KR102008280B1 - Binder composition for lithium ion secondary battery electrodes, slurry composition for lithium ion secondary battery electrodes, electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

An object of this invention is to provide the binder composition for lithium ion secondary battery electrodes which can improve dispersibility, suppressing foaming of a slurry composition, and can provide the high speed coating property excellent to the said slurry composition. The binder composition of the present invention contains an adhesive polymer, a diphenyl ether surfactant, an alkylbenzene sulfonic acid surfactant, and a solvent. Here, the binder composition of this invention has THF gel content of 70 mass% or more and 95 mass% or less, the weight average molecular weight of THF dissolution component is 5000 or more and 40000 or less, and the diphenyl ether with respect to the compounding quantity of an alkylbenzene sulfonic acid type surfactant. The ratio of the compounding quantity of system type surfactant is 1/9 or more and 9 or less.

Description

Binder composition for lithium ion secondary battery electrodes, slurry composition for lithium ion secondary battery electrodes, electrode for lithium ion secondary battery and lithium ion secondary battery

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

Lithium ion secondary batteries have a small size, light weight, high energy density, and can be repeatedly charged and discharged.

Here, the electrodes (positive electrode and negative electrode) of a lithium ion secondary battery usually comprise an electrical power collector and the electrode mixture layers (positive electrode mixture layer and negative electrode mixture layer) formed on the electrical power collector. The electrode mixture layer is formed by coating, for example, a binder composition and a slurry composition obtained by dissolving and / or dispersing an electrode active material in a solvent on a current collector and then drying the binder to bind the electrode active material to a binder component. have. In recent years, attempts have been made to improve the coatability of slurry compositions used for forming electrodes for the purpose of improving the production efficiency of electrodes and further improving the performance of lithium ion secondary batteries.

For example, Patent Literature 1 discloses a water-dispersible polymer binder resin containing a positive electrode active material, a polyurethane resin composed of a polyol and a polyisocyanate, a conductive material, and a slurry composition for a positive electrode containing a surfactant. It is reported that the slurry composition for positive electrodes is excellent in coating property on an electrical power collector. And according to this patent document 1, by adding surfactant, a positive electrode active material and a water dispersible polymer binder resin are disperse | distributed uniformly to an aqueous solvent in a short time, and also suppressing aggregation and sedimentation of these, and collecting the phase of the positive electrode slurry composition It can improve the coatability to.

Patent Document 1: Japanese Unexamined Patent Publication No. 2013-134884

In recent years, the speed | rate of the coating speed of a slurry composition is calculated | required from the viewpoint of further improving the production efficiency of an electrode.

However, when coating the slurry composition of the said patent document 1 on an electrical power collector, when a coating speed is raised, dispersion | variation will arise in coating amount due to insufficient dispersibility of a slurry composition, foaming by surfactant, etc., and There existed a problem that a defective location (stripes, coating nonuniformity, cratering, etc.) arose in the electrode mixture layer obtained.

That is, there existed room for improvement in the point that the slurry composition containing the surfactant of the said patent document 1 further improves dispersibility, fully suppressing foaming, and ensuring high speed coatability.

Therefore, an object of the present invention is to provide a binder composition for a lithium ion secondary battery electrode which can improve dispersibility while suppressing the foaming of the slurry composition for a lithium ion secondary battery electrode and can impart excellent high speed coating property to the slurry composition. It is done.

Moreover, an object of this invention is to provide the slurry composition for lithium ion secondary battery electrodes which is excellent in dispersibility and exhibits the outstanding high speed coating property, while foaming is suppressed.

Moreover, an object of this invention is to provide the lithium ion secondary battery electrode which can exhibit the outstanding battery characteristic to a lithium ion secondary battery, and the lithium ion secondary battery provided with this electrode.

MEANS TO SOLVE THE PROBLEM This inventor earnestly examined for the purpose of solving the said subject. In addition, in the binder composition for a lithium ion secondary battery electrode comprising an adhesive polymer, the present inventors blend two kinds of surfactants, such as a diphenyl ether surfactant and an alkylbenzene sulfonic acid surfactant, in a predetermined amount ratio, In addition, by suppressing the THF gel content of the binder composition and the weight average molecular weight (Mw) of the THF dissolving component, respectively, within a predetermined range, the foaming suppression and the improvement of dispersibility of the slurry composition obtained by using the binder composition are achieved in a balanced manner. Conceived of things. In addition, even when the slurry composition was coated on the current collector at high speed, variations in the coating amount were suppressed, and it was found that an electrode mixture layer having fewer defective points could be formed, thereby completing the present invention.

That is, this invention aims at solving the said subject advantageously, The binder composition for lithium ion secondary battery electrodes of this invention uses adhesive polymer, a diphenyl ether type surfactant, an alkylbenzene sulfonic acid type surfactant, and a solvent. THF gel content is 70 mass% or more and 95 mass% or less, the weight average molecular weight of THF melt | dissolution component is 5000 or more and 40000 or less, and the said diphenyl ether type surfactant with respect to the compounding quantity of the said alkylbenzene sulfonic-acid surfactant is included. It is characterized by the ratio of compounding quantity that is 1/9 or more and 9 or less. Thus, it comprises an adhesive polymer, and further comprises two kinds of surfactants, diphenyl ether-based surfactants and alkylbenzene sulfonic acid-based surfactants in a predetermined amount ratio, and also has a predetermined THF gel content and THF dissolution When the binder composition which has the weight average molecular weight of a component is used, the slurry composition for lithium ion secondary battery electrodes which dispersibility is favorable and exhibits the outstanding high speed coating property, while foaming is suppressed can be prepared.

In addition, "THF gel content" and "weight average molecular weight of THF melt | dissolution component" of the binder composition for lithium ion secondary battery electrodes can be measured using the method as described in the Example of this specification.

Here, the binder composition for lithium ion secondary battery electrodes of this invention contains 0.2 mass part or more and 1.5 mass parts or less of the said diphenyl ether type surfactant and the said alkylbenzene sulfonic acid type surfactant in total per 100 mass parts of said adhesive polymers. desirable. If the sum total of the compounding quantity of a diphenyl ether type surfactant and the compounding quantity of an alkylbenzene sulfonic acid type surfactant is in the above-mentioned range, it will further improve dispersibility, suppressing foaming of the slurry composition containing a binder composition, and said slurry composition It is possible to further improve the high-speed coatability of the. In addition, the adhesiveness of the electrode mixture layer obtained by using the slurry composition containing a binder composition and an electrical power collector can be improved, and the battery characteristics (output characteristics, cycling characteristics, etc.) of a lithium ion secondary battery can be improved.

And it is preferable that the binder composition for lithium ion secondary battery electrodes of this invention contains 0.1 mass part or more and 1 mass part or less of a polyacrylic acid compound per 100 mass parts of said adhesive polymers. By including a polyacrylic acid compound in the above-mentioned compounding quantity, the dispersibility of the slurry composition containing a binder composition can be improved further, and the high speed coatability of the said slurry composition can be improved further. In addition, the adhesiveness of an electrode mixture layer and an electrical power collector obtained using the slurry composition containing a binder composition can be improved, and the battery characteristic of a lithium ion secondary battery can be improved.

In addition, it is preferable that the binder composition for lithium ion secondary battery electrodes of this invention contains 0.5 mass part or more and 1.5 mass parts or less of a phosphoric acid compound per 100 mass parts of said adhesive polymers. When a phosphoric acid compound is included in the above-mentioned compounding quantity, the dispersibility of the slurry composition containing a binder composition can be improved further, and the high speed coatability of the said slurry composition can be improved further. In addition, the adhesiveness of an electrode mixture layer and an electrical power collector obtained using the slurry composition containing a binder composition can be improved, and the battery characteristic of a lithium ion secondary battery can be improved.

Moreover, in the binder composition for lithium ion secondary battery electrodes of this invention, it is preferable that the said adhesive polymer contains an aromatic vinyl monomeric unit and an aliphatic conjugated diene monomeric unit. The copolymer including the aromatic vinyl monomer unit and the aliphatic conjugated diene monomer unit can increase dispersibility of the electrode active material while having moderate flexibility. Therefore, when the said copolymer is used as an adhesive polymer, the electrode by which the adhesiveness of an electrode mixture layer and an electrical power collector is fully ensured can be manufactured, and when the said electrode is used especially as a negative electrode, it is the battery characteristic excellent in a lithium ion secondary battery. Can be exercised.

In addition, in this invention, "containing a monomeric unit" means that "the structural unit derived from a monomer is contained in the polymer obtained using the monomer."

Furthermore, in the binder composition for lithium ion secondary battery electrodes of this invention, the said adhesive polymer containing an aromatic vinyl monomer unit and an aliphatic conjugated diene monomeric unit further contains 0.1 mass% or more of ethylenically unsaturated carboxylic monomer units 10 It is preferable to contain mass% or less. In addition to the aromatic vinyl monomer unit and the aliphatic conjugated diene monomer unit, when a copolymer containing an ethylenically unsaturated carboxylic acid monomer unit in the above-mentioned range is used as the adhesive polymer, the dispersibility of the slurry composition comprising the binder composition It can further improve and the high speed coating property of the said slurry composition can further be improved. Moreover, the adhesiveness of an electrode mixture layer and an electrical power collector can fully be ensured, and the battery characteristic excellent in a lithium ion secondary battery can be exhibited.

Moreover, this invention aims at solving the said subject advantageously, and the slurry composition for lithium ion secondary battery electrodes of this invention contains any one of the binder compositions for lithium ion secondary battery electrodes mentioned above and an electrode active material. It features. The slurry composition comprising any one of the above-described binder compositions exhibits good dispersibility while suppressing foaming and exhibits excellent high-speed coating properties.

Here, it is preferable that the slurry composition for lithium ion secondary battery electrodes of this invention is a viscosity of 500 mPa * s or more and 3500 mPa * s or less, and solid content concentration is 40 mass% or more and 55 mass% or less. When the viscosity and solid content concentration of a slurry composition are respectively in the above-mentioned range, the drying efficiency at the time of drying and obtaining an electrode mixture layer can be ensured, further improving the high-speed coatability of a slurry composition.

In addition, "viscosity" of the slurry composition for lithium ion secondary battery electrodes is a viscosity measured using a single cylindrical rotational viscometer, and can be measured using the method as described in the Example of this specification specifically.

Moreover, this invention aims at solving the said subject advantageously, The electrode for lithium ion secondary batteries of this invention collects the electrode mixture layer prepared using the slurry composition for any one of lithium ion secondary battery electrodes mentioned above. It is characterized by comprising in the phase. The electrode mixture layer obtained using any one of the slurry compositions mentioned above has few defect points, and the electrode provided with the said electrode mixture layer can exhibit the outstanding battery characteristic to a lithium ion secondary battery.

Moreover, this invention aims at solving the said subject advantageously, The lithium ion secondary battery of this invention is equipped with the positive electrode, the negative electrode, electrolyte solution, and a separator, At least one of the said positive electrode and the negative electrode mentioned above is a lithium ion secondary battery. It is a battery electrode, It is characterized by the above-mentioned. The lithium ion secondary battery provided with the electrode mentioned above is excellent in battery characteristics, such as an output characteristic and a cycle characteristic.

According to the present invention, it is possible to provide a binder composition for a lithium ion secondary battery electrode capable of increasing dispersibility while suppressing foaming of the slurry composition for a lithium ion secondary battery electrode and providing excellent high speed coating property to the slurry composition. .

According to the present invention, it is possible to provide a slurry composition for a lithium ion secondary battery electrode which exhibits excellent dispersibility and exhibits excellent high-speed coating properties while suppressing bubble generation.

According to this invention, the electrode for lithium ion secondary batteries which can exhibit the outstanding battery characteristic to a lithium ion secondary battery, and the lithium ion secondary battery provided with the said electrode can be provided.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail.

Here, the binder composition for lithium ion secondary battery electrodes of this invention is used for preparation of the slurry composition for lithium ion secondary battery electrodes. In addition, the slurry composition for lithium ion secondary battery electrodes of this invention is used for the electrode formation of a lithium ion secondary battery. And the lithium ion secondary battery electrode of this invention is equipped with the electrode mixture layer formed from the slurry composition for lithium ion secondary battery electrodes of this invention. Moreover, the lithium ion secondary battery of this invention is characterized by including the electrode for lithium ion secondary batteries of this invention.

(Binder composition for lithium ion secondary battery electrode)

The binder composition for lithium ion secondary battery electrodes of this invention contains an adhesive polymer, surfactant, and a solvent. The binder composition of the present invention has a ratio of the compounding amount of the diphenyl ether surfactant and the alkylbenzene sulfonic acid surfactant to the compounding amount of the diphenyl ether surfactant to the blending amount of the alkylbenzene sulfonic acid surfactant as 1/9 or more. It is included in quantity becoming 9 or less. Moreover, the binder composition of this invention is 70 mass% or more and 95 mass% or less, and the weight average molecular weights of THF melt | dissolution component are 5000 or more and 40000 or less.

And according to the binder composition for lithium ion secondary battery electrodes of this invention mentioned above, dispersibility can be improved, suppressing foaming of the slurry composition for lithium ion secondary battery electrodes, and the high speed coating property of the said slurry composition can be improved.

<Adhesive Polymer>

When the adhesive polymer is formed using the binder composition for secondary battery electrodes of the present invention, in the produced electrode, a component (for example, an electrode active material) included in the electrode mixture layer does not detach from the electrode mixture layer. It is a component that can be maintained.

Here, as an adhesive polymer, if it can be used as a binder in the electrode for lithium ion secondary batteries, it will not specifically limit. As an adhesive polymer, a diene polymer, an acrylic polymer, a fluoropolymer, a silicone polymer, etc. can be used, for example. Especially, when using the binder composition of this invention for formation of a negative electrode mixture layer, it is preferable to use a diene polymer as an adhesive polymer, and to use the copolymer which has an aliphatic conjugated diene monomeric unit and an aromatic vinyl monomer unit. Particularly preferred. A copolymer having an aliphatic conjugated diene monomer unit which is a low rigidity, a flexible repeating unit, which can increase the adhesiveness, and an aromatic vinyl monomer unit which can decrease the solubility of the polymer in the electrolyte and increase the stability of the adhesive polymer in the electrolyte. This is because the function as an adhesive polymer can be exhibited favorably. The polymer mentioned above may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Hereinafter, the copolymer which has an aliphatic conjugated diene monomeric unit and an aromatic vinyl monomeric unit is mentioned as an example, and its suitable structure is explained in full detail.

[Furtherance]

When using the copolymer which has an aliphatic conjugated diene monomeric unit and an aromatic vinyl monomer unit as an adhesive polymer, it does not specifically limit as an aliphatic conjugated diene monomer which can form an aliphatic conjugated diene monomeric unit, 1, 3- butadiene, 2 -Methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted straight chain conjugated pentadienes, substituted and branched conjugated hexadienes, and the like can be used. Among these, 1,3-butadiene is preferable. In addition, an aliphatic conjugated diene monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In the adhesive polymer, the content ratio of aliphatic conjugated diene monomer units is preferably 10 mass% or more, more preferably 25 mass% or more, more preferably 30 mass% or more, preferably 50 mass% or less, More preferably, it is 45 mass% or less. Flexibility of an electrode can be improved because the content rate of an aliphatic conjugated diene monomeric unit is 10 mass% or more. On the other hand, when the content ratio of the aliphatic conjugated diene monomer unit is 50% by mass or less, the adhesion between the electrode mixture layer and the current collector is improved, and the electrolyte resistance of the electrode formed from the slurry composition containing the binder composition of the present invention is also excellent. Can be improved.

Moreover, it does not specifically limit as an aromatic vinyl monomer which can form the aromatic vinyl monomer unit of an adhesive polymer, Styrene, (alpha) -methylstyrene, vinyltoluene, divinylbenzene, etc. are mentioned, Especially, styrene is preferable. In addition, an aromatic vinyl monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In the adhesive polymer, the content ratio of the aromatic vinyl monomer unit is preferably 40% by mass or more, more preferably 50% by mass or more, preferably 80% by mass or less, more preferably 70% by mass or less, further Preferably it is 65 mass% or less. When the content ratio of the aromatic vinyl monomer unit is 40% by mass or more, the electrolyte resistance of the electrode can be improved, and by 80% by mass or less, the adhesion between the electrode mixture layer and the current collector can be made good.

Furthermore, it is preferable that an adhesive polymer contains an ethylenic unsaturated carboxylic monomer unit. It does not specifically limit as ethylenic unsaturated carboxylic monomer which can form an ethylenic unsaturated carboxylic monomer unit, Monocarboxylic acid, such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and dica Lenic acid, its anhydride, etc. are mentioned. Especially, acrylic acid, methacrylic acid, and itaconic acid are preferable, and itaconic acid is more preferable. In addition, an ethylenic unsaturated carboxylic monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In the adhesive polymer, the content ratio of the ethylenically unsaturated carboxylic monomer unit is preferably 0.1 mass% or more, more preferably 1.0 mass% or more, even more preferably 1.5 mass% or more, and preferably 10 mass%. % Or less, More preferably, it is 7 mass% or less, More preferably, it is 4 mass% or less. When the content rate of an ethylenic unsaturated carboxylic monomer unit is in the above-mentioned range, aggregation of an adhesive polymer is suppressed and it becomes possible to improve the dispersibility of a slurry composition, and also the electrode mixture layer obtained from the said slurry composition, and a collector Adhesion can be improved.

The adhesive polymer may contain monomer units other than the aliphatic conjugated diene monomeric unit, aromatic vinyl monomeric unit, and ethylenic unsaturated carboxylic monomer unit which were mentioned above. As a monomer which can form such another monomeric unit, For example, the vinyl cyanide monomer, the unsaturated carboxylic acid alkyl ester monomer, and the unsaturated monomer containing a hydroxyalkyl group of Unexamined-Japanese-Patent No. 2012/026462, and unsaturated carbohydrate are mentioned. Acid amide monomers, ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, etc. are mentioned.

[Manufacturing method]

Although the manufacturing method of an adhesive polymer is not specifically limited, An adhesive polymer is manufactured by superposing | polymerizing the monomer composition containing the monomer mentioned above in an aqueous solvent, for example. In addition, the content rate of each monomer in a monomer composition is made to be the same as the content rate of the repeating unit in a desired copolymer (adhesive polymer) normally.

In addition, the polymerization mode is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization or the like can be used. As the polymerization reaction, any of ionic polymerization, radical polymerization, living radical polymerization and the like can be used. And at the time of superposition | polymerization, a known emulsifier and a polymerization initiator can be used as needed.

Moreover, it is preferable that the adhesive polymer obtained is water-insoluble. In this invention, that a polymer is "insoluble in water" means that insoluble content becomes 90 mass% or more when it melt | dissolves 0.5 g of the polymers in 100 g of water at 25 degreeC.

<Surfactant>

The binder composition of this invention needs to contain a diphenyl ether type surfactant and an alkylbenzene sulfonic acid type surfactant in predetermined ratio as surfactant. According to the research of the present inventors, diphenyl ether type surfactant makes foaming a slurry composition relatively difficult among surfactants, whereas alkylbenzene sulfonic acid type surfactant can improve the dispersibility of slurry composition favorable. . And by using these two types of surfactants in a predetermined ratio, it becomes possible to suppress foaming, ensuring dispersibility of a slurry composition, and as a result, it becomes possible to improve the high speed coating property of a slurry composition. In addition, although the reason which makes a diphenyl ether type surfactant hardly generate | occur | produce a slurry composition is inferred, it is inferred that it is based on the following reasons. That is, the mechanism of foaming is considered to be because, for example, in the case of a slurry composition using water as a solvent, the surfactant forms micelles in water in order to reduce the contact area between the hydrophobic part and the water and lowers the surface energy. It is inferred that the diphenyl ether surfactant is because the diphenyl structure, which is a hydrophobic moiety, is difficult to form micelles and has an antifoaming effect.

Moreover, the binder composition of this invention may contain surfactant other than the said 2 types of surfactant.

[Diphenyl ether type surfactant]

Although it will not specifically limit, if it is surfactant which has a diphenyl ether skeleton as a diphenyl ether type surfactant, For example, the compound which has a diphenyl ether skeleton, a hydrophilic group (sulfonic acid group, a carboxyl group, a phosphoric acid group, etc.), and its salt are mentioned. have. And as a diphenyl ether type surfactant, an alkyl diphenyl ether disulfonate is preferable from a viewpoint of fully suppressing foaming of a slurry composition, a dodecyl diphenyl ether disulfonate is more preferable, and dodecyl diphenyl ether disulfonic acid Sodium is more preferred. In addition, a diphenyl ether type surfactant may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[Alkylbenzene sulfonic acid surfactant]

Examples of the alkylbenzene sulfonic acid surfactant include alkylbenzene sulfonic acid and salts thereof. And as an alkylbenzene sulfonic-acid type surfactant, linear alkylbenzene sulfonate is preferable, sodium linear alkylbenzene sulfonate is more preferable, sodium dodecylbenzene sulfonate is more preferable. In addition, a dialkyl benzene sulfonic acid type surfactant may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[Surfactant amount]

In the binder composition of the present invention, the ratio of the blending amount of the diphenyl ether surfactant to the blending amount of the alkylbenzenesulfonic acid surfactant (hereinafter referred to as "surfactant amount ratio") is 1/9 or more and 9 or less. It is necessary, and it is preferable that it is 1/4 or more, It is more preferable that it is 3/7 or more, It is preferable that it is 4 or less, It is more preferable that it is 7/3 or less. When surfactant amount ratio is less than 1/9, foaming of a slurry composition cannot fully be suppressed and the battery characteristic of a lithium ion secondary battery falls. On the other hand, when surfactant amount ratio is more than 9, the dispersibility of a slurry composition falls, and adhesiveness of an electrode mixture layer and an electrical power collector cannot be ensured, and battery characteristics (especially cycling characteristics) fall. And by making surfactant amount ratio into the above-mentioned range, foaming is suppressed also in high speed coating, and it becomes possible to obtain the slurry composition excellent in dispersibility.

[Total compounding quantity of 2 types of surfactant]

In the binder composition of the present invention, the total compounding amount of the diphenyl ether surfactant and the alkylbenzene sulfonic acid surfactant is not particularly limited, but the total compounding amount is preferably 100 parts by mass or more per 100 parts by mass of the adhesive polymer, and more. Preferably it is 0.3 mass part or more, More preferably, it is 0.35 mass part or more, Preferably it is 1.5 mass parts or less, More preferably, it is 1.2 mass parts or less, More preferably, it is 1.0 mass parts or less, Especially preferably, it is 0.9 mass parts Or less. If the total compounding quantity of these heterogeneous surfactant is 0.2 mass part or more, the dispersibility of a slurry composition will be improved and smooth coating will become easy in high speed coating. In addition, the adhesiveness of an electrode mixture layer and an electrical power collector can be improved, and the battery characteristic (especially an output characteristic) of a lithium ion secondary battery can be improved. On the other hand, foaming of a slurry composition can fully be suppressed as the total compounding quantity of these heterogeneous surfactant is 1.5 mass parts or less. In addition, the adhesiveness of an electrode mixture layer and an electrical power collector can be improved, and the battery characteristic of a lithium ion secondary battery can be improved.

<Solvent>

It does not specifically limit as a solvent of the binder composition of this invention, A known solvent can be used. Especially, it is preferable to use water as a solvent. In addition, at least one part of the solvent of a binder composition is not specifically limited, It can be set as the polymerization solvent contained in the monomer composition used when preparing an adhesive polymer.

<Other Ingredients>

In addition to the components described above, the binder composition of the present invention may contain components such as dispersion stabilizers, thickeners (excluding those corresponding to dispersion stabilizers), conductive materials, reinforcing materials, leveling agents, and electrolyte additives. These will not be specifically limited, if it does not affect battery reaction, A well-known thing can be used. In addition, these components may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Moreover, it is preferable that a binder composition contains a dispersion stabilizer from a viewpoint of stabilizing the dispersion state in the slurry composition obtained using a binder composition, and improving dispersibility. As a dispersion stabilizer, a polyacrylic acid compound and a phosphoric acid compound are mentioned, for example.

Polyacrylic acid and its salt are mentioned as a polyacrylic acid compound, From a viewpoint of improving the dispersibility of a slurry composition, polyacrylic acid salt is preferable and sodium polyacrylate is more preferable. Moreover, as a phosphate compound, a tripolyphosphate is preferable from a viewpoint of improving the dispersibility of a slurry composition, and sodium tripolyphosphate is more preferable.

In addition, a dispersion stabilizer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The compounding quantity in the binder composition of these dispersion stabilizers is not specifically limited. It is preferable that the compounding quantity of a polyacrylic-acid compound from a viewpoint of improving the dispersibility of a slurry composition is 0.1 mass part or more and 1 mass part or less per 100 mass parts of adhesive polymers, for example. In addition, it is preferable that the compounding quantity of a phosphate compound is 0.5 mass part or more and 1.5 mass parts or less per 100 mass parts of adhesive polymers from a viewpoint of raising the dispersibility of a slurry composition similarly.

And it is preferable that the binder composition of this invention contains both a polyacrylic acid compound and a phosphoric acid compound as a dispersion stabilizer from a viewpoint of further improving the dispersibility of a slurry composition.

<Preparation of binder composition>

Although the manufacturing method of the binder composition of this invention is not specifically limited, For example, it can prepare by mixing each said component. Specifically, a binder composition can be prepared by mixing the above components using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a brain trajectory, an ultrasonic disperser, a homogenizer, a planetary mixer, and a fill mix. .

Moreover, the binder composition of this invention polymerizes the monomer composition containing a diphenyl ether type surfactant and an alkylbenzene sulfonic acid type surfactant, for example, prepares the aqueous dispersion of an adhesive polymer, and the aqueous dispersion of the adhesive polymer obtained. It may also be prepared by optionally adding a solvent and other components.

<Properties of Binder Composition>

[THF gel content]

It is necessary that the binder composition of this invention is 70 mass% or more and 95 mass% or less, It is preferable that it is 75 mass% or more, It is more preferable that it is 80 mass% or more, It is preferable that it is 90 mass% or less. When THF gel content is less than 70 mass%, foam release property at the time of drying of a slurry composition cannot be ensured, and formation of the electrode mixture layer of uniform thickness becomes difficult. And the adhesiveness of an electrode mixture layer and an electrical power collector is impaired, and the battery characteristic of a lithium ion secondary battery falls. On the other hand, when THF gel content exceeds 95 mass%, the dispersibility of a slurry composition will be impaired, and smooth coating at the time of high speed coating will become difficult. Moreover, the adhesiveness of an electrode mixture layer and an electrical power collector is impaired, and the battery characteristic of a lithium ion secondary battery falls.

In addition, THF gel content of a binder composition can be suitably adjusted by changing the preparation conditions (for example, the monomer to be used, polymerization conditions, etc.) of an adhesive polymer. Specifically, the THF gel content can be adjusted by changing the polymerization temperature, the type of polymerization initiator, the amount of the chain transfer agent, and the polymerization conversion ratio (monomer consumption, etc.) at the time of stopping the reaction, for example, a chain transfer agent used at the time of polymerization. When the amount of phosphorus tert-dodecyl mercaptan (TDM) is reduced, the THF gel content can be increased. When the amount of TDM compounding is high, the THF gel content can be reduced. In addition, when the polymerization conversion rate at the time of stopping the reaction is increased, the THF gel content can be increased, and when the polymerization conversion rate is decreased, the THF gel content can be decreased.

[Weight Average Molecular Weight of THF Dissolution Component]

As for the binder composition of this invention, it is necessary that the weight average molecular weights of THF dissolving component are 5000 or more and 40000 or less, It is preferable that it is 7000 or more, It is more preferable that it is 8000 or more, It is more preferable that it is 10000 or more, It is especially preferable that it is 15000 or more, It is 40000 It is preferable that it is the following, It is more preferable that it is 30000 or less, It is more preferable that it is 25000 or less, It is especially preferable that it is 20000 or less. When the weight average molecular weight of the THF dissolving component is less than 5000, since the low molecular weight component increases, foaming of the slurry composition tends to occur, and coating to a uniform amount at the time of high-speed coating becomes difficult. In addition, the adhesiveness of an electrode mixture layer and an electrical power collector cannot be ensured, and the battery characteristic of a lithium ion secondary battery falls. On the other hand, when the weight average molecular weight of a THF melt | dissolution component exceeds 40000, the viscosity of a slurry composition will rise and high speed coating will become difficult.

In addition, the weight average molecular weight of the THF dissolving component of a binder composition can be suitably adjusted by changing the preparation conditions (for example, the monomer to be used, polymerization conditions, etc.) of an adhesive polymer. Specifically, the weight average molecular weight of the THF dissolving component can be adjusted by changing the polymerization temperature, the type and amount of the polymerization initiator, and the amount of the chain transfer agent. For example, the blending amount of the TDM which is the chain transfer agent used in the polymerization is reduced. The weight average molecular weight of the THF dissolving component can be increased, and the weight average molecular weight of the THF dissolving component can be reduced by increasing the blending amount of TDM. Moreover, when the compounding quantity of a polymerization initiator is reduced, the weight average molecular weight of a THF melt | dissolution component can be raised, and when the compounding quantity of a polymerization initiator is increased, the weight average molecular weight of a THF melt | dissolution component can be reduced.

[pH]

It is preferable that pH of the binder composition of this invention exists in the range of 7.5 +/- 1.5, ie, 6.0 or more and 9.0 or less. The binder composition whose pH is in the above-mentioned range is excellent in stability, and long-term storage is attained. In addition, pH of a binder composition can be adjusted with a known method. For example, when raising pH, aqueous alkali solution, such as ammonia water, may be added.

(Slurry Composition for Lithium Ion Secondary Battery Electrode)

The slurry composition for lithium ion secondary battery electrodes of this invention contains an electrode active material and the binder composition of this invention mentioned above. And since the slurry composition of this invention contains the binder composition of this invention mentioned above, while foaming is suppressed, dispersibility is favorable and it exhibits the outstanding high speed coating property.

<Electrode active material>

An electrode active material is a substance which exchanges electrons in the electrode (positive electrode, negative electrode) of a lithium ion secondary battery. And as an electrode active material (positive electrode active material, negative electrode active material) of a lithium ion secondary battery, the substance which can occlude and discharge | release lithium is usually used.

[Positive electrode active material]

Specifically, as the positive electrode active material, a compound containing a transition metal, for example, a transition metal oxide, a transition metal sulfide, a composite metal oxide of lithium and a transition metal, and the like can be used. Moreover, as a transition metal, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo etc. are mentioned, for example.

Here, as the transition metal oxide, for example, MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , amorphous MoO ₃ , amorphous V ₂ O _5, may be an amorphous V ₆ O ₁₃ and the like.

Examples of the transition metal sulfides include TiS ₂ , TiS ₃ , amorphous MoS ₂ , FeS, and the like.

Examples of the composite metal oxide of lithium and transition metal include lithium-containing composite metal oxides having a layered structure, lithium-containing composite metal oxides having a spinel structure, lithium-containing composite metal oxides having an olivine-type structure, and the like.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), and lithium-containing composite oxide (Li (Co Mn Ni) O). ₂ ), a lithium-containing composite oxide of Ni-Mn-Al, a lithium-containing composite oxide of Ni-Co-Al, and a solid solution of LiMaO ₂ and Li ₂ MbO ₃ . Examples of the lithium-containing composite oxide of Co-Ni-Mn include Li [Ni _0.5 Co _0.2 Mn _0.3 ] O ₂ , Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ , and the like. Further, as the solid solution of LiMaO ₂ and Li ₂ MbO _3, for example, there may be mentioned _{xLiMaO 2 · (1-x)} Li 2 MbO 3 and the like. Here, x represents a number satisfying 0 <x <1, Ma represents one or more kinds of transition metals having an average oxidation state of 3+, and Mb represents one or more kinds of transition metals having an average oxidation state of 4+. Such solid solution is Li [Ni _{0 . 17} Li _{0 . 2} Co _{0 . 07} Mn _{0 . 56} ] O ₂ , and the like.

In addition, in this specification, an "average oxidation state" shows the average oxidation state of said "one or more types of transition metals", and is calculated from the molar amount and valence of a transition metal. For example, when "one or more types of transition metal" is composed of the Ni ^{2 +} and Mn ^{+ 4} of 50mol% 50mol% of the average oxidation state of the "one or more types of transition metal" is (0.5) × (2+) + (0.5) x (4+) = 3+.

As the lithium-containing composite metal oxide having a spinel structure, for example, there may be mentioned a substituted compound with lithium manganese oxide (LiMn ₂ O ₄₎ or lithium manganese oxide (LiMn ₂ O ₄₎ a transition metal other part of the Mn of . Specific examples include LiNi _{0 . 5} Mn _{1 . 5} O ₄ can be given, such as the _{Li s [Mn 2-t Mc} t] O 4. Here, Mc represents one or more types of transition metals whose average oxidation state is 4+. Specific examples of Mc include Ni, Co, Fe, Cu, Cr, and the like. In addition, t represents a number satisfying 0 <t <1, and s represents a number satisfying 0 ≦ s ≦ 1. As the positive electrode active material, a lithium excess spinel compound represented _by Li _{1 + x} Mn _2-x O ₄ (0 <X <2) may be used.

Examples of the lithium-containing composite metal oxide having an olivine-type structure include olivine-type lithium phosphate compounds represented by Li _y MdPO ₄ such as olivine-type lithium iron phosphate (LiFePO ₄ ) and olivine-type manganese phosphate (LiMnPO ₄ ). have. Here, Md represents one or more types of transition metals having an average oxidation state of 3+, and examples thereof include Mn, Fe, Co, and the like. In addition, y represents the number which satisfy | fills 0 <= y <= 2. In addition, in the olivine-type lithium phosphate compound represented by Li _y MdPO ₄ , Md may be partially substituted with another metal. As a metal which can be substituted, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Mo, etc. are mentioned, for example.

Negative Electrode Active Material

Moreover, as a negative electrode active material, a carbon type negative electrode active material, a metal type negative electrode active material, the negative electrode active material which combined these, etc. are mentioned, for example.

Here, the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of inserting lithium (also referred to as "dope"). Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials. .

The carbonaceous material is a material having a low graphitization degree (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000 ° C. or lower. In addition, although the minimum of the heat processing temperature at the time of carbonizing is not specifically limited, For example, it can be 500 degreeC or more.

As the carbonaceous material, for example, digraphite carbon which easily changes the structure of the carbon depending on the heat treatment temperature, or non-graphitizing carbon having a structure close to the amorphous structure represented by glassy carbon, etc. Can be mentioned.

Here, the carbon material using the tar pitch obtained from petroleum or coal as a digraphite carbon is mentioned, for example. Specific examples thereof include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolytic vapor-grown carbon fibers.

Examples of the non-graphite carbon include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, pseudoisotropic carbon, furfuryl alcohol resin fired bodies (PFA), hard carbon, and the like.

The graphite material is a material having high crystallinity close to graphite obtained by heat treating digraphite carbon at 2000 ° C or higher. In addition, the upper limit of the heat processing temperature is not specifically limited, For example, it can be 5000 degrees C or less.

And as a graphite material, natural graphite, artificial graphite, etc. are mentioned, for example.

Here, as artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing digraphite carbon mainly at 2800 ° C or higher, graphitized MCMB obtained by heat treating MCMB at 2000 ° C or higher, and mesophase pitch-based carbon fiber at 2000 ° C or higher And one graphitized mesophase pitch-based carbon fiber.

In addition, a metal type negative electrode active material is an active material containing a metal, Usually, the element which can insert lithium is included in a structure, and means the active material whose theoretical electric capacity per unit mass when lithium is inserted is 500 mAh / g or more. As the metal-based active material, for example, a lithium metal, a single metal capable of forming a lithium alloy (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, and their oxides, sulfides, nitrides, silicides, carbides, phosphides and the like are used. Among these, as a metallic negative electrode active material, the active material containing a silicon (silicone negative electrode active material) is preferable. This is because the lithium ion secondary battery can be increased in capacity by using a silicon negative electrode active material.

Examples of the silicon-based negative electrode active material include silicon (Si), an alloy containing silicon, a composite material of Si-containing material and conductive carbon formed by coating or compounding SiO, SiO _x , and Si-containing material with conductive carbon. . In addition, these silicone negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 or more type.

As an alloy containing silicon, an alloy composition containing silicon, transition metals, such as aluminum and iron, and containing rare earth elements, such as tin and yttrium, is mentioned, for example.

SiO _x is a compound containing at least one and, Si of the SiO and SiO _2, x is usually 0.01 or more and less than 2. And SiO _x can be formed using the disproportionation reaction of silicon monoxide (SiO), for example. Specifically, SiO _x can be prepared by optionally heat treating SiO in the presence of a polymer such as polyvinyl alcohol and producing silicon and silicon dioxide. The heat treatment may be carried out at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher in an atmosphere containing organic gas and / or vapor after pulverizing and mixing SiO with a polymer.

As a composite material of Si-containing material and conductive carbon, for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated under an atmosphere containing, for example, an organic gas and / or vapor. The compound which consists of is mentioned. Moreover, the method of coating the surface with respect to SiO particle by the chemical vapor deposition method using organic substance etc., and the method of carrying out complex granulation (assembly) of SiO particle, graphite, or artificial graphite by a mechanochemical method. It can also obtain by well-known methods, such as these.

<Binder composition>

As a binder composition which can be mix | blended with a slurry composition, the binder composition for lithium ion secondary battery electrodes of this invention containing the adhesive polymer mentioned above, a diphenyl ether type surfactant, an alkylbenzene sulfonic acid type surfactant, and a solvent can be used. have.

In addition, the compounding quantity of a binder composition is not specifically limited, For example, an adhesive polymer is preferably 0.5 mass part or more, and preferably 5.0 mass part or less, More preferably 3.0 per 100 mass parts of electrode active materials in solid content conversion. It can be set as the quantity used as a mass part or less.

In addition, the adhesive polymer, diphenyl ether type surfactant, and alkylbenzene sulfonic acid type surfactant in a slurry composition were contained in the binder composition, The suitable abundance ratio of each component is the same as the suitable abundance ratio of each component in a binder composition. Do.

<Other Ingredients>

The other component that can be blended into the slurry composition is not particularly limited, and the same components as the other components that can be blended into the binder composition of the present invention can be mentioned. In addition, the other component may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

<Preparation of slurry composition>

The slurry composition mentioned above can be prepared by adding and mixing solvents, such as water, to each said component as needed. Specifically, a slurry composition is prepared by mixing the above components with an aqueous medium using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a brain trajectory, an ultrasonic disperser, a homogenizer, a planetary mixer, and a fill mix. can do. In addition, mixing of said each component can be normally performed for 10 minutes-several hours in the range of room temperature-80 degreeC.

Properties of Slurry Composition

[Viscosity]

It is preferable that a viscosity of a slurry composition is 500 mPa * s or more, It is preferable that it is 3500 mPa * s or less, It is more preferable that it is 3000 mPa * s or less, It is more preferable that it is 2500 mPa * s or less. By the viscosity of a slurry composition being in the range mentioned above, foaming can fully be suppressed, ensuring high dispersibility of a slurry composition, and high speed coatability can be improved.

[Solid content concentration]

It is preferable that solid content concentration is 40 mass% or more, It is more preferable that it is 43 mass% or more, It is more preferable that it is 45 mass% or more, It is preferable that it is 55 mass% or less, It is more preferable that it is 53 mass% or less, 52 It is more preferable that it is mass% or less, and it is especially preferable that it is 51 mass% or less. When the solid content concentration of the slurry composition is 40% by mass or more, the slurry composition has moderate fluidity, so that uniform coating is possible in high-speed coating, and drying efficiency when the slurry composition is dried to obtain an electrode mixture layer is secured. On the other hand, when solid content concentration of a slurry composition is 55 mass% or less, the dispersibility of a slurry composition becomes high and smooth coating in high speed coating is attained, and the concealment defect of a coating film is suppressed.

(Electrode for lithium ion secondary battery)

The slurry composition for a lithium ion secondary battery electrode (a slurry composition for a negative electrode and a slurry composition for a positive electrode) prepared by using the binder composition for a lithium ion secondary battery electrode of the present invention may be used for the production of lithium ion secondary battery electrodes (negative electrode and positive electrode). Can be.

Specifically, the electrode for lithium ion secondary batteries of this invention is equipped with an electrical power collector and the electrode mixture layer formed on the electrical power collector, and an electrode mixture layer consists of the dry matter of the slurry composition for lithium ion secondary battery electrodes mentioned above normally. The electrode mixture layer contains at least an electrode active material, the adhesive polymer described above, an alkylbenzene sulfonic acid surfactant, and a diphenyl ether surfactant. In addition, each component contained in the electrode mixture layer was contained in the said slurry composition, and the suitable abundance ratio of each of these components is the same as the suitable abundance ratio of each component in a slurry composition.

In addition, since the electrode for a lithium ion secondary battery includes an electrode mixture layer having excellent layer thickness uniformity and adhesion to a current collector, the lithium ion secondary battery can exhibit excellent battery characteristics.

(Method for producing electrode for lithium ion secondary battery)

In addition, the electrode for lithium ion secondary batteries of this invention is the process (coating process) of coating the above-mentioned slurry composition for lithium ion secondary battery electrodes on an electrical power collector, and the lithium ion secondary battery electrode coated on an electrical power collector, for example. It is manufactured through the process (drying process) of drying the slurry composition for forming an electrode mixture layer on an electrical power collector.

[Painting process]

It does not specifically limit as a method of coating the said slurry composition on an electrical power collector, A well-known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method and the like can be used. At this time, you may coat a slurry composition only on the single side | surface of an electrical power collector, and may coat on both surfaces. The thickness of the slurry film on the electrical power collector after drying after coating can be suitably set according to the thickness of the electrode mixture layer obtained by drying.

As the current collector for coating the slurry composition, a material having electrical conductivity and electrochemically durable is used. Specifically, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used as the current collector. In particular, as an electrical power collector used for a negative electrode, copper foil is especially preferable. Moreover, as an electrical power collector used for a positive electrode, aluminum foil is especially preferable. In addition, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[Drying process]

It does not specifically limit as a method of drying the slurry composition on an electrical power collector, A well-known method can be used, For example, the drying method by irradiation with warm air, hot air, low humidity wind, vacuum drying, irradiation with infrared rays, an electron beam, etc. Can be mentioned. Thus, by drying the slurry composition on an electrical power collector, an electrode mixture layer is formed on an electrical power collector, and the electrode for lithium ion secondary batteries provided with an electrical power collector and an electrode mixture layer can be obtained.

In addition, after a drying process, you may pressurize an electrode mixture layer using a metal mold | die press, a roll press, etc. By the pressure treatment, the adhesion between the electrode mixture layer and the current collector can be improved.

In addition, when an electrode mixture layer contains a curable polymer, it is preferable to harden the said polymer after formation of an electrode mixture layer.

(Lithium Ion Secondary Battery)

The lithium ion secondary battery of this invention is equipped with the positive electrode, the negative electrode, electrolyte solution, and a separator, and uses the electrode for lithium ion secondary batteries of this invention as at least one of a positive electrode and a negative electrode. And since the lithium ion secondary battery of this invention is equipped with the electrode for lithium ion secondary batteries of this invention, it is excellent in battery characteristics, such as an output characteristic and a cycle characteristic.

<Electrode>

As mentioned above, the electrode for lithium ion secondary batteries of this invention is used as at least one of a positive electrode and a negative electrode. That is, the positive electrode of a lithium ion secondary battery may be the electrode of this invention, a known negative electrode may differ from the negative electrode, the negative electrode of a lithium ion secondary battery may be an electrode of this invention, the positive electrode may be a known positive electrode different from a lithium ion secondary, and Both the positive electrode and the negative electrode of the battery may be the electrode of the present invention.

<Electrolyte amount>

As electrolyte solution, the electrolyte solution which melt | dissolved electrolyte in the solvent can be used.

Here, the organic solvent which can melt | dissolve electrolyte can be used as a solvent. Specifically, as the solvent, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and methyl acetate in alkyl carbonate solvents such as ethylene carbonate, propylene carbonate and γ-butyrolactone The thing which added viscosity adjusting solvents, such as dimethoxyethane, dioxolane, methyl propionate, and methyl formate, can be used.

Lithium salt can be used as electrolyte. As a lithium salt, the thing of Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among these lithium salts, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable as the electrolyte because they are easily dissolved in an organic solvent and exhibit high dissociation.

<Separator>

As a separator, the thing of Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among them, polyolefin-based resins (polyethylene, polypropylene, polybutene) can be made thinner, whereby the ratio of the electrode active material in the lithium ion secondary battery can be increased to increase the capacity per volume. , A microporous membrane made of polyvinyl chloride) is preferable.

<Method for manufacturing lithium ion secondary battery>

Lithium ion secondary batteries are manufactured by, for example, superimposing a positive electrode and a negative electrode through a separator and, if necessary, winding and folding them according to the shape of the battery, placing them in a battery container, and injecting and sealing an electrolyte solution into the battery container. can do. In order to prevent an increase in pressure inside the lithium ion secondary battery, generation of overcharge and discharge, and the like, an overcurrent preventing element such as a fuse or a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the lithium ion secondary battery may be any of a coin type, a button type, a sheet type, a cylindrical shape, a square shape, and a flat type.

Example

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In addition, in the following description, "%" and "part" which represent quantity are a mass reference | standard unless there is particular notice.

In Examples and Comparative Examples, the THF gel content of the binder composition and the weight average molecular weight of the THF dissolving component, the viscosity of the slurry composition, the dispersibility, the suppression of foaming, and the high speed coating property (smoothness and uniformity), the negative electrode mixture layer and The adhesiveness of an electrical power collector, the output characteristic, and cycling characteristics of a lithium ion secondary battery were evaluated using the following method, respectively.

<THF gel content>

The binder composition was dried under a 50% humidity and 23-25 ° C. environment, and formed into a film of about 0.3 mm in thickness. The film formed into a film was cut out to 3 mm square, and precisely weighed.

Let the mass of the film piece obtained by cutting be w0. This film piece was immersed in 100 g of tetrahydrofuran (THF) at 25 degreeC for 24 hours. Then, the film piece pulled up from THF was vacuum-dried at 105 degreeC for 3 hours, and the mass w1 of insoluble content was measured.

And THF gel content (mass%) was computed according to the following formula.

THF gel content (mass%) = (w1 / w0) x 100

<Weight average molecular weight of the THF dissolving component>

About 10 mg of binder composition was dissolved in 5 ml of THF, and left at 25 ° C. for 16 hours to obtain a sample for measurement through a 0.45 μm membrane filter.

The weight average molecular weight (Mw) of THF melt | dissolved component was calculated | required by the polypermeation chromatography (RI detection) by the following measurement conditions and the column using the obtained measurement sample then.

[Measuring conditions]

Temperature: 35 ℃

Solvent: THF

Flow rate: 1.0 ml / min

Concentration: 0.2 wt%

Sample injection volume: 100 μl

[column]

Toso Corporation make, "GPC TSKgel alpha-2500" (30 cm x 2 pieces) was used. (Measured under conditions where the linear correlation of Log ₁₀ (Mw) -dissolution time between Mw1000 and 300000 is 0.98 or greater)

<Viscosity>

According to JISZ8803: 1991, it measured by the single cylindrical rotational viscometer (25 degreeC, rotation speed = 60rpm, spindle shape: 4), and made the value of 60 second after the start of a measurement into the viscosity of a slurry composition.

Dispersibility

The solid content concentration of the slurry composition was adjusted to 15 mass%, and the dilution liquid which diluted 500 times the dispersion liquid after this solid content concentration adjustment was prepared. And particle size distribution was measured with the laser diffraction type particle size distribution measuring apparatus ("SALD-7100" by Shimadzu Corporation). About the obtained particle diameter distribution, the particle diameter which becomes 50% of the cumulative volume calculated from the small diameter side was calculated | required, and this was made into the volume average particle diameter D50 of the aggregated particle (made of negative electrode active material, an adhesive polymer, etc.) in a slurry composition. The ratio of the volume average particle diameter D50 of the aggregated particles in the slurry composition to the primary particle diameter of the negative electrode active material (the primary particle diameter of the negative electrode active material obtained by mixing these plural types when the negative electrode active material is composed of plural kinds of negative electrode active materials) Particle diameter) was calculated and evaluated according to the following criteria. It shows that the volume average particle diameter D50 of the aggregated particle in a slurry composition is closer to the primary particle diameter of a negative electrode active material, and this slurry composition is excellent in dispersibility, so that this particle ratio is small.

A: Particle cost is less than 1.4 times

B: Particle cost is 1.4 times or more but less than 1.6 times

C: Particle cost is 1.6 times or more but less than 1.8 times

D: Particle cost is 1.8 times or more

<Suppression of foam generation>

100 ml of the slurry composition was put into a container, and it sealed, and it depressurized to 0.9 kgf / cm <2>, stirring at 20 degreeC and 23 degreeC using a stirrer. And the time (time required for a package) from a pressure reduction start until foam | bubble does not generate | occur | produce was measured, and the following references | standards evaluated. It shows that foaming of a slurry composition is suppressed so that time required for defoaming is short.

A: Less than 3 minutes

B: The time required for a parcel is three minutes or more and less than five minutes

C: Time required for parcel is more than five minutes less than eight minutes

D: The time required for parcel is more than 8 minutes

<High speed coating property (smoothness)>

The slurry composition was discharged from a die using a die cutter and coated on a copper foil (15 mm thick, subjected to an organic solvent treatment) running at a speed of 30 m / min in the horizontal direction. After coating, it dried for 5 minutes at 120 degreeC, and formed the electrode mixture layer of thickness 70micrometer on copper foil. The center part of the obtained electrode mixture layer was cut out in rectangle of length 100mm and width 10mm. And the surface of the electrode mixture layer was observed using visual observation and an optical microscope (magnification: 10 times), and the following reference | standard evaluated.

A: There is no coating nonuniformity and it coats uniformly.

B: There is no coating nonuniformity, but fine streaks are observed by the observation by an optical microscope (stripes are not confirmed by the observation by visual observation).

C: There is no coating nonuniformity, but 1-3 streaks are confirmed by visual observation.

D: It corresponds to at least any one of the following (i)-(iii).

(i) There exist coating nonuniformity, and an uncoated point exists on copper foil.

(ii) Visually, four or more stripes are identified.

(iii) The occurrence of cratering is seen.

<High speed coating property (uniformity of coating amount)>

The slurry composition was discharged from a die using a die cutter and coated on a copper foil (15 mm thick, subjected to an organic solvent treatment) running at a speed of 30 m / min in the horizontal direction. After coating, it dried for 5 minutes at 120 degreeC, and formed the electrode mixture layer of thickness 70micrometer on copper foil. The obtained electrode (electrode mixture layer + copper foil) was blanked with a blanking blade having a diameter of 16 mm, 10 circular electrodes were produced, and the weight was measured to calculate the weight of the electrode mixture layer in each circular electrode. The deviation degree (%) obtained by multiplying the value obtained by subtracting the minimum value from the maximum value of the weights of the ten electrode mixture layers by the average value of the maximum value and the minimum value (100) was calculated and evaluated according to the following criteria. The smaller the deviation value, the more uniform the coating amount at the time of high speed coating.

A: deviation is less than 1.5%

B: deviation is more than 1.5% and less than 3.0%

C: deviation is more than 3.0% and less than 5.0%

D: deviation is more than 5.0%

<Adhesion between negative electrode mixture layer and current collector>

Cut the produced negative electrode for lithium ion secondary battery into a rectangle of 100mm in length and 10mm in width to make a test piece, and attach a cellophane tape (as defined in JIS Z1522) to the surface of the negative electrode mixture layer with the side having the negative electrode mixture layer face down. The stress when peeling off one end of the whole at a pulling rate of 50 mm / min in the vertical direction was measured (also, the cellophane tape was fixed to the test bench). The measurement was performed 3 times, the average value was obtained, and this was made into peel peel strength, and the following references | standards evaluated. It shows that the adhesiveness of a negative electrode mixture layer and an electrical power collector is excellent, so that the value of peeling peeling strength is large.

A: Peeling peel strength is 5N / m or more

B: Peel peel strength is 4N / m or more and less than 5N / m

C: Peeling peel strength is 3N / m or more and less than 4N / m

D: peel peel strength is less than 3N / m

<Output characteristics>

The produced lithium ion secondary battery was left still for 24 hours in 25 degreeC environment from the time of pouring electrolyte solution. Thereafter, charging operation was performed at 0.1C for 5 hours in an environment at 25 ° C, and the voltage V0 when one hour had elapsed after charging was measured. Thereafter, the discharge operation was performed at a discharge rate of 0.2 C in an environment of -30 ° C, and the voltage V1 15 seconds after the start of discharge was measured. And the voltage change represented by (DELTA) V = V0-V1 was calculated | required and the following reference | standard evaluated. The smaller this voltage change, the smaller the internal resistance and the better the low temperature output characteristics.

A: voltage change ΔV is less than 0.6V

B: voltage change ΔV is 0.6 V or more and less than 0.7 V

C: voltage change ΔV is 0.7 V or more and less than 0.8 V

D: voltage change ΔV is 0.8 V or more

<Cycle characteristics>

The produced lithium ion secondary battery was left to stand in 25 degreeC environment for 5 hours from the time of pouring the electrolyte solution. Thereafter, charging / discharging operation of charging to 4.2V and discharging up to 3.0V by a constant current / constant voltage method of 0.2C in a 25 ° C. environment was performed to measure the initial discharge capacity C0. In addition, the charging and discharging cycle of charging to 4.2V and discharging up to 3.0V by a constant current / constant voltage method of 0.5C in a 60 ° C environment was repeated, and the discharge capacity C1 after 100 cycles was measured. And the cycle characteristic was evaluated by the capacity retention ratio represented by (DELTA) C = (C1 / C0) * 100 (%). The higher the value of the capacity retention rate, the smaller the decrease in discharge capacity and the better the cycle characteristics.

A: Capacity retention rate ΔC is 80% or more

B: Capacity retention ΔC is 75% or more but less than 80%

C: Capacity retention ΔC is 70% or more but less than 75%

D: Capacity retention ΔC is less than 70%

(Example 1)

<Preparation of the binder composition for lithium ion secondary battery negative electrodes>

In the pressure-resistant container A equipped with a stirrer, 57.4 parts of styrene as an aromatic vinyl monomer, 1,3-butadiene as an aliphatic conjugated diene monomer, 2.6 parts of itaconic acid as an ethylenically unsaturated carboxylic acid monomer, 50 parts of ion-exchanged water, t as a chain transfer agent 0.4 parts of dodecyl mercaptan (TDM), 0.6 parts of ammonium persulfate as polymerization initiator, and 0.2 parts of sodium dodecylbenzenesulfonate as alkylbenzene sulfonic acid-based surfactant were added and stirred to obtain emulsion A. Subsequently, 100 parts of ion-exchange water and 0.25 parts of sodium dodecyl diphenyl ether disulfonate as a diphenyl ether type surfactant were thrown into the pressure-resistant container B with a stirrer, and it stirred. Then, it heated at 75 degree | times, 10 parts of ion-exchange water and 0.6 part of ammonium persulfate were added as a polymerization initiator, and the mixture B was obtained. The emulsion A was continuously added to the mixture B over 240 minutes. After the addition of the emulsion A was completed, the temperature was raised to 90 ° C, the reaction was carried out for 240 minutes, the reaction was stopped when the polymerization conversion rate reached 99.0%, and the reaction was stopped to obtain an aqueous dispersion of the adhesive polymer. Subsequently, after adding 0.5 part of sodium polyacrylate (Toagosei Co., Aaron T-50) as a dispersion stabilizer to this aqueous dispersion, pH was adjusted to 8.5 with ammonia water, and the binder composition of 40% of solid content concentration was obtained. The THF gel content of this binder composition and the weight average molecular weight of THF melt | dissolution component were evaluated. The results are shown in Table 1.

<Preparation of the slurry composition for lithium ion secondary battery negative electrodes>

70 parts of artificial graphite (volume average particle diameter D50: 20 m, specific surface area: 4 m 2 / g) and Si-OC-based active material (volume average particle diameter D50: 10 m, specific ratio as a negative electrode active material in a disper-mounted planetary mixer 30 parts of surface area: 6 m <2> / g) and 5 parts of acetylene black were added as a electrically conductive material, and it mixed for 20 minutes using only the low speed blade | wing.

Subsequently, 1.0 part of carboxymethyl cellulose ("Daicel 1380" by Daiichi Kyosei Chemical Co., Ltd.) was added as a thickener, and it adjusted to 55% of solid content concentration with ion-exchanged water, and 60 at 25 degreeC as a thickener. Min mixed. Then, it adjusted to 52% of solid content concentration with ion-exchange water, and mixed at 25 degreeC for 15 minutes, and obtained the liquid mixture.

1.0 part of binder compositions mentioned above per 100 parts of negative electrode active materials were added to the said liquid mixture as solid content of an adhesive polymer. Furthermore, ion-exchange water was added, it adjusted so that final solid content concentration might be 48%, and it mixed for 10 minutes, and obtained the slurry composition for lithium ion secondary battery negative electrodes. The viscosity, dispersibility, foaming inhibition, and high speed coatability (smoothness and uniformity) of this slurry composition were evaluated. The results are shown in Table 1.

<Manufacture of negative electrode for lithium ion secondary battery>

The slurry composition for lithium ion secondary battery negative electrodes mentioned above was coated by the die cutter at the speed | rate of 30 m / min so that thickness may be about 200 micrometers on the single side | surface of the copper foil (current collector) of thickness 20micrometer. Then, it dried for 2 minutes at 60 degreeC, and also heat-processed at 120 degreeC for 2 minutes, and obtained the negative electrode raw material.

The negative electrode fabric was rolled to obtain a negative electrode for a lithium ion secondary battery having a thickness of the negative electrode mixture layer of 70 μm and a density of 1.7 g / cm 3. The adhesion between the negative electrode mixture layer and the current collector was evaluated using this negative electrode. The results are shown in Table 1.

<Production of Lithium Ion Secondary Battery>

The negative electrode obtained above was vacuum-dried at 80 degreeC for 10 hours, and was cut out to the disk shape of diameter 12mm. Separator (porous membrane made of polypropylene, disk shape, diameter 18mm, thickness 25㎛), positive electrode (lithium cobalt oxide, disk shape, diameter 10mm, thickness 75㎛) and expanded metal are placed on the negative electrode mixture layer side of the disk-shaped negative electrode. It laminated in order and obtained the laminated body. This laminated body was accommodated in the stainless steel coin-type exterior container (diameter 20mm, height 1.8mm, stainless steel thickness 0.25mm) provided with the polypropylene packing. Subsequently, an electrolyte solution is injected into the container, and the outer container is fixed by capping a 0.2 mm thick stainless steel cap through a polypropylene packing, and the outer container is sealed to obtain a lithium ion secondary battery having a diameter of 20 mm and a thickness of about 2 mm (coin). Cell type). The output characteristic and the cycle characteristic were evaluated about the obtained lithium ion secondary battery. The results are shown in Table 1.

(Example 2)

The amount of sodium dodecyl diphenyl ether disulfonate as a diphenyl ether surfactant and sodium dodecylbenzene sulfonate as an alkylbenzene sulfonic acid surfactant was changed as shown in Table 1, and sodium tripolyphosphate was substituted for sodium polyacrylate as a dispersion stabilizer. A binder composition, a slurry composition, a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that 1.0 part was used. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Examples 3 and 4)

A binder composition, a slurry composition, a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the amounts of TDM as the chain transfer agent were changed to 0.50 parts and 0.35 parts, respectively. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Examples 5 and 6)

Except for changing the amount of sodium dodecyl diphenyl ether disulfonate as a diphenyl ether surfactant and sodium dodecylbenzene sulfonate as an alkylbenzene sulfonic acid surfactant as shown in Table 1 (the surfactant content ratio was the same as 4) and a binder composition, a slurry composition, a negative electrode, and the lithium ion secondary battery were produced like Example 1. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Example 7, 8)

Except for changing the amounts of sodium dodecyl diphenyl ether disulfonate as a diphenyl ether surfactant and sodium dodecylbenzene sulfonate as an alkylbenzene sulfonic acid surfactant as shown in Table 1 (surfactant ratios are 1/4 and 4, respectively). In the same manner as in Example 1, a binder composition, a slurry composition, a negative electrode, and a lithium ion secondary battery were produced. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Example 9)

A binder composition, a slurry composition, a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that sodium polyacrylate and sodium tripolyphosphate as the dispersion stabilizers were used in the amounts shown in Table 1. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Example 10)

A binder composition, a slurry composition, a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that sodium polyacrylate as the dispersion stabilizer was not used. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Examples 11 and 12)

A binder composition and a slurry were prepared in the same manner as in Example 1, except that the amount of ion-exchanged water added during preparation of the slurry composition was changed so that the solid content concentration of the slurry composition for lithium ion secondary battery negative electrodes was 52% and 43%, respectively. The composition, the negative electrode, and the lithium ion secondary battery were produced. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Comparative Example 1)

A binder composition, a slurry composition, a negative electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the polymerization reaction of the adhesive polymer was stopped at a polymerization conversion rate of 90%. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Comparative Examples 2-4)

The amount of TDM as a chain transfer agent was changed to 0.50 part, 0.60 part, and 0.30 part, respectively, and for Comparative Examples 2 and 3, Example 1 and 3 were used in addition to divinylbenzene, which is a crosslinking agent, as an aromatic vinyl monomer. In the same manner, a binder composition, a slurry composition, a negative electrode, and a lithium ion secondary battery were produced. And it evaluated similarly to Example 1. The results are shown in Table 1.

(Comparative Examples 5 and 6)

Binder composition and slurry in the same manner as in Example 1 except that the amounts of sodium dodecyl diphenyl ether disulfonate as diphenyl ether surfactant and sodium dodecylbenzene sulfonate as alkyl benzene sulfonic acid surfactant were changed as shown in Table 1, respectively. The composition, the negative electrode, and the lithium ion secondary battery were produced. And it evaluated similarly to Example 1. The results are shown in Table 1.

In addition, in Table 1,

`` ST '' represents styrene,

"DVB" represents divinylbenzene,

"BD" represents 1,3-butadiene,

"IA" represents itaconic acid,

"DPES" represents sodium dodecyldiphenyletherdisulfonate,

"DBS" represents sodium dodecylbenzenesulfonate,

"SPA" represents sodium polyacrylate,

"STPP" represents sodium tripolyphosphate,

"THF" represents tetrahydrofuran.

From Examples 1-12 and Tables 1-6 of Table 1, it turns out that in Examples 1-12, dispersibility is raised, suppressing foaming of a slurry composition, and ensuring the outstanding high speed coating property can be ensured. Moreover, in Examples 1-12, it is understood that the adhesiveness of an electrode mixture layer and an electrical power collector is fully ensured, and in addition, a lithium ion secondary battery can exhibit the outstanding battery characteristic (output characteristic, cycling characteristic).

Here, by adjusting the THF gel content of the binder composition and the weight average molecular weight of the THF dissolving component from Examples 1, 3 and 4 of Table 1, dispersibility of the slurry composition, high-speed coating property and suppression of foam generation, electrode mixture layer and current collector It turns out that the adhesiveness of and the battery characteristic of a lithium ion secondary battery can be improved further.

In addition, from Examples 1, 5, and 6 of Table 1, the dispersibility, high speed coatability, and foaming of the slurry composition were adjusted by adjusting the total amount of two kinds of surfactants (diphenyl ether surfactant and alkylbenzene sulfonic acid surfactant). It turns out that generation | occurrence | production suppression, adhesiveness of an electrode mixture layer and an electrical power collector, and the battery characteristic of a lithium ion secondary battery can be improved further.

And from Examples 1, 7, and 8 of Table 1, the dispersibility of a slurry composition, high speed coating property, and the amount of two types of surfactant (diphenyl ether type surfactant and alkylbenzene sulfonic acid type surfactant) are adjusted. It can be seen that foam generation suppression, adhesion between the electrode mixture layer and the current collector, and battery characteristics of the lithium ion secondary battery can be further improved.

In addition, from Examples 1, 2, 9, and 10 of Table 1, by using a dispersion stabilizer, dispersibility of the slurry composition, high-speed coating property and foam generation suppression, adhesion between the electrode mixture layer and the current collector, and the lithium ion secondary battery It can be seen that the battery characteristics can be further improved. It is clear from Examples 1, 2, and 9 that the dispersibility of the slurry composition can be further improved by using two kinds of polyacrylic acid compounds and phosphoric acid compounds together as dispersion stabilizers.

In addition, from Examples 1, 11 and 12 of Table 1, by controlling the solid content concentration of the slurry composition, high-speed coating property and foam generation suppression of the slurry composition, adhesion between the electrode mixture layer and the current collector, and output characteristics of the lithium ion secondary battery It can be seen that can be further improved.

Industrial availability

According to the present invention, it is possible to provide a binder composition for a lithium ion secondary battery electrode capable of increasing dispersibility while suppressing foaming of the slurry composition for a lithium ion secondary battery electrode and providing excellent high speed coating property to the slurry composition. .

According to the present invention, it is possible to provide a slurry composition for a lithium ion secondary battery electrode which exhibits excellent dispersibility and exhibits excellent high-speed coating properties while suppressing bubble generation.

According to this invention, the electrode for lithium ion secondary batteries which can exhibit the outstanding battery characteristic to a lithium ion secondary battery, and the lithium ion secondary battery provided with the said electrode can be provided.

Claims (10)

An adhesive polymer, a diphenyl ether type surfactant, an alkylbenzene sulfonic acid type surfactant, and a solvent,
THF gel content is 70 mass% or more and 95 mass% or less,
The weight average molecular weight of the THF dissolving component is 5000 or more and 40000 or less,
And the ratio of the blending amount of the diphenyl ether surfactant to the blending amount of the alkylbenzene sulfonic acid surfactant is 1/9 or more and 9 or less,
The total compounding quantity of the said diphenyl ether type surfactant and the said alkylbenzene sulfonic acid type surfactant is 0.2 mass part or more and 0.5 mass parts or less per 100 mass parts of said adhesive polymers,
The binder composition for lithium ion secondary battery electrodes containing 0.5 mass part or more and 1.5 mass parts or less of phosphoric acid compound per 100 mass parts of said adhesive polymers.
The method of claim 1,
The binder composition for lithium ion secondary battery electrodes containing 0.1 mass part or more and 1 mass part or less of polyacrylic acid compounds per 100 mass parts of said adhesive polymers.
The method of claim 1,
The binder composition for lithium ion secondary battery electrodes in which the said adhesive polymer contains an aromatic vinyl monomer unit and an aliphatic conjugated diene monomer unit.
The method of claim 3, wherein
The binder composition for lithium ion secondary battery electrodes in which the said adhesive polymer further contains 0.1 mass% or more and 10 mass% or less of ethylenic unsaturated carboxylic monomer unit.
The slurry composition for lithium ion secondary battery electrodes containing the binder composition for lithium ion secondary battery electrodes and electrode active material in any one of Claims 1-4.
The method of claim 5,
The slurry composition for lithium ion secondary battery electrodes whose viscosity is 500 mPa * s or more and 3500 mPa * s or less, and solid content concentration is 40 mass% or more and 55 mass% or less.
The electrode for lithium ion secondary batteries provided with the electrode mixture layer prepared using the slurry composition for lithium ion secondary battery electrodes of Claim 5 on an electrical power collector.
A lithium ion secondary battery provided with a positive electrode, a negative electrode, electrolyte solution, and a separator, and at least one of the said positive electrode and a negative electrode is the electrode for lithium ion secondary batteries of Claim 7. delete delete