JP2021034569A - Active material for power storage device positive electrode, positive electrode for power storage device, and power storage device - Google Patents

Abstract

To raise the initial discharge capacity of a power storage device.SOLUTION: An active material for a power storage device positive electrode according to the present invention comprises at least one of polyaniline and a polyaniline derivative, having an oxidant and a reductant. As to the active material for such a positive electrode, the ratio of a peak intensity of Mass number m/z:80 to a peak intensity of Mass number m/z:73, determined according to Time-Of-Flight secondary ion mass spectrometry (TOF-SIMS), is 1.30 or below.SELECTED DRAWING: None

Description

The present invention relates to an active material 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 containing polyaniline or a derivative thereof as an active material. Polyaniline in a reduction dedoping state is used for producing a positive electrode for a power storage device.

Japanese Unexamined Patent Publication No. 2014-53297

In Patent Document 1, no attempt has been made to produce a positive electrode for a power storage device using polyaniline in a semi-oxidized state having an oxidized body and a reduced body. Therefore, the present invention provides an active material for a positive electrode which is advantageous from the viewpoint of increasing the initial discharge capacity of a power storage device while containing at least one of a semi-oxidized polyaniline and a polyaniline derivative having an oxidized body and a reduced body.

The present invention
Containing at least one of a polyaniline and a polyaniline derivative having an oxidant and a reduced form,
The ratio of the peak intensity of mass number m / z: 80 to the peak intensity of mass number m / z: 73 determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is 1.30 or less. ,
Provided is an active material for a positive electrode of a power storage device.

The present invention also provides a positive electrode for a power storage device provided with an active material layer containing the above-mentioned active material 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 above-mentioned active material for the positive electrode of the power storage device is advantageous from the viewpoint of increasing the initial discharge capacity of the power storage device.

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

When polyaniline in a reduction dedoping state is used in the production of a positive electrode for a power storage device as in the technique described in Patent Document 1, it is difficult to improve the durability of the power storage device. Therefore, in order to eliminate the drawbacks of polyaniline in the reduction and dedoping state, it is possible to prepare a power storage device using a positive electrode active material containing at least one of a semi-oxidized polyaniline having an oxide and a reduced body and a polyaniline derivative. Conceivable. From this point of view, the present inventors have repeatedly studied the active material for the positive electrode, and found that a substance having a predetermined mass number near the surface of the active material for the positive electrode containing at least one of the semi-oxidized polyaniline and the polyaniline derivative. It was newly found that the amount affects the initial discharge capacity of the power storage device. Based on this new finding, the present inventors have devised an active material 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.

The active material for a positive electrode of a power storage device according to the present invention (hereinafter, may be referred to as “active material for positive electrode”) is referred to as at least one of a polyaniline and a polyaniline derivative (hereinafter, referred to as a “polyaniline compound”) having an oxidized substance and a reduced substance. May) include. In other words, the active material for the positive electrode contains a polyaniline-based compound in a semi-oxidized state. In addition, in the positive electrode active material, the ratio (Is / Ia) of the peak intensity Is of mass number m / z: 80 to the peak intensity Ia of mass number m / z: 73 determined by TOF-SIMS is 1. It is .30 or less.

When Is / Ia of the positive electrode active material is 1.30 or less, the initial discharge capacity of the power storage device manufactured by using the positive electrode active material tends to increase. In addition, the fact that Is / Ia of the active material for the positive electrode is 1.30 or less is advantageous from the viewpoint of increasing the discharge capacity of the power storage device at a low temperature (for example, −30 ° C.).

TOF-SIMS is a method of analyzing the surface of a sample. According to TOF-SIMS, the surface of the sample is irradiated with an ion beam (primary beam), and the ions (secondary ions) emitted from the surface of the sample are mass-separated by utilizing the flight time difference. When Is / Ia is 1.30 or less in the positive electrode active material, the amount of the substance having a mass number of m / z: 80 tends to decrease in the vicinity of the surface of the positive electrode active material. As a result, it is considered that the initial discharge capacity of the power storage device manufactured by using this positive electrode active material is likely to increase. Further, it is considered that this tends to increase the discharge capacity of the power storage device at a low temperature. TOF-SIMS measurements mass number of m / z: 80 peaks SO ₃ ^- may be attributed to. In other words, the mass number m / z: peak intensity of 80, for example SO ₃ ^- derived. Mass number m / z: 73 peaks of ion C ₆ H derived from an aromatic hydrocarbon structure ^- may belong to. In other words, the mass number m / z: peak intensity of 73, for example C ₆ H ^- derived.

If the content of S in the entire positive electrode active material is small, it is considered that Is / Ia in the positive electrode active material is likely to be adjusted to 1.30 or less. However, according to the studies by the present inventors, it has been found that a small content of S in the entire positive electrode active material is not necessarily associated with adjusting Is / Ia to a desired range. .. On the other hand, the present inventors have succeeded in adjusting the value of Is / Ia to a desired range as a result of repeated trial and error by reviewing the conditions for producing the active material for the positive electrode.

In the positive electrode active material, Is / Ia is preferably 1.00 or less, more preferably 0.80 or less, still more preferably 0.50 or less, and particularly preferably less than 0.50. In the positive electrode active material, Is / Ia can be, for example, 0.01 or more.

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.

The semi-oxidized polyaniline is typically obtained by electrolytic or chemical oxidative polymerization of aniline. The semi-oxidized polyaniline derivative is typically obtained by electrolytic or chemical oxidative polymerization of the aniline derivative. 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 semi-oxidized polyaniline-based compound is obtained by electrolytic polymerization or chemical oxidation polymerization of aniline or an aniline derivative, the polyaniline-based compound can be doped with a dopant such as 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 positive electrode active material. The protonic acid is, for example, hydrochloric acid or sulfuric acid.

When a polyaniline-based compound in a semi-oxidized state 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 not limited to a specific oxidizing agent as long as Is / Ia can be adjusted to 1.30 or less in the positive electrode active material. 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 and the polyaniline derivative contained in the active material for the positive electrode are preferably dedoping at the time of producing the positive electrode for the power storage device. Specifically, the polyaniline compound contained in the active material for the positive electrode is in a state in which a dopant such as a protonic acid is dedoping. In this case, the positive electrode active material is likely to be appropriately dispersed in the active material layer, 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 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 positive electrode active material 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 positive electrode active material 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 for the positive electrode is repeatedly doped and dedoping, so that it can be used as a power storage device.

For example, Is / Ia can be adjusted to 1.30 or less in the positive electrode active material by adjusting the production conditions of the polyaniline compound. For example, it is advantageous to use hydrochloric acid as the protonic acid for doping and to adjust the temperature of the polymerization reaction to a predetermined range from the viewpoint of adjusting Is / Ia to 1.30 or less in the positive electrode active material. The semi-oxidized polyaniline compound obtained as described above may be washed, classified, or pulverized. By performing such a treatment, Is / Ia may be adjusted to 1.30 or less in the positive electrode active material. 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 positive electrode active material 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. The average particle size of the positive electrode active material is the maximum of 50 or more positive electrode active materials when observing 50 or more positive electrode active materials using an electron microscope such as a scanning electron microscope (SEM). It can be determined by measuring the diameter. Alternatively, the average particle size of the positive electrode active material 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 positive electrode active material has, for example, a specific surface area of ^{1 m 2 / g or more.} The specific surface area of the positive electrode active material is typically measured according to the BET method. The positive electrode active material preferably has a specific surface area of ^{10 m 2 / g or more.} The positive electrode active material has, for example, a specific surface area of ^{100 m 2 / g or less.}

The positive electrode for a power storage device can be provided by using the above-mentioned active material for a positive electrode. As shown in FIG. 1, the positive electrode 1a for a power storage device includes an active material layer 10. The active material layer 10 contains the above-mentioned positive electrode active material (positive electrode active material 12). As a result, the initial discharge capacity of the power storage device manufactured by using the positive electrode 1a tends to increase. In addition, the discharge capacity of the power storage device manufactured by using the positive electrode 1a at a low temperature tends to be high.

The content of the positive electrode 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. Yes, especially preferably 60% or more. As a result, the energy density of the power storage device tends to increase. The content of the positive electrode 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, the first conductive auxiliary agent 14a. The first conductive auxiliary agent 14a has an aspect ratio of 10 or more. 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 conductive carbon material is, for example, a fibrous carbon material such as carbon fiber and carbon nanotube.

The aspect ratio of the first conductive auxiliary agent 14a is a value (L / W) obtained by dividing the maximum length L of the first conductive auxiliary agent 14a by the maximum width W of the first conductive auxiliary agent 14a in a specific direction. When the first conductive auxiliary agent 14a extends in a curved shape, the maximum length L is determined along the curved line. The maximum width W is the maximum value of the width of the first conductive auxiliary agent 14a in the direction perpendicular to the virtual straight line or curve that determines the maximum length L. 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 content of the first conductive additive 14a in the active material layer 10 is, for example, 1 to 30%, preferably 2 to 25%, more preferably 3 to 20%, and even more preferably 3 to 20% on a mass basis. It is 3 to 15%. As a result, the positive electrode active material 12 can be activated more reliably while suppressing the content of the first conductive auxiliary agent 14a. As a result, it is easy to increase the energy density of the power storage device.

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 positive electrode active material 12 and the outer surface of the first conductive auxiliary agent 14a. The binder 15 binds the positive electrode active material 12 and the first conductive auxiliary agent 14a. 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 manufactured by using the positive electrode 1a, the pores 16 are impregnated with the electrolytic solution. 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, it is considered that the desired characteristics related to rapid charging / discharging are likely to be exhibited in the power storage device.

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 positive electrode active material 12 have a good affinity, and the first conductive auxiliary agent 14a easily comes into contact with the positive electrode 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 positive electrode 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 positive electrode active material 12, if necessary. The active material other than the positive electrode 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.

As shown in FIG. 1, the positive electrode 1a 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 as long as the initial discharge capacity of the power storage device can be increased. 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 1a 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 positive electrode active material 12, the first conductive auxiliary agent 14a, and the binder 15 in a dispersion medium is applied to the surface of the conductive layer 30 to form a coating film, and the coating film is dried. The active material layer 10 can be formed by allowing the material to be formed. In this way, the positive electrode 1a can be manufactured. If necessary, an active material other than the positive electrode 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 1a, a slurry prepared by dispersing the positive electrode active material 12, the first conductive auxiliary agent 14a, and the binder 15 in a dispersion medium is applied to the main surface of the current collector 20. A coating film may be formed and the coating film may be dried to form the active material layer 10.

The positive electrode 1a may be changed as, for example, the positive electrode 1b shown in FIG. 2 and the positive electrode 1c shown in FIG. The positive electrodes 1b and 1c are configured in the same manner as the positive electrode 1a except for a portion to be particularly described. The components of the positive electrodes 1b and 1c that are the same as or correspond to the components of the positive electrode 1a are designated by the same reference numerals, and detailed description thereof will be omitted. The description of the positive electrode 1a also applies to the positive electrodes 1b and 1c, as long as there is no technical contradiction.

As shown in FIG. 2, in the positive electrode 1b, the active material layer 10 contains the second conductive auxiliary agent 14b instead of the first conductive auxiliary agent 14a. The second conductive auxiliary agent 14b has an aspect ratio of less than 10. 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 a conductive carbon material or a metallic material. The conductive carbon material is, for example, conductive carbon black such as acetylene black and Ketjen black.

The aspect ratio of the second conductive auxiliary agent 14b is a value (L / W) obtained by dividing the maximum diameter L of the second conductive auxiliary agent 14b by the maximum width W of the second conductive auxiliary agent 14b in a specific direction. The maximum width W is the maximum value of the width of the first conductive auxiliary agent 14a in the direction perpendicular to the virtual straight line extending in the direction defining the maximum diameter L. The aspect ratio of the second conductive auxiliary agent 14b may be 8 or less, 5 or less, or 3 or less.

Since the active material layer 10 contains the second conductive auxiliary agent 14b, the positive electrode active material 12 can be activated, and the energy density of the power storage device can be easily increased. In addition, the manufacturing cost of the positive electrode 1b tends to be low.

The content of the second conductive auxiliary agent 14b in the active material layer 10 is, for example, 1 to 30%, preferably 2 to 25%, and more preferably 3 to 20% on a mass basis. As a result, the positive electrode active material 12 can be activated more reliably while suppressing the content of the second conductive auxiliary agent 14b. As a result, it is easy to increase the energy density of the power storage device.

As shown in FIG. 3, in the positive electrode 1c, the active material layer 10 contains the first conductive auxiliary agent 14a and the second conductive auxiliary agent 14b. As a result, the first conductive auxiliary agent 14a and the second conductive auxiliary agent 14b can be arranged in a desired state around the positive electrode active material 12 in the active material layer 10. As a result, in particular, the discharge capacity of the power storage device manufactured by using the positive electrode 1c at a low temperature tends to be high.

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, for example, 1 to 30%, preferably 2 to 25%, based on the mass, and more. It is preferably 3 to 20%, and more preferably 4 to 15%.

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, for example, 1 to 9900%, and may be 10 to 900% on a mass basis. It may be 25 to 400%.

As shown in FIG. 4, the power storage device 5 can be provided by using the positive electrode 1a. The power storage device 5 includes an electrolyte layer 3, a negative electrode 2, and a positive electrode 1a. The negative electrode 2 is arranged in contact with the first main surface of the electrolyte layer 3. The positive electrode 1a is arranged in contact with the second main surface of the electrolyte layer 3. The active material layer 10 of the positive electrode 1a is in contact with the second main surface of the electrolyte layer 3. The electrolyte layer 3 is arranged between the positive electrode 1a and the negative electrode 2. Since the power storage device 5 includes the positive electrode 1a, it is easy to exhibit a high initial discharge capacity. The power storage device 5 may include a positive electrode 1b or 1c instead of the positive electrode 1a.

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 electrolyte layer 3 preferably contains an electrolyte having an imide anion. Such electrolytes are relatively readily available.

The electrolyte layer 3 more preferably contains at least one of lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethylsulfonyl) imide. In this case, the discharge capacity of the power storage device 5 at a low temperature tends to increase more reliably. When the electrolyte layer 3 contains at least one of lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethylsulfonyl) imide, the electrolyte layer 3 may contain only these electrolytes as an electrolyte. May contain electrolytes of the following types.

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) phenolic resin, polyimide, and calcined cellulose.
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 1a and the negative electrode 2. The separator prevents an electrical short circuit between the positive electrode 1a 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 1a 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>
(Preparation of positive electrode active material)
A semi-oxidized polyaniline powder (weight average molecular weight M _w : 100,000, distributor: Sigma-Aldrich) was obtained. Using a planetary rotary pot mill LP-4 manufactured by Ito Seisakusho, 10 g of polyaniline powder and a predetermined amount of water were mixed and stirred at a rotation speed of 200 rotations per minute (rpm). A zirconia crushed ball having a diameter of 1 mm was used for mixing and stirring. The capacity of the crushed balls was adjusted to 20% of the container capacity recommended by the manufacturer. After mixing and stirring, the polyaniline powder was taken out and dried to obtain an active material for a positive electrode according to Example 1.

The positive electrode active material according to Example 1 was vacuum-dried under the conditions of 100 ° C. and 3 hours to prepare a sample for measuring the specific surface area. The adsorption isotherm of nitrogen gas of the sample was measured using BELSORP-maxII manufactured by Microtrac Bell, and the specific surface area was determined according to the BET method (relative pressure range 0.05 to 0.3). The specific surface area of the positive electrode active material polyaniline according to Example 1 as measured by the BET method was 6 m ² / g.

The proportion of the oxidized substance in the polyaniline of the positive electrode active material according to Example 1 determined from the solid-state NMR spectrum was 50% by mass.

(Preparation of positive electrode)
5 g (69.9 parts by mass) of the positive electrode 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.), which is a conductive auxiliary agent, and a binder. As a result, 0.64 g (9 parts by mass) of styrene-butadiene copolymer (SBR) 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, and Shinky. Using a rotating and revolving vacuum mixer manufactured by 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 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. A sample prepared by fixing the conductive carbon black powder on the support film was observed with an electron microscope, and the aspect ratio of each powder was calculated from the images of 30 or more conductive carbon black powders arbitrarily selected. The arithmetic mean was calculated. As a result, the average aspect ratio of the conductive carbon black powder was 1.2. 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.

(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>
(Preparation of active material for positive electrode)
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. Then, 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 an active material for a positive electrode according to Example 2.

The specific surface area of the positive electrode active material according to Example 2 in polyaniline was measured according to the BET method in the same manner as in the positive electrode active material according to Example 1. The specific surface area of the positive electrode active material polyaniline according to Example 2 was 14 m ² / g.

The proportion of the oxidized substance in the polyaniline of the positive electrode active material according to Example 2 determined from the solid-state NMR spectrum was 45% by mass. The polyaniline contained in the positive electrode active material according to Example 2 was in a semi-oxidized state and in a de-doping state.

(Preparation of positive electrode)
5 g (69.9 parts by mass) of the positive electrode active material according to Example 2, 1.29 g (18 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 binder. As a result, 0.64 g (9 parts by mass) of the styrene-butadiene copolymer 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, and made by Shinky. Using a 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 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.

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.

(Manufacturing of power storage device)
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.

<Example 3>
The present invention relates to Example 3 in the same manner as in Example 2 except that a LiN (SO ₂ F) ₂ carbonate solution having a concentration of 1.2 M (mol / dm ³ _{) was used instead of the LiPF 6} carbonate solution as the electrolytic solution. A lithium ion capacitor was prepared.

<Example 4>
In Example 4 in the same manner as in Example 2 except that a LiN (SO ₂ CF ₃ ) ₂ carbonate solution having a concentration of 1.2 M (mol / dm ³ _{) was used instead of the LiPF 6} carbonate solution as the electrolytic solution. Such a lithium ion capacitor was manufactured.

<Example 5>
(Preparation of positive electrode)
CNT paste (manufactured by Cnano, product name: LB217-54) 12 containing 5 g (76.9 parts by mass) of the positive electrode active material and 5% by mass of carbon nanotube (CNT) powder as a conductive auxiliary agent according to Example 2. 9.9 g (9.9 parts by mass), 0.64 g (9.8 parts by mass) of styrene-butadiene copolymer as a binder, and 11.02 g (3.4 parts by mass) of sodium carboxymethyl cellulose diluted to 2% by mass. In addition to 6 g of water, 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 Example 5 was obtained. In the styrene-butadiene copolymer, the copolymerization ratio of styrene: butadiene [1,4 bodies]: butadiene [1,2 bodies] was 61:31: 8. The sample prepared by fixing the CNT powder used in Example 5 on the support film was observed with an electron microscope, and the aspect ratio of each powder was calculated from the images of 30 or more CNT powders arbitrarily selected, and the aspect ratio thereof was calculated. The arithmetic mean was calculated. As a result, the average value of the aspect ratio of the CNT powder was 50. An electron micrograph of the CNT powder is shown in FIG.

A positive electrode according to Example 5 was produced in the same manner as in Example 1 except that the slurry for the active material layer according to Example 5 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 Example 5 was 40 μm.

(Manufacturing of power storage device)
A lithium ion capacitor according to Example 5 was produced in the same manner as in Example 1 except that the positive electrode according to Example 5 was used instead of the positive electrode according to Example 1.

<Example 6>
(Preparation of positive electrode)
Separately from 5 g (76.9 parts by mass) of the positive electrode active material according to Example 2 and 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. CNT paste (manufactured by Cnano, product name: LB217-54) containing 5% by mass of carbon nanotube (CNT) powder, which is a conductive auxiliary agent of Add 0.64 g (9.8 parts by mass) of the combined product 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. Using the 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 Example 6 was obtained. In the styrene-butadiene copolymer, the copolymerization ratio of styrene: butadiene [1,4 bodies]: butadiene [1,2 bodies] was 61:31: 8.

A positive electrode according to Example 6 was produced in the same manner as in Example 1 except that the slurry for active material layer according to Example 6 was used instead of the slurry for active material layer according to Example 1. The thickness of the active material layer on the positive electrode according to Example 6 was 40 μm.

(Manufacturing of power storage device)
A lithium ion capacitor according to Example 6 was produced in the same manner as in Example 1 except that the positive electrode according to Example 6 was used instead of the positive electrode according to Example 1.

<Comparison example>
A semi-oxidized polyaniline powder (weight average molecular weight M _w : 100,000, distributor: Sigma-Aldrich) was used as it was as an active material for a positive electrode according to a comparative example. The specific surface area of the positive electrode active material according to the comparative example in polyaniline was measured according to the BET method in the same manner as in the positive electrode active material according to Example 1. The specific surface area of the positive electrode active material polyaniline according to the comparative example was 8 m ² / g.

5 g (69.9 parts by mass) of the positive electrode active material and 1.29 g (18 parts by mass) of conductive carbon black powder (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.), which is a conductive auxiliary agent, as a binder. 0.64 g (9 parts by mass) of a styrene-butadiene copolymer 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, and a rotation manufactured by Shinky Co., Ltd. was added. Using a revolving vacuum mixer Awatori Rentaro 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 the comparative example was obtained. In the styrene-butadiene copolymer, the copolymerization ratio of styrene: butadiene [1,4 bodies]: butadiene [1,2 bodies] was 61:31: 8.

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

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

<Particle size measurement>
Using a particle image analyzer (manufactured by Malvern, product name: Morphologi G3), the particle size distribution based on the number of positive electrode active materials according to Examples 1 and 2 was measured, and the average particle size (from the measurement results) D50) was determined. The average particle size of the positive electrode active material according to Example 1 was 3 μm, and the average particle size of the positive electrode active material according to Example 2 was 2 μm.

<TOF-SIMS>
A sample for TOF-SIMS was prepared from the positive electrode active material according to Examples 1 and 2 and the positive electrode active material according to Comparative Example. TOF-SIMS was performed on each sample using a TOF-SIMS device (manufactured by ULVAC-PHI, product name: TRIFT V). In this analysis, Bi ₃ ²⁺ was used as the primary ion, the primary ion acceleration voltage was adjusted to 30 kV, and the measurement area was adjusted to 100 μm square. From the analysis results, the peak intensity of mass number m / z: 73, the peak intensity of mass number m / z: 80, and the peak intensity of mass number m / z: 97 were determined. Next, these peaks were assigned. Mass number m / z: 73 peaks of C ₆ H ^- was assigned to be. Mass number m / z: 80 peaks SO ₃ ^- was assigned to be. Mass number m / z: 97 peaks HSO ₄ ^- was assigned to be. Then, C ₆ H ^- (mass number m / z: 73) to the peak intensity of (Ia), SO ₃ ^- (mass number m / z: 80) the ratio of the peak intensity of (Is) (Is / Ia) I asked. Then, C ₆ H ^- (mass number m / z: 73) to the peak intensity of (Ia), HSO ₄ ^- (mass number m / z: 97) the ratio of the peak intensity of (Ih) (Ih / Ia) I asked. The results are shown in Table 1.

<Ion chromatograph>
A sample of ion chromatography was prepared from the positive electrode active material according to Examples 1 and 2 and the positive electrode active material according to Comparative Example. Ion chromatography (IC) was performed on each sample using an ion chromatograph (manufactured by Thermo Fisher Scientific, product name: ICS-3000). As a measuring method, a combustion IC that completely burns each sample was used, S contained in the sample was _{detected as sulfate ion SO 4} ^2- , and the total S conversion amount was determined. The results are shown in Table 1.

<Initial discharge capacity>
The lithium-ion capacitors according to each example and comparative example are taken out from the glove box, and inside a constant temperature bath kept at 25 ° C., 10 cycles with a current value corresponding to 1C in a voltage range of 3.8V to 2.2V. After charging and discharging, the discharge capacity [mAh / g] in 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 the examples and comparative examples are charged and discharged at a current value corresponding to 10C in a voltage range of 3.8V to 2.2V inside a constant temperature bath kept at −30 ° C. to discharge. The volume Ac [mAh / g] was identified. The results are shown in Table 1.

As shown in Table 1, the initial discharge capacity Ai of the lithium-ion capacitor according to each example was higher than the initial discharge capacity Ai of the lithium-ion capacitor according to the comparative example. Comparing Example 1 and Comparative Example, the concentration of the total S conversion amount based on the IC in the sample prepared from the positive electrode active material of Example 1 is based on the IC in the sample prepared from the positive electrode active material of Comparative Example. It was higher than the concentration of the total S conversion amount. On the other hand, the value of Is / Ia in the sample prepared from the positive electrode active material of Example 1 is 1.30 or less, whereas the value of Is / Ia in the sample prepared from the positive electrode active material of Comparative Example is 1. It was over .30. Therefore, it was suggested that the Is / Ia value of 1.30 or less in the positive electrode active material is advantageous for increasing the initial discharge capacity of the power storage device and the discharge capacity at low temperature. In other words, in the TOF-SIMS, SO ₃ is detected from the vicinity of the surface of the positive electrode active material ^- it is less advantageous in terms of increasing the discharge capacity at the initial discharge capacity and low temperature of the electric storage device has been suggested ..

According to Example 2, the value of Is / Ia in the sample prepared from the active material for the positive electrode is less than 0.50, which suggests that this is advantageous for further increasing the discharge capacity at low temperature. It was.

According to the comparison between Example 2 and Examples 3 and 4, the use of LiN (SO ₂ F) ₂ and LiN (SO ₂ CF ₃ ) ₂ as the solute of the electrolytic solution further enhances the discharge capacity at low temperature. It was suggested that it is particularly advantageous. The maximum anion radius of LiN (SO ₂ F) ₂ is 3.5 angstroms, and the maximum anion radius of LiN (SO ₂ CF ₃ ) ₂ is 4.7 angstroms. On the other hand, the maximum anion radius of _{LiPF 6 is 2.7 angstroms.}

According to the comparison between Example 2 and Examples 5 and 6, it is advantageous that the active material layer contains a conductive auxiliary agent having a high aspect ratio in order to further increase the discharge capacity at low temperature, and the active material. It was suggested that it is particularly advantageous that the layer contains both a high aspect ratio conductive auxiliary agent and a low aspect ratio conductive auxiliary agent.

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

Claims (11)

Containing at least one of a polyaniline and a polyaniline derivative having an oxidant and a reduced form,
The ratio of the peak intensity of mass number m / z: 80 to the peak intensity of mass number m / z: 73 determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is 1.30 or less. ,
Active material for positive electrode of power storage device. Mass number m / z: peak intensity of 73 C ₆ H ^- derived from, the mass number m / z: peak intensity of 80 SO ₃ ^- from, storage device for the positive electrode active material according to claim 1. The active material for a positive electrode of a power storage device according to claim 1 or 2, wherein the polyaniline and the polyaniline derivative contain 35 to 60% of an oxidized substance on a mass basis. The active material for a positive electrode of a power storage device according to any one of claims 1 to 3, which has an average particle size of more than 0.5 μm and 20 μm or less. The active material for a positive electrode of a power storage device according to any one of claims 1 to 4, wherein the specific surface area measured according to the BET method is 10 m ^{2 / g or more.} A positive electrode for a power storage device, comprising an active material layer containing the active material for the positive electrode for the power storage device according to any one of claims 1 to 5. The positive electrode for a power storage device according to claim 6, wherein the active material layer further contains a first conductive auxiliary agent having an aspect ratio of 10 or more. The positive electrode for a power storage device according to claim 6, wherein the active material layer further contains a first conductive auxiliary agent having an aspect ratio of 10 or more and a second conductive auxiliary agent having an aspect ratio of less than 10. .. 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 any one of claims 6 to 8, which is arranged in contact with the second main surface of the electrolyte layer.
Power storage device. The storage device according to claim 9, wherein the electrolyte layer contains an electrolyte having an imide anion. The storage device according to claim 9, wherein the electrolyte layer contains at least one of lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethylsulfonyl) imide.