KR20240002930A - Binder for nonaqueous secondary battery, slurry for porous layer of li-ion secondary battery, porous layer of li-ion secondary battery, separator for li-ion secondary battery and li-ion secondary battery - Google Patents

Abstract

(Problem) Obtain a binder for non-aqueous secondary batteries that can form a layer that can suppress separator shrinkage even at high temperatures.
(Solution) A binder for a non-aqueous secondary battery comprising an aqueous medium and a particulate copolymer, wherein 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) relative to 100 parts by mass of the total mass of the vinyl monomer units are expressed by the following formula: (1) is satisfied,
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)

Description

Binder for non-aqueous secondary batteries, slurry for lithium ion secondary battery porous layers, lithium ion secondary battery porous layer, separator for lithium ion secondary batteries, and lithium ion secondary batteries {BINDER FOR NONAQUEOUS SECONDARY BATTERY, SLURRY FOR POROUS LAYER OF LI-ION SECONDARY BATTERY, POROUS LAYER OF LI-ION SECONDARY BATTERY, SEPARATOR FOR LI-ION SECONDARY BATTERY AND LI-ION SECONDARY BATTERY}

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

Conventionally, development of electrical storage devices represented by lithium ion secondary batteries has been actively carried out.

Usually, in the lithium ion secondary battery, a separator made of a microporous membrane is formed between the positive and negative electrodes. The separator has the function of preventing direct contact between positive and negative electrodes and also allowing ions to pass through the electrolyte solution held in the micropores.

Recently, in order to secure the electrical properties and safety of lithium ion secondary batteries while imparting various characteristics to the separator, a separator has been proposed in which a layer containing an inorganic filler and a resin binder is disposed on the surface of the substrate constituting the separator (e.g. For example, see Patent Document 1).

In Patent Document 1, a resin composition containing polymer particles formed of a first monomer having an acidic functional group, a second monomer having an amide group, and another third monomer and an inorganic filler is coated on a separator, and the resin is applied on the separator. A technology related to a lithium ion secondary battery having a protective layer made of a composition is disclosed.

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

Recently, there has been a demand for further improvement in the performance of secondary batteries. One of its performances is to further ensure safety when the secondary battery is used in a high temperature environment. As a technology for ensuring the safety of secondary batteries when used in such high-temperature environments, for example, a composition for a functional layer of a non-aqueous secondary battery containing organic particles and a solvent has been proposed, and the composition for a functional layer of a non-aqueous secondary battery includes , a technology for use as a material for forming a functional layer on a separator is disclosed (for example, see 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.

In secondary batteries, the micropores of the separator shrink when the battery generates heat, preventing passage of lithium ions and the like, and have the function of suppressing runaway of the secondary battery.

However, there is a problem that if the secondary battery runs away at a high temperature of about 150°C or higher, the separator shrinks and a short circuit of the electrode occurs. In particular, in recent years, the capacity of batteries has been increased, and the amount of heat generated during runaway tends to increase, so there is a demand 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 further optionally 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 in a predetermined range. In addition, 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.

Although the functional layer formed on the separator disclosed in Patent Document 3 has high heat resistance and shrinkage and is said to be able to ensure the safety of secondary batteries, there is still room for improvement with regard to suppressing shrinkage of the separator under high temperatures of 150°C or higher. There is a problem with this.

Additionally, Patent Document 4 discloses a material for a functional layer containing a predetermined amount of an epoxy group-containing monomer. The functional layer formed from the material for the functional layer disclosed in Patent Document 4 has excellent flexibility in a low temperature range (for example, 60°C) before heat shrinkage begins, and heat crosslinking proceeds at a high temperature of 150°C or higher. It is said to be hard, have high hot water resistance, and ensure the safety of secondary batteries.

However, since the material for the functional layer disclosed in Patent Document 4 has a low initial storage elastic modulus, the storage elastic modulus after thermal crosslinking at a high temperature of 150 ° C. or higher is not sufficiently high, and therefore, shrinkage of the separator is suppressed at a high temperature of 150 ° C. or higher. In terms of effectiveness, there is still a problem that there is room for improvement.

In addition, Patent Document 5 discloses a binder composition for electrical storage devices, the binder composition for electrical storage devices having a water-soluble polymer having a proportion of repeating units derived from (meth)acrylamide of 40 to 100% by mass as the main component, and there is. Such water-soluble polymers have excellent adhesion to inorganic pigments, but when the binder composition for electrical storage devices is applied on a separator together with an aqueous medium, the polymer dissolved in the aqueous medium penetrates into the pores, causing clogging, which reduces battery performance. It has a problem that it tends to deteriorate. In addition, since the water-soluble polymer increases the moisture content of the separator, the moisture content inside the battery increases, causing a side reaction in the electrolyte solution, which is highly likely to cause early deterioration of battery performance. There is also a problem in this respect that there is room for improvement. there is.

Furthermore, Patent Document 6 discloses a binder dispersion liquid for a non-aqueous secondary battery separator containing a particulate polymer containing 40 to 80 mass% of (meth)acrylamide. The binder dispersion for a non-aqueous secondary battery separator contains a particulate copolymer obtained by copolymerization of an ethylenically unsaturated monomer having a predetermined octanol/water partition coefficient and the (meth)acrylamide. A binder dispersion for a non-aqueous secondary battery separator having such a form can be considered to increase the heat resistance of the separator while not impairing conductivity when coated on a separator. However, the degree of water solubility of (meth)acrylamide, and Inferring from the viscosity of the binder dispersion, it contains a significant amount of water-soluble polymer, and like the binder composition for an electrical storage device disclosed in Patent Document 5 described above, the particulate polymer dissolved in the aqueous medium penetrates into the pores, causing clogging. , it has a problem that it tends to deteriorate battery performance.

Furthermore, Patent Document 7 and Patent Document 8 disclose a binder composition for a non-aqueous secondary battery containing a copolymer formed by copolymerizing a (meth)acrylamide monomer and a (meth)acrylic acid ester monomer. In these Patent Documents 7 and 8, it is described 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 composition for a non-aqueous secondary battery itself disclosed in Patent Documents 7 and 8 is not sufficiently high, and there is a problem that there is room for improvement in suppressing shrinkage of the separator at a high temperature of 150 ° C. or higher. there is.

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

As described above, the conventionally disclosed technology still has a problem in that a sufficient effect is not obtained in suppressing separator shrinkage at a high temperature of 150°C or higher.

Therefore, in the present invention, for example, a binder for non-aqueous secondary batteries capable of forming a layer capable of suppressing separator shrinkage even at high temperatures of about 150°C or higher, and a slurry for a porous layer of lithium ion secondary batteries containing the binder for non-aqueous secondary batteries. The purpose is to provide a lithium ion secondary battery porous layer containing the slurry for a lithium ion secondary battery porous layer, a separator for a lithium ion secondary battery containing the lithium ion secondary battery porous layer, and a lithium ion secondary battery.

The present inventors conducted intensive studies to achieve the above object and found that, in a binder for a non-aqueous secondary battery containing a particulate copolymer containing a vinyl monomer unit, the vinyl monomer unit is an acrylamide monomer unit (B1) and , a methacrylamide monomer unit (B2), and a content W1 (parts by mass) of the acrylamide monomer unit (B1) relative to 100 parts by mass of the total mass of the vinyl monomer unit, and the methacrylamide monomer unit ( By using a binder for a non-aqueous secondary battery in which the content W2 (parts by mass) of B2) has a predetermined relationship and the content W2 of the methacrylamide monomer unit (B2) is not less than a predetermined value, separator shrinkage can be prevented even at high temperatures. By finding out what could be suppressed, we came to complete the present invention.

That is, the present invention is as follows.

〔One〕

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) relative to 100 parts by mass of the total mass of the vinyl monomer units are expressed by the following formula: (1) is satisfied,

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〕

The binder for a non-aqueous secondary battery according to [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.

〔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 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the particulate copolymer,

The binder for a non-aqueous secondary battery according to any one of [1] to [3] above.

〔5〕

The ratio described in any one of [1] to [4] above, wherein the content W2 of the methacrylamide monomer unit (B2) relative to the total mass of 100 parts by mass of the vinyl monomer unit is 2 parts by mass or more and less than 20 parts by mass. Binder for aqueous secondary batteries.

〔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 non-aqueous secondary battery according to any one of [1] to [5] above, wherein the binder is 1 or more and 1.5 or less.

〔7〕

The particulate copolymer is,

The storage elastic modulus at 30°C is 7 × 10 ⁷ Pa or more and 5 × 10 ⁸ Pa or less,

A storage modulus at 130°C of 2×10 ⁶ Pa or more,

The binder for a non-aqueous secondary battery 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,

Inorganic filler,

Containing the binder for a non-aqueous secondary battery according to any one of [1] to [9] above,

Slurry for lithium ion secondary battery porous layer.

〔11〕

Containing the slurry for the lithium ion secondary battery porous layer described in [10] above,

Lithium ion secondary battery porous layer.

〔12〕

Containing 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 separator for a lithium ion secondary battery described in [12] above.

According to the present invention, a binder for a non-aqueous secondary battery capable of forming a layer capable of suppressing separator shrinkage even at high temperatures is obtained.

The mode for carrying out the present invention (hereinafter referred to as “present 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 of the present invention. possible.

In this specification, when referring to a “monomer”, this “monomer” includes all of the monomers constituting the particulate copolymer of the present embodiment.

In addition, in this specification, when a monomer is introduced into a polymer, it is described as a “monomer unit,” and the state before being introduced into a polymer is described as a “monomer” or “compound.”

In addition, in this specification, “(meth)acrylic acid ester” means both methacrylic acid ester and acrylic acid ester, and “(meth)acrylamide” includes both methacrylamide and acrylamide, respectively. It is used in the meaning of:

[Binder for non-aqueous secondary batteries]

The binder for a non-aqueous secondary battery of this embodiment contains an aqueous medium and a particulate copolymer.

The particulate copolymer includes a vinyl monomer unit, and 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) relative to 100 parts by mass of the total mass of the vinyl monomer units are expressed by the following formula: (1) is satisfied,

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 non-aqueous secondary batteries of this embodiment, it is possible to form a porous layer that can effectively suppress separator shrinkage even at a high temperature of about 150°C or higher, for example.

Usually, a microporous separator for a secondary battery is formed with a layer for the purpose of providing a function such as suppressing heat shrinkage of the separator. Examples of the method of forming the layer include a method of coating a composition containing an inorganic pigment, latex, a dispersant, a thickener, etc., and an aqueous medium. At this time, the separator and the above layer (also referred to as a coating layer) are required to have high adhesion to prevent peeling.

The present inventors studied the idea that by increasing the adhesion, the coating layer could strongly support the separator and effectively suppress heat shrinkage of the separator. However, as a result of examination, it was found that heat shrinkage of the separator could not be sufficiently suppressed in a coating layer adjusted to increase adhesive strength simply to strengthen the peel strength.

In addition, as a result of examination by the present inventors, in addition to adhesion under room temperature conditions, it is important to exhibit high adhesion even under high temperatures such as 150°C, where the polyolefin-based base material constituting the separator begins to shrink. Could know.

In addition, the present inventors have found that when the coating layer contains a predetermined amount of an amide group-containing vinyl monomer, especially a particulate copolymer containing a (meth)acrylamide monomer unit, as a polar component, the coating layer has It was found that the coating layer exhibited the desired behavior and could effectively suppress heat 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 the particulate copolymer, it is necessary to adjust the monomer distribution ratio between the aqueous medium and the particulate copolymer, specifically, the acrylamide monomer relative to the aqueous medium/particulate copolymer. Adjusting the distribution ratio and mainly using methacrylamide monomers from the viewpoint of copolymerization of the monomers, specifically, copolymerization of acrylamide monomers with other vinyl monomers, and methacrylamide monomers, By comparing the copolymerization with other vinyl monomers, we found that methacrylamide monomer has higher copolymerization and is easier to incorporate into the skeleton of the particulate copolymer, so it was important to mainly use methacrylamide monomer. .

(aqueous medium)

The binder for a non-aqueous secondary battery of this embodiment contains 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, lubricant, thickener, disinfectant, etc.

(particulate copolymer)

The binder for non-aqueous secondary batteries of this embodiment contains a particulate copolymer.

The particulate copolymer contains vinyl monomer units.

＜Vinyl monomer unit＞

A vinyl compound, which is a raw material monomer for forming the vinyl monomer unit constituting the particulate copolymer, is a monomer having a vinyl group, and includes both a vinyl compound (CH ₂ =CHX) and a vinylidene compound (CH ₂ =CXY), such as For example, (meth)acrylic acid ester, (meth)acrylic acid, (meth)acrylamide, aromatic vinyl compound, acrylonitrile, etc. are mentioned. Specifically, it is described in detail below.

These may be used individually by 1 type, or may be used in combination of 2 or more types.

<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.”

Raw material monomers 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 methacryl group, and specifically, a reactive interface described later. Compounds that can be used as activators include. These may be used individually by 1 type, or may be used in combination of 2 or more types.

The particulate copolymer using the vinyl monomer unit and “a monomer unit derived from a reactive surfactant having a functional group copolymerizable with a vinyl group” is excellent in chemical stability, and the separator using the binder for a non-aqueous secondary battery of the present embodiment is , its chemical structure tends to be difficult to decompose even when exposed to oxidizing conditions, reducing conditions, and high temperature conditions (for example, 150°C) inside the battery.

<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 the methacrylamide monomer unit (B2) contained in the particulate copolymer is 2 parts by mass or more, preferably 4 parts by mass or more, with respect to 100 parts by mass of the total mass of vinyl monomer units in the particulate copolymer, More preferably, it is 6 parts by mass or more, and even more preferably, it is 10 parts by mass or more.

The upper limit of the content of the methacrylamide monomer unit (B2) is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, with respect to 100 parts by mass of the total mass of vinyl monomer units in the particulate copolymer. It is preferably less than 20 parts by mass, and even more preferably is 15 parts by mass or less.

By setting the content of the methacrylamide monomer unit (B2) contained in the particulate copolymer to 2 parts by mass or more with respect to 100 parts by mass of the total mass of vinyl monomer units in the particulate copolymer, the binder for a non-aqueous secondary battery of the present embodiment is In addition to the increased adhesion at room temperature, the storage elastic modulus at high temperatures (for example, 130°C) increases, and there is a tendency to suppress heat shrinkage of the separator using the binder for non-aqueous secondary batteries of the present embodiment. there is. In addition, the content of the methacrylamide monomer unit (B2) is set to 30 parts by mass or less with respect to 100 parts by mass of the total mass of vinyl monomer units in the particulate copolymer, so that the ratio of the water-soluble component contained in the binder for a non-aqueous secondary battery of the present embodiment is This is suppressed and when coated as a slurry, clogging of the pores of the separator is reduced, so battery characteristics such as cycle characteristics and rate characteristics tend to improve.

As described above, the particulate copolymer 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) relative to 100 parts by mass of the total mass of the vinyl monomer units are expressed by the following formulas: (1) has the relationship.

0 ＜ W1/W2 ＜ 1··· (1)

Since the ratio of water-soluble components contained in the particulate copolymer is suppressed by satisfying the relationship of the above equation (1) and specifying W1 as less than W2, battery characteristics such as cycle characteristics and rate characteristics can be determined by the mechanism described above. This tends to improve.

A method of controlling the ratio of methacrylamide monomer units to 100 parts by mass of the total mass of vinyl monomer units in the particulate copolymer within the numerical range described above includes, for example, a method for producing a particulate copolymer described later. At the time of emulsion polymerization, a method of adjusting the mixing ratio of methacrylamide monomer to a value in accordance with the desired numerical range with respect to the total amount of vinyl monomer may be mentioned.

In addition, as a method of controlling to satisfy the relationship of the above formula (1), in the method for producing the particulate copolymer constituting the binder for a non-aqueous secondary battery of the present embodiment, the mixing ratio of methacrylamide monomer and acrylamide monomer is adjusted. , there is a method of adjusting the value according to the desired numerical range.

The content when the total mass of the vinyl monomer units of the methacrylamide monomer unit and the acrylamide monomer unit contained in the particulate copolymer of the present embodiment is 100 parts by mass is determined from the mixing ratio of the monomers at the time of production of the particulate copolymer. It may be calculated or calculated from various spectrum data using IR (ATR method) or the like. In addition, the amount of other monomer units contained in the particulate copolymer can be calculated by the same calculation method as that of the methacrylamide monomer unit.

(Storage modulus of particulate copolymer)

As described above, in order to suppress thermal shrinkage of the separator of a secondary battery even at a high temperature of, for example, 150° C. or higher, the binder for a non-aqueous secondary battery of the present embodiment sufficiently adheres to the separator and the inorganic filler and at the same time forms particulate aerial It is desirable for the polymer to have a high elastic modulus.

Since the particulate copolymer includes an acrylamide monomer unit (B1) and a methacrylamide monomer unit (B2), the binder for a non-aqueous secondary battery of the present embodiment has a high temperature range from room temperature to high temperature (e.g., 130°C). A particulate copolymer that has adhesion and maintains an excellent storage modulus E' is obtained.

The particulate copolymer contained in the binder for a non-aqueous secondary battery of the present embodiment has a storage elastic ^modulus of ⁷ × 10 ⁶ Pa or more is preferable. As a result, the coating layer containing the particulate copolymer exhibits the above-described behavior and tends to be able to suppress shrinkage of the separator having microporous even when the temperature of the separator is high.

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 more preferably 5 × 10 ⁶ Pa or more at 130°C.

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 more preferably 6 × 10 ⁶ Pa or more at 130°C.

In a preferred embodiment of the binder for a non-aqueous secondary battery of the present embodiment, the particulate copolymer contains one or more monomers selected from (meth)acrylic acid ester monomers, an acrylamide monomer, a methacrylamide monomer, and a carboxylic acid group. It is made of a copolymer containing a monomer and a crosslinkable monomer as monomer units, wherein the crosslinkable monomer contains an epoxy group-containing vinyl monomer, and the storage modulus of the particulate copolymer at 30°C is 1. It is 10 ⁷ Pa or more and 3 10 ⁸ Pa or less, and the storage elastic modulus at 130°C is 5 10 ⁶ Pa or more. The particulate copolymer having the above storage elastic modulus may be referred to as particulate copolymer I in this specification.

A method of controlling the storage modulus of the particulate copolymer to satisfy the above range includes using a (meth)acrylamide monomer in the particulate copolymer. Additionally, a method of further increasing the storage modulus of the particulate copolymer includes using an epoxy group-containing vinyl monomer. In this case, an epoxy group-containing vinyl monomer unit is included as the vinyl monomer unit in the particulate copolymer.

In addition, a method of controlling the storage elastic modulus of the particulate copolymer includes, as monomer units, one or more monomers selected from (meth)acrylic acid ester monomers, a carboxylic acid group-containing monomer, and a crosslinkable monomer, and these monomers A method of adjusting the type and mixing ratio may be mentioned.

As described above, the content W2 of the methacrylamide monomer unit (B2) contained in the particulate copolymer of the present embodiment is 2 parts by mass or more with respect to 100 parts by mass of the total mass of vinyl monomer units, more preferably. is 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 ratio of methacrylamide monomer is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably less than 20 parts by mass, with respect to 100 parts by mass of vinyl monomer unit mass, and even more preferably Preferably it is 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 more and 15 parts by mass, based on 100 parts by mass of the total mass of vinyl monomer units. or less, and more preferably 6 parts by mass or more and 10 parts by mass or less.

By setting the content of the methacrylamide monomer unit to 2 parts by mass or more, the particulate copolymer tends to have both high adhesion derived from hydrogen bonding force and a storage elastic modulus. Moreover, by setting it to 20 parts by mass or less, flexibility at room temperature increases and adhesion improves.

＜(meth)acrylic acid ester monomer＞

As described above, in order to appropriately control the storage modulus of the particulate copolymer, it is effective to use one or more monomers selected from (meth)acrylic acid ester monomers in the particulate copolymer.

The (meth)acrylic acid ester monomer is not limited to the following, but examples include (meth)acrylic acid ester having one ethylenically unsaturated bond.

In this specification, (meth)acrylic acid ester may be referred to as (meth)acrylate.

The (meth)acrylic acid ester having one ethylenically unsaturated bond is not limited to the following, but includes, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, and isobutyl acrylate. methyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, cyclohexyl acrylate, methyl methacrylate (in this specification, also referred to as methyl methacrylate). , ethyl methacrylate, propyl methacrylate, isopropyl acrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, (meth)acrylates having an alkyl group such as uryl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, and t-butylcyclohexyl acrylate; (meth)acrylates having an aromatic ring such as benzyl acrylate, phenyl acrylate, benzyl methacrylate, and phenyl methacrylate; etc. can be mentioned.

These (meth)acrylic acid ester monomers are used individually or in combination of two or more types.

The (meth)acrylate having an alkyl group is preferably a (meth)acrylate consisting of an alkyl group and a (meth)acryloyloxy group.

The (meth)acrylate having an aromatic ring is preferably a (meth)acrylate consisting of an aromatic ring and a (meth)acryloyloxy group.

The (meth)acrylic acid ester monomer is more preferably a (meth)acrylic acid ester monomer composed of an alkyl group having 4 or more carbon atoms and a (meth)acryloyloxy group, and (meth)acrylic acid ester monomer composed of an alkyl group having 6 or more carbon atoms and a (meth)acryloyloxy group. Acrylic acid ester monomers are more preferred, and include methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, and t-butylcyclohexyl acrylate. More preferably, one or more selected from the group consisting of methyl methacrylate, cyclohexyl methacrylate, butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate. It is more desirable. 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 adhesion to the electrode.

It is preferable that the (meth)acrylic acid ester monomer contains at least methyl methacrylate. Moreover, the content of methyl methacrylate is preferably 1.0 parts by mass or more with respect to 100 parts by mass of the total amount of (meth)acrylic acid ester monomers. By including 1.0 parts by mass or more of methyl methacrylate relative to 100 parts by mass of the total amount of (meth)acrylic acid ester monomer, the compatibility between the (meth)acrylic acid ester monomer and the (meth)acrylamide monomer increases, and copolymerization improves. In addition, the behavior of increasing the flexibility of the coating layer at low temperatures (that is, strengthening the peeling strength of the coating layer using the separator and the binder for non-aqueous secondary batteries of this embodiment) and hardening the coating layer at high temperatures is observed. It is easier to implement, and shrinkage of the separator tends to be more suppressed 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 even more preferably 8 parts by mass or more. The upper limit of the content of the 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 carboxylic acid group-containing monomer in the particulate copolymer.

The carboxylic acid group-containing monomer is not limited to the following, but examples include 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 acid monomers such as acrylic acid, methacrylic acid, half ester of itaconic acid, half ester of maleic acid, and half ester of fumaric acid; Dicarboxylic acid monomers such as itaconic acid, fumaric acid, and maleic acid; etc. can be mentioned.

The carboxylic acid group-containing monomer can be used individually or in combination of two or more types.

Among these, acrylic acid, methacrylic acid, and itaconic acid are preferable, and acrylic acid and methacrylic acid are more preferable.

The content of the carboxylic acid group-containing monomer is usually 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the vinyl monomer unit. 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, more preferably 1 part by mass, per 100 parts by mass of vinyl monomer unit mass. It is 4 parts by mass or less.

＜Crosslinkable monomer＞

As described above, in order to appropriately control the storage modulus of the 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-crosslinking structure during or after polymerization. These are used individually or in combination of two or more types.

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.

The epoxy group-containing vinyl monomer is not limited to the following, but examples include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methyl glycidyl acrylate, and methyl glycidyl methacrylate. Rates, etc. can be mentioned.

These are used individually or in combination of two or more types.

Monomers having a functional group that provides a self-crosslinking structure during or after polymerization include, in addition to the epoxy group-containing vinyl monomers described above, for example, hydroxyl group-containing vinyl monomers containing a hydroxyl group, and alkoxymethyl group-containing vinyl monomers containing an alkoxymethyl group. , and a hydrolyzable silyl group-containing vinyl monomer containing a hydrolyzable silyl group.

These are used individually or in combination of two or more types.

Crosslinkable monomers constituting the particulate copolymer include, in addition to epoxy group-containing vinyl monomers, monomers having two or more radically polymerizable double bonds, amino group-containing vinyl monomers, hydroxyl group-containing vinyl monomers, alkoxymethyl group-containing vinyl monomers, and hydrolyzable monomers. It is preferable to further include at least one member selected from the group consisting of vinyl monomers having a silyl group.

By using the crosslinkable monomer, for example, when the binder for non-aqueous secondary batteries containing the particulate copolymer of the present embodiment is used as an adhesive for electrodes or separators, it has excellent adhesiveness while maintaining appropriate fluidity. Therefore, it tends to be excellent in handling properties.

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

The polyfunctional (meth)acrylate may be bifunctional (meth)acrylate, trifunctional (meth)acrylate, or tetrafunctional (meth)acrylate.

The polyfunctional (meth)acrylate is not limited to the following, but includes, for example, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, and trimethylolpropane triacrylate. Acrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate can be mentioned. These are used individually or in combination of two or more types.

Among these, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate are preferred because they exhibit better resistance to electrolyte solution even in small amounts.

The amino group-containing vinyl monomer is not limited to the following, but examples include N,N-methylenebisacrylamide, diacetoneacrylamide, and N,N-dimethylaminoethylacrylamide.

The hydroxyl group-containing vinyl monomer is not limited to the following, but examples include hydroxyethyl (meth)acrylate such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; Hydroxypropyl (meth)acrylate such as 2-hydroxypropyl (meth)acrylate; Hydroxybutyl (meth)acrylate, such as 2-hydroxybutyl (meth)acrylate and 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 are used individually or in combination of two or more types.

Examples of the hydroxyl group-containing vinyl monomer include, in addition to the compounds described above, 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 are used individually or in combination of two or more types.

The alkoxymethyl group-containing vinyl monomer is not limited to the following, but includes, for example, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-butoxymethylmethacrylamide. Crylamide, etc. can be mentioned.

These are used individually or in combination of two or more types.

The hydrolyzable silyl group-containing vinyl monomer is not limited to the following, but includes, for example, vinyl silane, vinyl trimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ -Methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, etc. are mentioned. These are used individually or in combination of two or more types.

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 or more and 25 parts by mass or less, with respect to 100 parts by mass of the particulate copolymer. It is preferably 6 parts by mass or more and 25 parts by mass or less, and more preferably 8 parts by mass or more and 25 parts by mass or less.

By setting the content of the monomer unit formed by the crosslinkable monomer to a range of 2 parts by mass to 30 parts by mass, the layer containing the particulate copolymer formed on the separator of the secondary battery tends to be able to further suppress heat shrinkage of the separator. there is.

[Crosslinkable monomer containing 2 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 to 5 parts by mass, more preferably 0.3 to 3 parts by mass, and even more preferably 100 parts by mass of the particulate copolymer. Typically, it is 0.5 parts by mass or more and 2 parts by mass.

By setting the content of the crosslinkable monomer unit 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 can be improved. Moreover, by setting it to 5 parts by mass or less, the binder for non-aqueous secondary batteries of this embodiment has improved adhesion at room temperature and tends to be able to more effectively suppress shrinkage of the separator even at high temperatures.

(Form of particulate copolymer)

For example, the particulate copolymer of the present embodiment may be in the form of a dispersion in which a particulate copolymer (also referred to as latex particles) containing the various monomers described above as monomer units is dispersed in an aqueous medium.

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.

The solid content concentration in the aqueous medium dispersion is not particularly limited, but is usually 10% by mass or more and 60% by mass or less, and is 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, for example, improvement of dispersion stability due to high solid fractionation of the slurry. In addition, by setting it to 50% by mass or less, the viscosity of the aqueous medium dispersion containing the particulate copolymer is suppressed, and workability in slurry mixing work is improved.

(Viscosity of binder for non-aqueous secondary battery)

The viscosity of the binder for non-aqueous secondary batteries of this embodiment is not particularly limited, but is usually 2000 mPas or less, and is preferably 300 mPas or less.

If the viscosity of the binder for a non-aqueous secondary battery of this embodiment is 2000 mPas or less, handling properties improve, and workability in, for example, slurry mixing work improves.

Normally, the viscosity of the binder for non-aqueous secondary batteries can be reduced to an arbitrary value by adding adjustment water, but at the same time, the solid content concentration decreases, so a solid content concentration of at least 30% by mass or more that satisfies the above viscosity range This is particularly desirable.

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

(Glass transition temperature of particulate copolymer)

The upper limit of the glass transition temperature of the particulate copolymer contained in the binder for a non-aqueous secondary battery of the present embodiment is 10°C or lower, preferably 0°C or lower, and more preferably -5°C or lower.

Moreover, 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, there is a tendency that the composition containing the binder for non-aqueous secondary batteries can be easily applied when applying it on the separator of the secondary battery.

The glass transition temperature can be controlled, for example, by adjusting the type and content of the monomer units constituting the particulate copolymer, specifically, the content of (meth)acrylic acid ester monomer and/or unsaturated carboxylic acid. By adjusting , it can be controlled within the numerical range described above.

The glass transition temperature of the particulate copolymer can be measured by the method described in the Examples described above.

(Average particle diameter of particulate copolymer)

The particulate copolymer has a volume average particle diameter Dv of preferably 30 nm or more and 230 nm or less, more preferably 50 nm or more and 200 nm or less, and even more preferably 70 nm or more and 180 nm or less.

When 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 non-aqueous secondary batteries of the present embodiment to a separator, sufficient appropriate voids can be left, thereby removing the ions in the electrolyte solution. There is a tendency to maintain the permeable separator function.

The volume average particle diameter Dv and number average particle diameter Dn of the particulate copolymer can be controlled, for example, by manufacturing it using seed latex and surfactant in a desired ratio. Normally, as the amount of seed latex and surfactant used increases, the volume average particle diameter Dv and the number average particle diameter Dn tend to decrease.

The volume average particle diameter Dv and the number average particle diameter Dn can be measured by the method described in the Examples described later.

In the binder for non-aqueous secondary batteries of the present embodiment, the ratio Dv/Dn of the volume average particle diameter Dv and the number average particle diameter Dn of the particulate copolymer is preferably 1 or more and 2.5 or less, more preferably 1 or more and 2 or less, More preferably, it is 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 is obtained, and when used as a coating layer, The structure is also uniform, achieving high strength even at high temperatures, and heat 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. Methods for increasing dispersion stability include, for example, adding a surfactant into an aqueous medium during or after polymerization to increase steric and electronic repulsion between particulate copolymers.

The volume average particle diameter Dv and the number average particle diameter Dn can be measured by the method described in the Examples described later.

(Method for producing particulate copolymer)

The particulate copolymer used in the binder for non-aqueous secondary batteries of this embodiment can be produced by a known polymerization method. As a polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, or block polymerization is used.

In order to obtain the particulate copolymer as a dispersion, it is preferable to use an emulsion polymerization method as a polymerization method. The method of emulsion polymerization is not particularly limited, and conventionally known methods can be used.

As a method of emulsion polymerization, for example, in an aqueous medium, acrylamide monomer, methacrylamide monomer, if necessary, (meth)acrylic acid ester monomer, carboxylic acid group-containing monomer, and crosslinkable monomer, and also radical polymerization. In a dispersion system containing an initiator, a surfactant, and, if necessary, other additive components (for example, a molecular weight regulator) as basic components, a method of polymerizing the above-mentioned monomers is included.

During polymerization, a method of keeping the composition of the monomer supplied into the reaction system constant throughout the entire polymerization process, or a method of changing the composition of the supplied monomer sequentially or continuously during the polymerization process to change the composition of the particles of the resin dispersion produced, etc. , various methods can be used depending on need.

When the particulate copolymer is obtained by emulsion polymerization, for example, the obtained particulate copolymer may be in the form of an aqueous dispersion (latex) containing water and the particulate copolymer dispersed in the water.

As the (meth)acrylic acid ester monomer, the carboxylic acid group-containing monomer, and the crosslinkable monomer, the compounds described above 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 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 peroxo disulfate, peroxides, water-soluble azobis compounds, and redox systems of peroxide-reducing agents.

Examples of peroxo disulfate include potassium peroxo di sulfate (KPS), sodium peroxo di sulfate (NPS), and ammonium peroxo di sulfate (APS).

Examples of peroxides include hydrogen peroxide, t-butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide.

Water-soluble azobis compounds include, for example, 2,2-azobis(N-hydroxyethylisobutylamide), 2,2-azobis(2-amidinopropane)2hydrogen chloride, and 4,4-azo. Bis(4-cyanopentanoic acid) etc. can be mentioned.

The redox system of the peroxide-reducing agent includes, for example, the peroxide, sodium sulfooxylate formaldehyde, sodium bisulfite, sodium thiosulfate, sodium hydroxymethanesulfinate, L-ascorbic acid, and its salts, cuprous salts. , and a combination of one or two or more reducing agents such as 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 amount of monomers.

The surfactant forms micelles in an aqueous medium, provides a polymerization field for the polymerizable monomer, and provides dispersion stability by adsorbing to the surface of the particulate copolymer.

Ionic species of the surfactant include nonionic, anionic, and cationic species. However, from the viewpoint of dispersion stability, it is preferable to have nonionic, anionic, or both.

The surfactant may have an unsaturated double bond (for example, a vinyl group) capable of radical polymerization in its molecular structure. A surfactant having an unsaturated double bond capable of radical polymerization in its molecular structure is hereinafter described as a reactive surfactant.

Nonionic surfactants, which are non-reactive surfactants, are not limited to the following, but examples include non-reactive polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polycyclic phenyl ether, and polyoxyethylene. 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, alkylalkanolamide, polyoxyethylene alkyl Phenyl ether, etc. can be mentioned.

Anionic surfactants that are non-reactive surfactants include, but are not limited to, non-reactive alkyl sulfate esters, polyoxyethylene alkyl ether sulfate ester salts, alkyl benzene sulfonates, alkyl naphthalene sulfonates, and alkyl sulfonates. Succinate, alkyl diphenyl ether disulfonate, naphthalene sulfonic acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate ester, polyoxyethylene distyrenated phenyl ether sulfate ester, fatty acid salt, alkyl phosphate, polyoxyethylene alkyl phenyl. Ether sulfuric acid ester salts, etc. can be mentioned.

The anionic reactive surfactant, which is a reactive surfactant, is not limited to the following, but includes, for example, an ethylenically unsaturated monomer having a sulfonic acid group, a sulfonate group, or a sulfuric acid ester group and a salt thereof, and a sulfonic acid group or an ammonium salt thereof. A compound having a group that is an alkali metal salt (ammonium sulfonate group, or alkali metal sulfonate group) is preferable. Such anionic reactive surfactants are not limited to the following, but include, for example, alkylallyl sulfosuccinic acid salt (e.g., “Eleminol (trademark) JS-2” manufactured by Sanyo Chemical Company, “Eleminol ( Trademark) JS-5"; "Late water (trademark) S-120", "Late water (trademark) S-180A", "Late water (trademark) S-180" manufactured by Kao Corporation, etc.); Polyoxyethylene alkyl propenyl phenyl ether sulfate ester salt (for example, “Aquaron (trademark) SR-10” and “Aquaron (trademark) SR-1025” manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.). ) ; Ammonium = α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (examples include “Aquaron KH-1025” manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), etc. there is.

Nonionic reactive surfactants that are reactive surfactants include, but are not limited to, α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxy. Polyoxyethylene (for example, "Adekaria Soph NE-20", "Adekaria Soph NE-30", and "Adekaria Soph (trademark) NE-40" manufactured by Asahi Denka Industries, Ltd.) .) ; Polyoxyethylene alkylpropenylphenyl ether (for example, “Aquaron (trademark) RN-10”, “Aquaron (trademark) RN-20”, and “Aquaron (trademark) RN-30” manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd. ", "Aquaron (trademark) RN-50", etc.) can be mentioned.

The surfactant used in the polymerization process of the particulate copolymer preferably contains a reactive surfactant. Reactive surfactants may be used individually by one type, or may be used in combination of two or more types.

Since the particulate copolymer contained in the binder for a non-aqueous secondary battery of the present embodiment preferably has a vinyl monomer unit and a monomer unit derived from a reactive surfactant having a functional group copolymerizable with a vinyl group, the reactive surfactant is , it is preferable to use one that has excellent copolymerization with vinyl compounds. From this viewpoint, for example, polyoxyethylene alkylpropenylphenyl ether sulfate ester salt (for example, “Aquaron (trademark) SR-1025” manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., etc.) is preferred, and ammonium = It is preferable to use α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (for example, “Aquaron KH-1025” manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.). These are preferably used 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.

Reactive surfactants are effective for increasing the copolymerization of acrylamide monomers, methacrylamide monomers, and other vinyl monomers to produce a copolymer with uniform composition distribution.

The estimated mechanism is as follows.

First, a polymer elongation reaction is initiated between a portion of the methacrylamide monomer dissolved in water and the reactive surfactant. The growing polymer radicals form micelles, into which the remaining methacrylamide monomer and other vinyl monomers invade, and the copolymer grows.

By the above mechanism, the production of a water-soluble copolymer resulting from the homopolymerization of methacrylamide monomer is suppressed, and copolymerization with other vinyl monomers can proceed.

Uniform copolymer composition and suppression of the formation of water-soluble copolymer are important in terms of increasing the storage modulus of the particulate copolymer and preventing degradation of battery performance due to clogging when coated as a slurry on a separator. do.

From the viewpoint of opportunity for contact with the methacrylamide monomer in the water layer, it is particularly preferable to use an anionic reactive surfactant.

The molecular weight regulator is not limited to the following, but includes, for example, halogenated hydrocarbons such as chloroform and carbon tetrachloride, n-hexy mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, In addition to mercaptans such as thioglycolic acid and xantogens such as dimethylxanthogendisulfide and diisopropylxanthogendisulfide, terpinolene and α-methylstyrene dimer can be used in general emulsion polymerization. You can use everything. Among these, n-dodecyl mercaptan is preferably used.

The amount of the molecular weight regulator used is preferably 5 parts by mass or less with respect to 100 parts by mass of the total amount of monomers used when polymerizing each part.

[Adhesive for lithium ion secondary batteries]

The binder for non-aqueous secondary batteries of this embodiment is used as an adhesive for lithium ion secondary batteries.

Adhesives for lithium ion secondary batteries are used, for example, to bond separators and electrodes. 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 lithium ion secondary batteries can be manufactured by applying an adhesive for lithium ion secondary batteries on a separator to form an adhesive layer. For a more detailed configuration of the lithium ion secondary battery, refer to, for example, what is described in Japanese Patent Application Publication No. 2015-41603, etc.

[Binder for porous layer in non-aqueous secondary battery]

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 binder for a porous layer is used, for example, to form a porous layer on a separator by bonding an inorganic filler or the like by point adhesive, 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 the lithium ion secondary battery porous layer of this embodiment contains water, an inorganic filler, and the binder for non-aqueous secondary batteries of this embodiment.

The slurry for a lithium ion secondary battery porous layer of the present embodiment is applied, for example, to the surface of a separator substrate for an electrical storage device, dried, and a porous layer containing an inorganic filler and a particulate copolymer is formed on the substrate. It is a dispersion used to form. The slurry for the lithium ion secondary battery porous layer of this embodiment may contain a conductive additive, a thickener, a non-aqueous solvent, etc. as needed.

[Lithium ion secondary battery porous layer]

The porous layer of the lithium ion secondary battery of this embodiment contains an inorganic filler and the binder for non-aqueous secondary batteries of this embodiment.

(Inorganic filler)

The inorganic filler used in the porous layer of a lithium ion secondary battery is not particularly limited, but is preferably one that has a melting point of 200°C or higher, has high electrical insulation, and is electrochemically stable within the range of use of the lithium ion secondary battery.

The inorganic filler is not limited to the following, but examples include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; Nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride; Silicon carbide, calcium carbonate, barium sulfate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, Ceramics such as amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; Glass fiber, etc. can be mentioned. These may be used individually by 1 type, or may use 2 or more types together.

Among these, from the viewpoint of improving the electrochemical stability and heat resistance characteristics of the separator, aluminum oxide compounds such as alumina, aluminum hydroxide, and aluminum hydroxide (AlO(OH)); and aluminum silicate compounds without ion exchange ability, such as kaolinite, dickite, nacrite, halloysite, and pyrophyllite, or barium sulfate.

Additionally, alumina exists in many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and all can be used preferably. Among these, α-alumina is preferable from the viewpoint of thermal and chemical stability.

As the aluminum oxide compound, aluminum hydroxide (AlO(OH)) is preferable. As aluminum hydroxide, 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 a main component as the inorganic filler constituting the porous layer of the lithium ion secondary battery of this embodiment, a very lightweight lithium secondary battery porous layer is obtained while maintaining high permeability, and thinner lithium ion Even when a secondary battery porous layer is formed, heat shrinkage of the separator at high temperatures is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite, which can reduce ionic impurities that adversely affect the properties of electrochemical devices, is more preferable.

As an aluminum silicate compound without ion exchange ability, kaolin, which is mainly composed of kaolin mineral, is more preferable because it is inexpensive and easy to obtain. Among kaolin, wet kaolin and calcined kaolin obtained by calcining this are known.

In this embodiment, calcined kaolin is more preferred. Calcined kaolin tends to have excellent electrochemical stability because crystal water is released and impurities are removed during the calcining treatment.

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 2.0 μm or less, more preferably greater than 0.1 μm and 1.5 μm or less, and still more preferably greater than 0.2 μm and 1.0 μm or less. It is preferable to set the average particle diameter of the inorganic filler within the above range from the viewpoint of suppressing heat shrinkage of the separator at high temperatures even when the thickness of the porous layer is thin (for example, 4 μm or less). Methods for adjusting the average particle size and distribution of the inorganic filler include, for example, pulverizing the inorganic filler using an appropriate grinding device such as a ball mill, bead mill, or jet mill to reduce the particle size. .

The shape of the inorganic filler includes, for example, plate shape, scale shape, needle shape, column shape, spherical shape, polyhedral shape, block shape, etc. You may use a combination of multiple types of inorganic fillers having such shapes.

The proportion of the inorganic filler in the porous layer of the lithium ion secondary battery of the present embodiment can be appropriately determined from the viewpoint of the binding property of the inorganic filler, the permeability of the separator, and heat resistance. The ratio of the inorganic filler in the porous layer of the 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 or more and 99.99 parts by mass, when the total of the inorganic filler and the particulate copolymer is 100 parts by mass. parts by mass or less, more preferably 80 parts by mass or more and 99.9 parts by mass or less, and even more preferably 90 parts by mass or more and 99.5 parts by mass or less.

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

The layer density of the porous layer of the lithium ion secondary battery of this embodiment is preferably 0.5 g/cm3 or more and 3.0 g/cm3 or less, and more preferably 1.0 g/cm3 or more and 2.5 g/cm3 or less. When the layer density of the porous layer of the lithium ion secondary battery of this embodiment is 0.5 g/cm3 or more, the thermal contraction rate at high temperature tends to become good. When the layer density of the porous layer of the lithium ion secondary battery of this embodiment is 3.0 g/cm3 or less, the air permeability tends to decrease.

As a method of forming a porous layer for a lithium ion secondary battery of the present embodiment, for example, a coating liquid containing an inorganic filler and a binder for a non-aqueous secondary battery of the present embodiment is applied to at least one side of the porous substrate constituting the separator. Here's how to do it: 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 battery]

The separator (separator) for lithium ion secondary batteries of this embodiment includes the porous layer for lithium ion secondary batteries of this embodiment.

The separator may include a porous substrate and a porous layer disposed on at least a portion of at least one side of the porous substrate.

The said porous layer is a lithium ion secondary battery porous layer of this embodiment, and contains the particulate copolymer mentioned above.

This separator may be comprised only of the porous substrate and the lithium ion secondary battery porous layer of this embodiment, or may further have an adhesive layer with the electrode in addition to these.

When the separator for lithium ion secondary batteries has a lithium ion secondary battery porous layer, the porous layer is disposed on one side or both sides of the porous substrate of the separator.

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

(porous substrate)

A porous substrate is a substrate that has pores or voids inside, and the porous substrate itself can be one that has been conventionally used as a separator for secondary batteries. As a porous substrate, from the viewpoint of excellent coating properties when forming a porous layer through a coating process, and by making the film thickness of the separator thinner, the active material ratio in an electric storage device such as a battery is increased, thereby increasing the capacity per volume. From this point of view, a polyolefin microporous membrane containing a polyolefin-based resin as a main component is preferable. In addition, here, “containing as a main component” means containing more than 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more. Preferably it contains 95 mass% or more, more preferably 98 mass% or more, and may be 100 mass%.

By subjecting the surface of the polyolefin microporous membrane to surface treatment, it becomes easier to apply the coating solution thereafter and the adhesion between the polyolefin microporous membrane and the porous layer improves, so it is preferable to perform surface treatment.

Examples of surface treatment methods include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

(Method for placing lithium ion secondary battery porous layer containing inorganic filler)

The lithium ion secondary battery porous layer of the present embodiment includes, for example, an inorganic filler, a particulate copolymer, and, if necessary, a coating solution containing additional components such as a solvent (for example, water) and a dispersant, and the porous layer is It can be placed on a porous substrate by coating at least one side of the substrate.

The particulate copolymer may be synthesized by emulsion polymerization, and the obtained emulsion may be used as 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 substrate 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, the 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, Examples include the rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, and inkjet coating method. In particular, the gravure coater method is preferable because it has a high degree of freedom in the coating shape.

The method for removing the solvent from the coating film after coating is not limited as long as it does not adversely affect the porous substrate and the lithium ion secondary battery porous layer. For example, a method of drying at a temperature below the melting point of the substrate while fixing the substrate, a method of drying under reduced pressure at a low temperature, etc. can be mentioned.

The method for removing the solvent from the coating film after coating is not particularly limited as long as it is a method that does not adversely affect the porous substrate and the porous layer of the lithium ion secondary battery. For example, a method of drying a polyolefin porous substrate at a temperature below its melting point while fixing it, a method of drying under reduced pressure at a low temperature, or a method of immersing the particulate copolymer in a poor solvent to solidify the particulate copolymer into particulate form and simultaneously removing the solvent. Extraction methods, etc. may be mentioned.

[Lithium ion secondary battery]

The lithium ion secondary battery of this embodiment includes the separator for lithium ion secondary batteries of this embodiment.

The lithium ion secondary battery of the present embodiment has a configuration other than including the separator of the present embodiment, for example, as described in Japanese Patent Application Publication No. 2018-92701, a conventionally known lithium ion secondary battery. It may be the same as .

The particulate copolymer used in the binder for a non-aqueous secondary battery of this embodiment can be incorporated into a porous layer on a separator, and the film containing the separator and the porous layer is called a coating 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% for both MD and TD, more preferably 0% or more and 35% or less, and even more preferably It is 0% or more and 30% or less. When the thermal contraction rate at 150°C in both MD and TD is 30% or less, separator film rupture can be prevented even when the battery abnormally heats up, and contact between positive and negative electrodes can be suppressed, resulting in better safety. Performance tends to be achieved.

Example

Hereinafter, the present embodiment will be described in more detail using examples and comparative examples, but the present invention is not limited in any way to the following examples.

Various physical properties were measured and evaluated using the following measurement and evaluation methods.

[Solids concentration]

Approximately 1 g of the aqueous dispersion of the particulate copolymer obtained in the examples and comparative examples described later was accurately weighed on an aluminum dish, and the mass (g) of the measured aqueous dispersion was set to 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 set to b.

Solid content concentration was calculated using the following formula.

Solid content concentration (%) = b/a × 100

[PH of aqueous dispersion of particulate copolymer]

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

[Glass transition temperature of particulate copolymer]

An appropriate amount of the water dispersion (solid content concentration 38 to 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.

Approximately 17 mg of the dried film was placed in an aluminum container for measurement, and the DSC curve and DDSC curve under nitrogen atmosphere were obtained using a DSC measurement device (manufactured by Shimadzu Corporation, model number: DSC6220).

Additionally, the measurement was performed using the following program.

(1st stage temperature increase program)

Starting at 70°C, the temperature was increased at a rate of 15°C per minute. After reaching 110°C, it was maintained for 5 minutes.

(2nd stage temperature lowering 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 increased from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were acquired during the temperature increase in this third stage.

The intersection of the straight line extending the base line toward the high temperature side in the obtained DSC curve and the tangent at the inflection point was taken as the glass transition temperature (Tg).

[Average particle diameter of particulate copolymer]

Using a particle size measuring device by light scattering (LEED & NORTHRUP, brand name "MICROTRAC UPA150"), the 50% particle size (μm) was measured and taken as the average particle size.

As a result, the number average particle diameter (Dn) and volume average particle diameter (Dv) were obtained, and their ratio: Dv/Dn was calculated.

[Electrolyte swelling degree]

3 g of the water dispersion (solid content concentration 38 to 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. After drying, the dried film was cut to 0.5 g, placed in a 50 mL vial bottle along with 10 g of a mixed solvent of ethylene carbonate:ethylmethyl carbonate = 1:2 (volume ratio), shaken for 3 hours, then the sample was taken out and It was washed with a mixed solvent, and the mass (Wa) was measured. After that, the mass (Wb) was measured after leaving it in an oven at 150°C for 1 hour, and the degree of swelling of the particulate copolymer with respect to the electrolyte solution was measured using the following formula.

In addition, although the mixed solvent did not contain an electrolyte, it was confirmed that there was no difference in the swelling degree of the particulate copolymer regardless of the presence or absence of the electrolyte.

Swelling degree (fold) of particulate copolymer in electrolyte solution = (Wa - Wb)/Wb

[Viscosity, slurry mixing workability, solution stability]

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 was placed in a polypropylene bottle and measured using a BM type viscometer (TV manufactured by Toki Sangyo Co., Ltd.). -100B) was used to measure the viscosity under the condition of a spindle rotation speed of 60 rpm (initial viscosity: ηi).

After that, the sample was stored for 2 weeks in a thermostat maintained at 60°C, and then the viscosity was measured under the same conditions as above using a BM type viscometer (viscosity after storage: ηf).

Using these measurements, slurry mixing workability and solution stability were evaluated according to the following criteria.

<Evaluation criteria for slurry mixing 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 but less than 3.0

C: ηf/ηi is less than 0.5 or more than 3.0

[Storage modulus]

The storage elastic modulus of the particulate copolymer was measured according to the standards of JIS K 7244.

Approximately 12 g of the aqueous dispersion of the particulate copolymer (solid content concentration: 40%) obtained in the examples and comparative examples described later was poured onto a polypropylene plate divided into 15 cm by 15 cm, dried at room temperature for 1 day, and the resulting polymer was obtained. The film was molded into a size of 5 mm x 70 mm and used as a test piece.

The thickness of the obtained test piece was recorded as the average value at a total of three points ±20 mm from the center of the sample and along the long side from there using a membrane thickness meter (DIGIMATIC INDICATOR, manufactured by MITSUTOYO).

A viscoelasticity measuring device (manufactured by Rheometric Scientific, product name RSA3) was used, in tension-compression mode with a chuck distance of 50 mm, an initial temperature of 30°C, an end temperature of 140°C, a temperature increase rate of 5°C/min, 1.0 Hz, and a strain of 0.1%. The tensile storage modulus was measured, and the values of the storage modulus at 30°C and the storage elastic modulus at 130°C were obtained.

In Tables 1 to 6 below, the notation “E + a” in the numerical value of the storage elastic modulus means × 10 ^a .

[Adhesion (peel strength)]

Using the aqueous dispersion of the particulate copolymer obtained in the examples and comparative examples described later, a dispersion liquid for forming a porous layer was obtained according to (formation of a coating film) described later.

The dispersion liquid for forming a porous layer was applied to the surface of a corona-treated polyethylene porous substrate. After that, a drying treatment was performed to form a porous layer, and a coated film with a total film thickness of 17 µm was obtained.

This coating film was attached to a 15 mm × 75 mm prep plate with double-sided tape so that the polyethylene porous substrate side was adhered.

After that, a 12 mm wide mending tape was attached from above the porous layer, one end of the mending tape was pulled in the vertical direction at a tensile speed of 100 mm/min, and the stress when peeled off was measured. The measurement was performed three times, the average value was obtained, and this was used as the peeling strength.

The larger the peel strength value, the better the adhesion between the polyethylene porous substrate and the porous layer, which was evaluated according to the following criteria.

<Evaluation criteria for adhesion>

A: 300 gf/cm or more

B: More than 150 gf/cm but less than 300 gf/cm

C: Less than 150 gf/cm

[Heat resistance and shrinkage]

A coating film was obtained using the aqueous dispersion of the particulate copolymer obtained in the examples and comparative examples described later, and according to (formation of the coating film) described later.

It was cut into pieces of 100 mm in the MD direction and 100 mm in the TD direction, and left to stand in an oven at 150°C for 1 hour. At this time, the sample was sandwiched between two sheets of paper to prevent warm air from directly reaching the sample. After the sample was taken out of the oven and cooled, the length (mm) was measured, and the heat shrinkage rate was calculated using the following equation.

Measurements were conducted in the MD and TD directions, 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} × 100

<Evaluation criteria for heat resistance and shrinkage>

A: Heat shrinkage rate less than 3%

B: Heat shrinkage rate 3% or more but less than 10%

C: Heat shrinkage rate of 10% or more

[Moisture content of separator]

A separator provided with a porous layer was obtained using the aqueous dispersion of the particulate copolymer obtained in the Examples and Comparative Examples described later, and according to (formation of a coating film) described later.

The separator was cut to a size of 0.15 g to 0.20 g, and pretreated at 23°C and relative humidity of 40% for 12 hours. After that, the mass was measured and used as the sample mass (g).

The water mass (μg) of the sample after pretreatment was measured using a Curl Fischer apparatus. In addition, the heating and vaporization conditions during measurement were 150°C for 10 minutes. Additionally, Hydranal Coolomat CG-K (manufactured by SIGMA-ALDRICH) was used as the cathode reagent, and Hydranal Coolomat AK (manufactured by SIGMA-ALDRICH) was used as the anode reagent.

The water content of the separator was calculated according to the formula below and evaluated according to the following criteria.

Moisture content of separator W (ppm) = moisture mass (μg)/sample mass (g)

<Evaluation criteria for moisture content of separator>

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)]

<Production of a positive play>

LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as a positive electrode active material, carbon black as a conductive auxiliary agent, and a polyvinylidene fluoride solution as a binder were mixed at a solid mass ratio of 91:5:4, and used as a dispersion solvent. N-methyl-2-pyrrolidone was added to a solid content of 68% by mass and further mixed to prepare a slurry-like solution. This slurry-like 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, and the application amount was set to 175 g/m2. Additionally, the positive electrode mixture portion was rolled with a roll press so that the density was 2.8 g/cm3. After that, the applied area was cut to 30 mm

<Production of Negative Drama>

Artificial graphite as a negative electrode active material, styrene butadiene rubber as a binder, and carboxymethyl cellulose aqueous solution were mixed at a solid mass ratio of 96.4:1.9:1.7, water was added as a dispersing solvent to a solid content of 50 mass%, and further mixed to form a slurry. The upper solution was prepared. This slurry-like 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, and the application amount was set to 86 g/m 2 . Furthermore, the negative electrode mixture portion was rolled with a roll press so that the density was 1.45 g/cm3. After that, the application area was cut to 32 mm

<Preparation of non-aqueous electrolyte>

LiPF ₆ as a solute was dissolved in a mixed solvent of ethylene carbonate:ethylmethyl carbonate = 1:2 (volume ratio) at a concentration of 1.0 mol/L, and vinylene carbonate was further added at a concentration of 1.0 mass% to obtain a non-aqueous electrolyte solution. It was prepared.

<Assembly of cells>

A separator provided with a porous layer was obtained using the aqueous dispersion of the particulate copolymer obtained in the Examples and Comparative Examples described later, and according to (formation of a coating film) described later.

The separator was cut into 60 mm x 40 mm. The positive electrode, separator, and negative electrode were overlapped in that order to form a laminate. At this time, the porous layer side of the coating film obtained according to (formation of the coating film) described later was placed to face the positive electrode.

This laminate was inserted into an aluminum laminate exterior body of 80 mm x 60 mm.

Next, the non-aqueous electrolyte solution was injected into the exterior body, and the opening was then sealed to produce a small battery.

The assembled small battery is charged to a battery voltage of 4.2 V at a constant current of 2 mA (approximately 0.05 C) at 25°C, and further constant-voltage charging is maintained at 4.2 V, taking a total of approximately 21 hours, the first charge after manufacturing the battery. was performed, and then the battery was discharged to a voltage of 3.0 V at a current of 7 mA. After that, the battery is charged to a voltage of 4.2 V at a constant current of 12 mA (approximately 0.3 C), and further charged at a constant voltage maintaining 4.2 V for a total of approximately 5 hours. After that, the battery voltage is brought to 3.0 V at a current of 12 mA. Discharging was repeated three times until .

Next, at 25°C, the battery was charged to a voltage of 4.2 V at a constant current of 12 mA (approximately 0.3 C), and further charged at a constant voltage maintaining 4.2 V for a total of 5 hours, after which the current value was 36 mA ( The battery was discharged at about 1.0 C) to a battery voltage of 3.0 V, and the discharge capacity at that time was set to 1 C discharge capacity (mAh).

Next, at 25°C, the battery is charged to a voltage of 4.2 V with a constant current of 12 mA (approximately 0.3 C), and further charged at a constant voltage maintaining 4.2 V for a total of about 5 hours, after which the current value is 72 mA. (about 2.0 C) was discharged to a battery voltage of 3.0 V, and the discharge capacity at that time was set to 2 C discharge capacity (mAh).

The ratio of 2 C discharge capacity to 1 C discharge capacity was calculated, this value was used as the rate characteristic, and evaluation was made according to the following criteria.

Rate characteristics (%) = (2 C discharge capacity/1 C discharge capacity) × 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]

A small battery whose rate characteristics were evaluated as described above was charged to a battery voltage of 4.2 V at a current value of 6 mA (approximately 1.0 C) at 60°C. After reaching 4.2 V, the voltage was adjusted to 4.2 V while adjusting the current value. V was maintained continuously for a total of 3 hours, and the cycle of discharging to a battery voltage of 3.0 V at a current value of 6 mA was repeated 100 times, and the discharge capacity (mAh) at the 1st cycle and the 100th cycle was measured.

The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first time was calculated, this value was used as the cycle characteristic, and evaluation was made according to the following criteria.

Cycle characteristics (%) = (100th discharge capacity/1st discharge capacity) × 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, reflux condenser, dropping tank, and thermometer, 65 parts by mass of ion-exchanged water, and as a surfactant, “Aquaron KH1025” (registered trademark, Daiichi Kogyo Pharmaceutical Co., Ltd., 25% aqueous solution, “KH1025”) 0.06 part by mass of "Adecaria Soph SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd., also described as "SR1025") was added.

Next, the temperature inside the reaction vessel was raised to 75°C, and 1.5 parts by mass of a 2% aqueous solution of ammonium persulfate (also referred to as “APS”) was added while maintaining the temperature at 75°C. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the following emulsion liquid was added dropwise from the dropping tank to the reaction vessel over 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 butylacrylate (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 (meth)acrylamide monomer;

Acrylamide (also referred to as “AAm”) 0.1 part by mass,

Methacrylamide (also referred to 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;

Trimethylolpropane triacrylate (ATMPT, brand name manufactured by Shinnakamura Chemical Industry Co., Ltd., also referred to as “A-TMPT”) 2 parts by mass,

As a reactive surfactant;

“Aquaron KH1025” (registered trademark, Daiichi Kogyo Pharmaceutical Co., Ltd., 25% aqueous solution) 7.5 parts by mass,

“Adecaria Soph SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) 7.5 parts by mass,

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,

The mixture was prepared by mixing for 5 minutes using a homomixer.

After completion of the dropwise addition of the emulsion, 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 obtained emulsion was adjusted to pH 5.0 using an ammonium hydroxide aqueous solution (25% aqueous solution, also referred to as AW), and an aqueous dispersion with a solid content concentration of 40% was obtained.

For the particulate copolymer in the obtained aqueous dispersion, Tg, average particle diameter, and storage elastic modulus were measured by the above method, and heat shrinkage and peel strength were evaluated.

The evaluation results are shown in Tables 1 to 6.

(Formation of coating film)

100 parts by mass of aluminum hydroxide particles (average particle diameter 1.0 μm) as an inorganic filler (solids concentration 50%), 3.0 parts by mass of an aqueous dispersion containing the synthesized particulate copolymer as a resin binder (solids concentration 40%), and ion dissociation properties. A dispersion liquid for forming a porous layer was prepared by uniformly dispersing 0.5 parts by mass of polyamine salt (dispersant solid concentration: 1%) as an inorganic dispersant.

The prepared dispersion for forming a porous layer was applied to the surface of a previously corona-treated polyethylene porous substrate using a bar coater.

Thereafter, water was removed by drying at 60°C for 1 minute, thereby obtaining a coated film with a total film thickness of 17 µm, in which a 2 µm thick porous layer was formed on the polyethylene porous substrate.

The evaluation results are shown in Tables 1 to 6 below.

Additionally, tripolyphosphoric acid was used as “polyphosphoric acid.”

[Examples 2 to 21, Comparative Examples 1 to 10]

The monomers and surfactants for forming the particulate copolymer were mixed as shown in Tables 1 to 6 below. Other conditions: Emulsion polymerization was performed in the same manner as in Example 1, and an aqueous dispersion of the particulate copolymer was obtained.

Additionally, 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,

refers to each.

In addition, in the same manner as in Example 1, a porous layer was produced according to the above (formation of the coating film).

For the particulate copolymer in the obtained aqueous dispersion, Tg, average particle diameter, and storage elastic modulus were measured by the above method, and adhesion, heat shrinkage resistance, solution stability, slurry mixing workability, water content of the separator, rate characteristics, and cycle characteristics were evaluated. did.

The evaluation results are shown in Tables 1 to 6.

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

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) relative to 100 parts by mass of the total mass of the vinyl monomer units are expressed by the following formula: (1) is satisfied,
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) According to claim 1,
The particulate copolymer is a binder for a non-aqueous secondary battery having a glass transition temperature of 10°C or lower. According to claim 1,
A binder for a non-aqueous secondary battery, 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. According to claim 1,
The vinyl monomer unit includes a crosslinkable monomer unit containing two or more vinyl groups,
A binder for a non-aqueous secondary battery, wherein the content of the crosslinkable monomer unit containing two or more vinyl groups is 0.1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the particulate copolymer. According to claim 1,
The content W2 of the methacrylamide monomer unit (B2) relative to 100 parts by mass of the total mass of the vinyl monomer unit is,
A binder for a non-aqueous secondary battery comprising 2 parts by mass or more and less than 20 parts by mass. 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,
A binder for non-aqueous secondary batteries that is 1 or more and 1.5 or less. According to claim 1,
The particulate copolymer is,
The storage elastic modulus at 30°C is 7 × 10 ⁷ Pa or more and 5 × 10 ⁸ Pa or less,
A binder for non-aqueous secondary batteries having a storage modulus of 2×10 ⁶ Pa or more at 130°C. According to claim 1,
A binder for a non-aqueous secondary battery, wherein the vinyl monomer unit further includes an epoxy group-containing vinyl monomer unit. According to claim 1,
A binder for a non-aqueous secondary battery, wherein the binder for a non-aqueous secondary battery is a binder for a porous layer in a non-aqueous secondary battery. water,
Inorganic filler,
A slurry for a lithium ion secondary battery porous layer, comprising the binder for a non-aqueous secondary battery according to any one of claims 1 to 9. A lithium ion secondary battery porous layer comprising the slurry for a lithium ion secondary battery porous layer according to claim 10. A separator for lithium ion secondary batteries, comprising the lithium ion secondary battery porous layer according to claim 11. A lithium ion secondary battery comprising the separator for a lithium ion secondary battery according to claim 12.