Powder, Conductive Aid, Dispersion, Conductive Layer, Electrode Composite Layer, and Secondary Battery

Abstract

Provided is a powder containing fibrous carbon that can be easily dispersed and can impart electron conductivity to an electrode or the like with a small addition amount. 【Solution means】A powder containing fibrous carbon having a structure in which cylindrical carbon hexagonal net surfaces are laminated in the fiber thickness direction, wherein the average fiber diameter of the fibrous carbon is 110 nm to 300 nm, and when the powder is observed at a magnification of 20,000 times using a scanning electron microscope (SEM), the average value of the 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] The present disclosure relates to a powder, a conductive assistant, a dispersion liquid, a conductive layer, an electrode binder layer, and a secondary battery.

Background Art

[0002] Secondary batteries take advantage of the characteristics of being small, lightweight, and having a high voltage, and are widely used in electronic devices such as notebook PCs, mobile phones, smartphones, and tablet PCs. In recent years, against the backdrop of environmental issues, secondary batteries such as lithium-based secondary batteries have become popular in electric vehicles (EVs) that run solely on batteries and hybrid electric vehicles (HEVs) that combine a gasoline engine and a battery.

[0003] Carbon fibers such as vapor-grown carbon fibers have conventionally been used as conductive assistants 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, particles, 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 a high yield with a small amount of catalyst.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Mixing non-fibrous carbon as described in Patent Document 1 is a preferable aspect from the viewpoint of imparting conductivity to, for example, the electrodes of a lithium-ion secondary battery. However, the content of non-fibrous carbon needs to be precisely controlled. Further, the fiber diameter of the fine carbon fibers produced in Patent Document 1 is about 80 nm. Generally, carbon fibers with a fiber diameter of 100 nm or less tend to aggregate, and it may not be easy to obtain a desired dispersed state in the electrode slurry of a lithium-ion secondary battery. Therefore, a device capable of inputting a larger amount of energy is required to achieve a desired dispersed state of the fine carbon fibers.

[0006] It is also difficult to achieve a desired dispersed state in the electrode slurry for the highly branched carbon fibers described in Patent Document 2, and a device capable of inputting a larger amount of energy is required to achieve a desired dispersed state.

[0007] Furthermore, the fiber diameter of the carbon fibers produced in Patent Document 3 is about 100 nm, and it may not be easy to obtain a desired dispersed state in the electrode slurry of a lithium-ion secondary battery. Therefore, a device capable of inputting a larger amount of energy is required to achieve a desired dispersed state of the carbon fibers.

[0008] From the above points, fibrous carbon that can be easily dispersed and can impart electronic conductivity to electrodes and the like with a small addition amount is desirable.

[0009] The present disclosure has been made in view of the above circumstances, and an object thereof is 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 addition amount, a conductive auxiliary agent, a dispersion liquid, a conductive layer, an electrode mixture layer, and a secondary battery containing the powder.

Means for Solving the Problems

[0010] Specific means for achieving the above problems are as follows. <1> A powder containing fibrous carbon having a structure in which cylindrical carbon hexagonal network planes are laminated in the fiber thickness direction, wherein the average fiber diameter of the fibrous carbon is 110 nm to 300 nm, and when the powder is observed at a magnification of 20,000 times using a scanning electron microscope (SEM), the average value of the 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 <1>, wherein the fibrous carbon contains network-forming fibers. <3> The powder according to <1> or <2>, wherein the average length of the fibrous carbon is 3 μm to 20 μm. <4> The d 002 of the powder is 0.3370 nm to 0.3390 nm, which is the powder according to any one of <1> to <3>. <5> The powder according to any one of <1> to <4>, wherein the spherical carbon particles are particles generated during the production of the fibrous carbon. <6> The pressure when compressing to 0.8 g / cm 3 is 0.8 MPa to 2.5 MPa, which is the powder according to any one of <1> to <5>. <7> The volume resistivity when compressed to 0.8 g / cm 3 is 0.025 Ω·cm or less, which is the powder according to any one of <1> to <6>. <8> The R value in the Raman spectrum is 0.05 to 0.30, which is the powder according to any one of <1> to <7>. <9> A conductive auxiliary agent containing the powder according to any one of <1> to <8>. <10> A dispersion liquid containing the powder according to any one of <1> to <8>. <11> A conductive layer containing the powder according to any one of <1> to <8>. <12> An electrode mixture layer containing the powder according to any one of <1> to <8>. <13> A positive electrode including a positive electrode current collector and a positive electrode mixture layer including a positive electrode active material disposed on the positive electrode current collector, and a negative electrode including a negative electrode current collector and a negative electrode mixture layer including a negative electrode active material disposed on the negative electrode current collector. A secondary battery in which at least one of the positive electrode active material layer and the negative electrode active material layer contains the powder described in any one of <1> to <8>.

Advantages of the Invention

[0011] According to the present disclosure, it is possible to provide a powder containing fibrous carbon that can be easily dispersed and can impart electron conductivity to an electrode or the like with a small addition amount, a conductive auxiliary agent containing the powder, a dispersion liquid, a conductive layer, an electrode active material layer, and a secondary battery.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present disclosure.

[0014] In the present disclosure, the term "step" includes not only a step independent of other steps but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. In the present disclosure, the numerical range indicated by using "~" includes the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content rate or content of each component means the total content rate or content of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may contain a plurality of types. When there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component means a value for the mixture of the plurality of types of particles present in the composition, unless otherwise specified. In the present disclosure, the terms "layer" or "film" include cases where, when observing the region where the layer or film is present, it is formed not only over the entire region but also only in a part of the region. In the present disclosure, the term "lamination" indicates stacking layers, and two or more layers may be bonded or two or more layers may be detachable. In the present disclosure, the term "including" in a specific component (for example, a conductive auxiliary agent, a dispersion, a conductive layer, an electrode binder layer) means that other components other than the specific component may be included. In the present disclosure, the "conductive auxiliary agent" is added to the electrode binder layer to reduce the resistance of the electrode.

[0015] <Powder> The powder of the present disclosure is a powder containing fibrous carbon having a structure in which cylindrical carbon hexagonal net planes are laminated in the thickness direction of the fiber, the average fiber diameter of the fibrous carbon is 110 nm to 300 nm, and when the powder is observed at a magnification of 20,000 times using a scanning electron microscope (SEM), the average value of the 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 the present disclosure, it can be easily dispersed in a dispersion liquid, a conductive layer, an electrode binder layer, etc., and electron conductivity can be imparted to an electrode, etc. with a small addition amount.

[0016] The powder of the present disclosure contains fibrous carbon and spherical carbon particles, and the average maximum diameter of the spherical carbon particles is 0.30 μm or less. In the present disclosure, the spherical carbon particles mean carbon particles having an aspect ratio (maximum diameter / minimum diameter) of 1 to 3. The minimum diameter means the length of the spherical carbon particles in a direction orthogonal to the direction of the maximum diameter. Also, regarding the mode in which particulate carbon is located at the tip, in the middle, etc. of the fibrous carbon, if the contour of the particulate carbon can be determined and the aspect ratio of the particulate carbon is 1 to 3, it is treated as spherical carbon particles. However, when the fibrous carbon and the particulate carbon are joined or integrated and the contour of the particulate carbon cannot be determined, it is not included in the spherical carbon particles referred to here.

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

[0018] The powder of the present disclosure may contain other carbon materials in addition to the fibrous carbon and the spherical carbon particles. The shape of the other carbon materials is not particularly limited, and examples include flaky shapes and particulate shapes with a circularity of less than 0.90.

[0019] When the powder of the present disclosure is observed at a magnification of 20,000 times using a scanning electron microscope (SEM), the average value of the number of spherical carbon particles is 1 to 30. In other words, the powder is observed at a magnification of 20,000 times using a scanning electron microscope (SEM), and the number of spherical carbon particles in one field of view is counted. This operation is repeated a total of 64 times (8 positions vertically × 8 positions horizontally in the central part of the powder to be observed), and the average value of the number of spherical carbon particles in the counted one field of view is obtained, which is taken as the average value of the number of spherical carbon particles. When the average value of the number of spherical carbon particles is 1 or more, the number of contact points increases when fibrous carbon forms a network in the electrode. From this viewpoint, the average value of the number of spherical carbon particles is preferably 2 or more, more preferably 3 or more. Also, when the average value of the number of spherical carbon particles is 30 or less, the contact points between fibrous carbons are not reduced, which also contributes to the electron conductivity of the electrode. From this viewpoint, the average value of the number of spherical carbon particles is preferably 20 or less, more preferably 15 or less.

[0020] The average maximum diameter of the spherical carbon particles is 0.3 μm or less according to the SEM image. When the average maximum diameter is 0.3 μm or less, the spherical carbon particles can enter the gaps between the secondary particles of the active material or act as contact points between fibrous carbons, so that the resistance of the electrode can be reduced. The average maximum diameter of the spherical carbon particles is preferably 0.28 μm or less, more preferably 0.25 μm or less. The lower limit of the average maximum diameter of the spherical carbon particles is not particularly limited, and it may be 0.1 μm or more.

[0021] Regarding the spherical carbon particles contained in the powder of the present disclosure, when a plurality of spherical carbon particles seem to form a large lump by fusion, bonding, etc., when the roundness of the lump is 0.90 or more, the lump is counted as one spherical carbon particle, and the maximum diameter of the lump is regarded as the maximum diameter of one spherical carbon particle. Therefore, when the roundness of the lump is less than 0.90, the lump is not counted as one spherical carbon particle and is excluded from the measurement of the average maximum diameter. In addition, in the SEM image, spherical carbon particles whose entire contour cannot be seen are 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 contour of the projection view of the solid. The average maximum diameter of the spherical carbon particles can be measured by the method described in the examples below.

[0023] In the present disclosure, the structure in which cylindrical carbon hexagonal net planes are stacked in the thickness direction refers to a structure in which a structure formed by winding carbon hexagonal net planes into a cylindrical shape is stacked in the thickness direction (also referred to as a specific structure). The specific structure can be confirmed, for example, by observing the powder with a transmission electron microscope (TEM) as follows. Observe an image in which the longitudinal direction of fibrous carbon can be confirmed (hereinafter, also referred to as a "TEM longitudinal image") and an image in which a 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"). Then, in the TEM longitudinal image, when there are a plurality of lines along the longitudinal direction inside the fibrous carbon, and in the TEM cross-sectional image, when there are a plurality of closed curves with different maximum diameters, and the closed curves are arranged in order on the inner side as the maximum diameter decreases, it can be confirmed that the fibrous carbon has a specific structure. Further, in the X-ray diffraction method (XRD), a structure in which carbon hexagonal net planes are stacked can be confirmed by confirming diffraction lines similar to those of graphite particles for the planes of (002), (100), (101), (110), or (112). The structure in which cylindrical carbon hexagonal net planes are stacked in the thickness direction may be a structure in which a plurality of cylindrical carbon hexagonal net planes with different diameters are arranged in a concentric circular cross-section (such as a concentric multi-tube), and for a plurality of cylindrical carbon hexagonal net planes with different diameters, the central axes (lines connecting the centers of each of the cross-sections of a cylinder) may not all be aligned, or only a part of the central axes may be aligned. The shape of the cross-section of the cylinder is not limited to a perfect circle, and may be an elliptical shape, a polygonal shape, etc., and a part of the outer periphery may be a perfect circle, an ellipse, other curves, a polygonal shape, or a combination thereof (the above-mentioned "closed curve" refers to such a shape. Also, in these cases, the "central axis" is a line connecting the centroids of each of the cross-sections). The structure in which cylindrical carbon hexagonal net planes are stacked in the thickness direction may be a structure in which the central axes of a plurality of cylindrical (for example, the cross-section is an elliptical shape, a polygonal shape) carbon hexagonal net planes with different maximum widths of the cross-section are all aligned, or the central axes may not all be aligned, or only a part of the central axes may be aligned.

[0024] The BET specific surface area of the powder is 5 m 2 / g to 30 m 2It is preferably / g, and from the viewpoint of battery characteristics, it is 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 dispersible, 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 perfect 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 002refers to the average interplanar spacing d determined by the X-ray diffraction method for powders, specifically the Gakushin method. 002 Specifically, using a sample horizontal multi-purpose X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation), in accordance with the Gakushin method (Latest Carbon Material Experimental Techniques (Analysis and Analysis Edition), edited by the Carbon Materials Society), silicon powder is used as an internal standard to measure d 002 .

[0026] The average fiber diameter of the fibrous carbon is 110 nm to 300 nm. When the average fiber diameter is 110 nm or more, it can be easily dispersed in the slurry when coating the electrode. From this perspective, the average fiber diameter is preferably 120 nm or more, and more preferably 130 nm or more. When the average fiber diameter of the fibrous carbon is 300 nm or less, sufficient electron conductivity can be imparted with a small addition amount to the electrode. From this perspective, 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 the 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. When the average length of the fibrous carbon is 1 μm or more, electron conductivity can be imparted to the electrode with a small addition amount. When the average length of the fibrous carbon is 20 μm or less, the fibrous carbon can be easily dispersed. The average length of the fibrous carbon can be measured by the method described in the examples below.

[0028] The fibrous carbon preferably contains network-forming fibers. Here, the "network-forming fiber" refers to an aggregate of filamentous substances. The network-forming fiber refers to one having a structure in which the length of the fibrous carbon is 7 μm or more and it overlaps with another fiber or branches at some point when observed by SEM. More specifically, when observed at a magnification of 5000 times by SEM, it is confirmed that the length is 7 μm or more, and when the fibrous carbon is observed at, for example, 5000 to 20,000 times, if a location where it is intertwined with another fibrous carbon or a branched location can be confirmed, it can be determined that it is a network-forming fiber. Such fibrous carbon is particularly excellent in network formation in electrodes and the like, and thus has an excellent ability to impart electron conductivity with a small addition amount. The network-forming fiber can be formed, for example, by adjusting an additive used in the powder manufacturing method described later. As an example, by using sulfur, ethers, etc. as the additive, it becomes easier to form network-forming fibers, and by adjusting the ratio of the metal contained in the catalyst precursor to the sulfur component (for example, S / Fe), it becomes easier to adjust the amount of network-forming fibers.

[0029] From the viewpoint of achieving low resistance when the powder of the present disclosure is added to an electrode, it is preferable that the volume resistivity (also referred to as the consolidated resistivity) when the powder is compressed to 0.8 g / cm 3 is 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 consolidated resistivity can be measured as follows. First, use the measurement jig shown in FIG. 5. The cell 4 is made of resin, and the inside has a bottom area of (1×4) cm 2 and a depth of 10 cm. It is provided with a copper electrode 3 for passing an electric current through the object to be measured 5 and voltage measurement terminals 1 between the electrodes 3. Put a certain amount of sample into the cell 4, apply a force to the compression rod 2 from above to compress the sample. Pass a current of 0.1 A through the sample, and when the bulk density reaches 0.8 g / cm 3 , read the voltage between 2.0 cm of the two voltage measurement terminals 1 inserted from the bottom of the container, and calculate the resistivity ρ from the following formula. ρ = (E / 0.1) × S / 2 In the formula, ρ is the specific resistance [Ω·cm], S is the cross-sectional area (depth × width) = d × 1 [cm 2 in the direction in which current flows through the sample, and E is the voltage between terminals [V].

[0030] When consolidating the powder of the present disclosure to 0.8 g / cm 3 The pressure may be 0.8 MPa to 2.5 MPa, or may be 1.5 MPa to 2.3 MPa.

[0031] The powder of the present disclosure preferably has an R value in the Raman spectrum of 0.05 to 0.30. When the R value is 0.05 or more, the fibrous carbon or spherical carbon particles in the powder become flexible, so they are less likely to be broken when mixed or kneaded. From this viewpoint, the R value is more preferably 0.07 or more, and even more preferably 0.09 or more. When the R value is 0.30 or less, the fibrous carbon or spherical carbon particles in the powder have sufficient electron conductivity. From this viewpoint, the R value is more preferably 0.25 or less, and even more preferably 0.20 or less. Raman spectroscopic analysis of the powder can be performed under the following conditions to obtain the R value. Micro Raman spectroscopic measurement device: LabRAM (registered trademark) HR Evolution manufactured by Horiba, Ltd. Excitation wavelength: 532 nm Exposure time: 10 seconds Number of integrations: 2 times Diffraction grating: 300 lines / mm (600 nm) Measurement sample: Using a microspatula, place the powder on a glass preparation plate so that the powder becomes uniform. Make it wider than the following measurement range. Measurement range: 80 μm in length × 100 μm in width Number of points: Perform 100-point measurement with a vertical feed of 17.8 μm and a horizontal feed of 22.2 μm, obtain a spectrum obtained by averaging them, and perform the following analysis. 1350 cm -1 Peak intensity (I D ) and (I GLet the ratio of (ID / I G ) be the R value (ID / I Note that after correcting the baseline, the height from the baseline to the peak top is defined as the peak intensity.

[0032] The powder of the present disclosure may be used for conductive aids and the like, may also be used for the preparation of dispersion liquids, electrode binder layer forming compositions, etc., and may also be used for the formation of a conductive layer or an electrode binder layer such as a positive electrode binder layer or a negative electrode binder layer.

[0033] <Method for manufacturing powder> The method for manufacturing the powder of the present disclosure includes, for example, the following steps. (Step 1) Mix a carbon source, a catalyst precursor, and an additive to prepare a raw material mixture. (Step 2) Heat the reaction furnace to a predetermined temperature. (Step 3) Introduce the raw material mixture into the reaction furnace using a carrier gas to generate powder. (Step 4) Recover the powder.

[0034] <(Step 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 liquid or gaseous. To make it gaseous, the raw material mixture may be heated in advance to vaporize it, or components that are gaseous at room temperature may be used. Also, in the raw material mixture, the catalyst precursor or additive may be 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. When the raw material mixture is liquid, preferably, liquids containing carbon that are liquid at room temperature, such as benzene, toluene, styrene, xylene, cyclohexane, methanol, ethanol, etc., are exemplified. As carbon sources that are gaseous at room temperature, hydrocarbon gases such as methane, ethylene, acetylene, and gases such as CO and CO2 are exemplified. A plurality of types of carbon sources may be mixed and used.

[0036] The content rate of the carbon source in the raw material mixture is preferably such that the content rate of the carbon contained in the carbon source is 50% by mass to 99.9% by mass with respect to the total amount of the raw material mixture, more preferably 60% by mass to 99.8% by mass, still more preferably 70% by mass to 99.7% by mass, and particularly preferably 80% by mass to 99.6% by mass.

[0037] As the catalyst precursor, those that generate fine iron, cobalt, or nickel particles with a size of several nm to a dozen or so nm in a reactor under a reducing atmosphere such as hydrogen may be used. Examples of the catalyst precursor include organotransition metal compounds such as ferrocene, cobaltocene, and nickelocene, oxides of transition metals, chlorides of transition metals, nitrates of transition metals, and sulfates of transition metals. Instead of the catalyst precursor or in combination with the catalyst precursor, the catalyst itself may be used. For example, the aforementioned fine iron, cobalt, or nickel particles may be used.

[0038] The content rate of the catalyst precursor in the raw material mixture is preferably such that the content rate of the metal component contained in the catalyst precursor is 0.001% by mass to 10% by mass with respect to the total amount of the raw material mixture, more preferably 0.01% by mass to 5% by mass, and still more preferably 0.1% by mass to 3% by mass.

[0039] The additive may contain sulfur. Examples of the sulfur-containing additive include cyclic sulfur compounds such as thiophene, cyclopentanethiol, and dimethyldisulfide, thiols, and sulfides. Examples of the additive that is a gas at normal temperature include sulfur compounds such as H2S and CH3SH.

[0040] The content rate of sulfur in the raw material mixture is preferably 0.01% by mass to 1% by mass, more preferably 0.015% by mass to 0.5% by mass, and still more preferably 0.0225% by mass 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 ethers are polyethers with a molecular weight of 300 or more.

[0042] Although the mechanism by which ethers act is not clear, the inventors speculate that the size of the droplets of the carbon source or catalyst precursor is adjusted to be suitable for the formation of fibrous carbon, and in addition, the thickness or shape of the fibrous carbon produced changes compared to the case without addition, so it has some effect on the catalyst particles.

[0043] Generally, a carrier gas is used to accompany the raw material mixture and introduce the raw material mixture into the reaction tube. The type of carrier gas is not limited, and examples include inert gases such as hydrogen and argon, and gas mixtures of hydrogen and inert gases. From the perspective of the production efficiency of fibrous carbon, the carrier gas is preferably hydrogen or a gas mixture of hydrogen and an inert gas.

[0044] <(Step 2)> In Step 2, the reaction furnace is heated to a predetermined temperature. In one embodiment, a vertical furnace is used. In addition, the shape of the reaction furnace is not particularly limited as long as it can react.

[0045] The temperature of the heating zone of the reaction furnace 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, the raw material mixture is introduced into the reaction furnace using a carrier gas to generate powder. A method of spraying the liquid or slurry raw material mixture from a spray nozzle using a carrier gas may be employed, or the vaporized raw material mixture may be introduced into the reaction tube using a carrier gas.

[0047] It is considered that the carbon source, catalyst precursor, and additive introduced into the reaction tube are each decomposed. Among them, when the catalyst precursor decomposes, metal clusters are generated in the gas phase, and this is considered to be the catalyst for the formation reaction of fibrous carbon, spherical carbon particles, etc.

[0048] The carbon source and additive interact with the metal clusters in any of the states of being decomposed, partially decomposed, or not decomposed, and it is considered that fibrous carbon, spherical carbon particles, etc. are generated starting from the catalyst by a catalytic reaction.

[0049] <(Step 4)> In Step 4, the generated powder is recovered. In a vertical reaction furnace, the powder that has fallen down may be continuously carried out, or in a batch furnace, the furnace may be cooled and the reaction tube may be opened and then recovered. The powder may be transported with an inert gas.

[0050] <Subsequent process> The powder obtained after Step 4 has a large amount of pyrolyzate of the carbon source adhering to its surface, and its electron conductivity may be low. Therefore, the powder may be carbonized by heating it in an inert atmosphere. Thereby, the electron conductivity of the powder can be increased. This step is also referred to as the "firing step". Examples of the inert atmosphere in the firing step include nitrogen, argon, etc. The temperature in the firing step is preferably 800°C to 1600°C. The firing time can be determined by analyzing the exhaust gas and taking the point when the generated gas disappears as the end point.

[0051] Furthermore, after the firing step, by heating in an inert atmosphere, the graphitization degree of the powder may be increased. Thereby, the electron conductivity of the powder can be further increased, the chemical stability can be ensured, and the catalytic metal mixed in the product can be evaporated and removed. This step is also referred to as the "graphitization step". The temperature in the graphitization step is preferably 2500°C to 3300°C. The time in the graphitization step is not particularly limited and is usually several seconds to several hours. After the graphitization step, the shape of the powder may be adjusted by crushing.

[0052] <Conductive aid The conductive aid of the present disclosure contains the powder of the present disclosure described above. The said conductive aid can be used as a conductive aid in secondary batteries such as lithium ion secondary batteries. As a conductive aid for secondary batteries, generally carbon black such as acetylene black is used, but it may be used in combination with carbon black and the powder of the present disclosure, or the powder of the present disclosure may be used instead of carbon black.

[0053] Other conductive aids used in combination with the powder of the present disclosure include, in addition to carbon black, multi-walled carbon nanotubes (MWCNT), single-walled carbon nanotubes (SWCNT), graphene, graphite particles, amorphous carbon, and the like. Other conductive aids may be used alone or in combination of two or more.

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

[0055] <Dispersion liquid The dispersion liquid of the present disclosure contains the powder of the present disclosure described above. The dispersion liquid of the present disclosure may contain other components other than the powder, and examples of the other components include the other conductive aids, solvents, dispersants, etc. described above.

[0056] Examples of the solvent include water, organic solvents, etc. The organic solvent is not particularly limited, and examples include N-methyl-2-pyrrolidone (NMP), acetone, ethyl acetate, acetonitrile, tetrahydrofuran (THF), and dimethylformamide (DMF).

[0057] The dispersant is not particularly limited, and examples thereof include polyvinylpyrrolidone (PVP), Triton X-100, and sodium cholate.

[0058] The content of the powder is preferably 0.1% by mass to 30% by mass, more preferably 0.5% by mass to 20% by mass, and even more preferably 1% by mass to 10% by mass with respect to the total amount of the dispersion liquid.

[0059] The content of the dispersant is preferably 0.01% by mass to 10% by mass with respect to the total amount of the dispersion liquid.

[0060] When the powder of the present disclosure is used in combination with other conductive aids, the content of the powder with respect to the total of the powder and other conductive aids in the dispersion liquid of the present disclosure may be 1% by mass to 100% by mass, may be 10% by mass to 90% by mass, or may be 20% by mass to 80% by mass. Considering the stability of the dispersion liquid, the resistance when forming an electrode binder layer, etc., the above-mentioned content is appropriately adjusted.

[0061] <Conductive layer> The conductive layer of the present disclosure contains the powder of the present disclosure described above. The conductive layer of the present disclosure may contain components other than the powder of the present disclosure. For example, it may contain a binder, additives as required, other conductive aids, etc. The conductive layer is provided, for example, on a metal foil that is a current collector in a secondary battery such as a lithium ion secondary battery. By forming an electrode binder layer on the conductive layer, it is possible to achieve a lower resistance and an improvement in adhesion compared to the case where the electrode binder layer and the current collector are in direct contact.

[0062] The content of the powder is preferably 1% by mass to 60% by mass with respect to the total mass of the conductive layer. When the content of the powder described above is 1% by mass or more, a sufficiently low resistance can be obtained. From the viewpoint of low resistance, the content of the powder described above is more preferably 10% by mass or more, and even more preferably 20% by mass or more.

[0063] Since the content of the aforementioned powder is 60% by mass or less, the detachment of the powder from the conductive layer can be suppressed. From the viewpoint of suppressing the detachment of the powder, the content of the aforementioned powder is more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0064] The conductive layer of the present disclosure may contain a binder. The binder contained in the conductive layer is not particularly limited, and examples thereof include binders used in secondary batteries such as lithium ion secondary batteries. Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyimide, polyamideimide, polyacrylic acid, and the like.

[0065] The content of the binder is preferably 5% by mass to 80% by mass based on the total mass of the conductive layer. When the content of the binder is 5% by mass or more, it is easy to form into a layer and powder shedding can be suppressed. From the viewpoints of moldability and suppression of powder shedding, the content of the aforementioned binder is more preferably 10% by mass or more, and even more preferably 20% by mass or more.

[0066] Since the content of the aforementioned binder is 80% by mass or less, the resistance of the conductive layer can be suppressed. From the viewpoint of low resistance, the content of the aforementioned binder is more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0067] <Electrode binder layer> The electrode binder layer of the present disclosure contains the aforementioned powder of the present disclosure. Examples of the electrode binder layer include a positive electrode binder layer and a negative electrode binder layer. The forms of the positive electrode binder layer and the negative electrode binder layer will be described in the section on secondary batteries below.

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

[0069] <Secondary battery> The secondary battery of the present disclosure includes a positive electrode including a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, and a negative electrode including a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and at least one of the positive electrode mixture layer and the negative electrode mixture layer contains the powder of the present disclosure.

[0070] As the form of the secondary battery, a structure in which a plurality of positive and negative electrodes housed in an exterior material are laminated in the thickness direction may be used, a laminate type secondary battery may be used, or a wound type secondary battery may be used. As the wound type secondary battery, for example, a cylindrical secondary battery in which an electrode pair obtained by winding a laminate formed by laminating a positive electrode and a negative electrode via a separator and an electrolytic solution are enclosed in a cylindrical exterior body may be used, or alternatively, a cylindrical secondary battery in which a cell obtained by winding a laminate formed by laminating a positive electrode and a negative electrode via a solid electrolyte is enclosed in a cylindrical exterior body may be used.

[0071] The secondary battery may be a battery in which a laminate formed by laminating a positive electrode and a negative electrode via a separator and an electrolytic solution are housed in an exterior material, or may be a battery in which a laminate formed by laminating a positive electrode and a negative electrode via a solid electrolyte is housed in an exterior material.

[0072] The type of the secondary battery is not particularly limited, and examples thereof include lithium-based secondary batteries, sodium-based secondary batteries, potassium-based secondary batteries, magnesium-based secondary batteries, and aluminum-based secondary batteries. Among them, lithium-based secondary batteries capable of achieving high voltage and high energy density and sodium-based secondary batteries capable of reducing costs are preferable. Examples of lithium secondary batteries include lithium-ion secondary batteries and lithium secondary batteries in which the negative electrode is metallic lithium (including, for example, lithium-sulfur batteries and lithium-air batteries), and examples of battery types include liquid electrolyte type batteries and solid electrolyte type batteries that contain at least one of an electrolytic solution, a polymer electrolyte, a polymer gel electrolyte, a solid electrolyte, etc. Also, for secondary batteries other than lithium secondary batteries, similar to the aforementioned lithium secondary batteries, the positive electrode active material, negative electrode active material, electrolyte, etc. are not limited and can take various forms. Hereinafter, as an example, an example of a lithium secondary battery will be described, but the present invention is not limited thereto.

[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 the present disclosure includes a positive electrode including a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material.

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

[0076] The positive electrode mixture layer may contain the powder of the present disclosure. For example, a composition for forming a positive electrode mixture layer (a kind of composition for forming an electrode mixture layer) containing a positive electrode active material and the powder of the present disclosure on the positive electrode current collector, and further containing carbon black, other conductive aids, a binder (for example, the binder described in the item of the conductive layer), a solvent, etc. as necessary, is applied, the applied slurry is dried, and then pressed to form a positive electrode mixture layer on the positive electrode current collector.

[0077] The thickness of the positive electrode active material layer may be 30 μm or more, may be 50 μm to 70 μm, or may be 70 μm to 100 μm from the viewpoints of energy density and safety.

[0078] The density of the positive electrode active material layer may be 2.0 g / cm 3 or more, may be 3.0 g / cm 3 or more, and may be 3.0 g / cm 3 to 4.0 g / cm 3 from the viewpoints of energy density and safety.

[0079] The areal weight of the positive electrode active material layer may be 10.0 mg / cm 2 or more, and may be 10.0 mg / cm 2 to 30.0 mg / cm 2 from the viewpoints of energy density and safety.

[0080] The average electrode area (average positive electrode area and average negative electrode area) per sheet may be 20 cm 2 to 10000 cm 2 or may be 300 cm 2 to 10000 cm 2 from the viewpoints of energy density and safety.

[0081] (Positive electrode active material) The positive electrode active material layer contains a positive electrode active material. The positive electrode active material can be appropriately selected according to the type of the secondary battery. For example, compounds containing at least one of lithium, sodium, potassium, magnesium, and aluminum can be mentioned. Examples of the positive electrode active material include oxides containing nickel, phosphates having an olivine structure, etc. When the secondary battery is a lithium-based secondary battery, examples of the positive electrode active material include 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 O4 (a, b ≧ 0, a + b = 2), etc. The positive electrode active material may be used alone or in combination of two or more kinds.

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

[0083] LiNi x Mn y Co z Al w As LiNi x Mn y Co z )O2 (x ≥ 0.5, y ≤ 0.3, z ≤ 0.3, x + y + z = 1), it is more preferable that Li(Ni x Mn y Co z )O2 (x ≥ 0.5, y ≤ 0.3, z ≤ 0.3, x + y + z = 1). Examples of the positive electrode active material represented by Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 include, for example, 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, Li(Ni 0.5 Mn 0.2 Co 0.3 )O2, and Li(Ni

[0084] Examples of the positive electrode active material represented by LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni) include, for example, LiFePO4, LiFe0.5 Mn 0.5 PO4, LiFe 0.3 Mn 0.7 PO4, LiCoPO4, and LiCo 0.5 Mn 0.5 PO4 may be mentioned.

[0085] In the positive electrode mixture layer, the content of the positive 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 positive electrode capacity.

[0086] In the positive electrode mixture layer, the positive electrode active material, a conductive assistant such as the powder of the present disclosure, a binder, etc. may be simply mixed, or a conductive assistant such as the powder of the present disclosure may be compounded on the surface of the positive electrode active material. Examples of the conductive assistant include other conductive assistants other than the powder of the present disclosure (for example, other conductive assistants described in the item of the conductive assistant).

[0087] When the positive electrode mixture layer contains the above powder, in the positive electrode mixture 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.

[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 still more preferably 2.0% by mass or less.

[0089] The positive electrode mixture layer may contain fibrous carbon other than the powder of the present disclosure (other fibrous carbon). Examples of other fibrous carbon include carbon fiber (carbon fiber), vapor-grown carbon fiber, carbon nanotubes such as single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT), and carbon nanofiber.

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

[0091] The material of the negative electrode current collector is not particularly limited as long as it is a material with electron conductivity, and can be selected from copper, nickel, titanium, stainless steel, etc. The state of the negative electrode current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. As an example, a copper foil is used as the negative electrode current collector.

[0092] The negative electrode binder layer may contain the powder of the present disclosure. For example, 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. as required is applied on the negative electrode current collector, the applied slurry is dried, and then pressed to form a negative electrode binder layer on the negative electrode current collector.

[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 1.3 g / cm 3 or more, and may be 1.5 g / cm 3 to 2.0 g / cm 3 or more.

[0095] From the viewpoints of energy density and safety, the basis weight of the negative electrode binder layer may be 5.0 mg / cm 2 or more, and may be 10 mg / cm 2 to 20 mg / cm 2 or more.

[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 of (0 < x ≤ 1) etc. may 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] In the negative electrode binder layer, the content of the negative electrode active material is preferably 70% by mass to 99% by mass, 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 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. As the conductive aid, other conductive aids other than the powder of the present disclosure (for example, other conductive aids described in the item of conductive aids) may be mentioned.

[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 even 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 even more preferably 2.0% by mass or less.

[0101] (Outer packaging material) As the exterior material for housing the positive electrode and the negative electrode, there is no limitation as long as it can house the positive electrode and the negative electrode, and optionally a separator, an electrolytic solution, or a solid electrolyte, etc. Examples of the exterior material include commercially available battery packs, 18650-type cylindrical cells, those in a form packed with an aluminum wrapping material, etc., and the exterior material can be freely designed and used.

[0102] (Separator) The secondary battery may be provided with a separator between the positive electrode and the negative electrode. As the separator, it can be freely selected from those that can be used in general secondary batteries, and examples include microporous films made of polyethylene or polypropylene. Separators mixed with particles such as SiO2 and Al2O3 as fillers, and separators with these particles adhered to the surface can also be used.

[0103] (Electrolytic solution) The secondary battery may contain an electrolytic solution. There is no particular limitation on the electrolytic solution, and an electrolytic solution that can be used in a normal secondary battery can be preferably used. For example, an organic solvent in which a lithium salt of 0.5 mol / L to 2.0 mol / L is dissolved can be used.

[0104] Examples of the lithium salt include LiPF6, LiBF4, LiClO4, LiAsF6, LiN(SO2F)2 (LiFSI), etc.

[0105] Examples of the organic solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), and the like. The organic solvent may be appropriately selected from those listed herein and others and used after mixing. Examples of the additive for the electrolytic solution include vinylene carbonate (VC), propane sultone (PS), and fluoroethylene carbonate (FEC). When using an additive, the content of the additive is preferably 0.01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass, and even more preferably 0.5% by mass to 5% by mass with respect to 100% by mass of the organic solvent.

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

[0107] (Solid electrolyte) A solid electrolyte may be used as the electrolyte. When using a solid electrolyte, a separator becomes unnecessary, and a battery in a form in which a positive electrode and a negative electrode are sandwiched by the solid electrolyte (for example, an all-solid-state lithium ion secondary battery) can be formed.

[0108] Examples of the solid electrolyte include polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte is not particularly limited, and examples thereof include polymers such as polyethylene oxide (PEO), polymethyl methacrylic acid (PMMA), polyacrylonitrile (PAN), and polymer gels obtained by adding a plasticizer (for example, an organic solvent) to the polymer and impregnating the lithium salt. The inorganic solid electrolyte is not particularly limited, and includes sulfide-based solid electrolytes such as Li2S-P2S5, Li2S-GeS2, Li2S-SiS2-Li3PO4, 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 of oxide-based solid electrolytes include (PO4)3 such as Ge(PO4)3 and the like.

[0109] The secondary battery of the present disclosure can be used as a power source for electronic devices such as smartphones, tablet PCs, and portable information terminals; as a power source for electric motors such as power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and for storing electric power obtained by fuel cells, solar power generation, wind power generation, and the like.

Examples

[0110] Hereinafter, the present disclosure will be specifically described by way of examples, but the scope of the present disclosure is not limited to these examples.

[0111] The physical property values of the powders in Table 1 obtained in the examples and comparative examples were measured by the methods shown below. The physical property values of powders other than those in Table 1 may also be measured by the methods shown below.

[0112] <Observation of Transmission Electron Microscope (TEM) of Powders> The fibrous carbon contained in each of the powders of Examples 1 to 3 and the comparative example was dispersed in ethanol, scooped up with a microgrid, and dried to obtain a sample. The TEM observation of the sample was performed. It was confirmed as follows that the fibrous carbon contained in each of the powders of Examples 1 to 3 and the comparative examples all had a structure in which cylindrical carbon hexagonal net planes were laminated in the thickness direction of the fiber. First, the powder was observed by TEM-EDX, and an image capable of confirming the longitudinal direction of the fibrous carbon (hereinafter also referred to as a "TEM longitudinal image") and an image capable of confirming a cross section when the fibrous carbon was cut in a direction intersecting the longitudinal direction (hereinafter also referred to as a "TEM cross-sectional image") were observed. Then, in the TEM longitudinal image, it was confirmed that a plurality of lines along the longitudinal direction existed inside the fibrous carbon, and in the TEM cross-sectional image, a plurality of closed curves with different maximum diameters existed concentrically. From the above, it was confirmed that the fibrous carbon had a structure in which cylindrical carbon hexagonal net planes were laminated in the thickness direction of the fiber. Apparatus name: JEM-ARM200F (manufactured by JEOL Ltd.)

[0113] <Scanning Electron Microscope (SEM) Observation of Powder> (Measurement of Spherical Carbon Particles) A double-sided carbon tape was attached to the sample stage for SEM observation, and about half of a microspatula of the powder was scattered thereon. This was observed by SEM. The SEM images of the powders of Examples 1 to 3 and the comparative example are shown in FIGS. 1 to 4. Observation was carried out at a magnification of 20,000 times, and the number of spherical carbon particles appearing in one field of view was counted, and the average value of the number of spherical carbon particles was obtained in the same manner as described above. (Measurement of Fiber Diameter) A double-sided carbon tape was attached to the sample stage for SEM observation, and about half of a microspatula of the powder was scattered thereon. This was observed by SEM. Observation was carried out at a magnification of 20,000 times, and a plurality of SEM photographs were taken. The number of fibrous carbons for which the diameter was measured was 200 randomly selected. The average fiber diameter was obtained by taking the arithmetic mean of these 200. The diameter of the fibrous carbon is the dimension in the direction perpendicular to the direction in which the fibrous carbon extends. For one fibrous carbon, the diameter at one randomly selected location other than both ends was measured, and this was taken as the diameter of the fibrous carbon. (Measurement of Fiber Length) 50 mL of ethanol was put into a screw tube, about half of a microspatula of powder was added, and ultrasonic treatment was performed for 15 minutes. After the ultrasonic treatment, the dispersion was sprayed on the dull surface of the aluminum foil and air-dried. After air-drying, the aluminum foil was cut into a size that could be placed on the sample stage for SEM observation, and the fibrous carbon on the aluminum foil was observed and photographed at a magnification where both ends were captured. The lengths along the fiber axes of 200 randomly selected fibers were measured, and the average value was obtained. (Measurement of average maximum diameter) Using a scanning electron microscope (SEM), the powder was observed at a magnification of 20,000 times, and photos of randomly different fields of view were taken. Using these, the average value of the maximum diameter of the spherical carbon particles was measured. The fields of view were shifted as described above to continue measuring the spherical carbon particles until a total of 20 spherical carbon particles were obtained. 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 sample for resistance measurement> As the positive electrode active material, 97 parts by mass of LiCoO2 (50% diameter in the volume-based cumulative particle size distribution, D50 = 38 μm), 2 parts by mass of a conductive aid such as the powder obtained in the example or comparative example, 1 part by mass of PVDF as a binder, and N-methyl-2-pyrrolidone (NMP, manufactured by Kishida Chemical Co., Ltd.) as a solvent for slurry preparation were appropriately added to form a slurry. A kneader, Aotori Rentaro (manufactured by Shinky Co., Ltd., ARE-100), was used for kneading. The obtained slurry was applied onto thick paper using a doctor blade with a gap of 50 μm and dried. Then, it was cut into a size of 3 cm in length and 5 cm in width to obtain a measurement sample.

[0115] <Resistance measurement> Using a resistivity meter Loresta GP (manufactured by Dia Instruments Co., Ltd.), the volume resistivity of the above measurement sample was measured and compared. The evaluation criteria are as follows, and if it is A or B, it can be judged that the resistance evaluation is good. A: Sufficiently low (less than 10 Ω·cm) B: Low (10 Ω·cm or more and less than 30 Ω·cm) C: Slightly high (30 Ω·cm or more and less than 50 Ω·cm) D: High (50 Ω·cm or more and less than 100 Ω·cm) E: Considerably high (100 Ω·cm or more)

[0116] <Production of powder Powders of the examples and comparative examples were produced as shown below.

[0117] (Example 1) A raw material mixture was prepared by mixing 0.083% by mass of ferrocene (powder form, purity > 98%), 0.022% by mass of sulfur (powder form, purity 99.99%), 0.31% by mass of polypropylene glycol (D - 400, manufactured by NOF Corporation, molecular weight: 400, decomposition temperature: 290 °C), and 99.585% by mass of benzene. This was conveyed at a flow rate of benzene of 0.11 g / min using a pump and sprayed from the upper part of a vertical reaction tube using a triple - tube nozzle. The carrier gas was hydrogen and the flow rate was 946 NmL / min. The temperature inside the reaction tube was 1250 °C. After reacting for 10 minutes, the supply of the raw material mixture was stopped, the gas was switched from the 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 amount of necessary samples such as SEM observation from the recovered product, it was charged into the furnace again and heated to 1000 °C while flowing nitrogen gas. It was held at 1000 °C for 30 minutes, cooled, and the product was recovered. Thereafter, the recovered powder was charged into a graphitization furnace and heated to 2800 °C while flowing argon gas. After holding at 2800 °C for 30 minutes, it was cooled and the product was recovered. This was gently crushed with 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) A reaction was carried out in the same manner as in Example 1, except that a raw material mixture in which sulfur was 0% by mass and benzene was 99.607% by mass was prepared.

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

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

[0122]

Table 1

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

Claims

1. A powder containing fibrous carbon having a structure in which cylindrical carbon hexagonal mesh surfaces are laminated in the thickness direction of the fibers, the average fiber diameter of the fibrous carbon being 110 nm to 170 nm, and when the powder is observed at a magnification of 20,000 times using a scanning electron microscope (SEM), the average number of spherical carbon particles is 1 to 30, and the average maximum diameter of the spherical carbon particles is 0.20 μm to 0.30 μm.

2. 10. The powder of claim 1, wherein the fibrous carbon comprises network-forming fibers.

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

4. d of the powder ００２ The powder according to claim 1, wherein the average particle diameter is 0.3370 nm to 0.3390 nm.

5. 2. 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 2. The powder according to claim 1, wherein the pressure when compacting is 0.8 MPa to 2.5 MPa.

7. 0.8 g / cm ３ 2. The powder according to claim 1, which has a volume resistivity of 0.025 Ω·cm or less when compacted.

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

30.

9. A conductive assistant comprising the powder according to any one of claims 1 to 8.

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

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

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

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

Images