JP2013073961A - Electrochemical capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical capacitor in which energy density can be improved while Coulomb efficiency can be improved.SOLUTION: An electrochemical capacitor of the present invention includes a positive electrode 2, a negative electrode 3 and a separator 4 interposed between the positive electrode 2 and the negative electrode 3. The separator 4 includes: a positive electrode side separator 11 disposed adjacent to the positive electrode 2 and allowing the passage of gas generated at the positive electrode; a negative electrode side separator 12 disposed adjacent to the negative electrode 3 and capturing a negative electrode activity inhibitor derived from anions included in a nonaqueous electrolyte; and an intermediate separator 13 disposed between the positive electrode side separator 11 and the negative electrode side separator 12 and blocking the passage of a lithium deposit deposited at the negative electrode.

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.

  2. Description of the Related Art Conventionally, studies and development of secondary batteries such as lithium ion batteries, electrochemical capacitors such as electric double layer capacitors and hybrid capacitors have been underway as power storage devices mounted on hybrid vehicles and fuel cell vehicles. An electricity storage device generally includes a positive electrode, a negative electrode, a separator interposed between these electrodes, and an outer container that contains the electrode and the separator and is filled with an electrolyte so as to immerse them. Yes.

  As such an electricity storage device, for example, the electrolytic solution is an aprotic organic solvent containing a lithium salt, the separator is formed of cellulose, polyethylene, or the like, and at least two or more sheets are sandwiched between the positive electrode and the negative electrode. A lithium ion capacitor to be used has been proposed (see, for example, Patent Document 1).

JP 2009-59732 A

However, in the lithium ion capacitor described in Patent Document 1, when charging and discharging are repeated at a high voltage, Li dendrite (Li dendrite) is precipitated in the negative electrode, and in the positive electrode, by oxidative decomposition of the electrolytic solution. Gas (eg, CO ₂ ) may be generated.

  In such a lithium ion capacitor, when the separator is made of cellulose, Li dendrite (Li dendrites) may penetrate the separator, and the positive electrode and the negative electrode may be short-circuited. As a result, the coulomb efficiency may decrease.

On the other hand, when the separator is made of polyethylene, Li dendrite (Li dendrites) can be prevented from penetrating the separator, but the passage of gas (for example, CO ₂ ) due to oxidative decomposition of the electrolyte is suppressed. In some cases, the gas stays in the cell. As a result, the energy density may not be maintained well.

  Accordingly, an object of the present invention is to provide an electrochemical capacitor that can improve the energy density while improving the coulomb efficiency.

  In order to achieve the above object, an electrochemical capacitor of the present invention includes a positive electrode, a negative electrode made of a material capable of reversibly occluding and releasing lithium ions, a non-aqueous electrolyte containing lithium ions, the positive electrode, and the negative electrode A separator interposed between the first separator and the positive electrode, the first separator allowing the gas generated in the positive electrode to pass therethrough, and the negative electrode. A second separator that captures a negative electrode activity-inhibiting substance derived from an anion contained in the non-aqueous electrolyte, and the lithium contained in the non-aqueous electrolyte that is disposed between the first separator and the second separator. A third separator that is derived from ions and blocks the passage of lithium precipitates that are deposited in the negative electrode.

  In the electrochemical capacitor of the present invention, the first separator is disposed adjacent to the positive electrode, and the third separator is disposed between the first separator and the second separator. Therefore, gas generated in the positive electrode passes through the first separator and is removed from the electrochemical capacitor, and lithium precipitates precipitated in the negative electrode can be prevented from penetrating the separator.

  As a result, a short circuit between the positive electrode and the negative electrode can be prevented, and gas can be prevented from staying in the electrochemical capacitor.

  Therefore, the electrochemical capacitor of the present invention can improve the energy density while improving the coulomb efficiency. Thereby, the lifetime of an electrochemical capacitor can be improved and the cost can be reduced.

It is a schematic block diagram of the hybrid capacitor which shows one Embodiment of the electrochemical capacitor of this invention. It is a figure which shows the change of the Coulomb efficiency of the hybrid capacitor (test cell) in the charging / discharging cycle of an Example and a comparative example. It is a figure which shows the change of the energy density of the hybrid capacitor (test cell) in the charging / discharging cycle of an Example and a comparative example.

  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 as an example of an electrochemical capacitor includes a positive electrode 2, a negative electrode 3 disposed opposite to the positive electrode 2 with a space therebetween, and a separator interposed between the positive electrode 2 and the negative electrode 3. 4, a cell tank 6 that accommodates the positive electrode 2, the negative electrode 3, and the separator 4, and a nonaqueous electrolyte 5 that is stored in the cell tank 6 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 is a polarizable electrode and includes a positive electrode side coating layer 8 and a positive electrode side current collector 7.

  The positive electrode side coating layer 8 is formed in a predetermined shape (for example, a rectangular shape) and contains, for example, a positive electrode material made of polarizable carbon and a polymer binder, and further contains a conductive agent as necessary. ing.

  The positive electrode material is obtained by, for example, activating a carbon material.

  Examples of the carbon material include soft carbon and hard 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 cokes, coal needle cokes, anthracene, polyvinyl chloride, polyacrylonitrile, etc. Thermally decomposed products such as chemical coke.

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 hard carbons include, for example, phenol resins, melamine resins, urea resins, furan resins, epoxy resins, alkyd resins, unsaturated polyester resins, diallyl phthalate resins, furfural resins, resorcinol resins, silicone resins, xylene resins, urethanes. 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 carbon materials may be used alone or in combination.

  Among these carbon materials, soft carbon is preferable, and mesophase pitch is more 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 activation treatments, an alkali activation treatment is preferable, and an alkali activation treatment (KOH activation treatment) using potassium hydroxide (KOH) as an activator is more preferable.

  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 quantity of KOH used is 0.5-5 mass parts with respect to 1 mass part of carbon materials, for example.

In the hybrid capacitor 1 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 4.2 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 content rate of positive electrode material is 65-99 mass parts with respect to 100 mass parts of positive electrode side collectors, Preferably, it is 70-90 mass parts.

  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 polymer binders may be used alone or in combination.

  Of these polymer binders, preferably, polyvinylidene fluoride (PVdF) is used.

  The content rate of a polymer binder is 1-25 mass parts with respect to 100 mass parts of positive electrode side collectors, Preferably, it is 5-20 mass parts.

  Examples of the conductive agent include carbon black, ketjen black, and acetylene black.

  These conductive agents may be used alone or in combination.

  Of these conductive agents, carbon black is preferable.

  The content rate of a electrically conductive agent is 0-20 mass parts with respect to 100 mass parts of positive electrode side collectors, Preferably, it is 5-10 mass parts.

  The positive electrode side current collector 7 is formed of, for example, a metal foil, and examples of the metal foil include an aluminum foil, a copper foil, a stainless steel foil, and a nickel foil.

  Among these metal foils, aluminum foil is preferable.

  Moreover, although the thickness of these metal foils changes with the scales of the hybrid capacitor 1, it is 10-50 micrometers in a lab scale, for example.

  In order to form the positive electrode 2, for example, the above-described positive electrode material, polymer binder, and, if necessary, a conductive agent and the like are blended in the above-described ratio, and stirred in a solvent to obtain a slurry (solid content: 10 to 60% by mass). Next, the slurry is applied to the surface of the positive electrode current collector 7 to form the positive electrode side coating layer 8, and then subjected to pressure stretching using, for example, a roll press to obtain an electrode sheet. Next, the electrode sheet is cut into a predetermined shape (for example, a rectangular shape or a circular shape) and then further dried as necessary. Thereby, the positive electrode 2 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.

  These solvents may be used alone or in combination.

  Of these solvents, aprotic polar solvents are preferable, and N-methyl-2-pyrrolidone (NMP) is more preferable.

  Although the thickness of the positive electrode 2 obtained by such a method varies depending on the scale of the hybrid capacitor 1, for example, in the lab scale, the thickness is 30 to 150 μm.

  Moreover, although the magnitude | size of the positive electrode 2 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, preferably 10 to 10 mm. The length (direction in the direction perpendicular to the longitudinal direction) is, for example, 10 to 200 mm, preferably 10 to 100 mm. For example, in the case of a circular shape, the diameter is, for example, 5 to 30 mm, preferably Is 5 to 15 mm.

  The negative electrode 3 is an electrode that reversibly occludes / releases lithium ions, and includes a negative electrode side coating layer 10 and a negative electrode side current collector 9.

  The negative electrode side coating layer 10 is formed in a predetermined shape (for example, rectangular shape), and includes, for example, a negative electrode material capable of reversibly occluding and releasing lithium ions and a polymer binder, and further, if necessary. Contains a conductive agent.

  Examples of the negative electrode material include hard carbon and 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. Further, graphite is preferably used in the form of powder (for example, having an average particle size of 25 μm or less).

  These negative electrode materials may be used alone or in combination.

  Of these negative electrode materials, soft carbon and graphite are preferable, and a combination of soft carbon and graphite is more preferable.

  The content rate of negative electrode material is 80-99 mass parts with respect to 100 mass parts of negative electrode side coating layers, Preferably, it is 85-95 mass parts.

  Examples of the polymer binder include the polymer binder described above.

  These polymer binders may be used alone or in combination.

  Of these polymer binders, PVdF is preferable.

  The content rate of a polymer binder is 1-20 mass parts with respect to 100 mass parts of negative electrode side coating layers, Preferably, it is 5-15 mass parts.

  Examples of the conductive agent include the above-described conductive agents.

  These conductive agents may be used alone or in combination.

  The content rate of a electrically conductive agent is 0-20 mass parts with respect to 100 mass parts of negative electrode side coating layers, Preferably, it is 1-10 mass parts.

  The negative electrode side current collector 9 is formed from, for example, the metal foil described above.

  Among these metal foils, copper foil is preferable.

  Although the thickness of metal foil changes with the scales of the hybrid capacitor 1, it is 5-50 micrometers in a lab scale, for example.

  In order to form the negative electrode 3, for example, the above-described negative electrode material, polymer binder, and, if necessary, a conductive agent and the like are blended in the above ratio, and stirred in a solvent to obtain a slurry (solid content: 10 to 60% by mass).

  Next, the slurry is applied (applied) onto the negative electrode side current collector 9 to form the negative electrode side coating layer 10, and then subjected to pressure stretching using, for example, a roll press to obtain an electrode sheet. Next, the electrode sheet is cut into a predetermined shape (for example, a rectangular shape or a circular shape) and then further dried as necessary. Thereby, the negative electrode 3 is obtained.

  Examples of the solvent include the above-mentioned solvents, preferably an aprotic polar solvent, and more preferably N-methyl-2-pyrrolidone (NMP).

  The thickness of the negative electrode 3 varies depending on the scale of the hybrid capacitor 1, but is, for example, 5 to 70 μm on the lab scale.

  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. For example, in the case of a circular shape, the diameter is, for example, 5 to 30 mm, preferably 5 to 15 mm.

  The separator 4 includes a positive separator 11 as an example of a first separator, a negative separator 12 as an example of a second separator, and an intermediate separator 13 as an example of a third separator.

  The positive electrode side separator 11 is disposed adjacent to the positive electrode side coating layer 8 and is formed of, for example, natural fibers such as cellulose.

  Among such positive electrode side separators 11, a separator formed from cellulose is preferable.

  Moreover, the positive electrode side separator 11 has pores, and the pore diameter is, for example, 3 to 50 μm, preferably 5 to 25 μm.

  Moreover, although the thickness of the positive electrode side separator 11 changes with scales of the hybrid capacitor 1, in a laboratory scale, it is 10-100 micrometers, for example.

  The negative electrode side separator 12 is disposed adjacent to the negative electrode side coating layer 10 and contains, for example, a scavenger for capturing a negative electrode activity inhibitor and a polymer binder.

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 ), and alkaline earth such as magnesium oxide (MgO). And oxides of similar metals.

  Such scavengers may be used alone or in combination.

  Of these scavengers, lithium carbonate is preferable.

  The content rate of a trapping agent is 60-95 mass parts with respect to 100 mass parts of negative electrode side separators, Preferably, it is 70-90 mass parts.

  Examples of the polymer binder include the polymer binder described above.

  These polymer binders may be used alone or in combination.

  Of these polymer binders, PTFE is preferable.

  The content rate of a polymer binder is 5-40 mass parts with respect to 100 mass parts of negative electrode side separators, Preferably, it is 10-30 mass parts.

  And in order to form the negative electrode side separator 12, the mixture which mix | blended above-described scavenger and a polymer binder in the above-mentioned ratio is prepared, for example.

  Next, the mixture is subjected to pressure stretching using, for example, a roll press to obtain a capturing agent-containing sheet. Next, the scavenger-containing sheet is cut into a predetermined shape (for example, a rectangular shape or a circular shape), and then further dried as necessary. Thereby, the negative electrode side separator 12 is obtained.

  The intermediate separator 13 is disposed between the positive electrode side separator 11 and the negative electrode side separator 12, and is formed of, for example, organic fibers such as polyolefin (for example, polyethylene, polypropylene, ethylene / propylene copolymer, etc.).

  Among such intermediate separators 13, a separator formed of polyethylene is preferable.

  Such an intermediate separator 13 is formed with pores, and the pore diameter is, for example, 0.2 to 1 μm, preferably 0.2 to 0.8 μm.

  Moreover, although the thickness of the intermediate separator 13 changes with the scales of the hybrid capacitor 1, it is 5-50 micrometers in a laboratory scale, for example.

  Moreover, although the magnitude | size of these positive electrode side separator 11, the negative electrode side separator 12, and the intermediate | middle separator 13 changes with scales of the hybrid capacitor 1, for example, in a lab scale, in the case of a rectangular shape, for example, 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. For example, in the case of a circular shape, the diameter is, for example, 10 to 60 mm, preferably 20 to 20 mm. .

  Such a separator 4 is arranged such that the intermediate separator 13 is sandwiched between the positive electrode side separator 11 and the negative electrode side separator 12, and the one side surface of the intermediate separator 13 and the positive electrode side separator 11 are in contact with each other. The other side surface of the intermediate separator 13 and the negative electrode side separator 12 are in contact with each other.

  Moreover, the ratio of the thickness of the negative electrode side separator 12, the intermediate | middle separator 13, and the positive electrode side separator 11 is 1-4: 1: 1-4, for example, Preferably, it is 2-3: 1: 2-3.

  The nonaqueous electrolyte 5 is an organic solvent containing lithium ions, and 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 lithium salts may be used alone or in combination.

Of these lithium salts, LiPF ₆ is preferable.

  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 organic solvents may be used alone or in combination.

  Of these organic solvents, ethylene carbonate and diethyl carbonate are preferable, and a mixed solvent of ethylene carbonate and diethyl carbonate is more preferable.

  The density | concentration of the lithium salt in the nonaqueous electrolyte 5 is 0.5-5 mol / L, for example, Preferably, it is 0.5-2 mol / L.

  In order to prepare such a hybrid capacitor 1, first, the above-described positive electrode 2, negative electrode 3 and separator 4 are laminated. Specifically, the intermediate separator 13 is sandwiched between the positive electrode side separator 11 and the negative electrode side separator 12, and then the positive electrode 2 is laminated so that the positive electrode side coating layer 8 is adjacent to the positive electrode side separator 11. The negative electrode 3 is laminated so that the negative electrode side coating layer 10 is adjacent.

  Subsequently, the positive electrode side current collector 7 and the negative electrode side current collector 9 are joined to the current collecting tab, and the obtained laminate is accommodated in the cell tank 6 (for example, an aluminum laminate film). Then, the nonaqueous electrolyte 5 is injected into the cell tank 6.

  Thus, the hybrid capacitor 1 is prepared as a laminate cell.

In the hybrid capacitor 1, when the potential of the positive electrode 2 is set to a high potential such as 4.2 V vs Li / Li ⁺ or more, the anion ( For example, a negative electrode activity inhibitor that reduces the electric capacity of the negative electrode is generated from PF _6- ^{and the} like contained in LiPF ₆ .

  As a process in which the negative electrode activity inhibitor is generated, for example, a process in which HF as a negative electrode activity inhibitor is generated will be described below.

First, when a predetermined voltage (that is, 4.2 V vs Li / Li ⁺ or more) is applied to the positive electrode 2 and the negative electrode 3, in the non-aqueous electrolyte 5, for example, from moisture and organic substances contained in the positive electrode 2 and the non-aqueous electrolyte 5. 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, aqueous anions contained in the electrolyte 5 (e.g., PF ₆ contained in LiPF ₆ ^-, etc.) and react, HF is produced (the following formula (3) reference.).

(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.

  However, in the hybrid capacitor 1, since the negative electrode side separator 12 contains a scavenger (for example, lithium carbonate), even if a negative electrode activity inhibitor is generated due to the irreversible capacity of the positive electrode 2, the negative electrode activity inhibition is caused. The negative electrode side separator 12 captures the substance. Therefore, a decrease in the energy density of the hybrid capacitor 1 can be prevented.

In the hybrid capacitor 1, when charging / discharging is repeated at a high voltage, gas (for example, CO ₂ ) is generated in the positive electrode 2 due to oxidative decomposition of the nonaqueous electrolyte 5. On the other hand, in the negative electrode 3, lithium precipitates (lithium dendrites) are precipitated from lithium ions contained in the nonaqueous electrolyte 5.

  In this hybrid capacitor 1, since the positive electrode side separator 11 having a pore diameter of, for example, 3 to 50 μm is disposed adjacent to the positive electrode side coating layer 8, the gas generated in the positive electrode 2 passes through the positive electrode side separator 11, It is removed outside the hybrid capacitor 1. Therefore, it is possible to suppress the gas from staying in the hybrid capacitor 1 and to improve the energy density.

  In the hybrid capacitor 1, the intermediate separator 13 having a pore diameter of, for example, 0.2 to 1 μm is disposed between the positive electrode side separator 11 and the negative electrode side separator 12. The passage of lithium precipitates deposited in is blocked. Therefore, lithium deposits can be prevented from penetrating the separator 4, and a short circuit between the positive electrode 2 and the negative electrode 3 can be prevented. As a result, the coulomb efficiency can be improved.

  Therefore, the hybrid capacitor 1 can improve the energy density while improving the coulomb efficiency. Thereby, the lifetime of the hybrid capacitor 1 can be improved and the cost can be reduced.

Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example.
Example 1
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 mass of KOH was added to 1 part by mass 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 until the waste liquid became neutral. Thereby, KOH activated soft carbon (positive electrode 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.) having a solid content of 75: 8.3: A slurry of the mixture (solid content: 30% by mass) was added to an NMP (N-methyl-2-pyrrolidone) solvent at a mass 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, thereby obtaining an electrode sheet having a thickness of 72 μm of the positive electrode side coating layer (the positive electrode active material coating layer) excluding the aluminum foil.

Next, the electrode sheet was cut into a circular shape with a diameter of 10 mm to produce a positive electrode. (Electrode volume: about 5.7 mm ³ )
2. Production of Negative Electrode Artificial graphite, soft carbon, and polymer binder (PVdF manufactured by Kureha Co., Ltd.) in a mass ratio of solid content 67.5: 22.5: 10, NMP (N-methyl-2-pyrrolidone) solvent The mixture was stirred at room temperature (25 ° C. to 30 ° C.) for 12 hours to obtain a slurry of the mixture (solid content: 40% by mass).

  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. Subsequently, the dried copper foil was press-stretched with a roll press to obtain an electrode sheet having a negative electrode side coating layer (negative electrode active material coating layer) thickness of 14 μm excluding the copper foil.

Next, the electrode sheet was cut into a circular shape with a diameter of 10 mm to produce a negative electrode. (Electrode volume: about 1.1 mm ³ )
3. Production of Separator (3-1) Production of Positive Electrode Side Separator A 20 μm thick cellulose separator (TF40-50 made by Nippon Kogyo Paper Co., Ltd.) having a pore diameter of about 5 μm is cut into a circular shape with a diameter of Φ25 mm, thereby producing a positive electrode side. A separator was produced.
(3-2) Production of Intermediate Separator A polyethylene separator having a thickness of 9 μm (ND309 manufactured by Asahi Kasei Co., Ltd.) (pore diameter: 0.2 μm) was cut into a circular shape having a diameter of Φ25 mm to produce an intermediate separator.
(3-3) Production of negative electrode side separator Lithium carbonate (Li ₂ CO ₃ ) powder (Kishida Chemical Co., Ltd. average particle size 85.0 μm) and polymer binder (Daikin Industries, Ltd. PTFE dispersion) A mixture of them was obtained by kneading in a mortar at a mass ratio of 80:20.

Next, the mixture was subjected to pressure stretching using a manual roll press to obtain a capturing agent-containing sheet having a thickness of 20 μm. Next, the scavenger-containing sheet was cut into a circular shape having a diameter of Φ25 mm, 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 scavenger-containing sheet was carried into a glove box in a dry Ar atmosphere so as not to come into contact with the atmosphere. The negative electrode side separator was produced by the above operation.
4). Preparation of Electrolytic Solution An electrolytic solution was prepared by dissolving 1 mol / L of LiPF ₆ (lithium salt) in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1).
5. Assembly of Laminate Cell (Test Cell) One positive electrode, one negative electrode, and three separators (positive electrode side separator, intermediate separator, negative electrode side separator) were laminated. Specifically, first, the intermediate separator is sandwiched between the positive electrode side separator and the negative electrode side separator, and then the positive electrode is laminated on the positive electrode side separator so that the positive electrode side coating layer is adjacent to the negative electrode side separator. The negative electrode was laminated so that the side coating layers were adjacent.

Subsequently, the laminated positive electrode, negative electrode, and each separator were accommodated in a cell tank, and an electrolytic solution (1 cc) was injected. The test cell was assembled by the above operation.
Comparative Example 1
A test cell was prepared in the same manner as in Example 1 except that no intermediate separator was used.
Comparative Example 2
The positive electrode side separator is sandwiched between the intermediate separator and the negative electrode side separator, the positive electrode is laminated on the intermediate separator so that the positive electrode side coating layer is adjacent, and the negative electrode is applied so that the negative electrode side separator is adjacent to the negative electrode side coating layer. A test cell was prepared in the same manner as in Example 1 except that was laminated.
Charge / Discharge Test A charge / discharge test (charge / discharge cycle) was performed on each of the test cells assembled in the above Examples and Comparative Examples by the following method.
(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 0.3 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 FIG. 2 shows a change in coulomb efficiency (ratio of discharge capacity to charge capacity) of the hybrid capacitor (test cell) in the charge / discharge cycle of the example and each comparative example.

  In FIG. 3, the change of the energy density of the hybrid capacitor (test cell) in the charging / discharging cycle of an Example and each comparative example is shown.

  The Coulomb efficiency was calculated from the discharge capacity / charge capacity for each cycle of the test cell.

The change in energy density is the ratio of the energy of each cycle of the test cell to the electrode volume of the positive electrode / negative electrode, and was calculated from the change in energy density after the seventh cycle.
Consideration (1) Coulomb efficiency As shown in FIG. 1, in Comparative Example 1, a short circuit between the positive electrode and the negative electrode (a point where the Coulomb efficiency is remarkably low) was confirmed around 700 cycles in the charge / discharge cycle.

On the other hand, in Example 1 and Comparative Example 2, a short circuit between the positive electrode and the negative electrode was not confirmed.
(2) Energy Density As shown in FIG. 2, in Comparative Examples 1 and 2, a decrease in energy density was confirmed as the charge / discharge cycle was repeated.

  On the other hand, in Example 1, it was confirmed that a high energy density was satisfactorily maintained even when the charge / discharge cycle was repeated.

DESCRIPTION OF SYMBOLS 1 Hybrid capacitor 2 Positive electrode 3 Negative electrode 4 Separator 5 Nonaqueous electrolyte 11 Positive electrode side separator 12 Negative electrode side separator 13 Intermediate separator

Claims (1)

A positive electrode;
A negative electrode made of a material capable of reversibly inserting and extracting lithium ions;
A non-aqueous electrolyte containing lithium ions;
An electrochemical capacitor comprising a separator interposed between the positive electrode and the negative electrode,
The separator is
A first separator disposed adjacent to the positive electrode and allowing passage of gas generated in the positive electrode;
A second separator disposed adjacent to the negative electrode and capturing a negative electrode activity inhibitor derived from an anion contained in the nonaqueous electrolyte;
A third separator that is disposed between the first separator and the second separator and that is derived from lithium ions contained in the non-aqueous electrolyte and that blocks the passage of lithium precipitates deposited on the negative electrode. A feature of the electrochemical capacitor.

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