JP6623808B2 - Slurry for negative electrode and method for producing negative electrode - Google Patents

Description

  The present invention relates to a slurry for a negative electrode used to obtain a negative electrode of a power storage device, and a method for manufacturing a negative electrode using the slurry.

Portable devices such as mobile phones and notebook computers are widely used as products using secondary batteries. Secondary batteries are also attracting attention as large power sources for electric vehicles.
The electrode of the secondary battery includes, for example, a current collector formed of a metal material such as copper or aluminum, and an active material layer bound on the current collector. In general, the active material layer contains an electrode binder for binding the active material. In recent years, use of an anionic vinyl-based polymer having a carboxyl group such as polyacrylic acid as an electrode binder has been attempted. Patent Literature 1 discloses an electrode binder including lithium polyacrylate and sodium polyacrylate. Patent Document 2 discloses an electrode binder including polyacrylic acid and polyethyleneimine. Patent Document 3 discloses an electrode binder including polyacrylic acid and an amine compound.

JP 2009-080971 A JP 2009-135103 A JP 2003-003031 A

  The negative electrode has a current collector and a negative electrode active material layer laminated on the current collector. The negative electrode active material layer is obtained using a negative electrode electrode slurry that is a dispersion of the negative electrode active material. When carbon black is contained in the slurry for the negative electrode using N-methyl-2-pyrrolidone as a dispersion medium, a dispersant for dispersing carbon black is required. When the negative electrode slurry further contains a carboxyl group-containing anionic vinyl polymer and a polyfunctional amine as binder components, the viscosity of the negative electrode slurry may be excessively increased.

  An object of the present invention is to provide a negative electrode slurry capable of suppressing an increase in viscosity and a method for manufacturing a negative electrode using the same.

  The slurry for a negative electrode for solving the above-mentioned problem is a slurry for a negative electrode for obtaining a negative electrode of a power storage device, comprising a negative electrode active material, a binder component, carbon black, N-methyl-2-pyrrolidone, and a dispersant. And the binder component contains an anionic vinyl polymer having a carboxyl group and a polyfunctional amine, and the dispersant contains a nonionic polymer.

In the slurry for a negative electrode, the dispersant preferably includes at least one of polyvinyl alcohol and polyvinylpyrrolidone.
A method for manufacturing a negative electrode that solves the above problem is a method for manufacturing a negative electrode of a power storage device, and obtains a negative electrode using the slurry for a negative electrode.

  According to the present invention, it is possible to suppress an increase in viscosity.

Hereinafter, embodiments of the slurry for the negative electrode and the method for producing the negative electrode will be described.
The negative electrode slurry is used for obtaining a negative electrode of a power storage device.
The slurry for the negative electrode contains (A) a negative electrode active material, (B) carbon black, (C) a binder component, (D) N-methyl-2-pyrrolidone, and (E) a dispersant.

<(A) Negative electrode active material>
As the negative electrode active material, a known material used as a negative electrode active material of a power storage device such as a secondary battery can be used. Examples of the negative electrode active material include a carbon-based material, an element capable of being alloyed with lithium, and a compound having an element capable of being alloyed with lithium.

  As the carbon-based material, for example, a material capable of occluding and releasing lithium, for example, non-graphitizable carbon, natural graphite, artificial graphite, cokes, graphites, glassy carbons, and organic polymer compound fired bodies , Carbon fiber, and activated carbon.

  Elements that can be alloyed with lithium include, for example, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb and Bi are mentioned. Among elements that can be alloyed with lithium, Si is particularly preferable.

  Examples of the compound having an element that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, and In. , Si, Ge, Sn, Pb, Sb, and a compound having an element selected from Bi. Among these compounds, a silicon-based material that is a compound having Si is particularly preferable.

As the silicon-based material, for example, SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _V (0 <V ≦ 2), SnSiO ₃ , and LiSiO. Among the silicon-based materials, SiO _V (0 <V ≦ 2) is preferable.

Examples of the silicon-based material include a silicon material obtained from CaSi ₂ through a decalcification reaction disclosed in International Publication No. 2014/080608. The silicon material is obtained by, for example, decalcifying (for example, heating at 300 to 1000 ° C.) a layered polysilane obtained by treating CaSi ₂ with an acid (for example, hydrochloric acid or hydrogen fluoride).

As the negative electrode active material, only one type may be used, or two or more types may be used in combination.
The content of the negative electrode active material in the slurry for the negative electrode is preferably, for example, in the range of 5: 3 to 99: 1 in the mass ratio of the negative electrode active material and the binder component (negative electrode active material: binder component). , More preferably in the range of 3: 1 to 97: 3, even more preferably in the range of 16: 3 to 95: 5. When the negative electrode active material is the above-described silicon material disclosed in International Publication No. 2014/080608, the mass ratio between the silicon material and the binder component (silicon material: binder component) is 3: 1 to 7.5. : 1, preferably in the range of 4: 1 to 5: 1.

<(B) Carbon black>
Carbon black has a function as a conductive assistant. Examples of the carbon black include acetylene black, furnace black, and Ketjen black. Only one type of carbon black may be used, or two or more types may be used in combination. The carbon black preferably contains acetylene black. Acetylene black preferably has a 50% particle diameter (D50) in the range of 0.35 to 0.75 μm, from the viewpoint of further improving the characteristics (cycle characteristics) of the power storage device, and 0.18 to 0.25 μm. More preferably, it has a 10% particle diameter (D10) in the range of 1.6 to 3.5 and a 90% particle diameter (D90) in the range of 1.6 to 3.5 μm. The 50% particle diameter means a secondary particle diameter of acetylene black at an integrated value of 50% in a particle size distribution obtained by a laser diffraction / scattering method. The same applies to the 10% particle size and the 90% particle size.

The content of carbon black in the slurry for the negative electrode is preferably in the range of 0.5 to 1.5 parts by mass with respect to 1 part by mass of the binder component.
<(C) Binder component>
The binder component contains an anionic vinyl polymer having a carboxyl group and a polyfunctional amine. The anionic vinyl polymer having a carboxyl group and the polyfunctional amine are components that are condensed by heating to produce a binder having a crosslinked structure.

  Examples of the anionic vinyl polymer having a carboxyl group include polyacrylic acid, polymethacrylic acid, a copolymer of acrylic acid and methacrylic acid, and a copolymer of at least one of acrylic acid and methacrylic acid with a vinyl monomer. Coalescence. Examples of the vinyl monomer constituting the copolymer with at least one of acrylic acid and methacrylic acid include, for example, acrylic ester, methacrylic ester, butene, isobutene, maleic acid, itaconic acid, acrylamide, methacrylamide, styrene, acrylonitrile, At least one selected from compounds having a vinyl group, a vinylene group, and a vinylidene group, such as methacrylonitrile, is exemplified.

As the anionic vinyl polymer having a carboxyl group, only one kind may be used, or two or more kinds may be used in combination.
The weight average molecular weight of the anionic vinyl polymer having a carboxyl group is not particularly limited, but is preferably, for example, in the range of 10,000 to 2,000,000, and in the range of 25,000 to 1,800,000. Is more preferable, and the range is more preferably 50,000 to 1,500,000.

  A polyfunctional amine is a compound having two or more amino groups. Examples of the polyfunctional amine include an aromatic polyfunctional amine having a structure represented by the following general formula (1).

Y in the general formula (1) is a linear alkyl group having 1 to 4 carbon atoms, a phenylene group, or an oxygen atom. Further, the bonding position of Y in each benzene ring may be any of the ortho, meta and para positions with respect to the amino group.

  When Y in the general formula (1) is a linear alkyl group or a phenylene group, a substituent may be bonded to a carbon atom constituting the structure. For example, examples of the substituent bonded to the carbon atom constituting the linear alkyl group include a methyl group, an ethyl group, a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a methoxy group, an ethoxy group, and an oxo group. . One of these substituents may be bonded, or two or more thereof may be bonded. Further, the number of substituents bonded to one carbon atom may be one or two. Further, the substituent bonded to the carbon atom constituting the linear alkyl group and the phenylene group may be an amino group or a substituent containing an amino group, and in this case, it has three or more amino groups. It becomes a polyfunctional amine.

  R1 and R2 in the general formula (1) are each independently one or more hydrogen atoms, a methyl group, an ethyl group, a trifluoromethyl group, or a methoxy group. When R1 is a methyl group, an ethyl group, a trifluoromethyl group, or a methoxy group, the bonding position of R1 may be any of the ortho, meta, and para positions with respect to the amino group. The same applies to R2.

  Examples of the compound in which Y in the general formula (1) is a linear alkyl group include, for example, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, and 4,4′- Ethylene dianiline, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 1,1-bis (4-aminophenyl) cyclohexane, 9,9-bis (4-aminophenyl) fluorene, 2,2'- Bis (4-aminophenyl) hexafluoropropane, 4,4'-diaminobenzophenone, 4,4'-methylenebis (2-ethyl-6-methylaniline), and pararoseaniline. Examples of the compound in which Y in the general formula (1) is a phenylene group include 1,3,5-tris (4-aminophenyl) benzene. Examples of the compound in which Y in the general formula (1) is an oxygen atom include 4,4'-diaminodiphenyl ether. 1,3,5-tris (4-aminophenyl) benzene and pararoseaniline are trifunctional amines having three amino groups.

  Examples of the polyfunctional amine other than the aromatic polyfunctional amine represented by the general formula (1) include 1,4-diaminobutane, 1,6-diaminohexane, 1,8-diaminooctane, and 2-aminoaniline ( 1,2-phenylenediamine), 3-aminoaniline (1,3-phenylenediamine), 4-aminoaniline (1,4-phenylenediamine), 2,4-diaminopyridine, 2,5-diaminopyridine, 2, 6-diaminopyridine and 1,3-diiminoisoindoline.

As the polyfunctional amine, only one kind may be used, or two or more kinds may be used in combination.
When the total amount of the polyfunctional amine is 10 parts by mass, the amount of the polyfunctional amine other than the aromatic polyfunctional amine represented by the general formula (1) is preferably 1 part by mass or less.

  The mixing ratio of the anionic vinyl polymer having a carboxyl group and the polyfunctional amine is set so that the number of carboxyl groups of the anionic vinyl polymer is larger than the number of amino groups of the polyfunctional amine. In other words, the mixing ratio is set so that the carboxyl group of the anionic vinyl polymer is at least 1 equivalent to 1 equivalent of the amino group of the polyfunctional amine. The ratio of the number of carboxyl groups of the anionic vinyl polymer to the number of amino groups of the polyfunctional amine (carboxyl group / amino group ratio) is preferably in the range of 1.5 / 1 to 15/1, and More preferably, it is in the range of 1 to 10/1.

  It is preferable that the binder component containing the anionic vinyl polymer having a carboxyl group and the polyfunctional amine has been subjected to a preliminary heat treatment. The slurry for the negative electrode containing the binder component subjected to the preheating is formed by the association of the anionic vinyl polymer having a carboxyl group with the polyfunctional amine and the partial condensation of the carboxyl group and the amino group. The state is such that the condensation reaction between the system polymer and the polyfunctional amine is easily promoted. Thereby, for example, it is possible to shorten the heating time when using the slurry for the negative electrode.

  The binder component may further contain at least one reactive low molecular compound of a polyfunctional carboxylic acid and a monoamine from the viewpoint of adjusting the mechanical or chemical properties of the obtained binder. When a polyfunctional carboxylic acid is further contained in the slurry for the negative electrode as a binder component, a binder having a crosslinked structure derived from both the polyfunctional carboxylic acid and the polyfunctional amine can be formed. When a monoamine is contained as a binder component in the negative electrode slurry, the monoamine binds to the carboxyl group of the anionic vinyl-based polymer, and a non-crosslinked portion is formed in the binder. The monoamine may be an aliphatic monoamine or an aromatic monoamine. The content of the reactive low-molecular compound in the slurry for the negative electrode is preferably, for example, 1 part by mass or less based on 10 parts by mass of the aromatic polyfunctional amine represented by the general formula (1).

  The binder component may include a polymer other than the anionic vinyl-based polymer having a carboxyl group. Examples of this polymer include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyimide, polyamideimide, carboxymethylcellulose, polyvinyl chloride, methacrylic resin, polyacrylonitrile, modified polyphenylene oxide, polyethylene oxide, polyethylene, and polypropylene. And at least one selected from phenolic resins.

  The solid content composed of the anionic vinyl polymer and the polyfunctional amine is preferably 1% by mass or more, and more preferably 10% by mass or more, based on the total solid content of the binder component in the negative electrode slurry. Is more preferable.

<(D) N-methyl-2-pyrrolidone>
N-methyl-2-pyrrolidone functions as a dispersion medium for the negative electrode active material and carbon black and as a solvent for the binder component.

  The content of N-methyl-2-pyrrolidone in the slurry for the negative electrode is preferably in the range of 30 to 900 parts by mass with respect to 100 parts by mass of the total amount of the negative electrode active material, carbon black, and the binder component. .

  When the content of N-methyl-2-pyrrolidone in the slurry for the negative electrode is increased, the dispersibility of the negative electrode active material and carbon black and the solubility of the binder component can be increased. When the content of N-methyl-2-pyrrolidone in the slurry for the negative electrode is reduced, N-methyl-2-pyrrolidone is easily removed when the negative electrode is manufactured.

<(E) Dispersant>
The dispersant has a function of dispersing carbon black in N-methyl-2-pyrrolidone in the presence of the binder component. The dispersant is composed of a nonionic polymer.

  Examples of the nonionic polymer of the dispersant include polyvinyl alcohol, polyvinyl pyrrolidone (poly (N-vinyl-2-pyrrolidone)), polyvinyl butyral, polyacrylamide, polyethylene glycol, polypropylene glycol, polyacrylonitrile, polycaprolactone, polyethylene oxide, Examples thereof include polyisobutylene, dimethylpolysiloxane, and polyether polyol.

Only one type of dispersant may be used, or two or more types may be used in combination.
The dispersant preferably contains at least one of polyvinyl alcohol and polyvinyl pyrrolidone, and more preferably contains polyvinyl alcohol. In this case, characteristics of the power storage device can be improved.

  The degree of saponification of polyvinyl alcohol is preferably in the range of 72 to 90 mol%, more preferably in the range of 86 to 90 mol%. In this case, it is possible to further suppress an increase in viscosity of the slurry for the negative electrode.

  As defined in JIS K6726: 1994, the degree of saponification of polyvinyl alcohol can be determined by quantifying residual acetic acid groups (mol%) in a sample of polyvinyl alcohol with sodium hydroxide and subtracting from 100.

  The average degree of polymerization of polyvinyl alcohol is preferably in the range of 300 to 3500, and more preferably in the range of 1000 to 3000. In this case, it is easy to further suppress an increase in the viscosity of the slurry for the negative electrode.

  As defined in JIS K6726: 1994, the average degree of polymerization of polyvinyl alcohol was obtained by completely saponifying a sample of polyvinyl alcohol in advance using sodium hydroxide, and then measuring the relative viscosity with water using a viscometer. It can be calculated from this relative viscosity.

  The content of the dispersant in the slurry for the negative electrode is preferably in the range of 1 to 15 parts by mass, more preferably 1 to 10 parts by mass, and still more preferably 100 parts by mass of carbon black. It is in the range of 1 to 8 parts by mass. When the content of the dispersant is increased, the viscosity of the slurry for the negative electrode can be further suppressed. When the content of the dispersant is reduced, characteristics of the power storage device can be improved.

<Components other than the above components>
The slurry for the negative electrode may contain a conductive additive other than carbon black. Examples of the conductive assistant other than carbon black include carbon nanotubes. The content of the conductive additive other than carbon black in the slurry for the negative electrode is preferably, for example, 10 parts by mass or less based on 100 parts by mass of carbon black.

  The slurry for the negative electrode may contain a solvent other than N-methyl-2-pyrrolidone. Examples of the solvent other than N-methyl-2-pyrrolidone include a non-aqueous solvent or water compatible with N-methyl-2-pyrrolidone. The content of the solvent other than N-methyl-2-pyrrolidone in the slurry for the negative electrode is preferably, for example, 10 parts by mass or less based on 100 parts by mass of N-methyl-2-pyrrolidone.

  The slurry for the negative electrode can also contain a catalyst that promotes the condensation reaction between the anionic vinyl polymer having a carboxyl group and the polyfunctional amine. Examples of the catalyst include 1-methylimidazole, 2-methylimidazole, N, N′-dicyclohexylcarbodiimide, N, N′-carbonyldiimidazole, N, N′-diisopropylcarbodiimide, 1- [3- (dimethylamino) Propyl] -3-ethylcarbodiimide, 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride, diphenylphosphoric acid azide, a dehydration condensation catalyst such as a BOP reagent can be effectively used.

<Production method of slurry for negative electrode>
The slurry for the negative electrode is obtained by mixing the above components with a well-known stirrer. In the production of the negative electrode slurry, the order of mixing the plurality of components to be mixed is not particularly limited. As the order of compounding each component, for example, a negative electrode active material and a binder component may be compounded in a dispersion containing a dispersant, carbon black, and N-methyl-2-pyrrolidone, or a dispersant, a binder, And a solution containing N-methyl-2-pyrrolidone and carbon black and a negative electrode active material.

  When preheating the binder component, the heating temperature is preferably in the range of 40 to 140 ° C, more preferably in the range of 60 to 130 ° C. The preliminary heat treatment of the binder component is performed in a solvent such as N-methyl-2-pyrrolidone.

<Method of manufacturing negative electrode>
The method for producing a negative electrode is a method for obtaining a negative electrode using the slurry for a negative electrode. In the method for manufacturing the negative electrode, first, the negative electrode polarization slurry is applied to a current collector to form a film-shaped coating layer on the surface of the current collector. As the current collector, a known metal material used as a current collector for a negative electrode of a power storage device such as a secondary battery can be used. Examples of metal materials that can be used for the current collector include silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, molybdenum, and stainless steel. No.

  Next, a negative electrode active material layer is obtained by curing the binder component in a heating step of the coating layer. More specifically, in the heating step, a binder having a crosslinked structure is obtained by condensing an anionic vinyl-based polymer having a carboxyl group of a binder component and a polyfunctional amine. The heating temperature in the heating step is preferably from 150 to 230 ° C, more preferably from 180 to 200 ° C, from the viewpoint of promoting the formation of a crosslinked structure. The heating temperature in the heating step is preferably in the range of 180 to 230 ° C. from the viewpoint of forming an acid anhydride structure described later. In the negative electrode slurry containing the binder component, when the heating temperature is increased, the characteristics (cycle characteristics) of the power storage device such as a secondary battery are improved. The heating step can also be performed after a drying step or a pressing step for removing N-methyl-2-pyrrolidone contained in the coating layer.

As a method of the heat treatment and the drying treatment, for example, a method of heating under a normal pressure or a reduced pressure by using a heat source such as hot air, infrared rays, microwaves, and high-frequency waves is used.
The negative electrode obtained as described above has a current collector and a negative electrode active material layer laminated on the current collector. The binder contained in the negative electrode active material layer is formed by forming at least one of an amide bond and an imide bond between the carboxyl group of the anionic vinyl polymer and the amino group of the polyfunctional amine. The polymer has a crosslinked structure. More specifically, the binder has a chain structure composed of an anionic vinyl polymer and a crosslinked structure that connects carboxylic acid side chains within the chain structure or between the chain structures. The crosslinked structure is at least one type of crosslinked structure selected from the following general formulas (2) to (4).

“Poly” in the general formulas (2) to (4) indicates a chain structure composed of an anionic vinyl polymer. In the general formulas (3) and (4) having an imide structure, the two carbonyl groups constituting one imide structure may be carbonyl groups bonded to different chain structures or may be the same. It may be a carbonyl group bonded to a chain structure. For example, when the two carbokinyl groups constituting the imide structure are carbonyl groups bonded to adjacent carbons in the same chain structure, a maleimide structure is formed as the imide structure.

  X in the general formulas (2) to (4) is a structure derived from a polyfunctional amine. For example, when the polyfunctional amine is an aromatic polyfunctional amine represented by the general formula (1), X is The structure shown in Expression (5) is obtained.

Y, R1 and R2 in the general formula (5) have a structure corresponding to Y, R1 and R2 in the general formula (1), respectively.

  The crosslinked structure of the binder preferably has both an amide bond and an imide bond. That is, the crosslinked structure of the binder preferably has at least the crosslinked structure of the general formula (2) and the general formula (4), or at least the crosslinked structure of the general formula (3).

  The binder preferably has an acid anhydride structure (CO—O—CO) formed by dehydration condensation of two carboxyl groups in the molecular structure. The acid anhydride structure may be a structure formed in the same chain structure or a structure formed between different chain structures. That is, two carbonyl carbons contained in the acid anhydride structure may be bonded to the same chain structure, or may be bonded to different chain structures.

  The above-described negative electrode can be effectively used for a non-aqueous power storage device including a non-aqueous electrolyte as an electrolyte. Examples of the power storage device include a secondary battery, an electric double layer capacitor, and a lithium ion capacitor. In addition, such a power storage device is useful as a non-aqueous secondary battery for driving a motor of an electric vehicle or a hybrid vehicle, or a non-aqueous secondary battery used in personal computers, portable communication devices, home appliances, office equipment, industrial equipment, and the like. It is.

Next, the operation and effect of the present embodiment will be described.
(1) A slurry for a negative electrode for obtaining a negative electrode of a power storage device contains a negative electrode active material, a binder component, carbon black, N-methyl-2-pyrrolidone, and a dispersant. The binder component contains an anionic vinyl polymer having a carboxyl group and a polyfunctional amine, and the dispersant contains a nonionic polymer. According to this configuration, the non-polar portion of the nonionic polymer is adsorbed on the carbon black, and the polar portion of the nonionic polymer is spread in N-methyl-2-pyrrolidone, so that the Carbon black is suitably dispersed. Here, the nonionic polymer, unlike the cationic polymer, hardly affects the solubility of the anionic vinyl-based polymer having a carboxyl group. Further, the nonionic polymer is unlikely to affect the solubility of the polyfunctional amine unlike the anionic polymer. That is, the nonionic polymer that enhances the dispersibility of carbon black is easily compatible with the above-mentioned binder component in the presence of N-methyl-2-pyrrolidone. This makes it possible to suppress an increase in the viscosity of the slurry for the negative electrode. Therefore, for example, handling of the slurry for the negative electrode becomes easy. Therefore, it is possible to provide a negative electrode slurry which is excellent in mass productivity of the negative electrode.

  (2) The dispersant preferably contains at least one of polyvinyl alcohol and polyvinyl pyrrolidone. In this case, it is possible to further suppress an increase in the viscosity of the slurry for the negative electrode. For example, when the dispersant contains polyvinyl alcohol, it is possible to suppress the dispersant from affecting the characteristics of the power storage device.

Next, technical ideas that can be grasped from the above embodiment and other examples will be described below.
(A) The slurry for a negative electrode, wherein the dispersant contains polyvinyl alcohol, and the degree of saponification of the polyvinyl alcohol is in the range of 72 to 90 mol%.

  (B) A dispersion used by mixing with a binder component for a negative electrode of a power storage device, wherein the binder component contains an anionic vinyl polymer having a carboxyl group and a polyfunctional amine, and the dispersion is A dispersion comprising carbon black, N-methyl-2-pyrrolidone and a dispersant, wherein the dispersant comprises a nonionic polymer.

Next, examples will be described.
(Test Examples 1 to 7)
A test solution containing a binder component, carbon black, N-methyl-2-pyrrolidone, and a dispersant was prepared. As the binder component, polyacrylic acid (weight average molecular weight: 50,000) was used as an anionic vinyl polymer having a carboxyl group, and 4,4′-diaminodiphenylmethane was used as a polyfunctional amine. Preliminary heat treatment was performed at 80 ° C. for 3 hours using pyrrolidone as a solvent. The ratio of acrylic acid to amino groups was adjusted so that COOH: NH ₂ = 4: 1. Acetylene black was used as carbon black.

The mass ratio of each component in the test solution is as follows.
Binder component: 10.2 parts by mass Carbon black: 9.6 parts by mass N-methyl-2-pyrrolidone: 79.9 parts by mass Dispersant: 0.3 part by mass The content of the dispersant in the test liquid is carbon black. About 3 parts by mass for 100 parts by mass.

Table 1 shows details of the dispersants used in the test liquids of Test Examples 1 to 7. In Table 1, “PVA” in the type column of the dispersant indicates polyvinyl alcohol.
(Test Examples 8 and 9)
In Test Examples 8 and 9, the test liquid was the same as in Test Example 1, except that the dispersants shown in Table 1 were used and the content of the dispersant was changed to about 10 parts by mass with respect to 100 parts by mass of carbon black. Was prepared. In Table 1, “PVP” in the type column of the dispersant indicates polyvinylpyrrolidone.

(Reference Examples 1 and 2)
In Reference Example 1, a test liquid was prepared in the same manner as in Test Example 1, except that the dispersant in Test Example 1 was changed to a commercially available cationic polymer. In Reference Example 2, a test liquid was prepared in the same manner as in Test Example 1, except that the dispersant of Test Example 1 was changed to a commercially available anionic polymer.

<Viscosity measurement>
The viscosity of the test liquid of each test example was measured. The viscosity was measured using a B-type viscometer at a spindle rotation speed of 20 rpm and at room temperature. Table 1 shows the results.

<Measurement of particle size distribution>
As a result of measuring the 50% particle diameter (D50) of the carpon black in each of the test solutions of Test Examples 1 to 9, any of the test solutions was in the range of 0.35 to 0.75 μm, and the dispersion of carbon black was The condition was good. As a result of measuring the 10% particle diameter (D10) and the 90% particle diameter (D90) of the carpon black in each test solution, D10 was in the range of 0.18 to 0.25 μm, and D90 was 1. It was in the range of 6 to 3.5 μm.

In Test Examples 1 to 9, a test liquid having fluidity without being solidified was obtained. In Reference Examples 1 and 2, the test liquid was solidified (gelled) and did not have fluidity.

(Example 1)
A slurry for a negative electrode was prepared by mixing 60 parts by mass of a silicon-based active material as a negative electrode active material with the test liquid of Test Example 5.

As the silicon-based active material, a silicon-based material obtained through a decalcification reaction from CaSi ₂ disclosed in International Publication No. 2014/080608 was used.
Using this negative electrode slurry, a negative electrode active material layer was formed on the surface of a 30 μm electrolytic copper foil as a current collector. The negative electrode active material layer was formed by first applying a negative electrode slurry to a current collector using a doctor blade method to form a negative electrode slurry application layer. Next, N-methyl-2-pyrrolidone in the coating layer was removed by volatilization, and then pressed using a roll press so that the thickness of the coating layer was 20 μm. Subsequently, the coating layer was cured by heat treatment at 160 ° C. for 3 hours in a vacuum (under reduced pressure) to produce a sheet for a negative electrode.

  A negative ion electrode sheet was cut into a circular shape having a diameter of 11 mm, and a lithium ion secondary battery was prepared by using a metal lithium foil having a thickness of 500 μm cut into a circular shape having a diameter of 13 mm as a positive electrode, while using it as a negative electrode. . As a separator of the lithium ion secondary battery, a glass filter manufactured by Hoechst Celanese Corporation and Celgard 2400 manufactured by Celgard Corporation were used. As the non-aqueous electrolyte, a non-aqueous electrolyte obtained by dissolving lithium hexafluorophosphate to a concentration of 1 M in a mixed solvent of ethylene carbonate and diethyl carbonate mixed at a volume ratio of 1: 1 was used.

(Examples 2 and 3)
In Example 2, a lithium ion secondary battery was prepared in the same manner as in Example 1, except that a slurry for a negative electrode was prepared using the test liquid of Test Example 8. In Example 3, a lithium ion secondary battery was prepared in the same manner as in Example 1, except that a slurry for a negative electrode was prepared using the test liquid of Test Example 9.

<Evaluation of battery characteristics>
With respect to the lithium ion battery of each embodiment, discharging was performed at a direct current of 0.2 mA until the voltage of the negative electrode with respect to the positive electrode became 0.01 V, and 10 minutes after the discharge was completed, the negative electrode was discharged at a direct current of 0.2 mA. Charging was performed until the voltage of the electrode with respect to the positive electrode reached 1.0 V. The discharge capacity at this time was set as the initial discharge capacity, and the charge capacity was set as the initial charge capacity. Then, the initial efficiency was calculated based on the following equation.

Initial efficiency (%) = (initial charge capacity / initial discharge capacity) × 100
Further, the above-described discharge and charge were defined as one cycle, charge and discharge were performed in a specified cycle, and cycle characteristics were calculated based on the following equation.

Cycle characteristics (%) = (charge capacity after specified cycle / initial charge capacity) × 100
Table 2 shows the evaluation results of the battery characteristics of each example.

As shown in Table 2, in each of the examples, practical battery characteristics were obtained. From Examples 2 and 3, the effect of the type of the dispersant on the battery characteristics can be confirmed. It can be seen that Example 2 using PVA as a dispersing agent can obtain better battery characteristics than Example 3 using PVP as a dispersing agent.

Claims (3)

A slurry for a negative electrode for obtaining a negative electrode of a power storage device,
It contains a negative electrode active material, a binder component, carbon black, N-methyl-2-pyrrolidone and a dispersant,
The binder component includes an anionic vinyl polymer having a carboxyl group and a polyfunctional amine,
The slurry for a negative electrode, wherein the dispersant includes a nonionic polymer.   The slurry for a negative electrode according to claim 1, wherein the dispersant includes at least one of polyvinyl alcohol and polyvinyl pyrrolidone. A method for manufacturing a negative electrode of a power storage device,
A method for producing a negative electrode, comprising using the slurry for a negative electrode according to claim 1 or 2 to obtain a negative electrode.