Carbon nanoflower-coated carbon sphere material with core-shell structure, and preparation method and application thereof

Abstract

The application discloses a carbon nanoflower-coated carbon sphere material with a core-shell structure and a preparation method and application thereof, and the technical scheme is as follows: taking a thorn-shaped silica sphere as a template, glucose and resorcinol / formaldehyde as carbon precursors to construct a walnut-type core-shell structure nanoflower-coated carbon sphere, and taking the same as a sulfur host to be applied to a lithium-sulfur battery positive electrode. The carbon nanoflower-coated carbon sphere structure can effectively relieve problems such as strain caused by sulfur volume expansion, low electron / ion diffusion rate, polysulfide shuttling, poor conductivity and the like, so as to realize capacity exertion, rate performance improvement and cycle stability improvement of a high-performance lithium-sulfur battery.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically to carbon nanoflower-coated carbon sphere materials with core-shell structure, their preparation methods, and applications. Background Technology

[0002] Lithium-sulfur batteries are highly favored by researchers due to their high theoretical specific capacity and energy density. However, they also suffer from problems such as the poor conductivity of sulfur as the active material, severe volume expansion during charge and discharge, and the shuttle effect of polysulfides, which seriously limit the commercial application of lithium-sulfur batteries. To address these issues, combining sulfur with materials that have high conductivity and large specific surface area can significantly improve the problems of poor conductivity and volume expansion caused by sulfur.

[0003] Carbon materials are a promising sulfur host material due to their wide availability, easily controllable structure, good conductivity, and excellent chemical stability. Hollow microstructured carbon cathodes, serving as a sulfur matrix, utilize their porous and hollow nanostructure to shorten the ion diffusion path in the electrolyte, while the carbon shell mitigates the volume expansion / contraction of sulfur, showing attractive potential in lithium-sulfur batteries. Although hollow carbon spheres (HCS) are considered important matrix materials, the simple hollow structure still has a significant drawback: the high content of insulating sulfur and the discharge product lithium sulfide loaded inside the hollow structure is dispersed only by the inner carbon wall with a limited specific surface area, which cannot effectively improve the internal ionic / electron conductivity difference, thus reducing the utilization rate of active sulfur and ultimately affecting the battery's capacity and rate performance. Therefore, strategies to efficiently disperse sulfur and lithium sulfide by controlling the internal structure of hollow carbon spheres, thereby enhancing the affinity for polysulfide ions, improving sulfur utilization, and suppressing polysulfide ion loss, have become an effective method. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a carbon nanosphere with a core-shell structure, its preparation method and application.

[0005] To achieve the above objectives, the first aspect of the present invention is a method for preparing carbon nanospheres with a core-shell structure, the technical solution of which includes the following steps:

[0006] S1: Weigh hexadecyl bromopyridine and urea, mix and dissolve them in water. Separately, dissolve tetraethyl orthosilicate in a mixed solution of cyclohexane and n-pentanol. Mix the two solutions, stir evenly, and transfer them to a reaction vessel for reaction. After cooling, filter and wash to obtain a light yellow to white solid. After drying, transfer it to a muffle furnace for high-temperature calcination to obtain a white powder, which is the spiky silica spheres.

[0007] S2: The sea urchin-shaped silica spiky balls are aminated with 3-aminopropyltriethoxysilane to obtain aminated silica spiky balls.

[0008] S3: The aminated silica spikes and glucose are dispersed in deionized water and placed in a reaction vessel for hydrothermal reaction to obtain glucose-coated silica spikes.

[0009] S4: The glucose-coated silica spikes are ultrasonically dispersed in isopropanol solvent, and deionized water and ammonia are added and stirred continuously. Tetraethyl orthosilicate is added and stirred continuously. After centrifugation and drying, the core target substrate is obtained. The structure of the core target substrate is: a surface layer, a middle layer and an inner layer coated sequentially, wherein the surface layer is silica, the middle layer is glucose and the inner layer is silica spikes.

[0010] S5: The core target substrate is ultrasonically dispersed with deionized water and magnetically stirred. Then, hexadecyltrimethylammonium bromide, resorcinol, and ethanol ammonia are added rapidly in sequence and stirred continuously. Formaldehyde reagent is then added dropwise for reaction, and the mixture is allowed to stand for aging. The resulting solid powder is then centrifuged and dried. The powder is then placed in a ceramic boat and calcined in an atmosphere of argon and ammonia. The product is then etched with hydrofluoric acid to remove the SiO2 template, finally yielding core-shell structured carbon nanoflower-coated carbon spheres.

[0011] A further setting is that the mass ratio of hexadecyl bromide pyridine, urea and tetraethyl orthosilicate in step S1 is 10:6:25.

[0012] A further setting is that the volume ratio of water, cyclohexane, and n-pentanol in step S1 is 20:1:20.

[0013] A further setting is that the mechanical rotation speed in step S1 is 2000 rpm.

[0014] A further setting is that the furnace temperature in step S1 is 120°C and the time is 6 hours.

[0015] A further setting is that the hydrothermal reaction temperature in step S3 is 180°C and the time is 10 hours.

[0016] A further setting is that the mass ratio of aminated silica spikes to glucose in S3 is 1:2.

[0017] A further setting is that the volume ratio of deionized water, ammonia, and tetraethyl orthosilicate in step S4 is 180:100:7, and the concentration of the ammonia is 28%.

[0018] A further setting is that the mass ratio of hexadecyltrimethylammonium bromide to resorcinol in step S5 is 136:15.

[0019] A further setting is that the volume ratio of ethanol, ammonia, and formaldehyde in step S5 is 17:0.06:0.3.

[0020] A further setting is that the volume ratio of ammonia to argon in step S5 is 1:9.

[0021] A second aspect of the present invention is to provide carbon nanoflower-coated carbon spheres with a core-shell structure prepared by the preparation method described above.

[0022] A third aspect of the present invention is to provide an application of the carbon nanoflower-coated carbon sphere material as described above in a lithium-sulfur battery, wherein the carbon nanoflower-coated carbon sphere is used as a carrier for the positive electrode of a lithium-sulfur battery.

[0023] The beneficial effects of this invention are: using spiky silica spheres as templates and glucose and resorcinol / formaldehyde as carbon precursors to construct walnut-shaped core-shell structured nanoflowers@carbon spheres, and using these as hosts to support sulfur in lithium-sulfur battery cathodes, the structure is novel and highly innovative.

[0024] The walnut-shaped core-shell structured carbon nanosphere positive electrode sulfur fixation carrier of this invention combines the advantages of hollow carbon spheres and flower-shaped carbon spheres. The synergistic effect of the carbon shell absorption and the dispersion and adsorption of polysulfide ions by the carbon nanoflowers, the cavity's ability to cope with sulfur volume expansion, and the high conductivity of carbon materials, combined with these three factors, results in excellent rate performance and cycle stability.

[0025] See the example for specific performance tests. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0027] Figure 1 This is a scanning electron microscope image of the walnut-shaped core-shell carbon nanospheres (WSYCS) prepared in Specific Example 1 of the present invention;

[0028] Figure 2 Transmission electron micrographs of WSYCS, WSYCS1, and WSYCS3;

[0029] Figure 3 The following are performance graphs of WSYCS / S, WSYCS1 / S and WSYCS3 / S as specific comparative examples of the present invention as positive electrode materials for lithium-sulfur batteries at different rates.

[0030] Figure 4 The cycling stability diagrams of WSYCS / S, WSYCS1 / S and WSYCS3 / S as specific comparative examples of lithium-sulfur battery cathode materials in this invention are shown. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] (1) Preparation of WSYCS: 1) 2.5 g of hexadecylpyridinium bromide and 1.5 g of urea were dissolved in 75 mL of deionized water in a 250 mL three-necked round-bottom flask, and added to a stirred solution of tetraethoxysilane (6.25 g), 1-pentanol (3.75 mL), and cyclohexane (75 mL) at room temperature to produce an emulsion. The emulsion was stirred for 60 minutes (at 2200 rpm) and then transferred to four 250 mL polytetrafluoroethylene-lined autoclaves. The autoclaves were then rapidly heated to 120 °C and maintained at 120 °C for 6 hours. After cooling, suction filtration, and washing several times with deionized water, a yellow solid was obtained. The corresponding product was further calcined at 550 °C for 6 hours to obtain U-SiO2 (1.5 g of white powder). 2) Take 5g of urchin-shaped silica spheres (U-SiO2) with a diameter of approximately 200nm and ultrasonically disperse them in 300mL of anhydrous toluene solvent. Add 15mL of 3-aminopropyltriethoxysilane during stirring. After centrifugation and drying, obtain a solid powder (aminated U-SiO2 spiky spheres). Disperse this powder with glucose at a mass ratio of 1:2 in 75mL of deionized water until homogeneous. Transfer the powder to a 100mL reactor and hydrothermally react at 180℃ for 10h. Afterward, remove and dry to obtain a glucose-coated brownish-red product (G@U-SiO2). 3) Weigh 400mg of G@U-SiO2 and ultrasonically disperse it in 20mL of isopropanol solvent. Stir until homogeneous. Add 36mL of deionized water and 20mL of 28% ammonia solution and continue stirring. Add 1.4mL of tetraethyl orthosilicate (TEOS) and stir for 3h. Centrifuge and dry to obtain the core target substrate (SiO2@G@U-SiO2). 4) Weigh 480 mg of SiO2@G@U-SiO2 powder and 43 mL of deionized water. After ultrasonic dispersion and magnetic stirring, rapidly add 1360 mg of cetyltrimethylammonium bromide, 150 mg of resorcinol, 17 mL of ethanol, and 60 μL of ammonia water, and continue stirring for 0.5 h. Then, add 300 μL of formaldehyde reagent dropwise and react for 6 h, followed by overnight aging. Centrifuge and dry the resulting solid powder, then place it in a ceramic boat under an Ar / NH3 = 9:1 atmosphere and calcine at 900 °C for 2 h.

[0034] (2) WSYCS / S synthesis process: 100 mg of WSYCS and 400 mg of sulfur powder were thoroughly ground in an agate mortar. The mixture was then placed in a quartz tube, vacuum-sealed, and subsequently placed in a tube furnace at 155 °C for 48 h, with a heating rate of 1 °C / min. -1 Ensure that sulfur is fully melted and infiltrated into the core and shell. After the tube furnace cools to room temperature, remove the quartz tube to obtain the target product, the composite material.

[0035] (3) Synthesis process of composite electrode: The composite material obtained in the previous step was placed in a 25×40 weighing bottle with conductive carbon and 5% PVDF binder in a ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added and the mixture was magnetically stirred for 10 hours to adjust the viscosity of the slurry. The slurry was evenly coated onto a flat aluminum foil using a 200µm coater. After vacuum drying at 60℃ for 12 hours, the slurry was cut into electrode sheets using a 14mm punch for later use.

[0036] (4) Battery assembly: Place the weighed electrode sheets and accessories required for battery assembly into a glove box (H2O < 1ppm; O2 < 1ppm). Assemble the battery in the following order: positive electrode shell → positive electrode sheet → appropriate amount of electrolyte (a mixed solution of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide, 1% lithium nitrate in ethylene glycol dimethyl ether and 1,3-dioxane in a molar ratio of 1:1) → separator → appropriate amount of electrolyte → lithium sheet → gasket → spring sheet → negative electrode shell. (5) Performance testing: Use the LAND battery testing system (LAND-CT2001A) to perform cycle charge and discharge tests on the CNF@CS / S electrode battery. The battery operating voltage window range is 1.5-3.0V.

[0037] Comparative Example 1

[0038] (1) Preparation of WSYCS1: 1) 2.5 g of hexadecylpyridinium bromide and 1.5 g of urea were dissolved in 75 mL of deionized water in a 250 mL three-necked round-bottom flask, and added to a stirred solution of tetraethoxysilane (6.25 g), 1-pentanol (3.75 mL), and cyclohexane (75 mL) at room temperature to produce an emulsion. The emulsion was stirred for 60 minutes (at 2200 rpm) and then transferred to four 250 mL polytetrafluoroethylene-lined autoclaves. The autoclaves were then rapidly heated to 120 °C and maintained at 120 °C for 6 hours. After cooling, suction filtration, and washing several times with deionized water, a yellow solid was obtained. The corresponding product was further calcined at 550 °C for 6 hours to obtain U-SiO2 (1.5 g of white powder). 2) Take 5g of urchin-shaped silica spheres (U-SiO2) with a diameter of approximately 200nm and ultrasonically disperse them in 300mL of anhydrous toluene solvent. Add 15mL of 3-aminopropyltriethoxysilane during stirring. After centrifugation and drying, obtain a solid powder (aminated U-SiO2 spiky spheres). Disperse this powder with glucose at a mass ratio of 1:2 in 75mL of deionized water until homogeneous. Transfer the powder to a 100mL reactor and hydrothermally react at 180℃ for 10h. Afterward, remove and dry to obtain a glucose-coated brownish-red product (G@U-SiO2). 3) Weigh 400mg of G@U-SiO2 and ultrasonically disperse it in 20mL of isopropanol solvent. Stir until homogeneous. Add 36mL of deionized water and 20mL of 28% ammonia solution, continue stirring, and add 1.2mL of tetraethyl orthosilicate (TEOS). Stir for 3h. Centrifuge and dry to obtain the core target substrate (SiO2@G@U-SiO2). 4) Weigh 480 mg of SiO2@G@U-SiO2 powder and 43 mL of deionized water. After ultrasonic dispersion and magnetic stirring, rapidly add 1360 mg of cetyltrimethylammonium bromide, 150 mg of resorcinol, 17 mL of ethanol, and 60 μL of ammonia water, and continue stirring for 0.5 h. Then, add 300 μL of formaldehyde reagent dropwise and react for 6 h, followed by overnight aging. Centrifuge and dry the resulting solid powder, then place it in a ceramic boat under an Ar / NH3 = 9:1 atmosphere and calcine at 900 °C for 2 h.

[0039] (2) WSYCS1 / S Synthesis Process: 100 mg WSYCS and 400 mg sulfur powder were thoroughly ground in an agate mortar. The mixture was then placed in a quartz tube, vacuum-sealed, and subsequently placed in a tube furnace at 155 °C for 48 h, with a heating rate of 1 °C / min. -1 Ensure that sulfur is fully melted and infiltrated into the core and shell. After the tube furnace cools to room temperature, remove the quartz tube to obtain the target product, the composite material.

[0040] (3) Synthesis process of composite electrode: The composite material obtained in the previous step was placed in a 25×40 weighing bottle with conductive carbon and 5% PVDF binder in a ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added and the mixture was magnetically stirred for 10 hours to adjust the viscosity of the slurry. The slurry was evenly coated onto a flat aluminum foil using a 200µm coater. After vacuum drying at 60℃ for 12 hours, the slurry was cut into electrode sheets using a 14mm punch for later use.

[0041] (4) Battery Assembly: Place the weighed electrode plates and all necessary battery components into a glove box (H2O < 1 ppm; O2 < 1 ppm). Assemble the battery in the following order: positive electrode shell → positive electrode plate → appropriate amount of electrolyte (a mixed solution of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide, 1% lithium nitrate in ethylene glycol dimethyl ether, and 1,3-dioxane in a 1:1 molar ratio) → separator → appropriate amount of electrolyte → lithium plate → gasket → spring plate → negative electrode shell.

[0042] (5) Performance testing: The CNF@CS / S electrode battery was subjected to cyclic charge and discharge tests using the LAND battery test system (LAND-CT2001A). The battery operating voltage window range was 1.5-3.0V.

[0043] Comparative Example 2

[0044] (1) Preparation of WSYCS3: 1) 2.5 g of hexadecylpyridinium bromide and 1.5 g of urea were dissolved in 75 mL of deionized water in a 250 mL three-necked round-bottom flask, and added to a stirred solution of tetraethoxysilane (6.25 g), 1-pentanol (3.75 mL), and cyclohexane (75 mL) at room temperature to produce an emulsion. The emulsion was stirred for 60 minutes (at 2200 rpm) and then transferred to four 250 mL polytetrafluoroethylene-lined autoclaves. The autoclaves were then rapidly heated to 120 °C and maintained at 120 °C for 6 hours. After cooling, suction filtration, and washing several times with deionized water, a yellow solid was obtained. The corresponding product was further calcined at 550 °C for 6 hours to obtain U-SiO2 (1.5 g of white powder). 2) Take 5g of urchin-shaped silica spheres (U-SiO2) with a diameter of approximately 200nm and ultrasonically disperse them in 300mL of anhydrous toluene solvent. Add 15mL of 3-aminopropyltriethoxysilane during stirring. After centrifugation and drying, obtain a solid powder (aminated U-SiO2 spiky spheres). Disperse this powder with glucose at a mass ratio of 1:2 in 75mL of deionized water until homogeneous. Transfer the powder to a 100mL reactor and hydrothermally react at 180℃ for 10h. Afterward, remove and dry to obtain a glucose-coated brownish-red product (G@U-SiO2). 3) Weigh 400mg of G@U-SiO2 and ultrasonically disperse it in 20mL of isopropanol solvent. Stir until homogeneous, then add 36mL of deionized water and 20mL of 28% ammonia solution. Continue stirring and add 1.6mL of tetraethyl orthosilicate (TEOS). Stir for 3h. Centrifuge and dry to obtain the core target substrate (SiO2@G@U-SiO2). 4) Weigh 480 mg of SiO2@G@U-SiO2 powder and 43 mL of deionized water. After ultrasonic dispersion and magnetic stirring, rapidly add 1360 mg of cetyltrimethylammonium bromide, 150 mg of resorcinol, 17 mL of ethanol, and 60 μL of ammonia water, and continue stirring for 0.5 h. Then, add 300 μL of formaldehyde reagent dropwise and react for 6 h, followed by overnight aging. Centrifuge and dry the resulting solid powder, then place it in a ceramic boat under an Ar / NH3 = 9:1 atmosphere and calcine at 900 °C for 2 h.

[0045] (2) WSYCS3 / S synthesis process: 100 mg WSYCS and 400 mg sulfur powder were thoroughly ground in an agate mortar. The mixture was then placed in a quartz tube, vacuum-sealed, and subsequently placed in a tube furnace at 155 °C for 48 h, with a heating rate of 1 °C / min. -1 Ensure that sulfur is fully melted and infiltrated into the core and shell. After the tube furnace cools to room temperature, remove the quartz tube to obtain the target product, the composite material.

[0046] (3) Synthesis process of composite electrode: The composite material obtained in the previous step was placed in a 25×40 weighing bottle with conductive carbon and 5% PVDF binder in a ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added and the mixture was magnetically stirred for 10 hours to adjust the viscosity of the slurry. The slurry was evenly coated onto a flat aluminum foil using a 200µm coater. After vacuum drying at 60℃ for 12 hours, the slurry was cut into electrode sheets using a 14mm punch for later use.

[0047] (4) Battery Assembly: Place the weighed electrode plates and all necessary battery components into a glove box (H2O < 1 ppm; O2 < 1 ppm). Assemble the battery in the following order: positive electrode shell → positive electrode plate → appropriate amount of electrolyte (a mixed solution of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide, 1% lithium nitrate in ethylene glycol dimethyl ether, and 1,3-dioxane in a 1:1 molar ratio) → separator → appropriate amount of electrolyte → lithium plate → gasket → spring plate → negative electrode shell.

[0048] (5) Performance testing: The CNF@CS / S electrode battery was subjected to cyclic charge and discharge tests using the LAND battery test system (LAND-CT2001A). The battery operating voltage window range was 1.5-3.0V.

Claims

1. A method for preparing carbon nanoflower-coated carbon spheres with a core-shell structure, characterized in that... Includes the following steps: S1: Weigh hexadecyl bromopyridine and urea, mix and dissolve them in water. Separately, dissolve tetraethyl orthosilicate in a mixed solution of cyclohexane and n-pentanol. Mix the two solutions, stir evenly, and transfer them to a reaction vessel for reaction. After cooling, filter and wash to obtain a light yellow to white solid. After drying, transfer it to a muffle furnace for high-temperature calcination to obtain a white powder, which is the spiky silica spheres. S2: The spiky silica balls are aminated with 3-aminopropyltriethoxysilane to obtain aminated silica spiky balls. S3: The aminated silica spikes and glucose are dispersed in deionized water and placed in a reaction vessel for hydrothermal reaction to obtain glucose-coated silica spikes. S4: The glucose-coated silica spikes are ultrasonically dispersed in isopropanol solvent, and deionized water and ammonia are added and stirred continuously. Tetraethyl orthosilicate is added and stirred continuously. After centrifugation and drying, the core target substrate is obtained. The structure of the core target substrate is: a surface layer, a middle layer and an inner layer coated sequentially, wherein the surface layer is silica, the middle layer is glucose and the inner layer is silica spikes. S5: The core target substrate is ultrasonically dispersed with deionized water and magnetically stirred. Then, hexadecyltrimethylammonium bromide, resorcinol, ethanol, and ammonia are added rapidly in sequence and stirred continuously. Formaldehyde reagent is then added dropwise for reaction, and the mixture is allowed to stand for aging. The resulting solid powder is then centrifuged and dried. The powder is then placed in a ceramic boat and calcined in an atmosphere of argon and ammonia. The product is then etched with hydrofluoric acid to remove the SiO2 template, finally yielding core-shell structured carbon nanoflower-coated carbon spheres.

2. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: In step S1, the mass ratio of hexadecyl bromide pyridine, urea, and tetraethyl orthosilicate is 10:6:

25.

3. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: The volume ratio of water, cyclohexane, and n-pentanol in step S1 is 20:1:

20.

4. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: The mechanical rotation speed in step S1 is 2000 rpm.

5. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: The temperature of the muffle furnace in step S1 is 120°C, and the time is 6 hours.

6. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: The hydrothermal reaction temperature in step S3 is 180℃, and the time is 10h.

7. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: The mass ratio of aminated silica spikes to glucose in S3 is 1:

2.

8. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: In step S4, the volume ratio of deionized water, ammonia, and tetraethyl orthosilicate is 180:100:7, and the concentration of ammonia is 28%.

9. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: In step S5, the mass ratio of hexadecyltrimethylammonium bromide to resorcinol is 136:

15.

10. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: In step S5, the volume ratio of ethanol, ammonia, and formaldehyde is 17:0.06:0.

3.

11. The method for preparing a carbon nanoflower-coated carbon sphere material with a core-shell structure according to claim 1, characterized in that: The volume ratio of ammonia to argon in step S5 is 1:

9.

12. A carbon nanoflower-coated carbon sphere material with a core-shell structure prepared by the preparation method according to any one of claims 1-11.

13. The application of the carbon nanoflower-coated carbon sphere material as described in claim 12 in lithium-sulfur batteries, characterized in that: The carbon nanoflower-coated carbon sphere material was used as a carrier for sulfur in the positive electrode of a lithium-sulfur battery.

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