JP2015153638A - Method for forming protective layer and power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a protective film in which deterioration with charge/discharge suppresses non-uniform deterioration in a protective layer plane and excellent charge/discharge characteristics equipped with the protective layer are expressed, and also to provide a power storage device equipped with the protective layer created by the film forming method.SOLUTION: Disclosed is a film forming method which includes a binder particle (A1), a filler particle (A2) and liquid medium, and is further heated to 30 to 100°C after spraying a composition for protective layer formation which ranges 1 to 30 in the ratio (Da2/Da1) between the average particle diameter (Da1) of the binder particle (A1) and the average particle diameter (Da2) of the filler particle (A2) on a base material.

Description

  The present invention relates to a method for forming a protective layer that can be used in an electricity storage device and an electricity storage device including the protective layer.

  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.

  The electricity storage device having such a high voltage and high energy density is required to be further downsized. In order to achieve miniaturization of an electricity storage device, it is essential not only to reduce the thickness of power generation elements such as a positive electrode and a negative electrode, but also to reduce the thickness of a separator or the like 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 particular, in an electricity storage device using metal ions such as lithium ions, dendrites due to metal ions are likely to occur on the electrode surface by repeated charge and discharge. Such dendrites usually precipitate as needle-like crystals, so that they tend to grow through the separator, which is a porous film. When the dendrite grows through the separator and reaches the surface of the counter electrode, the electricity storage device is short-circuited and loses the charge / discharge function. As the separator becomes thinner and the distance between the positive electrode and the negative electrode becomes narrower, the risk of occurrence of such a phenomenon increases, and the reliability decreases accordingly.

  In order to avoid such a phenomenon, for example, in Patent Document 1 and Patent Document 2, battery characteristics are improved by forming a porous layer including a resin binder containing polyamide, polyimide, and polyamideimide on a porous separator substrate. Improvement techniques are being studied. On the other hand, Patent Document 3 discusses a technique for improving battery characteristics by forming a porous protective layer containing a binder containing a fluorine-based resin and a rubber-based resin on at least one surface of a positive electrode and a negative electrode. ing. In Patent Document 4, a battery is formed by forming a porous layer containing a copolymer containing a (meth) acrylonitrile monomer unit and a (meth) acrylate monomer unit on a porous separator substrate. Techniques for improving the characteristics are being studied.

International Publication No. 2009/041395 JP 2009-87562 A JP 2009-54455 A International Publication No. 2010/074202

  However, according to the conventional film forming method using a material as described in the above-mentioned patent document, a short circuit caused by dendrite generated by charging / discharging by forming a protective layer on the separator or electrode surface. However, it is difficult to form a uniform protective film over a wide film forming area. For this reason, there has been a problem that the deterioration of the protective layer accompanying charge / discharge proceeds non-uniformly in the surface of the protective layer, and the charge / discharge characteristics deteriorate.

  Therefore, the method for forming a protective layer according to the present invention solves the above-described problem, and forms a protective layer in which deterioration due to charging / discharging suppresses non-uniform deterioration in the surface of the protective layer. It is an object of the present invention to provide an electricity storage device having a layer and exhibiting good charge / discharge characteristics.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

[Application Example 1]
One aspect of a film forming method for producing a protective layer disposed between the positive electrode and the negative electrode of the electricity storage device according to the present invention is as follows.
Containing binder particles (A1), filler particles (A2), and a liquid medium,
A protective layer forming composition in which the ratio (Da2 / Da1) of the average particle size (Da1) of the binder particles (A1) to the average particle size (Da2) of the filler particles (A2) is 1 to 30 After being sprayed on, a method of forming a protective layer disposed between the positive electrode and the negative electrode of the electricity storage device by further heating to 30 to 100 ° C. is characterized.

[Application Example 2]
In the film forming method of Application Example 1,
The binder particles (A1) may have an average particle diameter (Da1) of 20 nm to 450 nm.

[Application Example 3]
In the film forming method of Application Example 1 or Application Example 2,
The binder particles (A1) can be contained in an amount of 0.1 parts by weight to 15 parts by weight with respect to 100 parts by weight of the filler particles (A2).

[Application Example 4]
In the film forming method of any one of Application Examples 1 to 3,
The binder particles (A1) may be particles in which at least one endothermic peak is observed in a temperature range of −50 to + 80 ° C. when differential scanning calorimetry (DSC) is performed in accordance with JIS K7121. it can.

[Application Example 5]
In the film forming method of any one of Application Examples 1 to 4,
The binder particles (A1) may be solid particles, and the filler particles (A2) may be particles having pores.

[Application Example 6]
One aspect of the protective layer according to the present invention is:
It is produced using the protective layer forming method of any one of Application Examples 1 to 5.

[Application Example 7]
One aspect of the separator according to the present invention is:
It is covered with the protective layer described in Application Example 6.

[Application Example 8]
One aspect of the electricity storage device according to the present invention is:
It has a positive electrode, a negative electrode, the protective layer of the application example 6 arrange | positioned between the said positive electrode and the said negative electrode, and electrolyte solution, It is characterized by the above-mentioned.

[Application Example 9]
In the electricity storage device of Application Example 8,
The protective layer may be in contact with at least one surface of the positive electrode and the negative electrode.

[Application Example 10]
In the electricity storage device of Application Example 8 or Application Example 9,
A separator disposed between the positive electrode and the negative electrode can be further provided.

  According to the method for forming a protective layer in which a protective layer usable for the electricity storage device according to the present invention is formed on a substrate, a uniform protective layer can be formed over a wide film-forming area. Furthermore, since the protective film is homogeneous, local deterioration of the protective film can be suppressed even if charging / discharging is repeated, and thus the electricity storage device according to the present invention can exhibit good charge / discharge characteristics.

  Furthermore, according to the method for forming a protective layer of the present invention, the film forming time and drying time can be shortened, and the amount of waste liquid at the time of coating can be suppressed.

FIG. 1 is a schematic diagram illustrating a cross section of the electricity storage device according to the first embodiment. FIG. 2 is a schematic diagram illustrating a cross section of the electricity storage device according to the second embodiment. FIG. 3 is a schematic diagram illustrating a cross section of the electricity storage device according to the third embodiment. FIG. 4 is a DSC chart of the binder particles (A1) obtained in Synthesis Example 3. FIG. 5 is a TGA chart of the filler particles (A2) obtained in Synthesis Example 15.

  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. Method for Forming Protective Layer The method for forming a protective layer of the present invention is a method for forming a porous protective layer on the substrate by spraying the composition for forming a protective layer onto the substrate.

  As a method for spraying the protective layer-forming composition onto the substrate, a known method can be applied. Examples thereof include a spray method, an inkjet printing method, an aerosol deposition method (AD method), an electrostatic fine particle coating method in which mixed particles are accelerated by electrostatic force, and a cold spray method. Among these methods, since it is easy to adjust the film thickness of the protective layer to be formed, a spray method or an ink jet printing method can be preferably used. There are various nozzle shapes depending on the discharge amount and the spray pattern, and the optimum nozzle shape can be used in a timely manner.

  In the spray method, pressurized gas may be used to spray the protective layer forming composition. In the case of using the spray method, since the protective layer forming composition is sprayed using a spray coater, the droplets of the protective layer forming composition can be made small. For this reason, it becomes possible to infiltrate the composition for protective layer formation to the deeper part of an electrode or a separator. When using the inkjet printing method, by using an inkjet printer, the droplets of the pregel can be made small as in the case of using the spray coater, and the protective layer forming composition is soaked deep into the electrodes and the separator. be able to.

  When a pressurized gas is used for spraying the protective layer forming composition in the spray method, optimum conditions can be used as appropriate depending on the purpose as the spray conditions. For example, pressure (hydraulic pressure) can be used with a spray gun. ) 5-16 MPa, removing or adding the liquid medium to adjust the viscosity of the protective layer forming composition to 0.5-10 mPs · s, and spraying the protective layer forming composition onto the base material to carry out the coating operation. Preferably it is done.

  In the spray method and the inkjet printing method, it is easy to adjust the thickness of the coating layer by changing the coating amount per unit area, so that the protective layer obtained by removing the liquid medium in the subsequent drying step The film thickness can be easily controlled.

  The composition for forming a protective layer according to the production method of the present embodiment includes binder particles (A1) (hereinafter also referred to as “(A1) component”) and filler particles (A2) (hereinafter also referred to as “(A2) component”). ) And a liquid medium, and the ratio (Da2 / Da1) of the average particle size (Da1) of the binder particles (A1) to the average particle size (Da2) of the filler particles (A2) is 1-30. Yes, preferably 1.5-20.

  In general, when a coating film is produced by spraying a dispersion containing powder by a method such as a spray method or an inkjet method, when the dispersibility of the powder in the dispersion is deteriorated or the particle size of the powder is large Are likely to clog and agglomerate particles at the nozzle orifice and strainer. In order to solve this problem, for example, Japanese Patent Publication No. 63-2996 discloses the addition of hygroscopic aliphatic polyhydric alcohols, aliphatic polyhydric alcohols, and acetate derivatives to the coating solution. . JP-A-2003-73229 discloses a spray composition to which an antibacterial agent and a humectant are added. However, when creating a protective layer for use in an electricity storage device as in the present application, these additives are unnecessary in the protective film if additives that improve these spraying properties are added only to improve the coatability. Therefore, the charge / discharge characteristics of the electricity storage device produced using the produced protective layer are deteriorated.

  However, the ratio (Da2 / Da1) between the average particle size (Da1) of the binder particles (A1) and the average particle size (Da2) of the filler particles (A2) contained in the protective layer forming composition is in the above range. In this case, it is possible to suppress the occurrence of the above-mentioned problems, and it is not necessary to add a component unnecessary for the charge / discharge characteristics of the electricity storage device. A protective layer can be created.

  Furthermore, by creating a uniform protective layer over a large area, it is possible to greatly suppress the deterioration of the charge / discharge characteristics due to local deterioration of the protective layer due to charge / discharge due to uneven thickness of the protective layer. Can do. If the ratio (Da2 / Da1) is not within the above range, aggregation is likely to occur at the nozzle orifice or strainer used when the coating film is produced by spraying the protective layer forming composition, and the foreign matter is buried in the coating layer. By doing so, the protective layer becomes inhomogeneous, and as a result, the heterogeneous protective layer deteriorates due to charge / discharge, which is not preferable.

  Moreover, since it contains the average particle diameter (Da1) of the binder particles (A1) and the filler particles (A2) contained in the protective layer-forming composition, these two types of particles have a flying distance when sprayed. It is easy to make a difference. As a result, there is a risk that two types of particles are easily unevenly distributed in the film thickness direction of the coating film.

  However, the ratio (Da2 / Da1) between the average particle size (Da1) of the binder particles (A1) and the average particle size (Da2) of the filler particles (A2) contained in the protective layer forming composition is in the above range. If it exists, generation | occurrence | production of the above problems can be suppressed and a favorable protective layer can be produced also in a favorable electrical property and a film thickness direction.

  In the production method of the present embodiment, the protective layer-forming composition described above is sprayed onto a substrate to prepare a coating layer for the protective film composition, and the prepared coating layer is heated to 30 to 100 ° C. create.

  After finishing forming the coating layer of the target thickness by spraying the protective layer-forming composition on the substrate as described above, the prepared coating layer is 30 to 100 ° C., preferably 40 to 80 ° C., more preferably Is heated to 45-70 ° C. to remove the liquid medium and create a protective layer. The atmosphere during heating can be selected in a timely manner depending on the material of the base material, the characteristics of the components (A1) and (A2), etc. If the atmosphere does not change even in an oxidizing atmosphere, it may be in the air, and easily changes in an oxidizing atmosphere. When it is a component, the liquid medium may be removed in an inert atmosphere such as nitrogen or a vacuum atmosphere of about 0.01 to 0.1 Torr.

  The heating method is not particularly limited. For example, drying by warm air, hot air, low-humidity air, vacuum drying, drying by irradiation with (far) infrared rays, electron beams or the like can be mentioned. The productivity is improved by adjusting the drying speed so that the liquid medium can be removed as quickly as possible within a range where the active material layer does not crack due to stress concentration or the protective layer does not peel from the substrate. Is preferred for.

  Since the protective layer-forming composition contains a liquid medium, the component (A1) and / or the component (A2) is the surface in the step of applying the protective layer-forming composition to the surface of the substrate and drying it. By being subjected to the action of tension, it moves along the thickness direction of the coating layer by drying (hereinafter, this phenomenon is also referred to as “migration”). Specifically, the component (A1) and / or the component (A2) tend to move to the side opposite to the surface in contact with the substrate of the coating layer, that is, the gas-solid interface side where the liquid medium evaporates.

  As a result, the distribution of the components (A1) and (A2) is not uniform in the thickness direction of the protective layer after drying, so that the properties of the protective layer are deteriorated and the adhesion between the substrate and the protective layer is impaired. Problems occur. For example, when the component (A1) acting as a binder bleeds (transfers) to the gas-solid interface side of the protective layer, and the amount of the component (A1) at the interface between the substrate and the protective layer becomes relatively small. The electrical characteristics deteriorate due to the inhibition of the electrolyte solution permeating into the protective layer, and the binding property between the base material and the protective layer tends to be lowered and peeling tends to occur. Furthermore, the smoothness of the surface of the protective layer tends to be impaired by bleeding of the component (A1).

  However, when the ratio (Da2 / Da1) is within the above range and the drying temperature is within the above range, the occurrence of the above-described problems can be suppressed, and good electrical characteristics and adhesion to the substrate can be achieved. It is possible to produce a protective layer that balances the above. In addition, when the ratio (Da2 / Da1) is less than the above range, the difference in average particle diameter between the component (A1) and the component (A2) is small, so that the area where the component (A1) and the component (A2) are in contact with each other It tends to be smaller and the component (A2) cannot be sufficiently retained. On the other hand, when the ratio (Da2 / Da1) exceeds the above range, the difference in average particle diameter between the component (A1) and the component (A2) becomes large, and the adhesive strength of the component (A1) becomes insufficient. There is a tendency that the binding property between the protective layer and the protective layer decreases.

1.1. The composition for producing a protective layer The 1st aspect of the composition for protective layer formation which concerns on this Embodiment contains binder particle | grains (A1), filler particle | grains (A2), and a liquid medium.

  Hereinafter, each component contained in the composition for protective layer formation of this invention is demonstrated 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.

1.1.1. Binder particles (A1)
The composition for forming a protective layer according to the present embodiment contains the binder particles (A1).

  The binder particles (A1) preferably have a repeating unit content of less than 15 parts by mass derived from a compound having two or more polymerizable unsaturated groups in 100 parts by mass of the binder particles (A1). More preferably, it is more preferably 0 part by mass, that is, substantially no content. When the repeating unit derived from the compound having two or more polymerizable unsaturated groups is in the above range, the flexibility of the binder particles (A1) becomes higher, and the adhesion between the polymer particles and the separator and the electrode Since adhesiveness becomes favorable, it is preferable.

  It is preferable that the binder particles (A1) function as a binder for closely adhering filler particles (A2), which will be described later, and further function as a binder for closely adhering the separator, electrode, and protective layer members. When the binder particles (A1) function as such a binder, they are preferably solid particles having no pores inside the particles. By being solid particles, better binder properties can be expressed.

  Hereinafter, the aspect which comprises the monomer which comprises the repeating unit contained in binder particle | grains (A1) and binder particle | grains (A1) is explained in full detail.

1.1.2.1. Compound having two or more polymerizable unsaturated groups The compound having two or more polymerizable unsaturated groups is not particularly limited, and examples thereof include polyfunctional (meth) acrylic acid esters and aromatic polyfunctional vinyl compounds. .

  Examples of the polyfunctional (meth) acrylic acid ester include compounds represented by the following general formula (2), (poly) (meth) acrylic acid esters of polyhydric alcohols, and other polyfunctional monomers.

(In the general formula (2), 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. It is an organic group having 1 to 18 carbon atoms.)
Preferable specific examples of R ^{2 in} the general formula (2) include, for example, vinyl group, isopropenyl group, allyl group, (meth) acryloyl group, epoxy group, glycidyl group, hydroxyalkyl group and the like.

  In the present invention, “polyfunctional (meth) acrylic acid ester” means (meth) acrylic acid ester having two or more (meth) acryloyl groups, one (meth) acryloyl group, and further polymerizable. (Meth) acrylic acid ester having at least one functional group selected from the group consisting of a carbon-carbon unsaturated bond, an epoxy group, and a hydroxyl group.

  Polyfunctional (meth) acrylic acid esters include ethylene glycol (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetra (meta) ) Pentaerythritol acrylate, dipentaerythritol hexa (meth) acrylate, glycidyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, allyl (meth) acrylate, di (meth) An ethylene glycol acrylate, propylene glycol di (meth) acrylate, etc. can be mentioned, It can be 1 or more types 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. Particularly 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 general formula (3), 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 (3) 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 (3) include a methyl group and an ethyl group.

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

1.1.2.2. Monomer having a fluorine atom The binder particle (A1) 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. As the (meth) acrylic acid ester having a fluorine atom, for example, a compound represented by the following general formula (4), (meth) acrylic acid 3 [4 [1-trifluoromethyl-2,2-bis [bis (tri Fluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl and the like.

(In the general formula (4), 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 (4) include a fluorinated alkyl group having 1 to 12 carbon atoms, a fluorinated aryl group having 6 to 16 carbon atoms, and a fluorinated aralkyl group having 7 to 18 carbon atoms. Among these, a fluorinated alkyl group having 1 to 12 carbon atoms is preferable. Preferred examples of R6 in the general formula (4) 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-hexa Fluorobutyl group, 1H, 1H, 5H-octafluoropentyl group, 1H, 1H, 9H-perfluoro-1-nonyl group, 1H, 1H, 11H-perfluoroundecyl group, perfluorooctyl group, etc. it can. 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 ratio of the repeating unit derived from the monomer having a fluorine atom in 100 parts by mass of the binder particles (A1) is preferably 5 to 50 parts by mass, and more preferably 15 to 40 parts by mass. It is especially preferable that it is -30 mass parts.

1.1.2.3. Unsaturated carboxylic acid It is preferable that the binder particles (A1) contain a repeating unit derived from an unsaturated carboxylic acid in addition to the repeating unit derived from the monomer having a fluorine atom. 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 ratio of the repeating unit derived from the unsaturated carboxylic acid in 100 parts by mass of the binder particles (A1) is preferably 1 to 10 parts by mass, and more preferably 2.5 to 7.5 parts by mass.

1.1.2.4. Conjugated Diene Compound The binder particles (A1) 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 ratio of the repeating unit derived from the conjugated diene compound in 100 parts by mass of the binder particles (A1) 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 within the above range, it is preferable because appropriate flexibility can be imparted and the binding property between the polymer particles becomes good.

1.1.2.5. Other unsaturated monomer In addition to the above-mentioned repeating unit, the binder particle (A1) may further contain a repeating unit derived from another unsaturated monomer copolymerizable therewith.

  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.

  As the unsaturated carboxylic acid ester, a (meth) acrylic acid ester can be preferably used, and 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. Among these, it is preferable that it is an alkyl ester of (meth) acrylic acid, and is 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.

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

  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.

  Examples of the other 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. An aminoalkylamide etc. can be mentioned and 1 or more types selected from these can be used.

1.1.2.6. Average particle diameter (Da1) of binder particles (A1)
The average particle diameter (Da1) of the binder particles (A1) 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 (Da1) of the binder particles (A1) is within the above range, the stability of the 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 (Da1) is less than the above range, the surface area of the binder particles (A1) becomes excessive and the solubility in the electrolytic solution increases, so that the particles (A1) binder particles ( A1) elutes into the electrolyte and contributes to an increase in internal resistance. On the other hand, if the average particle diameter (Da1) 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 size (Da1) of the binder particles (A1) is the cumulative number of particles when the particle size distribution is measured using a particle size distribution measuring apparatus based on the light scattering method and the particles are accumulated from small particles. This is the value of the particle diameter (D50) at which the frequency is 50%. Examples of such a particle size distribution measuring apparatus include Coulter LS230, LS100, LS13320 (above, manufactured by Beckman Coulter. Inc), FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.), and the like. These particle size distribution measuring devices are not intended to evaluate only the primary particles of the binder particles (A1), but can also evaluate the secondary particles formed by aggregation of the primary particles. Therefore, the particle size distribution measured by these particle size distribution measuring devices can be used as an indicator of the dispersion state of the binder particles (A1) contained in the composition.

1.1.2.7. Toluene-insoluble content The toluene-insoluble content of the binder particles (A1) 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 for the polymer particles (A) described above.

1.1.2.8. The temperature at which weight loss of 10 wt% in an air atmosphere _{(T 10)}
The temperature (T ₁₀ ) at which the weight of the binder particles (A1) 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 particles (A1) 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. Therefore, if the temperature (T ₁₀ ) at which the weight of the binder particles (A1) is reduced by 10% by weight in the air atmosphere is within the above temperature range, the stability against oxidation at high temperature and high voltage inside the battery is improved. As a result, the decomposition rate of the polymer particles is less likely to occur, so that the remaining capacity ratio is improved.

The temperature (T ₁₀ ) at which the weight of the binder particles (A1) is reduced by 10% by weight in an air atmosphere can be measured as follows. 10 g of an aqueous dispersion containing polymer particles (A1) 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. 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 polymer particles (A) 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 ).

1.1.2.9. Particle (A1) Aspect of Binder Particle (A1) As a specific aspect of the binder particle (A1), when a monomer having a fluorine atom is used, (1) a repeating unit derived from the monomer having a fluorine atom Copolymer particles obtained by synthesizing binder particles (A1) having a single-stage polymerization, (2) Polymer X having a repeating unit derived from a monomer having a fluorine atom and unsaturated carboxylic acid Two modes of composite particles having a polymer Y having a repeating unit are mentioned. Among these, from the viewpoint of excellent oxidation resistance, composite particles are preferable, and the composite particles are more preferably polymer alloy particles.

  “Polymer alloy” is a “generic name for multi-component polymers obtained by mixing or chemical bonding of two or more components” according to the definition in “Iwanami Physical and Chemical 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, An entangled IPN (Interpenetrating Polymer Network, etc.) ”. However, the polymer alloy as a polymer contained in the composition for forming a protective layer of the present invention is a polymer made of IPN among “a polymer alloy in which different types of polymer components are not bonded by a covalent bond”.

  By using polymer alloy particles containing polymer X and polymer Y, it is possible to simultaneously exhibit electrolyte permeability, liquid retention and oxidation resistance, adhesion and flexibility, and a rate of increase in resistance. Can be manufactured. In addition, when a polymer alloy particle consists only of the polymer X and the polymer Y, since oxidation resistance can be improved more, it is preferable.

  Such polymer alloy particles preferably have only one endothermic peak in the temperature range of −50 to 250 ° C. when measured by differential scanning calorimetry (DSC) in accordance with 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 particle 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 particles generally has an endothermic peak (glass transition temperature) different from that of the polymer X. For this reason, when the polymer X and the polymer Y exist in the binder particles (A1) in phase separation as in, for example, a core-shell structure, two endothermic peaks are observed in the temperature range of −50 to 250 ° C. Should be done. From this, when there is only one endothermic peak in the temperature range of −50 to 250 ° C., it can be estimated that the binder particles (A1) are polymer alloy particles.

  Furthermore, when the temperature of only one endothermic peak of the binder particles (A1) which are polymer alloy particles is in the range of −30 to + 80 ° C., the binder particles (A1) have good flexibility and adhesiveness. This is preferable because it can be imparted and, therefore, the adhesion can be further improved.

  The polymer X may further include 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.

  The more preferable aspect of the polymer X is 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; the repetition derived from ethylene tetrafluoride. The content of the unit is preferably 50 parts by mass or less, more preferably 1 to 30 parts by mass, particularly preferably 2 to 20 parts by mass; and the content of the repeating unit derived from propylene hexafluoride. 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 unsaturated carboxylic acid ester, the α, β-unsaturated nitrile compound and other monomers exemplified above can be used.

  The content ratio 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 particles have the above-described configuration, the synthesis method is not particularly limited. For example, the polymer alloy particles can be easily synthesized by 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 particles can be easily produced by the synthesis method. When polymer alloy particles are 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 the absorption time is too short, only a core-shell type polymer or a part of the surface layer becomes a polymer having an IPN type structure, and the polymer alloy particles in the present invention cannot be obtained. There are many. 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 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. Conditions under which 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) are appropriate.

  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 particles 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 particles contain the polymer X in the above range, the balance between the permeability, liquid retention and oxidation resistance of the electrolytic solution, and adhesion is improved. Further, 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 particles contain the polymer X in the above range, so that the polymer alloy It becomes possible to set the content ratio of each repeating unit in the whole particle within the above-mentioned preferable range, and this makes the ethylene carbonate (EC) / diethyl carbonate (DEC) insoluble content an appropriate value. The rate of increase in resistance is sufficiently low.

1.1.2.10. Production method of binder particle (A1) When the binder particle (A1) has a repeating unit derived from a monomer having a fluorine atom, its production, that is, having a repeating unit derived from a monomer having a fluorine atom. When the polymer is synthesized by 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 (surfactant) Agent) and the like.

  Further, when the binder particles (A1) have a repeating unit derived from a conjugated diene compound, they may be prepared by one-stage polymerization, two-stage polymerization, or multistage polymerization. It can be carried out in the presence of a polymerization initiator, 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 and organic peroxide. . These polymerization initiators can be used singly or in combination of two or more.

  When the binder particle (A1) has a repeating unit derived from a monomer having a fluorine atom, the total amount of monomers used (the binder particle (A1) is synthesized by one-step polymerization). The total amount of monomers used, the total number of monomers leading to the polymer X in the production of the polymer X, the polymer Y in the case of polymerizing the polymer Y in the presence of the polymer X, (The same applies hereinafter.) It is preferable that the amount is 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; 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 an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, and a fluorosurfactant.

  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; surface activity of amino acid types such as lauryl-β-alanine, lauryl di (aminoethyl) glycine, octyldi (aminoethyl) glycine, and the like. 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 fluoroalkylethylene 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-382, 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.); Footents 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 and more preferably 0.02 to 5 parts by mass with respect to 100 parts by mass in total of the monomers used.

  The emulsion polymerization is preferably carried out 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.

1.1.3. Filler particles (A2)
The protective layer forming composition according to the present embodiment contains the filler particles (A2).

  The filler particles (A2) are preferably inorganic particles or polymer particles.

1.1.3.1. Inorganic particles When the filler particles (A2) are inorganic particles, the toughness of the protective layer to be formed can be improved.

  As the inorganic particles, titanium oxide (titania), aluminum oxide (alumina), zirconium oxide (zirconia), magnesium oxide (magnesia), silica, or 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 (Db) of the inorganic particles is preferably 1 μm or less, and more preferably in the range of 0.1 to 0.8 μm. When the average particle diameter (Db) of the inorganic particles is in the above range, a smooth and flexible protective layer can be formed, and when an electricity storage device is produced, it comes into contact with a separator or an electrode disposed adjacent to the protective layer. However, 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 membrane, it is preferable that the average particle diameter (Db) of an inorganic particle is larger than the average pore diameter of this separator. Thereby, the damage to a separator can be reduced and it can prevent that an inorganic particle is clogged with the microporous of a separator.

  Here, the average particle diameter (Db) of the inorganic particles is the cumulative frequency of the number of particles when the particle size distribution is measured using a particle size distribution measuring apparatus based on the laser diffraction method and the particles are accumulated from small particles. Is the value of the particle diameter (D50) at which 50%. Examples of such a laser diffraction particle size distribution measuring apparatus include HORIBA LA-300 series, HORIBA LA-920 series (manufactured by Horiba, Ltd.) and the like. This particle size distribution measuring apparatus is not intended to evaluate only primary particles of inorganic particles, but also targets secondary particles formed by aggregation of primary particles. Therefore, the average particle diameter (Db) obtained by this particle size distribution measuring apparatus can be used as an indicator of the dispersion state of the inorganic particles contained in the protective layer forming slurry. The average particle diameter (Db) of the inorganic particles is measured by centrifuging the slurry for forming the protective layer to precipitate the inorganic particles, then removing the supernatant and measuring the precipitated inorganic particles by the above method. Can also be measured.

1.1.3.2. Polymer particles When the filler particles (A2) are polymer particles, the content of repeating units derived from a compound having two or more polymerizable unsaturated groups in 100 parts by mass of the polymer particles is 20 to 100 parts by mass. Yes, preferably 20 parts by mass or more, more preferably 50 parts by mass or more, still more preferably 80 parts by mass or more, and particularly preferably 90 parts by mass or more.

  When the content of the repeating unit derived from the compound having two or more polymerizable unsaturated groups is within the above range, the heat resistance, solvent resistance, and short circuit caused by dendrites of the protective layer prepared from the protective layer forming composition Since the function to prevent is improved, it is preferable. Furthermore, the composition for protective layer formation which concerns on this Embodiment can improve the toughness of the protective layer formed by containing a polymer particle.

  Hereinafter, the monomer constituting the repeating unit contained in the polymer particles, the mode of the polymer particles, the production method, and the like will be described in detail.

1.3.2.1. Compound having two or more polymerizable unsaturated groups As the compound having two or more polymerizable unsaturated groups, the compound exemplified in the binder particles (A1) can be used, and the polyfunctional (meth) described above. At least one selected from the group consisting of acrylic acid esters and aromatic polyfunctional vinyl compounds can be preferably used. Among these, aromatic divinyl compounds are more preferable, and divinylbenzene is particularly preferable. Further, when the binder particle (A1) has a repeating unit derived from a compound having two or more polymerizable unsaturated groups, the polymer particle functioning as a filler has two polymerizable unsaturated groups identical to the binder particle (A1). It is preferable to have a repeating unit derived from a compound having at least one.

  When the polymer particles contain a repeating unit derived from divinylbenzene, the content ratio of divinylbenzene is preferably 20 to 100% by mass, more preferably 50 to 100% by mass, and particularly preferably 80%, based on all monomers. ˜100 mass%. When the content ratio of divinylbenzene is less than 20% by mass, the resulting polymer particles may be inferior in terms of heat resistance, resistance to electrolytic solution, and the like.

1.3.2.2. Other unsaturated monomers In addition to the repeating units derived from the compound having two or more polymerizable unsaturated groups, the polymer particles are derived from other unsaturated monomers copolymerizable therewith. Repeating units may be further included.

  Examples of such unsaturated monomers include unsaturated carboxylic acid esters (excluding compounds having two or more polymerizable unsaturated groups) described in the above polymer particles, aromatic vinyl compounds (provided that Except for compounds having two or more polymerizable unsaturated groups), unsaturated carboxylic acids, α, β-unsaturated nitrile compounds, other unsaturated monomers, and the like. The polymer particles preferably have a repeating unit derived from a compound having two or more polymerizable unsaturated groups, a repeating unit derived from an unsaturated carboxylic acid ester, and a repeating unit derived from an aromatic vinyl compound. .

  The content ratio of the repeating unit derived from the unsaturated carboxylic acid ester in 100 parts by mass of the polymer particles is preferably 5 to 80 parts by mass, and more preferably 10 to 75 parts by mass.

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

1.3.2.3. Average particle diameter of polymer particles (Da2)
The average particle diameter (Da2) of the polymer particles 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 (Da2) of a polymer particle is larger than the average pore diameter of the separator which is a porous film. Thereby, the damage to a separator can be reduced and it can prevent that a polymer particle is clogged with the microporous of a separator.

  The average particle diameter (Da2) of the polymer particles can be measured by the same method as that for the binder particles (A1).

1.1.3.2.4. Toluene insoluble content The toluene insoluble content of the polymer particles is preferably 90% or more, more preferably 95% or more, and most preferably 100%, that is, not dissolved. 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 within the above range, it is possible to suppress the elution of the polymer into the electrolytic solution even when the power storage device is produced and charging / discharging is repeated over a long period of time. It is estimated that the change can be suppressed. In addition, a toluene insoluble content is computable by the method similar to the above-mentioned polymer particle (A).

1.1.3.2.5. The temperature at which weight loss of 10 wt% in an air atmosphere _{(T 10)}
The temperature (T ₁₀ ) at which the polymer particles are 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 polymer particles are reduced by 10% by weight in an air atmosphere is presumed to correlate with the chemical stability against oxidation at high temperature and high voltage inside the battery. Therefore, if the temperature (T ₁₀ ) at which the polymer particles are reduced by 10% by weight in the air atmosphere is within the above temperature range, the stability against oxidation at high temperature and high voltage inside the battery is improved, and the polymer Since the decomposition reaction of the particles is less likely to occur, the remaining capacity ratio is improved. The temperature (T ₁₀ ) at which the polymer particles are reduced by 10% by weight in an air atmosphere can be calculated by the same method as that for the binder particles (A1).

1.1.3.2.6. Embodiment of Polymer Particles When the polymer particles are measured by differential scanning calorimetry (DSC) according to JIS K7121, no endothermic peak is observed in the range of −50 ° C. to + 300 ° C. This indicates that the polymer particles 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 obtained from the composition for protective layer formation.

  The polymer particles are preferably particles having one or more pores therein. When the polymer particles have one or more pores therein, the permeability and liquid retention of the electrolytic solution of the protective layer obtained are improved, and good charge / discharge characteristics can be expressed. 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 polymer particles have one or more pores therein, the volume porosity is preferably 1% to 80%, more preferably 2% to 70%, and more preferably 5% to 60%. It is particularly preferred that 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 polymer particles was observed with an electron microscope (Hitachi High-Technologies Corporation, Hitachi Transmission Electron Microscope H-7650) for the polymer particles (A2) and filler particles (A2). The average particle diameter and particle inner diameter of the 100 particles were measured and calculated by the following formula (5).

Volume porosity (%) = ((particle inner diameter) ³ / (average particle diameter) ³ ) × 100 (5)
1.1.3.2.7. Production method of polymer particles The polymer particles contained in the composition for forming a protective layer according to the present embodiment are not particularly limited as long as the polymer particles have the above-described configuration. It is preferable to use methods such as emulsion polymerization, seeding emulsion polymerization, suspension polymerization, seeding suspension polymerization, and solution precipitation polymerization. Among these, emulsion polymerization and seeding emulsion polymerization are preferable. Of these, seeding emulsion polymerization is particularly preferred because the particle size distribution can be easily controlled uniformly.

  Further, when the polymer particles have a hollow structure, they are prepared according to the methods described in JP-A No. 2002-30113, JP-A No. 2009-120784, and JP-A No. 62-127336. In the case of the core-shell type, it can be produced according to the method described in JP-A-4-98201.

1.1.4. Liquid medium The protective layer forming composition according to the present embodiment further contains a liquid medium. The 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, based on the entire aqueous medium. Most preferably, the aqueous medium is composed only of water without containing a non-aqueous medium.

  The composition for forming a protective layer according to the present embodiment uses an aqueous medium as a liquid medium, and preferably does not contain a non-aqueous medium other than water, so that the degree of adverse effects on the environment is low, so High safety.

1.1.5. Other components The composition for protective layer formation concerning this Embodiment can contain other components, such as a thickener and surfactant, as needed.

1.1.5.1. Thickener The composition for protective layer formation concerning this Embodiment can contain a thickener from a viewpoint of improving the coating property. Examples of the thickener include cellulose compounds such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose; ammonium salts or alkali metal salts of the above cellulose compounds; poly (meth) acrylic acid, modified poly (meth) Polycarboxylic acids such as acrylic acid; alkali metal salts of the above polycarboxylic acids; polyvinyl alcohol (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; (meth) acrylic acid, maleic acid And a water-soluble polymer such as a saponified product of a copolymer of an unsaturated carboxylic acid such as fumaric acid and a vinyl ester. Among these, particularly preferred thickeners are alkali metal salts of carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, alkali metal salts of poly (meth) acrylic acid, and the like.

  Examples of commercially available thickeners include carboxymethyl cellulose 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. The alkali metal salt of can be mentioned.

  When the composition for protective layer formation which concerns on this Embodiment contains a thickener, the usage-amount of a thickener shall be 5 mass% or less with respect to the total solid content of the composition for protective layer formation. Is preferable, and it is more preferable that it is 0.1-3 mass%.

1.1.5.2. Surfactant The composition for forming a protective layer according to the present embodiment can contain a surfactant from the viewpoint of improving its dispersibility and dispersion stability. Examples of the surfactant include those described in “1.2.10. Method for producing binder particles (A1)”.

1.1.5. Method for Producing Protective Layer Forming Composition The protective layer forming composition according to the present embodiment includes binder particles (A1), filler particles (A2), a liquid medium, and additives used as necessary. Can be prepared by mixing. These can be mixed and stirred using a normal method, and for example, a stirrer, a defoaming machine, a bead mill, a high-pressure homogenizer, or the like can be used. The preparation of the protective layer forming composition is preferably performed under reduced pressure. Thereby, it can prevent that a bubble arises in the electrode layer obtained.

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

2. 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, a protective layer disposed between the positive electrode and the negative electrode, and an electrolytic solution, and the protective layer is for forming the protective layer described above. It is produced using the composition. Hereinafter, first to third embodiments will be described with reference to the drawings.

2.1. First Embodiment FIG. 1 is a schematic view showing a cross section of an electricity storage device according to a first embodiment. 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, a thickener used for dispersion of a fluorine-containing polymer such as polyvinylidene fluoride or polyfluorinated acrylate or a positive electrode active material, or a styrene butadiene rubber (SBR) or (meth) acrylate copolymer A polymer composition containing a coalescence 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-mentioned protective layer forming composition on the surface of the positive electrode 10 (or the negative electrode 20) and drying it. For example, a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method, or the like is applied as a method for applying the protective layer forming composition to the surface of the positive electrode 10 (or the negative electrode 20). be able to. The drying treatment of the coating film is preferably performed in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for a processing time of 1 to 120 minutes, more preferably 5 to 60 minutes.

  Although the film thickness of the protective layer 30 is not specifically limited, It is preferable that it is the range of 0.5-4 micrometers, and it is more preferable that it is the range of 0.5-3 micrometers. 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 power 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. The electrolyte concentration in this case 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; esters 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; Examples include sultone compounds such as 1,4-butane sultone, 2,4-butane sultone, and 1,8-naphtha sultone.

2.2. Second Embodiment FIG. 2 is a schematic view showing a cross section of an electricity storage device according to a second embodiment. 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 between the positive electrode 110 and the separator 150. In the power storage device 2 illustrated in FIG. 2, the protective layer 130 is disposed so as to be 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 a protective layer forming composition described later 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 forming composition to the surface of the separator 150, for example, a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method, or the like can be applied. The drying treatment of the coating film is preferably performed in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for a processing time of 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.

  The other configuration of the power storage device 2 according to the second embodiment is the same as that of the power storage device 1 according to the first embodiment described with reference to FIG.

2.3. Third Embodiment FIG. 3 is a schematic view showing a cross section of an electricity storage device according to a third embodiment. 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 by, for example, applying the above-described protective layer forming composition on the surface of the separator 250 and drying it. As a method for applying the protective layer forming composition to the surface of the separator 250, for example, a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method, or the like can be applied. The drying treatment of the coating film is preferably performed in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for a processing time of 1 to 120 minutes, more preferably 5 to 60 minutes.

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

2.4. Manufacturing method As a manufacturing method of an electricity storage device as described above, 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 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.

2.5. 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.

3. 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.

3.1. Synthesis of binder particles (A1) 3.1.1. 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. As a result of analyzing the obtained polymer X by ¹⁹ F-NMR, the mass composition ratio of each monomer was VDF / HFP = 21/4.

<Synthesis of binder particles (A1)>
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 and 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. Then, after cooling, the reaction was stopped, and the aqueous dispersion S1 containing 40% of the binder particles (A1) containing the polymer X and the polymer Y was adjusted to pH 7 with a 2.5N aqueous sodium hydroxide solution. Obtained.

  About the obtained water dispersion S1, a particle size distribution is measured using the particle size distribution measuring apparatus (The model "FPAR-1000" by Otsuka Electronics Co., Ltd.) which makes a dynamic light scattering method a measurement principle, From the particle size distribution, The average particle size (Da1) 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 1), the toluene insoluble content of the binder particles (A1) was 85%.

Toluene insoluble content (%) = ((1-Y) / 1) × 100 (1)
Furthermore, when the obtained film (film composed of binder particles (A1)) 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. Since Tg was observed at −5 ° C., the obtained binder particles (A1) are 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”). The temperature at which the polymer particles A1 were reduced by 10 wt% when heated in an air atmosphere at a rate of temperature increase of 20 ° C./min (hereinafter, this reduction start temperature is expressed as “T10”) was 338 ° C.

3.1.2. Synthesis Examples 2-12, 31
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 binder particles (A1) having the composition shown in Table 1 was prepared, and the solid of the aqueous dispersion was prepared. Water dispersions S2 to S12 and S15 having a solid content concentration of 40% were prepared by removing or adding water under reduced pressure according to the partial concentration. As a result of measurement of insoluble toluene in the same manner as in Synthesis Example 1 for the obtained binder particles (A1), results of DSC measurement (glass transition temperature Tg, melting temperature Tm) and results of TG measurement (weight reduction start temperature T10) are shown. These are also shown in Table 1. FIG. 4 is a DSC chart of the binder particles (A1) obtained in Synthesis Example 3. According to FIG. 4, since the melting temperature Tm is not observed and the single glass transition temperature Tg is observed at −15 ° C., it is estimated that the obtained binder particles (A1) are polymer alloy particles. The

3.1.3. Synthesis Example 13
In Synthesis Example 1, an aqueous dispersion containing binder particles (A1) having the composition shown in Table 1 was prepared without using polymer X, and water was removed under reduced pressure according to the solid content concentration of the aqueous dispersion. Alternatively, an aqueous dispersion S13 having a solid concentration of 40% was prepared by adding. As a result of measurement of insoluble toluene in the same manner as in Synthesis Example 1 for the obtained binder particles (A1), results of DSC measurement (glass transition temperature Tg, melting temperature Tm) and results of TG measurement (weight reduction start temperature T10) are shown. These are also shown in Table 1.

3.1.4. Synthesis Example 14
In a temperature-controllable autoclave equipped with a stirrer, water 200 parts by mass, sodium dodecylbenzenesulfonate 0.6 parts by mass, potassium persulfate 1.0 part by mass, sodium bisulfite 0.5 part by mass, α-methylstyrene The monomer shown in the column of 0.5 part by weight of dimer, 0.3 part by weight of dodecyl mercaptan and the polymer (A1) in Table 1 was 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 S14 containing 50% by mass of binder particles (A1). As a result of the measurement of insoluble toluene in the same manner as in Synthesis Example 1 for the obtained binder particles (A1), the result of DSC measurement (glass transition temperature Tg, melting temperature Tm) and the result of TG measurement (weight reduction start temperature T ₁₀ ) Is also shown in Table 1.

3.2. Synthesis of filler particles (A2) 3.2.1. Synthesis Example 15
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 performed for 6 hours. As a result, an aqueous dispersion containing polymer particles having a polymerization yield of 98% and an average particle diameter of 170 nm and a standard deviation of the particle diameter 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 number 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. Then, after cooling, the reaction was stopped, the pH was adjusted to 7 with a 2.5N aqueous sodium hydroxide solution, and an aqueous dispersion L1 containing 20% filler particles (A2) was obtained.

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

  100 g of this filler particle (A2) aqueous dispersion was weighed and dried at 120 ° C. for 1 hour. The obtained solid was pulverized in an agate mortar to obtain a powder (filler particles (A2)).

As a result of performing toluene insoluble content measurement, DSC measurement and TG measurement of the obtained powder (powder composed of filler particles (A2)) in the same manner as in Synthesis Example 1, the toluene insoluble content was 99%. The transition temperature Tg and the melting temperature Tm could not be observed, and the weight loss starting temperature T10 was 379 ° C. FIG. 5 is a TGA chart of the filler particles (A2) obtained in Synthesis Example 15. According to FIG. 5, it can be read that the temperature (T ₁₀ ) at which the weight of the filler particles (A2) obtained in Synthesis Example 15 is reduced by 10% by weight in an air atmosphere is 379 ° C.

3.2.2. Synthesis Examples 16-25
In the synthesis example 15, except that the composition and the amount of the emulsifier were appropriately changed, an aqueous dispersion containing filler particles (A2) having the composition shown in Table 2 was prepared, and water was added according to the solid content concentration of the aqueous dispersion. Were removed or added under reduced pressure to obtain aqueous dispersions L2 to L11 having a solid concentration of 20%. As a result of toluene insoluble matter measurement performed on the obtained filler particles (A2) in the same manner as in Synthesis Example 1, DSC measurement results (glass transition temperature Tg, melting temperature Tm) and TG measurement results (weight loss start temperature T ₁₀ ) Is also shown in Table 2.

3.2.3. Synthesis Example 26
In a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, 109.5 parts by mass of water, 0.2 part by mass of sodium dodecylbenzenesulfonate as an emulsifier, 0.5 part by mass of octyl glycol as a molecular weight regulator and polymerization As an initiator, 0.5 part by mass of sodium persulfate was added. Next, 20% of a monomer mixture obtained by mixing 20 parts by mass of methacrylic acid and 80 parts by mass of methyl methacrylate was charged into a pressure resistant reactor. Thereafter, the temperature is raised to 75 ° C. while stirring, and a polymerization reaction is carried out for 1 hour after reaching 75 ° C., and then the remaining monomer mixture is continuously put into a pressure-resistant reaction vessel over 2 hours while maintaining the temperature at 75 ° C. Added. Thereafter, aging was further performed for 2 hours to obtain an aqueous dispersion of polymer particles (A2a) having a solid content of 40% and an average particle diameter of 200 nm.

  186 parts by mass of water is put into a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, and 10 parts by mass of the polymer particles (A2a) having a particle size of 200 nm are solidified. Sodium persulfate 0.5 part by mass was added as an agent, and the temperature was raised to 80 ° C. with stirring. Next, a monomer mixture obtained by mixing 30 parts by weight of methacrylic acid, 69.5 parts by weight of methyl methacrylate and 0.5 parts by weight of divinylbenzene was kept in a pressure-resistant reaction vessel at a temperature of 80 ° C. and continuously 3 with stirring. I put it in over time. Thereafter, aging was further performed for 2 hours to obtain an aqueous dispersion of polymer particles (A2b) having a solid content of 31% and an average particle diameter of 400 nm.

  350 parts by mass of water is put into a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, and 15 parts by mass of the polymer particles (A2b) having a particle diameter of 400 nm as described above are started. As an agent, 0.4 part by mass of sodium persulfate was added, and the temperature was raised to 80 ° C. while stirring. Next, a monomer mixture obtained by mixing 50 parts by mass of styrene, 25 parts by mass of divinylbenzene, and 25 parts by mass of ethylvinylbenzene was continuously added to the pressure resistant reactor over 4 hours while stirring. While the monomer mixture was charged, the temperature of the pressure resistant reactor was maintained at 80 ° C. After completion of continuous addition of the monomer mixture, 5 parts by mass of 25% ammonium water was introduced into a pressure resistant reactor maintained at 80 ° C. and aged for 3 hours to obtain an aqueous dispersion L12 containing 20% filler particles (A2). Obtained.

As a result of toluene insoluble matter measurement performed on the obtained filler particles (A2) in the same manner as in Synthesis Example 1, DSC measurement results (glass transition temperature Tg, melting temperature Tm) and TG measurement results (weight loss start temperature T ₁₀ ) Is also shown in Table 2.

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

  Aqueous dispersion of polymer particles containing 20% filler particles (A2) obtained for analyzing the particle structure in more detail was dried and solidified, and adjusted to pH 10 that was 20 times the solid content. Water-soluble components were completely removed by washing with water three times and further with ion-exchanged water four times, and dried and solidified again to obtain a powder of filler particles (A2). When this powder was observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation), a hollow polymer having an average particle diameter of 1,000 particles and a particle inner diameter of 600 nm was observed. The particles had a volume porosity of 22%.

3.2.4. Synthesis Example 27
In the above synthesis example 26, the polymer particles (A2b) were replaced with 15 parts by mass of solids, 50 parts by mass of styrene, 25 parts by mass of divinylbenzene, and 25 parts by mass of ethylvinylbenzene. In the same manner as in Synthesis Example 26, except that 50 parts by mass, 77 parts by mass of styrene, 22 parts by mass of divinylbenzene, and 1 part by mass of acrylic acid were used, an aqueous dispersion L13 containing 20% filler particles (A2) was obtained. It was.

As a result of toluene insoluble matter measurement performed on the obtained filler particles (A2) in the same manner as in Synthesis Example 1, DSC measurement results (glass transition temperature Tg, melting temperature Tm) and TG measurement results (weight loss start temperature T ₁₀ ) Is also shown in Table 2.

  The particle size distribution is measured using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle, and the average particle diameter of filler particles (A2) is determined from the particle size distribution. When (Da2) was determined, it was 810 nm.

  Aqueous dispersion of polymer particles containing 20% filler particles (A2) obtained for analyzing the particle structure in more detail was dried and solidified, and adjusted to pH 10 that was 20 times the solid content. Water-soluble components were completely removed by washing with water three times and further with ion-exchanged water four times, and dried and solidified again to obtain a powder of filler particles (A2). When this powder was observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation), the observed 100 particles were hollow polymer particles having an average particle diameter of 810 nm and a particle inner diameter of 700 nm. Yes, the volume porosity was 65%.

3.2.5. Synthesis Example 28
In a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, 99 parts by mass of styrene, 1 part by mass of methacrylic acid and 8 parts by mass of t-dodecyl mercaptan, 0.4 parts by mass of sodium lauryl sulfate in 200 parts by mass of water And an aqueous solution in which 1.0 part by mass of potassium persulfate was dissolved and polymerized at 70 ° C. for 8 hours with stirring to obtain an aqueous dispersion of polymer particles having an average particle diameter of 250 nm.

  Next, 10 parts by mass of the polymer particles, 0.1 part by mass of polyoxyethylene nonylphenyl ether, 0.3 part by mass of sodium lauryl sulfate and 0.5 part by mass of potassium persulfate are added to 900 parts by mass of water. Distributed. A mixture of 60 parts by weight of methyl methacrylate, 30 parts by weight of divinylbenzene, 10 parts by weight of styrene and 20 parts by weight of toluene was added thereto and stirred at 30 ° C. for 1 hour, followed by stirring at 70 ° C. for 5 hours and cooling. When the steam strip treatment was performed, an aqueous dispersion L14 containing hollow filler particles (A2) was obtained.

As a result of toluene insoluble matter measurement performed on the obtained filler particles (A2) in the same manner as in Synthesis Example 1, DSC measurement results (glass transition temperature Tg, melting temperature Tm) and TG measurement results (weight loss start temperature T ₁₀ ) Is also shown in Table 2.

  The particle size distribution is measured using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle, and the average particle diameter of filler particles (A2) is determined from the particle size distribution. When (Da2) was determined, it was 490 nm. When the polymer particles were dried and then observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation), the average particle diameter of 100 particles observed was 490 nm, and the particle inner diameter was 350 nm. The hollow polymer particles had a volume porosity of 36%.

3.2.6. Synthesis Example 29
In Synthesis Example 28, instead of 60 parts by mass of methyl methacrylate, 30 parts by mass of divinylbenzene, 10 parts by mass of styrene and 20 parts by mass of toluene, 60 parts by mass of methyl methacrylate, 40 parts by mass of allyl methacrylate and 15 parts by mass of toluene An aqueous dispersion L15 containing filler particles (A2) was obtained in the same manner as in Synthesis Example 28 except that was used.

As a result of toluene insoluble matter measurement performed on the obtained filler particles (A2) in the same manner as in Synthesis Example 1, DSC measurement results (glass transition temperature Tg, melting temperature Tm) and TG measurement results (weight loss start temperature T ₁₀ ) Is also shown in Table 2.

  The particle size distribution is measured using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle, and the average particle diameter of filler particles (A2) is determined from the particle size distribution. When (Da2) was determined, it was 420 nm. When the polymer particles were dried and observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation), the average particle diameter of 100 particles observed was 420 nm, and the particle inner diameter was 220 nm. The hollow polymer particles had a volume porosity of 14%.

3.2.7. Synthesis Example 30
In a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, 109.5 parts by mass of water, 0.2 part by mass of sodium dodecylbenzenesulfonate as an emulsifier, 0.5 part by mass of octyl glycol as a molecular weight regulator and polymerization As an initiator, 0.5 part by mass of sodium persulfate was added. Next, 20% of a monomer mixture obtained by mixing 15 parts by mass of methacrylic acid and 85 parts by mass of methyl methacrylate was charged into a pressure resistant reactor. Thereafter, the temperature is raised to 75 ° C. while stirring, and a polymerization reaction is carried out for 1 hour after reaching 75 ° C., and then the remaining monomer mixture is continuously put into a pressure-resistant reaction vessel over 2 hours while maintaining the temperature at 75 ° C. Added. Thereafter, aging was further performed for 2 hours to obtain an aqueous dispersion of polymer particles having a solid content of 40% and an average particle size of 200 nm.

  Into a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, 186 parts by mass of water is charged, and 10 parts by mass of the polymer particles having a particle diameter of 200 nm as described above are added as a polymerization initiator. Sodium sulphate (0.5 parts by mass) was added and the temperature was raised to 80 ° C. with stirring. Next, a monomer mixture obtained by mixing 30 parts by weight of methacrylic acid, 69.5 parts by weight of methyl methacrylate and 0.5 parts by weight of divinylbenzene was kept in a pressure-resistant reaction vessel at a temperature of 80 ° C. and continuously 3 with stirring. I put it in over time. Thereafter, aging was further performed for 2 hours to obtain an aqueous dispersion of polymer particles having a solid content of 31% and an average particle diameter of 400 nm.

  350 parts by mass of water was put into a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, and 20 parts by mass of the polymer particles having a particle diameter of 400 nm as a polymerization initiator were added thereto as a polymerization initiator. 0.4 parts by mass of sodium sulfate was added, and the temperature was raised to 80 ° C. while stirring. Next, a monomer mixture obtained by mixing 90 parts by mass of styrene, 9 parts by mass of divinylbenzene, and 1 part by mass of acrylic acid was continuously added to the pressure resistant reactor over 4 hours while stirring. While the monomer mixture was charged, the temperature of the pressure resistant reactor was maintained at 80 ° C. After the completion of the continuous addition of the monomer mixture, 5 parts by mass of 25% ammonium water was placed in a pressure resistant reactor maintained at 80 ° C., and aged for 3 hours to obtain an aqueous dispersion L16 containing 20% filler particles (A2). Obtained.

As a result of toluene insoluble matter measurement performed on the obtained filler particles (A2) in the same manner as in Synthesis Example 1, DSC measurement results (glass transition temperature Tg, melting temperature Tm) and TG measurement results (weight loss start temperature T ₁₀ ) Is also shown in Table 2.

  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 the average particle diameter of filler particles (A2) is determined from the particle size distribution. When (Da2) was determined, it was 1000 nm.

  Aqueous dispersion of polymer particles containing 20% filler particles (A2) obtained for analyzing the particle structure in more detail was dried and solidified, and adjusted to pH 10 that was 20 times the solid content. Water-soluble components were completely removed by washing with water three times and further with ion-exchanged water four times, and dried and solidified again to obtain a powder of filler particles (A2). When this powder was observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation), a hollow polymer having an average particle size of 1,000 nm and a particle inner diameter of 800 nm was observed for 100 particles. The volume porosity was 51%.

  The abbreviations or names of the respective components in Table 1 and Table 2 mean the following compounds, respectively.

<Compound having two or more polymerizable unsaturated groups>
AMA: Allyl methacrylate EDMA: Ethylene glycol dimethacrylate DVB: Divinylbenzene <Monomer having a fluorine atom>
-VDF: Vinylidene fluoride-HFP: Propylene hexafluoride-TFE: Tetrafluoroethylene <Unsaturated carboxylic acid>
MAA: methacrylic acid TA: itaconic acid AA: acrylic acid <unsaturated carboxylic acid ester>
MMA: Methyl methacrylate EHA: 2-ethylhexyl acrylate BMA: n-butyl methacrylate CHMA: cyclohexyl methacrylate <Aromatic vinyl compound>
ST: Styrene EVB: Ethyl vinyl benzene <Conjugated diene compound>
BD: 1,3-butadiene <nitrile compound>
-AN: Acrylonitrile In addition, the notation of "-" in Table 1 and Table 2 shows that the applicable component was not used.

3.3. Example 1
3.3.1. Preparation of composition for forming protective layer The aqueous dispersion S1 and the aqueous dispersion L1 are mixed so that the binder particles (A1) are 10 parts by mass with respect to 100 parts by mass of the filler particles (A2). 1 part by weight of an agent (manufactured by Daicel Corporation, trade name “CMC1120”) and 275 parts by weight of water K. Mixing and dispersing treatment was performed using Fillmix (R) 56-50 type (manufactured by PRIMIX Co., Ltd.) to prepare a protective layer forming composition.

About the obtained composition for protective layer formation, toluene insoluble content measurement, DSC measurement (glass transition temperature Tg, melting temperature Tm) and TG measurement (start of weight loss) by the same method as “3.2.1. Synthesis Example 15” As a result of performing the temperature T10), the insoluble content in 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.

3.3.2. 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 (trade 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 electrode for 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 .

3.3.3. Production of protective layer (production of positive electrode with protective layer)
The protective layer-forming composition obtained above is placed in a stainless steel container on the surface of the positive electrode active material layer of the positive electrode obtained above, pressurized to an internal pressure of 0.1 MPa, and a one-fluid nozzle (unijet TG full cone, flow size) 0.3, manufactured by Spraying Systems Japan Co., Ltd.) and then dried at 60 ° C. for 5 minutes to form a protective layer on the surface of the positive electrode active material layer. The protective layer had a thickness of 3 μm.

3.3.4. Production of negative electrode <Preparation of slurry for negative 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), 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.

<Preparation of electrode for 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 .

3.3.5. Assembly of Lithium Ion Battery Cell A bipolar coin cell (Hosen Co., Ltd.) obtained by punching and molding the negative electrode produced above to a diameter of 16.16 mm in an Ar-substituted glove box with a dew point of −80 ° C. or lower. And product name “HS flat cell”). Next, a separator made of a polypropylene porous film punched to a diameter of 24 mm (product name “Celguard # 2400” manufactured by Celgard Co., Ltd.) was placed, and after injecting 500 μL of electrolyte so that air did not enter, The positive electrode with a protective layer manufactured in step 1 is punched and molded to a diameter of 15.95 mm, and placed so that the separator and the protective layer formed on the positive electrode face each other, and the outer body of the bipolar coin cell is closed with a screw. The lithium ion battery cell (electric storage device) was assembled by sealing. The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio).

3.3.6. Measurement of remaining capacity rate and resistance increase rate The battery cell produced above 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, it was continuously determined. Charging was continued at a voltage (4.1 V), and 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).

  An EIS measurement ("Electrochemical Impedance Spectroscopy", "electrochemical impedance measurement") was performed on the charged cell, and an 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.

Remaining capacity ratio (%) = (C2 / C1) × 100 (6)
Resistance increase rate (%) = (EISb / EISa) × 100 (7)
When this residual capacity ratio was 75% or more, it was judged as good and indicated as ◯ in the table, and when it was less than 75%, it was judged as defective and indicated as × in the table. Further, when the resistance increase rate was 300% or less, it was judged that the durability was good and indicated in the table as ○, and when exceeding 300%, it was judged as defective and indicated as × in the table.

  In the above measurement conditions, “1C” indicates a current value at which discharge is completed in one 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.

3.5. Examples 2 to 10 and 23, 1b to 10b and 23b, Comparative Examples 1 to 9 and 20 to 23, 1b to 9b and 20b to 23b
Except for blending the aqueous dispersions shown in Table 3, Table 3b, Table 4 or Table 4b in the proportions shown in Table 3, Table 3b, Table 4 or Table 4b, and changing the coating method to the method described in the table, In the same manner as in Example 1, the protective layer forming compositions described in Table 3 and Table 4 were prepared. About the obtained composition for protective layer formation, the result of the toluene insoluble content obtained by the same method as “3.2.1. Synthesis Example 15”, the result of DSC measurement (glass transition temperature Tg, melting temperature Tm ) And TG measurement results (weight loss start temperature T ₁₀ ) are shown in Table 3, Table 3b, Table 4, and Table 4b. Furthermore, an electricity storage device was produced and evaluated in the same manner as in Example 1 using the prepared protective layer forming composition. The evaluation results are shown in Table 3, Table 3b, Table 4, and Table 4b.

  In the ink jet method, coating was performed by using a model No. NanoPrinter-900 manufactured by Microjet Co., Ltd., holding the slurry and the nozzle head at 23 ° C., and discharging at a setting of 100 picoliters per drop of ink. In the die coating method, coating was performed using a model number YBA-5 manufactured by Yoshimitsu Seiki at a sweep rate of 100 mm / sec. In the bar coat method, coating was performed at a sweep speed of 100 mm / sec using model # 8 manufactured by Yasuda Seiki. In the dip coating method, coating was performed using a model number M300 manufactured by Asumi Giken at a lifting speed of 20 mm / second.

<Inorganic particles>
-Titanium oxide: The product name “KR380” (manufactured by Titanium Industry Co., Ltd., rutile type, number average particle size 0.38 μm) is used as it is, or the product name “KR380” is ground in an mortar and sieved. Thus, titanium oxide having a number average particle size of 0.08 μm and 0.12 μm was prepared and used.
Aluminum oxide: Product name “AKP-3000” (manufactured by Sumitomo Chemical Co., Ltd., number average particle size 0.74 μm), or product name “AKP-50” (manufactured by Sumitomo Chemical Co., Ltd., number average particle size 0.22 μm) Was used.
・ Zirconium oxide: Product name “UEP zirconium oxide” (manufactured by Daiichi Elemental Chemical Co., Ltd., number average particle diameter 0.67 μm)
Silica: Product name “Seahoster (R) KE-S50” (manufactured by Nippon Shokubai Co., Ltd., number average particle size 0.54 μm), or product name “Seahoster (R) KE-S100” (manufactured by Nippon Shokubai Co., Ltd., number An average particle size of 0.98 μm) was used.
Magnesium oxide: Product name “PUREMAG® FNM-G” (manufactured by Tateho Chemical Co., Ltd., number average particle size 0.50 μm)
In Table 3, Table 3b, Table 4, and Table 4b, the notation “−” indicates that the corresponding component was not used. In Comparative Example 8, “S7 / S9” is written in the column of the type of the aqueous dispersion of the binder particles (A1), and “10/100” is written in the column of the amount of the aqueous dispersion used. It shows that the dispersions S7 and S9 were mixed and used, and 10 parts by mass of binder particles (A1) contained in the aqueous dispersion S7 and 100 parts by mass of binder particles (A1) contained in the aqueous dispersion S9. It is shown that the mixture was used. The notation in Comparative Example 8b, Comparative Example 9, and Comparative Example 9b is the same.

3.5. Example 11
3.5.1. Production of Positive Electrode and Negative Electrode A positive electrode and a negative electrode were produced in the same manner as in Example 1.

3.5.2. Production of protective layer (production of separator with protective layer)
For forming a protective layer obtained in the above “3.3.1. Preparation of protective layer-forming composition” on both sides of a separator made of polypropylene porous film (trade name “Celguard # 2400” manufactured by Celgard Co., Ltd.) The composition was placed in a stainless steel container, pressurized to an internal pressure of 0.1 MPa, sprayed from a single fluid nozzle (Unijet TG full cone, flow rate size 0.3, manufactured by Spraying Systems Japan Co., Ltd.), and then applied to 60 Drying was performed at 10 ° C. for 10 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).

3.5.3. Assembly of Lithium Ion Battery Cell A bipolar coin cell (Hosen Co., Ltd.) obtained by punching and molding the negative electrode produced above to a diameter of 16.16 mm in an Ar-substituted glove box with a dew point of −80 ° C. or lower. And product name “HS flat cell”). Next, the separator with the protective layer prepared in “3.5.2. Preparation of protective layer (preparation of separator with protective layer)” punched to a diameter of 24 mm is placed, and electrolysis is performed so that air does not enter. After injecting 500 μL of the liquid, the positive electrode manufactured above was punched and molded to a diameter of 15.95 mm, and the outer body of the two-pole coin cell was closed with a screw and sealed, so that a lithium ion battery cell (Electric storage device) was assembled. The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio).

3.5.4. Measurement of Residual Capacity Rate and Resistance Increase Rate Residual capacity rate and resistance increase rate were measured in the same manner as in Example 1 above.

3.5.5. Adhesiveness between protective layer and electrode From the negative electrode, separator with protective layer, and positive electrode produced above, test pieces each having a width of 2 cm and a length of 5 cm were cut out, and the negative electrode active material layer and the positive electrode active material layer were each provided with a protective layer. A negative electrode / a separator with a protective layer / a positive electrode was laminated so as to face the separator. 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. Thereafter, before the solvent was 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 Is not transferred to the protective layer x: When either the negative electrode or the positive electrode is peeled off, there is no resistance, and it is already peeled 3.6. Examples 12-22, 1b-22b, Comparative Examples 10-19, 10b-19b
Tables 5 and 5b were prepared in the same manner as in Example 1 except that the aqueous dispersions shown in Tables 5 and 5b were blended in the usage ratios shown in Tables 5 and 5b and the coating method was changed to the method described in the table. The protective layer forming composition described in 5b was prepared. About the obtained composition for protective layer formation, the result of the toluene insoluble content obtained by the same method as “3.2.1. Synthesis Example 15”, the result of DSC measurement (glass transition temperature Tg, melting temperature Tm ) And the results of TG measurement (reduction start temperature T ₁₀ ) are shown together in Table 5. Furthermore, an electricity storage device was produced and evaluated in the same manner as in Example 11 using the obtained protective layer forming composition. The evaluation results are shown in Table 5 and Table 5b.

  As apparent from Tables 3 to 4 and Tables 3b to 4b, an electricity storage device (lithium) having a positive electrode having a protective layer according to the present invention shown in Examples 1 to 10 and 23, 1b to 10b and 23b. The ion battery was excellent in the remaining capacity after the durability test and the suppression of the increase in resistance. On the other hand, in Comparative Examples 1 to 5, 8 and 20 to 23, and Comparative Examples 1b to 5b, 8b and 20b to 23b, an electricity storage device satisfying both good residual capacity and suppression of the resistance increase rate was not obtained. Further, since Comparative Examples 6 and 6b did not function as a battery, it was impossible to evaluate the measurement of the remaining capacity rate and the resistance increase rate. The reason for this is considered that the positive electrode and the negative electrode are completely blocked by the protective layer formed only of the binder particles (A1) having a binder function. Comparative Examples 7 and 9 Since Comparative Examples 7b and 9b had a protective layer with poor binding force, the protective layer dropped off when the battery was produced, and a battery having a protective layer could not be produced.

  As apparent from Table 5 and Table 5b above, the electricity storage device (lithium ion battery) including the separator having the protective layer according to the present invention shown in Examples 11 to 22 and 11b to 22b remains after the durability test. It was confirmed that the capacity and resistance increase were excellent, and the adhesion between the protective layer and the electrode was good. On the other hand, in Comparative Examples 11, 12, 15, 17, 11b, 12b, 15b, and 17b, an electricity storage device that satisfies both good residual capacity and suppression of the resistance increase rate was not obtained. Further, Comparative Examples 13, 18, 13b, and 18b did not function as a battery, and thus could not be evaluated in the measurement of the remaining capacity rate and the resistance increase rate. The reason for this is considered that the positive electrode and the negative electrode are completely blocked by the protective layer formed only of the binder particles (A1) having a binder function. In Comparative Examples 10, 14, 19, 10b, 14b, and 19b, since the protective layer had a poor binding force, the protective layer dropped off when the battery was produced, and the battery having the protective layer could not be produced.

  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 (10)

Containing binder particles (A1), filler particles (A2), and a liquid medium,
A protective layer forming composition in which the ratio (Da2 / Da1) of the average particle size (Da1) of the binder particles (A1) to the average particle size (Da2) of the filler particles (A2) is 1 to 30 The method of forming the protective layer arrange | positioned between the positive electrode and negative electrode of an electrical storage device by further heating to 40-80 degreeC after spraying on.   The formation method of the protective layer of Claim 1 whose average particle diameter (Da1) of the said binder particle | grain (A1) is 20 nm or more and 450 nm or less.   The formation method of the protective layer of Claim 1 or Claim 2 which contains the said binder particle (A1) 0.1-15 mass parts with respect to 100 mass parts of said filler particles (A2).   When the differential scanning calorimetry (DSC) is performed on the binder particles (A1) in accordance with JIS K7121, at least one endothermic peak in a temperature range of −50 to + 80 ° C. is observed. 4. The method for forming a protective layer according to any one of 3 above.   The method for forming a protective layer according to any one of claims 1 to 4, wherein the binder particles (A1) are solid particles and the filler particles (A2) are particles having pores.   The protective layer produced using the formation method of the protective layer as described in any one of Claims 1 thru | or 5.   A separator coated with the protective layer according to claim 6.   An electricity storage device comprising: a positive electrode; a negative electrode; the protective layer according to claim 6 disposed between the positive electrode and the negative electrode; and an electrolytic solution.   The electricity storage device according to claim 8, wherein the protective layer is in contact with at least one surface of the positive electrode and the negative electrode. An electricity storage device comprising the separator according to claim 7.