Preparation and application of sulfur-nitrogen-doped monatomic cobalt supported porous carbon-sulfur composite positive electrode material

Abstract

The application provides preparation and application of a sulfur-nitrogen doped single-atom cobalt loaded porous carbon sulfur composite positive electrode material. The sulfur-nitrogen doped single-atom cobalt loaded porous carbon is obtained through high-temperature pyrolysis of the interaction among cobalt ions, dopamine and thiourea, the electronic structure of the active site of the catalyst is adjusted through common doping of sulfur and nitrogen, the catalytic activity of the single-atom cobalt is improved, the physical adsorption of the porous hollow carbon and the catalytic effect of the single-atom cobalt are synergistically exerted through the coordination between the porous carbon substrate and the single atom, the dissolution of polysulfides is greatly reduced, and the cycle stability of the battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to the preparation and application of a sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite cathode material. Background Technology

[0002] With the depletion of oil resources, electricity is bound to become one of the world's primary energy sources in the future. Developing batteries capable of long-term, stable storage of sustainable energy, possessing very long cycle life, and meeting environmental constraints is a significant challenge facing modern electrochemistry. Lithium-ion batteries, due to their high specific capacity, excellent rate performance, and reliable safety, are crucial for improving our quality of life. Currently, lithium-sulfur batteries have an absolute advantage in energy density (the theoretical value calculated based on lithium anodes and sulfur cathodes is approximately 2600 Wh / kg). -1 It is a commercially available graphite-cobalt oxide lithium-ion battery with a capacity of 387Wh / kg. -1 It is five times more than that of other energy sources (although the actual energy density in practical applications is still 400 to 600 Wh / kg), and its abundant raw materials and environmentally friendly characteristics have attracted widespread attention and research.

[0003] Sulfur cathode materials are a key component of lithium-sulfur batteries, and there are three main problems: First, sulfur and various discharge products (Li2S) x The poor ionic and electronic conductivity (x = 1-8) increases battery internal resistance and electrode polarization. Secondly, during electrochemical processes, the polysulfides (Li₂S₄-Li₂S₈) formed readily react with or dissolve in organic electrolytes, shuttling to the negative electrode and causing an irreversible decrease in the positive electrode capacity, thus reducing battery performance. Thirdly, the excessive volume change of the sulfur positive electrode during cycling (S₈ (2.07 g / cm³)...) -3 ) and Li2S (1.66 g / cm³) -3 During discharge, the volume expands by 79%, leading to fragmentation and extreme capacity decay. To construct cathode materials with high conductivity and stable cycle performance, various transition metal-doped porous hollow carbon materials are used for sulfur loading to increase the conductivity of the cathode, mitigate volume changes, and improve the cathode's resistance to polysulfides (Li₂S₂). x The adsorption capacity of x=4~8) reduces the shuttle effect of lithium-sulfur batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying a sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite cathode material. Firstly, sulfur-nitrogen co-doping is used to adjust the electronic structure of the active sites, improving the catalytic activity of single-atom cobalt. Then, through the coordination between the porous carbon substrate and the single atom, the physical adsorption of the porous hollow carbon and the catalytic effect of the single-atom cobalt are synergistically utilized, significantly reducing the dissolution of polysulfides and improving the cycle stability of the battery.

[0005] A sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite cathode material is characterized by hollow carbon spheres with cobalt single-atom dispersion derived from metal and polymer chelate materials, sulfur-nitrogen co-doped single-atom cobalt dispersed throughout the carbon shell, active sulfur distributed in the cavity, and the carbon content in the composite material being 10% to 40%, the single-atom Co content being 0.001% to 10%, and the sulfur content being 50% to 90%.

[0006] The sulfur-nitrogen-doped cobalt-supported porous carbon-sulfur composite cathode material has hollow nanospheres with a radius of 50–800 nm, a carbon shell thickness of 5–50 nm, micropores of 0–2 nm, mesopores of 2–50 nm, and a specific surface area of ​​100–1000 m². 2 g -1 The pore volume is 0.1–2 cm³. 3 g -1 .

[0007] The preparation method of sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite cathode material firstly involves improving... The method involves synthesizing a silica template, coating the silica template with a layer of polydopamine while chelating a cobalt source, separating and purifying it, mixing it with a sulfur source in a certain proportion, calcining it, removing the template, and heat-treating it to obtain the material. The method includes the following steps:

[0008] (1) Synthesis of SiO2@polydopamine-cobalt ions: Cobalt source and SiO2 are dissolved in water and dispersed to prepare a suspension; dopamine is added to the suspension and stirred continuously at a speed of 100-1000 rpm (more preferably, 400-700 rpm); then a Tris buffer solution with pH = 7.1-9 is added until the solution pH = 7.8-8.5 (more preferably, pH = 7.9-8.1), and finally stirring is continued for 5-10 h (more preferably, 7-8 h) to polymerize dopamine on the surface of SiO2 spheres to obtain SiO2@polydopamine-cobalt ions;

[0009] The final concentration of dopamine is 2-200 mg / ml (more preferably, the concentration of dopamine is 5-50 mg / ml); the mass ratio of cobalt source and SiO2 is 1:500-1000 (more preferably, 1:700-800); the final concentration of SiO2 is 5-200 mg / ml (more preferably, 10-30 mg / ml);

[0010] (2) Sulfur doping carbonization: The SiO2@polydopamine-cobalt ions obtained in step (1) are mixed and ground with thiourea and then placed in a tube furnace for high-temperature pyrolysis carbonization under argon and / or nitrogen atmosphere to obtain sulfur and nitrogen doped single-atom cobalt supported porous carbon coarse material; the carbonization temperature is 600-1000℃ (more preferably, 850-950℃), and the carbonization time is 1-10h (more preferably, 2.5-3.5h);

[0011] (3) Remove template: Add the material from step (2) to an appropriate amount of 0.01-5M (more preferably, 0.05-2M) sodium hydroxide aqueous solution or hydrofluoric acid aqueous solution with a mass fraction of 5-40% (more preferably, 10-30%) and stir for 1-5 hours. Centrifuge, wash and dry to obtain sulfur and nitrogen doped single-atom cobalt supported porous carbon material.

[0012] (4) Sulfur composite: The sulfur-nitrogen doped single-atom cobalt supported porous carbon material obtained in step (3) is mixed with sublimed sulfur and ground, transferred to a sealed bottle, and the sulfur is heat-treated under argon and / or nitrogen atmosphere to obtain sulfur-nitrogen doped single-atom cobalt supported porous carbon-sulfur composite material.

[0013] In step (1), the cobalt source is one or more of cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, cobalt chloride hexahydrate, cobalt acetate tetrahydrate, and cobalt acetylacetone (more preferably, cobalt nitrate hexahydrate and / or cobalt sulfate heptahydrate); the dispersion method is ultrasonic dispersion for 10 to 100 min (more preferably, ultrasonic dispersion for 40 to 70 min); the Tris buffer solution is Tris-HCl and / or Tris-EDTA.

[0014] In step (2), the mass ratio of SiO2@polydopamine-cobalt ions to thiourea is 1:1 to 10 (more preferably, 1:1.5 to 2.5); the grinding method is ball milling for 10 to 60 min; the protective atmosphere is high-purity nitrogen and / or argon; the gas flow rate is 50 to 200 ml / min (more preferably, 70 to 100 ml / min); and the heating rate is 1 to 10 °C / min (more preferably, 4 to 6 °C / min).

[0015] In step (4), the protective atmosphere is high-purity argon or high-purity nitrogen; the mass ratio of sulfur-nitrogen-doped single-atom cobalt-supported porous carbon and sulfur composite is 1:1 to 10 (more preferably, 1:2 to 4); the sulfur impregnation temperature is 150 to 160°C (more preferably, 154.5 to 155.5°C).

[0016] This invention obtains sulfur-nitrogen-doped single-atom cobalt-supported porous carbon material through the chemical bonding of thiourea with polydopamine and cobalt ions during the carbonization process, and then obtains sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite cathode material by heat treatment with sulfur.

[0017] This invention utilizes the interaction between cobalt ions, dopamine, and thiourea to obtain sulfur-nitrogen-doped single-atom cobalt-supported porous carbon through high-temperature pyrolysis. By adjusting the ratio of sulfur and cobalt sources, the sulfur-nitrogen ratio bonded to the central cobalt atom can be changed, thereby regulating the electronic structure of the cobalt atom. Furthermore, through the coordination between the porous carbon substrate and the single atom, the physical adsorption of porous hollow carbon and the catalytic effect of single-atom cobalt are synergistically utilized. This structure can be used for bidirectional catalysis of the electrochemical reaction process of the sulfur cathode in lithium-sulfur batteries, greatly reducing the dissolution of polysulfides and improving the cycle stability of the battery.

[0018] The advantages of this invention lie in its low raw material cost, mature synthesis process, and ability to be mass-produced. It allows for optimization of the sulfur-nitrogen-doped cobalt-supported hollow carbon nanosphere structure by controlling parameters in a single step, enabling it to function as a positive electrode material in different battery systems to suppress the shuttle effect of polysulfides. The sulfur-nitrogen-doped cobalt-supported porous carbon material prepared by this method possesses abundant pore structure and a large specific surface area, thus effectively loading sulfur, mitigating volume changes during charge and discharge, maintaining good wettability to the electrolyte, increasing the conductivity of the electrode material, improving rate performance, and maintaining the structural stability of the material. Furthermore, the cobalt atoms with their unique electronic structure exhibit a stronger catalytic conversion effect on polysulfides during the electrode reaction process, significantly reducing polysulfide accumulation. This not only accelerates the electrode reaction rate, reduces active material loss, and improves rate performance, but also mitigates the corrosion of the negative electrode by polysulfides in the electrolyte. Therefore, the application of sulfur-nitrogen-doped cobalt-supported porous carbon-sulfur composite positive electrode material can greatly improve the cycle stability and rate performance of batteries, making it a material with significant industrial application potential. Attached image description:

[0019] Figure 1 This is a SEM image of sulfur-nitrogen-doped single-atom cobalt-supported porous carbon.

[0020] Figure 2 This is a TEM image of sulfur-nitrogen-doped single-atom cobalt-supported porous carbon.

[0021] Figure 3 Nitrogen adsorption-desorption curves and pore size distribution of sulfur-nitrogen doped single-atom cobalt-supported porous carbon

[0022] Figure 4 This is a HAADF-STEM image of a sulfur-nitrogen-doped single-atom cobalt-supported porous carbon material.

[0023] Figure 5 XPS spectra of sulfur and nitrogen-doped single-atom cobalt-supported porous carbon.

[0024] Figure 6 This is a cycle diagram of the battery specific capacity in Example 1.

[0025] Figure 7 This is a cycle diagram of the battery specific capacity in Example 2.

[0026] Figure 8 The TEM image is a comparison of Example 1.

[0027] Figure 9 SEM image of Comparative Example 2 Detailed Implementation

[0028] The following embodiments are further illustrations of the present invention, but are not intended to limit the scope of the invention.

[0029] Example 1

[0030] 4g of SiO2 and 5mg of cobalt nitrate hexahydrate were added to 200ml of aqueous solvent and ultrasonically dispersed for 60min to obtain a suspension. Then, 2g of dopamine hydrochloride was dissolved in the suspension and stirred vigorously at 500rpm. Next, 200ml of Tris-HCl (pH=8.3) buffer solution was added to adjust the pH of the solution to 8. Finally, stirring was continued for 8h to polymerize dopamine on the surface of SiO2 spheres to obtain SiO2@polydopamine-cobalt ions.

[0031] 1g of SiO2@polydopamine-cobalt ions was mixed with thiourea at a ratio of 1:2 and ball-milled for 40min. The mixture was then placed in a tube furnace and heated to 900℃ under an argon atmosphere at a heating rate of 5℃ / min and a gas flow rate of 100ml / min. The temperature was maintained for 3h to obtain sulfur and nitrogen doped single-atom cobalt-supported porous carbon coarse material.

[0032] Take 0.3g of sulfur-nitrogen-doped single-atom cobalt-supported porous carbon crude material and add it to 50ml of 28% hydrofluoric acid. Stir for 4 hours, centrifuge, wash and dry to obtain sulfur-nitrogen-doped single-atom cobalt-supported porous carbon material.

[0033] SEM, SEM, BET, HAADF-STEM, and XPS images of sulfur-nitrogen-doped single-atom cobalt-supported porous carbon materials are shown below. Figure 1 As shown, Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown;

[0034] 0.1g of sulfur-nitrogen-doped single-atom cobalt-supported porous carbon material was ground with 0.3g of sublimed sulfur, transferred to a sealed glass bottle, and heat-treated at 155℃ for 12h to obtain carbon-sulfur composite material.

[0035] Take 0.1g of the sample, add 0.02g of conductive carbon and 0.267g of 5% (w / w) polyvinylidene fluoride (PVDF) solution, with N-methylpyrrolidone as the solvent. Grind for 1 hour, then use a scraper to coat a 200-micron thick film onto carbon-coated aluminum foil. Dry at 60℃ overnight, slice, weigh, and vacuum dry at 55℃ for 24 hours. Use this electrode as the positive electrode, lithium sheet as the negative electrode, Celgard 2500 as the separator, 1M lithium bis(trifluoromethanesulfonyl)imide solution (LITFSI) as the electrolyte, 0.2M lithium nitrate as the additive, and a mixture of 1,3-dioxolane (DOL) and dimethyl ether (DME) (volume ratio 1:1) as the solvent to assemble a coin-type lithium-sulfur battery. Charge-discharge tests were conducted at rates from 0.05C to 2C. At 1C rate, the first charge-discharge capacity was 1004 mAh / g. -1 After 500 cycles, the capacity is 698 mAhg. -1 The battery cycle diagram of Example 1 is as follows: Figure 6 As shown.

[0036] Example 2

[0037] The process and conditions for preparing sulfur-nitrogen-doped single-atom cobalt-supported porous carbon are the same as in Example 1;

[0038] The difference lies in the following: 0.1g of sulfur-nitrogen co-doped cobalt-supported porous carbon spheres were ground with 0.4g of sublimed sulfur, transferred to a sealed glass bottle, and heat-treated at 155℃ for 12 hours to obtain sulfur-nitrogen co-doped cobalt-supported porous carbon spheres. Subsequent electrode coating and battery assembly and testing were the same as in Example 1; the battery cycle diagram for Example 2 is shown below. Figure 7 As shown.

[0039] Depend on Figure 1 The particle size of the sulfur-nitrogen-doped single-atom cobalt-supported porous carbon material is observed to be 500–700 nm, and the size is uniform.

[0040] Depend on Figure 2 The scanning electron microscope image of the sulfur-nitrogen-doped single-atom cobalt-supported porous carbon material shows that its spherical shell thickness is 8 nm.

[0041] Depend on Figure 3 Sulfur-nitrogen-doped single-atom cobalt-supported porous carbon materials have a thickness of 698 μm. 2 Large specific surface area / g;

[0042] Depend on Figure 4 Aberration-corrected electron microscopy images of sulfur-nitrogen-doped cobalt-supported porous carbon materials confirm that cobalt atoms are indeed loaded onto the hollow porous carbon material (marked by red circles).

[0043] Depend on Figure 5 The XPS spectrum shows that S atoms are bonded to Co in the porous carbon spheres, confirming the doping and coordination of S.

[0044] Depend on Figure 6 In Example 1, the discharge capacity of the first cycle at a current density of 1C reached 1004 mAh g. -1 .

[0045] Depend on Figure 7 In Example 1, the discharge capacity of the first cycle at a current density of 1C reached 1050 mAh g. -1 .

[0046] This indicates that sulfur-nitrogen-doped single-atom cobalt-supported porous carbon materials have abundant pore structures, so their composite ratio with sublimed sulfur of 1:3 or 1:4 has no significant impact on battery cycle performance.

[0047] Comparative Example 1

[0048] The preparation of SiO2@polydopamine-cobalt ions is the same as in Example 1;

[0049] The difference lies in the following: 1g of SiO2@polydopamine-cobalt ions and thiourea were mixed and ground at a ratio of 1:20 and then placed in a tube furnace and heated at 5℃ for 1 minute under an argon atmosphere. -1 The heating rate was increased to 900℃ with a gas flow rate of 100 ml / min, and the temperature was kept constant for 3 h to obtain sulfur and nitrogen doped single-atom cobalt-supported porous carbon material.

[0050] TEM tests were performed on sulfur-nitrogen-doped single-atom cobalt-supported porous carbon materials. For example... Figure 8 As shown in the comparative example, due to the increase in the thiourea feed ratio, a large number of cobalt sulfide particles appeared in the material, indicating that the thiourea feed ratio is crucial to the generation of single-atom sulfur-doped single-atom cobalt.

[0051] Comparative Example 2

[0052] The preparation of SiO2@polydopamine-cobalt ions is the same as in Example 1;

[0053] Take 1g of SiO2@polydopamine-cobalt ions and thiourea in a 1:2 ratio, grind them thoroughly, and place them in a tube furnace. The difference is that the furnace is heated at 5℃ for 5 minutes under an argon atmosphere. -1 The heating rate was increased to 1100℃ with a gas flow rate of 100 ml / min, and the temperature was kept constant for 3 h to obtain sulfur and nitrogen doped single-atom cobalt-supported porous carbon material.

[0054] SEM analysis was performed on sulfur-nitrogen-doped single-atom cobalt-supported porous carbon materials. For example... Figure 9 As shown in the comparative example, due to the higher calcination temperature, the carbon shell in the second example showed a partially broken state under an electron microscope. Therefore, the physical confinement effect on sulfur was reduced, resulting in the dissolution of a large amount of polysulfides and a decrease in the cycle stability of the battery.

Claims

1. A method for preparing a sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite cathode material, characterized in that: Includes the following steps, (1) Synthesis of SiO2@polydopamine-cobalt ions: Cobalt source and SiO2 are dissolved in water and dispersed to prepare a suspension; dopamine is added to the suspension and stirred continuously at 100~1000 rpm; then a buffer solution with pH=7.1~9 Tris is added until the solution pH=7.8~8.5, and finally stirring is continued for 5-10 h to polymerize dopamine on the surface of SiO2 spheres to obtain SiO2@polydopamine-cobalt ions; The final concentration of dopamine is 2~200 mg / ml; the mass ratio of cobalt source and SiO2 is 1:500~1000; the final concentration of SiO2 is 5~200 mg / ml. (2) Sulfur doping carbonization: The SiO2@polydopamine-cobalt ions obtained in step (1) are mixed and ground with thiourea and placed in a tube furnace. The mixture is then pyrolyzed and carbonized at high temperature under argon and / or nitrogen atmosphere to obtain sulfur and nitrogen doped single-atom cobalt supported porous carbon coarse material. The carbonization temperature is 600~1000℃ and the carbonization time is 1~10h. (3) Remove template: Add the material from step (2) to an appropriate amount of sodium hydroxide aqueous solution or hydrofluoric acid aqueous solution and stir for 1-5 hours. Centrifuge, wash and dry to obtain sulfur and nitrogen doped single-atom cobalt supported porous carbon material. (4) Sulfur composite: The sulfur-nitrogen doped single-atom cobalt supported porous carbon material obtained in step (3) is mixed with sublimed sulfur and ground, transferred to a sealed bottle, and the sulfur is heat-treated under argon and / or nitrogen atmosphere to obtain sulfur-nitrogen doped single-atom cobalt supported porous carbon-sulfur composite material. In step (4), the mass ratio of sulfur-nitrogen doped single-atom cobalt-supported porous carbon and sulfur composite is 1:1~10; the sulfur impregnation temperature is 150~160℃.

2. The preparation method according to claim 1, characterized in that: Step (1) The cobalt source is one or more of cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, cobalt chloride hexahydrate, cobalt acetate tetrahydrate, and cobalt acetylacetonate.

3. The preparation method according to claim 1, characterized in that: Step (1) The cobalt source and SiO2 are dispersed in an aqueous solvent by ultrasonic dispersion for 10~100 min to obtain a suspension.

4. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of SiO2@polydopamine-cobalt ions to thiourea is 1:1~10.

5. The preparation method according to claim 1, characterized in that: The grinding method described in step (2) is ball milling, with a time of 10~60 min; Step (2) The protective atmosphere is high-purity nitrogen and / or argon; the gas flow rate is 50~200 ml / min; the heating rate is 1~10℃ / min.

6. The preparation method according to claim 5, characterized in that: Step (2) The protective atmosphere is high-purity nitrogen and / or argon; the gas flow rate is 70~100ml / min; the heating rate is 4~6℃ / min.

7. The preparation method according to claim 1, characterized in that... In step (3), the concentration of sodium hydroxide is 0.01~5M; the mass fraction of hydrofluoric acid is 5~40%.

8. The preparation method according to claim 7, characterized in that... In step (3), the concentration of sodium hydroxide is 0.05~2M; the mass fraction of hydrofluoric acid is 10~30%.

9. The preparation method according to claim 1, characterized in that: The sulfur loading time in step (4) is more than 6 hours.

10. A sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite cathode material prepared by any one of the preparation methods of claims 1-9.

11. The application of the sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite cathode material as described in claim 10 in lithium-sulfur batteries.

12. The application according to claim 11, characterized in that, A lithium-sulfur battery was assembled using a sulfur-nitrogen-doped single-atom cobalt-supported porous carbon-sulfur composite material as the positive electrode, a lithium sheet as the negative electrode, a polyolefin separator, an ether electrolyte, and additives. This structure can be used to catalyze the electrochemical reaction process of the sulfur cathode in lithium-sulfur batteries; the separator is made of PP and / or PE; the ether electrolyte is made of DOL and / or DME. The additive is one or more of lithium nitrate, lithium carbonate, lithium phosphate, or lithium acetate; the assembly can obtain the material for use in cylindrical lithium-sulfur batteries, pouch lithium-sulfur batteries, or coin lithium-sulfur batteries.

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