CN108400285B - Carbon-based metal-free electrocatalyst for promoting polysulfide conversion in lithium-sulfur battery - Google Patents

Carbon-based metal-free electrocatalyst for promoting polysulfide conversion in lithium-sulfur battery Download PDF

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CN108400285B
CN108400285B CN201810195789.9A CN201810195789A CN108400285B CN 108400285 B CN108400285 B CN 108400285B CN 201810195789 A CN201810195789 A CN 201810195789A CN 108400285 B CN108400285 B CN 108400285B
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nitrogen
carbon
doped carbon
based metal
lithium
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CN108400285A (en
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杜玲玉
李有彬
吴强
杨立军
王喜章
胡征
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Nanjing University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
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    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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Abstract

The invention provides aA sulfur-filled carbon-based metal-free electrocatalyst belongs to the field of lithium-sulfur batteries. The sulfur-filled carbon-based metal-free electrocatalyst provided by the invention can fill S into the cavity of the nano cage by utilizing micropores and nano-scale cavities on the wall of the nano cage, and has nitrogen-doped sp2The lithium-sulfur battery based on the carbon has the advantages of high power and long service life, and in the charging and discharging processes, the nitrogen is doped with sp2Carbon itself can effectively catalyze polysulfide conversion reactions, unlike nitrogen-doped sp2The carbon only has the function of chemisorbing lithium polysulfide reported in documents, and the cooperation of the functions realizes the high-efficiency adsorption and conversion of the lithium polysulfide, effectively inhibits the polarization effect and the shuttle effect, and improves the specific capacity, the power, the cycle life and the stability of the lithium-sulfur battery.

Description

Carbon-based metal-free electrocatalyst for promoting polysulfide conversion in lithium-sulfur battery
Technical Field
The invention relates to the technical field of lithium-sulfur batteries, in particular to a sulfur-filled carbon-based metal-free electrocatalyst, a preparation method thereof, a revelation of polysulfide conversion in a catalytic lithium-sulfur battery and an energy storage application of the lithium-sulfur battery.
Background
Lithium-sulfur batteries have the outstanding advantages of high energy density and low cost, and are one of the most promising next-generation secondary battery systems, but the current commercialization is faced with the challenges of low sulfur utilization, limited power density, and short cycle life.
The power density of a lithium-sulfur battery depends mainly on the electrochemical reaction rate of sulfur and lithium ions to lithium sulfide via polysulfide, charge transport rate, and the like. The rapid electrochemical reaction produces a large polarization effect, which increases the charge potential and decreases the discharge potential, resulting in a decrease in specific capacity and a decrease in lifetime. Large poleThe polarization effect mainly comes from slow charge transfer kinetics and high activation energy of lithium polysulfide conversion reaction, so that the inhibition of the polarization effect is the key for improving the energy density and the power density of the sulfur anode, and the approaches are as follows: (i) the method adopts a high-conductivity carbon material and designs a porous hierarchical structure to enhance charge transmission and material transportation capability; (ii) by introducing an electrocatalyst, the activation energy of the lithium polysulfide oxidation/reduction reaction is reduced to reduce the overpotential of the reaction, common catalysts include: elemental metals (e.g. Pt, Co), transition metal compounds (e.g. oxide MnO)2、Fe2O3Sulfide (WS)2、MoS2) Nitride (TiN, VN), metal free catalysts (phosphoalkene and quinoid imine) etc., which generally require a support of conductive carbon material dispersed in a high specific surface area to function better. Therefore, the development of an electrode material with excellent charge transfer kinetics and high catalytic activity is very important for improving the power density of the lithium-sulfur battery.
In view of the characteristics of high conductivity, high mechanical strength, rich and adjustable morphology, light weight, low price and easy availability, the carbon-based material becomes a carrier material which has the widest application and the most application prospect in the research of lithium-sulfur batteries, for example, CN104953089A in the prior art discloses that the inner cavity of a carbon nanocage with a hierarchical structure is filled with high-loading (79.8 wt%) sulfur, but the problem of poor electrochemical performance still exists.
Disclosure of Invention
In view of the above, the present invention provides a sulfur-filled carbon-based metal-free electrocatalyst, a preparation method thereof, and applications of the electrocatalyst in catalyzing polysulfide conversion in a lithium sulfur battery and energy storage in a lithium sulfur battery. The sulfur-filled carbon-based metal-free electrocatalyst provided by the invention has excellent energy storage performance of a lithium-sulfur battery.
In order to achieve the above object, the present invention provides the following technical solutions:
the utility model provides a S fills carbon base no metal electrocatalyst, uses nitrogen-doped carbon nanometer cage as the carrier, nitrogen-doped carbon nanometer cage includes nitrogen-doped carbon material' S cage wall with the cavity that the cage wall surrounds, the cavity intussuseption is filled with elemental sulfur.
Preferably, the specific surface area of the nitrogen-doped carbon nanocages is 500-2500 m2·g-1The pore volume is 2-8 cm3·g-1And the nitrogen content in the nitrogen-doped carbon nanocages is 0-20 at.%.
Preferably, the S filling amount in the sulfur-filled carbon-based metal-free electrocatalyst is 20-90 wt.%.
The invention also provides a preparation method of the sulfur-filled carbon-based metal-free electrocatalyst, which comprises the following steps:
(1) mixing steam of a volatile nitrogen-containing carbon source with a magnesium oxide precursor in an inert gas, and carrying out in-situ pyrolysis to obtain a core-shell structure nitrogen-doped carbon nanocage-coated magnesium oxide intermediate product, wherein the magnesium oxide precursor is basic magnesium carbonate or magnesium carbonate;
(2) soaking the core-shell structure intermediate product obtained in the step (1) in inorganic acid to remove a magnesium oxide template, so as to obtain a hollow nitrogen-doped carbon nanocage;
(3) and (3) in an inert gas, after the hollow nitrogen-doped carbon nanocages obtained in the step (2) and sulfur form a compound, sequentially carrying out melting and heat treatment to obtain the S-filled carbon-based metal-free electrocatalyst.
Preferably, the nitrogen-containing carbon source in step (1) comprises one or more of pyridine, ammonia gas, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 3-methylaminopyridine, 4-methylaminopyridine, 2-aminoisonicotinic acid, 3-aminoisonicotinic acid, 2, 3-diaminopyridine, 2, 4-diaminopyridine, 2, 5-diaminopyridine, 2, 6-diaminopyridine, 3, 4-diaminopyridine, pyrrole, N-methylpyrrole, pyrrole-2-carbonitrile and 1-aminopyrrole.
Preferably, the melting temperature in the step (3) is 145-170 ℃, and the melting time is more than 2 h.
Preferably, the temperature of the heat treatment in the step (3) is 180-250 ℃, and the time of the heat treatment is 0.5-5 h.
The invention also provides another preparation method of the carbon-based metal-free electrocatalyst, which comprises the following steps:
(1) mixing steam of a volatile nitrogen-containing carbon source with a magnesium oxide precursor in an inert gas, and carrying out in-situ pyrolysis to obtain a core-shell structure nitrogen-doped carbon nanocage-coated magnesium oxide intermediate product, wherein the magnesium oxide precursor is basic magnesium carbonate or magnesium carbonate;
(2) soaking the core-shell structure intermediate product obtained in the step (1) in inorganic acid to remove a magnesium oxide template, so as to obtain a hollow nitrogen-doped carbon nanocage;
(3) mixing the hollow nitrogen-doped carbon nanocage obtained in the step (2), sodium thiosulfate, inorganic acid and water to perform an oxidation-reduction reaction to obtain an S and nitrogen-doped carbon nanocage compound precursor;
(4) and (3) sequentially melting and thermally treating the S and nitrogen-doped carbon nanocage compound precursor obtained in the step (3) in inert gas to obtain the S-filled carbon-based metal-free electrocatalyst.
Preferably, the melting temperature in the step (4) is 145-170 ℃, and the melting time is 2-24 h.
The invention also provides application of the S-filled carbon-based metal-free electrocatalyst in the technical scheme in a lithium-sulfur battery.
The invention provides an S-filled carbon-based metal-free electrocatalyst, which takes nitrogen-doped carbon nanocages as carriers, and S is filled in cavities of the nitrogen-doped carbon nanocages. The carbon-based metal-free electrocatalyst provided by the invention can fill S into the nano cage cavity by utilizing micropores and nano-scale cavities on the nano cage wall, and has the nitrogen-doped sp2The lithium-sulfur battery based on the carbon has the advantages of high power and long service life, and in the charging and discharging processes, the nitrogen is doped with sp2The carbon can effectively catalyze polysulfide conversion reaction, is a novel lithium-sulfur battery metal-free electrocatalyst, and is different from nitrogen-doped sp2The carbon only has literature reports of chemical adsorption of lithium polysulfide, and the cooperation of the effects realizes the high-efficiency adsorption and conversion of the lithium polysulfide, effectively inhibits the polarization effect and the shuttle effect, and improves the ratio of the lithium-sulfur batteryCapacity, power and cycle life and stability. The data of the examples show that the carbon-based metal-free electrocatalyst provided by the invention is at 0.2 A.g-1The specific capacity under the current density can reach 1373 mAh.g-1、20A·g-1The specific capacity under the current density can reach 539 mAh.g-1、10A·g-1The specific capacity is kept at 438mAh g after the current density is cycled for 1000 times-1。
Furthermore, the nitrogen-doped carbon nanocage as the carrier of the sulfur-filled carbon-based metal-free electrocatalyst has the characteristics of large specific surface area, rich micropores, mesopores, macropores, large pore volume, nitrogen content and adjustable S filling amount, and the specific surface area is 500-2500 m2·g-1The pore volume is 2-8 cm3·g-1The nitrogen content in the nitrogen-doped carbon nanocages is 0-20 at.%; the filling amount of S in the carbon-based metal-free electrocatalyst is 20-90 wt.%.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a TEM micrograph of an S-filled carbon-based metal-free electrocatalyst prepared in example 1 of the present invention, N2Adsorption and desorption curves and pore distribution curves;
FIG. 2 is a CV curve (a) and a potential-current density plot (b) of a charge-discharge plateau of a battery prepared in example 1 of the present invention;
fig. 3 is a graph of the rate and cycle stability of an S-filled carbon-based metal-free electrocatalyst prepared in example 1 of the present invention and an electrocatalyst prepared in comparative example.
Detailed Description
The invention provides a sulfur-filled carbon-based metal-free electrocatalyst (S @ hNCNC), which takes a nitrogen-doped carbon nano cage as a carrier, wherein the nitrogen-doped carbon nano cage comprises a cage wall made of a nitrogen-doped carbon material and a cavity surrounded by the cage wall, and elemental sulfur (S) is filled in the cavity.
In the invention, the specific surface area of the nitrogen-doped carbon nanocages is preferably 500-2500 m2·g-1(ii) a The preferred pore volume is 2-8 cm3·g-1(ii) a The content of nitrogen in the nitrogen-doped carbon nanocages is preferably 0-20 at.%, and more preferably 8.9 at.%.
In the invention, the filling amount of S in the sulfur-filled carbon-based metal-free electrocatalyst is preferably 20-90 wt.%, and more preferably 74.5-75 wt.%.
The invention also provides a preparation method of the sulfur-filled carbon-based metal-free electrocatalyst, which comprises the following steps:
(1) mixing steam of a volatile nitrogen-containing carbon source with a magnesium oxide precursor in an inert gas, and carrying out in-situ pyrolysis to obtain a core-shell structure nitrogen-doped carbon nanocage-coated magnesium oxide intermediate product, wherein the magnesium oxide precursor is basic magnesium carbonate or magnesium carbonate;
(2) soaking the core-shell structure intermediate product obtained in the step (1) in inorganic acid to remove magnesium oxide, so as to obtain a hollow nitrogen-doped carbon nanocage;
(3) and (3) compounding the hollow nitrogen-doped carbon nanocages obtained in the step (2) with sulfur in an inert gas to obtain a precursor, and sequentially carrying out melting and heat treatment to obtain the S-filled carbon-based metal-free electrocatalyst.
In an inert gas, steam of a volatile nitrogen-containing carbon source is mixed with a magnesium oxide precursor for in-situ pyrolysis to obtain a core-shell structure nitrogen-doped carbon nanocage-coated magnesium oxide intermediate product, wherein the magnesium oxide precursor is basic magnesium carbonate or magnesium carbonate. In the present invention, the nitrogen-containing carbon source preferably includes one or more of pyridine, ammonia gas, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 3-methylaminopyridine, 4-methylaminopyridine, 2-aminoisonicotinic acid, 3-aminoisonicotinic acid, 2, 3-diaminopyridine, 2, 4-diaminopyridine, 2, 5-diaminopyridine, 2, 6-diaminopyridine, 3, 4-diaminopyridine, pyrrole, N-methylpyrrole, pyrrole-2-carbonitrile, and 1-aminopyrrole, and more preferably pyridine, ammonia gas, 2-aminopyridine, or pyrrole. When the nitrogen-containing carbon source is preferably a mixture, the amount of each component in the mixture is not particularly limited, and the mixture may be used in any ratio.
The source of the nitrogen-containing carbon source vapor is not particularly limited in the present invention, and any means known to those skilled in the art that can vaporize a nitrogen-containing carbon source, such as heating, may be used.
In the invention, the temperature of the in-situ pyrolysis is preferably 670-900 ℃, more preferably 690-800 ℃, and most preferably 750-800 ℃, and the time of the in-situ pyrolysis is preferably 5-240 minutes, more preferably 10-60 minutes, and most preferably 30-40 minutes. In the invention, in the in-situ pyrolysis process, volatile nitrogen-containing carbon source steam is carbonized and wrapped on the surfaces of magnesium oxide nano particles generated in situ.
The adding mode of the steam of the volatile nitrogen-containing carbon source and the magnesium oxide precursor is not specially limited, and the adding sequence known by the technicians in the field is adopted, specifically, basic magnesium carbonate or magnesium carbonate is added into a reaction tube, evenly spread and placed into a tubular furnace; then pumping out air and filling inert gas, and introducing volatile nitrogen-containing carbon source steam by a bubbling method.
After the magnesium oxide intermediate product wrapped by the core-shell structure nitrogen-doped carbon nanocage is obtained, the core-shell structure intermediate product is soaked in inorganic acid to obtain the hollow nitrogen-doped carbon nanocage (hNCNC). in the invention, the inorganic acid is preferably hydrochloric acid or sulfuric acid, and the concentration of the inorganic acid is preferably 0.1-6 mol/L.
In the invention, the time for soaking and removing the magnesium oxide template is preferably 5-720 minutes, and preferably 30-60 minutes; the soaking is preferably carried out at room temperature without additional heating or cooling. In the invention, the MgO inner core is removed in the inorganic acid soaking process to obtain the hollow nitrogen-doped carbon nanocages.
After the inorganic acid soaking is finished, the invention preferably sequentially filters, washes the soaked product to be neutral and dries the soaked product to obtain the hollow nitrogen-doped carbon nanocage. The specific modes of filtering, washing to neutrality and drying are not particularly limited in the present invention, and can be those well known to those skilled in the art.
After the hollow nitrogen-doped carbon nanocages are obtained, the hollow nitrogen-doped carbon nanocages are compounded with sulfur in inert gas to obtain a precursor, and melting and heat treatment are sequentially carried out to obtain the carbon-based metal-free electrocatalyst. In the invention, the melting temperature is preferably 700-900 ℃, more preferably 750-800 ℃, and the melting time is preferably more than 12 hours, more preferably 20-24 hours. In the melting process, sulfur is melted and filled into the hollow nitrogen-doped carbon nanocage cavity.
In the present invention, the sulfur is preferably sulfur powder.
In the present invention, the rate of temperature rise to the melting temperature is not particularly limited, and the melting temperature can be reached.
In the present invention, the inert gas is preferably N2Or argon.
In the invention, the heat treatment temperature is preferably 180-250 ℃, more preferably 190-200 ℃, and the heat treatment time is preferably 0.5-5 h, more preferably 2 h. In the invention, the adsorbed S on the outer surface of the hollow nitrogen-doped carbon nanocage is removed in the heat treatment process. The present invention is not particularly limited in the rate of temperature rise to the heat treatment temperature, and the heat treatment temperature can be reached.
After the heat treatment is completed, the present invention preferably cools the heat-treated product naturally to room temperature to obtain the sulfur-filled carbon-based metal-free electrocatalyst.
The invention also provides another preparation method of the sulfur-filled carbon-based metal-free electrocatalyst, which comprises the following steps:
(1) mixing steam of a volatile nitrogen-containing carbon source with a magnesium oxide precursor in an inert gas, and carrying out in-situ pyrolysis to obtain a core-shell structure nitrogen-doped carbon nanocage-coated magnesium oxide intermediate product, wherein the magnesium oxide precursor is basic magnesium carbonate or magnesium carbonate;
(2) soaking the core-shell structure intermediate product obtained in the step (1) in inorganic acid to remove a magnesium oxide template, so as to obtain a hollow nitrogen-doped carbon nanocage;
(3) mixing the hollow nitrogen-doped carbon nanocage obtained in the step (2), sodium thiosulfate, inorganic acid and water to perform an oxidation-reduction reaction to obtain an S and nitrogen-doped carbon nanocage compound precursor;
(4) and (3) sequentially melting and thermally treating the S and nitrogen-doped carbon nanocage compound precursor obtained in the step (3) in inert gas to obtain the S-filled carbon-based metal-free electrocatalyst.
The steps for obtaining the hollow carbon nanocages in the invention are the same as those in the scheme, and are not described again.
After the hollow nitrogen-doped carbon nanocages are obtained, the hollow nitrogen-doped carbon nanocages, sodium thiosulfate, inorganic acid and water are mixed to perform an oxidation-reduction reaction, and a precursor of the S and nitrogen-doped carbon nanocage compound is obtained. In the present invention, the inorganic acid is preferably a non-oxidizing acid, and more preferably hydrochloric acid, dilute sulfuric acid, acetic acid, or the like. The concentration and the dosage of the inorganic acid are not specially limited, and the full progress of the oxidation-reduction reaction can be ensured.
The adding sequence of the hollow nitrogen-doped carbon nanocage, the sodium thiosulfate, the inorganic acid and the water is not particularly limited, and the adding sequence known to a person skilled in the art can be adopted, specifically, for example, the sodium thiosulfate and the water are mixed to obtain a sodium thiosulfate solution, the hollow nitrogen-doped carbon nanocage is mixed with the water to obtain a hollow nitrogen-doped carbon nanocage suspension, and the inorganic acid is added after the sodium thiosulfate solution and the hollow nitrogen-doped carbon nanocage suspension are uniformly mixed.
In the present invention, the concentration of the sodium thiosulfate solution is preferably 5 to 50.0 g. L-1The concentration of the hollow nitrogen-doped carbon nanocage suspension is preferably 0.1-5.0 g. L-1The concentration of the inorganic acid is preferably 0.1-2.0 mol. L-1。
In the invention, the addition rate of the inorganic acid is preferably 1.0-5.0 m L & min-1。
The invention has no special limitation on the temperature and time of the oxidation-reduction reaction, and can ensure that the oxidation-reduction reaction is fully carried out, such as reaction for 2 hours at room temperature.
After the redox reaction is finished, preferably, the redox reaction product is sequentially filtered, washed and dried to obtain the precursor of the S and nitrogen-doped carbon nanocage compound. The present invention is not particularly limited in terms of the specific manner of filtration, washing with water and drying, and may be implemented in a manner known to those skilled in the art. The present invention is not limited to the specific mixing method, and the mixing method may be a method known to those skilled in the art.
After the precursor of the S and nitrogen-doped carbon nanocage compound is obtained, the precursor of the S and nitrogen-doped carbon nanocage compound is sequentially melted and thermally treated in inert gas to obtain the S-filled carbon-based metal-free electrocatalyst. In the invention, the melting temperature is preferably 145-170 ℃, more preferably 150-155 ℃, and the melting time is preferably 5-24 h, more preferably 12 h. In the present invention, the rate of temperature rise to the melting temperature is not particularly limited, and the melting temperature can be reached.
The requirements of the present invention for said heat treatment are in accordance with the above-mentioned schemes and will not be described herein again.
After the heat treatment is completed, the present invention preferably naturally cools the heat-treated product to room temperature to obtain the S-filled carbon-based metal-free electrocatalyst.
The invention also provides application of the S-filled carbon-based metal-free electrocatalyst in the technical scheme in a lithium-sulfur battery.
In the present invention, the application preferably includes: mixing the prepared S-filled carbon-based metal-free electrocatalyst, acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, taking N-methyl pyrrolidone as a solvent, uniformly stirring, uniformly coating the mixture on an aluminum foil, drying at 80 ℃ and tabletting to obtain the working electrode plate.
In the invention, the loading amount of the S-filled carbon-based metal-free electrocatalyst on the working electrode sheet is preferably 1.0-1.5 mg-cm-2More preferably 1.2 to 1.3 mg/cm-2。
The S-filled carbon-based metal-free electrocatalyst, the preparation method and the application thereof according to the present invention will be described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.
Example 1
Weighing 5.0g of basic magnesium carbonate, adding the basic magnesium carbonate into a quartz tube, uniformly spreading the basic magnesium carbonate, putting the quartz tube into a central area of a tube furnace, repeatedly filling argon and evacuating for 3 to 5 times by using a mechanical pump, heating the quartz tube to 800 ℃ in an argon atmosphere, introducing pyridine steam by a bubbling method, reacting for 60 minutes, cooling the tube to room temperature under the protection of the argon after the reaction is finished, collecting powder from the quartz tube, soaking the powder in 1 mol/L diluted hydrochloric acid for 1 hour, filtering, repeatedly washing the powder to be neutral by using deionized water, and drying the solution at 110 ℃ to obtain a hollow nitrogen-doped carbon nanocage (hNCNC). in the scheme, a picture 1a is a transmission electron microscope photograph of the hNCNC prepared in the embodiment, and a picture 1b is an N-doped carbon nanoc2As can be seen from FIG. 1b, the adsorption/desorption curves and the pore distribution curve, the specific surface area of hNCNC obtained in this example was 1300m2·g-1Pore volume of 4.3cm3·g-1The nitrogen content in the nitrogen-doped carbon nanocages is 8.9 at.%, the size of the nanocages is about 10-30 nm, the mesoporous rate is higher than 90%, and it can be seen that sulfur is uniformly filled in the nanocages, and the mesoporous volume is obviously reduced on a nitrogen adsorption and desorption curve.
5.0g of sodium thiosulfate is weighed and dissolved in a deionized water solution of 200m L to prepare 25.0 g. L-1Sodium thiosulfate solution is prepared by selecting hNCNC with N content of 8.9 at.%, dispersing 0.100g hNCNC in 100m L deionized water solution, and adding 200m L25.0.0 g. L-1Sodium thiosulfate solution, stirring well, at 3.0m L. min-1At a rate of 300m L0.2 mol L-1And (3) reacting the dilute hydrochloric acid solution for 2 hours, filtering, washing, drying at 70 ℃, putting the sample in Ar inert gas flow at 155 ℃ for 12 hours to melt sulfur and fill the sulfur into the cavity of the nanocage, and heating the sample to 250 ℃ under the Ar inert gas flow to treat for 1.5 hours to remove adsorbed S on the outer surface of the nanocage. After the sample had cooled naturally to room temperature, the catalyst S @ hNCNC was obtained, which had an S loading of 75.0 wt.% as determined by Thermogravimetric Analysis (TA).
Mixing 75.0 wt.% of S @ hNCNC carbon-based metal-free electrocatalyst, acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, taking N-methyl pyrrolidone as a solvent, and uniformly stirringThen evenly coating the mixture on an aluminum foil, drying and tabletting at 80 ℃ to obtain the working electrode slice (S @ hNCNC). The loading amount of the carbon-based metal-free electrocatalyst is 1.4mg cm-2The electrolyte solution is 1 mol. L-1Lithium bistrifluoromethanesulfonimide (L iTFSI)/dimethyl ether (DME) -dioxolane (DO L) (volume ratio 1:1), and 1 wt.% of L iNO3The diaphragm is a polypropylene/polyethylene microporous membrane (Celgard2500), all batteries (2032 type button batteries) are assembled in an anhydrous and oxygen-free glove box, a lithium sheet is used as a counter electrode, the battery test is carried out on a blue CT2001 multi-channel battery measuring device, a constant current charging and discharging method is adopted, the voltage range is 1.7-2.8V, the Cyclic Voltammetry (CV) test is carried out on Bio-L clinical VMP3 and VMP300 multi-channel electrochemical measuring devices, and the voltage scanning rate is 0.1 mV.min-1The voltage range is 1.7-2.8V.
Fig. 3 is a lithium sulfur battery performance test result of S @ hnnc electrode: at 0.2, 1, 5, 10 and 20A g-1Specific capacity under current density is 1373, 1157, 900, 777 and 539mAh g-1；1A·g-1The specific capacity is kept at 1058 mAh.g after circulating for 100 circles under the current density-1(ii) a At 5 and 10 A.g-1The specific capacity is still maintained at 555 and 438mAh g after the current density is cycled for 1000 circles-1It is demonstrated that L i-S @ hNCNC has excellent high rate capability and long cycle stability.
Comparative example
Same procedure as in example 1 except that pyridine vapor was replaced with benzene vapor, hollow carbon nanocages (hCNC) were obtained.
Mixing 76.0 wt.% of S @ hCNC carbon-based metal-free electrocatalyst, acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, taking N-methylpyrrolidone as a solvent, uniformly stirring, uniformly coating the mixture on an aluminum foil, drying at 80 ℃ and tabletting to obtain a working electrode piece (L i-S @ hCNC), wherein the loading amount of the carbon-based metal-free electrocatalyst is 1.4 mg-cm-2The electrolyte solution is 1 mol. L-1Lithium bistrifluoromethanesulfonimide (L iTFSI)/dimethyl ether (DME) -dioxolane (DO L) (volume ratio 1:1), and 1 wt.% of L iNO3. The separator was a polypropylene/polyethylene microporous membrane (Celgard 2500). All the batteries (2032 type button battery) are in the hands without water and oxygenThe battery test is carried out on a blue CT2001 multi-channel battery measuring device by adopting a constant current charging and discharging method, the voltage range is 1.7-2.8V, the cyclic volt-ampere (CV) test is carried out on a Bio-L ogic VMP3 and VMP300 multi-channel electrochemical measuring device, and the voltage scanning speed is 0.1 mV.min-1The voltage range is 1.7-2.8V.
The results of the performance test of the lithium sulfur battery with the S @ hCNC electrode of fig. 3 are: at 0.2, 1, 5, 10 and 20A g-1Specific capacity under current density is 1195, 998, 759, 619 and 251 mAh.g in sequence-1；1A·g-1The specific capacity of the capacitor is 829 mAh.g after circulating for 100 circles under the current density-1(ii) a At 5 and 10 A.g-1The specific capacity is 408 and 320 mAh.g after 1000 cycles of circulation under the current density-1。
FIG. 2 is a CV curve (a) and a cell charge-discharge plateau potential-current density plot (b) for S @ hNCC carbon-based metal-free electrocatalyst prepared in example 1 of the present invention and S @ hNCC prepared in comparative example versus L i2S6CV test results of the electrolyte show that S @ hNCNC catalyzes L i2S6The Tafel slopes for oxidation and reduction were 82.3 and 74.3mV dec, respectively-1And the corresponding values for S @ hCNC are 111 and 134mV · dec, respectively-1The cell charge-discharge plateau potential-current density plot of fig. 2b shows that the cell charge-discharge overpotential of S @ hnnc is lower, compared to L i-S @ hCNC, the oxidation peak and reduction peak of L i-S @ hnncnc appear negative-shifted and positive-shifted, respectively, consistent with the behavior of charge-discharge plateau potential under different current densities, i.e. the charge potential is reduced and the discharge potential is increased, indicating that the N-doped hnncnc has a catalytic effect.
Comparing the data of example 1 with the data of the comparative example, it can be seen that: the Tafel slope of the comparative example S @ hCNC electrocatalyst was significantly higher than the corresponding value for the S @ hnnc electrocatalyst of example 1; the cell charge-discharge overpotential for the comparative example S @ hCNC electrocatalyst was significantly higher than the corresponding value for the S @ hnnc electrocatalyst in example 1; the specific capacity, the multiplying power, the cycling stability and other electrochemical energy storage performances of the lithium-sulfur battery of the comparative example S @ hNCC electrocatalyst are obviously inferior to the corresponding numerical values of the S @ hNCNC electrocatalyst in example 1. These results show that: nitrogen heteroatom doped hnncc has significant catalytic effect on oxidation and reduction reactions of polysulfides, thus resulting in a significantly better electrochemical energy storage performance of S @ hnncc in example 1 than the comparative example.
Example 2
Nitrogen-doped carbon nanocages having a nitrogen content of 20.0 at.% were prepared using the same protocol as in example 1.
5.0g of sodium thiosulfate is weighed and dissolved in a deionized water solution of 200m L to prepare 25.0 g. L-1Sodium thiosulfate solution is prepared by selecting hNCNC with N content of 20.0 at.%, dispersing 0.100g of hNCNC in 100m L of deionized water, and adding 200m L25.0.0 g. L-1Sodium thiosulfate solution, stirring well, at 3.0m L. min-1At a rate of 300m L0.2 mol L-1And (3) reacting the dilute hydrochloric acid solution for 2 hours, filtering, washing, drying at 70 ℃, putting the sample in an Ar inert gas flow at 140 ℃ for 12 hours to melt sulfur and fill the sulfur into the cavity of the nano cage, and heating the sample to 180 ℃ under the Ar inert gas flow to treat for 1.5 hours to remove adsorbed S on the outer surface of the nano cage. After the sample had cooled naturally to room temperature, the catalyst S @ hNCNC was obtained with an S loading of 74.5 wt.% measured by TA.
Mixing 74.5 wt.% of S @ hNCNC carbon-based metal-free electrocatalyst, acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, uniformly stirring the mixture by taking N-methyl pyrrolidone as a solvent, uniformly coating the mixture on an aluminum foil, and drying and tabletting the aluminum foil at 80 ℃ to obtain the working electrode slice. The loading amount of the carbon-based metal-free electrocatalyst is 1.5mg cm-2The electrolyte solution is 1 mol. L-1Lithium bistrifluoromethanesulfonimide (L iTFSI)/dimethyl ether (DME) -dioxolane (DO L) (volume ratio 1:1), and 1 wt.% of L iNO3The diaphragm is a polypropylene/polyethylene microporous membrane (Celgard2500), all batteries (2032 type button batteries) are assembled in an anhydrous and oxygen-free glove box, a lithium sheet is used as a counter electrode, the battery test is carried out on a blue CT2001 multi-channel battery measuring device, a constant current charging and discharging method is adopted, the voltage range is 1.7-2.8V, the Cyclic Voltammetry (CV) test is carried out on Bio-L clinical VMP3 and VMP300 multi-channel electrochemical measuring devices, and the voltage scanning rate is 0.1 mV.min-1The voltage range is 1.7-2.8V.
The performance test result of the lithium-sulfur battery is as follows: at 0.21, 5, 10 and 20A g-1Specific capacity under current density is 1273, 1085, 820, 732 and 478 mAh.g-1；1A·g-1The specific capacity is kept at 944mAh g after circulating for 100 circles under the current density-1(ii) a At 5 and 10 A.g-1The specific capacity is still maintained at 427 and 335mAh g after 1000 cycles of circulation under the current density-1。
Example 3
Nitrogen-doped carbon nanocages having a nitrogen content of 8.9 at.% were prepared using the same protocol as in example 1.
5.0g of sodium thiosulfate is weighed and dissolved in a deionized water solution of 200m L to prepare 25.0 g. L-1Selecting hNCNC with N content of 8.9 at.%, dispersing 0.100g hNCNC into 100m L deionized water solution, adding 100m L25.0.0 g. L-1Sodium thiosulfate solution, stirring well, at 3.0m L. min-1At a rate of 300m L0.2 mol L-1And (3) reacting the dilute hydrochloric acid solution for 2 hours, filtering, washing, drying at 70 ℃, putting the sample in Ar inert gas flow at 170 ℃ for 12 hours to melt sulfur and fill the sulfur into the cavity of the nanocage, and heating the sample to 250 ℃ under the Ar inert gas flow to treat for 1.5 hours to remove adsorbed S on the outer surface of the nanocage. After the sample was naturally cooled to room temperature, the catalyst S @ hNCNC was obtained, the S loading of which was measured by TA as 20.0 wt.%.
Mixing 20.0 wt.% of S @ hNCNC carbon-based metal-free electrocatalyst, acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, uniformly stirring the mixture by taking N-methyl pyrrolidone as a solvent, uniformly coating the mixture on an aluminum foil, and drying and tabletting the aluminum foil at 80 ℃ to obtain the working electrode slice. The loading amount of the carbon-based metal-free electrocatalyst is 1.0mg cm-2The electrolyte solution is 1 mol. L-1Lithium bistrifluoromethanesulfonimide (L iTFSI)/dimethyl ether (DME) -dioxolane (DO L) (volume ratio 1:1), and 1 wt.% of L iNO3The diaphragm is a polypropylene/polyethylene microporous membrane (Celgard2500), all batteries (2032 type button batteries) are assembled in an anhydrous and oxygen-free glove box, a lithium sheet is used as a counter electrode, a battery test is carried out on a blue CT2001 multi-channel battery measuring device, a constant current charging and discharging method is adopted, the voltage range is 1.7-2.8V, and the multi-channel electrochemical test is carried out on Bio-L clinical VMP3 and VMP300The Cyclic Voltammetry (CV) test was performed on a measuring device with a voltage sweep rate of 0.1 mV. min-1The voltage range is 1.7-2.8V.
The performance test result of the lithium-sulfur battery is as follows: at 0.2, 1, 5, 10 and 20A g-1The specific capacity under the current density is 1103, 904, 750, 587 and 419 mAh.g in sequence-1；1A·g-1The specific capacity is kept at 758mAh & g after 100 cycles of circulation under the current density-1(ii) a At 5 and 10 A.g-1The specific capacity is still maintained at 322 and 204mAh g after the current density is cycled for 1000 circles-1。
Example 4
Nitrogen-doped carbon nanocages having a nitrogen content of 8.9 at.% were prepared using the same protocol as in example 1.
10.0g of sodium thiosulfate is weighed and dissolved in a deionized water solution of 200m L to prepare 25.0 g. L-1Sodium thiosulfate solution is prepared by selecting hNCNC with N content of 8.9 at.%, dispersing 0.100g hNCNC in 100m L deionized water solution, and adding 200m L25.0.0 g. L-1Sodium thiosulfate solution, fully stirred, added with 300m L0.2.2 mol L at the rate of 3.0m L min-1-1And (3) reacting the dilute hydrochloric acid solution for 2 hours, filtering, washing, drying at 70 ℃, putting the sample in Ar inert gas flow at 155 ℃ for 12 hours to melt sulfur and fill the sulfur into the cavity of the nanocage, and heating the sample to 250 ℃ under the Ar inert gas flow to treat for 2 hours so as to remove adsorbed S on the outer surface of the nanocage. After the sample had cooled naturally to room temperature, the catalyst S @ hNCNC was obtained with an S loading of 90.0 wt.% measured by TA.
Mixing 90.0 wt.% of S @ hNCNC carbon-based metal-free electrocatalyst, acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, uniformly stirring the mixture by taking N-methyl pyrrolidone as a solvent, uniformly coating the mixture on an aluminum foil, and drying and tabletting the aluminum foil at 80 ℃ to obtain the working electrode slice. The loading amount of the carbon-based metal-free electrocatalyst is 1.5mg cm-2The electrolyte solution is 1 mol. L-1Lithium bistrifluoromethanesulfonimide (L iTFSI)/dimethyl ether (DME) -dioxolane (DO L) (volume ratio 1:1), and 1 wt.% of L iNO3. The separator was a polypropylene/polyethylene microporous membrane (Celgard 2500). All batteries (2032 type button battery) are assembled in a water-free and oxygen-free glove box, and lithium sheets are used as pairsThe electrode is used for carrying out battery test on a blue CT2001 multi-channel battery measuring device, a constant current charging and discharging method is adopted, the voltage range is 1.7-2.8V, cyclic volt-ampere (CV) test is carried out on a Bio-L ogic VMP3 and VMP300 multi-channel electrochemical measuring device, and the voltage scanning rate is 0.1mV min-1The voltage range is 1.7-2.8V.
The performance test result of the lithium-sulfur battery is as follows: at 0.2, 1, 5, 10 and 20A g-1The specific capacity under the current density is 1023, 874, 703, 521 and 367 mAh.g-1；1A·g-1The specific capacity is kept at 701 mAh.g after circulating for 100 circles under the current density-1(ii) a At 5 and 10 A.g-1The specific capacity is still maintained at 284 and 190mAh & g after the current density is cycled for 1000 circles-1。
Example 5
Nitrogen-doped carbon nanocages having a nitrogen content of 8.9 at.% were prepared using the same protocol as in example 1.
In inert gas, 0.2g of nitrogen-doped carbon nanocages with the nitrogen content of 8.9 at.% and 1.0g of sulfur powder are uniformly mixed and ground for 30 minutes, and a sample is placed in Ar inert gas flow at 155 ℃ and kept for 12 hours; and raising the temperature to 250 ℃ for 2h to remove the adsorbed S on the outer surface of the nano cage, naturally cooling the sample to room temperature to obtain the catalyst S @ hNCNC, and measuring the S filling amount by using TA to be 75.5 wt.%.
Mixing 75.5 wt.% of S @ hNCNC carbon-based metal-free electrocatalyst, acetylene black and polyvinylidene fluoride according to the weight ratio of 8:1:1, uniformly stirring the mixture by taking N-methyl pyrrolidone as a solvent, uniformly coating the mixture on an aluminum foil, and drying and tabletting the aluminum foil at 80 ℃ to obtain the working electrode slice. The loading amount of the carbon-based metal-free electrocatalyst is 1.5mg cm-2The electrolyte solution is 1 mol. L-1Lithium bistrifluoromethanesulfonimide (L iTFSI)/dimethyl ether (DME) -dioxolane (DO L) (volume ratio 1:1), and 1 wt.% of L iNO3The diaphragm is polypropylene/polyethylene microporous membrane (Celgard2500), all batteries (2032 type button batteries) are assembled in an anhydrous and oxygen-free glove box, a lithium sheet is used as a counter electrode, battery test is carried out on a blue CT2001 multi-channel battery measuring device, a constant current charging and discharging method is adopted, the voltage range is 1.7-2.8V, and the batteries are subjected to multi-channel electrochemical testing in Bio-L clinical VMP3 and VMP300Cyclic Voltammetry (CV) measurements were performed on a chemical measurement device with a voltage sweep rate of 0.1mV min-1The voltage range is 1.7-2.8V.
The performance test result of the lithium-sulfur battery is as follows: at 0.2, 1, 5, 10 and 20A g-1The specific capacity under the current density is 1320, 1102, 873, 741 and 502 mAh.g in sequence-1；1A·g-1The specific capacity is kept at 1020mAh g after 100 cycles of circulation under the current density-1(ii) a At 5 and 10 A.g-1The specific capacity is still maintained at 531 and 422 mAh.g after 1000 cycles of circulation under the current density-1。
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (3)

1. An S-filled carbon-based metal-free electrocatalyst takes a nitrogen-doped carbon nanocage as a carrier, the nitrogen-doped carbon nanocage comprises a cage wall made of a nitrogen-doped carbon material and a cavity surrounded by the cage wall, and elemental sulfur is filled in the cavity; the loading of S in the S-filled carbon-based metal-free electrocatalyst was 75 wt.%; the specific surface area of the nitrogen-doped carbon nanocages is 1300m2·g-1Pore volume of 4.3cm3·g-1The nitrogen content in the nitrogen-doped carbon nanocages was 8.9 at.%;
the preparation method of the S-filled carbon-based metal-free electrocatalyst comprises the following steps:
(1) mixing steam of a volatile nitrogen-containing carbon source with a magnesium oxide precursor in an inert gas, and carrying out in-situ pyrolysis to obtain a core-shell structure nitrogen-doped carbon nanocage-coated magnesium oxide intermediate product, wherein the magnesium oxide precursor is basic magnesium carbonate or magnesium carbonate;
(2) soaking the core-shell structure intermediate product obtained in the step (1) in inorganic acid to remove a magnesium oxide template, so as to obtain a hollow nitrogen-doped carbon nanocage;
(3) mixing the hollow nitrogen-doped carbon nanocages obtained in the step (2), sodium thiosulfate, inorganic acid and waterCarrying out oxidation reduction reaction to obtain S and nitrogen doped carbon nanocage compound precursor, and mixing the sodium thiosulfate and water to obtain 25.0 g. L-1Mixing the hollow nitrogen-doped carbon nanocages with water to obtain a hollow nitrogen-doped carbon nanocage suspension, wherein the concentration of the hollow nitrogen-doped carbon nanocage suspension is 1.0 g. L-1At 3.0m L. min-1At a rate of 0.2 mol. L-1A dilute hydrochloric acid solution;
(4) and (3) sequentially melting and thermally treating the S and nitrogen-doped carbon nanocage compound precursor obtained in the step (3) in inert gas to obtain the S-filled carbon-based metal-free electrocatalyst.
2. The S-filled carbon-based metal-free electrocatalyst according to claim 1, characterized in that the temperature of melting in step (4) is 145-170 ℃ and the time of melting is 2-24 h.
3. Use of the S-filled carbon-based metal-free electrocatalyst according to claim 1 in a lithium sulfur battery.
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