JP6087728B2 - Secondary battery electrode binder - Google Patents

Description

  The present invention relates to a binder for a secondary battery electrode. More specifically, the present invention relates to a binder for a secondary battery electrode that is excellent in adhesiveness between the positive and negative active materials constituting the secondary battery electrode and each electrode metal current collector.

In secondary batteries such as nickel metal hydride batteries and lithium ion batteries, each electrode is made by bonding an active material of positive and negative electrodes to each electrode metal current collector with a binder. The binder is required to have oxidation resistance and resistance to swelling with respect to the electrolytic solution, and a solution in which polyvinylidene fluoride is dissolved in N-methyl-2-pyrrolidone (NMP) is used as the binder.
However, polyvinylidene fluoride is inferior in adhesion between the active material for positive and negative electrodes and each electrode metal current collector, and inferior in swelling resistance to the electrolytic solution (hereinafter sometimes simply referred to as swelling resistance). There was a problem in terms of electrochemical stability that the battery capacity was reduced (that is, the cycle characteristics were poor) by repeated charging and discharging of the secondary battery.
In order to solve this problem, a method of using an aqueous dispersion of an olefin polymer which is less swellable to an electrolytic solution and is electrochemically stable as a binder (for example, see Patent Document 1) is known.

JP-A-9-251856

However, in the method described in Patent Document 1, although there is swelling resistance against an electrolytic solution, the adhesion between each active material of the positive and negative electrodes and each electrode metal current collector is still insufficient, and electrochemical stability. It was not satisfying in terms of, and improvement was eagerly desired.
The objective of this invention is providing the binder for secondary battery electrodes which is excellent in the swelling resistance with respect to electrolyte solution, and excellent in the adhesiveness of each active material of positive and negative electrodes, and each electrode metal electrical power collector.

  The inventor of the present invention has arrived at the present invention as a result of intensive studies to solve the above problems. That is, the present invention contains a copolymer (X) having a polyolefin (A) and an unsaturated (poly) carboxylic acid (anhydride) (B) as structural units and an acid value of 50 to 250 mgKOH / g. The secondary battery electrode binder (N).

The binder (N) for secondary battery electrodes of the present invention has the following effects.
(1) Excellent swelling resistance to the electrolytic solution.
(2) Excellent adhesion between each active material of positive and negative electrodes and each electrode metal current collector.
(3) A secondary battery having an electrode formed using the binder is excellent in cycle characteristics.

[Polyolefin (A)]
The polyolefin (A) in the present invention includes one or two or more (co) polymers of olefins, and one or more of olefins and one or more of other monomers. A polymer is included.
Examples of the olefin include alkenes having 2 to 30 carbon atoms (hereinafter abbreviated as C) such as ethylene, propylene, 1- and 2-butene, and isobutene, and C5-30 α-olefins (1-hexene, 1-hexene, Decene, 1-dodecene, etc.); other monomers include C4-30 unsaturated monomers having copolymerizability with olefins, such as vinyl acetate.

Specific examples of (A) include ethylene unit-containing (propylene unit-free) (co) polymers such as high, medium and low density polyethylene, and ethylene and C4-30 unsaturated monomers [butene (1- Butene, etc.), C5-30 α-olefin (1-hexene, 1-dodecene, etc.), copolymer with vinyl acetate, etc. (weight ratio is adhesiveness of binder and terminal and / or molecular chain of (A)) Preferably from 30/70 to 99/1, more preferably from 50/50 to 95/5) and the like; propylene unit-containing (ethylene unit-free) (co) polymer such as polypropylene, Copolymer of propylene and C4-30 unsaturated monomer (same as above) (weight ratio is same as above); ethylene / propylene copolymer (weight ratio is binder adhesion and terminal of (A)) Oh And / or from the viewpoint of the amount of double bonds in the molecular chain, preferably 0.5 / 99.5 to 30/70, more preferably 2/98 to 20/80); Coalescence, such as polybutene, is included.
Among these, polyethylene, polypropylene, ethylene / propylene copolymer are preferable from the viewpoint of copolymerization with an unsaturated (poly) carboxylic acid (anhydride) (B) and an aliphatic unsaturated hydrocarbon (C) described later. Polymers, propylene / C4-30 unsaturated monomer copolymers, more preferably ethylene / propylene copolymers, and propylene / C4-30 unsaturated monomer copolymers.

  Number average molecular weight of (A) [hereinafter abbreviated as Mn. The measurement is based on a gel permeation chromatography (GPC) method described later. same as below. ] Is preferably 800 to 50,000, more preferably 1,000 to 45,000 from the viewpoint of the adhesiveness of the binder (N) for secondary battery electrodes of the present invention and the productivity of the (N). .

The measurement conditions of Mn by GPC in the present invention are as follows.
Apparatus: High-temperature gel permeation chromatograph [“Alliance
GPC V2000 ", manufactured by Waters Corporation]
Detector: Refractive index detector Solvent: Orthodichlorobenzene reference material: Polystyrene sample concentration: 3 mg / ml
Column stationary phase: PLgel 10 μm, MIXED-B 2 in series
[Made by Polymer Laboratories, Inc.]
Column temperature: 135 ° C

(A) is a molecular terminal and / or molecule from the viewpoint of copolymerization with an unsaturated (poly) carboxylic acid (anhydride) (B) or (B) and an aliphatic unsaturated hydrocarbon (C) described later. It is preferable to have a double bond in the chain.
The number of double bonds in the molecular end and / or molecular chain per 1,000 carbon atoms (also referred to as 1,000 carbon atoms) of (A) is (A) and (B) or (B) From the viewpoint of copolymerization with (C) and the productivity of (N), the number is preferably 0.1 to 20, more preferably 0.3 to 18, and particularly preferably 0.5 to 15.
Here, the number of double bonds can be determined from the spectrum of (A) ¹ H-NMR (nuclear magnetic resonance) spectroscopy. That is, the peak in the spectrum is assigned, and the number of double bonds in (A) and (A) are calculated from the integral value derived from double bonds and the integral value derived from (A) at 4.5 to 6 ppm in (A). Is calculated, and the number of double bonds in the molecular end and / or molecular chain per 1,000 carbon atoms in (A) is calculated. The number of double bonds in the examples described later followed this method.

  The production method of (A) includes polymerization methods (for example, those described in JP-A-59-206409) and degradation methods [thermal, chemical and mechanical degradation methods, etc. Examples of the formation method (hereinafter sometimes referred to as thermal degradation method) include those described in JP-B No. 43-9368, JP-B No. 44-29742, and JP-B No. 6-70094].

  The polymerization method includes a method of (co) polymerizing one or more of the olefins, and a method of copolymerizing one or more of the olefins and one or more of the other monomers. It is.

  In the degradation method, a polyolefin (A0) having a high molecular weight [preferably Mn 30,000 to 400,000, more preferably 50,000 to 200,000] obtained by the polymerization method is thermally, chemically or mechanically used. The method of degrading is included.

Among the degradation methods, in the thermal degradation method, the polyolefin (A0) is continuously introduced for 0.5 to 10 hours at 300 to 450 ° C. in the absence of an organic peroxide under nitrogen aeration. Alternatively, a method of thermally degrading discontinuously, and (2) a method of thermally degrading at 180 to 300 ° C. for 0.5 to 10 hours in the presence of an organic peroxide are included.
Among these (1) and (2), from the viewpoint of the copolymerizability between (A) and (B) or (B) and (C) obtained, it is preferable that the molecular terminal and / or in the molecular chain. It is the method of (1) that it is easy to obtain those having a larger number of double bonds.

  Among these production methods of (A), those having a larger number of double bonds in the molecular end and / or molecular chain are easily obtained, and (A) and (B) or (B) and (C) From the viewpoint of easy copolymerization of these, a degradation method is preferred, and a thermal degradation method is more preferred.

[Unsaturated (poly) carboxylic acid (anhydride) (B)]
The unsaturated (poly) carboxylic acid (anhydride) (B) in the present invention is a C3-30 (poly) carboxylic acid (anhydride) having one polymerizable unsaturated group. In the present invention, the unsaturated (poly) carboxylic acid (anhydride) means an unsaturated monocarboxylic acid, an unsaturated polycarboxylic acid and / or an unsaturated polycarboxylic anhydride.
Among these (B), as unsaturated monocarboxylic acid, aliphatic (C3-24, for example, acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, isocrotonic acid), alicyclic ring-containing (C6-24, Unsaturated poly (2-3 or more) carboxylic acids (anhydrides) include unsaturated dicarboxylic acids (anhydrides) [aliphatic dicarboxylic acids (anhydrides) (C4-24, for example, Maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, and anhydrides thereof), alicyclic dicarboxylic acids (anhydrides) (C8-24, such as cyclohexene dicarboxylic acid, cycloheptene dicarboxylic acid, bicyclo) Heptene dicarboxylic acid, methyltetrahydrophthalic acid, and their anhydrides)], etc.], and unsaturated tricarboxylic acids (anhydrides) [fats Tricarboxylic acid (anhydride) (C5-24, such as aconitic acid, 3-butene-1,2,3-tricarboxylic acid, 4-pentene-1,2,4-tricarboxylic acid, and anhydrides thereof), alicyclic ring Containing tricarboxylic acids (anhydrides) (C9-24, such as 4-cyclohexene-1,2,3-tricarboxylic acid, 4-cycloheptene-1,2,3-tricarboxylic acid and anhydrides thereof) and the like. (B) may be used alone or in combination of two or more.
Of the above (B), from the viewpoint of copolymerization with (A) and the aliphatic unsaturated hydrocarbon (C) described later, unsaturated dicarboxylic acid (anhydride) is preferable, and aliphatic unsaturated is more preferable. Dicarboxylic acids (anhydrides), particularly preferred are aliphatic unsaturated dicarboxylic anhydrides, most preferred are maleic anhydride.

[Aliphatic unsaturated hydrocarbon (C)]
In the aliphatic unsaturated hydrocarbon (C) in the present invention, a C2-30 alkene, a C6 to 36 (more preferably C8 to 30) linear α-olefin and a branched chain constituting the (A) are included. In addition to the α-olefin, C4-30 other unsaturated monomers (butadiene and the like) having copolymerizability with olefin are included.
Examples of the linear α-olefin include 1-hexene, 1-octene, 1-nonene, 1-decene, and a mixture of two or more thereof.
Examples of the α-olefin having a branched chain include propylene trimer, propylene tetramer, and a mixture of two or more thereof.
Of the above (C), C6 to 36 (more preferably C8 to 30) are preferable from the viewpoint of copolymerization with (A) and (B) and adhesiveness of the binder for secondary battery electrode (N). These are α-olefins having a straight chain α-olefin and a branched chain.

[Radical initiator (D)]
In the copolymer (X) in the present invention, the (A), (B), or (A), (B), (C) is a radical generation source [radical initiator (D), heat, light, etc. ] In the presence or absence of].
Examples of the radical initiator (D) include azo compounds [azobisisobutyronitrile, azobisisovaleronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile)], peroxides [monofunctional ( (Having one peroxide group in the molecule) (benzoyl peroxide, di-t-butyl peroxide, lauroyl peroxide, dicumyl peroxide, etc.) and polyfunctional (having two or more peroxide groups in the molecule) [2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, di-t-butylperoxyhexahydroterephthalate, diallyl peroxydicarbonate, etc.]] and the like.
Of these, (A), (B), or (A), (B), (C) graft copolymerization viewpoint, that is, to be described later, (A) is a trunk, (B) or (B) From the viewpoint of the formability of the graft copolymer having (C) (co) polymer as a branch, a peroxide is preferable, a monofunctional peroxide is more preferable, and di-t-butyl is particularly preferable. Peroxide, lauroyl peroxide, dicumyl peroxide.

  The use amount of (D) is preferably based on the total weight of (A), (B) or the total weight of (A), (B), (C) from the viewpoint of reactivity and side reaction suppression. 0.05 to 10%, more preferably 0.2 to 5%, particularly preferably 0.5 to 3%.

[Copolymer (X)]
The copolymer (X) in the present invention comprises the polyolefin (A) and the unsaturated (poly) carboxylic acid (anhydride) (B) as structural units.
In addition, (X) is an aliphatic unsaturated hydrocarbon (C) in the above structural unit, from the viewpoint of increasing the copolymerization ratio of (B) and further improving the adhesiveness of the binder (N) for secondary battery electrodes. It is good also as a copolymer which adds (A), (B), and (C) as a structural unit.
In the production of (X), styrene or a styrene derivative (thing of C9-15, for example, methylstyrene, α-methylstyrene, p-methoxystyrene, m-butylstyrene, etc.) is contained as a structural unit of the copolymer. It is preferable not to do it from the viewpoint of the adhesiveness of (N).

  In addition, the content of each component based on the total weight of (A), (B), and (C) is as follows. (A) is a binder for a secondary battery electrode (N) that contains the copolymer (X). From the viewpoint of productivity and adhesiveness, preferably 20 to 85%, more preferably 30 to 80%; (B) is preferably 8 to 45%, more preferably from the viewpoint of the adhesiveness and swelling resistance of (N). 10 to 40%; (C) is usually 70% or less, preferably 5 to 65%, more preferably 10 to 50% from the viewpoint of the adhesiveness and swelling resistance of (N).

  The weight ratio [(A) / (B)] of (A) and (B) in (X) is preferably 30/70 from the viewpoint of the swelling resistance, adhesion, and electrochemical stability of (N). ~ 92/8, more preferably 35/65 to 80/20; (A) to (C) weight ratio [(A) / (C)] is (N) swelling resistance and adhesion, electrochemical From the viewpoint of mechanical stability, it is preferably 23/77 to 94/6, more preferably 30/70 to 85/15; the weight ratio of (A) to the sum of (B) and (C) [(A) / [(B) + (C)]] is preferably 20/80 to 85/15, more preferably 30/70 to 80/20, from the viewpoint of the swelling resistance, adhesion, and electrochemical stability of (N). The weight ratio of (B) to (C) [(B) / (C)] is determined from the viewpoint of the adhesiveness, electrochemical stability and swelling resistance of (N); Mashiku is more preferably 11 / 89-90 / 10, 15 / 85-80 / 20.

  Copolymer (X) is preferably polyolefin (A) and unsaturated (poly) carboxylic acid (anhydride) (B) or (A), (B) and in the presence of radical initiator (D). It can be produced by copolymerizing an aliphatic unsaturated hydrocarbon (C).

The specific production method (X) includes the following methods [1] and [2].
[1] (A), (B), or (A), (B), (C) is a suitable organic solvent [C3-18, such as hydrocarbon (hexane, heptane, octane, dodecane, benzene, toluene, xylene) Etc.), halogenated hydrocarbons (di-, tri-, and tetrachloroethane, dichlorobutane, etc.), ketones (acetone, methyl ethyl ketone, di-t-butyl ketone, etc.), ethers (ethyl-n-propyl ether, di-n-) Butyl ether, di-t-butyl ether, dioxane, etc.)], and if necessary, (D) [or a solution in which (D) is dissolved in an appropriate organic solvent (the same as above)], which will be described later. A chain transfer agent (t) and a polymerization inhibitor (f), and stirring with heating (solution method);
[2] (A), (B), or (A), (B), (C) and, if necessary, (D), (t), (f) are mixed in advance, an extruder, a Banbury mixer, a kneader A method of melting and kneading using a method (melting method).

  The reaction temperature in the solution method may be a temperature at which (A) is dissolved in an organic solvent, and (A), (B), or (A), (B), (C) copolymerizability and productivity. From this viewpoint, it is preferably 50 to 220 ° C, more preferably 110 to 210 ° C, and particularly preferably 120 to 180 ° C.

  Further, the reaction temperature in the melting method may be a temperature at which (A) melts, and (A), (B) or (A), (B), (C) copolymerizability and reaction product. From the viewpoint of the decomposition temperature, it is preferably 120 to 260 ° C, more preferably 130 to 240 ° C.

Examples of the chain transfer agent (t) include alcohols (C1-24, such as methanol, ethanol, 1-propanol, 2-butanol, allyl alcohol); thiols (C1-24, such as ethanethiol, propanethiol, n- and sec). -Butanethiol, 1-octanethiol); aldehydes (C2-18, eg 1- and 2-butyraldehyde, 1-pentylaldehyde); phenols (C6-36, eg phenol, o-, m- and p-cresol) Amines (C3-24, such as diethyl methylamine, triethylamine, diphenylamine); disulfides (C2-24, such as diethyl disulfide, di-1-propyl disulfide) and the like.
The amount of (t) used is usually 30% or less based on the total weight of (A) and (B) or the total weight of (A), (B) and (C), (A) and (B) Or from the viewpoint of copolymerization and productivity of (A), (B), and (C), preferably 0.1 to 20%.

Examples of the polymerization inhibitor (f) include catechol (C6-36, such as 2-methyl-2-propylcatechol), quinone (C6-24, such as p-benzoquinone), nitro compound (C3-24, such as nitrobenzene), Stabilized radicals [C5-36, such as 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2,6,6-tetramethyl-1-piperidinyl oxide (TEMPO)].
The amount of (f) used is usually 5% or less based on the total weight of (A) and (B) or the total weight of (A), (B) and (C), productivity, (A), From the viewpoint of the stability of (B) and (C) and the reactivity of (A), (B) and (C), it is preferably 0.01 to 0.5%.

  Mn of (X) is preferably 1,500 to 70,000, more preferably 2,000 to 60,000, particularly preferably 2,500 to 50,000 from the viewpoint of swelling resistance and adhesiveness of (N). 000.

The acid value of (X) is 50 to 250 mg KOH / g (hereinafter, only numerical values are shown), preferably 65 to 200, more preferably 80 to 180. When the acid value of (X) is less than 50, the adhesiveness of (N) is poor, and when it exceeds 250, the swelling resistance of (N) is poor.
The acid value here is a value obtained by measurement according to the following procedures (i) to (iii) according to JIS K0070.
(I) 1 g of (X) is dissolved in 100 g of xylene adjusted to 100 ° C.
(Ii) Titration with 0.1 mol / L potassium hydroxide ethanol solution [trade name “0.1 mol / L ethanolic potassium hydroxide solution”, manufactured by Wako Pure Chemical Industries, Ltd.] using phenolphthalein as an indicator at the same temperature. I do.
(Iii) The amount of potassium hydroxide required for titration is converted to mg, and the acid value (unit: mgKOH / g) is calculated.
In the above measurement, one acid anhydride group is equivalent to one carboxyl group. The acid value in the examples described later was in accordance with this method.

Examples of the method for bringing the acid value of (X) into the above range include the following methods.
(1) A method of suspending or dissolving (A) and (B) adjusted in the amount used in an appropriate organic solvent, and copolymerizing the structural units of (A) and (B) under the condition of heating and stirring.
(2) A method in which (C) is further added to the structural unit to (A) and (B) and copolymerized in the same manner as in (1).
The above (1) specifically includes (A) and (B) as a suitable organic solvent [C3-18, such as hydrocarbon (hexane, heptane, octane, decane, dodecane, benzene, toluene, xylene, etc.), Halogenated hydrocarbons (di-, tri- and tetrachloroethane, dichlorobutane, etc.), ketones (acetone, methyl ethyl ketone, diethyl ketone, di-t-butyl ketone, etc.), ethers (ethyl-n-propyl ether, di-i-propyl) Ether, di-n-butyl ether, di-t-butyl ether, dioxane, etc.)], and if necessary, dissolve (D) [or (D) in an appropriate organic solvent (same as above). The above-mentioned chain transfer agent (t) and polymerization inhibitor (f) are added and heated and stirred.
Of the above (1) and (2), (2) can be easily controlled for the copolymerization ratio of (B) by adding (C) to the structural unit, thereby adjusting the acid value of (X) to the above range. This is a preferable method because it is easy.

Moreover, the following are contained in the form of copolymer (X).
[1] A graft copolymer in which (A) is a trunk and (B) or a (co) polymer of (B) and (C) is a branch.
[2] A random and / or block copolymer of (A) and (B) or (A), (B) and (C).
In the form of [1], (A) and (B) or (A), (B) and (C) are preferably heated and melted in the presence of (D) (more preferably a peroxide), or It can be formed by suspending or dissolving in an organic solvent, adding the chain transfer agent (t) and the polymerization inhibitor (f) if necessary, and stirring with heating.
The form of the above [2] is preferably (A) and (B), or (A), (B) and (C) are heated and melted in the presence of (D) (more preferably an azo compound), or appropriate It can be formed by suspending or dissolving in an organic solvent, and further adding a chain transfer agent (t) and a polymerization inhibitor (f), which will be described later, if necessary, followed by heating and stirring.
Of the forms [1] and [2], the form [1] is preferable from the viewpoint of the adhesiveness (N).

[Binder for secondary battery electrode (N)]
The binder (N) for secondary battery electrodes of the present invention is a co-polymer having an acid value of 50 to 250 mgKOH / g, comprising the polyolefin (A) and the unsaturated (poly) carboxylic acid (anhydride) (B) as structural units. It contains polymer (X).

Examples of the method for producing the secondary battery binder (N) of the present invention include the following methods (1) to (3).
(1) A method in which (X) and, if necessary, a basic compound (G) are added and emulsified and dispersed under conditions of high temperature (preferably 100 to 200 ° C.), and preferably 5 to 60% by weight of an aqueous dispersion. .
(2) A method in which (X) and an organic solvent are mixed and stirred to obtain a 5 to 60% by weight organic solvent dispersion or organic solvent solution.
(3) A method in which (X) is pulverized by a pulverizer (for example, a feather mill or the like) to form fine particles having a volume average particle diameter of 0.01 to 5 μm and a 5 to 60 wt% aqueous dispersion or organic solvent dispersion .
Of the above methods (1) to (3), the method (1) and (2) are more preferable, and the method (1) is more preferable from the viewpoint of the adhesiveness (N) and the industrial viewpoint. .

(G) in the method (1) includes inorganic compounds [alkali metal hydroxides (sodium hydroxide, potassium hydroxide, etc.)]; organic compounds [ammonia, amines [C3-15, such as aliphatic amines ( Mono-, di- and triethylamine, mono- and dipropylamine, isopropylamine, n-, sec- and isobutylamine, 2-methoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine, 2,2-dimethoxyethylamine , 3-diethylaminopropylamine, etc.), heterocyclic-containing amines (morpholine, N-methylmorpholine, N-ethylmorpholine, pyrrole, pyridine, etc.), alkanolamines (monoethanolamine, N, N-dimethylethanolamine, diethylaminoethanol, etc.) ) That.
Among these (G), from the viewpoint of the electrochemical stability of (N), preferred are organic compounds, and more preferred are ammonia, ethylamine, and propylamine.

Examples of the organic solvent in the method (2) include hydrocarbons [aliphatic hydrocarbons (C5-15, for example, hexane, heptane, octane), alicyclic hydrocarbons (C5-15, for example, cyclohexane, methylcyclohexane). , Ethylcyclohexane, cycloheptane, methylcycloheptane), aromatic ring-containing hydrocarbon (C6-15, such as toluene, xylene, ethylbenzene), etc.]; carboxylic acid ester (C4-15, such as ethyl acetate, -propyl) And -butyl, ethyl-propionate, -propyl and -butyl, ethyl butyrate, -propyl and -butyl); ether esters [C6-15, such as alkylene glycol alkyl ether acetates (ethylene glycol monoethyl ether acetate, ethylene glycol) mono Chill ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate); ketone (C3-12, eg acetone, methylethylketone, methylisobutylketone, cyclohexanone); ether [C4-16, eg n -Butyl ether, isobutyl ether, tetrahydrofuran, diethyl ether, ethylene glycol dialkyl (C1-6) ether, dioxane] and the like.
Of these, hydrocarbons are preferable from the viewpoint of swelling resistance, aliphatic hydrocarbons, aromatic ring-containing hydrocarbons and alicyclic ring-containing hydrocarbons are more preferable, and aliphatic hydrocarbons are particularly preferable.

[Secondary battery electrode]
The secondary battery electrode of the present invention comprises the binder (N), an active material (a positive electrode active material for the positive electrode, a negative electrode active material for the negative electrode), and a metal current collector. If necessary, a conductive additive (carbon material such as carbon black, amorphous whisker carbon, graphite) may be added to the electrode.

Examples of positive electrode active materials for lithium ion batteries include transition metal oxides (MnO ₂ , V ₂ O _5, etc.), transition metal sulfides (MoS ₂ , TiS _2, etc.), and complex oxides (LiCoO) composed of lithium and transition metals. ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi ^X Co _(1-X) O ₂ ), conductive polymer materials (polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole / polyaniline complex, etc. ).

  In addition, as the negative electrode active material for lithium ion batteries, lithium ions can be doped and dedoped, for example, metallic lithium, lithium alloy, tin oxide, niobium oxide, vanadium oxide, titanium oxide, silicon, transition metal nitriding Carbon materials (graphite, etc.). These may be used as a composite (metal lithium-niobium oxide composite or the like).

Examples of the positive electrode active material for a nickel-hydrogen secondary battery include nickel hydroxide, a composite of nickel hydroxide, cobalt, and zinc.
Examples of the active material for the negative electrode of the nickel metal hydride secondary battery include hydrogen storage alloys made of manganese, nickel, cobalt, aluminum, misch metal, and the like.

  The positive and negative metal current collectors may be any material having conductivity, and examples thereof include aluminum, nickel, and copper. The thickness of the current collector is usually 5 to 50 μm. Examples of the shape of the current collector include a foil, a film, a sheet, a net, a punched material, a porous body, a foam, a fiber group, and a molded body of a nonwoven fabric.

The production of the secondary battery electrode is specifically as follows.
That is, the binder paste is prepared by mixing the binder (N) and the positive electrode active material or the negative electrode active material, if necessary, a conductive additive and a thickener (carboxymethyl cellulose, etc.) in any order at room temperature or a controlled temperature. create. Next, the binder paste is applied on a metal current collector and dried to form a secondary battery electrode.
The weight ratio of the copolymer (X) and the positive electrode active material or (X) and the negative electrode active material in the binder paste is preferably from the viewpoint of the adhesiveness of the binder (N) and the electric capacity of the secondary battery. It is 99-20 / 80, More preferably, it is 5 / 95-10 / 90.

Examples of the method for applying the paste on the metal current collector include a method using a film applicator and a doctor blade.
Further, as a method for removing water and / or organic solvent after coating on the metal current collector, for example, drying at 60 to 150 ° C., preferably 70 to 130 ° C. for 5 to 120 minutes, and further reducing the pressure at 120 ° C. for 12 hours. The method of drying is mentioned. The thickness of the coating film on the electrode after application and drying is preferably 10 to 500 μm from the viewpoint of the electric capacity and internal resistance of the secondary battery described later. The thickness and density of the coating film on the electrode can be controlled by compression molding at a predetermined pressure using, for example, a roll press.

[Secondary battery]
The secondary battery of the present invention is produced by enclosing the electrode (positive electrode and negative electrode), separator and electrolyte of the present invention in a container. Examples of the separator include a porous film and a nonwoven fabric. Examples of the porous film include polyolefin, polyimide, polyvinylidene fluoride, polyester, and the like. Examples of the nonwoven fabric include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and glass fiber. Examples of the shape of the secondary battery include a cylindrical shape, a coin shape, a square shape, and a film shape.

Examples of the non-aqueous electrolyte used for the lithium ion secondary battery in the secondary battery include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ N / Li, and the like. Examples thereof include those obtained by dissolving the electrolyte alone or in combination of two or more thereof in an organic solvent (diethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyrolactone, etc.). Examples of the electrolytic solution used for the nickel metal hydride secondary battery include an aqueous solution obtained by combining electrolytes such as potassium hydroxide and sodium hydroxide alone or in combination.

The binder for secondary electrodes of this invention is excellent in the swelling resistance with respect to electrolyte solution, and is excellent in the adhesiveness of each active material of positive and negative electrodes, and each electrode metal electrical power collector. The swelling resistance can be evaluated by an electrolyte solution swelling test described later, and the adhesiveness can be evaluated by a peel test described later.
Moreover, the secondary battery which has the electrode formed using the binder of this invention is electrochemically stable, and is excellent in the battery capacity maintenance rate after 100 cycles of below-mentioned charging / discharging. The battery capacity maintenance rate is preferably 85% or more, and more preferably 90% or more.

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. The part in an Example represents a weight part. In the following, Example 19 is referred to as Reference Example 1.

[Polyolefin (A)]
Production Example 1
Polyolefin (A0-1) having a structural unit of 98 mol% propylene and 2 mol% ethylene in a reaction vessel [trade name “Sun Allomer PZA20A”, manufactured by Sun Allomer Co., Ltd., Mn 100,000, molecules per 1,000 carbons The number of double bonds in the terminal and / or molecular chain is 0, and so on. 100 parts were charged in a nitrogen atmosphere, heated and melted with a mantle heater while nitrogen was passed through the gas phase portion, and subjected to heat degradation at 360 ° C. for 70 minutes while stirring to obtain polyolefin (A-1). . In (A-1), the number of double bonds in molecular ends and / or molecular chains per 1,000 carbon atoms was 7.2, and Mn was 3,000.

Production Examples 2-7
Except having performed thermal degradation according to Table 1 in the manufacture example 1, it carried out similarly to the manufacture example 1 and obtained polyolefin (A-2)-(A-7). The results are shown in Table 1.

[Binder for secondary battery electrode]
Example 1
A reaction vessel was charged with 100 parts of (A-1), 24 parts of maleic anhydride (B-1), 18.5 parts of 1-decene (C-1) and 100 parts of xylene. The mixture was heated to 130 ° C. and dissolved uniformly. A solution prepared by dissolving 0.5 part of dicumyl peroxide [trade name “Park Mill D”, manufactured by NOF Corporation] (D-1) in 10 parts of xylene was added dropwise over 10 minutes, and then refluxed with xylene. Stirring was continued for 3 hours. Thereafter, xylene and unreacted maleic anhydride were distilled off under reduced pressure (1.5 kPa, the same shall apply hereinafter) to obtain a copolymer (X-1). (X-1) had an acid value of 95 and Mn of 5,000.
Further, 100 parts of (X-1) and 400 parts of water were charged into a mixing container, and stirred at 150 ° C. for 1 hour to disperse. Then, it cooled to normal temperature and obtained 500 parts of binders (N-1) which is a 20 weight% aqueous dispersion of (X-1). The results are shown in Table 2.

Examples 2-20, Comparative Examples 1-8
In Example 1, it carried out similarly to Example 1 except having used the raw material according to Table 2, 3, and binder (N-2)-(N-20), (RN-1)-(RN-8). ) The results are shown in Tables 2 and 3.

Example 21
In Example 1, in place of 100 parts of (A-1) and 400 parts of water, except that 100 parts of (A-7) and 400 parts of toluene were used, copolymer (X -21) 20 parts by weight of an organic solvent solution was obtained 500 parts of binder (N-21). The results are shown in Table 3.

[Secondary battery electrode and secondary battery]
Example 22
<Creation of positive electrode>
Binder (N-1) 7.5 parts, positive electrode active material lithium cobalt oxide [trade name "Cellseed C", manufactured by Nippon Chemical Industry Co., Ltd.] 100 parts, acetylene black ["DENKA BLACK" Made by Denki Kagaku Kogyo Co., Ltd. same as below. ] 4 parts, 25 parts by weight of 2% by weight aqueous solution of carboxymethyl cellulose [trade name “Serogen SBH-6”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.] as a thickener, and kneaded thoroughly in a mortar to give secondary A binder paste for battery positive electrode was prepared.
The paste was applied on one side of a copper foil of length 400 mm × width 150 mm × thickness 18 μm using a film applicator so that the thickness after drying was about 50 μm, dried at 80 ° C. for 30 minutes, In order to remove moisture and / or organic solvent, vacuum drying was performed at 120 ° C. for 12 hours to prepare a secondary battery positive electrode in which an active material layer was formed on a copper foil. The electrode was evaluated according to a peel test described later. The results are shown in Table 4.
<Creation of negative electrode>
7.5 parts of binder (N-1), graphite powder as a negative electrode active material [trade name “CGC-20”, manufactured by Nippon Graphite Industry Co., Ltd.] 94 parts, 4 parts of acetylene black as a conductive additive, as a thickener 25 parts by weight of a 2% by weight aqueous solution of carboxymethylcellulose (CMC) [trade name “Serogen BSH-6”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.] was blended, and then a binder paste for secondary battery negative electrode in the same manner as the positive electrode. Was prepared to prepare a secondary battery negative electrode. The electrode was evaluated according to a peel test described later. The results are shown in Table 4.
<Creation of secondary battery>
The obtained positive electrode and negative electrode are wound with a polyethylene microporous film [trade name “Hypore”, manufactured by Asahi Kasei Co., Ltd., film thickness 20 μm] as a separator, wound, cut into a predetermined length, and an electrode. Groups were created. Next, the electrode group was inserted into a Ni-plated Fe battery case, and 3 parts by weight of vinylene carbonate was added to 100 parts of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate mixed solvent (volume ratio 3: 3: 2). In addition, an electrolytic solution in which lithium hexafluorophosphate was dissolved to a concentration of 1 mol / L was added and sealed, and cylindrical lithium ions having a battery capacity of 2,000 mAh, a diameter of 18 mm, and a length of 65 mm A secondary battery was prepared. The obtained secondary battery was evaluated according to the battery capacity maintenance rate after 100 cycles of charge and discharge described later. The results are shown in Table 4.

Examples 23-42, Comparative Examples 9-16
About the obtained binders (N-2) to (N-21) and binders (RN-1) to (RN-8), a positive electrode, a negative electrode, and a secondary battery were prepared and evaluated in the same manner as in Example 22. did. The results are shown in Tables 4 and 5.

<Evaluation method>
[1] Electrolytic solution swelling test (evaluation of swelling resistance)
The copolymer (X) is cut into a 1 cm square cube (weight: W0), and 3 parts by weight of vinylene carbonate in 100 parts by weight of a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (volume ratio 3: 3: 2). And then immersed in an electrolytic solution in which lithium hexafluorophosphate is dissolved to a concentration of 1 mol / L at 50 ° C. for 24 hours. Thereafter, the electrolytic solution adhering to the surface of the resin is wiped off, and the electrolytic solution is immersed The weight (W1) of the later (X) was measured, the increase was calculated from the following formula, and evaluated as the electrolyte expansion coefficient (%) according to the following criteria.

Electrolytic solution expansion rate (%) = [(W1) − (W0)] × 100 / (W0)

However, W0: Weight of (X) before immersion in electrolyte
W1: Weight of (X) after immersion in electrolyte

Evaluation criteria A: The electrolyte expansion coefficient is less than 10%.
○: The expansion ratio of the electrolytic solution is 10% or more and less than 15%.
Δ: The electrolyte expansion coefficient is 15% or more and less than 25%.
X: The electrolyte expansion coefficient is 25% or more.

[2] Peel test (adhesion evaluation)
The obtained secondary battery positive electrode and negative electrode were each cut into a length of 20 mm x a width of 20 mm, and cut with a cutter knife every 1 mm to create a grid of 100 squares. When the cellophane tape was affixed on the grid and the tape was peeled off all at once, the evaluation was made with a grid having no peeling in 100 squares.

[3] Battery capacity retention rate after 100 cycles of charge / discharge (Evaluation of cycle characteristics)
The prepared lithium ion secondary battery was charged and discharged 100 times under the following conditions. Note that the discharge capacity at the first cycle was the initial discharge capacity, and the current value at the time of this discharge was 1C. Then, the percentage of the discharge capacity after 100 cycles with respect to the initial discharge capacity was determined as the battery capacity maintenance rate (%).
Charging / discharging conditions Constant current charging: 0.3C, final voltage 4.15V
Constant voltage charge: 4.15V, 0.05C, pause time 20 minutes Constant current discharge: 1.0C, final voltage 2.0V, pause time 20 minutes

  From the results of Tables 4 and 5, the secondary battery electrode binder of the present invention is superior in swelling resistance to the electrolytic solution as compared with the comparative one, and adheres to each active material of the positive and negative electrodes and each electrode metal current collector. It can be seen that a secondary battery having an excellent property and an electrode formed using the binder is excellent in cycle characteristics.

  The binder for secondary battery electrodes of the present invention is excellent in swelling resistance to an electrolytic solution and adhesion between each active material of positive and negative electrodes and each electrode metal current collector, and an electrode formed using the binder. Since the secondary battery is excellent in cycle characteristics, it can be suitably used as a binder for a wide variety of secondary battery (nickel metal hydride secondary battery, lithium ion secondary battery, etc.) electrodes and is extremely useful. It is.

Claims (10)

Selected from the group consisting of polyolefin (A) having 0.1 to 20 double bonds per 1,000 carbon atoms , and unsaturated monocarboxylic acid, unsaturated polycarboxylic acid and unsaturated polycarboxylic acid anhydride Binder for secondary battery electrode comprising copolymer (X) having at least one unsaturated (poly) carboxylic acid (anhydride) (B) as a structural unit and having an acid value of 50 to 250 mgKOH / g (N).   The binder according to claim 1, wherein (B) is an unsaturated dicarboxylic acid (anhydride).   Furthermore, the binder of Claim 1 or 2 formed by adding an aliphatic unsaturated hydrocarbon (C) to a structural unit.   The binder according to any one of claims 1 to 3, wherein (X) is a graft copolymer in which (A) is a trunk and (B) or a (co) polymer of (B) and (C) is a branch.   The binder according to any one of claims 1 to 4, wherein (A) and (B) or (A), (B) and (C) are copolymerized in the presence of the radical initiator (D). The binder according to any one of claims 1 to 5 , wherein a weight ratio of (A) to (B) is 30/70 to 92/8. The binder according to any one of claims 1 to 6, which is an aqueous dispersion. The secondary battery electrode comprised from an active material, a metal electrical power collector, and the binder in any one of Claims 1-7 . A secondary battery comprising an electrolyte, a separator, and the electrode according to claim 8 . The secondary battery according to claim 9 , wherein the battery capacity retention rate after 100 cycles of charge / discharge is 85% or more.