CN112886026B

CN112886026B - Reed flower biochar-based electrode material and preparation method thereof

Info

Publication number: CN112886026B
Application number: CN202110032339.XA
Authority: CN
Inventors: 杜彬; 周慧; 王斌; 胡博闻; 邓忠月; 陈龙; 何燕
Original assignee: Yangzhou Polytechnic Institute
Current assignee: Shenzhen Ruisiwei New Energy Co.,Ltd.
Priority date: 2021-01-11
Filing date: 2021-01-11
Publication date: 2022-03-25
Anticipated expiration: 2041-01-11
Also published as: CN112886026A

Abstract

The scheme relates to a reed peanut carbon-based electrode material and a preparation method thereof, and the preparation method comprises the steps of carbonizing reed flowers in a nitrogen atmosphere, carrying out high-temperature activation and nitrogen doping by using potassium hydroxide as an activating agent and a nitrogen-containing compound as a nitrogen doping agent to obtain reed flower biochar, mixing the reed flower biochar with acetylene black and polytetrafluoroethylene emulsion, tabletting and drying to obtain the reed flower biochar-based electrode material. In the invention, the electrode material is prepared from reed flowers, carbonization, activation pore-forming and nitrogen doping are completed in one step, and the preparation process is simple and easy to operate; the nitrogen-containing compound such as diethanol amine selected by the invention has hydroxyl and can carry out chemical reaction with carboxyl on the surface of reed flowers, so that the nitrogen-containing compound is better combined with biomass carbon and has high nitrogen content; meanwhile, the diethanol amine has alkalinity and water solubility, is easy to enter the interior of plant fibers, is easier to form pores in the high-temperature carbonization process, and is used as a nitrogen-doped agent and an auxiliary pore-forming agent in the preparation process of the biochar-based material.

Description

Reed flower biochar-based electrode material and preparation method thereof

Technical Field

The invention relates to the technical field of electrode material preparation, in particular to a reed flower biochar-based electrode material and a preparation method thereof.

Background

In the present day where environmental problems and shortage of fuel energy are highlighted, it has been an irreversible trend to vigorously develop clean renewable energy. The development of novel high-efficiency energy storage devices is an important component for researching the sustainable utilization of energy. Supercapacitors, lithium ion batteries, lithium-sulfur batteries and other rechargeable batteries are considered promising energy storage devices. The super capacitor has the advantages of environmental protection, high specific capacitance value, high charging and discharging speed, large storage capacity, long cycle life and the like, and is widely applied to the industrial fields of military, automobiles and the like. The electrode material in the super capacitor is the most important factor for determining the energy storage capacity, and the development of the super capacitor technology is mainly developed towards the research direction of the nano-structure electrode material. The super capacitor has high power density, high charge-discharge efficiency and long cycle service life, can effectively improve the efficiency of an energy storage system, and the electrode material of the super capacitor mainly comprises a metal oxide material, a conductive polymer material and a carbon-based material.

The porous biomass carbon material serving as an environment-friendly novel material has the advantages of rich raw material source, low price, easy obtainment, large specific surface area, good electrochemical performance and the like. Has wide application prospect in the fields of adsorbing materials, lithium electronic batteries, lithium-sulfur batteries, fuel batteries, super capacitor electrode materials and the like. At present, a research for preparing a porous carbon material by using a natural product is available, but the electrochemical activity is low, and the porous carbon material is not suitable for being used as a super capacitor electrode material.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to prepare the biological carbon material based on the reed flowers and prepare the electrode material, and the biological carbon material can be applied to a super capacitor and has good conductivity.

A preparation method of a reed peanut carbon-based electrode material comprises the steps of carbonizing reed flowers in a nitrogen atmosphere, carrying out high-temperature activation and nitrogen doping by using potassium hydroxide as an activating agent and a nitrogen-containing compound as a nitrogen doping agent to obtain reed flower biochar, mixing the reed flower biochar with acetylene black and polytetrafluoroethylene emulsion, tabletting and drying to obtain the reed flower biochar-based electrode material.

Further, the carbonization condition is that the temperature of the dried reed flowers is raised to 700 ℃ at the heating speed of 2-3 ℃/min under the nitrogen atmosphere, and then the constant temperature is kept for 1-3 h.

Further, the high-temperature activation condition is that carbonized reed flowers are soaked in 6mol/L potassium hydroxide solution for 12 hours, then dried to constant weight at 110 ℃, heated to 700 ℃ at a heating speed of 3 ℃/min in a nitrogen atmosphere, and then kept at the constant temperature for 1-3 hours.

Further, the nitrogen-containing compound is ethanolamine, diethanolamine or triethanolamine.

Further, the nitrogen doping condition is that the activated reed flowers are soaked in 6mol/L potassium hydroxide solution, nitrogen-containing compounds are added and uniformly stirred, the mixture is kept stand for 12 hours, then the mixture is dried to constant weight at 110 ℃, the temperature is raised to 700 ℃ at the heating speed of 2-3 ℃/min in the nitrogen atmosphere, and then the constant temperature is kept for 1-3 hours.

Further, the step of tabletting is to uniformly mix the reed flower biochar with acetylene black and polytetrafluoroethylene emulsion, add absolute ethyl alcohol to adjust the viscosity of the mixed material, press the mixed material to a sheet, place the sheet on a nickel foam sheet, compact the sheet by a tabletting machine, and then dry the sheet for 8 hours at 110 ℃.

Further, the mass ratio of the reed flower biochar to the acetylene black to the polytetrafluoroethylene emulsion is 85:10: 5.

The invention provides a reed flower biochar-based electrode material prepared by the preparation method.

The invention has the beneficial effects that: the reed is rich in lignin, cellulose, hemicellulose and the like, the preparation of the biochar-based material by utilizing the reed straw has been studied, however, the silicon content in the reed straw is high, the pretreatment of adding hydrofluoric acid and the like is usually needed in the preparation process, and the preparation process is complicated; in the invention, the electrode material is prepared from reed flowers, carbonization, activation pore-forming and nitrogen doping are completed in one step, and the preparation process is simple and easy to operate; the selected nitrogen-containing compound has hydroxyl and can perform chemical reaction with carboxyl on the surface of reed flowers, so that the nitrogen-containing compound is better combined with biomass carbon and has high nitrogen content; meanwhile, the nitrogen-containing compound has alkalinity and water solubility, is easy to enter the interior of the plant fiber and is easier to form pores in the high-temperature carbonization process; after the nitrogen-containing compound such as diethanol amine is used, the specific surface pore volume of the material is obviously enhanced under the same activation condition, and the nitrogen-containing compound serves as a nitrogen-doped agent and an auxiliary pore-forming agent in the preparation process of the biochar-based material.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is an SEM photograph of RFC/RFAC/RFAC-N (a and e are SEM photographs of RFC, b and f are SEM photographs of RFAC, c and d are SEM photographs of RFC, and d and g are SEM photographs of RFAC-N-2).

FIG. 2 is an XRD pattern of RFC/RFAC/RFAC-N/RFAC-N-2.

FIG. 3 is a Raman diagram of RFC/RFAC/RFAC-N/RFAC-N-2.

FIG. 4 is a graph of cyclic voltammograms of electrode materials made of RFC/RFAC/RFAC-N/RFAC-N-2, respectively.

FIG. 5 is a constant current charge and discharge curve diagram of the electrode materials made of RFC/RFAC/RFAC-N/RFAC-N-2 respectively.

FIG. 6 is a graph showing the change of specific capacitance with current density of electrode materials made of RFC/RFAC/RFAC-N/RFAC-N-2, respectively.

FIG. 7 is a graph showing the AC impedance curves of electrode materials made of RFC/RFAC/RFAC-N/RFAC-N-2, respectively.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

In the following examples of the present invention, the raw materials involved are as follows: the reed flowers are collected from \37015ofYangzhou city in Jiangsu province, and in the wetland in the river region, the reed flowers are cleaned by deionized water and dried for later use before experiments; absolute ethyl alcohol (analytically pure, 99.7%) potassium hydroxide (analytically pure), diethanolamine (chemically pure), hydrochloric acid (analytically pure, 36.0-38.0%) and hydrofluoric acid (analytically pure, 40%) were purchased from the national pharmaceutical group; acetylene black (battery grade) and polytetrafluoroethylene emulsion (60%) were purchased from alatin reagent inc.

Example 1:

3g of cleaned and dried reed flowers are put into a tube furnace, heated to 700 ℃ at a heating speed of 3 ℃/min under the nitrogen atmosphere, and then kept at the constant temperature for 2h for carbonization. And (3) cooling to room temperature, grinding the carbonized product, soaking the product in 1mol/L HCl to remove impurities, and washing the product to be neutral by using deionized water. Finally, drying at 110 ℃, and naming the obtained reed flower biochar sample as RFC;

soaking 3g of RFC in 80ml of potassium hydroxide solution with the concentration of 6mol/L for 12h, then drying at 110 ℃ to constant volume, heating to 700 ℃ at the heating speed of 3 ℃/min under the atmosphere of nitrogen, keeping the temperature constant for 2h for activation, wherein the cleaning method of the activated sample is the same as that of the RFC, and the sample is named as RFAC;

soaking 3g of RFAC in 80ml of potassium hydroxide solution with the concentration of 6mol/L, adding 0.6g of diethanolamine, uniformly stirring, standing for 12h, drying to constant volume at 110 ℃, heating to 700 ℃ at the heating speed of 3 ℃/min, keeping the temperature for 2h for activation, wherein the cleaning method is the same as RFC, and the obtained product is named as RFAC-N.

Comparative example 1:

the diethanolamine in example 1 was replaced with aniline, and the procedure was otherwise the same as in example 1 to give a product designated RFAC-N-2.

The application comprises the following steps: the RFC/RFAC/RFAC-N in the example 1 and the RFAC-N-2 in the comparative example 1 can be used for preparing the electrode material of the super capacitor, and the preparation method can be carried out according to the following steps.

Uniformly mixing 85 wt% of RFC/RFAC/RFAC-N/RFAC-N-2, 10 wt% of acetylene black and 5 wt% of polytetrafluoroethylene emulsion, adding absolute ethyl alcohol to adjust the viscosity of the mixed material, pressing the mixed material to a sheet, placing the sheet on a foamed nickel sheet, compacting the sheet by using a tabletting machine, and drying the sheet at 110 ℃ for 8 hours to obtain the reed peanut carbon-based supercapacitor electrode material.

The test method of the above materials of the invention is as follows:

on an electrochemical workstation (CHI 760E, Shanghai Chenghua instruments, Inc.), a two-electrode electrochemical test system was used, and 6mol/L KOH was used as an electrolyte to study the electrode material. The performance of the electrode material is evaluated by adopting a cyclic voltammetry test (CV), a constant current charge and discharge test (GCD) and an alternating current impedance test (EIS).

The specific capacitance of the material is tested by GCD and calculated by the formula Cg 2I delta t/m delta V, wherein Cg is the specific capacitance (F g)^-1) I is discharge current (A), delta t is discharge time(s), m is reed peanut charcoal mass (g) on the single electrode, and delta V is potential window (the potential range in the experiment is 0-1V).

A in figure 1 and e in figure 1 are SEM images of RFC, and it can be seen that the material prepared after carbonizing the reed flowers is a block structure with a smooth surface; b in FIG. 1 and f in FIG. 1 are SEM images of RFAC, and it can be seen that after pore formation by KOH, the surface of the nanosheet is relatively smooth, but the morphology of the material is changed into an interconnected porous carbon nanosheet structure; adding diethanolamine for nitrogen doping to obtain c in a figure 1 and g in the figure 1, wherein the shapes of the c in the figure 1 and the g in the figure 1 are similar to those of b in the figure 1 and f in the figure 1, but the pore diameter is reduced, namely the obtained product after nitrogen doping is still a porous carbon nanosheet structure, and due to the introduction of the diethanolamine, a plurality of small pores are generated on the surface of the carbon nanosheet, so that the carbon nanosheet structure not only serves as a nitrogen doping agent, but also serves as an auxiliary pore-forming agent; and the mode of doping N with aniline is used to obtain d in figure 1 and h in figure 1, and it can be seen from the enlarged view of h in figure 1 that the surface of the carbon nanosheet is relatively smooth, no small hole is generated as shown by g in figure 1, that is, aniline cannot serve as an auxiliary pore-forming agent, and the performance is single.

FIG. 2 is an XRD pattern of RFC, RFAC-N and RFAC-N-2, from which two broad peaks near 24 and 43 are seen, corresponding to the (002) and (100) crystal planes of the graphite interlayer structure, indicating that these four materials are in an amorphous state.

FIG. 3 is a Raman plot of RFC, RFAC-N and RFAC-N-2, 1340cm^-1The peak near (D band) represents lattice defects and disordered structure, 1590cm^-1The peak near the (G band) represents graphitized carbon, and the intensity ratio (I) of the D band and the G band_D/I_G) Representing the degree of disorder in the structure of the material. RFC, RFAC and RFAC-N I_D/I_G0.93, 1.08, 1.17 and 1.18 respectively. KOH activation can result in an increase in defects in the carbon matrix due to the high density of pores and expansion of the carbon lattice created during KOH activation.

The elemental analysis and BET results are shown in Table 1, RAFC nitrogen doping with diethanolamine and aniline respectively to obtain RAFC-N and RFAC-N-2, and the nitrogen content is measured, the data in Table 1 show that the nitrogen content of RAFC-N is obviously increased and is higher than RFAC-N-2, which indicates that the effect of diethanolamine as nitrogen doping agent is better than that of aniline; from the specific surface area and pore volume value conditions, the RFAC-N value is obviously increased compared with RFAC, however, the specific surface area of RFAC-N-2 is not increased or decreased, and the pore volume area is not greatly different, which also indicates that the RFAC-N material obtained by nitrogen doping with diethanolamine has excellent electrochemical performance.

TABLE 1

Sample (I)	C/％	H/％	N/％	Other%	Specific surface m²/g	Pore volume cm²/g
							RFAC	66.1	3.49	0.901	28.8	1325	0.7526
RFAC-N	80.2	2.63	1.73	15.4	1679	1.059
							RFAC-N-2	66.1	3.49	1.55	28.8	1229	0.7938

FIG. 4 is a cyclic voltammetry test of RFC/RFAC/RFAC-N/RFAC-N-2 electrode materials respectively prepared at a scanning rate of 10mV, the cyclic voltammetry curve of a tested sample is similar to a rectangle, the larger the area, the larger the specific capacitance, the larger the area, the RFAC-N electrode material area is, namely, the specific capacitance is, it can be seen from the figure that the RFAC-N electrode material area is the largest, while the RFAC-N-2 electrode material area is close to the RAFC, and the influence on the performance of the electrode material after nitrogen doping is small.

FIG. 5 shows 1A g^-1According to the constant current charge and discharge test condition under the current density, as shown in the figure, the constant current charge and discharge curves of the tested sample show slightly deformed isosceles triangles, which shows that the electrode material has good double-layer capacitance characteristics, the RFC is 10.4F/g, the RFAC is 214F/g, the RFAC-N is 252F/g, the RFAC-N-2 is 217.4F/g, and the RFAC-N has good capacitance performance and rate capability.

FIG. 6 shows that the specific capacitance of RFAC-N is obviously higher than that of RFC and RFAC, when the current density is increased from 0.5A/g to 10A/g, the capacitance retention rate of RFAC-N is also higher, 199F/g is achieved at 10A/g, the rate performance reaches 79.0%, and the rate performance is better.

Fig. 7 is an ac impedance test chart, and it can be seen that the ac impedance curves of all the samples are mainly composed of a semicircle and a straight line inclined upward. The nearly vertical inclined straight line shows that the porous carbon material has lower diffusion resistance, so that the porous carbon material is very favorable for the rapid transmission of electrons in the electrolyte, and the material has more excellent capacitance performance. The low frequency of the RFC sample the ideal vertical line deviates from the x-axis in part because of the relatively low specific surface area. The Nyquist curves for all samples exhibited approximately perpendicular lines in the low frequency region, indicating that the behavior of the EDLC is ideal. In the mid-frequency region, all samples exhibited a 45 ° slope, indicating a Warburg impedance. The shorter the projection length, the faster the electrolyte ions can reversibly diffuse. The RFAC and RFAC-N samples show a quasi-vertical line in the low frequency range, indicating that capacitance dominates the electric double layer mechanism. In the high frequency region, the Equivalent Series Resistance (ESR) was obtained in combination with the resistance of the electrolyte, the intrinsic resistance of the active material, and the contact resistance between the active material and the collector interface. The RFAC-N sample had the lowest ESR, indicating that it had the best conductivity and the lowest inherent resistance.

While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable in various fields of endeavor to which the invention pertains, and further modifications may readily be made by those skilled in the art, it being understood that the invention is not limited to the details shown and described herein without departing from the general concept defined by the appended claims and their equivalents.

Claims

1. A preparation method of a reed peanut charcoal-based electrode material is characterized by comprising the steps of carbonizing reed flowers in a nitrogen atmosphere, carrying out high-temperature activation and nitrogen doping by using potassium hydroxide as an activating agent and a nitrogen-containing compound as a nitrogen doping agent to obtain reed flower charcoal, mixing with acetylene black and polytetrafluoroethylene emulsion, tabletting and drying to obtain the reed flower charcoal-based electrode material; the carbonization condition is that the dried reed flowers are heated to 700 ℃ at the heating speed of 2-3 ℃/min under the nitrogen atmosphere and then are kept at the constant temperature for 1-3 h; the high-temperature activation condition is that carbonized reed flowers are soaked in 6mol/L potassium hydroxide solution for 12 hours, then dried to constant weight at 110 ℃, heated to 700 ℃ at a heating speed of 2-3 ℃/min in a nitrogen atmosphere, and then kept at the constant temperature for 1-3 hours; the nitrogen-containing compound is ethanolamine, diethanolamine or triethanolamine; the nitrogen doping condition is that the activated reed flowers are soaked in 6mol/L potassium hydroxide solution, nitrogen-containing compounds are added and evenly stirred, the mixture is kept stand for 12 hours, then the mixture is dried to constant weight at 110 ℃, the temperature is raised to 700 ℃ at the heating speed of 2-3 ℃/min in the nitrogen atmosphere, and then the constant temperature is kept for 1-3 hours.

2. The method for preparing a reed flower biochar-based electrode material as claimed in claim 1, wherein the tabletting step comprises uniformly mixing the reed flower biochar with acetylene black and polytetrafluoroethylene emulsion, adding absolute ethyl alcohol to adjust the viscosity of the mixed material, pressing the mixed material into a sheet, placing the sheet on a nickel foam sheet, compacting the sheet by using a tabletting machine, and then drying the sheet at 110 ℃ for 8 hours.

3. The method for preparing the reed flower biochar-based electrode material as claimed in claim 1, wherein the mass ratio of the reed flower biochar, the acetylene black and the polytetrafluoroethylene emulsion is 85:10: 5.

4. A reed flower biochar-based electrode material prepared by the preparation method of any one of claims 1-3.