WO2023037556A1 - Electrode for energy storage devices, energy storage device, production method for electrode for energy storage devices, and material for forming electrode - Google Patents

Electrode for energy storage devices, energy storage device, production method for electrode for energy storage devices, and material for forming electrode Download PDF

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WO2023037556A1
WO2023037556A1 PCT/JP2021/033591 JP2021033591W WO2023037556A1 WO 2023037556 A1 WO2023037556 A1 WO 2023037556A1 JP 2021033591 W JP2021033591 W JP 2021033591W WO 2023037556 A1 WO2023037556 A1 WO 2023037556A1
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electrode
energy storage
storage device
active material
acrylonitrile
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PCT/JP2021/033591
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French (fr)
Japanese (ja)
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学 平澤
真代 堀川
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株式会社レゾナック
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present disclosure relates to an energy storage device electrode, an energy storage device, a method for manufacturing an energy storage device electrode, and an electrode forming material.
  • Energy storage devices are widely used in which charge and discharge are performed by moving alkali metal ions such as lithium ions between the positive and negative electrodes.
  • the positive and negative electrodes of such energy storage devices generally contain particles of a material (active material) capable of absorbing and releasing alkali metal ions, and a binder for binding the particles of the active material.
  • the binder for the active material is required to be flexible enough to follow the volume change of the active material. For this reason, polymer compounds are mainly used as binders.
  • binders for active materials in addition to commonly used polymer compounds such as polyvinylidene fluoride and styrene-butadiene rubber, the application of polymer compounds with electronic conductivity is expected to increase the capacity of energy storage devices. being considered.
  • JP-A-2019-535116 proposes the use of polyacrylonitrile in which a cyclization reaction has occurred (cyclized polyacrylonitrile) as an electrode of an energy storage device.
  • heating to cause the cyclization reaction of polyacrylonitrile may affect the properties of the electrode.
  • an object of the present disclosure is to provide an electrode for an energy storage device that exhibits excellent properties even after heating, an energy storage device, a method for manufacturing an electrode for an energy storage device, and an electrode-forming material.
  • Means for solving the above problems include the following embodiments.
  • ⁇ 1> Contains particles containing a substance capable of absorbing and releasing alkali metal ions, and a binder containing cyclized polyacrylonitrile, wherein the cyclized polyacrylonitrile is a copolymer of acrylonitrile and a polymer component other than acrylonitrile.
  • An electrode for an energy storage device which is a cyclized product of ⁇ 2>
  • ⁇ 3> The electrode for an energy storage device according to ⁇ 1> or ⁇ 2>, wherein the copolymer contains an anionic group.
  • an electrode for an energy storage device comprising a step of heat-treating a composition containing particles containing a substance capable of absorbing and releasing alkali metal ions and a copolymer of acrylonitrile and a polymer component other than acrylonitrile Method.
  • a material for forming an electrode of an energy storage device comprising a copolymer of acrylonitrile and a polymerization component other than acrylonitrile.
  • an energy storage device electrode an energy storage device, a method for producing an energy storage device electrode, and an electrode-forming material that exhibit excellent properties even after heating are provided.
  • FIG. 4 is a scanning electron microscope image of the surface of the electrode produced in Example 1.
  • FIG. 4 is a scanning electron microscope image of the surface of the electrode produced in Comparative Example 1.
  • FIG. 4 is a scanning electron microscope image of the surface of the electrode produced in Comparative Example 1.
  • process includes a process that is independent of other processes, and even if the purpose of the process is achieved even if it cannot be clearly distinguished from other processes. .
  • the numerical range indicated using “ ⁇ ” includes the numerical values before and after “ ⁇ ” as the minimum and maximum values, respectively.
  • the upper limit or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described step by step.
  • the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
  • each component may contain multiple types of applicable substances.
  • the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition unless otherwise specified. means quantity.
  • a plurality of types of particles corresponding to each component in the present disclosure may be included.
  • the particle size of each component means a value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
  • the term "layer” includes not only the case where the layer is formed in the entire region when observing the region where the layer exists, but also the case where it is formed only in part of the region. included.
  • the energy storage device electrode of the present disclosure includes particles containing a substance capable of occluding and releasing alkali metal ions (hereinafter also referred to as active material particles) and a binder containing cyclized polyacrylonitrile.
  • Polyacrylonitrile polyacrylonitrile is an electrode for energy storage devices (hereinafter also referred to as electrode) which is a cyclized product of a copolymer of acrylonitrile and a polymerization component other than acrylonitrile (hereinafter also referred to as copolymer component).
  • particles containing a substance capable of absorbing and releasing alkali metal ions may be referred to as active material particles
  • polymerized components other than acrylonitrile may be referred to as copolymer components
  • electrodes for energy storage devices may be referred to as electrodes.
  • the ring closure reaction between adjacent nitrile groups contained in polyacrylonitrile is an exothermic reaction. Since this exothermic reaction progresses abruptly at around 293°C, the temperature in the reaction system rises sharply at around 293°C. As a result, the formation and volatilization of low-molecular-weight by-products due to scission of the molecular chains of polyacrylonitrile rapidly proceed.
  • a copolymerization component is introduced into polyacrylonitrile, the amount of nitrile groups is relatively reduced and the ring closure reaction occurs at a lower temperature (for example, around 278° C.), suppressing rapid heat generation. As a result, the formation and volatilization of low-molecular-weight by-products are suppressed, and the residual amount of cyclized polyacrylonitrile increases.
  • the ring closure reaction of nitrile groups includes those that occur intramolecularly and those that occur intermolecularly.
  • the intramolecular ring-closure reaction of nitrile groups is relatively reduced, and the intermolecular ring-closure reaction of nitrile groups is relatively increased.
  • formation of a three-dimensional crosslinked structure of the cyclized polyacrylonitrile is promoted.
  • a copolymerization component having an ionic functional group when introduced into polyacrylonitrile, in addition to the radical polymerization reaction between adjacent nitrile groups, an ionic polymerization reaction also occurs between the ionic functional group and the nitrile group. resulting in binding of the molecular chains. Ionic polymerization reactions proceed at lower temperatures than radical polymerization reactions. As a result, the formation and volatilization of low-molecular-weight by-products are suppressed, and the residual amount of cyclized polyacrylonitrile increases.
  • the binder contains cyclized polyacrylonitrile.
  • cyclized polyacrylonitrile means a material obtained by causing a cyclization reaction of polyacrylonitrile (that is, a cyclized product of polyacrylonitrile).
  • Characterization of the above reaction can be performed by infrared spectroscopy.
  • Infrared spectroscopy may be transmission or reflection.
  • a peak at 2939 cm ⁇ 1 for —CH 2 — before forming a double bond, and a peak at 806 cm ⁇ 1 for a —CH ⁇ C— group after forming a double bond by dehydrogenation can be confirmed.
  • the cyclized polyacrylonitrile can be said to have properties intermediate between those of carbon and polymers, and the greater the degree of ring closure of the nitrile group, the more similar the properties of the cyclized polyacrylonitrile to those of carbon.
  • this absorbance ratio is also referred to as absorbance ratio A.
  • the absorbance ratio A is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more.
  • the resulting binder has moderate flexibility and easily follows the expansion and contraction of the active material.
  • the absorbance ratio A is preferably 6 or less, more preferably 3 or less, and even more preferably 1 or less.
  • the absorbance ratio A is 6 or less, the structure of the binder obtained by sufficiently ring-closing the nitrile groups becomes strong.
  • Cyclized polyacrylonitrile can be said to be a polymer that has been given electronic conductivity through a cyclization reaction.
  • this absorbance ratio is also referred to as absorbance ratio B.
  • the absorbance ratio B is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more.
  • the resulting binder exhibits sufficient electronic conductivity.
  • the upper limit of the absorbance ratio B is not particularly limited, it may be 1 or less, for example.
  • the cyclized polyacrylonitrile itself has various bonding species, so each peak tends to overlap with other peaks, so it is preferable to draw a baseline for calculation.
  • a method of drawing by connecting the tails of both ends of the target peak can be exemplified.
  • the absorbance ratio in infrared spectroscopy is a mixture of cyclized polyacrylonitrile and active material (provided that the active material is catalytic to the cyclization and decomposition reactions of polyacrylonitrile), even if the measurement target is only cyclized polyacrylonitrile. A similar tendency is confirmed even in the state of the electrode combined with the current collector. Therefore, the absorbance ratio may be calculated in the state where the object to be measured is a mixture of cyclized polyacrylonitrile and an active material or an electrode in combination with a current collector.
  • the cyclized polyacrylonitrile preferably contains an acridone structure.
  • the acridone structure is the ring structure shown below (the wavy line indicates the binding site) generated during the cyclization reaction of polyacrylonitrile.
  • the cyclized polyacrylonitrile containing the acridone structure can be obtained by performing a heat treatment that causes a cyclization reaction of the polyacrylonitrile in an oxygen-containing environment.
  • cyclized polyacrylonitrile has an acridone structure
  • pyrolysis GC/MS analysis Panolysis Gas Chromatography Mass Spectrometry
  • known techniques for X-ray photoelectron spectrum analysis The presence of the acridone structure can be confirmed by a fragment of mass 177 in pyrolysis GC/MS analysis and by a peak around 532 eV in X-ray photoelectron spectroscopy.
  • the cyclized polyacrylonitrile contained in the binder is a cyclized product of a copolymer of acrylonitrile and a polymerization component other than acrylonitrile (hereinafter also referred to as an acrylonitrile copolymer).
  • the polymerization components other than acrylonitrile that constitute the acrylonitrile copolymer are not particularly limited.
  • it may be selected from polymer components having at least one functional group selected from the group consisting of a sulfo group, a carboxy group, an amino group and an alkyl ester group.
  • a sulfo group in the present disclosure is a monovalent group represented by —SO 3 H.
  • the sulfo group may form a salt with an alkali metal such as sodium.
  • a carboxy group in the present disclosure is a monovalent group represented by —COOH.
  • an amino group is a monovalent group represented by —NR 1 R 2 , where R 1 and R 2 are each independently a hydrogen atom or a monovalent organic group.
  • an alkyl ester group is a monovalent group represented by -COOR, and R is an alkyl group.
  • the number of carbon atoms in the alkyl group is preferably 1-15, more preferably 1-5, even more preferably 1-3.
  • Polymerization components containing a sulfo group include allylsulfonic acid, methallylsulfonic acid, vinylbenzenesulfonic acid, and alkali metal salts thereof.
  • Polymerization components containing a carboxy group include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, and alkali metal salts thereof.
  • Polymerization components containing amino groups include acrylamide, methacrylamide, dimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamide, and the like.
  • polymerizable components containing an alkyl ester group examples include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, and n-methacrylate. butyl, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate and the like.
  • Polymerization components other than the above include vinyl acetate, styrene, vinylidene chloride, and vinyl chloride.
  • the acrylonitrile copolymer preferably contains an ionic group such as a sulfo group, a carboxyl group and an amino group, and may contain an anionic group such as a sulfo group and a carboxyl group. More preferably, it has a sulfo group.
  • An acrylonitrile copolymer containing an ionic group can be obtained by using a polymerization component containing an ionic group as a polymerization component other than acrylonitrile.
  • the proportion of the polymerized components other than acrylonitrile in the acrylonitrile copolymer to the total polymerized components is preferably 0.1% by mass or more, and is 0.2% by mass or more. is more preferable, and 0.5% by mass or more is even more preferable.
  • the ratio of the polymer components other than acrylonitrile in the acrylonitrile copolymer to the total polymer components is preferably 20% by mass or less, and is 15% by mass or less. is more preferable, and 10% by mass or less is even more preferable.
  • the molecular weight of the acrylonitrile copolymer is not particularly limited, but the weight average molecular weight is preferably 5,000 to 3,000,000, more preferably 10,000 to 1,000,000. When the weight average molecular weight of the acrylonitrile copolymer is 5,000 or more, a good binder can be obtained. becomes easier.
  • the acrylonitrile copolymer may be an atactic type in which the nitrile group has no stereoregularity or an isotactic type with stereoregularity, but the isotactic type is preferred.
  • the degree of crystallinity of the acrylonitrile copolymer is high and the molecules are easily oriented. Therefore, there is a tendency to exhibit sufficient strength to withstand volume changes of the active material. In addition, a cyclization reaction easily occurs, and sufficient electron conductivity can be imparted.
  • Japanese Patent Publication No. 7-103189 can be referred to as a method for producing an isotactic type acrylonitrile copolymer.
  • the electrode of the present disclosure may contain a binder other than cyclized polyacrylonitrile as a binder.
  • Binders other than cyclized polyacrylonitrile include polyacrylic acid, polyvinyl acetate, polystyrene, polyvinylidene chloride, polyvinyl chloride, and polymethacrylic acid.
  • the proportion of the cyclized polyacrylonitrile in the entire binder is preferably 70% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and 90% by mass to 100% by mass. is more preferred.
  • the content of the binder contained in the electrode is preferably 10% by mass or more, more preferably 20% by mass or more, of the entire electrode (excluding the current collector). More preferably, it is 30% by mass or more.
  • the content of the binder contained in the electrode is preferably 50% by mass or less, more preferably 45% by mass or less, and 40% by mass or less of the entire electrode (excluding the current collector). is more preferred.
  • the active material particles contained in the electrode of the present disclosure are not particularly limited as long as they contain a material (active material) that can occlude and release alkali metal ions.
  • the active material particles contained in the electrode may be of one type or a combination of two or more types.
  • Alkali metal ions include lithium ions, potassium ions, sodium ions, and the like. Among these, lithium ion is preferred.
  • positive electrode active materials include lithium transition metal compounds such as lithium transition metal oxides and lithium transition metal phosphates.
  • Lithium transition metal oxides include compounds containing one or more of transition metals such as Mn, Ni, Co, etc., and some of the transition metals contained in these compounds, one or more of them or a lithium transition metal oxide substituted with a metal element (typical element) such as Mg or Al.
  • negative electrode active materials include carbon materials and active materials containing silicon atoms.
  • Carbon materials include graphite, hard carbon, and soft carbon.
  • active materials containing silicon atoms include Si (metallic silicon) and silicon oxides represented by SiOx (0.8 ⁇ x ⁇ 1.5).
  • the silicon oxide may have a structure in which nano-silicon is dispersed in a silicon oxide matrix by a disproportionation reaction.
  • the active material containing silicon atoms may be doped with boron, phosphorus, or the like to make it a semiconductor.
  • the active material particles may include active material particles made of a carbon material and having silicon present on the surface thereof.
  • Examples of methods for making silicon exist on the surface of active material particles made of a carbon material include a vapor deposition method and a plasma CVD (Chemical Vapor Deposition) method.
  • the plasma CVD method may be performed by decomposing raw materials such as silane and chlorosilane.
  • Active materials containing silicon atoms have a large theoretical capacity and are expected to contribute to increasing the capacity of energy storage devices. In addition, active materials containing silicon atoms themselves are not electronically conductive.
  • the cyclized polyacrylonitrile used as a binder in the electrode of the present disclosure has both sufficient flexibility and electronic conductivity to accommodate changes in the volume of the active material. Therefore, it can be particularly suitably used as a binder for active material particles containing silicon atoms.
  • the shape of the active material particles is not particularly limited.
  • it may be spherical, wire-shaped, scaly, massive, composite particles composed of a plurality of particles, or the like.
  • the volume average particle diameter (D50) of the active material particles is preferably 1 ⁇ m to 50 ⁇ m, more preferably 3 ⁇ m to 30 ⁇ m.
  • D50 volume average particle diameter of the active material particles
  • preparation of the slurry for forming the electrode is facilitated.
  • the volume average particle size of the active material particles is 50 ⁇ m or less, the electrode can be easily formed into a thin film, and the input/output characteristics of the energy storage device can be easily improved.
  • the volume average particle size of the active material particles is measured by a laser scattering diffraction method.
  • the volume-average particle diameter is defined as the particle diameter when the accumulation from the small diameter side is 50% in the volume-based particle diameter distribution obtained by the laser scattering diffraction method.
  • the volume average particle size is the volume average particle size of the secondary particles.
  • secondary particle means a particle that is the smallest unit of normal behavior formed by agglomeration of a plurality of primary particles
  • primary particle means that it can exist alone. It means the smallest unit particle that can be made.
  • the particle size of the primary particles that make up the secondary particles is not particularly limited.
  • the average primary particle size is preferably 10 nm to 50 ⁇ m. More preferably, it is 30 nm to 10 ⁇ m.
  • the average primary particle size of the active material particles is 10 nm or more, the influence of the natural oxide film formed on the surface can be suppressed.
  • the average primary particle size of the active material particles is 50 ⁇ m or less, deterioration due to charging and discharging is suppressed.
  • the primary particle diameter of the active material means the major diameter of the primary particles observed with a scanning electron microscope. Specifically, when the primary particles are spherical, it means the maximum diameter, and when the primary particles are tabular, it means the maximum diameter or maximum diagonal length in the projected image of the particles observed from the thickness direction. "Average primary particle diameter” is the arithmetic mean value of the measured values of the major diameters of 300 or more primary particles observed with a scanning electron microscope.
  • the active material particles are wire-shaped, there is no particular limit to their length. For example, it is preferably 10 nm to 10 ⁇ m. When the length of the wire-shaped active material particles is 10 nm or more, the handleability is improved, and when the length is 10 ⁇ m or less, stress during expansion of the active material particles tends to be easily dispersed.
  • the diameter of wire-like particles is preferably 1 nm to 5 ⁇ m.
  • the wire-shaped active material particles may contain a catalyst component for forming the wire-shaped active material particles. Specific examples of the wire-shaped active material particles include metallic silicon particles.
  • the method for adjusting the particle size of the active material particles is not particularly limited. Examples thereof include a method of selecting raw materials, a method of adjusting pulverization conditions, a vapor deposition method, a plasma method, and a method of surface treatment with silane or the like.
  • the BET specific surface area of the active material particles is preferably 0.5 m 2 /g to 100 m 2 /g, more preferably 1 m 2 /g to 30 m 2 /g.
  • the BET specific surface area of the active material particles is 0.5 m 2 /g or more, sufficient discharge capacity can be easily obtained.
  • the BET specific surface area of the active material particles is 100 m 2 /g or less, the handling property during electrode production is excellent.
  • the BET specific surface area of the active material particles can be calculated from the nitrogen adsorption isotherm at -196°C.
  • the active material particles may have a coating on their surfaces.
  • the active material particles may have a coating (carbon coating) made of a carbon material.
  • a coating carbon coating
  • electronic conductivity can be imparted to active material particles that do not have electrical conductivity.
  • the material of the carbon material is not particularly limited, and may be graphite or amorphous carbon.
  • the carbon material contained in the coating may be obtained by carbonizing an organic compound.
  • organic compounds include tar, pitch, and organic polymer compounds.
  • organic polymer compounds include polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, starch, and cellulose.
  • An embodiment of the electrode may include active material particles containing silicon and active material particles made of a carbon material.
  • the ratio of the active material particles containing silicon and the active material particles made of a carbon material is not particularly limited, but the ratio of the active material particles containing silicon is 5% by mass to 90% by mass of the total active material particles. is preferred, and 10% by mass to 70% by mass is more preferred.
  • the capacity of the energy storage device can be sufficiently increased.
  • the ratio of the active material particles containing silicon is 90% by mass or less of the entire active material particles, it is possible to sufficiently suppress the deterioration of the electrode due to the volume change of the active material.
  • the content of the active material particles contained in the electrode is preferably 50% by mass or more of the entire electrode (excluding the current collector), and is 55% by mass or more. is more preferable, and 60% by mass or more is even more preferable.
  • the content of the active material particles contained in the electrode is preferably 95% by mass or less of the entire electrode (excluding the current collector), and 90% by mass or less. and more preferably 80% by mass or less.
  • the electrodes may contain a conductive aid.
  • conductive aids include carbon materials such as carbon black, carbon nanotubes, carbon nanofibers, fullerenes and carbon nanohorns, conductive oxides, and conductive nitrides.
  • the content is not particularly limited, and may be 1% by mass to 20% by mass of the entire electrode (excluding the current collector).
  • the electrode may be in a state in which a layer containing active material particles, a binder, and optionally a conductive aid is formed on a current collector.
  • the type of current collector is not particularly limited, and metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel can be used.
  • the current collector may be carbon-coated, surface-roughened, or the like.
  • the electrode 10 shown in FIG. 1 is in a state in which a layer containing active material particles 2 and a binder 3 is formed on a current collector 1 .
  • the electrode 11 shown in FIG. 2 is a modification of the electrode 10 shown in FIG. is in a state.
  • Electrode 12 shown in FIG. 3 is a modification of electrode 10 shown in FIG. 1, and active material particles 2 have carbon coating 5 .
  • the energy storage device of the present disclosure comprises the electrodes of the present disclosure as described above.
  • the type of energy storage device is not particularly limited. Examples thereof include devices such as lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries, which utilize movement of alkali metal ions between electrodes for charging and discharging.
  • the energy storage device of the present disclosure is composed of a positive electrode, a negative electrode, an electrolytic solution, and the like.
  • the energy storage device electrode described above may be a positive electrode or a negative electrode, but is preferably a negative electrode.
  • organic solvents, ionic liquids, etc. in which electrolyte salts are dissolved can be used.
  • the ionic liquid include ionic liquids that are liquid at a temperature of less than 170° C., solvated ionic liquids, and the like.
  • electrolyte salts include LiPF 6 , LiClO 4 , LiBF 4 , LiClF 4 , LiAsF 6 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiN(FSO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiN( Lithium salts that generate poorly solvated anions such as C 2 F 5 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 , LiCl, and LiI are included.
  • electrolyte salt Only one electrolyte salt may be used, or two or more electrolyte salts may be used.
  • the electrolyte salt concentration in the electrolytic solution is, for example, preferably 0.3 mol or more, more preferably 0.5 mol or more, and even more preferably 0.8 mol or more per 1 L of the electrolytic solution.
  • the electrolyte salt concentration in the electrolytic solution is, for example, preferably 5 mol or less, more preferably 3 mol or less, and even more preferably 1.5 mol or less per 1 L of the electrolytic solution.
  • organic solvents include carbonates (propylene carbonate, ethylene carbonate, diethyl carbonate, etc.), lactones ( ⁇ -butyrolactone, etc.), chain ethers (1,2-dimethoxyethane, dimethyl ether, diethyl ether, etc.), Cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, diglyme, triglyme, tetraglyme, etc.), sulfolanes (sulfolane, etc.), sulfoxides (dimethylsulfoxide, etc.), nitriles (acetonitrile, propionitrile, etc.) , benzonitrile, etc.), amides (N,N-dimethylformamide, N,N-dimethylacetamide, etc.), polyoxyalkylene glycols (diethylene glycol, etc.), and other aprotic solvents (t
  • Only one type of organic solvent may be used, or two or more types may be used.
  • the cation part that constitutes the ionic liquid may be either an organic cation or an inorganic cation, but is preferably an organic cation.
  • organic cations that make up the ionic liquid include imidazolium cations, pyridinium cations, pyrrolidinium cations, phosphonium cations, ammonium cations, and sulfonium cations.
  • the anion part constituting the ionic liquid may be either an organic anion or an inorganic anion.
  • organic anions constituting the ionic liquid include alkyl sulfate anions such as methyl sulfate anion (CH 3 SO 4 ⁇ ) and ethyl sulfate anion (C 2 H 5 SO 4 ⁇ ); tosylate anion (CH 3 C 6 H 4 SO 3 ⁇ ); alkanesulfonate anions such as methanesulfonate anion (CH 3 SO 3 ⁇ ), ethanesulfonate anion (C 2 H 5 SO 3 ⁇ ), butanesulfonate anion (C 4 H 9 SO 3 ⁇ ); romethanesulfonate anion (CF 3 SO 3 ⁇ ), pentafluoroethanesulfonate anion (C 2 F 5 SO 3 ⁇ ), heptafluoropropanesulfonate anion (C 3 H 7 SO 3 ⁇ ), nonafluorobutanesulfonate anion (C 4 H 9 SO 3
  • Specific inorganic anions constituting the ionic liquid include bis(fluorosulfonyl)imide anion (N(SO 2 F) 2 ⁇ ); bis(trifluorosulfonyl)imide anion (N(SO 2 CF 3 ) 2 ⁇ ).
  • hexafluorophosphate anion PF 6 ⁇
  • tetrafluoroborate anion BF 4 ⁇
  • halide anions such as chloride ion (Cl ⁇ ), bromide ion (Br ⁇ ), iodide ion (I ⁇ ); tetrachloro aluminate anion (AlCl 4 ⁇ ); thiocyanate anion (SCN ⁇ ); and the like.
  • ionic liquids include those composed of a combination of any of the above cation moieties and any of the above anion moieties.
  • the ionic liquid whose cation moiety is an imidazolium cation include 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3 -methylimidazolium chloride, 1-ethyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium methanesulfonate, 1,2,3-trimethylimidazolium methylsulfate, methylimidazolium chloride, methylimid
  • ionic liquids in which the cation portion is a pyrrolidinium cation include 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) ) imide and the like.
  • solvated ionic liquids examples include glyme-lithium salt complexes.
  • lithium salt in the glyme-lithium salt complex examples include lithium bis(fluorosulfonyl)imide (LiN(SO 2 F) 2 , sometimes abbreviated as “LiFSI” in the present disclosure), lithium bis(trifluoro romethanesulfonyl)imide (LiN(SO 2 CF 3 ) 2 , sometimes abbreviated as “LiTFSI” in the present disclosure), and the like.
  • glyme in the glyme-lithium salt complex examples include triethylene glycol dimethyl ether (CH 3 (OCH 2 CH 2 ) 3 OCH 3 , triglyme), tetraethylene glycol dimethyl ether (CH 3 (OCH 2 CH 2 ) 4 OCH 3 , tetraglyme) and the like.
  • a glyme-lithium salt complex can be prepared, for example, by mixing a lithium salt and glyme so that the lithium salt:glyme (molar ratio) is preferably 10:90 to 90:10.
  • the electrolyte may contain additives.
  • additives include fluoroethylene carbonate, propanesultone, vinylene carbonate, methanesulfonic acid, cyclohexylbenzene, tert-amylbenzene, adiponitrile, and succinonitrile.
  • the amount of the additive in the electrolytic solution is, for example, preferably 0.1% by mass to 30% by mass, preferably 0.5% by mass to 10% by mass, based on the total amount of the electrolytic solution.
  • the energy storage device may further comprise commonly used members such as separators, gaskets, sealing plates, and cases in addition to the electrodes and electrolyte.
  • the separator used in the energy storage device is not particularly limited, and examples include polyolefin-based porous membranes such as porous polypropylene nonwoven fabrics and porous polyethylene nonwoven fabrics.
  • the shape of the energy storage device can be any shape, such as cylindrical, square, and button.
  • the method for producing an electrode for an energy storage device of the present disclosure includes particles (active material particles) containing a substance capable of absorbing and releasing alkali metal ions, and a copolymer of acrylonitrile and a polymer component other than acrylonitrile (acrylonitrile copolymer ) and a step of heat-treating a composition comprising:
  • an electrode containing, as a binder, cyclized polyacrylonitrile, which is a cyclization reaction product of an acrylonitrile copolymer can be produced.
  • the details and preferred aspects of the active material particles and acrylonitrile copolymer are the same as the details and preferred aspects of the active material particles and acrylonitrile copolymer used in the electrode described above.
  • the heat treatment in the above method is performed under conditions (for example, 278°C to 600°C) that cause a cyclization reaction of the acrylonitrile copolymer.
  • the temperature at which the cyclization treatment is performed is 278°C or higher, preferably 280°C or higher, more preferably 290°C or higher, and even more preferably 300°C or higher.
  • the temperature at which the cyclization treatment is performed is 600°C or lower, preferably 500°C or lower, more preferably 450°C or lower, and even more preferably 400°C or lower.
  • the oxygen concentration during the cyclization treatment is preferably 4 ppm or higher, more preferably 7.5 ppm or higher, even more preferably 10 ppm or higher, and particularly preferably 15 ppm or higher.
  • the oxygen concentration when performing the cyclization treatment is 100 ppm or less, preferably 80 ppm or less, more preferably 60 ppm or less, and 40 ppm or less. is more preferred.
  • the components other than oxygen in the atmosphere in which the cyclization treatment is performed are not particularly limited, and may be nitrogen, an inert gas such as argon, or a mixture thereof.
  • the time for performing the cyclization treatment is not particularly limited, and can be selected, for example, from 3 hours to 15 hours.
  • the time for performing the cyclization treatment in the present disclosure means the time during which the temperature of the composition is 278°C to 600°C.
  • the method of the present disclosure may include a step of heat-treating the composition at a temperature of 150°C or more and less than 278°C (hereinafter also referred to as pretreatment) before the cyclization treatment.
  • the time for performing pretreatment is not particularly limited, and can be selected, for example, from 3 hours to 15 hours.
  • the time during which the pretreatment is performed in the present disclosure means the time during which the temperature of the composition is 150°C or higher and lower than 278°C.
  • the atmosphere during the pretreatment is not particularly limited, and may be an inert atmosphere that does not contain oxygen or an atmosphere that contains oxygen (such as air). From the viewpoint of cycle characteristics, the atmosphere preferably contains 5% to 30% by volume of oxygen.
  • the pretreatment and the cyclization treatment may or may not be performed consecutively.
  • a step of cooling the composition may be performed between the pretreatment and the cyclization treatment.
  • the composition may contain a conductive aid, solvent, etc.
  • Solvents include those capable of dissolving polyacrylonitrile, such as N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and dimethylsulfoxide.
  • the composition is a mixture of the active material particles and the acrylonitrile copolymer, it is obtained by polymerizing the monomers in a state in which the active material particles and the monomer that is the raw material of the acrylonitrile copolymer are mixed. good too.
  • the composition may be pressurized.
  • pressurizing the composition By pressurizing the composition, a cyclization reaction occurs in the state where the molecules of the acrylonitrile copolymer are oriented, and the molecules stack to increase the crystallinity.
  • the acrylonitrile copolymer is highly crystallized, the obtained cyclized polyacrylonitrile tends to have an improved strength and an improved electronic conductivity.
  • the method of applying pressure to the composition is not particularly limited.
  • a method of sandwiching between members and applying surface pressure (for example, 0.1 MPa to 10 MPa) can be used.
  • the pressure treatment may be performed before the cyclization treatment, during the cyclization treatment, or after the cyclization treatment.
  • the composition for the cyclization treatment may be in a layered state on the current collector.
  • Electrode forming material is a material for forming an electrode of an energy storage device, and is an electrode-forming material containing a copolymer of acrylonitrile and a polymer component other than acrylonitrile (acrylonitrile copolymer). be.
  • Electrodes and energy storage devices formed using the above materials exhibit excellent characteristics.
  • the details and preferred aspects of the acrylonitrile copolymer contained in the above materials are the same as the details and preferred aspects of the acrylonitrile copolymer used in the electrode described above.
  • Example 1 Acrylonitrile copolymer (PAN) was added to N-methyl-2-pyrrolidone (NMP) and mixed at room temperature to dissolve PAN to prepare a PAN/NMP solution (PAN content: 10% by mass).
  • PAN Acrylonitrile copolymer
  • NMP N-methyl-2-pyrrolidone
  • the acrylonitrile copolymer contains sodium methallylsulfonate (0.3% by mass) and methyl acrylate (5.8% by mass) as polymerization components other than acrylonitrile, and has a weight average molecular weight of 80,000. board.
  • Si particles (average secondary particle diameter: about 5 ⁇ m) as an active material and a PAN/NMP solution were mixed so that the mass ratio of Si and PAN (Si:PAN) was 70:30 to obtain slurry A. .
  • the slurry A was applied to a copper foil as a current collector and dried to obtain a laminate of the electrode and the current collector (mass per area of the electrode: 7 g/m 2 ). This laminate was subjected to heat treatment (cyclization treatment) at 350° C. for 5 hours in a nitrogen atmosphere with an oxygen concentration of 20 ppm to obtain an electrode.
  • a polypropylene porous membrane is used as the separator, and 1M LiPF6 as the electrolyte is EC (ethylene carbonate), EMC (ethyl methyl carbonate) and DEC (diethyl carbonate) in a ratio of 1:1:1 (volume ratio).
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the initial efficiency was obtained from the following formula from the charge capacity of the first cycle (initial charge capacity) and the discharge capacity of the first cycle (initial discharge capacity).
  • Initial efficiency (%) (initial discharge capacity (mAh) / initial charge capacity (mAh)) x 100
  • the discharge capacity retention rate was obtained from the following formula from the initial discharge capacity and the discharge capacity at the 50th cycle.
  • Discharge capacity retention rate (%) (50th cycle discharge capacity (mAh) / initial discharge capacity (mAh)) x 100 The initial efficiency was 91% for Example 1, 71% for Example 2, and 56% for Comparative Example 1.
  • the discharge capacity retention rate after 50 cycles was 54% for Example 1, 25% for Example 2, and 27% for Comparative Example 1.
  • the discharge capacity per active material mass after 50 cycles was 2030 mAh/g for Example 1, 750 mAh/g for Example 2, and 558 mAh/g for Comparative Example 1.
  • ⁇ Electrode strength> As an index of electrode strength, when the electrodes prepared in Example 1 and Comparative Example 1 are divided into three equal parts in the thickness direction, the layer farthest from the current collector (upper layer), the middle layer (middle layer), and the current collector A SAICAS (Surface And Interfacial Cutting Analysis System) test was performed to examine the peel strength when the electrodes were scraped off in order from the closest layer (lower layer). The measurement conditions are as follows.
  • the battery of Example 1 which was produced using the electrode containing the cyclized acrylonitrile copolymer, was produced using the electrode containing the cyclized acrylonitrile homopolymer. As compared with the battery of Comparative Example 1, the number of cracks on the surface is small.

Abstract

An electrode for energy storage devices that includes particles containing a substance which can absorb and release alkali metal ions, and a binding material containing cyclized polyacrylonitrile, the cyclized polyacrylonitrile being a cyclized product of a copolymer of acrylonitrile and a polymerization component other than acrylonitrile.

Description

エネルギー貯蔵デバイス用電極、エネルギー貯蔵デバイス、エネルギー貯蔵デバイス用電極の製造方法及び電極形成用材料Electrode for energy storage device, energy storage device, method for producing electrode for energy storage device, and material for forming electrode
　本開示は、エネルギー貯蔵デバイス用電極、エネルギー貯蔵デバイス、エネルギー貯蔵デバイス用電極の製造方法及び電極形成用材料に関する。 The present disclosure relates to an energy storage device electrode, an energy storage device, a method for manufacturing an energy storage device electrode, and an electrode forming material.
　正極と負極との間をリチウムイオン等のアルカリ金属イオンが移動することによって充放電が行われるエネルギー貯蔵デバイスが広く用いられている。このようなエネルギー貯蔵デバイスの正極及び負極は一般に、アルカリ金属イオンを吸蔵及び放出可能な物質（活物質）の粒子と、活物質の粒子を結着するための結着材とを含んでいる。 Energy storage devices are widely used in which charge and discharge are performed by moving alkali metal ions such as lithium ions between the positive and negative electrodes. The positive and negative electrodes of such energy storage devices generally contain particles of a material (active material) capable of absorbing and releasing alkali metal ions, and a binder for binding the particles of the active material.
　活物質はアルカリ金属イオンの吸蔵及び放出に伴って体積が変化するため、活物質の結着材には活物質の体積変化に充分に追従しうる柔軟性が求められる。このため、結着材としては高分子化合物が主に用いられる。 Since the volume of the active material changes as it absorbs and releases alkali metal ions, the binder for the active material is required to be flexible enough to follow the volume change of the active material. For this reason, polymer compounds are mainly used as binders.
　活物質の結着材としては、ポリフッ化ビニリデン、スチレンブタジエンゴム等の一般に用いられている高分子化合物に加え、電子伝導性を有する高分子化合物の適用がエネルギー貯蔵デバイスの容量増大等の観点から検討されている。 As binders for active materials, in addition to commonly used polymer compounds such as polyvinylidene fluoride and styrene-butadiene rubber, the application of polymer compounds with electronic conductivity is expected to increase the capacity of energy storage devices. being considered.
　例えば、特表２０１９－５３５１１６号公報には、環化反応を生じさせたポリアクリロニトリル（環化ポリアクリロニトリル）をエネルギー貯蔵デバイスの電極に用いることが提案されている。 For example, JP-A-2019-535116 proposes the use of polyacrylonitrile in which a cyclization reaction has occurred (cyclized polyacrylonitrile) as an electrode of an energy storage device.
　環化ポリアクリロニトリルをエネルギー貯蔵デバイスの電極に適用する場合、ポリアクリロニトリルの環化反応を生じさせるための加熱が電極の特性に影響を与える恐れがある。 When applying cyclized polyacrylonitrile to the electrode of an energy storage device, heating to cause the cyclization reaction of polyacrylonitrile may affect the properties of the electrode.
　上記事情に鑑み、本開示は加熱を経ても優れた特性を示すエネルギー貯蔵デバイス用電極、エネルギー貯蔵デバイス、エネルギー貯蔵デバイス用電極の製造方法及び電極形成用材料を提供することを課題とする。 In view of the above circumstances, an object of the present disclosure is to provide an electrode for an energy storage device that exhibits excellent properties even after heating, an energy storage device, a method for manufacturing an electrode for an energy storage device, and an electrode-forming material.
　上記課題を解決するための手段には、以下の実施態様が含まれる。
＜１＞アルカリ金属イオンを吸蔵及び放出可能な物質を含む粒子と、環化ポリアクリロニトリルを含む結着材と、を含み、前記環化ポリアクリロニトリルはアクリロニトリルとアクリロニトリル以外の重合成分との共重合体の環化処理物である、エネルギー貯蔵デバイス用電極。
＜２＞前記共重合体はイオン性基を含む、＜１＞に記載のエネルギー貯蔵デバイス用電極。
＜３＞前記共重合体はアニオン性基を含む、＜１＞又は＜２＞に記載のエネルギー貯蔵デバイス用電極。
＜４＞前記共重合体におけるアクリロニトリル以外の重合成分の全重合成分に占める割合は０．１質量％～２０質量％である、＜１＞～＜３＞のいずれか１項に記載のエネルギー貯蔵デバイス用電極。
＜５＞前記アルカリ金属イオンを吸蔵及び放出可能な物質はケイ素原子を含む、＜１＞～＜４＞のいずれか１項に記載のエネルギー貯蔵デバイス用電極。
＜６＞＜１＞～＜５＞のいずれか１項に記載のエネルギー貯蔵デバイス用電極を含む、エネルギー貯蔵デバイス。
＜７＞アルカリ金属イオンを吸蔵及び放出可能な物質を含む粒子と、アクリロニトリルとアクリロニトリル以外の重合成分との共重合体と、を含む組成物を熱処理する工程を含む、エネルギー貯蔵デバイス用電極の製造方法。
＜８＞エネルギー貯蔵デバイスの電極を形成するための材料であって、アクリロニトリルとアクリロニトリル以外の重合成分との共重合体を含む、電極形成用材料。 Means for solving the above problems include the following embodiments.
<1> Contains particles containing a substance capable of absorbing and releasing alkali metal ions, and a binder containing cyclized polyacrylonitrile, wherein the cyclized polyacrylonitrile is a copolymer of acrylonitrile and a polymer component other than acrylonitrile. An electrode for an energy storage device, which is a cyclized product of
<2> The electrode for an energy storage device according to <1>, wherein the copolymer contains an ionic group.
<3> The electrode for an energy storage device according to <1> or <2>, wherein the copolymer contains an anionic group.
<4> The energy storage according to any one of <1> to <3>, wherein the ratio of the polymer components other than acrylonitrile in the copolymer to the total polymer components is 0.1% by mass to 20% by mass. Electrodes for devices.
<5> The electrode for an energy storage device according to any one of <1> to <4>, wherein the substance capable of absorbing and releasing alkali metal ions contains a silicon atom.
<6> An energy storage device comprising the electrode for an energy storage device according to any one of <1> to <5>.
<7> Production of an electrode for an energy storage device, comprising a step of heat-treating a composition containing particles containing a substance capable of absorbing and releasing alkali metal ions and a copolymer of acrylonitrile and a polymer component other than acrylonitrile Method.
<8> A material for forming an electrode of an energy storage device, comprising a copolymer of acrylonitrile and a polymerization component other than acrylonitrile.
　本開示によれば、加熱を経ても優れた特性を示すエネルギー貯蔵デバイス用電極、エネルギー貯蔵デバイス、エネルギー貯蔵デバイス用電極の製造方法及び電極形成用材料が提供される。 According to the present disclosure, an energy storage device electrode, an energy storage device, a method for producing an energy storage device electrode, and an electrode-forming material that exhibit excellent properties even after heating are provided.
エネルギー貯蔵デバイス用電極の構成の一例を示す概念図である。It is a conceptual diagram which shows an example of a structure of the electrode for energy storage devices. エネルギー貯蔵デバイス用電極の構成の一例を示す概念図である。It is a conceptual diagram which shows an example of a structure of the electrode for energy storage devices. エネルギー貯蔵デバイス用電極の構成の一例を示す概念図である。It is a conceptual diagram which shows an example of a structure of the electrode for energy storage devices. 実施例１で作製した電極の表面の走査電子顕微鏡像である。4 is a scanning electron microscope image of the surface of the electrode produced in Example 1. FIG. 比較例１で作製した電極の表面の走査電子顕微鏡像である。4 is a scanning electron microscope image of the surface of the electrode produced in Comparative Example 1. FIG.
　以下、本開示を実施するための形態について詳細に説明する。但し、本開示は以下の実施形態に限定されるものではない。以下の実施形態において、その構成要素（要素ステップ等も含む）は、特に明示した場合を除き、必須ではない。数値及びその範囲についても同様であり、本開示を制限するものではない。 A detailed description will be given below of the embodiment for implementing the present disclosure. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present disclosure.
　本開示において「工程」との語には、他の工程から独立した工程に加え、他の工程と明確に区別できない場合であってもその工程の目的が達成されれば、当該工程も含まれる。 In the present disclosure, the term "process" includes a process that is independent of other processes, and even if the purpose of the process is achieved even if it cannot be clearly distinguished from other processes. .
　本開示において「～」を用いて示された数値範囲には、「～」の前後に記載される数値がそれぞれ最小値及び最大値として含まれる。 In the present disclosure, the numerical range indicated using "~" includes the numerical values before and after "~" as the minimum and maximum values, respectively.
　本開示中に段階的に記載されている数値範囲において、一つの数値範囲で記載された上限値又は下限値は、他の段階的な記載の数値範囲の上限値又は下限値に置き換えてもよい。また、本開示中に記載されている数値範囲において、その数値範囲の上限値又は下限値は、実施例に示されている値に置き換えてもよい。 In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described step by step. . Moreover, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
　本開示において各成分は該当する物質を複数種含んでいてもよい。組成物中に各成分に該当する物質が複数種存在する場合、各成分の含有率又は含有量は、特に断らない限り、組成物中に存在する当該複数種の物質の合計の含有率又は含有量を意味する。 In the present disclosure, each component may contain multiple types of applicable substances. When there are multiple types of substances corresponding to each component in the composition, the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition unless otherwise specified. means quantity.
　本開示において各成分に該当する粒子は複数種含んでいてもよい。組成物中に各成分に該当する粒子が複数種存在する場合、各成分の粒子径は、特に断らない限り、組成物中に存在する当該複数種の粒子の混合物についての値を意味する。 A plurality of types of particles corresponding to each component in the present disclosure may be included. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means a value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
　本開示において「層」との語には、当該層が存在する領域を観察したときに、当該領域の全体に形成されている場合に加え、当該領域の一部にのみ形成されている場合も含まれる。
＜エネルギー貯蔵デバイス用電極＞
　本開示のエネルギー貯蔵デバイス用電極は、アルカリ金属イオンを吸蔵及び放出可能な物質を含む粒子（以下、活物質粒子ともいう）と、環化ポリアクリロニトリルを含む結着材と、を含み、前記環化ポリアクリロニトリルはアクリロニトリルとアクリロニトリル以外の重合成分（以下、共重合成分ともいう）との共重合体の環化処理物である、エネルギー貯蔵デバイス用電極（以下、電極ともいう）である。 In the present disclosure, the term "layer" includes not only the case where the layer is formed in the entire region when observing the region where the layer exists, but also the case where it is formed only in part of the region. included.
<Energy storage device electrodes>
The energy storage device electrode of the present disclosure includes particles containing a substance capable of occluding and releasing alkali metal ions (hereinafter also referred to as active material particles) and a binder containing cyclized polyacrylonitrile. Polyacrylonitrile polyacrylonitrile is an electrode for energy storage devices (hereinafter also referred to as electrode) which is a cyclized product of a copolymer of acrylonitrile and a polymerization component other than acrylonitrile (hereinafter also referred to as copolymer component).
　本開示において、アルカリ金属イオンを吸蔵及び放出可能な物質を含む粒子を活物質粒子と称し、アクリロニトリル以外の重合成分を共重合成分と称し、エネルギー貯蔵デバイス用電極を電極と称する場合がある。 In the present disclosure, particles containing a substance capable of absorbing and releasing alkali metal ions may be referred to as active material particles, polymerized components other than acrylonitrile may be referred to as copolymer components, and electrodes for energy storage devices may be referred to as electrodes.
　本発明者らの検討の結果、アクリロニトリルとアクリロニトリル以外の重合成分との共重合体の環化処理物である環化ポリアクリロニトリルを結着材として含む電極は、加熱を経ても優れた特性を示すことがわかった。その理由は、例えば、下記のように考えられる。 As a result of studies by the present inventors, it was found that an electrode containing, as a binder, cyclized polyacrylonitrile, which is a cyclized product of a copolymer of acrylonitrile and a polymerization component other than acrylonitrile, exhibits excellent properties even after being heated. I understand. The reason is considered as follows, for example.
　ポリアクリロニトリルに含まれる隣接するニトリル基同士の閉環反応は発熱反応である。この発熱反応は２９３℃付近を境に急激に進むため、２９３℃付近において反応系内の温度の急激な上昇を伴う。このため、ポリアクリロニトリルの分子鎖の切断による低分子副生成物の生成及び揮発が急激に進む。一方、ポリアクリロニトリルに共重合成分が導入されていると、ニトリル基の量が相対的に減少して閉環反応がより低温（例えば、２７８℃付近）で起き、急激な発熱も抑えられる。その結果、低分子副生成物の生成及び揮発が抑制されて環化ポリアクリロニトリルの残存量が増大する。 The ring closure reaction between adjacent nitrile groups contained in polyacrylonitrile is an exothermic reaction. Since this exothermic reaction progresses abruptly at around 293°C, the temperature in the reaction system rises sharply at around 293°C. As a result, the formation and volatilization of low-molecular-weight by-products due to scission of the molecular chains of polyacrylonitrile rapidly proceed. On the other hand, when a copolymerization component is introduced into polyacrylonitrile, the amount of nitrile groups is relatively reduced and the ring closure reaction occurs at a lower temperature (for example, around 278° C.), suppressing rapid heat generation. As a result, the formation and volatilization of low-molecular-weight by-products are suppressed, and the residual amount of cyclized polyacrylonitrile increases.
　さらに、ニトリル基の閉環反応には分子内で生じるものと分子間で生じるものとがある。ポリアクリロニトリルに共重合成分が導入されていると、分子内で生じるニトリル基の閉環反応が相対的に減少し、分子間で生じるニトリル基の閉環反応が相対的に増大する。その結果、環化ポリアクリロニトリルの３次元的な架橋構造の形成が促進される。 Furthermore, the ring closure reaction of nitrile groups includes those that occur intramolecularly and those that occur intermolecularly. When a copolymer component is introduced into polyacrylonitrile, the intramolecular ring-closure reaction of nitrile groups is relatively reduced, and the intermolecular ring-closure reaction of nitrile groups is relatively increased. As a result, formation of a three-dimensional crosslinked structure of the cyclized polyacrylonitrile is promoted.
　あるいは、ポリアクリロニトリルにイオン性の官能基を有する共重合成分が導入されていると、隣接するニトリル基間のラジカル重合反応に加えてイオン性の官能基とニトリル基との間でもイオン重合反応が生じ、分子鎖の結合が生じる。イオン重合反応は、ラジカル重合反応よりも低い温度で進行する。その結果、低分子副生成物の生成及び揮発が抑制されて環化ポリアクリロニトリルの残存量が増大する。 Alternatively, when a copolymerization component having an ionic functional group is introduced into polyacrylonitrile, in addition to the radical polymerization reaction between adjacent nitrile groups, an ionic polymerization reaction also occurs between the ionic functional group and the nitrile group. resulting in binding of the molecular chains. Ionic polymerization reactions proceed at lower temperatures than radical polymerization reactions. As a result, the formation and volatilization of low-molecular-weight by-products are suppressed, and the residual amount of cyclized polyacrylonitrile increases.
　以上の理由から、得られる電極の強度が向上し、優れた特性を示すと考えられる。
（結着材）
　結着材は、環化ポリアクリロニトリルを含む。本開示において環化ポリアクリロニトリルとは、ポリアクリロニトリルの環化反応を生じさせて得られる材料（すなわち、ポリアクリロニトリルの環化処理物）を意味する。 For the above reasons, it is considered that the obtained electrode has improved strength and exhibits excellent characteristics.
(Binder)
The binder contains cyclized polyacrylonitrile. In the present disclosure, cyclized polyacrylonitrile means a material obtained by causing a cyclization reaction of polyacrylonitrile (that is, a cyclized product of polyacrylonitrile).
　環化ポリアクリロニトリルは、原料となるポリアクリロニトリルの環化処理工程において、－Ｃ≡Ｎ（ニトリル）基が閉環して－Ｃ＝Ｎ－基になるだけでなく、脱水素化反応により、たとえば主鎖を構成する－ＣＨ２－ＣＨ－基が－ＣＨ＝Ｃ－基等に変化して二重結合を形成することが好ましい。環化反応と脱水素化反応の双方が生じることで、共役系の二重結合が形成され、電子伝導性が向上する傾向にある。 Cyclized polyacrylonitrile can be obtained not only by ring closure of -C≡N (nitrile) group to become -C=N- group in the cyclization treatment step of raw material polyacrylonitrile, but also by dehydrogenation reaction, for example, It is preferable that the -CH 2 -CH- group constituting the chain is changed to -CH=C- group or the like to form a double bond. Both the cyclization reaction and the dehydrogenation reaction tend to form a conjugated double bond and improve the electron conductivity.
　上記反応のキャラクタリゼーションは、赤外分光法で行うことができる。赤外分光法は透過法であっても反射法であってもよい。 Characterization of the above reaction can be performed by infrared spectroscopy. Infrared spectroscopy may be transmission or reflection.
　赤外分光法において、－Ｃ≡Ｎ（ニトリル）基は２２４０ｃｍ－１～２２４３ｃｍ－１におけるピークとして、閉環した－Ｃ＝Ｎ－基は１５７７ｃｍ－１～１６０４ｃｍ－１におけるピークとして、脱水素化により二重結合になる前の－ＣＨ２－は２９３９ｃｍ－１におけるピークとして、脱水素化により二重結合になった後の－ＣＨ＝Ｃ－基は８０６ｃｍ－１におけるピークとして、それぞれ確認できる。 In infrared spectroscopy, the -C≡N (nitrile) group as a peak at 2240 cm -1 to 2243 cm -1 and the ring-closed -C=N- group as a peak at 1577 cm -1 to 1604 cm -1 by dehydrogenation A peak at 2939 cm −1 for —CH 2 — before forming a double bond, and a peak at 806 cm −1 for a —CH═C— group after forming a double bond by dehydrogenation can be confirmed.
　閉環した－Ｃ＝Ｎ－基は、１５７７ｃｍ－１～１６０４ｃｍ－１の範囲で、形成される六員環の構造によってシフトする。具体的には、六員環構造に含まれる二重結合の数が多いほど、－Ｃ＝Ｎ－の結合距離が短くなり、低波数側にシフトする傾向にある。 The ring-closed —C═N— group shifts in the range of 1577 cm −1 to 1604 cm −1 depending on the structure of the 6-membered ring formed. Specifically, the larger the number of double bonds contained in the six-membered ring structure, the shorter the bond distance of -C=N-, which tends to shift to the lower wavenumber side.
　上記ピークの帰属は、The influence of thermal stabilization stage on the molecular structure of polyacrylonitrile fibers prior to the carbonization stage（Fibers and Polymers 2012, Vol.13, No.3, 295-302）、Structural transformation of polyacrylonitrile fibers during stabilization and low temperature carbonization（Polymer Degradation and Stability,Volume 128, June 2016, 39-45）等を参考にできる。 The above peaks are assigned to The influence of thermal stabilization stage on the molecular structure of polyacrylonitrile fibers prior to the carbonization stage (Fibers and Polymers 2012, Vol.13, No.3, 295-302), Structural transformation of polyacrylonitrile fibers during stabilization and low temperature carbonization (Polymer Degradation and Stability, Volume 128, June 2016, 39-45).
　環化ポリアクリロニトリルは、炭素とポリマーの中間の性質を有するということができ、ニトリル基の閉環の度合いが大きいほど、その環化ポリアクリロニトリルは炭素に近い性質を有するということができる。 The cyclized polyacrylonitrile can be said to have properties intermediate between those of carbon and polymers, and the greater the degree of ring closure of the nitrile group, the more similar the properties of the cyclized polyacrylonitrile to those of carbon.
　環化ポリアクリロニトリルにおけるニトリル基と閉環した－Ｃ＝Ｎ－基の比率は、－Ｃ≡Ｎ（ニトリル）基に対応するピークにおける吸光度と閉環した－Ｃ＝Ｎ－基に対応するピークにおける吸光度との比（ニトリル基／閉環した－Ｃ＝Ｎ－基）で表すことができ、この比の値が大きいほど、環化ポリアクリロニトリルはポリマーに近い性質を有するということができる。以下、この吸光度比を吸光度比Ａともいう。 The ratio of the nitrile group and the ring-closed -C=N- group in the cyclized polyacrylonitrile is the absorbance at the peak corresponding to the -C≡N (nitrile) group and the absorbance at the peak corresponding to the ring-closed -C=N- group. (nitrile group/ring-closed -C=N- group), and it can be said that the larger the value of this ratio, the closer the properties of the cyclized polyacrylonitrile to those of polymers. Hereinafter, this absorbance ratio is also referred to as absorbance ratio A.
　吸光度比Ａは、０．０１以上であることが好ましく、０．０２以上であることがより好ましく、０．０３以上であることがさらに好ましい。 The absorbance ratio A is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more.
　吸光度比Ａが０．０１以上であると、得られる結着材が適度な柔軟性を有し、活物質の膨張収縮に追従しやすい。 When the absorbance ratio A is 0.01 or more, the resulting binder has moderate flexibility and easily follows the expansion and contraction of the active material.
　吸光度比Ａは、６以下であることが好ましく、３以下であることがより好ましく、１以下であることがさらに好ましい。 The absorbance ratio A is preferably 6 or less, more preferably 3 or less, and even more preferably 1 or less.
　吸光度比Ａが６以下であると、ニトリル基が充分に閉環して得られる結着材の構造が強固になる。 When the absorbance ratio A is 6 or less, the structure of the binder obtained by sufficiently ring-closing the nitrile groups becomes strong.
　環化ポリアクリロニトリルは、環化反応によって電子伝導性が付与されたポリマーということができる。 Cyclized polyacrylonitrile can be said to be a polymer that has been given electronic conductivity through a cyclization reaction.
　環化ポリアクリロニトリルの電子伝導性の度合いは、脱水素化反応により二重結合になった後の－ＣＨ＝Ｃ－基に対応するピークにおける吸光度と閉環した－Ｃ＝Ｎ－基に対応するピークにおける吸光度との比（二重結合になった後の－ＣＨ＝Ｃ－基／閉環した－Ｃ＝Ｎ－基）で表すことができ、この比の値が大きいほど、環化ポリアクリロニトリルの電子伝導性が大きいということができる。以下、この吸光度比を吸光度比Ｂともいう。 The degree of electronic conductivity of the cyclized polyacrylonitrile is determined by the absorbance at the peak corresponding to the -CH=C- group after the double bond is formed by the dehydrogenation reaction and the peak corresponding to the ring-closed -C=N- group. It can be represented by the ratio of the absorbance in (-CH=C- group after becoming a double bond / -C=N- group after ring closure), and the larger the value of this ratio, the more electrons of the cyclized polyacrylonitrile It can be said that the conductivity is large. Hereinafter, this absorbance ratio is also referred to as absorbance ratio B.
　吸光度比Ｂは、０．０１以上であることが好ましく、０．０２以上であることがより好ましく、０．０３以上であることが更に好ましい。 The absorbance ratio B is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more.
　吸光度比Ｂが０．０１以上であると、得られる結着材が充分な電子伝導性を示す。 When the absorbance ratio B is 0.01 or more, the resulting binder exhibits sufficient electronic conductivity.
　吸光度比Ｂの上限は特に制限されないが、例えば、１以下であってもよい。 Although the upper limit of the absorbance ratio B is not particularly limited, it may be 1 or less, for example.
　赤外分光分析を実施する際は、環化ポリアクリロニトリル自体が種々の結合種を持つために、それぞれのピークが他のピークと重なりやすいため、ベースラインを引いて算出することが好ましい。ベースラインの引き方に特に制限はないが、対象のピークの両端の裾をつなげて引く方法を例示することができる。 When performing infrared spectroscopic analysis, the cyclized polyacrylonitrile itself has various bonding species, so each peak tends to overlap with other peaks, so it is preferable to draw a baseline for calculation. There is no particular limitation on how to draw the baseline, but a method of drawing by connecting the tails of both ends of the target peak can be exemplified.
　赤外分光法における吸光度比は、測定対象が環化ポリアクリロニトリルのみであっても、環化ポリアクリロニトリルと活物質の混合物（ただし、活物質がポリアクリロニトリルの環化及び分解反応に対して触媒的作用がある場合を除く）であっても、集電体と組み合わせた電極の状態であっても同様の傾向が確認される。したがって、測定対象が環化ポリアクリロニトリルと活物質の混合物又は集電体と組み合わせた電極の状態で吸光度比の算出を行ってもよい。 The absorbance ratio in infrared spectroscopy is a mixture of cyclized polyacrylonitrile and active material (provided that the active material is catalytic to the cyclization and decomposition reactions of polyacrylonitrile), even if the measurement target is only cyclized polyacrylonitrile. A similar tendency is confirmed even in the state of the electrode combined with the current collector. Therefore, the absorbance ratio may be calculated in the state where the object to be measured is a mixture of cyclized polyacrylonitrile and an active material or an electrode in combination with a current collector.
　環化ポリアクリロニトリルは、アクリドン構造を含むことが好ましい。アクリドン構造は、ポリアクリロニトリルの環化反応過程で生じる、下記に示す環構造（波線は結合部位を示す）である。 The cyclized polyacrylonitrile preferably contains an acridone structure. The acridone structure is the ring structure shown below (the wavy line indicates the binding site) generated during the cyclization reaction of polyacrylonitrile.
Figure JPOXMLDOC01-appb-C000001
Figure JPOXMLDOC01-appb-C000001
　アクリドン構造を含む環化ポリアクリロニトリルは、アクリドン構造が酸素原子を含むことからわかるように、ポリアクリロニトリルの環化反応を生じさせる熱処理を酸素を含む環境で行うことにより得られる。 As can be seen from the fact that the acridone structure contains oxygen atoms, the cyclized polyacrylonitrile containing the acridone structure can be obtained by performing a heat treatment that causes a cyclization reaction of the polyacrylonitrile in an oxygen-containing environment.
　環化ポリアクリロニトリルがアクリドン構造を有することは、熱分解ＧＣ／ＭＳ分析（Ｐｙｒｏｌｙｓｉｓ　Ｇａｓ　Ｃｈｒｏｍａｔｏｇｒａｐｈｙ　Ｍａｓｓ　Ｓｐｅｃｔｒｏｍｅｔｒｙ）、Ｘ線光電子スペクトル分析用の公知の手法によって確認することができる。アクリドン構造の存在は、熱分解ＧＣ／ＭＳ分析では質量１７７のフラグメントで確認でき、Ｘ線光電子スペクトル分析では５３２ｅＶ付近のピークで確認できる。 The fact that the cyclized polyacrylonitrile has an acridone structure can be confirmed by pyrolysis GC/MS analysis (Pyrolysis Gas Chromatography Mass Spectrometry) and known techniques for X-ray photoelectron spectrum analysis. The presence of the acridone structure can be confirmed by a fragment of mass 177 in pyrolysis GC/MS analysis and by a peak around 532 eV in X-ray photoelectron spectroscopy.
　本開示において、結着材に含まれる環化ポリアクリロニトリルは、アクリロニトリルとアクリロニトリル以外の重合成分との共重合体（以下、アクリロニトリル共重合体ともいう）の環化処理物である。 In the present disclosure, the cyclized polyacrylonitrile contained in the binder is a cyclized product of a copolymer of acrylonitrile and a polymerization component other than acrylonitrile (hereinafter also referred to as an acrylonitrile copolymer).
　アクリロニトリル共重合体を構成するアクリロニトリル以外の重合成分は、特に制限されない。例えば、スルホ基、カルボキシ基、アミノ基及びアルキルエステル基からなる群より選択される少なくとも１種の官能基を有する重合成分から選択してもよい。 The polymerization components other than acrylonitrile that constitute the acrylonitrile copolymer are not particularly limited. For example, it may be selected from polymer components having at least one functional group selected from the group consisting of a sulfo group, a carboxy group, an amino group and an alkyl ester group.
　本開示においてスルホ基は、－ＳＯ３Ｈで示される１価の基である。スルホ基は、ナトリウム等のアルカリ金属と塩を形成していてもよい。 A sulfo group in the present disclosure is a monovalent group represented by —SO 3 H. The sulfo group may form a salt with an alkali metal such as sodium.
　本開示においてカルボキシ基は、－ＣＯＯＨで示される１価の基である。 A carboxy group in the present disclosure is a monovalent group represented by —COOH.
　本開示においてアミノ基は、－ＮＲ１Ｒ２で示される１価の基であり、Ｒ１及びＲ２はそれぞれ独立に水素原子又は１価の有機基である。 In the present disclosure, an amino group is a monovalent group represented by —NR 1 R 2 , where R 1 and R 2 are each independently a hydrogen atom or a monovalent organic group.
　本開示においてアルキルエステル基は、－ＣＯＯＲで示される１価の基であり、Ｒはアルキル基である。アルキル基の炭素数は、１～１５が好ましく、１～５がより好ましく、１～３がさらに好ましい。 In the present disclosure, an alkyl ester group is a monovalent group represented by -COOR, and R is an alkyl group. The number of carbon atoms in the alkyl group is preferably 1-15, more preferably 1-5, even more preferably 1-3.
　スルホ基を含む重合成分としては、アリルスルホン酸、メタリルスルホン酸、ビニルベンゼンスルホン酸、これらのアルカリ金属塩等が挙げられる。 Polymerization components containing a sulfo group include allylsulfonic acid, methallylsulfonic acid, vinylbenzenesulfonic acid, and alkali metal salts thereof.
　カルボキシ基を含む重合成分としては、アクリル酸、メタクリル酸、イタコン酸、クロトン酸、マレイン酸、フマル酸、これらのアルカリ金属塩等が挙げられる。 Polymerization components containing a carboxy group include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, and alkali metal salts thereof.
　アミノ基を含む重合成分としては、アクリルアミド、メタクリルアミド、ジメチルアミノプロピルアクリルアミド、ジメチルアミノプロピルメタクリルアミド等が挙げられる。 Polymerization components containing amino groups include acrylamide, methacrylamide, dimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamide, and the like.
　アルキルエステル基を含む重合成分としては、アクリル酸メチル、アクリル酸エチル、アクリル酸イソプロピル、アクリル酸ｎ－ブチル、アクリル酸２－エチルヘキシル、メタクリル酸メチル、メタクリル酸エチル、メタクリル酸イソプロピル、メタクリル酸ｎ－ブチル、メタクリル酸ｎ－ヘキシル、メタクリル酸シクロヘキシル、メタクリル酸ラウリル等が挙げられる。 Examples of polymerizable components containing an alkyl ester group include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, and n-methacrylate. butyl, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate and the like.
　上記以外の重合成分としては、酢酸ビニル、スチレン、塩化ビニリデン、塩化ビニル等が挙げられる。 Polymerization components other than the above include vinyl acetate, styrene, vinylidene chloride, and vinyl chloride.
　電極及びエネルギー貯蔵デバイスの特性の観点からは、アクリロニトリル共重合体はスルホ基、カルボキシ基、アミノ基等のイオン性基を含むことが好ましく、スルホ基、カルボキシ基等のアニオン性基を含むことがより好ましく、スルホ基を有することがさらに好ましい。 From the viewpoint of the properties of electrodes and energy storage devices, the acrylonitrile copolymer preferably contains an ionic group such as a sulfo group, a carboxyl group and an amino group, and may contain an anionic group such as a sulfo group and a carboxyl group. More preferably, it has a sulfo group.
　イオン性基を含むアクリロニトリル共重合体は、アクリロニトリル以外の重合成分としてイオン性基を含む重合成分を用いることで得られる。 An acrylonitrile copolymer containing an ionic group can be obtained by using a polymerization component containing an ionic group as a polymerization component other than acrylonitrile.
　電極及びエネルギー貯蔵デバイスの特性の観点からは、アクリロニトリル共重合体におけるアクリロニトリル以外の重合成分の全重合成分に占める割合は０．１質量％以上であることが好ましく、０．２質量％以上であることがより好ましく、０．５質量％以上であることがさらに好ましい。 From the viewpoint of the properties of the electrode and the energy storage device, the proportion of the polymerized components other than acrylonitrile in the acrylonitrile copolymer to the total polymerized components is preferably 0.1% by mass or more, and is 0.2% by mass or more. is more preferable, and 0.5% by mass or more is even more preferable.
　環化ポリアクリロニトリルの特性を充分に発揮する観点からは、アクリロニトリル共重合体におけるアクリロニトリル以外の重合成分の全重合成分に占める割合は２０質量％以下であることが好ましく、１５質量％以下であることがより好ましく、１０質量％以下であることがさらに好ましい。 From the viewpoint of fully exhibiting the properties of the cyclized polyacrylonitrile, the ratio of the polymer components other than acrylonitrile in the acrylonitrile copolymer to the total polymer components is preferably 20% by mass or less, and is 15% by mass or less. is more preferable, and 10% by mass or less is even more preferable.
　アクリロニトリル共重合体の分子量に特に制限はないが、重量平均分子量で５０００～３００万であることが好ましく、１万～１００万であることがより好ましい。アクリロニトリル共重合体の重量平均分子量が５０００以上であると、良質な結着材を得ることができ、アクリロニトリル共重合体の重量平均分子量が３００万以下であると、粘度が低く活物質との混合が容易になる。 The molecular weight of the acrylonitrile copolymer is not particularly limited, but the weight average molecular weight is preferably 5,000 to 3,000,000, more preferably 10,000 to 1,000,000. When the weight average molecular weight of the acrylonitrile copolymer is 5,000 or more, a good binder can be obtained. becomes easier.
　アクリロニトリル共重合体は、ニトリル基が立体規則性をもたないアタクチック型であっても、立体規則性をもつアイソタクチック型であってもよいが、アイソタクチック型であることが好ましい。 The acrylonitrile copolymer may be an atactic type in which the nitrile group has no stereoregularity or an isotactic type with stereoregularity, but the isotactic type is preferred.
　アクリロニトリル共重合体がアイソタクチック型であると、アクリロニトリル共重合体の結晶化度が高く、分子が配向しやすい。このため、活物質の体積変化に耐えうる充分な強度を発現する傾向にある。また、環化反応が生じやすく、充分な電子伝導性を付与することができる。アイソタクチック型のアクリロニトリル共重合体の製造方法としては、特公平７－１０３１８９号公報等を参考にすることができる。 If the acrylonitrile copolymer is isotactic, the degree of crystallinity of the acrylonitrile copolymer is high and the molecules are easily oriented. Therefore, there is a tendency to exhibit sufficient strength to withstand volume changes of the active material. In addition, a cyclization reaction easily occurs, and sufficient electron conductivity can be imparted. Japanese Patent Publication No. 7-103189 can be referred to as a method for producing an isotactic type acrylonitrile copolymer.
　本開示の電極は、結着材として環化ポリアクリロニトリル以外の結着材を含んでもよい。 The electrode of the present disclosure may contain a binder other than cyclized polyacrylonitrile as a binder.
　環化ポリアクリロニトリル以外の結着材としては、ポリアクリル酸、ポリ酢酸ビニル、ポリスチレン、ポリ塩化ビニリデン、ポリ塩化ビニル、ポリメタクリル酸等が挙げられる。 　Binders other than cyclized polyacrylonitrile include polyacrylic acid, polyvinyl acetate, polystyrene, polyvinylidene chloride, polyvinyl chloride, and polymethacrylic acid.
　結着材全体に占める環化ポリアクリロニトリルの割合は、７０質量％～１００質量％であることが好ましく、８０質量％～１００質量％であることがより好ましく、９０質量％～１００質量％であることがさらに好ましい。 The proportion of the cyclized polyacrylonitrile in the entire binder is preferably 70% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and 90% by mass to 100% by mass. is more preferred.
　電極の強度を維持する観点からは、電極に含まれる結着材の含有率は、電極全体（集電体を除く）の１０質量％以上であることが好ましく、２０質量％以上であることがより好ましく、３０質量％以上であることがさらに好ましい。 From the viewpoint of maintaining the strength of the electrode, the content of the binder contained in the electrode is preferably 10% by mass or more, more preferably 20% by mass or more, of the entire electrode (excluding the current collector). More preferably, it is 30% by mass or more.
　電極に含まれる結着材の含有率は、電極全体（集電体を除く）の５０質量％以下であることが好ましく、４５質量％以下であることがより好ましく、４０質量％以下であることがさらに好ましい。
（活物質粒子）
　本開示の電極に含まれる活物質粒子は、アルカリ金属イオンを吸蔵及び放出可能な物質（活物質）を含む粒子であれば特に制限されない。電極に含まれる活物質粒子は、１種のみでも２種以上の組み合わせであってもよい。 The content of the binder contained in the electrode is preferably 50% by mass or less, more preferably 45% by mass or less, and 40% by mass or less of the entire electrode (excluding the current collector). is more preferred.
(Active material particles)
The active material particles contained in the electrode of the present disclosure are not particularly limited as long as they contain a material (active material) that can occlude and release alkali metal ions. The active material particles contained in the electrode may be of one type or a combination of two or more types.
　アルカリ金属イオンとしては、リチウムイオン、カリウムイオン、ナトリウムイオン等が挙げられる。これらの中でもリチウムイオンが好ましい。 Alkali metal ions include lithium ions, potassium ions, sodium ions, and the like. Among these, lithium ion is preferred.
　正極の活物質としては、リチウム遷移金属酸化物、リチウム遷移金属リン酸塩等のリチウム遷移金属化合物が挙げられる。 Examples of positive electrode active materials include lithium transition metal compounds such as lithium transition metal oxides and lithium transition metal phosphates.
　リチウム遷移金属酸化物としては、Ｍｎ、Ｎｉ、Ｃｏ等の遷移金属の１種又は２種以上を含む化合物、及びこれらの化合物に含まれる遷移金属の一部を、１種若しくは２種以上の他の遷移金属又はＭｇ、Ａｌ等の金属元素（典型元素）で置換したリチウム遷移金属酸化物が挙げられる。 Lithium transition metal oxides include compounds containing one or more of transition metals such as Mn, Ni, Co, etc., and some of the transition metals contained in these compounds, one or more of them or a lithium transition metal oxide substituted with a metal element (typical element) such as Mg or Al.
　負極の活物質としては、炭素材料、ケイ素原子を含む活物質等が挙げられる。 Examples of negative electrode active materials include carbon materials and active materials containing silicon atoms.
　炭素材料としては、黒鉛、ハードカーボン、ソフトカーボン等が挙げられる。 Carbon materials include graphite, hard carbon, and soft carbon.
　ケイ素原子を含む活物質としては、Ｓｉ（金属シリコン）、ＳｉＯｘ（０．８≦ｘ≦１．５）で表されるケイ素酸化物等が挙げられる。 Examples of active materials containing silicon atoms include Si (metallic silicon) and silicon oxides represented by SiOx (0.8≦x≦1.5).
　ケイ素酸化物は、不均化反応によりナノシリコンが酸化ケイ素マトリックスに分散された構造であってもよい。 The silicon oxide may have a structure in which nano-silicon is dispersed in a silicon oxide matrix by a disproportionation reaction.
　ケイ素原子を含む活物質は、ホウ素、リン等がドープされて半導体化されていてもよい。 The active material containing silicon atoms may be doped with boron, phosphorus, or the like to make it a semiconductor.
　活物質粒子は、炭素材料からなる活物質粒子の表面にケイ素が存在する活物質粒子を含んでもよい。 The active material particles may include active material particles made of a carbon material and having silicon present on the surface thereof.
　炭素材料からなる活物質粒子の表面にケイ素を存在させる方法としては、蒸着法、プラズマＣＶＤ（Ｃｈｅｍｉｃａｌ　Ｖａｐｏｒ　Ｄｅｐｏｓｉｔｉｏｎ）法等が挙げられる。プラズマＣＶＤ法はシラン、クロロシラン等の原料を分解して行ってもよい。 Examples of methods for making silicon exist on the surface of active material particles made of a carbon material include a vapor deposition method and a plasma CVD (Chemical Vapor Deposition) method. The plasma CVD method may be performed by decomposing raw materials such as silane and chlorosilane.
　ケイ素原子を含む活物質は理論容量が大きく、エネルギー貯蔵デバイスの高容量化への寄与が期待される一方で、充放電の際の体積変化が大きく、劣化しやすい。さらに、ケイ素原子を含む活物質はそれ自体に電子伝導性がない。 Active materials containing silicon atoms have a large theoretical capacity and are expected to contribute to increasing the capacity of energy storage devices. In addition, active materials containing silicon atoms themselves are not electronically conductive.
　本開示の電極に結着材として用いられる環化ポリアクリロニトリルは、活物質の体積変化に対応しうる充分な柔軟性と電子伝導性とを併せもつ。このため、ケイ素原子を含む活物質粒子の結着材として特に好適に使用できる。 The cyclized polyacrylonitrile used as a binder in the electrode of the present disclosure has both sufficient flexibility and electronic conductivity to accommodate changes in the volume of the active material. Therefore, it can be particularly suitably used as a binder for active material particles containing silicon atoms.
　活物質粒子の形状は、特に制限されない。例えば、球状、ワイヤ状、鱗片状、塊状、複数の粒子からなる複合粒子等であってよい。 The shape of the active material particles is not particularly limited. For example, it may be spherical, wire-shaped, scaly, massive, composite particles composed of a plurality of particles, or the like.
　活物質粒子（ワイヤ状の粒子を除く）は、体積平均粒子径（Ｄ５０）が１μｍ～５０μｍであることが好ましく、３μｍ～３０μｍであることがより好ましい。活物質粒子の体積平均粒子径が１μｍ以上であると、電極を形成するためのスラリーの調製が容易になる。活物質粒子の体積平均粒子径が５０μｍ以下であると、電極の薄膜化がしやすく、エネルギー貯蔵デバイスの入出力特性が向上しやすい。 The volume average particle diameter (D50) of the active material particles (excluding wire-like particles) is preferably 1 μm to 50 μm, more preferably 3 μm to 30 μm. When the volume-average particle size of the active material particles is 1 μm or more, preparation of the slurry for forming the electrode is facilitated. When the volume average particle size of the active material particles is 50 μm or less, the electrode can be easily formed into a thin film, and the input/output characteristics of the energy storage device can be easily improved.
　活物質粒子の体積平均粒子径は、レーザー散乱回折法によって測定される。具体的には、レーザー散乱回折法によって得られる体積基準の粒子径分布において小径側からの累積が５０％となるときの粒子径を体積平均粒子径とする。 The volume average particle size of the active material particles is measured by a laser scattering diffraction method. Specifically, the volume-average particle diameter is defined as the particle diameter when the accumulation from the small diameter side is 50% in the volume-based particle diameter distribution obtained by the laser scattering diffraction method.
　活物質粒子が二次粒子である場合、上記体積平均粒子径は二次粒子の体積平均粒子径である。 When the active material particles are secondary particles, the volume average particle size is the volume average particle size of the secondary particles.
　本開示において「二次粒子」とは、複数個の一次粒子が凝集して形成された通常挙動する上での最小単位の粒子を意味し、「一次粒子」とは、単独で存在することができる最小単位の粒子を意味する。 In the present disclosure, the term "secondary particle" means a particle that is the smallest unit of normal behavior formed by agglomeration of a plurality of primary particles, and the term "primary particle" means that it can exist alone. It means the smallest unit particle that can be made.
　活物質粒子が二次粒子である場合、二次粒子を構成する一次粒子の粒子径は、特に制限されない。例えば、平均一次粒子径は１０ｎｍ～５０μｍであることが好ましく。３０ｎｍ～１０μｍであることがより好ましい。活物質粒子の平均一次粒子径が１０ｎｍ以上であると、表面に形成される自然酸化膜の影響を抑えることができる。活物質粒子の平均一次粒子径が５０μｍ以下であると、充放電に伴う劣化が抑制される。 When the active material particles are secondary particles, the particle size of the primary particles that make up the secondary particles is not particularly limited. For example, the average primary particle size is preferably 10 nm to 50 μm. More preferably, it is 30 nm to 10 μm. When the average primary particle size of the active material particles is 10 nm or more, the influence of the natural oxide film formed on the surface can be suppressed. When the average primary particle size of the active material particles is 50 μm or less, deterioration due to charging and discharging is suppressed.
　本開示において活物質の一次粒子径は、走査型電子顕微鏡で観察される一次粒子の長径を意味する。具体的には、一次粒子が球状である場合はその最大直径を意味し、一次粒子が板状である場合はその厚み方向から観察した粒子の投影像における最大直径または最大対角線長を意味する。「平均一次粒子径」は、走査型電子顕微鏡で観察される３００個以上の一次粒子の長径の測定値の算術平均値である。 In the present disclosure, the primary particle diameter of the active material means the major diameter of the primary particles observed with a scanning electron microscope. Specifically, when the primary particles are spherical, it means the maximum diameter, and when the primary particles are tabular, it means the maximum diameter or maximum diagonal length in the projected image of the particles observed from the thickness direction. "Average primary particle diameter" is the arithmetic mean value of the measured values of the major diameters of 300 or more primary particles observed with a scanning electron microscope.
　活物質粒子がワイヤ状である場合、その長さに特に制限はない。例えば、１０ｎｍ～１０μｍであることが好ましい。ワイヤ状の活物質粒子の長さを１０ｎｍ以上とすることでハンドリング性が向上し、１０μｍ以下とすることで活物質粒子の膨張時の応力が分散されやすい傾向にある。 When the active material particles are wire-shaped, there is no particular limit to their length. For example, it is preferably 10 nm to 10 μm. When the length of the wire-shaped active material particles is 10 nm or more, the handleability is improved, and when the length is 10 μm or less, stress during expansion of the active material particles tends to be easily dispersed.
　ワイヤ状の粒子の径に特に制限はない。例えば、１ｎｍ～５μｍであることが好ましい。ワイヤ状の粒子の径を１ｎｍ以上とすることで、ワイヤ状の粒子の自立強度が向上し、５μｍ以下とすることで活物質粒子の膨張時の径方向への応力が抑えられ、長さ方向に応力を逃がすことができる。ワイヤ状の活物質粒子は、活物質粒子をワイヤ状に形成するための触媒成分を含んでいてもよい。ワイヤ状の活物質粒子として具体的には、金属シリコンの粒子が挙げられる。 There is no particular limit to the diameter of wire-like particles. For example, it is preferably 1 nm to 5 μm. By setting the diameter of the wire-shaped particles to 1 nm or more, the self-supporting strength of the wire-shaped particles is improved, and by setting the diameter to 5 μm or less, the stress in the radial direction when the active material particles expand is suppressed, and the length direction is reduced. can relieve stress. The wire-shaped active material particles may contain a catalyst component for forming the wire-shaped active material particles. Specific examples of the wire-shaped active material particles include metallic silicon particles.
　活物質粒子の粒子径を調節する方法は、特に制限されない。例えば、原料を選択する方法、粉砕条件を調節する方法、蒸着、プラズマ法、シラン等の表面処理を行う方法などが挙げられる。 The method for adjusting the particle size of the active material particles is not particularly limited. Examples thereof include a method of selecting raw materials, a method of adjusting pulverization conditions, a vapor deposition method, a plasma method, and a method of surface treatment with silane or the like.
　活物質粒子のＢＥＴ比表面積は、０．５ｍ２／ｇ～１００ｍ２／ｇであることが好ましく、１ｍ２／ｇ～３０ｍ２／ｇであることがより好ましい。活物質粒子のＢＥＴ比表面積が０．５ｍ２／ｇ以上であると、十分な放電容量が得られやすくなる。活物質粒子のＢＥＴ比表面積が１００ｍ２／ｇ以下であると、電極作製の際のハンドリング性に優れる。 The BET specific surface area of the active material particles is preferably 0.5 m 2 /g to 100 m 2 /g, more preferably 1 m 2 /g to 30 m 2 /g. When the BET specific surface area of the active material particles is 0.5 m 2 /g or more, sufficient discharge capacity can be easily obtained. When the BET specific surface area of the active material particles is 100 m 2 /g or less, the handling property during electrode production is excellent.
　活物質粒子のＢＥＴ比表面積は、－１９６℃における窒素の吸着等温線から算出できる。 The BET specific surface area of the active material particles can be calculated from the nitrogen adsorption isotherm at -196°C.
　活物質粒子は、表面に被覆を有していてもよい。 The active material particles may have a coating on their surfaces.
　例えば、活物質粒子は炭素材料からなる被覆（炭素被覆）を有していてもよい。活物質粒子を炭素材料で被覆することで、例えば、導電性を持たない活物質粒子に電子伝導性を付与することができる。 For example, the active material particles may have a coating (carbon coating) made of a carbon material. By coating the active material particles with a carbon material, for example, electronic conductivity can be imparted to active material particles that do not have electrical conductivity.
　活物質粒子を炭素材料で被覆する場合、炭素材料の材質は特に制限されず、黒鉛又は非晶質炭素であってもよい。 When the active material particles are coated with a carbon material, the material of the carbon material is not particularly limited, and may be graphite or amorphous carbon.
　被覆に含まれる炭素材料は、有機化合物を炭化して得られるものであってもよい。有機化合物としてはタール、ピッチ、有機高分子化合物等が挙げられる。有機高分子化合物としてはポリアクリロニトリル、ポリ塩化ビニル、ポリビニルアルコール、ポリ酢酸ビニル、ポリビニルブチラール、デンプン、セルロース等が挙げられる。 The carbon material contained in the coating may be obtained by carbonizing an organic compound. Examples of organic compounds include tar, pitch, and organic polymer compounds. Examples of organic polymer compounds include polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, starch, and cellulose.
　電極の一実施形態は、ケイ素を含む活物質粒子と、炭素材料からなる活物質粒子とを含んでもよい。 An embodiment of the electrode may include active material particles containing silicon and active material particles made of a carbon material.
　この場合、ケイ素を含む活物質粒子と炭素材料からなる活物質粒子との比率に特に制限はないが、ケイ素を含む活物質粒子の割合が活物質粒子全体の５質量％～９０質量％であることが好ましく、１０質量％～７０質量％であることがより好ましい。 In this case, the ratio of the active material particles containing silicon and the active material particles made of a carbon material is not particularly limited, but the ratio of the active material particles containing silicon is 5% by mass to 90% by mass of the total active material particles. is preferred, and 10% by mass to 70% by mass is more preferred.
　ケイ素を含む活物質粒子の割合が活物質粒子全体の５質量％以上であると、エネルギー貯蔵デバイスの高容量化を充分に達成できる。 When the ratio of the active material particles containing silicon is 5% by mass or more of the total active material particles, the capacity of the energy storage device can be sufficiently increased.
　ケイ素を含む活物質粒子の割合が活物質粒子全体の９０質量％以下であると、活物質の体積変化に伴う電極の劣化を充分に抑制できる。 When the ratio of the active material particles containing silicon is 90% by mass or less of the entire active material particles, it is possible to sufficiently suppress the deterioration of the electrode due to the volume change of the active material.
　エネルギー貯蔵デバイスの高容量化の観点からは、電極に含まれる活物質粒子の含有率は、電極全体（集電体を除く）の５０質量％以上であることが好ましく、５５質量％以上であることがより好ましく、６０質量％以上であることがさらに好ましい。 From the viewpoint of increasing the capacity of the energy storage device, the content of the active material particles contained in the electrode is preferably 50% by mass or more of the entire electrode (excluding the current collector), and is 55% by mass or more. is more preferable, and 60% by mass or more is even more preferable.
　結着材による電極の強度維持効果の観点からは、電極に含まれる活物質粒子の含有率は、電極全体（集電体を除く）の９５質量％以下であることが好ましく、９０質量％以下であることがより好ましく、８０質量％以下であることがさらに好ましい。
（導電助剤）
　必要に応じ、電極は導電助剤を含んでもよい。導電助剤としては、カーボンブラック、カーボンナノチューブ、カーボンナノファイバー、フラーレン、カーボンナノホーン等の炭素材料、導電性を示す酸化物、導電性を示す窒化物等が挙げられる。 From the viewpoint of the effect of maintaining the strength of the electrode by the binder, the content of the active material particles contained in the electrode is preferably 95% by mass or less of the entire electrode (excluding the current collector), and 90% by mass or less. and more preferably 80% by mass or less.
(Conductivity aid)
If necessary, the electrodes may contain a conductive aid. Examples of conductive aids include carbon materials such as carbon black, carbon nanotubes, carbon nanofibers, fullerenes and carbon nanohorns, conductive oxides, and conductive nitrides.
　電極が導電助剤を含む場合、その含有率は特に制限されず、電極全体（集電体を除く）の１質量％～２０質量％であってもよい。
（集電体）
　電極は、集電体の上に活物質粒子、結着材及び必要に応じて含まれる導電助剤を含む層が形成された状態であってもよい。 When the electrode contains a conductive aid, the content is not particularly limited, and may be 1% by mass to 20% by mass of the entire electrode (excluding the current collector).
(current collector)
The electrode may be in a state in which a layer containing active material particles, a binder, and optionally a conductive aid is formed on a current collector.
　集電体の種類は特に制限されず、アルミニウム、銅、ニッケル、チタン、ステンレス鋼等の金属又は合金が挙げられる。集電体はカーボンコート、表面粗化等が施された状態であってもよい。 The type of current collector is not particularly limited, and metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel can be used. The current collector may be carbon-coated, surface-roughened, or the like.
　電極の構成の例を、図面に基づいて説明する。 An example of the electrode configuration will be explained based on the drawings.
　図１に示す電極１０は、集電体１の上に、活物質粒子２と結着材３とを含む層が形成された状態である。 The electrode 10 shown in FIG. 1 is in a state in which a layer containing active material particles 2 and a binder 3 is formed on a current collector 1 .
　図２に示す電極１１は、図１に示す電極１０の変形例であり、集電体１の上に形成された層が活物質粒子２及び結着材３に加えて導電助剤４を含んだ状態である。 The electrode 11 shown in FIG. 2 is a modification of the electrode 10 shown in FIG. is in a state.
　図３に示す電極１２は、図１に示す電極１０の変形例であり、活物質粒子２が炭素被覆５を有する状態である。
＜エネルギー貯蔵デバイス＞
　本開示のエネルギー貯蔵デバイスは、上述した本開示の電極を備える。 Electrode 12 shown in FIG. 3 is a modification of electrode 10 shown in FIG. 1, and active material particles 2 have carbon coating 5 .
<Energy storage device>
The energy storage device of the present disclosure comprises the electrodes of the present disclosure as described above.
　エネルギー貯蔵デバイスの種類は特に制限されない。例えば、リチウムイオン電池、ナトリウムイオン電池、カリウムイオン電池等の、アルカリ金属イオンの電極間の移動を充放電に利用するデバイスが挙げられる。 The type of energy storage device is not particularly limited. Examples thereof include devices such as lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries, which utilize movement of alkali metal ions between electrodes for charging and discharging.
　本開示のエネルギー貯蔵デバイスは、正極、負極、電解液等から構成される。上述したエネルギー貯蔵デバイス用電極は正極であっても負極であってもよいが、負極であることが好ましい。 The energy storage device of the present disclosure is composed of a positive electrode, a negative electrode, an electrolytic solution, and the like. The energy storage device electrode described above may be a positive electrode or a negative electrode, but is preferably a negative electrode.
　エネルギー貯蔵デバイスに使用される電解液としては、電解質塩を溶解させた有機溶媒、イオン液体等を使用できる。イオン液体としては、１７０℃未満の温度で液状のイオン液体、溶媒和イオン液体等が挙げられる。 As the electrolyte used in energy storage devices, organic solvents, ionic liquids, etc. in which electrolyte salts are dissolved can be used. Examples of the ionic liquid include ionic liquids that are liquid at a temperature of less than 170° C., solvated ionic liquids, and the like.
　電解質塩として具体的には、ＬｉＰＦ６、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＣｌＦ４、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＡｌＯ４、ＬｉＡｌＣｌ４、ＬｉＮ（ＦＳＯ２）２、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ２Ｆ５ＳＯ２）２、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣｌ、ＬｉＩ等の溶媒和しにくいアニオンを生成するリチウム塩が挙げられる。 Specific examples of electrolyte salts include LiPF 6 , LiClO 4 , LiBF 4 , LiClF 4 , LiAsF 6 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiN(FSO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiN( Lithium salts that generate poorly solvated anions such as C 2 F 5 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 , LiCl, and LiI are included.
　電解質塩は、１種のみを用いても２種以上を用いてもよい。 Only one electrolyte salt may be used, or two or more electrolyte salts may be used.
　電解液中の電解質塩濃度は、例えば、電解液１Ｌあたり好ましくは０．３モル以上、より好ましくは０．５モル以上、さらに好ましくは０．８モル以上である。 The electrolyte salt concentration in the electrolytic solution is, for example, preferably 0.3 mol or more, more preferably 0.5 mol or more, and even more preferably 0.8 mol or more per 1 L of the electrolytic solution.
　電解液中の電解質塩濃度は、例えば、電解液１Ｌあたり好ましくは５モル以下、より好ましくは３モル以下、さらに好ましくは１．５モル以下である。 The electrolyte salt concentration in the electrolytic solution is, for example, preferably 5 mol or less, more preferably 3 mol or less, and even more preferably 1.5 mol or less per 1 L of the electrolytic solution.
　有機溶媒として具体的には、カーボネート類（プロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート等）、ラクトン類（γ－ブチロラクトン等）、鎖状エーテル類（１，２－ジメトキシエタン、ジメチルエーテル、ジエチルエーテル等）、環状エーテル類（テトラヒドロフラン、２－メチルテトラヒドロフラン、ジオキソラン、４－メチルジオキソラン、ジグライム、トリグライム、テトラグライム等）、スルホラン類（スルホラン等）、スルホキシド類（ジメチルスルホキシド等）、ニトリル類（アセトニトリル、プロピオニトリル、ベンゾニトリル等）、アミド類（Ｎ，Ｎ－ジメチルホルムアミド、Ｎ，Ｎ－ジメチルアセトアミド等）、ポリオキシアルキレングリコール類（ジエチレングリコール等）などの非プロトン性溶媒が挙げられる。 Specific examples of organic solvents include carbonates (propylene carbonate, ethylene carbonate, diethyl carbonate, etc.), lactones (γ-butyrolactone, etc.), chain ethers (1,2-dimethoxyethane, dimethyl ether, diethyl ether, etc.), Cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, diglyme, triglyme, tetraglyme, etc.), sulfolanes (sulfolane, etc.), sulfoxides (dimethylsulfoxide, etc.), nitriles (acetonitrile, propionitrile, etc.) , benzonitrile, etc.), amides (N,N-dimethylformamide, N,N-dimethylacetamide, etc.), polyoxyalkylene glycols (diethylene glycol, etc.), and other aprotic solvents.
　有機溶媒は、１種のみを用いても２種以上を用いてもよい。 Only one type of organic solvent may be used, or two or more types may be used.
　イオン液体を構成するカチオン部は、有機カチオン及び無機カチオンのいずれでもよいが、有機カチオンであることが好ましい。 The cation part that constitutes the ionic liquid may be either an organic cation or an inorganic cation, but is preferably an organic cation.
　イオン液体を構成する有機カチオンとして具体的には、イミダゾリウムカチオン、ピリジニウムカチオン、ピロリジニウムカチオン、ホスホニウムカチオン、アンモニウムカチオン、スルホニウムカチオン等が挙げられる。 Specific examples of organic cations that make up the ionic liquid include imidazolium cations, pyridinium cations, pyrrolidinium cations, phosphonium cations, ammonium cations, and sulfonium cations.
　イオン液体を構成するアニオン部は、有機アニオン及び無機アニオンのいずれでもよい。 The anion part constituting the ionic liquid may be either an organic anion or an inorganic anion.
　イオン液体を構成する有機アニオンとして具体的には、メチルサルフェートアニオン（ＣＨ３ＳＯ４ －）、エチルサルフェートアニオン（Ｃ２Ｈ５ＳＯ４ －）等のアルキルサルフェートアニオン；トシレートアニオン（ＣＨ３Ｃ６Ｈ４ＳＯ３ －）；メタンスルホネートアニオン（ＣＨ３ＳＯ３ －）、エタンスルホネートアニオン（Ｃ２Ｈ５ＳＯ３ －）、ブタンスルホネートアニオン（Ｃ４Ｈ９ＳＯ３ －）等のアルカンスルホネートアニオン；トリフルオロメタンスルホネートアニオン（ＣＦ３ＳＯ３ －）、ペンタフルオロエタンスルホネートアニオン（Ｃ２Ｆ５ＳＯ３ －）、ヘプタフルオロプロパンスルホネートアニオン（Ｃ３Ｈ７ＳＯ３ －）、ノナフルオロブタンスルホネートアニオン（Ｃ４Ｈ９ＳＯ３ －）等のパーフルオロアルカンスルホネートアニオン；ビス（トリフルオロメタンスルホニル）イミドアニオン（（ＣＦ３ＳＯ２）Ｎ－）、ビス（ノナフルオロブタンスルホニル）イミドアニオン（（Ｃ４Ｆ９ＳＯ２）Ｎ－）、ノナフルオロ－Ｎ－［（トリフルオロメタン）スルホニル］ブタンスルホニルイミドアニオン（（ＣＦ３ＳＯ２）（Ｃ４Ｆ９ＳＯ２）Ｎ－）、Ｎ，Ｎ－ヘキサフルオロ－１，３－ジスルホニルイミドアニオン（ＳＯ２ＣＦ２ＣＦ２ＣＦ２ＳＯ２Ｎ－）等のパーフルオロアルカンスルホニルイミドアニオン；アセテートアニオン（ＣＨ３ＣＯＯ－）；ハイドロジェンサルフェートアニオン（ＨＳＯ４ －）；などが挙げられる。 Specific examples of organic anions constituting the ionic liquid include alkyl sulfate anions such as methyl sulfate anion (CH 3 SO 4 − ) and ethyl sulfate anion (C 2 H 5 SO 4 − ); tosylate anion (CH 3 C 6 H 4 SO 3 − ); alkanesulfonate anions such as methanesulfonate anion (CH 3 SO 3 − ), ethanesulfonate anion (C 2 H 5 SO 3 − ), butanesulfonate anion (C 4 H 9 SO 3 − ); romethanesulfonate anion (CF 3 SO 3 − ), pentafluoroethanesulfonate anion (C 2 F 5 SO 3 − ), heptafluoropropanesulfonate anion (C 3 H 7 SO 3 − ), nonafluorobutanesulfonate anion (C 4 H 9 SO 3 − ) and other perfluoroalkanesulfonate anions ; N − ), nonafluoro-N-[(trifluoromethane)sulfonyl]butanesulfonylimide anion ((CF 3 SO 2 )(C 4 F 9 SO 2 )N − ), N,N-hexafluoro-1,3-di perfluoroalkanesulfonylimide anions such as sulfonylimide anions (SO 2 CF 2 CF 2 CF 2 SO 2 N − ); acetate anions (CH 3 COO − ); hydrogen sulfate anions (HSO 4 − );
　イオン液体を構成する無機アニオンとして具体的には、ビス（フルオロスルホニル）イミドアニオン（Ｎ（ＳＯ２Ｆ）２ －）；ビス（トリフルオロスルホニル）イミドアニオン（Ｎ（ＳＯ２CＦ3）２ －）；ヘキサフルオロホスフェートアニオン（ＰＦ６ －）；テトラフルオロボレートアニオン（ＢＦ４ －）；塩化物イオン（Ｃｌ－）、臭化物イオン（Ｂｒ－）、ヨウ化物イオン（Ｉ－）等のハライドアニオン；テトラクロロアルミネートアニオン（ＡｌＣｌ４ －）；チオシアネートアニオン（ＳＣＮ－）；などが挙げられる。 Specific inorganic anions constituting the ionic liquid include bis(fluorosulfonyl)imide anion (N(SO 2 F) 2 − ); bis(trifluorosulfonyl)imide anion (N(SO 2 CF 3 ) 2 − ). hexafluorophosphate anion (PF 6 − ); tetrafluoroborate anion (BF 4 − ); halide anions such as chloride ion (Cl − ), bromide ion (Br − ), iodide ion (I − ); tetrachloro aluminate anion (AlCl 4 − ); thiocyanate anion (SCN − ); and the like.
　イオン液体としては、例えば、上記のいずれかのカチオン部と、上記のいずれかのアニオン部と、の組み合わせで構成されたものが挙げられる。 Examples of ionic liquids include those composed of a combination of any of the above cation moieties and any of the above anion moieties.
　カチオン部がイミダゾリウムカチオンであるイオン液体として具体的には、１－エチル－３－メチルイミダゾリウムビス（トリフルオロメタンスルホニル）イミド、１－ブチル－３－メチルイミダゾリウムビス（トリフルオロメタンスルホニル）イミド、１－メチル－３－プロピルイミダゾリウムビス（トリフルオロメタンスルホニル）イミド、１－ヘキシル－３－メチルイミダゾリウムビス（トリフルオロメタンスルホニル）イミド、１－エチル－３－メチルイミダゾリウムクロライド、１－ブチル－３－メチルイミダゾリウムクロライド、１－エチル－３－メチルイミダゾリウムメタンスルホネート、１－ブチル－３－メチルイミダゾリウムメタンスルホネート、１，２，３－トリメチルイミダゾリウムメチルサルフェート、メチルイミダゾリウムクロライド、メチルイミダゾリウムハイドロジェンサルフェート、１－エチル－３－メチルイミダゾリウムハイドロジェンサルフェート、１－ブチル－３－メチルイミダゾリウムハイドロジェンサルフェート、１－ブチル－３－メチルイミダゾリウムハイドロジェンサルフェート、１－エチル－３－メチルイミダゾリウムテトラクロロアルミネート、１－ブチル－３－メチルイミダゾリウムテトラクロロアルミネート、１－エチル－３－メチルイミダゾリウムアセテート、１－ブチル－３－メチルイミダゾリウムアセテート、１－エチル－３－メチルイミダゾリウムエチルサルフェート、１－ブチル－３－メチルイミダゾリウムメチルサルフェート、１－エチル－３－メチルイミダゾリウムチオシアネート、１－ブチル－３－メチルイミダゾリウムチオシアネート、１－エチル－２，３－ジメチルイミダゾリウムエチルサルフェート等が挙げられる。 Specific examples of the ionic liquid whose cation moiety is an imidazolium cation include 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3 -methylimidazolium chloride, 1-ethyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium methanesulfonate, 1,2,3-trimethylimidazolium methylsulfate, methylimidazolium chloride, methylimidazolium Hydrogen sulfate, 1-ethyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium hydrogen sulfate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium thiocyanate, 1-ethyl-2,3-dimethylimidazolium Ethyl sulfate etc. are mentioned.
　カチオン部がピロリジニウムカチオンであるイオン液体として具体的には、１－メチル－１－プロピルピロリジニウムビス（トリフルオロメタンスルホニル）イミド、１－ブチル－１－メチルピロリジニウムビス（トリフルオロメタンスルホニル）イミド等が挙げられる。 Specific examples of ionic liquids in which the cation portion is a pyrrolidinium cation include 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) ) imide and the like.
　溶媒和イオン液体としては、グライム－リチウム塩錯体等が挙げられる。 Examples of solvated ionic liquids include glyme-lithium salt complexes.
　グライム－リチウム塩錯体におけるリチウム塩として具体的には、リチウムビス（フルオロスルホニル）イミド（ＬｉＮ（ＳＯ２Ｆ）２、本開示においては、「ＬｉＦＳＩ」と略記することがある）、リチウムビス（トリフルオロメタンスルホニル）イミド（ＬｉＮ（ＳＯ２ＣＦ３）２、本開示においては、「ＬｉＴＦＳＩ」と略記することがある）等が挙げられる。 Specific examples of the lithium salt in the glyme-lithium salt complex include lithium bis(fluorosulfonyl)imide (LiN(SO 2 F) 2 , sometimes abbreviated as “LiFSI” in the present disclosure), lithium bis(trifluoro romethanesulfonyl)imide (LiN(SO 2 CF 3 ) 2 , sometimes abbreviated as “LiTFSI” in the present disclosure), and the like.
　グライム－リチウム塩錯体におけるグライムとして具体的には、トリエチレングリコールジメチルエーテル（ＣＨ３（ＯＣＨ２ＣＨ２）３ＯＣＨ３、トリグライム）、テトラエチレングリコールジメチルエーテル（ＣＨ３（ＯＣＨ２ＣＨ２）４ＯＣＨ３、テトラグライム）等が挙げられる。 Specific examples of glyme in the glyme-lithium salt complex include triethylene glycol dimethyl ether (CH 3 (OCH 2 CH 2 ) 3 OCH 3 , triglyme), tetraethylene glycol dimethyl ether (CH 3 (OCH 2 CH 2 ) 4 OCH 3 , tetraglyme) and the like.
　グライム－リチウム塩錯体は、例えば、リチウム塩とグライムとを、リチウム塩：グライム（モル比）が、好ましくは１０：９０～９０：１０となるように、混合することで作製できる。 A glyme-lithium salt complex can be prepared, for example, by mixing a lithium salt and glyme so that the lithium salt:glyme (molar ratio) is preferably 10:90 to 90:10.
　電解液は、添加剤を含んでもよい。添加剤として具体的には、フルオロエチレンカーボネート、プロパンスルトン、ビニレンカーボネート、メタンスルホン酸、シクロヘキシルベンゼン、ｔｅｒｔ－アミルベンゼン、アジポニトリル、スクシノニトリル等が挙げられる。 The electrolyte may contain additives. Specific examples of additives include fluoroethylene carbonate, propanesultone, vinylene carbonate, methanesulfonic acid, cyclohexylbenzene, tert-amylbenzene, adiponitrile, and succinonitrile.
　電解液中の添加剤の量は、例えば、電解液全体の０．１質量％～３０質量％であることが好ましく、０．５質量％～１０質量％であることが好ましい。 The amount of the additive in the electrolytic solution is, for example, preferably 0.1% by mass to 30% by mass, preferably 0.5% by mass to 10% by mass, based on the total amount of the electrolytic solution.
　エネルギー貯蔵デバイスは、電極及び電解液に加え、通常使用されるセパレータ、ガスケット、封口板、ケース等の部材をさらに備えていてもよい。 The energy storage device may further comprise commonly used members such as separators, gaskets, sealing plates, and cases in addition to the electrodes and electrolyte.
　エネルギー貯蔵デバイスに使用されるセパレータは特に制限されず、多孔質ポリプロピレン製不織布、多孔質ポリエチレン製不織布等のポリオレフィン系の多孔質膜などが挙げられる。 The separator used in the energy storage device is not particularly limited, and examples include polyolefin-based porous membranes such as porous polypropylene nonwoven fabrics and porous polyethylene nonwoven fabrics.
　エネルギー貯蔵デバイスの形状は、円筒型、角型、ボタン型等の任意の形態とすることができる。 The shape of the energy storage device can be any shape, such as cylindrical, square, and button.
　エネルギー貯蔵デバイスの用途は特に制限されない。例えば、分散型又は可搬性の電池として、電子機器、電気機器、自動車、電力貯蔵等の電源又は補助電源として利用できる。
＜エネルギー貯蔵デバイス用電極の製造方法＞
　本開示のエネルギー貯蔵デバイス用電極の製造方法は、アルカリ金属イオンを吸蔵及び放出可能な物質を含む粒子（活物質粒子）と、アクリロニトリルとアクリロニトリル以外の重合成分との共重合体（アクリロニトリル共重合体）と、を含む組成物を熱処理する工程を含む、エネルギー貯蔵デバイス用電極の製造方法である。 Applications of the energy storage device are not particularly limited. For example, as a distributed or portable battery, it can be used as a power source or auxiliary power source for electronic devices, electrical devices, automobiles, power storage, and the like.
<Method for producing electrode for energy storage device>
The method for producing an electrode for an energy storage device of the present disclosure includes particles (active material particles) containing a substance capable of absorbing and releasing alkali metal ions, and a copolymer of acrylonitrile and a polymer component other than acrylonitrile (acrylonitrile copolymer ) and a step of heat-treating a composition comprising:
　上記方法によれば、アクリロニトリル共重合体の環化反応物である環化ポリアクリロニトリルを結着材として含む電極を製造することができる。 According to the above method, an electrode containing, as a binder, cyclized polyacrylonitrile, which is a cyclization reaction product of an acrylonitrile copolymer, can be produced.
　活物質粒子及びアクリロニトリル共重合体の詳細及び好ましい態様は、上述した電極に用いる活物質粒子及びアクリロニトリル共重合体の詳細及び好ましい態様と同様である。 The details and preferred aspects of the active material particles and acrylonitrile copolymer are the same as the details and preferred aspects of the active material particles and acrylonitrile copolymer used in the electrode described above.
　上記方法における熱処理は、アクリロニトリル共重合体の環化反応が生じる条件（例えば、２７８℃～６００℃）で行う。 The heat treatment in the above method is performed under conditions (for example, 278°C to 600°C) that cause a cyclization reaction of the acrylonitrile copolymer.
　以下、２７８℃～６００℃で組成物を熱処理する工程を「環化処理」ともいう。 Hereinafter, the process of heat-treating the composition at 278°C to 600°C is also referred to as "cyclization treatment".
　アクリロニトリル共重合体を上記温度で熱処理することで、アクリロニトリル共重合体の環化反応が進行するとともに脱水素化反応が進行して二重結合が形成され、得られる環化ポリアクリロニトリルの電子伝導性が向上する。 By heat-treating the acrylonitrile copolymer at the above temperature, the cyclization reaction of the acrylonitrile copolymer proceeds and the dehydrogenation reaction proceeds to form double bonds, resulting in the electronic conductivity of the resulting cyclized polyacrylonitrile. improves.
　環化処理を実施する際の温度は２７８℃以上であり、２８０℃以上であることが好ましく、２９０℃以上であることがより好ましく、３００℃以上であることがさらに好ましい。 The temperature at which the cyclization treatment is performed is 278°C or higher, preferably 280°C or higher, more preferably 290°C or higher, and even more preferably 300°C or higher.
　環化処理を実施する際の温度は６００℃以下であり、５００℃以下であることが好ましく、４５０℃以下であることがより好ましく、４００℃以下であることがさらに好ましい。環化処理を実施する温度を６００℃以下とすることで、アクリロニトリル共重合体の炭化が抑制され、得られる環化ポリアクリロニトリルの柔軟性が維持される。 The temperature at which the cyclization treatment is performed is 600°C or lower, preferably 500°C or lower, more preferably 450°C or lower, and even more preferably 400°C or lower. By setting the temperature at which the cyclization treatment is performed to 600° C. or lower, carbonization of the acrylonitrile copolymer is suppressed, and flexibility of the obtained cyclized polyacrylonitrile is maintained.
　環化処理を実施する際の酸素濃度は４ｐｐｍ以上であることが好ましく、７．５ｐｐｍ以上であることがより好ましく、１０ｐｐｍ以上であることがさらに好ましく、１５ｐｐｍ以上であることが特に好ましい。 The oxygen concentration during the cyclization treatment is preferably 4 ppm or higher, more preferably 7.5 ppm or higher, even more preferably 10 ppm or higher, and particularly preferably 15 ppm or higher.
　アクリロニトリル共重合体の分解を抑制する観点からは、環化処理を実施する際の酸素濃度は１００ｐｐｍ以下であり、８０ｐｐｍ以下であることが好ましく、６０ｐｐｍ以下であることがより好ましく、４０ｐｐｍ以下であることがさらに好ましい。 From the viewpoint of suppressing the decomposition of the acrylonitrile copolymer, the oxygen concentration when performing the cyclization treatment is 100 ppm or less, preferably 80 ppm or less, more preferably 60 ppm or less, and 40 ppm or less. is more preferred.
　環化処理を実施する雰囲気の酸素以外の成分は特に制限されず、窒素、アルゴン等の不活性ガス又はこれらの混合物であってもよい。 The components other than oxygen in the atmosphere in which the cyclization treatment is performed are not particularly limited, and may be nitrogen, an inert gas such as argon, or a mixture thereof.
　環化処理を実施する時間は特に制限されず、例えば、３時間～１５時間の間から選択できる。 The time for performing the cyclization treatment is not particularly limited, and can be selected, for example, from 3 hours to 15 hours.
　本開示において環化処理を実施する時間は、組成物の温度が２７８℃～６００℃である間の時間を意味する。 The time for performing the cyclization treatment in the present disclosure means the time during which the temperature of the composition is 278°C to 600°C.
　本開示の方法は、環化処理の前に、１５０℃以上２７８℃未満の温度で組成物を熱処理する工程（以下、前処理ともいう）を含んでもよい。 The method of the present disclosure may include a step of heat-treating the composition at a temperature of 150°C or more and less than 278°C (hereinafter also referred to as pretreatment) before the cyclization treatment.
　前処理を実施する時間は特に制限されず、例えば、３時間～１５時間の間から選択できる。 The time for performing pretreatment is not particularly limited, and can be selected, for example, from 3 hours to 15 hours.
　本開示において前処理を実施する時間は、組成物の温度が１５０℃以上２７８℃未満である間の時間を意味する。 The time during which the pretreatment is performed in the present disclosure means the time during which the temperature of the composition is 150°C or higher and lower than 278°C.
　前処理を行う際の雰囲気は特に制限されず、酸素を含まない不活性雰囲気であっても、酸素を含む雰囲気（空気等）であってもよい。サイクル特性の観点からは、酸素を５体積％～３０体積％含む雰囲気であることが好ましい。 The atmosphere during the pretreatment is not particularly limited, and may be an inert atmosphere that does not contain oxygen or an atmosphere that contains oxygen (such as air). From the viewpoint of cycle characteristics, the atmosphere preferably contains 5% to 30% by volume of oxygen.
　前処理と環化処理とをこの順に行う場合、前処理と環化処理とを連続して行っても、連続せずに行ってもよい。例えば、前処理と環化処理との間で組成物を冷却する工程を行ってもよい。 When the pretreatment and the cyclization treatment are performed in this order, the pretreatment and the cyclization treatment may or may not be performed consecutively. For example, a step of cooling the composition may be performed between the pretreatment and the cyclization treatment.
　必要に応じ、組成物は導電助剤、溶剤等を含んでもよい。溶媒としては、Ｎ－メチル－２－ピロリドン、ジメチルホルムアミド、ジメチルアセトアミド、ジメチルスルホキシド等のポリアクリロニトリルを溶解可能な溶媒が挙げられる。 If necessary, the composition may contain a conductive aid, solvent, etc. Solvents include those capable of dissolving polyacrylonitrile, such as N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and dimethylsulfoxide.
　組成物は、活物質粒子とアクリロニトリル共重合体との混合物であっても、活物質粒子とアクリロニトリル共重合体の原料となるモノマーとを混合した状態でモノマーを重合させて得られるものであってもよい。 Even if the composition is a mixture of the active material particles and the acrylonitrile copolymer, it is obtained by polymerizing the monomers in a state in which the active material particles and the monomer that is the raw material of the acrylonitrile copolymer are mixed. good too.
　組成物は、加圧されてもよい。組成物を加圧することで、アクリロニトリル共重合体の分子が配向した状態で環化反応が生じ、分子がスタッキングすることで結晶性が高まる。アクリロニトリル共重合体が高結晶化すると、得られる環化ポリアクリロニトリルの強度が向上し、電子伝導度も向上する傾向にある。 The composition may be pressurized. By pressurizing the composition, a cyclization reaction occurs in the state where the molecules of the acrylonitrile copolymer are oriented, and the molecules stack to increase the crystallinity. When the acrylonitrile copolymer is highly crystallized, the obtained cyclized polyacrylonitrile tends to have an improved strength and an improved electronic conductivity.
　組成物に圧力を加える方法に特に制限はないが、耐圧容器、オートクレーブ用容器等の内部にガス又は液体を封入し、加熱したてこれらを気化させて圧力を高める方法、組成物を板状の部材で挟み、面圧（たとえば０．１ＭＰａ～１０ＭＰａ）をかける方法などが挙げられる。加圧処理は環化処理の前に行っても、環化処理の間に行っても、環化処理の後に行ってもよい。 The method of applying pressure to the composition is not particularly limited. A method of sandwiching between members and applying surface pressure (for example, 0.1 MPa to 10 MPa) can be used. The pressure treatment may be performed before the cyclization treatment, during the cyclization treatment, or after the cyclization treatment.
　環化処理を行う際の組成物は、集電体の上に層状に形成された状態であってもよい。
＜電極形成用材料＞
　本開示の電極形成用材料は、エネルギー貯蔵デバイスの電極を形成するための材料であって、アクリロニトリルとアクリロニトリル以外の重合成分との共重合体（アクリロニトリル共重合体）を含む、電極形成用材料である。 The composition for the cyclization treatment may be in a layered state on the current collector.
<Electrode forming material>
The electrode-forming material of the present disclosure is a material for forming an electrode of an energy storage device, and is an electrode-forming material containing a copolymer of acrylonitrile and a polymer component other than acrylonitrile (acrylonitrile copolymer). be.
　上記材料を用いて形成される電極及びエネルギー貯蔵デバイスは、優れた特性を示す。 Electrodes and energy storage devices formed using the above materials exhibit excellent characteristics.
　上記材料に含まれるアクリロニトリル共重合体の詳細及び好ましい態様は、上述した電極に用いるアクリロニトリル共重合体の詳細及び好ましい態様と同様である。 The details and preferred aspects of the acrylonitrile copolymer contained in the above materials are the same as the details and preferred aspects of the acrylonitrile copolymer used in the electrode described above.
　以下、実施例に基づいて本開示をより具体的に説明するが、本開示は下記の実施例に制限されるものではない。
＜実施例１＞
　アクリロニトリル共重合体（ＰＡＮ）をＮ－メチル－２－ピロリドン（ＮＭＰ）へ加え、室温で混合してＰＡＮを溶解し、ＰＡＮ／ＮＭＰ溶液（ＰＡＮ含有率：１０質量％）を調製した。 Hereinafter, the present disclosure will be described more specifically based on examples, but the present disclosure is not limited to the following examples.
<Example 1>
Acrylonitrile copolymer (PAN) was added to N-methyl-2-pyrrolidone (NMP) and mixed at room temperature to dissolve PAN to prepare a PAN/NMP solution (PAN content: 10% by mass).
　アクリロニトリル共重合体としては、アクリロニトリル以外の重合成分としてメタリルスルホン酸ナトリウム（０．３質量％）及びメチルアクリレート（５．８質量％）を含み、重量平均分子量が８０，０００であるものを用いた。 The acrylonitrile copolymer contains sodium methallylsulfonate (0.3% by mass) and methyl acrylate (5.8% by mass) as polymerization components other than acrylonitrile, and has a weight average molecular weight of 80,000. board.
　活物質としてＳｉ粒子（平均二次粒子径：約５μｍ）とＰＡＮ／ＮＭＰ溶液とを、ＳｉとＰＡＮの質量比率（Ｓｉ：ＰＡＮ）が７０：３０となるように混合し、スラリーＡを得た。スラリーＡを集電体である銅箔に塗布して乾燥し、電極と集電体との積層体（電極の面積当たり質量：７ｇ／ｍ２）を得た。この積層体に対し、酸素濃度が２０ｐｐｍの窒素雰囲気中で３５０℃、５時間の熱処理（環化処理）を行って、電極を得た。
＜実施例２＞
　アクリロニトリル共重合体として、アクリロニトリル以外の重合成分としてメチルアクリレート（０．５質量％）を含み、重量平均分子量が２００，０００であるものを用いたこと以外は実施例１と同様にして電極を作製した。
＜比較例１＞
　アクリロニトリル共重合体に代えて、アクリロニトリルの単独重合体（重量平均分子量：１５０，０００）を用いたこと以外は実施例１と同様にして電極を作製した。
＜電池の作製＞
　負極電極として上記で作製した電極と、対極としてリチウム金属とを用い、コイン型の電池を作製した。セパレータとしてはポリプロピレン多孔質膜を使用し、電解液としては１ＭのＬｉＰＦ６をＥＣ（エチレンカーボネート）、ＥＭＣ（エチルメチルカーボネート）及びＤＥＣ（ジエチルカーボネート）を１：１：１（体積比）の割合で含む混合溶媒に溶解したものを使用した。
＜電池特性＞
　作製したコイン型電池に対し、０．０５Ｃ（２０時間かけてフル充電及びフル放電される電流）のレートでの充放電を３サイクル実施し、次いで、０．１Ｃ（１０時間かけてフル充電及びフル放電される電流）のレートでの充放電を４７サイクル実施した（計５０サイクル）。 Si particles (average secondary particle diameter: about 5 μm) as an active material and a PAN/NMP solution were mixed so that the mass ratio of Si and PAN (Si:PAN) was 70:30 to obtain slurry A. . The slurry A was applied to a copper foil as a current collector and dried to obtain a laminate of the electrode and the current collector (mass per area of the electrode: 7 g/m 2 ). This laminate was subjected to heat treatment (cyclization treatment) at 350° C. for 5 hours in a nitrogen atmosphere with an oxygen concentration of 20 ppm to obtain an electrode.
<Example 2>
An electrode was produced in the same manner as in Example 1 except that an acrylonitrile copolymer containing methyl acrylate (0.5% by mass) as a polymerization component other than acrylonitrile and having a weight average molecular weight of 200,000 was used. bottom.
<Comparative Example 1>
An electrode was prepared in the same manner as in Example 1, except that an acrylonitrile homopolymer (weight average molecular weight: 150,000) was used instead of the acrylonitrile copolymer.
<Production of battery>
Using the electrode prepared above as the negative electrode and lithium metal as the counter electrode, a coin-type battery was prepared. A polypropylene porous membrane is used as the separator, and 1M LiPF6 as the electrolyte is EC (ethylene carbonate), EMC (ethyl methyl carbonate) and DEC (diethyl carbonate) in a ratio of 1:1:1 (volume ratio). was dissolved in a mixed solvent containing
<Battery characteristics>
The prepared coin-type battery was charged and discharged at a rate of 0.05 C (current for full charge and full discharge over 20 hours) for 3 cycles, then 0.1 C (full charge and discharge for 10 hours). 47 cycles of charge/discharge were performed at a rate of (current for full discharge) (total of 50 cycles).
　上記条件の充放電において、１サイクル目の充電容量（初回充電容量）と１サイクル目の放電容量（初回放電容量）とから、下記式により初回効率を求めた。 In charging and discharging under the above conditions, the initial efficiency was obtained from the following formula from the charge capacity of the first cycle (initial charge capacity) and the discharge capacity of the first cycle (initial discharge capacity).
　初回効率（％）＝（初回放電容量（ｍＡｈ）／初回充電容量（ｍＡｈ））×１００
　上記条件の充放電において、初回放電容量と、５０サイクル目の放電容量とから、下記式により放電容量維持率を求めた。 Initial efficiency (%) = (initial discharge capacity (mAh) / initial charge capacity (mAh)) x 100
In charging and discharging under the above conditions, the discharge capacity retention rate was obtained from the following formula from the initial discharge capacity and the discharge capacity at the 50th cycle.
　放電容量維持率（％）＝（５０サイクル目の放電容量（ｍＡｈ）／初回放電容量（ｍＡｈ））×１００
　初回効率は、実施例１は９１％、実施例２は７１％、比較例１は５６％であった。 Discharge capacity retention rate (%) = (50th cycle discharge capacity (mAh) / initial discharge capacity (mAh)) x 100
The initial efficiency was 91% for Example 1, 71% for Example 2, and 56% for Comparative Example 1.
　５０サイクル後の放電容量維持率は、実施例１は５４％、実施例２は２５％、比較例１は２７％であった。 The discharge capacity retention rate after 50 cycles was 54% for Example 1, 25% for Example 2, and 27% for Comparative Example 1.
　５０サイクル後の活物質質量あたりの放電容量は、実施例１は２０３０ｍＡｈ／ｇ、実施例２は７５０ｍＡｈ／ｇ、比較例１は５５８ｍＡｈ／ｇであった。
＜電極強度＞
　電極強度の指標として、実施例１及び比較例１で作製した電極を厚み方向に３等分したときに集電体から最も遠い層（上層）、中間の層（中層）、集電体に最も近い層（下層）の順に電極を削り取るときの剥離強度を調べるＳＡＩＣＡＳ（Ｓｕｒｆａｃｅ　Ａｎｄ　Ｉｎｔｅｒｆａｃｉａｌ　Ｃｕｔｔｉｎｇ　Ａｎａｌｙｓｉｓ　Ｓｙｓｔｅｍ）試験を行った。測定条件は下記の通りである。 The discharge capacity per active material mass after 50 cycles was 2030 mAh/g for Example 1, 750 mAh/g for Example 2, and 558 mAh/g for Comparative Example 1.
<Electrode strength>
As an index of electrode strength, when the electrodes prepared in Example 1 and Comparative Example 1 are divided into three equal parts in the thickness direction, the layer farthest from the current collector (upper layer), the middle layer (middle layer), and the current collector A SAICAS (Surface And Interfacial Cutting Analysis System) test was performed to examine the peel strength when the electrodes were scraped off in order from the closest layer (lower layer). The measurement conditions are as follows.
　本実施例では、測定装置としてダイプラ・ウィンテス（株）製のＳＡＩＣＡＳ、型式:ＤＮ－２０Ｓを使用した。 In this example, SAICAS manufactured by Daipla Wintes Co., Ltd., model: DN-20S, was used as the measuring device.
　測定モード：低速度モード
　刃幅：１．０ｍｍ
　水平速度：５μｍ／ｓ
　垂直速度：０．５μｍ／ｓ
　試験回数：２
　試験環境：気温２４．３℃～２５．７℃、相対湿度２０％～２１％
　集電体から下層を削り取ったときの剥離強度（ｋＮ／ｍ、測定２回の平均値）を測定したところ、実施例１は０．６ｋＮ／ｍであり、比較例１の０．３ｋＮ／ｍよりも大きかった。
＜電極の表面観察＞
　電池の充放電を５０サイクル実施した後、実施例１及び比較例１で作製した電池から取り出した電極の表面を走査電子顕微鏡で観察した。図４に実施例１で作製した電極の表面の走査電子顕微鏡像を、図５に比較例１で作製した電極の表面の走査電子顕微鏡像をそれぞれ示す。 Measurement mode: Low speed mode Blade width: 1.0mm
Horizontal speed: 5 μm/s
Vertical velocity: 0.5 μm/s
Number of tests: 2
Test environment: temperature 24.3°C to 25.7°C, relative humidity 20% to 21%
When the peel strength (kN/m, average value of two measurements) was measured when the lower layer was scraped off from the current collector, it was 0.6 kN/m in Example 1 and 0.3 kN/m in Comparative Example 1. was bigger than
<Surface observation of electrode>
After 50 charge/discharge cycles of the battery, the surfaces of the electrodes taken out from the batteries produced in Example 1 and Comparative Example 1 were observed with a scanning electron microscope. FIG. 4 shows a scanning electron microscope image of the surface of the electrode produced in Example 1, and FIG. 5 shows a scanning electron microscope image of the surface of the electrode produced in Comparative Example 1. As shown in FIG.
　図４及び図５に示すように、アクリロニトリル共重合体の環化処理物を含む電極を用いて作製した実施例１の電池は、アクリロニトリル単独重合体の環化処理物を含む電極を用いて作製した比較例１の電池に比べて表面のひびが少ない。 As shown in FIGS. 4 and 5, the battery of Example 1, which was produced using the electrode containing the cyclized acrylonitrile copolymer, was produced using the electrode containing the cyclized acrylonitrile homopolymer. As compared with the battery of Comparative Example 1, the number of cracks on the surface is small.

Claims (8)

  1. 　アルカリ金属イオンを吸蔵及び放出可能な物質を含む粒子と、環化ポリアクリロニトリルを含む結着材と、を含み、前記環化ポリアクリロニトリルはアクリロニトリルとアクリロニトリル以外の重合成分との共重合体の環化処理物である、エネルギー貯蔵デバイス用電極。 Particles containing a substance capable of absorbing and releasing alkali metal ions; An electrode for an energy storage device, which is a processed product.
  2. 　前記共重合体はイオン性基を含む、請求項１に記載のエネルギー貯蔵デバイス用電極。 The electrode for energy storage device according to claim 1, wherein the copolymer contains an ionic group.
  3. 　前記共重合体はアニオン性基を含む、請求項１又は請求項２に記載のエネルギー貯蔵デバイス用電極。 The electrode for an energy storage device according to claim 1 or 2, wherein the copolymer contains an anionic group.
  4. 　前記共重合体におけるアクリロニトリル以外の重合成分の全重合成分に占める割合は０．１質量％～２０質量％である、請求項１～請求項３のいずれか１項に記載のエネルギー貯蔵デバイス用電極。 The electrode for an energy storage device according to any one of claims 1 to 3, wherein the ratio of the polymer components other than acrylonitrile in the copolymer to the total polymer components is 0.1% by mass to 20% by mass. .
  5. 　前記アルカリ金属イオンを吸蔵及び放出可能な物質はケイ素原子を含む、請求項１～請求項４のいずれか１項に記載のエネルギー貯蔵デバイス用電極。 The electrode for an energy storage device according to any one of claims 1 to 4, wherein the substance capable of absorbing and releasing alkali metal ions contains silicon atoms.
  6. 　請求項１～請求項５のいずれか１項に記載のエネルギー貯蔵デバイス用電極を含む、エネルギー貯蔵デバイス。 An energy storage device comprising the energy storage device electrode according to any one of claims 1 to 5.
  7. 　アルカリ金属イオンを吸蔵及び放出可能な物質を含む粒子と、アクリロニトリルとアクリロニトリル以外の重合成分との共重合体と、を含む組成物を熱処理する工程を含む、エネルギー貯蔵デバイス用電極の製造方法。 A method for producing an electrode for an energy storage device, comprising a step of heat-treating a composition containing particles containing a substance capable of absorbing and releasing alkali metal ions and a copolymer of acrylonitrile and a polymer component other than acrylonitrile.
  8. 　エネルギー貯蔵デバイスの電極を形成するための材料であって、アクリロニトリルとアクリロニトリル以外の重合成分との共重合体を含む、電極形成用材料。 An electrode-forming material that is a material for forming an electrode of an energy storage device and contains a copolymer of acrylonitrile and a polymer component other than acrylonitrile.
PCT/JP2021/033591 2021-09-13 2021-09-13 Electrode for energy storage devices, energy storage device, production method for electrode for energy storage devices, and material for forming electrode WO2023037556A1 (en)

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