JP6189730B2 - Positive electrode for secondary battery and non-aqueous secondary battery including the same - Google Patents

Description

  The present invention relates to a positive electrode for a secondary battery and a non-aqueous secondary battery including the same, preferably used for a non-aqueous secondary battery typified by a lithium secondary battery.

A lithium ion secondary battery (hereinafter simply referred to as a lithium secondary battery) as a non-aqueous secondary battery has characteristics of high voltage and high capacity, and is relatively easy to reduce in size and weight. Used as a power source for electronic devices. In recent years, in addition to vehicles such as electric bicycles, electric cars, and airplanes, they are used for backup power sources for mobile phone base stations, hospitals, etc., and their use is being studied. In a typical lithium secondary battery, a carbonaceous material that can occlude and release lithium is used as an active material for a negative electrode, and a composite oxide of a transition metal such as LiCoO ₂ and lithium is used as an active material for a positive electrode. ing. With this combination, high voltage and high capacity are realized. With the expansion of battery applications, power consumption increases and the temperature range used is wide. Therefore, it is desired to improve the characteristic deterioration accompanying the charge / discharge cycle under various use conditions and extend the life of the battery also in the lithium secondary battery.

  The deterioration of characteristics associated with the charge / discharge cycle of a non-aqueous secondary battery is caused by repeated swelling and shrinkage of the electrode during charge / discharge, which decreases the adhesive force between the current collector and the positive electrode active material layer or under high voltage. It is considered that the binder is oxidized and deteriorated, and the binding power of the binder is reduced. Therefore, in order to suppress the deterioration accompanying the charge / discharge cycle, it is necessary to increase the binding force between the current collector and the positive electrode active material layer. Moreover, it is necessary to select a material having high oxidation resistance as the binder.

  In order to increase the binding force between the current collector and the positive electrode active material layer, the surface area of the current collector is increased. For example, the surface of the current collector is generally roughened by etching the surface of the current collector or by depositing a constituent metal on the surface by electrodeposition (Patent Documents 1, 2 and 3). In addition, a method of forming minute irregularities by causing fine particles to collide with the surface of the rolled copper foil at a high speed has been proposed (see Patent Document 4). Furthermore, a method for forming irregularities by irradiating a metal foil with laser light has also been proposed (see Patent Document 5). In addition, it has also been proposed to provide unevenness on the surface by using a guide roller having unevenness on the surface (see Patent Document 6).

  On the other hand, as another method for increasing the binding force between the current collector and the positive electrode active material layer, there is a measure of increasing the adhesive strength of the binder to be used. As the positive electrode binder, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) is generally used. Since these materials are excellent in oxidation resistance, they are generally used as positive electrode binders. However, it is inferior in adhesive strength with an active material or a current collector. Therefore, in order to increase the adhesive strength, it is necessary to increase the addition amount. As a result, there is a problem that the ratio of covering the active material is increased and the battery characteristics are deteriorated.

  Moreover, a styrene-butadiene rubber (SBR) is mentioned as a binder for negative electrodes. Since SBR has high adhesive strength, the amount added can be reduced. However, there is a drawback that the oxidation resistance is low. As a measure for supplementing the oxidation resistance, hydrogen may be added to the double bond of SBR to improve the oxidation resistance, but there is a problem that the manufacturing cost increases. Furthermore, since PDVF and SBR have a high affinity with the electrolytic solution, there is a problem that if the battery is left at a high temperature or if charging and discharging are repeated, the resin swells and the battery tends to swell.

JP 2005-38797 A JP 7-272726 A JP 2008-060124 A JP 2002-79466 A JP 2003-258182 A JP-A-8-195202

  The present invention has been made in view of the above problems. A positive electrode for a secondary battery having a sufficiently low electrical resistance, a remarkably high adhesion strength between the positive electrode current collector and the positive electrode active material, excellent oxidation resistance, and remarkably high cycle characteristics when repeatedly used, and It aims at providing the non-aqueous secondary battery containing the positive electrode for secondary batteries.

That is, the first of the present invention is the following positive electrode for a secondary battery.
[1] A positive electrode for a secondary battery having a positive electrode active material-containing layer on the surface of a positive electrode current collector made of an aluminum alloy foil, wherein the positive electrode current collector is formed on the surface by dipping in an aqueous solution of a water-soluble amine compound. The positive electrode current collector (X) having irregularities, wherein the positive electrode active material-containing layer comprises a water-dispersible binder (A) containing the olefin copolymer (a), an active material (B), and a conductive assistant. A positive electrode for a secondary battery, comprising an agent (C).
[2] The secondary battery according to [1], wherein the water-soluble amine compound is one or more compounds selected from the group consisting of hydrazine, ammonia, and a water-soluble amine compound. Positive electrode.
[3] The olefin copolymer (a) has a weight average molecular weight of 50,000 or more (in terms of polystyrene) determined by gel permeation chromatography (GPC), and contains a structural unit derived from propylene. A random propylene copolymer (a-1) having a rate of 50% by weight or more and less than 85% by weight, an acid-modified random propylene copolymer (a) obtained by acid-modifying the random propylene copolymer (a-1) (a -2), and the content of the structural unit derived from (meth) acrylic acid is selected from the group consisting of an ethylene- (meth) acrylic acid copolymer (a-3) having a content of 5 wt% or more and 25 wt% or less. The positive electrode for a secondary battery according to [1] or [2], wherein the positive electrode is one or more compounds.
[4] The water-dispersible binder (A) is an acid-modified olefin (co) polymer (a) having a weight average molecular weight of less than 50,000 (polystyrene conversion) determined by gel permeation chromatography (GPC). -4) is further included, The positive electrode for secondary batteries in any one of [1]-[3] characterized by the above-mentioned.

The second of the present invention is the following non-aqueous secondary battery.
[5] A non-aqueous secondary battery comprising the positive electrode for a secondary battery according to any one of [1] to [4].

  The positive electrode for a secondary battery of the present invention has a sufficiently low electric resistance and a high adhesive strength between the positive electrode current collector and the positive electrode active material. Therefore, according to the positive electrode for secondary batteries, a secondary battery having high charge / discharge efficiency and a high capacity retention rate even when used repeatedly can be obtained.

A. Secondary Battery Positive Electrode The secondary battery positive electrode of the present invention has a structure in which a positive electrode active material-containing layer is formed on the surface of a positive electrode current collector made of an aluminum alloy foil.

(1) Positive electrode current collector The positive electrode current collector (X) in the positive electrode for a secondary battery of the present invention is made of an aluminum alloy foil treated with an aqueous solution of a water-soluble amine compound, and on the surface of the aluminum alloy foil. Unevenness is formed. When the aluminum alloy foil is dipped in an aqueous solution of a water-soluble amine compound, appropriate irregularities are generated on the current collector surface layer, and the adhesive strength between the positive electrode current collector and the positive electrode active material-containing layer is increased. Further, the presence of an amine compound on the surface of the positive electrode current collector further increases the adhesive strength with the water-dispersible binder (A) containing the olefin copolymer (a) contained in the positive electrode active material-containing layer. Rise.

  Examples of the amine compound include ammonia, hydrazine, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, ethanolamine, allylamine, ethanolamine, diethanolamine, triethanolamine, aniline, and other amines.

  Among these, hydrazine is particularly preferable from the viewpoints of low odor, effectiveness at low concentrations, and low cost. The immersion of the positive electrode current collector is preferably performed at 40 to 80 ° C, particularly preferably 50 to 70 ° C. The concentration of the aqueous solution of the water-soluble amine compound is appropriately selected according to the type of the water-soluble amine compound. When the amine compound is hydrazine, the monohydric hydrazine is preferably 2 to 10% by weight, more preferably 3 to 5% by weight. The immersion time of the positive electrode current collector is preferably 30 to 90 seconds. After immersion, it is washed with water and dried with hot air at 40 to 90 ° C.

  Moreover, it is preferable that the positive electrode current collector of the present invention is pretreated with an acidic, basic, or both aqueous solution before the treatment with the water-soluble amine compound. By the pretreatment, the oxide film present on the surface layer of the aluminum alloy foil is efficiently removed, and the charge / discharge efficiency of the secondary battery is improved.

  The basic liquid for pretreatment is preferably an aqueous alkali metal hydroxide solution of 0.5 to 3% by weight. In particular, it is preferable to use an aqueous caustic soda solution at 35 to 40 ° C. The acidic liquid for pretreatment is preferably 0.5 to 5% by weight of hydrohalic acid, hydrofluoric acid derivative or nitric acid. In particular, it is preferable to use hydrochloric acid, nitric acid, or an aqueous solution of ammonium difluoride with temperature controlled at 35 to 40 ° C.

  When the thickness of the positive electrode current collector is 5 mm or more, it is difficult for the electrolyte to penetrate into the positive electrode, and it becomes difficult to maintain the performance of the secondary battery. On the other hand, when the thickness of the positive electrode is smaller than 0.1 mm, the number of stacked electrodes per unit cell becomes several hundreds, and the unit cell manufacturing operation becomes complicated. For this reason, the thickness of the positive electrode current collector depends on the density of the active material, the type of water-dispersible binder to be mixed, the active material, the conductive assistant, the thickener, the press pressure of the electrode, and the like. It is preferably 0.1 mm or more and less than 5 mm.

(2) Positive electrode active material-containing layer The positive electrode active material-containing layer contains a water-dispersible binder (A) containing the olefin copolymer (a), an active material (B), and a conductive additive (C). . The positive electrode active material-containing layer is prepared by applying a paste obtained by mixing an aqueous dispersion of a water-dispersible binder (A), an active material (B), and a conductive additive (C) on the surface of the positive electrode current collector. Obtained by coating.

(2-1) Water dispersible binder (A)
The water-dispersible binder (A) includes the olefin copolymer (a), and includes a surfactant (x) and a viscosity modifier (y) as necessary. The aqueous dispersion of the water-dispersible binder (A) is obtained by dispersing the olefin copolymer (a) or the like in water.

  The method for dispersing the olefin copolymer (a) in water is not particularly limited, but in order to minimize the amount of emulsification aid and emulsifier, it is a method of adding a small amount of alkaline water to the melt-kneaded resin. Is preferred (Japanese Patent Publication No. 7-008933). In addition, neutralization with an alkali is required for emulsification and dispersion, but the alkali species for that purpose are not particularly limited, and examples thereof include alkali metals such as ammonia, organic amines, potassium hydroxide, sodium hydroxide, and lithium hydroxide. It is done.

  Total amount of water-dispersible binder (A) (solid content of olefin copolymer (a) and surfactant (x) and solid content of viscosity modifier (y)) contained in the positive electrode active material-containing layer Is preferably 0.5 to 30 parts by weight, more preferably 1 to 20 parts by weight with respect to 100 parts by weight of the active material (B). If it is this range, the adhesiveness of a positive electrode electrical power collector and a positive electrode active material content layer will increase easily. Further, if the amount of the water-dispersible binder (A) is less than 0.5 parts by weight, the positive electrode active material-containing layer may peel off from the positive electrode current collector, and if it exceeds 30 parts by weight, the electrical resistance May rise.

(Olefin copolymer (a))
When the olefin copolymer (a) according to the present invention is contained in the water-dispersible binder (A), the adhesion between the positive electrode current collector and the positive electrode active material-containing layer increases, and the battery cycle performance increases. . The olefin copolymer (a) is contained in the water-dispersible binder (A) in an amount of 5 to 80% by weight, preferably 10 to 70% by weight in terms of solid content. Within this range, good electrode plate adhesion can be obtained.

  The olefin copolymer (a) is preferably particulate. Although the volume average particle diameter of an olefin copolymer (a) is not specifically limited, It is preferable that it is 10-1,000 nm, More preferably, it is 10-800 nm, More preferably, it is 10-500 nm. The volume average particle diameter is measured by Microtrac HRA: Honneywell. If the particle diameter of the olefin copolymer (a) is in the above range, it is preferable because of excellent water dispersion stability. Moreover, if it is less than 10 nm, there exists a possibility that adhesiveness with a positive electrode electrical power collector may fall, and when it exceeds 1,000 nm, there exists a possibility that the dispersion stability in an aqueous dispersion may be impaired. The method for controlling the particle size is not particularly limited, and can be appropriately adjusted depending on, for example, the melting temperature during production, the amount of resin neutralization, the amount of emulsification aid, and the like.

  The olefin copolymer (a) has a melting point [Tm] measured by a differential scanning calorimeter (DSC) of 120 ° C. or lower, preferably not recognized, and is 110 ° C. or lower. More preferably not. If the melting point is 120 ° C. or lower or the melting point is not recognized, the flexibility of the positive electrode is increased. On the other hand, if the melting point exceeds 120 ° C., the flexibility of the positive electrode is insufficient and the workability may be impaired. Furthermore, the olefin copolymer (a) may or may not have crystallinity, but from the viewpoint of cycle characteristics of the secondary battery and adhesion to various base materials, crystallization by X-ray diffraction method. The degree is preferably 30% or less.

  The olefin copolymer (a) includes at least one selected from the following copolymer (a-1), copolymer (a-2), and copolymer (a-3). Moreover, (co) polymer (a-4) and / or copolymer (a-5) may be contained as needed.

(Random propylene copolymer (a-1))
The random propylene-based copolymer (a-1) is mainly composed of structural units derived from propylene, and in addition, ethylene, 1-butene, 4-methylpentene-1,1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-nonadecene, 1-eicosene, 9-methyldecene-1, It is a copolymer of α-olefins such as 11-methyldodecene-1 and 12-ethyltetradecene-1. Only one kind of these copolymers may be used, or a plurality of kinds may be used in combination.

  Among these, a random propylene-butene copolymer, a random ethylene-propylene-butene copolymer, and a random ethylene-propylene copolymer are preferable from the viewpoint that the flexibility of the positive electrode is increased.

  The weight average molecular weight calculated | required by the gel permeation chromatography (GPC) of a copolymer (a-1) is 50,000 or more in polystyrene conversion, and an upper limit is although it does not specifically limit, Preferably it is 50,000-500,000. Preferably, it is 50,000 to 300,000 from the viewpoint of controlling the dispersed particle size when the aqueous dispersion is formed. When it is less than 50,000, when the copolymer (a-1) binds the active material, the strength as the binder is insufficient, and the positive electrode active material-containing layer is easily peeled off from the positive electrode current collector. .

  From the viewpoint of the impact resistance, flexibility, and adhesion strength of the electrode, particularly the cycle characteristics of the electrode, the content of the structural unit derived from propylene is 50% by weight with respect to 100% by weight of the copolymer (a-1). It is preferable that it is less than 85 weight%, More preferably, it is 50-80 weight%, More preferably, it is 55-80 weight%.

(Acid-modified random propylene copolymer (a-2))
The acid-modified random propylene copolymer (a-2) is a copolymer obtained by modifying the random propylene copolymer (a-1) with an acid. It is preferable to use an acid-modified copolymer for adhesion to the positive electrode current collector.

  The weight average molecular weight of the copolymer (a-2) is the same as that of the copolymer (a-1). The type of acid that modifies the copolymer (a-1) is not particularly limited as long as it is a compound that can modify the random propylene copolymer (a-1), and examples thereof include carboxylic acid and sulfonic acid. Among these, carboxylic acid is preferable from the viewpoint of adhesion to the positive electrode current collector. Further, maleic acid having an unsaturated bond, benzoic acid and derivatives thereof may be mentioned, and maleated modified random polypropylene modified with maleic acid is particularly preferable from the viewpoint of the number of acid functional groups. More preferable are a maleated modified random propylene-butene copolymer, a maleated modified random ethylene-propylene-butene copolymer and a maleated modified random ethylene-propylene copolymer from the viewpoint of electrode plate flexibility.

  If the degree of acid modification (degree of modification) is high, it will cause thickening of the emulsion and increase in resin swellability with respect to the electrolyte. Therefore, the degree of modification is usually in the range of 0.1 to 5.0% by weight in terms of acid. For example, in the case of modification with maleic acid, the degree of modification is preferably 0.5 to 4.0% by weight in terms of maleic anhydride (maleinization modification degree 0.5 to 4.0), more preferably 0.5. 5 to 2.0% by weight (degree of maleic modification 0.5 to 2.0).

  The modification method with maleic acid is not particularly limited. For example, the random propylene copolymer (a-1) is dissolved or dispersed in a hydrocarbon solvent at a high temperature, and maleic anhydride and an organic peroxide are added to make anhydrous. Male peroxide and maleic anhydride are continuously added and extruded while continuously mixing and kneading the random propylene copolymer (a-1) with a twin screw extruder. There is a method of reacting in-flight.

(Ethylene- (meth) acrylic acid copolymer (a-3))
In the ethylene- (meth) acrylic acid copolymer (a-3), the content of structural units derived from (meth) acrylic acid is 5% by weight or more and 25% by weight or less, preferably 6 to 20% by weight, more preferably. Is 10 to 20% by weight in terms of electrode plate adhesion. When the content of the structural unit is less than 5% by weight, the stability of the aqueous dispersion is lowered and the adhesion as a binder is lowered. On the other hand, if it exceeds 25% by weight, it becomes a water-soluble polymer, not an aqueous dispersion, and the binding property in the low addition region is lowered.

  It is preferable that the weight average molecular weight of a copolymer (a-3) is the same range as a copolymer (a-1). The (meth) acrylic acid is preferably neutralized with an alkali. The alkali species is not particularly limited, and examples thereof include alkali metals such as ammonia, organic amines, potassium hydroxide, sodium hydroxide, and lithium hydroxide. In particular, ammonia, sodium hydroxide, and lithium hydroxide are suitable for forming an aqueous dispersion.

  The neutralization rate of the carboxylic acid possessed by the (meth) acrylic acid is not particularly limited, but is preferably 25 mol% or more and 85 mol% or less. If the amount is less than 25 mol%, the stability of the aqueous dispersion may decrease, and if it exceeds 85 mol%, the unneutralized carboxylic acid may be insufficient, and the adhesion as a binder may decrease. Preferably, they are 30 mol% or more and 80 mol% or less, More preferably, they are 35 mol% or more and 75 mol% or less.

  The copolymer (a-3) in the olefin copolymer (a) may be 100% by weight with respect to the olefin copolymer (a). Moreover, when mixing a copolymer (a-1) and a copolymer (a-2), with respect to a total of 100 weight part of a copolymer (a-1) and a copolymer (a-2). The amount is preferably 0 to 200 parts by weight, more preferably 0.5 to 150 parts by weight.

(Acid-modified olefin (co) polymer (a-4))
The acid-modified olefin (co) polymer (a-4) is an olefin (co) polymer modified with an acid. Examples of the olefin-based (co) polymer include homopolymers having 2 to 6 carbon atoms such as polyethylene and polypropylene, and those obtained by copolymerizing olefins having 2 to 6 carbon atoms. Among them, a propylene homopolymer, or a random copolymer or block copolymer of propylene and an α-olefin having 2 to 6 carbon atoms (excluding propylene). Usually, the unit derived from propylene is 50 mol% or more, preferably 60 mol, based on 100 mol% in total of the units derived from propylene and the units derived from α-olefin having 2 to 6 carbon atoms (excluding propylene). It is a copolymer containing in an amount of% or more. The kind of acid and the modification method are the same as those of the copolymer (a-2). As the acid, maleic acid is preferable from the viewpoint of the number of acid functional groups.

  The weight average molecular weight calculated | required by GPC of a (co) polymer (a-4) is less than 50,000 in a polystyrene conversion, Preferably it is less than 5,000-50,000, More preferably, it is 5,000-40,000. The low molecular weight copolymer (a-4) is used as a dispersion aid when dispersing the olefin copolymer (a) and mixed when the aqueous dispersion (A) is kneaded with the electrode active material. It has a role of improving stability, adhesion between the positive electrode current collector and the positive electrode active material-containing layer, and compatibility with a thickener (viscosity modifier), particularly carboxymethylcellulose.

  In particular, the random propylene copolymer (a-1) is that the (co) polymer (a-4) is a low molecular weight maleated modified olefin (co) polymer having a weight average molecular weight of less than 50,000. Or it is preferable from a viewpoint of improving the compatibility in an aqueous dispersion process with an acid-modified random propylene-based copolymer (a-2), and maleated modified polypropylene is more preferable.

  The degree of modification is usually 0.1 to 10% by weight, preferably 0.5 to 8% by weight, from the viewpoints of water dispersibility stability and electrode plate adhesion. If it exceeds this range, the emulsifying properties at the time of dispersing the emulsion may decrease, the mixing stability of the paste may decrease, and the viscosity may increase.

  The random propylene copolymer (a-1) from the viewpoints of adhesion of the olefin copolymer (a) and swellability with respect to the electrolytic solution, and also from the viewpoint of emulsifiability at the time of emulsion dispersion and paste mixing stability. It is preferable that the content of the (co) polymer (a-4) is 5 to 50 parts by weight with respect to a total of 100 parts by weight of the acid-modified random propylene copolymer (a-2), Preferably it is 10-40 weight part, More preferably, it is 10-30 weight part.

(Other copolymer (a-5))
In the olefin type copolymer (a) concerning this invention, the other copolymer (a-5) may be included in the range which does not impair the effect of this invention.

  The other copolymer (a-5) is different from the copolymers (a-1) to (a-4), and is styrene, ethylene, propylene, 1-butene, 1,3-butadiene, 3-methyl. Copolymerizable monomers such as -1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene, 1-decene and 1-dodecene; Examples thereof include copolymers singly or in combination of two or more, styrene-ethylene-butylene copolymers, and hydrogenated products thereof. In addition, polymers containing alicyclic structures such as norbornene polymers, monocyclic cyclic polyolefin polymers, cyclic conjugated diene polymers, vinyl alicyclic hydrocarbon polymers, and hydrogenated products thereof are also used. be able to.

  The copolymer (a-5) includes acid-modified products of these copolymers, and maleated modified products are particularly preferable. From the viewpoint of improving the adhesion between the positive electrode current collector and the positive electrode active material-containing layer and the flexibility of the electrode, the content of the copolymer (a-5) is 100 weights of the olefin copolymer (a). The amount is preferably 0 to 50 parts by weight, more preferably 0 to 30 parts by weight with respect to parts. Furthermore, the content of the copolymer (a-5) is preferably 0 to 50 parts by weight with respect to 100 parts by weight of the total of the copolymers (a-1) and (a-2). Preferably it is 0-30 weight part.

  In the case of using a copolymer modified with maleic acid, the maleation modification degree is not particularly limited, but is preferably 0.1 to 10% by weight, more preferably 0.1 to 8% by weight. Exceeding this range may cause a decrease in emulsification during dispersion of the emulsion, a decrease in the mixing stability of the paste, and a thickening. The weight average molecular weight of the copolymer (a-5) is not particularly limited, but is preferably 5,000 to 300,000.

(Surfactant (x))
In this invention, it is preferable that surfactant (x) is contained in a water-dispersible binder (A) as needed. The surfactant is a substance that modifies the surface of the substance or the parent or hydrophobic state of the interface. In the present invention, the surfactant functions as a dispersant, a wetting agent, and an antifoaming agent. When a surfactant is included, it is preferable from the viewpoint of forming an aqueous dispersion of the active material and the conductive assistant.

  The surfactant is preferably anionic, nonionic, or silicon-based, but is not particularly limited. The addition amount of the surfactant is 0 to 100 parts by weight, preferably in terms of solids, based on 100 parts by weight of the solids of the olefin copolymer (a) in the water-dispersible binder (A), preferably 3 to 80 parts by weight. If this range is exceeded, the compatibility of the resin particles with the electrolyte will increase, and the strength will be significantly reduced, and the resin will easily swell.

  Examples of the anionic surfactant include sulfonates having a saturated or unsaturated alkyl chain of C10 to C20, such as sodium dodecylbenzenesulfonate and sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, alkylnaphthalenesulfonic acid. Sodium, dialkylsulfosuccinate, sodium stearate, potassium oleate and other C10 to C20 saturated or unsaturated carboxylate, sodium dioctylsulfosuccinate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene Sodium alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium dialkylsulfosuccinate, stearin Sodium, sodium oleate, t-octyl phenoxy ethoxy polyethoxy ethyl sulfate sodium salt, and the like.

  Examples of the nonionic surfactant include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether, polyoxyalkylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene Ethylene styrenated phenyl ether, polyoxyethylene distyrenated phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl phenyl ether, oxyethylene / oxypropylene block copolymer, t-octylphenoxyethyl poly Polyols of ethoxyethanol, nonylphenoxyethyl polyethoxyethanol, acetylenic glycol derivatives Shi ethylene ether.

  Examples of the silicon surfactant include polydimethylsiloxane, polyether-modified polydimethylsiloxane, polymethylalkylsiloxane, and silicon-modified polyoxyethylene ether. Only one type of surfactant may be used, or a plurality of these types may be used in combination.

  Among these surfactants, potassium oleate and potassium stearate are preferable in that the active material and the conductive additive are dispersed in water. In addition, acetylenic glycol derivative polyoxyethylene ether and silicon-modified polyoxyethylene ether are preferable from the viewpoint of reducing the surface tension of water. As the surfactant, when at least one selected from potassium oleate, polyoxyethylene ether of an acetylenic glycol derivative and silicon-modified polyoxyethylene ether is used, the resulting aqueous dispersion is a good active material, conductive It is more preferable because a dispersion state of the auxiliary agent can be obtained.

  When the copolymer (a-3) is used alone as the olefin copolymer (a), the water-dispersible binder (A) is used from the viewpoint of improving the dispersibility of the active material and the conductive additive. It is preferable to contain a surfactant. Such surfactants are not particularly limited, but are preferably potassium oleate, potassium stearate, polyoxyethylene ethers of acetylenic glycol derivatives, silicon-modified polyoxyethylene ethers, more preferably potassium oleate, acetylene. These are polyoxyethylene ethers of renic glycol derivatives and silicon-modified polyoxyethylene ethers. In this case, the surfactant is not particularly limited, but is 0 to 100 parts by weight in terms of solid content with respect to 100 parts by weight of the solid content of the copolymer (a-3), preferably 3 to 80 from the viewpoint of cycle characteristics. Parts by weight. This range is preferred because a good capacity retention based on electrode plate adhesion can be obtained.

(Viscosity modifier (y))
In the present invention, it is preferable that the water dispersible binder (A) contains a viscosity modifier (y) as necessary.

  The addition amount of the viscosity modifier is 10 to 100 parts by weight, preferably 10 in terms of solid content, with respect to 100 parts by weight of solid content of the olefin copolymer (a), from the viewpoint of coating properties and workability. -95 parts by weight.

  Although a viscosity modifier is not specifically limited, The weight average molecular weight calculated | required by GPC becomes like this. Preferably it is 50,000-4,000,000 (polystyrene conversion), More preferably, it is 60,000-3,500,000, More preferably Is 65,000-3,000,000. If the weight average molecular weight is less than 50,000, the active material may be precipitated, and if it exceeds 4,000,000, the paste may have remarkable thixotropic characteristics. Moreover, it is preferable that it is in the above-mentioned range since good electrode plate coatability can be obtained.

  Although it does not specifically limit as a viscosity modifier, Cellulose derivatives, such as carboxymethylcellulose (CMC), carboxyethylcellulose, and hydroxyethylcellulose, polyoxyethylene or its modified body, polyvinyl alcohol or its modified body, polysaccharide, etc. are mentioned.

  Among these viscosity modifiers, CMC, polyoxyethylene or a modified product thereof, polyvinyl alcohol or a modified product thereof is more preferable from the viewpoint of sedimentation stability. Only one type of viscosity modifier may be used, or a plurality of these types may be used in combination.

(Other)
In the water-dispersible binder (A) according to the present invention, a heat-resistant stabilizer, an anti-slip agent, a foaming agent, a crystallization aid, a nucleating agent, and a pigment are included in the range not impairing the object of the invention. Various additives such as dyes, plasticizers, antioxidants, antioxidants, impact modifiers, fillers, crosslinking agents, co-crosslinking agents, crosslinking aids, adhesives, softeners, flame retardants, processing aids, etc. It may be blended.

(2-2) Active material (B)
The active material (B), is not particularly _limited, such as _{LiCoO 2, LiMn 2 O 4,} LiFePO 4 and the like. Moreover, you may use the carbon material of a conductive support agent suitably. For example, as a positive electrode active material for a lithium ion secondary battery, a sulfur-based compound such as Li ₂ S, S, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _X Co _(1-X) O ₂ , _{LiNi x Mn y Co (1-} x-y), LiNi x Co y Al (1-x-y), Li 2 MnO 3, a composite oxide consisting of lithium, such as a transition _metal, LiFePO _4, LiMnPO 4, etc. And conductive polymer materials such as polyaniline, polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, and dimercaptothiadiazole / polyaniline complex. Of these, composite oxides composed of lithium and a transition metal and phosphoric acid compounds such as LiFePO ₄ and LiMnPO ₄ are particularly preferable. When the negative electrode is lithium metal or a lithium alloy, a carbon material can also be used as the positive electrode. As the positive electrode, a mixture of lithium and transition metal composite oxide and a carbon material can be used.

  The positive electrode active material used in the present invention may be coated with an electron conductive material such as a carbon material on the particle surface in order to increase the electron conductivity of the particle itself.

(2-3) Conductive aid (C)
The conductive assistant (C) is not particularly limited, but carbon materials such as carbon black, amorphous whisker carbon, graphite, acetylene black and artificial graphite, conductive polymers such as polythiophene and polypyrrole and derivatives thereof, and metal fine particles such as cobalt. Etc. These may be used singly or in combination of two or more. You may use the carbon material of an active material suitably.

  The conductive assistant is preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by weight with respect to 100 parts by weight of the active material (B). Within this range, good lithium ion transportability and electrical conductivity can be obtained without impairing the charge capacity. Moreover, there exists a possibility that the electrical resistance of a compound material layer may be increased as it is less than 0.1 weight part, and when it exceeds 20 weight part, there exists a possibility that Li ion transport property may be reduced.

(2-4) Method for Forming Positive Electrode Active Material-Containing Layer As described above, the positive electrode active material-containing layer comprises an aqueous dispersion of the water-dispersible binder (A), the active material (B), and a conductive auxiliary agent ( It is obtained by applying a slurry containing C) onto the positive electrode current collector (X). For application of the slurry, an applicator, a bar coater, a comma coater, a die coater, or the like can be used. After applying the slurry, it is dried as necessary.

Moreover, you may press as needed after application | coating of a slurry. The packing density of the active material contained in the positive electrode active material-containing layer is in the range of 1.0 to 2.0 g / cm ² , and the amount of active material contained in the positive electrode active material-containing layer is in the range of 4 to 90 mg / cm ² . It is preferable to press so that it becomes. If the active material filling density of the positive electrode is less than 1.0 g / cm ² , the energy density of the battery is lowered, which is not preferable. When the packing density of the positive electrode active material is higher than 2.5 g / cm ² , the permeability of the electrolytic solution to the positive electrode plate is lowered, and the battery performance is deteriorated.

B. Non-aqueous secondary battery In one aspect of the present invention, the non-aqueous secondary battery according to the present invention comprises a positive electrode for a secondary battery according to the present invention, which is formed by stacking a negative electrode together with a negative electrode, a cylindrical type, a coin type It is formed by forming a rectangular shape, a film shape or any other shape and enclosing a non-aqueous electrolyte.

(1) Separator As the separator, those usually used for secondary batteries can be used, and a microporous membrane or a nonwoven fabric is used. Examples of the microporous film include polyolefin, polyimide, polyvinylidene fluoride, polyester, and the like. In particular, a porous polyolefin film is preferable, and specifically, a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and polypropylene can be exemplified. On the porous polyolefin film, other resin excellent in thermal stability may be coated.

(2) Electrolyte As the non-aqueous electrolyte, an electrolyte usually used in a non-aqueous secondary battery can be used singly or in combination of two or more and dissolved in an organic solvent. Examples of the solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate, and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, and dipropyl carbonate; Lactones such as γ-butyrolactone and γ-valerolactone;
Furans such as tetrahydrofuran and 2-methyltetrahydrofuran; ethers such as diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, dioxane; dimethyl sulfoxide, sulfolane, methylsulfolane, acetonitrile, formic acid Examples thereof include methyl, methyl acetate and the like, and one or more of these may be mixed and used. In particular, cyclic carbonates such as PC, EC and butylene carbonate are preferred because they are high-boiling solvents.

As electrolyte salts that can be used in the non-aqueous electrolyte used in the present invention, lithium borofluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), tri Examples thereof include lithium salts such as lithium fluoroacetate (LiCF ₃ COO) and lithium bis (trifluoromethanesulfone) imide (LiN (CF ₃ SO ₂ ) ₂ ), and one or more of these may be used in combination.

(3) Negative electrode As the negative electrode, a negative electrode usually used in a non-aqueous secondary battery can be used. For example, graphite material powder such as spheroidized natural graphite, artificial graphite, non-graphitizable carbon material powder, hard carbon A negative electrode using, for example, as an active material is preferable.

(4) Exterior material The exterior material of the non-aqueous secondary battery is preferably a metal can such as a can made of iron, stainless steel, aluminum or the like. Moreover, you may use the film-form bag which laminated the ultra-thin aluminum with resin. The shape of the exterior material may be any of a cylindrical shape, a rectangular shape, a thin shape, and the like, but since a large-sized lithium ion secondary battery has many opportunities to be used as an assembled battery, it is preferably a rectangular shape or a thin shape.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example 1]
<Adjustment of positive electrode current collector>
A commercially available aluminum degreasing agent “NE-6 (manufactured by Meltex)” was dissolved in water at a concentration of 15% by weight and adjusted to 75 ° C. An aluminum foil having a thickness of 20 μm was immersed in this aluminum degreasing tank for 5 minutes and washed with water, and then immersed in a tank containing a 1 wt% hydrochloric acid aqueous solution at 40 ° C. for 1 minute and washed with water. Subsequently, it was immersed for 1 minute in a tank containing a 1% by weight aqueous caustic soda solution at 40 ° C. and washed with water. Next, it was immersed for 1 minute in a tank containing 1% by weight hydrochloric acid aqueous solution at 40 ° C. and washed with water, and immersed in a first vidrazine treatment tank containing 2.5% by weight hydrated hydrazine aqueous solution at 60 ° C. for 1 minute, It was immersed in a second vitocerazine treatment tank containing a 0.5 wt% monohydric hydrazine aqueous solution at 40 ° C. for 0.5 minutes and washed with water. This was dried in warm air at 40 ° C. for 15 minutes and at 60 ° C. for about 5 minutes to obtain a positive electrode current collector (X).

<Preparation of aqueous dispersion of olefin copolymer (a)>
As the olefin copolymer (a), 50 parts by weight of a maleated random polypropylene (a-2) copolymerized with a weight average molecular weight of 100,000, a maleic modification degree of 1.0, and a total of 25% by weight of butene, 5 parts by weight of an ethylene-methacrylic acid copolymer having a weight average molecular weight of 90,000 (methacrylic acid content: 4% by weight) (a-3) was mixed. Furthermore, 50 parts of potassium oleate was mixed, melt-kneaded at 200 ° C. with a twin screw extruder, and then kneaded while adding an aqueous potassium hydroxide solution.
The discharged product was dispersed in water to obtain an aqueous dispersion containing an olefin copolymer (a) having a volume average particle diameter of 150 nm and a nonvolatile content of 45% by weight. The melting point of (a) was 80 ° C.

<Preparation of positive electrode for lithium secondary battery>
Carboxymethyl cellulose (Daicel Chemical Co., Ltd. CMC 1160, weight average molecular weight: 650,000), Hydroxyethyl cellulose (Daicel Chemical Co., Ltd. SP600, weight average molecular weight: 1,000,000), polyoxyethylene (Meisei Chemical Industry Co., Ltd., Alcox E) A viscosity modifier (y) selected from -75, weight average molecular weight: 2,000,000) and polyvinyl alcohol (Kuraray KL-318, weight average molecular weight: 70,000) is adjusted to 1% by weight, 1 part by weight in terms of solid content and 3 parts by weight of the above-mentioned aqueous dispersion of the olefin copolymer were mixed to obtain an aqueous dispersion (A1).
LiCoO ₂ (Honjo FMC Energy Systems Co., Ltd. HLC-22) 85.5 parts by weight (active material B), artificial graphite 8 parts by weight and acetylene black (Denka Black) 3 parts by weight (conducting aid C) The obtained water dispersion (A1) and distilled water were added to prepare a LiCoO ₂ mixture slurry (slurry A1) having a solid content concentration of 50% by weight. Next, this slurry A1 was applied to the positive electrode current collector (X), dried, and compression molded to prepare a positive electrode for a lithium secondary battery having a thickness of 70 μm.

<Evaluation of adhesion of positive electrode for lithium secondary battery>
About the obtained positive electrode for lithium secondary batteries, the created positive electrode was cut off, and the electrode plate was fixed to a stainless steel plate with a double-sided tape, and then a cellophane tape was attached to the surface to make a sample for evaluation. Using the sample for evaluation, a 90-degree peel test was performed with a tensile tester Intesco. The measurement was performed three times, and the peel strength at the interface between the active material-containing layer and the current collector was evaluated by observing the peeled state. As a result of the evaluation, peeling between the positive electrode active material-containing layer and the current collector was not observed three times, and peeling occurred between the cellophane tape and the surface of the positive electrode active material-containing layer.

<Production of negative electrode for lithium secondary battery>
Carboxymethylcellulose (Daicel Chemical Co., Ltd. CMC1160, weight average molecular weight: 650,000) is adjusted to 1.2% by weight, and 1 part by weight in terms of solid content and the water-dispersible binder (A) in terms of solid content. 2 parts by weight and an anionic type (Non-Sal OK-2 manufactured by NOF Corporation) were mixed to obtain an aqueous dispersion (A2).
The obtained water dispersion (A2) and distilled water were added to 90 parts by weight of artificial graphite (manufactured by Hitachi Chemical Co., Ltd .; MAGD) having an average particle diameter of 20 μm and 7 parts by weight of acetylene black (Denka Black: manufactured by Denki Kagaku Kogyo Co., Ltd.). Was added to prepare a slurry for negative electrode (slurry A2) having a solid concentration of 50% by weight.
Next, this slurry A2 was applied to a negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm, dried, and compression molded to prepare a negative electrode having a thickness of 70 μm.

<Preparation of non-aqueous electrolyte for lithium ion secondary battery>
As a non-aqueous solvent, ethylene carbonate (EC) and methyl ethyl carbonate (MEC) mixed at a ratio of EC: MEC = 4: 6 (weight ratio) were used, and then LiPF ₆ as an electrolyte was dissolved. A non-aqueous electrolyte was prepared so that the electrolyte concentration was 1.0 mol / liter.

<Production of coin-type lithium ion secondary battery>
As a negative electrode for a coin-type battery, the negative electrode was punched into a disk shape having a diameter of 14 mm to obtain a coin-shaped negative electrode having a weight of 20 mg / 14 mmφ. As a positive electrode for a coin-type battery, the positive electrode was punched into a disk shape having a diameter of 13.5 mm to obtain a coin-shaped positive electrode having a weight of 42 mg / 13.5 mmφ.

Using the coin-shaped negative electrode, the positive electrode, and a separator made of a microporous polypropylene film having a thickness of 25 μm and a diameter of 16 mm, the negative electrode, the separator, and the positive electrode are placed in the negative electrode can of a stainless steel 2032 size battery can. Laminated. Thereafter, 0.04 ml of the non-aqueous electrolyte was injected into the separator, and then an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were stacked on the laminate.
Finally, by covering the positive electrode can of the battery via a polypropylene gasket and caulking the can lid, the airtightness inside the battery was maintained, and a coin-type battery having a diameter of 20 mm and a height of 3.2 mm was produced. .

<Evaluation of battery cycle characteristics>
Using the coin-type battery, this battery is connected to Nagano Co., Ltd. under the condition of a constant current of 0.5 mA and a constant voltage of 4.2 V until the current value at a constant voltage of 4.2 V reaches 0.05 mA. The battery was charged, and then discharged under the conditions of a constant current of 1 mA and a constant voltage of 3.0 V until the current value at a constant voltage of 3.0 V was 0.05 mA. This cycle was repeated 500 times, and the capacity maintenance rate (%) after 500 cycles with respect to the battery capacity of the fifth cycle was evaluated. The capacity maintenance rate was 83%.

[Comparative Example 1]
In the adjustment of the positive electrode current collector, the commercially available aluminum degreasing agent “NE-6 (manufactured by Meltex)” implemented in Example 1 was dissolved in water at a concentration of 15% to 75 ° C. Example 1 except that a positive electrode current collector (X ′) prepared without any treatment other than immersing an aluminum foil having a thickness of 20 μm in an aluminum degreasing bath containing this aqueous solution for 5 minutes and washing with water was used. Similarly, the slurry A1 was applied to the positive electrode current collector (X ′), dried, and compression molded to produce a positive electrode for a lithium secondary battery having a thickness of 70 μm.
When the adhesive strength of the obtained positive electrode with the current collector was measured, it peeled between the positive electrode active material-containing layer and the current collector three times.
A coin-type battery was prepared in the same manner as in Example 1 except that the positive electrode current collector (X ′) was used as the positive electrode current collector, and the capacity retention rate (%) was evaluated. The rate was 68%.

[Comparative Example 2]
<Preparation of positive electrode for lithium secondary battery>
10 parts of PBR (Tuffmer XM5070; manufactured by Mitsui Chemicals, Inc.) having a weight average molecular weight of 300,000 and 200 parts of toluene are mixed and stirred for 1 hour at 110 ° C., and a binder containing an olefin copolymer having a melting point of 75 ° C. An agent (A ′) was obtained. LiCoO ₂ (Honjo FMC Energy Systems Co., Ltd. HLC-22) 85.5 parts by weight (active material B), artificial graphite 8 parts by weight and acetylene black (Denka Black) 3 parts by weight (conducting aid C) The obtained binder (A ′) was added and kneaded to prepare a LiCoO ₂ mixture slurry (slurry A1 ′) having a solid concentration of 50% by weight.

  Next, this slurry A1 'was applied to the positive electrode current collector (X), dried, and compression molded to produce a positive electrode for a lithium secondary battery having a thickness of 70 µm. An attempt was made to measure the adhesive strength of the obtained positive electrode with the current collector, but the binding force of the positive electrode active material layer was weak, and the active material layer collapsed during the evaluation process, and the evaluation was not possible.

Claims (4)

A positive electrode for a secondary battery having a positive electrode active material-containing layer on the surface of a positive electrode current collector made of an aluminum alloy foil,
The positive electrode current collector is a positive electrode current collector (X) in which irregularities are formed on the surface by immersion treatment in an aqueous solution of hydrazine ,
The positive electrode active material-containing layer contains a water-dispersible binder (A) containing an olefin copolymer (a), an active material (B), and a conductive additive (C) .
The olefin copolymer (a) has a weight average molecular weight of 50,000 or more (in terms of polystyrene) determined by gel permeation chromatography (GPC), and a content of a structural unit derived from propylene of 50. Random propylene copolymer (a-1) of not less than 85% by weight and acid-modified random propylene copolymer (a-2) obtained by acid-modifying the random propylene copolymer (a-1) And one type selected from the group consisting of ethylene- (meth) acrylic acid copolymers (a-3) whose content of structural units derived from (meth) acrylic acid is 5 wt% or more and 25 wt% or less A positive electrode for a secondary battery, which is the above compound . The water-dispersible binder (A) is an acid-modified olefin (co) polymer (a-4) having a weight average molecular weight of less than 50,000 (polystyrene conversion) determined by gel permeation chromatography (GPC). The positive electrode for a secondary battery according to claim 1, further comprising: Characterized in that it comprises a positive electrode for a secondary battery according to claim 1 or 2, a non-aqueous secondary battery.   Immersing the aluminum alloy foil in a hydrazine aqueous solution having a concentration of 2 to 10% by weight as a monohydrated hydrazine to obtain a positive electrode current collector (X);
  A positive electrode active material containing a water-dispersible binder (A) containing an olefin copolymer (a), an active material (B) and a conductive additive (C) on the surface of the positive electrode current collector (X) Forming a layer;
Including
  The olefin copolymer (a) has a weight average molecular weight of 50,000 or more (in terms of polystyrene) determined by gel permeation chromatography (GPC), and a content of a structural unit derived from propylene of 50. Random propylene copolymer (a-1) of not less than 85% by weight and acid-modified random propylene copolymer (a-2) obtained by acid-modifying the random propylene copolymer (a-1) And one type selected from the group consisting of ethylene- (meth) acrylic acid copolymers (a-3) whose content of structural units derived from (meth) acrylic acid is 5 wt% or more and 25 wt% or less The manufacturing method of the positive electrode for secondary batteries characterized by being the above compound.