CN113113570B - Simple construction method of nano carbon shell loaded molybdenum-based heterojunction and application of simple construction method in lithium-sulfur battery - Google Patents
Simple construction method of nano carbon shell loaded molybdenum-based heterojunction and application of simple construction method in lithium-sulfur battery Download PDFInfo
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Abstract
A simple construction method of a molybdenum-based heterojunction loaded on a nano carbon shell and application of the molybdenum-based heterojunction in a lithium-sulfur battery belong to the field of lithium-sulfur batteries. And (3) treating the molybdenum disulfide/carbon shell material with low-concentration hydrogen peroxide under a mild condition to generate a molybdenum trioxide heterojunction on the surface of the molybdenum disulfide to obtain the molybdenum disulfide-molybdenum trioxide/carbon shell modified diaphragm. The reaction condition is mild, the preparation method is simple, the obtained product has obvious structural advantages, the two-dimensional heterostructure can accelerate the transmission of electrons and ions and provide a large number of catalytic sites, and the two-dimensional heterostructure has strong polarity and can improve the adsorption capacity of polysulfide so as to improve the electrochemical performance; in addition, the introduction of the highly conductive carbon shell into the synthesized material can further increase the electron transport of the synthesized material and accelerate the polysulfide conversion.
Description
Technical Field
The invention belongs to the field of electrochemistry, relates to a carbon shell loaded molybdenum-based heterojunction material modified lithium-sulfur battery diaphragm, and particularly relates to a carbon shell loaded molybdenum disulfide and molybdenum trioxide heterojunction material modified lithium-sulfur battery diaphragm, which achieves adsorption capture and catalytic conversion of polysulfide.
Background
In recent years, the growth in demand for mobile devices and electric automobiles has greatly pushed the development of advanced rechargeable batteries. Lithium-sulfur batteries (Li-S) are based on their high theoretical capacity (1672mAh g)-1) And low sulfur costs, have become one of the most promising candidate energy storage devices today. However, commercialization of lithium-sulfur batteries has been hindered by technical difficulties such as low utilization of sulfur, the "shuttling effect" of soluble polysulfides, irreversible cathode structure during cycling, and large volume expansion.
In the past decades, various strategies have been developed to address these challenges, such as the use of porous carbon materials, novel binders, electrolyte additives, and modified separators. Among these approaches, membrane modification is considered a promising strategy to limit the "shuttling effect" of soluble polysulfides. A great deal of work has been done on diaphragm modification. For example, carbon-based materials such as graphene, porous carbon, carbon nanotubes, etc. have been widely used to modify membranes to confine polysulfides by physical adsorption. However, the weak physical interaction between polysulfides and carbon materials is not sufficient to limit the shuttling of polysulfides. Another strategy is to use polar materials whose strong chemisorption capacity helps to capture polysulfides. For example, Chen et al found TiO2The modified membranes are effective for immobilizing polysulfides. However, the slow redox kinetics of the immobilized polysulfides may block the pores of the separator, thereby hindering the migration of lithium ions.
To address these challenges, the most effective approach is to incorporate a catalyst as a membrane modifier, which can provide active sites to promote the conversion of polysulfides. Some nitrides, carbides and sulfides are capable of catalyzing the conversion of polysulfides. Among them, two-dimensional molybdenum disulfide has attracted much attention because of its adjustable structure, good catalytic activity, high ionic conductivity, and low cost. Li et al prepared MoS2/C microsphere modified partition board for regulating and controlling Li2Deposition of S, wherein MoS2the/C is effective in accelerating the polysulfide conversion. Tang et al also established MoS on Celgard membranes2The thin layer, the improved membrane can be used as an effective barrier to inhibit polysulfide dissipation. Molybdenum disulfide, particularly two-dimensional molybdenum disulfide, exhibits marginal adsorption and catalysis, while the presence of a large number of inert sites on the basal plane greatly limits the number of adsorption and catalysis sites. Thus, MoS2Are still insufficient for capturing and converting polysulfides. Therefore, there is a pressing need for a more efficient strategy to modify MoS2。
Molybdenum-based oxide (MoO)x) It is a good polysulfide host due to its strong metal-oxygen bond polarity. Thus, MoS2-MoOxThe heterostructure can effectively improve the adsorption capacity. Further, MoOxAnd MoS2Crystal distortion near the interface may create more active sites, thereby increasing catalytic activity. For the reasons mentioned above, we have designed a simple MoS2-MoO3Carbon shell composite material (MoS)2-MoO3/CS) with H2O2Preparation of MoS by oxidation2-MoO3A/carbon shell composite material. Under mild conditions, the molybdenum disulfide can be diluted with H in a short time2O2And (4) partial oxidation. During oxidation, the S atoms may be replaced by excess oxygen atoms to form MoO due to the higher bonding affinity of Mo-O (as compared to Mo-S)3。MoS2And MoO3The synergistic effect in the heterostructure enhances the adsorption capacity and catalytic activity towards polysulfides.
The foregoing demonstrates that molybdenum-based catalysts have wide application in lithium sulfur batteries and give good electrochemical performance. However, the catalytic action of the molybdenum-based catalyst on polysulfide is not deeply studied, and if a novel molybdenum-based heterojunction which is adsorbed and catalyzed on polysulfide is synthesized, not only can good lithium-sulfur battery performance be obtained, but also the use of a noble metal catalyst can be greatly reduced, and the cost of the lithium-sulfur battery is reduced.
Disclosure of Invention
The invention designs an effective, simple and low-cost nano carbon shell loaded molybdenum-based heterojunction material modified lithium-sulfur battery diaphragm. The material adopts a nano carbon shell as a loaded MoS2The growth substrate of (1)The carbon nano-shell has larger specific surface area and good conductivity, and on the other hand, the carbon shell material can provide good electron and ion transmission channels. Sodium molybdate and thiourea are added to synthesize the two-dimensional molybdenum disulfide nanosheet capable of repeatedly etching the carbon shell morphology through a hydrothermal reaction, so that an active site is provided for polysulfide conversion. And then, carrying out low-concentration hydrogen peroxide treatment to generate a molybdenum trioxide heterostructure on the surface of the two-dimensional molybdenum disulfide. The synthesized material is used for modifying a PP diaphragm of a commercial lithium-sulfur battery, and molybdenum-based heterojunction contained in the synthesized material is used for adsorbing and catalyzing polysulfide compounds, so that the shuttle effect of the polysulfide compounds is greatly reduced; in addition, the existence of the carbon shell can increase electron and ion transmission channels and improve the conductivity of the synthesized material. The synthesized material is applied to the lithium-sulfur battery, so that the utilization rate of sulfur can be increased, the coulombic efficiency is improved, and the cycling stability of the battery is improved.
In order to achieve the design of the materials, the invention adopts the following technical scheme:
a simple construction method for a nano carbon shell loaded molybdenum-based heterojunction is characterized in that a small amount of template-free carbon shells are used as a substrate, sodium molybdate is used as a molybdenum source, thiourea is used as a sulfur source, and a two-dimensional molybdenum disulfide material grows on the surfaces of the carbon shells. And mildly treating the molybdenum disulfide/carbon shell at room temperature by using low-concentration hydrogen peroxide to generate molybdenum trioxide heterojunction active catalytic sites on the surface of two-dimensional molybdenum disulfide. The method specifically comprises the following steps:
(1) the nano carbon shell is prepared by a template-free method.
Firstly, sodium citrate is dried for 12-24h in an oven at the temperature of 140-. The product obtained is stirred in 2-4M HCl solution for 2-6h and then washed with a large amount of deionized water. Drying at 60-80 ℃ overnight to obtain the nano carbon shell product.
(2) The molybdenum disulfide/carbon shell material is prepared by a hydrothermal method.
Dispersing the nano carbon shell product obtained in the step (1) in deionized water for ultrasonic treatment for 2-4h, then adding sodium molybdate dihydrate and thiourea, and stirring for 0.5-1h to obtain a mixed solution, wherein 50-150mg of the nano carbon shell product is dispersed in 50-80mL of deionized water, 0.5-1.0g of the sodium molybdate dihydrate and 1-2g of thiourea are added.
And (3) placing the mixed solution into a 100mL high-pressure kettle, sealing and heating at 200 ℃ for 16-24h, washing the obtained solid product with deionized water, and drying in a vacuum oven at 60 ℃ for 6-12h to obtain the molybdenum disulfide/carbon shell material.
(3) The molybdenum disulfide-molybdenum trioxide/carbon shell material is synthesized by simple and mild low-concentration hydrogen peroxide oxidation treatment.
Adding a molybdenum disulfide/carbon shell into deionized water, and dripping diluted hydrogen peroxide solution into the molybdenum disulfide/carbon shell dispersion liquid, wherein 100mg of molybdenum disulfide/carbon shell and 20-40ml of diluted hydrogen peroxide are added into every 20-30ml of deionized water; and continuously stirring for 15-30 minutes, washing with deionized water, and vacuum drying at 60-80 ℃ overnight to obtain the molybdenum disulfide-molybdenum trioxide/carbon shell material.
Further, the concentration of the diluted hydrogen peroxide is 1 wt.% to 4.5 wt.%.
The application of the carbon nano-shell loaded molybdenum-based heterojunction material in the lithium-sulfur battery modifies the synthesized carbon shell loaded molybdenum-based heterojunction material into a PP diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nano-shell loaded molybdenum-based heterojunction material in the lithium-sulfur battery comprises the following specific steps:
first, a modified separator is prepared
And loading the molybdenum disulfide-molybdenum trioxide/carbon shell material on a Celgard 2325 polypropylene (PP) diaphragm by adopting a filtering method. 3-5mg molybdenum disulfide-molybdenum trioxide/carbon shell powder and 0.4-0.5mL PVDF/NMP (1.0mg mL)-1) Ultrasonic dispersing in 30-40ml ethylene glycol for 2-4 h. Filtering the dispersion liquid on a PP membrane, and then drying the dispersion liquid for 6 to 12 hours in vacuum at the temperature of between 60 and 80 ℃;
second, a positive electrode material is prepared
60-80 wt.% sublimed sulphur and 20-40 wt.% carbon shell and heated in an ampoule at 155 ℃ for 12-24 h. Mixing a carbon shell/sulfur mixture, carbon nanotubes and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in NMP, coating the obtained slurry on an aluminum foil, and drying at 60-80 ℃ for 6-12 h;
thirdly, assembling the lithium-sulfur battery
The prepared anode material, the modified diaphragm and the cathode lithium sheet are assembled into a battery in sequence, wherein the adding amount of the electrolyte is 40-60 mu L, and the sulfur carrying amount is 1.2mg/cm2-4.7mg/cm2。
The invention has the beneficial effects that:
(1) under mild conditions, by simple H2O2The oxidation process synthesizes novel MoS with heterostructure2-MoO3Carbon Shell (MoS)2-MoO3/CS) composite material.
(2)MoS2-MoO3The strong polarity of the heterostructure can improve the adsorption capacity of polysulfides, thereby improving electrochemical performance.
(3) The formed nano carbon shell is coupled with MoS2-MoO3The heterojunction has obvious structural advantages, the two-dimensional heterostructure can accelerate the transmission of electrons and ions, provide a large number of catalytic sites and improve the cycle and rate performance of the battery; in addition, the introduction of the highly conductive carbon shell into the synthesized material can further increase the electron transport of the synthesized material and accelerate the polysulfide conversion.
Drawings
FIG. 1 is a schematic diagram of the synthesis process and a schematic diagram of barrier to polysulfide diffusion in example 1;
FIG. 2 is a scanning electron micrograph and a heterojunction transmission electron micrograph of a part of a material prepared in example 1; in which, fig. 2(a) is a scanning electron microscope image, and fig. 2(b) is a high-resolution transmission electron microscope image.
FIG. 3 is a graph of the high sulfur cycle performance of the material prepared in example 1;
FIG. 4 is a graph showing the long cycle performance of the sulfur loading of 1.2mg/cm2 for the material prepared in example 1;
FIG. 5 is a graph of the result of DFT binding energy simulation calculation of the material prepared in example 1; fig. 5(a) is a graph showing the binding energy between molybdenum disulfide and polysulfide, and fig. 5(b) is a graph showing the binding energy between molybdenum trioxide and polysulfide.
Detailed Description
The preparation method and performance of the nanocarbon shell supported molybdenum-based heterojunction according to the present invention will be described in further detail with reference to the following examples, which are not intended to limit the present invention in any way.
Reference case
(1) The carbon shell is prepared by a template-free method. In a typical preparation, 5g of sodium citrate was dried in an oven at 155 ℃ for 24h, ball milled for 12h, and then the powder sample was transferred to a quartz boat and annealed at 800 ℃ under argon atmosphere for 1h with a ramp rate of 5 ℃/min. The resulting product was stirred in 3M HCl solution for 4h and washed with copious amounts of deionized water. Drying at 60 ℃ overnight to obtain a carbon shell product;
(2) the molybdenum disulfide/carbon shell material is prepared by a hydrothermal method. In a detailed synthesis procedure, 100mg of carbon shell was dispersed in 70mL of deionized water and sonicated for 2h, followed by the addition of 0.5g of sodium molybdate dihydrate and 1g of thiourea and stirred for 0.5 h. The solution was placed in a 100mL autoclave and heated hermetically at 200 ℃ for 24 h. Washing the prepared solid product with deionized water, and drying in a vacuum oven at 60 ℃ for 12h to obtain a molybdenum disulfide/carbon shell material;
(3) application to lithium-sulfur battery
First, a modified separator is prepared
The molybdenum disulfide/carbon shell material was supported on a Celgard 2325 polypropylene (PP) membrane using a filtration process. 4.05mg of molybdenum disulfide/carbon shell powder and 0.45mL of PVDF/NMP (1.0mg mL)-1) Ultrasonic dispersion treatment is carried out for 2h in 30ml of ethylene glycol. Filtering the dispersion on a PP membrane, and then drying the dispersion for 6 hours in vacuum at the temperature of 60 ℃;
second, a positive electrode material is prepared
75 wt.% sublimed sulphur and 25 wt.% carbon shell were mixed and heated in an ampoule at 155 ℃ for 12 h. Mixing a carbon shell/sulfur mixture, carbon nanotubes and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in NMP, coating the obtained slurry on an aluminum foil, and drying at 60 ℃ for 6 h;
thirdly, assembling the lithium-sulfur battery
The prepared positive electrode material, the modified diaphragm and the negative electrode lithium sheet are assembled into a battery in sequence, wherein the adding amount of electrolyte is 50 mu L, and the sulfur carrying amount is 1.2mg/cm2。
Example 1
(1) The nano carbon shell is prepared by a template-free method.
Drying sodium citrate in a 140 ℃ oven for 12h, ball-milling for 6h, then transferring the powder sample into a quartz boat, annealing for 1h under the argon atmosphere at 700 ℃, and raising the temperature at the rate of 5 ℃/min. The resulting product was stirred in 2M HCl solution for 2h and washed with copious amounts of deionized water. Drying at 60 ℃ overnight to obtain a nano carbon shell product;
(2) the molybdenum disulfide/carbon shell material is prepared by a hydrothermal method.
50mg of carbon shell was dispersed in 50mL of deionized water and sonicated for 2h, then 0.5g of sodium molybdate dihydrate and 1g of thiourea were added and stirred for 0.5 h. The solution was placed in a 100mL autoclave and heated hermetically at 200 ℃ for 16 h. Washing the prepared solid product with deionized water, and drying in a vacuum oven at 60 ℃ for 6h to obtain a molybdenum disulfide/carbon shell material;
(3) the molybdenum disulfide-molybdenum trioxide/carbon shell material is synthesized by simple and mild low-concentration hydrogen peroxide oxidation treatment.
Adding 100mg of molybdenum disulfide/carbon shell into 20ml of deionized water, dripping 20ml of diluted hydrogen peroxide (1 wt.%) solution into the molybdenum disulfide/carbon shell dispersion liquid, continuously stirring for 15 minutes, washing with deionized water, and vacuum drying at 60 ℃ overnight to obtain the molybdenum disulfide-molybdenum trioxide/carbon shell material.
The application of the carbon nano-shell loaded molybdenum-based heterojunction material in the lithium-sulfur battery modifies the synthesized carbon shell loaded molybdenum-based heterojunction material into a PP diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nano-shell loaded molybdenum-based heterojunction material in the lithium-sulfur battery comprises the following specific steps:
first, a modified separator is prepared
And loading the molybdenum disulfide-molybdenum trioxide/carbon shell material on a Celgard 2325 polypropylene (PP) diaphragm by adopting a filtering method. 3mg of molybdenum disulfide-molybdenum trioxide/carbon shell powder and 0.4mL of PVDF/NMP (1.0mg mL)-1) Ultrasonic dispersion treatment is carried out for 2h in 30ml of ethylene glycol. Filtering the dispersion on a PP membrane, and then drying the dispersion for 6 hours in vacuum at the temperature of 60 ℃;
second, a positive electrode material is prepared
60 wt.% sublimed sulphur and 40 wt.% carbon shell were mixed and heated in an ampoule at 155 ℃ for 12 h. Mixing a carbon shell/sulfur mixture, carbon nanotubes and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in NMP, coating the obtained slurry on an aluminum foil, and drying at 60 ℃ for 6 h;
thirdly, assembling the lithium-sulfur battery
The prepared anode material, the modified diaphragm and the cathode lithium sheet are assembled into a battery in sequence, wherein the adding amount of the electrolyte is 40 mu L, and the sulfur carrying amount is 1.2mg/cm2。
Example 2
(1) The nano carbon shell is prepared by a template-free method.
Drying sodium citrate in an oven at 160 ℃ for 24h, performing ball milling for 12h, transferring a powder sample into a quartz boat, and annealing at 900 ℃ for 3h under an argon atmosphere, wherein the heating rate is 5 ℃/min. The resulting product was stirred in 4M HCl solution for 6h and washed with copious amounts of deionized water. Drying at 80 ℃ overnight to obtain a nano carbon shell product;
(2) the molybdenum disulfide/carbon shell material is prepared by a hydrothermal method.
150mg of carbon shell was dispersed in 80mL of deionized water and sonicated for 4h, then 1.0g of sodium molybdate dihydrate and 2g of thiourea were added and stirred for 1 h. The solution was placed in a 100mL autoclave and heated hermetically at 200 ℃ for 24 h. Washing the prepared solid product with deionized water, and drying in a vacuum oven at 60 ℃ for 12h to obtain a molybdenum disulfide/carbon shell material;
(3) the molybdenum disulfide-molybdenum trioxide/carbon shell material is synthesized by simple and mild low-concentration hydrogen peroxide oxidation treatment.
Adding 200mg of molybdenum disulfide/carbon shell into 30ml of deionized water, dripping 40ml of diluted hydrogen peroxide (4.5 wt.%) solution into the molybdenum disulfide/carbon shell dispersion liquid, continuing stirring for 30 minutes, washing with the deionized water, and carrying out vacuum drying at 80 ℃ overnight to obtain the molybdenum disulfide-molybdenum trioxide/carbon shell material.
The application of the carbon nano-shell loaded molybdenum-based heterojunction material in the lithium-sulfur battery modifies the synthesized carbon shell loaded molybdenum-based heterojunction material into a PP diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nano-shell loaded molybdenum-based heterojunction material in the lithium-sulfur battery comprises the following specific steps:
first, a modified separator is prepared
And loading the molybdenum disulfide-molybdenum trioxide/carbon shell material on a Celgard 2325 polypropylene (PP) diaphragm by adopting a filtering method. Adding 5mg of molybdenum disulfide-molybdenum trioxide/carbon shell powderEnd and 0.5mL PVDF/NMP (1.0mg mL)-1) Ultrasonic dispersion treatment is carried out for 4 hours in 40ml of ethylene glycol. Filtering the dispersion on a PP membrane, and then drying the dispersion for 12 hours in vacuum at 80 ℃;
second, a positive electrode material is prepared
80 wt.% sublimed sulphur and 20 wt.% carbon shell were mixed and heated in an ampoule at 155 ℃ for 24 h. Mixing a carbon shell/sulfur mixture, carbon nanotubes and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in NMP, coating the obtained slurry on an aluminum foil, and drying at 80 ℃ for 12 h;
thirdly, assembling the lithium-sulfur battery
The prepared positive electrode material, the modified diaphragm and the negative electrode lithium sheet are assembled into a battery in sequence, wherein the adding amount of electrolyte is 60 mu L, and the sulfur carrying amount is 4.7mg/cm2。
Embodiment 3
(1) The nano carbon shell is prepared by a template-free method.
Drying sodium citrate in an oven at 150 ℃ for 20h, ball-milling for 9h, transferring the powder sample into a quartz boat, annealing at 800 ℃ for 2h under argon atmosphere, and raising the temperature at the rate of 5 ℃/min. The resulting product was stirred in 3M HCl solution for 4h and washed with copious amounts of deionized water. Drying at 70 ℃ overnight to obtain a nano carbon shell product;
(2) the molybdenum disulfide/carbon shell material is prepared by a hydrothermal method.
100mg of carbon shell was dispersed in 65mL of deionized water and sonicated for 3h, then 0.75g of sodium molybdate dihydrate and 1.5g of thiourea were added and stirred for 0.75 h. The solution was placed in a 100mL autoclave and heated hermetically at 200 ℃ for 20 h. Washing the prepared solid product with deionized water, and drying in a vacuum oven at 70 ℃ for 9h to obtain a molybdenum disulfide/carbon shell material;
(3) the molybdenum disulfide-molybdenum trioxide/carbon shell material is synthesized by simple and mild low-concentration hydrogen peroxide oxidation treatment.
Adding 150mg of molybdenum disulfide/carbon shell into 25ml of deionized water, dripping 30ml of diluted hydrogen peroxide (2.25 wt.%) solution into the molybdenum disulfide/carbon shell dispersion liquid, continuing stirring for 25 minutes, washing with deionized water, and performing vacuum drying at 70 ℃ overnight to obtain the molybdenum disulfide-molybdenum trioxide/carbon shell material.
The application of the carbon nano-shell loaded molybdenum-based heterojunction material in the lithium-sulfur battery modifies the synthesized carbon shell loaded molybdenum-based heterojunction material into a PP diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nano-shell loaded molybdenum-based heterojunction material in the lithium-sulfur battery comprises the following specific steps:
first, a modified separator is prepared
And loading the molybdenum disulfide-molybdenum trioxide/carbon shell material on a Celgard 2325 polypropylene (PP) diaphragm by adopting a filtering method. 4mg of molybdenum disulfide-molybdenum trioxide/carbon shell powder and 0.45mL of PVDF/NMP (1.0mg mL)-1) Ultrasonic dispersion treatment is carried out for 3 hours in 35ml of ethylene glycol. Filtering the dispersion on a PP membrane, and then drying the dispersion for 9 hours in vacuum at 70 ℃;
second, a positive electrode material is prepared
70 wt.% sublimed sulphur and 30 wt.% carbon shell were mixed and heated in an ampoule at 155 ℃ for 18 h. Mixing a carbon shell/sulfur mixture, carbon nanotubes and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in NMP, coating the obtained slurry on an aluminum foil, and drying at 70 ℃ for 9 h;
thirdly, assembling the lithium-sulfur battery
The prepared positive electrode material, the modified diaphragm and the negative electrode lithium sheet are assembled into a battery in sequence, wherein the adding amount of electrolyte is 50 mu L, and the sulfur carrying amount is 3.2mg/cm2。
The invention comprises the following steps: 1) under mild conditions, a novel molybdenum disulfide-molybdenum trioxide/carbon shell composite material with a heterostructure is synthesized by a simple hydrogen peroxide oxidation process; 2) the strong polarity of the molybdenum disulfide-molybdenum trioxide heterostructure can improve the adsorption capacity of polysulfide, thereby improving the electrochemical performance. 3) The prepared nano carbon shell coupled molybdenum disulfide-molybdenum trioxide heterojunction has obvious structural advantages, the two-dimensional heterostructure can accelerate the transmission of electrons and ions, provide a large number of catalytic sites and improve the cycle and rate performance of the battery; in addition, the introduction of the highly conductive carbon shell into the synthesized material can further increase the electron transport of the synthesized material and accelerate the polysulfide conversion.
The above-mentioned embodiments only express the embodiments of the present invention, but not should be understood as the limitation of the scope of the invention patent, it should be noted that, for those skilled in the art, many variations and modifications can be made without departing from the concept of the present invention, and these all fall into the protection scope of the present invention.
Claims (5)
1. A simple construction method of a molybdenum-based heterojunction loaded on a nano carbon shell is characterized in that a small amount of template-free carbon shells are used as a substrate, sodium molybdate is used as a molybdenum source, thiourea is used as a sulfur source, and a two-dimensional molybdenum disulfide material grows on the surfaces of the carbon shells; mildly treating the molybdenum disulfide/carbon shell at room temperature by using low-concentration hydrogen peroxide, and generating molybdenum trioxide heterojunction active catalytic sites on the surface of two-dimensional molybdenum disulfide; the method comprises the following steps:
(1) preparing a nano carbon shell by a template-free method;
ball-milling the dried sodium citrate for 6-12h, transferring the powder sample into a quartz boat, and annealing for 1-3h under the argon atmosphere at the temperature of 700-; stirring the obtained product in HCl solution for 2-6h, washing with deionized water, and drying in a vacuum oven to obtain a nano carbon shell product;
(2) preparing a molybdenum disulfide/carbon shell material by a hydrothermal method;
dispersing the nano carbon shell product obtained in the step (1) in deionized water for ultrasonic treatment for 2-4h, then adding sodium molybdate dihydrate and thiourea, and stirring for 0.5-1h to obtain a mixed solution, wherein 50-150mg of the nano carbon shell product is dispersed in 50-80mL of deionized water, 0.5-1.0g of the sodium molybdate dihydrate and 1-2g of thiourea are added; placing the mixed solution in a high-pressure kettle, sealing and heating at 200 ℃ for 16-24h, washing the obtained solid product with deionized water, and drying in a vacuum oven to obtain a molybdenum disulfide/carbon shell material;
(3) synthesizing a molybdenum disulfide-molybdenum trioxide/carbon shell material through simple and mild low-concentration hydrogen peroxide oxidation treatment;
adding a molybdenum disulfide/carbon shell into deionized water, and dripping diluted hydrogen peroxide solution into the molybdenum disulfide/carbon shell dispersion liquid, wherein 100mg of molybdenum disulfide/carbon shell and 20-40ml of diluted hydrogen peroxide are added into every 20-30ml of deionized water; and continuously stirring for 15-30 minutes, washing with deionized water, and drying in a vacuum oven to obtain the molybdenum disulfide-molybdenum trioxide/carbon shell material.
2. The simple construction method of the nanocarbon shell supported molybdenum-based heterojunction as claimed in claim 1, wherein the drying temperature of the sodium citrate in the step (1) is 140-160 ℃, and the drying time is 12-24 h.
3. The simple construction method of the nanocarbon shell-supported molybdenum-based heterojunction as claimed in claim 1, wherein the concentration of the HCl solution in the step (1) is 2-4M.
4. The simple construction method of the molybdenum-based heterojunction loaded on the nano-carbon shell as claimed in claim 1, wherein the concentration of the diluted hydrogen peroxide in the step (3) is 1 wt.% to 4.5 wt.%.
5. The application of the nano carbon shell loaded molybdenum-based heterojunction obtained by the method of any one of claims 1 to 4 in the lithium-sulfur battery is characterized in that the synthesized carbon shell loaded molybdenum-based heterojunction material is used for modifying a PP diaphragm of a commercial lithium-sulfur battery and is applied to the lithium-sulfur battery, and the method specifically comprises the following steps:
first, a modified separator is prepared
Loading a molybdenum disulfide-molybdenum trioxide/carbon shell material on a polypropylene diaphragm by adopting a filtering method; performing ultrasonic dispersion treatment on molybdenum disulfide-molybdenum trioxide/carbon shell powder and PVDF/NMP in ethylene glycol for 2-4h to obtain a dispersion liquid, wherein 3-5mg of molybdenum disulfide-molybdenum trioxide/carbon shell powder and 0.4-0.5mL of PVDF/NMP are added into every 30-40mL of ethylene glycol; filtering the dispersion liquid on a PP membrane, and finally drying the dispersion liquid for 6 to 12 hours in vacuum at the temperature of between 60 and 80 ℃ to obtain a modified membrane;
second, a positive electrode material is prepared
Mixing sublimed sulfur and a carbon shell, and heating in an ampoule bottle at 155 ℃ for 12-24 hours to obtain a carbon shell/sulfur mixture; mixing a carbon shell/sulfur mixture, a carbon nano tube and polyvinylidene fluoride in NMP according to the mass ratio of 8:1:1, coating the obtained slurry on an aluminum foil, and drying at 60-80 ℃ for 6-12 h;
thirdly, assembling the lithium-sulfur battery
And sequentially assembling the prepared positive electrode material, the modified diaphragm and the negative electrode lithium sheet into a battery.
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