Powder, conductive additive, dispersion, composition, conductive layer, electrode mixture layer, electrode, secondary battery, method for manufacturing dispersion, method for manufacturing composition, and method for manufacturing electrode

Abstract

The present invention provides a powder capable of further reducing the volume resistivity of electrodes when used in the electrodes of a secondary battery, as well as a conductive additive, dispersion, composition, conductive layer, electrode mixture layer, electrode, and secondary battery containing the powder. [Solution] The powder is a fibrous carbon powder having a structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction. The powder is 0.6 g / cm³ 3 The volume resistivity when the powder is compressed to 0.8 g / cm³ 3 The ratio of volume resistivity when compressed is 0.545 or greater.

Description

[Technical Field]

[0001] This disclosure relates to powders, conductive additives, dispersions, compositions, conductive layers, electrode mixture layers, electrodes, secondary batteries, methods for producing dispersions, methods for producing compositions, and methods for producing electrodes. [Background technology]

[0002] Rechargeable batteries, with their small size, light weight, and high voltage characteristics, are widely used in electronic devices such as notebook PCs, mobile phones, smartphones, and tablet PCs. In recent years, due to environmental concerns, rechargeable batteries such as lithium-ion batteries have become popular in electric vehicles (EVs) that run solely on batteries, and hybrid electric vehicles (HEVs) that combine gasoline engines and batteries.

[0003] Carbon fibers, such as vapor-processed carbon fibers, are used as conductive additives in the electrodes of secondary batteries. For example, Patent Document 1 specifies a density of 10-50 kg / m³. 3 A conductive material dispersion is proposed containing bundle-type carbon nanotubes having a bulk density and conductivity that satisfies the condition of Equation 1: -X ≤ 10logR ≤ -0.6X (where X is the bulk density of the carbon nanotube and R is the powder resistance of the carbon nanotube under a pressure of 10 to 65 MPa). A lithium secondary battery manufactured using this conductive material dispersion is disclosed. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2018-534747 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, there is a need for a powder containing fibrous carbon that further reduces the volume resistivity of the electrodes when used in secondary battery electrodes. This disclosure has been made in view of the above circumstances, and aims to provide a powder that can further reduce the volume resistivity of an electrode when used in the electrodes of a secondary battery, as well as a conductive additive containing the powder, a dispersion, a composition, a conductive layer, an electrode mixture layer, an electrode, a secondary battery, a method for manufacturing the dispersion, a method for manufacturing the composition, and a method for manufacturing the electrode. [Means for solving the problem]

[0006] The specific means for achieving the aforementioned objectives are as follows: <1> This powder contains fibrous carbon having a structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction. The aforementioned powder is 0.6 g / cm³ 3 The volume resistivity when the powder is compressed to 0.8 g / cm³ 3 A powder in which the ratio of volume resistivity when compressed is 0.545 or greater. <2> BET specific surface area is 14.5m² 2 It is less than or equal to / g. <1> The powder described above. <3> Bulk density is 0.065 g / cm³ 3 The following is: <1> or <2> The powder described above. <4> The proportion of particles 4.6 μm or smaller in the cumulative particle size distribution based on volume of the powder is 6.00 volume% or less. <1> ~ <3> The powder described in any one of the items. <5> <1> ~ <4> A conductive additive comprising the powder described in any one of the items. <6> <1> ~ <4> A dispersion comprising the powder described in any one of the items and a solvent. <7> <1> ~ <4> A composition comprising the powder described in any one of the items and a binder. <8> <1> ~ <4> A conductive layer comprising the powder described in any one of the items. <9> <1> ~ <4> An electrode mixture layer comprising the powder described in any one of the items, a binder, and an electrode active material. <10> <1> ~ <3> An electrode containing the powder described in any one of the items. <11> It comprises a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode is <10> A secondary battery, which has electrodes as described above. <12> <1> ~ <4> A method for producing a dispersion, comprising mixing a powder described in any one of the items and a solvent. <13> <1> ~ <4> A method for producing a composition, comprising mixing a powder described in any one of the items and a binder. <14> <1> ~ <4> A method for manufacturing an electrode, comprising the step of applying an electrode mixture layer-forming composition containing the powder, binder, and electrode active material described in any one of the items to a current collector to form an electrode mixture layer. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a powder that can further reduce the volume resistivity of an electrode when used in the electrodes of a secondary battery, as well as a conductive additive containing the powder, a dispersion, a composition, a conductive layer, an electrode mixture layer, an electrode, a secondary battery, a method for manufacturing the dispersion, a method for manufacturing the composition, and a method for manufacturing the electrode. [Modes for carrying out the invention]

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

[0009] In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes, provided that the purpose of such process is achieved. In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content rate or content of each component means the total content rate or content of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may contain a plurality of types. When there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component means a value for a mixture of the plurality of types of particles present in the composition, unless otherwise specified. In the present disclosure, the term "layer" or "film" includes not only the case where it is formed over the entire region where the layer or film is present, but also the case where it is formed only in a part of the region when observing the region where the layer or film is present. In the present disclosure, the term "lamination" indicates stacking layers, and two or more layers may be bonded, or two or more layers may be detachable. In the present disclosure, the term "comprising" in a specific component (for example, conductive auxiliary agent, dispersion liquid, conductive layer, electrode binder layer) means that it may contain other components other than the specific component. In the present disclosure, the "conductive auxiliary agent" is added to the electrode binder layer and lowers the resistance of the electrode.

[0010] <Powder> The powder of the present disclosure is a powder containing fibrous carbon having a structure in which cylindrical carbon hexagonal mesh surfaces are laminated in the thickness direction, and the ratio of the volume specific resistance when the powder is compressed to 0.8 g / cm 3 to the volume specific resistance when the powder is compressed to 0.6 g / cm 3 is 0.545 or more. Hereinafter, the volume specific resistance when the powder is compressed to 0.6 g / cm 3 is also referred to as the "0.6 g / cm 3 compacted specific resistance". Further, the volume specific resistance when the powder is compressed to 0.8 g / cm 3 is also referred to as the "0.8 g / cm 3 compacted specific resistance". The ratio of the 0.8 g / cm 3 compacted specific resistance to the 0.6 g / cm 3 compacted specific resistance is also referred to as the "compacted resistance ratio". The reason why the powder having the above configuration can further reduce the volume resistivity of the electrodes when used as electrodes in a secondary battery is not clear, but it can be inferred as follows.

[0011] The fact that the consolidation resistance ratio is within the above range means that the change in volume resistivity is small with such pressure changes. This is 0.6 g / cm³. 3 This suggests that, at the point of compression, a certain degree of electrical contact between carbon fibers is already secured. In other words, the aggregation of carbon fibers is suppressed, and they are reasonably dispersed. In this state, the uneven distribution of areas that do not conduct electricity is suppressed, and as a result, it is possible to further reduce the volume resistance of the electrodes.

[0012] In this disclosure, the structure in which tubular carbon hexagonal mesh surfaces are stacked in the thickness direction refers to a structure in which multiple tubular structures formed by rolling up carbon hexagonal mesh surfaces are stacked along the thickness direction (also referred to as a specific structure). A specific structure can be confirmed, for example, by observing the powder with a transmission electron microscope (TEM) as follows: Observe an image that shows the longitudinal direction of the fibrous material (hereinafter also referred to as a "TEM longitudinal image") and an image that shows the cross-section when the fibrous material is cut in a direction intersecting the longitudinal direction (hereinafter also referred to as a "TEM cross-sectional image"). If, in the TEM longitudinal image, multiple lines exist inside the fibrous material along the longitudinal direction, and in the TEM cross-sectional image, multiple closed curves with different maximum diameters exist, and the closed curves are arranged sequentially towards the inside as the maximum diameter decreases, then it can be confirmed that the material is fibrous carbon having a specific structure. Furthermore, by using energy-dispersive X-ray spectroscopy (EDS) at that site, it can be confirmed that the element constituting that site is carbon. In one embodiment, in a particular structure, in a cylindrical cross-section, there are sections with smaller cross-sectional areas as you approach the center, and sections with larger cross-sectional areas as you move away from the center of the cross-section. A structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction may be a structure in which multiple cylindrical carbon hexagonal mesh surfaces of different diameters are arranged to have concentric cross-sections (for example, like a concentric multi-tube), and the central axes (lines connecting the centers of each cross-section of a given tube) of multiple cylindrical carbon hexagonal mesh surfaces of different diameters do not all have to be aligned, but some may have aligned central axes. The shape of the tube cross-section is not limited to a perfect circle, but may be an ellipse, a polygon, etc., and part of the outer circumference 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] 0.6 g / cm³ 3 0.8 g / cm³ relative to the compression resistivity 3 The ratio of the compression resistivity is 0.545 or higher, preferably 0.560 or higher, and more preferably 0.570 or higher. 0.6 g / cm³ 3 0.8 g / cm³ relative to the compression resistivity 3 The ratio of the consolidation resistivity is preferably 1.0 or less, more preferably 0.8 or less, and even more preferably 0.6 or less, from the viewpoint of ensuring electrical contacts when compressing powder at low pressure.

[0014] 0.8 g / cm³ 3 The compression resistivity is preferably 0.0120 Ω·cm to 0.0260 Ω·cm. (0.8 g / cm³) 3 When the compaction resistivity is within the above range, the resistance of the powder itself is low, making it possible to further reduce the volume resistivity of the electrode. 0.8 g / cm³ 3From the viewpoint of further reducing the volume resistance of the electrodes, the compaction 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, and most preferably 0.0155 Ω·cm or less. 0.8 g / cm³ 3 The compaction resistivity is preferably 0.0120 Ω·cm or higher, more preferably 0.013 Ω·cm or higher, even more preferably 0.014 Ω·cm or higher, and particularly preferably 0.0144 Ω·cm or higher, from the viewpoint that it is preferable for the fibrous carbon to contain defects in order to more efficiently form a network structure between them.

[0015] In measuring the compaction resistivity, 0.8 g / cm³ 3 The pressure used for consolidation may be 0.5 MPa to 3.0 MPa, or 1.5 MPa to 2.3 MPa.

[0016] 0.6 g / cm³ 3 The compression resistivity is preferably 0.0120 Ω·cm to 0.0310 Ω·cm. (0.6 g / cm³) 3 When the compaction resistivity is within the above range, the resistance of the powder itself is low, making it possible to further reduce the volume resistivity of the electrode. 0.6 g / cm³ 3 From the viewpoint of further reducing the volume resistance of the electrodes, 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. 0.6 g / cm³ 3 The compaction resistivity is preferably 0.0150 Ω·cm or higher, more preferably 0.0180 Ω·cm or higher, even more preferably 0.0210 Ω·cm or higher, and particularly preferably 0.0240 Ω·cm or higher, from the viewpoint that it is preferable for the fibrous carbon to contain defects in order to more efficiently form a network structure between them.

[0017] In measuring the compaction resistivity, 0.6 g / cm³ 3 The pressure used for consolidation may be 0.2 MPa to 2.5 MPa, or 0.5 MPa to 1.5 MPa. The compaction resistivity is measured by the method described in the examples.

[0018] The BET specific surface area of ​​the powder is 14.5 m², from the viewpoint of reducing the decomposition reaction of the electrolyte. 2 It is preferable that the amount be less than or equal to 14.0m 2 It is more preferable that the value be less than or equal to / g. The BET specific surface area of ​​the powder is set to 11.0 m² from the viewpoint of obtaining fibrous carbon of sufficient fineness. 2 It is preferable that the amount be 12.0m or more. 2 It is more preferable that it be 13.5m or more per gram. 2 It is even more preferable that the amount be 1 / g or more. The BET specific surface area of ​​the powder is calculated using the BET multipoint method with nitrogen as the adsorbent gas.

[0019] The bulk density of the powder is 0.065 g / cm³ from the standpoint of dispersibility. 3 Preferably, it is 0.060 g / cm³. 3 It is more preferable that the following is the case: 0.055 g / cm³ 3 It is even more preferable that the following is the case: 0.050 g / cm³ 3 The following is particularly preferable: The bulk density of the powder is measured by the method described in the examples. Furthermore, the bulk density of the powder is set to 0.036 g / cm³ to reduce aggregation caused by the fineness of the fibrous carbon. 3 Preferably, it is 0.039 g / cm³ or more. 3 It is more preferable that the concentration be greater than or equal to 0.040 g / cm³. 3 It is even more preferable that the above conditions are met. The bulk density of the powder is measured by the method described in the examples.

[0020] Average interlayer distance (d) of the graphite layer in the powder 002The average interlayer distance (d) of the graphite layer of the powder is preferably 0.3389 nm or less, more preferably 0.3385 nm or less, and even more preferably 0.3383 nm or less, from the viewpoint of eliminating conductivity and the activity of side reactions. 002 From the viewpoint of maintaining the flexibility of the fibers, the wavelength is preferably 0.3375 nm or greater, more preferably 0.3377 nm or greater, and even more preferably 0.3379 nm or greater.

[0021] From the viewpoint of imparting conductivity to the electrodes with a low amount of additive, the proportion of particles 4.6 μm or smaller in the cumulative particle size distribution based on the volume of the powder is preferably 6.00 volume% or less, more preferably 5.00 volume% or less, and even more preferably 4.00 volume% or less. Furthermore, from the viewpoint of reducing aggregates, the proportion of particles 4.6 μm or smaller in the cumulative particle size distribution based on the volume of the powder is preferably 1.00 volume% or more, more preferably 2.00 volume% or more, and even more preferably 3.00 volume% or more. The volume-based cumulative particle size distribution of the powder is obtained by measuring it with a laser diffraction particle size analyzer.

[0022] From the viewpoint of producing a secondary battery with 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. Furthermore, 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, particularly preferably 150 nm or more, and extremely preferably 160 nm or more.

[0023] The average fiber diameter of fibrous carbon can be determined 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 determined by measuring the width of a randomly selected point on the fiber, excluding both ends, as seen in the SEM image.

[0024] The variation in the average fiber diameter of the fibrous carbon is preferably low from the viewpoint of producing a secondary battery with good dispersibility and excellent cycle characteristics and rate characteristics. The standard deviation σ of the fiber diameter is preferably 55 nm or less, more preferably 53 nm or less, and even more preferably 50 nm or less.

[0025] The standard deviation σ of the fiber diameter of fibrous carbon is determined from the diameters of 200 samples measured by the method described above, based on the following formula. In the following formula, X i is the diameter of each fiber of the measured fibrous carbon, X is the average fiber diameter, and n represents the number of measured fibers (=200).

[0026]

number

[0027] From the viewpoint of producing a secondary battery with excellent cycle characteristics and rate characteristics, the average fiber length of the fibrous carbon is preferably 2.0 μm or more, more preferably 2.5 μm or more, even more preferably 3.0 μm or more, and particularly preferably 3.5 μm or more. Furthermore, 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.

[0028] The average fiber length of fibrous carbon can be measured as follows: Fibrous carbon is dispersed in a dispersion medium, spread on aluminum foil or the like, dried, and observed with a scanning electron microscope (SEM). The length of 200 randomly selected fibers along their fiber axes is measured, and the average fiber length is calculated by taking the arithmetic mean. Alternatively, the electrode may be washed with a solvent to remove binders and other contaminants, and the fibrous carbon can be extracted and its average fiber length determined.

[0029] The variation in the average fiber length of the fibrous carbon is preferably low from the viewpoint of producing a secondary battery with good dispersibility and excellent cycle and rate characteristics. 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.

[0030] The standard deviation σ of the fiber length of fibrous carbon is determined from the lengths of 200 fibers measured by the method described above, based on the following formula. In the following formula, X i is the length of each fiber of the measured fibrous carbon, X is the average fiber length, and n represents the number of measured fibers (=200).

[0031]

number

[0032] <Method for manufacturing powders> The method for producing the powder described herein is not particularly limited as long as it yields a powder that satisfies the above requirements. The method for producing the powder described herein includes, for example, the following steps: (Step 1) A raw material mixture is prepared by mixing a carbon source with at least one selected from the group consisting of a catalyst precursor and a catalyst. (Step 2) Heat the reactor to the specified temperature. (Step 3) The raw material mixture is introduced into the reactor using a carrier gas to generate a powder. (Step 4) Collect the powder.

[0033] (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 additives as needed. The raw material mixture may be a liquid or a gas at room temperature. If a gaseous raw material mixture is used, the mixture may be preheated to vaporize it, or components that are gaseous at room temperature may be used. The carbon source may be dissolved in the catalyst precursor or additive, or dispersed in the catalyst precursor or additive.

[0034] The carbon source is not particularly limited. When the raw material mixture is liquid at room temperature, it is preferable to use a carbon source that is liquid at room temperature, such as benzene, toluene, styrene, xylene, cyclohexane, methanol, and ethanol. When the raw material mixture is gaseous at room temperature, it is preferable to use a carbon source that is gaseous at room temperature, such as hydrocarbon gases like methane, ethylene, and acetylene, and gases like CO and CO2. The carbon source may be used alone, or two or more may be used in combination.

[0035] The carbon source content in the raw material mixture is preferably 50% to 99.9% by mass of the carbon source relative to the total amount of the raw material mixture, more preferably 60% to 99.8% by mass, even more preferably 70% to 99.7% by mass, and particularly preferably 80% to 99.6% by mass.

[0036] The catalyst precursor may be one which generates fine catalyst particles of iron, cobalt, nickel, etc., measuring several nanometers to more than ten nanometers in size in a reactor under a reducing atmosphere such as hydrogen. Examples of catalyst precursors include organotransition metal compounds such as ferrocene, cobaltocene, and nickerosene; oxides, chlorides, nitrates, or sulfates of transition metals; and so on. The catalyst precursor may be used alone or in combination of two or more types. The catalyst itself may be used instead of the catalyst precursor, or in combination with the catalyst precursor. The raw material mixture may contain at least one selected from the group consisting of a catalyst precursor and the catalyst.

[0037] 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% to 10% by mass relative to the total amount of the raw material mixture, more preferably 0.01% to 5% by mass, and even more preferably 0.1% to 3% by mass.

[0038] The raw material mixture may further contain additives. Preferably, the additives contain sulfur-containing compounds. Examples of sulfur-containing compounds include cyclic sulfur compounds such as thiophene, cyclopentanethiol, and dimethyl disulfide; and acyclic sulfur compounds such as thiols and sulfides. Examples of gaseous additives at room temperature include sulfur compounds such as H2S and CH3SH.

[0039] The sulfur atom content in the raw material mixture is preferably 0.01% to 1% by mass, more preferably 0.015% to 0.5% by mass, and even more preferably 0.0225% to 0.125% by mass.

[0040] Typically, a carrier gas is used to introduce the raw material mixture into the reaction tube. The type of carrier gas is not limited and includes hydrogen, inert gases such as argon, and a mixture of hydrogen and an inert gas.

[0041] (Process 2) In step 2, the reactor is heated to a predetermined temperature. In one embodiment, a vertical furnace is used. Otherwise, the shape of the reactor is not particularly limited as long as it is capable of carrying out the reaction.

[0042] 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.

[0043] (Step 3) In step 3, a carrier gas is used to introduce the raw material mixture into the reaction furnace to generate a powder. The raw material mixture may be sprayed from a spray nozzle using the carrier gas, or the vaporized raw material mixture may be introduced into the reaction tube using the carrier gas.

[0044] It is believed that the carbon source, catalyst precursor, and additives introduced into the reaction tube are all decomposed. In particular, when the catalyst precursor decomposes, metal clusters are formed in the gas phase, which are thought to act as catalysts for the formation of fibrous carbon, spherical particles, and other materials.

[0045] It is believed that the carbon source and additives interact with the metal clusters in either a decomposed, partially decomposed, or undecomposed state, and that fibrous carbon, spherical particles, etc., are generated starting from the catalyst through a catalytic reaction.

[0046] (Step 4) In step 4, the generated powder is recovered. In a vertical reactor, the powder that falls to the bottom may be continuously discharged, or in a batch furnace, the furnace may be cooled and the reaction tubes opened before recovery. The powder may also be transported using an inert gas.

[0047] <Post-process> After step 4, the obtained powder may be heated in an inert atmosphere. This heating carbonizes the thermal decomposition products 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 in the calcination step include nitrogen and argon. The temperature in the calcination step is preferably 800°C to 1600°C. The calcination time may be determined by analyzing the exhaust gas and ending when no more gas is generated.

[0048] Furthermore, the degree of graphitization of the powder may be increased by further heating in an inert atmosphere after the calcination process. This further enhances the electronic conductivity of the powder, ensures chemical stability, and allows for the evaporation and removal of catalyst metals present in the product. This process is also called the "graphitization process." The temperature in the graphitization process is preferably 2500°C to 3300°C. The time in the graphitization process is not particularly limited, and is usually from a few seconds to a few hours.

[0049] After the graphitization process, the powder may be pulverized. The bulk density of the powder may be adjusted by the degree of pulverization. Lowering the degree of pulverization tends to result in a lower bulk density. Examples of grinding equipment include microjet mills, jet mills, and laboratory grinders. Furthermore, the powder may be classified either after or without grinding. The bulk density of the powder can also be adjusted through classification.

[0050] The method for obtaining a powder with a consolidation resistance ratio within the above range is not particularly limited, but for example, it may be obtained by omitting the grinding and classification after the graphitization process. Alternatively, it may be obtained by adjusting the conditions of grinding and classification. Furthermore, by adjusting the grinding and classification conditions, the BET specific surface area, bulk density, and the proportion of particles smaller than 4.6 μm in the volume-based cumulative particle size distribution can be adjusted.

[0051] <Conductive additive> The conductive additives of this disclosure include the powders of this disclosure. The conductive additive may also be used as a conductive additive in secondary batteries such as lithium-ion secondary batteries. Generally, carbon black such as acetylene black is used as a conductive additive for secondary batteries, but carbon black may be used in combination with the powder of this disclosure, or the powder of this disclosure may be used instead of carbon black.

[0052] Other conductive additives used in combination with the powders of this disclosure include carbon black, multiwalled carbon nanotubes (MWCNTs), single-walled carbon nanotubes (SWCNTs), graphene, graphite particles, amorphous carbon, and the like. Other conductive additives may be used individually or in combination of two or more.

[0053] The powder content relative to the total of the powder and other conductive additives is preferably 1% to 100% by mass, more preferably 10% to 90% by mass, and even more preferably 20% to 80% by mass.

[0054] <Dispersion> The dispersion of the present disclosure comprises the powder of the present disclosure and a solvent. The dispersion of this disclosure may contain other components besides the powder and solvent, such as a dispersant and the other conductive additives mentioned above.

[0055] Examples of solvents include water and organic solvents. Organic solvents are not particularly limited and include N-methyl-2-pyrrolidone (NMP), acetone, ethyl acetate, acetonitrile, tetrahydrofuran (THF), and dimethylformamide (DMF).

[0056] The dispersant is not particularly limited and includes polyvinylpyrrolidone (PVP), Triton X-100, sodium cholate, and the like. The dispersant content is preferably 0.01% to 10% by mass relative to the total volume of the dispersion.

[0057] The powder content of the present disclosure is preferably 0.1% to 30% by mass, more preferably 0.5% to 20% by mass, and even more preferably 1% to 10% by mass, based on the total amount of the dispersion.

[0058] When the powder of this disclosure is used in combination with other conductive additives, the content of the powder in the dispersion of this disclosure relative to the total of the powder and other conductive additives may be 1% to 100% by mass, 10% to 90% by mass, or 20% to 80% by mass. The above content may be adjusted as appropriate, taking into consideration the stability of the dispersion, the resistance when used as an electrode mixture layer, etc.

[0059] The dispersions of this disclosure can be prepared by mixing the powders of this disclosure with a solvent. The mixing method is not particularly limited, and known methods can be applied.

[0060] <Composition> The compositions of this disclosure include the aforementioned powders of this disclosure and a binder. The compositions of this disclosure may contain other components besides the powder and binder, such as the aforementioned other conductive additives, solvents, and dispersants.

[0061] The binder is not particularly limited and can be any binder used in secondary batteries such as lithium-ion batteries. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), butadiene styrene rubber (SBR), sodium carboxymethylcellulose (CMC), polyimide, polyamide-imide, polyacrylic acid, and styrene-acrylic acid ester copolymers.

[0062] The binder content is preferably 0.5% to 5% by mass, more preferably 1% to 3% by mass, and even more preferably 1.5% to 2% by mass, based on the total amount of the composition.

[0063] The powder content is preferably 0.05% to 50% by mass, more preferably 0.1% to 30% by mass, and even more preferably 0.2% to 20% by mass, based on the total amount of the composition. When the powder of this disclosure is used in combination with other conductive additives, the powder content relative to the total amount of the powder and other conductive additives in the composition of this disclosure is the same as the range described in the section on dispersions.

[0064] When a dispersant is used, the dispersant content is preferably 0.01% to 10% by mass relative to the total amount of the composition.

[0065] The compositions of this disclosure can be prepared by mixing the powders of this disclosure with a binder and, if necessary, other components such as conductive additives. The mixing method is not particularly limited, and known methods can be applied.

[0066] <Conductive layer> The conductive layer of this disclosure comprises the powder of this disclosure. The conductive layer of this disclosure may contain components other than the powder of this disclosure, such as binders, additives, and other conductive aids. The binders, additives, and other conductive aids are the same as those described above.

[0067] The conductive layer is provided on a metal foil, which is a current collector, in a secondary battery such as a lithium-ion secondary battery. The conductive layer may be provided on one side of the metal foil or on both sides. 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. In this disclosure, the term "up" is not limited to "up" in the vertical direction, but may also refer to "down" in the vertical direction, or to the left or right.

[0068] The powder content of the present disclosure is preferably 1% to 60% by mass relative to the total mass of the conductive layer. A powder content of 1% by mass or more provides sufficiently low resistance. 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, the shedding of powder from the conductive layer can be suppressed. From the viewpoint of suppressing powder shedding, the powder content is more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0069] The binder content is preferably 5% to 80% by mass relative to the total mass of the conductive layer. A binder content of 5% by mass or more facilitates layered molding and suppresses powder shedding. From the viewpoint of moldability and suppression of powder shedding, a binder content of 10% by mass or more is more preferable, and 20% by mass or more is even more preferable. Furthermore, by having a binder content of 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.

[0070] <Electrode mixture layer> The electrode mixture layer of the present disclosure comprises the powder of the present disclosure, a binder, and an electrode active material. Examples of electrode mixture layers include a positive electrode mixture layer and a negative electrode mixture layer. The forms of the positive electrode mixture layer and the negative electrode mixture layer will be explained later in the section on secondary batteries.

[0071] 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.

[0072] The binder in the electrode mixture layer is the same as the binder described above. The binder content is preferably 0.5% to 10% by mass relative to the total mass of the electrode mixture layer. A binder content of 0.5% by mass or more facilitates layered molding and suppresses powder shedding. From the viewpoint of moldability and suppression of powder shedding, a binder content of 1.0% by mass or more is more preferable, and 1.5% by mass or more is even more preferable. Furthermore, from the viewpoint of low resistance in the electrode mixture layer, the binder content is more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0073] Electrode active materials include positive electrode active materials and negative electrode active materials, and these types will be explained later in the section on secondary batteries. The content of the electrode active material is preferably 70% to 99% by mass relative to the total mass of the electrode mixture layer, and from the viewpoint of electrode capacity, it is preferably 80% or more by mass, more preferably 90% or more by mass, and even more preferably 95% or more by mass. 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.

[0074] <Electrode> The electrode of this disclosure comprises the powder of this disclosure. The electrode of this disclosure may be either a positive electrode or a negative electrode. When the electrode of this disclosure is an electrode for a secondary battery, it comprises 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 this disclosure may be contained in the electrode mixture layer or in the conductive layer. If the conductive layer contains the powder of this disclosure, the conductive layer described above may be applied. If the electrode mixture layer contains the powder of this disclosure, the electrode mixture layer described above may be applied.

[0075] The method for manufacturing the electrodes of this disclosure is not particularly limited, and one example is a method that includes the step of applying an electrode mixture layer-forming composition containing the powder, binder, and electrode active material of this disclosure to a current collector to form an electrode mixture layer.

[0076] The electrodes of this disclosure preferably have 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.

[0077] <Secondary battery> The secondary battery of this disclosure comprises a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode has the electrode of this disclosure.

[0078] The secondary battery may take the form of a structure in which multiple positive and negative electrodes are stacked in the thickness direction within an outer casing, a laminated secondary battery, or a wound secondary battery. As an example of a wound secondary battery, it may be a cylindrical secondary battery in which an electrode pair and electrolyte obtained by winding a laminate in which positive and negative electrodes are stacked with a separator in between are sealed inside a cylindrical outer casing, or a cylindrical secondary battery in which a cell obtained by winding a laminate in which positive and negative electrodes are stacked with a solid electrolyte in between is sealed inside a cylindrical outer casing.

[0079] A secondary battery may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a separator in between, and an electrolyte are housed in an outer casing, or it may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a solid electrolyte in between is housed in an outer casing.

[0080] The types of secondary batteries are not particularly limited, and include lithium-based secondary batteries, sodium-based secondary batteries, potassium-based secondary batteries, magnesium-based secondary batteries, and aluminum-based secondary batteries. Among these, lithium-based secondary batteries, which can achieve high voltage and high energy density, and sodium-based secondary batteries, which can be cost-effective, are preferred. Examples of lithium-based secondary batteries include lithium-ion secondary batteries and lithium-based secondary batteries in which the negative electrode is metallic lithium (including, for example, lithium-sulfur batteries and lithium-air batteries). These include liquid electrolyte batteries and solid electrolyte batteries that contain at least one of the following: electrolyte, polymer electrolyte, polymer gel electrolyte, or solid electrolyte. Furthermore, for secondary batteries other than lithium-based secondary batteries, the positive electrode active material, negative electrode active material, electrolyte, etc., are not limited and can take various forms, similar to the lithium-based secondary batteries mentioned above. The following describes an example of a lithium-ion secondary battery, but the present invention is not limited to this example.

[0081] [Positive electrode] The positive electrode generally comprises a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The aforementioned conductive layer may be provided between the positive electrode current collector and the positive electrode mixture layer.

[0082] The material of the positive electrode current collector is not particularly limited as long as it does not oxidize and dissolve at high potential and is electrically conductive; it 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, aluminum foil is used as the positive electrode current collector.

[0083] The positive electrode mixture layer may contain the powder of this disclosure. For example, a positive electrode current collector is coated with a composition containing a positive electrode active material (a composition for forming a positive electrode mixture layer) according to the present disclosure, the coating layer is dried, and then pressed to form a positive electrode mixture layer on the positive electrode current collector.

[0084] The thickness of the positive electrode mixture layer may be 30 μm or more, 50 μm to 70 μm, or 70 μm to 100 μm, from the viewpoint of energy density, etc.

[0085] The density of the positive electrode mixture layer is 2.0 g / cm³, from the perspective of energy density and other factors. 3 It may be greater than or equal to 3.0 g / cm³. 3 It may be greater than or equal to 3.0 g / cm³. 3 ~4.0g / cm 3 That's fine.

[0086] The basis weight of the positive electrode mixture layer is 10.0 mg / cm³, from the perspective of energy density and other factors. 2 It may be greater than or equal to 10.0 mg / cm³. 2 ~30.0 mg / cm³ 2 That's fine.

[0087] (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 include compounds containing at least one of lithium, sodium, potassium, magnesium, and aluminum. Examples of positive electrode active materials include nickel-containing oxides and phosphates having an olivine-type structure. 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), etc. The positive electrode active material may be used alone or in combination of two or more types.

[0088] The positive electrode active material preferably contains LiNi x Mn y Co z Al w O2 (x, y, z, w ≥ 0, x + y + z + w = 1), or preferably contains LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni).

[0089] LiNi x Mn y Co z Al w As O2 (x, y, z, w ≥ 0, x + y + z + w = 1), it is preferably one with a relatively high nickel ratio, for example, x ≥ 0.5 or more. Li(Ni x Mn y Co z )O2 (x ≥ 0.5, y ≤ 0.3, z ≤ 0.3, x + y + z = 1) is more preferable. As the positive electrode active material represented by Li(Ni x Mn y Co z )O2 (x ≥ 0.5, y ≤ 0.3, z ≤ 0.3, x + y + z = 1), for example, Li(Ni 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 can be mentioned.

[0090] As the positive electrode active material represented by LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni), for example, LiFePO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn0.7 PO4, LiCoPO4 and LiCo 0.5 Mn 0.5 PO4 is one example.

[0091] In the positive electrode mixture layer, the content of the positive electrode active material is preferably 70% to 99% by mass, and from the viewpoint of positive electrode capacity, it is preferably 80% or more by mass, more preferably 90% or more by mass, and even more preferably 95% or more by mass. In the positive electrode mixture layer, the content of the positive electrode active material may be 99% or less by mass, 98% or less by mass, or 97% or less by mass.

[0092] In the positive electrode mixture layer, the positive electrode active material, a conductive additive such as the powder of this disclosure, a binder, etc., may simply be mixed together, or the conductive additive such as the powder of this disclosure may be compounded onto the surface of the positive electrode active material. Examples of conductive additives other than the powder of this disclosure (for example, other conductive additives described in the section on conductive additives) may be used.

[0093] When the positive electrode mixture layer contains the above powder, the content of the above powder in the positive electrode mixture layer 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.

[0094] In the positive electrode mixture 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.

[0095] The cathode mixture layer may contain fibrous carbon other than the powders of this disclosure (other fibrous carbon). Examples of other fibrous carbon include carbon fibers, vapor-phase carbon fibers, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and other carbon nanofibers.

[0096] [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. A conductive layer as described above may be provided between the negative electrode current collector and the negative electrode mixture layer.

[0097] 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.

[0098] The negative electrode mixture layer may contain the powder of the present disclosure. For example, a composition containing a negative electrode active material (a composition for forming a negative electrode mixture layer) in the composition 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 mixture layer on the negative electrode current collector.

[0099] From the perspective of energy density and the like, the thickness of the negative electrode mixture layer may be 30 μm or more, may be 50 μm to 100 μm, or may be 100 μm to 150 μm.

[0100] From the perspective of energy density and the like, the density of the negative electrode mixture 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 may be.

[0101] From the perspective of energy density and the like, the basis weight of the negative electrode mixture layer may be 5.0 mg / cm 2 or more, and may be 10 mg / cm 2 to 20 mg / cm 2 or may be.

[0102] (Negative electrode active material) The negative electrode mixture layer contains a negative electrode active material. As the negative electrode active material, a semi-metal or metal that forms an alloy with lithium such as Si, Sn, Al, SiO x (0 < x ≤ 2), soft carbon, hard carbon, graphite, a composite of silicon and carbon, Li4Ti5O12 , metallic Li, InO x (0 < x ≤ 1.5), AlO x (0 < x ≤ 1.5), AgO x (0 < x ≤ 0.5), CdO x (0 < x ≤ 1), SbO x (0 < x ≤ 1.5), BiO x (0 < x ≤ 1.5), ZnO x Oxides such as (0 < x ≤ 1) etc. can be mentioned. Among them, it is preferable that the negative electrode active material 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.

[0103] In the negative electrode binder layer, the content of the negative electrode active material is preferably 70% to 99% by mass, and from the viewpoint of the negative electrode capacity, it 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 negative electrode active material may be 99% by mass or less, may be 98% by mass or less, or may be 97% by mass or less.

[0104] 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).

[0105] 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.

[0106] 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.

[0107] The average electrode area per sheet (average positive electrode area and average negative electrode area) is 20 cm². 2 ~10,000cm 2 It may also be 300cm 2 ~10,000cm 2 That's fine.

[0108] (Exterior materials) The outer casing material for housing the positive and negative electrodes is not limited as long as it can accommodate the positive and negative electrodes, and optionally a separator and electrolyte, or a solid electrolyte. Examples of outer casing materials include commercially available battery packs, 18650 type cylindrical cells, and those packaged in aluminum foil, and the outer casing material can be freely designed and used.

[0109] (Separator) A secondary battery may be equipped with a separator between the positive and negative electrodes. The separator can be appropriately selected from those commonly used in secondary batteries. Examples of separators include microporous films made of polyethylene or polypropylene. Separators can also be made by mixing particles such as SiO2 or Al2O3 as fillers, or by attaching these particles to the surface.

[0110] (electrolyte) Secondary batteries may contain an electrolyte. There are no particular restrictions on the electrolyte, and an electrolyte that can be used in a typical secondary battery can be appropriately selected. For example, an organic solvent in which a lithium salt at a concentration of 0.5 mol / L to 2.0 mol / L can be dissolved can be used as the electrolyte.

[0111] Examples of lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, and LiN(SO2F)2(LiFSI).

[0112] Examples of organic solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and propylene carbonate (PC). Organic solvents listed here and others may be used in combination as appropriate. Examples of electrolyte additives include vinylene carbonate (VC), propane sultone (PS), and fluoroethylene carbonate (FEC). When additives are used, the additive content is preferably 0.01% to 20% by mass, more preferably 0.1% to 10% by mass, and even more preferably 0.5% to 5% by mass, based on 100% by mass of the organic solvent.

[0113] (Ionic liquid) Ionic liquids may be used as electrolytes, or ionic liquids may be used in combination with the aforementioned organic solvents. The ionic liquid is not particularly limited, and examples include combinations of cations such as imidazolium cations, pyrrolidinium cations, piperinidium cations, and ammonium cations with anions such as bis(trifluoromethane)sulfonamide anions.

[0114] (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 positive electrode and negative electrode are sandwiched between solid electrolytes.

[0115] Examples of solid electrolytes include polymer electrolytes and inorganic solid electrolytes. Polymer electrolytes are not particularly limited and include, for example, polymers such as polyethylene oxide (PEO), polymethyl methacrylic acid (PMMA), and polyacrylonitrile (PAN), as well as polymer gels impregnated with the lithium salt obtained by adding a plasticizer (e.g., organic solvent) to the polymer. Inorganic solid electrolytes are not particularly limited and include sulfide-based solid electrolytes such as Li2S-P2S5, Li2S-GeS2, and Li2S-SiS2-Li3PO4, and La 0.51 Li 0.34TiO 2.94 Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 , 50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N 0.46 (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.

[0116] The secondary battery of this disclosure preferably has a discharge capacity (capacity retention rate (%)) after 500 cycles, with the initial discharge capacity measured at 25°C being 100%, which is 85.0% or higher, more preferably 85.5% or higher, and even more preferably 86.0% or higher. The volume retention rate is measured under the conditions described in the examples.

[0117] The secondary battery of this disclosure preferably has a DC resistance (DCR) of 0.0870Ω or less during initial charging, more preferably 0.0860Ω or less, even more preferably 0.0850Ω or less, and particularly preferably 0.0840Ω or less. The lower the DC resistance (DCR) during initial charging, the better, and there is no particular limit to the lower limit, which may be 0.0010Ω or more, or 0.0001Ω or more. The DC resistance (DCR) during initial charging is measured under the conditions described in the examples.

[0118] The secondary battery of this disclosure preferably has a DCR of 0.1330Ω or less after 500 cycles of charging, more preferably 0.1300Ω or less, even more preferably 0.1250Ω or less, and particularly preferably 0.1240Ω or less. The lower the DCR after 500 cycles of charging, the better, and there is no particular limit to the lower limit, which may be 0.0100Ω or more, or 0.0010Ω or more. The DCR during charging after 500 cycles is measured under the conditions described in the examples.

[0119] In the secondary battery of this disclosure, the cell temperature when the charged cell is discharged at 5C after being brought to 45°C is preferably less than 49°C, and preferably 48.5°C or lower. The cell temperature is measured under the conditions described in the examples.

[0120] The secondary battery of this 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 such as power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and for storing electricity obtained from fuel cells, solar power generation, wind power generation, etc. [Examples]

[0121] The present disclosure will be described in detail below with reference to 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 following method.

[0122] <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, on the bottom surface with dimensions of 1 cm in length × 4 cm in width, two metal points (φ = 3 mm) for voltage measurement were provided and 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 resistivity.

[0123] <BET specific surface area> NOVA2200e manufactured by Quantachrome was used as the BET specific surface area measuring device. 3 g of the powder was put into 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.

[0124] <Bulk density> 1.000 g of the powder was weighed and put into a graduated cylinder, and it was vibrated for 30 seconds with a test tube mixer (model number 'Touch Mixer MT31' (manufactured by Yamato Scientific Co., Ltd.)). Intensity ON1 was selected. The top surface of the powder was leveled, and the scale of the graduated cylinder was read. The bulk density of the powder was calculated from the obtained volume and mass.

[0125] <Average fiber length and average fiber diameter> The powder was dispersed in ethanol and spread onto aluminum foil. After drying, the carbon fibers were photographed panoramically at 4000x magnification using a scanning electron microscope to prepare a field of view that allowed measurement of both ends of the fibrous carbon. The lengths of 200 randomly selected fibrous carbons were measured, and the average length was taken as the average fiber length. The powder was dispersed in ethanol, spread on aluminum foil, and after drying, the diameters of 200 randomly selected fibrous carbons were measured using a scanning electron microscope at 20,000x magnification. The average of these measurements was then defined as the average fiber diameter. The standard deviations for fiber length and fiber diameter were calculated.

[0126] [Comparative Example 1] (Fabrication of the positive electrode) NMC811(Li(Ni)) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 An NMP solution (solid content concentration 7.3% by mass) was prepared containing 96.5 parts by mass of O2 (manufactured by Amoy Tungsten Co., Ltd.), 1.0 part by mass of carbon black (C-NERGY Super C65, manufactured by Imerys Graphite & Carbon, primary particle size: 33 nm), 0.5 parts by mass of vapor-phase carbon fiber VGCF-H (manufactured by Resonaq Co., Ltd.), and 2.0 parts by mass of PVDF, and mixed in a kneader. Subsequently, a slurry was prepared by mixing in the kneader while adding NMP as needed to adjust the viscosity. The vapor-phase carbon fiber VGCF-H was separately confirmed by TEM observation to have a structure in which tubular carbon hexagonal mesh surfaces are stacked in the thickness direction. The average interlayer distance (d) of the graphite layer of the vapor-phase carbon fiber VGCF-H. 002 The particle size was 0.339 nm, and the volume fraction of particles smaller than 4.6 μm in the volume-based cumulative particle size distribution was 12.98%.

[0127] The slurry was coated onto a 20 μm thick aluminum foil using a roll coater and dried to obtain a positive electrode sheet. After vacuum drying, the basis weight of the positive electrode mixture layer was reduced to 11.2 mg / cm² by roll pressing. 2 , density 3.2 g / cm³ 3 I adjusted it to that.

[0128] (Evaluation of coating properties) The coating properties of the slurry when applied with a roll coater were evaluated according to the following criteria. A: The slurry has good smoothness, consistency, and drying speed. B: The slurry has a defect in either its smoothness, consistency, or drying speed.

[0129] (Evaluation of coated surface) The coated surface was visually inspected and evaluated according to the following criteria. A: No aggregation B: Aggregation present

[0130] (Volume resistivity of electrodes) The obtained positive electrode sheets were vacuum-dried in a dry room (dew point -70°C) at 100°C for 10 hours to prepare electrode samples. The volume resistivity of the positive electrode sheets was measured using the RM2610 electrode resistance measurement system (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.

[0131] (Fabrication of the negative electrode) Carboxymethylcellulose (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) was used as the negative electrode active material. 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 (per g) was used. As an aqueous binder, a dispersion of polysol LB150 (manufactured by Resonaq Corporation) fine particles was prepared. Note D V50 This represents the 50% particle size in the volume-based cumulative particle size distribution. Here, it was measured using a laser diffraction particle size analyzer.

[0132] 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 solids, and 1.5 parts by mass of aqueous binder were weighed out and mixed in a kneader to obtain a slurry for the negative electrode. The aforementioned negative electrode slurry was coated onto a 20 μm thick copper foil using a roll coater. After drying, it was further vacuum-dried to obtain a negative electrode sheet. The negative electrode sheet was roll-pressed at a pressure of 300 MPa to obtain a density of 1.4 g / cm³ of the negative electrode mixture layer. 3 I adjusted it to that.

[0133] (Creation of evaluation cells) The following batteries were fabricated in a dry room maintained at a dew point of -70°C or lower.

[0134] The obtained positive electrode sheet and negative electrode sheet were punched out to form an area of ​​36 cm². 2 Four positive electrodes and five negative electrodes were obtained. The obtained positive and negative electrodes were stacked alternately using an automatic laminating machine. A microporous film made of polypropylene was sandwiched between the positive and negative electrodes as a separator. An aluminum tab was attached to the positive electrode's aluminum foil, and a nickel tab was attached to the negative electrode's copper foil. The entire assembly, excluding the tabs, was wrapped in aluminum laminate packaging, and 2500 μL of electrolyte was injected inside. The opening was then sealed by heat fusion to create 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, to which vinylene carbonate (VC) was added at a concentration of 1% by mass. In addition, electrolyte LiPF6 was dissolved in this solution to a concentration of 1.2 mol / L.

[0135] (Evaluation of evaluation cells) [Measurement of cell temperature] A sheet thermocouple was attached to the center of the laminated surface of the evaluation cell so that the temperature sensor was positioned there, and then secured with a bakelite plate for electrochemical measurements. Constant current charging was performed at 114mA (0.2C) until the voltage reached 4.2V, followed by constant voltage charging at a constant voltage of 4.2V until the current was 0.05C. A fully charged cell was placed in a 45°C constant temperature bath until the temperature stabilized. Then, it was discharged to 2.5V with a constant current of 2850mA (5C), and the temperature during this discharge was recorded using a data logger.

[0136] [Comparative Example 2] A cell was prepared in the same manner as in Comparative Example 1, except that the gas-phase carbon fiber used in the positive electrode was replaced with carbon fiber obtained through the following process. The gas-phase carbon fiber used in the positive electrode of Comparative Example 2 had an average interlayer distance (d) of the graphite layer. 002 The particle size was 0.338 nm, and the volume fraction of particles smaller than 4.6 μm in the volume-based cumulative particle size distribution was 6.39%. Furthermore, it was confirmed by separate TEM observation that this vapor-phase carbon fiber has a structure in which tubular carbon hexagonal mesh surfaces are stacked in the thickness direction.

[0137] 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 for supplying raw materials was placed at the top of the reaction tube, and a conveyor belt was placed at the bottom of the reaction tube and connected to a tank equipped with a bag filter. The flammable gas that passed through the bag filter was burned in an incinerator. A starting liquid was prepared by dissolving ferrocene and sulfur in benzene. The composition of the starting liquid was 96.4% by mass of benzene, 3.5% by mass of ferrocene, and 0.1% by mass of sulfur. Using hydrogen as the carrier gas, the prepared raw material solution was supplied at a rate of 0.59 g / NL (benzene (g / min) / hydrogen (NL / min)). The raw material solution was sprayed into the reaction tube using a two-fluid nozzle and passed through a reaction furnace heated to 1300°C to synthesize carbon fibers. NL is a value measured under standard conditions of 0°C, 1013 hPa atmospheric pressure, and 0% relative humidity, and is a converted value under standard conditions. After supplying raw materials for 7 hours, the supply of raw material liquid and hydrogen was stopped, and nitrogen was supplied to expel the flammable gases. The carbon material produced by this operation is sometimes called "generated carbon material."

[0138] Step 2 (Castration of carbon material: Calcined carbon material) The carbon material produced in step 1 was placed in a firing furnace (120 mm inner diameter). It was heated to 1000°C under an argon atmosphere to remove the tar adhering to the carbon material. After firing, the carbon material obtained in this operation is sometimes called "fired carbon material".

[0139] Step 3 (Graphitization of calcined carbon material: Graphitized carbon material) The calcined carbon material obtained in step 2 was placed in a high-frequency heating furnace (120 mm inner diameter). Under an argon atmosphere, it was heated to 2800°C to graphitize the calcined carbon material. The carbon material obtained by this operation is sometimes called "graphitized carbon material". After graphitization treatment, the material was roughly crushed with a shovel, and then pulverized for 3 minutes using a Waring Food Blender (manufactured by FMI Co., Ltd., model: CB-15T) at High mode (approximately 18,500 rpm). The resulting powder was then processed using a Turbo Classifier (manufactured by Nisshin Engineering Co., Ltd., model: TC-15MS) at a rotation speed of 5,000 rpm and a classification airflow of 1.5 m³. 3 Classification was performed at a rate of / min, and the powder recovered on the fine powder side was used as the sample.

[0140] [Example 1] In Comparative Example 2, carbon fibers were prepared using the same gas-phase method as the positive electrode, except that the rough crushing, pulverization, and classification steps after graphitization were omitted. A cell was then fabricated in the same manner as in Comparative Example 1, except that these gas-phase carbon fibers were used as the positive electrode. The gas-phase carbon fiber used in the positive electrode of Example 1 had an average interlayer distance (d) of the graphite layer. 002 The particle size was 0.338 nm, and the volume fraction of particles smaller than 4.6 μm in the volume-based cumulative particle size distribution was 3.67%. Furthermore, it was confirmed by separate TEM observation that this gas-phase carbon fiber has a structure in which tubular carbon hexagonal mesh surfaces are stacked in the thickness direction.

[0141] Table 1 shows the average fiber diameter, standard deviation of fiber diameter, average fiber length, and standard deviation of fiber length of the carbon fibers used. Table 2 shows the evaluation results for Example 1, Comparative Examples 1 and 2.

[0142] [Table 1]

[0143] [Table 2]

[0144] As shown in Table 2, the powder contains fibrous carbon having a structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction, and the concentration is 0.6 g / cm³. 3 0.8 g / cm³ relative to the compression resistivity 3 Example 1, which used powder with a compaction resistivity ratio of 0.545 or higher, showed a lower volume resistivity of the prepared electrode compared to Comparative Examples 1 and 2, which used powder with a compaction resistivity ratio of less than 0.545. Furthermore, the cell temperature in Example 1 was kept lower compared to Comparative Examples 1 and 2.

Claims

1. This powder contains fibrous carbon having a structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction. The aforementioned powder is 0.6 g / cm³ ３ The volume resistivity when the powder is compressed to 0.8 g / cm³ ３ A powder in which the ratio of volume resistivity when compressed is 0.545 or greater.

2. The BET specific surface area is 14.5 m². ２ The powder according to claim 1, wherein the amount is less than or equal to / g.

3. Bulk density is 0.065 g / cm³ ３ The powder according to claim 1 or claim 2, which is as follows:

4. The powder according to claim 1 or claim 2, wherein the proportion of particles 4.6 μm or smaller in the cumulative particle size distribution based on the volume of the powder is 6.00 volume% or less.

5. A conductive additive comprising the powder described in claim 1 or claim 2.

6. A dispersion comprising the powder described in claim 1 or claim 2 and a solvent.

7. A composition comprising the powder described in claim 1 or claim 2, and a binder.

8. A conductive layer comprising the powder described in claim 1 or claim 2.

9. An electrode mixture layer comprising the powder according to claim 1 or claim 2, a binder, and an electrode active material.

10. An electrode comprising the powder described in claim 1 or claim 2.

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 described in claim 10.

12. A method for producing a dispersion, comprising mixing the powder described in claim 1 or claim 2 with a solvent.

13. A method for producing a composition, comprising mixing the powder described in claim 1 or claim 2 with a binder.

14. A method for manufacturing an electrode, comprising the step of applying an electrode mixture layer forming composition, comprising the powder, binder, and electrode active material described in claim 1 or claim 2, to a current collector to form an electrode mixture layer.

Images