JP2008091678A - Binder resin emulsion for hybrid capacitor electrode, hybrid capacitor electrode using binder resin emulsion, and hybrid capacitor including hybrid capacitor electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a binder resin emulsion for a hybrid capacitor electrode that improves high-speed charge/discharge characteristics of a hybrid capacitor, a hybrid capacitor electrode using the binder resin emulsion, and a hybrid capacitor including the hybrid capacitor electrode. <P>SOLUTION: It is devised to provide the binder resin emulsion for a hybrid capacitor electrode that includes water and an ethylene-(meta) acrylic acid copolymer, which is neutralized by a neutralizer and in which a mass ratio of an ethylene unit and a (meta) acrylic acid unit is 90/10-70/30 and an MI (melt index) is 200-3,000 g/10 min, the hybrid capacitor electrode using the binder resin emulsion, and the hybrid capacitor including the hybrid capacitor electrode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a resin emulsion for a hybrid capacitor electrode, a hybrid capacitor electrode using the resin emulsion, and a hybrid capacitor including the electrode.

  Energy storage devices are roughly classified into two types: secondary batteries such as lithium ion secondary batteries and electric double layer capacitors. In particular, the electric double layer capacitor can be charged / discharged with a large current, and therefore is promising for applications such as power source and brake regeneration of electric vehicles, load leveling and uninterruptible power supply.

Since this electric double layer capacitor is charged and discharged by a non-Faraday reaction, it can be rapidly charged and discharged as compared to a secondary battery that is charged and discharged by a Faraday reaction, and has the advantage that the cycle life is long and the durability during voltage application is high. is there.
On the other hand, the electrode of the electric double layer capacitor is made of activated carbon for both positive and negative electrodes, and its energy density is lower than that of the secondary battery.

  Then, the proposal which makes the positive electrode use the carbon material which occluded lithium ion in the negative electrode beforehand and expresses several times the energy of the electric double layer capacitor whose both electrodes are activated carbon is made (refer patent documents 1-3). ).

This device is charged / discharged by a non-Faraday reaction at the positive electrode and by a Faraday reaction at the negative electrode, so the charge / discharge mechanism is different from that of electric double layer capacitors and lithium ion secondary batteries, but it can be charged / discharged faster than secondary batteries. The energy density is higher than that of the electric double layer capacitor.
Hereinafter, this device is referred to as “hybrid capacitor”.

  Although the device was able to increase the energy as compared with the conventional electric double layer capacitor, the high-speed charge / discharge characteristics were inferior. This characteristic can be improved by increasing the adhesion between the electrode material particles or between the electrode material particles and the current collector to lower the internal resistance of the electrode, and a binder resin for an electrode having a high adhesion is required.

A conventional hybrid capacitor positive electrode is composed of activated carbon and carbon black. As a binder resin composition for adhering these particles or particles and a current collector, an aqueous dispersion emulsion of polytetrafluoroethylene (PTFE) particles. A two-component material consisting of sodium salt or ammonium salt of carboxymethyl cellulose (CMC) (as a water-soluble polymer thickener) has been used (see Patent Document 4).
However, these materials have a problem in the long-term reliability of the electrode because activated carbon is coated with a binder resin composition, making it difficult to adsorb and desorb ions.
Japanese Patent Application Laid-Open No. 64-014882 Japanese Patent Laid-Open No. 08-1007048 Japanese Patent No. 3807854 International Publication No. 98/058397 Pamphlet

On the other hand, the conventional hybrid capacitor negative electrode is a styrene-butadiene copolymer as a binder resin composition for adding a carbon material and, if necessary, carbon black, and adhering these particles or particles to a current collector. A two-component material comprising an aqueous dispersion emulsion (SBR) particles or SBR and a sodium salt or ammonium salt of carboxymethylcellulose (CMC) (as a water-soluble polymer thickener) has been used (see Patent Document 5). ).
Japanese Patent Laid-Open No. 05-074741

  However, SBR tends to be adsorbed on the carbon material that is the negative electrode active material and tends to cover the surface of the carbon material. Therefore, there is a problem that the electrolytic solution hardly penetrates into the composite layer of the carbon material, carbon black, and binder resin, and the charge / discharge characteristics are deteriorated.

  An object of the present invention is to provide a binder resin emulsion for a hybrid capacitor electrode that improves high-speed charge / discharge characteristics of the hybrid capacitor, a hybrid capacitor electrode using the resin emulsion, and a hybrid capacitor including this electrode.

  The present invention is an ethylene- (meth) neutralized with a neutralizer and having an ethylene unit / (meth) acrylic acid unit mass ratio of 90/10 to 70/30 and an MI (melt index) of 200 to 3000 g / 10 min. It is related with the binder resin emulsion for hybrid capacitor electrodes characterized by including an acrylic acid copolymer and water.

Moreover, this invention relates to the said binder resin emulsion for hybrid capacitor electrodes whose neutralizing agent is an amine compound.
Moreover, this invention relates to the said binder resin emulsion for hybrid capacitor electrodes whose neutralizing agent is an alkanolamine.
Moreover, this invention relates to the said binder resin emulsion for hybrid capacitor electrodes in which the carboxyl group of 10-100 mol% of the copolymer is neutralized.

The present invention is also a hybrid capacitor electrode having a current collector and a composite material layer provided on at least one surface of the current collector, wherein the composite material layer is used for an active material and the hybrid capacitor. The present invention relates to an electrode for a hybrid capacitor obtained by a step of applying a slurry containing a binder resin emulsion on a current collector and a step of removing a solvent from the applied slurry.
Furthermore, this invention relates to the hybrid capacitor containing the said electrode.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the binder resin emulsion for hybrid capacitor electrodes excellent in the high-speed charge / discharge characteristic and lifetime characteristic, the electrode for hybrid capacitors using the resin emulsion, and the hybrid capacitor containing this electrode.

  (1) The resin emulsion for an electrode for a hybrid capacitor of the present invention has an ethylene unit / (meth) acrylic acid unit mass ratio of 90/10 to 70/30 and an MI (melt index) neutralized with a neutralizing agent. 200-3000 g / 10 min ethylene- (meth) acrylic acid copolymer, solvent such as water and any other material.

(1-1) Ethylene- (meth) acrylic acid copolymer The ethylene- (meth) acrylic acid copolymer in the present invention is obtained by copolymerizing ethylene and (meth) acrylic acid as appropriate using a catalyst. can get. For the polymerization, an existing polymerization method such as pressure polymerization can be used.

  The resulting ethylene- (meth) acrylic acid copolymer is flexible in terms of electrode flexibility, flexibility, adhesion between the composite material layer and the current collector, and the balance of emulsification in a water-dispersed emulsion with a neutralizing agent. The mass ratio of ethylene unit / (meth) acrylic acid unit is 90/10 to 70/30, preferably 85/15 to 75/25, and MI (melt index, ASTM-D-1238, the same applies hereinafter) is 200 to 3000 g / 10 min, preferably 300 to 1500 g / 10 min. These ethylene- (meth) acrylic acid copolymers are used alone or in combination of two or more.

(1-2) Neutralizing agent In the present invention, the neutralizing agent is not particularly limited as long as it is a basic compound having the ability to neutralize the carboxyl group of the ethylene- (meth) acrylic acid copolymer. For example, amine compounds (monoamines such as ammonia, triethylamine, diethylamine, 2-amino-2-methyl-1-propanol, N, N-dimethylethanolamine, N, N-diethylethanolamine, 2-dimethylamino-2-methyl) -1-propanol, monoisopropanolamine, diisopropanolamine, triisopropanolamine, monoethanolamine, diethanolamine, triethanolamine, alkanolamines such as N-ethyldiethanolamine, N-methyldiethanolamine), hydroxides (sodium hydroxide, Potassium hydroxide), morpholine and the like.

  Among these, amine compounds are preferable because they are easily available and do not contain metal ions that remain without being volatilized even when heated. Among them, amine compounds are preferable, and they have high hydrophilicity and are excellent in water-dispersed emulsion ability. In view of the above, alkanolamine is more preferable. These neutralizing agents are used alone or in combination of two or more.

(1-3) Solvent The solvent added to the binder resin emulsion according to the present invention is water. Therefore, the binder resin emulsion according to the present invention exists in the form of an aqueous dispersion emulsion.
In addition, a solvent other than water can be added as necessary for adjusting the particle size of the obtained water-dispersed emulsion. Although there is no restriction | limiting in particular as solvents other than water, Lower alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol which have high hydrophilicity, are preferable. These solvents are used alone or in combination of two or more.

(1-4) Other materials Other materials can be added to the binder resin emulsion according to the present invention as necessary. Other materials include, for example, a cross-linking component to completely compensate the swelling resistance to the electrolyte, a rubber component to supplement the flexibility and flexibility of the electrode, and an increase to improve the electrode coatability of the slurry. Examples thereof include a viscosity agent (viscosity modifier), an anti-settling agent, an antifoaming agent, and a leveling agent.

  These other materials may be added to the binder resin emulsion of the present invention in advance, or may be added when adjusting the slurry by mixing the active material and the binder resin emulsion. These other materials are used alone or in combination of two or more.

(1-5)
The binder resin emulsion which becomes this invention contains what neutralized the ethylene- (meth) acrylic acid copolymer with the neutralizing agent as mentioned above.
The neutralization reaction between the ethylene- (meth) acrylic acid copolymer and the neutralizing agent is not particularly limited as long as it is in the presence of water, but usually proceeds at normal pressure. In the case of normal pressure, the temperature range in which the reaction is possible is preferably 0 to 100 ° C. in which water maintains a liquid state, more preferably 40 to 95 ° C., still more preferably 70 to 95 ° C., and more preferably 80 to 95 ° C. Particularly preferred.

  Further, it is more preferable to raise the temperature to the melting point or higher of the copolymer to be used from beginning to end. The reaction time is preferably 10 minutes or more in terms of reaction efficiency, work efficiency, etc., more preferably 30 minutes to 20 hours, and even more preferably 1 to 10 hours.

  The amount of the neutralizing agent is not particularly limited as long as it is at least the minimum amount necessary for the aqueous dispersion emulsion of the ethylene- (meth) acrylic acid copolymer, but the excess neutralizing agent does not remain. In this respect, 10 to 100 mol% of the carboxyl group of the copolymer is preferable, 30 to 100 mol% is more preferable, and 50 to 100 mol% is more preferable.

  Specifically, 0.1 to 1 mol of 1N neutralizer, preferably 0.3 to 1 mol of 1 mol of (meth) acrylic acid contained in the ethylene- (meth) acrylic acid copolymer. 1 mol, more preferably 0.5 to 1 mol.

  The amount of the solvent such as water is not particularly limited as long as it is more than the minimum amount necessary for making the above-mentioned copolymer into an aqueous dispersion emulsion, but the slurry is prepared by mixing the active material and the binder resin. In some cases, a solvent is added to adjust the viscosity, and therefore it is preferable that the binder resin emulsion is not excessively present.

For example, in the case of water, 30 to 95% by mass is preferable, 40 to 90% by mass is more preferable, and 50 to 85% by mass is further based on the total mass of the ethylene- (meth) acrylic acid copolymer and water. preferable.
Moreover, when adding other solvents other than water, 0.1-30 mass% is preferable with respect to the whole solvent containing water, for example, 0.1-20 mass% is more preferable, and other solvents are more preferable 1-10. More preferred is mass%.

  You may adjust suitably the quantity of the water of a neutralizing agent on the basis of the magnitude | size of the particle | grains of the binder resin emulsion obtained. For example, the average particle size of the binder resin emulsion is preferably 0.001 to 10 μm, more preferably 0.01 to 1 μm, and still more preferably 0.05 to 0.3 μm. When the average particle size is 0.001 μm or more, the voids existing on the surface of the hybrid capacitor electrode active material are not filled, and the agglomerates (spatters) are prepared when the active material and the binder resin emulsion are mixed to prepare a slurry. Without being formed, and good handleability of the slurry and applicability to the current collector can be obtained.

(2) Use of binder resin emulsion The binder resin emulsion which becomes this invention is manufactured as mentioned above, and is normally used in the state of water dispersion emulsion as it is.
The binder resin emulsion according to the present invention is suitably used as a binder used for an electrode of a hybrid capacitor, particularly a hybrid capacitor.

  Here, the “hybrid capacitor” is an energy device comprising an activated carbon as a positive electrode, a carbon material capable of inserting and extracting lithium in a negative electrode, and an organic solution containing a lithium salt as an electrolytic solution, in which lithium is previously stored in the negative electrode. Say.

  Any known active carbon can be used as the positive electrode active material of the hybrid capacitor according to the present invention, and examples thereof include aggregates such as powder formed bodies, fibrous forms, and sheet forms.

  Moreover, the aggregate | assembly should just contain activated carbon substantially, and may contain other positive electrode constituent materials, such as carbon black, other than that. The material for the positive electrode current collector is a metal such as aluminum, titanium, or tantalum, or an alloy thereof. In particular, aluminum or an alloy thereof is preferable in terms of energy density because it is lightweight.

  As the negative electrode active material of the hybrid capacitor according to the present invention, any known carbon material can be used, for example, natural graphite, artificial graphite, graphitized mesocarbon microsphere, graphite whisker, graphitized carbon fiber, One type or two or more types can be selected and used from the group consisting of non-graphitizable carbon material and amorphous carbon obtained by heat treatment of vapor grown carbon, petroleum coke, coal coke or pitch coke.

  Moreover, the negative electrode of the present invention may contain a positive electrode constituent material such as carbon black. As the negative electrode current collector, for example, a foil such as nickel or copper, a mesh, or the like can be used, but a mesh is preferable in order to increase the efficiency of occlusion of lithium in advance. The integration of the negative electrode mixture and the current collector can be performed, for example, by a molding method such as a roll press.

  By inserting lithium ions into the negative electrode thus obtained, and further disposing the positive electrode through a separator and injecting an electrolytic solution, for example, a hybrid capacitor can be obtained.

  In the present invention, the amount of lithium ions inserted into the negative electrode for a hybrid capacitor is preferably 50 to 100%, more preferably 90 to 100% of the Li storage capacity of the negative electrode active material. If it is less than 50%, the cycle life of the hybrid capacitor tends to deteriorate, and if it exceeds 100%, lithium is deposited on the negative electrode material and the cell safety tends to be lowered.

  As a method for inserting lithium ions into the negative electrode for a hybrid capacitor according to the present invention, any known method can be used. For example, a method in which a negative electrode and a lithium metal are directly opposed to each other and immersed in an electrolytic solution, or current / voltage There is a method of inserting electrochemically using a control device. Among these, a method using a control device is preferable from the viewpoint that the amount of lithium inserted into the negative electrode becomes clear, and a direct facing method is preferable from the viewpoint of simplicity of the process.

  The material and shape of the separator of the hybrid capacitor according to the present invention are not particularly limited, but are preferably selected from materials that are stable with respect to the electrolyte and excellent in liquid retention. , Porous sheets made of polyolefin such as polyethylene and polypropylene, and nonwoven fabrics.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , for example, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane. 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl Carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, acetic acid A so-called organic electrolyte solution dissolved in a simple substance such as ethyl, a non-aqueous solvent such as a two-component or three-component mixture can be used.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to these.
<Preparation of binder resin emulsion>

Example 1
A 2 liter separable flask equipped with a stirrer, thermometer and condenser was prepared. Ethylene- (meth) acrylic acid copolymer (MI: 1300 g / 10 min, ethylene unit / acrylic acid unit = 80/20 <mass ratio>, melting point: 75 ° C.) 300 g, purified water 1162.9 g and N, 37.14 g of N-dimethylethanolamine (an amount corresponding to neutralizing 50 mol% of the carboxyl group of the copolymer) was added to the above separable flask.

  The temperature of the flask was raised to 95 ° C. while stirring, and then kept at that temperature for 2 hours, and the copolymer was made into a water-dispersed emulsion by a neutralization reaction. Then, it cooled to room temperature and obtained the binder resin emulsion of this invention. The average particle size of the obtained emulsion was 0.06 μm, and the non-volatile content after drying at 150 ° C. for 2 hours under atmospheric pressure was 20.1% by mass.

Example 2
A binder resin emulsion of the present invention was obtained in the same manner as in Example 1 except that the MI of the ethylene-acrylic acid copolymer was changed to 300 g / 10 min. The average particle size of the obtained emulsion was 0.08 μm, and the non-volatile content after drying at 150 ° C. for 2 hours under atmospheric pressure was 20.2 mass%.

Comparative Example 1
A styrene-butadiene copolymer (SBR) 40 mass% water-dispersed emulsion manufactured by Nippon Zeon was prepared.

Comparative Example 2
A 60% by mass aqueous dispersion of polytetrafluoroethylene manufactured by Daikin Chemical Industries was prepared.

Example 3
Production of positive electrode:
A slurry was prepared by kneading and dispersing 100 parts by weight of activated carbon powder, 10 parts by weight of carbon black, 10 parts by weight of carboxymethylcellulose ammonium and 10 parts by weight of the binder resin emulsion of Example 1. This slurry was applied onto an etched aluminum foil (thickness 20 μm) and dried at 100 ° C. for 1 hour. This was pressed, punched to a diameter of 15 mm (φ), and vacuum-dried at 120 ° C. for 3 hours was used as the positive electrode.

Production of negative electrode:
A slurry was prepared by blending and kneading graphite, an aqueous sodium carboxymethyl cellulose solution, and the binder resin emulsion of Example 1 to 97.5 wt%, 1.25 wt%, and 1.25 wt%, respectively, in terms of solid content. . This slurry was applied onto a rolled copper foil (thickness: 18 μm) and dried at 80 ° C. for 1 hour. This was pressed, punched to a diameter of 15 mm (φ), and vacuum-dried at 120 ° C. for 3 hours to make a negative electrode.

Li insertion into the negative electrode (preliminary charge)
The negative electrode and lithium metal are opposed to each other with a separator interposed therebetween, and an electrolyte (LiPF ₆ is mixed in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) (volume ratio of EC and EMC is 1: 3) is 1. A cell was prepared by immersing in a cell dissolved in a concentration of 5 mol / liter.

When this cell was connected to a charge / discharge tester, Li was inserted into the negative electrode at a constant current (0.28 mA / cm ² ), and when the potential of the negative electrode became 0 V (vsLi / Li ⁺ ), Li was charged at a constant voltage. Inserted. The end was made when the current value reached 0.02 mA. Hereinafter, this operation is referred to as “preliminary charging”.

Fabrication of Hybrid Capacitor Cell The above positive electrode and the precharged negative electrode are opposed to each other with a separator interposed therebetween, and an electrolytic solution (LiPF ₆ is a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume of EC and EMC). The cell was prepared by dipping in a ratio of 1: 3) dissolved in a concentration of 1.5 mol / liter.

Discharge capacity and charge / discharge efficiency Place the cell prepared above in a constant temperature bath at 25 ° C., and charge it using a charge / discharge test device until the potential difference between the positive electrode and the negative electrode reaches 4V at a current value corresponding to the 4C rate. The battery was discharged at the same current value until the potential difference reached 2V. This operation was repeated four times, and the discharge amount in the fourth charge / discharge was defined as the discharge capacity. Furthermore, the ratio of discharge amount / charge amount at this time was defined as charge / discharge efficiency.

Cycle capacity maintenance rate In addition, the cell was charged at a current value corresponding to the 4C rate until the potential difference between the positive electrode and the negative electrode reached 4V, and discharged at the same current value until the potential difference reached 2V. This operation was repeated 10,000 times to measure the discharge capacity, and the value of the discharge capacity at the 10,000th cycle / the discharge capacity at the fourth cycle was defined as the cycle capacity retention rate.

Example 4
Production of positive electrode:
A binder resin emulsion was prepared in the same manner as in Example 3 except that Example 2 was used.
Production of negative electrode:
A binder resin emulsion was prepared in the same manner as in Example 3 except that Example 2 was used.
The preliminary charging, the production of the hybrid capacitor cell, the discharge capacity, the charge / discharge efficiency and the cycle capacity retention rate were the same as in Example 3.

Comparative Example 3
Production of positive electrode:
A binder resin emulsion was prepared in the same manner as in Example 3 except that Comparative Example 2 was used.
Preparation of Negative Electrode A negative electrode was prepared in the same manner as in Example 3 except that the binder resin emulsion was changed to Comparative Example 1.
The preliminary charging, the production of the hybrid capacitor cell, the discharge capacity, the charge / discharge efficiency and the cycle capacity retention rate were the same as in Example 3.
The results of Examples 3 and 4 and Comparative Example 3 are shown together in Table 1.

  As shown in Table 1, it is clear that Examples 3 and 4 are superior to Comparative Example 3 in all of discharge capacity, charge / discharge efficiency, and cycle capacity retention rate.

Claims (6)

  Ethylene- (meth) acrylic acid copolymer having a mass ratio of ethylene unit / (meth) acrylic acid unit of 90/10 to 70/30 and MI (melt index) of 200 to 3000 g / 10 min neutralized with a neutralizing agent A binder resin emulsion for hybrid capacitor electrodes, comprising coalescence and water.   The binder resin emulsion for hybrid capacitor electrodes according to claim 1, wherein the neutralizing agent is an amine compound.   The binder resin emulsion for hybrid capacitor electrodes according to claim 2, wherein the neutralizing agent is an alkanolamine.   The binder resin emulsion for hybrid capacitor electrodes according to any one of claims 1 to 3, wherein 10 to 100 mol% of carboxyl groups of the copolymer are neutralized.   It is a hybrid capacitor electrode which has an electrical power collector and the composite material layer provided in at least 1 surface of this electrical power collector, Comprising: The said composite material layer is an active material and any one of Claims 1-4. The electrode for hybrid capacitors obtained by the process of apply | coating the slurry containing the binder resin emulsion for hybrid capacitors on a collector, and the process of removing a solvent from the apply | coated slurry.   A hybrid capacitor comprising the electrode according to claim 5.