A composite sulfur electrode material, its preparation method and application

Abstract

The present invention belongs to the field of electrochemical energy storage, and relates to a composite sulfur electrode material, a preparation method thereof, and an application thereof. The composite sulfur electrode material uses a two-dimensional lamellar material as a matrix, and one-dimensional carbon nanotubes are in-situ grown on metal sites to form a two-dimensional-one-dimensional composite material. Sulfur is coated on the inner and outer walls of the carbon nanotubes and embedded in the gaps formed by the intersection of the carbon nanotubes. The two-dimensional-one-dimensional composite material is a unified whole with one-dimensional carbon nanotubes growing on the two-dimensional lamella. The two-dimensional lamellar material is a single-layer or multi-layer lamellar compound, preferably a metal compound; the one-dimensional carbon nanotube is a hollow tubular structure with excellent electrical conductivity. The two-dimensional-one-dimensional composite material provided by the present invention can improve its electrical conductivity while ensuring the excellent performance of the two-dimensional lamellar material when used as a sulfur carrier, promote the transmission of electrons / ions, and provide sufficient space to load sulfur and relieve the volume expansion during charge and discharge, thereby optimizing its electrochemical performance in the field of metal-sulfur batteries.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical energy storage, and relates to a composite sulfur electrode material, a preparation method thereof and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Two-dimensional materials have high specific surface area, high mechanical strength and high carrier mobility, and have very broad application prospects in the new energy field. Some two-dimensional materials reported currently, such as layered double hydroxides (LDH), transition metal sulfides (MoS2, WS2, etc.), transition metal selenides (MoSe2, WSe2, etc.), etc., exhibit excellent electrochemical properties. However, the conductivity of these two-dimensional transition metal compounds is relatively low when in use, which affects their practical applications in new energy fields such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, supercapacitors, and solar cells.

[0004] Carbon nanotubes have the advantages of low density, high conductivity, high mechanical stability, etc. Therefore, they have wide applications in fields such as electrochemical catalyst carriers and supercapacitors. Currently, the preparation methods of carbon nanofibers mainly include electrospinning, carbonization, hydrothermal treatment, microwave irradiation, and chemical vapor deposition. Among them, the chemical vapor deposition method has the advantages of simple operation and low cost. Therefore, the chemical vapor deposition method has been widely studied for the preparation of carbon nanofibers.

[0005] The theoretical specific capacity of elemental sulfur is 1675 mAh / g, and elemental sulfur has rich reserves and low prices. Metal-sulfur batteries prepared with elemental sulfur as the positive electrode and metals (such as lithium, sodium, potassium, magnesium, etc.) as the negative electrode have high theoretical specific energy. For example, the theoretical specific energy of lithium-sulfur batteries is as high as 2600 Wh / kg, which is a very promising electrochemical energy storage system. However, the application of metal-sulfur batteries faces many obstacles: 1) The conductivity of elemental sulfur is low, resulting in the inability to fully utilize the active substances and the inability to fully express the specific capacity; 2) During the charge and discharge process, intermediate polysulfides dissolve in the electrolyte and shuttle back and forth between the positive and negative electrodes to form a "shuttle effect", causing the battery capacity to continuously decay; 3) The density difference between sulfur and the discharge product leads to volume expansion during the charge and discharge process, damaging the electrode structure, etc. These obstacles result in the inability to fully express the capacity of metal-sulfur batteries and poor cycle stability, affecting the practical applications of metal-sulfur batteries.

[0006] The metal sites of two-dimensional transition metal compounds can adsorb polysulfides through chemical bonding, reduce their migration between the positive and negative electrodes, effectively inhibit the shuttle effect of metal-sulfur batteries, and improve the cycle stability of the batteries. They are the positive electrode sulfur carriers of high-efficiency metal-sulfur batteries. However, when in use, two-dimensional transition metal compounds have poor electrical conductivity and there is a problem of mutual stacking between two-dimensional sheets, which affects the effective utilization of the active substance sulfur. Therefore, it is necessary to improve the electrical conductivity of two-dimensional transition metal compounds and inhibit the stacking between two-dimensional nanosheets. Summary of the Invention

[0007] In order to improve the problem of poor electrical conductivity of some two-dimensional transition metal compounds in metal-sulfur batteries, the purpose of the present invention is to provide a composite sulfur electrode material, its preparation method and application. One-dimensional carbon nanotubes are grown on the surface of two-dimensional materials and then compounded with sulfur to form a composite sulfur electrode material. Carbon nanotubes have excellent electrical conductivity, and the hollow tubular structure and the gap structure formed between carbon nanotubes provide space allowance for the attachment of sulfur and the volume change caused by charge and discharge. Therefore, the electrochemical performance of the battery can be improved to the greatest extent.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] In the first aspect, a composite sulfur electrode material, the composite sulfur electrode material is one-dimensional carbon nanotubes grown on the surface of two-dimensional sheet materials, sulfur is uniformly coated on the inner and outer walls of the carbon nanotubes, and sulfur is embedded in the gaps formed by the entanglement and interlacing of numerous carbon nanotubes; the two-dimensional sheet material is a single-layer or multi-layer lamellar compound.

[0010] In the present invention, the two-dimensional sheet material is a two-dimensional layered metal compound, including layered double hydroxide (LDH), transition metal sulfide (MoS2, WS2, etc.), transition metal selenide (MoSe2, WSe2, etc.); the one-dimensional carbon nanotubes have a hollow structure and excellent electrical conductivity. Chemical vapor deposition process is a common process for preparing carbon nanotubes. This process requires a metal catalyst as the growth site of carbon nanotubes, and the surface of layered double hydroxide (LDH), transition metal sulfide (MoS2, WS2, etc.), transition metal selenide (MoSe2, WSe2, etc.) with low conductivity just exposes metal active sites, which provides the possibility for researchers to deposit and prepare carbon nanotubes on them.

[0011] The prepared composite sulfur electrode material maintains the basic morphology of the two-dimensional-one-dimensional material, and sulfur is uniformly coated on the tube wall of the one-dimensional carbon nanotubes. During the melting treatment process, sulfur experiences three phases: solid-liquid-gas. Therefore, sulfur can spread evenly on the tube wall of the carbon nanotubes and penetrate into the interior of the carbon nanotubes. Part of the sulfur is embedded in the gaps between the carbon nanotubes, but it can also be in contact with the carbon nanotubes. This structure helps the full contact between sulfur and the conductive carbon nanotubes, promoting the full utilization of the active substance sulfur.

[0012] The role of the composite sulfur electrode material constructed in the present invention as the sulfur carrier for the positive electrode of the metal-sulfur battery is as follows: the two-dimensional sheet material serves as the framework, and its metal sites are the growth sites of the one-dimensional carbon nanotubes; the one-dimensional carbon nanotubes provide a rich space for loading sulfur, and their hollow structure can promote the rapid transmission of ions. The conductivity of the carbon nanotubes is conducive to the transmission of electrons, and the intertwined and coiled gaps between the carbon tubes and the hollow structure can alleviate the volume expansion during charge and discharge, maximizing the electrochemical performance of the composite material.

[0013] During the charge and discharge process of the metal-sulfur battery, sulfur is completely converted into polysulfides, and the polysulfides will shuttle back and forth between the positive and negative electrodes to form a shuttle effect. Therefore, it is necessary to confine the polysulfides in the positive electrode region. In this application, the adsorption methods of polysulfides mainly include two types:

[0014] 1) Physical adsorption of carbon nanotubes;

[0015] 2) The metal sites of the metal compound can chemically bond polysulfides and adsorb the polysulfides in the positive electrode region through chemical action, with an obvious restricting effect on the polysulfides. The metal sites here are the same as those that catalyze the formation of one-dimensional carbon nanotubes, but the one-dimensional carbon nanotubes do not occupy all the metal sites, so it will not affect the chemical adsorption of polysulfides.

[0016] In the second aspect, a preparation method of a composite sulfur electrode material includes the following steps:

[0017] S1. Prepare a two-dimensional layered material or modify metal sites on the surface of the two-dimensional material; the metal sites on the two-dimensional layered material can serve as active sites, which can catalyze the deposition and growth of carbon elements at this position to form carbon nanotubes.

[0018] S2. Place a carbon precursor around the two-dimensional layered material, and carbon nanotubes can be in-situ grown on the two-dimensional layered material after high-temperature heat treatment in a tube furnace to obtain a two-dimensional-one-dimensional composite material; the carbon nanotubes grow at the metal sites, and the carbon nanotubes can improve the conductive ability of the material and provide positions and space for loading sulfur.

[0019] S3. Using a two-dimensional-one-dimensional composite material as a sulfur carrier, compounding sulfur to prepare a composite sulfur electrode material, which can be applied to the preparation of the positive electrode of a metal-sulfur battery. The abundant gaps between carbon nanotubes and the hollow structure of one-dimensional carbon nanotubes provide sufficient space for the attachment or volume change of sulfur, which is beneficial to the structural stability of the material, inhibits the shuttle effect, and improves the long-term durability of the battery positive electrode.

[0020] In a third aspect, an application of the above composite sulfur electrode material in the positive electrode of a metal-sulfur battery.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. While ensuring the excellent electrochemical performance of the two-dimensional material, the two-dimensional-one-dimensional composite material provided by the present invention in-situ grows one-dimensional carbon nanotubes on the two-dimensional lamellar material, effectively improving the conductivity of the composite material and promoting the rapid transport of ions.

[0023] 2. The prepared two-dimensional-one-dimensional composite material retains the metal sites of the two-dimensional material, can chemically bond polysulfides, inhibits the shuttle effect of polysulfides, and improves the cycle stability of the metal-sulfur battery.

[0024] 3. The abundant gaps and the hollow structure of one-dimensional carbon nanotubes provide sufficient space for the attachment or volume change of sulfur, which is beneficial to the structural stability of the material and improves the long-term durability of the battery positive electrode. The composite sulfur electrode material constructed by the present invention is expected to improve the comprehensive electrochemical performance of two-dimensional materials in the new energy field. Description of the Drawings

[0025] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0026] Figure 1 SEM image of the two-dimensional layered material NiCo-LDH prepared in the example;

[0027] Figure 2 SEM image of the two-dimensional-one-dimensional composite material prepared in the example;

[0028] Figure 3 Cycling performance graph of the composite sulfur electrode prepared in the example at 0.1C;

[0029] Figure 4 Rate performance of the composite sulfur electrode prepared in the example. Detailed Embodiments

[0030] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0031] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] In view of the problem of poor conductivity of some two-dimensional metal compound materials when used in the new energy field, the present invention proposes a composite sulfur electrode material, its preparation method and application.

[0033] A typical embodiment of the present invention provides a composite sulfur electrode material, including a two-dimensional layered material-one-dimensional carbon nanotube composite material. The two-dimensional layered material is a single-layer or multi-layer lamellar compound. The one-dimensional carbon nanotubes grow in-situ on the surface of the two-dimensional nanosheet material.

[0034] The characteristics of constructing a two-dimensional-one-dimensional composite material in the present invention are: using a two-dimensional metal compound lamellar material as the matrix, and growing one-dimensional carbon nanotubes in-situ on its metal sites. The two-dimensional metal compound lamellar material is a single-layer or multi-layer lamellar metal compound. The one-dimensional carbon nanotubes and the two-dimensional lamellar material are an integral whole.

[0035] In some embodiments, when constructing the composite sulfur electrode material, the sulfur loading in the composite material is 30-95% by mass, preferably 60-85%, and further preferably 65-75%.

[0036] In some embodiments, the two-dimensional metal compound layered material is one or more of layered double hydroxide (LDH), two-dimensional transition metal sulfide, two-dimensional transition metal selenide, transition metal carbon / nitride (MXene), etc., or modifying metal active sites on two-dimensional materials such as graphene and graphene oxide.

[0037] The layered double hydroxides include various LDH materials such as NiCo-LDH, NiFe-LDH, NiV-LDH, NiTi-LDH, CoAl-LDH, CoMn-LDH, etc.; the two-dimensional transition metal sulfides include MoS2, WS2, etc.; the two-dimensional transition metal selenides include MoSe2, WSe2, etc.; the MXene materials include Ti3C2T x 、Ti2CT x 、V2CTx , Mo2CT x , Nb2CT x , Nb4C3T x , Mo2TiC2T x and Mo2Ti2C3T x etc.

[0038] Another embodiment of the present invention provides a method for preparing a composite sulfur electrode material, which includes the following steps:

[0039] S1. Prepare a two-dimensional layered material or modify metal sites on the surface of a two-dimensional material. The metal sites on the two-dimensional layered material can serve as active sites, which can catalyze the deposition and growth of carbon elements at this position to form carbon nanotubes.

[0040] S2. Place a carbon precursor around the two-dimensional layered material, and carbon nanotubes can be in-situ grown on the two-dimensional layered material after high-temperature heat treatment in a tube furnace, obtaining a two-dimensional-one-dimensional composite material. The carbon nanotubes can improve the electrical conductivity of the material and provide a position and space for loading sulfur.

[0041] S3. Use the two-dimensional-one-dimensional composite material as a sulfur carrier, and compound it with elemental sulfur to prepare a composite sulfur electrode material, which can be applied to the preparation of the positive electrode of a metal-sulfur battery. The rich gaps and the hollow structure of the one-dimensional carbon nanotubes provide sufficient space for the attachment or volume change of sulfur, which is beneficial to the structural stability of the material and improves the long-term durability of the positive electrode of the battery.

[0042] In S1, the two-dimensional layered material is a two-dimensional material with metal active sites on the surface such as layered double hydroxide (LDH), two-dimensional transition metal sulfide, two-dimensional transition metal selenide, transition metal carbon / nitride (MXene), etc.; for other two-dimensional materials without metal sites on the surface such as graphene and graphene oxide, metal active sites need to be modified on their surfaces.

[0043] In S2, the carbon precursor is an organic matter rich in carbon elements such as dicyandiamide, melamine, urea, chitin, etc., or natural biomass such as soybean straw, wheat straw, ginkgo leaf, cotton, wool, sugarcane, reed, wood, etc. The temperature of the high-temperature heat treatment is not lower than 400 °C, preferably 400 - 2000 °C, further preferably 600 - 1500 °C, and more preferably 800 - 1200 °C. The inert atmosphere is formed by nitrogen or helium, argon, etc., and is preferably formed by nitrogen or argon.

[0044] In S3, the advantages of using two-dimensional-one-dimensional composites as sulfur carriers are as follows: The metal sites of two-dimensional metal compounds can chemically bond polysulfides, inhibiting the shuttle effect of polysulfides and improving the cycling stability of metal-sulfur batteries; one-dimensional carbon nanotubes can effectively improve the electrical conductivity of the composites and promote the rapid transport of ions; the abundant voids and the hollow structure of one-dimensional carbon nanotubes provide sufficient space for the attachment or volume change of sulfur, which is conducive to the structural stability of the material and improves the long-term durability of the battery cathode.

[0045] In some embodiments, to prepare the composite sulfur electrode material, the mass ratio of the two-dimensional-one-dimensional composite to sulfur is 1:9 to 9:1, further preferably 2:8 to 6:4, and more preferably 2:8 to 4:6.

[0046] The composite method of the two-dimensional-one-dimensional composite and sulfur is as follows: They can be directly mixed and ground; or the two-dimensional-one-dimensional composite can be immersed in a sulfur / CS2 solution, filtered by suction and slowly dried; or nano sulfur can be in-situ generated on the two-dimensional-one-dimensional composite. In some embodiments, the composite method of the two-dimensional-one-dimensional composite and sulfur is to directly mix and grind them, and then perform heat treatment.

[0047] In some embodiments, after the two-dimensional-one-dimensional composite and sulfur are combined, heat treatment is performed, and the heat treatment method is melt heat treatment. The melt heat treatment temperature is 145 to 300 °C, preferably 155 to 165 °C, and more preferably 155 °C; the heat treatment time is 1 to 50 h, preferably 10 to 24 h.

[0048] The third implementation mode of the present invention provides an application of the above composite sulfur electrode material in the field of metal-sulfur batteries.

[0049] Specifically, the metal-sulfur battery includes but is not limited to lithium-sulfur batteries, sodium-sulfur batteries, potassium-sulfur batteries, magnesium-sulfur batteries, etc.

[0050] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in combination with specific examples and comparative examples.

[0051] Example 1

[0052] (1) Preparation of two-dimensional layered material

[0053] The two-dimensional layered material NiCo-LDH was prepared by the co-precipitation method. The preparation method was as follows: Weigh 2 mmol of Ni(NO3)2·6H2O, 2 mmol of Co(NO3)2·6H2O, and 0.67 g of ammonium fluoride and dissolve them in 250 mL of water. After stirring evenly, gradually add 2.75 mL of ammonia water (concentration 25%) and mechanically stir for 3.5 h. Centrifuge the obtained flocculent product, wash it with water, and dry it in vacuum at 60 °C to obtain the nanosheets of the two-dimensional layered material NiCo-LDH.

[0054] The morphology of the two-dimensional layered material NiCo-LDH obtained in the above steps was tested. The scanning electron micrograph is as Figure 1 shown. It can be seen from Figure 1 that the two-dimensional layered material NiCo-LDH is generally fluffy blocky particles with irregular shapes and sizes ranging from 2 to 10 μm. After magnification, it is observed that the fluffy particles have very thin walls and are composed of many small nanosheets, indicating that the prepared two-dimensional layered material NiCo-LDH is a particulate structure formed by the cross-agglomeration of numerous nanosheets with different orientations. However, the size of the nanosheets is relatively small, so they agglomerate into macroscopic particulate materials.

[0055] (2) Preparation of two-dimensional-one-dimensional composite materials

[0056] Using the two-dimensional layered material NiCo-LDH containing bimetallic sites as the matrix and dicyandiamide as the carbon precursor, a two-dimensional-one-dimensional composite material was prepared. The preparation method was as follows: Grind the two-dimensional layered material NiCo-LDH in an agate mortar for 1 hour. Weigh a certain mass of the two-dimensional layered material NiCo-LDH and place it in a small corundum boat, and weigh a certain mass of dicyandiamide and place it in a large corundum boat (the mass ratio of NiCo-LDH to dicyandiamide is 1:10). Place the small corundum boat inside the large corundum boat and put it in a high-temperature tube furnace. Under the condition of passing argon gas (200 mL / min), carry out high-temperature carbonization to prepare the two-dimensional-one-dimensional composite material. The program set for the high-temperature tube furnace was: Heat from room temperature to 400 °C at a rate of 5 °C / min, keep it at a constant temperature for 1 h, heat to 800 °C at a rate of 5 °C / min, keep it at a constant temperature for 2 h, and then cool it naturally to room temperature to obtain the two-dimensional-one-dimensional composite material.

[0057] The morphology of the two-dimensional-one-dimensional composite material obtained in the above steps was analyzed. The scanning electron micrograph is as Figure 2As shown, it can be seen that the two-dimensional layered material NiCo-LDH no longer presents the fluffy particle morphology aggregated by nanosheets, but shows a large flake structure with a certain thickness. After magnification, it can be seen that there are many one-dimensional carbon nanotubes wound on the surface of the sheet layer. The diameter of the carbon nanotubes is about 50-200 nm, and the length can reach about 20 μm. Each carbon nanotube is independent of each other, and no branched structure is observed, indicating that the growth sites of the carbon nanotubes are independent of each other. The top of the hollow carbon nanotube is capped with a solid particle, and the bottom is connected to the two-dimensional layered material NiCo-LDH, which indicates that the hollow carbon nanotube grows gradually from top to bottom with the Ni and Co metal sites of the two-dimensional layered material NiCo-LDH as nodes. This structure of the two-dimensional-one-dimensional composite material not only improves the conductivity of the two-dimensional layered material NiCo-LDH through the carbon nanotube material, but also the pores formed by the interweaving and winding of the carbon nanotubes and its hollow structure provide a developed space to load sulfur. On the other hand, it can relieve the volume expansion during the charge and discharge process, so it is a good sulfur carrier.

[0058] (3) Preparation of composite sulfur electrode material

[0059] The composite material was prepared by the melt impregnation method: the ground two-dimensional-one-dimensional composite material and elemental sulfur (mass ratio 3:7) were ground for 40 min. A certain mass m1 was weighed and sealed in a test tube, and then placed in a muffle furnace and heated at 115 °C for 20 hours and then at 300 °C for 2 hours, and then taken out and weighed to get m2. The sulfur loading was calculated according to the mass difference, and the calculation method was 1 - 0.3*m1 / m2. In this example, m1 was taken as 0.6968 g and m2 was 0.6187 g. According to the calculation, the sulfur loading of the two-dimensional-one-dimensional composite material was 66.21%.

[0060] The prepared composite sulfur electrode material maintained the basic morphology of the two-dimensional-one-dimensional composite material, and sulfur was uniformly coated on the tube wall of the one-dimensional carbon nanotubes. This is because during the melting process, sulfur experienced three phases: solid, liquid, and gas, so it spread evenly on the tube wall of the carbon nanotubes and penetrated into the interior of the carbon nanotubes. Part of the sulfur was embedded in the gaps between the carbon nanotubes but could also be in contact with the carbon nanotubes. This structure helps the full contact between sulfur and the conductive carbon nanotubes and promotes the full utilization of the active material sulfur.

[0061] (4) Electrochemical performance test

[0062] The composite sulfur electrode material prepared in the above steps was subjected to an electrochemical performance test. Using the composite sulfur electrode material as the positive electrode material of the lithium-sulfur battery, metallic lithium as the negative electrode, adding a polypropylene separator, and the electrolyte was DOL / DME (1:1 / v:v) with 1 M LiTFSI + 1% LiNO3, and the battery was assembled in a glove box filled with high-purity argon.

[0063] The results of the cycling test (voltage range 1.7 - 2.8 V) are as follows Figure 3 shown. It can be seen from Figure 3 that for the lithium-sulfur battery prepared with two-dimensional NiCo-LDH as the sulfur electrode, the initial discharge specific capacity is 595.0 mAh / g, and the discharge specific capacity is only 112.9 mAh / g after 60 cycles. The capacity decay of the battery is relatively obvious. While the lithium-sulfur battery prepared with the two-dimensional-one-dimensional composite material as the sulfur carrier has excellent electrochemical performance. The initial discharge specific capacity at 0.1C is 708.9 mAh / g, and the discharge specific capacity is 564.7 mAh / g after 60 cycles. The battery decays significantly in the first ten cycles, but the capacity tends to be stable later, and the cycling performance is improved significantly.

[0064] The rate performance test is as follows Figure 4 shown. It can be seen that for the lithium-sulfur battery prepared with two-dimensional NiCo-LDH as the sulfur electrode, the specific capacity at 0.1C is 699.0 mAh / g, and the discharge specific capacities at 0.2C and 0.5C are 172.3 and 114.4 mAh / g respectively. When the current density is increased to 1C, the specific capacity decay is nearly zero. While for the battery prepared with the composite sulfur electrode material in this example, the discharge specific capacities at 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 4C are 751.1, 562.7, 529.8, 472.3, 465.8, 462.1, 421.1 mAh / g respectively. When the current density increases from 1C to 4C, the change in the discharge specific capacity is very small, indicating that the composite sulfur electrode material in this example can still achieve rapid ion / electron transport as the electrode material at high current densities.

[0065] This is because the one-dimensional carbon nanotubes grown on the two-dimensional layered material NiCo-LDH greatly improve the conductivity of the two-dimensional layered material NiCo-LDH. At the same time, the hollow tubular structure of the one-dimensional carbon nanotubes provides a space for ion / electron transport, and the rich interstitial structure can relieve the volume expansion of the lithium-sulfur battery during charge and discharge, so it exhibits excellent rate performance.

[0066] In summary, the present invention constructs a composite sulfur electrode material. Using this composite material as the positive sulfur carrier of the metal-sulfur battery can improve the utilization rate of sulfur, promote the rapid transport of ions / electrons, relieve the volume expansion of sulfur during charge and discharge, and inhibit the shuttle effect of the metal-sulfur battery through the dual effects of physical confinement and chemical adsorption, maximizing the electrochemical performance of the metal-sulfur battery.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A composite sulfur electrode material, characterized in that, Based on a two-dimensional layered material as the matrix, one-dimensional carbon nanotubes are in-situ grown on its metal sites to form a two-dimensional-one-dimensional composite material. Sulfur is coated on the inner and outer walls of the carbon nanotubes and embedded in the gaps formed by the interlaced carbon nanotubes. The two-dimensional layered material is NiCo-LDH; the sulfur loading in the composite material is 65-75% by mass. The preparation method of the composite sulfur electrode material includes the following steps: S1, Prepare a two-dimensional layered material containing metal sites. S2, Place a carbon precursor around the two-dimensional layered material and perform heat treatment in a tube furnace at a heat treatment temperature of 700-1200 °C to in-situ grow one-dimensional carbon nanotubes at the positions of the metal sites of the two-dimensional layered material. S3, Mix sulfur on the two-dimensional-one-dimensional composite material and perform heat treatment to obtain the composite sulfur electrode material. In S2, the carbon precursor is dicyandiamide. In S3, the heat treatment method is melt heat treatment.

2. The composite sulfur electrode material according to claim 1, wherein The two-dimensional layered material is a single-layer or multi-layer flaky compound; the one-dimensional carbon nanotube is a hollow tubular structure, and the one-dimensional carbon nanotube and the two-dimensional layered material are an integral whole.

3. A method for preparing the composite sulfur electrode material as described in claim 1, characterized in that, It includes the following steps: S1, Prepare a two-dimensional layered material containing metal sites. S2, Place a carbon precursor around the two-dimensional layered material and perform heat treatment in a tube furnace to in-situ grow one-dimensional carbon nanotubes at the positions of the metal sites of the two-dimensional layered material. S3, Mix sulfur on the two-dimensional-one-dimensional composite material and perform heat treatment to obtain the composite sulfur electrode material.

4. The preparation method of the composite sulfur electrode material according to claim 3, characterized in that, The mass ratio of the two-dimensional layered material to the carbon precursor is 1:2-1:

30.

5. The preparation method of the composite sulfur electrode material according to claim 3, characterized in that, The mass ratio of the two-dimensional layered material to the carbon precursor is 1:5-1:

20.

6. The preparation method of the composite sulfur electrode material according to claim 3, characterized in that, The mass ratio of the two-dimensional layered material to the carbon precursor is 1:5-1:

10.

7. The preparation method of the composite sulfur electrode material according to claim 3, characterized in that, The method of combining the two-dimensional-one-dimensional composite material with sulfur is: melt impregnation method.

8. The preparation method of the composite sulfur electrode material according to claim 7, characterized in that, The operation steps of the melt impregnation method are: put it in a muffle furnace and heat at 155 °C for 20 h, then heat at 300 °C for 2 h and take it out.

9. Application of the composite sulfur electrode material according to any one of claims 1-2 or the composite sulfur electrode material obtained by the preparation method according to any one of claims 3-8 as an electrode material in a metal-sulfur battery; The metal-sulfur battery is one or more of a lithium-sulfur battery, a sodium-sulfur battery, a potassium-sulfur battery, and a magnesium-sulfur battery.

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