CN114149028A - Method for doping molybdenum disulfide with oxygen induced by ethylene glycol and application of method in lithium-sulfur battery - Google Patents
Method for doping molybdenum disulfide with oxygen induced by ethylene glycol and application of method in lithium-sulfur battery Download PDFInfo
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Abstract
The invention provides a method for inducing oxygen-doped molybdenum disulfide by using ethylene glycol and application of the method in a lithium-sulfur battery, belongs to the field of lithium-sulfur batteries, and particularly relates to a method for preparing oxygen-doped molybdenum disulfide/carbon nanosheets by using a green and mild ethylene glycol competitive reduction method to modify a diaphragm. The invention has the beneficial effects that: 1) preparing an oxygen-doped molybdenum disulfide/carbon nanosheet by adopting a green and mild glycol competitive reduction method; 2) oxygen atoms have strong polarity and proper electronic regulation capacity, and absorb polysulfide by forming Li-O bonds; 3) the dopant of oxygen atoms can also disturb the structure of the molybdenum disulfide, creating crystal distortion and an amorphous structure, thereby creating rich adsorption and catalytic sites. In addition, the high-conductivity carbon nanosheets are introduced into the synthesized material, so that the electron transmission of the synthesized material can be further increased, and the polysulfide conversion is accelerated.
Description
Technical Field
The invention belongs to the field of electrochemistry, relates to an oxygen-doped molybdenum disulfide material modified lithium-sulfur battery diaphragm, and particularly relates to a glycol-induced oxygen-doped molybdenum disulfide-loaded carbon nanosheet material modified lithium-sulfur battery diaphragm, which achieves adsorption capture and catalytic conversion of soluble polysulfide.
Background
Gradual exhaustion of traditional energy sources and aggravation of environmental pollution require clean and efficient electrochemical energy storage devices. Among energy storage devices, lithium sulfur (Li-S) batteries are high due to the high theoretical energy density (2600Wh kg)-1) And the low cost and environmental friendliness of sulfur are considered to be one of the most promising next-generation rechargeable batteries. However, the practical development of lithium sulfur batteries is still hampered by technical problems such as low coulombic efficiency and poor cycle life caused by shuttling of soluble polysulfides between two electrodes during charging and discharging.
To solve these problems, numerous strategies have been proposed, such as the design of sulfur composite positive electrodes, the exploration of new binders, the construction of interlayers and the functionalization of separators. One of the most effective techniques is to modify the separator to block the migration path of polysulfides without affecting lithium ion transport. Various carbon materials have been used to modify the separator to physically capture polysulfides, such as porous carbon, carbon nanotubes, and graphene. However, between non-polar carbon materials and polar polysulphidesWeak physical interactions limit the binding capacity. Another strategy is to use a polar material with catalytic capabilities as a separator modifier to chemically anchor polysulfides and accelerate the conversion kinetics of lithium sulfur cells. In recent years, MoS2It is attracting attention because of its polar properties, remarkable catalytic activity, environmental friendliness and low cost. For example, Tang et al will thin MoS2The layers are deposited on a conventional PP separator to obtain an improved separator. Polysulfide shuttling is effectively inhibited, with MoS2the/PP separator battery has excellent cycle stability. Nevertheless, MoS2In particular two-dimensional MoS2Exhibiting 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 catalytic sites. Therefore, MoS should be further activated2To improve the performance of the Li-S cell.
Heteroatom doping is one of the effective material modification methods for improving adsorption capacity and catalytic activity. Due to the fact that the atom radius and electronegativity of the introduced heteroatoms are different, the lattice distance and the electron density can be well adjusted, and therefore more active sites are generated and the electronic performance is improved. For example, Zhang et al found that nitrogen doping can significantly increase Co in lithium sulfur batteries9S8Polysulfide immobilization and redox catalytic activity of the nanoparticles. Nitrogen doped Co9S8The battery is at 0.2A g-1The following shows 1233mAh g-1High capacity and low capacity fade after 1000 cycles of 0.037% per turn. The phosphorus atom can also enhance the chemical adsorption capacity and the high catalytic activity Fe4N to exhibit significant initial capacity and long-term cycling stability. Thus, doping of heteroatoms to MoS2Can effectively activate the basal plane to improve the electrochemical performance. However, current methods for the preparation of heteroatom-doped molybdenum disulfide are primarily based on time-consuming and harsh post-treatments. In addition, the post-doping reaction is generally carried out from MoS2At the beginning of the surface, it is difficult to achieve a uniform distribution of heteroatoms, thereby impairing the enhancement of intrinsic properties.
The foregoing illustrates that molybdenum disulfide catalysts have a wide range of applications in lithium sulfur batteries and give good electrochemical performance. However, the catalytic action of molybdenum disulfide on polysulfide is not enough to support a high-performance lithium sulfur battery, and if a novel modified molybdenum disulfide catalyst which has both adsorption and catalysis 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.
Here, we report a simple design to prepare oxygen-doped MoS by a green and mild competitive reduction of ethylene glycol process2Carbon nano-sheet (O-MoS)2CNS) for membrane modification. Ethylene glycol is a typical reducing agent and has been widely used to reduce metal salts. During the vulcanization reaction, ethylene glycol and thiourea compete with each other and react with the molybdenum-based precursor, resulting in insufficient vulcanization and formation of O-MoS2. The one-pot method can lead to in-situ doping, and oxygen atoms can be uniformly introduced into MoS2. Oxygen atoms are highly polar, have suitable electronic regulation capacity, and adsorb polysulfides by forming Li-O bonds. Therefore, the O can be doped in MoS2To provide structural and electronic regulation to enhance catalytic activity and polysulfide adsorption capacity.
Disclosure of Invention
The invention designs a mild, simple and low-cost oxygen-doped molybdenum disulfide material modified lithium-sulfur battery diaphragm. The material adopts the carbon nano sheet as a growth substrate for loading oxygen-doped molybdenum disulfide, on one hand, the carbon nano sheet has larger specific surface area and good conductivity, and on the other hand, the two-dimensional carbon nano sheet can provide good electron and ion transmission channels. Ethylene glycol, ammonium heptamolybdate and thiourea are added to synthesize the two-dimensional oxygen-doped molybdenum disulfide nanosheet capable of copying the morphology of the carbon nanosheet through hydrothermal reaction, and an active site is provided for the adsorption and conversion of polysulfide. The synthesized material is modified into a commercial polypropylene diaphragm, and the shuttle effect of polysulfide is greatly reduced by utilizing the adsorption and catalysis of oxygen-doped molybdenum disulfide contained in the synthesized material on the polysulfide; in addition, the existence of the carbon nano-sheet 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 method for doping molybdenum disulfide with oxygen through ethylene glycol induction comprises the steps of growing a two-dimensional oxygen-doped molybdenum disulfide material on the surface of a carbon nanosheet by taking a small number of template-free carbon nanosheets as substrates, ammonium heptamolybdate as a molybdenum source, thiourea as a sulfur source and ethylene glycol as an induction-doped reducing agent. The method specifically comprises the following steps:
(1) and preparing the carbon nano sheet by a template-free method.
In a typical preparation, sodium citrate is dried in an oven at 160 ℃ of 140-. The resulting product was stirred in 2-4M HCl solution for 2-6h and washed with copious amounts of deionized water. Drying at 40-80 ℃ overnight to obtain a carbon nano sheet product as a substrate.
(2) The oxygen-doped molybdenum disulfide/carbon nanosheet material is simply prepared by a green and mild ethylene glycol competitive reduction method.
Dispersing the carbon nano sheet material prepared in the step (1) in a mixed solution of deionized water and ethylene glycol, and carrying out ultrasonic treatment for 1-3h, wherein the ethylene glycol is used as a reducing agent; then adding ammonium heptamolybdate and thiourea and stirring for 0.5-1 h. The solution is placed in a 100mL autoclave and hermetically heated at 200 ℃ and 240 ℃ for 16-24 h. And washing the prepared solid product with deionized water, and drying in a vacuum oven at 40-80 ℃ for 6-10h to obtain the oxygen-doped molybdenum disulfide/carbon nanosheet material. Wherein 50-150mg of carbon nanosheet material, 200-400mg of ammonium heptamolybdate and 600-700mg of thiourea are correspondingly added into the mixed solution of 40-60mL of deionized water and 10-30mL of ethylene glycol.
The synthesis of oxygen-doped molybdenum disulfide is a competitive reduction process, and when a sulfurization reaction occurs in pure water, thiourea first reacts with water to generate H2S，H2S can simultaneously reduce and sulfide Mo6+And molybdenum disulfide is formed. Due to the presence of ethylene glycol, it can react with H2S compete for Mo reduction6+Thereby inhibiting the formation of oxygen-doped disulfides by sulfidationAnd (4) molybdenum melting. Thus, both ethylene glycol and thiourea can reduce Mo6+Form Mo4+And their co-existence competition can induce the synthesis of oxygen-doped molybdenum disulfide. The doping of oxygen atoms can activate the basal plane of molybdenum disulfide to provide abundant adsorption/catalytic sites, enlarge the interlayer distance to promote ion transport, increase the adsorption energy of polysulfide and enhance the electrocatalytic activity.
The application of the carbon nanosheet oxygen-loaded molybdenum disulfide material to the lithium-sulfur battery modifies the synthesized carbon nanosheet oxygen-loaded molybdenum disulfide material to a polypropylene diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nanosheet oxygen-loaded molybdenum disulfide material to the lithium-sulfur battery specifically comprises the following steps:
first, a modified separator is prepared
And loading the oxygen-doped molybdenum disulfide/carbon nanosheet material on the polypropylene diaphragm by adopting a suction filtration method. At room temperature, oxygen-doped molybdenum disulfide/carbon nanosheet powder and concentration of 1.0mg mL-1Adding the PVDF/NMP into isopropanol, and carrying out ultrasonic dispersion treatment for 1-3 h. Filtering the dispersion liquid on a polypropylene membrane, and then drying for 6-10h in vacuum at 40-80 ℃; wherein, 3-4mg of oxygen-doped molybdenum disulfide/carbon nanosheet powder and 0.3-0.5mL of PVDF/NMP are correspondingly added into each 20-40mL of isopropanol. After the modification by the oxygen-doped molybdenum disulfide/carbon nanosheet material, the open pore channels on the surface of the polypropylene can be covered by the active material and become rough, so that shuttling of polysulfide can be effectively adsorbed and blocked, and the polysulfide can be further activated and reused.
Second, a positive electrode material is prepared
Mixing 60-80 wt.% of sublimed sulfur and 20-40 wt.% of carbon nanosheets prepared by the template-free method in step one at room temperature, and heating in an ampoule bottle at 155 ℃ for 8-16 h. Mixing a carbon nano sheet/sulfur mixture, a carbon nano tube and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methyl pyrrolidone, coating the obtained slurry on an aluminum foil, and drying at 40-80 ℃ for 6-10 h;
thirdly, assembling the lithium-sulfur battery
Sequentially assembling the prepared positive electrode material, the modified diaphragm and the negative electrode lithium sheet into a battery, wherein the adding amount of the electrolyte is 40-50 mu L, and the sulfur carrying amount is 1.2mg/cm2-8.2mg/cm2。
The invention has the beneficial effects that:
(1) an oxygen-doped molybdenum disulfide/carbon nanosheet is prepared by a green and mild ethylene glycol competitive reduction method.
(2) Oxygen atoms are highly polar, have suitable electronic regulation capacity, and adsorb polysulfides by forming Li-O bonds.
(3) The dopant of oxygen atoms can also disturb the structure of the molybdenum disulfide, creating crystal distortion and an amorphous structure, thereby creating rich adsorption and catalytic sites. In addition, the high-conductivity carbon nanosheets are introduced into the synthesized material, so that the electron transmission of the synthesized material can be further increased, and the polysulfide conversion is accelerated.
Drawings
FIG. 1 is a schematic diagram of the synthesis process of example 3;
FIG. 2 is a scanning electron micrograph and a transmission electron micrograph of a part of a preparation material of example 3; 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 preparation material of example 3;
FIG. 4 is a graph showing long cycle properties of the preparation material of example 3;
FIG. 5 is a graph showing the result of DFT binding energy simulation calculation of the preparation material of embodiment 3.
Detailed Description
The following examples further illustrate the preparation method and properties of the ethylene glycol-induced oxygen-doped molybdenum disulfide according to the present invention, but should not be construed as limiting the present invention in any way.
Reference case
(1) And preparing the carbon nano sheet 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 nano sheet product as a substrate.
(2) And preparing the molybdenum disulfide/carbon nanosheet material by a hydrothermal method.
100mg of carbon nanosheets were dispersed in 70mL of deionized water and sonicated for 2h, then 309mg of ammonium heptamolybdate and 666mg of thiourea were added and stirred for 0.5 h. The solution was placed in a 100mL autoclave and heated hermetically at 220 ℃ for 20 h. And washing the prepared solid product with deionized water, and drying in a vacuum oven at 60 ℃ for 8h to obtain the molybdenum disulfide/carbon nanosheet material. Molybdenum disulfide can only adsorb and catalyze polysulfide through unpaired atomic sites on the edge, a large number of inert basal planes cannot be effectively utilized, the rapid redox dynamics required by a high-performance lithium-sulfur battery cannot be met, and the utilization of active substances and the exertion of specific capacity are limited;
the application of the carbon nanosheet-loaded molybdenum disulfide material to the lithium-sulfur battery modifies the synthesized carbon nanosheet-loaded molybdenum disulfide material to a polypropylene diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nanosheet-loaded molybdenum disulfide material to the lithium-sulfur battery comprises the following specific steps:
first, a modified separator is prepared
And loading the molybdenum disulfide/carbon nano sheet material on the polypropylene diaphragm by adopting a suction filtration method. At room temperature, molybdenum disulfide/carbon nanosheet powder and concentration of 1.0mg mL-1The PVDF/NMP of (1) is added into isopropanol and treated by ultrasonic dispersion for 2 hours. Filtering the dispersion liquid on a polypropylene membrane, and then drying the dispersion liquid for 8 hours in vacuum at the temperature of 60 ℃; wherein, 3.6mg of oxygen-doped molybdenum disulfide/carbon nanosheet powder and 0.4mL of PVDF/NMP are correspondingly added into each 30mL of isopropanol.
Second, a positive electrode material is prepared
At room temperature, 75 wt.% sublimed sulfur and 25 wt.% carbon nanoplates prepared using the templateless method in step one were mixed and heated in an ampoule at 155 ℃ for 12 h. Mixing a carbon nanosheet/sulfur mixture, a carbon nanotube and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methylpyrrolidone, coating the obtained slurry on an aluminum foil, and drying at 60 ℃ for 8 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, and the battery comprises the anode material, the modified diaphragm and the cathode lithium sheetThe adding amount of the medium electrolyte is 45 mu L, and the sulfur carrying amount is 1.2mg/cm2-8.2mg/cm2。
The assembled cell had only 50% capacity retention after 100 cycles at a rate of 0.5C.
Example 1
(1) And preparing the carbon nano sheet 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 nanosheet product as a substrate;
(2) the oxygen-doped molybdenum disulfide/carbon nanosheet material is simply prepared by a green and mild ethylene glycol competitive reduction method.
Dispersing the carbon nano sheet material prepared in the step (1) in a mixed solution of deionized water and ethylene glycol, and carrying out ultrasonic treatment for 2h, wherein the ethylene glycol is used as a reducing agent; then ammonium heptamolybdate and thiourea are added and stirred for 1 h. The solution was placed in a 100mL autoclave and heated at 220 ℃ for 22h with sealing. And washing the prepared solid product with deionized water, and drying in a vacuum oven at 60 ℃ for 10h to obtain the oxygen-doped molybdenum disulfide/carbon nanosheet material. Wherein, every 50mL of deionized water and 20mL of ethylene glycol are correspondingly added with 100mg of carbon nano sheet material, 309mg of ammonium heptamolybdate and 666mg of thiourea. In oxygen-doped molybdenum disulfide materials, oxygen atoms have a strong polarity with suitable electronic tuning capability to carry polysulfides by forming Li-O bonds. In addition, the oxygen atom dopant can also disturb the structure of the molybdenum disulfide, produce crystal distortion and an amorphous structure, thereby enriching rich adsorption and catalytic sites and expanding ion transport channels. Therefore, the oxygen is doped to provide structural and electronic regulation in the molybdenum disulfide, so that the catalytic activity and the adsorption capacity of polysulfide are improved, active species are effectively utilized, and the specific capacity is improved.
The application of the carbon nanosheet oxygen-loaded molybdenum disulfide material to the lithium-sulfur battery modifies the synthesized carbon nanosheet oxygen-loaded molybdenum disulfide material to a polypropylene diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nanosheet oxygen-loaded molybdenum disulfide material to the lithium-sulfur battery specifically comprises the following steps:
first, a modified separator is prepared
And loading the molybdenum disulfide/carbon nano sheet material on the polypropylene diaphragm by adopting a suction filtration method. At room temperature, molybdenum disulfide/carbon nanosheet powder and concentration of 1.0mg mL-1The PVDF/NMP of (1) is added into isopropanol and treated by ultrasonic dispersion for 2 hours. Filtering the dispersion liquid on a polypropylene membrane, and then drying the dispersion liquid for 8 hours in vacuum at the temperature of 60 ℃; wherein, 3.6mg of oxygen-doped molybdenum disulfide/carbon nanosheet powder and 0.4mL of PVDF/NMP are correspondingly added into each 30mL of isopropanol.
Second, a positive electrode material is prepared
At room temperature, 75 wt.% sublimed sulfur and 25 wt.% carbon nanoplates prepared using the templateless method in step one were mixed and heated in an ampoule at 155 ℃ for 12 h. Mixing a carbon nanosheet/sulfur mixture, a carbon nanotube and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methylpyrrolidone, coating the obtained slurry on an aluminum foil, and drying at 60 ℃ for 8 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 45 mu L, and the sulfur carrying amount is 1.2mg/cm2-8.2mg/cm2。
The assembled battery can have a capacity retention of 85% after 100 cycles at a rate of 0.5C.
Example 2
(1) And preparing the carbon nano sheet by a template-free method.
In a typical preparation, 3g of sodium citrate was dried in a 140 ℃ oven for 10h, ball milled for 5h, and then the powder sample was transferred to a quartz boat and annealed at 700 ℃ for 0.5h under argon atmosphere at a ramp 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 40 ℃ overnight to obtain a carbon nanosheet product as a substrate;
(2) the oxygen-doped molybdenum disulfide/carbon nanosheet material is simply prepared by a green and mild ethylene glycol competitive reduction method.
Dispersing the carbon nano sheet material prepared in the step (1) in a mixed solution of deionized water and ethylene glycol, and carrying out ultrasonic treatment for 1h, wherein the ethylene glycol is used as a reducing agent; then ammonium heptamolybdate and thiourea are added and stirred for 0.5 h. The solution was placed in a 100mL autoclave and heated hermetically at 200 ℃ for 16 h. And washing the prepared solid product with deionized water, and drying in a vacuum oven at 40 ℃ for 6h to obtain the oxygen-doped molybdenum disulfide/carbon nanosheet material. Wherein 50mg of carbon nanosheet material, 200mg of ammonium heptamolybdate and 600mg of thiourea are correspondingly added into the mixed solution of 40mL of deionized water and 30mL of ethylene glycol. The doping of oxygen atoms can activate the basal plane of molybdenum disulfide to provide abundant adsorption/catalytic sites, enlarge the interlayer distance to promote ion transport, increase the adsorption energy of polysulfide and enhance the electrocatalytic activity.
The application of the carbon nanosheet oxygen-loaded molybdenum disulfide material to the lithium-sulfur battery modifies the synthesized carbon nanosheet oxygen-loaded molybdenum disulfide material to a polypropylene diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nanosheet oxygen-loaded molybdenum disulfide material to the lithium-sulfur battery specifically comprises the following steps:
first, a modified separator is prepared
And loading the oxygen-doped molybdenum disulfide/carbon nanosheet material on the polypropylene diaphragm by adopting a suction filtration method. At room temperature, oxygen-doped molybdenum disulfide/carbon nanosheet powder and concentration of 1.0mg mL-1Adding the PVDF/NMP into isopropanol, and carrying out ultrasonic dispersion treatment for 1 h. Filtering the dispersion liquid on a polypropylene membrane, and then drying for 6 hours in vacuum at 40 ℃; wherein, 3mg of oxygen-doped molybdenum disulfide/carbon nanosheet powder and 0.3mL of PVDF/NMP are correspondingly added into each 20mL of isopropanol.
Second, a positive electrode material is prepared
At room temperature, 60 wt.% sublimed sulfur and 40 wt.% carbon nanosheets prepared using the template-free method of step one were mixed and heated in an ampoule at 155 ℃ for 8 h. Mixing a carbon nanosheet/sulfur mixture, a carbon nanotube and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methylpyrrolidone, coating the obtained slurry on an aluminum foil, and drying at 40 ℃ for 6 h;
thirdly, assembling the lithium-sulfur battery
The prepared anode material, the modified diaphragm and the cathode lithium sheet are sequentially arrangedThe battery is assembled, wherein the adding amount of the electrolyte is 40 mu L, and the sulfur carrying amount is 1.2mg/cm2-8.2mg/cm2。
The assembled battery can have 82% capacity retention after 100 cycles at a rate of 0.5C.
Embodiment 3
(1) And preparing the carbon nano sheet by a template-free method.
In a typical preparation, 7g of sodium citrate was dried in a 160 ℃ oven for 30h, ball milled for 15h, and then the powder sample was transferred to a quartz boat and annealed at 900 ℃ under argon atmosphere for 2h with a ramp rate of 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 carbon nanosheet product as a substrate;
(2) the oxygen-doped molybdenum disulfide/carbon nanosheet material is simply prepared by a green and mild ethylene glycol competitive reduction method.
Dispersing the carbon nano sheet material prepared in the step (1) in a mixed solution of deionized water and ethylene glycol, and carrying out ultrasonic treatment for 3 hours, wherein the ethylene glycol is used as a reducing agent; then ammonium heptamolybdate and thiourea are added and stirred for 1 h. The solution was placed in a 100mL autoclave and heated hermetically at 240 ℃ for 24 h. And washing the prepared solid product with deionized water, and drying in a vacuum oven at 80 ℃ for 10h to obtain the oxygen-doped molybdenum disulfide/carbon nanosheet material. Wherein, 150mg of carbon nano sheet material, 400mg of ammonium heptamolybdate and 700mg of thiourea are correspondingly added into the mixed solution of 60mL of deionized water and 10mL of ethylene glycol. The doping of oxygen atoms can activate the basal plane of molybdenum disulfide to provide abundant adsorption/catalytic sites, enlarge the interlayer distance to promote ion transport, increase the adsorption energy of polysulfide and enhance the electrocatalytic activity.
The application of the carbon nanosheet oxygen-loaded molybdenum disulfide material to the lithium-sulfur battery modifies the synthesized carbon nanosheet oxygen-loaded molybdenum disulfide material to a polypropylene diaphragm of a commercial lithium-sulfur battery, and the application of the carbon nanosheet oxygen-loaded molybdenum disulfide material to the lithium-sulfur battery specifically comprises the following steps:
first, a modified separator is prepared
Loading oxygen-doped molybdenum disulfide/carbon nanosheet material on a polypropylene diaphragm by adopting a suction filtration method. At room temperature, oxygen-doped molybdenum disulfide/carbon nanosheet powder and concentration of 1.0mg mL-1The PVDF/NMP of (1) was added to isopropanol and subjected to ultrasonic dispersion treatment for 3 hours. Filtering the dispersion liquid on a polypropylene membrane, and then drying the dispersion liquid for 10 hours in vacuum at the temperature of 80 ℃; wherein, 4mg of oxygen-doped molybdenum disulfide/carbon nanosheet powder and 0.5mL of PVDF/NMP are correspondingly added into each 40mL of isopropanol.
Second, a positive electrode material is prepared
80 wt.% sublimed sulfur and 20 wt.% carbon nanoplates prepared by the templateless method in step one were mixed at room temperature and heated in an ampoule at 155 ℃ for 16 h. Mixing a carbon nanosheet/sulfur mixture, a carbon nanotube and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methylpyrrolidone, coating the obtained slurry on an aluminum foil, and drying at 80 ℃ for 10 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/cm2-8.2mg/cm2。
The assembled battery can have 80% capacity retention after 100 cycles at a rate of 0.5C.
The above examples merely represent embodiments of the present invention and are not to be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.
Claims (3)
1. A method for inducing oxygen to dope molybdenum disulfide by ethylene glycol is characterized in that a two-dimensional oxygen-doped molybdenum disulfide material grows on the surface of a carbon nanosheet by taking a template-free carbon nanosheet as a substrate, ammonium heptamolybdate as a molybdenum source, thiourea as a sulfur source and ethylene glycol as a reducing agent for inducing doping; the method comprises the following steps:
(1) preparing carbon nano sheets as a substrate by a template-free method;
(2) the oxygen-doped molybdenum disulfide/carbon nanosheet material is simply prepared by a green and mild ethylene glycol competitive reduction method, and the method specifically comprises the following steps:
firstly, dispersing the carbon nano sheet material prepared in the step (1) in a mixed solution of deionized water and ethylene glycol for ultrasonic treatment for 1-3h, wherein the ethylene glycol is used as a reducing agent; secondly, adding ammonium heptamolybdate and thiourea and stirring for 0.5-1 h; thirdly, placing the solution in a high-pressure kettle, sealing and heating at 200-240 ℃ for 16-24h, washing the prepared solid product with deionized water, and then placing the solid product in a vacuum oven for drying treatment to obtain the oxygen-doped molybdenum disulfide/carbon nanosheet material; wherein 50-150mg of carbon nanosheet material, 200-400mg of ammonium heptamolybdate and 600-700mg of thiourea are correspondingly added into the mixed solution of 40-60mL of deionized water and 10-30mL of ethylene glycol.
2. The method for doping molybdenum disulfide by oxygen induced by ethylene glycol as claimed in claim 1, wherein the first step of preparing carbon nanosheets comprises the steps of: firstly, drying sodium citrate in an oven at the temperature of 140-; secondly, transferring the powder sample into a quartz boat, and annealing for 0.5-2h under the argon atmosphere at the temperature of 700-; and finally, stirring the obtained product in a 2-4M HCl solution for 2-6h, washing with deionized water, and drying overnight to obtain a carbon nanosheet product.
3. The application of the high-activity Mn/Co-N double-site doped carbon material catalyst prepared by the preparation method of claim 1 or 2 in a lithium-sulfur battery is characterized in that the synthesized catalyst is used for modifying a commercial PP (polypropylene) diaphragm of the lithium-sulfur battery and is applied to the lithium-sulfur battery.
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