JP2014220327A - Electrode for power storage device, power storage device, and method for manufacturing electrode for power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a power storage device which improves power-stored energy density by improving capacitance and cell voltage of a power storage device when the electrode is used as the electrode for the power storage device, a power storage device using the electrode for the power storage device, and a method for manufacturing the electrode for the power storage device.SOLUTION: An electrode for a power storage device comprises: a carbon nano-tube; an ion fluid; and a metal foil for holding the carbon nano-tube and the ion fluid and having at least one of a recessed part and a projection part on a surface.

Description

  The present invention relates to an electrode for an electricity storage device, an electricity storage device, and a method for producing an electrode for an electricity storage device.

  Among power storage devices, capacitors are widely used in various electric devices. Among many types of capacitors, electric double layer capacitors and lithium ion capacitors have large capacities and have attracted particular attention in recent years.

  The electric double layer capacitor is a power storage device including a cell, a sealed container for securing electrical insulation between the cells and preventing liquid leakage, a collecting electrode for taking out electricity, and a lead wire. The cell mainly includes a pair of opposed activated carbon electrodes, a separator that electrically separates the activated carbon electrodes, and an organic electrolyte that develops capacity.

  A lithium ion capacitor is an electricity storage device that uses an electrode such as an activated carbon electrode that can electrostatically absorb and desorb ions as a positive electrode, and an electrode that can store lithium ions such as hard carbon as a negative electrode.

The energy stored in the electric double layer capacitor is represented by the following formula (1).
W = (1/2) CU ² (1)
W is the stored energy (capacity), C is the electrostatic capacity (depending on the surface area of the electrode), and U is the cell voltage.

  From the above formula (1), it is considered that the improvement of the capacitance contributes to the improvement of the stored energy.

  JP-A-2005-07955 discloses that, in an electric double layer capacitor, in order to improve the capacitance, “carbon nanotubes obtained by applying a shearing force to carbon nanotubes in the presence of an ionic liquid and subdividing them” An electrode material for an electric double layer capacitor, characterized in that it is composed of a gel-like composition comprising an ionic liquid. "

JP 2009-267340 A discloses that a sheet on which a carbon nanotube having a specific surface area of 600 to 2600 m ² / g is paper-molded constitutes a current collector and has a concavo-convex portion on the surface, and the concavo-convex portion thereof. An electrode for an electric double layer capacitor, which is characterized by being integrated by the above. "

Japanese Patent Laying-Open No. 2005-07955 JP 2009-267340 A

  However, the gel composition described in Japanese Patent Application Laid-Open No. 2005-07955 is easily deformed and is not solidified, so that it is inconvenient to handle as an electrode material. Furthermore, since it is difficult to mount the gel composition on the current collector foil with a large thickness, there is a problem in increasing the capacitance per electrode unit area.

  Japanese Patent Application Laid-Open No. 2009-267340 also describes a technique using foamed nickel (a three-dimensional network nickel porous body) as a base material. There is a problem that it is difficult to disperse. Furthermore, gas such as CO is generated due to residual moisture and functional groups in the activated carbon, and there is a problem in increasing the cell voltage. It is also desired to increase the output in relation to the contact between the electrode material and the current collector.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an energy storage device capable of improving the energy density to be stored by improving the capacitance and cell voltage when used as an electrode of the energy storage device. Electrode, an electricity storage device using the electricity storage device electrode, and a method for producing the electricity storage device electrode.

  The present invention is an electrode for an electricity storage device comprising a carbon nanotube, an ionic liquid, and a metal foil that holds the carbon nanotube and the ionic liquid and has a concave portion or a convex portion on the surface.

  The electrode for an electricity storage device of the present invention uses carbon nanotubes as an active material. Since carbon nanotubes are fibrous, the contact property between the carbon nanotubes is good, and the electrical conductivity of the active material can be improved. Therefore, when an electrode for an electricity storage device using carbon nanotubes as an active material is used as an electrode of the electricity storage device, the output of the electricity storage device can be improved.

  Furthermore, the metal foil having at least one of a concave portion and a convex portion on the surface can favorably hold the carbon nanotubes in the concave portion or on the surface of the metal foil. Therefore, when the electrode for an electricity storage device of the present invention is used as an electrode of an electricity storage device, it can improve the electrostatic capacity and the cell voltage of the electricity storage device and improve the energy density of the electricity stored.

  When the thickness of the body portion of the metal foil is 10 μm or more and 500 μm or less, both sufficient strength and current collecting property can be achieved. If the thickness of the metal foil main body is too thin, the strength is reduced. If the metal foil is too thick, the proportion of the metal foil in the power storage device increases and the capacity density of the power storage device decreases, so the thickness of the metal foil main body is 15 μm. The thickness is preferably 100 μm or less, more preferably 18 μm or more and 60 μm or less.

  In the electrode for an electricity storage device of the present invention, preferably, the average pore diameter of the concave portion of the metal foil is 500 nm or more and 500 μm or less.

  When the average pore diameter of the recesses of the metal foil is 500 nm or more, the carbon nanotubes and the ionic liquid are likely to enter the recesses, and the contact between the carbon nanotubes and the metal foil is improved. Therefore, the internal resistance of the electrode is reduced, and the energy density of the electricity storage device can be improved. On the other hand, when the average pore diameter of the concave portion of the metal foil is 500 μm or less, the carbon nanotube can be satisfactorily held in the concave portion without using a binder component, and an electrode having sufficient strength can be obtained. it can.

  In the electrode for an electricity storage device of the present invention, preferably, a through hole penetrating the metal foil is present in the recess of the metal foil.

  When carbon nanotubes and ionic liquid are applied to metal foil using a squeegee, etc., if there are through holes in the recesses, air will not accumulate in the recesses, so the carbon nanotubes and ionic liquid will be fully filled in the recesses. can do. Therefore, the capacitance of the electricity storage device can be increased.

  In the electrode for an electricity storage device of the present invention, preferably, there is no through-hole penetrating the metal foil in the recess of the metal foil.

  If there is no through-hole penetrating the metal foil in the concave portion of the metal foil, the carbon nanotube can be held in the concave portion, and the life of the electricity storage device is prolonged.

  In the electrode for an electricity storage device of the present invention, preferably, the metal foil has a plurality of protrusions, and the pitch between the protrusions is 1 μm or more and 1000 μm or less.

  When the pitch between the protrusions is 1 μm or more, the carbon nanotubes and the ionic liquid are easily held on the metal foil by being supported in the space formed between the plurality of protrusions, Good contactability. Therefore, the internal resistance of the electrode is reduced, and the energy density of the electricity storage device can be improved. On the other hand, when the pitch between the convex portions is 1000 μm or less, the carbon nanotubes can be favorably retained on the metal foil without using a binder component.

In the electrode for an electricity storage device of the present invention, the metal foil is preferably a flocked metal.
When a flocked metal is used as the metal foil, the carbon nanotubes can be entangled with the flocked portion to hold the carbon nanotubes well, and the current collecting property of the electrode for the electricity storage device is improved.

  In the electrode for an electricity storage device of the present invention, preferably, the electrode for an electricity storage device does not contain a binder component.

  According to the electrode for an electricity storage device of the present invention, the active material can be held in the concave portion or on the surface of the metal foil having at least one of the concave portion and the convex portion on the surface. For this reason, an electrode can be produced even if it does not use the binder component which is an insulator. Therefore, the electrode for an electricity storage device of the present invention can hold carbon nanotubes at a high content rate in the electrode unit volume, and further the internal resistance is reduced, so that the capacitance and cell voltage of the electricity storage device are improved. The energy density of stored electricity can be improved.

The present invention is an electricity storage device including an electrode for an electricity storage device.
According to the electricity storage device of the present invention, the electrostatic capacity and the cell voltage can be improved, and the energy density of the electricity stored can be improved.

  The present invention relates to a power storage device comprising a step of kneading carbon nanotubes and an ionic liquid to produce a kneaded product, and a step of filling the kneaded product in a metal foil having at least one of a concave portion and a convex portion on the surface. It is a manufacturing method of the electrode for a vehicle.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for electrical storage devices in which the kneaded material containing a carbon nanotube and an ionic liquid is favorably hold | maintained in the recessed part of metal foil or the surface of metal foil can be obtained. When the electricity storage device electrode is used as an electrode of an electricity storage device, it can improve the electrostatic capacity and cell voltage of the electricity storage device and improve the energy density of the electricity stored.

  According to the present invention, when used as an electrode of an electricity storage device, the electricity storage device electrode capable of improving the electrostatic capacity and the cell voltage and improving the energy density of electricity stored, and the electricity storage using the electrode for the electricity storage device A device and a method for manufacturing the electrode for an electricity storage device can be provided.

It is a top view which shows an example of an expanded metal. It is an expansion perspective view of the A section of FIG. It is a top view which shows an example of a perforated foil. It is a perspective view which shows an example of a porous sheet. (A) is AA sectional drawing of FIG. 4, (b) is BB sectional drawing of FIG. 4, (c) is CC sectional drawing of FIG. (A) is a top view which shows an example of the metal foil which has a recessed part on the surface, (b) is DD sectional drawing of Fig.6 (a). It is sectional drawing which shows an example of a flocked metal. (A) is a top view which shows an example of the metal foil which has a convex part on the surface, (b) is EE sectional drawing of Fig.8 (a). (A) is a top view which shows an example of the metal foil which has a convex part on the surface, (b) is FF sectional drawing of Fig.9 (a). It is the schematic of the cell of the electric double layer capacitor in one embodiment of this invention. It is the schematic of the cell of the lithium ion capacitor in one embodiment of this invention.

  Hereinafter, the present invention will be described based on embodiments. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

[Embodiment 1]
(Electrode for power storage devices)
In one embodiment of the present invention, an electrode for an electricity storage device includes a carbon nanotube, an ionic liquid, and a metal foil having at least one of a concave portion and a convex portion on the surface.

(carbon nanotube)
Examples of the carbon nanotube include a single-walled carbon nanotube (hereinafter also referred to as single-walled CNT) in which only one carbon layer (graphene) is cylindrical, or a cylindrical shape in which a plurality of carbon layers are stacked. A cup-stacked structure in which double-walled carbon nanotubes (hereinafter also referred to as double-walled CNTs) or multi-walled carbon nanotubes (hereinafter also referred to as multi-walled CNTs) and graphene in the form of a paper cup with a bottom are stacked. Nanotubes and the like are known, and any of them can be used.

  The shape of the carbon nanotube is not particularly limited, and any carbon nanotube having a closed end or an open end can be used. Among them, it is preferable to use a carbon nanotube having a shape in which both ends are open. If both ends of the carbon nanotube are open, the ionic liquid or the electrolytic solution easily enters the inside of the carbon nanotube, so that the contact area between the carbon nanotube and the ionic liquid or the electrolytic solution increases. Therefore, the electrode for an electricity storage device using the carbon nanotube can increase the capacitance of the electricity storage device.

  The average length of the carbon nanotubes is preferably in the range of 100 nm to 2000 μm, and more preferably in the range of 500 nm to 100 μm. When the average length of the carbon nanotubes is in the range of 100 nm to 2000 μm, the dispersibility of the carbon nanotubes in the ionic liquid is good, and the carbon nanotubes are easily held in the recesses of the metal foil or on the metal foil. . Therefore, the contact area between the carbon nanotube and the ionic liquid is increased, and the capacitance of the electricity storage device can be increased. Furthermore, when the average length of the carbon nanotube is 500 nm or more and 100 μm or less, the effect of increasing the capacitance of the electricity storage device is significant.

  The average diameter of the carbon nanotubes is preferably in the range of 0.1 nm to 50 nm, and more preferably in the range of 0.5 nm to 5 nm. When the average diameter of the carbon nanotubes is in the range of 0.1 nm to 50 nm, the ionic liquid or the electrolytic solution easily enters the carbon nanotubes, so that the contact area between the carbon nanotubes and the ionic liquid or the electrolytic solution increases. The capacitance of the electricity storage device can be increased.

  The purity of the carbon nanotube is preferably 70% by mass or more, and more preferably 90% by mass or more. If the purity of the carbon nanotube is less than 70% by mass, there is a concern that the withstand voltage may be lowered or dendrite may be generated due to the influence of the catalyst metal.

  When the purity of the carbon nanotube is 90% by mass or more, the electrical conductivity is good. Therefore, the electrode for an electricity storage device manufactured using the carbon nanotube can improve the output of the electricity storage device.

(Ionic liquid)
An ionic liquid is a combination of an anion and a cation so as to have a melting point of about 100 ° C. or less. For example, hexafluorophosphate (PF ₆ ), tetrafluoroborate (BF ₄ ), bis (trifluoromethanesulfonyl) imide (TFSI), trifluoromethanesulfonate (TFS) or bis (perfluoroethylsulfonyl) imide (anion) BETI) can be used. As a cation, an imidazolium ion having an alkyl group having 1 to 8 carbon atoms, a pyridinium ion having an alkyl group having 1 to 8 carbon atoms, a piperidinium ion having an alkyl group having 1 to 8 carbon atoms, A pyrrolidinium ion having an alkyl group or a sulfonium ion having an alkyl group having 1 to 8 carbon atoms can be used.

Examples of the ionic liquid include 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF ₄ ), 1-ethyl-3-methylimidazolium-bis (fluorosulfonyl) imide (EMI-FSI), 1-ethyl. -3-Methylimidazolium-bis (trifluoromethanesulfonyl) imide (EMI-TFSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMI-TFSI), 1-hexyl-3-methyl Imidazolium tetrafluoroborate (HMI-BF ₄ ), 1-hexyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (HMI-TFSI), 1-ethyl-3-methylimidazolium-fluorohydrogenate ( _{EMI (FH) 2.3 F),} N, - Diethyl -N- methyl -N- (2-methoxyethyl) - tetrafluoroborate _{(DEME-BF 4), N} , N- diethyl--N- methyl -N- (2-methoxyethyl) - bis (trifluoromethanesulfonyl ) Imide (DEME-TFSI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13-TFSI), triethylsulfonium-bis (trifluoromethanesulfonyl) imide (TES-TFSI), N- Methyl-N-propylpyrrolidinium-bis (trifluoromethanesulfonyl) imide (P13-TFSI), triethyloctylphosphonium-bis (trifluoromethanesulfonyl) imide (P2228-TFSI), N-methyl-methoxymethylpyrrolidinium-tetrafluor It can be used Roboreto (C13-BF _4). These ionic liquids may be used alone or in appropriate combination. Furthermore, the ionic liquid may contain a supporting salt.

  When using the electrode for an electricity storage device for a lithium ion capacitor, as an ionic liquid, for example, an ion containing a lithium salt such as lithium-bis (fluorosulfonyl) imide (LiFSI) or lithium-bis (trifluoromethanesulfonyl) imide (LiTFSI) Use liquid.

  When the electrode for an electricity storage device is used for a lithium ion capacitor, a solution in which a supporting salt is dissolved in an ionic liquid is used.

Examples of the supporting salt include lithium-hexafluorophosphate (LiPF ₆ ), lithium-tetrafluoroborate (LiBF ₄ ), lithium-perchlorate (LiClO ₄ ), lithium-bis (trifluoromethanesulfonyl) imide (LiN (SO ₂ CF _{3) 2),} a lithium - bis (pentafluoroethanesulfonyl) imide _{(LiN (SO 2 C 2 F} 5) 2), a lithium - bis (pentafluoroethanesulfonyl) imide (LiBETI), lithium - trifluoromethanesulfonate ( LiCF ₃ SO ₃ ), lithium-bis (oxalate) borate (LiBC ₄ O ₈ ), or the like can be used.

  The concentration of the supporting salt in the ionic liquid is preferably from 0.1 mol / L to 5.0 mol / L, more preferably from 1 mol / L to 3.0 mol / L.

  The ionic liquid can include an organic solvent. When the ionic liquid contains an organic solvent, the viscosity of the ionic liquid decreases. Therefore, the electrode for an electricity storage device provided with an ionic liquid containing an organic solvent can improve the low temperature characteristics of the electricity storage device.

  As the organic solvent, for example, propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), acetonitrile (AN) or the like is mixed or single. Can be used.

(Metal foil)
The metal foil has at least one of a concave portion and a convex portion on the surface.

  When the metal foil has a recess on the surface, the carbon nanotube and the ionic liquid enter the recess, and therefore the metal foil can hold the carbon nanotube and the ionic liquid well. Therefore, the electrode for an electricity storage device using the metal foil can improve the electrostatic capacity and the cell voltage of the electricity storage device and improve the energy density of the electricity stored.

  The average pore diameter of the concave portions of the metal foil is preferably 500 nm or more and 500 μm or less, and more preferably 1000 nm or more and 100 μm or less.

  When the average pore diameter of the concave portions of the metal foil is 500 nm or more, the carbon nanotubes and the ionic liquid can easily enter the concave portions, and the contact between the carbon nanotubes and the metal foil is improved. Therefore, the internal resistance of the electrode is reduced, and the energy density of the electricity storage device can be improved. On the other hand, when the average pore diameter of the concave portion of the metal foil is 500 μm or less, the carbon nanotube can be favorably retained in the concave portion without using a binder component, and an electrode having sufficient strength can be obtained. .

  In addition, the average hole diameter of a recessed part can be confirmed by shaving the surface of the electrode for electrical storage devices, and observing the hole diameter of the recessed part exposed on the surface with a microscope.

It is preferable that the through-hole which penetrates metal foil exists in the recessed part of metal foil.
When carbon nanotubes and ionic liquids are applied to metal foil using a squeegee, etc., if there are through holes that penetrate the metal foil in the recesses of the metal foil, air does not accumulate in the recesses, so there is no problem in the recesses. Carbon nanotubes and ionic liquids can be filled. Therefore, the capacitance of the electricity storage device can be increased.

  For example, expanded metal, perforated foil, porous sheet (3DF), or the like can be used as the metal foil through which the concave portion penetrates.

  Further, as the metal foil, a metal foil having no through hole penetrating the metal foil can be used in the concave portion of the metal foil.

  If the concave portion of the metal foil does not penetrate, the carbon nanotube can be held in the concave portion, and the life of the electricity storage device is prolonged.

  Metal foil can also have a convex part on the surface. In particular, if the metal foil has a plurality of protrusions on the surface, the carbon nanotubes and ions can be supported on the surface of the metal foil because carbon nanotubes and ionic liquid can be carried in the space formed between the plurality of protrusions. Liquid can be retained. Further, when the pitch between the convex portions is 1 μm or more, the carbon nanotubes and the ionic liquid are easily carried by the plurality of convex portions, so that the contact property between the carbon nanotubes and the metal foil is improved. Therefore, the internal resistance of the electrode is reduced, and the energy density of the electricity storage device can be improved. On the other hand, when the pitch between the convex portions is 1000 μm or less, the carbon nanotubes can be favorably retained on the metal foil without using a binder component. Here, the distance between convex parts means the shortest distance between adjacent convex parts on the metal foil surface.

A flocked metal can be used as the metal foil having a convex portion.
Here, the flocked metal is a metal foil as if the needle-like, whisker-like, hairy, or fibrous metal is flocked to the metal foil obliquely or perpendicularly to the metal foil surface. The state adhering to the surface or the state integrated with the metal foil.

  When a flocked metal is used as the metal foil, the carbon nanotubes are entangled with the flocked portion, and the retention and current collecting properties are improved.

  The shape of the convex part of metal foil can have shapes other than the flocked metal. For example, the shape of the convex portion can be a hemispherical shape, a pot shape, a mountain shape, a cylindrical shape, or the like.

  The thickness of the main body of the metal foil is preferably 10 μm or more and 500 μm or less, and more preferably 15 μm or more and 100 μm or less. In addition, in this specification, the thickness of metal foil means the average thickness of the main-body part except the recessed part and convex part of the metal foil surface.

  The metal of the metal foil preferably contains at least one selected from the group consisting of aluminum, nickel, copper, an aluminum alloy, and a nickel alloy.

  Since the electrode for an electricity storage device using aluminum, nickel, copper, an aluminum alloy or a nickel alloy as the metal of the metal foil is difficult to elute even in the operating voltage range of the electricity storage device (about 0 V or more and 5 V or less with respect to the lithium potential) An electric storage device capable of stable charging even during long-term charge / discharge can be obtained. Particularly in a high voltage (3.5 V or more with respect to lithium potential) range, the metal of the metal foil preferably contains aluminum, an aluminum alloy or a nickel alloy, and more preferably aluminum.

The basis weight of the metal foil is preferably 500 g / m ² or less from the viewpoint of strength as an electrode for an electricity storage device and reduction in electric resistance of the electricity storage device. Furthermore, 150 g / m ² or less is preferable from the viewpoint of improving the energy density of the electricity storage device. Moreover, 10 g / m ² or more is preferable from the viewpoint of maintaining strength.

Hereinafter, specific examples of the metal foil will be described with reference to the drawings.
FIG. 1 is a plan view showing an example of “expanded metal” which is a metal foil having a concave portion on the surface, and FIG. 2 is an enlarged perspective view of a portion A in FIG.

  Expanded metal is a mesh-like metal foil in which a metal plate is spread and expanded in a zigzag pattern by an expanding machine, and the cut is formed into a rhombus or a turtle shell. When an expanded metal is used as the metal foil, the carbon nanotube and the ionic liquid can be held in the diamond-shaped or turtle shell-shaped space.

  The average hole diameter of the recessed portion of the expanded metal means an average value of the long diameter LW and the short diameter SW of the space portion shown in FIG. Moreover, when metal foil is an expanded metal, the average thickness of the main-body part of metal foil means the average thickness of the metal part shown by T of FIG.

FIG. 3 is a plan view showing an example of a “perforated foil” that is a metal foil having a concave portion on the surface.
The perforated foil is a metal foil having a plurality of through-holes obtained by drilling a metal foil with a punching press mold. When a perforated foil is used as the metal foil, the carbon nanotube and the ionic liquid can be held inside the through hole.

  The average hole diameter of the concave portion of the perforated foil means the average hole diameter (average diameter) of the through holes. Moreover, when metal foil is a perforated foil, the average thickness of the main-body part of metal foil means the average thickness of metal parts other than a through-hole.

  FIG. 4 is a perspective view showing an example of a “porous sheet (3DF, 3 Dimensional Fiol)” that is a metal foil having concave and convex portions on the surface, and FIG. 5A is a cross-sectional view taken along the line AA in FIG. 5B is a cross-sectional view taken along the line BB in FIG. 4, and FIG. 5C is a cross-sectional view taken along the line CC in FIG.

  The porous sheet is obtained by punching a metal foil from both sides with a press with a needle.

  As shown in FIGS. 5A and 5B, the porous sheet 110 has a planar portion 111 having a planar shape, and both surfaces are concave with respect to one surface and convex with respect to the other surface. And a bent portion 112.

In FIG.5 (c), the plane part 111 is not seen but only the bending part 112 is seen.
The bent portion 112 includes a rectangular through hole 113 that penetrates from one surface to the other surface. In the porous sheet, the through hole 113 punched in one surface direction (P surface) and the through hole 113 punched in the other surface direction (Q surface) are in a direction along the surface (left and right in the figure). Alternatingly arranged. The through hole 113 is not limited to a rectangle, and may be a circle.

  When a porous sheet is used as the metal foil, the carbon nanotube and the ionic liquid can be held in the hole 114 surrounded by the inner peripheral surface that is the concave shape of the bent portion 112.

  The average pore diameter of the concave portion of the porous sheet means the average pore diameter of the through holes. In addition, the hole diameter of a through-hole means the hole diameter (length of R in FIG. 5 (a), (b), (c)) of the opening part of a through-hole. Moreover, when metal foil is a porous sheet, the average thickness of the main-body part of metal foil means the average thickness of metal foil before drilling.

  Fig.6 (a) is a top view which shows an example of the metal foil which has a recessed part on the surface, FIG.6 (b) is DD sectional drawing of Fig.6 (a).

  In the metal foil shown in FIGS. 6A and 6B, the concave portion has a hemispherical shape and does not penetrate the metal foil. This metal foil can hold | maintain a carbon nanotube and an ionic liquid in a recessed part.

  The average pore diameter of the concave portions of the metal foil shown in FIGS. 6A and 6B means the average pore diameter of the concave portions on the surface of the metal foil indicated by R in FIG. Moreover, the average thickness of the main-body part of metal foil means the average thickness of metal foil except a recessed part shown by T in FIG.6 (b).

FIG. 7 is a cross-sectional view showing an example of “flocked metal” which is a metal foil having a convex portion on the surface.
Flocked metal is produced by bonding and welding the ends of metal fibers onto a metal foil, or by electroplating by applying a conductive treatment to a cloth having a brushed structure, etc. A metal foil provided with fibers. When a flocked metal is used as the metal foil, the carbon nanotube and the ionic liquid can be held in the space between the fine fibers formed on the surface of the metal foil.

  The pitch (P) between the fine fibers is preferably 1 μm or more and 1000 μm or less. In addition, the average thickness of the main-body part of metal foil means the average thickness of metal foil except a fine fiber shown by T in FIG.

  8 (a) and 9 (a) are plan views showing other examples of metal foils having convex portions on the surface, and FIGS. 8 (b) and 9 (b) are respectively E in FIG. 8 (a). -E sectional drawing, FF sectional drawing of Fig.9 (a). The convex portions shown in FIGS. 8A and 8B can be formed by conspicuous the surface of the metal foil. 9A and 9B, the convex portion has a hemispherical shape. In any metal foil, since the carbon nanotube and the ionic liquid can be carried in the space formed between the plurality of convex portions, the carbon nanotube and the ionic liquid can be held on the surface of the metal foil.

The pitch (P) between the convex portions is preferably 1 μm or more and 1000 μm or less. In addition, the average thickness of the main-body part of metal foil means the average thickness of metal foil except a convex part shown by T in FIG.8 (b) and FIG.9 (b).
(binder)
The role of the binder is to bind the current collector and the active material in the electrode. However, since the binder resin typified by polyvinylidene fluoride (PVdF) is an insulator, the binder resin itself increases the internal resistance of the electricity storage device including the electrodes, which in turn reduces the charge / discharge efficiency of the electricity storage device. It becomes a factor to reduce.

  According to the electrode for an electricity storage device of the present invention, the carbon nanotube (active material) can be held in the recess or on the surface of the metal foil (current collector) without using a binder. Therefore, in one embodiment of the present invention, the electrode for an electricity storage device preferably does not contain a binder.

In another embodiment of the present invention, a binder may be used for the electrode for the electricity storage device. Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polyethylene oxide-modified polymethacrylate crosslinked body (PEO-PMA), polyethylene oxide (PEO), polyethylene glycol diacrylate crosslinked body (PEO- PA), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyacrylic acid (PAA), polyvinyl acetate, pyridinium-1,4-diylinocarbonyl-1,4- _{phenylenemethylene (PICPM) -BF 4, PICPM} -PF 6, PICPM-TFSA, PICPM-SCN, such as PICPM-OTf It can be used. Among these, it is preferable to use a polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polymethyl methacrylate (PMMA), or a polyethylene oxide-modified polymethacrylate crosslinked product (PEO-PMA).

(Conductive aid)
The electrode for an electricity storage device may contain a conductive additive. The conductive auxiliary agent can reduce the resistance of the electricity storage device. The type of the conductive auxiliary agent is not particularly limited, and for example, acetylene black, ketjen black, carbon fiber, natural graphite (eg, flake graphite, earthy graphite), artificial graphite, ruthenium oxide and the like can be used. The content of the conductive assistant is preferably, for example, 2 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the active material. If the amount is less than 2 parts by mass, the effect of improving the conductivity is small, and if it exceeds 20 parts by mass, the capacitance may decrease.

(Method for producing electrode for power storage device)
A method for manufacturing an electrode for an electricity storage device according to an embodiment of the present invention will be described below.

  First, a carbon nanotube and an ionic liquid are kneaded to obtain a kneaded product. For example, a kneaded product in which carbon nanotubes are uniformly dispersed in an ionic liquid can be obtained by kneading for about 10 minutes to 120 minutes using a mortar. When the carbon nanotubes are dispersed in the ionic liquid, the aggregation of the carbon nanotubes is eliminated and the specific surface area of the carbon nanotubes is increased. For this reason, when an electrode is produced using a kneaded material, a larger electrostatic capacity can be obtained.

  The kneading ratio of the carbon nanotube and the ionic liquid is not particularly limited. For example, when the amount of the carbon nanotube in the kneaded material is in the range of 3% by mass to 70% by mass of the total amount of the kneaded material, It is preferable because it can be easily applied to a metal foil having at least one of a concave portion and a convex portion. In addition, when adding a supporting salt and a binder, it can add in this kneading | mixing process.

  Next, a kneaded material is apply | coated to the metal foil which has at least any one of a recessed part and a convex part on the surface. For example, a metal foil is installed on the upper surface of a mesh or porous plate or membrane that is permeable or liquid-permeable, with the concave or convex surface as the upper surface, and from the upper surface of the metal foil to the lower surface (mesh plate installation surface side) The kneaded material is applied in a direction so as to be squeezed with a squeegee or the like.

[Embodiment 2]
(Electric double layer capacitor)
As an example of an electricity storage device using the electrode for an electricity storage device of the present invention, an electric double layer capacitor will be described with reference to FIG.

  In the electric double layer capacitor using the electrode for an electricity storage device of the present invention, the positive electrode 2 and the negative electrode 3 are opposed to each other with the surfaces having at least one of the concave portion and the convex portion sandwiching the separator 1 therebetween. Is arranged. The separator 1, the positive electrode 2, and the negative electrode 3 are sealed between an upper cell case 7 and a lower cell case 8 filled with the electrolytic solution 6. The upper cell case 7 and the lower cell case 8 are provided with terminals 9 and 10. Terminals 9 and 10 are connected to a power source 20.

  In the electric double layer capacitor, the electrode for an electricity storage device of the present invention can be used for the positive electrode and the negative electrode.

As the electrolytic solution, an ionic liquid used for an electrode for an electricity storage device can be used.
As the separator of the electric double layer capacitor, for example, a highly electrically insulating porous film made of polyolefin, polyethylene terephthalate, polyamide, polyimide, cellulose, glass fiber or the like can be used.

(Method for manufacturing electric double layer capacitor)
First, two electrodes for an electricity storage device of the present invention are punched out to an appropriate size, and are opposed to each other with a separator interposed therebetween. And it accommodates in a cell case and impregnates electrolyte solution. Finally, the electric double layer capacitor can be manufactured by sealing the case with a lid. In order to reduce the moisture in the capacitor as much as possible, the capacitor is manufactured in an environment with little moisture, and the sealing is performed in a reduced pressure environment. In addition, as long as the electrode for electrical storage devices of this invention is used, you may produce by the method of other than this.

[Embodiment 3]
(Lithium ion capacitor)
As an example of an electricity storage device using the electrode for an electricity storage device of the present invention, a lithium ion capacitor will be described with reference to FIG.

  The structure of the lithium ion capacitor using the electrode for an electricity storage device of the present invention is basically the same as that of the electric double layer capacitor except that the lithium metal foil 16 is crimped to the surface of the negative electrode 3 facing the positive electrode 2. It is the same.

  In the lithium ion capacitor, the electrode for an electricity storage device of the present invention can be used for the positive electrode and the negative electrode. The negative electrode is not particularly limited, and a conventional negative electrode using a metal foil can also be used.

As the electrolytic solution, an ionic liquid containing a lithium salt used for an electrode for an electricity storage device is used.
A lithium metal foil for lithium doping is pressure-bonded to the negative electrode on a surface having at least one of a concave portion and a convex portion of the metal foil.

  The lithium ion capacitor preferably has a negative electrode capacity larger than the positive electrode capacity, and the amount of occlusion of lithium ions in the negative electrode is 90% or less of the difference between the positive electrode capacity and the negative electrode capacity. The amount of occlusion of lithium ions can be adjusted by the thickness of the lithium metal foil that is pressure-bonded to the negative electrode.

(Lithium ion capacitor manufacturing method)
First, the electrode for an electricity storage device of the present invention is punched out to an appropriate size to prepare a positive electrode and a negative electrode, and a lithium metal foil is pressure-bonded to the surface of the negative electrode having at least one of a concave portion and a convex portion. Next, the positive electrode and the negative electrode are opposed to each other with a separator interposed therebetween. At this time, the negative electrode is disposed so that the surface on which the lithium metal foil is pressure-bonded faces the positive electrode. And it accommodates in a cell case and impregnates electrolyte solution. Finally, a lithium ion capacitor can be produced by sealing the case with a lid.

  In addition, since it is lithium-doped, it is left for 0.5 to 100 hours at an environmental temperature of 0 to 60 ° C. with the electrolyte injected. When the potential difference between the positive and negative electrodes becomes 2 V or less, it can be determined that the lithium doping is completed.

  In this example, as the metal foil, an aluminum foil having a recess on the surface (expanded metal, perforated foil, porous sheet, aluminum foil having a hemispherical recess on the surface), or an aluminum foil without surface treatment is used. The performance of the electric double layer capacitor provided with the electrode was evaluated. In addition, the thickness of the main body part of the used metal foil, the average hole diameter of the recessed part, and the basis weight are as shown in Table 1.

(Preparation of kneaded product)
Single-walled CNT (“SO-P” manufactured by Meijo Nanocarbon Co., Ltd. (shape: single-walled CNT, average length: 1 to 5 μm, average diameter: 1.4 nm, purity: 98.3 mass%) and EMI-BF ₄ preparative amount of single-walled CNT was prepared to be 7 wt% of the total amount of single-walled CNT and EMI-BF _4. Next, a single-layer CNT and the EMI-BF ₄ in a mortar 10 A kneaded product was obtained by kneading for a minute.

(Production of electrodes for power storage devices)
The kneaded material was placed on the surface of the metal foil of each example and comparative example, and the kneaded material was applied using a squeegee to produce an electrode for an electricity storage device.

(Production of electric double layer capacitor)
^{Two of the} obtained electrodes for an electricity storage device were punched out into a circular shape having a diameter of 15 mm (electrode area: 1.77 cm ² ) to form a positive electrode and a negative electrode, respectively. Cellulose fiber separators (“TF4035” manufactured by Nippon Kogyo Paper Industries Co., Ltd., thickness 35 μm) were placed opposite to each other and stored in an R2032-type coin cell case. Next, EMI-BF ₄ was injected as an electrolyte into the coin cell case, and then the case was sealed to produce a coin-type electric double layer capacitor.

<Performance evaluation test>
At an environmental temperature of 25 ° C., the battery was charged to 3.5 V at a constant current of 1 A / g (the amount of current per mass of carbon nanotubes contained in a single electrode), and then charged at a constant voltage of 3.5 V for 5 minutes. Thereafter, the electrostatic capacity when discharged to 0 V with a constant current of 1 A / g (current amount per mass of carbon nanotube contained in a single electrode) was evaluated. In Table 1, the capacitance (F / g) is shown as the capacitance per mass of carbon nanotubes contained in the single electrode. The energy density WD (Wh / L) at this time is also shown. The energy density was calculated using the following formula (2).
WD = W / V (2)
W represents energy stored in the capacitor, and V represents volume. The volume V is a capacitor volume that ignores the coin cell case.

  The results are shown in Table 1.

<Evaluation results>
Examples 1-1 to 1-12 are electric double-layer capacitors provided with electrodes manufactured using an aluminum foil having a concave portion on the surface, and the electric double layer of Comparative Example 1 using an aluminum foil without surface treatment. The energy density increased compared to the multilayer capacitor.

  In this example, as the metal foil, an aluminum foil having a convex portion on the surface (flocked metal, an aluminum foil having a convex portion in the shape of FIG. 8 on the surface, an aluminum foil having a hemispherical convex portion on the surface), or The performance of an electric double layer capacitor provided with an electrode using an aluminum foil without surface treatment was evaluated. In addition, the thickness of the main-body part of the used metal foil and the pitch of a convex part are as showing in Table 2.

(Production of electric double layer capacitor)
An electric double layer capacitor was produced in the same manner as in Example 1 except that the metal foil was changed.

<Performance evaluation test>
The operating voltage range, capacitance, and energy density were evaluated in the same manner as in Example 1.

  The results are shown in Table 2.

<Evaluation results>
Examples 2-1 to 2-9 are electric double layer capacitors provided with electrodes manufactured using an aluminum foil having convex portions on the surface, and the electricity of Comparative Example 1 using an aluminum foil without surface treatment. The energy density increased compared to the double layer capacitor.

  In this example, the performance was evaluated for an electric double layer capacitor using carbon nanotubes having different shapes, average lengths, average diameters, and purity. Table 3 shows the shape, average length, average diameter, and purity of the carbon nanotubes used.

(Production of electric double layer capacitor)
An electric double layer capacitor was produced in the same manner as in Example 1 except that the carbon nanotube was changed.

<Performance evaluation test>
The operating voltage range, capacitance, and energy density were evaluated in the same manner as in Example 1.

  The results are shown in Table 3.

(1) Expanded metal: Main part thickness 20 μm, average pore diameter 150 μm, basis weight 32.6 g / m ² (same as Example 1-2).
(2) Perforated foil: Main part thickness 20 μm, average pore diameter 300 μm, basis weight 21.6 g / m ² (same as Example 1-5).
(3) Porous sheet: Main body thickness 20 μm, average pore diameter 100 μm, basis weight 54.0 g / m ² (same as Example 1-8).
(4) Flocked metal: Main part thickness 100 μm, pitch 50 μm (same as Example 2-2).

<Evaluation results>
When Example 3-1 to Example 3-3 were compared, the energy density was improved when the average length of the carbon nanotubes was in the range of 1.1 to 2.5.

  When Examples 3-3, 3-4, and 3-7 were compared, the energy density was improved when the carbon nanotubes with both ends opened were used, compared with when single-walled carbon nanotubes and double-walled carbon nanotubes were used.

In this example, the performance of the electric double layer capacitor was evaluated when the kneaded material contained an organic solvent and a binder.
(Preparation of kneaded product)
EMI-BF ₄ (“1-ethyl-3-methylimidazolium tetrafluoroborate” manufactured by Kishida Chemical Co., Ltd.), PC and PVdF-HFP were used in 76: 15: 8 (Example 4-1) or 62:31. : 7 (Example 4-2) by mass% to obtain a mixed solution.

Further, EMI-BF ₄ and PVdF-HFP were mixed at a mass ratio of 90:10 to obtain a mixed solution (Example 4-3).

In each mixed solution, single-wall CNT (“SO-P” manufactured by Meijo Nanocarbon Co., Ltd. (shape: single-wall CNT, average length: 1 to 5 μm, average diameter: 1.4 nm, purity: 98.3 mass%) ) Is added so that the amount of the single-walled CNT is 7% by mass of the total amount of the single-walled CNT and EMI-BF ₄ or the single-walled CNT, EMI-BF ₄ and PC, and 10 minutes using a mortar. A kneaded product was obtained by kneading.
(Production of electrodes for power storage devices)
An electrode was produced in the same manner as in Example 1 using the kneaded material of each Example.
(Production of electric double layer capacitor)
About each Example, the coin (R2032) type electric double layer capacitor was obtained by the same method as Example 1. Incidentally, it was a mixture of EMI-BF ₄ and the PC kneaded product produced during the same mixing ratio of each example in the electrolyte.
<Performance evaluation>
The environmental temperature was changed in the range of −40 ° C. to 80 ° C., and the capacitance was evaluated by the same method as in Example 1 at each temperature. The operating voltage range was 0V to 3.5V. As a control, the same evaluation was performed on the capacitor of Example 1-1. The evaluation results are shown in Table 4. In Table 4, capacitance (F / g) is shown as capacitance per mass of active material contained in a single electrode.

(1) Expanded metal: main body thickness 20 μm, average pore diameter 150 μm, basis weight 32.6 g / m ² (same as Example 1-2)
(5) PC: “Propylene carbonate” manufactured by Kishida Chemical Co., Ltd.
(6) PVdF-HFP: “Kynar Flex 2801” (polyvinylidene fluoride-hexafluoropropylene copolymer) manufactured by Arkema.
<Evaluation results>
From Table 4, the electric double layer capacitors of Example 4-1 and Example 4-2 produced using the kneaded material containing PC are suppressed in the decrease in capacitance even in the low temperature region, and the low temperature characteristics are improved. It was. This is considered to be derived from the fact that the organic solvent decreased the viscosity of the ionic liquid.

  An electricity storage device using the electrode for an electricity storage device of the present invention can be used for various applications including transportation equipment such as automobiles and railways.

  DESCRIPTION OF SYMBOLS 1 Separator, 2 Positive electrode, 3 Negative electrode, 6 Electrolyte, 7 Upper cell case, 8 Lower cell case, 9,10 terminal, 20 Power supply, 110 Porous sheet, 111 Plane part, 112 Bending part, 113 Through-hole, 114 hole.

Claims (10)

Carbon nanotubes,
An ionic liquid,
Holding the carbon nanotube and the ionic liquid, and comprising a metal foil having at least one of a concave portion and a convex portion on the surface,
Electrode for electricity storage devices.   The thickness of the main-body part of the said metal foil is an electrode for electrical storage devices of Claim 1 which are 10 micrometers or more and 500 micrometers or less.   The average hole diameter of the recessed part of the said metal foil is an electrode for electrical storage devices of Claim 1 or 2 which are 500 nm or more and 500 micrometers or less.   The electrode for electrical storage devices of any one of Claims 1-3 in which the through-hole which penetrates the said metal foil exists in the recessed part of the said metal foil.   The electrode for electrical storage devices of any one of Claims 1-3 in which the through-hole which penetrates the said metal foil does not exist in the recessed part of the said metal foil.   The electrode for an electricity storage device according to any one of claims 1 to 5, wherein the metal foil has a plurality of protrusions, and a pitch between the protrusions is 1 µm or more and 1000 µm or less.   The electrode for an electricity storage device according to claim 6, wherein the metal foil is a flocked metal.   The said electrode for electrical storage devices is an electrode for electrical storage devices of any one of Claims 1-7 which does not contain a binder component.   An electrical storage device provided with the electrode for electrical storage devices of any one of Claims 1-8. A step of kneading carbon nanotubes into an ionic liquid to produce a kneaded product;
Filling the kneaded material into a metal foil having at least one of a concave portion and a convex portion on the surface,
A method for producing an electrode for an electricity storage device.

Images