CN107799745B - Molybdenum carbide-sulfur composite material and preparation method and application thereof - Google Patents
Molybdenum carbide-sulfur composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the technical field of lithium-sulfur battery anode materials, and provides a molybdenum carbide-sulfur composite material and a preparation method and application thereof, wherein the molybdenum carbide-sulfur composite material comprises molybdenum carbide and a sulfur simple substance, the molybdenum carbide is of a porous rod-shaped structure, the length of the molybdenum carbide is 1-5 mu m, the diameter of the molybdenum carbide is 30-60 nm, the sulfur simple substance is doped in pores of the molybdenum carbide, and the mass ratio of the molybdenum carbide to the sulfur simple substance is 1-9: 9 to 1. The molybdenum carbide-sulfur composite material provided by the invention has higher specific surface area and electronic conductivity, and can improve the utilization rate of sulfur and relieve the shuttle flying effect. The lithium-sulfur battery prepared from the molybdenum carbide-sulfur composite material is subjected to charge and discharge tests, the reversible capacity of 623-653 mAh/g is still maintained after 500 times of circulation, the capacity is maintained at more than 70%, the coulombic efficiency is over 93%, and the circulation performance is remarkably improved.
Description
Technical Field
The invention relates to the technical field of lithium-sulfur battery positive electrode materials, in particular to a molybdenum carbide-sulfur composite material and a preparation method and application thereof.
Background
In recent years, with the rapid development of electric vehicles and energy storage devices, it is difficult for the current commercial lithium ion batteries to meet the demand of people for high energy density. Lithium-sulfur batteries are considered as one of the candidates for next-generation batteries because of their high energy density and low cost characteristics. However, polysulfide dissolves in an electrolyte due to low electronic conductivity of sulfur element, a large volume change in a cycle process causes a shuttle effect, the utilization rate of sulfur is low, and the cycle stability is poor, which all restrict the practical application of the lithium-sulfur battery.
In the prior art, use is made of materials such as Ti4O7And polar conductive substances such as TiN and the like are compounded as sulfur carriers to be used as the cathode materials of the lithium-sulfur battery, but the cathode materials have poor cycle stability due to weak constraint on polysulfide, and are not suitable for large-scale production.
Therefore, in the prior art, carbon-sulfur composite is more adopted to improve the performance of the lithium-sulfur battery, and carbon material is used as a sulfur carrier to improve the electrical conductivity of the whole composite material, and simultaneously, the free diffusion of polysulfide can be physically restrained. However, the interaction between the carbon material and polysulfide in the existing carbon-sulfur composite is weak, and the polysulfide still diffuses into the electrolyte along with the increase of the cycle times along with the cycle, so that the cycle performance and the service life of the carbon-sulfur composite cannot be met.
Disclosure of Invention
The invention aims to provide a molybdenum carbide-sulfur composite material, a preparation method thereof and application thereof in a lithium-sulfur battery; the molybdenum carbide-sulfur composite material provided by the invention has higher specific surface area and conductivity, can effectively relieve the shuttle flying effect, and improves the cycle stability and service life of the lithium-sulfur battery.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a molybdenum carbide-sulfur composite material which comprises molybdenum carbide and a sulfur simple substance in chemical composition, wherein the molybdenum carbide is in a porous rod-like structure, the length of the molybdenum carbide is 1-5 mu m, and the diameter of the molybdenum carbide is 30-60 nm; the sulfur simple substance is doped in pores of the molybdenum carbide, and the mass ratio of the molybdenum carbide to the sulfur simple substance is 1-9: 9 to 1.
The invention also provides a preparation method of the molybdenum carbide-sulfur composite material, which comprises the following steps:
1) mixing a molybdenum trioxide raw material, hydrogen peroxide and a nitric acid solution, and carrying out hydrothermal treatment to obtain rod-shaped molybdenum trioxide;
2) mixing and drying the rod-shaped molybdenum trioxide and a carbon precursor material, and carrying out reduction reaction under a protective atmosphere to obtain rod-shaped molybdenum carbide;
3) and mixing the rod-shaped molybdenum carbide and the elemental sulfur, and carrying out heat treatment under a protective atmosphere to obtain the molybdenum carbide-sulfur composite material.
Preferably, the concentration of the hydrogen peroxide is 0.01-0.35 g/mL; the concentration of the nitric acid solution is 0.01-0.7 g/mL.
Preferably, the temperature of the hydrothermal treatment is 90-200 ℃, and the time of the hydrothermal treatment is 1-72 h.
Preferably, the carbon precursor material includes one or a mixture of two or more of glucose, phenolic resin, aniline, pyrrole, thiophene, sucrose and carboxymethyl cellulose.
Preferably, the mass ratio of the rod-shaped molybdenum trioxide to the carbon precursor material is 1:0.05 to 200.
Preferably, the protective atmosphere in step 2) and step 3) is independently N2Ar, He and H2One or a mixture of two or more of them.
Preferably, the temperature of the reduction reaction in the step 2) is 400-1200 ℃, and the time of the reduction reaction is 1-72 hours.
Preferably, the temperature of the heat treatment in the step 3) is 140-200 ℃, and the time of the heat treatment is 10-30 h.
The invention also provides a lithium-sulfur battery which comprises a positive electrode, a lithium negative electrode and electrolyte, wherein the positive electrode comprises an active substance, and the active substance is the molybdenum carbide-sulfur composite material or the molybdenum carbide-sulfur composite material prepared by the preparation method.
The invention provides a molybdenum carbide-sulfur composite material which comprises molybdenum carbide and a sulfur simple substance in chemical composition, wherein the molybdenum carbide is in a porous rod-like structure, the length of the molybdenum carbide is 1-5 mu m, and the diameter of the molybdenum carbide is 30-60 nm; the sulfur simple substance is doped in pores of the molybdenum carbide, and the mass ratio of the molybdenum carbide to the sulfur simple substance is 1-9: 9 to 1. The molybdenum carbide with a rod-like structure in the molybdenum carbide sulfur composite material provided by the invention has higher specific surface area and electronic conductivity, can relieve volume expansion, physically binds polysulfide, reduces the diffusion phenomenon of polysulfide, and improves the utilization rate of sulfur; the higher electronic conductivity can improve the electronic transmission capability, and finally, the purposes of improving the cycle stability and prolonging the service life of the lithium-sulfur battery are achieved.
Meanwhile, the molybdenum carbide has a very strong adsorption effect on polar polysulfide, so that the free diffusion of the polysulfide is effectively inhibited, and the shuttle flying effect is relieved. Experimental results show that the length of the molybdenum carbide-sulfur composite material is 1-5 mu m, the diameter of the molybdenum carbide-sulfur composite material is 30-60 nm, and the specific surface area of the composite material is 289-352 m2Per g, conductivity 1.1X 102S·cm-1～1.02×102S·cm-1。
The invention also provides a preparation method of the molybdenum carbide-sulfur composite material, and the method is simple and convenient to operate and easy to implement.
The molybdenum carbide-sulfur composite material provided by the invention can be applied to lithium-sulfur batteries. Experimental results show that the lithium-sulfur battery prepared from the molybdenum carbide-sulfur composite material still maintains the reversible capacity of 623-653 mAh/g after being cycled for 500 times by performing charge-discharge tests at the constant temperature of 30 ℃ and within the voltage range of 1.5-3.0V, the capacity is maintained above 70%, the coulombic efficiency is over 93%, and good cycle stability is shown.
Drawings
FIG. 1 is an SEM image of a molybdenum carbide-sulfur composite prepared in example 1 of the present invention;
FIG. 2 is a graph of the cycle performance of a coin lithium-sulfur battery prepared in example 2 of the present invention;
FIG. 3 is a graph of the cycle performance of coin lithium sulfur batteries prepared in example 4 of the present invention.
Detailed Description
The invention provides a molybdenum carbide-sulfur composite material which comprises molybdenum carbide and a sulfur simple substance, wherein the molybdenum carbide is in a porous rod-like structure, the length of the molybdenum carbide is 1-5 mu m, and the diameter of the molybdenum carbide is 30-60 nm; the sulfur simple substance is doped in pores of the molybdenum carbide, and the mass ratio of the molybdenum carbide to the sulfur simple substance is 1-9: 9 to 1.
The molybdenum carbide-sulfur composite material provided by the invention comprises molybdenum carbide; in the invention, the molybdenum carbide is of a nanorod structure, and the length of the molybdenum carbide nanorod is preferably 1-5 μm, and more preferably 2-4 μm; the diameter of the molybdenum carbide nanorod is preferably 30-60 nm, more preferably 40-50 nm, and most preferably 45 nm; the molybdenum carbide in the invention can play a supporting role as a main skeleton structure of the molybdenum carbide sulfur composite material. In the present invention, the molybdenum carbide is preferably 10 to 90% by mass, more preferably 30 to 60% by mass, and most preferably 50% by mass.
In the invention, the molybdenum carbide has higher specific surface area and electronic conductivity, can relieve volume expansion, physically binds polysulfide, reduces the diffusion phenomenon of polysulfide and improves the utilization rate of sulfur; the higher electronic conductivity can improve the electronic transmission capability, and finally improve the cycling stability and the service life of the lithium-sulfur battery. Meanwhile, the molybdenum carbide has a very strong adsorption effect on polar polysulfide, so that the free diffusion of the polysulfide is effectively inhibited, and the shuttle flying effect is relieved.
The molybdenum carbide-sulfur composite material provided by the invention also comprises a sulfur simple substance doped in the pores of the rod-shaped molybdenum carbide; in the invention, the mass content of the elemental sulfur is preferably 10-90%, more preferably 30-60%, and most preferably 50%; in the invention, the sulfur elementary substance with specific content is doped as an active substance of the molybdenum carbide-sulfur composite material, so that the rate capability and the cycling stability of the lithium-sulfur battery can be obviously improved.
The molybdenum carbide sulfur composite material provided by the invention has a structure of a nano rod shape, the length of the nano rod shape is 1-5 mu m, and the diameter of the nano rod shape is 30-60 nm; the specific surface area of the molybdenum carbide-sulfur composite material provided by the invention is 289-352 m2Per g, conductivity 1.1X 102～1.02×102S·cm-1Compared with other existing carbon-sulfur composites, the specific surface area and the conductivity of the composite are remarkably improved.
The invention also provides a preparation method of the molybdenum carbide-sulfur composite material, which comprises the following steps:
1) mixing a molybdenum trioxide raw material, hydrogen peroxide and a nitric acid solution, and carrying out hydrothermal treatment to obtain rod-shaped molybdenum trioxide;
2) mixing the rod-shaped molybdenum trioxide, a carbon precursor material and a solvent, and carrying out a reduction reaction under a protective atmosphere to obtain molybdenum carbide;
3) and mixing the molybdenum carbide with a sulfur simple substance, and carrying out heat treatment under a protective atmosphere to obtain the molybdenum carbide-sulfur composite material.
According to the invention, a molybdenum trioxide raw material, hydrogen peroxide and a nitric acid solution are mixed to obtain a mixed solution. The method has no special requirements on the sources of the molybdenum trioxide raw material, hydrogen peroxide and nitric acid solution, and only needs to use reagents which are sold in the market or used for experiments; the molybdenum trioxide used in the invention is a non-rod-shaped raw material sold in the market; the purpose of selecting the hydrogen peroxide and the nitric acid solution in the invention is to dissolve molybdenum trioxide and prepare molybdenum carbide with a special rod-like structure.
In the invention, the concentration of the hydrogen peroxide is preferably 0.01-0.35 g/ml, more preferably 0.1-0.25 g/ml, and most preferably 0.15 g/ml; the concentration of the nitric acid solution is preferably 0.01-0.7 g/ml, more preferably 0.1-0.5 g/ml, and most preferably 0.2-0.4 g/ml. In the invention, the volume ratio of the hydrogen peroxide to the nitric acid solution is preferably 0.1-20: 1, more preferably 0.5 to 5: 1.
in the present invention, the solid-to-liquid ratio of the mixed solution (i.e., the mass content of molybdenum trioxide in the mixed solution) is preferably 0.001 to 100, more preferably 0.01 to 50, and most preferably 0.1 to 20.
In the invention, the mixing of the molybdenum trioxide raw material, hydrogen peroxide and nitric acid solution is preferably carried out under the condition of stirring, and the stirring is preferably magnetic stirring; the stirring speed is preferably 10-5000 r/min, more preferably 100-1000 r/min, and most preferably 200-500 r/min; the stirring time is preferably 1-72 h, more preferably 5-50 h, and most preferably 20-40 h. According to the invention, the raw materials can be uniformly mixed by adopting a stirring mixing mode, and the formation of the molybdenum trioxide with the rod-shaped structure is promoted.
The method has no special requirements on the mixing order of the molybdenum trioxide raw material, hydrogen peroxide and nitric acid solution, the molybdenum trioxide raw material, the hydrogen peroxide and the nitric acid solution can be mixed in any order, and the molybdenum trioxide with special morphology can be prepared. According to the invention, hydrogen peroxide and a nitric acid solution are preferably mixed, and then a molybdenum trioxide raw material is added for mixing, so that the condition of molybdenum trioxide is not controllable due to the change of the adding sequence of nitric acid and hydrogen peroxide, and the rod-shaped molybdenum trioxide is obtained.
After the mixed solution is obtained, the mixed solution is subjected to hydrothermal treatment to obtain the rod-shaped molybdenum trioxide. In the invention, the temperature of the hydrothermal treatment is preferably 90-200 ℃, more preferably 120-180 ℃, and most preferably 160 ℃; the time of the hydrothermal treatment is preferably 1-72 h, more preferably 12-60 h, and most preferably 24-32 h. The apparatus for hydrothermal treatment in the present invention is not particularly limited, and hydrothermal treatment in a hydrothermal reaction vessel is preferably performed in the embodiment of the present invention.
After the hydrothermal treatment is finished, the rod-shaped molybdenum trioxide solution is preferably cooled, separated and dried in sequence to obtain pure rod-shaped molybdenum trioxide; in the present invention, the temperature after cooling is preferably room temperature, and the present invention has no special requirement for the cooling manner, and may adopt a cooling manner that is conventional in the art, and in the embodiment of the present invention, a natural cooling manner is preferably adopted.
In the present invention, the separation comprises centrifugation and filtration; the centrifugal and filtering process is not particularly limited, and the solid-liquid separation of the rod-shaped molybdenum trioxide and the mixed solution can be realized by adopting the conventional centrifugal and filtering method in the field.
In the invention, the drying temperature is preferably 20-120 ℃, more preferably 50-100 ℃, and most preferably 60-80 ℃; the method has no special requirement on the drying time, and can completely volatilize the solution on the rod-shaped molybdenum trioxide obtained by solid-liquid separation.
After the rod-shaped molybdenum trioxide is obtained, the rod-shaped molybdenum trioxide and a carbon precursor material are mixed, and reduction reaction is carried out under a protective atmosphere to obtain molybdenum carbide.
In the present invention, the mass ratio of the rod-shaped molybdenum trioxide to the carbon precursor material is preferably 1:0.05 to 200, more preferably 1: 1-100, most preferably 1: 10 to 50. In the invention, the carbon precursor material comprises one or a mixture of more than two of glucose, phenolic resin, aniline, pyrrole, thiophene, sucrose and carboxymethyl cellulose. In the invention, a carbon precursor material is used as a reducing agent to reduce molybdenum trioxide to obtain molybdenum carbide.
In the invention, the mixing temperature is preferably-5-100 ℃, more preferably 0-80 ℃, and most preferably 10-50 ℃; the mixing is preferably carried out under stirring conditions; the stirring speed is preferably 10-5000 r/min, more preferably 100-1000 r/min, and most preferably 200-500 r/min; the stirring time is preferably 1-48 h, more preferably 10-32 h, and most preferably 18-24 h.
In the present invention, the rod-shaped molybdenum trioxide and the carbon precursor material are preferably dispersed in a solvent and mixed to obtain a more uniform mixture. In the invention, the concentration of the carbon precursor in the mixed solution is 0.01-10 mol/L. The solvent preferably comprises water and/or an organic solvent, and the organic solvent preferably comprises one or a mixture of more than two of ethanol, methanol, acetone, isopropanol, tetrahydrofuran and carbon tetrachloride. After dispersion and mixing in the solvent are completed, the present invention preferably dries the obtained mixture to obtain a solid mixed powder of rod-shaped molybdenum trioxide and a carbon precursor material. In the invention, the drying temperature is preferably 20-120 ℃, more preferably 40-100 ℃, and most preferably 50-70 ℃. The drying method of the invention is not particularly limited, and the drying method known to those skilled in the art can be adopted; in the present invention, the purpose of drying is to obtain a solid mixed powder of rod-shaped molybdenum trioxide and a carbon precursor material.
After drying is finished, the obtained solid powder is subjected to reduction reaction in a protective atmosphere to obtain the rod-shaped molybdenum carbide. In the present invention, the protective atmosphere is preferably N2Ar, He and H2One or a mixture of two or more of them. In the present invention, the protective atmosphere functions to prevent the precursor material from reacting with oxygen in the air.
In the invention, the temperature of the reduction reaction is preferably 400-1200 ℃, more preferably 500-1000 ℃, and most preferably 600-800 ℃; the time of the reduction reaction is preferably 1-72 h, more preferably 12-60 h, and most preferably 24-32 h; the reduction reaction is preferably carried out in a high temperature furnace for sintering treatment.
After the reduction reaction is finished, preferably, a product system obtained by the reduction reaction is cooled to room temperature to obtain rod-shaped molybdenum carbide; in the present invention, the cooling method is preferably natural cooling.
After the rod-shaped molybdenum carbide is obtained, the rod-shaped molybdenum carbide and a sulfur simple substance are mixed, and heat treatment is carried out under a protective atmosphere to obtain the molybdenum carbide-sulfur composite material. In the invention, the mass ratio of the molybdenum carbide to the elemental sulfur is preferably 1-9: 9-1, more preferably 1-5: 5-1, most preferably 1-2: 2 to 1. In the present invention, the protective atmosphere is preferably N2Ar, He and H2One or a mixture of two or more of them.
The operation of mixing the molybdenum carbide and the elemental sulfur is not particularly limited, and the technical scheme of powder mixing which is well known by the technical personnel in the field can be adopted; in the invention, the mixing of the molybdenum carbide and the elemental sulfur is preferably ball milling mixing, and the ball milling mixing time is 1-72 h, more preferably 12-60 h, and most preferably 24-32 h; the ball milling speed is preferably 10-5000 r/min, more preferably 100-1000 r/min, and most preferably 200-500 r/min.
In the invention, the temperature of the heat treatment is preferably 140-200 ℃, more preferably 150-180 ℃, and most preferably 160-170 ℃; the time of the heat treatment is preferably 1-72 h, more preferably 12-60 h, and most preferably 24-32 h. In the present invention, the heat treatment is selected so that the precursor is heated to react with each other to form molybdenum carbide, the carbon precursor is carbonized at a high temperature to form carbon, and the carbon can react with the rod-shaped molybdenum trioxide to form molybdenum carbide having pores.
The invention also provides a lithium-sulfur battery which comprises a positive electrode, a lithium negative electrode and electrolyte, wherein the positive electrode comprises an active substance, acetylene black and PVDF, and the active substance is the molybdenum carbide-sulfur composite material or the molybdenum carbide-sulfur composite material prepared by the preparation method.
The button lithium-sulfur battery is preferably assembled by taking metal lithium as a negative electrode, electrolyte and a positive plate in an argon-protected glove box; the preparation method of the lithium-sulfur battery is not particularly limited, and the technical scheme for assembling the lithium-sulfur battery, which is well known to those skilled in the art, can be adopted.
In the invention, the molybdenum carbide-sulfur composite material, the acetylene black and the PVDF are preferably mixed according to the mass ratio of 8: 1: 1, preparing uniform slurry (solid content is 50%) by taking N-methyl pyrrolidone as a solvent, coating the uniform slurry on an aluminum foil with proper thickness, and drying to obtain the positive plate. The invention has no special limitation on the types of the lithium cathode and the electrolyte, and the lithium cathode and the electrolyte of the lithium-sulfur battery well known to the technical personnel in the field can be adopted; in the present invention, LiTFSI and LiNO are preferable as the electrolyte3Lithium salt, DOL and DME are used as solvents, and the volume ratio of the two solvents is 1: 1, concentration of lithium salt 1M LiTFSI, 0.1M LiNO3。
The molybdenum carbide-sulfur composite material, the preparation method thereof and the application thereof in a lithium-sulfur battery provided by the present invention will be described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.
Example 1
Preparing a mixed solution (20 ml of 0.3g/ml hydrogen peroxide and 10ml of 0.65g/ml nitric acid solution), adding 0.4g of molybdenum trioxide into the mixed solution, and stirring for 72 hours at the stirring speed of 500 r/min; then carrying out hydrothermal treatment for 36 hours at 190 ℃, cooling to room temperature, centrifuging, filtering, and drying at 70 ℃ to obtain rod-shaped molybdenum trioxide;
mixing the prepared rod-shaped molybdenum trioxide with phenolic resin according to a mass ratio of 2: 1 in 40ml of ethanol solvent, stirred at 40 ℃ for 28 hours, and dried at 80 ℃ to obtain a solid mixed powder. Mixing the solid mixed powder in N2Sintering in a protected high-temperature furnace, heating to 900 ℃ at the heating rate of 5 ℃/min, carrying out sintering reaction for 18h, and naturally cooling to room temperature to obtain molybdenum carbide;
mixing the prepared molybdenum carbide and sulfur elementary substance according to the mass ratio of 2: 3, in the ball mill, the ballMilling for 4 hours, the product is in N2And (3) carrying out heat treatment for 30 hours at 160 ℃ in a protected high-temperature furnace, and naturally cooling to room temperature to obtain the molybdenum carbide-sulfur composite material.
The SEM image of the molybdenum carbide-sulfur composite material prepared in this example is shown in fig. 1. As can be seen from FIG. 1, the molybdenum carbide-sulfur composite material prepared in this example is a nanorod structure with a length of 2 μm and a nanorod diameter of 50 nm; the specific surface area and the conductivity of the material are tested by nitrogen adsorption and four probes, and the specific surface area of the molybdenum carbide-sulfur composite material is 352m2Per g, conductivity 1.02X 102S·cm-1。
Example 2
Preparation of lithium-sulfur battery: mixing the molybdenum carbide-sulfur composite material prepared in the example 1 with acetylene black and PVDF according to a mass ratio of 8: 1: 1, mixing, preparing uniform slurry (solid content is 50%) by taking N-methyl pyrrolidone as a solvent, coating the slurry on an aluminum foil, drying to obtain a positive plate, and putting the positive plate in an argon-protected glove box by taking metal lithium as a negative electrode, 1M LiTFSI and 0.1M LiNO3(DOL and DME are solvents with the volume ratio of 1: 1) are used as electrolyte, and the button lithium-sulfur battery is assembled.
And (3) testing the cycle performance: and (3) carrying out charge-discharge test at constant temperature of 30 ℃ and within the voltage range of 1.5-3.0V at the current density of 1C, and circulating for 500 times.
As can be seen from the cycle performance curve of the positive electrode material shown in fig. 2, the reversible capacity of 653mAh/g is maintained after 500 cycles, and the capacity is maintained at 70% or more after 500 cycles at 1C rate, so that the coulombic efficiency is over 93%, and the cycle stability is excellent.
Example 3
Preparing a mixed solution (10 ml of 0.1g/ml hydrogen peroxide and 40ml of 0.45g/ml nitric acid solution), adding 0.8g of molybdenum trioxide into the mixed solution, and stirring for 36 hours at the stirring speed of 100 r/min; then carrying out hydrothermal treatment for 24 hours at 160 ℃, cooling to room temperature, centrifuging, filtering, and drying at 60 ℃ to obtain rod-shaped molybdenum trioxide;
mixing the prepared rod-shaped molybdenum trioxide with glucose according to a mass ratio of 1: 1 was dispersed in 30ml of water, stirred at 30 ℃ for 20 hours, and dried at 50 ℃ to obtain a solid mixed powder. Putting the solid mixed powder into a high-temperature furnace in argon, heating to 800 ℃ at the heating rate of 10 ℃/min, carrying out sintering reaction for 12h, and naturally cooling to room temperature to obtain molybdenum carbide;
mixing the prepared molybdenum carbide and sulfur elementary substance according to the mass ratio of 3: and 4, ball-milling the mixture in a ball mill for 8 hours, carrying out heat treatment on the product in a high-temperature furnace under the protection of argon at the temperature of 170 ℃ for 20 hours, and naturally cooling the product to room temperature to obtain the molybdenum carbide-sulfur composite material.
The molybdenum carbide sulfur composite material prepared by the embodiment is of a nanorod structure, the length of the nanorod structure is 1 mu m, and the diameter of the nanorod structure is 30 nm; the specific surface area and the conductivity of the material are tested by nitrogen adsorption and a four-probe, and the specific surface area of the molybdenum carbide-sulfur composite material prepared in the embodiment is 289m2Per g, conductivity 1.1X 102S·cm-1。
Example 4
The molybdenum carbide sulfur composite prepared in example 3 was assembled into a button lithium sulfur battery in the same manner as in example 2.
And (3) testing the cycle performance: and (3) carrying out charge-discharge test at constant temperature of 30 ℃ and within the voltage range of 1.5-3.0V at the current density of 1C, and circulating for 500 times.
As can be seen from the cycle performance curve of the positive electrode material shown in fig. 3, the reversible capacity of 623mAh/g was maintained after 500 cycles, and the capacity was maintained at 70% or more after 500 cycles at 1C rate, which resulted in a coulombic efficiency of more than 97% and excellent cycle stability.
Example 5
Preparing a mixed solution (60 ml of 0.2g/ml hydrogen peroxide and 10ml of 0.35g/ml nitric acid solution), adding 2g of molybdenum trioxide into the mixed solution, and stirring for 5 hours at the stirring speed of 300 r/min; then carrying out hydrothermal treatment for 12 hours at the temperature of 90 ℃, cooling to room temperature, centrifuging, filtering, and drying at the temperature of 20 ℃ to obtain rod-shaped molybdenum trioxide;
mixing the prepared rodlike molybdenum trioxide with thiophene according to the mass ratio of 2: 1 in 80ml of carbon tetrachloride solvent, stirred at 100 ℃ for 5 hours, and dried at 20 ℃ to obtain a solid mixed powder. Putting the solid mixed powder into a high-temperature furnace of hydrogen, heating to 1200 ℃ at the heating rate of 5 ℃/min, carrying out sintering reaction for 12h, and naturally cooling to room temperature to obtain molybdenum carbide;
mixing the prepared molybdenum carbide and sulfur elementary substance according to the mass ratio of 1: and 9, ball-milling the mixture in a ball mill for 48 hours, carrying out heat treatment on the product in a high-temperature furnace under the protection of hydrogen at 140 ℃ for 24 hours, and naturally cooling the product to room temperature to obtain the molybdenum carbide-sulfur composite material.
The molybdenum carbide sulfur composite material prepared by the embodiment is of a nanorod structure, the length of the nanorod structure is 5 microns, and the diameter of the nanorod is 60 nm; the specific surface area and the conductivity of the material were tested by nitrogen adsorption and four probes, and the specific surface area of the molybdenum carbide-sulfur composite material prepared in this example was 320m2Per g, conductivity 1.05X 102S·cm-1。
Example 6
The molybdenum carbide sulfur composite prepared in example 5 was assembled into a button lithium sulfur battery in the same manner as in example 2.
And (3) testing the cycle performance: the charge-discharge test is carried out at constant temperature of 30 ℃ and within the voltage range of 1.5-3.0V and at the current density of 1C, the reversible capacity of 648 is still maintained after 500 cycles, the capacity can be maintained at more than 70% after 500 cycles at the multiplying power of 1C, the coulombic efficiency is more than 97%, and the excellent cycle stability is shown.
Example 7
Preparing a mixed solution (18 ml of 0.2g/ml hydrogen peroxide and 18ml of 0.35g/ml nitric acid solution), adding 3g of molybdenum trioxide into the mixed solution, and stirring for 12 hours at a stirring speed of 500 r/min; then carrying out hydrothermal treatment for 24 hours at 120 ℃, cooling to room temperature, centrifuging, filtering, and drying at 120 ℃ to obtain rod-shaped molybdenum trioxide;
mixing the prepared rodlike molybdenum trioxide and carboxymethyl cellulose according to a mass ratio of 1: 10 was dispersed in 50ml of acetone solvent, stirred at-5 ℃ for 48 hours, and dried at 120 ℃ to obtain a solid mixed powder. Putting the solid mixed powder into N2Heating to 600 ℃ at the heating rate of 10 ℃/min in the high-temperature furnace, sintering for 24 hours, and naturally cooling to room temperature to obtain molybdenum carbide;
mixing the prepared molybdenum carbide and sulfur elementary substance according to the mass ratio of 9: 1, ball milling in a ball mill for 12 hours, and grinding the product in a ball mill for 12 hours to obtain the product2And (3) carrying out heat treatment for 12 hours at 200 ℃ in a protected high-temperature furnace, and naturally cooling to room temperature to obtain the molybdenum carbide-sulfur composite material.
The molybdenum carbide sulfur composite material prepared by the embodiment is of a nanorod structure, the length of the nanorod structure is 3 microns, and the diameter of the nanorod is 50 nm; the specific surface area and the conductivity of the material were tested by nitrogen adsorption and four probes, and the specific surface area of the molybdenum carbide-sulfur composite material prepared in this example was 340m2Per g, conductivity 1.03X 102S·cm-1。
Example 8
The molybdenum carbide sulfur composite prepared in example 7 was assembled into a button lithium sulfur battery in the same manner as in example 2.
And (3) testing the cycle performance: the charge and discharge test is carried out at constant temperature of 30 ℃ and within the voltage range of 1.5-3.0V and at the current density of 1C, the reversible capacity of 635mAh/g is still kept after 500 times of circulation, the capacity can be kept above 70% after 500 times of 1C multiplying power circulation, the coulombic efficiency is over 97%, and the excellent circulation stability is shown.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. The molybdenum carbide-sulfur composite material is characterized by comprising molybdenum carbide and a sulfur simple substance in chemical composition, wherein the molybdenum carbide is in a porous rod-like structure, the length of the molybdenum carbide is 1-5 mu m, and the diameter of the molybdenum carbide is 30-60 nm; the sulfur simple substance is doped in pores of the molybdenum carbide, and the mass ratio of the molybdenum carbide to the sulfur simple substance is 1-9: 9-1;
the preparation method of the molybdenum carbide-sulfur composite material comprises the following steps:
1) mixing a molybdenum trioxide raw material, hydrogen peroxide and a nitric acid solution, and carrying out hydrothermal treatment to obtain rod-shaped molybdenum trioxide;
2) mixing and drying the rod-shaped molybdenum trioxide and a carbon precursor material, and carrying out reduction reaction under a protective atmosphere to obtain rod-shaped molybdenum carbide;
3) and mixing the rod-shaped molybdenum carbide and the elemental sulfur, and carrying out heat treatment under a protective atmosphere to obtain the molybdenum carbide-sulfur composite material.
2. A method of preparing a molybdenum carbide sulfur composite material as defined in claim 1, comprising the steps of:
1) mixing a molybdenum trioxide raw material, hydrogen peroxide and a nitric acid solution, and carrying out hydrothermal treatment to obtain rod-shaped molybdenum trioxide;
2) mixing and drying the rod-shaped molybdenum trioxide and a carbon precursor material, and carrying out reduction reaction under a protective atmosphere to obtain rod-shaped molybdenum carbide;
3) and mixing the rod-shaped molybdenum carbide and the elemental sulfur, and carrying out heat treatment under a protective atmosphere to obtain the molybdenum carbide-sulfur composite material.
3. The preparation method of the molybdenum carbide-sulfur composite material according to claim 2, wherein the concentration of the hydrogen peroxide is 0.01-0.35 g/mL; the concentration of the nitric acid solution is 0.01-0.7 g/mL.
4. The method for preparing the molybdenum carbide-sulfur composite material according to claim 2 or 3, wherein the temperature of the hydrothermal treatment is 90 to 200 ℃ and the time of the hydrothermal treatment is 1 to 72 hours.
5. The method of claim 2, wherein the carbon precursor material comprises one or a mixture of two or more of glucose, phenolic resin, aniline, pyrrole, thiophene, sucrose, and carboxymethyl cellulose.
6. The method for preparing the molybdenum carbide-sulfur composite material according to claim 2 or 5, wherein the mass ratio of the rod-shaped molybdenum trioxide to the carbon precursor material is 1:0.05 to 200.
7. The method for preparing the molybdenum carbide-sulfur composite material according to claim 2, wherein the protective atmosphere in the step 2) and the step 3) is one or a mixture of two or more of N2, Ar, He and H2.
8. The preparation method of the molybdenum carbide-sulfur composite material according to claim 2 or 7, wherein the temperature of the reduction reaction in the step 2) is 400 to 1200 ℃, and the time of the reduction reaction is 1 to 72 hours.
9. The preparation method of the molybdenum carbide-sulfur composite material according to claim 2 or 7, wherein the heat treatment temperature in the step 3) is 140 to 200 ℃ and the heat treatment time is 10 to 30 hours.
10. A lithium-sulfur battery, which comprises a positive electrode, a lithium negative electrode and an electrolyte, wherein the positive electrode comprises an active material, acetylene black and PVDF, and is characterized in that the active material is the molybdenum carbide-sulfur composite material in claim 1 or the molybdenum carbide-sulfur composite material obtained by the preparation method in any one of claims 2 to 9.
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| CN112216840A (en) * | 2020-10-13 | 2021-01-12 | 陕西科技大学 | Molybdenum disulfide/molybdenum nitride heterostructure composite material for lithium-sulfur battery electrode and preparation method thereof |
| CN114914426B (en) * | 2022-05-30 | 2024-02-23 | 大连理工大学 | Sulfur@carbon/molybdenum carbide sulfur cathode material and preparation method thereof |
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