JP2021034570A - Active material layer for power storage device positive electrode, positive electrode for power storage device, and power storage device - Google Patents

Abstract

To provide an active material layer for a power storage device positive electrode that is advantageous from the viewpoint of enhancing the characteristics of a power storage device at low temperatures.SOLUTION: An active material layer 10 for a positive electrode of a power storage device includes an active material 12, a first conductive aid 14a, and a second conductive aid 14b. The active material 12 contains an electrochemically active polymer. The first conductive aid 14a has an aspect ratio of 10 or greater. The second conductive aid 14b has an aspect ratio of less than 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to an active material layer for a positive electrode of a power storage device, a positive electrode for a power storage device, and a power storage device.

Conventionally, there has been known a technique of using an electrochemically active polymer such as polyaniline as an active material in the positive electrode of a power storage device.

For example, Patent Document 1 describes a positive electrode for a power storage device for a power storage device having excellent rapid charge / discharge properties. The positive electrode contains an active material containing at least one of polyaniline and a polyaniline derivative, a conductive additive, and a binder. The ratio of the oxidized form of polyaniline in the active material is 45% by mass or more of the total polyaniline active material. In the binder, the total of the polarity term and the hydrogen bond term of the Hansen solubility parameter is 20 MPa ^1/2 or less. In Patent Document 1, a positive electrode is produced by applying a slurry on a current collector layer such as aluminum foil. In the technique described in Patent Document 1, conductive carbon black is preferably used.

Japanese Unexamined Patent Publication No. 2018-26341

In Patent Document 1, although the rapid charge / discharge property of the power storage device has been studied, the characteristics of the power storage device at low temperature and the rapid charge / discharge performance at room temperature have not been studied. The technique described in Patent Document 1 has room for reexamination from the viewpoint of enhancing the characteristics of the power storage device at low temperature and the rapid charge / discharge performance at room temperature. Therefore, the present invention provides an active material layer for a positive electrode of a power storage device, which is advantageous from the viewpoint of enhancing the characteristics of the power storage device at low temperature and the rapid charge / discharge performance at room temperature.

The present invention
Active materials, including electrochemically active polymers,
A first conductive auxiliary agent having an aspect ratio of 10 or more,
Provided is an active material layer for a positive electrode of a power storage device, comprising a second conductive auxiliary agent having an aspect ratio of less than 10.

In addition, the present invention
Provided is a positive electrode for a power storage device provided with the above-mentioned active material layer for a positive electrode for a power storage device.

In addition, the present invention
With the electrolyte layer,
A negative electrode arranged in contact with the first main surface of the electrolyte layer,
The positive electrode for a power storage device, which is arranged in contact with the second main surface of the electrolyte layer, is provided.
Provides a power storage device.

The active material layer for the positive electrode of the power storage device is advantageous from the viewpoint of enhancing the rapid charge / discharge performance at room temperature and the characteristics of the power storage device at low temperature.

FIG. 1 is a cross-sectional view showing an example of a positive electrode for a power storage device according to the present invention. FIG. 2 is a cross-sectional view showing an example of a power storage device according to the present invention. FIG. 3 is an electron micrograph of carbon nanotube powder. FIG. 4 is an electron micrograph of the conductive carbon black powder. FIG. 5 is an electron micrograph of the active material layer according to Example 1. FIG. 6 is an electron micrograph of the active material layer according to Example 2.

According to the studies by the present inventors, an electrochemically active polymer such as polyaniline has a characteristic that it is easily electrochemically activated even at a low temperature (for example, −30 ° C.). On the other hand, an electrochemically active polymer does not easily maintain high conductivity at a low temperature, and it is not easy to improve the characteristics of a power storage device containing such a polymer as an active material of a positive electrode at a low temperature. As a result of a great deal of trial and error, the present inventors, by using a plurality of types of conductive auxiliaries having different aspect ratios in combination, the characteristics at low temperature of a power storage device containing an electrochemically active polymer as an active material of a positive electrode. It was newly found that it can be improved. Based on this new finding, the present inventors have devised an active material layer for a positive electrode of a power storage device according to the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments.

As shown in FIG. 1, the active material layer 10 for the positive electrode of the power storage device includes an active material 12, a first conductive auxiliary agent 14a, and a second conductive auxiliary agent 14b. The active material 12 contains an electrochemically active polymer. The first conductive auxiliary agent 14a has an aspect ratio of 10 or more. The second conductive auxiliary agent 14b has an aspect ratio of less than 10. The aspect ratio of the first conductive auxiliary agent 14a and the second conductive auxiliary agent 14b typically divides the maximum length or the maximum diameter L of each conductive auxiliary agent by the maximum width W of each conductive auxiliary agent in a specific direction. Value (L / W). If the conductive aid extends in a curved line, the maximum length L is determined along that curve. The maximum width W is the maximum value of the width of the conductive auxiliary agent in the direction perpendicular to the virtual straight line or curve extending in the direction defining the maximum length or the maximum diameter L.

It is considered that the active material 12 is electrochemically active at a low temperature (for example, −30 ° C.), but its conductivity is low. The active material layer 10 includes a first conductive auxiliary agent 14a, and the first conductive auxiliary agent 14a can, for example, adhere to the surface of the active material 12 to compensate for the decrease in conductivity of the active material 12 at a low temperature. it is conceivable that. However, according to the studies by the present inventors, if the active material layer includes only the first conductive auxiliary agent 14a as the conductive auxiliary agent, it is still difficult to increase the discharge capacity of the power storage device at a low temperature. According to the studies by the present inventors, it is considered that the first conductive auxiliary agent 14a is difficult to fill the gap between the active materials 12 due to its shape, and is disadvantageous for increasing the conductivity between the active materials 12. .. On the other hand, it is considered that the second conductive auxiliary agent 14b can appropriately fill the gap between the active materials 12 and easily enhance the conductivity between the active materials 12. As described above, according to the active material layer 10, the discharge capacity of the power storage device at a low temperature can be increased by the organic bonding between the function of the first conductive auxiliary agent 14a and the function of the second conductive auxiliary agent 14b. Conceivable.

Further, the power storage device manufactured by using the active material layer 10 tends to exhibit good characteristics with respect to rapid charging / discharging at room temperature (for example, 25 ° C.). In rapid charge / discharge, expansion and contraction of the electrochemically active polymer contained in the active material 12 occurs. Since the active material layer 10 includes the second conductive additive 14b, even if the electrochemically active polymer contained in the active material 12 expands and contracts, the conductivity between the active materials 12 becomes high. It is thought that it is easy to keep high. Therefore, it is considered that the power storage device manufactured by using the active material layer 10 tends to exhibit good characteristics with respect to rapid charging / discharging at room temperature. In addition, since the first conductive auxiliary agent 14a has an aspect ratio of 10 or more, it is not easily affected by the expansion and contraction of the electrochemically active polymer contained in the active material 12. Therefore, the discharge capacity of the power storage device manufactured by using the active material layer 10 at a low temperature is likely to be kept high even after rapid charging / discharging.

The sum of the content of the first conductive auxiliary agent 14a and the content of the second conductive auxiliary agent 14b in the active material layer 10 is not limited to a specific value. The sum is, for example, 1 to 30% on a mass basis. According to such a configuration, the discharge capacity of the power storage device at a low temperature can be increased more reliably. When the sum of the content of the first conductive auxiliary agent 14a and the content of the second conductive auxiliary agent 14b exceeds 30%, the amount of the active material 12 becomes relatively small, which is advantageous for the power storage device 5. It's hard to say.

The sum of the content of the first conductive auxiliary agent 14a and the content of the second conductive auxiliary agent 14b in the active material layer 10 is preferably 2 to 25%, more preferably 2 to 20% on a mass basis. Yes, more preferably 3-19%.

In the active material layer 10, the ratio of the content of the first conductive auxiliary agent to the content of the second conductive auxiliary agent is not limited to a specific value. The ratio is, for example, 1 to 9900% on a mass basis. According to such a configuration, the function of the first conductive auxiliary agent 14a and the function of the second conductive auxiliary agent 14b are satisfactorily exhibited, and the discharge capacity of the power storage device at a low temperature can be increased more reliably.

In the active material layer 10, the ratio of the content of the first conductive auxiliary agent 14a to the content of the second conductive auxiliary agent 14b is preferably 10 to 900%, more preferably 25 to 400% on a mass basis. is there.

The first conductive auxiliary agent 14a is present in a wider range than the second conductive auxiliary agent 14b on the surface of the active material 12, for example. According to such a configuration, it is easy to compensate for the decrease in the conductivity of the active material 12 at a low temperature.

The second conductive auxiliary agent 14b exists, for example, in the gap between the active materials 12. According to such a configuration, the conductivity between the active materials 12 tends to increase.

The aspect ratio of the first conductive auxiliary agent 14a may be 20 or more, 50 or more, or 150 or more. The aspect ratio of the first conductive auxiliary agent 14a is, for example, 5000 or less. The maximum length L of the first conductive auxiliary agent 14a is, for example, 0.5 μm or more, may be 1 μm or more, may be 3 μm or more, or may be 5 μm or more. The maximum length L of the first conductive auxiliary agent 14a is, for example, 30 μm or less.

The first conductive auxiliary agent 14a is, for example, rod-shaped, tubular-shaped, fibrous-shaped, or fibril-shaped. The first conductive auxiliary agent 14a is typically made of a conductive material having properties that do not change with the voltage applied for charging and discharging the power storage device. The first conductive auxiliary agent 14a can be a conductive carbon material or a metallic material. The first conductive auxiliary agent 14a preferably contains a first conductive carbon material.

The first conductive carbon material is, for example, a fibrous carbon material such as carbon fiber and carbon nanotube. The first conductive carbon material is preferably carbon nanotubes. In this case, the discharge capacity of the power storage device at a low temperature can be increased more reliably. The carbon nanotubes may be single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes.

The aspect ratio of the second conductive auxiliary agent 14b may be 8 or less, 5 or less, or 3 or less. The maximum diameter L of the second conductive auxiliary agent 14b is, for example, 20 nm or more, may be 30 nm or more, and may be 40 nm or more. The maximum diameter L of the second conductive auxiliary agent 14b is, for example, 1 μm or less.

The second conductive auxiliary agent 14b is typically made of a conductive material having properties that do not change with the voltage applied for charging and discharging the power storage device. The second conductive auxiliary agent 14b can be, for example, a conductive carbon material or a metallic material. The second conductive auxiliary agent 14b preferably contains a second conductive carbon material.

The second conductive carbon material is preferably a carbon black such as acetylene black and ketjen black. In this case, the discharge capacity of the power storage device at a low temperature can be increased more reliably. In addition, it is easy to reduce the manufacturing cost of the active material layer 10.

The electrochemically active polymer contained in the active material 12 is not limited to a specific polymer. The electrochemically active polymer contained in the active material 12 includes, for example, at least one of a polyaniline and a polyaniline derivative (hereinafter, may be referred to as “polyaniline-based compound”) having an oxidized body and a reduced product. In other words, the active material 12 contains a polyaniline-based compound in a semi-oxidized state. As a result, the power storage device tends to have high durability. On the other hand, at low temperatures, the conductivity of the semi-oxidized polyaniline compound tends to decrease. However, according to the active material layer 10, the active material 12 contains a polyaniline-based compound in a semi-oxidized state due to the organic bonding between the functions of the first conductive auxiliary agent 14a and the functions of the second conductive auxiliary agent 14b. Also, the discharge capacity of the power storage device at low temperature can be increased.

Polyaniline compounds contain, for example, 35-60% oxidants by mass. In this case, the storage stability of the polyaniline-based compound is good, and the durability of the power storage device can be more reliably increased. The chemical structures of the oxidized Ox and the reduced Red of the polyaniline compound are shown in the following formula (a). In the formula (a), each of x and y is an integer of 0 or more.

The content of the oxidant in the polyaniline compound can be determined from ^{, for example, the solid 13 CNMR spectrum.} The content of the oxidant in the polyaniline compound is the degree of oxidation represented by the ratio A640 / A340 of the maximum absorption A640 near 640 nm and the maximum absorption A340 near 340 nm in the electron spectrum of the spectrophotometer. It can also be calculated from the index. The content of the oxidant (ratio of the oxidant) in the polyaniline compound can be determined, for example, according to the method described in paragraphs 0040 to 0051 of JP-A-2018-26341.

Polyaniline is typically obtained by electrolytic or chemical oxidative polymerization of aniline. Polyaniline derivatives are typically obtained by electrolytic or chemical oxidative polymerization of aniline derivatives. The aniline derivative has, for example, at least one 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 a position other than the 4-position of aniline. Have. The aniline derivative is, for example, (i) o-substituted aniline such as o-methylaniline, o-ethylaniline, o-phenylaniline, o-methoxyaniline, and o-ethoxyaniline, or (ii) m-methylaniline. , M-Ethylaniline, m-methoxyaniline, m-ethoxyaniline, m-phenylaniline and the like may be m-substituted anilines. In the synthesis of the polyaniline derivative, only one kind of aniline derivative may be used, or two or more kinds of aniline derivatives may be used in combination.

When a polyaniline-based compound is obtained by electrolytic polymerization or chemical oxidation polymerization of an aniline or an aniline derivative, the polyaniline-based compound can be doped with a dopant such as a protonic acid in order to impart conductivity. The protonic acid used for doping is not limited to a particular protonic acid as long as it can impart the desired conductivity to the active material 12. The protonic acid is, for example, hydrochloric acid or sulfuric acid.

When a polyaniline-based compound is obtained by electrolytic polymerization or chemical oxidation polymerization of aniline or an aniline derivative, for example, a predetermined oxidizing agent is used. The oxidizing agent is selected from the group consisting of, for example, ammonium peroxodisulfate (APS), hydrogen peroxide, potassium dichromate, potassium permanganate, sodium chlorate, ammonium cerium nitrate, sodium iodate, iron chloride, and manganese dioxide. At least one.

As described above, the polyaniline compound may be doped with a dopant such as a protonic acid in order to impart conductivity. On the other hand, the polyaniline compound contained in the active material 12 is preferably dedoping at the time of producing the positive electrode for the power storage device. Specifically, the polyaniline compound contained in the active material 12 is in a state in which a dopant such as a protonic acid is dedoping. In this case, the active material 12 is likely to be appropriately dispersed in the active material layer 10, and the energy density of the power storage device is likely to increase. This is because the dedoping polyaniline compound disperses well in the slurry even if the dispersion medium of the slurry for forming the active material layer 10 is water. On the other hand, it may be difficult to satisfactorily disperse the doped polyaniline compound using water as a dispersion medium.

The polyaniline compound contained in the active material 12 is preferably dedoping during assembly of the power storage device. When the power storage device is in a charged state, the polyaniline compound contained in the active material 12 is in a doped state. It is conceivable to assemble a power storage device by combining a positive electrode chemically doped in advance and a negative electrode that has not been charged. In this case, in the initial charge of the power storage device, only the chemically undoped polyaniline compound at the positive electrode contributes to the charge. Therefore, the initial charge capacity of the power storage device is significantly reduced, which is not preferable for the power storage device. It is also conceivable to assemble a power storage device by combining a positive electrode chemically doped in advance and a negative electrode such as a lithium pre-doped negative electrode. In this case, it is possible to discharge immediately after assembling the power storage device, but the chemically doped positive electrode is difficult to be electrochemically doped and dedoping, resulting in a decrease in the capacity of the power storage device. Therefore, it is difficult to obtain a desired power storage device. Even if the polymer is electrochemically active in a dedoping state when the positive electrode is manufactured or when the power storage device is assembled, it is electrochemically doped from the time when charging is started after the power storage device is assembled. After that, the polyaniline compound contained in the active material 12 is repeatedly doped and dedoping, so that it can be used as a power storage device.

The semi-oxidized polyaniline compound obtained as described above may be washed, classified, or pulverized. By performing such a process, the power storage device manufactured by using the active material 12 may exhibit a high discharge capacity at a low temperature. The classification method is not limited to a specific method, and a known classification method can be applied. The method of pulverization is not limited to a specific method. The pulverization method is at least one selected from the group consisting of, for example, a ball mill, a bead mill, a sand mill, a jet mill, and a roll mill.

The active material 12 has, for example, an average particle size of more than 0.5 μm and 20 μm or less. As a result, the initial discharge capacity of the power storage device tends to increase more reliably. For the average particle size of the active material 12, for example, when 50 or more active materials 12 are observed using an electron microscope such as a scanning electron microscope (SEM), the maximum diameter of the 50 or more active materials 12 is measured. Can be determined by doing. Alternatively, the average particle size of the active material 12 may be determined using a particle image analyzer that images the shape of the particles using a microscope and analyzes them by image analysis. As used herein, the "average particle size" refers to the median diameter (D50). The median diameter is a particle size such that the number of particles having a particle size larger than that value is equal to the number of particles having a particle size smaller than that value.

The content of the active material 12 in the active material layer 10 is, for example, 1% or more, preferably 5% or more, more preferably 20% or more, and further preferably 40% or more on a mass basis. Especially preferably 60% or more. As a result, the energy density of the power storage device tends to increase. The content of the active material 12 in the active material layer 10 is, for example, 95% or less on a mass basis.

As shown in FIG. 1, the active material layer 10 further contains, for example, a binder 15. The binder 15 contains, for example, an elastomer. The elastomer can be natural rubber, synthetic rubber, or thermoplastic elastomer. The binder 15 is typically in contact with the outer surface of the active material 12, the outer surface of the first conductive auxiliary agent 14a, or the outer surface of the second conductive auxiliary agent 14b. The binder 15 binds the active material 12, the first conductive auxiliary agent 14a, and the second conductive auxiliary agent 14b. As shown in FIG. 1, the active material layer 10 has, for example, pores 16. The pores 16 are formed so as to be continuous from one main surface of the active material layer 10 to the other main surface, for example. In the power storage device, for example, the electrolytic solution is impregnated into the pores 16. Since the binder 15 contains an elastomer, the binder 15 is easily deformed without generating a large stress according to the dimensional change of the electrochemically active polymer particles accompanying the charging and discharging of the power storage device. As a result, the desired characteristics of the power storage device are likely to be exhibited with respect to rapid charging / discharging.

The binder 15 includes, for example, a rubber material. In this case, the rubber material can be, for example, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, or a methyl methacrylate-butadiene copolymer.

The total of the polar term and the hydrogen bond term in the Hansen solubility parameter of the binder 15 is, for example, 20 MPa ^1/2 or less. In this case, the binder 15 and the active material 12 have a good affinity, and the first conductive auxiliary agent 14a and the second conductive auxiliary agent 1ba are likely to come into proper contact with the active material 12. Calculations for determining this Hansen solubility parameter can be performed according to the method described in Charles M. Hansen, Hansen Solubility Parameters: A Users Handbook (CRC Press, 2007). In addition, by using the computer software Hansen Solubility Parameters in Practice (HSPiP), the Hansen solubility parameter can be calculated from the chemical structure. Further, the total of the polarity term and the hydrogen bond term in the Hansen solubility parameter of the binder made of the composite material is determined by summing the product of the Hansen solubility parameter of each component constituting the binder and the mass-based composition ratio of each component. it can. The sum of the polar term and the hydrogen bond term in the Hansen solubility parameter of the binder 15 is preferably 19 MPa ^1/2 or less, more preferably 12 MPa ^1/2 or less, and further preferably 8 MPa ^1/2 or less. ..

The content of the binder 15 in the active material layer 10 is, for example, 1 to 30%, preferably 4 to 25%, and more preferably 4 to 18% on a mass basis. As a result, the active material 12 can be appropriately dispersed in the active material layer 10 while suppressing the content of the binder 15. As a result, it is easy to increase the energy density in the power storage device.

The active material layer 10 may contain an active material other than the active material 12, if necessary. The active material other than the active material 12 is, for example, a carbon material such as activated carbon. The activated carbon can be an alkaline activated carbon, a steam activated carbon, a gas activated carbon, or a zinc chloride activated carbon.

The active material layer 10 may further contain an additive such as a thickener, if necessary. Thickeners are, for example, methyl cellulose, hydroxyethyl cellulose, polyethylene oxide, carboxymethyl cellulose (CMC), derivatives thereof, or salts thereof. Among them, carboxylmethyl cellulose, a derivative thereof, or a salt thereof is preferably used as a thickener.

The content of the thickener in the active material layer 10 is, for example, 1 to 20%, preferably 1 to 10%, and more preferably 1 to 8% on a mass basis.

The positive electrode for a power storage device can be provided by using the above-mentioned active material layer 10. As shown in FIG. 1, the positive electrode 1 for a power storage device includes an active material layer 10. As a result, the discharge capacity of the power storage device manufactured by using the positive electrode 1 at a low temperature tends to increase. In addition, the power storage device manufactured by using the positive electrode 1 tends to exhibit good characteristics with respect to rapid charging / discharging at room temperature.

As shown in FIG. 1, the positive electrode 1 further includes, for example, a current collector 20 and a conductive layer 30. The conductive layer 30 is arranged between the active material layer 10 and the current collector 20. The conductive layer 30 is in contact with the active material layer 10 and the current collector 20. Due to the conductive layer 30, peeling or the like is unlikely to occur between the active material layer 10 and the current collector 20. The conductive layer 30 may be omitted, and the active material layer 10 may be in direct contact with the current collector 20.

The conductive layer 30 is not limited to a specific aspect. The conductive layer 30 contains, for example, conductive particles 32 made of a carbon material such as graphite and a binder 35 in contact with the outer surface of the conductive particles 32. In this case, the conductive layer 30 easily adheres to the active material layer 10 and the current collector 20.

The thickness of the conductive layer 30 has, for example, a thickness of 0.1 μm to 20 μm. The conductive layer 30 may have a thickness of 0.1 μm to 10 μm, or may have a thickness of 0.1 μm to 5 μm.

The contact angle of water droplets on the surface formed by the conductive layer 30 is, for example, 100 ° or less. The contact angle of water droplets on the surface of the conductive layer 30 can be measured, for example, according to the static droplet method in Japanese Industrial Standard JIS R 3257: 1999 before forming the active material layer 10. The measurement temperature of the contact angle of the water droplet is 25 ° C. The contact angle of water droplets on the surface of the conductive layer 30 is determined by, for example, forming the active material layer 10 and then removing at least a part of the active material layer 10 by a method such as polishing or cutting to expose the conductive layer 30. It may be measured on the surface of the conductive layer 30. In addition, at least a part of the current collector 20 may be removed by a method such as polishing or cutting to expose the conductive layer 30, and measurement may be performed on the surface of the exposed conductive layer 30.

The small contact angle of water droplets on the main surface of the conductive layer 30 is advantageous from the viewpoint of enhancing the adhesion between the conductive layer 30 and the active material layer 10. The contact angle of the water droplets is preferably 90 ° or less, more preferably 80 ° or less, and even more preferably 70 ° or less. The contact angle of the water droplet is, for example, 10 ° or more.

The peel strength P of the active material layer 10 with respect to the conductive layer 30 measured by the Surface And Interfacial Cutting Analysis System (SAICAS) is, for example, 0.15 kN / m or more. The peel strength P is determined by, for example, the following formula (1). The measurement mode of SAICAS is the constant velocity mode. The cutting speed is 10 μm / sec. FH is the horizontal cutting stress [N] when the SAICAS diamond cutting edge (manufactured by Daipla, rake angle: 10 °) is horizontally moved at the interface between the active material layer 10 and the conductive layer 30. W is the blade width [m] of the cutting edge of SAICAS. SAICAS is a registered trademark of Daipla Co., Ltd.
P = FH / W (1)

The larger the peel strength P, the higher the adhesion between the conductive layer 30 and the active material layer 10. The peel strength P is preferably 0.15 kN / m or more, more preferably 0.17 kN / m or more, and further preferably 0.23 kN / m or more.

The binder 35 of the conductive layer 30 is not limited to a specific binder. The binder 35 contains, for example, at least one selected from the group consisting of methyl cellulose, hydroxyethyl cellulose, polyethylene oxide, carboxymethyl cellulose, derivatives thereof, salts thereof, polyolefins, natural rubbers, synthetic rubbers, and thermoplastic elastomers. In this case, the conductive layer 30 easily adheres to the active material layer 10 and the current collector 20. In particular, when the total of the polar term and the hydrogen bond term in the Hansen solubility parameter of the binder 15 is 20 MPa ^1/2 or less, and the binder 35 of the conductive layer 30 contains the above components, the active material layer 10 and Adhesion with the conductive layer 30 tends to be high.

As the synthetic rubber or thermoplastic elastomer, for example, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, or a methyl methacrylate-butadiene copolymer can be used.

The binder 35 may contain at least one selected from the group consisting of polyolefins, carboxymethyl cellulose, and styrene-butadiene copolymers. In this case, the adhesion between the conductive layer 30 and the active material layer 10 or the current collector 20 is likely to increase more reliably.

The binder 35 preferably contains at least one of carboxymethyl cellulose and a styrene-butadiene copolymer. In this case, the adhesion between the conductive layer 30 and the active material layer 10 tends to increase.

The current collector 20 is a foil or mesh made of a metal material such as nickel, aluminum, and stainless steel.

An example of a method for manufacturing the positive electrode 1 will be described. First, the current collector 20 is prepared, and the conductive layer 30 is formed on the main surface of the current collector 20. The conductive layer 30 is formed by, for example, coating, sputtering, vapor deposition, ion plating, or CVD using a predetermined raw material. Desirably, the conductive layer 30 is formed by applying a slurry prepared by dispersing the conductive particles 32 and the binder 35 in a dispersion medium to the main surface of the current collector 20 to form a coating film, and the coating film is dried. It can be formed by that. Then, a slurry prepared by dispersing the active material 12, the first conductive auxiliary agent 14a, the second conductive auxiliary agent 14b, and the binder 15 in a dispersion medium is applied to the surface of the conductive layer 30 to form a coating film. The active material layer 10 can be formed by drying this coating film. In this way, the positive electrode 1 can be manufactured. If necessary, an active material other than the active material 12 and an additive such as a thickener are added to the slurry for forming the active material layer 10.

When the conductive layer 30 is omitted in the positive electrode 1, a slurry prepared by dispersing the active material 12, the first conductive auxiliary agent 14a, the second conductive auxiliary agent 14b, and the binder 15 in a dispersion medium is mainly used in the current collector 20. It may be applied to a surface to form a coating film, and the coating film may be dried to form an active material layer 10.

As shown in FIG. 2, the power storage device 5 can be provided by using the positive electrode 1. The power storage device 5 includes an electrolyte layer 3, a negative electrode 2, and a positive electrode 1. The negative electrode 2 is arranged in contact with the first main surface of the electrolyte layer 3. The positive electrode 1 is arranged in contact with the second main surface of the electrolyte layer 3. The active material layer 10 of the positive electrode 1 is in contact with the second main surface of the electrolyte layer 3. The electrolyte layer 3 is arranged between the positive electrode 1 and the negative electrode 2. Since the power storage device 5 includes the positive electrode 1, it tends to exhibit a high discharge capacity at a low temperature.

The electrolyte layer 3 typically contains an electrolyte. The electrolyte layer 3 is, for example, a sheet in which a separator is impregnated with an electrolytic solution or a sheet made of a solid electrolyte. When the electrolyte layer 3 is a sheet made of a solid electrolyte, the electrolyte layer 3 itself may also serve as a separator.

The above electrolyte contains a solute and, if necessary, a solvent and various additives. In this case, the solute is a combination of, for example, a metal ion such as lithium ion and a predetermined counter ion for the metal ion. Counterions include, for example, sulfonic acid ion, perchlorate ion, tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroarsenic ion, bis (trifluoromethanesulfonyl) imide ion, bis (pentafluoroethanesulfonyl) imide ion, and bis. It is a (fluorosulfonyl) imide, a lithium bis (trifluoromethylsulfonyl) imide, or a halogen ion. Specific examples of electrolytes are LiCF ₃ SO ₃ , LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) _2. , And LiCl.

The solvent in the electrolyte is, for example, a non-aqueous solvent (organic solvent) such as a carbonate compound, a nitrile compound, an amide compound, and an ether compound. Specific examples of the solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, acetonitrile, propyronitrile, N, N'-dimethylacetamide, N-methyl-2-pyrrolidone, dimethoxyethane, and the like. Diethoxyethane and γ-butyrolactone. As the solvent in the electrolyte, one kind of solvent may be used alone, or two or more kinds of solvents may be used in combination. A solution in which a solute is dissolved in the above solvent may be referred to as an "electrolyte solution".

The electrolytic solution may contain additives, if necessary. Additives are, for example, vinylene carbonate or fluoroethylene carbonate.

The negative electrode 2 includes, for example, an active material layer 60 and a current collector 70. The active material layer 60 contains a negative electrode active material. The negative electrode active material is a substance capable of inserting and removing a metal or ions. As the negative electrode active material, metallic lithium, a carbon material capable of inserting and removing lithium ions by a redox reaction, a transition metal oxide, silicon, and tin are preferably used. The active material layer 60 is in contact with the first main surface of the electrolyte layer 3.

Carbon materials capable of inserting and removing lithium ions include, for example, (i) activated carbon, (ii) coke, (iii) pitch, (iv) phenol formaldehyde, polyimide, and calcined cellulose, and (v) artificial graphite. , (Vi) natural graphite, (vii) hard carbon, or (vii) soft carbon.

A carbon material capable of inserting and removing lithium ions is preferably used as the main component of the negative electrode. In the present specification, the principal component means the component contained most in terms of mass.

The current collector 70 is a foil or mesh made of a metal material such as nickel, aluminum, stainless steel, and copper.

As the negative electrode 2, it is also possible to use a lithium pre-doped negative electrode in which a carbon material such as graphite, hard carbon, or soft carbon is pre-doped with lithium ions.

In the power storage device 5, a separator is typically arranged between the positive electrode 1 and the negative electrode 2. The separator prevents an electrical short circuit between the positive electrode 1 and the negative electrode 2. The separator is, for example, a porous sheet that is electrochemically stable and has high ion permeability, desired mechanical strength, and insulating properties. The material of the separator is preferably a porous film made of a resin such as (i) paper, (ii) non-woven fabric, (iii) polypropylene, polyethylene, and polyimide.

An example of the manufacturing method of the power storage device 5 will be described. A separator is arranged between the positive electrode 1 and the negative electrode 2 to obtain a laminated body. This laminate is placed in a package made of an aluminum laminate film and vacuum dried. Next, the electrolytic solution is injected into the vacuum-dried package, the package is sealed, and the power storage device 5 is assembled. The process of assembling the power storage device 5 such as injecting the electrolytic solution into the package is preferably performed in an inert gas atmosphere such as ultra-high purity argon gas using a glove box.

The power storage device 5 may be manufactured in a film type, a sheet type, a square type, a cylindrical type, a button type, or the like by using a package other than the package made of the aluminum laminated film.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the examples shown below.

<Example 1>
165.3 g of ion-exchanged water, 54.69 g of hydrochloric acid (concentration: 36% by mass), and 41.9 g of aniline were added to a 500 ml separable flask, and the mixture was stirred while cooling to 15 ° C. Aniline-containing liquid was prepared. 238.4 g of ion-exchanged water and 128.4 g of ammonium peroxodisulfate (APS) were mixed to obtain an APS solution. The APS solution was added dropwise to the aniline-containing solution. At this time, the temperature of the reaction solution was adjusted to 35 ° C. After completion of dropping the APS solution, suction filtration was performed on the reaction solution to obtain a black-green powder. The powder was washed with ion-exchanged water, the obtained powder was placed in a flask, an aqueous sodium hydroxide solution was further added, and the mixture was stirred to perform dedoping. Next, the powder obtained by filtering the solution was filtered by suction filtration. Next, the powder was washed with ion-exchanged water until the filtrate became neutral. Then, the powder was vacuum dried at 60 ° C. for 10 hours to obtain the active material according to Example 1.

The proportion of the oxidized substance in the polyaniline of the active material according to Example 1 determined from the solid-state NMR spectrum was 45% by mass. The polyaniline contained in the active material according to Example 1 was in a semi-oxidized state and in a de-doping state.

Using a particle image analyzer (manufactured by Malvern, product name: Morphologi G3), the particle size distribution based on the number of active materials according to Example 1 was measured, and the average particle size (D50) was determined from the measurement results. did. The average particle size of the active material according to Example 1 was 2 μm.

(Preparation of positive electrode)
5 g (76.9 parts by mass) of the active material according to Example 1, 0.322 g (5 parts by mass) of conductive carbon black powder (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.), which is a conductive auxiliary agent, and a conductive auxiliary agent. 6.43 g (4.9 parts by mass) of CNT paste (manufactured by Cnano, product name: LB217-54) containing 5% by mass of carbon nanotube (CNT) powder, and styrene-butadiene copolymer (SBR) as a binder. Add 0.64 g (9.8 parts by mass) and 11.02 g (3.4 parts by mass) of sodium carboxymethyl cellulose diluted to 2% by mass to 4 g of water, and add Shinky's rotating and revolving vacuum mixer Awatori Kneading. Using Taro ARV-310, stirring was performed at 2000 rpm for 10 minutes, and defoaming operation was performed for 3 minutes. In this way, the slurry for the active material layer according to Example 1 was obtained. In the styrene-butadiene copolymer, the copolymerization ratio of styrene: butadiene [1,4 bodies]: butadiene [1,2 bodies] was 61:31: 8. Table 1 shows the content of each component in the solid content of the slurry for the active material layer according to Example 1. For the aspect ratio of the CNT powder and the carbon black powder, 30 or more CNT powders or 30 arbitrarily selected by fixing each powder on the support film and observing each sample prepared in this manner with an electron microscope. It was determined by calculating the aspect ratio of each powder from the images of one or more carbon black powders and calculating the arithmetic average. The carbon nanotube (CNT) powder contained carbon nanotubes having an aspect ratio of 50 or more. The conductive carbon black powder contained carbon black having an aspect ratio of less than 10. An electron micrograph of the carbon nanotube powder is shown in FIG. An electron micrograph of the conductive carbon black powder is shown in FIG.

As a current collector, an aluminum foil having a thickness of 20 μm was prepared. Using a desktop automatic coating device (manufactured by Tester Sangyo Co., Ltd.) and a doctor blade type applicator with a micrometer, apply the slurry for the active material layer according to Example 1 on the current collector at an application speed of 10 mm / sec. To form a coating film. Next, this coating film was left at room temperature (25 ° C.) for 45 minutes and then dried on a hot plate at a temperature of 100 ° C. to form the active material layer according to Example 1. In this way, the positive electrode according to Example 1 was produced. The thickness of the active material layer was 40 μm. An electron micrograph of the active material layer according to Example 1 is shown in FIG.

(Manufacturing of power storage device)
Inside a glove box kept in an environment with a dew point of -60 ° C or less and an oxygen concentration of 1 ppm or less, a separator (manufactured by Nippon Kodoshi Kogyo Co., Ltd., product name: TF40-) is attached to a graphite negative electrode sheet with a current collector tab attached. 50) was piled up. Next, an electrode having a metal lithium foil attached to a stainless steel mesh to which a current collector tab was attached was placed on the separator. At this time, the metallic lithium foil was brought into contact with the separator. This laminate was placed inside a bag-shaped package made of an aluminum laminate film. In this package, the three sides of the pair of square aluminum laminate films were sealed, and the other sides were separated from each other to form an opening. _{Next, a LiPF 6} carbonate solution having a concentration of ^{1.2 M (mol / dm 3} ) was injected into the inside of this package as an electrolytic solution. This carbonate solution contained ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) as carbonates. Next, the opening of the package was sealed with the current collector tab protruding from the opening of the package. In this way, a laminated cell for producing a lithium pre-doped negative electrode was obtained. Next, this laminated cell is taken out from the glove box, and inside a constant temperature bath kept at 25 ° C., in a potential range of 2.0 V to 0.01 V, it corresponds to 0.2 C with respect to the capacity of the graphite negative electrode sheet. Charging and discharging were carried out for 3 cycles with the current value to be applied, and finally, a reaction was carried out in which lithium ions were inserted into graphite up to a capacity of 75% of the capacity of the graphite negative electrode sheet. In this way, a laminated cell containing a lithium-predoped negative electrode sheet was produced.

The laminate cell containing the lithium pre-doped negative electrode sheet was reinserted into the glove box. The sealed portion of the laminate cell was cut off, and the lithium-predoped negative electrode sheet was taken out. Next, these were stacked so that the separator was located between the positive electrode according to Example 1 and the negative electrode sheet predoped with lithium. A non-woven fabric (manufactured by Nippon Kodoshi Kogyo Co., Ltd., product name: TF40-50) was used as the separator. A current collector tab was attached to the positive electrode. Next, the laminate of the positive electrode, the separator, and the negative electrode sheet was placed inside a bag-shaped package made of an aluminum laminate film. In this package, the three sides of the pair of square aluminum laminate films were sealed, and the other sides were separated from each other to form an opening. _{Next, a LiPF 6} carbonate solution having a concentration of 1.2 M (mol / dm ^{3) was injected into the package as an electrolytic solution.} This carbonate solution contained ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) as carbonates. Next, the opening of the package was sealed with the current collector tab of the positive electrode and the current collector tab of the negative electrode sheet protruding from the opening of the package. In this way, the lithium ion capacitor according to Example 1 was obtained.

<Example 2>
5 g (72.2 parts by mass) of the active material according to Example 1, 0.645 g (9.3 parts by mass) of conductive carbon black powder (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.), which is a conductive auxiliary agent, and conductivity. 12.9 g (9.3 parts by mass) of CNT paste (manufactured by Cnano, product name: LB217-54) containing 5% by mass of carbon nanotube (CNT) powder as an auxiliary agent, and a styrene-butadiene copolymer (9.3 parts by mass) as a binder. Add 0.414 g (6 parts by mass) of SBR) and 11.02 g (3.2 parts by mass) of sodium carboxymethyl cellulose diluted to 2% by mass to 5.74 g of water, and add Shinky's rotating and revolving vacuum mixer Awa. Using Tori-Nentaro ARV-310, stirring was performed at 2000 rpm for 10 minutes, and defoaming operation was performed for 3 minutes. In this way, the slurry for the active material layer according to Example 2 was obtained. In the styrene-butadiene copolymer, the copolymerization ratio of styrene: butadiene [1,4 bodies]: butadiene [1,2 bodies] was 61:31: 8. Table 1 shows the content of each component in the solid content of the slurry for the active material layer according to Example 2.

A positive electrode according to Example 2 was produced in the same manner as in Example 1 except that the slurry for the active material layer according to Example 2 was used instead of the slurry for the active material layer according to Example 1. The thickness of the active material layer in the positive electrode according to Example 2 was 40 μm. An electron micrograph of the active material layer on the positive electrode according to Example 2 is shown in FIG.

A lithium ion capacitor according to Example 2 was produced in the same manner as in Example 1 except that the positive electrode according to Example 2 was used instead of the positive electrode according to Example 1.

<Comparative example 1>
5 g (69.9 parts by mass) of the active material according to Example 1, 1.29 g (18 parts by mass) of conductive carbon black powder (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary agent, and styrene as a binder. -Postate copolymer (SBR) 0.64 g (9 parts by mass) and 11.02 g (3.1 parts by mass) of sodium carboxymethyl cellulose diluted to 2% by mass were added to 9.55 g of water, manufactured by Shinky Co., Ltd. Using the rotating and revolving vacuum mixer Awatori Rentaro ARV-310, stirring was performed at 2000 rpm for 10 minutes, and defoaming was performed for 3 minutes. In this way, the slurry for the active material layer according to Comparative Example 1 was obtained. In the styrene-butadiene copolymer, the copolymerization ratio of styrene: butadiene [1,4 bodies]: butadiene [1,2 bodies] was 61:31: 8. Table 1 shows the content of each component in the solid content of the slurry for the active material layer according to Comparative Example 1.

A positive electrode according to Comparative Example 1 was produced in the same manner as in Example 1 except that the slurry for the active material layer according to Comparative Example 1 was used instead of the slurry for the active material layer according to Example 1. The thickness of the active material layer on the positive electrode according to Comparative Example 1 was 40 μm.

A lithium ion capacitor according to Comparative Example 1 was produced in the same manner as in Example 1 except that the positive electrode according to Comparative Example 1 was used instead of the positive electrode according to Example 1.

<Comparative example 2>
12.86 g of CNT paste (manufactured by Cnano, product name: LB217-54) containing 5 g (76.9 parts by mass) of the active material according to Example 1 and 5 mass% of carbon nanotube (CNT) powder as a conductive auxiliary agent. (9.9 parts by mass), 0.64 g (9.8 parts by mass) of styrene-butadiene copolymer (SBR) as a binder, and 11.02 g (3.4 parts by mass) of sodium carboxymethyl cellulose diluted to 2% by mass. ) And 11 g of water were added, and the mixture was stirred at 2000 rpm for 10 minutes using a rotating and revolving vacuum mixer Awatori Rentaro ARV-310 manufactured by Shinky Co., Ltd., and a defoaming operation was performed for 3 minutes. In this way, the slurry for the active material layer according to Comparative Example 2 was obtained. In the styrene-butadiene copolymer, the copolymerization ratio of styrene: butadiene [1,4 bodies]: butadiene [1,2 bodies] was 61:31: 8. Table 1 shows the content of each component in the solid content of the slurry for the active material layer according to Comparative Example 2.

A positive electrode according to Comparative Example 2 was produced in the same manner as in Example 1 except that the slurry for the active material layer according to Comparative Example 2 was used instead of the slurry for the active material layer according to Example 1. The thickness of the active material layer on the positive electrode according to Comparative Example 2 was 40 μm.

A lithium ion capacitor according to Comparative Example 2 was produced in the same manner as in Example 1 except that the positive electrode according to Comparative Example 2 was used instead of the positive electrode according to Example 1.

<Initial discharge capacity>
The lithium-ion capacitors according to each example and each comparative example are taken out from the glove box, and inside a constant temperature bath kept at 25 ° C., the current value corresponding to 1C is 10 in the voltage range of 3.8V to 2.2V. Cycle charging and discharging were performed, and the discharge capacity [mAh / g] of the first cycle was determined to be the initial discharge capacity Ai [mAh / g] of the lithium ion capacitors according to each Example and Comparative Example. The results are shown in Table 1.

<Discharge capacity at low temperature>
The lithium ion capacitors according to each example and each comparative example were charged and discharged in a constant temperature bath kept at −30 ° C. in a voltage range of 3.8 V to 2.2 V with a current value corresponding to 10 C. The discharge capacity Ac [mAh / g] was specified. The results are shown in Table 1.

<Evaluation of rapid charge / discharge>
Charging with a current value equivalent to 10C and equivalent to 200C in a voltage range of 3.8V to 2.2V inside a constant temperature bath in which the lithium ion capacitors according to each example and each comparative example are kept at 25 ° C. Charging and discharging accompanied by discharging at the current value was performed, and the discharging capacity Arf [mAh / g] at that time was specified. The results are shown in Table 1.

Charging with a current value equivalent to 200C and equivalent to 200C in a voltage range of 3.8V to 2.2V inside a constant temperature bath in which the lithium ion capacitors according to each example and each comparative example are kept at 25 ° C. Charging and discharging accompanied by discharging at the current value was performed, and the discharging capacity Ars [mAh / g] at that time was specified. The results are shown in Table 1.

As shown in Table 1, the lithium ion capacitor according to the example showed a higher discharge capacity at a low temperature than the lithium ion capacitor according to the comparative example. According to the comparison between Examples and Comparative Examples, when the active material layer comprises an active material containing polyaniline, the active material layer further comprises a conductive auxiliary agent having a high aspect ratio and a conductive auxiliary agent having a low aspect ratio. This suggests that the discharge capacity of the power storage device at low temperatures increases.

In addition, the lithium-ion capacitor according to the example showed a higher discharge capacity in rapid charge / discharge than the lithium-ion capacitor according to the comparative example. When the active material layer includes an active material containing polyaniline, the active material layer further includes a conductive auxiliary agent having a high aspect ratio and a conductive auxiliary agent having a low aspect ratio, so that the power storage device in rapid charge / discharge can be used. It was suggested that the discharge capacity would increase.

As shown in FIGS. 5 and 6, in the active material layer of each example, the carbon nanotube powder was present on the surface of the active material in a wider range than that of the conductive carbon black powder. In addition, the conductive carbon black powder was present in the gaps between the active materials.

1 Positive electrode 2 Negative electrode 3 Electrolyte layer 5 Power storage device 10 Active material layer 12 Active material 14a First conductive auxiliary agent 14b Second conductive auxiliary agent 15 Binder 16 Vacancies 20 Current collector 30 Conductive layer 32 Conductive particles 35 Binder

Claims (14)

Active materials, including electrochemically active polymers,
A first conductive auxiliary agent having an aspect ratio of 10 or more,
An active material layer for a positive electrode of a power storage device, comprising a second conductive auxiliary agent having an aspect ratio of less than 10. The active material layer for a positive electrode of a power storage device according to claim 1, wherein the sum of the content of the first conductive auxiliary agent and the content of the second conductive auxiliary agent is 1 to 30% on a mass basis. The active material layer for a positive electrode of a power storage device according to claim 1 or 2, wherein the ratio of the content of the first conductive auxiliary agent to the content of the second conductive auxiliary agent is 1 to 9900% on a mass basis. The activity for a positive electrode of a power storage device according to any one of claims 1 to 3, wherein the first conductive auxiliary agent is present on the surface of the active material in a wider range than that of the second conductive auxiliary agent. Material layer. The active material layer for a positive electrode of a power storage device according to any one of claims 1 to 4, wherein the second conductive auxiliary agent exists in a gap between the active materials. The active material layer for a positive electrode of a power storage device according to any one of claims 1 to 5, wherein the first conductive auxiliary agent contains a first conductive carbon material. The active material layer for a positive electrode of a power storage device according to claim 6, wherein the first conductive carbon material is carbon nanotubes. The active material layer for a positive electrode of a power storage device according to any one of claims 1 to 7, wherein the second conductive auxiliary agent contains a second conductive carbon material. The active material layer for a positive electrode of a power storage device according to claim 8, wherein the second conductive carbon material is carbon black. The active material layer for a positive electrode of a power storage device according to any one of claims 1 to 9, wherein the polymer contains at least one of a polyaniline and a polyaniline derivative having an oxidized body and a reduced body. The active material layer for a positive electrode of a power storage device according to claim 10, wherein the polyaniline and the polyaniline derivative contain 35 to 60% of an oxidized substance on a mass basis. The active material layer for a positive electrode of a power storage device according to any one of claims 1 to 11, wherein the polymer has an average particle size of more than 0.5 μm and 20 μm or less. A positive electrode for a power storage device provided with the active material layer for the positive electrode of the power storage device according to any one of claims 1 to 12. With the electrolyte layer,
A negative electrode arranged in contact with the first main surface of the electrolyte layer,
The positive electrode for a power storage device according to claim 13, which is arranged in contact with the second main surface of the electrolyte layer.
Power storage device.