JP2024007380A - Binder for nonaqueous secondary battery, slurry for lithium ion secondary battery porous layer, lithium ion secondary battery porous layer, lithium ion secondary battery separator, and lithium ion secondary battery - Google Patents

Abstract

To provide a binder for a nonaqueous secondary battery, which enables the formation of a layer capable of suppressing separator shrinkage even under a high-temperature condition.SOLUTION: A binder for a nonaqueous secondary battery comprises: an aqueous medium; and a particulate copolymer. The particulate copolymer contains a vinyl monomer unit. The vinyl monomer unit contains an acrylamide monomer unit (B1) and a methacrylamide monomer unit (B2). A content W1(pts.mass) of the acrylamide monomer unit (B1) and a content W2 (pts.mass) of the methacrylamide monomer unit (B2) to a total mass, 100 pts.mass of the vinyl monomer unit satisfy the following requirement (1): 0<W1/W2<1 (1), and the content W2 of the methacrylamide monomer unit (B2) is equal to or larger than 2 pts.mass.SELECTED DRAWING: None

Description

The present invention relates to a binder for a non-aqueous secondary battery, a slurry for a lithium ion secondary battery porous layer, a lithium ion secondary battery porous layer, a lithium ion secondary battery separator, and a lithium ion secondary battery.

2. Description of the Related Art Power storage devices such as lithium ion secondary batteries have been actively developed.
Usually, in the lithium ion secondary battery, a separator made of a microporous membrane is provided between the positive and negative electrodes. The separator has the function of preventing direct contact between the positive and negative electrodes and allowing ions to pass through the electrolyte held in the micropores.
In recent years, separators have been proposed in which a layer containing an inorganic filler and a resin binder is placed on the surface of the base material that makes up the separator in order to provide the separator with various properties while ensuring the electrical properties and safety of lithium-ion secondary batteries. (For example, see Patent Document 1).
Patent Document 1 includes polymer particles formed from a first monomer having an acidic functional group, a second monomer having an amide group, and another third monomer and an inorganic filler. A technique related to a lithium ion secondary battery is disclosed in which a resin composition is coated on a separator to form a protective layer made of the resin composition on the separator.

In a lithium ion secondary battery, an adhesive layer or the like is sometimes provided on the surface of an electrode and/or a separator for the purpose of improving adhesiveness between battery members. For example, an electrode with an adhesive layer formed on the electrode and an adhesive layer formed on the separator, and a separator with an adhesive layer formed on the separator are used as battery members. Specifically, a technique has been disclosed in which a porous film containing polymer particles and an inorganic filler is provided on a separator, and then an adhesive layer is further provided between the porous film and the electrode (see, for example, Patent Document 2).

In recent years, there has been a demand for further improvement in the performance of secondary batteries. One of its features is that it further ensures safety when the secondary battery is used in a high-temperature environment. As a technique for ensuring the safety of secondary batteries when used in such high-temperature environments, for example, non-aqueous secondary battery functional layer compositions containing organic particles and solvents have been proposed. A technique has been disclosed in which the composition for a non-aqueous secondary battery functional layer is used as a material when forming a functional layer on a separator (see, for example, Patent Document 3). It is said that the functional layer of Patent Document 3 has high heat shrinkage resistance, can sufficiently suppress the occurrence of short circuit between the positive electrode and the negative electrode in a high-temperature environment, and can ensure safety.

The fine pores of the separator in a secondary battery contract when the battery generates heat, inhibiting the passage of, for example, lithium ions, and having the function of suppressing runaway of the secondary battery.
However, if the secondary battery runs out of control at a high temperature of about 150° C. or higher, there is a problem in that the separator shrinks and short circuits occur between the electrodes. In particular, in recent years, the capacity of batteries has been increasing, and the amount of heat generated during runaway tends to increase, so there is a need for technology to prevent separator shrinkage at high temperatures.

The composition for a non-aqueous secondary battery functional layer disclosed in Patent Document 3 contains organic particles and a solvent, and optionally further contains a binder and other components. The organic particles contain polyfunctional ethylenically unsaturated monomer units in a predetermined ratio, and have a volume average particle diameter within a predetermined range. Further, it is disclosed that the binder optionally included is a polymer containing a crosslinkable monomer unit such as allyl glycidyl ether and a repeating unit other than the crosslinkable monomer unit.
The functional layer formed on the separator disclosed in Patent Document 3 has high heat shrinkage resistance and is said to be able to ensure the safety of secondary batteries, but the separator shrinks at high temperatures of 150°C or higher. The problem is that there is still room for improvement in terms of suppression.

Further, Patent Document 4 discloses a material for a functional layer containing a predetermined amount of an epoxy group-containing monomer. The functional layer formed of the material for the functional layer disclosed in Patent Document 4 has excellent flexibility in the low temperature range (for example, 60°C) before thermal contraction begins, and is resistant to heat at high temperatures of 150°C or higher. It becomes hard as crosslinking progresses, has high heat resistance, and is said to be able to ensure the safety of secondary batteries.
However, since the material for the functional layer disclosed in Patent Document 4 has a low initial storage modulus, the storage modulus after thermal crosslinking at a high temperature of 150°C or higher is not sufficiently high. There is a problem in that there is still room for improvement in the effect of suppressing shrinkage of the separator at high temperatures of .degree. C. or higher.

Further, Patent Document 5 discloses a binder composition for an electricity storage device, and the binder composition for an electricity storage device is a water-soluble binder composition in which the proportion of repeating units derived from (meth)acrylamide is 40 to 100% by mass. The main component is a polymer. Such water-soluble polymers have excellent adhesion to inorganic pigments, but when the binder composition for power storage devices is coated on a separator together with an aqueous medium, the polymer dissolved in the aqueous medium may enter the inside of the pores. The problem is that the intrusion tends to cause clogging and reduce battery performance. In addition, since the water-soluble polymer increases the water content of the separator, the amount of water inside the battery increases, which is likely to cause side reactions in the electrolyte and cause early deterioration of battery performance. However, there is also a problem that there is room for improvement.

Furthermore, Patent Document 6 discloses a binder dispersion for a nonaqueous secondary battery separator containing a particulate polymer containing 40 to 80% by mass of (meth)acrylamide. The binder dispersion for a non-aqueous secondary battery separator contains a particulate copolymer obtained by copolymerizing an ethylenically unsaturated monomer having a predetermined octanol/water partition coefficient and the (meth)acrylamide. . It is thought that a binder dispersion for a non-aqueous secondary battery separator having such a form will increase the heat resistance of the separator while not impairing its conductivity when coated on the separator. Judging from the high water solubility of meth)acrylamide and the viscosity of the binder dispersion, it contains a large amount of water-soluble polymer, and is similar to the binder composition for power storage devices disclosed in Patent Document 5 mentioned above. Another problem is that the particulate polymer dissolved in the aqueous medium invades the inside of the pores, causing clogging, which tends to reduce battery performance.

Further, Patent Document 7 and Patent Document 8 disclose a binder composition for non-aqueous secondary batteries containing a copolymer formed by copolymerizing a (meth)acrylamide monomer and a (meth)acrylic acid ester monomer. things are disclosed. Patent Documents 7 and 8 describe that the binder composition for non-aqueous secondary batteries has a high effect of improving adhesion to electrodes and/or separators. However, the high-temperature strength of the binder compositions for non-aqueous secondary batteries themselves disclosed in Patent Documents 7 and 8 is not sufficiently high, and there is room for improvement in suppressing separator shrinkage at high temperatures of 150°C or higher. It has the following problem.

Patent No. 5708872 International publication 2019/065416 pamphlet International Publication 2021/141119 pamphlet Japanese Patent Application Publication No. 2015-118908 Patent No. 7004104 Japanese Patent Application Publication No. 2015-088484 Japanese Patent Application Publication No. 2015-185530

As described above, the conventionally disclosed techniques have a problem in that sufficient effects have not yet been achieved in suppressing separator shrinkage at high temperatures of 150° C. or higher.

Therefore, in the present invention, we have developed a binder for non-aqueous secondary batteries that can form a layer that can suppress separator shrinkage even at high temperatures of about 150°C or higher, and a lithium ion secondary battery containing the binder for non-aqueous secondary batteries. Slurry for a battery porous layer, a lithium ion secondary battery porous layer containing the slurry for a lithium ion secondary battery porous layer, a lithium ion secondary battery separator containing the lithium ion secondary battery porous layer, and a lithium ion secondary battery The purpose is to provide

As a result of intensive studies to achieve the above object, the present inventors have found that in a binder for non-aqueous secondary batteries containing a particulate copolymer containing vinyl monomer units, the vinyl monomer units are , containing an acrylamide monomer unit (B1) and a methacrylamide monomer unit (B2), the content W1 of the acrylamide monomer unit (B1) based on 100 parts by mass of the total mass of the vinyl monomer unit. (parts by mass) and the content W2 (parts by mass) of the methacrylamide monomer unit (B2) have a predetermined relationship, and the content W2 of the methacrylamide monomer unit (B2) is The inventors have discovered that separator shrinkage can be suppressed even at high temperatures by using a binder for non-aqueous secondary batteries that has a value equal to or higher than a predetermined value, and have completed the present invention.
That is, the present invention is as follows.

[1]
A binder for a non-aqueous secondary battery, comprising an aqueous medium and a particulate copolymer,
The particulate copolymer contains a vinyl monomer unit,
The vinyl monomer unit includes an acrylamide monomer unit (B1) and a methacrylamide monomer unit (B2),
The content W1 (parts by mass) of the acrylamide monomer unit (B1) and the content W2 (parts by mass) of the methacrylamide monomer unit (B2) with respect to 100 parts by mass of the total mass of the vinyl monomer units. ) satisfies the following formula (1),
The content W2 of the methacrylamide monomer unit (B2) is 2 parts by mass or more,
Binder for non-aqueous secondary batteries.
0<W1/W2<1...(1)
[2]
The binder for a non-aqueous secondary battery according to [1] above, wherein the particulate copolymer has a glass transition temperature of 10° C. or lower.
[3]
[1] or [2] above, wherein the particulate copolymer contains a vinyl monomer unit and a monomer unit derived from a reactive surfactant having a functional group copolymerizable with a vinyl group. The binder for non-aqueous secondary batteries described in .
[4]
The vinyl monomer unit includes a crosslinkable monomer unit containing two or more vinyl groups,
The content of the crosslinkable monomer unit containing two or more vinyl groups is 0.1 parts by mass or more and 5 parts by mass or less, based on 100 parts by mass of the particulate copolymer.
The binder for non-aqueous secondary batteries according to any one of [1] to [3] above.
[5]
[1] to [4] above, wherein the content W2 of the methacrylamide monomer unit (B2) is 2 parts by mass or more and less than 20 parts by mass with respect to 100 parts by mass of the total mass of the vinyl monomer units. The binder for non-aqueous secondary batteries according to any one of the above.
[6]
The particulate copolymer has a ratio Dv/Dn of the volume average particle diameter Dv and the number average particle diameter Dn,
The binder for a nonaqueous secondary battery according to any one of [1] to [5] above, which has a binder of 1 or more and 1.5 or less.
[7]
The particulate copolymer is
The storage modulus at 30° C. is 7×10 ⁷ Pa or more and 5×10 ⁸ Pa or less,
The storage modulus at 130° C. is 2×10 ⁶ Pa or more,
The binder for nonaqueous secondary batteries according to any one of [1] to [6] above.
[8]
The binder for a non-aqueous secondary battery according to any one of [1] to [7] above, wherein the vinyl monomer unit further includes an epoxy group-containing vinyl monomer unit.
[9]
The binder for a non-aqueous secondary battery according to any one of [1] to [8] above, wherein the binder for a non-aqueous secondary battery is a binder for a porous layer in a non-aqueous secondary battery.
[10]
water and,
Inorganic filler;
The binder for non-aqueous secondary batteries according to any one of [1] to [9] above,
including,
Slurry for porous layer of lithium ion secondary battery.
[11]
Comprising the slurry for a lithium ion secondary battery porous layer according to [10] above,
Lithium ion secondary battery porous layer.
[12]
Comprising the lithium ion secondary battery porous layer described in [11] above,
Separator for lithium ion secondary batteries.
[13]
A lithium ion secondary battery, comprising the lithium ion secondary battery separator described in [12] above.

According to the present invention, a binder for a nonaqueous secondary battery can be obtained that can form a layer that can suppress separator shrinkage even at high temperatures.

A mode for carrying out the present invention (hereinafter referred to as "this embodiment") will be described in detail below, but the present invention is not limited thereto, and various modifications may be made without departing from the gist thereof. is possible.

In the present specification, the term "monomer" includes all of the monomers that constitute the particulate copolymer of this embodiment.
In addition, in this specification, when a monomer is incorporated into a polymer, it is described as a "monomer unit", and when it is in a state before being incorporated into a polymer, it is described as a "monomer" or a "compound". do.

Furthermore, in this specification, "(meth)acrylic ester" means both methacrylic ester and acrylic ester, and "(meth)acrylamide" includes both methacrylamide and acrylamide, respectively. It is used in the sense of

[Binder for non-aqueous secondary batteries]
The binder for a non-aqueous secondary battery of this embodiment includes an aqueous medium and a particulate copolymer.
The particulate copolymer contains a vinyl monomer unit, and the vinyl monomer unit contains an acrylamide monomer unit (B1) and a methacrylamide monomer unit (B2).
The content W1 (parts by mass) of the acrylamide monomer unit (B1) and the content W2 (parts by mass) of the methacrylamide monomer unit (B2) with respect to 100 parts by mass of the total mass of the vinyl monomer units. ) satisfies the following formula (1),
The content W2 of the methacrylamide monomer unit (B2) is 2 parts by mass or more.
0<W1/W2<1...(1)
According to the binder for nonaqueous secondary batteries of the present embodiment, it is possible to form a porous layer that can effectively suppress separator shrinkage even at high temperatures of about 150° C. or higher, for example.

Usually, a microporous separator for a secondary battery is provided with a layer intended to provide functions such as suppressing thermal contraction of the separator. Examples of the method for forming the layer include a method of applying a composition containing an inorganic pigment, latex, dispersant, thickener, etc., and an aqueous medium. At this time, the separator and the layer (also referred to as a coating layer) are required to have high adhesion so that they do not peel off.
The present inventors considered that by increasing the adhesion, the coating layer could strongly support the separator and effectively suppress the thermal shrinkage of the separator, and conducted studies. However, as a result of investigation, it has become clear that the thermal shrinkage of the separator cannot be sufficiently suppressed with a coating layer that has been adjusted to have a high adhesive force simply to increase the peel strength.
In addition, as a result of studies conducted by the present inventors, in addition to adhesion at room temperature, the polyolefin base material constituting the separator starts to shrink, and has high adhesion even at high temperatures such as 150°C. It was found that it is important to express the
Furthermore, the present inventors have found that when the coating layer contains a predetermined amount of an amide group-containing vinyl monomer, particularly a particulate copolymer containing (meth)acrylamide monomer units, as a polar component, It has been found that the layer exhibits desired behavior at low and high temperatures, and that the coating layer can effectively suppress thermal shrinkage of the separator even at high temperatures such as 150°C.
Furthermore, the present inventors have found that in order to effectively introduce an amide group into a particulate copolymer, it is necessary to adjust the monomer distribution ratio between the aqueous medium and the particulate copolymer. Specifically, adjusting the distribution ratio of acrylamide monomer to the aqueous medium/particulate copolymer, and mainly using methacrylamide monomer from the viewpoint of copolymerizability between the monomers, Specifically, we compared the copolymerizability of acrylamide monomer with other vinyl monomers and the copolymerizability of methacrylamide monomer with other vinyl monomers. In view of the fact that methacrylamide monomers have higher copolymerizability and are more easily incorporated into the skeleton of particulate copolymers, it has been found that it is important to mainly use methacrylamide monomers.

(aqueous medium)
The binder for non-aqueous secondary batteries of this embodiment includes an aqueous medium.
Examples of the aqueous medium include solvents such as water, methanol, ethanol, and isopropyl alcohol.
The aqueous medium may contain a dispersant, a lubricant, a thickener, a bactericide, and the like.

(Particulate copolymer)
The binder for non-aqueous secondary batteries of this embodiment includes a particulate copolymer.
The particulate copolymer contains vinyl monomer units.

<Vinyl monomer unit>
The vinyl compound, which is a raw material monomer for forming the vinyl monomer units constituting the particulate copolymer, is a monomer having a vinyl group, and includes vinyl compounds (CH ₂ =CHX) and vinylidene compounds (CH ₂ =CXY), such as (meth)acrylic acid ester, (meth)acrylic acid, (meth)acrylamide, aromatic vinyl compound, acrylonitrile, and the like. Specifically, this will be explained in detail below.
These may be used alone or in combination of two or more.

<Monomer unit derived from a reactive surfactant having a functional group copolymerizable with a vinyl group>
The particulate copolymer preferably contains the vinyl monomer unit and a monomer unit derived from a "reactive surfactant having a functional group copolymerizable with a vinyl group."
Examples of the raw material monomer for forming a monomer unit having a functional group copolymerizable with the vinyl group, that is, the reactive surfactant, include compounds having a vinyl group, an acrylic group, or a methacrylic group. Specific examples include compounds that can be used as reactive surfactants as described below. These may be used alone or in combination of two or more.

A particulate copolymer using the vinyl monomer unit and "a monomer unit derived from a reactive surfactant and having a functional group copolymerizable with a vinyl group" has a high chemical stability. The separator using the binder for nonaqueous secondary batteries of this embodiment has excellent chemical structure that does not decompose even when exposed to oxidizing conditions, reducing conditions, and high temperature conditions (for example, 150°C) inside the battery. It tends to be difficult to

<Methacrylamide monomer unit in particulate copolymer>
As described above, the particulate copolymer includes a vinyl monomer unit, and the vinyl monomer unit includes an acrylamide monomer (B1) and a methacrylamide monomer unit (B2).
The content W2 of methacrylamide monomer units (B2) contained in the particulate copolymer is 2 parts by mass or more based on 100 parts by mass of the total vinyl monomer unit in the particulate copolymer. The amount is preferably 4 parts by mass or more, more preferably 6 parts by mass or more, and even more preferably 10 parts by mass or more.
The upper limit of the content of methacrylamide monomer units (B2) is preferably 30 parts by mass or less, more preferably It is 20 parts by mass or less, more preferably less than 20 parts by mass, even more preferably 15 parts by mass or less.
The content of the methacrylamide monomer unit (B2) contained in the particulate copolymer is 2 parts by mass or more based on 100 parts by mass of the total vinyl monomer unit in the particulate copolymer. As a result, the binder for non-aqueous secondary batteries of this embodiment has improved adhesion at room temperature and has increased storage elastic modulus at high temperatures (for example, 130°C), making the binder for non-aqueous secondary batteries of this embodiment There is a tendency that thermal shrinkage of the separator used can be suppressed. In addition, by setting the content of the methacrylamide monomer unit (B2) to 30 parts by mass or less with respect to 100 parts by mass of the total vinyl monomer unit in the particulate copolymer, The proportion of water-soluble components contained in the binder for water secondary batteries is suppressed, and when applied as a slurry, clogging of the pores of the separator is reduced, resulting in good battery characteristics such as cycle characteristics and rate characteristics. There is a tendency to

As mentioned above, the particulate copolymer includes an acrylamide monomer unit (B1) and a methacrylamide monomer unit (B2).
The content W1 (parts by mass) of the acrylamide monomer unit (B1) and the content W2 (parts by mass) of the methacrylamide monomer unit (B2) with respect to 100 parts by mass of the total mass of the vinyl monomer units. ) has the relationship of the following formula (1).
0<W1/W2<1...(1)
By satisfying the relationship of formula (1) and specifying W1 to be less than W2, the proportion of water-soluble components contained in the particulate copolymer is suppressed, so that the above-mentioned mechanism improves cycle characteristics and rate characteristics. Battery characteristics tend to be better.

As a method for controlling the ratio of methacrylamide monomer units to the total mass of 100 parts by mass of vinyl monomer units in the particulate copolymer within the above-mentioned numerical range, for example, When performing emulsion polymerization as in the manufacturing method, a method may be mentioned in which the blending ratio of methacrylamide monomers is adjusted to a value corresponding to a desired numerical range with respect to the total amount of vinyl monomers blended.
Further, as a method for controlling the relationship so as to satisfy the relationship of formula (1), in the method for producing a particulate copolymer constituting the binder for a non-aqueous secondary battery of the present embodiment, methacrylamide monomer and An example of this method is to adjust the blending ratio of acrylamide monomers to a value that corresponds to a desired numerical range.

The content of methacrylamide monomer units and acrylamide monomer units contained in the particulate copolymer of this embodiment, when the total mass of vinyl monomer units is 100 parts by mass, is It may be calculated from the blending ratio of monomers during polymer production, or may be calculated from various spectral data using IR (ATR method) or the like. Further, the amount of other monomer units contained in the particulate copolymer can be calculated using the same calculation method as for the methacrylamide monomer unit.

(Storage modulus of particulate copolymer)
As mentioned above, in order to suppress thermal shrinkage of the separator of a secondary battery even at high temperatures of, for example, 150°C or higher, the non-aqueous secondary battery binder of this embodiment sufficiently binds the separator and inorganic filler. It is preferable that the particulate copolymer has a high elastic modulus while adhering closely.
Since the particulate copolymer contains an acrylamide monomer unit (B1) and a methacrylamide monomer unit (B2), the non-aqueous secondary battery binder of this embodiment can be heated from room temperature to high temperature (for example, 130 A particulate copolymer which has high adhesion and maintains an excellent storage modulus E' over the temperature range (°C) can be obtained.

The particulate copolymer contained in the binder for non-aqueous secondary batteries of this embodiment has a storage modulus of 7×10 ⁶ Pa or more and 5×10 ⁸ Pa or less at 30° C., and It is preferable that it is 2×10 ⁶ Pa or more at 130°C. Thereby, the coating layer containing the particulate copolymer exhibits the above-mentioned behavior, and it tends to be possible to suppress shrinkage of the microporous separator even if the separator becomes high temperature.
It is more preferable that the particulate copolymer has a storage modulus of 1×10 ⁷ Pa or more and 3×10 ⁸ Pa or less at 30°C, and 5×10 ⁶ Pa or more at 130°C.
It is further preferable that the particulate copolymer has a storage modulus of 4×10 ⁷ Pa or more and 2×10 ⁸ Pa or less at 30°C, and 6×10 ⁶ Pa or more at 130°C.
In a preferred embodiment of the binder for non-aqueous secondary batteries of this embodiment, a particulate copolymer is combined with one or more monomers selected from (meth)acrylic acid ester monomers and an acrylamide monomer. A copolymer containing a methacrylamide monomer, a carboxylic acid group-containing monomer, and a crosslinkable monomer as monomer units, wherein the crosslinkable monomer has an epoxy group. The particulate copolymer has a storage modulus of 1×10 ⁷ Pa or more and 3×10 ⁸ Pa or less at 30°C, and a storage modulus of 5× It is 10 ⁶ Pa or more. The particulate copolymer having the above storage modulus may be referred to as particulate copolymer I in this specification.

A method for controlling the storage modulus of the particulate copolymer so that it satisfies the above range includes a method of using a (meth)acrylamide monomer in the particulate copolymer. Further, as a method for further increasing the storage modulus of the particulate copolymer, a method using an epoxy group-containing vinyl monomer can be mentioned. In this case, the particulate copolymer contains an epoxy group-containing vinyl monomer unit as a vinyl monomer unit.
Furthermore, as a method for controlling the storage modulus of a particulate copolymer, one or more monomers selected from (meth)acrylic acid ester monomers, a carboxylic acid group-containing monomer, and a crosslinkable Examples include a method of including monomers as monomer units and adjusting the types of these monomers and their blending ratio.

As mentioned above, the content W2 of the methacrylamide monomer unit (B2) contained in the particulate copolymer of this embodiment is 2 parts by mass based on 100 parts by mass of the total vinyl monomer unit. The amount is more preferably 4 parts by mass or more, still more preferably 6 parts by mass or more, and even more preferably 10 parts by mass or more.
The upper limit of the proportion of methacrylamide monomer is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably less than 20 parts by mass, per 100 parts by mass of vinyl monomer unit mass. and even more preferably 15 parts by mass or less.
The content of methacrylamide monomer units contained in the particulate copolymer is preferably 2 parts by mass or more and 20 parts by mass or less, more preferably 3 parts by mass or less, based on 100 parts by mass of the total vinyl monomer units. The content is from 6 parts by mass to 10 parts by mass, more preferably from 6 parts by mass to 10 parts by mass.
By setting the content of methacrylamide monomer units to 2 parts by mass or more, the particulate copolymer tends to have both high adhesiveness derived from hydrogen bonding strength and storage modulus. Further, by setting the amount to 20 parts by mass or less, flexibility at room temperature is increased and adhesion is improved.

<(meth)acrylic acid ester monomer>
As mentioned above, in order to appropriately control the storage modulus of the particulate copolymer, it is necessary to add one or more monomers selected from (meth)acrylic acid ester monomers to the particulate copolymer. It is effective to use
Examples of the (meth)acrylic ester monomer include, but are not limited to, a (meth)acrylic ester having one ethylenically unsaturated bond.
In this specification, (meth)acrylic acid ester may be referred to as (meth)acrylate.
Examples of (meth)acrylic esters having one ethylenically unsaturated bond include, but are not limited to, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n -Hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, cyclohexyl acrylate, methyl methacrylate (also referred to herein as methyl methacrylate), ethyl methacrylate, propyl methacrylate, isopropyl acrylate, butyl methacrylate, isobutyl methacrylate, t-butyl (Meth)acrylates having alkyl groups such as methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, t-butyl cyclohexyl acrylate; benzyl acrylate, phenyl acrylate, benzyl methacrylate, phenyl Examples include (meth)acrylates having an aromatic ring such as methacrylate.
These (meth)acrylic acid ester monomers may be used alone or in combination of two or more.
The (meth)acrylate having an alkyl group is preferably a (meth)acrylate comprising an alkyl group and a (meth)acryloyloxy group.
The (meth)acrylate having an aromatic ring is preferably a (meth)acrylate comprising an aromatic ring and a (meth)acryloyloxy group.

The (meth)acrylic ester monomer is more preferably a (meth)acrylic ester monomer consisting of an alkyl group having 4 or more carbon atoms and a (meth)acryloyloxy group, and an alkyl group having 6 or more carbon atoms and ( More preferred are (meth)acrylic acid ester monomers consisting of meth)acryloyloxy groups, such as methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, and t-butylcyclohexyl acrylate. One or more selected from the group consisting of methyl methacrylate, cyclohexyl methacrylate, butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate is even more preferable. It is preferable to use such a (meth)acrylic acid ester monomer from the viewpoint of improving polymerization stability during emulsion polymerization and from the viewpoint of improving adhesiveness with electrodes.

It is preferable that the (meth)acrylic acid ester monomer contains at least methyl methacrylate. Further, the content of methyl methacrylate is preferably 1.0 parts by mass or more based on 100 parts by mass of the total amount of (meth)acrylic acid ester monomers. By containing 1.0 parts by mass or more of methyl methacrylate based on 100 parts by mass of the total amount of (meth)acrylic ester monomers, a phase of (meth)acrylic ester monomers and (meth)acrylamide monomers can be formed. Solubility increases and copolymerizability improves. In addition, the flexibility of the coating layer is increased at low temperatures (that is, the peel strength between the separator and the coating layer using the binder for nonaqueous secondary batteries of this embodiment is strengthened), and the coating layer is This makes it easier to realize the behavior of hardening the separator, and it tends to suppress shrinkage of the separator even at high temperatures.
The content of methyl methacrylate relative to 100 parts by mass of the total amount of (meth)acrylic acid ester monomers is more preferably 5 parts by mass or more, and still more preferably 8 parts by mass or more. The upper limit of the content of methyl methacrylate is not particularly limited, but may be 50 parts by mass or less, preferably 40 parts by mass or less, and more preferably 20 parts by mass or less.

<Carboxylic acid group-containing monomer>
As described above, in order to appropriately control the storage modulus of the particulate copolymer, it is effective to use a monomer containing a carboxylic acid group in the particulate copolymer.
Examples of the carboxylic acid group-containing monomer include, but are not limited to, ethylenically unsaturated monomers having a carboxyl group.
In this specification, the carboxylic acid group-containing monomer is also referred to as unsaturated carboxylic acid.
Examples of the ethylenically unsaturated monomer having a carboxyl group include, but are not limited to, monocarboxylic acids such as acrylic acid, methacrylic acid, half ester of itaconic acid, half ester of maleic acid, and half ester of fumaric acid. Monomers; dicarboxylic acid monomers such as itaconic acid, fumaric acid and maleic acid; and the like.
One type of carboxylic acid group-containing monomer can be used alone or two or more types can be used in combination.
Among these, acrylic acid, methacrylic acid, and itaconic acid are preferred, and acrylic acid and methacrylic acid are more preferred.

The content of the carboxylic acid group-containing monomer may be generally 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the vinyl monomer unit mass. From the viewpoint of further suppressing shrinkage of the separator, the content of the carboxylic acid group-containing monomer is preferably 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the vinyl monomer unit mass. , more preferably 1 part by mass or more and 4 parts by mass or less.

<Crosslinkable monomer>
As mentioned above, in order to appropriately control the storage modulus of a particulate copolymer, it is effective to use a crosslinkable monomer.
Examples of the crosslinkable monomer include monomers having two or more radically polymerizable double bonds, and monomers having a functional group that provides a self-crosslinked structure during or after polymerization. These may be used alone or in combination of two or more.
The crosslinkable monomer constituting the particulate copolymer preferably contains an epoxy group-containing vinyl monomer. The epoxy group-containing vinyl monomer corresponds to a monomer having a functional group that provides a self-crosslinking structure during or after polymerization.
Examples of the epoxy group-containing vinyl monomer include, but are not limited to, glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methyl glycidyl acrylate, and methyl glycidyl methacrylate.
These may be used alone or in combination of two or more.

In addition to the above-mentioned epoxy group-containing vinyl monomers, monomers having functional groups that provide a self-crosslinked structure during or after polymerization include, for example, hydroxyl group-containing vinyl monomers containing hydroxyl groups, and alkoxymethyl group-containing monomers. and a hydrolyzable silyl group-containing vinyl monomer containing a hydrolyzable silyl group.
These may be used alone or in combination of two or more.

In addition to the epoxy group-containing vinyl monomer, the crosslinkable monomers constituting the particulate copolymer include monomers having two or more radically polymerizable double bonds, and amino group-containing vinyl monomers. , a hydroxyl group-containing vinyl monomer, an alkoxymethyl group-containing vinyl monomer, and a vinyl monomer having a hydrolyzable silyl group.
By using the above-mentioned crosslinkable monomer, for example, when the binder for non-aqueous secondary batteries containing the particulate copolymer of this embodiment is used as an adhesive for electrodes or separators, it can maintain appropriate fluidity. However, since it has excellent adhesive properties, it tends to be easy to handle.

Examples of the monomer having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth)acrylate. Among the monomers having two or more radically polymerizable double bonds, polyfunctional (meth)acrylates are more preferred because they exhibit better resistance to electrolytic solutions even in small amounts.

The polyfunctional (meth)acrylate may be a bifunctional (meth)acrylate, a trifunctional (meth)acrylate, or a tetrafunctional (meth)acrylate.
Examples of polyfunctional (meth)acrylates include, but are not limited to, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate. , pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more.
Among these, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate are preferred because they exhibit better resistance to electrolytic solutions even in small amounts.

Examples of the amino group-containing vinyl monomer include, but are not limited to, N,N-methylenebisacrylamide, diacetone acrylamide, and N,N-dimethylaminoethyl acrylamide.

Examples of the hydroxyl group-containing vinyl monomer include, but are not limited to, hydroxyethyl (meth)acrylates such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; hydroxyl groups such as 2-hydroxypropyl (meth)acrylate; Propyl (meth)acrylate; Hydroxybutyl (meth)acrylate such as 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate; 3-chloro-2-hydroxypropyl (meth)acrylate, di-(ethylene glycol) ) maleate, di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis(2-hydroxyethyl) maleate, and 2-hydroxyethylmethyl fumarate. These hydroxyl group-containing vinyl monomers may be used alone or in combination of two or more.
Examples of the hydroxyl group-containing vinyl monomer include, in addition to the above-mentioned compounds, a methylol group-containing vinyl monomer. Examples of the methylol group-containing vinyl monomer include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide. These may be used alone or in combination of two or more.

Examples of the alkoxymethyl group-containing vinyl monomer include, but are not limited to, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-butoxymethylmethacrylamide. .
These may be used alone or in combination of two or more.

Examples of hydrolyzable silyl group-containing vinyl monomers include, but are not limited to, vinylsilane, vinyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxy Examples include propyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, and 3-(methacryloyloxy)propyltrimethoxysilane. These may be used alone or in combination of two or more.

The content of the monomer unit formed by the above-mentioned crosslinkable monomer is usually 2 parts by mass or more and 30 parts by mass or less, preferably 4 parts by mass, based on 100 parts by mass of the particulate copolymer. It is 25 parts by mass or less, more preferably 6 parts by mass or more and 25 parts by mass or less, and even more preferably 8 parts by mass or more and 25 parts by mass or less.
A layer containing a particulate copolymer provided on a separator of a secondary battery by setting the content of the monomer unit formed by the crosslinkable monomer in the range of 2 parts by mass or more and 30 parts by mass or less. tends to further suppress thermal shrinkage of the separator.

[Crosslinkable monomer containing two or more vinyl groups]
Among the crosslinkable monomers mentioned above, it is preferable to use a crosslinkable monomer containing two or more vinyl groups. The content of the crosslinkable monomer unit containing two or more vinyl groups is preferably 0.1 parts by mass or more and 5 parts by mass or less, more preferably 0.1 parts by mass or more and 5 parts by mass or less, based on 100 parts by mass of the particulate copolymer. The amount is 3 parts by mass or more and 3 parts by mass, more preferably 0.5 parts by mass or more and 2 parts by mass.
By setting the content of crosslinkable monomer units containing two or more vinyl groups to 0.1 parts by mass or more per 100 parts by mass of the particulate copolymer, the electrolyte resistance of the particulate copolymer is improved. can be done. In addition, by setting the amount to 5 parts by mass or less, the binder for non-aqueous secondary batteries of the present embodiment tends to have improved adhesion at room temperature and can more effectively suppress shrinkage of the separator even at high temperatures.

(Form of particulate copolymer)
The particulate copolymer of this embodiment is, for example, in the form of a dispersion in which particulate copolymers (also referred to as latex particles) containing the various monomers mentioned above as monomer units are dispersed in an aqueous medium. may have.
Therefore, one form of the binder for a non-aqueous secondary battery of the present embodiment is an aqueous medium dispersion containing a particulate copolymer.
Although the solid content concentration in the aqueous medium dispersion is not particularly limited, it is generally 10% by mass or more and 60% by mass or less, preferably 30% by mass or more and 50% by mass or less. By setting the solid content concentration to 30% by mass or more, the degree of freedom in slurry design increases, such as improving dispersion stability due to high solid content of the slurry. Moreover, by controlling the content to 50% by mass or less, the viscosity of the aqueous medium dispersion containing the particulate copolymer is suppressed, and workability in slurry blending work is improved.

(Viscosity of binder for non-aqueous secondary batteries)
The viscosity of the binder for non-aqueous secondary batteries of this embodiment is not particularly limited, but is usually 2000 mPas or less, preferably 300 mPas or less.
When the viscosity of the binder for non-aqueous secondary batteries of this embodiment is 2000 mPas or less, handling properties are improved, and workability in, for example, slurry blending work is improved.
Normally, the viscosity of a binder for non-aqueous secondary batteries can be lowered to an arbitrary value by adding adjusting water, but at the same time the solid content concentration decreases, so at least 30% by mass or more. It is particularly preferable that the solid content concentration satisfies the above viscosity range.

The binder for a non-aqueous secondary battery of the present embodiment includes a particulate copolymer as particles (copolymer particles) dispersed in an aqueous medium. In addition to the aqueous medium and copolymer, the aqueous medium dispersion may contain other solvents, dispersants, lubricants, thickeners, bactericides, and the like.

(Glass transition temperature of particulate copolymer)
The upper limit of the glass transition temperature of the particulate copolymer contained in the binder for nonaqueous secondary batteries of the present embodiment is 10°C or lower, preferably 0°C or lower, and more preferably -5°C or lower. be.
Further, the lower limit of the glass transition temperature is -50°C or higher, preferably -40°C or higher, and more preferably -30°C or higher.
When the glass transition temperature is within the above range, a composition containing a non-aqueous secondary battery binder tends to be easily coated onto a separator of a secondary battery.
The glass transition temperature can be controlled, for example, by adjusting the type and content of monomer units constituting the particulate copolymer. Alternatively, by adjusting the content of unsaturated carboxylic acid, it can be controlled within the above numerical range.
The glass transition temperature of the particulate copolymer can be measured by the method described in the Examples above.

(Average particle diameter of particulate copolymer)
The volume average particle diameter Dv of the particulate copolymer is preferably 30 nm or more and 230 nm or less, more preferably 50 nm or more and 200 nm or less, and still more preferably 70 nm or more and 180 nm or less.
Since the volume average particle diameter Dv of the particulate copolymer is within the above range, when adhering the adhesive for lithium ion secondary batteries using the binder for nonaqueous secondary batteries of this embodiment to the separator, It is possible to leave a sufficient amount of appropriate voids, and it tends to be possible to maintain the separator's function of transmitting ions in the electrolytic solution.
The volume average particle diameter Dv and number average particle diameter Dn of the particulate copolymer can be controlled, for example, by using seed latex and a surfactant in desired proportions. Generally, by increasing the amount of seed latex and surfactant used, the volume average particle diameter Dv and the number average particle diameter Dn tend to become smaller.
The volume average particle diameter Dv and the number average particle diameter Dn can be measured by the method described in the Examples below.

In the binder for nonaqueous secondary batteries of the present embodiment, the ratio Dv/Dn of the volume average particle diameter Dv to the number average particle diameter Dn of the particulate copolymer is preferably 1 or more and 2.5 or less, and more preferably Preferably it is 1 or more and 2 or less, more preferably 1 or more and 1.5 or less.
The ratio Dv/Dn of the volume average particle diameter Dv and the number average particle diameter Dn is an index of the particle size distribution of the particulate copolymer, and by setting it to 2.5 or less, a dispersion with a narrow particle size distribution without coarse particles can be obtained. is obtained, the structure when used as a coating layer is uniform, high strength is achieved even at high temperatures, and thermal shrinkage of the separator tends to be suppressed.
By increasing the dispersion stability of the particulate copolymer in an aqueous medium during or after polymerization, the particle size distribution can be narrowed and Dv/Dn can be controlled within the above numerical range. Examples of methods for increasing dispersion stability include adding a surfactant to an aqueous medium during or after polymerization to increase steric and electronic repulsion between particulate copolymers. Can be mentioned.
The volume average particle diameter Dv and the number average particle diameter Dn can be measured by the method described in Examples described below.

(Method for producing particulate copolymer)
The particulate copolymer used in the binder for non-aqueous secondary batteries of this embodiment can be manufactured by a known polymerization method. As the polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization, etc. is used.

In order to obtain the particulate copolymer as a dispersion, it is preferable to use an emulsion polymerization method as the polymerization method. The emulsion polymerization method is not particularly limited, and conventionally known methods can be used.
As a method for emulsion polymerization, for example, in an aqueous medium, an acrylamide monomer, a methacrylamide monomer, optionally a (meth)acrylic acid ester monomer, a carboxylic acid group-containing monomer, and a crosslinking In a dispersion system whose basic composition components are a monomer, a radical polymerization initiator, a surfactant, and other additive components (e.g., a molecular weight regulator) used as necessary, the monomer is Examples include a method of polymerizing.
During polymerization, there are methods for keeping the composition of the monomers supplied into the reaction system constant during the entire polymerization process, and for resin dispersions produced by changing the composition of the monomers supplied sequentially or continuously during the polymerization process. Various methods can be used as needed, such as a method for changing the composition of particles.
When a particulate copolymer is obtained by emulsion polymerization, for example, the particulate copolymer obtained is in the form of an aqueous dispersion (latex) containing water and a particulate copolymer dispersed in the water. Good too.

As the (meth)acrylic acid ester monomer, the carboxylic acid group-containing monomer, and the crosslinkable monomer, the above-mentioned compounds can be used.

A radical polymerization initiator initiates addition polymerization of monomers by radical decomposition using heat or a reducing substance.
As the radical polymerization initiator, both inorganic initiators and organic initiators can be used.
As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used.

Examples of water-soluble polymerization initiators include peroxodisulfates, peroxides, water-soluble azobis compounds, and peroxide-reducing agent redox systems.
Examples of peroxodisulfates include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS).
Examples of the peroxide include hydrogen peroxide, t-butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide.
Examples of water-soluble azobis compounds include 2,2-azobis(N-hydroxyethylisobutyramide), 2,2-azobis(2-amidinopropane) hydrogen chloride, and 4,4-azobis(4-cyanopentanoic acid). ) etc.
Examples of the peroxide-reducing redox system include sodium sulfoxylate formaldehyde, sodium bisulfite, sodium thiosulfate, sodium hydroxymethanesulfinate, L-ascorbic acid and its salts, Examples include one or a combination of two or more reducing agents such as copper salts and ferrous salts.

The radical polymerization initiator can preferably be used in an amount of 0.05 to 0.4 parts by mass based on 100 parts by mass of the total monomers.

The surfactant forms micelles in an aqueous medium and provides a polymerization site for the polymerization monomer, and also imparts dispersion stability by adsorbing onto the surface of the particulate copolymer.
Ionic species of the surfactant include nonions, anions, and cations, and from the viewpoint of dispersion stability, it is preferable to have nonions, anions, or both.
The surfactant may have a radically polymerizable unsaturated double bond (for example, a vinyl group) in its molecular structure. A surfactant having an unsaturated double bond capable of radical polymerization in its molecular structure is hereinafter referred to as a reactive surfactant.

Examples of nonionic surfactants that are non-reactive surfactants include, but are not limited to, non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, and polyoxyethylene alkyl ethers. Ethylene distyrenated phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkyl alkanolamide, polyoxyethylene alkylphenyl Examples include ether.

Examples of anionic surfactants that are non-reactive surfactants include, but are not limited to, non-reactive alkyl sulfates, polyoxyethylene alkyl ether sulfate salts, alkylbenzene sulfonates, and alkylnaphthalene sulfonic acids. salt, alkyl sulfosuccinate, alkyldiphenyl ether disulfonate, naphthalene sulfonic acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate salt, polyoxyethylene distyrenated phenyl ether sulfate salt, fatty acid salt, alkyl phosphate , polyoxyethylene alkyl phenyl ether sulfate salt, and the like.

Examples of the anionic reactive surfactant that is a reactive surfactant include, but are not limited to, ethylenically unsaturated monomers having a sulfonic acid group, a sulfonate group, or a sulfuric acid ester group, and salts thereof. , a sulfonic acid group, or a group that is an ammonium salt or an alkali metal salt thereof (an ammonium sulfonate group or an alkali metal sulfonate group) is preferred. Examples of such anionic reactive surfactants include, but are not limited to, alkylaryl sulfosuccinates (for example, "Eleminol (trademark) JS-2" manufactured by Sanyo Chemical Co., Ltd., "Eleminol (trademark) JS Polyoxyethylene alkyl propenyl phenyl ether Sulfate ester salt (for example, "Aqualon (trademark) SR-10", "Aqualon (trademark) SR-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); ammonium = α-sulfonato-ω-1-( Allyloxymethyl)alkyloxypolyoxyethylene (eg, "Aqualon KH-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and the like.

Examples of the nonionic reactive surfactant include, but are not limited to, α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxy poly Oxyethylene (for example, "Adekaria Soap NE-20", "Adekarya Soap NE-30", "Adekaria Soap (trademark) NE-40" manufactured by Asahi Denka Kogyo Co., Ltd.); polyoxyethylene Alkyl propenyl phenyl ether (for example, "Aqualon (trademark) RN-10", "Aqualon (trademark) RN-20", "Aqualon (trademark) RN-30", "Aqualon (trademark) RN" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) -50'', etc.).

The surfactant used in the polymerization step of the particulate copolymer preferably includes a reactive surfactant. One type of reactive surfactant may be used alone, or two or more types may be used in combination.
The particulate copolymer contained in the binder for non-aqueous secondary batteries of this embodiment is a monomer derived from a vinyl monomer unit and a reactive surfactant having a functional group copolymerizable with a vinyl group. Since it is preferable that the surfactant has a unit, it is preferable to use a reactive surfactant that has excellent copolymerizability with a vinyl compound. From this point of view, for example, polyoxyethylene alkyl propenyl phenyl ether sulfate ester salt (for example, "Aqualon (trademark) SR-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is preferable, and ammonium = α-sulfonate-ω- It is preferable to use 1-(allyloxymethyl)alkyloxypolyoxyethylene (eg, "Aqualon KH-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). These are suitable because the steric repulsion of the polyoxyethylene group and the electronic repulsion due to the anionic nature of the sulfonic acid ester group are effective in improving the stability of the particulate copolymer during and/or after polymerization. used for.

Reactive surfactants are effective in increasing the copolymerizability of acrylamide monomers, methacrylamide monomers, and other vinyl monomers and producing copolymers with uniform composition distribution. be.
The presumed mechanism is as follows.
First, a polymer elongation reaction between part of the methacrylamide monomer dissolved in water and the reactive surfactant begins. The growing polymer radicals form micelles into which the remaining methacrylamide monomer and other vinyl monomers enter and the copolymer grows.
Due to the above mechanism, the formation of a water-soluble copolymer derived from homopolymerization of the methacrylamide monomer is suppressed, and copolymerization with other vinyl monomers can proceed.
The fact that the copolymer composition is uniform and that the formation of water-soluble copolymers is suppressed increases the storage modulus of the particulate copolymer and improves the visibility when applied to a separator as a slurry. This is important in preventing deterioration of battery performance due to clogging.
From the viewpoint of the opportunity of contact with the methacrylamide monomer in the aqueous layer, it is particularly preferable to use an anionic reactive surfactant.

Molecular weight regulators include, but are not limited to, chloroform, halogenated hydrocarbons such as carbon tetrachloride, n-hexymercaptan, n-octylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan, thioglycol. In addition to mercaptans such as acids, xanthogens such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide, terpinolene and α-methylstyrene dimer, all those usable in ordinary emulsion polymerization can be used. Among these, n-dodecyl mercaptan is preferably used.

The amount of the molecular weight regulator used is preferably 5 parts by mass or less based on 100 parts by mass of the total amount of monomers used in polymerizing each part.

[Adhesive for lithium ion secondary batteries]
The binder for nonaqueous secondary batteries of this embodiment is used as an adhesive for lithium ion secondary batteries.
The adhesive for lithium ion secondary batteries is used, for example, to bond a separator and an electrode. The adhesive for lithium ion secondary batteries is used, for example, when forming an adhesive layer on a separator or electrode of a lithium ion secondary battery. In particular, a separator with an adhesive layer for a lithium ion secondary battery can be manufactured by applying an adhesive for a lithium ion secondary battery onto a separator to form an adhesive layer. For a more detailed configuration of the lithium ion secondary battery, reference can be made to, for example, those described in Japanese Patent Application Laid-Open No. 2015-41603.

[Binder for porous layer in non-aqueous secondary batteries]
The binder for non-aqueous secondary batteries of this embodiment can be suitably used as a binder for porous layers in non-aqueous secondary batteries.
The porous layer binder is used, for example, to form a porous layer on a separator by bonding an inorganic filler or the like by point adhesion, and to improve the heat resistance of the separator while maintaining lithium ion permeability.

[Slurry for lithium ion secondary battery porous layer]
The slurry for a porous layer of a lithium ion secondary battery of this embodiment includes water, an inorganic filler, and the binder for a non-aqueous secondary battery of this embodiment.

The slurry for a porous layer of a lithium ion secondary battery of the present embodiment is prepared by applying the slurry to the surface of a separator substrate for an electricity storage device, for example, and then drying the slurry to coat the inorganic filler and particulate copolymer on the substrate. A dispersion liquid used to form a porous layer containing. The slurry for a porous layer of a lithium ion secondary battery according to the present embodiment may contain a conductive additive, a thickener, a non-aqueous solvent, and the like, if necessary.

[Lithium ion secondary battery porous layer]
The lithium ion secondary battery porous layer of this embodiment includes an inorganic filler and the nonaqueous secondary battery binder of this embodiment.

(Inorganic filler)
The inorganic filler used in the porous layer of lithium ion secondary batteries is not particularly limited, but it has a melting point of 200°C or higher, has high electrical insulation properties, and is electrochemically stable within the range of use of lithium ion secondary batteries. Something is preferable.

Inorganic fillers include, but are not limited to, oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitrides such as silicon nitride, titanium nitride, and boron nitride. Material ceramics; silicon carbide, calcium carbonate, barium sulfate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, seri Examples include ceramics such as Cyto, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; glass fiber, and the like. These may be used alone or in combination of two or more.

Among these, aluminum oxide compounds such as alumina, aluminum hydroxide, aluminum hydroxide oxide (AlO(OH)); and kaolinite, dickite, nacrite, It is preferable to use an aluminum silicate compound having no ion exchange ability, such as halloysite or pyrophyllite, or barium sulfate.

Note that alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Among these, α-alumina is preferred from the viewpoint of thermal and chemical stability.

As the aluminum oxide compound, aluminum hydroxide oxide (AlO(OH)) is preferable. As the aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing internal short circuits caused by the generation of lithium dendrites. By employing particles containing boehmite as the main component as the inorganic filler constituting the porous layer of the lithium ion secondary battery of this embodiment, the porous layer of the lithium secondary battery becomes extremely lightweight while maintaining high permeability. In addition, even when a thinner lithium ion secondary battery porous layer is formed, thermal shrinkage of the separator at high temperatures is suppressed, and excellent heat resistance tends to be exhibited. More preferred is synthetic boehmite, which can reduce ionic impurities that adversely affect the properties of electrochemical devices.

As the aluminum silicate compound without ion exchange ability, kaolin, which is mainly composed of kaolin minerals, is more preferable because it is inexpensive and easily available. As for kaolin, wet kaolin and calcined kaolin made by firing the same are known.
In this embodiment, calcined kaolin is more preferred. Calcined kaolin tends to have excellent electrochemical stability because water of crystallization is released and impurities are also removed during the firing process.

The average particle diameter of the inorganic filler used in the porous layer of a lithium ion secondary battery is preferably greater than 0.01 μm and less than or equal to 2.0 μm, more preferably greater than 0.1 μm and less than or equal to 1.5 μm. , more preferably more than 0.2 μm and 1.0 μm or less. Setting the average particle diameter of the inorganic filler within the above range is preferable from the viewpoint of suppressing thermal shrinkage of the separator at high temperatures even when the thickness of the porous layer is thin (for example, 4 μm or less). Examples of methods for adjusting the average particle size and distribution of the inorganic filler include a method of reducing the particle size by pulverizing the inorganic filler using an appropriate pulverizing device such as a ball mill, bead mill, jet mill, etc. can.

Examples of the shape of the inorganic filler include a plate, a scale, a needle, a column, a sphere, a polyhedron, and a lump. You may use multiple types of inorganic fillers having these shapes in combination.

The proportion of the inorganic filler in the porous layer of the lithium ion secondary battery of this embodiment can be appropriately determined from the viewpoints of the binding properties of the inorganic filler, the permeability of the separator, heat resistance, and the like. The proportion of the inorganic filler in the porous layer of a lithium ion secondary battery is preferably 20 parts by mass or more and less than 100 parts by mass, more preferably 50 parts by mass, when the total of the inorganic filler and particulate copolymer is 100 parts by mass. It is 99.99 parts by mass or less, more preferably 80 parts by mass or more and 99.9 parts by mass or less, even more preferably 90 parts by mass or more and 99.5 parts by mass or less.

The thickness of the lithium ion secondary battery porous layer of this embodiment is preferably 0.5 μm or more from the viewpoint of improving heat resistance and insulation properties, and from the viewpoint of increasing the capacity and permeability of the battery. It is preferable that it is 4 μm or less.

The layer density of the lithium ion secondary battery porous layer of this embodiment is preferably 0.5 g/cm ³ or more and 3.0 g/cm 3 or less, and 1.0 g/cm ^{3 or} more and 2.5 g/cm ³ or less. It is more preferable that When the layer density of the lithium ion secondary battery porous layer of this embodiment is 0.5 g/cm ³ or more, the thermal shrinkage rate at high temperatures tends to be good. When the layer density of the lithium ion secondary battery porous layer of this embodiment is 3.0 g/cm ³ or less, the air permeability tends to decrease.

As a method for forming the lithium ion secondary battery porous layer of this embodiment, for example, coating containing an inorganic filler and the non-aqueous secondary battery binder of this embodiment on at least one side of a porous base material constituting a separator is possible. An example is a method of applying a liquid. In this case, the coating liquid may contain a solvent, a dispersant, a thickener, etc. in order to improve dispersion stability, coating properties, and storage properties.

[Separator for lithium ion secondary batteries]
The lithium ion secondary battery separator (separator) of this embodiment includes the lithium ion secondary battery porous layer of this embodiment.
The separator can include a porous base material and a porous layer disposed on at least a portion of at least one side of the porous base material.
The porous layer is a lithium ion secondary battery porous layer of this embodiment, and contains the above-mentioned particulate copolymer.
This separator may be comprised only of the porous base material and the lithium ion secondary battery porous layer of this embodiment, and may further have an adhesive layer with the electrode in addition to these.

When a lithium ion secondary battery separator has a lithium ion secondary battery porous layer, the porous layer is arranged on one or both sides of the porous base material of the separator.

Preferred embodiments of each member constituting the separator and the method for manufacturing the separator will be described in detail below.

(Porous base material)
A porous base material is a base material that has holes or voids inside, and the porous base material itself is one that has been conventionally used as a separator for secondary batteries. be able to. As a porous base material, it is important to have excellent coating properties when forming a porous layer through a coating process, and to make the separator film thinner, so that it can be used as an active material in power storage devices such as batteries. From the viewpoint of increasing the ratio and increasing the capacity per volume, a polyolefin microporous membrane containing a polyolefin resin as a main component is preferable. Here, "containing as a main component" means containing in an amount exceeding 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, and even more. The content is preferably 95% by mass or more, more preferably 98% by mass or more, and may be 100% by mass.

Surface treatment on the surface of the polyolefin microporous membrane makes it easier to apply the coating solution afterwards, and improves the adhesion between the polyolefin microporous membrane and the porous layer. It is preferable to apply
Examples of the surface treatment method include a corona discharge treatment method, a plasma treatment method, a mechanical surface roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

(Method for arranging a lithium ion secondary battery porous layer containing inorganic filler)
The lithium ion secondary battery porous layer of the present embodiment is prepared by applying a coating liquid containing an inorganic filler, a particulate copolymer, and, if necessary, additional components such as a solvent (e.g., water) and a dispersant. It can be placed on a porous substrate by coating at least one side of the porous substrate.
The particulate copolymer may be synthesized by emulsion polymerization, and the resulting emulsion may be used as it is as a coating liquid.
The coating liquid preferably contains a poor solvent for the particulate copolymer, such as water or a mixed solvent of water and a water-soluble organic medium (for example, methanol or ethanol).

The method of applying the coating liquid to the porous base material of the separator is not particularly limited as long as the required layer thickness and coating area can be achieved.
Coating methods include, for example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, and rod coater method. , a squeeze coater method, a cast coater method, a die coater method, a screen printing method, a spray coating method, an inkjet coating method, and the like. In particular, the gravure coater method is preferable because it has a high degree of freedom in coating shape.

The method for removing the solvent from the coated film after coating is not limited as long as it does not adversely affect the porous base material and the porous layer of a lithium ion secondary battery. Examples include a method of drying at a temperature below the melting point of the base material while fixing the base material, a method of drying under reduced pressure at a low temperature, and the like.

The method for removing the solvent from the coated film after coating is not particularly limited as long as it does not adversely affect the porous base material and the porous layer of the lithium ion secondary battery. For example, methods include drying at a temperature below the melting point of the polyolefin porous substrate while fixing it, drying under reduced pressure at low temperature, and immersing the particulate copolymer in a poor solvent for the particulate copolymer to form particles. Examples include a method of coagulating and simultaneously extracting the solvent.

[Lithium ion secondary battery]
The lithium ion secondary battery of this embodiment includes the lithium ion secondary battery separator of this embodiment.
The structure of the lithium ion secondary battery of this embodiment other than including the separator of this embodiment is a conventionally known lithium ion secondary battery, for example, as described in JP 2018-92701A. It may be similar to a battery.

The particulate copolymer used in the binder for a non-aqueous secondary battery of this embodiment can be included in a porous layer on a separator, and a film containing a separator and a porous layer is referred to as a coated film.
The heat shrinkage rate at 150°C in the coating film is not particularly limited, but is preferably 0% or more and less than 40% in both MD and TD, more preferably 0% or more and less than 35%, and even more preferably 0% or more and less than 40%. % or more and 30% or less. By having a heat shrinkage rate of 30% or less at 150°C in both MD and TD directions, it is possible to prevent the separator from breaking even when the battery is abnormally heated, and to suppress contact between the positive and negative electrodes, making it even better. This tends to result in better safety performance.

Hereinafter, the present embodiment will be described in more detail using Examples and Comparative Examples, but the present invention is not limited to the following Examples.
Various physical properties were measured and evaluated using the following measurement methods and evaluation methods.

[Solid content concentration]
Approximately 1 g of an aqueous dispersion of a particulate copolymer obtained in the Examples and Comparative Examples described below was accurately weighed on an aluminum plate, and the mass (g) of the aqueous dispersion weighed at this time was designated as a. It was dried in a hot air dryer at 130° C. for 1 hour, and the dry mass (g) of the copolymer after drying was defined as b.
The solid content concentration was calculated using the following formula.
Solid content concentration (%) = b/a x 100

[pH of water dispersion of particulate copolymer]
The electrode of a pH meter (glass electrode hydrogen ion concentration indicator manufactured by Toa DK Co., Ltd.) was immersed in an aqueous dispersion of particulate copolymer with a solid content concentration of approximately 40%, and the displayed value was read. .

[Glass transition temperature of particulate copolymer]
An appropriate amount of an aqueous dispersion (solid content concentration 38-42%, pH 8.0) containing the particulate copolymer obtained in the Examples and Comparative Examples described later was placed in an aluminum dish, and dried in a hot air dryer at 130°C for 60 minutes. Dry for a minute.
Approximately 17 mg of the dried film was packed into an aluminum container for measurement, and a DSC curve and a DDSC curve were obtained in a nitrogen atmosphere using a DSC measurement device (manufactured by Shimadzu Corporation, model number: DSC6220).
Note that the measurements were performed using the following program.
(1st stage temperature increase program)
Starting at 70°C, the temperature was raised at a rate of 15°C per minute. After reaching 110°C, it was maintained for 5 minutes.
(Second stage temperature reduction program)
The temperature was lowered from 110°C at a rate of 30°C per minute. After reaching -50°C, it was maintained for 4 minutes.
(3rd stage temperature increase program)
The temperature was raised from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were acquired during this third stage of temperature rise.
The intersection of the straight line extending the baseline of the obtained DSC curve toward the high temperature side and the tangent at the inflection point was defined as the glass transition temperature (Tg).

[Average particle diameter of particulate copolymer]
The 50% particle diameter (μm) was measured using a particle diameter measuring device using a light scattering method (manufactured by LEED & NORTHRUP, trade name "MICROTRAC UPA150"), and was defined as the average particle diameter.
Thereby, the number average particle diameter (Dn) and the volume average particle diameter (Dv) were obtained, and their ratio: Dv/Dn was calculated.

[Electrolyte swelling degree]
3 g of an aqueous dispersion (solid content concentration 38-42%, pH 8.0) containing the particulate copolymer obtained in the Examples and Comparative Examples described later was placed in an aluminum dish, and dried in a hot air dryer at 130°C for 60 minutes. Dry for a minute. After drying, the dried film was cut into pieces of 0.5 g, placed in a 50 mL vial together with 10 g of a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1:2 (volume ratio), and shaken for 3 hours. A sample was taken out, washed with the above mixed solvent, and its mass (Wa) was measured. Thereafter, the particulate copolymer was left to stand in an oven at 150° C. for 1 hour, and then its mass (Wb) was measured, and the degree of swelling of the particulate copolymer with respect to the electrolytic solution was measured using the following formula.
Although the above mixed solvent did not contain an electrolyte, it was confirmed that there was no difference in the degree of swelling of the particulate copolymer regardless of the presence or absence of the electrolyte.
Swelling degree (times) of particulate copolymer in electrolyte solution = (Wa-Wb)/Wb

[Viscosity, slurry blending workability, solution stability]
Weighed 100 g of an aqueous dispersion (solid content concentration 30 to 42%, pH 5.0) containing the particulate copolymer obtained in the Examples and Comparative Examples described later into a polypropylene bottle, and measured it with a BM type viscometer ( The viscosity was measured at a spindle rotation speed of 60 rpm (initial viscosity: ηi) using a TV-100B (manufactured by Toki Sangyo Co., Ltd.).
Thereafter, the sample was stored for two weeks in a constant temperature bath maintained at 60° C., and then the viscosity was measured again under the same conditions as above using the BM type viscosity system (viscosity after storage: ηf).
Using these measured values, slurry blending workability and solution stability were evaluated according to the following criteria.
<Evaluation criteria for slurry blending workability>
A: ηi is less than 300 mPa・s B: ηi is 300 mPa・s or more and less than 2000 mPa・s C: ηi is 2000 mPa・s or more <Evaluation criteria for solution stability>
A: ηf/ηi is 0.8 or more and less than 2.0 B: ηf/ηi is 0.5 or more and less than 0.8 or 2.0 or more and less than 3.0 C: ηf/ηi is less than 0.5 or 3.0 or higher

[Storage modulus]
The storage modulus of the particulate copolymer was measured according to the JIS K 7244 standard.
Approximately 12 g of an aqueous dispersion (solid content concentration: 40%) of the particulate copolymer obtained in the Examples and Comparative Examples described below was poured onto a polypropylene plate divided into 15 cm squares, and dried at room temperature for one day. The resulting polymer film was molded into a 5 mm x 70 mm square to form a test piece.
The thickness of the obtained test piece was recorded using a film thickness meter (DIGIMATIC INDICATOR, manufactured by MITSUTOYO) as an average value at a total of three points: the center of the sample and points ±20 mm from the center in the long side direction.
Using a viscoelasticity measuring device (manufactured by Rheometric Scientific, product name RSA3), distance between chucks 50 mm, initial temperature 30 °C, final temperature 140 °C, heating rate 5 °C/min, 1.0 Hz, tensile strain at 0.1% strain. - The tensile storage modulus was measured in compression mode, and the values of the storage modulus at 30°C and the storage modulus at 130°C were obtained.
In Tables 1 to 6 below, the notation "E+a" in the storage modulus value means ×10 ^a .

[Adhesion (peel strength)]
A dispersion liquid for forming a porous layer was obtained using an aqueous dispersion of a particulate copolymer obtained in the Examples and Comparative Examples described later and according to (formation of a coating film) described later.
The above-mentioned dispersion liquid for forming a porous layer was applied to the surface of a corona-treated polyethylene porous substrate. Thereafter, a drying process was performed to form a porous layer, and a coated film having a total thickness of 17 μm was obtained.
This coating film was attached to a 15 mm x 75 mm preparation using double-sided tape so that the polyethylene porous substrate side was adhered.
Thereafter, a mending tape with a width of 12 mm was pasted onto the porous layer, one end of the mending tape was pulled in the vertical direction at a pulling speed of 100 mm/min, and the stress when peeled off was measured. The measurement was carried out three times, and the average value was calculated and used as the peel strength.
The larger the peel strength value, the better the adhesion between the polyethylene porous base material and the porous layer, and was evaluated based on the following criteria.
<Adhesion evaluation criteria>
A: 300gf/cm or more B: 150gf/cm or more but less than 300gf/cm C: Less than 150gf/cm

[Heat shrinkage resistance]
Coated films were obtained using aqueous dispersions of particulate copolymers obtained in Examples and Comparative Examples described below and in accordance with (formation of coated film) described below.
It was cut into pieces of 100 mm in the MD direction and 100 mm in the TD direction, and left in an oven at 150° C. for 1 hour. At this time, the sample was sandwiched between two sheets of paper so that the hot air did not directly hit the sample. After taking out the sample from the oven and cooling it, the length (mm) was measured, and the heat shrinkage rate was calculated using the following formula.
The measurement was performed in the MD direction and the TD direction, and the larger value was taken as the heat shrinkage rate, and the heat shrinkage resistance was evaluated according to the following criteria.
Heat shrinkage rate (%) = {(100-length after heating)/100} x 100
<Evaluation criteria for heat shrinkage resistance>
A: Heat shrinkage rate less than 3% B: Heat shrinkage rate 3% or more and less than 10% C: Heat shrinkage rate 10% or more

[Moisture content of separator]
A separator with a porous layer was obtained using an aqueous dispersion of a particulate copolymer obtained in the Examples and Comparative Examples described later, and in accordance with (formation of a coated film) described later.
The separator was cut into pieces ranging from 0.15 g to 0.20 g and pretreated at 23° C. and 40% relative humidity for 12 hours. Thereafter, the mass was measured and defined as the sample mass (g).
The water mass (μg) of the sample after pretreatment was measured using a Karl Fischer apparatus. The heating vaporization conditions during the measurement were 150° C. and 10 minutes. Further, Hydranal Coulomat CG-K (manufactured by SIGMA-ALDRICH) was used as the cathode reagent, and Hydranal Coulomat AK (manufactured by SIGMA-ALDRICH) was used as the anode reagent.
The water content of the separator was calculated according to the following formula and evaluated according to the following criteria.
Separator water content W (ppm) = water mass (μg) / sample mass (g)
<Evaluation criteria for separator moisture content>
A: W is less than 800 ppm B: W is 800 ppm or more and less than 1500 ppm C: W is 1500 ppm or more

[Characteristics of small batteries (rate characteristics)]
<Preparation of positive electrode>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as a positive electrode active material, carbon black as a conductive aid, and polyvinylidene fluoride solution as a binder at a solid content mass ratio of 91:5:4. After mixing, N-methyl-2-pyrrolidone was added as a dispersion solvent so that the solid content was 68% by mass, and further mixing was performed to prepare a slurry solution. This slurry solution was applied to one side of a 15 μm thick aluminum foil so that a portion of the aluminum foil was exposed, and then the solvent was removed by drying to give a coating amount of 175 g/m ² . Further, it was rolled using a roll press so that the density of the positive electrode mixture portion was 2.8 g/cm ³ . Thereafter, the coated area was cut to a size of 30 mm x 50 mm and included the exposed portion of the aluminum foil, and an aluminum lead piece was welded to the exposed portion of the aluminum foil to obtain a positive electrode.
<Preparation of negative electrode>
Artificial graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose aqueous solution are mixed at a solid content mass ratio of 96.4:1.9:1.7, and water is used as a dispersion solvent at a solid content of 50 mass. % and further mixed to prepare a slurry solution. This slurry solution was applied to one side of a 10 μm thick copper foil so that a portion of the copper foil was exposed, and then the solvent was removed by drying to give a coating amount of 86 g/m ² . Furthermore, it was rolled using a roll press so that the density of the negative electrode mixture portion was 1.45 g/cm ³ . Thereafter, the coated area was cut to be 32 mm x 52 mm and included the exposed copper foil portion, and a nickel lead piece was welded to the exposed copper foil portion to obtain a negative electrode.
<Preparation of non-aqueous electrolyte>
In a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1:2 (volume ratio), LiPF ₆ as a solute was dissolved at a concentration of 1.0 mol/L, and vinylene carbonate was further dissolved at a concentration of 1.0% by mass. was added to prepare a non-aqueous electrolyte.
<Cell assembly>
A separator with a porous layer was obtained using an aqueous dispersion of a particulate copolymer obtained in the Examples and Comparative Examples described below and according to (formation of a coating film) described later. I cut it out. The positive electrode, separator, and negative electrode were laminated in this order to form a laminate. At this time, the porous layer side of the coating film obtained according to (formation of coating film) described below was arranged so as to face the positive electrode.
This laminate was inserted into an 80 mm x 60 mm aluminum laminate exterior body.
Next, the non-aqueous electrolyte was injected into the exterior body, and the opening was then sealed to produce a small battery.

The assembled small battery was charged at 25°C with a constant current of 2mA (approximately 0.05C) to a battery voltage of 4.2V, and then with constant voltage charging to maintain 4.2V for a total of about 21 hours after battery creation. The battery was first charged, and then discharged to a battery voltage of 3.0V at a current value of 7mA. After that, the battery was charged at a constant current of 12 mA (approximately 0.3 C) until the battery voltage reached 4.2 V, and then the constant voltage was maintained at 4.2 V for a total of approximately 5 hours. Discharging to .0V was repeated three times.

Next, at 25°C, charge the battery to a voltage of 4.2V with a constant current of 12mA (approximately 0.3C), and then charge the battery at a constant voltage of 4.2V for a total of 5 hours, and then charge the battery with a current value of 36mA. (approximately 1.0 C) to a battery voltage of 3.0 V, and the discharge capacity at that time was defined as 1 C discharge capacity (mAh).

Next, at 25°C, charge the battery with a constant current of 12 mA (approximately 0.3 C) to a battery voltage of 4.2 V, and then charge with constant voltage charging to maintain 4.2 V for a total of about 5 hours, after which the current value The battery was discharged at 72 mA (approximately 2.0 C) to a battery voltage of 3.0 V, and the discharge capacity at that time was defined as 2C discharge capacity (mAh).

The ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was used as the rate characteristic, which was evaluated based on the following criteria.
Rate characteristics (%) = (2C discharge capacity/1C discharge capacity) x 100

<Evaluation criteria for rate characteristics>
A: Rate characteristic 90% or more B: Rate characteristic 80% or more but less than 90% C: Rate characteristic less than 80%

[Cycle characteristics]
The small battery whose rate characteristics were evaluated as described above was charged at 60°C with a current value of 6 mA (approximately 1.0 C) to a battery voltage of 4.2 V, and after reaching 4.2 V, while adjusting the current value. The cycle of maintaining the voltage at 4.2V, charging for a total of 3 hours, and discharging to a battery voltage of 3.0V at a current value of 6mA was repeated 100 times, and the discharge capacity (mAh) of the 1st and 100th cycles was was measured.
The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was calculated, and this value was used as the cycle characteristic, which was evaluated according to the following criteria.
Cycle characteristics (%) = (100th discharge capacity/1st discharge capacity) x 100
<Evaluation criteria for cycle characteristics>
A: 90% or more B: 80% or more but less than 90% C: less than 80%

[Example 1]
(Production of particulate copolymer)
In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 65 parts by mass of ion-exchanged water and a 25% aqueous solution of "Aqualon KH1025" (registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a surfactant were added. , also written as "KH1025"), and 0.06 parts by mass of "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd., also written as "SR1025"). I put it in.
Next, the temperature inside the reaction vessel was raised to 75°C, and while maintaining the temperature at 75°C, 1.5 parts by mass of a 2% aqueous solution of ammonium persulfate (also referred to as "APS") was added. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the following emulsion was dripped into the reaction vessel from the dropping tank over a period of 150 minutes.
In addition, the emulsion was produced by the following method.
As a (meth)acrylic acid ester monomer;
Methyl methacrylate (also referred to as "MMA") 6.4 parts by mass,
42 parts by mass of butyl acrylate (also referred to as "BA"),
34 parts by mass of 2-ethylhexyl acrylate (also referred to as "2EHA"),
60 parts by mass of 2-hydroxyethyl methacrylate (also referred to as "HEMA"),
As an unsaturated carboxylic acid;
1 part by mass of methacrylic acid (also referred to as "MAA"),
1.5 parts by mass of acrylic acid (also referred to as "AA"),
As a (meth)acrylamide monomer;
0.1 part by mass of acrylamide (also referred to as "AAm"),
Methacrylamide (also described as "MAAm") 7 parts by mass as an epoxy group-containing monomer;
2 parts by mass of glycidyl methacrylate (also referred to as "GMA"),
As a crosslinkable monomer containing two or more vinyl groups;
2 parts by mass of trimethylolpropane triacrylate (ATMPT, trade name manufactured by Shin Nakamura Chemical Co., Ltd., also referred to as "A-TMPT"),
As a reactive surfactant;
"Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 7.5 parts by mass,
7.5 parts by mass of "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.),
As a polymerization initiator;
0.25 parts by mass of a 2% aqueous solution of ammonium persulfate,
and 83.2 parts by mass of ion-exchanged water,
A mixture was prepared by mixing for 5 minutes using a homomixer.
After the emulsion was added dropwise, the temperature inside the reaction vessel was raised to 80°C, maintained for 120 minutes, and then cooled to room temperature to obtain an emulsion.
The resulting emulsion was adjusted to pH 5.0 using an ammonium hydroxide aqueous solution (25% aqueous solution, also referred to as AW) to obtain an aqueous dispersion with a solid content concentration of 40%.
Regarding the particulate copolymer in the obtained aqueous dispersion, Tg, average particle diameter, and storage modulus were measured by the above method, and heat shrinkability and peel strength were evaluated.
The evaluation results are shown in Tables 1 to 6.

(Formation of coating film)
An aqueous dispersion containing 100 parts by mass (solid content concentration 50%) of aluminum hydroxide oxide particles (average particle diameter 1.0 μm) as an inorganic filler and a synthesized particulate copolymer as a resin binder (solid content concentration 40%). ) and 0.5 parts by mass of a polyphosphoric acid amine salt (dispersant solid content concentration 1%) as an ion-dissociative inorganic dispersant were uniformly dispersed to prepare a dispersion liquid for forming a porous layer.
The prepared dispersion for forming a porous layer was applied to the surface of a polyethylene porous base material which had been subjected to corona treatment in advance using a bar coater.
Thereafter, water was removed by drying at 60° C. for 1 minute, thereby obtaining a coating film with a total thickness of 17 μm, in which a porous layer with a thickness of 2 μm was formed on the polyethylene porous base material.
The evaluation results are listed in Tables 1 to 6 below.
Note that tripolyphosphoric acid was used as the "polyphosphoric acid".

[Examples 2 to 21, Comparative Examples 1 to 10]
Monomers and surfactants for forming particulate copolymers were blended as shown in Tables 1 to 6 below. Emulsion polymerization was carried out under the same conditions as in Example 1 to obtain an aqueous dispersion of a particulate copolymer.
In addition, in Tables 1 to 6,
TMPT is trimethylolpropane triacrylate,
EDMA is ethylene glycol diacrylate,
MA is methyl acrylate,
EA is ethyl acrylate,
CHMA is cyclohexyl methacrylate,
NMAM is N-methylolacrylamide,
DBS-Na is dodecylbenzenesulfonic acid,
APS is ammonium persulfate;
respectively.
Further, in the same manner as in Example 1, a porous layer was produced according to the above (formation of a coated film).
The Tg, average particle diameter, and storage modulus of the particulate copolymer in the resulting aqueous dispersion were measured by the above method, and the adhesion, heat shrinkage resistance, solution stability, slurry blending workability, and separator properties were determined. Moisture content, rate characteristics, and cycle characteristics were evaluated.
The evaluation results are shown in Tables 1 to 6.

The non-aqueous secondary battery binder of the present invention has industrial applicability as a material for a secondary battery separator.

Claims (13)

A binder for a non-aqueous secondary battery, comprising an aqueous medium and a particulate copolymer,
The particulate copolymer contains a vinyl monomer unit,
The vinyl monomer unit includes an acrylamide monomer unit (B1) and a methacrylamide monomer unit (B2),
The content W1 (parts by mass) of the acrylamide monomer unit (B1) and the content W2 (parts by mass) of the methacrylamide monomer unit (B2) with respect to 100 parts by mass of the total mass of the vinyl monomer units. ) satisfies the following formula (1),
The content W2 of the methacrylamide monomer unit (B2) is 2 parts by mass or more,
Binder for non-aqueous secondary batteries.
0<W1/W2<1...(1) The particulate copolymer has a glass transition temperature of 10°C or less,
The binder for non-aqueous secondary batteries according to claim 1. The particulate copolymer contains a vinyl monomer unit and a monomer unit derived from a reactive surfactant having a functional group copolymerizable with a vinyl group.
The binder for non-aqueous secondary batteries according to claim 1. The vinyl monomer unit includes a crosslinkable monomer unit containing two or more vinyl groups,
The content of the crosslinkable monomer unit containing two or more vinyl groups is 0.1 parts by mass or more and 5 parts by mass or less, based on 100 parts by mass of the particulate copolymer.
The binder for non-aqueous secondary batteries according to claim 1. The content W2 of the methacrylamide monomer unit (B2) with respect to 100 parts by mass of the total mass of the vinyl monomer unit is
2 parts by mass or more and less than 20 parts by mass,
The binder for non-aqueous secondary batteries according to claim 1. The particulate copolymer has a ratio Dv/Dn of the volume average particle diameter Dv and the number average particle diameter Dn,
1 or more and 1.5 or less,
The binder for non-aqueous secondary batteries according to claim 1. The particulate copolymer is
The storage modulus at 30° C. is 7×10 ⁷ Pa or more and 5×10 ⁸ Pa or less,
The storage modulus at 130° C. is 2×10 ⁶ Pa or more,
The binder for non-aqueous secondary batteries according to claim 1. The vinyl monomer unit further includes an epoxy group-containing vinyl monomer unit,
The binder for non-aqueous secondary batteries according to claim 1. The binder for a non-aqueous secondary battery is a binder for a porous layer in a non-aqueous secondary battery,
The binder for non-aqueous secondary batteries according to claim 1. water and,
Inorganic filler;
The binder for a non-aqueous secondary battery according to any one of claims 1 to 9,
including,
Slurry for porous layer of lithium ion secondary battery. Comprising the slurry for a lithium ion secondary battery porous layer according to claim 10,
Lithium ion secondary battery porous layer. A lithium ion secondary battery porous layer according to claim 11,
Separator for lithium ion secondary batteries. A lithium ion secondary battery, comprising the lithium ion secondary battery separator according to claim 12.