KR101993811B1 - Positive electrode for secondary cell, method for manufacturing positive electrode secondary cell, and secondary cell - Google Patents

Abstract

The present invention provides a positive electrode for a secondary battery which is excellent in flexibility and binding property of a positive electrode composite material layer and can exhibit excellent low temperature output characteristics in a secondary battery. A positive electrode for a secondary battery according to the present invention comprises a current collector and a positive electrode mixture layer laminated on the current collector, wherein the positive electrode mixture layer includes a positive electrode active material and a binder, and the binder contains 95% by mass or more of vinylidene fluoride units A polymer (A) and a polymer (B) containing a nitrile group-containing monomer unit, wherein the crystallinity of the polymer (A) is 40% or less.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode for a secondary battery, a method for manufacturing the same,

The present invention relates to a positive electrode for a secondary battery, a manufacturing method thereof, and a secondary battery.

BACKGROUND ART [0002] A secondary battery such as a lithium ion secondary battery is small and light in weight, has a high energy density, and is capable of repeated charge / discharge, and is used in a wide variety of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of secondary batteries.

Here, the electrode for the secondary battery generally has a current collector and an electrode composite layer formed on the current collector. The electrode composite layer includes, for example, an electrode active material, a binder (binder), and a conductive material to be blended as required. In recent years, in order to further improve the performance of the secondary battery, improvement of the electrode composite layer has been attempted.

Specifically, it has been studied to increase the energy density of the secondary battery by increasing the density and thickness of the electrode composite layer (positive electrode composite layer) with respect to the positive electrode for the secondary battery. However, in the positive electrode composite material layer having a large density and a large thickness, it tends to be difficult to ensure the flexibility and binding properties of the positive electrode composite material layer.

Thus, for example, in Patent Document 1, as a binder capable of securing the flexibility and binding properties of the positive electrode composite material layer even when the density and thickness of the positive electrode composite material layer are increased, a nitrile group-containing monomer unit, a hydrophilic group- Methacrylate ester monomer unit and a straight chain alkylene unit having 4 or more carbon atoms, and a fluorine-containing polymer at a predetermined ratio. In Patent Document 1, a slurry containing a positive electrode active material, a conductive material, and a binder is applied as a positive electrode using the above-mentioned binder, and the coated slurry is dried under conditions of a temperature of 60 ° C and a temperature of 120 ° C Dried, and further subjected to a heat treatment at a temperature of 150 캜 to form a positive electrode composite material layer on the current collector.

Patent Document 1: International Publication No. 2013/129658

Here, according to the positive electrode using the binder described in Patent Document 1, even when the density and thickness of the positive electrode composite material layer are increased, flexibility and binding property of the positive electrode composite material layer can be ensured and the cycle characteristics etc. of the secondary battery can be improved have. However, there is still room for improvement in that the positive electrode using the binder described in Patent Document 1 further improves the flexibility and tackiness of the positive electrode composite material layer. Further, the secondary battery using the positive electrode described in Patent Document 1 has room for improvement in improving the output characteristics, particularly, the output characteristics under low temperature (hereinafter sometimes referred to as "low temperature output characteristics").

It is therefore an object of the present invention to provide a positive electrode for a secondary battery which is excellent in flexibility and binding property of a positive electrode composite material layer and can exhibit excellent output characteristics (in particular, low temperature output characteristics) do.

Another object of the present invention is to provide a secondary battery having excellent output characteristics (particularly low-temperature output characteristics).

Means for Solving the Problems The present inventors have conducted intensive studies for the purpose of solving the above problems. The inventors of the present invention have found that, in a positive electrode comprising a positive electrode composite material layer containing a polymer (A) containing a vinylidene fluoride unit and a polymer (B) containing a nitrile group-containing monomer unit as a binder, And the degree of crystallinity of the polymer (A) in the positive electrode composite material layer is set to a predetermined value or less to improve flexibility and tackiness of the positive electrode composite material layer and to improve the flexibility of the positive electrode The improvement of the characteristics can be achieved, and the present invention has been accomplished.

That is, the object of the present invention is to solve the above problems advantageously. The positive electrode for a secondary battery of the present invention is a positive electrode for a secondary battery comprising a current collector and a positive electrode composite material layer laminated on the current collector, (A) containing a vinylidene fluoride unit in an amount of 95 mass% or more and a polymer (B) containing a nitrile group-containing monomer unit, wherein the polymer A) has a crystallinity of 40% or less. When the polymer (A) containing 95% by mass or more of vinylidene fluoride units and having a degree of crystallinity of 40% or less and the polymer (B) containing a nitrile group-containing monomer unit are contained as the binder, The flexibility and bondability of the secondary battery can be improved and the low temperature output characteristics of the secondary battery can be improved.

In the present invention, the content ratio of the repeating units in the polymer is not particularly limited and can be measured by a known method such as pyrolysis gas chromatography or nuclear magnetic resonance (NMR).

In the present invention, the "degree of crystallinity of the polymer (A)" means the degree of crystallinity of the polymer (A) relative to the total amount of the? -Imine portion, the? -Imine portion and the amorphous portion in the polymer (A) (= ((Alpha positive part + beta positive part) / (alpha positive part + beta positive part + amorphous part)} 100%). In the present invention, the " degree of crystallization of the polymer (A) " is defined as the degree of crystallization of the polymer (A) by using the area of the peak detected at the positions of 80 ppm, 88 ppm and 95 ppm in the 19 F- I). ≪ / RTI > Incidentally, when the resolution of the 19 F-NMR spectrum is not sufficient, each peak area can be obtained by separating the peaks by peak fitting.

The crystallinity of the polymer (A) = ({(a 2) + (c-a)} / {(a 2) + (c-a) + b} 100%

Wherein a represents the area of the peak at the 80 ppm position, b represents the peak area at the 88 ppm position, and c represents the peak area at the 95 ppm position.

Further, in the 19 F-NMR spectrum, the peak detected at a position of 80 ppm is derived from the alpha positive portion, the peak detected at a position of 88 ppm is derived from an amorphous portion, And the beta positive part. In the formula (I), the area a of the peak at the 80 ppm position of the 19 F-NMR spectrum, the area b of the peak at the 88 ppm position, the area c of the peak at the 95 ppm position, (II) below exists between the amount of the positive part and the amount of the amorphous part.

(amount of amorphous part) / (amount of amorphous part): (amount of amodified part / 2) + amount of amodified part} (II)

Here, in the positive electrode for a secondary battery of the present invention, it is preferable that the polymer (B) further comprises a (meth) acrylic acid ester monomer unit. When the polymer (B) contains a (meth) acrylic acid ester monomer unit, the binding property of the polymer (B) can be increased and the binding property of the positive electrode mixture layer can be further improved. This is because the stability of the polymer (B) with respect to the electrolytic solution can be improved and the cycle characteristics of the secondary battery can be improved.

In the present invention, "(meth) acryl" means acryl and / or methacryl.

In the positive electrode for a secondary battery of the present invention, it is preferable that the polymer (B) further comprises an alkylene structural unit having 4 or more carbon atoms. When the polymer (B) contains an alkylene structural unit having 4 or more carbon atoms, the cycle characteristics and output characteristics of the secondary battery can be improved.

In the present invention, the term " including an alkylene structural unit having 4 or more carbon atoms " means repeating an alkylene structure represented by a general formula: -C _n H _2n - (wherein n is an integer of 4 or more) Unit is included.

In the positive electrode for a secondary battery of the present invention, the content ratio of the nitrile group-containing monomer units in the polymer (B) is preferably 2% by mass or more and 50% by mass or less. When the content of the nitrile group-containing monomer unit is from 2 to 50 mass%, the stability of the polymer (B) to the electrolyte solution can be improved, and the cycle characteristics and output characteristics of the secondary battery can be improved.

In the positive electrode for a secondary battery of the present invention, the content of the (meth) acrylic acid ester monomer unit in the polymer (B) is preferably 5 mass% or more and 50 mass% or less. (B) and the stability of the polymer (B), and the flexibility of the electrode composite layer using the polymer (B) and the cyclic characteristics of the secondary battery (B) can be improved by setting the content of the (meth) acrylic acid ester monomer unit to 5 to 50 mass% And it is possible to improve the output characteristics of the secondary battery.

In the positive electrode for a secondary battery of the present invention, the content of the alkylene structural unit having 4 or more carbon atoms in the polymer (B) is preferably 20 mass% or more and 70 mass% or less. When the proportion of the alkylene structural unit having 4 or more carbon atoms is 20 to 70 mass%, the content of the nitrile group-containing monomer units in the polymer (B) is sufficiently ensured and the binding property of the positive electrode material layer using the polymer (B) And the cycle characteristics and the output characteristics of the secondary battery can be sufficiently improved.

In the positive electrode for a secondary battery of the present invention, the iodine value of the polymer (B) is preferably 3 mg / 100 mg or more and 60 mg / 100 mg or less. This is because the cycle characteristics of the secondary battery can be sufficiently improved by setting the iodine value of the polymer (B) to 3 mg / 100 mg to 60 mg / 100 mg.

The secondary battery positive electrode of the present invention preferably has a ratio of the amount of the polymer (B) to the total amount of the polymer (A) and the polymer (B) is 5 mass% or more and 35 mass% or less. When the total amount of the polymer (A) and the polymer (B) is 100 mass%, the proportion of the polymer (B) is preferably 5 to 35 mass%, the flexibility and binding properties of the positive electrode mixture layer, The output characteristics and the cycle characteristics can be sufficiently improved.

The present invention also provides a positive electrode active material for a secondary battery, comprising a polymer (A) containing 95 mass% or more of vinylidene fluoride units, a polymer A step of forming a coating film containing a polymer (B) containing a fluorine-containing monomer unit on a current collector; and a step of cooling the coating film after heating the film at a temperature equal to or higher than the melting point of the polymer (A) Of the polymer (A) having a molecular weight of not more than 40% and a positive electrode composite material layer containing the polymer (B) on the current collector. As described above, the film formed on the current collector is heated at a temperature equal to or higher than the melting point of the polymer (A) and then cooled to form the positive electrode composite material layer by adjusting the degree of crystallinity of the polymer (A) contained in the film to 40% , A positive electrode for a secondary battery having a positive electrode composite material layer excellent in flexibility and binding property and capable of improving low temperature output characteristics of the secondary battery can be produced.

In the present invention, the " melting point of the polymer " can be obtained according to JIS K7121.

In the method for producing a positive electrode for a secondary battery according to the present invention, it is preferable that the temperature for heating the coating is 165 ° C or higher and 250 ° C or lower. This is because the crystallinity of the polymer (A) can be relatively easily controlled to an appropriate magnitude by heating the coating at 165 to 250 ° C.

In the method for producing a positive electrode for a secondary battery according to the present invention, it is preferable that the rate of cooling the coating is 100 ° C / hour or more and 500 ° C / hour or less. The reason for this is that the crystallization degree of the polymer (A) can be controlled to an appropriate degree while increasing the productivity of the positive electrode by setting the cooling rate of the coating film at 100 to 500 캜 / hour.

It is another object of the present invention to solve the above problems in an advantageous manner. The secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the positive electrode is any one of the above- . As described above, when the above-described positive electrode for a secondary battery is used as the positive electrode, the low-temperature output characteristics of the secondary battery can be improved.

According to the present invention, it is possible to provide a positive electrode for a secondary battery which is excellent in flexibility and binding property of a positive electrode composite material layer and can exhibit excellent output characteristics (particularly, low temperature output characteristics) for a secondary battery.

Further, according to the present invention, it is possible to provide a secondary battery having excellent output characteristics (particularly low-temperature output characteristics).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged view showing the essential part of a 19 F-NMR spectrum of the polymer (A). FIG.

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

Here, the positive electrode for a secondary battery of the present invention is used as a positive electrode of a secondary battery such as a lithium ion secondary battery. The positive electrode for a secondary battery of the present invention can be manufactured using the method for manufacturing a positive electrode for a secondary battery of the present invention. Further, the secondary battery of the present invention uses the positive electrode for a secondary battery of the present invention as a positive electrode.

Hereinafter, a positive electrode for a secondary battery according to the present invention, a manufacturing method thereof, and a positive electrode for a lithium ion secondary battery as an example of a secondary battery, a manufacturing method thereof, and a lithium ion secondary battery will be described. Method, and secondary battery are not limited to these examples.

(Positive electrode for lithium ion secondary battery)

A positive electrode for a lithium ion secondary battery according to the present invention comprises a current collector and a positive electrode composite material layer laminated on the current collector. The positive electrode for a lithium ion secondary battery is characterized in that the positive electrode mixture layer contains a positive electrode active material and a binder, the binder contains 95 mass% or more of vinylidene fluoride units and has a crystallinity of 40% or less and a nitrile group And a polymer (B) containing a monomer unit.

<Home>

Here, as the collector of the positive electrode for a lithium ion secondary battery, a material having electric conductivity and electrochemically durable is used. Specifically, the current collector may be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold or platinum. Among them, it is preferable to use a current collector made of aluminum or an aluminum alloy as the current collector for the positive electrode. In this case, aluminum and aluminum alloy may be used in combination, or aluminum alloys of different kinds may be used in combination. Aluminum and aluminum alloys have excellent heat resistance and are electrochemically stable, so they are excellent current collector materials.

The shape of the current collector is not particularly limited, but is preferably a sheet-like shape having a thickness of about 0.001 to 0.5 mm.

An intermediate layer (for example, a conductive adhesive layer) may be optionally formed on the surface of the current collector to increase the bonding strength and conductivity between the positive electrode current-collecting layer and the current collector.

&Lt; Positive electrode composite layer &

The positive electrode composite material layer contains a positive electrode active material and a binder, and optionally contains a conductive material and other components that are optionally compounded. The positive electrode composite material layer of the positive electrode for a lithium ion secondary battery according to the present invention is excellent in flexibility and binding property because the above-mentioned polymer (A) and polymer (B) are used in combination as a binder. Further, since the positive electrode for a lithium ion secondary battery according to the present invention uses the above-mentioned polymer (A) as a binder for the positive electrode composite material layer, the low temperature output characteristic of the lithium ion secondary battery can be improved.

Further, the positive electrode composite material layer may be laminated only on one side of the current collector, or may be laminated on both sides of the current collector.

[Positive electrode active material]

The positive electrode active material is not particularly limited and a known positive electrode active material can be used.

Specifically, the positive electrode active material is not particularly limited, and lithium-containing cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ), Co- 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 ), an olivine-type lithium manganese phosphate LiMnPO ₄ , Li _{1 + x} Mn _2-x A lithium-excess spinel compound represented by 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 them, lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium-containing complex oxide of Co-Ni-Mn, Ni-Co -Al lithium complex oxide, 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 preferably used.

Further, the mixing amount and the particle diameter of the positive electrode active material are not particularly limited and may be the same as those of the conventional positive electrode active material.

[Adhesive]

The binder is a component that can be supported in the positive electrode for a lithium ion secondary battery so that components contained in the positive electrode mixture layer do not separate from the positive electrode mixture layer. Generally, the binding material in the positive electrode composite material layer binds the positive electrode active material, the conductive material, or the conductive material between the positive electrode active material, the conductive material, or the conductive material, while the electrolyte is absorbed and swollen when immersed in the electrolyte solution to prevent the positive electrode active material and the like from falling off the current collector do.

In the present invention, from the viewpoints of improving the flexibility and binding properties of the positive electrode composite material layer and improving the low temperature output characteristics of the secondary battery, it is preferable that the binder contains 95% by mass or more of vinylidene fluoride units, It is necessary to use at least two polymers of a polymer (A) having a crystallinity of not more than 40% in the layer and a polymer (B) containing a nitrile group-containing monomer unit.

The reason why the flexibility and binding properties of the positive electrode composite material layer and the low temperature output characteristics of the secondary battery are improved by using the polymer (A) and the polymer (B) as a binder is not clear, but is presumed to be as follows.

That is, the polymer (A) has good flexibility and is excellent in binding property and the polymer (B) is excellent in flexibility and binding property. Therefore, by using the polymer (A) and the polymer (B) It is possible to enhance the flexibility and tackiness of the substrate. The polymer (A) has a crystallinity of 40% or less in the positive electrode composite material layer and has a large amount of amorphous portions. The amorphous portion of the polymer (A) is likely to swell in the electrolyte solution, and when swelled, exhibits good ion conductivity even at a low temperature. Therefore, by using the polymer (A), the low-temperature output characteristics of the secondary battery can be improved.

[[Polymer (A)]]

The polymer (A) is a vinylidene fluoride polymer containing a vinylidene fluoride unit which is a repeating unit derived from vinylidene fluoride. Specifically, the polymer (A) is a copolymer of vinylidene fluoride or vinylidene fluoride, which is a homopolymer of vinylidene fluoride, and a monomer copolymerizable with vinylidene fluoride.

Further, the monomer copolymerizable with vinylidene fluoride is not particularly limited, and fluorine-containing monomers such as tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride, vinyl fluoride, and perfluoroalkyl vinyl ether, ethylene, (Meth) acrylate, N (meth) acrylate, N-methylstyrene, vinyltoluene, chlorostyrene, methyl (meth) acrylate, (Meth) acrylamide, N-butoxymethyl (meth) acrylamide, (meth) acrylic acid, itaconic acid, fumaric acid, crotonic acid, maleic acid, allyl glycidyl ether, glycidyl (Meth) acrylic acid dimethylaminoethyl, diethylaminoethyl (meth) acrylate, styrenesulfonic acid, vinylsulfonic acid, (meth) allylsulfonic acid, 3-allyloxy- - chloro-2-phosphoric acid pro It can be cited 3-allyloxy-2-hydroxy-monomers containing no fluorine such as propane phosphoric acid. These may be used alone or in combination of two or more. Among them, from the viewpoint of polymerization easiness, a monomer copolymerizable with vinylidene fluoride is preferably a fluorine-containing monomer, and more preferably hexafluoropropylene.

The polymer (A) is prepared, for example, by polymerizing a monomer composition containing the above-described monomers in an aqueous solvent. The content of each monomer in the monomer composition can be determined in accordance with the content of the desired monomer units (repeating units) in the polymer (A).

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

- content of vinylidene fluoride units -

The content of the vinylidene fluoride unit in the polymer (A) is preferably 97% by mass or more, more preferably 100% by mass or less , A homopolymer of vinylidene fluoride). When the content of the vinylidene fluoride unit is less than 95% by mass, the flexibility and the binding property of the positive electrode composite material layer can not be sufficiently improved even when used in combination with the polymer (B). On the other hand, if the content of the vinylidene fluoride unit is 95 mass% or more, the flexibility and the binding property of the positive electrode composite material layer can be sufficiently improved, and the degree of crystallinity of the polymer (A) can be appropriately made large.

- Crystallinity -

The polymer (A), which is a vinylidene fluoride polymer, usually contains an alpha positive portion, a beta positive portion and an amorphous portion. The polymer (A) in the positive electrode mixture layer needs to have a degree of crystallinity of 40% or less, which is the ratio of the sum of the? -Imine portion and? -Imine portion to the total amount of the? -Imine portion,? -Imine portion and amorphous portion, A is preferably 15% or more, more preferably 20% or more, more preferably 25% or more, still more preferably 30% or more, still more preferably 38% or less and still more preferably 35% or less. When the degree of crystallinity of the polymer (A) exceeds 40%, the ratio of the crystalline portion increases (that is, the ratio of the amorphous portion decreases) and it becomes difficult to exhibit good ionic conductivity in the electrolytic solution. It is not possible to sufficiently improve the low-temperature output characteristics. When the degree of crystallinity of the polymer (A) exceeds 40%, the flexibility of the polymer (A) is lowered by the increase of the crystalline portion, and it becomes impossible to sufficiently increase the flexibility of the positive electrode composite material layer. From the viewpoint of suppressing the strength of the polymer (A) from lowering and lowering the binding force of the polymer (A), securing the binding property of the positive electrode composite material layer and securing the cycle characteristics of the secondary battery, the crystallinity of the polymer (A) % Or more.

The degree of crystallinity of the polymer (A) can be determined by, for example, changing the composition of the polymer (A), changing the heat treatment (heating and cooling) conditions of the coating film formed on the current collector described later, The type and the amount thereof, and the like. Concretely, when the content ratio of the vinylidene fluoride unit in the polymer (A) is reduced, the degree of crystallization of the polymer (A) in the positive electrode composite material layer can be lowered. When the film formed on the current collector is heated at a temperature higher than the melting point of the polymer (A), the crystallinity of the polymer (A) in the positive electrode mixture layer can be lowered. In addition, if the coating film formed on the current collector is heated at a temperature higher than the melting point of the polymer (A) and then cooled at a higher cooling rate, the crystallinity of the polymer (A) in the positive electrode composite material layer can be lowered. When the polymer (B) having a high compatibility with the polymer (A) is used or the blending amount of the polymer (B) is increased, crystallization of the polymer (A) And the degree of crystallization of the polymer (A) in the positive electrode composite material layer can be lowered.

[[Polymer (B)]]

The polymer (B) is a polymer containing a monomer unit containing a nitrile group. The polymer (B) may optionally contain a (meth) acrylic acid ester monomer unit, an alkylene structural unit having 4 or more carbon atoms, a hydrophilic group-containing monomer unit, and other monomer units. The polymer (B) preferably contains a (meth) acrylic acid ester monomer unit and / or an alkylene structural unit having 4 or more carbon atoms.

- Nitrile group-containing monomer unit -

The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer. The polymer (B) is required to contain a nitrile group-containing monomer unit from the viewpoint of enhancing the binding property of the positive electrode mixture layer using the polymer (B) as a binder.

As the nitrile group-containing monomer capable of forming a nitrile group-containing monomer unit, an?,? - ethylenically unsaturated nitrile monomer can be exemplified. 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; ? -halogenoacrylonitrile such as? -chloroacrylonitrile and? -bromoacrylonitrile; ? -Alkyl acrylonitrile such as methacrylonitrile and? -Ethyl acrylonitrile; And the like. Among these, acrylonitrile and methacrylonitrile are preferable as the nitrile group-containing monomer from the viewpoint of enhancing the binding force of the polymer (B) and improving the binding property of the positive electrode composite layer, 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 (B) is preferably 2% by mass or more when the total amount of the repeating units (sum of the monomer units and the structural units) in the polymer (B) is 100% By mass, more preferably not less than 5% by mass, more preferably not less than 10% by mass, further preferably not less than 15% by mass, more preferably not more than 50% by mass, more preferably not more than 30% Is particularly preferable. When the content of the nitrile group-containing monomer units in the polymer (B) is 2% by mass or more, the cycle characteristics and output characteristics of the secondary battery having the positive electrode using the polymer (B) can be improved. When the proportion of the nitrile group-containing monomer units in the polymer (B) is 50 mass% or less, the stability of the polymer (B) with respect to the electrolyte solution can be enhanced, and the secondary battery comprising the positive electrode Cycle characteristics can be improved.

- (meth) acrylic acid ester monomer unit -

The (meth) acrylic acid ester monomer unit is a repeating unit derived from a (meth) acrylic acid ester monomer. From the viewpoint of further improving the binding property of the positive electrode composite material layer by increasing the binding force of the polymer (B) and improving the stability of the polymer (B) with respect to the electrolyte solution, the polymer (B) Meth) acrylic acid ester monomer unit.

Examples of the (meth) acrylic acid ester monomer capable of forming the (meth) acrylic acid ester monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, Acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate , alkyl acrylate esters such as n-tetradecyl acrylate and stearyl acrylate; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, Hexyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate Methacrylic acid alkyl esters such as acrylate, stearyl methacrylate and glycidyl methacrylate; And the like. Among these, from the viewpoint of enhancing the binding force of the polymer (B) and improving the binding property of the positive electrode composite material layer, the (meth) acrylic acid ester monomer is preferably an acrylic acid alkyl ester having an alkyl group having 4 to 10 carbon atoms and bonded to a non- And n-butyl acrylate and 2-ethylhexyl acrylate are more preferable.

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

The content of the (meth) acrylic acid ester monomer unit in the polymer (B) is preferably 5% by mass or more, more preferably 10% by mass or more, based on 100% by mass of all the repeating units in the polymer (B) By mass, more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less. This is because the output characteristics of the secondary battery having the positive electrode using the polymer (B) can be improved by setting the content of the (meth) acrylic acid ester monomer unit in the polymer (B) to 50 mass% or less. The content of the (meth) acrylic acid ester monomer unit in the polymer (B) is 5 mass% or more, whereby the flexibility of the polymer (B) and the stability against the electrolyte can be increased. Flexibility and cycle characteristics of the secondary battery can be improved.

- an alkylene structural unit having 4 or more carbon atoms -

The alkylene structural unit having 4 or more carbon atoms is a repeating unit composed of an alkylene structure represented by the general formula: -C _n H _2n - (n is an integer of 4 or more). The polymer (B) preferably contains an alkylene structural unit having 4 or more carbon atoms from the viewpoint of further improving the cycle characteristics and output characteristics of the secondary battery.

Here, the alkylene structural unit having 4 or more carbon atoms may be linear or branched. From the viewpoint of improving the output characteristics of the secondary battery, the alkylene structural unit having 4 or more carbon atoms is preferably a straight chain, that is, a straight chain alkylene structural unit.

The method of introducing an alkylene structural unit having 4 or more carbon atoms into the polymer (B) is not particularly limited, and examples thereof include the following methods (1) and (2)

(1) a method of preparing a polymer from a monomer composition containing a conjugated diene monomer and adding hydrogen to the polymer to convert the conjugated diene monomer unit into an alkylene structural unit,

(2) a method of preparing a polymer from a monomer composition comprising a 1-olefin monomer having 4 or more carbon atoms

. Among them, the method (1) is preferable because the production of the polymer (B) is easy.

Examples of the conjugated diene monomer include conjugated diene compounds having 4 or more carbon atoms such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene. Of these, 1,3-butadiene is preferred. That is, the alkylene structural unit having 4 or more carbon atoms is preferably a structural unit (conjugated diene hydride unit) obtained by hydrogenating the conjugated diene monomer unit, and a structural unit (1,3-butadiene Hydride unit) is more preferable. Further, the selective hydrogenation of the conjugated diene monomer unit can be carried out by a known method such as an oil layer hydrogenation method or an aqueous layer hydrogenation method.

Examples of the 1-olefin monomer having 4 or more carbon atoms include 1-butene, 1-hexene, and the like.

These conjugated diene monomers and 1-olefin monomers having 4 or more carbon atoms may be used alone or in combination of two or more thereof

The content of the alkylene structural unit having 4 or more carbon atoms in the polymer (B) is preferably 20% by mass or more, more preferably 25% by mass or more, based on 100% by mass of all the repeating units in the polymer (B) , More preferably 30 mass% or more, and most preferably 70 mass% or less, and more preferably 60 mass% or less. When the content of the alkylene structural unit having 4 or more carbon atoms in the polymer (B) is within the above range, the cycle characteristics and output characteristics of the secondary battery can be sufficiently improved. The content of the nitrile group-containing monomer units in the polymer (B) is sufficiently ensured by setting the proportion of the alkylene structural units having 4 or more carbon atoms in the polymer (B) to 70 mass% or less, The binding property of the layer can be sufficiently enhanced.

- Hydrophilic group-containing monomer unit -

The hydrophilic group-containing monomer unit is a repeating unit derived from a hydrophilic group-containing monomer. The polymer (B) preferably contains a hydrophilic group-containing monomer unit from the viewpoint of enhancing the binding force of the polymer (B) to improve the binding property of the positive electrode mixture layer.

Examples of the hydrophilic group-containing monomer capable of forming a hydrophilic group-containing monomer unit 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.

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

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-? -Epoxy methacrylic acid and? -Diaminoacrylic 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, maleic acid methylallyl, maleic acid diphenyl, maleic acid nonyl, maleic decyl, Maleic acid esters such as dodecyl, octadecyl maleate, and 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 compound having a carboxylic acid group, an acid anhydride which generates a carboxyl group by hydrolysis can also be used.

And other monoethyl esters such as monoethyl maleate, monoethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, itaconic acid And monoesters and diesters of?,? - ethylenically unsaturated polycarboxylic acids such as monoethyl, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate.

Examples of the monomer having a sulfonic acid group include vinylsulfonic acid, methylvinylsulfonic acid, (meth) allylsulfonic acid, styrenesulfonic acid, ethyl (meth) acrylate-2-sulfonate, 3-allyloxy-2-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 2- (meth) acryloyloxyethyl phosphate, methyl 2- (meth) acryloyloxyethyl phosphate, ethyl- (meth) acryloyloxyethyl phosphate and the like.

In the present invention, &quot; (meth) acryloyl &quot; 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; 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, Alkanol esters of ethylenically unsaturated carboxylic acids such as 4-hydroxybutyl and di-2-hydroxypropyl itaconate; ^{_{Formula: CH 2 = CR 1 -COO- (}} C q H 2q O) p -H [ In the formula, p is an integer of 2 ~ 9, q is an integer of 2 ~ 4, R ¹ represents a hydrogen or a methyl group. Esters of polyalkylene glycol and (meth) acrylic acid represented by the following formula (Meth) acrylate of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2 '- (meth) acryloyloxyphthalate and 2-hydroxyethyl- Acrylic acid esters; Vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (Meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl- Mono (meth) allyl ethers of alkylene glycols such as allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether and (meth) allyl-6-hydroxyhexyl ether; Polyoxyalkylene glycol (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; (Poly) alkylene glycols such as glycerin mono (meth) allyl ether, (meth) allyl-2-chloro-3-hydroxypropyl ether and (meth) allyl- Mono (meth) allyl ether of hydroxy substituent; Mono (meth) allyl ethers and halogen substituents of polyhydric phenols such as eugenol and isoengener; (Meth) allyl-2-hydroxyethylthioether, and (meth) allyl-2-hydroxypropylthioether; And the like.

The content of the hydrophilic group-containing monomer units in the polymer (B) is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, more preferably 1.0% by mass or more , More preferably not less than 30 mass%, more preferably not more than 25 mass%, even more preferably not more than 20 mass%, particularly preferably not more than 6 mass%. This is because when the content of the hydrophilic group-containing monomer units in the polymer (B) is 0.05 mass% or more, the binding property of the polymer (B) is increased and the binding property of the positive electrode mixture layer can be further increased. This is because the content of the hydrophilic group-containing monomer units in the polymer (B) is 30 mass% or less, whereby the flexibility of the polymer (B) is prevented from being lowered and the flexibility of the positive electrode mixture layer can be suppressed from lowering.

- Other monomer units -

The polymer (B) may contain other monomer units other than the above-mentioned monomer units within the range not impairing the effect of the present invention. Other monomers capable of forming other monomer units are not particularly limited, and known monomers copolymerizable with the above-mentioned monomers can be used.

The content of other monomer units in the polymer (B) is preferably 30 mass% or less, more preferably 20 mass% or less, and further preferably 10 mass% or less.

- Method of preparing polymer (B)

The method of preparing the polymer (B) is not particularly limited, but it can be prepared, for example, by polymerizing a monomer composition containing the above-mentioned monomers to obtain a polymer and optionally hydrogenating the obtained polymer.

Here, 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 and structural unit (repeating unit) in the polymer (B).

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

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

The iodine value of the hydrogenated polymer (B) is preferably 60 mg / 100 mg or less, more preferably 30 mg / 100 mg or less, and particularly preferably 20 mg / 100 mg or less. The lower limit is preferably 3 mg / 100 mg or more, more preferably 8 mg / 100 mg or more. By setting the iodine value to such a range, the cycle characteristics of the secondary battery can be sufficiently improved. Further, the iodine value can be measured by the method described in the examples of this specification.

[[Compounding ratio of polymer (A) and polymer (B)]]

The blending ratio of the polymer (A) and the polymer (B) in the binder is such that when the total amount of the polymer (A) and the polymer (B) is 100 mass%, the proportion of the polymer (B) More preferably 15 mass% or more, further preferably 50 mass% or less, more preferably 35 mass% or less, still more preferably 30 mass% or less, and most preferably 25 mass% By mass or less. When the ratio of the polymer (B) in the polymer (A) and the polymer (B) is within the above range, the degree of crystallization of the polymer (A) in the positive electrode mixture layer can be made an appropriate level, This is because the binding property and the low-temperature output characteristics and the cycle characteristics of the secondary battery can be sufficiently improved.

[[Blending amount of binder]]

In the positive electrode composite material layer, the amount of the binder material containing the polymer (A) and the polymer (B) is preferably 0.1 part by mass or more, more preferably 0.5 parts by mass or more per 100 parts by mass of the positive electrode active material, Is not more than 10 parts by mass, more preferably not more than 5 parts by mass. This is because the binding property and flexibility of the positive electrode composite material layer can be sufficiently increased by making the amount of the binder to be 0.1 part by mass or more per 100 parts by mass of the positive electrode active material. This is because when the amount of the binder is less than or equal to 10 parts by mass per 100 parts by mass of the positive electrode active material, the increase in internal resistance can be suppressed when the positive electrode containing the binder is applied to the lithium ion secondary battery.

When the binder contains other polymers than the polymer (A) and the polymer (B), the proportion of other polymers in the binder is preferably 20% by mass or less, more preferably 5% by mass or less, It is more preferable that the binder does not contain any other polymer.

[Conductive material]

The conductive material is for securing electrical contact between the positive electrode active materials in the positive electrode composite material layer. The conductive material is not particularly limited, and a known conductive material can be used. Specifically, examples of the conductive material include acetylene black, Ketchen Black (registered trademark), furnace black, graphite, carbon fiber, carbon flake, carbon microfine fiber (for example, carbon nanotube or vapor phase growth carbon fiber) ; Fibers of various metals, foils and the like can be used. Of these, acetylene black and Ketchen black are preferable as the conductive material from the viewpoint of sufficiently improving the output characteristics of the lithium ion secondary battery.

The amount of the conductive material in the positive electrode composite material layer is preferably not less than 0.5 mass parts, more preferably not less than 1 mass parts, preferably not more than 3 mass parts, and more preferably not more than 2.5 mass parts, per 100 mass parts of the positive electrode active material. If the amount of the conductive material to be blended is too small, it is not possible to ensure sufficient electrical contact between the positive electrode active materials and the output characteristics of the secondary battery can not be sufficiently improved. On the other hand, if the blend amount of the conductive material is too large, the density of the positive electrode composite layer is lowered, and the secondary battery can not be sufficiently high capacity.

[Other ingredients]

The positive electrode for a lithium ion secondary battery may contain components such as a viscosity adjusting agent, a reinforcing agent, a leveling agent, and an electrolyte additive in addition to the above components. These are not particularly limited as long as they do not affect the cell reaction, and well-known ones such as those described in International Publication No. 2012/115096 can be used. These components may be used singly or in combination of two or more in an arbitrary ratio.

(Manufacturing Method of Positive Electrode for Lithium Ion Secondary Battery)

The method for manufacturing a positive electrode for a lithium ion secondary battery according to the present invention can be used for manufacturing the positive electrode for a lithium ion secondary battery described above. The method for producing a positive electrode for a lithium ion secondary battery according to the present invention comprises a positive electrode active material, a polymer (A) containing 95% by mass or more of vinylidene fluoride units and a polymer (B) containing a nitrile group- (Film forming step) for forming a film on the current collector; and a step of forming a film on the current collector by heating the film at a temperature equal to or higher than the melting point of the polymer (A) and then cooling the film to form a positive electrode active material and a polymer having a crystallinity of 40% A) and a polymer (B) on a current collector (a heat treatment step). That is, in the method for producing a positive electrode for a lithium ion secondary battery according to the present invention, a film to be a precursor of a positive electrode composite material layer is formed on a current collector in a film formation step, and then the film is heat treated in a heat treatment step, (A) having a crystallinity of not more than 40% is made into a positive electrode composite material layer, thereby producing a positive electrode for a lithium ion secondary battery comprising a current collector and a positive electrode composite material layer laminated on the current collector.

<Coating Formation Step>

In the film forming step, a film containing a component to be contained in the positive electrode composite material layer is formed on the current collector. Concretely, in the film-forming step, at least a positive electrode active material, a polymer (A) containing 95% by mass or more of vinylidene fluoride units and a polymer (B) containing a nitrile group-containing monomer unit, , And other components to be blended as required are formed on the current collector.

The kind and amount of components contained in the film are the same as those contained in the positive electrode composite material layer of the positive electrode for a lithium ion secondary battery described above, except that the crystallinity of the polymer (A) is not limited to 40% or less.

Here, the formation of the film on the current collector can be carried out using a known film-forming method using a slurry composition obtained by dispersing or dissolving the components contained in the film in a solvent such as water or an organic solvent. Specifically, the coating film is not particularly limited, and a method of (i) applying a slurry composition onto a current collector and drying the slurry composition applied on the current collector to form a film, or (ii) spray-drying the slurry composition A method in which a composite particle is prepared, a prepared composite particle is supplied onto a current collector, and the mixture is pressure-formed to form a coating film.

Here, in the above methods (i) and (ii), drying of the slurry composition is usually carried out at a temperature lower than the melting point of the polymer (A), for example, at a temperature of 40 to 140 ° C. In general, when the slurry composition is dried, crystallization of the polymer (A) proceeds by heating at a temperature lower than the melting point, so that the degree of crystallization of the polymer (A) increases. Therefore, the crystallinity of the polymer (A) in the coating film formed by forming the slurry composition usually becomes more than 40%.

&Lt; Heat treatment step &

In the heat treatment step, the film formed in the film forming step is first heated at a temperature equal to or higher than the melting point of the polymer (A). Subsequently, the heated film was cooled to obtain a polymer (A) having a crystallinity of 40% or less and a positive electrode active material, a polymer containing 95 mass% or more of vinylidene fluoride units and having a crystallinity of 40% or less A) and a polymer (B) containing a nitrile group-containing monomer unit are formed.

In the heat treatment step, the heated and cooled film may be optionally subjected to a pressure treatment using a mold press or a roll press to form a positive electrode composite material layer. By the pressure treatment, the adhesion between the positive electrode composite material layer and the current collector can be improved.

[Heating of Coating]

Here, in the heat treatment step, the film is heated at a temperature not lower than the melting point of the polymer (A) when the film is heated at a temperature lower than the melting point of the polymer (A), the crystallization of the polymer (A) A) becomes high, and it becomes difficult to make the degree of crystallinity of the polymer (A) 40% or less.

The heating of the coating film is not particularly limited, and can be carried out using a known drying furnace or a heating furnace. Concretely, the heating of the film can be carried out, for example, by heating a roll of the laminate formed by forming a film on the current collector in a vacuum dryer. In the case where the coating is formed by the method (i) in the coating step, the formation of the coating (drying of the slurry composition) and heating may be carried out simultaneously or continuously.

The temperature at which the coating film is heated is not lower than the melting point of the polymer (A) and can be any temperature as long as the component in the coating film is less than the thermal decomposition temperature. However, it is preferably 165 ° C or higher, more preferably 180 ° C or higher, Deg.] C or lower, more preferably 200 deg. C or lower. When the temperature for heating the coating film is set to 165 ° C or more and 250 ° C or less, it is easy to control the degree of crystallization of the polymer (A) to an appropriate degree.

The time for heating the coating film is not particularly limited, and can be, for example, from 1 hour to 24 hours. When the time for heating the coating film is set to 1 hour to 24 hours, it is easy to control the degree of crystallization of the polymer (A) to an appropriate degree.

[Coating of Coating]

Cooling of the heated film is not particularly limited, and can be carried out using a known method such as natural heat radiation or air cooling.

Here, when the film heated at a temperature higher than the melting point of the polymer (A) is rapidly cooled, the degree of crystallization of the polymer (A) is lowered (i.e., the amorphous portion of the polymer (A) is increased). On the other hand, when the coating film heated at a temperature higher than the melting point of the polymer (A) is slowly cooled, the degree of crystallization of the polymer (A) becomes higher (that is, the crystalline portion of the polymer (A) increases) as compared with the case where it is rapidly cooled. Also, the higher the temperature at which the film is heated, the more easily the crystallinity of the polymer (A) is likely to be lowered (that is, the amorphous portion of the polymer (A) is likely to increase). Therefore, in the heat treatment step, the temperature for heating the film and the rate for cooling the film are adjusted so that the degree of crystallinity of the polymer (A) is 40% or less to form the positive electrode composite material layer.

The rate at which the film is cooled is not particularly limited, and may be, for example, 100 占 폚 / hour or more and 500 占 폚 / hour or less. When the cooling rate of the coating film is 100 ° C / hour or more and 500 ° C / hour or less, it is easy to control the degree of crystallization of the polymer (A) to an appropriate degree while increasing the productivity of the positive electrode.

The polymer (A) present in the positive electrode composite material layer obtained by heating and cooling the coating film as described above is usually a vinylidene fluoride polymer composed of an alpha positive portion, a beta positive portion and an amorphous portion.

(Lithium ion secondary battery)

A lithium ion secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, and uses the positive electrode for a lithium ion secondary battery according to the present invention as a positive electrode. Since the lithium ion secondary battery according to the present invention uses the positive electrode for a lithium ion secondary battery according to the present invention, it has excellent low temperature output characteristics and high performance.

<Negative electrode>

As a negative electrode of a lithium ion secondary battery, a known negative electrode used as a negative electrode for a lithium ion secondary battery can be used. Specifically, as the negative electrode, for example, a negative electrode made of a thin metal lithium or a negative electrode having a negative electrode mixture layer formed on the current collector can 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. Among these, it is preferable to use a current collector made of copper as the current collector for the negative electrode. As the negative electrode composite material layer, a layer including a negative electrode active material and a binder may be used. The binder is not particularly limited, and any known materials 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, for example, a lithium salt is used. Examples of the lithium salt include 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. Among them, LiPF ₆ , LiClO ₄ and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable because it is easily soluble in a solvent and exhibits a high degree of dissociation. The electrolytes may be used singly or in combination of two or more at any ratio. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte having a high degree of dissociation is used, so that the lithium ion conductivity can be controlled by 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 Carbonates such as benzyl carbonate (BC), methyl ethyl carbonate (EMC) and the like; esters such as? -butyrolactone and methyl formate; Ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur compounds including sulfolane and dimethyl sulfoxide; Etc. are commonly used. A mixed solution of these solvents may also be used. Among them, it is preferable to use a carbonate having a high dielectric constant and a wide potential range, and more preferably a mixture of ethylene carbonate and ethylmethyl carbonate.

The concentration of the electrolyte in the electrolytic solution can be suitably adjusted. For example, it is preferably 0.5 to 15 mass%, more preferably 2 to 13 mass%, and still more preferably 5 to 10 mass%. In addition, a known additive such as fluoroethylene carbonate or ethyl methyl sulfone may be added to the electrolytic solution.

<Separator>

The separator is not particularly limited, and for example, those described in Japanese Patent Application Laid-Open No. 2012-204303 can be used. Among them, the total thickness of the separator can be made thinner, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery to increase the capacity per volume. Therefore, a polyolefin (polyethylene, polypropylene, polybutene, Vinyl) resin is preferable.

<Manufacturing Method of Lithium Ion Secondary Battery>

The lithium ion secondary battery of the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, and winding and folding the battery in accordance with the shape of the battery, And then sealing it. An overcurrent prevention element such as a fuse, a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary in order to prevent the rise of the internal pressure of the lithium ion secondary battery and the overcharge discharge. 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 quantities are on a mass basis unless otherwise specified.

The crystallinity of the polymer (A) in the positive electrode composite material layer, the iodine value of the polymer (B), the flexibility and binding property of the positive electrode composite material layer, and the high temperature cycle characteristics and low temperature output characteristics of the lithium ion secondary battery Were measured and evaluated using the following methods, respectively.

<Crystallinity>

The positive electrode composite material layer was peeled from the prepared positive electrode for a lithium ion secondary battery and filled in a zirconia rotor having a diameter of 2.5 mm. Then, a 19 F-NMR spectrum as shown in Fig. 1 was measured using a solid state NMR apparatus (Avance 400, manufactured by Bruker). Peak fitting was performed with a Gaussian function with the center value fixed for the peak of the 19 F-NMR spectrum (the peak shown by the solid line in FIG. 1) obtained next. Specifically, peak fitting was performed with respect to the peak of 19 F-NMR spectrum using peak fitting software (OriginLab, Origin 9.1). As a result, a peak indicated by a dashed line was detected at a position of 80 ppm, a peak indicated by a one-dot chain line was detected at a position of 88 ppm, and a peak indicated by a two-dot chain line was detected at a position of 95 ppm. Therefore, an area a of the peak originating from the alpha positive portion and a peak area b of the peak derived from the amorphous portion, which are detected at a position of 88 ppm, detected at a position of 80 ppm, And the area c of the peak derived from the static portion was obtained. The degree of crystallization of the polymer (A) was calculated using the following formula (I).

The crystallinity is calculated by the following formula: Crystallinity = [{(a × 2) + (c-a)} / {(a × 2) + (c-

<Iodine value>

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

<Flexibility>

Bars having different diameters were placed on the positive electrode composite material layer side of the prepared positive electrode for a lithium ion secondary battery so as to overlap in the width direction (short side direction) of the positive electrode. Then, the positive electrode was wound around a rod to evaluate whether or not the positive electrode composite layer was cracked. The smaller the diameter of the rod with the positive electrode not cracked, the higher the flexibility of the positive electrode composite layer and the better the turnability of the positive electrode.

A = not split in rod 0.7mm in diameter

B = not split in a rod 0.8 mm in diameter

C = not split in rod with 0.9mm diameter

D = not split in a rod with a diameter of 1.0 mm

E = not split in rod of diameter 1.2mm

&Lt; Adhesion property &

The prepared positive electrode for a lithium ion secondary battery was cut into a rectangle having a width of 1.0 cm and a length of 10 cm and used as a test piece to fix the surface of the positive electrode composite layer side up. Then, a cellophane tape was attached to the surface of the test piece on the side of the positive electrode composite layer. At this time, the cellophane tape specified in JIS Z1522 was used. Thereafter, the stress was measured when the cellophane tape was peeled from one end of the test piece at a speed of 50 mm / minute in the 180 占 direction (the other end side of the test piece). The measurement was carried out ten times, and an average value of the stress was obtained. The average stress value was determined as the peel strength (N / m) and evaluated according to the following criteria. The larger the fill strength, the better the bondability of the positive electrode composite layer to the current collector.

A = 120 N / m or more

B = 110 N / m or more and less than 120 N / m

C = 100 N / m or more and less than 110 N / m

D = less than 100 N / m

<High temperature cycle characteristics>

The produced lithium ion secondary battery was charged at 4.2 V by a constant current method of 0.5 C in an atmosphere at a temperature of 45 캜, and charged and discharged for discharging to 3.0 V were repeated for 200 cycles. Then, the charge / discharge capacity retention ratio expressed by the ratio of the electric capacity at the end of 200 cycles to the electric capacity at the end of 5 cycles (= (electric capacity at the end of 200 cycles / electric capacity at the end of 5 cycles) × 100 (%)) . These measurements were carried out on five cells of the lithium ion secondary battery, and the average of the charge / discharge capacity retention ratios of the respective cells was used as the charge / discharge capacity retention ratio and evaluated based on the following criteria. The larger this value is, the better the high-temperature cycle characteristics are.

A = 95% or more charge / discharge capacity retention rate

B = charge / discharge capacity retention rate of 90% or more and less than 95%

C = charge / discharge capacity retention rate 85% or more and less than 90%

D = charge / discharge capacity maintenance rate less than 85%

<Low Temperature Output Characteristics>

The produced lithium ion secondary battery was charged at a constant current and constant voltage (CCCV) to 4.2 V in an atmosphere at a temperature of 25 캜 to prepare a cell. The prepared cell was discharged to 2.5 V by the constant current method of 1 C in an atmosphere of a temperature of 25 캜 and a temperature of -10 캜 to obtain an electric capacity at each temperature. The discharge capacity retention rate expressed by the ratio of the electric capacity (= (electric capacity at 10 ° C-electric capacity / electric capacity at 25 ° C) × 100 (%)) was obtained. These measurements were performed on five cells of the lithium ion secondary battery, and the average of the discharge capacity retention ratios of the respective cells was evaluated as low temperature output characteristics by the following criteria. The larger this value is, the better the low temperature output characteristic is.

A = 70% or more

B = 60% or more and less than 70%

C = 50% or more and less than 60%

D = 40% or more and less than 50%

E = less than 40%

(Example 1)

&Lt; Preparation of Polymer (A) >

Polyvinylidene fluoride (KF Polymer # 7200, manufactured by Kureha Co., Ltd., melting point: 161 캜) was prepared as the polymer (A).

&Lt; Preparation of polymer (B) >

In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 20 parts of acrylonitrile as a nitrile group-containing monomer, 30 parts of butyl acrylate as a (meth) acrylic acid ester monomer, And the inside of the bottle was replaced with nitrogen. Then, 45 parts of 1,3-butadiene as the conjugated diene monomer was pushed in and 0.25 part of ammonium persulfate was added, and polymerization reaction was carried out at a reaction temperature of 40 캜. Then, a polymer comprising a nitrile group-containing monomer unit, a (meth) acrylic acid ester monomer unit, a hydrophilic group-containing monomer unit and a conjugated diene monomer unit was obtained. The polymerization conversion rate was 85%, and the iodine value of the polymer was 280 mg / 100 mg.

Subsequently, 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 added to a 1-liter autoclave equipped with a stirrer. The solution was allowed to flow to remove dissolved oxygen in the polymer solution. Thereafter, 75 mg of palladium acetate as a hydrogenation catalyst was dissolved in 180 ml of water to which 4-fold molar amount of nitric acid was added to Pd, and the solution was added. The contents of the autoclave were heated to 50 DEG C under the condition that the system was purged with hydrogen gas twice and then pressurized with hydrogen gas to 3 MPa and subjected to a hydrogenation reaction (referred to as &quot; first-stage hydrogenation reaction &quot;) for 6 hours . The iodine value of the polymer was 35 mg / 100 mg.

Subsequently, the autoclave was returned to atmospheric pressure, and 25 mg of palladium acetate as a hydrogenation catalyst was dissolved in 60 mL of water to which 4-fold molar amount of nitric acid was added relative to Pd. The contents of the autoclave were heated to 50 DEG C under the condition that the inside of the autoclave was replaced with hydrogen gas twice and then pressurized with hydrogen gas to 3 MPa and the hydrogenation reaction for 6 hours (referred to as &quot; hydrogenation in the second step & .

Thereafter, the contents were returned to room temperature, the inside of the system was brought to a nitrogen atmosphere, and the mixture was concentrated using an evapoator until the solid concentration became 40% to obtain an aqueous dispersion of the polymer (B). Further, 320 parts of N-methyl-2-pyrrolidone (NMP) was added to 100 parts of the aqueous dispersion of the polymer (B), and water was evaporated under reduced pressure to obtain an NMP solution of the polymer (B). 100 g of the NMP solution was solidified with 1 liter of methanol, and then dried at 60 DEG C overnight under vacuum to obtain a dried product. The obtained dried product was analyzed by NMR to find that the polymer (B) contained 20% by mass of a nitrile group-containing monomer unit (acrylonitrile unit), 45% by mass of a structural unit derived from 1,3-butadiene, Methacrylic acid unit) and 30 mass% of a (meth) acrylic acid ester monomer unit (butyl acrylate unit). Here, the structural unit derived from 1,3-butadiene was formed of 38.8% by mass of a linear alkylene structural unit having 4 or more carbon atoms, an anhydride-modified butadiene unit and a 1,2-addition polymerized structural unit. The iodine value of the polymer (B) was 10 mg / 100 mg.

&Lt; Preparation of slurry composition for positive electrode &

100 parts of lithium cobalt oxide having a layered structure as a positive electrode active material (LiCoO ₂ , particle diameter: 12 μm), 2.0 parts of acetylene black as a conductive material (Denkika Chemical Co., HS-100) (Solid content: 8.0%) in an amount corresponding to a solid content of 1.6 parts and an NMP solution (solid content concentration: 8.0%) of the polymer (B) in an amount corresponding to a solid content of 0.4 part and an appropriate amount of NMP were stirred with a planetary mixer, Lt; / RTI &gt;

&Lt; Preparation of positive electrode for lithium ion secondary battery &

An aluminum foil having a thickness of 20 mu m was prepared as a current collector. The slurry composition for positive electrode was coated on an aluminum foil with a comma coater so that the coating amount after drying was 20 mg / cm ² . Then, the aluminum foil was conveyed in an oven at a temperature of 60 ° C for 2 minutes and at an oven of 120 ° C for 2 minutes at a rate of 0.5 m / min to dry the positive electrode slurry composition to form a film on the aluminum foil Film forming process). Subsequently, the roll of the coated aluminum foil was vacuum dried at a temperature of 165 DEG C for 2 hours. Thereafter, the film was slowly cooled (cooling rate: 140 ° C / hour) to a temperature of 25 ° C over 1 hour to obtain a negative electrode raw material film. The density of the positive electrode green sheet before pressing was 2.42 g / cm &lt; ^{3 &} gt ;. The original plate of the positive electrode was rolled by a roll press to prepare a positive electrode composed of a positive electrode mixture layer having a density of 3.7 g / cm ³ and an aluminum foil (heat treatment step). The thickness of the positive electrode composite material layer was 70 mu m. The prepared positive electrode was subjected to measurement of flexibility and adhesion. The degree of crystallization of the polymer (A) in the positive electrode composite material layer was also measured. The results are shown in Table 1.

&Lt; Preparation of negative electrode for lithium ion secondary battery &

100 parts of artificial graphite (specific surface area: 4 m ² / g, average particle diameter: 24.5 μm) as a negative electrode active material and 1% aqueous solution of carboxymethylcellulose as a viscosity adjuster (manufactured by Daiichiko Kosei Yakuhin Co., BSH-12) was added in an amount of 1 part in terms of solid content, adjusted to a solid content concentration of 55% by ion-exchange water, and then mixed at 25 ° C for 60 minutes. Subsequently, the solid content was adjusted to 52% with ion-exchanged water. Thereafter, the mixture was further mixed at a temperature of 25 DEG C for 15 minutes to obtain a mixed solution.

To the obtained mixed solution, a 40% aqueous dispersion of styrene-butadiene copolymer (glass transition point: -15 占 폚) as a binder was added in an amount of 1.0 part in terms of solid content and ion-exchanged water to adjust the final solid concentration to 50% And mixed again for 10 minutes. The obtained mixture was subjected to defoaming treatment under reduced pressure to obtain a slurry composition for a negative electrode having good flowability.

The resulting negative electrode slurry composition was coated on a copper foil having a thickness of 20 mu m as a current collector by a comma coater so that the film thickness after drying was about 150 mu m and dried. This drying was carried out by conveying the copper foil in an oven at a temperature of 60 캜 for 2 minutes at a speed of 0.5 m / min. Thereafter, the substrate was subjected to heat treatment at a temperature of 120 占 폚 for 2 minutes to obtain a negative electrode raw disk. This original negative electrode plate was rolled by a roll press to obtain a negative electrode having a negative electrode composite material layer having a thickness of 80 mu m.

<Preparation of Separator>

The single-layered polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, manufactured by dry method, porosity 55%) was cut into a square of 5 cm × 5 cm.

&Lt; Preparation of lithium ion secondary battery >

As an exterior of the lithium ion secondary battery, an aluminum-containing sheath was prepared. The positive electrode thus obtained was cut out into a square of 4 cm x 4 cm, and the surface of the collector side was arranged so as to be in contact with the aluminum-covered sheath. On the surface of the positive electrode composite material layer of the positive electrode, the square separator obtained above was arranged. The negative electrode thus obtained was cut into a square of 4.2 cm x 4.2 cm and placed on the separator so that the surface of the negative electrode composite material layer side faced the separator. Further, a 1.0 M LiPF ₆ solution containing 1.5% of vinylene carbonate (VC) was charged. The solvent of the LiPF ₆ solution is a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC / EMC = 3/7 (volume ratio)). Further, in order to seal the openings of the aluminum-covered sheath, a heat-sealed at 150 ° C was used to obtain an aluminum-covered sheath, thereby manufacturing a lithium ion secondary battery. The obtained lithium ion secondary battery was evaluated for its high temperature cycle characteristics and low temperature output characteristics. The results are shown in Table 1.

(Example 2)

As a polymer (A), a copolymer of vinylidene fluoride and hexafluoropropylene (Kareflex 2850-00, content of vinylidene fluoride units: 97% by mass) was used instead of polyvinylidene fluoride, , Melting point: 155 占 폚), a positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced and evaluated. The results are shown in Table 1.

(Example 3)

As a polymer (A), a copolymer of vinylidene fluoride and hexafluoropropylene (Kareflex Kynar flex 2800-00, content ratio of vinylidene fluoride units: 95% by mass) was used instead of polyvinylidene fluoride, , Melting point: 140 占 폚), a positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced and evaluated. The results are shown in Table 1.

(Examples 4 to 6)

A slurry composition for a positive electrode, a positive electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a positive electrode slurry composition were prepared in the same manner as in Example 1 except that the blending amounts of the polymer (A) and the polymer (B) A negative electrode for an ion secondary battery and a lithium ion secondary battery were manufactured and evaluated. The results are shown in Table 1.

(Example 7)

Polymer (B) was prepared in the same manner as in Example 1 except that the amount of acrylonitrile was changed to 5 parts and the amount of 1,3-butadiene was changed to 60 parts at the time of preparing polymer (B). The polymer (B) was obtained by polymerizing 5% by mass of a nitrile group-containing monomer unit (acrylonitrile unit), 60% by mass of a 1,3-butadiene-derived structural unit, 5% by mass of a hydrophilic group-containing monomer unit (methacrylic acid unit) %, And 30 mass% of a (meth) acrylic acid ester monomer unit (butyl acrylate unit). The structural unit derived from 1,3-butadiene was formed of 52.5% by mass of a straight chain alkylene structural unit having 4 or more carbon atoms, an anhydride-modified butadiene unit and a 1,2-addition polymerized structural unit. The iodine value of the polymer (B) was 13 mg / 100 mg.

A positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1 except that the polymer (B) was used. The results are shown in Table 1.

(Example 8)

Polymer (B) was prepared in the same manner as in Example 1 except that the amount of acrylonitrile was changed to 40 parts and the amount of 1,3-butadiene was changed to 25 parts at the time of preparing polymer (B). The polymer (B) was obtained by polymerizing 40% by mass of a nitrile group-containing monomer unit (acrylonitrile unit), 25% by mass of a 1,3-butadiene-derived structural unit, 5% by mass of a hydrophilic group-containing monomer unit (methacrylic acid unit) %, And 30 mass% of a (meth) acrylic acid ester monomer unit (butyl acrylate unit). The structural unit derived from 1,3-butadiene was formed of 20.6% by mass of a straight chain alkylene structural unit having 4 or more carbon atoms, an anhydride-modified butadiene unit and a 1,2-addition polymerized structural unit. The iodine value of the polymer (B) was 8 mg / 100 mg.

A positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1 except that the polymer (B) was used. The results are shown in Table 1.

(Example 9)

In the preparation of the polymer (B), 68 parts of 2-ethylhexyl acrylate was used instead of 30 parts of butyl acrylate, the amount of acrylonitrile was changed to 15 parts, 1,3-butadiene was not used, Polymer (B) was prepared in the same manner as in Example 1 except that the amount of acid was changed to 17 parts and the hydrogenation reaction in the first step and the hydrogenation reaction in the second step were not carried out. The polymer (B) contained 15 mass% of a nitrile group-containing monomer unit (acrylonitrile unit), 17 mass% of a hydrophilic group-containing monomer unit (methacrylic acid unit), 17 mass% of a (meth) acrylic acid ester monomer unit Acrylate unit) by 68 mass%. The iodine value of the polymer (B) was 10 mg / 100 mg.

A positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1 except that the polymer (B) was used. The results are shown in Table 1.

(Example 10)

The procedure of Example 1 was repeated except that the amount of acrylonitrile was changed to 25 parts and the amount of 1,3-butadiene was changed to 70 parts without using butyl acrylate at the time of preparing the polymer (B) (B). In addition, the polymer (B) contains 25 mass% of a nitrile group-containing monomer unit (acrylonitrile unit), 70 mass% of a 1,3-butadiene-derived structural unit, 5 mass of a hydrophilic group- %. The structural unit derived from 1,3-butadiene was formed from 63.8 mass% of a straight-chain alkylene structural unit having 4 or more carbon atoms, an anhydride-modified butadiene unit and a 1,2-addition polymerized structural unit. The iodine value of the polymer (B) was 15 mg / 100 mg.

A positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1 except that the polymer (B) was used. The results are shown in Table 1.

(Example 11)

A slurry composition for a positive electrode, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a negative electrode were prepared in the same manner as in Example 1 except that the roll of the coated aluminum foil was vacuum- A negative electrode for a lithium ion secondary battery and a lithium ion secondary battery were produced and evaluated. The results are shown in Table 1.

(Example 12)

Polymer (B) was prepared in the same manner as in Example 1 except that the amount of acrylonitrile was changed to 25 parts and methacrylic acid was not used at the time of preparing polymer (B). The polymer (B) contains 25 mass% of a nitrile group-containing monomer unit (acrylonitrile unit), 45 mass% of a structural unit derived from 1,3-butadiene, a (meth) acrylic acid ester monomer unit (butyl acrylate unit) Was contained in an amount of 30% by mass. The structural unit derived from 1,3-butadiene was formed of 38.8% by mass of a straight-chain alkylene structural unit having 4 or more carbon atoms, an anhydride-modified butadiene unit and a 1,2-addition polymerized structural unit. The iodine value of the polymer (B) was 10 mg / 100 mg.

A positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1 except that the polymer (B) was used. The results are shown in Table 1.

(Comparative Example 1)

Except that the temperature for vacuum drying the roll of the aluminum foil on which the film was formed during the production of the positive electrode for a lithium ion secondary battery was changed to 150 占 폚 and quenched (cooling rate: 1500 占 폚 / hour) A positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)

As a polymer (A), a copolymer of vinylidene fluoride and hexafluoropropylene (Kareflex 275-01, content ratio of vinylidene fluoride units: 90% by mass) was used instead of polyvinylidene fluoride, , Melting point: 138 占 폚), a positive electrode slurry composition, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery were produced and evaluated. The results are shown in Table 1.

(Comparative Example 3)

A slurry composition for a positive electrode, a positive electrode for a lithium ion secondary battery, and a negative electrode were prepared in the same manner as in Example 1 except that the polymer (B) was not used in preparing the positive electrode slurry composition and the amount of the polymer (A) , A negative electrode for a lithium ion secondary battery and a lithium ion secondary battery were manufactured and evaluated. The results are shown in Table 1.

From Examples 1 to 12 and Comparative Examples 1 to 3 in Table 1, Examples 1 to 12 using the predetermined polymer (A) and polymer (B) as binder were excellent in the flexibility and binding property of the positive electrode composite material layer, It is also seen that the electrical characteristics (high temperature cycle characteristics and low temperature output characteristics) of the secondary battery are also good. On the other hand, in Comparative Examples 1 and 2 in which the predetermined polymer (A) was not used and in Comparative Example 3 in which the polymer (B) was not used, the flexibility and binding property of the positive electrode composite material layer and the electrical characteristics of the secondary battery Able to know.

It can also be seen from Examples 1 to 3 in Table 1 that the flexibility and binding properties of the positive electrode composite material layer and the electrical characteristics of the secondary battery can be improved by adjusting the composition of the polymer (A).

It can be seen from Example 1 and Examples 4 to 6 of Table 1 that the flexibility and binding properties of the positive electrode composite material layer and the electrical characteristics of the secondary battery can be improved by adjusting the compounding ratio of the polymer (A) and the polymer (B) .

It can also be seen from Example 1 and Examples 7 to 10 in Table 1 that the flexibility and binding properties of the positive electrode composite material layer and the electrical characteristics of the secondary battery can be improved by adjusting the composition of the polymer (B).

From Examples 1 and 11 of Table 1, the degree of crystallinity of the polymer (A) was adjusted by adjusting the cooling rate at the time of cooling after the film was heated, and the flexibility and tackiness of the positive electrode composite material layer, It can be seen that the electrical characteristics of the battery can be improved.

From Examples 1 and 12 in Table 1, it is also possible to improve the binding property of the positive electrode composite material layer by increasing the binding force of the polymer (B) by including the methacrylic acid unit as the hydrophilic group-containing monomer unit in the polymer (B) Can be seen.

Industrial availability

According to the present invention, it is possible to provide a positive electrode for a secondary battery which is excellent in flexibility and binding property of a positive electrode composite material layer and can exhibit excellent output characteristics (particularly, low temperature output characteristics) for a secondary battery.

Further, according to the present invention, it is possible to provide a secondary battery having excellent output characteristics (particularly low-temperature output characteristics).

Claims (12)

A process for producing a negative electrode active material, comprising the steps of: forming a positive electrode active material, a coating film containing a polymer (A) containing 95% by mass or more of vinylidene fluoride units and a polymer (B) containing a nitrile group-
The film is heated at a temperature equal to or higher than the melting point of the polymer (A) and then cooled to obtain a mixture of the positive electrode active material and the polymer (A) having a crystallinity of at least 15% and at most 40% And a step of forming the positive electrode collector on the current collector.
The method according to claim 1,
Wherein the polymer (B) further comprises a (meth) acrylic acid ester monomer unit.
The method according to claim 1,
Wherein the polymer (B) further comprises an alkylene structural unit having 4 or more carbon atoms.
4. The method according to any one of claims 1 to 3,
Wherein the content of the nitrile group-containing monomer units in the polymer (B) is 2% by mass or more and 50% by mass or less.
3. The method of claim 2,
Wherein the content of the (meth) acrylic acid ester monomer unit in the polymer (B) is 5 mass% or more and 50 mass% or less.
The method of claim 3,
Wherein the content of the alkylene structural unit having 4 or more carbon atoms in the polymer (B) is 20 mass% or more and 70 mass% or less.
4. The method according to any one of claims 1 to 3,
Wherein the iodine value of the polymer (B) is 3 mg / 100 mg or more and 60 mg / 100 mg or less.
4. The method according to any one of claims 1 to 3,
Wherein the ratio of the amount of the polymer (B) to the total amount of the polymer (A) and the polymer (B) is 5 mass% or more and 35 mass% or less.
4. The method according to any one of claims 1 to 3,
Wherein the temperature for heating the coating is not less than 165 ° C and not more than 250 ° C.
4. The method according to any one of claims 1 to 3,
Wherein the rate of cooling the coating is not less than 100 ° C / hour and not more than 500 ° C / hour. delete delete

Images