CN108832107B - Graphene quantum dot-bio-based activated carbon composite material and preparation method thereof - Google Patents
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Abstract
The invention discloses 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. The graphene quantum dot-bio-based active carbon composite material is obtained by modifying bio-based active carbon through the graphene quantum dot, and the graphene quantum dot-bio-based active carbon composite material has higher discharge specific capacity, higher coulombic efficiency value, better rate capability and conductivity, and good cycle performance compared with the original bio-based active carbon, and has good application prospect in the field of research of lithium battery negative materials.
Description
Technical Field
The invention relates to a graphene quantum dot-bio-based activated carbon composite material and a preparation method thereof, belonging to the technical field of lithium battery materials.
Background
Compared with other rechargeable secondary batteries, the lithium ion battery has obvious advantages, has good safety, accords with the theme that the development and production safety of the contemporary society is always put on the first place, has small volume and high capacity, and accords with the development trend of the times. The lithium ion battery has the advantage of no pollution, and is favored in various fields, from a mobile phone battery to an electric or hybrid automobile to aerospace and the like. With the continuous innovation of science and technology, people have higher requirements on lithium ion batteries, the innovation of the lithium ion batteries is imminent, and a large number of scholars at home and abroad are working on the research of the lithium ion batteries with better comprehensive performance. The research on the lithium ion cathode material has profound significance for improving the performance of the lithium ion battery, the real life and the scientific and technological development and the like.
In recent years, biomass waste has become a functional material with the most development potential due to the advantages of low cost, environmental protection, renewability and the like, is favored, and activated carbon prepared by taking the biomass waste as a raw material has high specific surface, is rich in micropores and shows certain good electrochemical properties, thereby attracting wide attention of researchers at home and abroad. Studies on electrochemical performance of activated carbon have been focused on the fields of electric double layer capacitance, super capacitor, and the like, and biomass carbon has been studied as a negative electrode material for lithium ion batteries relatively rarely. Fey and the like use rice hulls as raw materials, prepare rice hull activated carbon through high-temperature pyrolysis, and conduct research and analysis on electrochemical properties, and find that a battery assembled by using the self-made rice hull activated carbon as an electrode material has bright points in electrochemical properties, such as high discharge specific capacity, but low efficiency, and has the defects of insufficient cycle performance, insufficient conductivity and the like, and further research is still needed.
The graphene quantum dots are used as one member of a graphene family, the size of the graphene quantum dots is only a few nanometers, and compared with other members of the graphene family, the graphene quantum dots have unique advantages in quantum confinement effect and boundary effect, so that the graphene quantum dots which are often used for modifying certain materials have wide application potential in many fields, wherein the graphene quantum dots are already applied in the fields of super capacitors, photoelectric devices and the like. Although both biomass charcoal and graphene quantum dots have huge electrochemical application potential, few reports are made on the research on the electrochemical performance of the graphene quantum dot modified biomass charcoal.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a graphene quantum dot-bio-based activated carbon composite material, and the bio-based activated carbon modified by the graphene quantum dots has higher discharge specific capacity, higher coulombic efficiency value, better rate capability and conductivity, shows good cycle performance and has good application prospect in the research field of lithium battery cathode materials compared with the original bio-based activated carbon.
The invention provides a graphene quantum dot-bio-based activated carbon composite material, which comprises bio-based activated carbon, wherein the surface of the bio-based activated carbon is connected with graphene quantum dots through hydrogen bonds, the bio-based activated carbon is of a micro mesoporous structure, and the graphene quantum dots are physically adsorbed in 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 amino functionalized graphene quantum dots.
In an embodiment of the present invention, the amino acid functionalized graphene quantum dot is a phenylalanine functionalized graphene quantum dot, a histidine functionalized graphene quantum dot, a valine functionalized graphene quantum dot, or a lysine functionalized graphene quantum dot.
In one embodiment of the invention, the bio-based activated carbon is chaff activated carbon, straw activated carbon, fruit shell activated carbon, straw 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 shell activated carbon is walnut shell activated carbon, rice hull activated carbon or chestnut shell activated carbon.
In one embodiment of the invention, the grass stem activated carbon is weed stem activated carbon.
In one embodiment of the invention, the biomass residue activated carbon is bagasse activated carbon or beet pulp activated carbon.
In one embodiment of the invention, the graphene quantum dot-bio-based activated carbon composite material is prepared by the following method:
dissolving and dispersing graphene quantum dots to form a dispersion liquid;
step two, adding bio-based activated carbon into the dispersion liquid obtained in the step one, uniformly mixing, heating and drying;
and step three, calcining the dried sample obtained in the step two to obtain the graphene quantum dot-bio-based activated carbon composite material.
The second purpose of the invention is to provide a preparation method of the graphene quantum dot-bio-based activated carbon composite material, which comprises the following steps:
dissolving and dispersing graphene quantum dots to form a dispersion liquid;
step two, adding bio-based activated carbon into the dispersion liquid obtained in the step one, uniformly mixing, heating and drying;
and step three, calcining the dried sample obtained in the step two to obtain the graphene quantum dot-bio-based activated carbon composite material.
In one embodiment of the invention, in step one, ultrasonic dispersion is used, and the dispersion time is 1-4 h.
In one embodiment of the present invention, in the second step, the amount of the bio-based activated carbon added is 5 to 15 times the amount by mass of the graphene quantum dots.
In one embodiment of the present invention, in the second step, the heating is performed at 80-100 ℃ for 3-5 h.
In one embodiment of the present invention, in step three, the calcination is performed in a 400-500 ℃ calciner at Ar/H2Calcining for 6-8h in the atmosphere.
The third purpose of the invention is to provide the application of the graphene quantum dot-bio-based activated carbon composite material in the preparation of a lithium battery cathode.
The fourth purpose of the invention is to provide a lithium battery negative electrode material which comprises the graphene quantum dot-bio-based activated carbon composite material.
The fifth purpose of the invention is to provide a lithium battery, wherein the negative electrode of the lithium battery is prepared from the graphene quantum dot-bio-based activated carbon composite material.
The invention has the beneficial effects that:
compared with the original bio-based activated carbon, the bio-based activated carbon modified by the graphene quantum dots has higher discharge specific capacity, higher coulombic efficiency value, better rate performance and conductivity, shows good cycle performance, and has good application prospect in the research field of lithium battery cathode materials.
Drawings
FIG. 1 is a Fourier transform infrared spectrum diagram of a phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material;
fig. 2 is a cyclic voltammetry curve of rice hull activated carbon (a) and phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material (b);
fig. 3 is a first (solid line) and second (dotted line) charge and discharge curves of rice hull activated carbon (a) and phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material (b) at a current density of 100 mA/g;
fig. 4(a) is a discharge capacity curve of rice hull activated carbon and phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material under different current densities;
FIG. 4(b) shows the cycle performance of the rice hull activated carbon and phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material at a current density of 100 mA/g;
fig. 5 is an electrochemical alternating-current impedance spectrogram of the rice hull activated carbon (a) and the phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material (b) after 50 cycles.
Detailed Description
The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.
The lithium ion diffusion coefficient D is calculated from the low frequency region data according to the formula (1).
D＝R2T2/2A2n4F4C2σ2(1)
In the formula: r is the gas volume constant; t is the absolute temperature; a is the cathode material surface area; n is the number of electron transfers during redox; 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 dot-rice hull activated carbon composite material
10g of rice hulls are placed in 50g of phosphoric acid solution with the mass fraction of 60%, and are calcined at 500 ℃ under the protection of inert gas (argon), and then are cleaned and dried to obtain the rice hull-based activated carbon.
Citric acid is used as a precursor, phenylalanine is used as a functional reagent, and the phenylalanine functional graphene quantum dot is prepared by a high-temperature heating dry method. 3g of citric acid and 2.5g of phenylalanine are weighed, dissolved in 2mL of sodium hydroxide solution, and mixed together, evaporated and dried at 100 ℃ to obtain a viscous substance, and the viscous substance is dried in an oven at 80 ℃ for three days. Grinding the solid into powder, placing the powder in a porcelain crucible, heating the porcelain crucible in a muffle furnace at 200 ℃ for 2h, cooling the porcelain crucible to room temperature to obtain a brownish black product, dissolving the brownish black product in 25mL of ionized water, centrifuging the porcelain crucible in a centrifuge with the rotation speed of 10000rpm for 30min, separating insoluble particles, dialyzing the supernatant in ultrapure water by using a dialysis bag to further purify the product, and performing freeze drying on the dialyzed solution to obtain the final product, namely the phenylalanine functionalized graphene quantum dot.
Weighing 0.5g of prepared phenylalanine functionalized graphene quantum dot, dissolving the prepared phenylalanine functionalized graphene quantum dot in a small amount of deionized water, performing ultrasonic dispersion for 2 hours until the graphene quantum dot is completely dissolved to form a dispersion solution, adding 5g of self-made rice hull activated carbon, stirring while oscillating to uniformly mix the graphene quantum dot and the dispersion solution, placing the mixture in a constant-temperature water bath at 90 ℃ for heating for 3.5 hours, and then drying. The dried sample was placed in a 450 ℃ tube furnace at Ar/H2Calcining for 6h in the atmosphere to obtain the final product.
Example 2: preparation of phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material
10g of rice hulls are placed in 50g of phosphoric acid solution with the mass fraction of 60%, and are calcined at 500 ℃ under the protection of inert gas (argon), and then are cleaned and dried to obtain the rice hull-based activated carbon.
Citric acid is used as a precursor, phenylalanine is used as a functional reagent, and the phenylalanine functional graphene quantum dot is prepared by a high-temperature heating dry method. 3g of citric acid and 2.5g of phenylalanine are weighed, dissolved in 2mL of sodium hydroxide solution, and mixed, evaporated and dried at 100 ℃ to obtain a viscous substance, and the viscous substance is dried in an oven at 80 ℃ for three days. Grinding the solid into powder, placing the powder in a porcelain crucible, heating the porcelain crucible in a muffle furnace at 200 ℃ for 2h, cooling the porcelain crucible to room temperature to obtain a brownish black product, dissolving the brownish black product in 25mL of ionized water, centrifuging the porcelain crucible in a centrifuge with the rotation speed of 10000rpm for 30min, separating insoluble particles, dialyzing the supernatant in ultrapure water by using a dialysis bag to further purify the product, and performing freeze drying on the dialyzed solution to obtain the final product, namely the phenylalanine functionalized graphene quantum dot.
Weighing 0.5g of prepared phenylalanine functionalized graphene quantum dot, dissolving the prepared phenylalanine functionalized graphene quantum dot in a small amount of deionized water, performing ultrasonic dispersion for 2 hours until the graphene quantum dot is completely dissolved to form a dispersion solution, adding 3g of self-made rice hull activated carbon, stirring while oscillating to uniformly mix the graphene quantum dot and the dispersion solution, placing the mixture in a constant-temperature water bath at 90 ℃ for heating for 3.5 hours, and then drying. The dried sample was placed in a 450 ℃ tube furnace at Ar/H2Calcining for 6h in the atmosphere to obtain the final product.
Example 3: preparation of phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material
10g of rice hulls are placed in 50g of phosphoric acid solution with the mass fraction of 60%, and are calcined at 500 ℃ under the protection of inert gas (argon), and then are cleaned and dried to obtain the rice hull-based activated carbon.
Citric acid is used as a precursor, phenylalanine is used as a functional reagent, and the phenylalanine functional graphene quantum dot is prepared by a high-temperature heating dry method. 3g of citric acid and 2.5g of phenylalanine are weighed, dissolved in 2mL of sodium hydroxide solution, and mixed, evaporated and dried at 100 ℃ to obtain a viscous substance, and the viscous substance is dried in an oven at 80 ℃ for three days. Grinding the solid into powder, placing the powder in a porcelain crucible, heating the porcelain crucible in a muffle furnace at 200 ℃ for 2h, cooling the porcelain crucible to room temperature to obtain a brownish black product, dissolving the brownish black product in 25mL of ionized water, centrifuging the porcelain crucible in a centrifuge with the rotation speed of 10000rpm for 30min, separating insoluble particles, dialyzing the supernatant in ultrapure water by using a dialysis bag to further purify the product, and performing freeze drying on the dialyzed solution to obtain the final product, namely the phenylalanine functionalized graphene quantum dot.
Weighing 0.5g of prepared phenylalanine functionalized graphene quantum dot, dissolving the prepared phenylalanine functionalized graphene quantum dot in a small amount of deionized water, performing ultrasonic dispersion for 2 hours until the graphene quantum dot is completely dissolved to form a dispersion solution, adding 8g of self-made rice hull activated carbon, stirring while oscillating to uniformly mix the graphene quantum dot and the dispersion solution, placing the mixture in a constant-temperature water bath at 90 ℃ for heating for 3.5 hours, and then drying. The dried sample was placed in a 450 ℃ tube furnace at Ar/H2Calcining for 6h in the atmosphere to obtain the final product.
Example 4: preparation of histidine functionalized graphene quantum dot-rice hull activated carbon composite material
10g of rice hulls are placed in 50g of phosphoric acid solution with the mass fraction of 60%, and are calcined at 500 ℃ under the protection of inert gas (argon), and then are cleaned and dried to obtain the rice hull-based activated carbon.
Citric acid is used as a precursor, histidine is used as a functional reagent, and a high-temperature heating dry method is adopted to prepare the histidine functionalized graphene quantum dot. 3g of citric acid and 2.5g of histidine are weighed, dissolved in 2mL of sodium hydroxide solution, mixed, evaporated and dried at 100 ℃ to obtain a viscous substance, and the viscous substance is dried in an oven at 80 ℃ for three days. Grinding the solid into powder, placing the powder in a porcelain crucible and placing the porcelain crucible in a muffle furnace at 200 ℃ for heating for 2h, cooling to room temperature to obtain a brownish black product, dissolving the brownish black product in 25mL of ionized water, centrifuging the product in a centrifuge with the rotation speed of 10000rpm for 30min, separating insoluble particles, dialyzing the supernatant in ultrapure water by using a dialysis bag to further purify the product, and performing freeze drying on the dialyzed solution to obtain the final product, namely the histidine functionalized graphene quantum dots.
Weighing 0.5g of prepared histidine functionalized graphene quantum dot, dissolving in a small amount of deionized water, performing ultrasonic dispersion for 2 hours until the graphene quantum dot is completely dissolved to form a dispersion solution, adding 5g of self-made rice hull activated carbon, stirring while oscillating to uniformly mix the graphene quantum dot and the dispersion solution, placing in a constant-temperature water bath at 90 ℃ for heating for 3.5 hours, and then drying. And placing the dried sample in a 450 ℃ tube furnace, and calcining for 6H in Ar/H2 atmosphere to obtain the final product.
Example 5: preparation of phenylalanine functionalized graphene quantum dot-wheat straw activated carbon composite material
Weighing 10g of wheat straw, adding 80% phosphoric acid according to the dipping ratio of 3:1, and pre-activating for 60min at 140 ℃. And putting the mixture into a calcining furnace, heating to 450 ℃ at the heating rate of 3 ℃/min, and calcining for 60 min. Washing to be neutral, and drying to obtain the straw-based activated carbon.
Citric acid is used as a precursor, phenylalanine is used as a functional reagent, and the phenylalanine functional graphene quantum dot is prepared by a high-temperature heating dry method. 3g of citric acid and 2.5g of phenylalanine are weighed, dissolved in 2mL of sodium hydroxide solution, and mixed together, evaporated and dried at 100 ℃ to obtain a viscous substance, and the viscous substance is dried in an oven at 80 ℃ for three days. Grinding the solid into powder, placing the powder in a porcelain crucible, heating the porcelain crucible in a muffle furnace at 200 ℃ for 2h, cooling the porcelain crucible to room temperature to obtain a brownish black product, dissolving the brownish black product in 25mL of ionized water, centrifuging the porcelain crucible in a centrifuge with the rotation speed of 10000rpm for 30min, separating insoluble particles, dialyzing the supernatant in ultrapure water by using a dialysis bag to further purify the product, and performing freeze drying on the dialyzed solution to obtain the final product, namely the phenylalanine functionalized graphene quantum dot.
Weighing 0.5g of prepared phenylalanine functionalized graphene quantum dot, dissolving in a small amount of deionized water, ultrasonically dispersing for 2h until the graphene quantum dot is completely dissolved to form a dispersion solution, then adding 5g of self-made wheat straw activated carbon, stirring while oscillating to uniformly mix the graphene quantum dot and the dispersion solution, placing in a constant-temperature water bath at 90 ℃ for heating for 3.5h, and then drying. The dried sample was placed in a 450 ℃ tube furnace at Ar/H2Calcining for 6h in the atmosphere to obtain the final product.
Example 6: preparation of histidine functionalized graphene quantum dot-weed stem activated carbon composite material
Washing 10g of weed stem with clear water, and washing weedThe stems were cut into 10-20 mm pieces and dried in an oven at 105 ℃ for 1 day. It was ground and sieved to 20-50 mesh. The powder is immersed in a bath containing 40% ZnCl2ZnCl of2The solution was left for 18 hours. The slurry was then calcined in a calciner at 500 ℃ for 30 minutes. The product was washed successively with 0.5mol HCl, deionized water to remove residual ZnCl2And mixing with mineral substances, and drying to obtain the weed stem activated carbon.
Citric acid is used as a precursor, histidine is used as a functional reagent, and a high-temperature heating dry method is adopted to prepare the histidine functionalized graphene quantum dot. 3g of citric acid and 2.5g of histidine are weighed, dissolved in 2mL of sodium hydroxide solution, mixed, evaporated and dried at 100 ℃ to obtain a viscous substance, and the viscous substance is dried in an oven at 80 ℃ for three days. Grinding the solid into powder, placing the powder in a porcelain crucible and placing the porcelain crucible in a muffle furnace at 200 ℃ for heating for 2h, cooling to room temperature to obtain a brownish black product, dissolving the brownish black product in 25mL of ionized water, centrifuging the product in a centrifuge with the rotation speed of 10000rpm for 30min, separating insoluble particles, dialyzing the supernatant in ultrapure water by using a dialysis bag to further purify the product, and performing freeze drying on the dialyzed solution to obtain the final product, namely the histidine functionalized graphene quantum dots.
Weighing 0.5g of prepared histidine functionalized graphene quantum dot, dissolving in a small amount of deionized water, performing ultrasonic dispersion for 2 hours until the graphene quantum dot is completely dissolved to form a dispersion solution, adding 5g of self-made weed stem activated carbon, stirring while oscillating to uniformly mix the graphene quantum dot and the dispersion solution, placing in a constant-temperature water bath at 90 ℃ for heating for 3.5 hours, and then drying. The dried sample was placed in a 450 ℃ tube furnace at Ar/H2Calcining for 6h in the atmosphere to obtain the final product.
Example 7: preparation of amino functionalized graphene quantum dot-bagasse active carbon composite material
The bagasse was carbonized with concentrated sulfuric acid at a low temperature in a weight ratio of 4:3, 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. At high temperature of 900 deg.C and 2dm of air3·min-1Is metered into the reactor at a rate of 10 ℃/min to 160 ℃. The temperature was maintained for 2 hours, and then the reactor was pulled out of the furnace and allowed to cool. Washing and drying to obtain the bagasse active carbon.
And (3) preparing the amino functionalized graphene quantum dots by using citric acid as a precursor and ammonia water as a functionalized reagent by adopting a high-temperature heating dry method. 3g of citric acid is weighed, dissolved in 2mL of sodium hydroxide solution, mixed with 5mL of ammonia water, evaporated and dried at 100 ℃ to obtain a viscous substance, and the viscous substance is placed in an oven at 80 ℃ for drying for three days. Grinding the solid into powder, placing the powder in a porcelain crucible and placing the porcelain crucible in a muffle furnace at 200 ℃ for heating for 2h, cooling to room temperature to obtain a brownish black product, dissolving the brownish black product in 25mL of ionized water, centrifuging the product in a centrifuge with the rotation speed of 10000rpm for 30min, separating insoluble particles, dialyzing the supernatant in ultrapure water by using a dialysis bag to further purify the product, and performing freeze drying on the dialyzed solution to obtain the final product, namely the amino functionalized graphene quantum dot.
Weighing 0.5g of prepared amino-functionalized graphene quantum dots, dissolving the prepared amino-functionalized graphene quantum dots in a small amount of deionized water, ultrasonically dispersing for 2 hours until the graphene quantum dots are completely dissolved to form a dispersion solution, then adding 5g of self-made bagasse activated carbon, stirring while oscillating to uniformly mix the graphene quantum dots and the dispersion solution, heating in a constant-temperature water bath at 90 ℃ for 3.5 hours, and then drying. The dried sample was placed in a 450 ℃ tube furnace at Ar/H2Calcining for 6h in the atmosphere to obtain the final product.
Example 8: preparation of electrode and assembly of battery
Preparing an electrode: the composite material prepared in examples 1 to 7 and conductive agent acetylene black are mixed in an agate mortar according to the mass ratio of 8:1, and the mixture is fully ground for 1 hour for later use. Adding the ground mixture and sodium alginate (2%) as a binder into a small glass bottle according to the mass ratio of 9:1, stirring for 24h, and uniformly mixing. The mixed electrode slurry was uniformly coated on a copper foil wiped with absolute ethanol by an automatic coater, and then dried overnight in a vacuum drying oven at 110 ℃.
Assembling the battery: tabletting, weighing and numbering electrode plates, taking the obtained electrode plates as a negative electrode and a lithium plate as a positive electrode, and using 1mol/L LiPF6Electrolyte, polypropylene diaphragm, in chargeThe glove box filled with argon was assembled into a CR2025 button cell.
Example 9: analysis of surface area and pore structure of rice hull activated carbon
Detecting the specific surface area and the pore volume of the rice hull activated carbon prepared in the example 1 by using a specific surface area and pore size analyzer, wherein the specific surface area of the rice hull activated carbon obtained by detection is 1722m2The pore volume is 1.86mL/g, the aperture of the activated carbon is 1-50nm, and the pore structure of the rice hull-based activated carbon belongs to a micro-mesoporous coexisting structure. The phenylalanine functionalized quantum dots are adsorbed on the surface of the rice hull activated carbon through hydrogen bonding, and are also adsorbed in the pores of the micro mesopores through physical adsorption.
Example 10: infrared spectroscopic analysis of phenylalanine functionalized graphene quantum dot-rice hull activated carbon
An FT-IR spectrogram of the phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material prepared in the example 1 is detected, and the result is shown in FIG. 1. At 3400cm-1The broad peaks appearing nearby are related to the stretching vibration of O-H and N-H, 1040cm-1And 675cm-1The vibration peaks are attributed to the stretching vibration of the C-N and C-O bonds respectively. According to infrared analysis, the existence of hydroxyl, carbonyl, carboxyl, amino and other groups on the surface of the composite material indicates that part of phenylalanine functionalized graphene quantum dots are adsorbed on the surface of the rice hull activated carbon.
Example 11: phenylalanine functionalized graphene quantum dot-rice hull activated carbon cyclic voltammetry test analysis
Taking the phenylalanine functionalized graphene quantum dot-rice hull activated carbon in example 1 as an example, cyclic voltammetry curves of the rice hull activated carbon and the rice hull activated carbon composite material modified by the graphene quantum dot in a voltage range of 0.01-3V are detected, and the result is shown in fig. 2. In fig. 2, a reduction peak occurs between 0.5 and 1V, and during the second cycle, the reduction peak does not occur because lithium ions react with the electrolyte solution during the first cycle to cause the formation of an SEI film. A pair of reversible redox peaks appears between 0.1 and 0.5V and is switched with the insertion and extraction of lithium ions on the electrode material, and when the potential is scanned from a negative potential to a positive potential, an oxidation peak appears between 0.1 and 0.5V on both electrode materials, and the oxidation peak is the extraction peak of lithium ions. As can be seen from comparison between fig. 2(a) and (b), the cyclic voltammetry curves of the rice hull activated carbon composite material modified by the graphene quantum dots show better coincidence in two cyclic processes, which illustrates that the introduction of the graphene quantum dots makes the cyclic stability of the electrode material better.
Example 12: constant current charge and discharge test for phenylalanine functionalized graphene quantum dot-rice hull activated carbon
Taking the phenylalanine functionalized graphene quantum dot-rice hull activated carbon in example 1 as an example, the constant current charge and discharge test is performed on the rice hull activated carbon and the rice hull activated carbon composite material modified by the graphene quantum dot.
FIG. 3 is a graph of charge and discharge curves for the first and second cycles of two materials at a current density of 100 mA/g. In the first discharging process, the specific discharge capacity of the rice hull activated carbon is 350mAh/g, the graphene quantum dot-rice hull activated carbon composite material is 430mAh/g, the specific first discharge capacity of the rice hull activated carbon composite material modified by the graphene quantum dots is obviously higher than that of unmodified rice hull activated carbon, and the specific second discharge capacity is reduced compared with the specific first discharge capacity because a battery forms an SEI (solid electrolyte interphase) film in the first discharging process, and lithium ions react with the material in the process of being embedded into the electrode material, so that the electrode material is damaged and consumed, the lithium ion capacity is reduced, and the specific charge-discharge capacity is further influenced. The calculated first coulombic efficiencies of the rice hull activated carbon and the phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material are 82.8% and 88.9% respectively, and the first coulombic efficiencies of the rice hull activated carbon and the phenylalanine functionalized graphene quantum dot-rice hull activated carbon composite material are both high, but the first coulombic efficiency of the graphene quantum dot modified rice hull activated carbon composite material is obviously improved compared with that of unmodified rice hull activated carbon. The introduction of the graphene quantum dots is illustrated, the capacity of the rice hull activated carbon electrode material is increased, the first coulombic efficiency is obviously improved, and the improvement of the cycle performance of the battery is facilitated.
FIG. 4(a) is a graph of specific discharge capacities of rice hull activated carbon and phenylalanine graphene quantum dot-rice hull activated carbon composite materials at current densities of 100mA/g, 200mA/g, 400mA/g, 800mA/g, 1600mA/g and 100mA/g, wherein as shown in the graph, specific discharge capacities of the phenylalanine graphene quantum dot-rice hull activated carbon composite materials at different current densities are higher than those of the rice hull activated carbon, the specific discharge capacity of the composite material at the first discharge is 430mAh/g and is higher than that of the rice hull activated carbon at a discharge specific capacity of 350mAh/g by 80mAh/g, and specific discharge capacities of the composite material at current densities of 200mA/g, 400mA/g, 800mA/g, 1600mA/g and 100mA/g are higher than those of the rice hull activated carbon by 76 h/g, 76 mAh/g, and, 54mAh/g, 102mAh/g, 82mAh/g and 139mAh/g, which shows that the introduction of the graphene quantum dots has obvious specific capacity effect on the electrode material and improves the rate capability of the electrode material. It can also be seen from fig. 4(a) that the discharge specific capacity after the second cycle is much lower than that of the first cycle, again demonstrating that the SEI film is formed by the first discharge process as described above. Fig. 4(b) is a discharge cycle performance diagram of the rice hull activated carbon composite material modified by the rice hull activated carbon and the phenylalanine graphene quantum dots at a current density of 100mA/g, the discharge specific capacity of the composite material at the current density of 100mA/g is concentrated between 350 and 380mAh/g, and it can be seen from the diagram that the change of the discharge specific capacity is not large after 100 cycles (the first discharge specific capacity is not included, because an SEI film is formed in the first discharge process, the second discharge specific capacity is obviously reduced). The specific discharge capacity of the rice hull activated carbon is continuously reduced along with the circulation process, after the rice hull activated carbon is circulated for 100 times, the specific discharge capacity of the material is reduced to 157mAh/g from the beginning to be stabilized near 280mAh/g, which shows that the circulation performance of the rice hull activated carbon material is not ideal, the introduction of the graphene quantum dots improves the circulation performance of the rice hull activated carbon electrode material, and the rice hull activated carbon composite material modified by the phenylalanine functionalized graphene quantum dots shows good circulation performance.
Example 13: electrochemical impedance analysis of phenylalanine functionalized graphene quantum dot-rice hull activated carbon
Taking the phenylalanine functionalized graphene quantum dot-rice hull activated carbon in example 1 as an example, electrochemical impedance analysis is performed on the rice hull activated carbon and the rice hull activated carbon composite material modified by the graphene quantum dot.
Fig. 5 is an electrochemical alternating-current impedance spectrum of rice hull activated carbon and the rice hull activated carbon composite material modified by graphene quantum dots after 50 cycles, and table 1 shows relevant data.
TABLE 1 equivalent Circuit data
Note: rsRepresents the solution impedance, RctRepresenting the charge transfer resistance, D is the lithium ion diffusion coefficient.
In the electrochemical alternating-current impedance spectrogram of the rice hull-based activated carbon composite material modified by the rice hull-based activated carbon and the graphene quantum dots, a curve comprises a semicircular arc and an oblique line. The semicircular arc belongs to a high-frequency region, the diameter of the semicircle represents the impedance of the material as an electrode and is closely related to the formation of an SEI film in the high-frequency region, and the oblique line belongs to a low-frequency region and represents the diffusion blocking condition of the low-frequency region and is closely related to the diffusion of lithium ions into the electrode material. R of rice hull activated carbonsIs 228.3. omega., RctIs 577.7 omega, and R of the composite materialsIs 32.4. omega. RctThe resistance of the composite material electrode is less than that of the original rice hull-based activated carbon and has a larger lithium ion diffusion coefficient as can be known from alternating current impedance analysis, which shows that the introduction of the graphene quantum dots is beneficial to the diffusion of lithium ions in an SEI film and an electrode material, and the conductivity of the rice hull-based activated carbon electrode material is improved.
Example 14: examples 1-6 composite electrochemical parameters
The electrochemical parameters of the bio-based activated carbon prepared in examples 1 to 7 and the bio-based activated carbon composite material repaired by the graphene quantum dots were measured, including specific discharge capacity at a current density of 100mA/g, specific discharge capacity after 100 cycles at a current density of 100mA/g, and solution impedance RsCharge transfer resistance RctAnd lithium ion diffusion coefficient D, see table 2 for specific results.
Table 2 examples 1-7 composite electrochemical parameters
The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.
Claims (4)
1. The graphene quantum dot-bio-based activated carbon composite material is characterized by comprising bio-based activated carbon, wherein the surface of the bio-based activated carbon is connected with graphene quantum dots through hydrogen bonds, the bio-based activated carbon is of a micro mesoporous structure, and the graphene quantum dots are physically adsorbed in pores of the micro mesoporous structure;
the graphene quantum dots are phenylalanine functionalized graphene quantum dots; the phenylalanine functionalized graphene quantum dot is prepared by the following steps: weighing 3g of citric acid, dissolving in 2mL of sodium hydroxide solution, weighing 2.5g of phenylalanine, dissolving in 2mL of sodium hydroxide solution, mixing the two solutions, evaporating and drying at 100 ℃ to obtain a viscous substance, drying in an oven at 80 ℃ for three days to obtain a solid, crushing the solid into powder, placing the powder in a ceramic crucible, heating in a muffle furnace at 200 ℃ for 2 hours, cooling to room temperature to obtain a brownish black product, dissolving in 25mL of ionized water, centrifuging for 30min in a centrifuge at the rotating speed of 10000rpm, separating insoluble particles, dialyzing the supernatant in ultrapure water by using a dialysis bag to further purify the product, and freeze-drying the dialyzed solution to obtain the phenylalanine functionalized graphene quantum dots;
the bio-based activated carbon is rice hull activated carbon or wheat straw activated carbon; putting 10g of rice hulls into 50g of phosphoric acid solution with the mass fraction of 60%, calcining at 500 ℃ under the protection of inert gas, and then cleaning and drying to obtain the rice hull activated carbon; weighing 10g of wheat straw, adding a phosphoric acid solution with the mass fraction of 80% according to the dipping ratio of 3:1, pre-activating at 140 ℃ for 60min, putting the mixture into a calcining furnace, heating to 450 ℃ at the heating rate of 3 ℃/min, calcining for 60min, washing to be neutral, and drying to obtain the wheat straw activated carbon;
the graphene quantum dot-bio-based activated carbon composite material is prepared by the following steps:
weighing 0.5g of phenylalanine functionalized graphene quantum dot, dissolving the weighed quantum dot in a small amount of deionized water, ultrasonically dispersing for 2 hours until the phenylalanine functionalized graphene quantum dot is completely dissolved to form a dispersion solution, then adding 5g of bio-based activated carbon, stirring while oscillating to uniformly mix the two, heating the mixture in a constant-temperature water bath at 90 ℃ for 3.5 hours, drying, placing the dried sample in a tube furnace at 450 ℃, and performing Ar/H (argon/hydrogen) reaction on the sample in an Ar/H (argon/hydrogen) furnace2Calcining for 6 hours in the atmosphere to obtain the graphene quantum dot-bio-based activated carbon composite material.
2. The application of the graphene quantum dot-bio-based activated carbon composite material of claim 1 in preparation of a negative electrode of a lithium battery.
3. A negative electrode material for a lithium battery, comprising the graphene quantum dot-bio-based activated carbon composite material according to claim 1.
4. A lithium battery, which is characterized in that the graphene quantum dot-bio-based activated carbon composite material of claim 1 is adopted to prepare a negative electrode of the lithium battery.
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