WO2014006973A1 - Electrode for electricity storage devices, electricity storage device using same, and method for producing same - Google Patents

Abstract

For the purpose of obtaining a novel electricity storage device having high weight energy density and high rate characteristics, the present invention provides an electrode for electricity storage devices, which is provided with a porous layer (2) that is formed on at least a part of the surface of a collector (1). The porous layer is formed of at least the components (X) and (Y) described below, and the surface of the porous layer is configured of a recessed and projected structure wherein a plurality of recesses having an average diameter of 50-10,000 μm are distributed. (X) an active material which intercalates and deintercalates ions (Y) a binder

Description

Electrode for power storage device, power storage device using the same, and method for producing the same

TECHNICAL FIELD The present invention relates to an electrode for an electricity storage device, an electricity storage device using the electrode, and a method for producing the electrode, and more particularly relates to a novel electrode for an electricity storage device having high weight energy density and high rate characteristics, an electricity storage device using the electrode, and a method for producing the electrode. is there.

In recent years, with the advancement and development of electronic technology in portable PCs, mobile phones, personal digital assistants (PDAs), secondary batteries that can be repeatedly charged and discharged are widely used as power storage devices for these electronic devices. Yes. In such an electrochemical storage device such as a secondary battery, it is desired that the material used as an electrode has a high capacity and high rate characteristics.

The electrode of the electricity storage device contains an active material having a function capable of inserting and removing ions. The insertion / desorption of ions of the active material is also referred to as so-called doping / dedoping, and the amount of doping / dedoping per certain molecular structure is called the doping rate (or doping rate). As a result, the capacity can be increased.

Electrochemically, it is possible to increase the capacity of a battery by using a material having a large amount of ion insertion / desorption as an electrode. More specifically, lithium secondary batteries, which are attracting attention as power storage devices, use a graphite-based negative electrode that can insert and desorb lithium ions, and about one lithium ion is inserted per six carbon atoms. -Desorption and high capacity have been achieved.

Among such lithium secondary batteries, a lithium-containing transition metal oxide such as lithium manganate or lithium cobaltate is used for the positive electrode, and a carbon material capable of inserting and removing lithium ions is used for the negative electrode. Lithium secondary batteries that face each other in an electrolytic solution have a high energy density, and thus are widely used as power storage devices for the electronic devices described above.

However, the lithium secondary battery is a secondary battery that obtains electric energy by an electrochemical reaction, and has a drawback that the output density is low because the speed of the electrochemical reaction is low. Furthermore, since the internal resistance of the secondary battery is high, rapid discharge is difficult and rapid charge is also difficult. Moreover, since an electrode and electrolyte solution deteriorate by the electrochemical reaction accompanying charging / discharging, generally a lifetime, ie, a cycling characteristic, is not good.

Therefore, in order to improve the above problem, a lithium secondary battery using a conductive polymer such as polyaniline having a dopant as a positive electrode active material is also known (see Patent Document 1).

However, in general, a secondary battery having a conductive polymer as a positive electrode active material is an anion transfer type in which an anion is doped into the conductive polymer during charging and the anion is dedoped from the polymer during discharging. Therefore, when a carbon material that can insert and desorb lithium ions is used as the negative electrode active material, a cation-moving rocking chair type secondary battery in which cations move between both electrodes during charge and discharge cannot be configured. . That is, the rocking chair type secondary battery has the advantage that the amount of the electrolyte is small, but the secondary battery having the conductive polymer as the positive electrode active material cannot do so, and contributes to the miniaturization of the electricity storage device. I can't.

In order to solve such problems, a large amount of electrolyte solution is not required, and the ion concentration in the electrolyte solution is not substantially changed, thereby improving the capacity density per volume, weight, and energy density. A cation migration type secondary battery has also been proposed. In this method, a positive electrode is formed using a conductive polymer having a polymer anion such as polyvinyl sulfonic acid as a dopant, and lithium metal is used for the negative electrode (see Patent Document 2).

JP-A-3-129679 Japanese Patent Laid-Open No. 1-132052

However, the secondary battery is still not sufficient in performance. That is, the battery has a lower weight energy density and lower high rate characteristics than a lithium secondary battery using a lithium-containing transition metal oxide such as lithium manganate or lithium cobaltate for the positive electrode.

The present invention has been made in order to solve the above-described problems in an electricity storage device such as a conventional lithium secondary battery, and is a novel electrode for an electricity storage device having a high weight energy density and a high rate characteristic. A power storage device used and a method for manufacturing the same are provided.

The present invention is an electrode for an electricity storage device comprising a porous layer formed on at least a part of a current collector surface, wherein the porous layer comprises at least the following (X) and (Y), The first gist of the present invention is an electrode for an electricity storage device having a concavo-convex structure in which a plurality of concave portions having an average diameter of 50 to 10,000 μm are distributed.
(X) An active material that inserts and desorbs ions.
(Y) Binder.

Further, a positive electrode for an electricity storage device using the above electrode is a second summary, and an electricity storage device in which this is a positive electrode and the negative electrode contains the following (Z) is a third summary.
(Z) At least one selected from a compound or metal capable of inserting / extracting ions.
And the manufacturing method of the electrode for electrical storage devices provided with the process of carrying out the ultrasonic dispersion process of the porous layer composition which consists of an active material (X) and a binder (Y) at least, and a solvent makes a 4th summary.

That is, the present inventors made extensive studies to obtain an electricity storage device having a high weight energy density and a high rate characteristic. In general, in an electricity storage device, in order to improve the contact ratio with the current collector to achieve high weight energy density, etc., all electrode surfaces (all surfaces as well as the surface in contact with the current collector) are flat or submicron. Only the pores are present. However, the present inventors paid attention to the fact that the size of the recesses on the surface of the porous electrode affects battery characteristics such as high capacity density, and as a result of further research, the concavo-convex structure existing on the electrode surface In addition, if a relatively large recess is formed, thereby forming an electrolytic solution reservoir capable of storing a specific amount of electrolytic solution on the electrode surface, it is surprisingly contrary to conventional technical common sense that charging / discharging of the active material is performed. It has been found that ion migration at the time can be performed smoothly, whereby an electricity storage device having a high weight energy density and a high rate characteristic can be obtained.

As described above, an electrode for an electricity storage device comprising a porous layer formed on at least a part of a current collector surface, wherein the porous layer is composed of at least the above (X) and (Y), If the surface of the layer is an electrode for an electricity storage device having an uneven structure in which a plurality of recesses having an average diameter of 50 to 10,000 μm are distributed, the electricity storage device using this will have excellent weight energy density and high rate characteristics. become.

Further, when the liquid pool ratio of the concavo-convex structure is 3 to 70%, the obtained electricity storage device is further excellent in weight energy density.

Furthermore, when the active material (X) is a conductive polymer, it is possible to realize an electricity storage device that can reduce deterioration of electrodes and electrolyte.

When the main component of the binder (Y) is an anionic polymer, the ion concentration in the electrolytic solution does not substantially change, so that a large amount of the electrolytic solution is not required, and the storage device is downsized. Can be realized.

When the electrode for an electricity storage device is used as a positive electrode, the obtained electricity storage device can realize a high weight energy density.

Furthermore, an electricity storage device having an electrolyte layer and a positive electrode and a negative electrode provided to face each other with the electrolyte layer interposed therebetween, wherein the positive electrode is the electrode for the electricity storage device, and the negative electrode is an electricity storage device containing the following (Z) It has high performance battery characteristics.
(Z) At least one selected from a compound or metal capable of inserting / extracting ions.

In addition, according to the method for producing an electrode for an electricity storage device comprising a step of ultrasonically dispersing a porous layer composition composed of at least the active material (X) and the binder (Y) and a solvent, the electricity storage is more excellent in energy characteristics. A device can be obtained.

It is sectional drawing which shows the structure of the electrode for electrical storage devices. It is sectional drawing which shows the structure of an electrical storage device. It is sectional drawing for demonstrating the measurement of the liquid pool rate of the electrode for electrical storage devices.

Hereinafter, embodiments of the present invention will be described in detail. However, the description described below is an example of embodiments of the present invention, and the present invention is not limited to the following contents.

As shown in FIG. 1, the electrode for an electricity storage device of the present invention is an electrode 2 composed of a porous layer formed on at least a part of the surface of a current collector 1, and this electrode 2 has an uneven structure on the surface. And having a plurality of relatively large recesses having a specific average diameter. In addition, the hole 2 'indicates a hole in the porous layer.

As shown in FIG. 2, the electricity storage device of the present invention has an electrolyte layer 3 and a positive electrode 2 and a negative electrode 4 provided to face each other, and the positive electrode 2 is the electrode 2 described above. In addition, the negative electrode 4 includes at least one selected from a compound or metal capable of inserting / extracting ions. Hereinafter, it demonstrates in detail in order.

<About electrodes>
The electrode for an electricity storage device of the present invention is a porous layer composed of at least an active material (X) for inserting / extracting ions and a binder (Y).

Examples of the active material (X) from which ions are inserted / extracted (hereinafter sometimes referred to as “active material”) include, for example, polyacetylene, polypyrrole, polyaniline, polythiophene, polyfuran, polyselenophene, and polyisothianaphthene. , Polyphenylene sulfide, polyphenylene oxide, polyazulene, poly (3,4-ethylenedioxythiophene), and conductive polymer materials such as substituted polymers thereof, or polyacene, graphite, carbon nanotube, carbon nanofiber, graphene, etc. Examples thereof include carbon materials. In addition, inorganic materials such as lithium cobaltate, lithium manganate, lithium nickelate, and lithium iron phosphate are also included. In particular, polyaniline or polyaniline derivatives having a large electrochemical capacity are particularly preferably used.

Examples of the polyaniline derivative include at least a substituent such as an alkyl group, an alkenyl group, an alkoxy group, an aryl group, an aryloxy group, an alkylaryl group, an arylalkyl group, and an alkoxyalkyl group at positions other than the 4-position of the aniline. One that has one. Among them, o-substituted anilines such as o-methylaniline, o-ethylaniline, o-phenylaniline, o-methoxyaniline, o-ethoxyaniline, m-methylaniline, m-ethylaniline, m-methoxyaniline, m M-substituted anilines such as -ethoxyaniline and m-phenylaniline are preferably used. These may be used alone or in combination of two or more.

A conductive polymer material such as polyaniline is usually in a doped state (in which ions are inserted). Further, when the above (X) is not in a doped state, a doped state is obtained by performing a doping process. Specific examples of the doping treatment include a method of mixing a dopant containing atoms to be doped into a starting material (for example, aniline), a method of reacting a product material (for example, polyaniline) with a dopant, and the like.

As described above, the insertion / desorption of ions in (X) is also referred to as so-called doping / dedoping. The doping / dedoping amount per certain molecular structure is called the doping rate, and the doping rate is The higher the material, the higher the capacity of the battery. The ions at this time are sometimes called dopants.

For example, the doping rate of the conductive polymer as the X component is said to be 0.5 for polyaniline and 0.25 for polypyrrole. The higher the doping rate, the higher the capacity of the battery can be formed. At this time, for example, the conductivity of the conductive polyaniline is about 10 ⁰ to 10 ³ S / cm in the doped state, and 10 ⁻¹⁵ to 10 ⁻² S / cm in the undoped state.

Therefore, the above (X) may be in a doped state (during discharging) during charging or discharging, or may be in a dedope state or a reduced dedoping state (during charging).

By the way, in order to make the above (X) into the reduction-dedoped state in the initial stage, there is a method of making it directly into the reduction-dedoped state, but in general, a reduction step is required after making the dedope state. First, a dedope state is obtained by neutralizing the dopant which (X) has. For example, (X) in a dedope state is obtained by stirring in a solution for neutralizing the dopant (X) and then washing and filtering. Specifically, in order to dedope polyaniline having tetrafluoroboric acid as a dopant, a method of neutralizing by stirring in an aqueous sodium hydroxide solution can be mentioned.

Next, a reduced dedoped state is obtained by reducing (X) in the undoped state. For example, stirring in a solution for reducing (X) in the dedope state, followed by washing and filtering yields (X) in the reduced dedope state. Specifically, a method of reducing polyaniline in a dedoped state by stirring in an aqueous methanol solution of phenylhydrazine can be mentioned.

The electricity storage device of the present invention comprises an electrode using a material containing at least the above (X) and a binder (Y) described below.

<About binder (Y)>
Here, examples of the binder (Y) include not only binders such as vinylidene fluoride and styrene-butadiene rubber, but also polyanions, anion compounds having a relatively large molecular weight, anionic polymers having low solubility in an electrolyte solution, and the like. can give.

Especially, it is preferable that the main component of binder (Y) consists of the said anionic polymer. Here, the main component means a component that occupies the majority of the whole, and includes the case where the whole consists of only the main component.

Furthermore, among anionic polymers, compounds having a carboxyl group in the molecule are preferably used, and polycarboxylic acids that are polymers in particular are more preferably used.

Examples of the polycarboxylic acid include polymaleic acid, polyacrylic acid, polymethacrylic acid, polyvinylbenzoic acid, polyallylbenzoic acid, polymethallylbenzoic acid, polymaleic acid, polyfumaric acid, polyglutamic acid, and polyaspartic acid. Acrylic acid and polymethacrylic acid are particularly preferably used. These may be used alone or in combination of two or more.

In the electricity storage device according to the present invention, when a polymer such as the above polycarboxylic acid is used as the binder (Y), this polymer also functions as a dopant, so that it has a rocking chair type mechanism and has characteristics of the electricity storage device. It seems to be involved in improvement.

Examples of the polycarboxylic acid include those in which a carboxylic acid having a carboxyl group in the molecule is converted to a lithium type. The exchange rate for the lithium type is preferably 100%, but the exchange rate may be low depending on the situation, and is preferably 40% to 100%.

The binder (Y) is usually used in an amount of 1 to 100 parts by weight, preferably 2 to 70 parts by weight, and most preferably 5 to 40 parts by weight with respect to 100 parts by weight of the active material (X). . If the amount of the binder (Y) relative to the (X) is too small, a uniform electrode tends not to be obtained. On the other hand, even if the amount of the binder (Y) relative to the (X) is too large, the energy density is high. There is a tendency that an electricity storage device cannot be obtained.

The electrode according to the electricity storage device of the present invention is composed of a composite composed of at least the above (X) and (Y), and is preferably formed on a porous sheet. Usually, the thickness of the electrode is preferably 1 to 500 μm, and more preferably 10 to 300 μm.

The thickness of the electrode is obtained by measuring the electrode using a dial gauge (manufactured by Ozaki Mfg. Co., Ltd.) whose tip shape is a flat plate having a diameter of 5 mm, and obtaining the average of 10 measured values with respect to the surface of the electrode. When an electrode (porous layer) is provided on the current collector and composited, the thickness of the composite is measured in the same manner as described above, the average of the measured values is obtained, and the thickness of the aluminum foil is subtracted. The thickness of the electrode can be obtained by calculation.

The electrode for an electricity storage device of the present invention is formed, for example, as follows. Dissolve the binder (Y) in water to make an aqueous solution, and then add an active material (X) and, if necessary, a conductive assistant such as conductive carbon black to prepare a paste. To do. A composite having a layer of a uniform mixture of the X component and the Y component (and, if necessary, a conductive aid) on the current collector by evaporating water after applying this on the current collector As a result, a sheet electrode can be obtained.

And the electrode for electrical storage devices of this invention consists of a porous layer, and has an uneven structure in the surface (surface which contacts electrolyte solution). When an electricity storage device is manufactured, an electrolytic solution can be stored in the uneven structure, which is a feature of the present invention. In addition, the convex part which forms the uneven structure of this invention is formed from the porous layer, and the electrolyte solution which exists in a recessed part, and the electrolyte solution in a convex porous layer may be connected by the through-hole. .

Such a concavo-convex structure can be formed using, for example, the following method. When preparing the porous layer, a slurry solution is prepared by adding the active material (X) and the binder (Y) and, if necessary, a solvent, a conductive additive, etc. In the stirring and mixing step, the slurry-like solution is maintained in a dispersion state having a constant dispersion diameter larger than usual. Specifically, each main mixing condition is controlled so as to leave a certain large and constant dispersion diameter.

When the solvent of the slurry solution is a solvent having relatively low solubility in the binder, a porous layer having a relatively large dispersion diameter can be obtained when it is applied onto the current collector and dried. Therefore, a concavo-convex structure resulting from the dispersion diameter is formed on the surface of the porous layer.

It is also effective to reduce the circularity of the particles of the active material (X) so that it is difficult to close-pack.

<About the average diameter of the recesses>
As described above, there is a concavo-convex structure on the electrode surface, and the average diameter of the concave portions of this concavo-convex structure is 50 to 10,000 μm. In particular, the average diameter is preferably 100 to 10,000 μm, more preferably 500 to 5,000 μm.

Here, the average diameter is measured as follows.
First, the produced electrode is cut in the thickness direction to produce a measurement sample. A tomographic image is constructed by X-ray CT, a plurality of distances between convex portions of 50 μm or more are obtained, and the average value is taken as the average diameter. In addition, when only the convex part less than 50 micrometers exists, a scanning electron microscope (SEM) observation is performed and an average diameter is calculated | required by the same operation.

As described above, the recess is formed on the surface of the porous layer, and the average diameter of the recess is 50 to 10,000 μm, whereas the average diameter of the pores of the porous layer is less than 5 μm, Obviously different.

<About the liquid pool rate>
Further, contrary to the common technical knowledge that the surface of the electrode preferably has flat or fine pores, the present invention has a relatively large number of concave portions distributed, and this is a considerable amount of electrolyte solution. It is a liquid reservoir that can store water. The liquid pool ratio of the recesses on the electrode surface is preferably 3 to 70%, more preferably 5 to 50%, and still more preferably 10 to 30%. If the liquid pool rate is too small, the contact surface between the electrode and the electrolytic solution decreases, so that it tends to be difficult to achieve a high energy density or the like. If it is too large, the amount of active material in the electrode is insufficient. This is because it tends to be difficult to achieve high energy density and the like.

Here, the liquid pool rate on the electrode surface is expressed by the following formula (1) and will be described below with reference to FIG.

[Equation 1]
Liquid pool ratio (%) = (T ₁ −T ₂ ) / T ₁ × 1/100 (1)

In the above formula (1), T ₁ is the surface contact average thickness (T _{1 in} FIG. 3), and T ₂ is the point contact average thickness (T _{2 in} FIG. 3). By measuring these, the liquid pool rate is measured.

Specifically, a dial gauge (manufactured by Ozaki Mfg. Co., Ltd.) having a tip shape of 5 mm in diameter is used as T ₁ (surface contact average thickness). An electrode size of 70 mm (horizontal) × 140 mm (vertical) is measured at 78 points at 10 mm intervals. From the average value of the obtained values, the current collector thickness is subtracted to obtain the coating film thickness (T ₁ ). Normally the coating thickness using T _1.

Next, T ₂ (point contact average thickness) is measured using a spherical measuring element with a tip of the tip of the carbide contacting the electrode upper surface and the lower surface of 2 mm in diameter and a radius of curvature of 20 mm at the tip, and a measuring pressure of 0.40 N. Using a (40 gf) sheet thickness measuring device (manufactured by Mitutoyo Corporation), 78 points of thickness are measured as described above. A value obtained by subtracting the current collector thickness from the average value of the obtained values is defined as a coating film thickness (T ₂ ).

By using the obtained T ₁ and T ₂ and applying the above equation (1), the liquid pool ratio (%) of the present invention can be obtained.

The electrode formed as described above can be used as the positive electrode of the electricity storage device of the present invention.

<About the electrolyte layer>
The electrolyte layer according to the power storage device of the present invention is configured using an electrolyte material. For example, a sheet obtained by impregnating a separator with an electrolytic solution or a sheet formed of a solid electrolyte is preferably used. The sheet made of the solid electrolyte itself also serves as a separator.

The electrolyte layer material is composed of a solute (electrolyte), a solvent as necessary, and various additives. Examples of such solutes include metal ions such as lithium ions and appropriate counter ions, sulfonate ions, perchlorate ions, tetrafluoroborate ions, hexafluorophosphate ions, hexafluoroarsenic ions, bis ions. A combination of (trifluoromethanesulfonyl) imide ion, bis (pentafluoroethanesulfonyl) imide ion, halogen ion and the like is preferably used. Therefore, specific examples of such an electrolyte include LiCF ₃ SO ₃ , LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCl. Etc.

As the solvent used as necessary, for example, at least one non-aqueous solvent such as carbonates, nitriles, amides, ethers, that is, an organic solvent is used. Specific examples of such organic solvents include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile, propionitrile, N, N'-dimethylacetamide, N-methyl-2- Examples include pyrrolidone, dimethoxyethane, diethoxyethane, and γ-butyrolactone. These may be used alone or in combination of two or more. In addition, what melt | dissolved the solute in the solvent may be called "electrolyte solution."

In the present invention, as described above, the separator can be used in various modes. As the separator, it is possible to prevent an electrical short circuit between the positive electrode and the negative electrode that are arranged to face each other across the separator. Furthermore, the separator is electrochemically stable, has a large ion permeability, and has a certain level. Any insulating porous sheet having mechanical strength may be used. Therefore, as the material of the separator, for example, a porous film made of a resin such as paper, nonwoven fabric, polypropylene, polyethylene, or polyimide is preferably used. These may be used alone or in combination of two or more.

<About negative electrode>
The negative electrode in the electricity storage device according to the present invention is formed using at least one of a metal or a compound capable of inserting / extracting ions or a metal (hereinafter also referred to as “negative electrode active material”) (Z). As the negative electrode active material (Z), metallic lithium, a carbon material in which lithium ions can be inserted / extracted during oxidation / reduction, a transition metal oxide, silicon, tin, or the like is preferably used. In addition, in the present invention, “use” means not only the case where only the forming material is used, but also the case where the forming material is used in combination with another forming material. Is used at less than 50% by weight of the forming material.

Also, the thickness of the negative electrode preferably conforms to the thickness of the positive electrode.

<Production of power storage device>
Production of an electricity storage device using the above materials will be described with reference to FIG. The battery is preferably assembled in a glove box under an inert gas atmosphere such as ultra-high purity argon gas.

In FIG. 2, metal foils and meshes such as nickel, aluminum, stainless steel, and copper are appropriately used as current collectors (1, 5 in FIG. 2) for positive electrode 2 and negative electrode 4. Then, the current collectors 1 and 5 are connected to the current extraction connecting terminals (tab electrodes, not shown) of the positive electrode 2 and the negative electrode 4 using a spot welder.

Next, the positive electrode 2 and the current collector 1 are vacuum-dried. Thereafter, a negative electrode active material such as a metal lithium foil is pressed against the stainless steel mesh in a glove box having a dew point of −100 ° C. to produce a composite of the negative electrode 4 and the current collector 5.

Next, a predetermined number of various separators (not shown) are sandwiched between the positive electrode 2 and the negative electrode 4 in the glove box, and the positive electrode 2 and the negative electrode 4 are placed in a laminate cell heat-sealed on these three sides. Adjust the position of the separator so that they face each other correctly and do not short-circuit.

Then, after setting a sealant on the tab portions for the positive electrode and the negative electrode, the tab electrode portion is heat-sealed, leaving a little electrolyte inlet. Thereafter, a predetermined amount of battery electrolyte is sucked with a micropipette, and a predetermined amount is injected from the electrolyte solution inlet of the laminate cell. Finally, the electrolyte solution inlet at the top of the laminate cell is sealed by heat sealing to complete the electricity storage device (laminate cell) of the present invention.

<Power storage device>
The electricity storage device of the present invention is formed into various shapes such as a film type, a sheet type, a square type, a cylindrical type, and a button type in addition to the laminate cell. In addition, the positive electrode size of the electricity storage device is preferably 1 to 300 mm on one side in the case of a laminate cell, particularly preferably 10 to 50 mm, and the electrode size of the negative electrode is 1 to 400 mm. It is preferably 10 to 60 mm. The electrode size of the negative electrode is preferably slightly larger than the positive electrode size.

Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples.

First, prior to the production of electricity storage devices as examples and comparative examples, the following components were prepared and prepared.

[Preparation of active material (X)]
As the active material (X), conductive polyaniline powder using tetrafluoroboric acid as a dopant was prepared as follows. In the present invention, the powder means a collection of particles.

(Conductive polyaniline powder)
To a 300 mL glass beaker containing 138 g of ion-exchanged water, 84.0 g (0.402 mol) of a 42 wt% concentration tetrafluoroboric acid aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade) is added to a magnetic stirrer. While stirring, 10.0 g (0.107 mol) of aniline was added thereto. When aniline was added to the tetrafluoroboric acid aqueous solution, the aniline was dispersed as oily droplets in the tetrafluoroboric acid aqueous solution, but then dissolved in water within a few minutes, and the uniform and transparent aniline aqueous solution. Became. The aniline aqueous solution thus obtained was cooled to −4 ° C. or lower using a low temperature thermostat.

Next, 11.63 g (0.134 mol) of manganese dioxide powder (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade 1) as an oxidizing agent is added little by little to the above aniline aqueous solution, and the temperature of the mixture in the beaker is −1. The temperature was not exceeded. Thus, by adding an oxidizing agent to the aniline aqueous solution, the aniline aqueous solution immediately turned black-green. Thereafter, when stirring was continued for a while, a black-green solid started to be formed.

Thus, after adding the oxidizing agent over 80 minutes, the reaction mixture containing the produced reaction product was further stirred for 100 minutes while cooling. Then, using a Buchner funnel and a suction bottle, the obtained solid was No. Suction filtration was performed with two filter papers (manufactured by ADVANTEC) to obtain a powder. This powder was stirred and washed in a 2 mol / L tetrafluoroboric acid aqueous solution using a magnetic stirrer. Subsequently, it was stirred and washed several times with acetone, and this was filtered under reduced pressure. The obtained powder was vacuum-dried at room temperature (25 ° C.) for 10 hours to obtain 12.5 g of conductive polyaniline having tetrafluoroboric acid as a dopant (hereinafter simply referred to as “conductive polyaniline”). The conductive polyaniline was a bright green powder.

(Conductivity of conductive polyaniline powder)
After pulverizing 130 mg of the conductive polyaniline powder in a smoked mortar, vacuum-pressing was performed for 10 minutes under a pressure of 75 MPa using a KBr tablet molding machine for infrared spectrum measurement, and a conductive polyaniline disk having a thickness of 720 μm was formed. Obtained. The conductivity of the disk measured by the 4-terminal method conductivity measurement by the Van der Pau method was 19.5 S / cm.

(Undoped conductive polyaniline powder)
The conductive polyaniline powder in a doped state obtained as described above is placed in a 2 mol / L aqueous sodium hydroxide solution, stirred for 30 minutes in a 3 L separable flask, and the tetrafluoroboric acid as a dopant is removed by a neutralization reaction. Doped. The dedoped polyaniline was washed with water until the filtrate became neutral, then stirred and washed in acetone, and filtered under reduced pressure using a Buchner funnel and a suction bottle to obtain a dedoped polyaniline powder on No. 2 filter paper. . This was vacuum-dried at room temperature for 10 hours to obtain a brown undoped polyaniline powder.

(Reductive dedoped polyaniline powder)
Next, this dedope polyaniline powder was put into a methanol solution of phenylhydrazine and subjected to reduction treatment for 30 minutes with stirring. The color of the polyaniline powder changed from brown to gray by reduction. After the reaction, it was washed with methanol, washed with acetone, filtered, and vacuum dried at room temperature to obtain polyaniline in a reduced and dedoped state.

(Conductivity of polyaniline powder in reduced and undoped state)
After pulverizing 130 mg of the above polyaniline powder in the reduced dedope state in a smoked mortar, vacuum reduced pressure molding was performed for 10 minutes under a pressure of 75 MPa using a KBr tablet molding machine for infrared spectrum measurement, and a reduced dedope having a thickness of 720 μm. A polyaniline disk in state was obtained. The electric conductivity of the disk measured by the 4-terminal conductivity measurement by the Van der Pau method was 5.8 × 10 ⁻³ S / cm.

[Preparation of binder (Y)]
(Binder 1 solution: aqueous solvent)
Using polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight 1,000,000), this was heated and stirred to dissolve in water, and 20.5 g of 4.4 wt% concentration uniform and viscous polyacrylic acid aqueous solution. Got. To this aqueous solution, 0.15 g of lithium hydroxide was added and dissolved again to prepare a polyacrylic acid-polylithium acrylate complex solution (binder 1 solution) in which 50% of the acrylic acid sites were replaced with lithium.

(Binder 2 solution: water / methanol mixed solvent)
Using polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight 1,000,000), this was heated and stirred to dissolve in a water / methanol mixed solvent (weight ratio 1/1), and a uniform concentration of 4.4 wt% 20.5 g of a viscous polyacrylic acid aqueous solution was obtained. To this aqueous solution, 0.15 g of lithium hydroxide was added and dissolved again to prepare a polyacrylic acid-polylithium acrylate complex solution (binder 2 solution) in which 50% of the acrylic acid sites were replaced with lithium.

[Preparation of anode material]
A 50 μm thick metal lithium foil (Honjo Metal Co., Ltd., coin-type metal lithium) was prepared.

[Preparation of electrolyte]
An ethylene carbonate / dimethyl carbonate solution (manufactured by Kishida Chemical Co., Ltd.) of 1 mol / dm ³ concentration of lithium tetrafluoroborate (LiBF ₄ ) was prepared.

[Preparation of separator]
A non-woven fabric (manufactured by Hosen Co., Ltd., TF40-50 (porosity: 55%)) was prepared.

[Tab electrode]
An aluminum metal foil with a thickness of 50 μm was prepared as a tab electrode for current extraction of the positive electrode, and a nickel metal foil with a thickness of 50 μm was prepared as a tab electrode for current extraction of the negative electrode.

[Current collector]
An aluminum foil with a thickness of 30 μm was prepared as a current collector for positive electrode, and a stainless mesh with a thickness of 180 μm was prepared as a current collector for negative electrode.

[Example 1]
<Forming a positive electrode using (X) and (Y)>
After mixing 4 g of reduced dedope polyaniline powder prepared as X component, 0.5 g of conductive carbon black (Denka Black, Denki Kagaku Kogyo Co., Ltd.) and 4 g of water, this was prepared as described above. It was added to 20.5 g of the binder 1 solution and kneaded well with a spatula. This was subjected to ultrasonic treatment for 5 minutes with an ultrasonic homogenizer, and a paste having fluidity was obtained using a Fillmix 40-40 type (manufactured by Primix). The paste was further defoamed for 3 minutes with Awatori Nertaro (Sinky Corp.) to obtain a defoamed paste.

Using a tabletop automatic coating device (manufactured by Tester Sangyo Co., Ltd.), the solution coating thickness was adjusted to 360 μm with a doctor blade type applicator with a micrometer, and the above defoamed paste was removed at a coating speed of 10 mm / second. It apply | coated on the etching aluminum foil (made by Hosen company, 30 micrometers thickness) for multilayer capacitors. Subsequently, after leaving at room temperature for 45 minutes, it was dried on a hot plate at a temperature of 100 ° C. to produce a porous polyaniline sheet electrode.

<Production of electricity storage device>
The assembly of a laminate cell as an electricity storage device (lithium secondary battery) using the polyaniline sheet electrode obtained above as a positive electrode and the other materials prepared above will be described below.

The battery was assembled in a glove box under an ultra-high purity argon gas atmosphere (dew point in the glove box: −100 ° C.).

The electrode size of the positive electrode for the laminate cell is 27 mm × 27 mm, the negative electrode size is 29 mm × 29 mm, which is slightly larger than the positive electrode size.

First, the metal foils of the positive electrode and negative electrode tab electrodes were respectively connected to the corresponding metal foils of current collectors using a spot welder. A positive electrode, a negative electrode, and a separator on which a tab electrode was previously attached by a spot welder were vacuum dried at 80 ° C. for 2 hours. After that, it was put in a glove box with a dew point of −100 ° C., and the prepared metal lithium foil was pressed into the stainless steel mesh of the current collector in the glove box to make a composite of the negative electrode and the current collector. .

Next, in the glove box, various separators were sandwiched between the positive electrode and the negative electrode, and these were set in a laminate cell in which three sides were heat-sealed. Then, adjust the position of the separator so that the positive electrode and the negative electrode are correctly opposed to each other and do not short-circuit, set the sealing agent on the positive electrode and negative electrode tab parts, leave a little electrolyte injection port, tab electrode The part was heat sealed. Thereafter, a predetermined amount of electrolyte solution was sucked with a micropipette, and a predetermined amount was injected from the electrolyte solution inlet of the laminate cell. Finally, the electrolyte solution inlet at the top of the laminate cell was sealed by heat sealing to complete the laminate cell.

[Example 2]
A polyaniline sheet electrode was obtained in the same manner as in Example 1 except that the defoamed paste prepared in Example 1 was further subjected to ultrasonic treatment with an ultrasonic homogenizer for 1 minute, and then a lithium secondary battery was produced. .

Example 3
After 4 g of the conductive polyaniline powder was mixed with 0.5 g of conductive carbon black powder (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.), this was added to 20.5 g of the prepared binder 2 solution and kneaded well with a spatula. Thereafter, ultrasonic treatment was performed for 5 minutes with an ultrasonic homogenizer, and then a paste having fluidity was obtained using a Fillmix 40-40 type (manufactured by Primix). This paste was defoamed for 3 minutes with Awatori Nertaro (Sinky Corp.) to obtain a defoamed paste. Except for the preparation of this defoaming paste, a polyaniline sheet electrode was obtained by the same operation as in Example 1, and then a lithium secondary battery was produced.

[Comparative Example 1]
In place of the ultrasonic treatment using the ultrasonic homogenizer of Example 1 and the treatment using the Fillmix 40-40 type (manufactured by Primix), a planetary rotating ball mill (manufactured by Philitchu Co., P-6) is used and 5 mm The mixture was stirred for 1 hour at a rotational speed of 400 rpm while using zirconia balls. After separating the zirconia balls, the resulting paste was subjected to a defoaming operation for 3 minutes using Awatori Nertaro (manufactured by Shinky Corporation) to obtain a defoamed paste. Except for this, a polyaniline sheet electrode was obtained in the same manner as in Example 1, and then a lithium secondary battery was produced.

[Comparative Example 2]
90 parts by weight of lithium cobaltate, 5 parts by weight of acetylene black as a conductive additive, and 5 parts by weight of polyvinylidene fluoride powder as a binder were mixed, and this was further mixed with 95 parts by weight of N-methylpyrrolidone (NMP) solution After mixing with a part and kneading well with a spatula, a positive active material slurry was prepared by dispersing using a Philmix 40-40 type (manufactured by Primix). This slurry was applied to an aluminum current collector with a thickness of 30 μm by a doctor blade method to form an electrode layer on the positive electrode current collector. Then, it compressed so that the electrode application layer thickness might be set to 30 micrometers using a rolling roll, and the positive electrode was obtained. A lithium secondary battery was produced in the same manner as in Example 1 except that the positive electrode produced above was used in place of the polyaniline sheet electrode of Example 1.

Using each power storage device thus obtained, various characteristics were measured and evaluated according to the following measurement methods in addition to the above-described measurement methods of the average diameter and the liquid pool ratio, and the results are shown in Table 1 below. It was shown to.

<Porosity of electrode (%)>
Porosity of electrode (%) = {(apparent volume of electrode−true volume of electrode) / apparent volume of electrode} × 100

The apparent volume of the electrode means “the electrode area of the electrode × the electrode thickness excluding the aluminum foil that is the current collector”. On the other hand, the true volume of the electrode means “the volume of the electrode constituent material excluding the aluminum foil”. Specifically, as described above, using the constituent weight ratio of the electrode constituent material and the true density value of each constituent material, the average density of the entire electrode constituent material is calculated, and the total weight of the electrode constituent material is calculated. It is obtained by dividing by this average density.

<Weight energy density (Wh / kg)>
Each power storage device was measured in a constant current / constant voltage charge / constant current discharge mode in a 25 ° C. environment using a battery charging / discharging device (SD8, manufactured by Hokuto Denko). The end-of-charge voltage is 3.8 V. After the voltage reaches 3.8 V by constant current charging, constant voltage charging at 3.8 V is performed for 2 minutes, and then constant current discharge is performed until the end-of-discharge voltage is 2.0 V. went. The charge / discharge current was set so that the weight capacity density of polyaniline was 150 mAh / g, and the entire capacity was charged / discharged in 20 hours (0.05 C).

<Charging efficiency (%)>
When the measurement is performed in the constant current / constant voltage charge / constant current discharge mode using the battery charging / discharging device (Hokuto Denko, SD8), the voltage reaches the end-of-charge voltage of 3.8 V by constant current charging. Capacity (Ah) was measured, and the value obtained by the following formula (2) was defined as the charging efficiency (%).

[Equation 2]
Charging efficiency (%) = Charging capacity at 10 C / Charging capacity at 0.2 C × 100 (2)

<Discharge capacity maintenance rate (%)>
The discharge capacity retention rate (%) is obtained by charging and discharging at 0.2 C in a constant current / constant voltage charge / constant current discharge mode using a battery charge / discharge device (Hokuto Denko, SD8). Further, charging / discharging at 10 C was performed to determine the discharge capacity. The value obtained by the following formula (3) was defined as the discharge capacity retention rate (%).

[Equation 3]
Discharge capacity retention rate (%) = discharge capacity at 10 C / discharge capacity at 0.2 C × 100 (3)

Here, “0.2C” means a current value at which charging or discharging is completed after 5 hours of constant current charging or discharging using the assembled secondary battery, and “10C” is It means a current value at which charging or discharging is completed in 6 minutes after constant current charging or discharging.

As is clear from Examples 1 to 3 in Table 1 above, the electrode of this example product in which a plurality of recesses having an average diameter of 50 to 10,000 μm are distributed has a charge efficiency and a discharge capacity maintenance rate that are higher than those of the comparative example. It was found to have high rate performance. Moreover, it turned out that any Example has a high weight energy density except the comparative example 1. FIG.

This is because the specific uneven structure on the surface of the porous electrode forms a liquid reservoir layer in which the electrolyte can stay, so that the rate of movement of ions coming out of the porous interior is greater in the liquid reservoir layer. It is thought to be due to.

In the above embodiments, specific forms in the present invention have been described. However, the above embodiments are merely examples and are not construed as limiting. Various modifications apparent to those skilled in the art are contemplated to be within the scope of this invention.

The electricity storage device of the present invention can be suitably used as an electricity storage device such as a lithium secondary battery. The power storage device of the present invention can be used for the same applications as conventional secondary batteries. For example, portable electronic devices such as portable PCs, mobile phones, and personal digital assistants (PDAs), hybrid electric vehicles, Widely used in power sources for driving automobiles, fuel cell vehicles and the like.

DESCRIPTION OF SYMBOLS 1 Current collector 2 Electrode 2 'Hole 3 Electrolyte layer

Claims (7)

An electrode for an electricity storage device comprising a porous layer formed on at least a part of a current collector surface, wherein the porous layer comprises at least the following (X) and (Y), and the surface of the porous layer is: An electrode for an electricity storage device, characterized by having an uneven structure in which a plurality of recesses having an average diameter of 50 to 10,000 μm are distributed.
(X) An active material that inserts and desorbs ions.
(Y) Binder. The electrode for an electricity storage device according to claim 1, wherein a liquid pool ratio of the concavo-convex structure is 3 to 70%. The electrode for an electricity storage device according to claim 1 or 2, wherein the active material (X) is a conductive polymer. The electrode for an electricity storage device according to any one of claims 1 to 3, wherein a main component of the binder (Y) is an anionic polymer. A positive electrode for an electricity storage device, wherein the electrode for an electricity storage device according to any one of claims 1 to 5 is used. An electricity storage device having an electrolyte layer and a positive electrode and a negative electrode provided to face each other with the electrolyte layer interposed therebetween, the positive electrode being the electrode according to any one of claims 1 to 5, wherein the negative electrode is the following (Z) An electricity storage device comprising:
(Z) At least one selected from a compound or metal capable of inserting / extracting ions. The method according to any one of claims 1 to 5, further comprising an ultrasonic dispersion treatment of at least the porous layer composition comprising the active material (X) and the binder (Y) and a solvent. A method for producing electrodes for power storage devices.

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