JP2016103553A - Method for manufacturing electrochemical capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrochemical capacitor, by which an electrochemical capacitor superior in power storage capacity and low-temperature characteristic (capacitor performance under a low-temperature environment) can be obtained.SOLUTION: A method for manufacturing an electrochemical capacitor comprises: a preparation step for preparing a cell 10 including a positive electrode 2, a negative electrode 3, a cell bath 6 which contains the positive electrode 2 and the negative electrode 3, and a first electrolytic solution 5 stored in the cell bath 6 so that the positive electrode 2 and the negative electrode 3 are immersed therein, and including a first mix solvent in which the content of ethylene carbonate blended is 50 vol.% or more; a step for performing an electrochemical activating process on the cell 10; and a step for replacing the first electrolytic solution 5 with a second electrolytic solution including a second mix solvent in which the content of ethylene carbonate blended is less than 50 vol.% after the electrochemical activating process.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, secondary batteries such as lithium-ion batteries, electric double layer capacitors, and hybrid capacitors (in addition to electric double layers, energy is obtained by oxidation-reduction reactions in the positive electrode or negative electrode as power storage devices mounted in hybrid vehicles and fuel cell vehicles. Research and development of electrochemical capacitors such as storage capacitors) are underway.

  An electrochemical capacitor generally has a positive electrode, a negative electrode, a separator interposed between the electrodes, and a cell tank that contains the electrodes and the separator and is filled with an electrolyte so as to immerse them. doing.

For example, the electrolytic solution contains LiBF ₄ (lithium tetrafluoroborate) and a mixed solvent of ethylene carbonate and dimethyl carbonate, and ethylene carbonate is 50% by volume or more and 80% by volume with respect to the total amount of ethylene carbonate and dimethyl carbonate. A hybrid capacitor having a volume% or less range has been proposed (see, for example, Patent Document 1).

JP 2014-165187 A

  However, in the hybrid capacitor described in Patent Document 1, ethylene carbonate having a melting point of about 35 ° C. is contained in the mixed solvent at a high rate (50 to 80 volume%), so that the low temperature environment ( For example, at 10 ° C. or less, there is a problem that the electrolytic solution is solidified and the capacitor performance is deteriorated.

  On the other hand, if the ratio of ethylene carbonate in the mixed solvent is reduced, it is possible to suppress the solidification of the electrolyte solution in a low temperature environment, but there is a problem that a sufficient storage capacity cannot be ensured.

  Accordingly, an object of the present invention is to provide an electrochemical capacitor manufacturing method capable of obtaining an electrochemical capacitor having excellent storage capacity and low temperature characteristics (capacitor performance in a low temperature environment).

  The method for producing an electrochemical capacitor of the present invention includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a cell tank containing the positive electrode and the negative electrode, and the positive electrode and the negative electrode so as to be immersed therein. Electrochemical activation by applying a voltage to the positive electrode and the negative electrode in the presence of the first electrolytic solution in a preparation step of preparing a cell that is stored in a cell tank and includes a first electrolytic solution containing ethylene carbonate An activation step to be processed, and after the activation step, a replacement step of replacing the first electrolytic solution with a second electrolytic solution containing ethylene carbonate relatively less than the first electrolytic solution, The liquid is composed of a lithium salt and a first solvent containing ethylene carbonate, and the second electrolyte is composed of a lithium salt and a second solvent containing ethylene carbonate. In the first solvent, the mixing ratio of the ethylene carbonate is at least 50% by volume, in the second solvent, the mixing ratio of the ethylene carbonate is characterized in that less than 50% by volume.

  According to such a manufacturing method, in the activation step, the first electrolytic solution having a relatively high blending ratio of ethylene carbonate (specifically, the first solvent having a blending ratio of ethylene carbonate of 50% by volume or more is included). ), The positive electrode and the negative electrode are subjected to electrochemical activation treatment, so that an excellent storage capacity can be ensured.

  And after an activation process, 1st electrolyte solution contains the 2nd electrolyte solution (specifically, the 2nd solvent whose compounding ratio of ethylene carbonate is less than 50 volume%) with a comparatively low compounding ratio of ethylene carbonate ), The solidification of the electrolyte solution in a low temperature environment can be suppressed.

  Therefore, an electrochemical capacitor having excellent storage capacity and low temperature characteristics can be obtained.

Further, the respective lithium salt of the first electrolyte and the second electrolyte is suitably a LiBF _4.

However, LiBF ₄ (lithium tetrafluoroborate) has excellent thermal stability and low reactivity with moisture compared to other lithium salts (for example, lithium hexafluorophosphate). Therefore, when each of the first electrolyte solution and the second electrolyte solution contains LiBF ₄ , decomposition of the lithium salt can be suppressed, and generation of gas resulting therefrom can be suppressed. As a result, the electrochemical capacitor can be prevented from being damaged and the performance is lowered.

Also, each of the lithium salt of the first electrolyte and the second electrolyte is a LiBF _4, in activation step, in the presence of a proportion of the ethylene carbonate is relatively high first electrolytic solution, the positive and negative electrodes As a result of the electrochemical activation treatment, an excellent storage capacity can be ensured.

  As a result, an electrochemical capacitor having excellent storage capacity can be obtained while gas generation can be suppressed.

  According to the method for producing an electrochemical capacitor of the present invention, an electrochemical capacitor having excellent storage capacity and low temperature characteristics can be obtained.

It is a schematic block diagram of the hybrid capacitor which shows one Embodiment of the electrochemical capacitor of this invention. It is a graph which shows the energy density of the hybrid capacitor of an Example and a comparative example.

  As shown in FIG. 1, a hybrid capacitor 1 as an example of an electrochemical capacitor is interposed between a positive electrode 2, a negative electrode 3 arranged to face the positive electrode 2 with a space therebetween, and a positive electrode 2 and a negative electrode 3. And a cell tank 6 that accommodates the positive electrode 2, the negative electrode 3, and the separator 4. 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 formed by, for example, forming a mixture obtained by blending a positive electrode material (polarizable carbon material) and a binder, and further, for example, a conductive agent, if necessary, into an electrode shape, and then drying, Is formed.

  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%.

  Examples of soft carbon include pitches such as petroleum pitch, coal pitch, and mesophase pitch, and graphitizable cokes such as petroleum needle coke, coal needle coke, anthracene, polyvinyl chloride, and polyacrylonitrile. Thermal decomposition products such as These soft carbons may 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.

  As hard carbon, for example, 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 resin, etc. Thermosetting resin, for example, carbon black such as thermal black, furnace black, lamp black, channel black, acetylene black, non-graphitizable coke different from graphitizable coke such as flue coke and gilsonite coke, For example, plant raw materials such as coconut palm and wood flour, for example, pyrolysates such as glassy carbon, and the like can be mentioned. These hard carbons may be used alone or in combination of two or more.

  Among such carbon materials, soft carbon is preferable, pitches are more preferable, and mesophase pitches are particularly 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, for example, 500 ° C. to 800 ° C. in a nitrogen atmosphere, and then fired together with KOH at 700 to 1000 ° C. The quantity of KOH used is 0.5-5 mass parts with respect to 1 mass part of carbon materials, for example.

  A positive electrode material is mix | blended so that the mass ratio of solid content may be a ratio of 70-99 mass% with respect to the mixture whole quantity, for example.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluoroolefin copolymer crosslinked polymer, fluoroolefin vinyl ether copolymer crosslinked polymer, carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylic. An acid etc. are mentioned. These binders may be used alone or in combination of two or more.

  Of these binders, polyvinylidene fluoride (PVdF) is preferable.

  The mass ratio of the solid content of the binder is, for example, 1% by mass or more, preferably 5% by mass or more, for example, 20% by mass or less, preferably 15% by mass or less, with respect to the total amount of the mixture.

  Examples of the conductive agent include carbon black, ketjen black, and acetylene black. These conductive agents may be used alone or in combination of two or more. Among these conductive agents, carbon black is preferable.

  The mass ratio of the solid content of the conductive agent is, for example, 0% by mass or more, preferably 5% by mass or more, for example, 20% by mass or less, preferably 10% by mass or less, with respect to the total amount of the mixture. That is, the conductive agent may or may not be blended.

  In order to form the positive electrode 2, for example, a mixture containing the above-described positive electrode material, a binder, and, if necessary, a conductive agent is stirred in a solvent, for example, in a slurry (solid content: 10 to 60). Mass%).

  Examples of the solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, ethyl acetate, dimethyl phthalate, ethanol, methanol, butanol, Water etc. are mentioned. These solvents may be used alone or in combination of two or more. Among these solvents, N-methyl-2-pyrrolidone (NMP) is preferable.

  Next, the slurry is applied (coated) on a metal foil (current collector), dried, and then stretched under pressure using, for example, a roll press to obtain an electrode sheet. Thereafter, the electrode sheet is punched into a predetermined shape. Thereby, the positive electrode 2 is obtained.

  Examples of the metal foil include aluminum foil, copper foil, stainless steel foil, and nickel foil. Among these metal foils, aluminum foil is preferable.

  The thickness of the positive electrode 2 obtained by such a method varies depending on the scale of the hybrid capacitor 1. However, in the lab scale, for example, the thickness is 30 to 150 μm, and the thickness excluding the metal foil serving as the current collector is 10 to 10 mm. 140 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 mm to 200 mm, and is orthogonal to the longitudinal direction. The direction (width direction) length is, for example, 10 mm to 200 mm or less, and in the case of a circular shape, the diameter is, for example, 5 to 15 mm.

  The negative electrode 3 is formed, for example, by molding a mixture obtained by blending a negative electrode material and a binder into an electrode shape and then drying it.

  The negative electrode material is made of a material capable of reversibly occluding and releasing lithium ions, 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. 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 two or more.

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

  The mass ratio of the solid content of the negative electrode material is, for example, 80% by mass or more, preferably 85% by mass or more, for example, 99% by mass or less, preferably 95% by mass or less, with respect to the total amount of the mixture.

  Examples of the binder include the above-described binders. These binders may be used alone or in combination of two or more. Of these binders, polyvinylidene fluoride (PVdF) is preferable.

  The mass ratio of the solid content of the binder is, for example, 1% by mass or more, preferably 5% by mass or more, for example, 20% by mass or less, preferably 15% by mass or less, with respect to the total amount of the mixture.

  Moreover, in manufacture of the negative electrode 3, a electrically conductive agent can also be mix | blended as needed.

  Examples of the conductive agent include the above-described conductive agents. These conductive agents may be used alone or in combination of two or more.

  The mass ratio of the solid content of the conductive agent is, for example, 0% by mass or more, preferably 1% by mass or more, for example, 20% by mass or less, preferably 10% by mass or less, based on the total amount of the mixture.

  In order to form the negative electrode 3, for example, a mixture containing a negative electrode material, a binder, and, if necessary, a conductive agent is stirred in a solvent to obtain a slurry (solid content: 10 to 60% by mass). obtain.

  Examples of the solvent include the above-described solvents. These solvents may be used alone or in combination of two or more. Among these solvents, N-methyl-2-pyrrolidone (NMP) is preferable.

  Next, the slurry is applied (coated) on a metal foil (current collector), dried, and then stretched under pressure using, for example, a roll press to obtain an electrode sheet. Thereafter, the electrode sheet is punched into a predetermined shape. Thereby, the negative electrode 3 is obtained.

  Examples of the metal foil include the above-described metal foil. Among these metal foils, copper foil is preferable.

  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 metal foil serving as the current collector is 5. ~ 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.

  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. Among these separators, a separator made of ceramic fibers is preferable.

  Although the thickness of such a separator 4 changes with scales of the hybrid capacitor 1, it is 100-1000 micrometers in a lab scale, for example.

  Moreover, although the magnitude | size of the separator 4 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, 15 to 220 mm, and the length in the width direction. The length is, for example, 15 to 220 mm. In the case of a circular shape, the diameter is, for example, 10 to 30 mm.

  The cell tank 6 is not particularly limited and may be a known container or a bag for a metal laminate film. In such a cell tank 6, Preferably, the bag for metal laminate films is mentioned.

  Next, a method for producing a hybrid capacitor as an embodiment of the method for producing an electrochemical capacitor of the present invention will be described in detail.

  In this method, first, a positive electrode 2, a negative electrode 3, a separator 4, a cell tank 6 and a first electrolytic solution 5 are prepared, and a positive electrode 2, a negative electrode 3, a separator 4, a cell tank 6, and a first electrolytic solution are prepared. 5 is prepared (preparation step).

  To prepare the cell 10, first, the positive electrode 2 and the negative electrode 3 are laminated on one side of the separator 4 and the negative electrode 3 on the other side so that the positive electrode 2 and the negative electrode 3 are opposed to each other with a gap. The stacked body is placed in the cell tank 6.

  Next, the first electrolytic solution 5 is injected and stored in the cell tank 6 so that the positive electrode 2, the negative electrode 3, and the separator 4 are immersed therein. Thereby, the cell 10 is assembled.

  The 1st electrolyte solution 5 consists of a lithium salt as electrolyte, and the 1st mixed solvent as an example of the 1st solvent which melt | dissolves lithium salt.

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 two or more.

Of these lithium salts, LiBF ₄ (lithium tetrafluoroborate) is preferably used.

  The concentration of the lithium salt in the first electrolytic solution 5 is, for example, 0.5 mol / L or more, for example, 5 mol / L or less, preferably 2 mol / L or less.

  The first mixed solvent contains ethylene carbonate (EC), and specifically, is a mixed solvent of ethylene carbonate and the first organic solvent.

  Examples of the first organic solvent include propylene carbonate (melting point: −55 ° C.), propylene carbonate derivative, butylene carbonate (melting point: −45 ° C.), dimethyl carbonate (melting point: 2 to 4 ° C.), diethyl carbonate (melting point: − 43 ° C), ethyl methyl carbonate (melting point: -14.5 ° C), γ-butyrolactone (melting point: -43.5 ° C), 1,3-dioxolane (melting point: -95 ° C), dimethyl sulfoxide (DMSO, melting point: 19 ° C.), sulfolane (melting point: 27.5 ° C.), formamide (melting point: 2-3 ° C.), dimethylformamide (DMF, melting point: −61 ° C.), dimethylacetamide (DMA, melting point: −20 ° C.), phosphoric acid Triester, maleic anhydride (melting point: 52.6 ° C), succinic anhydride (melting point: 120 ° C), phthalic anhydride (melting point) 131 ° C.), 1,3-propane sultone (melting point: 31 ° C.), 4,5-dihydropyran derivative, nitrobenzene (melting point: 5.7 ° C.), 1,3-dioxane (melting point: −45 ° C.), 1, 4-dioxane (melting point: 11.8 ° C), 3-methyl-2-oxazolidinone (melting point: 15 ° C), 1,2-dimethoxyethane (melting point: -58 ° C), tetrahydrofuran (melting point: -108.4 ° C) 2-methyltetrahydrofuran (melting point: -136 ° C), tetrahydrofuran derivative, sydnone compound, acetonitrile (melting point: -45 ° C), nitromethane (melting point: -29 ° C), alkoxyethane, toluene (melting point: -95 ° C), etc. Can be mentioned.

  These first organic solvents may be used alone or in combination of two or more. Among these first organic solvents, an organic solvent having a melting point lower than that of ethylene carbonate (34 ° C. to 37 ° C.), more preferably an organic solvent having a melting point of 10 ° C. or less, particularly preferably, Examples include dimethyl carbonate.

  In such a first mixed solvent, the blending ratio of ethylene carbonate is 50% by volume or more, preferably 60% by volume or more, for example, 90% by volume or less, preferably 80% by volume or less.

  If the blending ratio of ethylene carbonate in the first mixed solvent is equal to or higher than the above lower limit, the storage capacity of the hybrid capacitor 1 can be reliably improved by an activation step described later. An excessive increase in the viscosity of the mixed solvent can be suppressed.

  In the first mixed solvent, the blending ratio of the first organic solvent is, for example, 10% by volume or more, preferably 20% by volume or more, for example, 40% by volume or less, preferably 35% by volume or less. When the first organic solvent contains dimethyl carbonate, the mixing ratio of dimethyl carbonate in the first mixed solvent is, for example, 10% by volume or more, preferably 20% by volume or more, for example, 40% by volume or less, preferably Is 35% by volume or less.

  If the blending ratio of the first organic solvent (dimethyl carbonate) in the first mixed solvent is not less than the above lower limit and not more than the upper limit, the viscosity of the first mixed solvent can be easily adjusted.

  The viscosity of the first mixed solvent at 25 ° C. is preferably as low as possible, and is, for example, 0.4 mPa · s or more, for example, 3 mPa · s or less, preferably 2 mPa · s or less. The viscosity of the first mixed solvent can be measured with a known tuning fork type vibration viscometer.

  Next, if necessary, the obtained cell 10 is arranged, for example, so that the surface directions of the positive electrode 2 and the negative electrode 3 are along the vertical direction, and along the opposing direction of the positive electrode 2 and the negative electrode 3 using a known restraining device. The cell 10 is pressurized. Thereby, the cell 10 is restrained (fixed) with a predetermined restraining pressure.

  The pressurizing condition (constraint pressure) of the cell 10 is, for example, 100 kPa or more, preferably 200 kPa or more, for example, 700 kPa or less, preferably 500 kPa or less.

  Next, a voltage is applied to the positive electrode 2 and the negative electrode 3 in the presence of the first electrolytic solution 5 to charge and discharge the cell 10 and to perform an electrochemical activation process (activation process).

In the electrochemical activation treatment, specifically, for example, constant current charging is performed at 0.5 mA / cm ² or more and ² mA / cm ² or less until the cell voltage rises to a range of 4.7 V or more and 4.9 V or less, for example. To do.

After charging, the cell voltage is maintained at, for example, 4.7 V or more and 4.9 V or less until the current value drops to, for example, 0.1 mA / cm ² or more and 0.3 mA / cm ² or less. The holding time is usually less than 5 hours, preferably less than 4 hours, for example, 1 hour or more.

Thereafter, constant current discharge is performed at, for example, 0.5 mA / cm ² or more and ² mA / cm ² or less until the cell voltage drops to 2.0 V or more and 3.0 V or less, for example.

  This charge / discharge cycle is performed, for example, 1 to 10 times, preferably once.

Thereafter, the cell voltage, for example, until the rise 4.7V below the range of 4.3 V, for example, a constant current charge at 0.01 mA / cm ² or more 7 mA / cm ² or less.

After charging, without holding the cell voltage, cell voltage, for example, until drops below than 2.0 V 3.0 V, for example, a constant current discharge at 0.01 mA / cm ² or more 7 mA / cm ² or less.

  This charge / discharge cycle is repeated, for example, 10 times or more, preferably 30 times or more, for example, 1000 times or less, preferably 80 times or less.

  In addition, an activation process is specifically implemented on the temperature conditions of 10 degreeC or more, for example, Preferably, 15 degreeC or more, for example, 40 degrees C or less, Preferably, it is 35 degrees C or less.

  Next, if necessary, the cell 10 is charged and discharged, and a warm-up process (break-in operation) is performed (warm-up process).

In the warm-up process, specifically, the cell 10 after the electrochemical activation process is performed until the cell voltage rises to, for example, 4.6 V or more and 4.7 V or less, preferably 4.6 V, for example, The constant current charging is performed at 0.1 mA / cm ² or more, preferably 1 mA / cm ² or more, for example, 20 mA / cm ² or less, preferably 10 mA / cm ² or less.

After charging, the voltage application state is maintained, for example, for 5 hours or more, preferably 10 hours or more, for example, 20 hours or less, preferably 15 hours or less. In addition, while maintaining the voltage application state in this way, the current value is, for example, 0.1 mA / cm ² or more, preferably 0.3 mA / cm ² or more, for example, 10 mA / cm ² or less, preferably Lower to 7 mA / cm ² or less.

Thereafter, for example, until the cell voltage drops to, for example, 1.5 V or more, preferably 2 V or more, for example, 3.5 V or less, preferably 3 V or less, for example, 0.1 mA / cm ² or more, preferably The constant current discharge is performed at 1 mA / cm ² or more, for example, 20 mA / cm ² or less, preferably 10 mA / cm ² or less.

  This charge / discharge cycle is performed, for example, 1 to 10 times, preferably once.

  By such warm-up processing, the amount of gas generated in the hybrid capacitor 1 can be reduced, and damage to the hybrid capacitor 1 and performance degradation can be suppressed.

  Such a warm-up process is distinguished from the above-described electrochemical activation process by the holding time in the voltage application state.

  That is, in the above-described electrochemical activation treatment, after the cell 10 is charged with a constant current, the holding time in which a voltage is applied is usually 1 hour or more and less than 5 hours.

  On the other hand, in the warm-up process, after the cell 10 is charged with a constant current, the holding time in which the cell 10 is held in a voltage application state is, for example, 5 hours or more and 20 hours or less as described above.

  Next, if necessary, the cell 10 after the warm-up process is further charged and discharged and subjected to a pre-cycle process (a pre-cycle process). Thereby, the gas is purged from the cell 10.

Specifically, in the pre-cycle process, the cell voltage after the warm-up process has a cell voltage of, for example, 3.5 V or more, preferably 4 V or more, for example 4.6 V or less, preferably 4.4 V. Until it rises below, constant current charging is performed at, for example, 1 mA / cm ² or more, preferably 3 mA / cm ² or more, for example, 10 mA / cm ² or less, preferably 7 mA / cm ² or less.

After charging, for example, 1 mA until the cell voltage drops to, for example, 1.5 V or more, preferably 2.1 V or more, for example, 3 V or less, preferably 2.5 V or less without holding the cell voltage. / Cm ² or more, preferably 3 mA / cm ² or more, for example, 10 mA / cm ² or less, preferably 7 mA / cm ² or less.

  This charge / discharge cycle is repeated, for example, 500 times or more, preferably 600 times or more, for example, 1000 times or less, preferably 800 times or less.

  By such pre-cycle processing, the amount of gas generated in the hybrid capacitor 1 can be surely reduced, and damage to the hybrid capacitor 1 and performance degradation can be reliably suppressed.

Furthermore, as a pre-cycling, preferably at 4.4V less voltage range of 2.1V, the charge and discharge by 1 mA / cm ² or more 10 mA / cm ² or less current is repeated below 1000 times more than 500 times.

  After the warm-up process, as a pre-cycle process, the internal resistance of the hybrid capacitor 1 can be reduced by repeating charging and discharging with a predetermined current for a predetermined number of times within a predetermined voltage range.

  Next, the first electrolytic solution 5 in the cell tank 6 is replaced with a second electrolytic solution 7 containing ethylene carbonate relatively less than the first electrolytic solution 5 (replacement step). That is, the replacement process is performed at least after the activation process and, if necessary, after the warm-up process or the pre-cycle process.

  More specifically, the first electrolytic solution 5 is taken out from the cell tank 6, and the second electrolytic solution 7 is injected and stored so that the positive electrode 2, the negative electrode 3, and the separator 4 are immersed in the cell tank 6.

  The second electrolytic solution 7 includes a lithium salt as an electrolyte and a second mixed solvent as an example of a second solvent that dissolves the lithium salt.

Examples of the lithium salt include the above-described lithium salt, preferably the same lithium salt as the lithium salt included in the first electrolytic solution 5, and more preferably LiBF ₄ . These lithium salts may be used alone or in combination of two or more.

  The concentration of the lithium salt in the second electrolyte solution 7 is, for example, 0.5 mol / L or more, for example, 5 mol / L or less, preferably 2 mol / L or less, and more preferably, the lithium salt in the first electrolyte solution 5. Is the same concentration.

  The second mixed solvent contains ethylene carbonate, and specifically, is a mixed solvent of ethylene carbonate and the second organic solvent.

  Examples of the second organic solvent include organic solvents having a melting point lower than that of ethylene carbonate (34 ° C. to 37 ° C.) among the first organic solvents described above. Specifically, propylene carbonate (melting point) : -55 ° C), propylene carbonate derivative, butylene carbonate (melting point: -45 ° C), dimethyl carbonate (melting point: 2 ° C), diethyl carbonate (melting point: -43 ° C), ethyl methyl carbonate (melting point: -14.5 ° C) ), Γ-butyrolactone (melting point: −43.5 ° C.), 1,3-dioxolane (melting point: −95 ° C.), dimethyl sulfoxide (DMSO, melting point: 19 ° C.), sulfolane (melting point: 27.5 ° C.), formamide (Melting point: 2-3 ° C.), dimethylformamide (DMF, melting point: −61 ° C.), dimethylacetamide (DMA, melting point: 20 ° C.), phosphoric acid triester, 1,3-propane sultone (melting point: 31 ° C.), 4,5-dihydropyran derivative, nitrobenzene (melting point: 5.9 ° C.), 1,3-dioxane (melting point: −45) ° C), 1,4-dioxane (melting point: 11.8 ° C), 3-methyl-2-oxazolidinone (melting point: 15 ° C), 1,2-dimethoxyethane (melting point: -58 ° C), tetrahydrofuran (melting point:- 108.4 ° C.), 2-methyltetrahydrofuran (melting point: −136 ° C.), tetrahydrofuran derivative, sydnone compound, acetonitrile (melting point: −45 ° C.), nitromethane (melting point: −29 ° C.), alkoxyethane, toluene (melting point: − 95 ° C.).

  These second organic solvents may be used alone or in combination of two or more. Among these second organic solvents, preferably, the same organic solvent as the first organic solvent, more preferably an organic solvent having a melting point of 5 ° C. or less, particularly preferably dimethyl carbonate is used.

  In such a second mixed solvent, the blending ratio of ethylene carbonate is, for example, 10% by volume or more, preferably 20% by volume or more and less than 50% by volume, preferably 45% by volume or less.

  If the blending ratio of ethylene carbonate in the second mixed solvent is equal to or higher than the above lower limit, the excellent storage capacity of the hybrid capacitor 1 can be reliably ensured, and if it is equal to or lower than the upper limit, the second electrolytic solution 7 is low in temperature. Solidification in the environment can be reliably suppressed.

  Moreover, the blending ratio of ethylene carbonate of the second mixed solvent is (the blending ratio of EC of the second mixed solvent / the blending ratio of EC of the first mixed solvent) with respect to the blending ratio of ethylene carbonate of the first mixed solvent, for example 20% or more, preferably 30% or more, for example 70% or less, preferably 60% or less.

  In the second mixed solvent, the blending ratio of the second organic solvent is, for example, 40% by volume or more, preferably 50% by volume or more, for example, 90% by volume or less, preferably 80% by volume or less. Further, when the organic solvent contains dimethyl carbonate, the mixing ratio of dimethyl carbonate in the second mixed solvent is, for example, 40% by volume or more, preferably 50% by volume or more, for example, 90% by volume or less, preferably 80% by volume or less.

  If the blending ratio of the second organic solvent (dimethyl carbonate) in the second mixed solvent is not less than the above lower limit and not more than the upper limit, the viscosity of the second mixed solvent can be easily adjusted.

  The viscosity of the second mixed solvent at 25 ° C. is preferably as low as possible, and is, for example, 0.4 mPa · s or more, for example, 3 mPa · s or less, preferably 2 mPa · s or less. The viscosity of the second mixed solvent can be measured with a known tuning fork type vibration viscometer.

  Thus, the hybrid capacitor 1 including the positive electrode 2, the negative electrode 3, the separator 4, the cell tank 6 and the second electrolytic solution 7 is manufactured.

    According to such a manufacturing method of the hybrid capacitor 1, in the activation step, the positive electrode 2 and the negative electrode 3 are subjected to the electrochemical activation treatment in the presence of the first electrolytic solution 5 in which the blending ratio of ethylene carbonate is relatively high. Excellent storage capacity can be ensured.

  And since the 1st electrolyte solution 5 is replaced by the 2nd electrolyte solution 7 with a comparatively low blending ratio of ethylene carbonate after an activation process, it can suppress that electrolyte solution solidifies in a low-temperature environment.

  Therefore, it is possible to obtain the hybrid capacitor 1 having excellent storage capacity and low temperature characteristics.

Further, each of the first electrolyte 5 and the second electrolytic solution 7, contains LiBF ₄ as a lithium salt.

Therefore, it is possible to suppress decomposition of LiBF _4, can suppress the generation of gas caused thereby. As a result, damage to the hybrid capacitor 1 and performance degradation can be suppressed.

Moreover, even if each lithium salt of the 1st electrolyte solution 5 and the 2nd electrolyte solution is LiBF ₄ , in the presence of the 1st electrolyte solution 5 with a relatively high blending ratio of ethylene carbonate in the activation step, Since the positive electrode 2 and the negative electrode 3 are subjected to an electrochemical activation treatment, an excellent storage capacity can be ensured.

  Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example. “Part” and “%” are based on mass unless otherwise specified. Specific numerical values such as blending ratio (content ratio), physical property values, and parameters used in the following description are described in the above-mentioned “Mode for Carrying Out the Invention”, and the corresponding blending ratio (content ratio) ), Physical property values, parameters, etc. The upper limit value (numerical value defined as “less than” or “less than”) or lower limit value (number defined as “greater than” or “exceeded”) may be substituted. it can.

Example 1
<Preparation process>
1. Production of Positive Electrode A mesophase pitch (AR resin manufactured by Mitsubishi Gas Chemical Company) 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. Washing was performed 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 (binder, PVdF manufactured by Kureha Co., Ltd.) with a solid content of 75: 8 .3: The mass ratio of 16.7 was charged into an NMP (N-methyl-2-pyrrolidone) solvent and stirred at room temperature (25 ° C. to 30 ° C.) for 12 hours, whereby a slurry of the mixture (solid content: 30 Mass%).

  Next, the obtained slurry was applied to the surface of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, dried at 80 ° C. for 12 hours, and then subjected to pressure stretching with a roll press to remove the aluminum foil. An electrode sheet having a work layer (positive electrode) thickness of 72 μm was obtained.

Next, the electrode sheet was cut into a rectangular shape having a length in the longitudinal direction of 60 mm and a length (direction in the width direction) orthogonal to the longitudinal direction of 41 mm, thereby producing a positive electrode.
2. Production of negative electrode NMP (N-methyl-2-pyrrolidone) with artificial graphite, soft carbon, and polymer binder (binder, PVdF manufactured by Kureha) at a solid content of 67.5: 22.5: 10. ) It was put in a solvent and 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 copper foil (negative electrode current collector) having a thickness of 10 μm, dried at 80 ° C. for 12 hours, and then subjected to pressure stretching with a roll press to remove the copper foil. An electrode sheet having a work layer (negative electrode) thickness of 14 μm was obtained.

Subsequently, the length in the longitudinal direction was 60 mm, and the length (direction in the width direction) perpendicular to the longitudinal direction was cut into a rectangular shape having a length of 45 mm, thereby producing a negative electrode.
3. Production of Separator A separator was produced by cutting a ceramic filter (GB-100R, manufactured by ADVANTEC) into a thickness of 50 mm × 54 mm.
4). Preparation of 1st electrolyte solution Ethylene carbonate and dimethyl carbonate were mixed in the ratio from which ethylene carbonate will be 66.7 volume% with respect to those total amounts, and the 1st mixed solvent was prepared. Then, the LiBF the first mixed solvent obtained ₄ (lithium salt), its concentration by dissolving as a 1.5 mol / L, to prepare a first electrolytic solution.
5. Preparation of Second Electrolytic Solution Ethylene carbonate and dimethyl carbonate were mixed at a ratio of 40.0% by volume of ethylene carbonate with respect to their total amount to prepare a second mixed solvent. Next, a second electrolytic solution was prepared by dissolving LiBF ₄ (lithium salt) in the obtained second mixed solvent so as to have a concentration of 1.5 mol / L.
6). Production of Cell One positive electrode, one negative electrode, and one separator were laminated.

  Specifically, the positive electrode was laminated on one side of the separator and the negative electrode on the other side so that the positive electrode and the negative electrode were opposed to each other with a gap therebetween.

  Next, the positive electrode current collector of the positive electrode and an aluminum plate (positive electrode current collection tab) on which a sealant was deposited were ultrasonically bonded. Similarly, the negative electrode current collector of the negative electrode and the nickel plate (negative electrode current collection tab) on which the sealant was welded were ultrasonically bonded. The electrode body was obtained by the above operation.

  Next, the electrode body was wrapped with an aluminum laminate film, and the three sides were joined by thermal welding of the aluminum laminate film to form a cell tank.

  Next, the electrode body wrapped with the aluminum laminate film was carried into a dryer and vacuum-dried at 120 ° C. for 12 hours. After the inside of the dryer was purged with nitrogen, it was carried into a glove box in a dry Ar atmosphere so as not to be exposed to the air.

  Next, the pressure was reduced in the chamber, and the first electrolytic solution was injected into the cell tank so that the positive electrode, the negative electrode, and the separator were immersed.

  Thereafter, the aluminum laminate film was thermally welded and sealed, and then returned to normal pressure. As a result, a hybrid capacitor cell was obtained.

Thereafter, the obtained cell was placed in a restraining device so that the longitudinal direction thereof was along the vertical direction, and the cell was restrained (pressurized) with a restraining pressure of 200 kPa along the opposing direction of the positive electrode unit and the negative electrode unit.
<Activation process>
The battery was charged at a constant current of 1 mA / cm ² until the cell voltage increased to 4.8V. After charging, the cell voltage is maintained at 4.8 V (2 hours) until the current value drops to 0.3 mA / cm ² (2 hours), and then constant current discharge at 1 mA / cm ² until the cell voltage drops to 2.3 V. did.

Next, constant current charging was performed at 5 mA / cm ² until the cell voltage increased to 4.6V. After charging, without being held at that voltage, constant current was discharged at 5 mA / cm ² until the cell voltage dropped to 2.3V. This charging / discharging was repeated 50 times in total.

Thereafter, constant current charging was performed at 1 mA / cm ² until the cell voltage increased to 4.4V. After charging, the battery was discharged at a constant current of 1 mA / cm ² until the cell voltage dropped to 2.3 V without being held at that voltage. This charging / discharging was repeated 50 times.
<Warm-up process>
The cell of the hybrid capacitor subjected to the electrochemical activation treatment as described above was charged / discharged under the following conditions and warmed up.

Specifically, first, constant current charging was performed at 1 mA / cm ² until the cell voltage increased to 4.6V. After charging, the cell voltage was maintained at 4.6V for 5 hours. During this time, the current value dropped to 0.3 mA / cm ² .

Thereafter, constant current discharge was performed at 1 mA / cm ² until the cell voltage dropped to 2.3V.
<Precycle process>
Next, the cell after the warm-up treatment was first charged at a constant current of 5 mA / cm ² until the cell voltage increased to 4.4V. After charging, constant current discharge was performed at 5 mA / cm ² until the cell voltage dropped to 2.1V. This charging / discharging was repeated 600 times in total.
<Replacement process>
Next, the cell after the pre-cycle treatment was carried into a glove box in an Ar atmosphere, a part of the aluminum laminate film was cut, and the cell was opened. And after taking out 1st electrolyte solution from the cell tank of the cell, it pressure-reduced in the chamber and inject | poured 2nd electrolyte solution in the cell tank so that a positive electrode, a negative electrode, and a separator might be immersed.

  Thereafter, the aluminum laminate film was thermally welded and sealed again, and then returned to normal pressure. Thereby, a hybrid capacitor was obtained.

  In Example 1, the preparation process, the activation process, the warm-up process, the precycle process, and the replacement process were performed under a temperature condition of 25 ° C.

Comparative Example 1
A hybrid capacitor was obtained in the same manner as in Example 1 except that the replacement process was not performed.
<Performance evaluation>
(1) Calculation of storage capacity The storage capacity of each of the hybrid capacitors obtained in Example 1 and Comparative Example 1 was calculated from the following formula (1).

Formula (1):
Storage capacity [F / cc] = C / EV
C: Capacitance [F]
EV: electrode volume [cc]
The storage capacity of the hybrid capacitor of Example 1 was 69.4 F / cc.

The storage capacity of the hybrid capacitor of Comparative Example 1 was 70 F / cc.
(2) Low-temperature characteristic evaluation Each of the hybrid capacitors obtained in Example 1 and Comparative Example 1 was placed in a thermostatic bath, cooled at each temperature shown in Table 1 for 8 hours, and then subjected to a charge / discharge test.

Specifically, each hybrid capacitor after cooling was charged with a constant current at 1 mA / cm ² until the cell voltage increased to 4.4V. After charging, constant current was discharged at 1 mA / cm ² until the cell voltage dropped to 2.3V. The volume energy density in this charge / discharge was determined. The results are shown in Table 1 and FIG.

DESCRIPTION OF SYMBOLS 1 Hybrid capacitor 2 Positive electrode 3 Negative electrode 5 1st electrolyte solution 6 Cell tank 7 2nd electrolyte solution 10 cell

Claims (2)

A positive electrode, a negative electrode disposed opposite to the positive electrode, a cell tank containing the positive electrode and the negative electrode, and a reservoir containing ethylene carbonate stored in the cell tank so that the positive electrode and the negative electrode are immersed therein A preparation step of preparing a cell comprising one electrolytic solution;
An activation step of applying a voltage to the positive electrode and the negative electrode in the presence of the first electrolytic solution to perform an electrochemical activation treatment;
After the activation step, including replacing the first electrolyte solution with a second electrolyte solution containing ethylene carbonate relatively less than the first electrolyte solution,
The first electrolyte solution includes a lithium salt and a first solvent containing ethylene carbonate,
The second electrolyte solution includes a lithium salt and a second solvent containing ethylene carbonate,
In the first solvent, the blending ratio of the ethylene carbonate is 50% by volume or more,
In the second solvent, the blending ratio of the ethylene carbonate is less than 50% by volume. 2. The method of manufacturing an electrochemical capacitor according to claim 1, wherein the lithium salt of each of the first electrolyte solution and the second electrolyte solution is LiBF ₄ .