CN112980436B - Carbon quantum dot derived carbon nano sheet composite silicon dioxide anode material and preparation method thereof - Google Patents

Abstract

The invention discloses a carbon quantum dot derived carbon nano sheet composite silicon dioxide anode material and a preparation method thereof. In the carbon quantum dot derived carbon nano sheet composite nano silicon dioxide anode material, the thickness of the carbon quantum dot derived carbon nano sheet is less than or equal to 2nm, the carbon quantum dot derived carbon nano sheet contains sulfur with the mass ratio of 0.8% -1.3%, the shape of silicon dioxide is spherical, the crystal structure is an amorphous structure, and the average particle size is about 150nm. Mixing carbon quantum dots and sulfur doping agents, preparing sulfur doped carbon quantum dot derivative carbon nano sheets by calcining and heating, ultrasonically dispersing the carbon quantum dot derivative carbon nano sheets in absolute ethyl alcohol, adding ammonia water, ethyl orthosilicate and deionized water, mixing, and preparing the sulfur doped carbon quantum dot derivative carbon nano sheet composite silicon dioxide anode material by a sol-gel method and freeze drying. The preparation process is simple and has low energy consumption; the carbon quantum dot derived carbon nano sheet is used as an inner core supporting framework, the material thickness is uniform, the structure is stable, and the electric conduction is enhanced, so that the circulation stability is enhanced.

Description

A carbon quantum dot derived carbon nanosheet composite silica negative electrode material and its preparation method

technical field

The invention belongs to the field of lithium-ion battery electrode materials, and in particular relates to a carbon quantum dot-derived carbon nanosheet composite silicon dioxide negative electrode material and a preparation method thereof.

Background technique

Lithium-ion batteries (LIBs) have attracted much attention due to their high energy density and long cycle life. Commercial graphite with a theoretical capacity of only 372mAh/g can no longer meet the growing demand for power. Therefore, silicon-based anode materials with a higher theoretical specific capacity (4200mAh/g) are considered to be the best anode for next-generation lithium-ion batteries. However, its huge volume expansion (>300%) during lithiation leads to structural fragmentation as well as disadvantages such as phase transition during electrochemical reactions, causing rapid capacity fading and significantly limiting its commercial applications.

In recent years, amorphous silica with a theoretical capacity of up to 1965mAh/g has attracted people's attention, and its lithiation reaction to generate Li ₂ O can be used as a buffer component for volume change. However, their applications are limited by their low initial Coulombic efficiency and low electrical conductivity. In order to solve the above-mentioned problems existing in the pure silicon dioxide negative electrode material, the present invention pioneered the use of carbon quantum dot-derived carbon nanosheet composite silicon dioxide to prepare the lithium battery negative electrode material. up to 1124.8mAh/g, the first charge specific capacity can reach 725.7mAh/g, and can maintain a reversible specific capacity of 568.7mAh/g after 60 cycles; at a current density of 4A/g, it can maintain 568.7mAh/g after 200 cycles The reversible specific capacity of g.

Contents of the invention

The object of the present invention is to provide a carbon quantum dot derived carbon nanosheet composite silicon dioxide negative electrode material and a preparation method thereof.

In the carbon quantum dot-derived carbon nanosheet composite nano-silica negative electrode material involved in the present invention, the carbon quantum dot-derived carbon nanosheet has a thickness of ≤2nm and contains sulfur with a mass ratio of 0.8%-1.3%, and the morphology of the silicon dioxide is: Spherical, crystal structure is amorphous structure, average particle size is about 150nm.

The specific steps of the preparation method of the carbon quantum dot derived carbon nanosheet composite nano-silica negative electrode material are as follows:

(1) Take 40mL of acetaldehyde solution with a concentration of 40% by volume and put it in a 100mL beaker. Under vigorous magnetic stirring, slowly add 8g of NaOH solid to react for 1 hour, then let it stand at room temperature for 72 hours, and then put the resulting Take out the black oily solid and place it in a beaker, add 50mL of hydrochloric acid solution with a concentration of 1mol/L and stir for 1 hour, then repeatedly centrifuge and wash it with deionized water until neutral, then put the solid powder in an oven and keep it warm at 70°C for 12 hours , that is, carbon quantum dots.

(2) Weigh 1g of carbon quantum dots obtained in step (1) and 6g of sulfur dopant and put them into a mortar, place them in a 5mL alumina crucible, put them into a tube furnace, and heat them at 3°C/min under a nitrogen atmosphere. Heating to 800°C, holding for 1 hour, cooling to room temperature, washing with deionized water and filtering for 3 to 5 times, putting in an oven, heating to 70°C, holding for 12 hours to obtain carbon quantum dot-derived carbon nanosheets.

(3) Disperse 50-200 mg of carbon quantum dot-derived carbon nanosheets obtained in step (2) in 8 mL of analytically pure absolute ethanol and ultrasonicate for 30 minutes, add ammonia water with a mass percentage concentration of 28% to make the pH of the system 8- 10. Add 0.5mL of analytically pure ethyl orthosilicate, let it stand for 12 hours, add 1mL of deionized water to form a gel, put it in a freeze dryer and freeze-dry it to obtain carbon quantum dot-derived carbon nanosheet composite silica negative electrode material .

(4) Mix 0.1 g of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material obtained in step (3), Ketjen Black and polyvinylidene fluoride in a mass ratio of 5:3:2, and add 1 to 1.5 mL Analytical pure N-methyl-2-pyrrolidone is ground into a slurry, coated on a copper foil current collector with a coating thickness of 10 μm, heated to 110°C in a vacuum drying oven, kept for 10 hours, and cooled to room temperature , Use a punching machine to punch a circular pole piece with a diameter of 16mm.

(5) With the metal lithium sheet as the counter electrode, the polypropylene of the microporous structure is selected as the diaphragm, and the electrolyte is dissolved with a concentration of 1mol/L LiPF ₆ EC+DMC+DEC solution, and the volume ratio of EC, DMC and DEC is 1: 1:1, assembled into a CR2025 battery in an argon-protected glove box, after sealing, let it stand for 12 hours, and carried out the electrochemical performance test, the test voltage was 3-0.01V, and the current density was 200mA/g-4A/g .

The sulfur dopant is one or more of sodium dodecylsulfate, sodium dodecylbenzenesulfonate and sulfur.

The present invention has the following advantages:

(1) In the prepared carbon quantum dot-derived carbon nanosheet composite silica negative electrode material, the carbon quantum dot-derived carbon nanosheet is used as the core support skeleton, which has a stable structure and enhanced electrical conductivity, thereby enhancing cycle stability.

(2) In terms of the cost advantage of preparation, this technology realizes the preparation of quantum dot-derived carbon nanosheet composite silica negative electrode material by simple sol-gel method and freeze-drying treatment, which has the characteristics of less operation steps and low energy consumption. Fully reflect the cost advantage.

Description of drawings

FIG. 1 is a scanning electron microscope (SEM) image of carbon quantum dot-derived carbon nanosheets prepared in Example 1 of the present invention.

Fig. 2 is an X-ray diffraction (XRD) pattern of carbon quantum dot-derived carbon nanosheets prepared in Example 1 of the present invention.

Fig. 3 is the charging and discharging curves of the first two times of the carbon quantum dot derived carbon nanosheet composite silicon dioxide negative electrode material prepared in Example 1 of the present invention.

Fig. 4 is a cycle performance graph of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material prepared in Example 1 of the present invention.

Fig. 5 is a graph showing charge and discharge curves of the carbon quantum dot derived carbon nanosheet composite silicon dioxide negative electrode material prepared in Example 2 of the present invention.

Fig. 6 is a cycle performance diagram of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material prepared in Example 2 of the present invention.

Fig. 7 is the charge-discharge curve diagram of the carbon quantum dot derived carbon nanosheet composite silicon dioxide negative electrode material prepared in Example 3 of the present invention,

Fig. 8 is a cycle performance diagram of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material prepared in Example 3 of the present invention.

9 is a scanning electron microscope (SEM) image of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material prepared in Example 4 of the present invention.

Figure 10 is the charge-discharge curve of the carbon quantum dot derived carbon nanosheet composite silicon dioxide negative electrode material prepared in Example 4 of the present invention

Fig. 11 is a cycle performance graph of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material prepared in Example 4 of the present invention.

Fig. 12 is a cycle performance diagram of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material prepared in Example 4 of the present invention at a current density of 2A g ^-1 .

Fig. 13 is a cycle performance diagram of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material prepared in Example 4 of the present invention at a current density of 4A g ^-1 .

Detailed ways

Example 1:

(1) Take 40mL of acetaldehyde solution with a concentration of 40% by volume and put it in a 100mL beaker. Under vigorous magnetic stirring, slowly add 8g of NaOH solid to react for 1 hour, then let it stand at room temperature for 72 hours, and then put the resulting Take out the black oily solid and place it in a beaker, add 50mL of hydrochloric acid solution with a concentration of 1mol/L and stir for 1 hour, then repeatedly centrifuge and wash it with deionized water until neutral, then put the solid powder in an oven and keep it warm at 70°C for 12 hours , that is, carbon quantum dots.

(2) Weigh 1g of carbon quantum dots obtained in step (1) and 6g of sodium lauryl sulfate and put them in a mortar, place them in a 5mL alumina crucible, put them into a tube furnace, and heat them at 3°C under a nitrogen atmosphere. /min heated to 800°C, kept for 1 hour, cooled to room temperature, washed with deionized water and filtered 3 times, placed in an oven, heated to 70°C, kept for 12 hours to obtain carbon quantum dot-derived carbon nanosheets. The carbon quantum dot-derived carbon nanosheets were analyzed by scanning electron microscopy (SEM). As shown in Figure 1, the microscopic appearance of the carbon quantum dot-derived carbon nanosheets is a sheet-like structure with a thickness ≤ 2nm. X-ray diffraction (XRD) analysis of carbon quantum dot-derived carbon nanosheets (Fig. 2) indicated that the material was amorphous carbon.

(3) Disperse 50 mg of carbon quantum dot-derived carbon nanosheets obtained in step (2) in 8 mL of analytically pure absolute ethanol and ultrasonicate for 30 minutes, add ammonia water with a mass percentage concentration of 28% to make the pH of the system 8, add 0.5 mL of analytically pure ethyl orthosilicate, after standing for 12 hours, add 1mL of deionized water to form a gel, put it into a freeze dryer and freeze-dry to obtain carbon quantum dot-derived carbon nanosheet composite silica negative electrode material.

(4) Mix 0.1 g of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material obtained in step (3), Ketjen Black and polyvinylidene fluoride in a mass ratio of 5:3:2, add 1 mL of analytically pure N -Methyl-2-pyrrolidone is ground into a slurry, coated on a copper foil current collector with a coating thickness of 10 μm, placed in a vacuum drying oven and heated to 110°C, kept for 10 hours, cooled to room temperature, and punched Machine punched into a circular pole piece with a diameter of 16mm.

(5) Use metal lithium sheet as counter electrode, polypropylene with microporous structure as separator, electrolyte solution as EC+DMC+DEC solution with LiPF ₆ dissolved at a concentration of 1mol/L, and the volume ratio of EC, DMC and DEC is 1 :1:1, assembled into a CR2025 battery in an argon-protected glove box, after sealing, let it stand for 12 hours, and carried out the electrochemical performance test, the test voltage was 3-0.01V, and the current density was 200mA/g. Electrochemical performance tests show that the first charge-discharge specific capacity of the composite is 408.7 and 1467mAh/g (Figure 3), the reversible capacity retained after 100 cycles is 379.8mAh/g, and the Coulombic efficiency is maintained above 90%. (Figure 4), showing better electrochemical performance.

Example 2:

(1) Take 40mL of acetaldehyde solution with a concentration of 40% by volume and put it in a 100mL beaker. Under vigorous magnetic stirring, slowly add 8g of NaOH solid to react for 1 hour, then let it stand at room temperature for 72 hours, and then put the resulting Take out the black oily solid and place it in a beaker, add 50mL of hydrochloric acid solution with a concentration of 1mol/L and stir for 1 hour, then repeatedly centrifuge and wash it with deionized water until neutral, then put the solid powder in an oven and keep it warm at 70°C for 12 hours , that is, carbon quantum dots.

(2) Weigh 1g of carbon quantum dots obtained in step (1) and 6g of sodium lauryl sulfate and put them in a mortar, place them in a 5mL alumina crucible, put them into a tube furnace, and heat them at 3°C under a nitrogen atmosphere. /min heated to 800°C, kept for 1 hour, cooled to room temperature, washed with deionized water and filtered 4 times, placed in an oven, heated to 70°C, kept for 12 hours to obtain carbon quantum dot-derived carbon nanosheets.

(3) Disperse 100 mg of carbon quantum dot-derived carbon nanosheets obtained in step (2) in 8 mL of analytically pure absolute ethanol and sonicate for 30 minutes, add ammonia water with a mass percentage concentration of 28% to make the pH of the system 9, add 0.5 mL of analytically pure ethyl orthosilicate, after standing for 12 hours, add 1mL of deionized water to form a gel, put it into a freeze dryer and freeze-dry to obtain carbon quantum dot-derived carbon nanosheet composite silica negative electrode material.

(4) Mix 0.1 g of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material obtained in step (3), Ketjen Black and polyvinylidene fluoride in a mass ratio of 5:3:2, add 1 mL of analytically pure N -Methyl-2-pyrrolidone is ground into a slurry, coated on a copper foil current collector with a coating thickness of 10 μm, placed in a vacuum drying oven and heated to 110°C, kept for 10 hours, cooled to room temperature, and punched Machine punched into a circular pole piece with a diameter of 16mm.

(5) Use metal lithium sheet as counter electrode, polypropylene with microporous structure as separator, electrolyte solution as EC+DMC+DEC solution with LiPF ₆ dissolved at a concentration of 1mol/L, and the volume ratio of EC, DMC and DEC is 1 :1:1, assembled into a CR2025 battery in an argon-protected glove box, after sealing, let it stand for 12 hours, and carried out the electrochemical performance test, the test voltage was 3-0.01V, and the current density was 200mA/g. Electrochemical performance tests show that the first charge-discharge specific capacity of the composite is 673.4 and 1990.7mAh/g (Figure 5), and the reversible capacity retained after 100 cycles is 510.2mAh/g, and the Coulombic efficiency is maintained at 90%. Above (Fig. 6), it shows better electrochemical performance.

Example 3:

(1) Take 40mL of acetaldehyde solution with a concentration of 40% by volume and put it in a 100mL beaker. Under vigorous magnetic stirring, slowly add 8g of NaOH solid to react for 1 hour, then let it stand at room temperature for 72 hours, and then put the resulting Take out the black oily solid and place it in a beaker, add 50mL of hydrochloric acid solution with a concentration of 1mol/L and stir for 1 hour, then repeatedly centrifuge and wash it with deionized water until neutral, then put the solid powder in an oven and keep it warm at 70°C for 12 hours , that is, carbon quantum dots.

(2) Weigh 1g of carbon quantum dots obtained in step (1) and 6g of sodium lauryl sulfate and put them in a mortar, place them in a 5mL alumina crucible, put them into a tube furnace, and heat them at 3°C under a nitrogen atmosphere. /min heated to 800°C, kept for 1 hour, cooled to room temperature, washed with deionized water and filtered 5 times, put in an oven, heated to 70°C, kept for 12 hours to obtain carbon quantum dot derived carbon nanosheets.

(3) Disperse 150 mg of carbon quantum dot-derived carbon nanosheets obtained in step (2) in 8 mL of analytically pure absolute ethanol and sonicate for 30 minutes, add ammonia water with a mass percentage concentration of 28% to make the pH of the system 10, add 0.5 mL of analytically pure ethyl orthosilicate, after standing for 12 hours, add 1mL of deionized water to form a gel, put it into a freeze dryer and freeze-dry to obtain carbon quantum dot-derived carbon nanosheet composite silica negative electrode material.

(4) Mix 0.1 g of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material obtained in step (3), Ketjen Black and polyvinylidene fluoride in a mass ratio of 5:3:2, add 1.2 mL of analytically pure Grind N-methyl-2-pyrrolidone to make a slurry, coat it on the copper foil current collector with a coating thickness of 10 μm, put it in a vacuum drying oven and heat it to 110 ° C, keep it warm for 10 hours, cool to room temperature, and use a punch The chip machine is punched into a circular pole piece with a diameter of 16mm.

(5) Use metal lithium sheet as counter electrode, polypropylene with microporous structure as separator, electrolyte solution as EC+DMC+DEC solution with LiPF ₆ dissolved at a concentration of 1mol/L, and the volume ratio of EC, DMC and DEC is 1 :1:1, assembled into a CR2025 battery in an argon-protected glove box, after sealing, let it stand for 12 hours, and carried out the electrochemical performance test, the test voltage was 3-0.01V, and the current density was 200mA/g. Electrochemical performance tests showed that the first charge-discharge specific capacity of the composite material was 725.7 and 1914.8mAh/g (Figure 7), and the reversible capacity remained at 638.2mAh/g after 80 cycles, and the coulombic efficiency was maintained at 90%. Above (Fig. 8), it shows better electrochemical performance.

Example 4:

(1) Take 40mL of acetaldehyde solution with a concentration of 40% by volume and put it in a 100mL beaker. Under vigorous magnetic stirring, slowly add 8g of NaOH solid to react for 1 hour, then let it stand at room temperature for 72 hours, and then put the resulting Take out the black oily solid and place it in a beaker, add 50mL of hydrochloric acid solution with a concentration of 1mol/L and stir for 1 hour, then repeatedly centrifuge and wash it with deionized water until neutral, then put the solid powder in an oven and keep it warm at 70°C for 12 hours , that is, carbon quantum dots.

(2) Weigh 1g of carbon quantum dots obtained in step (1) and 6g of sodium lauryl sulfate and put them in a mortar, place them in a 5mL alumina crucible, put them into a tube furnace, and heat them at 3°C under a nitrogen atmosphere. /min heated to 800°C, kept for 1 hour, cooled to room temperature, washed with deionized water and filtered 5 times, put in an oven, heated to 70°C, kept for 12 hours to obtain carbon quantum dot derived carbon nanosheets.

(3) Disperse 200 mg of carbon quantum dot-derived carbon nanosheets obtained in step (2) in 8 mL of analytically pure absolute ethanol and ultrasonicate for 30 minutes, add ammonia water with a mass percentage concentration of 28% to make the pH of the system 10, add 0.5 mL of analytically pure ethyl orthosilicate, after standing for 12 hours, add 1mL of deionized water to form a gel, put it into a freeze dryer and freeze-dry to obtain carbon quantum dot-derived carbon nanosheet composite silica negative electrode material. The carbon quantum dot derived carbon nanosheet composite silica negative electrode material was tested and analyzed by scanning electron microscopy (SEM). As shown in Figure 9, the microscopic morphology of the composite material is a sheet structure with uniform thickness.

(4) Mix 0.1 g of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material obtained in step (3), Ketjen Black and polyvinylidene fluoride in a mass ratio of 5:3:2, add 1.5 mL of analytically pure Grind N-methyl-2-pyrrolidone to make a slurry, coat it on the copper foil current collector with a coating thickness of 10 μm, put it in a vacuum drying oven and heat it to 110 ° C, keep it warm for 10 hours, cool to room temperature, and use a punch The chip machine is punched into a circular pole piece with a diameter of 16mm.

(5) Use metal lithium sheet as counter electrode, polypropylene with microporous structure as separator, electrolyte solution as EC+DMC+DEC solution with LiPF ₆ dissolved at a concentration of 1mol/L, and the volume ratio of EC, DMC and DEC is 1 :1:1, assembled into a CR2025 battery in an argon-protected glove box, after sealing, let it stand for 12 hours, and carried out the electrochemical performance test, the test voltage was 3-0.01V, and the current density was 200mA/g. Electrochemical performance tests showed that the first charge-discharge specific capacity of the composite was 1124.8 and 2812.9mAh/g (Figure 10), and the reversible capacity remained after 80 cycles was 775.9mAh/g (Figure 11), showing better electrochemical performance. The cycle performance of the composite material at a high current density of 2A/g and 4A/g is shown in Figures 12 and 13, the former still retains a reversible specific capacity of 501.9mAh/g after 120 cycles (Figure 12), and the latter The latter still retain a reversible specific capacity of 426.4mAh/g (Fig. 13) after 200 cycles, and the coulombic efficiencies are maintained above 90%.

Claims (1)

1. A method for preparing a carbon quantum dot derived carbon nanosheet composite silica negative electrode material, characterized in that in the carbon quantum dot derived carbon nanosheet composite nano silicon dioxide negative electrode material, the carbon quantum dot derived carbon nanosheet thickness≤2 nm, containing sulfur with a mass ratio of 0.8%-1.3%, the shape of silica is spherical, the crystal structure is amorphous, and the average particle size is 150nm; The specific steps of the preparation method of the carbon quantum dot derived carbon nanosheet composite silica negative electrode material are as follows: (1) Take 40 mL of acetaldehyde solution with a concentration of 40% by volume and put it into a 100 mL beaker. Under vigorous magnetic stirring, slowly add 8 g of NaOH solid to react for 1 hour, then let it stand at room temperature for 72 hours, and then Take out the black oily solid obtained from the reaction and place it in a beaker, add 50 mL of hydrochloric acid solution with a concentration of 1 mol/L and stir for 1 hour, then repeatedly centrifuge and wash it with deionized water until neutral, then put the solid powder in an oven at 70 ℃ for 12 hours to obtain carbon quantum dots; (2) Weigh 1 g of carbon quantum dots obtained in step (1) and 6 g of sulfur dopant into a mortar, place them in a 5 mL alumina crucible, put them into a tube furnace, and heat them at 3 ℃/min Heating to 800 ℃, heat preservation for 1 hour, after cooling to room temperature, wash and filter with deionized water 3~5 times, put in an oven, heat to 70 ℃, heat preservation for 12 hours, to obtain carbon quantum dot derived carbon nanosheets ; (3) Disperse 50-200 mg of carbon quantum dot-derived carbon nanosheets obtained in step (2) in 8 mL of analytically pure absolute ethanol and sonicate for 30 minutes, and add ammonia water with a concentration of 28% by mass to make the pH of the system to be 8 to 10, add 0.5 mL of analytically pure ethyl orthosilicate, let it stand for 12 hours, add 1 mL of deionized water to form a gel, put it in a freeze dryer and freeze-dry to obtain carbon quantum dot-derived carbon nanosheet composite carbon dioxide Silicon anode material; (4) Mix 0.1 g of the carbon quantum dot-derived carbon nanosheet composite silica negative electrode material obtained in step (3), Ketjen Black and polyvinylidene fluoride at a mass ratio of 5:3:2, and add 1~1.5 mL Analytical pure N-methyl-2-pyrrolidone is ground into a slurry, coated on a copper foil current collector with a coating thickness of 10 mm, heated in a vacuum drying oven to 110 °C, kept for 10 hours, and cooled to room temperature , using a punching machine to punch a circular pole piece with a diameter of 16 mm; (5) Lithium metal sheet is used as the counter electrode, polypropylene with a microporous structure is selected as the separator, and the electrolyte is EC+DMC+DEC solution with a concentration of 1 mol/L LiPF ₆ dissolved, and the volume ratio of EC, DMC and DEC is 1 :1:1, assembled into a CR2025 battery in an argon-protected glove box, after sealing, let it stand for 12 hours, and carried out electrochemical performance tests, the test voltage was 3~0.01 V, and the current density was 200 mA/g~4 A/g; The sulfur dopant is one or more of sodium dodecylsulfate, sodium dodecylbenzenesulfonate and sulfur.

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