WO2011071106A1

WO2011071106A1 - Negative electrode for secondary battery and secondary battery equipped with same, and resin precursor for binder, resin precursor solution and binder composition for use in production of secondary battery

Info

Publication number: WO2011071106A1
Application number: PCT/JP2010/072113
Authority: WO
Inventors: 利昌田中; 和徳小関; 真二及川; 大佐池田
Original assignee: 新日鐵化学株式会社
Priority date: 2009-12-11
Filing date: 2010-12-09
Publication date: 2011-06-16

Abstract

Disclosed are: a negative electrode and the like which enable the production of a secondary battery having a good balance among properties including discharge capacity and cycle properties; and a resin precursor for a binder and the like which can be used for the production of the secondary battery and the like. Specifically disclosed are: a negative electrode for a secondary battery, in which a negative electrode active material is integrated with a binder that comprises a polyimide resin having a repeating unit represented by general formula (1); and a resin precursor for a binder for use in the production of a secondary battery, which is characterized by containing 50 mol% or more of a precursor of the polyimide resin. [In general formula (1), Ar₁ represents a bivalent aromatic diamine residue having at least two ether bonds; and Ar₂ represents a tetravalent acid dianhydride residue represented by formula (2) or (3).] [In formula (3), Y represents a direct bond or -CO-.]

Description

Negative electrode for secondary battery, secondary battery using the same, and resin precursor for binder, resin precursor solution used for forming secondary battery, and binder composition

The present invention provides a negative electrode for a secondary battery, a secondary battery using the same, and an electrode for a lithium secondary battery by forming an active material layer (a mixture layer) on a current collector. The present invention relates to a binder resin precursor, a resin precursor solution, and a binder composition to be used.

Lithium secondary batteries, which are one of the secondary batteries, have a higher energy density than other secondary batteries, so they can be reduced in size and weight, such as mobile phones, personal computers, and personal digital assistants (PDAs). It is widely used as a power source for mobile electronic devices such as handy video cameras, and its demand is expected to increase in the future.

In particular, in recent years, demand for electric vehicles and hybrid electric vehicles (Hybrid Electric Vehicles: HEVs) that combine nickel-hydrogen battery-powered motors and gasoline engines to increase energy and environmental issues has increased. In addition to initial efficiency and charge / discharge capacity, further improvements in lithium secondary battery performance such as input / output characteristics and cycle life are required.

A lithium secondary battery (lithium ion secondary battery) has a structure in which an electrolyte containing lithium ions is filled between a positive electrode and a negative electrode. Of these, for example, a negative electrode that intercalates lithium. The active material is bound with a binder (binder) and includes an active material layer integrated on the current collector. As the binder, polyvinylidene fluoride (PVDF) has been mainly used so far.

However, PVDF has a problem in that the adhesive strength between the negative electrode and the positive electrode active materials or the current collector is not sufficient, the adhesiveness gradually deteriorates, and the cycle life is shortened. Further, if the battery temperature rises abnormally due to a short circuit or the like, PVDF is decomposed to generate HF, and this HF reacts violently with Li, so that the battery is damaged.

Therefore, in order to obtain a secondary battery having a longer cycle life and excellent reliability, a negative electrode and a positive electrode using a polyimide resin as a binder have been proposed (see Patent Document 1 and Patent Document 2). Furthermore, the following improved technologies have been proposed for the negative electrode using a polyimide resin as a binder. For example, the compounding ratio of a negative electrode active material made of carbonaceous powder and a polyimide resin is specified to improve the charge / discharge capacity (see Patent Document 3), or an active material layer made of a polyimide resin and a negative electrode active material. In addition to the technology for improving cycle characteristics (see Patent Document 4) by specifying three parameters: thickness, ratio of polyimide resin in the active material layer, and drying temperature when forming the active material layer, a specific acid anhydride By combining two types of polyimide resins using materials, the negative electrode active material and the binder are more reliably bonded to the current collector, and the binding force between the negative electrode active materials is increased to suppress an increase in resistance at the negative electrode. Technology (see Patent Document 5), a negative electrode active material containing silicon particles having a predetermined particle size is bound with a polyimide resin using a specific diamine to obtain a negative electrode. As withstand repeated electrodeposition, such techniques to improve the cycle characteristics (see Patent Document 6) are known.

Japanese Patent No. 3311402 Japanese Patent No. 3561701 JP 2008-252550 A JP 2008-84562 A Japanese Patent No. 4215532 JP 2008-34352 A

In particular, when lithium secondary batteries are used as in-vehicle power sources for hybrid vehicles and electric vehicles, in addition to the discharge capacity, which is a typical performance of secondary batteries, cycle life that shows repeated charge / discharge performance, It is important to have excellent input / output characteristics that show a balance between energy recovery and energy recovery. However, as described above, although various improvements have been made on the negative electrode using a polyimide resin as a binder, the cycle life and output characteristics are still not at a sufficient level.

Therefore, an object of the present invention is to provide a negative electrode capable of obtaining a secondary battery exhibiting performance such as discharge capacity, output characteristics, and cycle characteristics in a well-balanced manner. Another object of the present invention is to provide a secondary battery suitable as a power source for a hybrid vehicle or an electric vehicle, using such a negative electrode.

Furthermore, another object of the present invention is to provide a resin for a binder used for an electrode of a secondary battery that expresses performance such as discharge capacity, output characteristics, and cycle characteristics in a well-balanced manner required for a power source for a hybrid vehicle or an electric vehicle. The object is to provide a precursor, a resin precursor solution, and a binder composition.

Therefore, as a result of intensive studies on the above problems, the present inventors were excellent in the balance of discharge capacity, output characteristics, and cycle characteristics by using a polyimide resin made from a specific acid anhydride and diamine as a raw material. It discovered that the negative electrode for secondary batteries could be obtained, and completed this invention.

That is, the present invention is a negative electrode for a secondary battery including an active material layer in which a negative electrode active material is integrated with a binder, and the polyimide having a repeating unit represented by the following general formula (1) as the binder A negative electrode for a secondary battery using a resin.

[In the formula, Ar ₁ represents a divalent aromatic diamine residue having at least two ether bonds, and Ar ₂ represents a tetravalent acid diacid represented by the following formula (2) or formula (3). An anhydride residue is shown. ]

[In Formula (3), Y represents either a direct bond or —CO—. ]

Further, the present invention is a secondary battery using the above negative electrode.

The present invention also relates to a resin precursor for a binder used for forming an active material layer (a mixture layer) on a current collector to form an electrode of a lithium secondary battery, the following general formula (6) The resin precursor for binders is characterized by containing 50 mol% or more of a polyimide resin precursor having a repeating unit represented by:

[In Formula (3), Y represents either a direct bond or —CO—. ]

Furthermore, the present invention is a resin precursor solution characterized by containing the binder resin precursor in an organic solvent and having a viscosity in the range of 500 to 10,000 cP.

Furthermore, the present invention is a binder composition comprising the resin precursor solution and an active material.

The binder composition of the present invention preferably contains 0.1 to 10% by mass of a polyimide resin precursor having a repeating unit represented by the general formula (1) with respect to the active material. When used in the above, the active material is preferably a carbon material, and the average particle size of the active material is preferably in the range of 5 to 50 μm.

The negative electrode of the present invention can provide a negative electrode for a secondary battery having an excellent balance of discharge capacity, output characteristics, and cycle characteristics. Therefore, according to the negative electrode of the present invention, it is possible to obtain a secondary battery having a balance of practical characteristics required for a power source for in-vehicle use such as a hybrid vehicle or an electric vehicle.

In addition, according to the present invention, a binder resin precursor, a resin precursor solution, and a binder composition suitable for forming an electrode for a secondary battery having an excellent balance of discharge capacity, output characteristics, and cycle characteristics are obtained. Can do. By forming an electrode as a binder of an active material using these, a secondary battery having a balance of practical characteristics required for a vehicle-mounted power source such as a hybrid vehicle or an electric vehicle can be obtained.

Below, the negative electrode for secondary batteries of this invention and a secondary battery using the same are first demonstrated in detail based on embodiment of the negative electrode for secondary batteries.
In the present invention, a predetermined polyimide resin is used as a binder as described below. In general, the polyimide resin is excellent in the binding force between the negative electrode active materials, and more excellent in adhesiveness to the current collector forming the negative electrode than PVDF. In addition, unlike PVDF, which is a type of fluororesin, polyimide resin does not contain fluorine in the structure, and because it is thermally stable and has high heat resistance, the battery can be used even when the battery temperature rises abnormally. Low risk of breakage or rupture.

First, the polyimide resin used in the present invention has a repeating unit represented by the general formula (1), and Ar ₁ is a divalent aromatic diamine residue having at least two ether bonds. Can include:

[In formula (4), X represents a divalent organic group having one or more aromatic rings, and preferably has a structure shown in the following (5). ]

As a preferred diamine component that gives such an aromatic diamine residue, specifically, 2,2′-bis [4- (4-aminophenoxy) phenyl] propane (BAPP), 1,3-bis (4-amino) And phenoxy) benzene (TPE-R), 1,3-bis (3-aminophenoxy) benzene (APB), 4,4′-bis (4-aminophenoxy) biphenyl (BAPB), and the like. Among these diamine components, it is preferable to use BAPP as an essential component, and it is particularly preferable to use this in a proportion of 50 mol% or more.

In the polyimide resin used in the present invention, Ar ₂ shown in the general formula (1) is a tetravalent acid dianhydride residue represented by the following formula (2) or formula (3).

[In Formula (3), Y represents either a direct bond or —CO—. ]

Preferred acid dianhydrides that give such acid dianhydride residues are specifically pyromellitic anhydride (PMDA), 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and the like. In addition, the diamine and acid anhydride used as the raw material for the polyimide resin may be a mixture of two or more components, respectively, and a diamine or acid anhydride other than those represented by Ar ₁ and Ar ₂ may be used in combination. In that case, however, it is desirable that the ratio of the components other than those represented by Ar ₁ and Ar ₂ is less than 50% in terms of the molar ratio of each component.

As Ar ₁ and Ar ₂ constituting the polyimide structural unit other than the general formula (1), Ar ₁ is 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, m -Phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'- Diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diamino Diphenylsulfone, 3,3'-diaminodiphenylsulfone, benzidine, 3,3'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobi Diamine residues obtained from phenyl, 3,3′-dimethoxybenzidine, 4,4 ″ -diamino-p-terphenyl, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, etc., alone or Two or more kinds can be mixed and used. Further, a siloxane diamine having a siloxane chain having a repeating number of 1 to 20 may be used.

Furthermore, Ar ₂ may be used those comprising the formula (2) or (3) other than the acid dianhydride. Examples of the acid anhydride in which Ar ₂ gives an acid anhydride residue other than those represented by the general formulas (2) and (3) include 4,4′-oxydiphthalic dianhydride, naphthalene-2,3,6,7-tetracarboxylic Acid dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetra Carboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, 2,2-bis (2,3-dicarboxyphenyl) -propane dianhydride, 2,2-bis (3 , 4-dicarboxyphenyl) -propane dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-di Carboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, and the like. These can also be used.

When the polyimide resin of the general formula (1) is obtained, it is produced by polymerizing raw material diamine and acid anhydride in the presence of a solvent to obtain a polyimide precursor resin, followed by heat treatment and imidization. Can do. In addition, when setting it as a negative electrode material binder, generally it is set as the composition for disperse-mixing with an active material, a solvent, and other required additives in the state of a polyimide precursor resin, and forming an active material layer. Examples of the reaction solvent used here include dimethylacetamide, dimethylformamide, N-methylpyrrolidone, 2-butanone, diglyme, and xylene, and one or more of these may be used. In addition, the polyimide precursor resin has a weight average molecular weight of 10,000 to 500, 500, from the viewpoint of the balance between the binding property / adhesiveness as a binder and the viscosity of the slurry obtained by mixing with the active material. It is preferable to be in the range of 000.

Moreover, the negative electrode active material in this invention can be suitably selected according to the kind of secondary battery, for example, in the case of a lithium secondary battery (lithium ion secondary battery), lithium can be intercalated. Specifically, in addition to carbon materials such as graphite and amorphous carbon, lithium-transition metal compounds, lithium-titanium composite oxides, metal materials, and lithium aluminum alloys, lithium tin An alloy, a lithium alloy such as a lithium silicon alloy, or the like can be used. In some cases, these two or more negative electrode active materials may be used in combination. Of these, carbonaceous materials are generally used, and in particular, graphite materials are excellent materials having a high energy density obtained at a high temperature of at least about 2000 ° C., usually about 2600 to 3000 ° C. However, because it has problems with input / output characteristics and cycle characteristics, it is fired at a temperature lower than that of graphite materials for in-vehicle power sources such as hybrid cars and electric cars, and high input / output applications used for power storage. A low crystalline carbon material having a low degree of graphitization is preferably used.

As a low crystalline carbon material having a low degree of graphitization, for example, a petroleum-based or coal-based heavy oil is obtained by performing a thermal decomposition / polycondensation reaction at a maximum temperature of about 400 ° C. to 800 ° C. for about 24 hours. The raw coke produced and calcined coke obtained by calcining the raw coke at a maximum temperature of about 800 ° C. to 1500 ° C. may be mentioned, and these may be mixed at a predetermined ratio. In addition, a material obtained by adding a boron compound, a phosphorus compound, a nitrogen compound, or the like to these carbon materials, firing, and replacing a part of carbon with a specific element can also be used. Since such a carbon material is usually obtained in the form of a lump, it is better to pulverize it to a predetermined particle size using a pulverizer. In that case, from the viewpoint of energy efficiency when used in a secondary battery The average particle diameter determined as the median diameter is preferably 5 to 50 μm, more preferably 5 to 15 μm, and the BET specific surface area is preferably 5 m ² / g or less, more preferably. Is preferably 1 m ² / g or less. The pulverized carbon material can be used as a negative electrode active material by further firing at about 800 to 1400 ° C.

In the present invention, the polyimide resin or a precursor thereof and the negative electrode active material are mixed using a solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF), water, or alcohol. Thus, a negative electrode provided with an active material layer can be obtained by preparing a slurry and applying and drying the slurry on a current collector.

Here, the material of the conductive substrate used as the current collector is not particularly limited, but a metal foil such as aluminum, copper, nickel, titanium, and stainless steel can be used. Moreover, although the form of such an electroconductive base material can be made into various forms, such as a continuous sheet, a perforated sheet, and a net-like (net-like) sheet, it is particularly preferable to use a continuous sheet. Further, the thickness of the conductive substrate is preferably 2 to 30 μm.

In forming the active material layer on the current collector, a negative electrode active material and, if necessary, a conductive aid were mixed into a slurry obtained by dissolving a polyimide resin or a precursor thereof in an organic solvent such as NMP. Then, the active material layer is formed by coating the current collector with a uniform thickness by a known means such as extrusion coating, curtain coating, roll coating or gravure coating, drying to remove the organic solvent, and then heat curing. Form. At this time, from the viewpoint of the balance between the binding property and the discharge capacity, the content ratio of the polyimide resin with respect to the negative electrode active material is preferably in the range of 0.1 to 10% by mass, preferably 0.3 to It is good to make it the range of 8 mass%. Further, the thickness of the active material layer may be about the same as that for forming a known negative electrode for a secondary battery, and is not particularly limited, but is generally about 10 to 500 μm.

The negative electrode thus obtained can be suitably used as an electrode for a secondary battery such as a lithium secondary battery. When a lithium secondary battery is formed using the negative electrode of the present invention, the opposite positive electrode includes a lithium-containing transition metal oxide LiM (1) _x O ₂ (where x is a numerical value in the range of 0 ≦ x ≦ 1). Where M (1) represents a transition metal and is composed of at least one of Co, Ni, Mn, Ti, Cr, V, Fe, Zn, Al, Sn, and In), or LiM (1) _y M (2) _2-y O ₄ (wherein y is a numerical value in the range of 0 ≦ y ≦ 1, where M (1) and M (2) represent transition metals, Co, Ni, Mn , Ti, Cr, V, Fe, Zn, Al, Sn, In), LiM (1) _x M (2) _y M (3) _z O ₂ (where x, y and z are x + y + z = 1 in the range satisfying the relationship, where M (1), M (2) and M (3) represent transition metals, Co, Ni, Mn, Ti, Cr, V, Fe, Zn , Al, Sn, In Both consist of one _{type), LiM (1) x PO} 4 ( wherein x is a number in the range of 0 ≦ x ≦ 1, wherein M (1) represents a transition metal, Co, Ni, Mn, Ti , Cr, V, Fe, Zn, Al, Sn, In), transition metal chalcogenides (Ti, S ₂ , NbSe, etc.), vanadium oxide (V ₂ O ₅ , V ₆ O ₁₃ , V ₂ O ₄ , V ₃ O ₆ etc.) and lithium compounds, general formula M _x Mo ₆ Ch _6-y (wherein x is a numerical value in the range of 0 ≦ x ≦ 4, y is 0 ≦ y ≦ 1) In the formula, M represents a metal such as a transition metal, Ch represents a chalcogen metal), or a positive electrode active material such as activated carbon or activated carbon fiber.

Further, Examples of the electrolyte filling the space between the positive electrode and the negative electrode, and any known ones can be used, for example _{_{_{LiClO 4, LiBF 4, LiPF 6}}} , LiAsF 6, LiB (C 6 H 5), LiCl LiBr, Li ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, Li (CF ₃ CH ₂ OSO ₂ ) ₂ N, Li (CF ₃ CF ₂ CH ₂ OSO ₂ ) ₂ N, Li (HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ N, Li ((CF ₃ ) ₂ CHOSO ₂ ) ₂ N, LiB [C ₆ H ₃ (CF ₃ ) ₂ ] ₄ Mention may be made of mixtures of more than one species.

Examples of the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1, 2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, anisole, diethyl ether, sulfolane, methylsulfolane, acetonitrile, chloronitrile, propio Nitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene , Benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, sulfite, a single solvent or a mixture of two or more solvents such as dimethyl sulfite may be used.

Next, the binder resin precursor, the resin precursor solution, and the binder composition used for forming the secondary battery of the present invention will be described in detail.
In the present invention relating to a binder application for binding an active material, a predetermined polyimide resin precursor is used as described below.

The binder resin precursor of the present invention contains a polyimide resin precursor having a repeating unit represented by the general formula (6). In General Formula (6), Ar ₁ represents a divalent aromatic diamine residue having at least two ether bonds, and Ar ₂ is a tetravalent represented by Formula (2) or Formula (3). An acid dianhydride residue is shown. In the formula (3), Y represents either a direct bond or —CO—. Ar ₁ preferably includes the following.

[In Formula (4), X represents a divalent organic group having one or more aromatic rings, and preferably has a structure as shown in the following (5). ]

Favorable diamine components that give such aromatic diamine residues and preferred acid dianhydrides that give acid dianhydride residues include those mentioned above.

In the binder resin precursor, the ratio of the polyimide resin precursor having the repeating unit represented by the general formula (6) is preferably 50 mol% or more. In addition to the polyimide resin precursor having the repeating unit of the general formula (6), there is a possibility that it may be contained in less than 50 mol%. In the general formula (6), Ar ₁ is 4,4′-diaminodiphenyl ether. , 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'- Diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 4,4'-diamino Diphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, benzidine, 3,3'-diaminobiphenyl, 2, 2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4 ''-diamino-p-terphenyl, 1 Diamine residues obtained from 1,5-diaminonaphthalene, 2,6-diaminonaphthalene and the like can be mentioned, and these can be used alone or in admixture of two or more. Further, a siloxane diamine having a siloxane chain having a repeating number of 1 to 20 may be used. Furthermore, Ar ₂ may be used those comprising the formula (2) or (3) other than the acid dianhydride. Examples of the acid anhydride in which Ar ₂ gives an acid anhydride residue other than those represented by the general formulas (2) and (3) include 4,4′-oxydiphthalic dianhydride, naphthalene-2,3,6,7-tetracarboxylic Acid dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetra Carboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, 2,2-bis (2,3-dicarboxyphenyl) -propane dianhydride, 2,2-bis (3 , 4-Dicarboxyphenyl) -propane dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3.4-dicarboxyphenyl) ) Methane dianhydride, bis (2,3-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, and the like. The above can also be used.

The polyimide resin precursor having a repeating unit represented by the general formula (6) may be a resin precursor solution in a state dispersed in an organic solvent. Here, if necessary, a solvent may be added separately from the solvent used during polymerization of the polyimide resin precursor. Such a solvent may be the same as that used in the polymerization of the polyimide resin precursor, or may be another solvent. In general, dimethylacetamide, dimethylformamide, N-methylpyrrolidone, 2-butanone, diglyme, xylene and the like may be used, and one or more of these may be used. In consideration of application to the current collector, the viscosity of the resin precursor solution is preferably in the range of 500 to 10,000 cP, more preferably in the range of 1,000 to 5,000 cP. .

The resin precursor solution thus obtained is mixed with an active material and other additives used as necessary to obtain a binder composition. The binder composition is applied to the current collector constituting the electrode as described in detail later, and the polyimide resin precursor having the repeating unit of the general formula (6) in the composition is at this stage. It is imidized by a means such as heating to become a polyimide resin having a repeating unit represented by the following general formula (1).

The imidized polyimide resin having the repeating unit of the general formula (1) is obtained by imidizing the polyimide resin precursor represented by the general formula (6), and Ar ₁ and Ar ₂ are represented by the general formula ( This represents the same as 6). That is, Ar ₁ is a divalent aromatic diamine residue having at least two ether bonds. Ar ₂ shown in the general formula (4) is a tetravalent acid dianhydride residue represented by the above formula (2) or formula (3).

When obtaining a polyimide resin having a repeating unit of the general formula (1), the raw material diamine and acid anhydride are polymerized in the presence of a solvent to obtain a polyimide resin precursor, and then heat treated to imidize. When a polyimide resin precursor is used as a binder for an electrode, as described above, a binder composition in which an active material or the like and a polyimide resin precursor are mixed is usually on a current collector. And imidized by heat treatment. Examples of the solvent used for the polymerization include dimethylacetamide, dimethylformamide, N-methylpyrrolidone, 2-butanone, diglyme, xylene and the like, and one or more of these may be used. In addition, the polyimide resin precursor has a weight average molecular weight in the range of 10,000 to 500,000 from the viewpoint of the balance between the binding property / adhesiveness as the binder and the viscosity of the slurry obtained by mixing with the active material. It is preferable to do so.

The resin precursor solution of the present invention is mixed with a positive electrode active material or a negative electrode active material depending on the application to form a binder composition. Here, the positive electrode active material and the negative electrode active material are not particularly limited, and representative examples thereof include those described above. As described above, the resin precursor solution containing the polyimide resin precursor is made into a slurry using a predetermined solvent as necessary together with the positive electrode or the negative electrode active material, as exemplified above. The electrode provided with the active material layer can be obtained by applying and drying on the current collector.

In forming the active material layer on the current collector, the positive electrode or negative electrode active material and, if necessary, a conductive aid are mixed with the resin precursor solution to form a slurry, and then extrusion coating, curtain coating, roll The active material layer is formed by applying a uniform thickness to the current collector by a known means such as coating or gravure coating, drying and removing the organic solvent, followed by heating imidization. At this time, from the viewpoint of the balance between the binding property and the discharge capacity, the content ratio of the polyimide resin precursor having the repeating unit of the general formula (6) to the active material is in the range of 0.1 to 10% by mass. It is preferable to make it in the range of 0.3 to 8% by mass. The thickness of the active material layer may be about the same as that for forming a known electrode for a secondary battery, and is not particularly limited, but is generally about 10 to 500 μm.

Hereinafter, the present invention will be described in more detail on the basis of examples. However, the present invention is not limited to the following examples in any way, and can be implemented with appropriate modifications without departing from the scope of the present invention. .

(Binder composition production example-Example 1)
First, using a refined pitch from which heavy quinoline insolubles have been removed from coal-based heavy oil, a bulk coke produced by heat treatment at a temperature of 500 ° C. for 24 hours by a delayed coking method is obtained, and finely pulverized with a jet mill. The raw coke powder having an average particle size of 9.9 μm was obtained by pulverization and sizing.

The bulk raw coke obtained as described above is heat-treated for 1 hour or more at a temperature from the inlet temperature of 700 ° C. to the outlet temperature of 1500 ° C. (maximum temperature reached) by a rotary kiln to obtain massive calcined coke. The powder was pulverized and sized by a mill to obtain calcined coke powder having an average particle size of 9.5 μm.

Phosphoric acid ester (14% by mass active phosphorus solid resin: manufactured by Sanko Co., Ltd.) with respect to the total of 50 parts by mass of raw coke powder and 50 parts by mass of calcined coke powder obtained as described above (100 parts by mass of coke powder). Name HCA, chemical name: 9,10-dihydro-9-oxa-10-osfaphenanthrene-10-oxide) 17.9 parts by mass (phosphorus equivalent: 2.5 parts by mass), and boron carbide 3.2 parts by mass (Boron conversion: 2.5 parts by mass) was added to obtain a coke material.

Next, the coke material is heated from room temperature at a rate of 600 ° C./hour, reaches 900 ° C. (maximum temperature reached), and is further held for 2 hours for carbonization treatment (firing), and a lithium secondary battery Negative electrode active material A was obtained.

On the other hand, dimethylacetamide using pyromellitic anhydride (PMDA) as the acid dianhydride and 2,2'-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) as the diamine is used in approximately the same mole. A precursor of polyimide resin having a weight average molecular weight of 144,000 was obtained by reacting in (DMAC) at room temperature for 4 hours. The polyimide resin precursor thus obtained is used as a binder for a lithium secondary battery.

The negative electrode active material A obtained above and the precursor of the polyimide resin excluding the solvent (DMAC) at the time of polymerization are in a ratio of 95% by mass and 5% by mass, and dimethylacetamide (DMAC) is separately used as a solvent. The mixture was added and kneaded to prepare a slurry (binder composition). The composition of the obtained slurry is shown in Table 1. The amount of DMAC (solvent) in the binder composition was such that the solid content concentration (polyimide resin precursor + negative electrode active material) of the slurry excluding all solvents was 50% by weight. In addition, the viscosity of the polyimide resin precursor solution in Table 1 is a viscosity obtained by polymerizing raw material diamine and acid anhydride in the presence of a solvent using an E-type viscometer manufactured by TOKIMEC ( 25 ° C.). Furthermore, the weight average molecular weight is a value in terms of polystyrene of the polyimide resin precursor.

(Binder composition production example-Examples 2 to 6)
Polyimide resin precursors according to Examples 2 to 6 were obtained in the same manner as in Example 1 except that the combination of acid dianhydride and diamine was changed as shown in Table 1. In addition, the polyimide resin precursors according to Examples 2 to 5 were kneaded with negative electrode active material A using dimethylacetamide (DMAC) as a solvent in the same manner as in Example 1 to obtain slurries (binder compositions). . On the other hand, about the polyimide resin precursor which concerns on Example 6, the natural graphite was used instead of the negative electrode active material A, and the slurry (binder composition) was obtained like Example 1 except it.

(Binder composition production example-Comparative Examples 1 to 5)
Polyimide resin precursors according to Comparative Examples 2 to 5 were obtained in the same manner as in Example 1 except that the combination of acid dianhydride and diamine was changed as shown in Table 1. These were kneaded with negative electrode active material A using dimethylacetamide (DMAC) as a solvent in the same manner as in Example 1 to obtain slurries (binder compositions). On the other hand, the slurry which knead | mixed with the negative electrode active material A by using dimethylacetamide (DMAC) as a solvent was made into the comparative example 1 similarly to Example 1 using polyvinylidene fluoride (PVDF) instead of a polyimide resin precursor. . In addition, the meaning of the abbreviation described in Table 1 is as follows.
BTDA: 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride
BPDA: 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride
TPE-R: 1,3-bis (4-aminophenoxy) benzene
APB: 1,3-bis (3-aminophenoxy) benzene
DSDA: 3,3 ', 4,4'-diphenylsulfonetetracarboxylic dianhydride
BPADA: 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane dianhydride
PDA: p-Phenylenediamine
DAPE: 4,4'-diaminodiphenyl ether

(Negative electrode production example-Example 7)
Using the binder composition obtained in Example 1, the negative electrode was produced in the following manner, and the performance as a secondary battery was evaluated. That is, the obtained binder composition was applied to a copper foil having a thickness of 10 μm so as to have a uniform thickness, and then the polyimide resin precursor was imidized by heat treatment at 350 ° C. for 30 minutes in a nitrogen atmosphere to obtain copper. An active material layer was formed on the foil. The copper foil provided with the active material layer is dried and pressed to a predetermined electrode density to produce an electrode sheet having a total thickness of 60 μm, and a negative electrode is obtained by cutting the sheet into a circle having a diameter of 15 mmΦ. It was.

For the obtained negative electrode, in order to evaluate the electrode characteristics of the negative electrode single electrode, a test lithium secondary battery was prepared as follows. As the counter electrode, metallic lithium cut out to about 15.5 mmΦ was used. In addition, a coin cell was prepared by using a solution of LiPF ₆ dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio of 1: 1) as the electrolytic solution at a concentration of 1 mol / l, and using a porous membrane of propylene as the separator. did.

Using this coin cell thus obtained, a constant current discharge of 0.5 mA / cm ² was initially carried out at a constant temperature of 25 ° C., with a terminal voltage lower limit voltage of 0 V and a discharge upper limit voltage of 1.5 V. The discharge capacity was 313 mAh / g when the output characteristics and input characteristics at the time of carrying out constant current discharge and charging of 5 mA / cm ² were examined by the capacity maintenance ratio, and the capacity maintenance ratio related to the output characteristics was The capacity maintenance ratio related to the input characteristics was 78.2% and 56.2%. The product of these ratios was evaluated as the input / output balance and found to be 0.44. Here, the capacity maintenance rate related to the output characteristics is obtained from the ratio of the discharge capacity during 5 mA / cm ² constant current discharge to the initial discharge capacity, and the capacity maintenance ratio related to the input characteristics is 5 mA / cm ² constant relative to the initial charge capacity. It calculated | required from ratio of the charge capacity at the time of electric current charge. The capacity maintenance rate after 3 cycles obtained from the ratio of the discharge capacity at the 3rd cycle to the discharge capacity at the 1st cycle by repeating the constant current discharge and the charge at 0.5 mA / cm ² for 3 cycles is 95.2%. Met. Furthermore, constant capacity discharge and charging were repeated 100 cycles, and the capacity retention rate after 100 cycles, which was obtained from the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle, was 87.7%. As for the capacity retention ratio (cycle characteristics) after 100 cycles, ◎ if the capacity retention ratio is 80% or more, ◯ if it is 70% or more and less than 80%, △ if it is 60% or more and less than 70%. Table 2 shows the results of evaluation in four stages, with x being less than 60%.

(Negative electrode production example-Examples 8 to 12, Comparative Examples 6 to 10)
For the binder compositions obtained in Examples 2 to 5 and Comparative Examples 1 to 5, a negative electrode was produced in the same manner as in Example 7 for producing the negative electrode, and the discharge capacity, output characteristics, and cycle characteristics were determined. evaluated. The results are shown in Table 2. In addition, in the case of the comparative example 6 of negative electrode manufacture using the binder composition of the comparative example 1, the heat processing at 350 degreeC in the nitrogen atmosphere after apply | coating to copper foil was abbreviate | omitted. As a result, the negative electrode obtained in Comparative Example 6 for producing the negative electrode had a discharge capacity of 291 mAh / g, a capacity retention ratio of 61.2% for output characteristics, and a capacity maintenance ratio of 32.8 for input characteristics. %Met. The input / output balance obtained from the product of these ratios was 0.20, and the capacity retention rate after 3 cycles obtained by repeating 3 cycles of constant current discharge and charge was 88.0%. Furthermore, the capacity maintenance rate after 100 cycles obtained by repeating 100 cycles of constant current discharge and charge was 63.9%.

As is clear from the results of the above negative electrode production examples (Examples 7 to 12, Comparative Examples 6 to 10), in the case of Examples 7 to 12 using the binder composition according to Examples 1 to 6 of the present invention, Compared to Comparative Example 6 using PVDF as a binder and Comparative Examples 7 to 10 using polyimide resins other than those represented by the general formula (1), the discharge capacity, output characteristics, and cycle characteristics It turned out that the secondary battery excellent in the balance can be obtained.

(Negative electrode production example-Example 13)
Using refined pitch from which quinoline insolubles have been removed from coal-based heavy oil, bulk coke produced by heat treatment at a temperature of 500 ° C. for 24 hours by a delayed coking method (raw coke) is obtained. The size was adjusted to obtain a raw coke powder having an average particle size of 9.9 μm.

Phosphoric acid ester (14% by mass active phosphorus solid resin: manufactured by Sanko Co., Ltd.) with respect to the total of 50 parts by mass of raw coke powder and 50 parts by mass of calcined coke powder obtained as described above (100 parts by mass of coke powder). No. HCA, chemical name: 9,10-dihydro-9-oxa-10-osfaphenanthrene-10-oxide) 17.9 parts by mass (phosphorus equivalent: 2.5 parts by mass) was added to obtain a coke material.

Next, the coke material is heated from room temperature at a rate of 600 ° C./hour, reaches 900 ° C. (maximum temperature reached), and is further held for 2 hours for carbonization treatment (firing), and a lithium secondary battery Negative electrode active material B was obtained.

As a binder, a negative electrode was obtained in the same manner as in Example 7 of negative electrode production using the polyimide resin precursor used in Example 1 of binder composition production (Table 3). The obtained negative electrode was evaluated in the same manner as in Example 7. As a result, the discharge capacity was 313 mAh / g, the capacity maintenance ratio related to output characteristics was 80.1%, and the capacity maintenance ratio related to input characteristics was 57.0%. Met. The input / output balance obtained from the product of these ratios was 0.46. Further, the capacity retention rate after 3 cycles was 95.8%, and the evaluation of the cycle characteristics related to the capacity retention rate after 100 cycles was ◎.

(Negative electrode production example-Examples 14 to 18)
A negative electrode was obtained in the same manner as in Example 13 except that the binder used in Example 13 was changed to a polyimide resin precursor having the composition shown in Table 3. About the obtained negative electrode, it carried out similarly to Example 13, and evaluated discharge capacity, output characteristics, and cycling characteristics. The results are shown in Table 3. In addition, the meaning of the new abbreviation described in Table 3 is as follows, and others are as above-mentioned. Moreover, the polyimide resin was imidized by the heat processing at the time of forming an active material layer by polymerizing precursors in the same manner as in Example 1.
m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl

As is apparent from the results of Examples 12 to 18 of the negative electrode production example, it was found that any secondary battery having an excellent balance of discharge capacity, output characteristics, and cycle characteristics can be obtained.

The negative electrode of the present invention can provide a secondary battery with an excellent balance of discharge capacity, output characteristics, and cycle characteristics. Therefore, by using this negative electrode, it is possible to obtain a secondary battery having a balance of practical characteristics required for a power source for in-vehicle use such as a hybrid vehicle or an electric vehicle. Moreover, it is not restricted to these uses, It can utilize suitably as a power supply by which high output, a high capacity | capacitance, and a long life are requested | required, such as a power supply for electric power tools, including a power supply for fuel cell vehicles.

Further, the resin precursor for binder, the resin precursor solution, and the binder composition of the present invention provide an electrode useful for forming a secondary battery excellent in balance of discharge capacity, output characteristics, and cycle characteristics. Can do. Therefore, by using such an electrode, it is possible to obtain a secondary battery having a balance of practical characteristics required for a power source for use in a vehicle such as a hybrid vehicle or an electric vehicle.

Claims

A negative electrode for a secondary battery having an active material layer in which a negative electrode active material is integrated with a binder, wherein a polyimide resin having a repeating unit represented by the following general formula (1) is used as the binder. A negative electrode for a secondary battery.

[In the formula, Ar 1 represents a divalent aromatic diamine residue having at least two ether bonds, and Ar 2 represents a tetravalent acid diacid represented by the following formula (2) or formula (3). An anhydride residue is shown. ]

[In Formula (3), Y represents either a direct bond or —CO—. ]
The negative electrode for a secondary battery according to claim 1, wherein the content ratio of the polyimide resin with respect to the negative electrode active material is in the range of 0.1 to 10% by mass.
A secondary battery using the negative electrode according to claim 1 or 2.
The secondary battery according to claim 3, which is used as an in-vehicle power source for a hybrid vehicle or an electric vehicle.
A resin precursor for a binder used for forming an active material layer on a current collector to form an electrode of a lithium secondary battery, and a polyimide resin precursor having a repeating unit represented by the following general formula (6) The resin precursor for binders characterized by containing 50 mol% or more of a body.

[In the formula, Ar 1 represents a divalent aromatic diamine residue having at least two ether bonds, and Ar 2 represents a tetravalent acid diacid represented by the following formula (2) or formula (3). An anhydride residue is shown. ]

[In Formula (3), Y represents either a direct bond or —CO—. ]
A resin precursor solution comprising the binder resin precursor according to claim 5 in an organic solvent and having a viscosity in the range of 500 to 10,000 cP.
A binder composition comprising the resin precursor solution according to claim 6 and an active material.
The binder composition according to claim 7, comprising 0.1 to 10% by mass of a polyimide resin precursor having a repeating unit represented by the general formula (6) with respect to the active material.
The binder composition according to claim 7 or 8, wherein the active material is a carbon material, and the average particle diameter of the active material is in the range of 5 to 50 µm, and is used for forming a negative electrode.