TW201603363A - Composition for formation of lithium ion secondary battery electrode, electrode for lithium ion secondary battery, and lithium ion secondary battery, and method for producing composition for formation of lithium ion secondary battery electrode - Google Patents

Abstract

The present invention provides: a composition for the formation of a lithium ion secondary battery electrode, said composition making it possible to improve adhesiveness between an active material and a binder resin; an electrode for a lithium ion secondary battery; and a lithium ion secondary battery. This composition for the formation of a lithium ion secondary battery electrode comprises an active material and a binder resin. Therein, in the active material, the transverse relaxation time of water protons in a dispersion liquid as measured according to condition 1 below is 10 seconds or more, and in the binder resin, the transverse relaxation time of water protons in a water-based emulsion as measured according to condition 2 below is 200 seconds or more. Condition 1: A transverse relaxation time of water protons that is obtained by measuring, according to a pulse NMR method, an active material dispersion liquid formed by mixing, at a mass ratio of 52.8:0.5:46.6, an active material, carboxymethyl cellulose having a weight average molecular weight of 3000000 and a degree of substitution of 0.9, and water. Condition 2: A transverse relaxation time of water protons that is obtained by measuring, according to a pulse NMR method, an anionic water-based emulsion that includes 40 mass% of a binder resin.

Description

Lithium ion battery electrode forming composition, lithium ion battery electrode, lithium ion battery, and lithium ion battery electrode forming composition manufacturing method

The present invention relates to a composition for forming a lithium ion battery electrode, a lithium ion battery electrode, a lithium ion battery, and a method for forming a lithium ion battery electrode.

In recent years, lithium ion battery systems have attracted attention in terms of miniaturization and weight reduction of notebook computers, mobile phones, power tools, electronic devices, and communication devices. In addition, recently, lithium ion batteries for electric vehicles and hybrid electric vehicles are strongly demanded from the viewpoint of environmental application, and in particular, lithium ion batteries which are subjected to high voltage, high capacity, and high energy density.

Lithium ion battery is composed of a positive electrode containing a metal oxide such as lithium cobalt oxide as an active material, a negative electrode containing a carbon material such as graphite as an active material, and an electrolyte solution centered on a carbonate. A battery that moves between the negative electrode and thereby charges and discharges the battery.

In more detail, the positive electrode can be obtained by a positive electrode collector of aluminum foil or the like. The surface is formed by forming a positive electrode layer from a composition containing a positive electrode active material such as a metal oxide and a binder, and the negative electrode is made of a negative electrode active material containing a graphite or the like and a binder by a surface of a negative electrode current collector such as a copper foil. The composition was obtained by forming a negative electrode layer. Therefore, each of the binders serves to adhere the active material and the binder, and has a function of preventing aggregation and destruction of the positive electrode layer and the negative electrode layer.

In the past, the adhesives for the positive electrode layer and the negative electrode layer were From the viewpoint of the self-swelling resistance of the resin of the electrolytic solution, polyvinylidene fluoride (PVDF) using an organic solvent-based N-methylpyrrolidone (NMP) as a solvent can be used, and industrially, Can be used for more models. However, this adhesive has a low adhesion to an active material, and requires a large amount of a binder in actual use. As a result, there is a disadvantage that the capacity and energy density of the lithium ion secondary battery are lowered. Further, since NMP, which is a high-priced organic solvent, is used as the binder, there is also a problem in the price of the final product and the maintenance of the working environment at the time of preparation of the slurry or the current collector.

As a solution to solve such problems, Patent Document 1 The medium-sized proposal includes: a binder for a lithium ion battery electrode, which contains a specific amount of styrene, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid, and internal crosslinking for a wholly ethylenically unsaturated monomer. The glass transition temperature obtained by emulsion polymerization of an ethylenically unsaturated monomer which is an essential component as an essential component in the presence of an emulsifier is 30 ° C or less.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2011-243464

However, the adhesive of Patent Document 1 can be excellent in the adhesiveness of natural graphite which is used as a negative electrode active material, but the adhesiveness of other active materials such as artificial graphite is not necessarily good. Among other active materials, artificial graphite is expensive, but has less impurities and can reduce electrical resistance, and can improve battery performance. Therefore, in recent years, a binder suitable for artificial graphite has been required.

An object of the present invention is to provide a lithium ion battery electrode forming composition, an electrode for a lithium ion battery, and a lithium ion battery, which are excellent in the adhesion between the active material and the binder resin, even if it is an active material other than natural graphite. Further, an object of the present invention is to provide a method for efficiently producing a composition for forming a lithium ion battery electrode which is excellent in adhesion between an active material and a binder resin even when it is an active material other than natural graphite.

The inventors of the present invention have made an effort to solve the above problems, and have made the following estimation: First, the properties of the surface of the active material have a large influence on the adhesion between the active material and the binder resin. However, the nature of the surface of the active material is difficult to analyze. In particular, artificial graphite is characterized by the disappearance of the functional groups on the surface by firing, and the analysis of the properties of the surface. It is extremely difficult. In fact, if the active material layer is not formed, it is impossible to judge whether the adhesion is good or not. Therefore, the present inventors have further studied intensively, and as a means for specifying the properties of the surface of the active material, attention has been paid to the lateral relaxation time of the water proton by the pulse NMR method, thereby solving the above problems.

In other words, the present invention provides the lithium ion battery electrode electrode forming composition, the lithium ion battery electrode, the lithium ion battery, and the lithium ion battery electrode forming composition of the following [1] to [7].

[1] A lithium ion battery electrode forming composition comprising an active material and a binder resin, wherein the active material is a transverse relaxation time of 10% of water particles of the dispersion measured by the following condition 1 In the case of at least two seconds, the binder resin is a transverse relaxation time of water protons of the aqueous emulsion measured by the following condition 2 of 200 seconds or longer.

Condition 1: The transverse relaxation time of the water proton obtained by measuring the active material dispersion by a pulse NMR method, the active material dispersion being an active material, a carboxymethyl fiber having a weight average molecular weight of 3 million and a degree of substitution of 0.9 The mixture of water and water is mixed with a mass ratio of 52.8:0.5:46.6.

Condition 2: The transverse relaxation time of the water proton obtained by measuring the anionic aqueous emulsion containing 40% by mass of the binder resin by pulse NMR.

[2] The lithium ion battery electrode forming composition according to [1] above, wherein the active material is artificial graphite.

[3] The composition for forming a lithium ion battery electrode according to the above [1] or [2] wherein the acid value of the binder resin is 20 mgKOH/g or less.

[4] The lithium ion battery electrode forming composition according to any one of the above [1], wherein the binder resin is a copolymer of styrene and an ethylenically unsaturated carboxylic acid ester.

[5] A lithium ion battery electrode comprising a layer containing an active material formed of the lithium ion battery electrode electrode forming composition according to any one of the above [1] to [4].

[6] A lithium ion secondary battery using the lithium ion battery electrode of the above [5].

[7] A method for producing a composition for forming a lithium ion battery electrode, which comprises the step of mixing an active material with a binder resin, wherein

When the transverse relaxation time of the water proton of the dispersion of the active material measured by the following condition 1 is 10 seconds or more, the transverse relaxation time of the water proton of the aqueous emulsion measured by the following condition 2 is used. More than 200 seconds as a binder resin.

Condition 1: The transverse relaxation time of the water proton obtained by measuring the active material dispersion by a pulse NMR method, the active material dispersion being an active material, a carboxymethyl fiber having a weight average molecular weight of 3 million and a degree of substitution of 0.9 The mixture of water and water is mixed with a mass ratio of 52.8:0.5:46.6.

Condition 2: The laterality of the water proton obtained by measuring the anionic aqueous emulsion containing 40% by mass of the binder resin by pulse NMR Relaxation time.

According to the lithium ion battery electrode forming composition, the lithium ion battery electrode, and the lithium ion battery of the present invention, even if it is an active material other than natural graphite, the adhesion between the active material and the binder resin can be improved.

In addition, in the related art, if the layer containing the active material is not actually formed, the adhesion between the active material and the binder resin cannot be determined. According to the method for producing a composition for forming a lithium ion battery electrode according to the present invention, even if the active material is not actually formed, In the layer, an active material excellent in adhesion and a binder resin can be selected, and the production efficiency of the lithium ion battery electrode-forming composition can be improved.

[Lithium ion battery electrode forming composition]

The lithium ion battery electrode forming composition of the present invention (hereinafter sometimes referred to as "the composition of the present invention") is obtained by containing an active material and a binder resin, and the active material is measured by the following condition 1 The transverse relaxation time of the water proton of the dispersion is 10 seconds or longer, and the binder resin is a transverse relaxation time of the water proton of the aqueous emulsion measured by the following condition 2 of 200 seconds or longer.

Condition 1: Measurement of active substance dispersion by pulse NMR The transverse relaxation time of the water proton obtained, which is obtained by mass-producing the active material, carboxymethyl cellulose having a weight average molecular weight of 3 million and a degree of substitution of 0.9, and water at a mass ratio of 52.8:0.5:46.6. Mixed.

Condition 2: The transverse relaxation time of the water proton obtained by measuring the anionic aqueous emulsion containing 40% by mass of the binder resin by pulse NMR.

The composition of the present invention is measured by the condition 1 As the active material, the transverse relaxation time of the water proton (hydrogen nucleus) of the liquid dispersion is 10 seconds or longer, and the transverse relaxation time of the water proton of the aqueous emulsion measured by the condition 2 is 200 seconds or more as the adhesive. Resin.

In the present invention, the transverse relaxation time of water protons (hereinafter sometimes referred to as "transverse relaxation time") measured by pulse NMR is focused on the infiltration of water by the active material and the binder resin. Ease of use. That is to say, it means that if the transverse relaxation time is long, it is not easy to be infiltrated with water (the degree of hydrophilicity is low), and if the transverse relaxation time is short, it is easy to be infiltrated with water (the degree of hydrophilicity is high).

Conventionally, the properties of the surface of the active material are difficult to analyze. In particular, artificial graphite is used to cause the functional groups on the surface to disappear by firing, and the analysis of the properties of the surface is difficult. In the present invention, the hydrophilicity of the active material and the binder resin is used as an index for judging, and the transverse relaxation time of the water protons measured by the pulse NMR method is focused on, and further, the active material is The transverse relaxation time has a specific relationship with the transverse relaxation time of the binder resin, and becomes an active substance other than natural graphite. It is sufficient to make the adhesion between the active material and the binder resin good. In addition, the composition of the present invention which satisfies the conditions 1 and 2 is also excellent in that it is easy to improve the adhesion to the current collector to be described later.

The composition of the present invention can be used as a positive electrode forming composition of a lithium ion battery electrode or as a negative electrode forming composition. However, in the case of being used as a negative electrode forming composition, it is particularly effective.

(active substance)

In the active material, the transverse relaxation time of the water proton of the dispersion measured by the following condition 1 was 10 seconds or longer.

Condition 1: The transverse relaxation time of the water proton obtained by measuring the active material dispersion by a pulse NMR method, the active material dispersion being an active material, a carboxymethyl fiber having a weight average molecular weight of 3 million and a degree of substitution of 0.9 The mixture of water and water is mixed with a mass ratio of 52.8:0.5:46.6.

The measurement of Condition 1 was carried out by pulse NMR. More The pulse NMR apparatus is used, and the measurement core is a hydrogen nucleus, and the measurement conditions of a temperature of 25 ° C, a frequency of 13 MHz, and a pulse width of 2 μs are measured by the CPMG method (Carr-Purcell Meiboom-Gill method). And determine the transverse relaxation time of the water proton (spin-spin relaxation time). Further, in the measurement of Condition 1, the pH of the active material dispersion is preferably adjusted to 7.0.

Further, in the measurement of Condition 1, the transverse relaxation time of the water protons which are in contact with the active material is calculated as the transverse relaxation time of the water protons. The average of the two components of the transverse relaxation time of the water protons in the free state of the surface of the active material.

The transverse relaxation time of Condition 1 is preferably 11 seconds or more, more preferably 12 seconds or more. Further, the upper limit of the transverse relaxation time of Condition 1 is not particularly limited, but is preferably 50 seconds or shorter, more preferably 40 seconds or shorter, still more preferably 30 seconds or shorter.

Further, carboxymethyl cellulose (CMC) is a function of enhancing the dispersion and definition of the active material dispersion by viscosity-increasing action.

The active substance system is not limited as long as the condition 1 is satisfied. Used in the field. In terms of the active material, it is preferred to use a person capable of adsorbing and releasing lithium ions. The active material is a positive electrode active material and a negative electrode active material. The present invention is easy to exert an effect in the case of using a negative electrode active material as an active material, and it is easier to exert an effect in the case of using a carbonaceous material or artificial graphite among the negative electrode active materials, and in particular, it is difficult to analyze the properties of the surface to be used. In the case of artificial graphite, it can exert extremely remarkable effects.

The shape of the active material is not particularly limited, and a ball can be used. Shape, scale, etc. Among these, from the viewpoint of electron conductivity, it is preferable to have a spherical shape.

The average particle diameter of the active material is preferably from 5 to 100 μm, more preferably from 10 to 50 μm, still more preferably from 15 to 30 μm, from the viewpoint of dispersibility of the active material. Further, the average particle diameter can be calculated by a laser diffraction method.

The average specific surface area of active substance, based on the viewpoint of dispersibility of the active material, it is preferably 0.1 ~ 100m ² / g, more preferably 0.1 ~ 50m ² / g, and still more preferably 0.1 ~ 30m ² / g. Further, the average specific surface area can be obtained by measuring the specific surface area (according to JIS Z8830) by the BET nitrogen adsorption method.

Examples of the positive electrode active material include a metal composite oxide, particularly a metal composite oxide containing lithium and at least one metal of iron, cobalt, nickel, and manganese. Preferably, Li _x M _{y1 is included.} O ₂ (however, M represents one or more transition metals, preferably at least one of Co, Mn or Ni, and 1.10>x>0.05, 1≧y1>0), or Li _x M _y2 O ₄ (but M system represents one or more transition metals, preferably Mn or Ni, and 1.10>x>0.05, 2≧y2>0), or Li _x M _y1 PO ₄ (however, M system represents one or more transitions) The metal, preferably at least one of Fe, Co, Mn or Ni, and an active material of 1.10>x>0.05, 1≧y1>0), for example, LiCoO ₂ , LiNiO ₂ , Li _x Ni _y3 Mn _z Co _a O ₂ (wherein 1.10>x>0.05, 1>y3>0, 1>z>0, 1>a>0), a composite oxide represented by LiMn ₂ O ₄ or LiFePO ₄ , or the like.

Examples of the negative electrode active material include various cerium oxides (such as SiO ₂ ); carbonaceous materials; metal composite oxides such as Li ₄ Ti ₅ O _{12 ,} and the like, and artificial graphite is preferred.

The artificial graphite is obtained by firing a carbonaceous material such as amorphous carbon, graphite, natural graphite, pitch-based carbon fiber or polyacetylene at a temperature of about 3000 ° C, and the crystal structure is different from that of the carbonaceous material. Further, the atomic bonding of the artificial graphite is a hexagonal plate crystal, and the structure is a tortoise-like layer.

(Binder resin)

As the binder resin, the lateral relaxation time of the water proton (hydrogen nucleus) of the aqueous emulsion measured by the following condition 2 was 200 seconds or longer.

Condition 2: The lateral relaxation time of the water proton obtained by measuring the anionic aqueous emulsion containing 40% by mass of the binder resin by pulse NMR.

The measurement of Condition 2 was carried out by pulse NMR. More The pulse NMR apparatus is used, and the measurement core is a hydrogen nucleus, and the measurement conditions of a temperature of 25 ° C, a frequency of 13 MHz, and a pulse width of 2 μs are measured by the CPMG method (Carr-Purcell Meiboom-Gill method). And determine the transverse relaxation time of the water proton (spin-spin relaxation time). Further, in the measurement of Condition 2, the pH of the anionic aqueous emulsion is preferably adjusted to 7.0.

Further, in the measurement of Condition 2, the transverse relaxation time of the water protons contacting the surface of the binder resin particles and the free state of the surface not contacting the binder resin particles were calculated as the transverse relaxation time of the water protons. The average of the two components of the transverse relaxation time of the water proton.

The transverse relaxation time of Condition 2 is preferably 220 seconds or more, more preferably 300 seconds or more. Further, the upper limit of the transverse relaxation time of Condition 2 is not particularly limited, but is preferably 750 seconds or shorter, more preferably 600 seconds or shorter, and still more preferably 450 seconds or shorter.

An anionic aqueous emulsion used in the measurement of Condition 2, For example, modulation can be performed by the following methods (1) and (2).

(1) An aqueous emulsion containing 40% by mass of a binder resin was prepared using an anionic emulsifier.

(2) Using a reactive anionic emulsifier as a polymerizable monomer for forming a binder resin, an aqueous emulsion containing 40% by mass of a polymerized binder resin was prepared.

The average particle diameter of the binder resin particles in the aqueous emulsion does not particularly affect the transverse relaxation time of the water proton, but is preferably 50 to 500 nm, more preferably 100 to 250 nm. Further, the average particle diameter of the binder resin particles in the aqueous emulsion can be measured by a laser diffraction method.

The adhesive resin system is not particularly suitable as long as the condition 2 is satisfied. Use restricted. The binder resin satisfying the condition 2 is preferably a low acid value. Specifically, the acid value is preferably 20 mgKOH/g or less, more preferably 15 mgKOH/g or less, and still more preferably 10 mgKOH/g or less. By.

The binder resin is formed by the composition of the present invention. From the viewpoint that the electrode is not easily broken, the glass transition temperature is preferably 30° C. or lower, more preferably 20° C. or lower, and still more preferably 15° C. or lower. Further, from the viewpoint of handleability, the glass transition temperature of the binder resin is preferably set to -20 ° C or higher.

The glass transition temperature of the binder resin is a glass transition temperature Tgi of each of the homopolymers of the ethylenically unsaturated monomer Mi (i = 1, 2, ..., i) used for the emulsion polymerization of the binder resin. (i = 1, 2, ..., i), and each weight fraction of the ethylenically unsaturated monomer Mi (i = 1, 2, ..., i), and borrowed The following formula (I) was calculated as a theoretical value.

1/Tg=Σ(Xi/Tgi)..(I)

Examples of the binder resin include styrene-butadiene rubber; a copolymer of styrene and an ethylenically unsaturated carboxylic acid ester; an ethylene-vinyl acetate copolymer; an ethylene-vinyl neodecanoate copolymer, and ethylene. An ethylene-ethylenically unsaturated carboxylic acid ester copolymer or the like which is an acrylate copolymer or the like. Among these, a copolymer of styrene and an ethylenically unsaturated carboxylic acid ester can improve the adhesion between the active material and the binder resin, and is excellent in the swelling resistance of the electrolytic solution and excellent in charge and discharge cycle characteristics. The point of view is ideal. Further, the copolymer of styrene and an ethylenically unsaturated carboxylic acid ester is excellent from the viewpoint of excellent adhesion to a current collector.

A copolymer of styrene and an ethylenically unsaturated carboxylic acid ester (hereinafter, simply referred to as "copolymer") is a combination of styrene and an ethylenically unsaturated carboxylic acid ester. The copolymer can be obtained, for example, by emulsion polymerization of a raw material composition containing styrene, an ethylenically unsaturated carboxylic acid ester, and an internal crosslinking agent in an aqueous medium in the presence of an emulsifier.

The styrene-based system mainly has a function of improving the adhesion between the active material and the binder resin and the adhesion between the layer containing the active material and the current collector. In particular, in the case where artificial graphite is used as the active material, the effect thereof can be further exerted.

The amount of styrene used is preferably a total monomer formation of the above copolymer. The fraction is 15 to 70% by mass, more preferably 30 to 60% by mass, and even more preferably 35 to 55% by mass.

By using the amount of styrene in an amount of 15% by mass or more, the adhesion between the active material and the binder resin and the adhesion between the layer containing the active material and the current collector can be easily improved. Further, by using the amount of styrene in an amount of 70% by mass or less, the electrode formed of the composition of the present invention can be prevented from being broken.

Ethylene unsaturated carboxylic acid esters can be distinguished as having no functional groups Base and those with functional groups.

Examples of the ethylenically unsaturated carboxylic acid ester having no functional group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and (meth)acrylic acid. Isopropyl ester, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, (meth)acrylic acid 2 -ethylhexyl ester, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isodecyl (meth)acrylate, isodecyl (meth)acrylate, (Meth) acrylates such as benzyl (meth)acrylate. Among these, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate are preferred from the viewpoint of ease of emulsion polymerization or durability. , isodecyl (meth)acrylate.

The amount of the ethylenically unsaturated carboxylic acid ester having no functional group is preferably from 25 to 85% by mass, more preferably from 30 to 65% by mass, even more preferably 40%, based on the total monomer component of the copolymer. ~55 mass%.

By using an ethylenically unsaturated carboxylic acid ester having no functional group When it is 25% by mass or more, the flexibility and heat resistance of the formed electrode can be easily improved, and by setting it to 85% by mass or less, the adhesive property of the active material and the binder resin can be made and the activity can be contained. The adhesion between the layer of the substance and the current collector tends to be good.

The ethylenically unsaturated carboxylic acid ester having a functional group is Listed: an ethylenically unsaturated carboxylic acid ester having a hydroxyl group or a glycidyl group. For example, 2-hydroxyalkyl (meth)acrylate, glycidyl acrylate, etc., such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate, etc. are mentioned. Among these, 2-hydroxyethyl (meth)acrylate is preferred.

Amount of ethylenically unsaturated carboxylic acid ester having a functional group In particular, it is preferably from 0.1 to 10% by mass, more preferably from 0.5 to 5% by mass, even more preferably from 1 to 3% by mass, based on the total monomer component of the copolymer.

When the amount of the ethylenically unsaturated carboxylic acid having a functional group is 0.1% by mass or more, the emulsion polymerization stability or mechanical stability can be easily improved, and a dry film for the electrolyte can be used. The swell resistance is good. Further, when the amount of the ethylenically unsaturated carboxylic acid having a functional group is increased, the transverse relaxation time is shortened, and conversely, if the amount used is small, the transverse relaxation time tends to increase. Therefore, by using the amount of the ethylenically unsaturated carboxylic acid having a functional group of 10% by mass or less, the transverse relaxation time can be easily made into the range of the present invention, and the adhesion between the active material and the binder resin can be achieved. The adhesion between the layer containing the active material and the current collector is likely to be good.

An ethylenically unsaturated carboxylic acid may be further used in forming the monomer of the above copolymer.

Examples of the ethylenically unsaturated carboxylic acid include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid, or the like. A half ester of a dicarboxylic acid or the like, among which acrylic acid and itaconic acid are preferred. These ethylenically unsaturated carboxylic acids may be used alone or in combination of two or more.

When a small amount of the ethylenically unsaturated carboxylic acid is added, it may contribute to an improvement in emulsion polymerization stability or mechanical stability. However, if a large amount is added, the transverse relaxation time tends to be short, and the adhesion between the active material and the binder resin, The adhesion between the layer containing the active material and the current collector tends to decrease. Therefore, the amount of the ethylenically unsaturated carboxylic acid to be used is preferably 3% by mass or less, more preferably 2% by mass or less, still more preferably 1% by mass or less based on the total monomer component of the copolymer.

Further, a monomer other than the above having at least one polymerizable ethylenically unsaturated group may be further used for forming the monomer of the above copolymer. Examples of such a monomer include decylamine such as (meth) acrylamide, N-methylol (meth) acrylamide, (meth) acrylonitrile, vinyl acetate, vinyl propionate, and the like. A compound other than the ethylenically unsaturated carboxylic acid ester having a functional group such as a nitrile group or a nitrile group, or a sodium p-styrenesulfonate.

Further, as the monomer for forming the above copolymer, in order to adjust the molecular weight, a mercaptan, a thioglycolic acid and an ester thereof, a β-mercaptopropionic acid, an ester thereof, or the like may be used.

Further, as the monomer forming the above copolymer, a reactive emulsifier described later may be further used.

In order to improve the swell resistance of the dry film to the electrolyte, It is preferred that the raw material composition of the copolymer of styrene and the ethylenically unsaturated carboxylic acid ester further contains an internal crosslinking agent (internal crosslinking monomer).

As the internal crosslinking agent, a reactive group having at least one ethylenically unsaturated bond and having reactivity with a functional group of the above monomer, or having two or more ethylenically unsaturated bonds may be used. .

Examples of such an internal crosslinking agent include divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, triallyl cyanurate, and the like. a crosslinkable polyfunctional monomer having two or more unsaturated groups, ethylene trimethoxy decane, ethylene triethoxy decane, γ-methyl propylene oxypropyl trimethoxy decane, γ-methyl propylene oxy propylene A decane coupling agent such as a triethoxy decane or the like, among which, preferably, divinylbenzene, trimethylolpropane tri(meth)acrylate, and γ-methylpropenyloxypropyltrimethoxydecane are preferred. . These internal crosslinking agents may be used alone or in combination of two or more.

In terms of the amount of internal crosslinking agent used, it is preferred to form the above The total monomer component of the copolymer is 0.1 to 5% by mass, more preferably 0.1 to 3% by mass, still more preferably 0.2 to 2% by mass. By using the amount of the internal crosslinking agent in an amount of 0.1% by mass or more, the swell resistance of the dried film of the electrolytic solution can be improved, and the emulsification polymerization stability can be prevented by setting it to 5% by mass or less. reduce.

In order to copolymerize styrene and ethylenically unsaturated carboxylic acid ester The transverse relaxation time of the substance is in the range of the condition 2, and it is preferred that the total amount of the styrene and the ethylenically unsaturated carboxylic acid ester having no functional group is increased among the monomers forming the copolymer, and the internal use is used. Crosslinker. Specifically In general, the total amount of styrene and the ethylenically unsaturated carboxylic acid ester having no functional group is preferably 90% by mass or more, more preferably 93% by mass or more, and still more preferably 94% by mass. the above.

As the emulsifier used in the emulsion polymerization, a usual anionic emulsifier or a nonionic emulsifier can be used.

Examples of the anionic emulsifier include an alkylbenzenesulfonate, an alkylsulfate salt, a polyoxyethylene alkyl ether sulfate salt, and a fatty acid salt. Examples of the nonionic emulsifier include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene polycyclic phenyl ether, polyoxyalkylene alkyl ether, and sorbitan fatty acid ester. , polyoxyethylene sorbitan fatty acid ester and the like. These may be used alone or in combination of two or more.

Further, when a reactive emulsifier is used as the emulsifier, it is possible to prevent the emulsifier from leaking, and it is preferable from the viewpoint of improving the mechanical stability of the electrode formed of the composition of the present invention. Examples of the reactive emulsifier include those represented by the following general formulas (1) to (5).

In the formula, R represents an alkyl group, and m represents an integer of 10 to 40.

In the formula, n represents an integer of 10 to 12, and m represents an integer of 10 to 40.

In the formula, R represents an alkyl group, and M represents NH ₄ or Na.

In the formula, R represents an alkyl group.

In the formula, AO represents an alkylene oxide having 2 or 3 carbon atoms, and m represents an integer of 10 to 40.

The preferred amount of emulsifier used is in non-reactive milk. In the case of the chemical agent, it is preferably 0.1 to 3 parts by mass, more preferably 0.1 to 2 parts by mass, even more preferably 0.2 to 1 part by mass based on 100 parts by mass of the total monomer component forming the copolymer. Share. In the case of the reactive emulsifier, it is preferably from 0.3 to 5 parts by mass, more preferably from 0.5 to 4 parts by mass, even more preferably from 0.5 to 2 parts by mass, based on the total monomer component of the copolymer. Further, the non-reactive emulsifier or the reactive emulsifier may be used singly, but it is preferably used by mixing.

Free radical polymerization initiator used in emulsion polymerization A well-known person can be used, and examples thereof include ammonium persulfate, potassium persulfate, hydrogen peroxide, and t-butyl hydroperoxide. Further, these polymerization initiators may be used in combination with a reducing agent such as sodium metabisulfite, insurance powder (sodium hydroxymethanesulfinate), ascorbic acid or the like as needed for redox polymerization.

In terms of emulsion polymerization, it can be applied to the polymerization side A method in which the components are continuously supplied while being continuously supplied, and the like. The polymerization system is usually carried out under stirring at a temperature of 30 to 90 °C. Further, the pH can be adjusted by adding a basic substance during or after the polymerization of the above copolymer, thereby improving the polymerization stability, mechanical stability, and chemistry during emulsion polymerization. Stability. As the alkaline substance used at this time, ammonia, triethylamine, ethanolamine, caustic soda, or the like can be used. These may be used alone or in combination of two or more.

The composition of the present invention is preferably an active substance and a binder The resin is dispersed or dissolved in water or a mixture of water and a highly hydrophilic solvent. The preparation of the composition of the present invention may be, for example, a method in which the binder resin is dispersed, dissolved or kneaded in a solvent, and then the active material and an additive used as needed are further added to further disperse, dissolve or knead.

The content ratio of the active material and the binder resin in the composition of the present invention is preferably from 95.0 to 99.5 mass% based on the solid content, and the binder resin is from 0.5 to 5.0 mass%, more preferably active. The material composition is 98.0 to 99.5 mass%, the binder resin is 0.5 to 2.0% by mass, and more preferably the active material is 99.0 to 99.5% by mass, and the binder resin is 0.5 to 1.0% by mass.

[Li-ion battery electrode]

The lithium ion battery electrode of the present invention (hereinafter referred to as "the electrode of the present invention") has a layer containing an active material formed of the above-described composition for forming a lithium ion battery electrode of the present invention on a current collector. By.

Although the electrode of the present invention can be used as a positive electrode of a lithium ion secondary battery or as a negative electrode, it can particularly exhibit an effect when used as a negative electrode.

In terms of current collector, it is only iron, copper, aluminum, nickel, and stainless. There is no particular limitation on the metallic nature of steel or the like. Among these, the current collecting system for the positive electrode is preferably aluminum, and the current collecting system for the negative electrode is preferably copper.

The shape of the current collector is not particularly limited, but it is usually preferred to use a sheet having a thickness of 0.001 to 0.5 mm.

The electrode of the present invention can be coated, for example, by a current collector The composition for forming a lithium ion battery electrode of the present invention described above is obtained by drying.

As the coating method, a general method can be used, and examples thereof include a reverse roll method, a direct roll method, a doctor blade method, a knife coating method, an extrusion method, a curtain coating method, a gravure method, a bar coating method, a dipping method, and an extrusion method. law. In the above, the coating method is selected by blending various characteristics such as viscosity of the composition of the present invention and drying property, and it is preferable that the surface state of the layer containing the active material is good. Scraper method, knife coating method or extrusion method.

Further, the electrode of the present invention can be pressurized as needed after forming a layer containing the active material. Although a general method can be used for the method of pressurization, a molding method or a roll pressing method is particularly preferable. The pressurization pressure is not particularly limited, but is preferably 0.2 to 3 t/cm ² .

The electrode active material of the invention is connected with the binder resin The property is good, and the aggregation failure of the layer containing the active material can be prevented. Further, the electrode of the present invention can improve the adhesion between the layer containing the active material and the current collector. This effect is particularly excellent in the case of using copper as a current collector.

[Li-ion battery]

The lithium ion secondary battery of the present invention (hereinafter sometimes referred to as "the battery of the present invention") is obtained by using the above-described lithium ion battery electrode of the present invention.

The battery of the present invention can use a positive electrode and/or a negative electrode, and electrolysis The liquid, and the parts such as the spacers required, are manufactured in accordance with a known method. In the case of the electrode, the electrode of the present invention described above may be used for both the positive electrode and the negative electrode, and the electrode of the present invention described above may be used for one of the positive electrode or the negative electrode, but it is particularly effective in the case where the electrode of the present invention described above is used for the negative electrode. .

In the case of a battery outer casing, a metal outer casing or an aluminum laminated outer casing can be used. The shape of the battery may be any shape such as a button type, a button type, a sheet type, a cylinder type, a square shape, a flat type, or the like. As the electrolyte in the electrolyte of the battery, a well-known lithium salt can be used as long as it is selected in accordance with the kind of the active material. For example, LiClO ₄ , LiBF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , LiCl, LiBr, LiB(C ₂ H ₅ ) ₄ , CF ₃ SO ₃ Li, CH ₃ SO ₃ Li, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, lithium lower aliphatic acid carboxylate or the like.

As a solvent for dissolving the electrolyte, it is only necessary to The liquid to dissolve the electrolyte is usually not particularly limited, and examples thereof include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), and carbonic acid. a carbonate such as ethyl ester (DEC), methyl ethyl carbonate (MEC) or vinyl carbonate (VC); a lactone such as γ-butyrolactone or γ-valerolactone; trimethoxymethane; 1,2-dimethoxy An ether such as ethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran or 2-methyltetrahydrofuran; an anthracene such as dimethyl hydrazine; 1,3-dioxolane; An oxolane such as 4-methyl-1,3-dioxolane; a nitrogen-containing compound such as acetonitrile, nitromethane, formamide or dimethylformamide; methyl formate, Organic acid esters of methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, etc.; phosphotriester or diglyme; triethylene glycol dimethyl ether; Anthraquinones such as hydrazine and methylcyclobutyl hydrazine; oxazolidinones such as 3-methyl-2-oxazolidinone; 1,3-propane sultone and 1,4-butane sulfonate a sultone such as an ester or a naphthalene sultone. These may be used alone or in combination of two or more.

[Manufacturing Method of Composition for Forming Lithium Ion Battery Electrode]

The method for producing a lithium ion battery electrode forming composition of the present invention is a method for producing a lithium ion battery electrode forming composition comprising the step of mixing an active material and a binder resin.

When the transverse relaxation time of the water proton of the dispersion of the active material measured by the following condition 1 is 10 seconds or more, the transverse relaxation time of the water proton of the aqueous emulsion measured by the following condition 2 is used. It is used as a binder resin for 200 seconds or more.

Condition 1: The transverse relaxation time of the water proton detected by a pulsed NMR method, wherein the active material dispersion is an active material, a carboxymethyl cellulose having a weight average molecular weight of 3 million and a degree of substitution of 0.9, It is mixed with water in a mass ratio of 52.8:0.5:46.6.

Condition 2: The transverse relaxation time of the water proton obtained by measuring the anionic aqueous emulsion containing 40% by mass of the binder resin by pulse NMR.

In the past, it was difficult to introduce the properties of the surface of the active material. Since the analysis is performed, the layer containing the active material is not actually formed, and the adhesion between the active material and the binder resin cannot be judged. On the other hand, according to the method for producing a composition for forming a lithium ion battery electrode according to the present invention, by using the concept of the transverse relaxation time of water protons, it is possible to select an activity excellent in adhesion without actually forming a layer containing an active material. The substance and the binder resin can improve the manufacturing efficiency of the composition for forming an electrode of the lithium ion battery.

[Examples]

Hereinafter, the present invention will be described in more detail by showing examples and comparative examples, but the present invention is not limited thereto. In addition, "parts" and "%" in the examples and the comparative examples indicate the parts by mass and the mass %, respectively, unless otherwise stated.

In addition, the materials used in the examples and the comparative examples, and the lithium ion battery electrode-forming composition, the lithium ion battery electrode, and the lithium ion battery obtained in the examples and the comparative examples were subjected to the following measurement and evaluation. The results are shown in Table 1 or 2.

(Measurement of transverse relaxation time)

A pulse nuclear magnetic resonance apparatus (Acronarea, manufactured by XIGO Co., Ltd.) was used, and the measurement core was set as a hydrogen nucleus to measure a temperature of 25 ° C and a frequency. The measurement conditions of the 13 MHz and 90° pulse widths of 2 μs were measured by the CPMG method (Carr-Purcell Meiboom-Gill method), and the transverse relaxation time of the water protons of the anionic water emulsions A to F of the binder resin and the active materials were measured. The transverse relaxation time of the water protons of the dispersions i~iii.

Further, the active material dispersions i to iii were obtained by using the following active materials i to iii, carboxymethylcellulose having a weight average molecular weight of 3,000,000 and a degree of substitution of 0.9, and water at a mass ratio of 52.8:0.5:46.6. Mix and mix.

Active material i: natural graphite (spherical shape, average particle diameter 17 μm, average specific surface area 5.9 m ² /g)

Active material ii: artificial graphite (spherical shape, average particle diameter 18 μm, average specific surface area 1.3 m ² /g)

Active material iii: artificial graphite (scale, average particle diameter 22 μm, average specific surface area 1.3 m ² /g)

(adhesive)

On the copper foil as a current collector, a composition for forming a lithium ion battery electrode (negative electrode) was applied so that the thickness of Wet became 150 μm, and the resultant was dried by heating at 60 ° C for 30 minutes. Next, it was vacuum-dried at 120 ° C for 1 h, and left at 23 ° C and 50% RH for 24 hours to prepare a test piece. The test piece application surface was bonded to the SUS plate using a double-sided tape, and 180° peeling (peeling width 25 mm, peeling speed 100 mm/min) was performed to measure the peel strength. If the peel strength is small, it means that the layer containing the active material is easily agglomerated and destroyed, and the adhesive of the active material and the binder resin low.

(Charge and discharge high temperature cycle characteristics)

The battery cycle test was performed by CC-CV charging (upper limit voltage 4.2 V, current 1 C, CV time 1.5 hours), CC discharge (lower limit voltage 3.0 V, current 1 C), and both were carried out at 45 °C. The capacity retention ratio is a ratio of the discharge capacity at the 200th cycle to the discharge capacity at the first cycle.

(Synthesis of anionic water emulsion A of binder resin)

In a separate flask equipped with a cooling tube, a thermometer, a stirrer, and a dropping funnel, 40 parts of ion-exchanged water and a reactive anionic emulsifier represented by the above general formula (4) (manufactured by Sanyo Chemical Industry Co., Ltd.) were charged. The product name is ELEMINOL JS-20, active ingredient 40%) 0.2 parts, and the temperature is raised to 75 °C.

Then, the monomer emulsion was dropped for 3 hours, and the reactive anionic emulsifier represented by the above general formula (4) (manufactured by Sanyo Chemical Industry Co., Ltd., trade name ELEMINOL JS-20) was previously added. , active ingredient 40%) 2.3 parts, non-reactive anionic emulsifier (manufactured by Daiichi Kogyo Co., Ltd., trade name: HITENOL 08E, polyoxyethylene alkyl ether sulfate) 0.4 parts, styrene 50.4 parts, 44.1 parts of 2-ethylhexyl acrylate, 2.0 parts of 2-hydroxyethyl methacrylate, 1.6 parts of acrylic acid, 0.4 parts of sodium p-styrenesulfonate, 0.5 parts of trimethylolpropane methacrylate, and ion exchange water 85 The mixture is mixed. Simultaneously When 0.43 parts of potassium persulfate as a polymerization initiator was dissolved in 20 parts of ion-exchanged water, it took 3 hours to carry out dropwise polymerization at 80 °C. After the completion of the dropwise addition, the mixture was aged for 2 hours, and then cooled, and 1.8 parts of aqueous ammonia was added to obtain an anionic aqueous emulsion A. The ratio of the binder resin in the obtained anionic water-based emulsion A was 40%, the viscosity was 60 mPa·s, and the average particle diameter of the resin particles in the emulsion was 130 nm and pH 7.0.

Further, the viscosity was measured using a Brooke non-rotational viscosity agent at a liquid temperature of 23 ° C, a number of revolutions of 60 rpm, a No. 2 or No. 3 rotor.

(Synthesis of anionic water emulsion B~F of binder resin)

An anionic aqueous emulsion B to F was obtained in the same manner as above except that the composition of the monomer was changed to the blending of Table 1.

(Anionic water emulsion G of binder resin)

An anionic aqueous emulsion G as a binder resin is an anionic aqueous emulsion (40% of a binder resin) adjusted with a styrene-butadiene rubber (glass transition temperature of -7 ° C (measured by DSC)). The viscosity was 11 mPa·s, and the average particle diameter of the resin particles in the emulsion was 190 nm and pH 7.0).

(Example 1) 1. Preparation of positive electrode forming composition and positive electrode

N-methyl is added to a mixture of 90 parts of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , 5 parts of acetylene carbon as a conductive auxiliary agent, and 5 parts of polyvinylidene fluoride as a binder resin. 100 parts of pyrrolidone was further mixed to prepare a composition for forming a positive electrode.

Then, the composition was applied to one surface of an aluminum foil having a thickness of 20 μm as a current collector by a doctor blade method so that the thickness after the roll press treatment was 60 μm, and dried at 120 ° C for 5 minutes. The layer is pressurized to form a layer containing the positive electrode active material.

2. Preparation of negative electrode forming composition and negative electrode

50 parts of the above-mentioned active material ii, 3.75 parts of the above emulsion A, and 50 parts of a 2% aqueous solution of CMC (weight average molecular weight 3 million, degree of substitution 0.9) were mixed, and 28 parts of water were further added to obtain lithium ion of Example 1. A battery electrode (negative electrode) forming composition.

Then, the composition was applied to one surface of a ketone foil having a thickness of 10 μm as a current collector so as to have a thickness of 60 μm after the roll press treatment, and dried at 80° C. for 5 minutes, and subjected to a pressurization step. A layer containing a negative electrode active material is formed.

3. Battery production

a conductive paste is attached to the obtained layer containing the positive electrode active material and the layer containing the negative electrode active material, and a spacer composed of a polyolefin-based porous film is interposed between the positive electrode and the negative electrode to make the positive electrode and the positive electrode The active materials of the negative electrode are housed in an aluminum laminate outer casing (battery package) so as to face each other. Injecting LiPF ₆ into a 1.0 mol/L (liter) ethylene carbonate (EC) / diethyl carbonate (EMC) = 40 / 60 (volume ratio) electrolyte and vacuum impregnation in a separate package, the liquid injection portion The lithium ion battery of Example 1 was obtained by heat fusion.

(Examples 2 to 10) (Comparative Examples 1 to 9)

A lithium ion battery electrode-forming composition, a lithium ion battery electrode, and a lithium ion secondary battery were obtained in the same manner as in Example 1 except that the active material and the emulsion used for the production of the negative electrode were changed to the emulsion of Table 2.

As can be seen from Table 1, it can be confirmed that Examples 1 to 10 The lithium ion battery electrode forming composition, the lithium ion battery electrode, and the lithium ion battery have high peel strength and good adhesion between the active material and the binder resin. Further, in Examples 1 to 4 and Examples 6 to 9, since the binder resin is a copolymer of styrene and an ethylenically unsaturated carboxylic acid ester, It is excellent in charge and discharge high temperature cycle characteristics.

On the other hand, in Comparative Examples 1 to 9, since the transverse relaxation time of the active material or the transverse relaxation time of the binder resin did not satisfy the conditions of the present invention, the adhesion between the active material and the binder resin could not be made. Good, causing the coating film to be agglomerated and damaged, but the peeling strength is poor.

Claims (7)

A lithium ion battery electrode forming composition comprising an active material and a binder resin, wherein the active material is a transverse relaxation time of a water particle of a dispersion measured by the following condition 1 of 10 seconds or longer. The binder resin is a water-based emulsion having a transverse relaxation time of 200 seconds or more as measured by the following condition 2, and Condition 1 is a water quality obtained by measuring an active material dispersion by a pulse NMR method. In the transverse relaxation time of the sub-component, the active material dispersion is obtained by mixing an active material, a carboxymethyl cellulose having a weight average molecular weight of 3 million and a degree of substitution of 0.9, and water at a mass ratio of 52.8:0.5:46.6. Condition 2: The transverse relaxation time of the water proton obtained by measuring the anionic aqueous emulsion containing 40% by mass of the binder resin by pulse NMR. The composition for forming a lithium ion battery electrode according to claim 1, wherein the active material is artificial graphite. The composition for forming a lithium ion battery electrode according to claim 1 or 2, wherein the acid value of the binder resin is 20 mgKOH/g or less. The composition for forming a lithium ion battery electrode according to claim 1 or 2, wherein the binder resin is a copolymer of styrene and an ethylenically unsaturated carboxylic acid ester. A lithium ion battery electrode having a layer containing an active material formed of a composition for forming a lithium ion battery electrode according to claim 1 or 2 on a current collector. A lithium ion secondary battery using the lithium ion battery electrode of claim 5. A method for producing a composition for forming an electrode for a lithium ion battery, comprising the step of mixing an active material with a binder resin, wherein the transverse relaxation of the water proton of the dispersion of the active material measured by the following condition 1 When the time is 10 seconds or more, the transverse relaxation time of the water-based emulsion of the aqueous emulsion measured by the following condition 2 is 200 seconds or more as the binder resin, and Condition 1: The active material is dispersed by the pulse NMR method. The transverse relaxation time of the water proton obtained by measuring the liquid, the active material dispersion is an active material, a carboxymethyl cellulose having a weight average molecular weight of 3 million and a degree of substitution of 0.9, and water, 52.8:0.5:46.6 The mass ratio was mixed. Condition 2: The transverse relaxation time of the water proton obtained by measuring the anionic aqueous emulsion containing 40% by mass of the binder resin by pulse NMR.