CN112071657A - Carbon material-carbon nanofiber composite material and double-layer capacitor - Google Patents
Carbon material-carbon nanofiber composite material and double-layer capacitor Download PDFInfo
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- 239000002131 composite material Substances 0.000 title claims abstract description 50
- 239000003990 capacitor Substances 0.000 title claims abstract description 40
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 33
- 239000003575 carbonaceous material Substances 0.000 claims abstract description 55
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 39
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- 239000006258 conductive agent Substances 0.000 claims abstract description 14
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- 239000002184 metal Substances 0.000 claims description 39
- 239000003054 catalyst Substances 0.000 claims description 36
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- 238000002360 preparation method Methods 0.000 claims description 5
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- 239000000463 material Substances 0.000 abstract description 32
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- 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
- H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
-
- 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
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
-
- 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
- C01B32/354—After-treatment
-
- 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
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- 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
- H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
- H01G11/86—Processes for the manufacture of hybrid or EDL capacitors, or components thereof specially adapted for electrodes
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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
- Y02E60/13—Energy storage using capacitors
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- Power Engineering (AREA)
- Nanotechnology (AREA)
- Organic Chemistry (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Materials Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Manufacturing & Machinery (AREA)
- Composite Materials (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
Abstract
The invention provides a carbon material-carbon nanofiber composite material and an electric double layer capacitor. The composite material has a specific surface area of 100-1000 m2The carbon nano-fiber grows on the surface of the carbon material with the volume of the fine pores being more than 80 percent, can improve the density and the volume capacity of the electrode and can obviously inhibit the generation in the charging/discharging processThe volume expansion ratio of the electrode (2) is suitable for use as a capacitor material having an increased capacity per unit volume. In addition, the crystallinity of the carbon nanofibers is greater than that of conventional capacitor materials and can cause close contact between the materials, which is advantageous for high current characteristics, and can also function as a conductive agent.
Description
Technical Field
The invention relates to the technical field of electrode materials, in particular to a carbon material-carbon nanofiber composite material and a double-layer capacitor.
Background
The electric double layer capacitor has both double layer electrostatic capacity generated by a double layer generated at an interface where a solid electrode and a liquid electrolyte contact, and virtual static electricity generated by ions entering the double layer through adsorption to an electrode surface or a redox reaction process, and thus can be applied to a large capacity electric vehicle, a hybrid electric vehicle, and a large capacity power source.
An electrode of an electric double layer capacitor is generally used by mixing powdered activated carbon with carbon black as a conductive agent, and pasting it to a current collector, and adding a binder for binding between the activated carbon and the conductive agent and the current collector. An electric double layer capacitor is manufactured by forming a metal collector on carbon fibers or activated carbon fibers, or by compressing a carbon paste on conductive rubber or a metal collector or by applying a slurry containing activated carbon powder to a metal collector to form a polarized electrode.
Characteristics required for materials generally used as electrodes of electric double layer capacitors include high capacity, electrode density, cycle characteristics, and low volume expansion ratio. Therefore, the material for the electrode of the electric double layer capacitor has a specific surface area of 2000 to 3500m for reducing the volume expansion coefficient2The material per gram, however, these large specific surface materials produce products with low electrode density and too small a volume capacity. In addition, conversely, when a material having a small specific surface area is used to improve the volume expansion ratio, the electrode density and the capacity per unit volume may increase, but conversely, the volume expansion ratio also increases, and thus there is discomfort.
In general, the "volume expansion rate" of an electrode is a method mainly used for measuring the change in thickness of the electrode during charge/discharge of a secondary battery or the like, and a dilatometer (dillatometer) method proposed by Ozuku of the university of osaka, japan is generally employed, but in the present invention, the change in thickness of the electrode before and after charge/discharge is measured by using a disk-shaped electrode as shown in fig. 1, respectively, and will be changed.
In addition, in materials generally used for capacitor electrodes, a high "volume expansion rate" means that the volume expansion rate of an electrode manufactured using the material reaches 30% to 50% during charge and discharge. Therefore, when the volume expansion rate of the electrode, which is generally made of a material for a capacitor, is 30% to 50%, the electrode structure is broken to increase the internal resistance and decrease the capacity, and the capacitance profile is deformed, so that the factors to be controlled are required
Therefore, in order to use the material as an electrode of a capacitor, it is necessary to develop a material that can sufficiently satisfy the above-described contradictory properties, and particularly, it is necessary to satisfy a condition that a volume expansion ratio should not be too large in the production of the electrode.
Disclosure of Invention
The present invention has been made to solve the above-mentioned problems occurring in the prior art, and provides a carbon material-carbon nanofiber composite and a double layer capacitor, in which carbon nanofibers are grown on the surface of a carbon material and the surface is modified by the carbon nanofibers, thereby providing an electric double layer capacitor characterized in that the composite, which has changed characteristics such as specific surface area, pore diameter, and pore volume, is used as an electrode material.
In order to achieve the purpose, the invention adopts the following technical scheme:
the first aspect of the invention provides a carbon material-carbon nanofiber composite material, and the preparation method comprises the following steps:
adding a carbon material into a solution in which a metal catalyst is dissolved, and stirring until the weight of the metal catalyst loaded on the carbon material is 0.5-10% of the weight of the carbon material;
filtering the carbon material loaded with the metal catalyst, recovering the carbon material loaded with the metal catalyst and drying;
and step three, placing the dried carbon material carrying the metal catalyst in a vertical furnace or a horizontal furnace, introducing inert gas at the speed of 50-100 cc/min for replacing for 10-40 minutes, and then supplying mixed gas at the speed of 100-200 cc/min for 5-20 minutes to grow carbon nanofibers on the surface of the dried carbon material carrying the metal catalyst, thereby forming the carbon material-carbon nanofiber composite material.
Further, before the inert gas is introduced, air, oxygen, hydrogen, helium, argon or nitrogen is introduced to gasify the dried carbon material carrying the metal catalyst at the temperature of 250-500 ℃ for 5 minutes to 5 hours until mesopores with the diameter of 2-50nm are formed on the surface of the carbon material.
Further, the metal catalyst is selected from one or more of salts of Fe, Ni, Co, Mg, Cu, Mn, Mo and oxides thereof.
Further, the particle size of the metal catalyst is 5nm to 500 nm.
Further, the solvent of the above metal catalyst is distilled water or aliphatic alcohol.
Further, the mixed gas includes two or more of hydrogen, ethylene, carbon monoxide, methane, and acetylene.
Further, the temperature of the vertical furnace or the horizontal furnace in the third step is 400-700 ℃.
Further, the carbon material in the first step has a specific surface area of 100-1000 m2And/g, the volume of the micro pores is more than 80 percent of one or more of activated carbon, coke, asphalt and carbon nanofibers.
Further, the stirring temperature in the first step is 600-900 ℃, and the stirring time is 0.5-5 hours.
Further, the carbon nanofibers have a diameter of 5 to 500 nm.
A second aspect of the present invention is an electric double layer capacitor whose electrode material comprises the above-described carbon material-carbon nanofiber composite.
Further, the electrode material further comprises a conductive agent and a binder; the conductive agent comprises one or more of Ketjen black, carbon black and acetylene black; the adhesive is polytetrafluoroethylene and/or styrene butadiene rubber.
By adopting the technical scheme, compared with the prior art, the invention has the following technical effects:
the carbon material-carbon nanofiber composite material provided by the invention is obtained by synthesizing carbon nanofibers on the surface of a material with low specific surface area and low fine pore distribution, can improve the electrode density and volume capacity, can remarkably inhibit the volume expansion rate of an electrode generated in the charging/discharging process, and is suitable for being used as a capacitor material with increased unit volume capacity. In addition, the crystallinity of the carbon nanofibers is greater than that of conventional capacitor materials and can cause close contact between the materials, which is advantageous for high current characteristics, and can also function as a conductive agent.
Drawings
FIG. 1 is a schematic diagram for calculating the volumetric expansion ratio of an electrode;
FIG. 2 is a scanning electron microscope photograph of the surface of a composite material according to an embodiment of the present invention;
FIG. 3 is a scanning electron micrograph of a surface of a carbon material after gasification in accordance with an embodiment of the present invention;
FIG. 4 is a scanning electron micrograph of a composite of carbon nanofibers grown on the surface of a carbon material after gasification according to an embodiment of the present invention;
FIG. 5 is a scanning electron micrograph of the surface of alkali-activated coke in a comparative example of the present invention;
fig. 6 shows the discharge capacity per unit volume of the electrode including the materials provided in examples and comparative examples in the present invention as a function of current density.
Detailed Description
The invention provides a carbon material-carbon nanofiber composite material and a double-layer capacitor, and particularly provides a carbon material-carbon nanofiber composite material with the thickness of 100-1000 m2The carbon nanofibers having a specific surface area of/g and fine pores having a diameter of 2nm or less of 80% or more grow on the surface of the carbon material, and since the specific surface area of the carbon material employed in the present invention is smaller than that of a conventionally used material, the electrode density is increased to facilitate an increase in capacity per unit volume. However, when only the alkali-activated carbon material provided by the present invention is used as an electrode of an electric double layer capacitor, the volume expansion rate during charge/discharge reaches 30% to 50%. Therefore, when having a high volume expansion coefficient as described above, the resistance increases due to the destruction of the electrode structure. BySince it causes a reduction in capacity and a deformation in cell shape, there are many problems in using it as an electrode of a capacitor. Therefore, an electrode composite material usable as an electric double layer capacitor is obtained by growing carbon nanofibers on the surface of a carbon material having the above characteristics to change the specific surface area, pore diameter and volume.
In one aspect, the method for preparing the carbon material-carbon nanofiber composite material comprises the following steps:
adding a carbon material into a solution in which a metal catalyst is dissolved, and stirring for several minutes to several hours until the weight of the metal catalyst loaded on the carbon material is 0.5-10% of the weight of the carbon material;
filtering the carbon material loaded with the metal catalyst, recovering the carbon material loaded with the metal catalyst and drying;
and step three, placing the dried carbon material carrying the metal catalyst in a vertical furnace or a horizontal furnace, introducing inert gas at the speed of 50-100 cc/min for replacing for 10-40 min, and then supplying mixed gas at the speed of 100-200 cc/min for 5-20 min to grow and synthesize carbon nano fibers on the surface of the dried carbon material carrying the metal catalyst, thereby forming the carbon material-carbon nano fiber composite material.
In a preferred embodiment of the present invention, the preparation method further comprises introducing air, oxygen, hydrogen, helium, argon or nitrogen to gasify the dried carbon material carrying the metal catalyst for several minutes to several hours at the temperature of 250-500 ℃ before introducing the inert gas until mesopores with a diameter of 2-50nm are formed on the surface of the carbon material. It is known that the size of the mesopores generally increases the capacity of the capacitor.
Further, fine powder or the like may be present on the surface of the carbon nanofibers grown on the surface of the carbon material, and the fine powder may cause a side reaction in the performance evaluation of the electrode to degrade the performance of the electrode, so that the removal by heat treatment can be selectively performed by adding hydrogen gas at 400 to 800 ℃.
In a preferred embodiment of the present invention, the metal catalyst is selected from one or more of salts of Fe, Ni, Co, Mg, Cu, Mn, Mo and oxides thereof.
In a preferred embodiment of the present invention, the particle size of the metal catalyst is 5nm to 500 nm.
In a preferred embodiment of the present invention, the solvent of the metal catalyst is distilled water or aliphatic alcohol.
In a preferred embodiment of the present invention, the concentration of the metal catalyst is 0.5 to 10 wt%.
In a preferred embodiment of the present invention, the mixed gas includes two or more of hydrogen, ethylene, carbon monoxide, methane, and acetylene.
In a preferred embodiment of the present invention, the carbon material in the first step has a specific surface area of 100 to 1000m2(ii)/g, wherein fine pores having a diameter of 2nm or less account for 80% or more of the volume of one or more of activated carbon, coke, pitch and carbon nanofibers. More preferably, the volume of the fine pores is 80 to 97%.
In a preferred embodiment of the present invention, the temperature of the vertical furnace or the horizontal furnace in the third step is 400-700 ℃.
The carbon nanofibers grown on the surface of the carbon material described above obtain various different structures depending on the temperature of the synthesis reaction and the metal catalyst, specifically: nickel in the temperature range of 400-630 ℃, or a binary or ternary metal catalyst containing nickel can be used to obtain a herringbone structure; a platelet structure can be obtained with iron in the temperature range of 550-650 ℃ or when using an iron-containing binary or ternary metal catalyst; and carbon nanofibers having a tubular structure in a temperature range of 650 ℃ or higher. In the present invention, the growth of carbon nanofibers that can achieve various structures as described above is possible, and is not particularly limited. In addition, the diameter of the synthesized carbon nanofibers is generally about 5 to 500 nm.
The carbon material-carbon nanofiber composite material manufactured by the method can be used for an electrode of an electric double layer capacitor, the volume expansion rate of the carbon material-carbon nanofiber composite material is 5-25%, and compared with a conventional composite material, the volume expansion rate is greatly reduced. The electrode capacity of an electric double layer capacitor using the composite material as an electrode is 20F/cc or more, and the electrode density is 0.8 to 1.4g/cc, which is equivalent to or higher than that of a conventional composite material.
In the carbon material-carbon nanofiber composite of the present invention, the specific surface area is reduced and the average diameter of pores is changed from micropores to mesopores, wherein the range of micropores is 40% to 70% and the range of mesopores is 30% to 60%, as compared with the basic carbon material, and the surface of the carbon material is modified to be suitable for the characteristics of an electrode of an electric double layer capacitor.
In addition, the specific surface area of the carbon material is only 100 to 1000m2And 80% or more of micropores (micropores having a diameter of 2nm or less) are used, so that a breakthrough change in capacity increase per unit volume can be made as compared with the conventional electric double cell capacitor using only a large specific surface area material.
In another aspect, the present invention provides an electric double layer capacitor including the above-described carbon material-carbon nanofiber composite as an electrode material, further including a conductive agent and a binder.
In a preferred embodiment of the present invention, the conductive agent includes one or more of ketjen black, carbon black, and acetylene black; the adhesive is polytetrafluoroethylene and/or styrene butadiene rubber.
The present invention will be described in detail and specifically with reference to the following examples to facilitate better understanding of the present invention, but the following examples do not limit the scope of the present invention.
Example 1
This example provides a preferred carbon material-carbon nanofiber composite material, wherein the carbon material used is NaOH activated coke with a specific surface area of 662m2In terms of a specific molar mass per gram, the mean pore diameter was 1.64nm and the microporosity was 86.4%. The preparation method of the carbon material-carbon nanofiber composite material comprises the following steps:
(1) adding a nickel catalyst with the weight of 1% of that of the carbon material into the carbon material and loading;
(2) to the carbon material carrying the nickel catalyst, argon gas was introduced at 100cc/min, and the mixture was replaced at 500 ℃ for 20 minutes, and then a mixed gas of ethylene/hydrogen (4: 1) was injected at a rate of 200 cc/min, and synthesized at 500 ℃ for 10 minutes to grow carbon nanofibers. The carbon nanofibers formed on the surface of the carbon material are in a herringbone structure having a fiber diameter of 5 to 500nm, and a surface photograph measured by an electron microscope before is shown in fig. 2. As shown in fig. 2, it was confirmed that the carbon nanofibers completely surrounded the surface of the carbon material.
In addition, the specific surface area of the carbon material was from 662m due to the growth of carbon nanofibers2The/g is reduced to 271m2The decrease was 59%, the average diameter of pores increased from 1.64nm to 3.74nm, and the volume of micropores increased by 50.1%, and the volume of mesopores became 49.9%, which became a structure having a large number of mesopores.
Example 2
This example provides a preferred carbon material-carbon nanofiber composite, which is prepared by a method further comprising the step of gasifying the surface of the carbon material at 400 ℃ for 1 hour by selectively using air, before growing carbon nanofibers on the surface of the carbon material containing the metal catalyst, and the remaining steps are the same as in example 1.
The surface photographs of the prepared composite materials were measured using a Scanning Electron Microscope (SEM), and the results are shown in fig. 3 and 4. Fig. 3 is a photograph of the surface of a carbon material that has been subjected to a gasification process only prior to the growth of carbon nanofibers, the gasification causing a gap or etching phenomenon to occur on the surface of the material. Fig. 4 is a photograph of the surface of the composite material in which the carbon nanofibers have grown on the surface of the carbon material (fig. 3) after gasification, and it can be seen that the carbon nanofibers have grown uniformly on the surface of the gasified carbon material.
The carbon material-carbon nanofiber composite showed a specific surface area from 662m through a series of gasification and growth processes of carbon nanofibers and an average pore diameter2The/g is reduced to 375m2The decrease in the number of mesopores per gram was about 43%, the average pore diameter was increased from 1.64nm to 3.12nm, the volume of micropores was 59.2%, and the volume of mesopores was 40.8%, which became a structure having a large number of mesopores.
Comparative example 1
This comparative example is a representative material of a commercially available capacitor and was produced by thermochemical production in kansai japan.
The capacitor has a length of 3166m2Specific surface area/g, micropore volume of 97%, mesopore volume of 3% and material with pores of average diameter 2.09 nm.
Comparative example 2
The present comparative example is the base material of the present invention, and is not prepared in the form of a composite material as in the present invention, but a composite material prepared using an activation method with an alkali compound. That is, the coke is heat-treated at 800 ℃ for 1 hour in nitrogen to remove volatiles, and then pulverized to 125 μm or less. After mixing the coke powder/sodium hydroxide at a weight ratio of 1/4, a separate nickel container was prepared in a stainless steel container, placed in the nickel container and heat-treated. At this time, the heat treatment was carried out under a nitrogen atmosphere at a flow rate of 100cc/min and a temperature of 700 ℃ for 1 hour.
The specific surface area of the material prepared by the method is 662m2In terms of a specific volume, the micropore volume was 86.4%, the mesopore volume was 13.6%, and the average pore diameter was 1.64 nm. The surface photograph of the material prepared by activating coke with alkali is shown in fig. 5.
In addition, the relative surface area, the volume of pores, and the average diameter of pores of the composite materials prepared according to the above comparative examples and examples were measured using a specific surface area-fine pore distribution measuring apparatus (Belsorp-max, Nippon Bell) to measure the specific surface area, the pore volume, and the diameter at a nitrogen relative pressure (P/P0) ═ 1, and the results are shown in table 1 below.
TABLE 1 measurement parameters of electrode materials provided in examples 1-2 and comparative examples 1-2
As shown in Table 1, comparative example 1 was a commercially available product, and had a very large specific surface area of 3000m2More than g. The number of fine pores was large, and therefore the pore volume was 5 to 8 times as large as that of comparative example 2 and examples 1 to 2. In addition, comparative example 2 has a large number of micropores (2nm or less), and thus the volume of the pores is larger, and the average diameter is smaller than examples 1 to 2. In the growth of carbon nanofibers of examples 1 and 2, the carbon nanofibers are grown fromIn the increase of mesopores (2-50nm), the specific surface area decreases and the volume and average diameter of the pores increase.
Experimental examples: manufacture and evaluation of electrodes
In this experimental example, an experiment was performed in which the composite materials prepared in the above examples and comparative examples were applied to an electrode. First, the composite materials prepared in the above examples and comparative examples were pulverized to 45 μm or less. To manufacture the electrode, 80 wt% of the composite material for capacitor, 10 wt% of ketjen black as a conductive agent, 10 wt% of PTFE as a binder and 50 to 400 wt% of a lubricant, etc. according to the specific surface area of the material are added and mixed. After calendering to prepare a sheet electrode and drying, the electrode is prepared to have a diameter of
Disc-shaped. The conductive agent, binder, lubricant, and the like used in the production of the electrode are common materials used in the production of the electrode, and are not particularly limited.
The weight, thickness, etc. of the electrodes were measured and assembled into a coin-shaped unit in a glove box. In the case of an aqueous solution, the monomers are assembled into a capacitor monomer in the atmosphere. The assembled capacitor monomer is charged to 2.5V in a non-aqueous solution under the condition of constant current and constant voltage, and then the current density (1 mA/cm) is adopted under the condition of constant current2～50mA/cm2) Discharge to 0V. After completion of the discharge, the capacitor was disassembled to measure the thickness of the electrode, and the volume expansion rate of the electrode was calculated by comparing with the thickness before evaluation, and the results thereof are shown in tables 2 and 3 and fig. 6. For the current collector, stainless steel having a thickness of 0.5mm was used.
Here, the capacity per unit volume is calculated from (mAh 3.6/[ voltage range at discharge ] [ weight or volume of positive electrode/negative electrode ]), and the capacity per unit weight [ F/g ] or the capacity per unit volume [ F/cc ] is obtained.
TABLE 2 Performance parameters of electrodes made of the composite materials of examples and comparative examples
As can be seen from the results in table 2, the discharge capacity per unit volume tends to be inversely proportional to the specific surface area and the electrode density. In comparative example 1, at a low current density (1 mA/cm)2) The capacity per unit weight was 35F/g, but the electrode density was low, and the capacity per unit volume was 12.2F/cc, which was only 35% by weight. However, the volume ratio of comparative example 2 and examples 1 to 2 is 85 to 92% by weight because of the high electrode density. Even in the large current characteristic (50mA capacity/1 mA capacity [% ])]) Comparative example 1 was also 26.2%, comparative example 2 was 44.6%, and examples 1 to 2 were 51.6% and 57.8%, respectively, which are excellent.
TABLE 3 Performance parameters of electrodes made of the composite materials of examples and comparative examples
| Material | Specific surface area (m)2/g) | Electrode Density (g/cc) | Electrode volume expansion ratio (%) |
| Comparative example 1 | 3166 | 0.35 | 4～9 |
| Comparative example 2 | 662 | 0.91 | 38～48 |
| Example 1 | 271 | 0.92 | 5～9 |
| Example 2 | 375 | 0.9 | 6～10 |
From the results shown in Table 3, it is understood that comparative example 1 using a material having a large specific surface area has a very small volume expansion rate of 4% to 9%, and that the density of the electrode comprising a conductive agent and a binder is usually very low, 0.34 to 0.37g/cc, resulting in a discharge capacity per unit volume of 1mA/cm2Is only 12F/cc at the current density of (2). In comparative example 2 containing a conductive agent and a binder, the electrode had a very high density of 0.91g/cc and a capacity per unit volume of 24F/cc, but the electrode had a very high volume expansion rate of 38 to 48%, and therefore, it was not suitable as a capacitor material.
However, as in the present invention, the results of using the carbon material-carbon nanofiber composite as an electrode of an electric double layer capacitor by growing carbon nanofibers on the surface using a carbon material having a small specific surface area show that, as shown in examples 1 and 2, even by surface modification, the electrode density hardly changes, and the volume expansion rate of the electrode is 5 to 10%, which is reduced by 70% or more compared to comparative example 2.
The embodiments of the present invention have been described in detail, but the embodiments are merely examples, and the present invention is not limited to the embodiments described above. Any equivalent modifications and substitutions to those skilled in the art are also within the scope of the present invention. Accordingly, equivalent changes and modifications made without departing from the spirit and scope of the present invention should be covered by the present invention.
Claims (10)
1. A carbon material-carbon nanofiber composite material is characterized in that the preparation method comprises the following steps:
adding a carbon material into a solution in which a metal catalyst is dissolved, and stirring until the weight of the metal catalyst loaded on the carbon material is 0.5-10% of the weight of the carbon material;
filtering the carbon material loaded with the metal catalyst, recovering the carbon material loaded with the metal catalyst and drying;
and step three, placing the dried carbon material loaded with the metal catalyst in a vertical furnace or a horizontal furnace, introducing inert gas at the rate of 50-100 cc/min for replacing for 10-40 minutes, and then supplying mixed gas at the rate of 100-200 cc/min for 5-20 minutes to grow carbon nanofibers on the surface of the dried carbon material loaded with the metal catalyst to form the carbon material-carbon nanofiber composite material.
2. The carbon material-carbon nanofiber composite material as claimed in claim 1, wherein the preparation method further comprises before introducing the inert gas, introducing air, oxygen, hydrogen, helium, argon or nitrogen to gasify the dried metal catalyst-loaded carbon material at 500 ℃ for 5 minutes to 5 hours at 250 ℃ until mesopores with a diameter of 2 to 50nm are formed on the surface of the dried metal catalyst-loaded carbon material.
3. The carbon material-carbon nanofiber composite material according to claim 1, wherein the metal catalyst is selected from one or more of salts of Fe, Ni, Co, Mg, Cu, Mn, Mo, and oxides thereof.
4. The carbon material-carbon nanofiber composite material according to claim 1, wherein the particle size of the metal catalyst is 5nm to 500 nm.
5. The carbon material-carbon nanofiber composite material according to claim 1, wherein the solvent of the metal catalyst is distilled water or an aliphatic alcohol.
6. The carbon material-carbon nanofiber composite material according to claim 1, wherein the mixed gas includes two or more of hydrogen, ethylene, carbon monoxide, methane, and acetylene.
7. The carbon material-carbon nanofiber composite material as claimed in claim 1, wherein the temperature of the vertical furnace or the horizontal furnace in the third step is 400 to 700 ℃.
8. The carbon material-carbon nanofiber composite material as claimed in claim 1, wherein the carbon material in the first step has a specific surface area of 100 to 1000m2And/g, the volume of the micro pores is more than 80 percent of one or more of activated carbon, coke, asphalt and carbon nanofibers.
9. An electric double layer capacitor, wherein an electrode material of the electric double layer capacitor comprises the carbon material-carbon nanofiber composite material as set forth in any one of claims 1 to 8.
10. The double layer capacitor of claim 9 wherein the electrode material further comprises a conductive agent and a binder;
the conductive agent comprises one or more of Ketjen black, carbon black and acetylene black; the adhesive is polytetrafluoroethylene and/or styrene butadiene rubber.
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