KR20180094153A - Binder composition for secondary-cell positive electrode, slurry composition for secondary-cell positive electrode, positive electrode for secondary cell, and secondary cell - Google Patents

Abstract

An object of the present invention is to provide a binder composition for a secondary battery positive electrode excellent in high-potential durability. The binder composition for a secondary battery positive electrode of the present invention is a binder composition for a secondary battery positive electrode containing a polymer A containing a nitrile group-containing monomer unit and a conjugated diene monomer unit, a fluorine-containing polymer B and a solvent, Is 20 mg / 100 mg or more and 80 mg / 100 mg or less in iodine value, and the composite membrane obtained by forming the binder composition has 20 or less diameters of 20 mu m or more in diameter of 20 mu m or more in the range of 200 mu m square.

Description

TECHNICAL FIELD [0001] The present invention relates to a binder composition for a secondary battery positive electrode, a slurry composition for a negative electrode of a secondary battery, a positive electrode for a secondary battery, and a secondary battery. BACKGROUND OF THE INVENTION SECONDARY CELL}

The present invention relates to a binder composition for a secondary battery positive electrode, a slurry composition for a secondary battery positive electrode, a positive electrode for a secondary battery, and a secondary battery.

BACKGROUND ART [0002] A secondary battery such as a lithium ion secondary battery has characteristics such that it is small in size, light in weight, high in energy density, and can be repeatedly charged and discharged, and is used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of achieving high performance of the rechargeable battery.

Here, the positive electrode used in a secondary battery such as a lithium ion secondary battery generally has a current collector and an electrode composite layer (positive electrode composite layer) formed on the current collector. The positive electrode composite material layer is formed using a slurry composition obtained by dispersing, for example, a positive electrode active material and a binder composition containing a binder in a dispersion medium.

Therefore, in recent years, improvement of the binder composition used for forming the positive electrode composite layer has been attempted in order to achieve performance improvement of a further layer of the secondary battery.

Specifically, for example, Patent Document 1 discloses a binder composition capable of improving the flexibility of a positive electrode and the initial capacity of a secondary battery, wherein a monomer composition containing a nitrile group-containing monomer, a (meth) acrylic acid ester monomer and a conjugated diene monomer There has been proposed a positive electrode binder composition comprising a nitrile group-containing acrylic polymer composed of a hydride of a copolymer obtained by polymerizing a composition and a fluorine-containing polymer such as polyvinylidene fluoride as a binder.

In addition, for example, Patent Document 2 discloses a binder composition capable of improving the capacity and rate characteristics of a secondary battery by exhibiting at least an excellent binding capacity in an amount of use, and is a binder composition comprising an acrylic rubber, an acrylonitrile-butadiene rubber hydride, A binder composition for a positive electrode containing vinylidene fluoride as a binder has been proposed.

International Publication No. 2014/119790 Japanese Patent Application Laid-Open No. 2003-223895

However, the binder of the above-described conventional positive electrode binder composition did not have sufficient durability (high-potential durability) when repeatedly exposed to a high electric field. Therefore, in the secondary battery having the positive electrode formed using the above-described conventional positive electrode binder composition, there is a possibility that the battery performance may be deteriorated due to an increase in the amount of gas generation when the charge and discharge are repeated at a high potential There was room for.

Therefore, an object of the present invention is to provide a binder composition for a secondary battery positive electrode excellent in high-potential durability and a slurry composition for a secondary battery positive electrode.

It is another object of the present invention to provide a positive electrode for a secondary battery excellent in high-potential durability.

Further, it is an object of the present invention to provide a secondary battery having a small amount of gas generation even when charge / discharge is repeated over a high potential.

The present inventors have conducted intensive studies for the purpose of solving the above problems. The present inventors have also found that a composite film comprising a polymer having a nitrile group-containing monomer unit and a conjugated diene monomer unit and having a iodine value within a predetermined range and a fluorine-containing polymer as a binder, And that the binder composition exhibiting a predetermined property is excellent in high-potential durability, thereby completing the present invention.

The binder composition for a secondary battery positive electrode of the present invention is characterized in that it comprises a polymer A containing a nitrile group-containing monomer unit and a conjugated diene monomer unit, and a fluorine-containing Polymer B and a solvent, wherein the polymer A has an iodine value of 20 mg / 100 mg or more and 80 mg / 100 mg or less, and the composite membrane obtained by forming the binder composition has a volume of 200 m square And the number of existing spherical crystals having a diameter of 20 m or more is 20 or less. As described above, when the polymer A and the fluorine-containing polymer B are used together as a binder, the iodide value of the polymer A is set to 20 mg / 100 mg or more and 80 mg / 100 mg or less, , Excellent high-level durability can be exhibited in the binder composition.

Further, in the present invention, the term "the polymer includes a monomer unit" means that "a polymer obtained by using the monomer contains a structural unit derived from a monomer". Therefore, when the polymer A is a hydrogenated polymer obtained by hydrogenation after polymerization, the "conjugated diene monomer unit" also includes a structural unit derived from a hydrogenated conjugated diene monomer after polymerization. That is, the "conjugated diene monomer unit" includes all the structural units derived from the conjugated diene monomer (non-hydrogenated structural unit and hydrogenated structural unit).

In the present invention, " iodine value " can be measured in accordance with JIS K6235 (2006).

Further, in the present invention, in the present invention, the "composite film" is prepared by taking the binder composition on a Teflon chalet so as to have a thickness of 50 μm after drying, then drying it at 160 ° C. for 1.5 hours, Vacuum drying, and then quenched at a cooling rate of 100 캜 / min to 25 캜 or lower. In the present invention, the term " number of municipal water having a diameter of 20 占 퐉 or more " means that the composite membrane is observed using an optical microscope to determine whether the ratio of the long axis to the short axis is 0.7 or more and 1.0 or less, And measuring the number of municipalities having a diameter (maximum diameter) of 20 m or more.

Here, in the binder composition for a secondary battery positive electrode of the present invention, it is preferable that the fluorine-containing polymer B contains 50 mol% or more of vinylidene fluoride monomer units. When the fluorine-containing polymer B containing 50 mol% or more of the vinylidene fluoride monomer unit is used, in the secondary battery having the positive electrode formed by using the binder composition, the amount of gas generated when charge / Can be further reduced.

Further, in the binder composition for a secondary battery positive electrode of the present invention, it is preferable that the polymer A contains 30% by mass or more of the nitrile group-containing monomer units. The use of the polymer A containing 30% by mass or more of the nitrile group-containing monomer unit reduces the amount of gas generated when charging / discharging is repeated at a high potential in a secondary battery having a positive electrode formed using the binder composition .

In the present invention, the ratio of the monomer units in the polymer can be measured by a known method such as NMR or thermal decomposition gas chromatography.

In the binder composition for a secondary battery positive electrode of the present invention, it is preferable that the composite membrane has a storage elastic modulus E 'of 1 x 10 ⁸ Pa or more and 1 x 10 ⁹ Pa or less and a loss tangent (tan delta) of 0.001 or more and 0.1 or less . When the storage elastic modulus E 'and the loss tangent (tan delta) of the composite membrane are within the above range, the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently increased.

In the present invention, the "storage elastic modulus E '" and the "loss tangent (tan δ)" of the composite membrane can be obtained by measuring the solid viscoelasticity in a tensile mode at 25 ° C. and a frequency of 1 Hz .

The binder composition for a secondary battery positive electrode of the present invention preferably has a ratio of the amount of the polymer A to the total amount of the polymer A and the fluorine-containing polymer B of 5% by mass or more and 50% by mass or less. When the content of the polymer A in the polymer A and the fluorine-containing polymer B is within the above range, the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently increased, and in the secondary battery having the positive electrode , It is possible to further reduce the amount of gas generated when charging / discharging is repeated on a high potential.

It is another object of the present invention to solve the above problems in an advantageous manner. The present invention provides a slurry composition for a secondary battery positive electrode, which comprises a positive electrode active material and a binder composition for a secondary battery positive electrode . As described above, when the binder composition for secondary battery positive electrode is used, excellent high-level durability can be exhibited in the slurry composition.

It is a further object of the present invention to solve the above problems advantageously. The positive electrode for a secondary battery of the present invention is characterized by including a positive electrode composite material layer formed by using the above-described slurry composition for a secondary battery positive electrode . Thus, by using the above-described slurry composition for a secondary battery positive electrode, a positive electrode having excellent durability at high potential can be obtained.

It is an object of the present invention to solve the above problems advantageously. The secondary battery of the present invention is characterized by comprising the above-described positive electrode for a secondary battery, a negative electrode, an electrolyte, and a separator. As described above, by using the above-described positive electrode for secondary battery, it is possible to sufficiently suppress gas generation when charging / discharging is repeated at a high potential.

According to the present invention, it is possible to provide a binder composition for a secondary battery positive electrode excellent in high-potential durability and a slurry composition for a secondary battery positive electrode.

According to the present invention, it is possible to provide a positive electrode for a secondary battery excellent in high-potential durability.

Furthermore, according to the present invention, it is possible to provide a secondary battery having a small amount of gas generation even if charging / discharging is repeated over a high potential.

Fig. 1 (a) is an optical microscope photograph of a composite film formed using the binder composition of Example 1, and Fig. 1 (b) is a photograph of the composite film formed using the binder composition of Example 1, It is a processed photograph displayed surrounded by a red dashed line.
[Fig. 2] Fig. 2 (a) is an optical microscope photograph of a composite film formed using the binder composition of Comparative Example 6, and Fig. 2 (b) It is a processed photograph displayed surrounded by a red dashed line.

Hereinafter, embodiments of the present invention will be described in detail.

Here, the binder composition for a secondary battery positive electrode of the present invention can be used in preparing a slurry composition for a secondary battery positive electrode. The slurry composition for a secondary battery positive electrode prepared using the binder composition for a secondary battery positive electrode of the present invention can be used for forming a positive electrode of a secondary battery such as a lithium ion secondary battery. Furthermore, the secondary battery of the present invention is characterized by using a positive electrode for a secondary battery formed by using the slurry composition for a secondary battery positive electrode of the present invention.

(Binder Composition for Positive Electrode of Secondary Battery)

The binder composition for a secondary battery positive electrode of the present invention comprises a polymer A containing a nitrile group-containing monomer unit and a conjugated diene monomer unit, a fluorine-containing polymer B, and a solvent, optionally mixed with a positive electrode of a secondary battery And further contains other ingredients which can be used. The binder composition for a secondary battery positive electrode of the present invention is characterized in that the composite membrane obtained by forming the binder composition under a predetermined condition has an iodine value of 20 mg / 100 mg or more and 80 mg / 100 mg or less and has a diameter And 20 or less in number of 20 탆 or more.

According to the binder composition for a secondary battery positive electrode of the present invention, a polymer A having an iodine value of 20 mg / 100 mg or more and 80 mg / 100 mg or less is used and a composite film obtained from the binder composition satisfies a predetermined property, And the fluorine-containing polymer B, the high-potential durability can be sufficiently increased while securing the flexibility and peel strength of the positive electrode formed by using the binder composition. Therefore, by using the binder composition for a secondary battery positive electrode of the present invention, it is possible to obtain a secondary battery having a small amount of gas generation even when charging / discharging is repeated over a high potential.

Further, in the binder composition containing a polymer containing a conjugated diene monomer unit, it is generally considered that the lower the iodine value of the polymer including the conjugated diene monomer unit and the smaller the amount of double bonds in the polymer, the higher the durability of high potential . However, in the binder composition for a secondary battery positive electrode of the present invention, the reason is not clear, but it is preferable that the iodine value of the polymer A containing the nitrile group-containing monomer unit and the conjugated diene monomer unit is 20mg / 100mg or more and 80mg / And the composite film formed from the binder composition when the fluorine-containing polymer B is used in combination with the fluorine-containing polymer B satisfies a predetermined property, the fluorine-containing polymer B has a higher potential durability than the case where the polymer A having an iodine value of less than 20 mg / .

<Polymer A>

Polymer A is a component which functions as a binder together with fluorine-containing polymer B and is a positive electrode prepared by forming a positive electrode composite material layer on a current collector by using a slurry composition for secondary battery positive electrode prepared using a binder composition, So that the components contained in the positive electrode composite layer are not separated from the positive electrode composite layer. The polymer A includes a nitrile group-containing monomer unit and a conjugated diene monomer unit, and needs to have an iodine value of 20 mg / 100 mg or more and 80 mg / 100 mg or less. Further, as long as the effect of the present invention is not impaired, the polymer A may optionally contain other monomer units. The polymer A is preferably a hydrogenated polymer obtained by hydrogenating a polymer obtained by polymerizing a monomer composition containing a nitrile group-containing monomer and a conjugated diene monomer, optionally further containing another monomer, by a known method.

The proportion of the fluorine-containing monomer units in the polymer A is usually 30% by mass or less, preferably 20% by mass or less, and the proportion of the fluorine-containing monomer units in the polymer A (fluorine- Is different from the fluorine-containing polymer B described later.

[Nitrile group-containing monomer unit]

The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer. Since polymer A contains a monomer unit containing a nitrile group, excellent flexibility and binding force can be exerted.

Here, examples of the nitrile group-containing monomer capable of forming a nitrile group-containing monomer unit include an?,? - ethylenically unsaturated nitrile monomer. Specifically, the?,? - ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an?,? - ethylenically unsaturated compound having a nitrile group, and examples thereof include acrylonitrile,? -Chloroacrylonitrile, ? -Halogenoacrylonitrile such as methacrylonitrile,? -Halogenoacrylonitrile such as methacrylonitrile,? -Alkylacrylonitrile such as methacrylonitrile and? -Ethyl acrylonitrile, and the like. Of these, acrylonitrile and methacrylonitrile are preferable as the nitrile group-containing monomer from the viewpoint of enhancing the binding force of the polymer A, and acrylonitrile is more preferable.

These may be used alone or in combination of two or more.

The content of the nitrile group-containing monomer units in the polymer A is preferably 2% by mass or more, more preferably 10% by mass or more, and more preferably 25% by mass or more based on 100% by mass of all the repeating units in the polymer A. [ More preferably 30% by mass or more, particularly preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less. When the content of the nitrile group-containing monomer units in the polymer A is 2% by mass or more, the flexibility and binding force of the polymer A can be improved, and the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently increased. Therefore, it is possible to prevent the separation of the positive electrode composite layer and to obtain a secondary battery having a small amount of gas generation even when charge / discharge is repeated over a high potential. When the content of the nitrile group-containing monomer units in the polymer A is 50 mass% or less, the stability of the polymer A with respect to the electrolyte can be improved, so that the battery characteristics (e.g., output characteristics, etc.) Can be suppressed, and the amount of gas generated when charging / discharging over a high potential is repeated can be reduced.

[Conjugated diene monomer unit]

The conjugated diene monomer unit is a repeating unit derived from a conjugated diene monomer, and the conjugated diene monomer unit includes all the structural units derived from a conjugated diene monomer. Specifically, when the polymer A is a hydrogenated polymer obtained by hydrogenating a polymer obtained by polymerizing a monomer composition comprising a nitrile group-containing monomer and a conjugated diene monomer by a known method, the conjugated diene monomer unit of the polymer A may contain, Non-hydrogenated structural units that are not hydrogenated after polymerization, and hydrogenated structural units that are hydrogenated after polymerization. Since Polymer A contains a conjugated diene monomer unit, excellent stability can be exhibited with respect to an electrolytic solution.

Examples of the conjugated diene monomer capable of forming the conjugated diene monomer unit include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl- 1,3-pentadiene, 2-chloro-1,3-butadiene, and the like. Of these, 1,3-butadiene is preferred.

These may be used alone or in combination of two or more.

The content of the conjugated diene monomer units in the polymer A is preferably 50% by mass or more, more preferably 55% by mass or more, more preferably 60% by mass or more, based on 100% by mass of the total repeating units in the polymer A. More preferably 98% by mass or less, more preferably 90% by mass or less, even more preferably 75% by mass or less, and particularly preferably 70% by mass or less. When the content of the conjugated diene monomer unit in the polymer A is 50 mass% or more, the stability of the polymer A with respect to the electrolyte solution can be enhanced, so that deterioration of the battery characteristics of the secondary battery can be suppressed, It is possible to reduce the amount of gas generated when charging and discharging are repeated. When the content of the conjugated diene monomer unit in the polymer A is 98% by mass or less, the flexibility and binding force of the polymer A can be improved, and the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently increased. Therefore, it is possible to prevent the separation of the positive electrode composite material layer and obtain a secondary battery having a small amount of gas generation even when charge / discharge is repeated on a high potential.

[Other monomer units]

Other monomers capable of forming other monomer units are not particularly limited, and examples thereof include known monomers copolymerizable with the monomers described above, such as (meth) acrylic acid ester monomers and polymerizable monomers having a hydrophilic group. .

These monomers may be used singly or in combination of two or more. In the present invention, "(meth) acryl" means acryl and / or methacryl.

Examples of the (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, Acrylate, n-hexyl acrylate, hexyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n - pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate , Methacrylic acid alkyl esters such as octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate and stearyl methacrylate ; And the like.

Examples of the polymerizable monomer having a hydrophilic group include a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, and a monomer having a hydroxyl group.

Examples of the monomer having a carboxylic acid group include a monocarboxylic acid and a derivative thereof, a dicarboxylic acid and an acid anhydride thereof, and derivatives thereof.

Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.

Examples of the monocarboxylic acid derivative include 2-ethyl acrylic acid, isocrotonic acid,? -Acetoxy acrylic acid,? -Trans-aryloxy acrylic acid,? -Chloro-? -E-methoxy acrylic acid,? -Diamino acrylic acid, .

Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and the like.

Examples of the dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate, diphenylmaleic acid maleate, maleic acid dicylate, Maleic acid dodecyl maleate, octadecyl maleate, and maleic acid esters such as maleic acid fluoroalkyl.

Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic acid anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.

As the monomer having a carboxylic acid group, an acid anhydride which generates a carboxyl group by hydrolysis can also be used.

In addition, there may be mentioned monoethyl maleate, monoethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, Monoesters and diesters of?,? - ethylenically unsaturated polycarboxylic acids such as ethyl, diethyl itaconate, monobutyl itaconate, dibutyl itaconate, and the like.

Examples of the monomer having a sulfonic acid group include vinylsulfonic acid, methylvinylsulfonic acid, (meth) allylsulfonic acid, styrenesulfonic acid, ethyl (meth) acrylate-2-sulfonate, -Hydroxypropanesulfonic acid and the like.

In the present invention, "(meth) allyl" means allyl and / or methallyl.

Examples of the monomer having a phosphoric acid group include (meth) acryloyloxyethyl phosphate, methyl 2- (meth) acryloyloxyethyl phosphate and ethyl- (meth) acryloyloxyethyl phosphate.

In the present invention, "(meth) acryloyl" means acryloyl and / or methacryloyl.

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol and 5-hexen-1-ol; Hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di- St. alkanol ester of unsaturated carboxylic acid and the like; the formula CH ₂ = CR ¹ -COO- (H _2n C _n O) _m -H (the formula, m represents an integer of from 2 to 9, n is an integer of 2-4 , R ¹ represents a hydrogen or a methyl group) which is a polyalkylene glycol with (meth) acrylic acid esters represented by; 2-hydroxyethyl-2 '- oxy one (meth) acrylate phthalate, 2-hydroxyethyl - Mono (meth) acrylates of dihydroxy esters of dicarboxylic acids such as 2 '- (meth) acryloyloxy succinate (Meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-2-hydroxypropyl ether, (Meth) allyl-3-hydroxybutyl ether, (meth) allyl-2-hydroxybutyl ether, Mono (meth) allyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; polyoxyalkylene glycol mono (Meth) allyl ethers, such as glycerol mono (meth) allyl ether, (meth) allyl-2-chloro-3-hydroxypropyl ether, ) &Lt; / RTI &gt; of the halogen and hydroxy substituents of alkylene glycol (Meth) allyl-2-hydroxyethyl thioether, (meth) allyl-2-hydroxy (meth) allyl ether, (Meth) allylthioethers of alkylene glycols such as propylthioether and the like.

The content of the other monomer units in the polymer A is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, and the polymer A contains other monomer units (That is, the polymer A includes only a nitrile group-containing monomer unit and a conjugated diene monomer unit).

[Iodine]

Polymer A is required to have an iodine value of 20 mg / 100 mg or more and 80 mg / 100 mg or less, preferably 30 mg / 100 mg or more, more preferably 40 mg / 100 mg or more, and more preferably 50 mg / 100 mg or more And is preferably 75 mg / 100 mg or less, more preferably 65 mg / 100 mg or less, and even more preferably 60 mg / 100 mg or less. When the iodine value of the polymer A is less than 20 mg / 100 mg, the reason for this is not clear, but the high potential durability of the binder composition can not be sufficiently increased. When the iodine value of the polymer A is more than 80 mg / 100 mg, the stability of the polymer A with respect to the electrolytic solution is lowered, the battery characteristics of the secondary battery are lowered, and the gas generation amount . Further, when the iodine value of the polymer A is outside the above range, the binding force of the polymer A is lowered, and the peel strength of the positive electrode formed using the binder composition can not be sufficiently increased.

[Weight average molecular weight]

Further, the polymer A preferably has a weight average molecular weight of 100,000 or more, more preferably 125,000 or more, further preferably 150,000 or more, more preferably 2,000,000 or less, more preferably 1,000,000 or less, still more preferably 500,000 or less , And particularly preferably 300,000 or less. If the weight average molecular weight of the polymer A is 100,000 or more, the binding force of the polymer A can be further increased, and the battery characteristics of the secondary battery can be inhibited from being lowered. Therefore, it is possible to reduce the amount of gas generated when charging / discharging is repeated over a high potential. When the weight average molecular weight of the polymer A is 2,000,000 or less, the viscosity of the binder composition or the slurry composition is increased and handling and productivity are prevented from being lowered.

In the present invention, the &quot; weight average molecular weight &quot; can be measured using a gel permeation chromatograph.

[Preparation method of Polymer A]

The method of preparing the polymer A is not particularly limited. For example, it is possible to prepare a polymer by polymerizing a monomer composition containing the above-mentioned monomer, and optionally hydrogenating (hydrogenating) the obtained polymer.

In the present invention, the content of each monomer in the monomer composition can be determined in accordance with the content ratio of each monomer unit in the polymer A.

 The polymerization is not particularly limited, and any of a solution polymerization method, a suspension polymerization method, a bulk polymerization method, an emulsion polymerization method and the like can be used. As the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, and living radical polymerization can be used. When polymerization is carried out, a known emulsifier or a polymerization initiator may be used as needed.

The method of hydrogenating a polymer is not particularly limited, and a general method using a catalyst (see, for example, International Publication No. 2012/165120, International Publication No. 2013/080989 and Japanese Patent Laid-open No. 2013-8485) Can be used.

<Fluorine-Containing Polymer B>

The fluorine-containing polymer B functioning as a binder together with the above-mentioned polymer A is a polymer containing a fluorine-containing monomer unit. Concretely, as the fluorine-containing polymer B, homopolymers or copolymers of one or more fluorine-containing monomers, monomers containing one or more fluorine-containing monomers and fluorine-free monomers (hereinafter referred to as "fluorine-free monomers"), . &Lt; / RTI &gt;

The proportion of the fluorine-containing monomer units in the fluorine-containing polymer B is usually 70% by mass or more, and preferably 80% by mass or more. The proportion of the fluorine-free monomer unit in the fluorine-containing polymer B is usually 30 mass% or less, preferably 20 mass% or less.

[Fluorine-containing monomer unit]

Examples of the fluorine-containing monomer capable of forming the fluorine-containing monomer unit include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl chloride trifluoride, vinyl fluoride, trifluoroethylene, trifluorochloroethylene, 2 , 3,3,3-tetrafluoropropene, perfluoroalkyl vinyl ether, and the like. Among these, as the fluorine-containing monomer, vinylidene fluoride and tetrafluoroethylene are preferable.

The fluorine-containing polymer B preferably has at least a vinylidene fluoride monomer unit as the fluorine-containing monomer unit, more preferably a vinylidene fluoride monomer unit and a tetrafluoroethylene monomer unit.

The content of the vinylidene fluoride monomer unit in the fluorine-containing polymer B is preferably 50 mol% or more, more preferably 55 mol% or more, further preferably 60 mol% or more, and more preferably 89.5 mol% or less , And still more preferably not more than 89 mol%, further preferably not more than 70 mol%. When the content of the vinylidene fluoride monomer unit in the fluorine-containing polymer B is 50 mol% or more, the stability of the fluorine-containing polymer B with respect to the electrolytic solution can be enhanced, so that deterioration of the battery characteristics of the secondary battery can be suppressed At the same time, it is possible to reduce the amount of gas generated when charging / discharging is repeated on a high potential. When the content of vinylidene fluoride monomer units in the fluorine-containing polymer B is 89.5 mol% or less, the flexibility and binding force of the fluorine-containing polymer B can be improved, and the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently . Therefore, it is possible to prevent the separation of the positive electrode composite material layer and to obtain a secondary battery having a small amount of gas generation even when charging / discharging is repeated over a high potential.

The content of the tetrafluoroethylene monomer units in the fluorine-containing polymer B is preferably 9.9 mol% or more, more preferably 19.9 mol% or more, still more preferably 29.9 mol% or more, and 49.9 mol% or less , More preferably 44.9 mol% or less, and still more preferably 39.9 mol% or less. When the content ratio of the tetrafluoroethylene monomer units in the fluorine-containing polymer B is 9.9 mol% or more, the flexibility and binding force of the fluorine-containing polymer B can be improved and the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently increased . Therefore, it is possible to prevent the separation of the positive electrode composite material layer and to obtain a secondary battery having a small amount of gas generation even when charging / discharging is repeated over a high potential. When the proportion of the tetrafluoroethylene monomer units in the fluorine-containing polymer B is 49.9 mol% or less, the stability of the fluorine-containing polymer B with respect to the electrolyte solution can be enhanced, so that deterioration of the battery characteristics of the secondary battery can be suppressed It is possible to reduce the amount of gas generated when charging and discharging are repeated on a high potential.

[Fluorine-free monomer]

Examples of the fluorine-free monomer capable of forming a fluorine-free monomer unit include monomers that do not contain fluorine copolymerizable with the fluorine-containing monomer, such as 1-olefins such as ethylene, propylene and 1-butene; unsaturated nitrile compounds such as (meth) acrylonitrile, methyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylate, (Meth) acrylate, N-methyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N (Meth) acrylamide, N-phenyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (Meth) acrylate Amide group-containing unsaturated compounds such as N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide and 2- (meth) acrylamido- Vinyl compounds containing carboxyl groups such as acrylic acid, itaconic acid, fumaric acid, crotonic acid and maleic acid; unsaturated compounds containing epoxy groups such as allyl glycidyl ether and glycidyl (meth) acrylate; dimethylaminoethyl (meth) Unsaturated compounds containing amino groups such as diethylaminoethyl (meth) acrylate, unsaturated compounds containing sulfonic acid groups such as styrenesulfonic acid, vinylsulfonic acid and (meth) allylsulfonic acid, unsaturated compounds containing sulfuric acid groups such as 3-allyloxy- ; Unsaturated compounds containing a phosphoric acid group such as propyl (meth) acrylate-3-chloro-2-phosphate and 3-allyloxy-2-hydroxypropanephosphoric acid.

Among these, as the fluorine-free monomer, an amide group-containing unsaturated compound is preferable, and N-tert-butyl acrylamide is more preferable.

The fluorine-containing polymer B preferably has an amide group-containing unsaturated compound monomer unit as the fluorine-free monomer, and more preferably contains an N-tert-butyl acrylamide monomer unit.

The content of the amide group-containing unsaturated compound monomer unit in the fluorine-containing polymer B is preferably 0.01 mol% or more, more preferably 0.04 mol% or more, still more preferably 0.1 mol% or more, and 3 mol% or less , More preferably 2.5 mol% or less, further preferably 2 mol% or less, particularly preferably 0.5 mol% or less. When the content ratio of the amide group-containing unsaturated compound monomer unit in the fluorine-containing polymer B is from 0.01 mol% to 3 mol%, the peel strength of the positive electrode formed by using the binder composition and the battery characteristics of the secondary battery can be improved , A secondary battery with a small amount of gas generation can be obtained even when charging and discharging are repeated on a high potential.

[Viscosity of 5 mass% solution of fluorine-containing polymer B]

The fluorine-containing polymer B preferably has a viscosity of 25 mPa.s or more at 25 DEG C of a 5 mass% solution of N-methyl-2-pyrrolidone (NMP) as a solvent, more preferably 80 mPa.s or more More preferably 150 mPa · s or more, particularly preferably 450 mPa · s or more, more preferably 10,000 mPa · s or less, still more preferably 5,000 mPa · s or less, and 1,500 mPa · s or less And still more preferably not more than 600 mPa · s. When the viscosity of the 5 mass% NMP solution of the fluorine-containing polymer B is 20 mPa.s or more, the binding force of the fluorine-containing polymer B can be further increased and the battery characteristics of the secondary battery can be inhibited from being lowered. Therefore, it is possible to reduce the amount of gas generated when charging / discharging is repeated over a high potential. When the viscosity of the 5 mass% NMP solution of the fluorine-containing polymer B is 10,000 mPa 占 퐏 or less, the viscosity of the binder composition or the slurry composition is increased, and handling and productivity are prevented from being lowered.

In the present invention, the viscosity of the 5 mass% NMP solution of the fluorine-containing polymer B can be measured at 25 캜 using a B-type viscometer.

[Method of preparing fluorine-containing polymer B]

The method for producing the fluorine-containing polymer B is not particularly limited, and any of the solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method and the like can be used.

As the polymerization method, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used. As the polymerization initiator, a known polymerization initiator can be used.

<Containing Ratio of Polymer A and Fluorine-Containing Polymer B>

The content of the polymer A and the fluorine-containing polymer B in the binder composition is such that the ratio of the amount of the polymer A to the total amount of the polymer A and the fluorine-containing polymer B is 100 mass% More preferably 10 mass% or more, further preferably 50 mass% or less, more preferably 40 mass% or less, still more preferably 30 mass% or less, particularly preferably 20 mass% or less. When the ratio of the amount of the polymer A is 5% by mass or more, the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently increased. Therefore, it is possible to prevent the separation of the positive electrode composite material layer and to obtain a secondary battery having a small amount of gas generation even when charging / discharging is repeated over a high potential. When the ratio of the amount of the polymer A is 50 mass% or less, it is possible to reduce the amount of gas generated when charging / discharging is repeated over a high electric field, by setting the number of mounds having a diameter of 20 m or more, have.

<Solvent>

The solvent is not particularly limited and an organic solvent can be used. Examples of the organic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, Alcohols such as methanol and ethanol, alcohols such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as diethyl ether, dioxane and tetrahydrofuran, N, N-dimethylform Amide and N-methyl-2-pyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene. These may be used singly or in combination of two or more kinds.

Among them, NMP is preferable as the solvent.

&Lt; Other components &gt;

The binder composition of the present invention may contain, in addition to the above components, components such as a reinforcing material, a leveling agent, a viscosity adjusting agent, and an electrolyte additive. These are not particularly limited as long as they do not affect the cell reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. These components may be used singly or two or more of them may be used in combination at an arbitrary ratio.

<Properties of composite membrane>

The binder composition of the present invention was prepared so that the thickness of the binder composition after drying was 50 占 퐉 on a Teflon chalet and then dried at 160 占 폚 for 1.5 hours and then vacuum dried at 110 占 폚 for 5 hours and then dried at 100 占 폚 At a cooling rate of not more than 25 DEG C per minute to form a composite film comprising the polymer A and the fluorine-containing polymer B, it is necessary that the composite film has a predetermined property.

[Number of New Year's Day]

Specifically, the composite membrane formed by using the binder composition of the present invention needs to have a number of 20 to 20 or less diameters of 20 mu m or more in diameter within a range of 200 mu m square, and a diameter of 20 mu m It is preferable that the number of Chinese characters or more is 1 or more and 10 or less. When the number of mats is 20 or less, the high-potential durability of the binder composition can be sufficiently increased. Therefore, when the binder composition is used, a secondary battery having a small amount of gas generation when charge / discharge is repeated over a high electric field is obtained. Here, it is presumed that the reclamation of the composite membrane is derived from the fluorine-containing polymer B.

It is also presumed that the number of mugworts having a diameter of 20 m or more in the composite membrane changes due to the compatibility of the polymer A with the fluorine-containing polymer B. The number of mugworts having a diameter of 20 m or more in the composite membrane can be determined by, for example, the kind and ratio of the monomer units constituting the polymer A and the fluorine-containing polymer B, the iodine value of the polymer A, Can be adjusted by changing the content ratio of the polymer B. [

[Storage elastic modulus]

The composite membrane described above preferably has a storage elastic modulus E 'of 1 x 10 ⁸ Pa or more and 1 x 10 ⁹ Pa or less. When the storage elastic modulus E 'of the composite film is within the above range, the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently increased.

The storage elastic modulus E 'of the composite film can be calculated, for example, by the kind and ratio of the monomer units constituting the polymer A and the fluorine-containing polymer B, the iodine content of the polymer A, and the polymer A and the fluorine-containing polymer B in the binder composition The content ratio can be changed to adjust the diameter and the number of the reclamation existing in the composite membrane.

[Loss tangent]

The composite membrane described above preferably has a loss tangent (tan delta) of not less than 0.001 and not more than 0.1. If the loss tangent (tan delta) of the composite membrane is within the above range, the flexibility and peel strength of the positive electrode formed using the binder composition can be sufficiently increased.

The loss tangent (tan delta) of the composite film is, for example, a ratio of the type and ratio of the monomer units constituting the polymer A and the fluorine-containing polymer B, the ratio of iodine to the polymer A in the binder composition, The content ratio of B can be changed to adjust the diameter and number of the reclamation present in the composite film.

(Slurry Composition for Secondary Battery Positive Electrode)

The slurry composition for a secondary battery positive electrode of the present invention comprises a positive electrode active material and the above-described binder composition, and optionally further contains a conductive material and other components. That is, the slurry composition for a secondary battery positive electrode of the present invention contains a positive electrode active material, the polymer A described above, the fluorine-containing polymer B, and a solvent, and optionally further contains a conductive material and other components. And, since the secondary battery positive electrode slurry composition of the present invention includes the above-described binder composition, the positive electrode formed using the slurry composition can sufficiently enhance high-potential durability while securing flexibility and peel strength.

In the following, a description will be given of a case where the slurry composition for a secondary battery positive electrode is a slurry composition for a lithium ion secondary battery positive electrode, but the present invention is not limited to the following examples.

&Lt; Positive electrode active material &

The positive electrode active material is a substance exchanging electrons at the positive electrode of the secondary battery. As the positive electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium is generally used.

Concretely, the positive electrode active material for a lithium ion secondary battery is not particularly limited, and lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ) (Li (CoMnNi) O ₂ ) of Mn, a lithium-containing complex oxide of Ni-Mn-Al, a lithium-containing complex oxide of Ni-Co-Al, an olivine-type lithium iron phosphate (LiFePO ₄ ) Lithium manganese lithium (LiMnPO ₄ ), lithium excess spinel compound represented by Li _{1 + x} Mn _{2 -x} O ₄ (0 <X <2), Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ , LiNi _0.5 Mn _1.5 O _4, and the like.

Among the above, lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium-containing complex oxide of Co-Ni-Mn, and the like are preferable as the positive electrode active material from the viewpoint of improving the battery capacity and the like of the secondary battery. _{Li [Ni 0.17 Li 0.2 Co 0.07} Mn 0.56] O 2 , or LiNi _0.5 is preferred to use the Mn _1.5 O ₄ and lithium-containing cobalt oxide _{(LiCoO 2), Li [Ni} 0.17 Li 0.2 Co 0.07 Mn 0.56] O 2 , or LiNi _0.5 Mn _1.5 O ₄ is more preferably used.

The blending amount and the particle diameter of the positive electrode active material are not particularly limited and may be the same as those of the conventionally used positive electrode active material.

* &Lt; Binder composition &gt;

As the binder composition, the above-described binder composition for a secondary battery positive electrode of the present invention is used.

The amount of the binder composition to be blended is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and more preferably 2 parts by mass or less, in terms of solid content, per 100 parts by mass of the positive electrode active material, Or less. When the amount of the binder composition blended per 100 parts by mass of the positive electrode active material is 0.5 part by mass or more in terms of solid content, the peak strength of the positive electrode formed using the slurry composition can be sufficiently increased. Therefore, it is possible to prevent the separation of the positive electrode composite material layer and to obtain a secondary battery having a small amount of gas generation even when charging / discharging is repeated over a high potential. When the amount of the binder composition is less than 2 parts by mass in terms of solid content per 100 parts by mass of the positive electrode active material, increase in the ratio of the polymer A and the fluorine-containing polymer B in the positive electrode composite material layer formed using the slurry composition is suppressed, The capacity decrease of the secondary battery can be suppressed.

&Lt; Conductive material &

The conductive material is for securing electrical contact between the positive electrode active materials. Examples of the conductive material include carbon black (for example, acetylene black, Ketjenblack (registered trademark), furnace black, etc.), graphite, carbon fiber, carbon flake, carbon short- Grown carbon fiber, etc.), fiber of various metals, foil and the like can be used. Among them, carbon black is preferable as the conductive material, and acetylene black is more preferable.

These may be used alone or in combination of two or more.

The amount of the conductive material to be blended is preferably at least 1 part by mass, more preferably at least 1.2 parts by mass, further preferably at least 1.5 parts by mass, and most preferably at most 3 parts by mass per 100 parts by mass of the positive electrode active material, More preferably at most 2.5 parts by mass, and still more preferably at most 2.5 parts by mass. If the amount of the conductive material is too small, electrical contact between the positive electrode active materials may not be sufficiently secured. On the other hand, if the blending amount of the conductive material is too large, there is a fear that the viscosity stability of the slurry composition is lowered, and the density of the positive electrode composite material layer in the positive electrode is lowered, so that the secondary battery can not be sufficiently high capacity.

&Lt; Other components &gt;

Other components that can be blended into the slurry composition are not particularly limited, and the same components as the other components that can be blended in the binder composition of the present invention can be mentioned. The other components may be used singly or in combination of two or more in an arbitrary ratio.

<Preparation of slurry composition>

The above-mentioned slurry composition can be prepared by dissolving or dispersing the respective components in a solvent such as an organic solvent. Specifically, each of the components and the solvent are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a brain ball, an ultrasonic disperser, a homogenizer, a planetary mixer and a fill mix, Can be prepared. As the solvent used for preparing the slurry composition, a solvent contained in the binder composition may be used.

(Positive electrode for secondary battery)

The positive electrode for a secondary battery of the present invention comprises a current collector and a positive electrode composite material layer formed on the current collector, and the positive electrode material mixture layer is formed by using the slurry composition for the secondary battery positive electrode. That is, at least the positive electrode active material, the polymer A, and the fluorine-containing polymer B are contained in the positive electrode composite material layer. Further, each component contained in the electrode composite layer was included in the slurry composition for the positive electrode of the secondary battery, and the favorable abundance ratio of each component thereof is the same as that of each component in the slurry composition.

Since the positive electrode for a secondary battery of the present invention is manufactured by using the slurry composition containing the binder composition for a secondary battery positive electrode of the present invention, even if charging / discharging is repeated over a high potential, A secondary battery with a small amount of generation is obtained.

&Lt; Preparation method of positive electrode &gt;

The positive electrode for a secondary battery of the present invention can be obtained by, for example, a step of applying the above-described slurry composition onto a current collector (coating step), a step of drying the slurry composition applied on the current collector, (Drying step).

[Application step]

The method of applying the slurry composition onto the current collector is not particularly limited and a known method can be used. Specifically, as a coating method, a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method and the like can be used. At this time, the slurry composition may be applied to only one surface of the current collector, or may be applied to both surfaces. The thickness of the slurry film on the collector on the current collector after application and drying can be appropriately set in accordance with the thickness of the positive electrode composite material layer obtained by drying.

Here, as the current collector to which the slurry composition is applied, a material having electric conductivity and electrochemically durable is used. Specifically, as the current collector, a current collector made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold or platinum can be used. Among them, an aluminum foil is particularly preferable as a collector used as a positive electrode. The above materials may be used singly or in combination of two or more in an arbitrary ratio.

[Drying process]

The method for drying the slurry composition on the current collector is not particularly limited and a known method can be used. For example, a drying method by hot air, hot air, low-humidity air, vacuum drying, . By drying the slurry composition on the current collector in this way, a positive electrode composite material layer is formed on the current collector to obtain a positive electrode for a secondary battery having a current collector and a positive electrode material layer.

After the drying step, the positive electrode composite material layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the positive electrode composite material layer and the current collector can be improved.

In addition, when the positive electrode composite material layer contains a curable polymer, it is preferable to cure the polymer after formation of the positive electrode composite material layer.

(Secondary battery)

The secondary battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator, and the positive electrode for a secondary battery of the present invention is used as the positive electrode. Since the secondary battery of the present invention is provided with the positive electrode for secondary battery of the present invention, the amount of generated gas is small even when charge / discharge is repeated at a high potential (for example, 4.4 V or higher).

In the following, a case where the secondary battery is a lithium ion secondary battery is described as an example, but the present invention is not limited to the following examples.

<Negative electrode>

As the negative electrode, a known negative electrode can be used. Specifically, as the negative electrode, for example, a negative electrode comprising a thin metal plate of lithium, or a negative electrode comprising a negative electrode mixture layer formed on a current collector may be used.

The current collector may be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold or platinum. As the negative electrode composite material layer, a layer containing a negative electrode active material and a binder may be used. Further, the binder is not particularly limited, and any known material can be used.

<Electrolyte>

As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte of the lithium ion secondary battery, for example, a lithium salt is used. As the lithium salt, _{e.g., LiPF 6, LiAsF 6, LiBF} 4, LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) 2 NLi, and the like _{(CF 3 SO 2) 2 NLi} , (C 2 F 5 SO 2) NLi. Of these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable because it is easy to dissolve in a solvent and exhibits a high degree of dissociation. The electrolytes may be used singly or in combination of two or more in an arbitrary ratio. Generally, the lithium ion conductivity tends to increase with the use of a supporting electrolyte having a high degree of dissociation, so that the lithium ion conductivity can be controlled depending on the type of the supporting electrolyte.

The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Examples of the organic solvent include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate Examples of the organic solvent include carbonates such as butylene carbonate (BC) and ethyl methyl carbonate (EMC), esters such as? -Butyrolactone and methyl formate, ethers such as 1,2-dimethoxyethane and tetrahydrofuran, Sulfoxide compounds such as dimethyl sulfoxide and the like are preferably used. A mixed solution of these solvents may also be used. Among them, carbonates are preferably used because they have a high dielectric constant and a wide stable potential range, and it is more preferable to use a mixture of ethylene carbonate and ethylmethyl carbonate.

The concentration of the electrolyte in the electrolytic solution can be adjusted arbitrarily, and is preferably 0.5 to 15 mass%, more preferably 2 to 13 mass%, and more preferably 5 to 10 mass% . To the electrolytic solution, known additives such as fluoroethylene carbonate, ethylmethylsulfone and the like may be added.

<Separator>

The separator is not particularly limited, and for example, those described in Japanese Laid-Open Patent Publication No. 2012-204303 can be used. Among them, polyolefins such as polyethylene, polypropylene, polybutene, poly (ethylene terephthalate), polybutylene terephthalate, polybutylene terephthalate, polybutylene terephthalate, Polyvinyl chloride) resin is preferable.

<Manufacturing Method of Secondary Battery>

In the secondary battery of the present invention, for example, the positive electrode and the negative electrode are overlapped with each other with a separator interposed therebetween. The battery is wound into a battery container by winding or folding according to the necessity, It can be manufactured by punching. An overcurrent prevention element such as a fuse, a PTC element, an expansion metal, a lead plate, or the like may be provided as necessary in order to prevent internal pressure rise and overcharge discharge of the secondary battery from occurring. The shape of the secondary battery may be, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, or a flat shape.

Example

Hereinafter, the present invention will be described concretely based on examples, but the present invention is not limited to these examples. In the following description, &quot;% &quot; and &quot; part &quot; representing amounts are on a mass basis unless otherwise specified.

In the polymer produced by copolymerizing a plurality of kinds of monomers, the proportion of the structural units formed by polymerizing certain monomers in the polymer is generally, unless otherwise specified, (Input ratio) of the monomer to the total amount of the monomer.

In Examples and Comparative Examples, the iodine content of the polymer was determined by measuring the weight average molecular weight and the solution viscosity of 5 mass%, the water retention of the composite membrane, the storage elastic modulus, the loss elastic modulus and the loss tangent (tan delta) The high potential gas generation amount of the secondary battery was measured and evaluated by the following method.

&Lt; Iodine of Polymer &gt;

 100 g of the aqueous dispersion of the polymer was solidified with 1 liter of methanol, and then vacuum-dried at 60 DEG C for 12 hours. Then, the iodine value of the obtained dry polymer was measured according to JIS K6235 (2006).

&Lt; Weight average molecular weight of polymer &

 The polymer was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an NMP solution having a concentration of 8 mass%. Then, 130 mg of an NMP solution having a concentration of 8 mass% was dissolved in 5 ml of N, N-dimethylformamide (DMF), and the measurement was carried out using a gel permeation chromatograph. As the column, TSK gel α-M, α-3000 (φ 7.8 mm × 30 cm) manufactured by Tosoh Corporation was used. Then, the weight average molecular weight was calculated from the obtained data.

&Lt; Viscosity of 5 mass% solution of polymer &

 The polymer was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an NMP solution having a concentration of 5 mass%. Then, the viscosity at 25 캜 was measured using a B-type viscometer (TV-10M, manufactured by TOKI INDUSTRIAL CO., LTD.).

<Numbers of composite membranes>

[Production of composite membrane]

The binder composition was taken on a Teflon chalet to a length of 50 mu m after drying. Thereafter, it was dried at 160 ° C for 1.5 hours, vacuum-dried at 110 ° C for 5 hours, and then rapidly cooled to 25 ° C or less at a cooling rate of 100 ° C / minute to obtain a composite film.

[How to check the local water supply]

Using the optical microscope (VHX-9000, manufactured by KEEN), the obtained composite membrane was observed at a magnification of 1000 times. Then, four images (optical microscope photographs) of 100 mu m x 100 mu m were taken at an arbitrary position of the composite film, and the number of midsummer with a diameter of 20 mu m or more was measured for each image. Then, the sum of the numbers of the municipalities having a diameter of 20 mu m or more measured was obtained, and the number of municipalities existing within the range of 200 mu m square was obtained.

1 (a), the position of the moon phase of 20 mu m or more in diameter in Fig. 1 (a) was surrounded by a red dashed line to obtain a composite film formed by using the binder composition of Example 1, Respectively. 2 (a), the position of the orbital of 20 탆 or more in diameter in Fig. 2 (a) was surrounded by a red dashed line and Fig. 2 (b) Respectively.

&Lt; Storage elastic modulus, loss elastic modulus and loss tangent (tan delta) of composite film &gt;

[Production of composite membrane]

A composite membrane was obtained in the same manner as described above.

[Measurement of viscoelasticity of composite membrane]

The obtained composite membrane was subjected to a tensile mode (adjustment of the elongation of the sample: adjusted in the automatic measurement mode) at a temperature of 25 DEG C with a minimum tension of 98.0 mN using a viscoelastic spectrometer (DMS, manufactured by SII Nanotechnology Co., Ltd., DMS6100 standard type) , The distance between the chucks was 10 mm, and the sample width was 10 mm to measure the storage elastic modulus and the loss elastic modulus at 0.1 to 10 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, And loss tangent (tan delta) were measured.

<Flexibility of positive electrode>

The sheet-like positive electrode and the sheet-like negative electrode were wound using a core having a diameter of 20 mm via a separator to obtain a rolled body. As the separator, a microporous membrane made of polypropylene having a thickness of 20 mu m was used. Then, the obtained winding body was compressed from one direction until the thickness became 4.5 mm at a speed of 10 mm / sec. Thereafter, the compacted body was disassembled, and the state of the positive electrode was observed with a naked eye to evaluate the following criteria.

A: No crack

B: There is a minute crack, but no separation of the positive electrode composite layer

C: Peeling of the positive electrode composite layer

&Lt; Peel strength of positive electrode &

The prepared sheet-like positive electrode was cut into squares with a width of 2.5 cm and a length of 1 cm to prepare a test piece, and the surface of the positive electrode material layer side was fixed with the surface facing upward. Then, an adhesive tape (cellophane tape specified in JIS Z1522) was attached to the surface of the positive electrode composite material layer side of the test piece, and then the adhesive tape was peeled from one end of the test piece in the direction of 180 ° (the other end side of the test piece) at a rate of 50 mm / The stress was measured. The measurement was carried out 10 times to obtain an average value of the stress, and this was evaluated as the peel strength based on the following criteria. The larger the fill strength, the better the adhesion of the positive electrode composite layer to the current collector.

A: Peel strength of 12 N / m or more

B: Peel strength of 10 N / m or more and less than 12 N / m

C: Peel strength less than 10 N / m

&Lt; Amount of high potential gas generation in secondary battery &

The prepared lithium ion secondary battery was charged at a temperature of 25 캜 under a pressure of 600 mA until the voltage became 4.4 V, and then the initial volume of the battery was measured. Subsequently, charging (float charging) was performed for one week under a 60 ° C environment so that the voltage became 4.4 V, and the volume of the battery (volume after float charging) was measured again. Then, the amount of increase in volume of the battery (volume after float filling-initial volume) was calculated, and this was evaluated according to the following criteria as the amount of high-potential gas generation. The lower the amount of high potential gas generation, the better the high-potential durability of the binder composition.

A: volume increase is less than 5mL

B: Volume increase exceeding 5 mL and below 8 mL

C: Volumetric increase is more than 8mL and less than 11mL

D: Volumetric increase exceeds 11mL to 15mL or less

E: volume increase exceeds 15 mL

(Example 1)

<Preparation of Polymer A>

In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate and 35 parts of acrylonitrile as a nitrile group-containing monomer were charged in this order, and the inside of the bottle was replaced with nitrogen. Thereafter, 65 parts of 1,3-butadiene as a conjugated diene monomer was pressed, and 0.25 part of ammonium persulfate was added, and polymerization reaction was carried out at a reaction temperature of 40 占 폚. Then, a polymer comprising a nitrile group-containing monomer unit and a conjugated diene monomer unit was obtained. The polymerization conversion rate was 85%, and the iodine value was 280 mg / 100 mg.

Next, water was added to the obtained polymer, and 400 mL (total solid content: 48 g) of a polymer solution having a total solid content concentration adjusted to 12 mass% was charged into a 1 liter autoclave equipped with a stirrer, And the solution was allowed to flow for a minute to remove dissolved oxygen in the polymer solution. Thereafter, 50 mg of palladium acetate as a hydrogenation catalyst was dissolved in 180 ml of water to which 4 moles of nitric acid relative to Pd had been added, and the solution was added. The inside of the system was replaced with hydrogen gas twice, and the contents of the autoclave were heated to 50 DEG C under a pressure of 3 MPa with hydrogen gas, and hydrogenation was carried out for 6 hours.

Thereafter, the contents were returned to room temperature, the inside of the system was brought to a nitrogen atmosphere, and the mixture was concentrated to a solid concentration of 40% by using an evaporator to obtain a polymer containing a nitrile group-containing monomer unit and a conjugated diene monomer unit A water dispersion. Further, 320 parts of N-methyl-2-pyrrolidone (NMP) was added to 100 parts of this aqueous dispersion, and water and residual monomer were completely evaporated under reduced pressure. Then, N-methyl- To obtain an NMP solution of Polymer A having a concentration of 8 mass%.

Then, the weight average molecular weight and the iodine value of the obtained polymer A were measured. The results are shown in Table 1.

<Preparation of fluorine-containing polymer B>

1.1 kg of pure water was added to an autoclave having an internal volume of 4 L and sufficiently purged with nitrogen. 880 g of octafluorocyclobutane was then added, and the inside of the system was kept at 45 캜 and a stirring speed of 580 rpm. Thereafter, 45 g of tetrafluoroethylene as a fluorine-containing monomer, 130 g of vinylidene fluoride, and 2 g of a 10 mass% methanol solution of N-tert-butyl acrylamide as a fluorine-free monomer were charged in the autoclave. Then, 1 g of a 50 mass% methanol solution of di-n-propyl peroxydicarbonate was added to initiate polymerization. As the polymerization progressed, the pressure in the system was lowered. Therefore, a mixed gas of tetrafluoroethylene / vinylidene fluoride = 33/67 (molar ratio) was continuously supplied to maintain the pressure in the system at 1.5 MPa (gauge pressure) . Further, 3.1 g of a total of 3.1 g of N-tert-butyl acrylamide in a 10 mass% methanol solution was continuously added, and stirring was continued for 5 hours. After repressurizing and returning to atmospheric pressure, the reaction product was washed with water and dried to obtain 50 g of white powder of fluorine-containing polymer B.

The obtained fluorine-containing polymer B contained 66.4 mol% of vinylidene fluoride monomer units, 33.4 mol% of tetrafluoroethylene monomer units, and 0.2 mol% of N-tert-butyl acrylamide monomer units.

Then, the viscosity of the obtained fluorine-containing polymer B in a 5 mass% solution was measured. The results are shown in Table 1.

&Lt; Preparation of binder composition for secondary battery positive electrode &

 0.3 part of the NMP solution of the polymer A in terms of solid fraction, 1.7 parts of the fluorine-containing polymer B and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to obtain a total amount of the polymer A and the fluorine- To obtain a binder composition in which the ratio of the amount of the polymer A to the amount of the polymer A was 15 mass%.

Then, a composite membrane was formed by using the binder composition to evaluate the water retention, storage elastic modulus, loss elastic modulus and loss tangent (tan delta) of the composite membrane. The results are shown in Table 1.

&Lt; Preparation of slurry composition for secondary battery positive electrode &

100 parts of LiCoO ₂ (volume average particle diameter: 12 μm) as a positive electrode active material and _2.0 parts of acetylene black as an electroconductive material (DENKA BLACK CHEMICAL INDUSTRIES, DENKA BLACK IND., Volume average particle diameter: 35 nm, BET specific surface area: 68 m ² / g) , 2 parts of the binder composition in terms of solid content, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were stirred with a planetary mixer to prepare a slurry composition for a secondary battery positive electrode.

&Lt; Preparation of positive electrode for secondary battery &

An aluminum foil having a thickness of 15 mu m was prepared as a current collector. Then, the slurry composition for the secondary battery positive electrode was coated on both sides of the aluminum foil so that the coating amount after drying was 20 mg / cm ² , and dried at 60 ° C for 20 minutes and at 120 ° C for 20 minutes. Thereafter, it was heat-treated at 150 DEG C for 2 hours to obtain a positive electrode cloth. The positive electrode was rolled by a roll press to produce a positive electrode composite layer having a density of 3.9 g / cm &lt; ³ &gt; and a sheet-like positive electrode made of an aluminum foil. Then, the sheet-like positive electrode was cut to a width of 4.8 mm and a length of 50 cm to obtain a positive electrode for a secondary battery.

The peel strength was measured using a sheet-like positive electrode. Further, the flexibility of the positive electrode was evaluated using a sheet-like positive electrode and a sheet-like negative electrode to be described later. The results are shown in Table 1.

<Fabrication of negative electrode for secondary battery>

A mixture of 90 parts of spherical artificial graphite (volume average particle diameter: 12 占 퐉) as a negative electrode active material and 10 parts of SiO _x (volume average particle diameter: 10 占 퐉), 1 part of a styrene butadiene copolymer as a binder, 1 part of carboxymethyl cellulose as a thickener, , And an appropriate amount of water as a dispersion medium was stirred with a planetary mixer to prepare a slurry composition for a secondary battery negative electrode.

Next, a copper foil having a thickness of 15 mu m was prepared as a current collector. Then, the slurry composition for a secondary battery negative electrode was applied to both surfaces of the copper foil so that the coating amount after drying was 10 mg / cm ² , and dried at 60 ° C for 20 minutes and at 120 ° C for 20 minutes. Thereafter, the resultant was heat-treated at 150 DEG C for 2 hours to obtain a negative electrode cloth. The negative electrode material was rolled by a roll press to produce a negative electrode composite material layer having a density of 1.8 g / cm ³ and a sheet-like negative electrode made of a copper foil. Then, the sheet-like negative electrode was cut into 5.0 mm in width and 52 cm in length to obtain a negative electrode for a secondary battery.

<Fabrication of secondary battery>

The fabricated positive electrode for a secondary battery and negative electrode for a secondary battery were wound using a core having a diameter of 20 mm through a separator (microporous membrane made of polypropylene) having a thickness of 15 m to obtain a winding. Then, the obtained winding body was compressed from one direction until the thickness became 4.5 mm at a speed of 10 mm / sec. Further, the rolled body after compression had an elliptical shape in plan view, and the ratio of the long diameter to the short diameter (long diameter / short diameter) was 7.7.

A mixed solution obtained by adding 5 mass% of fluoroethylene carbonate to a mixed solvent of a non-aqueous electrolyte (a 1.0 M LiPF ₆ solution (solvent: ethylene carbonate / ethyl methyl carbonate = 3/7 (mass ratio) 2% by volume of vinylene carbonate) was prepared.

Thereafter, the wound body after compression was accommodated in the aluminum laminate case together with 3.2 g of the nonaqueous electrolyte solution. Then, a nickel lead wire was connected to a predetermined point of the negative electrode for the secondary battery, an aluminum lead wire was connected to a predetermined point of the positive electrode for the secondary battery, and the opening of the case was sealed with heat to obtain a lithium ion secondary battery. This lithium ion secondary battery was a pouch type having a width of 35 mm, a height of 48 mm, and a thickness of 5 mm, and the nominal capacity of the battery was 700 mAh.

Then, using the produced lithium ion secondary battery, the amount of high potential gas generation was measured. The results are shown in Table 1.

(Example 2)

 Polymer A, fluorine-containing polymer B, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, and a separator were prepared in the same manner as in Example 1 except that the amount of palladium acetate as a hydrogenation catalyst was changed to 47 mg, Negative electrode and secondary battery were produced, and evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)

 Polymer A, fluorine-containing polymer B, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, and a negative electrode were prepared in the same manner as in Example 1 except that the amount of palladium acetate used as a hydrogenation catalyst was changed to 58 mg, Negative electrode and secondary battery were produced, and evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Example 4)

The fluorine-containing monomer to be charged into the autoclave was changed to 70 g of tetrafluoroethylene and 105 g of vinylidene fluoride at the time of preparing the fluorine-containing polymer B, and the composition of the mixed gas supplied into the system during the polymerization was changed to tetrafluoroethylene / vinylidene fluoride Polymer A, fluorine-containing polymer B, positive electrode binder composition, positive electrode slurry composition, positive electrode, negative electrode and secondary battery were produced in the same manner as in Example 1, Evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)

Polymer A, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode and a secondary battery were produced in the same manner as in Example 1 except that polyvinylidene fluoride (solef 6020, manufactured by Solvay Co., Ltd.) was used as the fluorine- , And evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Examples 6 to 7)

Except that the ratio of the amount of the polymer A to the total amount of the polymer A and the fluorine-containing polymer B at the time of preparing the positive electrode binder composition was set to the ratio shown in Table 1, the polymer A, the fluorine-containing Polymer B, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode and a secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)

The binder composition for positive electrode was prepared in the same manner as in Example 1 except that the fluorine-containing polymer B was not used and the NMP solution of the polymer A and an appropriate amount of N-methyl-2-pyrrolidone (NMP) , A polymer composition A, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode and a secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)

Except that the binder composition was obtained by mixing the fluorine-containing polymer B with an appropriate amount of N-methyl-2-pyrrolidone (NMP) without using the NMP solution of the polymer A in preparing the binder composition for the positive electrode, , A fluorine-containing polymer B, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode and a secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3)

 Polymer A, fluorine-containing polymer B, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, and a negative electrode were prepared in the same manner as in Example 1 except that the amount of palladium acetate used as a hydrogenation catalyst was changed to 40 mg, Negative electrode and secondary battery were produced, and evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 4)

 Polymer A, fluorine-containing polymer B, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, and a negative electrode were prepared in the same manner as in Example 1 except that the amount of palladium acetate used as a hydrogenation catalyst was changed to 61 mg, Negative electrode and secondary battery were produced, and evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 5)

A fluorine-containing polymer B, a binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode and a secondary battery were prepared in the same manner as in Example 1 except that an acrylic polymer prepared as described below was used instead of the polymer A Evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

<Acrylic Polymer>

240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 20 parts of acrylonitrile as a nitrile group-containing monomer, and 80 parts of butyl acrylate as a (meth) acrylic acid ester monomer were put in an autoclave equipped with a stirrer in this order, After replacing the inside of the bottle with nitrogen, 0.25 part of ammonium persulfate was added and polymerization reaction was carried out at a reaction temperature of 70 캜 to obtain an acrylic polymer.

(Comparative Example 6)

At the time of preparation of the polymer A, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 20 parts of acrylonitrile as a monomer containing a nitrile group, and 20 parts of butyl acrylate as a (meth) acrylic acid ester monomer were added to an autoclave equipped with a stirrer. 35 parts were placed in this order, the inside of the bottle was replaced with nitrogen, 45 parts of 1,3-butadiene as a conjugated diene monomer was pressed, and 0.25 part of ammonium persulfate was added and polymerization was carried out at 40 DEG C to obtain a hydrogenated polymer Except that the polymer A, the fluorine-containing polymer B, the positive electrode binder composition, the positive electrode slurry composition, the positive electrode, the negative electrode and the secondary battery were produced in the same manner as in Example 1, . The results are shown in Table 1.

It can be seen from Table 1 that the secondary battery produced by using the binder compositions of Examples 1 to 7 has a small amount of gas generation even if charge and discharge are repeated over a high electric field.

According to the present invention, it is possible to provide a binder composition for a secondary battery positive electrode excellent in high-potential durability and a slurry composition for a secondary battery positive electrode.

According to the present invention, it is possible to provide a positive electrode for a secondary battery excellent in high-potential durability.

Furthermore, according to the present invention, it is possible to provide a secondary battery having a small amount of gas generation even if charging / discharging is repeated over a high potential.

Claims (8)

As a binder composition for a secondary battery positive electrode containing a polymer A containing a nitrile group-containing monomer unit and a conjugated diene monomer unit, a fluorine-containing polymer B and a solvent,
The polymer A has an iodine value of 20 mg / 100 mg or more and 80 mg / 100 mg or less,
Wherein the composite membrane obtained by forming the binder composition has a number of spherical crystals of 20 mu m or more in diameter within a range of 200 mu m square and 20 or less. The method according to claim 1,
Wherein the fluorine-containing polymer B comprises 50 mol% or more of vinylidene fluoride monomer units. 3. The method according to claim 1 or 2,
Wherein the polymer A contains 30% by mass or more of the nitrile group-containing monomer unit. 4. The method according to any one of claims 1 to 3,
Wherein the composite membrane has a storage elastic modulus E 'of 1 x 10 ⁸ Pa or more and 1 x 10 ⁹ Pa or less and a loss tangent (tan delta) of 0.001 or more to 0.1 or less. 5. The method according to any one of claims 1 to 4,
Wherein the ratio of the amount of the polymer A to the total amount of the polymer A and the fluorine-containing polymer B is 5 mass% or more and 50 mass% or less. A slurry composition for a secondary battery positive electrode, comprising a positive electrode active material and a binder composition for a secondary battery positive electrode according to any one of claims 1 to 5. A positive electrode for a secondary battery, comprising a positive electrode composite material layer formed by using the slurry composition for a positive electrode of a secondary battery according to claim 6. A secondary battery comprising the positive electrode for a secondary battery according to claim 7, a negative electrode, an electrolyte, and a separator.

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