JP2009295665A - Electrode for electrochemical element, its manufacturing method, and electrical double layer capacitor using electrode for electrochemical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for an electrochemical element capable of obtaining a capacitor suitable for a high-speed charge and discharge at a high current by intending to reduce an internal resistance of the capacitor and to improve an electrode strength. <P>SOLUTION: In the electrode for the electrochemical element, an electrode composition layer is formed through a conductive adhesive layer on a collector with plural protrusions in at least one direction. Especially, it is desirable that a protrusion-formation-density in the collector may be one piece/mm<SP>2</SP>or more, moreover it is desirable that an effective surface area (A) of the collector per unit area (B) of the collector may exceed 1 by A/B ratio. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode for an electrochemical device, and more particularly to an electrode for an electrochemical device that has both a low internal resistance and a high electrode strength, and is preferably used for an electric double layer capacitor. Moreover, this invention relates to the manufacturing method of this electrode for electrochemical devices, and the electric double layer capacitor using this electrode for electrochemical devices.

In recent years, electric double layer capacitors (hereinafter sometimes simply referred to as “capacitors”) are attracting attention in high-power applications and regenerative energy applications because they can be charged and discharged at high speed, and their applications are expanding. In capacitors, reduction of internal resistance is considered to be an important issue because it reduces heat loss caused by I ² R during large current charge / discharge and leads to improvement of charge / discharge efficiency.

  The improvement of the electrode strength leads to an improvement in the capacity because the handling property and the winding diameter of the wound cell can be reduced. From the above, reduction of internal resistance and improvement of electrode strength are important issues for improving the performance of electric double layer capacitors.

In order to reduce the internal resistance of a capacitor, it has heretofore been proposed to reduce the internal resistance of an electrode by forming a plurality of protrusions on a current collector. For example, in the electrochemical device described in Patent Document 1, a metal foil serving as a current collector is punched, and a through hole and a protrusion having a height of 300 μm and a size of 0.4 mm × 0.4 mm are formed at 4 / mm ^2. The internal resistance of the capacitor is reduced. At this time, the height of the protrusion is preferably 0.5 to 0.8 when the electrode thickness is 1.0. However, in the method described in Patent Document 1, the number of protrusions protruding from the electrode composition layer is small, and the area where the electrode composition layer and the current collector are in contact is small. For this reason, the reduction of internal resistance was still insufficient. Furthermore, since the method described in Patent Document 1 merely forms the electrode composition layer on the current collector, it cannot be said that the electrode composition layer and the current collector are sufficiently adhered to each other. The contact resistance generated at the interface between the electrode composition layer and the current collector cannot be sufficiently reduced. And since sufficient contact | adhesion was not aimed at, there existed a problem that electrode strength also became weak.

  On the other hand, in the electric double layer capacitor described in Patent Document 2, it is possible to improve the adhesion with the polarizable electrode and reduce the internal resistance by adhering the conductive material and the polarizable electrode using a conductive adhesive. Proposed.

JP-A-9-134726 JP-A-7-161589

  The object of the present invention is to achieve a capacitor suitable for high-speed charge / discharge with a large current by reducing the internal resistance of the capacitor and improving the electrode strength, which cannot be said to be sufficiently solved by the method described in the above-mentioned document. The object is to provide an electrode for an electrochemical element.

  As a result of intensive studies to solve the above problems, the present inventors have improved the contact area between the electrode composition layer and the current collector by forming a plurality of protrusions on the current collector, By forming the electrode composition layer on the current collector through the conductive adhesive layer, the interface resistance between the electrode composition layer and the current collector can be drastically reduced and the electrode strength can be improved. I found.

  Further, in order to increase the contact area between the electrode composition layer and the current collector, by controlling the formation density and shape of the protrusions on the current collector, the internal resistance is further reduced and the electrode strength is reduced. I found it to improve. In addition, by forming an opening in the current collector, electrolyte ions permeate the electrodes, so that the active material in the electrode composition layer can be effectively used, the capacitance is further improved, and between the products. It has been found that the variation in capacity is reduced.

  Furthermore, by applying a conductive adhesive to the current collector and then providing a protrusion, a conductive adhesive layer can be formed on the side of the protrusion, and the opening of the protrusion is blocked. It has been found that the adhesion between the current collector and the electrode composition layer can be improved.

  Based on these findings, the present inventors have completed the present invention. That is, this invention which solves the said subject contains the following matter as a summary.

(1) An electrode for an electrochemical device, wherein an electrode composition layer is formed on a current collector having a plurality of protrusions on at least one surface via a conductive adhesive layer.

(2) The electrode for an electrochemical element according to (1), wherein a protrusion forming density of the current collector is 1 piece / mm ² or more.

(3) The electrode for an electrochemical element according to (1) or (2), wherein the effective surface area (A) of the current collector per unit area (B) of the current collector exceeds 1 in terms of A / B ratio.

(4) The electrode composition surrounded by the protrusion protruding into the electrode composition layer is 1% by volume or more of the total volume of the electrode composition layer, according to any one of (1) to (3) Electrode for electrochemical elements.

(5) The electrochemical element according to any one of (1) to (4), wherein the height (H) of the protrusion has a relationship of H / T <1 with respect to the thickness (T) of the electrode composition layer. Electrode.

(6) The electricity according to any one of (1) to (5), wherein the current collector has a hole portion, and the hole area ratio is 10 to 90% with respect to a unit area of the current collector. Electrode for chemical elements.

(7) The electrode for an electrochemical element according to (6), wherein the opening is formed on the top of the protrusion.

(8) The electrode for an electrochemical element according to (1), wherein the shape of the protrusion is a triangular frustum shape or a quadrangular frustum shape whose upper base area is smaller than the lower base area.

(9) The electrode for an electrochemical element according to any one of (1) to (8), wherein the electrode composition layer contains an electrode active material, a conductive additive, and a binder.

(10) A step of applying a conductive adhesive to the current collector,
Forming a protrusion on the current collector;
Applying an electrode composition onto the current collector;
The manufacturing method of the electrode for electrochemical elements which has the process of hot-pressing the apply | coated electrode composition.

(11) An electric double layer capacitor having the electrode for an electrochemical element according to any one of (1) to (9).

  According to the present invention, the contact area between the electrode composition layer and the current collector is improved by forming a plurality of protrusions on the current collector, and the conductive adhesive layer is further formed on the current collector having the protrusions. By forming the electrode composition layer via the electrode, an electrode for an electrochemical device having a low interface resistance between the electrode composition layer and the current collector and a high electrode strength is provided.

  Hereinafter, the present invention will be described in more detail with reference to the drawings including the best mode. As shown in the figure, an electrode for an electrochemical element 4 of the present invention is an electrode composition layer on a current collector 1 having a plurality of protrusions (10, 12) on at least one surface via a conductive adhesive layer 2. 3 is formed. First, the current collector 1 having protrusions used in the present invention will be described.

<Current collector with protrusion>
FIG. 1 is a partial perspective view of a current collector 1 used in the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a sectional view thereof.

 As the type of material constituting the current collector 1, for example, metal, carbon, conductive polymer, or the like can be used, and metal is preferably used. As the current collector metal, aluminum, platinum, nickel, tantalum, titanium, stainless steel, other alloys and the like are usually used.

 The current collector 1 is subjected to surface chemical treatment and surface roughening treatment in advance as necessary for reducing contact resistance with the electrode composition layer or improving adhesion with the electrode composition layer. Also good. Examples of the surface chemical treatment include acid treatment and chromate treatment. Examples of the surface roughening treatment include electrochemical etching treatment and etching treatment with acid or alkali.

  The thickness of the current collector 1 is usually 1 to 200 μm, preferably 5 to 100 μm, more preferably 10 to 60 μm in the flat portion.

 As shown in the figure, the current collector 1 is formed with a convex protrusion 10 protruding from at least one surface thereof. Moreover, as shown in the drawing, a concave protrusion 12 protruding on the other surface may be formed. These protrusions are particularly preferably formed so as to protrude toward the surface on which the electrode composition layer 3 is formed. Therefore, when the electrode composition layer 3 is formed only on one side of the current collector 1, only the convex projections 10 protruding on the surface may be formed. In addition, when the electrode composition layer 3 is formed on both surfaces of the current collector 1, it is particularly preferable to form a convex protrusion 10 protruding on one surface and a concave protrusion 12 protruding on the other surface. Here, the protrusions (10, 12) in the present invention are protrusions having a height of 1 μm or more in a direction perpendicular to the current collector plane, and are generated by etching or roughening the current collector surface. Does not include fine irregularities. That is, the height (H) of the protrusion in the present invention is 1 μm or more, preferably 2 to 200 μm.

A plurality of protrusions are formed on the current collector 1. The number of protrusions is preferably greater than 1 piece / mm ² , more preferably 2-30 pieces / mm ² , and particularly preferably 10-25 pieces / mm ² in terms of formation density. Here, the formation density of protrusions is the number of protrusions formed per unit area of the current collector surface, and is obtained by observing the current collector surface in an enlarged manner. The number of protrusions is the sum of the convex protrusions 10 and the concave protrusions 12.

The protrusions as described above are formed by embossing a foil-like metal or the like and extending the metal of the embossed portion as described later. Therefore, the total surface area (effective surface area) is increased by the amount that the metal foil is stretched. That is, the effective surface area (A) per unit area (B) of the current collector 1 exceeds 1 in the A / B ratio. In other words, the effective surface area in the 1 mm × 1 mm region (1 mm ² ) of the current collector surface exceeds 1 mm ² . The effective surface area of the current collector 1 is the sum of the areas of the flat portions where the protrusions are not formed and the areas of the side surfaces of the protrusions. The area of the protrusion side surface is the area of the protrusion side portion 11 from the current collector flat portion to the rising top portion in the protrusion 10. When the concave protrusion 12 is formed, the area of the taper portion 13 depending from the current collector flat portion is also included in the area of the protrusion side surface. Further, when the opening 3 is not formed in the protrusion, the area of the upper surface or the lower surface of the protrusion is also included in the effective surface area of the current collector 1.

  The effective surface area of the current collector 1 is the number of protrusions (10, 12) formed per unit area of the current collector 1, the dimensions of the protrusions, and the dimensions in the case where apertures are formed. It is determined by measurement using an electron microscope (SEM). By increasing the effective surface area of the current collector 1, the contact area between the electrode composition layer 3 and the current collector 1 increases, so that the contact resistance between the electrode composition layer 3 and the current collector 1 decreases, In addition, the electrode strength is improved. As a result, the internal resistance of the electric double layer capacitor can be reduced and the durability is improved. Accordingly, the effective surface area (A) per unit area (B) of the current collector 1 exceeds 1 in terms of A / B ratio, preferably 1.5 or more, more preferably 1.5 to 6, particularly preferably 1. In the range of 5-4.

  As shown in FIGS. 5 and 6, the protrusion formed on the current collector 1 penetrates into the electrode composition layer 3. Since the electrode composition is also filled in the internal space of the protrusion, the bonding between the electrode composition layer 3 and the current collector 1 is strengthened, the electrode strength is improved, and the current collection efficiency is also improved. Therefore, it is preferable that the ratio of the electrode composition filled in the internal space of the protrusion, that is, the amount of the electrode composition surrounded by the protrusion, to the total electrode composition amount is larger. That is, in the electrode 4 for an electrochemical element of the present invention, the electrode composition surrounded by the protrusions is preferably 1% by volume or more, more preferably 10% by volume of the total volume of the electrode composition layer 3. As mentioned above, More preferably, it exists in the range of 10-30 volume%.

 Here, the volume of the electrode composition surrounded by the protrusions is the number of protrusions formed on the current collector 1, the protrusion dimensions, and the dimensions when the openings 14 are formed. SEM), and the height of the protrusion is obtained from a thickness meter (the height of the protrusion = the thickness of the protrusion current collector−the thickness before the protrusion processing), and the total volume of the protrusion calculated from these equal.

  In the electrochemical element electrode 4 of the present invention, the ratio between the height (H) of the protrusion formed on the current collector 1 and the thickness (T) of the electrode composition layer 3 provided on the protrusion forming surface, H / T is preferably less than 1, and more preferably in the range of 0.2 to 0.9. By setting the H / T ratio in the above range, the reduction in internal resistance and the improvement in electrode strength become more remarkable. On the other hand, if the height H of the protrusion is equal to or greater than the thickness T of the electrode composition layer 3, the protrusion protrudes from the electrode composition layer 3 and damages the separator formed between the electrodes, or the electrodes come into contact with each other to cause a short circuit. There is.

  The current collector 1 preferably has an aperture. The position where the opening 14 is formed is not particularly limited. The opening 14 may be formed by forming a through hole in the flat portion of the current collector 1, and the opening 14 may be formed by breaking through the top of the protrusion. May be formed. The formation amount of the opening 14, that is, the opening ratio is preferably 10% to 90%, more preferably 20% to 60%, particularly preferably 30% to 60% with respect to the unit area of the current collector 1. Is in range. The aperture ratio is obtained by planar observation of the current collector 1. Specifically, the aperture ratio is determined by performing planar observation of the current collector 1 and calculating the area of the through holes per unit area.

 By setting the aperture ratio of the current collector 1 in the above range, capacity variation between lots when an electric double layer capacitor is manufactured can be suppressed. In an electrochemical device using a current collector that does not have a normal aperture, if a non-facing surface where the electrodes do not face each other is created when a multilayer electric double layer capacitor is produced, from the non-facing surface Capacitance cannot be taken out. Further, when the amount of active material per unit area of the electrode varies, the actual capacitance that can be taken out may be smaller than the capacitance calculated from the weight of the active material amount. Therefore, there may be a variation in capacity between lots of electric double layer capacitor cells. This is because the diffusion of electrolyte ions occurs only on the opposing surface of the positive and negative electrodes. However, by forming the apertures in the current collector 1, electrolyte ions pass through the current collector 1 and diffuse, so that the capacitance can be taken out from the non-facing surface where the electrodes do not face each other. Furthermore, even when using electrodes with different amounts of active material per unit area of the electrode, it is possible to easily balance the capacitance within the capacitor cell as long as the total weight of the electrode active material is matched. Capacity variation between lots of cells can be suppressed.

  When the opening 14 is provided in the current collector 1, the opening diameter is 0.01 to 10 μm, preferably 1 to 5 μm (when the opening is rectangular, the length is one side of the opening). When the opening is too small, the passage of electrolyte ions becomes insufficient, and the above-described effects cannot be obtained. On the other hand, when the opening diameter is too large, the effective surface area of the current collector 1 may decrease.

  The shape of the protrusion formed on the current collector 1 is not particularly limited, and may be a pyramid shape, a cone shape, a prismatic shape, or a cylindrical shape as illustrated. However, in order to maintain the strength of the protrusion, as shown in the figure, the upper base area (upper opening) is smaller than the lower base area (lower opening), and has a triangular or truncated pyramid shape. Is preferred.

  The method for imparting protrusions to the current collector 1 is not particularly limited, and various known methods can be used. Among them, a pair of upper and lower embossing rolls rotating in opposite directions are used from the viewpoint of productivity and cost. The method is preferred. Protrusions are formed on the current collector by passing a current collector to which the protrusions are not provided through the gap between the embossing rolls. On the surface of each pair of upper and lower embossing rolls, a large number of convex portions and concave portions are alternately arranged in a grid pattern alternately in the vertical and horizontal directions, and the arrangement of the convex concave portions is given to the current collector 1. It is preferable that the protrusions are arranged in a triangular frustum shape or a quadrangular frustum shape. Further, it is more preferable that each of the convex portions and the concave portions provided on the embossing roll is a sharp blade, and an opening is provided at the top of the protrusion.

<Conductive adhesive>
An electrode composition layer 3 is formed on the surface of the current collector via the conductive adhesive layer 2. By providing the conductive adhesive layer 2, the adhesion between the electrode composition layer 3 and the current collector 1 is improved, and the interface resistance between the electrode composition layer 3 and the current collector 1 can be reduced. As the conductive adhesive, known ones can be used, and among them, a conductive adhesive obtained by dissolving or dispersing a conductive agent, a binder, and a thickener in a solvent is preferable.

  The conductive agent is not particularly limited as long as it has conductivity, among which conductive carbon black, graphite and the like are particularly preferable. The volume average particle diameter of the conductive agent is usually in the range of 0.001 to 10 μm, preferably 0.05 to 5 μm, more preferably 0.01 to 1 μm. These conductive agents can be used alone or in combination of two or more.

  The binder is not particularly limited, and examples thereof include polymer compounds such as a fluorine polymer, a diene polymer, an acrylate polymer, polyimide, polyamide, and polyurethane. Furthermore, a cellulose derivative may be used as a thickener, and an ammonium salt of carboxymethyl cellulose is particularly preferable.

  The conductive adhesive used in the present invention may contain a solvent as required. Examples of the solvent component include toluene, acetone, water, methanol, ethanol, propanol, butanol, tetrachloroethylene, trichloroethylene, and bromochloro. Examples include methane, diacetone, dimethylformamide, ethyl ether, cresol, xylene, chloroform, and dimethyl ether, and these can be used alone or in combination of two or more.

  The amount ratio of the conductive agent, the binder and the solvent in the conductive adhesive may be appropriately determined depending on the purpose. For example, 1 to 10 parts by weight of the binder with respect to 100 parts by weight of the conductive carbon black powder, The range of 0-300 weight part of a solvent can be mentioned.

  The conductive adhesive can be produced by mixing the above components using a mixer. As the mixer, a ball mill, a sand mill, a pigment disperser, a pulverizer, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, and the like can be used.

  The method for applying the conductive adhesive to the current collector 1 is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

  The thickness of the conductive adhesive layer 2 applied to the current collector 1 is usually 1 to 15 μm, preferably 2 to 10 μm, more preferably 2 to 5 μm. When the thickness of the conductive adhesive layer is within the above range, the anchor effect is satisfactorily exhibited and the electron transfer resistance can be reduced.

  The conductive adhesive layer 2 may be formed after the protrusions are applied to the current collector. However, the conductive adhesive layer 2 is formed on the flat current collector before the protrusions are applied, and then the protrusions are formed on the current collector. It is preferable to provide the protrusion-coated current collector 1 on which the conductive adhesive is formed efficiently. The conductive adhesive layer 2 can be formed on the side of the protrusion by applying a conductive adhesive to the current collector before the protrusion is applied, and then providing the protrusion. The adhesion between the current collector 1 and the electrode composition layer 3 can be improved without blocking the opening 14 with the conductive adhesive.

<Electrode active material>
The electrode composition layer 3 preferably contains an electrode active material, a conductive aid and a binder.
The electrode active material is preferably an allotrope of carbon, and specific examples include activated carbon, polyacene, carbon whisker, and graphite. In particular, activated carbon is preferable as the electrode active material for the electric double layer capacitor, and specific examples thereof include phenol-based, rayon-based, acrylic-based, pitch-based, and coconut shell-based activated carbon. These carbonaceous materials can be used alone or in combination of two or more. Further, as the electrode active material, non-porous carbon having a microcrystalline carbon similar to graphite and having an increased interlayer distance of the microcrystalline carbon can be used. Such non-porous carbon is obtained by dry-distilling graphitized charcoal with microcrystals of a multilayer graphite structure at 700 to 850 ° C., then heat-treating with caustic at 800 to 900 ° C., and if necessary with heated steam. It is obtained by removing the residual alkali component.

The electrode active material used in the present invention preferably has a large specific surface area that can form an interface having a larger area even with the same mass. Specifically, the specific surface area of the electrode active material is preferably ^{30 m} 2 / g or more, more preferably 500~5,000m ² / g, particularly preferably from 1,000~3,000m ² / g. The shape of the electrode active material may be either powder or fiber.

  The volume average particle diameter of the electrode active material is preferably 0.1 to 100 μm, more preferably 1 to 50 μm, and still more preferably 3 to 35 μm. When the volume average particle diameter is in this range, it is preferable because the electrode can be easily molded and the capacity can be increased. The electrode active material described above can be used alone or in combination of two or more depending on the type of electrode for the electric double layer capacitor. When the electrode active materials are used in combination, two or more types of electrode active materials having different average particle diameters or particle size distributions may be used in combination.

<Conductive aid>
The type of the conductive aid is not particularly limited as long as it has conductivity, and examples thereof include carbon allotropes or metals, and carbon allotropes are preferably used. Specifically, conductive carbon black such as furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennaut Shap); natural graphite, graphite such as artificial graphite; Particulate conductive aids that are: Moreover, the fibrous conductive support agent which consists of carbon allotropes, such as carbon fibers, such as a polyacrylonitrile type | system | group carbon fiber, a pitch type | system | group carbon fiber, and a vapor-grown carbon fiber; Examples of conductive assistants made of metal include particulate conductive assistants such as titanium oxide, ruthenium oxide, aluminum, and nickel; and fibrous conductive assistants such as metal fibers. Among these, carbon black is preferable, and acetylene black and furnace black are more preferable.

  The volume average particle diameter of the conductive auxiliary agent is preferably smaller than the volume average particle diameter of the electrode active material, and is usually in the range of 0.001 to 10 μm, preferably 0.05 to 5 μm, more preferably 0.01 to 1 μm. It is. When the particle size of the conductive assistant is within this range, high conductivity can be obtained with a smaller amount of use. These conductive assistants can be used alone or in combination of two or more.

  The amount of the conductive assistant is usually 0.1 to 50 parts by weight, preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. By forming the electrode for the electric double layer capacitor containing the amount of the conductive auxiliary in this range, the capacity of the capacitor can be increased and the internal resistance can be decreased.

<Binder>
The binder is not particularly limited as long as it is a compound having a binding force. Examples of the binder include polymer compounds such as a fluorine polymer, a diene polymer, an acrylate polymer, polyimide, polyamide, and polyurethane. Among them, the binder is preferably an acrylate polymer, and has good binding properties with the current collector 1, improved electrode density by pressing, and internal resistance and flexibility of the obtained electrode. These binders can be used alone or in combination of two or more. Further, the binder may be a binder having a core-shell structure obtained by stepwise polymerization of a mixture of two or more monomers.

  The fluorine-based polymer is a polymer containing a monomer unit containing a fluorine atom. Specific examples of the fluoropolymer include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, ethylene / tetrafluoroethylene copolymer, ethylene / chlorotri Fluoroethylene copolymer and perfluoroethylene / propene copolymer may be mentioned. Among them, it is preferable to include polytetrafluoroethylene because it is easy to fibrillate and retain the electrode active material.

  The diene polymer is a homopolymer of a conjugated diene or a copolymer obtained by polymerizing a monomer mixture containing a conjugated diene, or a hydrogenated product thereof. The proportion of the conjugated diene in the monomer mixture is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Specific examples of the diene polymer include conjugated diene homopolymers such as polybutadiene and polyisoprene; aromatic vinyl / conjugated diene copolymers such as carboxy-modified styrene / butadiene copolymer (SBR); Examples thereof include vinyl cyanide / conjugated diene copolymers such as acrylonitrile / butadiene copolymer (NBR); hydrogenated SBR, hydrogenated NBR, and the like.

  The acrylate polymer is preferably an acrylate polymer containing a monomer unit obtained by polymerizing an acrylic ester and / or a methacrylic ester, usually 50% by weight or more, preferably 70% by weight or more, and has high heat resistance. And the internal resistance of the electrode for electric double layer capacitors obtained can be made small. Specific examples of the acrylate polymer include, for example, 2-ethylhexyl acrylate / methacrylic acid / acrylonitrile copolymer, 2-ethylhexyl acrylate / methacrylic acid / methacrylonitrile copolymer, butyl acrylate / acrylonitrile copolymer. , Butyl acrylate / acrylic acid copolymer, 2-ethylhexyl acrylate / styrene / methacrylic acid copolymer, and butyl acrylate / methyl methacrylate / methacrylic acid copolymer, acrylic acid-2-ethylhexyl / acrylonitrile / itacon An acid polymer etc. are mentioned.

  The glass transition temperature (Tg) of the binder is preferably 50 ° C. or lower, more preferably −100 to 0 ° C. When the Tg of the binder is within this range, the binding property is excellent with a small amount of use, the electrode strength is high, the flexibility is high, and the electrode density can be easily increased by a pressing process during electrode formation.

  The shape of the binder is most preferably particulate in order to minimize binding, increase in electrode capacity, and increase in internal resistance, for example, a binder such as latex. In a state in which the above particles are dispersed in a solvent, and powders obtained by drying such a dispersion.

  The particle size of the binder is not particularly limited, but is usually 0.001 to 100 μm, preferably 0.01 to 10 μm, more preferably 0.05 to 1 μm. When the average particle size of the binder is within this range, an excellent binding force can be imparted to the active material layer even when a small amount of the binder is used.

  The method for producing the binder is not particularly limited, and a known polymerization method such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, or a solution polymerization method can be employed. Among them, it is preferable to produce by an emulsion polymerization method because the particle diameter of the binder is easy to control.

  The usage-amount of a binder is 1-20 weight part normally with respect to 100 weight part of electrode active materials, Preferably it is the range of 3-15 weight part.

<Electrode composition>
The electrode composition preferably used in the present invention is composed of an electrode active material, a conductive additive and a binder, and may further contain a cellulose derivative. When a cellulose derivative is used, the stability of the slurry containing the electrode composition is high, and solid matter precipitation and aggregation are unlikely to occur. Furthermore, the coating property and fluidity | liquidity of a slurry improve by using a cellulose derivative.

  The cellulose derivative is a compound obtained by etherifying or esterifying at least a part of the hydroxyl group of cellulose, and is preferably water-soluble. Cellulose derivatives usually do not have a glass transition point. Specific examples include carboxymethyl cellulose, carboxymethyl ethyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose. These salts can also be used. Examples of the salt include ammonium salt and alkali metal salt. Among these, a salt of carboxymethyl cellulose is preferable, and an ammonium salt of carboxymethyl cellulose is particularly preferable.

  The degree of etherification of the cellulose derivative is preferably 0.5 to 2, more preferably 0.5 to 1.5. Here, the degree of etherification is a value representing how many hydroxyl groups contained per 3 glucose units of cellulose are etherified on average. When the degree of etherification is within this range, the stability of the slurry containing the electrode composition is high, and solid matter sedimentation and aggregation are unlikely to occur. Furthermore, the coating property and fluidity | liquidity of a slurry improve by using a cellulose derivative.

  The amount of the cellulose derivative used is appropriately selected according to the type of electrode for an electrochemical element produced using the electrode composition, but is usually 0.1 to 10 parts by weight, preferably with respect to the electrode active material. 0.5 to 5 parts by weight.

<Method for producing electrode for electrochemical device>
As a method for producing the electrode 4 for an electrochemical element of the present invention, the electrode composition layer 3 is formed on the current collector 1 having protrusions by wet molding or dry molding via the conductive adhesive layer 2. Is mentioned. Specifically, wet molding is performed by dispersing or dissolving an electrode active material, a conductive additive, a cellulose derivative, and a binder in water or an organic solvent to prepare a slurry, and applying the slurry onto the current collector 1 and drying. Thus, the electrode composition layer 3 is formed on the current collector 1. Dry molding is a concept for the above-mentioned wet molding, and includes a step of mixing a binder and an electrode active material to obtain a mixture, and a step of molding the obtained mixture into a sheet-like electrode composition layer 3. Including. In dry molding, the mixture may contain a small amount of water or an organic solvent as a molding aid, but the solid content concentration in the molding step is usually more than 70% by weight, preferably 80% by weight or more. It is. Specific examples of the dry molding method include an extrusion molding method, a roll rolling method, a powder molding method, and a pressure molding method.

  The slurry can be produced by mixing water and each of the above components using a mixer. As the mixer, a ball mill, a sand mill, a pigment disperser, a pulverizer, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, and the like can be used. Also, the electrode active material and the conductivity imparting material are first mixed using a mixer such as a crusher, a planetary mixer, a Henschel mixer, and an omni mixer, and then the binder composition is added and mixed uniformly. Is also preferable. By adopting this method, a uniform slurry can be easily obtained.

  The viscosity of the slurry varies depending on the type of coating machine and the shape of the coating line, but is usually 100 to 100,000 mPa · s, preferably 1,000 to 50,000 mPa · s, and more preferably 5,000 to 5,000. It is 20,000 mPa · s.

  The method for applying the slurry to the current collector 1 is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

  Examples of the drying method of the coated slurry include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. Among these, a drying method by irradiation with far infrared rays is preferable.

  The drying temperature and the drying time are preferably a temperature and a time at which the solvent in the applied slurry can be completely removed, and the drying temperature is 100 to 300 ° C, preferably 120 to 250 ° C. The drying time is usually 10 minutes to 100 hours, preferably 20 minutes to 20 hours.

  In the present invention, it is preferable to hot press the applied electrode composition. The hot press may be performed before the drying or after the drying. By performing the pressing, an electrode having a smooth surface and a uniform surface can be obtained. In addition, pressing after drying is preferable because the electrode density can be easily increased.

  The hot pressing method is preferably a die press or roll press. The temperature of hot pressing is preferably in the range of 50 ° C to 150 ° C, more preferably 80 ° C to 130 ° C.

<Electric double layer capacitor>
The electric double layer capacitor of the present invention has the electrochemical element electrode 4 of the present invention. The electric double layer capacitor can be produced according to a conventional method using the electrode of the present invention and components such as an electrolytic solution and a separator. Specifically, for example, the electrode is cut into an appropriate size, then the electrodes are overlapped via a separator, and this is wound into a capacitor shape, folded into a container, and an electrolytic solution is injected into the container. Can be manufactured by sealing.

  The type of the electrolytic solution used in the present invention is not particularly limited, but a nonaqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent is preferable.

As the electrolyte, conventionally known ones can be used, and (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , (C ₂ H ₅ ) ₄ NPF ₆ , LiClO ₄ , Examples of the salt include LiAsF ₆ , LiBF ₄ , LiPF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , and LiN (CF ₃ SO ₂ ) ₂ . The concentration of the electrolyte in the electrolytic solution is preferably at least 0.1 mol / liter or more in order to reduce the internal resistance due to the electrolytic solution, and more preferably in the range of 0.5 to 1.5 mol / liter. preferable.

  The solvent (electrolytic solution solvent) is not particularly limited as long as it is generally used as an electrolytic solution solvent. Specific examples include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone; sulfolanes; nitriles such as acetonitrile. These can be used alone or as a mixed solvent of two or more. Of these, carbonates are preferred.

  Examples of separators used in electric double layer capacitors include microporous membranes or non-woven fabrics made of polyolefins such as polyethylene and polypropylene, porous membranes mainly made of pulp called electrolytic capacitor paper, and rayon-based porous membranes. Can be used. Moreover, it can replace with a separator and a solid electrolyte can also be used.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, the part and% in a present Example are a basis of weight unless there is particular notice.

The tests and evaluations in the examples and comparative examples are performed by the following methods.
(Measurement of effective surface area of current collector)
The effective surface area of the current collector is measured by observing the current collector with protrusions with a scanning electron microscope (SEM), the number of protrusions formed on a unit area (1 mm length × 1 mm width) on the current collector plane, and Measure the aperture (vertical x horizontal) dimensions of the truncated pyramidal projections. The height of the quadrangular frustum-shaped protrusion is measured using a thickness meter (the height of the protrusion (H) = the thickness of the current collector of the protrusion−the thickness before processing the protrusion), and the height of the quadrangular frustum-shaped protrusion is calculated. To do. From these values, the surface area of the current collector per unit volume on one side of the electrode is calculated and used as the effective surface area. From the above, the ratio of the effective surface area (A) of the current collector to the unit area (B) of the current collector, A / B, is obtained. Further, after forming the electrode composition layer on the current collector having protrusions, the fractured surface is confirmed using SEM, and it is confirmed that the quadrangular frustum-shaped protrusions are not crushed, and A / B is the electrode composition layer. It is confirmed that there is no change even after the formation of.

(Measurement of the ratio of electrode composition surrounded by protrusions)
The ratio (volume%) of the electrode composition surrounded by the protrusions was determined by observing the current collector with protrusions with an SEM, the number of protrusions formed on the current collector plane length 1 mm × width 1 mm, and the truncated pyramid shape Measure the aperture (vertical x horizontal) dimensions. The height of the quadrangular frustum-shaped protrusion is measured using a thickness meter (the height of the protrusion = the thickness of the protrusion current collector−the thickness before the protrusion processing), and the height of the quadrangular frustum-shaped protrusion is calculated. From these values, the volume of the protrusions formed on the current collector (the volume of the internal space) is calculated, and the ratio of the electrode composition surrounded by the protrusions in the unit volume on one side of the electrode is determined. In addition, after forming the electrode composition layer on the protrusion current collector, the fractured surface is confirmed using SEM, it is confirmed that the quadrangular frustum-shaped protrusions are not crushed, and the proportion of the protrusion volume is confirmed to be correct. .

(Measurement of hole area ratio)
Measurement of the aperture ratio of the current collector is performed by observing the current collector with protrusions from the direction perpendicular to the current collector plane with an SEM, and measuring the size of the aperture, thereby opening the aperture per unit area. Calculate the area percentage.

(Measurement of electrode composition layer thickness)
The thickness of the electrode composition layer was determined by forming an electrode composition layer on both sides of the current collector and then using an eddy current displacement sensor (sensor head part EX-110V, amplifier unit part EX-V02: manufactured by Keyence Corporation). taking measurement. The thickness of each electrode composition layer is measured at intervals of 2 cm, and the average value thereof is defined as the thickness (T) of the electrode composition layer.

(Peel strength of electrode)
The electrode is cut into a rectangle having a length of 100 mm and a width of 10 mm so that the coating direction of the electrode composition is the long side to obtain a test piece, and the cell composition tape (to JIS Z1522) is applied to the surface of the electrode composition layer with the electrode composition layer side down. The stress is measured when one end of the current collector is pulled in the vertical direction and pulled at a pulling speed of 50 mm / min. The measurement is performed three times, the average value is obtained, and this is taken as the peel strength. The higher the peel strength, the greater the binding force of the electrode composition layer to the current collector.

(Electrical characteristics of electric double layer capacitor)
The electric characteristics of the electric double layer capacitor were determined by a charge / discharge test of the electric double layer capacitor. Charging current is performed using a current value at which the current value per unit area of the electrode is 3.3 mA / cm ^2, and when the voltage reaches 2.7 V, the voltage is maintained and constant voltage charging is performed. Charging is completed when the current value drops to 0.165 mA / cm ² . Then, immediately after the end of charging, constant current discharging is performed until the voltage reaches 0 V at a current value similar to that used during charging. The capacitance is calculated from the amount of electric power at the time of discharge using an energy conversion method.

  Next, using this capacitance, charging is started at a constant current of 5 mA / F so that the charging / discharging speed of the electric double layer capacitor is constant, and the charging times of constant current charging and constant voltage charging are matched. When the charging is completed for 20 minutes, the charging is completed. Then, immediately after the charging is completed, constant current discharging is performed until the voltage reaches 0 V at a current value similar to that used for charging. The internal resistance is calculated using a voltage 0.2 seconds after the start of discharge, and is expressed as a resistivity per volume. The capacitance is calculated from the amount of electric power during discharge using an energy conversion method, and is calculated as the capacitance per volume of the electrode composition layer used in the electric double layer capacitor.

<Example 1>
Carboxymethylcellulose ammonium salt having a degree of etherification of 0.6 and a 1% aqueous solution having a viscosity of 30 mPa · s is dissolved in 213.2 parts of ion-exchanged water, and a volume average particle diameter of 0. 50 parts of 035 μm acetylene black (Denka black powder: manufactured by Denki Kagaku Kogyo Co., Ltd.) was added and mixed and dispersed using a planetary mixer to obtain a conductivity imparting agent dispersion having a solid concentration of 20%.

26 parts of the resulting conductivity imparting agent dispersion, 100 parts of activated carbon powder having an average particle size of 5 μm and a specific surface area of 2000 m ² / g as an electrode active material, and an aqueous dispersion 7.5 having an acrylate polymer solid content concentration of 40% A suitable amount of water is added to 1 part of carboxymethylcellulose ammonium salt having a etherification degree of 0.6 and a 1% aqueous solution having a viscosity of 900 mPa · s, and the mixture is dispersed by using a planetary mixer. A slurry (electrode composition) falling between ˜20,000 mPa · s was obtained. As the acrylate polymer, a copolymer having a Tg of −20 ° C. obtained by emulsion polymerization of 76 parts of 2-ethylhexyl acrylate, 20 parts of acrylonitrile and 4 parts of itaconic acid was used.

  The conductive adhesive is 80 parts of graphite having a volume average particle diameter of 3.7 μm (KS-6: manufactured by Timcal) and 20 parts of carbon black (Super-P: manufactured by Timcal) having a volume average particle diameter of 0.4 μm as a conductive agent. 4 parts of carboxymethylcellulose ammonium salt having a degree of etherification of 0.6 and a viscosity of 1 m aqueous solution of 30 mPa · s as a dispersant, and 8 parts of an aqueous dispersion of 40% solid content of an acrylate polymer as a binder. 261 parts were added and mixed and dispersed using a planetary mixer to obtain a slurry (conductive adhesive) having a solid content concentration of 30%. As the acrylate polymer, a copolymer having a Tg of −20 ° C. obtained by emulsion polymerization of 76 parts of 2-ethylhexyl acrylate, 20 parts of acrylonitrile and 4 parts of itaconic acid was used. This conductive adhesive was applied to an aluminum foil current collector with a thickness of 30 μm with a bar coater and dried at 120 ° C. for 5 minutes to obtain a current collector with a 4 μm conductive adhesive layer.

By passing the current collector with the conductive adhesive layer through the opposing gaps between a pair of upper and lower embossing rolls rotating in the opposite direction, the upper part with 11 protrusions / mm ² and a protrusion height of 66 μm is opened. In addition, a projection current collector with a conductive adhesive layer having a porosity of 36% and having a truncated pyramidal projection (bottom dimension of the bottom of the projection, length 15 μm × width 21 μm) was obtained.

  After applying the slurry of the electrode composition to both sides of the current collector using a roll coater on the current collector with protrusions having a conductive adhesive layer, drying at 60 ° C. for 20 minutes, and then heat-treating at 120 ° C. for 20 minutes Then, a roll press was performed at a roll temperature of 100 ° C. to obtain an electrode for an electrochemical element having a thickness (the thickness of the electrode composition layers on both sides, the thickness of the conductive adhesive layer and the thickness of the current collector) of 110 μm. When the electrode composition layer thickness was measured using an eddy current displacement sensor (sensor head portion EX-110V, amplifier unit portion EX-V02: manufactured by Keyence Corporation), the thickness of the electrode composition layer was 72 μm.

  In the electrode obtained above, the uncoated part where the conductive adhesive layer and the electrode composition layer are not formed is left 2 cm × 2 cm wide, and the electrode composition layer is 5 cm × 5 cm wide. Cut out. A tab material made of aluminum having a length of 7 cm, a width of 1 cm, and a thickness of 0.01 cm was ultrasonically welded to the uncoated portion. Two sets were prepared and dried at 160 ° C. for 40 minutes, and then the two electrode composition layer surfaces were opposed to each other, and a separator made of a rayon-based porous film having a length of 6 cm × width of 6 cm and a thickness of 35 μm was sandwiched therebetween. This was housed in a laminate film, vacuum impregnated with an electrolyte solution so that no air remained, the laminate film was pressure-bonded with a laminator, and sealed to produce an electric double layer capacitor. In addition, as electrolyte solution, what melt | dissolved tetraethylammonium borofluoride in the density | concentration of 1.0 mol / L in propylene carbonate was used. The storage of the electrode after the heat treatment and the assembly of the capacitor were performed in a dry room having a dew point temperature of −60 ° C. Table 1 shows the capacitance density and volume resistivity of the obtained electric double layer capacitor.

<Example 2>
An electrode for an electrochemical element was obtained in the same manner as in Example 1 except that the height of the protrusion of the current collector to be used was 36 μm. Table 1 shows the evaluation results of the electrical characteristics of the obtained electrode.

<Comparative Example 1>
An electrode for an electrochemical element was obtained in the same manner as in Example 1 except that a current collector with protrusions not coated with a conductive adhesive was used. Table 1 shows the evaluation results of the electrical characteristics of the obtained electrode.

<Comparative Example 2>
An electrode for an electrochemical device was obtained in the same manner as in Example 1 except that a flat plate current collector not subjected to protrusion processing was used. Table 1 shows the evaluation results of the electrical characteristics of the obtained electrode.

<Comparative Example 3>
An electrode for an electrochemical device was obtained in the same manner as in Comparative Example 1 except that a flat plate current collector not coated with a conductive adhesive was used. Table 1 shows the evaluation results of the electrical characteristics of the obtained electrode.

  In Examples 1 and 2, the volume resistivity of the electric double layer capacitor is reduced as compared with Comparative Examples 1 to 3. This is because by adding protrusions to the current collector, the effective surface area of the current collector is increased, the area where the electrode composition layer and the current collector are in contact with each other is increased, and the protrusions occupying the electrode composition layer are further increased. In addition to increasing the ratio (volume%) and increasing the protrusion height (H) / electrode thickness (T), it is possible to efficiently collect current from within the electrode composition layer. It is considered that the effect of providing the protrusions was synergistically extracted by providing the layer.

FIG. 1 is a partial perspective view of a current collector used in the present invention. FIG. 2 is a partial plan view of a current collector used in the present invention. FIG. 3 is a partial cross-sectional view of a current collector used in the present invention. FIG. 4 shows a state where a conductive adhesive layer is formed on the current collector surface. FIG. 5 is a partial cross-sectional view of an electrode for an electrochemical element according to the present invention. FIG. 6 is a partially enlarged view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Current collector with protrusion 2 ... Conductive adhesive layer 3 ... Electrode composition layer 4 ... Electrode for electrochemical elements 10 ... Convex protrusion 11 ... Side surface of convex protrusion 12 ... Concave protrusion 13 ... Tapered part of concave protrusion 14 ... opening

Claims (11)

  An electrode for an electrochemical element, wherein an electrode composition layer is formed on a current collector having a plurality of protrusions on at least one surface via a conductive adhesive layer. The electrode for electrochemical devices according to claim 1, wherein the current collector has a protrusion formation density of 1 piece / mm ² or more.   The electrode for an electrochemical element according to claim 1 or 2, wherein an effective surface area (A) of the current collector per unit area (B) of the current collector exceeds 1 in terms of an A / B ratio.   The electrode for an electrochemical element according to any one of claims 1 to 3, wherein the electrode composition surrounded by the protrusion protruding into the electrode composition layer is 1% by volume or more of the total volume of the electrode composition layer. .   The electrode for an electrochemical element according to claim 1, wherein the height (H) of the protrusion has a relationship of H / T <1 with respect to the thickness (T) of the electrode composition layer.   The electrode for an electrochemical element according to any one of claims 1 to 5, wherein the current collector has a hole portion, and the hole area ratio is 10 to 90% with respect to a unit area of the current collector.   The electrode for an electrochemical element according to claim 6, wherein the opening is formed at the top of the protrusion.   2. The electrode for an electrochemical element according to claim 1, wherein the shape of the protrusion is a triangular frustum shape or a quadrangular frustum shape having an upper base area smaller than a lower base area.   The electrode for an electrochemical element according to any one of claims 1 to 8, wherein the electrode composition layer contains an electrode active material, a conductive additive and a binder. Applying a conductive adhesive to the current collector;
Forming a protrusion on the current collector;
Applying an electrode composition onto the current collector;
The manufacturing method of the electrode for electrochemical elements which has the process of hot-pressing the apply | coated electrode composition.   The electric double layer capacitor which has an electrode for electrochemical elements in any one of Claims 1-9.

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