the precursor and tellurium powder under the protection of argon to obtain a composite material in which carbon-limited CoTe2 nanoparticles are uniformly loaded on the surface of MXene. The obtained composite material has the physical limitation, chemical adsorption and high catalytic activity of the CoTe2 nanoparticles of the high-conductivity MXene matrix, can effectively inhibit the polysulfide shuttle effect, buffer volume expansion and accelerate the reaction kinetics. When applied to a room-temperature sodium-sulfur battery positive electrode as a sulfur host material, the composite material significantly improves the specific capacity, rate performance and cycle stability of the battery. The method is simple, has good repeatability and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage, and specifically relates to a CoTe2 / C@MXene composite material, its preparation method and application. Background Technology

[0002] With the increasing global demand for large-scale energy storage systems, the development of rechargeable battery technologies that combine high energy density, long cycle life, and low cost has become a key research focus. Room temperature sodium-sulfur (RT Na-S) batteries, due to their extremely high theoretical specific capacity (1675 mAh / g) and energy density (1274 Wh / kg), as well as the abundance and low cost of sulfur and sodium resources, are considered one of the important development directions for next-generation large-scale energy storage technologies.

[0003] However, the practical application of room-temperature sodium-sulfur batteries faces numerous challenges stemming from the sulfur cathode. Firstly, elemental sulfur and its discharge products (such as sodium sulfide) have extremely low electronic conductivity (the electronic conductivity of sulfur is approximately 5 × 10⁻⁶). -28 The sulfur-to-sodium ratio (S / m) results in slow electrochemical reaction kinetics and low utilization of active materials. Secondly, during charge and discharge, the reaction between sulfur and sodium involves a series of formations and transformations of soluble sodium polysulfides, accompanied by approximately 170% volume expansion. More seriously, these polysulfides readily dissolve in the electrolyte and migrate across the separator to the negative electrode side under the drive of the concentration gradient, resulting in a "shuttle effect," causing irreversible loss of active materials, negative electrode corrosion, and rapid capacity decay. Therefore, effectively overcoming these defects of the sulfur cathode is crucial for advancing the practical application of room-temperature sodium-sulfur batteries.

[0004] Therefore, researchers typically develop functional materials with excellent conductivity and catalytic activity as additives or host materials for sulfur cathodes to promote the conversion of polysulfides and regulate their reaction kinetics. However, constructing composite materials with both high catalytic activity and high conductivity, and achieving uniform dispersion of catalytic components in the host material, remains a challenge. Based on this, this invention proposes a CoTe2 / C@MXene composite material and its preparation method, and explores its application as a high-performance sulfur host in room-temperature sodium-sulfur batteries. Summary of the Invention

[0005] This invention aims to overcome key technical bottlenecks in existing room-temperature sodium-sulfur batteries, such as poor conductivity, significant volume expansion, and severe polysulfide shuttle effect of the sulfur cathode. It provides a CoTe2 / C@MXene composite material, its preparation method, and its applications. This method uses freeze-drying and high-temperature tellurization processes to uniformly load highly catalytically active carbon-confined CoTe2 nanoparticles onto two-dimensional layered MXene to form a CoTe2 / C@MXene composite structure, constructing a heterostructure host material with both excellent conductivity and synergistic catalytic effects. As a functional host for the sulfur cathode in room-temperature sodium-sulfur batteries, the CoTe2 / C@MXene composite material fully leverages the synergistic effect of its multiple components: the MXene matrix, with its highly conductive network and abundant polar surface sites, effectively improves the overall conductivity of the electrode, buffers volume expansion during cycling, and inhibits the dissolution and migration of polysulfides through physical confinement and chemical adsorption; the loaded carbon-confined CoTe2 component further enhances the interfacial anchoring ability for polysulfides, while its high catalytic activity significantly accelerates the redox conversion kinetics of sodium polysulfides, fundamentally suppressing the shuttle effect. Based on the above structural design, the CoTe2 / C@MXene composite material prepared by this invention can significantly improve the utilization rate and reversibility of sulfur active materials, thereby endowing room temperature sodium-sulfur batteries with high specific capacity, excellent rate performance and long cycle stability, showing good application prospects.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a CoTe2 / C@MXene composite material includes the following steps:

[0008] (1) Add MXene, cobalt salt and melamine to 10 mL of water at a mass ratio of 1:(2-20):(2-20), stir ultrasonically for 30 minutes to form a mixed solution, then freeze in liquid nitrogen and dry in a freeze dryer.

[0009] (2) The dried precursor and tellurium powder obtained above were placed in two ceramic boats at a mass ratio of 1:(1-10). The ceramic boat containing tellurium powder was placed upstream of the tube furnace. Then, under the protection of argon, the temperature was raised to 400-600℃ at 2℃ / min and held for 2 hours to obtain CoTe2 / C@MXene composite material.

[0010] Preferably, the MXene in step (1) is Ti3C2T. x Ti2CT x Mo2CT x V2CT x Or V4C3T x One or more of them.

[0011] Preferably, the cobalt salt in step (1) is one or more of cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, or cobalt sulfate heptahydrate.

[0012] The present invention also provides a CoTe2 / C@MXene composite material obtained according to the aforementioned preparation method.

[0013] The present invention also provides the application of the above-mentioned CoTe2 / C@MXene composite material as a S carrier to fabricate a hybrid S electrode and in a room temperature sodium-sulfur battery.

[0014] The method for creating the application is as follows:

[0015] (1) The CoTe2 / C@MXene composite material and S are ground and mixed in a mass ratio of 1:(1-5). Then, the mixture is sealed in a glove box filled with argon gas and placed in a polytetrafluoroethylene reactor liner. The mixture is then kept at 155°C in an oven for 12-24 hours to obtain the composite S cathode material (i.e., S@CoTe2 / C@MXene).

[0016] (2) Grind and mix the S@CoTe2 / C@MXene cathode material, conductive agent and binder in a mass ratio of 7:2:1 or 8:1:1, add an appropriate amount of deionized water or NMP, stir evenly, and coat the resulting slurry evenly on the rough surface of the copper current collector and vacuum dry at 60-120℃ to obtain the Na-S battery composite S electrode.

[0017] (3) The above-mentioned composite S electrode is used as the positive electrode of the Na-S battery, and metallic sodium is used as the negative electrode. The electrolyte is 1M NaSO3CF3 dissolved in DEGDME solvent or 1M NaPF6 dissolved in DEGDME solvent or 1M NaPF6 dissolved in DME solvent. The membrane is made of glass fiber GF / D and Celgard2325 as a double-layer membrane, wherein the Celgard2325 membrane is closer to the composite S electrode side. They are assembled in sequence to form a CR2032 button-type room temperature Na-S battery.

[0018] Preferably, the conductive agent in step (2) is one or more of conductive carbon black, graphene, MXene, or carbon nanotubes.

[0019] Preferably, the adhesive in step (2) is one or more of polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, or sodium alginate.

[0020] Advantages and beneficial effects of the present invention:

[0021] (1) The CoTe2 / C@MXene composite material constructed in this invention fully leverages the synergistic effect of multiple components. The highly conductive two-dimensional MXene matrix provides a fast electron transport channel and abundant polar surfaces, effectively improving the overall conductivity of the sulfur cathode; at the same time, the CoTe2 nanoparticles uniformly loaded on the carbon confinement of MXene have excellent polysulfide catalytic conversion ability, significantly accelerating the reaction kinetics and suppressing the shuttle effect from the root.

[0022] (2) The flexibility and interlayer voids of the MXene matrix can effectively accommodate the volume change of sulfur during the charging and discharging process, avoiding the pulverization failure of the electrode structure; the presence of the carbon matrix further disperses the CoTe2 nanoparticles, preventing them from agglomerating during cycling and ensuring the long-term stability of the electrode structure.

[0023] (3) The present invention adopts a synthesis strategy of electrostatic self-assembly combined with high-temperature tellurization, which is simple and reproducible. By controlling the ratio of cobalt salt to melamine and the tellurization conditions, the size and loading of CoTe2 nanoparticles can be controlled. The nitrogen-rich carbon matrix plays a dual role in protecting MXene from oxidation and inhibiting CoTe2 aggregation during the high-temperature treatment process.

[0024] (4) The CoTe2 / C@MXene composite material prepared in this invention was used as a sulfur host in a room temperature sodium-sulfur battery. The resulting S@CoTe2 / C@MXene cathode exhibited high specific capacity, excellent rate performance and long cycle stability, which were significantly better than single CoTe2 or MXene host materials, showing good application prospects. Attached Figure Description

[0025] Figure 1 These are (a) low-magnification and (b) high-magnification scanning electron microscope images of the CoTe2 / C@MXene composite material synthesized in Example 1;

[0026] Figure 2 This is a low-magnification transmission electron microscope image and particle size distribution of the CoTe2 / C@MXene composite material synthesized in Example 1;

[0027] Figure 3 These are high-magnification transmission electron microscope images (a, b) of the CoTe2 / C@MXene composite material synthesized in Example 1 at different locations;

[0028] Figure 4 This is the X-ray diffraction pattern of the CoTe2 / C@MXene composite material synthesized in Example 1;

[0029] Figure 5The graphs show the rate performance of the S@CoTe2 / C@MXene electrode prepared in Example 7, the S@CoTe2 electrode prepared in Comparative Example 1, and the S@MXene electrode prepared in Comparative Example 2 at current densities of 0.2, 0.5, 1, 2, and 5 A / g, respectively.

[0030] Figure 6 The graph shows the cycling stability of the S@CoTe2 / C@MXene electrode prepared in Example 7, the S@CoTe2 electrode prepared in Comparative Example 1, and the S@MXene electrode prepared in Comparative Example 2 at a current density of 2A / g.

[0031] Figure 7 The images show the UV absorption spectra and visualizations of the solutions (insets) of the CoTe2 / C@MXene composite material prepared in Example 1, the CoTe2 synthesized in Comparative Example 1, and the MXene used in Comparative Example 2 after being immersed in sodium polysulfide solution.

[0032] Figure 8 The CV diagrams are of the CoTe2 / C@MXene composite material prepared in Example 1, the CoTe2 synthesized in Comparative Example 1, and the symmetric cells prepared using MXene in Comparative Example 2. Detailed Implementation

[0033] To make the above-mentioned objectives and advantages of the present invention clear and easy to understand, the technical solutions of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments. Unless otherwise specified, all materials mentioned are commercially available.

[0034] Example 1:

[0035] This embodiment provides a synthesis and characterization analysis of a CoTe2 / C@MXene composite material. The specific synthesis process is as follows:

[0036] (1) Add 25 mg of MXene, 125 mg of cobalt acetate tetrahydrate and 100 mg of melamine to 10 mL of water, stir ultrasonically for 30 minutes to form a mixed solution, then quickly freeze in liquid nitrogen and dry in a freeze dryer.

[0037] (2) Take 100 mg of the dried precursor and 200 mg of tellurium powder obtained above and place them in two ceramic boats respectively. Place the ceramic boat containing tellurium powder upstream of the tube furnace and place the precursor downstream of the tube furnace. Then, under the protection of argon, heat to 500℃ at 2℃ / min and hold for 2 hours to obtain CoTe2 / C@MXene composite material.

[0038] Figure 1 This is a scanning electron microscope (SEM) image of the synthesized CoTe2 / C@MXene composite material. From Figure 1 As can be seen from image a, the synthesized CoTe2 / C@MXene composite material basically retains the lamellar morphology of the original MXene, while exhibiting a multidimensional wrinkled structure. This structure provides ample space for sulfur loading and electrochemical conversion. Further magnified SEM images (…) Figure 1 (b) Clearly, ultrafine CoTe2 nanoparticles are uniformly loaded and modified on the surface of the MXene substrate without obvious aggregation, indicating that the spatial confinement effect of the carbon substrate is effectively utilized.

[0039] Figure 2 The low-magnification transmission electron microscopy (TEM) image of the CoTe2 / C@MXene composite material further confirms that the composite material possesses a micron-scale layered structure, and shows that the size distribution of the CoTe2 nanoparticles is between 20 and 140 nm. These ultrafine and highly dispersed nanoparticles can expose more active sites, effectively participating in subsequent structural reconstruction and related catalytic reactions.

[0040] Figure 3 This is a high-magnification transmission electron microscope image of the CoTe2 / C@MXene composite material. Figure 3 The measured lattice spacing of the nanoparticles in a is 0.33 nm, which corresponds to the (100) crystal plane of CoTe2 (PDF#79-062-5401), confirming that the CoTe2 nanoparticles were successfully prepared and the phase is pure. Figure 3 In step b, a distinct confined carbon layer with a thickness of approximately 5 nm was observed around the CoTe2 particles. This carbon layer further inhibits the aggregation of CoTe2 nanoparticles and provides protection. Furthermore, the MXene substrate exhibits a clear (002) crystal plane, and analysis of the interlayer spacing and number of layers indicates that its thickness corresponds to a few-layer structure of approximately 1–3 layers, suggesting that MXene maintains a well-defined layered crystal structure during the composite process.

[0041] Figure 4 The X-ray diffraction pattern of the synthesized CoTe2 / C@MXene composite material is shown in this example. Figure 4 It can be seen that the XRD diffraction peaks of the composite material can be indexed to the (001), (100), (011), (002), (012), (110), (103), and (112) crystal planes of CoTe2 (PDF#97-062-5401). Since the MXene surface is covered by CoTe2 particles, no MXene diffraction peaks were detected.

[0042] Example 2:

[0043] The preparation method is the same as that described in Example 1, except that:

[0044] In step (2), the calcination temperature is 400℃, and other conditions and parameters are the same as in Example 1.

[0045] Example 3:

[0046] The preparation method is the same as that described in Example 1, except that:

[0047] In step (2), the calcination temperature is 600℃, and other conditions and parameters are the same as in Example 1.

[0048] Example 4:

[0049] The preparation method is the same as that described in Example 1, except that:

[0050] In step (1), the amount of melamine added is 500 mg, and other conditions and parameters are as in Example 1.

[0051] Example 5:

[0052] The preparation method is the same as that described in Example 1, except that:

[0053] In step (1), the amount of cobalt acetate tetrahydrate and melamine added is 200 mg and 400 mg, respectively, and other conditions and parameters are as in Example 1.

[0054] Example 6:

[0055] The preparation method is the same as that described in Example 1, except that:

[0056] In step (1), the amounts of cobalt acetate tetrahydrate and melamine added were 200 mg and 600 mg, respectively, and other conditions and parameters were as in Example 1.

[0057] Example 7:

[0058] This embodiment provides a method for preparing a composite S electrode and testing the performance of a room-temperature Na-S battery. The detailed operation procedure is as follows:

[0059] (1) The CoTe2 / C@MXene composite material obtained in Example 1 and S were ground and mixed at a mass ratio of 1:2. Then, the mixture was sealed in a glove box filled with argon gas and placed in a polytetrafluoroethylene reactor liner. The mixture was then kept at 155°C in an oven for 12 hours to obtain the composite S cathode material (i.e., S@CoTe2 / C@MXene).

[0060] (2) Grind and mix the S@CoTe2 / C@MXene cathode material, conductive agent and binder in a mass ratio of 7:2:1, add an appropriate amount of deionized water, stir evenly, and coat the resulting slurry evenly on the rough surface of the copper current collector and vacuum dry at 60°C to obtain the Na-S battery composite S electrode.

[0061] (3) The above-mentioned composite S electrode is used as the positive electrode of the Na-S battery, metallic sodium is used as the negative electrode, the electrolyte is 1M NaPF6 dissolved in DME solvent, and the membrane is made of glass fiber GF / D and Celgard2325 as a double-layer membrane, wherein the Celgard2325 membrane is close to the side of the composite S electrode, and they are assembled in sequence to form a CR2032 button-type room temperature Na-S battery.

[0062] (4) The button cell assembled in step (3) is tested for performance in the Xinwei Battery Test System. The battery charge and discharge voltage range is 0.4 to 3V. The current density for rate performance testing is 0.2, 0.5, 1, 2, 5 and 0.2A / g. Its cycle performance is 1000 cycles at a current density of 2A / g.

[0063] Figure 5 The rate performance graph for the S@CoTe2 / C@MXene cathode shows average capacities of 1600.5, 1632.0, 1587.6, 1559.7, and 1507.2 mAh / g at current densities of 0.2, 0.5, 1.0, 2.0, and 5.0 A / g, respectively. Even when the current density is restored to 0.2 A / g, the cathode still provides a high capacity of 1612.2 mAh / g.

[0064] Figure 6 The graph shows the cycling performance of the S@CoTe2 / C@MXene electrode. After 1000 cycles at a current density of 2A / g, it can maintain a high sodium storage performance of 1533.0mAh / g, with a capacity decay rate of only 0.005% per cycle and a capacity retention rate of approximately 95.0%.

[0065] Figure 7 The UV absorption spectrum and visualization of the solution are shown for the CoTe2 / C@MXene composite material after immersion in sodium polysulfide solution. The results demonstrate its moderate adsorption performance for sodium polysulfide.

[0066] Figure 8 The CV curves of the symmetric cells prepared from the CoTe2 / C@MXene composite material show obvious redox peaks, indicating excellent catalytic performance for sodium polysulfide.

[0067] Comparative Example 1:

[0068] This example provides the preparation and electrochemical performance characterization of a control electrode (S@CoTe2 electrode) for the S@CoTe2 / C@MXene electrode. The specific preparation process of CoTe2 is the same as that described in Example 1, except that:

[0069] In step (1), MXene and melamine are not added, and other conditions and parameters are the same as in Example 1.

[0070] The specific fabrication process of the S@CoTe2 electrode is the same as the preparation method described in Example 7, except that:

[0071] In step (1), the CoTe2 / C@MXene composite material was replaced with the pure phase CoTe2 obtained above. Other conditions and parameters were performed as in Example 7.

[0072] Figure 5 The rate performance of the S@CoTe2 electrode prepared for this example at current densities of 0.2-5 A / g is compared with that of the S@CoTe2 / C@MXene electrode in Example 7. It can be seen that the composite material (S@CoTe2 / C@MXene) with added MXene as an S-supported catalyst significantly improves the performance of room temperature Na-S batteries. Figure 6 The cycling performance of the S@CoTe2 electrode fabricated for this example is shown, and its discharge capacity is significantly lower than that of the S@CoTe2 / C@MXene electrode. This is because the highly conductive MXene can provide rapid electron transport for the system, while providing a two-dimensional space for the dispersion of CoTe2 and the subsequent conversion of S species. This allows the CoTe2 nanoparticles to expose more active sites, thereby promoting the catalytic reaction and significantly improving the sodium storage performance of S.

[0073] Figure 7 The UV absorption spectrum and visualization of the solution are shown for CoTe2 material after immersion in sodium polysulfide solution. The results demonstrate that the adsorption performance of CoTe2 material for sodium polysulfide is poor.

[0074] Figure 8 To obtain the CV curves of symmetrical cells assembled using CoTe2 material, CoTe2 material exhibited a relatively broad redox peak, indicating that it has certain catalytic performance for sodium polysulfide, but its peak intensity and catalytic characteristics are not as good as those of the CoTe2 / C@MXene composite material.

[0075] Comparative Example 2:

[0076] This example provides the preparation and electrochemical performance characterization of a control electrode (S@MXene electrode) for the S@CoTe2 / C@MXene electrode. The specific preparation process is the same as that described in Example 7, except that:

[0077] In step (1), the CoTe2 / C@MXene composite material was replaced with Ti3C2 MXene. Other conditions and parameters were performed as in Example 7.

[0078] Figure 5 and Figure 6The figures show the rate performance and cycle performance curves of the S@MXene electrode. It can be seen that the discharge capacity of this electrode is also significantly lower than that of the S@CoTe2 / C@MXene electrode.

[0079] Figure 7 The image shows the UV absorption spectrum and visualization of the solution after MXene was immersed in sodium polysulfide solution. MXene exhibits strong adsorption performance for sodium polysulfide, and its sodium polysulfide solution becomes clear.

[0080] Figure 8 The CV curves of symmetrical cells assembled using MXene materials were obtained. MXene materials exhibited significant polarization, indicating weak catalytic performance for sodium polysulfides.

[0081] These results further confirm that the synergistic effect between the highly conductive MXene and the CoTe2 catalyst can effectively alleviate the bottleneck problems of low intrinsic conductivity of elemental sulfur and slow sodium conversion kinetics. The CoTe2 / C@MXene composite material can not only enhance the chemisorption of sodium polysulfides, but also efficiently catalyze the redox conversion process of sodium polysulfides, ultimately significantly improving the sodium storage performance of sulfur-based electrodes.

[0082] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a CoTe2 / C@MXene composite material, characterized in that, Includes the following steps: (1) Add MXene, cobalt salt and melamine to 10 mL of water in a mass ratio of 1:(2-20):(2-20), stir ultrasonically for 30 minutes to form a mixed solution, then freeze in liquid nitrogen and dry in a freeze dryer; (2) The dried precursor and tellurium powder obtained in step (1) are placed in two ceramic boats at a mass ratio of 1:(1-10). The ceramic boat containing tellurium powder is placed upstream of a tube furnace and heated to 400-600℃ at 2℃ / min under the protection of argon gas. The temperature is held for 2 hours to obtain CoTe2 / C@MXene composite material.

2. The preparation method according to claim 1, characterized in that, The MXene mentioned in step (1) is Ti3C2T x Ti2CT x Mo2CT x V2CT x Or V4C3T x One or more of them.

3. The preparation method according to claim 1, characterized in that, The cobalt salt mentioned in step (1) is one or more of cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, or cobalt sulfate heptahydrate.

4. A CoTe2 / C@MXene composite material prepared by the preparation method according to any one of claims 1-3.

5. An application of the CoTe2 / C@MXene composite material as described in claim 4, characterized in that, The CoTe2 / C@MXene composite material was used as a sulfur carrier to fabricate a hybrid sulfur electrode, which was then applied to the sulfur cathode of a room-temperature sodium-sulfur battery.

6. The application according to claim 5, characterized in that, The specific method for fabricating a hybrid S-electrode includes the following steps: (1) CoTe2 / C@MXene composite material and S are ground and mixed at a mass ratio of 1:(1-5), sealed in an argon glove box in a polytetrafluoroethylene reactor liner, and kept in an oven at 155℃ for 12-24 hours to obtain composite S cathode material S@CoTe2 / C@MXene; (2) Grind and mix the S@CoTe2 / C@MXene cathode material, conductive agent and binder in a mass ratio of 7:2:1 or 8:1:1, add an appropriate amount of deionized water or NMP, stir evenly to obtain a slurry, coat the slurry evenly on the rough surface of the copper current collector, and vacuum dry at 60-120℃ to obtain the Na-S battery composite S electrode.

7. The application according to claim 6, characterized in that, The conductive agent mentioned in step (2) is one or more of conductive carbon black, graphene, MXene, or carbon nanotubes.

8. The application according to claim 6, characterized in that, The adhesive mentioned in step (2) is one or more of polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose or sodium alginate.

9. The application according to claim 5, characterized in that, The room temperature sodium-sulfur battery is a CR2032 button cell, with the composite S electrode prepared according to claim 6 as the positive electrode, metallic sodium as the negative electrode, and the electrolyte being one of 1M NaSO3CF3 dissolved in DEGDME, 1M NaPF6 dissolved in DEGDME, or 1M NaPF6 dissolved in DME. The separator is a double-layer separator composed of glass fiber GF / D and Celgard 2325, with the Celgard 2325 separator located on the side closer to the composite S electrode.

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