Electrode and lithium ion secondary battery

Abstract

The present invention provides an electrode for a lithium ion secondary battery, the electrode having an active material layer containing a particulate active material containing an organic sulfur compound and an iron compound, in which AS, AF, and D satisfy the following inequality (1): AS * AF * D > 7000, where As represents the content of elemental sulfur in the active material, in mass%, A represents the content of elemental sulfur in the active material, and D represents the content of elemental sulfur in the active material, in mass%, and D represents the content of elemental sulfur in the active material. AF represents the iron element content in the active material in mass%, and D represents the coating density of the active material in mg / cm < 2 >. The purpose of the present invention is to improve the overall performance of a lithium ion secondary battery, such as charge / discharge capacity, capacity retention rate, and energy density.

Description

Technical Field

[0001] The present invention relates to a novel electrode and a lithium-ion secondary battery including the electrode. Background Art

[0002] Lithium-ion secondary batteries are mainly used as batteries for portable electronic devices due to their large charge-discharge capacity. In addition, lithium-ion secondary batteries are increasingly being used as batteries for electric vehicles and are expected to improve their performance.

[0003] Patent Document 1 describes an active material for an electrode 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, materials that can absorb and release more lithium ions, such as silicon (Si), tin (Sn), etc., have been proposed to increase the battery capacity of lithium-ion secondary batteries.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: JP2020-167144A. Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, there is still room for further improvement in an electrode using an active material such as that in Patent Document 1.

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

[0011] Means for Solving the Problems

[0012] That is, the present invention relates to the following electrode.

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

[0014] The electrode has an active material layer, and the active material layer contains particulate active material,

[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 ×A FA×D > 7000,

[0018] In the formula, A S represents the sulfur element content in the active material, in mass %, and A F represents the iron element content in the active material, in mass %, and D represents the coating density of the active material, in mg / cm 2 .

[0019] Effects of the Invention

[0020] According to the present invention, an electrode (i.e., a positive electrode or a negative electrode) of a lithium-ion battery capable of achieving high comprehensive performance of charge-discharge capacity, capacity retention rate, and energy density, and a lithium-ion secondary battery including the electrode can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a cross-sectional view schematically showing a reaction apparatus for manufacturing an active material in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in detail below. In addition, for the description of a numerical range, the upper and lower limit values involving "above" and "below" can be arbitrarily combined values, and the numerical values in the embodiments can also be these upper and lower limits. In addition, unless contrary to the purpose of the present invention, a numerical range shown as including its two end values should be interpreted as also disclosing a numerical range that does not include one of the two end values, and a numerical range that does not include its two end values.

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

[0024] An electrode for a lithium-ion secondary battery,

[0025] wherein the electrode has an active material layer, and the active material layer contains particulate active material,

[0026] the active material contains an organic sulfur compound and an iron compound,

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

[0028] (1) A S × A F × D > 7000,

[0029] In the formula, A S represents the sulfur element content in the active material, in mass %, and A F represents the iron element content in the active material, in mass %, and D represents the coating density of the active material, in mg / cm 2 .

[0030] Although not bound by theory, the reasons why the electrode of the present invention is considered to be able to improve the comprehensive performance of charge-discharge capacity, capacity retention rate, and energy density are as follows.

[0031] Sulfur and lithium are likely to form soluble compounds during the charge-discharge process, so there is a drawback that the charge-discharge capacity gradually decreases due to repeated charge-discharge. In contrast, the present invention 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 maintained at a value equal to or greater than a certain value. Under such conditions, the sulfur and iron retained on the electrode interact with each other under given conditions, and thus it is considered 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 the inequality (1) is 8000.

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

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

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

[0036] When the above electrode is used as the positive electrode, when the initial discharge capacity is referred to as DC 3 (mAh / g), DC 3 is preferably greater than 400 mAh / g, and more preferably greater than 600 mAh / g.

[0037] The above electrode has a current collector, and the current collector has a metal foil. 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 ×D / T > 24.0.

[0039] By making the quotient obtained by dividing the product value of the amount of sulfur and the coating density by the thickness value of the metal foil current collector equal to or greater than a certain value, each value restricts each other, and thus it is considered that the performance of the electrode and / or the battery is improved.

[0040] When the above electrode is used as the 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 invention is a lithium-ion secondary battery having the above electrodes.

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

[0043] (3) A S × D / V > 240.

[0044] By making the quotient obtained by dividing the product value of the amount of sulfur and the coating density by the volume value of the electrolyte equal to or greater than a certain value, each value restricts each other, and thus it is considered that the performance of the electrode and / or the battery is improved.

[0045] <Definition>

[0046] The term "granular" means that the active material is made fine enough to be suitable for mixing with another material for the purpose of the present invention. For the particles constituting the active material, there is no particular limitation on their size as long as the size enables proper mixing.

[0047] "Active material" refers to a material that plays a role in the redox reaction for energy conversion in a lithium-ion secondary battery.

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

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

[0050] Unless otherwise specified, in this specification, the "initial discharge capacity" refers to the third discharge capacity.

[0051] <Measurement method>

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

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

[0054] "Median particle size" is the volume-based cumulative 50% size (median particle size 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 the electrode for a lithium ion secondary battery of the present invention and the lithium ion secondary battery of the present invention.

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

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

[0058] (1) A S × A F × D > 7000,

[0059] wherein A S represents the sulfur element content in the active material, in mass %, A F represents the iron element content 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 related to the present invention contains particulate active material. The active material layer is composed of the following electrode material (i.e., positive electrode material or negative electrode material) containing particulate active material. Here, the phrase "the active material is particulate" means that the active material is made fine enough to be suitable for mixing with another material constituting the electrode for the purpose of the present invention, and as long as the active material is in this state, the meaning of this phrase is not particularly limited. For example, when the term "particulate" is represented by the median particle size, it can be in the range of 1 nm to 1000 μm.

[0062] The median particle size (median particle size 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 size 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 size 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 size can be measured by the method described in the following Examples section.

[0063] [Active material]

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

[0065] Organic sulfur compounds are compounds in which at least carbon atoms, hydrogen atoms, and sulfur atoms are bonded to each other. Since the active material is obtained through a step of firing a raw material containing a polymer (such as rubber, resin, etc.), an iron ion compound, and sulfur, it is difficult to analyze the detailed structure of the product obtained in this step, but it has been confirmed that carbon atoms, hydrogen atoms, and sulfur atoms are bonded to each other. In this case, it is speculated that the organic sulfur compound contains a carbon-sulfur structure, for example, a long-chain polymeric thiophenobenzene structure in which thiophene rings are condensed to form a chain, and structures similar thereto. In addition, depending on other raw materials used for firing or the gas atmosphere employed, other atoms (such as nitrogen atoms, etc.) can further bond to the organic sulfur compound.

[0066] An iron compound is a compound in which an iron atom is bonded to an atom other than an iron atom. Examples of atoms other than an iron atom include, for example, a sulfur atom. Examples of iron compounds include iron(II) sulfide (FeS), iron(III) sulfide (Fe 2 S 3 ), iron disulfide (FeS 2 ), etc. Among them, iron disulfide (FeS 2 ) is typical or preferred.

[0067] Therefore, in the present invention, "the particulate active material contains an organic sulfur compound" can be expressed as "the particulate active material contains at least carbon atoms and sulfur atoms", or "the particulate active material contains an organic sulfur compound and an iron compound" can be expressed as "the particulate active material contains at least carbon atoms, sulfur atoms, and iron atoms". In addition, when it contains carbon atoms, sulfur atoms, and iron atoms, the carbon element content, sulfur element content, and iron element content are measured by the methods described in the Examples 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 iron element content (mass %) in the active material is preferably greater than 10.0 mass %, more preferably greater than 11.0 mass %, further preferably greater than 12.0 mass %, further preferably greater than 13.0 mass %, further preferably greater than 13.5 mass %, further preferably greater than 14.0 mass %, further preferably greater than 14.5 mass %, further preferably 14.9 mass % or more, further preferably greater than 15.0 mass %, further 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 %. The upper limit of the iron element content is usually 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 greater than 2.5 mg / cm 2 , more preferably greater than 6.2 mg / cm 2 , further 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 . Its upper limit is not particularly limited, and the higher the upper limit, the more preferred. Therefore, although it is not very meaningful to mention the upper limit of the coating density, the upper limit can usually be assumed to be about 15.0 mg / cm 2 , only as a reference value.

[0074] (Carbon element content)

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

[0076] (Hydrogen element content)

[0077] Since the hydrogen atoms in the polymer react with sulfur by firing to form hydrogen sulfide and the hydrogen sulfide is released outside the system, the hydrogen element content in the active material (mass %) is relatively small. The hydrogen element content in the active material is preferably 1.6 mass % or less. This 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 (mass %) of the hydrogen element content 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 size)

[0079] The active material is pulverized to obtain a specified particle size and is preferably particles having a size suitable for manufacturing an electrode. From the perspective of improving the performance of the electrode and / or the 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 size (median particle size d 50 ). The median particle size 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 size 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 size can be measured by the method described in the Examples section below.

[0080] [Inequality (1)]

[0081] For the electrode of the present invention, as described in the above Inequality (1), the sulfur element content A S (mass %) and the iron element content A F (mass %) in the active material and the coating density D (mg / cm 2 ) of the active material have a product 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. There is no particular limitation on the upper limit of the left side value of Inequality (1), and the higher the upper limit, the more preferable. Therefore, although it is not very meaningful to mention the upper limit of the left side value of Inequality (1), it can generally be assumed to be about 20000, about 15000, or about 12000 as a reference value only.

[0082] [Inequality (2)]

[0083] For the electrode of the present invention, as described in the above inequality (2), the content A of sulfur element in the active material S (mass %) and the coating density D (mg / cm 2 ) of the active material, the quotient obtained by dividing the product of them 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, further preferably 36.0. There is no particular limitation on the upper limit of the left side value of inequality (2), and the higher the upper limit, the more preferable. Therefore, although it is not very meaningful to mention the upper limit of the left side value of inequality (2), generally, the upper limit can be assumed to be about 100, about 80 or about 60, only as reference values.

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

[0085] [Charge and discharge capacity]

[0086] The electrode of the present invention exhibits excellent charge and discharge capacity. In addition, in the following description, unless otherwise specified, the initial discharge capacity refers to the third discharge capacity (DC 3 ). Here, the third discharge capacity is the discharge capacity when charging and discharging three times after manufacturing the electrode and the battery (the third discharge is defined in the following cycle: the first discharge, the first charge, the second discharge, the second charge, the third discharge, the third charge), where the discharge cut-off voltage is 1.0 V and the charge cut-off voltage is 3.0 V. In the case of discharge, when discharging at a constant current (the current value corresponding to 1 g of the positive electrode active material is 50 mA), the voltage of 3.0 V finally drops to 1.0 V. Measure the total time (h) spent during the voltage drop from 3.0 V to 1.0 V, multiply the measured total time by the applied current (mA) to obtain the capacity (mAh), and then divide the capacity by the weight of the active material to obtain the specific capacity (mAh / g). On the other hand, in the case of charging, charge at a constant current, whereby the voltage rises instead, and when the voltage finally reaches 3.0 V, the charging terminates. This also applies to the 10th discharge capacity described below.

[0087] (Initial discharge capacity (DC 3 ))

[0088] When the electrode of the present invention is used as the positive electrode, the initial discharge capacity (DC 3 )(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 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. There is no particular limitation on the upper limit of the initial discharge capacity, and the higher the upper limit, the more preferable. Therefore, although it is not very meaningful to mention the upper limit of the initial discharge capacity, the upper limit can generally be assumed to be, for example, about 1000 mAh / g as a reference value only.

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

[0090] When the electrode of the present invention is used as the positive electrode, the discharge capacity during 10 charge-discharge cycles, that is, the 10th discharge capacity (DC 10 )(in 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 more, further preferably greater than 650 mAh / g, further preferably 671 mAh / g or more, further preferably 681 mAh / g or more, further preferably 690 mAh / g or more, further preferably 723 mAh / g or more, further preferably 743 mAh / g or more. There is no particular limitation on the upper limit of the discharge capacity, and the higher the upper limit, the more preferable. Therefore, although it is not very meaningful to mention the upper limit of the discharge capacity, the upper limit can generally be assumed to be, for example, a value approximately equal to the initial discharge capacity or about 900 mAh / g as a reference value only.

[0091] In addition, when measuring the 3rd discharge capacity and the 10th discharge capacity of the electrode of the present invention used as the positive electrode, a negative electrode and an electrolyte that can be used persistently (such that lithium is not immediately depleted) within the scope of common technical knowledge are used. The electrode can fully exhibit the performance related to the discharge capacity of the positive electrode, and the 3rd discharge capacity and the 10th discharge capacity are determined by the structure of the positive electrode. For example, regarding the negative electrode, it is sufficient to use a negative electrode in which the lithium content (in molar amount) is greater than one percent (preferably one-tenth, more preferably one-half) of the amount of sulfur (in molar amount) 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 × 4 cm × coating density), and the mixture layer also contains other components besides sulfur, so the amount of sulfur (in molar amount) is necessarily less than 0.004491 (≒ 0.144 / 32.065) (this value is equal to or less than 71.5%). On the other hand, the weight of the negative electrode is 534 mg (4 cm × 5 cm × 0.5 mm × specific gravity of lithium), and the amount of lithium (in molar amount) is 0.076934 (≒ 0.534 / 6.941), so the amount of lithium (in molar amount) in the negative electrode is large enough. In addition, for example, regarding the electrolyte, it is sufficient to make the amount of lithium (in molar amount) greater than one percent (preferably one-tenth, more preferably one-half) of the amount of sulfur (in molar amount) in the positive electrode. In the following examples, the amount of lithium (in molar amount) in the electrolyte is 0.002 = volume V of the electrolyte (= 2.0 mL) × concentration (= 1.0 mol / L), so the amount of lithium (in molar amount) in the electrolyte is large enough. When using a negative electrode and an electrolyte containing a large enough amount of lithium (in molar amount) as described above, the discharge capacity of the positive electrode can be fully exhibited. Here, the volume V (mL) of the electrolyte refers to the total volume of the electrolyte solution or solid electrolyte containing the solute.

[0092] [Use]

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

[0094] The electrode for a lithium ion secondary battery can be manufactured in the same manner as described in the following manufacturing method section by using the materials described in the manufacturing method section. That is, when the above electrode for a lithium ion secondary battery is used as the positive electrode, conductive aids, binders, current collectors, etc. described in the following manufacturing method section are used in the same manner as described in the manufacturing method section, so as to manufacture the above electrode for a lithium ion secondary battery into a positive electrode. And when the above electrode for a lithium ion secondary battery is used as the negative electrode, conductive aids, binders, current collectors, etc. described in the following manufacturing method section are used in the same manner as described in the manufacturing method section, so as to manufacture the above electrode for a lithium ion secondary battery into a negative electrode. As described above, these descriptions in the following manufacturing method section 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 invention is a lithium ion secondary battery including the above electrode for a lithium ion secondary battery.

[0097] A lithium ion secondary battery can be manufactured in the same manner as described in the following manufacturing method section by using the materials described in the following manufacturing method section. That is, when the above electrode for a lithium ion secondary battery is used as the positive electrode, a negative electrode, an electrolyte, a separator, etc. described in the following manufacturing method section are used in the same manner as described in the manufacturing method section, so as to manufacture a lithium ion secondary battery. On the other hand, when the above electrode for a lithium ion secondary battery is used as the negative electrode, a positive electrode, an electrolyte, a separator, etc. described in the following manufacturing method section are used in the same manner as described in the manufacturing method section, so as to manufacture a lithium ion secondary battery. As described above, these descriptions in the following manufacturing method section 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 invention, as described in the above inequality (3), the sulfur element content A S (mass %) and the coating density D (mg / cm 2The quotient obtained by dividing the product of ()) 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. There is no particular limitation on the upper limit of the value on the left side of inequality (3), and the higher the upper limit, the more preferred. Therefore, although it doesn't make much sense to mention the upper limit of the value on the left side of inequality (3), generally, the upper limit can be assumed to be about 1000, about 800, or about 600 as reference values only.

[0100] Since the range of the volume V (mL) of the electrolyte varies depending on the size of the battery, there is no clear regulation for this range. Just use the minimum amount that can exhibit the performance of the active material and enable the battery to operate fully. As a reference value only, 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 invention can be used as a lithium ion secondary battery having comprehensive performance of improved charge-discharge capacity, capacity retention rate, and energy density.

[0103] [Preparation Method]

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

[0105] [Preparation of Active Material]

[0106] The active material related to the present invention can be prepared by a preparation method including: (1) mixing raw materials containing a polymer, an iron ion compound, and sulfur to obtain a fired raw material; (2) firing the fired raw material in a non-oxidizing atmosphere.

[0107] (Polymer)

[0108] The polymer is not particularly limited as long as it is a compound containing at least carbon atoms and hydrogen atoms and absorbs sulfur to form an organic sulfur compound when fired with an iron ion compound and sulfur in a non-oxidizing atmosphere. In addition, the polymer may be a polymer containing heteroatoms such as nitrogen atoms and sulfur atoms. Specific examples of the polymer include, for example, polymers of unsaturated hydrocarbon group monomers, condensates of substituted aromatic hydrocarbons and sulfur chloride, etc. The polymer may be used alone, or two or more of them may be used in combination.

[0109] <<Polymer of unsaturated hydrocarbon group monomer>>

[0110] Examples of the polymer of unsaturated hydrocarbon group monomers include, for example, resins such as acrylic resins. In addition, examples of the polymer of unsaturated hydrocarbon group monomers include diene rubbers and the like. One or more polymers of unsaturated hydrocarbon group monomers can be used.

[0111] Examples of the acrylic resin include, for example, polymers obtained by polymerizing at least one monomer selected from the group consisting of acrylate compounds represented by the following chemical formula (1); or polymers obtained by polymerizing at least one monomer selected from acrylate compounds represented by the following formula (1) and at least one monomer selected from diacrylate compounds represented by the following chemical formula (2). One or more acrylic resins can be used, and one or more acrylate compounds can also be used.

[0112] CH 2 =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] CH 2 =C(R 21 )COO-Y-OCO(R 22 )C=CH 2 (2)

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

[0116] In chemical formula (1), R 11 is preferably a methyl group, R12 Preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and among them, more preferably methyl, n-butyl, isobutyl, tert-butyl. Examples of the compound represented by Chemical Formula (1) include, for example, methyl (meth)acrylate, butyl (meth)acrylate, etc., and more preferably methyl methacrylate, butyl methacrylate. Here, the “(meth)acrylate” in methyl (meth)acrylate and butyl (meth)acrylate means “acrylate” or “methacrylate” (the same hereinafter). A further preferred example of the compound represented by Chemical Formula (1) is butyl methacrylate.

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

[0118] -(CH 2 )l-(CH 2 CH 2 O) m -(CH 2 CH 2 CH 2 O) n -(3)

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

[0120] In Chemical Formula (3), preferably, l is 1, 2, 3, 4, 5, or 6, and m and n are 0; m is 1, 2, or 3, and l and n are 0; or n is 1 or 2, and l 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, etc. Among them, ethylene glycol dimethacrylate is preferred.

[0122] Preferred examples of the acrylic resin include homopolymers of (meth)acrylic acid methyl ester, homopolymers of (meth)acrylic acid butyl ester, copolymers of (meth)acrylic acid methyl ester and ethylene glycol di(meth)acrylate, copolymers of (meth)acrylic acid butyl ester and ethylene glycol di(meth)acrylate, etc. Among them, as the acrylic resin, a methacrylate-type acrylic resin is preferred. More preferred examples of the acrylic resin include copolymers of methyl methacrylate and ethylene glycol dimethacrylate.

[0123] In the present invention, the acrylic resin preferably has a fine particle form. Here, the fine particle means a particle having a particle size of 300.0 μm or less. The particle size 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 size is not particularly limited, and is usually, for example, 0.1 μm or more, preferably 1.0 μm or more. This particle size is a value (median particle size) measured by a particle size distribution measuring device (PSA1090L manufactured by Anton Paar GmbH).

[0124] The acrylic resin may be spherical fine particles or porous fine particles. When the acrylic resin is porous, its oil absorption amount 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 JP2017-88501A.

[0125] The acrylic resin only needs to have the above structure, and its Mw is not particularly limited. However, the Mw of the acrylic resin is usually in the range of 2000 to 1500000. Mw is a value measured by gel permeation chromatography (GPC) (calibrated with polystyrene).

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

[0127] Examples of diene rubbers include, for example, natural rubber, isoprene rubber, butadiene rubber (such as high cis - polybutadiene rubber, etc.). Diene rubbers are commercially available or can be manufactured by conventional methods within the knowledge of those skilled in the art.

[0128] [[Condensates of substituted aromatic hydrocarbons and sulfur monochloride]]

[0129] Examples of condensates of substituted aromatic hydrocarbons and sulfur monochloride include, for example, condensates of alkylphenols and sulfur monochloride. Specific examples of condensates of alkylphenols and sulfur monochloride include, for example, TACKIROLV200, TS3108, TS3109 manufactured by Tago Chemical Co., Ltd., Vultac 3 manufactured by Arkema Co., Ltd., etc. One or more condensates of substituted aromatic hydrocarbons and sulfur monochloride can be used.

[0130] (sulfur)

[0131] As 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 types of sulfur can be used.

[0132] Based on 100 parts by mass of the polymer, the content of sulfur is preferably greater than 50 parts by mass, more preferably greater than 100 parts by mass, further preferably greater than 300 parts by mass, further preferably greater than 400 parts by mass, and further preferably 500 parts by mass or more. When the content is greater than 50 parts by mass, there is a tendency to improve the charge - discharge capacity and cycle characteristics. On the other hand, there is no upper limit to the content of sulfur, but it 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, and further preferably less than 700 parts by mass. When the content is less than 1000 parts by mass, there is a tendency to have an advantage in terms of cost. In addition, in this specification, the term "cycle characteristics" refers to the characteristics in which the charge - discharge capacity of the secondary battery remains despite repeated charging / discharging. Therefore, a secondary battery with a high degree of decline in charge - discharge capacity and a low capacity retention rate during repeated charging and discharging has poor cycle characteristics, while conversely, a secondary battery with a low degree of decline in charge - discharge capacity and a high capacity retention rate has excellent cycle characteristics.

[0133] As sulfur, any of various allotropes can be used, but preferably sulfur contains S that is solid at normal temperature and pressure 8 sulfur, S 8 The monomer of sulfur is more preferred.

[0134] (iron - containing ionic compound)

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

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

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

[0138] Examples of iron complexes include, for example, complexes of divalent iron (Fe 2+ ), complexes of trivalent iron (Fe 3+ ), 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, halogen atoms (such as chlorine atoms, bromine atoms, etc.), cyano groups, dicyclopentadienyl, N,N'-bis(salicylidene)ethylenediamine, etc. Examples of iron complexes include: potassium hexacyanoferrate(II) ([Fe(CN) 6 K 4 ), potassium hexacyanoferrate(III) ([Fe(CN) 6 K 3 ), sodium iron(III) chloride ([FeCl4 Na), ferrocene (dicyclopentadienyliron(II)), iron(III) chloride N,N'-bis(salicylidene)ethylenediamine, etc. One or more iron complexes can be used.

[0139] As the iron ion-containing compound, at least one selected from the above-mentioned organic acid salts of iron, inorganic acid salts of iron, neutral iron complexes, and iron complex salts can be used. Among them, organic acid salts of iron, inorganic acid salts of iron, or neutral iron complexes are preferred.

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

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

[0142] (Polymer in which iron ion-containing compound is dispersed)

[0143] In the present invention, the polymer and the iron ion-containing compound can be used as a polymer in which the iron ion-containing compound is dispersed, and the polymer in which the iron ion-containing compound is dispersed is obtained by previously dispersing the iron ion-containing compound in the polymer. Such a polymer in which the iron ion-containing compound is dispersed can be prepared by polymerizing the polymer in a state where the iron ion-containing compound is previously dispersed in the monomers constituting the polymer. The polymerization reaction can be carried out by a conventional method.

[0144] As the polymer in which the iron ion-containing compound is dispersed, for example, a polymer in which the iron ion-containing compound is dispersed in an acrylic resin can be appropriately used. Preferred examples of the acrylic resin for this purpose include: homopolymers of (meth)acrylic acid methyl ester, copolymers of (meth)acrylic acid methyl ester and ethylene glycol dimethacrylate, etc. In addition, preferred examples of the iron ion-containing compound for this purpose include iron(II) oxalate, etc.

[0145] (Other materials)

[0146] The raw materials may appropriately contain other materials commonly used in the art as needed. Examples of such materials include, for example, conductive carbon materials and the like.

[0147] <<Conductive carbon material>>

[0148] The raw materials may contain a conductive carbon material. This is because it can improve the conductivity of the active material. As such a conductive carbon material, a carbon material having a graphite structure is preferred. As the carbon material, for example, porous carbon materials (such as activated carbon, etc.), graphite, carbon black, acetylene black, Ketjen black, carbon fiber (CF), and nanocarbon materials (such as carbon nanotubes (CNT), carbon nanofibers, graphene, fullerenes, etc.) can be used. One or more conductive carbon materials can be used.

[0149] Among them, acetylene black, carbon black, and Ketjen black are preferred because of their low price and excellent dispersibility. In addition, a small amount of CNT, graphene, etc. 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. In addition, the total combined amount of CNT or graphene is preferably 8% by mass or more and 12% by mass or less of the total amount of the conductive carbon material.

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

[0151] (Mixing step (1))

[0152] The mixing step is a step of preparing the firing raw materials.

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

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

[0155] <<WET method>>

[0156] In the present invention, the WET method includes the following steps for preparing the raw materials:

[0157] (a-1) Adding a polymer and an iron ion compound to a solvent (such as an organic solvent, etc.) to obtain a mixture, or adding monomers capable of forming a polymer and an iron ion compound and carrying out a polymerization reaction to obtain a mixture containing a polymer, in which the iron ion 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 sub-step (a-1), the method of adding the polymer or monomer, iron ion 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 monomer) and the iron ion compound can be added to the organic solvent simultaneously and mixed, (2) the polymer (or monomer) can be added to the organic solvent and mixed, and then the iron ion compound can be added and mixed, or (3) the iron ion compound can be added to the organic solvent and mixed, and then the polymer (or monomer) can be added and mixed.

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

[0162] Sub-step (a-1) can be carried out 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 a drying method (such as heat drying, reduced pressure drying, reduced pressure heat drying, etc.) on the mixture in sub-step (a-1).

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

[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, the method of mixing them using a blender, etc.

[0166] <<DRY method>>

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

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

[0169] Here, the powder means a state in which each of the solid raw materials has been made fine enough to be suitable for mixing for the purposes of the present invention. The size of each particle constituting the powder is not particularly limited as long as the mixing can be carried out appropriately, but is usually in the range of, for example, 1 μm or more to 40 μm or less. From the perspective of improving the performance of the electrode and / or the battery, the size of the particles 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 size. The median particle size can be measured by the method described in the following Examples section.

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

[0171] In the WET method and the DRY method, it is preferably to mix the raw materials sufficiently in advance for firing. In addition, when adding a conductive carbon material or the like to the raw materials, these additives can also be mixed in advance for firing so that they are contained in the raw materials in advance.

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

[0173] (Firing step (2))

[0174] The firing step is a step of firing the raw materials obtained above. The firing of the raw materials can be carried out by a conventional method, for example, by heating the raw materials at a predetermined heating 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 carried out in a non-oxidizing atmosphere. A non-oxidizing atmosphere refers to an atmosphere substantially free of oxygen, which is used to inhibit the oxidative degradation and excessive pyrolysis of the constituent components. Specifically, it refers to an inert gas atmosphere such as nitrogen, argon, a sulfur gas atmosphere, an ammonia gas atmosphere, etc. Therefore, the firing can be appropriately carried out in a quartz tube under an inert gas atmosphere, for example.

[0177] <<Heating rate>>

[0178] The heating rate is preferably in the range of, for example, 50 °C / h or more and 500 °C / h or less. The heating 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 heating 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 heating rate is within such a range, there is a tendency to easily achieve the purpose of improving the charge-discharge capacity and cycle characteristics.

[0179] <<Firing temperature / time>>

[0180] The firing temperature refers to the temperature after the raw material has completed heating, and the raw material is held at this temperature for a certain period of time for firing. This 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 sulfidation reaction and prevent the charge-discharge capacity of the object from decreasing. On the other hand, when it is lower than 550 °C, there is a tendency to prevent the decomposition of the raw material, prevent the decrease in the yield and the charge-discharge capacity. 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, further preferably lower than 450 °C.

[0181] From the perspective of improving the performance of the electrode and / or battery, preferably, the firing temperature in the firing step is higher than the thermal decomposition temperature of the iron ion compound.

[0182] The holding time of the firing temperature only needs to be appropriately set according to the type of raw material, the firing temperature, etc., 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 to be able to carry out firing sufficiently, while when it is 6 hours or less, there is a tendency to prevent excessive pyrolysis of the constituent components.

[0183] <<Apparatus>>

[0184] The firing can be carried out by, for example, a muffle furnace ( Figure 1 ), or can be carried out using a continuous device (such as a twin-screw extruder, etc.). When using a continuous device, there is an advantage: a sulfur-based active material can be continuously manufactured through a series of operations, such as kneading, pulverizing, and mixing the raw material in the device while also carrying out firing, etc.

[0185] A muffle furnace ( Figure 1 ) is a furnace partitioned by a heating plate or the like, and in order to prevent contamination of the sample, the heat source (heater) is not exposed inside the furnace. Figure 1 In, the muffle furnace 1 has a heater 2 at the lower part of the furnace, and the heater is separated by a heating plate. A lid 3 is installed on the front surface (the left end side in the figure) of the furnace, and it has a structure that enables the furnace to be maintained in an atmosphere of an inert gas 4 inside the furnace. A thermocouple (not shown) is installed on the lid so that the temperature inside the furnace during firing can be measured. Two-layer stainless steel (SUS) rectangular trays 5 and 6 for firing raw materials are installed in the upper and lower layers inside the furnace.

[0186] The inside of the furnace is configured so that a gas (for example, 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 containing an aqueous sodium hydroxide solution 9, and the exhaust gas discharged from the muffle furnace 1 to the outside through the gas discharge pipe 8 is discharged to the outside once it passes through the aqueous sodium hydroxide solution 9 in the trap tank 10. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the reaction, the hydrogen sulfide gas is neutralized by the aqueous sodium hydroxide solution and removed from the exhaust gas.

[0187] (Step of removing residues)

[0188] In the processed product obtained after firing, unreacted sulfur precipitated from sulfur that sublimated and then cooled during the firing process remains. In the presence of these residues, it is preferable to remove as many of these residues as possible because they may cause deterioration of the cycle characteristics. Removal of the residues can be carried out according to a conventional method (for example, by drying under reduced pressure heating, drying with hot air, cleaning with a solvent, etc.).

[0189] (Crushing / Classification)

[0190] In order to obtain particles having a size suitable for manufacturing an electrode, it is preferable to crush the obtained active material to have a specified particle size and classify it. The preferred size (particle size distribution) of the particulate active material is as described above.

[0191] The pulverization can be carried out by conventional methods. For example, it can be implemented by pulverizing the active substance under predetermined conditions using a pulverizer (such as a cutter mill, jet mill, etc.). The pulverization conditions vary depending on the mill used, etc. For example, in the case of using a cutter mill (such as the Free Speed Mill FS-20 manufactured by Labonect), it can be processed for 1 second or more and 30 seconds or less under the conditions of a rotational speed of 20,000 rpm or more and 30,000 rpm or less. In addition, in the case of using a dry jet mill (such as the Nano Jetmizer NJ-30 manufactured by Aishin Nano Technologies CO., LTD.), it can be processed at a processing 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] In addition, in the firing method using a twin-screw extruder as described above, the manufactured active substance can also be pulverized into particles by shearing during kneading while manufacturing the active substance.

[0193] [Manufacture of Lithium-Ion Secondary Battery Electrodes]

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

[0195] (In the case of using the granular active substance as the positive electrode active material)

[0196] Except for using the above granular active substance as the positive electrode active material, the positive electrode for a lithium-ion secondary battery can be manufactured in the same manner as the positive electrode for an ordinary lithium-ion secondary battery. For example, a positive electrode can be manufactured by mixing the granular active substance with a conductive additive, 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. In addition, as another method, for example, the granular active substance can also be kneaded with a conductive additive, a binder, and a small amount of solvent using a mortar, etc. to form a film, and then pressed onto a current collector using a press, etc. to manufacture the positive electrode. However, in this case, the active substance is coated so that the coating density D (mg / cm 2 ) satisfies the above inequality (1).

[0197] <<Conductive Additive>>

[0198] Examples of the conductive additive include, for example, vapor-grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), Ketjen black (KB), graphite, or fine metal powder that is stable at a positive electrode potential, such as aluminum, titanium, etc. In addition, as the conductive additive, the above-mentioned conductive carbon materials can also be used. One or more of these conductive additives can be used.

[0199] <<Binder>>

[0200] Examples of the binder include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (PAI), carboxymethyl cellulose (CMC), polyvinyl chloride (PVC), acrylic resin, polymethacrylic acid resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), etc. One or more of these binders can be used.

[0201] <<Solvent>>

[0202] Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformaldehyde, alcohols, hexane, water, etc. 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. However, preferably, based on 100 parts by mass of the active material, for example, 2 to 100 parts by mass of the conductive additive, 2 to 50 parts by mass of the binder, and an appropriate amount of solvent are mixed. However, in this case, for the sulfur element content A S (mass%) and iron element content A F (mass%) of the active material and the coating density D (mg / cm 2 ) of the active material, the relationship between them 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, any current collector commonly used for the positive electrode of a lithium-ion secondary battery can be used. For example, examples of the current collector include those composed of metal foils (such as aluminum foil, aluminum mesh, perforated aluminum sheet, expanded aluminum sheet, stainless steel foil, stainless steel mesh, perforated stainless steel sheet, expanded stainless steel sheet, nickel foam, nickel non-woven fabric, copper foil, copper mesh, perforated copper sheet, expanded copper sheet, titanium foil, titanium mesh, etc.), as well as carbon non-woven fabric, carbon woven fabric, etc. Among them, a current collector composed of a metal foil is preferred. 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 with a surface coated with carbon or the like include, for example, carbon-coated aluminum foil. In this case, the current collector includes a carbon-coated portion.

[0207] (In the case of using particulate active material as the negative electrode active material)

[0208] In addition to using the above particulate active material as the negative electrode active material, the negative electrode for a lithium-ion secondary battery can be manufactured in the same manner as a common negative electrode for a lithium-ion secondary battery. For example, a negative electrode can be manufactured by mixing particulate active material with a conductive additive, 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 particulate active material can also be kneaded with a conductive additive, a binder, and a small amount of solvent using a mortar or the like to form a film, and then pressed onto a current collector using a press or the like to manufacture the negative electrode. However, in this case, the coating of the active material is carried out such that the coating density D (in mg / cm 2 as the unit) satisfies the above inequality (1).

[0209] For the conductive additive, the binder, and the solvent, the same conductive additive, binder, and solvent as those used in the case of using particulate active material as the positive electrode active material can be used, and the same conductive additive, binder, and solvent can also be coated on the current collector.

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

[0211] In addition to using the electrodes for a lithium-ion secondary battery obtained above, the lithium-ion secondary battery of the present invention can be manufactured in the same manner as in the case of manufacturing a common lithium-ion secondary battery.

[0212] (In the case of using particulate active material as the positive electrode active material)

[0213] In addition to the positive electrode containing the above particulate active material (positive electrode active material), a negative electrode, an electrolyte, and further components such as a separator can be used as needed to manufacture the lithium-ion secondary battery of the present invention according to a conventional method.

[0214] <<Negative electrode>>

[0215] As the negative electrode material, well-known metallic lithium, carbon-based materials (such as graphite, etc.), silicon-based materials (such as silicon thin films, etc.), alloy-based materials (such as copper tin, cobalt tin, etc.) can be used. Among the above-mentioned negative electrode materials, when using lithium-free materials (such as carbon-based materials, silicon-based materials, alloy-based materials, etc.) as the negative electrode material, its advantage is that it is not easy to cause a short circuit between the positive electrode and the negative electrode due to the generation of dendrites. However, when these lithium-free negative electrode materials are used in combination with the positive electrode of the present invention, neither the positive electrode nor the negative electrode contains lithium. Therefore, a lithium pre-doping process for pre-doping lithium into either one or both of the negative electrode and the positive electrode is required. As the lithium pre-doping method, only known methods can be used. For example, examples of the lithium pre-doping method of doping lithium into the negative electrode include: the method of doping lithium by electrolytic doping (using metallic lithium as the counter electrode, assembling a half-cell and electrochemically doping lithium), and the method of doping lithium by attachment pre-doping (attaching a metallic lithium foil to the electrode, then placing it in the electrolyte, and using the diffusion of lithium into the electrode for doping). In addition, when pre-doping lithium into the positive electrode, the above electrolytic doping method can be used. As the lithium-free negative electrode material, a silicon-based material, which is particularly preferably a high-capacity negative electrode material, is more preferably thin-film silicon with a thin electrode thickness and an advantage in terms of the capacity per unit volume.

[0216] <<Electrolyte>>

[0217] The electrolyte compensates for the charge generated by the discharge of electrons to the external circuit through ion flow, and is accompanied by the oxidation / reduction of the active substances at the positive electrode / negative electrode. As the electrolyte for a lithium-ion secondary battery, an electrolyte obtained by dissolving an alkali metal salt as the electrolyte in an organic solvent can be used. As the organic solvent, at least one non-aqueous solvent selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl ether, γ-butyrolactone, acetonitrile, etc. is preferably used. As the electrolyte, LiPF 6 、LiBF 4 、LiAsF 6 、LiCF 3 SO 3 、LiI、LiClO 4 etc. 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 (for example, a polymer gel state).

[0218] <<Separator>>

[0219] In addition to the above-mentioned negative electrode, positive electrode, and electrolyte, a lithium-ion secondary battery may further include components such as a separator. The separator is interposed between the positive electrode and the negative electrode, allows ion migration between the positive electrode and the negative electrode, and prevents internal short circuits between the positive electrode and the negative electrode. If the lithium-ion secondary battery is a sealed type, the separator is required to have the function of retaining the electrolyte. As the separator, a thin and microporous or non-woven fabric film made of polyethylene, polypropylene, polyacrylonitrile, aromatic polyamide, polyimide, cellulose, glass, etc. is preferably used.

[0220] <<Shape>>

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

[0222] (In the case of using granular active material as the negative electrode active material)

[0223] In addition to the negative electrode containing the above-mentioned granular active material (negative electrode active material), a positive electrode and an electrolyte can also be used, and components such as a separator can be used as needed. The lithium-ion secondary battery of the present invention is manufactured according to a conventional method.

[0224] <<Positive Electrode>>

[0225] The positive electrode material is not particularly limited as long as it is a lithium-containing transition metal oxide or solid solution oxide, or a substance capable of electrochemically absorbing and releasing lithium ions. Examples of the lithium-containing transition metal oxide include, for example, Li-Co-based composite oxides (such as LiCoO 2 etc.), Li-Ni-Co-Mn-based composite oxides (such as LiNi x Co y Mn z O 2 etc.), Li-Ni-based composite oxides (such as LiNiO 2 etc.), Li-Mn-based composite oxides (such as LiMn 2 O 4 etc.). Examples of the solid solution oxide include, for example, Li a Mn x Co y Ni z O 2 (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 O 2(0.300 ≤ x ≤ 0.850, 0.100 ≤ y ≤ 0.300, 0.100 ≤ z ≤ 0.300), LiMn 1.5 Ni 0.5 O 4 etc. These compounds can be used alone or in combination of multiple kinds.

[0226] For the electrolyte, separator, and the shape of the lithium-ion secondary battery, the same electrolyte, separator, and the shape of the lithium-ion secondary battery as those in the case of using particulate active material as the positive electrode active material can be adopted.

[0227] Examples

[0228] Although the present invention is described based on examples, the present invention is not limited to the examples only.

[0229] Hereinafter, various chemicals used in the examples and comparative examples are shown in summary.

[0230] <Materials Used in the Tests>

[0231] Iron ion compound: Ferrous oxalate (II) dihydrate prepared in Synthesis Example 1

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

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

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

[0235] Synthesis Example 1 (Iron Ion Compound)

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

[0237] Synthesis Example 2 (Polymer in which Iron Ion Compound is Dispersed)

[0238] 80 parts by mass of methyl methacrylate (MMA) and 20 parts by mass of ethylene glycol dimethacrylate (EGDMA) were mixed to prepare a mixture, and 100 parts of an iron ion compound was further dispersed therein, and the mixture was subjected to a polymerization reaction to obtain an acrylic resin in which the iron ion 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 Granular Active Substance>

[0241] (Firing Raw Material)

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

[0243] (Reaction Apparatus for Firing)

[0244] A muffle furnace ( Figure 1 ) was used to fire the raw material. Figure 1 The muffle furnace in

[0245] (Firing Step)

[0246] First, the atmosphere in the muffle furnace was replaced with Ar gas three times using a vacuum pump, and the raw material for firing was accommodated in a tray (which is a SUS container). Then, while continuously supplying Ar gas at a flow rate of 100 mL / min from the gas inlet pipe, the muffle furnace was heated for 30 minutes after the start of the supply. The temperature was increased at a rate of 5 °C / h, and when the temperature of the raw material for firing reached the firing temperature described in Table 2, heat treatment was carried out for 2 hours while maintaining the firing temperature. Next, while adjusting the flow rate of the Ar gas, the temperature of the fired material was naturally cooled to 25 °C in an Ar gas atmosphere, and then the fired product was taken out of the muffle furnace.

[0247] (Crushing Step)

[0248] The fired product was crushed using a cutting machine, a dry jet mill, etc. The crushing steps for Manufacturing Examples 1-7 will be described below.

[0249] For Manufacturing Examples 1-6, as shown in Table 1, crushing was carried out by treating the fired product for a predetermined period of time at a predetermined rotational speed using a cutting machine (Free Speed Mill, FS-20, manufactured by Labonect).

[0250] Table 1

[0251]

[0252] On the other hand, for Manufacturing Example 7, the fired product was pulverized 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 fired product, the fired product was classified using a 32-μm stainless steel sieve to obtain the active material.

[0255] (Physical properties of the active substance)

[0256] (Elemental analysis)

[0257] Elemental analysis was performed on the active substances manufactured in the examples and comparative examples.

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

[0259] (Iron element content)

[0260] Thermogravimetric analysis was performed on the active substances manufactured in the examples and comparative examples, and based on the obtained measurement results, the amount (mass %) of each iron element was calculated.

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

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

[0263] In addition, it has been confirmed that the iron element in this example and the comparative example exists in the form of iron disulfide (FeS 2 ) Therefore, by the following calculation method, the ratio (mass %) of iron disulfide was calculated based on the ash content ratio (mass %) of each of this example and the comparative example. That is, from the weight reduction rate (100 mass %) of Manufacturing Example 8 in Table 2, it can be seen that after the polymer 1 (acrylic resin) was converted into a sulfide, the polymer 1 was completely decomposed. On the other hand, from the weight reduction rate (36 mass %) of Manufacturing Example 9, it can be seen that iron disulfide (FeS 2) decreased by 36 mass%. Therefore, by the following calculation method, the proportion (mass%) of iron disulfide (FeS 2 ) in each active material was calculated,

[0264] FeS 2 Proportion (mass%) = Ash content proportion × {100 / (100 - 36)}.

[0265] In addition, by the following calculation method, the iron element content (Fe proportion, mass%) was calculated from the proportion (mass%) of FeS 2 ,

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

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

[0268] (Median particle size)

[0269] Using a laser diffraction / scattering type particle size distribution analyzer (Particle Size Analyzer PSA1090L manufactured by Anton Paar GmbH), with water as the dispersion medium, the volume-based cumulative 50% size (median particle size d 50 ) was measured.

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

[0271] Table 2

[0272]

[0273] <Manufacture of positive electrode and lithium-ion secondary battery>

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

[0275] (Positive electrode)

[0276] Using the active material obtained above as the active material, acetylene black as the conductive additive, and acrylic resin as the binder. Weigh them so that the ratio of active material:conductive additive:binder is 90:5:5 (mass %), put them into a container, and stir and mix using a rotation-revolution mixer (ARE-250 manufactured by THINKY CORPORATION). Use milliQ water as the dispersant to produce a uniform slurry. Using a coater with a slit width of 200 - 300 μm, coat the produced slurry on a 20-μm carbon-coated aluminum foil, and press it using a roll press to obtain an electrode. Then, use a drying device to heat and dry the electrode at 120 °C for 3 hours. After drying, cut the electrode into the following shape: the part forming the mixed layer containing the active material has a width of 4 cm and a length of 3 cm, and the electrode also has an exposed part of the positive current collector as the positive electrode groove, thereby obtaining the electrode (positive electrode). Then, measure the mass of the electrode, and calculate the amount of the active material in the electrode from the above ratio. In addition, the "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, use a metallic lithium foil (manufactured by Honjo Metal Co., Ltd., with a thickness of 0.5 mm), and use a copper foil as the negative current collector. Cut the metallic lithium foil into a width of 5 mm and a length of 4 cm and attach it to the copper foil to obtain an electrode (negative electrode).

[0279] (Electrolyte)

[0280] As the electrolyte, use a non-aqueous electrolyte prepared by dissolving LiPF 6 in a mixed solvent of ethylene carbonate and diethyl carbonate. Ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1:1. The concentration of LiPF 6 in the electrolyte is 1.0 mol / L.

[0281] (Lithium ion secondary battery)

[0282] Use the above positive electrode and negative electrode to fabricate a laminated battery. Specifically, in a drying chamber, sandwich a separator (Celgard 2400 manufactured by Celgard LLC, a polypropylene microporous membrane with a thickness of 25 μm) and a glass non-woven fabric filter (with a thickness of 440 μm, GA100 manufactured by ADVANTEC) between the positive electrode and the negative electrode to form an electrode body battery. Place the electrode body battery in a laminate package formed by an aluminum laminate film (manufactured by MTI Corporation). Inject the above electrolyte (2.0 mL) into the laminate package. Seal the laminate package using 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] For each laminated lithium-ion secondary battery fabricated in the examples and comparative examples, charge and discharge were performed at a current value of 50 mA per 1 g of the positive electrode active material under the condition of a test temperature of 30°C. The discharge cut-off voltage was set to 1.0 V, and the charge cut-off voltage was set to 3.0 V. In addition, while repeating charge and discharge, the battery discharge capacities (mAh) at the 1st, 2nd, 3rd, and 10th times were observed.

[0286] Define the 3rd discharge capacity DC 3 (mAh / g) as the initial capacity. The larger the initial capacity, the larger the charge and discharge capacity of the lithium-ion secondary battery, and it can be evaluated as preferable. In addition, the capacity retention rate (%) is calculated from the 10th discharge capacity DC 10 (mAh / g) and the 3rd discharge capacity DC 3 (mAh / g) by the following formula. It can be said that the higher the capacity retention rate, the more excellent the cycle characteristics of the lithium-ion secondary battery.

[0287] Capacity retention rate (%) = (DC 10 / DC 3 ) × 100.

[0288] (Energy Density)

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

[0290] (Charge and Discharge Capacity Index)

[0291] Express the 10th discharge capacity (DC 10 )(mAh / g) in each of the examples and comparative examples as an index using the following formula. The larger this index, the larger the discharge capacity and the more preferable. Measurement was performed using a battery performance evaluation device (BLS system manufactured by Kikakkei Center Co., Ltd.).

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

[0293] (Capacity Retention Rate Index)

[0294] Express the capacity retention rate (DC10 / DC 3 )(%) is expressed as an exponent. The larger the exponent, the larger the capacity retention rate, and the more preferable it is.

[0295] Capacity retention rate index = Capacity retention rate of each example and comparative example / Capacity retention rate of Comparative Example 1 × 100.

[0296] (Energy density index)

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

[0298] Energy density index = Energy density of each example and comparative example / Energy density of Comparative Example 1 × 100.

[0299] (Comprehensive performance index)

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

[0301]

[0302] According to Table 3, the examples show an improvement in the comprehensive performance of charge-discharge capacity, capacity retention rate, and 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, and the active material layer contains 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 × A F × D > 7000,

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

[0311] [2] The electrode described in [1] above, wherein the value on the right side of 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 described in [1] or [2] above, wherein the sulfur element content A in the active material S is greater than 65.0% by mass, preferably greater than 66.0% by mass, more preferably greater than 70.0% by mass.

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

[0314] [5] The electrode according to any one of [1] to [4] above, 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 [1] to [5] above, wherein the initial discharge capacity DC when the electrode is used as a positive electrode 3 is greater than 400 mAh / g.

[0316] [7] The electrode according to [6] above, wherein the initial discharge capacity DC 3Greater 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 [1] to [7] above,

[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 × 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 [1] to [8] above, 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, where DC 10 represents the 10th discharge capacity (mAh / g) when the electrode is used as the positive electrode.

[0324]

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

[0325]

[11] The lithium-ion secondary battery according to

[10] above, 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 Signs

[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 inlet pipe

[0338] 8. Gas discharge pipe

[0339] 9. Aqueous sodium hydroxide solution

[0340] 10. Collection tank

Claims

1. An electrode for a lithium-ion secondary battery, The electrode has an active material layer, and the active material layer contains particulate active material, The active material contains an organic sulfur compound and an iron compound, Wherein, A S 、A F and D satisfy the following inequality (1), (1)A S ×A F ×D > 7000, Wherein, A S represents the sulfur element content in the active material, with the unit of mass%, and A F represents the iron element content in the active material, with the unit of mass%, and D represents the coating density of the active material, with the unit of mg / cm 2 .

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

3. The electrode according to claim 1, Wherein, The sulfur element content A in the active substance S is greater than 65.0% by mass.

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

5. The electrode according to claim 1 or 3, Wherein, The coating density D of the active substance is greater than 2.5 mg / cm 2 .

6. The electrode according to claim 1 or 3, Wherein, The initial discharge capacity DC when the electrode is used as the positive electrode 3 is greater than 400 mAh / g.

7. The electrode according to claim 6, Wherein, The initial discharge capacity DC 3 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 ×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, The 10th discharge capacity DC when the electrode is used as the positive electrode 10 is 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 9, Wherein, The lithium-ion secondary battery further has an electrolyte, A S , D, and V satisfy the following inequality (3), (3)A S ×D / V > 240, In the formula, V represents the volume of the electrolyte, in mL.

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