CN107732202B - Preparation method of lithium-sulfur battery positive electrode material - Google Patents
Preparation method of lithium-sulfur battery positive electrode material Download PDFInfo
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Abstract
The invention relates to a preparation method of a lithium-sulfur battery anode material. According to the method, a graphene oxide solution and a silicon dioxide dispersion solution are mixed and then added with ammonium bicarbonate, and then the sulfur/nitrogen-doped porous graphene composite lithium-sulfur battery positive electrode material is prepared through a process of ball milling and sulfur doping by a hot melting method. The invention overcomes the defects of low effective load capacity of sulfur, obvious shuttle effect of polysulfide, obvious volume expansion effect of the lithium-sulfur battery and unstable electrochemical performance of the battery in the anode material of the lithium-sulfur battery prepared by the prior art.
Description
Technical Field
The technical scheme of the invention relates to a preparation method of a high-specific-capacity lithium-sulfur battery positive electrode material, in particular to a method for preparing a sulfur/porous nitrogen-doped graphene composite lithium-sulfur battery positive electrode material by preparing porous nitrogen-doped graphene as a sulfur carrier material through a template method and then doping sulfur through a ball milling method and a hot melting method, and belongs to the field of material chemistry.
Background
With the rapid development of the related fields of portable electronic products, electric vehicles, energy storage and the like, higher and higher requirements are put forward on the performance of the battery. Therefore, it is of great strategic importance to develop a novel lithium ion secondary battery having high performance, low cost and environmental friendliness. At present, the theoretical specific capacity of the commercialized lithium ion battery is limited by the theoretical specific capacity of 300mAh/g, and obviously cannot meet the requirement on the practical application quality of the lithium ion battery, and the theoretical specific capacity of the novel lithium-sulfur battery is about five times of the theoretical specific capacity of the commercial lithium ion battery (the theoretical specific capacity is 1675mAh/g, and the specific energy is 2500Wh/kg), and the novel lithium-sulfur battery is considered to be one of the high-energy batteries with the most development potential.
However, lithium sulfur batteries still present some key challenges in practical applications. First, pure sulfur is an electronic and ionic insulator at room temperature (conductivity 5X 10-30)S·cm-1) The transport of electrons and ions in the positive electrode using sulfur as a positive electrode material is very difficult. Secondly, the intermediate product lithium polysulfide formed in the charging and discharging process is easily dissolved in the electrolyte solution, so that the electroactive substance on the positive electrode is pulverized, dropped and dissolved to lose, the lithium polysulfide dissolved in the electrolyte is diffused to the lithium metal negative electrode, and the lithium sulfide generated by the reaction is precipitatedAnd precipitates on the surface of the negative electrode, resulting in an increase in the internal resistance of the battery, and ultimately in a decline in the capacity of the battery. Third, sulfur and final product Li2The sulfur positive electrode undergoes volume expansion and fragmentation (expansion ratio of 76%) depending on the density of S, which results in poor cycle stability of the lithium-sulfur battery. In the prior art, a scheme for improving the performance of a lithium-sulfur battery is to mechanically compound elemental sulfur and a porous material with a high pore structure by a filling, mixing or coating method to form a positive electrode composite material, so that the lithium ion conductivity of a sulfur-based positive electrode and the cycle performance of the battery are improved. The porous material is required to: firstly, the catalyst has chemical stability and does not react with polysulfide and metallic lithium; secondly, insoluble in electrolyte; and thirdly, the lithium ion conductivity is higher.
Graphene has the excellent characteristics of excellent conductivity, high chemical stability, large specific surface area, strong mechanical property, unique two-dimensional porous network geometric structure and the like, can form a coating structure with sulfur simply and easily, and can improve the electrochemical activity of elemental sulfur, shorten an electron and ion transmission path, limit the dissolution of polysulfide and further improve the overall performance of the lithium-sulfur battery by utilizing the graphene to modify the lithium-sulfur battery. The prior art on the research of sulfur/graphene composite cathode materials is also reported: CN105609773A reports a preparation method of a sulfur-doped three-dimensional structure lithium-sulfur battery positive electrode material, wherein a hydrothermal method is adopted to generate three-dimensional sulfur-doped graphene by taking sodium benzenesulfonate as a sulfur source, and the sulfur-doped graphene is added into an N-methylpyrrolidone solution to perform ultrasonic reaction with Ketjen black to form the three-dimensional structure lithium-sulfur battery positive electrode material. CN201310153983.8 reports a preparation method of a sulfur-graphene composite structure positive electrode material for a lithium-sulfur battery, which comprises the steps of firstly preparing sulfur powder, an organic amine dispersion liquid and a graphene organic solvent, mixing the two solutions to obtain a third dispersion liquid, and performing solid-liquid separation by dropping water or an acid solution to obtain the positive electrode material for the lithium-sulfur battery. CN201610671807.7 reports a preparation method of a foamed graphene lithium sulfur battery positive electrode plate, which includes ball-milling and mixing graphene oxide and polyacrylonitrile, dispersing the mixture in a mixed solution of ethanol and water, soaking the solution in nickel foam to make the graphene oxide enter the nickel foam, performing heat treatment to obtain the foamed graphene, and finally smearing sulfur on the surface of a sample to perform sulfur doping to obtain the lithium sulfur battery positive electrode material. CN201710242972.5 reports a preparation method of a lithium-sulfur battery positive electrode material, which is a method for preparing a boron-doped graphene/sulfur composite three-dimensional structure lithium-sulfur battery positive electrode material by one-step completion of graphene oxide reduction, boron doping and solvothermal reaction.
Although the prior art of the sulfur/graphene composite cathode material improves the performance of the lithium-sulfur battery to a certain extent, the common defects are as follows: the effective load capacity of sulfur in the positive electrode material is low, the shuttle effect of polysulfide is obvious, the volume expansion effect of the lithium-sulfur battery is obvious, the electrochemical performance of the battery is unstable, the material yield is low, and the feasibility of industrial production is poor.
Disclosure of Invention
The invention aims to provide a preparation method of a lithium-sulfur battery cathode material aiming at the defects in the prior art. According to the method, silicon dioxide microspheres are introduced as a sulfur carrier material, and then a sulfur/nitrogen-doped porous graphene composite lithium-sulfur battery positive electrode material is prepared through a process of ball milling and sulfur doping by a hot melting method. The invention overcomes the defects of low effective load capacity of sulfur, obvious shuttle effect of polysulfide, obvious volume expansion effect of the lithium-sulfur battery and unstable electrochemical performance of the battery in the anode material of the lithium-sulfur battery prepared by the prior art.
The technical scheme adopted by the invention for solving the technical problem is as follows:
the preparation method of the lithium-sulfur battery positive electrode material comprises the following steps
Step one, preparing graphene oxide:
preparing 1-10 mg/mL graphene oxide aqueous solution;
step two, preparing nitrogen-doped porous graphene:
mixing the solution A and the solution B to obtain a mixed dispersion liquid C, adding ammonium bicarbonate into the mixed dispersion liquid C to obtain a mixed dispersion liquid D, performing ultrasonic dispersion on the mixed dispersion liquid D by using an ultrasonic dispersion instrument for 1-5 hours to obtain a graphene oxide-silicon dioxide uniformly mixed suspension containing nitrogen source ammonium bicarbonate, placing the suspension in a high-pressure reaction kettle with a polytetrafluoroethylene lining, and performing hydrothermal reduction at 100-200 ℃ for 6-24 hours; washing a product obtained by the reaction with deionized water, and then carrying out vacuum drying treatment to obtain the nitrogen-doped graphene-silicon dioxide composite material; then soaking the graphene in hydrofluoric acid for 6-24 hours to obtain nitrogen-doped porous graphene;
wherein the solution A is a graphene oxide solution with the concentration of 1-10 mg/mL, and the solution B is a silicon dioxide dispersion liquid with the concentration of 1-100 mg/mL and the diameter of microspheres of 10-300 nm; the volume ratio is solution A: the solution B is 1: 1-3; adding 0.1-0.5 g of ammonium bicarbonate into every 10-50 mL of the mixed dispersion liquid C;
step three, preparing the positive electrode material of the sulfur/nitrogen-doped porous graphene composite structure lithium-sulfur battery:
putting the porous nitrogen-doped graphene prepared in the second step and pure-phase nano sulfur powder into a ball milling tank, mixing and processing for 3-5 h by using a planetary ball mill, putting the mixture obtained after ball milling into a tubular furnace under the protection of nitrogen, and carrying out heat treatment for 8-24 h at 100-200 ℃ to obtain the sulfur/porous nitrogen-doped graphene composite lithium-sulfur battery anode material;
wherein the mass ratio of porous nitrogen-doped graphene: pure-phase nano sulfur powder is 1: 3-10.
In the second step, ultrasonic dispersion is carried out by an ultrasonic dispersion instrument under the power of 300-650W.
In the second step, the hydrofluoric acid is 5-40% in mass percentage concentration.
In the third step, the rotating speed of the planetary ball mill is 200-600 rpm.
And in the third step, the flow rate of the nitrogen is 100-250 mL/min.
According to the preparation method of the positive electrode material of the lithium-sulfur battery, the graphene can be prepared by a plurality of existing well-known technologies (such as hummers method, solid/liquid phase stripping and the like);
in the above method for preparing the positive electrode material of the lithium-sulfur battery, the raw materials are commercially available, and silica dispersions with different particle sizes are commercially available as template materials, and the equipment and process used are well known to those skilled in the art.
The invention has the following beneficial effects:
the hydrothermal method adopted in the preparation of the porous nitrogen-doped graphene sulfur-carrying material is the most convenient and high-yield synthesis method, and the commercial production is easy; the selected silicon dioxide pellets as the template are carefully selected, the silicon dioxide pellets are low in price, high in chemical stability and high in thermal stability in the current commercially available template, the pore-forming effect in the hydrothermal synthesis process is obvious, and the pore-forming scale controllability is high; in the introduction of nitrogen doping, the ammonium bicarbonate is low in price, the raw material graphene oxide subjected to hydrothermal synthesis has oxygen-containing groups such as-COOH, -OH and the like, the nitrogen doping effect introduced by the ammonium bicarbonate in the hydrothermal process is more obvious, and the nitrogen doping is carefully designed when the nitrogen doping is introduced in situ.
The conductivity of the graphene is good, but the pore-forming easiness degree is possibly inferior to that of the polymer and the metal oxide, but the conductivity of the polymer and the metal oxide is too poor, so that the benefit of modifying the graphene into a porous structure is huge, the experimental scheme is skillfully and meticulously designed, the difficulty is broken through, the experimental scheme is simple, the yield is high, and the industrial production prospect is achieved.
The concrete expression is as follows:
(1) in the design process, in order to solve the problems of low active material loading capacity and low active material utilization rate in the conventional lithium-sulfur battery positive electrode material, the invention innovatively provides a method for preparing the sulfur/nitrogen-doped porous graphene composite structure lithium-sulfur battery positive electrode material by combining a template method and a nitrogen doping technology, completing nitrogen element doping and pore-forming of graphene in one step through a hydrothermal approach, and then carrying out sulfur doping through a ball milling and hot melting method. Firstly, through structural modification of graphene, the graphene is converted from an original lamellar structure into a porous structure, so that the energy barrier of the graphene structure is reduced, and the efficiency of a sulfur inlet hole structure in a sulfur carrying process is improved; secondly, the nitrogen-doped porous graphene structure has a higher specific surface area than a common lamellar stack type graphene structure in the prior art, ensures that sulfur can completely enter the porous graphene, ensures that the real sulfur-carrying amount of the nitrogen-doped porous graphene structure is obviously superior to that of the conventional common lamellar graphene structure, has an effective sulfur-carrying amount up to 76% (shown in figure 2), obviously improves the electrochemical performance of the lithium-sulfur battery anode material, has small discharge capacity attenuation in the circulating process, and obviously improves the circulating stability.
(2) In the design process, the structural problem of the carbon-sulfur composite material in the lithium-sulfur battery anode material is fully considered, the graphene is structurally modified before sulfur doping, silicon dioxide is used as a template, the graphene is reduced in one step by a hydrothermal method, and nitrogen doping is carried out to obtain a porous nitrogen-doped graphene structure, so that the microstructure of the sulfur carrier material is regulated. The sulfur is doped by adopting a hot melting method so that the sulfur uniformly enters the preset micro-nano pore channel, a carbon-sulfur core-shell structure is effectively formed, the modified nitrogen-doped porous graphene structure can effectively coat the sulfur, and the volume expansion effect of the lithium-sulfur battery is effectively solved while the conductivity of the anode material is remarkably improved. Therefore, the lithium-sulfur battery positive electrode material prepared by the invention effectively inhibits the volume expansion effect in the charging and discharging processes, and the conductivity is obviously improved.
(3) In the design process of the invention, the problem of structural control of the carbon/sulfur composite material in the lithium-sulfur battery anode material is fully considered, and the excellent electrochemical performance of the electrode material is ensured through the microstructure control of the composite material, namely the microstructure of the carbon/sulfur composite material is regulated and controlled by a nitrogen doping method. According to the invention, ammonium bicarbonate is used as a nitrogen source and graphene oxide is used for preparing the nitrogen-doped porous graphene through a hydrothermal method, and nitrogen atoms have strong electron adsorption capacity, so that part of carbon atoms can be replaced without changing the crystal structure of the graphene, thereby improving the conductivity of the carbon material, generating an adsorption effect on polysulfide in the charge-discharge process, remarkably reducing the shuttle effect of the polysulfide, and further effectively improving the cycle performance of the lithium-sulfur battery. Therefore, the invention improves the cycle performance of the lithium-sulfur battery anode material by controlling the microstructure of the lithium-sulfur battery anode material.
Compared with the prior art, the method provided by the invention has the following remarkable improvements:
(1) the prior art CN201710242972.5 has the following fundamental defects in the process of preparing the positive electrode material of the lithium-sulfur battery: (a) according to the technology, sulfur is doped in situ by a hydrothermal method, graphene and sulfur are compounded in the hydrothermal process, the sulfur and the graphene are suspended in water respectively and do not form a composite structure inevitably in the hydrothermal process, even if the sulfur and the graphene are compounded together, the sulfur is only attached to the surface of the graphene, the real sulfur carrying capacity is not high, the initial capacity is high in the circulating process, the capacity reduction speed is high, the problems that the active substance loading capacity is small and the active substance utilization rate is low in the existing lithium-sulfur battery positive electrode material can not be effectively solved, and the discharge stability of the lithium-sulfur battery is difficult to realize. More importantly, the graphene is not structurally modified, the original layer sheet structure of the graphene is still maintained, the graphene sheets are inevitably stacked again in the drying process, the specific surface area of the graphene sheets is reduced, and the volume expansion effect of the lithium-sulfur battery is difficult to solve. In addition, the diffusion of sulfur is difficult to effectively inhibit by the lamellar graphene structure, the energy barrier of the stacked graphene structure is high, the difficulty of sulfur entering the graphene structure is correspondingly increased, and the effective load of sulfur is difficult to form. (b) A large number of researches show that the graphene has excellent mechanical property, heat conducting property and electric conducting property, and can improve the electrochemical property of the lithium-sulfur battery after being compounded with sulfur, but the structure of the carbon-sulfur composite material can directly influence the electric conducting property of the positive electrode material of the lithium-sulfur battery and the inhibiting capability of the positive electrode material on the volume expansion effect of an electrode. The patent technology adopts an in-situ sulfur doping method, and is limited by the influence of different required reaction energies in different areas in the hydrothermal reduction process of graphene in the sulfur doping process. The graphene oxide prepared by the improved Hummers method is not uniform in layer number, and usually shows that 2-20 layers are different, and the number of oxygen-containing groups included in the graphene oxide with different layer numbers is different inevitably in the hydrothermal process, so that the energy required by the graphene with the large layer number is large, and the energy required by the graphene with the small layer number is small in the reaction process, so that the phenomenon of uneven loading of sulfur is generated in different areas in the in-situ sulfur doping process, the carbon-sulfur composite material has structural defects, and sulfur in partial areas is exposed on the surface of the graphene, so that the conductivity of the cathode material is reduced. In conclusion, the lithium-sulfur battery cathode material prepared in the patent has low and uneven sulfur loading amount and high capacity reduction speed, and cannot effectively solve the problems of low active material loading amount and low utilization rate, obvious volume expansion effect and poor conductivity of the conventional lithium-sulfur battery cathode material. The sulfur/nitrogen-doped porous graphene composite lithium-sulfur battery positive electrode material prepared by the method completely overcomes the defects of CN201710242972.5 in the prior art.
(2) The basic defects of the prior art CN201610671807.7 in the process of preparing the positive plate of the foam graphene lithium-sulfur battery are as follows: this patent is to the structural modification of graphite alkene be through the porosity of foam nickel material to it prepares porous graphite alkene as the template, accomplish the complex of sulphur-carbon through scribbling the technology that sulphur powder carries out heat treatment, the foam graphite alkene of not only preparing has structural defect, use to scribble the mode and also can't realize the good complex of sulphur and graphite alkene in addition, lead to the uneven distribution of sulphur, graphite alkene is not high to the effective load capacity of sulphur, positive electrode material electric conductivity is poor, do not solve lithium sulphur battery positive electrode material sulphur and carry the low, electric conductivity is poor, shuttle effect obvious shortcoming. The sulfur/nitrogen-doped porous graphene composite lithium-sulfur battery cathode material prepared by the method completely overcomes the defects of CN201610671807.7 in the prior art.
(3) The CN201310153983.8 in the prior art has the following fundamental defects in the process of preparing the positive electrode material of the sulfur-graphene composite structure lithium-sulfur battery: the method adopts a solid-liquid separation process to prepare the lithium-sulfur battery cathode material with a sulfur-graphene composite structure, firstly, an organic amine dispersion liquid of sulfur and an organic solvent dispersion liquid of graphene are mixed in a sulfur doping process, and then, a graphene-sulfur compound is separated out in a mode of adding water or acid liquid, sulfur and graphene can only be simply mixed in the process of separating out the graphene-sulfur compound from a mixed solution, and the sulfur loading is low and uneven; in the dripping process, the solution concentration is continuously reduced due to the precipitation of the graphene-sulfur compound, the sulfur-carrying amount of successively precipitated samples is obviously different, the sulfur-carrying amount of the later precipitated sample is obviously lower than that of the first precipitated sample, the uneven sulfur-carrying amount can cause a shuttle effect of polysulfide, the volume expansion effect of the electrode material is obvious, and the circulation stability in the charging and discharging process is poor. The sulfur/nitrogen-doped porous graphene composite lithium-sulfur battery positive electrode material prepared by the method completely overcomes the defects of CN201310153983.8 in the prior art.
(4) According to the method, through selection and proportion regulation of raw materials, design of a preparation process and control of an implementation process, the nitrogen-doped porous graphene with low cost, high yield and a stable structure is prepared innovatively, and the industrial applicability is strong; through the design and regulation of the sulfur doping process, sulfur is completely coated on the nitrogen-doped porous graphene to form a stable carbon-sulfur coating structure, the effective load of sulfur in the lithium-sulfur battery anode material is obviously improved, as shown in (figure 2), the mass percentage of sulfur is about 76%, the shuttle effect of polysulfide and the volume expansion effect of the lithium-sulfur battery are effectively avoided, and the lithium-sulfur battery has excellent electrochemical performance and extremely strong cycle stability.
(5) As shown in figure 4, the first charge-discharge specific capacity of the lithium-sulfur battery prepared by the method is 1537mAh/g at 0.1 ℃, the lithium-sulfur battery has high discharge capacity and excellent cycling stability, and the electrochemical performance of the lithium-sulfur battery is obviously superior to that of the lithium-sulfur battery prepared by the prior art.
(6) The invention relates to a preparation method of a lithium-sulfur battery positive electrode material with the characteristics of high yield and industrial feasibility.
Drawings
The invention is further illustrated with reference to the following figures and examples.
Fig. 1X-ray diffraction pattern of the sulfur/nitrogen-doped porous graphene composite prepared in example 1.
Fig. 2 is a thermogravimetric plot of the sulfur/nitrogen-doped porous graphene composite material prepared in example 1.
Fig. 3 is a scanning electron microscope photograph of the nitrogen-doped porous graphene prepared in example 1.
Fig. 4 is a first electrochemical charge-discharge curve of the positive electrode material of the sulfur/nitrogen-doped porous graphene composite structure lithium-sulfur battery prepared in example 1.
Detailed Description
Example 1:
step one, preparing graphene oxide:
preparing 2mg/mL graphene oxide aqueous solution; the graphene oxide is a known material, and is prepared by an improved Hummers method. The following examples are the same;
step two, preparing nitrogen-doped porous graphene:
uniformly mixing a graphene oxide solution A with the concentration of 2mg/mL and a silicon dioxide dispersion liquid B with the concentration of 50mg/mL and the diameter of a microsphere of 300nm according to the volume ratio of the solution of 1:1 to obtain a mixed dispersion liquid C, adding 0.5g of ammonium bicarbonate into the 50m mixed dispersion liquid C to obtain a mixed dispersion liquid D, performing ultrasonic dispersion on the mixed dispersion liquid D by using an ultrasonic disperser for 5 hours to obtain a graphene oxide-silicon dioxide uniformly mixed suspension containing ammonium bicarbonate as a nitrogen source, placing the suspension in a high-pressure reaction kettle with a polytetrafluoroethylene lining, and performing hydrothermal reduction for 12 hours at the temperature of 200 ℃; washing a product obtained by the reaction with deionized water, then carrying out vacuum drying treatment, and soaking the nitrogen-doped graphene-silicon dioxide composite material obtained by drying in hydrofluoric acid with the mass percentage concentration of 10% for 24 hours to etch the silicon dioxide ball serving as the template, thus obtaining a nitrogen-doped porous graphene sample;
step three, preparing the positive electrode material of the sulfur/nitrogen-doped porous graphene composite structure lithium-sulfur battery:
putting the porous nitrogen-doped graphene prepared in the second step and pure-phase nano sulfur powder into a ball milling tank, mixing and processing for 5 hours by using a planetary ball mill, putting a mixture obtained after ball milling into a tubular furnace under the protection of nitrogen, and carrying out heat treatment for 12 hours at 150 ℃ to obtain a sulfur/porous nitrogen-doped graphene composite lithium-sulfur battery positive electrode material;
wherein the mass ratio of porous nitrogen-doped graphene: pure phase nano sulfur powder is 1: 4;
in the second step, ultrasonic dispersion is carried out by an ultrasonic dispersion instrument under 650W power.
In the third step, the rotating speed of the planetary ball mill is 400 rpm.
The flow rate of nitrogen in the third step is 150 mL/min.
According to the preparation method of the positive electrode material of the lithium-sulfur battery, the graphene can be prepared by a plurality of existing well-known technologies (such as hummers method, solid/liquid phase stripping and the like);
in the above method for preparing the positive electrode material of the lithium-sulfur battery, the raw materials are commercially available, and silica dispersions with different particle sizes are commercially available as template materials, and the equipment and process used are well known to those skilled in the art.
Fig. 1 is data obtained by an X-ray diffraction test, and X-ray diffraction patterns of the sulfur/nitrogen-doped porous graphene composite material (shown by a curve ● in the figure), the nitrogen-doped porous graphene material (shown by a curve ■ in the figure) and pure-phase nano sulfur (shown by a curve a in the figure) are respectively shown in the figure. The characteristic peak of sulfur accompanying the graphene characteristic peak in the sulfur/nitrogen-doped porous graphene composite electrode material is obvious, and the characteristic peak indicates that the sulfur in the composite material is rich and uniformly coated by the graphene. The nitrogen-doped porous graphene sample without introduced sulfur has no characteristic peak (about 10 degrees) of graphite oxide, and only has characteristic peaks (23 degrees and 43 degrees) of graphene, which shows that the reduction is relatively thorough in the hydrothermal process, and the purity of the sample is high.
Fig. 2 is data obtained by a differential thermal analyzer test, and the data in the graph shows that the sulfur content in the sulfur/nitrogen-doped porous graphene composite material is about 76% by mass, which indicates that the composite material has a large specific surface area, an obvious porous structure and a good sulfur coating effect.
Fig. 3 is a microscopic structure diagram photographed by a scanning electron microscope, and it can be seen from the diagram that the nitrogen-doped porous graphene has an extremely rich pore structure, which is a great help for sulfur storage, and sulfur is difficult to run away after entering the pore structure, so that the lithium-sulfur battery cathode material prepared by the present invention has excellent cycle performance.
Fig. 4 is an electrochemical constant current charge and discharge curve of a button-type test assembled by the electrode material and a lithium sheet prepared in the patent and tested by a novei charge and discharge tester, and it can be seen from the figure that the first discharge capacity of the material is up to 1537mAh/g at a current density of 0.1C, a reaction platform is arranged in the charging process, two reaction platforms are arranged in the discharging process, and no redundant side reaction platform indicates that the anode material has excellent charge and discharge stability in the circulating process.
Example 2:
step one, preparing graphene oxide:
preparing 5mg/mL graphene oxide aqueous solution;
step two, preparing nitrogen-doped porous graphene:
uniformly mixing a graphene oxide solution A with the concentration of 5mg/mL and a silicon dioxide dispersion liquid B with the concentration of 30mg/mL and the diameter of a microsphere of 200nm according to the volume ratio of the solution of 1:2 to obtain a mixed dispersion liquid C, adding 0.35g of ammonium bicarbonate into the mixed dispersion liquid C with the diameter of 30m to obtain a mixed dispersion liquid D, performing ultrasonic dispersion on the mixed dispersion liquid D by using an ultrasonic dispersion instrument for 2 hours to obtain a graphene oxide-silicon dioxide uniformly mixed suspension containing ammonium bicarbonate as a nitrogen source, placing the suspension in a high-pressure reaction kettle with a polytetrafluoroethylene lining, and performing hydrothermal reduction at 150 ℃ for 24 hours; washing a product obtained by the reaction with deionized water, then carrying out vacuum drying treatment, and soaking the nitrogen-doped graphene-silicon dioxide composite material obtained by drying in hydrofluoric acid with the mass percentage concentration of 20% for 12h to etch the silicon dioxide ball serving as the template, thus obtaining a nitrogen-doped porous graphene sample;
step three, preparing the positive electrode material of the sulfur/nitrogen-doped porous graphene composite structure lithium-sulfur battery:
putting the porous nitrogen-doped graphene prepared in the second step and pure-phase nano sulfur powder into a ball milling tank, mixing and processing for 5 hours by using a planetary ball mill, putting a mixture obtained after ball milling into a tubular furnace under the protection of nitrogen, and carrying out heat treatment for 12 hours at 180 ℃ to obtain a sulfur/porous nitrogen-doped graphene composite lithium-sulfur battery positive electrode material;
wherein the mass ratio of porous nitrogen-doped graphene: pure phase nano sulfur powder is 1: 3;
in the second step, the ultrasonic dispersion is carried out by an ultrasonic dispersion instrument under the power of 550W.
In the third step, the rotating speed of the planetary ball mill is 300 rpm.
The flow rate of nitrogen in the third step is 200 mL/min.
According to the preparation method of the positive electrode material of the lithium-sulfur battery, the graphene can be prepared by a plurality of existing well-known technologies (such as hummers method, solid/liquid phase stripping and the like);
in the above method for preparing the positive electrode material of the lithium-sulfur battery, the raw materials are commercially available, and silica dispersions with different particle sizes are commercially available as template materials, and the equipment and process used are well known to those skilled in the art.
The invention is not the best known technology.
Claims (4)
1. The preparation method of the positive electrode material of the lithium-sulfur battery is characterized by comprising the following steps
Step one, preparing graphene oxide:
preparing 1-10 mg/mL graphene oxide aqueous solution;
step two, preparing nitrogen-doped porous graphene:
mixing the solution A and the solution B to obtain a mixed dispersion liquid C, adding ammonium bicarbonate into the mixed dispersion liquid C to obtain a mixed dispersion liquid D, performing ultrasonic dispersion on the mixed dispersion liquid D by using an ultrasonic dispersion instrument for 1-5 hours to obtain a graphene oxide-silicon dioxide uniformly mixed suspension containing nitrogen source ammonium bicarbonate, placing the suspension in a high-pressure reaction kettle with a polytetrafluoroethylene lining, and performing hydrothermal reduction at 100-200 ℃ for 6-24 hours; washing a product obtained by the reaction with deionized water, and then carrying out vacuum drying treatment to obtain the nitrogen-doped graphene-silicon dioxide composite material; then soaking the graphene in hydrofluoric acid for 6-24 hours to obtain nitrogen-doped porous graphene;
wherein the solution A is a graphene oxide solution with the concentration of 1-10 mg/mL, and the solution B is a silicon dioxide dispersion liquid with the concentration of 1-100 mg/mL and the diameter of microspheres of 10-300 nm; the volume ratio is solution A: the solution B is 1: 1-3; adding 0.1-0.5 g of ammonium bicarbonate into every 10-50 mL of the mixed dispersion liquid C;
step three, preparing the positive electrode material of the sulfur/nitrogen-doped porous graphene composite structure lithium-sulfur battery:
putting the porous nitrogen-doped graphene prepared in the second step and pure-phase nano sulfur powder into a ball milling tank, mixing and processing for 3-5 h by using a planetary ball mill, putting the mixture obtained after ball milling into a tubular furnace under the protection of nitrogen, and carrying out heat treatment for 8-24 h at 100-200 ℃ to obtain the sulfur/porous nitrogen-doped graphene composite lithium-sulfur battery anode material;
wherein the mass ratio of porous nitrogen-doped graphene: pure-phase nano sulfur powder is 1: 3-10;
in the second step, the hydrofluoric acid is 5-40% in mass percentage concentration.
2. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 1, wherein the ultrasonic dispersion is performed at 300 to 650W using an ultrasonic disperser in the second step.
3. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 1, wherein the rotation speed of the planetary ball mill in the third step is 200 to 600 rpm.
4. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 1, wherein the flow rate of nitrogen in the third step is 100 to 250 mL/min.
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| CN201710957364.2A CN107732202B (en) | 2017-10-16 | 2017-10-16 | Preparation method of lithium-sulfur battery positive electrode material |
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| CN108511722A (en) * | 2018-04-04 | 2018-09-07 | 青岛大学 | A kind of cladding sulfur doping graphene ternary material and its preparation method and application |
| CN109103439B (en) * | 2018-08-30 | 2021-09-03 | 广东工业大学 | Flexible self-supporting lithium-sulfur battery positive electrode material, preparation method and battery thereof |
| CN109786690B (en) * | 2018-12-24 | 2020-10-20 | 肇庆市华师大光电产业研究院 | Lithium-sulfur battery positive electrode material and preparation method thereof |
| CN109980217A (en) * | 2019-03-26 | 2019-07-05 | 华南理工大学 | A kind of flexible self-supporting lithium-sulphur cell positive electrode and preparation method thereof based on natural fiber |
| CN110061220A (en) * | 2019-04-28 | 2019-07-26 | 西安交通大学 | A kind of FeOOH/ graphene active material and preparation method thereof, lithium sulfur battery anode material and preparation method thereof |
| CN110323443A (en) * | 2019-05-27 | 2019-10-11 | 北京理工大学 | A kind of spherical N doping redox graphene material and its application |
| CN110773198B (en) * | 2019-11-19 | 2022-10-04 | 肇庆市华师大光电产业研究院 | Carbon dioxide electrochemical reduction catalyst and preparation method thereof |
| CN111029526A (en) * | 2019-11-28 | 2020-04-17 | 西南科技大学 | Preparation method of porous positive pole piece for lithium-sulfur battery and product thereof |
| CN111554891B (en) * | 2020-04-24 | 2022-03-04 | 天津大学 | Method for preparing lithium-sulfur battery cathode material from three-dimensional mesoporous biochar |
| CN111740084B (en) * | 2020-06-15 | 2021-11-23 | 石家庄尚太科技股份有限公司 | Sulfur-doped pre-lithiated silicon-carbon composite material and preparation method thereof |
| CN113659142A (en) * | 2021-08-06 | 2021-11-16 | 欣旺达电动汽车电池有限公司 | Nitrogen-doped graphene aerogel and preparation method thereof, lithium-sulfur battery positive electrode material and preparation method thereof, and lithium-sulfur battery |
| CN113809301B (en) * | 2021-09-17 | 2023-03-10 | 中国海洋大学 | High-voltage nitrogen-doped nickel lithium manganate electrode material with yolk-like structure and lithium storage application thereof |
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