Electrode active material, electrode, and lithium ion secondary battery

Abstract

The purpose of the present invention is to improve the charge / discharge capacity and capacity retention rate of an active material constituting an electrode of a lithium ion secondary battery. Provided is an electrode active material comprising particles, the electrode active material comprising: an organic sulfur compound; and a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, in which the powder resistivity of the particles is less than 1.0 * 103 Omega * cm, and in which AS and R [rho] satisfy the following inequality: (1) AS / R [rho] > = 0.05, in which AS represents the sulfur content (mass%) in the electrode active material, and R [rho] represents the powder resistivity.

Description

TECHNICAL FIELD

[0001] The present application relates to a novel electrode active material, an electrode comprising the electrode active material, and a lithium-ion secondary battery comprising the electrode. BACKGROUND

[0002] Since lithium-ion secondary batteries have large charge and discharge capacities, they are mainly used as batteries for portable electronic devices. In addition, they are increasingly used as batteries for electric vehicles, and their performance is expected to be further improved.

[0003] Patent Document 1 describes a sulfur-based active material obtained by calcining a raw material comprising a polymer containing methacrylonitrile as a monomer component and sulfur.

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

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

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

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, it is still desired to develop an active material other than the active material described in Patent Document 1.

[0010] In addition, the above-mentioned materials that have been proposed as negative electrode active materials have a large volume change during the absorption and release of lithium ions, and thus have a problem of poor cycle characteristics when repeatedly charged and discharged. Although carbon materials such as graphite, hard carbon, and the like are also used, their capacities have almost reached their theoretical limits, and it is not expected that their capacities will be significantly increased.

[0011] An object of the present application is to provide a novel electrode active material capable of improving the charge and discharge capacities and the capacity retention rate, an electrode (i.e., a positive electrode or a negative electrode) comprising the electrode active material, and a lithium-ion secondary battery comprising the electrode.

[0012] MEANS FOR SOLVING THE PROBLEM

[0013] The present application relates to the following electrode active material.

[0014] An electrode active material composed of particles, comprising:

[0015] an organic sulfur compound; and

[0016] a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium,

[0017] wherein the powder resistivity of the particles is less than 1.0 x 10 3 Ω·cm, and

[0018] wherein A S and R ρ satisfy the following inequality:

[0019] (1) A S / R ρ ≥ 0.05

[0020] wherein A S represents the sulfur content (mass %) in the electrode active material, and R ρ represents the powder resistivity.

[0021] Effects of the Invention

[0022] According to the present invention, it is possible to provide a novel electrode active material capable of improving the charge / discharge capacity and the capacity retention rate, an electrode (i.e., a positive electrode or a negative electrode) containing the electrode active material, and a lithium-ion secondary battery containing the electrode.

[0023] In the present specification, the term "cycle characteristics" refers to the characteristics of a secondary battery in maintaining the charge / discharge capacity when charging / discharging is repeated. Thus, the cycle characteristics of a secondary battery in which the degree of decrease in the charge / discharge capacity is high and the capacity retention rate is low are poor, while, on the contrary, the cycle characteristics of a secondary battery in which the degree of decrease in the charge / discharge capacity is low and the capacity retention rate is high are excellent. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a cross-sectional view schematically showing a reaction apparatus for manufacturing an electrode active material in an embodiment of the present invention.

[0025] REFERENCE NUMERALS

[0026] 1. Muffle furnace

[0027] 2. Heater

[0028] 3. Cover

[0029] 4. Inert gas

[0030] 5. Tray (upper layer)

[0031] 6. Tray (lower layer)

[0032] 7. Gas introduction pipe

[0033] 8. Gas discharge pipe

[0034] 9. aqueous sodium hydroxide solution

[0035] 10. catch tank DETAILED DESCRIPTION

[0036] Hereinafter, the constitution of one embodiment of the present application will be described in detail. In addition, the numerical values of the upper limit and the lower limit of the relative terms such as "above", "below", "greater than", "less than" and the like used to describe a numerical range can be arbitrarily combined numerical values, and the numerical values in the examples can also be these upper limit values and / or lower limit values. Also, unless it is contrary to the purpose of the present specification, the numerical range shown to include the lower limit or the upper limit is interpreted as disclosing the numerical range not including the lower limit or the upper limit; conversely, unless it is contrary to the purpose of the present specification, the numerical range shown not to include the lower limit or the upper limit is interpreted as disclosing the numerical range including the lower limit or the upper limit.

[0037] One embodiment of the present application is an electrode active material composed of a particle, comprising: an organic sulfur compound; and a metal compound containing at least one metal selected from iron, molybdenum, vanadium, and titanium, wherein a powder resistivity of the particle is less than 1.0 x 10 3 Ω·cm, where A S and R ρ satisfies the following inequality:

[0038] (1) A S / R ρ ≥ 0.05

[0039] In the formula, A S represents the sulfur content (mass %) in the electrode active material, R ρ represents the powder resistivity.

[0040] Although not intended to be bound by theory, the following can be considered as the reason why the electrode active material of the present embodiment can improve the charge-discharge capacity and the capacity retention rate. That is, when the powder resistivity is less than 1.0 x 10 3 Ω·cm, the electrical conductivity of the inside and the surface of the particle of the electrode active material is improved, and thus it is considered that the charge-discharge capacity and the capacity retention rate are improved.

[0041] The right side of inequality (1) is preferably 0.50, more preferably 5.00.

[0042] The powder resistivity is preferably less than 111, more preferably less than 10.

[0043] The metal compound is preferably an iron compound.

[0044] Another embodiment of the present application is an electrode containing the electrode active material.

[0045] Preferably, the electrode includes a current collector having a metal foil, D and A S satisfy the following inequality,

[0046] (2) D x A S > 150

[0047] In the formula, D represents the coating density of the electrode active material on the current collector (unit: mg / cm 2 ).

[0048] By setting the product of the coating density and the sulfur content to exceed a predetermined value, it is considered that the performance of the electrode and / or the battery can be improved.

[0049] Preferably, the electrode includes a current collector having a metal foil, D, T and A S satisfy the following inequality,

[0050] (3) D x A S / T > 10.0

[0051] In the formula, D represents the coating density of the electrode active material on the current collector (unit: mg / cm 2 ), and T represents the thickness of the metal foil (unit: μm).

[0052] By causing the coating density, the sulfur content, and the thickness of the metal foil to satisfy the above inequality, it is considered that the performance of the electrode and / or the battery can be improved.

[0053] Preferably, the electrode includes a current collector having a metal foil, D is greater than 2.5 mg / cm 2 , wherein D represents the coating density of the electrode active material on the current collector (unit: mg / cm 2 ).

[0054] DC3 is preferably greater than 400 mAh / g, wherein DC3 represents the 3rd discharge capacity when the electrode is used as a positive electrode.

[0055] DC 10 is preferably greater than 350 mAh / g, wherein DC 10 represents the 10th discharge capacity when the electrode is used as a positive electrode.

[0056] The electrode is preferably a positive electrode.

[0057] It is considered that the use of the electrode as a positive electrode can improve the performance of the electrode and / or the battery. In particular, by combining the electrode with a lithium negative electrode having a large specific capacity, a battery having a large weight energy density can be realized.

[0058] Another embodiment of the present application is a lithium ion secondary battery including the electrode.

[0059] Preferably, the lithium ion secondary battery further comprises an electrolyte, D, V and A S satisfies the following inequality,

[0060] (4) D x A S / V > 600

[0061] In the formula, V represents the volume of the electrolyte (unit: mL), D represents the coating density of the electrode active material on the current collector (unit: mg / cm 2 ).

[0062] By satisfying the above inequality with the coating density, the sulfur content, and the volume of the electrolyte, it is considered that the performance of the electrode and / or the battery can be improved.

[0063] <Definitions>

[0064] The "electrode active material" is one of the electrode materials of a battery, and refers to a material that participates in a reaction that generates electric energy. The electrode active material includes a positive electrode active material and a negative electrode active material.

[0065] The "particle" refers to a particle in which the electrode active material is made to be fine enough to be suitable for mixing with other materials for the purpose of the present application. As for the particle that constitutes the electrode active material, the size of such a particle is not particularly limited as long as the above-mentioned mixing can be appropriately performed. For example, if the "particle" is expressed in terms of the median particle diameter, it can be in the range of 1 nm to 1000 μm.

[0066] The "particle diameter" is expressed as the median particle diameter (d50) unless otherwise specified.

[0067] The "sulfur content in the electrode active material" is the amount of the sulfur element contained in the electrode active material (unit: mass %).

[0068] The "average fiber length" is calculated by taking a photograph of the fiber with a transmission or scanning electron microscope, measuring the length of 50 fibers in the fiber axial direction, and then calculating the arithmetic average thereof. The average fiber length is applicable to carbon fibers and the like.

[0069] The "average fiber diameter" is calculated by taking a photograph of the fiber with a transmission or scanning electron microscope, measuring the diameter of 50 fibers, and then calculating the arithmetic average thereof. The average fiber diameter is applicable to carbon fibers and the like.

[0070] The "active material" refers to a material that is responsible for an oxidation-reduction reaction that occurs in a lithium ion secondary battery.

[0071] The "coating density" is the mass of the active material per unit area (cm 2 ) coated on the current collector (unit: mg).

[0072] "Volume of electrolyte" refers to the total volume of an electrolyte solution or a solid electrolyte containing solutes. The unit is mL.

[0073] "Initial discharge capacity" refers to the 3rd discharge capacity unless otherwise specified.

[0074] <Measurement method>

[0075] "Powder resistivity" is measured using an automatic powder resistivity analyzer (MCP-PD600 manufactured by Nippon Denshoku Analysis & Technology Corp.) for a granular measurement sample (obtained by setting 1 g of a measurement object composed of particles in a 20 mm probe unit and compressing it with a load of 20 kN to harden it), in a normal temperature and humidity environment (temperature: 23°C, relative humidity: 50%), using a four-probe method (electrode diameter: 3 mm). The unit is Ω·cm.

[0076] "Amount of each element" is each measured by the method described in the examples. For example, it is applicable to sulfur, carbon, metals including iron, hydrogen, nitrogen, and the like.

[0077] "Particle size distribution" is measured using a laser diffraction / scattering type particle size distribution analyzer (Particle Size Distribution Analyzer PSA1090L manufactured by Anton Paar GmbH) using water as a dispersion medium.

[0078] "Median particle size d50" is the cumulative 50% particle size by volume (unit: μm) in the particle size distribution.

[0079] Hereinafter, the electrode active material, the electrode, and the lithium-ion secondary battery of the present embodiment will be described.

[0080] <Electrode active material>

[0081] The electrode active material of the present embodiment is an electrode active material composed of particles, the electrode active material containing: an organic sulfur compound; and a metal compound containing at least one metal selected from iron, molybdenum, vanadium, and titanium, wherein the powder resistivity (unit: Ω·cm) of the particles is less than a predetermined value, and the ratio of the sulfur content (unit: mass%) in the electrode active material to the powder resistivity is equal to or greater than a predetermined value. The organic sulfur compound and the metal compound in the electrode active material of the present embodiment are formed by reacting an organic compound, a raw material metal compound, and sulfur as raw materials thereof by the following calcination. Furthermore, when the raw material metal compound is a raw material iron compound, the presence of iron disulfide as the metal compound is confirmed.

[0082] (Amount of each element)​

[0083] The amount of sulfur element, the amount of carbon element, the amount of hydrogen element, the amount of nitrogen element, and the amount of metal element as shown below are the amounts of each element contained in the electrode active material. Further, when the electrode active material contains an iron compound, it is based on the knowledge that iron disulfide is contained as the iron compound based on a comparison of the peak distribution of the diffraction intensity of iron disulfide (pyrite) obtained by X-ray diffraction measurement.

[0084] <<Amount of sulfur element>>

[0085] From the viewpoint of improving the performance of the electrode and / or battery, the amount of sulfur element in the electrode active material is preferably greater than 45.0 mass%, more preferably greater than 50.0 mass%, further preferably greater than 55.0 mass%, further preferably greater than 60.0 mass%. There is no particular limitation on the upper limit of the amount of sulfur element, but it is usually 80 mass%, or it can be 70 mass% or 65 mass%.

[0086] <<Amount of carbon element>>

[0087] From the viewpoint of improving the performance of the electrode and / or battery, the amount of carbon element is preferably greater than 5.0 mass%, more preferably greater than 10.0 mass%, further preferably greater than 15.0 mass%. On the other hand, the amount of this element is preferably less than 30.0 mass%, more preferably less than 25.0 mass%, further preferably less than 23.0 mass%.

[0088] <<Amount of hydrogen element>>

[0089] Hydrogen (H) in the organic compound is changed to hydrogen sulfide by reacting with sulfur by calcination, and is released to the outside of the system. Therefore, the amount of hydrogen element in the electrode active material is preferably less than 1.0 mass%, more preferably less than 0.7 mass%, further preferably less than 0.5 mass%. When the amount is less than 1.0 mass%, it tends to indicate that the calcination (sulfidation reaction) is sufficient. Therefore, in this case, the charge and discharge capacity tends to be improved.

[0090] <<Amount of nitrogen element>>

[0091] If a nitrogen source is not used as a raw material, the amount of nitrogen element in the electrode active material (unit: mass%) can be 0 mass%. For example, in the case of preparing a raw material by a wet (WET) method, if a solvent containing a nitrogen atom is used as a solvent thereof, the nitrogen element can be detected.

[0092] <<Amount of metal element>>

[0093] From the viewpoint of improving the electrode and / or battery performance, the amount of the metal element in the electrode active material (unit: mass%) is preferably greater than 10.0 mass%, more preferably greater than 15.0 mass%, further preferably greater than 20.0 mass%, while the amount of the metal element is preferably less than 30 mass%, more preferably less than 25.0 mass%, further preferably less than 24.0 mass%.

[0094] (Powder resistivity)

[0095] In the electrode active material composed of the predetermined particles according to the present embodiment, the powder resistivity of the particles is less than 1.0 x 10 3 Ω·cm. When the powder resistivity is 1.0 x 10 3 Ω·cm or greater, the improvement in the electrode and / or battery performance cannot be achieved.

[0096] The powder resistivity is preferably less than 500, more preferably less than 300, further preferably less than 150, further preferably less than 111, further preferably less than 100, further preferably less than 72, further preferably less than 50, further preferably less than 30, further preferably less than 10. Further, the lower the powder resistivity, the more preferable it is, and it is not meaningful to set a lower limit, but as a reference value, it can be assumed to be about 1.

[0097] The powder resistivity is appropriately adjusted by changing the kind or amount of the organic compound, the raw material metal compound, and sulfur as raw materials, or the kind or amount of the carbon material as an optional component.

[0098] (Inequality (1))

[0099] A S and R ρ satisfy the following inequality, where A S represents the sulfur content (unit: mass%) in the electrode active material according to the present embodiment, and R ρ represents the powder resistivity. When the following inequality is not satisfied, the sulfur content is too low or the powder resistivity is too high, and thus the improvement in the electrode and / or battery performance cannot be achieved.

[0100] (1) A S / R ρ ≥ 0.05

[0101] The right side of Inequality (1) is preferably 0.10, more preferably 0.50, further preferably 0.56, further preferably 0.80, further preferably 0.86, further preferably 1.00, further preferably 3.00, further preferably 5.00, further preferably 6.00, further preferably 6.70. Further, the higher the value on the left side of Inequality (1), the more preferable it is, and it is not meaningful to set an upper limit, but as a reference value, it can be assumed to be about 20.00.

[0102] (Median particle diameter)

[0103] The electrode active material of the present embodiment is composed of particles, and the size of the particles is suitable for manufacturing an electrode. From the viewpoint of improving the performance of the electrode and / or the battery, the particle diameter of the electrode active material is preferably in the range of about greater than 1.0 μm and less than 40.0 μm in terms of the median particle diameter (median particle diameter d50). The median particle diameter is more preferably greater than 1.5 μm, further preferably greater than 2.0 μm, further preferably greater than 3.0 μm. In addition, the median particle diameter is more preferably less than 30.0 μm, further preferably less than 25.0 μm, further preferably less than 20.0 μm, further preferably less than 15.0 μm, further preferably less than 10.0 μm, further preferably less than 8.0 μm. The median particle diameter can be measured by the method described in the Example section below.

[0104] (Other components)

[0105] The electrode active material of the present embodiment can contain the materials described in the manufacturing method section below in the same manner as described in the section.

[0106] <Electrode>

[0107] The electrode of the present embodiment is an electrode containing the electrode active material described above. The electrode is preferably an electrode obtained by mixing the particulate electrode active material containing the organic sulfur compound and the carbon material with necessary other electrode materials (for example, a conductive aid, a binder, and the like) and coating the mixture on a current collector.

[0108] The lithium ion secondary battery electrode of the present embodiment can be configured in the same manner as described in the manufacturing method section below by using the materials described in the section. That is, when the above-described lithium ion secondary battery electrode is used as a positive electrode, a positive electrode for a lithium ion secondary battery can be formed in the same manner as described in the manufacturing method section below by using the conductive aid, the binder, the current collector, and the like described in the section; when the above-described lithium ion secondary battery electrode is used as a negative electrode, a negative electrode for a lithium ion secondary battery can be formed in the same manner as described in the manufacturing method section below by using the conductive aid, the binder, the current collector, and the like described in the section. Therefore, the description in the manufacturing method section below can be regarded as a description of the electrode for a lithium ion secondary battery of the present embodiment.

[0109] (Inequality (2))

[0110] Preferably, the electrode of the present embodiment includes a current collector having a metal foil, and D and A satisfy the following inequality, S satisfy the following inequality,

[0111] (2) D x AS >150

[0112] wherein D represents the coating density of the electrode active material on the current collector, in mg / cm 2 .

[0113] The right side of inequality (2) is more preferably 190, further preferably 193, further preferably 195, further preferably 200, further preferably 210, further preferably 220, further preferably 230, further preferably 240, further preferably 242, further preferably 244. Furthermore, the higher the value on the left side of inequality (2) is, the more preferable it is, and it is not meaningful to set an upper limit, but as a reference value, it can be assumed to be about 1000.

[0114] (coating density (in mg / cm 2 )

[0115] The coating density (in mg / cm 2 ) of the electrode active material on the electrode is preferably greater than 2.50 mg / cm 2 , more preferably greater than 3.00 mg / cm 2 , further preferably greater than 3.50 mg / cm 2 , further preferably greater than 3.80 mg / cm 2 , further preferably greater than 3.90 mg / cm 2 . The higher the value of the coating density is, the more preferable it is, and it is not meaningful to set an upper limit, but as a reference value, it can be assumed to be about 15.0 mg / cm 2 .

[0116] (inequality (3))

[0117] Preferably, the electrode of the present embodiment includes a current collector having a metal foil, and D, T, and A S satisfy the following inequality:

[0118] (3) D x A S / T > 10.0

[0119] wherein D represents the coating density of the electrode active material on the current collector (in mg / cm 2 ), and T represents the thickness of the metal foil (in μm).

[0120] The right side of inequality (3) is more preferably 11.0, further preferably 11.3, further preferably 11.4, further preferably 12.0, further preferably 13.0, further preferably 14.0, further preferably 14.2, further preferably 14.3. The value of the left side of inequality (3) is more preferable the higher, and there is no meaning to set an upper limit, but it is a reference value. It can be assumed to be about 100.

[0121] (thickness of metal foil (T))

[0122] The thickness T of the metal foil (unit: pm) is preferably 5 pm or more, more preferably 10 pm or more. On the other hand, T is preferably 40 pm or less, more preferably 30 pm or less, further preferably 25 pm or less.

[0123] (charge / discharge capacity)

[0124] The electrode of the present embodiment exhibits an excellent charge / discharge capacity. The third discharge capacity (DC3), that is, the initial discharge capacity, is the discharge capacity when three charge / discharge cycles are performed after the preparation of the electrode and the battery, with a discharge termination voltage of 1.0 V and a charge termination voltage of 3.0 V (that is, when the charge / discharge cycles are repeated as the first discharge, the first charge, the second discharge, the second charge, the third discharge, and the third charge). In the case of discharge, when the discharge is performed at a constant current (the current value corresponds to 50 mA / 1 g of positive electrode active material), the voltage of 3.0 V eventually decreases to 1.0 V. The total time (unit: h) required for the measurement voltage to decrease from 3.0 V to 1.0 V is multiplied by the applied current (unit: mA) to obtain the capacity (unit: mAh), and then divided by the weight of the active material to obtain the specific capacity (unit: mAh / g). On the other hand, in the case of charge, since the charge is performed at a constant current, the voltage is reversely increased, and when the voltage eventually reaches 3.0 V, the charge is terminated. The same applies to the tenth discharge capacity described below.

[0125] [initial discharge capacity (DC3)]

[0126] When the electrode of the present embodiment is used as a positive electrode, the initial discharge capacity (DC3) (unit: mAh / g) is preferably greater than 400 mAh / g. The initial discharge capacity is more preferably greater than 450 mAh / g, further preferably greater than 500 mAh / g, further preferably 514 mAh / g or greater, further preferably greater than 550 mAh / g, further preferably greater than 600 mAh / g, further preferably greater than 650 mAh / g, further preferably greater than 700 mAh / g, further preferably greater than 710 mAh / g. There is no particular limitation on the upper limit of the initial discharge capacity, and the higher the better. Therefore, the upper limit of the initial discharge capacity is not particularly meaningful, but only as a reference value, it can be generally assumed to be about 1000 mAh / g.

[0127] [10th discharge capacity (DC 10 ) ]

[0128] When the electrode of the present embodiment is used as a positive electrode, the discharge capacity at the time of repeating charge and discharge 10 times (i.e., the 10th discharge capacity (DC 10 , unit: mAh / g) is preferably greater than 350 mAh / g. The discharge capacity is more preferably greater than 400 mAh / g, further preferably 478 mAh / g or greater, further preferably greater than 500 mAh / g, further preferably 536 mAh / g or greater, further preferably greater than 600 mAh / g, further preferably greater than 700 mAh / g, further preferably 710 mAh / g or greater. There is no particular limitation on the upper limit of the discharge capacity, and the higher the better. Therefore, the upper limit of the discharge capacity is not particularly meaningful, but only as a reference value, it can be generally assumed to be about the value of the initial discharge capacity or about 900 mAh / g.

[0129] Further, when the electrode of the present embodiment is used as a positive electrode, if the performance related to the discharge capacity of the positive electrode is sufficiently exerted within the range of common knowledge that the lithium ion secondary battery can be used for a long time (i.e., Li is not depleted) by measuring using a negative electrode and an electrolyte, the discharge capacity at the 3rd or 10th time is determined by the configuration of the positive electrode. For example, for the negative electrode, the amount of lithium can be preferably 2 times or more, more preferably 5 times or more, further preferably 10 times or more, and further preferably 50 times or more (mol amount) of the amount (mol amount) of sulfur in the positive electrode. Further, for example, for the electrolyte, when the amount (microliters) of the electrolyte solution is preferably 10 times or more, more preferably 20 times or more, and further preferably 50 times or more of the amount (mg) of sulfur in the positive electrode, the discharge capacity of the positive electrode can be sufficiently exerted, resulting in a longer battery life. On the other hand, in view of the energy density of the battery, the amount of the electrolyte solution is preferably small. For example, the amount (microliters) of the electrolyte solution is preferably 5 times or less, more preferably 3 times or less, and further preferably 1 times or less of the amount (mg) of sulfur in the positive electrode. Here, the volume V (mL) of the electrolyte represents the total volume of the electrolyte solution including solutes. Further, the electrolyte can be in the form of an electrolyte solution or in the form of a solid (solid electrolyte), or a combination thereof can be used.

[0130] (Application)

[0131] The electrode for lithium ion secondary battery of the present embodiment can be used as a positive electrode or a negative electrode of a lithium ion secondary battery. Further, the electrode for lithium ion secondary battery of the present embodiment is preferably used as a positive electrode of a lithium ion secondary battery.

[0132] <Li-ion secondary battery>

[0133] The lithium ion secondary battery of the present embodiment is a lithium ion secondary battery containing the above-described electrode.

[0134] The lithium ion secondary battery of the present embodiment can be configured in the same manner as described in the following manufacturing method section by using the materials described in the section. That is, when the above-described electrode for lithium ion secondary battery is used as a positive electrode, a negative electrode, an electrolyte, a separator, and the like described in the following manufacturing method section can be used to be configured in the same manner as described in the section. On the other hand, when the above-described electrode for lithium ion secondary battery is used as a negative electrode, a positive electrode, an electrolyte, a separator, and the like described in the following manufacturing method section can be used to be configured in the same manner as described in the section. Therefore, the description in the following manufacturing method section can be regarded as a description of the present lithium ion secondary battery.

[0135] (Inequality (4))

[0136] Preferably, the lithium ion secondary battery of the present embodiment further contains an electrolyte, and D, V, and A S satisfies the following inequality (4),

[0137] (4) D x A S > 600

[0138] In the formula, V represents the volume of the electrolyte (unit: mL), D represents the coating density of the electrode active material on the current collector (unit: mg / cm 2 ).

[0139] The right side of inequality (4) is more preferably 650, further preferably 700, further preferably 750, further preferably 800, further preferably 850, further preferably 860, further preferably 865. The value of the left side of inequality (4) is more preferably higher, and there is no meaning to set an upper limit, but as a reference value, it can be assumed to be about 1500.

[0140] (Volume of electrolyte V)

[0141] Since the range of the volume V (mL) of the electrolyte varies depending on the size of the battery, it is not generally limited, and only the minimum amount that can exert the performance of the electrode active material and make the battery satisfactorily operate is used. As a reference value, for example, in the case of the coin-type battery shown in the examples, the volume is preferably 0.1 mL or more, more preferably 0.12 mL or more, further preferably 0.15 mL or more. On the other hand, V is preferably 0.40 mL or less, more preferably 0.30 mL or less, further preferably 0.28 mL or less, further preferably 0.25 mL or less.

[0142] (Application)

[0143] The lithium ion secondary battery of the present embodiment can be used as a lithium ion secondary battery having improved comprehensive performance of charge-discharge capacity, capacity retention rate, and energy density, and can be used as a battery for a portable information terminal (such as a smartphone, a notebook computer, and the like), a portable electronic device (such as a music player, a digital camera, and the like), and a medical device, and can be used as a battery for a next-generation clean energy automobile (such as a hybrid electric vehicle (HEV), an electric vehicle (EV), a plug-in hybrid electric vehicle (PHEV), and the like).

[0144] <Manufacturing method>

[0145] The manufacturing method of the electrode active material, the electrode, and the lithium ion secondary battery of the present embodiment will be described below in order.

[0146] (Manufacture of electrode active material)

[0147] The electrode active material of the present embodiment can be produced, for example, by the following steps: (1) a step of mixing sulfur, an organic compound, and a raw material metal compound to obtain a calcination raw material; (2) a step of calcining the calcination raw material to obtain a calcination product; and (3) a step of pulverizing the calcination product into particles to obtain an electrode active material.

[0148] [Raw material]

[0149] The raw material will be described below.

[0150] [Organic compound]

[0151] The organic compound is not particularly limited as long as it is a compound containing at least carbon and hydrogen atoms and absorbs sulfur to form an organic sulfur compound when calcined with sulfur in a non-oxidizing hot atmosphere. In addition, the organic compound can be an organic compound containing a hetero atom such as a nitrogen atom, a sulfur atom, or the like. Specific examples of the organic compound include, for example, a polymer of an unsaturated chain hydrocarbon-based monomer, a condensed compound of a substituted aromatic hydrocarbon and sulfur chloride, and the like. The organic compound can be used alone or in combination with two or more thereof.

[0152] [Polymer of unsaturated chain hydrocarbon-based monomer]

[0153] Examples of the polymer of an unsaturated chain hydrocarbon-based monomer include, for example, a resin such as an acrylic resin, and the like. In addition, examples of the polymer of an unsaturated chain hydrocarbon-based monomer include diene-based rubber, and the like. One or more polymers of an unsaturated chain hydrocarbon-based monomer can be used.

[0154] Examples of the acrylic resin include, for example, a polymer obtained by polymerization of monomers containing at least one of an acrylate compound represented by the following Chemical Formula (1); a polymer obtained by polymerization of monomers consisting of only at least one of an acrylate compound represented by the following Chemical Formula (1); a polymer obtained by polymerization of monomers containing at least one of an acrylate compound represented by the following Chemical Formula (1) and at least one of a diacrylate compound represented by the following Chemical Formula (2); and a polymer obtained by polymerization of monomers consisting of only at least one of an acrylate compound represented by the following Chemical Formula (1) and at least one of a diacrylate compound represented by the following Chemical Formula (2), selected from at least one of the following. One or more acrylic resins can be used.

[0155] CH2=C(R 11 )COOR 12 (1)

[0156] (wherein, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group.)

[0157] CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2(2)

[0158] (wherein R 21 and R 22 are the same or different, each being a hydrogen atom or a methyl group; Y is a straight-chain hydrocarbon group, which can have at least one substituent selected from a hydroxyl group and an alkyl group; the carbon skeleton constituting the hydrocarbon group can have an ether bond formed with an oxygen atom, provided that, when there are two or more ether bonds, there are always two or more carbon atoms interposed between any adjacent oxygen atoms.)

[0159] In Chemical Formula (1), R 11 is preferably a methyl group, and R 12 is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, of which, more preferably, a methyl group, a n-butyl group, an iso-butyl group, or a t-butyl group. Examples of the compound represented by Chemical Formula (1) include, for example, (meth) methyl acrylate, (meth) butyl acrylate, and the like, of which, more preferably, methyl methacrylate and butyl methacrylate. Here, “(meth) acrylate” in (meth) methyl acrylate and (meth) butyl acrylate means “acrylate” or “methacrylate” (also applicable hereinafter). A further preferred example of the compound represented by Chemical Formula (1) is butyl methacrylate.

[0160] In Chemical Formula (2), R 21 and R 22 are each preferably a methyl group. The number of carbon atoms in the hydrocarbon group (straight-chain) Y is preferably 2 to 6, more preferably 2 or 3. The number of substituents in Y is preferably 1 to 4, more preferably 1 or 2. As the substituents of Y, one or more substituents selected from a hydroxyl group and an alkyl group having 1 to 4 carbon atoms are preferred, and as the alkyl group having 1 to 4 carbon atoms, a methyl group is preferred. When the carbon skeleton of Y has an ether bond formed with an oxygen atom, for example, the portion corresponding to –Y–O– is preferably represented by the following Chemical Formula (3) (provided that the substituents in Y are not considered in Chemical Formula (3)):

[0161] –(CH2) l –(CH2CH2O) m –(CH2CH2CH2O) n –(3)

[0162] (wherein l is 0 to 6, m is 0 to 3, and n is 0 to 2. Of these, l, m, and n cannot be 0 at the same time.)

[0163] In Chemical Formula (3), preferably, 1 is 1, 2, 3, 4, 5, or 6, and m and n are 0; m is 1, 2, or 3, and 1 and n are 0; or, n is 1 or 2, and 1 and m are 0.

[0164] Examples of the compound represented by Chemical Formula (2) include, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, and the like. Among them, ethylene glycol dimethacrylate is preferable.

[0165] Preferred examples of the acrylic resin include a homopolymer of (meth)acrylic acid methyl ester, a homopolymer of (meth)acrylic acid butyl ester, a copolymer of (meth)acrylic acid methyl ester and ethylene glycol di(meth)acrylate, a copolymer of (meth)acrylic acid butyl ester and ethylene glycol di(meth)acrylate, and the like. Among them, as the acrylic resin, a methacrylate-based acrylic resin is preferable. More preferred examples of the acrylic resin include a copolymer of methacrylic acid methyl ester and ethylene glycol dimethacrylate.

[0166] In the present embodiment, the acrylic resin is preferably in the form of fine particles. Here, the fine particles refer to particles having a particle diameter of 300.0 μm or less. The particle diameter is preferably 270.0 μm or less, more preferably 200.0 μm or less, further preferably 100.0 μm or less, further preferably 50.0 μm or less, further preferably 20.0 μm or less, further preferably 15.0 μm or less, further preferably 13.0 μm or less, further preferably 10.0 μm or less, further preferably 6.0 μm or less. On the other hand, the lower limit of the particle diameter is not particularly limited, but is typically, for example, 0.1 μm or more, preferably 1.0 μm or more. The particle diameter is a value (median particle diameter) measured by a particle size distribution analyzer PSA1090L manufactured by Anton Paar GmbH.

[0167] The acrylic resin can be a spherical fine particle or a porous fine particle. When the acrylic resin is porous, the oil absorption amount thereof is preferably 100 mL / 100 g or more, more preferably 110 mL / 100 g or more, further preferably 120 mL / 100 g or more, further preferably 130 mL / 100 g or more, further preferably 140 mL / 100 g or more. The oil absorption amount is a value measured in accordance with JIS K5101-13-2:2004. More specifically, it can be measured by the method described in paragraph 0069 of JP 2017-88501 A.

[0168] The Mw of the acrylic resin is not particularly limited as long as the acrylic resin has the above structure. The Mw of the acrylic resin is usually in the range of 2000 to 1500000. The Mw is a value determined by gel permeation chromatography (GPC) (calibrated with polystyrene).

[0169] The acrylic resin is commercially available or can be produced by a conventional method within the knowledge of those skilled in the art. Examples of the commercially available acrylic resin include, for example, those manufactured by Sekisui Kasei Co., Ltd.

[0170] Examples of the diene-based rubber include, for example, natural rubber, isoprene rubber, butadiene rubber (such as high-cis polybutadiene rubber), and the like. The diene-based rubber is commercially available or can be produced by a conventional method within the knowledge of those skilled in the art.

[0171] <<Condensate of substituted aromatic hydrocarbon and chlorinated sulfur>>

[0172] Examples of the condensate of substituted aromatic hydrocarbon and chlorinated sulfur include a condensate of alkylphenol and chlorinated sulfur, and the like. Specific examples of the condensate of alkylphenol and chlorinated sulfur include, for example, TACKIROL V200, TS3108, and TS3109 manufactured by NOKA CHEMICAL CO., LTD., Vultac 3 manufactured by Arkema, and the like. One or more condensates of substituted aromatic hydrocarbon and chlorinated sulfur can be used.

[0173] <<Raw material metal compound>>

[0174] As the raw material metal compound, the following raw material metal compound can be used.

[0175] <<Raw material iron compound>>

[0176] Examples of the raw material iron compound include an iron compound containing a divalent or trivalent iron ion, but as long as it is decomposed and reacts with sulfur to produce iron disulfide in the calcination process, various compounds can be used without particular limitation. Examples of the raw material iron compound include an acid salt of iron, a complex of iron, and the like. Examples of the acid salt of iron include both an organic acid salt of iron and an inorganic acid salt of iron. On the other hand, examples of the complex of iron include a neutral iron complex and an iron complex salt (a complex salt of iron). Among them, the organic acid salt of iron, the inorganic acid salt of iron, or the neutral iron complex is preferred. One or more iron compounds can be used.

[0177] Examples of the organic acid salt of iron include, for example, a salt of divalent iron (Fe 2+ ) and an organic acid, a salt of trivalent iron (Fe 3+) and the like. Among them, a salt of divalent iron and an organic acid is preferable. The organic acid is not particularly limited, and includes an organic acid having a carboxyl group (-COOH), an organic acid having a sulfonic acid group (-SO3H), and the like. Among them, an organic acid having a carboxyl group is preferable. Specific examples of the organic acid include a fatty acid, oxalic acid, tartaric acid, citric acid, malic acid, succinic acid, and the like. Specific examples of the fatty acid include, for example, a fatty acid having 1 or more and 6 or less carbon atoms, such as acetic acid, propionic acid, butyric acid, and the like. Among them, acetic acid, oxalic acid, and the like are preferable. Preferred examples of the organic acid salt of iron include ferrous acetate (II) and ferrous oxalate (II), and the like. They can be hydrates. One or more kinds of the organic acid salt of iron can be used.

[0178] Examples of the inorganic acid salt of iron include, for example, a salt of divalent iron (Fe 2+ ) and an inorganic acid, a salt of trivalent iron (Fe 3+ ) and an inorganic acid, and the like. Specific examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, and the like. Among them, nitric acid and the like are preferable. Preferred examples of the inorganic acid salt of iron include ferrous chloride (II), ferric chloride (III), ferrous sulfate (II), ferric sulfate (III), ferrous nitrate (II), ferric nitrate (III), and the like. They can be hydrates. One or more kinds of the inorganic acid salt of iron can be used.

[0179] Examples of the complex of iron include a complex of divalent iron (Fe 2+ ), a complex of trivalent iron (Fe 3+ ), and the like. The complex of iron can be in the form of a neutral complex or in the form of a complex salt. The ligand coordinated to the iron ion is not particularly limited, and examples thereof include, for example, a halogen atom (such as a chlorine atom, a bromine atom, and the like), a cyano group, a bis-cyclopentadienyl group, N,N'-bis(salicylidene)ethylenediamine, and the like. Examples of the complex of iron include, for example, potassium hexacyanoferrate (II) ([Fe(CN)6]K4), potassium hexacyanoferrate (III) ([Fe(CN)6]K3), sodium tetrachloroferrate (III) ([FeCl4]Na), bis-cyclopentadienyl iron (II) (ferrocene), N,N'-bis(salicylidene)ethylenediamine chloroferrate (III) (N,N'-bis(salicylidene)ethylenediaminato iron (III) chloride), and the like. One or more kinds of the complex of iron can be used.

[0180] <Raw material molybdenum compound>

[0181] Examples of the raw material molybdenum compound include molybdenum trioxide (VI), sodium molybdate (VI), hexaammonium heptamolybdate (VI), diammonium molybdate (VI), calcium molybdate (VI), molybdic acid (VI), phosphomolybdic acid (VI), molybdenum disulfide (VI), and the like. One or more kinds of the molybdenum compound can be used.

[0182] <Raw material vanadium compound>

[0183] Examples of the raw material vanadium compound include vanadium pentoxide (V), ammonium metavanadate (V), vanadium oxytrichloride (V), sodium metavanadate (V), potassium vanadate (V), sodium vanadate (V), vanadium tetrachloride (IV), vanadyl sulfate (IV), vanadyl dichloride (IV), vanadium oxide (IV), vanadium trichloride (IV), vanadium oxide (III), vanadium trioxide (IV, V), and the like. One or more vanadium compounds can be used.

[0184] <Raw material titanium compound>

[0185] Examples of the raw material titanium compound include titanium oxide, titanium dioxide, titanium trioxide, titanium tetrachloride, and the like. One or more titanium compounds can be used.

[0186] <Content of raw material metal compound>

[0187] From the viewpoint of improving the performance of the electrode and / or the battery, the content of the raw material metal compound in the calcination raw material is preferably 50 parts by mass or more and 300 parts by mass or less, based on 100 parts by mass of the organic compound. 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 100 parts by mass or less.

[0188] <Median particle diameter of raw material metal compound>

[0189] When the raw material metal compound is used as the calcination raw material, it is preferably previously pulverized. The median particle diameter (d50) of the metal compound is preferably 12.00 μm or less, more preferably 10.00 μm or less, more preferably 8.00 μm or less, further preferably 6.00 μm or less, further preferably 4.00 μm or less, further preferably 3.00 μm or less. On the other hand, the lower limit of the median particle diameter is not particularly limited, but is usually about 0.10 μm or more, and can be about 1.00 μm or about 2.00 μm. The median particle diameter can be measured by the above-described method.

[0190] <Specific surface area of raw material metal compound>

[0191] The specific surface area of the raw material metal compound is preferably 1.0 m 2 / g or more, more preferably 2.0 m 2 / g or more, further preferably 3.0 m 2 / g or more, further preferably 4.0 m 2 / g or more, further preferably 4.5 m 2 / g or more. On the other hand, the upper limit of the specific surface area is not particularly limited, but is usually about 40.0 m 2 / g or less, and can be about 20.0 m 2 / g or less, or about 10.0 m 2 / g or less. The specific surface area can be measured by a full-automatic specific surface area analyzer Macsorb (HM-model 1201, manufactured by MOUNTECH Co., Ltd.).

[0192] The raw material metal compound having the median particle diameter or the specific surface area as described above can be manufactured by a conventional method, for example, by pulverizing the raw material metal compound using a pulverizer. As such a pulverizer, for example, a pulverizer manufactured by Nikkiso Analytical Instruments Co., Ltd. (for example, JFC-2000 or the like) can be used.

[0193] <<Sulfur>>

[0194] As the sulfur, sulfur in various forms such as powdered sulfur, insoluble sulfur, precipitated sulfur, colloidal sulfur, and the like can be used. Among them, precipitated sulfur and colloidal sulfur are preferred. One or more kinds of sulfur can be used.

[0195] From the viewpoint of improving the performance of the electrode and / or the battery, the content of sulfur in the calcination raw material is preferably more than 50 parts by mass, more preferably more than 100 parts by mass, further preferably more than 300 parts by mass, further preferably more than 400 parts by mass, further preferably 500 parts by mass or more, based on 100 parts by mass of the organic compound. When the content is more than 50 parts by mass, there is a tendency that the charge and discharge capacity and the cycle characteristics can be improved. On the other hand, there is no particular upper limit to the content of sulfur, but it is preferably less than 1000 parts by mass, more preferably less than 900 parts by mass, further preferably less than 800 parts by mass, further preferably less than 700 parts by mass. When the content is less than 1000 parts by mass, there is a tendency that there is an advantage in terms of cost. Furthermore, in the present specification, the term "cycle characteristics" means a characteristic in which the charge and discharge capacity of a secondary battery remains unchanged despite repeated charge and discharge. Therefore, the cycle characteristics of a secondary battery in which the degree of decrease in the charge and discharge capacity is high and the capacity retention rate is low are poor with repeated charge and discharge, and on the contrary, the cycle characteristics of a secondary battery in which the degree of decrease in the charge and discharge capacity is low and the capacity retention rate is high are excellent.

[0196] As the sulfur, any one of various allotropes can be used, but those containing S8 sulfur which is a solid at normal temperature and pressure are preferred, and S8 sulfur alone is more preferred.

[0197] <<Other materials>>

[0198] The raw material can appropriately include other materials commonly used in the art as needed. Examples of such materials include carbon materials.

[0199] <<Carbon materials>>

[0200] In the electrode active material of the present embodiment, the carbon material is preferably a carbon material having a graphite structure. Furthermore, the carbon material is preferably electrically conductive. Examples of the carbon material can include, for example, porous carbon materials (e.g., activated carbon, etc.), graphite, carbon black, acetylene black, and Ketjen black, and carbon fiber-based materials (e.g., carbon fiber, vapor grown carbon fiber (VGCF), carbon nanotube (CNT), carbon nanofiber, etc.); and other forms of nanocarbon materials (e.g., graphene, fullerene, etc.) other than carbon fiber. Among these, carbon fiber-based materials (e.g., carbon fiber, vapor grown carbon fiber (VGCF), CNT, carbon nanofiber, etc.) are preferable, and CNT is particularly preferable. One or more carbon materials can be used.

[0201] When the carbon material is carbon fiber, it is preferable that, as a form constituting the carbon fiber, the average fiber length be equal to or greater than a predetermined value, and the average fiber diameter be equal to or less than a predetermined value, from the viewpoint of improving the performance of the electrode and / or the battery. This is because it is thought that the electrical conductivity of the electrode active material can be improved. The average fiber length is preferably greater than 1 μm, more preferably greater than 1.5 μm, and further preferably 2 μm or greater. There is no particular limitation on the upper limit of the average fiber length, and it can be 100 μm, 50 μm, or 20 μm. Furthermore, the average fiber diameter is preferably less than 100 nm, more preferably less than 50 nm, and further preferably less than 10 nm. There is no particular limitation on the lower limit of the average fiber diameter, but it is generally about 1 nm.

[0202] The aspect ratio of the carbon material is preferably greater than 10, more preferably greater than 100, and further preferably greater than 1,000, and it is preferably less than 100,000, more preferably less than 50,000, and further preferably less than 10,000.

[0203] From the viewpoint of the effects of the present application, the specific surface area of the carbon material is preferably 400 m 2 / g or more, and preferably 2400 m 2 / g or less. The specific surface area is more preferably 500 m 2 / g or more, and further preferably 600 m 2 / g or more. On the other hand, the specific surface area is more preferably 2000 m 2 / g or less, and further preferably 1800 m 2 / g or less. Furthermore, the specific surface area is measured by the BET multipoint method.

[0204] From the viewpoint of the effects of the present application, the G / D ratio of the carbon material is preferably 10 or greater. The G / D ratio is more preferably 20 or greater, further preferably 30 or greater, and further preferably 40 or greater. On the other hand, there is no particular limitation on the upper limit of the G / D ratio, but if it is not less than 90, it can be said that the carbon material has few defects. Here, the G / D ratio is the ratio of the representative Raman shift peak in the Raman spectrum of the carbon material, and more specifically, it is the ratio of the G band peak derived from the graphite structure to the D band peak derived from defects. In addition, the Raman spectrum is measured using RAMAN touch manufactured by Nanophoton (excitation wavelength λ = 532 nm, grating: 1200 gr / mm, resolution: 1.2 cm -1 ).

[0205] From the viewpoint of the effects of the present application, the amount of metal impurities in the carbon material is preferably 5% by mass or less. The amount of metal impurities is preferably 3% by mass or less, further preferably 2% by mass or less, and further preferably 1% by mass or less. The amount of metal impurities is preferably as small as possible, but for example, 0.1% by mass is sufficient as a small amount of metal impurities. In addition, the metal impurities are measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0206] From the viewpoint of improving the performance of the electrode and / or the battery, the content of the carbon material in the calcination raw material is preferably less than 5 parts by mass, based on 100 parts by mass of the organic compound. The content is more preferably less than 1 part by mass, and further preferably less than 0.5 parts by mass. On the other hand, the content is preferably greater than 0.05 parts by mass, more preferably greater than 0.07 parts by mass, and further preferably 0.10 parts by mass or greater.

[0207] (Manufacturing steps)

[0208] [Step of mixing (1)]

[0209] The mixing step is a step of preparing the calcination raw material. The mixing step can be performed by mixing sulfur, the organic compound, the raw material metal compound, and other optional components (as needed).

[0210] The above mixing can be performed by a conventional method, and there is no particular limitation as long as it is a method in which these components are sufficiently mixed. In the present embodiment, at least the following mixing by wet method or mixing by dry (DRY) method to be mentioned below can be cited as a preferred mixing method.

[0211] <<Wet method>>

[0212] In the present embodiment, the wet method includes: for the preparation of the raw material,

[0213] (a-1) a step of adding an organic compound and a raw material metal compound to a solvent such as an organic solvent, to obtain a mixture,

[0214] (a-2) a step of removing the solvent from the mixture, to obtain a dry mixture, and

[0215] (a-3) a step of mixing the dry mixture and sulfur.

[0216] In step (a-1), the method of adding the organic compound and the raw material metal compound to the organic solvent is not particularly limited, as long as a mixture can be obtained by mixing them. For example, (1) the organic compound and the raw material metal compound can be mixed by being added to the organic solvent at the same time; or (2) one of them can be mixed by being added to the organic solvent first, and then the remainder can be further added and mixed, in which case the combination of the raw material added first and the combination of the raw material added later are not particularly limited.

[0217] In step (a-1), as the organic solvent, an organic solvent commonly used in the field can be used, examples of which include, for example, N-methyl-2-pyrrolidone, N,N-dimethylformamide, an alcohol, hexane, water, acetone, an ether such as tetrahydrofuran, and the like. Furthermore, as the organic solvent, an organic solvent that dissolves the organic compound is preferred. This is because it contributes to good mixing. One or more of these solvents can be used.

[0218] Step (a-1) can be performed by stirring in a container such as a beaker.

[0219] In step (a-2), the removal of the organic solvent can be performed by a conventional method. For example, the removal can be performed by a drying method such as heat drying, reduced pressure drying, reduced pressure and heat drying, and the like, on the mixture in step (a-1).

[0220] Preferably, the dry mixture thus obtained is pulverized before the next step is performed. This is because, by this means, it is expected that the mixing in step (a-3) will be performed more appropriately.

[0221] In step (a-3), the mixing of the dry mixture and sulfur can be performed by a conventional method, examples of which can include, for example, a method of mixing using a blender, and the like.

[0222] When any component is used, the any component can be mixed in step (a-1). In this case, the order in which the raw material metal compound is added to the organic solvent is not particularly limited, and it can be added in any order, similarly to the other raw materials.

[0223] <<Dry process>>

[0224] In the present embodiment, the dry method includes: mixing the organic compound, the raw material metal compound, and sulfur (all in powder form),

[0225] (b-1) a step of mixing an organic compound, a raw material metal compound, and sulfur (all in powder form).

[0226] Here, the powder refers to each material being made into a state fine enough to be suitable for mixing for the purpose of the present application. The size of each particle constituting the powder is not particularly limited as long as mixing is appropriately performed, but is generally, for example, in the range of 1 μm or more and 40 μm or less. From the viewpoint of improving the performance of the electrode and / or the battery, the particle size (in terms of median particle diameter) is preferably 2 μm or more, more preferably 3 μm or more, further preferably 4 μm or more, and it is preferably 30 μm or less, further preferably 20 μm or less, further preferably 15 μm or less, further preferably 10 μm or less. The median particle diameter can be measured by the above-described method.

[0227] Mixing can be performed by a conventional method, for example, in the same manner as the mixing in step (a-3) described above. Furthermore, when an arbitrary component is added to the raw material, it can also be mixed together.

[0228] In both the wet method and the dry method, it is desirable to sufficiently mix the raw material in advance for the calcination.

[0229] The raw material thus obtained can be directly used in the next calcination step, or it can be formed into a pellet as needed, which can then be used in the next step.

[0230] [Calcination Step (2)]

[0231] The calcination step is a step of calcining the calcined raw material obtained above. Calcination can be performed by a conventional method, for example, by a method of heating the calcined raw material at a predetermined temperature increase rate until a predetermined temperature is reached, and maintaining it at the predetermined temperature for a predetermined time, and then naturally cooling it.

[0232] <<Non-Oxidizing Atmosphere>>

[0233] Calcination is preferably performed under a non-oxidizing atmosphere. The non-oxidizing atmosphere refers to an atmosphere substantially free of oxygen, for the purpose of suppressing oxidative deterioration and excessive pyrolysis of the constituent components. Specifically, it refers to an inert gas atmosphere (for example, nitrogen, argon, or the like), a sulfur gas atmosphere, an ammonia gas atmosphere, or the like. Thus, calcination can be appropriately performed, for example, in a quartz tube under an inert gas atmosphere.

[0234] <<Temperature Increase Rate>>

[0235] The heating rate is preferably in the range of, for example, 50°C / h or higher and 500°C / h or lower. The heating rate is preferably 80°C / h or higher, more preferably 100°C / h or higher, and even more preferably 120°C / h or higher. On the other hand, the heating rate is preferably 400°C / h or lower, even more preferably 300°C / h or lower, and even more preferably 200°C / h or lower. When the heating rate is within such a range, there is a tendency to easily achieve the goal of improving charge / discharge capacity and cycle characteristics.

[0236] <<Caking Temperature / Time>>

[0237] The roasting temperature refers to the temperature at which the raw material is heated and maintained for a certain period of time for roasting. The temperature is preferably within the range of greater than 250°C and less than 550°C. At temperatures greater than 250°C, there is a tendency to avoid incomplete sulfidation and prevent a decrease in the charge / discharge capacity of the target material. On the other hand, at temperatures less than 550°C, there is a tendency to prevent the decomposition of the raw material and to prevent a decrease in yield and charge / discharge capacity. More preferably, this temperature is greater than 300°C, even more preferably greater than 350°C, and even more preferably greater than 370°C. On the other hand, it is more preferably less than 500°C, and even more preferably less than 450°C.

[0238] From the perspective of improving electrode and / or battery performance, the roasting temperature in the roasting step is preferably higher than the temperature during the pyrolysis of the raw material metal compound.

[0239] The time for maintaining the roasting temperature can be appropriately set according to the type of raw material and the roasting temperature, but it is preferred to be, for example, more than 1 hour and less than 6 hours. When it is more than 1 hour, there is a tendency to fully roast the raw material, and when it is less than 6 hours, there is a tendency to prevent excessive pyrolysis of the constituent components.

[0240] <<Device>>

[0241] Firing can be achieved, for example, in a muffle furnace ( Figure 1 It can be implemented either directly or using a continuous process (such as a twin-screw extruder). When using a continuous process, there are advantages such as the ability to continuously produce sulfide electrode active materials through a series of operations, such as kneading, crushing and mixing raw materials while simultaneously calcining them in the process.

[0242] muffle furnace ( Figure 1 A furnace is a type of furnace separated by a hot plate or similar structure, preventing the heat source (heater) from being exposed inside the furnace and thus preventing sample contamination. Figure 1In this embodiment, the muffle furnace 1 has a heater 2 in the lower portion of the furnace, which is separated by a heat plate. A lid 3 is installed on the front surface (left end side in the figure) of the furnace, which makes the furnace have a structure in which the inside of the furnace can be kept in an atmosphere of an inert gas 4. A thermocouple (not shown) is connected to the lid, so that the temperature inside the furnace during calcination can be measured. In the furnace, two layers of trays 5 and 6 for rectangular stainless steel reaction containers for calcination of raw materials are installed in the upper and lower layers.

[0243] The inside of the furnace is configured so that a gas (for example, argon (Ar) gas or the like) can be continuously supplied into and discharged to the outside through a gas introduction pipe 7 and a gas discharge pipe 8. The gas discharge pipe 8 is connected to a collection tank 10 that contains an aqueous sodium hydroxide solution 9, and the exhaust gas discharged to the outside from the muffle furnace 1 through the gas discharge pipe 8 is discharged to the outside after passing through the aqueous sodium hydroxide solution 9 in the collection tank 10. Thus, even if the exhaust gas contains hydrogen sulfide gas generated by the reaction, the hydrogen sulfide gas is neutralized in the aqueous sodium hydroxide solution and removed from the exhaust gas.

[0244] [Residue removal step]

[0245] In the processed product obtained after calcination, unreacted sulfur or the like, which sublimates during calcination and then precipitates by cooling, can remain. Since these residues can cause deterioration of the cycle characteristics, if any residues are present, they should be removed as much as possible. The removal of the residues can be performed according to conventional methods (for example, reduced-pressure heat drying, hot-air drying, and solvent cleaning, etc.).

[0246] [Crushing, classification]

[0247] Preferably, the obtained electrode active material is crushed to have a predetermined particle size and classified to obtain particles of a size suitable for the manufacture of electrodes. The preferred size range of the electrode active material particles is as described above.

[0248] The pulverization can be performed by a conventional method, for example, it can be performed by subjecting the material to a pulverization treatment under predetermined conditions using a pulverizer such as a cutting pulverizer, an air flow pulverizer, or the like. The pulverization conditions differ depending on the pulverizer used and the like, for example, when a cutting pulverizer (for example, Free Speed Mill FS-20 manufactured by Labonect) is used, the treatment can be performed at a rotation speed of 20,000 rpm or more and 30,000 rpm or less for 1 second or more and 30 seconds or less. Further, when a dry-type air flow pulverizer (for example, Nano Jetmizer NJ-30 manufactured by Aishin Nano Technologies CO., LTD.) is used, the treatment can be performed at a processing speed of 1 g / min or more and 3 g / min or less at a pulverization pressure of 0.5 MPa or more and 2.0 MPa or less. Further, the pulverization can be performed using a sieve or the like.

[0249] Further, in the calcination method using the twin-screw extruder as described above, while the electrode active material is manufactured, the manufactured electrode active material can be pulverized into particles by shearing during kneading.

[0250] (MANUFACTURE OF ELECTRODE FOR LITHIUM-ION SECONDARY BATTERY)

[0251] Using the electrode active material obtained as described above, an electrode for a lithium-ion secondary battery including an electrode active material layer containing the electrode active material can be prepared by a conventional method. That is, an electrode can be obtained in the same manner as in the case of preparing a general electrode for a lithium-ion secondary battery except that the electrode active material described above is used as an active material.

[0252] [USE OF ELECTRODE ACTIVE MATERIAL AS POSITIVE ELECTRODE ACTIVE MATERIAL]

[0253] A positive electrode for a lithium-ion secondary battery can be manufactured in the same manner as in the case of a general positive electrode for a lithium-ion secondary battery except that the electrode active material described above is used as a positive electrode active material. For example, the positive electrode can be manufactured by mixing the electrode active material with a conductive aid, a binder, and a solvent, preparing a paste-like positive electrode material, coating the positive electrode material to a current collector, and then drying it. As another method, the positive electrode can be manufactured, for example, by kneading the electrode active material with a conductive aid, a binder, and a small amount of solvent using a mortar or the like, shaping them into a film, and then pressure-bonding it to a current collector using a press or the like.

[0254] <CONDUCTIVE AID>

[0255] Examples of the conductive aid include, for example, vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, or a fine powder of a metal stable at the potential of the positive electrode (e.g., aluminum, titanium, etc.). In addition, as the conductive aid, a conductive carbon material among the above-described carbon materials can also be used. One or more of these conductive aids can be used.

[0256] [Binder]

[0257] Examples of the binder include polyvinylidene fluoride (polyvinylidene difluoride: PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamide-imide (PAI), carboxymethyl cellulose (CMC), polyvinyl chloride (PVC), acrylic resin, methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene ether (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), etc. One or more of these binders can be used.

[0258] [Solvent]

[0259] Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformamide, alcohol, hexane, water, etc. One or more of these solvents can be used.

[0260] [Blending amount]

[0261] The blending amount of these materials constituting the positive electrode is not particularly limited, but, for example, 2 to 100 parts by mass of the conductive aid, 2 to 50 parts by mass of the binder, and an appropriate amount of the solvent are preferably blended with respect to 100 parts by mass of the electrode active material.

[0262] [Current collector]

[0263] As the current collector, those generally used for the positive electrode of a lithium ion secondary battery can be used. 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 nonwoven fabric, a copper foil, a copper mesh, a punched copper sheet, an expanded copper sheet, a titanium foil, a titanium mesh, etc., and a current collector composed of a carbon nonwoven fabric, a carbon woven fabric, etc. Among them, a current collector containing a metal foil is preferred. The current collector can be used alone or two or more kinds thereof can be used in combination. In addition, the surface of the current collector can be coated with carbon or the like. Specific examples of such a current collector having the surface coated with carbon or the like include, for example, a carbon-coated aluminum foil, etc. In this case, the current collector contains a carbon-coated portion.

[0264] [Use of the electrode active material as a negative electrode active material]

[0265] The negative electrode for a lithium-ion secondary battery can be manufactured in the same manner as in the case of a negative electrode for a general lithium-ion secondary battery, except that the above-described electrode active material is used as the negative electrode active material. For example, the negative electrode can be manufactured by mixing the electrode active material with a conductive aid, a binder, and a solvent, preparing a paste-like negative electrode material, coating the negative electrode material to a current collector, and then drying it. As another method, the negative electrode can also be manufactured, for example, by kneading the electrode active material with a conductive aid, a binder, and a small amount of solvent using a mortar or the like, shaping them into a film, and then pressure-bonding it to a current collector using a press or the like.

[0266] As the conductive aid, the binder, and the solvent, the same conductive aid, binder, and solvent as in the case of using the electrode active material as the positive electrode active material can be used, and this is also applicable to the current collector.

[0267] (MANUFACTURE OF LITHIUM-ION SECONDARY BATTERY)

[0268] The lithium-ion secondary battery of the present embodiment can be manufactured in the same manner as in the case of a general lithium-ion secondary battery, except that the above-described electrode for a lithium-ion secondary battery is used.

[0269] [USE OF ELECTRODE ACTIVE MATERIAL AS POSITIVE ELECTRODE ACTIVE MATERIAL]

[0270] The lithium-ion secondary battery of the present embodiment can be manufactured in a conventional manner, except that a positive electrode containing the above-described electrode active material (positive electrode active material) is used, and a negative electrode and an electrolyte, and further components such as a separator, as needed, are used.

[0271] <<NEGATIVE ELECTRODE>>

[0272] As the negative electrode material, known metal lithium, carbon-based materials (e.g., graphite, etc.), silicon-based materials (e.g., silicon thin film, etc.), and alloy-based materials (e.g., copper-tin alloy, cobalt-tin alloy, etc.) can be used. When a material not containing lithium (e.g., carbon-based materials, silicon-based materials, alloy-based materials, etc., among the above negative electrode materials) is used as the negative electrode material, it is advantageous that short-circuiting between the positive electrode and the negative electrode due to generation of dendrites is less likely to occur. However, when these negative electrode materials not containing lithium are used in combination with the positive electrode of the present embodiment, both the positive electrode and the negative electrode do not contain lithium. Therefore, a lithium pre-doping process in which lithium is inserted into either or both of the negative electrode and the positive electrode in advance is required. As the lithium pre-doping method, known methods can be used. For example, when lithium is doped into the negative electrode, there are a method in which lithium is inserted by an electrolytic doping method (using metal lithium as a counter electrode, assembling a half-cell, and electrochemically doping lithium) and a method in which lithium is inserted by a pre-doping method (attaching a metal lithium foil to an electrode, and then placing it in an electrolyte, and doping by utilizing diffusion of lithium into the electrode). Further, when lithium is pre-doped into the positive electrode, the above electrolytic doping method can be employed. As the negative electrode material not containing lithium, a silicon-based material (which is a negative electrode material having a high capacity) is particularly preferable, and among them, a thin film silicon (which is advantageous in terms of unit volume capacity because of a thin electrode thickness) is more preferable.

[0273] < electrolyte >

[0274] The electrolyte compensates for the electric charge generated by release of electrons to the outside circuit accompanying oxidation / reduction of the electrode active material at the positive electrode / negative electrode through ion flow. As the electrolyte for a lithium ion secondary battery, those obtained by dissolving an alkali metal salt as an electrolyte in an organic solvent can be used. As the organic solvent, at least one selected from non-aqueous solvents such as dimethoxyethane, vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, γ-butyrolactone, acetonitrile, etc. is preferably used. As the electrolyte, Li(FSO2)2N, LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiI, LiClO4, etc. can be used. The concentration of the electrolyte only needs to be about 0.5 mol / L to 5.0 mol / L. Further, 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).

[0275] < separator >

[0276] In addition to the negative electrode, the positive electrode, and the electrolyte as described above, the lithium-ion secondary battery can include components such as a separator and the like. The separator is located between the positive electrode and the negative electrode, allows the migration of ions between the positive electrode and the negative electrode, and prevents internal short-circuiting between the positive electrode and the negative electrode. If the lithium-ion secondary battery is of a sealed type, the separator needs to have a function of retaining the electrolyte. As the separator, a thin and microporous or non-woven fabric film made of polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, glass, or the like is preferably used.

[0277] <<Shape>>

[0278] The shape of the lithium-ion secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a stacked shape, a coin shape, a laminated shape, a button shape, and the like can be used.

[0279] [Use of Electrode Active Material as Negative Electrode Active Material]

[0280] The lithium-ion secondary battery of the present embodiment can be manufactured in accordance with a conventional method, using a positive electrode and an electrolyte, and further components such as a separator and the like as needed, in addition to a negative electrode containing the electrode active material (negative electrode active material) described above.

[0281] <<Positive Electrode>>

[0282] The positive electrode material is not particularly limited, and is, for example, a transition metal oxide or a solid solution oxide containing lithium, or a substance that can electrochemically absorb and release lithium ions. Examples of the transition metal oxide containing lithium include, for example, Li-Co-based composite oxides (for example, LiCoO2and the like), Li-Ni-Co-Mn-based composite oxides (for example, LiNi x Co y Mn z O2and the like), Li-Ni-based composite oxides (for example, LiNiO2and the like), Li-Mn-based composite oxides (for example, LiMn2O4and the like), and the like. Examples of the solid solution oxide include, for example, Li a Mn x Co y Ni z O2(1.150≤a≤1.430, 0.450≤x≤0.600, 0.100≤y≤0.150, 0.200≤z≤0.280), LiMn x Co y Ni z O2(0.300≤x≤0.850, 0.100≤y≤0.300, 0.100≤z≤0.300), LiMn 1.5 Ni 0.5 O4and the like. These compounds can be used alone or a plurality thereof can be used in mixture.

[0283] <<Other>>

[0284] As for the electrolyte, the separator, and the shape of the lithium ion secondary battery, the same electrolyte, separator, and shape of the lithium ion secondary battery as in the case where the electrode active material is used as the positive electrode active material can be employed. Example

[0285] While the present application will be described based on examples, the present application is not limited to the examples.

[0286] Various chemicals used in the examples and comparative examples are summarized below. The various chemicals were purified according to a conventional method as needed.

[0287] <Materials used in the test>

[0288] Organic compound: spherical acrylic resin made of methyl methacrylate homopolymer (TECHPOLYMER MB-4 manufactured by Sekisui Plastics Co., Ltd., particle diameter: 4 μm)

[0289] Source metal compound (iron compound): ferrous oxalate dihydrate (ferrous oxalate dihydrate manufactured by Wako Pure Chemical Industries, Ltd., guaranteed reagent)

[0290] Carbon material: carbon nanotube (CNT) (CNT dispersion liquid manufactured by Nanobridge Co., Ltd., dispersion medium: N-methyl-2-pyrrolidone, average fiber diameter: 1.6 nm, average fiber length: 2 to 10 μm, specific surface area: 800 to 1600 m 2 / g, G / D ratio: 40 or more, metal impurity amount: 1% by mass or less)

[0291] Sulfur: precipitated sulfur manufactured by Tsukishima Kika K.K.

[0292] Organic solvent (wet method): N-methyl-2-pyrrolidone (manufactured by Yamanouchi Pharmaceutical Co., Ltd.)

[0293] Production Example 1 (fine pulverization of source metal compound)

[0294] Before using the source metal compound as a raw material, the source metal compound was pulverized for 10 minutes in advance using a freezer mill (JFC-2000 manufactured by Japan Analytical Industry Co., Ltd.).

[0295] Production Example 2 (preparation of dry mixture by wet method)

[0296] In the examples in which the mixing method is noted as wet in Table 1, a dry mixture composed of the organic compound, the raw material metal compound, and the carbon material is prepared in advance by wet method before preparing the calcination raw material. In preparing the dry mixture, first, the organic compound is added to an organic solvent and mixed well, and then the raw material metal compound and the carbon material are added and mixed, to obtain a liquid mixture. Next, the organic solvent is removed from the liquid mixture, and it is pulverized using a cutting mill (LAB MILL manufactured by Osaka Chemical Co., Ltd.), to obtain the dry mixture.

[0297] <Manufacture of electrode active material>

[0298] (Preparation of calcination raw material)

[0299] In the examples in which the dry mixture is prepared in advance by wet method, the dry mixture is mixed with sulfur using a stirrer, to obtain a raw material for calcination. In other examples (for example, Reference Example y, Reference Example z), the raw materials are mixed using a stirrer, to prepare a raw material for calcination.

[0300] (Reaction apparatus)

[0301] The raw material is calcined using a muffle furnace. Figure 1 The muffle furnace in Reference Example x is as described above. Figure 1

[0302] (Calcination step)

[0303] First, in a case where the calcination raw material is housed in a tray which is a stainless steel reaction vessel, the atmosphere in the muffle furnace is replaced with Ar gas three times using a vacuum pump. Then, while continuously supplying Ar gas at a flow rate of 100 mL / min from a gas introduction pipe, heating of the muffle furnace is started 30 minutes after the start of the supply. The temperature is increased at a temperature increase rate of 5°C / min, and when the temperature of the calcination raw material reaches the calcination temperature described in Table 1, heat treatment is performed for 2 hours while maintaining the temperature. Then, while adjusting the Ar gas flow rate, the temperature of the calcination product is naturally cooled to 25°C under an Ar gas atmosphere, and then the calcination product is taken out of the muffle furnace.

[0304] (Removal of unreacted sulfur)

[0305] In order to remove unreacted sulfur (sulfur alone in a free state) remaining in the product after the calcination step, the following step is performed. That is, the calcination product is pulverized in a mortar, and then the pulverized product is housed in a glass tube furnace, heated at 250°C for 3 hours while vacuum suction, to obtain an electrode active material in which unreacted sulfur has been removed (or contains only a trace amount of unreacted sulfur). The temperature increase rate is set to 10°C / min.

[0306] (Pulverization step) ​

[0307] The calcined material from which unreacted sulfur had been removed was pulverized with a cutting pulverizer (free speed pulverizer, FS-20, manufactured by Labonect).

[0308] (Classification work)

[0309] In order to remove coarse particles from the pulverized calcined material, the calcined material was classified using a stainless steel sieve with a mesh size of 32 μm, and an electrode active material was obtained.

[0310] <Physical properties of the electrode active material>

[0311] The following properties were measured with respect to the electrode active material obtained above.

[0312] (Elemental analysis)

[0313] With respect to the amounts of carbon, hydrogen, nitrogen, and sulfur, a mass was measured using a fully automatic elemental analyzer varioMICRO cube manufactured by Elementar, and a mass ratio (%) of each of them in the total amount of the electrode active material was calculated from the mass. The results are shown in Table 1.

[0314] (Amount of iron element)

[0315] Each of the electrode active materials was subjected to thermogravimetric analysis, and from the obtained measurement results, the amount of the iron element (mass %) was calculated.

[0316] The thermogravimetric analysis was performed using a TGA Q500 manufactured by TA Instruments, Inc. The measurement conditions were that after the electrode active material was heated to 750°C under an Ar gas atmosphere, air was introduced to completely decompose the measurement sample. From the measured weight reduction ratio (mass %), the ash content ratio (mass %) in each of the electrode active materials was calculated using the following calculation.

[0317] Ash content ratio (mass %) = 100 - weight reduction ratio (mass %)

[0318] Further, it has been confirmed that the iron element in each of the electrode active materials exists in the form of iron disulfide (FeS2), and therefore, from the ash content ratio (mass %) of each of the electrode active materials, the iron disulfide ratio (mass %) was calculated using the following calculation. That is, from the weight reduction ratio (100 mass %) of Reference Example y in Table 1, it is known that the organic compound is completely decomposed after being converted into a sulfide, and from the weight reduction ratio (36 mass %) of Reference Example z, it is known that the weight of the iron disulfide (FeS2) in the electrode active material is reduced by 36 mass %. Therefore, from the following calculation, the iron disulfide (FeS2) ratio (mass %) in each of the electrode active materials was calculated.

[0319] FeS2 ratio (mass %) = ash content ratio x {100 / (100-36)

[0320] Further, the amount of iron element (Fe ratio, mass %) was calculated from the FeS2 ratio (mass %) by the following calculation.

[0321] Fe ratio (mass %) = FeS2 ratio x Fe atomic weight / (Fe atomic weight + S atomic weight x 2)

[0322] (wherein, Fe atomic weight is 55.845, and S atomic weight is 32.065.)

[0323] (Particle size distribution, median particle size)

[0324] A laser diffraction / scattering type particle size distribution analyzer (particle size distribution analyzer PSA1090L manufactured by Anton Paar) was used to measure the particle size distribution using water as the dispersion medium, and a particle size distribution curve was obtained. From the particle size distribution curve, the volume-based cumulative 50% size (median particle size d50) was measured.

[0325] (Powder resistivity)

[0326] The powder resistivity (Ω-cm) was measured using an automatic powder resistivity analyzer (MCP-PD600 manufactured by Nittoseiko Analytech Co., Ltd.), and the measurement sample (which was obtained by setting 1 g of the measurement target composed of particles in a 20 mm probe unit with a load of 20 kN to compress the hardening) was measured using a 4-probe method (electrode diameter: 3 mm) in a normal temperature and humidity (temperature: 23°C, relative humidity: 50%) environment.

[0327] The results are shown in Table 1 below.

[0328] Table 1

[0329]

[0330] Manufacture of lithium ion secondary battery

[0331] A lithium ion secondary battery was manufactured as follows.

[0332] (Positive electrode)

[0333] ​As the active material, the electrode active material obtained above was used, as the conductive agent, acetylene black (HS-100 manufactured by Denka) and vapor grown carbon fiber (VGCF manufactured by Showa Denko) were used, and as the binder, an acrylic resin (manufactured by FUJIFILM and Wako Pure Chemical Industries, Ltd., average molecular weight: 2700 to 7500) was used. They were weighed so that the ratio of the active material: acetylene black: vapor grown carbon fiber: binder would be 95: 1.25: 1.25: 2.5 (% by mass), and they were put in a container, and using a planetary centrifugal mixer (ARE-250 manufactured by THINKY CORPORATION), milliQ water was used as the dispersant, and they were mixed by stirring to prepare a uniform slurry. The slurry obtained was coated on an aluminum foil of 17 μm using an applicator with a slit width of 100 μm, and using a roll press, it was compressed to obtain an electrode, and then the electrode was heated at 120°C for 3 hours, and dried with a drier, and then punched into a disk shape of 14 mm in diameter and 1.5 mm in thickness to obtain an electrode (positive electrode). Then, the mass of the electrode was measured, and the amount of the active material in the electrode was calculated according to the above ratio. 11 mm, to obtain an electrode (negative electrode). Then, the mass of the electrode was measured, and the amount of the active material in the electrode was calculated according to the above ratio.

[0334] (Negative electrode)

[0335] As the negative electrode, a metal lithium foil (disk-shaped with a diameter of 14 mm and a thickness of 500 μm, manufactured by Hitojyo Metal Co., Ltd.) was used. A stainless steel sheet was used as the negative electrode current collector.

[0336] (Electrolyte)

[0337] As the electrolyte, a non-aqueous electrolyte in which LiPF6 was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate was used. Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1. The concentration of LiPF6 in the electrolyte was 1.0 mol / L.

[0338] (Lithium ion secondary battery)

[0339] A coin battery was prepared using the positive electrode and the negative electrode described above. Specifically, in a dry room, a separator (Celgard 2400 manufactured by Celgard LLC, polypropylene microporous film with a thickness of 25 μm) and a glass non-woven fabric filter (thickness 440 μm, GA100 manufactured by ADVANTEC) were sandwiched between the positive electrode and the negative electrode to form an electrode body battery. This electrode body battery was loaded into a battery case made of stainless steel (part for a CR2032 type coin battery, manufactured by Hohsen Corporation). The electrolyte described above was injected into the battery case. The amount of the electrolyte was 0.28 mL in terms of the volume of the electrolyte. The battery case was sealed using a sealer to obtain a lithium ion secondary battery of each example and comparative example.

[0340] <Evaluation of lithium ion secondary battery>

[0341] (discharge capacity and capacity retention rate)

[0342] Each of the button-type lithium ion secondary batteries produced in each of the examples and comparative examples was subjected to charge and discharge at a current value equivalent to 50 mA / 1 g of positive electrode active material at a test temperature of 30°C. The discharge termination voltage was set to 1.0 V, and the charge termination voltage was set to 3.0 V. When the charge and discharge was repeated, the 1st, 2nd, 3rd, and 10th battery discharge capacities (mAh) were observed. The measurement was performed using a battery performance evaluation device (BLS system, manufactured by Measuring Instrument Center Co., Ltd.).

[0343] The 3rd discharge capacity DC3 (mAh / g) was defined as the initial capacity. The greater the initial capacity, the greater the charge and discharge capacity of the lithium ion secondary battery, and this can be evaluated as being preferable. Furthermore, the capacity retention rate (%) was calculated from the 3rd discharge capacity DC3 (mAh / g) and the 10th discharge capacity DC10 (mAh / g) according to the following equation. 10 (mAh / g). It can be said that the higher the capacity retention rate, the more excellent the cycle characteristics of the lithium ion secondary battery.

[0344] Capacity retention rate (%) = (DC 10 / DC3) x 100

[0345] The results are shown in Table 2 below.

[0346] Table 2

[0347]

[0348] <Embodiments>

[0349] Hereinafter, a preferred embodiment will be shown.

[0350] [1] An electrode active material composed of particles, comprising:

[0351] an organic sulfur compound; and

[0352] a metal compound containing at least one metal selected from iron, molybdenum, vanadium, and titanium,

[0353] wherein the powder resistivity of the particles is less than 1.0 x 10 3 Ω·cm, preferably less than 500, more preferably less than 300, further preferably less than 150, and

[0354] wherein A S and R ρsatisfies the following inequality, the right side of inequality (1) is preferably 0.10,

[0355] (1) A S / R ρ ≥ 0.05

[0356] wherein A S represents the sulfur content in the electrode active material (mass %), R ρ represents the powder resistivity.

[0357] [2] The electrode active material according to the above [1], wherein the right side of inequality (1) is 0.50, preferably 0.56, more preferably 0.80, further preferably 0.86, further preferably 1.00, further preferably 3.00.

[0358] [3] The electrode active material according to the above [1], wherein the right side of inequality (1) is 5.00, preferably 6.00, more preferably 6.70.

[0359] [4] The electrode active material according to any one of the above [1] to [3], wherein the powder resistivity is less than 111, preferably less than 100, more preferably less than 72, further preferably less than 50, further preferably less than 30.

[0360] [5] The electrode active material according to any one of the above [1] to [3], wherein the powder resistivity is less than 10.

[0361] [6] The electrode active material according to any one of the above [1] to [5], wherein the metal compound is an iron compound.

[0362] [7] An electrode comprising the electrode active material according to any one of the above [1] to [6].

[0363] [8] The electrode according to the above [7],

[0364] wherein the electrode includes a current collector,

[0365] wherein the current collector has a metal foil, and

[0366] wherein D and A S satisfies the following inequality, the right side of inequality (2) is preferably 190, more preferably 193, further preferably 195, further preferably 200, further preferably 210, further preferably 220, further preferably 230, further preferably 240, further preferably 242, further preferably 244,

[0367] (2) D x A S>150

[0368] wherein D represents a coating density of the electrode active material on the current collector (mg / cm 2 ).

[0369] [9] The electrode according to any one of the above [7] or [8],

[0370] wherein the electrode includes a current collector,

[0371] wherein the current collector has a metal foil, and

[0372] wherein D, T and A S satisfy the following inequality, the right side of inequality (3) is preferably 11.0, more preferably 11.3, further preferably 11.4, further preferably 12.0, further preferably 13.0, further preferably 14.0, further preferably 14.2, further preferably 14.3,

[0373] (3) DxA S / T > 10.0

[0374] wherein D represents a coating density of the electrode active material on the current collector (mg / cm 2 ), and T represents a thickness of the metal foil (μm).

[0375]

[10] The electrode according to any one of the above [7] to [9],

[0376] wherein the electrode includes a current collector,

[0377] wherein the current collector has a metal foil, and

[0378] wherein D is greater than 2.5 mg / cm 2 , preferably greater than 3.00 mg / cm 2 , more preferably greater than 3.50 mg / cm 2 , further preferably greater than 3.80 mg / cm 2 , further preferably greater than 3.90 mg / cm 2 wherein D represents a coating density of the electrode active material on the current collector (mg / cm 2 ).

[0379]

[11] The electrode according to any one of the above [7] to

[10] , wherein DC3 is greater than 400 mAh / g, preferably greater than 450 mAh / g, more preferably greater than 500 mAh / g, further preferably 514 mAh / g or more, further preferably greater than 550 mAh / g, further preferably greater than 600 mAh / g, further preferably greater than 650 mAh / g, further preferably greater than 700 mAh / g, further preferably greater than 710 mAh / g, wherein DC3 represents the 3rd discharge capacity when the electrode is used as a positive electrode.

[0380]

[12] The electrode according to any one of the above [7] to

[11] , wherein DC 10 is greater than 350 mAh / g, preferably greater than 400 mAh / g, more preferably 478 mAh / g or more, further preferably greater than 500 mAh / g, further preferably 536 mAh / g or more, further preferably greater than 600 mAh / g, further preferably greater than 700 mAh / g, further preferably 710 mAh / g or more, wherein DC 10 represents the 10th discharge capacity when the electrode is used as a positive electrode.

[0381]

[13] The electrode according to any one of the above [7] to

[12] , wherein the electrode is a positive electrode.

[0382]

[14] A lithium ion secondary battery comprising the electrode according to any one of the above [7] to

[13] .

[0383]

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

[14] , further comprising an electrolyte, wherein D, V and A S satisfy the following inequality, the right side of inequality (4) is preferably 650, more preferably 700, further preferably 750, further preferably 800, more preferably 850, further preferably 860, further preferably 865,

[0384] (4) D x A S / V > 600

[0385] wherein V represents the volume of the electrolyte (mL), D represents the coating density of the electrode active material on the current collector (mg / cm 2 ).

Claims

1. An electrode active material, comprising particles, including: Organic sulfur compounds; and A metal compound comprising at least one metal selected from iron, molybdenum, vanadium, and titanium. in, The powder resistivity of the particles is less than 1.0 × 10⁻⁶. 3 Ω·cm, A S and R ρ The following inequalities must be satisfied. (1)A S / R ρ ≥ 0.05 In the formula, A S R indicates the sulfur content in the electrode active material, expressed in mass %. ρ This indicates the resistivity of the powder.

2. The electrode active material according to claim 1, wherein, The right side of inequality (1) is 0.

50.

3. The electrode active material according to claim 1, wherein, The right side of inequality (1) is 5.

00.

4. The electrode active material according to any one of claims 1 to 3, wherein, The resistivity of the powder is less than 111.

5. The electrode active material according to any one of claims 1 to 3, wherein, The resistivity of the powder is less than 10.

6. The electrode active material according to any one of claims 1 to 3, wherein, The metal compound is an iron compound.

7. An electrode comprising the electrode active material according to any one of claims 1 to 3.

8. The electrode according to claim 7, in, The electrode includes a current collector. The current collector has a metal foil. D and A S The following inequalities must be satisfied. (2)D×A S >150 In the formula, D represents the coating density of the electrode active material on the current collector, with units of mg / cm³. 2 .

9. The electrode according to claim 7, in, The electrode includes a current collector. The current collector has a metal foil. D, T, and A S The following inequalities must be satisfied. (3)D×A S / T>10.0 In the formula, D represents the coating density of the electrode active material on the current collector, with units of mg / cm³. 2 T represents the thickness of the metal foil, in μm.

10. The electrode according to claim 7, in, The electrode includes a current collector. The current collector has a metal foil. D > 2.5 mg / cm 2 Where D represents the coating density of the electrode active material on the current collector, in mg / cm³. 2 .

11. The electrode according to claim 7, wherein, DC3 is greater than 400 mAh / g, where DC3 represents the third discharge capacity when the electrode is used as the positive electrode.

12. The electrode according to claim 7, wherein, DC 10 Greater than 350mAh / g, of which DC 10 This indicates the 10th discharge capacity when the electrode is used as the positive electrode.

13. The electrode according to claim 7, wherein, The electrode is a positive electrode.

14. A lithium-ion secondary battery having the electrode as described in claim 7.

15. The lithium-ion secondary battery according to claim 14, further comprising an electrolyte, wherein, D, V, and A S The following inequalities must be satisfied. (4)L×W S / V>600 In the formula, V represents the volume of the electrolyte in mL, and D represents the coating density of the electrode active material on the current collector in mg / cm³. 2 .

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