CN111106322B

CN111106322B - Nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material

Info

Publication number: CN111106322B
Application number: CN201811262170.1A
Authority: CN
Inventors: 郭金; 廖莎; 张会成; 王少军; 凌凤香
Original assignee: China Petroleum and Chemical Corp; Sinopec Dalian Research Institute of Petroleum and Petrochemicals
Current assignee: Sinopec Dalian Petrochemical Research Institute Co ltd; China Petroleum and Chemical Corp
Priority date: 2018-10-27
Filing date: 2018-10-27
Publication date: 2021-07-09
Anticipated expiration: 2038-10-27
Also published as: CN111106322A

Abstract

A nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material is prepared by using formaldehyde as a bridge, enabling the formaldehyde to be appropriately crosslinked with melamine to form a nitrogen-doped precursor, carrying out hydrothermal reaction to enable the nitrogen-doped precursor, an active component precursor and graphene to be mutually and uniformly fused, and carrying out solvent-free microwave reaction to synthesize the high-nitrogen-content doped molybdenum disulfide/three-dimensional graphene composite material. The composite material avoids the loss caused by sublimation of the nitrogen-doped precursor in the heating process in the traditional nitrogen-doping process, improves the nitrogen-doping efficiency, and realizes the uniform fusion of the interaction of the nitrogen-doped precursor, the active component precursor and the graphene under mild to strong reaction conditions. The prepared nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material has good stability, is not easy to denature in air, is easy to store, has a large specific surface area, is used as a lithium ion battery cathode material, provides a good channel for lithium ion transmission, and shows a large specific capacity and a good cycling stability performance.

Description

Nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material

Technical Field

The invention relates to a nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material, in particular to a high-nitrogen-content doped molybdenum disulfide/three-dimensional graphene lithium battery cathode material and a preparation method thereof, and belongs to the technical field of nano composite materials and application thereof.

Background

Graphene is a carbonaceous material having a two-dimensional honeycomb lattice structure formed by close packing of single-layer carbon atoms, and has received great attention in experimental science and theoretical science since the discovery of Andre K heim (Andre K. Geim) and the like at manchester university in 2004 england. Graphene, which is only one carbon atom thick, is the thinnest of known materials, but is very strong and hard, stronger than diamond, and 100 times stronger than the hardest steel in the world. The catalyst has a special nano structure and excellent performance, and has potential application prospects in the fields of catalysis, lithium storage, composite materials, electrochemistry and the like.

Graphene has hydrophobic properties and is difficult to directly modify and process in practical research. Graphene Oxide (GO), a derivative of the Graphene oxide, has good water-soluble dispersibility due to the fact that oxygen-containing functional groups such as carboxyl, hydroxyl and carbonyl are enriched on the surface, and good operability is provided for further modification of GO. GO can be collapsed to form a three-dimensional hydrogel, such as by adding certain cross-linking agents and providing certain temperatures and pressures. The three-dimensional graphene has a high actual specific surface area, a rich pore structure and an excellent electron transmission speed, and good conditions are created for improving the electron transmission and the quality transmission of the catalyst.

CN102887502B provides a chemical vapor deposition method for preparing nitrogen-doped graphene material, which firstly provides a clean and dry substrate; coating a solution containing a catalyst on the surface of the substrate, heating the substrate to 500-1300 ℃ under an oxygen-free condition, introducing a reducing gas and the reducing catalyst, and then introducing a gaseous organic carbon source compound and a gaseous nitrogen source compound for reaction to finally obtain the nitrogen-doped graphene. CN104393254B provides a solid-phase reaction method for preparing a nitrogen-doped molybdenum disulfide/graphene composite material, which comprises the steps of firstly mixing a graphene oxide solution, a nitrogen-containing precursor, a sulfur-containing precursor and a molybdenum-containing precursor in a solvent, then evaporating to obtain a precursor material, then removing the solvent and heteroatoms to obtain the precursor material, and then calcining at the temperature of 500-700 ℃ in an inert atmosphere to obtain the nitrogen-doped molybdenum disulfide/graphene composite material. However, these methods generally have the problems of multiple steps, long time (more than one week is needed in the whole composite material preparation process of CN 104393254B), difficulty in controlling the nitrogen doping content, and low nitrogen doping efficiency due to the large loss of the nitrogen doping precursor caused by the intensive sublimation of the nitrogen doping precursor during the heating process in the solid phase reaction. The preparation of high nitrogen content doped graphene and molybdenum disulfide/graphene composite materials is difficult, thereby limiting the wide application of such materials.

Disclosure of Invention

The invention provides a method for efficiently, quickly and massively synthesizing a high-nitrogen-content doped molybdenum disulfide/three-dimensional graphene composite material, which aims to solve the problems that in the prior art, the preparation of a nitrogen-doped graphene material has complex equipment, complex process, complex and time-consuming operation, low product utilization rate, difficult raw material acquisition, low nitrogen doping content caused by the loss of a large amount of nitrogen-doped precursors in the nitrogen-doping process, and the aggregation and accumulation of active components and nanoparticles in the long-time heat treatment process of graphene.

In order to achieve the technical purpose, the invention provides a preparation method of a nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material, which comprises the following steps:

(1) dispersing graphene oxide and cysteine in a formaldehyde solution to obtain a dispersion liquid A;

(2) dispersing melamine and ammonium tetrathiomolybdate into deionized water to obtain a dispersion liquid B;

(3) mixing the dispersion liquid A and the dispersion liquid B, heating to 50-80 ℃ for reaction for 10-60min, adjusting the pH of the reaction liquid to 7-9, heating in a sealed environment to 100-200 ℃ for hydrothermal reaction for 12-24 h, and drying the product to obtain a solid material;

(4) and (4) placing the solid material obtained in the step (3) in a microwave reaction cavity, and heating for 10-60min at the microwave power of 300-1200W to obtain the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material.

In the above-mentioned production method, the concentration of the aqueous formaldehyde solution in the step (1) is not particularly limited, and in a preferred embodiment of the present invention, the concentration of formaldehyde is 37% to 40% by mass. And mixing the graphene oxide and the formaldehyde solution according to the solid-to-liquid ratio of 1g (10-100) mL. The mixing mass ratio of the graphene oxide to the cysteine is 1:1-20, preferably 1: 3-8; the cysteine is L-cysteine; the obtained solution is preferably mixed and dispersed uniformly in an ultrasonic mode, and the ultrasonic time is 5-30 min.

In the above production method, the dispersion liquid a and the dispersion liquid B are mixed in the step (3), and the dispersion liquid a is preferably poured into the dispersion liquid B. Mixing the graphene in the dispersion liquid A, the melamine in the dispersion liquid B and the ammonium tetrathiomolybdate in the dispersion liquid B according to the mass ratio of 1:1-20: 1-20. After mixing, the mixture is preferably mixed and dispersed uniformly in an ultrasonic mode, and the ultrasonic time is 5-30 min.

In the above preparation method, the pH of the reaction solution in the step (3) may be adjusted by using an organic base or an inorganic base, and as a more specific embodiment, the pH is selected from one or more of triethanolamine, methylamine, ethylamine, ethylenediamine, propylamine, isopropylamine, aniline, cyclohexylamine, o-aminophenol, 2-chlorophenol, potassium carbonate, sodium bicarbonate, potassium hydroxide, and sodium hydroxide.

In the preparation method, the hydrothermal reaction temperature in the step (3) is preferably 120-160 ℃, and the time is preferably 12-18 h.

In the above production method, the drying in the step (3) is freeze-drying. The freeze drying can maintain the graphene skeleton structure, effectively relieve the agglomeration phenomenon of graphene materials, and further ensure the characteristics of the interior of graphene.

In the preparation method, the power of the microwave reaction in the step (4) is preferably 600-1000W, and the time is preferably 10-30 min.

In the preparation method, the microwave reaction cavity is purged by nitrogen or inert gas before and during the microwave reaction, and preferably, argon is used for purging.

In the above preparation method, the graphene oxide is selected from among graphene oxides having the following properties: the area of the sheet layer is 100 mu m²The conductivity is 3500S/m or more.

In the above preparation method, the graphene oxide is obtained by oxidizing graphite, and the graphene oxide of the present invention is synthesized by Hummers method, and as a more specific embodiment, the present invention discloses a specific preparation method of the graphene oxide as follows: adding natural crystalline flake graphite into ice-bath concentrated sulfuric acid under stirring, cooling to 0-10 ℃, adding sodium nitrate and potassium permanganate, stirring for reaction, adding deionized water, heating to 50-100 ℃, reacting at constant temperature until the reaction solution turns to bright yellow, adding hydrogen peroxide, stirring for reaction, cooling, washing and drying to obtain graphene oxide.

The specification of the natural crystalline flake graphite is 100-500 meshes. After the reaction is finished, repeatedly settling with deionized water during post-treatment to remove unreacted graphite particles, centrifuging with hydrochloric acid, cleaning, removing Cl ions in the reaction solution, washing with deionized water until the pH value is close to neutral, drying, and grinding.

The stripping efficiency of the Hummers method is more than 93%, the yield is more than 90%, the structural integrity of the obtained graphene oxide sheet layer is high, and the crystal lattice is complete after thermal reduction.

The technical purpose of the second aspect of the invention is to provide the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material prepared by the method. In the preparation process of the method, formaldehyde and melamine are mixed firstly to generate moderate crosslinking reaction to form a water-soluble nitrogen-doped precursor, and then the hydrothermal reaction is carried out to carry out graphene nitrogen doping, so that the nitrogen-doped precursor and graphene components are easy to interact, conditions are created for uniformly fusing composite materials, and the nitrogen-doped process and MoS are more favorably realized₂Compounding with graphene; the subsequent microwave reaction has high heating speed and uniform heating, the graphene oxide is rapidly thermally reduced into graphene, and the nitrogen-doped precursor and the active component single-source precursor are thermally decomposed, so that the graphene nitrogen doping and the active component dispersion are more uniform due to the fact that the graphene oxide, the nitrogen-doped precursor and the active component are uniformly fused in the previous preparation process, and the high-content nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material is more favorably synthesized.

The technical purpose of the third aspect of the invention is to provide application of the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material, and the material can be used as a lithium ion battery cathode material and shows good cycle stability and rate capability.

Compared with the prior art, the invention has the following advantages:

(1) according to the invention, formaldehyde is used as a bridge in the preparation process of the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material, and the formaldehyde and melamine are subjected to moderate crosslinking to form the nitrogen-doped precursor, so that the problem of low nitrogen-doping efficiency caused by large loss of the nitrogen-doped precursor due to strong sublimation of the nitrogen-doped precursor in the heating process in the traditional solid nitrogen-doping reaction is solved.

(2) In the preparation process, the formaldehyde and the melamine are subjected to a cross-linking reaction to form a water-soluble nitrogen-doped precursor, and the nitrogen-doped precursor is uniformly coated on the three-dimensional graphene skeleton, so that the nitrogen-doped precursor, the active component precursor and the graphene are uniformly interacted and fused in the subsequent hydrothermal reaction, and the preparation of the high-nitrogen-content doped material is realized.

(3) The microwave reaction stage in the preparation process has the advantages that the heating speed is high, the heating is uniform, on one hand, the loss caused by sublimation of the nitrogen-doped precursor due to slow temperature rise in the traditional reaction can be avoided, on the other hand, under the microwave condition, the graphene oxide is rapidly thermally reduced into the graphene, and meanwhile, the nitrogen-doped precursor and the active component single-source precursor are thermally decomposed.

(4) The microwave reaction has high heating speed and MoS₂The combination of the nanosheets and the nitrogen-doped graphene is firm, the particles are not easy to accumulate, the time required by the synthetic material is greatly shortened, and the graphene and MoS are relieved₂The problem of agglomeration under the condition of long-term heating is more favorable for synthesizing the high-performance nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material.

(5) The microwave reaction in the preparation process adopts a solvent-free treatment mode, so that the post-treatment processes of washing, separating, drying and the like of the product are omitted, and the production process is simplified.

(6) The nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material prepared by the method has good stability, is not easy to denature in air, is easy to store, has a large specific surface area, is used as a lithium ion battery cathode material, provides a good channel for lithium ion transmission, and shows a large specific capacity and a good cycling stability performance.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

Fig. 1 is an XRD pattern of graphene oxide prepared according to the present invention;

fig. 2 is an SEM image of the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material prepared in example 8;

FIG. 3 is a graph of the current density of 100 mA-g for the N-doped molybdenum disulfide/three-dimensional graphene composite material in example 8^-1Time charge and discharge cycle curve.

Detailed Description

The following non-limiting examples are presented to enable those of ordinary skill in the art to more fully understand the present invention and are not intended to limit the invention in any way.

The graphene oxide used in the following examples was prepared by the following method:

100mL of 98% concentrated sulfuric acid was slowly added to a 500mL dry three-necked flask, and the three-necked flask was placed on a magnetic stirrer with ice-bath cooling. 2.0g of natural crystalline flake graphite (180 mesh) was added with rapid stirring, and when the temperature of the reaction solution was reduced to about 0 ℃, 4.0g of sodium nitrate was slowly added, and stirring was continued for 2 hours. Then slowly adding 10g of potassium permanganate in batches within 1h, continuously stirring for 2h, and controlling the reaction temperature below 10 ℃. The three-necked flask is transferred into a water bath at 40 ℃, and the reaction is continuously stirred for 2 hours. Subsequently, 200mL of warm deionized water was added slowly and the reaction solution was kept at a temperature within 100 ℃. The reaction was carried out at a constant temperature of 98 ℃ until the reaction solution became bright yellow. 20mL of 30% hydrogen peroxide was added to the reaction solution, and the mixture was stirred continuously to allow the mixture to react sufficiently. And after cooling, replacing deionized water with the obtained solution for repeated sedimentation, removing unreacted graphite particles, centrifugally cleaning with hydrochloric acid to remove Cl ions in the reaction solution, and then washing with deionized water until the pH value is close to neutral. And finally, vacuum drying for 12h at 80 ℃ to obtain graphene oxide, and grinding the graphene oxide into powder for later use. Its XRD pattern is shown in FIG. 1 and is located at 11^oLeft and right are oxidationThe 001 diffraction peak typical of graphene is mainly due to intercalation of a large number of oxygen-containing functional groups between graphene sheets. The distance between graphite oxide sheets can be calculated to be 0.7 nm through the Sherle formula, and is obviously larger than the interlayer spacing 0.3254 nm of graphite. The increased interlayer spacing is primarily due to oxygen-containing functional groups intercalated between graphene sheets.

The nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material is prepared in the embodiments 1-8:

example 1

(1) 1.0g of graphene oxide and 3.0g L-cysteine were weighed and dispersed in 20mL of 37% formaldehyde aqueous solution, and the mixture was placed in an ultrasonic instrument and uniformly dispersed to obtain dispersion A.

(2) 3.0g of melamine and 5.0g of ammonium tetrathiomolybdate were weighed into 40mL of deionized water, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed by ultrasonic, and the dispersion B was recorded.

(3) Mixing the dispersion A and the dispersion B, heating in water bath to 60 ℃, and stirring for 10 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 8.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. The solid obtained was freeze-dried.

(4) And (4) placing the product in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. And heating for 10min at 600W of microwave power to obtain the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material.

Example 2

(1) 1.0g of graphene oxide and 3.0g L-cysteine were weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic instrument and uniformly dispersed to obtain dispersion A.

(2) 5.0g of melamine and 8.0g of ammonium tetrathiomolybdate were weighed into 40mL of deionized water, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed by ultrasonic, and the dispersion B was recorded.

Example 3

(1) 1.0g of graphene oxide and 4.0g L-cysteine were weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic instrument and uniformly dispersed to obtain dispersion A.

(2) 10.0g of melamine and 10.0g of ammonium tetrathiomolybdate were weighed into 40mL of deionized water, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed by ultrasonic, and the dispersion B was recorded.

(3) Mixing the dispersion A and the dispersion B, heating in water bath to 70 ℃, and stirring for 10 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 8.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. The solid obtained was freeze-dried.

(4) And (4) placing the product in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. And heating for 20min at 600W of microwave power to obtain the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material.

Example 4

(1) 1.0g of graphene oxide and 5.0g of 5.0g L-cysteine were weighed out and dispersed in 30mL of 37% formaldehyde aqueous solution, and the mixture was placed in an ultrasonic instrument and uniformly dispersed to obtain dispersion A.

(2) 10.0g of melamine and 12.0g of ammonium tetrathiomolybdate were weighed into 40mL of deionized water, and the mixture was placed in an ultrasonic apparatus and uniformly dispersed by ultrasonic, and the dispersion B was recorded.

(3) Mixing the dispersion A and the dispersion B, heating in water bath to 70 ℃, and stirring for 20 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 9.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. The solid obtained was freeze-dried.

(4) And (4) placing the product in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. And heating for 30min at 600W of microwave power to obtain the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material.

Example 5

(1) 1.0g of graphene oxide and 6.0g L-cysteine were weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic instrument and uniformly dispersed to obtain dispersion A.

(3) Mixing the dispersion A and the dispersion B, heating in water bath to 70 ℃, and stirring for 20 min. And then adding potassium hydroxide into the reaction liquid, adjusting the pH value of a reaction liquid system to 9.0, carrying out ultrasonic mixing uniformly, then pouring the reaction liquid into a high-pressure reaction kettle, and heating to 120 ℃ for reaction for 12 hours. The solid obtained was freeze-dried.

(4) And (4) placing the product in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. And heating for 10min at the microwave power of 800W to obtain the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material.

Example 6

(1) 1.0g of graphene oxide and 7.0g of 7.0g L-cysteine were weighed out and dispersed in 30mL of 37% formaldehyde aqueous solution, and the mixture was placed in an ultrasonic instrument and uniformly dispersed to obtain dispersion A.

(3) Mixing the dispersion A and the dispersion B, heating in water bath to 80 ℃, and stirring for 30 min. And then adding potassium hydroxide into the reaction liquid, adjusting the pH value of a reaction liquid system to 9.0, carrying out ultrasonic mixing uniformly, then pouring the reaction liquid into a high-pressure reaction kettle, and heating to 140 ℃ for reaction for 15 hours. The solid obtained was freeze-dried.

Example 7

(1) 1.0g of graphene oxide and 8.0g of 8.0g L-cysteine were weighed and dispersed in 30mL of 37% aqueous formaldehyde solution, and the mixture was placed in an ultrasonic instrument and uniformly dispersed to obtain dispersion A.

(3) Mixing the dispersion A and the dispersion B, heating in water bath to 80 ℃, and stirring for 30 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 9.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 160 ℃ for reaction for 15 hours. The solid obtained was freeze-dried.

Example 8

(3) Mixing the dispersion A and the dispersion B, heating in water bath to 80 ℃, and stirring for 30 min. And adding triethanolamine into the reaction solution, adjusting the pH value of a reaction solution system to 9.0, ultrasonically mixing uniformly, pouring the reaction solution into a high-pressure reaction kettle, and heating to 160 ℃ for reacting for 18 hours. The solid obtained was freeze-dried.

(4) And (4) placing the product in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. And heating for 30min at the microwave power of 1000W to obtain the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material.

SEM image of nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material obtained in example 8As shown in FIG. 2, the MoS of the two-dimensional structure can be seen₂Grows on a three-dimensional graphene framework and shows a compact three-dimensional structure, which is beneficial to good conductivity of nitrogen-doped three-dimensional graphene and MoS₂The active components are combined to exert more excellent electrochemical performance.

Comparative example 1

In the step (1), formaldehyde solution is not used, and deionized water is used for replacing:

(1) 1.0g of graphene oxide and 8.0g of 8.0g L-cysteine were weighed and dispersed in 30mL of deionized water, and the mixture was placed in an ultrasonic instrument and uniformly dispersed, and the dispersion A was recorded.

(4) And (4) placing the product in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating the mixture for 30min at the microwave power of 1000W to obtain a comparative composite material.

Comparative example 2

In the step (2), ammonium tetrathiomolybdate is not added:

(1) 1.0g of graphene oxide and 8.0g of 8.0g L-cysteine were weighed and dispersed in 30mL of 37% formaldehyde solution deionized water, and the mixture was placed in an ultrasonic instrument and uniformly dispersed to be recorded as dispersion A.

(2) 10.0g of melamine is weighed and added into 40mL of deionized water, and the mixture is placed in an ultrasonic instrument to be uniformly dispersed by ultrasonic, and the dispersion liquid B is marked.

(4) And (4) placing the product in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating for 30min with 1000W of microwave power to obtain the composite material.

Comparative example 3

And (3) adjusting the pH value of the reaction solution without adding alkali liquor, uniformly mixing the dispersion solution A and the dispersion solution B, and then directly carrying out hydrothermal reaction:

(3) And mixing the dispersion liquid A and the dispersion liquid B, uniformly mixing by ultrasonic waves, pouring the reaction liquid into a high-pressure reaction kettle, and heating to 160 ℃ for reacting for 18 hours. The solid obtained was freeze-dried.

(4) And (4) placing the black solid powder obtained in the step (3) in a microwave reaction chamber, and purging for 1h by 100mL/min argon. Heating for 30min with 1000W of microwave power to obtain the composite material.

The materials of examples 1-8 and comparative examples 1-3 are used as the negative electrode material of the lithium ion battery. Taking the synthesized nitrogen-doped graphene as an active component, selecting a 2016 type battery shell, a metal lithium sheet (phi 16 mm multiplied by 1mm), and 1.0M LiPF₆The mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DEC) (volume ratio of 1:1) is used as electrolyte, and Celgard2300 microporous polypropylene coal membrane is used as battery diaphragm. The materials are assembled into a button cell in a glove box filled with Ar gas, and the test is carried out after the working electrode is fully soaked by the electrolyte. The method comprises the following five steps:

(1) size mixing

The material used has a large specific surface and is easy to adsorb moisture in the air, so the material for preparing the electrode is firstly dried fully in a vacuum drying oven at 120 ℃ to remove the surface moisture. Then adding active material and conductive additive (acetylene black)) And a binder (PVDF) are added into the dispersant according to the mass percentage of 80:10:10N-methylpyrrolidone (NMP) mixed grinding, resulting in uniform mixing of the materials, making a viscous slurry.

(2) Coating film

The resulting viscous paste was uniformly coated on a copper foil (thickness of about 100 μm). The specific operation is as follows: 1) the copper foil of moderate size is cut and laid flat on a table top. 2) Removing stains on the surface of the copper foil. 3) The slurry was dispersed on a copper foil and uniformly spread on the copper foil using a die. 4) The copper foil coated with the slurry was dried in a vacuum drying oven at 120 ℃ for 12 hours.

(3) Roller compaction

After the completion of drying, the copper foil coated with the slurry was rolled with a small-sized rolling machine to prevent the electrode material from falling off from the surface of the copper foil.

(4) Tabletting

And cutting the rolled film into a plurality of circular electrode slices with the diameter of 12mm by using a manual slicer. In order to prevent the coating film from falling off during charge and discharge cycles, it was pressed into a sheet by an oil press. And taking out and weighing after drying, and waiting for battery loading.

(5) Assembled battery

The process of assembling the button cells was carried out in a glove box filled with Ar gas. The battery is assembled according to the sequence of negative battery shell/electrolyte/working electrode plate/electrolyte/diaphragm/lithium plate/positive battery shell. And standing for 24 hours, and carrying out electrochemical test after the electrolyte is fully soaked.

And carrying out charge and discharge tests on the assembled button type simulation battery. The material of example 8 was used at a voltage in the range of 0.01 to 3.0V and at a current of 100mA g^-1The results of the cycle stability test at the current density of (a) are shown in fig. 3. The first charge and discharge capacities and the discharge capacities after 100 charge and discharge tests of examples 1 to 8 and comparative examples 1 to 3 are shown in table 1, wherein the nitrogen content was measured by elemental analysis.

The test data show that the nitrogen doping content in the composite material is improved, and the nitrogen content can reach 9.3 percent at most. Secondly, the first discharge specific capacity of the button cell is increased, and the first maximum discharge capacity of the embodiment 8 can be reached1398.0 mAh·g^-1Compared with the comparative example 1, the reversible capacity retention rate is close to 90.0 percent and is up to 91.8 percent, the reversible capacity retention rate is improved by 14.0 percent, the reversible capacity retention rate is improved by 245.6 percent, the reversible capacity retention rate is improved by 12.7 percent, and the reversible capacity is still kept after 100 times of circulation, which shows that the composite material prepared by the invention has higher reversible capacity and good cycle performance.

TABLE 1

Claims

1. A preparation method of a nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material comprises the following steps:

(1) dispersing graphene oxide and cysteine in a formaldehyde aqueous solution to obtain a dispersion liquid A;

2. The preparation method according to claim 1, wherein in the step (1), the graphene oxide and the aqueous formaldehyde solution are mixed according to a solid-to-liquid ratio of 1g to 10-100 mL.

3. The preparation method according to claim 1, wherein the mixing mass ratio of the graphene oxide to the cysteine in the step (1) is 1:1-20, and the cysteine is L-cysteine.

4. The preparation method according to claim 3, wherein the mixing mass ratio of the graphene oxide to the cysteine in the step (1) is 1: 3-8.

5. The method according to claim 1, wherein the dispersion A and the dispersion B are mixed in the step (3) by pouring the dispersion A into the dispersion B.

6. The preparation method according to claim 1, wherein the dispersion liquid A and the dispersion liquid B are mixed in the step (3), and the ratio of graphene in the dispersion liquid A to melamine in the dispersion liquid B to ammonium tetrathiomolybdate in the dispersion liquid B is 1:1-20:1-20 by mass.

7. The process according to claim 1, wherein an organic base or an inorganic base is used for adjusting the pH of the reaction solution in the step (3).

8. The method according to claim 7, wherein the organic or inorganic base is selected from one or more of triethanolamine, methylamine, ethylamine, ethylenediamine, propylamine, isopropylamine, aniline, cyclohexylamine, o-aminophenol, 2-chlorophenol, potassium carbonate, sodium bicarbonate, potassium hydroxide, and sodium hydroxide.

9. The preparation method according to claim 1, wherein the hydrothermal reaction in the step (3) is carried out at a temperature of 120 to 160 ℃ for 12 to 18 hours.

10. The preparation method according to claim 1, wherein the microwave reaction in the step (4) has a power of 600-1000W and a time of 10-30 min.

11. The preparation method according to claim 1, characterized in that the graphene oxide is chosen in particular from graphene oxides having the following properties: the area of the sheet layer is 100 mu m²The conductivity is 3500S/m or more.

12. The preparation method according to claim 11, wherein the graphene oxide is obtained by oxidizing graphite.

13. The preparation method according to claim 12, wherein the graphene oxide is synthesized by a Hummers method, and the preparation method comprises the following steps: adding natural crystalline flake graphite into ice-bath concentrated sulfuric acid under stirring, cooling to 0-10 ℃, adding sodium nitrate and potassium permanganate, stirring for reaction, adding deionized water, heating to 50-100 ℃, reacting at constant temperature until the reaction solution turns to bright yellow, adding hydrogen peroxide, stirring for reaction, cooling, washing, and drying to obtain graphene oxide.

14. The nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material prepared by the method of any one of claims 1 to 13.

15. The use of the nitrogen-doped molybdenum disulfide/three-dimensional graphene composite material of claim 14 as a negative electrode material for a lithium ion battery.