Powder, conductive additive, dispersion, conductive layer, electrode mixture layer, and secondary battery

Abstract

The present invention provides a powder containing fibrous carbon that can be easily dispersed and can impart electronic conductivity to electrodes and the like with only a small amount of additive. [Solution] A powder containing fibrous carbon having a structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, wherein the average fiber diameter of the fibrous carbon is 110 nm to 300 nm, and when the powder is observed using a scanning electron microscope (SEM) at a magnification of 20,000 times, the average number of spherical carbon particles is 1 to 30, and the average maximum diameter of the spherical carbon particles is 0.30 μm or less.

Description

[Technical Field]

[0001] This disclosure relates to powders, conductive additives, dispersions, conductive layers, electrode mixture layers, and secondary batteries. [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 those produced by vapor-phase carbon fiber processing, have traditionally been used as conductive additives for the electrodes of secondary batteries. For example, Patent Document 1 proposes a fine carbon fiber mixture characterized by being a mixture of fine carbon fibers and non-fibrous carbon in the form of flakes, particulates, or sheets. Patent document 2 proposes carbon fibers with many branches. Patent Document 3 discloses that by adding polypropylene glycol or the like as a specific additive component, carbon fibers can be obtained in high yield with a small amount of catalyst. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2003-89930 [Patent Document 2] Japanese Patent Publication No. 2004-176244 [Patent Document 3] Japanese Patent Publication No. 2004-44064 [Overview of the project] [Problems that the invention aims to solve]

[0005] The inclusion of non-fibrous carbon, as described in Patent Document 1, is a desirable configuration, for example, from the viewpoint of imparting conductivity to the electrodes of a lithium-ion secondary battery. However, the content of non-fibrous carbon needs to be strictly controlled. Furthermore, the fiber diameter of the fine carbon fibers produced in Patent Document 1 is about 80 nm, and generally, carbon fibers with a fiber diameter of 100 nm or less tend to aggregate, making it difficult to obtain the desired dispersion state in the electrode slurry of a lithium-ion secondary battery. Therefore, an apparatus capable of supplying greater energy is needed to achieve the desired dispersion state of fine carbon fibers.

[0006] Even the highly branched carbon fibers described in Patent Document 2 are difficult to disperse in the desired state in an electrode slurry, and a device capable of supplying greater energy is required to achieve the desired dispersion state.

[0007] Furthermore, the carbon fibers produced in Patent Document 3 have a fiber diameter of approximately 100 nm, which may make it difficult to achieve the desired dispersion state in the electrode slurry of a lithium-ion secondary battery. Therefore, a device capable of supplying greater energy is needed to achieve the desired dispersion state of the carbon fibers.

[0008] For the reasons mentioned above, fibrous carbon is desirable because it can be easily dispersed and imparts electronic conductivity to electrodes and the like with only a small amount of additive.

[0009] This disclosure is made in view of the above circumstances and aims to provide a powder containing fibrous carbon that can be easily dispersed and impart electronic conductivity to electrodes etc. with a small amount of addition, as well as a conductive additive, dispersion, conductive layer, electrode mixture layer, and secondary battery containing said powder. [Means for solving the problem]

[0010] The specific means for achieving the aforementioned objectives are as follows: <1> A powder containing fibrous carbon having a structure in which tubular carbon hexagonal network surfaces are stacked in the direction of fiber thickness, wherein the average fiber diameter of the fibrous carbon is 110 nm to 300 nm, and when the powder is observed using a scanning electron microscope (SEM) at a magnification of 20,000 times, the average number of spherical carbon particles is 1 to 30, and the average maximum diameter of the spherical carbon particles is 0.30 μm or less. <2> The fibrous carbon includes network-forming fibers. <1> The powder described above. <3> The average length of the fibrous carbon is 3 μm to 20 μm. <1> or <2> The powder described above. <4> The powder d 002 This range is 0.3370nm to 0.3390nm. <1> ~ <3> The powder described in any one of the following. <5> The spherical carbon particles are particles generated during the production of the fibrous carbon. <1> ~ <4> The powder described in any one of the following. <6> 0.8 g / cm³ 3 The pressure used for compaction is 0.8 MPa to 2.5 MPa. <1> ~ <5> The powder described in any one of the following. <7> 0.8 g / cm³ 3 The volume resistivity when compacted is 0.025 Ω·cm or less. <1> ~ <6> The powder described in any one of the following. <8> The R-value in the Raman spectrum is between 0.05 and 0.30. <1> ~ <7> The powder described in any one of the following. <9> <1> ~ <8> A conductive additive containing the powder described in any one of the following. <10> <1> ~ <8> A dispersion containing any one of the powders described in the following. <11> <1> ~ <8> A conductive layer containing the powder described in any one of the following. <12> <1> ~ <8> An electrode mixture layer containing the powder described in any one of the following. <13> A positive electrode comprising a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, and a negative electrode comprising a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, At least one of the positive electrode mixture layer and the negative electrode mixture layer <1> ~ <8> A secondary battery containing the powder described in any one of the following. [Effects of the Invention]

[0011] According to this disclosure, it is possible to provide a powder containing fibrous carbon that can be easily dispersed and can impart electronic conductivity to electrodes and the like with a small amount of addition, as well as a conductive additive, dispersion, conductive layer, electrode mixture layer, and secondary battery containing the powder. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an SEM image of the powder from Example 1. [Figure 2] This figure shows an SEM image of the powder from Example 2. [Figure 3] This figure shows an SEM image of the powder from Example 3. [Figure 4] This figure shows an SEM image of the powder of Comparative Example 1. [Figure 5] This is a cross-sectional view of a cell used for measuring compaction resistivity. [Modes for carrying out the invention]

[0013] 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.

[0014] 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 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 refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the terms “layer” or “film” include cases where, when the region in which the layer or film exists is observed, it is formed not only over the entire region but also over only a portion of the region. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together or detachable. In this disclosure, the term "contains" in reference to a specific component (e.g., a conductive additive, a dispersion, a conductive layer, an electrode mixture layer) means that it may contain other components in addition to that specific component. In this disclosure, the "conductive additive" is added to the electrode mixture layer to reduce the resistance of the electrode.

[0015] <Powder> The powder of this disclosure is a powder containing fibrous carbon having a structure in which tubular carbon hexagonal network surfaces are stacked in the direction of fiber thickness, wherein the average fiber diameter of the fibrous carbon is 110 nm to 300 nm, and when the powder is observed using a scanning electron microscope (SEM) at a magnification of 20,000 times, the average number of spherical carbon particles is 1 to 30, and the average maximum diameter of the spherical carbon particles is 0.30 μm or less. By using the powder of this disclosure, it can be easily dispersed in dispersions, conductive layers, electrode mixture layers, etc., and electron conductivity can be imparted to electrodes, etc., with a small amount of addition.

[0016] The powder of this disclosure comprises fibrous carbon and spherical carbon particles, wherein the average maximum diameter of the spherical carbon particles is 0.30 μm or less. In this disclosure, spherical carbon particles mean carbon particles having an aspect ratio (maximum diameter / minor diameter) of 1 to 3. The minor diameter means the length of the spherical carbon particle in a direction perpendicular to the direction of the maximum diameter. Furthermore, in configurations where particulate carbon is located at the tip or in the middle of fibrous carbon, if the outline of the particulate carbon can be determined and the aspect ratio of the particulate carbon is 1 to 3, it will be treated as a spherical carbon particle. However, if the fibrous carbon and particulate carbon are joined or integrated, and the outline of the particulate carbon cannot be determined, it will not be included in the definition of spherical carbon particles.

[0017] The spherical carbon particles contained in the powder of this disclosure are preferably particles generated during the production of fibrous carbon. The method for producing fibrous carbon is as described in the powder production method described later.

[0018] The powders of this disclosure may contain carbon materials other than fibrous carbon and spherical carbon particles. The shape of the other carbon materials is not particularly limited and may include flakes, particulates with a circularity of less than 0.90, etc.

[0019] The powder of this disclosure has an average number of spherical carbon particles of 1 to 30 when observed at a magnification of 20,000x using a scanning electron microscope (SEM). In other words, the powder is observed at a magnification of 20,000x using a scanning electron microscope (SEM), and the number of spherical carbon particles in one field of view is counted. This operation is repeated in a total of 64 locations (8 vertical x 8 horizontal locations in the central part of the observed powder), and the average number of spherical carbon particles in each field of view is calculated and taken as the average number of spherical carbon particles. Having an average number of spherical carbon particles of 1 or more increases the number of contact points when fibrous carbon forms a network within the electrode. From this viewpoint, an average number of spherical carbon particles of 2 or more is preferable, and 3 or more is more preferable. Furthermore, having an average number of spherical carbon particles of 30 or less does not reduce the number of contact points between fibrous carbon, which also contributes to the electronic conductivity of the electrode. From this viewpoint, an average number of spherical carbon particles of 20 or less is preferable, and 15 or less is more preferable.

[0020] The spherical carbon particles have an average maximum diameter of 0.3 μm or less as determined by SEM imaging. This average maximum diameter of 0.3 μm or less allows the spherical carbon particles to fill the gaps between secondary particles of the active material and act as contact points between fibrous carbon particles, thereby reducing electrode resistance. The average maximum diameter of the spherical carbon particles is preferably 0.28 μm or less, and more preferably 0.25 μm or less. The lower limit of the average maximum diameter of spherical carbon particles is not particularly limited and may be 0.1 μm or greater.

[0021] With respect to the spherical carbon particles contained in the powder of this disclosure, if multiple spherical carbon particles appear to form a single large mass through fusion, joining, etc., the mass will be counted as a single spherical carbon particle if its circularity is 0.90 or greater, and the maximum diameter of the mass will be considered as the maximum diameter of a single spherical carbon particle. Therefore, if the circularity of the mass is less than 0.90, the mass will not be counted as a single spherical carbon particle and will be excluded from the measurement of the average maximum diameter. Furthermore, spherical carbon particles whose entire outline is not visible in the SEM image will be excluded from the measurement of the average maximum diameter.

[0022] Here, the maximum diameter is the length of the longest line segment connecting two different points on the outline of the projection of the solid. The average maximum diameter of spherical carbon particles can be measured by the method described in the examples below.

[0023] 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 in which the longitudinal direction of the fibrous carbon can be confirmed (hereinafter also referred to as a "TEM longitudinal image") and an image in which the cross-section can be confirmed when the fibrous carbon 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 along the longitudinal direction exist inside the fibrous carbon, 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 fibrous carbon has a specific structure. Furthermore, by observing diffraction lines similar to those of graphite particles for the (002), (100), (101), (110), or (112) planes using X-ray diffraction (XRD), the structure in which carbon hexagonal mesh surfaces are stacked can be confirmed. The 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 so as 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, and only some of the central axes may be aligned. The shape of the cross-section of the tube is not limited to a perfect circle, but may be an ellipse, a polygon, etc., and a part of the outer circumference may be a perfect circle, ellipse, other curve, polygon, or a combination thereof (the above "closed curve" refers to such a shape. In these cases, the "central axis" is the line connecting the centroids of each cross-section). The structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction may be a structure in which the central axes of multiple cylindrical carbon hexagonal mesh surfaces with different maximum cross-sectional widths (for example, elliptical or polygonal cross-sections) are all arranged to coincide, or the central axes may not all be aligned, or only some of the central axes may be aligned.

[0024] The BET specific surface area of ​​the powder is 5 m². 2 / g~30m 2It is preferably / g, and from the viewpoint of battery characteristics, 10 m 2 / g to 20 m 2 / g is more preferable, and 11 m 2 / g to 19 m 2 / g is even more preferable, and 12 m 2 / g to 18 m 2 / g is particularly preferable, and 12.5 m 2 / g to 17 m 2 / g is extremely preferable. When the BET specific surface area of the powder is 5 m 2 / g to 30 m 2 / g, the fibrous carbon in the powder is sufficiently thin and easily dispersed, and a sufficiently low resistance can be obtained by adding only a small amount to the electrode. The BET specific surface area of the powder is calculated by the BET multipoint method using nitrogen as the adsorbed gas. Specifically, it can be measured by the method shown below. First, use NOVA2200e (registered trademark) manufactured by Quantachrome as the BET specific surface area measuring device, put 3 g of the sample into the sample cell (9 mm × 135 mm), dry it at 300 °C under vacuum conditions for 1 hour, and then perform the measurement. Use N2 as the gas for BET specific surface area measurement. Calculate the specific surface area by the BET three-point method from the nitrogen adsorption amounts when the relative pressure is 0.1, 0.2, and 0.3. At this time, calculate using the density of liquid nitrogen as 0.808 (g / cm 3 ), the volume of 1 mole of nitrogen in the standard state as 22.4133 L, and the atomic weight of nitrogen as 14.0067.

[0025] The d 002 of the powder is preferably 0.3370 nm to 0.3390 nm, more preferably 0.3373 nm to 0.3385 nm, and even more preferably 0.3375 nm to 0.3383 nm. d 002 approaching 0.3354 nm means approaching a more complete graphite crystal, and it is considered that the electron conductivity increases accordingly. Therefore, when the d 002 of the powder is 0.3390 nm or less, a lower-resistance electrode can be obtained. The d 002This refers to the average interplanar spacing d, which was determined by X-ray diffraction of powder, specifically by the JSPS method. 002 This means that, specifically, using a horizontal sample multi-purpose X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation), and following the JSPS method (Latest Experimental Techniques for Carbon Materials (Analysis and Analysis Edition), edited by the Carbon Materials Society), silicon powder was used as the internal standard. 002 Measurements will be taken.

[0026] The average fiber diameter of the fibrous carbon is 110 nm to 300 nm. An average fiber diameter of 110 nm or more allows for easy dispersion in the slurry during electrode coating. From this perspective, an average fiber diameter of 120 nm or more is preferable, and 130 nm or more is more preferable. The average fiber diameter of the fibrous carbon is 300 nm or less, which allows sufficient electronic conductivity to be imparted to the electrode with only a small amount of additive. From this viewpoint, the average fiber diameter is preferably 190 nm or less, more preferably 180 nm or less, and even more preferably 170 nm or less. The average fiber diameter of fibrous carbon can be measured by the method described in the examples below.

[0027] The average length of the fibrous carbon is preferably 1 μm to 20 μm, more preferably 2 μm to 15 μm, and even more preferably 3 μm to 10 μm. An average length of 1 μm or more of fibrous carbon allows for the imparting of electronic conductivity to the electrode with a small amount of additive. An average length of 20 μm or less allows for easy dispersion of the fibrous carbon. The average length of fibrous carbon can be measured by the method described in the examples below.

[0028] The fibrous carbon preferably contains network-forming fibers. Here, "network-forming fibers" refers to aggregates of filamentous material. Network-forming fibers are defined as fibrous carbon with a length of 7 μm or more, and which, when observed with a scanning electron microscope (SEM), overlap with other fibers or have a branched structure at some point. More specifically, if the length is confirmed to be 7 μm or more when observed with an SEM at 5000x magnification, and if, for example, when the fibrous carbon is observed at 5000 to 20,000x magnification, it can be determined that it is a network-forming fiber if it shows areas where it is intertwined with other fibrous carbon or where it is branched. Such fibrous carbon is particularly excellent at forming networks in electrodes and other environments, and therefore has a superior ability to impart electronic conductivity with small amounts of additive. Network-forming fibers can be formed, for example, by adjusting the additives used in the powder manufacturing method described later. For example, using sulfur, ethers, etc. as additives facilitates the formation of network-forming fibers, and the amount of network-forming fibers can be easily adjusted by adjusting the ratio of metal to sulfur component (e.g., S / Fe) contained in the catalyst precursor.

[0029] The powder disclosed herein is prepared to have low resistance when added to an electrode, with a concentration of 0.8 g / cm³. 3 The volume resistivity (also called compaction resistivity) when compressed is preferably 0.025 Ω·cm or less, more preferably 0.020 Ω·cm or less, and even more preferably 0.019 Ω·cm or less. The compaction resistivity can be measured as follows. First, use the measurement jig shown in Figure 5. Cell 4 is made of resin and has a bottom area of ​​(1 × 4) cm². 2 The depth is 10 cm. A copper electrode 3 for passing an electric current through the object to be measured 5 and a voltage measuring terminal 1 between the electrodes 3 are provided. A certain amount of sample is placed in the cell 4, and force is applied to the compression rod 2 from above to compress the sample. A current of 0.1 A is passed through the sample, and the bulk density is 0.8 g / cm³. 3 At this point, the voltage between the two voltage measuring terminals 1 inserted from the bottom of the container at a distance of 2.0 cm is read, and the resistivity ρ is calculated from the following formula. ρ = (E / 0.1) × S / 2 In the formula, ρ is the resistivity [Ω·cm], and S is the cross-sectional area (depth × width) in the direction of current flow in the sample = d × 1 [cm²]. 2 ], where E is the terminal voltage [V].

[0030] The powder of this disclosure is 0.8 g / cm³ 3 The pressure used for consolidation may be 0.8 MPa to 2.5 MPa, or 1.5 MPa to 2.3 MPa.

[0031] The powders of this disclosure preferably have an R value of 0.05 to 0.30 in the Raman spectrum. An R value of 0.05 or higher makes the fibrous carbon or spherical carbon particles in the powder more flexible, making them less likely to break when mixed or kneaded. From this viewpoint, an R value of 0.07 or higher is more preferable, and an R value of 0.09 or higher is even more preferable. When the R value is 0.30 or less, the fibrous carbon or spherical carbon particles in the powder have sufficient electronic conductivity. From this viewpoint, the R value is more preferably 0.25 or less, and even more preferably 0.20 or less. The R value can be determined by performing Raman spectroscopy on the powder under the following conditions. Micro-Raman spectroscopy system: LabRAM® HR Evolution, manufactured by Horiba, Ltd. Excitation wavelength: 532nm Exposure time: 10 seconds Number of times: 2 Diffraction grating: 300 lines / mm (600nm) Measurement sample: Using a micro spatula, place the powder onto a glass slide and ensure the powder is uniform. The measurement range should be wider than the range specified below. Measurement range: 80 μm (vertical) x 100 μm (horizontal) Number of points: 100 points were measured with a vertical feed of 17.8 μm and a horizontal feed of 22.2 μm. The average spectrum was obtained from these measurements, and the following analysis was performed. 1350cm -1 Nearby peak intensity (I D ) and (I GThe ratio of ) is the R value (ID / I G ) Furthermore, the peak intensity is defined as the height from the baseline to the peak top after baseline correction.

[0032] The powder of this disclosure may be used as a conductive additive, or in the preparation of dispersions, compositions for forming electrode mixture layers, or in the formation of a conductive layer, or an electrode mixture layer such as a positive electrode mixture layer or a negative electrode mixture layer.

[0033] <Method for manufacturing powders> The method for producing the powder described herein includes, for example, the following steps: (Step 1) Mix the carbon source, catalyst precursor, and additives to prepare a raw material mixture. (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.

[0034] <(Process 1)> In (Step 1), a carbon source, a catalyst precursor, and an additive are mixed to prepare a raw material mixture. The raw material mixture may be a liquid or a gas. To make it a gas, the raw material mixture may be preheated and vaporized, or components that are gaseous at room temperature may be used. In addition, the raw material mixture may have the catalyst precursor or additive dissolved in the carbon source, or the carbon source may be dispersed in the catalyst precursor or additive.

[0035] The carbon source is not particularly limited, but when a liquid raw material mixture is used, preferred examples include liquids containing carbon that are liquid at room temperature, such as benzene, toluene, styrene, xylene, cyclohexane, methanol, and ethanol. Examples of gaseous carbon sources at room temperature include hydrocarbon gases such as methane, ethylene, and acetylene, and gases such as CO and CO2. Multiple carbon sources may be used in combination.

[0036] 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.

[0037] The catalyst precursor may be one which generates fine iron, cobalt, or nickel particles of several nanometers to more than ten nanometers in a reactor under a reducing atmosphere such as hydrogen. Examples of catalyst precursors include organotransition metal compounds such as ferrocene, cobaltocene, and nickerosene, as well as oxides of transition metals, chlorides of transition metals, nitrates of transition metals, and sulfates of transition metals. The catalyst itself may be used instead of the catalyst precursor, or in combination with the catalyst precursor; for example, the aforementioned fine iron, cobalt, or nickel particles may be used.

[0038] 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.

[0039] Additives may contain sulfur. Examples of sulfur-containing additives include cyclic sulfur compounds such as thiophene, cyclopentanethiol, and dimethyl disulfide, as well as thiols and sulfides. Examples of additives that are gaseous at room temperature include sulfur compounds such as H2S and CH3SH.

[0040] The sulfur 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.

[0041] The additive may contain ethers. The additive may contain sulfur or ethers, or both. Examples of ethers include polyethers such as polypropylene glycol and ethylene glycol, cyclic ethers such as tetrahydrofuran, low molecular weight ethers such as diethyl ether (for example, ethers with a molecular weight of 100 or less), and polyethers with a molecular weight of 300 or more. Preferably, the ether is a polyether with a molecular weight of 300 or more.

[0042] Although the mechanism by which ethers work is not clear, the inventors surmise that they have some effect on the catalyst particles, as they adjust the size of the droplets of the carbon source or catalyst precursor to be suitable for the generation of fibrous carbon, and also because the thickness or shape of the generated fibrous carbon changes compared to the case without ethers.

[0043] Typically, a carrier gas is used to guide 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. From the viewpoint of the efficiency of fibrous carbon production, hydrogen or a mixture of hydrogen and an inert gas is preferred as the carrier gas.

[0044] <(Step 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.

[0045] 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.

[0046] <(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.

[0047] It is believed that the carbon source, catalyst precursor, and additives introduced into the reaction tube are each 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 carbon particles, and other materials.

[0048] It is believed that the carbon source and additives interact with the metal clusters in one of the following states: decomposition, partial decomposition, or an undecomposed state, and that fibrous carbon, spherical carbon particles, etc., are generated starting from the catalyst through a catalytic reaction.

[0049] <(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.

[0050] <Post-process> The powder obtained after step 4 may have a large amount of thermal decomposition products of the carbon source adhering to its surface, resulting in low electronic conductivity. Therefore, the powder may be carbonized by heating it in an inert atmosphere. This can increase 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 preferred temperature in the calcination step is 800°C to 1600°C. The calcination time can be determined by analyzing the exhaust gas and ending the process when the generated gas is no longer present.

[0051] Furthermore, the degree of graphitization of the powder may be increased by heating it 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. After the graphitization process, the powder may be reshaped by crushing.

[0052] <Conductive additive> The conductive additive of this disclosure includes the powder of this disclosure as described above. The aforementioned conductive additive can 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.

[0053] Other conductive additives used in combination with the powders of this disclosure include, in addition to 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.

[0054] When the powder of this disclosure is used in combination with other conductive additives, the content of the powder relative to the total of the powder and other conductive additives is preferably 1% to 100% by mass, more preferably 10% to 90% by mass, and even more preferably 20% to 80% by mass.

[0055] <Dispersion> The dispersion of this disclosure comprises the powder of this disclosure as described above. The dispersion of this disclosure may contain other components besides the powder, such as the aforementioned conductive additives, solvents, and dispersants.

[0056] Examples of solvents include water and organic solvents. Examples of organic solvents are not particularly limited, but include N-methyl-2-pyrrolidone (NMP), acetone, ethyl acetate, acetonitrile, tetrahydrofuran (THF), and dimethylformamide (DMF).

[0057] The dispersant is not particularly limited and includes polyvinylpyrrolidone (PVP), Triton X-100, sodium cholate, and the like.

[0058] The powder content 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.

[0059] The dispersant content is preferably 0.01% to 10% by mass relative to the total volume of the dispersion.

[0060] 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.

[0061] <Conductive layer> The conductive layer of this disclosure comprises the powder of this disclosure as described above. The conductive layer of this disclosure may contain components other than the powder of this disclosure, for example, a binder or, if necessary, additives, other conductive aids, etc. The conductive layer is provided on top of a metal foil current collector in a secondary battery, such as a lithium-ion secondary battery. By forming an electrode mixture layer on top of 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.

[0062] The powder content 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.

[0063] By having a powder content of 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.

[0064] The conductive layer of this disclosure may contain a binder. The binder included in the conductive layer is not particularly limited, and examples include binders used in secondary batteries such as lithium-ion secondary batteries. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethylcellulose (CMC), polyimide, polyamide-imide, and polyacrylic acid.

[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, the binder content is more preferably 10% by mass or more, and even more preferably 20% by mass or more.

[0066] 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.

[0067] <Electrode mixture layer> The electrode mixture layer of this disclosure comprises the powder of this disclosure as described above. 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.

[0068] In the electrode mixture layer of this disclosure, the powder content is preferably 1% to 10% by mass, more preferably 2% to 9% by mass, and even more preferably 3% to 8% by mass.

[0069] <Secondary battery> The secondary battery of the present disclosure comprises a positive electrode having a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, and a negative electrode having a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, wherein at least one of the positive electrode mixture layer and the negative electrode mixture layer contains the powder of the present disclosure.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] The aforementioned conductive layer may be provided between the positive electrode current collector and the positive electrode mixture layer, or between the negative electrode current collector and the negative electrode mixture layer.

[0074] [Positive electrode] The secondary battery of this disclosure comprises a positive electrode having a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector.

[0075] 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.

[0076] The positive electrode mixture layer may contain the powder of this disclosure. For example, a positive electrode mixture layer is formed on a positive electrode current collector by coating it with a positive electrode active material and the powder of the present disclosure, and further optionally containing carbon black, other conductive additives, a binder (for example, the binder described in the section on conductive layers), a solvent, etc., coating the slurry with the coating, drying it, and then pressing it.

[0077] 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 and safety.

[0078] The density of the positive electrode mixture layer is 2.0 g / cm³, from the viewpoint of energy density and safety. 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.

[0079] The basis weight of the positive electrode mixture layer is 10.0 mg / cm³, considering energy density and safety. 2 It may be greater than or equal to 10.0 mg / cm³. 2 ~30.0 mg / cm³ 2 That's fine.

[0080] 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.

[0081] (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.

[0082] The positive electrode active material is LiNi x Mn y Co z Al w It is preferable that the mixture contains O2 (x, y, z, w≧0, x+y+z+w=1) or LiMPO4 (where M is one or more selected from Fe, Co, Mn, and Ni).

[0083] LiRing x Mn y Co z Al w For O2(x, y, z, w≧0, x+y+z+w=1), it is preferable that the nickel content is relatively high, for example, x≧0.5 or higher, and Li(Ni x Mn y Co z It is more preferable that O2(x≧0.5, y≦0.3, z≦0.3, x+y+z=1). Li(Ni x Mn y Co z As a positive electrode active material represented by 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 is one example.

[0084] Examples of positive electrode active materials represented as LiMPO4 (where M is one or more selected from Fe, Co, Mn, and Ni) include LiFePO4, LiFe0.5 Mn 0.5 PO4, LiFe 0.3 Mn 0.7 PO4, LiCoPO4 and LiCo 0.5 Mn 0.5 PO4 is one example.

[0085] 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.

[0086] 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.

[0087] 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 0.5% by mass or more.

[0088] 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.

[0089] 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.

[0090] [Negative electrode] The secondary battery comprises a negative electrode which includes a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector.

[0091] 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, a copper foil is used as the negative electrode current collector.

[0092] The negative electrode binder layer may contain the powder of the present disclosure. For example, on the negative electrode current collector, a composition for a negative electrode binder layer (a kind of composition for forming an electrode binder layer) containing a negative electrode active material and the powder of the present disclosure, and further containing other conductive aids, a binder (for example, the binder described in the item of the conductive layer), a solvent, etc. is applied, the applied slurry is dried, and then pressed to form a negative electrode binder layer on the negative electrode current collector.

[0093] From the viewpoints of energy density and safety, the thickness of the negative electrode binder layer may be 30 μm or more, may be 50 μm to 100 μm, or may be 100 μm to 150 μm.

[0094] From the viewpoints of energy density and safety, the density of the negative electrode binder layer may be 3 1.3 g / cm 3 or more, and may be 3 1.5 g / cm

[0095] From the viewpoints of energy density and safety, the basis weight of the negative electrode binder layer may be 2 5.0 mg / cm 2 or more, and may be 2 10 mg / cm

[0096] (Negative electrode active material) The negative electrode binder 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, Li4Ti5O 12, 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 those described above (0 < x ≤ 1.5) and others such as (0 < x ≤ 1) can be mentioned. Among them, the negative electrode active material preferably contains graphite. Also, at least a part of the surface of the negative electrode active material may be coated with amorphous carbon. The negative electrode active material may be used alone or in combination of two or more.

[0097] <e In the negative electrode binder layer, the content of the negative electrode active material is preferably 70% to 99% by mass, more preferably 80% or more, even more preferably 90% or more, and still more preferably 95% or more from the viewpoint of the negative electrode capacity.

[0098] 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).

[0099] 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 still more preferably 0.5% by mass or more.

[0100] 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 still more preferably 2.0% by mass or less.

[0101] (Outer packaging material) 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.

[0102] (Separator) A secondary battery may include a separator between the positive and negative electrodes. The separator can be freely selected from those commonly used in secondary batteries, such as microporous films made of polyethylene or polypropylene. Separators containing particles such as SiO2 or Al2O3 as fillers, or separators with these particles attached to the surface, can also be used.

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

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

[0105] 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 mixed. 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.

[0106] (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.

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

[0108] 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 0.34 TiO2.94 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.

[0109] 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]

[0110] 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.

[0111] The physical properties of the powders obtained in the examples and comparative examples, as shown in Table 1, were measured by the method described below. The physical properties of powders other than those in Table 1 may also be measured by the method described below.

[0112] <Transmission electron microscope (TEM) observation of powders> The fibrous carbon contained in each powder from Examples 1-3 and the Comparative Example was dispersed in ethanol, scooped up with a microgrid, and dried to obtain the sample. The sample was then observed using TEM. The fibrous carbon contained in each powder of Examples 1-3 and the Comparative Example was confirmed to have a structure in which tubular carbon hexagonal network surfaces are stacked in the direction of fiber thickness, as described below. First, the powder was observed using TEM-EDX to obtain an image showing the longitudinal direction of the fibrous carbon (hereinafter also referred to as the "TEM longitudinal image") and an image showing the cross-section when the fibrous carbon is cut in a direction intersecting the longitudinal direction (hereinafter also referred to as the "TEM cross-sectional image"). The TEM longitudinal image showed that there were multiple lines along the longitudinal direction inside the fibrous carbon, and the TEM cross-sectional image showed that there were multiple closed curves with different maximum diameters arranged concentrically. Thus, the structure in which tubular carbon hexagonal network surfaces are stacked in the direction of fiber thickness in the fibrous carbon was confirmed. Device name: JEM-ARM200F (manufactured by JEOL Ltd.)

[0113] <Scanning electron microscope (SEM) observation of powder> (Measurement of spherical carbon particles) Double-sided carbon tape was attached to a sample stage for SEM observation, and powder approximately half the size of a microspatula was sprinkled on top of it. This was then observed using SEM. SEM images of the powders from Examples 1-3 and the comparative example are shown in Figures 1-4. The particles were observed at a magnification of 20,000x, and the number of spherical carbon particles in each field of view was counted. The average number of spherical carbon particles was then calculated in the same manner as described above. (Measurement of fiber diameter) Double-sided carbon tape was attached to the sample stage for SEM observation, and a powder equivalent to about half a microspatula was sprinkled on top of it. This was then observed using SEM. Observations were made at 20,000x magnification, and multiple SEM images were taken. 200 fibrous carbon fibers were randomly selected for diameter measurement. The average fiber diameter was determined by taking the arithmetic mean of these 200 fibers. The diameter of a fibrous carbon fiber is the dimension perpendicular to the direction in which the fiber extends. For each fibrous carbon fiber, the diameter was randomly measured at one point other than the ends, and this was taken as the diameter of that fibrous carbon fiber. (Measurement of fiber length) 50 mL of ethanol was placed in a screw-cap tube, and powder was added to about half a microspatula's worth. Ultrasonic treatment was performed for 15 minutes. After ultrasonic treatment, the dispersion was sprayed onto the non-glossy side of aluminum foil and air-dried. After air-drying, the aluminum foil was cut to a size that could fit on the sample stage for SEM observation, and the fibrous carbon on the aluminum foil was observed and photographed at a magnification that showed both ends. The length along the fiber axis was measured for 200 randomly selected fibers, and the average value was calculated. (Measurement of average maximum diameter) Using a scanning electron microscope (SEM), the powder was observed at 20,000x magnification, and photographs of randomly selected fields of view were taken. These were used to measure the average maximum diameter of the spherical carbon particles. Measurements of spherical carbon particles were continued by shifting the field of view as described above until a total of 20 spherical carbon particles were found. ImageJ (National Institutes of Health, USA) was used as the image analysis software. Scanning electron microscope: JSM-7600F, manufactured by JEOL Ltd.

[0114] <Preparation of samples for resistance measurement> As the positive electrode active material, 97 parts by mass of LiCoO2 (50% diameter in the cumulative particle size distribution based on volume, D50 = 38 μm), 2 parts by mass of a conductive additive such as the powder obtained in the examples or comparative examples, 1 part by mass of PVDF as a binder, and N-methyl-2-pyrrolidone (NMP, manufactured by Kishida Chemical Co., Ltd.) was added as appropriate as a solvent for slurry preparation to make a slurry. The mixture was kneaded using a foam remover mixer (Sinky Co., Ltd., ARE-100). The obtained slurry was spread onto cardboard using a doctor blade with a gap of 50 μm and dried. A sample measuring 3 cm in length and 5 cm in width was cut from this and used as the measurement sample.

[0115] <Resistance Measurement> The volume resistivity of the above-mentioned samples was measured and compared using a resistivity meter, the Rolester GP (manufactured by Dia Instruments Co., Ltd.). The evaluation criteria are as follows; a score of A or B indicates good resistance evaluation. A: Sufficiently low (less than 10Ω·cm) B: Low (10Ω·cm or more, less than 30Ω·cm) C: Slightly high (30Ω·cm or more, less than 50Ω·cm) D: High (50Ω·cm or more, less than 100Ω·cm) E: Quite high (100Ω·cm or more)

[0116] <Preparation of powders> The powders of the examples and comparative examples were prepared as shown below.

[0117] (Example 1) A raw material mixture was prepared by mixing 0.083% by mass of ferrocene (powder, purity >98%), 0.022% by mass of sulfur (powder, purity 99.99%), 0.31% by mass of polypropylene glycol (D-400, manufactured by Nippon Oil & Fats Co., Ltd., molecular weight: 400, decomposition temperature: 290°C), and 99.585% by mass of benzene. This mixture was transported using a pump at a benzene flow rate of 0.11 g / min and sprayed from the top of a vertical reaction tube using a triple-tube nozzle. The carrier gas was hydrogen at a flow rate of 946 NmL / min. The temperature inside the reaction tube was 1250°C. After 10 minutes of reaction, the supply of the raw material mixture was stopped, the gas was switched from carrier gas to nitrogen gas, and the furnace was cooled. After cooling to room temperature, the gas was stopped, the reaction tube was opened, and the product was recovered. After extracting a small sample necessary for SEM observation and other purposes from the recovered product, it was placed back into the furnace and heated to 1000°C while flowing nitrogen gas through it. It was maintained at 1000°C for 30 minutes, then cooled and the product was recovered. Subsequently, the recovered powder was placed in a graphitization furnace and heated to 2800°C while argon gas was flowed through it. After holding it at 2800°C for 30 minutes, the temperature was lowered and the product was recovered. This was then lightly crushed in a mixer.

[0118] (Example 2) The reaction was carried out in the same manner as in Example 1, except that a raw material mixture was prepared by mixing 0.125% by mass of sulfur and 99.482% by mass of benzene.

[0119] (Comparative Example 1) The reaction was carried out in the same manner as in Example 1, except that a raw material mixture was prepared by mixing 0% by mass of sulfur and 99.607% by mass of benzene.

[0120] (Comparative Example 2) The reaction was carried out in the same manner as in Example 1, except that the mixture consisted of 7% by mass of ferrocene, 3% by mass of polypropylene glycol, 0.4% by mass of sulfur, and 89.6% by mass of benzene.

[0121] (Comparative Example 3) The reaction was carried out in the same manner as in Example 1, except that a raw material mixture was prepared by mixing 0.045% by mass of sulfur and 99.562% by mass of benzene.

[0122] [Table 1]

[0123] As shown in Table 1, using the powders of Examples 1 and 2 resulted in lower resistance than when using the powders of Comparative Examples 1 to 3.

Claims

1. A powder containing fibrous carbon having a structure in which tubular carbon hexagonal network surfaces are stacked in the direction of fiber thickness, wherein the average fiber diameter of the fibrous carbon is 110 nm to 300 nm, and when the powder is observed using a scanning electron microscope (SEM) at a magnification of 20,000 times, the average number of spherical carbon particles is 1 to 30, and the average maximum diameter of the spherical carbon particles is 0.30 μm or less.

2. The powder according to claim 1, wherein the fibrous carbon includes network-forming fibers.

3. The powder according to claim 1, wherein the average length of the fibrous carbon is 1 μm to 20 μm.

4. The powder d ００２ The powder according to claim 1, wherein the wavelength is 0.3370 nm to 0.3390 nm.

5. The powder according to claim 1, wherein the spherical carbon particles are particles generated during the production of the fibrous carbon.

6. 0.8 g / cm ３ The powder according to claim 1, wherein the pressure used for compaction is 0.8 MPa to 2.5 MPa.

7. 0.8 g / cm ３ The powder according to claim 1, wherein the volume resistivity when compacted is 0.025 Ω·cm or less.

8. The powder according to claim 1, wherein the R value in the Raman spectrum is 0.05 to 0.

30.

9. A conductive additive comprising the powder described in any one of claims 1 to 8.

10. A dispersion containing the powder according to any one of claims 1 to 8.

11. A conductive layer comprising the powder described in any one of claims 1 to 8.

12. An electrode mixture layer comprising the powder described in any one of claims 1 to 8.

13. A positive electrode comprising a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, and a negative electrode comprising a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, A secondary battery comprising at least one of the positive electrode mixture layer and the negative electrode mixture layer, which is the powder described in any one of claims 1 to 8.

Images