KR20200141530A - Adhesive composition, separator structure, electrode structure, nonaqueous electrolyte secondary battery, and manufacturing method thereof - Google Patents

Abstract

An adhesive resin composition comprising an adhesive resin formed on the surface of a separator or electrode of a nonaqueous electrolyte secondary battery, and the adhesive resin is derived from a constituent unit derived from vinylidene fluoride and a monomer copolymerizable with the vinylidene fluoride. At least one vinylidene fluoride copolymer (a) containing structural units of the adhesive resin is included, the turbidity of the NMP solution of the adhesive resin is 2 or more and 95 or less, and the solution viscosity (A) of the acetone solution is 350 to 20000 mPa·s, and the ratio (A)/(B) of the solution viscosity (A) to the solution viscosity (B) of the NMP solution of the adhesive resin is 1 or more and 15 or less.

Description

Adhesive composition, separator structure, electrode structure, nonaqueous electrolyte secondary battery, and manufacturing method thereof

The present invention relates to an adhesive composition, a separator structure, an electrode structure, a nonaqueous electrolyte secondary battery, and a manufacturing method thereof.

Since non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have high voltage and high energy density, they are used in various applications, for example, as power sources for mobile electronic devices such as smartphones and electric vehicles.

A lithium ion secondary battery has a positive electrode, a negative electrode, a separator disposed therebetween, and an electrolyte. The separator serves as an ion passage in the battery, and has a function of preventing short circuit by direct contact between the positive electrode and the negative electrode.

In recent years, with the increase in capacity of lithium ion secondary batteries, the safety of batteries has become more important. For example, as one of the higher capacity of the battery, it is also considered to increase the charging voltage of the battery, but the oxidation environment in the battery is likely to become more severe and the separator is likely to be oxidatively deteriorated. When the separator is oxidatively deteriorated, the shutdown function or the like is liable to be impaired, and an internal short circuit is liable to occur. Therefore, it is required to increase the oxidation resistance of the separator. In addition, when the internal resistance of the battery increases due to the expansion and contraction of the electrode active material during charging and discharging of the battery, the battery characteristics (especially cycle characteristics) tend to decrease. Therefore, it is also required to suppress an increase in the internal resistance of the battery by bonding the separator and the electrode. From the viewpoint of realizing these, by forming an adhesive composition layer on the surface of a separator or electrode, and bonding the separator and the electrode through the adhesive composition layer, it has been studied to improve the oxidation resistance of the separator and the adhesion between the separator and the electrode. have.

As a separator having an adhesive composition layer, for example, having an adhesive composition layer of a coating liquid obtained by mixing a dispersion containing a copolymer particle of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) and an aqueous CMC solution. A separator is disclosed (for example, Patent Document 1).

Patent Document 1: International Publication No. 2014/185378

By the way, a battery having a separator or an electrode having such an adhesive composition layer may be exposed to a high temperature environment. Therefore, it is required that the adhesion between the separator and the electrode does not decrease even under a high temperature environment.

For example, for a battery having a separator or electrode on which an adhesive composition layer is formed, take a laminate cell as an example: 1) a process of obtaining a laminate by laminating a positive electrode and a negative electrode through a separator, 2) encapsulating the laminate in the laminate cell Then, after impregnating the electrolyte solution, it is produced through a process of sealing, and 3) heating or hot pressing the sealed laminate cell, and bonding the separator and the anode or the cathode through the adhesive composition layer. Since the battery is exposed to high-temperature heat in the heating or heat pressing step of 3), it is desired that the separator and the electrode can exhibit high adhesion even when exposed to such high temperature. In addition, in the heating or heat pressing process of 3), it is necessary to strictly perform temperature control, and a poor battery in which the electrode and the separator are not adhered is likely to be manufactured simply by a slight temperature shift. Accordingly, from the viewpoint of reducing the defective rate of the battery, it is required that the allowable heating or heat press temperature range (process window) be as wide as possible.

Also in the separator of Patent Document 1, it has been desired to have a high adhesion between the separator and the electrode when exposed to a high temperature and to have a wide process window. In particular, the adhesion between the separator and the negative electrode has not been sufficiently studied so far.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an adhesive composition comprising an adhesive resin having a wide process window while maintaining high adhesiveness between a separator and an electrode even when exposed to high temperatures. Further, an object of the present invention is to provide a separator structure, an electrode structure, a nonaqueous electrolyte secondary battery, and a manufacturing method thereof using the adhesive composition.

The adhesive composition of the nonaqueous electrolyte secondary battery of the present invention for solving the above problems is an adhesive composition comprising an adhesive resin formed on the surface of a separator or electrode of a nonaqueous electrolyte secondary battery, and the adhesive resin is vinylidene fluoride At least one vinylidene fluoride copolymer (a) comprising a constituent unit derived from and a constituent unit derived from a monomer copolymerizable with the vinylidene fluoride, and the adhesive resin in a solution having a concentration of 5% by mass The turbidity when dissolved in N-methyl-2-pyrrolidone (hereinafter simply referred to as "NMP") is 2 or more and 95 or less, and acetone so that the concentration in the solution is 10% by mass. The solution viscosity (A) when dissolved in NMP is 350 to 20000 mPa·s, and the adhesive resin is dissolved in NMP so that the concentration in the solution is 5% by mass. The ratio (A)/(B) of A) is 1 or more and 15 or less.

The separator structure of the present invention has a separator and an adhesive composition layer obtained by using the adhesive composition of the present invention formed on at least one surface thereof.

The electrode structure of the present invention comprises a current collector, an electrode having an electrode active material layer including an electrode active material formed on the current collector, and an adhesive composition layer obtained by using the adhesive composition of the present invention formed on the surface of the electrode active material layer. Have.

The nonaqueous electrolyte secondary battery of the present invention uses the adhesive composition of the present invention formed on at least one of a positive electrode, a negative electrode, a separator disposed therebetween, and between the separator and the positive electrode, and between the separator and the negative electrode. It has an adhesive composition layer obtained by doing.

The method of manufacturing a non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator disposed therebetween, and the adhesiveness of the present invention formed on at least one of between the separator and the positive electrode, and between the separator and the negative electrode. A step of obtaining a laminate having an adhesive composition layer obtained by using the composition, and bonding the separator and the positive electrode to the laminate through the adhesive resin composition layer, and/or bonding the separator and the negative electrode It includes a process to let you do.

According to the present invention, high adhesion between the separator and the electrode can be maintained even when exposed to high temperatures, and an adhesive composition having a wide process window in a heating or heat press process, and a separator structure, electrode structure, and battery and adhesion using the same It is possible to provide a method for preparing the composition.

The high adhesion between the separator and the electrode is that "the components of the adhesive composition layer formed between the separator and the electrode do not dissolve in the electrolyte solution even at a certain temperature or higher, but remain between the separator and the electrode" and "the adhesive composition layer. It is considered to be obtained by "having a high modulus of elasticity". In addition, the wide process window indicates that ``when exposed to high temperatures (such as a heating or heat press process), the components of the adhesive composition layer do not dissolve in the electrolyte solution even at a certain temperature or higher, and remain between the separator and the electrode." I think it is valid. In other words, in order to obtain an adhesive resin having a wide process window while maintaining high adhesion between the separator and the electrode even when exposed to high temperatures, it is effective to 1) lower the solubility in the electrolyte and 2) have a high modulus of elasticity. I think it is.

1) About

A polymer having low solubility in an electrolytic solution usually exhibits a low solubility in NMP and a high solubility in acetone. If the solubility in NMP is low, the turbidity when dissolved in NMP is likely to increase. When the solubility in acetone is high, the solution viscosity (A) is likely to increase when dissolved in acetone.

As a result of intensive study, the present inventors found that if the turbidity when the adhesive resin containing the vinylidene fluoride copolymer (a) was dissolved in NMP was 2 or more and 95 or less, the solubility in the electrolyte solution tends to be moderately low, and furthermore, When the solution viscosity (A) when dissolved is 350 to 20000 mPa·s, the affinity of the adhesive resin to the electrolyte solution can be partially controlled, and the solubility of the adhesive resin in the electrolyte solution can be reduced. Revealed (i) the requirements).

2) About

On the contrary, a polymer having a high modulus of elasticity usually tends to have a high solubility in NMP and a low solubility in acetone. When the solubility in NMP is high, the solution viscosity (B) tends to increase when dissolved in NMP. If the solubility in acetone is low, the solution viscosity (A) tends to be low when dissolved in acetone.

As a result of intensive study, the present inventors found that the ratio of the solution viscosity (A) of the acetone solution and the solution viscosity (B) of the NMP solution of the adhesive resin containing the vinylidene fluoride copolymer (a) (A)/(B) It was found that by setting the value of 1 or more and 15 or less, a high modulus of elasticity and low solubility in an electrolytic solution can be balanced in balance (requirement of (ii)).

That is, the adhesive resin containing the vinylidene fluoride copolymer (a) and satisfying the requirements of i) and ii) may have a low solubility in an electrolyte solution and a high modulus of elasticity.

i) The turbidity when the adhesive resin is dissolved in NMP is 2 or more and 95 or less, and the solution viscosity (A) when the adhesive resin is dissolved in acetone is 350 to 20000 mPa·s, and

ii) The ratio (A)/(B) of the solution viscosity (A) to the solution viscosity (B) when the adhesive resin is dissolved in NMP is 1 or more and 15 or less

In addition, in the present specification, when the adhesive resin is ``mixed'' in a solvent, even when the adhesive resin is partially dissolved in the solvent, it is referred to as ``dissolved'' in the same manner as when all of the adhesive resin is dissolved, and the mixture Is called "solution".

The turbidity or solution viscosity (B) when the adhesive resin containing the vinylidene fluoride copolymer (a) is dissolved in NMP, and the solution viscosity (A) when dissolved in acetone are the vinylidene fluoride copolymer (a) Molecular weight and branching amount of, vinylidene fluoride copolymer (a), content and distribution of a monomer (HFP or CTFE) copolymerizable with vinylidene fluoride or crosslinkable monomer in the vinylidene fluoride copolymer (a), and their distribution, vinylidene fluoride copolymer (a) in the adhesive resin It can be adjusted by the content ratio of, alkali treatment to the adhesive resin, or the like.

For example, in order to increase the turbidity of the NMP solution of i) or the solution viscosity (A) of the acetone solution, for example, a monomer (HFP or CTFE) capable of copolymerizing with vinylidene fluoride in the vinylidene fluoride copolymer (a) or crosslinking It is preferable to increase the content of the sex monomer, control the distribution, increase the molecular weight or branch amount of the vinylidene fluoride copolymer (a), and perform alkali treatment on the adhesive resin. On the other hand, in order to make the viscosity ratio (A)/(B) of ii) 15 or less, for example, the content of a monomer (HFP or CTFE) copolymerizable with vinylidene fluoride or a crosslinkable monomer should not be excessively increased, It is preferable that the molecular weight and branching amount of the vinylidene fluoride copolymer (a) are not excessively increased, and that the alkali treatment for the adhesive resin is not excessively performed.

In particular, the positive electrode often contains a vinylidene fluoride polymer as a binder, but the negative electrode often contains a resin different from a vinylidene fluoride polymer such as carboxymethyl cellulose (CMC) as a binder. Therefore, when an adhesive resin containing a vinylidene fluoride polymer is used, it is difficult to obtain the adhesiveness between the separator and the negative electrode compared to the adhesiveness between the separator and the positive electrode. On the other hand, the adhesive resin of the present invention that satisfies the requirements of i) and ii) and the adhesive composition comprising the same can maintain high adhesiveness between the separator and the negative electrode even under high temperature, and can widen the process window. have. The present invention was made on the basis of this knowledge.

1. Adhesive composition

The adhesive composition of the present invention contains at least an adhesive resin.

1-1. Adhesive resin

The adhesive resin contains at least a vinylidene fluoride copolymer (a).

(Vinylidene fluoride copolymer (a))

The vinylidene fluoride copolymer (a) contains a structural unit derived from vinylidene fluoride and a structural unit derived from a monomer copolymerizable with vinylidene fluoride.

Examples of the monomer copolymerizable with vinylidene fluoride include a fluorine-based monomer copolymerizable with vinylidene fluoride, a hydrocarbon-based monomer, and a monomer having a hydrogen bonding polar functional group (preferably a carboxyl group-containing monomer).

Examples of fluorine-based monomers copolymerizable with vinylidene fluoride include fluorine-containing monomers such as vinyl fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene, chlorotrifluoroethylene (CTFE), and hexafluoropropylene (HFP). Alkyl vinyl compounds are included.

Examples of the hydrocarbon-based monomer copolymerizable with vinylidene fluoride include ethylene and propylene.

Examples of the carboxyl group-containing monomer copolymerizable with vinylidene fluoride include unsaturated monobasic acids such as acrylic acid, methacrylic acid, 2-carboxyethyl acrylate, and 2-carboxyethyl methacrylate; Unsaturated dibasic acids such as maleic acid and citraconic acid; Monoesters of unsaturated dibasic acids such as maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester, acryloyloxyethyl succinic acid, acryloyloxypropyl succinic acid, methacrylic Royloxyethyl succinic acid and methacryloyloxypropyl succinic acid are included.

Among these, from the viewpoint of making crystallinity control easier, a fluorine-based monomer is preferable, tetrafluoroethylene, chlorotrifluoroethylene, and hexafluoropropylene are preferable, and hexafluoropropylene is more preferable.

The content of the structural unit derived from vinylidene fluoride in the vinylidene fluoride copolymer (a), and the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride differs depending on the form of the adhesive resin, and thus will be detailed later. Explain.

Further, the vinylidene fluoride copolymer (a) may be crosslinked from the viewpoint of further lowering the solubility in NMP and further increasing the adhesive strength with the electrode surface. That is, the vinylidene fluoride copolymer (a) is a structural unit derived from a crosslinkable fluorinated alkyl vinyl compound (hereinafter, also simply referred to as a "crosslinkable monomer") in addition to a monomer copolymerizable with vinylidene fluoride or vinylidene fluoride. It may contain more.

As the crosslinkable monomer, a polyfunctional monomer may be used, or after obtaining an uncrosslinked copolymer, a crosslinking reaction may be further performed using a polyfunctional monomer.

Examples of the crosslinkable monomer include perfluoro divinyl ether and perfluoro alkylene divinyl ether. In addition, perfluoroalkylene divinyl ether is a compound having a structure in which two vinyl ether groups in which all hydrogen atoms are substituted with fluorine atoms are bonded to a linear or branched divalent perfluoroalkylene group having 1 to 6 carbon atoms. can do.

The content of the constituent units derived from the crosslinkable monomer in the vinylidene fluoride copolymer (a) is preferably less than 5% by mass with respect to the total amount of all structural units constituting the vinylidene fluoride copolymer (a), and 0.5 to 4 mass. It is more preferable that it is %, and it is still more preferable that it is 1.2-3 mass %.

The form of the adhesive resin is not particularly limited, but it is preferably in the form of particles, for example, from the viewpoint of forming a porous adhesive composition layer when water is used as a dispersion medium. The shape of the adhesive resin particles is not particularly limited, but it is easy to satisfy the requirements (turbidity of NMP solution, solution viscosity (A) and viscosity ratio (A)/(B)) of the aforementioned i) and ii). In view of that, (1) a core portion (or shell portion) made of a vinylidene fluoride copolymer (a), and a different amount of vinylidene fluoride, a structural unit derived from a monomer copolymerizable with vinylidene fluoride than (a). It is preferable that they are core-shell-type particles containing a shell portion (or core portion) made of polymer (b), or (2) slanted-type particles made of vinylidene fluoride copolymer (a).

For example, in (1), after the core is polymerized, a monomer required to polymerize the shell is re-added, and the shell is polymerized on the outside of the core particle to obtain the core shell particles, whereas in (2), a single By controlling the polymer structure by polymerization, it is possible to impart variations in the resin composition and obtain an adhesive resin having physical properties equivalent to those of the core-shell particles.

(1) Core-shell particle

The core-shell particles containing the vinylidene fluoride copolymer (a) may have a core portion made of the vinylidene fluoride copolymer (a) and a shell portion made of a different vinylidene fluoride polymer (b); It may have a core portion made of a vinylidene fluoride polymer (b) and a shell portion made of a vinylidene fluoride copolymer (a). Among them, since the viscosity tends to increase when the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride is large, the vinylidene fluoride polymer having a small content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride (b ) Constituting the shell portion is preferable from the viewpoint of improving stability during coating and winding. That is, core-shell particles having a core portion made of a vinylidene fluoride copolymer (a) and a shell portion made of a different vinylidene fluoride polymer (b) are preferable.

When the total amount of the structural units derived from vinylidene fluoride in the vinylidene fluoride copolymer (a) constituting the core part and the structural units derived from a monomer copolymerizable with vinylidene fluoride is 100% by mass, a vinylidene fluoride copolymer The content of the structural unit derived from vinylidene fluoride in (a) is preferably 20 to 70% by mass, more preferably 30 to 60% by mass, and even more preferably 30 to 50% by mass. When the content of the structural unit derived from vinylidene fluoride is more than a certain level, it is easy to increase the solution viscosity (B) of the NMP solution of the core-shell particles containing the vinylidene fluoride copolymer (a), and the solution viscosity of the acetone solution (A) It is easy to lower it. Thereby, it is easy to make the viscosity ratio (A)/(B) below a certain level, and it is easy to increase the elastic modulus of the core-shell particle|grains containing the vinylidene fluoride copolymer (a). On the other hand, if the content of the structural unit derived from vinylidene fluoride is below a certain level, the turbidity of the NMP solution of the core-shell particles containing the vinylidene fluoride copolymer (a) or the solution viscosity (A) of the acetone solution is not too low. . Thereby, the solubility of the core-shell particles containing the vinylidene fluoride copolymer (a) in the electrolytic solution is not too high.

In addition, when the total amount of the structural units derived from vinylidene fluoride in the vinylidene fluoride copolymer (a) and the structural units derived from a monomer copolymerizable with vinylidene fluoride is 100% by mass, the vinylidene fluoride copolymer (a The content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride in) is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, and even more preferably 50 to 70% by mass. If the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride is more than a certain level, it is easy to increase the turbidity of the NMP solution of the particles containing the vinylidene fluoride copolymer (a) and the viscosity of the acetone solution (A). This makes it easy to lower the solubility of the core-shell particles containing the vinylidene fluoride copolymer (a) in the electrolytic solution. On the other hand, if the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride is not more than a certain amount, the solution viscosity (B) of the NMP solution of the core-shell particles containing the vinylidene fluoride copolymer (a) is not too low, Since the solution viscosity (A) of the acetone solution is not too high, it is easy to make the viscosity ratio (A)/(B) to a certain or less. Thereby, the elastic modulus of the core-shell particles containing the vinylidene fluoride copolymer (a) is not too low.

In particular, the vinylidene fluoride copolymer (a) may be crosslinked from the viewpoint of further lowering the solubility of the core-shell particles in the electrolytic solution. Further, from the viewpoint of not impairing the elastic modulus of the core-shell particles, the vinylidene fluoride copolymer (a) may not be crosslinked.

The vinylidene fluoride polymer (b) constituting the shell portion contains at least a structural unit derived from vinylidene fluoride.

The content of the structural unit derived from vinylidene fluoride in the vinylidene fluoride polymer (b) is preferably larger than the content of the structural unit derived from vinylidene fluoride in the vinylidene fluoride copolymer (a). Specifically, the content of the structural unit derived from vinylidene fluoride in the vinylidene fluoride polymer (b) is copolymerized with the structural unit derived from vinylidene fluoride in the vinylidene fluoride polymer (b) and any vinylidene fluoride described later. When the total amount of structural units derived from possible monomers is 100% by mass, it is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass. When the content of the structural unit derived from vinylidene fluoride in the vinylidene fluoride polymer (b) is 80% by mass or more, the solution viscosity (B) of the NMP solution of the core-shell particles containing the vinylidene fluoride copolymer (a) increases. It is easy, and since the solution viscosity (A) of the acetone solution tends to be low, it is easy to make the viscosity ratio (A)/(B) to a constant or less. Thereby, it is easy to increase the elastic modulus of the core-shell particle|grains containing the vinylidene fluoride copolymer (a).

If necessary, the vinylidene fluoride polymer (b) may further contain a structural unit derived from a monomer copolymerizable with vinylidene fluoride or a structural unit derived from a crosslinkable monomer. The monomers or crosslinkable monomers copolymerizable with vinylidene fluoride in the vinylidene fluoride polymer (b) may be the same as the monomers or crosslinkable monomers copolymerizable with vinylidene fluoride in the above-described vinylidene fluoride copolymer (a). have.

In particular, from the viewpoint of further lowering the solubility of the vinylidene fluoride polymer (b) in the electrolyte solution, the vinylidene fluoride polymer (b) may be crosslinked, that is, it may further contain a structural unit derived from a crosslinkable monomer. . For example, when the content of structural units derived from a monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) constituting the core part is small (for example, less than 50% by mass), or a vinylidene fluoride copolymer When the solution viscosity (A) of the acetone solution of the particles containing (a) is low (for example, less than 600 mPa·s), the turbidity of the NMP solution is difficult to increase with only the core portion, and the solubility in the electrolyte solution is not sufficiently low. There are cases that do not. In this case, it is preferable that the vinylidene fluoride polymer (b) constituting the shell portion is crosslinked.

Conversely, when the content of structural units derived from a monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) constituting the core portion is large (for example, 50% by mass or more), or a vinylidene fluoride copolymer When the solution viscosity (A) of the particles containing (a) is high (for example, 600 mPa·s or more), it is easy to increase the turbidity of the NMP solution only by the core portion, and the solubility in the electrolyte solution is likely to be sufficiently low. In this case, the vinylidene fluoride polymer (b) constituting the shell portion may not be crosslinked.

In addition, when forming the adhesive resin composition layer containing inorganic fine particles, from the viewpoint of improving the coating property by increasing the dispersion stability between the inorganic fine particles and the adhesive resin, the vinylidene fluoride polymer (b) is copolymerized with vinylidene fluoride. As possible monomers, it is preferable to include a structural unit derived from a monomer having a hydrogen bonding polar functional group (preferably a carboxyl group-containing monomer).

When the amount of all the monomers contained in the core-shell particle is 100% by mass, the content of vinylidene fluoride is preferably 97% by mass or less, more preferably 50 to 97% by mass, and even more 60 to 95% by mass. desirable.

In core-shell particles having a core portion made of a vinylidene fluoride copolymer (a) and a shell portion made of a vinylidene fluoride polymer (b), the mass ratio of the core portion and the shell portion is not particularly limited, but, for example, the core portion/ It is preferable that it is a shell part = 40/60 to 99/1, it is more preferable that it is 50/50 to 90/10, and it is still more preferable that it is 50/50 to 70/30. When the mass ratio of the core portion is high, it is easy to sufficiently lower the solubility in the electrolyte solution, and when the mass ratio of the shell portion is high, it is easy to sufficiently increase the elastic modulus. The adhesive resin composition layer obtained from such core-shell particles is easy to maintain good adhesion to the electrode even under high temperature, and at the same time, it is easy to further widen the process window in the heating or hot pressing process.

(2) About slanted particles

It is preferable that the slanted particles made of the vinylidene fluoride copolymer (a) have a compositional variation from the center of the particles to the surface layer.

For example, slanted particles with a low content of structural units derived from a monomer copolymerizable with vinylidene fluoride on the outside of the particles (a slanted particles having a large content of structural units derived from vinylidene fluoride on the outside of the particles) are polymers. It can be obtained by controlling the structure of By increasing the amount of structural units derived from monomers that can be copolymerized with vinylidene fluoride inside the particles, and increasing the amount of vinylidene fluoride outside the particles, as in the case of the core-shell type particles in (1), during coating or winding It is possible to improve the stability. Such slanted particles include, for example, a part of vinylidene fluoride during polymerization and a monomer copolymerizable with vinylidene fluoride more than a part of vinylidene fluoride, initiating polymerization, and after the pressure is lowered, vinylidene fluoride It can be obtained by adding the remainder of and polymerization.

On the other hand, when the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride is relatively small compared to the core-shell type particle, the viscosity that affects the stability during coating or winding is difficult to develop. Structural units derived from leade may be unevenly distributed, and structures derived from a monomer copolymerizable with vinylidene fluoride and a crosslinked structure may be unevenly distributed in the surface layer. This makes it possible to increase the elastic modulus of the center portion while lowering the solubility of the inclined particles in the electrolyte solution in the surface layer portion. Such slanted particles, for example, when a crosslinked structure is unevenly distributed in the surface layer, a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride are polymerized during polymerization, and the crosslinkable monomer and vinylidene fluoride are reduced after the pressure is reduced. The remainder of can be obtained by polymerization by post-adding while maintaining a constant pressure.

In the slanted particles comprising the vinylidene fluoride copolymer (a), the total amount of the constituent units derived from vinylidene fluoride in the vinylidene fluoride copolymer (a) and the constituent units derived from a monomer copolymerizable with vinylidene fluoride When it is set as 100 mass%, the content of the structural unit derived from vinylidene fluoride in the vinylidene fluoride copolymer (a) is preferably 50 to 99 mass%, more preferably 60 to 95 mass%, and 70 to Even more preferably 95% by mass. In addition, when the total amount of the structural units derived from vinylidene fluoride in the vinylidene fluoride copolymer (a) and the structural units derived from a monomer copolymerizable with vinylidene fluoride is 100% by mass, the vinylidene fluoride copolymer (a The content of the structural unit derived from the monomer copolymerizable with vinylidene fluoride in) is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 5 to 30% by mass.

1-2. Properties of adhesive resin

(Acetone solution properties)

(1) Preparation of acetone solution

The powdered adhesive resin is dissolved in acetone so that the concentration in the acetone solution becomes 10% by mass. Specifically, after dispersing the adhesive resin in a sample bottle taken by weighing acetone at room temperature, putting it in a water bath set at 45°C and stirring for about 2 hours, acetone solution in which some or all of the adhesive resin is dissolved Prepare it. The turbidity and solution viscosity of the acetone solution are preferably measured immediately after the prepared acetone solution is allowed to cool to room temperature.

(2) turbidity

The turbidity of the prepared acetone solution is preferably 80 or less, more preferably 1 to 60, and even more preferably 2 to 55. When the turbidity is 80 or less, the solubility of the adhesive resin in the electrolytic solution tends to be low.

The turbidity of the solution can be measured with a turbidity meter (turbidity meter). Specifically, acetone was put in a linear cell (size 10×36×55 mm) so that the height was 4 cm or more and less than 4.5 cm, and a turbidimeter (NIPPON DENSHOKU INDUSTRIES CO. ., LTD.)) Product, NDH2000) after putting it into the measuring part, standardized under the conditions of room temperature 20±2℃, humidity 50±5%, light source D65·C, and measurement method 3 (measurement method in accordance with JIS K7136) Perform. Then, the acetone solution in which the adhesive resin was dissolved is placed in a cell, and the turbidity of the solution is measured under the same conditions.

(3) Solution viscosity (A)

It is preferable that the solution viscosity (A) of the prepared acetone solution is 350 to 20000 mPa·s. If the solution viscosity (A) is 350 mPa·s or more, the solubility of the adhesive resin in the electrolyte solution tends to be low because the molecular weight (branching amount) of the adhesive resin is large, and if it is 20000 mPa·s or less, the solubility in NMP is too high. Does not deteriorate. From these viewpoints, the solution viscosity (A) of the adhesive resin is more preferably 200 to 10000 mPa·s, and still more preferably 500 to 6200 mPa·s.

The viscosity of the solution can be measured with an E-type viscometer. Specifically, 1.1 ml of the solution was put in the measuring unit of a viscometer (RE550 type viscometer manufactured by Toki Sangyo Co., Ltd.), and a cone rotor 1°34'×R24, rotation speed 10 The measurement was performed at rpm, measurement time 300 seconds, and measurement temperature of 25°C. The viscosity at the time of 300 seconds is taken as the solution viscosity.

(NMP solution properties)

(1) Preparation of NMP solution

The powdered adhesive resin is added to NMP (N-methylpyrrolidone) so that the concentration in the NMP solution is 5% by mass, and part or all of it is dissolved. Specifically, the adhesive resin was put in a sample bottle measuring NMP, dispersed at room temperature, heated so that the solution temperature was 50°C, stirred for about 5 hours to dissolve part or all of the adhesive resin, Prepare a solution.

(2) turbidity

It is preferable that the turbidity of the prepared NMP solution is 2 to 95. When the turbidity is 2 or more, the solubility of the adhesive resin in the electrolytic solution tends to be low. When the turbidity is 95 or less, the melting point of the adhesive resin does not fall too low. The turbidity of the NMP solution of the adhesive resin is more preferably 2 to 75 from the above viewpoint, and even more preferably 2.5 to 60. The turbidity of the NMP solution can be measured in the same manner as described above. In addition, standardization is performed by putting NMP in the cell.

(3) Solution viscosity (B)

The solution viscosity (B) of the prepared NMP solution may be within a range in which the ratio (A)/(B) of the solution viscosity (A) to (B) becomes a range described later. Solution viscosity (B) can be measured in the same manner as described above.

In order to appropriately increase the turbidity of the NMP solution and increase the viscosity (A) of the acetone solution, for example, a monomer that can be copolymerized with vinylidene fluoride in the vinylidene fluoride copolymer (a) constituting the adhesive resin (HFP or CTFE) It is preferable to increase the content of) or the crosslinkable monomer, control the distribution, or increase the molecular weight or branch amount of the vinylidene fluoride copolymer (a).

(Viscosity ratio (A)/(B))

It is preferable that the ratio (A)/(B) of the solution viscosity (A) of the acetone solution of the adhesive resin and the solution viscosity (B) of the NMP solution is 1 or more and 15 or less. When the ratio (A)/(B) is 1 or more, the solution viscosity (B) of the NMP solution tends to be low, and the solution viscosity (A) of the acetone solution tends to be high, that is, the solubility in NMP tends to be low (for acetone. It is easy to increase the solubility). Therefore, it is easy to lower the solubility of the adhesive resin in the electrolytic solution. If the ratio (A)/(B) is 15 or less, the solution viscosity (B) of the NMP solution is not too low, and the solution viscosity (A) of the acetone solution is not too high, that is, the solubility in NMP is not too low ( Solubility in acetone is not too high), it is easy to obtain a high modulus of elasticity. It is even more preferable that the ratio (A)/(B) is 1 or more and 10 or less.

In order to make the viscosity ratio (A)/(B) below a certain level, for example, a monomer (HFP or CTFE) copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) constituting the adhesive resin or a crosslinkable monomer It is preferable that the content and distribution of, and the molecular weight and branching amount of the vinylidene fluoride copolymer (a) be a certain or less, or the content of the vinylidene fluoride copolymer (a) in the adhesive resin be a certain or less.

(Average particle diameter)

The average particle diameter of the adhesive resin particles is not particularly limited, but is preferably 10 nm to 1 μm, more preferably 50 to 500 nm, and even more preferably 70 to 300 nm.

When the adhesive resin particles are obtained by emulsion polymerization, the average particle diameter of the adhesive resin particles is normalized by the dynamic light scattering method in the state where the adhesive resin particles are dispersed in a liquid medium (e.g., water) after polymerization. It can be measured by (regularization) analysis. Specifically, using "DelsaMaxCORE" manufactured by BECKMAN COULTER, the particle diameter of the polymer particles is measured in accordance with JIS Z 8828, and the larger peak among the two peaks obtained by regularization analysis is taken as the average particle diameter. . On the other hand, in the case of obtaining the adhesive resin by suspension polymerization, 3,000 particles of the powdered vinylidene fluoride copolymer are photographed, and the average particle diameter is taken as the average particle diameter of the particles when it is assumed that each photographed particle is circular. .

(Melting point)

The melting point of the adhesive resin is not particularly limited, but it is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 105°C or higher.

The melting point of the adhesive resin can be measured by the following method. That is, between two aluminum foils sprayed with a release agent, a mold of 5 cm long x 5 cm wide x 150 µm thick and about 1 g of adhesive resin are put, and pressed at 200°C to obtain a film. The melting point of the obtained film is measured in accordance with ASTM d 3418 using DSC ("DSC-1" manufactured by METTLER).

The melting point of the adhesive resin can be adjusted by the monomer composition of the vinylidene fluoride copolymer (a) contained therein. In order to increase the melting point of the adhesive resin, for example, it is preferable to increase the content of the structural unit derived from vinylidene fluoride in the vinylidene fluoride copolymer (a).

(Inherent viscosity)

The intrinsic viscosity (ηi) of the adhesive resin obtained by the suspension polymerization method is preferably 0.50 to 5.0 dl/g, more preferably 1.0 to 4.0 dl/g, and 1.0 to 3.5 dl/g from the viewpoint of coatability. Even more desirable.

The intrinsic viscosity (ηi) can be calculated as the logarithmic viscosity at 30°C of a solution in which 4 g of an adhesive resin is dissolved in 1 liter of N,N-dimethylformamide (hereinafter simply referred to as “DMF”). have.

1-3. Method for producing adhesive resin

The adhesive resin (resin containing the vinylidene fluoride copolymer (a)) can be obtained through a process of polymerizing vinylidene fluoride and a monomer copolymerizable therewith by a known polymerization method including emulsion polymerization and suspension polymerization. .

(Emulsion polymerization method)

In the emulsion polymerization method, a polymerization initiator soluble in the liquid medium is additionally added to a liquid medium in which each monomer is poorly soluble, each monomer, an emulsifier, and a chain transfer agent as needed, and a mixture obtained by mixing, and a polymerization initiator soluble in the liquid medium is added to polymerize the monomer.

The liquid medium only needs to be poorly soluble in each monomer, and, for example, it is preferably water.

The emulsifier can be used as long as it can stably disperse the polymer synthesized by the emulsion polymerization method in the liquid medium while forming micelles of each monomer in a liquid medium, and can be appropriately selected from known surfactants. The emulsifier may be a surfactant conventionally used for synthesis of a vinylidene fluoride copolymer, and may be, for example, a perfluorinated surfactant, a partially fluorinated surfactant, a non-fluorinated surfactant, or the like. Among these surfactants, perfluoroalkyl sulfonic acids and salts thereof, perfluoroalkyl carboxylic acids and salts thereof, and fluorine-based surfactants having a fluorocarbon chain or fluoropolyether chain are preferred, and perfluoroalkyl carboxylic acids and their Salts are more preferred.

Examples of the chain transfer agent include ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propylaldehyde, ethyl propionate, carbon tetrachloride, and the like.

The polymerization initiator is a polymerization initiator soluble in a liquid medium, and may be, for example, a water-soluble peroxide, a water-soluble azo-based compound, and a redox-based initiator. Examples of the water-soluble peroxide include ammonium persulfate and potassium persulfate. Examples of the water-soluble azo-based compound include 2,2'-azobis-isobutyronitrile (AIBN) and 2,2'-azobis-2-methylbutyronitrile (AMBN). Examples of redox initiators include ascorbic acid-hydrogen peroxide and the like. Among these, the polymerization initiator is preferably a water-soluble peroxide.

Further, the emulsion polymerization method may be a soap-free emulsion polymerization method or a miniemulsion polymerization method.

In the soap-free emulsion polymerization method, it is preferable to use a reactive emulsifier, which is a substance having a polymerizable double bond in the molecule and also acting as an emulsifier. The reactive emulsifier forms micelles in the system at the beginning of the polymerization, but as the polymerization proceeds, since it is used and consumed in the polymerization reaction as a monomer, it hardly exists in an advantageous state in the reaction system finally obtained. Therefore, the reactive emulsifier is difficult to bleed out to the surface of the particles of the polymer to be obtained.

Examples of the reactive emulsifier include polyoxyalkylene alkenyl ether, sodium alkyl allyl sulfosuccinate, sodium methacryloyloxy polyoxypropylene sulfate ester, and alkoxy polyethylene glycol methacrylate.

Further, when each monomer is dispersed in a liquid medium without a reactive emulsifier, soap-free polymerization can be performed without using a reactive emulsifier.

In the mini-emulsion polymerization method, a strong shearing force is applied using an ultrasonic oscillator or the like, and the micelles are refined to a submicron size to perform polymerization. At this time, in order to stabilize the micronized micelles, a known hydrophobe is added to the mixture. In the mini-emulsion polymerization method, since a polymerization reaction typically occurs only inside each of the micelles, and each of the micelles becomes fine particles of a polymer, it is easy to control the particle size and particle size distribution of the resulting polymer fine particles.

(Suspension polymerization method)

In the suspension polymerization method, a monomer dispersion obtained by dissolving an oil-soluble polymerization initiator in each monomer is heated while mechanically stirring in water containing a suspending agent, a chain transfer agent, a stabilizer, and a dispersing agent, thereby suspending and dispersing the monomer. A polymerization reaction occurs in droplets. In the suspension polymerization method, since a polymerization reaction typically occurs only inside each droplet of a monomer, and each droplet of a monomer becomes fine particles of a polymer, it is easy to control the particle size and particle diameter distribution of the resulting polymer fine particles.

Examples of the polymerization initiator include diisopropyl peroxydicarbonate, dinormalpropyl peroxydicarbonate, dinormalheptafluoropropyl peroxydicarbonate, diisopropyl peroxydicarbonate, isobutyryl peroxide, di(chlorofluoroacyl). Peroxide, di(perfluoroacyl) peroxide and t-butyl peroxypivalate, and the like.

Examples of the suspending agent include methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, partially saponified polyvinyl acetate, and acrylic acid-based polymer.

The chain transfer agent may be the same as described above.

Next, a method of manufacturing the adhesive resin particles will be described for each form.

1-3-1. In the case of core shell type particles

Core-shell particles containing the vinylidene fluoride copolymer (a) can be obtained by a sequential polymerization method. For example, core-shell particles having a core portion made of a vinylidene fluoride copolymer (a) and a shell portion made of a vinylidene fluoride polymer (b) include, for example, vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride. Through a step of copolymerizing to form a core part made of a vinylidene fluoride copolymer (a), and a step of polymerizing at least vinylidene fluoride around the obtained core part to form a shell part made of a vinylidene fluoride copolymer (b). Can be manufactured.

When the vinylidene fluoride copolymer (a) or the vinylidene fluoride polymer (b) further contains a structural unit derived from the above-described crosslinkable monomer, these monomers may be further copolymerized during polymerization in each step.

The polymerization in each step can be carried out by a known polymerization method such as the above-described emulsion polymerization method or suspension polymerization method.

1-3-2. For slanted particles

The slanted particles made of the vinylidene fluoride copolymer (a) can be obtained through a step of polymerizing a vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride. As described above, polymerization can be performed by a known polymerization method such as an emulsion polymerization method or a suspension polymerization method.

And, from the viewpoint of satisfying the turbidity of the above-described NMP solution or the solution viscosity (A) and viscosity ratio (A)/(B) of the acetone solution, it is possible to impart a variation in composition or structure from the center of the particle to the surface layer. desirable.

For example, in order to obtain particles with a large content of structural units derived from a monomer copolymerizable with vinylidene fluoride inside the particles, and a large content of structural units derived from vinylidene fluoride in the surface layer of the particles, for example, during polymerization It can be obtained by adding a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride more than a part of vinylidene fluoride, initiating polymerization, and then adding the remainder of vinylidene fluoride after polymerization after the pressure is lowered.

For example, in order to obtain particles having an uneven crosslinked structure in the surface layer, a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride are added to a polymerization can during polymerization, and the pressure is reduced after starting polymerization. After lowering, it is preferable to perform polymerization while dividing the balance of the crosslinkable monomer and vinylidene fluoride into a plurality of times so that the pressure becomes constant and subjected to post-adding (including continuous post-adding continuously) (Method 1).

The post-addition of vinylidene fluoride is preferably carried out after starting the polymerization and after the pressure is lowered. Specifically, it is preferable to perform the post-addition of vinylidene fluoride after starting the polymerization and after the pressure is lowered. Specifically, the post-addition of vinylidene fluoride is preferably performed when the pressure in the reactor is lowered by 2% or more with respect to the initial pressure, and more preferably performed when the pressure in the reactor is lowered by 15% or more.

In addition, the monomers to be added post-add are only vinylidene fluoride and crosslinkable monomers, and do not substantially contain a monomer copolymerizable with vinylidene fluoride (e.g., 1% by mass or less, preferably, based on the total of the monomers to be added post Is preferably 0% by mass). The mass ratio of the post-added vinylidene fluoride and the pre-added vinylidene fluoride is preferably post-added vinylidene fluoride: pre-added vinylidene fluoride = 1:1 to 10:1 (mass ratio), and 2.5:1 to 7 It is more preferable that it is :1 (mass ratio).

The blending amount of the crosslinkable monomer is preferably 0.1 to 4% by mass, and more preferably 1.2 to 3.5% by mass with respect to the total amount of vinylidene fluoride and the monomers copolymerizable with vinylidene fluoride. The blending amount of vinylidene fluoride is preferably 15% by mass or more, and more preferably 12% by mass or more with respect to the total amount of all monomers constituting the vinylidene fluoride copolymer (a).

Further, even when a crosslinkable monomer is not used, it can be carried out in the same manner as in Method 1. That is, as a method of imparting deviation to the composition or structure of the particles, a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride are added to a polymerization can during polymerization, and polymerization is started, and after the pressure is lowered, the pressure It is preferable to perform polymerization while dividing the remainder of vinylidene fluoride into a plurality of times so as to become constant and performing post addition (including successive addition of successively post addition). The specific timing for performing the post-addition, or the mass ratio of the vinylidene fluoride post-added and the pre-added vinylidene fluoride may be the same as in Method 1.

In addition, in order to obtain particles having an uneven branched structure in the surface layer, in the step of polymerizing a vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride, the amount of the chain transfer agent is reduced, specifically, vinylidene fluoride and vinylidene fluoride. It is preferable to reduce it with respect to the total amount of copolymerizable monomers (Method 2). By reducing the blending amount of the chain transfer agent, the molecular weight (branching amount) of the resulting vinylidene fluoride copolymer (a) can be increased. Thereby, the obtained particle|grains are easy to raise the turbidity of an NMP solution, and it is easy to raise the viscosity (A) of acetone solution.

The blending amount of the chain transfer agent is preferably 0.2% by mass or less, more preferably 0.15% by mass or less, even more preferably 0.08% by mass or less with respect to the total amount of vinylidene fluoride and the monomer copolymerizable with vinylidene fluoride. desirable.

In these methods 1 and 2, a crosslinked structure or a branched structure can be formed in the surface layer portion of the particles obtained by performing polymerization in an environment containing a large amount of vinylidene fluoride.

In addition, as another method of imparting variation in composition or structure to the adhesive resin, a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride are copolymerized with vinylidene fluoride at the beginning of polymerization so that the number of monomers copolymerizable with vinylidene fluoride is greater than that of vinylidene fluoride. A method (Method 3) of adding the remainder of vinylidene fluoride and polymerizing at a stage in which the polymerization proceeds and the pressure is lowered than when the polymerization is initiated after the addition (to an excess amount); A method of alkali treating the adhesive resin containing the vinylidene fluoride copolymer (a)' (Method 4), etc. are also included.

For example, in Method 3 as well, the specific timing for performing the post-addition or the mass ratio of the vinylidene fluoride post-added and the pre-added vinylidene fluoride may be the same as in Method 1.

For example, as a method for alkali treatment of vinylidene fluoride copolymer (a)' (Method 4), specifically, a vinylidene fluoride copolymer (a)' is dissolved in NMP so that the polymer concentration in the solution is 5 parts by mass. (The turbidity at this time is less than 2), powder of lithium hydroxide (LiOH) is added thereto, and the mixture is stirred under heating. Thereby, the vinylidene fluoride copolymer (a)' can be modified (for example, dehydrofluoric acid), and the solubility in the electrolytic solution can be lowered.

The content of LiOH in the solution is preferably 0.01 to 20 parts by mass, and more preferably 0.1 to 10 parts by mass per 100 parts by mass of the vinylidene fluoride copolymer (a).

The heating temperature and the stirring time during the alkali treatment may be such that the solubility of the resulting vinylidene fluoride copolymer (a)' in the electrolytic solution can be lowered. The heating temperature can be, for example, 45 to 60°C. Stirring time can be made into 30 minutes-12 hours, for example.

1-4. Other ingredients

The adhesive resin composition may further contain components other than the adhesive resin. Examples of other components include water-soluble polymers, inorganic fillers, organic fillers, solvents (dispersion medium), and various additives.

The water-soluble polymer can increase the adhesion between the adhesive resin composition layer and the separator, and the adhesiveness between the adhesive resin composition layer and the electrode. The water-soluble polymer is preferably an adhesive resin or a polymer having adhesiveness to an electrode or a separator.

Examples of the water-soluble polymer include cellulose compounds such as carboxymethyl cellulose (CMC), methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose; Ammonium salt or alkali metal salt of the cellulose compound, polyacrylic acid (PAA), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene oxide (PEO). Among them, carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) are preferable from the viewpoint of a long-term battery use.

When the total solid content of the adhesive resin composition is 100 parts by mass, the content of the water-soluble polymer is preferably 0.01 to 20 parts by mass, and more preferably 0.01 to 15 parts by mass.

The inorganic filler prevents the occurrence of a short circuit even when the battery obtained is exposed to a high temperature at which the separator or the adhesive resin is melted, thereby improving the safety of the battery.

Examples of such inorganic fillers include silicon dioxide (SiO ₂ ), alumina (Al ₂ O ₃ ), titanium dioxide (TiO ₂ ), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), and magnesium oxide ( Oxides such as MgO), zinc oxide (ZnO), and barium titanate (BaTiO ₃ ); Hydroxides such as magnesium hydroxide (Mg(OH) ₂ ), calcium hydroxide (Ca(OH) ₂ ), zinc hydroxide (Zn(OH) ₂ ) aluminum hydroxide (Al(OH) ₃ ); Carbonates such as calcium carbonate (CaCO ₃ ); Sulfates such as barium sulfate; It includes nitrides, clay minerals, and the like. Inorganic fillers may be used singly or in combination of two or more. Among them, alumina, silicon dioxide, magnesium oxide, and zinc oxide are preferable from the viewpoint of battery safety and coating solution stability.

When the total solid content of the adhesive resin composition is 100 parts by mass, the content of the inorganic filler is preferably 0.01 to 99 parts by mass, and more preferably 50 to 95 parts by mass.

The average particle diameter of the inorganic filler is preferably 5 nm to 2 μm, more preferably 10 nm to 1 μm. The average particle diameter can be measured by the same method as described above.

Examples of the inorganic filler include AKP3000 (made by Sumitomo Chemical Company, LIMITED) sold as high-purity alumina particles.

Examples of the solvent include water or NMP. The content of the solvent is not particularly limited as long as the coatability becomes good, but when the total mass of the adhesive resin composition is 100 parts by mass, it is preferably 30 to 99 parts by mass, and more preferably 35 to 98 parts by mass.

2. Separator structure

The separator structure of the present invention has a separator and an adhesive resin composition layer formed on at least one surface thereof.

2-1. Separator

The material of the separator is not particularly limited, but examples thereof include polyolefin resins such as polyethylene and polypropylene; Polyester resins such as polyethylene terephthalate; Aromatic polyamide resin; Polyimide resins such as polyetherimide; Polyethersulfone, polysulfone, polyether ketone, polystyrene, polyethylene oxide, polycarbonate, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, ceramic, etc., and a single-layer or multi-layer porous membrane made of a mixture thereof Included. Among them, a porous membrane made of a polyolefin resin (for example, polyethylene or polypropylene) is preferable from the viewpoint of excellent shutdown function and meltdown function.

Examples of the polyolefin resin porous membrane include a single layer polypropylene separator, a single layer polyethylene separator, and a polypropylene/polyethylene/polypropylene 3 commercially available as Celgard (registered trademark, manufactured by Polypore International, Inc.). A layer separator is included.

2-2. Adhesive resin composition layer

The adhesive resin composition layer is formed on at least one surface of the separator. The adhesive resin composition layer is a layer obtained by using at least the adhesive resin composition described above, and may further contain other components as necessary.

The thickness of the adhesive resin composition layer may be such that the adhesiveness between the separator and the electrode can be maintained satisfactorily, and is not particularly limited, but, for example, it is preferably 0.5 to 25 μm, more preferably 1 to 20 μm. .

The adhesive resin composition layer can be formed through a step of drying the above-described adhesive resin composition on a separator, followed by a step of making it porous if necessary. The application method is not particularly limited, and may be a method of applying with a bar coater, a die coater, and a comma coater.

It is preferable that drying is performed to the extent that the solvent in the coating film can be sufficiently removed. For example, the drying temperature is preferably 40 to 180°C, more preferably 50 to 150°C. Drying time may be 1 minute to 15 hours.

In addition, after drying, heat treatment may be additionally performed if necessary. For example, when the adhesive resin composition layer does not contain a water-soluble polymer as another component, it is preferable to perform heat treatment. The heat treatment temperature is preferably 40 to 180°C, more preferably 50 to 170°C. The heat treatment time may be, for example, 1 minute to 5 hours.

3. Electrode structure

The electrode structure has an electrode and an adhesive resin composition layer formed on the surface thereof.

3-1. electrode

The electrode has a current collector and an electrode active material layer formed on the surface thereof. The electrode may be an anode or a cathode.

(The current collector)

Copper is contained in an example of the current collector for negative electrode. Copper may be metallic copper, but may be coated with copper foil on the surface of another medium.

Aluminum is contained in an example of the current collector for positive electrode. Aluminum may be coated with aluminum foil on the surface of other media, or may be added with reticulated aluminum.

The negative electrode or the current collector for positive electrode preferably has a thickness of 5 to 100 μm, more preferably 5 to 20 μm.

(Electrode active material layer)

The electrode active material layer includes an electrode active material and a binder, and may further include a conductive aid if necessary.

Examples of the positive electrode active material include a lithium-based positive electrode active material. Examples of the lithium-based positive electrode active material include general formula LiMY ₂ such as LiCoO ₂ , LiNi _x Co _1-x O ₂ (0<x≤1) (M is a transition metal such as Co, Ni, Fe, Mn, Cr, and V) One or two or more of them, Y is a chalcogen element such as O and S), a complex metal chalcogen compound, a complex metal oxide having a spinel structure such as LiMn ₂ O ₄ and an olivine type lithium compound such as LiFePO ₄ This includes. In addition, the positive electrode active material may be a commercial item.

From the viewpoint of suppressing decomposition of the electrolyte solution and suppressing an increase in initial irreversible capacity, the specific surface area of the positive electrode active material is preferably 0.05 to 50 m ² /g, more preferably 0.1 to 30 m ² /g. .

Examples of the negative electrode active material include carbon materials, metal materials, alloy materials, and metal oxides that have been conventionally used as negative electrode active materials. Among these, a carbon material is preferable from the viewpoint that stable battery characteristics are easily obtained, and artificial graphite, natural graphite, non-graphitized carbon, easily graphitized carbon, and the like are more preferable. Examples of artificial graphite include artificial graphite obtained by carbonizing an organic material, performing heat treatment at a high temperature again, pulverizing and classifying. Examples of the non-graphitized carbon include non-graphitized carbon obtained by firing a material derived from petroleum pitch at 1000 to 1500°C. Further, the negative active material may be a commercial item.

From the viewpoint of suppressing decomposition of the electrolyte solution and suppressing an increase in initial irreversible capacity, the specific surface area of the negative electrode active material is preferably 0.3 to 10 m ² /g, more preferably 0.6 to 6 m ² /g. .

The binder can improve the binding property between electrode active materials, an electrode active material and a conductive aid, or between an electrode active material and a current collector. The binder is not particularly limited, and one widely used in lithium ion secondary batteries may be used. Examples of the binder include fluorinated resins such as polytetrafluoroethylene, polyvinylidene fluoride (including vinylidene fluoride (co)polymers such as vinylidene fluoride maleic acid monomethyl ester copolymer) and fluorine rubber, Styrene butadiene rubber latex (SBR), cellulose compounds (such as carboxymethyl cellulose), and polyacrylonitrile (PAN). Among them, preferred examples of the binder for the positive electrode include vinylidene fluoride (co)polymer, and examples of the binder for the negative electrode include styrene butadiene rubber latex (SBR) and carboxymethyl cellulose (CMC).

The content of the binder is preferably 0.2 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, when the total amount of the electrode active material and the binder is 100 parts by mass.

The conductive aid can further increase the conductivity between the electrode active materials or between the electrode active material and the current collector. Examples of the conductive aid include acetylene black, Ketjen black, carbon nanofibers, carbon nanotubes, carbon fibers, and the like.

The content of the conductive aid is preferably 0.5 to 15 parts by mass, and more preferably 0.5 to 5 parts by mass, when the total amount of the electrode active material and the binder is 100 parts by mass.

The electrode active material layer can be formed by applying a mixture on the current collector and drying it.

The mixture is obtained by mixing the above-described electrode active material, a binder, and optionally a conductive aid and a non-aqueous solvent to form a uniform slurry. Examples of non-aqueous solvents include acetone, dimethyl sulfoxide, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane, ethyl acetate, γ-butyrolactone, tetrahydrofuran, acetamide, N-methylpi Rolidone, N,N-dimethylformamide, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, and the like.

The coating method is not particularly limited, but a bar coater, a die coater, a comma coater, or the like may be employed. Drying after application is usually performed at 50 to 150°C for 1 to 300 minutes. Drying may be performed multiple times at different temperatures. During drying, pressure may be applied, but drying is usually carried out under atmospheric pressure or reduced pressure. Heat treatment may be performed after drying. The heat treatment is usually performed at 100 to 300° C. for 10 seconds to 300 minutes.

After application and drying, a press treatment may be further performed. Press treatment is usually carried out at 1 to 200 MPa. By performing the press treatment, the electrode density can be improved.

The thickness of the positive electrode active material layer is preferably 40 to 500 μm, more preferably 100 to 400 μm. The thickness of the negative electrode active material layer is preferably 20 to 400 μm, more preferably 40 to 300 μm.

The weight per unit area of the electrode active material layer is preferably 20 to 700 g/m ² , more preferably 30 to 500 g/m ² .

3-2. Adhesive resin composition layer

The adhesive resin composition layer is a layer obtained by using the adhesive resin composition described above, and is formed on an electrode. The configuration and formation method of the adhesive resin composition layer are the same as the configuration and formation method of the above-described adhesive resin composition layer.

4. Non-aqueous electrolyte secondary battery

The nonaqueous electrolyte secondary battery of the present invention has a positive electrode, a negative electrode, a separator disposed therebetween, and an adhesive resin composition layer formed on at least one of between the separator and the positive electrode, and between the separator and the negative electrode.

The adhesive resin composition layer is a layer obtained from the above-described adhesive resin composition layer, and is formed on at least one of between the separator and the positive electrode and between the separator and the negative electrode. Among them, it is preferable that the adhesive resin composition layer is formed between the separator and the negative electrode.

Such a non-aqueous electrolyte secondary battery obtains a laminate having the above-described adhesive resin composition layer formed on at least one of a positive electrode, a negative electrode, a separator disposed therebetween, a separator and a negative electrode, and a separator and a positive electrode. It can be manufactured through a process and a process of heating or hot pressing the obtained laminated product.

The above-described laminate can be produced by any method. For example, a laminate may be obtained by laminating an anode, a cathode, and the above-described separator structure; A laminate can also be obtained by laminating a negative electrode structure having an adhesive resin composition layer (or a positive electrode structure having an adhesive resin composition layer), a positive electrode (or negative electrode), and a separator.

Heating or hot pressing of the obtained laminate may be performed before or after the step of impregnating the laminate with an electrolyte solution. From the viewpoint of promoting impregnation of the electrolytic solution into the adhesive resin composition layer and reducing the increase in the internal resistance due to the adhesive resin composition layer when used as a battery, or from the viewpoint of lowering the temperature during heating or hot pressing, heating or The heat press is preferably performed after impregnating the obtained laminate with an electrolytic solution.

That is, in the nonaqueous electrolyte secondary battery of the present invention, taking a laminate cell as an example, 1) the process of obtaining the above-described laminate, 2) the obtained laminate is put in a (bag-shaped) laminate cell, and the electrolyte is impregnated, and then laminated. It can be obtained through the process of sealing a cell, 3) heating or heat-pressing the sealed laminated cell, and bonding an electrode and a separator through an adhesive resin composition layer.

The heating or heat press temperature may be such that the separator and the electrode can be bonded to each other, and is not particularly limited. For example, it is preferably 40 to 180°C, and more preferably 60 to 110°C. As described above, the adhesive resin composition layer obtained by using the adhesive resin composition of the present invention is easy to obtain adhesion between the separator and the electrode in a wide temperature range (for example, 20 to 50°C), and has a wide process window. . The heating or hot pressing time is, for example, 20 seconds to 30 minutes. In addition, the pressure of the hot press is 1 to 30 MPa, for example.

In this way, in the heating or heat pressing process, the adhesive resin composition layer is exposed to a high temperature environment in the presence of an electrolytic solution. Even at such a high temperature, the adhesive resin composition layer obtained by using the adhesive resin composition of the present invention is difficult to dissolve in the electrolyte solution even at a certain temperature or higher and has a high elastic modulus. As a result, not only can the high adhesion between the separator and the electrode be maintained, but also the heating or heat press temperature range (process window) can be widened, so that the defective rate of the battery can be reduced.

In particular, compared to the positive electrode that often contains a vinylidene fluoride polymer as a binder, the negative electrode that often contains a resin other than the vinylidene fluoride polymer is a separator through an adhesive resin composition layer containing a vinylidene fluoride polymer. It is difficult to bond well with. Even in such a case, the adhesive resin composition layer obtained by using the adhesive resin composition of the present invention can maintain high adhesiveness between the separator and the negative electrode under high temperature and can widen the process window.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. The scope of the present invention is limited by these examples and is not interpreted.

1. Preparation of adhesive resin particles and measurement of physical properties

<Preparation of polymer particle 1 (core-shell particle)>

(1) polymerization of the core part

333 parts by mass of ion-exchanged water and 0.53 parts by mass of sodium pyrophosphate as a neutral buffer were placed in an autoclave and degassed by bubbling nitrogen for 30 minutes. Next, 1.3 parts by mass of perfluorooctanoic acid ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.125 parts by mass of ethyl acetate, 20 parts by mass of vinylidene fluoride (VDF), and 30 parts by mass of chlorotrifluoroethylene (CTFE) were placed in a charge pot for a monomer. A part of 27 parts by mass of this monomer mixture was added in a batch to the autoclave. After raising the temperature to 80°C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.07 parts by mass in terms of APS, and polymerization was initiated. After the start of the reaction, when the pressure dropped by 2% or more, 23 parts by mass of the remaining monomer mixture was continuously added so that the pressure became constant. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain a core portion made of the vinylidene fluoride copolymer (a-1). The average particle diameter of the obtained core part was 98 nm.

(2) Polymerization of the shell part

A monomer mixture was prepared by weighing 50 parts by mass of vinylidene fluoride (VDF) and 0.125 parts by mass of ethyl acetate in advance in a monomer charging port. Following the above-described emulsion polymerization of the core portion, polymerization was carried out by continuously supplying the monomer mixture at 80°C to maintain the pressure in the can. After completion of the monomer addition, when the pressure in the can was reduced to 2.5 MPa, polymerization of the shell portion was completed to form a shell portion made of a vinylidene fluoride polymer (b-1). The average particle diameter of the obtained core-shell polymer particle 1 (adhesive resin particle) was 135 nm.

<Preparation of polymer particle 2 (core-shell particle)>

(1) polymerization of the core part

330 parts by mass of ion-exchanged water was put in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 1.0 mass part of perfluorooctanoic acid ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.05 parts by mass of ethyl acetate, 10 parts by mass of vinylidene fluoride (VDF), and 30 parts by mass of hexafluoropropylene (HFP) were added all at once into the autoclave. After raising the temperature to 80 DEG C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.1 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 2.6 MPa. After the initiation of the reaction, when the pressure dropped to 2.5 MPa, 1 part by mass of perfluorodivinyl ether (PFDVE) was added as a crosslinking monomer, and then 60 parts by mass of vinylidene fluoride (VDF) in the can was at 2.5 MPa. It was added continuously to keep. When the pressure was lowered to 1.5 MPa, the polymerization was terminated to obtain particles of the core portion made of the vinylidene fluoride copolymer (a-2). The average particle diameter of the obtained particles was 158 nm.

(2) Polymerization of the shell part

700 parts by mass of ion-exchanged water and 0.5 parts by mass of disodium hydrogen phosphate were placed in an autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 100 parts by mass of particles of the water-dispersed core part and 0.5 parts by mass of PFOA were put, pressurized to 4.5 MPa, and nitrogen substitution was performed three times. 0.05 parts by mass of ethyl acetate and 100 parts by mass of vinylidene fluoride (VDF) were added at once into the autoclave. After heating up to 80° C. under stirring, a 5 wt% APS aqueous solution was added in an amount equivalent to 0.1 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 4.1 MPa. After the initiation of the reaction, when the pressure was lowered to 1.5 MPa, polymerization of the shell portion was completed to form a shell portion made of a vinylidene fluoride polymer (b-1) to obtain core-shell polymer particles 2. The average particle diameter of the obtained particles was 199 nm.

<Preparation of polymer particle 3 (core-shell particle)>

(1) polymerization of the core part

333 parts by mass of ion-exchanged water and 0.53 parts by mass of sodium pyrophosphate were put into the autoclave, and degassed by bubbling nitrogen for 30 minutes. Next, 1.33 parts by mass of ammonium perfluorooctanoate (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed three times. 0.25 parts by mass of ethyl acetate, 29 parts by mass of vinylidene fluoride (VDF), 21 parts by mass of chlorotrifluoroethylene (CTFE), and 0.5 parts by mass of perfluorodivinyl ether (PFDVE) as a crosslinkable monomer were placed in the charge port for the monomer. . A part of 27 parts by mass of this monomer mixture was added in a batch to the autoclave. After raising the temperature to 80°C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.07 parts by mass in terms of APS, and polymerization was initiated. After the initiation of the reaction, when the pressure dropped by 2% or more, 23 parts by mass of the remaining monomer mixture was continuously added so that the pressure became constant. When the pressure decreased to 1.5 MPa, polymerization was terminated, and emulsion polymerization of the core portion made of the vinylidene fluoride polymer (a-3) was terminated. The average particle diameter of the particles of the obtained core portion was 97 nm.

(2) Polymerization of the shell part

A monomer mixture was prepared by weighing 50 parts by mass of vinylidene fluoride (VDF) and 0.25 parts by mass of ethyl acetate in a monomer charging port in advance. Following the above-described core part emulsion polymerization, polymerization was carried out by continuously supplying the monomer mixture at 80°C so that the pressure in the can was maintained at 3.2 MPa. After completion of the monomer addition, when the pressure in the can was reduced to 2.5 MPa, polymerization of the shell portion was completed, and a shell portion made of a vinylidene fluoride polymer (b-2) was formed to obtain core-shell polymer particles 3. The average particle diameter of the obtained particles was 132 nm.

<Preparation of polymer particle 4 (core-shell particle)>

(1) polymerization of the core part

333 parts by mass of ion-exchanged water and 0.53 parts by mass of sodium pyrophosphate were put into the autoclave, and degassed by bubbling nitrogen for 30 minutes. Next, 1.33 parts by mass of ammonium perfluorooctanoate (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed three times. 0.25 parts by mass of ethyl acetate, 15 parts by mass of vinylidene fluoride (VDF), and 35 parts by mass of chlorotrifluoroethylene (CTFE) were placed in a charge pot for a monomer. A part of 27 parts by mass of this monomer mixture was added in a batch to the autoclave. After raising the temperature to 80°C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. After the initiation of the reaction, when the pressure fell by 2% or more, 23 parts by mass of the remaining monomer mixture was continuously added so that the pressure was kept constant. When the pressure was lowered to 1.5 MPa, the polymerization was terminated to obtain particles of the core portion made of the vinylidene fluoride copolymer (a-4). The average particle diameter of the particles of the obtained core portion was 94 nm.

(2) Polymerization of the shell part

A monomer mixture was prepared by weighing 50 parts by mass of vinylidene fluoride (VDF) and 0.25 parts by mass of ethyl acetate in a monomer charging port in advance. Following the above-described core part emulsion polymerization, polymerization was carried out by continuously supplying the monomer mixture at 80°C so that the pressure in the can was maintained at 3.2 MPa. After the completion of the monomer addition, when the pressure in the can was reduced to 2.5 MPa, the polymerization of the shell portion was completed to form a shell portion made of a vinylidene fluoride polymer (b-1) to obtain core-shell polymer particles 4. The average particle diameter of the obtained particles was 153 nm.

<Preparation of polymer particle 5 (inclined particle)>

330 parts by mass of ion-exchanged water and 0.2 parts by mass of disodium hydrogen phosphate were placed in the autoclave, and deaeration was performed by bubbling nitrogen for 30 minutes. Next, 1.0 mass part of perfluorooctanoic acid ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 18.0 parts by mass of vinylidene fluoride (VDF) and 7.0 parts by mass of hexafluoropropylene (HFP) were added together into the autoclave. After raising the temperature to 80°C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 2.6 MPa. After the initiation of the reaction, when the pressure was lowered to 2.5 MPa, 75.0 parts by mass of vinylidene fluoride (VDF) was continuously added so that the pressure in the can was maintained at 2.5 MPa. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 5 comprising a vinylidene fluoride copolymer (a-5). The average particle diameter of the obtained particles was 146 nm.

<Preparation of polymer particle 6 (inclined particle)>

(1) Preparation of PVDF/HFP copolymer

8271 g of ion-exchanged water, 1.61 g of methyl cellulose (manufactured by Shin-Etsu Chemical Co., Ltd., SM-100) in an autoclave with an inner volume of 14 liters, and diisopropyl peroxydicarbonate ( IPP) 12.9 g, vinylidene fluoride (VDF) 2936 g, and hexafluoropropylene (HFP) 290 g were added thereto, followed by polymerization at 29°C. After the polymerization was completed, the polymer slurry was heat-treated at 95°C for 60 minutes, then dehydrated, washed with water, and dried again at 80°C for 20 hours, and the vinylidene fluoride copolymer (a-6) (vinylidene fluoride/hexafluoropropylene copolymer) Polymer particle 6 consisting of coalescence) was obtained. The average particle diameter of the obtained particles was 170 μm.

(2) Lithium hydroxide treatment-1

5 mass% of the obtained copolymer (PVDF/HFP) was put into NMP, and it heated up to 50 degreeC, stirring at room temperature, and was completely dissolved. To this, 1% by mass of lithium hydroxide was added to the copolymer (PVDF/HFP), followed by stirring at 50°C for 3 hours. Using this solution, the turbidity, viscosity, and peel strength of the NMP solution of polymer particles 6 were measured.

(3) Lithium hydroxide treatment-2

10 mass% of the obtained copolymer (PVDF/HFP) was put in acetone, and dispersed while stirring at room temperature, and then heated to 45° C. in a water bath and dissolved. To this, 1% by mass of lithium hydroxide was added to the copolymer (PVDF/HFP), followed by stirring at 50°C for 3 hours. Using this solution, the turbidity and viscosity of the acetone solution of the polymer particles 6 were measured.

<Preparation of polymer particle 7 (inclined particle)>

330 parts by mass of ion-exchanged water and 0.25 parts by mass of disodium hydrogen phosphate as a neutral buffer were placed in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 1.0 mass part of perfluorooctanoic acid ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.2 parts by mass of ethyl acetate, 24.7 parts by mass of vinylidene fluoride (VDF), and 10.0 parts by mass of hexafluoropropylene (HFP) were added together into the autoclave. After the temperature was raised to 80°C under stirring, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. After the initiation of the reaction, after the pressure decreased by 2% or more, 2 parts by mass of perfluorodivinyl ether (PFDVE) and 63.3 parts by mass of vinylidene fluoride (VDF) were continuously added so that the pressure in the can became constant. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 7 comprising a vinylidene fluoride copolymer (a-7). The average particle diameter of the obtained particles was 154 nm.

<Preparation of polymer particle 8 (inclined particle)>

8230 g of ion-exchanged water, 0.96 g of methyl cellulose (Shin-Etsu Chemical Co., Ltd., SM-100), 27.48 g of di-n-propyl peroxydicarbonate, and 3146 vinylidene fluoride (VDF) in an autoclave with an inner volume of 14 L g and 64 g of hexafluoropropylene (HFP) were added, followed by polymerization at 29°C. After the polymerization was completed, the polymer slurry was heat-treated at 95°C for 60 minutes, dehydrated, washed with water, and dried again at 80°C for 20 hours, and the vinylidene fluoride copolymer (c-1) (vinylidene fluoride-hexafluoropropylene copolymer) Polymer particles 8 consisting of coalescence) were obtained. The average particle diameter of the obtained particles was 173 μm.

<Preparation of polymer particle 9 (inclined particle)>

330 parts by mass of ion-exchanged water and 0.2 parts by mass of disodium hydrogen phosphate were placed in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 0.7 parts by mass of perfluorooctanoate ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 8.0 parts by mass of vinylidene fluoride (VDF) and 47.0 parts by mass of hexafluoropropylene (HFP) were added together into the autoclave. After raising the temperature to 80°C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 3.83 MPa. After the initiation of the reaction, 45.0 parts by mass of vinylidene fluoride (VDF) was continuously added so that the pressure in the can was maintained at 2.5 MPa when the pressure was lowered to 2.5 MPa. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 9 comprising a vinylidene fluoride copolymer (c-2). The average particle diameter of the obtained particles was 187 nm.

<Preparation of polymer particle 10 (inclined particle)>

8271 g of ion-exchanged water, 1.61 g of methyl cellulose (made by Shin-Etsu Chemical Co., Ltd., SM-100), 12.9 g of diisopropyl peroxydicarbonate, 2903 g of vinylidene fluoride, and hexafluoro 323 g of propylene was put in, and polymerization was carried out at 29°C. After the polymerization was completed, the polymer slurry was heat-treated at 95°C for 60 minutes, then dehydrated, washed with water, and dried again at 80°C for 20 hours, and the vinylidene fluoride copolymer (c-3) (vinylidene fluoride/hexafluoropropylene copolymer) Polymer particle 10 consisting of coalescence) was obtained. The average particle diameter of the obtained particles was 165 μm.

<Preparation of polymer particle 11 (inclined particle)>

330 parts by mass of ion-exchanged water and 0.2 parts by mass of disodium hydrogen phosphate were placed in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 1.0 mass part of perfluorooctanoate ammonium salt (PFOA) was added, pressurized to 4.5 MPa, and nitrogen substitution was performed three times. 0.25 parts by mass of ethyl acetate, 23.7 parts by mass of vinylidene fluoride (VDF), and 8 parts by mass of hexafluoropropylene (HFP) were added together into the autoclave. After raising the temperature to 80°C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 3.3 MPa. After the initiation of the reaction, when the pressure drops to 2.5 MPa, 5 parts by mass of perfluorodivinyl ether (PFDVE) was added, and then 63.3 parts by mass of vinylidene fluoride (VDF) was continuously added so that the pressure in the can was maintained at 2.5 MPa. did. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 11 comprising a vinylidene fluoride copolymer (c-4). The average particle diameter of the obtained particles was 152 nm.

<Preparation of polymer particle 12 (inclined particle)>

330 parts by mass of ion-exchanged water and 0.2 parts by mass of disodium hydrogen phosphate were placed in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 1.0 mass part of perfluorooctanoic acid ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.25 parts by mass of ethyl acetate, 28.7 parts by mass of vinylidene fluoride (VDF), and 8.0 parts by mass of hexafluoropropylene (HFP) were added together into the autoclave. After the temperature was raised to 80°C under stirring, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 3.83 MPa. After the initiation of the reaction, when the pressure dropped to 2.5 MPa, 63.3 parts by mass of vinylidene fluoride (VDF) were continuously added so that the pressure in the can was maintained at 2.5 MPa. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 12 made of vinylidene fluoride copolymer (c-5). The average particle diameter of the obtained particles was 187 nm.

<Preparation of polymer particle 13 (inclined particle)>

250 parts by mass of ion-exchanged water and 0.2 parts by mass of sodium pyrophosphate as a neutral buffer were added to the autoclave, and degassed by bubbling nitrogen for 30 minutes. Next, 1.0 parts by mass of perfluorooctanoic acid ammonium salt (PFOA) was added, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.5 parts by mass of ethyl acetate, 80 parts by mass of vinylidene fluoride (VDF), 20 parts by mass of chlorotrifluoroethylene (CTFE), and 1 part by mass of perfluorodivinyl ether (PFDVE) were placed in the charge pot for a monomer. A part of 20 parts by mass of this monomer mixture was added in a batch to the autoclave. After raising the temperature to 80° C. while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.08 parts by mass in terms of APS, and polymerization was initiated. Immediately after the start of the reaction, 80 parts by mass of the remaining monomer mixture was continuously added so that the pressure was kept constant. When the pressure was lowered to 1.3 MPa, polymerization was terminated to obtain polymer particles 13 made of vinylidene fluoride copolymer (c-6). The average particle diameter of the obtained particles was 154 nm.

<Preparation of polymer particle 14 (core-shell particle)>

(1) polymerization of the core part

333 parts by mass of ion-exchanged water and 0.53 parts by mass of sodium pyrophosphate as a neutral buffer were placed in the autoclave, and degassed by bubbling nitrogen for 30 minutes. Next, 1.33 parts by mass of ammonium perfluorooctanoate (PFOA) was added, and the pressure was pressurized to 4.5 MPa, followed by nitrogen substitution three times. 0.53 parts by mass of ethyl acetate, 18 parts by mass of vinylidene fluoride (VDF), 12 parts by mass of chlorotrifluoroethylene (CTFE), and 0.3 parts by mass of perfluorodivinyl ether (PFDVE) were placed in the charge pot for a monomer. A part of 27 parts by mass of this monomer mixture was added in a batch to the autoclave. After raising the temperature to 80°C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.07 parts by mass in terms of APS, and polymerization was initiated. Immediately after the start of the reaction, 3 parts by mass of the remaining monomer mixture was continuously added so that the pressure was maintained at 2.6 MPa. When the pressure decreased to 1.5 MPa, polymerization was terminated, and emulsion polymerization of the core portion made of the vinylidene fluoride copolymer (a-8) was terminated. The average particle diameter of the obtained particles was 88 nm.

(2) Polymerization of the shell part

A monomer mixture was prepared by weighing 70 parts by mass of vinylidene fluoride (VDF) and 0.35 parts by mass of ethyl acetate in a monomer charging pot in advance. Following the above-described core part emulsion polymerization, polymerization was carried out by continuously supplying the monomer mixture at 80°C so that the pressure in the can was maintained at 3.2 MPa. After completion of the monomer addition, polymerization of the shell portion was completed when the pressure in the can was reduced to 2.7 MPa. Then, after cooling to 40°C, the residual monomer was purged to form a shell portion made of a vinylidene fluoride polymer (b-2) to obtain core-shell polymer particles 14. The average particle diameter of the obtained particles was 133 nm.

<Preparation of polymer particle 15 (inclined particle)>

330 parts by mass of ion-exchanged water and 0.2 parts by mass of disodium hydrogen phosphate as a neutral buffer were placed in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 1.0 mass part of perfluorooctanoic acid ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.25 parts by mass of ethyl acetate, 27.7 parts by mass of vinylidene fluoride (VDF), and 8.0 parts by mass of hexafluoropropylene (HFP) were added together into the autoclave. After the temperature was raised to 80°C under stirring, a 5 wt% ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.1 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 3.5 MPa. After the initiation of the reaction, when the pressure dropped to 2.5 MPa, 1 part by mass of perfluorodivinyl ether (PFDVE) was added, and then 63.3 parts by mass of vinylidene fluoride was continuously added so that the pressure in the can was maintained at 2.5 MPa. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 15 comprising a vinylidene fluoride copolymer (c-7). The average particle diameter of the obtained particles was 98 nm.

<Preparation of polymer particle 16 (core-shell particle)>

(1) polymerization of the core part

330 parts by mass of ion-exchanged water was put in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 1.0 mass part of perfluorooctanoic acid ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.05 parts by mass of ethyl acetate, 10 parts by mass of vinylidene fluoride (VDF), and 30 parts by mass of hexafluoropropylene (HFP) were added all at once into the autoclave. After raising the temperature to 80 DEG C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.1 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 2.5 MPa. After the start of the reaction, when the pressure was lowered to 2.0 MPa, 60 parts by mass of vinylidene fluoride (VDF) was continuously added so that the pressure in the can was maintained at 2.0 MPa. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain particles of the core portion made of the vinylidene fluoride copolymer (a-9). The average particle diameter of the obtained particles was 160 nm.

(2) Polymerization of the shell part

700 parts by mass of ion-exchanged water and 0.5 parts by mass of disodium hydrogen phosphate were placed in an autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 100 parts by mass of particles of the water-dispersed core part and 0.5 parts by mass of PFOA were put, pressurized to 4.5 MPa, and nitrogen substitution was performed three times. 0.05 parts by mass of ethyl acetate and 100 parts by mass of vinylidene fluoride (VDF) were added at once into the autoclave. After heating up to 80° C. under stirring, a 5 wt% APS aqueous solution was added in an amount equivalent to 0.1 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 4.0 MPa. After the initiation of the reaction, when the pressure was lowered to 1.5 MPa, polymerization of the shell portion was completed to form a shell portion made of the vinylidene fluoride copolymer (b-1) to obtain core-shell polymer particles 16. The average particle diameter of the obtained particles was 203 nm.

<Preparation of polymer particle 17 (inclined particle)>

330 parts by mass of ion-exchanged water was put in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 0.7 parts by mass of perfluorooctanoate ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.1 parts by mass of ethyl acetate, 14.7 parts by mass of vinylidene fluoride (VDF), and 22 parts by mass of hexafluoropropylene (HFP) were added all at once to the autoclave. After raising the temperature to 80° C. while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 3.7 MPa. After the initiation of the reaction, when the pressure was lowered to 2.5 MPa, 63.3 parts by mass of vinylidene fluoride (VDF) was continuously added so that the pressure in the can was maintained at 2.5 MPa. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 17 comprising a vinylidene fluoride copolymer (a-10). The average particle diameter of the obtained particles was 175 nm.

<Preparation of polymer particle 18 (inclined particle)>

330 parts by mass of ion-exchanged water was put in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 0.7 parts by mass of perfluorooctanoate ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.1 parts by mass of ethyl acetate, 9.7 parts by mass of vinylidene fluoride (VDF), and 27 parts by mass of hexafluoropropylene (HFP) were all added to the autoclave. After raising the temperature to 80°C while stirring this, a 5% by mass ammonium persulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 3.7 MPa. After the initiation of the reaction, when the pressure dropped to 2.5 MPa, 63.3 parts by mass of vinylidene fluoride (VDF) were continuously added so that the pressure in the can was maintained at 2.5 MPa. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 18 made of vinylidene fluoride copolymer (a-11). The average particle diameter of the obtained particles was 183 nm.

<Preparation of polymer particle 19 (inclined particle)>

330 parts by mass of ion-exchanged water was put in the autoclave, and degassed by nitrogen bubbling for 30 minutes. Next, 0.7 parts by mass of perfluorooctanoate ammonium salt (PFOA) was put, pressurized to 4.5 MPa, and nitrogen substitution was performed 3 times. 0.1 parts by mass of ethyl acetate, 9.5 parts by mass of vinylidene fluoride (VDF), and 27.3 parts by mass of hexafluoropropylene (HFP) were added all at once into the autoclave. After raising the temperature to 80° C. while stirring this, a 5% by mass ammonium sulfate (APS) aqueous solution was added in an amount equivalent to 0.06 parts by mass in terms of APS, and polymerization was initiated. The pressure in the can at this time was 2.6 MPa. Immediately after the start of the reaction, 63.4 parts by mass of vinylidene fluoride (VDF) was continuously added so that the pressure in the can was maintained at 2.6 MPa. When the pressure was lowered to 1.5 MPa, polymerization was terminated to obtain polymer particles 19 made of vinylidene fluoride copolymer (c-8). The average particle diameter of the obtained particles was 213 nm.

The melting point of the obtained polymer particles 1 to 19, the solution viscosity when dissolved in acetone (A), the turbidity when dissolved in NMP, the solution viscosity when dissolved in NMP (B), the intrinsic viscosity and the average particle diameter are as follows: Each was measured by the method.

[Melting point]

The melting point of the obtained polymer particles was measured in the form of a film. The film was produced by the following method. That is, between two aluminum foils sprayed with a release agent, a mold having a length of 5 cm x 5 cm x 150 µm in thickness and about 1 g of polymer particles were put, and pressed at 200°C. Using the obtained film, the melting point of the vinylidene fluoride copolymer was measured in accordance with ASTM d 3418 using DSC ("DSC-1" manufactured by METTLER).

[Solution viscosity of acetone solution (A)]

(Preparation of acetone solution)

The obtained polymer particles were dissolved in acetone. Specifically, the polymer particles were added so that the polymer concentration in the solution was 10% by mass, dispersed in acetone at room temperature, and then stirred in a water bath at 45°C to dissolve the vinylidene fluoride copolymer.

(Measurement of solution viscosity)

The viscosity of the obtained acetone solution was measured with an E-type viscometer. Specifically, 1.1 ml of acetone solution was put into the measuring unit of a viscometer (RE550 type viscometer manufactured by Toki Sangyo Co., Ltd.), cone rotor 1°34'×R24, rotation speed 10 rpm, measurement time 300 seconds, measurement temperature 25°C. Measurements were carried out. The viscosity at the elapse of 300 seconds was taken as the viscosity of the acetone solution.

[Turbidity of NMP solution]

(Preparation of NMP solution)

The obtained polymer particles were dissolved in NMP. Specifically, the polymer particles were added so that the polymer concentration in the solution was 5% by mass, dispersed in NMP at room temperature, and then stirred at 50° C. using a hot stirrer to dissolve the polymer particles.

The turbidity of the obtained NMP solution was measured with a turbidity meter (turbidity meter). Specifically, NMP was placed in a linear cell (size 10×36×55 mm) so that it had a height of 4 cm or more and less than 4.5 cm, and placed in the measurement unit of a turbidimeter (Nippon Denshoku Kogyo Co., Ltd. NDH2000), and then at room temperature. Standardization was carried out under the conditions of 20±2°C, humidity 50±5%, light source D65·C, and measurement method 3 (measurement method based on JIS K7136 (a method for obtaining haze of a plastic-transparent material)). Then, the NMP solution in which the adhesive resin was dissolved was put into the cell, and the turbidity of the solution was measured under the same conditions.

[Solution Viscosity of NMP Solution (B)]

(Preparation of NMP solution)

An NMP solution was obtained in the same manner as described above.

(Measurement of solution viscosity)

The viscosity of the obtained NMP solution was measured by the same method as the method of measuring the solution viscosity (A) of the acetone solution described above.

[Intrinsic Viscosity]

The intrinsic viscosity of the polymer particles (polymer particles 6, 8 and 10) obtained by the suspension polymerization method was measured. Specifically, 80 mg of the obtained polymer particles were dissolved in 20 mL of DMF to obtain a solution. For each of the obtained solution and DMF, the viscosity in a 30° C. thermostat was measured using an Ubbelohde viscometer, and the intrinsic viscosity was calculated by the following equation.

ηi=(1/C)·ln(η/η0)

η is the measured viscosity of the solution, η 0 is the measured viscosity of DMF, and C is the concentration of the particles containing the vinylidene fluoride copolymer in the solution, where it is 0.4 (g/dl).

[Average particle diameter]

For the polymer particles (polymer particles 1 to 5, 7, 9, and 11 to 19) obtained by the emulsion polymerization method, the average particle diameter was calculated by the regularization analysis of the dynamic light scattering method. Specifically, using "DelsaMaxCORE" manufactured by BECKMAN COULTER, the particle diameter of the polymer particles was measured in accordance with JIS Z 8828, and the large peak among the two peaks obtained by regularization analysis was taken as the average particle diameter. .

On the other hand, when polymer particles were obtained by suspension polymerization, 3,000 powdered polymer particles were photographed, and the average particle diameter of the particles was taken as the average particle diameter when it was assumed that each photographed particle was circular.

The composition of the obtained polymer particles 1 to 19 is shown in Table 1, and the measurement results of physical properties are shown in Table 2. In addition, "-" in Table 2 shows that measurement is impossible.

No. Composition of polymer particles Remark Core/Shelby
(Mass ratio) core Shell No. VDF CTFE HFP Crosslinkable monomer No. VDF Crosslinkable monomer One 50/50 a-1 40 60 b-1 100 The present invention 2 50/50 a-2 70 30 One b-1 100 The present invention 3 50/50 a-3 58 42 One b-2 100 One The present invention 4 50/50 a-4 30 70 b-1 100 The present invention 5 100/0 a-5 93 7 - The present invention 6 100/0 a-6 91 9 - The present invention 7 100/0 a-7 88 10 2 - The present invention 8 100/0 c-1 98 2 - compare 9 100/0 c-2 53 47 - compare 10 100/0 c-3 90 10 - compare 11 100/0 c-4 87 8 5 - compare 12 100/0 c-5 92 8 - compare 13 100/0 c-6 80 20 One - compare 14 30/70 a-8 60 40 One b-2 100 One compare 15 100/0 c-7 91 8 One - compare 16 50/50 a-9 70 30 b-1 100 The present invention 17 100/0 a-10 78 22 - The present invention 18 100/0 a-11 73 27 - The present invention 19 100/0 c-8 73 27 - compare

No. Properties of polymer particles Remark Melting point
(℃) Acetone solution properties NMP solution properties Viscosity ratio
(A)/(B) Intrinsic viscosity
(g/dl) Average
Particle diameter Turbidity
(-) Solution viscosity (A)
(mPa·s) Turbidity
(-) Solution viscosity
(B)
(mPa·s) One 163 10.1 926 2.2 389 2.4 - 135 nm The present invention 2 162 13.8 985 45.4 660 1.5 - 199 nm The present invention 3 161 7 497 7.4 276 1.8 - 132 nm The present invention 4 164 54.3 1260 2.3 217 5.8 - 153 nm The present invention 5 148 7.9 6000 35.7 720 8.3 - 146 nm The present invention 6 152 22.7 1369 2.8 670 2 2.3 170 μm The present invention 7 137 1.0 369 5.9 315 1.2 - 154 nm The present invention 8 162 - - 0.1 1467 - 1.5 173 μm compare 9 87 37 425 98.6 243 1.7 - 187 nm compare 10 151 1.3 1659 0.6 1502 1.1 2.8 165 μm compare 11 132 9.3 130 69 23 5.7 - 152 nm compare 12 149 0.4 170 One 195 0.9 - 187 nm compare 13 83 17.7 94 1.8 123 0.8 - 154 nm compare 14 161 1.2 537 0.6 261 2.1 - 133 nm compare 15 143 1.5 110 0.4 163 0.7 - 98 nm compare 16 162 24.3 1487 26.7 581 2.6 - 203 nm The present invention 17 140 4.4 3925 21.2 650 6.0 - 175 nm The present invention 18 134 3.5 4500 24.9 715 6.3 - 183 nm The present invention 19 110 2.5 405 1.6 490 0.8 - 213 nm compare

2. Preparation and evaluation of adhesive resin composition

[Examples 1 to 10, Comparative Examples 1 to 9]

The polymer particles (adhesive resin particles) shown in Tables 1 and 2 were dispersed in NMP so that the polymer concentration in the solution was 5% by mass to obtain an adhesive resin composition.

Using the adhesive resin composition obtained in Examples 1 to 10 and Comparative Examples 1 to 9, a separator structure having an adhesive resin composition layer was prepared, and the peel strength between the separator and the electrode and the adhesive temperature range (process window) were determined. It was measured by the following method.

[Measurement of peeling strength]

(1) Fabrication of separator structure

The adhesive resin composition was used as a separator (a single layer separator made of polyethylene, thickness 20 μm, porosity 40%, air permeability 300 sec, tensile strength (MD) 150 MPa, (TD) 130 MPa, tensile elongation (MD) 50%, (TD) 100%) was coated with a wire bar having a wet coating amount of 24 μm (count 12), and then immersed in a coagulation bath (water) of 23±2° C. for 3 minutes. Thereafter, it was immersed in a washing liquid (water) for 1 minute, and dried at 70° C. for 30 minutes under nitrogen. Further, heat treatment was performed at 60° C. for 3 hours in vacuum to obtain a separator structure having an adhesive resin composition layer having a thickness of 2 μm.

(2) Fabrication of cathode

BTR918 (modified natural graphite BTR product) 95 parts by mass as negative electrode active material, conductive aid (SuperP TIMCAL product) 2 parts by mass, SBR (styrene butadiene rubber) latex (BM-400 manufactured by Zeon Corporation) 2 parts by mass as a binder Part, as a thickener, CMC (carboxymethyl cellulose) (CELLOGEN 4H manufactured by DKS Co. Ltd.) 1 part by mass of water was added to prepare a slurry, and a copper foil (thickness 10 μm) Applied to. After drying the applied slurry, it was pressed and heat-treated at 150°C for 3 hours. As a result, a negative electrode active material layer having an electrode bulk density of 1.6 g/cm ³ and a weight per unit area of 60 g/m ² was formed to obtain a negative electrode.

(3) Fabrication of Al laminate cell

The obtained negative electrode was cut out into 2.5 x 5.0 cm. Further, the produced separator was cut out to 3.0 x 6.0 cm. The obtained negative electrode and the separator were laminated and placed in a bag of an Al laminate film. 180 μL of an electrolytic solution (ethylene carbonate (EC)/ethyl methyl carbonate (EMC) = 3/7 (mass ratio), LiPF ₆ : 1.2 M, VC: 1 mass%) was injected into the laminate placed in the bag of the Al laminate film. After infiltrating, vacuum degassing, sealing, and left standing overnight.

(4) Heat press

The obtained Al laminate cell was hot-pressed, and the adhesive resin composition layer on the separator and the negative electrode were thermally fused to obtain a sample for measuring peel strength. Specifically, after preheating the obtained Al laminate cell for 1 minute, it was hot pressed at 50° C. for 2 minutes at a surface pressure of about 4 MPa, and the peel strength was measured by the following method.

From the obtained sample for measuring peel strength, a laminate of an electrode and a separator was taken out. The negative electrode of the obtained laminate was fixed, and a 180° peel test was performed at a head speed of 200 mm/min using a tensile tester ("STA-1150 UNIVERSAL TESTING MACHINE" manufactured by ORIENTEC) to measure the peel strength.

Then, the same measurement was repeated while changing the heat press temperature in the range of 50 to 110°C. Specifically, three samples were prepared for each hot press temperature, the peel strength was measured, and the average value of these was taken as "peel strength at each hot press temperature". And the maximum value of "peel strength at each heat press temperature" when the same measurement was repeated while changing the heat press temperature within the range of 50 to 110°C was taken as "peel strength".

[Measurement of adhesive temperature range]

An Al laminate cell was produced in the same manner as the preparation of the sample for peel strength measurement. The obtained Al laminate cell was subjected to heat retention at an arbitrary temperature for 1 minute, and then hot pressed at a surface pressure of about 4 MPa for 2 minutes, and the adhesive resin composition layer on the separator and the negative electrode were thermally fused to obtain a sample for measuring peel strength. With respect to the obtained sample for measuring peel strength, the peel strength was measured in the same manner as described above. These series of operations were repeatedly performed while increasing the heat press temperature step by step in the range of 50 to 110°C, and a temperature range (adhesable temperature range, process window) in which the peel strength became 1.0 gf/mm or more was determined.

Table 3 shows the evaluation results of the peel strength and adhesive temperature range of the adhesive resin compositions of Examples 1 to 10 and Comparative Examples 1 to 9.

Properties of polymer particles evaluation No. Melting point
(℃) Acetone solution NMP solution Viscosity ratio
(A)/(B) Peel strength
(gf/mm) Adhesive temperature range Solution viscosity (A)
(mPa·s) Turbidity
(-) Solution viscosity (B)
(mPa·s) Example 1 One 163 926 2.2 389 2.4 2.0 30℃ or higher Example 2 2 162 985 45.4 660 1.5 2.4 30℃ or higher Example 3 3 161 497 7.4 276 1.8 1.1 20℃ or higher Example 4 4 164 1260 2.3 217 5.8 1.0 30℃ or higher Example 5 5 148 6000 35.7 720 8.3 2.0 30℃ or higher Example 6 6 152 1369 2.8 670 2.0 4.0 30℃ or higher Example 7 7 140 369 5.9 315 1.2 1.2 20℃ or higher Comparative Example 1 8 162 - 0.1 1467 - <0.5 10℃ or less Comparative Example 2 9 87 425 98.6 243 1.7 <0.5 10℃ or less Comparative Example 3 10 151 1659 0.6 1502 1.1 <0.5 10℃ or less Comparative Example 4 11 132 130 69 23 5.7 <0.5 10℃ or less Comparative Example 5 12 149 170 One 195 0.9 <0.5 10℃ or less Comparative Example 6 13 83 94 1.8 123 0.8 <0.5 10℃ or less Comparative Example 7 14 161 537 0.6 261 2.1 <0.5 10℃ or less Comparative Example 8 15 143 110 0.4 163 0.7 <0.5 10℃ or less Example 8 16 162 1487 26.7 581 2.6 2.7 20℃ or higher Example 9 17 140 3925 21.2 650 6.0 3.2 30℃ or higher Example 10 18 134 4500 24.9 715 6.3 3.2 30℃ or higher Comparative Example 9 19 110 405 1.6 490 0.8 <0.5 10℃ or less

The adhesive resin composition of Examples 1 to 10 using polymer particles (adhesive resin particles) having the turbidity of the NMP solution, the solution concentration (A) of the acetone solution, and the viscosity ratio (A)/(B) satisfying the scope of the present application It can be seen that the peeling strength between the separator and the negative electrode is high, and the adhesive temperature range is also wider than 20°C.

On the other hand, at least Comparative Examples 1, 3, 5 to 7 and 9 using polymer fine particles having too low turbidity of the NMP solution, or at least the adhesive resin composition of Comparative Example 2 using polymer fine particles having too high turbidity of the NMP solution, acetone In Comparative Example 4 using polymer particles having a low solution viscosity (A) of the solution, and the adhesive resin composition of Comparative Example 8 in which the solution viscosity (A) of the acetone solution was low and the viscosity ratio (A)/(B) was less than 1, It can be seen that the peel strength between the separator and the negative electrode is low, and the adhesive temperature range is also narrow to 10°C or less.

This application claims priority based on Japanese Patent Application No. 2018-104685 filed on May 31, 2018. All the contents described in this application specification are incorporated in the specification of this application.

Industrial availability

According to the present invention, it is possible to provide an adhesive resin composition including adhesive resin particles having a wide process window in a heating or heat press process while maintaining high adhesion between a separator and an electrode even when exposed to high temperatures .

Claims (15)

An adhesive composition comprising an adhesive resin formed on the surface of a separator or electrode of a nonaqueous electrolyte secondary battery,
The adhesive resin includes at least one vinylidene fluoride copolymer (a) comprising a structural unit derived from vinylidene fluoride and a structural unit derived from a monomer copolymerizable with vinylidene fluoride,
When the adhesive resin was dissolved in N-methyl-2-pyrrolidone so that the concentration in the solution was 5% by mass, the turbidity was 2 or more and 95 or less, and the concentration of the adhesive resin in the solution was 10% by mass. The solution viscosity (A) when dissolved in acetone as possible is 350 to 20000 mPa·s,
The ratio of the solution viscosity (A) to the solution viscosity (B) when the adhesive resin is dissolved in N-methyl-2-pyrrolidone so that the concentration in the solution is 5% by mass (A)/(B) Is 1 or more and 15 or less, the adhesive composition. The method of claim 1, wherein the adhesive resin is a particle comprising the vinylidene fluoride copolymer (a),
The average particle diameter of the particles is 10 nm to 1 μm, the adhesive composition. The vinylidene fluoride polymer (b) according to claim 2, wherein the particles surround a core portion made of the vinylidene fluoride copolymer (a), and surround the core portion, and have a higher ratio of vinylidene fluoride than the core portion. It is a core-shell particle comprising a shell portion consisting of ),
When the total amount of monomers contained in the core-shell particles is 100% by mass, the content of the vinylidene fluoride is 97% by mass or less. The adhesive composition according to claim 3, wherein the vinylidene fluoride copolymer (a) is not crosslinked. The adhesive composition according to claim 3 or 4, wherein the vinylidene fluoride polymer (b) is not crosslinked. The adhesive composition according to any one of claims 3 to 5, wherein the vinylidene fluoride polymer (b) further contains a structural unit derived from a carboxyl group-containing monomer. The adhesive composition according to any one of claims 1 to 6, wherein the monomer copolymerizable with vinylidene fluoride is at least one of chlorotrifluoroethylene and hexafluoropropylene. The adhesive composition according to any one of claims 1 to 7, wherein the adhesive resin has a melting point of 90°C or higher. With a separator,
A separator structure having an adhesive composition layer obtained by using the adhesive composition according to any one of claims 1 to 8 formed on at least one surface thereof. An electrode having a current collector, an electrode active material layer including an electrode active material formed on the current collector,
An electrode structure having an adhesive composition layer obtained by using the adhesive composition according to any one of claims 1 to 8 formed on the surface of the electrode active material layer. The adhesiveness according to any one of claims 1 to 8 formed on at least one of an anode, a cathode, a separator disposed therebetween, and between the separator and the anode, and between the separator and the cathode. A nonaqueous electrolyte secondary battery having an adhesive composition layer obtained by using the composition. The adhesiveness according to any one of claims 1 to 8 formed on at least one of an anode, a cathode, a separator disposed therebetween, and between the separator and the anode, and between the separator and the cathode. A step of obtaining a laminate having an adhesive composition layer obtained by using the composition, and
A method of manufacturing a non-aqueous electrolyte secondary battery comprising the step of bonding the laminate to the separator and the positive electrode through the adhesive composition, and/or bonding the separator and the negative electrode. The method of claim 12, wherein the bonding step is performed by heating at 40 to 180°C. The method of claim 12, wherein the bonding process is performed by a heat press at 40 to 180°C. The method for manufacturing a nonaqueous electrolyte secondary battery according to any one of claims 12 to 14, wherein the bonding step is performed after impregnating the laminate with an electrolyte solution.