KR101079317B1

KR101079317B1 - Manufacturing method of graphene electrode for supercapacitor and supercapacitor graphene electrode manufactured by the method

Info

Publication number: KR101079317B1
Application number: KR1020090114933A
Authority: KR
Inventors: 노광철; 박선민; 이재원; 이선영; 조민영; 박진배; 신달우
Original assignee: 한국세라믹기술원
Priority date: 2009-11-26
Filing date: 2009-11-26
Publication date: 2011-11-04
Also published as: KR20110058223A

Abstract

The present invention, polytetrafluoroethylene for improving the flexibility of the electrode by inhibiting brittleness of the electrode by the addition of molasses, molasses to improve the adhesion between the graphene powder, conductive material, the graphene powder particles to increase the filling density And mixing the dispersion medium to form a graphene mixture on a dough, filling the graphene mixture into a mold according to the shape of an electrode, pressing molding the press and sintering the compacted molding at 150 ° C to 400 ° C. It relates to a method for producing a graphene electrode for a supercapacitor comprising, and a graphene electrode for a supercapacitor prepared thereby. According to the present invention, it is possible to manufacture a graphene electrode for supercapacitors having improved conductivity and excellent output characteristics compared to existing activated carbon, high specific storage capacity, and no electrode loss, which are advantageous in yield and manufacturing cost.

Supercapacitors, graphene, molasses, polytetrafluoroethylene

Description

Manufacturing method of graphene electrode for supercapacitor and supercapacitor graphene electrode manufactured by this method {Manufacturing method of graphene electrode for supercapacitor and supercapacitor graphene electrode manufactured by the method}

The present invention relates to a supercapacitor electrode and a manufacturing method thereof, and more particularly, to a supercapacitor having improved conductivity and superior output characteristics compared to existing activated carbon, and having a high specific capacitance, and having no electrode loss, which is advantageous for yield and manufacturing cost. The present invention relates to a graphene electrode and a graphene electrode for a supercapacitor manufactured accordingly.

Supercapacitors are also commonly referred to as Electric Double Layer Capacitors (EDLCs), Supercapacitors or Ultracapacitors, which are the interface between electrodes and conductors and the electrolyte solution impregnated therewith. By using a pair of charge layers (electric double layers) each having a different sign, the deterioration due to repetition of the charge / discharge operation is very small and requires no maintenance. Accordingly, supercapacitors are mainly used in the form of backing up IC (integrated circuit) of various electric and electronic devices. Recently, the use of supercapacitors has been widely applied to toys, solar energy storage, and hybrid electric vehicle (HEV) power supply. have.

Such a supercapacitor generally includes two electrodes of a positive electrode and a negative electrode impregnated with an electrolyte, a separator made of a porous material interposed between the two electrodes to allow only ion conduction, and to prevent insulation and short circuit, and an electrolyte solution. It has a unit cell consisting of a gasket for preventing leakage and preventing insulation and short circuit, and a metal cap as a conductor for packaging them. One or more unit cells (usually, 2 to 6 in the case of a coin type) configured as described above are stacked in series and completed by combining two terminals of a positive electrode and a negative electrode.

The electrode constituting the supercapacitor mainly uses activated carbon as an electrode active material. The capacitance of the supercapacitor is determined by the amount of charge accumulated in the electric double layer, and the amount of charge becomes larger as the surface area of the electrode is larger. Therefore, since activated carbon has a high specific surface area of 300 m 2 / g or more, it is suitable as an electrode material of a supercapacitor requiring a large surface area.

A supercapacitor using activated carbon powder as an electrode is disclosed in Japanese Patent Laid-Open No. 4-44407. The electrode proposed in this publication is a solid activated carbon electrode obtained by solidifying a mixture of activated carbon powder with a thermosetting resin such as a phenol resin.

In general, the activated carbon for producing the electrode of the supercapacitor mainly has a specific surface area of 1500 m 2 / g or more. Recently, however, the most difficult point in manufacturing an electrode for a supercapacitor has been newly faced with a problem that it is difficult to increase the capacity per volume due to an electrode active material having a high specific surface area. In other words, when activated carbon having a high specific surface area is used, the capacity per unit mass is increased, but the electrode density is decreased due to the high specific surface area, and thus the capacity of the activated carbon is lowered compared to the unit volume.

2. Description of the Related Art Conventionally, two methods are mainly used to manufacture activated carbon electrodes for supercapacitors.

The first method is a method of manufacturing an electrode by coating an activated carbon mixture in the form of a slurry, which is a mixture of activated carbon, a binder, a conductive material, and a dispersion medium on an aluminum foil, and then cutting or punching to a predetermined size after drying (coating method). ).

In the second method, the activated carbon mixture in the form of a paste mixed with activated carbon, a binder, a conductive material, and a dispersion medium is stretched and rolled into two rolls and processed into a sheet, and the sheet is cut or punched to form an electrode. It is a method of manufacturing (rolling method).

1 is a process chart for explaining a manufacturing method (rolling method) of a supercapacitor electrode according to the prior art, in which the activated carbon mixture in a paste state is stretched and rolled onto a sheet 10 and then the sheet 10 Shows an electrode 20 fabricated by punching.

However, the conventional activated carbon electrode 20 manufactured as described above has a limitation in rolling the electrode due to the porosity and high specific surface area of the activated carbon, and generally exhibits an electrode density of about 0.5 to 0.6 g / cm 3, which is a sieve. It acts as a big factor to limit the appropriate dose. In addition, since only a portion of the electrode is used by cutting and punching, there is a problem that the loss rate of the electrode is also higher than 10%. That is, the electrode density is small, so that it does not exhibit a high capacity per volume, and as shown in FIG. 1, the excess sheet 10 is discarded after being cut or punched, resulting in a large amount of electrode loss, resulting in a decrease in yield and an increase in manufacturing cost. There is a problem.

The present invention has been made to solve the above problems, the object of the present invention is to improve the conductivity and excellent output characteristics compared to the existing activated carbon, the specific capacity is high, there is no electrode loss amount, the supercapacitor advantageous for the yield and manufacturing cost The present invention provides a method for manufacturing a graphene electrode and a graphene electrode for a supercapacitor prepared accordingly.

The present invention, in the manufacturing method of the electrode for the supercapacitor, the electrode by inhibiting the brittleness of the electrode by the addition of molasses, molasses to increase the filling density by improving the adhesion between the graphene powder, the conductive material, the graphene powder particles Mixing the polytetrafluoroethylene and the dispersion medium to improve the flexibility of the to form a graphene mixture on the dough, filling the graphene mixture into a mold according to the shape of the electrode and press-molded by a press and the compacted molding Sintering at 150 ° C. to 400 ° C., wherein the conductive material is added in an amount of 1 to 35 parts by weight based on 100 parts by weight of graphene powder, and the molasses is added in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of graphene powder. The polytetrafluoroethylene is added in an amount of 1 to 20 parts by weight based on 100 parts by weight of graphene powder, and the dispersion medium is 100 parts by weight of graphene powder. About 5 to 80 provides a method of manufacturing a graphene electrode for the supercapacitor of adding parts by weight.

The graphene powder may be made of a single layer graphene, bilayer graphene, multilayer graphene or graphene in the form of a tube.

The specific surface area of the graphene powder is in the range of 300 to 2800 m 2 / g, and the particle size of the graphene powder is preferably in the range of 0.9 to 20 μm in order to facilitate electrode molding and dispersion.

It is preferable to apply press molding at a pressure of 5 to 20 ton / cm 2 to perform compression molding.

The present invention also provides a graphene electrode for a supercapacitor, which is manufactured by a method for producing a graphene electrode for a supercapacitor and has a pellet form.

The graphene electrode for the supercapacitor may have an electrode density of 0.5 to 2 g / cm 3.

According to the present invention, the electrode density is drastically increased by the addition of graphene powder and molasses, and the pressing process is performed by pressing, thereby having a high capacity per unit volume. Graphene has a higher electrode density than conventional activated carbon, and when graphene powder is used, the capacity increases per unit volume compared to the case of using activated carbon powder, as well as the conductivity and output characteristics are excellent, thereby increasing the specific storage capacity. Graphene powder particles (especially in the form of tubes) have elasticity due to the voids formed in them and the spaces between the particles, which are difficult to solidify into tight tissues even when compressed, and are spaced apart from each other, causing reduction in electrode density. As the molasses is added, the adhesion strength between the graphene particles is increased to increase the filling density, and the pressing process by the press further increases the density, thereby increasing the electrode density, thereby increasing the graphene electrode for the supercapacitor of the present invention. Has capacity.

The addition of molasses can increase the packing density by improving the adhesion between the graphene powder particles, but the electrode brittle (brittle) has a problem of falling flexibility of the electrode, in order to suppress the polytetrafluoroethylene with molasses When added, the flexibility of the electrode is improved.

In addition, it is possible to obtain the electrode of the desired shape according to the shape of the mold without cutting or punching process, the production is simple, and most of all there is no electrode loss amount, it has a great effect on yield and cost reduction.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments are provided to those skilled in the art to fully understand the present invention, and may be modified in various forms, and the scope of the present invention is limited to the embodiments described below. It doesn't happen. Like numbers refer to like elements in the figures.

In order to manufacture a graphene electrode for a supercapacitor according to a preferred embodiment of the present invention by improving the adhesion between the graphene powder, the conductive material, the graphene powder particles to increase the filling density by the addition of molasses, molasses A graphene mixture is prepared by mixing polytetrafluoroethylene (PTFE) and a dispersion medium for improving the flexibility of the electrode by suppressing brittleness of the electrode.

In the blending amount of the graphene mixture, 1 to 35 parts by weight of conductive material, 0.1 to 20 parts by weight of molasses, and 1 to 20 parts by weight of polytetrafluoroethylene (PTFE) are added to 100 parts by weight of graphene powder. desirable. The content of the dispersion medium is not particularly limited, but is 80 parts by weight or less, preferably 5 to 80 parts by weight based on 100 parts by weight of the graphene powder.

Graphene is a two-dimensional, one-atomic carbon structure created by Andre Gaming's team at the University of Manchester, UK, and a team at the Russian Institute of Microelectronics, and can be made into tubes by rolling or bending it. Graphene is a stack of epitaxial layers of graphene, a plate of carbon atoms one atom thick, and each graphene layer may have an electronic structurally independent structure. It is called Multilayer Epitaxial Graphene (MEG). Multilayer epitaxial graphene can also be rolled or bent to form a tube. In the present invention, such a single layer graphene, bilayer graphene, multilayer graphene or a powder consisting of graphene in the form of a tube can be used. Graphene has a higher electrode density than conventional activated carbon, and when graphene powder is used, the capacity increases per unit volume compared to the case of using activated carbon powder, as well as the conductivity and output characteristics are excellent, thereby increasing the specific storage capacity. In addition, molasses serves to bind the graphene powder and the conductive material particles. It is preferable that the specific surface area of the graphene powder used is 300-2800 m <2> / g. The particle size of the graphene powder is preferably in the range of 0.9 to 20 μm in order to facilitate electrode molding and dispersion.

However, the graphene powder particles (especially in the form of tubes) have elasticity due to the voids formed in them and the spaces between the particles, so that the graphene powder particles cannot be solidified into a tight structure even when pressed, and are separated from each other unless there is any binder. It causes a decrease in electrode density.

To this end, in the present invention, molasses is added as a functional additive (binder), and a pressing process by a press 130 (see FIG. 2) is performed. That is, the molasses increases the packing density by improving the adhesion between the graphene particles, and the pressing process by the press 130 further improves the density. This in turn improves the electrode density resulting in a high capacity per unit volume.

The conductive material is not particularly limited as long as it is an electronic conductive material that does not cause chemical change, and examples thereof include metal powder or metal such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel, aluminum, silver, and the like. Fiber and the like.

The polytetrafluoroethylene (PTFE) is added to improve brittleness of the electrode by suppressing brittleness of the electrode by adding molasses. The addition of molasses can increase the packing density by improving the adhesion between the graphene powder particles, but the electrode brittle (brittle) has a problem that the flexibility of the electrode is inferior, when poly tetrafluoroethylene is added with molasses of the electrode Flexibility is improved. In addition, polytetrafluoroethylene serves to bond the graphene powder and the conductive material particles. Instead of the polytetrafluoroethylene, a material capable of improving the flexibility of the electrode may be used. Examples of the flexible material include polyvinylidenefloride (PVDF), carboxymethylcellulose (CMC), and polyvinyl alcohol ( poly vinyl alcohol (PVA), poly vinyl butyral (PVB), poly-N-vinylpyrrolidone (PVP), styrene butadiene rubber (SBR) and the like can be used.

The dispersion medium may be an organic solvent such as ethanol (EtOH), acetone, isopropyl alcohol, methyl pyrrolidone (NMP), propylene glycol or water.

As such, the graphene mixture used in the preparation of the electrode of the present invention is a dough phase in which a small amount of a dispersion medium is used, and includes graphene powder, a conductive material, molasses, polytetrafluoroethylene and a dispersion medium.

Hereinafter, a method of obtaining the graphene mixture will be described in more detail.

First, the powdery conductive material is dry mixed with the graphene powder to obtain a powder mixture. Then, a dispersion medium is added to molasses and polytetrafluoroethylene (PTFE) and sufficiently dispersed by wet mixing to obtain a mixed solution of molasses and polytetrafluoroethylene. Then, the powder mixture and the mixed solution are mixed to obtain a graphene mixture on dough. In this case, since the graphene mixture is in the form of dough, it may be difficult to uniformly mix (complete dispersion), using a mixer such as a planetary mixer for a predetermined time (for example, 10 minutes to 12 hours). Stirring to obtain a graphene mixture suitable for the preparation of the electrode of the present invention. Mixers, such as planetary mixers, allow for the production of uniformly mixed graphene mixtures.

The graphene mixture prepared as above is press-molded using a press molding machine as shown in FIG.

Figure 2 is a process chart for explaining the manufacturing method of the graphene electrode according to the present invention, which is a schematic configuration of a press molding machine used in the production of the electrode of the present invention is illustrated.

Referring to FIG. 2, the press molding machine includes a molding die 110 in which the mold 120 is formed, and a press 130 installed on an upper end of the molding die 110 and moved up and down. The graphene mixture 100 ′ is charged into the mold 120 of the mold 110 and then press-molded by press 130. At this time, the shape of the mold 120 is the same as the shape of the electrode 100 to be intended. In addition, although FIG. 2 illustrates a state in which one mold 120 is formed in the mold 110, it is preferable that a plurality of molds 120 are formed in the mold 110. Of course, when a plurality of mold 120 is formed, a plurality of presses 130 are installed in the same number. And the vertical movement of the press 130 may be used, such as hydraulic, pneumatic or electric press (cam method). At this time, it is preferable that the pressurization pressure of the press 130 is 5-20 ton / cm <2>.

The electrode 100 that has undergone the press-compression process as described above is subjected to the sintering process according to the present invention. The sintering process is carried out at a temperature of 150 ° C to 400 ° C, preferably 150 ° C to 300 ° C. In this case, when the sintering temperature is less than 150 ℃ difficult evaporation of the dispersion medium is not preferable, and when the high temperature sintering exceeding 400 ℃ is not preferable because the oxidation of the conductive material and molasses and polytetrafluoroethylene (PTFE) occurs. Therefore, it is preferable that sintering temperature is at least 150 degreeC or more and does not exceed 400 degreeC. And the sintering process is preferably carried out for about 10 minutes to 6 hours at the above temperature. In this sintering process, the electrode 100 is dried (dispersed medium evaporates) and at the same time, the powder particles are bound to improve the strength of the electrode 100.

The electrode 100 according to the present invention manufactured as described above can be applied directly to the capacitor (product) without a separate finishing process (cutting, punching, etc.), which is the same shape as the shape of the mold 120 as a pellet (pellet) Has And the electrode 100 of the present invention manufactured as described above has an electrode density of 0.5 ~ 2g / ㎠, it is possible to implement a capacity of 30F / cc or more.

A supercapacitor that realizes a high energy density per unit volume may be manufactured using the electrode manufactured by using the graphene mixture described above.

For example, the graphene electrode 100 manufactured using the graphene mixture according to the present invention may be usefully applied to a small coin-type capacitor as an ultra high capacity. 3 is a state diagram of the use of the graphene electrode 100 according to the present invention, showing a cross-sectional view of a coin-type capacitor to which the graphene electrode 100 is applied. In FIG. 3, reference numeral 150 denotes a metal cap as a conductor, 160 denotes a separator made of a porous material for preventing insulation and short circuit between the upper and lower graphene electrodes 100, and reference numeral 170 denotes a leakage of electrolyte solution. Gaskets for insulation and short circuit protection. At this time, the electrode 100 is firmly fixed by the metal cap 150 and the adhesive.

The method of manufacturing the supercapacitor will be described in more detail, to prevent a short circuit between the positive electrode manufactured by using the graphene mixture, the negative electrode manufactured by using the graphene mixture, and the positive electrode and the negative electrode between the positive electrode and the negative electrode. A separator may be prepared, and an electrolyte solution in which an electrolyte is dissolved may be injected between the anode and the cathode, and then sealed by a gasket.

The separator may be a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyester nonwoven fabric, a polyacrylonitrile porous separator, a poly (vinylidene fluoride) hexafluoropropane copolymer porous separator, a cellulose porous separator, a kraft paper or a rayon fiber, and the like. If the separator is generally used in the field is not particularly limited.

On the other hand, the electrolyte of the electrolyte solution filled in the hybrid supercapacitor of the present invention can be used that the lithium salt is dissolved as a non-aqueous electrolyte. The lithium salt is not particularly limited as a lithium salt commonly used in capacitors, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , Li (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiSbF ₆ or LiAsF ₆ Etc.

Although the solvent of the said electrolyte solution is not specifically limited, A cyclic carbonate solvent, a linear carbonate solvent, an ester solvent, an ether solvent, a nitrile solvent, and an amide solvent can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, or the like may be used as the cyclic carbonate solvent, and dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, or the like may be used as the chain carbonate solvent. The ester solvent may be methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, etc., and the ether solvent may be 1,2-dimethoxyethane, 1 , 2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran, etc. may be used, and acetonitrile may be used as the nitrile solvent, and the amide solvent may be used. Dimethylformamide and the like can be used.

Hereinafter, specific test examples and comparative examples of the present invention will be described. However, the following examples are merely provided to explain the present invention in more detail, and do not limit the technical scope of the present invention.

100 parts by weight of graphene powder and 10 parts by weight of Super-p black (manufactured by Kuraray Chemical Co., Ltd., Japan) were dry mixed. The graphene powder is a powder synthesized by the Hummer's method, which is a compound synthesized with graphene by hydrazine reduction of graphite oxide chemically oxidized and exfoliated graphite powder. Used. Separately, 5 parts by weight of molasses (domestic, Ltd. Yuwon Molasses) and 10 parts by weight of polyvinyl alcohol (PVA) as a softener were added to 35 parts by weight of distilled water and mixed. Then, the two mixtures were added to a planetary mixer (manufacturer: T.K, model name: Hivis disper), mixed and stirred for 40 minutes, and dispersed to obtain a graphene mixture on a dough.

Next, the graphene mixture was filled in an appropriate amount into the mold 120 of the press molding machine as shown in FIG. 2, and then compressed at a pressure of 12 ton / cm 2 for 2 seconds. The pressed molding was put into an electric oven (manufactured by International Engineering Co., Ltd.) maintained at 250 ° C. and sintered for 3 hours to prepare an electrode specimen having a diameter of 12 mm and a height of 1.2 mm.

Electrode density, capacitance, equivalent series resistance (ESR), and leakage current were measured by applying the prepared electrode specimens to a 20 mm diameter 32 mm coin cell, and the results are shown in Table 1 below. In this case, in preparing a coin cell, propylene carbonate (PC) / TEABF4 (tetraethylammonium tetrafluoborate) 1M was used. The charge was carried out for 30 minutes to 2.5V at 10mA, discharge was carried out in 1V from 2.5V to 1V. Equivalent series resistance (ESR) was performed at 1 kHz, and the leakage current was charged at 2.5V for 30 minutes.

Comparative Example

An activated carbon electrode made by a conventional manufacturing method was used as this comparative example. YP17 activated carbon powder (Japan, Kuraray Chemical Co., Ltd.), Super-p black, polytetrafluoroethylene (PTFE) and ethanol are mixed (YP17 activated carbon: Super-p black: polytetrafluoroethylene: acetone 100: 8: 15 Mixed at a weight ratio of 80) to obtain a mixture of activated carbon on the dough. The activated carbon mixture on the dough was subjected to a rolling stretching process and then punched to prepare electrode specimens. The prepared electrode specimens were applied to a coin cell having a diameter of 20 mm and a height of 32 mm. And the electrode density, capacity, equivalent series resistance (ESR), leakage current was measured in the same manner as in the above embodiment, the results are shown in Table 1 below.

division Comparative example Example Electrode Density (g / cm 3) 0.61 0.87 Capacity (F / cc) 18.4 25.8 ESR (Ω) 2.6 2.4 Leakage Current 160 160

As shown in Table 1, the coin cell manufactured using the electrode according to the present invention (example) can be seen that the electrode density is improved by more than 30% compared to the coin cell prepared according to the comparative example, It can be seen that the proper dose is also improved by 30% or more.

In addition, the ESR also shows an improved value due to the electrode density improvement, and it can be seen that the present invention implements the overall characteristic improvement of the supercapacitor.

As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation by a person of ordinary skill in the art within the scope of the technical idea of this invention is carried out. This is possible.

1 is a process chart for explaining a manufacturing method (rolling method) of a supercapacitor electrode according to the prior art.

Figure 2 is a process chart for explaining the manufacturing method of the graphene electrode according to the present invention.

3 is a state diagram of use of the graphene electrode 100 according to the present invention.

100: graphene electrode 110: mold

120: mold 130: press

150: metal cap 160: separator

170: gasket

Claims

In the manufacturing method of the electrode for a supercapacitor,

A mixture of polytetrafluoroethylene and a dispersion medium for improving the flexibility of the electrode by improving the adhesion between the graphene powder, the conductive material, and the graphene powder particles to suppress the brittleness of the electrode by adding molasses and molasses to increase the filling density. To form a graphene mixture on the dough;

Filling the graphene mixture into a mold according to the shape of an electrode and pressing molding the press mixture; And

Sintering the compacted molding at 150 ° C to 400 ° C,

The conductive material is added 1 to 35 parts by weight based on 100 parts by weight of graphene powder, the molasses is added to 0.1 to 20 parts by weight based on 100 parts by weight of graphene powder, the polytetrafluoroethylene is 100 parts by weight of graphene powder 1 to 20 parts by weight with respect to the dispersion medium, 5 to 80 parts by weight based on 100 parts by weight of the graphene powder,

Specific surface area of the graphene powder is in the range of 300 ~ 2800 m 2 / g, the particle size of the graphene powder is used for graphene supercapacitors, characterized in that in the range of 0.9 to 20㎛ to facilitate electrode molding and dispersion Method for producing a pin electrode.

The method of claim 1, wherein the graphene powder,

Method for producing a graphene electrode for a supercapacitor, characterized in that consisting of graphene of single layer, double layer graphene, multilayer graphene or tube form.

delete

The method of manufacturing a graphene electrode for a supercapacitor according to claim 1, wherein the press is press-molded by applying a pressure of 5 to 20 ton / cm 2.

A graphene electrode for supercapacitors, which is prepared by the method for producing a graphene electrode for supercapacitors according to claim 1 and has a pellet form.

The graphene electrode of claim 5, wherein the graphene electrode has an electrode density of 0.5 to 2 g / cm 3.