JP2011066325A - Electrochemical capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical capacitor for improving charging and discharging cycle durability, using a simple constitution. <P>SOLUTION: A hybrid capacitor 1 includes: a positive electrode 2 for supporting a positive electrode active material containing a polarizable carbon material; a negative electrode 3 that supports a negative electrode active material containing a material, capable of reversibly occluding and discharging lithium ions and is disposed so that the negative electrode active material faces the positive electrode active material; and an electrolyte 6 that contains an organic solvent, including lithium salts and immerses the positive electrode 2 and the negative electrode 3. In the hybrid capacitor 1, the ratio of a support area Sa of the positive electrode active material to a support area Sb of the negative electrode active material is set to less than 1, within a projection surface where the support area of the negative electrode active material is projected toward the support area of the positive electrode active material along the facing direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrochemical capacitor, and more particularly, to a hybrid capacitor having both power storage by an electric double layer and power storage by an oxidation-reduction reaction.

Conventionally, an electric double layer capacitor having a high output and a long life is known as an electric storage device mounted on a hybrid vehicle or a fuel cell vehicle.
In the electric double layer capacitor, when a voltage is applied between the positive electrode and the negative electrode, anions and cations are attracted to the positive electrode and the negative electrode, respectively, and a charge layer (electric double layer) is formed. The electric double layer capacitor can store energy by forming the electric double layer.

Furthermore, in recent years, in order to improve the energy density of the capacitor, a hybrid capacitor that stores energy by an oxidation-reduction reaction in the positive electrode or the negative electrode in addition to the electric double layer has been proposed. The hybrid capacitor includes, for example, an electrolytic solution made of an organic solvent containing a lithium salt (for example, LiPF ₆ ), a separator, and a positive electrode and a negative electrode that are opposed to each other with the separator interposed therebetween. The positive electrode is made of, for example, a polarizable carbon electrode that stores charges by physical adsorption / desorption of anions. On the other hand, the negative electrode is made of, for example, a carbon electrode capable of electrochemically occluding and releasing lithium ions.

However, in the hybrid capacitor, when the positive electrode potential becomes excessively high (for example, 4.23 V vs. Li / Li ⁺ or more), the anion (for example, PF ₆ ⁻ contained in LiPF ₆ ) in the electrolyte solution causes the negative electrode In some cases, a negative electrode activity inhibitor such as a free acid (for example, HF) that lowers the electric capacity of the negative electrode is generated. When the electric capacity of the negative electrode is reduced, the energy density of the capacitor is reduced, so it is necessary to capture such free acid.

Therefore, for example, a separator made of a ceramic filter, a positive electrode composed of a mixture of KOH activated soft carbon, ketjen black ECP and PTEF dispersion in a weight ratio of 85: 5: 10, artificial graphite, soft carbon and PVdF A negative electrode made of a mixture of 22.5: 67.5: 10, an electrolytic solution made of ethylene carbonate + diethyl carbonate solvent containing LiPF ₆ , a Li ₂ CO ₃ powder and PTFE, 80: There has been proposed a hybrid capacitor including a scavenger composed of a mixture blended at a weight ratio of 20 (see, for example, Patent Document 1 (Example 2)).

In the hybrid capacitor described in Patent Document 1, even when a high voltage (for example, 4.23 V vs. Li / Li ⁺ or more) is applied to the positive electrode, deterioration of the negative electrode can be suppressed and energy density can be increased. Can do.

JP 2008-103697 A (Example 2)

However, the charge / discharge cycle durability (maintenance rate of energy density) of the hybrid capacitor described in Patent Document 1 is still not sufficient, and further improvements in charge / discharge cycle durability are required in various fields dealing with capacitors. .
The objective of this invention is providing the electrochemical capacitor which can aim at the improvement of charging / discharging cycle durability by simple structure.

  In order to achieve the above object, the electrochemical capacitor of the present invention comprises a positive electrode carrying a positive electrode active material containing a polarizable carbon material, and a negative electrode active material containing a material capable of reversibly occluding and releasing lithium ions. A negative electrode disposed so that the negative electrode active material faces the positive electrode active material, and an electrolyte containing an organic solvent containing a lithium salt and in which the positive electrode and the negative electrode are immersed , In the projection plane obtained by projecting the negative electrode active material support area toward the positive electrode active material support area along the facing direction, the positive electrode active material support area with respect to the negative electrode active material support area The ratio is less than 1.

In the electrochemical capacitor of the present invention, the positive electrode active material support region is projected in a projection plane in which the positive electrode active material support region is projected toward the negative electrode active material support region along the facing direction. It is preferable that the negative electrode active material is entirely contained in the supporting region.
In the electrochemical capacitor according to the present invention, it is preferable that a ratio of the supported area of the positive electrode active material to the supported area of the negative electrode active material is 0.6 or more.

In the electrochemical capacitor of the present invention, it is preferable that the positive electrode active material contains KOH activated soft carbon.
In the electrochemical capacitor of the present invention, the potential of the positive electrode is 4.23 V vs. It is suitable that it is more than Li / Li ⁺ .
Moreover, in the electrochemical capacitor of the present invention, the negative electrode activity-inhibiting substance derived from the anion contained in the electrolytic solution is captured between the positive electrode and the negative electrode, at least one of the positive electrode and the negative electrode. It is preferred to contain a scavenger.

  According to the electrochemical capacitor of the present invention, the negative electrode active material supporting region is projected in the projection plane projected toward the positive electrode active material supporting region along the direction in which the positive electrode active material and the negative electrode active material face each other. Since the ratio of the positive electrode active material support area to the active material support area is less than 1, the charge / discharge cycle durability can be easily improved.

It is a schematic block diagram of the hybrid capacitor which shows one Embodiment of the electrochemical capacitor of this invention. It is a front view of the positive electrode and negative electrode which are employ | adopted as the hybrid capacitor shown in FIG. It is the schematic which shows the state by which the positive electrode and negative electrode which were formed in the rectangular shape were opposingly arranged. It is the schematic which shows the state by which the positive electrode and negative electrode which were formed in circular shape were opposingly arranged. It is a graph which shows the maintenance rate of the energy density of Example 1 and Comparative Examples 1-2. 4 is a graph showing charge / discharge cycle durability of Examples 1 to 3 and Comparative Example 1. It is a graph which shows the energy density of the 2nd cycle of Examples 1-3 and the comparative example 1. FIG.

FIG. 1 is a schematic configuration diagram of a hybrid capacitor showing an embodiment of an electrochemical capacitor of the present invention.
In FIG. 1, a hybrid capacitor 1 includes a positive electrode 2, a negative electrode 3 disposed opposite to the positive electrode 2 with a gap, a separator 4 interposed between the positive electrode 2 and the negative electrode 3, a positive electrode 2, a negative electrode 3 and the cell tank 5 which accommodates the separator 4, and the electrolyte solution 6 which is stored in the cell tank 5 and in which the positive electrode 2, the negative electrode 3, and the separator 4 are immersed. The hybrid capacitor 1 is a battery cell employed on a lab scale, and industrially a hybrid capacitor 1 that is appropriately scaled up by a known technique is employed.

The positive electrode 2 carries a positive electrode active material containing a positive electrode material (polarizable carbon material) made of polarizable carbon.
Such a positive electrode 2 is formed by, for example, applying a mixture obtained by blending a positive electrode active material containing a positive electrode material, a conductive agent, and a polymer binder to a positive electrode side current collector 8a (described later). The electrode sheet carrying the active material is manufactured, and the electrode sheet is formed into a predetermined shape (for example, a rectangular shape or a circular shape), and then dried as necessary.

The positive electrode material is obtained by, for example, activating a carbon material.
Examples of the carbon material include hard carbon and soft carbon.
With soft carbon, for example, by heat treatment in an inert atmosphere, the hexagonal network surface composed of carbon atoms tends to form a relatively regular laminated structure (graphite structure) than the hexagonal network surface of hard carbon. A general term for carbon. Specifically, when heat-treated in an inert atmosphere at 2000 to 3000 ° C., preferably 2500 ° C., the (002) plane average plane distance d ₀₀₂ is 3.40 mm or less, preferably 3.35 to It is a general term for carbon that forms a crystal structure of 3.40%.

  Specific soft carbons include, for example, pitches such as petroleum pitches, coal pitches, and mesophase pitches, and graphites such as petroleum needle coke, coal needle coke, anthracene, polyvinyl chloride, polyacrylonitrile, and the like. Thermally decomposed products such as chemical coke. These can be used alone or in combination of two or more.

Also, hard carbon, for example, in an inert atmosphere, when it is heat treated at 2500 ° C., is a general term for carbon to form a crystal structure of greater than 3.40Å average spacing _{d 002} of (002) plane.
Specific examples of the hard carbon include phenol resin, melamine resin, urea resin, furan resin, epoxy resin, alkyd resin, unsaturated polyester resin, diallyl phthalate resin, furfural resin, resorcinol resin, silicone resin, xylene resin, urethane. Thermosetting resin such as resin, for example, carbon black such as thermal black, furnace black, lamp black, channel black, acetylene black, for example, non-graphitizable coke such as flue coke and gilsonite coke Examples include coke, for example, plant raw materials such as palm, wood flour, and the like, for example, pyrolysates such as glassy carbon.

These can be used alone or in combination. Of these, soft carbon is preferable.
As the activation treatment, for example, alkaline activation treatment using potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), cesium hydroxide (CsOH), rubidium hydroxide (RbOH) or the like as an activator. For example, chemical activation treatment using zinc chloride (ZnCl ₂ ), phosphoric acid (H ₃ PO ₄ ) or the like as an activator, for example, gas activation treatment using carbon dioxide (CO ₂ ), air or the like as an activator, for example, Examples include steam activation treatment using steam (H ₂ O) as an activator. Among these, Preferably, an alkali activation process is mentioned, More preferably, the alkali activation process (KOH activation process) which uses potassium hydroxide (KOH) as an activator is mentioned.

In the activation treatment, for example, in the case of KOH activation treatment, the carbon material is pre-fired at 500 to 800 ° C., for example, and then fired together with KOH at 700 to 1000 ° C. in a nitrogen atmosphere. The amount of KOH used is, for example, 0.5 to 5 parts by weight with respect to 1 part by weight of the carbon material.
In the hybrid capacitor using the positive electrode material obtained by the activation process as the positive electrode 2, for example, the potential of the positive electrode 2 is 4.23 V vs. A relatively large irreversible capacity can be developed in the positive electrode 2 in a charge / discharge cycle of Li / Li ⁺ or more. Therefore, in the discharge process, the positive electrode can be discharged to a lower potential. As a result, the electric capacity of the positive electrode 2 can be increased.

The positive electrode material is blended so that, for example, the weight ratio of the solid content is 70 to 99% by weight with respect to the total amount of the mixture.
Examples of the conductive agent include carbon black, ketjen black, and acetylene black. These can be used alone or in combination of two or more.
Moreover, a electrically conductive agent is mix | blended so that the weight ratio of solid content may be a ratio of 0-20 weight% with respect to the mixture whole quantity, for example. That is, the conductive agent may or may not be blended.

  Examples of the polymer binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluoroolefin copolymer crosslinked polymer, fluoroolefin vinyl ether copolymer crosslinked polymer, carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, and polyacryl. An acid etc. are mentioned. These can be used alone or in combination of two or more. Of these, PVdF is preferable.

Moreover, a polymer binder is mix | blended so that the weight ratio of solid content may become a ratio of 1-20 weight% with respect to the mixture whole quantity, for example.
And in order to form the positive electrode 2, the mixture which mix | blended the positive electrode material (positive electrode active material), the electrically conductive agent, and the polymer binder is stirred in a solvent, and a slurry (solid content: 10 to 60 weight%) is obtained. Next, the slurry is applied to the surface of the positive electrode current collector 8a to form the positive electrode side coating layer 9a, and then, for example, the electrode sheet on which the positive electrode active material is supported is subjected to pressure stretching using a roll press. Get. Next, the electrode sheet is cut or punched into a predetermined shape (for example, a rectangular shape or a circular shape), and then further dried as necessary. Thereby, the positive electrode 2 carrying the positive electrode active material is obtained.

  Examples of the solvent include aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF), for example, protic polar solvents such as ethanol, methanol, propanol, butanol, and water, for example, Low polar solvents such as toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, dimethyl phthalate and the like can be mentioned. Among these, Preferably, an aprotic polar solvent is mentioned, More preferably, N-methyl-2-pyrrolidone (NMP) is mentioned.

Examples of the positive electrode side current collector 8a include metal foils such as aluminum foil, copper foil, stainless steel foil, and nickel foil.
The thickness of the positive electrode side current collector 8a varies depending on the scale of the hybrid capacitor 1, but is, for example, 10 to 50 μm in a lab scale.
The thickness of the positive electrode 2 obtained by such a method differs depending on the scale of the hybrid capacitor 1. For example, in the lab scale, the thickness is 30 to 150 μm and the thickness excluding the positive electrode side current collector 8 a ( That is, the thickness of the positive electrode side coating layer 9a) is 10 to 140 μm.

Moreover, although the magnitude | size of the positive electrode 2 changes with scales of the hybrid capacitor 1, for example, in the case of a lab scale, for example, in the case of a rectangular shape, the length in the longitudinal direction is, for example, 10 to 200 mm, orthogonal to the longitudinal direction. The direction (width direction) length is, for example, 10 to 200 mm, and in the case of a circular shape, the diameter is, for example, 5 to 15 mm.
Further, in such a positive electrode 2, the size of the surface on which the positive electrode active material is carried (the surface on which the positive electrode side coating layer 9 a is applied) is the length in the longitudinal direction when the positive electrode 2 is rectangular. However, the length in the width direction is, for example, 5 to 185 mm, and in the case of a circular shape, the diameter is, for example, 13 mm.

Moreover, the support area of the positive electrode active material (coating area of the positive electrode side coating layer 9a) in the positive electrode 2 is, for example, 25 to 34225 mm ² .
The negative electrode 3 is an electrode that reversibly stores and releases lithium ions, and carries a negative electrode active material that contains a negative electrode material that can reversibly store and release lithium ions.
Such a negative electrode 3 is, for example, an electrode on which a negative electrode active material is supported by applying a mixture obtained by blending a negative electrode active material containing a negative electrode material and a polymer binder to the negative electrode current collector 8b. A sheet is manufactured, and the electrode sheet is formed into a predetermined shape (for example, a rectangular shape or a circular shape), and then dried if necessary.

The negative electrode material is not particularly limited, and examples thereof include the hard carbon described above, the soft carbon described above, and graphite.
Examples of graphite include pyrolytic products of condensed polycyclic hydrocarbon compounds such as natural graphite, artificial graphite, graphitized mesophase carbon microspheres, graphitized mesophase carbon fiber, graphite whisker, graphitized carbon fiber, pitch, and coke. A graphite-type carbon material is mentioned.

These can be used alone or in combination of two or more. Further, graphite is preferably used in the form of powder (for example, having an average particle size of 25 μm or less).
And the above negative electrode materials are mix | blended so that the weight ratio of solid content may become a ratio of 80 to 99 weight% with respect to the mixture whole quantity, for example.
Examples of the polymer binder include the polymer binder described above, and preferably PVdF. Moreover, a polymer binder is mix | blended so that the weight ratio of solid content may become a ratio of 1 to 10 weight% with respect to the mixture whole quantity, for example.

Moreover, in manufacture of a negative electrode, a electrically conductive agent can also be mix | blended as needed.
Examples of the conductive agent include the above-described conductive agents. Moreover, a electrically conductive agent is mix | blended so that the weight ratio of solid content may be a ratio of 0-20 weight% with respect to the mixture whole quantity, for example.
And in order to form the negative electrode 3, for example, first, the mixture which mix | blended negative electrode material (negative electrode active material) and the polymer binder is stirred in a solvent, and a slurry (solid content: 10 to 60 weight%) is obtained. Next, the slurry is applied to the surface of the negative electrode side current collector 8b to form the negative electrode side coating layer 9b, and then, for example, the electrode sheet on which the negative electrode active material is supported is subjected to pressure stretching using a roll press. Get. Next, the electrode sheet is cut or punched into a predetermined shape (for example, a rectangular shape or a circular shape), and then further dried as necessary. Thereby, the negative electrode 3 carrying the negative electrode active material is obtained.

Examples of the solvent include the above-mentioned solvents, preferably an aprotic polar solvent, and more preferably N-methyl-2-pyrrolidone (NMP).
Moreover, as the negative electrode side current collector 8b, for example, the metal foil described above can be used.
Although the thickness of the negative electrode side collector 8b changes with scales of the hybrid capacitor 1, it is 10-50 micrometers in a laboratory scale, for example.

The thickness of the negative electrode 3 obtained by the method as described above varies depending on the scale of the hybrid capacitor 1. For example, in the lab scale, the thickness is 5 to 70 μm, and the thickness excluding the negative electrode side current collector 8b (that is, The thickness of the negative electrode side coating layer 9b) is 5 to 60 μm.
Moreover, although the magnitude | size of the negative electrode 3 changes with scales of the hybrid capacitor 1, for example, in a lab scale, for example, in the case of a rectangular shape, the length in the longitudinal direction is, for example, 10 to 200 mm and orthogonal to the longitudinal direction. The direction (width direction) length is, for example, 10 to 200 mm, and in the case of a circular shape, the diameter is, for example, 5 to 15 mm.

In addition, in such a negative electrode 3, the size of the surface on which the negative electrode active material is supported (the surface on which the negative electrode side coating layer 9b is applied) is the length in the longitudinal direction when the negative electrode 3 is rectangular. However, for example, the width direction length is 6 to 190 mm, and in the case of a circular shape, the diameter is 14 mm, for example.
Moreover, the supporting area of the negative electrode active material (the coating area of the negative electrode side coating layer 9b) in the negative electrode 3 is, for example, 36 to 36100 mm ² .

As shown in FIG. 1, such a negative electrode 3 is arranged such that the negative electrode active material (negative electrode side coating layer 9 b) faces the positive electrode active material (positive electrode side coating layer 9 a).
Examples of the separator 4 include separators made of inorganic fibers such as glass fibers, ceramic fibers, and whiskers, natural fibers such as cellulose, and organic fibers such as polyolefin and polyester.

Moreover, although the thickness of the separator 4 changes with scales of the hybrid capacitor 1, for example, in the lab scale, the thickness is 15 to 100 μm.
The size of the separator 4 is not particularly limited as long as the area of the surface facing the positive electrode 2 and the negative electrode 3 is larger than that of the positive electrode 2 and the negative electrode 3, and differs depending on the scale of the hybrid capacitor 1. For example, in the case of a rectangular shape, the length in the longitudinal direction is, for example, 15 to 220 mm, and the length in the width direction is, for example, 15 to 220 mm. In the case of a circular shape, the diameter is, for example, 10 to 25 mm.

The electrolytic solution 6 contains an organic solvent containing a lithium salt. Specifically, for example, the electrolytic solution 6 is prepared by dissolving a lithium salt in an organic solvent.
The lithium salt has an anion component containing halogen. For example, LiClO ₄ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiC ₄ F ₉ SO ₃ , LiC ₈ F ₁₇ SO ₃ , LiB [C _{6 H 3 (CF 3) 2} -3,5] 4, LiB (C 6 F 5) 4, LiB [C 6 H 4 (CF 3) -4] 4, LiBF 4, LiPF 6, LiAsF 6, LiSbF 6 , LiCF ₃ CO ₂ , LiN (CF ₃ SO ₂ ) _{2 and the} like. In the above formula, [C ₆ H ₃ (CF ₃ ) ₂ -3, 5] is the 3rd and 5th positions of the phenyl group, and [C ₆ H ₄ (CF ₃ ) -4] is the 4th position of the phenyl group. Each of which is substituted with —CF ₃ . These can be used alone or in combination of two or more.

  Examples of the organic solvent include propylene carbonate, propylene carbonate derivatives, ethylene carbonate, ethylene carbonate derivatives, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, 1,3-dioxolane, dimethyl sulfoxide (DMSO), Sulfolane, formamide, dimethylformamide (DMF), dimethylacetamide (DMA), dioxolane, phosphoric acid triester, maleic anhydride, succinic anhydride, phthalic anhydride, 1,3-propane sultone, 4,5-dihydropyran derivative, Nitrobenzene, 1,3-dioxane, 1,4-dioxane, 3-methyl-2-oxazolidinone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl Tetrahydrofuran, tetrahydrofuran derivatives, sydnone compounds, acetonitrile, nitromethane, alkoxy ethane, and toluene. These can be used alone or in combination of two or more.

In order to prepare the electrolytic solution 6, for example, the concentration of the lithium salt is, for example, 0.5 to 5 mol / L, preferably 1 to 3 mol / L. The lithium salt is dissolved in an organic solvent so that the amount is, for example, 50 ppm or less, preferably 10 ppm or less.
FIG. 2 is a front view of a positive electrode and a negative electrode employed in the hybrid capacitor shown in FIG.

  As shown in FIG. 2, in this hybrid capacitor 1, the positive electrode 2 and the negative electrode 3 are formed in substantially the same shape (both substantially rectangular shapes having rectangular convex portions), and as shown in FIG. 1, the positive electrode 2 When the negative electrode 3 and the negative electrode 3 are opposed to each other, a region where the positive electrode active material is not supported on the positive electrode 2 (that is, an exposed portion of the positive electrode side current collector 8a) and a region where the negative electrode active material is not supported on the negative electrode 3 The exposed portion of the current collector 8b is disposed without facing each other.

As shown in FIG. 2, in this hybrid capacitor 1, the negative electrode active material supporting region is formed in the positive electrode active material along the direction in which the positive electrode 2 (positive electrode active material) and the negative electrode 3 (negative electrode active material) face each other. In the projection plane P ₁ projected toward the support region, the ratio of the support area Sa of the positive electrode active material in the positive electrode 2 to the support area Sb of the negative electrode active material in the negative electrode 3 is designed to be less than 1. Yes.

Further, in the hybrid capacitor 1, the backprojection of the projection (i.e., the holding region of the positive electrode active material, negative electrode active towards the carrying region of the material projection along the opposite direction of the above) in the the projection plane P ₂ In addition, the positive electrode active material supporting region is entirely included in the negative electrode active material supporting region.
That is, in this hybrid capacitor 1, the positive electrode active material carrying area Sa (the coated area of the positive electrode side coating layer 9a) is less than the negative electrode active material carrying area Sb (the coated area of the negative electrode side coating layer 9b). (Sa <Sb).

By making the support area Sa of the positive electrode active material less than the support area Sb of the negative electrode active material, the oxidative decomposition of the electrolytic solution 6 can be suppressed, and the charge / discharge cycle durability can be improved.
That is, in the hybrid capacitor 1, since the positive electrode side coating layer 9a normally expands with use, for example, the positive electrode active material carrying area Sa is equal to or larger than the negative electrode active material carrying area Sb (for example, Sa = if it is designed to be sb) is expanded portions of the positive-side coating layer 9a is arranged without facing the negative electrode coating layer 9b, outside the projection plane P ₁ to which they are opposed .

In such a case, the potential becomes excessively high in the expanded portion of the positive electrode side coating layer 9a (the portion not facing the negative electrode side coating layer 9b), and electrolysis of the electrolytic solution 6 may be caused.
When the electrolytic solution 6 is decomposed, gas is generated in the hybrid capacitor 1 and, for example, bubbles adhere to the surface of the positive electrode 2 and / or the negative electrode 3 and contribute to charge / discharge of the positive electrode 2 and / or the negative electrode 3. In some cases, the area decreases, the organic solvent of the electrolytic solution 6 volatilizes, and the ion permeability decreases. As a result, the energy density maintenance rate (charge / discharge cycle durability) decreases.

On the other hand, in the projection plane P _1, bearing area Sa of the positive electrode active material, according to the hybrid capacitor 1, which is designed to be less than carrying area of the anode active material Sb, positive-side coated negative electrode side coating layer 9b Since it is formed to have a larger area than the working layer 9a, even when the positive electrode side coating layer 9a expands due to use, at least a part of the expanded portion is in relation to the negative electrode side coating layer 9b. opposite.

Therefore, according to such a hybrid capacitor 1, it can suppress that the electric potential of the expansion part of the positive electrode side coating layer 9a becomes high too much. As a result, decomposition of the electrolytic solution 6 can be suppressed, charge / discharge cycle durability can be improved, and an excellent energy density maintenance rate can be obtained.
The ratio of the positive electrode active material support area Sa in the positive electrode 2 to the negative electrode active material support area Sb in the negative electrode 3 is less than 1, preferably less than 0.98, more preferably less than 0.95, preferably Is 0.4 or more, more preferably 0.5 or more, and particularly preferably 0.6 or more.

When the ratio of the supported area Sa of the positive electrode active material to the supported area Sb of the negative electrode active material is equal to or higher than the above upper limit, a high energy density can be obtained in the initial stage of use, but the charge / discharge durability is inferior and the energy density is excellent. The maintenance rate may not be obtained.
On the other hand, if the ratio of the positive electrode active material support area Sa to the negative electrode active material support area Sb is less than the lower limit, the potential of the positive electrode 2 becomes excessively high, and the electrolytic solution 6 is decomposed and charge / discharge is performed. Cycle durability may be reduced.

FIG. 3 is a schematic diagram showing a state in which a positive electrode and a negative electrode formed in a rectangular shape are opposed to each other, and FIG. 4 is a schematic diagram showing a state in which a positive electrode and a negative electrode formed in a circular shape are arranged to face each other.
In FIG. 2, the positive electrode 2 and the negative electrode 3 are both formed in a substantially rectangular shape having a rectangular convex portion, but the shape of the positive electrode 2 and the negative electrode 3 is not particularly limited. As shown, both the positive electrode 2 and the negative electrode 3 can be formed in a rectangular shape. In such a case, the positive electrode 2 and the negative electrode 3 are alternately disposed opposite to each other in the longitudinal direction, so that the positive electrode active material in the positive electrode 2 is not supported (that is, the exposed portion of the positive electrode side current collector 8a), the negative electrode 3 can be disposed without facing each other (ie, an exposed portion of the negative electrode side current collector 8b).

Moreover, the positive electrode 2 and the negative electrode 3 can also be formed in a shape that does not have a portion where the positive electrode side current collector 8a is exposed and a portion where the negative electrode side current collector 8b is exposed. As shown, both the positive electrode 2 and the negative electrode 3 can be formed in a circular shape.
Furthermore, although not shown, the positive electrode 2 and the negative electrode 3 can be formed in other different shapes.

In the hybrid capacitor 1, the potential of the positive electrode 2 is preferably 4.23 V vs Li / Li ⁺ or more.
In order to set the potential of the positive electrode 2 to 4.23 V vs Li / Li ⁺ or higher, for example, when soft carbon and / or hard carbon is used for the negative electrode 3, the cell voltage is applied at 3 V or higher.

If the potential of the positive electrode 2 is 4.23 V vs Li / Li ⁺ or more, the energy density of the hybrid capacitor 1 can be improved.
On the other hand, in this hybrid capacitor 1, when the potential of the positive electrode 2 is set to a high potential of 4.23 V vs Li / Li ⁺ or higher, the anion contained in the electrolyte 6 is caused by the irreversible capacity of the positive electrode 2. (e.g., PF ₆ contained in LiPF ₆ ^-, etc.) negative active inhibitor derived from in some cases be generated.

The process in which the negative electrode activity inhibitor is generated, for example, the process in which HF is generated due to the development of the irreversible capacity of the positive electrode 2 is presumed as follows.
First, when the above-described predetermined voltage (that is, 4.23 V vs Li / Li ⁺ or more) is applied to the positive electrode 2 and the negative electrode 3, in the electrolytic solution 6, for example, from moisture and organic substances contained in the positive electrode 2 and the electrolytic solution 6. As shown in the following formulas (1) and (2), protons (H ⁺ ) are generated.

(1) 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻
(2) R—H → R + H ⁺ + e ⁻ (R is an alkyl group)
Then, the generated protons, anion contained in the electrolytic solution 6 (for example, PF ₆ contained in LiPF ₆ ^-, etc.) and react, HF is generated (see the following formula (3)).
(3) PF ₆ ⁻ + H ⁺ → PF ₅ + HF
A negative electrode activity-inhibiting substance such as HF may reduce the electric capacity of the negative electrode 3 and reduce the energy density of the hybrid capacitor 1.

Therefore, in this hybrid capacitor 1, it is preferable to capture a negative electrode activity inhibiting substance derived from an anion contained in the electrolytic solution 6 between the positive electrode 2 and the negative electrode 3 and at least one of the positive electrode 2 and the negative electrode 3. The scavenger to be contained is included.
By including a capture agent in the hybrid capacitor 1, for example, even if a negative electrode activity inhibitor is generated due to the irreversible capacity of the positive electrode 2, the negative electrode activity inhibitor can be captured by the capture agent.

Examples of the scavenger include alkali metal carbonates such as lithium carbonate (Li ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), and potassium carbonate (K ₂ CO ₃ ). These can be used alone or in combination of two or more. Of these, lithium carbonate is preferable.
More specifically, for example, when the capture agent is contained (arranged) between the positive electrode 2 and the negative electrode 3, the capture agent is preferably formed as the capture member 7.

The capturing member 7 is, for example, a sheet obtained by press-stretching a capturing agent for capturing a negative electrode activity inhibitor and a polymer binder.
Examples of the polymer binder include the above-described polymer binder, and preferably PTFE.
And in order to form the capture | acquisition member 7, for example, first, a capture | acquisition agent and a polymer binder are used, for example, the mixture ratio of capture | acquisition agent: polymer binder is 20: 80-98: 2 in the weight ratio of solid content, Preferably, it mix | blends so that it may become 50: 50-90: 10, and prepares a mixture. Next, the mixture is pressurized and stretched using, for example, a roll press to obtain a capturing agent-containing sheet.

The scavenger-containing sheet is punched into a predetermined shape (for example, a rectangular shape or a circular shape) and then dried as necessary. Thereby, the capture member 7 is obtained.
In this hybrid capacitor 1, for example, as shown in FIG. 1, as the separator 4, a separator 4a disposed on the positive electrode 2 side and a separator 4b disposed on the negative electrode 3 side are provided, and these separators 4a and 4b are provided. The capturing member 7 is provided between the two.

By providing the capture member 7, for example, even if a negative electrode activity inhibitor is generated due to the irreversible capacity of the positive electrode 2, the negative electrode activity inhibitor can be captured by the capture member 7. Moreover, such a capture | acquisition member 7 can serve as a separator as a capture agent containing separator.
In the hybrid capacitor 1, for example, the above carbonate can be disposed between the separator 4 a and the separator 4 b as a capturing agent without forming the capturing member 7.

In order to arrange the carbonate between the separator 4a and the separator 4b, for example, powdery carbonate is added to one surface of the separator 4a or the separator 4b, and the surface and the surface of the other separator 4a (4b) are added. And sandwich the carbonate.
In the hybrid capacitor 1, the carbonate may be coated on the surface of the positive electrode 2 and / or the negative electrode 3.

In order to coat the carbonate on the surface of the positive electrode 2 and / or the negative electrode 3, for example, a mixture containing carbonate and a binder is stirred and mixed in a solvent, and then applied onto the positive electrode 2 and / or the negative electrode 3 After that, it is dried.
Examples of the binder include the polymer binder described above.
Examples of the solvent include the above-mentioned solvents, preferably NMP (N-methyl-2-pyrrolidone) and water.

Furthermore, in this hybrid capacitor 1, lithium foil can also be used as a scavenger.
As the lithium foil, a known lithium foil can be used. For example, the lithium foil is formed in a circular shape or a rectangular shape.
The lithium foil is preferably formed so that the surface area thereof is substantially the same as or larger than the surface areas of the positive electrode 2 and the negative electrode 3. When the surface area of the lithium foil is such an area, the negative electrode activity inhibiting substance (for example, HF) can be efficiently captured.

Furthermore, the thickness is 0.01-0.1 mm, for example, Preferably, it is 0.01-0.05 mm.
The lithium foil has a plurality of holes in the thickness direction. By forming such a hole, the electrolytic solution 6 can pass between the separator 4a and the separator 4b, and can be charged and discharged.

The lithium foil may be any lithium metal. For example, lithium powder or paste-like lithium may be provided as a scavenger.
In addition to the lithium metal described above, the negative electrode activity inhibitor can also be captured by including in the cell tank 5 a compound having a Si—N bond (for example, perhydropolysilazane, methylpolysilazane, etc.). In this case, the negative electrode activity inhibiting substance is captured and stabilized by the compound having a Si—N bond.

When the scavenger is contained in the positive electrode 2 and / or the negative electrode 3, the scavenger is used as a material component of the positive electrode 2 and / or the negative electrode 3, for example.
That is, in such a case, a scavenger (for example, carbonate, lithium powder, etc.) is blended with the positive electrode material or the negative electrode material in the manufacturing process of the positive electrode 2 and / or the negative electrode 3. Thereby, the scavenger is contained in the positive electrode 2 and / or the negative electrode 3.

Then, such scavenger (catching member 7), to the irreversible capacity 1mAh expressed in the positive electrode 2, preferably in a ratio of ^{2 × 10 -5 mol~175 × 10 -5} mol.
When the amount of the scavenger is within such a range, a further excellent energy density can be expressed.
For example, referring to the above formulas (1) to (3), 1 mol of HF is generated with the flow of 1 mol of electrons. In other words, the irreversible capacity expressed in positive electrode 2 and Q (mAh), a Faraday constant 96500 (C / mol) Then, the amount _{M HF} of HF generated in the hybrid capacitor _1, M HF = 3.6 × Q × F ⁻¹ (mol).

In the case of using the _Li 2 CO ₃ as a scavenger, as shown in the following formula (4), HF is (reacts with _Li 2 CO ₃₎ is trapped in _Li 2 CO _3, LiF and _H 2 CO ₃ is generated.
(4) Li ₂ CO ₃ + 2HF → 2LiF + H ₂ CO ₃
As shown in the above formula (4), 0.5 mol of Li ₂ CO ₃ is required to capture 1 mol of HF. More specifically, the required amount M _Li2CO3 of Li ₂ CO ₃ is M _Li2CO3 = 0.5M _HF = 1.8 × Q × F ⁻¹ (mol). When F = 96500 is substituted, M _Li2CO3 = 2 × 10 ⁻⁵ × Q (mol). That is, when Li ₂ CO ₃ is contained 2 × 10 ⁻⁵ × Qmol or more with respect to the irreversible capacity Q (mAh), HF can be sufficiently captured. As a result, since a decrease in energy density due to the negative electrode activity inhibitor (HF) can be suppressed, a further excellent energy density can be expressed.

And according to this hybrid capacitor 1, the carrying area of the positive electrode active material (positive electrode side coating layer 9a) in the positive electrode 2 relative to the carrying area of the negative electrode active material in the negative electrode 3 (coating area of the negative electrode side coating layer 9b) Sb. The coating area) Sa ratio is less than 1, so that it is possible to easily improve the charge / discharge cycle durability.
Therefore, the electrochemical capacitor of the present invention can be suitably used, for example, as various industrial products such as a drive battery mounted in an automobile (such as a hybrid vehicle), a memory backup power source such as a notebook personal computer and a mobile phone.

Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example.
Examples 1-3 and Comparative Examples 1-2
1. Production of positive electrode Mesophase pitch (AR resin manufactured by Mitsubishi Gas Chemical Co., Ltd.) was heated in the atmosphere at 350 ° C. for 2 hours. Next, the heated pitch was pre-fired at 800 ° C. for 2 hours in a nitrogen atmosphere. Thereby, soft carbon was obtained. The obtained soft carbon was put in an alumina crucible, and 4 parts by weight of KOH was added to 1 part by weight of the soft carbon. Next, the soft carbon was calcined with KOH at 800 ° C. for 2 hours under a nitrogen atmosphere to activate KOH. Next, the KOH activated soft carbon was washed with ultrapure water. Washing was performed until the waste liquid became neutral. Thereby, KOH activated soft carbon (positive electrode material (positive electrode active material)) was obtained. After washing, KOH activated soft carbon was pulverized in a mortar and classified with a sieve (32 μm). Then, the grinding operation in the mortar was repeated until almost all the KOH-activated soft carbon had a particle size that could pass through the sieve.

  After classification, a KOH activated soft carbon powder, a conductive agent (carbon black, VXC-72R manufactured by Cabot Specialty Chemicals, Inc.), and a polymer binder (PVdF manufactured by Kureha Co., Ltd.) with a solid content of 75: 8.3: A slurry of the mixture (solid content: 30% by weight) was added to an NMP (N-methyl-2-pyrrolidone) solvent at a weight ratio of 16.7 and stirred at room temperature (25 ° C. to 30 ° C.) for 12 hours. Got.

Next, the obtained slurry was coated on the surface of an aluminum foil (positive electrode side current collector) having a thickness of 15 μm and dried at 80 ° C. for 12 hours to form a positive electrode side coating layer. Next, the dried aluminum foil was subjected to pressure stretching with a roll press to obtain an electrode sheet having a thickness of 72 μm.
Next, the electrode sheet was punched into a circular shape having a diameter of 13 mm, and then carried into a dryer and vacuum-dried at 120 ° C. for 12 hours. After the inside of the dryer was purged with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so as not to be exposed to the atmosphere. The positive electrode was produced by the above operation.

Table 1 shows the carrying area of the positive electrode active material (coating area of the positive electrode side coating layer) in each example and each comparative example.
2. Production of negative electrode Artificial graphite (negative electrode material (negative electrode active material)), soft carbon (negative electrode material (negative electrode active material)), and polymer binder (PVdF manufactured by Kureha Co., Ltd.) with a solid content of 67.5: 22.5 The slurry (solid content: 40% by weight) of the mixture was put into NMP (N-methyl-2-pyrrolidone) solvent at a weight ratio of 10 and stirred at room temperature (25 ° C. to 30 ° C.) for 12 hours. Obtained.

Next, the obtained slurry was applied to the surface of a 10 μm thick copper foil (negative electrode side current collector) and dried at 80 ° C. for 12 hours to form a negative electrode side coating layer. Next, the dried copper foil was subjected to pressure stretching with a roll press to obtain an electrode sheet having a thickness of 14 μm.
Next, the electrode sheet was punched into a circular shape having a diameter of 14 mm, and then carried into a dryer and vacuum-dried at 120 ° C. for 12 hours. After the inside of the dryer was purged with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so as not to be exposed to the atmosphere. The negative electrode was produced by the above operation.

Table 1 shows the carrying area of the negative electrode active material (coating area of the negative electrode side coating layer) in each Example and each Comparative Example.
3. Preparation of capture agent-containing separator Lithium carbonate (Li ₂ CO ₃ ) powder (manufactured by Kishida Chemical Co., Ltd., average particle size 85.0 μm) and polymer binder (PTFE dispersion manufactured by Daikin Industries, Ltd.) having a solid content of 80:20 A mixture thereof was obtained by kneading in a mortar in a weight ratio.

Next, the mixture was subjected to pressure stretching using a manual roll press to obtain a separator sheet having a thickness of 50 μm. Next, the separator sheet was punched into a circular shape having a diameter of 2.4 cm, and then carried into a dryer and vacuum-dried at 120 ° C. for 12 hours. Then, after purging the inside of the dryer with nitrogen, the scavenger-containing separator was carried into a glove box in a dry Ar atmosphere so as not to be exposed to the air. By the above operation, a scavenger-containing separator was produced.
4). Production of Separator A separator made of cellulose having a thickness of 25 μm (TF40-25 made by Nippon Kohatsu Paper Co., Ltd.) was punched into a circular shape having a diameter of 2.4 cm.
5. Preparation of Electrolytic Solution LiPF ₆ (lithium salt) was prepared by dissolving in an ethylene carbonate-ethyl methyl carbonate mixed solvent (volume ratio 1: 1) so that the concentration was 2 mol / L.
6). Assembly of Laminate Cell A test cell was assembled using 1 positive electrode, 1 negative electrode, 1 capture agent-containing separator and 2 separators, and 1 mL of electrolyte.

More specifically, first, a separator containing a scavenger is sandwiched between two separators, and then, after laminating a positive electrode on one side and a negative electrode on the other side of the laminated separator, It accommodated in the cell tank and inject | poured electrolyte solution.
In the assembly of the test cell, the positive electrode and the negative electrode are opposed to the positive electrode side coating layer (positive electrode active material) and the negative electrode side coating layer (negative electrode active material). In the projection plane P ₁ (see FIG. 2) projected toward the positive electrode active material supporting region along the facing direction of the positive electrode side coating layer (positive electrode active material) and the negative electrode side coating layer (negative electrode active material). In Examples 1 to 3, the ratio of the positive electrode active material support area to the negative electrode active material support area was 0.862, 0.538, and 0.444, respectively. Was also arranged to be 1.000.

In each of Examples 1 to 3 and Comparative Examples 1 and 2, the projection plane P ₂ (projected from the positive electrode active material supporting region toward the negative electrode active material supporting region along the facing direction). In FIG. 2), the positive electrode active material supporting region was included in the negative electrode active material supporting region.
Table 1 shows the ratio of the supported area of the positive electrode active material in the positive electrode to the supported area of the negative electrode active material in the negative electrode in each example and each comparative example.

  In Comparative Example 2, a test cell was assembled using one positive electrode, one negative electrode, four separators (total thickness 100 μm), and 1 mL of electrolyte without using the capture agent-containing separator.

Evaluation experiment 1. Charge / Discharge Test A charge / discharge test was carried out by the following method for each of the test cells assembled in the above Examples and Comparative Examples.
(1) 1st cycle It charged with constant current at 1 mA / cm < ² > until the cell voltage rose to 4.8V. After charging, the cell voltage was held at 4.8 V until the current value dropped to 0.5 mA / cm ² , and then constant current discharge was performed at 1 mA / cm ² until the cell voltage dropped to 2.3 V.
(2) 2nd to 6th cycles The battery was charged at a constant current of 1 mA / cm ² until the cell voltage increased to 4.6V. After charging, constant current was discharged at 1 mA / cm ² until the cell voltage dropped to 2.3V.
(3) From the 7th cycle Onward, constant current charging was performed at 5 mA / cm ² until the cell voltage increased to 4.6V. After charging, constant current discharge was performed at 5 mA / cm ² until the cell voltage dropped to 2.3V.
2. Evaluation Based on the test result obtained by the charge / discharge test, the energy density in the charge / discharge cycle after the pre-cycle of each test cell and its maintenance rate were calculated, and the charge / discharge cycle durability of each test cell was evaluated.
(1) Energy density maintenance rate From the following formula, the energy in the charge / discharge cycle (after the 7th cycle) of each test cell of Example 1 and Comparative Examples 1 and 2 after the pre-cycle (above 1 to 6 cycles). The density maintenance rate was calculated, and the relationship between the number of cycles (number of charge / discharge cycles) and the energy density was confirmed. The result is shown in FIG.
_{ER = (DE X / V P} + N) / (DE 7 / V P + N) = DE X / DE 7
ER: Energy density retention rate (Energy density retention)
DE _X : Discharge energy of the X cycle (Discharging energy) [Wh]
DE ₇ : Discharge energy of the seventh cycle (Discharge energy) [Wh]
_{VP + N} : product of the sum of the thickness of the positive electrode side coating layer and the thickness of the negative electrode side coating layer and the area of the coating layer (Volume) [L]
In addition, in _{VP + N} of said formula, as a coating layer area, the larger coating area (negative electrode side coating layer) was employ | adopted by the positive electrode side coating layer and the negative electrode side coating layer.
(2) Charging / discharging cycle life From the following formula | equation, the energy density in the charging / discharging cycle (after the 7th cycle) of the test cell of Examples 1-3 and the comparative example 1 after the precycle (the said 1-6 cycles) is shown. The number of cycles (number of charge / discharge cycles) until the energy density was reduced to 80% was measured when the energy density at the seventh cycle was calculated as 100%. The result is shown in FIG.
ED = DE _X / V _{P + N}
ED: Energy density [Wh / L]
DE _X : Discharge energy of the X cycle (Discharging energy) [Wh]
_{VP + N} : product of the sum of the thickness of the positive electrode side coating layer and the thickness of the negative electrode side coating layer and the area of the coating layer (Volume) [L]
In addition, in _{VP + N} of said formula, as a coating layer area, the larger coating area (negative electrode side coating layer) was employ | adopted by the positive electrode side coating layer and the negative electrode side coating layer.
(3) Energy density From the above formula, the energy density of the second cycle was calculated for each of the test cells of Examples 1 to 3 and Comparative Example 1. The result is shown in FIG.

DESCRIPTION OF SYMBOLS 1 Hybrid capacitor 2 Positive electrode 3 Negative electrode 4 Separator 5 Cell tank 6 Electrolyte 7 Capture member 8a Positive electrode side collector 8b Negative electrode side collector 9a Positive electrode side coating layer 9b Negative electrode side coating layer

Claims (6)

A positive electrode carrying a positive electrode active material containing a polarizable carbon material;
A negative electrode carrying a negative electrode active material containing a material capable of reversibly occluding and releasing lithium ions, and arranged so that the negative electrode active material faces the positive electrode active material;
An organic solvent containing a lithium salt, and an electrolyte solution in which the positive electrode and the negative electrode are immersed,
In the projection plane obtained by projecting the negative electrode active material carrying region toward the positive electrode active material carrying region along the facing direction,
The electrochemical capacitor according to claim 1, wherein a ratio of a supported area of the positive electrode active material to a supported area of the negative electrode active material is less than 1. In a projection plane in which the positive electrode active material supporting region is projected toward the negative electrode active material supporting region along the facing direction,
2. The electrochemical capacitor according to claim 1, wherein the positive electrode active material supporting region is entirely included in the negative electrode active material supporting region.   3. The electrochemical capacitor according to claim 1, wherein a ratio of a supported area of the positive electrode active material to a supported area of the negative electrode active material is 0.6 or more.   The electrochemical capacitor according to claim 1, wherein the positive electrode active material contains KOH-activated soft carbon. The positive electrode has a potential of 4.23 V vs. The electrochemical capacitor according to claim 1, wherein the electrochemical capacitor is Li / Li ⁺ or more. Between the positive electrode and the negative electrode, at least one of the positive electrode and the negative electrode,
The electrochemical capacitor according to claim 1, further comprising a capturing agent that captures a negative electrode activity inhibiting substance derived from an anion contained in the electrolytic solution.

Images