Electrode active material, electrode, lithium ion secondary battery, and method for manufacturing the same

Abstract

To improve the charge-discharge capacity and the capacity maintenance rate of an active material forming an electrode of a lithium ion secondary battery.SOLUTION: An electrode active material is formed of particles containing an organic sulfur compound and carbon material.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a novel electrode active material, an electrode comprising the electrode active material, a lithium ion secondary battery comprising the electrode, and a method for producing the same. [Background technology]

[0002] Lithium-ion secondary batteries have a large charge / discharge capacity and are primarily used as batteries for portable electronic devices. They are also increasingly being used as batteries for electric vehicles, and there are high hopes for improved performance.

[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 materials capable of absorbing and releasing more lithium ions, such as silicon (Si) and tin (Sn), as the negative electrode active material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-167144 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, development of active materials other than the active material of Patent Document 1 is still desired.

[0007] In addition, the above-mentioned materials proposed as negative electrode active materials have a problem that the volume change caused by the absorption and release of lithium ions is large, so that the cycle characteristics when repeatedly charged and discharged are not good. Carbon materials such as graphite and hard carbon are also used, but they have already reached the theoretical capacity, and a significant improvement in capacity cannot be expected.

[0008] The present invention provides a novel electrode active material capable of improving 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, and a method for producing the same. [Means for solving the problem]

[0009] The present invention relates to an electrode active material comprising particles containing an organosulfur compound and a carbon material. Effect of the Invention

[0010] According to the present invention, it is possible to provide a novel electrode active material capable of improving 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, and a method for producing the same.

[0011] In this specification, the term "cycle characteristic" refers to the characteristic of maintaining the charge / discharge capacity of a secondary battery despite repeated charging and discharging. Therefore, a secondary battery that experiences a large decrease in charge / discharge capacity and a low capacity retention rate with repeated charging and discharging 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. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view that illustrates a reaction apparatus used in the production of an electrode active material in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The configuration of one embodiment of the present invention will be described in detail below. The upper and lower limit values ​​of "more than", "less than", "over", "less than", etc. in the description of a numerical range can be arbitrarily combined, and the numerical values ​​in the examples can be these upper and / or lower limits. In addition, a numerical range shown as including a lower limit or an upper limit is understood to simultaneously disclose a numerical range not including the upper limit or lower limit, unless it is contrary to the spirit of this specification, and conversely, a numerical range shown as not including a lower limit or an upper limit is understood to simultaneously disclose a numerical range including 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 made of particles containing an organosulfur compound and a carbon material.

[0015] Although it is not intended 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 believed to be as follows: That is, the electrode active material of the present embodiment is made of particles containing an organic sulfur compound and a carbon material, and it is believed that the carbon material forms a three-dimensional conductive network while linking the organic sulfur compound, which is believed to contribute to the improvement of the charge / discharge capacity and capacity retention rate.

[0016] It is preferable that the carbon material is carbon fiber, and that the fibers constituting the carbon fiber have an average fiber length of more than 1 μm and an average fiber diameter of less than 100 nm.

[0017] It is believed that such a configuration makes it easier to form a three-dimensional conductive network.

[0018] The fibers constituting the carbon fiber are preferably carbon nanotubes.

[0019] It is believed that the carbon nanotubes form an excellent three-dimensional conductive network.

[0020] The content of the carbon material in the electrode active material is preferably less than 4.00 mass %.

[0021] The electrode active material preferably further contains a metal compound containing at least one selected from the group consisting of iron, molybdenum, vanadium and titanium.

[0022] The metal compound is preferably an iron compound.

[0023] Another embodiment of the present invention is an electrode comprising the electrode active material.

[0024] The electrode includes a current collector, and the current collector includes a metal foil. The content (mass%) of the carbon material in the electrode active material is A CM , the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then A CM It is preferable that and D satisfy the following formula: (1) DxA CM ×10>1.00

[0025] It is believed that by setting the product of the coating density and the content of the carbon material to exceed a predetermined value, the effect of adding the carbon material can be fully exerted.

[0026] The electrode includes a current collector, and the current collector includes a metal foil. The content (mass%) of the carbon material in the electrode active material is A CM , 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), A CM It is preferable that D and T satisfy the following formula. (2) D×A CM / T×10>0.100

[0027] It is believed that the effect of adding the carbon material can be fully exerted by making the coating density, the content of the carbon material, and the thickness of the metal foil satisfy the above formula.

[0028] 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 2.50mg / cm 2 It is preferable that the range is 100 to 2000 nm.

[0029] The third discharge capacity when the above electrode was used as a positive electrode was measured using a DC 3 Then, DC 3 It is preferable that the capacity is more than 400 mAh / g.

[0030] The 10th discharge capacity when the above electrode was used as a positive electrode was measured by DC 10 Then, DC 10 It is preferable that the capacity is more than 350 mAh / g.

[0031] Another embodiment of the present invention is a lithium ion secondary battery comprising the electrode.

[0032] The lithium ion secondary battery further comprises an electrolyte, the volume of the electrolyte being V (mL), and the content (mass%) of the carbon material in the electrode active material being A CM , the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then A CM It is preferable that D and V satisfy the following formula: (3) DxA CM / V×10>1.00

[0033] It is believed that the effect of adding the carbon material can be fully exerted by making the coating density, the content of the carbon material, and the volume of the electrolyte satisfy the above formula.

[0034] Another embodiment of the present invention comprises: (1) A step of mixing sulfur, an organic compound, and a carbon material to obtain a firing raw material; (2) A step of calcining the calcination raw material to obtain a calcined product; (3) pulverizing the fired product into particles to obtain an electrode active material; (4) preparing an electrode using the electrode active material; and (5) A step of producing a lithium ion secondary battery using the electrode. The method for producing a lithium ion secondary battery includes the steps of:

[0035] <Definition> "Electrode active material" refers to one of the electrode materials of a battery, and refers to a substance that is involved in the reaction that generates electricity. Electrode active materials are divided into positive electrode active materials and negative electrode active materials.

[0036] The term "particles" refers to a state in which the electrode active material is sufficiently fine to be suitable for mixing with other materials for the purpose of the present invention. The size of the particles constituting the electrode active material is not particularly limited as long as the above-mentioned mixing can be suitably carried out. For example, when the "particles" are expressed by a median diameter, the size can be within the range of 1 nm to 1000 μm.

[0037] "Particle size" is expressed as the median size (d50) unless otherwise specified.

[0038] The "average fiber length" is calculated by photographing the fibers with a transmission or scanning electron microscope, measuring the lengths of 50 fibers along their fiber axes, and taking the arithmetic average. The average fiber length is applicable to carbon fibers, etc.

[0039] The "average fiber diameter" is calculated by photographing the fibers with a transmission or scanning electron microscope, measuring the diameters of 50 fibers, and taking the arithmetic average. The average fiber diameter is applicable to carbon fibers, etc.

[0040] 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.

[0041] "Coating density" refers to the unit area (cm2) of the active material coated on the current collector. 2 ) mass (mg).

[0042] "Volume of electrolyte" means the total volume of the electrolyte solution, including the solute, or the solid electrolyte, in mL.

[0043] "Initial discharge capacity" refers to the third discharge capacity unless otherwise specified.

[0044] <Measurement method> 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.

[0045] The "particle size distribution" is measured using a laser diffraction / scattering particle size distribution analyzer (Anton Paar's PSA1090L particle size distribution analyzer) with water as the dispersion medium.

[0046] The "median diameter d50" is the volume-based cumulative 50% diameter (μm) in the particle size distribution.

[0047] The "carbon material content" refers to the content ratio (mass %) of the carbon material relative to the entire electrode active material, and is measured by the method described in the Examples section below.

[0048] The electrode active material, the electrode, and the lithium ion secondary battery of the present embodiment will be described below.

[0049] <Electrode active material> The electrode active material of the present embodiment is an electrode active material made of particles containing an organic sulfur compound and a carbon material.

[0050] The electrode active material of the present embodiment is obtained by calcining a raw material in which sulfur, an organic compound, and a carbon material are mixed, and pulverizing the calcined product to form particles. It is believed that the calcination causes the sulfur and the organic compound to react with each other to become an organic sulfur compound, and that the carbon material links the organic sulfur compound to form a three-dimensional conductive network.

[0051] (element content) The sulfur, carbon, hydrogen, nitrogen, and metal element amounts shown below are the amounts of each element contained in the electrode active material. 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.

[0052] ≪Sulfur element content≫ From the viewpoint of improving the performance of the electrode and / or the battery, the amount of elemental sulfur 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 even more preferably more than 60.0 mass%. There is no particular upper limit on the amount of elemental sulfur, but it is usually 80.0 mass%, may be 70.0 mass%, or may be 65.0 mass%.

[0053] <Carbon element content> From the viewpoint of improving the performance of the electrode and / or the battery, the amount of carbon element 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 amount of the element is preferably less than 30.0 mass%, more preferably less than 25.0 mass%, and even more preferably less than 23.0 mass%.

[0054] <Amount of hydrogen element> By calcination, hydrogen (H) in the organic compound reacts with sulfur to become hydrogen sulfide, which 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%, there is a tendency that the calcination (sulfurization reaction) is sufficient. Therefore, in this case, the charge / discharge capacity tends to be improved.

[0055] <Nitrogen element content> The amount of nitrogen element (mass%) in the electrode active material may be 0 mass% if 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, the nitrogen element may be detected.

[0056] ≪Metal element content≫ The electrode active material of the present embodiment preferably further contains a metal compound containing at least one selected from the group consisting of iron, molybdenum, vanadium, and titanium. The metal compound is preferably an iron compound. One or more kinds of metal compounds can be used.

[0057] When the electrode active material of the present embodiment contains the metal compound, the amount of metal element (mass %) in the electrode active material is, from the viewpoint of improving the performance of the electrode and / or battery, preferably more than 10.0 mass %, more preferably more than 15.0 mass %, and even more preferably more than 20.0 mass %, while the amount of the same element is preferably less than 30.0 mass %, more preferably less than 25.0 mass %, and even more preferably less than 24.0 mass %.

[0058] (Carbon materials) In the electrode active material of this embodiment, the carbon material preferably has a graphite structure. In addition, the carbon material is preferably conductive. Examples of the carbon material include porous carbon materials such as activated carbon, graphite, carbon black, acetylene black, and ketjen black, as well as carbon fibers such as carbon fibers, vapor-grown carbon fibers (VGCF), carbon nanotubes (CNT), and carbon nanofibers, and nanocarbon materials in a form other than carbon fibers such as graphene and fullerene. Among these, carbon fibers such as carbon fibers, vapor-grown carbon fibers (VGCF), CNT, and carbon nanofibers are preferred, and CNT is particularly preferred. One or more types of carbon materials can be used.

[0059] 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 the battery. This is because it is considered that the conductivity of the electrode active material can be improved. The average fiber length is preferably more than 1 μm, more preferably more than 1.5 μm, and even more preferably 2 μm or more. There is no particular limit to the upper limit of 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 limit to the lower limit of the average fiber diameter, but it is usually about 1 nm.

[0060] 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.

[0061] 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 2 / g or more is more preferable, and 600m 2 On the other hand, the specific surface area is preferably 2000 m 2 / g or less is more preferable, and 1800m 2 The specific surface area is measured by the BET multipoint method.

[0062] From the viewpoint of the effect 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, more preferably 30 or more, and even more preferably 40 or more. On the other hand, there is no particular limit on the upper limit of the G / D ratio, but if it is 90, it can be said that the carbon material has very few defects. Here, the G / D ratio is 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.

[0063] From the viewpoint of the effect of the present invention, the carbon material preferably has a metal impurity content of 5 mass% or less. The metal impurity content is preferably 3 mass% or less, more preferably 2 mass% or less, and even more preferably 1 mass% or less. The smaller the metal impurity content, the better, and for example, 0.1 mass% is a sufficiently small amount of metal impurities. The metal impurities are measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0064] The content of carbon material in the electrode active material (A CM ) is preferably less than 4.00% by mass. The content of the carbon material is preferably less than 2.00% by mass, more preferably less than 1.00% by mass, even more preferably less than 0.50% by mass, even more preferably less than 0.40% by mass, and even more preferably 0.35% by mass or less. On the other hand, the content is preferably more than 0.04% by mass, more preferably more than 0.05% by mass, even more preferably more than 0.06% by mass, even more preferably 0.07% by mass or more, even more preferably more than 0.10% by mass, even more preferably more than 0.15% by mass, even more preferably 0.19% by mass or more, even more preferably more than 0.20% by mass, and even more preferably more than 0.30% by mass.

[0065] (Median diameter) The electrode active material of this embodiment is made of particles, and the size of the particles is suitable for the manufacture of an electrode. From the viewpoint of improving the performance of an electrode and / or a battery, the preferred range of the particle size of the electrode active material is preferably a median diameter (d50) of more than 1.0 μm and less than 40.0 μm. The median diameter is more preferably more than 1.5 μm, 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, 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.

[0066] (Other Ingredients) The electrode active material of this embodiment can contain the materials described in the manufacturing method section below in the same manner as described in the same section.

[0067] <Electrode> The electrode of the present embodiment is an electrode containing the above-mentioned electrode active material.

[0068] The lithium ion secondary battery electrode of this embodiment can be constructed by using the materials described in the manufacturing method column below in the same manner as described in the same column. That is, when the lithium ion secondary battery electrode is used as a positive electrode, the conductive assistant, binder, current collector, etc. described in the manufacturing method column below can be used in the same manner as described in the same column to form a lithium ion secondary battery positive electrode, and when the lithium ion secondary battery electrode is used as a negative electrode, the conductive assistant, binder, current collector, etc. described in the manufacturing method column below can be used in the same manner as described in the same column to form a lithium ion secondary battery negative electrode. In this way, these explanations in the manufacturing method column below can be taken into consideration as explanations of the lithium ion secondary battery electrode of the embodiment.

[0069] The electrode of this embodiment includes a current collector, the current collector includes a metal foil, and the content (mass%) of the carbon material in the electrode active material is A CM, the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then A CM It is preferable that and D satisfy the following formula: (1) DxA CM ×10>1.00

[0070] (Formula (1)) The right side of formula (1) is more preferably 1.50, even more preferably 2.00, even more preferably 2.50, even more preferably 2.75, even more preferably 5.00, even more preferably 10.0, even more preferably 50.0, even more preferably 100. The upper limit of the value on the left side of formula (1) can be assumed to be about 500 as a reference value.

[0071] (Coating density (mg / cm 2 )) The coating density of the 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, 3.50 mg / cm 2 More preferably, 3.80 mg / cm 2 More preferably, 3.90 mg / cm 2 There is no particular upper limit to the coating density, and the higher the better, but the form of formula (1) naturally limits it. Therefore, there is little point in mentioning an upper limit to the coating density. However, the coating density is usually 15.0 mg / cm 2 It can also be estimated to be.

[0072] (Formula (2)) The electrode of this embodiment includes a current collector, the current collector includes a metal foil, and the content (mass%) of the carbon material in the electrode active material is A CM , 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), A CM It is preferable that D and T satisfy the following formula. (2) D×A CM / T×10>0.100

[0073] The right side of formula (2) is more preferably 0.120, even more preferably 0.140, even more preferably 0.160, even more preferably 0.400, even more preferably 0.600, even more preferably 1.00, even more preferably 3.00, even more preferably 5.00, even more preferably 6.00. The upper limit of the value of the left side of formula (2) can be assumed to be about 15.0 as a reference value.

[0074] (Thickness of metal foil (T)) The thickness T (μm) of the metal foil is preferably in the range of 5 μm or more, more preferably 10 μm or more, while T is preferably 40 μm or less, more preferably 30 μm or less, and further preferably 25 μm or less.

[0075] (Charge / discharge capacity) The electrode of this embodiment exhibits excellent charge / discharge capacity. 3 ) is the discharge capacity when three charge / discharge cycles are performed after the electrodes and batteries are fabricated, with the discharge cutoff voltage at 1.0 V and the charge cutoff voltage at 3.0 V (the third discharge when the cycle is repeated: first discharge, first charge, second discharge, second charge, third discharge, and third charge). In the case of discharge, when the battery is discharged at a constant current (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 current (mA) applied to obtain the capacity (mAh), and the specific capacity (mAh / g) is obtained by dividing the total time by the weight of the active material. On the other hand, in the case of charging, the voltage rises due to charging at a constant current, and when it finally reaches 3.0 V, charging is completed. The same applies to the 10th discharge capacity described later.

[0076] [Initial discharge capacity (DC 3 )] The initial discharge capacity (DC 3) (mAh / g) is preferably more than 400mAh / g. The initial discharge capacity is more preferably more than 450mAh / g, even more preferably more than 500mAh / g, even more preferably 514mAh / g or more, even more preferably more than 550mAh / g, even more preferably more than 600mAh / g, even more preferably more than 650mAh / g, even more preferably more than 700mAh / g, even more preferably more than 710mAh / g. There is no particular limit to the upper limit of the initial discharge capacity, and the higher the capacity, the better. Therefore, there is little meaning in mentioning the upper limit of the initial discharge capacity, but it can be assumed to be, for example, about 1000mAh / g as a reference value.

[0077] [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 more than 350mAh / g. The discharge capacity is preferably more than 400mAh / g, more preferably more than 478mAh / g, even more preferably more than 500mAh / g, even more preferably more than 536mAh / g, even more preferably more than 600mAh / g, even more preferably more than 700mAh / g, even more preferably more than 710mAh / g. There is no particular limit to the upper limit of the discharge capacity, and the higher the better. Therefore, there is little meaning in mentioning the upper limit of the discharge capacity, but it can be assumed to be, for example, about the value of the initial discharge capacity or about 900mAh / g as a reference value.

[0078] In addition, 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, if the negative electrode and electrolyte are within the technical common sense that can be used as a lithium ion secondary battery (i.e., Li is not depleted) and the performance related to the discharge capacity of the positive electrode is fully exhibited, and the measurement is performed in such a way that the performance related to the discharge capacity of the positive electrode is fully exhibited. For example, for the negative electrode, it is sufficient to use lithium in an amount (molar amount) preferably 2 times or more, more preferably 5 times or more, even more preferably 10 times or more, and even more preferably 50 times or more of the amount of sulfur (molar amount) in the positive electrode. Also, for example, for the electrolyte, if the amount of electrolyte (μL) is preferably 10 times or more, more preferably 20 times or more, and even more preferably 50 times or more of the amount of sulfur (mg) in the positive electrode, the discharge capacity of the positive electrode can be fully exhibited, leading to a long life of the battery. On the other hand, considering the energy density of the battery, it is preferable that the amount of electrolyte is small. For example, the amount of electrolyte (μL) 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 means the total volume of the electrolyte solution including the solute. The electrolyte may be in the form of an electrolyte solution or a solid (solid electrolyte), or the electrolyte may be a combination of both.

[0079] (Application) 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.

[0080] <Lithium-ion secondary battery> The lithium ion secondary battery of this embodiment is a lithium ion secondary battery including the above-mentioned electrode.

[0081] The lithium ion secondary battery of this embodiment can be constructed by using the materials described in the manufacturing method column below in the same manner as described in the same column. That is, when the lithium ion secondary battery electrode is used as a positive electrode, a lithium ion secondary battery can be constructed by using the negative electrode, electrolyte, separator, etc. described in the manufacturing method column below in the same manner as described in the same column. 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 by using the positive electrode, electrolyte, separator, etc. described in the manufacturing method column below in the same manner as described in the same column. In this way, these explanations in the manufacturing method column below can be taken into consideration as explanations of the present lithium ion secondary battery.

[0082] (Formula (3)) The lithium ion secondary battery of the present embodiment further comprises an electrolyte, the volume of the electrolyte being V (mL), and the content (mass%) of the carbon material in the electrode active material being A CM , the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then A CM It is preferable that D and V satisfy the following formula: (3) DxA CM / V×10>1.00

[0083] The right side of formula (3) is more preferably 3.00, even more preferably 5.00, even more preferably 9.90, even more preferably 20.0, even more preferably 26.0, even more preferably 30.0, even more preferably 38.0, even more preferably 100, even more preferably 300, even more preferably 370. The upper limit of the value on the left side of formula (3) can be assumed to be about 700 as a reference value.

[0084] (volume of electrolyte V) The volume V (mL) range of the electrolyte is not generally specified because it may vary depending on the size of the battery, and the minimum amount that draws out the performance of the electrode active material and operates sufficiently as a battery may be used. For example, in the case of a coin-type battery presented in the examples, as a reference value only, it is preferably 0.10mL or more, more preferably 0.12mL or more, and even more preferably 0.15mL or more. On the other hand, the V is preferably 0.40mL or less, more preferably 0.30mL or less, even more preferably 0.28mL or less, and even more preferably 0.25mL or less.

[0085] (Application) 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 as a battery for next-generation clean energy automobiles, such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs), as well as for portable information terminals such as smartphones and notebook personal computers, portable electronic devices such as music players and digital cameras, and medical devices.

[0086] <Production method> The electrode active material, the electrode, and the method for producing the lithium ion secondary battery according to this embodiment will be described below in order.

[0087] (Production of electrode active material) The electrode active material of the present embodiment can be produced, for example, by the steps of: (1) mixing sulfur, an organic compound, and a carbon material to obtain a calcination raw material; (2) calcining the calcination raw material to obtain a calcined product; and (3) pulverizing the calcined product into particles to obtain the electrode active material.

[0088] [Raw materials] The raw materials will be described below.

[0089] ≪Organic compounds≫ The organic compound is not particularly limited as long as it is a compound containing at least carbon atoms and hydrogen atoms, and when it is baked with sulfur in a non-oxidizing thermal atmosphere in the presence of a carbon material, it takes in 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, a condensate of a substituted aromatic hydrocarbon and sulfur chloride, and the like. The organic compound may be used alone or in combination of two or more kinds.

[0090] <Polymer of unsaturated chain hydrocarbon monomer> Examples of the polymer of the unsaturated chain hydrocarbon monomer include resins such as acrylic resins. Examples of the polymer of the unsaturated chain hydrocarbon monomer include diene rubbers. One or more types of the polymer of the unsaturated chain hydrocarbon monomer may be used.

[0091] Examples of the acrylic resin include a polymer obtained by polymerizing a monomer containing at least one selected from the group consisting of acrylate compounds represented by the following chemical formula (1); a polymer obtained by polymerizing a monomer containing at least one selected from the group consisting of acrylate compounds represented by the following chemical formula (1); a polymer 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 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 2 =C(R 11 )COOR 12 (1) (where R 11is a hydrogen atom or a methyl group, and R 12 is an alkyl group. CH 2 =C(R 21 )COO-Y-OCO(R 22 )C=CH 2 (2) (where R 21 and R 22 are the same or different and each is 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. However, when there are two or more ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.

[0092] In the chemical formula (1), R 11 is preferably a methyl group, R 12 is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and among these, a methyl group, an n-butyl group, an i-butyl group, or a t-butyl group is preferable. Examples of the compound represented by formula (1) include methyl (meth)acrylate, butyl (meth)acrylate, and the like, and more preferably, methyl methacrylate, butyl methacrylate. Here, the "(meth)acrylate" of methyl (meth)acrylate and butyl (meth)acrylate means either "acrylate" or "methacrylate" (hereinafter the same). A more preferable example of the compound represented by chemical formula (1) is butyl methacrylate.

[0093] In chemical formula (2), R 21 and R 22are preferably a methyl group. 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 through an oxygen atom, for example, the portion corresponding to -YO- is preferably one represented by the following chemical formula (3) (however, in chemical formula (3), the substituents in Y are not taken into consideration). -(CH 2 ) l -(CH 2 CH 2 O) m -(CH 2 CH 2 CH 2 O) n - (3) (Here, l is a number between 0 and 6, m is a number between 0 and 3, and n is a number between 0 and 2. However, l, m, and n cannot all be 0 at the same time.)

[0094] 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; alternatively, n is 1 or 2, and l and m are 0.

[0095] 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. Among these, ethylene glycol dimethacrylate is preferred.

[0096] Preferred examples of the acrylic resin 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, the acrylic resin is preferably a methacrylate type. More preferred examples of the acrylic resin include copolymers of methyl methacrylate and ethylene glycol dimethacrylate.

[0097] In this embodiment, the acrylic resin is preferably in the form of fine particles. Here, fine particles refer to particles with 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 by a particle size distribution measuring device PSA1090L manufactured by Anton Paar.

[0098] The acrylic resin may be spherical fine particles or porous fine particles. When the acrylic resin is porous, its oil absorption is preferably 100mL / 100g or more, more preferably 110mL / 100g or more, even more preferably 120mL / 100g or more, even more preferably 130mL / 100g or more, and even more preferably 140mL / 100g or more. The oil absorption is a value measured according to JIS K 5101-13-2:2004. More specifically, it can be measured by the method of paragraph 0069 of JP2017-88501A.

[0099] As long as the acrylic resin has the above structure, Mw is not particularly limited. However, the Mw of the acrylic resin is usually in the range of 2,000 to 1,500,000. Mw is a value measured by gel permeation chromatography (GPC) (calibrated with polystyrene).

[0100] The acrylic resin can be commercially available or can be produced by a conventional method within the knowledge of those skilled in the art. Examples of commercially available acrylic resins include those manufactured by Sekisui Chemical Co., Ltd.

[0101] Examples of the diene rubber include butadiene rubbers such as natural rubber, isoprene rubber, and high-cis polybutadiene rubber. The diene rubber can be commercially available or can be produced by a conventional method within the knowledge of those skilled in the art.

[0102] 《Condensate of Substituted Aromatic Hydrocarbon and Sulfur Chloride》 Examples of the condensate of substituted aromatic hydrocarbon and sulfur chloride include condensates of alkylphenol and sulfur chloride. Specific examples of the condensate of alkylphenol and sulfur chloride include Tackiol V200, TS3108, and TS3109 manufactured by Tago Chemical Industry Co., Ltd., and Vultac 3 manufactured by Arkema. One or more condensates of substituted aromatic hydrocarbon and sulfur chloride can be used.

[0103] ≪Carbon Material≫ As the carbon material, the above-mentioned ones can be used.

[0104] 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 with respect to 100 parts by mass of the organic compound. The content is more preferably less than 1 part by mass, still more preferably less than 0.5 part by mass. On the other hand, the content is preferably more than 0.05 part by mass, more preferably more than 0.07 part by mass, and still more preferably 0.10 part by mass or more.

[0105] Sulfur As the sulfur, any of various forms such as powdered sulfur, insoluble sulfur, precipitated sulfur, colloidal sulfur, etc. can be used, among which precipitated sulfur and colloidal sulfur are preferred. One or more types of sulfur can be used.

[0106] The sulfur content in the calcination raw material is preferably more than 50 parts by mass, more preferably more than 100 parts by mass, more preferably more than 300 parts by mass, more preferably more than 400 parts by mass, and more preferably 500 parts by mass or more, relative to 100 parts by mass of the organic compound, from the viewpoint of improving the performance of the electrode and / or the battery. By being more than 50 parts by mass, the charge / discharge capacity and cycle characteristics tend to be improved. 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, more preferably less than 800 parts by mass, and more preferably less than 700 parts by mass. By being less than 1000 parts by mass, there tends to be an advantage in terms of cost. In this specification, the term "cycle characteristics" refers to the characteristic that the charge / discharge capacity of a secondary battery is maintained despite repeated charging and discharging. Therefore, a secondary battery that experiences a large decrease in charge / discharge capacity and a low capacity retention rate with repeated charging and discharging 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.

[0107] Any of the various sulfur allotropes can be used. However, S, which is solid at room temperature and pressure, is preferred. 8 It is preferable that it contains sulfur, and S 8 It is more preferable that the sulfur is an elemental substance.

[0108] ≪Raw metal compound≫ When the electrode active material contains a metal compound containing at least one selected from the group consisting of iron, molybdenum, vanadium and titanium, a raw material metal compound containing a metal corresponding to these metals is used as the firing raw material.

[0109] {Raw material iron compound} When the metal is iron, 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 and reacts with sulfur to generate iron disulfide, and various compounds may be used. Examples of the raw iron compound include iron acid salts and iron complexes. 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 raw iron compounds may be used.

[0110] Examples of organic acid salts of iron include divalent iron (Fe 2+ ) and organic acid salts, and trivalent iron (Fe 3+ Among these, the salts of divalent iron and organic acids are preferred. Organic acids include those with a carboxyl group (-COOH) and those with a sulfo group (-SO 3 H), but those having a carboxyl group are preferred. Specific examples of organic acids include fatty acids, oxalic acid, tartaric acid, citric acid, malic acid, succinic acid, etc. Specific examples of fatty acids include those having 1 to 6 carbon atoms, such as acetic acid, propionic acid, and butyric acid. Of these, acetic acid, oxalic acid, etc. are preferred. Preferred examples of organic acid salts of iron include iron(II) acetate and iron(II) oxalate, etc. These may be hydrates. One or more types of organic acid salts of iron can be used.

[0111] Examples of inorganic salts of iron include divalent iron (Fe 2+ ) and salts with inorganic acids, 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 chloride (II), iron chloride (III), iron sulfate (II), iron sulfate (III), iron nitrate (II), and iron nitrate (III). These may be hydrates. One or more inorganic acid salts of iron may be used.

[0112] As an example of an iron complex, 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 coordinated to the iron ion is not particularly limited, and examples thereof include halogen atoms such as chlorine atoms and bromine atoms, cyano groups, dicyclopentadienyl groups, and N,N'-bis(salicylidene)ethylenediamine. Examples of iron complexes include potassium hexacyanidoferrate(II) ([Fe(CN) 6 ]K 4 ), potassium hexacyanidoferrate(III) ([Fe(CN) 6 ]K 3 ), sodium tetrachloroferrate(III) ([FeCl 4 ]Na), dicyclopentadienyl iron (II) (ferrocene), N,N'-bis (salicylidene) ethylenediaminato iron (III) chloride, etc. One or more kinds of iron complexes can be used.

[0113] <Raw material molybdenum compound> When the metal is molybdenum, examples of the raw 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 raw molybdenum compounds can be used.

[0114] <Raw material vanadium compound> When the metal is vanadium, 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), hexavanadium trioxide (IV, V), etc. One or more raw vanadium compounds can be used.

[0115] {Raw titanium compound} When the metal is titanium, examples of the raw titanium compound include titanium oxide, titanium dioxide, titanium trioxide, titanium tetrachloride, etc. One or more raw titanium compounds can be used.

[0116] <Content of raw metal compounds> From the viewpoint of improving the performance of the electrode and / or the battery, the content of the raw material metal compound in the calcination raw material is preferably 50 parts by mass or more and 300 parts by mass or less relative to 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.

[0117] <Median diameter of raw metal compound> It is preferable that the raw metal compound is crushed in advance when used as a firing raw material. The median diameter (d50) of the raw metal compound is preferably 12.00 μm or less, more preferably. The median diameter is 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 above-mentioned method.

[0118] 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 on 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 by a fully automatic specific surface area measuring device, Macsorb (HM-model 1201, manufactured by Mountec Co., Ltd.).

[0119] 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 metal compound with a pulverizer. As such a pulverizer, for example, a pulverizer manufactured by Japan Analytical Industry Co., Ltd. (e.g., JFC-2000, etc.) can be used.

[0120] Other ingredients The raw material may optionally contain other materials commonly used in this field.

[0121] (manufacturing process) [Mixing process (1)] The mixing step is a step of preparing a raw material to be fired. The mixing step can be carried out by mixing sulfur, an organic compound, a carbon material, and, if desired, an optional component such as a raw material metal compound.

[0122] The above mixing can be carried out by a conventional method, and is not particularly limited as long as the components are sufficiently mixed. In the present embodiment, at least the following mixing by the WET method or the DRY method can be mentioned as a preferred mixing method.

[0123] ≪WET method≫ In this embodiment, the WET method is a method for preparing a raw material, (a-1) a step of adding an organic compound and a carbon material 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 It includes.

[0124] In step (a-1), the method of adding the organic compound and the carbon material 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 carbon material may be simultaneously added to the organic solvent and mixed, (2) the organic compound may be added to the organic solvent and mixed, and then the carbon material may be added and mixed, or (3) the carbon material may be added to the organic solvent and mixed, and then the organic compound may be added and mixed.

[0125] 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, etc. In addition, the organic solvent is preferably one that dissolves organic compounds, because this contributes to good mixing. These solvents may be used alone or in combination.

[0126] Step (a-1) can be carried out, for example, by stirring in a container such as a beaker.

[0127] 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 drying by heating, drying under reduced pressure, or drying by heating under reduced pressure.

[0128] The dry mixture thus obtained is preferably pulverized before being subjected to the next step, since this is expected to facilitate more efficient mixing in step (a-3).

[0129] In the step (a-3), the dry mixture and sulfur can be mixed by a conventional method, for example, a method of mixing them using a blender can be mentioned.

[0130] When a raw metal compound is used as an optional component, the raw metal compound can be mixed in step (a-1). In this case, the order in which the raw metal compound is added to the organic solvent is not particularly limited, as with the other raw materials, and the raw metal compound may be added in any order.

[0131] ≪DRY method≫ In this embodiment, the DRY method is a method for preparing a raw material, (b-1) The method includes a step of mixing an organic compound, a carbon material, and sulfur, all of which are in a powder state.

[0132] Here, the powder refers to a state in which each solid raw material is sufficiently finely divided to a degree suitable for mixing for the purpose of this embodiment. The size of each particle constituting the powder is not particularly limited as long as the mixing is carried out suitably, but is usually, for example, in the range of 1 μm or more and 40 μm or less. From the viewpoint of improving the performance of the electrode and / or battery, the size of the particles 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, even more preferably 10 μm or less, in terms of the median diameter. The median diameter can be measured by the above-mentioned method.

[0133] 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). When a raw material metal compound is added to the raw material, this may also be mixed together.

[0134] In either the WET method or the DRY method, it is desirable to thoroughly mix the raw materials in advance in preparation for firing.

[0135] The raw material thus obtained may be used as it is in the next firing step, or may be formed into pellets, if desired, and then used in the next step.

[0136] [Firing process (2)] The calcination step is a step of calcining the calcination raw material obtained above. Calcination can be performed by a conventional method, for example, by heating the calcination raw material at a predetermined temperature increase rate until it reaches a predetermined temperature, maintaining the temperature at the predetermined temperature for a predetermined time, and then naturally cooling it.

[0137] <Non-oxidizing atmosphere> The firing is preferably carried out in a non-oxidizing atmosphere. The non-oxidizing atmosphere refers to an atmosphere that is substantially free of oxygen, and is adopted to suppress oxidative deterioration of the 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.

[0138] <Heating rate> The heating rate is preferably, for example, within 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 purpose of improving the charge / discharge capacity and cycle characteristics.

[0139] <Baking temperature and time> The calcination temperature is the temperature after the temperature rise of the raw material is completed, and is maintained for a certain period of time for calcination of the raw material. The temperature is preferably in the range of more than 250°C and less than 550°C. By being more than 250°C, the sulfurization reaction tends to be avoided from being insufficient, and the charge / discharge capacity of the target product tends to be prevented from decreasing. On the other hand, by being less than 550°C, the decomposition of the raw material tends to be prevented, and the decrease in yield and the decrease in charge / discharge capacity tend to be prevented. The temperature is more preferably more than 300°C, even more preferably more than 350°C, and even more preferably 370°C or more. On the other hand, less than 500°C is more preferable, and less than 450°C is even more preferable.

[0140] From the viewpoint of improving the performance of the electrode and / or the battery, the firing temperature in the firing step is preferably higher than the temperature at which the raw metal compound is thermally decomposed.

[0141] The time for which the firing temperature is maintained may be appropriately set depending on the type of raw material, the firing temperature, etc., but is preferably, for example, from 1 hour to 6 hours. A time of 1 hour or more tends to allow firing to proceed sufficiently, while a time of 6 hours or less tends to prevent excessive thermal decomposition of the components.

[0142] ≪Device≫ The calcination can be carried out, for example, by a muffle furnace (FIG. 1), or can be carried out by 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 produced continuously by a series of operations, such as kneading, pulverizing, and mixing the raw materials and calcining them in the apparatus.

[0143] A muffle furnace (Figure 1) is a furnace partitioned by a hot plate or the like so that the heat source (heater) is not exposed inside the furnace in order to prevent contamination of samples. In Figure 1, a muffle furnace 1 has a heater 2 at the bottom of the furnace, which is partitioned by a hot plate. A lid 3 is installed on the front side of the furnace (the left end side in the figure), and the furnace is structured so that an atmosphere of inert gas 4 can be maintained inside the furnace. A thermocouple (not shown) is attached to the lid, and the temperature inside the furnace during sintering can be measured. Inside the furnace, two trays 5 and 6, which are rectangular parallelepiped reaction vessels made of stainless steel and used to sinter the raw materials, are installed on the upper and lower levels.

[0144] 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 exhaust pipe 8. The gas exhaust pipe 8 is connected to a trap tank 10 containing an aqueous sodium hydroxide solution 9, and exhaust air attempting to exit from the muffle furnace 1 through the gas exhaust pipe 8 to the outside passes through the aqueous sodium hydroxide solution 9 in the trap tank 10 before being discharged to the outside. Therefore, even if the exhaust air contains hydrogen sulfide gas generated by the reaction, it is neutralized with the aqueous sodium hydroxide solution and removed from the exhaust air.

[0145] [Residue removal process] In the treated product obtained after calcination, unreacted sulfur may remain, which is the sulfur that sublimed during calcination and then cooled and precipitated. Since these residues are a factor in reducing cycle characteristics, it is desirable to remove the residues as much as possible if any remain. The removal of the residues can be carried out according to a conventional method, such as reduced pressure heating drying, hot air drying, and solvent washing.

[0146] [Crushing, classification] The obtained electrode active material is preferably pulverized to a predetermined particle size and classified to obtain particles of a size suitable for the production of an electrode. The preferred size range of the particles of the electrode active material is as described above.

[0147] The pulverization can be carried out by a conventional method, for example, by subjecting the mixture to a pulverization treatment under predetermined conditions using a pulverizer such as a cutter mill or a jet mill. The pulverization conditions vary depending on the mill used, but for example, when a cutter mill (e.g., Free Speed ​​Mill, FS-20, manufactured by Labnect Co., Ltd.) is used, the treatment can be carried out at a rotation speed of 20,000 rpm to 30,000 rpm for 1 second to 30 seconds. When a dry jet mill (e.g., Nano Jet Mizer, NJ-30, manufactured by Aisin Nano Technologies Co., Ltd.) is used, the treatment can be carried out at a treatment speed of 1 g / min to 3 g / min and a pulverization pressure of 0.5 MPa to 2.0 MPa. Classification can be carried out, for example, using a sieve.

[0148] In the firing method using the twin-screw extruder described above, the electrode active material can be produced and at the same time, the produced electrode active material can be pulverized into particles by shearing during kneading.

[0149] (Manufacturing electrodes for lithium-ion secondary batteries) 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 lithium ion secondary battery electrode, except that the electrode active material is used as the active material.

[0150] [When the electrode active material is used as a positive electrode active material] The positive electrode for lithium ion secondary batteries can be prepared in the same manner as the positive electrode for general lithium ion secondary batteries, except that the above-mentioned electrode active material is used as the positive electrode active material. For example, the positive electrode can be prepared by mixing the electrode active material with a conductive assistant, 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 the same. In addition, as another method, the positive electrode can also be prepared by kneading the electrode active material with a conductive assistant, a binder, and a small amount of solvent using a mortar or the like, forming it into a film, and then pressing it onto a current collector using a press or the like.

[0151] <Conductive assistant> Examples of the conductive assistant include vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, and fine powder of metals such as aluminum and titanium that are stable at the positive electrode potential. In addition, the conductive assistant may be one of the above carbon materials that is conductive. These conductive assistants may be used alone or in combination.

[0152] <Binder> Examples of binders include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamide-imide (PAI), carboxymethyl cellulose (CMC), polyvinyl chloride (PVC), acrylic resin, methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), etc. These binders can be used alone or in combination of two or more.

[0153] <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.

[0154] ≪Blend amount≫ The amounts of the materials constituting the positive electrode are not particularly limited, but it is preferable to mix, for example, 2 to 100 parts by mass of a conductive assistant, 2 to 50 parts by mass of a binder, and an appropriate amount of a solvent with respect to 100 parts by mass of an electrode active material.

[0155] <Current collector> As the current collector, one generally used for a positive electrode for a lithium ion secondary battery may be used. For example, the current collector may be made of metal foil such as aluminum foil, aluminum mesh, punched aluminum sheet, aluminum expand sheet, stainless steel foil, stainless steel mesh, punched stainless steel sheet, stainless steel expand sheet, foamed nickel, nickel nonwoven fabric, copper foil, copper mesh, punched copper sheet, copper expand sheet, titanium foil, titanium mesh, carbon nonwoven fabric, carbon woven fabric, etc. Among these, a current collector containing a metal foil is 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, for example, carbon-coated aluminum foil. In this case, the current collector includes a carbon-coated portion.

[0156] [When the electrode active material is used as the negative electrode active material] The negative electrode for lithium ion secondary batteries can be prepared in the same manner as a general negative electrode for lithium ion secondary batteries, except that the above-mentioned electrode active material is used as the negative electrode active material. For example, the negative electrode can be prepared by mixing the electrode active material with a conductive assistant, 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 the paste. In addition, as another method, the negative electrode can also be prepared by kneading the electrode active material with a conductive assistant, a binder, and a small amount of solvent using a mortar or the like, forming it into a film, and then pressing the film onto a current collector using a press or the like.

[0157] The conductive assistant, 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 current collector can also be the same as those used in the above case.

[0158] (manufacturing lithium-ion secondary batteries) The lithium ion secondary battery of this embodiment can be manufactured in the same manner as in the manufacture of a general lithium ion secondary battery, except that the lithium ion secondary battery electrode obtained above is used.

[0159] [When the electrode active material is used as a positive electrode active material] The lithium ion secondary battery of this embodiment can be produced in accordance with a conventional method by using a positive electrode containing the above-mentioned electrode active material (positive electrode active material), a negative electrode, an electrolyte, and, if desired, components such as a separator.

[0160] ≪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 using a material that does not contain lithium as the negative electrode material, for example, among the above-mentioned negative electrode materials, when using a carbon-based material, a silicon-based material, an alloy-based material, etc., it is advantageous in that it is difficult to cause a short circuit between the positive and negative electrodes due to the generation of dendrites. However, when using these lithium-free negative electrode materials in combination with the positive electrode of the present embodiment, neither the positive electrode nor the negative electrode contains lithium. Therefore, a lithium pre-doping process for inserting lithium into either one or both of the negative electrode and the positive electrode in advance is required. The lithium pre-doping method may follow a known method. For example, when doping lithium into the negative electrode, 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 sticking pre-doping method in which a metallic lithium foil is attached to the electrode and then left in the electrolytic solution to utilize the diffusion of lithium into the electrode to perform doping. Also, when pre-doping lithium into the positive electrode, the above-mentioned electrolytic doping method can be used. As the lithium-free negative electrode material, in particular, a silicon-based material, which is a high-capacity negative electrode material, is preferable, and among them, thin-film silicon, which has a thin electrode thickness and is advantageous in terms of capacity per volume, is more preferable.

[0161] ≪Electrolyte≫ The electrolyte compensates for the charge generated by the release of electrons to the external circuit as the electrode active material in the positive and negative electrodes is oxidized / reduced with the flow of ions. As the electrolyte used in a lithium-ion secondary battery, a solution obtained by dissolving an alkali metal salt, which is an electrolyte, in an organic solvent can be used. As the organic solvent, it is preferable to use 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. As the electrolyte, Li(FSO 2 ) 2 N, LiPF 6 、LiBF 4, LiAsF 6 , LiCF 3 SO 3 , LiI, LiClO 4 etc. can be used. The concentration of the electrolyte may be about 0.5 mol / L to 5.0 mol / L. The electrolyte is not limited to a liquid state. For example, when the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid state (for example, in a polymer gel state).

[0162] <Separator> The lithium ion secondary battery may include a separator and other components in addition to the above-mentioned negative electrode, positive electrode, and electrolyte. The separator is interposed between the positive electrode and the negative electrode, and allows the movement of ions between the positive electrode and the negative electrode, and prevents internal short circuit between the positive electrode and the negative electrode. If the lithium ion secondary battery is a sealed type, the separator is also required to have a function of retaining the electrolyte. As the separator, it is preferable to use a thin, microporous or nonwoven membrane made of polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, glass, or the like.

[0163] ≪Shape≫ The shape of the lithium ion secondary battery is not particularly limited, and it can be in various shapes such as a cylindrical type, a stacked type, a coin type, a laminated type, and a button type.

[0164] [When the electrode active material is used as the negative electrode active material] The lithium ion secondary battery of this embodiment can be produced in accordance with a conventional method by using a negative electrode containing the above-mentioned electrode active material (negative electrode active material), a positive electrode, an electrolyte, and, if desired, components such as a separator.

[0165] ≪Positive electrode≫ The positive electrode material is not particularly limited as long as it is, for example, a transition metal oxide or solid solution oxide containing lithium, or a substance capable of electrochemically absorbing and releasing lithium ions. Examples of transition metal oxides containing lithium include LiCoO 2 Li·Co based composite oxides such as LiNi x Coy Mn z O 2 Li·Ni·Co·Mn-based composite oxides such as LiNiO 2 Li·Ni composite oxides such as LiMn 2 O 4 Examples of the solid solution oxide include Li·Mn-based composite oxides such as Li a Mn x Co y Ni z O 2 (1.150≦a≦1.430, 0.450≦x≦0.600, 0.100≦y≦0.150, 0.200≦z≦0.280), LiMn x Co y Ni z O 2 (0.300≦x≦0.850, 0.100≦y≦0.300, 0.100≦z≦0.300), LiMn 1.5 Ni 0.5 O 4 These compounds may be used alone or in combination of two or more.

[0166] <Other> The electrolyte, separator, and shape of the lithium ion secondary battery can be the same as those in the above-mentioned case where the electrode active material is used as the positive electrode active material. EXAMPLES

[0167] The present invention will be described based on examples, but the present invention is not limited to only the examples.

[0168] The various chemicals used in the Examples and Comparative Examples are listed below. The various chemicals were purified according to conventional methods as necessary.

[0169] <Materials used in the test> Organic compound: Spherical acrylic resin consisting of homopolymer of methyl methacrylate (Techpolymer MB-4 manufactured by Sekisui Chemical 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 (CNTs) (CNT dispersion liquid 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 amount: 1% by 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.)

[0170] Production Example 1 (Fine Grinding of Raw Metal Compounds) Before use as a raw material, the raw material metal compound was ground in advance for 10 minutes with a freeze grinder (JFC-2000 manufactured by Japan Analytical Industry Co., Ltd.).

[0171] Production Example 2 (Preparation of dry mixture by WET method) In Table 1, in the examples 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 raw material to be fired. In preparing the dry mixture, first, the organic compound was added to an organic solvent and mixed thoroughly, 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 with a cutter mill (LAB MILL manufactured by Osaka Chemical Co., Ltd.) to obtain a dry mixture.

[0172] <Preparation of electrode active material> (Preparation of firing raw materials) In the examples where the dry mixture was prepared in advance by the WET method, the dry mixture and sulfur were mixed in a blender to obtain a raw material for calcination. In the other examples (e.g., Reference Example y and Reference Example z), the raw materials were mixed in a blender to obtain a raw material for calcination.

[0173] (Reaction Apparatus) The raw materials were fired in a muffle furnace (Fig. 1). The muffle furnace in Fig. 1 was as described above.

[0174] (Firing process) First, the atmosphere in the muffle furnace was replaced with Ar gas three times using a vacuum pump while the raw material to be fired was placed in a tray, which was a stainless steel reaction vessel. After that, 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 raw material to be fired reached the firing temperature shown in Table 1, the temperature was maintained while performing heat treatment for 2 hours. Next, the temperature of the fired product was naturally cooled to 25°C under an Ar gas atmosphere while adjusting the flow rate of Ar gas, and then the fired product was taken out of the muffle furnace.

[0175] (Removal of unreacted sulfur) In order to remove the unreacted sulfur (free elemental sulfur) remaining in the product after the firing process, the following process was carried out. That is, the fired product was crushed in a mortar, and the crushed product was placed in a glass tube oven and heated at 250°C for 3 hours while suctioning under vacuum to obtain an electrode active material from which the unreacted sulfur had been removed (or which contained only a trace amount of unreacted sulfur). The heating rate was 10°C / min.

[0176] (Crushing process) 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.).

[0177] (Classification work) In order to remove coarse particles from the pulverized fired product, the product was classified using a 32 μm mesh stainless steel sieve to obtain an electrode active material.

[0178] <Physical properties of electrode active materials> The electrode active material obtained above was examined for the following properties.

[0179] (Elemental analysis) The amounts of carbon, hydrogen, nitrogen, and sulfur were calculated as the mass ratio (%) of the total amount of the electrode active material based on the mass measured using a fully automatic elemental analyzer vario MICRO cube manufactured by Elementar. The results are shown in Table 1.

[0180] (iron element content) Each electrode active material was subjected to thermogravimetry, and the amount of iron element (mass %) was calculated based on the obtained measurement results.

[0181] Thermogravimetry was 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 ratio (mass%) of each electrode active material was calculated from the measured weight loss rate (mass%) using the following calculation. Ash content ratio (mass%) = 100-weight reduction rate (mass%)

[0182] In addition, the iron element in each electrode active material is iron disulfide (FeS 2 ), the iron disulfide ratio (mass%) was calculated from the ash ratio (mass%) of each electrode active material by the following calculation. That is, the weight loss rate (100 mass%) of Reference Example y in Table 1 shows that the organic compound is completely decomposed after being converted to a sulfide, while the weight loss rate (36 mass%) of Reference Example z shows that the iron disulfide (FeS) in the electrode active material is completely decomposed. 2 ) in each electrode active material is found to decrease in weight by 36 mass%. 2 ) ratio (mass %) was calculated by the following formula. FeS 2 Ratio (mass%) = ash content × {100 / (100-36)}

[0183] In addition, FeS 2 From the ratio (mass %), the amount of iron element (Fe ratio, mass %) was calculated by the following formula. Fe ratio (mass%) = FeS2 Ratio x Fe atomic weight / (Fe atomic weight + S atomic weight x 2) (However, the Fe atomic weight is 55.845 and the S atomic weight is 32.065.)

[0184] (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 the 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.

[0185] (Carbon material content) The content of the carbon material in the electrode active material was calculated from the ratio of the mass of the obtained electrode active material to the mass of the carbon material in the electrode active material. The mass of the carbon material in the electrode active material was calculated assuming that the carbon material does not undergo reactions such as sulfurization or decomposition during firing and that the weight remains unchanged before and after firing.

[0186] The results are shown in Table 1 below.

[0187] [Table 1]

[0188] <Production of lithium-ion secondary battery> A lithium ion secondary battery was fabricated as follows.

[0189] (positive electrode) As the active material, the electrode active material obtained above was used. As the conductive aid, acetylene black (manufactured by Denka Co., Ltd., HS-100) and vapor-grown carbon fiber (manufactured by Showa Denko K.K., VGCF) were used. As the binder, an acrylic resin (manufactured by Fujifilm Wako Pure Chemical Corporation, average molecular weight 2700 to 7500) was used. 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 rotation-revolution mixer (ARE-250 manufactured by Shinchi Co., Ltd.) with milliQ water as the dispersant to prepare a uniform slurry. The prepared slurry was coated on 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 (positive electrode) was obtained by punching out a φ11 mm disk. Then, the mass of the electrode was measured, and the amount of the active material in the electrode was calculated from the above ratio.

[0190] (Negative electrode) As the negative electrode, a metallic lithium foil (disk-shaped with a diameter of 14 mm and a thickness of 500 μm, manufactured by Honjo Metal Co., Ltd.) was used. As the negative electrode current collector, a stainless steel sheet was used.

[0191] (Electrolyte) As the electrolyte, a non-aqueous electrolyte in which LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate was used. Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1. The concentration of LiPF 6 in the electrolyte was 1.0 mol / L.

[0192] (Lithium ion secondary battery) A coin battery was produced using the above positive and negative electrodes. In detail, in a dry room, a separator (Celgard2400 manufactured by Celgard, a polypropylene microporous membrane having a thickness of 25 μm) and a glass nonwoven fabric filter (440 μm thick, GA100 manufactured by ADVANTEC) were sandwiched between the positive and negative electrodes to produce an electrode body battery. This electrode body battery was housed in a battery case (a material for CR2032 type coin batteries, manufactured by Hosen Co., Ltd.) made of a stainless steel container. The above electrolyte was injected into the battery case. The amount was 0.28 mL in terms of the volume of the electrolyte. The battery case was sealed with a crimping machine to obtain the lithium ion secondary batteries of each of the Examples and Comparative Examples.

[0193] <Evaluation of lithium-ion secondary batteries> (discharge capacity, capacity maintenance rate) The coin-type lithium-ion secondary batteries produced in each of the Examples and Comparative Examples were charged and discharged at a current value equivalent to 50 mA per 1 g of positive electrode active material under the condition of a test temperature of 30°C. The discharge end voltage was 1.0 V, and the charge end voltage was 3.0 V. In addition, charging and discharging were repeated, and the battery discharge capacity (mAh) was observed for the first, second, third, and tenth cycles. The measurements were performed using a battery performance evaluation device (BLS system, manufactured by Measuring Instrument Center Co., Ltd.).

[0194] 3rd Discharge Capacity DC 3 The initial capacity was determined as (mAh / g). The larger the initial capacity, the greater the charge / discharge capacity of the lithium-ion secondary battery, and the more favorable it is. 3 (mAh / g) and 10th discharge capacity DC 10 The capacity retention rate (%) was calculated from (mAh / g) using the following formula. It can be said that the higher the capacity retention rate, the more excellent the cycle characteristics of the lithium ion secondary battery. Capacity maintenance rate (%)=(DC 10 / DC 3 ) x 100

[0195] The results are shown in Table 2 below.

[0196] [Table 2]

[0197] <Embodiment> The following are preferred embodiments.

[0198] [1] Organic sulfur compounds, Carbon materials and An electrode active material comprising particles comprising: [2] The electrode active material according to the above [1], wherein the carbon material is carbon fiber, and the fibers constituting the carbon fiber have an average fiber length of more than 1 μm and an average fiber diameter of less than 100 nm, preferably less than 50 nm, and more preferably less than 10 nm. [3] The electrode active material according to [2] above, wherein the fibers constituting the carbon fiber are carbon nanotubes. [4] The electrode active material according to any one of the above [1] to [3], wherein the content of the carbon material in the electrode active material is less than 4.00 mass%, preferably less than 2.00 mass%, more preferably less than 1.00 mass%, even more preferably less than 0.50 mass%, even more preferably less than 0.40 mass%, and even more preferably 0.35 mass% or less. [5] The electrode active material according to any one of the above [1] to [4], further comprising a metal compound containing at least one selected from the group consisting of iron, molybdenum, vanadium and titanium. [6] The electrode active material according to [5] above, 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 comprises a current collector; The current collector includes a metal foil, The content (mass%) of the carbon material in the electrode active material is A CM , the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then A CMand D satisfy the following formula, and preferably the right side of formula (1) is 1.50, more preferably 2.00, even more preferably 2.50, even more preferably 2.75, even more preferably 5.00, even more preferably 10.0, even more preferably 50.0, even more preferably 100. (1) DxA CM ×10>1.00 [9] The electrode comprises a current collector; The current collector includes a metal foil, The content (mass%) of the carbon material in the electrode active material is A CM , 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), A CM The electrode according to the above [7] or [8], wherein D and T satisfy the following formula, and the right side of formula (2) is preferably 0.120, more preferably 0.140, even more preferably 0.160, even more preferably 0.400, even more preferably 0.600, even more preferably 1.00, even more preferably 3.00, even more preferably 5.00, even more preferably 6.00. (2) D×A CM / T×10>0.100

[10] The electrode comprises a current collector; The current collector includes a metal foil, The coating density (mg / cm) of the electrode active material on the current collector 2 ) is D, where D is 2.50 mg / cm 2 More preferably, 3.00 mg / cm 2 More preferably, 3.50 mg / cm 2 More preferably, 3.80 mg / cm 2 More preferably, 3.90 mg / cm 2 The electrode according to any one of the above [7] to [9], wherein the electrode is greater than 100%.

[11] The third discharge capacity when the electrode is used as a positive electrode is measured by DC 3 Then, DC 3The electrode according to any one of the above [7] to

[10] , wherein the capacity is more than 400 mAh / g, preferably more than 450 mAh / g, more preferably more than 500 mAh / g, even more preferably 514 mAh / g or more, even more preferably more than 550 mAh / g, even more preferably more than 600 mAh / g, even more preferably more than 650 mAh / g, even more preferably more than 700 mAh / g, even more preferably more than 710 mAh / g.

[12] The 10th discharge capacity when the electrode is used as a positive electrode is measured by DC 10 Then, DC 10 The electrode according to any one of the above [7] to

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

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

[12] .

[14] Further comprising an electrolyte, the volume of the electrolyte being V (mL); The content (mass%) of the carbon material in the electrode active material is A CM , the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then A CM and D and V satisfy the following formula, and the right side of formula (3) is preferably 3.00, more preferably 5.00, even more preferably 9.90, even more preferably 20.0, even more preferably 26.0, even more preferably 30.0, even more preferably 38.0, even more preferably 100, even more preferably 300, and even more preferably 370. (3) DxA CM / V×10>1.00

[15] (1) A process for obtaining a firing raw material by mixing sulfur, an organic compound, and a carbon material; (2) A step of calcining the calcination raw material to obtain a calcined product; (3) pulverizing the fired product into particles to obtain an electrode active material; (4) A step of fabricating an electrode using the electrode active material, and (5) A step of fabricating a lithium-ion secondary battery using the electrode A method for manufacturing a lithium-ion secondary battery, comprising the above steps.

Explanation of symbols

[0199] 1 Muffle furnace 2 Heater 3 Lid 4 Inert gas 5 Tray (upper stage) 6 Tray (lower stage) 7 Gas inlet pipe 8 Gas discharge pipe 9 Aqueous sodium hydroxide solution 10 Trap tank

Claims

1. Organosulfur compounds; Carbon materials and An electrode active material comprising particles comprising:

2. 2. The electrode active material according to claim 1, wherein the carbon material is carbon fiber, and the fibers constituting the carbon fiber have an average fiber length of more than 1 μm and an average fiber diameter of less than 100 nm.

3. 3. The electrode active material according to claim 2, wherein the fibers constituting the carbon fiber are carbon nanotubes.

4. The electrode active material according to claim 1 or 2, wherein the content of the carbon material in the electrode active material is less than 4.00 mass%.

5. 3. The electrode active material according to claim 1, further comprising a metal compound containing at least one selected from the group consisting of iron, molybdenum, vanadium and titanium.

6. 6. The electrode active material according to claim 5, wherein the metal compound is an iron compound.

7. An electrode comprising the electrode active material according to claim 1 or 2.

8. the electrode comprises a current collector; The current collector includes a metal foil, The content (mass%) of the carbon material in the electrode active material is A CM , the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then A CM 8. The electrode of claim 7, wherein and D satisfy the following formula: (1) D×A CM ×10>1.00

9. the electrode comprises a current collector; The current collector includes a metal foil, The content (mass%) of the carbon material in the electrode active material is A CM , 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), A CM 8. The electrode of claim 7, wherein D and T satisfy the following formula: (2) D×A CM / T×10>0.100

10. the electrode comprises a current collector; The current collector includes a metal foil, The coating density (mg / cm) of the electrode active material on the current collector 2 ) is D, D is 2.50 mg / cm 2 The electrode of claim 7 ,

11. The third discharge capacity when the electrode was used as a positive electrode was measured using a DC 3 Then, DC 3 The electrode of claim 7, wherein the capacitance is greater than 400 mAh / g.

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

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

14. Further comprising an electrolyte, the volume of the electrolyte being V (mL); The content (mass%) of the carbon material in the electrode active material is A CM , the coating density of the electrode active material on the current collector (mg / cm 2 ) is D, then A CM The lithium ion secondary battery according to claim 13 , wherein D and V satisfy the following formula: (3) D×A CM / V×10>1.00

15. (1) A step of mixing sulfur, an organic compound, and a carbon material to obtain a firing raw material; (2) A step of calcining the calcination raw material to obtain a calcined product; (3) A step of pulverizing the fired product into particles to obtain an electrode active material; (4) preparing an electrode using the electrode active material; and (5) A step of producing a lithium ion secondary battery using the electrode. The method for producing a lithium ion secondary battery comprises the steps of:

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