Carbon materials, conductive additives, dispersions, electrode mixture layer forming compositions, and secondary batteries

Abstract

This invention provides a carbon material that has a high oxidation current of 4.1V and enables the fabrication of secondary batteries with excellent battery characteristics. [Solution] A carbon material containing fibrous carbon having a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, d 002 The wavelength is 0.3391 nm or less, and the BET specific surface area is 10.5 m². 2 / g or more 18.0m 2 It is less than / g, and the compressed density is 0.8g / cm³. 3 A carbon material having a compaction resistivity greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm.

Description

[Technical Field]

[0001] This disclosure relates to carbon materials, conductive additives, dispersions, compositions for forming 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] A composite carbon fiber has been proposed in which multilayer carbon nanotubes are homogeneously dispersed between graphitized carbon nanofibers and near the surface of the graphitized carbon nanofibers as a conductivity imparting agent to the electrodes of secondary batteries (for example, Patent Document 1). This composite carbon fiber disperses easily in a matrix such as resin without leaving aggregates and has an excellent effect in reducing resistance. When this composite carbon fiber is included as a conductivity imparting agent in the electrodes of a secondary battery, battery characteristics such as capacity retention rate are improved. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5497109 [Overview of the project] [Problems that the invention aims to solve]

[0005] For additives in secondary batteries, such as additives to electrodes like the positive and negative electrodes, there is a demand for materials that can improve battery characteristics. For example, in the positive electrode, there is a +4.1V vs. Li / Li desorption current, which is considered to be almost entirely due to lithium desorption from the active material. +A carbon material is desirable that allows for the fabrication of secondary batteries with a high oxidation current at 4.1V (hereinafter sometimes simply referred to as "4.1V oxidation current"; the same applies to oxidation currents at other potentials).

[0006] This disclosure is made in view of the above circumstances and aims to provide a carbon material that has a large 4.1V oxidation current value and can be used to produce a secondary battery with excellent battery characteristics, as well as a conductive additive, dispersion, electrode mixture layer forming composition and secondary battery containing the same. [Means for solving the problem]

[0007] The specific means for achieving the aforementioned objectives are as follows: <1> A carbon material containing fibrous carbon having a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, d 002 The wavelength is 0.3391 nm or less, and the BET specific surface area is 10.5 m². 2 / g or more 18.0m 2 It is less than / g, and the compressed density is 0.8g / cm³. 3 A carbon material having a compaction resistivity greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm. <2> In the nitrogen adsorption test of the carbon material, the cumulative pore volume up to a relative pressure of 0.00295 is 0.0030 mL / g to 0.0050 mL / g. <1> The carbon material described above. <3> The carbon material d 002 This range is 0.3370nm to 0.3390nm. <1> or <2> The carbon material described above. <4> The total pore volume (cumulative pore volume up to a relative pressure of 0.99) in the nitrogen adsorption test of the carbon material is 0.1000 mL / g or less. <1> ~ <3> A carbon material as described in any one of the following. <5> In the nitrogen adsorption test of the carbon material, the ratio of the micropore volume (cumulative pore volume up to relative pressure = 0.1537) to the total pore volume (cumulative pore volume up to relative pressure = 0.99) using the BJH method with the Halsey formula, φ2, is 14.0% or less. <1> ~ <4> A carbon material as described in any one of the following. <6> The oxygen content of the carbon material is 0.10% by mass or less. <1> ~ <5> A carbon material as described in any one of the following. <7> <1> ~ <6> A conductive additive containing any one of the carbon materials described in one of the following. <8> <1> ~ <6> A dispersion containing any one of the carbon materials described in one of the following. <9> <1> ~ <6> A composition for forming an electrode mixture layer, comprising any one of the carbon materials described in one of the following. <10> 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> ~ <6> A secondary battery containing a carbon material as described in any one of the following. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a carbon material that has a large 4.1V oxidation current value and can be used to produce a secondary battery with excellent battery characteristics, as well as a conductive additive, dispersion, electrode mixture layer forming composition, and secondary battery containing the same. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing a longitudinal cross-section of a cell used for measuring powder resistance. [Modes for carrying out the invention]

[0010] 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.

[0011] 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 the present disclosure, in the numerical range indicated by using "~", the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise 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 stepwise. Further, in the numerical range 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 not only the case where the layer or film is formed over the entire region when observing the region where the layer or film exists, but also the case where it is formed only in a part of the region. In the present disclosure, the term "lamination" indicates laminating layers, and two or more layers may be bonded, and two or more layers may be detachable. [[ID=~]] [[ID=~]]

[0012] [[ID=~]] <Carbon material> The carbon material of the present disclosure is a carbon material containing fibrous carbon having a structure in which cylindrical carbon hexagonal net planes are laminated in the fiber thickness direction, where d 002 is 0.3391 nm or less, the BET specific surface area is 10.5 m 2 / g or more and less than 18.0 m 2 [[ID=~]] / g, and the consolidation resistivity at a bulk density of 0.8 g / cm 3 is greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm. By using the carbon material of the present disclosure, it is possible to produce a secondary battery having a large value of 4.1 V oxidation current and excellent battery characteristics.

[0013] The carbon material disclosed herein has a compressive density of 0.8 g / cm³. 3 The compression resistivity is greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm. In the carbon material disclosed herein, a compaction resistivity greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm enables the fabrication of secondary batteries with superior battery characteristics. More specifically, a compaction resistivity greater than 0.0165 Ω·cm corresponds to adequate oxygen bonding to the surface of the carbon material, for example, to the fibrous and non-fibrous carbon contained in the carbon material, or to a disordered hexagonal network surface of the carbon material. This is presumed to result in good affinity and miscibility with the positive electrode active material, and a tendency for the 4.1V oxidation current to be higher. On the other hand, a compaction resistivity less than 0.0140 Ω·cm may reduce affinity and miscibility with the positive electrode active material, but it is presumed that the carbon material has sufficient conductivity, which tends for the 4.1V oxidation current to be higher. Compression density of carbon material: 0.8 g / cm³ 3 The compaction resistivity can be measured by the method described in the examples below.

[0014] The carbon material disclosed herein has a compressive density of 0.8 g / cm³. 3 The compression resistivity in this case may be 0.0166 Ω·cm or higher, or 0.0170 Ω·cm or higher. Compression density: 0.8 g / cm³ 3 The compression resistivity in this case may be 0.0200 Ω·cm or less, or 0.0180 Ω·cm or less.

[0015] The carbon material disclosed herein has a compressive density of 0.8 g / cm³. 3 The compression resistivity in this case may be 0.0138 Ω·cm or less, or 0.0136 Ω·cm or less. Compression density: 0.8 g / cm³ 3 The compression resistivity in this case may be 0.0120 Ω·cm or higher, or 0.0130 Ω·cm or higher.

[0016] d of carbon materials 002 The wavelength is 0.3391 nm or less, and from the viewpoint of battery characteristics, it is preferably 0.3370 nm to 0.3390 nm, more preferably 0.3375 nm to 0.3388 nm, and even more preferably 0.3380 nm to 0.3386 nm. d of carbon materials 002 This refers to the average interplanar spacing d of carbon materials, specifically determined by X-ray diffraction, or more precisely, by the JSPS method. 002 It means...

[0017] The BET specific surface area of ​​carbon materials is 10.5 m². 2 / g or more 18.0m 2 It is less than / g, and from the perspective of battery characteristics, 11.0m 2 / g~17.5m 2 It is preferable that it be / g, and 11.5m 2 / g~17.0m 2 It is more preferable that it be / g, and 13.5m 2 / g~17.0m 2 It is even more preferable that it be / g. The BET specific surface area of ​​carbon materials is calculated using the BET multipoint method from adsorption isotherm data at three points near relative pressures of 0.1, 0.2, and 0.3.

[0018] In the nitrogen adsorption test of the carbon material of this disclosure, the total pore volume (cumulative pore volume up to a relative pressure of 0.99) is preferably 0.1000 mL / g or less, more preferably 0.0300 mL / g to 0.0800 mL / g, and even more preferably 0.0360 mL / g to 0.0600 mL / g. The nitrogen adsorption test of carbon materials can be performed by the method described in the examples below.

[0019] In the nitrogen adsorption test of the carbon material of this disclosure, the cumulative pore volume of the pores up to a relative pressure of 0.00295 is preferably 0.0030 mL / g to 0.0050 mL / g, more preferably 0.0031 mL / g to 0.0045 mL / g, and even more preferably 0.0032 mL / g to 0.0042 mL / g.

[0020] In the nitrogen adsorption test of the carbon material of this disclosure, the ratio of the cumulative pore volume of pores up to a relative pressure of 0.00295 to the total pore volume (cumulative pore volume up to a relative pressure of 0.99) (hereinafter also referred to as φ1) is preferably 13.0% or less, more preferably 10.0% or less, and even more preferably 5.0% to 9.0%.

[0021] In the nitrogen adsorption test of the carbon material of this disclosure, the cumulative pore volume up to a relative pressure of 0.1537 is preferably 0.0040 mL / g to 0.0070 mL / g, more preferably 0.0042 mL / g to 0.0065 mL / g, and even more preferably 0.0045 mL / g to 0.0060 mL / g.

[0022] In the nitrogen adsorption test of the carbon material of this disclosure, the ratio of the micropore volume (cumulative pore volume up to a relative pressure of 0.1537) to the total pore volume (cumulative pore volume up to a relative pressure of 0.99) using the BJH method with the Halsey formula (hereinafter also referred to as φ2) is preferably 16.0% or less, more preferably 14.0% or less, and even more preferably 9.0% to 13.0%.

[0023] In the nitrogen adsorption test of the carbon material of this disclosure, the φ2 / φ1 ratio is preferably 1.350 or higher, and from the viewpoint of enabling the production of a secondary battery with a larger 4.1V oxidation current value and superior battery characteristics, it is preferably 1.370 to 1.450, more preferably 1.390 to 1.445, and even more preferably 1.405 to 1.440.

[0024] From the viewpoint of reducing the 4.5V oxidation current / 4.1V oxidation current values ​​when carbon materials are applied to secondary batteries, the oxygen content of the carbon material is preferably 0.10% by mass or less, more preferably 0.08% by mass or less, even more preferably 0.06% by mass or less, and particularly preferably 0.05% by mass or less. The lower limit of the oxygen content of the carbon material is not particularly limited and may be 0% by mass, 0.02% by mass or more, or 0.03% by mass or more. The oxygen content of a carbon material may also be determined by heating the carbon material in an inert gas and quantifying the generated CO and CO2 using infrared absorption spectroscopy.

[0025] Oxygen content correlates with, for example, the specific surface area of ​​the BET (Body-Ester Elastomer), with higher BET specific surface area tending to correlate with higher oxygen content. Therefore, adjusting the conditions for increasing the BET specific surface area (such as calcination steps, activation treatments, and grinding conditions) tends to allow for adjustment of the oxygen content. The carbon material of this disclosure may or may not be subjected to magnetic separation using an electromagnetic separator. It is believed that the oxygen content of the carbon material can be adjusted by performing magnetic separation using an electromagnetic separator.

[0026] From the viewpoint of producing a secondary battery with excellent cycle characteristics and rate characteristics, the average fiber diameter of the fibrous carbon is preferably 1 nm to 200 nm, more preferably 100 nm to 200 nm, and even more preferably 120 nm to 180 nm.

[0027] The average fiber diameter of fibrous carbon can be determined from the arithmetic mean of the diameters of 200 randomly selected fibers observed by SEM of the electrodes. The diameter of a single fiber can be determined by measuring the width at one point excluding both ends of a fiber from an SEM image and taking the arithmetic mean. Here, fiber width refers to the dimension of the fiber in the direction perpendicular to the longitudinal direction.

[0028] From the viewpoint of producing a secondary battery with excellent cycle characteristics and rate characteristics, the average fiber length of the fibrous carbon is preferably 1 μm to 20 μm, more preferably 3 μm to 15 μm, and even more preferably 4 μm to 10 μm.

[0029] The average fiber length of fibrous carbon can be measured as follows: The powder is dispersed in a dispersion medium, spread on aluminum foil or the like, dried, and observed by SEM. The length along the fiber axis of 200 randomly selected fibers is measured, and the average fiber length is determined by taking the arithmetic mean. Alternatively, the electrode may be washed with a solvent to remove binders and other contaminants, and the average fiber length of the carbon fibers may be determined using the extracted powder.

[0030] A test electrochemical cell was fabricated using the carbon material disclosed herein, and linear sweep voltammetry (LSV) was performed under the following conditions, yielding +4.1V vs. Li / Li + +4.5V vs. Li / Li for oxidation current + The ratio of oxidation currents (4.5V oxidation current / 4.1V oxidation current) is preferably 3.00 or less, more preferably 2.50 or less, and even more preferably 2.35 or less. The lower limit of the 4.5V oxidation current / 4.1V oxidation current is not particularly limited and may be, for example, 1.00 or more. By having a 4.5V oxidation current / 4.1V oxidation current of 3.00 or less, sufficient electrons and ions can be delivered to the electrode, and an electrode (especially the positive electrode) with few side reactions can be provided. -Measurement conditions- Scanning range: From natural immersion potential to +5.2V vs. Li / Li + to Scanning speed: 3mV / s Measurement temperature: 45℃ A test electrochemical cell can be prepared as follows: Use NMC811(Li(Ni) as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 Weigh 6 parts by mass of O296, 2 parts by mass of the carbon material of this disclosure, and 2.0 parts by mass of PVdF, and mix them in a kneader. Then, while adding NMP as appropriate, mix in the kneader to prepare an electrode mixture layer forming composition with adjusted viscosity. The prepared electrode mixture layer forming composition is coated onto a 20 μm thick aluminum foil using a roll coater, dried, and then vacuum dried to produce a test electrode with a positive electrode mixture layer. The basis weight (mass of electrode mixture layer per unit area) is 17 mg / cm².2 The dimensions of the test electrode shall be 20 mm x 20 mm. Next, a test electrochemical cell shall be prepared using the test electrode, the counter electrode and reference electrode (Li metal), and the electrolyte. As the electrolyte, a solution obtained by dissolving lithium hexafluoride phosphate (LiPF6) at a concentration of 1 M (mol / L) in a solvent obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) in a volume ratio of 3:7 shall be used.

[0031] The carbon material of this disclosure may consist solely of fibrous carbon having a structure in which tubular carbon hexagonal network surfaces are stacked in the direction of fiber thickness, or it may consist of such fibrous carbon and other carbon materials. The fibrous carbon content in the carbon material of this disclosure may be 50% to 100% by mass, 70% to 100% by mass, or 90% to 100% by mass, based on the total amount of carbon material.

[0032] The method for synthesizing the carbon material of this disclosure is not particularly limited and may be, for example, synthesized by a gas-phase method, or synthesized by a suspended catalyst method followed by heat treatment at 2000°C or higher under an inert atmosphere. The floating catalyst method is a method for obtaining carbon fibers by introducing a raw material solution, or a gaseous version thereof, prepared by dissolving catalyst sources such as ferrocene and sulfur compounds in a carbon source such as benzene, into a reactor heated to over 1000°C using a carrier gas such as hydrogen. Generally, a hollow tube is formed starting from the catalyst metal in the initial stages of the reaction, and carbon fibers grow in the longitudinal direction. Growth in the longitudinal direction continues until catalytic activity is lost, such as when the surface of the catalyst particles is covered with carbon. Once growth in the longitudinal direction is complete, pyrolysis carbon deposits on the surface of the hollow tube, and growth in the thickness direction progresses, forming a structure in which tubular carbon hexagonal mesh surfaces are stacked in the thickness direction of the fiber. Therefore, the fiber diameter can be adjusted by controlling the amount of pyrolysis carbon deposited on the carbon fibers during the reaction, i.e., the reaction time, the concentration of raw materials in the atmosphere, and the reaction temperature. The carbon material obtained by this reaction may have low conductivity because it is covered with pyrolysis carbon with low crystallinity. Therefore, in order to improve the crystallinity of the carbon fibers, heat treatment is performed at 800-1500°C under an inert gas atmosphere such as argon, followed by graphitization treatment at 2000-3000°C. The graphitization treatment simultaneously evaporates and removes the catalyst metal, enabling high-purity processing of the fibrous carbon. It is preferable to perform a heat treatment (first firing step) at 800°C to 1500°C, preferably 900°C to 1300°C, under an inert gas atmosphere such as argon, and then raise the temperature to 200°C to 500°C, preferably 1200°C to 1700°C, and hold it for 30 minutes to 3 hours (second firing step). This tends to increase the value of the 4.1V oxidation current and improve the battery characteristics. Furthermore, the temperature for the graphitization treatment is preferably 2500°C to 3000°C, and more preferably 2600°C to 3000°C.

[0033] 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 winding 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 a carbon material with a transmission electron microscope (TEM) as follows: Observe an image in which the longitudinal direction of the carbon fiber 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 carbon fiber 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 carbon fiber, 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 carbon fiber 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.

[0034] The carbon material d of the disclosure 002The BET specific surface area and consolidation resistivity can be adjusted as follows. Note that the following adjustment method is just one example and is not limited to this disclosure. d 002 This can be adjusted, for example, by changing the graphitization treatment conditions such as the graphitization temperature and the grinding conditions. For example, by increasing the graphitization temperature, d 002 It tends to decline. The BET specific surface area can be adjusted by changing conditions such as the heating time and holding time during graphitization, the heating time and holding time at each calcination step, the conditions for various processes such as grinding, and the powder synthesis reaction conditions. For example, increasing the holding time during graphitization tends to decrease the BET specific surface area, while adding a second calcination step or increasing the rotation speed during grinding tends to increase the BET specific surface area. The resistivity can be adjusted by changing, for example, the conditions of the graphitization process, such as the heating time and holding time during graphitization; the conditions of each calcination step, such as the heating time and holding time; the conditions of various processes such as grinding; and the conditions of the powder synthesis reaction.

[0035] The carbon material of this disclosure may be used as a conductive additive, or in the preparation of dispersions, electrode mixture layer forming compositions, etc.

[0036] The carbon material of this disclosure may be used in the form of a dispersion in a solvent or the like. The dispersion may contain other components such as a positive electrode active material, a negative electrode active material, a binder, and additives.

[0037] The carbon material of this disclosure may be used in the preparation of a composition for forming an electrode mixture layer (composition for forming an electrode mixture layer). Examples of compositions for forming electrode mixture layers include compositions for forming a positive electrode mixture layer and compositions for forming a negative electrode mixture layer. The composition for forming the positive electrode mixture layer comprises a positive electrode active material and the carbon material of this disclosure, and may further optionally contain carbon black, a binder, a solvent, etc. The negative electrode mixture layer forming composition comprises a negative electrode active material and the carbon material of this disclosure, and may further optionally contain a conductive additive, binder, solvent, etc.

[0038] <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 carbon material of the present disclosure.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] [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.

[0043] 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.

[0044] The positive electrode mixture layer may contain the carbon material 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 carbon material of this disclosure, and optionally further containing carbon black, a binder, a solvent, etc., using a composition for forming a positive electrode mixture layer (a type of composition for forming an electrode mixture layer), drying the coated slurry, and then pressing it.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] (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.

[0050] The positive electrode active material is LiNi x Mn y Co z Al wIt is preferable to contain O2 (x, y, z, w ≧ 0, x + y + z + w = 1) or LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni).

[0051] LiNi x Mn y Co z Al w As O2 (x, y, z, w ≧ 0, x + y + z + w = 1), it is preferable that the ratio of nickel is relatively high, for example, x ≧ 0.5 or more, and Li(Ni x Mn y Co z )O2 (x ≧ 0.5, y ≦ 0.3, z ≦ 0.3, x + y + z = 1) is more preferable. As the positive electrode active material represented by Li(Ni x Mn y Co z [[ID=|24]])O2 (x ≧ 0.5, y ≦ 0.3, z ≦ 0.3, x + y + z = 1), for example, Li(Ni[[ID=|25]] 0.8 [[ID=|26]]Mn[[ID=|27]] 0.1 [[ID=|28]]Co[[ID=|29]] 0.1 [[ID=|30]])O2, Li(Ni[[ID=|31]] 0.7 [[ID=|32]]Mn[[ID=|33]] 0.2 [[ID=|34]]Co[[ID=|35]] 0.1 [[ID=|36]])O2, Li(Ni[[ID=|37]] 0.7 [[ID=|38]]Mn[[ID=|39]] 0.1 [[ID=|40]]Co[[ID=|41]] 0.2 [[ID=|42]])O, Li(Ni[[ID=|43]] 0.6 [[ID=|44]]Mn[[ID=|45]] 0.2 [[ID=|46]]Co[[ID=|47]] 0.2 [[ID=|48]])O2, Li(Ni[[ID=|49]] 0.5 [[ID=|50]]Mn[[ID=|51]] 0.3 [[ID=|52]]Co[[ID=|53]] 0.2 [[ID=|54]])O2 and Li(Ni[[ID=|55]] 0.5 [[ID=|56]]Mn[[ID=|57]] 0.2 [[ID=|58]]Co[[ID=|59]] 0.3 [[ID=|60]])O2 can be mentioned.[[ID=|61]] [[ID=|62]]

[0052] [[ID=|63]] [[ID=|64]]As the positive electrode active material represented by LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni), for example, LiFePO4, LiFe[[ID=|65]] 0.5 [[ID=|66]]Mn[[ID=|67]] 0.5 [[ID=|68]]PO4, LiFe[[ID=|69]]<0OO0089>[[ID=|70]]Mn[[ID=|71]] 0.7 [[ID=|72]]PO4, LiCoPO4 and LiCo[[ID=|73]] 0.5 [[ID=|74]]Mn[[ID=|75]] 0.5 [[ID=|76]]PO4 can be mentioned.[[ID=|77]] [[ID=|78]]

[0053] In the positive electrode mixture layer, the content of the positive electrode active material is preferably 90.0% by mass or more, more preferably 93.0% by mass or more, and even more preferably 95.0% by mass or more, from the viewpoint of positive electrode capacity.

[0054] In the positive electrode mixture layer, the content of the positive electrode active material is preferably 98.0% by mass or less, more preferably 97.0% by mass or less, and even more preferably 96.5% by mass or less, from the viewpoint of ensuring the amount of other components.

[0055] The positive electrode mixture layer may contain the carbon material of this disclosure. When the positive electrode mixture layer contains the above-mentioned carbon material, the content of the above-mentioned carbon material 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.

[0056] In the positive electrode mixture layer, the content of the carbon material 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.

[0057] The cathode mixture layer may contain fibrous carbon other than the carbon material of this disclosure (other fibrous carbon). Examples of other fibrous carbon include carbon fibers, vapor-phase carbon fibers, carbon nanotubes such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and carbon nanofibers.

[0058] (Carbon Black) The positive electrode mixture layer may further contain carbon black. Carbon black is used as a conductive additive in secondary batteries. Examples of carbon black include Denka Black (registered trademark, manufactured by Denka Co., Ltd.), C-NERGY (registered trademark) Super C45, C65 (manufactured by Imerys Graphite & Carbon), and Ketjen Black (manufactured by Ketjen Black International).

[0059] The primary particle size of carbon black may be between 10 nm and 100 nm. Here, primary particles refer to the part corresponding to a single bead in a bead-like structure called an aggregate. When the primary particle size of carbon black is within this range, it tends to disperse uniformly on the surface of the active material. From the viewpoint of improving dispersibility, the primary particle size of carbon black is preferably between 20 nm and 80 nm, and more preferably between 30 nm and 70 nm.

[0060] The primary particle size of carbon black can be determined by selecting 100 arbitrary primary carbon black particles from SEM images of the electrode and cross-sectional SEM images, and then taking the arithmetic mean of the maximum particle length measurements using image recognition software.

[0061] When the positive electrode mixture layer contains carbon black, the carbon black content is preferably 0.2% by mass or more, more preferably 0.6% by mass or more, and even more preferably 1.0% by mass or more, from the viewpoint of obtaining excellent cycle characteristics and rate characteristics.

[0062] In the positive electrode mixture layer, the carbon black content is preferably 6.0% by mass or less, more preferably 4.0% by mass or less, and even more preferably 2.0% by mass or less, from the viewpoint of ensuring the capacity of the positive electrode.

[0063] (binder) The positive electrode mixture layer may contain a binder. Suitable binders include those commonly used in positive electrode mixture layers for lithium-ion secondary batteries. Examples of binders include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).

[0064] If the positive electrode mixture layer contains a binder, the binder content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2.0% by mass or more, from the viewpoint of obtaining the function of a binder.

[0065] In the positive electrode mixture layer, the binder content is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4.0% by mass or less, from the viewpoint of suppressing an increase in the resistance of the positive electrode.

[0066] (Other ingredients) In addition to the above, the positive electrode mixture layer may contain other components such as dispersants and additives. For example, it may contain various dispersants for dispersing the positive electrode active material, and agents for surface modification of the positive electrode active material.

[0067] [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.

[0068] The material of the negative electrode current collector is not particularly limited as long as it is an electronically conductive material, and can be selected from copper, nickel, titanium, stainless steel, etc. The state of the negative electrode current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. As an example, copper foil is used as the negative electrode current collector.

[0069] The negative electrode mixture layer may contain the carbon material of this disclosure. For example, a negative electrode mixture layer composition (a type of electrode mixture layer forming composition) containing a negative electrode active material and the carbon material of this disclosure, and further containing a conductive additive, binder, solvent, etc. as needed, is coated onto a negative electrode current collector, the coated slurry is dried, and then pressed to form a negative electrode mixture layer on the negative electrode current collector.

[0070] From the perspective of energy density and safety, the thickness of the negative electrode active material layer may be 30 μm or more, may be 50 μm to 100 μm, or may be 100 μm to 150 μm.

[0071] From the perspective of energy density and safety, the density of the negative electrode active material layer may be 1.3 g / cm 3 or more, may be 1.5 g / cm 3 ~2.0 g / cm 3 or more.

[0072] From the perspective of energy density and safety, the areal density of the negative electrode active material layer may be 5.0 mg / cm 2 or more, may be 10 mg / cm 2 ~20 mg / cm 2 or more.

[0073] (Negative electrode active material) The negative electrode active material layer contains a negative electrode active material. Examples of the negative electrode active material include Si, 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 (0 < x ≤ 1), and other oxides. Among them, it is preferable that the negative electrode active material contains graphite. Further, at least a part of the surface of the negative electrode active material may be coated with amorphous carbon.

[0074] In the negative electrode active material layer, the content of the negative electrode active material is preferably not less than 90.0% by mass, more preferably not less than 93.0% by mass, and still more preferably not less than 95.0% by mass.

[0075] In the negative electrode mixture layer, the content of the negative electrode active material is preferably 98.0% by mass or less, more preferably 97.0% by mass or less, and even more preferably 96.5% by mass or less, from the viewpoint of ensuring the amount of other components.

[0076] The negative electrode mixture layer may contain the carbon material of this disclosure. When the negative electrode mixture layer contains the above-mentioned carbon material, the content of the above-mentioned carbon material in the negative electrode mixture layer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0077] In the negative electrode mixture layer, the content of the carbon material 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.

[0078] (Conductive additive) The negative electrode mixture layer may contain a conductive additive. Examples of conductive additives include carbon materials such as carbon black and graphene.

[0079] (binder) The negative electrode mixture layer may contain a binder. Examples of binders include PVdF, PTFE, etc., as with the positive electrode mixture layer, as well as styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), etc.

[0080] If the negative electrode mixture layer contains a binder, the binder content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2.0% by mass or more, from the viewpoint of obtaining the function of a binder.

[0081] In the negative electrode mixture layer, the binder content is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4.0% by mass or less, from the viewpoint of suppressing an increase in the resistance of the negative electrode.

[0082] (Other ingredients) In addition to the above, the negative electrode mixture layer may contain other components such as dispersants and additives. For example, it may contain various dispersants for dispersing the negative electrode active material, and agents for surface modification of the negative electrode active material.

[0083] (Exterior materials) The outer casing material for housing the positive and negative electrodes is not limited as long as it can accommodate the positive and negative electrodes, and optionally a separator and electrolyte, or a solid electrolyte. Examples of outer casing materials include commercially available battery packs, 18650 type cylindrical cells, and those packaged in aluminum foil, and the outer casing material can be freely designed and used.

[0084] (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.

[0085] (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.

[0086] Examples of lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, and LiFSI.

[0087] 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.

[0088] (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.

[0089] (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.

[0090] Examples of solid electrolytes include polymer electrolytes and inorganic solid electrolytes. Polymer electrolytes are not particularly limited, and examples include polymers such as polyethylene oxide impregnated with the above-mentioned lithium salt. Inorganic solid electrolytes are not particularly limited, and examples include Li 13 Ti 1.7 Al 0.3 Examples include (PO4)3 and Li2S-P2S5.

[0091] 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 of electric tools, vacuum cleaners, electric bicycles, drones, electric vehicles, etc.; and for storing electric power obtained by fuel cells, solar power generation, wind power generation, etc.

Example

[0092] 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. The physical property values of the carbon materials obtained in the examples and comparative examples were measured by the methods shown below.

[0093] <BET specific surface area, total pore volume, cumulative pore volume at a specific relative pressure (nitrogen adsorption test)> Using NOVA4200e (manufactured by Quantachrome Instruments) as the measuring device, the sample was placed in a sample cell (9 mm × 135 mm) so that the total surface area of the sample was 2 m 2 ~5 m 2 The sample was put in, dried at 300 °C under vacuum conditions for 1 hour, and then the sample weight was measured and the measurement was carried out. Nitrogen was used as the gas for measurement.

[0094] The set minimum relative pressure during measurement was 0.005, and the set maximum relative pressure was 0.995. The BET specific surface area of the carbon material was calculated by the BET multi-point method from the adsorption isotherm data at three points near relative pressures of 0.1, 0.2, and 0.3. The total pore volume was calculated by linear approximation of the adsorption amount at a relative pressure of 0.99 from the adsorption isotherm data at two points around a relative pressure of 0.99, and was determined using the volume of 1 mole of nitrogen under standard conditions, the density of liquid nitrogen, and the atomic weight of nitrogen. The cumulative pore volume at a relative pressure of 0.1537 was calculated by linear approximation of the adsorption amount at a relative pressure of 0.1537 from the adsorption isotherm data at two points around a relative pressure of 0.1537, and was determined in the same manner as the total pore volume. Also, the cumulative pore volume at a relative pressure of 0.00295 was determined in the same manner as the cumulative pore volume at a relative pressure of 0.1537. ​3 The calculation was performed using the following assumptions: the volume of 1 mole of nitrogen at standard conditions (0°C, 1 atm) is 22.4133 liters, and the atomic weight of nitrogen is 14.0067.

[0095] The cumulative pore volume at a relative pressure of 0.1537 is calculated using the BJH method, which assumes the pore shape is cylindrical, by considering the average thickness t of the multi-molecular-weight nitrogen adsorption film and the Kelvin radius r. K The sum of (t+r K The radius of the cylinder is expressed by ), and furthermore, t is given by the Halsey formula, and r K If this is expressed by the Kelvin equation, it can be considered to be the sum of the volumes of pores with a diameter of 2 nm or less. In this disclosure, the radius of the cylinder (t+r K The diameter of the pore is defined as twice the value obtained from the given formula, and the diameter is rounded to the first decimal place.

[0096] The Halsey equation is known as equation (1) below. t = 0.354 [-5 / ln(p / p0)] 1 / 3 ...(1) In equation (1), t is the average thickness (nm) of the multi-molecule adsorbed film, p is the pressure, and p0 is the saturated vapor pressure. Therefore, p / p0 is the relative pressure.

[0097] It is known that the Kelvin equation becomes the following equation (2) in the case of nitrogen adsorption. r K =-0.953 / ln(p / p0)···(2) In formula (2), r K p is the Kelvin radius (the distance from the central axis of the cylinder to the surface of the multi-molecule adsorption film, assuming the pore shape is cylindrical), and its unit is nm. Also, p is pressure, and p0 is the saturated vapor pressure. Therefore, p / p0 is the relative pressure.

[0098] <d 002 (Powder X-ray diffraction) Using a horizontal sample multi-purpose X-ray diffractometer (Ultima IV, Rigaku Corporation), and following the JSPS method (Latest Experimental Techniques for Carbon Materials (Analysis and Analysis), edited by the Carbon Society of Japan), silicon powder was used as the internal standard. 002 Measurements were taken.

[0099] <Oxygen content> The oxygen content of carbon materials was measured under the following conditions. Approximately 20 mg of carbon material was weighed into a nickel capsule and placed in the graphite crucible of the oxygen, nitrogen, and hydrogen analyzer described below. The capsule was heated in an inert gas atmosphere, and the generated CO and CO2 were quantified by infrared absorption spectroscopy. (Measurement conditions) Oxygen, Nitrogen, and Hydrogen Analyzer: EMGA-920, manufactured by Horiba, Ltd. Carrier gas: Argon

[0100] <Transmission Electron Microscope (TEM) Observation> The carbon fibers contained in each carbon material were dispersed in ethanol, scooped up with a microgrid, and dried to obtain the sample. TEM observation was then performed on the sample. The carbon fibers contained in each carbon material were confirmed to have a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of the fiber thickness, as described below. First, the carbon materials were observed using TEM-EDX to obtain images showing the longitudinal direction of the carbon fibers (hereinafter also referred to as "TEM longitudinal images") and images showing the cross-section when the carbon fibers are cut in a direction intersecting the longitudinal direction (hereinafter also referred to as "TEM cross-sectional images"). In the TEM longitudinal images, it was confirmed that there are multiple lines along the longitudinal direction inside the carbon fibers, and in the TEM cross-sectional images, it was confirmed that there are multiple closed curves with different maximum diameters arranged concentrically. Thus, the structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of the fiber thickness in the carbon fibers was confirmed. Device name: JEM-ARM200F (manufactured by JEOL Ltd.)

[0101] <Average 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.

[0102] <Average 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.

[0103] <Consolidation Resistivity, Load-Compression Density Curve> The measuring jig shown in Figure 11 was used. Cell 4 has a flat area of ​​(1 × 4) cm². 2 It is made of resin, 10 cm deep, and has copper plate current terminals 3 for passing current through the object to be measured 5, and voltage measurement terminals 1 in the middle. 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 that point, the voltage between the two voltage measuring terminals 1 inserted from the bottom of the container at a distance of 2.0 cm was read, and the resistivity R was calculated from the following formula. R = (E / 0.1) × D / 2 In the formula, R is the resistivity [Ω·cm], and D is the cross-sectional area of ​​the powder in the direction of the current (depth × width) = 10d [cm²]. 2 ], where E is the terminal voltage [V]. In this example, the bulk density is 0.8 g / cm³. 3 The resistivity when compressed is defined as the compaction resistivity.

[0104] <Electrochemical Measurement> Using the carbon materials of each example and comparative example, the following test electrochemical cells were prepared, and electrochemical measurements were performed under the conditions shown below. (Preparation of test electrochemical cells) NMC811(Li(Ni)) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 )O2)96 Parts by mass of the carbon material from the example or comparative example, and 2.0 parts by mass of PVdF were weighed and mixed in a kneader. Then, NMP was added as needed while mixing in the kneader to prepare an electrode mixture layer-forming composition with adjusted viscosity. The prepared electrode mixture layer-forming composition was coated onto a 20 μm thick aluminum foil using a roll coater, dried, and then vacuum-dried to produce a test electrode with a positive electrode mixture layer. The basis weight (mass of the electrode mixture layer per unit area) was 17 mg / cm². 2 The dimensions of the test electrode were 20mm x 20mm. A test electrochemical cell was prepared using the Li metal test electrode, counter electrode, and reference electrode, as well as the electrolyte, from the examples or comparative examples. The electrolyte was a solution obtained by dissolving lithium hexafluoride phosphate (LiPF6) at a concentration of 1 M (mol / L) in a solvent prepared by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) in a volume ratio of 3:7. (Conditions for electrochemical measurement) Linear sweep voltammetry (LSV) was performed using the prepared test electrochemical cell under the following conditions. -Measurement conditions- Scanning range: From natural immersion potential to +5.2V vs. Li / Li + to Scanning speed: 3mV / s Measurement temperature: 45℃

[0105] <Fabrication of carbon materials> The carbon materials for the examples and comparative examples were prepared as shown below.

[0106] [Example 1] Manufacturing Example 1 (Synthesis of Carbon Materials: Produced Carbon Materials) A reactor was prepared consisting of a reaction tube with an inner diameter of 500 mm and a length of 2000 mm, and a heater. A two-fluid mixing nozzle for supplying raw materials was placed at the top of the reaction tube, and a conveyor belt was placed at the bottom of the reaction tube and connected to a tank equipped with a bag filter. The flammable gas that passed through the bag filter was burned in an incinerator. A starting liquid was prepared by dissolving ferrocene and sulfur in benzene. The composition of the starting liquid was 96.4% by mass of benzene, 3.5% by mass of ferrocene, and 0.1% by mass of sulfur. Using hydrogen as the carrier gas, the prepared raw material solution was supplied at a rate of 0.59 g / NL (benzene (g / min) / hydrogen (NL / min)). The raw material solution was sprayed into the reaction tube using a two-fluid nozzle and passed through a reaction furnace heated to 1300°C to synthesize carbon fibers. After supplying the raw materials for 7 hours, the supply of raw material solution and hydrogen was stopped, and nitrogen was supplied to expel the flammable gases. The carbon material produced by this operation is sometimes called "generated carbon material." Manufacturing Example 2 (Castration of Carbon Materials: Calcined Carbon Materials) The carbon material produced by Manufacturing Example 1 was placed in a firing furnace (120 mm inner diameter). It was heated to 1000°C under an argon atmosphere to remove the tar adhering to the carbon material. After firing, the carbon material obtained by this operation is sometimes called "fired carbon material". Manufacturing Example 3 (Graphitization of Calcined Carbon Materials: Graphitized Carbon Materials) The calcined carbon material obtained in Manufacturing Example 2 was placed in a high-frequency heating furnace (inner diameter 120 mm). The calcined carbon material was graphitized by heating to 2800°C under an argon atmosphere. The carbon material obtained by this operation is sometimes called "graphitized carbon material". After the graphitization treatment, the recovered graphitized carbon material was pulverized using a jet mill type pulverizer. The resulting powder was then passed through an electromagnetic separator for magnetic separation. The carbon material was obtained in the manner described above.

[0107] [Example 2] The carbon material was prepared in the same manner as in Example 1, except that the powder was not passed through the electromagnetic separator at the end.

[0108] [Example 3] The carbon material was prepared in the same manner as in Example 1, except that the inner diameter of the reaction tube was changed from 500 mm to 370 mm, the benzene flow rate / hydrogen flow rate ratio was set to 0.54 (g / NL), grinding was not performed after graphitization, and the powder was not passed through an electromagnetic separator at the end.

[0109] [Example 4] The carbon material was prepared in the same manner as in Example 1, except that the powder was not passed through the electromagnetic separator at the end.

[0110] [Comparative Example 1] In Example 1, a carbon material was prepared by following the same procedure as in Example 1, except that the graphitization process and pulverization after graphitization were omitted.

[0111] [Comparative Example 2] In Example 1, the carbon material was prepared by following the same procedure as in Example 1, except that the temperature during graphitization was changed from 2800°C to 2200°C and pulverization after the graphitization treatment was omitted.

[0112] [Comparative Example 3] In Example 1, the carbon material was prepared by following the same procedure as in Example 1, except that grinding after graphitization treatment was not performed.

[0113] [Comparative Example 4] A carbon material was prepared in the same manner as in Example 1, except that the reaction time was set to 2 hours, the calcination temperature to 1300°C, and pulverization was not performed after the graphitization treatment.

[0114] [Comparative Example 5] The carbon material was prepared in the same manner as in Example 1, except that the inner diameter of the reaction tube was changed from 500 mm to 370 mm and the benzene flow rate / hydrogen flow rate ratio was set to 0.54 (g / NL).

[0115] The carbon materials obtained in the examples and comparative examples were subjected to the aforementioned physical property measurements and electrochemical measurements. The results are shown in Tables 1 and 2. In Table 1, Volume 1 is the cumulative pore volume measured by nitrogen adsorbed onto the sample up to a relative pressure of 0.00295 in the nitrogen adsorption test, and the inventors believe that this value reflects the cumulative pore volume of pores with a diameter of 1 nm or less. φ1 is the ratio of Volume 1 to the total pore volume, and Volume 2 is the cumulative pore volume measured by nitrogen adsorbed onto the sample up to a relative pressure of 0.1537 in the nitrogen adsorption test, and is considered to be the cumulative pore volume of pores with a diameter of 2 nm or less based on the BJH method and the above assumptions. φ2 is the ratio of Volume 2 to the total pore volume.

[0116] [Table 1]

[0117] [Table 2]

[0118] The 4.1V oxidation current is largely thought to be due to lithium desorption from the positive electrode active material, NMC811, so a larger value is desirable in terms of battery characteristics. Furthermore, the 4.5V oxidation current is thought to be the sum of the current due to lithium desorption from the positive electrode active material NMC811 and the current due to the decomposition of the electrolyte. Therefore, a large 4.5V oxidation current is not necessarily desirable; rather, it is desirable for the 4.5V oxidation current to be large when the value of 4.5V oxidation current / 4.1V oxidation current is small (i.e., when the effect of electrolyte decomposition is small). As shown in Tables 1 and 2, the 4.1V oxidation current values ​​were higher in Examples 1-4 compared to Comparative Examples 1-5. Furthermore, the 4.5V oxidation current / 4.1V oxidation current values ​​in Examples 1-4 tended to be equal to or lower than those of the comparative examples.

Claims

1. A carbon material containing fibrous carbon having a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, d ００２ The wavelength is 0.3391 nm or less, and the BET specific surface area is 10.5 m². ２ / g or more 18.0m ２ The amount is less than 0.8 g / cm³, and the compressive density is 0.8 g / cm³. ３ A carbon material having a compaction resistivity greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm.

2. The carbon material according to claim 1, wherein in a nitrogen adsorption test of the carbon material, the cumulative pore volume up to a relative pressure of 0.00295 is 0.0030 mL / g to 0.0050 mL / g.

3. The carbon material d ００２ The carbon material according to claim 1, wherein the wavelength is 0.3370 nm to 0.3390 nm.

4. The carbon material according to claim 1, wherein the total pore volume (cumulative pore volume up to relative pressure = 0.99) in the nitrogen adsorption test of the carbon material is 0.1000 mL / g or less.

5. The carbon material according to claim 1, wherein in a nitrogen adsorption test of the carbon material, the ratio of the micropore volume (cumulative pore volume up to relative pressure = 0.1537) to the total pore volume (cumulative pore volume up to relative pressure = 0.99) by the BJH method using the Halsey formula, φ2, is 14.0% or less.

6. The carbon material according to claim 1, wherein the oxygen content of the carbon material is 0.10% by mass or less.

7. A conductive additive comprising the carbon material described in any one of claims 1 to 6.

8. A dispersion comprising the carbon material according to any one of claims 1 to 6.

9. A composition for forming an electrode mixture layer, comprising the carbon material described in any one of claims 1 to 6.

10. 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, wherein the carbon material is as described in any one of claims 1 to 6.

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