JP2009170287A - Non-aqueous electrolyte secondary battery electrode and non-aqueous electrolyte secondary battery using the same - Google Patents

Abstract

An electrode for a non-aqueous electrolyte secondary battery that can be manufactured by a simple process and exhibits high initial charge / discharge efficiency, high electrode plate strength, and low irreversible capacity.
An electrode for a non-aqueous electrolyte secondary battery in which an active material layer containing an active material and a binder is formed on a current collector, wherein the binder includes a metal salt, The problem has been solved by an electrode for a non-aqueous electrolyte secondary battery, characterized by containing an ion of a metal salt and a water-soluble polymer that forms an intramolecular crosslinked structure or an inclusion compound.
[Selection figure] None

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a specific non-aqueous electrolyte secondary battery electrode and a non-aqueous electrolyte secondary battery including this electrode.

  With the downsizing of electronic devices, it is desired to increase the capacity of secondary batteries. Therefore, lithium ion secondary batteries with higher energy density are attracting attention as compared to nickel / cadmium batteries and nickel / hydrogen batteries.

  As the electrode material, lithium metal oxides such as lithium cobaltate, lithium nickelate, and lithium manganate are often used for the positive electrode, and graphite, amorphous carbon, metal / alloy that can be combined with lithium, etc. are used for the negative electrode. Is often used. However, since many of these materials are powders, a binder is usually required to obtain an electrode body.

  As the binder, a polymer compound is used, and polyethylene, polymethyl methacrylate, styrene / butadiene copolymer, Teflon (registered trademark), poly (vinylidene fluoride), tetrafluoroethylene / perfluorovinyl ether copolymer are used. (Trade name Nafion), polyethylene oxide, polyethylene oxide / polypropylene oxide copolymer and the like are often used.

  However, many of the aforementioned compounds are hydrophobic, and many of them need to be dispersed in an organic solvent or dispersed in water as an aqueous dispersion. In the former, since an organic solvent removal / recovery facility is required after the electrode is formed, the latter aqueous system is often used in recent years.

  However, since the wettability of the dispersion to the electrode material powder is low and it is difficult to disperse the binder, a polysaccharide, usually a cellulosic organic polymer, particularly carboxymethylcellulose (CMC), coexists with the binder. Often used as a "dispersant" binder.

  On the other hand, as the solvent of the non-aqueous electrolyte, cyclic carbonates represented by ethylene carbonate, propylene carbonate, butylene carbonate, etc., which are high dielectric constant solvents, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc., which are low viscosity solvents, etc. Chain carbonates, cyclic esters such as γ-butyrolactone, cyclic ethers such as tetrahydrofuran 1,3-dioxolane, and chain ethers such as 1,2-dimethoxyethane are used alone or in combination. .

It is also common to add a small amount of a solvent having an unsaturated bond in the intramolecular structure such as vinylene carbonate or vinyl ethyl carbonate. As described above, a high dielectric constant solvent and a low viscosity solvent are often mixed and used, and as the electrolyte, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) _2, etc. These Li salts are used alone or in combination of two or more.

  However, when the electrode formed by combining the electrolytic solution and the binder is used in a battery, the “dispersant” binder often shows swelling / solubility with respect to the electrolytic solution. When the battery is in contact with the electrolyte for a long time, or when the battery temperature is raised, peeling from the active material as the battery material or exposure of the new surface is caused. For example, the irreversible capacity is increased or new gas is generated. .

  On the other hand, a binder mainly composed of a rubber system forms an essentially Li-impermeable film in the electrode body, and is thus resistant to lithium insertion / extraction reaction. In order to avoid this, it is known that the amount of the binder is reduced, for example, but since the role of maintaining the electrode as a structure is in the presence of this binder, the resistance is reduced, The binding property of the active material powder is inferior, and as a result, it is inferior in handleability when the electrode is wound.

As a technique related to the negative electrode active material, Patent Document 1 discloses that when carbon particles in which a calcium compound is added to the inside of a battery, particularly the negative electrode active material, are used, fluorine anions present in the electrolyte solution It has been disclosed that it can suppress coming to the interface, and exhibits a charge / discharge cycle with a high capacity, a high energy density, and a low irreversible capacity even during rapid charge / discharge. However, in the examples of Patent Document 1, since Teflon (registered trademark) is used as the negative electrode binder, the wettability with the electrolytic solution is insufficient, and the binder and Li react during charging. There was drowning and the loss reduction effect was not sufficient. In addition, the effect of filling the metal salt is not sufficient with polyvinylidene fluoride (PVdF) compared to the case of the rubber-based binder, and the electrode strength cannot be improved, the amount of the binder is reduced, and the electrode resistance is reduced. It was also not sufficient to reduce.
JP-A-11-111342

  The present invention has been made in view of the above-described background art, and its problem is to provide a non-aqueous electrolyte secondary battery electrode that exhibits high initial charge / discharge efficiency, high electrode plate strength, and small irreversible capacity in a simple process. It is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have at least a metal salt as an electrode binder and “form an intramolecular cross-linked structure or inclusion compound with an ion of the metal salt. It has been found that by containing a “water-soluble polymer”, an electrode having high physical strength and resistance to an electrolyte can be produced, and the present invention has been completed. In particular, by incorporating a metal salt exhibiting a crosslinking action or an inclusion action into a water-soluble polymer such as a cellulose-based polymer used as a “dispersant” -like binder, a high strength can be obtained. It is possible to produce an electrode body, it is possible to reduce the amount of binder, and to reduce the swelling / solubility of water-soluble polymers such as cellulosic polymers in electrolytes. As a result, the irreversible capacity was found to be reduced, and the present invention was completed. Furthermore, the present inventors have found that the metal salt has a filling effect with respect to a binder mainly composed of a rubber system, so that the performance can be further improved, and the present invention has been completed.

  That is, the present invention relates to an electrode for a non-aqueous electrolyte secondary battery in which an active material layer containing an active material and a binder is formed on a current collector, and the binder includes a metal salt and The present invention provides an electrode for a non-aqueous electrolyte secondary battery characterized in that it contains an ion of the metal salt and a water-soluble polymer that forms an intramolecular crosslinked structure or an inclusion compound. Moreover, this invention provides the nonaqueous electrolyte secondary battery characterized by using said electrode for nonaqueous electrolyte secondary batteries.

  According to the present invention, it is possible to provide an electrode for a non-aqueous electrolyte secondary battery that is inexpensive, has a simple process, and has excellent initial charge / discharge efficiency, electrode plate strength, and irreversible capacity.

  Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these specific contents. Various modifications can be made within the scope of the gist.

<Electrode for non-aqueous electrolyte secondary battery>
The electrode for a non-aqueous electrolyte secondary battery of the present invention is an electrode for a non-aqueous electrolyte secondary battery formed by forming an active material layer containing an active material and a binder on a current collector. The adhesive contains at least a metal salt and an ion of the metal salt and a water-soluble polymer that forms an intramolecular crosslinked structure or an inclusion compound.

[Active material]
(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium ions. For example, carbon materials having various degrees of graphitization ranging from graphite to amorphous materials can be alloyed with Li. It is preferable to use those selected from the group consisting of metal particles and metal oxide particles that can be alloyed with Li. Among these, graphite is particularly preferable because it can be easily obtained commercially.

  As the graphite, either natural graphite or artificial graphite can be used. It is preferable that graphite has few impurities, and it is used after being subjected to various purification treatments as necessary. Among these, it is particularly preferable to use graphite having a high degree of graphitization with a (002) plane spacing (d002) of less than 3.37 mm by the X-ray wide angle diffraction method.

  Specific examples of artificial graphite include coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride, Polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin, and other organic substances, usually graphitized at a firing temperature of 2500 to 3200 ° C. Is mentioned.

  Further, as the carbon material having a low graphitization degree, a material obtained by firing an organic substance at a temperature of usually 2500 ° C. or lower is used. Specific examples of organic substances include coal-based heavy oils such as coal tar pitch and dry-distilled liquefied oil; straight-run heavy oils such as atmospheric residual oil and vacuum residual oil; by-product during thermal decomposition of crude oil, naphtha, etc. Petroleum heavy oils such as cracked heavy oil such as ethylene tar; Aromatic hydrocarbons such as acenaphthylene, decacyclene and anthracene; Nitrogen-containing cyclic compounds such as phenazine and acridine; Sulfur-containing cyclic compounds such as thiophene; Aliphatic cyclic compounds; polyphenylenes such as biphenyl and terphenyl; polyvinyl compounds such as polyvinyl chloride, polyvinyl acetate, and polyvinyl butyral; thermoplastic polymers such as polyvinyl alcohol;

  The firing temperature of the carbon material having a low degree of graphitization is usually 600 ° C. or higher, preferably 900 ° C. or higher, more preferably 950 ° C. or higher. The upper limit varies depending on the degree of graphitization desired for the carbon material, but is usually 2500. It is below ℃. The firing is preferably performed at 2000 ° C. or lower, particularly preferably 1400 ° C. or lower. At the time of baking, acids such as phosphoric acid, boric acid and hydrochloric acid, and alkalis such as sodium hydroxide may be mixed with the organic matter.

  As the negative electrode active material, one or more selected from the above graphite, a carbon material having a low graphitization degree, metal particles that can be alloyed with Li, and metal oxide particles that can be alloyed with Li are appropriately mixed. It is also preferable to use them. For example, carbonaceous particles having a structure in which the surface of graphite is coated with a carbon material having a low degree of graphitization, and those obtained by aggregating graphite particles with an appropriate organic substance and regraphitizing are preferable. Furthermore, it is preferable that the composite particles contain a metal that can be alloyed with Li, such as Sn, Si, Al, and Bi.

<Particle size of negative electrode active material>
The average particle diameter of the negative electrode active material is usually 50 μm or less, preferably 25 μm or less, particularly preferably 18 μm or less, while the upper limit is usually 5 μm or more. In addition, when the negative electrode active material is a carbon material, secondary particles in which a plurality of particles are aggregated may be used. In this case, the average particle size of the secondary particles is preferably in the above-mentioned range, and the average particle size of the primary particles is usually 15 μm or less. If the particle size is too small, the specific surface area increases, the reaction surface with the electrolyte increases, and the irreversible capacity may increase. On the other hand, if the particle size is too large, when applying a slurry of the active material and the binder to the current collector, so-called striations due to large lumps occur, resulting in the formation of an active material layer with a uniform thickness. It can be difficult.

<Shape of negative electrode active material>
The shape is not particularly limited. For example, a raw material selected from the above-described graphite, a carbon material having a low degree of graphitization, metal particles that can be alloyed with Li, and metal oxide particles that can be alloyed with Li is used as a machine. Preferred is a spheroid formed by chemical treatment such as oxidation or plasma treatment. The circularity of particles having a volume average particle size in the range of 10 to 40 μm is preferably 0.80 or more, particularly preferably 0.90 or more, and further preferably 0.93 or more. This is preferable because the shape of the interparticle voids is uniform.

  “Circularity” is defined as [perimeter of a circle having the same area as the area of the particle projection image] / [perimeter of the particle projection image]. The case of a circularity of 1 is a theoretical sphere. Using an FPIA manufactured by Sysmex Industrial Co., which is a flow type particle image analyzer, 0.2 g of a measurement target (here, negative electrode material) is 0.2% by volume aqueous solution of polyoxyethylene (20) sorbitan monolaurate as a surfactant. After mixing with about 50 mL and irradiating 28 kHz ultrasonic waves at an output of 60 W for 1 minute, the detection range is specified as 0.6 to 400 μm, and the values measured for particles in the range of 10 to 40 μm are used.

(Positive electrode active material)
Examples of the positive electrode active material include metal chalcogen compounds that can occlude and release alkali metal cations such as lithium ions during charge and discharge. Examples of metal chalcogen compounds include vanadium oxide, molybdenum oxide, manganese oxide, chromium oxide, titanium oxide, tungsten oxide, and other transition metal oxides; vanadium sulfide, molybdenum sulfide things, sulfides of titanium, transition metal sulfides such as CuS; NiPS _3, FePS ₃ phosphate of a transition metal such as - sulfur compounds; VSe _2, NbSe selenium compound of a transition metal such as _{3; Fe 0.25 V 0.75 S 2} , Examples include composite oxides of transition metals such as Na _0.1 CrS ₂ ; composite sulfides of transition metals such as LiCoS ₂ and LiNiS _{2, and the} like.

Among these, V ₂ O ₅ , V ₅ O ₁₃ , VO ₂ , Cr ₂ O ₅ , MnO ₂ , TiO, MoV ₂ O ₈ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , TiS ₂ , V ₂ S ₅ , Cr _0.25 V _0.75 S ₂ , Cr _0.5 V _0.5 S _2, etc. are preferable, and particularly preferable are LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, and lithium transitions in which some of these transition metals are substituted with other metals. It is a metal complex oxide. These positive electrode active materials may be used alone or in combination.

  The positive electrode active material layer may contain a conductive material in order to improve the conductivity of the electrode. The conductive material is not particularly limited as long as an appropriate amount can be mixed with the active material to impart conductivity, but is usually carbon powder such as acetylene black, carbon black, graphite, etc .; fiber, powder, foil of various metals Etc.

[Binder]
The binder in the non-aqueous electrolyte secondary battery of the present invention is used for both the negative electrode and the positive electrode. That is, it is suitably contained in both the negative electrode active material layer and the positive electrode active material layer.
1) Water-soluble polymer which forms intramolecular cross-linked structure or clathrate compound with metal salt ion The binder in the non-aqueous electrolyte secondary battery of the present invention includes a metal salt, “ion of the metal salt and intramolecular It is essential to contain a “water-soluble polymer that forms a crosslinked structure or an inclusion compound”. Water-soluble polysaccharides can be widely and suitably used as “water-soluble polymers that form intramolecular cross-linked structures or inclusion compounds with metal salt ions” (hereinafter simply referred to as “water-soluble polymers”). For example, a polymer in which a pentose or hexose skeleton has a glucoside bond can be preferably used. Those having a thickening effect and a wetting effect are preferable. Among them, celluloses are particularly preferable because they are inexpensive and easily available. Examples of water-soluble polymers include hydroxymethylcellulose, ethylcellulose, methylcellulose, carboxymethylcellulose, carboxyethylcellulose, agar, carrageenan, fercelan, pectin, starch, mannan, curdlan, Ernest gum, starch, pullulan, guar gum, xanthan gum (xanthan gum) Polysaccharides such as gelatin; Polyethers such as polyethylene oxide and polypropylene oxide; Vinyl alcohols such as polyvinyl alcohol and polyvinyl butyral; Polyacids such as polyacrylic acid and polymethacrylic acid; and metal salts thereof Can be mentioned.

  Among these, polysaccharides or proteins are preferable, and carboxymethylcellulose can be selected from those having a wide variety of molecular weights and counterions, and can be adjusted to an appropriate viscoelasticity when slurried with an active material, in particular. preferable.

  The content of the water-soluble polymer is usually 0.5 parts by weight or more, preferably 0.7 parts by weight or more, more preferably 1 part by weight or more, usually 3 parts by weight or less, preferably 2 parts per 100 parts by weight of the active material. The amount is not more than parts by weight, more preferably not more than 1.5 parts by weight. If the content of the water-soluble polymer is too small, the dispersibility of the active material is deteriorated, and the dispersibility of the following rubber-based binder that controls the binding property is lacking. There are cases where the adhesive is ubiquitous. On the other hand, if the content of the water-soluble polymer is too large, the active material may be coated too much, and resistance to Li insertion / desorption may occur easily, and the performance for a non-aqueous electrolyte secondary battery is deteriorated. There is a case.

  The water-soluble polymer, when used in combination with a rubber-based binder described later, is responsible for improving the dispersibility of the rubber-based binder in the electrode, improving malleability, and loosening the agglomerates of the active material. Yes. Moreover, when compared with the same amount, it has an electrode strength that is not as good as that of a rubber system.

  The water-soluble polymer preferably has a cellulose skeleton and, when a metal salt coexists, forms an intramolecular crosslinked structure or an inclusion compound with ions of the metal salt. Many of the cellulose skeletons have so-called amphipathic properties that have both a hydrophobic part and a hydrophilic part, so that they can be made into aqueous solutions and adsorb to the surface of hydrophobic active materials. The active material powder can be handled as a pseudo hydrophilic powder. Moreover, the oxygen atom in a cellulose molecule has an ionic interaction with the metal cation which is a dissociation body of the following metal salt, and can be made into a crosslinked body.

2) Metal salt The metal salt can be used without limitation as long as it can dissociate the metal ion having the above-mentioned interaction, but it is possible to use 1A group or 2A group carbonate, sulfate, nitrate, phosphorus. Preference is given to acid salts, oxalates or hydrochlorides. Moreover, it is preferable that it is a salt of Li, Na, K, Mg, Ca, Sr, or Ba. For example, carbonates, sulfates, nitrates, phosphates, oxalates, hydrochlorides, and the like of Group 1A, Group 2A metals such as Li, Na, K, Mg, Ca, Sr, and Ba are particularly preferable. Specifically, carbonates such as calcium carbonate, sodium carbonate, lithium carbonate, potassium carbonate, nickel carbonate, and barium carbonate are preferable, and calcium carbonate salts such as heavy calcium carbonate, light calcium carbonate, and colloidal calcium carbonate are inexpensive. It is particularly preferable because it is available in large quantities.

  The content of the metal salt is usually 5% by mass or less, more preferably 3% by mass or less, usually 0.001% by mass or more, more preferably 0.1% by mass or more with respect to the entire water-soluble polymer solid content. . If the content is too small, the crosslinking effect due to sufficient interaction may not be obtained. On the other hand, when the content is too large, the interaction with the water-soluble polymer is too strong, the metal salt is not sufficiently dissociated, and the flexibility of the electrode body may be insufficient.

3) Rubber-based binder The binder in the non-aqueous electrolyte secondary battery of the present invention preferably further contains a rubber-based binder in addition to the water-soluble polymer and the metal salt. As the rubber binder, those having an olefinically unsaturated bond in the molecule are preferable. The type is not particularly limited, but specific examples include styrene / butadiene rubber, styrene / isoprene / styrene rubber, isoprene rubber, acrylonitrile / butadiene rubber, butadiene rubber, chloroprene rubber, neoprene rubber, ethylene / propylene / diene copolymer. Etc. Of these, styrene-butadiene rubber that can be obtained as an aqueous dispersion is particularly preferred.

  The molecular weight of the rubber-based binder is not particularly limited, but it is desirable that the weight average molecular weight is usually 10,000 or more, preferably 50,000 or more, usually 1,000,000 or less, preferably 300,000 or less.

  The rubber-based binder has a styrene unit, and the metal salt acts as a filler for the rubber-based binder, so that a high-strength electrode body can be produced. This is preferable in that the swelling and solubility of the water-soluble polymer in the electrolyte can be reduced. “Action as a filler” means increasing the strength of a rubber-based binder.

  By using such a rubber-based binder in combination with the above-mentioned active material, water-soluble polymer and metal salt, the strength of an electrode plate such as a negative electrode plate can be increased. When the strength of the electrode plate is high, deterioration of the electrode plate due to charge / discharge is suppressed, and the cycle life can be extended. In the present invention, since the adhesive strength between the active material layer and the current collector is high, even when the content of the binder in the active material layer is reduced, the battery is manufactured by winding the electrode plate. The problem that the active material layer peels from the current collector does not occur.

4) Combination of binder components The combination of components contained in the binder can be handled as an aqueous solution or aqueous dispersion, so that the cellulose-based polysaccharides, metal carbonates, and rubber-based binders can be used. Is particularly preferred. Of these, a combination of carboxymethylcellulose, calcium carbonate and styrene-butadiene rubber is most preferable.

5) Content ratio The ratio of the water-soluble polymer to the metal salt is usually 0.1 parts by weight or more, preferably 10 parts by weight or more, more preferably 50 parts by weight with respect to 100 parts by weight of the solid content of the water-soluble polymer. Part or more, usually 500 parts by weight or less, preferably 300 parts by weight or less, more preferably 150 parts by weight or less. If the lower limit is not reached, the crosslinking effect may not be sufficient. If the upper limit is exceeded, the metal salt may be difficult to dissociate, or the crosslinking may be too strong to interfere with the Li insertion / release reaction.

  When the rubber-based binder is contained, the total amount of the water-soluble polymer and the metal salt is usually 30 parts by weight or more, preferably 50 parts by weight or more, more preferably with respect to 100 parts by weight of the rubber-based binder. Is 100 parts by weight or more, usually 300 parts by weight or less, preferably 200 parts by weight or less, more preferably 160 parts by weight or less. Below the lower limit, the adhesion of the rubber-based binder to the negative electrode material is inferior, so that sufficient strength of the electrode cannot be obtained, and for example, it is easy to peel off from the current collector. On the other hand, if the upper limit is exceeded, the initial resistance when the battery is made increases, and a sufficient charge capacity cannot be obtained. “Negative electrode material” or “positive electrode material” refers to all materials that form an active material layer of a negative electrode or a positive electrode provided on a current collector. The same shall apply hereinafter.

  In the present invention, all the components forming the active material layer, that is, the negative electrode material or the positive electrode material, will be described later in addition to the binder (water-soluble polymer, metal salt, rubber-based binder). "Other components" such as a conductive material can be contained, but the binder is usually 90 parts by weight or more by dry weight with respect to 100 parts by weight of all the components forming the active material layer. Is 92 parts by weight or more, particularly preferably 95 parts by weight or more, and the upper limit is usually 99.9 parts by weight or less, preferably 99 parts by weight or less, particularly preferably 98.5 parts by weight or less. If the amount of the binder is too large, the capacity may be decreased and the resistance may be increased. If the amount of the binder is too small, the electrode plate strength may be inferior.

6) Other binders The binder in the non-aqueous electrolyte secondary battery of the present invention is used for both the negative electrode and the positive electrode. When the binder in the present invention is used for a negative electrode, the binder can also be used as a binder for binding a positive electrode active material. Used. Specific examples include inorganic compounds such as silicate and water glass, resins having no unsaturated bond, such as Teflon (registered trademark) and polyvinylidene fluoride. Among these, a resin having no unsaturated bond is particularly preferable. If a resin having an unsaturated bond is used as the resin for binding the positive electrode active material, it may be decomposed during the oxidation reaction. The weight average molecular weight of these resins is usually 10,000 or more, preferably 100,000 or more, and usually 3 million or less, preferably 1 million or less.

[Action]
The reason why the effect of the present invention is obtained is not clear, but the following can be considered. However, the present invention is not limited to the range of the following effects.

  The metal salt is ionized into a metal cation and an anion in the solvent slurry, and it is known that the water-soluble polymer and the metal cation described above have an ion-ion or ion-dipole interaction. This form includes a form in which a helix of a water-soluble polymer wraps around a metal ion, and a form in which metal ions are pinched between two water-soluble polymer β sheets. It is considered that the metal ions bring about the above-mentioned crosslinking action on the water-soluble polymer to be covered, thereby reducing the free volume of the water-soluble polymer molecular chain and making it difficult to swell against the electrolytic solution. Therefore, the area where the negative electrode active material active surface is in contact with the electrolytic solution is reduced, and it is considered that generation of irreversible capacity represented by SEI (Solid Electrolyte Interface solid electrolyte interface) formation is suppressed.

  Furthermore, when a rubber-based binder is used, the physical strength of the rubber is improved by a so-called filling effect (filler effect), and it is considered that the same effect can be exhibited in the negative electrode.

[Electrode manufacturing method]
The negative electrode in the non-aqueous secondary battery of the present invention is formed by dispersing a negative electrode active material, the above-described binder and other components in a solvent to form a slurry, which is applied to a current collector. The positive electrode in the non-aqueous secondary battery of the present invention is formed by dispersing a positive electrode active material, the above-described binder and other components in a solvent to form a slurry, which is applied to a current collector. As the solvent, an organic solvent such as alcohol or water can be used. If desired, the slurry may contain a conductive material. Examples of the conductive material include carbon black such as acetylene black, ketjen black, and furnace black, and fine powder made of Cu, Ni, or an alloy thereof having an average particle size of 1 μm or less. The amount of the conductive material added is usually 10% by mass or less with respect to the active material.

  A conventionally well-known thing can be used as a collector which apply | coats a slurry. Specific examples include metal thin films such as rolled copper foil, electrolytic copper foil, and stainless steel foil. The thickness of the current collector is usually 5 μm or more, preferably 9 μm or more, and usually 30 μm or less, preferably 20 μm or less. After apply | coating a slurry on a collector, it is normally dried at 60-200 degreeC, Preferably it is 80-195 degreeC in dry air or an inert atmosphere, and an active-physical property layer is formed.

  The thickness of the active material layer obtained by applying and drying the slurry is usually 5 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and usually 200 μm or less, preferably 100 μm or less, more preferably 75 μm or less. It is. If the active material layer is too thin, the practicality as a negative electrode or a positive electrode is lacking due to the balance with the particle size of the active material, and if it is too thick, it is difficult to obtain a sufficient Li occlusion / release function for high-density current values.

<Non-aqueous electrolyte secondary battery>
The electrode for a non-aqueous electrolyte secondary battery of the present invention is particularly suitable for use as a negative electrode for a non-aqueous electrolyte secondary battery. Hereinafter, a non-aqueous electrolyte secondary battery using this negative electrode will be described.

  The basic configuration of this non-aqueous electrolyte secondary battery is the same as that of a conventionally known non-aqueous electrolyte secondary battery. Usually, the positive electrode and the negative electrode are interposed through a porous membrane impregnated with the non-aqueous electrolyte. In the case. Therefore, the structure of the secondary battery according to the present invention is not particularly limited. For example, the secondary battery can be used in any form such as a coin-type battery, a cylindrical battery, and a square battery.

  The positive electrode is manufactured by slurrying an active material, a binder, and the like with a solvent, applying the mixture on a current collector, and drying in the same manner as the above-described negative electrode. The current collector for the positive electrode is not particularly limited, and aluminum, nickel, SUS or the like is used.

  The main component of the non-aqueous electrolyte solution is usually a lithium salt and a non-aqueous solvent that easily dissolves the lithium salt, as in known non-aqueous electrolyte solutions.

  As the non-aqueous solvent, any non-aqueous solvent conventionally proposed as a solvent for non-aqueous electrolytes can be appropriately selected and used. For example, chain carbonates such as ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain ethers such as 1,2-dimethoxyethane; tetrahydrofuran, Cyclic ethers such as 2-methyltetrahydrofuran, sulfolane and 1,3-dioxolane; chain esters such as methyl formate, methyl acetate and methyl propionate; cyclic esters such as γ-butyrolactone and γ-valerolactone It is done.

  These non-aqueous solvents may be used alone or in combination of two or more, but a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferred.

The lithium salt is not particularly limited as long as it is known to be usable in this application. For example, a halide such as LiCl or LiBr; a perhalogenate such as LiClO ₄ , LiBrO ₄ , or LiClO ₄ Inorganic lithium salts such as inorganic fluoride salts such as LiPF ₆ , LiBF ₄ and LiAsF ₆ ; perfluoroalkane sulfonates such as LiCF ₃ SO ₃ and LiC ₄ F ₉ SO ₃ ; Li trifluorosulfonimide ((CF ₃ And fluorine-containing organic lithium salts such as perfluoroalkanesulfonic acid imide salts such as SO ₂ ) ₂ NLi). Lithium salts may be used alone or in admixture of two or more.

  The concentration of the lithium salt in the non-aqueous electrolyte is usually about 0.5 to 2.0M.

  The nonaqueous electrolytic solution may contain an organic polymer compound in the electrolytic solution, and may be in the form of a gel, rubber, or solid sheet. Specific examples of organic polymer compounds include polyether polymer compounds such as polyethylene oxide and polypropylene oxide; cross-linked polymers of polyether polymer compounds; vinyl alcohol polymer compounds such as polyvinyl alcohol and polyvinyl butyral; vinyl Insoluble matter of alcohol-based polymer compound; polyepichlorohydrin; polyphosphazene; polysiloxane; vinyl-based polymer compound such as polyvinylpyrrolidone, polyvinylidene carbonate, polyacrylonitrile; poly (ω-methoxyoligooxyethylene methacrylate), poly (ω Examples thereof include polymer copolymers such as -methoxyoligooxyethylene methacrylate-methyl methacrylate) and poly (hexafluoropropylene-vinylidene fluoride).

  The nonaqueous electrolytic solution may contain a film forming agent. Examples of film forming agents include carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate, and methylphenyl carbonate; alkene sulfides such as ethylene sulfide and propylene sulfide; sultone compounds such as 1,3-propane sultone and 1,4-butane sultone; maleic acid Acid anhydrides such as anhydride and succinic anhydride are listed. The content of the film forming agent is usually 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, and most preferably 2% by mass or less with respect to the entire non-aqueous electrolyte solution. If the content of the film forming agent is too large, other battery characteristics such as an increase in initial irreversible capacity, low temperature characteristics, and deterioration in rate characteristics may be adversely affected.

  Further, as the nonaqueous electrolytic solution, a polymer solid electrolyte that is a conductor of an alkali metal cation such as lithium ion can be used. Examples of the polymer solid electrolyte include a polymer obtained by dissolving a Li salt in the above-described polyether polymer compound, and a polymer in which a polyether terminal hydroxyl group is substituted with an alkoxide.

  In order to prevent a short circuit, a porous separator such as a porous film or a nonwoven fabric is usually interposed between the positive electrode and the negative electrode. In this case, the electrolytic solution is used by impregnating a porous separator. As a material for the separator, polyolefin such as polyethylene and polypropylene; polyethersulfone and the like are used, and polyolefin is preferable.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples unless it exceeds the gist.

Example 1
1 part by weight of 1% by weight carboxymethylcellulose (CMC) aqueous solution and 0.5 part by weight of 50% by weight styrene by solid content with respect to 100 parts by weight of graphite coated with amorphous (d50 = 15 μm) -A butadiene rubber (SBR) dispersion was added, stirred and mixed, and 1 part by weight of colloidal calcium carbonate was further added thereto, followed by further stirring. After defoaming, the slurry was applied and dried on a copper thin film having a thickness of 20 μm to a dry film thickness of 11 mg / cm ² to obtain a negative electrode plate. This was rolled by a roll press to an electrode active material density of 1.6 g / cc to obtain a test specimen.

Example 2
A specimen was obtained in the same manner as in Example 1 except that spherical natural graphite particles were used in place of the amorphous coated graphite (d50 = 15 μm) in Example 1.

Example 3
A test body was obtained in the same manner as in Example 1 except that soft calcium carbonate was used instead of colloidal calcium carbonate in Example 1.

Comparative Example 1
A test body was obtained in the same manner as in Example 1 except that heavy calcium carbonate was not added in Example 1.

Comparative Example 2
A test body was obtained in the same manner as in Example 2 except that heavy calcium carbonate was not added in Example 2.

Comparative Example 3
A test specimen was obtained in the same manner as in Example 1 except that 1 part by weight of anhydrous silica having a diameter of 250 nm was added instead of heavy calcium carbonate in Example 1.

Comparative Example 4
Implemented except that 12.5% by weight of polyvinylidene fluoride (PVdF) dispersion in solid content was used in place of the carboxymethyl cellulose (CMC) aqueous solution and styrene-butadiene rubber (SBR) dispersion of Example 1. A test body was obtained in the same manner as in Example 1.

  Using the test bodies obtained in Examples 1 to 3 and Comparative Examples 1 to 4, the measurement was carried out by the measurement method described in the section <Battery Evaluation> below. The results are shown in Table 1.

<Battery evaluation>
(Plate strength)
The specimen was subjected to a scratch test using a continuous load type scratch tester manufactured by Heidon Co., Ltd., which was loaded with a zirconia scratch needle having a tip of 0.1 mmR. The test was an average of four measurements, and the “electrode strength” was the load (g) when the copper foil surface first appeared, that is, the minimum load (g) at which the copper foil surface appeared.

(3rd discharge capacity and irreversible capacity)
From the specimen, it was punched into a circle of 1.23 cm ² , using Li as the counter electrode, ethylene carbonate / ethyl methyl carbonate = 3/7 (volume ratio) as a solvent, and 1M LiPF ₆ electrolyte solution, polyethylene (PE) A half cell was created through a separator, and charged and discharged three times (three times) at a constant current density of 0.16 mA and an interelectrode potential of 0 to 1.5 V (vs. Li). The “irreversible capacity generated up to the third time” was measured. Each measured value was an average of 4 trials.

  As is clear from the results in Table 1, the electrode plate strength and irreversible capacity could be improved in those using the nonaqueous electrolyte secondary battery electrode of the present invention (Examples 1 to 3). . Further, the “third discharge capacity” was sufficiently large and had no problem.

  On the other hand, the non-aqueous electrolyte secondary battery electrodes of the present invention (Comparative Examples 1 to 4) were all inferior in electrode plate strength and large in irreversible capacity as compared with Examples.

  The non-aqueous electrolyte secondary battery using the electrode for the non-aqueous electrolyte secondary battery of the present invention is a very simple process and exhibits high initial charge / discharge efficiency, high electrode plate strength, and a small irreversible capacity. Useful for.

Claims (12)

  An electrode for a non-aqueous electrolyte secondary battery in which an active material layer containing an active material and a binder is formed on a current collector, the metal salt and ions of the metal salt as the binder And a water-soluble polymer that forms an intramolecular cross-linked structure or an inclusion compound, and a nonaqueous electrolyte secondary battery electrode.   2. The non-aqueous electrolyte solution according to claim 1, wherein the water-soluble polymer has a cellulose skeleton and, when coexisting with a metal salt, forms an intramolecular crosslinked structure or an inclusion compound with ions of the metal salt. Secondary battery electrode.   The water-soluble polymer is at least one selected from the group consisting of hydroxymethylcellulose, ethylcellulose, carboxymethylcellulose, agar, carrageenan, fercelan, pectin, starch, starch, mannan, curdlan, xanthan gum, Ernest gum and gelatin. The electrode for a non-aqueous electrolyte secondary battery according to claim 1 or claim 2.   The non-aqueous electrolysis according to any one of claims 1 to 3, wherein the metal salt contains a group 1A or group 2A carbonate, sulfate, nitrate, phosphate, oxalate or hydrochloride. Electrode for liquid secondary battery.   The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the metal salt is a salt of Li, Na, K, Mg, Ca, Sr or Ba.   The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the metal salt contains heavy calcium carbonate, light calcium carbonate, or colloidal calcium carbonate.   The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the binder further contains a rubber-based binder.   8. The rubber-based binder contains styrene / butadiene rubber, styrene / isoprene rubber, isoprene rubber, acrylonitrile / butadiene rubber, neoprene rubber, chloroprene rubber, butadiene rubber or ethylene / propylene / diene copolymer rubber. The electrode for non-aqueous electrolyte secondary batteries as described in 2.   The electrode for a non-aqueous electrolyte secondary battery according to claim 7 or 8, wherein the rubber-based binder has a styrene unit, and the metal salt acts as a filler for the rubber-based binder.   The active material is at least one selected from the group consisting of a carbon material, metal particles that can be alloyed with Li, and metal oxide particles that can be alloyed with Li. The electrode for a non-aqueous electrolyte secondary battery according to claim 9.   The electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 10, wherein the electrode is a negative electrode.   A nonaqueous electrolyte secondary battery using the electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 11.