JP2007273508A - Process for producing coating type electrode sheet for electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the matter of a conventional coating type electrode sheet that since gas adsorbed to activated carbon is discharged in large quantities when paste is mixed, applied or dried and the electrode sheet is dried on a current collecting foil while biting small bubbles in the electrode layer before shrinking softly, it is difficult to enhance bulk density and the capacitance decreases and the internal resistance increases. <P>SOLUTION: Paste containing fine particles 2 of a conductive material, a binder 1 and a solvent 4 is heated at 30°C or above and mixed to produce heated paste A. On the other hand, activated carbon particles 3 are heated at 80°C or above to discharge gas adsorbed to the activated carbon particles 3. The heat treated activated carbon particles 3 are added, at a temperature higher that of the heated paste A, to the heated paste A and mixed to produce electrode paste B. Thereafter, the electrode paste B is applied to a current collection foil 11 and a coating film 14 is dried by heating in a drying section 13 thus producing an electrode layer 15. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a coated electrode sheet for an electric double layer capacitor.

  The electric double layer capacitor is provided with polarizable electrodes (positive electrode and negative electrode) facing each other with a separator interposed therebetween, and utilizes the capacitance of the electric double layer formed on the surface of the polarizable electrode in the electrolytic solution. . The electric double layer capacitor is characterized by having an extremely large capacitance compared to a general capacitor such as an aluminum capacitor. Therefore, it is used for backup of electronic devices, power storage for home appliances and photocopiers, power supply for start-up when the vehicle is idle, power supply for hybrid vehicles, power for peak shaving and leveling of wind power and solar power generation A wide range of uses has been started up to storage applications, and electric double layer capacitors are expected as key devices that help save energy and reduce carbon dioxide. In addition, since the electric double layer capacitor does not involve a chemical reaction during charging and discharging, it has an advantage that a large current can be charged and discharged instantaneously and charging and discharging efficiency is good. In addition, the electric double layer capacitor can be charged / discharged 100,000 times or more and has a lifetime of 10 years or more, and thus has an advantage of high reliability.

  On the other hand, compared with a lithium ion battery or the like, the electric double layer capacitor has a drawback of low energy density. Therefore, in order to increase the energy density of the electric double layer capacitor, the combination of the pore size of carbon and the size of the electrolyte is optimized, and the type and electrode thickness of the activated carbon of the positive electrode and the negative electrode are changed, or as the activated carbon, A device has been devised to increase the energy density by using the specification-activated alkali activated carbon, nanogate carbon, nanocarbon or the like.

  The electric double layer capacitor has different shapes such as a button type and a laminated type, but in either case, a positive electrode and a negative electrode made of a polarizable electrode mainly composed of carbon particles such as activated carbon, and a separator that separates these two electrodes Are alternately laminated in the outer case and impregnated with an electrolytic solution (such as an electrolyte dissolved in a solution or an ionic liquid).

  There are two indicators of the performance of the electric double layer capacitor: capacitance and internal resistance. Capacitance and internal resistance are related to the electrode bulk density. When the electrode bulk density is low, there are many isolated activated carbons that cannot contribute to the capacitance, and the binding between the activated carbon and the activated carbon is insufficient and the electrical resistance is low. There is an influence such as becoming higher. Therefore, it was necessary to increase the bulk density. However, in the coated electrode sheet with excellent mass productivity, the catalyst paste is coated on the current collector foil and then dried in the process of drying without applying pressure. In addition, there is a drawback that the bulk density is significantly lower than that of a mold press type electrode.

  For this reason, the coating type electrode sheet has been devised to increase the bulk density by applying a press using a press machine such as a roll press. However, after drying once, the binder and thickener added to the catalyst paste are firmly solidified, hindering the movement of activated carbon particles by the press and increasing the press pressure, other rolling molds and molds There is a problem that the bulk density is lower than that of a press-type electrode.

  Further, the bulk density of the coating type electrode sheet greatly depends on the paste composition to be coated. Therefore, efforts have been made to increase the dispersibility of the paste and increase the binding effect with a small amount of binder.

  Here, Example 1 of Patent Document 1 discloses a method in which PTFE dispersion as a binder and ammonium salt of carboxymethyl cellulose as a binder and thickener are mixed in water, and activated carbon particles and conductive fine particles are added. In that claim, a method is disclosed in which the electrode paste is subjected to a high-pressure disperser and highly dispersed. PTFE is mixed first, and activated carbon particles and conductive material fine particles are mixed at the same time. However, Patent Document 1 does not touch on the treatment of activated carbon before charging and the temperature at the time of mixing.

  In the second embodiment of Patent Document 2, a sodium salt of carboxymethyl cellulose, a butadiene-styrene copolymer (hereinafter referred to as SBR) and PTFE dispersion are mixed, and then activated carbon particles and conductive material fine particles are mixed. Thus, a method of forming a slurry of electrode paste is disclosed. After mixing NaCMC, SBR, and PTFE first, activated carbon particles and conductive material fine particles are mixed. However, Patent Document 2 does not touch on the treatment of activated carbon before charging and the temperature at the time of mixing.

  In Example 1 of Patent Document 3, activated carbon particles and conductive material fine particles are mixed, carboxymethyl cellulose is added as a thickener and binder, and an acrylate polymer is further added to form a slurry of a coated electrode sheet. A method is disclosed. CMC is added after the activated carbon particles and the conductive material fine particles are first mixed, but Patent Document 3 does not mention the treatment of activated carbon before charging and the temperature at the time of mixing.

  Further, in the example of Patent Document 4, activated carbon particles, conductive material fine particles, and polyvinylidene fluoride (hereinafter referred to as PVDF) are mixed, and 1-methyl-2-pyrrolidone (NMP) is added as a solvent to form a slurry. A method for producing a coated electrode sheet for an electric double layer capacitor that is applied to a sheet and dried is disclosed. In this document, activated carbon particles, conductive material fine particles, and PVDF are mixed together, and Patent Document 4 does not touch on the treatment of activated carbon before charging and the temperature at the time of mixing.

Special table WO98-58397 JP 2001-307965 A JP 2005-116855 A JP 2006-24611 A

  In all cases, the coated electrode sheet of the conventional electric double layer capacitor is mixed with activated carbon from the initial stage, and the processing conditions of the activated carbon before mixing, the temperature conditions during mixing, and the temperature of the electrode paste are completely considered. Was not. In addition, even when activated carbon is mixed in a highly dispersed state, the bulk density of the coated electrode is still lower than that of the rolling type electrode and the molded type electrode, and the electrode paste is dried on the current collector foil and softly contracts. For this reason, efforts to increase the bulk density depended exclusively on roll presses. However, since the thickener and binder are hardened after the electrode paste is dried, it is difficult to improve the bulk density even if the pressure of the roll press is increased to a high level. In comparison with mold-type electrodes, there are problems in that the capacitance is low and the internal resistance is high.

  Even if the composition of the electrode paste is the same, the bulk density after coating and drying varies depending on the season, and even when the same type of activated carbon is used, the bulk density after coating and drying depends on the storage period and processing conditions of the activated carbon. Noticed a change. For example, the electrode layer produced in winter has a lower bulk density than the electrode layer produced in summer, and activated carbon that has been refrigerated for longer than when activated carbon stored at room temperature is used. The one that was used had a lower bulk density. Also, from the electron micrographs, large bubbles are encased in the electrode paste during coating and drying, the bulk density is low, the activated carbon particles and the conductive material fine particles are not in close contact, and a space is formed between them. In many cases, the present inventors have noticed.

  Furthermore, it was discovered that small bubbles were generated when the activated carbon particles were mixed, and bubbles were generated from the surface even during drying.

  Considering the discovery of these facts, a large amount of the gas adsorbed on the activated carbon particles is generated when the activated carbon particles are mixed into the paste, and when the paste is applied to the current collector foil and dried, especially during heating and drying. It was found that this gas was released and the drying of the paste proceeded while bubbles remained in the paste, which caused the density of the bulk to be lowered. The difference between the seasons is that in winter, the temperature during mixing is low, and most of the gas adsorbed on the activated carbon is released all at once during drying, which leaves a structure with air bubbles and lowers the bulk density. To happen. In addition, when activated carbon is stored in a refrigerator for a long time, the activated carbon absorbs a huge amount of gas, so that adsorption gas is generated during mixing into the paste and applying / drying the paste to the current collector foil. This enormously causes small bubbles to be taken into the structure of the coating film, resulting in a situation where the bulk density is lower than when stored at room temperature.

  Therefore, the present inventors placed activated carbon dried at 80 ° C. in an environment of 7 ° C. and 25 ° C. for a whole day and night, and confirmed how much gas each activated carbon adsorbs by a gravimetric method. Then, at 25 ° C., 0.69% (530 ml / 100 g activated carbon) gas of activated carbon is adsorbed on each activated carbon, and at 7 ° C., 0.91% (702 ml / 100 g activated carbon) gas of activated carbon is adsorbed on each activated carbon. It has been found. Usually, activated carbon is often refrigerated and stored in a nitrogen atmosphere, and during this time, activated carbon adsorbs more gas, and during charging into the paste, during stirring, during application, and during drying, Gas is gradually released from the activated carbon. In particular, during drying at high temperatures, the gas is released all at once from the activated carbon, and the volume of the gas increases due to the high temperature, but the activated carbon particles are covered with conductive material fine particles, a binder and a thickener, and the paste Since the viscosity of is extremely high, it is difficult to release the gas contained in the activated carbon, and bubbles tend to remain in the electrode layer structure.

  The present inventors have found these facts and have come up with the present invention.

  The present invention has been made to solve the above-described problems, and an object thereof is to increase the bulk density of a coated electrode sheet of an electric double layer capacitor. Another object of the present invention is to eliminate fluctuation of the bulk density due to the season and shorten the stirring time.

  The subject of the present invention is a method for producing a coated electrode sheet for an electric double layer capacitor, wherein a paste containing conductive material fine particles, a binder and a solvent is heated and mixed to 30 ° C. or higher to produce a heated paste; A step of heating the activated carbon particles to 80 ° C. or higher, a step of adding the activated carbon particles after the heat treatment to the heating paste at a temperature higher than the paste temperature of the heating paste, and mixing them to prepare an electrode paste; The subsequent electrode paste is applied as a coating paste on a current collector foil, and is heated and dried.

  Hereinafter, various embodiments of the subject of the present invention will be described in detail along with the effects and advantages thereof with reference to the accompanying drawings.

  According to the subject of the present invention, it is possible to prevent a large amount of adsorbed gas from being generated from the activated carbon particles during electrode paste preparation, and further, a space is formed in the applied paste when the applied paste is dried by the gas generated from the activated carbon particles. As a result, it is possible to prevent the bulk density from being lowered. As a result, the bulk density after drying can be increased. Moreover, according to the subject matter of the present invention, the stirring time of the paste can be shortened, work efficiency can be increased, and fluctuations in the bulk density of the paste due to the season can be eliminated.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each figure, the element which attached | subjected the same code | symbol shall show the same or equivalent element.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram of an electrode paste adjustment and coating production line showing a method for producing a coated electrode sheet for an electric double layer capacitor according to the present embodiment.

(Adjustment of electrode paste and its application / drying)
The adjustment of the electrode paste shown in FIG. 1 is only schematically shown. First, the solvent 4 is put in the container 7, the stirring blade is put, and the binder 1 is put in while stirring the solvent 4. Next, after putting the conductive material fine particles 2 to prepare a paste, the paste is stirred while being heated to 30 ° C. or higher. The heating paste A is produced or adjusted by this heating / mixing step. At this stage, the activated carbon particles 3 are not added to the heating paste A.

  The activated carbon particles 3 are vacuum-dried and deaerated in the vacuum dryer 9 while being heated by the heater 8 at a temperature of 80 ° C. or higher. The activated carbon particles 3 after the gas adsorbed by the heat treatment is released are kept at a temperature of 80 ° C. or higher and returned to normal pressure using nitrogen gas. While maintaining a temperature higher than the paste temperature, the mixture is put into the heating paste A and mixed. As a result, the produced electrode paste B was transferred to the paste reservoir of the coating machine 12 heated to 30 ° C. or higher while maintaining the temperature of 30 ° C. or higher, and the current of the current collector foil 11 drawn out from the feed roller. It is applied on top. In FIG. 1, reference numeral 14 indicates the electrode paste B immediately after the electrode paste B is applied as a coating paste on the current collector foil 11.

  After the application, the application paste 14 is quickly heated and dried in the drying unit 13, and the application paste 15 after the completion of the heating and drying is taken up by a take-up roller. Here, the drying temperature in the drying unit 13 depends on the selection of the solvent 4. For example, when the solvent 4 is distilled water or pure water, the drying temperature of the drying unit 13 is 95 ° C. The coating machine 12 and the drying unit 13 are disposed separately in a space in which dry nitrogen is flowed, that is, a nitrogen atmosphere 16.

  By adopting the above steps, the activated carbon particles 3 are mixed with the heated paste A with almost no gas adsorption after heating and vacuum drying at a temperature of 80 ° C. or higher, and then the particles in the electrode paste B. Thus, gas generation from the activated carbon particles 3 hardly occurs during mixing, coating, and heat drying of the electrode paste B. Accordingly, small bubbles are stirred into the electrode paste B or the coating paste, the coating film is softly dried while the coating film is held at the time of drying, or the conductive material fine particles 2 on the surface of the activated carbon particles are formed. There is no worry about peeling. Therefore, the density of the produced electrode sheet is higher than that of the conventional electrode sheet, and an electrode layer in which the conductive material fine particles 2 and the binder 1 are in close contact with the activated carbon particles 3 can be obtained.

(Comparative example: State of activated carbon particles in the conventional coating film)
FIG. 2 is a schematic longitudinal sectional view showing a change in the vicinity of activated carbon particles of a coated cloth film of a coated electrode sheet of a conventional electric double layer capacitor. Among them, (a) shows a state of a coating film immediately after coating, and (b) shows a state in which a huge amount of gas is generated from the activated carbon particles 3 at the time of drying, and bubbles are caught in the structure. Show.

  A mixed film 18 of the conductive material fine particles 2 and the binder 1 is formed so as to cover the geometric surface of the activated carbon particles 3. When the coating film is dried, the solvent evaporates, and the mixed film 18 of the conductive material fine particles 2 and the binder 1 is concentrated and contracts in a form of reducing the thickness. At the same time, as the temperature rises, a large amount of the gas adsorbed on the activated carbon particles 3 is released, and is released into the mixed coating 18 and into the coating film in such a manner as to push the mixed coating 18 away. Go out with the solvent. However, as the coating film dries and the viscosity of the paste increases, the gas released from the activated carbon particles 3 is less likely to be released to the outside. As shown in FIG. One of the mixed coatings 18 remains taken in as small bubbles 22 or remains as large bubbles 21 between the activated carbon particles 3 and the activated carbon particles 3 to reduce the bulk density.

  These situations became clear by detailed observation of conventional coating films by electron micrographs. It was 0.582 when the bulk density was investigated.

Example 1
First, steam activated charcoal having an average particle diameter of 15 μm was vacuum-dried at 200 ° C. for 1 hour, then dried nitrogen was fed back to normal pressure, and the activated carbon was held while the temperature was set at 150 ° C.

  Next, in a stainless steel container 7, N-methyl-2-pyrrolidone (N-methylpyrrolidone: also referred to as NMP) as the solvent 4 and polyvinylidene fluoride (polyvinylidene fluoride: PVDF) as the binder 1 are also referred to. ) 12% solution (Kureha Chemical KF Polymer) is added, and further 10 g of acetylene black is added as the conductive material fine particles 2, the temperature is set to 50 ° C., and the planetary mixer is heated. The paste was stirred for 10 minutes. Further, 300 g of N-methyl-2-pyrrolidone (NMP) was added, and the paste was stirred for 10 minutes while maintaining the temperature at 50 ° C. to prepare a heated paste A.

  Furthermore, 80 g of activated carbon kept at 150 ° C. in dry nitrogen was quickly weighed and added to heating paste A. The charging temperature of the activated carbon at this time was about 80 ° C. Further, it was confirmed that the weight of the activated carbon was increased during the weighing of the activated carbon for a short time, and the gas started to be adsorbed on the activated carbon particles whose temperature was lowered, and the weight of the activated carbon particles themselves was increased. Then, the heating paste A to which the activated carbon particles 3 were added was stirred for 10 minutes with a planetary mixer, and the activated carbon particles 3 were mixed with the heating paste A, whereby the electrode paste B was produced.

  In the application of the electrode paste B onto the current collector foil 11 and the heat drying step, a high-purity aluminum plain foil having a width of 300 mm, a thickness of 30 μm and a roll length of 250 m is used as the current collector foil 11, and the coating machine 12 is used. The reverse roll coater was used, the rotation ratio of the comma roll and the backing roll was set to 1, and the wet coating thickness was 220 μm. The length of the paste drying section 13 in the longitudinal direction is 2 m, the temperature setting in the first half 1 m is 90 ° C., the temperature setting in the second half 1 m is 120 ° C., and the solvent 4 NMP was removed by drying.

  The time until the electrode paste B formed by mixing the activated carbon particles 3 in the heating paste A was applied or coated on the current collector foil 11 as a coating paste and dried was 30 minutes.

  On the other hand, when the electrode is produced using the electrode paste B that has been passed for a whole day and night after the activated carbon particles 3 are charged, the bulk density is reduced and the performance as a capacitor cell is also lowered. It was confirmed. This is because the activated carbon particles 3 in the electrode paste B absorb gas from the atmosphere during storage, and the adsorbed gas is released when the electrode paste B is applied and dried.

  Then, the activated carbon particles 3 are mixed with the heating paste A to produce the electrode paste B, and the time until the electrode paste B is applied to the current collector foil 11 as a coating paste and heated and dried is within one hour. It is desirable. If the time is longer than that, NMP as the solvent 4 penetrates into the pores of the activated carbon particles 3, the remaining amount of NMP increases, and it becomes difficult to dry the coating paste.

  When the bulk density of the electrode produced in this example was examined, it was 0.631, and it was confirmed that it was greatly improved compared to the bulk density of 0.582 of the comparative example described above. Moreover, in the electrode produced in this example, the small bubbles 22 and the activated carbon particles 3 in the mixed coating 18 of the conductive material fine particles 2 and the binder 1 as seen in the comparative example (FIG. 2) are obtained by an electron microscope. There was almost no evidence that large bubbles 21 remained between the activated carbon particles 3 and the activated carbon particles 3.

(Production of capacitor cell)
Each electrode sheet of Example 1 and Comparative Example 1 was cut out, and an electrode layer having a size of 30 mm × 30 mm continuous thereto was cut using an aluminum plane foil portion not coated with an electrode layer as a current terminal, After vacuum drying at 150 ° C. for 18 hours, sandwiched between cellulose-based separators having a thickness of 35 μm, quaternary ammonium salt is used as an electrolyte, propylene carbonate is added as an electrolytic solution, housed in an aluminum laminate container and sealed. The capacitance and internal resistance were examined by examining the charge / discharge characteristics at 2.7 V at ° C.

  The capacitance and internal resistance of Example 1 are 2.05 F and 1.72 Ω, respectively, and the capacitance increases compared to the capacitance of 1.82 F and internal resistance of 1.96 Ω of the comparative example. It has been found that the internal resistance is reduced. This is because, in addition to the increase in the bulk density, the adhesion between the conductive material fine particles 2 and the binder 1 on the surface of the activated carbon particles is improved.

  FIG. 3 shows the value of the bulk density after coating when only the storage temperature of the paste (and hence the heating temperature of the paste when producing the heated paste A) is changed under the conditions of Example 1. It is a graph. As apparent from FIG. 3, by heating the paste to 30 ° C. or higher to produce heated paste A, the bulk density of the electrode layer after coating and drying is kept at a value of 0.62 or higher. The reason why the bulk density of the electrode layer is lowered at 25 ° C. or lower is that the viscosity is increased, stirring is insufficient, and the dispersibility is deteriorated. When the paste is stirred at 30 ° C. or higher to produce the heated paste A, the viscosity is remarkably lowered, the dispersion is improved, and the stirring time can be shortened as compared with the case of stirring at room temperature or low temperature. This is the same as cooking faster when cooking. When the paste temperature is below 30 ° C., the temperature becomes higher in the summer, and the stirring conditions of the paste are different from those of other seasons, making it difficult to maintain the same quality. On the other hand, in this example, when the paste temperature exceeds 80 ° C., the evaporation of NMP as the solvent 4 increases and the composition of the paste changes, and the thickener reacts with the activated carbon particles 3 to hydrolyze, There is a problem that impurities such as acids are generated. Therefore, it is most desirable in this example to stir the paste at a temperature of 30 ° C. or higher and lower than 80 ° C. to produce the heated paste A, and stirring can be completed in the shortest time. Note that the upper limit value of the paste temperature in FIG. 3 depends on the material selection of the solvent 4, and when NMP, distilled water, or pure water of this example is used as the solvent 4, as described above, the upper limit value of the paste temperature. Is 80 ° C.

  FIG. 4 is a graph showing the value of the bulk density of the electrode layer after coating and drying when only the heat treatment temperature of the activated carbon particles 3 added to the heating paste A is changed under the conditions of Example 1. It is. In order to obtain the observation results shown in FIG. 4, activated carbon that had been refrigerated at 7 ° C. for 2 weeks in the atmosphere before the heat treatment of the activated carbon particles 3 was used. As shown in FIG. 4, before the addition to the heating paste A, the activated carbon or the activated carbon particles 3 are heated to 80 ° C. or higher, whereby the bulk density is maintained at a high value exceeding 0.62. Although the activated carbon particles 3 can be dried even by heating at 70 ° C., the drying time required is long, so a drying temperature of 80 ° C. or higher is desirable. When the heating temperature of the activated carbon particles 3 before addition to the heating paste A is lower than 80 ° C., the gas and moisture adsorbed on the activated carbon particles 3 while being refrigerated at 7 ° C. are not removed, and the activated carbon particles 3 Since the activated carbon particles 3 generate a large amount of gas in each step of paste mixing, coating and drying after the heat treatment, the bulk density is low.

  In this example, when the heating temperature of the activated carbon particles 3 before addition to the heating paste A exceeds 400 ° C., there is a possibility that a part of the activated carbon is oxidized and deteriorated. Moreover, there are few general dryers that can achieve a temperature exceeding 400 ° C., and maintaining the heating temperature at a high temperature exceeding 400 ° C. is not preferable from the viewpoint of cost because the energy loss increases. Therefore, in this example, the heat treatment temperature of the activated carbon particles 3 is desirably 80 ° C. or higher and lower than 400 ° C., and does not depend on the type of the activated carbon. However, since the upper limit value of the heat treatment temperature of the activated carbon particles 3 is determined by the degree of the oxidation phenomenon, it depends on the treatment atmosphere (the amount of oxygen contained in the ambient gas). Therefore, the lower the ambient oxygen amount, the higher the upper limit value of the heat treatment temperature of the activated carbon particles 3. Therefore, the upper limit value of the heat treatment temperature of the activated carbon particles 3 is not generally determined.

Embodiment 2. FIG.
The present embodiment corresponds to a modification of the manufacturing method in the first embodiment for satisfying the requirement to use a second binder in the electrode paste B, which will be described later, as an application of the electric double layer capacitor. is doing.

  FIG. 5 is a diagram showing a method for manufacturing a coated electrode sheet of the electric double layer capacitor according to the present embodiment, and is a schematic diagram showing an electrode paste adjustment process in particular.

(Adjustment of electrode paste)
A different point from Embodiment 1 is that the second binder 5 is a binder that is rubberized by heating exceeding 30 ° C. Examples of such a binder that is rubberized by heating include fluorine resins such as polytetrafluoroethylene (PTFE), rubber binders such as styrene butadiene rubber (SBR), and mixtures thereof.

  As shown in FIG. 5, after the electrode paste B is cooled to 0 ° C. or higher and 30 ° C. or lower with ice water 10 or a refrigerator, the second binder 5 is added to the cooled electrode paste B to obtain the second A binder mixed electrode paste C is produced, and the paste C is applied onto the current collector foil 11 using the coating machine 12 in the same manner as in the first embodiment, and then the applied paste is heated and dried. The cooling temperature is preferably 0 ° C. or higher and 30 ° C. or lower. When the cooling temperature is lowered to less than 0 ° C., there is a possibility that a part of the solvent 4 such as water (distilled water or pure water) is solidified and deteriorated. On the other hand, when the temperature exceeds 30 ° C., the second binder 5 starts to be rubberized and gradually changes, and eventually the paste becomes like a candy.

  With respect to the activated carbon particles 3 contained in the second binder mixed electrode paste C, the pores become negative pressure by the above cooling process, but since the activated carbon particles 3 are not open to the atmosphere, the gas is immediately activated carbon. It does not adsorb to the particles 3. However, it is not desirable to store the second binder mixed electrode paste C for a long time. It is desirable to finish the coating / drying process within 4 hours after charging the activated carbon particles 3.

(Example 2)
After steam-activated charcoal having an average particle diameter of 15 μm was vacuum dried at 80 ° C. for 1 hour, dry nitrogen was fed back to normal pressure, and the temperature was kept at 80 ° C.

  100 g of water (distilled water or pure water) is added as a solvent 4 to a stainless steel container 7, and 2 g of NaCMC (NaC salt of CMC) is added as a thickener and binder to this as 60 ° C. It set and it stirred for 10 minutes with the planetary mixer, heating. Further, 10 g of acetylene black was added as the conductive material fine particles 2, and the mixture was further stirred for 10 minutes with a planetary mixer while maintaining the temperature at 60 ° C. to prepare a heated paste A.

  Next, 80 g of activated carbon kept at 80 ° C. in dry nitrogen was quickly weighed and added to heating paste A. The temperature of the activated carbon particles 3 at the time of charging was about 70 ° C.

  Then, it mixed for 10 minutes using the planetary mixer in the state heated at 60 degreeC, and after obtaining the electrode paste B, the paste B was cooled with the ice water 10, and when the paste temperature fell to 5 degreeC, PTFE dispersion was added as the second binder 5 and stirred for 10 minutes with a planetary mixer to prepare a second binder mixed electrode paste C. The addition amount of PTFE was 8 g as a resin amount.

  Using a coated electrode sheet having a thickness of 300 μm and a thickness of 30 μm and a roll length of 250 m, each coated with an electrode layer having a thickness of 200 μm on each of the front and back surfaces of a high-purity aluminum plain foil having a roll length of 250 m. The density of the electrode layer was examined by changing the type of impregnation solvent.

  A high-purity aluminum plain foil having a width of 300 mm, a thickness of 30 μm and a roll length of 150 m was used as the current collector foil 11, and the wet coating thickness was 220 μm. After drying, the thickness became 100 μm. The length of the paste drying part was 2 m, the temperature setting of the first 1 m part was set to 85 ° C., and the temperature setting of the latter 1 m part was set to 95 ° C., and water as the solvent 4 was removed by drying.

  The activated carbon particles 3 are mixed with the heating paste A to prepare the electrode paste B, and then the second binder mixed electrode paste C obtained by adding the second binder 5 to the electrode paste B is placed on the current collector foil 11. The time required to apply and dry was 50 minutes. When the electrode layer is produced using the second binder mixed electrode paste C that has been passed for a day and night in the refrigerator after the activated carbon particles 3 are charged, the bulk density of the electrode layer is reduced and the performance as a capacitor cell is also lowered. It was confirmed. This is because the second binder mixed electrode paste C absorbed gas from the atmosphere during storage, and the adsorbed gas was released during the coating / drying process. As a result of repeating the coating test under various conditions, the time until the activated carbon particles 3 are mixed with the heated paste A and then the second binder mixed electrode paste C is applied to the current collector foil 11 and dried is 1 It has been found that it is desirable to be within time. When it exceeds 1 hour, additives, such as a thickener, will react with activated carbon in the state heated, and will hydrolyze and produce impurities, such as an organic acid. In addition, moisture penetrates into the pores of the activated carbon including additives, making it difficult to remove by drying.

  When the bulk density was examined, it was 0.601, confirming that it was greatly improved compared to the bulk density 0.582 of the comparative example. In addition, by observation with an electron microscope, as shown in FIG. 2, small bubbles 22 in the mixed coating 18 of the conductive material fine particles 2 and the binder 1 and large bubbles 21 between the activated carbon particles 3 and the activated carbon particles 3 are formed. There was almost no evidence of remaining.

(Production of capacitor cell)
The electrode sheet of Example 2 was cut out, an aluminum plane foil portion not coated with the electrode layer was used as a current terminal, a continuous electrode layer having a size of 30 mm × 30 mm was cut, and vacuum dried at 200 ° C. for 18 hours. After that, sandwiched between cellulose-based separators with a thickness of 35 μm, quaternary ammonium salt as an electrolyte, propylene carbonate as an electrolytic solution, and sealed in an aluminum laminate container, sealed at 25 ° C. and 2.7 V By examining charge / discharge characteristics, capacitance and internal resistance were investigated.

  The capacitance and internal resistance of Example 2 were 1.93 F and 1.87Ω, respectively, and it was confirmed that the same capacitance and internal resistance as in Example 1 were obtained. This is because, as in the case of the first embodiment, in addition to the increase in the bulk density, the adhesion between the conductive material fine particles 2 and the binder 1 on the surface of the activated carbon particles is improved.

  In addition, what plays the role of both a binder and a thickener includes ammonium salt of carboxymethyl cellulose (CMC) (referred to as ammonia CMC), Na salt (referred to as NaCMC), polyvinyl alcohol, methyl cellulose, and hydroxyethyl cellulose. , Polyethylene oxide, polyethylene glycol, and mixtures thereof can be used.

  As the conductive material fine particles, carbon black, furnace black, acetylene black, carbon whisker, carbon fiber, natural graphite, artificial graphite and the like can be used.

  As the organic solvent, N-methyl-2-pyrrolidone (referred to as NMP), tetrahydrofuran, or the like can be used.

  As the activated carbon, steam activated carbon, alkali activated carbon, nanogate carbon, or the like can be used, and the particle diameter is preferably about 10 μm.

  As the current collector foil, a thickness of about 20 μm to 50 μm is desirable, and it is desirable to use a high purity aluminum plain foil, an aluminum etched foil or a copper foil whose surface is etched.

(Appendix)
While the embodiments of the present invention have been disclosed and described in detail above, the above description exemplifies aspects to which the present invention can be applied, and the present invention is not limited thereto. In other words, various modifications and variations to the described aspects can be considered without departing from the scope of the present invention.

It is a schematic diagram of the adjustment of the electrode paste of the coating type electrode sheet of the electric double layer capacitor and the coating production line according to Embodiment 1 of the present invention. It is a cross-sectional schematic diagram which shows the change of the activated carbon particle vicinity of the coating cloth film of the coating type electrode sheet | seat of the conventional electric double layer capacitor, (a) is a figure which shows the mode immediately after application | coating, (b) is huge from activated carbon at the time of drying It is a figure which shows a mode that a sufficient amount of gas was generated and the bubble was bitten in the structure. It is a graph which shows the paste temperature dependence of the bulk density of the coating type electrode sheet of the electric double layer capacitor which concerns on Embodiment 1 of this invention. It is a graph which shows the activated carbon heating temperature dependence of the bulk density of the coating type electrode sheet of the electric double layer capacitor which concerns on Embodiment 1 of this invention. It is a schematic diagram of adjustment of the electrode paste in the manufacturing method of the coating type electrode sheet of the electric double layer capacitor which concerns on Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Binder, 2 Conductive material fine particle, 3 Activated carbon particle, 4 Solvent, 5 2nd binder, 8 Heater, 9 Dryer, 10 Ice water, 11 Current collector foil, 12 Coating machine, 13 Drying part, 16 Nitrogen atmosphere, 18 Conductivity Mixed coating of material fine particles and binder, 20 expanded mixed coating, 21 bubbles, 22 bubbles entrained in the mixed coating.

Claims (6)

A step of heating and mixing a paste containing conductive material fine particles, a binder and a solvent at 30 ° C. or higher to produce a heated paste;
Heating the activated carbon particles to 80 ° C. or higher;
Adding the activated carbon particles after the heat treatment to the heating paste at a temperature higher than the paste temperature of the heating paste and mixing them to produce an electrode paste;
The electrode paste after production is applied as a coating paste on a current collector foil, and has a step of heating and drying,
A method for producing a coated electrode sheet for an electric double layer capacitor. It is a manufacturing method of the application type electrode sheet for electric double layer capacitors according to claim 1,
The binder is polyvinylidene fluoride,
The solvent is N methylpyrrolidone,
A method for producing a coated electrode sheet for an electric double layer capacitor. It is a manufacturing method of the application type electrode sheet for electric double layer capacitors according to claim 1,
The binder is carboxymethylcellulose;
The solvent is distilled water or pure water,
Instead of applying and drying the electrode paste,
A step of cooling the electrode paste to 0 ° C. or higher and 30 ° C. or lower and then adding a second binder that is rubberized by heating at a temperature exceeding 30 ° C. to produce the second binder mixed electrode paste C; ,
Applying the produced second binder mixed electrode paste onto the current collector foil as a coating paste, and drying by heating.
A method for producing a coated electrode sheet for an electric double layer capacitor. It is a manufacturing method of the application type electrode sheet for electric double layer capacitors according to claim 3,
The second binder is polytetrafluoroethylene or styrene butadiene rubber or a mixture thereof,
A method for producing a coated electrode sheet for an electric double layer capacitor. A method for producing a coated electrode sheet for an electric double layer capacitor according to any one of claims 1 to 4,
The activated carbon particles are mixed with the heating paste, and the time until the coating paste is applied to the current collector foil and dried is within one hour,
A method for producing a coated electrode sheet for an electric double layer capacitor. A method for producing a coated electrode sheet for an electric double layer capacitor according to any one of claims 1 to 5,
After applying the coating paste on the current collector foil, performing a heat drying step in a nitrogen atmosphere,
A method for producing a coated electrode sheet for an electric double layer capacitor.

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