CN111785943A - Preparation method and application of NPC @ C/S composite material - Google Patents
Preparation method and application of NPC @ C/S composite material Download PDFInfo
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Abstract
The invention discloses a preparation method and application of an NPC @ C/S composite material2Coating to form a core-shell structure ZIF @ SiO2(ii) a Preliminary carbonization to convert ZIF nuclei into nitrogen-doped porous coresCarbon to obtain NPC @ mSiO2And (5) secondary template. Followed by SiO2Introducing cyanamide into the mesoporous channel, carbonizing, and removing mSiO2And (3) obtaining an NPC @ C porous carbon nano polyhedron with a yolk-eggshell structure after a template, and finally compounding the NPC @ C porous carbon nano polyhedron with sulfur powder to obtain the NPC @ C/S composite material. The carbon material prepared by the method not only has an optimized yolk-eggshell porous structure, but also can be adjusted by mSiO2The thickness of the carbon shell layer is controlled by the thickness of the secondary template, and the heteroatom doping of the carbon core and the carbon shell can be realized, so that the loading capacity of active substances is improved in the application of the secondary template in the lithium-sulfur battery, and the shuttle effect is overcome, thereby improving the performance of the lithium-sulfur battery.
Description
Technical Field
The invention belongs to the technical field of carbon materials, and particularly relates to a preparation method and application of an NPC @ C/S composite material.
Background
With the continuous acceleration of the industrialization process, the demand of people for mineral resources is continuously increased, and various mineral resources are greatly exploited, so that various environmental pollution problems are more and more serious, and the life and health of human beings are seriously threatened. In order to prevent and control environmental pollution, efforts are being made to find and develop clean new energy sources to replace the conventional energy sources.
Li-S batteries are one of the core battery technologies in the post-lithium ion battery age. The S anode material has the advantages of ultrahigh energy density, low price and easy availability of S, light weight and the like, so that the Li-S battery becomes an excellent candidate in a new energy technology with low price and high energy density. In recent years, research on Li-S batteries has been rapidly progressing, however, sulfur-carrying capacity of Li-S battery positive electrodes reported so far is mostly less than 3.5 mg cm–2The percentage of sulfur is generally less than 70 wt%, and the energy density requirements for Li-S batteries in practical applications are not yet met. In order to further improve the performance of the battery, researchers have conducted more intensive research and found that: 1. the interaction between the positive electrode material and polysulfide is increased, so that the dissolution and diffusion of polysulfide can be effectively relieved; 2. the anode material is doped with proper elements, so that the effect of the surface binding force of the material can be effectively improved.
The carbon material derived from the metal organic framework Material (MOF) has the advantages of high specific surface area, good conductivity, controllable morphology and the like, and becomes a powerful candidate for the Li-S battery positive electrode material. However, MOF derived carbon materials tend to exhibit a single microporous structure that can accommodate only small amounts of the active species sulfur. Therefore, the performance of the battery using this as a positive electrode material is still not very desirable. The MOF derived special structural materials, such as yolk-eggshell structures and hollow structure carbon materials, can contain more active substance sulfur due to the optimized pore structure, and meanwhile, the confinement effect of the hollow structure can effectively inhibit the shuttle effect, so that the performance of the Li-S battery can be theoretically improved.
These materials of particular structure are generally prepared by templating. Wherein the preparation of the yolk @ eggshell structure requires a complex surface modification process: the yolk nucleus is introduced by surface chemical modification to solve the yolk nucleus/template, the problem of template/carbon precursor interface compatibility is overcome, and a template removing process is also needed. The whole preparation process is complicated and difficult, and the application of the structure in the Li-S battery is limited.
In order to prepare a high-performance Li-S battery electrode material, simplify the preparation process and improve the practical popularization and application value of the material, a more efficient and simple preparation method of a porous carbon nano polyhedron with a yolk-eggshell structure is needed. The product material has the advantages of a pore passage of a yolk-eggshell structure, and the characteristics of high comparative area, high conductivity and rich active sites of a common heteroatom doped carbon material, so that the finally prepared anode material can solve the problem of low active substance load, overcome the shuttle effect and further realize the improvement of the Li-S battery performance.
Disclosure of Invention
In order to overcome the defects that an MOF derived carbon material is single in pore structure, low in energy density and low in sulfur carrying capacity in Li-S battery application, the invention provides a preparation method and application of an NPC @ C/S composite material.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for preparing NPC @ C/S composite material comprises the steps of firstly preparing monodisperse yolk-eggshell structure porous carbon nano polyhedron NPC @ C, and then mixing the NPC @ C with sulfur powderCompounding to obtain an NPC @ C/S composite material; NPC @ C is prepared by adopting a two-stage template method, takes zeolite-like imidazole ester framework ZIF nano-particles as a primary template and a carbon source respectively, and takes mesoporous mSiO2Cyanamide is used as a secondary template and a carbon source, and the monodisperse yolk-eggshell structure porous carbon nano polyhedral NPC @ C with controllable carbon wall thickness is prepared through multi-step carbonization.
The preparation method comprises the following specific steps:
1) preparing a ZIF template:
rapidly adding a 2-methylimidazole methanol solution into a methanol solution of Zn salt or Co salt under stirring, uniformly mixing, standing at room temperature, centrifuging, washing to obtain ZIF nanoparticles (ZIF represents a zeolite imidazolate framework material), and sealing and storing the ZIF in methanol for later use;
2）ZIF@SiO2the preparation of (1):
adding the ZIF nano-particle methanol solution prepared in the step 1) into a methanol/water mixed solution containing 2-methylimidazole, and performing ultrasonic treatment at room temperature until the mixture is fully diffused; adding Cetyl Trimethyl Ammonium Bromide (CTAB) water solution, continuing to perform ultrasonic treatment until the mixture is fully diffused, then dropwise adding tetraethyl orthosilicate (TEOS) by using a syringe pump, continuing to stir at room temperature for 2-3 h, centrifuging, washing and drying to obtain ZIF @ SiO2；
3）NPC@mSiO2The preparation of (1):
ZIF @ SiO prepared in the step 2)2Placing the mixture in a tube furnace, carbonizing the mixture in an inert gas atmosphere, and naturally cooling the mixture to obtain the NPC @ mSiO2(NPC denotes ZIF-derived nitrogen-doped porous carbon, mSiO2Represents mesoporous silica);
4）NPC@mSiO2preparation of cyanamide:
the NPC @ mSiO prepared in the step 3) is added2Putting the sample and cyanamide into a flask, performing ultrasonic treatment for 2-3 h in a water bath at 45-55 ℃ under the vacuum condition, then stirring overnight in an oil bath at 55 ℃, centrifuging and washing to obtain NPC @ mSiO2Cyanamide, and drying in an oven;
5）NPC@mSiO2/g-C3N4the preparation of (1):
the NPC @ mSiO prepared in the step 4) is added2Placing cyanamide in a tubular furnace, calcining in an inert gas atmosphere, and naturally cooling to obtain NPC @ mSiO2/g-C3N4（g-C3N4Carbon nitride obtained after thermal polymerization of cyanamide);
6）NPC@g-C3N4the preparation of (1):
the NPC @ mSiO prepared in the step 5) is added2/g-C3N4Is placed in NH4HF2Soaking for 2-3 days, washing with distilled water until salinity is 0, performing solvent exchange with ethanol, and drying overnight to obtain NPC @ g-C3N4；
7) Preparation of NPC @ C:
the NPC @ g-C prepared in the step 6) is3N4Placing the mixture in a tubular furnace, carbonizing the mixture at a high temperature in an inert gas atmosphere, and naturally cooling the mixture to obtain a monodisperse yolk-eggshell structure porous carbon nano polyhedron NPC @ C;
8) preparation of NPC @ C/S composite material:
mixing and grinding the NPC @ C prepared in the step 7) and sulfur powder, calcining at the constant temperature of 155 ℃ for 10-12 h under a vacuum condition, and cooling to the normal temperature to obtain the NPC @ C/S composite material.
Further, in the step 1), the Zn salt is zinc nitrate or zinc acetate, and the Co salt is cobalt nitrate or cobalt acetate;
the molar ratio of the 2-methylimidazole to the Zn salt or the Co salt is 8-10: 1.
Further, in the step 2), the volume ratio of methanol to water is 0.5-0.8:1, and the molar mass of 2-methylimidazole is 4-8 mmol; the molar mass of CTAB is 0.8-1.6 mmol, and the mass fraction of aqueous solution of CTAB is 17% -25%; the volume of TEOS is 0.8-1.6 mL.
Further, in the step 3), the inert gas is nitrogen or argon, and the flow rate of the inert gas is 50-150 mL/min–1The carbonization temperature is 500-550 ℃, and the carbonization time is 5-8 h.
Further, in the step 5), the flow rate of the inert gas is 50-150 mL/min–1The reaction temperature is 500-550 ℃, and the reaction time is 4-6 h.
Further, in the step 7), the flow rate of the inert gas is 50-150 mL/min–1The carbonization temperature is 800-900 ℃, and the reaction time is 1-3 h.
The NPC @ C/S composite material prepared by the method not only has a yolk-eggshell porous structure, but also can be adjusted by adjusting mSiO2The thickness of the secondary template controls the thickness of the carbon shell layer, and the carbon core and the carbon shell are doped with heteroatoms.
The NPC @ C/S composite material prepared by the method can be applied to a lithium-sulfur battery, and the NPC @ C/S composite material, a conductive agent and a binder are mixed, a solvent is added for grinding to obtain uniform slurry, then the uniform slurry is coated on the surface of an aluminum foil, and the aluminum foil is dried and sliced to obtain the anode material of the lithium-sulfur battery.
Further, the mass fraction of sulfur in the NPC @ C/S positive electrode material is 60-80%.
The beneficial effects are that:
(1) the NPC @ C composite material is prepared by adopting a two-stage template method, the process is simple and controllable, the practical operability is strong, the expanded production application is facilitated, and the prepared material has the characteristics of monodispersity, controllable appearance, uniform particle size, a yolk-eggshell structure and controllable carbon wall thickness;
(2) the NPC @ C composite material prepared by adopting a two-stage template method has the following composition advantages: the carbon core and the carbon wall are doped with N, and the carbon core is doped with transition metal, so that the active material loading capacity can be improved in the application of the lithium-sulfur battery, and the performance of the lithium-sulfur battery is improved;
(3) by combining the structure and composition advantages of the obtained NPC @ C composite material, the optimized pore structure improves the loading capacity of active substances, thereby improving the battery capacity and showing the 'confinement effect', thereby improving the cycle stability, enhancing the conductivity by doping heteroatoms, and being beneficial to Li+Thereby effectively mitigating the "shuttling effect" of the cell.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) image of the NPC @ C composite prepared in example 1;
FIG. 2 is a schematic representation of the NPC @ C composite prepared in example 1N2Isothermal adsorption-desorption curve (BET) plot;
FIG. 3 is a plot of the pore size distribution curve (BJH) of the NPC @ C composite prepared in example 1;
fig. 4 is a charge-discharge curve diagram of the lithium sulfur battery positive electrode material obtained in test example 1, which was cycled for 200 cycles at 0.2C.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the following describes the technical solution of the present invention with reference to fig. 1 and the embodiment.
It should be noted that the embodiment provided by the present invention is only for effectively explaining the technical features of the present invention, and the terms of positioning such as left side, right side, upper end, lower end, etc. are only for better describing the embodiment of the present invention and should not be construed as limiting the technical solution of the present invention.
Example 1
1) Preparation of ZIF nanocrystals:
25 mL of 2.7 mol. L–12-Methylimidazole aqueous solution 25 mL of 0.27 mol. L was quickly added with stirring–1Zn (CH) of3COO)2·2H2Uniformly mixing the solution in the O aqueous solution, standing the solution for 24 hours at room temperature, centrifuging and washing to obtain a ZIF precursor, and hermetically storing the ZIF in 20 mL of methanol;
2）ZIF@SiO2the preparation of (1):
adding 10 mL of the methanol solution containing ZIF prepared in the step 1) into a mixed solution of 42 mL of methanol, 64 mL of water and 0.5 g of 2-methylimidazole, and performing ultrasonic treatment at room temperature until the mixture is fully diffused; then 2 mL of 0.6 mol. L was added–1Ultrasonic treatment is carried out at room temperature until the hexadecyl trimethyl ammonium bromide (CTAB) aqueous solution is fully diffused, 1.2 mL tetraethyl orthosilicate (TEOS) is dripped by a syringe pump, the mixture is stirred for 2 hours at room temperature, and then the mixture is centrifuged, washed and dried to obtain ZIF @ SiO2。
3）NPC@mSiO2Preparation of
ZIF @ SiO prepared in the step 2)2Placing in a tube furnace under nitrogen atmosphereAt 5 deg.C/min–1The temperature is increased to 550 ℃ at the rate of (2) for carbonization, the carbonization time is 4 h, and the mixture is naturally cooled to room temperature to obtain NPC @ mSiO2. (NPC denotes nitrogen-doped porous carbon, mSiO2Represents mesoporous silica)
4）NPC@mSiO2Preparation of cyanamide
To the above NPC @ mSiO2Adding cyanamide 10 times of the mass of the cyanamide into a sample, performing ultrasonic treatment for 3 hours in a vacuum state at the water temperature of 55 ℃, then stirring overnight in an oil bath at the temperature of 55 ℃, cooling, centrifuging and washing the sample to obtain NPC @ mSiO2Cyanamide, and left to dry in an oven.
5）NPC@mSiO2/g-C3N4Preparation of
Reaction of NPC @ mSiO2Cyanamide was placed in a tube furnace at 5 ℃ min under nitrogen atmosphere–1The temperature is raised to 550 ℃ at the rate of (1) and calcined for 4 h, and the mixture is naturally cooled to room temperature to obtain NPC @ mSiO2/g-C3N4。
6）NPC@g-C3N4Preparation of
The NPC @ mSiO prepared in the step 5) is added2/g-C3N4Is placed in 20 mL of 2 mol. L–1NH of (2)4HF2Soaking for 2 days, washing with distilled water to salinity of 0, performing solvent exchange with ethanol, and drying overnight to obtain NPC @ g-C3N4。
7) Preparation of NPC @ C
The NPC @ g-C prepared in the step 6) is3N4Placing in a tube furnace, and heating at 5 deg.C/min in nitrogen atmosphere–1And raising the temperature to 900 ℃ at the speed rate, carrying out high-temperature carbonization for 2 h, and naturally cooling to room temperature to obtain the porous carbon nano polyhedron NPC @ C with the yolk-eggshell structure.
8) Preparation of NPC @ C/S composite material
Mixing and grinding 40 mg of NPC @ C prepared in the step 7) and 80 mg of sulfur powder for 30 min, calcining at the constant temperature of 155 ℃ for 10 h under a vacuum condition, and cooling to room temperature to obtain the NPC @ C/S cathode material.
FIG. 1 is a Scanning Electron Microscope (SEM) image of NPC @ C composite material under different magnifications, and it can be seen that the prepared NPC @ C carbon nanoparticles are in a regular rhombic regular dodecahedron structure and are uniform in size; from the broken NPC @ C of one carbon wall, it can be seen that the carbon particle has an obvious core-shell structure, and the carbon wall thickness is about 3 nm.
FIG. 2 is the isothermal N of the prepared NPC @ C composite2Adsorption-desorption curve (BET) diagram, FIG. 3 is a pore size distribution curve (BJH) diagram of the prepared NPC @ C composite material, from N2An obvious hysteresis curve can be seen from an adsorption-desorption curve, and the pore size distribution range of the NPC @ C is 1-120 nm from a pore size distribution curve graph, so that the NPC @ C has a micropore-mesopore-macropore hierarchical pore system.
Example 2
1) Preparation of ZIF nanocrystals:
25 mL of 2.7 mol. L–125 mL of 0.27 mol. L aqueous solution of 2-methylimidazole (K) was rapidly added thereto under stirring–1Co (CH)3COO)2·4H2Uniformly mixing the solution in the O aqueous solution, standing the solution for 24 hours at room temperature, centrifuging and washing to obtain a ZIF precursor, and hermetically storing the ZIF in 20 mL of methanol;
2）ZIF@SiO2the preparation of (1):
adding 10 mL of the methanol solution containing ZIF prepared in the step 1) into a mixed solution of 42 mL of methanol, 63 mL of water and 0.5 g of 2-methylimidazole, and performing ultrasonic treatment at room temperature until the mixture is fully diffused; then 3 mL of 0.5 mol. L was added–1Ultrasonic treatment is carried out at room temperature until the hexadecyl trimethyl ammonium bromide (CTAB) aqueous solution is fully diffused, 1.4 mL tetraethyl orthosilicate (TEOS) is dripped by a syringe pump, stirred for 3h at room temperature, centrifuged, washed and dried to obtain ZIF @ SiO2。
3）NPC@mSiO2Preparation of
Preparing the prepared ZIF @ SiO2Placing in a tube furnace, and heating at 5 deg.C/min in nitrogen atmosphere–1The temperature is raised to 500 ℃ at the speed of the reaction for carbonization, the carbonization time is 6 h, the reaction product is naturally cooled to room temperature, and the NPC @ mSiO is obtained2。
4）NPC@mSiO2Preparation of cyanamide
To the above NPC @ mSiO2Adding cyanamide 10 times of the mass of the cyanamide into a sample, carrying out ultrasonic treatment for 3h in a vacuum state at the water temperature of 55 ℃, then stirring overnight in an oil bath at the temperature of 55 ℃, cooling, centrifuging and washing the sample to obtain NPC @ mSiO2Cyanamide, and left to dry in an oven.
5）NPC@mSiO2/g-C3N4Preparation of
Reaction of NPC @ mSiO2Cyanamide was placed in a tube furnace at 5 ℃ min under nitrogen atmosphere–1The temperature is increased to 550 ℃ at the speed rate for carbonization, the carbonization time is 5 h, the mixture is naturally cooled to room temperature, and the NPC @ mSiO is obtained2/g-C3N4。
6）NPC@g-C3N4Preparation of
The NPC @ mSiO prepared in the step 5) is added2/g-C3N420 mL of 2 mol. L–1NH of (2)4HF2Soaking for 2 days, washing with distilled water until salinity is 0, performing solvent exchange with ethanol, and drying overnight to obtain NPC @ g-C3N4。
7) Preparation of NPC @ C
Adding NPC @ g-C3N4Placing in a tube furnace, and heating at 5 deg.C/min in nitrogen atmosphere–1The temperature is raised to 800 ℃ at the speed rate, high-temperature carbonization is carried out, the carbonization time is 2 hours, and natural cooling is carried out to the room temperature, so as to obtain the porous carbon nano polyhedron NPC @ C with the yolk-eggshell structure.
8) Preparation of NPC @ C/S composite material
And (3) mixing and grinding 40 mg of NPC @ C prepared in the step (7) and 80 mg of sulfur powder for 30 min, calcining at the constant temperature of 155 ℃ for 12 h under a vacuum condition, and cooling to room temperature to obtain the NPC @ C/S cathode material.
Example 3
1) Preparation of ZIF nanocrystals:
25 mL of 2.7 mol. L–12-Methylimidazole aqueous solution 25 mL of 0.27 mol. L was quickly added with stirring–1Zn(CH3COO)2·2H2O and Co (CH)3COO)2·4H2O waterUniformly mixing the solution, standing the solution at room temperature for 24 hours, centrifuging and washing to obtain a ZIF precursor, and hermetically storing the ZIF in 20 mL of methanol;
2）ZIF@SiO2the preparation of (1):
adding 10 mL of methanol solution containing ZIF into a mixed solution of 42 mL of methanol, 65 mL of water and 0.5 g of 2-methylimidazole, and performing ultrasonic treatment at room temperature until the mixture is fully diffused; then 1 mL of 0.7 mol. L was added–1Ultrasonic treatment is carried out at room temperature until the hexadecyl trimethyl ammonium bromide (CTAB) aqueous solution is fully diffused, 0.8 mL tetraethyl orthosilicate (TEOS) is dripped by a syringe pump, stirred for 3h at room temperature, centrifuged, washed and dried to obtain ZIF @ SiO2。
3）NPC@mSiO2Preparation of
Mixing the above ZIF @ SiO2Placing in a tube furnace, and heating at 5 deg.C/min in nitrogen atmosphere–1The temperature is raised to 550 ℃ at the rate of (2) for carbonization, and the mixture is naturally cooled to room temperature to obtain NPC @ mSiO2。
4）NPC@mSiO2Preparation of cyanamide
To the above NPC @ mSiO2Adding cyanamide 10 times of the mass of the cyanamide into a sample, performing ultrasonic treatment for 3 hours in a vacuum state at the water temperature of 45 ℃, then stirring overnight in an oil bath at the temperature of 55 ℃, cooling, centrifuging and washing the sample to obtain NPC @ mSiO2Cyanamide, and left to dry in an oven.
5）NPC@mSiO2/g-C3N4Preparation of
Reaction of NPC @ mSiO2Cyanamide was placed in a tube furnace at 5 ℃ min under nitrogen atmosphere–1The temperature is increased to 550 ℃ at the rate of (2) for carbonization, the carbonization time is 6 h, and the NPC @ mSiO is obtained2/g-C3N4。
6）NPC@g-C3N4Preparation of
Reaction of NPC @ mSiO2/g-C3N420 mL of 2 mol. L–1NH of (2)4HF2Soaking for 2 days, washing with a large amount of water until salinity is 0, performing solvent exchange with ethanol, and drying overnight to obtain NPC @ g-C3N4。
7) Preparation of NPC @ C
Adding NPC @ g-C3N4Placing in a tube furnace, and heating at 5 deg.C/min in nitrogen atmosphere–1And raising the temperature to 900 ℃ at the speed rate, carrying out high-temperature carbonization for 3h, and naturally cooling to room temperature to obtain the porous carbon nano polyhedron NPC @ C with the yolk-eggshell structure.
8) Preparation of NPC @ C/S composite material
Mixing and grinding 40 mg of NPC @ C prepared in the step 7) and 60 mg of sulfur powder for 30 min, calcining at the constant temperature of 155 ℃ for 12 h under a vacuum condition, and cooling to room temperature to obtain the NPC @ C/S cathode material.
Comparative example 1
1) Preparation of ZIF nanocrystals:
25 mL of 2.7 mol. L–12-Methylimidazole aqueous solution 25 mL of 0.27 mol. L was quickly added with stirring–1Zn (CH) of3COO)2·2H2Uniformly mixing the solution in the O aqueous solution, standing the solution for 24 hours at room temperature, centrifuging and washing to obtain a ZIF precursor, and hermetically storing the ZIF in 20 mL of methanol;
2) putting the ZIF nano-crystal prepared in the step 1) into a tube furnace, and heating at 5 ℃ for min in a nitrogen atmosphere–1The temperature is increased to 900 ℃ at the speed of the ZIF derivative carbon nano-particles, the high-temperature carbonization is carried out, the carbonization time is 2 hours, the natural cooling is carried out to the room temperature, and the ZIF derivative carbon nano-particles are marked as ZIFC;
3) mixing and grinding 40 mg of ZIFC prepared in the step 2) and 80 mg of sulfur powder for 30 min, calcining at the constant temperature of 155 ℃ for 12 h under a vacuum condition, and cooling to room temperature to obtain the ZIFC/S positive electrode material.
Test example 1
Mixing the NPC @ C/S composite material obtained in the example 1, a conductive agent (Super P) and a binder (PVDF) according to a mass ratio of 8:1:1, adding a proper amount of N-methylpyrrolidone (NMP) solvent, continuously grinding for 30 min until uniform slurry is formed, then coating the uniform slurry on an aluminum foil current collector, drying the uniform slurry in vacuum at 60 ℃ for 12 h, and cutting the dried uniform slurry into disks with the diameter of 12 mm to be used as a positive electrode plate of a lithium-sulfur battery.
Assembly and testing of lithium sulfur batteries:
the obtained electrode piece is taken as a positive electrode, the metal lithium piece is taken as a negative electrode, the diaphragm is a Celgard-2500 type polypropylene film, and the electrolyte is a solution (added with 2.0 percent LiNO) of 1.0M LiTFSI dissolved in DOL (dimethyl ether) DME (volume ratio of 1: 1)3). A 2016 type button cell was assembled in a glove box filled with argon and its charge and discharge performance was tested on a blue system.
FIG. 4 is a graph of cycle performance at 0.2C of the prepared positive electrode material for lithium-sulfur battery, from which it can be seen that the specific first discharge capacity is 1010.6 mAh g–1After 200 cycles, the circulation still can reach 654.6 mAh g–1The specific capacity is higher and more stable.
The ZIFC/S composite material prepared in the comparative example 1 is used for preparing an electrode plate by the same method and assembling a lithium-sulfur battery by the same method, the charge and discharge performance of the lithium-sulfur battery is tested by the same method, and the test result is compared with that of the example 1.
The result shows that the first discharge specific capacity of the lithium-sulfur battery anode material prepared from the ZIFC/S composite material prepared in the comparative example 1 is only 870 mAh.g at 0.2C–1About 450 mAh g after 200 cycles–1The specific capacity is lower and the performance is poorer. Compared with the positive electrode material prepared by the prior art, the NPC @ C/S positive electrode material prepared by taking the porous carbon nano polyhedron NPC @ C with the yolk-eggshell structure prepared by the preparation method disclosed in the embodiment 1 as the basis and combining sulfur powder is greatly improved in performance, and the performance of the lithium-sulfur battery can be effectively improved.
The foregoing illustrates and describes the principles, general features, and advantages of the present invention. However, the above description is only an example of the present invention, the technical features of the present invention are not limited thereto, and any other embodiments that can be obtained by those skilled in the art without departing from the technical solution of the present invention should be covered by the claims of the present invention.
Claims (10)
1. The preparation method of the NPC @ C/S composite material is characterized by firstly preparing the porous carbon nano polyhedron NPC @ C with the monodisperse yolk-eggshell structure, and then compounding the NPC @ C with sulfur powder to obtain the NPC @ C/S composite materialA composite material; NPC @ C is prepared by adopting a two-stage template method, takes zeolite-like imidazole ester framework ZIF nano-particles as a primary template and a carbon source respectively, and takes mesoporous mSiO2Cyanamide is used as a secondary template and a carbon source, and the monodisperse yolk-eggshell structure porous carbon nano polyhedral NPC @ C with controllable carbon wall thickness is prepared through multi-step carbonization.
2. The method of preparing the NPC @ C/S composite material of claim 1, comprising the steps of:
1) preparing a ZIF template:
rapidly adding the 2-methylimidazole methanol solution into a Zn salt or Co salt methanol solution under stirring, uniformly mixing, standing at room temperature, centrifuging, washing to obtain ZIF nanoparticles, and hermetically storing the ZIF in methanol for later use;
2）ZIF@SiO2the preparation of (1):
adding the ZIF nano-particle methanol solution prepared in the step 1) into a methanol/water mixed solution containing 2-methylimidazole, and performing ultrasonic treatment at room temperature until the mixture is fully diffused; adding CTAB aqueous solution, continuing to perform ultrasonic treatment until the CTAB aqueous solution is fully diffused, dropwise adding TEOS (tetraethyl orthosilicate) by using an injection pump, continuing to stir at room temperature, centrifuging, washing and drying to obtain ZIF @ SiO2；
3）NPC@mSiO2The preparation of (1):
ZIF @ SiO prepared in the step 2)2Placing the mixture in a tube furnace, carbonizing the mixture in an inert gas atmosphere, and naturally cooling the mixture to obtain the NPC @ mSiO2；
4）NPC@mSiO2Preparation of cyanamide:
the NPC @ mSiO prepared in the step 3) is added2Putting the sample and cyanamide into a flask, performing ultrasonic treatment for 2-3 h in a water bath at 45-55 ℃ under the vacuum condition, then stirring overnight in an oil bath at 55 ℃, centrifuging and washing to obtain NPC @ mSiO2Cyanamide, and drying in an oven;
5）NPC@mSiO2/g-C3N4the preparation of (1):
the NPC @ mSiO prepared in the step 4) is added2Cyanamide is put into a tube furnace and is fed in an inert gas atmosphereCalcining, and naturally cooling to obtain NPC @ mSiO2/g-C3N4；
6）NPC@g-C3N4The preparation of (1):
the NPC @ mSiO prepared in the step 5) is added2/g-C3N4Is placed in NH4HF2Soaking for 2-3 days, washing with distilled water until salinity is 0, performing solvent exchange with ethanol, and drying overnight to obtain NPC @ g-C3N4；
7) Preparation of NPC @ C:
the NPC @ g-C prepared in the step 6) is3N4Placing the mixture in a tubular furnace, carbonizing the mixture at a high temperature in an inert gas atmosphere, and naturally cooling the mixture to obtain a monodisperse yolk-eggshell structure porous carbon nano polyhedron NPC @ C;
8) preparation of NPC @ C/S composite material:
mixing and grinding the NPC @ C prepared in the step 7) and sulfur powder, calcining at the constant temperature of 155 ℃ for 10-12 h under a vacuum condition, and cooling to the normal temperature to obtain the NPC @ C/S composite material.
3. The method of claim 2, wherein in step 1), the Zn salt is zinc nitrate or zinc acetate, and the Co salt is cobalt nitrate or cobalt acetate; the molar ratio of the 2-methylimidazole to the Zn salt or the Co salt is 8-10: 1.
4. The process of claim 2, wherein in step 2), the volume ratio of methanol to water is 0.5-0.8:1, and the molar mass of 2-methylimidazole is 4-8 mmol; the molar mass of CTAB is 0.8-1.6 mmol, and the mass fraction of CTAB aqueous solution is 17% -25%; the volume of TEOS is 0.8-1.6 mL.
5. The method of claim 2, wherein in step 3), the inert gas is nitrogen or argon, and the flow rate of the inert gas is 50-150 mL-min–1The carbonization temperature is 500-550 ℃, and the carbonization time is 5-8 h.
6. The method of claim 2, wherein the inert gas is supplied at a flow rate of 50 to 150 mL-min in step 5)–1The reaction temperature is 500-550 ℃, and the reaction time is 4-6 h.
7. The method of claim 2, wherein the inert gas is supplied at a flow rate of 50 to 150 mL-min in step 7)–1The carbonization temperature is 800-900 ℃, and the reaction time is 1-3 h.
8. The NPC @ C/S composite material as claimed in any one of claims 1 to 7, which has a porous yolk-shell structure and is prepared by adjusting the mSiO2The thickness of the secondary template controls the thickness of the carbon shell layer, and the carbon core and the carbon shell are doped with heteroatoms.
9. The use of the NPC @ C/S composite material as defined in claim 8 in a lithium sulfur battery, wherein the NPC @ C/S composite material is used as a positive electrode material for a lithium sulfur battery, and the NPC @ C/S composite material, a conductive agent and a binder are mixed, a solvent is added to the mixture to grind the mixture to obtain a uniform slurry, the uniform slurry is coated on the surface of an aluminum foil, and the aluminum foil is dried and sliced to obtain the positive electrode material for the lithium sulfur battery.
10. The use of the NPC @ C/S composite of claim 9 in a lithium sulfur battery, wherein the mass fraction of sulfur in the NPC @ C/S positive electrode material is between 60% and 80%.
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