JP5828633B2 - Lithium ion capacitor - Google Patents

Description

  The present invention relates to a lithium ion capacitor having low resistance and high output.

  In recent years, electricity storage devices with high output and high energy density have been demanded in the market, and accordingly, electricity storage devices such as lithium ion capacitors have been developed.

For example, Patent Document 1 uses a negative electrode formed from negative electrode active material particles having a 50% volume cumulative diameter (D50) of 0.1 to 2.0 μm, thereby improving low-temperature characteristics and high energy density and high output. A lithium ion capacitor is disclosed.
Patent Document 2 includes a polarizable electrode containing activated carbon, carbon black, and a binder, and 5 wt% to 50 wt% of carbon black having a specific surface area of 1000 m ² / g or more based on the total amount thereof. An electric double layer capacitor having at least one of the above is disclosed.

  Patent Document 3 discloses a high energy density lithium ion capacitor containing ketjen black or the like in the negative electrode coating.

JP 2006-303330 A Japanese Patent Laid-Open No. 9-275041 JP 2010-98020 PR

However, in order to further increase the output of the lithium ion capacitor, it is necessary to further reduce the internal resistance.
Ketjen Black has a highly developed structure and high electron conductivity, but because it is a material with a large specific surface area, it has a large irreversible capacity in conventional lithium ion secondary batteries and so on, so it can be used as a negative electrode forming material. It was difficult. On the other hand, since the irreversible capacity can be supplemented in advance by pre-doping in a lithium ion capacitor, it can be used as a negative electrode forming material. Patent Document 3 describes that ketjen black is used as a negative electrode forming material for a lithium ion capacitor. However, since the amount added is small, the internal resistance has not been sufficiently reduced.

The present invention has been made to solve the above-described problems, and can be realized in the following manner.
The lithium ion capacitor of the present invention includes a positive electrode, a negative electrode having a negative electrode active material layer, and an electrolytic solution. The negative electrode contains 4% by mass to 20% by mass of ketjen black with respect to 100% by mass of the negative electrode active material layer. To do.

  The negative electrode preferably contains graphite having a 50% volume cumulative diameter (D50) in the range of 1.0 to 10 μm.

  In the lithium ion capacitor of the present invention, the positive electrode potential after the positive electrode and the negative electrode are short-circuited is preferably 2.0 V or less.

  According to the present invention, a lithium ion capacitor having a small charge transfer resistance and a high output can be provided.

FIG. 1 is a cross-sectional view schematically showing an example of a lithium ion capacitor according to this embodiment. FIG. 2 is a plan view schematically showing an example of the lithium ion capacitor according to the present embodiment. FIG. 3 is a schematic diagram illustrating an example of a lithium ion capacitor according to the present embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications can be made.

<Lithium ion capacitor>
A lithium ion capacitor is an electricity storage device that includes a positive electrode, a negative electrode, and an electrolyte, and further includes a lithium electrode as necessary.
The positive electrode and the negative electrode preferably include a positive electrode active material and a negative electrode active material, respectively. The positive electrode active material can be reversibly doped / dedoped with lithium ions and anions, and the negative electrode active material can include lithium ions. It is preferable to use materials that can be reversibly doped and dedoped.

  In addition, the lithium ion capacitor of the present invention has a positive electrode potential after short-circuiting the positive electrode and the negative electrode, preferably 2.0 V or less, preferably 0.1 to 1.5 V, from the lithium electrode to the negative electrode. It is preferable to increase the capacity by previously supporting a predetermined amount of lithium ions on at least one of the positive electrodes.

In the present invention, the potential of the positive electrode after the positive electrode and the negative electrode are short-circuited is 2.0 V or less. The potential of the positive electrode determined by any of the following methods (A) or (B) is 2.0 V. It means the following cases.
(A) Doping with lithium ions, and then leaving the positive electrode terminal and negative electrode terminal of the capacitor cell electrically connected (short circuited) for 12 hours or more, then releasing the short circuit, 0.5 ~ Positive electrode potential measured within 1.5 hours (B) A constant current discharge to 0 V over 12 hours in a charge / discharge tester, and then the positive electrode terminal and the negative electrode terminal are electrically connected (short-circuited) The positive electrode potential was measured within 0.5 to 1.5 hours after the short circuit was released after being left at

  A lithium ion capacitor having a positive electrode potential of 2.0 V or less after the positive electrode and the negative electrode are short-circuited uses, for example, an electrolytic solution in which activated carbon is used for the positive electrode, carbon material and lithium salt are dissolved in an organic solvent for the negative electrode. In a conventional hybrid capacitor, the negative electrode can be obtained by pre-doping a predetermined amount of lithium ions in advance.

FIG. 1 is a cross-sectional view schematically showing a lithium ion capacitor 100 which is an example of the present embodiment. 1 is a cross-sectional view taken along the line II ′ of FIG. 2 and FIG.
FIG. 2 is a plan view schematically showing the lithium ion capacitor 100 according to the present embodiment. 2 is a top view of the lithium ion capacitor 100 of FIG. 3 (viewed from the second laminate film 3 side). In FIG. 2, for convenience, a portion under the second laminate film 3 is indicated by a dotted line.
FIG. 3 is a schematic diagram three-dimensionally showing the lithium ion capacitor 100 according to the present embodiment.

  As shown in FIGS. 1 and 2, the lithium ion capacitor 100 includes, for example, a laminate outer body 5 having a first laminate film 1 and a second laminate film 3, a positive electrode terminal 16, a negative electrode terminal 26, and a laminate 50. And an electrolytic solution. The stacked body 50 includes a positive electrode 10, a negative electrode 20, a lithium electrode 30, and a separator 40. In FIG. 1, the electrolyte solution is not shown for convenience.

  The shape of the laminate outer package 5 is rectangular in the example shown in FIG. 2, but is not particularly limited. As the 1st laminate film 1 and the 2nd laminate film 3, what laminated | stacked synthetic resin, such as a polypropylene and nylon, and metal foil, such as aluminum foil and copper foil, etc. are mentioned. In the laminate outer package 5, a laminate 50 and an electrolytic solution are accommodated.

  The positive electrode terminal 16 is provided between the first laminate film 1 and the second laminate film 3, for example. The positive electrode terminal 16 extends outward from the outer periphery of the laminate outer package 5 as shown in FIG. A positive electrode lead 18 is electrically connected to the positive electrode terminal 16. The positive electrode lead 18 can electrically connect the positive electrode terminal 16 and the positive electrode current collector 12 of the positive electrode 10. Examples of the material of the positive electrode terminal 16 and the positive electrode lead 18 include aluminum and stainless steel.

  The negative electrode terminal 26 is provided between the first laminate film 1 and the second laminate film 3, for example, apart from the positive electrode terminal 16. The negative electrode terminal 26 extends outward from the outer periphery of the laminate outer package 5 as shown in FIG. A negative electrode lead 28 is electrically connected to the negative electrode terminal 26. The negative electrode lead 28 can electrically connect the negative electrode terminal 26 and the negative electrode current collector 22 of the negative electrode 20. Examples of the material of the negative electrode terminal 26 and the negative electrode lead 28 include copper, stainless steel, and nickel. In the example shown in FIG. 1, the positive terminal 16 is provided at the left end (one end) of the laminate outer body 5, and the negative terminal 26 is the right end (the other end) of the laminate outer body 5. However, the positions of the terminals 16 and 26 are not particularly limited.

  The negative electrode lead 28 can further electrically connect (short-circuit) the lithium current collector 32 of the lithium electrode 30 and the negative electrode current collector 22 of the negative electrode 20. With such a configuration, when the electrolyte solution is injected and sealed in the laminate outer package 5 and left to stand for a predetermined time (for example, 10 days), the lithium foil 34 of the lithium electrode 30 is oxidized, and the electrons are negative. Flows into the electrolyte and is released into the electrolyte as lithium ions. Lithium ions are electrochemically doped into the negative electrode 20 via the electrolytic solution (“pre-dope”), and as a result, the potential of the negative electrode 20 can be lowered.

  The lithium foil 34 releases lithium ions into the electrolytic solution by pre-doping. FIG. 1 illustrates the lithium foil 34 before releasing lithium ions into the electrolytic solution.

  The laminated body 50 is accommodated in the laminate outer package 5 and immersed in the electrolytic solution. In the example illustrated in FIG. 1, the laminate 50 includes a separator 40, a lithium electrode 30, a negative electrode 20, a positive electrode 10, a negative electrode 20, a positive electrode 10, a negative electrode 20, a lithium electrode 30 and a separator from the bottom surface inside the first laminate film 1. The layers are stacked in the order of 40, and the separator 40 is interposed between the poles. That is, in the example illustrated in FIG. 1, the stacked body 50 includes two layers of positive electrodes 10 and three layers of negative electrodes 20, but the number thereof is not particularly limited. Each of the positive electrode 10 and the negative electrode 20 may have about 10 layers. Similarly, the number and location of the lithium electrodes 30 are not particularly limited. The positive electrode 10, the negative electrode 20, the lithium electrode 30, and the separator 40 are sheet-like.

  In addition, the laminated body 50 is not limited to the example shown in FIG. 1, For example, the laminated structure formed by laminating | stacking this laminated sheet by forming a laminated sheet by laminating | stacking a positive electrode, a negative electrode, a lithium electrode, and a separator, for example. But you can.

  Hereinafter, each member which comprises the laminated body 50 is demonstrated.

<Positive electrode>
As shown in FIG. 1, the positive electrode 10 preferably includes a positive electrode current collector 12 and a positive electrode active material layer 14.

  As the positive electrode current collector 12, a porous metal foil is preferably used. More specifically, the positive electrode current collector 12 may be a metal foil having through holes formed on the front and back surfaces thereof, such as a punching metal, an expanded metal, and an etching foil having holes penetrating the front and back surfaces. The lithium ion can move through the positive electrode current collector 12 if it has a hole penetrating the front and back surfaces. Therefore, lithium ions can be pre-doped into the negative electrode 20 through the positive electrode current collector 12. Examples of the material of the positive electrode current collector 12 include aluminum and stainless steel. The thickness of the positive electrode current collector 12 is not particularly limited, but is, for example, 10 μm to 50 μm.

  The positive electrode active material layer 14 is formed on the surface of the positive electrode current collector 12. In the example illustrated in FIG. 1, the positive electrode active material layer 14 is formed on both surfaces of the positive electrode current collector 12, but may be formed only on one surface. Although the thickness of the positive electrode active material layer 14 is not specifically limited, For example, they are 60 micrometers-90 micrometers, Preferably, they are 70 micrometers-80 micrometers.

For example, the positive electrode active material layer 14 is prepared by dispersing a powdered positive electrode active material, a binder (binder), and, if necessary, a thickener in a dispersion medium such as an aqueous solvent or an organic solvent. The slurry is applied to the surface of the positive electrode current collector 12 and dried.
The slurry may further be mixed with a positive electrode conductive additive as necessary.

  Hereinafter, the material which comprises the positive electrode active material layer 14 is demonstrated.

[Positive electrode active material]
The positive electrode active material is preferably a material capable of reversibly supporting anions such as hexafluorophosphate (PF ₆ ⁻ ) and tetrafluoroborate (BF ₄ ⁻ ). The positive electrode active material may be capable of supporting lithium ions, for example. Specific examples of the positive electrode active material include activated carbon, polyacene-based material (PAS) which is a heat-treated product of an aromatic condensation polymer, and activated carbon is preferable. Below, the case where activated carbon is used as a positive electrode active material is demonstrated.

The specific surface area of the activated carbon is preferably 1900m ² / g~2800m ² / g, further preferably a 1950m ² / g~2600m ² / g. In addition, the 50% volume cumulative diameter (D50) (average particle diameter) of the activated carbon is preferably 2 μm to 8 μm, particularly preferably 3 μm to 8 μm, from the viewpoint of the packing density of the activated carbon.

  When the specific surface area of activated carbon and D50 are in the above ranges, the energy density of the lithium ion capacitor can be further improved. In addition, the value of 50% volume cumulative diameter (D50) in this embodiment is calculated | required by the microtrack method, for example.

  Examples of the raw material of activated carbon include phenol resin, petroleum coke, petroleum pitch, coconut shell, and coal-based coke. Among these, it is preferable to use phenol resin or coal-based coke because the specific surface area can be increased. Activated carbon is obtained, for example, by firing and carbonizing raw materials, then activating treatment, and then pulverizing.

  Although the compounding quantity of a positive electrode active material is not restrict | limited in particular, It is preferable that it is 70-95 mass% when the whole positive electrode active material layer is 100 mass%, and it is more preferable that it is 80-90 mass%.

[Binder]
As the binder (binder), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), fluorine acrylic resin, etc. can be used, but fluorine acrylic resin should be used. Is preferred. More specifically, the fluoroacrylic resin includes a fluoropolymer obtained from a monomer component containing vinylidene fluoride (VDF), hexafluoropropylene (HFP), and the like, and (meth) acrylic acid alkyl esters. And a composite polymer obtained by compounding an acrylic polymer obtained from a monomer component containing a functional group-containing unsaturated monomer and the like. The composite polymer can be obtained, for example, by seed polymerization of an acrylic polymer using a fluorine-containing polymer as a seed.

  When an aprotic organic solvent is used as the electrolytic solution, the fluoroacrylic resin is less likely to swell with respect to the solvent as compared with, for example, cellulose. This is because it is considered that the fluoroacrylic resin is cured into a resin state when dried, and as a result, has an effect of suppressing excessive penetration of the electrolytic solution.

  Further, in the electrolytic solution, the fluorine acrylic resin is less likely to swell as compared with a fluorine-based binder such as an acrylic resin binder not containing fluorine atoms or polyvinylidene fluoride (PVDF). This is because, when the fluoroacrylic polymer is a composite polymer, the SP (Solubility Parameter) value changes due to the composite of the fluoropolymer and the acrylic polymer, and the affinity with the electrolytic solution changes. This is because it is considered to be.

  In addition, the composite can be expected to improve the potential resistance. By using a fluoroacrylic resin as the binder, the positive electrode active material layer 14 can be stably bound to the positive electrode current collector 12.

  Bonded by mixing a fluorine-based acrylic resin with a rubber binder such as SBR (styrene butadiene rubber); a fluorine-based resin such as polytetrafluoroethylene or polyvinylidene fluoride; a thermoplastic resin such as polypropylene or polyethylene. It may be an agent.

  The amount of the binder used is preferably, for example, from 5% by mass to 15% by mass, and more preferably from 6% by mass to 12% by mass with respect to the positive electrode active material.

[Thickener]
Examples of the thickener include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyethylene glycol (PEG), and the like. These are particularly preferably used as necessary when preparing a water-based paint that can be used at the time of producing the positive electrode, and may be used singly or in combination of two or more. The use amount of the thickener is, for example, preferably 1% by mass to 10% by mass, and more preferably 4% by mass to 10% by mass with respect to the positive electrode active material.

[Positive electrode conductive aid]
As the positive electrode conductive assistant, acetylene black, graphite, ketjen black, metal powder, and the like can be used. It is preferable that the usage-amount of a conductive support agent is about 1 mass%-10 mass% with respect to a positive electrode active material, for example.

[Dispersion medium]
The dispersion medium that can be used in manufacturing the positive electrode is not particularly limited as long as the positive electrode active material, the binder, and a thickener as necessary can be dispersed, but water and the like can be mentioned.

<Negative electrode>
As shown in FIG. 1, the negative electrode 20 preferably includes a negative electrode current collector 22 and a negative electrode active material layer 24.

  As the negative electrode current collector 22, a porous metal foil is preferably used. More specifically, the negative electrode current collector 22 may be a metal foil or the like in which through holes are formed on the front and back surfaces, such as a punching metal, an expanded metal, and an etching foil having holes that penetrate the front and back surfaces. Examples of the material of the negative electrode current collector 22 include copper, stainless steel, and nickel. Although the thickness of the negative electrode collector 22 is not specifically limited, For example, they are 10 micrometers-50 micrometers.

  The negative electrode active material layer 24 is formed on the surface of the negative electrode current collector 22. In the example shown in FIG. 1, the negative electrode active material layer 24 is formed on both surfaces of the negative electrode current collector 22, but may be formed only on one surface. Although the thickness of the negative electrode active material layer 24 is not specifically limited, For example, they are 10 micrometers-40 micrometers.

The negative electrode active material layer 24 is obtained by, for example, dispersing a powdered negative electrode active material, a conductive additive, a binder (binder), and a thickener as necessary in a dispersion medium such as an aqueous solvent or an organic solvent. The slurry is prepared, and the slurry is applied to the surface of the negative electrode current collector 22 and dried.
Hereinafter, the material which comprises the negative electrode active material layer 24 is demonstrated.

[Negative electrode active material]
The negative electrode active material is preferably a material capable of inserting and extracting lithium ions. More specifically, examples of the negative electrode active material include graphite (graphite), non-graphitizable carbon, and PAS. Among these, graphite having a 50% volume cumulative diameter (D50) in the range of 1.0 to 10 μm is preferable and graphite having a D50 in the range of 2 to 5 μm is more preferable from the viewpoint of output improvement.
The 50% volume cumulative diameter (D50) is a value measured using a particle size distribution measuring device.

  Although the compounding quantity of the said negative electrode active material is not restrict | limited in particular, It is preferable that it is 70-95 mass% when the whole negative electrode active material layer is 100 mass%, and it is more preferable that it is 80-90 mass%.

[Binder (binder), thickener]
Examples of the binder and thickener used when forming the negative electrode active material layer 24 include the compounds mentioned as the binder and thickener that can be used when forming the positive electrode active material layer 14. Can be mentioned.

The amount of the binder used is, for example, preferably 2% by mass to 15% by mass, and more preferably 3% by mass to 12% by mass with respect to the negative electrode active material.
The use amount of the thickener is, for example, preferably 1% by mass to 10% by mass, and more preferably 2% by mass to 10% by mass with respect to the negative electrode active material.

[Negative Conductive Aid (Ketjen Black)]
The negative electrode active material layer includes ketjen black as a negative electrode conductive additive. The content of ketjen black is 4% by mass to 20% by mass, preferably 5.5% by mass to 20% by mass, and more preferably 7% by mass to 100% by mass with respect to 100% by mass of the negative electrode active material layer. 20% by mass.

  By including the above amount of ketjen black in the negative electrode active material layer, the coulomb efficiency of the negative electrode is high, the capacitor characteristics such as the low DC resistance of the lithium ion capacitor are excellent in balance, the charge transfer resistance is small, and the high An output lithium ion capacitor can be obtained.

  If the ketjen black content exceeds the above range, side reactions increase and gas may be generated in the resulting lithium ion capacitor. If the ketjen black content is less than the above range, the resulting lithium ion There is a possibility that the ion capacitor has a large DC resistance.

[Other negative electrode conductive additives]
The active material layer may include other negative electrode conductive assistants in addition to ketjen black. Examples of other negative electrode conductive assistants include acetylene black, graphite, and metal powder. The content of the other negative electrode conductive assistant is, for example, preferably 1% by mass to 20% by mass, and more preferably 2% by mass to 18% by mass with respect to 100% by mass of the negative electrode active material layer.

  When graphite is contained in the active material layer, graphite is used as an active material and a conductive additive. Therefore, the content of graphite is 70 to 95% by mass when the entire negative electrode active material layer is 100% by mass. It is preferable that it is 80 to 90% by mass.

[Dispersion medium]
The dispersion medium that can be used in manufacturing the positive electrode is not particularly limited as long as the positive electrode active material, the binder, and a thickener as necessary can be dispersed, but water and the like can be mentioned.

<Lithium electrode>
As shown in FIG. 1, the lithium electrode 30 preferably includes a lithium electrode current collector 32 and a lithium foil 34.

  As the lithium electrode current collector 32, it is preferable to use a porous metal foil, a metal net or the like. The material of the lithium electrode current collector 32 is preferably a material that does not react with lithium ions, and specific examples include copper and stainless steel. The thickness of the lithium electrode current collector 32 is not particularly limited, but is, for example, 10 μm to 200 μm.

  The lithium foil 34 is a material that can function as a lithium ion supply source, such as metallic lithium, and is preferably pressure-bonded or vapor-deposited on at least one surface of the lithium electrode current collector 32. That is, when the lithium electrode current collector 32 and the negative electrode current collector 22 are electrically connected (short-circuited) and immersed in the electrolytic solution, the lithium foil 34 is oxidized, and electrons flow into the negative electrode. Ionized and released into the electrolyte as lithium ions. The lithium ions are electrochemically pre-doped into the negative electrode active material layer 24 via the electrolytic solution. The thickness of the lithium foil 34 is not particularly limited, but may be, for example, 1 μm to 300 μm, preferably 1 μm to 200 μm, and more preferably 10 μm to 200 μm.

  The pre-doping may be performed on at least one of the positive electrode active material layer 14 and the negative electrode active material layer 24. However, in consideration of the complexity of the process and the capacity of the lithium ion capacitor, the pre-doping of lithium ions is This is preferably performed only on the negative electrode active material layer 24.

<Separator>
As the separator 40, a porous material having durability against the electrolytic solution, the positive electrode active material, and the negative electrode active material can be used. More specifically, as the separator 40, a nonwoven fabric or a porous film made of cellulose, rayon, polyethylene, polypropylene, aramid resin, amideimide, polyphenylene sulfide, polyimide, polyisocyanurate, cellulose / rayon, or the like can be used. Although the thickness of the separator 40 is not specifically limited, For example, they are 20 micrometers-50 micrometers. The separator 40 can isolate the positive electrode 10, the negative electrode 20, and the lithium electrode 30 from each other. Moreover, it is preferable that the separator 40 is infiltrated with the electrolytic solution.

<Electrolyte>
As the electrolytic solution, an electrolytic solution using a supporting electrolyte such as a lithium salt as an electrolyte and an aprotic organic solvent as a solvent is preferable. An arbitrary additive may be mixed in the electrolytic solution as necessary. Examples of the aprotic organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl ketone, γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride, sulfolane and the like. These solvents may be used alone or in combination of two or more.

[Supporting electrolyte]
The supporting electrolyte is preferably a compound comprising a lithium salt. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , and LiN (C ₂ F ₅ SO ₂ ) ₂ . The concentration of the lithium salt in the electrolytic solution is, for example, 0.5 mol / l to 1.5 mol / l.

[Optional additives]
Although it does not restrict | limit especially as arbitrary additives, The compound etc. which are represented by following formula (1) can be mentioned.

The electrolytic solution preferably contains a compound represented by the following formula (1). A lithium ion capacitor having an appropriate resistance value can be produced by adding a compound represented by the following formula (1) to the electrolytic solution in a range of 0.05 to 0.5 wt%.
The compound represented by the following formula (1) is preferably a compound in which M is a transition metal or a Group 13 to Group 15 element, and more preferably a phosphoric acid derivative or a boric acid derivative in which M is P or B. .

In Formula (1), R ¹ represents a halogen atom, and R ² represents a methylene group, an alkylene group or a halogenated alkylene group which may have a substituent having 2 to 10 carbon atoms, or a carbon number. 6 to 20 arylene group or halogenated arylene group (all these alkylenes and arylenes may contain a substituent or a hetero atom, and q R ^{2 s} may be bonded to each other) X ¹ and X ² are each independently a hetero atom or NR ³ (R ³ is a hydrogen atom, an alkyl group or a halogenated alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms. Group or a halogenated aryl group (both these alkylene and arylene may contain a substituent or a hetero atom), M represents a transition metal or a thirteenth group. Shows a fifteenth group element, A ^{a +} is a metal ion represents a proton or onium ion, n is an integer of 0 to 8, m is an integer of 1 to 4, a and b are 1 3 represents an integer, q represents an integer of 1 to 4, and p represents p = b / a.

Examples of the compound represented by the above formula (1) include a compound represented by the following formula (2) (lithium bis (oxalato) borate, a compound represented by the following formula (3) (lithium difluorobis (oxalato) phosphate). Preferably there is.

[Example]
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited at all by these Examples.

[Binder synthesis method]
The fluoropolymer was synthesized as follows. The inside of an autoclave having an internal volume of about 6 liters equipped with an electromagnetic stirrer was sufficiently purged with nitrogen, then charged with 2.5 liters of deoxygenated pure water and 25 g of ammonium perfluorodecanoate as an emulsifier, The temperature was raised to 60 ° C. while stirring at 350 rpm. Next, a mixed gas consisting of 70% vinylidene fluoride (VDF) and 30% propylene hexafluoride (HFP) was charged until the internal pressure reached 20 kg / cm ² G. Thereafter, 25 g of Freon 113 solution containing 20% of diisopropyl peroxydicarbonate as a polymerization initiator was injected using nitrogen gas to initiate polymerization. During the polymerization, a mixed gas consisting of 60.2% VDF and 39.8% HFP was sequentially injected so that the internal pressure was maintained at 20 kg / cm ² G. In addition, since the polymerization rate decreased as the polymerization progressed, after 3 hours, the same amount of the polymerization initiator as that used before was injected using nitrogen gas, and the reaction was further continued for 3 hours. Thereafter, the reaction solution was cooled and the stirring was stopped, the unreacted monomer was released to stop the reaction, and a latex containing fine particles made of a fluoropolymer was obtained.

  Next, the polymerization process of the (meth) acrylic polymer was performed as follows. After fully replacing the inside of a 7-liter separable flask with nitrogen, 10 parts by mass of the latex obtained in the flask (in terms of solid content), a polymerizable emulsifier “ADEKA rear soap SR1025” (manufactured by Asahi Denka Co., Ltd.) ) 0.1 parts by weight, 9 parts by weight of methyl methacrylate (MMA), 0.4 parts by weight of acrylic acid (AA) and 170 parts by weight of water, and 0.3 parts by weight of potassium persulfate as a polymerization initiator Sodium sulfite 0.1 mass part was thrown in, and it was made to react at 50 degreeC for 2 hours.

  On the other hand, in another container, 80 parts by weight of water, 0.5 part by weight of “ADEKA rear soap SR1025” (manufactured by Asahi Denka), 54 parts by weight of 2-ethylhexyl acrylate (2EHA), 17 parts by weight of methyl methacrylate, styrene ( ST) 9 parts by mass and 0.6 parts by mass of acrylic acid were added and mixed, and the mixture was uniformly emulsified to obtain an emulsion. This emulsion was put into the separable flask and reacted at 50 ° C. for 3 hours and further at 80 ° C. for 1 hour. Thereafter, the reaction is stopped by cooling, the pH is adjusted to 7 with an aqueous sodium hydroxide solution, and 0.05 part by mass of “Nopco NXZ” (manufactured by San Nopco) is added as an antifoaming agent, whereby polymer particles are contained. An aqueous dispersion (hereinafter also referred to as “fluorine acrylic resin (1)”) was obtained. The obtained aqueous dispersion was used as a binder for positive and negative electrodes.

(Example 1: S1)
<Positive electrode>
[Method for preparing positive electrode slurry]
85% by mass of a commercially available activated carbon powder having a specific surface area of 2100 m ² / g as a positive electrode active material, 5.5% by mass of acetylene black powder as a conductive additive, 5.5% by mass of a fluoroacrylic resin (1) as a binder, As a thickener, 4% by mass of CMC was dispersed in ion-exchanged water, and sufficiently mixed with a mixing stirrer to obtain a positive electrode slurry.

[Production method of positive electrode]
A non-aqueous carbon-based conductive paint (manufactured by Nippon Atchison Co., Ltd .: EB-815) is formed on both surfaces of an aluminum expanded metal (manufactured by Nippon Metal Industry Co., Ltd.) having a thickness of 35 μm (porosity 50%) as a positive electrode current collector. It was coated by a spray method and dried. The through hole of the positive electrode current collector was almost closed with a conductive paint. The total thickness of the positive electrode current collector and the conductive paint was 52 μm.

  Next, the positive electrode slurry (1) having a thickness of 180 μm was manufactured by applying the positive electrode slurry to both surfaces of the positive electrode current collector to which the conductive coating material was applied, using a roll coater and then pressing.

<Negative electrode>
[Method for preparing negative electrode slurry]
Ketjen black powder with a 50% volume cumulative diameter (D50) measured by using a particle size distribution measuring apparatus LA920 (HORIBA Mfg. Co., Ltd.) of 57.5 m, 87.5% by mass of graphite, an area of 1270 m ² / g, and a hollowness of 78% (Ketjen Black International Co., Ltd. (trade name: ECP600JD)) 5.5% by mass, 3% by mass of CMC and 4% by mass of fluoroacrylic resin (1) are added and dispersed, and mixed thoroughly with a mixing stirrer. A negative electrode slurry (1) was obtained. The ketjen black content is 5.5% by mass with respect to the total mass of the negative electrode active material layer.

[Production method of negative electrode]
The negative electrode slurry (1) was applied to both surfaces of a copper expanded metal (manufactured by Nippon Metal Industry Co., Ltd.) having a thickness of 32 μm (porosity 50%) as a negative electrode current collector with a die coater and dried to form a negative electrode ( 1) was produced. The thickness of the negative electrode was 80 μm. In addition, the negative electrode after drying was punched out to a size of φ13 mm, and the negative electrode weight was measured. The weight of the current collector was subtracted to calculate the density of the negative electrode active material layer.

[Method of manufacturing negative electrode single electrode cell]
Cut the negative electrode (1) prepared in the above procedure into a size of 2.6 x 4.0 cm ^{2 in} length and width, and use 150 μm thick metallic lithium of the same size as the counter electrode in copper of 80 μm thickness. Two lithium electrodes were prepared by pressure bonding to a net (lithium electrode current collector). The negative electrode 1 and the lithium electrode 2 were alternately laminated as a separator via a cellulose / rayon mixed nonwoven fabric to obtain a first laminated sheet.

  The negative electrode current collector and the nickel negative electrode terminal were electrically connected via the negative electrode lead, and the lithium electrode current collector and the nickel lithium electrode terminal were electrically connected via the lithium electrode lead. The nickel terminals had a width of 5 mm, a length of 20 mm, and a thickness of 100 μm. The negative electrode lead and the lithium electrode lead were connected by ultrasonic welding.

Next, the first laminated sheet is placed inside a deep-drawn exterior container (first laminate film) having a length × width of 3 × 6.4 cm ² and a height of 1 mm in the squeezed region, and is rectangular as a sealing plate The laminate film (second laminate film) was used to cover the opening of the outer container, and the three sides of the laminate film and the outer container were fused. Subsequently, an electrolytic solution (a solution in which LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a weight ratio of 1: 1 to a concentration of 1 mol / l) was vacuum impregnated. Thereafter, the remaining one side of the laminate film was fused to the outer container. The negative electrode single electrode cell was produced by the above process.

[Negative electrode single electrode cell characteristic evaluation]
The negative electrode single electrode cell was charged to 0 V at a constant current of 10 mA, and after reaching 0 V, charging was continued for 24 hours at a constant voltage. Thereafter, the battery was discharged to 1.5 V at a constant current of 1 mA, and the charge capacity, discharge capacity, and coulomb efficiency of the negative electrode were determined. The results are shown in Table 1.

[Method for manufacturing lithium ion capacitor tripolar cell]
Next, the negative electrode (1) vertical × horizontal is cut six to a size of 2.6 × 4.0 cm ^2, said positive electrode (1) vertical × horizontal is 2.4 × 3.8 cm ² size Then 5 sheets were cut. And the negative electrode and the positive electrode were alternately laminated | stacked through the separator (35-micrometer-thick cellulose / rayon mixed nonwoven fabric) so that the outermost part of the laminated body at the time of lamination | stacking might become a negative electrode, and the laminated body was obtained. Next, as a separator, one cellulose / rayon mixed nonwoven fabric having a thickness of 35 μm was disposed on the outermost part (uppermost surface and lowermost surface) of the obtained laminate and fixed with a polyimide tape to obtain an electricity storage device element. Next, the positive electrode current collector and the aluminum positive electrode terminal were electrically connected via the positive electrode lead, and the negative electrode current collector and the nickel negative electrode terminal were electrically connected via the negative electrode lead. The positive electrode lead and the negative electrode lead were connected by ultrasonic welding. The positive electrode terminal and the negative electrode terminal had a width of 5 mm, a length of 20 mm, and a thickness of 100 μm.

As the lithium electrode, a lithium foil (thickness 150 μm, length × width 2.6 × 4.0 cm ² ) bonded to an 80 μm thick copper mesh (lithium electrode current collector) was used. One lithium electrode was arranged on the outermost part (lowermost part) of the electricity storage device element so as to face the outermost separator of the electricity storage device element to obtain a laminate (1). Next, the lithium electrode current collector and the nickel lithium electrode terminal were electrically connected via the lithium electrode lead. The lithium electrode lead was connected by ultrasonic welding. The lithium electrode terminal had a width of 5 mm, a length of 20 mm, and a thickness of 100 μm.

The obtained laminate (1) was placed inside a deep-drawn outer container (first laminate film) having a length of 3 × 6.4 cm ² and a height of 3 mm in the squeezed region, as a sealing plate The opening of the outer container was covered with a rectangular laminate film (second laminate film), and the three sides of the laminate film and the outer container were fused. Next, an electrolytic solution (a solution in which LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a weight ratio of 1: 1 to a concentration of 1 mol / l) was vacuum impregnated. Thereafter, the remaining one side of the laminate film was fused to the outer container. Through the above steps, a lithium ion capacitor tripolar cell was produced.

[Evaluation of lithium ion capacitor tripolar cell]
In the obtained lithium ion capacitor tripolar cell, pre-doping was first performed. The pre-doping amount is equivalent to 75% of the charging capacity in the negative electrode single electrode cell evaluation described above. The lithium electrode is charged from the negative electrode to the negative electrode at a constant current of 10 mA up to 0 V. The time when lithium ions were doped was regarded as the end.

  Next, charging is performed between the positive electrode and the negative electrode of the lithium ion capacitor tripolar cell at a constant current of 200 mA until the cell voltage reaches 3.8 V, and then a constant voltage of 3.8 V is applied. Voltage charging was performed for 1 hour. Next, the battery was discharged at a constant current of 200 mA until the cell voltage reached 2.2 V (hereinafter also referred to as “3.8 V-2.2 V cycle”). This cycle of 3.8V-2.2V was repeated, and the cell capacity and DC resistance were measured in the third discharge. The results are shown in Table 1.

(Example 2: S2)
In the preparation method of the negative electrode slurry, the same as Example 1 except that 89% by mass of graphite, 3% by mass of CMC, 4% by mass of fluoroacrylic resin (1) and 4% by mass of Ketjen black were added and dispersed to prepare the negative electrode slurry. A negative electrode monopolar cell and a lithium ion capacitor tripolar cell were manufactured, and the same measurements as in Example 1 were performed. The results are shown in Table 1.

(Example 3: S3)
In the method for preparing the negative electrode slurry, 86% by mass of graphite, 3% by mass of CMC, 4% by mass of the fluoroacrylic resin (1) and 7% by mass of Ketjen black were added and dispersed to prepare a negative electrode slurry. A negative electrode monopolar cell and a lithium ion capacitor tripolar cell were manufactured, and the same measurements as in Example 1 were performed. The results are shown in Table 1.

(Example 4: S4)
In the preparation method of the negative electrode slurry, the same as Example 1 except that 73% by mass of graphite, 3% by mass of CMC, 4% by mass of fluoroacrylic resin (1) and 20% by mass of ketjen black were added and dispersed to prepare the negative electrode slurry. A negative electrode monopolar cell and a lithium ion capacitor tripolar cell were manufactured, and the same measurements as in Example 1 were performed. The results are shown in Table 1.

(Example 5: S5)
In the preparation method of the negative electrode slurry, the same as Example 1 except that 81% by mass of graphite, 3% by mass of CMC, 4% by mass of fluoroacrylic resin (1) and 12% by mass of Ketjen black were added and dispersed to prepare the negative electrode slurry. A negative electrode monopolar cell and a lithium ion capacitor tripolar cell were manufactured, and the same measurements as in Example 1 were performed. The results are shown in Table 1.

(Example 6: S6)
A negative electrode single electrode cell and a lithium ion capacitor tripolar cell were produced in the same manner as in Example 4 except that 0.2% by mass of the compound represented by the above formula (2) was added to the electrolytic solution. Measurements were performed. The results are shown in Table 1.

(Comparative Example 1: C1)
In the preparation method of the negative electrode slurry, the same as Example 1 except that 90% by mass of graphite, 3% by mass of CMC, 4% by mass of fluoroacrylic resin (1) and 3% by mass of Ketjen black were added and dispersed to prepare the negative electrode slurry. A negative electrode monopolar cell and a lithium ion capacitor tripolar cell were manufactured, and the same measurements as in Example 1 were performed. The results are shown in Table 1.

(Comparative Example 2: C2)
In the preparation method of the negative electrode slurry, the same as Example 1 except that 68% by mass of graphite, 3% by mass of CMC, 4% by mass of the fluoroacrylic resin (1) and 25% by mass of Ketjen black were added and dispersed to prepare the negative electrode slurry. A negative electrode monopolar cell and a lithium ion capacitor tripolar cell were manufactured, and the same measurements as in Example 1 were performed. The results are shown in Table 1.

(Comparative Example 3: C3)
In place of the negative electrode slurry (1), 87.5% by mass of graphite having a D50 of 5 μm, 5.5% by mass of acetylene black, 3% by mass of CMC, and 4% by mass of fluoroacrylic resin were added and dispersed. A negative electrode single electrode cell and a lithium ion capacitor tripolar cell were produced in the same manner as in Example 1 except that the slurry obtained by thorough mixing was used, and the same measurements as in Example 1 were performed. The results are shown in Table 1.

Regarding the charge capacity, cell capacity, and DC resistance in Table 1, Example 1 was normalized to 100 and other examples and comparative examples were shown as relative values.
As a result of comprehensive judgment, a case where the coulombic efficiency was 40.0% or more and a direct current resistance value was 150 (mΩ) or less was evaluated as “◯”, and otherwise “×”.

  In the tripolar cells of Examples 1 to 6, when the positive electrode potential after the positive electrode and the negative electrode were short-circuited was measured, all were 2.0 V or less.

  Examples 1 to 6 resulted in excellent balance in capacitor characteristics such as coulomb efficiency, charge / discharge capacity, and direct current resistance. In Example 4, a slight amount of gas was generated, but there is no practical problem. In Example 6, the addition of the additive was good with almost no gas generation.

In Comparative Example 1, the content of ketjen black in the negative electrode active material layer was small, so that the coulomb efficiency of the negative electrode was high and gas generation was difficult, but the DC resistance value was large.
In Comparative Example 2, since the content of ketjen black in the negative electrode active material layer was large, the coulomb efficiency of the negative electrode was less than 40%, and side reactions increased, so that gas generation occurred and the cell expanded.

Since the comparative example 3 used acetylene black as a negative electrode conductive support agent, direct current | flow resistance became large.
From the above, it can be seen that when increasing the output of the lithium ion capacitor or the like, it is preferable to use ketjen black in a specific amount as a conductive aid for the negative electrode.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

1: first laminated film, 3: second laminated film, 5: laminated outer package,
10: positive electrode, 12: positive electrode current collector, 14: positive electrode active material layer, 16: positive electrode terminal, 18: positive electrode lead,
20: negative electrode, 22: negative electrode current collector, 24: negative electrode active material layer, 26: negative electrode terminal, 28: negative electrode lead,
30: Lithium electrode, 32: Lithium electrode current collector, 34: Lithium foil,
40: separator,
50: laminate,
100: Lithium ion capacitor

Claims (9)

A negative electrode having a positive electrode, a copper negative electrode current collector having holes penetrating the front and back surfaces, and a negative electrode active material layer, and an electrolyte solution,
A lithium ion capacitor in which the negative electrode satisfies the following requirement (I) and contains 4% by mass to 20% by mass of ketjen black with respect to 100% by mass of the negative electrode active material layer.
Requirement (I): A tripolar cell using the negative electrode and further using a positive electrode and a lithium electrode was prepared, and a cell voltage of 3. mA was applied between the positive electrode and the negative electrode of the tripolar cell at a constant current of 200 mA. Charging to 8V, then applying constant current-constant voltage charging with a constant voltage of 3.8V for 1 hour, repeating the charging / discharging cycle with 200mA constant current discharging until the cell voltage reaches 2.2V The value of the DC resistance measured in the third discharge is 150 mΩ or less.   2. The lithium ion capacitor according to claim 1, wherein the negative electrode contains graphite having a 50% volume cumulative diameter (D50) in a range of 1.0 to 10 μm.   The lithium ion capacitor according to claim 1, wherein the negative electrode includes a binder.   The lithium ion capacitor of any one of Claims 1-3 in which the said positive electrode contains a binder.   The lithium ion capacitor according to claim 1, wherein the positive electrode includes a positive electrode current collector having a hole penetrating the front and back surfaces and a positive electrode active material layer. The lithium ion capacitor further comprises a lithium electrode having a lithium electrode current collector,
The lithium ion capacitor according to any one of claims 1 to 5, wherein the lithium electrode current collector and the negative electrode current collector are electrically connected.   The lithium ion capacitor according to claim 1, wherein the electrolytic solution is an aprotic organic solvent. The lithium ion capacitor of any one of Claims 1-7 in which the said electrolyte solution contains the compound represented by following formula (1).

[In Formula (1), R ¹ represents a halogen atom, and R ² represents a methylene group, an alkylene group or a halogenated alkylene group which may have a substituent having 2 to 10 carbon atoms, or carbon. Arylene group or halogenated arylene group represented by formulas 6 to 20 (all of these alkylenes and arylenes may contain a substituent or a hetero atom, and q R ^{2 s} may be bonded to each other). X ¹ and X ² are each independently a hetero atom or NR ³ (R ³ is a hydrogen atom, an alkyl group or halogenated alkyl group having 1 to 10 carbon atoms, or 6 to 20 carbon atoms, An aryl group or a halogenated aryl group (both these alkylene and arylene may contain a substituent or a hetero atom), and M is a transition metal or a first Indicates ~ 15 group element, A ^{a +} is a metal ion represents a proton or onium ion, n is an integer of 0 to 8, m is an integer of 1 to 4, a and b are 1 Represents an integer of ˜3, q represents an integer of 1 to 4, and p represents p = b / a.]   The lithium ion capacitor according to claim 1, wherein a positive electrode potential after the positive electrode and the negative electrode are short-circuited is 2.0 V or less.

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