Secondary battery binder, slurry, electrode, method for manufacturing secondary battery, and secondary battery

Abstract

To provide a novel secondary battery binder or a slurry containing the secondary battery binder that can suitably contribute to the production of a battery and / or battery characteristics. [Solution means] containing an aqueous polymer, when the aqueous polymer is dissolved in water at a concentration of 2% by mass, the Na concentration of the obtained aqueous solution is 0.05% by mass or more and 0.25% by mass or less, a secondary battery binder having an electrolyte liquid absorption rate (25 °C) of the aqueous polymer of 8.0% or less.

Description

Technical Field

[0001] The present disclosure relates to a secondary battery binder, a slurry, an electrode, a method for manufacturing a secondary battery, and a secondary battery.

Background Art

[0002] In the manufacturing process of secondary batteries, particularly in the manufacturing process of electrodes, a slurry containing a binder is used. In recent years, from the perspective of concerns about environmental impact, there has been increasing interest in aqueous slurries with water as the solvent instead of slurries using organic solvents. Patent Document 1 discloses the use of an aqueous slurry containing a latex-based binder.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, the types and properties of the binder have not been sufficiently studied. An object of the present disclosure is to provide a novel secondary battery binder or a slurry containing the secondary battery binder that can suitably contribute to the manufacturing of batteries and / or battery characteristics.

Means for Solving the Problems

[0005] The present disclosure includes the following aspects: [Item 1] including an aqueous polymer, wherein the Na concentration of the aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2% by mass is 0.05% by mass or more and 0.25% by mass or less, and the electrolyte liquid absorption rate (25°C) of the aqueous polymer is 8.0% or less, a secondary battery binder. [Item 2] The secondary battery binder according to item 1, wherein the electrolyte liquid absorption rate (25 ° C) is 2% or more and 6.5% or less. [Item 3] The secondary battery binder according to item 1 or 2, wherein the aqueous polymer is a vinyl polymer having an acidic functional group-containing repeating unit. [Item 4] The aqueous polymer is Formula: -[CH 2 -C(R 1 )(C(=O)R 2 )]- [In the formula, R 1 is a hydrogen atom or CH 3 and R 2 is NH 2 , OM (M is a hydrogen atom or a counter cation.), O(CH 2 ) n OH, NH(CH 2 ) n OH (n is, independently of each other, 1 or more and 6 or less).] The repeating unit (1) represented by, and Formula: -[CH 2 -CH(OH)]- The repeating unit (2) represented by The secondary battery binder according to any one of items 1 to 3, including a repeating unit selected from [Item 5] In the aqueous polymer, The amount of the repeating unit selected from the repeating unit (1) and the repeating unit (2) is 40 mol% or more, The amount of the acidic functional group-containing repeating unit is 0.8 mol% or more, The amount of the nonionic repeating unit is 40 mol% or more, the secondary battery binder according to item 4. [Item 6] The secondary battery binder according to any one of items 1 to 5, including SBR. [Item 7] A slurry containing the secondary battery binder according to any one of items 1 to 6, and water. [Item 8] The slurry according to Item 7, further comprising an electrode active material. [Item 9] A method for manufacturing a secondary battery, comprising a step of applying the slurry according to Item 7 or 8. [Item 10] An electrode comprising the secondary battery binder according to any one of Items 1 to 6 or a component derived from the secondary battery binder. [Item 11] An electrode comprising a heat-dried product of the slurry according to Item 7 or 8. [Item 12] A secondary battery comprising the electrode according to Item 10 or 11. [Advantages of the Invention]

[0006] The secondary battery binder or the slurry containing the secondary battery binder in the present disclosure has one or more characteristics suitable for a battery or its manufacture. In particular, by using the secondary battery binder or the slurry containing the secondary battery binder in the present disclosure, expansion after charge and discharge cycles of the battery can be preferably suppressed. [Modes for Carrying Out the Invention]

[0007] [Definitions of Terms, etc.] In the present specification, unless otherwise specified, when a term (symbol) that may appear multiple times in a chemical structure is defined, the definition is applied independently for each appearance, regardless of whether the expression "independently of each other" or a similar expression is explicitly described.

[0008] In the present specification, "(meth)acryl" means "acryl or methacryl", and "(meth)allyl" means "allyl or methallyl".

[0009] In the present specification, when a plurality of lower limit values and a plurality of upper limit values are separately described, any lower limit value and upper limit value can be selected, and a numerical range of a combination of the lower limit value and the upper limit value can be selected.

[0010] [Secondary Battery Binder] The secondary battery binder in the present disclosure is used for enhancing the binding property between particles inside the electrode in a secondary battery, the binding property between the active material layer and the current collector, and the like.

[0011] [Aqueous polymer] The secondary battery binder in the present disclosure contains an aqueous polymer. The aqueous polymer in the present disclosure is a polymer that can be dispersed in water alone and is particularly water-soluble.

[0012] [Properties of aqueous polymer, etc.] The properties of the aqueous polymer are shown below.

[0013] (Water solubility) When 2.0 g of the aqueous polymer is dissolved in 100 g of water at 25°C, the insoluble matter may be 20% by mass or less, or 15% by mass or less with respect to the aqueous polymer, preferably 5% by mass or less, more preferably 1% by mass or less.

[0014] (Molecular weight, etc.)

[0015] The Mw (weight average molecular weight) of the aqueous polymer determined by GPC-RI may be 100,000 or more, 300,000 or more, 500,000 or more, 750,000 or more, or 1,500,000 or more, preferably 100,000 or more, more preferably 500,000 or more. Also, it may be 3,000,000 or less, 1,000,000 or less, 500,000 or less, or 250,000 or less, preferably 1,000,000 or less, more preferably 800,000 or less. This value is determined by the method described in the examples.

[0016] (pH) When the aqueous solution obtained by dissolving an aqueous polymer at a concentration of 2% by mass in water, the pH (25 °C) may be 5.0 or higher, 5.5 or higher, 6.0 or higher, 6.5 or higher, 7.0 or higher, 7.5 or higher, 8.0 or higher, 8.5 or higher, or 9.0 or higher, preferably 5.5 or higher, more preferably 6.5 or higher. Also, it may be 10 or lower, 9.5 or lower, 9.0 or lower, 8.5 or lower, 8.0 or lower, 7.5 or lower, or 7.0 or lower, preferably 9.0 or lower, more preferably 8.5 or lower. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water. When the pH is at or above the above lower limit value (especially 7.0 or above (neutral to alkaline)), the flexibility of the polymer component containing the aqueous polymer increases, and it can show high followability to the expansion and contraction of the active material. Similarly, when the pH is at or above the above lower limit value, the dispersibility of the slurry can be improved. When the pH is within the above range (especially 5.0 or above and 7.5 or below), the viscosity stability of the aqueous polymer solution is good, which is suitable from the viewpoint of the productivity of battery manufacturing.

[0017] (Viscosity) When the aqueous solution obtained by dissolving an aqueous polymer at a concentration of 2% by mass in water, the viscosity (25 °C) may be 1 mPa·s or higher, 5 mPa·s or higher, 10 mPa·s or higher, 25 mPa·s or higher, or 50 mPa·s or higher, preferably 5 mPa·s or higher, more preferably 25 mPa·s or higher. Also, it may be 2000 mPa·s or lower, 1000 mPa·s or lower, 500 mPa·s or lower, 100 mPa·s or lower, 50 mPa·s or lower, or 25 mPa·s or lower, preferably 300 mPa·s or lower, more preferably 100 mPa·s or lower. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water. By setting the viscosity within the above range (for example, 5 mPa·s or higher and 200 mPa·s or lower), the dispersibility of the active material and the binder in the slurry increases, the film of the binder on the active material is formed well, and the expansion of the electrode (especially the initial expansion rate) when made into a battery can be suppressed. Similarly, by setting the viscosity within the above range, the dispersibility of the slurry can be improved.

[0018] (Conductivity) When an aqueous solution is obtained by dissolving an aqueous polymer in water at a concentration of 2% by mass, the conductivity of the aqueous solution may be 0.5 mS / cm or more, 1.5 mS / cm or more, 2.5 mS / cm or more, 3.0 mS / cm or more, 3.5 mS / cm or more, or 4.5 mS / cm or more, preferably 2.0 mS / cm or more, more preferably 2.5 mS / cm or more, and may be 10 mS / cm or less, 7.5 mS / cm or less, or 5.0 mS / cm or less, preferably 7.5 mS / cm or less, more preferably 4.0 mS / cm or less. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water. When the conductivity is relatively low (for example, 3.3 mS / cm or less, particularly 3.0 mS / cm or less), it is suitable for suppressing foaming during stirring of the aqueous solution. Also, when the conductivity is within the above range, it is considered that the concentration of ionic components does not become too high, the properties of the ionic components as surfactants are suppressed, and foaming can be suppressed. When the conductivity is relatively high (particularly 3.3 mS / cm or more), the viscosity stability of the aqueous solution is suitable. This is considered because when the conductivity is high, the concentration of polar functional groups derived from the structure of the aqueous polymer increases, and the ionic interaction becomes stronger, stabilizing the viscosity of the aqueous solution.

[0019] (Na concentration) When an aqueous solution is obtained by dissolving an aqueous polymer in water at a concentration of 2% by mass, the Na concentration of the aqueous solution is 0.05% by mass or more and 0.25% by mass or less. When the Na concentration is within the above range, the expansion of the electrode after charge-discharge cycles can be suppressed. When the Na concentration is equal to or higher than the above lower limit value, the uneven distribution of the aqueous polymer in the slurry can be suppressed, the uneven distribution of the binder in the battery can also be suppressed, and it is considered that the expansion of the active material can be easily suppressed. A preferable lower limit value is 0.10% by mass or more. When the Na concentration is equal to or lower than the above upper limit value, since the adhesion to the active material becomes good, it is considered that the expansion is also suppressed. In addition, it is considered that the uniformity of the slurry is improved and an increase in the resistance of the battery can be suppressed. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water.

[0020] (Electrolyte absorption rate (25 °C)) The electrolyte absorption rate (25 °C) of the aqueous polymer is 8.0% or less. When the electrolyte absorption rate is within the above range, it is suitable for suppressing the DC resistance of the battery after charge-discharge cycles. From the same viewpoint, preferably, it is 6.5% or less, more preferably 2% or more and 6.5% or less. An aqueous polymer with an electrolyte absorption rate (25 °C) equal to or lower than the above upper limit value has relatively high rigidity and a tendency for the strength of the binder film to increase. As a result, it is considered that breakage or peeling of the binder film is less likely to occur during swelling and shrinkage of the active material due to charge and discharge of the battery, the coverage of the active material can be maintained high, the formation of a high-resistance film accompanying the decomposition of the electrolyte due to contact with the electrolyte can be suppressed, and an increase in the DC resistance of the battery can be suppressed. This value is determined by the method described in the examples.

[0021] [Structure, etc. of aqueous polymer] The aqueous polymer is obtained by polymerizing one or more monomers. The aqueous polymer may be a vinyl polymer. The vinyl polymer is a polymer obtained by polymerizing vinyl monomers. Here, the vinyl monomer may be any compound having a polymerizable carbon-carbon double bond (ethylenically unsaturated double bond) (>C=C<), and may be a monomer containing a vinyl group, vinylene group, vinylidene group, acryloyl group, methacryloyl group, or a derivative group thereof. The aqueous polymer may particularly be a (meth)acrylic polymer containing a repeating unit derived from a monomer having an acryloyl group or a methacryloyl group.

[0022] The aqueous polymer may be a random polymer or a block polymer, and is, for example, a random polymer.

[0023] (Hydrophilic repeating unit) The aqueous polymer has a hydrophilic repeating unit. The hydrophilic repeating unit contains a hydrophilic group. Examples of the hydrophilic group include anionic groups such as carboxy group, sulfonic acid group, phosphoric acid group, and nitric acid group, cationic groups such as amino group, hydroxy group, polyoxyethylene group (for example, the repeating number is 2 or more, 5 or more, or 10 or more), and nonionic hydrophilic groups such as amide group. The anionic group and the cationic group may be in the state of free acid / base, or a part or all of them may be in the form of salt.

[0024] In this specification, when referring to an anionic group, a cationic group, or a structure containing such a group (for example, an acidic functional group-containing repeating unit), unless explicitly stated, it is intended to include not only the anionic group and the cationic group but also their salts.

[0025] Examples of the counter cation of the anionic group include metal ions, preferably light metal ions, more preferably lithium ion, sodium ion, or potassium ion, particularly lithium ion or sodium ion. The counter cation may be monovalent to trivalent, monovalent to divalent, or monovalent, preferably monovalent. Examples of the counter anion of the cationic group include inorganic acid ions such as phosphate ion, nitrate ion, and sulfate ion, and halide ions. The aqueous polymer may be anionic and may not have a cationic group.

[0026] The aqueous polymer in the present disclosure preferably has a repeating unit having an acidic functional group as a hydrophilic repeating unit. The acidic functional group may be an anionic group such as a carboxy group, a sulfonic acid group, a phosphoric acid group, or a nitric acid group, preferably a carboxy group or a sulfonic acid group, and more preferably a carboxy group. These groups may exist in a salt state, and examples of the counter cation in that case include the above-described metal ions. Examples of the repeating unit having an acidic functional group include repeating units derived from (meth) acrylic acid, maleic acid, vinyl sulfonic acid, or (meth) allyl sulfonic acid.

[0027] The aqueous polymer in the present disclosure may have a nonionic hydrophilic repeating unit. Examples of the nonionic hydrophilic repeating unit include (meth) acrylamide, hydroxyalkyl (meth) acrylate, hydroxyalkyl (meth) acrylamide, polyoxyalkylene (meth) acrylate, polyoxyalkylene (meth) acrylamide, vinyl alcohol, and the like.

[0028] Examples of suitable hydrophilic repeating units include Formula: -[CH 2 -C(R 1 )(C(=O)R 2 )]- [In the formula, R 1 is a hydrogen atom or CH 3 , and R 2 is NH 2 , OM (M is a hydrogen atom or a counter cation.), O(CH 2 ) n OH, NH(CH 2 ) n OH (n is, independently of each other, 1 or more and 6 or less).] The repeating unit (1) represented by Formula: -[CH 2 -CH(OH)]- The repeating unit (2) represented by The repeating units selected from

[0029] In the repeating unit (1), R 1 is preferably a hydrogen atom.

[0030] In the repeating unit (1), R 2 The M in may be a metal cation, preferably a light metal cation, more preferably a lithium ion, a sodium ion, or a potassium ion, and particularly may be a lithium ion or a sodium ion. M may be monovalent to trivalent, monovalent to divalent, or monovalent, and is preferably monovalent.

[0031] In the repeating unit (1), R 2 The n in may be 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less, preferably 3 or less, and particularly 2 or less.

[0032] The repeating unit (1) preferably contains at least one of R 2 being an NH 2 group, an OH group, an ONa group, and an OLi group. The repeating unit (1) may be such that R 2 is only an NH 2 group, R 2 is only an OH group, R 2 is an ONa group, or R 2 is only an OLi group. The repeating unit (1) may contain those with R 2 being an ONa group and those with an OH group, or may contain those with R 2 being an OLi group and those with an OH group, or may contain those with an NH 2 group and those with an OH group, or may contain those with an NH 2 group, those with an OH group, and those with an ONa group, or may contain those with an NH 2 group, those with an OH group, those with an ONa group, and those with an OLi group, or may contain those with R 2 being an OH group, those with an OLi group, and those with an NH 2 group.

[0033] The repeating unit (2) can be introduced, for example, by a method of polymerizing a vinyl ester (such as vinyl acetate, vinyl propionate, etc., particularly vinyl acetate) and then saponifying it, a method of reacting a polymer having a vinyl alcohol-based repeating unit (such as polyvinyl alcohol), or the like.

[0034] The aqueous polymer preferably contains a repeating unit derived from (meth)acrylic acid (particularly the sodium salt or lithium salt).

[0035] (Non-hydrophilic repeating unit) The aqueous polymer may have a non-hydrophilic repeating unit. The non-hydrophilic repeating unit does not have a hydrophilic group (such as an ionic group). Examples of the non-hydrophilic repeating unit include repeating units derived from (meth)acrylonitrile, (meth)acrylic acid alkyl ester, vinyl chloride, and the like.

[0036] [Composition, etc. of the aqueous polymer] The amount of the hydrophilic repeating unit in the aqueous polymer may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 20 mol% or more, more preferably 40 mol% or more, and may also be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less.

[0037] The amount of the acidic functional group-containing repeating unit in the aqueous polymer may be 0.8 mol% or more, 3 mol% or more, 5 mol% or more, 10 mol% or more, 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 5 mol% or more, more preferably 10 mol% or more, and may also be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 60 mol% or less.

[0038] The amount of the nonionic hydrophilic repeating unit may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 20 mol% or more, more preferably 40 mol% or more, and may also be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 80 mol% or less.

[0039] The amount of the non-hydrophilic repeating unit may be 0 mol% or more, 1 mol% or more, 3 mol% or more, 5 mol% or more, 20 mol% or more, 40 mol% or more, or 50 mol% or more in the aqueous polymer, and may also be 70 mol% or less, 50 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, 10 mol% or less, 5 mol% or less, or 3 mol% or less. The aqueous polymer may not contain a non-hydrophilic repeating unit.

[0040] The amount of the nonionic repeating unit may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 20 mol% or more, more preferably 40 mol% or more, and may also be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 80 mol% or less.

[0041] The total amount of the repeating unit (1) and the repeating unit (2) may be 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 40 mol% or more, more preferably 50 mol% or more, and may also be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 80 mol% or less.

[0042] The amount of the repeating unit (1) may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 40 mol% or more, more preferably 50 mol% or more, and may also be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 80 mol% or less.

[0043] The amount of the repeating unit (2) may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 20 mol% or more, more preferably 40 mol% or more, and may also be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 70 mol% or less. The aqueous polymer may not contain the repeating unit (2).

[0044] (The amount of the repeating unit derived from (meth)acrylamide (wherein R in formula (1) 2 is NH 2 ) may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 20 mol% or more, more preferably 30 mol% or more, and may also be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 70 mol% or less.

[0045] (The amount of the repeating unit derived from (meth)acrylic acid or its salt (wherein R in formula (1) 2 is OM) may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 10 mol% or more, more preferably 20 mol% or more, and may also be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 70 mol% or less.

[0046] [Method for producing aqueous polymer] The method for producing the aqueous polymer is not particularly limited, and it can be produced by using a known method for producing a copolymer. Preferably, it can be synthesized by an aqueous solution radical polymerization method. Specifically, a radical polymerization initiator and, if necessary, a chain transfer agent are added to a monomer mixture solution, and the polymerization reaction may be carried out at a reaction temperature of about 50 to 100 °C (for example, 60 to 70 °C) while stirring. The reaction time is not particularly limited and may be about 1 to 10 hours. After the elapse of the reaction time, it may be further aged at a temperature of the reaction temperature +3 °C to +10 °C (for example, +4 °C to +8 °C) for 15 minutes to 2 hours (for example, 30 minutes to 1.5 hours). Aging can reduce the amount of unreacted monomer. When the aqueous polymer has a vinyl alcohol unit, for example, the saponification conditions may be set with reference to the method for producing a copolymer of vinyl alcohol and an alkali metal neutralized product of an ethylenically unsaturated carboxylic acid described in WO2017 / 168947.

[0047] The monomer concentration at the start of polymerization may be 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, or 25% by mass or more, and may also be 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less. In one aspect, it is 10% by mass or more and 11% by mass or less, 15% by mass or more and 17% by mass or less, or 11% by mass or more and 13% by mass or less.

[0048] As the initiator, various known ones can be used without particular limitation. Examples of the radical polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate; redox polymerization initiators obtained by combining such persulfates with reducing agents such as sodium bisulfite; azo-based initiators such as 2,2'-azobis-2-amidinopropane dihydrochloride (NC-32) (V-50) and 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044). The amount of the radical polymerization initiator used is preferably about 0.05 to 2% by mass, more preferably about 0.1 to 1.5% by mass, based on 100% by mass of the monomer group that is the raw material of the aqueous polymer in the present disclosure.

[0049] Each overlapping condition and the like can be appropriately set according to the structure of the target compound.

[0050] [Amount of aqueous polymer] The amount of the aqueous polymer may be 25% by mass or more, 50% by mass or more, 75% by mass or more, 95% by mass or more, or 99% by mass or more in the secondary battery binder, preferably 50% by mass or more, more preferably 75% by mass or more, and may also be 99% by mass or less, 90% by mass or less, 80% by mass or less, or 70% by mass or less. The secondary battery binder may be the aqueous polymer alone.

[0051] [Other binder components] The secondary battery binder in the present disclosure may contain other binder components in addition to the aqueous polymer. Examples of other components include known binder resins and the like, for example, styrene-butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), polyimide (PI), polyamide, ethylene-vinyl acetate copolymer (EVA), and the like.

[0052] The amount of other binder components may be 0% by mass or more, 0.5% by mass or more, 5% by mass or more, 10% by mass or more, or 25% by mass or more in the secondary battery binder, and may also be 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, for example, 3% by mass or less.

[0053] <Slurry> The slurry of the present disclosure contains the aforementioned secondary battery binder and water, and may further contain an electrode active material. The slurry may contain battery particles such as a conductive aid and other liquid media, and is typically an electrode slurry containing an electrode active material. The slurry may be a positive electrode slurry containing a positive electrode active material or a negative electrode slurry containing a negative electrode active material.

[0054] [Liquid medium] The slurry contains a liquid medium (aqueous medium) containing water. The liquid medium is preferably water alone from the perspective of environmental impact concerns, but may also contain an organic solvent such as alcohol (ethanol, methanol, isopropyl alcohol, etc.). The amount of the organic solvent may be 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less in the liquid medium, and is preferably 10% by mass or less.

[0055] [Amount of liquid medium] The amount of the liquid medium is adjusted according to the desired slurry solid content concentration. The amount of the liquid medium may be 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more in the slurry solid content (total amount of the secondary battery binder, active material, and conductive assistant), and is preferably 30% by mass or more, more preferably 50% by mass or more. Also, it may be 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less, and is preferably 70% by mass or less, more preferably 60% by mass or less.

[0056] [Secondary battery binder] The slurry contains a secondary battery binder. The types of the secondary battery binder are as described above.

[0057] [Amount of secondary battery binder] The amount of the secondary battery binder may be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, 3.0% by mass or more, or 5.0% by mass or more in the slurry solid content (total amount of the secondary battery binder, active material, and conductive assistant), and is preferably 0.3% by mass or more. Also, it may be 10% by mass or less, 7.5% by mass or less, 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, and is preferably 3.0% by mass or less, more preferably 1.0% by mass or less. Being above the above lower limit is suitable from the perspective of achieving good binder effects. Being below the above upper limit is suitable from the perspective of making the battery have a high capacity.

[0058] [Active material] The active material is an electrode active material, including a negative electrode active material or a positive electrode active material. When the active material is, for example, a negative electrode active material, it can include, for example, a carbon material, and can also include at least one of silicon and silicon oxide. Specific materials of the negative electrode active material and the positive electrode active material are exemplified below.

[0059] (Negative electrode active material) As the negative electrode active material, a negative electrode active material used in this technical field may be used.

[0060] As the negative electrode active material, carbon materials such as crystalline carbon and amorphous carbon may be used. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of amorphous carbon include soft carbon (easily graphitizable carbon) or hard carbon (difficultly graphitizable carbon), mesophase pitch carbide, calcined coke, etc.

[0061] As the negative electrode active material, materials such as silicon (Si), tin (Sn), and titanium (Ti) that can absorb and release a large amount of lithium ions may be used. These materials can be used in the form of a single substance, alloy, compound, solid solution, or composite active material containing a silicon-containing material, tin-containing material, or titanium-containing material. Examples of silicon-containing materials include Si, Si / C, SiOx (0.05 < x < 1.95), or an alloy, compound, or solid solution in which at least one element selected from the group consisting of B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn replaces a part of Si in any of these. The silicon-containing material may be a silicon oxide. Examples of tin-containing materials include Ni 2 Sn 4 ,Mg 2 Sn, SnOx (0 < x < 2), SnO 2 ,SnSiO 3 ,LiSnO, etc. Examples of titanium-containing materials include Li 2 TiO 3 ,Li 4 Ti5 O 12 Examples include lithium titanate, titanium niobium composite compounds, etc. These materials can be used alone or in combination of two or more. Among these, silicon or silicon oxide is preferred, and it may be, for example, elemental Si or silicon oxide.

[0062] As the negative electrode active material, it is more preferable to use a composite obtained by mixing a silicon or silicon oxide as the first negative electrode active material and a carbon material as the second negative electrode active material as the negative electrode active material. As the carbon material, any carbon material generally used in secondary batteries, particularly non-aqueous electrolyte secondary batteries, can be used, and crystalline carbon, amorphous carbon, or a combination of these may be used. Examples of the crystalline carbon include those described above.

[0063] The method for manufacturing the negative electrode active material is not particularly limited. When manufacturing an active material composite in which the first negative electrode active material and the second negative electrode active material are mixed, a method in which both are uniformly dispersed may be adopted. For example, a method of mixing the first negative electrode active material and the second negative electrode active material with a ball mill can be mentioned.

[0064] (Positive electrode active material) The positive electrode active material is not particularly limited, and a positive electrode active material used in this technical field may be used.

[0065] The positive electrode active material may be a lithium-containing composite oxide. The lithium-containing composite oxide is, for example, LiMnO 2 , LiFeO 2 , LiCoO 2 , LiMn 2 O 4 , Li 2 FeSiO 4 , LiNi 1 / 3 , Co 1 / 3 , Mn 1 / 3 O 2 , LiNi 0.5 , Co 0.2 , Mn 0.3 O 2 , LiNi 0.6 , Co0.2 Mn 0.2 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi x Co y M z O 2 (However, 0 ≦ x < 1, 0 ≦ y < 1, 0 ≦ z < 1, x + y + z = 1, and M is at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb, Fe, Cu, and Al.), LiMn (1-w) Fe w PO 4 (However, 0 < w < 1), LiFePO 4 etc. can be mentioned.

[0066] [Amount of active material] The amount of the active material may be 35% by mass or more, 45% by mass or more, 55% by mass or more, 65% by mass or more, 75% by mass or more, 95% by mass or more in the slurry solid content (total amount of the secondary battery binder, the active material, and the conductive assistant), preferably 55% by mass or more, more preferably 75% by mass or more, and also 99% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less.

[0067] [Conductive assistant] As the conductive assistant, the conductive assistants used in the technical field can be used. The conductive assistant is not particularly limited as long as it has conductivity, but carbon powder is preferred. Examples of the carbon powder include commonly used ones, such as acetylene black (AB), ketjen black (KB), graphite, carbon fiber, carbon nanotube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, carbon nanotube, and other carbon materials. These may be used alone or in combination of two or more.

[0068] [Amount of conductive assistant] The amount of the conductive assistant may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 3.0% by mass or more, or 5.0% by mass or more in the slurry solid content (total amount of the secondary battery binder, the active material, and the conductive assistant), preferably 0.3% by mass or more, and may be 10% by mass or less, 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, preferably 3.0% by mass or less, more preferably 1.0% by mass or less.

[0069] [Dispersion assistant] The slurry of the present disclosure may further contain a dispersion assistant. As the dispersion assistant, an organic acid containing at least one substituent selected from the group consisting of a hydroxy group, an amino group, and an imino group and a carboxy group, or humic acid is preferable. Examples of the organic acid having a hydroxy group and a carboxy group include lactic acid, tartaric acid, citric acid, malic acid, glycolic acid, tartronic acid, glucuronic acid, and humic acid. Examples of the organic acid having an amino group and a carboxy group include glycine, alanine, phenylalanine, 4-aminobutyric acid, leucine, isoleucine, lysine, glutamic acid, aspartic acid, glutamine, asparagine, histidine, tryptophan, cysteine, and polymers thereof. Examples of the organic acid having an imino group and a carboxy group include proline, 3-hydroxyproline, 4-hydroxyproline, and pipecolic acid. Among these, from the viewpoint of easy availability, glucuronic acid, humic acid, glycine, polyglycine, aspartic acid, or glutamic acid is preferable.

[0070] [Amount of dispersion assistant] The amount of the dispersion assistant may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, or 3.0% by mass or more in the slurry solid content (total amount of the secondary battery binder, the active material, and the conductive assistant), preferably 0.3% by mass or more, and may be 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, preferably 3.0% by mass or less, more preferably 1.0% by mass or less.

[0071] [Other components] The slurry of the present disclosure may contain other components, such as conventional additives and the like.

[0072] [Amount of other components] The amount of other components (each amount or total amount) may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 3.0% by mass or more, or 5.0% by mass or more in the slurry solid content (total amount of the secondary battery binder, active material, and conductive assistant), preferably 0.3% by mass or more, and may be 10% by mass or less, 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, preferably 3.0% by mass or less, more preferably 1.0% by mass or less.

[0073] [Method for producing slurry] The method for producing the slurry of the present disclosure is not particularly limited and is produced by mixing the components. For example, a binder, a liquid medium, an active material, and further, if necessary, a conductive assistant, a dispersion assistant, etc. are mixed to form a slurry. The timing of adding the liquid medium is not particularly limited. The binder of the present disclosure may be dispersed or dissolved in the liquid medium in advance, and then the active material and the like are mixed to form a slurry, or the active material, the binder of the present disclosure, and further, if necessary, a conductive assistant, a dispersion assistant, etc. are mixed in a solid state, and then the liquid medium is added to form a paste-like slurry.

[0074] <Electrode> The electrode of the present disclosure is an electrode for a secondary battery and contains the aforementioned secondary battery binder (or a component derived from the secondary battery binder) and active material in the present disclosure. That is, the electrode of the present disclosure can be produced, for example, by coating the aforementioned slurry of the present disclosure on a current collector and drying it. Therefore, the electrode may contain a heat-dried product of the slurry. The secondary battery binder may be decomposed or reacted by heat drying and converted into a component derived from the secondary battery binder.

[0075] The temperature during heat drying may be 50°C or higher, 70°C or higher, 90°C or higher, 110°C or higher, or 130°C or higher, preferably 70°C or higher, and may also be 300°C or lower, 250°C or lower, 200°C or lower, 175°C or lower, 150°C or lower, or 125°C or lower, preferably 150°C or lower. The heat drying may be performed under reduced pressure (for example, 0.05 MPa or lower, 0.03 MPa or lower, or 0.01 MPa or lower). The time for heat drying may be 1 hour or longer, 3 hours or longer, 6 hours or longer, 10 hours or longer, or 15 hours or longer, preferably 6 hours or longer, and may also be 72 hours or shorter, 48 hours or shorter, 36 hours or shorter, 24 hours or shorter, or 18 hours or shorter, preferably 24 hours or shorter.

[0076] When the electrode of the present disclosure is a negative electrode, as the material constituting the current collector, for example, conductive substances such as C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al, etc., and alloys containing two or more of these conductive substances (for example, stainless steel) can be used. Also, the current collector may be Fe plated with Cu. From the viewpoints of high electrical conductivity, excellent stability and oxidation resistance in the electrolytic solution, Cu, Ni, stainless steel, etc. are preferable as the material of the current collector of the negative electrode, and Cu or Ni is more preferable from the viewpoint of material cost.

[0077] When the electrode of the present disclosure is a positive electrode, as the material constituting the current collector, for example, conductive substances such as C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al, etc., and alloys containing two or more of these conductive substances (for example, stainless steel) can be used. From the viewpoints of high electrical conductivity, excellent stability and oxidation resistance in the electrolytic solution, C, Al, stainless steel, etc. are preferable as the material of the current collector of the positive electrode, and Al is more preferable from the viewpoint of material cost.

[0078] The shape of the current collector is not particularly limited, and for example, a foil-shaped substrate, a three-dimensional substrate, etc. can be used. When using a three-dimensional substrate (foamed metal, mesh, woven fabric, non-woven fabric, expand, etc.), the high-rate charge-discharge characteristics are also likely to be good.

[0079] <Battery> The secondary battery of the present disclosure includes the electrode for secondary battery of the present disclosure described above. The secondary battery of the present disclosure may be provided with the electrode for secondary battery of the present disclosure as either one or both of the positive electrode and the negative electrode. The secondary battery of the present disclosure is manufactured by using the electrode for secondary battery of the present disclosure (that is, by using the secondary battery binder in the present disclosure) and by a method used in the art.

[0080] The secondary battery of the present disclosure is preferably a non-aqueous electrolyte secondary battery, and particularly preferably a lithium ion secondary battery. Since a lithium ion secondary battery needs to contain lithium ions, a lithium salt is preferable as the electrolyte. Examples of this lithium salt include lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium trifluoromethanesulfonimide, and the like. The electrolyte can be used alone or in combination of two or more.

[0081] As the electrolytic solution, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, etc. can be used. The electrolytic solution can be used alone or in combination of two or more. In particular, propylene carbonate alone, a mixture of ethylene carbonate and diethyl carbonate, or γ-butyrolactone alone is preferable. The mixing ratio of the above-mentioned mixture of ethylene carbonate and diethyl carbonate can be arbitrarily adjusted within the range where one component is 10 to 90% by volume.

[0082] For the configurations of other secondary batteries, the configurations of known secondary batteries can be adopted.

[0083] Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

Examples

[0084] Hereinafter, the present disclosure will be described in detail with reference to examples, but the present disclosure is not limited to these examples.

[0085] The meanings of the abbreviations are as follows. AA: Acrylic acid AAm: Acrylamide 2-HEA: 2-Hydroxyethyl acrylate MAS: Methallylsulfonic acid VA: Vinyl alcohol CMC: Carboxymethyl cellulose SBR: Styrene-butadiene rubber

[0086] <Preparation of polymer> A polymer was prepared according to the procedure described below.

[0087] [Example 1] To a sealable vial with an internal volume of 500 ml, 35.3 g (0.49 mol) of acrylamide, 0.2 g (0.001 mol) of sodium methallylsulfonate, 35.3 g (0.49 mol) of acrylic acid, 48.6 g (0.42 mol) of 2-hydroxyethyl acrylate, 1.36 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (product name "VA-044" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 210.0 g of ion-exchanged water were added and mixed to prepare a monomer aqueous solution, which was deoxygenated. Separately from the above, into a 2 L reaction vessel equipped with a stirrer, a thermometer, an N 2 gas inlet tube, a reflux condenser and a dropping funnel, 858.3 g of ion-exchanged water was charged, and N 2After blowing in gas to deoxygenate the system, the internal temperature was raised to 68°C. Subsequently, under stirring in the reaction tank, the deoxygenated aqueous monomer solution was added dropwise from a dropping funnel over 3 hours. After the addition, the internal temperature was maintained at 68°C for 2 hours. Further, it was stirred at 73°C for 1 hour, cooled to 30°C, and 30.3 g of a 48 mass% NaOH aqueous solution was added until the pH reached 5.5, obtaining an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was AAm / AA(H / Na) / 2-HEA / MAS(H / Na) = 35 / 35 / 29.9 / 0.1 (molar ratio).

[0088] [Example 2] To a sealable vial with an internal volume of 500 ml, 40.0 g (0.56 mol) of acrylic acid, 60.0 g (0.52 mol) of 2-hydroxyethyl acrylate, 0.367 g of ammonium persulfate, and 50.0 g of ion-exchanged water were added and mixed to prepare an aqueous monomer solution, which was then deoxygenated. Separately from the above, a 1 L reaction tank equipped with a stirrer, thermometer, N 2 was charged with 500.0 g of ion-exchanged water, and N 2 After blowing in gas to deoxygenate the system, the internal temperature was raised to 75°C. Subsequently, under stirring in the reaction tank, the prepared aqueous monomer solution was added dropwise from a dropping funnel over 3 hours. After the addition, it was held for 2 hours. Then, the internal temperature was raised to 80°C and held for 1 hour. Thereafter, the internal temperature was cooled to 40°C, and 124.9 g (0.53 mol) of a 5 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 6.5, obtaining an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was 2-HEA / AA(H / Na) = 48 / 52 (molar ratio).

[0089] 〔Example 3〕 To a sealable vial with an internal volume of 500 ml, 23.8 g (0.33 mol) of acrylic acid, 22.6 g (0.19 mol) of 2-hydroxyethyl acrylate, 69.3 g (0.97 mol) of acrylamide, 0.608 g of ammonium persulfate, and 225.0 g of ion-exchanged water were added and mixed to prepare an aqueous monomer solution. Separately from the above, a stirrer, thermometer, N 2A 1-L reaction vessel equipped with a gas inlet tube, a reflux condenser, and a dropping funnel was charged with 607.6 g of ion-exchanged water and N 2 gas was blown in to deoxygenate the system, and then the internal temperature was raised to 75°C. Subsequently, the prepared aqueous monomer solution was added dropwise to the reaction vessel with stirring through the dropping funnel over 3 hours. After the addition, it was held for 2 hours. Then, the internal temperature was raised to 80°C and held for 1 hour. The internal temperature was cooled to 30°C, and 70.57 g (0.30 mol) of a 5 mol / L aqueous sodium hydroxide solution was added to adjust the pH to 6.5, obtaining an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was 2-HEA / AA(H / Na) / AAm = 13 / 22 / 65 (molar ratio).

[0090] [Example 4] To a 500-ml beaker, 46.5 g (0.54 mol) of methyl acrylate and 211.8 g (2.46 mol) of vinyl acetate were added to a 500-ml sealable vial and mixed to prepare an aqueous monomer solution. Separately from the above, a 2-L reaction vessel equipped with a stirrer, a thermometer, N 2 gas inlet tube, a reflux condenser, and a dropping funnel was charged with 768 g of ion-exchanged water and 12 g of anhydrous sodium sulfate, and N 2 gas was blown in to deoxygenate the system. Subsequently, 1 g of partially saponified polyvinyl alcohol (saponification degree 88%) and 1.2 g of lauryl peroxide were added, and the internal temperature was raised to 60°C. Subsequently, the prepared aqueous monomer solution was added dropwise to the reaction vessel with stirring through the dropping funnel over 4 hours. After the addition, the internal temperature was held at 65°C for 2 hours, and the precipitated solid content was filtered. To the same reaction vessel as above, the obtained solid content, 450 g of methanol, 420 g of ion-exchanged water, 140 g of sodium hydroxide, and 0.52 g of hydrazine were charged and stirred at 35°C for 3 hours. Subsequently, the internal temperature was cooled to 30°C, acetic acid was added to adjust the pH to 7.5, and after filtering off the solid content, the solid content was washed with methanol and dried at 60°C under reduced pressure for 8 hours to obtain an aqueous polymer. The composition of the repeating unit of the aqueous polymer was VA / AA(H / Na) = 82 / 18 (molar ratio).

[0091] [Comparative Example 1] Stirrer, thermometer, N2 831.0 g of ion-exchanged water was charged into a 2-L reaction vessel equipped with a gas inlet tube, a reflux condenser, and a dropping funnel. After introducing N 2 gas to deoxygenate the system, the internal temperature was raised to 68 °C. A previously prepared mixed solution of 126.6 g (1.78 mol) of acrylamide, 2.9 g (0.02 mol) of sodium methallylsulfonate, 1.45 g of 2,2’-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (product name “VA-044” manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 250.0 g of ion-exchanged water was added dropwise from the dropping funnel over 3 hours. After the addition, the mixture was held at the same temperature for 1.5 hours. Subsequently, 1.45 g of VA-044 and 20 g of ion-exchanged water were added, and the mixture was stirred at the same temperature for 1 hour and then stirred at 73 °C for 1 hour to obtain an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was AAm / MAS (H / Na) = 99 / 1 (molar ratio).

[0092] [Comparative Example 2] A 1-L reaction vessel equipped with a stirrer, a thermometer, an N 2 gas inlet tube, a reflux condenser, and a dropping funnel was charged with 485.3 g of ion-exchanged water and 100.0 g of terminal thiol-modified polyvinyl alcohol (degree of polymerization 375, degree of saponification 98.7 mol%). After introducing N 2 gas to deoxygenate the system, the internal temperature was raised to 95 °C and then cooled to room temperature. Subsequently, the pH was adjusted to 3.0 with 0.5 N sulfuric acid. Next, the internal temperature was raised to 62 °C, and 9.9 g (0.14 mol) of acrylic acid, 1.70 g of ammonium persulfate, and 75.2 g of ion-exchanged water were added dropwise from the dropping funnel over 1.5 hours with stirring. After the addition, the mixture was held for 0.5 hour while maintaining the internal temperature at 62 °C and then stirred at 67 °C for 1 hour. Thereafter, the internal temperature was cooled to 30 °C, and 5.72 g (0.69 mol) of a 48% by mass aqueous sodium hydroxide solution was added to obtain an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was VA / AA (H / Na) = 94 / 6 (molar ratio).

[0093] [Comparative Example 3] A mixture of carboxymethyl cellulose and styrene-butadiene rubber (CMC / SBR = 1 / 2 (solid weight ratio)) was used.

[0094] <Measurement of Polymer Properties> The properties of the aqueous polymers obtained in the above Examples / Comparative Examples were measured. The test methods are as follows.

[0095] [Molecular Weight, etc.] Regarding the aqueous polymers obtained in the above Examples / Comparative Examples, in terms of standard polyethylene glycol / polyethylene oxide conversion, Mw (weight-average molecular weight) was measured using GPC-RI. The details of the conditions are as follows. [GPC-RI] GPC apparatus: HLC-8320GPC (manufactured by Tosoh Corporation) Column: TSK GMPW XL (manufactured by Tosoh Corporation) Carrier: 0.1 M sodium nitrate Column temperature: 40 °C Flow rate: 1.0 mL / min Injection volume: 200 μL Concentration: 0.5 mg / mL

[0096] [pH] An aqueous polymer solution was prepared by dissolving the aqueous polymer in water so that the solid content concentration was 2% by mass. After maintaining the aqueous solution at 25 °C, the pH was measured using a pH meter (manufactured by Horiba, Ltd., model "D-71", glass pH electrode: model "9681S-10D"). The pH was calculated by rounding the second decimal place of the measured value.

[0097] [Viscosity] An aqueous polymer solution was prepared by dissolving the aqueous polymer in water so that the solid content concentration was 2% by mass. After maintaining the aqueous solution at 25 °C, the viscosity of the aqueous polymer solution was measured using a B-type viscometer (manufactured by BROOKFIELD, model "DV1MLVTJ0"). When measuring, the spindle and rotation speed corresponding to the viscosity were adopted as follows. LV-2, 12 rpm: 250 - 2500 mPa·s LV-1, 30 rpm: 20 - 200 mPa·s

[0098] 〔Conductivity〕 An aqueous polymer solution was prepared by dissolving an aqueous polymer in water so that the solid content concentration was 2% by mass. After keeping the temperature at 25 °C, the conductivity was measured using a conductivity meter (manufactured by AS ONE, model "AS710"). The conductivity was calculated by rounding the second decimal place of the measured value.

[0099] 〔Na Concentration〕 60% by mass nitric acid was added to an aqueous polymer solution prepared by dissolving an aqueous polymer in water so that the solid content concentration was 2% by mass to prepare a measurement solution by heating and dissolving. The mass of Na contained in the measurement solution was measured by analysis using an inductively coupled plasma optical emission spectrometer (manufactured by Thermo Fisher). The Na concentration of the 2% by mass aqueous polymer solution was calculated by the following formula. Na concentration = mass of Na in the measurement solution / mass of the added aqueous polymer solution × 100 [%]

[0100] 〔Electrolyte Absorption Rate (25 °C)〕 20 g of an aqueous polymer solution prepared by dissolving an aqueous polymer in water so that the solid content concentration was 2% by mass was added to a polypropylene tray (manufactured by AS ONE, model "DT-1"), and dried in a forced-air constant-temperature thermostat (manufactured by Yamato Scientific, model "DKM300") at 60 °C for 15 hours. Then, additional drying was performed in a vacuum dryer (manufactured by AS ONE, model "AVO-310N") at 60 °C and a reduced pressure of 0.1 MPa for 24 hours to produce a film. The film produced by the above method was cut into 40 mg (about 2 cm square) in a dry booth with a dew point of -70 °C, and the weight of the film before immersion in the electrolyte was measured. Then, the cut film was placed in a 50 mL screw tube bottle, 20 g of an electrolyte (ethylene carbonate / dimethyl carbonate = 1 / 1 v / v%, manufactured by Kishida Chemical) was added to immerse the film, the screw tube bottle was sealed, and stored in a safety tester (manufactured by ESPEC, model "CSH112") set at 25 °C for 22 hours. After storage, the film was taken out of the electrolyte in the drive booth, sandwiched with Kimwipes, and a load of about 700 g was applied from above for 2 seconds to wipe off the electrolyte. Then, the weight after immersion in the electrolyte was measured, and the electrolyte absorption rate was calculated using the following formula. Electrolyte absorption rate = (weight after immersion in electrolyte - weight before immersion in electrolyte) / weight before immersion in electrolyte × 100 [%] <Characteristics of battery / slurry / binder liquid, etc.> Using the aqueous polymer obtained in the above Examples / Comparative Examples, a battery / slurry / binder liquid was prepared, and its characteristics were measured. The test method is as follows.

[0101] [Capacity retention rate after 100 cycles] The capacity retention rate after 100 cycles was determined according to the following procedure. [Fabrication of electrode] As the electrode active material, 23.3 parts by mass of artificial graphite (manufactured by Jiangxi Zichen Technology, G-49), 5.8 parts by mass of silicon monoxide (manufactured by Shin-Etsu Chemical Co., Ltd., KSC-1265), and 0.9 parts by mass of the polymer aqueous solution in terms of solid content were kneaded. Further, water was added and kneaded so that the solid content concentration became 58% by mass to prepare a slurry-like negative electrode slurry. The obtained negative electrode slurry was applied onto a rolled copper foil with a thickness of 18 μm, dried, and then the rolled copper foil and the coating film were adhesively bonded by a roll press machine (manufactured by Ohno Roll Co., Ltd.). Next, heat treatment (under reduced pressure, 100 °C, 12 hours or more) was performed to fabricate a negative electrode. The thickness of the active material layer in the obtained negative electrode was 36 μm, and the capacity density of the negative electrode was 3.5 mAh / cm 2 It was.

[0102] [Assembly of coin cell] A coin cell (CR2032) was fabricated, which included the negative electrode fabricated above, the following positive electrode, a separator, and an electrolyte. · Positive electrode: LiNi 0.5 Co 0.2 Mn 0.3 O 2 (manufactured by Yama Co., Ltd.) · Separator: Glass filter (product name GA-100, manufactured by Advantec Co., Ltd.) ·Electrolyte: A solution prepared by dissolving LiPF 6 in a solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1:1, adding 1 mass% of vinylene carbonate (VC), which is an additive for the electrolyte, and 1 mass% of fluoroethylene carbonate (FEC).

[0103] [Measurement of Capacity Retention Rate] For each coin cell fabricated as described above, at 30 °C, charge up to 4.2 V at a current corresponding to 0.1C, discharge to 2.5 V at a current corresponding to 0.1C, charge up to 4.2 V at a current corresponding to 0.5C, and discharge to 2.5 V at a current corresponding to 0.5C. Repeat these operations for 3 cycles to age the battery. Subsequently, after charging up to 4.2 V at a current corresponding to 0.5C, discharge to SOC50 at a current corresponding to 0.5C, perform constant current discharge for 12 seconds at a current corresponding to 0.2C, charge for 24 seconds at a current corresponding to 0.1C, perform constant current discharge for 12 seconds at a current corresponding to 0.5C, charge for 1 minute at a current corresponding to 0.1C, perform constant current discharge for 12 seconds at a current corresponding to 1C, charge for 2 minutes at a current corresponding to 0.1C, perform constant current discharge for 12 seconds at a current corresponding to 2C, and then discharge to 2.5 V at a current corresponding to 0.2C to measure the initial discharge capacity. Subsequently, charge up to 4.2 V at a current corresponding to 1C and discharge to 2.5 V at a current corresponding to 1C. Repeat these operations for 97 cycles (cycles 4 to 100). Thereafter, perform the same operations as when measuring the initial discharge capacity to measure the discharge capacity after 100 cycles. Capacity retention rate after 100 cycles = [Discharge capacity after 100 cycles (mAh / g)] / [Initial discharge capacity after aging (mAh / g)] × 100 [%]

[0104] [Discharge Capacity after 100 Cycles] Measure the discharge capacity after 100 cycles in the test of the above [Capacity Retention Rate after 100 Cycles].

[0105] [Swelling Rate after 100 Cycles] The expansion rate after 100 cycles was determined according to the following procedure. [Fabrication of Electrodes] Electrodes were fabricated in the same manner as described in the above [Capacity Retention Rate after 100 Cycles].

[0106] [Assembly of Coin Cells] Coin cells (CR2032) equipped with a negative electrode, the following positive electrode, a separator, and an electrolyte were fabricated in the same manner as described in the above [Capacity Retention Rate after 100 Cycles].

[0107] [Measurement of Expansion Rate] For each of the coin cells fabricated as described above, at 30 °C, charging was performed up to 4.2 V at a current corresponding to 0.1C, discharging was performed up to 2.5 V at a current corresponding to 0.1C, charging was performed up to 4.2 V at a current corresponding to 0.5C, and discharging was performed up to 2.5 V at a current corresponding to 0.5C. This operation was repeated for 3 cycles to age the battery. Subsequently, after charging up to 4.2 V at a current corresponding to 0.5C, discharging was performed up to SOC50 at a current corresponding to 0.5C, constant current discharging was performed for 12 seconds at a current corresponding to 0.2C, charging was performed for 24 seconds at a current corresponding to 0.1C, constant current discharging was performed for 12 seconds at a current corresponding to 0.5C, charging was performed for 1 minute at a current corresponding to 0.1C, constant current discharging was performed for 12 seconds at a current corresponding to 1C, charging was performed for 2 minutes at a current corresponding to 0.1C, constant current discharging was performed for 12 seconds at a current corresponding to 2C, and then discharging was performed up to 2.5 V at a current corresponding to 0.2C (initial discharging operation). Subsequently, charging was performed up to 4.2 V at a current corresponding to 1C, and discharging was performed up to 2.5 V at a current corresponding to 1C for 97 cycles (cycles 4 to 100). Thereafter, the secondary battery was disassembled in a dry booth, and the negative electrode was taken out. It was washed with dimethyl carbonate, dried under reduced pressure at 23 °C for 1 hour, and the electrode thickness was measured with a micrometer. The active material layer thickness was calculated by subtracting the copper foil thickness from the electrode thickness, and the expansion rate was calculated using the following formula. Expansion rate after 100 cycles = (Active material layer thickness after disassembly after 100 cycles) / (Active material layer thickness at the time of battery fabrication) × 100 [%]

[0108] [DC Resistance (DCR) after 100 Cycles] [Fabrication of Electrodes] Electrodes were fabricated in the same manner as described in the above [Capacity Retention Rate after 100 Cycles]. [Assembly of Coin Cells] Coin cells (CR2032) equipped with a negative electrode, the following positive electrode, a separator, and an electrolyte were fabricated in the same manner as described in the above [Capacity Retention Rate after 100 Cycles].

[0109] [Measurement of DC Resistance after 100 Cycles] For each of the coin cells fabricated as described above, at 30 °C, charging was performed up to 4.2 V with a current corresponding to 0.1C, discharging was performed down to 2.5 V with a current corresponding to 0.1C, charging was performed up to 4.2 V with a current corresponding to 0.5C, and discharging was performed down to 2.5 V with a current corresponding to 0.5C. This operation was repeated 3 cycles to age the battery. Subsequently, after charging up to 4.2 V with a current corresponding to 0.5C, discharging was performed down to SOC50 with a current corresponding to 0.5C, constant current discharging was performed for 12 seconds with a current corresponding to 0.2C, charging was performed for 24 seconds with a current corresponding to 0.1C, constant current discharging was performed for 12 seconds with a current corresponding to 0.5C, charging was performed for 1 minute with a current corresponding to 0.1C, constant current discharging was performed for 12 seconds with a current corresponding to 1C, charging was performed for 2 minutes with a current corresponding to 0.1C, constant current discharging was performed for 12 seconds with a current corresponding to 2C, and then discharging was performed down to 2.5 V with a current corresponding to 0.2C (initial discharging operation). Subsequently, charging was performed up to 4.2 V with a current corresponding to 1C, and discharging was performed down to 2.5 V with a current corresponding to 1C. This operation was repeated 97 cycles (cycles 4 to 100). Thereafter, the same operation as the initial discharging operation was performed. The DC resistance of the cell was calculated from the values of the discharging current and voltage at 10.0 seconds of the C-rate of each coin cell, and this was taken as the DC resistance after 100 cycles.

[0110] [Peel Strength] The peel strength (adhesion strength) was determined according to the following procedure. [Fabrication of Electrodes] As the electrode active material, 23.3 parts by mass of artificial graphite (manufactured by Jiangxi Zichen Technology, G-49), 5.8 parts by mass of silicon monoxide (manufactured by Shin-Etsu Chemical Co., Ltd., KSC-1265), and 0.9 parts by mass of an aqueous polymer solution in terms of solid content were kneaded. Further, water was added and kneaded so that the solid content concentration became 58% by mass to prepare a negative electrode slurry. The obtained negative electrode slurry was applied onto a rolled copper foil with a thickness of 18 μm and dried. Then, the rolled copper foil and the coating film were adhesively bonded by a roll press machine (manufactured by Ohno Roll Co., Ltd.). Next, heat treatment (under reduced pressure, 100 °C, 12 hours or more) was performed to fabricate a negative electrode. The thickness of the active material layer in the obtained negative electrode was 36 μm, and the capacity density of the negative electrode was 3.5 mAh / cm 2 It was. [Measurement of peel strength] For the obtained electrodes, the peel strength (N / 15 mm) when the active material layer was peeled from the current collector foil was measured respectively. As a specific method, the electrode was cut into a size of 80 mm in width × 15 mm, and an adhesive tape was attached to the surface (electrode active material layer side). Then, it was attached to a stainless-steel plate with a double-sided tape to fix the electrode (current collector foil side), and this was used as an evaluation sample. Using this evaluation sample, a 90-degree peel test of the electrode with respect to the stainless-steel plate (90-degree peel test of the adhesive tape with respect to the negative electrode fixed to the stainless-steel plate) was performed with a tensile testing machine (manufactured by Shimadzu Corporation, small desktop testing machine EZ-SX), and the peel strength between the active material layer and the current collector foil in the electrode was measured.

[0111] [Mandrel test] The mandrel test was conducted according to the following procedure. [Fabrication of electrode] An electrode was fabricated in the same manner as described in the above [Peel strength]. [Mandrel test] In accordance with JIS K 5600-5-1, with the active material surface of the electrode facing outward, a bending test was performed on 4 electrodes using a mandrel with a diameter of 3 mm so that the active material layer was on the outside, and the number of electrodes with cracks and fractures on the electrode surface was recorded.

[0112] [Viscosity change rate after one week at 20 °C] An aqueous polymer solution was prepared by dissolving an aqueous polymer in water so that the solid content concentration was 2% by mass. After keeping the aqueous solution at 25°C, the viscosity before storage was measured using a B-type viscometer (manufactured by BROOKFIELD, model "DV1MLVTJ0"). Then, the 2% by mass aqueous solution was allowed to stand and stored at 20°C for 1 week. After keeping it at 25°C, the viscosity after storage was measured using a B-type viscometer (manufactured by BROOKFIELD, model "DV1MLVTJ0"). The viscosity change rate was calculated using the following formula. Viscosity change rate = (viscosity after storage - viscosity before storage) / viscosity before storage × 100 [%] In addition, the spindle and rotation speed corresponding to the viscosity were adopted as follows. LV-2, 12 rpm: 250 - 2500 mPa·s LV-1, 30 rpm: 20 - 200 mPa·s

[0113] The test results are summarized in the following table. TIFF0007684497000001.tif87164

Industrial Applicability

[0114] The present disclosure is suitably used for power sources of mobile communication devices, portable electronic devices, electric bicycles, electric motorcycles, electric vehicles, etc.

Claims

1. Contains water-based polymers, The aqueous solution obtained by dissolving the aqueous polymer in water at a concentration of 2% by mass has a Na concentration of 0.05% by mass or more and 0.25% by mass or less; The aqueous polymer has an electrolyte absorption rate (25° C.) of 8.0% or less, and the electrolyte has a composition in which the ratio of ethylene carbonate to dimethyl carbonate is 1 / 1 v / v%, A secondary battery binder, wherein an aqueous solution obtained by dissolving the aqueous polymer in water at a concentration of 2 mass % has a pH of 6.5 or more and 8.5 or less at 25°C.

2. The secondary battery binder according to claim 1 , wherein the electrolyte absorption rate (25° C.) is 2% or more and 6.5% or less.

3. 3. The secondary battery binder according to claim 1, wherein the aqueous polymer is a vinyl polymer having an acidic functional group-containing repeating unit.

4. The water-based polymer is formula: -[CH ２ -C(R １ )(C(=O)R ２ )]- [In the formula, R 1 is a hydrogen atom or CH ３ and R 2 NH ２ , OM (M is a hydrogen atom or a counter cation), O(CH ２ ) ｎ OH, NH(CH ２ ) ｎ OH (wherein each n is independently 1 or more and 6 or less). A repeating unit (1) represented by the formula: formula: -[CH ２ -CH(OH)]- Repeating unit (2) represented by the formula: The secondary battery binder according to claim 1 or 2, comprising a repeat unit selected from

5. In the water-based polymer, the amount of the repeating unit selected from the repeating unit (1) and the repeating unit (2) is 40 mol % or more, The amount of the acidic functional group-containing repeating unit is 0.8 mol % or more, 5. The secondary battery binder of claim 4, wherein the amount of non-ionic repeat units is 40 mol % or more.

6. 3. The secondary battery binder of claim 1 or 2, comprising SBR.

7. A slurry comprising the secondary battery binder according to claim 1 or 2 and water.

8. The slurry of claim 7 further comprising an electrode active material.

9. A method for producing a secondary battery, comprising the step of applying the slurry according to claim 7 .

10. 3. An electrode comprising the secondary battery binder according to claim 1 or 2 or a component derived from said secondary battery binder.

11. An electrode comprising the heat-dried slurry according to claim 8.

12. A secondary battery comprising the electrode according to claim 10.

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