CN106129407A - Synthesis method of MoS2@graphene composite nanomaterials - Google Patents

Abstract

The invention relates to a method for synthesizing MoS ₂ @graphene composite nanomaterials. The present invention adopts a one-step hydrothermal synthesis method, uses pyrolysis-reduced graphene oxide, sodium molybdate, and thiourea as raw materials, and a tris buffering agent as a solvent, and under the auxiliary action of dopamine, prepares a homogeneous _MoS2 @graphene composite nanomaterials. The TEM/SEM results show that a large number of MoS ₂ ultrathin nanosheets grow uniformly on the graphene surface, forming a network-like structure tightly wrapped on the graphene. It can be seen from the XRD spectrum that MoS ₂ crystallizes well and belongs to the 2H‑MoS ₂ crystal phase of the hexagonal system. The invention has the advantages of simple process, controllable conditions and high material load uniformity, and the prepared MoS ₂ @graphene composite nanomaterial has broad application prospects in new energy fields such as lithium-ion battery negative electrode materials.

Description

Synthesis method of MoS2@graphene composite nanomaterials

technical field

The invention relates to a method for synthesizing MoS ₂ @graphene composite nanomaterials, which belongs to the field of preparation of new energy materials such as lithium ion batteries.

Background technique

The transition metal sulfide MS ₂ (M=Mo,Ti,V) with two-dimensional layered structure usually has more active sites than zero-dimensional and one-dimensional, and can show more effective surfaces. It has the characteristics of small weight, large surface area and uniform distribution, and shows many excellent properties in terms of light, electricity, and magnetism. Among these materials, molybdenum disulfide nanomaterials (MoS ₂ ) with a graphite-like structure have attracted widespread attention in new energy fields such as lithium-ion battery anode materials due to their high theoretical capacity and special structure.

However, when MoS ₂ is deeply discharged, it will inevitably undergo serious volume expansion, resulting in changes in the microstructure of the material, which in turn affects the rate and cycle performance of the material; coupled with the limitations of its own electrical conductivity, it greatly limits its further application. Therefore, pure MoS ₂ as an electrode material can no longer meet the actual needs. At present, an effective way to improve and enhance the performance of materials is to form composite nanostructures with carbon materials with good electrical conductivity and stable structure. Graphene's unique two-dimensional structure, high specific surface area, and excellent electrical conductivity make it an ideal carrier for loading MoS ₂ . Many methods have been used to prepare MoS ₂ @graphene composites, such as synthesis with the assistance of surfactants; nitrogen-doped modified graphene and MoS ₂ composites, etc. Although some progress has been made in this area, the synthesis process of composite materials is relatively complicated. Therefore, developing a simple and effective preparation process to successfully combine _MoS2 with graphene and improve its electrochemical performance has important research significance in the fields of new energy.

Contents of the invention

The purpose of the present invention is to provide a preparation method of MoS ₂ @graphene lithium ion battery negative electrode material.

To achieve the above object, the present invention adopts the following technical solutions:

A method for preparing MoS ₂ @graphene composite nanomaterial, characterized in that the specific steps of the method are:

a. Graphene oxide is added to tris buffering agent to prepare a mixed solution with a concentration of 0.0350-0.0450mol/L; then add dopamine, continue to stir evenly, then add sodium molybdate, and continue to stir evenly; Add thiourea at last; The molar ratio of described graphene oxide, dopamine, sodium molybdate, thiourea is: 1:0.075～0.235:0.33:2.10;

b. React the mixed solution obtained in step a at 180-240°C for 12-24 hours; after the reaction is completed, centrifuge the product, wash it with deionized water and ethanol, and dry it to obtain a black powder;

c. Calcining the black powder obtained in step b in an inert atmosphere at 600-800° C. for 1-3 hours to obtain the MoS ₂ @graphene composite nanomaterial prepared in the present invention.

In the present invention, sodium molybdate is used as a molybdenum source, thiourea is used as a sulfur source, and graphene is compounded under the auxiliary action of dopamine to prepare a sheet-shaped MoS ₂ @graphene composite nanomaterial with uniform loading. In the process of the present invention, dopamine is firstly adsorbed on the surface of reduced graphene oxide by electrostatic action, then the molybdate ions produced by the hydrolysis of the added sodium molybdate are adsorbed on the dopamine, and the hydrogen sulfide decomposed by the finally added thiourea at high temperature The molybdate is reduced to MoS ₂ , and finally a uniformly loaded composite nanomaterial is formed.

Compared with the existing synthesis technology, the technology of the present invention has the following significant advantages: simple process, controllable conditions, high material load uniformity, and potential application prospects in the field of lithium ion battery materials.

Description of drawings

Fig. 1 is the XRD spectrum of the MoS ₂ @graphene composite nanomaterial obtained in the embodiment of the present invention.

Fig. 2 is a TEM picture of the MoS ₂ @graphene composite nanomaterial obtained in the embodiment of the present invention.

Fig. 3 is a SEM picture of the MoS ₂ @graphene composite nanomaterial obtained in the embodiment of the present invention.

Fig. 4 is a diagram of the electrochemical cycle performance of MoS ₂ @graphene composite nanomaterials obtained in the examples and comparative examples of the present invention.

detailed description

All embodiments are operated according to the operation steps of the above-mentioned technical solutions. For the preparation method of graphene oxide used in the present invention, please refer to J.Am.Chem.Soc., 2008, 130, 5856-5857. The details are as follows: Dissolve potassium persulfate (K ₂ S ₂ O ₈ ) and phosphorus pentoxide (P ₂ O ₅ ) in concentrated sulfuric acid, stir evenly with ultrasonic waves, add the weighed graphite powder, and complete the pre-oxidation process . It is then fully oxidized with potassium permanganate (KMnO ₄ ) and concentrated sulfuric acid at low temperature. Graphene oxide can be obtained by washing with dilute hydrochloric acid and washing with water several times. Finally, pyrolysis-reduced graphene oxide was obtained by calcination at 500°C.

Embodiment one:

a. Weigh 30 mg of pyrolysis-reduced graphene oxide, and ultrasonically disperse it in 60 ml of pre-prepared 10 mM tris buffer;

b. Add 90 mg of dopamine to the mixed solution of a above, stir for 2 hours, and fully dissolve;

c. Add 0.2g of sodium molybdate to the above solution b, and continue to stir for 1h; then add 0.4g of thiourea, and stir for 1h;

d. Pour the reacted mixed solution into a polytetrafluoroethylene-lined autoclave and react at 200°C for 24 hours;

e. After the reaction is completed, the product is taken out from the reaction kettle, centrifuged, washed repeatedly with deionized water and ethanol, dried in vacuum at 60°C overnight, and calcined at 600°C for 2 hours in a nitrogen atmosphere to obtain The MoS ₂ @graphene composite nanomaterial prepared by the present invention.

The physical properties of the obtained samples were characterized, and some of the results are shown in the accompanying drawings. It can be seen from the results that the obtained MoS ₂ @graphene composite has a uniform morphology, and the ultrathin MoS ₂ nanosheets are loaded on the surface of graphene, forming a network-like structure tightly wrapped on the graphene.

comparative example

The preparation process and steps of this embodiment are basically the same as those of this embodiment, except that the b step:

No dopamine added.

The results obtained are obviously different from those in Examples, MoS ₂ is difficult to load evenly on graphene and some of them agglomerate severely.

Referring to the accompanying drawings, Fig. 1 is the XRD spectrum of the MoS ₂ @graphene composite nanomaterial obtained in the embodiment of the present invention. XRD analysis: carried out on RigaKu D/max-2550 X-ray diffractometer in Japan; using CuKα diffraction. It can be seen that, in the composite material obtained by the present invention, the peak positions of the diffraction peaks are at 2θ=14.5°, 40.2°, 50.3°, and 59.9° respectively corresponding to (002), (103), (105), (110 ₎ of MoS ) crystal plane, consistent with the standard spectrum (JCPDF No.37-1492), is a typical hexagonal 2H-MoS ₂ crystal phase. And no other miscellaneous peaks appear, indicating that the obtained product is a high _- purity MoS2 nanosheet with good crystallization.

Referring to the accompanying drawings, Fig. 2 is a transmission electron microscope (TEM) picture of the MoS ₂ @graphene composite nanomaterial obtained in the embodiment of the present invention. TEM analysis: JEOL-200CX transmission electron microscope from Japan Electronics Co., Ltd. was used to observe the morphology and structure of the material. In the composite material obtained in the present invention, flake MoS2 is evenly supported _on the surface of graphene.

Referring to the accompanying drawings, Fig. 3 is a scanning electron microscope (SEM) picture of the MoS ₂ @graphene composite nanomaterial obtained in the embodiment of the present invention. SEM analysis: The morphology of the material was observed with a JSM-20CX emission scanning electron microscope from Japan Electronics Corporation. It can be seen from the SEM results that a large number of MoS2 ultrathin nanosheets grow uniformly _on the graphene surface, forming a network-like structure tightly wrapped on the graphene, which is consistent with the TEM results.

Referring to the accompanying drawings, Fig. 4 is a graph showing the electrochemical cycle performance of MoS ₂ @graphene composite nanomaterials obtained in the examples and comparative examples of the present invention. Among them, the test method of electrochemical performance is as follows: MoS ₂ @ graphene composite nanomaterial and carbon black are prepared, and PVDF (polyvinylidene fluoride, 2.5wt.% aqueous solution) is mixed uniformly to make the negative electrode of the battery; As the positive electrode, the microporous polypropylene material is used as the diaphragm; the electrolyte is prepared by dissolving LiPF ₆ in ethylene carbonate (EC), propylene carbonate (DMC) and ethylene carbonate (DEC) (the corresponding mass ratio is 1: 1:1). The assembly of the simulated cells was done in an argon-filled glove box. As can be seen from Figure 4, the first discharge capacity of the composite nanomaterial obtained in the embodiment is 1732.3mAh/g under the condition of a current density of 100mA/g, and the capacity still reaches 1100.0mAh/g after 50 cycles. Still can reach 63.5%. However, the material obtained in the comparative example is 1430.0mAh/g for the first discharge at the same current density, and the capacity is only 413.6mAh/g after 50 cycles, and the capacity retention rate is very low.

Claims (1)

1. A preparation method of MoS ₂ @graphene composite nanomaterial, characterized in that the specific steps of the method are: a. Add graphene oxide to tris buffering agent to prepare a mixed solution with a concentration of 0.0350~0.0450mol/L; then add dopamine, continue to stir evenly, then add sodium molybdate, and continue to stir evenly; Add thiourea at last; The mol ratio of described graphene oxide, dopamine, sodium molybdate, thiourea is: 1: 0.075～0.235: 0.33: 2.10; b. react the mixed solution obtained in step a at 180-240 °C for 12-24 h; after the reaction is completed, centrifuge the product, wash it with deionized water and ethanol, and dry it to obtain a black powder; c. Calcining the above product at 600-800° C. for 1-3 h in a nitrogen atmosphere to obtain the MoS ₂ @graphene composite nanomaterial prepared in the present invention.