Few-layer two-dimensional transition metal sulfide and graphene ribbon composite material and preparation method and application thereof

Abstract

The present invention discloses a composite material of a few-layer two-dimensional transition metal sulfide and graphene ribbons, as well as its preparation method and application. The method places a two-dimensional transition metal sulfide (MoS2), metallic potassium, and a certain proportion of carbon nanotubes into a vacuum reaction vessel, and heats the reaction vessel for different times and temperatures, causing the metallic potassium to vaporize and enter the MoS2 layer while also entering the interior of the carbon nanotubes. After a certain reaction time, when the distribution of the embedded potassium atoms stabilizes, the reaction vessel is cooled and removed, and methanol is added to react the metallic potassium with the methanol to form potassium methoxide. The potassium methoxide is removed by washing, and the carbon nanotubes are simultaneously stripped to prepare the composite material of the few-layer two-dimensional transition metal sulfide and graphene ribbons. When the composite material of the few-layer two-dimensional transition metal sulfide and graphene ribbons of the present invention is used as a negative electrode material, the battery has excellent rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary ion battery electrode materials, and specifically relates to a composite material of a few-layer two-dimensional transition metal sulfur compound and graphene strips, and a preparation method and application thereof. Background Art

[0002] In recent years, with the continued development of global industrialization, humanity's demand for energy has increased dramatically. At the same time, the environmental pollution caused by industrialization has further intensified. The search for green, environmentally friendly, and renewable energy sources is a key focus for current researchers. Since EXXON's discovery in 1976 that TiS2 can reversibly intercalate and deintercalate lithium ions, leading to the development of the first lithium-ion secondary battery, and Sony's commercial launch of the lithium cobalt oxide / carbon lithium-ion secondary battery in 1991, lithium-ion secondary batteries have achieved substantial development over the past 30 years. However, their development has been plagued by issues such as unstable safety factors, the inability to further increase energy density, and insufficient and uneven lithium resource reserves. Sodium, potassium, zinc, and magnesium ion secondary batteries are similar in principle and structure to lithium-ion batteries, all consisting of a positive and negative electrode and different electrolytes. Compared to lithium-ion batteries, new ion batteries offer the natural advantages of lower raw material costs: these elements are much more abundant on Earth than lithium, are evenly distributed globally, and are inexpensive to mine. In addition, the new type of ion secondary battery has advantages such as higher specific capacity and cycle efficiency than lithium-ion secondary batteries, and is more suitable for application scenarios of large-scale energy storage, such as large-scale high-voltage power grid energy storage, high-speed mobile communication network base station energy storage, big data center energy storage, cloud computing center energy storage and other scenarios.

[0003] At present, the negative electrode material of commercial lithium-ion secondary batteries is still mainly graphitized carbon materials. The theoretical lithium storage capacity of graphite carbon materials is 372mAhg -1 However, in the process of studying sodium-ion secondary batteries, researchers such as Stevens and Fouletier discovered that, while lithium ions can be reversibly embedded and deintercalated in graphite sheets, sodium ions, potassium ions, zinc ions, and magnesium ions with increasingly larger ionic radii cannot be efficiently embedded and deintercalated in graphite sheets with an interlayer spacing of 0.355 nm like lithium ions with smaller ionic spacing. However, non-graphite carbon materials suffer from significant irreversible capacity loss when storing such ions, resulting in poor cycling performance during high-current and high-rate tests. Furthermore, the decomposition of the battery electrolyte during high-current testing can also affect the performance of non-graphite carbon materials in embedding ions.

[0004] In the search for suitable new negative electrode materials for ion secondary batteries, researchers have discovered that the low charge-discharge efficiency and poor cycle performance commonly associated with carbon-based materials are difficult to overcome. Therefore, finding new negative electrode materials to replace carbon-based materials has become a top priority. Since the discovery of graphene, researchers have conducted extensive research on two-dimensional materials. Transition metal sulfides and transition metal selenides have garnered significant attention due to their unique electrical properties. Transition metal sulfides (TMDs) generally have a sandwich-like structure: a stacked structure similar to XMX. In this XMX structure, M represents a transition metal element such as Mo, W, Co, or Ni, while X represents a chalcogenide element such as S, Se, or Te. Among the many known transition metal sulfides, researchers have focused extensively on transition metal sulfides such as molybdenum sulfide and tungsten sulfide, and transition metal selenides such as molybdenum selenide.

[0005] Researchers have conducted extensive research on transition metal sulfides, but the energy storage applications of related materials still have a lot of room for improvement. Generally speaking, relevant researchers have used the following methods to improve the electrochemical properties of related materials: First, by regulating the morphology of transition metal sulfide compounds to obtain a larger specific surface area to accelerate the reaction with related ions. Second, by regulating and improving the conductivity of related transition metal sulfides to improve their performance as energy storage materials. In short, as an energy storage material, the self-limiting growth advantage of two-dimensional transition metal sulfides gives them a natural advantage when used in combination with other two-dimensional carbon materials such as graphene strips as energy storage materials. Summary of the Invention

[0006] In response to the deficiencies in the prior art, the present invention aims to provide a method for in-situ preparation of a composite material of a few-layer two-dimensional transition metal sulfide and graphene ribbons. The method comprises placing a two-dimensional transition metal sulfide MoS2, metallic potassium, and a certain proportion of carbon nanotubes in a vacuum reaction vessel, heating the reaction vessel for different times and temperatures, causing the metallic potassium to vaporize and enter the MoS2 layer while also entering the interior of the carbon nanotubes. After a certain reaction time, when the distribution of the embedded potassium atoms stabilizes, the reaction vessel is cooled and removed, and methanol is added to react the metallic potassium with the methanol to form potassium methoxide. The potassium methoxide is removed by washing, and the carbon nanotubes are simultaneously stripped to prepare a composite material of few-layer MoS2 in which the graphene ribbons are bound to the graphene ribbons (i.e., the composite material of few-layer two-dimensional transition metal sulfide and graphene ribbons of the present invention).

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] A method for in-situ preparation of a composite material of a few-layer two-dimensional transition metal sulfide compound and graphene ribbons comprises the following steps:

[0009] Step 1: Place MoS2 powder, potassium metal, and carbon nanotube powder into a container, create a nitrogen or inert gas environment in the container, seal the container, mix the materials in the container evenly, keep the temperature at 200-450°C for 1-24 hours, and then cool to room temperature;

[0010] In step 1, the ratio of the MoS2 powder, metallic potassium and carbon nanotube powder is 50:50:(1-20) by mass.

[0011] In step 1, the method for making the container into a nitrogen or inert gas environment is: repeating the following steps multiple times: evacuating the container and then filling it with nitrogen or inert gas.

[0012] In step 1, the method for uniformly mixing the substances in the container is to shake the sealed container.

[0013] In step 1, the temperature is kept at 200-450° C. for 6-24 hours.

[0014] In the above technical solution, the shaking time is 10 to 60 minutes.

[0015] Step 2: Take out the material in the container obtained in step 1, mix it with methanol, stir it for reaction, wash it, and dry it.

[0016] In step 2, the washing is carried out using methanol, ethanol and deionized water in sequence to remove elemental potassium and potassium methoxide.

[0017] In step 2, the ratio of the substance taken out from the container to methanol is 1:(5-20) by mass.

[0018] In step 2, the stirring reaction time is 60 to 120 minutes.

[0019] In step 2, the drying temperature is 80 to 120° C., and the drying time is 8 to 24 hours.

[0020] The composite material of the few-layer two-dimensional transition metal sulfur compound and graphene strips of the present invention has excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The SEM image of the few-layer two-dimensional transition metal sulfur compound obtained in Example 1;

[0022] Figure 2 TEM images of a few-layer two-dimensional transition metal sulfur compound obtained for Example 1, wherein a, b, c, and d are TEM images of a few-layer MoS2;

[0023] Figure 3A TEM spectrum of a few-layer two-dimensional transition metal sulfur compound was obtained for Example 1;

[0024] Figure 4 The SEM image of the composite material of a few-layer two-dimensional transition metal sulfide and graphene ribbons obtained in Example 2;

[0025] Figure 5 The charge-discharge diagram of the composite material of a few-layer two-dimensional transition metal sulfur compound and graphene ribbon obtained in Example 2 when used as the negative electrode material of a potassium ion battery;

[0026] Figure 6 This is the SEM image of the composite material prepared in Comparative Example 1;

[0027] Figure 7 This is the SEM image of the composite material prepared in Comparative Example 2.

[0028] FIG8( a ) is a TEM image of a composite material of a few-layer two-dimensional transition metal sulfide and graphene ribbons obtained in Example 2;

[0029] FIG8( b ) is an energy spectrum diagram of the composite material of a few-layer two-dimensional transition metal sulfur compound and graphene ribbons obtained in Example 2.

[0030] Figure 9 This is a cycle diagram obtained in Example 2 when the composite material of a few-layer two-dimensional transition metal sulfur compound and graphene ribbon is used as the negative electrode material of a potassium ion battery;

[0031] Figure 10 This is a cycle diagram when the few-layer two-dimensional transition metal sulfur compound obtained in Example 1 is used as the negative electrode material of potassium ion battery. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below with reference to specific embodiments.

[0033] Example 1

[0034] A method for preparing a few-layer two-dimensional transition metal sulfide compound comprises the following steps:

[0035] Step 1: Place MoS2 powder and potassium metal into a quartz tube and evacuate the tube three times, each time to a vacuum of 1×10 -3 After pa, nitrogen is filled in. The quartz tube is sealed and shaken for 60 minutes using a shaker to mix the materials in the quartz tube evenly. The tube is placed in a muffle furnace and heated to 450°C at a rate of 5°C / min and kept at 450°C for 24 hours, then cooled to room temperature (20-25°C). The ratio of MoS2 powder to potassium metal is 1:1 by mass.

[0036] Step 2: Disassemble the quartz tube in the glove box, take out the substance in the quartz tube obtained in step 1, mix it with methanol, and stir the reaction for 60 minutes to allow the methanol and metallic potassium to fully react to form potassium methoxide. Wash with methanol, ethanol and deionized water in sequence to remove elemental potassium and potassium methoxide, and dry at 80°C for 12 hours to obtain a few-layer two-dimensional transition metal sulfur compound, wherein the ratio of the substance taken out from the quartz tube to methanol is 5:50 by mass.

[0037] Example 2

[0038] A method for in-situ preparation of a composite material of a few-layer two-dimensional transition metal sulfide compound and graphene ribbons comprises the following steps:

[0039] Step 1: Place MoS2 powder, potassium metal and carbon nanotube powder into a quartz tube, and evacuate the tube three times, each time to 1×10 -3 After pa, nitrogen is filled in. The quartz tube is sealed and shaken for 60 minutes using a shaker to mix the materials in the quartz tube evenly. The tube is placed in a muffle furnace and heated to 450°C at a rate of 5°C / min and kept at 450°C for 24 hours, then cooled to room temperature (20-25°C). The ratio of MoS2 powder, potassium metal, and carbon nanotube powder is 50:50:5 by mass.

[0040] Step 2: Disassemble the quartz tube in the glove box, take out the substance in the quartz tube obtained in step 1, mix it with methanol, and stir the reaction for 60 minutes to allow the methanol and metallic potassium to fully react to form potassium methoxide. Wash with methanol, ethanol and deionized water in sequence to remove elemental potassium and potassium methoxide, and dry at 80° C. for 12 hours to obtain a composite material of a few-layer two-dimensional transition metal sulfur compound and graphene ribbons, wherein the ratio of the substance taken out from the quartz tube to methanol is 5:50 by mass.

[0041] Example 3

[0042] A method for in-situ preparation of a composite material of a few-layer two-dimensional transition metal sulfide compound and graphene ribbons comprises the following steps:

[0043] Step 1: Place MoS2 powder, potassium metal and carbon nanotube powder into a quartz tube, and evacuate the tube three times, each time to 1×10 -3 After pa, nitrogen is filled in. The quartz tube is sealed and shaken for 60 minutes using a shaker to mix the materials in the quartz tube evenly. The tube is placed in a muffle furnace and heated to 450°C at a rate of 5°C / min and kept at 450°C for 24 hours, then cooled to room temperature (20-25°C). The ratio of MoS2 powder, potassium metal, and carbon nanotube powder is 50:50:10 by mass.

[0044] Step 2: Disassemble the quartz tube in the glove box, take out the substance in the quartz tube obtained in step 1, mix it with methanol, and stir the reaction for 60 minutes to allow the methanol and metallic potassium to fully react to form potassium methoxide. Wash with methanol, ethanol and deionized water in sequence to remove elemental potassium and potassium methoxide, and dry at 80° C. for 12 hours to obtain a composite material of a few-layer two-dimensional transition metal sulfur compound and graphene ribbons, wherein the ratio of the substance taken out from the quartz tube to methanol is 5:50 by mass.

[0045] Example 4

[0046] A method for in-situ preparation of a composite material of a few-layer two-dimensional transition metal sulfide compound and graphene ribbons comprises the following steps:

[0047] Step 1: Place MoS2 powder, potassium metal and carbon nanotube powder into a quartz tube, and evacuate the tube three times, each time to 1×10 -3 After pa, nitrogen is then filled in. The quartz tube is sealed and shaken in an oscillator for 60 minutes to mix the materials in the quartz tube evenly. The tube is placed in a muffle furnace and heated to 450°C at a rate of 5°C / min and kept at 450°C for 24 hours, then cooled to room temperature (20-25°C). The ratio of MoS2 powder, potassium metal, and carbon nanotube powder is 50:50:20 by mass.

[0048] Step 2: Disassemble the quartz tube in the glove box, take out the substance in the quartz tube obtained in step 1, mix it with methanol, and stir the reaction for 60 minutes to allow the methanol and metallic potassium to fully react to form potassium methoxide. Wash with methanol, ethanol and deionized water in sequence to remove elemental potassium and potassium methoxide, and dry at 80° C. for 12 hours to obtain a composite material of a few-layer two-dimensional transition metal sulfur compound and graphene ribbons, wherein the ratio of the substance taken out from the quartz tube to methanol is 5:50 by mass.

[0049] Comparative Example 1

[0050] A method for preparing a composite material comprises the following steps:

[0051] Step 1: Place MoS2 powder and carbon nanotube powder into a quartz tube and evacuate the tube three times, each time to 1×10 -3 After pa, nitrogen is filled in. The quartz tube is sealed and shaken for 60 minutes using a shaker to mix the materials in the quartz tube evenly. The tube is placed in a muffle furnace and heated to 450°C at a rate of 5°C / min and kept at 450°C for 24 hours before being cooled to room temperature (20-25°C). The ratio of MoS2 powder to carbon nanotube powder is 50:10 by mass.

[0052] Step 2: dismantle the quartz tube in the glove box, take out the material in the quartz tube obtained in step 1, and obtain a composite material.

[0053] Comparative Example 2

[0054] A method for preparing a composite material, comprising the steps of:

[0055] Step 1: Place carbon nanotube powder into a quartz tube and evacuate the tube three times, each time to 1×10 -3 After pa, nitrogen is filled in. Place in a muffle furnace and heat at 5℃ / min to 450℃ and keep at 450℃ for 24h, then cool to room temperature (20-25℃);

[0056] Step 2: Disassemble the quartz tube in the glove box, take out the substance in the quartz tube obtained in step 1, mix it with methanol, stir and react for 60 minutes, wash it with methanol, ethanol and deionized water in sequence, and dry it at 80°C for 12 hours. The ratio of the substance taken out from the quartz tube to methanol is 5:50 by mass.

[0057] The method for in situ preparation of a composite material of a few-layer two-dimensional transition metal sulfur compound and graphene strips of the present invention uses potassium vapor to enter the interlayer space and react with methanol to form potassium methoxide. Figure 4 、 Figure 6 By comparison, the diameter of the carbon nanotubes becomes significantly thicker, which increases the distance between the MoS layers and breaks the carbon nanotubes into graphene strips.

[0058] Figure 1 、 Figure 2 The SEM and TEM images of the few-layer two-dimensional transition metal sulfur compound prepared in Example 1 are shown. Figure 1 、 Figure 2 It can be clearly seen that the few-layer MoS2 exfoliated by metallic potassium intercalation is in the form of thin flakes.

[0059] Figure 3 This is a TEM image of the few-layer two-dimensional transition metal sulfur compound prepared in Example 1. As shown in the figure, after the carbon nanotube strips are intercalated and exfoliated by metallic potassium, the diameter of the carbon tubes becomes significantly thicker, and the compact carbon nanotube array is transformed into a fluffy graphene strip.

[0060] The prepared electrodes were assembled into CR2032 button cells for electrochemical performance testing. The active material (800 mg) of the composite material of the two-dimensional transition metal sulfide compound and graphene ribbons prepared in Example 2 or the two-dimensional transition metal sulfide compound obtained in Example 1, 10 wt% of a conductive agent (100 mg), and 10 wt% of a binder (CMC) (100 mg) were added to 3 ml of deionized water. The mixture was then stirred evenly for 8 hours to obtain an electrode slurry. The electrode slurry was evenly coated on copper foil to obtain an electrode sheet. The electrode sheet was placed in a vacuum drying oven and dried at 110°C for 24 hours to obtain a working electrode sheet. A potassium metal sheet was used as a reference electrode. The reference electrode, working electrode, and Celgard microporous polypropylene membrane as a diaphragm were assembled in sequence in a purified glove box filled with Ar gas (O2 < 0.1ppm, H2O < 0.1ppm) to form a potassium ion battery. The active material was used as the negative electrode material of the potassium ion battery. The electrode liquid was a mixture of KPF6 and a solvent. The concentration of KPF6 in the electrode liquid was 0.8M, and the solvent was a mixed solution of ethyl carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1. It should be noted that the electrolyte must fully infiltrate the diaphragm and no gas can enter between the diaphragm and the positive electrode sheet.

[0061] Figure 5 This is the charge and discharge diagram of the composite material of the few-layer two-dimensional transition metal sulfur compound and graphene ribbon prepared in Example 2 when used as the negative electrode material of the potassium ion battery. Through charge and discharge, it can be seen that the prepared potassium ion battery has a high conductivity at 0.1-5Ag -1 The charge and discharge capacity is good at current density of 0.1Ag -1 At the current density, the capacity is as high as 830mAhg -1 , at a current density of 5Ag -1 When the battery is fully charged, there is still 256mAh g -1 This shows that the prepared few-layer two-dimensional transition metal sulfur compound and graphene strip composite material is an ideal potassium ion battery negative electrode material.

[0062] like Figure 6 and 7 As shown, the SEM images of Comparative Examples 1 and 2 prove that, in the absence of metallic potassium vapor intercalation, it is impossible to exfoliate carbon nanotubes into graphene strips and MoS2 simply by heating and shaking.

[0063] Figure 8 shows the TEM image (a) and energy spectrum (b) of the composite material of a few-layer two-dimensional transition metal sulfide and graphene ribbons obtained in Example 2. Figure 8(a) shows the presence of a large amount of few-layer MoS2 on the graphene nanosheets evolved from carbon nanotubes exfoliated from metal K. Furthermore, Figure 8(b) shows that the sample contains only three elements: carbon, sulfur, and molybdenum. During the exfoliation process, the MoS2 was not oxidized, and the metallic potassium was effectively removed.

[0064] Figure 9 、 Figure 10 The cycle diagrams of the composite material of the few-layer two-dimensional transition metal sulfur compound and graphene strip prepared in Example 2 and the few-layer two-dimensional transition metal sulfur compound obtained in Example 1 when used as the negative electrode material of potassium ion battery are shown respectively. Figure 9 、 Figure 10 By comparing the results of the experiments, it can be found that when the few-layer two-dimensional transition metal sulfur compounds and graphene strip samples stripped by potassium ion intercalation are used as negative electrode materials for potassium ion batteries, the cycling effect is much better than that of the samples without graphene strips.

[0065] The few-layer two-dimensional transition metal sulfur compound and graphene ribbon composite materials prepared in Example 3 and Example 4 can both achieve the same technical effects as the few-layer two-dimensional transition metal sulfur compound and graphene ribbon composite materials prepared in Example 2.

[0066] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A method for in-situ preparation of a composite material of a few-layer two-dimensional transition metal sulfide compound and graphene ribbons, characterized in that: The following steps are involved: Step 1: Place MoS2 powder, potassium metal, and carbon nanotube powder into a container, create a nitrogen or inert gas environment in the container, seal the container, mix the materials in the container evenly, keep the temperature at 200-450°C for 1-24 hours, and then cool to room temperature; Step 2: Take out the material in the container obtained in step 1, mix it with methanol, stir it for reaction, wash it, and dry it.

2. The method according to claim 1, characterized in that In step 1, the ratio of the MoS2 powder, metallic potassium and carbon nanotube powder is 50:50:(1-20) by mass.

3. The method according to claim 1, characterized in that In step 1, the method for making the container into a nitrogen or inert gas environment is: repeating the following steps multiple times: evacuating the container and then filling it with nitrogen or inert gas.

4. The method according to claim 1, wherein In step 1, the method for uniformly mixing the substances in the container is to shake the sealed container.

5. The method according to claim 1, wherein In step 1, the temperature is kept at 200-450° C. for 6-24 hours.

6. The method according to claim 4, characterized in that The shaking time is 10 to 60 minutes.

7. The method according to claim 1, characterized in that In step 2, the washing is carried out using methanol, ethanol and deionized water in sequence to remove elemental potassium and potassium methoxide.

8. The method according to claim 1, characterized in that In step 2, the ratio of the substance taken out from the container to methanol is 1:(5-20) by mass.

9. The method according to claim 1, characterized in that In step 2, the stirring reaction time is 60 to 120 minutes.

10. The method according to claim 1, characterized in that In step 2, the drying temperature is 80 to 120° C., and the drying time is 8 to 24 hours.

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