Electrode active material, electrode, and lithium ion secondary battery

Abstract

To improve the charge / discharge capacity and the capacity retention rate of an electrode active material constituting an electrode of a lithium ion secondary battery.SOLUTION: An electrode active material comprises particles containing an organic sulfur compound. When the oxygen content (mass%) in the electrode active material is AO and the sulfur content (mass%) therein is AS, AO and AS satisfy the following formulae: (1) AO>9.0; (2) AS>45.0; and (3) AO×AS>550.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Since lithium-ion secondary batteries have a large charge-discharge capacity, they are mainly used as batteries for portable electronic devices. In addition, the usage amount of lithium-ion secondary batteries is also increasing as batteries for electric vehicles, and an improvement in performance is expected.

[0003] Patent Document 1 describes a positive electrode active material obtained by heat-treating high-cis polybutadiene rubber together with sulfur and a vulcanization accelerator, and Patent Document 2 describes an electrode active material obtained by firing polymethyl methacrylate together with sulfur.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the active materials of Patent Document 1 and Patent Document 2 have only a low oxygen content, and there is still room for improvement in the charge-discharge capacity and the capacity retention rate.

[0006] The present invention aims to provide a novel electrode active material, 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, which can improve the charge-discharge capacity and the capacity retention rate.

Means for Solving the Problems

[0007] The present invention relates to the following electrode active material. An electrode active material comprising particles containing an organic sulfur compound, wherein the oxygen content (mass %) in the electrode active material is A O and the sulfur content (mass %) is A S and in the case where A O and A S satisfy the following formula. (1) A O > 9.0 (2) A S > 45.0 (3) A O × A S > 550

Advantages of the Invention

[0008] 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, that is, a positive electrode or a negative electrode, and a lithium ion secondary battery comprising the electrode.

[0009] Although not intended to be bound by theory, in the present invention, the following reasons are considered for the ability to improve the charge-discharge capacity and capacity retention rate. That is, sulfur functions as an active material that can be repeatedly charged and discharged by undergoing a reversible electrochemical reaction with lithium. Also in the present invention, as in the prior art, sulfur is mixed with a polymer and fixed to the polymer through heat treatment, thereby suppressing elution and contributing to a reversible reaction. For this reason, it is considered that the greater the number of sulfur atoms, the larger the charge-discharge capacity. On the other hand, in the present invention, oxygen atoms are bonded to carbon and sulfur to form bonds such as C-O bonds. For this reason, (1) since the active material contains these polar bonds, the dispersibility of the active material in the electrode slurry using water as a solvent is improved, and a uniform electrode is produced. Therefore, it is considered that the cycle capacity is easily maintained even after expansion and contraction accompanying the charge-discharge cycle. Also, (2) since the oxygen content is high and this exists in the skeleton of the active material, the S-S bond can be more stably retained inside the structure of the active material. Therefore, in the reaction between sulfur and lithium accompanying the insertion and desorption of lithium ions due to charge and discharge, it is considered that the ability to maintain sulfur inside the structure of the active material is high. Therefore, it is considered that the cycle capacity is easily maintained even after undergoing an electrochemical reaction accompanying the charge-discharge cycle.

[0010] As used herein, "cycle characteristics" refers to the characteristic that the charge-discharge capacity of a secondary battery is maintained despite repeated charge and discharge. Therefore, with repeated charge and discharge, a secondary battery with a large degree of decrease in charge-discharge capacity and a low capacity retention rate has poor cycle characteristics, whereas conversely, a secondary battery with a small degree of decrease in charge-discharge capacity and a high capacity retention rate has excellent cycle characteristics.

Brief Description of the Drawings

[0011]

Figure 1

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described. Regarding the description of numerical ranges, the upper and lower limit values such as "or more", "or less", "exceeding", and "less than" can be arbitrarily combined numerical values, and the numerical values in the examples can also be used as these upper and lower limits. In addition, a numerical range shown as including the lower limit or the upper limit is construed as simultaneously disclosing a numerical range not including the upper limit or the lower limit as long as it does not contravene the gist of the present invention. Conversely, a numerical range shown as not including the lower limit or the upper limit is construed as simultaneously disclosing a numerical range including the lower limit or the upper limit as long as it does not contravene the gist of the present invention.

[0013] One embodiment of the present invention is an electrode active material composed of particles containing an organic sulfur compound, wherein the oxygen content (mass%) in the electrode active material is A O and the sulfur content (mass%) is A S In the case where it is, A O and A S is an electrode active material that satisfies the following formula. (1) A O > 9.0 (2) A S > 45.0 (3) A O × A S > 550

[0014] The right side of formula (1) is preferably 11.0. The right side of formula (2) is preferably 50.0. The right side of formula (3) is preferably 570. By satisfying at least any one of the formulas under stricter conditions, it is considered that the effects of the present invention are more achieved.

[0015] The active material preferably further contains a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium.

[0016] The metal compound is preferably an iron compound.

[0017] Another embodiment of the present invention is an electrode comprising the electrode active material.

[0018] The electrode includes a current collector, the current collector includes a metal foil, and when the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, it is preferable that D and A O and A S satisfy the following formula. (4) D×(A O ×A S )>1000

[0019] It is considered that the performance of the electrode and / or the battery can be improved by making the product of the coating density, the oxygen content, and the sulfur content exceed a predetermined value.

[0020] The electrode includes a current collector, the current collector includes a metal foil, and when the coating density (mg / cm 2 ) of the electrode active material on the current collector is D and the thickness of the metal foil is T (μm), it is preferable that D, T, and A O and A S satisfy the following formula. (5) D×(A O ×A S ) / T>60

[0021] It is considered that the performance of the electrode and / or the battery can be improved by making the coating density, the oxygen content, the sulfur content, and the thickness of the metal foil satisfy the above formula.

[0022] The electrode includes a current collector, the current collector includes a metal foil, and when the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, it is preferable that D is greater than 2.50 mg / cm 2 .

[0023] The electrode is preferably a positive electrode.

[0024] It is considered that the performance of the electrode and / or the battery can be improved by using it as a positive electrode.

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

[0026] The lithium ion secondary battery further comprises an electrolyte. Let the volume of the electrolyte be V (mL), and the coating density (mg / cm 2 ) of the electrode active material on the current collector be D. When D, V, and A O and A S satisfy the following formula, it is preferable. (6) D×(A O ×A S ) / V>4000

[0027] By making the coating density, oxygen content, sulfur content, and volume of the electrolyte satisfy the above formula, it is considered that the performance of the electrode and / or the battery can be improved.

[0028] Another embodiment of the present invention is a method for manufacturing an electrode active material, comprising: (1) A mixing step of mixing a raw material containing cellulose and sulfur in an amount equal to or more than the mass of the cellulose to obtain a fired raw material; (2) A firing step of firing the fired raw material to obtain a fired product; and (3) A granulation step of pulverizing the fired product to obtain particles of the fired product is a method for manufacturing an electrode active material.

[0029] The cellulose is preferably cellulose that has not been chemically modified.

[0030] This is because, by not being chemically modified, the reaction between sulfur and cellulose can be prevented from being insufficient due to chemical modification, and as a result, a decrease in sulfur content can be avoided.

[0031] <Definition> "Particle" 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. Regarding the particles constituting the electrode active material, the size of such particles is not particularly limited as long as the above mixing can be suitably carried out. For example, when representing "particles" by the median diameter, it can be in the range of 1 nm to 1000 μm.

[0032] "Particle diameter" is expressed as the median diameter (d50) unless otherwise specified.

[0033] "Electrode active material" is one of the electrode materials of a battery and refers to a substance involved in the reaction that generates electricity. The electrode active material includes a positive electrode active material and a negative electrode active material.

[0034] "Oxygen content in the electrode active material" is the amount (mass %) of oxygen element contained in the electrode active material.

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

[0036] "Active material" refers to a substance responsible for the oxidation-reduction reaction carried out for energy conversion in a lithium-ion secondary battery.

[0037] "Coating density" is the mass (mg) per unit area (cm 2 ) of the active material coated on the current collector.

[0038] "Volume of the electrolyte" means the total volume of the electrolyte solution containing the solute or the solid electrolyte. The unit is mL.

[0039] "Initial discharge capacity" refers to the second discharge capacity unless otherwise specified.

[0040] <Measurement method>

[0041] "The content of oxygen, sulfur, etc. in the electrode active material" is measured by the method described in the examples, respectively. That is, the elemental amounts of carbon, hydrogen, nitrogen, and sulfur are measured by combustion-infrared absorption method in an oxygen stream using a fully automatic elemental analyzer vario MICRO cube manufactured by Elementar. The elemental amount of oxygen is measured by inert gas fusion-infrared absorption method using an oxygen, nitrogen, and hydrogen analyzer EMGA-930 manufactured by Horiba, Ltd.

[0042] "Particle size distribution" is measured using a laser diffraction / scattering particle size distribution measuring device (PSA1090L particle size distribution measuring device manufactured by Anton Paar) with water as the dispersion medium.

[0043] "Median diameter" is measured as the volume-based cumulative 50% diameter (μm) in the particle size distribution unless otherwise specified.

[0044] Hereinafter, the electrode active material, electrode, and lithium-ion secondary battery of the present embodiment will be described.

[0045] <Electrode active material> The electrode active material is an electrode active material composed of particles containing an organic sulfur compound. As shown in the above formulas (1) to (3), the oxygen content (mass%) A in the electrode active material O and the sulfur content (mass%) A S each exceed a predetermined value, and the product of A O and A S exceeds a predetermined value.

[0046] The organic sulfur compound is a compound formed by incorporating sulfur by firing sulfur with an organic compound typified by cellulose or the like in a non-oxidizing atmosphere. In the present embodiment, the organic sulfur compound is not particularly limited as long as it constitutes particles and the electrode active material composed of the particles satisfies the above formulas (1) to (3).

[0047] (Formulas (1) to (3)) The oxygen content (mass%) in the electrode active material is AO and when the sulfur content (mass%) is A S in this case, A O and A S and A satisfy the following formula. (1) A O > 9.0 (2) A S > 45.0 (3) A O × A S > 550

[0048] The right side of formula (1) is preferably 10.0, more preferably 11.0, still more preferably 12.0, still more preferably 13.0, still more preferably 14.0, still more preferably 15.0, still more preferably 16.0, still more preferably 17.0, still more preferably 18.0. The upper limit of the value of A O is not particularly limited, but as a reference value, it can also be assumed to be about 30.00.

[0049] A O can be increased by using an organic compound containing a large number of oxygen atoms as a raw material for firing, and conversely, can be decreased by using an organic compound containing a small number of oxygen atoms as a raw material for firing. Examples of the organic compound containing a relatively large number of oxygen atoms include cellulose.

[0050] (Formula (2)) The right side of formula (2) is preferably 46.0, more preferably 47.0, still more preferably 48.0, still more preferably 49.0, still more preferably 50.0, still more preferably 51.0, still more preferably 52.0, still more preferably 53.0, still more preferably 54.0, still more preferably 55.0, still more preferably 56.0, still more preferably 57.0, still more preferably 58.0, still more preferably 59.0. The upper limit of the value of A S is not particularly limited, but as a reference value, it can also be assumed to be about 70.0.

[0051] A Scan be increased by using a large amount of sulfur as a raw material for firing, and conversely, can be decreased by reducing the amount of sulfur used as a raw material for firing.

[0052] (Formula (3)) The right side of formula (3) is preferably 560, more preferably 570, still more preferably 600, still more preferably 650, still more preferably 700, still more preferably 750, still more preferably 800, still more preferably 830, still more preferably 840. A O ×A S The upper limit of is not particularly limited, but as a reference value, it can also be assumed to be about 1500.

[0053] A O ×A S is A O 's value and A S 's value can be adjusted by adjusting each of them.

[0054] (Elements other than oxygen and sulfur) The electrode active material may contain elements other than oxygen and sulfur. Such elements include carbon, hydrogen, nitrogen, and the like.

[0055] [Carbon content] The amount of carbon element is preferably more than 5.0% by mass, more preferably more than 10.0% by mass, still more preferably more than 15.0% by mass, from the viewpoint of improving the performance of the electrode and / or the battery. On the other hand, the amount of the element is preferably less than 50.0% by mass, more preferably less than 45.0% by mass, still more preferably less than 40.0% by mass.

[0056] [Hydrogen content] Upon firing, hydrogen (H) in the organic compound reacts with sulfur to form hydrogen sulfide, which is released outside the system. Therefore, the hydrogen content of the electrode active material is preferably less than 1.0% by mass, more preferably less than 0.7% by mass, and even more preferably less than 0.5% by mass. When it is less than 1.0% by mass, the firing (sulfidation reaction) tends to be sufficient. Therefore, in this case, the charge-discharge capacity tends to improve.

[0057] [Nitrogen content] The amount of nitrogen element (mass %) in the electrode active material can be 0 mass % when no nitrogen source is used in the raw materials. For example, if a compound containing a nitrogen atom is used as the organic compound, the nitrogen element can be detected.

[0058] (Amount of metal element) The electrode active material preferably further contains a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium. Also, the metal compound is preferably an iron compound. One or more metal compounds can be used.

[0059] When the electrode active material contains a metal compound, the amount of metal element (mass %) is preferably more than 10.0% by mass, more preferably more than 15.0% by mass, and even more preferably more than 20.0% by mass from the viewpoint of improving the performance of the electrode and / or the battery. On the other hand, the amount of the same element is preferably less than 30% by mass, more preferably less than 25.0% by mass, and even more preferably less than 24.0% by mass. Here, the amount of metal element means the total amount of those plural metal elements when the metal compound contains plural metal elements.

[0060] (Median diameter) The electrode active material consists of particles, and the size thereof is a size suitable for the production of the electrode. From the viewpoint of improving the performance of the electrode and / or the battery, the preferable range of the particle size of the electrode active material is about more than 1.0 μm and less than 40.0 μm in terms of the median diameter (median diameter d50). More preferably, the median diameter is more than 1.5 μm, still more preferably more than 2.0 μm, and still more preferably more than 3.0 μm. Also, more preferably, the median diameter is less than 30.0 μm, still more preferably less than 25.0 μm, still more preferably less than 20.0 μm, still more preferably less than 15.0 μm, still more preferably less than 10.0 μm, and still more preferably less than 8.0 μm. The median diameter can be measured by the method described in the column of Examples below.

[0061] (Other components) The electrode active material of the present embodiment can contain the materials described in the column of the production method below in the same manner as described in the same column.

[0062] <Electrode> The electrode according to one embodiment of the present invention is an electrode containing the above electrode active material.

[0063] The electrode according to the present embodiment can be used in a lithium ion secondary battery, and the electrode can be configured by using the materials described in the column of the production method below in the same manner as described in the same column. That is, when the above electrode is used as a positive electrode, a conductive assistant, a binder, a current collector, etc. described in the column of the production method below can be used in the same manner as described in the same column to form a positive electrode for a lithium ion secondary battery. When the above electrode is used as a negative electrode, a conductive assistant, a binder, a current collector, etc. described in the column of the production method below can be used in the same manner as described in the same column to form a negative electrode for a lithium ion secondary battery. Thus, these explanations in the column of the production method below can be referred to as the explanation of this electrode.

[0064] The electrode of the present embodiment includes a current collector, the current collector includes a metal foil, and when the coating density (mg / cm 2 ) on the current collector of the electrode active material is D, D and A O and AS It is preferable that they satisfy the following formula. (4) D×(A O ×A S )>1000

[0065] (Formula (4)) The right side of formula (4) is more preferably 1500, even more preferably 1700, even more preferably 1900, even more preferably 2100, even more preferably 2200, even more preferably 2300. Although there is no significance in setting an upper limit as the higher the value of the left side of formula (4) is, the better, it can be assumed to be about 5000 as a reference value.

[0066] (Coating density) The coating density D (mg / cm 2 ) of the electrode active material on the electrode is preferably more than 2.50 mg / cm 2 , more preferably more than 3.00 mg / cm 2 , even more preferably more than 3.50 mg / cm 2 , even more preferably more than 3.80 mg / cm 2 , even more preferably more than 3.90 mg / cm 2 . Although there is no significance in setting an upper limit as the higher the coating density value is, the better, it can be assumed to be about 15.0 mg / cm 2 as a reference value.

[0067] (Formula (5)) The electrode of this embodiment includes a current collector, the current collector contains a metal foil, when the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, and the thickness of the metal foil is T (μm), it is preferable that D, T, and A O and A S satisfy the following formula. (5) D×(A O ×A S ) / T>60

[0068] The right side of formula (5) is more preferably 80, even more preferably 90, even more preferably 110, even more preferably 120, even more preferably 130. Although the higher the value of the left side of formula (5), the better, there is no meaning in setting an upper limit. As a reference value, it can be assumed to be about 300.

[0069] (Thickness of metal foil) As a preferable range of the thickness T (μm) of the metal foil, it is 5 μm or more, more preferably 10 μm or more. On the other hand, the T is preferably 40 μm or less, more preferably 30 μm or less, even more preferably 25 μm or less.

[0070] (Charge and discharge capacity) The electrode of the present embodiment exhibits excellent charge and discharge capacity. The second discharge capacity (DC 2 ) which is the initial discharge capacity is the discharge capacity when charge and discharge are performed twice with the discharge cut-off voltage set to 1.0 V and the charge cut-off voltage set to 3.0 V after the production of the electrode and the battery (it is the second discharge when repeating the first discharge, the first charge, the second discharge, and the second charge). In the case of discharge, when discharging at a constant current (a current value corresponding to 50 mA per 1 g of the positive electrode active material), the voltage of 3.0 V finally drops to 1.0 V. Measure the total time (h) from 3.0 V to 1.0 V, multiply it by the current (mA) passed, and the capacity (mAh) can be obtained. Divide it by the weight of the active material to obtain the specific capacity (mAh / g). On the other hand, in the case of charging, the voltage rises conversely by charging with a constant current, and when it finally reaches 3.0 V, the charging is completed. The same applies to the 10th and 20th discharge capacities described later.

[0071] [Initial discharge capacity (DC 2 )] The initial discharge capacity DC 2 (mAh / g) when the electrode of the present embodiment is used as the positive electrode is preferably more than 455 mAh / g. DC 2is more preferably more than 460 mAh / g, still more preferably more than 470 mAh / g, still more preferably 480 mAh / g or more, still more preferably more than 490 mAh / g, still more preferably more than 500 mAh / g, and still more preferably more than 550 mAh / g. There is no particular limitation on the upper limit of the initial discharge capacity, and the higher it is, the more preferable it is. Therefore, although the significance of referring to the upper limit of the initial discharge capacity is small, as a reference value, it can usually be assumed to be, for example, about 1000 mAh / g.

[0072] [Discharge capacity at the 20th cycle (DC 20 )] When the electrode of this embodiment is used as the positive electrode, the discharge capacity when charging and discharging are repeated 20 times, that is, the discharge capacity DC at the 20th cycle 20 (mAh / g) is preferably more than 375 mAh / g. DC 20 is more preferably more than 400 mAh / g, still more preferably more than 430 mAh / g, still more preferably more than 450 mAh / g, still more preferably more than 480 mAh / g, still more preferably more than 490 mAh / g, still more preferably more than 500 mAh / g, and still more preferably more than 550 mAh / g. There is no particular limitation on the upper limit of the discharge capacity, and the higher it is, the more preferable it is. Therefore, although the significance of referring to the upper limit of the discharge capacity is small, as a reference value, it can usually be assumed to be, for example, about the value of the initial discharge capacity or about 900 mAh / g.

[0073] When the electrode of this embodiment is used as the positive electrode, the discharge capacity at the second or 20th time can be measured by using a negative electrode and an electrolyte within the common general knowledge of technologies that can be durable as a lithium-ion secondary battery (i.e., technologies in which Li does not run out), so that the performance related to the discharge capacity of the positive electrode can be fully exerted. In this case, it is determined by the configuration of the positive electrode. For example, for the negative electrode, lithium in an amount (mol amount) preferably 2 times or more, more preferably 5 times or more, still more preferably 10 times or more, and even more preferably 50 times or more the amount (mol amount) of sulfur in the positive electrode may be used. Also, for example, for the electrolyte, if the amount of the electrolytic solution (microliters) is preferably 10 times or more, more preferably 20 times or more, still more preferably 50 times or more the amount (mg) of sulfur in the positive electrode, the discharge capacity of the positive electrode can be fully exerted, leading to an extended battery life. On the other hand, considering the energy density of the battery, it is preferable that the amount of the electrolytic solution is small. For example, the amount of the electrolytic solution (microliters) is preferably 5 times or less, more preferably 3 times or less, still more preferably 1 time or less with respect to the amount (mg) of sulfur in the positive electrode. Here, the volume V (mL) of the electrolyte means the total volume of the electrolytic solution including the solute. Note that the electrolyte may be in the form of a solid (solid electrolyte) in addition to the form of the electrolytic solution, and both can be combined.

[0074] (Use) The electrode of this embodiment can be used as the positive electrode or the negative electrode of a lithium-ion secondary battery. Also, it is preferable to use the electrode of this embodiment as the positive electrode of a lithium-ion secondary battery.

[0075] <Lithium-ion secondary battery> A lithium-ion secondary battery according to an embodiment of the present invention is a lithium-ion secondary battery including the above electrode.

[0076] The lithium-ion secondary battery of the present embodiment can be configured by using the materials described in the column of the manufacturing method below in the same manner as described in the same column. That is, when using the above electrode as the positive electrode, a negative electrode, an electrolyte, a separator, etc. described in the column of the manufacturing method below can be used in the same manner as described in the same column to configure a lithium-ion secondary battery. On the other hand, when using the above electrode as the negative electrode, a positive electrode, an electrolyte, a separator, etc. described in the column of the manufacturing method below can be used in the same manner as described in the same column to configure a lithium-ion secondary battery. Thus, these explanations in the column of the manufacturing method below can be referred to as the explanation of this lithium-ion secondary battery.

[0077] (Formula (6)) The lithium-ion secondary battery of the present embodiment further comprises an electrolyte. Let the volume of the electrolyte be V (mL), and when the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, it is preferable that D, V, and A O and A S satisfy the following formula (6). (6) D×(A O ×A S ) / V>4000

[0078] The right side of formula (6) is more preferably 4500, further preferably 5000, further preferably 5500, further preferably 6000, further preferably 7000, further preferably 7500, further preferably 8000. Although there is no significance in setting an upper limit as the higher the value of the left side of formula (6) is, the better, it can be assumed to be about 20000 as a reference value.

[0079] (Volume V of the electrolyte) Since the volume V (mL) range of the electrolyte can vary depending on the size of the battery, it is not uniformly defined. Instead, the minimum amount sufficient to draw out the performance of the electrode active material and operate the battery properly can be used. As a reference value only, for example, in the case of the coin-type battery presented in the examples, it is preferably 0.1 mL or more, more preferably 0.12 mL or more, and even more preferably 0.15 mL or more. On the other hand, the V is preferably 0.40 mL or less, more preferably 0.30 mL or less, even more preferably 0.28 mL or less, and even more preferably 0.25 mL or less.

[0080] (Use) The lithium-ion secondary battery of this embodiment is useful as a lithium-ion secondary battery with improved comprehensive performance of charge-discharge capacity and capacity retention rate. It can be used as a battery for portable information terminals such as smartphones and notebook personal computers, portable electronic devices such as music players and digital cameras, medical devices, and next-generation clean energy vehicles such as hybrid vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHEVs).

[0081] <Manufacturing method> The manufacturing methods of the electrode active material, electrode, and lithium-ion secondary battery of this embodiment will be described below in order.

[0082] (Manufacture of electrode active material) The electrode active material of this embodiment can be manufactured by various methods. For example, as a method using cellulose in the organic compound as a raw material, the following methods can be mentioned.

[0083] That is, the electrode active material of this embodiment is (1) A mixing step of mixing a raw material containing cellulose and sulfur in an amount equal to or greater than the mass of the cellulose to obtain a fired raw material, (2) A firing step of firing the fired raw material to obtain a fired product, and (3) A granulation step of pulverizing the fired product to obtain particles of the fired product can be manufactured by a manufacturing method including.

[0084] [Raw materials] The raw materials used as the firing raw materials will be described below.

[0085] ≪Cellulose≫ Cellulose (Cellulose, Cell-OH, Ce) is a natural polymer that is the main component of the cell walls of plant cells and fibers, and is a carbohydrate represented by (C 12 H 20 O 10 ). n Cellulose has the following chemical structural formula. In this chemical structural formula, n indicating the average number of repetitions is a number of 1 or more, preferably 10 to 10000, more preferably 50 to 2000.

[0086] [Chemical formula]

[0087] As is clear from the above chemical structural formula, since cellulose has a plurality of hydroxyl groups, there exists an ester form in which all or part of them are esterified by an esterifying agent. The esterifying agent is not particularly limited as long as it can impart a carboxy group to the hydrophilic group of cellulose, and various ones can be used. For example, carboxylic acid-based compounds can be used, such as compounds having two or more carboxy groups, acid anhydrides of compounds having two or more carboxy groups, etc. can be used. In the present embodiment, cellulose includes such an ester form.

[0088] Cellulose as a plant material is composed of cellulose fibers of 20 to 40 μm. These cellulose fibers are bundles of cellulose microfibrils, and further, the cellulose microfibrils are bundles of cellulose molecular chains. Therefore, such cellulose as a plant material is preferably defibrated before use.

[0089] The defibrillation treatment includes mechanical defibrillation and chemical defibrillation, and any of these defibrillation treatments can be used in this embodiment. Here, examples of the mechanical defibrillation treatment include the high-pressure homogenizer method, the microfluidizer method (opposing jet collision method), the grinder method, the ball mill pulverization method, the bead mill pulverization method, and the cryogenic pulverization method. Among these, the cryogenic pulverization method is preferred. Examples of the chemical defibrillation treatment include the TEMPO method, the phosphoric acid esterification method, the phosphorous acid esterification method, the carboxymethylation method, the Sunday method, the sulfonation method, the enzymatic hydrolysis method, the acid hydrolysis method, and the ionic liquid selective dissolution method.

[0090] When cellulose is defibrillated by mechanical defibrillation treatment, no chemical modification is made, but when it is defibrillated by chemical defibrillation treatment, chemical modification is made. In this embodiment, from the viewpoint of improving the performance of the electrode and / or battery, cellulose that has been defibrillated by mechanical defibrillation treatment and has not been chemically modified is preferred.

[0091] Note that prior to the defibrillation treatment, it is preferable to perform a chemical or enzymatic pretreatment on cellulose.

[0092] One type or two or more types of cellulose can be used.

[0093] ≪Sulfur≫ As sulfur, various forms such as powdered sulfur, insoluble sulfur, precipitated sulfur, and colloidal sulfur can all be used. Among these, precipitated sulfur and colloidal sulfur are preferred. One type or two or more types of sulfur can be used.

[0094] From the viewpoint of improving the performance of the electrode and / or the battery, the sulfur content in the firing raw material is preferably 100 parts by mass or more, more preferably more than 100 parts by mass, still more preferably 200 parts by mass or more, still more preferably more than 200 parts by mass, and still more preferably 300 parts by mass or more, with respect to 100 parts by mass of cellulose. On the other hand, regarding the sulfur content, there is no particular upper limit, but it is preferably less than 1000 parts by mass, more preferably less than 900 parts by mass, still more preferably less than 800 parts by mass, still more preferably less than 700 parts by mass, still more preferably less than 600 parts by mass, still more preferably less than 500 parts by mass, and still more preferably 400 parts by mass or less. Being less than 1000 parts by mass tends to be cost - advantageous.

[0095] As sulfur, any of various allotropes can be used, but S which is solid at normal temperature and normal pressure 8 It is preferably something containing sulfur, S 8 It is more preferably elemental sulfur.

[0096] ≪Raw material metal compound≫ When the electrode active material further contains a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, as a raw material for firing, a raw material metal compound can further be used. Examples of the raw material metal compound include the following raw material metal compounds. It is preferable to use a raw material iron compound as the raw material metal compound.

[0097] 《Raw material iron compound》 Examples of the raw material iron compound include iron compounds containing divalent or trivalent iron ions. Any iron compound that decomposes during firing to react with sulfur to produce iron disulfide is not particularly limited, and various compounds can be used. Examples of the raw material iron compound include iron acid salts and iron complexes. Examples of the iron acid salts include both organic acid salts of iron and inorganic acid salts of iron. On the other hand, examples of the iron complexes include neutral iron complexes and salts of iron complex ions (iron complex salts). Among these, organic acid salts of iron, inorganic acid salts of iron, or neutral iron complexes are preferred. One or more iron compounds can be used.

[0098] Examples of the organic acid salts of iron include salts of divalent iron (Fe 2+ ) and organic acids, salts of trivalent iron (Fe 3+ ) and organic acids, etc. Among these, salts of divalent iron and organic acids are preferred. The organic acids are not particularly limited as long as they have a carboxyl group (-COOH) or a sulfo group (-SO 3 H), etc., but those having a carboxyl group are preferred. Specific examples of the organic acids include fatty acids, oxalic acid, tartaric acid, citric acid, malic acid, succinic acid, etc. Specific examples of the fatty acids include those having 1 to 6 carbon atoms such as acetic acid, propionic acid, and butyric acid. Among these, acetic acid, oxalic acid, etc. are preferred. Preferred examples of the organic acid salts of iron include iron(II) acetate, iron(II) oxalate, etc. These may be hydrates. One or more organic acid salts of iron can be used.

[0099] Examples of the inorganic acid salts of iron include salts of divalent iron (Fe 2+ ) and inorganic acids, salts of trivalent iron (Fe 3+ ) and inorganic acids, etc. Specific examples of the inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, etc. Among these, nitric acid, etc. are preferred. Preferred examples of the inorganic acid salts of iron include iron(II) chloride, iron(III) chloride, iron(II) sulfate, iron(III) sulfate, iron(II) nitrate, iron(III) nitrate, etc. These may be hydrates. One or more inorganic acid salts of iron can be used.

[0100] Examples of iron complexes include complexes of divalent iron (Fe 2+ ) and complexes of trivalent iron (Fe 3+ ). The iron complex may be in the form of a neutral complex or a complex salt. The ligands coordinated to the iron ion are not particularly limited, and examples include halogen atoms such as chlorine atoms and bromine atoms, cyano groups, dicyclopentadienyl groups, N,N'-bis(salicylidene)ethylenediamine, and the like. Examples of iron complexes include potassium hexacyanoferrate(II) ([Fe(CN) 6 K 4 ), potassium hexacyanoferrate(III) ([Fe(CN) 6 K 3 ), sodium tetrachloroferrate(III) ([FeCl 4 Na), dicyclopentadienyliron(II) (ferrocene), N,N'-bis(salicylidene)ethylenediaminatoiron(III) chloride, and the like. One or more iron complexes can be used.

[0101] 《Raw material molybdenum compound》 Examples of the raw material molybdenum compound include molybdenum(VI) trioxide, sodium(VI) molybdate, hexaammonium(VI) heptamolybdate, diammonium(VI) molybdate, calcium(VI) molybdate, molybdic(VI) acid, phosphomolybdic(VI) acid, molybdenum(VI) disulfide, and the like. One or more molybdenum compounds can be used.

[0102] 《Raw material vanadium compound》 Examples of the raw vanadium compound include vanadium(V) pentoxide, ammonium metavanadate(V), vanadium(V) oxytrichloride, sodium metavanadate(V), potassium vanadate(V), sodium vanadate(V), vanadium(IV) tetrachloride, vanadium(IV) oxysulfate, vanadium(IV) oxydichloride, vanadium(IV) oxide, vanadium(IV) trichloride, vanadium(III) oxide, hexavanadium(IV,V) tridecoxide, etc. One or more vanadium compounds can be used.

[0103] 《Raw Titanium Compound》 Examples of the raw titanium compound include titanium oxide, titanium dioxide, titanium dioxide, dititanium trioxide, titanium tetrachloride, etc. One or more titanium compounds can be used.

[0104] 《Content of the Raw Metal Compound》 From the perspective of improving the performance of the electrode and / or battery, the content of the raw metal compound in the fired raw material is preferably 50 to 300 parts by mass, more preferably more than 50 parts by mass, still more preferably more than 60 parts by mass, still more preferably more than 70 parts by mass, still more preferably more than 75 parts by mass, based on 100 parts by mass of cellulose. On the other hand, the content is more preferably less than 250 parts by mass, still more preferably less than 200 parts by mass, still more preferably less than 150 parts by mass, still more preferably 100 parts by mass or less.

[0105] 《Median Diameter of the Raw Metal Compound》 When using the raw material metal compound as a fired raw material, it is preferably pulverized in advance. The median diameter (d50) of the 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, still more preferably 6.00 μm or less, still more preferably 4.00 μm or less, still more preferably 3.00 μm or less. On the other hand, there is no particular limitation on the lower limit of the median diameter, but usually it is about 0.10 μm or more, and may be about 1.00 μm or about 2.00 μm. The median diameter can be measured by the method described above.

[0106] 《Specific Surface Area of Raw Material Metal Compound》 The specific surface area of the raw material metal compound is preferably 1.0 m 2 / g or more, more preferably 2.0 m 2 / g or more, still more preferably 3.0 m 2 / g or more, still more preferably 4.0 m 2 / g or more, still more preferably 4.5 m 2 / g or more. On the other hand, there is no particular limitation on the upper limit of the specific surface area, but usually it is about 40.0 m 2 / g or less, and may be about 20.0 m 2 / g or less, and may be about 10.0 m 2 / g or less. The specific surface area can be measured by a fully automatic specific surface area measuring device Macsorb (HM-model 1201, manufactured by Mountech Co., Ltd.).

[0107] The raw material metal compound having the median diameter or specific surface area as described above can be prepared by a conventional method. For example, the raw material metal compound can be prepared by pulverizing it with a pulverizer. As such a pulverizer, for example, those manufactured by Nippon Analytical Industry Co., Ltd. (such as JFC-2000) can be used.

[0108] ≪Other Materials≫ The raw material may optionally contain other materials commonly used in this field as desired. Such raw materials include carbon materials.

[0109] "Carbon Materials" In the electrode active material of this embodiment, the carbon material preferably has a graphite structure. Further, the carbon material is preferably conductive. Examples of the carbon material include porous carbon materials such as activated carbon, graphite, carbon black, acetylene black, ketjen black, and in addition, carbon fibers such as carbon fiber, vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), carbon nanofiber, and nano-carbon materials having shapes other than carbon fibers such as graphene and fullerene. Among these, carbon fibers such as carbon fiber, vapor-grown carbon fiber (VGCF), CNT, and carbon nanofiber are preferable, and particularly, CNT is preferable. One or more kinds of carbon materials can be used.

[0110] When the carbon material is a carbon fiber, from the viewpoint of improving the performance of the electrode and / or the battery, the form of the fiber constituting the carbon fiber preferably has an average fiber length of a predetermined value or more and an average fiber diameter of a predetermined value or less. 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 limitation on the upper limit of the average fiber length, and it may be 100 μm, 50 μm, or 20 μm. Also, 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 limitation on the lower limit of the average fiber diameter, but it is usually about 1 nm.

[0111] The aspect ratio of the carbon material is preferably more than 10, more preferably more than 100, and even more preferably more than 1000, and is preferably less than 100000, more preferably less than 50000, and even more preferably less than 10000.

[0112] From the viewpoint of the effects of the present invention, the specific surface area of the carbon material is 400 m 2It is preferably at least / g, and preferably at most 2400 m 2 / g. The specific surface area is preferably at least 500 m 2 / g, more preferably at least 600 m 2 / g, and even more preferably at least 600 m / g. On the other hand, the specific surface area is more preferably at most 2000 m 2 / g, even more preferably at most 1800 m 2 / g. The specific surface area is measured by the BET multi-point method.

[0113] From the viewpoint of the effects of the present invention, the carbon material preferably has a G / D ratio of 10 or more. The G / D ratio is more preferably 20 or more, even more preferably 30 or more, and even more preferably 40 or more. On the other hand, there is no particular limitation on the upper limit of the G / D ratio, but if it is 50, it can be said that the carbon material has extremely few defects. Here, the G / D ratio is the ratio of the peaks of typical Raman shifts in the Raman spectrum of the carbon material. More specifically, it is 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 RAMANtouch manufactured by Nanophoton Co., Ltd. (excitation wavelength λ = 532 nm, grating: 1200 gr / mm, resolution: 1.2 cm-1).

[0114] From the viewpoint of the effects of the present invention, the carbon material preferably has a metal impurity content of 5% by mass or less. The metal impurity content is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. The less the metal impurity content, the better. For example, if it is 0.1% by mass, the metal impurity content is in a sufficiently low state. Here, the metal impurities referred to herein mean metal elements other than iron, molybdenum, vanadium, and titanium.

[0115] 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 cellulose. 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.

[0116] (Manufacturing process) [Mixing step (1)] The mixing step is a step of mixing a raw material containing cellulose and sulfur in an amount equal to or greater than the mass of the cellulose to obtain a firing raw material.

[0117] The above mixing is not particularly limited as long as these components are sufficiently mixed, and can be carried out by a conventional method. In the present embodiment, for example, a method of directly mixing a raw material containing cellulose in a powder state and sulfur in a powder state in an amount equal to or greater than the mass of the cellulose using a blender or the like can be mentioned. Further, when an optional component such as a raw material metal compound or a carbon material is added to the raw material, the optional component may also be mixed together with a blender or the like.

[0118] Here, the powder refers to a state in which each solid raw material is sufficiently fine to be suitable for mixing under the object of the present invention. The size of each particle constituting the powder is not particularly limited as long as the mixing is preferably carried out, but usually, for example, it is 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, still more preferably 4 μm or more, preferably 30 μm or less, still more preferably 20 μm or less, still more preferably 15 μm or less, and still more preferably 10 μm or less in terms of median diameter. The median diameter can be measured by the above method.

[0119] The raw material thus obtained may be directly used in the next firing step, or may be formed into pellets if desired and then used in the next step.

[0120] [Firing Process (2)] The firing process is a process of firing the fired raw material obtained above to obtain a fired product. Firing can be carried out by a conventional method. For example, the fired raw material can be heated at a predetermined heating rate until it reaches a predetermined temperature, maintained at the predetermined temperature for a predetermined time, and then cooled naturally.

[0121] Non-oxidizing atmosphere Firing is preferably carried out under a non-oxidizing atmosphere. A non-oxidizing atmosphere means an atmosphere substantially free of oxygen and is adopted to suppress oxidation degradation of the constituent components and excessive thermal decomposition. Specifically, it refers to an inert gas atmosphere such as nitrogen or argon, a sulfur gas atmosphere, an ammonia gas atmosphere, etc. Therefore, firing can be preferably carried out, for example, in a quartz tube under an inert gas atmosphere.

[0122] Heating rate The heating rate is preferably, for example, in the range of 50°C / h or more and 500°C / h or less. The heating rate is preferably 80°C / h or more, more preferably 100°C / h or more, and still more preferably 120°C / h or more. On the other hand, the heating rate is more preferably 400°C / h or less, still more preferably 300°C / h or less, and still more preferably 200°C / h or less. When the heating rate is within such a range, it tends to be easy to achieve the purpose of improving the charge-discharge capacity and cycle characteristics.

[0123] Firing temperature and time The firing temperature refers to the temperature after the raw material has completed its temperature rise and is maintained for a certain period of time for firing the raw material. Preferably, this temperature is in the range of exceeding 250°C and less than 550°C. By exceeding 250°C, it is possible to avoid insufficient vulcanization reaction and tend to prevent a decrease in the charge-discharge capacity of the target product. On the other hand, by setting it to less than 550°C, it is possible to prevent decomposition of the raw material and tend to prevent a decrease in yield and a decrease in charge-discharge capacity. More preferably, the temperature exceeds 270°C, even more preferably exceeds 290°C, and even more preferably is 300°C or higher. On the other hand, more preferably, the temperature is less than 500°C, even more preferably less than 470°C, and even more preferably 450°C or lower.

[0124] When using a raw material metal compound as the raw material, from the perspective of improving the performance of the electrode and / or battery, the firing temperature in the firing process is preferably higher than the temperature at which the raw material metal compound thermally decomposes.

[0125] The time for maintaining at the firing temperature may be appropriately set according to the type of raw material, firing temperature, etc. For example, it is preferably 0.5 hours or more and 6 hours or less. By being 0.5 hours or more, the firing tends to proceed sufficiently, and by being 6 hours or less, excessive thermal decomposition of the constituent components can be prevented. More preferably, the time is 0.6 hours or more, and even more preferably 0.7 hours or more. On the other hand, more preferably, the time is 4 hours or less, and even more preferably 2 hours or less.

[0126] ≪Apparatus≫ Firing can be carried out, for example, by a muffle furnace (Figure 1), or alternatively, it can also be carried out using a continuous apparatus such as a twin-screw extruder. When using a continuous apparatus, there is an advantage that a sulfur-based electrode active material can be continuously manufactured by a series of operations such as kneading, pulverizing, and mixing the raw material while firing it within the apparatus.

[0127] The 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 the sample. In Figure 1, the muffle furnace 1 has a heater 2 at the lower part of the furnace, and the heater is partitioned by a hot plate. A lid 3 is installed on the front of the furnace (the left end side in the figure), and it has a structure that can maintain the inside of the furnace in an atmosphere of an inert gas 4. A thermocouple (not shown) is attached to the lid, and the temperature inside the furnace during firing can be measured. Inside the furnace, trays 5 and 6, which are rectangular parallelepiped reaction vessels made of stainless steel for firing the raw material, are installed in two stages, one on the upper stage and the other on the lower stage.

[0128] Inside the furnace, gas (for example, an inert gas such as argon (Ar) gas) can be continuously supplied from the outside and discharged through a gas introduction pipe 7 and a gas discharge pipe 8. The gas discharge pipe 8 is connected to a trap tank 10 containing an aqueous sodium hydroxide solution 9, and the exhaust gas that tries to go out from the muffle furnace 1 through the gas discharge pipe 8 to the outside is once passed through the aqueous sodium hydroxide solution 9 in the trap tank 10 and then discharged to the outside. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the reaction, it is neutralized with the aqueous sodium hydroxide solution and removed from the exhaust gas.

[0129] [Residue removal step] The residue removal step is a step of removing residues such as unreacted sulfur in which sulfur sublimated during firing has cooled and precipitated from the fired product. Since these residues are factors that reduce the cycle characteristics, it is desirable to remove them as much as possible if there are residues. The removal of residues can be carried out, for example, by subjecting the fired product to conventional methods such as drying under reduced pressure heating, hot air drying, and solvent washing.

[0130] [Grinding step (3)] The grinding step is a step of grinding the fired product to obtain particles of the fired product. The fired product is preferably ground into particles of a size suitable for the production of the electrode. The preferable size range of the particles of the electrode active material is as described above.

[0131] The pulverization can be carried out by a conventional method. For example, it can be carried out by subjecting 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. For example, when using a cutter mill (e.g., Free Speed Mill, FS-20 manufactured by Labonekt Co., Ltd.), the rotation speed can be set at 20,000 rpm or more and 30,000 rpm or less, and the treatment time can be 1 second or more and 30 seconds or less. Also, when using a dry jet mill (e.g., Nano Jet Mizor, NJ-30 manufactured by Aisin Nanotechnology Co., Ltd.), the treatment speed can be 1 g / min or more and 3 g / min or less, and the pulverization pressure can be 0.5 MPa or more and 2.0 MPa or less.

[0132] The particles of the pulverized fired product obtained above can be classified if desired, and the particle size can be further made uniform. Classification can be carried out, for example, using a sieve with a desired sieve mesh size.

[0133] In addition, in the firing method using the twin-screw extruder described above, due to the shear during kneading, pulverization of the produced electrode active material particles can be carried out simultaneously with the production of the electrode active material.

[0134] (Manufacture of Electrode for Lithium Ion Secondary Battery) Using the electrode active material obtained above, an electrode for a lithium ion secondary battery including an electrode active material layer containing the electrode active material can be manufactured by a conventional method. That is, the electrode can be obtained in the same manner as in the case of manufacturing a general electrode for a lithium ion secondary battery, except that the above electrode active material is used as the active material.

[0135] [When Using the Electrode Active Material as the Positive Electrode Active Material] The positive electrode for a lithium-ion secondary battery can be produced in the same manner as a general positive electrode for a lithium-ion secondary battery, except that the above electrode active material is used as the positive electrode active material. For example, the positive electrode can be produced by mixing the electrode active material with a conductive 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 it. As another method, the positive electrode can be produced, for example, by kneading the electrode active material together 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 crimping it to a current collector using a press or the like.

[0136] <<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, or fine powders of metals such as aluminum and titanium that are stable at the positive electrode potential. Also, as the conductive assistant, a conductive one among the above carbon materials can be used. These conductive assistants can be used alone or in combination of two or more.

[0137] <<Binder>> Examples of the binder include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (PAI), carboxymethyl cellulose (CMC), polyvinyl chloride (PVC), acrylic resin, 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.

[0138] <<Solvent>> Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformaldehyde, alcohol, hexane, water, etc. One or more of these solvents can be used.

[0139] <<Blending amount>> Although the blending amount of the materials constituting these positive electrodes is not particularly limited, for example, it is preferable to blend 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 the electrode active material.

[0140] <<Current collector>> As the current collector, those generally used for the positive electrode of a lithium-ion secondary battery may be used. For example, as the current collector, in addition to metal foils such as aluminum foil, aluminum mesh, punched aluminum sheet, expanded aluminum sheet, stainless steel foil, stainless steel mesh, punched stainless steel sheet, expanded stainless steel sheet, foamed nickel, nickel non-woven fabric, copper foil, copper mesh, punched copper sheet, expanded copper sheet, titanium foil, titanium mesh, etc., those made of carbon non-woven fabric, carbon woven fabric, etc. are exemplified. Among these, a current collector containing a metal foil is preferable. The current collector may be used alone or in combination of two or more. In addition, the surface of the current collector may be coated with carbon or the like. Specific examples of such a current collector whose surface is coated with carbon or the like include, for example, carbon-coated aluminum foil. In this case, the current collector includes the carbon-coated portion.

[0141] [When using the electrode active material as the negative electrode active material] The negative electrode for the lithium-ion secondary battery can be produced in the same manner as a general negative electrode for a lithium-ion secondary battery, except that the above electrode active material is used as the negative electrode active material. For example, the negative electrode can be produced by mixing the electrode active material with a conductive 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 it. As another method, the negative electrode can be produced, for example, by kneading the electrode active material together with a conductive assistant, a binder, and a small amount of solvent using a mortar or the like, forming it into a film shape, and then pressing it onto a current collector using a press or the like.

[0142] 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 and used in the same manner.

[0143] (Manufacture of Lithium-Ion Secondary Battery) The lithium-ion secondary battery of this embodiment can be manufactured in the same manner as in the case of manufacturing a general lithium-ion secondary battery, except that the electrode for the lithium-ion secondary battery obtained above is used.

[0144] [When the Electrode Active Material is Used as the Positive Electrode Active Material] The lithium-ion secondary battery of this embodiment can be produced according to a conventional method by using a negative electrode, an electrolyte, and, if desired, a member such as a separator on the positive electrode containing the above electrode active material (positive electrode active material).

[0145] ≪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, a silicon-based material, which is a high-capacity negative electrode material in particular, is preferable, and among them, thin-film silicon with a thin electrode thickness and advantageous capacity per volume is more preferable.

[0146] ≪Electrolyte≫ The electrolyte compensates for the charge generated by the release of electrons into the external circuit as the electrode active material in the positive and negative electrodes is oxidized / reduced, by 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. Note that the electrolyte is not limited to liquid. For example, when the lithium-ion secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid state (e.g., polymer gel state).

[0147] <<Separator>> In addition to the negative electrode, positive electrode, and electrolyte described above, a lithium-ion secondary battery may include components such as a separator. The separator is interposed between the positive electrode and the negative electrode, 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 holding the electrolyte solution. As the separator, it is preferable to use a thin and microporous or non-woven fabric-like film made of materials such as polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, and glass.

[0148] <<Shape>> The shape of the lithium-ion secondary battery is not particularly limited and can be various shapes such as cylindrical, laminated, coin type, laminate type, button type, etc.

[0149] [When using the electrode active material as the negative electrode active material] The lithium-ion secondary battery of this embodiment can be manufactured according to a conventional method by using a negative electrode containing the above electrode active material (negative electrode active material), a positive electrode, an electrolyte, and further, if desired, components such as a separator.

[0150] <<Positive Electrode>> As the positive electrode material, for example, a transition metal oxide or solid solution oxide containing lithium, or a substance that can electrochemically occlude and release lithium ions is not particularly limited. As the transition metal oxide containing lithium, for example, LiCoO 2 such as Li·Co-based composite oxides, LiNi x Coy Mn z O 2 Li-Ni-Co-Mn composite oxides such as, LiNiO 2 Li-Ni composite oxides such as, or LiMn 2 O 4 Li-Mn composite oxides such as, etc. can be exemplified. As the solid solution oxide, for example, Li a Mn x Co y Ni z O 2 (1.150 ≦ a ≦ 1.430, 0.450 ≦ x ≦ 0.600, 0.100 ≦ y ≦ 0.150, 0.200 ≦ z ≦ 0.280), LiMn x Co y Ni z O 2 (0.300 ≦ x ≦ 0.850, 0.100 ≦ y ≦ 0.300, 0.100 ≦ z ≦ 0.300), LiMn 1.5 Ni 0.5 O 4 etc. can be exemplified. These compounds may be used alone or in combination of two or more.

[0151] <<Others>> Regarding the electrolyte, separator, and the shape of the lithium-ion secondary battery, those similar to the above case where the electrode active material is used as the positive electrode active material can be used in the same manner.

Examples

[0152] The present invention will be described based on examples, but the present invention is not limited only to the examples.

[0153] The various chemicals used in the examples and comparative examples are summarized below. The various chemicals were purified according to conventional methods as necessary.

[0154] <Materials used in the test> Cellulose: Cellulose (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., white powder, passing through 38 μm (400 mesh)) Diene rubber: high cis - butadiene rubber (UBEPOL (registered trademark) BR150L manufactured by UBE Industries, Ltd., cis content (cis - 1,4 - bonded butadiene unit amount): 98% by mass) PP: polypropylene (available from Sigma - Aldrich, catalog number 428116, melting point: 157 °C) Cross - linked PMMA: cross - linked polymethyl methacrylate (Tech Polymer MB30X - 8 manufactured by Sekisui Chemical Co., Ltd., spherical acrylic resin composed of a copolymer of methyl methacrylate and ethylene glycol dimethacrylate, particle diameter: 8 μm) Sulfur: precipitated sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0155] Production Example 1 (Grinding of raw materials) Cellulose and polypropylene were each ground for 10 minutes in a cryogenic grinder (JFC - 2000 manufactured by Nippon Analytical Industry Co., Ltd.) before being used as raw materials.

[0156] <Preparation of electrode active material> (Mixing step) The raw materials were charged according to the compounding ratios shown in the following table and mixed using a blender (LAB MILL manufactured by Osaka Chemical Co., Ltd.) to obtain a fired raw material.

[0157] (Firing step) A muffle furnace (Figure 1) was used for firing the raw materials. The muffle furnace in Figure 1 is as described above.

[0158] First, with the fired raw material contained in a tray which is a stainless - steel reaction vessel, the atmosphere in the muffle furnace was replaced three times with Ar gas using a vacuum pump. Then, while continuously supplying Ar gas at a flow rate of 100 mL / min from the gas inlet tube, heating of the muffle furnace was started 30 minutes after the start of supply. The temperature was raised at a rate of 5 °C / min. When the temperature of the fired raw material reached the firing temperature shown in Table 1, heat treatment was performed for 45 minutes while maintaining the temperature. Next, while adjusting the flow rate of Ar gas, after naturally cooling the temperature of the fired product to 25 °C under an Ar gas atmosphere, the fired product was taken out from the muffle furnace.

[0159] (Removal of unreacted sulfur) In order to remove the unreacted sulfur (elemental sulfur in a free state) remaining in the product after the firing process, the following steps were carried out. That is, the fired product was pulverized in a mortar, the pulverized product was placed in a glass tube oven, and heated at 290 °C for 3 hours while performing vacuum suction, to obtain an electrode active material from which unreacted sulfur was removed (or which contains only a trace amount of unreacted sulfur). The heating rate was 10 °C / min.

[0160] (Pulverization process) The fired product from which unreacted sulfur was removed was pulverized using a cutter mill (LAB MILL manufactured by Osaka Chemical Co., Ltd.).

[0161] (Classification operation) In order to remove coarse particles from the pulverized fired product, classification was performed using a 32 μm mesh stainless steel sieve to obtain an electrode active material.

[0162] (Physical properties of the electrode active material) Regarding the electrode active material obtained above, the following characteristics were examined.

[0163] (Particle size distribution, median diameter) The particle size distribution was measured using a laser diffraction / scattering type particle size distribution measuring device (PSA1090L, a particle size distribution measuring device manufactured by Anton Paar GmbH), 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.

[0164] (Elemental composition) The mass ratios (%) in the total amount of the electrode active material were calculated from the masses measured using a fully automatic elemental analyzer vario MICRO cube manufactured by Elementar for the elemental amounts of carbon, hydrogen, nitrogen, and sulfur. The mass ratio (%) in the total amount in the electrode active material was calculated from the mass measured using an oxygen / nitrogen / hydrogen analyzer EMGA-930 manufactured by Horiba, Ltd. for the elemental amount of oxygen.

[0165] <Fabrication of Lithium-Ion Secondary Battery> A lithium-ion secondary battery was fabricated as follows.

[0166] (Positive Electrode) As the active material, the electrode active material obtained above was used. As the conductive assistant, acetylene black (manufactured by Denka Co., Ltd., HS-100) was used, and as the binder, an acrylic resin (manufactured by Fujifilm Wako Pure Chemical Corporation, average molecular weight 2700 - 7500) was used. These were weighed so that the ratio was active material:acetylene black:binder = 85:10:5 (mass %), placed in a container, and stirred and mixed using a rotation-revolution mixer (ARE-250 manufactured by Shinki 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, an electrode (positive electrode) was obtained by punching out a φ11-mm disc. Then, the mass of the electrode was measured, and the amount of active material in the electrode was calculated from the above ratio.

[0167] (Negative Electrode) As the negative electrode, a metallic lithium foil (disc-shaped with a diameter of 14 mm and a thickness of 500 μm, manufactured by Honjo Metal Co., Ltd.) was used. A stainless steel sheet was used as the negative electrode current collector.

[0168] (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.

[0169] (Lithium-Ion Secondary Battery) Using the above positive electrode and negative electrode, coin cells were fabricated. Specifically, in a dry room, a separator (Celgard 2400 made by Celgard, a polypropylene microporous membrane with a thickness of 25 μm) and a glass nonwoven fabric filter (with a thickness of 440 μm, GA100 made by ADVANTEC) were sandwiched between the positive electrode and the negative electrode to form an electrode body cell. This electrode body cell was housed in a battery case made of a stainless steel container (a member for a CR2032 type coin cell, manufactured by Takizawa Co., Ltd.). The above electrolyte was injected into the battery case. The amount was 0.28 mL as the volume of the electrolyte. The battery case was sealed with a caulking machine to obtain the lithium-ion secondary batteries of each example and comparative example.

[0170] <Evaluation of Lithium-Ion Secondary Batteries> (Discharge Capacity, Capacity Retention Rate) Regarding the coin-type lithium-ion secondary batteries fabricated in each example and comparative example, under the condition of a test temperature of 30 °C, per 1 g of the positive electrode active material, the charge and discharge were carried out at a current value corresponding to 50 mA from the 1st to the 10th cycles, and at a current value corresponding to 100 mA from the 11th to the 20th cycles. The discharge cut-off voltage was 1.0 V and the charge cut-off voltage was 3.0 V. Also, the charge and discharge were repeated, and the battery discharge capacities (mAh) at the 1st, 2nd, 10th, and 20th cycles were observed. This measurement was performed using a battery performance evaluation device (manufactured by Measuring Instrument Center Co., Ltd., BLS system).

[0171] The discharge capacity DC at the 2nd cycle 3 (mAh / g) was taken as the initial capacity. The larger the initial capacity, the more favorably the lithium-ion secondary battery can be evaluated in terms of having a large charge and discharge capacity. Also, the discharge capacity DC at the 2nd cycle 2 (mAh / g) and the discharge capacity DC at the 20th cycle 20 (mAh / g) were used to obtain the capacity retention rate (%) according to the following formula. The higher the capacity retention rate, the better the cycle characteristics of the lithium-ion secondary battery can be said to be. Capacity retention rate (%) = (DC 20 / DC 2 ) × 100

[0172] The results are as shown in Table 1 below.

[0173]

Table 1

[0174] Examples 1 to 4 showed a higher initial discharge capacity than Comparative Examples 2 and 3. This is presumably because a higher sulfur content enables more binding with lithium ions. Note that, although Comparative Example 1 has a high sulfur content, its initial discharge capacity is only lower than those of Examples 1 to 4. Also, Examples 1 to 4 showed a higher capacity retention rate than Comparative Examples 1, 3, and 4. This is presumably because the sulfur content is sufficiently high and the oxygen content is high, suppressing side reactions in the charge-discharge reaction.

[0175] <Embodiment> Preferred embodiments are shown below.

[0176] [1] An electrode active material composed of particles containing an organic sulfur compound, wherein the oxygen content (mass %) in the electrode active material is A O and the sulfur content (mass %) is A S such that A O and A S satisfy the following formula, or at least one of the right sides of Formulas (1) to (3) takes a more preferable value, the preferable value for the right side of Formula (1) being 10.0, the preferable value for the right side of Formula (2) being 46.0, more preferably 47.0, still more preferably 48.0, still more preferably 49.0, and the preferable value for the right side of Formula (3) being 560: (1) A O > 9.0 (2) A S > 45.0 (3) A O × A S > 550 [2] The right side of formula (1) is 11.0, preferably 12.0, more preferably 13.0, still more preferably 14.0, still more preferably 15.0, still more preferably 16.0, still more preferably 17.0, still more preferably 18.0, and the electrode active material described in the above [1]. [3] The right side of formula (2) is 50.0, preferably 51.0, more preferably 52.0, still more preferably 53.0, still more preferably 54.0, still more preferably 55.0, still more preferably 56.0, still more preferably 57.0, still more preferably 58.0, still more preferably 59.0, and the electrode active material described in the above [1] or the above [2]. [4] The right side of formula (3) is 570, preferably 600, more preferably 650, still more preferably 700, still more preferably 750, still more preferably 800, still more preferably 830, still more preferably 840, and the electrode active material described in any one of the above [1] to the above [3]. [5] The active material further includes a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium, and the electrode active material described in the above [1] to the above [4]. [6] The metal compound is an iron compound, and the electrode active material described in the above [5]. [7] An electrode comprising the electrode active material described in any one of the above [1] to the above [6]. [8] The electrode includes a current collector, The current collector includes a metal foil, When the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, when D and A O and A S satisfy the following formula, or the right side of formula (4) is preferably 1500, more preferably 1700, still more preferably 1900, still more preferably 2100, still more preferably 2200, still more preferably 2300, and the electrode described in the above [7]. (4) D×(A O ×A S )>1000 [9] The electrode includes a current collector, The current collector includes a metal foil, The coating density (mg / cm 2 ) of the electrode active material on the current collector is D, and when the thickness of the metal foil is T (μm), D, T, and A O and A S satisfy the following formula, or the right side of formula (5) is preferably 80, more preferably 90, still more preferably 110, still more preferably 120, still more preferably 130. The electrode according to [7] or [8] above. (5) D×(A O ×A S ) / T > 60

[10] The electrode includes a current collector, the current collector includes a metal foil, when the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, D is more than 2.50 mg / cm 2 , preferably more than 3.00 mg / cm 2 , more preferably more than 3.50 mg / cm 2 , still more preferably more than 3.80 mg / cm 2 , still more preferably more than 3.90 mg / cm 2 . The electrode according to any one of [7] to [9] above.

[11] The electrode is a positive electrode. The electrode according to any one of [7] to

[10] above.

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

[11] above.

[13] Further comprising an electrolyte, with the volume of the electrolyte being V (mL), when the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, V, D, and A O and A S satisfy the following formula, or the right side of formula (6) is preferably 4500, more preferably 5000, still more preferably 5500, still more preferably 6000, still more preferably 7000, still more preferably 7500, still more preferably 8000. The lithium-ion secondary battery according to

[12] above. (6) D×(A O ×A S ) / V > 4000

[14] A method for manufacturing an electrode active material, comprising: (1) A mixing step of mixing a raw material containing cellulose and sulfur having a mass equal to or greater than the mass of the cellulose to obtain a fired raw material; (2) A firing step of firing the fired raw material to obtain a fired product; and (3) A granulation step of pulverizing the fired product to obtain particles of the fired product. A method for manufacturing an electrode active material, comprising the above steps.

[15] The manufacturing method according to

[14] above, wherein the cellulose is cellulose that has not been chemically modified.

Explanation of reference numerals

[0177] 1 Muffle furnace 2 Heater 3 Lid 4 Inert gas 5 Tray (upper stage) 6 Tray (lower stage) 7 Gas introduction pipe 8 Gas discharge pipe 9 Aqueous sodium hydroxide solution 10 Trap tank

Claims

1. An electrode active material comprising particles containing an organic sulfur compound, The oxygen content (mass %) in the electrode active material is A O and the sulfur content (mass %) is A S In the case where it is, A O and A S An electrode active material in which and satisfy the following formula. (1) A O > 9.0 (2) A S > 45.0 (3) A O × A S > 550

2. The electrode active material according to claim 1, wherein the right side of formula (1) is 11.

0.

3. The electrode active material according to claim 1, wherein the right side of formula (2) is 50.

0.

4. The electrode active material according to claim 1, wherein the right side of formula (3) is 570.

5. The electrode active material according to claims 1 to 4, further comprising a metal compound containing at least one metal selected from the group consisting of iron, molybdenum, vanadium, and titanium.

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 any one of claims 1 to 4.

8. The electrode includes a current collector, The current collector includes a metal foil, When the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, D and A O and A S satisfy the following formula, the electrode according to claim 7. (4) D × (A O × A S ) > 1000

9. The electrode includes a current collector, The current collector includes a metal foil, The coating density (mg / cm 2 2) of the electrode active material on the current collector is D, and the thickness of the metal foil is T (μm). When D, T, A O and A S and A satisfy the following formula, the electrode according to claim 7. (5) D × (A O × A S ) / T > 60

10. The electrode includes a current collector, The current collector includes a metal foil, When the coating density (mg / cm 2 ) of the electrode active material on the current collector is D, and D is more than 2.50 mg / cm 2 , the electrode according to claim 7.

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

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

13. Further comprising an electrolyte, and the volume of the electrolyte is V (mL), When the coating density (mg / cm 2 ) of the electrode active material on the current collector is defined as D, the lithium-ion secondary battery according to claim 12, wherein V, D, and A O and A S satisfy the following formula. (6) D × (A O × A S ) / V > 4000

14. A method for manufacturing an electrode active material, (1) A mixing step of mixing a raw material containing cellulose and sulfur having a mass equal to or greater than the mass of the cellulose to obtain a fired raw material, (2) A firing step of firing the fired raw material to obtain a fired product, and (3) A particle forming step of pulverizing the fired product to obtain particles of the fired product The manufacturing method of the electrode active material including.

15. The manufacturing method according to claim 14, wherein the cellulose is cellulose that has not been chemically modified.

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