WO2016027715A1

WO2016027715A1 - Protective layer, method for producing same, separator and electricity storage device

Info

Publication number: WO2016027715A1
Application number: PCT/JP2015/072624
Authority: WO
Inventors: 政宏上田; 振範金; 一聡伊藤; 智隆篠田; 悠太浅井
Original assignee: Jsr株式会社
Priority date: 2014-08-21
Filing date: 2015-08-10
Publication date: 2016-02-25

Abstract

Provided are: a protective layer for achieving an electricity storage device that has excellent charge/discharge characteristics, while being suppressed in gas generation within the electricity storage device caused by decomposition of an electrolyte contained in an electrolyte solution, or the like; a separator; and an electricity storage device which is provided with the protective layer or the separator. A protective layer according to the present invention is characterized by being arranged between a positive electrode and a negative electrode of an electricity storage device and containing a filler (A) and a water-soluble polymer (B), while having a water content of from 0.1 mg/cm³ to 35 mg/cm³ (inclusive). A separator according to the present invention is characterized by containing a filler (A) and a water-soluble polymer (B) and having a water content of from 0.1 mg/cm³ to 5 mg/cm³ (inclusive).

Description

Protective layer and method for producing the same, separator and power storage device

The present invention relates to a protective layer usable for an electricity storage device, a method for producing the same, a separator, and an electricity storage device.

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.

Such power storage devices having high voltage and high energy density are required to be further downsized. In order to achieve miniaturization of an electricity storage device, it is essential not only to make a power generation element such as a positive electrode and a negative electrode thin, but also to make a thin film such as a separator that separates the positive electrode and the negative electrode. However, when the interval between the positive electrode and the negative electrode is reduced due to the miniaturization of the electricity storage device, there may be a problem that a short circuit is likely to occur.

In the event of an abnormality such as a short circuit or overcharge, there is a greater risk of excessive heat generation than before due to the high voltage and high energy density of the electricity storage device. For this reason, the electric storage device is provided with several means for ensuring safety even in the event of an abnormality, and one of the means is a separator shutdown function. The shutdown function is a function of suppressing excessive heat generation by stopping the battery reaction by blocking the movement of ions when the temperature of the battery rises for some reason and blocking the movement of ions. In particular, one of the reasons why polyethylene porous membranes are frequently used as power storage device separators using metal ions such as lithium ions is that they have an excellent shutdown function. However, as the electricity storage device increases in voltage and energy density, the amount of heat generated during abnormal heat generation increases rapidly, and when the temperature suddenly reaches high temperatures or when heat is required after shutdown and the high temperature state is maintained for a long time. There is. In such a case, there is a risk that the separator contracts or breaks and short-circuits between the positive and negative electrodes, causing further heat generation.

In order to avoid such a phenomenon, for example, Patent Document 1 and Patent Document 2 propose a technique for improving battery characteristics by using a porous separator formed by melting and kneading a polymer and inorganic particles. . On the other hand, Patent Document 3 proposes a technique for improving battery characteristics by forming a porous film (protective layer) on at least one surface of a positive electrode and a negative electrode. Patent Document 4 proposes a technique for improving battery characteristics by forming a porous layer on a porous separator substrate using a polymer and inorganic particles.

International Publication No. 2006/0253323 JP 2008-214425 A JP 2009-54455 A International Publication No. 2010/074202

However, according to the prior art using inorganic particles as described in the above-mentioned patent document, a short circuit caused by dendrite generated due to charge / discharge is suppressed by forming a protective layer on the separator or electrode surface. Although it is possible, it is difficult to remove moisture sufficiently from the protective layer because the inorganic particles adsorb a large amount of moisture. Moisture contained in the protective layer or the separator reacts with the electrolyte contained in the electrolytic solution to generate gas, which contributes to deterioration of charge / discharge characteristics and life of the electricity storage device.

In particular, when a protective layer is formed on a separator having an excellent shutdown function, the separator base material is closed (hereinafter also simply referred to as “shutdown”) when heated and dried at a high temperature. However, it is difficult to completely remove moisture from the inorganic particles at such temperatures. Further, if a process such as forming a protective layer and separately storing it in a dry atmosphere to reduce the amount of moisture in the protective layer is necessary, the production process becomes complicated, leading to a decrease in productivity.

Therefore, some aspects according to the present invention provide an electricity storage device that suppresses gas generation in the electricity storage device due to decomposition of the electrolyte contained in the electrolyte and has excellent charge / discharge characteristics. A protective layer and a separator, and an electricity storage device including these layers are provided.

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 protective layer according to the present invention is:
A protective layer disposed between the positive electrode and the negative electrode of the electricity storage device,
A filler (A);
A water-soluble polymer (B);
Containing
The water content is from 0.1 mg / cm ^{3 to} 35 mg / cm ³ .

[Application Example 2]
In the protective layer of Application Example 1,
Furthermore, a binder (C) can be contained.

[Application Example 3]
In the protective layer of Application Example 2,
The water-soluble polymer (B) can be contained in an amount of 5 parts by mass to 15 parts by mass with respect to a total of 100 parts by mass of the filler (A) and the binder (C).

[Application Example 4]
In the protective layer of any one of Application Examples 1 to 3,
The filler (A) contains water-insoluble polymer particles (A2),
The content ratio of the repeating unit derived from the compound having two or more polymerizable unsaturated groups in 100 parts by mass of the water-insoluble polymer particles (A2) may be 20 parts by mass or more and 100 parts by mass or less.

[Application Example 5]
In the protective layer of any one of Application Examples 1 to 3,
The filler (A) can contain inorganic particles (A1) and water-insoluble polymer particles (A2).

[Application Example 6]
In the protective layer of Application Example 5,
The ratio between the content (MA1) of the inorganic particles (A1) and the content (MA2) of the water-insoluble polymer particles (A2) is MA1 / MA2 = 0.1 to 10 on a mass basis. Can do.

[Application Example 7]
In the protective layer of Application Example 5 or Application Example 6,
In 100 parts by mass of the protective layer, the water-soluble polymer (B) can be contained in an amount of 1 part by mass to 15 parts by mass.

[Application Example 8]
In the protective layer of any one of Application Examples 5 to 7,
The content ratio of the repeating unit derived from the compound having two or more polymerizable unsaturated groups in 100 parts by mass of the water-insoluble polymer particles (A2) may be 20 parts by mass or more and 100 parts by mass or less.

[Application Example 9]
One aspect of the separator according to the present invention is:
A filler (A);
A water-soluble polymer (B);
Containing
The water content is 0.1 mg / cm ³ or more and 5 mg / cm ³ or less.

[Application Example 10]
In the separator of Application Example 9,
Furthermore, a binder (C) can be contained.

[Application Example 11]
In the separator of Application Example 9 or Application Example 10,
The filler (A) can contain inorganic particles (A1) and water-insoluble polymer particles (A2).

[Application Example 12]
In the separator of any one of Application Example 9 to Application Example 11,
At least a part of the surface can be covered with the protective layer according to any one of Application Examples 1 to 8.

[Application Example 13]
One aspect of the electricity storage device according to the present invention is:
It has a positive electrode, a negative electrode, a protective layer of any one of application examples 1 to 8 arranged between the positive electrode and the negative electrode, and an electrolytic solution.

[Application Example 14]
One aspect of the electricity storage device according to the present invention is:
It is characterized by comprising a positive electrode, a negative electrode, the separator of any one of Application Examples 9 to 12 disposed between the positive electrode and the negative electrode, and an electrolytic solution.

[Application Example 15]
One aspect of the method for forming a protective layer according to the present invention is:
Inorganic particles (A1) containing a filler (A), a water-soluble polymer (B), a binder (C), and a liquid medium, wherein the filler (A) has an average particle diameter (Da1) and It contains at least one selected from the group consisting of water-insoluble polymer particles (A2) having an average particle size (Da2), and the average particle size (Da1) and the average particle size (Dc) of the binder (C) A composition in which at least one of the ratio (Da1 / Dc) and the ratio (Da2 / Dc) of the average particle diameter (Da2) to the average particle diameter (Dc) of the binder (C) is 1 to 30 A process to prepare;
After applying the composition, heating at 30 to 120 ° C .;
It is characterized by including.

[Application Example 16]
In the method for forming the protective layer of Application Example 15,
The ratio (Da1 / Da2) between the average particle diameter (Da1) of the inorganic particles (A1) and the average particle diameter (Da2) of the water-insoluble polymer particles (A2) may be 0.5 to 10. .

According to the electricity storage device including the protective layer or the separator according to the present invention, gas generation in the electricity storage device due to decomposition of the electrolyte or the like can be effectively suppressed. And since an electrical storage device provided with the protective layer or separator which concerns on this invention can suppress generation | occurrence | production of an internal gas also by repetition and overcharge of charging / discharging, a charging / discharging characteristic becomes favorable.

FIG. 1 is a schematic view showing a cross section of an electricity storage device according to a first specific example. FIG. 2 is a schematic diagram illustrating a cross section of the electricity storage device according to the second specific example. FIG. 3 is a schematic view showing a cross section of the electricity storage device according to the third specific example. FIG. 4 is a TGA chart of the water-insoluble polymer particles (A2-1) obtained in Synthesis Example 4.

Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be understood that the present invention is not limited to only the embodiments described below, and includes various modifications that are implemented without departing from the scope of the present invention.

1. Protective layer The protective layer which concerns on one Embodiment of this invention is arrange | positioned between the positive electrode and negative electrode of an electrical storage device, contains a filler (A) and a water-soluble polymer (B), and has a water content. It is 0.1 mg / cm ³ or more and 35 mg / cm ³ or less.

The moisture content of the protective layer according to the present embodiment is 0.1 mg / cm ³ or more and 35 mg / cm ³ or less, and preferably 0.1 mg / cm ³ or more and 25 mg / cm ³ or less. When the moisture content of the protective layer is within the above range, gas generation in the electricity storage device due to decomposition of the electrolyte by moisture or the like can be suppressed. As a result, the electricity storage device including the protective layer according to the present embodiment has excellent charge / discharge characteristics, and can suppress generation of internal gas even by repeated charge / discharge or overcharge.

The moisture content of the protective layer according to the present embodiment can be measured as follows. In a dry room with a dew point of -60 ° C, put the measurement sample into the heating furnace of the moisture vaporizer VA-230 (Mitsubishi Chemical Analytech Co., Ltd.), flow nitrogen gas at 150 ° C for 1 minute, and the Karl Fischer moisture meter CA200 (Mitsubishi). It is introduced into a measurement cell of Chemical Analytech Co., Ltd. and the water content is measured. The water content per unit volume is calculated by calculating the water content weight from the integrated value up to the titration end point and dividing this by the volume determined by the product of the area and film thickness of the sample.

When using an inorganic filler as in the prior art, it is very difficult to remove moisture from the inorganic filler contained in the protective layer. For example, in order to reduce the water content of the inorganic filler contained in the protective layer, there is a method of increasing the drying temperature. However, in this case, since the base material is damaged by heating, the charge / discharge characteristics of the electricity storage device are deteriorated.

For this reason, in the protective layer according to the present embodiment, a uniform coating film is formed with the filler (A) (inorganic filler (A1) and / or water-insoluble polymer (A2) having a sufficiently low water content). In the prior art, the water content in the protective layer is controlled within the aforementioned range by blending the water-soluble polymer (B) in a well-balanced manner and further controlling the film forming conditions of the coating film. It succeeded in producing the protective layer which gave the favorable charge / discharge characteristic which was difficult.

Hereinafter, each component contained in the protective layer of the present invention will be described in detail. “(Meth) acrylic acid” in the following description is a concept including both acrylic acid and methacrylic acid. Similar terms such as “(meth) acrylonitrile” should be understood similarly.

The “water-soluble polymer” in the present invention refers to a polymer having a solubility in 1 g of water at 1 atm and 23 ° C. of 0.01 g or more. The “water-insoluble polymer” in the present invention refers to a polymer having a solubility in 1 g of water at 1 atm and 23 ° C. of less than 0.01 g.

1.1. Filler (A)
The protective layer according to the present embodiment includes a filler (A). The filler (A) is preferably inorganic particles (A1) and / or water-insoluble polymer particles (A2). The protective layer according to the present embodiment preferably contains both inorganic particles (A1) and water-insoluble polymer particles (A2) as the filler (A). By using not only the inorganic particles (A1) but also the water-insoluble polymer particles (A2) as the filler (A), the water content in the protective layer can be reduced within the above-mentioned range without deteriorating the properties as the protective layer. It becomes easy to control. Then, by controlling the film forming conditions of the coating film, a protective layer whose water content is controlled within the above-mentioned range can be produced, and a protective layer that provides good charge / discharge characteristics that has been difficult with the prior art is produced. Can do.

When the protective layer according to the present embodiment contains both the inorganic particles (A1) as the filler (A) and the water-insoluble polymer particles (A2), the content (MA1) of the inorganic particles (A1) and The blending ratio with the content (MA2) of the water-insoluble polymer particles (A2) is preferably MA1 / MA2 = 0.1 to 10 on a mass basis, and MA1 / MA2 = 0.3 to 5 More preferably. When the blending ratio is in the above range, the moisture content in the protective layer can be effectively reduced, and the toughness of the protective layer formed is well balanced.

1.1.1. Inorganic particles (A1)
When the inorganic particles (A1) are contained as the filler (A), the toughness of the protective layer to be formed can be improved. Since the inorganic particles (A1) have high hygroscopicity, it is inevitable that a certain amount of moisture is brought into the electric storage device when no treatment is performed. Therefore, when inorganic particles are used as the filler (A), it is preferable to remove moisture as much as possible by heat treatment or the like in advance. Furthermore, it is preferable to keep the hygroscopicity low by forming a hydrophobic film on the surface of the inorganic particles from which moisture has been removed.

As the inorganic particles (A1), titanium oxide (titania), aluminum oxide (alumina), zirconium oxide (zirconia), magnesium oxide (magnesia), silica and the like can be used. Among these, titanium oxide and aluminum oxide are preferable from the viewpoint of further improving the toughness of the protective layer. Further, as the titanium oxide, rutile type titanium oxide is more preferable from the viewpoint of further improving the toughness of the protective layer.

The average particle diameter (Da1) of the inorganic particles (A1) is preferably 1 μm or less, and more preferably in the range of 0.1 to 0.8 μm. When the average particle diameter (Da1) of the inorganic particles (A1) is in the above range, a smooth and flexible protective layer can be formed, and when an electricity storage device is produced, a separator or electrode disposed adjacent to the protective layer; Even if it contacts, since the risk of damaging them is reduced, the durability of the electricity storage device is improved. In addition, when using the separator which is a porous film, the average particle diameter (Da1) of the inorganic particles (A1) is preferably larger than the average pore diameter of the separator. Thereby, damage to a separator can be reduced and it can prevent that an inorganic particle (A1) is clogged with the microporous of a separator.

Here, the average particle diameter (Da1) of the inorganic particles (A1) is a particle size distribution measuring apparatus using a particle size distribution measuring apparatus based on the laser diffraction / light scattering method, and the light scattering intensity is expressed as the particle diameter. This is the value of the particle diameter (D50) at which the cumulative frequency of scattering intensity is 50% when the particles are accumulated in order from small particles to large particles. As such a laser diffraction type particle size distribution measuring apparatus, for example, HORIBA LA-300 series, HORIBA LA-920 series (manufactured by Horiba, Ltd.), Coulter LS230, LS100, LS13 320 (manufactured by Beckman Coulter. Inc) And FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.). This particle size distribution measuring apparatus does not only evaluate the primary particles of the inorganic particles (A1) but also evaluates the secondary particles formed by aggregation of the primary particles. Therefore, the average particle diameter (Da1) obtained by this particle size distribution measuring apparatus is an inorganic particle (A1) contained in a composition for producing a protective layer (hereinafter also referred to as “composition for protective layer”). ) As an indicator of the dispersion state. The average particle diameter (Da1) of the inorganic particles (A1) is determined by centrifuging the protective layer composition to settle the inorganic particles, then removing the supernatant liquid, and removing the precipitated inorganic particles by the above method. It can also be measured by measuring.

1.1.2. Water-insoluble polymer particles (A2)
When the water-insoluble polymer particles (A2) are contained as the filler (A), the water content of the formed protective layer can be effectively reduced.

The water-insoluble polymer particle (A2) has a content of repeating units derived from a compound having two or more polymerizable unsaturated groups in 100 parts by mass of the polymer constituting the water-insoluble polymer particle (A2). It is preferably 20 parts by mass or more and 100 parts by mass or less, more preferably 50 parts by mass or more and 100 parts by mass or less, further preferably 80 parts by mass or more and 100 parts by mass or less, and 90 parts by mass or more and 100 parts by mass or less. It is particularly preferred that the amount is not more than parts.

When the content of the repeating unit derived from the compound having two or more polymerizable unsaturated groups is within the above range, not only can the moisture content of the protective layer be reduced, but also the heat resistance, solvent resistance, and short circuit due to dendrite of the protective layer. This is preferable because the function of preventing the problem is improved. Furthermore, since the hardness of the water-insoluble polymer particles (A2) is increased, the toughness of the protective layer to be formed can be improved.

Hereinafter, the monomer constituting the repeating unit contained in the water-insoluble polymer particles (A2), the characteristics, aspects and production methods of the water-insoluble polymer particles (A2) will be described in detail.

1.1.2.1. Monomer <Compound having two or more polymerizable unsaturated groups>
Although it does not restrict | limit especially as a compound which has two or more polymerizable unsaturated groups, For example, a polyfunctional (meth) acrylic acid ester, an aromatic polyfunctional vinyl compound, etc. are mentioned.

Examples of the polyfunctional (meth) acrylic acid ester include compounds represented by the following general formula (1), (poly) (meth) acrylic acid esters of polyhydric alcohols, and other polyfunctional monomers.

(In the general formula (1), R ¹ represents a hydrogen atom or a methyl group, and R ² represents at least one functional group selected from the group consisting of a polymerizable carbon-carbon unsaturated bond, an epoxy group and a hydroxyl group. And an organic group having 1 to 18 carbon atoms.)

Preferable specific examples of R ^{2 in} the general formula (1) include, for example, vinyl group, isopropenyl group, allyl group, (meth) acryloyl group, epoxy group, glycidyl group, hydroxyalkyl group and the like.

The “polyfunctional (meth) acrylic acid ester” in the present invention has one (meth) acryloyl group in addition to a (meth) acrylic acid ester having two or more (meth) acryloyl groups, and is further polymerizable. Also included are (meth) acrylic acid esters having at least one functional group selected from the group consisting of carbon-carbon unsaturated bonds, epoxy groups, glycidyl groups and hydroxy groups.

Specific examples of such polyfunctional (meth) acrylic acid esters include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and tetra (meth) acrylic. Examples include pentaerythritol acid, dipentaerythritol hexa (meth) acrylate, glycidyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, allyl (meth) acrylate, and the like. It can be one or more selected from these. Among these, at least one selected from the group consisting of ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate and allyl (meth) acrylate is preferable. More preferred is ethylene glycol acrylate. The polyfunctional (meth) acrylic acid ester exemplified above may be used alone or in combination of two or more.

As the aromatic polyfunctional vinyl compound, for example, a compound represented by the following general formula (2) can be preferably used.

(In the above general formula (2), a plurality of R ³ are each independently an organic group having a polymerizable carbon-carbon unsaturated bond, and a plurality of R ⁴ are each independently represented by 1 to 18 carbon atoms. And n is an integer of 2 to 6, and m is an integer of 0 to 4.)

Examples of R ³ in the general formula (2) include a vinylene group having 2 to 12 carbon atoms, an allyl group, a vinyl group, and an isopropenyl group, and among these, a vinylene group having 2 to 12 carbon atoms. It is preferable that Examples of R ⁴ in the general formula (2) include a methyl group and an ethyl group.

Examples of aromatic polyfunctional vinyl compounds include, but are not limited to, aromatic divinyl compounds such as divinylbenzene and diisopropenylbenzene. Of these, divinylbenzene is preferred. The aromatic polyfunctional vinyl compounds exemplified above may be used alone or in combination of two or more.

Among the compounds having two or more polymerizable unsaturated groups exemplified above, aromatic divinyl compounds are more preferable, and divinylbenzene is particularly preferable. When the water-insoluble polymer particles (A2) contain a repeating unit derived from divinylbenzene, the content of divinylbenzene is preferably 20 to 100% by mass, more preferably 50 to 100% by mass with respect to the total monomers. %, Particularly preferably 80 to 100% by mass. When the content ratio of divinylbenzene is less than 20% by mass, the obtained water-insoluble polymer particles (A2) may be inferior in terms of heat resistance, electrolytic solution resistance, and the like.

<Other unsaturated monomers>
In the water-insoluble polymer particles (A2), in addition to the repeating unit derived from the compound having two or more polymerizable unsaturated groups, a repeating unit derived from another unsaturated monomer copolymerizable with these units. Units may be further included.

Such unsaturated monomers include unsaturated carboxylic acid esters (excluding compounds having two or more polymerizable unsaturated groups), aromatic vinyl compounds (provided that two polymerizable unsaturated groups are present). And the like, and unsaturated carboxylic acids, α, β-unsaturated nitrile compounds, and other unsaturated monomers. The water-insoluble polymer particle (A2) is a repeating unit derived from a compound having two or more polymerizable unsaturated groups, a repeating unit derived from an unsaturated carboxylic acid ester, or a repeating derived from an aromatic vinyl compound. It is preferable to have a unit.

<Unsaturated carboxylic acid ester>
As the unsaturated carboxylic acid ester, a (meth) acrylic acid ester can be preferably used. Examples thereof include an alkyl ester of (meth) acrylic acid and a cycloalkyl ester of (meth) acrylic acid. The alkyl ester of (meth) acrylic acid is preferably an alkyl ester of (meth) acrylic acid having an alkyl group having 1 to 10 carbon atoms, such as methyl (meth) acrylate, ethyl (meth) acrylate, (meth ) N-propyl acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, n-amyl (meth) acrylate, i- (meth) acrylate Examples include amyl, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, and decyl (meth) acrylate. Examples of the cycloalkyl ester of (meth) acrylic acid include cyclohexyl (meth) acrylate. The unsaturated carboxylic acid ester exemplified above may be used alone or in combination of two or more. Of these, alkyl esters of (meth) acrylic acid are preferred and are selected from methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate and 2-ethylhexyl acrylate. It is more preferable to use one or more.

The content of the repeating unit derived from the unsaturated carboxylic acid ester in 100 parts by mass of the water-insoluble polymer particles (A2) is preferably 5 to 80 parts by mass, and more preferably 10 to 75 parts by mass. preferable.

<Aromatic vinyl compound>
Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, and the like, and can be one or more selected from these. Among the above, the aromatic vinyl compound is particularly preferably styrene.

The content of the repeating unit derived from the aromatic vinyl compound in 100 parts by mass of the water-insoluble polymer particles (A2) is preferably 5 to 85 parts by mass, and more preferably 10 to 80 parts by mass. .

<Unsaturated carboxylic acid>
Examples of the unsaturated carboxylic acid include monocarboxylic acids or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and one or more selected from these are used. can do. As the unsaturated carboxylic acid, it is preferable to use one or more selected from acrylic acid and methacrylic acid, and acrylic acid is more preferable.

The content of the repeating unit derived from the unsaturated carboxylic acid in 100 parts by mass of the water-insoluble polymer particles (A2) is preferably 1 to 10 parts by mass, and 2.5 to 7.5 parts by mass. It is more preferable.

<Α, β-unsaturated nitrile compound>
Examples of the α, β-unsaturated nitrile compound include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, and one or more selected from these can be used. . Among these, at least one selected from the group consisting of acrylonitrile and methacrylonitrile is preferable, and acrylonitrile is particularly preferable.

The content of the repeating unit derived from the α, β-unsaturated nitrile compound in 100 parts by mass of the water-insoluble polymer particles (A2) is preferably 1 to 10 parts by mass, and 2.5 to 7.5. More preferably, it is part by mass.

<Other unsaturated monomers>
Other unsaturated monomers include alkyl amides of unsaturated carboxylic acids such as (meth) acrylamide and N-methylol acrylamide; unsaturated carboxylic acids such as aminoethyl acrylamide, dimethylaminomethyl methacrylamide and methylaminopropyl methacrylamide And one or more selected from these can be used.

1.1.2.2. Characteristics of water-insoluble polymer particles (A2) <toluene insoluble matter>
The toluene insoluble content of the water-insoluble polymer particles (A2) at 50 ° C. is preferably 90% or more, more preferably 95% or more, and particularly preferably 100%. It is presumed that the toluene insoluble content is approximately proportional to the amount of insoluble content in the electrolytic solution used in the electricity storage device. For this reason, if the toluene insoluble content is in the above range, it is possible to suppress the elution of the water-insoluble polymer particles (A2) into the electrolytic solution even when an electricity storage device is produced and charging / discharging is repeated for a long period of time. Can be guessed.

The toluene insoluble content can be calculated as follows. 10 g of an aqueous dispersion containing water-insoluble polymer particles (A2) is weighed into a Teflon (registered trademark) petri dish having a diameter of 8 cm and dried at 120 ° C. for 1 hour to form a film. 1 g of the obtained film (polymer) is immersed in 400 mL of toluene and shaken at 50 ° C. for 3 hours. Next, the toluene phase was filtered through a 300-mesh wire mesh to separate insoluble components, and the weight (Y (g)) of the residue obtained by evaporating and removing the dissolved toluene was measured. 3) Determine the toluene insoluble content.
Toluene insoluble content (%) = ((1-Y) / 1) × 100 (3)

<Temperature for reducing 10% by weight in an air atmosphere (T ₁₀ )>
The temperature (T ₁₀ ) at which the weight of the water-insoluble polymer (A2) is reduced by 10% by weight in an air atmosphere is preferably 320 ° C. or higher, and more preferably 350 ° C. or higher. The temperature (T ₁₀ ) at which the weight of the water-insoluble polymer particles (A2) is reduced by 10% by weight in an air atmosphere is estimated to correlate with the chemical stability against oxidation at high temperature and high voltage inside the battery. . For this reason, if the temperature (T ₁₀ ) at which the weight of the water-insoluble polymer particles (A2) is reduced by 10% by weight in an air atmosphere is within the above temperature range, the battery is stable against oxidation at high temperatures and high voltages. As a result, the decomposition reaction of the water-insoluble polymer particles (A2) is less likely to occur, and the remaining capacity ratio is improved.

The temperature (T ₁₀ ) at which the weight of the water-insoluble polymer particles (A2) is reduced by 10% by weight in an air atmosphere can be measured as follows. 10 g of an aqueous dispersion containing water-insoluble polymer particles (A2) is weighed into a Teflon (registered trademark) petri dish having a diameter of 8 cm and dried at 120 ° C. for 1 hour to form a film. The obtained film (polymer) is pulverized into powder, and this powder is subjected to thermogravimetric analysis with a thermal analyzer (for example, model “DTG-60A” manufactured by Shimadzu Corporation). As a result, the temperature at which the weight of the water-insoluble polymer particles (A2) is reduced by 10% by weight in the air atmosphere when heated at a heating rate of 20 ° C./min in an air atmosphere is defined as (T ₁₀ ).

<Endothermic characteristics of water-insoluble polymer particles (A2)>
As the thermal characteristics of the water-insoluble polymer particles (A2), no endothermic peak is observed in the range of −50 ° C. to + 300 ° C. when differential scanning calorimetry (DSC) is performed according to JIS K7121. It is preferable. This indicates that the water-insoluble polymer particles (A2) are crosslinked with a compound having two or more polymerizable unsaturated groups. Thereby, heat resistance and intensity | strength can be provided to the protective layer formed.

1.1.2.3. Embodiment of water-insoluble polymer particles (A2) The average particle diameter (Da2) of the water-insoluble polymer particles (A2) is preferably in the range of 100 to 3000 nm, and preferably in the range of 100 to 1500 nm. Is more preferable. When the average particle diameter (Da2) of the water-insoluble polymer particles (A2) is in the above range, a smooth and flexible protective layer can be formed, and when an electricity storage device is produced, it is disposed adjacent to the protective layer. Even if it contacts with a separator and an electrode, since the risk of damaging them is reduced, the durability of the electricity storage device is improved. In addition, when using the separator which is a porous film, the average particle diameter (Da2) of the water-insoluble polymer particles (A2) is preferably larger than the average pore diameter of the separator. Thereby, the damage to a separator can be reduced and it can prevent that a water-insoluble polymer particle (A2) is clogged with the microporous of a separator. In addition, the average particle diameter (Da2) of the water-insoluble polymer particles (A2) can be measured by the same method as the average particle diameter (Da1) of the above-mentioned inorganic particles (A1).

When the water-insoluble polymer particles (A2) are present in the protective layer, the water-insoluble polymer particles (A2) are preferably particles having one or more pores therein. The water-insoluble polymer particles (A2) have one or more pores inside thereof, thereby improving the electrolyte permeability and liquid retention of the protective layer obtained, and exhibiting better charge / discharge characteristics. Can be made. The particle structure may be, for example, a hollow structure having pores inside the particle, or a core-shell type structure having a plurality of pores from the surface of the particle to the inside (core). Also good.

When the water-insoluble polymer particles (A2) have one or more pores therein, the volume porosity is preferably 1% to 80%, more preferably 2% to 70%. It is particularly preferably 5% to 60%. When the volumetric porosity is within this range, it is possible to achieve both the permeability and liquid retention of the electrolytic solution of the protective layer obtained and the improvement of toughness.

The volume porosity of the water-insoluble polymer particles (A2) is observed with, for example, the water-insoluble polymer particles (A2) with an electron microscope (manufactured by Hitachi High-Technologies Corporation, Hitachi transmission electron microscope H-7650). The average particle diameter and particle inner diameter of 100 randomly extracted particles can be measured and calculated by the following formula (4).
Volume porosity (%) = ((particle inner diameter) ³ / (average particle diameter) ³ ) × 100 (4)

1.1.2.4. Method for producing water-insoluble polymer particles (A2) The method for synthesizing the water-insoluble polymer particles (A2) contained in the protective layer according to the present embodiment is not particularly limited. Specifically, emulsion polymerization, seeding emulsification It is preferable to use a method such as polymerization, suspension polymerization, seeding suspension polymerization, or solution precipitation polymerization. Among these, emulsion polymerization and seeding emulsion polymerization are preferable, and seeding emulsion polymerization is more preferable because the particle size distribution can be easily controlled uniformly.

In addition, when the water-insoluble polymer particles (A2) have a hollow structure, the methods described in JP-A No. 2002-30113, JP-A No. 2009-120784, and JP-A No. 62-127336 are disclosed. In the case of the core-shell type, it can be manufactured according to the method described in JP-A-4-98201.

1.2. Water-soluble polymer (B)
The protective layer according to the present embodiment includes a water-soluble polymer (B). By containing the water-soluble polymer (B), a uniform coating film is easily formed, and the function as a protective layer is improved.

The water-soluble polymer (B) used in the electricity storage device is basically required to be stable at a high potential. Moreover, when using as a protective layer use, it is requested | required that the dispersibility of a filler (A) is favorable. In addition, it is required that the protective layer composition has a certain degree of viscosity and exhibits fluidity because of the necessity of coating on the electrode surface or the separator surface. Thus, selection of materials is necessary from many viewpoints.

From such a viewpoint, the water-soluble polymer (B) is preferably a natural polymer, a semi-synthetic polymer, or a synthetic polymer.

Examples of natural polymers include, for example, plant- or animal-derived polysaccharides and proteins, and, in some cases, natural polymers that have been subjected to fermentation treatment with microorganisms or heat treatment. . These natural polymers can be classified as plant natural polymers, animal natural polymers, microbial natural polymers, and the like.

Examples of plant-based natural polymers include gum arabic, gum tragacanth, galactan, guar gum, carob gum, caraya gum, carrageenan, pectin, cannan, quince seed (malmello), arche colloid (gasso extract), starch (rice, corn, potato, Derived from wheat and the like), glycyrrhizin and the like. Examples of animal-based natural polymers include collagen, casein, albumin, gelatin and the like. Examples of the microbial natural polymer include xanthan gum, dextran, succinoglucan, and bullulan.

Cellulosic semisynthetic polymers can be classified into nonionic, anionic and cationic.

Nonionic cellulose semisynthetic polymers include, for example, alkylcelluloses such as methylcellulose, methylethylcellulose, ethylcellulose, and microcrystalline cellulose; hydroxyethylcellulose, hydroxybutylmethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, hydroxypropyl Examples thereof include hydroxyalkyl celluloses such as methyl cellulose stearoxy ether, carboxymethyl hydroxyethyl cellulose, alkyl hydroxyethyl cellulose, and nonoxynyl hydroxyethyl cellulose.

Examples of the anionic cellulose semisynthetic polymer include alkyl celluloses obtained by substituting the above nonionic cellulose semisynthetic polymer with various derivative groups, and sodium salts and ammonium salts thereof. Specific examples include sodium cellulose sulfate, methyl cellulose, methyl ethyl cellulose, ethyl cellulose, carboxymethyl cellulose (CMC), and salts thereof.

Examples of cationic cellulose semisynthetic polymers include low nitrogen hydroxyethyl cellulose dimethyl diallyl ammonium chloride (polyquaternium-4), O- [2-hydroxy-3- (trimethylammonio) propyl] hydroxyethyl cellulose (polyquaternium- 10), and O- [2-hydroxy-3- (lauryldimethylammonio) propyl] hydroxyethylcellulose chloride (polyquaternium-24).

Among these, a cellulose-based semisynthetic polymer, a sodium salt thereof, or an ammonium salt thereof is more preferable because it can have cationic, anionic, or amphoteric characteristics. Among these, an anionic cellulose semisynthetic polymer is particularly preferable from the viewpoint of dispersibility of the filler.

The degree of etherification of the cellulose semisynthetic polymer is preferably in the range of 0.5 to 1.0, more preferably 0.6 to 0.8. The degree of substitution of a hydroxyl group (3) per anhydroglucose unit in cellulose with a carboxymethyl group or the like is referred to as the degree of etherification. Theoretically, values from 0 to 3 can be taken. When the degree of etherification is in the above range, compatibility with water is also observed while adsorbing on the filler surface, so that the dispersibility is excellent and the filler can be finely dispersed to the primary particle level. In addition, by providing an optimum average degree of polymerization, the stability over time can be improved, and coating without agglomerates and thickness unevenness can be achieved.

Examples of commercially available cellulose polymers include carboxy such as CMC1120, CMC1150, CMC2200, CMC2280, CMC2450 (manufactured by Daicel Corporation), Metroles SH type, Metroles SE type (manufactured by Shin-Etsu Chemical Co., Ltd.), and the like. Examples thereof include alkali metal salts of methylcellulose.

Examples of synthetic polymers include polycarboxylic acids such as poly (meth) acrylic acid and modified poly (meth) acrylic acid; alkali metal salts of the above polycarboxylic acids; polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers And water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid and fumaric acid and vinyl esters. .

The average degree of polymerization calculated from the intrinsic viscosity obtained from the Ubbelohde viscometer of the water-soluble polymer (B) is preferably in the range of 500 to 2500, more preferably 1000 to 2000, and particularly preferably 1000 to 1500. . When the average degree of polymerization of the water-soluble polymer (B) is in the above range, the balance between the solubility of the water-soluble polymer (B) in water and the adsorptivity to the filler (A) surface is improved, and the protective layer is used. The dispersion stability of the filler (A) in the composition tends to be good. Moreover, the viscosity of the composition for protective layers also becomes moderate. As a result, a uniform coating film is easily formed during coating.

The content ratio of the water-soluble polymer (B) in the protective layer according to the present embodiment is 5 parts by mass or more and 15 parts by mass or less with respect to a total of 100 parts by mass of the filler (A) and the binder (C) described above. It is preferable that Moreover, it is preferable that the content rate of the water-soluble polymer (B) in 100 mass parts of protective layers concerning this Embodiment is 1 mass part or more and 15 mass parts or less. When the content ratio of the water-soluble polymer (B) is within the above range, the water content in the protective layer can be easily controlled to 0.1 mg / cm ³ or more and 35 mg / cm ³ or less, and the composition for the protective layer Therefore, it is easy to form a uniform coating film.

1.3. Binder (C)
The protective layer according to the present embodiment may contain a binder (C) for binding the fillers (A) to each other and further improving the adhesion to the electrode surface or the separator surface. The binder (C) may be a water-insoluble polymer and does not have a specific shape in the protective layer. However, the binder (C) is preferably present in the form of particles in the protective layer composition before coating. When the binder (C) is present in the form of particles, the filler (A) can be efficiently bound to each other when forming a coating film, and the formed protective layer and the electrode surface or separator surface Adhesion is improved.

When the binder (C) is in the form of particles, the particles are preferably solid particles having no pores inside. By being a solid particle, a better binder characteristic can be expressed in the protective layer.

Hereinafter, the monomer constituting the repeating unit contained in the binder (C), the mode of the binder (C1), the production method, and the like will be described in detail.

1.3.1. Monomer <Compound having two or more polymerizable unsaturated groups>
Here, the “compound having two or more polymerizable unsaturated groups” has the same meaning as the compound described in the above-mentioned filler (A). The content ratio of the repeating unit derived from the compound having two or more polymerizable unsaturated groups in 100 parts by mass of the binder (C) is preferably less than 15 parts by mass, and more preferably 5 parts by mass or less. , 0 parts by mass, that is, it is particularly preferable not to contain substantially. When the content ratio of the repeating unit derived from the compound having two or more polymerizable unsaturated groups in the binder (C) is within the above range, the flexibility of the binder (C) increases, This is preferable because the adhesion is improved. On the other hand, if it exceeds the above range, the flexibility of the binder (C) becomes poor, and the adhesion to the electrode surface or separator surface may be lowered, which is not preferable.

<Monomer having a fluorine atom>
The binder (C) preferably contains a repeating unit derived from a monomer having a fluorine atom. Examples of the monomer having a fluorine atom include an olefin compound having a fluorine atom and a (meth) acrylic acid ester having a fluorine atom. Examples of the olefin compound having a fluorine atom include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, ethylene trifluoride chloride, and perfluoroalkyl vinyl ether. Examples of the (meth) acrylic acid ester having a fluorine atom include a compound represented by the following general formula (5): (meth) acrylic acid 3 [4 [1-trifluoromethyl-2,2-bis [bis (tri Fluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl and the like.

(In the above general formula (5), R ⁵ is a hydrogen atom or a methyl group, and R ⁶ is a C 1-18 hydrocarbon group containing a fluorine atom.)

Examples of R ⁶ in the general formula (5) include fluorinated alkyl groups having 1 to 12 carbon atoms, fluorinated aryl groups having 6 to 16 carbon atoms, and fluorinated aralkyl groups having 7 to 18 carbon atoms. Among these, a fluorinated alkyl group having 1 to 12 carbon atoms is preferable. Preferable specific examples of R ^{6 in} the general formula (5) include, for example, 2,2,2-trifluoroethyl group, 2,2,3,3,3-pentafluoropropyl group, 1,1,1, 3,3,3-hexafluoropropan-2-yl group, β- (perfluorooctyl) ethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,4,4,4- Hexafluorobutyl group, 1H, 1H, 5H-octafluoropentyl group, 1H, 1H, 9H-perfluoro-1-nonyl group, 1H, 1H, 11H-perfluoroundecyl group, perfluorooctyl group, etc. Can do. Of these, the monomer having a fluorine atom is preferably an olefin compound having a fluorine atom, more preferably at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene. preferable. The monomer having a fluorine atom may be used alone or in combination of two or more.

The content of the repeating unit derived from the monomer having a fluorine atom in 100 parts by mass of the binder (C) is preferably 5 to 50 parts by mass, more preferably 15 to 40 parts by mass, It is particularly preferably 30 to 30 parts by mass.

<Unsaturated carboxylic acid>
The binder (C) preferably contains a repeating unit derived from an unsaturated carboxylic acid in addition to the repeating unit derived from the monomer having a fluorine atom. As unsaturated carboxylic acid, the compound illustrated in the above-mentioned filler (A) is mentioned.

The content of the repeating unit derived from the unsaturated carboxylic acid in 100 parts by mass of the binder (C) is preferably 1 to 10 parts by mass, and more preferably 2.5 to 7.5 parts by mass.

<Conjugated diene compound>
The binder (C) may further contain a repeating unit derived from a conjugated diene compound. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene and the like. , One or more selected from these. Among these, 1,3-butadiene is particularly preferable.

The content of the repeating unit derived from the conjugated diene compound in 100 parts by mass of the binder (C) is preferably 30 to 60 parts by mass, and more preferably 40 to 55 parts by mass. When the content ratio of the repeating unit derived from the conjugated diene compound is in the above range, it is preferable because appropriate flexibility can be imparted and the binding property between the fillers (A) becomes good.

<Other unsaturated monomers>
The binder (C) may further contain a repeating unit derived from another unsaturated monomer copolymerizable with these, in addition to the above-mentioned repeating unit.

As such an unsaturated monomer, for example, an unsaturated carboxylic acid ester (excluding those corresponding to the compound having two or more polymerizable unsaturated groups and the monomer having a fluorine atom), Examples include α, β-unsaturated nitrile compounds, aromatic vinyl compounds (excluding those corresponding to the compounds having two or more polymerizable unsaturated groups) and other monomers. About these compounds, the compound illustrated in the above-mentioned filler (A) is mentioned.

1.3.2. Properties of binder (C) <average particle size>
The average particle diameter (Dc) of the binder (C) is preferably in the range of 20 to 450 nm, more preferably in the range of 30 to 420 nm, and particularly preferably in the range of 50 to 400 nm.

When the average particle diameter (Dc) of the binder (C) is in the above range, the stability of the protective layer composition itself is improved, and the internal resistance is increased even when a protective layer is formed on the electricity storage device (resistance increase rate). ) Can be kept low. When the average particle diameter (Dc) is less than the above range, the surface area of the binder (C) becomes excessive and the solubility in the electrolytic solution increases, so that the binder (C) gradually changes into the electrolytic solution as the electricity storage device is charged and discharged. Elutes and contributes to an increase in internal resistance. On the other hand, if the average particle diameter (Dc) exceeds the above range, the surface area of the particles becomes too small and the adhesion is reduced, so that it becomes difficult to form a strong protective layer, and sufficient durability performance of the electricity storage device is obtained. Disappear.

The average particle diameter (Dc) of the binder (C) can be measured by the same method as the average particle diameter (Da2) of the water-insoluble polymer particles (A2) described above.

<Toluene insoluble matter>
The toluene insoluble content of the binder (C) at 50 ° C. is preferably 80% or more, and more preferably 85% or more. It is presumed that the toluene insoluble content is approximately proportional to the amount of insoluble content in the electrolytic solution used in the electricity storage device. For this reason, if a toluene insoluble content is the said range, even if it manufactures an electrical storage device and it repeats charging / discharging over a long period of time, since it can suppress the elution of the polymer to electrolyte solution, it can be estimated that it is favorable. The toluene insoluble matter can be calculated by the same method as that described for the filler (A).

<Temperature for reducing 10% by weight in an air atmosphere (T ₁₀ )>
The temperature (T ₁₀ ) at which the weight of the binder (C) is reduced by 10% by weight in an air atmosphere is preferably 320 ° C. or higher, and more preferably 350 ° C. or higher. The temperature (T ₁₀ ) at which the weight of the binder (C) is reduced by 10% by weight in an air atmosphere is presumed to correlate with chemical stability against oxidation at high temperature and high voltage inside the battery. For this reason, if the temperature (T ₁₀ ) at which the weight of the binder (C) is reduced by 10% by weight in an air atmosphere is within the above temperature range, the stability against oxidation at high temperature and high voltage inside the battery is improved. Since the decomposition reaction of the binder (C) is difficult to occur, the remaining capacity ratio is improved. The temperature (T ₁₀ ) at which the weight of the binder (C) is reduced by 10% by weight in an air atmosphere can be calculated by a method similar to the method described for the filler (A).

<Endothermic characteristics of binder (C)>
Regarding the thermal properties of the binder (C), only one endothermic peak in the temperature range of −50 ° C. to + 250 ° C. is observed when differential scanning calorimetry (DSC) is performed according to JIS K7121. Is preferred. The endothermic behavior of the binder (C) is presumed to correlate with the shape stability of the particles when the binder (C) is in the form of particles. For this reason, if one endothermic peak of the binder (C) is observed in the temperature range, the shape stability of the particles of the binder (C) becomes good, and the formed protective layer can have sufficient strength. It is guessed.

1.3.3. Embodiment of Binder (C) As a specific embodiment of the binder (C), when a monomer having a fluorine atom is used, (1) a water-insoluble polymer having a repeating unit derived from the monomer having a fluorine atom A copolymer obtained by synthesizing by a one-step polymerization, (2) a polymer X having a repeating unit derived from a monomer having a fluorine atom, and a polymer Y having a repeating unit derived from an unsaturated carboxylic acid; Two embodiments of the composite polymer having Among these, from the viewpoint of excellent oxidation resistance, a composite polymer is preferable, and the composite polymer is more preferably a polymer alloy.

“Polymer alloy” is a general term for multi-component polymers obtained by mixing or chemical bonding of two or more components, according to the definition in “Iwanami Riken Dictionary 5th edition. Iwanami Shoten” “Polymer blends physically mixed with different polymers, block and graft copolymers in which different polymer components are covalently bonded, polymer complexes in which different polymers are associated by intermolecular forces, Intertwined IPN (Interpenetrating Polymer Network, interpenetrating polymer network), etc. ”. However, the polymer alloy as the water-insoluble polymer contained in the protective layer according to the present embodiment is a polymer composed of IPN among “a polymer alloy in which different types of polymer components are not bonded by a covalent bond”. is there.

The polymer X constituting the polymer alloy is excellent in electrolyte permeability and liquid retention, and the hard segments of the crystalline resin aggregate to form a pseudo-crosslinking point such as C—H—FC in the main chain. It is thought that When only such a polymer X is mixed with the filler (A) and used for the protective layer of the electricity storage device, the electrolyte has good permeability, liquid retention and oxidation resistance, but has good adhesion and flexibility. There is a tendency to become insufficient. As a result, the filler (A) in the protective layer cannot be sufficiently bound, and the protective layer has become non-homogeneous, for example, the filler (A) is peeled off. Can't get. On the other hand, although the polymer Y constituting the polymer alloy is excellent in adhesion and flexibility, it tends to have low oxidation resistance. When this is used alone as a protective layer of an electricity storage device, charge and discharge are performed. Since it is deteriorated by oxidative decomposition or the like by repeated or overcharging, an electricity storage device having a low resistance increase rate cannot be obtained.

However, by using a polymer alloy containing the polymer X and the polymer Y, it is possible to simultaneously exhibit electrolyte permeability, liquid retention and oxidation resistance, adhesion and flexibility, and increase resistance. It becomes possible to manufacture an electricity storage device with a low rate. In addition, when a polymer alloy consists only of the polymer X and the polymer Y, since oxidation resistance can be improved more, it is preferable.

Such a polymer alloy preferably has only one endothermic peak in the temperature range of −50 to 250 ° C. when measured by differential scanning calorimetry (DSC) according to JIS K7121. The temperature of this endothermic peak is more preferably in the range of −30 to + 80 ° C.

The polymer X constituting the polymer alloy generally has an endothermic peak (melting temperature) at −50 to 250 ° C. when it exists alone. In addition, the polymer Y constituting the polymer alloy generally has an endothermic peak (glass transition temperature) different from that of the polymer X. Therefore, when the polymer X and the polymer Y are present in phase separation in the binder (C), two endothermic peaks should be observed in the temperature range of −50 to 250 ° C. From this, it can be estimated that the binder (C) is a polymer alloy when there is only one endothermic peak in the temperature range of −50 to 250 ° C.

Furthermore, when the temperature of only one endothermic peak of the binder (C) which is a polymer alloy is in the range of −30 to + 80 ° C., the binder (C) can impart good flexibility and tackiness. Therefore, the adhesiveness can be further improved, which is preferable.

Polymer X may further have a repeating unit derived from another unsaturated monomer in addition to the repeating unit derived from the monomer having a fluorine atom. Here, as the other unsaturated monomer, the above-exemplified unsaturated carboxylic acid, unsaturated carboxylic acid ester, α, β-unsaturated nitrile compound and other monomers can be used.

The content ratio of the repeating unit derived from the monomer having a fluorine atom in 100 parts by mass of the polymer X is preferably 80 parts by mass or more, and more preferably 90 parts by mass or more. In such a case, the monomer having a fluorine atom is preferably at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and propylene hexafluoride.

Further preferred embodiments of the polymer X are as follows. That is, the content ratio of the repeating unit derived from vinylidene fluoride in 100 parts by mass of the polymer X is preferably 50 to 99 parts by mass, more preferably 80 to 98 parts by mass; derived from ethylene tetrafluoride. The content of the repeating unit is preferably 50 parts by mass or less, more preferably 1 to 30 parts by mass, and particularly preferably 2 to 20 parts by mass; and the content of the repeating unit derived from propylene hexafluoride The ratio is preferably 50 parts by mass or less, more preferably 1 to 30 parts by mass, and particularly preferably 2 to 25 parts by mass. The polymer X is most preferably composed of only a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene.

On the other hand, the polymer Y may further have a repeating unit derived from another unsaturated monomer in addition to the repeating unit derived from the unsaturated carboxylic acid. Here, as the other unsaturated monomer, the above-exemplified unsaturated carboxylic acid ester, α, β-unsaturated nitrile compound and other monomers can be used.

The content of the repeating unit derived from the unsaturated carboxylic acid in 100 parts by mass of the polymer Y is preferably 2 to 20 parts by mass, and more preferably 3 to 15 parts by mass.

As long as the polymer alloy has the above-described configuration, the synthesis method is not particularly limited, but it can be easily synthesized by, for example, a known emulsion polymerization step or an appropriate combination thereof.

For example, first, a polymer X having a repeating unit derived from a monomer having a fluorine atom is synthesized by a known method, and then a monomer for constituting the polymer Y is added to the polymer X. After the monomer is sufficiently absorbed in the stitch structure of the polymer particles made of the polymer X, the absorbed monomer is polymerized in the stitch structure of the polymer X to obtain the polymer Y. The polymer alloy can be easily produced by the synthesis method. When a polymer alloy is produced by such a method, it is essential that the polymer X sufficiently absorbs the monomer of the polymer Y. When the absorption temperature is too low or when the absorption time is too short, it becomes a simple phase-separated polymer mixture, and the polymer alloy in the present invention cannot be obtained in many cases. However, if the absorption temperature is too high, the pressure of the polymerization system becomes too high, which is disadvantageous in terms of reaction system handling and reaction control, and even if the absorption time is excessively long, further advantageous results are not obtained. .

From the above viewpoint, the absorption temperature is preferably 30 to 100 ° C., more preferably 40 to 80 ° C., and the absorption time is preferably 1 to 12 hours, and preferably 2 to 8 hours. It is more preferable. At this time, it is preferable to lengthen the absorption time when the absorption temperature is low, and a short absorption time is sufficient when the absorption temperature is high. Appropriate conditions are such that the value obtained by multiplying the absorption temperature (° C.) and the absorption time (h) is approximately 120 to 300 (° C. · h), preferably 150 to 250 (° C. · h).

The operation of absorbing the monomer of the polymer Y in the stitch structure of the polymer X is preferably performed in a known medium used for emulsion polymerization, for example, in water.

The content ratio of the polymer X in 100 parts by mass of the polymer alloy is preferably 5 to 50 parts by mass, more preferably 15 to 40 parts by mass, and particularly preferably 20 to 30 parts by mass. When the polymer alloy contains the polymer X in the above-described range, the balance between the permeability, liquid retention and oxidation resistance of the electrolytic solution, and adhesion is improved. Moreover, when the polymer Y in which the content ratio of the repeating unit derived from each monomer is in the above preferable range is used, the polymer alloy contains the polymer X in the above range, so that the entire polymer alloy It is possible to set the content ratio of each repeating unit in the above-mentioned preferable range, and this makes the ethylene carbonate (EC) / diethyl carbonate (DEC) insoluble content an appropriate value. The rate of increase will be sufficiently low.

1.3.4. Production method of binder (C) When the binder (C) has a repeating unit derived from a monomer having a fluorine atom, its production, that is, a polymer having a repeating unit derived from a monomer having a fluorine atom. The polymerization in the case of one-step polymerization, the polymerization of the polymer X, and the polymerization of the polymer Y in the presence of the polymer X are respectively known polymerization initiators, molecular weight regulators, emulsifiers (surfactants), etc. Can be carried out in the presence of

Further, when the binder (C) has a repeating unit derived from a conjugated diene compound, it may be prepared by one-stage polymerization, may be prepared by two-stage polymerization, and further by multi-stage polymerization. Can be carried out in the presence of an agent, a molecular weight regulator, an emulsifier (surfactant) and the like.

Examples of the polymerization initiator include water-soluble polymerization initiators such as sodium persulfate, potassium persulfate, and ammonium persulfate; oil-soluble polymerization such as benzoyl peroxide, lauryl peroxide, and 2,2′-azobisisobutyronitrile. Initiators; redox polymerization initiators composed of a combination of a reducing agent such as sodium bisulfite, iron (II) salt, tertiary amine and the like and an oxidizing agent such as persulfate or organic peroxide. These polymerization initiators can be used singly or in combination of two or more.

When the binder (C) has a repeating unit derived from a monomer having a fluorine atom, the total amount of monomers used (when the binder (C) is synthesized by one-step polymerization) Is the total amount of monomers used, the total amount of monomers leading to polymer X in the production of polymer X, and the single amount leading to polymer Y when polymer Y is polymerized in the presence of polymer X The same applies to the following.) It is preferably 0.3 to 3 parts by mass with respect to 100 parts by mass.

Examples of the molecular weight regulator include halogenated hydrocarbons such as chloroform and carbon tetrachloride; mercaptan compounds such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dotezyl mercaptan, and thioglycolic acid; dimethyl Examples thereof include xanthogen compounds such as xanthogen disulfide and diisopropylxanthogen disulfide; and other molecular weight regulators such as terpinolene and α-methylstyrene dimer. These molecular weight regulators can be used singly or in combination of two or more. The use ratio of the molecular weight regulator is preferably 5 parts by mass or less with respect to 100 parts by mass in total of the monomers used.

Examples of the emulsifier include anionic surfactants, nonionic surfactants, amphoteric surfactants, and fluorosurfactants.

Examples of the anionic surfactant include sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, sulfates of polyethylene glycol alkyl ethers, etc .; examples of the nonionic surfactants include polyethylene glycol Examples thereof include alkyl esters, alkyl ethers of polyethylene glycol, alkyl phenyl ethers of polyethylene glycol, and the like.

As the amphoteric surfactant, for example, the anion portion is composed of a carboxylate salt, a sulfate ester salt, a sulfonate salt or a phosphate ester salt, and the cation portion is composed of an amine salt, a quaternary ammonium salt or the like. Things can be mentioned. Specific examples of such amphoteric surfactants include betaine compounds such as lauryl betaine and stearyl betaine; amino acid type surfactants such as lauryl-β-alanine, lauryl di (aminoethyl) glycine, and octyldi (aminoethyl) glycine. An agent can be mentioned.

Examples of the fluorosurfactant include fluorobutyl sulfonate, phosphoric acid ester having a fluoroalkyl group, carboxylate having a fluoroalkyl group, and a fluoroalkyl ethylene oxide adduct. Examples of such commercially available fluorosurfactants include F-top EF301, EF303, EF352 (above, manufactured by Tochem Products Co., Ltd.); Megafac F171, F172, F173 (above, manufactured by DIC Corporation); FC430, FC431 (above, manufactured by Sumitomo 3M Limited); Asahi Guard AG710, Surflon S-381, S-382, SC101, SC102, SC103, SC104, SC105, SC106, Surfinol E1004, KH-10, KH-20, KH-30, KH-40 (above, manufactured by Asahi Glass Co., Ltd.); tergent 250, 251, 222F, FTX-218 (above, manufactured by Neos Co., Ltd.), and the like. As an emulsifier, the 1 type (s) or 2 or more types selected from the above can be used.

The use ratio of the emulsifier is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass with respect to 100 parts by mass in total of the monomers used.

Emulsion polymerization is preferably performed in a suitable aqueous medium, particularly preferably in water. The total content of the monomers in the aqueous medium can be 10 to 50% by mass, and preferably 20 to 40% by mass.

The conditions for emulsion polymerization are preferably a polymerization time of 2 to 24 hours at a polymerization temperature of 40 to 85 ° C., and more preferably a polymerization time of 3 to 20 hours at a polymerization temperature of 50 to 80 ° C.

2. Next, the manufacturing method of the protective layer which concerns on one Embodiment of this invention is demonstrated. In the protective layer according to the present embodiment, a composition for a protective layer containing a filler (A), a water-soluble polymer (B), a binder (C), and a liquid medium is applied onto a suitable support and dried. Thus, the protective layer can be produced by setting the water content in the protective layer to 0.1 mg / cm ³ or more and 35 mg / cm ³ or less. The protective layer produced in this way is a porous film, can permeate the electrolytic solution satisfactorily, and does not deteriorate the charge / discharge characteristics even if it is disposed between the positive electrode and the negative electrode.

The moisture content of the protective layer adjusts the concentration and ratio of the filler (A), water-soluble polymer (B) and binder (C) in the protective layer composition and the conditions for removing the liquid medium from the coating film. Can be controlled.

The method for applying the protective layer composition to the support is not particularly limited, and can be carried out by a method commonly used industrially, such as coating by a coater (also referred to as a doctor blade) or coating by brush coating. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, an extrusion method, and a brush coating method. Among these, the dip method is preferable in that a uniform protective layer can be obtained. As the support, a resin film, a metal belt, a drum, or the like can be used.

The composition for protective layer is applied on a support, and after removing the liquid medium, the protective layer obtained can be peeled off from the support and laminated with an electrode or a separator substrate. Examples of the laminating method include a method of thermocompression bonding using a heating roll and a method of using an adhesive film of a porous film.

Moreover, when using a separator base material as a support without peeling off the protective layer, the adhesiveness between the support and the protective layer is applied by pressure treatment using a mold press or a roll press, if necessary. Can also be improved. However, at this time, if the pressure treatment is excessively performed, the porosity of the protective layer, which is a porous film, may be impaired. Therefore, the pressure and the pressurization time are appropriately controlled.

Examples of the method for forming the protective layer by removing the liquid medium from the coating film include drying by warm air, hot air, low-humidity air, vacuum drying, and (irradiation) irradiation with infrared rays, electron beams, and the like. In particular, when a separator substrate is used as a support, the heating temperature is set to 0.1 mg / cm ³ or more and 35 mg / cm ³ or less without deteriorating the air permeability of the separator substrate. Is preferably 30 to 120 ° C, more preferably 30 to 90 ° C, and particularly preferably 40 to 80 ° C.

The optimum heating temperature varies depending on the type of liquid medium contained in the protective layer composition. For example, when a low-volatility liquid medium such as N-methylpyrrolidone is used as the liquid medium, it is preferably heated at 90 to 180 ° C. for 30 to 180 minutes. When a highly volatile solvent is used, it is preferably heated at 120 to 160 ° C. for 60 to 120 minutes. By setting it as the above-mentioned heating conditions, the water content of the protective layer can be controlled to 0.1 mg / cm ³ or more and 35 mg / cm ³ or less without providing a separate drying step.

<Composition for protective layer>
The composition for a protective layer used in the method for producing a protective layer according to the present embodiment contains a filler (A), a water-soluble polymer (B), a binder (C), and a liquid medium. The filler (A) and the binder (C) are preferably dispersed as particles in the liquid medium.

Average particle size (Da) of filler (A) contained in the protective layer composition (average particle size after mixing when inorganic particles (A1) and water-insoluble polymer particles (A2) are mixed) Is preferably in the range of 100 to 3000 nm, and more preferably in the range of 100 to 1500 nm. In addition, it is preferable that the average particle diameter (Da) of a filler (A) is larger than the average hole diameter of the separator which is a porous film. Thereby, damage to a separator can be reduced and it can prevent that a filler (A) is clogged with the microporous of a separator.

The ratio (Da / Dc) between the average particle size (Da) of the filler (A) and the average particle size (Dc) of the binder (C) is preferably 1-30. When the ratio (Da / Dc) is within the above range, the binder (C) is formed at the contact point between the filler (A) particles when the protective layer composition is applied and dried to form the protective layer. From the viewpoint of maintaining the shape of the protective layer.

When the filler (A) is inorganic particles (A1) and / or water-insoluble polymer particles (A2), the average particle diameter (Da1) of the inorganic particles (A1) and the average particle diameter of the binder (C) The ratio (Da1 / Dc) to (Dc) is preferably from 1 to 30, more preferably from 1 to 10, and particularly preferably from 1.5 to 5. The ratio (Da2 / Dc) of the average particle size (Da2) of the water-insoluble polymer particles (A2) to the average particle size (Dc) of the binder (C) is preferably 1 to 30. 1 to 5 is more preferable, and 1.1 to 2 is particularly preferable. When at least one of the ratio (Da1 / Dc) and the ratio (Da2 / Dc) is in the above range, the filler (A) is formed when the protective layer composition is applied and dried to form the protective layer. Since the binder (C) tends to gather at the contact point between the particles and the binding force between the particles is improved, it is preferable from the viewpoint of maintaining the shape of the protective layer.

Furthermore, when both the inorganic particles (A1) and the water-insoluble polymer particles (A2) are contained as the filler (A), the average particle diameter (Da1) of the inorganic particles (A1) and the water-insoluble polymer particles (A2) ) To the average particle diameter (Da2) (Da1 / Da2) is preferably 0.5 to 10, more preferably 0.7 to 5, and preferably 0.9 to 3. Particularly preferred. When the ratio (Da1 / Da2) is in the above range, the inorganic particles (A1) and the water-insoluble polymer particles (A2) are formed when the protective layer composition is applied and dried to form the protective layer. It is considered that the migration of either of the particles can be suppressed and the uneven distribution of either particle on the surface of the protective film can be suppressed. For this reason, it is preferable from the viewpoint of the homogeneity of the protective layer.

The protective layer composition contains a liquid medium. This liquid medium is preferably an aqueous medium containing water. This aqueous medium can contain a small amount of non-aqueous medium in addition to water. Examples of such non-aqueous media include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, and the like, and one or more selected from these are used. can do. The content ratio of such a non-aqueous medium is preferably 10% by mass or less, more preferably 5% by mass or less, when the total mass of the liquid medium is 100% by mass. It is particularly preferable that the aqueous medium is composed only of water without containing a non-aqueous medium.

The composition for the protective layer uses an aqueous medium as a liquid medium, and preferably contains no non-aqueous medium other than water, so that the degree of adverse effects on the environment is low and the safety for handling workers is high.

If necessary, other components such as a surfactant may be added to the protective layer composition.

<The manufacturing method of the composition for protective layers>
The protective layer composition described above preferably contains 0.1 to 2000 parts by weight of binder (C) with respect to 100 parts by weight of filler (A), preferably 3 to 1500 parts by weight. More preferably, it is contained in a proportion of 5 to 1000 parts by mass. In addition, said content rate is the case where a protective layer is formed on one surface of the positive electrode or the negative electrode or the surface of the separator, and the case where a protective layer is formed as an adhesive layer interposed between the positive electrode or the negative electrode and the separator. The preferred range is different.

When the protective layer is formed on one surface of the positive electrode or the negative electrode or the surface of the separator using the protective layer composition described above, the binder (C) is 0.1 to 15 parts per 100 parts by mass of the filler (A). It is preferably contained at a ratio of 3 parts by mass, more preferably 3 to 12 parts by mass, and particularly preferably 5 to 10 parts by mass. When the content ratio of the filler (A) and the binder (C) contained in the protective layer composition is within the above range, the balance between the toughness of the protective layer to be formed and the lithium ion permeability is improved, As a result, the rate of increase in resistance of the obtained electricity storage device can be further reduced.

Moreover, when forming the protective layer as a contact bonding layer interposed between a positive electrode or a negative electrode, and a separator using the above-mentioned composition for protective layers, a binder (C) is 100 mass parts of fillers (A). The content is preferably 1 to 2000 parts by mass, more preferably 5 to 1500 parts by mass, and particularly preferably 10 to 1000 parts by mass. When the content ratio of the filler (A) and the binder (C) contained in the protective layer composition is within the above range, the balance between the adhesion of the protective layer formed to the electrode and the lithium ion permeability is balanced. As a result, the rate of increase in resistance of the obtained electricity storage device can be further reduced.

The protective layer composition described above is prepared by mixing the filler (A), the water-soluble polymer (B), the binder (C), the liquid medium, and other components as necessary. The As a means for mixing them, for example, a known mixing device such as a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer can be used.

For mixing and stirring for producing the protective layer composition, a mixer capable of stirring to such an extent that the aggregate of the filler (A) does not remain in the protective layer composition and a sufficient dispersion condition as necessary are selected. There is a need to. The degree of dispersion is preferably mixed and dispersed so that aggregates larger than at least 20 μm are eliminated. The degree of dispersion can be measured with a grain gauge.

The composition for a protective layer of an electricity storage device as described above forms an electrode including a protective layer having excellent adhesion between fillers (A), between fillers (A) and electrodes, and between fillers (A) and separators. In addition, an electricity storage device including such an electrode has a sufficiently low resistance increase rate.

3. Separator The separator according to one embodiment of the present invention contains a filler (A) and a water-soluble polymer (B), and has a water content of 0.1 mg / cm ³ or more and 5 mg / cm ³ or less. It is characterized by. Such a separator may contain the above-mentioned binder (C), and preferably includes the above-described protective layer on the surface.

In the case where the separator according to this embodiment has a structure in which a protective layer is laminated on the surface, the above-described composition for a protective layer is applied onto a separator substrate, and the moisture content in the separator is reduced to 0.00 by drying or the like. it can be prepared by a 1 mg / cm ³ or more 5 mg / cm ³ or less. The separator produced in this way is a porous film, can permeate the electrolytic solution satisfactorily, and does not deteriorate the charge / discharge characteristics even if it is disposed between the positive electrode and the negative electrode.

In the separator according to the present embodiment, the protective layer composition is applied onto a suitable support, the liquid medium is removed by drying or the like, and the resulting film is peeled off from the support to produce a protective layer. It can also be produced by pressure bonding with the porous film. Alternatively, the protective layer composition can be produced by extruding it with a T-die into a film shape and press-bonding it with a polyolefin porous film. Furthermore, it can also be produced by applying the protective layer composition to a polyolefin porous film and removing the liquid medium by drying or the like. In addition, about a polyolefin porous membrane, a commercial item can be used. Alternatively, a porous polyolefin raw film containing calcium carbonate as an inorganic filler is immersed in an equal amount of a mixed solution of hydrochloric acid and methanol, and manufactured by a known manufacturing method such as a manufacturing method by dissolving and removing calcium carbonate Can be used.

4). Hereinafter, preferred embodiments of an electricity storage device according to the present invention will be described in detail with reference to the drawings.

An electricity storage device according to an embodiment of the present invention includes a positive electrode, a negative electrode, the above-described protective layer disposed between the positive electrode and the negative electrode, and an electrolytic solution. Hereinafter, such an electricity storage device will be described with reference to the drawings while showing a first specific example.

In addition, an electricity storage device according to an embodiment of the present invention includes a positive electrode, a negative electrode, the separator disposed between the positive electrode and the negative electrode, and an electrolytic solution. Hereinafter, such an electricity storage device will be described with reference to the drawings while showing a second specific example and a third specific example.

4.1. First Specific Example FIG. 1 is a schematic diagram illustrating a cross section of an electricity storage device according to a first specific example. As shown in FIG. 1, the electricity storage device 1 includes a positive electrode 10 in which a positive electrode active material layer 14 is formed on the surface of a positive electrode current collector 12 and a negative electrode 20 in which a negative electrode active material layer 24 is formed on the surface of a negative electrode current collector 22. And a protective layer 30 provided between the positive electrode 10 and the negative electrode 20, and an electrolyte solution 40 that fills between the positive electrode 10 and the negative electrode 20. In the electricity storage device 1, no separator is provided between the positive electrode 10 and the negative electrode 20. This is because if the positive electrode 10 and the negative electrode 20 are completely fixed with a solid electrolyte or the like, the positive electrode 10 and the negative electrode 20 do not come into contact with each other to cause a short circuit.

The positive electrode 10 shown in FIG. 1 is formed so that the positive electrode active material layer 14 is not provided on one surface along the longitudinal direction and the positive electrode current collector 12 is exposed. A layer 14 may be provided. Similarly, the negative electrode 20 shown in FIG. 1 is formed such that the negative electrode active material layer 24 is not provided on one surface along the longitudinal direction and the negative electrode current collector 22 is exposed, A negative electrode active material layer 24 may be provided.

As the positive electrode current collector 12, for example, a metal foil, an etching metal foil, an expanded metal, or the like can be used. Specific examples of these materials include metals such as aluminum, copper, nickel, tantalum, stainless steel, and titanium, and can be appropriately selected and used according to the type of the target power storage device. For example, when forming the positive electrode of a lithium ion secondary battery, it is preferable to use aluminum among the above as the positive electrode current collector 12. In such a case, the thickness of the positive electrode current collector 12 is preferably 5 to 30 μm, and more preferably 8 to 25 μm.

The positive electrode active material layer 14 includes one or more positive electrode active materials of a positive electrode material that can be doped / dedoped with lithium, and is configured to include a conductivity-imparting agent such as graphite as necessary. . In addition, as a binder, fluorine-containing polymers such as polyvinylidene fluoride and polyfluorinated acrylic esters, water-soluble polymers such as carboxymethyl cellulose used for dispersion of positive electrode active materials, styrene butadiene rubber (SBR) and (meth) acrylic. A polymer composition containing an acid ester copolymer may be used.

The positive electrode active material is not particularly limited as long as it is a positive electrode material that can be doped / undoped with lithium and contains a sufficient amount of lithium. Specifically, a composite metal composed of lithium and a transition metal represented by the general formula LiMO ₂ (wherein M contains at least one of Co, Ni, Mn, Fe, Al, V, and Ti). It is preferable to use an oxide or an intercalation compound containing lithium. In addition, Li _a MX _b (M is one selected from transition metals, X is selected from S, Se, PO ₄ and 0 <a, b is an integer) can also be used. In particular, when a lithium composite oxide represented by Li _x M _I O ₂ or Li _y M _{II 2} O ₄ is used as the positive electrode active material, a high voltage can be generated and the energy density can be increased, which is preferable. . In these composition formulas, M _I represents one or more transition metal elements, preferably at least one of cobalt (Co) and nickel (Ni). M _II represents one or more transition metal elements, and is preferably manganese (Mn). The values of x and y vary depending on the charge / discharge state of the battery, and are usually in the range of 0.05 to 1.10. Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , LiNi _z Co _1-z O ₂ (where 0 <z <1), LiMn ₂ O _{4, and the} like.

As the negative electrode current collector 22, for example, a metal foil, an etching metal foil, an expanded metal, or the like can be used. Specific examples of these materials include metals such as aluminum, copper, nickel, tantalum, stainless steel, and titanium, and can be appropriately selected and used according to the type of the target power storage device. Of the above, copper is preferably used as the negative electrode current collector 22. In such a case, the thickness of the current collector is preferably 5 to 30 μm, and more preferably 8 to 25 μm.

The negative electrode active material layer 24 is configured to include any one or two or more negative electrode materials that can be doped / undoped with lithium as a negative electrode active material, and if necessary, a binder similar to the positive electrode It is comprised including.

As the negative electrode active material, for example, a carbon material, a crystalline or amorphous metal oxide, or the like can be suitably used. Examples of carbon materials include non-graphitizable carbon materials such as coke and glassy carbon, and graphites of highly crystalline carbon materials having a developed crystal structure. Specifically, pyrolytic carbons, cokes ( Pitch coke, needle coke, petroleum coke, etc.), graphite, glassy carbons, polymer compound fired bodies (phenol resins, furan resins, etc. fired and carbonized at an appropriate temperature), carbon fibers, activated carbon, etc. Can be mentioned. As crystalline or amorphous metal oxides, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn) ), Lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd) or platinum (Pt) ) As a constituent element. In particular, those containing silicon (Si) or tin (Sn) as constituent elements can be suitably used.

Note that the above-described active material layer is preferably subjected to press working. Examples of means for performing the press working include a roll press machine, a high-pressure super press machine, a soft calendar, and a 1-ton press machine. The conditions for the press working are appropriately set according to the type of processing machine used and the desired thickness and density of the active material layer. In the case of a lithium ion secondary battery positive electrode, the thickness is preferably 40 to 100 μm, and the density is preferably 2.0 to 5.0 g / cm ³ . In the case of a lithium ion secondary battery negative electrode, the thickness is preferably 40 to 100 μm and the density is preferably 1.3 to 1.9 g / cm ³ .

The protective layer 30 is disposed between the positive electrode 10 and the negative electrode 20. 1, the protective layer 30 is disposed between the positive electrode 10 and the negative electrode 20 so as to be in contact with the positive electrode active material layer 14, but is disposed so as to be in contact with the negative electrode active material layer 24. May be. Further, the protective layer 30 may be disposed as a self-supporting film between the positive electrode 10 and the negative electrode 20 without being in contact with the positive electrode 10 or the negative electrode 20. Thereby, even if it is a case where dendrites precipitate by repeating charging / discharging, since it is guarded by the protective layer 30, a short circuit does not occur. Therefore, the function as an electricity storage device can be maintained.

The protective layer 30 can be formed, for example, by applying the above-described protective layer composition to the surface of the positive electrode 10 (or the negative electrode 20) and drying it. As a method for applying the protective layer composition to the surface of the positive electrode 10 (or the negative electrode 20), for example, a doctor blade method, a reverse roll method, a comma bar method, an air knife method, a die coating method, or the like can be applied. The coating film is preferably dried in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for 1 to 120 minutes, more preferably 5 to 60 minutes.

The thickness of the protective layer 30 is not particularly limited, but is preferably in the range of 0.5 to 4 μm, and more preferably in the range of 0.5 to 3 μm. When the thickness of the protective layer 30 is in the above range, the permeability of the electrolytic solution into the electrode and the liquid retaining property are improved, and an increase in the internal resistance of the electrode can be suppressed.

The electrolytic solution 40 is appropriately selected and used according to the type of the target electricity storage device. As the electrolytic solution 40, a solution in which an appropriate electrolyte is dissolved in a solvent is used.

When manufacturing a lithium ion secondary battery, a lithium compound is used as an electrolyte. Specifically, for example _{_{_{LiClO 4, LiBF 4, LiI,}}} LiPF 6, LiCF 3 SO 3, LiAsF 6, LiSbF 6, LiAlCl 4, LiCl, LiBr, LiB (C 2 H 5) 4, LiCH 3 SO 3, LiC _{_{_{_{4 F 9 SO 3, Li (}}}} CF 3 SO 2) can be cited ₂ N or the like. In this case, the electrolyte concentration is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.

The type and concentration of the electrolyte in the case of manufacturing a lithium ion capacitor are the same as in the case of the lithium ion secondary battery.

In any of the above cases, examples of the solvent used in the electrolytic solution include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; lactones such as γ-butyrolactone; trimethoxy Silane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, ether such as 2-methyltetrahydrofuran; Sulfoxide such as dimethyl sulfoxide; 1,3-dioxolane, 4-methyl-1,3-dioxolane, etc. Oxolane derivatives; nitrogen-containing compounds such as acetonitrile and nitromethane; Estes such as methyl formate, methyl acetate, butyl acetate, methyl propionate, ethyl propionate, and phosphate triester Glyme compounds such as diglyme, triglyme and tetraglyme; ketones such as acetone, diethyl ketone, methyl ethyl ketone and methyl isobutyl ketone; sulfone compounds such as sulfolane; oxazolidinone derivatives such as 2-methyl-2-oxazolidinone; 1,3-propane sultone; Sultone compounds such as 1,4-butane sultone, 2,4-butane sultone and 1,8-naphtha sultone.

4.2. Second Specific Example FIG. 2 is a schematic view showing a cross section of an electricity storage device according to a second specific example. As shown in FIG. 2, the electricity storage device 2 includes a positive electrode 110 in which a positive electrode active material layer 114 is formed on the surface of a positive electrode current collector 112 and a negative electrode 120 in which a negative electrode active material layer 124 is formed on the surface of a negative electrode current collector 122. A protective layer 130 provided between the positive electrode 110 and the negative electrode 120, an electrolyte solution 140 that fills between the positive electrode 110 and the negative electrode 120, and a separator 150 provided between the positive electrode 110 and the negative electrode 120. It is provided.

The electricity storage device 2 is different from the electricity storage device 1 described above in that the protective layer 130 is disposed so as to be sandwiched between the positive electrode 110 and the separator 150. 2, the protective layer 130 is sandwiched between the positive electrode 110 and the separator 150, but the protective layer 130 is sandwiched between the negative electrode 120 and the separator 150. It may be arranged so that. By adopting such a configuration, even when dendrites are deposited by repeated charge and discharge, the protective layer 130 guards and no short circuit occurs. Therefore, the function as an electricity storage device can be maintained.

The protective layer 130 can be formed by, for example, applying the above-described protective layer composition on the surface of the separator 150, bonding the positive electrode 110 (or the negative electrode 120), and then drying. As a method for applying the protective layer composition to the surface of the separator 150, for example, a doctor blade method, a reverse roll method, a comma bar method, an air knife method, a die coating method, or the like can be applied. The coating film is preferably dried in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for 1 to 120 minutes, more preferably 5 to 60 minutes.

Any separator 150 may be used as long as it is electrically stable, chemically stable with respect to the positive electrode active material, the negative electrode active material, or the solvent, and has no electrical conductivity. . For example, a polymer nonwoven fabric, a porous film, glass or ceramic fibers in a paper shape can be used, and a plurality of these may be laminated. In particular, a porous polyolefin film is preferably used, and a composite of this with a heat-resistant material made of polyimide, glass, ceramic fibers or the like may be used.

Other configurations of the power storage device 2 according to the second specific example are the same as those of the power storage device 1 according to the first specific example described with reference to FIG.

4.3. Third Specific Example FIG. 3 is a schematic diagram illustrating a cross section of an electricity storage device according to a third specific example. As shown in FIG. 3, the electricity storage device 3 includes a positive electrode 210 in which a positive electrode active material layer 214 is formed on the surface of a positive electrode current collector 212, and a negative electrode 220 in which a negative electrode active material layer 224 is formed on the surface of a negative electrode current collector 222. An electrolyte 240 filling between the positive electrode 210 and the negative electrode 220, a separator 250 provided between the positive electrode 210 and the negative electrode 220, and a protective layer 230 formed so as to cover the surface of the separator 250. It is provided.

The electricity storage device 3 is different from the electricity storage device 1 and the electricity storage device 2 described above in that the protective layer 230 is formed so as to cover the surface of the separator 250. By adopting such a configuration, even when dendrite is deposited by repeated charge and discharge, the protective layer 230 guards and no short circuit occurs. Therefore, the function as an electricity storage device can be maintained.

The protective layer 230 can be formed, for example, by applying the above-described protective layer composition to the surface of the separator 250 and drying it. As a method of applying the protective layer composition to the surface of the separator 250, for example, a doctor blade method, a reverse roll method, a comma bar method, an air knife method, a die coating method, or the like can be applied. The coating film is preferably dried in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for 1 to 120 minutes, more preferably 5 to 60 minutes.

Regarding other configurations of the power storage device 3 according to the third specific example, the power storage device 1 according to the first specific example described with reference to FIG. 1 and the power storage according to the second specific example described with reference to FIG. Since it is the same as the device 2, the description thereof is omitted.

4.4. Manufacturing Method As a manufacturing method of the above-described power storage device, for example, two electrodes (two of a positive electrode and a negative electrode or two of a capacitor electrode) are overlapped via a separator as necessary, and this is used as a battery. Examples of the method include a method of winding, folding, etc. in a battery container according to the shape, injecting an electrolyte into the battery container, and sealing. The shape of the battery can be an appropriate shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, or a flat shape.

4.5. Applications The power storage device as described above is suitable as a secondary battery or a capacitor mounted on an automobile such as an electric vehicle, a hybrid car, and a truck, as well as a secondary battery used for AV equipment, OA equipment, communication equipment, It is also suitable as a capacitor.

5. EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. “Part” and “%” in Examples and Comparative Examples are based on mass unless otherwise specified.

5.1. Synthesis of binder (C) 5.1.1. Synthesis example 1
<Synthesis of Polymer X>
The inside of an autoclave with an internal volume of 6 L equipped with an electromagnetic stirrer was sufficiently purged with nitrogen, then 2.5 L of deoxygenated pure water and 25 g of ammonium perfluorodecanoate as an emulsifier were charged, and the mixture was stirred at 350 rpm up to 60 ° C. The temperature rose. Next, a mixed gas composed of 70% of vinylidene fluoride (VDF) as a monomer and 30% of propylene hexafluoride (HFP) was charged until the internal pressure reached 20 kg / cm ² . 25 g of Freon 113 solution containing 20% of diisopropyl peroxydicarbonate as a polymerization initiator was injected using nitrogen gas to initiate polymerization. During the polymerization, a mixed gas composed of 60.2% VDF and 39.8% HFP was sequentially injected so that the internal pressure was maintained at 20 kg / cm ² to maintain the pressure at 20 kg / cm ² . Further, since the polymerization rate decreased as the polymerization progressed, the same amount of the same polymerization initiator solution as that described above was injected using nitrogen gas after 3 hours, and the reaction was continued for 3 hours. Then, simultaneously with cooling the reaction liquid, the stirring was stopped and the reaction was stopped after releasing the unreacted monomer, whereby an aqueous dispersion containing 40% of the particles of the polymer X was obtained. The obtained polymer X was analyzed by ¹⁹ F-NMR. As a result, the mass composition ratio of each monomer was VDF / HFP = 21/4.

<Synthesis of binder (C1)>
After the inside of the 7-L separable flask was sufficiently purged with nitrogen, 25 parts by mass of an aqueous dispersion containing the particles of the polymer X obtained in the above step in terms of the polymer X was added to the emulsifier “ADEKA rear soap SR1025”. (Trade name, manufactured by ADEKA Corporation) 0.5 parts by mass, methyl methacrylate (MMA) 30 parts by mass, 2-ethylhexyl acrylate (EHA) 40 parts by mass, methacrylic acid (MAA) 5 parts by mass and water 130 parts by mass The portions were sequentially charged and stirred at 70 ° C. for 3 hours to allow the polymer X to absorb the monomer. Next, 20 mL of a tetrahydrofuran solution containing 0.5 part by mass of azobisisobutyronitrile, which is an oil-soluble polymerization initiator, is added, heated to 75 ° C., reacted for 3 hours, and further reacted at 85 ° C. for 2 hours. went. Thereafter, the reaction was stopped after cooling, and the aqueous dispersion S1 containing 40% of the binder (C1) containing the polymer X and the polymer Y was obtained by adjusting the pH to 7 with a 2.5N sodium hydroxide aqueous solution. It was.

For the obtained water dispersion S1, the particle size distribution is measured 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 size (Dc) was determined to be 330 nm.

10 g of the obtained aqueous dispersion S1 was weighed into a Teflon (registered trademark) petri dish having a diameter of 8 cm and dried at 120 ° C. for 1 hour to form a film. 1 g of the obtained film (polymer) was immersed in 400 mL of toluene and shaken at 50 ° C. for 3 hours. Next, the toluene phase was filtered through a 300-mesh wire mesh to separate insoluble components, and the weight of the residue (Y (g)) obtained by evaporating and removing the dissolved toluene was measured from the following formula ( When the toluene insoluble content was determined by 3), the toluene insoluble content of the binder (C1) was 85%.
Toluene insoluble content (%) = ((1-Y) / 1) × 100 (3)

Furthermore, when the obtained film (film composed of the binder (C1)) was measured by a differential scanning calorimeter (manufactured by NETZSCH, DSC204F1, Phoenix), the melting temperature Tm was not observed, and the single glass transition temperature Tg Was observed at −5 ° C., the obtained binder (C1) is presumed to be polymer alloy particles.

Further, the obtained film (polymer) was subjected to thermogravimetric analysis with a thermal analyzer (manufactured by Shimadzu Corporation, model “DTG-60A”). When heated in an air atmosphere at a heating rate of 20 ° C./min, the temperature at which the polymer particles lose 10% by weight (hereinafter, this reduction starting temperature is expressed as “T ₁₀ ”) was 338 ° C.

5.1.2. Synthesis example 2
In the synthesis example 1, except that the composition of the monomer gas and the amount of the emulsifier were appropriately changed, an aqueous dispersion containing the binder (C2) with the composition shown in Table 1 was prepared, and the solid content of the aqueous dispersion was By removing or adding water under reduced pressure according to the concentration, an aqueous dispersion S2 having a solid content concentration of 40% was produced. As a result of average particle diameter (Dc) carried out in the same manner as in Synthesis Example 1 for the obtained binder (C2), as a result of measuring toluene insoluble matter, as a result of DSC measurement (glass transition temperature Tg, melting temperature Tm), and as measured by TG The results (weight loss starting temperature T ₁₀ ) are also shown in Table 1.

5.1.3. Synthesis example 3
In a temperature-controllable autoclave equipped with a stirrer, 200 parts by weight of water, 0.6 parts by weight of sodium dodecylbenzenesulfonate, 1.0 part by weight of potassium persulfate, 0.5 part by weight of sodium bisulfite, α-methylstyrene 0.5 parts by mass of dimer, 0.3 parts by mass of dodecyl mercaptan and the monomers shown in Table 1 were charged all at once, and the temperature was raised to 70 ° C. to conduct a polymerization reaction for 8 hours. Thereafter, the temperature was raised to 80 ° C., and the reaction was further performed for 3 hours to obtain a latex. The pH of this latex was adjusted to 7.5, and 5 parts by mass of sodium tripolyphosphate (added as an aqueous solution having a solid content conversion value and a concentration of 10% by mass) was added. Thereafter, the residual monomer was removed by steam distillation, and concentrated under reduced pressure to obtain an aqueous dispersion S3 containing 50% by mass of the binder (C3). As a result of average particle diameter (Dc) performed on the obtained binder (C3) in the same manner as in Synthesis Example 1, as a result of measuring toluene insolubles, as a result of DSC measurement (glass transition temperature Tg, melting temperature Tm), and as measured by TG The results (weight loss starting temperature T ₁₀ ) are also shown in Table 1.

5.2. Synthesis of water-insoluble polymer particles (A2) 5.2.1. Synthesis example 4
100 parts by mass of styrene, 10 parts by mass of t-dodecyl mercaptan, 0.8 parts by mass of sodium dodecylbenzenesulfonate, 0.4 parts by mass of potassium persulfate, and 200 parts by mass of water were placed in a 2 L flask and stirred. Then, the temperature was raised to 80 ° C. in a nitrogen gas atmosphere, and polymerization was carried out for 6 hours. As a result, an aqueous dispersion containing polymer particles having a polymerization yield of 98% and an average particle size of 170 nm and a standard deviation of the particle size of 0.02 μm was obtained. The polymer particles had a toluene dissolved content of 98%, and the molecular weight measured by gel permeation chromatography was weight average molecular weight (Mw) = 5,000 and average molecular weight (Mn) = 3,100.

After sufficiently substituting the inside of the reaction vessel with nitrogen, 5 parts by mass of polymer particles (in terms of solid content) and 1.0 part by mass of sodium lauryl sulfate were obtained. Then, 0.5 parts by mass of potassium persulfate, 400 parts by mass of water, 45 parts by mass of styrene, and 50 parts by mass of divinylbenzene were mixed and stirred at 30 ° C. for 10 minutes to allow the polymer particles to absorb the monomer. Then, it heated up at 70 degreeC and reacted for 3 hours. Thereafter, after cooling, the reaction was stopped, and the pH was adjusted to 7 with a 2.5N aqueous sodium hydroxide solution to obtain an aqueous dispersion L1 containing 20% of water-insoluble polymer particles (A2-1).

The particle size distribution is measured using a particle size distribution measuring apparatus (model “FPAR-1000”, manufactured by Otsuka Electronics Co., Ltd.) using the dynamic light scattering method as a measurement principle, and water-insoluble polymer particles (A2- When the average particle diameter (Da2) of 1) was determined, it was 380 nm.

100 g of the water dispersion L1 of the water-insoluble polymer particles (A2-1) was weighed and dried at 120 ° C. for 1 hour. The obtained solid was pulverized in an agate mortar to obtain a powder (water-insoluble polymer particles (A2-1)).

As a result of performing toluene insoluble content measurement, DSC measurement and TG measurement of the obtained powder (powder composed of water-insoluble polymer particles (A2-1)) in the same manner as in Synthesis Example 1, the toluene insoluble content was 99%, a glass transition temperature Tg and the melting temperature Tm can not be observed, weight loss initiation temperature _{T 10} was 379 ° C.. FIG. 4 is a TGA chart of the water-insoluble polymer particles (A2-1) obtained in Synthesis Example 4. According to FIG. 4, it can be read that the temperature (T ₁₀ ) at which the weight of the water-insoluble polymer particles (A2-1) obtained in Synthesis Example 4 is reduced by 10% by weight in an air atmosphere is 379 ° C. .

The obtained powder (powder composed of water-insoluble polymer particles (A2-1)) was observed with an electron microscope (Hitachi High-Technologies Corporation, Hitachi transmission electron microscope H-7650). No vacancies were observed.

5.2.2. Synthesis example 5
In Synthesis Example 4, an aqueous dispersion containing water-insoluble polymer particles (A2-2) having the composition shown in Table 2 was prepared except that the composition and the amount of emulsifier were appropriately changed. By removing or adding water under reduced pressure according to the partial concentration, an aqueous dispersion L2 having a solid concentration of 20% was obtained. The obtained water-insoluble polymer particles (A2-2) were subjected to the same average particle diameter (Da2) as in Synthesis Example 1, as a result of measuring toluene insolubles, as a result of volumetric porosity, and as a result of DSC measurement. Table 2 also shows (glass transition temperature Tg, melting temperature Tm) and the results of TG measurement (weight reduction start temperature T ₁₀ ).

The abbreviations or names of the components in Table 1 and Table 2 represent the following compounds, respectively.
<Compound having two or more polymerizable unsaturated groups>
EDMA: ethylene glycol dimethacrylate DVB: divinylbenzene <monomer having a fluorine atom>
・ VDF: Vinylidene fluoride ・ HFP: Propylene hexafluoride <Unsaturated carboxylic acid>
MAA: methacrylic acid TA: itaconic acid AA: acrylic acid <unsaturated carboxylic acid ester>
-MMA: methyl methacrylate-EHA: 2-ethylhexyl acrylate <aromatic vinyl compound>
ST: Styrene <conjugated diene compound>
-BD: 1,3-butadiene The notation "-" in Tables 1 and 2 indicates that the corresponding component was not used.

5.3. Example 1
5.3.1. Preparation of Composition for Protective Layer The aqueous dispersion S1 and the aqueous dispersion L1 are mixed so that the binder (C) is 5 parts by mass with respect to 95 parts by mass of the filler (A), and a water-soluble polymer ( B) (product name “CMC1120” manufactured by Daicel Corporation) 5 parts by mass and 275 parts by mass of water K. Mixing and dispersing treatment was performed using Fillmix (R) type 56-50 (manufactured by PRIMIX Co., Ltd.) to prepare a protective layer composition.

About the obtained composition for protective layers, toluene insoluble content measurement, DSC measurement (glass transition temperature Tg, melting temperature Tm) and TG measurement (weight loss start temperature) by the same method as “5.2.1. Synthesis Example 4” As a result of T ₁₀ ), the insoluble content of toluene was 99%, the transition temperature Tg was −4 ° C., the melting temperature Tm was not observed, and the weight loss starting temperature T ₁₀ was 360 ° C.

5.3.2. Production of positive electrode <Preparation of positive electrode active material>
Commercially available lithium iron phosphate (LiFePO ₄ ) was pulverized in an agate mortar and classified using a sieve to prepare active material particles having a particle diameter (D50 value) of 0.5 μm.

<Preparation of slurry for positive electrode>
A biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation), 4 parts by mass of polyvinylidene fluoride (PVDF) (in terms of solid content), 100 parts by mass of the above active material particles, and acetylene black 5 Part by mass and 68 parts by mass of N-methylpyrrolidone (NMP) were added and stirred at 60 rpm for 1 hour. Further, 32 parts by mass of NMP was added and stirred for 1 hour to obtain a paste. The resulting paste was stirred at 200 rpm for 2 minutes, 1,800 rpm for 5 minutes, and further under vacuum (5.0 ×) using a stirring defoaming machine (trade name “Awatori Nertaro” manufactured by Shinky Co., Ltd.). The slurry for positive electrode was prepared by stirring and mixing at 1,800 rpm for 1.5 minutes at 10 ³ Pa).

<Preparation of positive electrode>
The positive electrode slurry was uniformly applied to the surface of a current collector made of aluminum foil by a doctor blade method so that the film thickness after drying was 100 μm, and dried at 120 ° C. for 20 minutes. Then, the positive electrode with the positive electrode active material layer formed on the surface of the current collector was obtained by pressing with a roll press so that the density of the film (active material layer) was 2.0 g / cm ³ .

5.3.3. Production of negative electrode <Preparation of slurry for negative electrode>
A biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Co., Ltd.), 4 parts by mass of polyvinylidene fluoride (PVDF) (in terms of solid content) and 100 parts by mass of graphite as a negative electrode active material (solid) Minute conversion), 80 parts by mass of N-methylpyrrolidone (NMP) was added, and the mixture was stirred at 60 rpm for 1 hour. Then, after adding 20 parts by mass of NMP, using a stirring defoaming machine (product name “Awatori Netaro” manufactured by Shinky Co., Ltd.) for 2 minutes at 200 rpm, then for 5 minutes at 1,800 rpm, further vacuum Below, the slurry for negative electrodes was prepared by stirring and mixing for 1.5 minutes at 1,800 rpm.

<Production of negative electrode>
The negative electrode slurry was uniformly applied to the surface of a current collector made of copper foil by a doctor blade method so that the film thickness after drying was 150 μm, and dried at 120 ° C. for 20 minutes. Then, the negative electrode in which the negative electrode active material layer was formed on the surface of the current collector was obtained by pressing using a roll press machine so that the film density was 1.5 g / cm ³ .

5.3.4. Production of protective layer (production of separator provided with protective layer)
Protection obtained in the above “5.3.1. Preparation of composition for protective layer” on both sides of a separator made of a porous polypropylene film (manufactured by Celgard, trade name “Celguard # 2400”, film thickness 25 μm) After the layer composition was applied using the dip coating method, it was dried at 50 ° C. for 60 minutes to form protective layers on both sides of the separator. The thickness of the protective layer obtained was 2 μm on one side (total of 4 μm on both the front and back sides).

<Moisture content per unit volume>
In a dry room with a dew point of -60 ° C, put the sample for measurement of the separator in the heating furnace of the moisture vaporizer VA-230 (Mitsubishi Chemical Analytech), flow nitrogen gas at 150 ° C for 1 minute, and Karl Fischer moisture meter It was introduced into a measurement cell of CA200 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and the water content was measured. Calculate the moisture content per unit volume of the protective layer by calculating the moisture content from the integrated value up to the end of the titration and dividing this by the volume determined by the product of the area of the measurement sample and the thickness of the protective layer 4 μm. As a result, it was 0.6 mg / cm ³ . Further, the water content per unit volume of the separator was calculated by dividing this by the volume determined by the product of the area of the measurement sample and the film thickness of the separator of 29 μm, and was 0.1 mg / cm ³ . .

5.3.5. Assembly of lithium ion battery cell In a glove box substituted with Ar so that the dew point is −80 ° C. or lower, the negative electrode produced above was cut out to 50 mm × 25 mm on a film-like outer aluminum seal made of aluminum. A negative terminal was attached and placed. Next, the separator manufactured above was cut out to 54 mm × 27 mm and placed on the negative electrode. Finally, a positive electrode terminal was attached to the positive electrode produced as described above and cut out to 48 mm × 23 mm, and placed on the separator. And the exterior aluminum seal similar to the said exterior aluminum seal was mounted on this positive electrode. Thus, the laminated body which consists of an exterior aluminum seal, a negative electrode, a microporous film, a positive electrode, and an exterior aluminum seal was obtained. Thereafter, the outer peripheral aluminum seals on the three sides of this laminate were sealed by bonding the outer peripheral edges of the two outer aluminum seals with a heating sealing device. Then, 1M LiPF ₆ ethylene carbonate / diethyl carbonate (3/7 weight ratio) (manufactured by Kishida Chemical Co., Ltd.) was injected so that air did not enter between the layers, and after degassing under reduced pressure, The negative electrode terminal and the positive electrode terminal were exposed to the outside of the exterior aluminum seal, and the fourth side was sealed and sealed to produce a laminate type battery cell composed of a bipolar single layer laminate cell.

5.3.6. Evaluation of electricity storage device <Measurement of remaining capacity rate and resistance increase rate>
The battery cell produced above is placed in a constant temperature bath at 25 ° C., charging is started at a constant current (0.2 C), and charging is continued at a constant voltage (4.1 V) when the voltage reaches 4.1 V. The charging was completed (cut off) when the current value reached 0.01C. Next, discharging was started at a constant current (0.2 C), and the time when the voltage reached 2.5 V was regarded as discharging completion (cut-off) (aging charge / discharge).

The cell after the aging charge / discharge is put in a thermostat at 25 ° C., and charging is started at a constant current (0.2 C). When the voltage reaches 4.1 V, the cell is continuously maintained at a constant voltage (4.1 V). Charging was continued, and charging was completed (cut off) when the current value reached 0.01C. Next, discharge was started at a constant current (0.2 C), and when the voltage reached 2.5 V, the discharge was completed (cut off), and C1 which was the value of the discharge capacity (initial) at 0.2 C was measured. did.

The cell after the discharge capacity (initial) measurement was placed in a constant temperature bath at 25 ° C., charging was started at a constant current (0.2 C), and when the voltage reached 4.1 V, the constant voltage (4.1 V) was continued. The charging was continued at), and the time when the current value reached 0.01 C was defined as the completion of charging (cut-off).

The EIS measurement (“Electrochemical Impedance Spectroscopy”, “electrochemical impedance measurement”) was performed on the charged cell, and the initial resistance value EISA was measured.

Next, the cell in which the initial resistance value EISa was measured was placed in a constant temperature bath at 60 ° C., and charging was started at a constant current (0.2 C). When the voltage reached 4.4 V, the constant voltage (4 4V), charging was continued for 168 hours (overcharge acceleration test).

After that, the charged cell was placed in a constant temperature bath at 25 ° C., the cell temperature was lowered to 25 ° C., and then discharging was started at a constant current (0.2 C), and the voltage became 2.5V. Was completed (cutoff), and C2 as a value of the discharge capacity at 0.2 C (after the test) was measured.

The cell having the above discharge capacity (after the test) is placed in a constant temperature bath at 25 ° C., and charging is started at a constant current (0.2 C). When the voltage reaches 4.1 V, the constant voltage (4.1 V) continues. The charging was continued at, and the time when the current value reached 0.01 C was regarded as charging completion (cut-off). Next, discharging was started at a constant current (0.2 C), and the time when the voltage reached 2.5 V was regarded as completion of discharging (cut-off). EIS measurement of this cell was performed, and EISb which is a resistance value after application of thermal stress and overcharge stress was measured.

The remaining capacity rate obtained by substituting the above measured values into the following formula (6) is 93%, and the resistance increase rate obtained by substituting the above measured values into the following formula (7) is 150%. there were.
Residual capacity ratio (%) = (C2 / C1) × 100 (6)
Resistance increase rate (%) = (EISb / EISa) × 100 (7)
When this remaining capacity ratio is 75% or more and the resistance increase rate is 300% or less, it can be evaluated that the durability is good.

In the above measurement conditions, “1C” indicates a current value at which discharge is completed in 1 hour after constant-current discharge of a cell having a certain electric capacity. For example, “0.1 C” is a current value at which discharge is completed over 10 hours, and “10 C” is a current value at which discharge is completed over 0.1 hours.

<Battery swelling>
The above laminated battery was charged with 0.2 C, 4.2 V constant voltage / constant current charging for 8 hours. When it was put in an oven with a load of 1.8 kg / cm ² applied and stored at 85 ° C. for 3 days and observed for appearance, there was no swelling of the battery. The case where the battery was clearly swollen was judged as x, and the case where the battery swollen was not apparent from the appearance was judged as good, and was marked in the table. Note that the swelling of the battery in this case is considered to be due to the generation of gas in the battery.

<Adhesiveness between protective layer and electrode>
From the negative electrode produced above, the separator with protective layer, and the positive electrode, test pieces each having a width of 2 cm and a length of 5 cm were cut out so that the negative electrode active material layer and the positive electrode active material layer were respectively opposed to the separator with the protective layer. / Separator with protective layer / Positive electrode was laminated. The obtained laminate was impregnated with a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio) and sandwiched between polyester films (Toray Industries, Lumirror S10, 250 μm thickness), 80 ° C. × 5 minutes, 0 Heated and pressurized at 1 MPa. Then, before the solvent dried, the negative electrode and the positive electrode were peeled off from the separator with the protective layer, and evaluated as follows.
A: When both the negative electrode and the positive electrode are peeled off, there is resistance, and a part or all of the active material layer is adhered and transferred to the protective layer. ○: When both the negative electrode and the positive electrode are peeled off, there is resistance, but the active material layer X is not transferred to the protective layer x: When there is no resistance when either the negative electrode or the positive electrode is peeled off, it has already been peeled off

5.4. Examples 2 to 10, Comparative Examples 1 to 8
A protective layer composition described in Tables 3 to 4 was prepared in the same manner as in Example 1 except that the aqueous dispersions shown in Tables 3 to 4 were blended in the usage ratios shown in Tables 3 to 4. . About the obtained composition for protective layers, as a result of the toluene insoluble content measurement obtained by the same method as “5.2.1. Synthesis Example 4”, the results of DSC measurement (glass transition temperature Tg, melting temperature Tm) The results of TG measurement (starting weight reduction temperature T ₁₀ ) are also shown in Tables 3 to 4. Further, an electricity storage device was produced and evaluated in the same manner as in Example 1 using the obtained protective layer composition. The evaluation results are also shown in Tables 3 to 4.

The abbreviations and names of the components in Table 3 and Table 4 represent the following compounds, respectively.
<Inorganic particles>
-Titania: Product name “KR380” (manufactured by Titanium Industry Co., Ltd., rutile type, average particle size 0.38 μm)
Alumina: Product name “AKP-3000” (manufactured by Sumitomo Chemical Co., Ltd., average particle size 0.74 μm)
<Water-soluble polymer (B)>
CMC: trade name “CMC1120” (manufactured by Daicel Corporation, sodium carboxymethylcellulose)
-PVA: trade name "GH-20" (Nippon Synthetic Chemical Co., Ltd., polyvinyl alcohol)
PAA: trade name “A-10H” (manufactured by Toa Gosei Co., Ltd., polyacrylic acid, weight average molecular weight 200,000)

5.5. Evaluation results As is apparent from Tables 3 to 4 above, in the electricity storage device (lithium ion battery) including the separator having the protective layer according to the present invention shown in Examples 1 to 10, no battery swelling was observed. It was confirmed that the residual capacity after the durability test and the resistance increase were excellent, and the adhesion between the protective layer and the electrode was good.

On the other hand, according to the electrical storage device (lithium ion battery) including the separator having the protective layer (the protective layer that is not the present invention) shown in Comparative Examples 1, 2, 4, 7, and 8, the charge / discharge characteristics are poor. Further, battery swelling was observed. Further, Comparative Example 6 is an example in which the moisture content is reduced by heat-treating a separator not provided with a protective layer. In this case, the water content could be reduced to 0 mg / cm ³ (below the measurement limit), but the film contracted, and it was impossible to create an electricity storage device using the contracted film. . Further, with respect to Comparative Example 5 and Comparative Example 3, it was possible to reduce the moisture content by heating the separator at 180 ° C. until each ^{0.2mg / cm 3, 2mg / cm} 3. However, although the structure of the electrical storage device was created using the film after the heat treatment and the charge / discharge evaluation was performed, it was found that the film could not be charged / discharged at all and the film after the heating could not function as a separator.

The present invention is not limited to the above embodiment, and various modifications can be made. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). The present invention also includes a configuration in which a non-essential part of the configuration described in the above embodiment is replaced with another configuration. Furthermore, the present invention includes a configuration that achieves the same effects as the configuration described in the above embodiment or a configuration that can achieve the same object. Furthermore, the present invention includes a configuration obtained by adding a known technique to the configuration described in the above embodiment.

1, 2, 3 ...

Electric storage device

10, 110, 210 ... Positive electrode, 12, 112, 212 ... Positive electrode current collector, 14, 114, 214 ... Positive electrode active material layer, 20, 120, 220 ... Negative electrode, 22, 122 222, negative electrode current collector, 24, 124, 224 ... negative electrode active material layer, 30, 130, 230 ... protective layer, 40, 140, 240 ... electrolyte, 150, 250 ... separator

Claims

A filler (A);
A water-soluble polymer (B);
Containing
Water content is less than 0.1 mg / cm 3 or more 35 mg / cm 3, a protective layer disposed between the positive electrode and the negative electrode of the power storage device.
The protective layer according to claim 1, further comprising a binder (C).
The protective layer according to claim 2, comprising 5 parts by mass or more and 15 parts by mass or less of the water-soluble polymer (B) with respect to a total of 100 parts by mass of the filler (A) and the binder (C).
The filler (A) contains water-insoluble polymer particles (A2),
The content ratio of the repeating unit derived from the compound having two or more polymerizable unsaturated groups in 100 parts by mass of the water-insoluble polymer particles (A2) is 20 parts by mass or more and 100 parts by mass or less. The protective layer according to claim 3.
The protective layer according to any one of claims 1 to 3, wherein the filler (A) contains inorganic particles (A1) and water-insoluble polymer particles (A2).
The ratio of the content (MA1) of the inorganic particles (A1) to the content (MA2) of the water-insoluble polymer particles (A2) is MA1 / MA2 = 0.1 to 10 on a mass basis. The protective layer according to claim 5.
The protective layer according to claim 5 or 6, comprising 1 part by mass or more and 15 parts by mass or less of the water-soluble polymer (B) in 100 parts by mass of the protective layer.
The content ratio of the repeating unit derived from the compound having two or more polymerizable unsaturated groups in 100 parts by mass of the water-insoluble polymer particles (A2) is 20 parts by mass or more and 100 parts by mass or less. The protective layer according to claim 7.
A filler (A);
A water-soluble polymer (B);
Containing
A separator having a water content of 0.1 mg / cm 3 or more and 5 mg / cm 3 or less.
Furthermore, the separator of Claim 9 containing a binder (C).
The separator according to claim 9 or 10, wherein the filler (A) contains inorganic particles (A1) and water-insoluble polymer particles (A2).
The separator according to any one of claims 9 to 11, wherein at least a part of the surface is coated with the protective layer according to any one of claims 1 to 8.
An electricity storage device comprising: a positive electrode; a negative electrode; the protective layer according to any one of claims 1 to 8 disposed between the positive electrode and the negative electrode; and an electrolytic solution.
An electricity storage device comprising: a positive electrode; a negative electrode; the separator according to any one of claims 9 to 12 disposed between the positive electrode and the negative electrode; and an electrolytic solution.
Inorganic particles (A1) containing a filler (A), a water-soluble polymer (B), a binder (C), and a liquid medium, wherein the filler (A) has an average particle diameter (Da1) and It contains at least one selected from the group consisting of water-insoluble polymer particles (A2) having an average particle size (Da2), and the average particle size (Da1) and the average particle size (Dc) of the binder (C) A composition in which at least one of the ratio (Da1 / Dc) and the ratio (Da2 / Dc) of the average particle diameter (Da2) to the average particle diameter (Dc) of the binder (C) is 1 to 30 A process to prepare;
After applying the composition, heating at 30 to 120 ° C .;
A method for forming a protective layer, comprising:
The ratio (Da1 / Da2) between the average particle diameter (Da1) of the inorganic particles (A1) and the average particle diameter (Da2) of the water-insoluble polymer particles (A2) is 0.5 to 10. 15. The method for forming a protective layer according to 15.