JP7327942B2 - Composition for forming porous insulating layer, electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for producing electrode for non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composition for forming a porous insulating layer, an electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a method for producing an electrode for a non-aqueous electrolyte secondary battery.

While non-aqueous electrolyte secondary batteries have relatively high energy densities, they are also required to ensure safety. For this reason, for example, a shutdown function is used to increase the internal resistance inside the battery by closing the pores of the separator by melting when the battery is abnormally heated due to an internal short circuit or the like. In addition to the shutdown function of the separator, a method of preventing an internal short circuit by forming a porous insulating layer directly on the electrode surface has also been studied (see, for example, Patent Document 1).

Such an electrode having heat resistance and insulation properties is produced, for example, as follows. First, an active material-containing paste as a water-based slurry is applied onto a current collector, dried, and then pressed to form an active material layer. Next, a material slurry for forming a porous insulating layer is applied onto the active material layer and dried to form a porous insulating layer.

JP 2008-226566 A

Here, the present inventors have found that when the material slurry is applied onto the active material layer, the active material layer swells due to the solvent in the material slurry, thereby lowering the density. That is, since the active material layer has voids even after rolling, when the material slurry is applied, the liquid component in the slurry partially penetrates into the active material layer. The permeated liquid component affects constituent materials in the active material layer. The electrode after rolling has residual stress, but as a result of the infiltrated liquid component affecting physical properties such as the elastic modulus of the constituent materials, the balance of the residual stress is lost and some of the residual strain is released, and the active material This leads to the phenomenon that the layer thickness of the layer increases. If the layer thickness of the active material layer is greater than the designed thickness, problems may occur when inserting the battery element into the exterior case. Although the increase in the layer thickness of the active material layer per layer is slight, the battery element is usually a laminate in which a plurality of electrodes and separators are laminated, or a wound body in which long electrodes are wound. Therefore, the increase in the thickness of the battery element due to the increase in the thickness of the plurality of active material layers cannot be ignored.

Such a problem becomes even more pronounced when the active material layer is rolled under a higher pressure in order to increase the energy density of the non-aqueous electrolyte secondary battery. That is, when the battery design electrode density (filling rate of the active material layer) is low, the designed electrode density of the active material layer is adjusted in advance during electrode rolling in consideration of the increase in electrode thickness after the formation of the porous insulating layer. It was possible to deal with it by evaluating it highly. However, as the energy density of non-aqueous electrolyte secondary batteries has increased in recent years, the design electrode density has increased, so it tends to be difficult to roll the active material layer to a density higher than the design electrode density in advance. It is in. In addition, due to the demand for longer battery life, there is a tendency to use, for example, poorly oriented graphite particles as the negative electrode active material. As a result, the pressure applied during electrode rolling is increasing. Rolled electrodes contain a large amount of residual stress and strain, so the problem of increased film thickness when the material slurry is applied and dried becomes even more serious. It can also develop into production problems such as not being able to load.

Therefore, in the present invention, it is possible to suppress an increase in the layer thickness of the active material layer of the electrode, to prevent detachment and peeling of the composition for forming a porous insulating layer during the manufacturing process, and to improve battery performance. It is an object of the present invention to provide a composition for forming a porous insulating layer and a method for producing an electrode for a non-aqueous electrolyte secondary battery, which do not have an adverse effect. Another object of the present invention is to provide an electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery manufactured by the method.

In order to solve the above problems, according to one aspect of the present invention, there is provided a composition for forming a porous insulating layer for forming a porous insulating layer on an active material layer disposed on a main surface of a current collector, There is
The active material layer includes at least an active material capable of electrochemically intercalating and deintercalating lithium ions and an active material layer binder,
The composition for forming a porous insulating layer includes at least a solvent containing an organic solvent, insulating inorganic particles, and a binder,
the distance between the Hansen solubility parameter of the active material layer binder and the Hansen solubility parameter of the organic solvent is 8.0 (MPa) ^1/2 or more;
The distance between the Hansen solubility parameter of the active material and the Hansen solubility parameter of the organic solvent is 5.0 (MPa) ^1/2 or more,
The binder contains 30% by mass or more and 60% by mass or less of an aromatic vinyl compound and 20% by mass or more and 69% by mass or less of a (meth)acrylic acid ester, as structural units, relative to the total mass of the binder. , a polymer containing 5% by mass or more and 35% by mass or less of a (meth)acrylic acid ester containing a hydroxyl group or an ether group and 1% by mass or more and 10% by mass or less of a vinyl compound having an acidic functional group. A composition for forming an insulating layer is provided.

According to this aspect, when the porous insulating layer is formed, the thickness of the active material layer of the electrode is prevented from increasing. In addition, the composition for forming a porous insulating layer does not detach or peel off during the manufacturing process, and the battery performance is not adversely affected.

A distance between the Hansen solubility parameter of the active material and the Hansen solubility parameter of the organic solvent may be 8.0 (MPa) ^1/2 or more.

According to this aspect, an increase in the thickness of the active material layer of the electrode is further suppressed. In addition, detachment and peeling of the composition for forming a porous insulating layer during the manufacturing process are further suppressed, and adverse effects on battery performance are further suppressed.

The organic solvent may have a Hansen solubility parameter distance Ra of 5.0 (MPa) ^1/2 or more represented by the following formula (I).

(wherein δ _{D (solvent)} (MPa) ^1/2 is the dispersion term of the organic solvent, δ _{P (solvent)} (MPa) ^1/2 is the polar term of the organic solvent, δ _{H (solvent)} ( MPa) ^1/2 indicates the hydrogen bonding term of the organic solvent, respectively.)

According to this aspect, an increase in the thickness of the active material layer of the electrode is further suppressed. In addition, detachment and peeling of the composition for forming a porous insulating layer during the manufacturing process are further suppressed, and adverse effects on battery performance are further suppressed.

Moreover, the boiling point of the organic solvent at 1 atm may be 160° C. or higher.

According to this aspect, changes in physical properties of the composition for forming a porous insulating layer can be suppressed.

Also, the organic solvent may contain an alcohol-based compound.

Alcohol-based compounds are preferably used from the viewpoint of the dispersibility of insulating inorganic particles and polyolefin-based polymer particles and the solubility of the active material layer binder, and further suppresses the increase in the thickness of the active material layer of the electrode. be done.

In addition, the composition for forming a porous insulating layer may further contain polyolefin polymer particles.

According to this aspect, the safety of the non-aqueous electrolyte secondary battery can be improved.

Further, according to another aspect of the present invention, a current collector,
an active material layer disposed on the main surface of the current collector;
a porous insulating layer formed on the active material layer from the porous insulating layer-forming composition;
An electrode for a non-aqueous electrolyte secondary battery is provided in which the active material layer includes at least an active material capable of electrochemically intercalating and deintercalating lithium ions and an active material layer binder.

According to this aspect, an increase in the thickness of the active material layer is suppressed in the manufactured electrode for a non-aqueous electrolyte secondary battery.

According to another aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery including the electrode for a non-aqueous electrolyte secondary battery.

According to this aspect, an increase in the thickness of the active material layer is suppressed in the manufactured non-aqueous electrolyte secondary battery.

According to another aspect of the present invention, the step of forming a porous insulating layer on the active material layer disposed on the main surface of the current collector using a porous insulating layer-forming composition,
The active material layer includes at least an active material capable of electrochemically intercalating and deintercalating lithium ions and an active material layer binder,
The composition for forming a porous insulating layer includes at least a solvent containing an organic solvent, insulating inorganic particles, and a binder,
the distance between the Hansen solubility parameter of the active material layer binder and the Hansen solubility parameter of the organic solvent is 8.0 (MPa) ^1/2 or more;
The distance between the Hansen solubility parameter of the active material and the Hansen solubility parameter of the organic solvent is 5.0 (MPa) ^1/2 or more,
The binder contains 30% by mass or more and 60% by mass or less of an aromatic vinyl compound and 20% by mass or more and 69% by mass or less of a (meth)acrylic acid ester, as structural units, relative to the total mass of the binder. , a polymer containing 5% by mass or more and 35% by mass or less of a (meth)acrylic acid ester containing a hydroxyl group or an ether group and 1% by mass or more and 10% by mass or less of a vinyl compound having an acidic functional group. A method for manufacturing an electrode for an electrolyte secondary battery is provided.

According to this aspect, it is possible to improve the cycle life of the non-aqueous electrolyte secondary battery when it is charged and discharged at high temperature and high voltage.

As described above, according to the present invention, the increase in the layer thickness of the active material layer of the electrode of the non-aqueous electrolyte secondary battery, the separation of the composition for forming the porous insulating layer, and the performance deterioration in the high temperature life test are suppressed. be able to.

1 is an explanatory diagram showing a schematic configuration of a non-aqueous electrolyte secondary battery according to an embodiment of the invention; FIG.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

<1. Composition for Forming Porous Insulating Layer>
First, a composition for forming a porous insulating layer according to one embodiment of the present invention will be described. The composition for forming a porous insulating layer according to this embodiment is used to form a porous insulating layer on an active material layer of an electrode for a non-aqueous electrolyte secondary battery. The composition for forming a porous insulating layer according to this embodiment contains at least a solvent containing an organic solvent, insulating inorganic particles, and an active material layer binder.

(1.1 solvent)
As described above, the composition for forming a porous insulating layer according to this embodiment contains a solvent containing an organic solvent. The Hansen solubility parameter (hereinafter also referred to as “HSP”) of the active material layer binder in the active material layer and the HSP distance (hereinafter also referred to as “first HSP distance”) of the organic solvent are 8.0. (MPa) ^1/2 or more.

The distance (first HSP distance) between the HSP of the organic solvent contained in the porous insulating layer-forming composition and the HSP of the active material layer binder in the active material layer satisfies the above-described relationship, whereby the active material is Even when the composition for forming a porous insulating layer is applied onto the material layer, swelling of the active material layer is prevented. This prevents the thickness of the active material layer of the electrode from increasing.

Since the active material layer is generally subjected to rolling for the purpose of density adjustment, it contains residual stress.
The reason why the shape is stable even when residual stress is included is that the residual stress included in the active material layer is balanced.

Organic solvents generally used in conventional porous insulating layer-forming compositions swell the active material layer binder because the first HSP distance does not satisfy the above range. As a result, the elastic modulus of the binder for the active material layer is greatly reduced, the balance of the residual stress in the active material layer is lost, and the residual strain is released in the form of an increase in the thickness of the active material layer. On the other hand, in the present embodiment, the organic solvent has the above first HSP distance relationship. Therefore, even when the composition for forming a porous insulating layer is applied onto the active material layer, the swelling of the binder for the active material layer is suppressed, and as a result, the release of the residual strain is suppressed, and the active material layer is An increase in the layer thickness of is also suppressed.

HSP is an extended concept in which the Hildebrand SP value derived from regular solution theory and obtained from the latent heat of vaporization and density of the material is divided into three components: the polarity term δ _P , the hydrogen bonding term δ _H , and the dispersion term δ _D . be. This is expressed as one point in three-dimensional space. Therefore, in calculating the first HSP distance, the comparison of the HSPs of the active material layer binder and the solvent is discussed as the distance between two points (HSP distance) in the three-dimensional space shown in the following formula. In the present specification, HSP, the distance between HSPs and each component (polar term δ _P , hydrogen bonding term δ _H , dispersion term δ _D ) are “(MPa) ^1/2 ” unless otherwise defined. It is displayed based on the unit represented by .

In the formula, δD _(binder) is the dispersion term of the binder for the active material layer, δD _(solvent) is the dispersion term of the organic solvent, δP _(binder) is the polarity term of the binder for the active material layer, δ _{P (solvent)} indicates the polar term of the organic solvent, δ _{H (binder)} indicates the hydrogen bonding term of the active material layer binder, and δ _{H (solvent)} indicates the hydrogen bonding term of the organic solvent.

Although the upper limit of the first HSP distance is not particularly limited, it falls within a numerical value of 30 (MPa) ^1/2 or less in general solvents.

When a plurality of organic solvents are mixed, the HSP of the mixed solvent is calculated from the HSP of each organic solvent and the volume mixing ratio, and the distance between that HSP and the HSP of the active material layer binder (first HSP distance) should be 8.0 (MPa) ^1/2 or more. The HSP of the mixed solvent is obtained by weighting one point of each solvent arranged on the three-dimensional space of the HSP by the respective volume mixing ratio and calculating the center of gravity.

Furthermore, when the active material layer contains a plurality of types of active material layer binders, the organic solvent is 45% by mass or more of the active material layer binder with respect to the total mass of the active material layer binder, It is necessary to satisfy the first HSP distance relationship described above. The organic solvent is preferably 50 mass % or more, more preferably 70 mass % or more and 100 mass % or less of the active material layer binder with respect to the total mass of the active material layer binder in the active material layer; Satisfies the first HSP distance above. Furthermore, it is preferable that all types of active material layer binders in the active material layer satisfy the above first HSP distance relationship. This makes it possible to more reliably prevent swelling of the active material layer.

In addition, the distance between the Hansen solubility parameter of the active material and the Hansen solubility parameter of the organic solvent in the active material layer (hereinafter also referred to as "second HSP distance") is 5.0 (MPa) ^1/2 or more. is preferred.

The active material in the active material layer is mainly bound by the active material layer binder. It can contribute to maintaining the layer thickness.

When the second HSP distance satisfies the above relationship between the active material and the organic solvent, interaction with the active material surface, penetration of the active material and the active material layer binder into the adhesive interface, and Permeation of the organic solvent into the internal voids is suppressed.

As a result, the frictional force between the active materials is reduced, the peeling of the interface between the active material and the active material layer binder is suppressed, and the increase in the layer thickness of the active material layer is further reduced.

The upper limit of the second HSP distance is not particularly limited, but it falls within a numerical value of 20 (MPa) ^1/2 or less in general solvents other than water. Moreover, the second HSP distance is more preferably 8.0 (MPa) ^1/2 or more, thereby further suppressing an increase in the layer thickness of the active material layer.

The second HSP distance is calculated in the same manner as the first HSP distance described above, except that the Hansen solubility parameter of the active material layer binder is replaced with the Hansen solubility parameter of the active material. Further, even when a plurality of organic solvents are mixed in the composition for forming a porous insulating layer, the first HSP except that the Hansen solubility parameter of the active material layer binder is replaced with the Hansen solubility parameter of the active material A second HSP distance can be calculated in the same manner as the distance.

In addition, when the active material layer contains a plurality of types of active materials, the organic solvent is preferably 45% by mass or more, more preferably 50% by mass or more, and still more preferably 70% by mass with respect to the total mass of the active materials. The above second HSP distance is satisfied with an active material of 100 mass % or less. Furthermore, it is preferable that all types of active materials in the active material layer satisfy the second HSP distance relationship. This makes it possible to more reliably prevent swelling of the active material layer.

HSPs of various solvents can be used as a database on software such as Hansen Solubility Parameter in Practice 4th Edition.

The HSP of the active material layer binder is determined as follows. The active material layer binder (in a dried solid state) is immersed in a solvent known for HSP, and the degree of weight swelling with respect to each solvent is measured. Solvents used here include dimethyl sulfoxide, acetonitrile, dimethylformamide, methanol, ethanol, 1-butanol, 1,4-dioxane, tetrahydrofuran, toluene, methyl ethyl ketone, acetone, N-methyl-2-pyrrolidone (NMP), n-hexane, cyclohexane, methyl isobutyl ketone, n-butyl acetate, chloroform, methyl acetate, pyridine, hexafluoroisopropanol, diethylene glycol, γ-butyrolactone, 2-aminoethanol, cyclohexanone, 1,1,2,2-tetrabromoethane , 1-bromonaphthalene, aniline, etc., a wide selection of hydrophilic and hydrophobic solvents. Solvents with a degree of swelling of 3.0 or more by weight are classified as "swelling solvents", and solvents with a degree of swelling of less than 3.0 are classified as "non-swelling solvents". For each point of the solvent used in the test placed on the HSP three-dimensional space, the point of the solvent classified as "swelling solvent" is included and the point of the solvent classified as "non-swelling solvent" is included. Calculate no spheres. The central coordinate of the sphere when the radius of this sphere is maximized is defined as the HSP of the binder for the active material layer. If it is difficult to experimentally determine the HSP of the binder for the active material layer, the HSP may be obtained based on literature values.

The HSP of the active material may be obtained experimentally, but if it is difficult, the HSP may be obtained based on literature values. In addition, when it is difficult to obtain the literature value for HSP of a specific active material, the literature value for a compound corresponding to the same active material can be substituted. For example, HSPs may be obtained based on literature values for graphene as described in Langmuir 2008;24;10560-4. According to the literature, the dispersion term _δD of graphene is 18.0 (MPa) ^1/2 , the polar term _δP of graphene is 9.3 (MPa) ^1/2 , and the hydrogen bond term _δH of graphene is 7.0 (MPa) 1/2 . 7 (MPa) ^1/2 . Therefore, the organic solvent preferably has an HSP distance Ra of 5.0 (MPa) ^1/2 or more, more preferably 8.0 (MPa) ^1/2 or more, as shown in the following formula (I). This further reduces the increase in the layer thickness of the active material layer.

In formula (I), δ _{D (solvent)} represents the dispersion term of the organic solvent, δ _{P (solvent)} represents the polar term of the organic solvent, and δ _{H (solvent)} represents the hydrogen bonding term of the organic solvent.

Such an organic solvent is not particularly limited as long as it satisfies the above HSP relationship, particularly the first HSP distance relationship. For example, various known organic solvents such as glycol alkyl ether-based compounds and alcohol-based compounds can be used. These organic solvents easily satisfy the relationship between the general active material layer binder of the active material layer and the above first HSP distance, and the dispersibility of the insulating inorganic particles and the active material layer binder described later. is preferably used from the viewpoint of the solubility of Alcohol-based compounds are particularly preferable from the viewpoint of simultaneously increasing the first HSP distance and the second HSP distance. In addition, an organic solvent may be used individually by 1 type, and may be used in mixture of 2 or more types.

Examples of the alcohol-based compound include linear or branched lower alkyl alcohols or aliphatic alcohols having 3 to 10 carbon atoms, preferably 4 to 8 carbon atoms, and unsubstituted or substituted with an alkoxy group. Specific examples of such alcohol compounds include 2-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 2-methyl-1-pentanol, 2 -ethyl-1-pentanol, 2-methyl-1-hexanol, 2-ethyl-1-hexanol, 2-methyl-1-heptanol, 2-ethyl-1-heptanol, 2-propyl-1-heptanol , 1-methoxy-2-propanol, 3-methoxy-3-methyl-1-butanol, 3-ethoxy-3-methyl-1-butanol, 3-methoxy-3-methyl-1-pentanol, 3-ethoxy- 3-methyl-1-pentanol, 1-nonanol, 1-decanol and the like. When the alcohol compound is substituted with an alkoxy group, the number of carbon atoms in the alkoxy group is not particularly limited, but is, for example, 1 to 4, preferably 1 to 3, more preferably 1 or 2.

Note that the alcohol-based compound may be a monohydric alcohol or a polyhydric alcohol. However, the alcoholic compound is preferably a monohydric alcohol. This further suppresses an increase in the layer thickness of the active material layer.

Among those mentioned above, preferred alcoholic compounds are 1-butanol, 1-hexanol, 2-ethyl-1-hexanol, and 3-methoxy-3-methyl-1-butanol. Particularly preferred alcoholic compounds are 2-ethyl-1-hexanol and 3-methoxy-3-methyl-1-butanol. 3-Methoxy-3-methyl-1-butanol is the most preferable alcoholic compound because of its low odor and toxicity.

Glycol alkyl ether compounds include, for example, ethylene glycol monomethyl ether, monoalkylene glycol monoalkyl ethers such as ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, dialkylene glycol monoalkyl ether such as diethylene glycol monoethyl ether, trialkylene glycol monoalkyl such as triethylene glycol monomethyl ether, triethylene glycol monoethyl ether Ethers and other alkylene glycol monoalkyl ethers having a degree of polymerization of 3 or more can be mentioned. The number of carbon atoms in the alkoxy group in the glycol alkyl ether compound is not particularly limited, but is, for example, 1 or more and 4 or less, preferably 1 or more and 3 or less, more preferably 1 or 2.

Also, the glycol alkyl ether compound preferably has an ethylene glycol skeleton. Particularly preferred glycol alkyl ether compounds are triethylene glycol monomethyl ether, diethylene glycol monomethyl ether, and ethylene glycol monoethyl ether.

The boiling point of the organic solvent is preferably 100°C or higher, more preferably 130°C or higher and 250°C or lower. This prevents volatilization of the solvent during the formation of the porous insulating layer and a change in viscosity associated therewith, so that the porous insulating layer can be formed with a uniform thickness.

Moreover, the solvent may contain water. Water has excellent solubility of the active material layer binder in the active agent layer, and is suitable for dissolving and dispersing each material of the composition for forming a porous insulating layer. The content of water in the solvent is, for example, 70% by mass or less, preferably 50% by mass or less, relative to the solvent.

The content of the solvent in the composition for forming a porous insulating layer is not particularly limited, and can be appropriately selected according to production conditions. It is 45% by mass or less.

(1.2 Insulating inorganic particles)
Moreover, the composition for forming a porous insulating layer contains insulating inorganic particles. The insulating inorganic particles are the main component in the solid content of the composition for forming a porous insulating layer. The insulating inorganic particles ensure insulation between the separator and the active material layer and prevent unwanted internal short circuits.

_Such insulating _inorganic particles _{are not} particularly limited _. Nitride particles such as aluminum nitride and silicon nitride, refractory ion crystal particles such as calcium fluoride, barium fluoride, and barium sulfate, covalent crystal particles such as silicon and diamond, clay particles such as montmorillonite, boehmite, and zeolite. , apatite, kaolin, mullite, spinel, olivine, and other mineral resource-derived substances or artificial products thereof.

In addition, the surfaces of conductive particles such as metal particles, oxide particles such as SnO ₂ and tin-indium oxide (ITO), and carbonaceous particles such as carbon black and graphite are surface-treated with an electrically insulating material. Thus, the fine particles may be electrically insulating.

The average particle diameter of the insulating inorganic particles is not particularly limited, but is, for example, 0.01 μm or more and 5 μm or less, preferably 0.1 μm or more and 1 μm or less. In the present specification, the average particle size indicates the volume-based frequency cumulative D50 particle size, which can be measured by a laser diffraction/scattering particle size distribution analyzer.
The content of the insulating inorganic particles in the composition for forming a porous insulating layer is, for example, 20% by mass or more and 98% by mass or less, preferably 30% by mass, based on the solid content in the composition for forming a porous insulating layer. It is more than mass % and below 95 mass %.

(1.3 Binder)
The composition for forming a porous insulating layer contains a binder.

The binder contains, as structural units, 30% by mass or more and 60% by mass or less of an aromatic vinyl compound, 20% by mass or more and 69% by mass or less of a (meth)acrylic acid ester, and a hydroxyl group, based on the total mass of the binder. Alternatively, it is a polymer containing from 5% by mass to 35% by mass of (meth)acrylic ester containing an ether group and from 1% by mass to 10% by mass of a vinyl compound having an acidic functional group.

Examples of aromatic vinyl compounds include styrene, p-methylstyrene, m-methylstyrene, o-methylstyrene, ot-butylstyrene, mt-butylstyrene, pt-butylstyrene, p-chlorostyrene, and o-chlorostyrene. Among these, styrene is preferred.

(Meth)acrylate esters include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isopropyl (meth)acrylate, octyl (meth)acrylate, and (meth)acrylic acid 2 - Ethylhexyl, isobutyl (meth)acrylate, pentyl (meth)acrylate, n-hexyl (meth)acrylate, isoamyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, (meth)acrylate and isobornyl acrylate.

Examples of (meth)acrylic acid esters containing a hydroxyl group include 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 2-hydroxy(meth)acrylate. -3-phenoxypropyl, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid and the like.

Examples of (meth)acrylic acid esters containing an ether group include ethoxy (meth)acrylate-diethylene glycol, methoxy-triethylene glycol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenoxy (meth)acrylate- polyethylene glycol, phenoxydiethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, glycidyl (meth)acrylate and the like.

Examples of vinyl compounds containing acidic functional groups include acrylic acid, methacrylic acid, itaconic acid, maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-methacryloyloxyethyl acid phosphate.

The binding mode of the polymer, copolymer, and macromolecules that can be contained in the binder is not particularly limited, and the macromolecules are random copolymers, alternating copolymers, periodic copolymers, and block copolymers. Alternatively, it may be a graft copolymer.
The weight average molecular weight of the polymer, copolymer, and polymer that can be contained in the binder is not particularly limited, and is, for example, 50,000 or more and 2,000,000 or less, preferably 100,000 or more and 1,000,000. It is below. The weight average molecular weight can be measured by gel permeation chromatography using polyethylene oxide (PEO) as a standard substance.

The content of the aromatic vinyl compound in the binder is 30% by mass or more and 60% by mass or less, preferably 35% by mass or more and 55% by mass or less, and more preferably It is 40 mass % or more and 50 mass % or less.
If the content of the aromatic vinyl compound is at least the above lower limit, the strength against deformation of the binder is ensured. Flexibility with suppressed cracking against is ensured.

The content of the (meth)acrylic acid ester in the binder is 20% by mass or more and 69% by mass or less, preferably 40% by mass or more and 60% by mass or less, relative to the total mass of the binder. It is preferably 45% by mass or more and 55% by mass or less.
If the content of the (meth)acrylic acid ester is at least the above lower limit, the binding function as a binder can be expressed, and if the content of the (meth)acrylic acid ester is below the above upper limit, If there is, the strength can be maintained in the non-aqueous electrolyte secondary battery without dissolving in the non-aqueous solvent that dissolves the non-aqueous electrolyte and causing excessive swelling.

The content of the (meth)acrylic acid ester containing a hydroxyl group or an ether group in the binder is 5% by mass or more and 35% by mass or less, preferably 10% by mass or more and 30% by mass, based on the total mass of the binder. % by mass or less, more preferably 15% by mass or more and 25% by mass or less.
If the content of the (meth)acrylic acid ester containing a hydroxyl group or an ether group is at least the above lower limit, the solubility in an organic solvent in the composition for forming a porous insulating layer is ensured, and the hydroxyl group or ether group If the content of the (meth) acrylic acid ester containing strength can be maintained within

The content of the acidic functional group-containing vinyl compound is 1% by mass or more and 10% by mass or less, preferably 3% by mass or more and 8% by mass or less, relative to the total mass of the binder. If the content of the acidic functional group-containing vinyl compound is within the above range, good binding strength can be exhibited when the composition for forming a porous insulating layer is applied to an electrode. If the content of the acidic functional group-containing vinyl compound is below the above lower limit or above the above upper limit, the binding strength is lowered in any case.

The content of the binder in the composition for forming a porous insulating layer is, for example, 2% by mass or more and 10% by mass or less, preferably 3% by mass, based on the solid content in the composition for forming a porous insulating layer. It is more than 7 mass % or less.

(1.4 Polyolefin polymer particles)
The composition for forming a porous insulating layer may also contain polyolefin polymer particles. Since the polyolefin polymer particles have a relatively low melting point, they melt when the non-aqueous electrolyte secondary battery is abnormally heated, blocking the movement of lithium ions. This further improves the safety performance of the non-aqueous electrolyte secondary battery.

Examples of polyolefin polymer particles include polyethylene polymer particles and polypropylene polymer particles.

The average particle size of the polyolefin polymer particles is not particularly limited, but is, for example, 0.5 μm or more and 6 μm or less. A porous insulating layer is generally formed as a relatively thin (for example, 4 μm or less) thin film. Therefore, it is required that the average particle size of the polyolefin polymer particles is also relatively small. However, depending on the production method of the polyolefin-based polymer particles, there are particles that are not spherical but flat. In such cases, it is also possible to form a porous insulating layer with a film thickness thinner than the average particle diameter measured by a particle size distribution meter. It is possible. Polyolefin-based polymer particles are relatively difficult to disperse when the particle size is small, but contain the above-mentioned aromatic vinyl compound, (meth)acrylic acid ester, and (meth)acrylic acid ester containing a hydroxyl group or an ether group. It is possible to uniformly disperse in the porous insulating layer by using a polymer that has a high molecular weight as the binder for the active material layer.

Moreover, the content of the polyolefin polymer particles in the composition for forming a porous insulating layer is, for example, 20% by mass or more and 80% by mass or less with respect to the solid content in the composition for forming a porous insulating layer.

In the composition for forming a porous insulating layer according to the present embodiment described above, the Hansen solubility parameter of the active material layer binder of the active material layer has a distance of 8.0 (MPa) ^1/2 or more, An organic solvent with a Hansen solubility parameter having a distance of 5.0 (MPa) ^1/2 or more from the Hansen solubility parameter of the active material of the active material layer is used. Based on the total mass of the binder, 30% by mass or more and 60% by mass or less of an aromatic vinyl compound, 20% by mass or more and 69% by mass or less of a (meth)acrylic acid ester, and a (meth) containing a hydroxyl group or an ether group A polymer containing 5% to 35% by mass of acrylic acid ester and 1% to 10% by mass of a vinyl compound having an acidic functional group is employed. Therefore, even when the composition for forming a porous insulating layer is applied onto the active material layer, swelling of the active material layer is suppressed.

<2. Configuration of Nonaqueous Electrolyte Secondary Battery>
A specific configuration of the above-described non-aqueous electrolyte secondary battery 10 according to one embodiment of the present invention will be described below with reference to FIG. FIG. 1 is an explanatory diagram illustrating the configuration of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. The non-aqueous electrolyte secondary battery 10 also has a negative electrode 30 as an electrode for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

A non-aqueous electrolyte secondary battery 10 shown in FIG. 1 is an example of a secondary battery according to the present embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes a positive electrode 20 , a negative electrode 30 and a separator layer 40 . The shape of the non-aqueous electrolyte secondary battery 10 is not particularly limited, but may be, for example, cylindrical, prismatic, laminate, button, or the like.

The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22 arranged on the main surface of the current collector 21 . The current collector 21 may be any conductor, such as aluminum (Al), stainless steel, and nickel-plated steel.

In this specification, the term "principal surface" refers to a surface of a thin plate whose area is much larger than that of other surfaces. For example, in the current collector 21, the main surface means the front surface and the back surface of the foil-shaped current collector 21, and does not mean an end surface, a side surface, or the like.

The positive electrode active material layer 22 contains at least a positive electrode active material and a positive electrode active material layer binder, and may further contain a conductive agent. The contents of the positive electrode active material, the conductive agent, and the positive electrode active material layer binder are not particularly limited, and any content applicable to conventional non-aqueous electrolyte secondary batteries can be used. good.

The positive electrode active material is, for example, a transition metal oxide or solid solution oxide containing lithium, and is not particularly limited as long as it is a material capable of electrochemically intercalating and deintercalating lithium ions. Examples of transition metal oxides containing lithium include Li.Co-based composite oxides such as _LiCoO2 , _{Li.Ni.Co.Mn -} based composite oxides _such as _{LiNixCoyMnzO2} , and _Li.Co. Examples include Ni-based composite oxides and Li/Mn-based composite oxides such as LiMn ₂ O ₄ . Solid solution oxides include _{LiaMnxCoyNizO2 (} 1.150≤a≤1.430 _, 0.45≤x≤0.6, 0.10≤y≤0.15 _{, 0.20} ≦z≦0.28), LiMn _1.5 Ni _0.5 O ₄ and the like. The content (content ratio) of the positive electrode active material is not particularly limited as long as it is applicable to the positive electrode active material layer of the non-aqueous electrolyte secondary battery. Also, these compounds may be used singly or in combination.

Examples of conductive agents include carbon black such as ketjen black and acetylene black, natural graphite, artificial graphite, carbon nanotubes, graphene, and carbon nanofibers. fibrous carbon such as (carbon nanofibers), or a composite of these fibrous carbon and carbon black. However, the conductive agent can be used without particular limitation as long as it is for increasing the conductivity of the positive electrode. The content of the conductive agent is not particularly limited as long as it is applicable to the positive electrode active material layer of the non-aqueous electrolyte secondary battery.

Examples of the positive electrode active material layer binder include fluorine-containing resins such as polyvinylidene difluoride, styrene-containing resins such as styrene-butadiene rubber, and ethylene-propylene-diene terpolymers. propylene-diene terpolymer), acrylonitrile-butadiene rubber, fluoroelastomer, polyvinyl acetate, polymethylmethacrylate, polyethylene ( polyethylene), polyvinyl alcohol, carboxy Examples include carboxymethylcellulose, derivatives thereof (carboxymethylcelluloses (eg, salts of carboxymethylcellulose)), nitrocellulose, and the like. However, the positive electrode active material layer binder is capable of binding the positive electrode active material and the conductive agent onto the current collector 21, and has oxidation resistance and electrolyte solution stability that can withstand the high potential of the positive electrode. If there is, it is not particularly limited. Also, the content of the positive electrode active material layer binder is not particularly limited as long as it is applicable to the positive electrode active material layer of the non-aqueous electrolyte secondary battery.

The positive electrode active material layer 22 is formed by dissolving, for example, a positive electrode active material, a conductive agent, and a positive electrode active material layer binder in an appropriate organic solvent (eg, N-methyl-2-pyrrolidone, etc.). It can be formed by dispersing to form a positive electrode slurry, coating the positive electrode slurry on the current collector 21, drying and rolling it, and forming the positive electrode active material layer 22 after rolling. is not particularly limited as long as the density is applicable to the positive electrode active material layer of the non-aqueous electrolyte secondary battery.

The negative electrode 30 is an example of a secondary battery negative electrode according to this embodiment. The negative electrode 30 has a foil-shaped current collector 31 , a negative electrode active material layer 32 arranged in contact with the current collector 31 , and a porous insulating layer 33 arranged on the negative electrode active material layer 32 .

The current collector 31 is not particularly limited, and can be made of, for example, copper, aluminum, iron, nickel, stainless steel, alloys thereof, or plated steel thereof, such as nickel-plated steel. The current collector 31 is preferably made of copper, nickel, or alloys thereof.

The negative electrode active material layer 32 is arranged in contact with the current collector 31 , more specifically, such that one main surface thereof is adhered onto the current collector 31 . The negative electrode active material layer 32 contains at least a negative electrode active material. In the present embodiment, the negative electrode active material layer 32 includes a negative electrode active material and a negative electrode active material layer binder.

The negative electrode active material is not particularly limited as long as it is a material that can electrochemically occlude and release lithium ions. natural graphite coated with artificial graphite, etc.), Si-based active materials or Sn-based active materials (for example, fine particles of silicon (Si) or tin (Sn) or their oxides, alloys based on silicon or tin), metals Titanium oxide-based compounds such as lithium and Li ₄ Ti ₅ O ₁₂ and the like are included. At least one of the above materials can be used as the negative electrode active material. Silicon oxide is represented by SiO _x (0≦x≦2).

The content of the negative electrode active material in the negative electrode active material layer 32 is not particularly limited. It is 90% by mass or more and 99% by mass or less.

As the negative electrode active material layer binder, the same binder as the positive electrode active material layer binder that constitutes the positive electrode active material layer 22 can be used. Among the above, it is preferable to include at least one binder selected from the group consisting of styrene-containing resins, fluorine-containing resins, polyethylene, polyvinyl alcohol and carboxymethylcelluloses. Styrene-butadiene rubber is preferable as the styrene-containing resin, and polyvinylidene fluoride is preferable as the fluorine-containing resin. Carboxymethylcelluloses include carboxymethylcellulose and carboxymethylcellulose derivatives such as carboxymethylcellulose salts. Examples of carboxymethylcellulose salts include salts of carboxymethylcellulose and alkali metal ions, more specifically sodium carboxymethylcellulose, potassium carboxymethylcellulose, and lithium carboxymethylcellulose.

The content of the negative electrode active material layer binder in the negative electrode active material layer 32 is not particularly limited. , more preferably 1% by mass or more and 10% by mass or less.

The negative electrode active material layer 32 is formed by, for example, dispersing the above-described negative electrode active material and the negative electrode active material layer binder in an appropriate solvent (for example, water) to form a negative electrode slurry. It can be formed by coating on top, drying, and rolling. The thickness of the negative electrode active material layer 32 after rolling is not particularly limited as long as it is applicable to the negative electrode active material layer of a lithium ion secondary battery. Also, the negative electrode active material layer 32 may be formed by selectively including a graphite active material.

The negative electrode active material layer 32 is not limited to the method described above, and can be formed by physical vapor deposition such as thermal vapor deposition, ion plating, sputtering, or chemical vapor deposition (CVD).

The porous insulating layer 33 is formed on the negative electrode active material layer 32 so as to be arranged between the negative electrode 30 and the separator layer 40 . The porous insulating layer 33 prevents unwanted internal short circuits in the non-aqueous electrolyte secondary battery 10 . In the present embodiment, the porous insulating layer 33 is formed by applying the porous insulating layer-forming composition described above and drying it. Thus, the porous insulating layer contains, for example, insulating inorganic particles, a binder, and optionally polyolefinic polymer particles. The configurations relating to the insulating inorganic particles, the binder, and the polyolefin polymer particles are as described above.

Separator layer 40 typically includes a separator and an electrolyte. The separator is not particularly limited, and any separator can be used as long as it is used as a separator for lithium ion secondary batteries. As the separator, it is preferable to use a porous film, a non-woven fabric, or the like, which exhibits excellent high-rate discharge performance, alone or in combination. Also, the separator may be coated with an inorganic material such as Al ₂ O ₃ , Mg(OH) ₂ , SiO ₂ or the like, and may contain the above inorganic material as a filler.

Examples of materials constituting such a separator include polyolefin resins such as polyethylene and polypropylene, polyethylene terephthalate, and polybutylene terephthalate. Representative polyester resins, polyvinylidene difluoride, vinylidene difluoride-hexafluoropropylene copolymer, and vinylidene fluoride-perfluorovinyl ether copolymer. ifluoride- perfluoroninylether copolymer, vinylidene difluoride-tetrafluoroethylene copolymer, vinylidene difluoride-trifluoroethylene copolymer polymer), vinylidene fluoride-fluoroethylene copolymer ( vinylidene difluoride-fluoroethylene copolymer), vinylidene fluoride-hexafluoroacetone copolymer (vinylidene difluoride-hexafluoroacetone copolymer), vinylidene fluoride-ethylene copolymer (vinylidene difluoride- ethylene copolymer), vinylidene fluoride-propylene copolymer ( vinylidene difluoride-propylene copolymer, vinylidene difluoride-trifluoropropylene copolymer, vinylidene difluoride-tetrafluoroethylene-hexafluoropropylene copolymer de-tetrafluoroethylene copolymer), fluorinated A vinylidene difluoride-ethylene-tetrafluoroethylene copolymer and the like can be used. The porosity of the separator is not particularly limited, and any porosity of a conventional lithium ion secondary battery separator can be applied.

The electrolytic solution contains an electrolyte salt and a solvent.

An electrolyte salt is an electrolyte such as a lithium salt. The electrolyte salt is, for example, _LiClO4 , _LiBF4 , LiAsF6, _LiPF6 , LiSCN, LiBr, _LiI , _Li2SO4 , _Li2B10Cl10 , _NaClO4 , NaI, _NaSCN , NaBr, _{KClO4 , KSCN} , etc. inorganic ion salt containing one of lithium (Li), sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN ( _{CF3SO2 )} ( _{C4F9SO2 )} , LiC( _{CF3SO2 ) 3 ,} LiC( _{C2F5SO2 ) 3} , ( _CH3 ) _{4NBF4 ,} ( _{CH3 ) 4NBr} , (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C ₄ H ₉ ) ₄ NI , (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, lithium stearylsulfate, lithium octylsulfate ), an organic ion salt such as lithium dodecylbenzenesulpgonate, and the like can be used. These electrolyte salts may be used alone or in combination of two or more. Also, the concentration of the electrolyte salt is not particularly limited, but for example, a concentration of about 0.5 mol/L or more and 2.0 mol/L or less can be used.

The solvent is a non-aqueous solvent that dissolves the electrolyte salt. Solvents include, for example, cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; gamma-butyrolactone cyclic esters such as (γ-butyrolactone), γ-valerolactone (γ-valerolactone), chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, formic acid Chain esters such as methylformate, methylacetate, methylbutyrate, propyl acetate, ethyl propionate, propyl propionate, tetrahydrofuran uran) or derivatives thereof, 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxy Ethers such as 1,4-dibutoxyethane or methyldiglyme, nitriles such as acetonitrile and benzonitrile, dioxolane or its derivatives, ethylene sulfide , sulfolane, sultone or derivatives thereof and the like can be used alone or in combination of two or more thereof. When two or more solvents are mixed and used, the mixing ratio of each solvent can be the mixing ratio used in conventional lithium-ion secondary batteries.

Various additives such as a negative electrode SEI (Solid Electrolyte Interface) forming agent and a surfactant may be added to the electrolytic solution.

Such additives include, for example, succinic anhydride, lithium bis(oxalate) borate, lithium tetrafluoroborate, dinitrile compounds, propane PROPANE SULTONE (PROPANE SULTONE), Butanston, Propenseton (Propene Sultone), 3 -Sulfolene, Fluorinated AllyletheD AryletheD AryletheD AryletheD AllyletheD. To use ER), fluorinated methacrylate, etc. can. Moreover, as the content concentration of such an additive, the content concentration of the additive in a general lithium-ion secondary battery can be used.

In the non-aqueous electrolyte secondary battery 10 according to the present embodiment described above, the porous insulating layer-forming composition according to the present embodiment is used to form the porous insulating layer 33 when the negative electrode 30 is manufactured. Therefore, an unwanted increase in the layer thickness of the negative electrode active material layer 32 is suppressed.

In the above description, the negative electrode 30 is provided with the porous insulating layer 33, but the present invention is not limited to the illustrated embodiment. For example, positive electrode 20 may comprise a porous insulating layer. Also in this case, an increase in the layer thickness of the positive electrode active material layer 22 of the positive electrode 20 is suppressed. Further, in this case, the negative electrode 30 may not have a porous insulating layer.

<3. Method for manufacturing non-aqueous electrolyte secondary battery>
Next, a method for manufacturing the non-aqueous electrolyte secondary battery 10 will be described. In the method for manufacturing the non-aqueous electrolyte secondary battery 10 according to the present embodiment, a porous insulating layer is formed on an active material layer arranged on the main surface of a current collector using a porous insulating layer-forming composition. have a step of However, the manufacturing method of the non-aqueous electrolyte secondary battery 10 is not limited to the following method, and any manufacturing method can be applied.

The positive electrode 20 is manufactured as follows. First, a mixture of a positive electrode active material, a conductive agent, and a positive electrode active material layer binder in a desired ratio is dispersed in an organic solvent (eg, N-methyl-2-pyrrolidone) to form a positive electrode slurry. Next, the cathode active material layer 22 is formed by forming (for example, coating) the cathode slurry on the current collector 21 and drying it.

Although the coating method is not particularly limited, for example, a knife coater method, a gravure coater method, a reverse roll coater, a slit die coater, etc. may be used. The following coating steps are also carried out in the same manner.

Further, the positive electrode active material layer 22 is compressed to a desired thickness using a compressor. Thereby, the positive electrode 20 is manufactured. Here, the thickness of the positive electrode active material layer 22 is not particularly limited as long as it has the thickness of the positive electrode active material layer of a conventional non-aqueous electrolyte secondary battery.

Anode 30 is also manufactured in the same manner as cathode 20 . First, a negative electrode slurry is formed by dispersing a mixture of a negative electrode active material and a negative electrode active material layer binder at a desired ratio in a solvent (for example, water). A graphite active material may be optionally mixed in the negative electrode slurry.

Next, the negative electrode slurry is formed (for example, coated) on the current collector 31 and dried to form the negative electrode active material layer 32 . Further, the negative electrode active material layer 32 is compressed to a desired thickness using a compressor. Here, the thickness of the negative electrode active material layer 32 is not particularly limited as long as it has the thickness of the negative electrode active material layer of a conventional non-aqueous electrolyte secondary battery.

After that, the porous insulating layer 33 is formed using the composition for forming a porous insulating layer. Specifically, the porous insulating layer 33 is formed by applying a composition for forming a porous insulating layer onto the negative electrode active material layer 32 and drying the composition. Thus, the negative electrode 30 is manufactured.

In addition, since the porous insulating layer 33 is formed using the porous insulating layer-forming composition according to the present embodiment, the negative electrode active material layer 32 is Swelling is suppressed. As a result, an unwanted increase in the thickness of the negative electrode 30 is prevented.

Subsequently, the electrode structure is manufactured by sandwiching the separator 40 between the positive electrode 20 and the negative electrode 30 . Next, the manufactured electrode structure is processed into a desired shape (for example, cylindrical, rectangular, laminated, button-shaped, etc.) and inserted into a container having the desired shape. Further, by injecting a desired electrolytic solution into the container, each pore in the separator 40 is impregnated with the electrolytic solution. Thereby, the non-aqueous electrolyte secondary battery 10 is manufactured.

Although the porous insulating layer 33 is formed on the negative electrode active material layer 32 in the above description, the present invention is not limited to the embodiment described above. For example, a porous insulating layer may be formed on the positive electrode active material layer 22 using a composition for forming a porous insulating layer. In this case, it is not necessary to form a porous insulating layer on the negative electrode active material layer 32 .

Hereinafter, the present invention will be described in more detail based on specific examples. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

(Synthesis of binder)
<Synthesis of Binder 1>
22.0 g of styrene, 4.0 g of 2-ethylhexyl acrylate, 12.0 g of methoxyethyl acrylate, 2.0 g of methacrylic acid, 0.8 g of sodium dodecylbenzenesulfonate, ion After 115 g of exchanged water was charged and stirred, the inside of the system was replaced with nitrogen, and the temperature inside the system was raised to 70° C. while stirring at 600 rpm. After the temperature in the system reached 70° C., an aqueous solution prepared by dissolving 0.27 g of potassium persulfate in 5.0 g of ion-exchanged water was added and reacted for 12 hours. The non-volatile content of the aqueous dispersion after the reaction was measured and found to be 25.0% by mass (conversion rate 100%). After that, 200 mL of ethanol was added to a liquid obtained by concentrating the reaction liquid to a non-volatile content of 40% by mass by distillation under reduced pressure with heating, thereby precipitating and separating a solid matter. This solid was collected, washed twice with 100 mL of ethanol, and dried under reduced pressure at 80° C. for 10 hours. A colorless and transparent copolymer solution was obtained. Solids content was 8%.

<Synthesis of Binder 2>
In the synthesis of Binder 1, the composition in the reaction system was changed. A colorless transparent copolymer was prepared in the same manner as in the synthesis of Binder 1, except that 14.0 g of styrene, 20.0 g of 2-ethylhexyl acrylate, 4.0 g of methoxyethyl acrylate, and 2.0 g of methacrylic acid were added in order. A solution was obtained. Solids content was 8%.

<Synthesis of Binder 3>
In the synthesis of Binder 1, the composition in the reaction system was changed. A colorless transparent copolymer was prepared in the same manner as in the synthesis of Binder 1, except that 18.0 g of styrene, 12.0 g of 2-ethylhexyl acrylate, 8.0 g of methoxyethyl acrylate, and 2.0 g of methacrylic acid were added in order. A solution was obtained. Solids content was 8%.

<Synthesis of Binder 4>
In the synthesis of Binder 1, the composition in the reaction system was changed. A colorless transparent copolymer was prepared in the same manner as in the synthesis of Binder 1, except that 18.8 g of styrene, 12.0 g of 2-ethylhexyl acrylate, 8.0 g of methoxyethyl acrylate, and 1.2 g of methacrylic acid were added in order. A solution was obtained. Solids content was 8%.

<Synthesis of Binder 5>
In the synthesis of Binder 1, the composition in the reaction system was changed. A colorless transparent copolymer was prepared in the same manner as in the synthesis of Binder 1 except that 16.8 g of styrene, 12.0 g of 2-ethylhexyl acrylate, 8.0 g of methoxyethyl acrylate and 3.2 g of methacrylic acid were added in order. A solution was obtained. Solids content was 8%.

<Synthesis of Binder 6>
In the synthesis of Binder 1, the composition in the reaction system was changed. A colorless and transparent copolymer solution was obtained in the same manner as in the synthesis of Binder 1 except that 20.0 g of styrene, 12.0 g of 2-ethylhexyl acrylate and 8.0 g of methoxyethyl acrylate were added in order. Solids content was 8%.

<Synthesis of Binder 7>
In the synthesis of Binder 1, the composition in the reaction system was changed. A cloudy copolymer solution was obtained in the same manner as in the synthesis of Binder 1 except that 26.0 g of styrene, 12.0 g of 2-ethylhexyl acrylate and 2.0 g of methacrylic acid were added in order. Solids content was 8%.

<Synthesis of Binder 8>
In the synthesis of Binder 1, the composition in the reaction system was changed. A colorless transparent copolymer was prepared in the same manner as in the synthesis of Binder 1 except that 10.0 g of styrene, 12.0 g of 2-ethylhexyl acrylate, 16.0 g of methoxyethyl acrylate and 2.0 g of methacrylic acid were added in order. A solution was obtained. Solids content was 8%.

<Preparation of Binder 9>
A vinyl butyral-vinyl alcohol-vinyl acetate (mass ratio of 80/18/2) copolymer powder having a weight average molecular weight of 70,000 or more and 100,000 or less (manufactured by Aldrich) was mixed with 3-methoxy-3-methyl-1-butanol. to obtain a copolymer solution having a solid content of 10%.

<Production of Binder 10>
In a 500 mL flask equipped with a stirrer and a thermometer, 70.6 mg of azoisobutyronitrile, 14.0 g of acryloylmorpholine, and 6.0 g of acrylic acid were charged and stirred, followed by 3-methoxy-3-methyl. 180.0 g of -1-butanol and 5.088 g of ethanolamine were added in order. The inside of the system was replaced with nitrogen, and the temperature inside the system was raised to 65° C. while stirring at 600 rpm, and the reaction was carried out for 12 hours. When the non-volatile content of the solution after cooling was measured, it was 9.7% by mass (conversion rate 96%). After that, the residue of the initiator and the unreacted monomer were removed from the solution after the reaction by heating under reduced pressure distillation. After cooling this solution to room temperature, the copolymer solution was obtained by adding ethanolamine and adjusting to pH8. Solids content was 10%.

(Preparation of negative electrode)
Artificial graphite (flaky granules, specific surface area: 1.7 m ² /g, average particle size: 15 µm), carboxymethylcellulose sodium salt, and styrene-butadiene-based aqueous dispersion were mixed at a solid mass ratio of 97.5:1.0:1. A negative electrode mixture slurry was prepared by dissolving and dispersing in a water solvent in step 5. Next, this negative electrode mixture slurry is applied to both sides of a copper foil current collector having a thickness of 10 μm to form a coating film, and after drying the coating film, it is rolled by a roll press, and the copper foil current collector is coated with the slurry. A negative electrode having a negative electrode active material layer was produced. The electrode coating amount was 26 mg/cm ² (converted to both sides), and the electrode density was 1.65 g/cm ³ . Here, the binder in the negative electrode active material layer is styrene-butadiene rubber and carboxymethylcellulose.

(Preparation of composition for forming porous insulating layer)
(Example 1)
Binder 1 and boehmite particles having an average particle diameter (D50) of 0.9 μm were mixed at a solid content mass ratio of 5:45, and 3-methoxy-3-methyl-1-butanol (MMB) was added. In addition, the solid content was adjusted to 40% and dispersed by a bead mill to obtain a dispersion liquid. The particle size of this dispersion was checked with a grind gauge of 50 μm, and the composition in which the absence of aggregates was confirmed was evaluated as “good”, and the composition in which the aggregates did not disappear even after repeated dispersion was evaluated as “with aggregates”. did.

This composition for forming a porous insulating layer was applied on both sides of the negative electrode active material layer (active material layer) of the negative electrode using a wire bar so that the thickness of each side after drying was 3 μm. Drying was performed in an oven at 60°C for 15 minutes. The thickness of the negative electrode active material layer of the obtained porous insulating layer formed negative electrode was measured and compared with the film thickness before forming the porous insulating layer to calculate the amount of increase in film thickness per one side. The thickness of the negative electrode active material layer and the porous insulating layer was measured by scanning electron microscope (SEM) observation after cross-sectional processing of the electrode with a cryocross section polisher, and the average value of the thickness measurements in 10 fields of view was calculated. . This negative electrode was punched out with a Thomson blade, and a nickel lead wire (negative electrode tab) was welded to the end to obtain a negative electrode. After punching with a Thomson blade, if cracks are found at the edges, and if boehmite particles in the porous insulating layer are clearly detached by touching the surface of the porous insulating layer with a finger, it is judged as “peeled”. Those in which no significant detachment was observed were evaluated as "no detachment".

(Preparation of positive electrode)
Lithium nickel-cobalt manganate (nickel/cobalt/manganese=8/1/1 mol ratio), carbon black, and polyvinylidene fluoride (PVDF) are dissolved and dispersed in N-methylpyrrolidone at a solid content mass ratio of 96:2:2. Thus, a positive electrode mixture slurry was produced. Next, the positive electrode mixture slurry was applied to both sides of a 12 μm thick aluminum foil current collector, and then dried. A positive electrode active material layer was produced by rolling the dried coating layer. The electrode coating amount was 42 mg/cm ² (converted to both sides), and the electrode density was 3.6 g/cm ³ . The total thickness of the current collector and the positive electrode active material layer was 120 µm. Then, an aluminum lead wire (positive electrode tab) was welded to the end of the current collector to obtain a positive electrode.

(Preparation of non-aqueous electrolyte secondary battery)
An electrode laminate was produced by laminating the separator, the negative electrode, the separator, and the positive electrode in this order. Next, the electrode laminate and the electrolytic solution were enclosed in a laminate film (packaging material) composed of three layers of polypropylene/aluminum/nylon. Here, each lead wire previously welded to each electrode was led out of the laminate film. The electrolytic solution used was prepared by dissolving 1M LiPF ₆ and 1% by mass of vinylene carbonate in a solvent in which ethylene carbonate/dimethyl carbonate was mixed at a ratio of 3:7 (volume ratio). The resulting secondary battery was fixed by sandwiching it between two SUS plates, and a secondary battery before initial charging was produced in such a manner that the laminate film was not deformed.

Next, the secondary battery before initial charge was subjected to constant current charging to 4.3 V at 1/10 CA of the design capacity (1 CA is 1 hour discharge rate), and then constant voltage charging to 4.30 V to 1/20 CA. . After that, constant current discharge was performed to 2.7 V at 1/2 CA. Through this process, a non-aqueous electrolyte secondary battery was produced. The discharge capacity at this time was taken as the initial discharge capacity.

(High temperature life test)
This non-aqueous electrolyte secondary battery was subjected to 200 cycles of charging at 0.5 CA and discharging at 1 CA at a temperature of 25°C. Then, the capacity retention rate was measured by dividing the discharge capacity after 100 cycles by the initial discharge capacity. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 1 was 88%. Table 1 shows the results.

(Example 2)
A composition for forming a porous insulating layer of Example 2 was prepared in the same manner as in Example 1 except that Binder 1 was changed to Binder 2, and the composition was applied to a negative electrode. Also, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Example 2 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 2 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 2 was 88%. Table 1 shows the results.

(Example 3)
A composition for forming a porous insulating layer of Example 3 was prepared in the same manner as in Example 1 except that Binder 1 was changed to Binder 3, and the composition was applied to a negative electrode. Also, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Example 3 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 3 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 3 was 91%. Table 1 shows the results.

(Example 4)
A composition for forming a porous insulating layer of Example 4 was prepared in the same manner as in Example 1 except that Binder 1 was changed to Binder 4, and the composition was applied to a negative electrode. Further, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Example 4 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 4 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 4 was 90%. Table 1 shows the results.

(Example 5)
A composition for forming a porous insulating layer of Example 5 was prepared in the same manner as in Example 1 except that Binder 1 was changed to Binder 5, and the composition was applied to a negative electrode. Further, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Example 5 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 5 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 5 was 90%. Table 1 shows the results.

(Example 6)
High-density polyethylene wax and 3-methoxy-3-methyl-1-butanol (MMB) were added as polyolefin-based polymer particles to adjust the solid content to 15%, and dispersed in a bead mill to obtain a dispersion. The average particle diameter (D50) was 5.2 μm, and the shape was flattened by an electron microscope. Binder 3 and boehmite particles having an average particle diameter (D50) of 0.9 μm were mixed at a solid content mass ratio of 5:22.5, and 3-methoxy-3-methyl-1-butanol (MMB ) was added to adjust the solid content to 40%, and dispersed in a bead mill to obtain a dispersion liquid. The dispersion was checked for particle size with a 50 μm grind gauge to confirm the absence of aggregates. The porous insulation of Example 4 containing polymer particles and boehmite particles having a solid content of 23% by mixing the polymer particle dispersion and the boehmite particle dispersion at a solid content mass ratio of 22.5:27.5 A layer-forming composition was prepared.
This was applied to the negative electrode in the same manner as in Example 1.
Also, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Example 6 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 6 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Example 6 was 90%. Table 1 shows the results.

(Comparative example 1)
A composition for forming a porous insulating layer of Comparative Example 1 was prepared in the same manner as in Example 1 except that Binder 1 was changed to Binder 9, and the composition was applied to a negative electrode. Also, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Comparative Example 1 was produced. Regarding the non-aqueous electrolyte secondary battery of Comparative Example 1, the capacity retention rate was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 1 was 79%. Table 1 shows the results.

(Comparative example 2)
A composition for forming a porous insulating layer of Comparative Example 2 was prepared in the same manner as in Example 1 except that Binder 1 was changed to Binder 10 in Example 1, and was applied to a negative electrode. Also, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Comparative Example 2 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 2 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 2 was 85%. Table 1 shows the results.

(Comparative Example 3)
A composition for forming a porous insulating layer of Comparative Example 3 was prepared in the same manner as in Example 6 except that binder 10 was used instead of binder 3, and the composition was applied to a negative electrode. Also, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Comparative Example 3 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 3 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 3 was 84%. Table 1 shows the results.

(Comparative Example 4)
A composition for forming a porous insulating layer of Comparative Example 4 was prepared in the same manner as in Example 1 except that Binder 6 was used instead of Binder 1 in Example 1, and the composition was applied to a negative electrode. Since aggregates were found in the composition for forming a porous insulating layer, coating defects due to aggregates were partially observed in the coating with a thickness of 3 μm. A non-aqueous electrolyte secondary battery of Comparative Example 4 was produced in the same manner as in Example 1 using the well-coated portion. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 4 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 4 was 86%. Table 1 shows the results.

(Comparative Example 5)
A composition for forming a porous insulating layer of Comparative Example 5 was prepared in the same manner as in Example 1 except that Binder 7 was used instead of Binder 1 in Example 1, and the composition was applied to a negative electrode. , the aggregates in the composition for forming a porous insulating layer were large, and good coating with a thickness of 3 µm was not possible. Table 1 shows the results.

(Comparative Example 6)
A composition for forming a porous insulating layer of Comparative Example 6 was prepared in the same manner as in Example 1 except that Binder 8 was used instead of Binder 1 in Example 1, and the composition was applied to a negative electrode. Also, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Comparative Example 6 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 6 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 6 was 81%. Table 1 shows the results.

(Comparative Example 7)
The procedure of Example 1 was repeated except that acrylic rubber (polyn-butyl acrylate) was used instead of Binder 1, and N-methyl-2-pyrrolidone (NMP) was used as the solvent. A composition for forming a porous insulating layer of Comparative Example 7 was prepared and applied to a negative electrode. Also, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery of Comparative Example 7 was produced. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 7 was measured in the same manner as in Example 1. The capacity retention rate of the non-aqueous electrolyte secondary battery of Comparative Example 7 was 84%. Table 1 shows the results.

In the table, "St" is styrene, "2EHA" is 2-ethylhexyl acrylate, "MeOEA" is methoxyethyl acrylate, "MAA" is methacrylic acid, and "VB" is vinyl butyrate (vinyl butyral). , "VA" for vinyl alcohol, "VAc" for vinyl acetate, "ACMO" for acryloylmorpholine, and "AA" for acrylic acid. In addition, "HSP distance 1" is the distance between the Hansen solubility parameter of the binder (styrene-butadiene rubber, SBR) and the Hansen solubility parameter of the organic solvent, and "HSP distance 2" is the distance of the binder (carboxymethylcellulose, CMC). The distance between the Hansen solubility parameter and the Hansen solubility parameter of the organic solvent, and "HSP distance 3" indicates the distance between the Hansen solubility parameter of the active material and the Hansen solubility parameter of the organic solvent.

<Consideration of the results>
In Examples 1 to 6, since the composition for forming a porous insulating layer was within the scope of the present invention, a good composition for forming a porous insulating layer was obtained, and the composition for forming a porous insulating layer was removed. There was no separation, and high temperature life characteristics were also good.
In Comparative Examples 1 to 6, the effect of suppressing the negative electrode thickness was about the same as in Examples, but Comparative Examples 1 and 6 were inferior in high-temperature life characteristics, and Comparative Examples 2, 3, and 6 were inferior. In No. 4, peeling was observed in cutting out the negative electrode. In Comparative Example 4, agglomerates were observed, which was considered to be due to insufficient dispersion of boehmite. In Comparative Example 5, agglomerates were generated, probably due to the low solubility of the binder in the solvent, and a good composition for forming a porous insulating layer could not be obtained. In Comparative Example 7, the Hansen solubility parameter of the solvent was not within the range of the present invention, so the amount of increase in the thickness of the negative electrode after forming the porous insulating layer was large.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

10 Non-aqueous electrolyte secondary battery 20 Positive electrode 21 Positive electrode current collector 22 Positive electrode active material layer 30 Negative electrode 31 Negative electrode current collector 32 Negative electrode active material layer 33 Porous insulating layer 40 Separator layer

Claims (9)

A composition for forming a porous insulating layer for forming a porous insulating layer on an active material layer disposed on a main surface of a current collector,
The active material layer includes at least an active material capable of electrochemically intercalating and deintercalating lithium ions and an active material layer binder,
The composition for forming a porous insulating layer includes at least a solvent containing an organic solvent, insulating inorganic particles, and a binder,
the distance between the Hansen solubility parameter of the active material layer binder and the Hansen solubility parameter of the organic solvent is 8.0 (MPa) ^1/2 or more;
The distance between the Hansen solubility parameter of the active material and the Hansen solubility parameter of the organic solvent is 5.0 (MPa) ^1/2 or more,
The binder contains 30% by mass or more and 60% by mass or less of an aromatic vinyl compound and 20% by mass or more and 69% by mass or less of a (meth)acrylic acid ester, as structural units, relative to the total mass of the binder. , a polymer containing 5% by mass or more and 35% by mass or less of a (meth)acrylic acid ester containing a hydroxyl group or an ether group and 1% by mass or more and 10% by mass or less of a vinyl compound having an acidic functional group. A composition for forming an insulating layer. 2. The composition for forming a porous insulating layer according to claim 1, wherein the distance between the Hansen solubility parameter of said active material and the Hansen solubility parameter of said organic solvent is 8.0 (MPa) ^<1/2> or more. 3. The composition for forming a porous insulating layer according to claim 1, wherein the organic solvent has a distance Ra of the Hansen solubility parameter represented by the following formula (I) of 5.0 (MPa) ^1/2 or more. .
(wherein δ _{D (solvent)} (MPa) ^1/2 is the dispersion term of the organic solvent, δ _{P (solvent)} (MPa) ^1/2 is the polar term of the organic solvent, δ _{H (solvent)} ( MPa) ^1/2 indicates the hydrogen bonding term of the organic solvent, respectively.) 4. The composition for forming a porous insulating layer according to claim 1, wherein the organic solvent has a boiling point of 160° C. or higher at 1 atm. 5. The composition for forming a porous insulating layer according to claim 1, wherein the organic solvent contains an alcohol compound. 6. The composition for forming a porous insulating layer according to any one of claims 1 to 5, further comprising polyolefin polymer particles. a current collector;
an active material layer disposed on the main surface of the current collector;
a porous insulating layer formed on the active material layer from the composition for forming a porous insulating layer according to any one of claims 1 to 6,
An electrode for a non-aqueous electrolyte secondary battery, wherein the active material layer includes at least an active material capable of electrochemically intercalating and deintercalating lithium ions and an active material layer binder. A nonaqueous electrolyte secondary battery comprising the electrode for a nonaqueous electrolyte secondary battery according to claim 7 . forming a porous insulating layer on the active material layer disposed on the main surface of the current collector using a porous insulating layer-forming composition;
The active material layer includes at least an active material capable of electrochemically intercalating and deintercalating lithium ions and an active material layer binder,
The composition for forming a porous insulating layer includes at least a solvent containing an organic solvent, insulating inorganic particles, and a binder,
the distance between the Hansen solubility parameter of the active material layer binder and the Hansen solubility parameter of the organic solvent is 8.0 (MPa) ^1/2 or more;
The distance between the Hansen solubility parameter of the active material and the Hansen solubility parameter of the organic solvent is 5.0 (MPa) ^1/2 or more,
The binder contains 30% by mass or more and 60% by mass or less of an aromatic vinyl compound and 20% by mass or more and 69% by mass or less of a (meth)acrylic acid ester, as structural units, relative to the total mass of the binder. , a polymer containing 5% by mass or more and 35% by mass or less of a (meth)acrylic acid ester containing a hydroxyl group or an ether group and 1% by mass or more and 10% by mass or less of a vinyl compound having an acidic functional group. A method for producing an electrode for an electrolyte secondary battery.

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