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, the active material containing an organic sulfur compound and an iron compound, AS, AF, and M satisfying the following inequality (1): AS * AF * Mgt; in the formula, AS represents the content (mass%) of elemental sulfur in the active material, AF represents the content (mass%) of elemental iron in the active material, and M represents the median diameter ([mu] m) of the active material. The purpose of the present invention is to improve the overall performance of the charge / discharge capacity and the capacity retention ratio of a lithium ion secondary battery.

Description

Technical Field

[0001] The present invention relates to a new 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 used as batteries for electric vehicles and are expected to have improved performance.

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

[0004] In addition, in order to increase the battery capacity of lithium-ion secondary batteries, materials that can absorb and release more lithium ions, such as silicon (Si), tin (Sn), etc., have been proposed as negative electrode active materials. Prior Art Documents Patent Document

[0005] Patent Document 1: JP 2020-167144 A Summary of the Invention Problems to be Solved by the Invention

[0006] However, there is still room for further improvement in electrodes using the active material of Patent Document 1.

[0007] An object of the present invention is to provide an electrode (i.e., a positive electrode or a negative electrode) of a lithium-ion battery that can achieve high comprehensive performance of charge-discharge capacity and capacity retention rate, and a lithium-ion secondary battery including the electrode. Means for Solving the Problems

[0008] That is, the present invention relates to the following electrode. An electrode for a lithium-ion secondary battery, the electrode having an active material layer containing particulate active material, the active material containing an organic sulfur compound and an iron compound, wherein, A S 、A F and M satisfy the following inequality (1), (1)A S ×A F ×M>1600, 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 M represents the median particle size of the active material, in μm. Effects of the present invention

[0009] According to the present invention, it is possible to provide an electrode (i.e., a positive electrode or a negative electrode) of a lithium-ion battery that can achieve high comprehensive performance of charge-discharge capacity and capacity retention rate, and a lithium-ion secondary battery including the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a cross-sectional view schematically showing a reaction apparatus for preparing an active material in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below. In addition, the upper and lower limit values related to "above" and "below" for describing a numerical range are values that can be arbitrarily combined, and the numerical values in the examples 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 its two end values and a numerical range that does not include its two end values.

[0012] One embodiment of the present invention is the following electrode. An electrode for a lithium-ion secondary battery, The electrode has an active material layer containing particulate active material, The active material contains an organic sulfur compound and an iron compound, wherein, A S 、A F and M satisfy the following inequality (1), (1)A S ×A F ×M>1600, In the formula, A S represents the sulfur element content (mass %) in the active material, A F represents the iron element content (mass %) in the active material, and M represents the median particle size (μm) of the active material.

[0013] Although not wishing to be bound by theory, the reasons for believing that the electrode of the present invention can improve the comprehensive performance of charge-discharge capacity and capacity retention rate are as follows.

[0014] During the charge and discharge process, sulfur and lithium are prone to form soluble compounds together. Therefore, there is a drawback that repeated charge and discharge leads to a gradual decrease in the charge and discharge capacity. In addition, as the active material expands or contracts during the charge and discharge process, the volume of the electrode mixture layer changes. As a result, cracks will appear in the mixture material, and the mixture material will peel off from the current collector, etc., thus reducing the capacity. In contrast, the feature of the present invention is that the active material contains iron, and the product of the sulfur content ratio in the active material, the iron content ratio in the active material, and the median particle size (μm) of the active material is maintained at a certain value or more. Under such conditions, sulfur and iron retained on the electrode interact with each other under given conditions, so it is considered that the comprehensive performance of the charge and discharge capacity and the capacity retention rate can be improved.

[0015] The value on the right side of the inequality (1) is preferably 2400.

[0016] Sulfur element content A in the active material S is preferably greater than 65.0% by mass.

[0017] Iron element content A in the active material F is preferably greater than 15.0% by mass.

[0018] The median particle size M is preferably 1.0 μm or more.

[0019] When the electrode as described above is used as the positive electrode, the initial discharge capacity is expressed as DC 3 (mAh / g), DC 3 is preferably greater than 400 mAh / g, more preferably greater than 600 mAh / g.

[0020] The electrode as described above has a current collector, and the current collector has a metal foil. When the thickness of the metal foil is expressed as T (μm), A S , M, T preferably satisfy the following inequality (2), (2)A S ×M / T > 6.0.

[0021] The quotient obtained by dividing the product value of the amount of sulfur and the median particle size by the thickness value of the current collector is a certain value or more, and each value restricts each other, so it is considered that the performance of the electrode and / or the battery is improved.

[0022] When the coating density of the active material is expressed as D (mg / cm 2 ), A S , A F and D preferably satisfy the following inequality (3), (3)A S ×A F ×D > 7000.

[0023] When the product of the sulfur content ratio and the iron content ratio in the active material and the coating density (mg / cm 2 ) of the active material is maintained at a certain value or more, sulfur and iron retained on the electrode interact with each other under given conditions, and thus it is considered that the performance of the electrode and / or the battery is improved.

[0024] When the electrode as described above is used as the positive electrode, the 10th discharge capacity is expressed as DC 10 (mAh / g), and DC 10 is preferably greater than 350 mAh / g.

[0025] Another embodiment of the present invention is a lithium ion secondary battery including the above electrode.

[0026] The lithium ion secondary battery preferably further has an electrolyte, and when the volume of the electrolyte is expressed as V (mL), A S , M, and V satisfy the following inequality (4), (4) A S ×M / V>60.

[0027] By making the quotient obtained by dividing the product value of the amount of sulfur and the median particle diameter by the volume value of the electrolyte be a certain value or more, each value restricts each other, and thus it is considered that the performance of the electrode and / or the battery is improved.

[0028] <Definition> The term "granular" refers to a state in which the active material is made fine enough to be suitable for mixing with another material for the purpose of the present invention. Regarding the particles constituting the active material, the size of the particles is not particularly limited as long as the mixing can be appropriately carried out.

[0029] "Active material" refers to a material that plays a role in a redox reaction for energy conversion in a lithium ion secondary battery.

[0030] "Active material layer" refers to a layer formed on a current collector constituting an electrode and made of an electrode material (including an active material).

[0031] "Coating density" refers to the mass (mg) per unit area (cm 2 ) of the active material coated on the current collector.

[0032] In this specification, unless otherwise specified, "initial discharge capacity" refers to the 3rd discharge capacity.

[0033] <Measurement method> "Sulfur element content" is the mass ratio (%) of sulfur element in the active material, which is measured by the element analysis method described below in this specification.

[0034] "Iron element content" is the mass ratio (%) of iron element in the active material, which is measured by the thermogravimetric analysis method described below in this specification.

[0035] "Median particle size" is the volume-based cumulative 50% size (median particle size d 50 ) measured with a laser diffraction / scattering type particle size distribution analyzer (particle size distribution analyzer PSA1090L manufactured by Anton Paar GmbH) using water as the dispersion medium.

[0036] The electrode for a lithium ion secondary battery of the present invention and the lithium ion secondary battery of the present invention will be described below.

[0037] <Electrode for Lithium Ion Secondary Battery> The electrode for a lithium ion secondary battery of the present invention has an active material layer containing particulate active material, the active material containing an organic sulfur compound and an iron compound, wherein A S 、A F and M satisfy the following inequality (1), (1) A S ×A F ×M > 1600, wherein, A S represents the sulfur element content (mass %) in the active material, A F represents the iron element content (mass %) in the active material, and M represents the median particle size (μm) of the active material.

[0038] [Active Material Layer] The active material layer according to the present invention contains particulate active material. The active material layer is composed of an electrode material (i.e., a positive electrode material or a negative electrode material), and the electrode material contains the particulate active material described below. Herein, the phrase "the active material is particulate" refers to a state in which 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. In addition, the meaning of this phrase is not intended to be particularly limited as long as the active material is in this state. For example, when the term "particulate" is represented by the median particle size, its range can be from 1 nm to 1000 μm.

[0039] 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, and 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, and further preferably 15.0 μm or less. The median particle size can be measured by the method described in the following Examples section.

[0040] [Active material] The active material involved in the present invention comprises an organic sulfur compound and an iron compound.

[0041] The organic sulfur compound is a compound 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 from this step. However, it can be 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, such as a long-chain polymerized thienobenzene structure (wherein thiophene rings are condensed to form a chain), a structure similar thereto, etc. 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.

[0042] The iron compound is a compound in which an iron atom is bonded to an atom other than the iron atom. Examples of the atom other than the iron atom include, for example, a sulfur atom. Examples of the iron compound include iron(II) sulfide (FeS), iron(III) sulfide (Fe 2 S 3 ), iron disulfide (FeS 2 ), etc. Among them, iron disulfide (FeS 2 ) is typical or preferred.

[0043] Therefore, in the present invention, the statement "the granular active material comprises an organic sulfur compound" can be expressed as "the granular active material contains at least carbon atoms and sulfur atoms", or the statement "the granular active material comprises an organic sulfur compound and an iron compound" can be expressed as "the granular active material contains at least carbon atoms, sulfur atoms, and iron atoms". In addition, in the case of containing 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 following Examples section.

[0044] (Sulfur element content (A S , in mass %)) 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 there is no particular limitation.

[0045] (The iron element content (A F , by mass %) 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 there is no particular limitation.

[0046] (Coating density (D, in mg / cm 2 ) 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。There is no particular limitation on the upper limit of the coating density, 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 generally be assumed to be about 15.0 mg / cm 2 , merely as a reference value.

[0047] (Carbon element content) The carbon element content (mass %) in the active material is preferably greater than 15.0 mass %, more preferably greater than 17.0 mass %, and 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 %, and further preferably less than 24.0 mass %.

[0048] (Hydrogen element content) Since the hydrogen atoms in the polymer react with sulfur during firing to produce hydrogen sulfide, and the hydrogen sulfide is released outside the system, thereby reducing the hydrogen element content, the hydrogen element content (mass %) in the active material 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, and 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 below the detection limit.

[0049] (Median particle size) The active material is pulverized to have a specified particle size, and is preferably particles having a size suitable for preparing an electrode. From the perspective of improving the performance of the electrode and / or battery, the preferred particle size distribution of the active material preferably has a median particle size d of about 1.0 μm or more and 40.0 μm or less 50 . The median particle size is more preferably 1.5 μm or more, further preferably 2.0 μm or more, and 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, and further preferably 15.0 μm or less. The median particle size can be measured by the method described in the following Examples section.

[0050] [Inequality (1)] For the electrode of the present invention, as described in the above Inequality (1), the sulfur element content A in the active material S (mass %), the iron element content A in the active material F(Mass %) multiplied by the median particle size M (μm) of the active material is greater than 1600. The right side of Inequality (1) is preferably 2000, more preferably 2400, further preferably 2800, further preferably 2900, further preferably 3600, further preferably 3700, further preferably 3800, further preferably 10000, further preferably 10800. There is no particular limitation on the upper limit of the left side value of Inequality (1), but it is usually about 20000, about 15000 or about 12000.

[0051] [Inequality (2)] For the electrode of the present invention, as described in the above Inequality (2), the sulfur element content A S (Mass %) multiplied by the median particle size M (μm) of the active material and divided by the thickness T (μm) of the metal foil constituting the current collector, the obtained quotient is preferably greater than 6.0. The right side of Inequality (2) is more preferably 7.0, further preferably 7.9, further preferably 8.1, further preferably 10.0, further preferably 11.0, further preferably 12.0, further preferably 12.4, further preferably 15.0, further preferably 20.0, further preferably 30.0. There is no particular limitation on the upper limit of the value on the left side of Inequality (2), and the higher the upper limit, the more preferred. Therefore, although it is not very meaningful to mention the upper limit of the left side value of Inequality (2), the upper limit is usually about 90.0, about 60.0 or about 50.0, only as a reference value.

[0052] 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, further preferably 25 μm or less.

[0053] [Inequality (3)] For the electrode of the present invention, as described in the above Inequality (3), the sulfur element content A s (Mass %), the iron element content A F (Mass %) in the active material and the coating density D (mg / cm 2) The product is preferably greater than 7000. More preferably, the right side of inequality (3) is 7500, further preferably 8000, further preferably 8500, further preferably 9000, further preferably 9100, further preferably 9200, further preferably 9400, further preferably 9500, and 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 preferred. Therefore, although it is not very meaningful to mention the upper limit of the left side value of inequality (1), the upper limit can generally be assumed to be about 20000, about 15000, or about 12000 only as reference values.

[0054] [Charge-discharge capacity] The electrode of the present invention exhibits excellent charge-discharge capacity. In addition, in the following description, unless otherwise specified, the initial discharge capacity refers to the 3rd discharge capacity (DC 3 ). Herein, the 3rd discharge capacity is the discharge capacity when, after preparing the electrode and the battery, three charge and discharge cycles are performed (the definition of the 3rd discharge is the following cycle: the 1st discharge, the 1st charge, the 2nd discharge, the 2nd charge, the 3rd discharge, the 3rd 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 each 1 g of the positive electrode active material is 50 mA), the voltage finally decreases from 3.0 V to 1.0 V. The total time (hours (h)) taken for the voltage to decrease from 3.0 V to 1.0 V is measured, and the capacity (mAh) is obtained by multiplying the measured total time by the applied current (mA), and then the specific capacity (mAh / g) is obtained by dividing the capacity by the weight of the active material. On the other hand, in the case of charging, charging is performed at a constant current, whereby the voltage rises instead, and when the voltage finally reaches 3.0 V, the charging is terminated. This also applies to the 10th discharge capacity described below.

[0055] (Initial discharge capacity (DC 3 )) 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, and further preferably greater than 730 mAh / g. There is no particular limitation on the upper limit of the initial discharge capacity, and the higher the upper limit, the more preferred. 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 only as a reference value.

[0056] (Discharge capacity after 10 charge-discharge cycles (DC 10 )) When the electrode of the present invention is used as the positive electrode, the discharge capacity during 10 charge-discharge cycles (i.e., the discharge capacity after 10 charge-discharge cycles (DC 10 )) (mAh / g) is preferably greater than 350 mAh / g. The discharge capacity is preferably greater than 400 mAh / g, more preferably greater than 500 mAh / g, further preferably greater than 600 mAh / g, further preferably greater than 650 mAh / g, further preferably 681 mAh / g or more, further preferably greater than 690 mAh / g, further preferably 723 mAh / g or more, and 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, generally, the upper limit can be assumed to be, for example, approximately equal to the value of the initial discharge capacity or approximately 900 mAh / g, only as a reference value.

[0057] In addition, when measuring the 3rd discharge capacity and the 10th discharge capacity of the electrode of the present invention as the positive electrode, in order for the electrode to fully exhibit the performance related to the discharge capacity of the positive electrode, a negative electrode and an electrolyte that can be used persistently as a lithium-ion secondary battery (so that lithium is not immediately exhausted) within the scope of common technical knowledge are used, 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 amount (molar amount) of lithium is greater than one percent (preferably one-tenth, more preferably one-half) of the amount (molar amount) of sulfur in the positive electrode. In the examples described below, 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 (molar amount) of sulfur is necessarily less than 0.004491 (≒ 0.144 / 32.065) (this value is 71.5% or less). 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 (molar amount) of lithium is 0.076934 (≒ 0.534 / 6.941), so the amount (molar amount) of lithium in the negative electrode is large enough. In addition, for example, regarding the electrolyte, it is sufficient to make the amount (molar amount) of lithium greater than one percent (preferably one-tenth, more preferably one-half) of the amount (molar amount) of sulfur in the positive electrode. In the examples described below, the amount (molar amount) of lithium in the electrolyte is 0.002 = volume V of the electrolyte (= 2.0 mL) × concentration (= 1.0 mol / L), so the amount (molar amount) of lithium in the electrolyte is large enough. As described above, when using a negative electrode and an electrolyte containing a large enough amount of lithium (molar amount), the discharge capacity of the positive electrode can be fully exhibited. Herein, the volume V (mL) of the electrolyte refers to the total volume of the electrolyte or solid electrolyte containing the solute.

[0058] [Application] The electrode for a lithium ion secondary battery of the present invention can be used as a positive electrode or a 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 a positive electrode of a lithium ion secondary battery.

[0059] The electrode for a lithium ion secondary battery can be prepared in the same manner as described in the preparation method section below by using the materials described in the preparation method section below. That is, in the case where the electrode for a lithium ion secondary battery as described above is used as a positive electrode, a conductive aid, a binder, a current collector, etc. described in the preparation method section below are used in the same manner as described in the preparation method section below, so that the electrode for a lithium ion secondary battery as described above can be prepared as a positive electrode; in the case where the electrode for a lithium ion secondary battery as described above is used as a negative electrode, a conductive aid, a binder, a current collector, etc. in the preparation method section below are used in the same manner as described in the preparation method section below, so that the electrode for a lithium ion secondary battery as described above can be prepared as a negative electrode. As described above, the description in the following preparation method section can be regarded as an explanation of the electrode for a lithium ion secondary battery.

[0060] <Lithium ion secondary battery> The lithium ion secondary battery of the present invention is a lithium ion secondary battery including the electrode for a lithium ion secondary battery as described above.

[0061] The lithium ion secondary battery can be prepared in the same manner as described in the preparation method section below by using the materials in the preparation method section below. That is, in the case where the electrode for a lithium ion secondary battery as described above is used as a positive electrode, a negative electrode, an electrolyte, a separator, etc. in the preparation method section below are used in the same manner as described in the preparation method section below, so that the lithium ion secondary battery can be prepared. On the other hand, in the case where the electrode for a lithium ion secondary battery as described above is used as a negative electrode, a positive electrode, an electrolyte, a separator, etc. in the preparation method section below are used in the same manner as described in the preparation method section below, so that the lithium ion secondary battery can be prepared. As described above, the description in the following preparation method section is regarded as an explanation of the lithium ion secondary battery.

[0062] [Inequality (4)] For the lithium ion secondary battery of the present invention, as described in the above inequality (4), the sulfur element content A in the active material SThe quotient obtained by dividing the product of (mass %) and the median particle diameter M (μm) of the active material by the electrolyte volume V (mL) is preferably greater than 60. The right side of inequality (4) is more preferably 70, further preferably 79, further preferably 81, further preferably 100, further preferably 110, further preferably 120, further preferably 150, further preferably 200, further preferably 250, further preferably 300. There is no particular limitation on the upper limit of the left side value of inequality (4), 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 (4), the upper limit is usually about 900, about 600 or about 500, only as a reference value.

[0063] Since the range of the electrolyte volume V (mL) varies depending on the size of the battery, this range is not clearly defined, and it is sufficient to use the minimum amount that can exhibit the performance of the active material and enable the battery to operate sufficiently. Only as a reference value, for example, in the case of the laminated battery described in the examples, the volume V is preferably 1.0 mL or more, more preferably 1.2 mL or more, and further preferably 1.5 mL or more. On the other hand, the volume V is preferably 4.0 mL or less, more preferably 3.0 mL or less, and further preferably 2.5 mL or less.

[0064] [Application] The lithium ion secondary battery of the present invention can be used as a lithium ion secondary battery having improved comprehensive performance of charge-discharge capacity and capacity retention rate.

[0065] [Preparation Method] Hereinafter, the preparation methods of the electrode and the lithium ion secondary battery of the present invention will be described in the order of the preparation method of the active material constituting the electrode.

[0066] [Preparation of Active Material] The active material of the present invention can be prepared by the following preparation method, including: (1) mixing a raw material 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.

[0067] (Polymer) The polymer is not particularly limited as long as it is a compound containing at least carbon atoms and hydrogen atoms and is a compound that 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 can be a polymer containing heteroatoms (such as nitrogen atoms, sulfur atoms, etc.). Specific examples of the polymer include, for example, polymers of unsaturated hydrocarbon group monomers, condensates of substituted aromatic hydrocarbons and sulfur chloride, etc. The polymers can be used alone or in combination of two or more of them.

[0068] <<Polymer of unsaturated hydrocarbon group monomers>> Examples of the polymer of unsaturated hydrocarbon group monomers include, for example, resins (such as acrylic resins, etc.). In addition, examples of the polymer of unsaturated hydrocarbon group monomers include diene rubbers, etc. One or more polymers of unsaturated hydrocarbon group monomers can be used.

[0069] Examples of acrylic resins include, for example, at least one polymer selected from the following: a polymer obtained by polymerizing at least one monomer selected from acrylate compounds represented by the following chemical formula (1); or a polymer obtained by polymerizing at least one monomer selected from acrylate compounds represented by the following chemical 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. CH 2 =C(R 11 )COOR 12 (1) (In the formula, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group.) CH 2 =C(R 21 )COO-Y-OCO(R 22 )C=CH 2 (2) (In the formula, R 21 is the same as or different from R 22 , R 21 and R 22 are each a hydrogen atom or a methyl group, Y is a straight-chain alkylene group, Y can have at least one substituent selected from a hydroxyl group and an alkyl group, and the carbon skeleton constituting the alkylene group can form an ether bond with an oxygen atom. Among them, when there are two or more ether bonds, there must be two or more intermediate carbon atoms between any adjacent oxygen atoms.)

[0070] In chemical formula (1), R 11 is preferably a methyl group, R 12 is 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 a methyl group, a n-butyl group, an isobutyl group, and a tert-butyl group. Examples of the compound represented by chemical formula (1) include, for example, methyl (meth)acrylate, butyl (meth)acrylate, etc., and more preferably methyl methacrylate and butyl methacrylate. In this article, "(meth)acrylate" in methyl (meth)acrylate and butyl (meth)acrylate means "acrylate" or "methacrylate" (the same applies hereinafter). A further preferred example of the compound represented by chemical formula (1) is butyl methacrylate.

[0071] 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 from 2 to 6, more preferably 2 or 3. The number of substituents in Y is preferably from 1 to 4, more preferably 1 or 2. As the substituent in Y, one or more substituents selected from a hydroxyl group and an alkyl group having 1 to 4 carbon atoms are preferred; as the alkyl group having 1 to 4 carbon atoms, methyl is preferred. For example, when the carbon skeleton of Y forms an ether bond with an oxygen atom, the part corresponding to -Y-O- is preferably represented by the following Chemical Formula (3) (wherein, the substituents in Y are not considered in Chemical Formula (3)). -(CH 2 ) I -(CH 2 CH 2 O) m -(CH 2 CH 2 CH 2 O) n -(3) (In the formula, I is from 0 to 6, m is from 0 to 3, and n is from 0 to 2. However, I, m, and n cannot be 0 at the same time.)

[0072] In Chemical Formula (3), preferably, I is 1, 2, 3, 4, 5, or 6, and m and n are 0; m is 1, 2, or 3, and I and n are 0; or n is 1 or 2, and I and m are 0.

[0073] 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.

[0074] 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 a copolymer of methyl methacrylate and ethylene glycol dimethacrylate.

[0075] In the present invention, the acrylic resin preferably has a fine particle form. Herein, 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, but is usually, for example, 0.1 μm or more, preferably 1.0 μm or more. The particle size is a value (median particle size) measured by a particle size distribution measuring device (PSA1090L manufactured by Anton Paar GmbH).

[0076] The acrylic resin may be spherical fine particles or porous fine particles. When the acrylic resin is porous, its oil absorption 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 is a value measured according to JIS K 5101-13-2:2004. More specifically, it can be measured by the method described in paragraph 0069 of JP 2017-88501A.

[0077] The acrylic resin only needs to have the structure as described above, and there is no particular limitation on its Mw. However, the Mw of the acrylic resin is usually in the range of 2000 to 1500000. The Mw is a value measured by gel permeation chromatography (GPC) (calibrated with polystyrene).

[0078] The acrylic resin is commercially available or can be prepared 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 Kasei Co., Ltd.

[0079] Examples of the diene rubber include, for example, natural rubber, isoprene rubber, butadiene rubber (such as high cis-polybutadiene rubber, etc.). The diene rubber is commercially available or can be prepared by a conventional method within the knowledge of those skilled in the art.

[0080] <<Condensate of substituted aromatic hydrocarbon and sulfur chloride>> Examples of condensates of substituted aromatic hydrocarbons and sulfur dichloride include, for example, condensates of alkylphenols and sulfur dichloride, etc. Specific examples of condensates of alkylphenols and sulfur dichloride include, for example, TACKIROL V200, TS3108, and TS3109 manufactured by Taoka Chemical Co., Ltd., Vultac 3 manufactured by Arkema, etc. More than one condensate of substituted aromatic hydrocarbons and sulfur dichloride can be used.

[0081] (sulfur) As sulfur, various forms of sulfur such as powdered sulfur, insoluble sulfur, precipitated sulfur, and colloidal sulfur can be used. Among them, precipitated sulfur and colloidal sulfur are preferred. More than one sulfur can be used.

[0082] 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 for the charge-discharge capacity and cycle characteristics to be improved. 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 be advantageous in terms of cost. In addition, in this specification, the term "cycle characteristics" refers to the characteristics of maintaining the charge-discharge capacity of the secondary battery 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, and conversely, a secondary battery with a low degree of decline in charge-discharge capacity and a high capacity retention rate has excellent cycle characteristics.

[0083] As sulfur, any of various allotropes can be used, but preferably sulfur contains S which is a solid under normal temperature and pressure 8 sulfur, more preferably S 8 monomer of sulfur.

[0084] (iron ion compound) The iron ion compound is not particularly limited as long as it is a compound that forms an iron compound when fired together with the polymer and sulfur in a non-oxidizing atmosphere. Examples of such iron ion compounds can include ferrites, iron complexes, etc. that contain divalent or trivalent iron ions. Examples of ferrites can include organic acid salts of iron and inorganic acid salts of iron. On the other hand, examples of iron complexes can include neutral iron complexes and iron complex ion salts (iron complex salts).

[0085] Examples of organic acid salts of iron include, for example, divalent iron (Fe2+ ) and salts of organic acids, ferric iron (Fe 3+ ) and salts of organic acids, etc. Among them, salts of ferrous 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 the organic acid include fatty acids, oxalic acid, tartaric acid, citric acid, malic acid, succinic acid, etc. Specific examples of the fatty acid 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 the organic acid salts of iron include iron(II) acetate, iron(II) oxalate, etc. They may be hydrates. More than one kind of organic acid salt of iron can be used.

[0086] Examples of the inorganic acid salts of iron include, for example, salts of ferrous iron (Fe 2+ ) and inorganic acids, salts of ferric iron (Fe 3+ ) and inorganic acids, etc. Among them, salts of ferrous iron and inorganic acids are preferred. Specific examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, etc. Among them, nitric acid, etc. are preferred. Preferred examples of the 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. More than one kind of inorganic acid salt of iron can be used.

[0087] Examples of the iron complex include, for example, ferrous iron (Fe 2+ ) complex, ferric iron (Fe 3+ ) complex, etc. The iron complex can be in the form of a neutral complex or in the form of a complex salt. The ligand coordinated with the iron ion is not particularly limited, and examples include, for example, halogen atoms (such as chlorine atoms, bromine atoms, etc.), cyano groups, dicyclopentadienyl groups, N,N'-bis(salicylidene)ethylenediamine, etc. Examples of the iron complex include potassium hexacyanoferrate(II) ([Fe(CN) 6 K 4 ), potassium hexacyanoferrate(III) ([Fe(CN) 6 K 3 ), sodium iron(III) chloride ([FeCl 4 Na), ferrocene (iron(II) dicyclopentadienyl), iron(III) chloride N,N'-bis(salicylidene)ethylenediamine, etc. More than one kind of iron complex can be used.

[0088] As the iron ion-containing compound, at least one selected from the group consisting of the organic acid salts of iron, the inorganic acid salts of iron, neutral iron complexes, and iron complex salts as described above can be used. Among them, organic acid salts of iron, inorganic acid salts of iron, or neutral iron complexes are preferred.

[0089] There is no particular limitation on the particle size of the iron ion compound, but 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, further preferably 15 μm or less. The median particle size can be measured by the method described in the Examples section as described below.

[0090] 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 compound is preferably 50 parts by mass or more and 300 parts by mass or less. The content is more preferably greater than 50 parts by mass, further preferably greater than 60 parts by mass, further preferably greater than 70 parts by mass, further preferably greater than 75 parts by mass. On the other hand, the content is more preferably less than 250 parts by mass, further preferably less than 200 parts by mass, further preferably less than 150 parts by mass, further preferably less than 125 parts by mass.

[0091] (Iron ion compound-dispersed polymer) In the present invention, the polymer and the iron ion compound can be used as an iron ion compound-dispersed polymer obtained by previously dispersing the iron ion compound in the polymer. Such an iron ion compound-dispersed polymer can be prepared by subjecting the polymer to a polymerization reaction in a state where the iron ion compound is previously dispersed in the monomers constituting the polymer. The polymerization reaction can be carried out by a conventional method.

[0092] As the iron ion compound-dispersed polymer, for example, an iron ion compound-dispersed acrylic resin obtained by dispersing the iron ion compound in an acrylic resin can be suitably used. Preferred examples of the acrylic resin for this purpose include homopolymers of (meth)acrylic acid methyl esters, copolymers of methyl methacrylate and ethylene glycol dimethacrylate, etc. In addition, preferred examples of the iron ion compound for this purpose include iron(II) oxalate, etc.

[0093] (Other materials) The raw materials can appropriately contain other materials commonly used in the art as needed. Examples of such materials include, for example, conductive carbon materials, etc.

[0094] <<Conductive carbon material>> The raw materials can contain a conductive carbon material. This is because it can improve the conductivity of the active material. A carbon material having a graphite structure is preferably used as the conductive carbon material. As the carbon material, for example, porous carbon materials (e.g., activated carbon, etc.), graphite, carbon black, acetylene black, Ketjen black, carbon fiber (CF), and nanocarbon materials (e.g., carbon nanotube (CNT), carbon nanofiber, graphene, fullerene, etc.) can be used. One or more conductive carbon materials can be used.

[0095] 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 CNTs, graphene, etc. can be used in combination with acetylene black, carbon black, or Ketjen black. Such a combined system makes it possible to further improve the cycle characteristics of the lithium-ion secondary battery without significantly increasing the cost. In addition, the total combined amount of CNTs or graphene is preferably 8% by mass or more and 12% by mass or less of the total amount of the conductive carbon material.

[0096] 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 decrease relatively, and there is a tendency to easily achieve the purpose of further improving the charge-discharge capacity and cycle characteristics.

[0097] (Mixing step (1)) The mixing step is a step for preparing the firing raw material. The mixing step can be carried out by mixing the polymer, the iron ion compound, sulfur, and any other components. In this case, the iron ion compound-dispersed polymer as described above can also be used instead of the polymer and the iron ion compound.

[0098] The mixing as described above can be carried out by a conventional method, and there is no particular limitation as long as it is a method for sufficiently mixing these components. In the present invention, examples of the preferred mixing method can at least include mixing by a wet method or mixing by a dry method, which will be mentioned below.

[0099] <<Wet method>> In the present invention, the wet method includes the following steps for preparing the raw material, (a-1) Adding the polymer and the iron ion compound to a solvent (such as an organic solvent, etc.) to obtain a mixture, or adding a monomer capable of forming a polymer and the iron ion compound and carrying out a polymerization reaction to obtain a mixture containing the polymer, wherein the iron ion compound is dispersed inside and on the surface of the polymer; (a-2) Removing the solvent from the mixture to obtain a dry mixture; and (a-3) Mixing the dry mixture with sulfur.

[0100] In sub-step (a-1), the method of adding a polymer or monomer, an iron ion-containing compound, etc. to an 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-containing 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-containing compound can be added and mixed, or (3) the iron ion-containing compound can be added to the organic solvent and mixed, and then the polymer (or monomer) can be added and mixed.

[0101] 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 preferably used. This is because it contributes to good mixing. More than one of these solvents can be used. In addition, when a liquid monomer is used in sub-step (a-1), a solvent is not necessary, and when no solvent is used, sub-step (a-2) can be omitted.

[0102] Sub-step (a-1) can be carried out by stirring in a container (such as a beaker, etc.).

[0103] In sub-step (a-2), the removal of the organic solvent can be carried out by a conventional method. For example, this removal can be carried out by a drying method (such as heating drying, reduced-pressure drying, reduced-pressure heating drying, etc.) on the mixture in sub-step (a-1).

[0104] Preferably, the dried mixture thus obtained is pulverized before proceeding to the next step. This is because, in this way, it can be expected that the mixing in sub-step (a-3) will be carried out more appropriately.

[0105] In sub-step (a-3), the mixing of the dried mixture and sulfur can be carried out by a conventional method, and examples thereof can include, for example, a method of mixing them using a blender, etc.

[0106] <<Dry method>> In the present invention, the dry method includes the following steps for preparing the raw materials, (b-1) Mix the polymer, the iron ion-containing compound, and sulfur in a powder state, or disperse the iron ion compound in the polymer and sulfur in a powder state.

[0107] In this text, the powder refers to a state in which each raw material in solid form has been made fine enough to be suitable for mixing for the purposes of the present invention. There is no particular limitation on the size of each particle constituting the powder, as long as mixing can be appropriately carried out, but it is generally 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 battery, the particle size 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, and further preferably 10 μm or less in terms of median particle size. The median particle size can be measured by the method described in the following Examples section.

[0108] Mixing can be carried out by a conventional method, for example, in the same manner as the mixing in sub-step (a-3) described above.

[0109] In both the wet method and the dry method, it is preferable to fully mix the raw materials in advance for firing. In addition, when adding a conductive carbon material or the like to the raw materials, these additives can also be pre-mixed for firing so that they are pre-included in the raw materials.

[0110] The raw materials thus obtained can be directly used in the next firing step, or, if necessary, they can be formed into granules and used in the next step.

[0111] (Firing step (2)) The firing step is a step of firing the raw materials obtained as described 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 is reached, holding it at the predetermined temperature for a predetermined time, and then allowing it to cool naturally.

[0112] [[Non-oxidizing atmosphere]] The firing is preferably 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, a non-oxidizing atmosphere refers to an inert gas atmosphere (such as nitrogen, argon, etc.), a sulfur gas atmosphere, an ammonia gas atmosphere, etc. Therefore, the firing can be appropriately carried out in an inert gas atmosphere in, for example, a quartz tube.

[0113] [[Heating rate]] 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 this range, there is a tendency to easily achieve the purpose of improving the charge-discharge capacity and cycle characteristics.

[0114] <<Firing Temperature / Time>> The firing temperature refers to the temperature after the raw materials have been heated up, and the raw materials are fired while maintaining this temperature for a certain period of time. This temperature is preferably in the range of above 250°C and below 550°C. When this temperature is higher than 250°C, there is a tendency to avoid insufficient vulcanization reaction and prevent the charge-discharge capacity of the object from decreasing. On the other hand, when this temperature is lower than 550°C, there is a tendency to prevent the decomposition of raw materials, prevent the decrease in yield, and prevent the charge-discharge capacity from decreasing. This temperature is more preferably higher than 300°C, further preferably higher than 350°C, and further preferably 370°C or higher. On the other hand, this temperature is more preferably lower than 500°C, further preferably lower than 450°C.

[0115] From the perspective of improving the performance of the electrode and / or battery, the firing temperature in the firing step is preferably higher than the thermal decomposition temperature of the iron ion compound.

[0116] The holding time of the firing temperature only needs to be appropriately set according to the raw material type, firing temperature, etc. For example, it is preferably 1 hour or more and 6 hours or less. When it is 1 hour or more, there is a tendency to fully promote firing, and when it is 6 hours or less, there is a tendency to prevent excessive pyrolysis of the constituent components.

[0117] <<Apparatus>> Firing can be carried out, for example, in a muffle furnace ( Figure 1 ), or it can be carried out using a continuous apparatus (such as a twin-screw extruder, etc.). When using a continuous apparatus, there are the following advantages: Through a series of operations (such as kneading, pulverizing, and mixing raw materials in the apparatus while firing, etc.), a sulfur-based active material can be continuously prepared.

[0118] The muffle furnace ( Figure 1 ) is a furnace separated by a hot plate or the like, so that the heat source (heater) is not exposed in the furnace to prevent contamination of the sample. Figure 1 In the muffle furnace 1, a heater 2 is provided at the lower part of the furnace, and the heater is separated by a heating plate. A lid 3 is provided on the front of the furnace (the left end side in the figure), which maintains an inert gas 4 atmosphere inside the furnace. A thermocouple is connected to the lid (not shown), so that the temperature inside the furnace during firing can be measured. Two layers of stainless steel (SUS) rectangular trays 5, 6 are provided in the upper and lower layers inside the furnace for firing raw materials.

[0119] The internal structure of the furnace enables a gas (e.g., an inert gas such as argon (Ar)) to be continuously supplied through the gas introduction pipe 7 and discharged to the outside through the gas discharge pipe 8. The gas discharge pipe 8 is connected to the trapping tank 10 containing the sodium hydroxide aqueous solution 9, and the exhaust gas leaving the muffle furnace 1 through the gas discharge pipe 8 is discharged to the outside once it passes through the sodium hydroxide aqueous solution 9 in the trapping tank 10. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the reaction, the hydrogen sulfide gas is neutralized by the sodium hydroxide aqueous solution and removed from the exhaust gas.

[0120] (Step of removing residues) In the processed product obtained after firing, there are cases where unreacted sulfur that sublimates during firing and then precipitates after cooling remains. In the presence of these residues, it is necessary to remove them as much as possible because they may cause deterioration of the cycle characteristics. The removal of the residues can be carried out according to a conventional method, for example, by drying under reduced pressure and heating, drying with hot air, washing with a solvent, etc.

[0121] (Crushing / Classification) In order to obtain particles having a size suitable for preparing an electrode, it is preferable to crush the obtained active material to a predetermined particle size and classify it. The preferred size (particle size distribution) of the particulate active material is as described above.

[0122] The crushing can be carried out by a conventional method. For example, the active material can be crushed under predetermined conditions by using a crusher (e.g., a cutting crusher, a jet mill, etc.). The crushing conditions vary depending on the crusher used. For example, in the case of using a cutting crusher (e.g., Free Speed Mill FS - 20 manufactured by Labonect), the treatment can be carried out under the conditions of a rotational speed of 20,000 rpm or more and 30,000 rpm or less for 1 second or more and 30 seconds or less. In addition, in the case of using a dry jet mill (e.g., Nano Jetmizer NJ - 30 manufactured by Aishin Nano Technologies CO., LTD (Aishin Nano Technology Co., Ltd.)), the treatment can be carried out at a processing speed of 1 g / min or more and 3 g / min or less and a crushing pressure of 0.5 MPa or more and 2.0 MPa or less.

[0123] In addition, in the firing method using a twin - screw extruder as described above, the prepared active material can also be crushed into particles by shearing during the kneading process while preparing the active material.

[0124] [Preparation of an electrode for a lithium - ion secondary battery] Using the granular active material obtained as described above, an electrode for a lithium ion secondary battery can be prepared by a conventional method, and the electrode has an active material layer containing the granular active material. That is, except for using the granular active material as described above as the active material, the electrode can be obtained in the same manner as in the case of preparing a normal lithium ion secondary battery.

[0125] (Case of using the granular active material as the positive electrode active material) Except for using the granular active material as described above as the positive electrode active material, the positive electrode for a lithium ion secondary battery can be prepared in the same manner as in the case of a normal positive electrode for a lithium ion secondary battery. For example, the positive electrode can be prepared by mixing the granular active material with a conductive assistant, 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, the granular active material can also be kneaded with a conductive assistant, a binder, and a small amount of solvent using, for example, a mortar, etc., to form a film, and then crimped onto the current collector using a press, etc. However, in this case, the coating of the active material is preferably carried out in such a way that the coating density D (mg / cm 2 ) satisfies the above inequality (3).

[0126] <<Conductive assistant>> Examples of the conductive assistant include, for example, vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), Ketjen black (KB), graphite, or fine metal powders stable at the positive electrode potential, such as aluminum, titanium, etc. In addition, as the conductive assistant, the conductive carbon material as described above can also be used. One or more of these conductive assistants can be used.

[0127] <<Binder>> 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. More than one of these binders can be used.

[0128] <<Solvent>> Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformaldehyde, alcohols, hexane, water, etc. More than one of these solvents can be used.

[0129] <<Mixing amount>> The mixing amount of these materials constituting the positive electrode is not particularly limited. However, for example, based on 100 parts by mass of the active material, it is preferable to mix 2 to 100 parts by mass of a conductive assistant, 2 to 50 parts by mass of a binder, and an appropriate amount of a solvent. 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 product of A S , A F and D is preferably determined to satisfy the inequality (3) as described above.

[0130] <<Current collector>> As the current collector, it is only necessary to use a current collector generally used for the positive electrode of a lithium ion secondary battery. For example, examples of the current collector include a current collector composed of a metal foil (such as an aluminum foil, an aluminum mesh, a punched aluminum sheet, an expanded aluminum sheet, a stainless steel foil, a stainless steel mesh, a punched stainless steel sheet, an expanded stainless steel sheet, a nickel foam, a nickel non-woven fabric, a copper foil, a copper mesh, a punched copper sheet, an expanded copper sheet, a titanium foil, a titanium mesh, etc.) and a carbon non-woven fabric, a carbon woven fabric, etc. Among them, a current collector containing a metal foil is preferable. The current collector can be used alone or two or more of them can be used in combination. In addition, the surface of the current collector can be coated with carbon or the like. Specific examples of the current collector having a surface coated with carbon or the like include, for example, a carbon-coated aluminum foil. In this case, the current collector includes a carbon-coated portion.

[0131] (In the case of using a particulate active material as the negative electrode active material) In addition to using the particulate active material as described above as the negative electrode active material, the negative electrode for a lithium ion secondary battery can be prepared in the same manner as in the case of a normal negative electrode for a lithium ion secondary battery. For example, a paste-like negative electrode material can be prepared by mixing a particulate active material with a conductive assistant, a binder, and a solvent, the negative electrode material can be coated on a current collector, and then dried to prepare the negative electrode. In addition, as another method, for example, a particulate active material can be kneaded with a conductive assistant, a binder, and a small amount of a solvent using a mortar or the like to form a film, and then it can be crimped to a current collector using a press or the like to prepare the negative electrode. However, in this case, the coating of the active material is preferably performed in such a manner that the coating density D (mg / cm 2 ) of the active material satisfies the inequality (3) as described above.

[0132] As the conductive assistant, the binder, and the solvent, the same conductive assistant, binder, and solvent as those in the case of using a particulate active material as the positive electrode active material can be used, and they can also be coated on the current collector.

[0133] [Preparation of Lithium Ion Secondary Battery] Except for using the electrodes for lithium ion secondary batteries obtained as above, the lithium ion secondary battery of the present invention can be prepared in the same manner as in the case of preparing ordinary lithium ion secondary batteries.

[0134] (Case of using granular active material as the positive electrode active material) Except for the positive electrode containing the granular active material (positive electrode active material) as described above, a negative electrode and an electrolyte can also be used, and further components such as a separator can be used as needed, and the lithium ion secondary battery of the present invention can be prepared according to a conventional method.

[0135] [[Negative Electrode]] As the negative electrode material, 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.) well-known to those skilled in the art can be used. Among the negative electrode materials described above, when using lithium-free materials (such as carbon-based materials, silicon-based materials, alloy-based materials, etc.) as the negative electrode material, it is advantageous that short circuits are not likely to occur 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 of pre-incorporating 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 need to be used. For example, the lithium pre-doping methods for doping lithium into the negative electrode include: a method of embedding lithium by electrolytic doping (using metallic lithium as the counter electrode, assembling a half-cell and electrochemically doping lithium); and a method of embedding lithium by the attachment pre-doping method (attaching a metallic lithium foil to the electrode and then placing it in the electrolyte to perform doping by utilizing the diffusion of lithium into the electrode). In addition, when pre-doping lithium into the positive electrode, the electrolytic doping method described above can be used. As the lithium-free negative electrode material, a silicon-based material (a negative electrode material with high capacity) is particularly preferred, and among them, thin film silicon with a thin electrode thickness and thus an advantage in terms of capacity per volume is more preferred.

[0136] [[Electrolyte]] The electrolyte compensates for the charge generated by the emission of electrons to the external circuit accompanying the oxidation / reduction of the active material at the positive electrode / negative electrode through ion flow. As the electrolyte for the 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, ethyl methyl 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 (e.g., a polymer gel state).

[0137] [[Separator]] In addition to the negative electrode, positive electrode, and electrolyte described above, a lithium ion secondary battery may further include components such as a separator, for example. The separator is located between the positive electrode and the negative electrode, allows ion migration between the positive electrode and the negative electrode, and prevents internal short circuit between the positive electrode and the negative electrode. If the lithium ion secondary battery is a sealed type, the separator needs to have the function of retaining the electrolyte. As the separator, it is preferable to use a thin and microporous film or nonwoven fabric film made of polyethylene, polypropylene, polyacrylonitrile, aromatic polyamide, polyimide, cellulose, glass, etc.

[0138] [[Shape]] 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.

[0139] (In the case of using a granular active material as the negative electrode active material) In addition to the negative electrode containing the granular active material (negative electrode active material) described above, a positive electrode and an electrolyte can also be used, and further components such as a separator can be used as needed, and the lithium ion secondary battery of the present invention is prepared according to a conventional method.

[0140] [[Positive Electrode]] The positive electrode material is not particularly limited, and it only needs to be, for example, 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 (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, LiaMn x Co y Niz 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 ones.

[0141] 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. Examples

[0142] Although the present invention will be described based on examples, the present invention is not limited to the examples.

[0143] The following shows a summary of various chemicals used in the examples and comparative examples.

[0144] <Materials Used in Tests> Iron ion compound: Ferrous oxalate (II) dihydrate prepared in Synthesis Example 1 Iron ion compound-dispersed polymer: Iron ion compound-dispersed acrylic resin (copolymer of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) (MMA: EGDMA = 80:20 (mass ratio)) and in a state where the iron ion compound is dispersed inside or on the surface of the acrylic resin)) prepared in Synthesis Example 2 Polymer: Acrylic resin obtained by polymerization in the same manner as in Preparation Example 2 except without using the iron ion compound (MMA: EGDMA = 80:20 (mass ratio)) Sulfur: Precipitated sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0145] Synthesis Example 1 (Iron Ion Compound) The material obtained by pulverizing iron(II) oxalate dihydrate (ultrapure iron(II) oxalate dihydrate manufactured by KANTO CHEMICAL CO., INC.) for 10 minutes using a cryogenic mill (JFC-2000 manufactured by Japan Analytical Industry Co., Ltd.) was used as the iron ion compound-containing material. Particle size (median particle size d 50 ): 2.10 μm, specific surface area: 6.6 m 2 / g.

[0146] Synthesis Example 2 (Iron Ion Compound-Dispersed Polymer) 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 the iron ion compound-containing material 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%.

[0147] Examples and Comparative Examples <Preparation of Granular Active Material> (Firing Raw Material) According to Table 2, each component was mixed with a stirrer to obtain a raw material for firing.

[0148] (Reaction Apparatus for Firing) A muffle furnace ( Figure 1 ) was used to fire the raw material. Figure 1 The muffle furnace in

[0149] (Firing Step) First, the firing raw material was placed in a tray (SUS container), and the atmosphere in the muffle furnace was replaced with Ar gas three times using a vacuum pump. Then, Ar gas was continuously supplied from the gas inlet tube at a flow rate of 100 mL / min, and the muffle furnace was heated 30 minutes after the start of the supply. The temperature was raised at a rate of 5 °C / h, and when the temperature of the firing raw material reached the firing temperature described in Table 2, heat treatment was performed for 2 hours while maintaining the firing temperature. Then, while adjusting the flow rate of Ar gas, the temperature of the fired material was naturally cooled to 25 °C in an Ar gas atmosphere, and then the fired substance was taken out of the muffle furnace.

[0150] (Pulverization Step) The fired substance was pulverized using a cutting mill, a dry jet mill, etc. The pulverization steps of Preparation Examples 1-7 will be described below.

[0151] For Preparation Examples 1-6, as shown in Table 1, the fired material was pulverized by using a cutting mill (free speed mill, FS-20, manufactured by Labonect) at a predetermined rotational speed for a predetermined period of time.

[0152] Table 1

[0153] On the other hand, for Preparation Example 7, a dry jet mill (Nano Jetmizer NJ-30 manufactured by Aishin Nanotechnology Co., Ltd.) was used to pulverize the fired product at a processing speed of 2 g / min and a pulverization pressure of 1.1 MPa.

[0154] (Classification step) In order to remove coarse particles from the pulverized fired material, the fired material was classified using a 32-μm stainless steel sieve to obtain the active material.

[0155] (Physical properties of the active material) (Elemental analysis) Elemental analysis was performed on the active materials prepared in the examples and comparative examples.

[0156] For carbon, hydrogen, nitrogen, and sulfur, a vario MICROcube, a fully automatic elemental analyzer manufactured by Elementar, was used, and based on the measured mass, the mass ratio (%) in the total amount of the active material was calculated. The results are shown in Table 2.

[0157] (Iron element content) Thermogravimetric analysis was performed on the active materials prepared in the examples and comparative examples, and based on the obtained measurement results, the amount of each iron element (mass %) was calculated.

[0158] Thermogravimetric analysis was performed using a TGAQ500 manufactured by TA Instruments. The measurement conditions were as follows: after heating the active material to 750 °C in an Ar atmosphere, air was introduced to completely decompose the measurement sample. Then, the ash content ratio (mass %) in each active material was calculated from the measured weight loss rate (mass %) by the following calculation method. Ash content ratio (mass %) = 100 - weight loss rate (mass %)

[0159] In addition, since it was confirmed that the iron element in the examples and comparative examples of the present invention was iron disulfide (FeS 2)Exists. Therefore, through the calculation method shown below, the proportion (mass %) of iron disulfide is calculated from the ash content ratio (mass %) of each of the examples and comparative examples of the present invention. That is, it can be seen from the weight reduction rate (100 mass %) of Preparation Example 8 in Table 2 that Polymer 1 (acrylic resin) completely decomposes after being converted into sulfide. On the other hand, from the weight reduction rate (36 mass %) of Preparation Example 9, it can be seen that the weight of iron disulfide (FeS 2 ) in the active material decreased by 36 mass %. Therefore, through the following calculation method, the proportion (mass %) of iron disulfide (FeS 2 ) in each active material is calculated, FeS 2 Proportion (mass %) = Ash content ratio × {100 / (100 - 36)}.

[0160] In addition, through the following calculation method, the iron element content (Fe proportion, mass %) is calculated from the proportion (mass %) of FeS 2 , Fe proportion (mass %) = Proportion of FeS 2 × Atomic mass of Fe / (Atomic mass of Fe + Atomic mass of S × 2), (where, assume 55.845 is used as the atomic mass of Fe and 32.065 is used as the atomic mass of S).

[0161] (Median particle size) 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 ) is measured.

[0162] The results are shown in Table 2 below

[0163] Table 2

[0164] <Preparation of Positive Electrode and Lithium-Ion Secondary Battery> According to Table 3, using the active material obtained as described above, the positive electrode is prepared as follows, and further using this positive electrode, the lithium-ion secondary battery is prepared as follows.

[0165] (Positive electrode) Using the active material obtained as described 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 rotary mixer (ARE-250 manufactured by THINKY Corporation), using milliQ water as the dispersant to prepare a uniform slurry. Coat the prepared slurry on a 20-μm carbon-coated aluminum foil using a coater with a slit width of 200 to 300 μm, and press it using a roll press to obtain an electrode. Then, heat and dry it at 120 °C for 3 hours using a drying device. After drying, cut the electrode into the following shape: the part forming the mixture 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 tab, thereby obtaining an electrode (positive electrode). Then, measure the mass of the electrode and calculate the amount of the active material in the electrode from the ratio described above. In addition, the "coating density (mg / cm 2 )" described in Table 3 refers to the coating density of the active material.

[0166] (Negative electrode) For the negative electrode, a metallic lithium foil (manufactured by Honjo Metal Co., Ltd., with a thickness of 0.5 mm) is used, and a copper foil is used as the negative current collector. Cut the metallic lithium foil into a width of 5 mm and a length of 4 cm and connect it to the copper foil to obtain an electrode (negative electrode).

[0167] (Electrolyte) Use a non-aqueous electrolyte in which LiPF is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate as the electrolyte. Ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1:1. The concentration of LiPF in the electrolyte is 1.0 mol / L. 6 6

[0168] (Lithium-ion secondary battery) Prepare a laminated battery using the positive electrode and negative electrode as described above. 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 nonwoven 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. Accommodate this electrode body battery in a laminated package formed of an aluminum laminated film (manufactured by MTI). Inject the above-described electrolyte (2.0 mL) into the laminated package. Seal the laminated package using an air degassing sealer to obtain the lithium-ion secondary battery of Example 1.

[0169] <Evaluation of lithium-ion secondary battery> ​​(Discharge capacity, capacity retention rate) Under the condition of a test temperature of 30 °C, each laminated lithium-ion secondary battery prepared in the examples and comparative examples was charged and discharged at a current value corresponding to 50 mA per 1 g of the positive electrode active material. 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 charging and discharging, the battery discharge capacities (mAh) at the 1st, 2nd, 3rd, and 10th times were observed.

[0170] 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 (%) was 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. Capacity retention rate (%) = (DC 10 / DC 3 ) × 100.

[0171] (Charge and discharge capacity index) The 10th discharge capacity (DC 10 )(mAh / g) in each of the examples and comparative examples was expressed 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 KEISOKUKI CENTER CO., LTD.). Charge and discharge capacity index = 10th discharge capacity in each of the examples and comparative examples / discharge capacity in Comparative Example 1 × 100.

[0172] (Capacity retention rate index) The capacity retention rate (DC 10 / DC 3 )(%) in each of the examples and comparative examples was expressed as an index using the following formula. The larger this index, the larger the capacity retention rate, and the more preferable. Capacity retention rate index = capacity retention rate in each of the examples and comparative examples / capacity retention rate in Comparative Example 1 × 100.

[0173] (Comprehensive performance index) Define the average value of the total value of the charge and discharge capacity index and the capacity retention rate index as the comprehensive performance index.

[0174] Table 3

[0175] According to Table 3, improvements in the comprehensive performance of charge-discharge capacity and capacity retention rate were exhibited in the examples.

[0176] <Embodiment> The following shows preferred embodiments.

[0177] [1] An electrode for a lithium-ion secondary battery, The electrode has an active material layer containing particulate active material, The active material contains an organic sulfur compound and an iron compound, wherein, A s , A F and M satisfy the following inequality (1), and the right side of the following inequality (1) is preferably 2000, (1) A s × A F × M > 1600, 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 M represents the median particle size of the active material, in μm. [2] The electrode of [1] above, wherein the value on the right side of inequality (1) is 2400, preferably 2800, more preferably 2900, further preferably 3600, further preferably 3700, further preferably 3800, further preferably 10000, and further preferably 10800. [3] The electrode of [1] or [2] above, wherein the sulfur element content A S in the active material is greater than 65.0 mass %, preferably greater than 66.0 mass %, and more preferably greater than 70.0 mass %. [4] The electrode of any one of [1] to [3] above, wherein the iron element content A F in the active material is greater than 15.0 mass %, preferably 15.4 mass % or more, more 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 %, and further preferably greater than 17.3 mass %. [5] The electrode of any one of [1] to [4] above, wherein the median particle size M is 1.0 μm or more, preferably 1.0 μm or more and 40.0 μm or less, more preferably 1.0 μm or more and 30.0 μm or less, further preferably 1.5 μm or more and 25.0 μm or less, further preferably 2.0 μm or more and 20.0 μm or less, and further preferably 2.4 μm or more and 15.0 μm or less. The electrode according to any one of [1] to [5] above, 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 [6] above, wherein the initial discharge capacity DC 3 is greater than 600 mAh / g, preferably 634 mAh / g or more, more 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. [8] The electrode according to any one of [1] to [7] above, wherein the electrode has a current collector, the current collector has a metal foil, A S 、M and T satisfy the following inequality (2), and the right side of inequality (2) is preferably 7.0, more preferably 7.9, further preferably 8.1, further preferably 10.0, further preferably 11.0, further preferably 12.0, further preferably 12.4, further preferably 15.0, further preferably 20.0, further preferably 30.0, (2) A S ×M / T > 6.0, wherein T represents the thickness of the metal foil, in μm. [9] The electrode according to any one of [1] to [8] above, wherein A S 、A F and D satisfy the following inequality (3), and the right side of inequality (3) 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, (3) A S ×A F ×D > 7000, wherein D represents the coating density of the active material, in mg / cm 2 .

[10] The electrode according to any one of [1] to [9] above, wherein the 10th discharge capacity DC when the electrode is used as the positive electrode 10Greater 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 greater than 650 mAh / g, 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.

[11] A lithium ion secondary battery, the lithium ion secondary battery having an electrode according to any one of [1] to

[10] above.

[12] The lithium ion secondary battery of

[11] above, wherein the lithium ion secondary battery further has an electrolyte, A S , M and V satisfy the following inequality (4), and the right side of inequality (4) is preferably 70, more preferably 79, further preferably 81, further preferably 100, further preferably 110, further preferably 120, further preferably 150, further preferably 200, further preferably 250, further preferably 300, (4)A S ×M / V > 60, wherein, V represents the volume of the electrolyte, in mL. List of reference symbols

[0178] 1. Muffle furnace 2. Heater 3. Lid 4. Inert gas 5. Tray (upper layer) 6. Tray (lower layer) 7. Gas inlet pipe 8. Gas discharge pipe 9. Aqueous sodium hydroxide solution 10. Trapping tank

Claims

1. An electrode for a lithium-ion secondary battery, The electrode has an active material layer containing particulate active material, The active material contains an organic sulfur compound and an iron compound, Wherein, A S 、A F and M satisfy the following inequality (1), (1)A S ×A F ×M > 1600, Wherein, 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 M represents the median particle size of the active material, in μm.

2. The electrode according to claim 1, Wherein, The value on the right side of inequality (1) is 2400.

3. The electrode according to claim 1, Wherein, Sulfur element content A in the active material S Greater than 65.0% by mass.

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

5. The electrode according to claim 1 or 3, Wherein, The median particle size M is 1.0 μm or more.

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, Initial discharge capacity DC 3 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 , M and T satisfy the following inequality (2), (2)A S ×M / T > 6.0 In the formula, T represents the thickness of the metal foil in μm.

9. The electrode according to claim 1 or 3, Wherein, A S 、A F and D satisfy the following inequality (3), (3)A S ×A F ×D > 7000, where D represents the coating density of the active material, with the unit of mg / cm 2 .

10. 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.

11. A lithium-ion secondary battery, Wherein, The lithium-ion secondary battery has the electrode according to claim 1 or 3.

12. The lithium-ion secondary battery according to claim 10, Wherein, The lithium-ion secondary battery further has an electrolyte, A S , M and V satisfy the following inequality (4), (4)A S ×M / V > 60, In the formula, V represents the volume of the electrolyte in mL.

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