Double-monatomic loaded porous carbon material and preparation and application thereof

Abstract

The invention relates to a double-monatomic-supported porous carbon material as well as preparation and application thereof, and belongs to the field of application of a sulfur positive electrode of a lithium-sulfur battery. The preparation method comprises the following steps: by taking multiple nitrogen-containing hydrocarbons as precursors, metal salt as a monatomic metal source and silicon dioxide spheres as a hard template, carrying out mixing, heating and stirring treatment, and then carrying out high-temperature sintering and acid etching on the silicon dioxide template, so as to obtain the double monatomic loaded porous carbon material. When the material is used as a positive electrode sulfur carrier, an assembled lithium-sulfur battery shows relatively excellent cycling stability. The method can be universally suitable for synthesis of various bimetallic monatomic catalysts, has the advantages of high metal monatomic loading capacity, good stability, low raw material cost, simple preparation process, mild conditions and good repeatability, and has the advantage of large-scale production.

Description

Technical Field

[0001] The present invention belongs to the field of new energy technology, and specifically relates to a double single atom-loaded porous carbon material and its preparation and application Background Art

[0002] With the increasing concern about environmental pollution, the "dual carbon" goal has been proposed. It is crucial to the efficient use of renewable resources to reduce carbon emissions, so there is an urgent need to develop large-scale energy storage technology and power battery technology. Secondary batteries can be used as key carriers for energy storage and conversion. With the rapid development of portable electronic devices, electric vehicles, energy storage power stations, aerospace and submarine technologies, the requirements for the energy density of secondary batteries are getting higher and higher. However, the energy density of commercial lithium-ion batteries is close to the theoretical upper limit, so it is necessary to develop and manufacture battery systems with high specific energy density. Among them, lithium-sulfur batteries are considered to be potential high-specific energy secondary battery systems because of their high theoretical discharge capacity (1675mAh / g) and specific energy (2567Wh / kg), low raw material cost and environmental friendliness.

[0003] Lithium-sulfur battery is a battery system with sulfur as positive electrode and metallic lithium as negative electrode, but the development of lithium-sulfur battery still faces the following problems: the reaction kinetics of sulfur positive electrode are slow and the utilization rate of active materials is low, resulting in low specific energy of battery; the intermediate product lithium polysulfide (LiPSs) produced during the charging and discharging process of sulfur positive electrode is easily dissolved in lithium-sulfur battery electrolyte, and under the action of electric field and concentration gradient, it is easy to pass through the diaphragm to shuttle to the metallic lithium negative electrode for reduction reaction, thereby causing battery self-discharge; the side reaction of LiPSs shuttling with lithium negative electrode will cause lithium negative electrode corrosion, electrolyte depletion and other problems, and the uneven dissolution and deposition of lithium will cause lithium dendrites and dead lithium, thereby reducing the stripping / deposition efficiency of lithium, so it will cause the coulombic efficiency and cycle performance of lithium-sulfur battery to decay rapidly during the cycle.

[0004] In the Chinese patent with the authorization publication number CN113707884A, an in-situ preparation method and application of a 3D Mo2C-Mo3N2 / rGO heterostructure material are mentioned. Although the metal particle material has a certain adsorption and catalytic conversion effect on lithium polysulfide, due to the low atomic utilization rate, the amount of material used to provide the metal source is large; the active center is single, and the catalytic conversion efficiency of lithium polysulfide is not high, so the lithium-sulfur battery cycle performance is not ideal. In addition, in the Chinese patent with the publication number CN115360352A, a preparation method of a single-atom catalyst material for the sulfur positive electrode of a lithium-sulfur battery is mentioned, and it is applied to the positive electrode of a lithium-sulfur battery. Although the metal single-atom site loaded by the material has a high catalytic efficiency, since the single-atom catalyst material contains only one metal active center, it can only catalyze the single-step reaction of the sulfur positive electrode, and cannot simultaneously catalyze the reduction and oxidation reaction steps of sulfur, resulting in unsatisfactory battery cycle performance. Summary of the Invention

[0005] The present invention aims to solve the problems that existing metal compound catalysts have low catalytic efficiency for the sulfur cathode of lithium-sulfur batteries, can only catalyze single-step reactions of sulfur, etc., and it is difficult to effectively inhibit the shuttle effect, resulting in unsatisfactory cycle performance of lithium-sulfur batteries; the metal utilization rate is low, and the consumption of raw materials is large. The present invention provides a general preparation method of a porous carbon material loaded with dual single atoms. The porous carbon prepared by this method has a rich pore structure, which can not only construct a conductive network for electron transport, but also have a high specific surface area to better disperse and anchor metal single atoms, with the advantage of a high loading amount of dual single atoms. In addition, the porous carbon material loaded with dual single atoms has a strong adsorption effect on dissolved polysulfides, and can simultaneously catalyze the redox reaction of the sulfur cathode, with a dual-selective catalytic conversion effect, which can effectively alleviate the "shuttle effect" of polysulfides. When this material is used as a cathode sulfur carrier, the prepared lithium-sulfur battery exhibits excellent cycle stability. The preparation process has simple technological process, low raw material cost, good repeatability, and is suitable for large-scale production.

[0006] The technical solution of the present invention is as follows:

[0007] A porous carbon material loaded with dual single atoms, its preparation and application, which is characterized by including the following steps:

[0008] Step 1: Dissolve a nitrogen-carbon-hydrogen compound and metal salts of two different metals in deionized water. The metals in the metal salts are any two of iron, cobalt, and nickel; and the molar ratio of the two metals is 1:0.5 - 2;

[0009] Step 2: Add silicon dioxide powder to the above solution and stir evenly;

[0010] Step 3: Heat and stir the above solution, evaporate the water and boil the solution until it becomes thick caramel color and then perform drying treatment.

[0011] Step 4: Grind the above material and place it in a tube furnace for calcination and carbonization treatment to obtain a carbon composite material;

[0012] Step 5: Etch the carbonized material with hydrofluoric acid, wash it with water, and dry it to obtain a porous carbon material loaded with dual single atoms.

[0013] In the above technical solution, the nitrogen-carbon-hydrogen compound selected in step 1 is one or a mixture of two or more of glucosamine, glucosamine hydrochloride, melamine, dicyandiamide, cyanoguanidine, alanine, lysine, g-C3N4, 2-methylimidazole, methionine, cysteine, and mercaptopropionic acid; the metal salts include a mixture of metal salts of two different metals among ferric nitrate, cobalt nitrate, nickel nitrate, ferric chloride, cobalt chloride, nickel chloride, iron phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, iron acetate, cobalt acetate, nickel acetate, iron acetylacetonate, cobalt acetylacetonate, and nickel acetylacetonate; the molar ratio of the nitrogen-carbon-hydrogen compound to the metal salt is 10 to 2000:1 (preferably 10 to 500:1); the mass concentration of the nitrogen-carbon-hydrogen compound in water is 50 to 200 g / L (preferably 100 to 150 g / L); the volume of water is 50 to 200 mL (preferably 100 to 150 mL);

[0014] In step 2, the molar ratio of the silica to the nitrogen-carbon-hydrogen compound is 1 to 300:1 (preferably 10 to 200:1), and the particle size of SiO2 is between 10 and 500 nm (preferably 50 to 200); the stirring time is 2 to 3 h;

[0015] In step 3, the heating temperature is 60 to 100 °C, and the heating and stirring time is 2 to 5 h;

[0016] In step 4, the calcination temperature is 500 to 1000 °C (preferably 700 to 900 °C), the calcination time is 1 to 10 h (preferably 2 to 4 h), and the calcination atmosphere is high-purity nitrogen and / or argon;

[0017] In step 5, the mass fraction of the HF solution is 5 to 50% (preferably 10 to 20%), the mass ratio of silica to hydrofluoric acid is 1:1 to 10 (preferably 1:4 to 7), and the etching time is 4 to 30 h (preferably 6 to 24 h).

[0018] The specific surface area of the prepared dual single-atom loaded porous carbon material is 300 to 2000 m 2 / g, the mass fraction of the metal single atom is 0.1% to 10%, and the material has dual metal single-atom sites;

[0019] The dual single-atom loaded porous carbon catalyst described in the present invention is used as a carrier material for elemental sulfur to prepare a sulfur cathode for a lithium-sulfur battery.

[0020] The present invention uses various nitrogen-containing hydrocarbons as precursors, metal salts as the metal source for single atoms, and silica spheres as hard templates. After mixing, heating, and stirring, and then through high-temperature sintering and acid etching of the silica template, a porous carbon material loaded with double single atoms is obtained. The characteristics of the present invention are that a large number of defect sites are generated during the pyrolysis of nitrogen-containing hydrocarbons, which is conducive to anchoring metal elements to form double single-atom sites; the porous carbon obtained after silica etching has a high specific surface area and a rich pore structure, which can further expose more double single-atom active sites, and then more effectively adsorb and catalyze the redox reaction of the sulfur cathode; the double single-atom sites can not only increase the active sites of metal elements, but also catalyze the reduction reaction and oxidation reaction of the sulfur cathode simultaneously, with a strong dual-selective catalytic conversion effect, thus effectively inhibiting the "shuttle effect" of polysulfide intermediate products. When this material is used as a cathode sulfur carrier, the assembled lithium-sulfur battery exhibits excellent cycle stability. The present invention can be generally applied to the synthesis of various bimetallic single-atom catalysts. One or more porous carbon materials loaded with different metal double single atoms can be prepared by adjusting the types of different metal salt precursors. At the same time, by changing the types of nitrogen-containing hydrocarbons, double single-atom active centers with different element (C / N / S) coordinations can be obtained, thereby realizing the controllable adjustment of catalytic performance; moreover, the metal single-atom loading is high, the stability is good, and at the same time, the raw material cost is low, the preparation process is simple, the conditions are mild, and the repeatability is good, having the advantages of large-scale production. Description of the Drawings

[0021] Figure 1 is the XRD diffraction pattern of the material of Example 1;

[0022] Figure 2 is the transmission electron microscope image of the material of Example 1;

[0023] Figure 3 is the BET adsorption test result of the material of Example 1;

[0024] Figure 4 is the aberration-corrected transmission electron microscope image of the material of Example 1;

[0025] Figure 5 is the comparative diagram of cyclic voltammograms of the lithium-sulfur batteries of Example 1, Comparative Example 1, and Comparative Example 2;

[0026] Figure 6 is the comparative diagram of the cycling performance of the lithium-sulfur batteries of Example 1, Comparative Example 1, and Comparative Example 2;

[0027] Figure 7 is the XRD diffraction pattern of the material of Example 2;

[0028] Figure 8 is the BET adsorption test result of the material of Example 2;

[0029] Figure 9 It is the aberration-corrected transmission electron microscopy image of the material in Example 2;

[0030] Figure 10 It is the comparative diagram of cyclic voltammetry curves of the lithium-sulfur batteries in Example 2, Comparative Example 3 and Comparative Example 4;

[0031] Figure 11 It is the comparative diagram of the cycling performance of the lithium-sulfur batteries in Example 2, Comparative Example 3 and Comparative Example 4;

[0032] Figure 12 It is the aberration-corrected transmission electron microscopy image of Example 3;

[0033] Figure 13 It is the aberration-corrected transmission electron microscopy image of Example 4;

[0034] Figure 14 It is the aberration-corrected transmission electron microscopy image of Example 5; Specific Embodiments

[0035] The following examples are further illustrations of the present invention rather than limiting the scope of the present invention.

[0036] Example 1

[0037] Take 0.07 mol of glucosamine hydrochloride, 0.001 mol of iron nitrate and 0.001 mol of cobalt nitrate, add 150 ml of deionized water and stir to mix evenly. Then add 1.5 mol of silicon dioxide (particle size 20 - 100 nm) and stir for 2 h. Subsequently, heat with stirring at 100 °C for 2 h, evaporate the water and boil the solution until it becomes thick caramel color and dries. After drying and grinding, spread the powder on a magnetic boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it constant for 2 h, then raise the temperature to 900 °C and keep it constant for 3 h, and cool to room temperature with the furnace. Add the carbonized material to 450 g of 20% HF aqueous solution by mass, stir for 12 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral. Then place the product in an oven at 75 °C and dry for 12 h to obtain the porous carbon material loaded with N-coordinated dual single atoms of Fe and Co (Fe / Co-N-C). According to the XRD results ( Figure 1 ), it shows that there are no impurities such as Fe and Co compounds, proving that the metal is dispersed on the carbon carrier in the form of single atoms. According to the transmission electron microscopy image ( Figure 2 ), it can be seen that the Fe / Co-N-C material has a rich pore structure, and the pore size range is 20 - 100 nm. According to the BET adsorption test results ( Figure 3 ), it can be known that the specific surface area of the material is 800 mg / cm 2 . Figure 4It is a spherical aberration corrected transmission electron microscope image of Fe / Co-N-C material. It can be seen that the surface of the carbon material has abundant single-atom sites. Through ICP results, it is obtained that this material has dual-metal single-atom sites, with the mass fraction of Fe metal single atoms being 0.4% and the mass fraction of Co metal single atoms being 0.6%.

[0038] Take 0.1 g of Fe / Co-N-C, grind it with 0.3 g of sublimed sulfur, and transfer it to a sealed autoclave. Heat-treat it at 155 °C for 12 h to obtain a porous carbon-sulfur composite material (S@Fe / Co-N-C) loaded with Fe-Co dual single atoms.

[0039] Take 0.08 g of S@Fe / Co-N-C and 0.01 g of conductive carbon, add 0.2 g of polyvinylidene fluoride (PVDF, mass concentration 5%) solution, use 2 ml of N-methylpyrrolidone as the solvent, grind for 1 h, then coat it on a carbon-coated aluminum foil current collector with a thickness of 300 μm, dry it overnight at 60 °C, cut it into 12 mm diameter circular pieces, weigh them, and vacuum dry them at 55 °C for 24 h. Use this electrode as the positive electrode, a lithium sheet as the negative electrode, Celgard 2500 as the separator, 1 M lithium bis(trifluoromethylsulfonyl)imide solution (LITFSI) as the electrolyte, 0.2 M lithium nitrate as the additive, and a mixed solution of 1,3-dioxolane (DOL) and dimethyl ether (DME) (volume ratio 1:1) as the solvent to assemble a coin-type lithium-sulfur battery and conduct cyclic voltammetry tests and charge-discharge tests at a 1C rate. Figure 5 It is the cyclic voltammetry curve of a lithium-sulfur battery with S@Fe / Co-N-C and the control groups S@Fe-N-C and S@Co-N-C as the positive electrodes. It can be seen that Fe-N-C is more conducive to catalyzing the reduction of the sulfur positive electrode, Co-N-C is more conducive to catalyzing the oxidation of the sulfur positive electrode, and Fe / Co-N-C is a dual-selective catalyst with the ability to catalyze both sulfur oxidation and reduction simultaneously. Figure 6 It is the charge-discharge cycle performance test of a lithium-sulfur battery at 1C. It can be seen that S@Fe / Co-N-C has a higher discharge specific capacity and better cycle stability compared to S@Fe-N-C and S@Co-N-C.

[0040] Example 2

[0041] Take 0.07 mol of glucosamine, 0.12 mol of melamine, 0.001 mol of iron acetate, and 0.001 mol of nickel acetate. Add 100 ml of deionized water, stir and mix evenly, then add 2 mol of silica (particle size 50 - 200 nm), and stir for 3 h. Subsequently, heat with stirring at 90 °C for 2 h, evaporate the water and boil the solution until it becomes thick and caramel-colored and then dry. After drying and polishing, spread the powder on a porcelain boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it at a constant temperature for 2 h, then raise the temperature to 800 °C and keep it at a constant temperature for 4 h, and then cool to room temperature with the furnace. Place the carbonized material in 800 g of an HF aqueous solution with a mass concentration of 10%, stir for 24 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral, and then place the product in an oven at 75 °C and dry for 12 h to obtain a porous carbon material (Fe / Ni-N-C) loaded with N-coordinated dual single atoms of Fe and Ni. According to the XRD results ( Figure 7 ), it shows that there are no impurities such as Fe and Ni compounds, proving that the metals are dispersed on the carbon carrier in the form of single atoms. According to the BET adsorption test results ( Figure 8 ), it can be known that the specific surface area of the material is 1000 mg / cm 2 . Figure 9 is the aberration-corrected transmission electron microscope image of the Fe / Ni-N-C material. It can be seen that the surface of the carbon material has abundant single-atom sites, and the pore size range is 50 - 200 nm. Through ICP results, it is obtained that the material has dual-metal single-atom sites, the mass fraction of Fe metal single atoms is 1%, and the mass fraction of Ni metal single atoms is 1%.

[0042] The process and conditions of sulfur impregnation of the material, positive electrode coating, and electrochemical testing of the coin lithium-sulfur battery are the same as those in Example 1. Figure 10 are the cyclic voltammograms of lithium-sulfur batteries with S@Fe / Ni-N-C and the control groups S@Fe-N-C and S@Ni-N-C as the positive electrodes. It can be seen that Fe-N-C is more conducive to catalyzing the reduction of the sulfur positive electrode, Ni-N-C is more conducive to catalyzing the oxidation of the sulfur positive electrode, and Fe / Ni-N-C is a dual-selective catalyst with simultaneous catalytic sulfur redox. Figure 11 is the charge-discharge cycling performance test of the lithium-sulfur battery at 1C. It can be seen that S@Fe / Ni-N-C has a higher discharge specific capacity and better cycling stability compared to S@Fe-N-C and S@Ni-N-C.

[0043] Example 3

[0044] Take 0.07 mol of glucosamine hydrochloride, 0.06 mol of melamine, 0.02 mol of cyanoguanidine, 0.08 mol of mercaptopropionic acid, 0.001 mol of iron phthalocyanine and 0.001 mol of cobalt phthalocyanine. Add 200 ml of deionized water, stir and mix evenly, then add 1.5 mol of silica (particle size 200 - 500 nm), and stir for 3 h. Subsequently, heat with stirring at 80 °C for 3 h, evaporate the water and boil the solution until it becomes thick and caramel-colored and then dry. After drying and polishing, spread the powder on a boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it constant for 2 h, then raise the temperature to 700 °C and keep it constant for 5 h, and then cool down to room temperature with the furnace. Place the carbonized material in 300 g of an HF aqueous solution with a mass concentration of 20%, stir for 10 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral, and then place the product in an oven at 75 °C and dry for 10 h to obtain a porous carbon material (Fe / Co-NS-C) loaded with N-coordinated double single atoms of Fe and Co. Its aberration-corrected transmission electron microscope is as shown in Figure 12 It can be seen that the carbon material surface has abundant single-atom sites. The specific surface area of the material is 700 mg / cm 2 , and the pore size range is 200 - 500 nm. Through ICP results, it is concluded that the material has double-metal single-atom sites. The mass fraction of Fe metal single atoms is 1%, and the mass fraction of Co metal single atoms is 1.2%.

[0045] The process and conditions of sulfur impregnation, positive electrode coating, and electrochemical testing of the button lithium-sulfur battery for the material are the same as those in Example 1. Fe-NS-C is more conducive to catalyzing the reduction of the sulfur cathode, Co-NS-C is more conducive to catalyzing the oxidation of the sulfur cathode, and Fe / Co-NS-C is a dual-selective catalyst with simultaneous catalysis of sulfur redox. Therefore, S@Fe / Co-NS-C has a higher discharge specific capacity and better cycle stability in the charge-discharge cycle performance test at 1C compared to S@Fe-NS-C and S@Co-NS-C.

[0046] Example 4

[0047] Take 0.12 mol of alanine, 0.12 mol of melamine, 0.08 mol of cysteine, 0.001 mol of iron acetylacetonate and 0.001 mol of nickel acetylacetonate. Add 80 ml of deionized water, stir and mix evenly, then add 0.8 mol of silica (particle size 50 - 300 nm) and stir for 3 h. Subsequently, heat with stirring at 60 °C for 5 h, evaporate the water and boil the solution until it becomes viscous caramel color and dries. After drying and grinding, spread the powder evenly in a boat and place it in a tube furnace. Under an argon atmosphere, first heat to 500 °C and keep it constant for 2 h, then raise the temperature to 1000 °C and keep it constant for 2 h, and then cool it to room temperature with the furnace. Place the carbonized material in 300 g of 20% HF aqueous solution by mass, stir for 15 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral. Then place the product in an oven at 75 °C and dry for 12 h to obtain a porous carbon material (Fe / Ni-NS-C) loaded with N-coordinated double single atoms of Fe and Ni. Its aberration-corrected transmission electron microscope is as Figure 13 shown. It can be seen that the surface of the carbon material has abundant single-atom sites. The specific surface area of the material is 500 mg / cm 2 , and the pore size range is 50 - 300 nm. Through ICP results, it is concluded that the material has double-metal single-atom sites. The mass fraction of single Fe metal single atoms is 1.2%, and the mass fraction of single Ni metal single atoms is 1.3%.

[0048] The process and conditions of sulfur impregnation, positive electrode coating and electrochemical testing of coin lithium-sulfur batteries for the material are the same as those in Example 1. Fe-NS-C is more conducive to catalyzing the reduction of the sulfur positive electrode, Ni-NS-C is more conducive to catalyzing the oxidation of the sulfur positive electrode, and Fe / Ni-NS-C is a dual-selective catalyst with simultaneous catalysis of sulfur redox. Therefore, S@Fe / Ni-NS-C has a higher discharge specific capacity and better cycle stability than S@Fe-NS-C and S@Ni-NS-C in the charge-discharge cycle performance test at 1C.

[0049] Example 5

[0050] Take 0.08 mol of lysine, 0.1 mol of g-C3N4, 0.08 mol of methionine, 0.001 mol of ferric chloride and 0.001 mol of cobalt chloride. Add 50 ml of deionized water, stir and mix evenly, then add 1.2 mol of silicon dioxide (particle size 10 - 100 nm), and stir for 3 h. Subsequently, heat with stirring at 60 °C for 3 h, evaporate the water and boil the solution until it becomes viscous and caramel-colored until dry. After drying and grinding, spread the powder evenly in a boat and place it in a tube furnace. Under an argon atmosphere, first heat to 500 °C and keep it at a constant temperature for 2 h, then raise the temperature to 900 °C and keep it at a constant temperature for 3 h, and cool down to room temperature with the furnace. Place the carbonized material in 480 g of an HF aqueous solution with a mass concentration of 10%, stir for 6 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral. Then place the product in an oven at 75 °C and dry for 10 h to obtain a porous carbon material (Fe / Co-NS-C) loaded with N-coordinated dual single atoms of Fe and Co. Its aberration-corrected transmission electron microscope is as Figure 14 shown, and it can be seen that the surface of the carbon material has abundant single-atom sites. The specific surface area of the material is 600 mg / cm 2 , and the pore size range is 10 - 100 nm. Through ICP results, it is concluded that the material has dual-metal single-atom sites. The mass fraction of single Fe metal single atoms is 1.6%, and the mass fraction of Co metal single atoms is 1.8%.

[0051] The process of sulfur impregnation, positive electrode coating, and electrochemical testing (process and conditions) of the coin-type lithium-sulfur battery of the material are the same as those in Example 1. Fe-NS-C is more conducive to catalyzing the reduction of the sulfur cathode, Co-NS-C is more conducive to catalyzing the oxidation of the sulfur cathode, and Fe / Co-NS-C is a dual-selective catalyst with simultaneous catalytic sulfur redox. Therefore, S@Fe / Co-NS-C has a higher discharge specific capacity and better cycle stability than S@Fe-NS-C and S@Co-NS-C in the charge-discharge cycle performance test at 1C.

[0052] Example 6

[0053] Take 0.07 mol of glucosamine hydrochloride, 0.18 mol of dicyandiamide, 0.02 mol of cyanoguanidine, 0.04 mol of mercaptopropionic acid, 0.04 mol of cysteine, 0.001 mol of iron phthalocyanine and 0.001 mol of nickel phthalocyanine drugs. Add 150 ml of deionized water, stir and mix evenly, then add 1 mol of silicon dioxide (particle size 20 - 80 nm), stir for 3 h, then heat with stirring at 80 °C for 3 h, evaporate the water and boil the solution until it becomes thick caramel color and dries. After drying and grinding, spread the powder on a magnetic boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it at a constant temperature for 1 h, then raise the temperature to 850 °C and keep it at a constant temperature for 4 h, and cool it to room temperature with the furnace. Place the carbonized material in 150 g of 40% mass concentration HF aqueous solution, stir for 4 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral, and then place the product in an oven at 75 °C and dry for 10 h to obtain a porous carbon material (Fe / Ni-NS-C) loaded with N-coordinated double single atoms of Fe and Ni. The carbon material surface has abundant single atom sites, and the specific surface area is 600 mg / cm 2 , and the pore size range is 20 - 80 nm. Through ICP results, it is concluded that the material has bimetallic single atom sites, the mass fraction of Fe metal single atoms is 1.6%, and the mass fraction of Ni metal single atoms is 1.3%.

[0054] The process and conditions of sulfur impregnation of the material, coating of the positive electrode sheet and electrochemical testing of the coin-type lithium-sulfur battery are the same as those in Example 1. Fe-NS-C is more conducive to catalyzing the reduction of the sulfur positive electrode, Ni-NS-C is more conducive to catalyzing the oxidation of the sulfur positive electrode, and Fe / Ni-NS-C is a dual-selective catalyst with simultaneous catalytic sulfur redox. Therefore, S@Fe / Ni-NS-C has a higher discharge specific capacity and better cycle stability than S@Fe-NS-C and S@Ni-NS-C in the charge-discharge cycle performance test at 1C.

[0055] Example 7

[0056] Take 0.07 mol of glucosamine, 0.02 mol of cyanoguanidine, 0.08 mol of mercaptopropionic acid, 0.001 mol of iron acetylacetonate and 0.001 mol of cobalt acetylacetonate. Add 100 ml of deionized water, stir and mix evenly, then add 2 mol of silica (particle size 50 - 200 nm), and stir for 2 h. Subsequently, heat with stirring at 100 °C for 2 h, evaporate the water and boil the solution until it becomes viscous caramel color and dries. After drying and grinding, spread the powder on a boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it constant for 1 h, then raise the temperature to 900 °C and keep it constant for 3 h, and cool to room temperature with the furnace. Place the carbonized material in 200 g of 50% mass concentration HF aqueous solution, stir for 4 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral. Then place the product in an oven at 75 °C and dry for 10 h to obtain a porous carbon material (Fe / Co-NS-C) loaded with N-coordinated double single atoms of Fe and Co. The carbon material surface has abundant single-atom sites, and the specific surface area is 850 mg / cm 2 , and the pore size range is 50 - 200 nm. The ICP results show that the material has double-metal single-atom sites. The mass fraction of Fe metal single atoms is 0.8%, and the mass fraction of Co metal single atoms is 1.0%.

[0057] The process and conditions of sulfur impregnation of the material, coating of the positive electrode and electrochemical testing of the coin-type lithium-sulfur battery are the same as those in Example 1. Fe-NS-C is more conducive to catalyzing the reduction of the sulfur cathode, Co-NS-C is more conducive to catalyzing the oxidation of the sulfur cathode, and Fe / Co-NS-C is a dual-selective catalyst with simultaneous catalysis of sulfur redox. Therefore, S@Fe / Co-NS-C has a higher discharge specific capacity and better cycle stability than S@Fe-NS-C and S@Co-NS-C in the charge-discharge cycle performance test at 1C. Example 8

[0058] Take 0.12 mol of alanine, 0.12 mol of melamine, 0.02 mol of cyanoguanidine, 0.001 mol of iron nitrate and 0.001 mol of nickel nitrate. Add them to 100 ml of deionized water, stir and mix evenly, then add 1 mol of silicon dioxide (particle size 50 - 100 nm) and stir for 2 h. Subsequently, heat with stirring at 60 °C for 4 h, evaporate the water and boil the solution until it becomes thick and caramel-colored and dries. After drying and grinding, spread the powder on a boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it at a constant temperature for 1 h, then raise the temperature to 900 °C and keep it at a constant temperature for 4 h, and cool it to room temperature with the furnace. Place the carbonized material in 600 g of an HF aqueous solution with a mass concentration of 5%, stir for 30 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral. Then place the product in an oven at 75 °C and dry for 10 h to obtain a porous carbon material (Fe / Ni-N-C) loaded with N-coordinated dual single atoms of Fe and Ni. The carbon material surface has abundant single-atom sites, and the specific surface area is 580 mg / cm 2 , and the pore size range is 50 - 100 nm. The ICP results show that the material has dual-metal single-atom sites. The mass fraction of Fe metal single atoms is 1.4%, and the mass fraction of Ni metal single atoms is 1.7%.

[0059] The process and conditions of sulfur impregnation of the material, positive electrode coating, and electrochemical testing of the coin lithium-sulfur battery are the same as in Example 1. Fe-N-C is more conducive to catalyzing the reduction of the sulfur cathode, Ni-N-C is more conducive to catalyzing the oxidation of the sulfur cathode, and Fe / Ni-N-C is a dual-selective catalyst with simultaneous catalysis of sulfur redox. Therefore, S@Fe / Ni-N-C has a higher discharge specific capacity and better cycle stability than S@Fe-N-C and S@Ni-N-C in the charge-discharge cycle performance test at 1C.

[0060] Example 9

[0061] Take 0.08 mol of lysine, 0.12 mol of melamine, 0.01 mol of g-C3N4, 0.001 mol of iron acetate, and 0.001 mol of cobalt acetate. Add 150 ml of deionized water, stir and mix evenly, then add 1.5 mol of silicon dioxide (particle size 100 - 200 nm), and stir for 2 h. Subsequently, heat with stirring at 80 °C for 3 h, evaporate the water and boil the solution until it becomes thick caramel-colored and dries. After drying and grinding, spread the powder evenly in a boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it at a constant temperature for 1 h, then raise the temperature to 1000 °C and keep it at a constant temperature for 2 h, and then cool down to room temperature with the furnace. Place the carbonized material in 450 g of an HF aqueous solution with a mass concentration of 20%, stir for 10 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral. Then place the product in an oven at 75 °C and dry for 10 h to obtain a porous carbon material (Fe / Co-N-C) loaded with N-coordinated dual single atoms of Fe and Co. The carbon material surface has abundant single-atom sites, and the specific surface area is 750 mg / cm 2 , and the pore size range is 100 - 200 nm. Through ICP results, it is concluded that the material has dual-metal single-atom sites. The mass fraction of Fe metal single atoms is 1.2%, and the mass fraction of Co metal single atoms is 1.3%.

[0062] The process and conditions of sulfur impregnation of the material, positive electrode coating, and electrochemical testing of the coin-type lithium-sulfur battery are the same as in Example 1. Fe-N-C is more conducive to catalyzing the reduction of the sulfur cathode, Co-N-C is more conducive to catalyzing the oxidation of the sulfur cathode, and Fe / Co-N-C is a dual-selective catalyst with simultaneous catalytic sulfur redox. Therefore, S@Fe / Co-N-C has a higher discharge specific capacity and better cycle stability than S@Fe-N-C and S@Co-N-C in the charge-discharge cycle performance test at 1C.

[0063] Example 10

[0064] Take 0.08 mol of lysine, 0.18 mol of dicyandiamide, 0.01 mol of g-C3N4, 0.08 mol of cysteine, 0.001 mol of ferric chloride and 0.001 mol of nickel chloride. Add 80 ml of deionized water, stir and mix evenly, then add 1 mol of silicon dioxide (particle size 300 - 500 nm), and stir for 2 h. Subsequently, heat with stirring at 90 °C for 2 h, evaporate the water and boil the solution until it becomes viscous caramel color and dries. After drying and grinding, spread the powder on a magnetic boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it constant for 1 h, then raise the temperature to 900 °C and keep it constant for 3 h, and cool to room temperature with the furnace. Place the carbonized material in 200 g of 40% mass concentration HF aqueous solution, stir for 8 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral. Then place the product in an oven at 75 °C and dry for 10 h to obtain a porous carbon material (Fe / Ni-NS-C) loaded with N-coordinated double single atoms of Fe and Ni. The carbon material surface has abundant single-atom sites, and the specific surface area is 620 mg / cm 2 , and the pore size range is 300 - 500 nm. From the ICP results, it can be concluded that the material has double-metal single-atom sites. The mass fraction of Fe metal single atoms is 1.1%, and the mass fraction of Ni metal single atoms is 1.3%.

[0065] The sulfur impregnation of the material, the coating of the positive electrode sheet, and the electrochemical (process and conditions) test of the coin lithium-sulfur battery are the same as in Example 1. Fe-NS-C is more conducive to catalyzing the reduction of the sulfur positive electrode, Ni-NS-C is more conducive to catalyzing the oxidation of the sulfur positive electrode, and Fe / Ni-NS-C is a dual-selective catalyst with simultaneous catalysis of sulfur redox. Therefore, S@Fe / Ni-NS-C has a higher discharge specific capacity and better cycle stability than S@Fe-NS-C and S@Ni-NS-C in the charge-discharge cycle performance test at 1C.

[0066] Comparative Example 1

[0067] Take 0.07 mol of glucosamine hydrochloride and 0.002 mol of ferric nitrate drugs, add 150 ml of deionized water, stir and mix evenly, then add 1.5 mol of silicon dioxide (particle size 20 - 100 nm), stir for 2 h, then heat with stirring at 100 °C for 2 h, evaporate the water and boil the solution until it becomes thick and caramel-colored and dries. After drying and polishing, spread the powder on a boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it constant for 2 h, then raise the temperature to 900 °C and keep it constant for 3 h, and cool to room temperature with the furnace. Add the carbonized material to 450 g of 20% HF aqueous solution by mass, stir for 12 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral, and then place the product in an oven at 75 °C and dry for 12 h to obtain a porous carbon material (Fe-N-C) loaded with N-coordinated single-atom Fe. The carbon material surface has abundant single-atom sites, and the specific surface area is 800 mg / cm 2 , and the pore size range is 20 - 100 nm. The ICP results show that the material has dual-metal single-atom sites, and the mass fraction of single-atom Fe metal is 1.0%.

[0068] The process and conditions of sulfur impregnation of the material, coating of the positive electrode sheet, and electrochemical testing of the coin-type lithium-sulfur battery are the same as those in Example 1. From Figure 5 The cyclic voltammetry curve shows that FeNC is beneficial to catalyze the reduction of the sulfur positive electrode but not beneficial to catalyze the oxidation of the sulfur positive electrode. Therefore, the cycling performance ( Figure 6 ) is poor.

[0069] Comparative Example 2

[0070] Take 0.07 mol of glucosamine hydrochloride and 0.002 mol of cobalt nitrate drugs, add 150 ml of deionized water, stir and mix evenly, then add 1.5 mol of silicon dioxide (particle size 20 - 100 nm), stir for 2 h, then heat with stirring at 100 °C for 2 h, evaporate the water and boil the solution until it becomes thick and caramel-colored and dries. After drying and polishing, spread the powder on a boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it constant for 2 h, then raise the temperature to 900 °C and keep it constant for 3 h, and cool to room temperature with the furnace. Add the carbonized material to 450 g of 20% HF aqueous solution by mass, stir for 12 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral, and then place the product in an oven at 75 °C and dry for 12 h to obtain a porous carbon material (Co-N-C) loaded with N-coordinated single-atom Co. The carbon material surface has abundant single-atom sites, and the specific surface area is 800 mg / cm 2 , and the pore size range is 20 - 100 nm. The ICP results show that the material has dual-metal single-atom sites, and the mass fraction of single-atom Co metal is 1.0%.

[0071] The sulfur immersion of the material, the coating of the positive electrode sheet, and the electrochemical testing (process and conditions) of the coin-type lithium-sulfur battery were the same as those in Example 1. From Figure 5 the cyclic voltammetry curve, it can be seen that CoNC is not conducive to catalyzing the reduction of the sulfur cathode but is conducive to catalyzing the oxidation of the sulfur cathode. Therefore, the cycling performance ( Figure 6 ) is poor.

[0072] Comparative Example 3

[0073] Take 0.07 mol of glucosamine, 0.12 mol of melamine, and 0.002 mol of iron acetate. Add 100 ml of deionized water and stir to mix evenly. Then add 2 mol of silicon dioxide (particle size 50 - 200 nm) and stir for 3 h. Subsequently, heat with stirring at 90 °C for 2 h, evaporate the water and boil the solution until it becomes viscous and caramel-colored until dry. After drying and grinding, spread the powder in a porcelain boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it at a constant temperature for 2 h, then raise the temperature to 800 °C and keep it at a constant temperature for 4 h, and cool it to room temperature with the furnace. Immerse the carbonized material in 800 g of an HF aqueous solution with a mass concentration of 10% and stir for 24 h to etch the SiO2 template. Then filter by suction and wash with deionized water until neutral. Then place the product in an oven at 75 °C and dry for 12 h to obtain a porous carbon material (Fe-N-C) loaded with N-coordinated single-atom Fe. The carbon material surface has abundant single-atom sites, with a specific surface area of 1000 mg / cm 2 , and the pore size range is 20 - 100 nm. The ICP results show that the material has dual-metal single-atom sites, and the mass fraction of Fe metal single atoms is 2.0%.

[0074] The sulfur immersion of the material, the coating of the positive electrode sheet, and the electrochemical testing (process and conditions) of the coin-type lithium-sulfur battery were the same as those in Example 1. From Figure 10 the cyclic voltammetry curve, it can be seen that FeNC is conducive to catalyzing the reduction of the sulfur cathode but is not conducive to catalyzing the oxidation of the sulfur cathode. Therefore, the cycling performance ( Figure 11 ) is poor.

[0075] Comparative Example 4

[0076] Take 0.07 mol of glucosamine, 0.12 mol of melamine, and 0.002 mol of nickel acetate. Add 100 ml of deionized water, stir and mix evenly, then add 2 mol of silica (particle size 50 - 200 nm) and stir for 3 h. Subsequently, heat with stirring at 90 °C for 2 h, evaporate the water and boil the solution until it becomes viscous and caramel-colored until dry. After drying and polishing, spread the powder on a porcelain boat and place it in a tube furnace. Under an argon atmosphere, first heat to 600 °C and keep it at a constant temperature for 2 h, then raise the temperature to 800 °C and keep it at a constant temperature for 4 h, and then cool to room temperature with the furnace. Place the carbonized material in 800 g of an HF aqueous solution with a mass concentration of 10%, stir for 24 h to etch the SiO2 template, then filter by suction and wash with deionized water until neutral, and then place the product in an oven at 75 °C and dry for 12 h to obtain a porous carbon material (Ni-N-C) loaded with N-coordinated single-atom Ni. The carbon material surface has abundant single-atom sites, and the specific surface area is 1000 mg / cm 2 , and the pore size range is 20 - 100 nm. From the ICP results, it can be concluded that the material has dual-metal single-atom sites, and the mass fraction of Ni metal single atoms is 2.0%.

[0077] The process and conditions of sulfur impregnation of the material, coating of the positive electrode sheet, and electrochemical testing of the coin-type lithium-sulfur battery are the same as those in Example 1. From Figure 10 the cyclic voltammetry curve, it can be seen that NiNC is not conducive to catalyzing the reduction of the sulfur positive electrode but is conducive to catalyzing the oxidation of the sulfur positive electrode. Therefore, the cycling performance ( Figure 11 ) is poor.

Claims

1. A preparation method of a dual single-atom loaded porous carbon material, characterized by the following steps: Step 1): Dissolve nitrogen-carbon-hydrogen compounds and metal salts of two different metals in water. The metals in the metal salts are any two of iron, cobalt, and nickel; and the molar ratio of the two metals is 1:0.5 - 2. Step 2): Add silicon dioxide powder to the above solution and stir evenly. Step 3): Heat and stir the above solution, evaporate water and boil the solution until it becomes thick caramel-colored and then conduct drying treatment. Step 4): Grind the above materials and place them in a tube furnace for calcination and carbonization treatment to obtain a carbon composite material. Step 5): Etch the above carbonized materials with hydrofluoric acid, wash them with water, and dry them to obtain a porous carbon material loaded with dual single atoms.

2. The preparation method according to claim 1, characterized in that: The nitrogen-carbon-hydrogen compounds selected in Step 1) are one or a mixture of two or more of glucosamine, glucosamine hydrochloride, melamine, dicyandiamide, cyanoguanidine, alanine, lysine, g-C3N4, 2-methylimidazole, methionine, cysteine, and mercaptopropionic acid. The metal salts described in Step 1) include one or a mixture of two or more of metal salts of two different metals selected from ferric nitrate, cobalt nitrate, nickel nitrate, ferric chloride, cobalt chloride, nickel chloride, iron phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, iron acetate, cobalt acetate, nickel acetate, iron acetylacetonate, cobalt acetylacetonate, and nickel acetylacetonate.

3. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of nitrogen-carbon-hydrogen compounds to metal salts in Step 1) is 10 - 2000:1 (preferably 10 - 500:1). The mass concentration of nitrogen-carbon-hydrogen compounds in water is 50 - 200 g / L (preferably 100 - 150 g / L).

4. The preparation method according to claim 1, characterized in that: The molar ratio of silicon dioxide to nitrogen-carbon-hydrogen compounds in Step 2) is 1 - 300:1 (preferably 10 - 200:1), the particle size of SiO2 is between 10 - 500 nm (preferably 50 - 200); the stirring time is 2 - 3 h.

5. The preparation method according to claim 1, characterized in that: The heating temperature in Step 3) is 60 - 100 °C, and the heating and stirring time is 2 - 5 h.

6. The preparation method according to claim 1, characterized in that: The calcination temperature in Step 4) is 500 - 1000 °C (preferably 700 - 900 °C), the calcination time is 1 - 10 h (preferably 2 - 4 h), and the calcination atmosphere is high-purity nitrogen and / or argon.

7. The preparation method according to claim 1, characterized in that: The mass fraction of the HF solution in Step 5) is 5 - 50% (preferably 10 - 20%), the mass ratio of silicon dioxide to hydrofluoric acid is 1:1 - 10 (preferably 1:4 - 7), and the etching time is 4 - 30 h (preferably 6 - 24 h).

8. A dual single-atom loaded porous carbon material prepared by the preparation method according to any one of claims 1-7.

9. The dual single-atom loaded porous carbon material according to claim 8, characterized in that: The specific surface area of the prepared porous carbon material loaded with dual single atoms is 300-2000 m 2 / g, the mass fraction of the metal single atom is 0.1%-10%, and the material has dual metal single atom sites.

10. An application of the dual single-atom loaded porous carbon material according to claim 8 or 9, which can be used as a carrier material for elemental sulfur to prepare a sulfur cathode of a lithium-sulfur battery; and can be a dual-selective catalyst for simultaneously catalyzing the sulfur redox process.

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