CN108832107B - Graphene quantum dot-bio-based activated carbon composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a graphene quantum dot-bio-based activated carbon composite material and a preparation method thereof, belonging to the technical field of lithium battery materials. The graphene quantum dot-bio-based activated carbon composite material of the present invention is obtained by modifying the bio-based activated carbon with graphene quantum dots. The graphene quantum dot-bio-based activated carbon composite material of the present invention is used as a negative electrode material for a lithium battery, which is more efficient than the original one. Bio-based activated carbon has higher specific discharge capacity, higher coulombic efficiency value, better rate performance and electrical conductivity, and exhibits good cycle performance, which has a good application prospect in the field of lithium battery anode material research.

Description

Graphene quantum dots-biobased activated carbon composite material and preparation method thereof

technical field

The invention relates to a graphene quantum dot-bio-based activated carbon composite material and a preparation method thereof, and belongs to the technical field of lithium battery materials.

Background technique

Compared with other rechargeable secondary batteries, lithium-ion batteries have obvious advantages. First of all, it has good safety and conforms to the theme that production safety is always the first priority in contemporary social development. Li-ion batteries are small in size and high in capacity, which is in line with the development trend of the times. The non-polluting advantages of lithium-ion batteries are favored by various fields, from mobile phone batteries to electric or hybrid vehicles to aerospace and other fields. With the continuous innovation of science and technology, people have higher requirements for lithium-ion batteries, and the innovation of lithium-ion batteries is imminent. A large number of scholars at home and abroad are working on the research of lithium-ion batteries with better comprehensive performance. The research on lithium-ion anode materials has far-reaching significance for improving the performance of lithium-ion batteries, real life and scientific and technological development.

In recent years, biomass waste has become a functional material with the most development potential because of its advantages of low cost, environmental protection, and renewability. pore, and showed some good electrochemical properties, which attracted extensive attention of researchers at home and abroad. So far, the research on the electrochemical properties of activated carbon has mainly focused on the fields of electric double layer capacitors and supercapacitors. Fey et al. used rice husk as raw material to prepare rice husk activated carbon through high temperature pyrolysis, and conducted research and analysis on electrochemical properties. They found that the battery assembled with homemade rice husk activated carbon as electrode material had bright spots in electrochemical performance, such as high discharge specific capacity, However, the efficiency is very low, and there are defects such as insufficient cycle performance and insufficient electrical conductivity, which still need further research.

As a member of the graphene family, graphene quantum dots are only a few nanometers in size. Compared with other members of the graphene family, they have unique advantages in quantum confinement effect and boundary effect. Therefore, they are often used as Modified graphene quantum dots have broad application potential in many fields, including supercapacitors, optoelectronic devices and other fields. Although both biomass carbon and graphene quantum dots have great potential for electrochemical applications, however, there are few reports on the electrochemical properties of graphene quantum dots-modified biomass carbon.

SUMMARY OF THE INVENTION

In order to solve these problems, the purpose of the present invention is to provide a kind of graphene quantum dot-bio-based activated carbon composite material, and the bio-based activated carbon after the present invention is modified with graphene quantum dots has higher discharge specific capacity than the original bio-based activated carbon. , higher coulombic efficiency value, better rate performance and electrical conductivity, and showed good cycle performance, which has a good application prospect in the field of lithium battery anode material research.

The first object of the present invention is to provide a graphene quantum dot-bio-based activated carbon composite material, including bio-based activated carbon, the surface of the bio-based activated carbon is connected to the graphene quantum dots through hydrogen bonds, and the bio-based activated carbon is a micro-intermediate Pore structure, the graphene quantum dots are physically adsorbed in the pores of the micro-mesoporous structure.

In one embodiment of the present invention, the graphene quantum dots are amino acid functionalized graphene quantum dots, amino functionalized graphene quantum dots or amine functionalized graphene quantum dots.

In one embodiment of the present invention, the amino acid functionalized graphene quantum dots are phenylalanine functionalized graphene quantum dots, histidine functionalized graphene quantum dots, and valine functionalized graphene quantum dots or lysine-functionalized graphene quantum dots.

In one embodiment of the present invention, the bio-based activated carbon is rice husk activated carbon, straw activated carbon, fruit shell activated carbon, grass stem activated carbon or biomass residue activated carbon.

In one embodiment of the present invention, the straw activated carbon is wheat straw activated carbon, rice straw activated carbon, corn straw activated carbon, soybean straw activated carbon or pepper straw activated carbon.

In one embodiment of the present invention, the nut shell activated carbon is walnut shell activated carbon, rice husk activated carbon or chestnut shell activated carbon.

In one embodiment of the present invention, the grass stem activated carbon is weed stem activated carbon.

In an embodiment of the present invention, the biomass residue activated carbon is bagasse activated carbon or beet bagasse activated carbon.

In one embodiment of the present invention, the graphene quantum dot-bio-based activated carbon composite material is prepared by the following method:

Step 1, dissolving and dispersing the graphene quantum dots to form a dispersion;

Step 2, adding bio-based activated carbon to the dispersion in step 1, mixing, heating, and then drying;

Step 3: calcining the dried sample in step 2 to obtain a graphene quantum dot-bio-based activated carbon composite material.

The second object of the present invention is to provide a preparation method of the graphene quantum dot-bio-based activated carbon composite material, and the preparation method comprises the following steps:

Step 1, dissolving and dispersing the graphene quantum dots to form a dispersion;

Step 2, adding bio-based activated carbon to the dispersion in step 1, mixing, heating, and then drying;

Step 3: calcining the dried sample in step 2 to obtain a graphene quantum dot-bio-based activated carbon composite material.

In an embodiment of the present invention, in step 1, ultrasonic waves are used for dispersion, and the dispersion time is 1-4 hours.

In an embodiment of the present invention, in step 2, the amount of bio-based activated carbon added is 5-15 times that of graphene quantum dots in terms of mass.

In an embodiment of the present invention, in step 2, the heating condition is heating at 80-100 °C for 3-5 h.

In an embodiment of the present invention, in step 3, the calcination is calcination in a calcination furnace at 400-500° C. in an Ar/H ₂ atmosphere for 6-8 hours.

The third object of the present invention is to provide the application of the graphene quantum dot-bio-based activated carbon composite material in the preparation of a lithium battery negative electrode.

The fourth object of the present invention is to provide a lithium battery negative electrode material, the lithium battery negative electrode material comprising the graphene quantum dot-bio-based activated carbon composite material.

The fifth object of the present invention is to provide a lithium battery, wherein the lithium battery is prepared from the graphene quantum dot-bio-based activated carbon composite material to prepare the negative electrode of the lithium battery.

Beneficial effects of the present invention:

Compared with the original bio-based activated carbon, the bio-based activated carbon modified with graphene quantum dots has higher discharge specific capacity, higher coulombic efficiency value, better rate performance and electrical conductivity, and shows good cycle performance , has a good application prospect in the research field of lithium battery anode materials.

Description of drawings

Fig. 1 is the Fourier transform infrared spectrogram of phenylalanine functionalized graphene quantum dots-rice husk activated carbon composite material;

Fig. 2 is the cyclic voltammetry curves of rice husk activated carbon (a) and phenylalanine functionalized graphene quantum dots-rice husk activated carbon composite material (b);

Figure 3 shows the first (solid line) and second (dotted line) charging of rice husk activated carbon (a) and phenylalanine-functionalized graphene quantum dots-rice husk activated carbon composite (b) at a current density of 100 mA/g. discharge curve;

Figure 4(a) shows the discharge capacity curves of rice husk activated carbon and phenylalanine functionalized graphene quantum dots-rice husk activated carbon composites at different current densities;

Figure 4(b) shows the cycling performance of rice husk activated carbon and phenylalanine functionalized graphene quantum dots-rice husk activated carbon composites at a current density of 100 mA/g;

Figure 5 is the electrochemical AC impedance spectra of rice husk activated carbon (a) and phenylalanine-functionalized graphene quantum dots-rice husk activated carbon composite (b) after 50 cycles.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

The lithium ion diffusion coefficient D is calculated from the data in the low frequency region according to formula (1).

D=R ² T ² /2A ² n ⁴ F ⁴ C ² σ ² (1)

where R is the gas volume constant; T is the absolute temperature; A is the surface area of the cathode material; n is the electron transfer number in the redox process; F is the Faraday constant; C is the concentration of lithium ions in the electrolyte; σ is the Warburg coefficient .

Example 1: Preparation of phenylalanine-functionalized graphene quantum dots-rice husk activated carbon composite material

10 g of rice husks were placed in 50 g of phosphoric acid solution with a mass fraction of 60%, calcined at 500° C. under the protection of inert gas (argon), and then washed and dried to obtain rice husk-based activated carbon.

Using citric acid as the precursor and phenylalanine as the functionalizing reagent, the phenylalanine-functionalized graphene quantum dots were prepared by a high-temperature heating dry method. Weigh 3g of citric acid and dissolve in 2mL of sodium hydroxide solution, and 2.5g of phenylalanine and dissolve in 2ml of sodium hydroxide solution, mix the two, then evaporate and dry at 100 ° C to obtain a viscous substance, put Dry in an oven at 80°C for three days. The solid was crushed into powder, placed in a porcelain crucible and placed in a 200 ℃ muffle furnace for 2 hours, cooled to room temperature to obtain a brown-black product, dissolved in 25 mL of ionized water, centrifuged in a centrifuge at 10,000 rpm for 30 min, and separated. For insoluble particles, the supernatant was dialyzed in ultrapure water with a dialysis bag to further purify the product, and the dialyzed solution was subjected to a freeze-drying step to obtain the final product, phenylalanine-functionalized graphene quantum dots.

Weigh 0.5 g of the prepared phenylalanine-functionalized graphene quantum dots, dissolve in a small amount of deionized water, and ultrasonically disperse for 2 h until the graphene quantum dots are completely dissolved to form a dispersion, then add 5 g of self-made rice husk activated carbon, while Stir while shaking to make the two evenly mixed, heat in a constant temperature water bath at 90°C for 3.5h, and then dry. The dried samples were placed in a tube furnace at 450 °C and calcined in an Ar/H ₂ atmosphere for 6 h to obtain the final product.

Example 2: Preparation of phenylalanine-functionalized graphene quantum dots-rice husk activated carbon composite material

10 g of rice husks were placed in 50 g of phosphoric acid solution with a mass fraction of 60%, calcined at 500° C. under the protection of inert gas (argon), and then washed and dried to obtain rice husk-based activated carbon.

Using citric acid as the precursor and phenylalanine as the functionalizing reagent, the phenylalanine-functionalized graphene quantum dots were prepared by a high-temperature heating dry method. Weigh 3g of citric acid and dissolve it in 2mL of sodium hydroxide solution, and 2.5g of phenylalanine and dissolve it in 2mL of sodium hydroxide solution, mix the two, and then evaporate and dry at 100 ° C to obtain a viscous substance. Dry in an oven at 80°C for three days. Crush the solid into powder, place it in a porcelain crucible and place it in a 200 ℃ muffle furnace for 2 hours, cool to room temperature to obtain a brown-black product, dissolve it in 25 mL of ionized water, and centrifuge it in a centrifuge at a speed of 10,000 rpm for 30 minutes to separate the insoluble product. The product was further purified by dialyzing the supernatant in ultrapure water with a dialysis bag, and the dialyzed solution was subjected to a freeze-drying step to obtain the final product, phenylalanine-functionalized graphene quantum dots.

Weigh 0.5 g of the prepared phenylalanine-functionalized graphene quantum dots, dissolve in a small amount of deionized water, and ultrasonically disperse for 2 h until the graphene quantum dots are completely dissolved to form a dispersion liquid, then add 3 g of self-made rice husk activated carbon, while Stir while shaking to make the two evenly mixed, heat in a constant temperature water bath at 90°C for 3.5h, and then dry. The dried samples were placed in a tube furnace at 450 °C and calcined in an Ar/H ₂ atmosphere for 6 h to obtain the final product.

Example 3: Preparation of phenylalanine-functionalized graphene quantum dots-rice husk activated carbon composite material

10 g of rice husks were placed in 50 g of phosphoric acid solution with a mass fraction of 60%, calcined at 500° C. under the protection of inert gas (argon), and then washed and dried to obtain rice husk-based activated carbon.

Using citric acid as the precursor and phenylalanine as the functionalizing reagent, the phenylalanine-functionalized graphene quantum dots were prepared by a high-temperature heating dry method. Weigh 3g of citric acid and dissolve it in 2mL of sodium hydroxide solution, and 2.5g of phenylalanine and dissolve it in 2mL of sodium hydroxide solution, mix the two, and then evaporate and dry at 100 ° C to obtain a viscous substance. Dry in an oven at 80°C for three days. Crush the solid into powder, place it in a porcelain crucible and place it in a 200 ℃ muffle furnace for 2 hours, cool to room temperature to obtain a brown-black product, dissolve it in 25 mL of ionized water, and centrifuge it in a centrifuge at a speed of 10,000 rpm for 30 minutes to separate the insoluble product. The product was further purified by dialyzing the supernatant in ultrapure water with a dialysis bag, and the dialyzed solution was subjected to a freeze-drying step to obtain the final product, phenylalanine-functionalized graphene quantum dots.

Weigh 0.5 g of the prepared phenylalanine-functionalized graphene quantum dots, dissolve in a small amount of deionized water, ultrasonically disperse for 2 h until the graphene quantum dots are completely dissolved to form a dispersion, and then add 8 g of self-made rice husk activated carbon, while the Stir while shaking to make the two evenly mixed, heat in a constant temperature water bath at 90°C for 3.5h, and then dry. The dried samples were placed in a tube furnace at 450 °C and calcined in an Ar/H ₂ atmosphere for 6 h to obtain the final product.

Example 4: Preparation of histidine-functionalized graphene quantum dots-rice husk activated carbon composite material

10 g of rice husks were placed in 50 g of phosphoric acid solution with a mass fraction of 60%, calcined at 500° C. under the protection of inert gas (argon), and then washed and dried to obtain rice husk-based activated carbon.

Using citric acid as the precursor and histidine as the functionalization reagent, the histidine-functionalized graphene quantum dots were prepared by a high-temperature heating dry method. Weigh 3g of citric acid and dissolve it in 2mL of sodium hydroxide solution, and 2.5g of histidine and dissolve it in 2mL of sodium hydroxide solution, mix the two, and then evaporate and dry at 100 ° C to obtain a viscous substance, which is placed in Dry in an oven at 80°C for three days. Crush the solid into powder, place it in a porcelain crucible and place it in a 200 ℃ muffle furnace for 2 hours, cool to room temperature to obtain a brown-black product, dissolve it in 25 mL of ionized water, and centrifuge it in a centrifuge at a speed of 10,000 rpm for 30 minutes to separate the insoluble product. The product is further purified by dialyzing the supernatant in ultrapure water with a dialysis bag, and the dialyzed solution is subjected to a freeze-drying step to obtain the final product, histidine-functionalized graphene quantum dots.

Weigh 0.5 g of the prepared histidine-functionalized graphene quantum dots, dissolve in a small amount of deionized water, and ultrasonically disperse for 2 h until the graphene quantum dots are completely dissolved to form a dispersion, then add 5 g of homemade rice husk activated carbon, and stir while stirring. The two were mixed evenly by shaking, placed in a constant temperature water bath at 90°C for 3.5h, and then dried. The dried samples were placed in a tube furnace at 450 °C and calcined in an Ar/H2 atmosphere for 6 h to obtain the final product.

Example 5: Preparation of phenylalanine-functionalized graphene quantum dots-wheat straw activated carbon composite material

Weigh 10 g of wheat straw, add phosphoric acid with a mass fraction of 80% according to the impregnation ratio of 3:1, and pre-activate at 140° C. for 60 min. The mixture was put into a calciner, heated to 450°C at a heating rate of 3°C/min, and calcined for 60min. Washed with water until neutral, and dried to obtain wheat straw-based activated carbon.

Using citric acid as the precursor and phenylalanine as the functionalizing reagent, the phenylalanine-functionalized graphene quantum dots were prepared by a high-temperature heating dry method. Weigh 3g of citric acid and dissolve in 2mL of sodium hydroxide solution, and 2.5g of phenylalanine and dissolve in 2ml of sodium hydroxide solution, mix the two, then evaporate and dry at 100 ° C to obtain a viscous substance, put Dry in an oven at 80°C for three days. The solid was crushed into powder, placed in a porcelain crucible and placed in a 200 ℃ muffle furnace for 2 hours, cooled to room temperature to obtain a brown-black product, dissolved in 25 mL of ionized water, centrifuged in a centrifuge at 10,000 rpm for 30 min, and separated. For insoluble particles, the supernatant was dialyzed in ultrapure water with a dialysis bag to further purify the product, and the dialyzed solution was subjected to a freeze-drying step to obtain the final product, phenylalanine-functionalized graphene quantum dots.

Weigh 0.5 g of the prepared phenylalanine-functionalized graphene quantum dots, dissolve them in a small amount of deionized water, and ultrasonically disperse for 2 h until the graphene quantum dots are completely dissolved to form a dispersion, and then add 5 g of self-made wheat straw activated carbon. Stir while shaking to make the two evenly mixed, heat in a constant temperature water bath at 90°C for 3.5h, and then dry. The dried samples were placed in a tube furnace at 450 °C and calcined in an Ar/H ₂ atmosphere for 6 h to obtain the final product.

Example 6: Preparation of histidine-functionalized graphene quantum dots-weed stem activated carbon composite material

Take 10 g of weed stems and wash them with clean water, cut the washed weed stems into 10-20 mm pieces, and dry the stems in an oven at 105° C. for 1 day. Grind and sieve to 20-50 mesh. _The powder was immersed in a ZnCl solution containing 40% ZnCl for ₁₈ hours. The slurry was then calcined in a calciner at 500°C for 30 minutes. The product was sequentially washed with 0.5mol HCl, deionized water to remove residual _ZnCl and minerals, and dried to obtain weed stem activated carbon.

Using citric acid as the precursor and histidine as the functionalization reagent, the histidine-functionalized graphene quantum dots were prepared by a high-temperature heating dry method. Weigh 3g of citric acid and dissolve it in 2mL of sodium hydroxide solution, and 2.5g of histidine and dissolve it in 2mL of sodium hydroxide solution, mix the two, and then evaporate and dry at 100 ° C to obtain a viscous substance, which is placed in Dry in an oven at 80°C for three days. Crush the solid into powder, place it in a porcelain crucible and place it in a 200 ℃ muffle furnace for 2 hours, cool to room temperature to obtain a brown-black product, dissolve it in 25 mL of ionized water, and centrifuge it in a centrifuge at a speed of 10,000 rpm for 30 minutes to separate the insoluble product. The product is further purified by dialyzing the supernatant in ultrapure water with a dialysis bag, and the dialyzed solution is subjected to a freeze-drying step to obtain the final product, histidine-functionalized graphene quantum dots.

Weigh 0.5 g of the prepared histidine-functionalized graphene quantum dots, dissolve them in a small amount of deionized water, and ultrasonically disperse for 2 h until the graphene quantum dots are completely dissolved to form a dispersion, then add 5 g of self-made weed stem activated carbon, while the Stir while shaking to make the two evenly mixed, heat in a constant temperature water bath at 90 °C for 3.5 h, and then dry. The dried samples were placed in a tube furnace at 450 °C and calcined in an Ar/H ₂ atmosphere for 6 h to obtain the final product.

Example 7: Preparation of amino-functionalized graphene quantum dots-bagasse activated carbon composite material

According to the weight ratio of 4:3, the bagasse is carbonized with concentrated sulfuric acid at low temperature, and then mixed in a mixer for about 30 minutes. The acid-impregnated bagasse was charged into a Pyrex reactor heated by a tube furnace. Air was metered into the reactor at a rate of 2 dm ³ ·min ⁻¹ at a high temperature of 900°C, while the fibers were heated to 160°C at a rate of 10°C/min. This temperature was maintained for 2 hours, then the reactor was pulled out of the furnace and allowed to cool. Wash and dry to obtain bagasse activated carbon.

Using citric acid as the precursor and ammonia water as the functionalization reagent, the amino-functionalized graphene quantum dots were prepared by a high-temperature heating dry method. 3 g of citric acid was weighed and dissolved in 2 mL of sodium hydroxide solution, mixed with 5 mL of ammonia water, and then evaporated and dried at 100 °C to obtain a viscous substance, which was dried in an oven at 80 °C for three days. Crush the solid into powder, place it in a porcelain crucible and place it in a 200 ℃ muffle furnace for 2 hours, cool to room temperature to obtain a brown-black product, dissolve it in 25 mL of ionized water, and centrifuge it in a centrifuge at a speed of 10,000 rpm for 30 minutes to separate the insoluble product. The product is further purified by dialyzing the supernatant in ultrapure water with a dialysis bag, and the dialyzed solution is subjected to a freeze-drying step to obtain the final product, amino-functionalized graphene quantum dots.

Weigh 0.5 g of the prepared amino-functionalized graphene quantum dots, dissolve in a small amount of deionized water, ultrasonically disperse for 2 h until the graphene quantum dots are completely dissolved to form a dispersion, then add 5 g of self-made bagasse activated carbon, and oscillate while stirring. The two were evenly mixed, placed in a constant temperature water bath at 90°C for 3.5 hours, and then dried. The dried samples were placed in a tube furnace at 450 °C and calcined in an Ar/H ₂ atmosphere for 6 h to obtain the final product.

Example 8: Preparation of electrodes and assembly of batteries

Preparation of electrodes: The composite materials prepared in Examples 1-7 and the conductive agent acetylene black were mixed in an agate mortar in a mass ratio of 8:1, fully ground for 1 hour and then used for later use. The ground mixture and the binder sodium alginate (2%) were added into a small glass bottle in a mass ratio of 9:1, stirred for 24 hours, and mixed evenly. The mixed electrode slurry was uniformly coated on the copper foil wiped with absolute ethanol by an automatic coater, and then placed in a vacuum drying oven at 110° C. to dry overnight.

Assembly of the battery: Press the sheet, weigh and number the electrode sheet, take the obtained electrode sheet as the negative electrode and the lithium sheet as the positive electrode, use 1 mol/L LiPF ₆ electrolyte, polypropylene separator, and assemble in an argon-filled glove box. CR2025 button battery.

Example 9: Rice husk activated carbon surface area and pore structure analysis

The specific surface area and pore volume of the rice husk activated carbon prepared in Example ¹ were detected by a specific surface area and pore diameter analyzer. In the range of 1-50nm, the pore structure of the rice husk-based activated carbon belongs to the coexistence structure of micro-mesoporous pores. Phenylalanine-functionalized quantum dots were not only adsorbed on the surface of rice husk activated carbon through hydrogen bonding, but also in the pores of micro-mesoporous pores through physical adsorption.

Example 10: Phenylalanine functionalized graphene quantum dots-rice husk activated carbon infrared spectroscopy analysis

Detect the FT-IR spectrum of the phenylalanine-functionalized graphene quantum dots-rice husk activated carbon composite material prepared in Example 1, and the results are shown in Figure 1. The broad peaks around 3400 cm ^-1 are related to the stretching vibrations of OH and NH, and the vibrational peaks at 1040 cm ^-1 and 675 cm ^-1 are attributed to the stretching vibrations of CN and CO bonds, respectively. Infrared analysis showed that there were hydroxyl, carbonyl, carboxyl and amino groups on the surface of the composite material, indicating that some phenylalanine-functionalized graphene quantum dots were adsorbed on the surface of rice husk activated carbon.

Example 11: Cyclic voltammetry analysis of phenylalanine-functionalized graphene quantum dots-rice husk activated carbon

Taking the phenylalanine functionalized graphene quantum dots-rice husk activated carbon of Example 1 as an example, the cycling of the rice husk activated carbon and the rice husk activated carbon composite material modified by the graphene quantum dots under the voltage range of 0.01-3V was detected. The voltammetry curve, the results are shown in Figure 2. In Fig. 2, a reduction peak appeared between 0.5-1V, and during the second cycle, the reduction peak no longer appeared, because during the first cycle, the reaction of lithium ions with the electrolyte solution resulted in the SEI film Formation. A pair of reversible redox peaks appearing between 0.1-0.5V is related to the intercalation and de-intercalation of lithium ions on the electrode material. When the potential is scanned from negative potential to positive potential, the two electrode materials are between 0.1-0.5V. There is an oxidation peak between them, which is the desorption peak of lithium ions. The comparison of Figure 2(a) and (b) shows that the cyclic voltammetry curves of the rice husk activated carbon composites modified by graphene quantum dots show better coincidence during the two cycles, indicating that the introduction of graphene quantum dots, This makes the cycle stability of the electrode material better.

Example 12: Phenylalanine-functionalized graphene quantum dots-rice husk activated carbon galvanostatic charge-discharge test

Taking the phenylalanine-functionalized graphene quantum dots-rice husk activated carbon of Example 1 as an example, the galvanostatic charge-discharge test was carried out on the rice husk activated carbon and the rice husk activated carbon composite material modified with graphene quantum dots.

Figure 3 is a graph of the charge-discharge curves of the two materials at the first and second cycles at a current density of 100 mA/g. During the first discharge process, the specific discharge capacity of rice husk activated carbon was 350mAh/g, while that of the graphene quantum dot-rice husk activated carbon composite was 430mAh/g. The first discharge ratio of the graphene quantum dot-modified rice husk activated carbon composite was The capacity is obviously higher than that of the unmodified rice husk activated carbon in the first discharge. Compared with the specific capacity of the first discharge, the specific capacity of the second discharge is decreased. This is because a layer of SEI film is formed in the battery during the first discharge. , the lithium ions react with the material during the process of intercalating the electrode material, resulting in the loss of the electrode material and the reduction of the amount of lithium ions, which in turn affects the charge-discharge specific capacity. The calculated first Coulomb efficiencies of rice husk activated carbon and phenylalanine-functionalized graphene quantum dots-rice husk activated carbon composites are 82.8% and 88.9%, respectively. Compared with the unmodified rice husk activated carbon, the first coulombic efficiency of the point-modified rice husk activated carbon composite was significantly improved. It shows that the introduction of graphene quantum dots increases the capacity of the rice husk activated carbon electrode material, and the first Coulomb efficiency is also significantly improved, which is beneficial to improve the cycle performance of the battery.

Figure 4(a) shows the performance of rice husk activated carbon and phenylalanine graphene quantum dots-rice husk activated carbon composites at 100 mA/g, 200 mA/g, 400 mA/g, 800 mA/g, 1600 mA/g, and 100 mA/g. The discharge specific capacity diagram under current density, as shown in the figure, the discharge specific capacity of phenylalanine graphene quantum dots-rice husk activated carbon composites at different current densities is higher than that of rice husk activated carbon, at 100mA/g Under the current density, the discharge specific capacity of the composite material for the first discharge is 430mAh/g, which is 80mAh/g higher than the discharge specific capacity of rice husk activated carbon of 350mAh/g. At the current density of 100 mA/g and 100 mA/g, the discharge specific capacity of the composite material is 76 mAh/g, 54 mAh/g, 102 mAh/g, 82 mAh/g, and 139 mAh/g higher than that of the rice husk activated carbon, respectively. The introduction has obvious effect on the specific capacity of the electrode material and improves the rate performance of the electrode material. It can also be seen from Figure 4(a) that the discharge specific capacity after the second cycle is much lower than that of the first cycle, which again proves that the SEI film is formed during the first discharge process described above. Figure 4(b) is the discharge cycle performance of the rice husk activated carbon composites modified with rice husk activated carbon and phenylalanine graphene quantum dots at a current density of 100 mA/g. The discharge specific capacity is concentrated between 350-380mAh/g. It can be seen from the figure that the discharge specific capacity does not change much after 100 cycles (excluding the first discharge specific capacity, because the SEI film is formed during the first discharge process, lead to a significant decrease in the specific capacity of the second discharge). However, the discharge specific capacity of rice husk activated carbon decreased continuously with the cycle process. After 100 cycles, the discharge specific capacity of the material decreased from the initial stable around 280mAh/g to 157mAh/g, indicating that the cycle performance of the rice husk activated carbon material itself is not good. Ideal, and the introduction of graphene quantum dots improves the cycling performance of rice husk activated carbon electrode materials, and the rice husk activated carbon composites modified with phenylalanine-functionalized graphene quantum dots show good cycling performance.

Example 13: Phenylalanine functionalized graphene quantum dots-rice husk activated carbon electrochemical impedance analysis

Taking the phenylalanine-functionalized graphene quantum dots-rice husk activated carbon of Example 1 as an example, electrochemical impedance analysis was performed on the rice husk activated carbon and the rice husk activated carbon composite material modified with graphene quantum dots.

Figure 5 is the electrochemical AC impedance spectrum of the rice husk activated carbon and the rice husk activated carbon composite material modified with graphene quantum dots after 50 cycles, and Table 1 is the relevant data.

Table 1 Equivalent circuit data

Note: R _s represents solution impedance, R _ct represents charge transfer impedance, and D is lithium ion diffusion coefficient.

In the electrochemical AC impedance spectra of rice husk-based activated carbon and graphene quantum dots-modified rice husk-based activated carbon composites, the curve includes a semicircle and a diagonal line. The semicircular arc belongs to the high frequency region, and the diameter of the semicircle represents the impedance of the material used as the electrode, which is closely related to the formation of the SEI film in the high frequency region. closely related to the material. The R _s of the rice husk activated carbon is 228.3 Ω and the R _ct is 577.7 Ω, while the R _s of the composite material is 32.4 Ω and the R _ct is 123.9 Ω. The AC impedance analysis shows that the electrode impedance of the composite material is lower than that of the original rice husk-based activated carbon. , and has a larger lithium ion diffusion coefficient, indicating that the introduction of graphene quantum dots is beneficial to the diffusion of lithium ions in the SEI film and electrode materials, and improves the conductivity of rice husk-based activated carbon electrode materials.

Example 14: Electrochemical parameters of the composite materials of Examples 1-6

Electrochemical parameters were detected on the bio-based activated carbon prepared in Examples 1-7 and the bio-based activated carbon composites repaired by graphene quantum dots, including the discharge specific capacity at a current density of 100 mA/g, and the current at a current density of 100 mA/g. The discharge specific capacity, solution impedance R _s , charge transfer impedance R _ct and lithium ion diffusion coefficient D after 100 cycles under the density are shown in Table 2 for specific results.

Table 2 Example 1-7 Electrochemical parameters of composite materials

The above-mentioned embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims (4)

1. a graphene quantum dot-bio-based activated carbon composite material, is characterized in that, comprises bio-based activated carbon, and described bio-based activated carbon surface connects graphene quantum dots by hydrogen bond, and described bio-based activated carbon is micro-mesoporous structure, Physical adsorption of graphene quantum dots in the pores of the micro-mesoporous structure; The graphene quantum dots are phenylalanine-functionalized graphene quantum dots; the phenylalanine-functionalized graphene quantum dots are prepared by the following steps: 3 g of citric acid is weighed and dissolved in 2 mL of sodium hydroxide solution 2.5 g of phenylalanine was weighed and dissolved in 2 ml of sodium hydroxide solution, the two were mixed, and then evaporated and dried at 100 °C to obtain a viscous substance, which was dried in an oven at 80 °C for three days. The solid was obtained, and the solid was crushed into powder, placed in a porcelain crucible and placed in a muffle furnace at 200 °C for 2 h, cooled to room temperature to obtain a brown-black product, dissolved in 25 mL of ionized water, and centrifuged at 10,000 rpm. Centrifuge in medium for 30 min to separate insoluble particles, dialyze the supernatant against ultrapure water with a dialysis bag to further purify the product, and freeze-dry the dialyzed solution to obtain the phenylalanine-functionalized graphene quantum dots; The bio-based activated carbon is rice husk activated carbon or wheat straw activated carbon; 10 g of rice husks are placed in 50 g of a phosphoric acid solution with a mass fraction of 60%, calcined at 500° C. under the protection of inert gas, and then washed and dried The rice husk activated carbon was obtained; 10 g of wheat straw was weighed, and a phosphoric acid solution with a mass fraction of 80% was added according to the impregnation ratio of 3:1, and the mixture was pre-activated at 140 ° C for 60 min, and the mixture was put into a calciner at a rate of 3 ° C/min. The heating rate is heated to 450 ° C, calcined for 60 min, washed with water until neutral, and dried to obtain the wheat straw activated carbon; The graphene quantum dot-bio-based activated carbon composite material is prepared by the following steps: Weigh 0.5 g of phenylalanine-functionalized graphene quantum dots, dissolve in a small amount of deionized water, and ultrasonically disperse for 2 h until the phenylalanine-functionalized graphene quantum dots are completely dissolved to form a dispersion, and then add 5 g of the biological base activated carbon, stir and shake to make the _two evenly mixed, heat in a constant temperature water bath at 90 °C for 3.5 h, and then dry, and place the dried samples in a 450 °C tube furnace in an Ar/H atmosphere After calcination for 6 h, the graphene quantum dot-bio-based activated carbon composite material was obtained. 2. the application of a graphene quantum dot-bio-based activated carbon composite material according to claim 1 in the preparation of lithium battery negative electrode. 3. A lithium battery negative electrode material, wherein the lithium battery negative electrode material comprises the graphene quantum dot-bio-based activated carbon composite material according to claim 1. 4. A lithium battery, characterized in that, the graphene quantum dot-bio-based activated carbon composite material according to claim 1 is used to prepare the negative electrode of the lithium battery.

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