JP2011204704A - Electrode for lithium ion capacitor and lithium ion capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for lithium ion capacitor increasing the durability of the lithium ion capacitor, excellent in dispersibility and increasing electrode density and energy density and the lithium ion capacitor using the same.SOLUTION: The electrode for lithium ion capacitor is configured by forming an electrode composition layer consisting of an electrode active material, a conductive material, a carboxymethyl cellulose salt and a (meth) acrylate polymer on a collector. The lithium ion capacitor uses the same.

Description

  The present invention relates to an electrode for a lithium ion capacitor and a lithium ion capacitor. More specifically, the present invention relates to a lithium ion capacitor electrode and a lithium ion capacitor having excellent dispersibility and high durability.

  The demand for lithium-ion capacitors that are compact and lightweight, have high energy density, and can be repeatedly charged and discharged is rapidly expanding due to their characteristics. In addition, since the lithium ion capacitor has a high energy density and output density, it is expected to be used in small applications such as mobile phones and notebook personal computers, and in large applications such as in-vehicle use. For this reason, lithium ion capacitors are required to be further improved in accordance with expansion and development of applications, such as lowering resistance, increasing capacity, increasing withstand voltage, and improving mechanical characteristics.

  Lithium ion capacitors have a polarizable electrode on the positive electrode and a non-polarizable electrode on the negative electrode. By using an organic electrolyte, the operating voltage can be increased and the energy density can be increased, but the withstand voltage (durability) is low. There was a problem.

Then, using the binder containing the acrylate polymer which has a nitrile group for the purpose of improving a withstand voltage is proposed (patent document 1). The electrode for a lithium ion capacitor in Patent Document 1 is formed by forming an electrode composition layer made of an acrylate polymer having an electrode active material, a conductive material, carboxymethyl cellulose, and a nitrile group on a current collector. However, such an electrode has a low dispersibility, so that the electrode density and energy density are low and insufficient.
JP 2007-019108 A

  The present invention provides an electrode for a lithium ion capacitor that is excellent in dispersibility and can increase the electrode density and energy density in addition to enhancing the durability of the lithium ion capacitor, and a lithium ion capacitor using the electrode. For the purpose.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor, as an electrode for a lithium ion capacitor of the present invention, an electrode composition layer comprising an electrode active material, a conductive material, a carboxymethyl cellulose salt, and a (meth) acrylate polymer It has been found that by using a material formed on a current collector, the electrode density is increased and the energy density and durability of a lithium ion capacitor using the electrode are increased.

  The present invention has been completed based on these findings.

  Thus, according to the present invention, there is provided an electrode for a lithium ion capacitor in which an electrode composition layer comprising an electrode active material, a conductive material, a carboxymethylcellulose salt and a (meth) acrylate polymer is formed on a current collector. .

  According to the present invention, there is provided a lithium ion capacitor using the lithium ion capacitor electrode.

  Thus, according to the electrode for a lithium ion capacitor of the present invention, it is possible to easily manufacture a lithium ion capacitor that increases the electrode density and increases the energy density and durability. The lithium ion capacitor of the present invention includes a memory backup power source for a personal computer or a portable terminal, a power source for instantaneous power failure such as a personal computer, application to an electric vehicle or a hybrid vehicle, a solar power generation energy storage system used in combination with a solar cell, a battery, It can be suitably used for various applications such as a combined load leveling power source.

  The electrode for a lithium ion capacitor of the present invention is formed by forming an electrode composition layer comprising an electrode active material, a conductive material, a carboxymethyl cellulose salt and a (meth) acrylate polymer on a current collector.

(Electrode active material)
The electrode active material used for the lithium ion capacitor electrode of the present invention is a substance that transfers electrons in the lithium ion capacitor electrode.

Electrode active materials used for electrodes for lithium ion capacitors include positive electrodes and negative electrodes.
The electrode active material used for the positive electrode of the lithium ion capacitor electrode is not particularly limited as long as it can reversibly carry lithium ions and anions such as tetrafluoroborate. Specifically, an allotrope of carbon is usually used, and electrode active materials used in electric double layer capacitors can be widely used. Specific examples of the allotrope of carbon include activated carbon, polyacene (PAS), carbon whisker, and graphite, and these powders or fibers can be used. Among these, activated carbon is preferable. Specific examples of the activated carbon include activated carbon made from phenol resin, rayon, acrylonitrile resin, pitch, coconut shell, and the like. When carbon allotropes are used in combination, two or more types of carbon allotropes having different average particle diameters or particle size distributions may be used in combination. Moreover, as an electrode active material used for the positive electrode, in addition to the above materials, a polyacene-based skeleton structure which is a heat-treated product of an aromatic condensation polymer and has an atomic ratio of hydrogen atom / carbon atom of 0.50 to 0.05 A polyacene-based organic semiconductor (PAS) having the following can also be suitably used.

  The electrode active material used for the negative electrode of the lithium ion capacitor electrode may be any material that can reversibly carry lithium ions. Specifically, electrode active materials used in the negative electrode of lithium ion secondary batteries can be widely used. Of these, crystalline carbon materials such as graphite and non-graphitizable carbon, carbon materials such as hard carbon and coke, and polyacene-based materials (PAS) described as the electrode active material of the positive electrode are preferable. These carbon materials and PAS are obtained by carbonizing a phenol resin or the like, activated as necessary, and then pulverized.

  The shape of the electrode active material used for the electrode for a lithium ion capacitor is preferably a granulated particle. When the shape of the particles is spherical, a higher density electrode can be formed during electrode molding.

  The volume average particle diameter of the electrode active material used for the lithium ion capacitor electrode is usually 0.1 to 100 μm, preferably 0.5 to 50 μm, more preferably 1 to 20 μm for both the positive electrode and the negative electrode. These electrode active materials can be used alone or in combination of two or more.

(Conductive material)
The conductive material used for the electrode for the lithium ion capacitor of the present invention is composed of an allotrope of particulate carbon that has conductivity and does not have pores that can form an electric double layer, specifically, furnace black, Examples thereof include conductive carbon blacks such as acetylene black and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennaut Shap). Among these, acetylene black and furnace black are preferable.

  The volume average particle diameter of the conductive material used for the electrode for the lithium ion capacitor of the present invention is preferably smaller than the volume average particle diameter of the electrode active material, and the range is usually 0.001 to 10 μm, preferably 0.05 to. It is 5 μm, more preferably 0.01 to 1 μm. When the volume average particle diameter of the conductive material is within this range, high conductivity can be obtained with a smaller amount of use. These conductive materials can be used alone or in combination of two or more. The amount of the conductive material is usually 0.1 to 50 parts by weight, preferably 0.5 to 15 parts by weight, and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. When the amount of the conductive material is within this range, the capacity of the lithium ion capacitor using the obtained lithium ion capacitor electrode can be increased and the internal resistance can be decreased.

(Carboxymethylcellulose salt)
The carboxymethyl cellulose salt used for the electrode for the lithium ion capacitor of the present invention is a dispersant in the slurry composition for forming the electrode composition layer, specifically, carboxymethyl cellulose ammonium, carboxymethyl cellulose alkali metal, carboxymethyl cellulose alkaline earth. And similar metals. Among these, carboxymethyl cellulose ammonium and carboxymethyl cellulose alkali metal are preferable, and carboxymethyl cellulose ammonium is particularly preferable. When carboxymethyl cellulose ammonium is used in the carboxymethyl cellulose salt, the electrode active material, the conductive material and the binder of the (meth) acrylate polymer can be uniformly dispersed, the electrode density can be increased, and the energy density can be increased.

  The molecular weight of the carboxymethylcellulose salt used for the lithium ion capacitor electrode of the present invention is usually 10,000 to 450,000, preferably 100,000 to 400,000, particularly preferably 250,000 to 350,000. The molecular weight is a polystyrene equivalent value measured by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent. When the molecular weight is within this range, the electrode active material, the conductive material and the (meth) acrylate polymer can be uniformly dispersed, the electrode density can be increased, and the energy density can be increased. These carboxymethylcellulose salts can be used alone or in combination of two or more. The amount of the carboxymethyl cellulose salt is usually 0.01 to 15 parts by weight, preferably 0.1 to 10 parts by weight, more preferably 1 to 5 parts by weight with respect to 100 parts by weight of the electrode active material. When the amount of the carboxymethyl cellulose salt is within this range, the capacity of the lithium ion capacitor using the obtained lithium ion capacitor electrode can be increased and the internal resistance can be decreased.

((Meth) acrylate polymer)
Specifically, the (meth) acrylate polymer used for the electrode for a lithium ion capacitor of the present invention is represented by the general formula (1): CH ₂ = CR ¹ -COOR ² (wherein R ¹ represents a hydrogen atom or a methyl group). , R ² represents an alkyl group or a cycloalkyl group.) A polymer containing a total of 60 wt% or more, preferably 80 wt% or more of monomer units derived from the compound represented by The upper limit of the total monomer units in the polymer is 90% by weight. The (meth) acrylate polymer is obtained by copolymerizing a compound represented by the general formula (1) and a monomer copolymerizable therewith.

  Specific examples of the compound represented by the general formula (1) include ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-amyl acrylate, Acrylic acid alkyl esters such as isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate; cycloalkyl acrylate esters such as isobornyl acrylate, etc. Acrylate: ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-he methacrylate Methacrylic acid alkyl esters such as sil, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate and stearyl methacrylate; methacrylic acid cycloalkyl esters such as cyclohexyl methacrylate; and methacrylates It is done. Among these, acrylate is preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable in that the strength of the obtained electrode can be improved.

  In addition to the compound represented by the general formula (1), the (meth) acrylate polymer can be copolymerized with a compound copolymerizable therewith. Specifically, a nitrile compound or a dibasic acid can be used. Can be mentioned.

  Specific examples of the nitrile compound include acrylonitrile and methacrylonitrile. Among them, acrylonitrile is preferable in that the binding strength with the current collector is increased and the electrode strength can be improved. The amount of acrylonitrile in the copolymerization is usually 0.1 to 40 parts by weight, preferably 0.5 to 30 parts by weight, more preferably 100 parts by weight of the compound represented by the general formula (1). It is in the range of 1 to 20 parts by weight. When the amount of acrylonitrile is within this range, the binding property with the current collector is excellent, and the obtained electrode strength is increased.

The dibasic acid is an acid having a structure capable of separating two protons in water. Specific examples include itaconic acid, fumaric acid, maleic acid, etc. Among them, itaconic acid and fumaric acid are preferable. Itaconic acid is particularly preferable because it can enhance the binding property with the current collector and improve the electrode strength.
The amount of the dibasic acid in the copolymerization is usually 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight, particularly preferably 100 parts by weight of the compound represented by the general formula (1). Is in the range of 1 to 10 parts by weight. When the amount of the dibasic acid is within this range, the binding property with the current collector is excellent, and the obtained electrode strength is increased.

  The shape of the (meth) acrylate polymer used for the electrode for the lithium ion capacitor of the present invention is not particularly limited, but has good binding properties, and suppresses deterioration of the capacity of the prepared electrode due to repeated charge / discharge. Therefore, it is preferably particulate. Examples of the particulate binder include those in which binder particles such as latex are dispersed in water, and powders obtained by drying such a dispersion.

  The glass transition temperature (Tg) of the (meth) acrylate polymer used for the lithium ion capacitor electrode of the present invention is preferably 50 ° C. or lower, more preferably −40 to 0 ° C. When the glass transition temperature (Tg) of the (meth) acrylate polymer is in this range, it is excellent in binding property with a small amount of use, strong in electrode strength, rich in flexibility, and the electrode density is increased by a pressing process at the time of electrode formation. Can be easily increased.

  The number average particle diameter of the (meth) acrylate polymer of the electrode for a lithium ion capacitor of the present invention is not particularly limited, but is usually 0.0001 to 100 μm, preferably 0.001 to 10 μm, more preferably 0.00. It has a number average particle diameter of 01 to 1 μm. When the number average particle diameter of the (meth) acrylate polymer is in this range, an excellent binding force can be imparted to the polarizable electrode even with a small amount of use. Here, the number average particle diameter is a number average particle diameter calculated by measuring the diameter of 100 randomly selected (meth) acrylate polymer particles in a transmission electron micrograph and calculating the arithmetic average value thereof. The shape of the particles can be either spherical or irregular. These (meth) acrylate polymers can be used alone or in combination of two or more. The amount of the (meth) acrylate polymer is usually 0.1 to 50 parts by weight, preferably 0.5 to 20 parts by weight, and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. It is. When the amount of the (meth) acrylate polymer is within this range, sufficient adhesion between the obtained electrode composition layer and the current collector can be secured, the capacity of the lithium ion capacitor can be increased, and the internal resistance can be decreased. it can.

(Electrode composition layer)
The electrode composition layer of the lithium ion capacitor electrode of the present invention is provided on the current collector, but the formation method is not limited. Specifically, 1) an electrode-forming composition formed by kneading an electrode active material, a conductive material, and a (meth) acrylate polymer is formed into a sheet, and the obtained sheet-like electrode layer composition is converted into a current collector. Method of laminating on top (kneading sheet molding method) 2) A paste-like electrode forming composition comprising an electrode active material, a conductive material and a (meth) acrylate polymer is prepared, and the surface has a conductive adhesive layer Method of applying and drying on current collector (wet molding method) 3) Preparing composite particles consisting of electrode active material, conductive material and (meth) acrylate polymer, sheet molding on current collector, roll press And the like (dry molding method). Among them, 2) a wet molding method, 3) a dry molding method are preferable, and 3) a lithium ion capacitor from which the dry molding method can be obtained is more preferable in that the capacity can be increased and the internal resistance can be reduced.

  Alternatively, a sheet-like electrode layer composition can be prepared, a conductive adhesive can be formed on the sheet, and a current collector can be further laminated to obtain a lithium ion capacitor electrode.

The density of the electrode composition layer of the lithium ion capacitor electrode of the present invention is not particularly limited, but is usually 0.30 to 10 g / cm ³ , preferably 0.35 to 5.0 g / cm ³ , more preferably 0. .40-3.0 g / cm ³ . The thickness of the electrode composition layer is not particularly limited, but is usually 5 to 1000 μm, preferably 20 to 500 μm, more preferably 30 to 300 μm.

(Current collector)
Specifically, the current collector used for the electrode for the lithium ion capacitor of the present invention may be a metal, carbon, conductive polymer, or the like, and preferably a metal. As the current collector metal, aluminum, platinum, nickel, tantalum, titanium, other alloys and the like are usually used. Among these, it is preferable to use copper, aluminum, or an aluminum alloy in terms of conductivity and voltage resistance.

  The shape of the current collector is not particularly limited, but is in the form of a film or a sheet, and the sheet-like current collector may have pores. The sheet-like current collector may have a shape such as an expanded metal, a punching metal, or a net. When a sheet-like current collector having pores is used, the capacity per volume of the obtained electrode can be increased. When the sheet-like current collector has holes, the ratio of the holes is preferably 10 to 79 area%, more preferably 20 to 60 area%.

  Although the thickness of a collector is suitably selected according to the intended purpose, it is 1-200 micrometers normally, Preferably it is 5-100 micrometers, More preferably, it is 10-50 micrometers.

  The current collector is suitable when a conductive adhesive layer is formed on the surface thereof, because the adhesion between the electrode composition layer and the current collector can be improved and the internal resistance of the resulting lithium ion capacitor can be reduced. It is.

  The conductive adhesive layer has a conductive material and a (meth) acrylate polymer as essential components, and water or a conductive material, a (meth) acrylate polymer, and a dispersant added as necessary. The conductive adhesive slurry obtained by kneading in an organic solvent can be formed by applying to a current collector and drying. By forming the conductive adhesive layer, the binding property between the electrode composition layer and the current collector is improved and the internal resistance is reduced.

  As the conductive material, (meth) acrylate polymer and dispersant used for the conductive adhesive layer, any of those exemplified as the components used for the electrode composition layer can be used. The amount of each component is preferably 5 to 20 parts by weight based on the dry weight of the (meth) acrylate polymer and 1 to 5 parts by weight based on the dry weight based on 100 parts by weight of the conductive material. If the amount of the (meth) acrylate polymer is too small, adhesion between the electrode composition layer and the current collector may be insufficient. On the other hand, if the amount of the (meth) acrylate polymer is too large, the conductive material may not be sufficiently dispersed and the internal resistance may increase. Moreover, even if there is too little quantity of the said dispersing agent, dispersion | distribution of an electrically conductive material may become inadequate. On the other hand, if the amount of the dispersant is too large, the conductive material may be covered with the dispersant, and the internal resistance may increase.

  The method for forming the conductive adhesive layer on the current collector is not particularly limited. For example, it is formed by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating, or the like.

  The thickness of the conductive adhesive layer is usually 0.5 to 10 μm, preferably 2 to 7 μm.

  The lithium ion capacitor of this invention uses the said electrode for lithium ion capacitors.

(Lithium ion capacitor)
Specifically, the lithium ion capacitor of the present invention includes the lithium ion capacitor electrode, separator, and electrolyte solution obtained above.

  A separator will not be specifically limited if it can insulate between the electrodes for lithium ion capacitors, and can allow a cation and an anion to pass through. Specifically, polyolefins such as polyethylene and polypropylene, microporous membranes or nonwoven fabrics made of rayon or glass fiber, and porous membranes mainly made of pulp called electrolytic capacitor paper can be used. A separator is arrange | positioned between the electrodes for lithium ion capacitors so that said pair of electrode composition layer may oppose, and an element is obtained. Although the thickness of a separator is suitably selected according to a use purpose, it is 1-100 micrometers normally, Preferably it is 10-80 micrometers, More preferably, it is 20-60 micrometers.

The electrolytic solution is usually composed of an electrolyte and a solvent. The electrolyte can use lithium ions as cations. As anions, PF ₆ ⁻ , BF ₄ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ²⁻ , C (RfSO ₃ ) ³⁻ , RfSO ₃ ⁻ (Rf is a fluoro having 1 to 12 carbon atoms, respectively) Represents an alkyl group), F ⁻ , ClO ₄ ⁻ , AlCl ₄ ⁻ , AlF ₄ ^{− and the} like. These electrolytes can be used alone or in combination of two or more.

  The solvent of the electrolytic solution is not particularly limited as long as it is generally used as a solvent for the electrolytic solution. Specifically, carbonates such as propylene car boat, ethylene carbonate and butylene carbonate; lactones such as γ-butyrolactone; sulfolanes; nitriles such as acetonitrile; These solvents can be used alone or as a mixed solvent of two or more. Of these, carbonates are preferred.

  A lithium ion capacitor is obtained by impregnating the above element with an electrolytic solution. Specifically, the device can be manufactured by winding, laminating, or folding the device in a container as necessary, and pouring the electrolyte into the container and sealing it. Further, a device in which an element is previously impregnated with an electrolytic solution may be stored in a container. Any known container such as a coin shape, a cylindrical shape, or a square shape can be used as the container.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples. In the examples and comparative examples, “part” and “%” are based on weight unless otherwise specified. Each characteristic in an Example and a comparative example is measured in accordance with the following method.

(Battery characteristics and durability of lithium-ion capacitors)
A lithium-ion capacitor of a laminated laminate cell is produced using the electrodes for lithium-ion capacitors produced in Examples and Comparative Examples. As the battery characteristics of this lithium ion capacitor, the capacity and the internal resistance are measured by performing a charge / discharge operation after standing for 24 hours. Here, charging starts with a constant current of 2 A, and when the voltage reaches 3.6 V, the voltage is maintained for 1 hour to be constant voltage charging. Discharging is performed immediately after the end of charging until it reaches 1.9 V at a constant current of 0.9 A.
The capacity is calculated as the capacity per weight of the electrode active material from the energy amount at the time of discharge. The internal resistance is calculated from the voltage drop immediately after discharge.
Further, the durability is evaluated by calculating a capacity maintenance ratio with respect to an initial capacity after continuously applying a lithium ion capacitor in a constant temperature bath at 70 ° C. for 3.6 V for 1000 hours. The greater the capacity retention rate, the better the durability.

(Peel strength of electrode)
The electrode for the lithium ion capacitor is cut into a rectangular shape having a length of 100 mm and a width of 10 mm so that the coating direction of the electrode composition layer becomes a long side to obtain a test piece, and the cell composition is formed on the surface of the electrode composition layer with the electrode composition layer side down. Apply a tape (specified in JIS Z1522), and measure the stress when one end of the current collector is pulled vertically and pulled at a pulling speed of 50 mm / min. ing.). This measurement was performed 3 times, the average value was calculated | required, and this was made into peel strength. The higher the peel strength, the greater the binding force of the electrode composition layer to the current collector.

(Electrode density)
A lithium ion capacitor electrode having an electrode composition layer formed on a current collector was cut into 5 cm × 5 cm, and its thickness d1 (μm) and weight m1 (g) were measured. (Μm) and m0 (g) are measured, and the electrode density (g / cc) is calculated from the following equation.
Electrode density (g / cc) = (m1−m0) / [{(5 × 5) × (d1−d0)} × 10000]
It shows that it is excellent in a dispersibility, so that an electrode density is large.

Example 1
As an electrode active material for the positive electrode, 100 parts of activated carbon powder (MSP-20; manufactured by Kansai Thermochemical Co., Ltd.) having a volume average particle diameter of 8 μm, which is an alkali-activated activated carbon made from phenol resin, and a carboxy having a molecular weight of 335,000 as a dispersant. 1.5 parts aqueous solution of sodium methylcellulose (2200; manufactured by Daicel Chemical Industries, Ltd.) corresponding to a solid content of 2.0 parts, acetylene black (denka black powder; manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, number average particles 40% aqueous dispersion of (meth) acrylate polymer (copolymer obtained by emulsion polymerization of 80 parts of 2-ethylhexyl acrylate, 15 parts of acrylonitrile and 5 parts of acrylic acid) with a diameter of 0.25 μm To prepare a slurry for the electrode composition layer of the positive electrode by mixing 3.0 parts and ion-exchanged water so that the total solid content is 35%. The

  The positive electrode composition slurry was applied onto a 30 μm thick aluminum current collector by a doctor blade at an electrode forming speed of 10 m / min, and dried at 60 ° C. for 20 minutes and then at 120 ° C. for 20 minutes. After that, it is punched out into a square of 5 cm to obtain a positive electrode for a lithium ion capacitor having a thickness of 100 μm.

  As an electrode active material for the negative electrode, 100 parts of graphite (KS-6; manufactured by Timcal) having a volume average particle diameter of 4 μm, and as a dispersant, a 1.5% aqueous solution of sodium carboxymethylcellulose having a molecular weight of 335,000 (2200; Daicel Chemical) (Manufactured by Kogyo Co., Ltd.) 2.0 parts in terms of solid content, 5 parts of acetylene black (Denka black powder; manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material, and a (meth) acrylate polymer ( 80 parts of 2-ethylhexyl acrylate, 15 parts of acrylonitrile, a copolymer obtained by emulsion polymerization of 5 parts of acrylic acid) 40% aqueous dispersion of 3.0 parts in terms of solid content, and ion-exchanged water in total solids Mixing so that the partial concentration becomes 40%, to prepare a slurry for the electrode composition layer of the negative electrode.

  The negative electrode composition layer slurry was applied onto a 20 μm thick copper current collector by a doctor blade at an electrode forming speed of 10 m / min, and dried at 60 ° C. for 20 minutes and then at 120 ° C. for 20 minutes. After that, it is punched out in a square of 5 cm to obtain a negative electrode for lithium ion capacitor having a thickness of 100 μm.

Cellulose / rayon nonwoven fabric is used as the positive electrode and negative electrode for lithium ion capacitor and the separator is impregnated with an electrolytic solution at room temperature for 1 hour, and then two lithium ion capacitor electrodes pass through the separator to form an electrode composition layer. Arrange the 10 pairs of positive electrodes and 11 pairs of negative electrodes so that the electrodes for electrochemical elements do not come into electrical contact with each other so that the opposing surfaces of the positive and negative electrodes are 20 layers. A lithium ion capacitor having a laminated laminate cell shape is produced. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1.0 mol / liter in a mixed solvent of ethylene carbonate, diethyl carbonate and propylene carbonate in a weight ratio of 3: 4: 1 is used.

  As a lithium electrode of the laminated laminate cell, a lithium metal foil (82 μm thick, 5 cm long × 5 cm wide) bonded to an 80 μm thick stainless steel mesh is used, and the lithium electrode is completely opposed to the outermost negative electrode. One electrode is disposed on each of the upper and lower electrodes of the stacked electrodes. The terminal welding part (two sheets) of the lithium electrode current collector is resistance-welded to the negative electrode terminal welding part. Table 1 shows the measurement results of the characteristics of the lithium ion capacitor electrode and the lithium ion capacitor.

(Example 2)
In Example 1, as a binder, a (meth) acrylate polymer having a number average particle diameter of 0.25 μm (a copolymer obtained by emulsion polymerization of 80 parts of 2-ethylhexyl acrylate, 15 parts of acrylonitrile, and 5 parts of acrylic acid) ), A (meth) acrylate polymer (80 parts ethyl 2-ethylhexyl acrylate, 15 parts acrylonitrile, 5 parts itaconic acid) is obtained by emulsion polymerization. A lithium ion capacitor electrode (positive electrode, negative electrode) and lithium ion capacitor are prepared in the same manner as in Example 1 except that a 40% aqueous dispersion of copolymer) is used. Table 1 shows the measurement results of the characteristics of the lithium ion capacitor electrode and the lithium ion capacitor.

(Example 3)
In Example 1, a 1.5% aqueous solution of carboxymethyl cellulose ammonium having a molecular weight of 335,000 (DN-800H; manufactured by Daicel Chemical Industries, Ltd.) was used as the solid content instead of the 1.5% aqueous solution of sodium carboxymethyl cellulose as a dispersant. A lithium ion capacitor electrode (positive electrode, negative electrode) and lithium ion capacitor are prepared in the same manner as in Example 1 except that 2.0 parts are used. Table 1 shows the measurement results of the characteristics of the lithium ion capacitor electrode and the lithium ion capacitor.

Example 4
In Example 1, instead of a 1.5% aqueous solution of sodium carboxymethylcellulose as a dispersant, a 1.5% aqueous solution of molecular weight 335,000 carboxymethylcellulose ammonium (DN-800H; manufactured by Daicel Chemical Industries, Ltd.) corresponds to the solid content. 2.0 parts, (meth) acrylate polymer having a number average particle size of 0.25 μm as binder (copolymer obtained by emulsion polymerization of 80 parts of 2-ethylhexyl acrylate, 15 parts of acrylonitrile and 5 parts of acrylic acid Obtained by emulsion polymerization of (meth) acrylate polymer (80 parts of 2-ethylhexyl acrylate, 15 parts of acrylonitrile, 5 parts of itaconic acid) having a number average particle size of 0.25 μm instead of a 40% aqueous dispersion. Lithium ion in the same manner as in Example 1, except that a 40% aqueous dispersion of Capacitor electrodes (positive electrode and negative electrode) and a lithium ion capacitor are prepared. Table 1 shows the measurement results of the characteristics of the lithium ion capacitor electrode and the lithium ion capacitor.

(Comparative Example 1)
In Example 1, in place of the 1.5% aqueous solution of sodium carboxymethylcellulose as a dispersant, carboxymethylcellulose having a molecular weight of 590,000 was used in the same manner as in Example 1 except that 2.0 parts in terms of solid content was used. A lithium ion capacitor electrode (positive electrode and negative electrode) and a lithium ion capacitor are prepared. Table 1 shows the measurement results of the characteristics of the lithium ion capacitor electrode and the lithium ion capacitor.

(Table 1)

  As is clear from the above Examples and Comparative Examples, when the lithium ion capacitor electrode of the present invention is used, the electrode density is high, the electrode strength is excellent, and the energy density and durability can be increased.

Claims (3)

An electrode for a lithium ion capacitor, in which an electrode composition layer comprising an electrode active material, a conductive material, a carboxymethyl cellulose salt and a (meth) acrylate polymer is formed on a current collector. The electrode for a lithium ion capacitor according to claim 1, wherein the carboxymethylcellulose salt is carboxymethylcellulose ammonium. The lithium ion capacitor which uses the electrode for lithium ion capacitors of Claim 1 or 2.