WO2012144439A1

WO2012144439A1 - Electrode for electrical storage device, and electrical storage device

Info

Publication number: WO2012144439A1
Application number: PCT/JP2012/060134
Authority: WO
Inventors: 一郎梶原; 達朗本多; 真希前川; 修小瀬
Original assignee: Jsr株式会社
Priority date: 2011-04-21
Filing date: 2012-04-13
Publication date: 2012-10-26
Also published as: JPWO2012144439A1

Abstract

This electrode for an electrical storage device is provided with a current collector, and an active material layer formed on the surface of the current corrector. The electrode is characterized in that the active material layer includes at least a polymer and an active material, and that polymer distribution coefficient of the active material layer is 1.1-3.

Description

Electrode for power storage device and power storage device

The present invention relates to an electrode for an electricity storage device and an electricity storage device including the electrode.

In recent years, a power storage device having a high voltage and a high energy density has been required as a power source for driving electronic equipment. In particular, lithium ion batteries and lithium ion capacitors are expected as power storage devices having high voltage and high energy density.

An electrode for an electricity storage device used for such an electricity storage device is produced by applying and drying a mixture of polymer particles and active material particles on the surface of a current collector. Properties required for such polymer particles include bonding between the active material particles and adhesion between the active material particles and the current collector (hereinafter also simply referred to as “binding property”), and a step of winding the electrode. Scratch resistance of the active material (hereinafter also simply referred to as “active material layer”) applied by the subsequent cutting, etc. And so on). When the electrodes satisfy these required characteristics, the electrode folding method, the winding radius, and the like can be easily designed, and the power storage device can be reduced in size.

Generally, polymer particles used for producing an active material layer are non-conductive and therefore tend to hinder the movement of electrons. For this reason, reducing the amount of polymer particles used is effective in improving the electrical characteristics of the electricity storage device. However, if the amount of the polymer particles used is reduced, the above-described binding property and powder falling property are deteriorated, and the workability is greatly deteriorated, which is not practical. For this reason, there is a limit in reducing the amount of polymer particles used, and there is a trade-off relationship between improvement in electrical characteristics.

It is also known that the polymer component is unevenly distributed along the thickness direction of the active material layer. For example, when the polymer component in the active material layer is relatively reduced at the interface between the current collector and the active material layer, the adhesion between the current collector and the active material layer is significantly reduced. It has been known. In order to control the uneven distribution of such polymer components, for example, Japanese Patent Application Laid-Open No. 10-270013 discloses that an active material layer is coated on a current collector in the vicinity of the current collector. A technique for increasing the concentration of the polymer component is disclosed.

However, even though the above-described technology can improve the binding property and powder-off property by controlling the uneven distribution of the polymer component in the active material layer, it can sufficiently exhibit the electrical characteristics of the electricity storage device. I couldn't.

Therefore, some embodiments according to the present invention provide an electrode for an electricity storage device that is excellent in binding properties and powder-off properties and has excellent electrical characteristics by solving the above-described problems.

The present invention has been made to solve at least a part of the above-described problems, and can be realized as the following aspects or application examples.

[Application Example 1]
One aspect of the electrode for an electricity storage device according to the present invention is:
An electrode for an electricity storage device comprising a current collector and an active material layer formed on a surface of the current collector,
The active material layer includes at least a polymer and an active material,
The active material layer has a polymer distribution coefficient of 1.1 to 3.

[Application Example 2]
In the electricity storage device electrode of Application Example 1,
When the thickness of the active material layer is T, the content of the polymer per unit volume contained in the active material layer from the surface in contact with the current collector to the thickness direction T / 2 is expressed as Ma (g / cm ³ ), When the polymer content per unit volume contained in the active material layer from the thickness direction T / 2 to T is Mb (g / cm ³ ), the ratio (Ma / Mb) is 3-6. Can be in range.

[Application Example 3]
In the electricity storage device electrode of Application Example 1 or Application Example 2,
The active material may contain a silicon active material.

[Application Example 4]
In the electrode for an electricity storage device of any one of Application Examples 1 to 3,
The active material layer was formed by applying a slurry for an electrode containing at least (A) polymer particles, (B) active material particles, and (C) water on the surface of the current collector, and then drying the electrode slurry. It may include a first layer and a second layer formed by applying the electrode slurry to the surface of the first layer and further drying.

[Application Example 5]
In the electrode for the electricity storage device of Application Example 4,
The thickness of the first layer can be smaller than the thickness of the second layer.

[Application Example 6]
In the electricity storage device electrode of Application Example 4 or Application Example 5,
One or more layers may be formed on the second layer by applying the electrode slurry and further drying the slurry.

[Application Example 7]
In the electrode for an electricity storage device according to any one of Application Example 4 to Application Example 6,
In the electrode slurry, the ratio (Db / Da) of the average particle diameter (Da) of the (A) polymer particles to the average particle diameter (Db) of the (B) active material particles is in the range of 20-100. Can be.

[Application Example 8]
In the electrode for the electricity storage device of any one of Application Examples 4 to 7,
The distribution of the polymer particles (A) is 2 to 60% by volume in a particle diameter section of 0.01 μm or more and less than 0.25 μm, and 40 to 98% by volume in a particle diameter section of 0.25 μm or more and 0.5 μm or less. Can have.

[Application Example 9]
In the electrode for the electricity storage device of any one of Application Example 4 to Application Example 8,
The average particle diameter (Db) of the (B) active material particles may be 1 to 200 μm.

[Application Example 10]
One aspect of the electricity storage device according to the present invention is:
The power storage device electrode according to any one of Application Examples 1 to 9 is provided.

According to the electrode for an electricity storage device according to the present invention, the binding property between the current collector and the active material layer is good, the powdering property is excellent, and the electrical characteristics are also excellent. Moreover, according to the electricity storage device provided with such an electrode for electricity storage devices, the charge / discharge rate characteristic which is one of the electrical characteristics is improved.

FIG. 1 is a cross-sectional view schematically showing an electricity storage device electrode according to the present embodiment.

Hereinafter, preferred embodiments according to the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, Various modifications implemented in the range which does not change the summary of this invention are also included.

1. Electrode for electricity storage device 1.1. Configuration and Features FIG. 1 is a cross-sectional view schematically showing an electricity storage device electrode according to the present embodiment. As shown in FIG. 1, the electrode 100 for an electricity storage device includes a current collector 10 and an active material layer 20 formed on the surface of the current collector 10.

The shape of the current collector 10 is not particularly limited, but usually a sheet-like one having a thickness of about 0.001 to 0.5 mm is used. The current collector 10 is not particularly limited as long as it is made of a conductive material. In the case of a lithium ion secondary battery, metal foils such as iron, copper, aluminum, nickel, and stainless steel can be used, and it is preferable to use aluminum for the positive electrode and copper for the negative electrode. In the case of a nickel metal hydride secondary battery, a punching metal, an expanded metal, a wire mesh, a foam metal, a mesh metal fiber sintered body, a metal plated resin plate, and the like can be given.

The active material layer 20 is a layer formed by applying an electrode slurry, which will be described later, to the surface of the current collector 10 and further drying it. Since the slurry for electrodes contains (A) polymer particles and (B) active material particles, the active material layer 20 includes at least a polymer and an active material. The thickness of the active material layer 20 is not particularly limited, but is usually 0.005 to 5 mm, preferably 0.01 to 2 mm.

The method for applying the electrode slurry to the surface of the current collector 10 is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, an immersion method, and a brush coating method. What is necessary is just to adjust suitably the quantity of the slurry for electrodes to apply | coat so that it may become the thickness of the active material layer mentioned above.

The method for drying the applied electrode slurry is not particularly limited. For example, drying by warm air, hot air, low-humidity air, vacuum drying, drying by irradiation with (far) infrared rays, electron beams or the like can be mentioned. The drying speed is usually adjusted so that the liquid medium can be removed as quickly as possible within a speed range in which the active material layer does not crack due to stress concentration or the active material layer does not peel from the current collector.

Furthermore, the density of the electrode for the electricity storage device may be increased by pressing the dried current collector. Examples of the pressing method include a mold press and a roll press.

The electrode 100 for an electricity storage device according to the present embodiment is characterized in that the polymer distribution coefficient of the active material layer 20 is in the range of 1.1 to 3, which is in the range of 1.2 to 2.5. Preferably, it is in the range of 1.4 to 2.

In the present invention, the “polymer distribution coefficient” is a coefficient defined by the following measurement method.

That is,
(1) The active material layer 20 is formed on one surface of the current collector 10 by the method described above. This is divided into two to produce two electrodes 100 for an electricity storage device having the same active material layer 20.
(2) A double-sided tape (product number “NW-25” manufactured by Nichiban Co., Ltd.) is pasted on an aluminum plate prepared in advance, and a Kapton tape (product number “650S” manufactured by Terraoka Co., Ltd.) is further applied on the double-sided tape. )) With the adhesive side facing up.
(3) On the adhesive surface of the Kapton tape prepared in (2), it is bonded to one active material layer side of the electrode prepared in (1) and is pressure-bonded with a roller.
(4) The current collector 10 is faced up and the aluminum plate produced in (3) is fixed on a horizontal plane, and then the current collector 10 is directed upward so that the angle with the aluminum plate is 90 degrees. The current collector 10 is peeled off from the adhesive surface between the current collector 10 and the active material layer 20.
(5) From both sides of the peeled interface, that is, from the surface of the active material layer remaining on the current collector 10 to a depth of 1.5 μm (all remaining if only a thickness of 1.5 μm or less remains) The active material layer 20 and the active material layer 20 having a depth of 1.5 μm from the surface of the active material layer remaining on the adhesive tape side are scraped off, and this is designated as “measurement sample A”.
(6) The entire active material layer 20 is scraped off from the other electrode for electricity storage device 100 produced in (1), and this is designated as “measurement sample B”.
(7) About each of the measurement sample A and the measurement sample B, it analyzes using the pyrolysis gas chromatography which has a high frequency induction heating system pyrolyzer, and content (mass%) of the polymer component per unit weight of each sample is calculated | required. calculate. A polymer distribution coefficient is calculated by substituting the obtained value into the following formula (1).
Polymer distribution coefficient = (polymer content of measurement sample A: mass%) / (polymer content of measurement sample B: mass%) (1)

In addition, according to the said Formula (1), if a polymer distribution coefficient is 1, it will represent that the polymer component in the active material layer 20 is distributed uniformly. Further, if the polymer distribution coefficient is a value exceeding 1, the polymer component is unevenly distributed in the vicinity of the peeling interface between the current collector 10 and the active material layer 20, and if the polymer distribution coefficient is less than 1, the current collector is present. It can be interpreted that the polymer component in the vicinity of the peeling interface between 10 and the active material layer 20 is sparse.

Generally, an active material repeatedly expands and contracts in volume as lithium ions are stored and released. In particular, it is known that an active material such as a carbonaceous material or a silicon material undergoes a large volume change due to insertion and extraction of lithium ions. When the electrode for an electricity storage device has an active material layer containing such an active material, the active material layer repeatedly expands and contracts as the electricity storage device is charged and discharged, and therefore the active material layer does not change in volume at all. There was a problem that the charge and discharge characteristics deteriorated rapidly due to peeling from the electric body.

However, when the polymer distribution coefficient of the active material layer is 1.1 to 3 as in the electrode for the electricity storage device according to the present embodiment, the polymer component is sufficiently near the interface between the current collector and the active material layer. Therefore, even if the active material layer repeats a large volume expansion and contraction, the binding property between the current collector and the active material layer can be sufficiently maintained, and the powder falling property is excellent. An electrode for an electricity storage device that is also excellent in electrical characteristics can be obtained. In particular, when an active material containing silicon (Si) having a large volume expansion / contraction rate is used as the negative electrode active material, the electrode for an electricity storage device according to the present embodiment has excellent binding properties and good charge / discharge characteristics. Show.

In the power storage device electrode 100 according to the present embodiment, the density of the active material layer 20 is preferably 1.2 to 1.8 g / cm ³ , and preferably 1.3 to 1.7 g / cm ^3. Is more preferably 1.4 to 1.6 g / cm ³ . If the density of the active material layer is in the above range, particularly the lower limit value or more, the polymer component sufficiently functions as a binder in the active material layer, so that the active material layer is agglomerated and peeled off, resulting in a decrease in powder fallability. Can be prevented. In addition, when the density of the active material layer is equal to or less than the upper limit value, the active material layer can sufficiently follow the flexibility of the current collector, and therefore, interface peeling between the current collector and the active material layer can be prevented.

In the present invention, the “density of the active material layer” is a value measured by the following measuring method. That is, by the method described above, an active material layer having an area C (cm ² ) and a thickness D (μm) is formed on one surface of the current collector to produce an electrode for an electricity storage device. When the mass of the current collector is A (g) and the mass of the produced electricity storage device electrode is B (g), the density of the active material layer is calculated by the following formula (2).
Active material layer density (g / cm ³ )
= (B (g) -A ( g)) / (C (cm 2) × D (μm) × 10 -4) ····· (2)

In the electricity storage device electrode 100 according to the present embodiment, when the thickness of the active material layer 20 is T, the unit included in the active material layer 20 from the surface in contact with the current collector 10 to the thickness direction T / 2. The polymer content per volume is Ma (g / cm ³ ), and the polymer content per unit volume contained in the active material layer 20 from the thickness direction T / 2 to T is Mb (g / cm 3). ³ ), the ratio (Ma / Mb) is preferably in the range of 3 to 6, and more preferably in the range of 3.5 to 5.

When the ratio (Ma / Mb) is in the above range, the binding property between the current collector and the active material layer is good, and an electrode for an electricity storage device that is excellent in powder fall-off property and excellent in electrical characteristics can be obtained. When the ratio (Ma / Mb) is less than the above range, the polymer component that functions as a binder is relatively less at the interface between the current collector and the active material layer, and thus the adhesion between the current collector and the active material layer. Tends to decrease. When the ratio (Ma / Mb) exceeds the above range, the binder component as an insulator is localized at the interface between the current collector and the active material layer, thereby increasing the internal resistance of the electrode and impairing the electrical characteristics. There is a tendency to be.

The ratio (Ma / Mb) is calculated from the following measurement method.

That is,
(1) First, an electricity storage device electrode 100 in which the active material layer 20 is formed on one surface of the current collector 10 is prepared.
(2) When the thickness of the active material layer 20 is T, the active material layer 20 is cut from the surface in contact with the current collector 10 in the thickness direction T / 2. If it cannot be cut, the upper layer portion from the thickness direction T / 2 to T may be scraped off. The active material layer 20 cut or scraped in this way is referred to as “measurement sample B”. On the other hand, all the active material layer 20 remaining on the current collector 10 is scraped off, and this is referred to as “measurement sample A”.
(3) About each of the measurement sample A and the measurement sample B, it analyzes using the pyrolysis gas chromatography which has a high frequency induction heating system pyrolyzer, Polymer content Ma per unit volume of the measurement sample A Ma (g / cm ³ ) and the polymer content Mb (g / cm ³ ) per unit volume of the measurement sample B are determined, and the ratio (Ma / Mb) is calculated.

The electricity storage device electrode 100 according to the present embodiment is preferably produced by a method in which an active material layer 20 is formed by multilayer coating of electrode slurry described later. Hereinafter, this method will be specifically described.

First, an electrode slurry described later is applied to the surface of the current collector 10, and is preferably dried at a temperature of 100 ° C. or higher to form a first layer that is a lower layer of the active material layer 20. Next, after applying an electrode slurry, which will be described later, to the surface of the first layer, it is preferably dried at a temperature of 100 ° C. or higher to form a second layer that is an upper layer of the active material layer. That is, the active material layer 20 is formed by applying a slurry for electrodes described later on the surface of the current collector 10 in a multilayer manner. In addition, it is preferable to dry at the temperature of 100 degreeC or more because it is necessary to evaporate the water contained in the slurry for electrodes.

The first layer of the active material layer 20 is considered to have a porous structure. Then, it is considered that the electrode slurry is infiltrated into the first layer by applying the electrode slurry to the surface of the first layer. Thereby, the content of the polymer component in the first layer in contact with the current collector 10 is increased. Therefore, according to this method, it is possible to easily produce an electrode for an electricity storage device in which the binding property between the current collector and the active material layer is good.

According to the above method, it is not necessary to change the polymer content for each of the electrode slurry used when forming the first layer and the electrode slurry used when forming the second layer. A slurry for use may be used. Thereby, a coating process can be simplified in the said method.

In the active material layer 20 manufactured by the above method, the thickness of the first layer is preferably thinner than the thickness of the second layer. Since a large amount of water is contained in the electrode slurry described later, it is considered that when the electrode slurry is applied to the surface of the first layer, water penetrates into the first layer. The second layer formed by drying in this state tends to have a rough surface. However, by making the thickness of the first layer thinner than the thickness of the second layer, the amount of water soaked becomes appropriate, and a good surface state in which the surface roughness of the second layer is reduced can be formed.

In the above method, one or more layers serving as the upper layer of the active material layer 20 are formed on the second layer by applying an electrode slurry described later, and preferably drying at a temperature of 100 ° C. or higher. Further, it may be formed.

1.2. As described above, the active material layer 20 is formed by collecting, on the surface of the current collector 10, an electrode slurry containing (A) polymer particles, (B) active material particles, and (C) water. It is formed by applying to the surface of the body 10 and further drying. Hereinafter, a slurry for an electrode that can be used for producing an electrode for an electricity storage device according to the present embodiment will be described in detail.

The electrode slurry used in the present embodiment is a dispersion for forming an active material layer by coating and drying on the surface of a current collector. (A) Polymer particles (hereinafter referred to as “(A) Component)), (B) active material particles (hereinafter also referred to as “component (B)”), and (C) water (hereinafter also referred to as “component (C)”).

The electrode slurry used in the present embodiment is a ratio (Db / Da) between the average particle diameter (Da) of the polymer particles (A) and the average particle diameter (Db) of the active material particles (B). Is preferably in the range of 20 to 100, more preferably in the range of 25 to 95, and particularly preferably in the range of 30 to 90.

When water is contained as a dispersion medium in the electrode slurry, in the step of applying and drying the electrode slurry on the surface of the current collector, the component (A) and / or the component (B) has surface tension. It has been confirmed that the film moves along the thickness direction of the coating film (hereinafter, also referred to as “migration”). Specifically, the component (A) and / or the component (B) tend to move to the side opposite to the surface in contact with the current collector of the coating film, that is, the gas-solid interface side where water evaporates.

As a result, since the distribution of the component (A) and the component (B) is not uniform in the thickness direction of the coating film, the electrode characteristics are deteriorated or the adhesion between the current collector and the active material layer is impaired. A problem occurs. For example, the component (A) acting as a binder bleeds (transfers) to the gas-solid interface side of the active material layer, and the amount of the component (A) at the interface between the current collector and the active material layer is relatively small. In such a case, the electrical characteristics deteriorate due to the inhibition of the penetration of the electrolytic solution into the active material layer, and the binding between the current collector and the active material layer tends to decrease and peeling tends to occur. is there. Furthermore, the smoothness of the surface of the active material layer tends to be impaired by bleeding of the component (A).

However, when the ratio (Db / Da) is within the above range, the occurrence of the above-described problems can be suppressed, and an electrode having both good electrical characteristics and adhesion can be produced.

Further, the electrode slurry used in the present embodiment preferably has a spinnability of 30 to 80%, more preferably 33 to 79%, and particularly preferably 35 to 78%. . When the spinnability is less than the above range, the leveling property is insufficient when the electrode slurry is applied onto the current collector, so that it is difficult to obtain the uniformity of the electrode thickness. If such an electrode having a non-uniform thickness is used, an in-plane distribution of charge / discharge reaction occurs, making it difficult to achieve stable battery performance. On the other hand, if the spinnability exceeds the above range, dripping easily occurs when the electrode slurry is applied onto the current collector, and it is difficult to obtain an electrode with stable quality. If the spinnability is within the above range, the occurrence of these problems can be suppressed, and an electrode having both good electrical characteristics and binding properties can be produced.

It should be noted that the “threadability” in the present invention can be measured as follows.

First, a Zaan cup (made by Dazai Equipment Co., Ltd., Zaan Biscocity Cup No. 5) having an opening with a diameter of 5.2 mm at the bottom is prepared. With the opening of the Zahn cup closed, 40 g of electrode slurry is poured into the Zahn cup. Thereafter, when the opening is opened, the electrode slurry flows out from the opening. Here, when T ₀ when opening the _opening, the T _A when the thread of the electrode slurry is _completed, when the outflow of the electrode slurry is completed the T _B, "spinnability in the present invention The “characteristic” can be obtained from the following formula (3).
Spinnability (%) = ((T _A −T ₀ ) / (T _B −T ₀ )) × 100 (3)

Next, each component contained in the electrode slurry used in the present embodiment will be described in detail.

1.2.1. (A) Polymer particles (A) The polymer particles contained in the electrode slurry used in the present embodiment are components that function as a binder for binding the active material particles to the current collector (B). is there.

(A) The average particle diameter (Da) of the polymer particles is preferably in the range of 0.05 to 0.4 μm, more preferably in the range of 0.06 to 0.39 μm, and 0.07 to A range of 0.38 μm is particularly preferable. (A) When the average particle diameter (Da) of the polymer particles is in the above range, the balance of the adsorption amount of the (A) polymer particles to the (B) active material particle surface becomes good, and the occurrence of migration is suppressed. be able to.

Further, (A) the polymer particles preferably satisfy the following requirements [1] and [2].
[1] 2 to 60% by volume, preferably 3 to 55% by volume, more preferably 4 to 50% by volume of polymer particles are present in a particle diameter section of 0.01 μm or more and less than 0.25 μm.
[2] Polymer particles should be present in a particle size interval of 0.25 μm to 0.5 μm in an amount of 40 to 98% by volume, preferably 45 to 97% by volume, more preferably 50 to 96% by volume.

When the ratio of the polymer particles in the above requirements [1] and [2] is in the above range, it is possible to effectively suppress the uneven distribution of the polymer particles at the interface between the obtained active material layer and air. Therefore, the penetration of the electrolytic solution into the active material layer can be promoted. This is preferable because electrical characteristics such as charge / discharge characteristics are improved and the binding between the current collector and the active material layer can be improved to prevent peeling and the like. Furthermore, when the abundance ratio of the polymer particles in the above requirements [1] and [2] is in the above range, there is a tendency that the powder falling property can be improved.

(A) The average particle diameter (Da) and particle size distribution of the polymer particles are measured by using a particle size distribution measuring apparatus based on the light scattering method. Examples of such a particle size distribution measuring apparatus include Coulter LS230, LS100, LS13 320 (manufactured by Coulter, Inc.) and FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.). This particle size distribution measuring apparatus is not intended to evaluate only primary particles of polymer particles, but also evaluates secondary particles formed by aggregation of primary particles. Therefore, the particle size distribution obtained by this particle size distribution measuring apparatus can be used as an index of the dispersion state of the (A) polymer particles contained in the electrode slurry.

In addition, (A) The average particle diameter (Da) and particle size distribution of the polymer particles are measured by centrifuging the electrode slurry and (B) precipitating the active material particles, and then measuring the supernatant liquid by the above method. Can be obtained.

(A) The polymer constituting the polymer particles is not particularly limited as long as it functions as a binder for binding the active material particles to the current collector (B). For example, (meth) acrylic acid Known materials such as ester (co) polymers, styrene- (meth) acrylic acid ester copolymers, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and polybutadiene can be used.

The polymer is preferably a rubbery polymer having a glass transition temperature (hereinafter referred to as “Tg”) of −80 to + 50 ° C., more preferably −75 to + 30 ° C., particularly preferably −70 to + 10 ° C. It is preferable that If a polymer with a Tg too low is used, the battery capacity may be reduced. If a polymer with a Tg too high is used, the binding force may be reduced, or the battery characteristics may vary greatly with temperature. is there.

(A) The method for producing the polymer particles is not particularly limited, and examples thereof include emulsion polymerization, seeding emulsion polymerization, suspension polymerization, seeding suspension polymerization, and solution precipitation polymerization. A solution-dispersion method is also possible in which polymer particles are dissolved or swollen in a solvent, stirred and mixed in a medium incompatible with the solvent, and then desolvated. Moreover, you may perform physical modification | denaturation, such as chemical modification and electron beam irradiation, with respect to the polymer particle obtained by these.

(A) The polymer particles can be synthesized in one stage by separately adding a dispersion stabilizer to the polymerization system during the reaction using emulsion polymerization or suspension polymerization among the above polymerization methods. 2 to 60% by volume in a particle size interval of 0.01 μm or more and less than 0.25 μm and 40 to 40 μm in a particle size interval of 0.25 μm or more and 0.5 μm or less so as to satisfy the above requirements [1] and [2]. A method of synthesizing a liquid medium dispersion in which polymer particles having a distribution of 98% by volume are dispersed in a liquid medium in one step is preferable from the viewpoint of improving productivity. Such a dispersion can be prepared by controlling the particle size distribution of the polymer particles by the known synthesis method described above.

In addition, the (A) polymer particles not only use a liquid medium dispersion containing the polymer particles synthesized in one stage as described above, but also include small particle size polymer particle components and large particle size polymer particles. It is also possible to obtain the components in two stages by separately obtaining the components by the polymerization method and mixing them.

As a specific method for obtaining the polymer particles (A) satisfying the requirements of the above [1] and [2], the liquid particles of the polymer particles having a mode diameter of 0.01 μm or more and less than 0.25 μm are used. 2 to 60 parts by mass of the medium dispersion liquid (I) in terms of polymer particles and the liquid medium dispersion liquid (II) of polymer particles having a mode particle diameter of 0.25 μm to 0.5 μm in terms of polymer particles And a method of mixing 40 to 98 parts by mass. However, the polymer particles after mixing the liquid medium dispersion (I) and the liquid medium dispersion (II) are 100 parts by mass in total. Here, the "moderate particle size" is the median value of the most frequent interval obtained from the particle size distribution measured using a particle size distribution measuring apparatus based on the light scattering method for the liquid medium dispersion. Say.

In the specific method described above, when the liquid medium dispersion (I) of polymer particles having a mode particle size of 0.01 μm or more and less than 0.25 μm is more than 60 parts by mass based on the polymer particles (mode particle size) The liquid medium dispersion of polymer particles having a particle size of 0.25 μm to 0.5 μm is less than 40 parts by mass with respect to the polymer particles), and the electrode slurry is applied to the current collector and dried. When the liquid medium is evaporated, relatively small polymer particles move (migrate) toward the air interface due to the influence of the surface tension accompanying the evaporation of the liquid medium. As a result, since the polymer particles are unevenly distributed on the electrode surface, there is a tendency that transfer of electrons with the electrolytic solution is hindered. On the other hand, at the interface between the active material layer and the current collector, the amount of polymer particles is relatively small, so that the adhesive force between the active material layer and the current collector tends to decrease and the binding property tends to be impaired. is there. As described above, when the balance of the polymer particles contained in the electrode slurry is lost, the electrical characteristics and the binding property between the active material layer and the current collector tend to be impaired.

Examples of the polymerizable unsaturated monomer (A) for obtaining polymer particles include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, ethoxyethyl acrylate, and methyl methacrylate. Ethylenically unsaturated carboxylic acid esters such as 2-ethylhexyl methacrylate, n-decyl methacrylate, 2-hydroxyethyl methacrylate, isoamyl crotonic acid, n-hexyl crotonic acid, dimethylaminoethyl methacrylate, monomethyl maleate; , 3-butadiene, 1,3-pentadiene, 2,3-pentadiene, isoprene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3 -Conjugated diene compounds such as heptadiene; acrylic acid, meta Ethylenically unsaturated carboxylic acids such as lauric acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride; aromatic vinyl compounds such as styrene, α-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, vinylnaphthalene; Examples include cyano group-containing vinyl compounds such as acrylonitrile and methacrylonitrile; vinyl ester compounds such as vinyl acetate and vinyl propionate; vinyl ether compounds such as ethyl vinyl ether, cetyl vinyl ether, and hydroxybutyl vinyl ether. These can be used alone or in admixture of two or more.

In addition, by adding a small amount of a crosslinkable monomer to the above monomer and polymerizing the monomer, the polymer particles are given a crosslinked structure by dissolving the polymer particles in a dispersion solvent or an electrolytic solution. This is preferable in that it is difficult to perform. Examples of such crosslinkable monomers include divinyl compounds such as divinylbenzene; polyfunctional dimethacrylates such as diethylene glycol dimethacrylate and ethylene glycol dimethacrylate; polyfunctional trimethacrylates such as trimethylolpropane trimethacrylate; Examples thereof include polyfunctional diacrylates such as polyethylene glycol diacrylate and 1,3-butylene glycol diacrylate; polyfunctional triacrylates such as trimethylolpropane triacrylate. The crosslinkable monomer is usually used in a proportion of 0.1 to 20% by mass, preferably 0.5 to 15% by mass, based on the entire polymerizable monomer.

Furthermore, liquid medium dispersions of polymer particles obtained by emulsion polymerization or suspension polymerization described above include ammonia, alkali metal (lithium, sodium, potassium, rubidium, cesium, etc.) hydroxide, inorganic ammonium compounds (ammonium chloride). Etc.), an aqueous solution of an organic amine compound (ethanolamine, diethylamine, etc.) can be added to adjust the pH. In particular, the binding between the current collector and the active material layer can be improved by adjusting the pH to be in the range of 5 to 13, preferably 6 to 12, using ammonia or alkali metal hydroxide. Is preferable.

As described above, the polymer particles (A) used in the electrode slurry can be used as polymer particles as they are, as a liquid medium dispersion of polymer particles obtained by emulsion polymerization or suspension polymerization. It is not limited to this. For example, when the dispersion medium used in the polymerization is a non-aqueous liquid medium, the non-aqueous liquid medium may be replaced with water to disperse the polymer particles in water. When the polymer particles are powder particles, they may be dispersed in a dispersion medium to prepare the electrode slurry according to the present embodiment.

The content of (A) polymer particles in the electrode slurry used in the present embodiment is usually 0.3 to 10 parts by mass in the positive electrode with respect to 100 parts by mass of (B) active material particles, The amount is preferably 0.5 to 5 parts by mass. On the other hand, the negative electrode is usually 0.2 to 5 parts by mass, preferably 0.5 to 2.5 parts by mass. According to the slurry for electrodes used in the present embodiment, a sufficient binding force can be obtained even when the content of the polymer particles is set to a small amount of about half to 1/10 of the conventional amount. An electric storage device using the electrode according to the above can obtain a high capacity and a charging speed.

1.2.2. (B) Active material particles The material constituting the active material particles (B) contained in the electrode slurry used in the present embodiment is not particularly limited, and an optimal material is appropriately selected according to the type of the target power storage device. can do. For example, in the case of a lithium ion secondary battery, both of the negative electrode active material and the positive electrode active material can be those used for manufacturing an electrode of a normal lithium ion secondary battery.

That is, as the negative electrode active material, carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch-based carbon fibers; conductive polymers such as polyacene; A _X B _Y O _Z (however, , A is an alkali metal or transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin and manganese, O represents an oxygen atom, and X, Y and Z are each 1.10>X> 0.05, 4.00>Y> 0.85, 5.00>Z> 1.5)), a Si-containing alloy, Si Examples include compounded compounds containing other metal oxides and the like.

In particular, when using silicon (Si) as an active material as an anode active material, silicon can occlude up to 22 pieces of lithium per 5 atoms _{_{(5Si + 22Li → Li 22 Si}} 5). As a result, the theoretical silicon capacity reaches 4200 mAh / g.

However, silicon undergoes a large volume change when it occludes lithium. Specifically, the graphite-based negative electrode active material expands in volume up to about 1.2 times by occlusion of lithium, whereas the silicon-based active material increases in volume up to about 4.4 times by occlusion of lithium. Volume expansion. For this reason, the silicon-based active material is pulverized, repeatedly peeled off from the current collector, and separated from the active material by repeated expansion and contraction, and the conductive network inside the active material layer is severed. Therefore, the cycle characteristics are extremely deteriorated in a short time.

However, when a silicon-based active material is used as the active material particles (B) contained in the electrode slurry used in the present embodiment, the above-mentioned problem does not occur, and the electrode for an electricity storage device that exhibits good electrical characteristics Can be produced. This is because (A) the polymer particles can firmly bind the silicon-based active material, and at the same time, even if the silicon-based active material expands by occluding lithium, the (A) polymer particles expand. This is considered to be because the silicon-based active material can be kept in a state of being shrunk and firmly bound. Further, in the aqueous dispersion, (A) polymer particles aggregate around the silicon-based active material to suppress hydrolysis of the silicon-based active material, thereby deteriorating the silicon-based active material when forming the active material layer. It is thought that it can be suppressed. In the present invention, the silicon-based active material refers to an active material mainly composed of silicon (Si), and more specifically refers to an active material having a silicon content of 90% by mass or more.

(B) When a carbon-based active material and a silicon-based active material are used in combination as active material particles, the amount of silicon-based active material used is that from the viewpoint of maintaining sufficient binding properties, When the mass is 100 parts by mass, it is preferably 4 to 40 parts by mass, more preferably 5 to 35 parts by mass, and particularly preferably 5 to 30 parts by mass. If the amount of the silicon-based active material used relative to the total mass of the active material particles is within the above range, the volume expansion of the carbon-based active material is smaller than the volume expansion of the silicon-based active material due to charge / discharge. Expansion and contraction accompanying charging / discharging of the active material layer containing the substance can be suppressed, and adhesion between the active material layer and the current collector can be further improved.

As the silicon-based active material, in addition to the silicon material described in JP-A-2004-185810, SiO _x (X = 0 to 2) produced by a disproportionation reaction of silicon monoxide represented by the following formula: ) (For example, materials described in JP-A-2004-47404 and JP-A-2005-259697) can be used. As the carbon-based active material used in combination with the silicon-based active material, the above-described carbonaceous materials can be preferably used, and among them, graphite is more preferable.

As the positive electrode active material, any material that can occlude / release lithium ions can be used without particular limitation. For example, sulfides such as TiS ₂ , TiS ₃ , MoS ₃ , LiFeS ₂ , Cu ₂ V ₂ O ₃ , V ₂ O—P ₂ O ₅ , MoO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , LiCoO ₂ , Transition metal oxides such as LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _0.4 Mn _1.6 O ₄ , LiCo _0.3 Ni _0.7 O ₂ , V ₂ O ₅ , MnO ₂ , LiCoPO ₄ , Spinel structures such as olipine-based oxides such as LiFePO ₄ , LiCoPO ₄ F and LiFePO ₄ F, Li ₄ Ti ₅ O ₁₂ , Li ₄ Fe _0.5 Ti ₅ O ₁₂ and Li ₄ Zn _0.5 Ti ₅ O ₁₂ Examples thereof include lithium titanium oxides and mixtures thereof. Furthermore, organic compounds such as conductive polymers such as polyacetylene and poly-p-phenylene can also be used.

Also, in the case of a nickel metal hydride secondary battery, any active material used in a normal nickel metal hydride secondary battery can be used. A hydrogen storage alloy can be used as the negative electrode active material. As the positive electrode active material, nickel oxyhydroxide, nickel hydroxide, or the like can be used.

(B) The average particle diameter (Db) of the active material particles is selected so as to satisfy the ratio (Db / Da) described above, but is usually in the range of 1 to 200 μm, and in the range of 10 to 100 μm. Preferably, it is in the range of 20 to 50 μm.

Here, (B) the average particle diameter (Db) of the active material particles means that the particle size distribution is measured using a particle size distribution measuring apparatus based on a laser diffraction method, and the cumulative frequency is 50% in volume percentage. It is a value of a particle diameter (D50). Examples of such a laser diffraction particle size distribution measuring apparatus include HORIBA LA-300 series, HORIBA LA-920 series (above, manufactured by Horiba, Ltd.), and the like. This particle size distribution measuring apparatus does not only evaluate the primary particles of the active material particles, but also evaluates secondary particles formed by aggregation of the primary particles. Therefore, the average particle diameter (Db) obtained by this particle size distribution measuring apparatus can be used as an index of the dispersion state of (B) active material particles contained in the electrode slurry.

The average particle diameter (Db) of the active material particles (B) is determined by centrifuging the slurry for the electrode to precipitate the active material particles (B), and then removing the supernatant liquid to settle the active material particles (B) It is obtained by measuring the substance particles by the above method.

1.2.3. (C) Water The electrode slurry used in the present embodiment contains (C) water. (C) By containing water, the stability of the electrode slurry is improved, and the electrode can be produced with good reproducibility. Further, the drying rate is faster than that of a high boiling point solvent (for example, N-methylpyrrolidone, etc.) generally used in electrode slurries, and improvement in productivity and migration suppression can be expected by shortening the drying time.

1.2.4. Other additives In addition to the components (A) to (C) described above, a conductivity-imparting agent, a non-aqueous medium, a thickener, etc. are added to the electrode slurry used in the present embodiment as necessary. May be.

As a specific example of the conductivity-imparting agent, carbon such as graphite and activated carbon is used in the lithium ion secondary battery. In the nickel metal hydride secondary battery, cobalt oxide is used for the positive electrode, and nickel powder, cobalt oxide, titanium oxide, carbon, or the like is used for the negative electrode. In both the batteries, examples of carbon include ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerenes. Among these, ketjen black, acetylene black, and furnace black are preferable. The amount of the conductivity-imparting agent used is usually 1 to 20 parts by mass, preferably 2 to 10 parts by mass with respect to 100 parts by mass of the active material particles (B).

In the electrode slurry used in the present embodiment, a non-aqueous medium having a normal boiling point of 80 to 350 ° C. may be added from the viewpoint of improving the coating property. Specific examples of the non-aqueous medium include amides such as N-methylpyrrolidone, dimethylformamide and dimethylacetamide; hydrocarbons such as toluene, xylene, n-dodecane and tetralin; 2-ethyl-1-hexanol, 1-nonanol Alcohols such as lauryl alcohol; ketones such as methyl ethyl ketone, cyclohexanone, phorone, acetophenone and isophorone; esters such as benzyl acetate, isopentyl butyrate, methyl lactate, ethyl lactate and butyl lactate; o-toluidine, m-toluidine, p Amines such as toluidine; amides such as N, N-dimethylacetamide and dimethylformamide; lactones such as γ-butyrolactone and δ-butyrolactone; sulfoxides and sulfones such as dimethyl sulfoxide and sulfolane . These can be used alone or as a mixed solvent of two or more. Among these, N-methylpyrrolidone is preferable from the viewpoint of the stability of the polymer particles and the workability during coating.

A thickener may be added to the electrode slurry used in the present embodiment from the viewpoint of improving the coatability. Specific examples of the thickener include celluloses such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose, and ammonium salts or alkali metal salts thereof; polycarboxylic acids such as poly (meth) acrylic acid and modified poly (meth) acrylic acid Acids, and alkali metal salts thereof; polyvinyl alcohol (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, and fumaric acid Water-soluble polymers such as a saponified product of a copolymer of an acid and a vinyl ester; Among these, particularly preferred thickeners are alkali metal salts of carboxymethyl cellulose, alkali metal salts of poly (meth) acrylic acid, and the like.

When the electrode slurry used in the present embodiment contains a thickener, the use ratio of the thickener is usually 5 to 200% by mass, preferably based on the total polymer particle mass (total solid content). Is 10 to 150% by mass, more preferably 20 to 100% by mass.

1.2.5. Method for Producing Slurry for Electrode The slurry for an electrode used in the present embodiment includes (A) polymer particles, (B) active material particles, (C) water, and additives used as necessary. Can be prepared by mixing. These can be mixed and stirred using a normal method, and for example, a stirrer, a defoaming machine, a bead mill, a high-pressure homogenizer, or the like can be used. The preparation of the electrode slurry is preferably performed under reduced pressure. Thereby, it can prevent that a bubble arises in the electrode layer obtained.

The mixing and stirring for preparing the electrode slurry used in the present embodiment includes a mixer capable of stirring to such an extent that no agglomerates of active material particles remain in the slurry, and sufficient dispersion conditions as necessary. It is necessary to select. The degree of dispersion can be measured with a particle gauge, but should be mixed and dispersed so that there are no aggregates larger than at least 100 μm. Examples of the mixer include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer.

2. Power Storage Device The power storage device according to the present embodiment includes the above-described power storage device electrode, and further includes an electrolytic solution and is manufactured according to a conventional method using components such as a separator. As a specific manufacturing method, for example, a negative electrode and a positive electrode are overlapped via a separator, and this is wound into a battery container according to a battery shape, put into a battery container, an electrolyte is injected into the battery container, and sealing is performed. The method of doing is mentioned. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

The electrolytic solution may be liquid or gel as long as it is used for a normal power storage device, and may be selected from those exhibiting a function as a battery according to the type of the negative electrode active material and the positive electrode active material.

As the electrolyte, a lithium ion secondary battery, any conventionally known lithium salts can be _{_{_{used, LiClO 4, LiBF 4, LiPF}}} 6, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiAlCl 4 , LiCl, LiBr, LiB (C ₂ H ₅ ) ₄ , LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, lower fatty acid carboxylate, etc. . Further, in a nickel metal hydride secondary battery, for example, a potassium hydroxide aqueous solution having a conventionally known concentration of 5 mol / liter or more can be used.

The solvent for dissolving the electrolyte is not particularly limited. Specific examples include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; lactones such as γ-butyl lactone; trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, Examples include ethers such as 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide, and these can be used alone or as a mixture of two or more.

3. EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, “parts” and “%” are based on mass unless otherwise specified.

3.1. Synthesis and preparation of polymer particle dispersions 3.1.1. Synthesis of polymer particle dispersion A In a reactor, 100 parts of water, 42 parts of butadiene, 30 parts of styrene, 8 parts of acrylonitrile, 18 parts of methyl methacrylate and 2 parts of itaconic acid, and a chain transfer agent 1 part of t-dodecyl mercaptan as a surfactant, 1.5 parts of sodium alkyldiphenyl ether disulfonate as a surfactant, 0.4 part of potassium persulfate as an initiator, and 0.3 part of sodium carbonate were added with stirring. Polymerization was performed at 0 ° C. for 8 hours, and the reaction was terminated at a polymerization conversion of 96%. Subsequently, the reactor was started with 10 parts of water, 14 parts of butadiene, 15 parts of styrene and 6 parts of methyl methacrylate, 0.1 part of sodium alkyldiphenyl ether disulfonate as a surfactant, After adding 0.2 parts of potassium persulfate and 0.1 part of sodium carbonate as an agent and continuing the polymerization reaction at 80 ° C. for 8 hours, the reaction was terminated. The polymerization conversion rate at this time was 98%. Unreacted monomers are removed from the obtained polymer particle dispersion, and after concentration, a 10% aqueous sodium hydroxide solution and water are added to adjust the solid content concentration and pH of the polymer particle dispersion. A polymer particle dispersion A having a concentration of 41% and a pH of 7.2 was obtained.

3.1.2. Synthesis of Polymer Particle Dispersions B to F In general, in the emulsion polymerization method, increasing the amount of the surfactant used can reduce the particle size of the polymer particles and conversely reduce the amount of the surfactant used. And the particle diameter of the polymer particles can be increased. Utilizing this property, polymer particle dispersions B to F were prepared by appropriately increasing or decreasing the amount of the surfactant used in “3.1.1. Synthesis of polymer particle dispersion A”. .

3.1.3. Measurement of the mode particle size of the polymer particle dispersion liquid For each of the obtained polymer particle dispersions A to F, a particle size distribution measuring apparatus (made by Otsuka Electronics Co., Ltd., model “ FPAR-1000 ") was used to measure the particle size distribution, and the mode particle size was determined from the particle size distribution. The data was calculated on a volume basis. The result was as follows. Here, for convenience, a polymer particle dispersion having a mode particle size of 0.01 μm or more and less than 0.25 μm is referred to as “liquid medium dispersion (I)”, and a mode particle size of 0.25 μm or more and 0.5 μm or less. A polymer particle dispersion is classified as “liquid medium dispersion (II)” (same in Table 1).
<Liquid medium dispersion (I)>
Polymer particle dispersion A: mode diameter 0.15 μm
Polymer particle dispersion E: mode diameter 0.20 μm
・ Polymer particle dispersion F; mode diameter 0.08 μm
<Liquid medium dispersion (II)>
Polymer particle dispersion B: mode diameter 0.37 μm
Polymer particle dispersion C: mode diameter 0.40 μm
-Polymer particle dispersion D: mode diameter 0.26 μm

3.1.4. Preparation of Polymer Particle Dispersions P1 to P9 Polymer Particle Dispersion A and Polymer Particle Dispersion B obtained as described above are mixed at a solid content mass ratio of 10:90 to disperse polymer particles. A liquid P1 was obtained. The obtained polymer particle dispersion P1 was measured for particle size distribution using a particle size distribution measuring apparatus (manufactured by Otsuka Electronics Co., Ltd., model “FPAR-1000”) based on the dynamic light scattering method. The average particle diameter (Da) of the combined particle dispersion P1 was 0.35 μm. The polymer particle dispersion P1 contains 11% by volume of polymer particles having a particle size of 0.01 μm or more and less than 0.25 μm, and 89 volumes of polymer particles having a particle size of 0.25 μm or more and 0.5 μm or less. % Content was confirmed. The data was calculated on a volume basis.

Except for the composition shown in Table 1, polymer particle dispersions P2 to P9 were prepared in the same manner as the polymer particle dispersion P1, and their particle size distribution was measured. The measurement results are also shown in Table 1.

3.2. Preparation of electrode slurry 1 part of a thickener (trade name “CMC2200”, manufactured by Daicel Chemical Industries, Ltd.) in a biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation) And 100 parts of graphite having an average particle diameter of 22 μm (in terms of solids) and 68 parts of water were added as the negative electrode active material, followed by stirring at 60 rpm for 1 hour. Thereafter, 1 part (in terms of solid content) of the polymer particle dispersion P1 prepared in the above-mentioned section “3.1.4. Preparation of polymer particle dispersions P1 to P9” was added, and the mixture was further stirred for 1 hour. A paste was obtained. Water was added to the obtained paste to adjust the solid content to 50%, and then the mixture was stirred at 200 rpm for 2 minutes at 1800 rpm at 200 rpm using a stirring defoamer (trade name “Netaro Awatori” manufactured by Shinky Co., Ltd.). The electrode slurry S1 was prepared by stirring and mixing for 5 minutes at 1800 rpm and 1800 rpm for 1.5 minutes under vacuum.

In Table 2, (A) the average particle diameter (Da) of the polymer particles is determined by centrifuging a part of the obtained electrode slurry, and measuring the supernatant liquid using a dynamic light scattering method as a measurement principle. It is a value obtained by measuring the particle size distribution using a distribution measuring apparatus (manufactured by Otsuka Electronics Co., Ltd., type “FPAR-1000”).

In Table 2, the graphite used as the active material particles (B) is a fine product by grinding commercially available graphite (manufactured by Hitachi Chemical Co., Ltd., product name “MAGD”) in an agate mortar and changing the grinding time. By performing the conversion, graphites having different average particle diameters (Db) described in Table 2 were obtained. In addition, the average particle diameter (Db) of the graphite used as (B) active material particles described in Table 2 is obtained by centrifuging the obtained electrode slurry, allowing the graphite to settle, and removing the supernatant liquid. It is a value obtained by measuring the product with a laser diffraction particle size distribution measuring device (HORIBA LA-300 series, manufactured by Horiba, Ltd.).

In Table 3, (B) mixed particles of graphite and silicon active material used as active material particles were prepared according to the method described in JP-A No. 2004-185810.

That is, a silicon powder (99.6%) having an average particle diameter of 10 microns obtained by grinding and crushing a silicon ingot in an agate mortar and a commercially available graphite (product name “MAGD, manufactured by Hitachi Chemical Co., Ltd.) )) Was mixed at a mass ratio shown in Table 3, and pulverized in nitrogen for 3 hours in a medium stirring mill apparatus. Then, it cooled to room temperature and took out in the air, without performing an antioxidant coating process, and obtained the mixed particle of the graphite and the silicon active material. By appropriately changing the pulverization time and performing atomization, mixed particles of graphite and silicon active material having different average particle diameters (Db) shown in Table 3 were obtained. In addition, the average particle diameter (Db) of the mixed particles of graphite and silicon active material used as (B) active material particles shown in Table 3 is determined by centrifuging the obtained slurry for electrodes and graphite and silicon active material. And the supernatant liquid is removed, and the sediment is measured with a laser diffraction particle size distribution analyzer (HORIBA LA-300 series, manufactured by Horiba, Ltd.).

Electrode slurries S2 to S17 were prepared in the same manner as the electrode slurry S1 except that the compositions shown in Tables 2 and 3 were used. The characteristics of the prepared electrode slurry are also shown in Tables 2 and 3.

3.3. Production of electrode and battery for electricity storage device 3.3.1. Example Doctor blade S1 prepared on the surface of a current collector made of copper foil with the electrode slurry S1 prepared in the above section "3.2. Preparation of electrode slurry" was dried so that the film thickness after drying was 40 µm. The film was uniformly coated by the method and dried at 120 ° C. for 20 minutes. Furthermore, the same electrode slurry S1 was uniformly applied by a doctor blade method so that the total film thickness after drying was 80 μm, and dried at 120 ° C. for 20 minutes. Finally, an electrode for an electricity storage device of Example 1 was obtained by pressing with a roll press machine (manufactured by Tester Sangyo Co., Ltd., gap-adjustable roll press machine “SA-601”).

In addition, the above examples except that the compression conditions of the roll press machine were changed so that the density of the active material layer described in Table 2 and Table 3 was obtained using the slurry for electrodes described in Table 2 and Table 3. Example 2 to 12 and Comparative Examples 1 to 5 were obtained in the same manner as for the electricity storage device electrode 1. The polymer distribution coefficient of the active material layer, the ratio (Ma / Mb) and the density in the active material layer in the obtained electrode for an electricity storage device are shown together in Tables 2 and 3.

In addition, the polymer distribution coefficient of the active material layer in the obtained electrode for an electricity storage device was calculated as follows. First, the obtained electrode for an electricity storage device was divided into two. Next, double-sided tape (product number “NW-25”, manufactured by Nichiban Co., Ltd.) is 120 mm on an aluminum plate of 70 mm × 150 mm prepared in advance, and Kapton tape (product number, manufactured by Terraoka Co., Ltd.) on the double-sided tape. A fixing stage was prepared by attaching “650S”) with the adhesive surface facing upward. On the fixing stage, the active material layer side of the test piece obtained by cutting the obtained electrode for an electricity storage device into a size of 20 mm × 100 mm was attached and pressure-bonded with a roller. The fixed stage to which the test piece was fixed was placed on a horizontal plane, and the test piece was pulled upward at a constant speed so that the angle with the fixing stage was 90 degrees, and the current collector was peeled off from the adhesive surface. . Thereafter, the active material layer having a depth of 1.5 μm from the surface of the active material layer remaining on the current collector side and a depth of 1.5 μm from the surface of the active material layer remaining on the adhesive tape side is scraped, and this is measured sample A It was. On the other hand, the entire active material layer was scraped off from the other divided electrode, and this was used as measurement sample B. About each of the measurement sample A and the measurement sample B, it analyzed by the pyrolysis gas chromatography which has a high frequency induction heating system pyrolyzer, and content (mass%) of the polymer component per unit weight of each sample was computed. The polymer distribution coefficient was calculated by substituting the obtained value into the following formula (1).
Polymer distribution coefficient = (polymer content of measurement sample A: mass%) / (polymer content of measurement sample B: mass%) (1)

Further, the mass A (g) of the current collector, the mass B (g) of the produced power storage device electrode, the area C (cm ² ) of the active material layer formed on the current collector, and the thickness D (μm) ) Was measured, and the density (g / cm ³ ) of the active material layer was calculated by the following formula (2).
Active material layer density (g / cm ³ )
= (B (g) -A ( g)) / (C (cm 2) × D (μm) × 10 -4) ····· (2)

Furthermore, with respect to the obtained electrode for an electricity storage device, the upper layer (up to 40 μm from the surface) of the active material layer was scraped, and this was designated as “measurement sample B”. Further, the active material layer remaining on the current collector was scraped off and used as “measurement sample A”. Each of the measurement sample A and the measurement sample B is analyzed by pyrolysis gas chromatography having a high frequency induction heating type pyrolyzer. The polymer content per unit volume (Ma) contained in the measurement sample A and the measurement sample B are The content (Mb) of the polymer per unit volume contained was determined, and the ratio (Ma / Mb) was calculated.

3.3.2. Production of counter electrode Biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Co., Ltd.) and electrode binder (product name “KF polymer # 1120” manufactured by Kureha Co., Ltd.) 4.0 parts (In terms of solid content), conductive assistant (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name “Denka Black 50% press product”) 3.0 parts, LiCoO _{2 having a} particle diameter of 5 μm as a positive electrode active material (manufactured by Hayashi Kasei Co., Ltd.) 100 parts (in terms of solid content) and 36 parts of N-methylpyrrolidone (NMP) were added, and the mixture was stirred at 60 rpm for 2 hours. After adding NMP to the obtained paste to adjust the solid content to 65%, using a stirring defoaming machine (trade name “Awatori Netaro”, manufactured by Shinky Co., Ltd.), 2 minutes at 200 rpm, 1800 rpm The mixture was stirred and mixed for 5 minutes at 1,800 rpm for 1.5 minutes under vacuum to prepare a slurry for electrodes. The prepared electrode slurry was uniformly applied to the surface of the current collector made of aluminum foil by a doctor blade method so that the film thickness after drying was 80 μm, and was dried at 120 ° C. for 20 minutes. Then, by pressing by a roll press as the membrane density is 3.0 g / cm ³ (Tester Sangyo Co., Ltd., the gap between the adjustable roll press "SA-601"), the "3 The counter electrode of the electrode for an electricity storage device obtained in “.3.1.

3.3.3. Assembling of the lithium ion battery cell In the glove box substituted with Ar so that the dew point is −80 ° C. or lower, the bipolar battery cell (trade name “HS Flat Cell” manufactured by Hosen Co., Ltd.) is placed in the above-mentioned “3.3. The electrode produced in the section “1. Example” was punched into a diameter of 15.95 mm and placed. Next, a separator made of a polypropylene porous membrane punched to a diameter of 24 mm (trade name “Celguard # 2400” manufactured by Celgard Co., Ltd.) was placed, and 500 μL of electrolyte was injected so that air did not enter. Thereafter, the counter electrode produced in the section “3.3.2. Production of counter electrode”, which was punched and molded to a diameter of 16.16 mm, was placed, and the outer body of the bipolar coin cell was closed with a screw. The lithium ion battery cell was assembled by sealing. The electrolytic solution used was a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / liter in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1.

3.4. Evaluation method (1) Evaluation of powder fall-off property Five 10 cm x 5 cm samples were cut out from the electrode produced in the above-mentioned "3.3.1. Example", and they were piled up. A commercially available high-quality paper was placed on the experimental table, and a 100 mesh stainless steel mesh was placed thereon. Five electrode test pieces stacked on the mesh were cut with scissors nine times at 1 cm intervals from the long side, and the state of the active material powder that passed through the stainless steel mesh and spilled on the fine paper was observed. The following evaluations were made based on the observation results. The evaluation criteria are as follows, and the results are also shown in Tables 2 and 3.
○: No powder fall off or very little powder fall off. Good.
X: A large amount of powder falling is observed. Bad.

(2) Evaluation of binding force Five 10 cm square samples were cut out from the electrode produced in the above section "3.3.1. Example", and compressed and molded by 120 ° C hot pressing for 5 minutes. Using a knife on the surface of the electrode for the electricity storage device, 6 incisions from the active material layer to the depth reaching the current collector were made at 2 mm intervals in both vertical and horizontal directions, and 25 square incisions were made in a grid pattern. An adhesive tape was affixed to the surface of the cut-in portion and immediately peeled off, and the number of cells where the active material layer was peeled off from the copper foil was counted. This was carried out once for one sample (one side), and the number of squares peeled out of a total of 125 squares of a total of 5 samples was counted, and the following evaluation was made based on this number. The evaluation criteria are as follows, and the results are also shown in Tables 2 and 3.
◯: Good with 0 to 20 cells dropped.
X: Defects with 21 or more missing cells.

(3) Evaluation of Charging / Discharging Rate Characteristics Charging of the cell produced in the section “3.3.3 Assembly of lithium ion battery cell” at a constant current (0.2 C) was started, and the voltage was 4. When the voltage reached 2 V, charging was continued at a constant voltage (4.2 V), and when the current value reached 0.01 C, charging was completed (cut off), and the charge capacity at 0.2 C was measured. Thereafter, discharge was started at a constant current (0.2 C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 0.2 C was measured. The ratio (%) of the discharge capacity at 3C to the discharge capacity at 0.2C was calculated, and the discharge rate characteristic (%) was calculated.

Next, charging of the same cell is started at a constant current (3C), and when the voltage reaches 4.2V, charging is continued at a constant voltage (4.2V). The charging capacity at 3C was measured with the point of time at which charging was completed (cut-off). Thereafter, discharge was started at a constant current (3C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 3C was measured. The ratio (%) of the charge capacity at 3C to the charge capacity at 0.2C was calculated, and the charge rate characteristic (%) was calculated. The evaluation criteria are as follows, and the results are also shown in Tables 2 and 3.
Good: Good discharge rate characteristics and charge rate characteristics of 80% or more.
X: The discharge rate characteristic or the charge rate characteristic is less than 80%, which is poor.

3.5. Evaluation Results As shown in Tables 2 and 3, according to the electricity storage device electrodes of Examples 1 to 12, the binding property between the current collector and the active material layer was good, and the powder falling property was excellent. In addition, the lithium ion batteries provided with the electrodes for the electricity storage device of Examples 1 to 12 had good charge / discharge rate characteristics, which is one of the electrical characteristics.

On the other hand, in the electricity storage device electrodes of Comparative Examples 1 to 5, the polymer distribution coefficient is out of the range of 1.1 to 3. Therefore, for the reasons described above, the binding property and powder-off property of the electricity storage device electrode, lithium ion The charge / discharge rate characteristics of the battery could not be made compatible.

The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 10 ... Current collector, 20 ... Active material layer, 100 ... Electrode for electrical storage device

Claims

An electrode for an electricity storage device comprising a current collector and an active material layer formed on a surface of the current collector,
The active material layer includes at least a polymer and an active material,
An electrode for an electricity storage device, wherein the active material layer has a polymer distribution coefficient of 1.1 to 3.
When the thickness of the active material layer is T, the content of the polymer per unit volume contained in the active material layer from the surface in contact with the current collector to the thickness direction T / 2 is expressed as Ma (g / cm 3 ), When the polymer content per unit volume contained in the active material layer from the thickness direction T / 2 to T is Mb (g / cm 3 ), the ratio (Ma / Mb) is 3-6. The electrode for an electricity storage device according to claim 1, wherein the electrode is in a range.
The electrode for an electrical storage device according to claim 1 or 2, wherein the active material contains a silicon active material.
The active material layer is
A first layer formed by applying a slurry for an electrode containing at least (A) polymer particles, (B) active material particles, and (C) water to the surface of the current collector;
A second layer formed by applying the electrode slurry on the surface of the first layer and then drying the slurry;
The electrode for electrical storage devices as described in any one of Claims 1 thru | or 3 containing these.
The electrode for an electricity storage device according to claim 4, wherein the thickness of the first layer is thinner than the thickness of the second layer.
Above the second layer,
The electrode for an electrical storage device according to claim 4, which has one or more layers formed by applying the electrode slurry and further drying the slurry.
In the electrode slurry, the ratio (Db / Da) of the average particle diameter (Da) of the (A) polymer particles to the average particle diameter (Db) of the (B) active material particles is in the range of 20-100. The electrode for electrical storage devices as described in any one of Claims 4 thru | or 6.
The distribution of the polymer particles (A) is 2 to 60% by volume in a particle diameter section of 0.01 μm or more and less than 0.25 μm and 40 to 98% by volume in a particle diameter section of 0.25 μm or more and 0.5 μm or less The electrode for an electrical storage device according to any one of claims 4 to 7, comprising:
The electrode for an electricity storage device according to any one of claims 4 to 8, wherein an average particle diameter (Db) of the (B) active material particles is 1 to 200 µm.
An electricity storage device comprising the electrode for an electricity storage device according to any one of claims 1 to 9.