JP2010123766A - Electrode sheet, and electric double-layer capacitor and lithium ion capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode sheet excelling in performance of internal resistance and the like and capable of keeping its excellent condition over a long time even if charge and discharge are repeated, and to provide a capacitor, in an electrode sheet for forming a polarizable electrode by applying a coating fluid containing an active material and the like to a surface of a collector such as metal foil and thereafter drying the coating fluid, and an electric double-layer capacitor and a lithium ion capacitor using the same. <P>SOLUTION: As an organic solvent constituent of the coating fluid, N, N-dimethylformamide is used, the coating fluid is applied, thereafter the weight ratio of the N, N-dimethylformamide in a coating composition is reduced to be set ≤5 wt.% to form a polarizable sheet, and thereby this electrode sheet is provided. This electric double-layer capacitor and this lithium ion capacitor each using the electrode sheet are also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode sheet, an electric double layer capacitor using the same, and a lithium ion capacitor. More specifically, a coating liquid containing an active material or the like is applied to the surface of a current collector such as a metal foil. Then, it is related with the electrode sheet | seat which forms a polarizable electrode by drying, an electric double layer capacitor using the same, and a lithium ion capacitor.

  In recent years, electrochemical capacitors such as an electric double layer capacitor that accumulates electricity in an electric double layer that is an interface between a polarizable electrode such as activated carbon and an electrolytic solution have begun to be put into practical use as a storage medium. As a general structure of an electrochemical capacitor, an electrode sheet made of a current collector such as a metal foil and a polarizable electrode such as activated carbon and a separator are alternately laminated to form a laminate, and further impregnated with an electrolyte. The laminated body is sealed in a container to form an electrochemical capacitor cell.

  In addition, an electrochemical capacitor cell is manufactured by forming a laminate of an electrode sheet and a separator in a sandwich shape for a square electrochemical capacitor and in a roll shape for a cylindrical electrochemical capacitor. Lead body and negative electrode body) are connected to the respective terminals, and the laminate is stored in a container, and then an electrolyte is injected from the opening of the container to impregnate the laminate with the electrolyte, and the tip of the electrode terminal is Many methods have been implemented to seal the container while it is exposed to the outside.

In such an electrochemical capacitor, the electrode sheet is generally manufactured by forming a polarizable electrode by applying and drying a coating liquid containing an active material on the surface of a current collector such as a metal foil. Conventionally, as coating components, there are many coating liquids in which conductive materials such as carbon black, activated carbon, and binders such as polytetrafluoroethylene and cellulose are dispersed in an organic solvent or an aqueous solvent. in use.
After applying these coating solutions, the solvent of constituent components, moisture, etc. are reduced by drying, and by strengthening the bond between the collector such as metal foil and the polarizable electrode formed on the surface, It is thought that important performances such as the capacitance and internal resistance of chemical capacitors and their lifetimes are improved. Therefore, many electrode sheet drying methods have been developed so far, and for example, the following patent applications have been filed.

  That is, Patent Document 1 discloses a method of evaporating the solvent in the coating liquid by irradiating infrared rays to form a polarizable electrode on the surface of the current collector, and Patent Document 2 discloses a solvent in the coating liquid. A method of forming a polarizable electrode on the surface of a current collector by evaporating by applying hot air is disclosed. Patent Document 3 discloses a method of applying a liquid having a low compatibility or a low surface tension to the surface of a metal foil in advance, and Patent Document 4 discloses hydroxy in an aprotic polar solvent. A method of using a coating liquid obtained by adding an active material to a solution containing an alkyl chitosan and an organic acid and / or a derivative thereof and kneading is disclosed.

JP 2001-222992 A JP 2001-345095 A JP 2008-36607 A Japanese Patent Laid-Open No. 2008-60060

However, even in the case of a capacitor for which an electrode sheet drying method has been developed as described above, performance such as electrostatic capacity and internal resistance gradually deteriorates due to repeated charge and discharge, and good performance is maintained for a long period of time. There was an inconvenience that it was not possible.
Therefore, the problem to be solved by the present invention is to apply a coating liquid containing an active material or the like to the surface of a current collector such as a metal foil, and then dry the electrode sheet to form a polarizable electrode, and Provided are an electrode sheet and a capacitor which have good performance such as internal resistance in an electric double layer capacitor and a lithium ion capacitor using the same, and can maintain the good state for a long time even after repeated charge and discharge. That is.

  As a result of intensive studies to solve these problems, the present inventors have developed a coating solution using N, N-dimethylformamide as an organic solvent for dissolving a solid component such as an active material, an alkali metal silicate and N / N-dimethylformamide in a polarizable electrode thus formed, applied to an aluminum foil via a conductive adhesive layer containing an alkaline earth metal silicate or directly to a copper foil The present invention has found that an electrode sheet capable of solving the above-mentioned problems, an electric double layer capacitor using the same, and a lithium ion capacitor can be obtained by reducing the weight ratio to 5% by weight or less by drying. Reached.

  That is, the present invention provides a coating liquid obtained by mixing a solid component containing activated carbon, carbon black, and polyvinylidene fluoride and an organic solvent containing N, N-dimethylformamide, an alkali metal silicate and / or Alternatively, after applying to an aluminum foil formed with a conductive adhesive layer containing an alkaline earth metal silicate, the coating composition (the coating liquid applied to the aluminum foil is solidified by drying) Electrode sheet (first form of electrode sheet), characterized in that a polarizable electrode is formed by reducing the weight ratio of N, N-dimethylformamide in the composition) to 5% by weight or less. ).

  In addition, the present invention provides a coating liquid obtained by mixing a solid component containing an active material and polyvinylidene fluoride and an organic solvent containing N, N-dimethylformamide on a copper foil, followed by drying. Polarized electrode by reducing the weight ratio of N, N-dimethylformamide in the composition (composition formed by drying the coating solution applied to the aluminum foil) to 5% by weight or less. It is an electrode sheet (2nd form electrode sheet) characterized by forming.

In addition, the present invention is an electric double layer capacitor comprising a laminate in which the electrode sheet of the first embodiment and a separator are laminated, and an electrolyte solution sealed in a container.
The present invention is also characterized in that the electrode sheet of the first form, the laminate of the electrode sheet of the second form and the separator, and the electrolyte solution are sealed in a container. This is a lithium ion capacitor.

  The electric double layer capacitor and lithium ion capacitor of the present invention using the electrode sheet of the present invention have excellent performance with low electrostatic capacity and low internal resistance. However, the performance can be maintained for a long time in a good state.

The electrode sheet of the present invention is a storage medium such as an electric double layer capacitor, a lithium ion capacitor, or a hybrid battery, and includes a solid component including activated carbon and at least N, N-dimethylformamide (hereinafter referred to as “DMF”). A coating liquid prepared by mixing with an organic solvent containing (a) is applied to the surface of a metal foil or the like and then dried to be applied to an electrode sheet forming a polarizable electrode.
Moreover, the electric double layer capacitor and the lithium ion capacitor of the present invention are applied to a capacitor using the above electrode sheet as an electrode sheet for a positive electrode and / or an electrode sheet for a negative electrode. Further, the electrode sheet and the capacitor of the present invention can be applied to both a square capacitor and a cylindrical capacitor.

Hereinafter, the coating liquid used in the present invention will be described in detail.
As the carbon black used in the electrode sheet of the present invention, any of furnace black, acetylene black, channel black, thermal black and the like can be used.

  As the activated carbon used in the electrode sheet of the first embodiment of the present invention, activated carbon such as coconut shell charcoal, wood powder charcoal, peat charcoal activated by water vapor or carbon dioxide, or graphitizable carbon activated by an alkali metal compound. The alkali activated charcoal performed etc. are mentioned. However, it is preferable to use an electrode sheet having a high capacitance per unit volume and activated carbon from which a capacitor can be obtained.

  Therefore, in the electrode sheet according to the first aspect of the present invention, petroleum pitch, coal pitch, synthetic pitch, or coke using these as starting materials (graphitizable coke) is heat-treated at 600 to 800 ° C. An activated carbon obtained by subjecting the carbonized material prepared by nitriding to a nitrogen content of 10 wt% or less and then activating the carbonized product is preferably used. The activated carbon after the activation treatment usually has a nitrogen content of 1 wt% or less. Further, as the above pitch, a synthetic pitch obtained by polymerizing condensed polycyclic hydrocarbons such as naphthalene, methylnaphthalene, anthracene, phenanthrene, acenaphthene, acenaphthylene, and pyrene in the presence of hydrogen fluoride and boron trifluoride. More preferably, it is used. Unlike other pitches, these are particularly preferably used because they have high chemical purity and the properties can be freely controlled.

The nitriding treatment of the carbonized material is not particularly limited, but is a method of performing a heat treatment in an atmosphere containing a nitrogen-containing gas (the nitrogen-containing gas here includes a nitrogen gas which is inert to carbon). A method using nitrogen plasma, and co-carbonization with a nitrogen-containing organic substance.
With regard to the heat treatment temperature of the carbonized product in a nitrogen-containing gas atmosphere, the amount of nitrogen introduced is reduced if the temperature is too high or too low, and the capacitance is not improved. If the heat treatment temperature is too high, the carbon network surface develops too much and the formation of the pore structure by activation is inhibited.

  The heat treatment temperature is preferably 600 to 1000 ° C, more preferably 600 to 950 ° C, and further preferably 600 to 850 ° C. The heat treatment time is preferably 0.1 to 10 hours, more preferably 0.1 to 8 hours, and further preferably 0.1 to 6 hours. Of the nitrogen-containing gases, ammonia is preferable because of its reactivity with carbon. The nitrogen-containing gas may be diluted with an inert gas such as nitrogen or argon, and its concentration is preferably 0.1 to 100% by volume, more preferably 0.5 to 100% by volume, and still more preferably 1 to 100%. % By volume.

The shape of the carbonized product during the heat treatment with the nitrogen-containing gas is not limited, but in order to contact more nitrogen-containing gas and introduce more nitrogen, it must be fine particles desirable. The particle diameter is preferably 10 mm or less, more preferably 7 mm or less, and still more preferably 5 mm or less.
The nitride obtained by such heat treatment is activated after pulverization, but chemical activation is preferable to obtain higher capacitance, and lithium hydroxide, sodium hydroxide, potassium hydroxide, potassium carbonate is further preferable. Alkaline activation with an alkali metal compound such as potassium chloride is more preferable.

The active material used in the electrode sheet according to the second embodiment of the present invention is obtained by blending carbon black with pitch and heat treating it, or blending carbon black after heat treating the pitch.
The pitch used in the electrode sheet of the second embodiment of the present invention is the same as the pitch described above.

When carbon black is blended in the pitch, it is usually 2 to 10 parts by weight of carbon black with respect to 100 parts by weight of the pitch, and preferably 3 to 8 parts by weight of carbon black with respect to 100 parts by weight of the pitch. Outside this range, when manufacturing a capacitor, the internal resistance may not be kept low.
In the present invention, the heat treatment is preferably performed at 500 ° C. to 800 ° C. after carbon black is added to the pitch. The heat treatment time is usually 0.5 to 4 hours, preferably 1 to 2 hours. These heat treatments are usually performed in a non-oxidizing gas atmosphere such as nitrogen or ammonia.

  The obtained heat-treated product is usually pulverized. As the pulverization method, an optimum model is appropriately selected from an impact pulverizer, a ball mill, a roller mill, a jet mill and the like. A classifier may be used in combination to obtain the desired particle size. In the pulverization treatment, the particle size is adjusted so that the average particle size is usually 1 to 50 μm, preferably 5 to 30 μm, and more preferably 10 to 25 μm.

  The heat-treated product (pulverized product) after the pulverization treatment is cleaned using a solvent. The type of the solvent is not particularly limited, and examples thereof include acetone, methanol, ethanol, propanol, isopropyl alcohol, butanol, hexane, heptane, benzene, toluene, xylene, quinoline, pyridine, and tetrahydrofuran. Preferably, the organic solvent has a boiling point of 50 ° C. or higher. Particularly preferred are quinoline and pyridine.

  It is preferable to use 10 to 50 parts by weight of the solvent with respect to 1 part by weight of the pulverized product. The pulverized product is washed using the above solvent at a temperature of 10 to 250 ° C, preferably 60 to 250 ° C, more preferably 120 to 230 ° C. The cleaning treatment time is 1 to 240 hours, preferably 12 to 72 hours, and more preferably 48 to 72 hours.

In order to collect the pulverized processed product (cleaned processed product) after the cleaning treatment, a known separation method can be used. For example, filtration and centrifugation can be used. When the recovered material in which the solvent remains is used as the active material of the electrode sheet, the long-term performance of the capacitor is deteriorated. Therefore, a drying process (solvent removal process) is performed after the separation and recovery. For example, using a solvent having a boiling point lower than that of the solvent used for the cleaning process, the recovered pulverized product after the cleaning process is again cleaned, and vacuum drying or the like is performed in an inert atmosphere.
By using the dried product thus obtained as an active material, a capacitor having a small electrode expansion due to electrolytic activation and a high energy density can be obtained.

When the pitch or the like is heat-treated, the carbon network surface grows by thermal polymerization. As shown in the present invention, the specific surface area of the heat-treated product obtained by heat-treating the pitch or the like at 500 ° C. or more and 800 ° C. or less with a solvent is 90 m ² / g or less, but exhibits a high capacitance. This is because solvent cleaning removes low-molecular substances at the carbon network edge, exposes the carbon network edge, penetrates the carbon cluster voids due to electrolytic activation, and further, ions between the layers of the carbon network. It is considered that the capacity is developed by facilitating the insertion of.

  The coating liquid used for the electrode sheet of the first embodiment of the present invention contains the above-mentioned activated carbon, carbon black, and polyvinylidene fluoride as solid components, and N, N -A coating liquid obtained by mixing an organic solvent containing dimethylformamide. Moreover, the coating liquid used for the electrode sheet of the second embodiment of the present invention contains the above-mentioned active material and polyvinylidene fluoride as solid components, and N, N-dimethyl is added to such solid components. A coating liquid obtained by mixing an organic solvent containing formamide. The content of N, N-dimethylformamide in the coating liquid is usually 50% by weight or more.

Next, the electrode sheet of the present invention will be described in detail.
In the electrode sheet according to the first aspect of the present invention, a conductive adhesive layer containing an alkali metal silicate and / or an alkaline earth metal silicate is formed as a conductive adhesive layer on the surface of the aluminum foil. The electrode sheet is obtained by applying a coating liquid containing activated carbon, carbon black, polyvinylidene fluoride, and N, N-dimethylformamide on the outer surface and then drying. The electrode sheet according to the second aspect of the present invention is an electrode sheet obtained by applying a coating liquid containing an active material, polyvinylidene fluoride, and N, N-dimethylformamide on the surface of a copper foil and then drying it. It is. The electrode sheet of the first form is usually used as an electrode sheet for a positive electrode and an electrode sheet for a negative electrode, and the electrode sheet of the second form is usually used as an electrode sheet for a negative electrode.

  As the alkali metal silicate used in the electrode sheet of the first embodiment, lithium silicate, sodium silicate, potassium silicate, etc., and as the alkaline earth metal silicate, calcium silicate Can be illustrated. Two or more of these can be used. In addition to these silicates, the conductive adhesive layer requires conductive components such as graphite and carbon black. In addition, although activated carbon, thermosetting resin, etc. may be contained, the content rate with respect to the whole electroconductive contact bonding layer of a silicate is 1-80 weight% normally, Preferably it is 2-50 weight%.

  In the electrode sheet of the first embodiment, the method for forming the conductive adhesive layer on the surface of the aluminum foil is not particularly limited, but for example, the constituent components of the conductive adhesive layer as described above may be water, A conductive adhesive layer can be formed on the surface of the aluminum foil by preparing a coating solution by dissolving or dispersing in an aqueous solvent or an organic solvent, coating the solution on the surface of the aluminum foil, and drying. The thickness of the conductive adhesive layer is usually 2 to 40%, preferably 5 to 25% of the thickness of the aluminum foil. When the thickness of the conductive adhesive layer is less than 2% of the thickness of the aluminum foil, the adhesive strength with the aluminum foil becomes weak, and when it exceeds 40%, the effect of suppressing the increase in the internal resistance of the capacitor is reduced.

  As shown in FIG. 1, the basic form of the electrode sheet of the present invention is that the polarizable electrode obtained by applying and drying the above-mentioned coating liquid is directly or via a conductive adhesive layer. It is formed on both surfaces (shaded portions) of the metal foil 2 excluding the portion to be. In applying the coating liquid, in order to obtain a desired film thickness, the viscosity of the coating liquid can be finely adjusted by diluting with a solvent such as ethylene glycol monomethyl ether or xylene. An appropriate amount of an antifoaming agent may be added. The method of applying the coating liquid to the surface of the metal foil is not particularly limited. For example, after applying the coating liquid on one side and drying, the coating liquid on the other side is similarly applied. Application and drying can be performed. The coating liquid in the present invention has high uniformity, can maintain a constant viscosity and characteristics for a long time, and has excellent wetting characteristics, so that the film thickness can be easily and precisely controlled.

  The drying in the present invention is performed until the content of N, N-dimethylformamide in the polarizable electrode becomes 5% by weight or less. Usually, it is dried (or heat-treated) at a temperature of 100 to 400 ° C., preferably 200 to 300 ° C., in a heat treatment furnace or the like. Moreover, the ultimate vacuum is performed under conditions of an absolute pressure of 0.1 Torr or less, preferably an absolute pressure of 0.01 Torr or less. If the temperature inside the dryer is too low, there is a problem that DMF does not volatilize sufficiently. Conversely, if the temperature is too high, the adhesive strength between the current collector and the polarizable electrode is lowered, and the polarizable electrode may be easily peeled off. is there.

  Although the solvent is mainly volatilized by the above-mentioned drying treatment, functional groups (-OH, -COOH, -C = O, etc.) remaining on activated carbon, carbon black, polyvinylidene fluoride, etc. in the coating solution are decomposed and removed at the same time. At the same time, the binding of activated carbon, carbon black, and polyvinylidene fluoride is strengthened. The polarizable electrode of the electrode sheet of the present invention obtained as described above has a density of usually 0.5 to 0.7 g / cc, preferably 0.55 to 0.65 g / cc, and a thickness of usually 0.00. It is 02 to 0.2 mm, preferably 0.05 to 0.1 mm.

Next, the electric double layer capacitor and the lithium ion capacitor of the present invention will be described in detail.
The capacitor of the present invention uses a laminate in which the above electrode sheets and separators are alternately laminated. In the electric double layer capacitor of the present invention, the electrode sheet of the first form is used as the positive electrode sheet and the negative electrode sheet. Moreover, in the lithium ion capacitor of this invention, the electrode sheet of a 1st form is used as an electrode sheet for positive electrodes, and the electrode sheet of a 2nd form is used as an electrode sheet for negative electrodes. In the present invention, when laminating the electrode sheet and the separator, as shown in FIG. 2, the lead part 4 of the electrode sheet (positive electrode body) for the positive electrode of the electrode sheet and the lead part of the electrode sheet (negative electrode body) for the negative electrode 5 are laminated so that they can be connected to the positive terminal 6 and the negative terminal 7, respectively.

  Thereafter, as shown in FIG. 3, the laminate 8 is housed in a flat container 9 made of a metal foil covered with a plastic film having an opening on at least one side, but the electrode terminal is on the opening side. Stored. In the production of a capacitor, the laminated body and the flat container are usually dried before the electrolytic solution is injected. In the present invention, the capacitor is continuously produced after the production of the electrode sheet. In the case of manufacturing, the drying process time of the laminate can be shortened, or the drying process can be omitted in some cases.

In the present invention, an electrolytic solution is then injected into the container and the capacitor cell is impregnated with electrolysis. The electrolyte used for the electric double layer capacitor of the present invention is not particularly limited, but examples of the solvent include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and the like. Examples of the electrolyte include tetraethylammonium, trimethylethylammonium, dimethyldiethylammonium, trimethylethylammonium, and tetramethylammonium. As the electrolyte used in the lithium ion capacitor of the present invention, it can be exemplified by the same solvents as the solvent, as an electrolyte, can be exemplified for example LiBF _4, LiPF ₆ or the like.

In addition, an operation is performed to remove gas such as water vapor adsorbed on the polarizable electrode by reducing the pressure in the container. By doing in this way, a laminated body can be efficiently impregnated with electrolyte solution. Furthermore, if necessary, between the injection of the electrolytic solution and the sealing of the container, the electrode terminal is energized and subjected to electrolytic purification in order to electrolyze and remove moisture and functional groups contained in the polarizable electrode. You can also.
After that, for example, the heated two heat seal bars are pressed in a sandwiched state in the opening of the flat container made of metal foil covered with a plastic film, and the container is sealed. A capacitor is obtained. In the present invention, the process from injection of the electrolytic solution to sealing of the container is performed under reduced pressure or in an inert gas atmosphere.

  The performance (capacitance and internal resistance) of the electrochemical capacitor manufactured as described above is measured by a charge / discharge test. Further, by continuing the charge / discharge test and repeating the above measurement, it is possible to investigate a decrease in capacitance and an increase in internal resistance.

  A sample for measuring the weight ratio of DMF remaining on the polarizable electrode (hereinafter referred to as “DMF residual ratio”) can be prepared, for example, by the following method. Under the same reduced pressure drying conditions as the electrode sheet used for the production of the laminate, the electrode sheet is excessively dried and used for DMF residual ratio measurement. Only the polarizable electrode is peeled off from one side of the dried electrode sheet with a razor and further pulverized using an agate mortar to obtain a measurement sample.

  When only DMF is used as the organic solvent of the coating liquid, volatile components contained in the sample prepared as described above are absorbed from the air after drying in addition to DMF remaining on the polarizable electrode. Water is considered. If the sample can be heated and volatile water and DMF can be separated and quantified based on the difference in boiling points, it is possible to determine the DMF residual rate in the sample, that is, in the polarizable electrode.

  As a simple method, using a thermal analysis (TGA), the weight reduction rate due to sample heating may be obtained in two stages from room temperature to 140 ° C. and from 140 ° C. to 380 ° C. A sample amount of about 50 mg is sufficient. Although moisture is mainly volatilized during the first stage of heating, the weight reduction is stopped by maintaining the temperature at 140 ° C. for about 10 minutes. The weight concentration of water in the sample is determined from the weight reduction in the first stage. Thereafter, DMF is mainly volatilized during the second stage of heating, but weight reduction is stopped by maintaining the temperature at 380 ° C. for about 10 minutes. From the weight reduction in the second stage, the weight concentration of DMF in the sample is obtained.

  Here, the weight loss in the first stage is mainly due to moisture mixed in from the atmosphere at the time of sample preparation, so it is not directly related to the residual amount of solvent after drying the electrode sheet, and the measured value depends on the environment of the measurement location. Changes significantly. Therefore, based on the weight obtained by subtracting the weight reduction amount of the first stage from the weight of the sample used for the thermal analysis measurement, the ratio of the weight reduction of the second stage at this time is regarded as the DMF residual ratio in the polarizable electrode. be able to.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these.

[Examples 1 to 4]
(Preparation of activated carbon)
In the presence of hydrogen fluoride and boron trifluoride, naphthalene is polymerized to synthesize pitch (softening point by Mettler method: 283 ° C, optical anisotropy of carbonized product: 100%, Lc value of graphitized product:> 100 nm) did. Next, 1000 g of the pitch is placed in a stainless steel square container having a height of 400 mm and a bottom surface of 400 mm × 400 mm, heated in a vertical furnace to 730 ° C. in a nitrogen atmosphere, and held at this temperature for 1 hour. To obtain a carbonized product.

The carbonized product was pulverized to 40 μm or less, and then placed in an alumina container, and subjected to nitriding treatment by holding at 750 ° C. for 4 hours in an ammonia / nitrogen (30/70 vol%) mixed gas atmosphere. The nitrogen content of this nitride was 4.8% by weight.
1 part by weight of the nitride powder and 1.8 parts by weight of 95% potassium hydroxide were uniformly mixed, heated to 750 ° C. at 5 ° C./min under a nitrogen atmosphere, and maintained at this temperature for 3 hours. . Activated carbon having a nitrogen content of 0.5% by weight after cooling to room temperature and then charging into a methanol-water mixture until the filtrate is neutral, followed by acid washing with 0.1 mol / L hydrochloric acid aqueous solution, filtration, and water washing. Got.

(Preparation of coating solution)
After charging activated carbon, carbon black (Denka black) and polyvinylidene fluoride in a weight ratio of 88: 5: 7 to the planetary mixer, DMF of about 2.5 times the total weight of the above components was injected, Mixing while kneading. At that time, heat generation of the mixture was confirmed, but the mixture was mixed so as not to approach the boiling point of 153 ° C. of DMF. The obtained slurry-like coating solution was a coating solution with extremely good dispersion stability that did not precipitate activated carbon, carbon black, and polyvinylidene fluoride even when allowed to stand for one day.

(Production of electrode sheet)
A mixer was charged with 2.3 kg of potassium silicate, 1 kg of graphite, 0.2 kg of carbon black, and 6.5 kg of 1% aqueous ammonia containing 2% of an anionic surfactant, and then stirred to conduct conductive bonding. A coating solution for the layer was prepared. This coating solution was applied with a width of 105 mm to the central portion of one side of an aluminum foil having a width of 150 mm and a thickness of 30 μm using a single-side coating apparatus. The unwinding speed and winding speed of the aluminum foil were 4 m / min. Moreover, 120-150 degreeC dry air was introduce | transduced from the hot air introduction port of the coating apparatus, and it was made to dry. The other side was coated in the same manner. As a result, conductive adhesive layers each having a thickness of about 4 μm were formed on both surfaces of the aluminum foil.

  Next, the coating liquid prepared as described above was applied to the aluminum foil having the conductive adhesive layer formed on the surface as described above, using a single-side coating apparatus. In addition, the part used as the lead part of an electrode sheet was sealed. The unwinding speed and winding speed of the aluminum foil at the time of application of the coating liquid were 4 m / min. Moreover, 40-80 degreeC dry air was introduce | transduced from the hot air introduction port of the coating apparatus, and it was made to dry. The other side was coated in the same manner. Further, the wound material is heat treated in a heat treatment furnace for 30 minutes, and then the seal is peeled off and cut into a shape as shown in FIG. 1 to form a polarizable electrode having a thickness of about 60 to 70 μm on the surface of the current collector. The obtained electrode sheet was obtained.

(Pressure drying of electrode sheet)
In order to efficiently volatilize the DMF remaining on the electrode sheet manufactured as described above, the electrode sheets were arranged in a vacuum dryer set at a temperature of 250 ° C. so as not to overlap each other and dried under reduced pressure.
The ultimate vacuum of the vacuum dryer was an absolute pressure of 0.01 Torr, and the drying time was 3 hours, 6 hours, 18 hours, and 120 hours. 57 electrode sheets were dried at each drying time.

(Production of electric double layer capacitor)
As described above, one electric double layer capacitor was manufactured for each of the electrode sheets that had been dried in four drying times (total of four). The manufacturing method is the same for all four, but details are given below.
A total of 56 dried electrode sheets and paper separators (thickness 50 μm) were stacked so that the lead portions could be alternately connected to the positive electrode and negative electrode terminals, and one side excluding the lead portions was 100 mm. A square laminate (thickness 15 mm) was produced. Next, the lead portion of the positive electrode body and the lead portion of the negative electrode body of the laminate were bonded to the electrode terminals by welding. In addition, the separator used what was left still for one day in the dry nitrogen atmosphere with a dew point of -50 degrees C or less, and the operation | work of lamination | stacking and adhesion | attachment was also performed in the dry nitrogen atmosphere with a dew point of -50 degrees C or less.
In addition, four square flat containers each having a side of 150 mm and having an aluminum foil whose surface is coated with a plastic film are prepared and left to stand in a dry nitrogen atmosphere having a dew point of −50 ° C. or less for one day. Oita.

  As shown in FIG. 3, each laminate was inserted into a container in a dry nitrogen atmosphere having a dew point of −50 ° C. or less for each of the aforementioned laminate and four flat containers. Next, 40 ml of an electrolytic solution in which an ammonium salt or the like was dispersed in a propylene carbonate solvent was injected from the opening of a flat container. After completing the injection of the electrolytic solution, the laminate was decompressed by a vacuum pump for 30 minutes, and the laminate was decompressed. During this period, the electrode terminal was energized to perform electrolytic purification. Thereafter, the opening of the container was heat sealed at 150 ° C., and the flat container was sealed to obtain an electric double layer capacitor.

(Investigation of the performance of electric double layer capacitors)
The electric double layer capacitors of Examples 1 to 4 were charged and discharged at 0 V to 2.7 V at room temperature (25 ° C.) (1 hour after the start of charging, and discharged to 0 V over 30 minutes) 10 times. As a result of measuring the capacitance and the internal resistance, it was confirmed that the performance was excellent as shown in Table 1. (Initial performance) The longer the drying time, the better the performance.

  Next, with respect to these electric double layer capacitors, charging / discharging (discharged to 0 V over 30 minutes after 5 hours of charging) was repeated 182 times (about 1000 hours) in an environment of 60 ° C. Thereafter, capacitance and internal resistance were measured. (Acceleration test) As a result, as shown in Table 1, the capacitance reduction rate was 15.6 to 19.6%, the internal resistance increase rate was 0.06 to 0.2%, and it was confirmed that the performance was excellent. It was. The longer the drying time, the better the performance.

(Measurement of residual DMF)
Of the electrode sheets whose drying times were changed in four ways as described above, about 50 mg each of the coating sheets (polarizable electrodes) that were not used in the laminate (total 4 sheets) were shaved with a razor, and an agate mortar was used. The pulverized sample was used as a sample for measuring DMF residual ratio.
Thermal analysis (TGA) was used as a DMF residual ratio measurement method. The temperature increase program was in two stages from room temperature to 140 ° C and from 140 ° C to 380 ° C.
Here, the weight loss at the first stage is mainly due to moisture mixed in from the atmosphere during sample preparation, so the weight obtained by subtracting the weight loss at the first stage from the weight of the sample used for the thermal analysis measurement is the standard. The ratio of weight reduction at the second stage at this time was regarded as the DMF residual ratio in the polarizable electrode.

[Examples 5 to 8]
(Production of electrode sheet)
In the production of the electrode sheets of Examples 1 to 4, the preparation of the active material was performed in the same manner as in Examples 1 to 4, except that a copper foil without a conductive adhesive layer formed on the surface was used as a current collector. A coating solution was prepared, and electrode sheets were produced in the same manner as in Examples 1 to 4, respectively.

(Pressure drying of electrode sheet)
For the two types of electrode sheets of Examples 1 to 4 and the electrode sheets manufactured as described above, both electrodes were placed in a vacuum dryer whose temperature was set to 250 ° C. in order to efficiently evaporate the remaining DMF. The sheets were lined up so as not to overlap each other and dried under reduced pressure.
The ultimate vacuum of the vacuum dryer was an absolute pressure of 0.01 Torr, and the drying time was 3 hours, 6 hours, 18 hours, and 120 hours. Each of the two types of electrode sheets was dried 11 times for each drying time.

(Production of lithium ion capacitors)
The electrode sheet of Examples 1 to 4 was used as the electrode sheet for the positive electrode, the electrode sheet using the copper foil was used as the electrode sheet for the negative electrode, and these and a paper separator (thickness 50 μm) were connected to the lead portion. A total of 20 layers were laminated so that the electrodes could be alternately connected to the positive electrode terminal and the negative electrode terminal, and a square laminate (thickness 7 mm) having a side of 100 mm excluding the lead portion was manufactured.
Next, the lead part of the positive electrode body and the lead part of the negative electrode body of the laminate were bonded to the electrode terminals by welding in the same manner as in Examples 1 to 4. Also, four flat containers similar to those of Examples 1 to 4 were prepared and allowed to stand for one day in a dry nitrogen atmosphere having a dew point of −50 ° C. or lower.

  As shown in FIG. 3, each laminate was inserted into a container in a dry nitrogen atmosphere having a dew point of −50 ° C. or less with respect to the aforementioned four laminates and four flat containers. Next, 40 ml of an electrolytic solution in which a lithium salt or the like was dispersed in an ethylene carbonate solvent was injected from the opening of the flat container. After completing the injection of the electrolytic solution, the laminate was decompressed by a vacuum pump for 30 minutes, and the laminate was decompressed. During this period, the electrode terminal was energized to perform electrolytic purification. Thereafter, the opening of the container was heat sealed at 150 ° C., and the flat container was sealed to obtain a lithium ion capacitor.

(Lithium ion capacitor performance survey)
For the lithium ion capacitors of Examples 5 to 8, charging and discharging at 2.3 V to 4.0 V (discharging to 2.3 V over 30 minutes after 4 hours from the start of charging) was repeated 1000 times at room temperature (25 ° C.). . (Cycle characteristic test) As a result of measuring the capacitance and internal resistance after the end of the first cycle, it was confirmed that the performance was excellent as shown in Table 2. (Initial performance) Further, the longer the drying time of the electrode sheet, the better performance was obtained.

  Next, after completion of the cycle characteristic test (after 1000 cycles), capacitance and internal resistance were measured. When the results were compared with the initial performance, as shown in Table 2, the capacitance reduction rate was 15.9 to 18.7%, the internal resistance increase rate was 1.3 to 1.6%, and the performance was excellent. I was able to confirm. In addition, the better performance was obtained as the drying time of the electrode sheet was longer.

(Measurement of residual DMF)
Of the electrode sheets for positive and negative electrodes, which were changed in drying time in four ways as described above, one that was not used for the laminate (total of 8 sheets) was coated with about 25 mg of coating film (polarizable electrode) each. And then pulverized using an agate mortar. Equal amounts of samples sampled from the positive and negative electrodes with the same drying time were mixed to obtain a DMF residual rate measurement sample for each drying time.
The DMF residual ratio was measured by thermal analysis (TGA), and the DMF residual ratio in the polarizable electrode was determined in the same manner as in Examples 1 to 4.

[Comparative Example 1]
After heat-treating the electrode sheets of Examples 1 to 4, the same process as in Examples 1 to 4 was performed until the step of cutting into a shape as shown in FIG. 57 cut electrode sheets were prepared, and the electrode sheets were arranged so as not to overlap each other in a vacuum dryer set at a temperature of 250 ° C., as in Examples 1 to 4, so that the ultimate vacuum was 0.01 Torr. Vacuum drying was performed. However, the drying time was 0.5 hours.
Of the dried electrode sheets, 56 laminates were produced in the same manner as in Examples 1 to 4, and one electric double layer capacitor was produced from this laminate, and the remaining one electrode sheet. Was used for measuring the DMF residual ratio in the same manner as in Examples 1 to 4.

  The electric double layer capacitor of Comparative Example 1 was charged and discharged at 0 V to 2.7 V at room temperature (25 ° C.) (1 hour after the start of charging, and discharged to 0 V over 30 minutes) 10 times, and then the capacitance As a result of measuring the internal resistance, as shown in Table 1, it was confirmed that the capacitance was smaller and the internal resistance was larger than those of Examples 1 to 4. (Initial performance)

  Next, with respect to these electric double layer capacitors, charging / discharging (discharged to 0 V over 30 minutes after 5 hours of charging) was repeated 182 times (about 1000 hours) in an environment of 60 ° C. Thereafter, capacitance and internal resistance were measured. (Acceleration test) As a result, as shown in Table 2, the capacitance decrease rate was 50.3% and the internal resistance increase rate was 435.0%, and the capacitance decrease rate and internal resistance increase compared to Examples 1 to 4. It was confirmed that the rate was large.

  About one electrode sheet which was not used for manufacture of a laminated body, the DMF residual rate in a polarizable electrode was calculated | required by the method similar to Examples 1-4 using thermal analysis (TGA).

[Comparative Example 2]
After heat-treating the two types of electrode sheets of Examples 5 to 8, the same steps as in Examples 5 to 8 were performed until the stage of cutting into a shape as shown in FIG. Prepare 11 pieces of each of the positive and negative electrode sheets, and arrange the electrode sheets in a vacuum dryer set at a temperature of 250 ° C. so that they do not overlap each other in the same manner as in Examples 5 to 8. Vacuum drying was performed at a pressure of 0.01 Torr. However, the drying time was 0.5 hours.
Of the dried electrode sheets, 10 positive and negative electrodes, respectively, were manufactured in the same manner as in Examples 5 to 8, and one lithium ion capacitor was manufactured from the stacked body. The electrode sheets for each negative electrode were used for measuring the DMF residual rate in the same manner as in Examples 5-8.

(Lithium ion capacitor performance survey)
With respect to the lithium ion capacitor of Comparative Example 2, charging and discharging at 2.3 V to 4.0 V (discharging to 2.3 V over 30 minutes after 4 hours from the start of charging) was repeated 1000 times at room temperature (25 ° C.). (Cycle characteristic test) As a result of measuring the capacitance and internal resistance after the end of the first cycle, as shown in Table 2, it was confirmed that the capacitance was smaller and the internal resistance was larger than in Examples 5-8. did it. (Initial performance)

  Next, after completion of the cycle characteristic test (after 1000 cycles), capacitance and internal resistance were measured. When the results were compared with the initial performance, the capacitance reduction rate was 48.0% and the internal resistance increase rate was 151.7% as shown in Table 2, and the capacitance reduction rate compared to Examples 5-8. It was also confirmed that the rate of increase in internal resistance was large.

  As described above, the electrochemical capacitor using the electrode sheet in which the DMF residual ratio is reduced to 5 wt% or less, more preferably 4 wt% or less by drying, like the electrode sheet of the example of the present invention, It was confirmed that the capacitance was high, the internal resistance was controlled low, and the performance could be maintained for a long time in a good state.

The top view which shows an example of the application part of a coating liquid in the electrode sheet of this invention The perspective view which shows an example of the laminated body in this invention Configuration diagram showing an example of the electric double layer capacitor of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lead part 2 Metal foil 3 Electrode sheet 4 Lead part of positive electrode body 5 Lead part of negative electrode body 6 Positive electrode terminal 7 Negative electrode terminal 8 Laminated body 9 Container

Claims (4)

  A coating liquid obtained by mixing a solid component containing activated carbon, carbon black, and polyvinylidene fluoride and an organic solvent containing N, N-dimethylformamide is used, and an alkali metal silicate and / or alkaline earth metal is used on the surface. After applying to the aluminum foil on which the conductive adhesive layer containing silicate is formed, the weight ratio of N, N-dimethylformamide in the coating composition is reduced to 5% by weight or less by drying. An electrode sheet comprising a polarizable electrode.   A coating liquid obtained by mixing a solid component containing an active material and polyvinylidene fluoride and an organic solvent containing N, N-dimethylformamide is applied to a copper foil, and then dried to form N, An electrode sheet formed by forming a polarizable electrode by reducing the weight ratio of N-dimethylformamide to 5% by weight or less.   An electric double layer capacitor comprising: a laminated body in which the electrode sheet according to claim 1 and a separator are laminated; and an electrolyte solution sealed in a container.   A lithium ion capacitor comprising: the electrode sheet according to claim 1, a laminate in which the electrode sheet according to claim 2 and a separator are laminated, and an electrolyte solution sealed in a container.

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