JP5623191B2 - Method for manufacturing electrochemical capacitor - Google Patents

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, lithium secondary batteries that can be charged and discharged by an oxidation-reduction reaction of lithium between electrodes are known as power storage devices mounted on hybrid vehicles and fuel cell vehicles.

A lithium secondary battery usually includes a positive electrode current collector made of aluminum having excellent electrical conductivity. However, when a high voltage of 4 V or higher is reached, aluminum in the positive electrode current collector may react with the electrolytic solution, resulting in increased self-discharge or poor storage characteristics. Thus, it has been proposed to use LiBF ₄ as the electrolyte of the electrolytic solution to suppress the reaction between aluminum and the electrolytic solution (see, for example, Patent Document 1).

  On the other hand, in recent years, a hybrid capacitor has been proposed as an electricity storage device, in addition to electricity storage by an electric double layer, in addition to electricity storage by a redox reaction of lithium.

  Such a hybrid capacitor includes a positive electrode containing a polarizable carbon material and a negative electrode containing a material capable of reversibly occluding and releasing lithium ions. Also in the hybrid capacitor, the positive electrode current collector is formed of aluminum.

Japanese Patent Laid-Open No. 7-142088

In such a hybrid capacitor, if LiBF ₄ is used as the electrolyte of the electrolytic solution in order to suppress the reaction between the positive electrode current collector aluminum and the electrolytic solution, there is a problem that the charge / discharge cycle durability is lowered. .

  Then, this invention is providing the manufacturing method of the electrochemical capacitor which can prevent the corrosion of the positive electrode electrical power collector which consists of aluminum effectively.

In order to achieve the above object, a method for producing an electrochemical capacitor of the present invention includes a positive electrode unit containing a polarizable carbon material, and a positive electrode unit comprising a positive electrode current collector that is in contact with the positive electrode and contains aluminum, Accommodates a negative electrode containing a negative electrode containing a material capable of reversibly occluding and releasing lithium ions facing the positive electrode, a negative electrode current collector in contact with the negative electrode, and the positive electrode unit and the negative electrode unit A first electrolytic solution for injecting a first electrolytic solution containing lithium ions into the cell tank so that the positive electrode unit and the negative electrode unit are immersed. An electrochemical activation treatment step in which a voltage is applied to the positive electrode and the negative electrode to perform an electrochemical activation treatment after the injection step and the first electrolyte solution injection step. After the electrochemical activation treatment step, further, in the cell bath, and further comprising a second electrolyte injection step of injecting a second electrolyte containing LiBF _4.

In the method for producing an electrochemical capacitor of the present invention, it is preferable that the first electrolytic solution contains LiPF ₆ .

In the method for producing an electrochemical capacitor of the present invention, it is preferable that the concentration of LiBF ₄ with respect to the total amount of the first electrolytic solution and the second electrolytic solution is 1.0 mol / L or less.

In the method for producing an electrochemical capacitor according to the present invention, since an electrolytic solution containing LiBF ₄ is injected after the electrochemical activation treatment step, decomposition of LiBF ₄ due to the electrochemical activation treatment is suppressed. Therefore, corrosion of aluminum can be effectively prevented and charge / discharge cycle durability can be improved.

  Therefore, according to the method for producing an electrochemical capacitor of the present invention, an electrochemical capacitor having excellent charge / discharge cycle durability can be produced.

It is a schematic block diagram of the hybrid capacitor which shows one Embodiment of the electrochemical capacitor manufactured by the manufacturing method of the electrochemical capacitor of this invention. It is a figure which shows the change of the energy density of the hybrid capacitor in the charging / discharging cycle of an Example and a comparative example. It is a figure which shows the change of the energy density maintenance factor of the hybrid capacitor 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 manufactured by the method for manufacturing an electrochemical capacitor of the present invention.

  In the manufacturing method of the hybrid capacitor 1 as one embodiment of the electrochemical capacitor of the present invention, the hybrid capacitor 1 is first assembled.

  In assembling the hybrid capacitor 1, first, the positive electrode unit 8 is prepared.

  The positive electrode unit 8 includes a flat plate-shaped positive electrode current collector 3 and a positive electrode 2 laminated on the surface of the positive electrode current collector 3.

  The positive electrode current collector 3 is not particularly limited as long as it contains aluminum, but an aluminum foil may be mentioned in consideration of electric conductivity.

  The thickness of the positive electrode current collector 3 varies depending on the scale of the hybrid capacitor 1, but is, for example, 10 to 50 μm, preferably 10 to 30 μm on a lab scale.

  The positive electrode 2 is formed by, for example, applying a mixture obtained by blending a positive electrode material, a polymer binder, and, if necessary, a conductive agent, for example, to the positive electrode current collector 3, and then drying as necessary. Is formed.

  The positive electrode material is made of polarizable carbon, and the polarizable carbon is obtained, for example, by activating the carbon material.

  Examples of the carbon material include 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 carbon is not particularly limited, but for example, pitches such as petroleum pitch, coal pitch, and mesophase pitch, such as petroleum needle coke, coal needle coke, anthracene, polyvinyl chloride, poly chloride. Thermally decomposed products such as graphitizable cokes such as acrylonitrile.

  These carbon materials may be used alone or in combination.

  Among these carbon materials, a thermal decomposition product of mesophase pitch is preferable.

  Although it does not restrict | limit especially as activation processing, For example, potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), cesium hydroxide (CsOH), a rubidium hydroxide (RbOH) activator, etc. And alkali activation treatment used as

  Among these activation treatments, an alkali activation treatment (KOH activation treatment) using potassium hydroxide (KOH) as an activator is 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, Preferably, it is 1-4 mass parts.

In the hybrid capacitor 1 using the positive electrode material obtained by the activation treatment for the positive electrode 2, for example, in a charge / discharge cycle in which the potential of the positive electrode 2 is 4.2 V vs Li / Li ⁺ or more, a relatively large irreversible capacity is applied to the positive electrode 2. Can be expressed. 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 average particle diameter of the positive electrode material is, for example, 0.5 μm to 20 μm, preferably 3 μm to 10 μm.

  The average particle diameter can be measured by a laser diffraction method.

  The mixing ratio of the positive electrode material is, for example, 70 to 99% by mass, preferably 75 to 90% by mass, based on the total amount of the mixture.

  The polymer binder is not particularly limited. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluoroolefin copolymer crosslinked polymer, fluoroolefin vinyl ether copolymer crosslinked polymer, carboxymethylcellulose, polyvinylpyrrolidone, Examples thereof include polyvinyl alcohol and polyacrylic acid.

  These polymer binders may be used alone or in combination.

  Of these polymer binders, PVdF is preferable.

  The blending ratio of the polymer binder is, for example, 1 to 20% by mass, preferably 10 to 20% by mass, based on the total amount of the mixture.

  The conductive agent is not particularly limited, and examples thereof 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 blending ratio of the conductive agent is, for example, 0 to 20% by mass, preferably 5 to 10% by mass 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 unit 8, for example, the above-described positive electrode material, polymer binder, and, if necessary, a mixture containing a conductive agent or the like is stirred in a solvent to obtain a slurry (solid content: 10 to 10). 60% by weight). Next, the slurry is applied to the surface of the positive electrode current collector 3, and then dried to form the positive electrode 2. Then, for example, the electrode sheet provided with the positive electrode 2 is subjected to pressure stretching using a roll press. obtain. Next, after the electrode sheet is cut or punched into a predetermined shape, the electrode sheet is subjected to slitting or the like as necessary.

  The solvent is not particularly limited, but for example, aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF), for example, protic properties such as ethanol, methanol, propanol, butanol and water Examples include polar solvents such as toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, and dimethyl phthalate.

  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.

  The thickness of the positive electrode unit 8 obtained by the above method varies 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 current collector 3. (That is, the thickness of the positive electrode 2) 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 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 width direction) perpendicular to the longitudinal direction is 100 mm, for example, 10 to 200 mm, preferably 10 to 100 mm.

  Moreover, although the magnitude | size of the positive electrode collector 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, preferably 10 to 100 mm, and the length (direction in the width direction) orthogonal to the longitudinal direction is, for example, 10 to 200 mm, preferably 10 to 100 mm.

  For example, in the case of a rectangular shape, the length of the positive electrode current collector 3 in the longitudinal direction is preferably longer than the length of the positive electrode 2 in the longitudinal direction, and is orthogonal to the longitudinal direction of the positive electrode current collector 3 and the positive electrode 2. It is preferable that the direction (width direction) length is the same length.

  Further, in assembling the hybrid capacitor 1, a negative electrode unit 9 is separately prepared.

  The negative electrode unit 9 includes a plate-shaped negative electrode current collector 5 and a negative electrode 4 laminated on the surface of the negative electrode current collector 5.

  Although it does not restrict | limit especially as the negative electrode electrical power collector 5, For example, aluminum foil, copper foil, stainless steel foil, nickel foil, etc. are mentioned.

  Among these negative electrode current collectors 5, a copper foil is preferable.

  The thickness of the negative electrode current collector 5 varies depending on the scale of the hybrid capacitor 1, but is, for example, 10 to 50 μm, preferably 10 to 30 μm on a lab scale.

  The negative electrode 4 is formed, for example, by applying a mixture obtained by blending a negative electrode material and a polymer binder to the negative electrode current collector 5 and drying it as necessary.

  The negative electrode material is made of a material capable of reversibly occluding and releasing lithium ions, and is not particularly limited, and examples thereof include the above-described soft carbon, hard carbon, and graphite.

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 carbon is not particularly limited, and examples thereof include phenol resin, melamine resin, urea resin, furan resin, epoxy resin, alkyd resin, unsaturated polyester resin, diallyl phthalate resin, furfural resin, resorcinol resin, and silicone resin. Thermosetting resins such as xylene resin and urethane resin, for example, carbon black such as thermal black, furnace black, lamp black, channel black, acetylene black, and graphitizable coke such as fluid coke and gilsonite coke. Are different non-graphitizable cokes, for example, plant-based materials such as coconut palm and wood flour, for example, pyrolysates such as glassy carbon.

  The graphite is not particularly limited. For example, natural graphite, artificial graphite, graphitized mesophase carbon microspheres, graphitized mesophase carbon fiber, graphite whisker, graphitized carbon fiber, pitch, coke, etc. Examples thereof include graphite-based carbon materials such as pyrolysates. 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 mixing ratio of the negative electrode material is, for example, 80 to 99% by mass, preferably 85 to 95% by mass, based on the total amount of the mixture.

  Although it does not restrict | limit especially as a polymer binder, For example, the above-mentioned polymer binder is mentioned.

  These polymer binders may be used alone or in combination.

  Of these polymer binders, PVdF is preferable.

  The blending ratio of the polymer binder is blended so that, for example, the mass ratio of the solid content is 1 to 20 mass%, preferably 5 to 10 mass% with respect to the total amount of the mixture.

  Moreover, in manufacture of the negative electrode unit 9, a electrically conductive agent can also be mix | blended as needed.

  Although it does not restrict | limit especially as a electrically conductive agent, For example, an above-described electrically conductive agent is mentioned.

  These conductive agents may be used alone or in combination.

  The blending ratio of the conductive agent is blended so that, for example, the mass ratio of the solid content is 0 to 20 mass%, preferably 1 to 10 mass% with respect to the total amount of the mixture.

  And in order to form the negative electrode unit 9, for example, the mixture which mix | blended the above-mentioned negative electrode material and a polymer binder is stirred in a solvent, and a slurry (solid content: 10-60 mass%) is obtained. Next, the slurry is applied to the surface of the negative electrode current collector 5, and then dried to form the negative electrode 4. Then, for example, the electrode sheet including the negative electrode 4 is formed by pressure stretching using a roll press. obtain. Next, after the electrode sheet is cut or punched into a predetermined shape, the electrode sheet is subjected to slitting or the like as necessary.

  Although it does not restrict | limit especially as a solvent, For example, the above-mentioned solvent is 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.

  The thickness of the negative electrode unit 9 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 current collector 5 (that is, The thickness of the negative electrode 4) is 5 to 60 μm.

  Moreover, although the magnitude | size of the negative electrode 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, 10 to 200 mm, preferably 10 to 10 mm. The length (direction in the width direction) perpendicular to the longitudinal direction is 100 mm, for example, 10 to 200 mm, preferably 10 to 100 mm.

  Moreover, although the magnitude | size of the negative electrode collector 5 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 100 mm, and the length (direction in the width direction) orthogonal to the longitudinal direction is, for example, 10 to 200 mm, preferably 10 to 100 mm.

  For example, in the case of a rectangular shape, the length of the negative electrode current collector 5 in the longitudinal direction is preferably longer than the length of the negative electrode 2 in the longitudinal direction, and is orthogonal to the longitudinal directions of the negative electrode current collector 5 and the negative electrode 4. It is preferable that the direction (width direction) length is the same length.

  Next, in the assembly of the hybrid capacitor 1, the positive electrode unit 8, the negative electrode unit 9, and the separator 6 are stacked.

  Specifically, the positive electrode unit 8 is laminated on one side of the separator 6 and the negative electrode unit 9 is laminated on the other side so that the positive electrode 2 and the negative electrode 4 are opposed to each other with a gap therebetween.

  Although it does not restrict | limit especially as the separator 6, For example, the separator which consists of inorganic fibers, such as glass fiber, ceramic fiber, a whisker, For example, natural fibers, such as a cellulose, For example, organic fibers, such as polyolefin and polyester, is mentioned.

  Among these separators, a separator made of cellulose is preferable.

  Specifically, the thickness of the separator 6 varies depending on the scale of the hybrid capacitor 1, but is 15 to 100 μm, for example, in the laboratory scale.

  In addition, although mentioned later in detail, when the capture agent is contained in the hybrid capacitor 1, when the capture agent is provided between the two separators 6 (the separator 6a and the separator 6b), the thickness of the separator 6 is The sum of the two separators 6 (separator 6a and separator 6b) and the scavenger is used.

  Moreover, although the magnitude | size of the separator 6 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. The length is, for example, 15 to 220 mm.

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 higher, the electrolyte stored in the cell tank 10 is caused by the irreversible capacity of the positive electrode 2. In some cases, a negative electrode activity inhibitor derived from an anion contained therein (for example, PF ₆ ⁻ contained in LiPF ₆ or the like) may 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-mentioned predetermined voltage (that is, 4.2 V vs Li / Li ⁺ or more) is applied to the positive electrode 2 and the negative electrode 4, in the electrolytic solution, for example, from the moisture and organic matter contained in the positive electrode 2 and the electrolytic solution, As shown in 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 (e.g., 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 4 and reduce the energy density of the hybrid capacitor 1.

  Therefore, in this hybrid capacitor 1, preferably, the negative electrode activity inhibitor derived from an anion contained in the electrolytic solution is captured between the positive electrode 2 and the negative electrode 4, or at least one of the positive electrode 2 and the negative electrode 4. A scavenger 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 scavengers may be used alone or in combination.

  Of these scavengers, lithium carbonate is preferable.

  More specifically, for example, when the capture agent is contained (arranged) between the positive electrode 2 and the negative electrode 4, the capture agent is preferably formed as the capture member 7.

  The capturing member 7 is, for example, a sheet obtained by press-drawing a mixture of a capturing agent for capturing a negative electrode activity inhibitor and a polymer binder.

  Although it does not restrict | limit especially as a polymer binder, For example, the above-mentioned polymer binder is mentioned, Preferably, PTFE is mentioned.

  And in order to form the capture member 7, for example, first, the capture agent and the polymer binder, for example, the blending ratio of the capture agent: polymer binder is 20:80 to 98: 2, as a mass 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.

  Then, after the scavenger-containing sheet is cut or punched into a predetermined shape, it is dried if necessary. Thereby, the capture member 7 is obtained.

  Although the thickness of the capture member 7 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 10 to 100 μm, preferably 20 to 50 μm.

  Moreover, although the magnitude | size of the capture member 7 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, preferably 10 The length (direction in the width direction) orthogonal to the longitudinal direction is, for example, 10 to 200 mm, preferably 10 to 100 mm.

  In this hybrid capacitor 1, for example, as shown in FIG. 1, as the separator 6, a separator 6a disposed on the positive electrode 2 side and a separator 6b disposed on the negative electrode 4 side are provided, and these separators 6a and 6b 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 6 a and the separator 6 b as a capturing agent without forming the capturing member 7.

  In order to arrange the carbonate between the separator 6a and the separator 6b, for example, powdery carbonate is added to one surface of the separator 6a or the separator 6b, and the surface and the surface of the other separator 6a (6b) 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 4.

  In order to coat the carbonate on the surface of the positive electrode 2 and / or the negative electrode 4, for example, a mixture containing a carbonate and a polymer binder is stirred and mixed in a solvent, and then applied onto the positive electrode 2 and / or the negative electrode 4. After that, it is dried.

  Although it does not restrict | limit especially as a polymer binder, For example, the above-mentioned polymer binder etc. are mentioned.

  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 a lithium foil, a well-known lithium foil can be used, for example, it forms in a rectangular shape.

  Further, the lithium foil is preferably formed so that the surface area thereof is substantially the same as the surface areas of the positive electrode 2 and the negative electrode 4 or a wider area. 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 can pass between the separator 6a and the separator 6b, 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 10 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.

  Further, when the scavenger is contained in the positive electrode 2 and / or the negative electrode 4, the scavenger is used as a material component of the positive electrode 2 and / or the negative electrode 4, 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 4. Thereby, the scavenger is contained in the positive electrode 2 and / or the negative electrode 4.

  Next, in the assembly of the hybrid capacitor 1, the positive electrode current collector 3 of the positive electrode unit 8 and the positive electrode current collector tab are joined, and the negative electrode current collector 5 of the negative electrode unit 9 and the negative electrode current collector tab are joined. .

  The positive electrode current collecting tab is not particularly limited as long as it is a metal plate on which a sealant is deposited, and examples thereof include an aluminum plate, a copper plate, a stainless steel plate, and a nickel plate.

  Among these positive electrode current collecting tabs, an aluminum plate on which a sealant is deposited is preferable.

  The negative electrode current collecting tab is not particularly limited as long as it is a metal plate on which a sealant is deposited, and examples thereof include an aluminum plate, a copper plate, a stainless steel plate, and a nickel plate.

  Among these positive electrode current collecting tabs, a nickel plate on which a sealant is deposited is preferable.

  The joining means of the positive electrode current collecting tab and the negative electrode current collecting tab is not particularly limited, and examples thereof include spot welding, ultrasonic bonding, and laser welding.

  Among these joining means, ultrasonic joining is preferable.

  Then, the stacked positive electrode unit 8, negative electrode unit 9 and separator 6 are arranged in the cell tank 10.

  The cell tank 10 is not particularly limited, but may be, for example, the container shown in FIG. 1 or a bag formed of a metal laminate film as in the examples described later.

  Next, in the method of manufacturing the hybrid capacitor 1, after the assembled hybrid capacitor 1 is dried, the first containing lithium ions in the cell tank 10 is immersed so that the positive electrode unit 8, the negative electrode unit 9, and the separator 6 are immersed therein. An electrolytic solution is injected (first electrolytic solution injection step).

  The 1st electrolyte solution contains the organic solvent containing lithium salt, for example, is prepared by dissolving lithium salt in an organic solvent.

The lithium salt is not particularly limited, has an anionic component containing a 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 , 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, but are not limited to, 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, phosphate triester, maleic anhydride, succinic anhydride, phthalic anhydride, 1,3-propane sultone, 4,5 -Dihydropyran derivatives, nitrobenzene, 1,3-dioxane, 1,4-dioxane, 3-methyl-2-oxazolidinone, 1,2-dimethoxyethane, tetrahydro Rofuran, 2-methyltetrahydrofuran, 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 ethyl methyl carbonate are preferable, and a mixed solvent of ethylene carbonate and ethyl methyl carbonate is more preferable.

  The concentration of the lithium salt in the first electrolytic solution is, for example, 1.0 to 5.0 mol / L, preferably 1 to 3 mol / L.

  Moreover, the density | concentration of the lithium salt in the whole quantity of a 1st electrolyte solution and the 2nd electrolyte solution mentioned later is 0.5-3.0 mol / L, for example, Preferably, it is 1-2 mol / L.

  Next, in the method for manufacturing the hybrid capacitor 1, voltage is applied to the positive electrode 2 and the negative electrode 4, and the positive electrode 2 and the negative electrode 4 are subjected to electrochemical activation treatment (electrochemical activation treatment step).

Specifically, constant current charging is performed at, for example, 0.5 to ² mA / cm ² until the cell voltage rises to, for example, 4.7 to 4.9 V. After charging, the current value, for example, the cell voltage to drop to 0.1~0.3mA / cm ^2, for example, held in 4.7～4.9V, then the cell voltage, e.g., 2. Until the voltage drops to 0 to 2.5 V, for example, constant current discharge is performed at 0.5 to ² mA / cm ² . This charge / discharge cycle is performed once.

Thereafter, until the cell voltage rises to 4.5 to 4.7 V, for example, constant current charging is performed at 0.5 to ² mA / cm ² , for example. After charging, for example, constant current discharge is performed at 0.5 to ² mA / cm ² until the cell voltage drops to 2.0 to 2.5 V, for example. This charge / discharge cycle is performed five times.

Then, constant current charging is performed at, for example, 3 to 7 mA / cm ² until the cell voltage rises to, for example, 4.5 to 4.7 V. After charging, for example, constant current discharge is performed at 3 to 7 mA / cm ² until the cell voltage drops to 2.0 to 2.5 V, for example. This charge / discharge cycle is performed 50 times.

  By such an electrochemical activation treatment, a hybrid capacitor having a high energy density and good durability can be obtained.

Next, in the method for manufacturing the hybrid capacitor 1, a second electrolytic solution containing LiBF ₄ is further injected into the cell tank 10 (second electrolytic solution injection step). Thereby, the hybrid capacitor 1 can be obtained.

The second electrolyte solution is contains an organic solvent containing LiBF _4, for example, be prepared by dissolving LiBF ₄ in an organic solvent.

  Although it does not restrict | limit especially as an organic solvent, For example, the above-mentioned organic solvent is mentioned.

  These organic solvents may be used alone or in combination.

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

The concentration of LiBF ₄ in a second electrolytic solution, for example, 1.0~5.0mol / L, preferably from 1~3mol / L.

The concentration of LiBF ₄ in the total amount of the first electrolytic solution and the second electrolytic solution is 1.0 mol / L or less, preferably in the range of 0.1 to 1.0 mol / L, more preferably 0. The range is from 1 to 0.5 mol / L.

  The volume ratio of the first electrolyte solution to the second electrolyte solution is, for example, 9: 1 to 4: 6, preferably 8: 2 to 6: 4.

In the hybrid capacitor 1, the first electrolytic solution containing LiPF ₆ is injected, and after the electrochemical activation treatment, the second electrolytic solution containing LiBF ₄ is injected. Therefore, the decomposition of LiBF ₄ by the electrochemical activation treatment is performed. It is suppressed. Therefore, the hybrid capacitor 1 sufficiently contains LiBF ₄ in the electrolytic solution stored in the cell tank 10 and can suppress the reaction between the positive electrode current collector 3 made of aluminum and the electrolytic solution. As a result, the charge / discharge cycle durability can be improved.

  Therefore, according to the method for producing an electrochemical capacitor of the present invention, an electrochemical capacitor having excellent charge / discharge cycle durability can be produced.

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 unit 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 (PVdF manufactured by Kureha Co., Ltd.) with 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 applied to the surface of an aluminum foil (positive electrode current collector) having a thickness of 15 μm and dried at 80 ° C. for 12 hours to form a positive electrode. Next, the dried aluminum foil was subjected to pressure stretching with a roll press to obtain an electrode sheet having a coating layer (positive electrode) thickness excluding the aluminum foil of 72 μm.

Next, the electrode sheet is cut into a rectangular shape having a length in the longitudinal direction of 60 mm and a direction (width direction) orthogonal to the length direction of 41 mm, and then the slit processing is performed on the cut electrode sheet at intervals of about 4 mm. Was given. The positive electrode unit was produced by the above operation.
2. Production of negative electrode unit NMP (N-methyl-2-pyrrolidone) solvent with artificial graphite, soft carbon, and polymer binder (PVdF manufactured by Kureha Co., Ltd.) in a solid content of 67.5: 22.5: 10 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 current collector) and dried at 80 ° C. for 12 hours. Subsequently, the dried copper foil was subjected to pressure stretching with a roll press, thereby obtaining an electrode sheet having a coating layer (negative electrode) excluding the copper foil having a thickness of 14 μm.

Next, after cutting into a rectangular shape having a longitudinal length of 60 mm and a direction (width direction) perpendicular to the longitudinal direction of 45 mm, the cut electrode sheet was slit at intervals of about 4 mm. The negative electrode unit was produced by the above operation.
3. Production of Capture Agent-Containing 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) are in a mass of 80:20 solids. Mixtures of these were obtained by kneading in a mortar.

Next, the mixture was subjected to pressure stretching using a manual roll press to obtain a separator sheet having a thickness of 30 μm. Next, the separator sheet was cut into 49 mm × 54 mm, 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 manufactured by Nippon Kogyo Paper Co., Ltd.) was cut into 50 mm × 54 mm.
5. Preparation of Electrolytic Solution LiPF ₆ or LiBF ₄ 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 Hybrid Capacitor One positive electrode unit, one negative electrode unit, one capture agent-containing separator and two auxiliary separators were laminated.

  Specifically, first, one capture agent-containing separator is sandwiched between two separators, and then placed on one side of the stacked separators so that the positive electrode 2 and the negative electrode 4 are opposed to each other with a gap therebetween. The positive electrode unit and the negative electrode unit on the other side were laminated.

  Next, the positive electrode current collector of the positive electrode unit and the aluminum plate (positive electrode current collection tab) on which the sealant was welded were ultrasonically bonded. Similarly, the negative electrode current collector of the negative electrode unit was ultrasonically bonded to a nickel plate (negative electrode final electricity tab) on which a sealant was deposited. 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. The hybrid capacitor was assembled by the above operation.
7). Preparation of Hybrid Capacitor The assembled hybrid capacitor was depressurized in the chamber, and an electrolytic solution containing LiPF ₆ was injected into the cell tank so that the positive electrode unit, the negative electrode unit, and the separator were immersed therein.

  Subsequently, the hybrid capacitor was sealed by heat welding of an aluminum laminate film, and then returned to normal pressure.

  Next, a voltage was applied to the positive electrode and the negative electrode to perform an electrochemical activation treatment.

Specifically, constant current charging was performed at 1 mA / cm ² until the cell voltage increased to 4.8V. After charging, the cell voltage was held at 4.8 V until the current value dropped to 0.1 mA / cm ² , and then constant current discharge was performed at 1 mA / cm ² until the cell voltage dropped to 2.3 V. This charge / discharge cycle was performed once.

Thereafter, constant current charging was performed at 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. This charge / discharge cycle was performed five times.

Thereafter, 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. This charge / discharge cycle was performed 50 times.

  Next, the hybrid capacitor was carried into a glove box in an Ar atmosphere, a part of the aluminum laminate film was cut, and the hybrid capacitor was opened.

Next, an electrolytic solution containing LiBF ₄ was injected so that the molar concentration of LiBF ₄ in the electrolytic solution stored in the cell tank was 1 mol / L. After the injection, the hybrid capacitor was sealed again by heat welding of an aluminum laminate film. The test cell was obtained by the above operation.

Example 2
Test cell in the same manner as in Example 1 except that an electrolyte containing LiBF ₄ was injected so that the molar concentration of LiBF ₄ in the electrolyte stored in the cell tank was 0.4 mol / L. Got.

Comparative Example 1
A test cell was obtained in the same manner as in Example 1 except that the hybrid capacitor was opened and the electrolyte containing LiBF ₄ was not injected.

Comparative Example 2
A hybrid capacitor was assembled in the same manner as in Example 1, and the assembled hybrid capacitor was decompressed in the chamber, and an electrolytic solution containing LiBF ₄ was placed in the cell tank so that the positive electrode unit, the negative electrode unit, and the separator were immersed therein. After the injection, the hybrid capacitor was sealed by thermal welding of an aluminum laminate film and returned to normal pressure.

  Next, a voltage was applied to the positive electrode and the negative electrode, and the above-described electrochemical activation treatment was performed. The test cell was obtained by the above operation.

Comparative Example 3
The hybrid capacitor was assembled in the same manner as in Example 1, and the assembled hybrid capacitor was decompressed in the chamber, and LiPF ₆ and LiBF ₄ were contained in the cell tank so that the positive electrode unit, the negative electrode unit, and the separator were immersed therein. After injecting each electrolytic solution, the hybrid capacitor was sealed by heat welding of an aluminum laminate film and returned to normal pressure. The concentration of LiBF ₄ in a mixed electrolyte solution was a 0.4 mol / L.

Next, a voltage was applied to the positive electrode and the negative electrode, and the above-described electrochemical activation treatment was performed. The test cell was obtained by the above operation.
Evaluation experiment 1. Energy Density of Hybrid Capacitor in Charge / Discharge Cycle A charge / discharge test was performed on the test cells obtained in Examples 1 and 2 and Comparative Examples 1 to 3 by the following method.

Endurance evaluation cycle 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.
(Discussion)
As shown in FIG. 2 and FIG. 3, the test cells (Examples 1 and 2) into which an electrolyte containing LiBF ₄ was injected after the electrochemical activation treatment showed an energy density even when the number of durability evaluation cycles was increased. A test cell (Comparative Example 1) in which an electrolyte containing LiBF ₄ can be kept high, and a test cell in which an electrolyte containing LiBF ₄ was injected before the electrochemical activation treatment (Comparative Example) Compared with 2 and 3), the charge / discharge cycle durability was excellent.

DESCRIPTION OF SYMBOLS 1 Hybrid capacitor 2 Positive electrode 3 Positive electrode collector 4 Negative electrode 5 Negative electrode collector 8 Positive electrode unit 9 Negative electrode unit

Claims (2)

A positive electrode containing a polarizable carbon material, a positive electrode unit which is in contact with the positive electrode and includes a positive electrode current collector containing aluminum, and a material facing the positive electrode and capable of reversibly occluding and releasing lithium ions A negative electrode containing, a negative electrode unit comprising a negative electrode current collector in contact with the negative electrode, and a method for producing an electrochemical capacitor comprising a cell tank containing the positive electrode unit and the negative electrode unit,
A first electrolyte injection step of injecting a first electrolyte containing LiPF ₆ into the cell tank so that the positive electrode unit and the negative electrode unit are immersed;
An electrochemical activation treatment step of applying a voltage to the positive electrode and the negative electrode after the first electrolyte injection step and performing an electrochemical activation treatment;
A method of manufacturing an electrochemical capacitor, further comprising a second electrolyte solution injection step of injecting a second electrolyte solution containing LiBF ₄ into the cell tank after the electrochemical activation treatment step. 2. The method of manufacturing an electrochemical capacitor according to claim 1, wherein the concentration of LiBF ₄ with respect to the total amount of the first electrolytic solution and the second electrolytic solution is 1.0 mol / L or less.

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