Electrode and lithium-ion secondary battery

Abstract

The present application provides an electrode for a lithium ion secondary battery, the electrode having an active material layer containing a particulate active material, the active material containing an organic sulfur compound and an iron compound, wherein A S , A F , and D satisfy the following inequality (1) A S × A F × D > 7000, wherein A s represents the content of sulfur element in the active material, in mass%, A F represents the content of iron element in the active material, in mass%, and D represents the coating density of the active material, in mg / cm 2 The present application aims to improve the comprehensive performance of the charge-discharge capacity, capacity retention rate, and energy density of a lithium ion secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to a novel electrode and a lithium ion secondary battery including the same. BACKGROUND

[0002] Lithium ion secondary batteries are mainly used as batteries for portable electronic devices because of their large charge-discharge capacity. In addition, lithium ion secondary batteries are increasingly used as batteries for electric vehicles, and it is desired to improve the performance.

[0003] Patent Literature 1 describes an active material for an electrode, which is obtained by firing a raw material containing a polymer and sulfur, the polymer containing methacrylonitrile as a monomer component.

[0004] In addition, as a negative electrode active material, it has been proposed to use a material capable of absorbing and releasing more lithium ions, such as silicon (Si), tin (Sn), etc., in order to improve the battery capacity of lithium ion secondary batteries.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: JP 2020-167144 A. SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, there is room for further improvement in electrodes using active materials such as those of Patent Literature 1.

[0010] An object of the present application is to provide an electrode (i.e., a positive electrode or a negative electrode) capable of realizing a lithium ion battery having high comprehensive performance in terms of charge-discharge capacity, capacity retention rate, and energy density, and a lithium ion secondary battery including the same.

[0011] MEANS FOR SOLVING THE PROBLEMS

[0012] That is, the present application relates to an electrode.

[0013] An electrode for a lithium ion secondary battery,

[0014] The electrode has an active material layer containing an active material in a particulate form,

[0015] The active material contains an organic sulfur compound and an iron compound,

[0016] wherein A S , A F and D satisfy the following inequality (1),

[0017] (1) A S x A F×D>7000,

[0018] In the formula, A S The sulfur content in the active substance is expressed in mass %. A F The value represents the iron content in the active material, expressed as a percentage by mass (%). D represents the coating density of the active material, expressed as mg / cm³. 2 .

[0019] The effects of the invention

[0020] According to the present invention, an electrode (i.e., a positive electrode or a negative electrode) for a lithium-ion battery that can achieve high overall performance in terms of charge / discharge capacity, capacity retention rate and energy density can be provided, as well as a lithium-ion secondary battery including the electrode. Attached Figure Description

[0021] Figure 1 A cross-sectional view of a reaction apparatus for producing active substances in an embodiment of the present invention is shown schematically. Detailed Implementation

[0022] The present invention will now be described in detail. Furthermore, the descriptions of numerical ranges involving "above" and "below" upper and lower limits are arbitrary combinations of values, and the values ​​in the embodiments may also be these upper and lower limits. Additionally, unless contrary to the purpose of the present invention, numerical ranges shown as including their two endpoints should be interpreted as also disclosing numerical ranges excluding one of their two endpoints, and numerical ranges excluding both endpoints.

[0023] One embodiment of the present invention is the following electrode.

[0024] An electrode for lithium-ion secondary batteries.

[0025] The electrode has an active material layer, which contains particulate active material.

[0026] The active substance contains organosulfur compounds and iron compounds.

[0027] Among them, A S A F D and D satisfy the following inequality (1),

[0028] (1)A S ×A F ×D>7000,

[0029] In the formula, A S Indicates the sulfur content in the active substance, in mass %. A F The value represents the iron content in the active material, expressed as a percentage by mass (%). D represents the coating density of the active material, expressed as mg / cm³. 2 .

[0030] While not being bound by theory, it is believed that the electrode of the present application is able to improve the comprehensive performance of charge-discharge capacity, capacity retention rate, and energy density for the following reasons.

[0031] Sulfur easily generates a soluble compound together with lithium during charge-discharge, and thus there is a disadvantage that repeated charge-discharge causes the charge-discharge capacity to gradually decrease. In contrast, the present application is characterized in that the active material contains iron, and the product of the content ratio of sulfur in the active material, the content ratio of iron in the active material, and the coating density (mg / cm 2 ) of the active material is kept equal to or greater than a certain value. Under such conditions, the sulfur and iron remaining on the electrode interact with each other under given conditions, and thus it is believed that the comprehensive performance of charge-discharge capacity, capacity retention rate, and energy density can be improved.

[0032] Preferably, the value on the right side of inequality (1) is 8000.

[0033] Preferably, the sulfur element content A S in the active material is greater than 65.0 mass %.

[0034] Preferably, the iron element content A F in the active material is greater than 15.0 mass %.

[0035] Preferably, the coating density D of the active material is greater than 2.5 mg / cm 2 .

[0036] In the case where the above-described electrode is used as a positive electrode, when the initial discharge capacity is referred to as DC3 (mAh / g), DC3 is preferably greater than 400 mAh / g, and more preferably greater than 600 mAh / g.

[0037] The above-described electrode has a current collector having a metal foil, and when the thickness of the metal foil is referred to as T (μm), A S , D, and T preferably satisfy the following inequality (2),

[0038] (2) A S x D / T > 24.0.

[0039] By making the quotient of the product value of the amount of sulfur and the coating density divided by the thickness value of the metal foil current collector equal to or greater than a certain value, the respective values are mutually restricted, and thus it is believed that the performance of the electrode and / or the battery is improved.

[0040] In the case where the above-described electrode is used as a positive electrode, when the 10th discharge capacity is referred to as DC 10 (mAh / g), DC 10 is preferably greater than 350 mAh / g.

[0041] Another embodiment of the present application is a lithium ion secondary battery having the above electrode.

[0042] Preferably, the lithium ion secondary battery further has an electrolyte, and when the volume of the electrolyte is referred to as V (mL), A S , D, and V satisfy the following inequality (3),

[0043] (3) A S × D / V > 240.

[0044] By making the product value of the amount of sulfur and the coating density divided by the volume value of the electrolyte equal to or greater than a certain value, each value is mutually restricted, thereby considering that the performance of the electrode and / or the battery is improved.

[0045] <DEFINITIONS>

[0046] The term "particulate" means that the active material is made into a state fine enough to be mixed with another material for the purpose of the present application. As for the size of the particles constituting the active material, it is not particularly limited as long as it is a size that enables proper mixing.

[0047] "Active material" means a material that plays a role in a redox reaction for performing energy conversion in a lithium ion secondary battery.

[0048] "Active material layer" means a layer formed on a current collector constituting an electrode and made of an electrode material containing an active material.

[0049] "Coating density" means the mass (mg) of the active material per unit area (cm 2 ) coated on the current collector.

[0050] Unless otherwise specified, "initial discharge capacity" in the present specification means the 3rd discharge capacity.

[0051] <MEASURING METHODS>

[0052] "Sulfur element content" is the mass proportion (%) of sulfur element in the active material, measured by the elemental analysis method described below in the present specification.

[0053] "Iron element content" is the mass proportion (%) of iron element in the active material, measured by the thermogravimetric method described below in the present specification.

[0054] "Median particle diameter" is the volume-based cumulative 50% size (median particle diameter d 50 ) measured using a laser diffraction / scattering type particle size distribution analyzer (particle size distribution analyzer PSA 1090L manufactured by Anton Paar GmbH) with water as the dispersion medium.

[0055] The following describes an electrode for a lithium-ion secondary battery according to the present application and a lithium-ion secondary battery according to the present application.

[0056] <Electrode for a lithium-ion secondary battery>

[0057] The electrode for a lithium-ion secondary battery according to the present application has an active material layer containing a particulate active material containing an organic sulfur compound and an iron compound, wherein A S , A F and D satisfy the following inequality (1),

[0058] (1) A S x A F xD > 7000,

[0059] wherein A S represents the content of sulfur element in the active material, in mass%, A F represents the content of iron element in the active material, in mass%, and D represents the coating density of the active material, in mg / cm 2 .

[0060] [Active material layer]

[0061] The active material layer according to the present application contains a particulate active material. The active material layer is composed of an electrode material (i.e., a positive electrode material or a negative electrode material) containing a particulate active material. Here, the phrase "the active material is particulate" means that the active material is prepared in a state fine enough to be mixed with another material constituting an electrode for the purpose of the present application, and the meaning of the phrase is not particularly limited as long as the active material is in such a state. For example, when the term "particulate" is expressed by a median particle diameter, it can be in the range of 1 nm to 1000 μm.

[0062] The median particle diameter (median particle diameter d 50 ) of the particles constituting the active material is preferably about 1.0 μm or more and 40.0 μm or less. The median particle diameter is more preferably 1.5 μm or more, further preferably 2.0 μm or more, further preferably 2.4 μm or more. In addition, the median particle diameter is more preferably 30.0 μm or less, further preferably 25.0 μm or less, further preferably 20.0 μm or less, further preferably 15.0 μm or less. The median particle diameter can be measured by the method described in the following Examples section.

[0063] [Active material]

[0064] The active material according to the present application contains an organic sulfur compound and an iron compound.

[0065] The organic sulfur compound is a compound in which at least a carbon atom, a hydrogen atom, and a sulfur atom are combined with each other. Since the active material is obtained by a step of firing a raw material containing a polymer (e.g., rubber, resin, etc.), a compound containing an iron ion, and sulfur, it is difficult to analyze the detailed structure of the product obtained by the step, but it has been confirmed that a carbon atom, a hydrogen atom, and a sulfur atom are combined with each other. In this case, it is presumed that the organic sulfur compound contains a carbon-sulfur structure, for example, a long-chain polythiophene and benzene structure condensed by a thiophene ring, a structure similar thereto, or the like. In addition, depending on other raw materials used for firing or a gas atmosphere used, other atoms (e.g., a nitrogen atom, etc.) can further be combined with the organic sulfur compound.

[0066] The iron compound is a compound in which an iron atom is combined with an atom other than an iron atom. Examples of the atom other than the iron atom include, for example, a sulfur atom. Examples of the iron compound include iron (II) sulfide (FeS), iron (III) sulfide (Fe2S3), iron disulfide (FeS2), and the like. Among them, iron disulfide (FeS2) is typical or preferred.

[0067] Therefore, in the present application, the expression "the particulate active material contains an organic sulfur compound" can be expressed as "the particulate active material contains at least a carbon atom and a sulfur atom", or the expression "the particulate active material contains an organic sulfur compound and an iron compound" can be expressed as "the particulate active material contains at least a carbon atom, a sulfur atom, and an iron atom". In addition, when it contains a carbon atom, a sulfur atom, and an iron atom, the carbon element content, the sulfur element content, and the iron element content are measured by the method described in the Example section below.

[0068] (Sulfur element content (A S , mass %)

[0069] The sulfur element content (mass %) in the active material is preferably greater than 50.0 mass %, more preferably greater than 55.0 mass %, further preferably greater than 60.0 mass %, further preferably greater than 61.0 mass %, further preferably 61.2 mass % or more, further preferably greater than 62.0 mass %, further preferably greater than 63.0 mass %, further preferably 63.6 mass % or more, further preferably greater than 64.0 mass %, further preferably 65.0 mass % or more, further preferably greater than 65.0 mass %, further preferably greater than 66.0 mass %, further preferably greater than 70.0 mass %. The upper limit of the sulfur element content is usually about 80 mass %, but is not particularly limited thereto.

[0070] (Iron element content (AF, mass %)

[0071] The content of iron element in the active material (mass %) is preferably more than 10.0 mass %, more preferably more than 11.0 mass %, further preferably more than 12.0 mass %, further preferably more than 13.0 mass %, further preferably more than 13.5 mass %, further preferably more than 14.0 mass %, further preferably more than 14.5 mass %, further preferably more than 14.9 mass %, further preferably more than 15.0 mass %, further preferably more than 15.4 mass %, further preferably more than 15.5 mass %, further preferably more than 16.0 mass %, further preferably more than 16.1 mass %, further preferably more than 17.0 mass %, further preferably more than 17.3 mass %. The upper limit of the content of iron element is generally about 25.0 mass %, but is not particularly limited thereto.

[0072] (coating density (D, mg / cm 2 )

[0073] The coating density (mg / cm 2 ) of the active material on the electrode is preferably more than 2.5 mg / cm 2 , more preferably more than 6.2 mg / cm 2 , further preferably more than 6.5 mg / cm 2 , further preferably more than 6.6 mg / cm 2 , further preferably more than 7.0 mg / cm 2 , further preferably more than 8.0 mg / cm 2 , further preferably more than 8.5 mg / cm 2 , further preferably more than 8.6 mg / cm 2 , further preferably more than 9.0 mg / cm 2 , further preferably more than 9.2 mg / cm 2 , further preferably more than 9.5 mg / cm 2 . The upper limit thereof is not particularly limited, and the higher the upper limit is, the more preferable it is. Thus, although the upper limit of the coating density is not particularly meaningful, the upper limit can also be assumed to be about 15.0 mg / cm 2 , as a reference value only.

[0074] (content of carbon element)

[0075] The content of carbon element in the active material (mass %) is preferably more than 15.0 mass %, more preferably more than 17.0 mass %, further preferably more than 18.0 mass %. On the other hand, the content of carbon element (mass %) is preferably less than 27.0 mass %, more preferably less than 25.0 mass %, further preferably less than 24.0 mass %.

[0076] (content of hydrogen element)

[0077] The hydrogen element content in the active material (mass %) is relatively small because the hydrogen atoms in the polymer react with sulfur to form hydrogen sulfide by firing and the hydrogen sulfide is released to the outside of the system, thereby reducing the hydrogen element content. The hydrogen element content in the active material is preferably 1.6 mass % or less. The value is less than 1.5 mass %, more preferably 1.2 mass % or less, further preferably less than 1.1 mass %, further preferably less than 1.0 mass %, further preferably less than 0.5 mass %, further preferably 0.4 mass % or less, further preferably 0.3 mass % or less, further preferably 0.2 mass % or less. On the other hand, the lower limit of the hydrogen element content (mass %) can be 0.1 mass %, can be less than 0.1 mass %, or can be equal to or less than the detection limit.

[0078] (Median particle diameter)

[0079] The active material is pulverized to obtain a prescribed particle size, and preferably has particles of a size suitable for manufacturing an electrode. From the viewpoint of performance improvement of the electrode and / or battery, the preferred particle size distribution of the particles of the active material is preferably about 1.0 μm or more and 40.0 μm or less in terms of the median particle diameter (median particle diameter d 50 ). The median particle diameter is more preferably 1.5 μm or more, further preferably 2.0 μm or more, further preferably 2.4 μm or more. In addition, the median particle diameter is more preferably 30.0 μm or less, further preferably 25.0 μm or less, further preferably 20.0 μm or less, further preferably 15.0 μm or less. The median particle diameter can be measured by the method described in the Example section below.

[0080] [Inequality (1)]

[0081] For the electrode of the present application, as described in the above inequality (1), the product of the sulfur element content A S (mass %) in the active material, the iron element content A F (mass %) in the active material, and the coating density D (mg / cm 2 ) of the active material is greater than 7000. The right side of inequality (1) is preferably 7500, more preferably 8000, further preferably 8500, further preferably 9000, further preferably 9100, further preferably 9200, further preferably 9400, further preferably 9500, further preferably 10000. The upper limit of the left side value of inequality (1) is not particularly limited, and the higher the upper limit, the more preferable. Thus, although the upper limit of the left side value of inequality (1) is not particularly meaningful, it can be assumed to be about 20000, about 15000, or about 12000, as a reference value.

[0082] [Inequality (2)]

[0083] For the electrode of the present invention, as described in the above inequality (2), the sulfur content A in the active material is... S (mass%) and coating density D of active material (mg / cm³) 2 The quotient obtained by dividing the product of the two inequalities (2) by the thickness T (μm) of the metal foil constituting the current collector is preferably greater than 24.0. The right side of inequality (2) is more preferably 25.0, further preferably 26.0, further preferably 27.0, further preferably 28.0, further preferably 28.5, further preferably 29.0, further preferably 29.4, further preferably 30.0, further preferably 30.8, further preferably 35.0, and further preferably 36.0. There is no particular upper limit on the value on the left side of inequality (2), but a higher upper limit is preferred. Therefore, although mentioning the upper limit of the value on the left side of inequality (2) is not very meaningful, it can generally be assumed to be approximately 100, approximately 80, or approximately 60, only as a reference value.

[0084] The thickness T (μm) of the metal foil is preferably in the range of 5 μm or more, and more preferably in the range of 10 μm or more. On the other hand, T is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.

[0085] [Charge / Discharge Capacity]

[0086] The electrode of the present invention exhibits excellent charge and discharge capacity. Furthermore, in the following description, unless otherwise stated, the initial discharge capacity refers to the third discharge capacity (DC3). Here, the third discharge capacity is the discharge capacity after three charge and discharge cycles following the fabrication of the electrode and battery (the third discharge is defined in the following cycle: first discharge, first charge, second discharge, second charge, third discharge, third charge), where the discharge termination voltage is 1.0V and the charge termination voltage is 3.0V. In the case of discharge, when discharged with a constant current (50mA per 1g of positive electrode active material), the voltage eventually drops from 3.0V to 1.0V. The total time (h) taken during the voltage drop from 3.0V to 1.0V is measured, and the total measured time is multiplied by the applied current (mA) to obtain the capacity (mAh), which is then divided by the weight of the active material to obtain the specific capacity (mAh / g). On the other hand, in the case of charging, charging is performed with a constant current, thereby increasing the voltage, and charging terminates when the voltage finally reaches 3.0V. This also applies to the 10th discharge capacity described below.

[0087] (Initial discharge capacity (DC3))

[0088] In the case where the electrode of the present application is used as a positive electrode, the initial discharge capacity (DC3) (mAh / g) is preferably greater than 400 mAh / g. The initial discharge capacity is preferably greater than 500 mAh / g, more preferably greater than 600 mAh / g, further preferably 634 mAh / g or greater, further preferably 681 mAh / g or greater, further preferably 690 mAh / g or greater, further preferably greater than 700 mAh / g, further preferably greater than 730 mAh / g, further preferably greater than 745 mAh / g. The upper limit of the initial discharge capacity is not particularly limited, and the higher the upper limit, the more preferable. Thus, although the upper limit of the initial discharge capacity is not particularly meaningful, the upper limit can be assumed to be, for example, about 1000 mAh / g, only as a reference value.

[0089] (the 10th discharge capacity (DC 10 ))

[0090] In the case where the electrode of the present application is used as a positive electrode, the discharge capacity at the time of repeated charging and discharging 10 times, i.e., the 10th discharge capacity (DC 10 ) (mAh / g) is preferably greater than 350 mAh / g. The discharge capacity is preferably greater than 400 mAh / g, more preferably greater than 500 mAh / g, further preferably greater than 600 mAh / g, further preferably 634 mAh / g or greater, further preferably greater than 650 mAh / g, further preferably 671 mAh / g or greater, further preferably 681 mAh / g or greater, further preferably 690 mAh / g or greater, further preferably 723 mAh / g or greater, further preferably 743 mAh / g or greater. The upper limit of the discharge capacity is not particularly limited, and the higher the upper limit, the more preferable. Thus, although the upper limit of the discharge capacity is not particularly meaningful, the upper limit can be assumed to be, for example, approximately equal to the value of the initial discharge capacity or about 900 mAh / g, only as a reference value.

[0091] Further, when measuring the 3rd discharge capacity and the 10th discharge capacity of the electrode using the electrode of the present application as the positive electrode, the negative electrode and the electrolyte which can be used as the lithium ion secondary battery for a long time (so that lithium is not immediately depleted) within the range of common technical knowledge are used, and the electrode can sufficiently exhibit the performance related to the discharge capacity of the positive electrode, the 3rd discharge capacity and the 10th discharge capacity being determined by the structure of the positive electrode. For example, as for the negative electrode, it is sufficient to use the negative electrode having the lithium content (molar amount) greater than one percent (preferably one-tenth, more preferably one-half) of the amount (molar amount) of sulfur in the positive electrode. In the following examples, the weight of the mixture layer containing the positive electrode active material is 103.4 mg to 144 mg (3 cm x 4 cm x coating density), and the mixture layer further contains other components other than sulfur, and therefore the amount (molar amount) of sulfur is necessarily lower than 0.004491 (≈ 0.144 / 32.065) (the value is equal to or less than 71.5%). On the other hand, the weight of the negative electrode is 534 mg (4 cm x 5 cm x 0.5 mm x specific gravity of lithium), and the amount (molar amount) of lithium is 0.076934 (≈ 0.534 / 6.941), and therefore the amount (molar amount) of lithium in the negative electrode is sufficiently large. Further, for example, as for the electrolyte, it is sufficient to make the amount (molar amount) of lithium greater than one percent (preferably one-tenth, more preferably one-half) of the amount (molar amount) of sulfur in the positive electrode. In the following examples, the amount (molar amount) of lithium in the electrolyte is 0.002 = the volume V (= 2.0 mL) of the electrolyte containing solute x the concentration (= 1.0 mol / L), and therefore the amount (molar amount) of lithium in the electrolyte is sufficiently large. When the negative electrode and the electrolyte containing the amount of lithium (molar amount) sufficient as described above are used, the discharge capacity of the positive electrode can be sufficiently exhibited. Here, the volume V (mL) of the electrolyte refers to the total volume of the electrolyte containing solute or the solid electrolyte.

[0092] [Use]

[0093] The electrode for a lithium ion secondary battery of the present application can be used as the positive electrode or the negative electrode of the lithium ion secondary battery. Further, the electrode for a lithium ion secondary battery of the present application is preferably used as the positive electrode of the lithium ion secondary battery.

[0094] The electrode for a lithium-ion secondary battery can be manufactured in the same manner as described in the manufacturing method section by using the materials described in the manufacturing method section. That is, in the case where the above-described electrode for a lithium-ion secondary battery is used as a positive electrode, the conductive aid, the binder, the current collector, and the like described in the manufacturing method section below are used in the same manner as described in the manufacturing method section, whereby the above-described electrode for a lithium-ion secondary battery is manufactured as a positive electrode, and, in the case where the above-described electrode for a lithium-ion secondary battery is used as a negative electrode, the negative electrode, the electrolyte, the separator, and the like described in the manufacturing method section below are used in the same manner as described in the manufacturing method section, whereby the above-described electrode for a lithium-ion secondary battery is manufactured as a negative electrode. As described above, these descriptions in the manufacturing method section below can be regarded as an explanation of the electrode for a lithium-ion secondary battery.

[0095] < Lithium-ion secondary battery >

[0096] The lithium-ion secondary battery of the present application is a lithium-ion secondary battery containing the above-described electrode for a lithium-ion secondary battery.

[0097] The lithium-ion secondary battery can be manufactured in the same manner as described in the manufacturing method section by using the materials described in the manufacturing method section below. That is, in the case where the above-described electrode for a lithium-ion secondary battery is used as a positive electrode, the negative electrode, the electrolyte, the separator, and the like described in the manufacturing method section below are used in the same manner as described in the manufacturing method section, whereby the lithium-ion secondary battery is manufactured. On the other hand, in the case where the above-described electrode for a lithium-ion secondary battery is used as a negative electrode, the positive electrode, the electrolyte, the separator, and the like described in the manufacturing method section below are used in the same manner as described in the manufacturing method section, whereby the lithium-ion secondary battery is manufactured. As described above, these descriptions in the manufacturing method section below can be regarded as an explanation of the lithium-ion secondary battery.

[0098] [Inequality (3)]

[0099] For the lithium-ion secondary battery of the present application, the sulfur element content A S (mass %) in the active material and the coating density D (mg / cm 2The quotient of the product of the above-mentioned values divided by the volume V (mL) of the electrolyte is preferably greater than 240. The right side of inequality (3) is more preferably 250, further preferably 260, further preferably 270, further preferably 280, further preferably 285, further preferably 290, further preferably 294, further preferably 300, further preferably 310, further preferably 350, further preferably 360. The upper limit of the left side of inequality (3) is not particularly limited, and the higher the upper limit, the more preferable. Thus, while the upper limit of the left side of inequality (3) is not particularly meaningful, it can be assumed to be about 1000, about 800, or about 600, as a reference value.

[0100] Since the volume V (mL) of the electrolyte varies depending on the size of the battery, the range is not particularly limited, and the minimum amount that can exhibit the performance of the active material and sufficiently operate the battery can be used. As a reference value, for example, in the case of the laminated battery described in the examples, the volume V is preferably 1.0 mL or more, more preferably 1.2 mL or more, and further preferably 1.5 mL or more. On the other hand, the volume V is preferably 4.0 mL or less, more preferably 3.0 mL or less, and further preferably 2.5 mL or less.

[0101] [Use]

[0102] The lithium ion secondary battery of the present application can be used as a lithium ion secondary battery having improved comprehensive performance of charge-discharge capacity, capacity retention rate, and energy density.

[0103] [Production method]

[0104] Hereinafter, the production method of the electrode and the lithium ion secondary battery of the present application will be described in the order of the production method of the active material constituting the electrode.

[0105] [Production of active material]

[0106] The active material according to the present application can be produced by a production method comprising: (1) mixing raw materials containing a polymer, an iron ion-containing compound, and sulfur, thereby obtaining a sintering raw material; and (2) sintering the sintering raw material in a non-oxidizing atmosphere.

[0107] (Polymer)

[0108] The polymer is not particularly limited, provided that it is a compound containing at least carbon and hydrogen atoms and a compound that absorbs sulfur to form an organic sulfur compound when fired together with an iron ion-containing compound and sulfur under a non-oxidizing atmosphere. In addition, the polymer can be a polymer containing a heteroatom such as a nitrogen atom, a sulfur atom, or the like. Specific examples of the polymer include, for example, a polymer of an unsaturated chain hydrocarbon-based monomer, a condensate of a substituted aromatic hydrocarbon and chlorinated sulfur, or the like. The polymer can be used alone or in combination of two or more kinds thereof.

[0109] <<unsaturated chain hydrocarbon-based monomer polymer>>

[0110] Examples of the unsaturated chain hydrocarbon-based monomer polymer include, for example, an acrylic resin, and the like. In addition, examples of the unsaturated chain hydrocarbon-based monomer polymer include a diene-based rubber, and the like. One or more kinds of the unsaturated chain hydrocarbon-based monomer polymer can be used.

[0111] Examples of the acrylic resin include, for example, at least one polymer selected from the group consisting of a polymer obtained by polymerizing at least one monomer selected from an acrylic ester compound represented by the following formula (1); or a polymer obtained by polymerizing at least one monomer selected from an acrylic ester compound represented by the following formula (1) and at least one monomer selected from a diacrylic ester compound represented by the following formula (2). One or more kinds of the acrylic resin can be used, and one or more kinds of the acrylic ester compound can be used.

[0112] CH2=C(R 11 )COOR 12 (1)

[0113] (Wherein, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group.)

[0114] CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2 (2)

[0115] (In the formula, R 21 and R 22 are the same or different, and each is a hydrogen atom or a methyl group; Y is a linear hydrocarbylene group, which can have at least one substituent selected from a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbylene group can have an ether bond formed with an oxygen atom, provided that when the ether bond is two or more, there are always two or more carbon atoms interposed between any adjacent oxygen atoms.)

[0116] In formula (1), R 11 is preferably a methyl group, and R 12The alkyl group having 1 to 6 carbon atoms is more preferably an alkyl group having 1 to 4 carbon atoms, and among them, methyl group, n-butyl group, isobutyl group, and t-butyl group are more preferable. Examples of the compound represented by Chemical Formula (1) include, for example, methyl (meth)acrylate, butyl (meth)acrylate, and the like, and methyl methacrylate and butyl methacrylate are more preferable. Here, "(meth)acrylate" of the methyl (meth)acrylate and butyl (meth)acrylate means "acrylate" or "methacrylate" (the same applies hereinafter). As a further preferable example of the compound represented by Chemical Formula (1), butyl methacrylate is exemplified.

[0117] In Chemical Formula (2), R 21 and R 22 are each preferably a methyl group. The number of carbon atoms in the alkylene group (straight chain) of Y is preferably 2 to 6, and more preferably 2 or 3. The number of substituents in Y is preferably 1 to 4, and more preferably 1 or 2. As the substituents in Y, one or more substituents selected from a hydroxyl group and an alkyl group having 1 to 4 carbon atoms are preferable; and as the alkyl group having 1 to 4 carbon atoms, a methyl group is preferable. When the carbon skeleton of Y has an ether bond formed with an oxygen atom, for example, the portion corresponding to -Y-O- is preferably represented by the following Chemical Formula (3) (provided that the substituents in Y are not taken into account in Chemical Formula (3)).

[0118] -(CH2)l-(CH2CH2O) m -(CH2CH2CH2O) n -(3)

[0119] (In the formula, 1 is 0 to 6, m is 0 to 3, and n is 0 to 2. However, 1, m, and n cannot be 0 at the same time.)

[0120] In Chemical Formula (3), preferably, 1 is 1, 2, 3, 4, 5, or 6, and m and n are 0; m is 1, 2, or 3, and 1 and n are 0; or n is 1 or 2, and 1 and m are 0.

[0121] Examples of the compound represented by Chemical Formula (2) include, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, and the like. Among them, ethylene glycol dimethacrylate is preferable.

[0122] Preferred examples of the acrylic resin include a homopolymer of methyl (meth)acrylate, a homopolymer of butyl (meth)acrylate, a copolymer of methyl (meth)acrylate and ethylene glycol di(meth)acrylate, a copolymer of butyl (meth)acrylate and ethylene glycol di(meth)acrylate, and the like. Among them, as the acrylic resin, an acrylic resin of the methacrylate type is preferred. More preferred examples of the acrylic resin include a copolymer of methyl methacrylate and ethylene glycol dimethacrylate.

[0123] In the present application, the acrylic resin is preferably in the form of fine particles. Here, fine particles refer to particles having a particle diameter of 300.0 μm or less. The particle diameter is preferably 270.0 μm or less, more preferably 200.0 μm or less, further preferably 100.0 μm or less, further preferably 50.0 μm or less, further preferably 20.0 μm or less, further preferably 15.0 μm or less, further preferably 13.0 μm or less, further preferably 10.0 μm or less, further preferably 6.0 μm or less. On the other hand, the lower limit of the particle diameter is not particularly limited, and is typically, for example, 0.1 μm or more, preferably 1.0 μm or more. This particle diameter is a value (median particle diameter) measured by a particle size distribution measuring device (PSA1090L manufactured by Anton Paar GmbH).

[0124] The acrylic resin can be a spherical fine particle or a porous fine particle. When the acrylic resin is porous, the oil absorption amount thereof is preferably 100 mL / 100 g or more, more preferably 110 mL / 100 g or more, further preferably 120 mL / 100 g or more, further preferably 130 mL / 100 g or more, further preferably 140 mL / 100 g or more. The oil absorption amount is a value measured according to JIS K5101-13-2:2004. More specifically, it can be measured by the method described in paragraph 0069 of JP 2017-88501 A.

[0125] The acrylic resin is not particularly limited as long as it has the above structure, and the Mw thereof is not particularly limited. However, the Mw of the acrylic resin is typically in the range of 2000 to 1500000. The Mw is a value measured by gel permeation chromatography (GPC) (calibrated with polystyrene).

[0126] The acrylic resin is commercially available or can be produced by a conventional method within the knowledge of those skilled in the art. Examples of the commercially available acrylic resin include, for example, an acrylic resin manufactured by Sekisui Plastics Co., Ltd.

[0127] Examples of the diene-based rubber include, for example, natural rubber, isoprene rubber, butadiene rubber (e.g., high-cis polybutadiene rubber, etc.), and the like. The diene-based rubber is commercially available or can be manufactured by a conventional method within the knowledge of those skilled in the art.

[0128] <<Condensate of substituted aromatic hydrocarbon and chlorinated sulfur>>

[0129] Examples of the condensate of substituted aromatic hydrocarbon and chlorinated sulfur include, for example, condensate of alkylphenol and chlorinated sulfur, etc. Specific examples of the condensate of alkylphenol and chlorinated sulfur include, for example, TACKIROL V200, TS3108, TS3109 manufactured by TAKACHIMICA CO., LTD., Vultac 3 manufactured by Arakawa Chemical Industries, Ltd., etc. One or more kinds of condensate of substituted aromatic hydrocarbon and chlorinated sulfur can be used.

[0130] (Sulfur)

[0131] As the sulfur, various forms of sulfur such as powdered sulfur, insoluble sulfur, precipitated sulfur, colloidal sulfur, etc. can be used. Among them, precipitated sulfur and colloidal sulfur are preferred. One or more kinds of sulfur can be used.

[0132] The content of the sulfur is preferably more than 50 parts by mass, more preferably more than 100 parts by mass, further preferably more than 300 parts by mass, further preferably more than 400 parts by mass, further preferably 500 parts by mass or more, based on 100 parts by mass of the polymer. When the content is more than 50 parts by mass, there is a tendency that the charge-discharge capacity and the cycle characteristics can be improved. On the other hand, the content of the sulfur has no upper limit, but is generally preferably less than 1000 parts by mass, more preferably less than 900 parts by mass, further preferably less than 800 parts by mass, further preferably less than 700 parts by mass. When the content is less than 1000 parts by mass, there is a tendency that there is an advantage in terms of cost. Furthermore, in the present specification, the term "cycle characteristics" means characteristics in which the charge-discharge capacity of the secondary battery is maintained despite repetition of charging / discharging. Thus, a secondary battery in which the charge-discharge capacity decreases to a high degree and the capacity retention rate is low with repetition of charging and discharging has poor cycle characteristics, whereas, on the contrary, a secondary battery in which the charge-discharge capacity decreases to a low degree and the capacity retention rate is high has excellent cycle characteristics.

[0133] As the sulfur, any one of various allotropes can be used, but it is preferred that the sulfur include S8 sulfur which is a solid at normal temperature and normal pressure, and a monomer of S8 sulfur is more preferred.

[0134] (Iron ion-containing compound)

[0135] The iron ion-containing compound is not particularly limited as long as it is a compound that forms an iron compound when fired with the polymer and sulfur under a non-oxidizing atmosphere. Examples of such an iron ion-containing compound can include ferrite salts, iron complexes, and the like that contain divalent or trivalent iron ions. Examples of the ferrite salt can include organic acid salts of iron and inorganic acid salts of iron. On the other hand, examples of the iron complex can include neutral iron complexes and iron complex ion salts (iron complex salts).

[0136] Examples of the organic acid salt of iron include, for example, a salt of divalent iron (Fe 2+ ) and an organic acid, a salt of trivalent iron (Fe 3+ ) and an organic acid, and the like. Among them, a salt of divalent iron and an organic acid is preferred. The organic acid is an organic acid having a carboxyl group (-COOH), an organic acid having a sulfonic group (-SO3H), or the like, but is not particularly limited thereto. Among them, an organic acid having a carboxyl group is preferred. Specific examples of the organic acid include aliphatic acids, oxalic acid, tartaric acid, citric acid, malic acid, succinic acid, and the like. Specific examples of the aliphatic acid include, for example, aliphatic acids having 1 to 6 carbon atoms, such as acetic acid, propionic acid, butyric acid, and the like. Among them, acetic acid, oxalic acid, and the like are preferred. Preferred examples of the organic acid salt of iron include iron (II) acetate, iron (II) oxalate, and the like. They can be hydrates. One or more kinds of the organic acid salt of iron can be used.

[0137] Examples of the inorganic acid salt of iron include, for example, a salt of divalent iron (Fe 2+ ) and an inorganic acid, a salt of trivalent iron (Fe 3+ ) and an inorganic acid, and the like. Among them, a salt of divalent iron and an inorganic acid is preferred. Specific examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, and the like. Among them, nitric acid and the like are preferred. Preferred examples of the inorganic acid salt of iron include iron (II) chloride, iron (III) chloride, iron (II) sulfate, iron (III) sulfate, iron (II) nitrate, iron (III) nitrate, and the like. They can be hydrates. One or more kinds of the inorganic acid salt of iron can be used.

[0138] Examples of the iron complex include, for example, a divalent iron (Fe 2+ ) complex, a trivalent iron (Fe 3+) complex, etc. The iron complex can be in the form of a neutral complex or in the form of a complex salt. The ligand coordinated with the iron ion is not particularly limited, and examples thereof include, for example, a halogen atom (e.g., a chlorine atom, a bromine atom, etc.), a cyano group, a dicyclopentadienyl group, N,N'-bis(salicylidene)ethylenediamine, etc. Examples of the iron complex include: potassium hexacyanoferrate(II) ([Fe(CN)6]K4), potassium hexacyanoferrate(III) ([Fe(CN)6]K3), sodium ferric chloride ([FeCl4]Na), dicyclopentadienyl iron(II) (ferrocene), N,N'-bis(salicylidene)ethylenediamine ferric chloride, etc. One or more kinds of iron complexes can be used.

[0139] As the iron ion-containing compound, at least one selected from the group consisting of the above-described organic acid salt of iron, the inorganic acid salt of iron, the neutral iron complex, and the iron complex salt can be used. Among them, the organic acid salt of iron, the inorganic acid salt of iron, or the neutral iron complex is preferred.

[0140] Although the particle diameter of the iron ion-containing compound is not particularly limited, the particle diameter (e.g., the median particle diameter) is preferably 1 μm or more, more preferably 2 μm or more. In addition, the particle diameter is preferably 40 μm or less, further preferably 30 μm or less, further preferably 20 μm or less, further preferably 15 μm or less. The median particle diameter can be measured by the method described in the following Example section.

[0141] From the viewpoint of improving the performance of the electrode and / or the battery, the content of the iron ion-containing compound is preferably 50 parts by mass or more and 300 parts by mass or less, based on 100 parts by mass of the polymer. The content is more preferably greater than 50 parts by mass, further preferably greater than 60 parts by mass, further preferably greater than 70 parts by mass, further preferably greater than 75 parts by mass. On the other hand, the content is more preferably less than 250 parts by mass, further preferably less than 200 parts by mass, further preferably less than 150 parts by mass, further preferably less than 125 parts by mass.

[0142] (Iron ion-containing compound-dispersed polymer)

[0143] In the present application, the polymer and the iron ion-containing compound can be used as an iron ion-containing compound-dispersed polymer obtained by dispersing the iron ion-containing compound in the polymer in advance. Such an iron ion-containing compound-dispersed polymer can be produced by causing the polymer to undergo a polymerization reaction in a state in which the iron ion-containing compound is dispersed in advance in a monomer constituting the polymer. The polymerization reaction can be performed by a conventional method.

[0144] As the polymer in which the iron ion-containing compound is dispersed, for example, an iron ion-containing compound-dispersed acrylic resin obtained by dispersing an iron ion-containing compound in an acrylic resin can be appropriately used. Preferred examples of the acrylic resin used for this purpose include a homopolymer of methyl (meth)acrylate, a copolymer of methyl (meth)acrylate and ethylene glycol dimethacrylate, and the like. Furthermore, preferred examples of the iron ion-containing compound used for this purpose include ferrous oxalate (II) and the like.

[0145] (Other materials)

[0146] The raw material can appropriately contain other materials commonly used in the field as needed. Examples of such materials include, for example, an electrically conductive carbon material and the like.

[0147] <<Electrically conductive carbon material>>

[0148] The raw material can contain an electrically conductive carbon material. This is because it can improve the electrical conductivity of the active material. As such an electrically conductive carbon material, a carbon material having a graphite structure is preferred. As the carbon material, for example, a porous carbon material (for example, activated carbon and the like), graphite, carbon black, acetylene black, ketjen black, carbon fiber (CF), and a nano carbon material (for example, carbon nanotube (CNT), carbon nanofiber, graphene, fullerene, and the like) can be used. One or more electrically conductive carbon materials can be used.

[0149] Among them, acetylene black, carbon black, and ketjen black are preferred because they are inexpensive and have excellent dispersibility. Furthermore, a small amount of CNT, graphene, or the like can be used in combination with acetylene black, carbon black, or ketjen black. Such a combination system can further improve the cycle characteristics of the lithium ion secondary battery without significantly increasing the cost. Furthermore, the total amount of CNT or graphene is preferably 8 mass% or more and 12 mass% or less of the total amount of the electrically conductive carbon material.

[0150] The content of the electrically conductive carbon material is preferably more than 5 mass parts, more preferably more than 10 mass parts, based on 100 mass parts of the polymer. When the content is more than 5 mass parts, there is a tendency to easily achieve the purpose of further improving the charge and discharge capacity and the cycle characteristics. On the other hand, the content is preferably less than 50 mass parts, more preferably less than 40 mass parts. When the content is less than 50 mass parts, the proportion of the sulfur-containing structure in the active material does not decrease relatively, and there is a tendency to easily achieve the purpose of further improving the charge and discharge capacity and the cycle characteristics.

[0151] (Mixing step (1))

[0152] The mixing step is a step of preparing a sintering raw material.

[0153] The mixing step can be performed by mixing the polymer, the iron ion-containing compound, the sulfur, and any other components. In this case, the polymer dispersed with the iron ion-containing compound described above can also be used instead of the polymer and the iron ion-containing compound.

[0154] The above mixing can be performed by a conventional method, and there is no particular limitation as long as the mixing is a method of sufficiently mixing the components. In the present application, examples of the preferred mixing method can include at least: mixing by a wet method (WET method) or mixing by a dry method (DRY method), which will be mentioned below.

[0155] <<WET method>>

[0156] In the present application, the WET method includes the following steps for preparing a raw material:

[0157] (a-1) adding a polymer and an iron ion-containing compound to a solvent (e.g., an organic solvent, etc.) to obtain a mixture, or adding a monomer capable of forming a polymer and an iron ion-containing compound and performing a polymerization reaction to obtain a mixture containing a polymer, in which the iron ion-containing compound is dispersed inside and on the surface of the polymer;

[0158] (a-2) removing the solvent from the mixture to obtain a dry mixture; and

[0159] (a-3) mixing the dry mixture and sulfur.

[0160] In the sub-step (a-1), the method of adding the polymer or the monomer, the iron ion-containing compound, etc. to the organic solvent is not particularly limited as long as a mixture can be obtained by mixing them. For example, (1) the polymer (or the monomer) and the iron ion-containing compound can be simultaneously added to the organic solvent and mixed, (2) the polymer (or the monomer) can be added to the organic solvent and mixed, and then the iron ion-containing compound can be added and mixed, or (3) the iron ion-containing compound can be added to the organic solvent and mixed, and then the polymer (or the monomer) can be added and mixed.

[0161] In the sub-step (a-1), as the organic solvent, an organic solvent commonly used in the art can be used, examples of which include, for example, N-methyl-2-pyrrolidone, N,N-dimethylformamide, alcohols, hexane, water, acetone, ethers (such as tetrahydrofuran, etc.), and the like. In addition, as the organic solvent, an organic solvent capable of dissolving the polymer is preferred. This is because it contributes to good mixing. One or more of these solvents can be used. Furthermore, in the case of using a liquid monomer in the sub-step (a-1), the solvent is not essential, and when the solvent is not used, the sub-step (a-2) can be omitted.

[0162] The sub-step (a-1) can be performed by stirring them in a container (such as a beaker, etc.).

[0163] In sub-step (a-2), the removal of the organic solvent can be carried out by a conventional method. For example, the removal can be carried out by subjecting the mixture in sub-step (a-1) to a drying method (e.g., heat drying, drying under reduced pressure, drying under reduced pressure with heating, etc.).

[0164] Preferably, the dried mixture thus obtained is pulverized before the next step is carried out. This is because, by this means, it is expected that the mixing in sub-step (a-3) can be more appropriately carried out.

[0165] In sub-step (a-3), the mixing of the dried mixture and sulfur can be carried out by a conventional method, examples of which can include, for example, a method in which they are mixed using a blender, etc.

[0166] <<DRY method>>

[0167] In the present application, the DRY method includes the following steps for preparing the raw material:

[0168] (b-1) mixing the polymer, the iron ion-containing compound, and sulfur in a powder state.

[0169] Here, the powder means that each of the raw materials of the solid has been made fine enough to be suitable for the purpose of mixing used in the present application. The size of each particle constituting the powder is not particularly limited, as long as the mixing can be appropriately carried out, but is generally in the range of, for example, 1 μm or more to 40 μm or less. From the viewpoint of improving the performance of the electrode and / or the battery, the size of the particle is preferably 2 μm or more, more preferably 3 μm or more, further preferably 4 μm or more, and preferably 30 μm or less, further preferably 20 μm or less, further preferably 15 μm or less, further preferably 10 μm or less, in terms of the median particle diameter. The median particle diameter can be measured by the method described in the Examples section below.

[0170] The mixing can be carried out by a conventional method, for example, in the same manner as the mixing in sub-step (a-3) described above.

[0171] In the WET method and the DRY method, it is preferable to previously mix the raw materials sufficiently for the firing. In addition, when an electrically conductive carbon material or the like is added to the raw materials, it is also possible to previously mix these additives for the firing, so that they are previously contained in the raw materials.

[0172] The raw materials thus obtained can be directly used for the next firing step, or if necessary, they can be made into particles and used for the next step.

[0173] (Firing step (2))

[0174] The firing step is a step of firing the raw material obtained above. The firing of the raw material can be performed by a conventional method, for example, by heating the raw material at a predetermined temperature- increasing rate until a predetermined temperature, holding them at the predetermined temperature for a predetermined time, and then allowing them to cool naturally.

[0175] <non-oxidizing atmosphere>

[0176] Preferably, the firing is performed under a non-oxidizing atmosphere. The non-oxidizing atmosphere refers to an atmosphere substantially free of oxygen, for the purpose of suppressing oxidative deterioration and excessive pyrolysis of the constituent components. Specifically, it refers to an inert gas atmosphere such as nitrogen gas, argon gas, a sulfur gas atmosphere, an ammonia gas atmosphere, and the like. Thus, the firing can be suitably performed in a quartz tube under an inert gas atmosphere, for example.

[0177] <temperature- increasing rate>

[0178] The temperature-increasing rate is preferably in the range of, for example, 50°C / h or more and 500°C / h or less. The temperature-increasing rate is preferably 80°C / h or more, more preferably 100°C / h or more, and further preferably 120°C / h or more. On the other hand, the temperature-increasing rate is more preferably 400°C / h or less, further preferably 300°C / h or less, and further preferably 200°C / h or less. When the temperature-increasing rate is in such a range, there is a tendency to easily achieve the purpose of improving the charge and discharge capacity and the cycle characteristics.

[0179] <temperature and time of firing>

[0180] The firing temperature refers to the temperature after the temperature increase of the raw material is completed, at which the raw material is held for a certain period of time for the purpose of firing. The temperature is preferably in the range of 250°C or more and 550°C or less. When it is higher than 250°C, there is a tendency to avoid insufficient vulcanization reaction and prevent the target charge and discharge capacity from decreasing. On the other hand, when it is lower than 550°C, there is a tendency to prevent the raw material from decomposing and to prevent the yield and the charge and discharge capacity from decreasing. The temperature is more preferably higher than 300°C, further preferably higher than 350°C, and further preferably 370°C or more. On the other hand, the temperature is more preferably lower than 500°C, and further preferably lower than 450°C.

[0181] From the viewpoint of improving the performance of the electrode and / or the battery, preferably, the firing temperature in the firing step is higher than the temperature at which the iron ion-containing compound thermally decomposes.

[0182] The holding time of the firing temperature only needs to be appropriately set depending on the type of the raw material, the firing temperature, and the like, but is preferably, for example, 1 hour or more and 6 hours or less. When it is 1 hour or more, there is a tendency that the firing can be sufficiently performed, and when it is 6 hours or less, there is a tendency that excessive pyrolysis of the constituent components can be prevented.

[0183] <apparatus>

[0184] Firing can be performed by, for example, a muffle furnace Figure 1 ) or can be implemented using a continuous device (e.g., a twin-screw extruder or the like). When a continuous device is used, there is an advantage that the chalcogenide active material is continuously manufactured by a series of operations, such as mixing, pulverizing, and mixing of raw materials while firing is implemented in the device.

[0185] A muffle furnace Figure 1 ) is a furnace that is partitioned by a heating plate or the like, and in order to prevent contamination of a sample, a heat source (heater) is not exposed in the furnace. Figure 1 In the muffle furnace 1, a heater 2 is provided in the lower portion of the furnace, and the heater is partitioned by a heating plate. A lid 3 is provided on the front surface (left end side in the drawing) of the furnace, and the lid allows the furnace to have a structure in which an atmosphere of an inert gas 4 can be maintained in the furnace. A thermocouple (not shown) is provided on the lid to allow the temperature in the furnace during firing to be measured. Two layers of stainless steel (SUS) rectangular parallelepiped trays 5 and 6 for firing raw materials are provided in the upper and lower layers in the furnace.

[0186] The furnace is configured so that a gas (e.g., an inert gas such as argon (Ar)) can be continuously supplied and discharged to the outside through a gas introduction pipe 7 and a gas discharge pipe 8. The gas discharge pipe 8 is connected to a trap tank 10 that contains a sodium hydroxide aqueous solution 9, and exhaust gas discharged to the outside from the muffle furnace 1 through the gas discharge pipe 8 is discharged to the outside once it passes through the sodium hydroxide aqueous solution 9 in the trap tank 10. Thus, even if the exhaust gas contains hydrogen sulfide gas generated by the reaction, the hydrogen sulfide gas is neutralized by the sodium hydroxide aqueous solution and removed from the exhaust gas.

[0187] (Step of removing residues)

[0188] In the processed product obtained after firing, unreacted sulfur that has been separated from sulfur that sublimates during the firing process and then cools is left. In the presence of these residues, it is preferable to remove as many of these residues as possible because they can cause deterioration of the cycle characteristics. The removal of residues can be implemented according to a conventional method (e.g., by drying by heating under reduced pressure, drying with hot air, washing with a solvent, or the like).

[0189] (Pulverization / classification)

[0190] In order to obtain particles having a size suitable for use in the manufacture of electrodes, it is preferable to pulverize the obtained active material to have a prescribed particle size and classify it. The preferable size (particle size distribution) of the particulate active material is as described above.

[0191] The pulverization can be performed by a conventional method, for example, it can be performed by subjecting the active material to a pulverization treatment under predetermined conditions using a pulverizer such as a chopper, a jet mill, or the like. The pulverization conditions differ depending on the pulverizer used, for example, in the case of using a chopper (for example, Free Speed Mill FS-20 manufactured by Labonect), it can be treated under conditions of a rotation speed of 20,000 rpm or more and 30,000 rpm or less for 1 second or more and 30 seconds or less. Further, in the case of using a dry jet mill (for example, Nano Jetmizer NJ-30 manufactured by Aishin Nano Technologies CO., LTD.), it can be treated at a treatment speed of 1 g / minute or more and 3 g / minute or less and a pulverization pressure of 0.5 MPa or more and 2.0 MPa or less.

[0192] Further, in the firing method using the twin-screw extruder as described above, it is also possible to pulverize the manufactured active material into particles by performing shearing during kneading while manufacturing the active material.

[0193] [Manufacture of lithium-ion secondary battery electrode]

[0194] Using the above-obtained particulate active material, a lithium-ion secondary battery electrode including an active material layer containing the particulate active material can be manufactured by a conventional method. That is, the electrode can be obtained in the same manner as in the case of manufacturing a general lithium-ion secondary battery electrode, except that the above particulate active material is used as the active material.

[0195] (Case where particulate active material is used as positive electrode active material)

[0196] The lithium-ion secondary battery positive electrode can be manufactured in the same manner as a general lithium-ion secondary battery positive electrode, except that the above particulate active material is used as the positive electrode active material. For example, the positive electrode can be manufactured by mixing the particulate active material with a conductive aid, a binder, and a solvent to prepare a paste-like positive electrode material, coating the positive electrode material on a current collector, and then drying. Further, as another method, for example, the positive electrode can also be manufactured by kneading the particulate active material together with a conductive aid, a binder, and a small amount of solvent using a mortar or the like and forming a thin film, and then pressing it onto a current collector using a press or the like. However, in this case, the coating of the active material is performed so that the coating density D (mg / cm2) of the active material satisfies the above inequality (1). 2 ) satisfies the above inequality (1).

[0197] [Conductive aid]

[0198] Examples of the conductive auxiliary agent include, for example, vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, or a fine powder of a metal stable at a positive electrode potential, such as aluminum, titanium, or the like. In addition, as the conductive auxiliary agent, the above-described conductive carbon material can also be used. One or two or more of these conductive auxiliary agents can be used.

[0199] <Adhesive>

[0200] Examples of the adhesive include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamide-imide (PAI), carboxymethyl cellulose (CMC), polyvinyl chloride (PVC), acrylic resin, methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene ether (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), or the like. One or more of these adhesives can be used.

[0201] <Solvent>

[0202] Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformamide, an alcohol, hexane, water, or the like. One or more of these solvents can be used.

[0203] <Mixing amount>

[0204] The mixing amount of these materials constituting the positive electrode is not particularly limited, but preferably, 2 to 100 parts by mass of the conductive auxiliary agent, 2 to 50 parts by mass of the adhesive, and an appropriate amount of the solvent are mixed, based on 100 parts by mass of the active material. However, in this case, the relationship between the sulfur element content A S (mass %) and the iron element content A F (mass %) of the active material and the coating density D (mg / cm 2 ) of the active material should be determined so that the product of A S , A F , and D satisfies the above inequality (1).

[0205] <Current collector>

[0206] As the current collector, a current collector commonly used for the positive electrode of a lithium-ion secondary battery can be used. Examples of the current collector include, for example, a current collector composed of a metal foil such as an aluminum foil, an aluminum mesh, a punched aluminum sheet, an expanded aluminum sheet, a stainless steel foil, a stainless steel mesh, a punched stainless steel sheet, an expanded stainless steel sheet, a nickel foam, a nickel nonwoven fabric, a copper foil, a copper mesh, a punched copper sheet, an expanded copper sheet, a titanium foil, a titanium mesh, and the like, and a carbon nonwoven fabric, a carbon woven fabric, and the like. Among them, a current collector composed of a metal foil is preferable. The current collector can be used alone or in combination of two or more. In addition, the surface of the current collector can be coated with carbon or the like. Specific examples of such a current collector having a surface coated with carbon or the like include, for example, a carbon-coated aluminum foil, and the like. In this case, the current collector includes a carbon-coated portion.

[0207] (Case where particulate active material is used as negative electrode active material)

[0208] The negative electrode for a lithium-ion secondary battery can be manufactured in the same manner as a general negative electrode for a lithium-ion secondary battery, except that the above-described particulate active material is used as the negative electrode active material. For example, the negative electrode can be manufactured by mixing the particulate active material with a conductive aid, a binder, and a solvent to prepare a paste-like negative electrode material, coating the negative electrode material on a current collector, and then drying. In addition, as another method, for example, the negative electrode can be manufactured by kneading the particulate active material with a conductive aid, a binder, and a small amount of a solvent using a mortar or the like to form a thin film, and then pressing the thin film on a current collector using a press or the like. However, in this case, the coating of the active material is performed so that the coating density D (in mg / cm 2 of the active material satisfies the above inequality (1).

[0209] As the conductive aid, the binder, and the solvent, the same conductive aid, the same binder, and the same solvent as in the case where the particulate active material is used as the positive electrode active material can be used, and the same conductive aid, the same binder, and the same solvent can be coated on the current collector.

[0210] [Manufacture of lithium-ion secondary battery]

[0211] The lithium-ion secondary battery of the present application can be manufactured in the same manner as in the case of manufacturing a general lithium-ion secondary battery, except that the above-described electrode for a lithium-ion secondary battery is used.

[0212] (Case where particulate active material is used as positive electrode active material)

[0213] The lithium-ion secondary battery of the present application can be manufactured according to a conventional method, except that a negative electrode and an electrolyte are used, and further, a separator or the like is used as necessary, in addition to the positive electrode containing the above-described particulate active material (positive electrode active material).

[0214] <<Negative electrode>>

[0215] As the negative electrode material, known metal lithium, carbon-based materials (e.g., graphite, etc.), silicon-based materials (e.g., silicon thin film, etc.), and alloy-based materials (e.g., copper tin, cobalt tin, etc.) can be used. Among the above-mentioned negative electrode materials, when a lithium-free material (e.g., carbon-based material, silicon-based material, alloy-based material, etc.) is used as the negative electrode material, it is advantageous in that short circuiting between the positive electrode and the negative electrode due to the generation of dendrites is less likely to occur. However, when these lithium-free negative electrode materials are used in combination with the positive electrode of the present application, neither the positive electrode nor the negative electrode contains lithium. Therefore, a lithium pre-doping process in which lithium is pre-doped into either or both of the negative electrode and the positive electrode is required. As the lithium pre-doping method, a known method can be used. For example, examples of the lithium pre-doping method in which lithium is doped into the negative electrode include a method in which lithium is doped by an electrolytic doping method (a half-cell is assembled using metal lithium as a counter electrode, and lithium is electrochemically doped), and a method in which lithium is doped by a pasting pre-doping method (a metal lithium foil is pasted to an electrode, which is then placed in an electrolyte, and doping is performed using diffusion of lithium into the electrode). In addition, when lithium is pre-doped into the positive electrode, the above-mentioned electrolytic doping method can be used. As the lithium-free negative electrode material, a silicon-based material, which is particularly preferable as a high-capacity negative electrode material, is more preferable, in which a thin film silicon, which is thin in electrode thickness and has an advantage in terms of capacity per unit volume, is more preferable.

[0216] < electrolyte >

[0217] The electrolyte compensates for the electric charge generated by the discharge of electrons to the external circuit, while accompanying oxidation / reduction of the active material at the positive electrode / negative electrode. As the electrolyte for the lithium ion secondary battery, an electrolyte obtained by dissolving an alkali metal salt as an electrolyte in an organic solvent can be used. As the organic solvent, at least one selected from non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, γ-butyrolactone, acetonitrile, etc. is preferably used. As the electrolyte, LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiI, LiClO4, etc. can be used. The concentration of the electrolyte only needs to be about 0.5 to 1.7 mol / L. In addition, the electrolyte is not limited to a liquid electrolyte. For example, when the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid state (e.g., a polymer gel state).

[0218] < separator >

[0219] In addition to the above-described negative electrode, positive electrode, and electrolyte, the lithium ion secondary battery can include components such as a separator. The separator is interposed between the positive electrode and the negative electrode, allows migration of ions between the positive electrode and the negative electrode, and prevents internal short-circuiting between the positive electrode and the negative electrode. If the lithium ion secondary battery is of a sealed type, the separator is required to have a function of retaining the electrolyte. As the separator, a thin and microporous or nonwoven fabric film made of polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, glass, or the like is preferably used.

[0220] <<Shape>>

[0221] The shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical type, a stacked type, a coin type, a laminated type, a button type, and the like can be used.

[0222] (Case in which a particulate active material is used as a negative electrode active material)

[0223] In addition to the negative electrode containing the above-described particulate active material (negative electrode active material), a positive electrode and an electrolyte are used, and components such as a separator are used as necessary, and the lithium ion secondary battery of the present application is manufactured according to a conventional method.

[0224] <<Positive Electrode>>

[0225] The positive electrode material is not particularly limited, and is only required to be a lithium-containing transition metal oxide or a solid solution oxide, or a substance capable of electrochemically absorbing and releasing lithium. Examples of the lithium-containing transition metal oxide include, for example, Li-Co-based composite oxides (such as LiCoO2and the like), Li-Ni-Co-Mn-based composite oxides (such as LiNi x Co y Mn z O2and the like), Li-Ni-based composite oxides (such as LiNiO2and the like), Li-Mn-based composite oxides (such as LiMn2O4and the like), and the like. Examples of the solid solution oxide include, for example, Li a Mn x Co y Ni z O2(1.150≤a≤1.430, 0.450≤x≤0.600, 0.100≤y≤0.150, 0.200≤z≤0.280), LiMn x Co y Ni z O2(0.300≤x≤0.850, 0.100≤y≤0.300, 0.100≤z≤0.300), LiMn 1.5 Ni 0.5 O4and the like. These compounds can be used alone or in a mixture of a plurality of kinds.

[0226] As for the electrolyte, the separator, and the shape of the lithium ion secondary battery, the same electrolyte, separator, and shape of the lithium ion secondary battery as in the case where the particulate active material is used as the positive active material can be employed.

[0227] Example

[0228] While the present application is illustrated based on the examples, the present application is not limited to the examples only.

[0229] The following summarizes various chemicals used in the examples and comparative examples.

[0230] Materials used in the test

[0231] Iron ion-containing compound: ferrous (II) oxalate dihydrate prepared in Synthetic Example 1

[0232] Iron ion-containing compound-dispersed polymer: iron ion-containing compound-dispersed acrylic resin (copolymer of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) (MMA:EGDMA = 80:20 (mass ratio) and acrylic resin in which iron ion-containing compound is dispersed inside or on the surface of the acrylic resin)) prepared in Synthetic Example 2

[0233] Polymer: acrylic resin (MMA:EGDMA = 80:20 (mass ratio)) obtained by polymerization in the same manner as in Production Example 2 except that the iron ion-containing compound was not used

[0234] Sulfur: precipitated sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0235] Synthetic Example 1 (iron ion-containing compound)

[0236] A substance obtained by pulverizing ferrous (II) oxalate dihydrate (ferrous (II) oxalate dihydrate manufactured by Kanto Chemical Co., Inc., Extrapure) using a freezer mill (JFC-2000 manufactured by Japan Analytical Industry Co., Ltd.) for 10 minutes was used as the iron ion-containing compound. Particle diameter (median particle diameter d 50 ): 2.10 μm, specific surface area: 6.6 m 2 / g.

[0237] Synthetic Example 2 (iron ion-containing compound-dispersed polymer)

[0238] A mixture of 80 parts by mass of methyl methacrylate (MMA) and 20 parts by mass of ethylene glycol dimethacrylate (EGDMA) was prepared, 100 parts of an iron ion-containing compound was further dispersed therein, and the mixture was subjected to a polymerization reaction, thereby obtaining an acrylic resin in which the iron ion-containing compound was dispersed inside or on the surface of the acrylic resin. The polymerization conversion rate was 100%.

[0239] Examples and Comparative Examples

[0240] Manufacture of Particulate Active Material

[0241] (Baking raw material)

[0242] According to Table 2, the respective components were mixed together in a blender to obtain a raw material for baking.

[0243] (Reaction apparatus for baking)

[0244] The raw material was baked using a muffle furnace (Model No. 550, manufactured by NAPSON Co., Ltd.). Figure 1 The muffle furnace in the Model No. 550 is as described above. Figure 1

[0245] (Baking step)

[0246] First, the atmosphere in the muffle furnace in which the baking raw material was housed in a tray (which is a SUS container) was replaced with Ar gas three times using a vacuum pump. Then, while Ar gas was continuously supplied at a flow rate of 100 mL / min from a gas introduction tube, heating of the muffle furnace was started 30 minutes after the start of the supply of the Ar gas. The temperature was increased at a temperature increase rate of 5°C / h, and when the temperature of the baking raw material reached the baking temperature described in Table 2, heat treatment was performed for 2 hours while the baking temperature was maintained. Next, while adjusting the flow rate of the Ar gas, the temperature of the baked material was naturally cooled to 25°C under an Ar gas atmosphere, and then the baked product was taken out of the muffle furnace.

[0247] (Pulverization step)

[0248] The baked product was pulverized using a cutter, a dry jet mill, or the like. The pulverization step for Manufacturing Examples 1 to 7 will be described below.

[0249] For Manufacturing Examples 1 to 6, pulverization was performed by processing the baked product for a predetermined period of time at a predetermined rotation speed using a cutter (free speed mill, FS-20, manufactured by Labonect) as shown in Table 1.

[0250] Table 1

[0251]

[0252] ​On the other hand, for Production Example 7, the calcine was pulverized by using a dry jet mill (Nano Jetmizer NJ-30 manufactured by Aishin NanoTechnologies CO., LTD.) at a processing speed of 2 g / min and a pulverization pressure of 1.1 MPa.

[0253] (Classification step)

[0254] In order to remove coarse particles from the pulverized calcine, the calcine was classified using a stainless steel sieve with a mesh size of 32 μm to obtain an active material.

[0255] <Physical properties of active materials>

[0256] (Elemental analysis)

[0257] The active materials produced in the examples and comparative examples were subjected to elemental analysis.

[0258] For carbon, hydrogen, nitrogen, and sulfur, a fully automatic elemental analyzer vario MICROcube manufactured by Elementar was used to calculate the mass ratio (%) in the total amount of the active material based on the measured mass. The results are shown in Table 2.

[0259] (Iron element content)

[0260] The active materials produced in the examples and comparative examples were subjected to thermogravimetric analysis, and based on the obtained measurement results, the amount of each iron element (mass %) was calculated.

[0261] Thermogravimetric analysis was performed using a TGA Q500 manufactured by TA Instruments. The measurement conditions were such that after the active material was heated to 750°C under an argon atmosphere, air was introduced to completely decompose the sample. Then, the ash content ratio (mass %) in each active material was calculated from the measured weight reduction ratio (mass %) by the following calculation method,

[0262] Ash content ratio (mass %) = 100 - weight reduction ratio (mass %)

[0263] Further, it was confirmed that the iron element in the present example and the comparative examples existed in the form of iron disulfide (FeS2), and therefore, the proportion of iron disulfide (mass %) was calculated from the ash content proportion (mass %) of each of the present example and the comparative examples by the following calculation method. That is, it was seen from the weight reduction rate (100 mass %) of Production Example 8 in Table 2 that the polymer 1 (acrylic resin) was completely decomposed after being converted into sulfide. On the other hand, it was seen from the weight reduction rate (36 mass %) of Production Example 9 that the weight of iron disulfide (FeS2) in the active material was reduced by 36 mass %. Therefore, the proportion of iron disulfide (FeS2) in each active material (mass %) was calculated by the following calculation method,

[0264] Proportion of FeS2 (mass %) = Ash content proportion x {100 / (100-36)}.

[0265] Further, the iron element content (Fe proportion, mass %) was calculated from the proportion of FeS2 (mass %) by the following calculation method,

[0266] Fe proportion (mass %) = Proportion of FeS2 x Atomic mass of Fe / (Atomic mass of Fe + Atomic mass of S x 2),

[0267] (assuming that 55.845 is used as the atomic mass of Fe and 32.065 is used as the atomic mass of S).

[0268] (Median particle diameter)

[0269] The volume-based cumulative 50% size (median particle diameter d50) was measured using a laser diffraction / scattering type particle size distribution analyzer (particle size distribution analyzer PSA1090L manufactured by Anton Paar GmbH) using water as the dispersion medium. 50 ).

[0270] The results are shown in Table 2 below.

[0271] Table 2

[0272]

[0273]

[0274] According to Table 3, the positive electrode was manufactured using the active material obtained above, and furthermore, the lithium ion secondary battery was manufactured using the positive electrode.

[0275] (Positive electrode)

[0276] ​Using the active material obtained above as an active material, using acetylene black as a conductive aid, and using an acrylic resin as a binder, they were weighed so that the ratio of the active material : the conductive aid : the binder would be 90 : 5 : 5 (mass %), put into a container, and stirred and mixed with a rotation-revolution mixer (ARE-250 manufactured by THINKY CORPORATION), using milliQ water as a dispersant, to produce a uniform slurry. Using an applicator with a slit width of 200 to 300 μm, the produced slurry was applied to a 20-μm carbon-coated aluminum foil, and pressed with a roll press to obtain an electrode, which was then heated and dried at 120°C for 3 hours using a drying device. After drying, the electrode was cut into a shape in which a portion including a mixed layer of the active material had a width of 4 cm and a length of 3 cm, and the electrode also had an exposed portion of a positive electrode current collector as a positive electrode groove, to obtain an electrode (positive electrode). Then, the mass of the electrode was measured, and the amount of the active material in the electrode was calculated from the above ratio. In addition, "coating density (mg / cm 2 )" described in Table 3 refers to the coating density of the active material.

[0277] (Negative electrode)

[0278] For the negative electrode, a metal lithium foil (manufactured by Hitojyo Metal Co., Ltd., having a thickness of 0.5 mm) was used, and a copper foil was used as a negative electrode current collector. The metal lithium foil was cut into a width of 5 mm and a length of 4 cm and attached to the copper foil to obtain an electrode (negative electrode).

[0279] (Electrolyte)

[0280] As the electrolyte, a nonaqueous electrolyte in which LiPF6was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate was used. Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1 : 1. The concentration of LiPF6in the electrolyte was 1.0 mol / L.

[0281] (Lithium-ion secondary battery)

[0282] A laminated battery was produced using the above positive electrode and negative electrode. Specifically, in a dry room, a separator (Celgard 2400 manufactured by Celgard LLC, a polypropylene microporous film having a thickness of 25 μm) and a glass nonwoven fabric filter (having a thickness of 440 μm, GA100 manufactured by ADVANTEC) were sandwiched between the positive electrode and the negative electrode to form an electrode body battery. The electrode body battery was placed in a laminated pack formed of an aluminum laminated film (manufactured by MTI Corporation). The above electrolyte (2.0 mL) was injected into the laminated pack. The laminated pack was sealed with an air-degassing sealer to obtain the lithium-ion secondary battery of Example 1.

[0283] <Evaluation of lithium-ion secondary battery>

[0284] (discharge capacity, capacity retention rate)

[0285] Each of the laminated lithium ion secondary batteries produced in the examples and comparative examples was subjected to charge and discharge at a current value of 50 mA per 1 g of positive electrode active material at a test temperature of 30°C. The discharge termination voltage was set to 1.0 V, and the charge termination voltage was set to 3.0 V. Further, while repeating the charge and discharge, the battery discharge capacity (mAh) at the 1st, 2nd, 3rd, and 10th times was observed.

[0286] The 3rd discharge capacity DC3 (mAh / g) was defined as the initial capacity. The greater the initial capacity, the greater the charge and discharge capacity of the lithium ion secondary battery, and this was evaluated as being preferable. Further, the capacity retention rate (%) was calculated from the 10th discharge capacity DC10 (mAh / g) and the 3rd discharge capacity DC3 (mAh / g) by the following equation. 10 The greater the capacity retention rate, the more excellent the cycle characteristics of the lithium ion secondary battery.

[0287] Capacity retention rate (%) = (DC 10 / DC3) x 100.

[0288] (energy density)

[0289] Using the discharge capacity of the active material and the average discharge voltage at the 10th cycle, the amount of energy mWh (i.e., mAh x V) per 1 cm 2 of the electrode was calculated, and the amount of energy was divided by the weight per 1 cm 2 to calculate the energy density (mWh / mg) of the electrode.

[0290] (charge and discharge capacity index)

[0291] The 10th discharge capacity (DC 10 ) (mAh / g) in each of the examples and comparative examples was expressed as an index using the following equation. The greater the index, the greater the discharge capacity, and this was more preferable. The measurement was performed using a battery performance evaluation device (BLS system manufactured by Soken Kagaku Keiki K.K.).

[0292] Charge and discharge capacity index = 10th discharge capacity in each of the examples and comparative examples / discharge capacity in Comparative Example 1 x 100.

[0293] (capacity retention rate index)

[0294] The capacity retention rate (DC 10 / DC3) (%) in each of the examples and comparative examples was expressed as an index using the following equation. The greater the index, the greater the capacity retention rate, and this was more preferable.

[0295] Capacity retention rate index = capacity retention rate of each example and comparative example / capacity retention rate of comparative example 1 x 100.

[0296] (Energy density index)

[0297] The energy density of each example and comparative example was expressed as an index using the following formula. The larger the index, the larger the energy density, and the more preferable.

[0298] Energy density index = energy density of each example and comparative example / energy density of comparative example 1 x 100.

[0299] (Comprehensive performance index)

[0300] The average value of the total values of the charge-discharge capacity index, the capacity retention rate index, and the energy density index was defined as the comprehensive performance index.

[0301]

[0302] According to Table 3, the examples exhibited an improvement in the comprehensive performance of the charge-discharge capacity, the capacity retention rate, and the energy density.

[0303] <Embodiment>

[0304] The following shows a preferred embodiment.

[0305] [1] An electrode for a lithium ion secondary battery,

[0306] The electrode has an active material layer containing a particulate active material,

[0307] The active material contains an organic sulfur compound and an iron compound,

[0308] wherein A S , A F and D satisfy the following inequality (1), and the right side of the following inequality (1) is preferably 7500,

[0309] (1) A S x A F x D > 7000,

[0310] In the formula, A S represents the content of sulfur element in the active material, in mass%, A F represents the content of iron element in the active material, in mass%, and D represents the coating density of the active material, in mg / cm 2 .

[0311] [2] The electrode according to the above [1], wherein the value on the right side of the inequality (1) is 8000, preferably 8500, more preferably 9000, further preferably 9100, further preferably 9200, further preferably 9400, further preferably 9500, further preferably 10000.

[0312] [3] The electrode according to the above [1] or [2], wherein the content of sulfur element A in the active material S is greater than 65.0 mass%, preferably greater than 66.0 mass%, more preferably greater than 70.0 mass%.

[0313] [4] The electrode according to any one of the above [1] to [3], wherein the content of iron element A in the active material F is greater than 15.0 mass%, more preferably 15.4 mass% or more, further preferably 15.5 mass% or more, further preferably greater than 16.0 mass%, further preferably greater than 16.1 mass%, further preferably greater than 17.0 mass%, further preferably greater than 17.3 mass%.

[0314] [5] The electrode according to any one of the above [1] to [4], wherein the coating density D of the active material is greater than 2.5 mg / cm 2 , preferably greater than 6.2 mg / cm 2 , more preferably greater than 6.5 mg / cm 2 , further preferably greater than 6.6 mg / cm 2 , further preferably greater than 7.0 mg / cm 2 , further preferably greater than 8.0 mg / cm 2 , further preferably greater than 8.5 mg / cm 2 , further preferably 8.6 mg / cm 2 or more, further preferably 9.0 mg / cm 2 or more, further preferably 9.2 mg / cm 2 or more, further preferably greater than 9.5 mg / cm 2 .

[0315] [6] The electrode according to any one of the above [1] to [5], wherein the initial discharge capacity DC3 when the electrode is used as a positive electrode is greater than 400 mAh / g.

[0316] [7] The electrode according to the above [6], wherein the initial discharge capacity DC3 is greater than 600 mAh / g, more preferably 634 mAh / g or more, further preferably 681 mAh / g or more, further preferably 690 mAh / g or more, further preferably greater than 700 mAh / g, further preferably greater than 730 mAh / g, further preferably greater than 745 mAh / g.

[0317] [8] The electrode according to any one of the above [1] to [7],

[0318] wherein the electrode has a current collector,

[0319] the current collector has a metal foil,

[0320] A S D and T satisfy the following inequality (2), and the right side of inequality (2) is preferably 25.0, more preferably 26.0, further preferably 27.0, further preferably 28.0, further preferably 28.5, further preferably 29.0, further preferably 29.4, further preferably 30.0, further preferably 30.8, further preferably 35.0, further preferably 36.0,

[0321] (2) A S x D / T > 24.0,

[0322] In the formula, T represents the thickness of the metal foil in μm.

[0323] [9] The electrode according to any one of the above [1] to [8], wherein DC10 is greater than 350 mAh / g, preferably greater than 400 mAh / g, more preferably greater than 500 mAh / g, further preferably greater than 600 mAh / g, further preferably 634 mAh / g or more, further preferably greater than 650 mAh / g, further preferably 671 mAh / g or more, further preferably 681 mAh / g or more, further preferably greater than 690 mAh / g, further preferably 723 mAh / g or more, further preferably 743 mAh / g or more, wherein DC 10 represents the 10th discharge capacity (mAh / g) in the case where the electrode is used as a positive electrode.

[0324]

[10] A lithium ion secondary battery having the electrode according to any one of the above [1] to [9].

[0325]

[11] The lithium ion secondary battery according to the above

[10] , wherein

[0326] the lithium ion secondary battery further has an electrolyte,

[0327] A S, D and V satisfy the following inequality (3), and the right side of inequality (3) is preferably 250, more preferably 260, further preferably 270, further preferably 280, further preferably 285, further preferably 290, further preferably 294, further preferably 300, further preferably 310, further preferably 350, further preferably 360,

[0328] (3) A S × D / V > 240,

[0329] wherein V represents the volume of the electrolyte, in mL.

[0330] List of Reference Symbols

[0331] 1. Muffle furnace

[0332] 2. Heater

[0333] 3. Lid

[0334] 4. Inert gas

[0335] 5. Tray (upper layer)

[0336] 6. Tray (lower layer)

[0337] 7. Gas introduction pipe

[0338] 8. Gas discharge pipe

[0339] 9. Sodium hydroxide aqueous solution

[0340] 10. Trapping tank

Claims

1. An electrode for a lithium-ion secondary battery, the electrode having an active material layer containing a particulate active material, the active material containing an organic sulfur compound and an iron compound, The iron element content A in the active material F more than 10.0 mass% and 25.0 mass% or less, wherein A S , A F and D satisfy the following inequality (1), (1) A S x A F x D > 7000, wherein A S represents the content of sulfur element in the active material, unit: mass%, A F represents the content of iron element in the active material, unit: mass%, D represents the coating density of the active material, unit: mg / cm 2 .

2. The electrode of claim 1, wherein, the value on the right side of the inequality (1) is 8000.

3. The electrode of claim 1, wherein, The sulfur element content A in the active material S greater than 65.0 mass %.

4. The electrode according to claim 1 or 3, wherein The iron element content A in the active material F greater than 15.0 mass %.

5. The electrode according to claim 1 or 3, wherein The active substance has a coating density D of more than 2.5 mg / cm2 2 .

6. The electrode according to claim 1 or 3, wherein the initial discharge capacity DC3 in the case where the electrode is used as a positive electrode is greater than 400 mAh / g.

7. The electrode of claim 6, wherein, the initial discharge capacity DC3 is greater than 600 mAh / g.

8. The electrode according to claim 1 or 3, wherein, the electrode has a current collector, the current collector has a metal foil, A S D and T satisfy the following inequality (2), (2) A S x D / T > 24.0, in the formula, T represents the thickness of the metal foil, in μm.

9. The electrode according to claim 1 or 3, wherein, 10th discharge capacity DC in the case where the electrode is used as a positive electrode 10 greater than 350 mAh / g.

10. A lithium-ion secondary battery having the electrode according to claim 1 or 3.

11. The lithium-ion secondary battery according to claim 10, wherein, the lithium-ion secondary battery further has an electrolyte, A S D and V satisfy the following inequality (3), (3) A S x D / V > 240, in the formula, V represents the volume of the electrolyte, in mL.

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