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

Abstract

A powder according to the present invention contains fibrous carbon having a structure in which cylindrical carbon hexagonal network planes are stacked in the thickness direction, and has a bulk density of 0.0360 g / cm3 to 0.0799 g / cm3.

Description

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

[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.

[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 10 to 50 kg / m 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 ≤ 10 log R ≤ -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.

[0004] Special table 2018-534747 publication

[0005] However, there is a need for a powder containing fibrous carbon that further reduces the volume resistivity of the electrode when used in the electrodes of a secondary battery. 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 the electrode when used in the electrodes of a secondary battery, as well as a conductive additive, dispersion, composition, conductive layer, electrode mixture layer, electrode, secondary battery, method for manufacturing the dispersion, method for manufacturing the composition, and method for manufacturing the electrode containing the powder.

[0006] The specific means for achieving the above objectives are as follows: <1> A fibrous carbon material having a structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction, with a bulk density of 0.0360 g / cm³ ３ ~0.0799g / cm ３ It is a powder. <2> 0.8 g / cm ３ The powder described in <1>, wherein the volume resistivity when compressed is 0.0120 Ω·cm to 0.0260 Ω·cm. <3> The BET specific surface area is 11.0 m². ２ / g ~ 25.0m ２ <1> or <2> is a powder in the form of / g. <4> A conductive additive comprising the powder described in any one of <1> to <3>. <5> A dispersion comprising the powder described in any one of <1> to <3> and a solvent. <6> A composition comprising the powder described in any one of <1> to <3> and a binder. <7> A conductive layer comprising the powder described in any one of <1> to <3>. <8> An electrode mixture layer comprising the powder described in any one of <1> to <3>, a binder, and an electrode active material. <9> An electrode comprising the powder described in any one of <1> to <3>. <10> 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 <9>. <11> A method for producing a dispersion comprising mixing the powder described in any one of <1> to <3> and a solvent. <12> A method for producing a composition, comprising mixing the powder described in any one of <1> to <3> with a binder. <13> A method for producing an electrode, comprising the step of applying an electrode mixture layer forming composition containing the powder described in any one of <1> to <3>, a binder, and an electrode active material to a current collector to form an electrode mixture layer.

[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.

[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 the process is achieved. In this disclosure, numerical ranges indicated using "~" include the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced by the values ​​shown in the examples. In this disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance 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 types of substances present in the composition, unless otherwise specified. In this disclosure, each component may contain multiple types of particles. If 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 this disclosure, the terms “layer” or “film” include cases where the layer or film is formed over the entire region when observed, as well as cases where it is formed only on a portion of the region. In this disclosure, the term “laminated” indicates stacking layers, and two or more layers may be bonded together or detachable. In this disclosure, the term “contains” in reference to a particular component (e.g., conductive additive, dispersion, conductive layer, electrode mixture layer) means that it may contain other components in addition to that particular component. In this disclosure, “conductive additive” is added to the 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 net planes are laminated in the thickness direction, and has a bulk density of 0.0360 g / cm ３ to 0.0799 g / cm ３ It is not clear why the powder having the above configuration can further reduce the volume resistance of the electrode when used in the electrode of the secondary battery, but it is speculated as follows.

[0011] The fibrous carbon contained in the powder of the present disclosure has a structure in which cylindrical carbon hexagonal net planes are laminated in the thickness direction, and thus is excellent in conductivity in the length direction of the fibrous carbon. However, when the bulk density of the powder exceeds 0.0799 g / cm ３ the fibrous carbon tends to be short, and it is difficult to obtain the advantage of conductivity due to the fibrous carbon. Also, when the bulk density of the powder is less than 0.0360 g / cm ３ the fibrous carbon tends to be too long and the fibrous carbon is likely to become entangled. Therefore, it is speculated that when the electrode binder layer is formed, the dispersibility decreases, locally low-conductivity portions are generated, and it is difficult for the volume resistance of the electrode to decrease. In the present disclosure, the numerical value of the bulk density of the powder comprehensively captures the dispersibility of the fibrous carbon, the effect of the conductive path by the fibrous carbon, etc. By setting the bulk density of the powder within a specific range, it has been found that it is possible to reduce the volume resistance of the electrode produced using the powder.

[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 along the longitudinal direction inside the fibrous material, and in the TEM cross-sectional image, multiple closed curves with different maximum diameters exist, and the closed curves are arranged sequentially towards the interior as the maximum diameter decreases, then it can be confirmed that it 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 whose cross-sectional area decreases as you approach the center, and sections whose cross-sectional area increases as you move away from the center of the cylinder's 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 cylinder) of multiple cylindrical carbon hexagonal mesh surfaces of different diameters do not all have to be aligned, but only some of the central axes may be aligned. The shape of the cylinder's 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] The bulk density of the powder is 0.0360 g / cm³. ３ The above is 0.0385 g / cm³. ３ Preferably, it is 0.0400 g / cm³ or more. ３ It is more preferable that the concentration be greater than or equal to 0.0500 g / cm³. ３ It is even more preferable that the concentration be greater than or equal to 0.0600 g / cm³.３ The above is particularly preferable. The bulk density of the powder is 0.0799 g / cm³. ３ The following is the result: 0.0750 g / cm³ ３ Preferably, it is 0.0700 g / cm³. ３ The following is more preferable. The bulk density of the powder is measured by the method described in the examples.

[0014] Average interlayer distance (d) of the graphite layer in the powder ００２ The 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.

[0015] From the viewpoint of imparting conductivity to the electrode with a low amount of additive, the volume fraction of 4.6 μm or smaller 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. There is no particular lower limit to the volume fraction of 4.6 μm or smaller in the volume-based cumulative particle size distribution of the powder, but it 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 with a laser diffraction particle size analyzer.

[0016] 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, and particularly preferably 150 nm or more.

[0017] The average fiber diameter of fibrous carbon can be determined from the arithmetic mean of the diameters of 200 fibers randomly observed by scanning electron microscopy (SEM) of the powder or electrode. The diameter of a single fiber can be determined by measuring the width of one randomly selected point excluding both ends of the fiber as seen in the SEM image. For electrodes containing fibrous carbon, the electrode may be washed with a solvent to remove binders and other substances, and the fibrous carbon may be extracted and its average fiber diameter measured.

[0018] 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, and more preferably 2.5 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.

[0019] 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 then observed by SEM. The length along the fiber axis of 200 randomly selected fibers is measured, and the average fiber length is determined by taking the arithmetic mean. Alternatively, the electrode may be washed with a solvent to remove binders and other substances, and the fibrous carbon can be extracted and its average fiber length determined.

[0020] 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.

[0021] Fiber length and diameter will be measured only for specimens that are clearly fibrous carbon. Fibrous carbon specimens will be selected if both ends are included in a single field of view. Even if the fiber is curved, it will be measured if it can be confirmed to be a single fiber. Specimens that are not clearly a single fiber due to overlapping or branching, specimens that are in contact with each other (e.g., fixed or aggregated specimens), specimens with a fiber length of less than 1 μm along the fiber axis, and specimens that cannot be determined to be fibrous carbon will be excluded.

[0022] The powder of this disclosure contains fibrous carbon (also called "specific fibrous carbon") having a structure in which cylindrical carbon hexagonal network surfaces are stacked in the thickness direction, and may further contain carbon materials other than specific fibrous carbon. In the powder of this disclosure, the proportion of specific fibrous carbon is preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, even more preferably 70% or more, and most preferably 90% or more, when the entire powder is considered as 100% or more in an image of the powder taken by SEM or TEM. The proportion of specific fibrous carbon is not particularly limited as long as it is 100% or less, for example, it may be 99% or less, or 95% or less. In this disclosure, "fibrous" preferably refers to a shape with an aspect ratio of 5 or more. The aspect ratio can be determined by the ratio of length to diameter (length / diameter). For any fibrous carbon sample being measured, a centerline (also called the fiber axis) is defined, and the length along the fiber axis is defined as the length in terms of aspect ratio. The centerline can be determined using image analysis software such as ImageJ.

[0023] The method for determining the proportion of specific fibrous carbon is not particularly limited. For example, one method involves dispersing the powder in a dispersion medium such as ethanol, spreading it onto aluminum foil and drying it, then observing it with a SEM at an appropriate magnification and counting the number of specific fibrous carbons and the number of other carbon materials. Another method involves dispersing the powder in a dispersion medium such as ethanol, scooping it up with a microgrid and drying it, then observing it with a TEM and counting the number of specific fibrous carbons and the number of other carbon materials.

[0024] Powder 0.8 g / cm³ ３ The volume resistivity when compressed (hereinafter referred to as "0.8 g / cm²") ３ The compression-resistivity (also called the "compression-resistivity ratio") is preferably 0.0120 Ω·cm to 0.0260 Ω·cm. 0.8 g / cm 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 ３ From 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, extremely preferably 0.0157 Ω·cm or less, and may also be 0.0153 Ω·cm or less. 0.8 g / cm 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.

[0025] 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.

[0026] Powder: 0.6 g / cm³ ３ The volume resistivity when compressed (hereinafter referred to as "0.6 g / cm²") ３ The compression-resistivity (also called the "compression-resistivity ratio") is preferably 0.0120 Ω·cm to 0.0310 Ω·cm. 0.6 g / cm 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 ３From 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 / cm 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.

[0027] 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 consolidation resistivity is measured by the method described in the examples.

[0028] The BET specific surface area of ​​the powder is 11.0 m², from the viewpoint of battery characteristics. ２ / g ~ 25.0m ２ It is preferable that the amount is / g. The BET specific surface area of ​​the powder is 11.0 m². ２ It is preferable that the amount be 12.0 m or more. ２ It is more preferable that the amount be 12.5 m or more. ２ It is even more preferable that the amount is 1 / g or more. The BET specific surface area of ​​the powder is 25.0 m². ２ It is preferable that the amount is less than or equal to 20.0 m ２ It is more preferable that it be less than or equal to 19.0 m ２ It is even more preferable that it be less than or equal to 18.0 m ２ It is particularly preferable that the amount be less than or equal to 17.0 m ２ It is extremely preferable that the amount is less than or equal to / g. The BET specific surface area of ​​the powder is calculated using the BET multipoint method with nitrogen as the adsorbent gas.

[0029] <Method for producing powder> The method for producing powder according to this disclosure includes, for example, the following steps: (Step 1) A raw material mixture is prepared by mixing a carbon source and at least one selected from the group consisting of a catalyst precursor and a catalyst. (Step 2) A reactor is heated to a predetermined temperature. (Step 3) The raw material mixture is introduced into the reactor using a carrier gas to produce powder. (Step 4) The powder is recovered.

[0030] (Step 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. When using a gaseous raw material mixture, the mixture may be preheated to vaporize it, or each component may be a gas at room temperature. The carbon source may be dissolved in the catalyst precursor or additive, or dispersed in the catalyst precursor or additive.

[0031] 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 CO, CO ２ Examples of such gases include the following. The carbon source may be used alone or in combination of two or more.

[0032] The carbon source content in the raw material mixture is preferably 50% to 99.9% by mass of the total amount of carbon in the carbon source, 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.

[0033] 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 organic transition 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. The catalyst itself may be used instead of the catalyst precursor, or in combination with the catalyst precursor. The raw material mixture should contain at least one selected from the group consisting of catalyst precursors and catalysts.

[0034] 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, more preferably 0.01% to 5% by mass, and even more preferably 0.1% to 3% by mass, relative to the total amount of the raw material mixture.

[0035] The raw material mixture may further contain additives. The additives preferably 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. As for additives that are gaseous at room temperature, H ２ S, CH ３ Examples include sulfur compounds such as SH.

[0036] 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.

[0037] 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.

[0038] (Step 2) In Step 2, the reactor is heated to a predetermined temperature. In one embodiment, a vertical reactor is used. Otherwise, the shape of the reactor is not particularly limited as long as it is capable of carrying out the reaction.

[0039] 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.

[0040] (Step 3) In Step 3, the raw material mixture is introduced into the reaction furnace using a carrier gas to generate a powder. A method may be employed in which the liquid or slurry-like raw material mixture is sprayed from a spray nozzle using a carrier gas, or the vaporized raw material mixture may be introduced into the reaction tube using a carrier gas.

[0041] 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.

[0042] 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.

[0043] (Step 4) In Step 4, the generated powder is recovered. The powder may be continuously discharged from a vertical reactor as it falls to the bottom, or it may be recovered from a batch furnace after the furnace has cooled down and the reaction tubes have been opened. The powder may also be transported using an inert gas.

[0044] <Post-processing> 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 electron conductivity of the powder. This process is also called the "calcination process". Examples of inert atmospheres in the calcination process include nitrogen and argon. The temperature in the calcination process 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.

[0045] 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.

[0046] 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 pulverization equipment include microjet mills, jet mills, and laboratory pulverizers. The powder may also be classified after or without pulverization. The bulk density of the powder can also be adjusted by classification.

[0047] <Conductive Additive> The conductive additive of this disclosure includes the powder of this disclosure. The conductive additive may 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 and the powder of this disclosure may be used in combination, or the powder of this disclosure may be used instead of carbon black.

[0048] Other conductive additives that can be used in combination with the powders of this disclosure include carbon black, multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes (SWCNTs), graphene, graphite particles, amorphous carbon, and the like. These other conductive additives may be used individually or in combination of two or more.

[0049] The content of the powder 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.

[0050] <Dispersion> The dispersion of the present disclosure comprises the powder of the present disclosure and a solvent. The dispersion of the present disclosure may also contain other components other than the powder and solvent, such as a dispersant and the other conductive additives mentioned above.

[0051] 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).

[0052] The dispersant is not particularly limited and examples include polyvinylpyrrolidone (PVP), Triton X-100, and sodium cholate. The dispersant content is preferably 0.01% to 10% by mass relative to the total volume of the dispersion.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] <Composition> The composition of the present disclosure comprises the aforementioned powder and a binder. The composition of the present disclosure may also contain other components other than the powder and the binder, such as the aforementioned other conductive additives, solvents, dispersants, etc.

[0057] 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.

[0058] 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.

[0059] 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 range as described in the section on dispersions.

[0060] When a dispersant is used, the dispersant content is preferably 0.01% to 10% by mass relative to the total amount of the composition.

[0061] 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.

[0062] <Conductive Layer> The conductive layer of this disclosure includes the powder of this disclosure. The conductive layer of this disclosure may also contain components other than the powder of this disclosure, such as binders, additives, and other conductive aids. Binders, additives, and other conductive aids are the same as those described above.

[0063] The conductive layer is provided on a metal foil that acts as a current collector in a secondary battery, such as a lithium-ion secondary battery. The conductive layer may be provided on one surface of the metal foil or on both surfaces. 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 "above" is not limited to "above" in the vertical direction, but may also refer to "below" in the vertical direction, or to the left or right.

[0064] 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, a powder content of 60% by mass or less suppresses powder shedding from the conductive layer. 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.

[0065] 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 preferable. Furthermore, a binder content of 80% by mass or less suppresses the resistance of the conductive layer. From the viewpoint of low resistance, the aforementioned binder content is more preferably 70% by mass or less, and 60% by mass or less is even preferable.

[0066] <Electrode Mixture Layer> The electrode mixture layer of this disclosure comprises the powder of this 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 described in the section on secondary batteries below.

[0067] 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.

[0068] 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 makes it easy to form into layers and suppresses powder shedding. From the viewpoint of moldability and suppression of powder shedding, the binder content is more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more. Furthermore, from the viewpoint of low resistance of the electrode mixture layer, the binder content is more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0069] Examples of electrode active materials include positive electrode active materials and negative electrode active materials, the types of which will be explained later in the section on secondary batteries. The content of the electrode active material is preferably 70% to 99% by mass of the total mass of the electrode mixture layer, and from the viewpoint of 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 electrode active material may be 99% by mass or less, 98% by mass or less, or 97% by mass or less.

[0070] <Electrodes> The electrodes of the present disclosure include the powder of the present disclosure. The electrodes of the present disclosure may be either a positive electrode or a negative electrode. When the electrodes of the present disclosure are electrodes for a secondary battery, they 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. If the conductive layer contains the powder of the present disclosure, the conductive layer described above may be applied. If the electrode mixture layer contains the powder of the present disclosure, the electrode mixture layer described above may be applied.

[0071] 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.

[0072] 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 electrodes is measured by the method described in the examples.

[0073] <Secondary Battery> The secondary battery of the present 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 the present disclosure.

[0074] 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.

[0075] 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.

[0076] 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, aluminum-based secondary batteries, etc. Among these, lithium-based secondary batteries that can achieve high voltage and high energy density and sodium-based secondary batteries that 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 (for example, lithium-sulfur batteries and lithium-air batteries are also included), and include liquid electrolyte type batteries and solid electrolyte type batteries that contain at least one of the following: electrolyte, polymer electrolyte, polymer gel electrolyte, solid electrolyte, etc. 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-based secondary battery, but the present invention is not limited thereto.

[0077] [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.

[0078] 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, 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, aluminum foil is used as the positive electrode current collector.

[0079] The positive electrode mixture layer may contain the powder of the present disclosure. For example, a positive electrode mixture layer is formed on a positive electrode current collector by coating it with a composition containing a positive electrode active material (a composition for forming a positive electrode mixture layer), drying the coating layer, and then pressing it.

[0080] 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.

[0081] The density of the positive electrode mixture layer is 2.0 g / cm³, from the viewpoint of energy density, etc.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 ~4.0 g / cm ３ That's fine.

[0082] The basis weight of the positive electrode mixture layer is 10.0 mg / cm³, from the viewpoint of energy density and other factors. ２ It may be greater than or equal to 10.0 mg / cm³. ２ ~30.0mg / cm ２ That's fine.

[0083] (Positive Electrode 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 O ２ (x, y, z, w≧0, x+y+z+w=1), LiMPO ４ (M is one or more selected from Fe, Co, Mn, and Ni), LiMn ａ Ni ｂ O ４ Examples include (a, b ≥ 0, a + b = 2). The positive electrode active material may be used alone or in combination of two or more types.

[0084] The positive electrode active material is LiNi ｘ Mn ｙ Co ｚ Al ｗ O ２ (x, y, z, w≧0, x+y+z+w=1) or LiMPO ４ (It is preferable that M contains one or more selected from Fe, Co, Mn, and Ni.)

[0085] LiNi ｘ Mn ｙ Co ｚ Al ｗ O ２As (x, y, z, w ≥ 0, x + y + z + w = 1), it is preferable that the proportion of nickel is relatively high, for example, x ≥ 0.5 or more. Li(Ni ｘ Mn ｙ Co ｚ )O ２ (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 )O ２ (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 )O ２ , Li(Ni ０．７ Mn ０．２ Co ０．１ )O ２ , Li(Ni ０．７ Mn ０．１ Co ０．２ )O ２ , Li(Ni ０．６ Mn ０．２ Co ０．２ )O ２ , Li(Ni ０．５ Mn ０．３ Co ０．２ )O ２ and Li(Ni ０．５ Mn ０．２ Co ０．３ )O ２ can be mentioned.

[0086] As the positive electrode active material represented by LiMPO ４ (M is one or more selected from Fe, Co, Mn and Ni), for example, LiFePO ４ , LiFe ０．５ Mn ０．５ PO ４ , LiFe ０．３ Mn ０．７ PO ４ , LiCoPO ４ and LiCo ０．５ Mn ０．５ PO ４ can be mentioned.

[0087] In the positive electrode mixture layer, the content of the positive electrode active material is preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, from the viewpoint of positive electrode capacity. 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.

[0088] 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.

[0089] When the positive electrode mixture layer contains the above-mentioned powder, the content of the above-mentioned 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.

[0090] 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.

[0091] 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, carbon nanotubes such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and carbon nanofibers.

[0092] [Negative electrode] The negative electrode generally comprises 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.

[0093] The material of the negative electrode current collector is not particularly limited as long as it is an electronically conductive material, 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, copper foil is used as the negative electrode current collector.

[0094] 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) is coated onto a negative electrode current collector, the coated slurry is dried, and then pressed to form a negative electrode mixture layer on the negative electrode current collector.

[0095] The thickness of the negative electrode mixture layer may be 30 μm or more, 50 μm to 100 μm, or 100 μm to 150 μm, from the viewpoint of energy density, etc.

[0096] The density of the negative electrode mixture layer is 1.2 g / cm³, from the viewpoint of energy density, etc. ３ It may be greater than or equal to 1.3 g / cm³. ３ ~2.0 g / cm ３ That's fine.

[0097] The basis weight of the negative electrode mixture layer is 5.0 mg / cm³, from the viewpoint of energy density, etc. ２ It may be greater than or equal to 10 mg / cm³. ２ ~20 mg / cm³ ２ That's fine.

[0098] (Negative electrode active material) The negative electrode mixture layer contains a negative electrode active material. The negative electrode active material may be a metalloid or metal that forms an alloy with lithium, such as Si, Sn, Al, or SiO ｘ (0 < x ≤ 2), soft carbon, hard carbon, graphite, silicon-carbon composite, Li ４ Ti ５ O １２ , metal 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), ZnOｘ Examples include oxides such as (0 < x ≤ 1). Among these, the negative electrode active material preferably contains graphite. Furthermore, at least a portion 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 types.

[0099] In the negative electrode mixture layer, the content of the negative electrode active material is preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, from the viewpoint of 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.

[0100] In the negative electrode mixture layer, the negative 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 negative 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.

[0101] When the negative electrode mixture layer contains the above powder, the content of the above powder in the negative electrode mixture layer 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.

[0102] In the negative 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.

[0103] The average electrode area per sheet (average positive electrode area and average negative electrode area) is 20 cm². ２ ~10,000 cm ２ It may also be 300 cm ２ ~10,000 cm ２ That's fine.

[0104] (Outer packaging) The outer packaging 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, etc. Examples of outer packaging include commercially available battery packs, 18650 type cylindrical cells, and those packaged in aluminum foil, and the outer packaging can be freely designed and used.

[0105] (Separator) A secondary battery may be provided with a separator between the positive and negative electrodes. The separator can be appropriately selected from those that can be used in general secondary batteries. Examples of separators include microporous films made of polyethylene or polypropylene. ２ Al ２ O ３ Separators containing particles such as these as fillers, or separators with these particles attached to the surface, can also be used.

[0106] (Electrolyte) Secondary batteries may contain an electrolyte. There are no particular restrictions on the electrolyte, and an electrolyte that can be used in a normal secondary battery can be appropriately selected. For example, an organic solvent in which a lithium salt is dissolved in an amount of 0.5 mol / L to 2.0 mol / L can be used as the electrolyte.

[0107] LiPF is an example of a lithium salt. ６ LiBF ４ LiClO ４ LiAsF ６ , LiN (SO ２ F) ２ Examples include (LiFSI).

[0108] 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 appropriately selected and used in combination. 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.

[0109] (Ionic Liquids) Ionic liquids may be used as electrolytes, or they may be used in combination with the aforementioned organic solvents. The ionic liquids are 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.

[0110] (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 in which the solid electrolyte is sandwiched between the positive and negative electrodes (for example, an all-solid-state lithium-ion secondary battery) can be formed.

[0111] 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 methacrylate (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 Li ２ S-P ２ S ５ Li ２ S-GeS ２ Li ２ S-SiS ２ -Li ３ PO ４Sulfide-based solid electrolytes such as La ０．５１ Li ０．３４ TiO ２．９４ Li １．３ Al ０．３ Ti １．７ (PO ４ ) ３ Li ７ La ３ Zr ２ O １２ , 50Li ４ SiO ４ ・50Li ３ BO ３ Li ２．９ PO ３．３ N ０．４６ (LIPON), Li ３．６ Si ０．６ P ０．４ O ４ Li １．０７ Al ０．６９ Ti １．４６ (PO ４ ) ３ Li １．５ Al ０．５ Ge １．５ (PO ４ ) ３ Examples include oxide-based solid electrolytes such as the following.

[0112] The secondary battery of this disclosure preferably has a discharge capacity (capacity retention rate (%)) after 500 cycles of 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.

[0113] The secondary battery of this disclosure preferably has a DC resistance (DCR) of 0.0870 Ω or less during initial charging, 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 DC resistance (DCR) during initial charging, the better, and there is no particular limit to the lower limit, which may be 0.0010 Ω or more, or 0.0001 Ω or more. The DC resistance (DCR) during initial charging is measured under the conditions described in the examples.

[0114] The secondary battery of this disclosure preferably has a DCR of 0.1330 Ω or less after 500 cycles of charging, more preferably 0.1300 Ω or less, even more preferably 0.1250 Ω or less, and particularly preferably 0.1240 Ω or less. A lower DCR after 500 cycles of charging is preferable, and there is no particular limit to the lower limit, which may be 0.0100 Ω or more, or 0.0010 Ω or more. The DCR after 500 cycles of charging is measured under the conditions described in the examples.

[0115] 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.

[0116] 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.

[0117] 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 methods shown below.

[0118] <Bulk Density> 1,000 g of powder was weighed, placed in a graduated cylinder, and vibrated for 30 seconds using a test tube mixer (model "Touch Mixer MT31" (manufactured by Yamato Scientific Co., Ltd.)). The intensity was set to ON1. The surface of the powder was leveled, and the scale on the graduated cylinder was read. The bulk density of the powder was calculated from the obtained volume and mass.

[0119] <Consolidation Resistivity> 1 g of powder was placed in a dedicated jig. The dedicated jig had a space of 1 cm (length) x 4 cm (width) x 9 cm (height), and the two sides of the 1 cm x 4 cm section were made of metal and electrically conductive. In addition, two metal points (φ = 3 mm) for voltage measurement were provided on the 1 cm x 4 cm bottom surface and electrically conductive. The distance between the metal points was 1 cm. The non-metal parts were made of plastic and were insulating. The push rod attached to the dedicated jig had a section of 0.999 cm (length) x 3.999 cm (width) x 9 cm (height), and the space of the dedicated jig was compressed in the height direction. While a current of 100 mA was passed through the metal on the side, 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 the density of the powder and volume resistivity were recorded from these measurements. Powder density: 0.8 g / cm ３ and 0.6 g / cm³ ３ The volume resistivity when compressed was determined as the compaction resistivity.

[0120] <BET Specific Surface Area> A NOVA2200e manufactured by Quantachrome was used as the BET specific surface area measuring device. 3 g of powder was placed in a sample cell (9 mm x 135 mm), dried at 300°C under vacuum conditions for 1 hour, and then measured. N was used as the gas for BET specific surface area measurement. ２ The specific surface area was calculated using the BET three-point method from the nitrogen adsorption amounts at relative pressures of 0.1, 0.2, and 0.3. At this time, the density of the nitrogen liquid was 0.808 (g / cm³). ３ The calculation was performed using the following assumptions: the volume of one mole of nitrogen at standard conditions is 22.4133 L, and the atomic weight of nitrogen is 14.0067.

[0121] [Comparative Example 1] (Preparation of the positive electrode) NMC811 (Li(Ni) as the positive electrode active material ０．８ Mn ０．１ Co ０．１ ) O ２An NMP solution (solid content concentration 7.3% by mass) was prepared containing 96.5 parts by mass of (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 adjusting the viscosity by mixing in the kneader while adding NMP as appropriate. It was separately confirmed by TEM observation that the vapor-phase carbon fiber VGCF-H has a structure in which cylindrical 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%.

[0122] 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.

[0123] (Evaluation of Coatability) The coatability of the slurry when applied with a roll coater was evaluated according to the following criteria: A: The slurry has good smoothness, consistency, and drying speed. B: The slurry has a defect in one or more of the following: smoothness, consistency, or drying speed.

[0124] (Evaluation of the coated surface) The coated surface was visually observed and evaluated according to the following criteria: A: No aggregation B: Aggregation present

[0125] (Volume Resistivity of the Electrode) The obtained positive electrode sheet was vacuum-dried in a dry room (dew point -70°C) at 100°C for 10 hours to prepare an electrode sample. The volume resistivity of the positive electrode sheet 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.

[0126] (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 : 5.7 μm, specific surface area: 3.2 m ２ A mixture with a mass ratio of 7:3 ( / g) was used. As an aqueous binder, a dispersion of polysol LB150 (manufactured by Resonaq Corporation) fine particles was prepared. 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.

[0127] 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 and mixed in a kneader to obtain a negative electrode slurry. The negative electrode slurry was coated onto a copper foil with a thickness of 20 μm 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.

[0128] (Preparation of evaluation cells) The following cells were prepared in a dry room maintained at a dew point of -70°C or lower.

[0129] The obtained positive electrode sheet and negative electrode sheet were punched out to form an area of ​​36 cm². ２Four positive electrodes and five negative electrodes were obtained. The obtained positive 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. Al tabs were attached to the Al foil of the positive electrode, and Ni tabs were attached to the Cu foil of the negative electrode. 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, which was a battery for evaluation. The electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:5:2, and then mixing vinylene carbonate (VC) to a concentration of 1% by mass, to which the electrolyte LiPF was further added. ６ A solution was used that was dissolved to a concentration of 1.2 mol / L.

[0130] (Evaluation of evaluation cells) [Capacity retention rate] The initial discharge capacity measured at 25°C was set as 100%, and the discharge capacity after 500 cycles was defined as the capacity retention rate (%). In measuring the capacity retention rate, charging was performed with a constant current of 114 mA (0.2 C) until the voltage reached 4.2 V, followed by constant voltage charging at a constant voltage of 4.2 V until the current decreased to 0.05 C. Discharging was performed with a constant current of 114 mA (0.2 C) until the voltage reached 2.8 V.

[0131] [DCR Evaluation] (DCR during initial discharge) Constant current charging was performed at 114 mA (0.2 C) until the voltage reached 4.2 V, followed by constant voltage charging at a constant voltage of 4.2 V until the current was 0.05 C. Discharge was then performed at a constant current of 57 mA (0.1 C) for 5 hours to reach 50% capacity. The voltage and current after 5 seconds were plotted when discharge currents of 114 mA (0.2 C), 285 mA (0.5 C), 570 mA (1 C), and 855 mA (1.5 C) were applied, and the DCR was calculated from the slope.

[0132] (DCR during discharge after 500 cycles) For the evaluation cell after 500 cycles, the DCR was determined using the same method as the DCR during the initial discharge described above.

[0133] [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 it was secured with a bakelite plate for electrochemical measurement. Constant current charging was performed at 114 mA (0.2 C) until the voltage reached 4.2 V, and then constant voltage charging was performed at a constant voltage of 4.2 V until the current reached 0.05 C. The fully charged cell was placed in a 45°C constant temperature bath until the temperature stabilized, and then discharged to 2.5 V with a constant current of 2850 mA (5 C). The temperature during this discharge was recorded with a data logger.

[0134] [Example 1] A cell was prepared in the same manner as in Comparative Example 1, except that the vapor-phase carbon fiber used in the positive electrode was replaced with a carbon material obtained through the following process. The vapor-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 6.39%. Separate TEM observation confirmed that the material has a structure in which tubular carbon hexagonal network surfaces are stacked in the thickness direction.

[0135] Process 1 (Synthesis of Carbon Material: Produced Carbon Material) A reactor consisting of a reaction tube with an inner diameter of 500 mm and a length of 2000 mm and a heater was prepared. A two-fluid mixing nozzle for supplying raw materials was placed at the top of the reaction tube, and a conveyor was placed at the bottom of the reaction tube and 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 the raw material solution. The composition of the raw material solution was 96.4% by mass of benzene, 3.5% by mass of ferrocene, and 0.1% by mass of sulfur. Hydrogen was used as the carrier gas, and 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 the 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 gas. The carbon material produced by this operation is sometimes called "produced carbon material."

[0136] Step 2 (Castration of Carbon Material: Calcined Carbon Material) The carbon material obtained in Step 1 was placed in a calcination furnace. It was heated to 1000°C under an argon atmosphere to remove the tar adhering to the carbon material. After calcination, the carbon material obtained in this operation is sometimes called "calcined carbon material".

[0137] 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. Under an argon atmosphere, the calcined carbon material was graphitized by heating to 2800°C. The carbon material obtained by this operation is sometimes called "graphitized carbon material". After the graphitization treatment, rough crushing was performed with a shovel, and then the material was crushed for 3 minutes using a Waring Food Blender (manufactured by FMI Co., Ltd., model: CB-15T) at a high intensity (approximately 18,500 rpm). The crushed 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 air volume of 1.5 m³. ３ Classification was performed using / min, and the powder recovered on the fine powder side was used as the sample.

[0138] [Example 2] In the gas-phase carbon fiber manufacturing method used for the positive electrode in Example 1, gas-phase carbon fiber was prepared in the same manner as in Example 1, except that the rough crushing, pulverization, and classification steps after graphitization treatment were omitted. A cell was manufactured in the same manner as in Comparative Example 1, except that this gas-phase carbon fiber was used as the positive electrode. The gas-phase carbon fiber used for the positive electrode in 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 3.67%. Furthermore, TEM observation separately confirmed that the material has a structure in which tubular carbon hexagonal network surfaces are stacked in the thickness direction.

[0139] [Comparative Example 2] The reaction was carried out in the same manner as in Example 1, except that the raw material solution from Example 1 was supplied at a rate of 0.71 g / NL (benzene (g / min) / hydrogen (NL / min)) and the raw material was supplied for 3 hours, to synthesize gas-phase carbon fibers. A cell was prepared 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 fibers used as the positive electrode in Example 1 had an average interlayer distance (d) of the graphite layer. ００２The 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 0.41%. Separate TEM observation confirmed that the material has a structure in which tubular carbon hexagonal network surfaces are stacked in the thickness direction.

[0140]

[0141] As shown in Table 1, it contains fibrous carbon and has a bulk density of 0.0360 g / cm³. ３ ~0.0799g / cm ３ Examples 1 and 2, which used the powder, had a bulk density of 0.0360 g / cm³. ３ ~0.0799g / cm ３ Compared to Comparative Examples 1 and 2, which used powders outside the specified range, the volume resistivity of the fabricated electrodes was significantly lower. Furthermore, the cells of Examples 1 and 2 exhibited lower DCR during initial charging and lower DCR after 500 cycles compared to the cell of Comparative Example 1, resulting in a higher capacity retention rate.

[0142] The disclosure of Japanese Patent Application No. 2024-208837 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. Contains fibrous carbon having a structure in which tubular carbon hexagonal mesh surfaces are stacked in the thickness direction, with a bulk density of 0.0360 g / cm³. ３ ~0.0799g / cm ３ It is a powder.

2. 0.8 g / cm³ ３ The powder according to claim 1, wherein the volume resistivity when compressed is 0.0120 Ω·cm to 0.0260 Ω·cm.

3. BET specific surface area is 11.0 m² ２ / g ~ 25.0m ２ The powder according to claim 1 or claim 2, wherein the weight is / g.

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

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

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

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

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

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

10. 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 9.

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

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

13. 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 claim 1 or claim 2 to a current collector to form an electrode mixture layer.

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