JP2016048633A - Slurry composition for lithium ion secondary battery negative electrode, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium ion secondary battery, which enables the suppression of the expansion accompanying the charge and discharge thereof and enables the enhancement in electric characteristics including a lithium ion secondary battery cycle characteristic even in the case of using a negative electrode active material including a silicon-based negative electrode active material to increase a battery capacity.SOLUTION: A slurry composition for a lithium ion secondary battery negative electrode comprises: a Si-containing negative electrode active material; a particulate polymer; an alginate; and water. The slurry composition includes 5 pts.mass or more of the alginate to 100 pts.mass of the particulate polymer.SELECTED DRAWING: None

Description

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

  Lithium ion secondary batteries are small and lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion secondary batteries.

  Here, the electrode for lithium ion secondary batteries is normally provided with the electrical power collector and the electrode compound-material layer formed on the electrical power collector. For example, the electrode mixture layer is formed on a current collector with a slurry composition obtained by dispersing an electrode active material and a binder (binder) and a conductive material blended as necessary in a dispersion medium. It is formed by applying and drying. Therefore, in recent years, attempts have been made to improve various materials blended in the slurry composition used for forming the electrode mixture layer in order to achieve further performance improvement of the lithium ion secondary battery.

  For example, it has been proposed to improve the performance of a lithium ion secondary battery by improving the formulation of the slurry composition for a negative electrode used for forming a negative electrode for a lithium ion secondary battery. Specifically, the slurry composition is collected by using a slurry composition for a negative electrode containing a carbon material active material and a binder composed of a water-dispersed emulsion resin having a specific property and a water-soluble polymer. It has been proposed to improve the film-forming property when applied to a body and to improve the cycle characteristics of a lithium ion secondary battery (see, for example, Patent Document 1). In addition, by using a slurry composition for negative electrode containing a semi-synthetic water-soluble polymer such as cellulose polymer having specific properties and polymer particles having specific properties, the coating property of the slurry composition is improved and lithium is added. It has been proposed to improve the manufacturability of ion secondary batteries (see, for example, Patent Document 2).

JP 2003-308441 A JP 2011-34962 A

Incidentally, in recent years, it has been proposed to employ a silicon-based negative electrode active material as a negative electrode active material from the viewpoint of increasing the capacity of a lithium ion secondary battery for a negative electrode for a lithium ion secondary battery. However, a negative electrode active material including a silicon-based negative electrode active material is likely to expand and contract with charge / discharge. Therefore, a negative electrode for a lithium ion secondary battery using a negative electrode active material containing a silicon-based negative electrode active material is prone to swelling of the negative electrode from the beginning when charging and discharging are repeated, and the lithium ion secondary battery using the negative electrode However, electrical characteristics such as cycle characteristics are likely to deteriorate.
Therefore, in the lithium ion secondary battery, even when a negative electrode active material containing a silicon-based negative electrode active material is used, the swelling of the negative electrode accompanying charge / discharge is suppressed, and the electrical characteristics such as cycle characteristics are improved. It is requested to do.

  However, when the negative electrode active material is changed to a negative electrode active material containing a silicon-based negative electrode active material in the conventional negative electrode slurry composition, the negative electrode formed sufficiently suppresses the swelling of the negative electrode accompanying charge / discharge. It was not possible to improve electrical characteristics such as cycle characteristics.

Therefore, the present invention can suppress swelling due to charging / discharging even when the battery capacity is increased by using a negative electrode active material containing a silicon-based negative electrode active material, and also provides cycle characteristics of a lithium ion secondary battery. It aims at providing the negative electrode for lithium ion secondary batteries which can improve electrical characteristics, such as. Moreover, an object of this invention is to provide the slurry composition for lithium ion secondary battery negative electrodes which can form the said negative electrode for lithium ion secondary batteries.
Furthermore, an object of the present invention is to provide a lithium ion secondary battery that can suppress swelling of the negative electrode and is excellent in electrical characteristics such as cycle characteristics.

  The inventor has intensively studied to achieve the above object. Then, the inventor of the present invention has a slurry composition containing a negative electrode active material containing Si (hereinafter sometimes referred to as “silicon-based negative electrode active material”), a particulate polymer, and a predetermined amount of alginate. Can suppress swelling of the negative electrode accompanying charge / discharge even when a negative electrode active material containing a silicon-based negative electrode active material is used, and improve the electrical characteristics of the lithium ion secondary battery The present invention has been completed by newly discovering that it is possible.

  That is, this invention aims to solve the above-mentioned problem advantageously, and the slurry composition for a lithium ion secondary battery negative electrode of the present invention comprises a negative electrode active material containing Si and a particulate polymer. And alginate and water, and 5 parts by mass or more of the alginate per 100 parts by mass of the particulate polymer. Thus, by using the slurry composition containing the negative electrode active material containing Si, the particulate polymer, and the alginate in a predetermined ratio, it is possible to suppress swelling associated with charge / discharge and lithium ion A negative electrode for a lithium ion secondary battery that can improve the electrical characteristics of the secondary battery can be formed.

Here, in the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, the negative electrode active material containing Si preferably contains a silicon oxide represented by SiO _x (0 <x <2). This is because the use of such a negative electrode active material can further increase the capacity of the lithium ion secondary battery produced using the slurry composition.

  In the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, the surface acid amount of the particulate polymer is preferably 0.25 mmol / g or more and 3.0 mmol / g or less. If the surface acid amount of the particulate polymer is within the above range, the swelling of the negative electrode formed using the slurry composition is sufficiently suppressed and the cycle characteristics of the lithium ion secondary battery having such a negative electrode are improved. Because you can.

  Furthermore, in the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, the THF gel content of the particulate polymer is preferably 80% by mass or more and 98% by mass or less. If the THF gel content of the particulate polymer is within the above range, the swelling of the negative electrode formed using the slurry composition is further suppressed, and the cycle characteristics of the lithium ion secondary battery having such a negative electrode are further improved. Because it can.

  And the slurry composition for lithium ion secondary battery negative electrodes of this invention WHEREIN: As for the said alginate, it is preferable that the viscosity of 10 mass% aqueous solution is 5 mPa * s or more and 1000 mPa * s or less. By controlling the viscosity of a 10% by mass aqueous solution of alginate within the above range, the swelling of the negative electrode formed using the slurry composition is further suppressed, and the cycle characteristics of the lithium ion secondary battery having such a negative electrode are further improved. It is because it can be made. Moreover, it is because it can suppress that stability of a slurry composition falls.

  Moreover, it is preferable that the slurry composition for lithium ion secondary battery negative electrodes of this invention contains the water-soluble polymer whose viscosity of 1 mass% aqueous solution is 1000 mPa * s or more and 5000 mPa * s or less further. By including a water-soluble polymer having a viscosity of 1% by mass in the above range, the swelling of the negative electrode formed using the slurry composition is further suppressed while suppressing an increase in the internal resistance of the lithium ion secondary battery. Because it can.

  Moreover, this invention aims at solving the said subject advantageously, The negative electrode for lithium ion secondary batteries of this invention is either of the slurry composition for lithium ion secondary battery negative electrodes mentioned above. A negative electrode mixture layer is formed on the current collector by coating the current collector and drying the lithium ion secondary battery negative electrode slurry composition coated on the current collector. To do. Thus, if the negative electrode mixture layer is formed using the above-described slurry composition for a negative electrode of a lithium ion secondary battery, swelling of the negative electrode accompanying charge / discharge can be suppressed, and lithium ion using the negative electrode can be used. The electrical characteristics of the secondary battery can be improved.

  And this invention aims at solving the said subject advantageously, The lithium ion secondary battery of this invention is the negative electrode for lithium ion secondary batteries mentioned above, a positive electrode, electrolyte solution, And a separator. If the negative electrode for lithium ion secondary batteries described above is used, the swelling of the negative electrode accompanying repeated charge / discharge can be suppressed, and excellent electrical characteristics can be obtained.

According to the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, even if the battery capacity is increased by using a negative electrode active material containing a silicon-based negative electrode active material, the swelling associated with charge / discharge is suppressed. In addition, it is possible to form a negative electrode for a lithium ion secondary battery that can improve electrical characteristics such as cycle characteristics of the lithium ion secondary battery.
Moreover, according to the negative electrode for lithium ion secondary batteries of this invention, even if it is a case where battery capacity is increased using the negative electrode active material containing a silicon type negative electrode active material, the swelling accompanying the repetition of charging / discharging is suppressed. In addition, the electrical characteristics such as the cycle characteristics of the lithium ion secondary battery can be improved.
And according to the lithium ion secondary battery of this invention, even if it is a case where battery capacity is increased using the negative electrode active material containing a silicon type negative electrode active material, the swelling of the negative electrode accompanying the repetition of charging / discharging is suppressed. And excellent electrical characteristics can be obtained.

When calculating the surface acid amount of a particulate polymer, it is the graph which plotted the electric conductivity (mS) with respect to the cumulative amount (mmol) of the added hydrochloric acid.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention is used when forming a negative electrode of a lithium ion secondary battery. And the negative electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for lithium ion secondary batteries negative electrode of this invention. The lithium ion secondary battery of the present invention is characterized by using the negative electrode for a lithium ion secondary battery of the present invention.

(Slurry composition for negative electrode of lithium ion secondary battery)
The slurry composition for a negative electrode of a lithium ion secondary battery of the present invention includes a negative electrode active material containing Si, a particulate polymer, an alginate, and water, and optionally further includes a water-soluble polymer. And the slurry composition for lithium ion secondary battery negative electrodes of this invention is characterized by containing 5 mass parts or more of alginates per 100 mass parts of particulate polymers.

<Negative electrode active material>
The negative electrode active material is an electrode active material for a negative electrode, and is a material that transfers electrons in the negative electrode of a lithium ion secondary battery.
The slurry composition of the present invention includes at least a negative electrode active material containing silicon (Si) as a negative electrode active material. By using the negative electrode active material containing Si, the capacity of the lithium ion secondary battery can be increased.

Examples of the negative electrode active material containing Si include silicon, an alloy of silicon and cobalt, nickel, iron, and the like, and a material containing Si such as SiO _x (hereinafter, also referred to as “Si-containing material”). Examples thereof include composites of Si-containing material and conductive carbon obtained by coating or compounding Si-containing material with conductive carbon. Among them, the slurry composition of the present invention is preferably a negative electrode active material containing Si is silicon oxide represented by _{SiO x (0 <x <2} ). This is because the capacity of the lithium ion secondary battery produced using the slurry composition of the present invention can be increased.

Here, SiO _x can be formed using, for example, a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO _x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed in an inert gas atmosphere after grinding and mixing SiO and optionally a polymer.

Examples of the composite of the Si-containing material and the conductive carbon include a compound obtained by heat-treating, for example, a ground mixture of SiO, a polymer such as polyvinyl alcohol, and an optional carbon material in an inert gas atmosphere. be able to. Here, when the temperature at which the pulverized mixture is heat-treated is high (for example, 900 ° C. or higher), SiO disproportionate in a matrix of conductive carbon made of carbonized polymer or a carbon material blended as an optional component. A composite (Si—SiO _x —C composite) in which SiO _x produced by the chemical reaction is dispersed is produced. Moreover, when the temperature at which the pulverized mixture is heat-treated is relatively low, a composite (SiO-C) in which a part of Si in SiO is replaced with conductive carbon is generated.

  Here, when the negative electrode active material containing Si is used, the negative electrode active material containing Si greatly expands and contracts with charge and discharge. Therefore, the negative electrode manufactured using the negative electrode active material containing Si is likely to lose its electrode plate structure, and there is a possibility that the conductive path may be interrupted at the initial stage of use of the lithium ion secondary battery. Therefore, normally, when a lithium ion secondary battery is manufactured using a negative electrode active material containing Si, when the obtained lithium ion secondary battery is subjected to a cycle test, rapid capacity deterioration occurs from the beginning of the test. There was a problem. However, in the negative electrode formed using the slurry composition of the present invention, since the negative electrode active material containing Si, the particulate polymer, and a predetermined amount or more of the alginate are used in combination, the initial use in the lithium ion secondary battery is started. The battery characteristics of the lithium ion secondary battery can be sufficiently improved by suppressing the rapid capacity deterioration.

  In addition to the negative electrode active material containing Si described above, the slurry composition of the present invention may contain another negative electrode active material capable of inserting and extracting lithium as the negative electrode active material. Examples of such other negative electrode active materials include carbon-based negative electrode active materials, metal-based negative electrode active materials other than Si, and negative electrode active materials obtained by combining these.

  As a mixture of a negative electrode active material containing Si and a carbon-based negative electrode active material, the negative electrode active material containing Si described above, and a material that can be used as a carbon-based negative electrode active material such as a carbonaceous material or a graphite material, Are optionally pulverized and mixed in the presence of a polymer such as polyvinyl alcohol. Here, the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton, into which lithium can be inserted (also referred to as “dope”).

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.
Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitic carbon having a structure close to an amorphous structure typified by glassy carbon. .
Here, as the graphitizable carbon, for example, a carbon material using tar pitch obtained from petroleum or coal as a raw material can be mentioned. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, pyrolytic vapor grown carbon fibers, and the like.
In addition, examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.

The graphite material is a material having high crystallinity close to that of graphite obtained by heat-treating graphitizable carbon at 2000 ° C. or higher. In addition, although the upper limit of heat processing temperature is not specifically limited, For example, it can be 5000 degrees C or less.
Examples of the graphite material include natural graphite and artificial graphite.
Here, as the artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2500 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, and mesophase pitch-based carbon fiber at 2000 ° C. Examples thereof include graphitized mesophase pitch-based carbon fibers that have been heat-treated.

  In addition, when using the mixture of a carbon-type negative electrode active material and the negative electrode active material containing Si as a negative electrode active material, artificial graphite can be used as a carbon-type negative electrode active material, for example.

  Furthermore, when a mixture of a carbon-based negative electrode active material and a negative electrode active material containing Si is used as the negative electrode active material, from the viewpoint of sufficiently suppressing deterioration of cycle characteristics while increasing the capacity of the lithium ion secondary battery, The negative electrode active material preferably includes 1 part by mass or more and 15 parts by mass or less of the negative electrode active material containing Si, with the total amount of the negative electrode active material containing Si and the carbon-based negative electrode active material being 100 parts by mass. It is particularly preferable to contain 10 parts by mass or more and 10 parts by mass or less. It is because the capacity of the lithium ion secondary battery can be sufficiently increased by containing 1 part by mass or more of the negative electrode active material containing Si. Moreover, if the content of the negative electrode active material containing Si is 15 parts by mass or less, deterioration of the cycle characteristics of the lithium ion secondary battery can be sufficiently suppressed.

  Furthermore, examples of the metal-based negative electrode active material that can be used in combination with the Si-containing negative electrode active material described above include known metal-based negative electrode active materials as described in JP2013-012357A.

  Here, the particle size and specific surface area of the negative electrode active material are not particularly limited, and can be the same as those of conventionally used negative electrode active materials.

<Particulate polymer>
In the negative electrode produced by forming the negative electrode mixture layer on the current collector using the slurry composition of the present invention, the particulate polymer is separated from the negative electrode mixture layer in the components contained in the negative electrode mixture layer. It is a component that can be retained so that it does not. In general, when the particulate polymer in the negative electrode mixture layer is immersed in the electrolytic solution, the particulate polymer maintains the particulate shape while absorbing and swelling the electrolytic solution, and binds the negative electrode active materials to each other. , Acts as a binder to prevent the negative electrode active material from falling off the current collector. The particulate polymer also binds particles other than the negative electrode active material contained in the negative electrode mixture layer, and also plays a role of maintaining the strength of the negative electrode mixture layer. The particulate polymer is insoluble in water. Here, the particulate polymer being “water-insoluble” means that when 0.5 g of the compound is dissolved in 100 g of water at 25 ° C., the insoluble content becomes 90% by mass or more.

[Surface acid amount of particulate polymer]
Here, the particulate polymer used in the slurry composition of the present invention preferably has a surface acid amount of 0.25 mmol / g or more, more preferably 0.5 mmol / g or more, and 1.0 mmol. / G or more is more preferable, 3.0 mmol / g or less is preferable, 2.8 mmol / g or less is more preferable, and 2.5 mmol / g or less is more preferable.
When the surface acid amount of the particulate polymer is less than 0.25 mmol / g, the strength of the negative electrode having the electrode mixture layer obtained by using the slurry composition of the present invention is lowered, and the negative electrode swells due to charge and discharge. May not be sufficiently suppressed. On the other hand, when the surface acid amount of the particulate polymer exceeds 3.0 mmol / g, the adhesion between the negative electrode mixture layer obtained using the slurry composition of the present invention and the current collector is reduced, and the negative electrode composite is reduced. There is a possibility that the cycle characteristics of the lithium ion secondary battery having the material layer and the current collector are deteriorated. Therefore, by setting the surface acid amount of the particulate polymer in the slurry composition of the present invention within the above-mentioned range, the negative electrode formed using the slurry composition is sufficiently suppressed and the negative electrode is provided. The cycle characteristics of the lithium ion secondary battery can be sufficiently improved.
In the present invention, the “surface acid amount” of the particulate polymer means the surface acid amount per 1 g of the solid content of the particulate polymer, and is measured using the measuring method described in the examples of the present specification. be able to.

[THF gel content of particulate polymer]
Furthermore, the particulate polymer used in the slurry composition of the present invention preferably has a tetrahydrofuran (THF) gel content of 80% by mass or more, more preferably 88% by mass or more, and 98% by mass or less. It is preferable that it is 96 mass% or less. When the THF gel content of the particulate polymer is less than 80% by mass, the strength of the negative electrode having the negative electrode mixture layer obtained by using the slurry composition of the present invention decreases, and the negative electrode swells due to charge / discharge. There is a possibility that it cannot be sufficiently suppressed. On the other hand, when the THF gel content of the particulate polymer exceeds 98% by mass, the adhesion between the negative electrode mixture layer obtained using the slurry composition of the present invention and the current collector is reduced, and the negative electrode mixture The cycle characteristics of the lithium ion secondary battery having the layer and the current collector may be deteriorated. Therefore, by making the THF gel content of the particulate polymer in the slurry composition of the present invention within the above range, it is possible to sufficiently suppress swelling of the negative electrode formed using such a slurry composition and The cycle characteristics of the lithium ion secondary battery can be sufficiently improved.
In the present invention, the “THF gel content” of the particulate polymer can be measured using the measuring method described in the examples of the present specification.

Here, examples of the particulate polymer used in the slurry composition of the present invention include known polymers such as a diene polymer, an acrylic polymer, and a silicon polymer. These polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
Among these, as the particulate polymer, it is preferable to use a diene polymer, particularly a copolymer having an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit, or a hydrogenated product thereof. An aliphatic conjugated diene monomer unit that is a low-rigidity and flexible repeating unit that can enhance the binding property, and the solubility of the polymer in the electrolytic solution is reduced to form particles in the electrolytic solution. This is because a copolymer having an aromatic vinyl monomer unit capable of enhancing the stability of the polymer can satisfactorily function as a binder.
In the present invention, “comprising a monomer unit” means “a monomer-derived structural unit is contained in a polymer obtained using the monomer”.
In the following, as an example, for the case where a copolymer having an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit is used as the particulate polymer, each monomer unit constituting the particulate polymer is explain. The particulate polymer used in the present invention is not limited to a copolymer having an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit.

[Aromatic vinyl monomer unit]
The aromatic vinyl monomer that can form the aromatic vinyl monomer unit of the particulate polymer is not particularly limited, and examples thereof include styrene, α-methylstyrene, vinyl toluene, and divinylbenzene. Styrene is preferred. 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.

  The content ratio of the aromatic vinyl monomer unit in the particulate polymer is preferably 25% by mass or more, based on 100% by mass of all monomer units contained in the particulate polymer. It is more preferably at least mass%, preferably at most 50 mass%, more preferably at most 45 mass%. If the content ratio of the aromatic vinyl monomer unit is out of the above range, the electrolyte solution resistance of the negative electrode mixture layer formed using the slurry composition may be insufficient, and the negative electrode mixture layer This is because the adhesiveness between the electrode and the current collector cannot be ensured, and the cycle characteristics may be deteriorated.

[Aliphatic conjugated diene monomer unit]
The aliphatic conjugated diene monomer that can form the aliphatic conjugated diene monomer unit of the particulate polymer is not particularly limited, and 1,3-butadiene, 2-methyl-1,3-butadiene, Examples include 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and among them, 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.

  Further, the content ratio of the aliphatic conjugated diene monomer unit in the particulate polymer is preferably 35% by mass or more, based on 100% by mass of all monomer units contained in the particulate polymer, It is more preferably 40% by mass or more, preferably 60% by mass or less, and more preferably 56% by mass or less. When the content of the aliphatic conjugated diene monomer unit is less than the above lower limit value, the flexibility of the particulate polymer cannot be ensured, and cycle characteristics may be deteriorated. The adhesion between the layer and the current collector cannot be ensured, and the cycle characteristics may also deteriorate.

  The particulate polymer may have a monomer unit other than the above-described aliphatic conjugated diene monomer unit and aromatic vinyl monomer unit.

  Specifically, the particulate polymer preferably contains an ethylenically unsaturated carboxylic acid monomer unit in addition to the aliphatic conjugated diene monomer unit and the aromatic vinyl monomer unit. The ethylenically unsaturated carboxylic acid monomer unit includes a carboxyl group (—COOH group) that enhances the adsorptivity to the negative electrode active material and the current collector, and is a repeating unit having high strength. Therefore, the particulate polymer having an ethylenically unsaturated carboxylic acid monomer unit can stably prevent the detachment of the negative electrode active material from the negative electrode mixture layer and can improve the strength of the negative electrode. .

Examples of the ethylenically unsaturated carboxylic acid monomer that can be used for the production of the particulate polymer having an ethylenically unsaturated carboxylic acid monomer unit include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itacone. Examples thereof include monocarboxylic acids and dicarboxylic acids such as acids, and anhydrides thereof. Among these, acrylic acid, methacrylic acid and itaconic acid are preferable as the ethylenically unsaturated carboxylic acid monomer from the viewpoint of the stability of the slurry composition of the present invention.
In addition, an ethylenically unsaturated carboxylic acid monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the particulate polymer, the content ratio of the ethylenically unsaturated carboxylic acid monomer unit is preferably 5% by mass or more, based on 100% by mass of all monomer units contained in the particulate polymer. Preferably it is 8 mass% or more, Especially preferably, it is 10 mass% or more, Preferably it is 40 mass% or less, More preferably, it is 30 mass% or less, Most preferably, it is 25 mass% or less. By making the content rate of an ethylenically unsaturated carboxylic acid monomer unit more than the said lower limit, stability of the slurry composition of this invention can be improved. Moreover, by setting it as the said upper limit or less, it can prevent that the viscosity of the slurry composition of this invention becomes high too much, and can make a slurry composition easy to handle.

  The particulate polymer is a styrene-butadiene copolymer containing a styrene unit as an aromatic vinyl monomer unit and a 1,3-butadiene unit as an aliphatic conjugated diene monomer unit. preferable.

  Further, the particulate polymer may contain any repeating unit other than those described above as long as the effects of the present invention are not significantly impaired. Examples of the monomer corresponding to the arbitrary repeating unit include a vinyl cyanide monomer, an unsaturated carboxylic acid alkyl ester monomer, an unsaturated monomer containing a hydroxyalkyl group, and an unsaturated carboxylic acid. And acid amide monomers. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like. Of these, acrylonitrile and methacrylonitrile are preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, and dimethyl itaco. Nate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. Of these, methyl methacrylate is preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Examples of the unsaturated monomer containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2- Examples include hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate and the like. Among these, 2-hydroxyethyl acrylate is preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide and the like. Of these, acrylamide and methacrylamide are preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Furthermore, the particulate polymer may contain any repeating unit other than these. For example, the particulate polymer may be produced using a monomer used in usual emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride and the like. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

And a particulate polymer is manufactured by superposing | polymerizing the monomer composition containing the monomer mentioned above in an aqueous solvent, for example.
Here, the content ratio of each monomer in the monomer composition is usually the same as the content ratio of the repeating unit in the desired particulate polymer.

The aqueous solvent is not particularly limited as long as the prepared particulate polymer is dispersible in a particle state, and usually has a boiling point at normal pressure of usually 80 ° C. or higher, preferably 100 ° C. or higher. It is usually selected from aqueous solvents at 350 ° C. or lower, preferably 300 ° C. or lower.
Specifically, examples of the aqueous solvent include water; ketones such as diacetone alcohol and γ-butyrolactone; alcohols such as ethyl alcohol, isopropyl alcohol, and normal propyl alcohol; propylene glycol monomethyl ether, methyl cellosolve, and ethyl cellosolve. Glycol ethers such as ethylene glycol tertiary butyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether; And ethers such as 3-dioxolane, 1,4-dioxolane and tetrahydrofuran; Among these, water is particularly preferred from the viewpoint that it is not flammable and a dispersion of particulate polymer particles can be easily obtained. In addition, water may be used as the main solvent, and an aqueous solvent other than the above water may be mixed and used within a range in which the dispersed state of the particulate polymer particles can be ensured.

  The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. As the polymerization format, any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used. Production efficiency, such as being easy to obtain a high molecular weight, and being able to be used in the production of a slurry composition as it is, since the polymer is obtained in the state of being dispersed in water, so that redispersion treatment is unnecessary. From this viewpoint, the emulsion polymerization method is particularly preferable. The emulsion polymerization can be performed according to a conventional method.

  And generally used emulsifiers, dispersants, polymerization initiators, polymerization aids, chain transfer agents and the like used for polymerization can be used, and the amount used is also generally used. In the polymerization, seed particles may be employed to perform seed polymerization, or batch polymerization or semi-batch polymerization may be performed. It is preferable to use semi-batch polymerization in which the monomer is continuously or intermittently added to the reaction system. By using semi-batch polymerization, it is possible to effectively control the THF gel content of the particulate polymer as compared to the case of using batch polymerization. In addition, by using semi-batch polymerization, the surface acid amount of the particulate polymer can be effectively controlled. The polymerization conditions can also be arbitrarily selected depending on the polymerization method and the type of polymerization initiator.

Here, the aqueous dispersion of particulate polymer particles obtained by the above-described polymerization method is, for example, alkali metal (for example, Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium compound (for example, NH ₄ Cl and the like) and a basic aqueous solution containing an organic amine compound (eg ethanolamine, diethylamine and the like) may be adjusted so that the pH is usually in the range of 5 to 10, preferably 5 to 9. . Among these, pH adjustment with an alkali metal hydroxide is preferable because it improves the binding property (peel strength) between the current collector and the negative electrode active material.

The above-mentioned THF gel content and surface acid amount can be appropriately adjusted by changing the preparation conditions of the particulate polymer (for example, the monomers used, the polymerization conditions, etc.).
Specifically, the surface acid amount of the particulate polymer can be controlled, for example, by changing the type and ratio of the monomer units constituting the particulate polymer and the polymerization method. More specifically, for example, the amount of surface acid can be efficiently controlled by adjusting the type and ratio of the ethylenically unsaturated carboxylic acid monomer unit. Normally, when ethylenically unsaturated carboxylic acid monomer having a large difference in reactivity with other monomers (such as itaconic acid) is used, the ethylenically unsaturated carboxylic acid monomer Since the copolymerization on the surface of the polymer is easy, the surface acid amount tends to increase. Furthermore, by employing the semi-batch polymerization described above, the surface acid amount of the particulate polymer can be effectively controlled.
Furthermore, the THF gel content can be adjusted by changing the polymerization temperature, the type of polymerization initiator, the conversion rate when the reaction is stopped (monomer consumption, etc.), for example, the chain transfer agent used during polymerization Decreasing the amount of a certain tert-dodecyl mercaptan (TDM) can increase the THF gel content, and increasing the TDM amount can decrease the THF gel content. Also, the THF gel content can be effectively controlled.

  In the slurry composition of the present invention, the particulate polymer having the properties and composition as described above is preferably added in an amount of 0.5 parts by mass or more per 100 parts by mass of the negative electrode active material containing the silicon-based negative electrode active material. Preferably it contains 0.8 parts by mass or more, preferably 10 parts by mass or less, more preferably 3 parts by mass or less. By setting the content of the particulate polymer to 0.5 parts by mass or more, sufficient adhesion between the negative electrode mixture layer and the current collector can be secured. Further, by controlling the content of the particulate polymer to 10 parts by mass or less, it is possible to suppress an increase in the internal resistance of the lithium ion secondary battery using the negative electrode formed using the slurry composition, The electrical characteristics of the secondary battery can be improved.

<Alginate>
The alginate is blended in the slurry composition of the present invention to suppress the swelling of the negative electrode produced using the slurry composition, and the rapid start of use in the lithium ion secondary battery using the negative electrode In addition to suppressing the capacity deterioration, it acts to sufficiently suppress the deterioration of the cycle characteristics of the lithium ion secondary battery.
And in the slurry composition of this invention, the compounding quantity of alginate needs to be 5 mass parts or more per 100 mass parts of particulate polymers mentioned above, 7 mass parts or more are preferable, and 15 mass parts or more are preferable. More preferably, it is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and particularly preferably 30 parts by mass or less. When the blending amount of the alginate in the slurry composition of the present invention is less than 5 parts by mass per 100 parts by mass of the particulate polymer, a rapid initial use in a lithium ion secondary battery produced using such a slurry composition is used. Capacitance deterioration and cycle characteristic deterioration cannot be sufficiently suppressed. Moreover, when the compounding amount of the alginate in the slurry composition of the present invention exceeds 50 parts by mass per 100 parts by mass of the particulate polymer, the internal resistance of the lithium ion secondary battery produced using the slurry composition increases. The cycle characteristics may be deteriorated. Therefore, the lithium ion manufactured using this slurry composition by making the compounding quantity of the alginate in the slurry composition of this invention into 5 mass parts or more per 100 mass parts of particulate polymers, Preferably it is 50 mass parts or less. It is possible to sufficiently suppress rapid capacity deterioration at the beginning of use of the secondary battery and to sufficiently improve cycle characteristics.

Here, in the alginate used for the production of the slurry composition of the present invention, the viscosity of a 10% by mass aqueous solution is preferably 5 mPa · s or more, more preferably 10 mPa · s or more, and 20 mPa · s or more. It is particularly preferably, 1000 mPa · s or less is preferred, 900 mPa · s or less is more preferred, and 700 mPa · s or less is particularly preferred. When the viscosity of a 10% by mass aqueous solution of an alginate used in the production of the slurry composition of the present invention is less than 5 mPa · s, the strength of the negative electrode formed using the slurry composition becomes insufficient, and charging and discharging are accompanied. There is a possibility that swelling of the negative electrode cannot be sufficiently suppressed. Further, when the viscosity of a 10% by mass aqueous solution of an alginate used in the production of the slurry composition of the present invention exceeds 1000 mPa · s, the particulate polymer blended in the slurry composition of the present invention aggregates, and the slurry composition There is a risk that the product may be difficult to prepare, and the cycle characteristics of the lithium ion secondary battery may be degraded.
The “viscosity of a 10% by mass aqueous solution” of alginate can be measured using the measurement method described in the examples of the present specification.

  There are no particular limitations on the alginates that can be used in blending the alginate with the slurry composition of the present invention, and common alkali salts such as ammonium, potassium, sodium, and lithium salts of alginic acid can be used. Can be mentioned. Among these, sodium salt and lithium salt are particularly preferable from the viewpoint of improving the electrical characteristics of the lithium ion secondary battery produced using the slurry composition of the present invention.

<Water-soluble polymer>
The water-soluble polymer that is an optional component elastically deforms following the expansion or contraction of the negative electrode active material when the negative electrode is formed using the slurry composition, and suppresses the swelling of the negative electrode due to charge / discharge. Furthermore, the water-soluble polymer can also function as a viscosity modifier that adjusts the viscosity of the slurry composition to facilitate application of the slurry composition onto the current collector.
Here, the polymer being water-soluble means that the insoluble content is less than 0.5% by mass when 0.5 g of the polymer is dissolved in 100 g of water at 25 ° C.

Here, as for the water-soluble polymer mix | blended with the slurry composition of this invention, it is preferable that the viscosity of 1 mass% aqueous solution is 1000 mPa * s or more, It is more preferable that it is 1300 mPa * s or more, 5000 mPa * s or less. It is preferable that it is 4000 mPa · s or less. When the viscosity of the 1% by mass aqueous solution of the water-soluble polymer to be blended with the slurry composition of the present invention is less than 1000 mPa · s, the strength of the negative electrode formed using the slurry composition becomes insufficient, and charging and discharging are accompanied. There is a possibility that swelling of the negative electrode cannot be sufficiently suppressed. Moreover, when the viscosity of a 1% by mass aqueous solution of the water-soluble polymer to be blended with the slurry composition of the present invention exceeds 5000 mPa · s, the internal resistance of the lithium ion secondary battery produced using the slurry composition increases. The cycle characteristics may be deteriorated. Therefore, by setting the viscosity of the 1% by mass aqueous solution of the water-soluble polymer to be blended in the slurry composition of the present invention within the above range, the swelling associated with charging / discharging of the negative electrode formed using such a slurry composition is sufficient. And the cycle characteristics of the lithium ion secondary battery having such a negative electrode can be sufficiently improved.
The “viscosity of a 1% by mass aqueous solution” of the water-soluble polymer can be measured using the measuring method described in the examples of the present specification.

  Here, the water-soluble polymer is not particularly limited, and examples thereof include a cellulose polymer, a polymer having an acidic group-containing monomer unit, and a mixture thereof.

  Examples of the cellulose polymer include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like. Among these, carboxymethyl cellulose is preferable from the viewpoint of improving the stability of the slurry composition.

Polymers having acidic group-containing monomer units include sulfonic acid polymers such as polystyrene sulfonic acid, ethylenically unsaturated carboxylic acid monomer units, (meth) acrylic acid ester monomer units, and fluorine-containing polymers. And a polymer containing a (meth) acrylic acid ester monomer unit. These monomer units are not particularly limited, and known ones can be used as long as the effects of the present invention are not impaired.
In the present specification, “(meth) acrylic acid” means acrylic acid and / or methacrylic acid. Among (meth) acrylic acid ester monomers, those containing fluorine are distinguished from (meth) acrylic acid ester monomers as fluorine-containing (meth) acrylic acid ester monomers.

  The water-soluble polymer as described above is preferably contained in the slurry composition at a ratio of 0.05 parts by mass or more per 100 parts by mass of the negative electrode active material containing a silicon-based negative electrode active material. 0.08 parts by mass or more is more preferable, 10 parts by mass or less is preferable, and 3 parts by mass or less is more preferable. This is because if the content of the water-soluble polymer is 0.05 parts by mass or more, the adhesion between the negative electrode mixture layer and the current collector can be improved while sufficiently suppressing the swelling of the negative electrode. Further, if the content of the water-soluble polymer is 10 parts by mass or less, the increase in the internal resistance of the lithium ion secondary battery using the negative electrode formed using the slurry composition is suppressed, and the lithium ion secondary This is because the electrical characteristics of the secondary battery can be improved.

<Other ingredients>
The slurry composition of this invention may contain components, such as a electrically conductive agent, a reinforcing material, a leveling agent, an electrolyte solution additive, other than the said component. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. Moreover, these components 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 of the present invention can be prepared by dispersing each of the above components in an aqueous medium as a dispersion medium. Specifically, the above components and the aqueous medium are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, or a fill mix. Thus, a slurry composition can be prepared. The particulate polymer can be added in the form of an aqueous dispersion.
Here, water is usually used as the aqueous medium, but an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used. The solid content concentration of the slurry composition is a concentration at which each component can be uniformly dispersed, for example, 30% by mass to 90% by mass, and more preferably 40% by mass to 80% by mass. Can do. Furthermore, mixing of each of the above-mentioned components and the aqueous medium can be usually carried out in the range of room temperature to 80 ° C. for 10 minutes to several hours.

(Anode for lithium ion secondary battery)
The negative electrode for lithium ion secondary batteries of the present invention can be produced using the slurry composition of the present invention.
The negative electrode for a lithium ion secondary battery according to the present invention includes a current collector and a negative electrode mixture layer formed on the current collector, and the negative electrode mixture layer includes at least a negative electrode active material containing Si. A substance, a particulate polymer, and an alginate are included. In addition, the negative electrode active material containing Si, the particulate polymer, and the alginate contained in the negative electrode were contained in the slurry composition of the present invention, and suitable for each of these components. The abundance ratio is the same as the preferred abundance ratio of each component in the slurry composition of the present invention.

  In the negative electrode for a lithium ion secondary battery according to the present invention, the negative electrode mixture layer contains a negative electrode active material containing Si, a particulate polymer, and an alginate, so that charging and discharging are repeated. The swelling can be suppressed and the electrical characteristics of the lithium ion secondary battery can be improved.

  The negative electrode for a lithium ion secondary battery of the present invention is applied, for example, to a step of applying the above-described slurry composition for a negative electrode of a lithium ion secondary battery on a current collector (application step), and a current collector. The lithium ion secondary battery negative electrode slurry composition is dried to form a negative electrode mixture layer on the current collector (drying step).

[Coating process]
A method for applying the slurry composition for a lithium ion secondary battery negative electrode on the current collector is not particularly limited, and a 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, or the like can be used. At this time, the slurry composition may be applied to only one side of the current collector or may be applied to both sides. The thickness of the slurry film on the current collector after coating and before drying can be appropriately set according to the thickness of the negative electrode mixture layer obtained by drying.

  Here, as the current collector to which the slurry composition is applied, an electrically conductive and electrochemically durable material is used. Specifically, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used. Among these, a copper foil is particularly preferable as the current collector used for the negative electrode. 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]
A method for drying the slurry composition on the current collector is not particularly limited, and a known method can be used. For example, drying with warm air, hot air, low-humidity air, vacuum drying, irradiation with infrared rays, electron beams, or the like. A drying method is mentioned. Thus, by drying the slurry composition on the current collector, a negative electrode mixture layer is formed on the current collector, and a negative electrode for a lithium ion secondary battery comprising the current collector and the negative electrode mixture layer is obtained. be able to.

Note that after the drying step, the negative electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the negative electrode mixture layer and the current collector can be improved.
Furthermore, when the negative electrode mixture layer contains a curable polymer, the polymer is preferably cured after the formation of the negative electrode mixture layer.

(Lithium ion secondary battery)
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the negative electrode for a lithium ion secondary battery of the present invention is used as the negative electrode. And since the lithium ion secondary battery of this invention uses the negative electrode for lithium ion secondary batteries of this invention, while being able to suppress the swelling of the negative electrode accompanying the repetition of charging / discharging, it was excellent in the electrical property. (In particular, cycle characteristics) can be obtained.

<Positive electrode>
As a positive electrode of a lithium ion secondary battery, a known positive electrode used as a positive electrode for a lithium ion secondary battery can be used. Specifically, as the positive electrode, for example, a positive electrode formed by forming a positive electrode mixture layer on a current collector can be used.
As the current collector, one made of a metal material such as aluminum can be used. Moreover, as a positive electrode compound material layer, the layer containing a known positive electrode active material, a electrically conductive material, and a binder can be used.

<Electrolyte>
As the electrolytic solution, an electrolytic solution in which an electrolyte is dissolved in a solvent can be used.
Here, as the solvent, an organic solvent capable of dissolving the electrolyte can be used. Specifically, examples of the solvent include alkyl carbonate solvents such as ethylene carbonate, propylene carbonate, γ-butyrolactone, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane. , Dioxolane, methyl propionate, methyl formate and the like can be used.
A lithium salt can be used as the electrolyte. As lithium salt, the thing as described in 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 a high degree of dissociation.

<Separator>
As a separator, the thing of Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among these, it is possible to reduce the thickness of the entire separator, thereby increasing the ratio of the electrode active material in the secondary battery and increasing the capacity per volume. A microporous film made of a resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred.

<Method for producing lithium ion secondary battery>
In the lithium ion secondary battery of the present invention, for example, a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the battery shape as necessary, and placed in the battery container. It can manufacture by inject | pouring electrolyte solution into and sealing. In order to prevent an increase in pressure inside the lithium ion secondary battery, overcharge / discharge, etc., an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. . The shape of the secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, and a flat shape.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, the surface acid amount and THF gel content of a particulate polymer, the viscosity of a 10% by weight aqueous solution of alginate, the viscosity of a 1% by weight aqueous solution of a water-soluble polymer, and a lithium ion secondary battery The initial swelling, initial cycle characteristics, cycle characteristics, and post-cycle swelling were evaluated using the following methods.

<Surface acid amount>
The surface acid amount of the particulate polymer is indicated by the amount of acid groups per gram of the particulate polymer.
First, an aqueous dispersion containing a particulate polymer (solid concentration 2%) is prepared. In a glass container having a capacity of 150 ml washed with distilled water, 50 g of the aqueous dispersion containing the particulate polymer is put into a solution conductivity meter (manufactured by Kyoto Electronics Co., Ltd .: CM-117, used cell type: K-121). Set and stir. Stirring is continued until addition of hydrochloric acid described later is completed.
Next, an aqueous 0.1 N sodium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd .: reagent grade) is used so that the electrical conductivity of the aqueous dispersion containing the particulate polymer is 2.5 to 3.0 mS. Add to aqueous dispersion containing particulate polymer. Thereafter, after 6 minutes, the electrical conductivity is measured. This value is the electrical conductivity at the start of measurement.
Further, 0.5 ml of 0.1 N hydrochloric acid is added to the aqueous dispersion containing the particulate polymer, and the electrical conductivity is measured after 30 seconds. Thereafter, 0.5 ml of 0.1 N hydrochloric acid is added again, and the electrical conductivity is measured after 30 seconds. This operation is repeated at intervals of 30 seconds until the electrical conductivity of the aqueous dispersion containing the particulate polymer becomes equal to or higher than the electrical conductivity at the start of measurement.
The obtained electric conductivity data is plotted on a graph with the electric conductivity (unit “mS”) on the vertical axis (Y coordinate axis) and the cumulative amount of added hydrochloric acid (unit “mmol”) on the horizontal axis (X coordinate axis). Plot. As a result, a hydrochloric acid amount-electric conductivity curve having three inflection points as shown in FIG. 1 is obtained. The X coordinates of the three inflection points are P1, P2, and P3 in order from the smallest value. Approximation lines L1, L2, and L3 are obtained by the least square method for the data in the three sections of the X coordinate from zero to coordinate P1, from coordinate P1 to coordinate P2, and from coordinate P2 to coordinate P3, respectively. Ask. The X coordinate of the intersection of the approximate straight line L1 and the approximate straight line L2 is A1 (mmol), and the X coordinate of the intersection of the approximate straight line L2 and the approximate straight line L3 is A2 (mmol).
The surface acid amount per 1 g of the particulate polymer is given as a value (mmol / g) in terms of hydrochloric acid from the following formula (a).
(A) Amount of surface acid per gram of particulate polymer = (A2-A1)

<THF gel content>
An aqueous dispersion containing a particulate polymer was prepared, and the aqueous dispersion was dried in an environment of 50% humidity and 23 to 25 ° C. to form a film having a thickness of 3 ± 0.3 mm. The film formed was cut into 1 mm square, and about 1 g was precisely weighed.
The mass of the film piece obtained by cutting is defined as w0. This piece of film was immersed in 100 g of tetrahydrofuran (THF) for 24 hours at 25 ° C. Then, the film piece pulled up from THF was vacuum-dried at 105 degreeC for 3 hours, and the mass w1 of insoluble matter was measured.
And THF gel content (mass%) was computed according to the following formula.
THF gel content (mass%) = (w1 / w0) × 100

<Viscosity of 10 mass% aqueous solution of alginate>
The viscosity of a 10% by mass aqueous solution of an alginate can be measured by preparing a 10% by mass aqueous solution of an alginate and using the B-type viscometer for the aqueous solution at 25 ° C. and a rotation speed of 60 rpm.
<Viscosity of 1% by weight aqueous solution of water-soluble polymer>
The viscosity of the 1% by weight aqueous solution of the water-soluble polymer is prepared by adjusting the water-soluble polymer by the adjusting method described later. Can be measured.

<Initial bulge>
The produced laminate cell type lithium ion secondary battery was allowed to stand in a 25 ° C. environment for 5 hours, and then charged at a rate of 4.2 V and 0.5 C in a 25 ° C. environment.
Thereafter, the charged cell was disassembled, the negative electrode was taken out, and the thickness (d1) of the negative electrode mixture layer was measured. Then, the change rate (initial bulging property = {(d1−d0) / d0} × 100 (%)) with respect to the thickness (d0) of the negative electrode (excluding the thickness of the current collector) before the production of the lithium ion secondary battery. And determined according to the following criteria. The smaller the initial bulge characteristic, the smaller the initial bulge of the negative electrode.
A: Initial swell characteristic is less than 30% B: Initial swell characteristic is 30% or more and less than 35% C: Initial swell characteristic is 35% or more and less than 40% D: Initial swell characteristic is 40% or more

<Initial cycle characteristics>
The prepared laminate cell type lithium ion secondary battery was allowed to stand for 5 hours in an environment of 25 ° C., and then charged and discharged at a charge / discharge rate of 4.2 V and 0.5 C in an environment of 25 ° C. The initial capacity C0 was measured. Furthermore, the same charge / discharge was repeated under an environment of 45 ° C., and the capacity C2 after 50 cycles was measured.
For the initial cycle characteristics, a capacity change rate ΔCC represented by ΔCC = (C2 / C0) × 100 (%) was calculated and evaluated according to the following criteria. The higher the capacity change rate ΔCC, the better the initial cycle characteristics.
A: ΔCC is 93% or more B: ΔCC is 88% or more and less than 93% C: ΔCC is 83% or more and less than 88% D: ΔCC is less than 83%

<Cycle characteristics>
The prepared laminate cell type lithium ion secondary battery was allowed to stand for 24 hours in an environment of 25 ° C., and then charged and discharged at a charge / discharge rate of 4.2 V and 0.5 C in an environment of 25 ° C. The initial capacity C3 was measured, and charging and discharging were repeated in an environment of 45 ° C., and the capacity C4 after 200 cycles was measured.
For the cycle characteristics, a capacity change rate ΔC represented by ΔC = (C4 / C3) × 100 (%) was calculated and evaluated according to the following criteria. It shows that it is excellent in cycle characteristics, so that the value of this capacity | capacitance change rate (DELTA) C is high.
A: ΔC is 86% or more B: ΔC is 80% or more and less than 86% C: ΔC is 75% or more and less than 80% D: ΔC is less than 75%

<Bulge after cycle>
The lithium ion secondary battery after the cycle characteristics were evaluated as described above was charged at 0.5 C in a 25 ° C. environment, the charged cell was disassembled, the negative electrode was taken out, and the negative electrode mixture layer The thickness (d2) of was measured. And the rate of change with respect to the thickness (d0) of the negative electrode (excluding the thickness of the current collector) before the production of the lithium ion secondary battery (post-cycle swelling characteristics = {(d2−d0) / d0} × 100 (%)) Was determined according to the following criteria. The smaller the bulge characteristic after cycling, the smaller the bulge of the negative electrode after cycling.
A: Swelling characteristic after cycle is less than 35% B: Swelling characteristic after cycle is 35% or more and less than 40% C: Swelling characteristic after cycle is 40% or more and less than 45% D: Swelling characteristic after cycle is 45% or more

(Example 1)
<Preparation of particulate polymer>
In a 5 MPa pressure vessel with a stirrer, 33 parts of styrene as an aromatic vinyl monomer, 46 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 20 parts of acrylic acid as an ethylenically unsaturated carboxylic acid monomer, hydroxy 1 part 2-hydroxyethyl acrylate as an unsaturated monomer containing an alkyl group, 0.3 part t-dodecyl mercaptan (TDM) as a chain transfer agent, 5 parts sodium dodecylbenzenesulfonate as an emulsifier, 150 parts ion-exchanged water And 1 part of potassium persulfate was added as a polymerization initiator, and after sufficiently stirring, the mixture was heated to 55 ° C. to initiate polymerization. The reaction was stopped by cooling when the monomer consumption reached 95.0%. The aqueous dispersion containing the polymer was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution. Then, the unreacted monomer was removed by heating under reduced pressure. Furthermore, it cooled to 30 degrees C or less after that, and obtained the aqueous dispersion of the particulate polymer.

<Preparation of slurry composition for negative electrode of lithium ion secondary battery>
In a planetary mixer with a disper, 95 parts of artificial graphite (“MAG-E” manufactured by Hitachi Chemical Co., Ltd., specific surface area: 4 m ² / g, volume average particle diameter: 24.5 μm) as negative electrode active material, and Si Negative electrode active material containing 5 parts of SiO _x (x = 1.1, volume average particle diameter: 5 μm) coated with conductive carbon, carboxymethyl cellulose (“MAC200HC” manufactured by Nippon Paper Chemical Co., Ltd.) as a water-soluble polymer 1 part of a 1% by weight aqueous solution (viscosity of 1% by weight aqueous solution: 2000 mPa · s) was added in an amount corresponding to the solid content, and the mixture was adjusted to a solid content concentration of 60% with ion-exchanged water, and then at 25 ° C. Next, after adjusting to a solid content concentration of 52% with ion-exchanged water, the mixture was further mixed for 15 minutes at 25 ° C. Next, the above mixture was mixed as described above. 1.20 parts of the aqueous dispersion of the particulate polymer obtained in a solid content equivalent, solid solution of sodium alginate ("ULV-L3" manufactured by Kimika Co., Ltd., viscosity of 10% by mass aqueous solution: 50 mPa · s) Add 0.30 parts in a substantial amount, add ion-exchanged water so that the final solid content concentration is 50%, and mix for another 10 minutes, defoaming under reduced pressure to obtain a negative electrode slurry composition. It was.

<Preparation of negative electrode for lithium ion secondary battery>
The prepared negative electrode slurry composition was applied on a copper foil having a thickness of 15 μm by a comma coater so that the applied amount was 9 to 10 mg / cm ² and dried. This drying was performed by transporting the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s).
The obtained negative electrode original fabric was pressed with a roll press machine so that the density was 1.6 to 1.7 g / cm ³ , thereby obtaining a negative electrode.
<Preparation of positive electrode for lithium ion secondary battery>
In a planetary mixer, 100 parts of LiCoO ₂ as a positive electrode active material, ₂ parts of acetylene black as a conductive material (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.), PVDF (polyvinylidene fluoride, manufactured by Kureha Chemical Co., Ltd.) as a binder 2 parts of KF-1100) was added, and further, 2-methylpyrrhodone was added and mixed so that the total solid content concentration was 67% to obtain a positive electrode slurry composition. And the obtained positive electrode slurry composition was apply | coated with the comma coater on the 20-micrometer-thick aluminum foil (current collector), and was dried. In addition, this drying was performed by conveying aluminum foil over 2 minutes at a speed | rate of 0.5 m / min in 60 degreeC oven. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material.
The obtained positive electrode original fabric was pressed with a roll press machine so that the density after pressing was 3.45 to 3.54 g / cm ³ to obtain a positive electrode.
<Production of lithium ion secondary battery>
A single-layer polypropylene separator (“Celgard # 2500” manufactured by Polypore Corporation, width 65 mm, length 500 mm, thickness 25 μm; manufactured by dry method; porosity 55%) was prepared and cut into a square of 5 cm × 5 cm. . Moreover, the aluminum packaging material exterior was prepared as a battery exterior.
And the produced positive electrode was cut out into a 4 cm x 4 cm square, and it has arrange | positioned so that the surface at the side of a collector may contact | connect the aluminum packaging material exterior. Next, a square separator was disposed on the surface of the positive electrode mixture layer side of the positive electrode. Further, the produced negative electrode was cut into a square of 4.2 cm × 4.2 cm, and arranged on the separator so that the surface on the negative electrode mixture layer side faced the separator. Thereafter, a LiPF ₆ solution having a concentration of 1.0 M as an electrolytic solution (the solvent is ethylene carbonate / ethyl methyl carbonate = 3/7 (volume ratio) mixed solvent is 100% by mass, and vinylene is used as an additive. To which 2% by mass of carbonate was added). Further, in order to seal the opening of the aluminum packaging material exterior, heat sealing at 150 ° C. was performed to close the aluminum packaging material exterior, and a laminated cell type lithium ion secondary battery was manufactured.
The manufactured lithium ion secondary battery was evaluated for initial bulge, initial cycle characteristics, cycle characteristics, and post-cycle bulge. The results are shown in Table 1.

(Example 2)
In preparing a slurry composition for a negative electrode of a lithium ion secondary battery, 1.27 parts of an aqueous dispersion of a particulate polymer in an amount corresponding to a solid content, a sodium alginate aqueous solution (“ULV-L3” manufactured by Kimika Co., Ltd., 10% by mass aqueous solution) The viscosity was 50 mPa · s) in an amount corresponding to a solid content of 0.23 parts (particulate polymer per 100 parts, sodium alginate 18 parts). Other than that was carried out similarly to Example 1, and manufactured the negative electrode for lithium ion secondary batteries, the positive electrode for lithium ion secondary batteries, and the lithium ion secondary battery. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
In preparing the slurry composition for a negative electrode of a lithium ion secondary battery, the aqueous dispersion of the particulate polymer was 1.36 parts in terms of solid content, an aqueous sodium alginate solution ("ULV-L3" manufactured by Kimika Co., Ltd., 10% by mass aqueous solution). The viscosity was 50 mPa · s) in an amount of 0.14 parts corresponding to the solid content (per 100 parts of the particulate polymer and 10 parts of sodium alginate). Other than that was carried out similarly to Example 1, and manufactured the negative electrode for lithium ion secondary batteries, the positive electrode for lithium ion secondary batteries, and the lithium ion secondary battery. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 4
In preparing the slurry composition for the negative electrode of a lithium ion secondary battery, the aqueous dispersion of the particulate polymer was 1.09 parts in terms of solid content, a sodium alginate aqueous solution ("ULV-L3" manufactured by Kimika Co., Ltd., 10% by mass aqueous solution). The viscosity was 50 mPa · s) in an amount of 0.41 part corresponding to the solid content (per 100 parts of the particulate polymer and 37 parts of sodium alginate). Other than that was carried out similarly to Example 1, and manufactured the negative electrode for lithium ion secondary batteries, the positive electrode for lithium ion secondary batteries, and the lithium ion secondary battery. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)
In preparing the slurry composition for a negative electrode of a lithium ion secondary battery, the aqueous dispersion of the particulate polymer was 1.17 parts in terms of solid content, a sodium alginate aqueous solution ("ULV-L3" manufactured by Kimika Co., Ltd., 10% by mass aqueous solution). The viscosity was 50 mPa · s) in an amount of 0.33 parts corresponding to the solid content (per 100 parts of the particulate polymer and 28 parts of sodium alginate). Other than that was carried out similarly to Example 1, and manufactured the negative electrode for lithium ion secondary batteries, the positive electrode for lithium ion secondary batteries, and the lithium ion secondary battery. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 6)
In preparing a slurry composition for a negative electrode of a lithium ion secondary battery, 1.06 parts of an aqueous dispersion of a particulate polymer in an amount corresponding to a solid content, a sodium alginate aqueous solution (“ULV-L3” manufactured by Kimika Co., Ltd., 10% by mass aqueous solution) The viscosity was 50 mPa · s) in an amount of 0.44 parts corresponding to the solid content (100 parts of the particulate polymer and 42 parts of sodium alginate). Other than that was carried out similarly to Example 1, and manufactured the negative electrode for lithium ion secondary batteries, the positive electrode for lithium ion secondary batteries, and the lithium ion secondary battery. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Examples 7 to 8)
In preparing the particulate polymer, a slurry composition for a lithium ion secondary battery negative electrode, a lithium ion secondary battery, and the like, except that the blending ratio of each monomer unit was changed as shown in Table 1. A negative electrode for a secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 9
In preparing the particulate polymer, a slurry composition for a lithium ion secondary battery negative electrode, a lithium ion secondary battery, and the like, except that the blending amount of t-dodecyl mercaptan (TDM) was 0.7 parts. A negative electrode for a secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 10)
In preparing the slurry composition for a lithium ion secondary battery negative electrode, the sodium alginate aqueous solution to be blended was changed to a sodium alginate aqueous solution ("ULV-5" manufactured by Kimika Co., Ltd.) having a viscosity of 600 mPa · s of a 10 mass% aqueous solution. In the same manner as in Example 1, a negative electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 11)
In preparing the slurry composition for a negative electrode of a lithium ion secondary battery, the sodium alginate aqueous solution to be blended was changed to a sodium alginate aqueous solution ("ULV-20" manufactured by Kimika Argin Co., Ltd.) having a viscosity of 2000 mPa · s of a 10% by mass aqueous solution. Produced a negative electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery in the same manner as in Example 1. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 12)
In preparing the slurry composition for the negative electrode of the lithium ion secondary battery, the lithium ion secondary solution was changed in the same manner as in Example 1 except that the aqueous sodium alginate solution was changed to a sodium alginate aqueous solution having a viscosity of 950 mPa · s. A negative electrode for a secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Examples 13 to 14)
In preparing the slurry composition for a lithium ion secondary battery negative electrode, the viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose as a water-soluble polymer to be blended was changed. Specifically, in Example 13, carboxymethyl cellulose (“Daicel 1380” manufactured by Daicel Finechem Co., Ltd.) having a viscosity of 1200 mPa · s as a water-soluble polymer was blended as a water-soluble polymer. Carboxymethylcellulose (“MAC350HC” manufactured by Nippon Paper Chemical Co., Ltd.) having a viscosity of 4500 mPa · s in a 1% by mass aqueous solution was blended as a combination. Except this, it carried out similarly to Example 1, and manufactured the negative electrode for lithium ion secondary batteries, the positive electrode for lithium ion secondary batteries, and the lithium ion secondary battery. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 15)
In preparing the particulate polymer, a slurry composition for a lithium ion secondary battery negative electrode, a lithium ion secondary battery, and the like, except that the blending ratio of each monomer unit was changed as shown in Table 1. A negative electrode for a secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
<Preparation of particulate polymer>
In preparing the particulate polymer, the amount of 1,3-butadiene, which is an aliphatic conjugated diene monomer, was changed to 62 parts, and 4 parts of itaconic acid was added as an ethylenically unsaturated carboxylic acid monomer. Prepared a particulate polymer in the same manner as in Example 1.
<Preparation of slurry composition for negative electrode of lithium ion secondary battery>
For the preparation of a slurry composition for a lithium ion secondary battery negative electrode, a lithium ion secondary battery negative electrode was prepared in the same manner as in Example 1 except that 1.5 parts of a particulate polymer was blended without blending an alginate. A slurry composition was prepared.

  A negative electrode for a lithium ion secondary battery was prepared in the same manner as in Example 1 except that the slurry composition for a negative electrode of a lithium ion secondary battery thus obtained was used. A positive electrode for an ion secondary battery and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
In preparing a slurry composition for a negative electrode of a lithium ion secondary battery without preparing a particulate polymer, an aqueous solution of sodium alginate ("ULV-L3" manufactured by Kimika Co., Ltd., 10% by mass aqueous solution) is not blended. Was added in an amount of 1.5 parts in terms of solid content. Except this, it carried out similarly to Example 1, and manufactured the negative electrode for lithium ion secondary batteries, the positive electrode for lithium ion secondary batteries, and the lithium ion secondary battery. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

  In Table 1, the Si-containing active material is a negative electrode active material containing Si, ST is styrene, BD is 1,3-butadiene, AA is acrylic acid, IA is itaconic acid, and 2-HEA is 2-hydroxyethyl acrylate, TDM represents t-dodecyl mercaptan, THF represents tetrahydrofuran, and CMC represents carboxymethylcellulose.

  From Table 1, in Examples 1-15 using the slurry composition containing the negative electrode active material containing Si, a particulate polymer, and the alginate of a predetermined ratio, it is charge / discharge in both the initial stage and after a cycle. It can be seen that the accompanying swelling of the negative electrode can be suppressed and the cycle characteristics of the lithium ion secondary battery can be improved. On the other hand, in Comparative Examples 1 and 2 using a slurry composition that does not contain a particulate polymer or a predetermined proportion of alginate, the cycle characteristics of the lithium ion secondary battery cannot be improved while suppressing swelling of the negative electrode. I understand.

In particular, from Examples 1 to 6 in Table 1, by adjusting the amount of alginate blended in the slurry composition, the cycle characteristics of the lithium ion secondary battery can be sufficiently improved while sufficiently suppressing the swelling of the negative electrode. I understand that.
Further, from Examples 1, 7 to 8 and 15 in Table 1, by adjusting the surface acid amount of the particulate polymer, the cycle characteristics of the lithium ion secondary battery are sufficiently suppressed while sufficiently suppressing the swelling of the negative electrode. It can be seen that it can be improved.
Further, from Examples 1 and 9 in Table 1, by adjusting the THF gel content of the particulate polymer, it is possible to sufficiently suppress the swelling of the negative electrode, and thus the cycle characteristics of the lithium ion secondary battery are improved. It turns out that it can fully improve.
Moreover, from Examples 1 and 10 to 12 in Table 1, it can be seen that the cycle characteristics of the lithium ion secondary battery can be sufficiently improved by adjusting the viscosity of the aqueous alginate solution to be blended in the slurry composition.
Moreover, from Examples 1 and 13 to 14 in Table 1, by adjusting the viscosity of the water-soluble polymer to be blended in the slurry composition, the cycle characteristics of the lithium ion secondary battery can be improved while sufficiently suppressing the swelling of the negative electrode. It turns out that it can fully improve.

According to the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, even if the battery capacity is increased by using a negative electrode active material containing a silicon-based negative electrode active material, the swelling associated with charge / discharge is suppressed. In addition, it is possible to form a negative electrode for a lithium ion secondary battery that can improve electrical characteristics such as cycle characteristics of the lithium ion secondary battery.
In addition, according to the negative electrode for a lithium ion secondary battery of the present invention, even when the battery capacity is increased by using a negative electrode active material containing a silicon-based negative electrode active material, it is possible to suppress swelling associated with charge / discharge. In addition, electrical characteristics such as cycle characteristics of the lithium ion secondary battery can be improved.
According to the lithium ion secondary battery of the present invention, it is possible to suppress the swelling of the negative electrode even when the battery capacity is increased by using the negative electrode active material containing the silicon-based negative electrode active material, and excellent Electrical characteristics can be obtained.

Claims (8)

A negative electrode active material containing Si, a particulate polymer, an alginate, and water;
A slurry composition for a negative electrode of a lithium ion secondary battery, containing 5 parts by mass or more of the alginate per 100 parts by mass of the particulate polymer. The slurry composition for a lithium ion secondary battery negative electrode according to claim 1, wherein the negative electrode active material containing Si contains a silicon oxide represented by SiO _x (0 <x <2).   The slurry composition for a lithium ion secondary battery negative electrode according to claim 1 or 2, wherein a surface acid amount of the particulate polymer is 0.25 mmol / g or more and 3.0 mmol / g or less.   The slurry composition for lithium ion secondary battery negative electrodes as described in any one of Claims 1-3 whose THF gel content of the said particulate polymer is 80 mass% or more and 98 mass% or less.   The said alginate is a slurry composition for lithium ion secondary battery negative electrodes as described in any one of Claims 1-4 whose viscosity of 10 mass% aqueous solution is 5 mPa * s or more and 1000 mPa * s or less.   Furthermore, the slurry composition for lithium ion secondary battery negative electrodes as described in any one of Claims 1-5 containing the water-soluble polymer whose viscosity of 1 mass% aqueous solution is 1000 mPa * s or more and 5000 mPa * s or less. The slurry composition for a lithium ion secondary battery negative electrode according to any one of claims 1 to 6 is applied on a current collector,
A negative electrode for a lithium ion secondary battery, which is obtained by drying the slurry composition for a negative electrode of a lithium ion secondary battery coated on the current collector to form a negative electrode mixture layer on the current collector.   A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 7, a positive electrode, an electrolytic solution, and a separator.

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