JP2004186195A - Method of manufacturing electrode sheet for electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable an electric double layer capacitor to be improved in long-term durability and reliability. <P>SOLUTION: A method of manufacturing an electrode sheet for an electric double layer capacitor includes a drying process composed of two steps, one is a continuous drying step where the electrode sheet is dried up passing through a drying chamber as it is fed from a rolled-up electrode sheet and then rolled up again into the rolled-up electrode sheet, and the other is a vacuum drying step where the rolled-up electrode sheet subjected to the continuous drying step is housed in a vacuum chamber and then dried out, whereby the electrode sheet can be made extremely small in residual moisture content and residual IPA content. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an electrode sheet for an electric double layer capacitor, and more particularly to an improved method for drying an electrode sheet.
[0002]
[Prior art]
Electric double-layer capacitors (capacitors) have farad-class large capacities and have excellent charge-discharge cycle characteristics, so they are used as backup power supplies for electric equipment and batteries for various transport vehicles such as automobiles. From the viewpoint of effective use of energy, use in applications such as storage of nighttime electric power is being studied in the future.
[0003]
The structure of the electric double layer capacitor and the mechanism of charge and discharge will be briefly described. First, the structure is a sheet (hereinafter, referred to as an electrode sheet) in which a current collector foil is sandwiched between two sheets of activated carbon (sheet electrodes). ) And an insulating separator capable of penetrating ions (hereinafter referred to as a separator), in which a polarizable electrode for an electric double-layer capacitor is immersed in an ionic solution. A voltage that does not cause electrolysis is applied to the polarized electrode for an electric double layer capacitor, and positive and negative electricity are applied to the interface to charge and discharge.
[0004]
Therefore, due to the nature of the electric double layer capacitor as described above, when a voltage is applied when moisture remains on the electrode sheet, the moisture may cause electrolysis and cause a decrease in the performance of the electric double layer capacitor. In the manufacturing process, a drying step for removing the water content of the electrode sheet to a practically acceptable level is required.
[0005]
As a method of manufacturing such an electric double layer capacitor including a drying step for removing water, for example, a polarizable electrode for an electric double layer capacitor including an electrode sheet and a separator is used as a container for an electric double layer capacitor. After being accommodated in the bottom cylindrical container, the container was sealed with a lid having a liquid inlet, and then the container was dried in an atmosphere having a dew point of −20 ° C. or less, and a non-aqueous electrolyte was injected from the liquid inlet. There is a method of closing the liquid inlet (for example, see Patent Document 1).
Further, for example, there is a method of mixing and kneading raw materials for a sheet-like electrode composed of a carbon-based powder, a conductive auxiliary agent, and a binder, and performing a drying step of removing moisture on the kneaded material (for example, see Patent Document 2). ).
[0006]
[Patent Document 1]
JP-A-2000-49052 (pages 3-4)
[0007]
[Patent Document 2]
JP 2001-307964 A (page 4-5)
[0008]
[Problems to be solved by the invention]
As described above, when water is mixed in the electrode sheet when a voltage is applied to the polarizable electrode for an electric double layer capacitor, the water causes electrolysis, and thus the capacitance of the electric double layer capacitor is increased. Problems such as a decrease in resistance, an increase in resistance, and a deterioration in durability occur.
[0009]
However, since the activated carbon (carbonaceous powder) constituting the electrode sheet is porous, it has a very high water absorption property. In addition, when mixing the respective raw materials, an alcohol-based organic material is used to facilitate the mixing. Since the solvent is added, there is a contradictory problem that water is inevitably present in the raw material.
[0010]
Therefore, in order to ensure long-term durability and reliability of the electric double-layer capacitor, a drying step in which the remaining amount of water and organic solvent in the electrode sheet is extremely low is indispensable in the manufacturing process.
However, in Patent Document 1 described above, since the polarizable electrode for an electric double layer capacitor composed of an electrode sheet and a separator is rolled in a cylindrical shape and dried in a container, the center of the polarizable electrode for an electric double layer capacitor is dried. It is difficult to dry the part well.
[0011]
Further, in Patent Document 2 described above, since the drying is performed at the stage where the raw materials of the sheet electrode are mixed and kneaded instead of the electrode sheet, the kneaded material is then rolled to produce a sheet electrode, and further the sheet electrode is formed. There is a problem that the sheet-shaped electrode absorbs moisture again until the electrode is bonded to the foil and completed as an electrode sheet.
[0012]
The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the remaining amount of water and the like in an electrode sheet to an extremely low value. An object of the present invention is to provide a method for manufacturing an electrode sheet for an electric double layer capacitor that can maintain durability and reliability over a long period of time.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing an electrode sheet for an electric double layer capacitor according to the present invention comprises the steps of mixing and kneading raw materials including a carbonaceous powder, a conductive auxiliary agent and a binder to form a molding material; Forming and rolling a material to form a long sheet-like electrode, laminating the sheet-like electrode and a current collector foil to form an electrode sheet, and drying the electrode sheet. In particular, the drying step is a continuous drying in which the electrode sheet is fed through a drying chamber of a continuous dryer while being fed out, and the rolled electrode sheet that has passed through the continuous drying is housed in a vacuum chamber of a vacuum dryer. And vacuum drying for drying (claim 1).
[0014]
According to this configuration, the drying step is performed after the electrode sheet is formed, that is, the electrode sheet itself is dried in a completed state, and the drying step is performed in a state where the electrode sheet is spread, and continuous drying and vacuum drying are performed. Therefore, the residual amounts of water and organic solvent in the electrode sheet can be set to extremely low values.
[0015]
By the way, the drying of the sheet-shaped electrode is usually performed by blowing heated air from a nozzle onto the sheet-shaped electrode, and the heated air is subjected to fine metal powder in a pipe (for example, a pipe connecting the heater and the nozzle) or a heating wire in the heater. In this case, the powder may be mixed with the surface of the electrode sheet and become an impurity, thereby contributing to a reduction in the durability of the electric double layer capacitor.
[0016]
Therefore, in order to ensure long-term durability and reliability of the electric double layer capacitor, when using heated air in the drying process of the electrode sheet, it is very important to strictly control the amount of impurities mixed in the heated air. Is important.
In this regard, in the present invention, the continuous drying is performed by blowing heated air through a hepa filter (Claim 2). These impurities can be removed by a hepafilter capable of collecting 99.97% or more of particles of 0.3 μm or more, so that the impurities do not adhere to the electrode sheet.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a manufacturing process for manufacturing an electrode sheet for an electric double layer capacitor (hereinafter, referred to as an electrode sheet). The raw materials for producing the sheet-like electrode constituting the electrode sheet include activated carbon as a carbonaceous powder, carbon black as a conductive aid, PTFE (polytetrafluoroethylene) powder as a binder, and liquid IPA as a binder aid. Isopropyl alcohol).
[0018]
First, each raw material is measured. Next, activated carbon and carbon black are put into a container of a mixer, and these are mixed by a rotating stirring blade. Thereby, activated carbon and carbon black are mixed as uniformly as possible.
Then, PTFE and IPA are charged into the container of the mixer, and these are mixed with the mixture of activated carbon and carbon black. Thereby, the activated carbon, the carbon black, and the PTFE are mixed, and the PTFE is fiberized, so that the activated carbon and the carbon black are entangled.
[0019]
Next, the mixed mixture is accommodated in a container of a kneader (kneader), covered with a lid, and kneaded by rotating a blade while pressing the mixture with the lid. By this kneading, the mixture is kneaded in a clay state, and the PTFE is further fiberized to bind the activated carbon and the carbon black. At this time, the temperature of the container, the lid and the blade of the kneading machine is controlled to, for example, 90 ° C.
Next, the kneaded material kneaded by the above kneading machine is accommodated in a container of the knurling machine 9 to be made into fine particles, and then charged into a calendering machine, and the mixture is formed into a sheet by two rollers. The formed sheet-shaped body is wound up by a winding roller. At this time, the thickness of the sheet-shaped molded body is, for example, 200 μm.
[0020]
Next, in a roll rolling step, the sheet-shaped compact is rolled through two rollers. By performing this roll rolling step a plurality of times, a sheet-like electrode having a predetermined thickness, for example, 160 μm is formed. Incidentally, in the final step of the roll rolling, both end portions in the width direction of the sheet electrode are cut by a cutter. What has been described above is the step of forming the sheet-like electrode.
Next, in a laminating step, the rolled sheet electrode is formed into an aluminum foil-bonded electrode sheet as a current collector foil. This is the step of preparing an electrode sheet. Then, a drying step including continuous drying and vacuum drying is performed on the roll-shaped electrode sheet.
[0021]
Here, the details of the continuous drying and the vacuum drying in the above-described drying step will be described with reference to FIGS.
First, in the continuous drying, as shown in FIG. 2, in a continuous drying device 2 for the electrode sheet 1, the electrode sheet 1 wound in a roll shape is passed through one of the rollers and dried through a drying chamber 3. The rolled electrode sheet 1 is wound by another roller and rolled again.
[0022]
In this case, the roller that feeds out the electrode sheet 1 performs tension control for applying a braking force according to the roll diameter (the wound thickness) of the electrode sheet 1, and the roller that rewinds the dried electrode sheet 1. In the roller 4 one stage before, edge control for displacing the electrode sheet 1 in the width direction is performed so that the tension of the electrode sheet 1 is constant in each portion in the width direction.
[0023]
A plurality of nozzles 5 for blowing heated air from above and below to the electrode sheet 1 to be continuously dried are provided in the drying chamber 3 described above. The number of nozzles 5 may be any number as long as it is sufficient to dry the electrode sheet 1. The heated air is generated by a first heated air supply means 6 having a heater 6a and a fan 6b as shown in FIG. 3 and then passed through a hepa filter 7 (High Efficiency Particulate Air Filter) to have a second air having a heater 8a and a fan 8b. The hot air is supplied to the nozzle 5 via the hot air supply means 8.
[0024]
The hepa filter 7 has a capability of collecting 99.97% of particles having a size of 0.3 μm or more by improving the dust collection area by forming a nonwoven fabric of resin fibers into a pleated shape. Metal powder and powder degraded by the heater are removed. However, since the density of the hepa filter 7 is very high due to its high trapping ability, the resistance reduces the momentum of the heated air. Further, the heat capacity of the hepa filter 7 is high because of its density, and the temperature of the heated air that has passed through the hepa filter 7 also decreases. Therefore, in this embodiment, the heated air that has passed through the hepa filter 7 is again blown onto the electrode sheet 1 from the nozzle 5 after the temperature and pressure are increased using the second heated air supply unit 8. I have.
[0025]
As described above, since the heated air that has passed through the hepa filter 7 has very little impurities in the air, the pipe connecting the second heated air supply means 8 and the nozzle 5 in this embodiment is made of corrosion-resistant stainless steel. In addition, for example, a nichrome wire serving as the heater 8b is covered with a stainless steel pipe having the same corrosion resistance to prevent dust generation.
[0026]
For this reason, the heating air from the second heating air supply means 8 also has very few impurities, but the configuration for generating the heating air is not necessarily limited to this depending on the environment of the drying process.
[0027]
As described above, the continuous drying performed by spreading the electrode sheet 1 effectively removes moisture and IPA residues contained in the electrode sheet 1.
The temperature of the heated air blown to the electrode sheet 1 is, for example, about 120 ° C. If the temperature is higher than this, a problem of deterioration of the adhesive or the like occurs.
In the drying chamber 3, the electrode sheet 1 is meandered and dried while being folded several times, or a far-infrared ray device or the like is installed in the drying chamber 3 while blowing hot air. There is no problem even if the drying ability is further increased.
[0028]
Further, in order to prevent dust from being generated on the electrode sheet 1, not only the heater of the above-mentioned second heated air supply means 8 but also the heater coated with stainless steel or the like in the first heated air supply means 6 or Piping may be used.
In vacuum drying, the electrode sheet 1 wound up in a roll after continuous drying is stored in a vacuum chamber 10 of a vacuum drying device 9 and dried in a rolled state.
[0029]
The vacuum chamber 10 adjusts the degree of vacuum or adjusts the airflow in the vacuum chamber by a vacuum pipe 11 and a purge pipe 12 connected to a vacuum pump (not shown), and the degree of vacuum can be measured using a vacuum gauge 13. it can. The door 15 to which the observation window 14 is attached seals the vacuum chamber 10 and is opened and closed by a handle 15a.
A heater 16 is provided on the peripheral wall of the vacuum chamber 10, and the temperature in the vacuum chamber 10 is controlled by the heater 16. A core support 17 is provided on the inner wall surface of the vacuum chamber 10, and the core support 17 can support a core 19 passed through a bobbin (winding core) 18 of the roll-shaped electrode sheet 1.
[0030]
Since the roll-shaped electrode sheet 1 supported by the core 19 and the core support 17 in the vacuum chamber 10 is placed under vacuum while being heated as described above, moisture that cannot be completely removed by continuous drying, and IPA is removed.
As described above, since the drying of the electrode sheet 1 is performed not during the formation but after the completion, it is possible to remove water and IPA contained in the electrode sheet 1 (sheet-like electrode) as much as possible, and as a result, high quality is achieved. It becomes possible to manufacture electric double layer capacitors.
[0031]
Here, the electrode sheet 1 after the vacuum drying is inspected for its residual moisture content, residual IPA content, overall appearance and the like. The residual moisture content is, for example, 2000 ppm or less, and the residual IPA content is 900 ppm. The following is assumed.
[0032]
The step of winding the electrode sheet 1 after the continuous drying into a roll is performed by providing a continuous dries (a dew point lower than in a dry area of −20 ° C. or less) in the drying chamber 3. By doing so, re-adsorption of moisture or the like may be prevented when the electrode sheet 1 is wound.
[Brief description of the drawings]
FIG. 1 shows an embodiment of the present invention and is a view showing a method for manufacturing an electrode sheet for an electric double layer capacitor. FIG. 2 is a side view showing a drying chamber. FIG. 3 is a supply flow of heated air in the drying chamber. FIG. 4 is a perspective view showing a vacuum chamber.
In the figure, 1 is an electrode sheet, 2 is a continuous drying device, 3 is a drying chamber, 4 is a roller, 5 is a nozzle, 6 is a first heated air supply means, 6a is a heater, 6b is a fan, 7 is a hepa filter, 8 Is a second heating air supply means, 8a is a heater, 8b is a fan, 9 is a vacuum dryer, 10 is a vacuum chamber, 11 is a vacuum pipe, 12 is a purge nozzle, 13 is a vacuum gauge, 14 is an observation window, and 15 is a door. , 15a are handles, 16 is a heater, 17 is a core support, 18 is a bobbin (winding core), and 19 is a core.

Claims (2)

A step of mixing and kneading the raw materials including the carbonaceous powder, the conductive auxiliary agent and the binder to form a molding material,
Forming and rolling this molding material to form a long sheet-like electrode;
Bonding the sheet electrode and the current collector foil to form an electrode sheet;
Performing a drying step of drying the electrode sheet, a method of manufacturing an electrode sheet for an electric double layer capacitor,
The drying step is continuous drying in which the electrode sheet is passed through a drying chamber while being fed and dried.
A method of manufacturing an electrode sheet for an electric double layer capacitor, comprising: vacuum drying in which, after the continuous drying, the electrode sheet wound into a roll is housed in a vacuum chamber and dried. The method for producing an electrode sheet for an electric double layer capacitor according to claim 1, wherein the continuous drying is performed by blowing heated air that has passed through a hepa filter in the drying chamber onto the electrode sheet.

Images