CN111864209B - Preparation method and application of lithium-sulfur battery positive electrode material - Google Patents
Preparation method and application of lithium-sulfur battery positive electrode material Download PDFInfo
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- CN111864209B CN111864209B CN202010405900.XA CN202010405900A CN111864209B CN 111864209 B CN111864209 B CN 111864209B CN 202010405900 A CN202010405900 A CN 202010405900A CN 111864209 B CN111864209 B CN 111864209B
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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Abstract
The invention discloses a preparation method and application of a lithium-sulfur battery positive electrode material. The preparation method comprises the steps of 1) mixing a molybdenum source, a sulfur source, a carbon source, a silicon dioxide ball and an N, N-dimethylformamide solvent, and carrying out hydrothermal reaction on the mixed solution; 2) annealing the hydrothermal reaction product in an inert atmosphere; 3) removing the silica ball template in the product obtained in the step 2) so as to obtain a molybdenum disulfide/carbon composite hollow ball; 4) and mixing the molybdenum disulfide/carbon composite hollow sphere with sublimed sulfur, and heating to load sulfur in the hollow sphere so as to obtain the lithium-sulfur battery cathode material. The positive electrode material prepared by the method can improve the overall conductivity of the sulfur positive electrode material, can buffer the volume expansion of the sulfur positive electrode material, simultaneously avoids or remarkably reduces the shuttle effect caused by the dissolution of the long-chain lithium polysulfide compound, and slows down the capacity attenuation of the positive electrode material, thereby improving the electrochemical performance, the cycle performance and the service life of the battery.
Description
Technical Field
The invention belongs to the field of batteries, and particularly relates to a preparation method and application of a lithium-sulfur battery positive electrode material.
Background
With the coming of the energy crisis, the demand of people for energy conversion and storage devices is increasing, and the development of some novel energy storage devices is promoted. Lithium-sulfur batteries have an ultra-high theoretical specific capacity due to their unique conversion reaction mechanism, and are considered as candidates for next-generation novel high-performance energy storage devices. The anode is elemental sulfur, the cathode is metallic lithium, and based on the oxidation-reduction reaction of the anode and the cathode, the theoretical specific capacities are 1675 mAh.g–1And 3861mAh · g–1So that the batteryThe capacity density of the high-density glass is 2600 Wh/kg–1Is more than 5 times of the current lithium ion battery system. However, since elemental sulfur itself has poor conductivity, it is difficult to achieve good electron transfer between itself and the current collector as an active material. In addition, complete lithiation of elemental sulfur to the final product Li2S, which expands in volume to a large extent (80%), easily falls off from the current collector, resulting in loss of active material and capacity deterioration. Most importantly, a series of LiPSs (lithium polysulfide compounds) are generated in the discharge process of the sulfur positive electrode, and as long-chain LiPSs are easily dissolved in electrolyte, the long-chain LiPSs continuously migrate and are consumed between the positive electrode and the negative electrode in the electrode reaction process, so that active substances are continuously lost, which is called shuttle effect and is also a unique and urgent problem to be solved in the lithium sulfur battery.
Disclosure of Invention
The present invention is directed to solving the above-described related art problems to some extent. Therefore, the invention aims to provide a preparation method and application of a positive electrode material of a lithium-sulfur battery. The positive electrode material prepared by the method can improve the overall conductivity of the sulfur positive electrode material, relieve the volume expansion of the sulfur positive electrode material, simultaneously avoid or remarkably reduce the shuttle effect caused by the dissolution of long-chain LiPSs, slow down the capacity attenuation of the positive electrode material, improve the electrochemical performance and the cycle performance of a battery and prolong the service life of the battery.
According to a first aspect of the present invention, a method of making a positive electrode material for a lithium sulfur battery is presented. According to an embodiment of the invention, the method comprises:
(1) mixing a molybdenum source, a sulfur source, a carbon source, a silicon dioxide ball and an N, N-dimethylformamide solvent, and carrying out hydrothermal reaction on the mixed solution;
(2) annealing the hydrothermal reaction product in an inert atmosphere;
(3) removing the silica ball template in the product obtained in the step (2) so as to obtain a molybdenum disulfide/carbon composite hollow ball;
(4) and mixing the molybdenum disulfide/carbon composite hollow sphere with sublimed sulfur, and heating to load sulfur in the hollow sphere so as to obtain the lithium-sulfur battery cathode material.
According to the method for preparing the lithium-sulfur battery cathode material, provided by the embodiment of the invention, the molybdenum disulfide/carbon composite hollow sphere is synthesized by a sacrificial template method, and elemental sulfur is injected into the hollow sphere by a melting-diffusion method, so that the molybdenum disulfide/carbon hollow superstructure sulfur-loaded lithium-sulfur battery cathode material can be finally obtained. Compared with the prior art, the preparation method has at least the following advantages: 1) the elemental sulfur can be bound in the molybdenum disulfide/carbon composite hollow sphere, so that the function of physical confinement is achieved, and the volume expansion of the material can be buffered; 2) molybdenum disulfide is used as a polar material, has a strong adsorption effect on LiPSs, and can reduce shuttle effect caused by dissolution of long-chain LiPSs, so that capacity attenuation is slowed down; 3) the uniform composition of carbon and molybdenum disulfide can obviously improve the overall conductivity of the anode material and improve the electron transmission capability, thereby further improving the reaction rate of the battery; 4) the method is simple to operate and mild in condition, and the prepared anode material is novel in appearance, stable in structure, capable of being produced in a large scale and strong in practicability; 5) the prepared lithium-sulfur battery positive electrode material has the effects of sulfur confinement and chemical adsorption, can effectively solve the problems of poor conductivity, volume expansion and shuttle effect of a sulfur positive electrode, and obviously improves the electrochemical performance, the cycle performance and the service life of the battery.
In addition, the method for preparing the positive electrode material for the lithium-sulfur battery according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the invention, in the step (1), the mixed solution is stirred at a speed of 200 to 500r/min in advance, and then the hydrothermal reaction is performed.
In some embodiments of the present invention, in the step (1), the temperature of the hydrothermal reaction is 180 to 250 ℃, and the reaction time is 10 to 20 hours.
In some embodiments of the invention, in step (1), the molybdenum source is ammonium molybdate, the sulfur source is thiourea, and the carbon source is glucose.
In some embodiments of the present invention, the molar ratio of the thiourea to the ammonium molybdate is (1.5 to 3): 1, the mass ratio of the glucose to the ammonium molybdate is (4-6): 10, the mass ratio of the silicon dioxide balls to the ammonium molybdate is (5-7): 10.
in some embodiments of the present invention, performing step (2) further comprises: and cooling, centrifuging, washing and drying the hydrothermal reaction product.
In some embodiments of the invention, the centrifugation product is alternately washed with ethanol and deionized water 2-4 times, and then vacuum-dried for 12-24 hours.
In some embodiments of the invention, in step (2), the annealing treatment comprises: heating to 500-700 ℃ at a rate of 3-6 ℃/min and maintaining for 6-12 h.
In some embodiments of the invention, in the step (3), the product obtained in the step (2) reacts with 10% hydrofluoric acid solution for 2-4 hours, and then is washed to be neutral, so as to obtain the molybdenum disulfide/carbon composite hollow sphere.
In some embodiments of the invention, in the step (4), the mass ratio of the sublimed sulfur to the molybdenum disulfide/carbon composite hollow spheres is (2-4): 1, heating to 150-180 ℃ at the speed of 5-10 ℃/min and keeping for 12-15 h.
According to a second aspect of the present invention, a positive electrode material for a lithium-sulfur battery is provided. According to the embodiment of the invention, the lithium-sulfur battery cathode material is obtained by adopting the method for preparing the lithium-sulfur battery cathode material. The lithium-sulfur battery positive electrode material has better conductivity and relatively lower volume expansion rate, is not easy to have shuttle effect, and can obviously improve the electrochemical performance, the cycle performance and the service life of the battery.
According to a third aspect of the present invention, the present invention proposes the use of the positive electrode material obtained by the above method for preparing a positive electrode material for a lithium-sulfur battery in a lithium-sulfur battery. According to the embodiment of the invention, the lithium-sulfur battery cathode material obtained by the preparation method is applied to the lithium-sulfur battery, so that the battery has higher capacity, better cycling stability and longer service life.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a flowchart of a method of preparing a positive electrode material for a lithium sulfur battery according to one embodiment of the present invention.
Fig. 2 is a topographical view of a positive electrode material for a lithium-sulfur battery prepared according to one embodiment of the present invention.
Fig. 3 is a surface element analysis diagram of a positive electrode material of a lithium-sulfur battery prepared according to an embodiment of the present invention, in which fig. 3(a) is a topographical structure diagram of the positive electrode material of the lithium-sulfur battery, fig. 3(b) is a distribution diagram of elemental sulfur on the surface of the positive electrode material, fig. 3(c) is a distribution diagram of elemental molybdenum on the surface of the positive electrode material, and fig. 3(d) is a distribution diagram of elemental carbon on the surface of the positive electrode material.
Fig. 4 is a thermogravimetric analysis of a positive electrode material for a lithium sulfur battery prepared according to an embodiment of the present invention.
Fig. 5 is a graph comparing the cycle performance of cells assembled using final samples prepared according to examples of the present invention and comparative examples.
Fig. 6 is a comparison of the morphology of a positive electrode material for a lithium sulfur battery prepared according to an example of the present invention, in which fig. 6(a) is a graph showing the morphology of the positive electrode material for the lithium sulfur battery prepared in example 7, and fig. 6(b) is a graph showing the morphology of the positive electrode material for the lithium sulfur battery prepared in example 6; fig. 6(c) is a structural view of the morphology of the positive electrode material of the lithium sulfur battery prepared in example 8.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
According to a first aspect of the present invention, a method of making a positive electrode material for a lithium sulfur battery is presented. According to an embodiment of the invention, with reference to fig. 1, the method comprises: (1) mixing a molybdenum source, a sulfur source, a carbon source, a silicon dioxide ball and an N, N-dimethylformamide solvent, and carrying out hydrothermal reaction on the mixed solution; (2) annealing the hydrothermal reaction product in an inert atmosphere; (3) removing the silica ball template in the product obtained in the step (2) so as to obtain a molybdenum disulfide/carbon composite hollow ball; (4) and mixing the molybdenum disulfide/carbon composite hollow sphere with sublimed sulfur, and heating to load sulfur in the hollow sphere so as to obtain the lithium-sulfur battery cathode material. According to the method, a molybdenum disulfide/carbon composite hollow sphere is synthesized by a sacrificial template method, elemental sulfur is injected into the hollow sphere by a melting-diffusion method, and the molybdenum disulfide/carbon hollow superstructure sulfur-loaded lithium sulfur battery positive electrode material can be finally obtained, so that the overall conductivity of the sulfur positive electrode material can be improved, the volume expansion of the sulfur positive electrode material can be buffered, the shuttle effect caused by long-chain LiPSs dissolution is avoided or remarkably reduced, the capacity attenuation of the positive electrode material is slowed down, the electrochemical performance and the cycle performance of the battery are improved, and the service life of the battery is prolonged.
The method of preparing the positive electrode material for a lithium-sulfur battery in the above-described embodiment of the present invention is described in detail mainly from two aspects below.
Firstly, preparing molybdenum disulfide/carbon composite hollow ball
According to the embodiment of the invention, a molybdenum source, a sulfur source, a carbon source, silica spheres and an N, N-dimethylformamide solvent are mixed, and the mixed solution is subjected to hydrothermal reaction; and (3) annealing the hydrothermal reaction product in an inert atmosphere, and then removing a silicon dioxide ball template in the product so as to obtain the molybdenum disulfide/carbon composite hollow ball.
According to a specific embodiment of the invention, the mixed solution can be stirred at a speed of 200-500 r/min in advance and then subjected to hydrothermal reaction, so that a more uniform and stable mixed solution can be obtained, the morphology structure of a reaction product can be further improved, and the molybdenum disulfide/carbon composite hollow sphere with uniform two phases and a regular surface can be obtained.
According to another embodiment of the present invention, the temperature of the hydrothermal reaction may be 180 to 250 ℃, for example, 180 ℃, 190 ℃, 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃ or 250 ℃, and the reaction time may be 10 to 20 hours, for example, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours or 20 hours, and the inventors found that the two-phase uniform molybdenum disulfide/carbon hollow superstructure cannot be formed at too high or too low a hydrothermal reaction temperature, and the prepared molybdenum disulfide/carbon composite hollow spherical morphology is irregular. Further, if the hydrothermal reaction time is too short, the material cannot nucleate and grow, and if the reaction time is too long, the molybdenum disulfide lamella is too thick and stacked. According to the invention, by controlling the hydrothermal reaction conditions, the composite hollow sphere with regular appearance and uniform molybdenum disulfide/carbon two phases can be finally obtained.
According to another embodiment of the present invention, the type of the carbon source in the present invention is not particularly limited, and can be selected by those skilled in the art according to actual needs, for example, the carbon source can be glucose, dopamine, polyvinylpyrrolidone, etc.
According to another embodiment of the present invention, the molybdenum source may preferably be ammonium molybdate, the sulfur source may preferably be thiourea, and the carbon source may preferably be glucose, thereby being more advantageous in obtaining a molybdenum disulfide/carbon composite hollow sphere structure. More preferably, the molar ratio of thiourea to ammonium molybdate may be (1.5 to 3): 1, for example, 1.5, 2 or 3, and the mass ratio of glucose to ammonium molybdate may be (4 to 6): 10, the inventor finds that by controlling the ratio of thiourea to ammonium molybdate to glucose, the molybdenum disulfide/carbon composite hollow sphere is more favorably obtained, the uniformity of two phases of molybdenum disulfide/carbon can be further improved, and the molybdenum disulfide/carbon composite hollow sphere with a more regular shape is obtained; further, the mass ratio of the silicon dioxide balls to the ammonium molybdate can be (5-7): 10, the inventor finds that the shell thickness of the finally formed molybdenum disulfide/carbon composite hollow sphere can be adjusted by adjusting the mass ratio of the silicon dioxide spheres to the ammonium molybdate, and if the mass ratio of the silicon dioxide spheres to the ammonium molybdate is too small, the molybdenum disulfide/carbon composite layer formed on the silicon dioxide spheres is too thick, which not only affects the subsequent sulfur load, but also reduces the structural stability of the material and is not beneficial to the transmission of electrons. If the mass ratio of the silicon dioxide balls to the ammonium molybdate is too large, the molybdenum disulfide/carbon composite layer formed on the silicon dioxide balls is too thin, which is not only unfavorable for forming the molybdenum disulfide/carbon composite hollow balls, but also seriously influences the physical confinement effect on sulfur. According to the invention, by controlling the proportion of the silicon dioxide spheres and the ammonium molybdate, a molybdenum disulfide/carbon composite layer with a proper thickness can be formed on the silicon dioxide sphere template, so that the prepared molybdenum disulfide/carbon composite hollow sphere has a good confinement effect on sulfur and an effect of buffering volume expansion, and finally the anode material with a stable structure and excellent electrochemical performance is prepared.
According to still another embodiment of the present invention, before the annealing treatment, the annealing treatment may further include: and cooling, centrifuging, washing and drying the hydrothermal reaction product. The centrifugal product can be alternately washed for 2-4 times by adopting ethanol and deionized water, and then is dried in vacuum for 12-24 hours, and compared with the mode of singly washing by adopting ethanol or singly washing by adopting deionized water, the removal rate of impurity ions and organic solvents can be obviously improved by alternately washing the centrifugal product by adopting ethanol and deionized water, so that the preparation of the single and stable molybdenum disulfide/carbon composite hollow ball is facilitated.
According to yet another specific embodiment of the present invention, the annealing process may include: heating to 500-700 ℃ at the speed of 3-6 ℃/min and keeping for 6-12 hours, and the inventor finds that the annealing temperature directly influences the crystallization degree of the material, when the temperature is too low, organic carbon cannot be carbonized completely, and the crystallization of molybdenum disulfide is poor; and when the annealing temperature is too high, the molybdenum disulfide nanosheets can be sintered and agglomerated to form particles, which is not beneficial to the transmission of electrons.
According to another embodiment of the invention, a 10% hydrofluoric acid solution and the annealed hydrothermal reaction product can be mixed and reacted for 2-4 hours, so that the silica ball template is effectively removed, and a molybdenum disulfide/carbon composite hollow ball structure is obtained; and further, washing the obtained molybdenum disulfide/carbon composite hollow ball to be neutral.
Secondly, loading sulfur in the molybdenum disulfide/carbon composite hollow sphere to obtain the lithium-sulfur battery anode material
According to the embodiment of the invention, the molybdenum disulfide/carbon composite hollow sphere is mixed with sublimed sulfur and is subjected to heating treatment, so that sulfur can be loaded in the hollow sphere to obtain the lithium-sulfur battery cathode material.
The material feeding ratio, the reaction temperature and time and the calcination temperature in the process parameters have decisive influence on the performance of the final product. If the feeding ratio is not proper, the final product cannot be formed directly; if the reaction temperature is too high or too low, a two-phase uniform molybdenum disulfide/carbon hollow superstructure cannot be formed, and other irregular appearances can be formed; if the calcining temperature is too high or too low, the loading of sulfur is affected, and the sulfur cannot be well limited physically, so that the product performance is affected.
According to another embodiment of the invention, the mass ratio of the sublimed sulfur to the molybdenum disulfide/carbon composite hollow spheres can be (2-4): 1, preferably (2 to 3.5): the inventor finds that if the mass ratio of the sublimed sulfur to the molybdenum disulfide/carbon composite hollow sphere is too small, the loading amount of the sulfur is too low, and the comprehensive performance of the battery is directly influenced, and if the mass ratio of the sublimed sulfur to the molybdenum disulfide/carbon composite hollow sphere is too large, redundant sulfur can be attached to the outer surface of the hollow sphere, the contact between the material and electrolyte is influenced, and the electrochemical performance of the material is finally influenced. By controlling the proportion, the lithium-sulfur battery cathode material with moderate sulfur carrying capacity and excellent electrochemical performance can be obtained.
According to another embodiment of the invention, the heating treatment can be carried out at a rate of 5-10 ℃/min to 150-180 ℃ and kept for 12-15 h, the inventors found that if the temperature of the heating treatment is too low or too short, sulfur cannot sufficiently enter the hollow sphere, and if the temperature of the heating treatment is too high or too long, sulfur can be evaporated or attached to the outer surface of the hollow sphere again, that is, the temperature of the heating treatment is too low or too high, and the time of the heating treatment is too long or too short, both of which can affect the electrochemical performance of the material.
According to another embodiment of the invention, ammonium molybdate, thiourea, glucose and silica spheres are mixed with N, N-dimethylformamide solvent, stirred for a certain time at a speed of 200 to 500r/min, and then transferred to a polytetrafluoroethylene reaction kettle to be placed in a muffle furnace for high-temperature heating, wherein the temperature is controlled to be 200 to 250 ℃, the hydrothermal reaction time is 10 to 20 hours, the molar ratio of thiourea to ammonium molybdate is 1.5 to 3, the addition amount of glucose is (40 to 60) mg/10mg of ammonium molybdate, and the addition amount of silica spheres is (50 to 70) mg/100mg of ammonium molybdate; cooling, centrifuging, washing and drying the obtained hydrothermal reaction product, wherein the hydrothermal reaction product is alternately washed by ethanol and deionized water after being cooled, and then is dried in vacuum for 12-24 hours; placing the washed and dried hydrothermal reaction product in a tubular furnace, and annealing in an inert atmosphere, wherein the heating rate is controlled to be 5 ℃/min, the temperature is kept at 500-700 ℃, and the time is 6-12 h; removing a silicon dioxide template in the annealed hydrothermal reaction product by using a 10% hydrofluoric acid solution, reacting for 2-4 h, washing the reaction product to be neutral by using pure water, and drying in a vacuum drying oven at the temperature of 60-80 ℃ for 12-24 h to obtain a molybdenum disulfide/carbon composite hollow sphere; and blending the molybdenum disulfide/carbon composite hollow spheres and sublimed sulfur, then placing the mixture in a tubular heating furnace for heating, and then blowing to obtain the lithium-sulfur battery cathode material, wherein the mass ratio of the sublimed sulfur to the molybdenum disulfide/carbon composite hollow spheres is 2-4, the temperature rise rate of the tubular furnace is controlled at 5 ℃/min, the final temperature is 150-170 ℃, and the heating time is 12-15 hours.
In summary, according to the method for preparing the positive electrode material of the lithium sulfur battery in the embodiment of the invention, the molybdenum disulfide/carbon composite hollow sphere is synthesized by the sacrificial template method, and elemental sulfur is injected into the hollow sphere by the melting-diffusion method, so that the positive electrode material of the lithium sulfur battery with the molybdenum disulfide/carbon hollow superstructure carrying sulfur can be finally obtained. Compared with the prior art, the preparation method has at least the following advantages: 1) the elemental sulfur can be bound in the molybdenum disulfide/carbon composite hollow sphere, so that the function of physical confinement is achieved, and the volume expansion of the material can be buffered; 2) molybdenum disulfide has a strong adsorption effect on LiPSs as a polar material, and can reduce a shuttle effect caused by dissolution of long-chain LiPSs, so that capacity attenuation is slowed down; 3) the uniform composition of carbon and molybdenum disulfide can obviously improve the overall conductivity of the anode material and improve the electron transmission capability, thereby further improving the reaction rate of the battery; 4) the method is simple to operate and mild in condition, and the prepared anode material is novel in appearance, stable in structure, capable of being produced in a large scale and strong in practicability; 5) the prepared lithium-sulfur battery positive electrode material has the effects of sulfur confinement and chemical adsorption, can effectively solve the problems of poor conductivity, volume expansion and shuttle effect of a sulfur positive electrode, and obviously improves the electrochemical performance, the cycle performance and the service life of the battery.
According to a second aspect of the present invention, a positive electrode material for a lithium-sulfur battery is provided. According to the embodiment of the invention, the lithium-sulfur battery cathode material is obtained by adopting the method for preparing the lithium-sulfur battery cathode material. The lithium-sulfur battery positive electrode material has better conductivity and relatively lower volume expansion rate, is not easy to have shuttle effect, and can obviously improve the electrochemical performance, the cycle performance and the service life of the battery. It should be noted that the features and effects described for the above method for preparing the positive electrode material of the lithium-sulfur battery are also applicable to the positive electrode material of the lithium-sulfur battery, and are not repeated herein.
According to a third aspect of the present invention, the present invention proposes the use of the positive electrode material obtained by the above method for preparing a positive electrode material for a lithium-sulfur battery in a lithium-sulfur battery. According to the embodiment of the invention, the lithium-sulfur battery cathode material obtained by the preparation method is applied to the lithium-sulfur battery, so that the battery has higher capacity, better cycling stability and longer service life.
The scheme of the invention will be explained with reference to the examples. It will be appreciated by those skilled in the art that the following examples are illustrative of the invention only and should not be taken as limiting the scope of the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Example 1
Weighing 100mg of ammonium molybdate tetrahydrate, 60mg of thiourea, 40mg of glucose and 50mg of silicon dioxide spheres, adding 30mL of N, N-dimethylformamide, carrying out ultrasonic treatment for 20min to uniformly disperse, and then placing on a stirring table to stir for 30min at the stirring speed of 200 r/min. Then the mixed solution is transferred to a 100mL polytetrafluoroethylene reaction kettle with a stainless steel shell, sealed and put into an oven, the temperature is set to be 180 ℃, and the time is 10 hours. Washing the product after the hydrothermal reaction with pure water and absolute ethyl alcohol for 3 times respectively, and then placing the product in a vacuum drying oven for drying for 12 hours. And (3) placing the dried sample in a tube furnace, annealing at 500 ℃ in an argon atmosphere, wherein the heating rate is 5 ℃/min, the annealing time is 10h, and then naturally cooling to room temperature. And finally, removing the silicon dioxide template by using 10% hydrofluoric acid, reacting for 2 hours, washing to be neutral by using pure water, and drying at 60 ℃ for 12 hours to obtain the black powder which is the molybdenum disulfide/carbon composite hollow sphere. And weighing sublimed sulfur and the prepared molybdenum disulfide/carbon composite hollow sphere in a ratio of 2: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, placing the mixture in a heating furnace, heating at the rate of 10 ℃/min and the final temperature of 150 ℃ for 12 hours, and naturally cooling to obtain the final product, namely the molybdenum disulfide/carbon/sulfur composite cathode material, namely the lithium-sulfur battery cathode material. The prepared sample of the positive electrode material is shown in fig. 2.
Example 2
Weighing 100mg of ammonium molybdate tetrahydrate, 120mg of thiourea, 50mg of glucose and 60mg of silicon dioxide spheres, adding 30mL of N, N-dimethylformamide, carrying out ultrasonic treatment for 20min to uniformly disperse, and then placing on a stirring table to stir for 30min at the stirring speed of 200 r/min. Then the mixed solution is transferred to a 100mL polytetrafluoroethylene reaction kettle with a stainless steel shell, sealed and put into an oven, the temperature is set to be 180 ℃, and the time is 10 hours. Washing the product after the hydrothermal reaction with pure water and absolute ethyl alcohol for 3 times respectively, and then placing the product in a vacuum drying oven for drying for 12 hours. And (3) placing the dried sample in a tube furnace, annealing at 500 ℃ in an argon atmosphere, wherein the heating rate is 5 ℃/min, the annealing time is 10h, and then naturally cooling to room temperature. And finally, removing the silicon dioxide template by using 10% hydrofluoric acid, reacting for 2 hours, washing to be neutral by using pure water, and drying at 60 ℃ for 12 hours to obtain the black powder which is the molybdenum disulfide/carbon composite hollow sphere. And weighing sublimed sulfur and the prepared molybdenum disulfide/carbon composite hollow sphere in a ratio of 2: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, placing the mixture in a heating furnace, heating at the rate of 10 ℃/min and the final temperature of 150 ℃ for 12 hours, and then naturally cooling to obtain the final product, namely the molybdenum disulfide/carbon/sulfur composite cathode material. The surface element distribution of the prepared positive electrode material sample is shown in fig. 3.
Example 3
Weighing 100mg of ammonium molybdate tetrahydrate, 60mg of thiourea, 40mg of glucose and 50mg of silicon dioxide spheres, adding 30mL of N, N-dimethylformamide, carrying out ultrasonic treatment for 20min to uniformly disperse, and then placing on a stirring table to stir for 30min at the stirring speed of 200 r/min. Then the mixed solution is transferred to a 100mL polytetrafluoroethylene reaction kettle with a stainless steel shell, sealed and put into an oven, the temperature is set to be 200 ℃, and the time is 10 hours. Washing the product after the hydrothermal reaction with pure water and absolute ethyl alcohol for 3 times respectively, and then placing the product in a vacuum drying oven for drying for 12 hours. And (3) placing the dried sample in a tube furnace, annealing at 500 ℃ in an argon atmosphere, wherein the heating rate is 5 ℃/min, the annealing time is 10h, and then naturally cooling to room temperature. And finally, removing the silicon dioxide template by using 10% hydrofluoric acid, reacting for 2 hours, washing to be neutral by using pure water, and drying at 60 ℃ for 12 hours to obtain the black powder which is the molybdenum disulfide/carbon composite hollow sphere. And weighing sublimed sulfur and the prepared molybdenum disulfide/carbon composite hollow sphere in a ratio of 2: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, placing the mixture in a heating furnace, heating at the rate of 10 ℃/min and the final temperature of 150 ℃ for 12 hours, and then naturally cooling to obtain the final product, namely the molybdenum disulfide/carbon/sulfur composite cathode material.
Example 4
Weighing 100mg of ammonium molybdate tetrahydrate, 60mg of thiourea, 40mg of glucose and 50mg of silicon dioxide spheres, adding 30mL of N, N-dimethylformamide, carrying out ultrasonic treatment for 20min to uniformly disperse, and then placing on a stirring table to stir for 30min at the stirring speed of 200 r/min. Then the mixed solution is transferred to a 100mL polytetrafluoroethylene reaction kettle with a stainless steel shell, sealed and put into an oven, the temperature is set to be 200 ℃, and the time is 10 hours. Washing the product after the hydrothermal reaction with pure water and absolute ethyl alcohol for 3 times respectively, and then placing the product in a vacuum drying oven for drying for 12 hours. And (3) placing the dried sample in a tube furnace, annealing at 700 ℃ in an argon atmosphere, wherein the heating rate is 5 ℃/min, the annealing time is 6h, and then naturally cooling to room temperature. And finally, removing the silicon dioxide template by using 10% hydrofluoric acid, reacting for 2 hours, washing to be neutral by using pure water, and drying for 24 hours at the temperature of 60 ℃ to obtain the black powder which is the molybdenum disulfide/carbon composite hollow sphere. And weighing sublimed sulfur and the prepared molybdenum disulfide/carbon composite hollow sphere in a ratio of 2: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, placing the mixture in a heating furnace, heating at the rate of 10 ℃/min and the final temperature of 150 ℃ for 12 hours, and then naturally cooling to obtain the final product, namely the molybdenum disulfide/carbon/sulfur composite cathode material.
Example 5
Weighing 100mg of ammonium molybdate tetrahydrate, 60mg of thiourea, 40mg of glucose and 50mg of silicon dioxide spheres, adding 30mL of N, N-dimethylformamide, carrying out ultrasonic treatment for 20min to uniformly disperse, and then placing on a stirring table to stir for 30min at the stirring speed of 200 r/min. Then the mixed solution is transferred to a 100mL polytetrafluoroethylene reaction kettle with a stainless steel shell, sealed and put into an oven, the temperature is set to be 250 ℃, and the time is 10 hours. Washing the product after the hydrothermal reaction with pure water and absolute ethyl alcohol for 3 times respectively, and then placing the product in a vacuum drying oven for drying for 12 hours. And (3) placing the dried sample in a tube furnace, annealing at 600 ℃ in an argon atmosphere, wherein the heating rate is 5 ℃/min, the annealing time is 6h, and then naturally cooling to room temperature. And finally, removing the silicon dioxide template by using 10% hydrofluoric acid, reacting for 2 hours, washing to be neutral by using pure water, and drying for 24 hours at the temperature of 60 ℃ to obtain the black powder which is the molybdenum disulfide/carbon composite hollow sphere. And weighing sublimed sulfur and the prepared molybdenum disulfide/carbon composite hollow sphere in a ratio of 2: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, placing the mixture in a heating furnace, heating at the rate of 10 ℃/min and the final temperature of 150 ℃ for 12 hours, and then naturally cooling to obtain the final product, namely the molybdenum disulfide/carbon/sulfur composite cathode material.
Example 6
Weighing 100mg of ammonium molybdate tetrahydrate, 60mg of thiourea, 40mg of glucose and 50mg of silicon dioxide spheres, adding 30mL of N, N-dimethylformamide, carrying out ultrasonic treatment for 20min to uniformly disperse, and then placing on a stirring table to stir for 30min at the stirring speed of 200 r/min. Then the mixed solution is transferred to a 100mL polytetrafluoroethylene reaction kettle with a stainless steel shell, sealed and put into an oven, the temperature is set to be 200 ℃, and the time is 10 hours. Washing the product after the hydrothermal reaction with pure water and absolute ethyl alcohol for 3 times respectively, and then placing the product in a vacuum drying oven for drying for 12 hours. And (3) placing the dried sample in a tube furnace, annealing at 600 ℃ in an argon atmosphere, wherein the heating rate is 5 ℃/min, the annealing time is 6h, and then naturally cooling to room temperature. And finally, removing the silicon dioxide template by using 10% hydrofluoric acid, reacting for 2 hours, washing to be neutral by using pure water, and drying for 24 hours at the temperature of 60 ℃ to obtain the black powder which is the molybdenum disulfide/carbon composite hollow sphere. And then weighing sublimed sulfur and the prepared molybdenum disulfide/carbon composite hollow sphere in a ratio of 3: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, placing the mixture in a heating furnace, heating at the rate of 5 ℃/min and the final temperature of 160 ℃ for 12 hours, and naturally cooling to obtain the final product, namely the molybdenum disulfide/carbon/sulfur composite cathode material. Wherein, the thermogravimetric analysis chart of the prepared cathode material sample is shown as 4, the morphology thereof is shown as 6(b), and the cycle performance chart of the lithium-sulfur battery assembled by adopting the cathode material sample is shown as 5.
Comparative example 1
Sublimed sulfur was mixed with acetylene black in a ratio of 3: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, transferring the mixture into an ampoule bottle, exhausting air in the bottle by using a vacuum pump, and sealing the bottle. Placing the anode material in a heating furnace, heating at the rate of 5 ℃/min and the final temperature of 160 ℃ for 12h, and then naturally cooling to obtain the final product, namely the carbon/sulfur composite anode material. The cycle performance of the lithium-sulfur battery assembled by using the positive electrode material sample is shown in fig. 5.
Example 7
Weighing 100mg of ammonium molybdate tetrahydrate, 60mg of thiourea, 40mg of glucose and 50mg of silicon dioxide spheres, adding 30mL of N, N-dimethylformamide, carrying out ultrasonic treatment for 20min to uniformly disperse, and then placing on a stirring table to stir for 30min at the stirring speed of 200 r/min. Then the mixed solution is transferred to a 100mL polytetrafluoroethylene reaction kettle with a stainless steel shell, sealed and put into an oven, the temperature is set to be 200 ℃, and the time is 20 hours. Washing the product after the hydrothermal reaction with pure water and absolute ethyl alcohol for 3 times respectively, and then placing the product in a vacuum drying oven for drying for 12 hours. And (3) placing the dried sample in a tube furnace, annealing at 700 ℃ in an argon atmosphere, wherein the heating rate is 5 ℃/min, the annealing time is 6h, and then naturally cooling to room temperature. And finally, removing the silicon dioxide template by using 10% hydrofluoric acid, reacting for 2 hours, washing to be neutral by using pure water, and drying for 24 hours at the temperature of 60 ℃ to obtain the black powder which is the molybdenum disulfide/carbon composite hollow sphere. And weighing sublimed sulfur and the prepared molybdenum disulfide/carbon composite hollow sphere in a ratio of 2: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, placing the mixture in a heating furnace, heating at the rate of 5 ℃/min and the final temperature of 170 ℃ for 12 hours, and then naturally cooling to obtain the final product, namely the molybdenum disulfide/carbon/sulfur composite cathode material. The prepared cathode material has a morphological structure as shown in fig. 6 (a).
Example 8
Weighing 100mg of ammonium molybdate tetrahydrate, 60mg of thiourea, 40mg of glucose and 50mg of silicon dioxide spheres, adding 30mL of N, N-dimethylformamide, carrying out ultrasonic treatment for 20min to uniformly disperse, and then placing on a stirring table to stir for 30min at the stirring speed of 200 r/min. Then the mixed solution is transferred to a 100mL polytetrafluoroethylene reaction kettle with a stainless steel shell, sealed and put into an oven, the temperature is set to be 200 ℃, and the time is 10 hours. Washing the product after the hydrothermal reaction with pure water and absolute ethyl alcohol for 3 times respectively, and then placing the product in a vacuum drying oven for drying for 12 hours. And (3) placing the dried sample in a tube furnace, annealing at 700 ℃ in an argon atmosphere, wherein the heating rate is 5 ℃/min, the annealing time is 6h, and then naturally cooling to room temperature. And finally, removing the silicon dioxide template by using 10% hydrofluoric acid, reacting for 2 hours, washing to be neutral by using pure water, and drying for 24 hours at the temperature of 60 ℃ to obtain the black powder which is the molybdenum disulfide/carbon composite hollow sphere. And weighing sublimed sulfur and the prepared molybdenum disulfide/carbon composite hollow sphere in a ratio of 4: 1, grinding the mixture by using a mortar until the mixture is uniformly mixed, placing the mixture in a heating furnace, heating at the rate of 5 ℃/min and the final temperature of 180 ℃ for 12 hours, and then naturally cooling to obtain the final product, namely the molybdenum disulfide/carbon/sulfur composite cathode material. The morphology structure of the prepared cathode material is shown in fig. 6 (c).
Results and conclusions:
1. referring to fig. 2, it can be seen that the molybdenum disulfide/carbon/sulfur composite positive electrode material synthesized by the method of the above embodiment of the present invention has regular surface morphology and uniform particle size; referring to the elemental analysis of fig. 3, it can be seen that the cathode material product synthesized by the method of the above embodiment of the present invention contains three elements, i.e., Mo, S, and C, indicating that sulfur is successfully loaded into the molybdenum disulfide/carbon composite hollow sphere; referring to fig. 4, the thermogravimetric analysis shows that the sulfur content of the cathode material prepared in example 4 is about 75 wt%, indicating that the molybdenum disulfide/carbon composite hollow sphere is almost completely loaded with sulfur.
2. The molybdenum disulfide/carbon/sulfur composite cathode material prepared in examples 1-8 and the molybdenum disulfide/carbon/composite hollow sphere prepared in comparative examples 1-2 were evaluated respectively.
Under the same conditions, the positive electrode material prepared in example 6, the molybdenum disulfide/carbon/composite hollow sphere prepared in comparative example 1, and the carbon/sulfur composite positive electrode material prepared in comparative example 1 were used to prepare positive electrode sheets, and a lithium foil was used as a negative electrode sheet to assemble batteries, and the assembled batteries were subjected to a capacity retention rate test at a rate of 0.2C for 200 charge and discharge cycles, respectively, and the results are shown in fig. 5. As can be seen from fig. 5, the capacity retention rate of the battery assembled by the molybdenum disulfide/carbon/sulfur composite positive electrode material synthesized by the method according to the above embodiment of the present invention is higher after 200 cycles, and the cycle stability is better, which indicates that the molybdenum disulfide/carbon/sulfur composite positive electrode material synthesized by the method according to the above embodiment of the present invention has higher specific capacity and cycle stability.
3. Comparing the morphology structures of the molybdenum disulfide/carbon/sulfur composite cathode materials prepared in examples 6 to 8, it can be seen from fig. 6 that the addition amount of the sublimed sulfur has a great influence on the morphology structure of the finally prepared cathode material. As shown in fig. 6(a) and 6(b), when the added amount of sulfur is 67 wt% and 75 wt%, respectively, the sulfur content is less, the elemental sulfur attached to the surface of the nanosphere is less, and most of the sulfur has been injected into the interior of the hollow nanosphere; referring to fig. 6(c), when the amount of sulfur loaded in the positive electrode material reaches 80 wt%, the amount of sulfur loaded is too large, and an excessive amount of elemental sulfur is coated on the surface of the hollow spheres. Therefore, the mass ratio of the sublimed sulfur to the molybdenum disulfide/carbon composite hollow spheres has great influence on the shape structure of the finally prepared cathode material, and the final electrochemical performance of the material is also determined.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (9)
1. A method of making a positive electrode material for a lithium sulfur battery, comprising:
(1) mixing a molybdenum source, a sulfur source, a carbon source, a silicon dioxide ball and an N, N-dimethylformamide solvent, and carrying out hydrothermal reaction on the mixed solution;
(2) annealing the hydrothermal reaction product in an inert atmosphere;
(3) removing the silica ball template in the product obtained in the step (2) so as to obtain a molybdenum disulfide/carbon composite hollow ball;
(4) mixing the molybdenum disulfide/carbon composite hollow sphere with sublimed sulfur, heating the mixture to load sulfur into the hollow sphere, and finally obtaining the lithium-sulfur battery cathode material,
in the step (1), the molybdenum source is ammonium molybdate, the sulfur source is thiourea, the carbon source is glucose, and the molar ratio of thiourea to ammonium molybdate is (1.5-3): 1, the mass ratio of the glucose to the ammonium molybdate is (4-6): 10, the mass ratio of the silicon dioxide balls to the ammonium molybdate is (5-7): 10,
in the step (4), the mass ratio of the sublimed sulfur to the molybdenum disulfide/carbon composite hollow spheres is (2-3.5): 1, heating to 150-180 ℃ at the speed of 5-10 ℃/min and keeping for 12-15 h.
2. The method according to claim 1, wherein in the step (1), the hydrothermal reaction is further performed after the mixed solution is stirred at a rate of 200 to 500r/min in advance.
3. The method according to claim 1 or 2, wherein in the step (1), the temperature of the hydrothermal reaction is 180-250 ℃ and the reaction time is 10-20 h.
4. The method of claim 1, wherein step (2) is further preceded by: and cooling, centrifuging, washing and drying the hydrothermal reaction product.
5. The method as claimed in claim 4, wherein the centrifuged product is alternately washed with ethanol and deionized water 2-4 times and then vacuum-dried for 12-24 hours.
6. The method of claim 4, wherein in step (2), the annealing process comprises: heating to 500-700 ℃ at a rate of 3-6 ℃/min and maintaining for 6-12 h.
7. The method according to claim 1 or 6, wherein in the step (3), the product obtained in the step (2) is reacted with 10% hydrofluoric acid solution for 2-4 h and then washed to be neutral, so as to obtain the molybdenum disulfide/carbon composite hollow sphere.
8. A lithium-sulfur battery positive electrode material prepared by the method of any one of claims 1 to 7.
9. The use of the positive electrode material of the lithium-sulfur battery according to claim 8 or the positive electrode material prepared by the method according to any one of claims 1 to 7 in a lithium-sulfur battery.
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| CN104934602A (en) * | 2015-06-19 | 2015-09-23 | 上海交通大学 | Molybdenum disulfide/carbon composite material and preparation method thereof |
| CN105047914A (en) * | 2015-05-28 | 2015-11-11 | 东南大学 | Lithium-ion battery anode material molybdenum disulfide/carbon and preparation method thereof |
| CN107275600A (en) * | 2017-05-31 | 2017-10-20 | 浙江大学 | The preparation method of molybdenum disulfide/carbon composite of hollow sphere |
| CN108232164A (en) * | 2018-01-15 | 2018-06-29 | 中南大学 | A kind of lithium sulfur battery anode material and preparation method thereof |
| CN108649194A (en) * | 2018-04-26 | 2018-10-12 | 复旦大学 | Graphene-supported molybdenum disulfide lithium sulfur battery anode material and preparation method thereof |
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| CN105047914A (en) * | 2015-05-28 | 2015-11-11 | 东南大学 | Lithium-ion battery anode material molybdenum disulfide/carbon and preparation method thereof |
| CN104934602A (en) * | 2015-06-19 | 2015-09-23 | 上海交通大学 | Molybdenum disulfide/carbon composite material and preparation method thereof |
| CN107275600A (en) * | 2017-05-31 | 2017-10-20 | 浙江大学 | The preparation method of molybdenum disulfide/carbon composite of hollow sphere |
| CN108232164A (en) * | 2018-01-15 | 2018-06-29 | 中南大学 | A kind of lithium sulfur battery anode material and preparation method thereof |
| CN108649194A (en) * | 2018-04-26 | 2018-10-12 | 复旦大学 | Graphene-supported molybdenum disulfide lithium sulfur battery anode material and preparation method thereof |
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