Powder, conductive aid, dispersion, composition, conductive layer, electrode mixture layer, electrode, secondary battery, method for producing dispersion, method for producing composition, and method for producing electrode

Abstract

Provided are a powder that, when used in an electrode of a secondary battery, can further reduce the volume resistance of the electrode, as well as a conductive assistant, dispersion, composition, conductive layer, electrode mixture layer, electrode, and secondary battery that contain the powder. The powder contains fibrous carbon having a structure in which cylindrical carbon hexagonal mesh planes are stacked in the thickness direction, and has a bulk density of 0.0360 g / cm 3 ~0.0799g / cm 3 is.

Description

[Technical Field]

[0001] The present disclosure relates to a powder, a conductive additive, a dispersion, a composition, a conductive layer, an electrode mixture layer, an electrode, a secondary battery, a method for producing a dispersion, a method for producing a composition, and a method for producing an electrode. [Background technology]

[0002] Taking advantage of their small size, light weight, and high voltage characteristics, secondary batteries are widely used in electronic devices such as notebook PCs, mobile phones, smartphones, tablet PCs, etc. In recent years, against the backdrop of environmental concerns, secondary batteries such as lithium-based secondary batteries have become widespread in electric vehicles (EVs) that run solely on batteries, and hybrid electric vehicles (HEVs) that combine gasoline engines with batteries.

[0003] Carbon fibers such as vapor grown carbon fibers are used as a conductive additive for electrodes of secondary batteries. For example, in Patent Document 1, 3 and bundle-type carbon nanotubes having conductivity that satisfies the condition of formula 1: -X≦10logR≦-0.6X (where X is the bulk density of the carbon nanotubes and R is the powder resistance of the carbon nanotubes under a pressure of 10 to 65 MPa), and a lithium secondary battery produced using this conductive material dispersion has been disclosed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2018-534747 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is a demand for a powder containing fibrous carbon that, when used in an electrode of a secondary battery, further reduces the volume resistivity of the electrode. The present disclosure has been made in view of the above circumstances, and aims to provide a powder that, when used in an electrode of a secondary battery, can further reduce the volume resistance of the electrode, as well as a conductive assistant, dispersion, composition, conductive layer, electrode mixture layer, electrode, secondary battery, method for producing dispersion, method for producing composition, and method for producing electrode, each of which contains the powder. [Means for solving the problem]

[0006] Specific means for achieving the above object are as follows. <1> It contains fibrous carbon having a structure in which cylindrical carbon hexagonal mesh planes are stacked in the thickness direction, and has a bulk density of 0.0360 g / cm 3 ~0.0799g / cm 3 That is, powder. <2> 0.8g / cm 3 When compressed to 0.0120 Ω·cm to 0.0260 Ω·cm, <1> The powder according to claim 1. <3> BET specific surface area is 11.0m 2 / g~25.0m 2 / g, <1> or <2> The powder according to claim 1. <4> <1> ~ <3> A conductive additive comprising the powder according to any one of claims 1 to 4. <5> <1> ~ <3> 10. A dispersion comprising the powder according to any one of claims 1 to 9 and a solvent. <6> <1> ~ <3> A composition comprising the powder according to any one of claims 1 to 4 and a binder. <7> <1> ~ <3> A conductive layer comprising the powder according to any one of claims 1 to 4. <8> <1> ~ <3> 10. An electrode mixture layer comprising the powder according to any one of claims 1 to 9, a binder, and an electrode active material. <9> <1> ~ <3> An electrode comprising the powder according to any one of claims 1 to 4. <10> A battery comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode is <9> A secondary battery comprising the electrode according to claim 1. <11> <1> ~ <3> 10. A method for producing a dispersion, comprising mixing the powder according to any one of the above items with a solvent. <12> <1> ~ <3> 10. A method for producing a composition, comprising mixing the powder according to any one of the above items with a binder. <13> <1> ~ <3> 10. A method for producing an electrode, comprising the step of applying an electrode mixture layer-forming composition containing the powder according to any one of claims 1 to 9, a binder, and an electrode active material to a current collector to form an electrode mixture layer. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a powder that, when used in an electrode of a secondary battery, can further reduce the volume resistance of the electrode, as well as a conductive assistant, dispersion, composition, conductive layer, electrode mixture layer, electrode, secondary battery, method for producing dispersion, method for producing composition, and method for producing electrode, each containing the powder. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0009] In the present disclosure, the term "process" includes not only a process that is independent of other processes, but also a process that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together, or two or more layers may be detachable. In the present disclosure, the term "comprise" of a specific component (for example, a conductive assistant, a dispersion liquid, a conductive layer, an electrode mixture layer) means that other components besides the specific component may be included. In the present disclosure, the term "conductive assistant" refers to an agent that is added to an electrode mixture layer to reduce the resistance of the electrode.

[0010] <Powder> The powder of the present disclosure contains fibrous carbon having a structure in which cylindrical carbon hexagonal mesh planes are stacked in the thickness direction, and has a bulk density of 0.0360 g / cm 3 ~0.0799g / cm 3 The reason why the powder having the above structure can further reduce the volume resistance of the electrode when used in an electrode of a secondary battery is not clear, but is presumed to be as follows.

[0011] The fibrous carbon contained in the powder of the present disclosure has a structure in which cylindrical carbon hexagonal mesh planes are stacked in the thickness direction, and therefore has excellent electrical conductivity in the length direction of the fibrous carbon. However, when the bulk density of the powder is 0.0799 g / cm 3When the bulk density of the powder exceeds 0.0360 g / cm, the fibrous carbon tends to be short, and the advantage of electrical conductivity of the fibrous carbon tends to be difficult to obtain. 3 If the length is less than 1 / 2 mm, the fibrous carbon tends to be too long and easily entangled, which is presumably why the dispersibility of the electrode mixture layer decreases when it is formed, resulting in localized areas of low conductivity and making it difficult to reduce the volume resistance of the electrode. In this disclosure, the bulk density of the powder is used to comprehensively grasp the dispersibility of the fibrous carbon, the effect of the conductive path provided by the fibrous carbon, etc., and it has been found that by setting the bulk density of the powder within a specific range, it is possible to reduce the volume resistance of electrodes made using the powder.

[0012] In the present disclosure, a structure in which cylindrical carbon hexagonal mesh planes are stacked in the thickness direction refers to a structure in which multiple cylindrical structures in which carbon hexagonal mesh planes are rolled up are stacked along the thickness direction (also referred to as a specific structure). The specific structure can be confirmed, for example, by observing the powder with a transmission electron microscope (TEM) as follows: An image in which the longitudinal direction of the fibrous material can be confirmed (hereinafter also referred to as a "TEM longitudinal image") and an image in which a cross section of the fibrous material cut in a direction intersecting the longitudinal direction can be confirmed (hereinafter also referred to as a "TEM cross-sectional image") are observed. If the TEM longitudinal image shows multiple lines running along the longitudinal direction within the fibrous material, and the TEM cross-sectional image shows multiple closed curves with different maximum diameters, the closed curves being arranged in order from the largest diameter to the smallest, the fibrous carbon can be confirmed to have a specific structure. Furthermore, energy dispersive X-ray spectroscopy (EDS) of that portion can be used to confirm that the element constituting that portion is carbon. In one embodiment, in a specific structure, in the cross section of a certain cylindrical shape, there are some where the cross-sectional area decreases as one approaches the center, and there are some where the cross-sectional area of ​​each tube increases as one moves away from the center of the cross section of the tube. The structure in which cylindrical carbon hexagonal mesh planes are stacked in the thickness direction may be a structure in which multiple cylindrical carbon hexagonal mesh planes of different diameters are arranged so as to have concentric cross sections (e.g., like a concentric multi-tube), and the central axes (lines connecting the centers of each cross section of a certain tube) of multiple cylindrical carbon hexagonal mesh planes of different diameters do not all need to be aligned, or may be aligned only partially. The cross-sectional shape of the tube is not limited to a perfect circle but may be an ellipse, a polygon, etc., and a portion of the periphery may be a perfect circle, an ellipse, another curve, a polygon, or a combination thereof. The above-mentioned "closed curve" refers to such a shape.

[0013] The bulk density of the powder is 0.0360 g / cm 3 or more, 0.0385 g / cm 3 It is preferable that the concentration is 0.0400 g / cm or more. 3 More preferably, it is 0.0500 g / cm or more. 3 More preferably, it is 0.0600 g / cm or more. 3 More preferably, it is equal to or greater than this. The bulk density of the powder is 0.0799 g / cm 3 is less than or equal to 0.0750 g / cm 3 Preferably, it is 0.0700 g / cm or less. 3 More preferably, it is: The bulk density of the powder is measured by the method described in the examples.

[0014] The average interlayer distance (d 002 From the viewpoint of electrical conductivity and eliminating the activity of side reactions, the average interlayer distance (d002 ) is preferably 0.3375 nm or more, more preferably 0.3377 nm or more, and even more preferably 0.3379 nm or more, from the viewpoint of maintaining the flexibility of the fiber.

[0015] From the viewpoint of imparting electrical conductivity to an electrode with a small amount of addition, the volume fraction of particles of 4.6 μm or less in the volume-based cumulative particle size distribution of the powder is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less. The lower limit of the volume fraction of particles of 4.6 μm or less in the volume-based cumulative particle size distribution of the powder is not particularly limited, but may be 1% or more, 3% or more, or 5% or more. The volume-based cumulative particle size distribution of the powder is obtained by measurement using a laser diffraction particle size distribution analyzer.

[0016] From the viewpoint of producing a secondary battery having excellent cycle characteristics and rate characteristics, the average fiber diameter of the fibrous carbon is preferably 180 nm or less, more preferably 170 nm or less, and even more preferably 165 nm or less. From the viewpoint of dispersibility, the average fiber diameter of the fibrous carbon is preferably 100 nm or more, more preferably 120 nm or more, even more preferably 130 nm or more, and particularly preferably 150 nm or more.

[0017] The average fiber diameter of fibrous carbon can be calculated from the arithmetic mean of the diameters of 200 fibers randomly observed by SEM of the electrode. The diameter of a single fiber can be calculated by measuring the width of a single randomly selected point on the fiber in the SEM photograph, excluding both ends.

[0018] The average fiber length of the fibrous carbon is preferably 2.0 μm or more, and more preferably 2.5 μm or more, from the viewpoint of producing a secondary battery having excellent cycle characteristics and rate characteristics. From the viewpoint of dispersibility, the average fiber length of the fibrous carbon is preferably 4.5 μm or less, more preferably 4.0 μm or less, and even more preferably 3.8 μm or less.

[0019] The average fiber length of fibrous carbon can be measured as follows. The fibrous carbon is dispersed in a dispersion medium, spread on aluminum foil or the like, and then dried. The resulting dispersion is observed under SEM, and the lengths of 200 randomly selected fibers along the fiber axis are measured, and the arithmetic average is taken to determine the average fiber length. Alternatively, the electrode may be washed with a solvent, and the fibrous carbon from which the binder and other materials have been removed is taken out, and the average fiber length of the fibrous carbon may be determined.

[0020] The variation in the average fiber length of the fibrous carbon is preferably low from the viewpoint of producing a secondary battery having good dispersibility and excellent cycle and rate characteristics, and the standard deviation σ of the average fiber length is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 2 μm or less.

[0021] Powder at 0.8g / cm 3 The volume resistivity when compressed to 0.8 g / cm 3 The compressive resistivity (also called "density resistivity") is preferably 0.0120 Ω·cm to 0.0260 Ω·cm. 3 When the compacted resistivity is within the above range, the resistance of the powder itself is low, and it is possible to further reduce the volume resistance of the electrode. 0.8g / cm 3 From the viewpoint of further reducing the volume resistivity of the electrode, the compacted resistivity is preferably 0.0260 Ω·cm or less, more preferably 0.0220 Ω·cm or less, even more preferably 0.0180 Ω·cm or less, particularly preferably 0.0160 Ω·cm or less, extremely preferably 0.0157 Ω·cm or less, and may be 0.0153 Ω·cm or less. 0.8g / cm 3 The compaction resistivity is preferably 0.0120 Ω·cm or more, more preferably 0.013 Ω·cm or more, even more preferably 0.014 Ω·cm or more, and particularly preferably 0.0144 Ω·cm or more, from the viewpoint that it is desirable for the fibrous carbon to contain defects in order to more efficiently form a network structure.

[0022] In the measurement of compaction resistivity, 0.8 g / cm 3 The pressure at the time of compaction may be 0.5 MPa to 3.0 MPa, or 1.5 MPa to 2.3 MPa.

[0023] Powder at 0.6g / cm 3 The volume resistivity when compressed to 0.6 g / cm 3 The compressive resistivity (also called "density resistivity") is preferably 0.0120 Ω·cm to 0.0310 Ω·cm. 3 When the compacted resistivity is within the above range, the resistance of the powder itself is low, and it is possible to further reduce the volume resistance of the electrode. 0.6g / cm 3 From the viewpoint of further reducing the volume resistivity of the electrode, the compaction resistivity is preferably 0.0300 Ω·cm or less, more preferably 0.0290 Ω·cm or less, even more preferably 0.0280 Ω·cm or less, and particularly preferably 0.0270 Ω·cm or less. 0.6g / cm 3 The compaction resistivity is preferably 0.0150 Ω·cm or more, more preferably 0.0180 Ω·cm or more, even more preferably 0.0210 Ω·cm or more, and particularly preferably 0.0240 Ω·cm or more, from the viewpoint that it is desirable for the fibrous carbon to contain defects in order to more efficiently form a network structure.

[0024] In the measurement of compaction resistivity, 0.6 g / cm 3 The pressure at the time of compaction may be 0.2 MPa to 2.5 MPa, or may be 0.5 MPa to 1.5 MPa. The compaction resistivity is measured by the method described in the Examples.

[0025] From the viewpoint of battery characteristics, the BET specific surface area of ​​the powder is 11.0 m 2 / g~25.0m 2 / g is preferred. The BET specific surface area of ​​the powder is 11.0m 2 / g or more, and 12.0m 2 / g or more is more preferable, and 12.5m 2 It is more preferable that the saturation coefficient is 1 / g or more. The BET specific surface area of ​​the powder is 25.0m 2 / g or less, and 2 / g or less is more preferable, and 19.0m 2 / g or less is more preferable, and 18.0m 2 / g or less is particularly preferable, and 17.0m 2 It is highly preferred that the saturation coefficient is 0.1 / g or less. The BET specific surface area of ​​the powder is calculated by the BET multipoint method using nitrogen as the adsorption gas.

[0026] <Powder manufacturing method> The method for producing powder according to the present disclosure includes, for example, the following steps. (Step 1) A carbon source and at least one selected from the group consisting of a catalyst precursor and a catalyst are mixed to prepare a raw material mixture. (Step 2) The reactor is heated to a predetermined temperature. (Step 3) The raw material mixture is introduced into a reactor using a carrier gas to generate powder. (Step 4) Collect the powder.

[0027] (Process 1) In (Step 1), a raw material mixture is prepared by mixing at least one selected from the group consisting of a carbon source, a catalyst precursor, and a catalyst, and, if necessary, an additive. The raw material mixture may be liquid or gaseous at room temperature. When a gaseous raw material mixture is used, the raw material mixture may be preheated and vaporized, or each component may be gaseous at room temperature. The carbon source may be dissolved in the catalyst precursor or the additive, or may be dispersed in the catalyst precursor or the additive.

[0028] The carbon source is not particularly limited. When a raw material mixture that is liquid at room temperature is prepared, it is preferable to use a carbon source that is liquid at room temperature, and examples of such a carbon source include benzene, toluene, styrene, xylene, cyclohexane, methanol, and ethanol. When a raw material mixture that is gaseous at room temperature is prepared, it is preferable to use a carbon source that is gaseous at room temperature, and examples of such a carbon source include hydrocarbon gases such as methane, ethylene, and acetylene, and gases such as CO and CO2. The carbon source may be used alone or in combination of two or more kinds.

[0029] The content of the carbon source in the raw material mixture is preferably such that the content of carbon contained in the carbon source is 50% by mass to 99.9% by mass, more preferably 60% by mass to 99.8% by mass, even more preferably 70% by mass to 99.7% by mass, and particularly preferably 80% by mass to 99.6% by mass, relative to the total amount of the raw material mixture.

[0030] The catalyst precursor may be one that generates fine catalyst particles of iron, cobalt, nickel, or the like, measuring several to several tens of nanometers, in a reactor under a reducing atmosphere such as hydrogen. Examples of the catalyst precursor include organic transition metal compounds such as ferrocene, cobaltocene, and nickelocene; and oxides, chlorides, nitrates, or sulfates of transition metals. One type of catalyst precursor may be used alone, or two or more types may be used in combination. The catalyst itself may be used in place of or in combination with the catalyst precursor. The raw material mixture may contain at least one selected from the group consisting of catalyst precursors and catalysts.

[0031] The content of the catalyst precursor in the raw material mixture is preferably such that the content of the metal component contained in the catalyst precursor is 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 5% by mass, and even more preferably 0.1% by mass to 3% by mass, relative to the total amount of the raw material mixture.

[0032] The raw material mixture may further contain an additive, which preferably contains a sulfur-containing compound. Examples of sulfur-containing compounds include cyclic sulfur compounds such as thiophene, cyclopentanethiol, and dimethyl disulfide; and non-cyclic sulfur compounds such as thiols and sulfides. Examples of additives that are gaseous at room temperature include sulfur compounds such as H2S and CH3SH.

[0033] The content of sulfur atoms in the raw material mixture is preferably 0.01% by mass to 1% by mass, more preferably 0.015% by mass to 0.5% by mass, and even more preferably 0.0225% by mass to 0.125% by mass.

[0034] Usually, a carrier gas is used to introduce the raw material mixture into the reaction tube. The type of carrier gas is not limited, and examples thereof include hydrogen, inert gases such as argon, and mixed gases of hydrogen and inert gases.

[0035] (Process 2) In step 2, the reactor is heated to a predetermined temperature. In one embodiment, a vertical furnace is used. The shape of the reactor is not particularly limited as long as it can accommodate the reaction.

[0036] The temperature of the heating zone of the reactor may be, for example, 300°C to 1600°C, 600°C to 1400°C, or 800°C to 1300°C.

[0037] (Step 3) In step 3, the raw material mixture is introduced into a reactor using a carrier gas to produce powder. A method of spraying a liquid or slurry raw material mixture from a spray nozzle using a carrier gas may be employed, or a vaporized raw material mixture may be introduced into a reactor tube using a carrier gas.

[0038] It is believed that the carbon source, catalyst precursor, and additives introduced into the reaction tube are each decomposed. When the catalyst precursor decomposes, metal clusters are generated in the gas phase, which are thought to act as catalysts for the reaction to produce fibrous carbon, spherical particles, etc.

[0039] It is believed that the carbon source and additives interact with the metal clusters in either a decomposed, partially decomposed, or non-decomposed state, and a catalytic reaction generates fibrous carbon, spherical particles, etc., starting from the catalyst.

[0040] (Step 4) In step 4, the produced powder is collected. In a vertical reactor, the powder that falls to the bottom can be continuously carried out, or in a batch furnace, the furnace can be cooled and the reaction tube can be opened before collection. The powder can also be transported using an inert gas.

[0041] <Post-process> After step 4, the obtained powder may be heated in an inert atmosphere. This heating carbonizes the pyrolyzed product of the carbon source adhering to the surface of the powder, thereby increasing the electronic conductivity of the powder. This step is also called the "calcination step." Examples of inert atmospheres used in the calcination step include nitrogen and argon. The temperature used in the calcination step is preferably 800°C to 1600°C. The calcination time may be determined by analyzing the exhaust gas and setting the end point as the time when no more gas is generated.

[0042] Furthermore, after the calcination step, the powder may be further heated in an inert atmosphere to increase the degree of graphitization. This further increases the powder's electronic conductivity, ensures chemical stability, and evaporates and removes catalytic metals present in the product. This step is also referred to as the "graphitization step." The temperature in the graphitization step is preferably 2500°C to 3300°C. The time required for the graphitization step is not particularly limited and is usually several seconds to several hours.

[0043] After the graphitization step, the powder may be pulverized. The bulk density of the powder may be adjusted by the degree of pulverization. A weaker degree of pulverization tends to result in a lower bulk density. Examples of the grinding device include a microjet, a jet mill, and a laboratory grinder. The powder may be classified after or without being crushed. The bulk density of the powder can also be adjusted by classification.

[0044] <Conductive additive> The conductive aid of the present disclosure includes the powder of the present disclosure. The conductive additive may be used as a conductive additive in a secondary battery such as a lithium ion secondary battery. Carbon black such as acetylene black is generally used as a conductive additive for secondary batteries, but carbon black may be used in combination with the powder of the present disclosure, or the powder of the present disclosure may be used instead of carbon black.

[0045] Other conductive additives that can be used in combination with the powder of the present disclosure include carbon black, multi-walled carbon nanotubes (MWCNT), single-walled carbon nanotubes (SWCNT), graphene, graphite particles, amorphous carbon, and the like. The other conductive assistants may be used alone or in combination of two or more.

[0046] The content of the powder relative to the total of the powder and other conductive additives is preferably 1% by mass to 100% by mass, more preferably 10% by mass to 90% by mass, and even more preferably 20% by mass to 80% by mass.

[0047] <Dispersion> The dispersion of the present disclosure includes the powder of the present disclosure and a solvent. The dispersion of the present disclosure may contain other components in addition to the powder and the solvent, and examples of the other components include a dispersant and the other conductive assistants described above.

[0048] Examples of the solvent include water, organic solvents, etc. The organic solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), acetone, ethyl acetate, acetonitrile, tetrahydrofuran (THF), dimethylformamide (DMF), etc.

[0049] The dispersant is not particularly limited, and examples thereof include polyvinylpyrrolidone (PVP), Triton X-100, sodium cholate, and the like. The content of the dispersant is preferably 0.01% by mass to 10% by mass relative to the total amount of the dispersion.

[0050] The content of the powder of the present disclosure is preferably 0.1% by mass to 30% by mass, more preferably 0.5% by mass to 20% by mass, and even more preferably 1% by mass to 10% by mass, relative to the total amount of the dispersion.

[0051] When the powder of the present disclosure is used in combination with other conductive additives, the content of the powder relative to the total of the powder and other conductive additives in the dispersion of the present disclosure may be 1% by mass to 100% by mass, 10% by mass to 90% by mass, or 20% by mass to 80% by mass. The content is appropriately adjusted taking into consideration the stability of the dispersion, the resistance when formed into an electrode mixture layer, etc.

[0052] The dispersion of the present disclosure can be prepared by mixing the powder of the present disclosure with a solvent. The mixing method is not particularly limited, and known methods can be applied.

[0053] <Composition> The composition of the present disclosure includes the powder of the present disclosure described above and a binder. The composition of the present disclosure may contain other components in addition to the powder and binder, and examples of the other components include the aforementioned other conductive assistants, solvents, dispersants, and the like.

[0054] The binder is not particularly limited, and examples thereof include binders used in secondary batteries such as lithium ion secondary batteries, etc. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), butadiene styrene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyimide, polyamide-imide, polyacrylic acid, and styrene-acrylic acid ester copolymers.

[0055] The content of the binder is preferably 0.5% by mass to 5% by mass, more preferably 1% by mass to 3% by mass, and even more preferably 1.5% by mass to 2% by mass, relative to the total amount of the composition.

[0056] The content of the powder is preferably 0.05% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass, and even more preferably 0.2% by mass to 20% by mass, relative to the total amount of the composition. When the powder of the present disclosure is used in combination with other conductive additives, the content of the powder relative to the total of the powder and other conductive additives in the composition of the present disclosure is the same as the range described in the dispersion section.

[0057] When a dispersant is used, the content of the dispersant is preferably 0.01% by mass to 10% by mass relative to the total amount of the composition.

[0058] The composition of the present disclosure can be prepared by mixing the powder of the present disclosure, a binder, and, if necessary, other components such as a conductive additive. The mixing method is not particularly limited, and known methods can be used.

[0059] <Conductive layer> The conductive layer of the present disclosure comprises the powder of the present disclosure. The conductive layer of the present disclosure may contain components other than the powder of the present disclosure, such as binders, additives, other conductive aids, etc. The binders, additives, and other conductive aids are the same as those described above.

[0060] The conductive layer is provided on a metal foil, which serves as a current collector, in a secondary battery such as a lithium-ion secondary battery. The conductive layer may be provided on one side or both sides of the metal foil. By forming an electrode mixture layer on the conductive layer, it is possible to achieve lower resistance and improved adhesion compared to when the electrode mixture layer and the current collector are in direct contact with each other. In the present disclosure, the term "upper" is not limited to "upper" in the vertical direction, but may also refer to "lower" in the vertical direction, or left and right.

[0061] The powder content of the present disclosure is preferably 1% by mass to 60% by mass relative to the total mass of the conductive layer. When the powder content is 1% by mass or more, a sufficiently low resistance can be obtained. From the viewpoint of low resistance, the powder content is more preferably 10% by mass or more, and even more preferably 20% by mass or more. Furthermore, by keeping the powder content at 60% by mass or less, it is possible to prevent the powder from falling off from the conductive layer. From the viewpoint of preventing the powder from falling off, the powder content is more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0062] The binder content is preferably 5% by mass to 80% by mass relative to the total mass of the conductive layer. When the binder content is 5% by mass or more, it is easy to form into a layer and powder falling can be suppressed. From the viewpoints of formability and suppression of powder falling, the binder content is more preferably 10% by mass or more, and even more preferably 20% by mass or more. Furthermore, by keeping the binder content at 80% by mass or less, the resistance of the conductive layer can be suppressed. From the viewpoint of low resistance, the binder content is more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0063] <Electrode mixture layer> The electrode mixture layer of the present disclosure contains the powder of the present disclosure, a binder, and an electrode active material. Examples of the electrode mixture layer include a positive electrode mixture layer, a negative electrode mixture layer, etc. The configurations of the positive electrode mixture layer and the negative electrode mixture layer will be described later in the section on secondary batteries.

[0064] In the electrode mixture layer, the powder content is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.4% by mass or more. In the electrode mixture layer, the powder content is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less.

[0065] The binder in the electrode mixture layer is the same as the binder described above. The binder content is preferably 0.5% by mass to 10% by mass relative to the total mass of the electrode mixture layer. When the binder content is 0.5% by mass or more, forming into a layer is easy and powder falling can be suppressed. From the viewpoints of formability and suppression of powder falling, the binder content is more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more. Moreover, from the viewpoint of low resistance of the electrode mixture layer, the content of the binder is more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0066] Examples of electrode active materials include positive electrode active materials and negative electrode active materials, and the types of these will be explained in the section on secondary batteries below. The content of the electrode active material is preferably 70% by mass to 99% by mass relative to the total mass of the electrode mixture layer, and from the viewpoint of electrode capacity, is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The content of the electrode active material may be 99% by mass or less, 98% by mass or less, or 97% by mass or less.

[0067] <Electrode> The electrode of the present disclosure includes the powder of the present disclosure. The electrode of the present disclosure may be either a positive electrode or a negative electrode. When the electrode of the present disclosure is an electrode for a secondary battery, it may include an electrode current collector and an electrode mixture layer disposed on the electrode current collector, and a conductive layer may be provided between the electrode current collector and the electrode mixture layer. The powder of the present disclosure may be contained in the electrode mixture layer or in the conductive layer. When the powder of the present disclosure is contained in the conductive layer, the above-mentioned conductive layer may be applied. When the powder of the present disclosure is contained in the electrode mixture layer, the above-mentioned electrode mixture layer may be applied.

[0068] The method for producing the electrode of the present disclosure is not particularly limited, and one example is a method including a step of applying an electrode mixture layer-forming composition containing the powder of the present disclosure, a binder, and an electrode active material to a current collector to form an electrode mixture layer.

[0069] The electrode of the present disclosure preferably has a volume resistivity of 24.20 Ω·cm or less, more preferably 24.00 Ω·cm or less, even more preferably 23.80 Ω·cm or less, and particularly preferably 23.60 Ω·cm or less. The volume resistivity of the electrode is measured by the method described in the examples.

[0070] <Secondary battery> The secondary battery of the present disclosure includes a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode has the electrode of the present disclosure.

[0071] The secondary battery may have a structure in which a plurality of positive electrodes and negative electrodes housed in an outer casing are stacked in the thickness direction, or may be a laminated secondary battery or a wound secondary battery. The wound secondary battery may be, for example, a cylindrical secondary battery in which an electrode pair obtained by winding a laminate formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween and an electrolyte solution are enclosed in a cylindrical outer casing, or a cylindrical secondary battery in which a cell obtained by winding a laminate formed by stacking a positive electrode and a negative electrode with a solid electrolyte interposed therebetween is enclosed in a cylindrical outer casing.

[0072] The secondary battery may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween and an electrolytic solution are housed in an exterior packaging material, or may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a solid electrolyte interposed therebetween is housed in an exterior packaging material.

[0073] The type of secondary battery is not particularly limited, and examples include lithium-based secondary batteries, sodium-based secondary batteries, potassium-based secondary batteries, magnesium-based secondary batteries, aluminum-based secondary batteries, etc. Among these, lithium-based secondary batteries that can achieve high energy density at high voltage and sodium-based secondary batteries that can be reduced in cost are preferred. Examples of lithium-based secondary batteries include lithium ion secondary batteries, lithium secondary batteries in which the negative electrode is metallic lithium (including, for example, lithium-sulfur batteries and lithium-air batteries), and liquid electrolyte type batteries and solid electrolyte type batteries containing at least one of an electrolytic solution, a polymer electrolyte, a polymer gel electrolyte, a solid electrolyte, etc. Similarly to the aforementioned lithium-based secondary batteries, secondary batteries other than lithium-based secondary batteries are not limited in terms of the positive electrode active material, the negative electrode active material, the electrolyte, etc., and can take various forms. In the following, an example of a lithium-based secondary battery will be described, but the present invention is not limited to this.

[0074] [Positive electrode] The positive electrode generally includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The conductive layer may be disposed between the positive electrode current collector and the positive electrode mixture layer.

[0075] The material of the positive electrode current collector is not particularly limited as long as it is an electron-conductive material that does not oxidize and dissolve at high potential, and can be selected from aluminum, nickel, titanium, stainless steel, etc. The state of the positive electrode current collector is not particularly limited, and can be selected from foil, perforated foil, mesh, etc. As an example, an aluminum foil is used as the positive electrode current collector.

[0076] The positive electrode mixture layer may contain the powder of the present disclosure. For example, a composition according to the present disclosure containing a positive electrode active material (a composition for forming a positive electrode mixture layer) is applied onto a positive electrode current collector, the coating layer is dried, and then pressed to form a positive electrode mixture layer on the positive electrode current collector.

[0077] From the viewpoint of energy density and the like, the thickness of the positive electrode mixture layer may be 30 μm or more, may be 50 μm to 70 μm, or may be 70 μm to 100 μm.

[0078] The density of the positive electrode mixture layer is set to 2.0 g / cm from the viewpoint of energy density, etc. 3 It may be 3.0 g / cm or more.3 It may be 3.0 g / cm or more. 3 ~4.0g / cm 3 may be.

[0079] The weight of the positive electrode mixture layer is set to 10.0 mg / cm from the viewpoint of energy density, etc. 2 It may be 10.0 mg / cm or more. 2 ~30.0mg / cm 2 may be.

[0080] (Cathode active material) The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material can be appropriately selected depending on the type of secondary battery, and examples thereof include compounds containing at least one of lithium, sodium, potassium, magnesium, and aluminum. Examples of the positive electrode active material include oxides containing nickel, phosphates having an olivine structure, etc. When the secondary battery is a lithium-based secondary battery, the positive electrode active material is LiNi x Mn y Co z Al w O2 (x, y, z, w≧0, x+y+z+w=1), LiMPO4 (M is one or more selected from Fe, Co, Mn and Ni), LiMn a Ni b Examples include O4 (a, b≧0, a+b=2). The positive electrode active material may be used alone or in combination of two or more kinds.

[0081] The positive electrode active material is LiNi x Mn y Co z Al w It preferably contains O2 (x, y, z, w≧0, x+y+z+w=1) or LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni).

[0082] LiNi x Mn y Co z Al wO2 (x, y, z, w≧0, x+y+z+w=1) preferably has a relatively high proportion of nickel, for example, x≧0.5 or more, and Li(Ni x Mn y Co z )O2(x≧0.5, y≦0.3, z≦0.3, x+y+z=1) is more preferable. x Mn y Co z )O2(x≧0.5, y≦0.3, z≦0.3, x+y+z=1) 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.7 Mn 0.1 Co 0.2 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2 and Li(Ni 0.5 Mn 0.2 Co 0.3 )O2 is one example.

[0083] Examples of the positive electrode active material represented by LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni) include LiFePO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn 0.7 PO4, LiCoPO4 and LiCo 0.5 Mn 0.5 PO4 is an example.

[0084] In the positive electrode mixture layer, the content of the positive electrode active material is preferably 70% by mass or more, and from the viewpoint of positive electrode capacity, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. In the positive electrode mixture layer, the content of the positive electrode active material may be 99% by mass or less, 98% by mass or less, or 97% by mass or less.

[0085] In the positive electrode mixture layer, a positive electrode active material, a conductive additive such as the powder of the present disclosure, a binder, etc. may be simply mixed, or a conductive additive such as the powder of the present disclosure may be complexed on the surface of the positive electrode active material. Examples of the conductive additive include conductive additives other than the powder of the present disclosure (for example, other conductive additives described in the section on conductive additives).

[0086] When the positive electrode mixture layer contains the powder, the content of the powder in the positive electrode mixture layer is preferably 0.1 mass % or more, more preferably 0.3 mass % or more, and even more preferably 0.4 mass % or more.

[0087] In the positive electrode mixture layer, the content of the powder is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less.

[0088] The positive electrode mixture layer may contain fibrous carbon (other fibrous carbon) other than the powder of the present disclosure. Examples of other fibrous carbon include carbon fiber, vapor-grown carbon fiber, carbon nanotubes such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and carbon nanofibers.

[0089] [Negative electrode] The negative electrode generally includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. The aforementioned conductive layer may be provided between the negative electrode current collector and the negative electrode mixture layer.

[0090] The material of the negative electrode current collector is not particularly limited as long as it is a material with electron conductivity, and can be selected from copper, nickel, titanium, stainless steel, etc. The state of the negative electrode current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. As an example, a copper foil is used as the negative electrode current collector.

[0091] The negative electrode binder layer may contain the powder of the present disclosure. For example, a composition containing a negative electrode active material (composition for forming a negative electrode binder layer) of the present disclosure is applied onto the negative electrode current collector, the applied slurry is dried, and then pressed to form a negative electrode binder layer on the negative electrode current collector.

[0092] From the perspective of energy density and the like, the thickness of the negative electrode binder layer may be 30 μm or more, may be 50 μm to 100 μm, or may be 100 μm to 150 μm.

[0093] From the perspective of energy density and the like, the density of the negative electrode binder layer may be 1.2 g / cm 3 or more, and may be 1.3 g / cm 3 to 2.0 g / cm 3 or more.

[0094] From the perspective of energy density and the like, the basis weight of the negative electrode binder layer may be 5.0 mg / cm 2 or more, and may be 10 mg / cm 2 to 20 mg / cm 2 or more.

[0095] (Negative electrode active material) The negative electrode binder layer contains a negative electrode active material. Examples of the negative electrode active material include semimetals or metals that form alloys with lithium such as Si, Sn, and Al, SiO x (0 < x ≤ 2), soft carbon, hard carbon, graphite, composites of silicon and carbon, Li4Ti5O 12 , metallic Li, InO x (0 < x ≤ 1.5), AlO <00​​​​(0 < x ≤ 1), SbO x (0 < x ≤ 1.5), BiO x (0 < x ≤ 1.5), ZnO x Examples thereof include oxides such as (0 < x ≤ 1), etc. Among them, the negative electrode active material preferably contains graphite. Also, at least a part of the surface of the negative electrode active material may be coated with amorphous carbon. The negative electrode active material may be used alone or in combination of two or more.

[0096] In the negative electrode binder layer, the content of the negative electrode active material is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and even more preferably 95% by mass or more from the viewpoint of the negative electrode capacity. The content of the negative electrode active material may be 99% by mass or less, 98% by mass or less, or 97% by mass or less.

[0097] In the negative electrode binder layer, the negative electrode active material, a conductive aid such as the powder of the present disclosure, a binder, etc. may be simply mixed, or a conductive aid such as the powder of the present disclosure may be compounded on the surface of the negative electrode active material. Examples of the conductive aid include other conductive aids other than the powder of the present disclosure (for example, other conductive aids described in the item of conductive aids).

[0098] When the negative electrode binder layer contains the above powder, in the negative electrode binder layer, the content of the above powder is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0099] In the negative electrode binder layer, the content of the above powder is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less.

[0100] The average electrode area (average positive electrode area and average negative electrode area) per sheet may be 20 cm 2 ~10000 cm 2 and may also be 300 cm 2 ~10000 cm 2may be.

[0101] (exterior materials) The exterior material for housing the positive electrode and the negative electrode is not limited as long as it can house the positive electrode, the negative electrode, and, if necessary, a separator and an electrolytic solution or a solid electrolyte, etc. Examples of the exterior material include commonly available battery packs, 18650-type cylindrical cells, and those packed in aluminum packaging, and the exterior material can be freely designed and used.

[0102] (separator) The secondary battery may include a separator between the positive electrode and the negative electrode. The separator can be appropriately selected from those that can be used in general secondary batteries. Examples of the separator include microporous films made of polyethylene or polypropylene. Separators that contain particles of SiO2, Al2O3, or the like as a filler, or separators that have these particles attached to their surfaces, can also be used.

[0103] (electrolyte) The secondary battery may contain an electrolytic solution. There are no particular limitations on the electrolytic solution, and an electrolytic solution that can be used in a typical secondary battery can be appropriately selected. For example, an organic solvent in which 0.5 mol / L to 2.0 mol / L of lithium salt is dissolved can be used as the electrolytic solution.

[0104] Examples of lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, and LiN(SO2F)2 (LiFSI).

[0105] Examples of the organic solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), etc. The organic solvent may be selected from the above and other organic solvents and used in combination. Examples of additives for the electrolyte solution include vinylene carbonate (VC), propane sultone (PS), and fluoroethylene carbonate (FEC). When an additive is used, the content of the additive is preferably 0.01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass, and even more preferably 0.5% by mass to 5% by mass, relative to 100% by mass of the organic solvent.

[0106] (ionic liquid) An ionic liquid may be used as the electrolyte, or an ionic liquid may be used in combination with the organic solvent described above. The ionic liquid is not particularly limited, and examples thereof include a combination of a cation such as an imidazolium cation, a pyrrolidinium cation, a piperidinium cation, or an ammonium cation with an anion such as a bis(trifluoromethane)sulfonamide anion.

[0107] (solid electrolyte) A solid electrolyte may be used as the electrolyte. When a solid electrolyte is used, a separator is not required, and a battery (for example, an all-solid-state lithium ion secondary battery) can be formed in which the solid electrolyte is sandwiched between a positive electrode and a negative electrode.

[0108] Examples of the solid electrolyte include polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte is not particularly limited, and examples thereof include polymers such as polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyacrylonitrile (PAN), and polymer gels obtained by adding a plasticizer (e.g., an organic solvent) to the polymer and impregnating the lithium salt. The inorganic solid electrolyte is not particularly limited, and examples thereof include sulfide-based solid electrolytes such as Li2S-P2S5, Li2S-GeS2, and Li2S-SiS2-Li3PO4, La 0.51 Li 0.34 TiO 2.94 , Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 , 50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N0.46 (LIPON), Li 3.6 Si 0.6 P 0.4 O4, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 Examples include oxide-based solid electrolytes such as (PO4)3.

[0109] In the secondary battery of the present disclosure, the discharge capacity (capacity retention rate (%)) after 500 cycles is preferably 85.0% or more, more preferably 85.5% or more, and even more preferably 86.0% or more, with the initial discharge capacity measured at 25°C being 100%. The capacity retention rate is measured under the conditions described in the examples.

[0110] The secondary battery of the present disclosure preferably has a direct current resistance (DCR) at initial charge of 0.0870 Ω or less, more preferably 0.0860 Ω or less, even more preferably 0.0850 Ω or less, and particularly preferably 0.0840 Ω or less. The lower the direct current resistance (DCR) at initial charge, the better, and there is no particular lower limit, and it may be 0.0010 Ω or more, or 0.0001 Ω or more. The direct current resistance (DCR) during initial charging is measured under the conditions described in the Examples.

[0111] In the secondary battery of the present disclosure, the DCR during charging after 500 cycles is preferably 0.1330 Ω or less, more preferably 0.1300 Ω or less, even more preferably 0.1250 Ω or less, and particularly preferably 0.1240 Ω or less. The lower the DCR during charging after 500 cycles, the better, and there is no particular lower limit, and it may be 0.0100 Ω or more, or 0.0010 Ω or more. The DCR during charging after 500 cycles is measured under the conditions described in the Examples.

[0112] In the secondary battery of the present disclosure, the cell temperature when the cell is charged to 45°C and then discharged at 5C is preferably less than 49°C, and more preferably 48.5°C or less. The cell temperature is measured under the conditions described in the Examples.

[0113] The secondary battery of the present disclosure can be used as a power source for electronic devices such as smartphones, tablet PCs, and personal digital assistants; as a power source for electric motors for power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and for storing electricity obtained from fuel cells, solar power generation, wind power generation, and the like. [Example]

[0114] The present disclosure will be specifically described below using examples, but the scope of the present disclosure is not limited to these examples. The physical properties of the powders obtained in the examples and comparative examples were measured by the methods shown below.

[0115] <Bulk density> 1,000 g of powder was weighed out, placed in a measuring cylinder, and vibrated for 30 seconds using a test tube mixer (model number "Touch Mixer MT31" manufactured by Yamato Scientific Co., Ltd.). The intensity was set to ON1. The top surface of the powder was smoothed, and the scale on the measuring cylinder was read. The bulk density of the powder was calculated from the obtained volume and mass.

[0116] <Consolidation specific resistance> 1 g of the powder was placed in a dedicated jig. The dedicated jig had a space of 1 cm in length × 4 cm in width × 9 cm in height. The two surfaces with dimensions of 1 cm in length × 4 cm in width were made of metal and were electrically conductive. Also, two metal points (φ = 3 mm) for voltage measurement were provided on the bottom surface with dimensions of 1 cm in length × 4 cm in width, and they were electrically conductive. The distance between the metal points was 1 cm. The parts other than the metal were made of plastic and were insulating. The push rod attached to the dedicated jig had a part with dimensions of 0.999 cm in length × 3.999 cm in width × 9 cm in height, and the space of the dedicated jig could be compressed in the height direction. While flowing a current of 100 mA through the metal on the side surface, the height of the powder and the voltage between the voltage terminals were measured when a predetermined load was applied from above the push rod, and from this, the density and volume resistivity of the powder were recorded. The powder was compressed to 0.8 g / cm 3 and 0.6 g / cm 3 The volume resistivity when compressed was determined as the consolidation specific resistivity.

[0117] <BET specific surface area> Using NOVA2200e manufactured by Quantachrome as the BET specific surface area measurement device, 3 g of the powder was placed in a sample cell (9 mm × 135 mm), dried at 300 °C under vacuum conditions for 1 hour, and then the measurement was carried out. N2 was used as the gas for BET specific surface area measurement. The specific surface area was calculated by the BET three-point method from the nitrogen adsorption amounts when the relative pressure was 0.1, 0.2, and 0.3. At this time, the density of liquid nitrogen was 0.808 (g / cm 3 ), the volume of 1 mole of nitrogen under standard conditions was 22.4133 L, and the atomic weight of nitrogen was 14.0067 for calculation.

[0118] [Comparative Example 1] (Fabrication of the positive electrode) As the positive electrode active material, NMC811 (Li(Ni 0.8 Mn 0.1 Co 0.1An NMP solution (solids concentration 7.3% by mass) containing 96.5 parts by mass of PO2 (Xiamen Tungsten Co., Ltd.), 1.0 part by mass of carbon black (C-NERGY Super C65, Imerys Graphite & Carbon, primary particle diameter: 33 nm), 0.5 parts by mass of vapor-grown carbon fiber VGCF-H (Resonac Co., Ltd.), and 2.0 parts by mass of PVDF was prepared and mixed in a kneader. Subsequently, the mixture was mixed in the kneader while appropriately adding NMP to prepare a slurry with adjusted viscosity. It was confirmed by TEM observation that the vapor grown carbon fiber VGCF-H has a structure in which cylindrical carbon hexagonal mesh planes are stacked in the thickness direction. The average interlayer distance (d 002 ) was 0.339 nm, and the volume fraction of particles with a size of 4.6 μm or less in the volume-based cumulative particle size distribution was 12.98%.

[0119] The slurry was applied to an aluminum foil having a thickness of 20 μm using a roll coater and dried to obtain a positive electrode sheet, which was then vacuum dried and roll pressed to obtain a positive electrode mixture layer with a weight per unit area of ​​11.2 mg / cm. 2 , density 3.2g / cm 3 was adjusted to.

[0120] (Evaluation of Coatability) The coating properties of the slurry when applied with a roll coater were evaluated according to the following criteria. A: The slurry is smooth, firm, and dries quickly. B: There is a problem with either the smoothness, hardness, or drying speed of the slurry.

[0121] (Evaluation of coated surface) The coated surface was visually observed and evaluated according to the following criteria. A: No aggregation B: Aggregation

[0122] (volume resistivity of electrode) The resulting positive electrode sheet was vacuum dried at 100°C for 10 hours in a dry room (dew point -70°C) to prepare an electrode sample. The volume resistivity of the positive electrode sheet was measured using an electrode resistance measurement system RM2610 (manufactured by Hioki E.E. Corporation). Five measurement points were randomly selected, and the average of the measured values ​​was taken as the volume resistivity of the electrode.

[0123] (Preparation of negative electrode) Carboxymethyl cellulose (CMC1380, manufactured by Daicel) was used as the binder. Specifically, CMC powder was dissolved in water to prepare an aqueous solution with a solid content of 2% by mass. Carbon black (C-NERGY Super C45, manufactured by Imerys Graphite & Carbon) was used as the conductive additive. Artificial graphite 1 (D V50 :14.4μm, specific surface area: 1.7m 2 / g), and artificial graphite 2 (D V50 :5.7μm, specific surface area: 3.2m 2 A mixture with a mass ratio of 7:3 (wt / g) was used. As the aqueous binder, a dispersion of Polysol LB150 (manufactured by Resonac Co., Ltd.) fine particles was prepared. In addition, D V50 is the 50% particle size in the cumulative particle size distribution on a volume basis. Here, it was measured using a laser diffraction particle size distribution analyzer.

[0124] 96.5 parts by mass of negative electrode active material, 1.3 parts by mass of conductive additive, 1.5 parts by mass of CMC solid content, and 1.5 parts by mass of aqueous binder were weighed and mixed in a kneader to obtain a negative electrode slurry. The negative electrode slurry was applied to a copper foil having a thickness of 20 μm using a roll coater. After drying, the negative electrode was further dried in a vacuum to obtain a negative electrode sheet. The negative electrode sheet was roll-pressed at a pressure of 300 MPa to reduce the density of the negative electrode mixture layer to 1.4 g / cm. 3 was adjusted to.

[0125] (Preparation of evaluation cells) The following battery was fabricated in a dry room where the atmosphere was maintained at a dew point of −70° C. or less.

[0126] The obtained positive electrode sheet and negative electrode sheet were punched out into pieces with an area of ​​36 cm 2 Four positive electrodes and five negative electrodes were obtained. The obtained positive electrodes and negative electrodes were stacked alternately using an automatic laminating machine. A microporous polypropylene membrane was sandwiched between the positive and negative electrodes as a separator. An Al tab was attached to the Al foil of the positive electrode, and a Ni tab was attached to the Cu foil of the negative electrode. The entire assembly, excluding the tab, was wrapped in aluminum laminate packaging, and 2500 μL of electrolyte was poured into it. The opening was then sealed by heat sealing to prepare a laminated full cell for evaluation. The electrolyte used was a solvent mixture of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:5:2, mixed with vinylene carbonate (VC) at 1% by mass, and further dissolved in the electrolyte LiPF6 to a concentration of 1.2 mol / L.

[0127] (Evaluation of the evaluation cell) [Capacity maintenance rate] The initial discharge capacity measured at 25°C was defined as 100%, and the discharge capacity after 500 cycles was defined as the capacity retention rate (%). In measuring the capacity retention rate, the battery was charged at a constant current of 114 mA (0.2 C) until the battery reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current decreased to 0.05 C. The battery was discharged at a constant current of 114 mA (0.2 C) until the battery reached 2.8 V.

[0128] [DCR Rating] (DCR during initial discharge) The battery was charged at a constant current of 114 mA (0.2 C) until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.05 C. The battery was then discharged at a constant current of 57 mA (0.1 C) for 5 hours to reach 50% capacity. The voltage and current were plotted after 5 seconds when discharge currents of 114mA (0.2C), 285mA (0.5C), 570mA (1C), and 855mA (1.5C) were applied, and the DCR was calculated from the slope.

[0129] (DCR after 500 cycles of discharge) After 500 cycles, the DCR of the evaluation cell was determined in the same manner as the DCR during initial discharge described above.

[0130] [Cell temperature measurement] A sheet thermocouple was attached to the surface of the evaluation cell so that the temperature sensor was positioned in the center of the laminate, and the cell was fastened with a bakelite board to perform electrochemical measurements. The battery was charged at a constant current of 114 mA (0.2 C) until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.05 C. The fully charged cell was placed in a thermostatic chamber at 45°C, and once the temperature had stabilized, it was discharged to 2.5V at a constant current of 2850mA (5C), and the temperature during this discharge was recorded with a data logger.

[0131] [Example 1] A cell was fabricated in the same manner as in Comparative Example 1, except that the vapor grown carbon fiber used in the positive electrode was replaced with a carbon material obtained through the following process. The vapor grown carbon fiber used in the positive electrode of Example 1 had an average interlayer distance (d 002 ) was 0.338 nm, and the volume fraction of particles of 4.6 μm or less in the volume-based cumulative particle size distribution was 6.39%. In addition, it was confirmed by separate TEM observation that the tubular carbon hexagonal network planes had a structure in which they were stacked in the thickness direction.

[0132] Step 1 (synthesis of carbon material: produced carbon material) A reactor was prepared, consisting of a reaction tube with an inner diameter of 500 mm and a length of 2000 mm, and a heater. A two-fluid mixing nozzle was placed at the top of the reaction tube to supply the raw materials, and a conveyor was placed at the bottom of the reaction tube, which was connected to a tank equipped with a bag filter. The combustible gas that passed through the bag filter was burned in an incinerator. Ferrocene and sulfur were dissolved in benzene to prepare a raw material solution having a composition of 96.4 mass % of benzene, 3.5 mass % of ferrocene, and 0.1 mass % of sulfur. Using hydrogen as a carrier gas, the prepared raw material solution was supplied at 0.59 g / NL (benzene (g / min) / hydrogen (NL / min)), sprayed into a reaction tube using a two-fluid nozzle, and passed through a reactor heated to 1300°C to synthesize carbon fiber. NL is a value measured under standard conditions of a temperature of 0°C, atmospheric pressure of 1013 hPa, and relative humidity of 0%, and is a converted value under standard conditions. After feeding the raw materials for 7 hours, the feed of the raw material liquid and hydrogen was stopped, and nitrogen was fed to expel the flammable gas. The carbon material produced by this operation is sometimes called the "produced carbon material."

[0133] Step 2 (firing of carbon material: fired carbon material) The carbon material obtained in step 1 was placed in a calcination furnace (inner diameter 120 mm). It was heated to 1000°C in an argon atmosphere to remove tar adhering to the carbon material. After calcination, the carbon material obtained by this operation is sometimes called the "calcined carbon material."

[0134] Step 3 (Graphitization of fired carbon material: graphitized carbon material) The sintered carbon material obtained in step 2 was placed in a high-frequency heating furnace (inner diameter 120 mm). The sintered carbon material was graphitized by heating to 2800°C under an argon atmosphere. The carbon material obtained by this operation is sometimes called "graphitized carbon material." After graphitization, the powder was roughly crushed with a scoop and then pulverized for 3 minutes using a Waring food blender (manufactured by FMI Co., Ltd., model: CB-15T) at high intensity (approximately 18,500 rpm). The crushed powder was then passed through a turbo classifier (manufactured by Nisshin Engineering Co., Ltd., model: TC-15MS) at a rotation speed of 5,000 rpm and a classification air volume of 1.5 m. 3 The classification process was carried out at 1 / min, and the powder recovered on the fine powder side was used as the sample.

[0135] [Example 2] Vapor-grown carbon fiber was prepared in the same manner as in the manufacturing method of vapor-grown carbon fiber used in the positive electrode of Example 1, except that the rough crushing, pulverization, and classification steps after the graphitization treatment were not performed. A cell was produced in the same manner as in Comparative Example 1, except that this vapor-grown carbon fiber was used for the positive electrode. The vapor grown carbon fiber used in the positive electrode of Example 2 had an average interlayer distance (d 002 ) was 0.338 nm, and the volume fraction of particles of 4.6 μm or less in the volume-based cumulative particle size distribution was 3.67%. In addition, it was confirmed by separate TEM observation that the tubular carbon hexagonal network planes had a structure in which they were stacked in the thickness direction.

[0136] Comparative Example 2 Vapor-grown carbon fiber was synthesized by carrying out the reaction in the same manner as in Example 1, except that the raw material solution of Example 1 was supplied under the conditions of 0.71 g / NL (benzene (g / min) / hydrogen (NL / min)) and the raw material was supplied for 3 hours. A cell was produced in the same manner as in Comparative Example 1, except that this vapor-grown carbon fiber was used for the positive electrode. The vapor grown carbon fiber used in the positive electrode of Example 1 had an average interlayer distance (d 002 ) was 0.338 nm, and the volume fraction of particles with a particle size of 4.6 μm or less in the volume-based cumulative particle size distribution was 0.41%. Furthermore, it was confirmed by separate TEM observation that the tubular carbon hexagonal network planes were stacked in the thickness direction.

[0137] [Table 1]

[0138] As shown in Table 1, the bulk density of the fibrous carbon fiber was 0.0360 g / cm 3 ~0.0799g / cm 3 In Examples 1 and 2, the bulk density of the powder was 0.0360 g / cm 3 ~0.0799g / cm 3 The volume resistivity of the produced electrode was clearly lower than that of Comparative Examples 1 and 2, which used powders outside the range. Furthermore, compared with the cell of Comparative Example 1, the cells of Examples 1 and 2 had a lower DCR at the time of initial charge, and the DCR at the time of charge after 500 cycles was also kept low, resulting in a higher capacity retention rate.

Claims

1. It contains fibrous carbon having a structure in which cylindrical carbon hexagonal mesh planes are stacked in the thickness direction, and has a bulk density of 0.0400 g / cm ３ ~0.0750g / cm ３ and A powder having a BET specific surface area of ​​15.0 m 2 / g or less.

2. 0.8 g / cm ３ 2. The powder according to claim 1, wherein the powder has a volume resistivity of 0.0120 Ω cm to 0.0260 Ω cm when compressed to 0.0120 Ω cm.

3. The powder according to claim 1, wherein the average interlayer distance (d 002 ) of the graphite layers is 0.3385 nm or less.

4. The powder according to claim 2, wherein the average interlayer distance (d 002 ) of the graphite layers is 0.3385 nm or less.

5. A conductive additive comprising the powder according to any one of claims 1 to 4.

6. A dispersion comprising the powder according to any one of claims 1 to 4 and a solvent.

7. A composition comprising the powder according to any one of claims 1 to 4 and a binder.

8. A conductive layer comprising the powder according to any one of claims 1 to 4.

9. An electrode mixture layer comprising the powder according to any one of claims 1 to 4, a binder, and an electrode active material.

10. An electrode comprising the powder according to any one of claims 1 to 4.

11. A secondary battery comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode according to claim 10.

12. A method for producing a dispersion, comprising mixing the powder according to any one of claims 1 to 4 with a solvent.

13. A method for producing a composition, comprising mixing the powder according to any one of claims 1 to 4 with a binder.

14. A method for manufacturing an electrode, comprising a step of applying an electrode mixture layer-forming composition containing the powder according to any one of claims 1 to 4, a binder, and an electrode active material to a current collector to form an electrode mixture layer.

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