CN112786870B

CN112786870B - Polypyrrole coated MoS2/C composite material and preparation method thereof

Info

Publication number: CN112786870B
Application number: CN202110184091.9A
Authority: CN
Inventors: 黄清; 高忠贵; 孔文婕; 刘富池
Original assignee: Guangxi Normal University
Current assignee: Guangxi Normal University
Priority date: 2021-02-10
Filing date: 2021-02-10
Publication date: 2022-05-13
Anticipated expiration: 2041-02-10
Also published as: CN112786870A

Abstract

The invention discloses polypyrrole-coated MoS₂a/C composite material and a preparation method thereof. The preparation method of the composite material comprises the following steps: 1) dissolving sodium molybdate dihydrate and thiourea in ethanol, adding polyvinylpyrrolidone, stirring, placing in a high-pressure kettle, and reacting at 150 deg.C or higher to obtain the final product₂C assembled hollow nanospheres; 2) get from MoS₂And C, uniformly mixing the hollow nanospheres assembled by the/C and an oxidant, taking the obtained mixture as a raw material, taking pyrrole as a coating source, taking a high-pressure kettle as a reaction chamber, and carrying out heat preservation reaction under the condition that the mixture and the pyrrole are not in contact with each other under the heating condition or the non-heating condition to obtain the composite material. The composite material is in a hollow spherical shape and has excellent Li⁺Storage performance and reversible capacity, and the preparation method is simpler and more environment-friendly.

Description

Polypyrrole coated MoS2/C composite material and preparation method thereof

Technical Field

The invention relates to an anode material of a lithium ion battery, in particular to polypyrrole-coated MoS₂a/C composite material and a preparation method thereof.

Background

In recent years, molybdenum disulfide (MoS) has a layered structure₂) Have attracted a great deal of interest and attention because of their unique chemical and physical properties. MoS₂The lithium ion battery has high specific capacity as an electrode material, and is considered as an anode material with great development prospect for lithium batteries. MoS₂Has a larger interlayer spacing of 0.62nm, compared with conventional graphite (372mAh g)^-1) In contrast, MoS₂Can contain more lithium ions and has higher lithium storage capacity (669mAh g)^-1) However, it still has the disadvantages of poor conductivity, severe volume expansion, rapid cycle degradation, poor electrochemical performance, etc., which hinders MoS₂Further development in the field of energy storage.

Existing research has shown that electrochemical performance is improved on the nano-scale by designing attractive graded molybdenum disulfide composites and by further expanding MoS₂Interlayer spacing to improve intrinsic capacitance of layered materialThe amount is an effective way. Researchers have designed and prepared carbon-coated MoS with yolk shell structure by hydrothermal method and etching process₂Hollow nanosphere and yolk shell type MoS₂the/C nanosphere has the advantages of high capacity and clear cavity space, and allows MoS₂Free expansion without damaging the outer layer and good performance retention (830mA h g)^-1at 5Ag^-1)(Guo,B.,Feng,Y.,Chen,X.,Li,B.&Yu,K. Preparation of yolk-shell MoS₂Applied Surface Science 434, 1021. 1029, doi:10.1016/j. apsusc.2017.11.018(2018). However, in the document, the solid molybdenum disulfide nanospheres are prepared by a hydrothermal method, then the solid molybdenum disulfide nanospheres are converted into hollow structures by a weak alkaline etching method, and then the yolk shell-shaped MoS coated with carbon is obtained by a hydrothermal process₂and/C, the process is complex and not environment-friendly after twice hydrothermal methods.

At present, no polypyrrole coated MoS with a hollow spherical structure is seen₂the/C composite material and the preparation method thereof are related reports.

Disclosure of Invention

The technical problem to be solved by the invention is to provide Li with a hollow spherical structure and excellent performance⁺Polypyrrole coated MoS for storage performance and reversible capacity₂The preparation method is simpler in process and environment-friendly.

In order to solve the technical problems, the invention adopts the following technical scheme:

polypyrrole coated MoS₂The preparation method of the/C composite material comprises the following steps:

1) preparation of MoS₂C assembled hollow nanospheres: taking sodium molybdate dihydrate (Na)₂MoO₄·2H₂O) and thiourea (CH)₄N₂S) dissolving in ethanol, adding polyvinylpyrrolidone (PVP), stirring, placing in a high-pressure autoclave, and reacting at 150 deg.C or higher to obtain MoS₂C assembled hollow nanospheres;

2) preparation of polypyrrole coated MoS₂the/C composite material: get by MoS₂Uniformly mixing the hollow nanospheres assembled by the/C and an oxidant, taking the obtained mixture as a raw material, taking pyrrole as a coating source, taking a high-pressure kettle as a reaction chamber, and carrying out heat preservation reaction under the condition that the mixture and the pyrrole are not in contact with each other under the heating condition or the non-heating condition to obtain the polypyrrole coated MoS₂a/C composite material.

The polypyrrole coated MoS of the invention₂the/C composite material is a hollow spherical structure, and the core of the composite material is ultrathin MoS containing mesoporous carbon₂Nano-flakes (MoS)₂/C) assembled hollow microspheres (i.e. MoS from step 1)₂C assembled hollow nanosphere), the surface of the hollow microsphere is coated with a layer of conductive polypyrrole (PPy), and the hollow structure of the inner core is combined with the coating of the surface conductive polypyrrole to ensure that the obtained composite material has excellent Li⁺Storage performance and reversible capacity. Applicants have found in experiments that hollow nanospheres can be prepared only when polyvinylpyrrolidone is used as the surfactant, and that MoS cannot be obtained when polyvinylpyrrolidone is replaced with other conventional surfactants such as oxalic acid or cetyltrimethylammonium bromide₂C assembled hollow nanospheres.

The autoclave involved in the invention is a conventional reaction kettle which can realize high-temperature and high-pressure reaction in the prior art and is provided with a lining (usually a polytetrafluoroethylene lining), such as a hydrothermal reaction kettle, a high-pressure digestion tank and the like. In carrying out the reaction, the starting materials are generally placed in the inner lining of an autoclave for the reaction.

In the step 1) of the preparation method, the average molecular weight of the polyvinylpyrrolidone is preferably 8000-24000, and the addition amount of the polyvinylpyrrolidone is usually more than 10% by mass of sodium molybdate dihydrate, preferably more than 20% by mass of sodium molybdate dihydrate, and more preferably 40-50% by mass of sodium molybdate dihydrate.

In the step 1) of the preparation method, the mass ratio of the sodium molybdate dihydrate to the thiourea is 1: 1-1: 1.5, preferably 4: 3. the amount of ethanol used is preferably such that the raw materials to be reacted can be dissolved. Specifically, the total amount of ethanol used in all raw materials is generally 10-30 ml calculated by taking 0.1g of sodium molybdate dihydrate as a reference. After the polyvinylpyrrolidone is added, the stirring time is preferably greater than or equal to 10 hours, and preferably 12-24 hours.

In the step 1) of the preparation method, the reaction is preferably carried out at 200-230 ℃. When the reaction is carried out at 200-230 ℃, the reaction time is usually greater than or equal to 10 hours, preferably 15-50 hours. After the reaction is finished and the reaction is cooled, the nano microspheres in the high-pressure kettle are MoS₂The hollow nanospheres assembled by the method/C need to be washed conventionally (usually, ethanol and deionized water are used for alternately washing for multiple times), dried (usually, dried to constant weight under the condition of 50-70 ℃) and annealed (specifically, the process is to anneal for 1-3 hours under the condition of 700-900 ℃) in argon after being collected.

In step 2) of the preparation method, the oxidant is ferric chloride and/or ammonium persulfate. The oxidizing agent is generally added in an amount of MoS₂The mass of the/C-assembled hollow nanospheres is more than 5%, and MoS is preferred₂The mass of the/C hollow nanospheres is 8-15%.

In step 2) of the above preparation method, the amount of the pyrrole added is determined as required, preferably, 1g of MoS₂The hollow nanospheres assembled by the/C are taken as a reference, and the adding amount of the pyrrole is calculated according to 40-150 mu L. The added pyrrole gradually vaporizes in the subsequent reaction process and drifts to MoS₂PPy polymerization is carried out on the surface of the/C hollow nanosphere, and finally the polymerization is carried out on the surface of the hollow nanosphere₂The surface of the hollow nanosphere assembled by the method is coated with a layer of conductive polypyrrole.

In step 2) of the above production method, the reaction is preferably performed at 20 ℃ or higher, more preferably at a heating temperature, and still more preferably at 40 to 60 ℃. When the reaction is carried out at 40-60 ℃, the reaction time is usually greater than or equal to 3 hours, and preferably 5-15 hours.

In step 2) of the above preparation method, the existing conventional method can be adopted to realize MoS₂Mixture of/C hollow nanospheres and oxidant with pyrrole monomers in polytetrafluoroethylene under high pressureThe liners are not contacted with each other, in the application, a polytetrafluoroethylene liner matched with the high-pressure autoclave is provided with an overhead layer, the mixture is placed on the overhead layer, and the pyrrole monomer is placed at the bottom of the liner, so that the mixture and the pyrrole monomer are not contacted with each other. When the inner lining matched with the high-pressure kettle has no overhead layer, a device for placing MoS can be placed in the inner lining₂Support of mixture of/C hollow nanospheres and oxidizing agent MoS₂The mixture of the/C hollow nanospheres and the oxidant is placed on the support frame, and then the pyrrole monomer is placed at the bottom of the lining, so that the mixture and the pyrrole monomer are not contacted with each other.

The invention also discloses polypyrrole coated MoS with a hollow spherical structure prepared by the method₂a/C composite material.

Compared with the prior art, the invention is characterized in that:

1. obtained by MoS under a specific process by using a specific surfactant₂the/C assembled hollow nanospheres can form a regular hollow structure without template materials and etching processes, and the process is simpler and the cost is lower. On the other hand, the MoS₂Hollow structures of the/C assembly, unlike carbon coatings, form MoS₂-C-MoS₂A sandwich structure, wherein a cross-linked carbonaceous network is formed between each molybdenum disulfide nano-flake, so that the ultra-thin mesoporous carbon layer is in MoS₂The nano thin sheet framework is more uniformly distributed, and the structure not only effectively improves electrons and lithium ions in MoS₂Permeability in/C microspheres and good improvement of MoS₂The pulverization and aggregation of the nano-sheets during the lithium intercalation and lithium deintercalation process.

2. In MoS₂Polypyrrole is coated on MoS on the basis of/C hollow nanospheres₂PPy @ MoS formed on surface of hollow structure of/C₂The special structure obviously improves the stability and the conductivity of the material, so that the obtained composite material has excellent Li when being used as the anode material of the lithium ion battery⁺Storage Properties and reversible Capacity (resulting polypyrrole coated MoS₂The discharge capacity and charge capacity of the first cycle of the/C composite material are 1265 and 884mAh g^-1(ii) a After 200 cycles, polypyrrole coats MoS₂the/C composite material is 0.5Ag^-1At a high current density of 1063mAh g^-1Good reversible capacity).

3. The embedded molybdenum disulfide hollow sphere (MoS) can be obtained by only one step of hydrothermal process without adopting an etching process₂and/C), the process is simpler and more environment-friendly.

Drawings

FIG. 1 is a MoS prepared according to example 1 of the present invention₂SEM image of/C assembled hollow nanosphere, wherein FIG. 1(a) is MoS₂SEM image of 10 μm of/C assembled hollow nanosphere, FIG. 1(b) is an enlarged view at box in FIG. 1(a), FIG. 1(C) is a graph showing MoS₂and/C is an SEM image of a hollow structure.

FIG. 2 shows a polypyrrole coated MoS prepared in example 1 of the present invention₂SEM image of/C composite material.

FIG. 3 shows a polypyrrole coated MoS prepared in example 1 of the present invention₂TEM image of the/C composite.

FIG. 4 shows pure MoS prepared as a comparison in example 1 according to the invention₂SEM image of (d).

FIG. 5 is a MoS prepared according to example 1 of the present invention₂/C assembled hollow nanosphere and polypyrrole coated MoS₂Composite material/C and pure MoS prepared as a comparison₂The raman spectrum of (a).

FIG. 6 is a MoS prepared according to example 1 of the present invention₂/C assembled hollow nanosphere and polypyrrole coated MoS₂Composite material/C and pure MoS prepared as a comparison₂The battery assembled as an active material is 0.5Ag^-1Lithium battery performance plots of 200 cycles at current density.

FIG. 7 is a MoS prepared in example 1 of the present invention₂/C assembled hollow nanosphere and polypyrrole coated MoS₂Composite material/C and pure MoS prepared as a comparison₂Rate cycle plot for cells assembled as active materials.

FIG. 8 is a MoS prepared in comparative example 1 of the present invention₂SEM image of/C.

FIG. 9 is a comparison of the present inventionMoS prepared in example 2₂SEM image of/C.

Detailed Description

In order to better explain the technical solution of the present invention, the following describes the present invention in further detail with reference to the examples and the accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, technical features used in the embodiments may be replaced with other technical features known in the art having equivalent or similar functions or effects without departing from the inventive concept.

Example 1

1) Preparation of MoS₂C assembled hollow nanospheres: 0.24g of sodium molybdate dihydrate and 0.18g of thiourea are weighed and dissolved in 40mL of ethanol, 0.1g of polyvinylpyrrolidone (average molecular weight is 8000) is added, the mixture is stirred for 12h (the system is milky white suspension), then the mixture is transferred to a 100 mL polytetrafluoroethylene lining, the lining is sealed and then placed in an autoclave, and the reaction is maintained for 42h by heating to 230 ℃. After the autoclave is cooled, collecting the hollow nanospheres, alternately washing the nanospheres for 5 times by using ethanol and deionized water, then putting the nanospheres into a vacuum drying oven, drying the nanospheres for 12 hours at 70 ℃, and annealing the nanospheres for 2 hours at 800 ℃ in argon to obtain the product of MoS₂C assembled hollow nanospheres. The obtained MoS is characterized by adopting a scanning electron microscope₂The surface topography of the/C assembled hollow nanospheres is shown in FIG. 1. Wherein, as shown in FIGS. 1(a) and 1(b), the MoS was prepared₂the/C hollow nanospheres are of uniform size, have an average diameter of about 800nm and a wall thickness of about 52-92 nm, and the outer surface of the nanospheres is composed of a plurality of curled graded nanosheets having a thickness of about 21-29 nm. FIG. 1(c) clearly shows the MoS₂Hollow structure of/C assembled hollow nanosphere.

For comparison, pure molybdenum disulfide (also referred to as pure MoS) was prepared in the same manner as in example 1 except that polyvinylpyrrolidone was not added₂)。

The pure MoS obtained₂Is shown in fig. 4. As can be seen from fig. 4, the sample prepared without polyvinylpyrrolidone addition had no hollow structure and exhibited a large irregular shape.

2) Preparation of polypyrrole coated MoS₂the/C composite material: getFrom MoS₂Neutralization of FeCl equivalent to 10% of its mass by C-assembled hollow nanospheres₃Fully grinding in a glove box filled with argon, placing the obtained mixed mixture on an overhead layer of a polytetrafluoroethylene lining, adding 5 mu L of pyrrole monomer at the bottom of the polytetrafluoroethylene lining, sealing the lining, placing the sealed lining in a high-pressure kettle, heating to 40 ℃, preserving heat and reacting for 10 hours to ensure that liquid pyrrole gradually vaporizes and drifts to MoS₂PPy polymerization is carried out on the surface of/C, and the obtained material is washed for 5 times by using deionized water and ethanol alternately to remove residual FeCl₃Then putting the mixture into a vacuum drying oven to dry for 12 hours at 70 ℃ to obtain polypyrrole coated MoS₂/C composite materials (also known as PPy @ MoS)₂/C hollow nanospheres). FIG. 2 shows the resulting PPy @ MoS₂The core-shell structure of the/C nanosphere can be seen from figure 2 that the PPy nanolayer is uniformly covered on the MoS₂The surface of the/C nano sheet. FIG. 3 shows the resulting PPy @ MoS₂Transmission Electron Microscope (TEM) image of/C hollow nanospheres, MoS is shown in FIG. 3₂the/C surface is obviously coated with a thin polypyrrole (PPy) layer and presents a hollow structure.

MoS prepared for this example₂/C assembled hollow nanosphere and polypyrrole coated MoS₂composite/C material and pure MoS prepared as a comparison₂The Raman spectrum of (A) was tested, as shown in FIG. 5, in which the MoS₂The symbol of/C is represented by MoS₂Hollow nanosphere/C assembly, PPy @ MoS₂[ C ] polypyrrole coated MoS₂Composite material of/C, Pure MoS₂Represents pure MoS₂. As can be seen from FIG. 5, pure MoS₂Are located at 379 and 404cm, respectively^-1E corresponding to hexagonal phase molybdenum disulfide_2gAnd A_1gA vibration mode. E_2gThe mode involves intra-layer displacement of Mo and S atoms, while A_1gThe mode involves an out-of-layer symmetric displacement of the S atoms along the C axis. For the product formed by MoS₂/C assembled hollow nanosphere and polypyrrole coated MoS₂the/C composite material is pure MoS₂In addition to the typical peaks observed, two peaks associated with the carbon material were observed, at 1370cm and 1600cm, respectively^-1To (3). MoS₂Broad peaks of D and G of/C from MoS₂The nano-flakes contain mesoporous carbonIt was caused, and it was clearly observed, that the introduction of PPy resulted in a significant enhancement of the D/G peak intensity, since the aromatic backbone of PPy was able to enhance raman activity.

MoS prepared in this example₂/C assembled hollow nanosphere and polypyrrole coated MoS₂composite/C material and pure MoS prepared as a comparison₂As active materials, respectively, they were mixed with carbon black (carbon black) and polyvinylidene (polyvinylidene) in a weight ratio of 7:2:1 in N-methyl-2-pyrrolidone (nmp), respectively, and then the slurry was spread uniformly on a copper foil. After drying at 100 ℃ in vacuum for 24h, electrode disks with a diameter of 12mm were cut. The loading capacity of the active substance on the electrode slice is 1.06-1.7 mg cm^-2. Electrochemical testing used button cells (CR2032) assembled in a glove box filled with Ar, lithium metal as the counter electrode, Celgard 2300 membrane as the separator, and 1M LiPF₆A mixed solvent (volume ratio is 1:1:1) dissolved in ethyl ester, diethyl carbonate and dimethyl carbonate (EC-DEC-DMC) is taken as electrolyte. Records that the voltage is 0.01-3V and Li/Li on a Land battery measuring system⁺The cycle performance and the rate performance at the off-voltage of (1) are shown in FIGS. 6 and 7, respectively, and in FIGS. 6 and 7, MoS₂The symbol of/C is represented by MoS₂Hollow nanosphere/C assembly, PPy @ MoS₂[ C ] polypyrrole coated MoS₂Composite material of/C, Pure MoS₂Represents pure MoS₂。

As shown in FIG. 6, at 0.5Ag^-1Pure MoS at Current Density of₂In the first cycle of (2) the discharge capacity and the charge capacity are 599 and 515mAh g, respectively^-1From MoS₂the/C assembled hollow nanospheres are 888 mAh g and 743mAh g respectively^-1All are lower than polypyrrole coated MoS₂Discharge and charge capacity in the first cycle of the/C composite (1265 and 884mAh g, respectively^-1). After 200 cycles, polypyrrole coats MoS₂the/C composite material is 0.5Ag^-1At a high current density of 1063mAh g^-1Good reversible capacity.

As shown in FIG. 7, polypyrrole coated MoS₂the/C composite material has excellent rate capability compared with the other two electrodes0.1, 0.2, 0.5, 1 and 2Ag at different current densities^-1Polypyrrole coated MoS₂The discharge capacity of the/C composite material is 1027, 995, 910, 823 and 767mAh g respectively^-1. When the current density is recovered to 0.1Ag^-1In time, through 60 cycles, 1218mAh g can be reached^-1The reversible capacity of (a).

Comparative example 1

Step 1) of example 1 was repeated, except that ethylene glycol methyl ether was used instead of ethanol. As a result, fibrous MoS was obtained₂(iv) MoS, SEM image of/C shown in FIG. 8₂The diameter of the/C fiber is about 400 nm.

Comparative example 2

Step 1) of example 1 was repeated except that deionized water was used in place of ethanol. As a result, a MoS having a large size and an irregular shape was obtained₂The SEM image of the/C sample is shown in FIG. 9.

Comparative example 3

Step 1) of example 1 was repeated, except that oxalic acid was used instead of polyvinylpyrrolidone.

The result was pure MoS₂The resulting sample was a solid structure, exhibiting a large irregular shape.

Comparative example 4

Step 1) of example 1 was repeated, except that cetyltrimethylammonium bromide was used instead of polyvinylpyrrolidone.

Example 2

Example 1 was repeated except that:

in the step 1), the dosage of ethanol is changed to 50mL, the dosage of polyvinylpyrrolidone is changed to 0.024g, and the reaction is changed to be carried out for 30h under the condition of 200 ℃;

in step 2), FeCl₃The dosage of the active ingredient is changed into MoS₂5% of the mass of the/C assembled hollow nanospheres.

The obtained composite material is characterized by a scanning electron microscope and a transmission electron microscope, and the polypyrrole coated MoS with a hollow spherical structure is determined₂a/C composite material.

Example 3

Example 1 was repeated except that:

in the step 1), polyvinylpyrrolidone with the average molecular weight of 10000 is used for replacing polyvinylpyrrolidone with the average molecular weight of 8000, and the reaction is carried out for 50 hours at the temperature of 150 ℃;

in step 2), FeCl₃The dosage of the active ingredient is changed into MoS₂The mass of the hollow nanospheres assembled by the/C is 15 percent, and the reaction is carried out for 5 hours under the condition of 60 ℃.

Example 4

Example 1 was repeated except that:

in the step 1), polyvinylpyrrolidone with the average molecular weight of 24000 is used for replacing polyvinylpyrrolidone with the average molecular weight of 8000, the adding amount of the polyvinylpyrrolidone is changed to 0.12g, and the stirring time is changed to 2h after the polyvinylpyrrolidone is added;

in step 2), FeCl is replaced by ammonium persulfate₃The dosage of the ammonium persulfate is changed into MoS₂The mass of the hollow nanospheres assembled by the/C is 15 percent, and the reaction is carried out for 12 hours under the condition of 25 ℃.

Claims

1. Polypyrrole coated MoS₂The preparation method of the/C composite material comprises the following steps:

1) preparation of MoS₂C assembled hollow nanospheres: dissolving sodium molybdate dihydrate and thiourea in ethanol, adding polyvinylpyrrolidone, stirring, placing in a high-pressure kettle, reacting at 150 deg.C or higher, washing, drying, and annealing to obtain MoS₂C assembled hollow nanospheres; wherein, theThe addition amount of the polyvinylpyrrolidone is more than 10% of the mass of the sodium molybdate dihydrate, and the annealing is carried out for 1-3 h in argon at the temperature of 700-900 ℃;

2) preparation of polypyrrole coated MoS₂the/C composite material: get by MoS₂The hollow nanospheres assembled by the method are uniformly mixed with an oxidant, the mixture is used as a raw material, pyrrole is used as a coating source, an autoclave is used as a reaction chamber, and the mixture and the pyrrole are reacted under a heating condition without contacting each other to obtain polypyrrole coated MoS₂a/C composite material; wherein, the oxidant is ferric chloride and/or ammonium persulfate.

2. The preparation method according to claim 1, wherein in the step 1), the polyvinylpyrrolidone is added in an amount of 40 to 50% by mass of the sodium molybdate dihydrate.

3. The preparation method according to claim 1, wherein in the step 1), the mass ratio of the sodium molybdate dihydrate to the thiourea is 1: 1-1: 1.5.

4. the process according to claim 1, wherein the reaction time in the step 1) is 10 hours or more.

5. The method according to claim 1, wherein the oxidizing agent is added in step 2) in an amount of MoS₂The mass of the hollow nanospheres assembled by the/C is more than 5 percent.

6. The method according to claim 1, wherein the reaction is carried out at 40 to 60 ℃ in step 2).

7. Polypyrrole coated MoS prepared according to the method of any one of claims 1-6₂a/C composite material.