JP6566622B2 - Thickening / stabilizing agent for electrode coating liquid of power storage device, coating liquid prepared using the thickening / stabilizing agent, electrode manufactured using the coating liquid, and power storage device using the electrode - Google Patents

Description

  The present invention relates to a thickener / stabilizer for an electrode coating solution of an electricity storage device, a coating solution prepared using the thickener / stabilizer, an electrode manufactured using the coating solution, and the electrode It relates to the electricity storage device used.

In recent years, a power storage device having a high voltage and a high energy density has been required as a power source for driving electronic devices. In particular, lithium ion secondary batteries, lithium ion capacitors, and the like are expected as power storage devices with high voltage and high energy density. Thus, the electrode used for an electrical storage device is normally manufactured by apply | coating and drying the mixture with an active material particle and a binder to the collector surface. Examples of the electricity storage device include a lithium ion secondary battery, an electric double layer capacitor, and a lithium ion capacitor.
These power storage devices are mainly composed of members such as electrodes, a non-aqueous electrolyte, and a normal separator. Among these, for the electrode for the electricity storage device, for example, the electrode mixture for the electricity storage device in which the battery active material and the conductive material are dispersed in an organic solvent or water together with the binder is applied onto the metal foil on the surface of the current collector and dried. Is formed. The characteristics of the electricity storage device are largely influenced by the main constituent materials such as the electrode active material, the electrolyte, and the current collector, but are also greatly affected by the binder and thickening stabilizer used as additives. It depends.

  The electrode mixture for an electricity storage device is mainly classified into an organic solvent-based binder in which a polymer is dissolved in an organic solvent and an aqueous binder in which a polymer is dissolved or dispersed in water. Particularly recently, an electrode mixture for an aqueous storage device using an aqueous binder has attracted attention because it can reduce the cost of manufacturing an electrode by using an organic solvent and can improve the environmental load and the working environment.

  However, since electrode active materials and conductive materials are usually highly hydrophobic, it is difficult to uniformly disperse them in an aqueous medium. If an electrode mixture with insufficient dispersion is used, the applicability to the current collector may deteriorate and the electrode may become non-uniform, or agglomerates may remain on the surface of the electrode, causing a short circuit. is there.

  The thickening stabilizer is added for the purpose of stabilizing the dispersion of the electrode active material and imparting viscosity suitable for application of the electrode coating solution. Conventionally, a water-soluble polymer is used as the thickening stabilizer, and among them, carboxymethylcellulose is used as a thickening stabilizer because of its excellent dispersion stability. (Patent Documents 1 and 2) However, this is not satisfactory, and a thickening stabilizer having further excellent dispersion stability is required for the purpose of improving battery performance.

  The electrode active material is dispersed by mixing an electrode active material, a thickening stabilizer, a dispersion medium, and other components to prepare an electrode coating solution. In this case, in order to increase the dispersibility of the electrode active material, it is preferable to use a mixer / disperser having a large dispersion capacity (Patent Document 3 and Patent Document 4). The conventionally known thickening stabilizers of this type cause the molecular chain breakage due to the shearing force of the mixer / disperser, resulting in a decrease in the viscosity of the electrode coating solution, resulting in a decrease in coating properties and a decrease in the stability of the electrode coating solution. was there.

  In Patent Document 5, streaky defects (streaks) are generated on the surface of the electrode coating liquid applied on the current collector substrate due to the undissolved carboxymethylcellulose in the electrode coating liquid. Describes the use of fine and water-soluble carboxymethylcellulose having a particle diameter of less than 50 μm in order to prevent defects such as streaks and pinholes from occurring in the electrode. However, undissolved carboxymethyl cellulose is not sufficiently removed, and defects such as streaks and pinholes may occur in the electrode.

JP 2011-192610 A JP 2010-238575 A JP 2010-279896 A International Publication No. 10/018771 International Publication No. 10/061871

  The present invention is excellent in dispersion stability of an electrode active material and a conductive material, does not cause a decrease in viscosity due to a stirring shear force during the dispersion process, is excellent in binding property and resistance to electrolytic solution, and has a streak ( It is an object of the present invention to provide a thickener / stabilizer for an electrode coating solution of an electricity storage device that does not cause defects such as streak) and pinholes.

That is, this invention relates to the invention hung up below.
[1] A thickener / stabilizer for an electrode coating solution of an electricity storage device containing cellulose fiber, wherein a carboxymethyl group is introduced into a hydroxyl group in the cellulose molecule of the cellulose fiber, and the degree of substitution is 0.01 Is 0.5 or less,
The cellulose has a crystal structure of type I and / or type II,
The aspect ratio of the cellulose fiber is 50 or more,
A thickener / stabilizer for an electrode coating solution of an electricity storage device, wherein the number average fiber width of the cellulose fibers is 2 nm or more and 500 nm or less.
[2] A coating solution composition for an electricity storage device containing the thickener / stabilizer for the electrode coating solution.
[3] As a preferred embodiment, the cellulose fiber content is 0.05 mass% or more and 5.00 mass% or less based on 100 mass parts of the solid content of the electrical storage device coating liquid composition. Liquid composition.
[4] An electrode for an electricity storage device produced using the coating solution composition for an electricity storage device.
[5] As a preferred embodiment, an electrode for an electricity storage device in which variation in the thickness direction of the active material density is within ± 5%.
[6] An electricity storage device using the electrode for an electricity storage device.

The thickener / stabilizer for the electrode coating liquid of the electricity storage device of the present invention has high dispersion stability, and since the electrode active material is uniformly dispersed, the obtained electricity storage device has high electron conductivity, Accordingly, the internal resistance is low, and the electrode manufactured with the coating solution is excellent in binding property and electrolytic solution resistance, so that the battery performance is enhanced.
Furthermore, since the thickener / stabilizer for electrode coating liquid of the electricity storage device of the present invention does not decrease the viscosity due to the stirring shear force even under strong mechanical dispersion conditions, dispersion under strong mechanical dispersion conditions is possible. As a result, the electrode active material can be uniformly dispersed. Moreover, since the viscosity can be maintained even after dispersion, an electrode coating solution excellent in coating property and storage stability can be obtained.

  Next, embodiments of the present invention will be described in detail.

The thickener / stabilizer for electrode coating solution of the electricity storage device of the present invention contains the following cellulose fiber.
A substituent is introduced into the hydroxyl group in the cellulose molecule, the degree of substitution is 0.01 or more and 0.5 or less,
The cellulose has a crystal structure of type I and / or type II,
The aspect ratio of the cellulose fiber is 50 or more,
The number average fiber width of the cellulose fibers is 2 nm or more and 500 nm or less.

  In the cellulose fiber, a substituent is introduced into a hydroxyl group in the cellulose molecule. The substituent is not particularly limited as long as it is a substituent that generates an ether bond with a hydroxyl group in the cellulose molecule. Specific examples include carboxymethyl group, methyl group, ethyl group, cyanoethyl group, hydroxyethyl group, hydroxypropyl group, ethylhydroxyethyl group, hydroxypropylmethyl group and the like. Of these, a carboxymethyl group is preferred.

  The degree of substitution represents the average value of the number of moles of substituents per mole of anhydroglucose unit.

  The degree of substitution is 0.01 or more and 0.5 or less, preferably 0.01 or more and 0.25 or less. When the degree of substitution is less than 0.01, it is difficult to defibrate the cellulose fiber, and when it exceeds 0.50, a part of the cellulose fiber is dissolved, resulting in poor dispersion stability of the electrode coating solution.

  The cellulose has a crystal structure of type I and / or type II. The cellulose has a crystal structure of type I and / or type II. For example, in a diffraction profile obtained by wide-angle X-ray diffraction image measurement, cellulose type I (diffraction angle 2θ = 14.8 °, 16.8 ° 22.6 °) or cellulose type II (diffractive angles 2θ = 12.1 °, 19.8 °, 22.0 °), which has a typical X-ray diffraction pattern.

  The aspect ratio of the cellulose fiber is 50 or more, more preferably 100 or more. When the aspect ratio is less than 50, there arises a problem that the dispersion stability of the electrode coating solution is deteriorated.

The aspect ratio of the cellulose can be measured, for example, by the following method, that is, a TEM image (magnification: magnification: cellulose is cast on a carbon film-coated grid that has been hydrophilized and then negatively stained with 2% uranyl acetate. The number average width of the short width and the number average width of the long width were observed. That is, the number average width of the shorter width and the number average width of the longer width are calculated according to the methods described above, and the aspect ratio is calculated according to the following formula (1) using these values. .

上記セルロース繊維の数平均繊維幅が２ｎｍ以上５００ｎｍ以下であるが、２ｎｍ以上２００ｎｍ以下であることがより好ましい。短幅の方の数平均幅が２ｎｍ未満であれば、電極塗工液の分散安定性が悪くなるという不具合が生じ、５００ｎｍを超える場合はセルロースが沈降するという不具合が生じる。

The number average fiber width of the cellulose fibers is 2 nm or more and 500 nm or less, and more preferably 2 nm or more and 200 nm or less. If the number average width of the shorter width is less than 2 nm, there is a problem that the dispersion stability of the electrode coating solution is deteriorated, and if it exceeds 500 nm, the problem that cellulose is precipitated occurs.

  The number average fiber width can be measured by the following method. That is, an aqueous dispersion of fine cellulose having a solid content of 0.05 to 0.1% by weight was prepared, and the dispersion was cast on a carbon film-coated grid that had been subjected to a hydrophilization treatment. (TEM) observation sample. In addition, when the fiber of a big fiber diameter is included, you may observe the scanning electron microscope (SEM) image of the surface cast on glass. Then, observation with an electron microscope image is performed at a magnification of 5000 times, 10000 times, or 50000 times depending on the size of the constituent fibers. At that time, an axis having an arbitrary vertical and horizontal image width is assumed in the obtained image, and the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers intersect the axis. Then, after obtaining an observation image that satisfies this condition, two random axes, vertical and horizontal, per image are drawn on this image, and the width of the fiber that intersects the axis is visually read. In this way, images of at least three non-overlapping surface portions are taken with an electron microscope and the width values of the fibers intersecting each other on two axes are read (thus, at least 20 × 2 × 3 = 120). Information on the width of The number average width of the short width and the long width is calculated from the data of the number average width of the fibers thus obtained.

  In order to obtain the cellulose fiber of the present invention, it is necessary to anion-modify the cellulose exemplified below using a known method. The following manufacturing method can be mention | raise | lifted as the example. Cellulose is used as a raw material, and the solvent is 3 to 20 times lower alcohol, specifically methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, etc. Use a mixture of two or more mixtures and water. In addition, the mixing ratio of a lower alcohol is 60-95 mass%. As the mercerizing agent, 0.5 to 20 times moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide is used per glucose residue of cellulose. Cellulose is formed by mixing cellulose, a solvent, and a mercerizing agent. The reaction temperature at this time is 0 to 70 ° C., preferably 10 to 60 ° C., and the reaction time is 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, the etherification reaction is carried out by adding 0.05 to 10.0 times mole of carboxymethylating agent per glucose residue. The reaction temperature at this time is 30 to 90 ° C., preferably 40 to 80 ° C., and the reaction time is 30 minutes to 10 hours, preferably 1 to 4 hours.

  The cellulose raw material of the present invention is a natural cellulose such as cellulose produced by microorganisms such as bleached or unbleached wood pulp, refined linter, and acetic acid bacteria, and cellulose is dissolved in some solvent such as a copper ammonia solution and a morpholine derivative. Examples include spun regenerated cellulose and fine cellulose that has been depolymerized by hydrolysis, alkali hydrolysis, enzymatic decomposition, explosion treatment, vibration ball mill treatment, or the like, or mechanically processed fine cellulose.

  The cellulose fiber of the present invention can be obtained by fibrillating an anion-modified cellulose with a high-pressure homogenizer or the like. A high-pressure homogenizer is a device that pressurizes a fluid with a pump and ejects it from a very delicate gap provided in a flow path. It is possible to emulsify, disperse, defibrate, grind, and make ultrafine particles by using total energy such as collision between particles and shear force due to pressure difference.

  The treatment conditions with the homogenizer of the present invention are not particularly limited, but the pressure conditions are 30 MPa or more, preferably 100 MPa or more, more preferably 140 MPa or more. In addition, prior to defibration / dispersion treatment with a high-pressure homogenizer, if necessary, pretreatment of anion-modified cellulose is performed using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer. Is also possible.

  The electrode coating liquid composition for an electricity storage device of the present invention contains the cellulose fiber as a thickener / stabilizer as a thickener / stabilizer.

  The cellulose content is preferably 0.05% by mass or more and 5.00% by mass or less, more preferably 0.2% by mass or more, with respect to 100% by mass of the solid content of the coating liquid composition for an electricity storage device. It is 2.0 mass% or less. When the cellulose content is less than 0.05% by mass, there is a problem that the dispersion stability is deteriorated, and when it exceeds 5.00% by mass, there is a problem that the internal resistance of the battery is increased.

  The electrode coating liquid composition for an electricity storage device of the present invention contains an electrode active material, a conductive agent, and a binder that binds them to a current collector according to the type of the electricity storage device used. Can do. Examples of the electricity storage device include known electricity storage devices, but are not particularly limited, and specific examples include a lithium secondary battery, an electric double layer capacitor, and a lithium ion capacitor. Hereinafter, the electrode active material, the conductive agent, and the binder that binds these to the current collector used in each power storage device will be described.

In the electricity storage device of the present invention, the positive electrode active material used for the positive electrode of the lithium secondary battery is not particularly limited as long as it can insert and desorb lithium ions. Examples include metal oxides such as CuO, Cu ₂ O, MnO ₂ , MoO ₃ , V ₂ O ₅ , CrO ₃ , MoO ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , CoO ₃ , LixCoO ₂ , LixNiO _2. , LixMn ₂ O ₄ , LiFePO ₄ and other complex oxides of lithium and transition metals, TiS ₂ , MoS ₂ , NbSe _{3 and} other metal chalcogenides, polyacene, polyparaphenylene, polypyrrole, polyaniline and other conductive polymers Compounds and the like.

Among these, a composite oxide of lithium and one or more selected from transition metals such as cobalt, nickel, and manganese, which is generally called a high voltage system, is preferable in terms of lithium ion release properties and high voltage. . Specific examples of the composite oxide of cobalt, nickel, manganese and lithium include LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNixCo (1-x) O ₂ , LiMnaNibCoc (a + b + c = 1) and the like. It is done. In addition, these lithium composite oxides doped with a small amount of elements such as fluorine, boron, aluminum, chromium, zirconium, molybdenum, iron, etc., or the surface of lithium composite oxide particles are made of carbon, MgO, Al ₂ O ₃ , those treated with SiO ₂ or the like can also be used. Two or more kinds of the positive electrode active materials can be used in combination.

As the negative electrode active material used for the negative electrode of the lithium secondary battery, any known active material can be used without particular limitation as long as it can insert / extract metallic lithium or lithium ions. For example, carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and graphitizable carbon can be used. In addition, metallic materials such as metallic lithium, alloys, tin compounds, lithium transition metal nitrides, crystalline metal oxides, amorphous metal oxides, silicon compounds, conductive polymers, etc. can be used. , Li ₄ Ti ₅ O ₁₂ , NiSi ₅ C _{6 and the} like.

  Among the electricity storage devices of the present invention, for example, an allotrope of carbon is usually used as an electrode active material used for an electrode for an electric double layer capacitor. Specific examples of the allotrope of carbon include activated carbon, polyacene, carbon whisker, and graphite, and these powders or fibers can be used. A preferred electrode active material is activated carbon, and specific examples include activated carbon made from phenol resin, rayon, acrylonitrile resin, pitch, coconut shell, and the like.

  The electrode active material used for the positive electrode of the lithium ion capacitor electrode may be any material that can reversibly carry lithium ions and anions such as tetrafluoroborate. Specifically, an allotrope of carbon is usually used, and electrode active materials used in electric double layer capacitors can be widely used.

  The electrode active material used for the negative electrode of the said lithium ion capacitor electrode is a substance which can carry | support a lithium ion reversibly. Specifically, electrode active materials used in the negative electrode of lithium ion secondary batteries can be widely used. Preferred examples include crystalline carbon materials such as graphite and non-graphitizable carbon, and polyacene-based materials (PAS) described as the positive electrode active material. These carbon materials and PAS are obtained by carbonizing a phenol resin or the like, activated as necessary, and then pulverized.

  A conductive agent is used as necessary in the electrode coating liquid composition for an electricity storage device of the present invention. Any electrically conductive material that does not adversely affect battery performance can be used as the conductive agent. Usually, carbon black such as acetylene black and ketchin black is used, but natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon whisker, carbon fiber and metal (copper, nickel, aluminum, A conductive material such as silver, gold, etc.) powder, metal fiber, or conductive ceramic material may be used. These can be included as a mixture of two or more. The addition amount is preferably 0.1 to 30% by weight, particularly preferably 0.2 to 20% by weight, based on the amount of the active material.

  Examples of the electrode binder used in the electrode coating liquid composition for the electricity storage device of the present invention include water-soluble and / or water-dispersible polymer compounds, such as polyvinylidene fluoride and polyfluoride. Polyvinylidene fluoride copolymer resins such as copolymers of vinylidene with hexafluoropropylene, perfluoromethyl vinyl ether and tetrafluoroethylene, fluorine resins such as polytetrafluoroethylene and fluororubber, styrene-butadiene rubber, ethylene- Polymers such as propylene rubber and styrene-acrylonitrile copolymer, and aqueous dispersions of resins such as polyurethane, polyacrylic acid, polyester, polyimide, polyamide, and epoxy can be used, but are not limited thereto. These binders may be used alone or in combination of two or more.

  Other thickening / stabilizing agents can be added to the electrode liquid coating composition for an electricity storage device of the present invention as long as the effects of the present invention are not hindered. As the thickener / stabilizer, known ones can be used and are not particularly limited. Specifically, hydroxymethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, etc. Celluloses; polycarboxylic acid compounds such as polyacrylic acid and polyacrylic acid soda; compounds having a vinylpyrrolidone structure such as polyvinylpyrrolidone; polyacrylamide, polyethylene oxide, polyvinyl alcohol, sodium alginate, xanthan gum, carrageenan, guar gum, One or more selected from agar, starch and the like can be used.

  The electrode of the electricity storage device of the present invention is produced using the coating solution composition for an electrode of the electricity storage device.

  The electrode of the electricity storage device of the present invention can be produced by a known method. Although not particularly limited, specifically, a slurry obtained by mixing a thickener / stabilizer for an electrode coating solution, an electrode active material, a conductive agent, a binder, and the like (hereinafter referred to as an electrode material). It can manufacture by preparing the electrode-shaped coating liquid composition for electrodes, apply | coating to the aluminum foil or copper foil etc. which become a collector, and volatilizing a dispersion medium.

  The method and order of mixing the electrode materials and the like are not particularly limited. For example, the active material and the conductive agent can be mixed in advance and used for mixing. In this case, the mortar, mill mixer, planetary type can be used. A ball mill such as a ball mill or a shaker type ball mill, a mechano-fusion, or the like can be used. Furthermore, since the viscosity-increasing / stabilizing agent of the present invention does not decrease in viscosity due to shear during mixing, a high-shear disperser such as a high-pressure homogenizer, an ultrahigh-pressure homogenizer, a high-speed rotating mixer, or a thin-film swirling disperser may be used. This further improves the dispersibility of the electrode active material.

  In the electrode of the electricity storage device of the present invention, the variation in the thickness direction of the active material density is preferably within ± 5%, more preferably within 4%. When the variation in the thickness direction of the active material density is more than ± 5%, the active material density in the electrode becomes non-uniform, which causes a problem that the electronic conductivity is adversely affected.

  In the present invention, the variation in the thickness direction of the active material density is measured by the following method. That is, the active material density distribution of the electrode cross section was measured with an electron beam probe microanalyzer (EPMA), and the variation in the thickness direction of the active material density was measured.

  The electricity storage device of the present invention is manufactured using an electrode of the electricity storage device.

  The power storage device of the present invention is manufactured using members generally used for power storage devices in addition to the electrodes of the power storage device. Specific examples include, but are not limited to, a current collector, a separator, an electrolytic solution, and an electrolyte salt.

  As the current collector of the electrode active material used in the electricity storage device of the present invention, any electronic conductor that does not adversely affect the constructed battery can be used. For example, as a positive electrode current collector, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc., in addition to aluminum for the purpose of improving adhesiveness, conductivity, and oxidation resistance. A material obtained by treating the surface of copper or copper with carbon, nickel, titanium, silver or the like can be used. In addition to the current collector for negative electrode, copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., adhesion, conductivity, oxidation resistance For the purpose of improving the properties, it is possible to use a surface of copper or the like treated with carbon, nickel, titanium, silver or the like. The surface of these current collector materials can be oxidized. Moreover, about the shape, molded bodies, such as a film form, a sheet form, a net form, the punched or expanded thing, a lath body, a porous body, and a foam other than foil shape, are also used. The thickness is not particularly limited, but a thickness of 1 to 100 μm is usually used.

  As the separator used in the electricity storage device of the present invention, a separator used in an ordinary electricity storage device can be used without any particular limitation. Examples thereof include porous resins made of polyethylene, polypropylene, polyolefin, polytetrafluoroethylene, ceramics, and the like. And non-woven fabric.

The electrolytic solution used for the electricity storage device of the present invention may be an electrolyte solution used for a normal electricity storage device, and common ones such as an organic electrolyte solution and an ionic liquid can be used.
Examples of the electrolyte salt used in the electricity storage device of the present invention include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCl, LiBr, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LII, LiAlCl ₄ , NaClO ₄ , NaBF ₄ , NaI and the like, in particular, inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (SO ₂ CxF2x + 1) (SO An organic lithium salt represented by ₂ CyF2y + 1) can be given. Here, x and y represent 0 or an integer of 1 to 4, and x + y is 2 to 8. Specifically, as the organic lithium salt, LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₅ ), LiN (SO ₂ CF ₃ ) (SO ₂ C ₃ F ₇ ) LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) (SO ₂ C ₃ F ₇ ), LiN (SO ₂ C ₂ F ₅ ) (SO ₂ C ₄ F ₉ ) and the like. Among them, it is preferable to use LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ or the like as the electrolyte because it has excellent electrical characteristics. The above electrolyte salt may be used alone or in combination of two or more. Such a lithium salt is usually contained in the electrolytic solution at a concentration of 0.1 to 2.0 mol / liter, preferably 0.3 to 1.5 mol / liter.

  The organic solvent for dissolving the electrolyte salt used in the electricity storage device of the present invention is not particularly limited as long as it is an organic solvent used in the nonaqueous electrolytic solution of the electricity storage device. For example, a carbonate compound, a lactone compound, an ether compound, sulfolane Examples include compounds, dioxolane compounds, ketone compounds, nitrile compounds, halogenated hydrocarbon compounds and the like. Specifically, carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol dimethyl carbonate, propylene glycol dimethyl carbonate, ethylene glycol diethyl carbonate, vinylene carbonate, lactones such as γ-butyl lactone, Ethers such as dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, sulfolanes such as sulfolane and 3-methylsulfolane, dioxolanes such as 1,3-dioxolane, 4-methyl-2- Ketones such as pentanone, nitriles such as acetonitrile, pyropionitrile, valeronitrile, benzonitrile, 1,2-di Halogenated hydrocarbons such as Roroetan, other methyl formate, dimethyl formamide, diethyl formamide, dimethyl sulfoxide, imidazolium salts, and ionic liquids such as such as quaternary ammonium salts. Furthermore, a mixture thereof may be used.

  Among these organic solvents, it is particularly preferable to contain one or more types of non-aqueous solvents selected from the group consisting of carbonates because they are excellent in electrolyte solubility, dielectric constant and viscosity.

In the electricity storage device of the present invention, when used for a polymer electrolyte or a polymer gel electrolyte, ethers, esters, siloxane, acrylonitrile, vinylidene fluoride, hexafluoropropylene, acrylate monomer, methacrylate monomer, styrene, which are polymer compounds, Examples thereof include polymers such as vinyl acetate, vinyl chloride, and oxetane, polymers having a copolymer structure thereof, and crosslinked products thereof, and the polymer may be one type or two or more types. The polymer structure is not particularly limited, but a polymer having an ether structure such as polyethylene oxide is particularly preferable.
As an electricity storage device of the present invention, a liquid battery is an electrolytic solution, a gel battery is a precursor solution in which a polymer is dissolved in an electrolytic solution, and a solid electrolyte battery is a polymer before crosslinking in which an electrolyte salt is dissolved in a battery container. To house.

  The electricity storage device according to the present invention can be formed in a cylindrical shape, a coin shape, a square shape, or any other shape, and the basic configuration of the battery is the same regardless of the shape, and the design is changed according to the purpose. can do. For example, in a cylindrical type, a wound body in which a negative electrode formed by applying a negative electrode active material to a negative electrode current collector and a positive electrode formed by applying a positive electrode active material to a positive electrode current collector are wound through a separator. It is housed in a battery can, sealed with a non-aqueous electrolyte injected, and insulating plates placed on top and bottom. When applied to a coin-type battery, the disc-shaped negative electrode, separator, disc-shaped positive electrode, and stainless steel plate are stacked and stored in a coin-type battery can, and a non-aqueous electrolyte is injected and sealed. .

Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples.
<Measurement method of substitution degree per glucose unit>
Cellulose fiber is prepared in a slurry of 0.6% by mass, 0.1M hydrochloric acid aqueous solution is added to adjust the pH to 2.4, and 0.05N sodium hydroxide aqueous solution is added dropwise until the pH reaches 11. The amount of carboxyl groups was measured from the amount of sodium hydroxide consumed in the neutralization step of the weak acid with a gradual change in electrical conductivity, and calculated using the following equation (2). The degree of substitution referred to here represents the average value of the number of moles of substituents per mole of anhydroglucose unit.

＜数平均繊維径の測定方法＞
セルロース繊維に水を加えて２質量％のスラリーとして、ディスパー型ミキサーを用いて回転数８，０００ｒｐｍで１０分間微細化処理を行った。各セルロース繊維の最大繊維径および数平均繊維径を、透過型電子顕微鏡（ＴＥＭ）（日本電子社製、ＪＥＭ−１４００）を用いて観察した。すなわち、各セルロース繊維を親水化処理済みのカーボン膜被覆グリッド上にキャストした後、２％ウラニルアセテートでネガティブ染色したＴＥＭ像（倍率：１００００倍）から、先に述べた方法に従い、数平均繊維径を算出した。

<Measurement method of number average fiber diameter>
Water was added to the cellulose fiber to make a slurry of 2 mass%, and a finer treatment was performed for 10 minutes at a rotation speed of 8,000 rpm using a disper type mixer. The maximum fiber diameter and the number average fiber diameter of each cellulose fiber were observed using a transmission electron microscope (TEM) (JEM-1400, manufactured by JEOL Ltd.). That is, after each cellulose fiber was cast on a hydrophilized carbon film-coated grid and negatively stained with 2% uranyl acetate, the number average fiber diameter was determined according to the method described above. Was calculated.

<Measurement method of crystal structure>
Using an X-ray diffractometer (Rigaku Corporation, RINT-Utima3), the diffraction profile of each cellulose fiber was measured, and cellulose I type (diffraction angle 2θ = 14.8 °, 16.8 °, 22.6 °). Alternatively, when a typical X-ray diffraction pattern is observed in cellulose type II (diffraction angle 2θ = 12.1 °, 19.8 °, 22.0 °), the crystal structure (type I and / or type II) is “ “No” was evaluated, and when no peak was observed, “No” was evaluated.

<Aspect ratio measurement method>
From the TEM image (magnification: 10000 times) that was negatively stained with 2% uranyl acetate after the cellulose was cast on a hydrophilic membrane-coated carbon film grid, the number average width and the long width of the short width of cellulose The number average width of was observed. That is, the number average width of the shorter width and the number average width of the longer width are calculated according to the methods described above, and the aspect ratio is calculated according to the following formula (1) using these values. .

＜セルロース繊維の製造＞
〔製造例１〕
撹拌機にパルプ（ＬＢＫＰ、日本製紙（株）製）を乾燥重量で２００ｇ、水酸化ナトリウムを１８ｇ加え、パルプ固形濃度が１５％になるように水を加えた。その後、３０℃で３０分攪拌した後に７０℃まで昇温し、モノクロロ酢酸ナトリウムを２３ｇ（有効成分換算）添加した。１時間反応した後に、反応物を取り出して中和、洗浄して、グルコース単位当たりの置換度０．０１のアニオン変性されたセルロースを得た。その後、アニオン変性したパルプを固形濃度１％とし、高圧ホモジナイザーにより、液温２０℃から冷却操作を伴いながら１４０ＭＰａの圧力で５回処理し、数平均繊維径９７nm、アスペクト比８１で、結晶構造を有するセルロース繊維１の水分散液を得た。

<Manufacture of cellulose fiber>
[Production Example 1]
To the stirrer, 200 g of dry pulp (LBKP, Nippon Paper Industries Co., Ltd.) and 18 g of sodium hydroxide were added, and water was added so that the pulp solid concentration was 15%. Then, after stirring for 30 minutes at 30 ° C., the temperature was raised to 70 ° C., and 23 g (in terms of active ingredient) of sodium monochloroacetate was added. After reacting for 1 hour, the reaction product was taken out, neutralized and washed to obtain anion-modified cellulose having a substitution degree of 0.01 per glucose unit. Thereafter, the anion-modified pulp was treated at a solid concentration of 1% and treated with a high-pressure homogenizer five times at a pressure of 140 MPa while being cooled from a liquid temperature of 20 ° C., with a number average fiber diameter of 97 nm and an aspect ratio of 81. An aqueous dispersion of cellulose fiber 1 was obtained.

[Production Example 2]
An aqueous dispersion of cellulose fiber 2 was obtained in the same manner as in Production Example 1, except that 176 g of sodium hydroxide and 234 g of sodium monochloroacetate (active ingredient conversion) were changed. In addition, the substitution degree per glucose unit of the obtained cellulose fiber was 0.10, the number average fiber diameter was 21 nm, the aspect ratio was 160, and it had a crystal structure.

[Production Example 3]
An aqueous dispersion of cellulose fiber 3 was obtained in the same manner as in Production Example 1, except that sodium hydroxide was changed to 308 g and sodium monochloroacetate was changed to 410 g (converted to active ingredients). In addition, the substitution degree per glucose unit of the obtained cellulose fiber was 0.25, the number average fiber diameter was 10 nm, the aspect ratio was 171 and had a crystal structure.

[Production Example 4]
An aqueous dispersion of cellulose fiber 4 was obtained in the same manner as in Production Example 1 except that sodium hydroxide was changed to 9 g and sodium monochloroacetate was changed to 12 g (in terms of active ingredient). In addition, the substitution degree per glucose unit of the obtained cellulose fiber was 0.005, the number average fiber diameter was 710 nm, the aspect ratio was 19, and it had a crystal structure.

[Production Example 5]
An aqueous dispersion of cellulose fiber 5 was obtained in the same manner as in Production Example 1, except that sodium hydroxide was changed to 476 g and sodium monochloroacetate was changed to 632 g (in terms of active ingredient). In addition, the substitution degree per glucose unit of the obtained cellulose was 0.60. When this was observed, a fibrous TEM image was not obtained, and the number average fiber diameter could not be measured. Moreover, it did not have a crystal structure.

[Production Example 6]
An aqueous dispersion of cellulose fiber 6 was obtained in the same manner as in Production Example 1 except that 308 g of sodium hydroxide, 410 g of sodium monochloroacetate (converted to active ingredient), and the treatment with the high-pressure homogenizer were changed to 20 times. In addition, the substitution degree per glucose unit of the obtained cellulose fiber was 0.25, and when this was observed, a fibrous TEM image was not obtained and the number average fiber diameter could not be measured. Moreover, it did not have a crystal structure.

[Production Example 7]
To a stirrer, 200 g of pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) in dry mass and 308 g of sodium hydroxide in dry mass were added, and water was added so that the pulp solid content concentration was 15%. Then, after stirring for 9 hours at 70 ° C., 410 g of sodium monochloroacetate (in terms of active ingredient) was added. After reacting for 1 hour, the reaction product was taken out, neutralized and washed to obtain anion-modified cellulose having a substitution degree of 0.28 per glucose unit. Thereafter, water was added to the anion-modified pulp to a solid content concentration of 1%, and the mixture was treated 5 times at a pressure of 140 MPa with a cooling operation from a liquid temperature of 20 ° C. with a high-pressure homogenizer to obtain a dispersion of cellulose fibers 7. It was. When this was observed, a fibrous TEM image was not obtained, and the number average fiber diameter could not be measured. Moreover, it did not have a crystal structure.

<Production of electrode>
[Negative electrode 1]
As a negative electrode active material, 100 g of natural graphite, 0.5 g of carbon black as a conductive agent (Super-P, manufactured by Timcal) and 50 g of a 1% by weight aqueous dispersion of cellulose fiber 1 as a thickener, and styrene / butadiene as a binder 4.0 g of a 50% by weight rubber aqueous dispersion (SBR) solution was mixed with a planetary mixer to prepare a negative electrode slurry so as to have a solid content of 50%. This negative electrode slurry was coated on an electrolytic copper foil having a thickness of 10 μm with a coating machine, dried at 120 ° C., and then subjected to a roll press treatment, to obtain a negative electrode 1 having a negative electrode active material of 7 mg / cm ² .

[Negative electrodes 2 to 21]
Negative electrodes 2 to 21 were obtained in the same manner as negative electrode 1 except that the types and addition amounts of the negative electrode active material, conductive agent, thickener, and binder were changed as shown in Table 1 below.

[Positive electrode 1]
100 g of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NMC) which is a positive electrode active material, 7.8 g of carbon black (manufactured by Timcal, Super-P) as a conductive agent, and cellulose fiber 1 as a thickener 1 g of an aqueous dispersion of 50 g and 4.0 g of a 50 wt% solution of styrene-butadiene rubber aqueous dispersion (SBR) as a binder are mixed with a planetary mixer, and the positive electrode slurry is mixed so that the solid content is 50%. Prepared. This positive electrode slurry was coated on a 20 μm-thick aluminum foil as a current collector with a coating machine, dried at 130 ° C., and then subjected to a roll press treatment to obtain a positive electrode having a positive electrode active material of 13.8 mg / cm ² . .

[Positive electrodes 2 to 20]
Production was performed in the same manner as in the positive electrode 1 except that the types and addition amounts of the negative electrode active material, the conductive agent, the thickener, the binder, and the current collector were changed as shown in Table 2, and positive electrodes 2 to 18 were obtained. .

<Evaluation of electrode>
The obtained electrode was evaluated for the following items. The evaluation results are shown in Tables 1 and 2 [Examples 1 to 24, Comparative Examples 1 to 17].

[Evaluation of binding properties]
After the coated surface of the electrode obtained above was bent 180 ° outward and returned, the extent of the area where the active material on the coated surface was removed was visually judged.
Evaluation criteria:
5 points: 0% dropout 4 points: 25% dropout 3 points: 50% dropout 2 points: 75% dropout 1 point: 100% dropout

[Electrolytic solution resistance evaluation]
The electrode obtained above was EC (ethylene carbonate) / PC (propylene carbonate) / DMC (dimethyl carbonate) / EMC (ethyl methyl carbonate) / DEC (diethyl carbonate) = 1/1/1/1/1 (vol). The appearance of the coating film after being immersed in the mixed solvent at 60 ° C. for 7 days was visually judged.
Evaluation criteria:
○: No change in the coating film Δ: Several points of swelling occur in the coating film ×: The coating film peels off.

[Presence / absence of aggregates]
The range of 5 cm × 5 cm of the electrode obtained above was observed, and the presence or absence of aggregates that could be visually confirmed was determined.
Evaluation criteria:
○: Aggregates cannot be confirmed. Δ: 1 to 5 aggregates can be confirmed.
X: Five or more aggregates can be confirmed.

[Evaluation of active material density variation]
The active material density distribution of the electrode cross section obtained above was measured with an electron beam probe microanalyzer (EPMA), and the variation in the thickness direction of the active material density was evaluated.
Evaluation criteria:
○: Within ± 5% △: Over ± 5% and less than 10% ×: ± 10% or more

[Stripes and presence of pinholes]
The range of 5 cm × 5 cm of the obtained electrode was observed, and the presence or absence of streaks and pinholes that could be visually confirmed was determined.
Evaluation criteria
○: Lines or pinholes cannot be confirmed
X: A streak or a pinhole can be confirmed

表１および表２より、セルロース繊維１ないし３を使用した電極は、活物質、結着剤等の部材によらず、各種評価項目（結着性、耐電解液性、凝集物、活物質密度バラツキ、スジピンホール）において良好な結果となった。これに対し、セルロース繊維４及び５を使用した場合は、各種評価項目においてセルロース繊維１ないし３に対して劣る結果となった。

From Table 1 and Table 2, the electrode using cellulose fibers 1 to 3 is not affected by members such as active materials and binders, but various evaluation items (binding properties, electrolytic solution resistance, aggregates, active material density) Good results were obtained for variations and stripe pinholes. On the other hand, when cellulose fibers 4 and 5 were used, the results were inferior to cellulose fibers 1 to 3 in various evaluation items.

<Production of lithium secondary battery>
[Examples 25 to 41, Comparative Examples 18 to 25]
The positive and negative electrodes obtained above are combined as shown in Table 3 below, and a polyolefin (PE / PP) separator is sandwiched between the electrodes as a separator, and the positive and negative terminals are ultrasonically welded to each positive and negative electrode. did. This laminate was put in an aluminum laminate packaging material, and heat sealed, leaving an opening for injection. The positive electrode area of 18cm ^2, to prepare a liquid injection before batteries with anode area 19.8cm ^2. Next, an electrolytic solution in which LiPF ₆ (1.0 mol / L) was dissolved in a solvent in which ethylene carbonate and diethyl carbonate (30/70 vol ratio) were mixed was poured, the opening was heat sealed, and an evaluation battery was prepared. Obtained.

<Evaluation of battery performance>
About the produced lithium secondary battery, the performance test in 20 degreeC was done. The test method is as follows. The test results are shown in Table 5.

[Cell impedance]
For the cell impedance, an impedance analyzer (manufactured by ZAHNER) was used to measure the resistance value at a frequency of 1 kHz.

[Charge / discharge cycle characteristics]
The charge / discharge cycle characteristics were measured under the following conditions.
When LiNi _1/3 Co _1/3 Mn _1/3 O ₂ or LiMn ₂ O ₄ is used as the positive electrode active material and natural graphite is used as the negative electrode active material, CC (constant current) up to 4.2 V at a current density equivalent to 1C. ) Charging, followed by switching to CV (constant voltage) charging at 4.2V, charging for 1.5 hours, and then performing a CC discharge to 2.7V at a current density equivalent to 1C for 300 cycles at 20 ° C. The 1C discharge capacity ratio after 300 cycles to the initial 1C discharge capacity at this time was defined as the 1C charge / discharge cycle retention rate.

When LiFePO ₄ is used as the positive electrode active material and natural graphite is used as the negative electrode active material, CC (constant current) charging is performed up to 4.0 V at a current density equivalent to 1 C, followed by CV (constant voltage) charging at 4.0 V. After charging for 1.5 hours, a cycle of CC discharge to 2.0 V at a current density equivalent to 1 C is performed 300 cycles at 20 ° C., and the 1 C discharge capacity ratio after 300 cycles to the initial 1 C discharge capacity at this time is 1 C The charge / discharge cycle retention rate was used.

When LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the positive electrode active material and Li ₄ Ti ₅ O ₁₂ is used as the negative electrode active material, CC (constant current) up to 2.9 V at a current density equivalent to 1C. Charge, then switch to CV (constant voltage) charge at 2.9V, charge for 1.5 hours, and then perform a cycle of CC discharge to 1.0V at a current density equivalent to 1C, 300 cycles at 20 ° C. The 1C discharge capacity ratio after 300 cycles with respect to the initial 1C discharge capacity was defined as the 1C charge / discharge cycle retention rate.

When LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the positive electrode active material and SiO is used as the negative electrode active material, CC (constant current) charging is performed up to 4.2 V at a current density equivalent to 1 C, and then After switching to CV (constant voltage) charging at 4.2V and charging for 1.5 hours, 50 cycles of CC discharge to 2.7V at a current density equivalent to 1C were performed at 20 ° C, and the initial 1C discharge at this time The 1C discharge capacity ratio after 50 cycles with respect to the capacity was defined as the 1C charge / discharge cycle retention rate.

表３より、セルロース繊維１ないし３を使用した負極及び正極を組み合わせたリチウム二次電池（実施例２５ないし４１）は、電池特性においてセルロース繊維４又は５を使用したリチウム二次電池（比較例１４ないし１９）に対し、セルインピーダンス及び容量保持率において優れていることが判明した

From Table 3, the lithium secondary battery (Examples 25 to 41) combining the negative electrode and the positive electrode using the cellulose fibers 1 to 3 (Examples 25 to 41) is a lithium secondary battery using the cellulose fibers 4 or 5 (Comparative Example 14). To 19), the cell impedance and the capacity retention were found to be excellent.

The thickening / stabilizing agent of the present invention can be used as a thickening / stabilizing agent for an electrode coating solution of an electricity storage device, and the electrodes produced therefrom are used for producing various electricity storage devices. The obtained power storage devices are used in various portable devices such as mobile phones, notebook computers, personal digital assistants (PDAs), video cameras, and digital cameras, as well as medium- or large-sized power storage devices installed in electric bicycles and electric vehicles. Can be used.

Claims (6)

A thickener / stabilizer for an electrode coating solution of an electricity storage device containing a cellulose fiber, wherein a carboxymethyl group is introduced into a hydroxyl group in the cellulose molecule of the cellulose fiber, and the degree of substitution is 0.01 or more and 0.00. 5 or less,
The cellulose has a crystal structure of type I and / or type II,
The aspect ratio of the cellulose fiber is 50 or more,
A thickener / stabilizer for an electrode coating solution of an electricity storage device, wherein the number average fiber width of the cellulose fibers is 2 nm or more and 500 nm or less.   A coating liquid composition for an electricity storage device, comprising the thickener / stabilizer for an electrode coating liquid according to claim 1.   3. The electricity storage device according to claim 2, wherein the content of the cellulose fiber is 0.05% by mass or more and 5.00% by mass or less with respect to 100% by mass of the solid content of the coating liquid composition for an electricity storage device. Coating liquid composition.   An electrode for an electricity storage device manufactured using the coating liquid composition for an electricity storage device according to claim 2.   The electrode for an electricity storage device according to claim 4, wherein the variation in the thickness direction of the active material density is within ± 5%. An electrical storage device using the electrode for an electrical device according to claim 4 or 5.