CN116119661A - Lignin-based porous carbon material, preparation method and application thereof, and lithium ion energy storage device - Google Patents
Lignin-based porous carbon material, preparation method and application thereof, and lithium ion energy storage device Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/318—Preparation characterised by the starting materials
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/342—Preparation characterised by non-gaseous activating agents
- C01B32/348—Metallic compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/30—Electrodes characterised by their material
- H01G11/32—Carbon-based
- H01G11/34—Carbon-based characterised by carbonisation or activation of carbon
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/30—Electrodes characterised by their material
- H01G11/32—Carbon-based
- H01G11/44—Raw materials therefor, e.g. resins or coal
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Power Engineering (AREA)
- Inorganic Chemistry (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Carbon And Carbon Compounds (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a lignin-based porous carbon material, a preparation method and application thereof and a lithium ion energy storage device, and relates to the technical field of carbon materials. The method comprises the steps of purifying the dealkalized lignin by hydrochloric acid to obtain purified lignin; pre-carbonizing the purified lignin under the condition of inert atmosphere to obtain a lignin-based carbon precursor; and (3) carrying out solid phase mixing on the lignin-based carbon precursor and an activating agent, and carbonizing and activating the obtained mixture under the inert atmosphere condition to obtain the lignin-based porous carbon material. According to the invention, lignin is purified and pre-carbonized, so that the composition and structure of the carbon precursor are regulated, the molecular structure stability of the carbon precursor is improved, and the formation and reservation of micropores and small mesopores (the pore diameter is smaller than 5 nm) are facilitated. The lignin-based porous carbon material prepared by the invention has high specific surface area and a micropore/small mesoporous composite pore structure, and is used as a positive electrode active material for a lithium ion energy storage device, and has excellent specific capacity and rate capability.
Description
Technical Field
The invention relates to the technical field of carbon materials, in particular to a lignin-based porous carbon material, a preparation method and application thereof and a lithium ion energy storage device.
Background
Lignin is one of the main organic components of plants, the content of which in lignocellulosic biomass is next to cellulose. In industrial processes lignin is discarded as a by-product, such as black liquor from paper mills and residues from the ethanol fermentation industry. Lignin molecules are mainly composed of three aromatic compounds, and the molecules have a high-content benzene ring structure, so that the lignin molecules are ideal carbon material precursors. Therefore, the preparation of the lignin-based carbon material is an effective way for the high-value utilization of lignin.
The porous carbon is widely applied to the fields of energy storage, environmental purification and the like due to the characteristics of high specific surface area, high chemical stability and the like. The porous carbon prepared from biomass such as lignin is generally obtained by directly carrying out pyrolysis activation (physical activation or chemical activation) on raw materials, and the prepared lignin-based porous carbon has higher specific surface area. However, in practice, because of the high pyrolysis reaction activity of lignin and the existence of inorganic impurities in industrial lignin, severe pyrolysis and activation reactions easily damage the pore structure of porous carbon, and finally cause the reduction of the specific surface area and the deterioration of the pore structure of lignin-based porous carbon materials, thereby damaging the performance of lignin-based porous carbon materials in various application fields.
Disclosure of Invention
In view of the above, the invention aims to provide a lignin-based porous carbon material, a preparation method and application thereof, and a lithium ion energy storage device. The lignin-based porous carbon material prepared by the invention has high specific surface area and a micropore/small mesoporous composite pore structure, and is used as a positive electrode active material for a lithium ion energy storage device, and has excellent specific capacity and rate capability.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a preparation method of a lignin-based porous carbon material, which comprises the following steps:
(1) Hydrochloric acid purification is carried out on the dealkalized lignin to obtain purified lignin;
(2) Pre-carbonizing the purified lignin under the condition of inert atmosphere to obtain a lignin-based carbon precursor; the temperature of the pre-carbonization is 300-500 ℃;
(3) Solid phase mixing is carried out on the lignin-based carbon precursor and an activating agent, and carbonization-activation is carried out on the obtained mixture under the inert atmosphere condition, so as to obtain a lignin-based porous carbon material; the carbonization-activation temperature is 600-1200 ℃.
Preferably, the method for purifying hydrochloric acid in the step (1) comprises the following steps:
mixing dealkalized lignin, water and first hydrochloric acid for first purification, and carrying out solid-liquid separation to obtain a solid;
mixing the solid with second hydrochloric acid for second purification, and carrying out solid-liquid separation and solid phase drying to obtain the purified lignin.
Preferably, the concentration of the first hydrochloric acid is 1-3 mol/L, the first purification is carried out under the stirring condition, and the time of the first purification is 1-60 min; the concentration of the second hydrochloric acid is 0.01-0.5 mol/L, the second purification is carried out under the ultrasonic condition, and the second purification time is 1-30 min.
Preferably, the flow rate of the inert atmosphere in the step (2) is 50-100 mL/min; the heat preservation time of the pre-carbonization is 0.5-12 h; the heating rate of the pre-carbonization temperature is 1-5 ℃/min.
Preferably, the activator in the step (3) comprises KOH, K 2 CO 3 NaOH and Na 2 CO 3 One or more of the following; the mass ratio of the lignin-based carbon precursor to the activator is 1:0.5-10.
Preferably, the flow rate of the inert atmosphere in the step (3) is 50-100 mL/min; the carbonization-activation heat preservation time is 0.5-3 h; the heating rate of the carbonized-activated temperature is 3-20 ℃/min.
Preferably, after carbonization-activation in the step (3), the obtained carbon material is further subjected to acid washing, water washing and drying in sequence.
The invention provides the preparation method of the technical proposalThe lignin-based porous carbon material is prepared; the pore structure of the lignin-based porous carbon material consists of micropores and mesopores, and the pore diameter of the mesopores is smaller than 5nm; the specific surface area of the lignin-based porous carbon material is more than or equal to 2500m 2 Per g, total pore volume of 1-2 cm 3 /g。
The invention provides application of the lignin-based porous carbon material in the lithium ion energy storage device as an anode active material.
The invention provides a lithium ion energy storage device, and a positive electrode active material of the lithium ion energy storage device comprises the lignin-based porous carbon material.
The invention provides a preparation method of a lignin-based porous carbon material, which comprises the following steps: (1) Hydrochloric acid purification is carried out on the dealkalized lignin to obtain purified lignin; (2) Pre-carbonizing the purified lignin under the condition of inert atmosphere to obtain a lignin-based carbon precursor; the temperature of the pre-carbonization is 300-500 ℃; (3) Solid phase mixing is carried out on the lignin-based carbon precursor and an activating agent, and carbonization-activation is carried out on the obtained mixture under the inert atmosphere condition, so as to obtain a lignin-based porous carbon material; the carbonization-activation temperature is 600-1200 ℃. According to the invention, the lignin raw material is purified, so that the influence of inorganic impurities on the lignin carbonization process is avoided; according to the invention, lignin is pre-carbonized within a certain temperature range, so that the molecular structure stability of a carbon precursor is improved, the formation and the reservation of micropores and small mesopores (the aperture is smaller than 5 nm) are facilitated, and the existence of the micropores and the small mesopores is favorable for improving the specific surface area of the porous carbon and simultaneously maintaining a proper pore volume, thereby improving the specific capacity of the porous carbon serving as the anode of a lithium ion energy storage device and avoiding the excessive electrolyte consumption requirement caused by high pore volume; the method uses the solid phase mixing and the co-pyrolysis of the activator and the lignin-based carbon precursor, is favorable for the penetration and etching of the activator to the lignin-based carbon precursor, realizes carbonization and chemical activation in one step, and has important influence on the regulation and control of the pore structure.
The invention provides the lignin-based porous carbon material prepared by the preparation method.The lignin-based porous carbon material provided by the invention has high specific surface area (2500 m) 2 Above/g) and a narrower pore size distribution (consisting of micropores and mesopores, with mesopore diameters of less than 5 nm). The example results show that compared with the lignin-based porous carbon which is not pre-carbonized, the lignin-based porous carbon obtained after pre-carbonization has higher specific surface area and larger total pore volume, and particularly the mesoporous volume is obviously increased, so that the rapid migration and diffusion of ions on the surface of the carbon are facilitated; the lignin-based porous carbon provided by the invention is used as a positive electrode active material for a lithium ion energy storage device, and the half cell of the lignin-based porous carbon shows high specific capacity and good rate capability.
Drawings
FIG. 1 is a scanning electron micrograph of lignin-based porous carbon prepared in example 1;
FIG. 2 is a nitrogen adsorption/desorption curve and a pore size distribution curve of lignin-based porous carbon prepared in example 1;
FIG. 3 is a nitrogen adsorption/desorption curve and a pore size distribution curve of lignin-based porous carbon prepared in example 2;
FIG. 4 is a nitrogen adsorption/desorption curve and a pore size distribution curve of lignin-based porous carbon prepared in example 3;
FIG. 5 is a nitrogen adsorption/desorption curve and a pore size distribution curve of lignin-based porous carbon prepared in comparative example 1;
fig. 6 is a graph showing the rate performance of half batteries of lithium ion capacitors assembled using the lignin-based porous carbon obtained in examples 1 to 3 and comparative example 1 as a positive electrode active material.
Detailed Description
The invention provides a preparation method of a lignin-based porous carbon material, which comprises the following steps:
(1) Hydrochloric acid purification is carried out on the dealkalized lignin to obtain purified lignin;
(2) Pre-carbonizing the purified lignin under the condition of inert atmosphere to obtain a lignin-based carbon precursor; the temperature of the pre-carbonization is 300-500 ℃;
(3) Solid phase mixing is carried out on the lignin-based carbon precursor and an activating agent, and carbonization-activation is carried out on the obtained mixture under the inert atmosphere condition, so as to obtain a lignin-based porous carbon material; the carbonization-activation temperature is 600-1200 ℃.
The method performs hydrochloric acid purification on the dealkalized lignin to obtain purified lignin. The method has no special requirement on the source of the dealkalized lignin, and adopts commercial products well known to the person skilled in the art; in the embodiment of the invention, the dealkalized lignin is purchased from Shanghai Micin Biochemical technologies Co., ltd. In the present invention, the method for purifying hydrochloric acid preferably comprises the steps of:
mixing dealkalized lignin, water and first hydrochloric acid for first purification, and carrying out solid-liquid separation to obtain a solid;
mixing the solid with second hydrochloric acid for second purification, and carrying out solid-liquid separation and solid phase drying to obtain the purified lignin.
In the present invention, the water is preferably deionized water, and the dosage ratio of the dealkalized lignin to the water is preferably 10g:100mL; the concentration of the first hydrochloric acid is preferably 1-3 mol/L, more preferably 1-2 mol/L, and the dosage ratio of the dealkalized lignin to the first hydrochloric acid is preferably 10g:80mL. In the present invention, the method for mixing the dealkalized lignin, water and the first hydrochloric acid is preferably as follows: adding water into the dealkalized lignin to stir to obtain lignin dispersion liquid; adding first hydrochloric acid into the lignin dispersion liquid. In the present invention, the first purification is preferably performed under stirring conditions, the stirring speed is preferably 400rpm, and the time of the first purification is preferably 1 to 60 minutes, more preferably 15 to 35 minutes; the first purification time is calculated from the completion of the first hydrochloric acid addition. The solid-liquid separation method is not particularly limited, and may be any method known to those skilled in the art, such as centrifugation or filtration. According to the method, through the first purification, water-soluble and acid-soluble impurities in the lignin raw material are removed, the purity of lignin is improved, hydrochloric acid with higher concentration is needed in the step, hydrolysis of lignin is accelerated by the hydrochloric acid with too high concentration, and the method comprehensively considers that the hydrochloric acid with the concentration of 1-3 mol/L is selected.
The present invention preferably adds a second hydrochloric acid to the solid; the concentration of the second hydrochloric acid is preferably 0.01-0.5 mol/L, more preferably 0.1-0.2 mol/L, and the dosage ratio of the second hydrochloric acid to the dealkalized lignin is preferably 150-300 mL/10 g, more preferably 200 mL/10 g. In the present invention, the second purification is preferably performed under ultrasonic conditions, the power of the ultrasonic wave is preferably 240W, and the time of the second purification (i.e., the time of the ultrasonic wave) is preferably 1 to 30min, more preferably 10min. The method of the invention has no special requirement on the solid-liquid separation mode, and the solid phase is collected through the solid-liquid separation. In the present invention, the second purification and solid-liquid separation operations are preferably repeated, and the number of times of the repetition is preferably 1 to 3 times. According to the invention, through the second purification, the impurity dissolved by hydrochloric acid in the first purification is washed away, and the second purification adopts hydrochloric acid with lower concentration, so that the weak acid environment of lignin aqueous dispersion can be maintained, the solubility of lignin in water is reduced, and the yield of purified lignin is improved. In the present invention, the temperature of the solid phase drying is preferably 60 to 100 ℃, and the time of the solid phase drying is not particularly limited, and the drying may be carried out to a constant weight, and the solid phase drying is preferably carried out in a forced air drying oven. According to the invention, the lignin raw material is purified, so that the influence of inorganic impurities on the lignin carbonization process is avoided.
After the purified lignin is obtained, the invention pre-carbonizes the purified lignin under the condition of inert atmosphere to obtain lignin-based carbon precursor. The inert atmosphere is not particularly limited in the present invention, and inert atmosphere well known to those skilled in the art, such as argon atmosphere; the flow rate of the inert atmosphere is preferably 50 to 100mL/min, more preferably 70 to 100mL/min. In the present invention, the temperature of the pre-carbonization is preferably 300 to 500 ℃, more preferably 350 to 450 ℃, and even more preferably 400 ℃; the heat preservation time of the pre-carbonization is preferably 0.5-12 h, more preferably 3-10 h; the heating rate from room temperature to the pre-charring temperature is preferably 1 to 5 ℃/min, more preferably 3 to 4 ℃/min. The invention preferably places the purified lignin in a corundum boat and then in a tube furnace for the pre-carbonization. According to the preparation method, the molecular structure stability of the carbon precursor is improved through the pre-carbonization, the formation and the reservation of micropores and small mesopores (the aperture is smaller than 5 nm) are facilitated, and the existence of the micropores and the small mesopores is beneficial to maintaining proper pore volume while improving the specific surface area of the porous carbon, so that the specific capacity of the porous carbon serving as the anode of the lithium ion energy storage device is improved, and the requirement of excessive electrolyte consumption caused by high pore volume is avoided. After the pre-carbonization, the obtained product is cooled to room temperature along with furnace temperature and then ground to obtain the powdery lignin-based carbon precursor.
After the lignin-based carbon precursor is obtained, the lignin-based carbon precursor and an activating agent are subjected to solid phase mixing, and the obtained mixture is subjected to carbonization-activation under the inert atmosphere condition to obtain the lignin-based porous carbon material. In the present invention, the activator preferably comprises KOH, K 2 CO 3 NaOH and Na 2 CO 3 One or more of them, more preferably KOH; the mass ratio of the lignin-based carbon precursor to the activating agent is preferably 1:0.5-10, more preferably 1:3-5; the solid phase mixing is preferably carried out in a pulverizer. Taking an activating agent as KOH as an example, most of the activation in the prior art is to mix KOH solution with a carbon precursor and then dry the mixture to obtain a reactant, and the method is long in time consumption and nonuniform in mixing; or the KOH solution and the carbon precursor are mixed and then are frozen and dried to obtain a mixture, and the mixture obtained by the method is more uniform, but takes longer time and has higher energy consumption; the invention mixes the carbon precursor and the activator solid phase by the pulverizer, which is simple and efficient and has good mixing effect.
The inert atmosphere is not particularly limited in the present invention, and inert atmosphere well known to those skilled in the art, such as argon atmosphere; the flow rate of the inert atmosphere is preferably 50 to 100mL/min, more preferably 70 to 100mL/min. In the present invention, the carbonization-activation temperature is preferably 600 to 1200 ℃, more preferably 900 to 1000 ℃; the heating rate from the temperature to the carbonization-activation temperature is preferably 3 to 20 ℃/min, more preferably 5 to 10 ℃/min; the heat-insulating time for the carbonization-activation is preferably 0.5 to 3 hours, more preferably 1 to 2 hours. The lignin-based carbon precursor is preferably placed in a corundum boat and then placed in a tube furnace for carbonization-activation. According to the invention, the activator and the lignin-based carbon precursor are mixed and pyrolyzed together, carbonization and chemical activation are realized in one step, and the method has an important influence on the regulation and control of a pore structure; in addition, the carbon precursor adopted by the invention is a lignin pre-carbonization product, and the lignin and KOH activation process is influenced by regulating and controlling the composition and structure of the lignin pre-carbonization product.
After carbonization-activation, the obtained carbon material is cooled to room temperature along with furnace temperature, and then is subjected to acid washing, water washing and drying in sequence, so that the lignin-based porous carbon material is obtained. In the invention, the acid reagent used for acid washing is preferably hydrochloric acid, and the concentration of the hydrochloric acid is preferably 1mol/L; the acid washing is preferably performed under boiling or ultrasonic conditions, and the acid washing is preferably performed multiple times to ensure that the residual activator in the carbon material is sufficiently removed by reaction. In the present invention, deionized water is preferably used for the water washing, and the water washing is preferably performed under ultrasonic conditions; the invention has no special requirement on the times of water washing, and ensures that the water washing is neutral. In the present invention, the drying temperature is preferably 100 ℃, and the drying time is based on drying to constant weight.
The invention provides the lignin-based porous carbon material prepared by the preparation method. In the invention, the pore structure of the lignin-based porous carbon material consists of micropores and mesopores, wherein the pore diameter of the mesopores is smaller than 5nm, i.e. the pore structure of the lignin-based porous carbon material is a micropore/mesopore composite pore structure with the pore diameter smaller than 5nm; the specific surface area of the lignin-based porous carbon material is more than or equal to 2500m 2 Per g, total pore volume of 1-2 cm 3 And/g. In the embodiment of the invention, the specific surface area of the lignin-based porous carbon material is 2863-3218 m 2 Per gram, the total pore volume is 1.272-1.545 cm 3 And/g. In the invention, the main constituent element of the lignin-based porous carbon material is carbon, and contains a small amount of oxygen element.
The invention provides application of the lignin-based porous carbon material in the lithium ion energy storage device as an anode active material. The lithium ion energy storage device is not particularly limited, and lithium ion energy storage devices well known to those skilled in the art, such as lithium ion batteries, lithium ion capacitors, and the like, are exemplified as lithium ion capacitors in the embodiment of the present invention. The lignin-based porous carbon material provided by the invention has high specific surface area and moderate total pore volume, and is used as an anode active material for a lithium ion energy storage device, and has excellent specific capacity and rate capability.
The invention provides a lithium ion energy storage device, and a positive electrode active material of the lithium ion energy storage device comprises the lignin-based porous carbon material. The present invention is not particularly limited to the construction of the lithium ion energy storage device, and may be constructed as is well known to those skilled in the art. In the embodiment of the invention, the lithium ion energy storage device is specifically a lithium ion capacitor; the positive electrode material of the lithium ion capacitor comprises a positive electrode active material, a conductive agent, a binder and a solvent; the positive electrode active material comprises the lignin-based porous carbon material according to the technical scheme, the conductive agent is preferably conductive carbon black, the binder is preferably polyvinylidene fluoride, and the solvent is preferably N-methyl pyrrolidone; the mass ratio of the positive electrode active material, the conductive agent and the binder is preferably 8:1:1; the negative electrode of the lithium ion capacitor is a metal lithium sheet; the electrolyte of the lithium ion capacitor comprises ethylene carbonate, dimethyl carbonate, diethyl carbonate and an additive, wherein the volume ratio of the ethylene carbonate to the dimethyl carbonate to the diethyl carbonate is preferably 1:1:1, and the additive is preferably LiPF 6 The concentration of the additive in the electrolyte is preferably 1mol/L.
The lignin-based porous carbon material, the preparation method and application thereof and the lithium ion energy storage device provided by the invention are described in detail below with reference to examples, but they are not to be construed as limiting the scope of the invention.
Example 1
The preparation method of the lignin-based porous carbon material comprises the following steps:
s1, adding 100mL of deionized water into 10g of dealkalized lignin, uniformly stirring, adding 80mL of 1mol/L hydrochloric acid, magnetically stirring for 15min at a rotating speed of 400rpm, separating solid and liquid by a decompression suction filtration mode, and retaining a solid product. 200mL of 0.1mol/L hydrochloric acid was added to the obtained solid product, and the mixture was sonicated at 240W for 10min, and the solid and liquid were separated by suction filtration under reduced pressure to leave the solid product, and the procedure was repeated 1 time. And (5) placing the obtained solid product in a blast drying oven at 60 ℃ for drying for 12 hours to obtain the purified lignin.
S2, placing 3g of purified lignin in a corundum boat, placing the corundum boat in a tube furnace, heating from room temperature to 400 ℃ at a heating rate of 3 ℃/min under the protection of argon, keeping the flow of the argon to be 100mL/min, and preserving the heat for 3 hours for pre-carbonization; cooling to room temperature along with the furnace temperature, collecting a solid product, and grinding to obtain the pre-carbonized lignin.
S3, solid-phase mixing 1.5g of pre-carbonized lignin and 4.5g of potassium hydroxide by using a pulverizer, placing the obtained mixed powder into a corundum boat, placing the corundum boat into a tube furnace, heating from room temperature to 900 ℃ at a heating rate of 5 ℃/min under the protection of argon, keeping the flow of the argon to be 100mL/min, and preserving the heat for 1h. Cooling to room temperature along with furnace temperature, adding 200mL 1mol/L hydrochloric acid into the obtained solid product, standing for 3h, boiling, filtering and retaining the solid product, and pickling twice according to the operation. 200mL of deionized water is added into the solid product, after ultrasonic cleaning is carried out for 10min, the solid is filtered and retained, and deionized water is repeatedly washed until the filtrate is neutral. And (3) placing the solid product in a blast drying oven at 100 ℃ for drying for 12 hours to obtain lignin-based porous carbon, which is named PDLPC-400-3.
FIG. 1 is a scanning electron micrograph of lignin-based porous carbon prepared in example 1. As can be seen from the results of FIG. 1, the lignin-based porous carbon has a porous structure, and obvious potassium hydroxide etching traces are formed on the surfaces of carbon particles.
FIG. 2 is a nitrogen adsorption/desorption curve and a pore size distribution curve of lignin-based porous carbon prepared in example 1. From the results of FIG. 2, it can be calculated that the lignin-based porous carbon has a specific surface area of 3218m 2 Per gram, total pore volume of 1.465cm 3 /g; as can also be seen from the results of figure 2,the pore structure of the lignin-based porous carbon consists of micropores and mesopores with the pore diameter smaller than 3 nm.
Example 2
A lignin-based porous carbon was prepared in the same manner as in example 1 except that the temperature of the pre-carbonization in step S2 was 350℃and the other conditions were the same as in example 1, to obtain a lignin-based porous carbon designated PDLPC-350-3.
FIG. 3 is a nitrogen adsorption/desorption curve and a pore size distribution curve of lignin-based porous carbon prepared in example 2. From the results of FIG. 3, it can be calculated that the specific surface area of the lignin-based porous carbon is 3093m 2 Per gram, total pore volume of 1.545cm 3 /g; it can also be seen from the results of fig. 3 that the pore structure of the lignin-based porous carbon is composed of micropores and mesopores with a pore diameter of less than 4 nm.
Example 3
A lignin-based porous carbon was prepared in the same manner as in example 1 except that the temperature of the pre-carbonization in step S2 was 450℃and the other conditions were the same as in example 1, to obtain a lignin-based porous carbon designated PDLPC-450-3.
FIG. 4 is a nitrogen adsorption/desorption curve and a pore size distribution curve of lignin-based porous carbon prepared in example 3. From the results of FIG. 4, it can be calculated that the lignin-based porous carbon has a specific surface area of 2863m 2 Per gram, total pore volume of 1.272cm 3 /g; it can also be seen from the results of fig. 4 that the pore structure of the lignin-based porous carbon is composed of micropores and mesopores with a pore diameter of less than 3.2 nm.
Comparative example 1
Lignin-based porous carbon was prepared in the same manner as in example 1 except that step S2 was omitted, and steps S1 to S3 were directly carried out, and the remainder was the same as in example 1, to obtain lignin-based porous carbon, which was designated PDLPC-3.
FIG. 5 is a nitrogen adsorption/desorption curve and a pore size distribution curve of lignin-based porous carbon prepared in comparative example 1. From the results of FIG. 5, it can be calculated that the lignin-based porous carbon has a specific surface area of 1923m 2 Per gram, total pore volume of 0.820cm 3 /g; it can also be seen from the results of FIG. 5 that the lignin-based porous carbonThe pore structure of the porous material consists of micropores and mesopores with the pore diameter smaller than 2.5nm, and the mesoporous volume is obviously reduced. Compared with comparative example 1, the lignin-based porous carbon obtained in example 1 has 67% increase in specific surface area and 78% increase in total pore volume.
Application example
The lignin-based porous carbon obtained in examples 1 to 3 and comparative example 1 was used as a positive electrode active material for lithium ion capacitors, and the electrochemical properties thereof were tested as follows:
mixing positive electrode active materials (lignin-based porous carbon obtained in examples 1 to 3 and comparative example), a conductive agent (conductive carbon black, super C45), a binder (polyvinylidene fluoride, PVDF) and a solvent (N-methylpyrrolidone, NMP) to obtain positive electrode slurry (wherein the mass ratio of positive electrode active materials, conductive agent and binder is 8:1:1); coating positive electrode slurry on a current collector (carbon-coated aluminum foil), drying in a blast drying oven at 80 ℃ for 12 hours, transferring to a vacuum drying oven, and drying at 60 ℃ for 12 hours; cutting the dried positive pole piece into a circular piece with the diameter of 11mm, standing for 10s under the pressure of 15MPa by using a hydraulic press, taking out, weighing, and transferring into a glove box protected by argon atmosphere for later use.
The lithium metal plate (diameter 15.6mm, thickness 450 μm) was used as the negative electrode, and the above positive electrode plate, separator (Celgard 2400) and electrolyte (ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and 1mol/L LiPF was added 6 As an additive) are assembled together into a CR2032 type button cell; and placing the assembled button cell on a Xinwei charge-discharge tester for constant-current charge-discharge test, wherein the voltage window is 2.0-4.2V, and a series of current densities are set for testing the multiplying power performance.
FIG. 6 is a graph showing the rate performance of half cells of lithium ion capacitors assembled using the lignin-based porous carbons obtained in examples 1 to 3 and comparative example 1 as positive electrode active materials, wherein cells using PDLPC-3 were tested at current densities of 0.5A/g, 1A/g, 2A/g, 3A/g, 5A/g and 8A/g, and cells using other lignin-based porous carbons were tested at current densities of 0.5A/g, 1A/g, 2A/g, 3A/g, 5A/g and 10A/g. As can be seen from fig. 6, the lignin-based porous carbon prepared after the pre-carbonization of the example shows higher specific discharge capacity and better rate performance at different current densities than the lignin-based porous carbon prepared without the pre-carbonization of comparative example 1, and specific performance data are shown in table 1:
table 1 electrochemical properties of lithium ion capacitor half cells assembled from lignin-based porous carbons obtained in examples 1 to 3 and comparative example 1 as positive electrode active materials
From the above examples, it can be seen that the lignin-based porous carbon material prepared by the present invention has a high specific surface area, a micropore/small mesoporous composite pore structure and a moderate total pore volume, and is used as a positive electrode active material for lithium ion energy storage devices, and has excellent specific capacity and rate capability.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (10)
1. The preparation method of the lignin-based porous carbon material is characterized by comprising the following steps of:
(1) Hydrochloric acid purification is carried out on the dealkalized lignin to obtain purified lignin;
(2) Pre-carbonizing the purified lignin under the condition of inert atmosphere to obtain a lignin-based carbon precursor; the temperature of the pre-carbonization is 300-500 ℃;
(3) Solid phase mixing is carried out on the lignin-based carbon precursor and an activating agent, and carbonization-activation is carried out on the obtained mixture under the inert atmosphere condition, so as to obtain a lignin-based porous carbon material; the carbonization-activation temperature is 600-1200 ℃.
2. The method of claim 1, wherein the method of purifying hydrochloric acid in step (1) comprises the steps of:
mixing dealkalized lignin, water and first hydrochloric acid for first purification, and carrying out solid-liquid separation to obtain a solid;
mixing the solid with second hydrochloric acid for second purification, and carrying out solid-liquid separation and solid phase drying to obtain the purified lignin.
3. The preparation method according to claim 2, wherein the concentration of the first hydrochloric acid is 1-3 mol/L, the first purification is performed under stirring, and the time of the first purification is 1-60 min; the concentration of the second hydrochloric acid is 0.01-0.5 mol/L, the second purification is carried out under the ultrasonic condition, and the second purification time is 1-30 min.
4. The method according to claim 1, wherein the flow rate of the inert atmosphere in the step (2) is 50 to 100mL/min; the heat preservation time of the pre-carbonization is 0.5-12 h; the heating rate of the pre-carbonization temperature is 1-5 ℃/min.
5. The method according to claim 1, wherein the activator in the step (3) comprises KOH, K 2 CO 3 NaOH and Na 2 CO 3 One or more of the following; the mass ratio of the lignin-based carbon precursor to the activator is 1:0.5-10.
6. The method according to claim 1, wherein the flow rate of the inert atmosphere in the step (3) is 50 to 100mL/min; the carbonization-activation heat preservation time is 0.5-3 h; the heating rate of the carbonized-activated temperature is 3-20 ℃/min.
7. The method according to claim 1, 5 or 6, wherein after the carbonization-activation in the step (3), the obtained carbon material is further subjected to acid washing, water washing and drying in this order.
8. The lignin-based porous carbon material prepared by the preparation method of any one of claims 1 to 7; the pore structure of the lignin-based porous carbon material consists of micropores and mesopores, and the pore diameter of the mesopores is smaller than 5nm; the specific surface area of the lignin-based porous carbon material is more than or equal to 2500m 2 Per g, total pore volume of 1-2 cm 3 /g。
9. The use of the lignin-based porous carbon material of claim 8 as a positive electrode active material in a lithium ion energy storage device.
10. A lithium ion energy storage device, characterized in that a positive electrode active material of the lithium ion energy storage device comprises the lignin-based porous carbon material of claim 8.
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