WO2025115526A1 - 電極形成用組成物、添加剤、及びゲル化抑制剤 - Google Patents

電極形成用組成物、添加剤、及びゲル化抑制剤 Download PDF

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WO2025115526A1
WO2025115526A1 PCT/JP2024/039199 JP2024039199W WO2025115526A1 WO 2025115526 A1 WO2025115526 A1 WO 2025115526A1 JP 2024039199 W JP2024039199 W JP 2024039199W WO 2025115526 A1 WO2025115526 A1 WO 2025115526A1
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active material
positive electrode
forming composition
electrode active
electrode
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English (en)
French (fr)
Japanese (ja)
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辰也 畑中
綾子 久保
幸雄 浅香
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Nissan Chemical Corp
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Nissan Chemical Corp
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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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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 invention relates to an electrode-forming composition, an additive, and a gelation inhibitor. Furthermore, the present invention relates to an electrode layer, a secondary battery, a method for producing an electrode-forming composition, and a method for inhibiting gelation of an electrode-forming composition.
  • Lithium-ion secondary batteries have a high energy density per unit weight and volume, which contributes to making electronic devices smaller and lighter.
  • the spread of electric vehicles has accelerated as part of efforts toward zero-emission automobiles, and there is a demand for even lower resistance, longer life, higher capacity, safety, and lower cost.
  • Lithium-ion secondary batteries generally have a three-layer structure of a positive electrode, a separator, and a negative electrode, which contains an electrolyte.
  • the positive and negative electrodes are manufactured, for example, by coating a current collector with an electrode slurry made by mixing an active material, a conductive material, and a binder.
  • the mainstream method for manufacturing negative electrodes is to coat the negative electrode slurry on copper foil, which serves as the current collector, and then dry it.
  • the mainstream method for manufacturing positive electrodes is to prepare a positive electrode slurry using an organic solvent such as N-methyl-2-pyrrolidone as the solvent, and then coat the resulting positive electrode slurry on aluminum foil, which serves as the current collector.
  • Inorganic compounds such as transition metal oxides and transition metal chalcogens that contain alkali metals are known as positive electrode active materials for lithium-ion secondary batteries that can obtain a battery voltage of around 4 V.
  • highly alkaline positive electrode active materials that contain large amounts of nickel and manganese are used to obtain high-capacity lithium-ion secondary batteries.
  • high-nickel positive electrode active materials such as Li x NiO 2 have a high discharge capacity and are attractive positive electrode materials, but they contain alkaline components such as LiOH, Li 2 O, LiHCO 3 , and Li 2 CO 3 on their surface, which are generated through proton exchange reactions with raw material residues or moisture, and through reactions with moisture and carbon dioxide in the air.
  • the electrode slurry When such positive electrode active materials are used, the electrode slurry will thicken or gel, causing it to gradually lose fluidity. When the electrode slurry loses fluidity, not only does it become difficult to achieve a uniform coating thickness, but in some cases, coating may not be possible, resulting in waste of material.
  • the main cause of this is thought to be that during the process of manufacturing the positive electrode, alkaline components present on the surface of the positive electrode active material, in the presence of trace amounts of moisture, promote the dehydrofluorination reaction of the fluorine-based binder, such as polyvinylidene fluoride (PVdF), which has a vinylidene fluoride structure and is used as a binder.
  • PVdF polyvinylidene fluoride
  • the alkaline components corrode the aluminum foil that is generally used as the current collector for the positive electrode, thereby increasing the resistance of the battery.
  • the alkaline components also react with the electrolyte inside the battery, increasing the resistance of the battery and potentially shortening its lifespan.
  • the thickening and gelling mentioned above can be suppressed by handling the raw materials and electrode slurry in a dry environment and controlling the water content, but the entire mass production process from preparing the electrode slurry to manufacturing the battery requires large-scale equipment, and the use of large amounts of electricity leads to increased costs and increased environmental impact, which can be problematic.
  • Patent Document 1 discloses a technique for suppressing gelation of an electrode slurry by preparing the electrode slurry (positive electrode material slurry) so that it does not become strongly alkaline even when dispersed in water.
  • preparing an electrode slurry so that it does not become strongly alkaline using the method described in Patent Document 1 not only requires strict pH control, but also requires a process in which the positive electrode active material is dispersed in water once, filtered from the dispersion to extract the positive electrode active material, and then dried. This results in cumbersome work and reduced yields.
  • the above-mentioned process may cause a decrease in the performance of the positive electrode active material itself.
  • Patent Document 2 reports a technology that uses a compound such as ultra-high molecular weight (weight average molecular weight of 2.2 million or more) polyethylene oxide to bind water through interaction with water (e.g., hydrogen bonding), thereby suppressing the reaction between the alkaline component of the positive electrode active material and water, thereby suppressing thickening and gelation.
  • ultra-high molecular weight polymers with strong thickening effects have handling problems, such as the time and cost required for uniform dissolution processing in a solvent, and the difficulty of making a high-concentration solution.
  • the above-mentioned ultra-high molecular weight polymers have a high ability to bind water, there is a concern that the polymer itself may bring in water, and to prevent this, strict management of prior drying is required.
  • Patent Document 3 and Patent Document 4 propose adding an organic acid or an inorganic acid to the positive electrode of a lithium-ion secondary battery to suppress gelation of the electrode slurry (positive electrode mixture slurry).
  • maleic acid, citraconic acid, and malonic acid are used in the positive electrode mixture
  • Patent Document 4 acetic acid, phosphoric acid, sulfuric acid, etc. are used in the electrode slurry (positive electrode paste).
  • a large amount of acid must be added to neutralize the alkali, which may result in a decrease in the energy density of the battery and an increase in the resistance of the battery.
  • the acid corrodes the device used to make the electrode.
  • the high acidity of the organic acid or inorganic acid may cause a neutralization reaction with the lithium ions in the active material, which may lead to a deterioration in battery performance.
  • Patent Document 5 reports a method in which the positive electrode active material is treated with fluorine gas and the remaining LiOH is fixed as LiF, thereby preventing gelation and suppressing gas generation.
  • fluorine gas is highly toxic and difficult to handle, and LiF produced as a by-product increases the internal resistance of the battery, reducing capacity, and capacity also decreases due to corrosion of the positive electrode active material by fluorine gas.
  • the residual fluorine reacts with traces of moisture present in the active material and electrolyte to produce hydrogen fluoride, which is prone to cycle deterioration.
  • Patent Document 6 reports that unreacted lithium hydroxide and impurities derived from the raw materials can be removed by washing with an aqueous solution containing a lithium salt.
  • this method such as the increased environmental burden caused by the wastewater generated during washing and the costs associated with treating the wastewater.
  • the present invention aims to provide an electrode-forming composition that suppresses thickening and gelling and improves storage stability by a simple method, as well as an additive for the electrode-forming composition and gelling suppression.
  • the present invention also aims to provide an electrode layer and a secondary battery that use the electrode-forming composition, as well as a method for producing the electrode-forming composition and a method for suppressing gelling of the electrode-forming composition.
  • the present invention includes the following.
  • An electrode-forming composition comprising a compound having a ring structure and an unsaturated bond, a positive electrode active material, a binder, and a solvent, The compound has a dissociable proton in the molecule, The proton dissociation energy of the compound is less than 1484.2 (kJ/mol); the highest occupied molecular orbital (HOMO) of the compound is greater than -0.27736 (a.u.); Composition for forming electrodes.
  • the positive electrode active material includes a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a single crystal body.
  • the positive electrode active material contains Ni, and the Ni content in the positive electrode active material is 30% by mass or more and 61% by mass or less.
  • the solvent is an aprotic solvent.
  • a secondary battery comprising the electrode layer according to [14].
  • a method for producing an electrode-forming composition comprising producing the electrode-forming composition according to any one of [1] to [13], a first positive electrode active material that is a polycrystalline body, and a second positive electrode active material that is a single crystal, comprising: [17] The method for producing an electrode-forming composition according to [16], wherein a mass ratio of the first positive electrode active material to the second positive electrode active material in the electrode-forming composition (first positive electrode active material:second positive electrode active material) is 2:8 to 8:2.
  • An additive for an electrode-forming composition comprising a first positive electrode active material that is a polycrystalline body, a second positive electrode active material that is a single crystal body, a binder, and a solvent, An additive having a dissociable proton in the molecule, a proton dissociation energy of less than 1484.2 (kJ/mol), and a highest occupied molecular orbital (HOMO) of more than -0.27736 (au).
  • a method for suppressing gelation of an electrode-forming composition including a first positive electrode active material that is a polycrystalline body, a second positive electrode active material that is a single crystal body, a binder, and a solvent comprising:
  • the method for suppressing gelation includes making the electrode-forming composition contain a compound having a dissociable proton in a molecule, a proton dissociation energy of less than 1484.2 (kJ/mol), and a highest occupied molecular orbital (HOMO) of more than -0.27736 (a.u.).
  • an electrode-forming composition that suppresses thickening and gelation and improves storage stability by a simple method, as well as an additive for the electrode-forming composition and gelation suppression.
  • an electrode layer and a secondary battery using the electrode-forming composition, as well as a method for producing the electrode-forming composition and a method for suppressing gelation of the electrode-forming composition.
  • FIG. 1 is a diagram in which proton dissociation energy is plotted on the horizontal axis and HOMO is plotted on the vertical axis for additives A1 to A28, a1 to a12, a25 and a26.
  • the specific compound has a dissociable proton in the molecule.
  • the proton dissociation energy of the specific compound is less than 1484.2 (kJ/mol).
  • the highest occupied molecular orbital (HOMO) of a particular compound is greater than -0.27736 (au).
  • the electrode-forming composition of the present invention is resistant to thickening and gelling, has high storage stability, and can be suitably used for forming a positive electrode for a secondary battery.
  • a secondary battery equipped with an electrode made using the composition When a secondary battery equipped with an electrode made using the composition is manufactured, merits such as improved quality and yield due to improved storage stability of the composition, cost reduction and reduction of environmental load due to high concentration of solids, and suppression of deterioration in the battery caused by alkaline components are expected, which can contribute to reducing the manufacturing cost of the secondary battery and improving the battery characteristics.
  • the electrode-forming composition is more likely to thicken and gel when it contains two types of positive electrode active materials (particularly, a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a single crystal body).
  • a compound has a dissociative proton and the proton dissociation energy of the compound is small, the compound is likely to release a proton, and the released proton is easily reduced by one electron and easily generates hydrogen radicals. If the highest occupied molecular orbital (HOMO) of a compound is high, the compound is easily radicalized and easily generates hydrogen radicals. This can be illustrated as follows.
  • the hydrogen radicals react (e.g., radical coupling) with the binder that has been radicalized due to an alkaline component present or generated in the composition.
  • the binder radicals are inactivated by the above reaction, the binder reaction that promotes thickening and gelation is suppressed.
  • the present invention is not limited to these mechanisms.
  • By suppressing thickening and gelation of the electrode-forming composition it is possible to form a homogeneous positive electrode layer.
  • the specific compound is composed of, for example, hydrogen and at least one of nonmetallic elements from Group 14 to Group 17.
  • the nonmetallic elements from Group 14 to Group 17 include boron, carbon, silicon, nitrogen, phosphorus, oxygen, sulfur, and halogens.
  • the specific compound may or may not have a heteroatom.
  • the heteroatom include an oxygen atom, a nitrogen atom, a phosphorus atom, a silicon atom, a sulfur atom, and a halogen atom.
  • the halogen atom include a fluorine atom, a chlorine atom, an iodine atom, and a bromine atom.
  • the molecular weight of the specific compound is not particularly limited, and may be, for example, 60 to 1,000, 60 to 700, 100 to 700, or 100 to 350.
  • the number of dissociable protons possessed by the specific compound is not particularly limited, and may be one or may be two or more. If the proton dissociation energy can be calculated, the compound is said to have a dissociable proton.
  • the content of the specific compound in the electrode-forming composition is not particularly limited, but is preferably 0.001 to 4 mass %, more preferably 0.001 to 2 mass %, even more preferably 0.001 to 0.5 mass %, still more preferably 0.001 to 0.3 mass %, and particularly preferably 0.001 to 0.2 mass %, based on the solid content. Moreover, an even more preferable lower limit of the content of the specific compound is 0.01 mass% of the solid content.
  • the solid content means the components other than the solvent that constitute the composition (hereinafter the same).
  • the content of the specific compound in the electrode-forming composition is preferably 0.1 to 50 parts by mass, more preferably 0.1 to 30 parts by mass, and even more preferably 0.1 to 20 parts by mass, relative to 100 parts by mass of the binder.
  • the content of the specific compound in the electrode-forming composition is preferably 0.1 to 50 parts by mass, more preferably 0.1 to 30 parts by mass, and even more preferably 0.1 to 20 parts by mass, per 100 parts by mass of the conductive assistant.
  • the positive electrode active material is not particularly limited.
  • An electrode-forming composition containing a positive electrode active material with a high nickel content has a strong tendency to thicken and gel. Therefore, in order to suppress thickening and gelling in an electrode-forming composition containing a positive electrode active material with a high nickel content, it is preferable for the positive electrode active material to contain Ni, and it is more preferable for the Ni content to be 30 mass% or more, and particularly preferable for the Ni content to be 40 mass% or more. There is no particular limit to the upper limit of the Ni content in the positive electrode active material, but for example, the Ni content is 61 mass% or less.
  • the general formula Li a Ni (1-x-y) Co x M 1 y M 2 z O 2 (wherein M 1 represents at least one selected from the group consisting of Mn and Al, M 2 represents at least one selected from the group consisting of Zr, Ti, Mg, B, W and V, and 1.00 ⁇ a ⁇ 1.50, 0.00 ⁇ x ⁇ 0.50, 0.00 ⁇ y ⁇ 0.50, 0.000 ⁇ z ⁇ 0.020) is preferred.
  • x may be in the range of 0.01 ⁇ x ⁇ 0.30, or 0.03 ⁇ x ⁇ 0.20.
  • the value of y may be in the range of 0.01 ⁇ x ⁇ 0.30, or in the range of 0.03 ⁇ x ⁇ 0.20.
  • These active materials can be used alone or in combination of two or more.
  • the electrode-forming composition is more likely to thicken and gel when it contains two types of positive electrode active materials (particularly, a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a monocrystalline body).
  • a specific compound to an electrode-forming composition that contains a positive electrode active material that contains two types of positive electrode active materials (particularly, a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a monocrystalline body)
  • the positive electrode active material contains a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a monocrystalline body.
  • the first positive electrode active material which is a polycrystalline body, is, for example, a lithium-containing transition metal oxide particle having a layered rock salt structure.
  • the crystallite size determined by Scherrer's formula based on the diffraction peak of the (104) plane obtained from the X-ray diffraction pattern using a CuK ⁇ radiation source of the lithium-containing transition metal oxide particle that is the first positive electrode active material is, for example, 20 nm or more and less than 500 nm.
  • the second positive electrode active material which is a single crystal, is, for example, a lithium-containing transition metal oxide particle having a layered rock salt structure.
  • the crystallite diameter of the first positive electrode active material and the crystallite diameter of the second positive electrode active material satisfy the relationship of the following formula (X).
  • X formula (X).
  • ⁇ 1 crystallite diameter (nm) of the first positive electrode active material
  • ⁇ 2 crystallite diameter (nm) of the second positive electrode active material
  • x1 is 0 nm, preferably 10 nm, more preferably 30 nm, and particularly preferably 70 nm.
  • x2 is 400 nm, preferably 350 nm, more preferably 300 nm, and particularly preferably 250 nm.
  • the crystallite size can be determined, for example, as follows.
  • X-ray diffraction measurement X-ray diffraction patterns of the positive electrode active material are collected using an X'Pert Pro MPD (PANaltical) using a CuK ⁇ radiation source (45 kV, 40 mA) emitting at a wavelength of 1.5418 ⁇ .
  • the instrument is configured with 0.02 rad Soller slits, 10 mm automatic variable divergence slits and 1/2° anti-scatter slits on the entrance side, and 8 mm anti-scatter slits and 0.02 rad Soller slits on the receiving side.
  • the radius of the goniometer is 240 mm.
  • XRD diffraction patterns are obtained in the range of 10 to 100° (2 ⁇ ) with a step size of 0.013°/scan and a time per step of 250 seconds.
  • the crystallite size of the positive electrode active material is calculated using the known Scherrer equation from the diffraction angle of the (104) plane peak obtained from the X-ray diffraction pattern and the full width at half maximum (FWHM) obtained by subtracting the device-specific half width.
  • ⁇ crystallite diameter (unit: nm) (Crystallite size refers to the average size of the ordered (crystalline) domains, which may be less than or equal to the grain size.)
  • ⁇ FWHM ⁇ : 1/2 of the diffraction angle 2 ⁇ of the diffraction peak assigned to the (104) plane
  • a peak of the (104) plane is observed, which is assigned to a crystal structure having space group R-3m.
  • the half-width characteristic of the device is 47.3° obtained by using Si powder (SRM640f, manufactured by NIST).
  • the mass ratio of the first positive electrode active material to the second positive electrode active material in the electrode forming composition is not particularly limited, but is preferably 2:8 to 8:2, more preferably 4:6 to 8:2, and particularly preferably 4:6 to 7:3.
  • the amount of the positive electrode active material in the electrode-forming composition is not particularly limited, but is preferably 88.0 to 99.949% by mass, more preferably 88.0 to 99.899% by mass, and even more preferably 95.0 to 99.0% by mass, based on the solid content.
  • the binder can be appropriately selected from known materials and is not particularly limited, but examples thereof include fluorine-based binders, polyimide, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, polyethylene, polypropylene, etc. These are non-aqueous binders.
  • fluorine-based binder include polyvinylidene fluoride (PVdF); polytetrafluoroethylene (PTFE); and copolymers containing at least one monomer selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene.
  • a fluorine-based binder In order to improve the storage stability of the electrode-forming composition, it is preferable to use a fluorine-based binder.
  • the fluorine-based binder is preferably modified with a polar functional group such as a carboxyl group or a hydroxyl group.
  • the polar functional group can be confirmed by the presence or absence of a clear peak detected in the range of 10 to 15 ppm in measurement using a nuclear magnetic resonance (NMR) device.
  • the binder can be used alone or in combination of two or more types.
  • the weight average molecular weight (Mw) of the binder is not particularly limited, but from the viewpoint of improving the adhesion between the current collector and the electrode layer, it is 600,000 to 3,000,000, preferably 700,000 to 2,000,000, and more preferably 700,000 to 1,500,000.
  • the weight average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).
  • the content of the binder in the electrode-forming composition is not particularly limited, but from the viewpoint of reducing costs and obtaining a high energy density, it is preferably 0.05 to 8 mass% of the solid content, more preferably 0.05 to 5 mass%, even more preferably 0.05 to 4 mass%, even more preferably 0.1 to 3 mass%, particularly preferably 0.2 to 2 mass%, and most preferably 0.3 to 1.5 mass%.
  • the solvent is not particularly limited, and examples thereof include solvents that are conventionally used in the preparation of electrode-forming compositions.
  • examples of the solvent include water and organic solvents.
  • organic solvents examples include ethers, halogenated hydrocarbons, amides, ketones, alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, glycol ethers, glycols, carbonates, and other organic solvents.
  • Examples of the alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, and t-butanol.
  • Examples of the aliphatic hydrocarbons include n-heptane, n-hexane, and cyclohexane.
  • Examples of aromatic hydrocarbons include benzene, toluene, xylene, and ethylbenzene.
  • Examples of glycol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether. Examples of glycols include ethylene glycol and propylene glycol.
  • carbonates examples include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.
  • organic solvents include, for example, ⁇ -butyrolactone, dimethylsulfoxide (DMSO), dioxolane, and sulfolane.
  • the organic solvent may be either a protic solvent or an aprotic solvent, with the aprotic solvent being preferred.
  • the aprotic solvent may, for example, be polar or non-polar.
  • amides, ketones and carbonates are preferred, and amides are more preferred.
  • solvents can be used alone or in combination of two or more.
  • the solids concentration of the electrode-forming composition is set appropriately taking into consideration the coatability of the composition and the thickness of the electrode to be formed, but is usually 60 to 92% by mass, preferably 65 to 90% by mass, and more preferably 70 to 85% by mass.
  • the conductive assistant is used, for example, to improve electrical conductivity.
  • the conductive assistant is not particularly limited, but examples thereof include carbon materials and conductive polymers.
  • carbon materials include graphite, carbon black, acetylene black (AB), vapor-grown carbon fibers, carbon nanotubes (CNT), carbon nanohorns, and graphene.
  • the conductive polymer include polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene.
  • the conductive assistant may be used alone or in combination of two or more kinds.
  • the content of the conductive assistant in the electrode-forming composition is not particularly limited, but is preferably 0.05 to 5 mass% of the solid content, more preferably 0.05 to 4 mass%, even more preferably 0.1 to 3 mass%, and even more preferably 0.2 to 2 mass%. By keeping the content of the conductive assistant within the above range, good electrical conductivity can be obtained.
  • the electrode-forming composition does not contain graphene, for example.
  • the graphene content in the conductive assistant is not particularly limited, but is preferably 45 mass % or less, more preferably 40 mass % or less, and particularly preferably 10 mass % or less.
  • the dispersant is used to improve the dispersibility of substances such as the positive electrode active material and the conductive assistant.
  • the dispersant can be appropriately selected from those that have been conventionally used as dispersants for conductive carbon materials such as CNTs.
  • a non-ionic polymer is preferred from the viewpoint of stability within the battery. Examples of nonionic polymers include polyvinylpyrrolidone (PVP) and polymers containing at least one functional group selected from the group consisting of a nitrile group, a hydroxyl group, a carbonyl group, an amino group, a sulfonyl group, and an ether group.
  • the functional group-containing polymer examples include polyvinyl alcohol, polyacrylonitrile, polylactic acid, polyester, polyimide, polyphenyl ether, polyphenyl sulfone, polyethyleneimine, and polyaniline.
  • a polymer containing a pyrrolidone structure or a nitrile group is preferred, and polyvinylpyrrolidone and polyacrylonitrile are more preferred.
  • the dispersants can be used alone or in combination of two or more.
  • the content of the dispersant in the electrode-forming composition is not particularly limited, but is preferably 0.001 to 0.5 mass % of the solid content, more preferably 0.001 to 0.3 mass %, and even more preferably 0.001 to 0.2 mass %. An even more preferable lower limit of the content of the dispersant is 0.01 mass % of the solid content.
  • the total amount of the specific compound and the dispersant is preferably 0.001 to 1 mass % of the solid content, and more preferably 0.01 to 1 mass %.
  • the viscosity of the electrode-forming composition is set appropriately taking into consideration the coating method and the thickness of the electrode to be formed, but is usually about 100 to 2,000,000 mPa ⁇ s, preferably about 300 to 1,000,000 mPa ⁇ s, and more preferably about 400 to 800,000 mPa ⁇ s.
  • the above viscosity is measured at 25°C using an E-type viscometer.
  • the electrode-forming composition of the present invention can be obtained by mixing the above-mentioned components.
  • the composition contains optional components other than the gelation inhibitor (specific compound) which is the additive of the present invention, the positive electrode active material, and the binder, the gelation inhibitor which is the additive and the positive electrode active material may be mixed together with the optional components, or both components may be mixed in advance and then mixed with the optional components. Either method can produce the effects of the present invention.
  • the electrode layer of the present invention is obtained from the electrode-forming composition of the present invention.
  • a method for forming an electrode layer for example, a method of applying an electrode-forming composition onto a substrate to form a coating film and then drying the coating film can be mentioned. This method is not particularly limited, and various conventionally known methods can be used. Specific examples of the coating method include various printing methods such as offset printing and screen printing, blade coating, dip coating, spin coating, bar coating, slit coating, inkjet printing, and die coating.
  • the temperature is preferably 50 to 400°C, and more preferably 70 to 150°C.
  • the thickness of the electrode layer is not particularly limited, but is preferably 0.01 to 1,000 ⁇ m, and more preferably 5 to 300 ⁇ m. In the case where the electrode layer is used alone as an electrode in the secondary battery, the thickness of the electrode layer is preferably 10 ⁇ m or more.
  • sulfide-based solid electrolytes include thiolithium-based materials such as Li 2 S—SiS 2 -lithium compound (wherein the lithium compound is at least one selected from the group consisting of Li 3 PO 4 , LiI, and Li 4 SiO 4 ), Li 2 S—P 2 O 5 , Li 2 S—B 2 S 5 , and Li 2 S—P 2 S 5 -GeS 2 .
  • Li 2 S—SiS 2 -lithium compound wherein the lithium compound is at least one selected from the group consisting of Li 3 PO 4 , LiI, and Li 4 SiO 4
  • Li 2 S—P 2 O 5 Li 2 S—B 2 S 5
  • Li 2 S—P 2 S 5 -GeS 2 Li 2 S—P 2 S 5 -GeS 2 .
  • the additive of the present invention is an additive for an electrode-forming composition containing a positive electrode active material, a binder, and a solvent.
  • the gelation inhibitor of the present invention is a gelation inhibitor for an electrode-forming composition including a positive electrode active material, a binder, and a solvent.
  • the gelation inhibitor is added to the electrode-forming composition including a positive electrode active material, a binder, and a solvent to suppress gelation of the electrode-forming composition.
  • the additive and the gelation inhibitor are the above-mentioned specific compounds, and examples and preferred examples thereof include the examples and preferred examples given in the description of the above-mentioned specific compounds.
  • the apparatus used in this example is as follows: (1) Rotation and revolution type mixer: Thinky Corporation, Awatori Mixer, atmospheric pressure type, ARE-310 (2) Dry Boss: Manufactured by Nihon Spindle Mfg. Co., Ltd. (3) Rheometer (Condition 1): Manufactured by Anton Paar, MCR302, Jig: CP40-1, Measurement GAP: 0.08 mm, Measurement temperature: Shear viscosity measurement was performed while sweeping the shear rate from 0.01 to 1000 sec -1 under the measurement conditions of 25°C. The viscosity of the slurry was measured at 100 sec -1 .
  • the raw materials used in this example are as follows: ⁇ Cathode active material> As the first positive electrode active material which is a polycrystalline body, S-800 was used, and as the second positive electrode active material which is a single crystal, T81RS was used.
  • S-800 Lithium nickel manganese cobalt oxide ( LiNi0.8Co0.1Mn0.1O2 , polycrystalline type, manufactured by Ningbo Ronbay New Energy Technology Co., Ltd., Ni ratio: 50% by mass, crystallite size determined by X-ray diffraction: 97 nm)
  • T81RS Lithium nickel manganese cobalt oxide ( LiNi0.8Co0.1Mn0.1O2 , single crystal type, manufactured by Hunan Shanshan Energy Technology Co., Ltd., Ni ratio: 50 mass%, crystallite size determined by X-ray diffraction: 296 nm)
  • A22 Irganox 3114 (trade name) is 1,3,5-Tris(3,5-di-tert.-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione manufactured by BASF.
  • A23 Irganox MD1024 (trade name) is 2',3-Bis[[3-[3,5-di-tert.-butyl-4-hydroxyphenyl]propionyl]]propionohydrazide manufactured by BASF.
  • A24, Adeka STAB AO-40 (trade name), is 6,6'-di-tert-butyl-4,4'-butylidene di-m-cresol manufactured by ADEKA Corporation.
  • Examples 17 to 20, Comparative Examples 26 to 27 The positive electrode active material, binder powder, conductive assistant, additive, NMP, and water were mixed in a dry mixer so as to obtain the composition ratios shown in Tables 2-2 and 2-4, and mixed using a rotation/revolution mixer to obtain an electrode slurry.
  • the water was added to intentionally create a state in which the slurry had a high water content.
  • Example 21 A 5% by mass NMP solution (additive solution) was prepared for additive A2.
  • the positive electrode active material, binder powder, conductive assistant, additive solution, NMP, and water were mixed in a dry mixer so as to obtain the composition ratio shown in Table 2-2, and mixed using a rotation/revolution type mixer to obtain an electrode slurry.
  • the water was added to intentionally create a state in which the slurry has a high water content.
  • Example 22 A 5% by mass NMP solution (additive solution) was prepared for additive A2.
  • the positive electrode active material, binder powder, conductive assistant, additive solution, NMP, and water were mixed in a dry mixer so as to obtain the composition ratio shown in Table 2-2, and mixed using a rotation/revolution type mixer to obtain an electrode slurry.
  • the water was added to intentionally create a state in which the slurry has a high water content.
  • Examples 23 to 29 A 5% by mass NMP solution (additive solution) was prepared for each of the additives A21 to A27.
  • the positive electrode active material, binder powder, conductive assistant, additive solution, NMP, and water were mixed in a dry mixer so as to obtain the composition ratio shown in Table 2-2, and mixed using a rotation/revolution type mixer to obtain an electrode slurry.
  • the water was added to intentionally create a state in which the slurry had a high water content.
  • Example 30 The positive electrode active material, binder powder, conductive assistant, additive, NMP, and water were mixed in a dry mixer so as to obtain the composition ratio shown in Table 2-2, and mixed using a rotation/revolution type mixer to obtain an electrode slurry.
  • the water was added to intentionally create a state in which the slurry has a high water content.
  • the slurries obtained above were subjected to viscosity measurement using a rheometer (condition 1) or a rheometer (condition 2) immediately after preparation. In addition, the presence or absence of gelation was confirmed visually after storage at 40°C for 24 hours. For those that did not gel, the viscosity was similarly measured using a rheometer (condition 1) or a rheometer (condition 2) to confirm the presence or absence of thickening and gelation tendency, and judged based on the following criteria. These evaluations are also summarized in each table.
  • the electrode slurries obtained in Examples 1 to 30 and Comparative Examples 1 to 30 were each uniformly applied to an aluminum foil current collector (15 ⁇ m thick, UACJ Corporation) using a doctor blade, dried at 80°C for 30 minutes to form an active material layer, and then pressed twice with a roll press at a linear pressure of 0.25 kN/cm, twice at 1 kN/cm, and twice at 3 kN/cm to produce electrodes.

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