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 that include an organosulfur compound and a metal compound including at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, wherein: the powder resistivity of the particles is less than 1.0×103 Ω·cm; and, where the sulfur content (mass%) in the electrode active material is AS and the powder resistivity is RP, AS and RP satisfy the following formula. Formula (1): AS / RP ≥ 0.05

Description

Electrode active material, electrode, and lithium ion secondary battery

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

[0002] Lithium-ion secondary batteries have a large charge / discharge capacity and are primarily used as batteries for portable electronic devices. Their use in electric vehicles is also increasing, and improvements in their performance are expected.

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

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

[0005] Japanese Patent Application Laid-Open No. 2020-167144

[0006] However, development of active materials other than those disclosed in Patent Document 1 is still desired.

[0007] In addition, the materials proposed as negative electrode active materials have the problem of poor cycle characteristics during repeated charge and discharge due to the large volume change caused by the absorption and release of lithium ions. Carbon materials such as graphite and hard carbon are also used, but they have already reached their theoretical capacity and no significant capacity improvement is expected.

[0008] The present invention provides a novel electrode active material that can improve charge / discharge capacity and capacity retention rate, an electrode comprising the electrode active material, i.e., a positive electrode or a negative electrode, and a lithium ion secondary battery comprising the electrode.

[0009] The present invention relates to the following electrode active material: an electrode active material comprising particles containing an organic sulfur compound and a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, wherein the particles have a powder resistivity of 1.0×10 3 the sulfur content (mass%) in the electrode active material is less than A S and the powder resistivity is R P In the case where A S and R P and an electrode active material that satisfies the following formula: (1) A S / R P ≧0.05

[0010] According to the present invention, it is possible to provide a novel electrode active material that can improve charge / discharge capacity and capacity retention rate, an electrode comprising the electrode active material, i.e., a positive electrode or a negative electrode, and a lithium ion secondary battery comprising the electrode.

[0011] In this specification, the term "cycle characteristics" refers to the ability of a secondary battery to maintain its charge / discharge capacity despite repeated charge / discharge. Therefore, a secondary battery that experiences a large decrease in charge / discharge capacity and a low capacity retention rate with repeated charge / discharge has poor cycle characteristics, whereas a secondary battery that experiences a small decrease in charge / discharge capacity and a high capacity retention rate has excellent cycle characteristics.

[0012] FIG. 1 is a cross-sectional view schematically showing a reaction apparatus used in the production of an electrode active material in an example of the present invention.

[0013] The configuration of one embodiment of the present invention will be described in detail below. The upper and lower limit values ​​associated with terms such as "greater than or equal to," "less than," "greater than," and "less than" used to describe a numerical range can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and / or lower limit values. Furthermore, a numerical range indicated as including a lower limit or an upper limit is understood to also disclose a numerical range that does not include the upper limit or lower limit, unless it is contrary to the spirit of this specification. Conversely, a numerical range indicated as excluding a lower limit or an upper limit is understood to also disclose a numerical range that includes the lower limit or upper limit, unless it is contrary to the spirit of this specification.

[0014] One embodiment of the present invention is an electrode active material comprising particles containing an organic sulfur compound and a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, wherein the powder resistivity of the particles is 1.0×10 3 Ω cm or less, and the sulfur content (mass%) in the electrode active material is A S and the powder resistivity is R P In the case where A S and R P and are electrode active materials that satisfy the following formula: (1) A S / R P ≧0.05

[0015] Although not intending to be bound by theory, the reason why the electrode active material of the present embodiment can improve the charge / discharge capacity and capacity retention rate is thought to be as follows: That is, when the powder resistivity is 1.0×10 3 If the electrical resistance is less than Ω·cm, the electrical conductivity inside and on the surface of the particles of the electrode active material is improved, which is thought to improve the charge / discharge capacity and capacity retention rate.

[0016] The right side of formula (1) is preferably 0.50, and more preferably 5.00.

[0017] The powder resistivity is preferably less than 111, and more preferably less than 10.

[0018] The metal compound is preferably an iron compound.

[0019] Another embodiment of the present invention is an electrode comprising the electrode active material.

[0020] The electrode includes a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector is 2 ) is D, then D and A S It is preferable that D×A satisfies the following formula: (2) S >150

[0021] It is believed that by making the product of the coating density and the sulfur content exceed a predetermined value, the performance of the electrode and / or the battery can be improved.

[0022] The electrode includes a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector is 2 ) is D and the thickness of the metal foil is T (μm), D, T and A S It is preferable that D×A satisfy the following formula: (3) S / T>10.0

[0023] It is believed that by ensuring that the coating density, sulfur content, and metal foil thickness satisfy the above formula, the performance of the electrode and / or battery can be improved.

[0024] The electrode includes a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector is 2 ) is D, D is 2.5 mg / cm 2 Preferably, it is greater than 1000 .mu.m.

[0025] When the third discharge capacity when the electrode is used as a positive electrode is defined as DC3, DC3 is preferably more than 400 mAh / g.

[0026] The tenth discharge capacity when the electrode was used as a positive electrode was measured by DC 10 When this is done, DC 10 is preferably greater than 350 mAh / g.

[0027] The electrode is preferably a positive electrode.

[0028] It is believed that the use of these materials as positive electrodes can improve the performance of electrodes and / or batteries. In particular, by combining them with lithium negative electrodes with high specific capacity, batteries with high weight energy density can be realized.

[0029] Another embodiment of the present invention is a lithium ion secondary battery comprising the electrode.

[0030] The lithium ion secondary battery further comprises an electrolyte, the volume of the electrolyte being V (mL), and the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then D, V and A S It is preferable that D×A satisfies the following formula: (4) S / V>600

[0031] It is believed that by ensuring that the coating density, sulfur content, and electrolyte volume satisfy the above formula, the performance of the electrode and / or battery can be improved.

[0032] <Definition> "Electrode active material" refers to one of the electrode materials in a battery, and refers to a substance that is involved in the reaction that generates electricity. Electrode active materials include positive electrode active materials and negative electrode active materials.

[0033] The term "particles" refers to an electrode active material that has been sufficiently finely divided to be suitable for mixing with other materials for the purposes of the present invention. The size of the particles that make up the electrode active material is not particularly limited as long as the mixing can be carried out suitably. For example, when the median diameter of the "particles" is expressed as a particle size, the particle size can be in the range of 1 nm to 1000 μm.

[0034] "Particle size" is expressed as the median size (d50) unless otherwise specified.

[0035] The "sulfur content in the electrode active material" is the amount (mass %) of elemental sulfur contained in the electrode active material.

[0036] The "average fiber length" is determined by photographing the fibers with a transmission or scanning electron microscope, measuring the lengths of 50 fibers along their fiber axes, and calculating the arithmetic average. The average fiber length is applicable to carbon fibers and the like.

[0037] The "average fiber diameter" is determined by photographing the fibers with a transmission or scanning electron microscope, measuring the diameters of 50 fibers, and calculating the arithmetic average. The average fiber diameter is applicable to carbon fibers and the like.

[0038] The term "active material" refers to a substance that is responsible for the oxidation-reduction reaction that takes place for energy conversion in a lithium ion secondary battery.

[0039] "Coating density" refers to the density per unit area (cm ) of the active material coated on the current collector. 2 ) is the mass (mg) per

[0040] "Electrolyte volume" refers to the total volume of the electrolyte solution containing the solute or the solid electrolyte, expressed in mL.

[0041] Unless otherwise specified, the "initial discharge capacity" refers to the third discharge capacity.

[0042] <Measurement Method> "Powder resistivity" is measured using an automatic powder resistivity measurement system (MCP-PD600 manufactured by Nitto Seiko Air Analytec Co., Ltd.), in which 1 g of a measurement object made of particles is set in a φ20 mm probe unit and compressed with a load of 20 kN to form a pellet-shaped measurement sample, and the measurement sample is measured as a volume resistivity using a four-probe method (electrode diameter 3 mm) under an environment of normal temperature and normal humidity (temperature 23°C, relative humidity 50%). The unit is Ω cm.

[0043] The "element content" is measured by the method described in the Examples. For example, it applies to sulfur, carbon, metals including iron, hydrogen, nitrogen, etc.

[0044] The "particle size distribution" is measured using a laser diffraction / scattering particle size distribution analyzer (Anton Paar PSA1090L particle size distribution analyzer) with water as the dispersion medium.

[0045] The "median diameter d50" is the volume-based cumulative 50% diameter (μm) in the particle size distribution.

[0046] The electrode active material, electrode, and lithium ion secondary battery of this embodiment will be described below.

[0047] <Electrode Active Material> The electrode active material of this embodiment is an electrode active material consisting of particles containing an organic sulfur compound and a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, wherein the powder resistivity (Ω cm) of the particles is less than a predetermined value, and the ratio of the sulfur content (mass %) in the electrode active material to the powder resistivity is equal to or greater than a predetermined value. The organic sulfur compound and metal compound in the electrode active material of this embodiment are formed by the reaction of the organic compound, the raw material metal compound, and sulfur through the calcination process described below. Furthermore, when the raw material metal compound is a raw material iron compound, the presence of iron disulfide has been confirmed as the metal compound.

[0048] (Elemental Amounts) The sulfur, carbon, hydrogen, nitrogen, and metal element amounts shown below are the amounts of each element contained in the electrode active material. Note that when the electrode active material contains an iron compound, the fact that the iron compound contains iron disulfide is based on a comparison with the peak profile of the diffraction intensity of iron disulfide (pyrite) obtained by X-ray diffraction measurement.

[0049] <Sulfur Element Content> From the viewpoint of improving the performance of the electrode and / or battery, the sulfur element content in the electrode active material is preferably more than 45.0 mass%, more preferably more than 50.0 mass%, even more preferably more than 55.0 mass%, and still more preferably more than 60.0 mass%. There is no particular upper limit for the sulfur element content, but it is usually 80 mass%, may be 70 mass%, or may be 65 mass%.

[0050] <<Carbon Element Content>> From the viewpoint of improving the performance of the electrode and / or battery, the carbon element content is preferably more than 5.0 mass%, more preferably more than 10.0 mass%, and even more preferably more than 15.0 mass%, while the carbon element content is preferably less than 30.0 mass%, more preferably less than 25.0 mass%, and even more preferably less than 23.0 mass%.

[0051] <<Hydrogen element content>> By calcination, hydrogen (H) in the organic compound reacts with sulfur to become hydrogen sulfide and is released outside the system. Therefore, the hydrogen element content of the electrode active material is preferably less than 1.0 mass%, more preferably less than 0.7 mass%, and even more preferably less than 0.5 mass%. When it is less than 1.0 mass%, calcination (sulfurization reaction) tends to be sufficient. Therefore, in this case, the charge / discharge capacity tends to be improved.

[0052] <<Nitrogen Element Amount>> The nitrogen element amount (mass %) in the electrode active material can be 0 mass % when no nitrogen source is used in the raw material. For example, when the raw material is prepared by the WET method, if a solvent containing nitrogen atoms is used as the solvent, nitrogen element can be detected.

[0053] <<Amount of Metal Element>> The amount of metal element (% by mass) in the electrode active material is preferably more than 10.0% by mass, more preferably more than 15.0% by mass, and even more preferably more than 20.0% by mass, from the viewpoint of improving the performance of the electrode and / or battery. On the other hand, the amount of the metal element is preferably less than 30% by mass, more preferably less than 25.0% by mass, and even more preferably less than 24.0% by mass.

[0054] (Powder Resistivity) In the electrode active material made of predetermined particles of this embodiment, the powder resistivity of the particles is 1.0 × 10 3 The powder resistivity is less than 1.0 × 10 3 If the resistance is Ω·cm or more, improvement in the performance of the electrode and / or battery cannot be achieved.

[0055] The powder resistivity is preferably less than 500, more preferably less than 300, even more preferably less than 150, even more preferably less than 111, even more preferably less than 100, even more preferably less than 72, even more preferably less than 50, even more preferably less than 30, and even more preferably less than 10. The lower the powder resistivity, the better, and there is no point in setting a lower limit, but a value of about 1 can be assumed as a reference value.

[0056] The powder resistivity can be adjusted appropriately by changing the type and amount of the organic compound, raw metal compound, and sulfur used as raw materials, or the type and amount of the carbon material used as an optional component.

[0057] (Formula (1)) The sulfur content (mass%) in the electrode active material of this embodiment is A S and the powder resistivity is R P In the case where A S and R P If the following formula is not satisfied, the sulfur content is too low or the powder resistivity is too high, and therefore, improvement in the performance of the electrode and / or battery cannot be achieved. S / R P ≧0.05

[0058] The right side of formula (1) is preferably 0.10, more preferably 0.50, even more preferably 0.56, even more preferably 0.80, even more preferably 0.86, even more preferably 1.00, even more preferably 3.00, even more preferably 5.00, even more preferably 6.00, and even more preferably 6.70. The higher the value of the left side of formula (1), the better, and there is no point in setting an upper limit, but as a reference value, a value of about 20.00 can be assumed.

[0059] (Median diameter) The electrode active material of this embodiment is composed of particles, and the size thereof is suitable for the production of an electrode. From the viewpoint of improving the performance of an electrode and / or a battery, the preferred range of particle size of the electrode active material is, in terms of median diameter (median diameter d50), preferably more than 1.0 μm and less than 40.0 μm. The median diameter is more preferably more than 1.5 μm, even more preferably more than 2.0 μm, and even more preferably more than 3.0 μm. The median diameter is more preferably less than 30.0 μm, even more preferably less than 25.0 μm, even more preferably less than 20.0 μm, even more preferably less than 15.0 μm, even more preferably less than 10.0 μm, and even more preferably less than 8.0 μm. The median diameter can be measured by the method described in the Examples section below.

[0060] (Other Components) The electrode active material of this embodiment can contain the materials described in the production method section below, in the same manner as described in the same section.

[0061] The electrode of this embodiment is an electrode containing the electrode active material described above. The electrode is preferably an electrode in which an electrode active material made of particles containing an organic sulfur compound and a carbon material is mixed with other electrode materials such as a conductive additive and a binder as necessary, and the mixture is applied to a current collector.

[0062] The lithium-ion secondary battery electrode of this embodiment can be constructed using the materials described in the manufacturing method section below in the same manner as described in that section. That is, when the lithium-ion secondary battery electrode is used as a positive electrode, the conductive additive, binder, current collector, etc. described in the manufacturing method section below can be used in the same manner as described in that section to form a lithium-ion secondary battery positive electrode. When the lithium-ion secondary battery electrode is used as a negative electrode, the conductive additive, binder, current collector, etc. described in the manufacturing method section below can be used in the same manner as described in that section to form a lithium-ion secondary battery negative electrode. In this way, the explanations in the manufacturing method section below can be taken into consideration as explanations of the present lithium-ion secondary battery electrode.

[0063] (Formula (2)) The electrode of this embodiment includes a current collector, and the current collector includes a metal foil. The coating density (mg / cm) of the electrode active material on the current collector is 2 ) is D, then D and A S It is preferable that D×A satisfy the following formula: (2) S >150

[0064] The right side of formula (2) is more preferably 190, even more preferably 193, even more preferably 195, even more preferably 200, even more preferably 210, even more preferably 220, even more preferably 230, even more preferably 240, even more preferably 242, and even more preferably 244. Note that the higher the value of the left side of formula (2), the more preferable it is, and there is no significance in setting an upper limit, but as a reference value, a value of about 1000 can be assumed.

[0065] (Coating density (mg / cm2 )) Coating density of electrode active material on the electrode (mg / cm 2 ) is 2.50 mg / cm 2 More preferably, it is greater than 3.00 mg / cm 2 More preferably, greater than 3.50 mg / cm 2 More preferably, greater than 3.80 mg / cm 2 More preferably, greater than 3.90 mg / cm 2 The higher the coating density value, the more preferable it is, and there is no point in setting an upper limit. However, as a reference value, 15.0 mg / cm 2 It can also be assumed to be the extent.

[0066] (Formula (3)) The electrode of this embodiment includes a current collector, and the current collector includes a metal foil. The coating density of the electrode active material on the current collector (mg / cm 2 ) is D and the thickness of the metal foil is T (μm), D, T and A S It is preferable that D×A satisfy the following formula: (3) S / T>10.0

[0067] The right side of formula (3) is more preferably 11.0, even more preferably 11.3, even more preferably 11.4, even more preferably 12.0, even more preferably 13.0, even more preferably 14.0, even more preferably 14.2, and even more preferably 14.3. The higher the value of the left side of formula (3), the better, and there is no point in setting an upper limit, but as a reference value, a value of about 100 can be assumed.

[0068] (Thickness (T) of Metal Foil) The thickness T (μm) of the metal foil is preferably 5 μm or more, more preferably 10 μm or more. On the other hand, T is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.

[0069] (Charge / Discharge Capacity) The electrode of this embodiment exhibits excellent charge / discharge capacity. The third discharge capacity (DC3), which is the initial discharge capacity, is the discharge capacity when three charge / discharge cycles are performed after the electrode and battery are fabricated, with the discharge end voltage being 1.0 V and the charge end voltage being 3.0 V (this is the third discharge when repeating the cycle of first discharge, first charge, second discharge, second charge, third discharge, and third charge). In the case of discharge, when discharged at a constant current (a current value equivalent to 50 mA per 1 g of positive electrode active material), the voltage of 3.0 V eventually drops to 1.0 V. The total time (h) from 3.0 V to 1.0 V is measured and multiplied by the applied current (mA) to obtain the capacity (mAh), which is divided by the weight of the active material to obtain the specific capacity (mAh / g). On the other hand, in the case of charging, the voltage rises conversely when charging at a constant current, and when it finally reaches 3.0 V, the charging is completed. The same applies to the tenth discharge capacity described later.

[0070] [Initial Discharge Capacity (DC3)] When the electrode of this embodiment is used as a positive electrode, the initial discharge capacity (DC3) (mAh / g) is preferably greater than 400 mAh / g. The initial discharge capacity is more preferably greater than 450 mAh / g, even more preferably greater than 500 mAh / g, even more preferably greater than 514 mAh / g, even more preferably greater than 550 mAh / g, even more preferably greater than 600 mAh / g, even more preferably greater than 650 mAh / g, even more preferably greater than 700 mAh / g, and even more preferably greater than 710 mAh / g. There is no particular limit to the upper limit of the initial discharge capacity, and the higher the better. Therefore, although there is little point in mentioning the upper limit of the initial discharge capacity, it can be assumed to be, for example, about 1000 mAh / g as a reference value.

[0071] [10th discharge capacity (DC 10 ) )] When the electrode of this embodiment is used as a positive electrode, the discharge capacity after 10 repeated charge and discharge cycles, that is, the 10th discharge capacity (DC 10) (mAh / g) is preferably greater than 350 mAh / g. The discharge capacity is more preferably greater than 400 mAh / g, even more preferably 478 mAh / g or greater, even more preferably greater than 500 mAh / g, even more preferably 536 mAh / g or greater, even more preferably greater than 600 mAh / g, even more preferably greater than 700 mAh / g, and even more preferably 710 mAh / g or greater. There is no particular limit to the upper limit of the discharge capacity, and the higher the capacity, the better. Therefore, although there is little meaning in mentioning the upper limit of the discharge capacity, it can be assumed, for example, to be approximately the value of the initial discharge capacity or approximately 900 mAh / g, merely as a reference value.

[0072] The third and tenth discharge capacities when the electrode of this embodiment is used as a positive electrode are determined by the configuration of the positive electrode, provided that the negative electrode and electrolyte are within the technical knowledge required for a lithium-ion secondary battery (i.e., that Li is not depleted) and are measured so that the performance related to the discharge capacity of the positive electrode can be fully demonstrated. For example, for the negative electrode, the amount of lithium used is preferably at least 2 times, more preferably at least 5 times, even more preferably at least 10 times, and even more preferably at least 50 times the amount (molar amount) of sulfur in the positive electrode. Furthermore, for example, for the electrolyte, the amount of electrolyte (microliters) is preferably at least 10 times, more preferably at least 20 times, and even more preferably at least 50 times the amount (mg) of sulfur in the positive electrode, so that the discharge capacity of the positive electrode can be fully demonstrated and the battery life can be extended. On the other hand, considering the energy density of the battery, a small amount of electrolyte is preferable. For example, the amount of electrolyte (microliters) is preferably 5 times or less, more preferably 3 times or less, and even more preferably 1 time or less, relative to the amount of sulfur (mg) in the positive electrode. Here, the volume V (mL) of the electrolyte refers to the total volume of the electrolyte including the solute. The electrolyte may be in the form of an electrolyte solution or a solid (solid electrolyte), or a combination of both.

[0073] (Uses) The lithium ion secondary battery electrode of this embodiment can be used as a positive electrode or a negative electrode of a lithium ion secondary battery. In addition, the lithium ion secondary battery electrode of this embodiment is preferably used as a positive electrode of a lithium ion secondary battery.

[0074] <Lithium-ion secondary battery> The lithium-ion secondary battery of this embodiment is a lithium-ion secondary battery including the above-described electrode.

[0075] The lithium ion secondary battery of this embodiment can be constructed using the materials described in the manufacturing method section below in the same manner as described in the same section. That is, when the lithium ion secondary battery electrode is used as a positive electrode, a lithium ion secondary battery can be constructed using the negative electrode, electrolyte, separator, etc. described in the manufacturing method section below in the same manner as described in the same section. On the other hand, when the lithium ion secondary battery electrode is used as a negative electrode, a lithium ion secondary battery can be constructed using the positive electrode, electrolyte, separator, etc. described in the manufacturing method section below in the same manner as described in the same section. In this way, the explanations in the manufacturing method section below can be taken into consideration as explanations of the present lithium ion secondary battery.

[0076] (Formula (4)) The lithium ion secondary battery of this embodiment further contains an electrolyte, the volume of the electrolyte being V (mL), and the coating density of the electrode active material on the current collector being V (mg / cm 2 ) is D, then D, V and A S It is preferable that D×A satisfies the following formula (4): S / V>600

[0077] The right side of formula (4) is more preferably 650, even more preferably 700, even more preferably 750, even more preferably 800, even more preferably 850, even more preferably 860, and even more preferably 865. The higher the value of the left side of formula (4), the more preferable it is, and there is no point in setting an upper limit, but as a reference value, a value of about 1500 can be assumed.

[0078] (Electrolyte Volume V) The range of the electrolyte volume V (mL) can vary depending on the size of the battery, so it is not generally specified. It is sufficient to use the minimum amount that brings out the performance of the electrode active material and allows the battery to function satisfactorily. For example, as a reference value, in the case of a coin-type battery presented in the examples, the volume is preferably 0.1 mL or more, more preferably 0.12 mL or more, and even more preferably 0.15 mL or more. Meanwhile, the volume V is preferably 0.40 mL or less, more preferably 0.30 mL or less, even more preferably 0.28 mL or less, and even more preferably 0.25 mL or less.

[0079] (Applications) The lithium ion secondary battery of the present embodiment is useful as a lithium ion secondary battery with improved overall performance in terms of charge / discharge capacity, capacity retention rate, and energy density, and can be used in mobile information terminals such as smartphones and notebook personal computers, mobile electronic devices such as music players and digital cameras, medical devices, as well as batteries for next-generation clean energy automobiles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs).

[0080] <Production Method> The methods for producing the electrode active material, electrode, and lithium ion secondary battery of this embodiment will be described below in order.

[0081] (Production of Electrode Active Material) The electrode active material of the present embodiment can be produced by, for example, (1) a step of mixing sulfur, an organic compound, and a raw metal compound to obtain a calcined raw material, (2) a step of calcining the calcined raw material to obtain a calcined product, and (3) a step of pulverizing the calcined product into particles to obtain an electrode active material.

[0082] [Raw Materials] Raw materials will be described below.

[0083] <Organic Compound> The organic compound is not particularly limited as long as it is a compound containing at least carbon atoms and hydrogen atoms, and when baked with sulfur under a non-oxidizing thermal atmosphere, it incorporates sulfur to form an organic sulfur compound. The organic compound may also contain a heteroatom such as a nitrogen atom or a sulfur atom. Specific examples of the organic compound include a polymer of an unsaturated chain hydrocarbon monomer and a condensate of a substituted aromatic hydrocarbon and sulfur chloride. The organic compound may be used alone or in combination of two or more.

[0084] <<Polymer of Unsaturated Chain Hydrocarbon Monomer>> Examples of polymers of unsaturated chain hydrocarbon monomers include resins such as acrylic resins. Examples of polymers of unsaturated chain hydrocarbon monomers include diene rubbers. One or more types of polymers of unsaturated chain hydrocarbon monomers can be used.

[0085] Examples of acrylic resins include polymers obtained by polymerizing a monomer containing at least one selected from the group consisting of acrylate compounds represented by the following chemical formula (1); polymers obtained by polymerizing a monomer containing at least one selected from the group consisting of acrylate compounds represented by the following chemical formula (1); polymers obtained by polymerizing a monomer containing at least one selected from the group consisting of acrylate compounds represented by the following chemical formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following chemical formula (2); and at least one polymer selected from the group consisting of polymers obtained by polymerizing a monomer containing at least one selected from the group consisting of acrylate compounds represented by the following chemical formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following chemical formula (2). One or more types of acrylic resins can be used. CH═C(R 11 ) COOR 12 (1) (where R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group.) CH2=C(R 21 )COO-Y-OCO(R 22) C=CH2 (2) (where R 21 and R 22 are the same or different and are a hydrogen atom or a methyl group, and Y is a linear hydrocarbylene group, which may have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbylene group may have an ether bond via an oxygen atom, provided that when there are two or more ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.

[0086] In the 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, and among these, a methyl group, an n-butyl group, an i-butyl group, or a t-butyl group is preferred. Examples of compounds represented by chemical formula (1) include methyl (meth)acrylate, butyl (meth)acrylate, etc., and more preferably methyl methacrylate and butyl methacrylate. Here, the "(meth)acrylate" in methyl (meth)acrylate and butyl (meth)acrylate refers to either "acrylate" or "methacrylate" (the same applies hereinafter). An even more preferred example of a compound represented by chemical formula (1) is butyl methacrylate.

[0087] In chemical formula (2), R 21 and R 22are preferably methyl groups. The number of carbon atoms in the hydrocarbylene group (straight chain) of Y is preferably 2 to 6, more preferably 2 or 3. The number of substituents in Y is preferably 1 to 4, more preferably 1 or 2. The substituents in Y are preferably one or more substituents selected from the group consisting of hydroxyl groups and alkyl groups having 1 to 4 carbon atoms, and the alkyl groups having 1 to 4 carbon atoms are preferably methyl groups. When the carbon skeleton of Y has an ether bond via an oxygen atom, for example, the portion corresponding to -Y-O- is preferably one represented by the following chemical formula (3) (however, in chemical formula (3), the substituents in Y are not taken into consideration). -(CH2) l -(CH2CH2O) m -(CH2CH2CH2O) n - (3) (where l is a number from 0 to 6, m is a number from 0 to 3, and n is a number from 0 to 2. However, l, m, and n cannot all be 0 at the same time.)

[0088] In chemical formula (3), it is preferred that l is 1, 2, 3, 4, 5, or 6, and m and n are 0; alternatively, m is 1, 2, or 3, and l and n are 0; or alternatively, n is 1 or 2, and l and m are 0.

[0089] Examples of the compound represented by chemical formula (2) include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyne glycol di(meth)acrylate, glycerin di(meth)acrylate, etc. Of these, ethylene glycol dimethacrylate is preferred.

[0090] Preferred examples of acrylic resins include homopolymers of methyl (meth)acrylate, homopolymers of butyl (meth)acrylate, copolymers of methyl (meth)acrylate and ethylene glycol di(meth)acrylate, and copolymers of butyl (meth)acrylate and ethylene glycol di(meth)acrylate. Of these, methacrylate-type acrylic resins are preferred. More preferred examples of acrylic resins include copolymers of methyl methacrylate and ethylene glycol dimethacrylate.

[0091] In this embodiment, the acrylic resin is preferably in the form of fine particles. Here, fine particles refer to particles having a particle diameter of 300.0 μm or less. The particle diameter is preferably 270.0 μm or less, more preferably 200.0 μm or less, even more preferably 100.0 μm or less, even more preferably 50.0 μm or less, even more preferably 20.0 μm or less, even more preferably 15.0 μm or less, even more preferably 13.0 μm or less, even more preferably 10.0 μm or less, even more preferably 6.0 μm or less. On the other hand, the lower limit of the particle diameter is not particularly limited, but is usually, for example, 0.1 μm or more, preferably 1.0 μm or more. The particle diameter is a value (median diameter) measured using a particle size distribution analyzer PSA1090L manufactured by Anton Paar.

[0092] The acrylic resin may be spherical fine particles or porous fine particles. When the acrylic resin is porous, its oil absorption is preferably 100 mL / 100 g or more, more preferably 110 mL / 100 g or more, even more preferably 120 mL / 100 g or more, even more preferably 130 mL / 100 g or more, and even more preferably 140 mL / 100 g or more. The oil absorption is a value measured in accordance with JIS K 5101-13-2:2004. More specifically, it can be measured by the method described in paragraph 0069 of JP 2017-88501 A.

[0093] The Mw of the acrylic resin is not particularly limited as long as it has the above structure. However, the Mw of the acrylic resin is usually within the range of 2,000 to 1,500,000. The Mw is a value measured by gel permeation chromatography (GPC) (calibrated with polystyrene).

[0094] The acrylic resins are commercially available or can be prepared by conventional methods within the knowledge of one skilled in the art, such as those manufactured by Sekisui Plastics Co., Ltd.

[0095] Diene rubbers include, for example, natural rubber, isoprene rubber, butadiene rubber such as high-cis polybutadiene rubber, etc. Diene rubbers are commercially available or can be prepared by conventional methods within the purview of those skilled in the art.

[0096] <<Condensate of Substituted Aromatic Hydrocarbon and Sulfur Chloride>> Examples of the condensate of substituted aromatic hydrocarbon and sulfur chloride include a condensate of alkylphenol and sulfur chloride. Specific examples of the condensate of alkylphenol and sulfur chloride include Tackirol V200, TS3108, and TS3109 manufactured by Taoka Chemical Co., Ltd., and Vultac3 manufactured by Arkema. One or more types of condensates of substituted aromatic hydrocarbon and sulfur chloride may be used.

[0097] <<Raw Metal Compound>> As the raw metal compound, the following raw metal compounds can be used.

[0098] <<Raw Iron Compound>> The raw iron compound may be an iron compound containing divalent or trivalent iron ions, but is not particularly limited as long as it decomposes during firing, reacts with sulfur, and produces iron disulfide, and various compounds can be used. Examples of the raw iron compound include iron acid salts, iron complexes, etc. Examples of iron acid salts include both organic iron acid salts and inorganic iron acid salts. On the other hand, examples of iron complexes include neutral iron complexes and salts of iron complex ions (iron complex salts). Of these, organic iron acid salts, inorganic iron acid salts, and neutral iron complexes are preferred. One or more iron compounds can be used.

[0099] Examples of organic acid salts of iron include divalent iron (Fe 2+ ) and organic acid salts, and trivalent iron (Fe 3+ ) and an organic acid salt. Of these, a salt of divalent iron and an organic acid is preferred. The organic acid is not particularly limited, and may include those having a carboxyl group (-COOH) or a sulfo group (-SO3H), but those having a carboxyl group are preferred. Specific examples of organic acids include fatty acids, oxalic acid, tartaric acid, citric acid, malic acid, and succinic acid. Specific examples of fatty acids include those having 1 to 6 carbon atoms, such as acetic acid, propionic acid, and butyric acid. Of these, acetic acid and oxalic acid are preferred. Preferred examples of iron organic acid salts include iron(II) acetate and iron(II) oxalate. These may be hydrates. One or more iron organic acid salts can be used.

[0100] Examples of inorganic salts of iron include divalent iron (Fe 2+ ) and inorganic acid salts, and trivalent iron (Fe 3+ ) and an inorganic acid. Specific examples of inorganic acids include hydrochloric acid, sulfuric acid, and nitric acid. Of these, nitric acid is preferred. Preferred examples of inorganic acid salts of iron include iron(II) chloride, iron(III) chloride, iron(II) sulfate, iron(III) sulfate, iron(II) nitrate, and iron(III) nitrate. These may also be hydrates. One or more inorganic acid salts of iron can be used.

[0101] Examples of iron complexes include divalent iron (Fe 2+ ) complexes and trivalent iron (Fe 3+ ) complexes. The iron complex may be in the form of a neutral complex or a complex salt. The ligand coordinating with the iron ion is not particularly limited and includes, for example, halogen atoms such as chlorine and bromine atoms, cyano groups, dicyclopentadienyl groups, and N,N'-bis(salicylidene)ethylenediamine. Examples of iron complexes include potassium hexacyanidoferrate(II) ([Fe(CN)6]K4), potassium hexacyanidoferrate(III) ([Fe(CN)6]K3), sodium tetrachloroferrate(III) ([FeCl4]Na), dicyclopentadienyl iron(II) (ferrocene), and N,N'-bis(salicylidene)ethylenediaminatoiron(III) chloride. One or more iron complexes can be used.

[0102] <<Raw Material Molybdenum Compound>> 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), etc. One or more types of molybdenum compounds can be used.

[0103] <<Raw Vanadium Compound>> Examples of the raw vanadium compound include vanadium pentoxide (V), ammonium metavanadate (V), vanadium oxytrichloride (V), sodium metavanadate (V), potassium vanadate (V), sodium vanadate (V), vanadium tetrachloride (IV), vanadium oxysulfate (IV), vanadium oxydichloride (IV), vanadium oxide (IV), vanadium trichloride (IV), vanadium oxide (III), and hexavanadium trioxide (IV, V). One or more vanadium compounds can be used.

[0104] <<Raw Titanium Compound>> Examples of the raw titanium compound include titanium oxide, titanium dioxide, titanium trioxide, titanium tetrachloride, etc. One or more types of titanium compounds can be used.

[0105] <<Content of Raw Metal Compound>> From the viewpoint of improving the performance of the electrode and / or battery, the content of the raw metal compound in the calcined raw material is preferably 50 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the organic compound. The content is more preferably more than 50 parts by mass, even more preferably more than 60 parts by mass, even more preferably more than 70 parts by mass, and even more preferably more than 75 parts by mass. On the other hand, the content is more preferably less than 250 parts by mass, even more preferably less than 200 parts by mass, even more preferably less than 150 parts by mass, and even more preferably 100 parts by mass or less.

[0106] <<Median diameter of raw metal compound>> The raw metal compound is preferably pulverized before use as a firing raw material. The median 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, even more preferably 6.00 μm or less, even more preferably 4.00 μm or less, and even more preferably 3.00 μm or less. On the other hand, there is no particular restriction on the lower limit of the median diameter, but it is usually about 0.10 μm or more, and may be about 1.00 μm or about 2.00 μm. The median diameter can be measured by the method described above.

[0107] <Specific surface area of ​​raw metal compound> The specific surface area of ​​the raw metal compound is 1.0 m 2 / g or more, and more preferably 2.0m 2 / g or more, more preferably 3.0m 2 / g or more, more preferably 4.0m 2 / g or more, more preferably 4.5m 2 On the other hand, there is no particular upper limit to the specific surface area, but it is usually 40.0 m 2 / g or less, and 2 / g or less, and 2 The specific surface area can be measured using a fully automatic specific surface area measuring device Macsorb (HM-model 1201, manufactured by Mountec Co., Ltd.).

[0108] The raw metal compound having the above-mentioned median diameter or specific surface area can be prepared by a conventional method, for example, by pulverizing the raw metal compound using a pulverizer, such as a pulverizer manufactured by Japan Analytical Industry Co., Ltd. (e.g., JFC-2000).

[0109] Sulfur can be used in various forms such as powdered sulfur, insoluble sulfur, precipitated sulfur, and colloidal sulfur, among which precipitated sulfur and colloidal sulfur are preferred. One or more types of sulfur can be used.

[0110] From the viewpoint of improving the performance of the electrode and / or battery, the sulfur content in the calcined raw material is preferably more than 50 parts by mass, more preferably more than 100 parts by mass, even more preferably more than 300 parts by mass, even more preferably more than 400 parts by mass, and even more preferably 500 parts by mass or more, relative to 100 parts by mass of the organic compound. A sulfur content of more than 50 parts by mass tends to improve charge / discharge capacity and cycle characteristics. On the other hand, there is no particular upper limit for the sulfur content, but it is preferably less than 1000 parts by mass, more preferably less than 900 parts by mass, even more preferably less than 800 parts by mass, and even more preferably less than 700 parts by mass. A sulfur content of less than 1000 parts by mass tends to be advantageous in terms of cost. In this specification, "cycle characteristics" refers to the property of maintaining the charge / discharge capacity of a secondary battery despite repeated charge / discharge. Therefore, a secondary battery that experiences a large decrease in charge / discharge capacity and a low capacity retention rate with repeated charge / discharge has poor cycle characteristics, whereas a secondary battery that experiences a small decrease in charge / discharge capacity and a high capacity retention rate has excellent cycle characteristics.

[0111] Although various allotropes of sulfur can be used, sulfur containing S8 sulfur, which is solid at room temperature and pressure, is preferred, and simple S8 sulfur is more preferred.

[0112] <<Other Materials>> The raw material may contain other materials commonly used in this field, as desired. Examples of such raw materials include carbon materials.

[0113] <<Carbon Material>> In the electrode active material of this embodiment, the carbon material preferably has a graphite structure. Furthermore, the carbon material is preferably conductive. Examples of carbon materials include porous carbon materials such as activated carbon, graphite, carbon black, acetylene black, and ketjen black, as well as carbon fibers such as carbon fiber, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofiber, and nanocarbon materials in a form other than carbon fiber, such as graphene and fullerene. Among these, carbon fibers such as carbon fiber, vapor-grown carbon fiber (VGCF), CNT, and carbon nanofiber are preferred, with CNT being particularly preferred. One or more types of carbon materials can be used.

[0114] When the carbon material is carbon fiber, the form of the fibers constituting the carbon fiber is preferably such that the average fiber length is a predetermined value or more and the average fiber diameter is a predetermined value or less, from the viewpoint of improving the performance of the electrode and / or battery. This is because it is believed that the 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 even more preferably greater than 2 μm. There is no particular upper limit to the average fiber length, and it may be 100 μm, 50 μm, or 20 μm. In addition, the average fiber diameter is preferably less than 100 nm, more preferably less than 50 nm, and even more preferably less than 10 nm. There is no particular lower limit to the average fiber diameter, but it is usually about 1 nm.

[0115] The aspect ratio of the carbon material is preferably greater than 10, more preferably greater than 100, and even more preferably greater than 1,000, and is preferably less than 100,000, more preferably less than 50,000, and even more preferably less than 10,000.

[0116] From the viewpoint of the effect of the present invention, the carbon material has a specific surface area of ​​400 m 2 / g or more, and 2 The specific surface area is preferably 500 m / g or less. 2 / g or more is more preferable, and 600m 2 On the other hand, the specific surface area is preferably 2000 m / g or more. 2 / g or less is more preferable, and 1800m 2 The specific surface area is measured by the BET multipoint method.

[0117] From the viewpoint of the effects of the present invention, the carbon material preferably has a G / D ratio of 10 or more. The G / D ratio is more preferably 20 or more, even more preferably 30 or more, and even more preferably 40 or more. On the other hand, there is no particular upper limit to the G / D ratio, but a G / D ratio of 90 or more can be said to be a carbon material with extremely few defects. Here, the G / D ratio refers to the ratio of a representative Raman shift peak in the Raman spectrum of the carbon material, and more specifically, the ratio of the G-band peak derived from the graphite structure to the D-band peak derived from defects. The Raman spectrum was measured using a RAMANTouch (excitation wavelength λ=532 nm, grating: 1200 gr / mm, resolution: 1.2 cm-1) manufactured by Nanophoton Co., Ltd.

[0118] From the viewpoint of the effects of the present invention, the carbon material preferably has a metal impurity content of 5% by mass or less. The metal impurity content is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. The lower the metal impurity content, the better, and for example, 0.1% by mass is a sufficiently low metal impurity content. The metal impurities are measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0119] From the viewpoint of improving the performance of the electrode and / or battery, the content of the carbon material in the firing raw material is preferably less than 5 parts by mass relative to 100 parts by mass of the organic compound. The content is more preferably less than 1 part by mass, and even more preferably less than 0.5 parts by mass. On the other hand, the content is preferably more than 0.05 parts by mass, more preferably more than 0.07 parts by mass, and even more preferably 0.10 parts by mass or more.

[0120] (Production Process) [Mixing Step (1)] The mixing step is a step of preparing a raw material for firing. The mixing step can be carried out by mixing sulfur, an organic compound, a raw material metal compound, and, if desired, other optional components.

[0121] The mixing can be carried out by a conventional method, and is not particularly limited as long as the components are sufficiently mixed. In this embodiment, at least the following wet method or dry method is preferred.

[0122] <<WET Method>> In the present embodiment, the WET method includes, in preparing a raw material, the steps of: (a-1) adding an organic compound and a raw material metal compound to a solvent such as an organic solvent to obtain a mixture; (a-2) removing the solvent from the mixture to obtain a dry mixture; and (a-3) mixing the dry mixture with sulfur.

[0123] In step (a-1), the method for adding the organic compound and the raw material metal compound to the organic solvent is not particularly limited, as long as they can be mixed to obtain a mixture. For example, (1) the organic compound and the raw material metal compound may be simultaneously added to the organic solvent and mixed, or (2) one of them may be added to the organic solvent first and mixed, and then the other may be added and mixed. In this case, the combination of raw materials added first and the combination of raw materials added later are not particularly limited.

[0124] In step (a-1), the organic solvent may be any organic solvent commonly used in this field, and examples of such solvents include N-methyl-2-pyrrolidone, N,N-dimethylformaldehyde, alcohol, hexane, water, acetone, ethers such as tetrahydrofuran, and the like. Furthermore, the organic solvent is preferably one that dissolves organic compounds, as this contributes to good mixing. One or more of these solvents may be used.

[0125] Step (a-1) can be carried out, for example, by stirring in a container such as a beaker.

[0126] In step (a-2), the organic solvent can be removed by a conventional method, for example, by subjecting the mixture of step (a-1) to a drying method such as heat drying, drying under reduced pressure, or drying under reduced pressure with heat.

[0127] The dry mixture thus obtained is preferably pulverized before being subjected to the next step, since this is expected to enable more efficient mixing in step (a-3).

[0128] In the step (a-3), the dry mixture and sulfur can be mixed by a conventional method, for example, by using a blender.

[0129] When an optional component is used, the optional component can be mixed in step (a-1). In this case, the order in which the raw material metal compounds are added to the organic solvent is not particularly limited, as with the other raw materials, and the raw materials may be added in any order.

[0130] <DRY Method> In the present embodiment, the DRY method is a method for preparing a raw material, which includes the step of: (b-1) mixing an organic compound, a raw material metal compound, and sulfur, all in a powder state.

[0131] Here, the term "powder" refers to a state in which the solid raw materials are sufficiently finely divided to be suitable for mixing for the purposes of the present invention. The size of each particle constituting the powder is not particularly limited as long as mixing is carried out appropriately, but is usually, for example, in the range of 1 μm to 40 μm. From the viewpoint of improving the performance of the electrode and / or battery, the particle size, in terms of median diameter, is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, and preferably 30 μm or less, even more preferably 20 μm or less, even more preferably 15 μm or less, and even more preferably 10 μm or less. The median diameter can be measured by the method described above.

[0132] The mixing can be carried out by a conventional method, for example, in the same manner as in the mixing in the above step (a-3). In addition, when an optional component is added to the raw material, this may also be mixed together.

[0133] In either the wet method or the dry method, it is desirable to thoroughly mix the raw materials in advance in preparation for firing.

[0134] The raw material thus obtained may be used as it is in the next firing step, or may be formed into pellets as desired and then used in the next step.

[0135] [Firing step (2)] The firing step is a step of firing the firing raw material obtained above. Firing can be performed by a conventional method, for example, by heating the firing raw material at a predetermined temperature increase rate until it reaches a predetermined temperature, maintaining the predetermined temperature for a predetermined time, and then allowing it to cool naturally.

[0136] <Non-oxidizing atmosphere> The firing is preferably carried out in a non-oxidizing atmosphere. A non-oxidizing atmosphere refers to an atmosphere that is substantially free of oxygen and is adopted to suppress oxidative degradation of the constituent components and excessive thermal decomposition. Specifically, the non-oxidizing atmosphere refers to an inert gas atmosphere such as nitrogen or argon, a sulfur gas atmosphere, an ammonia gas atmosphere, etc. Therefore, the firing can be suitably carried out, for example, in a quartz tube under an inert gas atmosphere.

[0137] <<Heating Rate>> The heating rate is preferably, for example, in the range of 50°C / h or more and 500°C / h or less. The heating rate is preferably 80°C / h or more, more preferably 100°C / h or more, and even more preferably 120°C / h or more. On the other hand, the heating rate is more preferably 400°C / h or less, even more preferably 300°C / h or less, and even more preferably 200°C / h or less. When the heating rate is within such a range, it tends to be easier to achieve the objective of improving the charge / discharge capacity and cycle characteristics.

[0138] <<Firing temperature and time>> The firing temperature refers to the temperature after the temperature rise of the raw materials is completed, and is maintained for a certain period of time to fire the raw materials. The temperature is preferably in the range of more than 250°C and less than 550°C. A temperature above 250°C tends to avoid insufficient sulfurization reaction and prevent a decrease in the charge / discharge capacity of the target product. On the other hand, a temperature below 550°C tends to prevent decomposition of the raw materials and prevent a decrease in yield and a decrease in charge / discharge capacity. The temperature is more preferably above 300°C, even more preferably above 350°C, and even more preferably 370°C or higher. On the other hand, less than 500°C is more preferably, and even more preferably less than 450°C.

[0139] From the viewpoint of improving the performance of the electrode and / or battery, the firing temperature in the firing step is preferably higher than the temperature at which the raw metal compound thermally decomposes.

[0140] The time for maintaining the calcination temperature may be appropriately set depending on the type of raw material, the calcination temperature, etc., but is preferably, for example, 1 hour or more and 6 hours or less. A time of 1 hour or more tends to allow the calcination to proceed sufficiently, while a time of 6 hours or less tends to prevent excessive thermal decomposition of the constituent components.

[0141] <Apparatus> The calcination can be carried out, for example, using a muffle furnace (FIG. 1), or can be carried out using a continuous apparatus such as a twin-screw extruder. When a continuous apparatus is used, there is an advantage that the sulfur-based electrode active material can be continuously produced by a series of operations, such as kneading, pulverizing, and mixing the raw materials in the apparatus while calcining.

[0142] A muffle furnace (Figure 1) is a furnace partitioned by a hot plate or the like to prevent the heat source (heater) from being exposed inside the furnace in order to prevent sample contamination. In Figure 1, muffle furnace 1 has heater 2 at the bottom of the furnace, which is partitioned by a hot plate. A lid 3 is installed on the front of the furnace (on the left end in the figure), and the furnace is designed to maintain an atmosphere of inert gas 4 inside the furnace. A thermocouple (not shown) is attached to the lid, allowing the temperature inside the furnace to be measured during firing. Inside the furnace, two trays 5 and 6, which are rectangular parallelepiped stainless steel reaction vessels for firing the raw materials, are installed on the upper and lower levels.

[0143] Gas (e.g., an inert gas such as argon (Ar) gas) can be continuously supplied to and discharged from the inside of the furnace through a gas inlet pipe 7 and a gas outlet pipe 8. The gas outlet pipe 8 is connected to a trap tank 10 containing an aqueous sodium hydroxide solution 9, and exhaust gas attempting to exit the muffle furnace 1 through the gas outlet pipe 8 to the outside first passes through the aqueous sodium hydroxide solution 9 in the trap tank 10 before being released to the outside. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the reaction, it is neutralized by the aqueous sodium hydroxide solution and removed from the exhaust gas.

[0144] [Residue Removal Step] The treated product obtained after calcination may contain unreacted sulfur, which is the sulfur that sublimed during calcination and then cooled and precipitated. Since these residues can cause a decrease in cycle characteristics, it is desirable to remove as much of the residue as possible if any. The residue removal can be carried out by a conventional method, such as reduced pressure heating drying, hot air drying, or solvent washing.

[0145] [Pulverization and Classification] The obtained electrode active material is preferably pulverized to a predetermined particle size and classified to obtain particles of a size suitable for producing an electrode. The preferred size range of the electrode active material particles is as described above.

[0146] Pulverization can be carried out by conventional methods, for example, by subjecting a pulverizer such as a cutter mill or a jet mill to pulverization under specified conditions. The pulverization conditions vary depending on the mill used, but for example, when using a cutter mill (e.g., a free speed mill, FS-20, manufactured by Labnect Co., Ltd.), the processing can be carried out at a rotation speed of 20,000 rpm to 30,000 rpm and for 1 second to 30 seconds. Furthermore, when using a dry jet mill (e.g., a nanojetmizer, NJ-30, manufactured by Aisin Nano Technologies Co., Ltd.), the processing speed can be 1 g / min to 3 g / min and the pulverization pressure can be 0.5 MPa to 2.0 MPa. Furthermore, classification can be carried out using, for example, a sieve.

[0147] In the firing method using the twin-screw extruder described above, the electrode active material can be produced and simultaneously pulverized into particles by shearing during kneading.

[0148] (Production of Electrode for Lithium-Ion Secondary Battery) Using the electrode active material obtained above, a lithium-ion secondary battery electrode having an electrode active material layer containing the electrode active material can be produced by a conventional method. That is, the electrode can be obtained in the same manner as in the production of a general electrode for a lithium-ion secondary battery, except that the electrode active material described above is used as the active material.

[0149] [When the electrode active material is used as the positive electrode active material] The positive electrode for a lithium ion secondary battery can be produced in the same manner as a general positive electrode for a lithium ion secondary battery, except that the above-mentioned electrode active material is used as the positive electrode active material. For example, the positive electrode can be produced by mixing the electrode active material with a conductive additive, a binder, and a solvent to prepare a paste-like positive electrode material, applying the positive electrode material to a current collector, and then drying it. Alternatively, the positive electrode can be produced by kneading the electrode active material with the conductive additive, the binder, and a small amount of solvent in a mortar or the like, forming it into a film, and then pressing it onto a current collector using a press or the like.

[0150] <Conductive Aid> Examples of conductive aids include vapor-grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, or fine powders of metals that are stable at a positive electrode potential, such as aluminum and titanium. Furthermore, conductive carbon materials among the above-mentioned carbon materials can also be used as the conductive aid. One or more of these conductive aids can be used.

[0151] <Binder> Examples of binders include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (PAI), carboxymethyl cellulose (CMC), polyvinyl chloride (PVC), acrylic resin, methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), etc. One or more of these binders can be used.

[0152] <Solvent> Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformaldehyde, alcohol, hexane, water, etc. These solvents can be used alone or in combination of two or more.

[0153] <<Bundling Amount>> The blending amounts of these materials constituting the positive electrode are not particularly limited, but for example, it is preferable to blend 2 to 100 parts by mass of a conductive additive, 2 to 50 parts by mass of a binder, and an appropriate amount of a solvent with respect to 100 parts by mass of an electrode active material.

[0154] <Current Collector> The current collector may be one generally used for the positive electrode of a lithium ion secondary battery. Examples of current collectors include metal foils such as aluminum foil, aluminum mesh, punched aluminum sheet, aluminum expanded sheet, stainless steel foil, stainless steel mesh, punched stainless steel sheet, stainless steel expanded sheet, foamed nickel, nickel nonwoven fabric, copper foil, copper mesh, punched copper sheet, copper expanded sheet, titanium foil, and titanium mesh, as well as carbon nonwoven fabric and carbon woven fabric. Among these, current collectors containing metal foil are preferred. One type of current collector may be used, or two or more types may be used in combination. The surface of the current collector may be coated with carbon or the like. A specific example of such a current collector whose surface is coated with carbon or the like is carbon-coated aluminum foil. In this case, the current collector includes a carbon-coated portion.

[0155] [When the electrode active material is used as the negative electrode active material] The negative electrode for a lithium ion secondary battery can be produced in the same manner as a general negative electrode for a lithium ion secondary battery, except that the above-mentioned electrode active material is used as the negative electrode active material. For example, the negative electrode can be produced by mixing the electrode active material with a conductive additive, a binder, and a solvent to prepare a paste-like negative electrode material, applying the negative electrode material to a current collector, and then drying it. Alternatively, the negative electrode can be produced by kneading the electrode active material together with the conductive additive, the binder, and a small amount of solvent in a mortar or the like, forming it into a film, and then pressing it onto a current collector using a press or the like.

[0156] The conductive additive, binder, and solvent can be the same as those used in the above case where the electrode active material is used as the positive electrode active material, and the same current collector can also be used.

[0157] (Manufacturing of Lithium-Ion Secondary Battery) The lithium-ion secondary battery of this embodiment can be manufactured in the same manner as in the case of manufacturing a general lithium-ion secondary battery, except that the lithium-ion secondary battery electrode obtained above is used.

[0158] [When the electrode active material is used as a positive electrode active material] The lithium ion secondary battery of the present embodiment can be produced according to a conventional method by using a positive electrode containing the electrode active material (positive electrode active material), a negative electrode, an electrolyte, and, if desired, components such as a separator.

[0159] <Negative Electrode> As the negative electrode material, known metallic lithium, carbon-based materials such as graphite, silicon-based materials such as silicon thin films, and alloy-based materials such as copper-tin and cobalt-tin can be used. When a lithium-free material is used as the negative electrode material, for example, a carbon-based material, silicon-based material, or alloy-based material among the above-mentioned negative electrode materials, it is advantageous in that it is less likely to cause a short circuit between the positive and negative electrodes due to the generation of dendrites. However, when these lithium-free negative electrode materials are used in combination with the positive electrode of this embodiment, neither the positive electrode nor the negative electrode contains lithium. For this reason, a lithium pre-doping process is required to pre-insert lithium into either the negative electrode or the positive electrode, or both. Known methods can be used for pre-doping lithium. For example, when doping lithium into the negative electrode, a method is used in which a half-cell is assembled using metallic lithium as the counter electrode and lithium is inserted by an electrolytic doping method in which lithium is electrochemically doped, or a method is used in which metallic lithium foil is attached to the electrode and then left in an electrolyte solution to dope lithium into the electrode by utilizing the diffusion of lithium into the electrode. The above-mentioned electrolytic doping method can also be used when pre-doping the positive electrode with lithium. As a lithium-free negative electrode material, a silicon-based material, which is a high-capacity negative electrode material, is particularly preferred, and among them, thin-film silicon, which has a thin electrode thickness and is advantageous in terms of capacity per volume, is more preferred.

[0160] <Electrolyte> The electrolyte compensates for the charge generated by the release of electrons into an external circuit due to the oxidation / reduction of the electrode active material at the positive and negative electrodes with the flow of ions. The electrolyte used in lithium-ion secondary batteries can be an electrolyte obtained by dissolving an alkali metal salt in an organic solvent. The organic solvent is preferably at least one selected from non-aqueous solvents such as dimethoxyethane, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, γ-butyrolactone, and acetonitrile. Examples of electrolytes that can be used include Li(FSO2)2N, LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiI, and LiClO4. The electrolyte concentration may be approximately 0.5 mol / L to 5.0 mol / L. The electrolyte is not limited to a liquid form. For example, when the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid state (for example, a polymer gel state).

[0161] <<Separator>> A lithium ion secondary battery may include components such as a separator in addition to the above-mentioned negative electrode, positive electrode, and electrolyte. The separator is interposed between the positive electrode and negative electrode, allowing ion migration between the positive electrode and negative electrode and preventing internal short-circuiting between the positive electrode and negative electrode. If the lithium ion secondary battery is a sealed type, the separator is also required to have the function of retaining the electrolyte. As the separator, it is preferable to use a thin, microporous or nonwoven membrane made of a material such as polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, or glass.

[0162] <<Shape>> 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, and a button shape can be used.

[0163] [When the electrode active material is used as a negative electrode active material] The lithium ion secondary battery of the present embodiment can be produced in accordance with a conventional method by using a negative electrode containing the electrode active material (negative electrode active material), a positive electrode, an electrolyte, and, if desired, components such as a separator.

[0164] <<Positive Electrode>> The positive electrode material is not particularly limited as long as it is, for example, a lithium-containing transition metal oxide or solid solution oxide, or a substance that can electrochemically absorb and release lithium ions. Examples of lithium-containing transition metal oxides include Li-Co composite oxides such as LiCoO2, LiNi x Co y Mn z Examples of the solid solution oxide include Li, Ni, Co, Mn-based composite oxides such as LiNiO, LiNiO, LiMn ... 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 O4, etc. These compounds may be used alone or in combination.

[0165] Others The electrolyte, separator, and shape of the lithium ion secondary battery can be the same as those in the above case where the electrode active material is used as the positive electrode active material.

[0166] The present invention will be described based on examples, but the present invention is not limited to only the examples.

[0167] The various chemicals used in the examples and comparative examples are listed below. The various chemicals were purified according to conventional methods as necessary.

[0168] <Materials used in the test> Organic compound: spherical acrylic resin made of a homopolymer of methyl methacrylate (Techpolymer MB-4 manufactured by Sekisui Plastics Co., Ltd., particle size: 4 μm) Raw metal compound (iron compound): iron (II) oxalate dihydrate (iron (II) oxalate dihydrate, special grade manufactured by Kanto Chemical Co., Ltd.) Carbon material: carbon nanotubes (CNT) (CNT dispersion manufactured by Kusumoto Chemicals 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 content: 1 mass% or less) Sulfur: precipitated sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Organic solvent (WET method): N-methyl-2-pyrrolidone (manufactured by Yoneyama Pharmaceutical Co., Ltd.)

[0169] Production Example 1 (Fine Grinding of Raw Metal Compound) Before use as a raw material, the raw metal compound was pulverized for 10 minutes in a frozen pulverizer (JFC-2000 manufactured by Japan Analytical Industry Co., Ltd.).

[0170] Production Example 2 (Preparation of Dry Mixture by WET Method) In examples in Table 1 where the mixing method is indicated as WET, a dry mixture consisting of an organic compound, a raw metal compound, and a carbon material was prepared by the WET method before preparing the calcined raw material. In preparing the dry mixture, the organic compound was first added to an organic solvent and thoroughly mixed, and then the raw metal compound and the carbon material were added and mixed to obtain a liquid mixture. Next, the organic solvent was removed from the liquid mixture, and the mixture was pulverized using a cutter mill (LAB MILL, manufactured by Osaka Chemical Co., Ltd.) to obtain a dry mixture.

[0171] <Preparation of electrode active material> (Preparation of raw material for calcination) In examples in which a dry mixture was prepared in advance by the WET method, the dry mixture and sulfur were mixed using a blender to obtain a raw material for calcination. In other examples (e.g., Reference Example y and Reference Example z), the raw materials were mixed using a blender to obtain a raw material for calcination.

[0172] (Reaction Apparatus) A muffle furnace (FIG. 1) was used to calcinate the raw materials. The muffle furnace in FIG. 1 is as described above.

[0173] (Firing process) First, the firing raw materials were placed in a tray, which was a stainless steel reaction vessel, and the atmosphere in the muffle furnace was replaced with Ar gas three times using a vacuum pump. Then, Ar gas was continuously supplied from the gas inlet tube at a flow rate of 100 mL / min, and 30 minutes after the start of supply, heating of the muffle furnace was started. The temperature was increased at a rate of 5 ° C. / min, and when the temperature of the firing raw materials reached the firing temperature listed in Table 1, heat treatment was performed for 2 hours while maintaining that temperature. Next, while adjusting the flow rate of Ar gas, the temperature of the fired product was naturally cooled to 25 ° C. under an Ar gas atmosphere, and then the fired product was removed from the muffle furnace.

[0174] (Removal of Unreacted Sulfur) In order to remove unreacted sulfur (free elemental sulfur) remaining in the product after the calcination step, the following step was carried out. That is, the calcined product was pulverized in a mortar, and the pulverized product was placed in a glass tube oven and heated at 250°C for 3 hours while evacuating to obtain an electrode active material from which unreacted sulfur had been removed (or which contained only a trace amount of unreacted sulfur). The temperature increase rate was 10°C / min.

[0175] (Pulverization Step) The calcined product from which the unreacted sulfur had been removed was pulverized using a cutter mill (free speed mill, FS-20, manufactured by Labnect Co., Ltd.).

[0176] (Classification Operation) In order to remove coarse particles from the pulverized fired product, the product was classified using a stainless steel sieve with a mesh of 32 μm to obtain an electrode active material.

[0177] <Physical Properties of Electrode Active Material> The electrode active material obtained above was examined for the following properties.

[0178] (Elemental Analysis) The elemental amounts of carbon, hydrogen, nitrogen, and sulfur were calculated as the mass ratio (%) of each element to the total amount of the electrode active material from the masses measured using a fully automatic elemental analyzer, Vario MICRO Cube, manufactured by Elementar. The results are shown in Table 1.

[0179] (Amount of Iron Element) Each electrode active material was subjected to thermogravimetry, and the amount of iron element (mass %) was calculated based on the obtained measurement results.

[0180] Thermogravimetric measurements were performed using a TGA Q500 manufactured by TA Instruments. The measurement conditions were as follows: the electrode active material was heated to 750°C in an Ar atmosphere, and then air was introduced to completely decompose the measurement sample. The ash content (mass%) of each electrode active material was then calculated from the measured weight loss rate (mass%) using the following formula: Ash content (mass%) = 100 - weight loss rate (mass%)

[0181] Furthermore, since it was confirmed that the iron element in each electrode active material was present as iron disulfide (FeS), the iron disulfide ratio (mass%) was calculated from the ash ratio (mass%) of each electrode active material using the following formula. That is, the weight loss rate (100 mass%) of Reference Example y in Table 1 indicates that the organic compound is completely decomposed after conversion to sulfide, while the weight loss rate (36 mass%) of Reference Example z indicates that the iron disulfide (FeS) in the electrode active material is reduced in weight by 36 mass%. Therefore, the iron disulfide (FeS) ratio (mass%) in each electrode active material was calculated using the following formula: FeS ratio (mass%) = ash ratio × {100 / (100-36)}

[0182] Furthermore, the iron element content (Fe content, mass %) was calculated from the FeS content (mass %) by the following formula: Fe content (mass %) = FeS content × Fe atomic weight / (Fe atomic weight + S atomic weight × 2) (where the Fe atomic weight was 55.845 and the S atomic weight was 32.065).

[0183] (Particle size distribution, median diameter) The particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (Anton Paar PSA1090L particle size distribution analyzer) with water as a dispersion medium to obtain a particle size distribution curve. From the particle size distribution curve, the volume-based cumulative 50% diameter (median diameter d50) was measured.

[0184] (Powder Resistivity) Powder resistivity (Ω cm) was measured using an automatic powder resistivity measurement system (MCP-PD600 manufactured by Nitto Seiko Air Analytec Co., Ltd.), in which 1 g of a measurement object made of particles was set in a φ20 mm probe unit and compressed under a load of 20 kN to form a pellet-shaped measurement sample, and the measurement sample was measured using a four-probe method (electrode diameter 3 mm) in an environment of normal temperature and normal humidity (temperature 23°C, relative humidity 50%).

[0185] The results are shown in Table 1 below.

[0186]

[0187] <Fabrication of Lithium-Ion Secondary Battery> A lithium-ion secondary battery was fabricated as follows.

[0188] (Positive electrode) The electrode active material obtained above was used as the active material, acetylene black (manufactured by Denka Co., Ltd., HS-100) and vapor-grown carbon fiber (manufactured by Showa Denko K.K., VGCF) as a conductive additive, and acrylic resin (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average molecular weight 2700 to 7500) was used as a binder. These were weighed so that the ratio was active material: acetylene black: vapor-grown carbon fiber: binder = 95: 1.25: 1.25: 2.5 (mass%), placed in a container, and stirred and mixed using a centrifugal mixer (manufactured by Thinky Corporation, ARE-250) using milliQ water as a dispersant to prepare a uniform slurry. The prepared slurry was applied to a 17 μm aluminum foil using an applicator with a slit width of 100 μm, and the electrode compressed using a roll press was heated in a dryer at 120° C. for 3 hours. After drying, the electrode was punched out to a diameter of 11 mm to obtain an electrode (positive electrode). The mass of the electrode was then measured, and the amount of active material in the electrode was calculated from the above ratio.

[0189] (Negative Electrode) A metallic lithium foil (disk-shaped, 14 mm in diameter and 500 μm in thickness, manufactured by Honjo Metals Co., Ltd.) was used as the negative electrode. A stainless steel sheet was used as the negative electrode current collector.

[0190] (Electrolyte) A non-aqueous electrolyte prepared by dissolving LiPF in a mixed solvent of ethylene carbonate and diethyl carbonate was used as the electrolyte. The ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1. The concentration of LiPF in the electrolyte was 1.0 mol / L.

[0191] (Lithium-ion secondary battery) A coin battery was fabricated using the above positive and negative electrodes. Specifically, in a dry room, a separator (Celgard 2400, a 25 μm thick polypropylene microporous membrane manufactured by Celgard) and a glass nonwoven fabric filter (440 μm thick, GA100 manufactured by Advantec) were sandwiched between the positive and negative electrodes to form an electrode battery. This electrode battery was housed in a battery case (CR2032 type coin battery material, manufactured by Hosen Co., Ltd.) made of a stainless steel container. The above electrolyte solution was poured into the battery case. The volume of the electrolyte was 0.28 mL. The battery case was sealed using a crimping machine to obtain the lithium-ion secondary batteries of each example and comparative example.

[0192] <Evaluation of Lithium-Ion Secondary Battery> (Discharge Capacity, Capacity Retention Rate) The coin-type lithium-ion secondary batteries produced in each Example and Comparative Example were charged and discharged at a current value equivalent to 50 mA per 1 g of positive electrode active material at a test temperature of 30°C. The discharge end voltage was 1.0 V, and the charge end voltage was 3.0 V. Charging and discharging were repeated, and the battery discharge capacity (mAh) was observed after 1, 2, 3, and 10 cycles. The measurements were performed using a battery performance evaluation device (BLS System, manufactured by Measuring Instrument Center Co., Ltd.).

[0193] The third discharge capacity DC3 (mAh / g) was taken as the initial capacity. The larger the initial capacity, the larger the charge / discharge capacity of the lithium ion secondary battery, and the more preferable it can be evaluated. The third discharge capacity DC3 (mAh / g) and the tenth discharge capacity DC 10 The capacity retention rate (%) was calculated from the capacity (mAh / g) using the following formula. The higher the capacity retention rate, the better the cycle characteristics of the lithium ion secondary battery. Capacity retention rate (%) = (DC 10 / DC3) x 100

[0194] The results are shown in Table 2 below.

[0195]

[0196] <Embodiments> Preferred embodiments are described below.

[0197] [1] An electrode active material comprising particles containing an organic sulfur compound and a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, wherein the powder resistivity of the particles is 1.0×10 3 Ω cm, preferably less than 500, more preferably less than 300, and even more preferably less than 150, and the sulfur content (mass%) in the electrode active material is A S and the powder resistivity is R P In the case where A S and R P and satisfies the following formula, and preferably the right side of formula (1) is 0.10. S / R P ≧0.05 [2] The electrode active material according to the above [1], wherein the right-hand side of formula (1) is 0.50, preferably 0.56, more preferably 0.80, even more preferably 0.86, even more preferably 1.00, and even more preferably 3.00. [3] The electrode active material according to the above [1], wherein the right-hand side of formula (1) is 5.00, preferably 6.00, and even more preferably 6.70. [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, even more preferably less than 50, and even more preferably less than 30. [5] The electrode active material according to any one of the above [1] to [3], wherein the powder resistivity is less than 10. [6] The electrode active material according to any one of the above [1] to [5], wherein the metal compound is an iron compound. [7] An electrode comprising the electrode active material according to any one of the above [1] to [6]. [8] The electrode includes a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector is 2 ) is D, then D and A Sand satisfy the following formula, and the right side of formula (2) is preferably 190, more preferably 193, even more preferably 195, even more preferably 200, even more preferably 210, even more preferably 220, even more preferably 230, even more preferably 240, even more preferably 242, and even more preferably 244. S [9] The electrode includes a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector 2 ) is D and the thickness of the metal foil is T (μm), D, T and A S and satisfy the following formula, and the right side of formula (3) is preferably 11.0, more preferably 11.3, even more preferably 11.4, even more preferably 12.0, even more preferably 13.0, even more preferably 14.0, even more preferably 14.2, even more preferably 14.3. S / T>10.0

[10] The electrode includes a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector 2 ) is D, D is 2.5 mg / cm 2 More than 3.00 mg / cm 2 More preferably, greater than 3.50 mg / cm 2 More preferably, greater than 3.80 mg / cm 2 More preferably, greater than 3.90 mg / cm 2

[11] The electrode according to any one of the above [7] to [9], wherein DC3 is greater than 400 mAh / g, preferably greater than 450 mAh / g, more preferably greater than 500 mAh / g, even more preferably 514 mAh / g or more, even more preferably greater than 550 mAh / g, even more preferably greater than 600 mAh / g, even more preferably greater than 650 mAh / g, even more preferably greater than 700 mAh / g, and even more preferably greater than 710 mAh / g, when the third discharge capacity when the electrode is used as a positive electrode is DC3.

[12] 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, even more preferably greater than 514 mAh / g, even more preferably greater than 550 mAh / g, even more preferably greater than 600 mAh / g, even more preferably greater than 650 mAh / g, even more preferably greater than 700 mAh / g, and even more preferably greater than 710 mAh / g when the tenth discharge capacity when the electrode is used as a positive electrode is DC 10 When this is done, DC 10The electrode according to any one of the above [7] to

[11] , wherein the average capacitance is greater than 350 mAh / g, preferably greater than 400 mAh / g, more preferably 478 mAh / g or more, even more preferably greater than 500 mAh / g, even more preferably 536 mAh / g or more, even more preferably greater than 600 mAh / g, even more preferably greater than 700 mAh / g, even more preferably 710 mAh / g or more.

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

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

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

[13] .

[15] A lithium ion secondary battery further comprising an electrolyte, wherein the volume of the electrolyte is V (mL), and the coating density (mg / cm) of the electrode active material on the current collector is 2 ) is D, then D, V and A S and satisfy the following formula, and are preferably 650, more preferably 700, even more preferably 750, even more preferably 800, even more preferably 850, even more preferably 860, and even more preferably 865. S / V>600

[0198] REFERENCE SIGNS LIST 1 muffle furnace 2 heater 3 lid 4 inert gas 5 tray (upper stage) 6 tray (lower stage) 7 gas inlet pipe 8 gas outlet pipe 9 sodium hydroxide aqueous solution 10 trap tank

Claims

1. An electrode active material comprising particles containing an organic sulfur compound and a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, wherein the powder resistivity of the particles is 1.0×10 3 The sulfur content (mass%) in the electrode active material is less than A S and the powder resistivity is R P In the case where A S and R P and an electrode active material that satisfies the following formula. S / R P ≧0.05 2. The electrode active material according to claim 1, wherein the right side of formula (1) is 0.

50.

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

00.

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

5. The electrode active material according to any one of claims 1 to 3, which has a powder resistivity of 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 includes a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector is 2 ) is D, then D and A S The electrode according to claim 7, wherein (2) D x A satisfies the following formula: S >150 9. The electrode comprises a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector 2 ) is D and the thickness of the metal foil is T (μm), D, T and A S The electrode according to claim 7, wherein (3) D x A satisfies the following formula: S / T>10.0 10. The electrode comprises a current collector, the current collector includes a metal foil, and the coating density (mg / cm) of the electrode active material on the current collector 2 ) is D, D is 2.5 mg / cm 2 The electrode of claim 7 , 11. The electrode according to claim 7, wherein DC3 is greater than 400 mAh / g when the third discharge capacity when the electrode is used as a positive electrode is DC3.

12. The 10th discharge capacity when the electrode is used as a positive electrode is measured using a DC 10 Then, DC 10 The electrode of claim 7, wherein the capacitance is greater than 350 mAh / g.

13. The electrode of claim 7, wherein said electrode is a positive electrode.

14. A lithium ion secondary battery comprising the electrode according to claim 7.

15. The electrode further comprises an electrolyte, the volume of the electrolyte being V (mL), and the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then D, V and A S The lithium ion secondary battery according to claim 14, wherein (4) D x A satisfies the following formula: S / V>600

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