Carbon material, conductive assistant, dispersion liquid, composition for forming an electrode mixture layer, and secondary battery

Abstract

To provide a carbon material that enables the production of a secondary battery with a large value of 4.1 V oxidation current and excellent battery characteristics. 【Solution means】A carbon material containing fibrous carbon having a structure in which cylindrical carbon hexagonal net surfaces 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 / g, and the oxygen content is 0.10 mass% or less.

Description

Technical Field

[0001] The present disclosure relates to a carbon material, a conductive assistant, a dispersion liquid, a composition for forming an electrode binder layer, and a secondary battery.

Background Art

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

[0003] As a conductive agent for an electrode of a secondary battery, a composite carbon fiber in which multi-walled carbon nanotubes are homogeneously dispersed between graphitized carbon nanofibers and in the vicinity of the surface of the graphitized carbon nanofibers has been proposed (for example, Patent Document 1). The composite carbon fiber is easily dispersed in a matrix such as a resin without leaving aggregates and has an excellent effect of reducing resistance. When the composite carbon fiber is contained as a conductive agent in an electrode of a secondary battery, battery characteristics such as a capacity retention rate are improved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As an additive to a secondary battery, for example, as an additive to an electrode such as a positive electrode and a negative electrode, a material capable of improving battery characteristics is required. For example, in the positive electrode, +4.1V vs. Li / Li, which is considered to be approximately the lithium desorption current from the active material +It is desirable to have a carbon material that enables the production of a secondary battery with a large oxidation current at 4.1 V (hereinafter, may be simply referred to as "oxidation current at 4.1 V". The same applies to the oxidation current at other potentials).

[0006] The present disclosure has been made in view of the above circumstances, and aims to provide a carbon material having a large oxidation current value at 4.1 V and enabling the production of a secondary battery with excellent battery characteristics, as well as a conductive auxiliary agent, a dispersion, a composition for forming an electrode mixture layer, and a secondary battery containing the same.

Means for Solving the Problems

[0007] Specific means for achieving the above problems are as follows. <1> A carbon material containing fibrous carbon having a structure in which cylindrical carbon hexagonal net surfaces 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 / g, and the oxygen content is 0.10 mass% or less. <2> The carbon material according to <1>, wherein 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. <3> The carbon material according to <1> or <2>, wherein d 002 of the carbon material is 0.3370 nm to 0.3390 nm. <4> The carbon material according to any one of <1> to <3>, wherein the oxygen content of the carbon material is 0.08 mass% or less. <5> The carbon material according to any one of <1> to <4>, wherein 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. <6> The carbon material according to any one of <1> to <5>, wherein in the nitrogen adsorption test of the carbon material, φ2, which is the ratio of the micropore volume (cumulative pore volume up to a relative pressure of 0.1537) by the BJH method using the Harkins-Jura equation to the total pore volume (cumulative pore volume up to a relative pressure of 0.99), is 14.0% or less. <7> The carbon material according to any one of <1> to <6>, wherein the oxygen content is 0.03% by mass or more. <8> In the nitrogen adsorption test of the carbon material, when the ratio of the cumulative pore volume up to a relative pressure of 0.00295 to the total pore volume (cumulative pore volume up to a relative pressure of 0.99) is defined as φ1, and the ratio of the micropore volume (cumulative pore volume up to a relative pressure of 0.1537) by the BJH method using the Harkins-Jura equation to the total pore volume (cumulative pore volume up to a relative pressure of 0.99) is defined as φ2, the carbon material according to any one of <1> to <7>, wherein φ2 / φ1 is 1.350 or more. <9> The compression density is 0.8 g / cm 3 The carbon material according to any one of <1> to <8>, wherein the consolidation resistivity at is greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm. <10> A conductive assistant containing the carbon material according to any one of <1> to <9>. <11> A dispersion containing the carbon material according to any one of <1> to <9>. <12> A composition for forming an electrode binder layer containing the carbon material according to any one of <1> to <9>. <13> A positive electrode including a positive electrode current collector and a positive electrode binder layer disposed on the positive electrode current collector and containing a positive electrode active material, and a negative electrode including a negative electrode current collector and a negative electrode binder layer disposed on the negative electrode current collector and containing a negative electrode active material, A secondary battery in which at least one of the positive electrode binder layer and the negative electrode binder layer contains the carbon material according to any one of <1> to <9>.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a carbon material capable of manufacturing a secondary battery having a large value of 4.1 V oxidation current and excellent battery characteristics, and a conductive assistant, a dispersion, a composition for forming an electrode binder layer, and a secondary battery containing the same.

Brief Description of the Drawings

[0009]

Figure 1

Mode for Carrying Out the Invention

[0010] 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, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present disclosure.

[0011] 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 numerical range indicated by "~" in the present disclosure, the numerical values described before and after "~" are included 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. Also, 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 a 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 where it exists but also the case where it is formed only in a part of the region when observing the region where the layer or film exists. 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.

[0012] <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, and 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 / g, the oxygen content is 0.10 mass% or less, and in the nitrogen adsorption test of the carbon material, the ratio of the cumulative pore volume up to a relative pressure of 0.00295 to the total pore volume (cumulative pore volume up to a relative pressure of 0.99) is defined as φ1, and the ratio of the micropore volume (cumulative pore volume up to a relative pressure of 0.1537) obtained by the BJH method using the Harkins-Jura equation to the total pore volume (cumulative pore volume up to a relative pressure of 0.99) is defined as φ2. When φ2 / φ1 is 1.350 or more. By using the carbon material of the present disclosure, it is possible to produce a secondary battery having a large value of the oxidation current at 4.1 V and excellent battery characteristics.

[0013] The d of the carbon material 002 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. The d of the carbon material 002 means the average interplanar spacing d obtained by the X-ray diffraction method of the carbon material, specifically, the Gakushin method. 002

[0014] The BET specific surface area of the carbon material is 10.5 m 2 / g or more and less than 18.0 m 2 / g, and from the viewpoint of battery characteristics, it is preferably 11.0 m 2 / g to 17.5 m 2 / g, more preferably 11.5 m 2 / g to 17.0 m 2 / g, and even more preferably 13.5 m 2 / g to 17.0 m 2 / g. ​The BET specific surface area of the carbon material is calculated by the BET multipoint method from the adsorption isotherm data at three points near relative pressures of 0.1, 0.2, and 0.3.

[0015] The oxygen content of the carbon material is 0.10 mass% or less, and from the viewpoint of reducing the value of 4.5V oxidation current / 4.1V oxidation current when the carbon material is applied to a secondary battery, it is preferably 0.08 mass% or less, more preferably 0.06 mass% or less, and even more preferably 0.05 mass% or less. The lower limit of the oxygen content of the carbon material is not particularly limited and may be 0 mass%, may be 0.02 mass% or more, or may be 0.03 mass% or more. The oxygen content of the carbon material may be determined by heating the carbon material in an inert gas and quantifying the generated CO and CO2 by infrared absorption method.

[0016] From the viewpoint of manufacturing a secondary battery having 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.

[0017] The average fiber diameter of the fibrous carbon can be determined from the arithmetic mean of the diameters of 200 randomly selected fibers observed by SEM of the electrode. The diameter of one fiber can be determined by measuring the width at one location excluding both ends of a certain fiber from the SEM photograph and taking the arithmetic mean. Here, the width of the fiber refers to the dimension of the fiber in the direction perpendicular to the longitudinal direction.

[0018] From the viewpoint of manufacturing a secondary battery having 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.

[0019] The average fiber length of the fibrous carbon can be measured as follows. The powder is dispersed in a dispersion medium, and the sample spread on aluminum foil or the like is observed by SEM after drying. The lengths of 200 randomly selected fibers along the fiber axis are measured, and the average fiber length can be measured by taking the arithmetic mean. The electrode can be washed with a solvent, the powder with the binder or the like removed is taken out, and the average fiber length of the carbon fiber may be determined using the taken-out powder.

[0020] The total pore volume (cumulative pore volume up to a relative pressure of 0.99) in the nitrogen adsorption test of the carbon material of the present disclosure 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 the carbon material can be carried out by the method described in the examples below.

[0021] The cumulative pore volume of the pores up to a relative pressure of 0.00295 in the nitrogen adsorption test of the carbon material of the present disclosure 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.

[0022] The ratio (hereinafter also referred to as φ1) of the cumulative pore volume of the 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) in the nitrogen adsorption test of the carbon material of the present disclosure is preferably 13.0% or less, more preferably 10.0% or less, and even more preferably 5.0% to 9.0%.

[0023] The cumulative pore volume of the pores up to a relative pressure of 0.1537 in the nitrogen adsorption test of the carbon material of the present disclosure 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.

[0024] In the nitrogen adsorption test of the carbon material of the present disclosure, the ratio of the micropore volume (cumulative pore volume of pores up to a relative pressure of 0.1537) by the BJH method using the Harkins-Jura equation to the total pore volume (cumulative pore volume up to a relative pressure of 0.99) (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%.

[0025] In the nitrogen adsorption test of the carbon material of the present disclosure, φ2 / φ1 is 1.350 or more, and from the viewpoint of enabling the production of a secondary battery with a larger value of the 4.1V oxidation current and more excellent 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.

[0026] In the carbon material of the present disclosure, the compression density is 0.8 g / cm 3 and the consolidation specific resistance is preferably greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm. In the carbon material of the present disclosure, when the consolidation specific resistance is greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm, it tends to enable the production of a secondary battery with more excellent battery characteristics. More specifically, when the consolidation specific resistance is greater than 0.0165 Ω·cm, it is speculated that oxygen is moderately bonded to the surface of the carbon material, for example, the surface of fibrous carbon or non-fibrous carbon contained in the carbon material, or the hexagonal network plane of the carbon material is disordered, thereby improving the affinity and miscibility with the positive electrode active material, and the value of the 4.1V oxidation current tends to increase. On the other hand, when the consolidation specific resistance is less than 0.0140 Ω·cm, although there is a risk of decreasing the affinity and miscibility with the positive electrode active material, it is speculated that the value of the 4.1V oxidation current tends to increase because the carbon material has sufficient conductivity. The measurement of the consolidation specific resistance at a compression density of 0.8 g / cm of the carbon material 3 can be performed by the method described in the examples below.

[0027] A test electrochemical cell was fabricated using the carbon material of the present disclosure, and linear sweep voltammetry (LSV) was performed under the following conditions. The oxidation current at +4.1 V vs. Li / Li + versus the oxidation current at +4.5 V vs. Li / Li + The ratio of the oxidation current at 4.5 V to the oxidation current at 4.1 V (4.5 V oxidation current / 4.1 V 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 4.5 V oxidation current / 4.1 V oxidation current is not particularly limited, and for example, it may be 1.00 or more. When the 4.5 V oxidation current / 4.1 V oxidation current is 3.00 or less, sufficient electrons and ions can be transported to the electrode, and an electrode (especially the positive electrode) with small side reactions can be provided. -Measurement conditions- Scanning range: from the natural immersion potential to +5.2 V vs. Li / Li + up to Scanning rate: 3 mV / s Measurement temperature: 45 °C The test electrochemical cell may be fabricated as follows. Weigh 96 parts by mass of NMC811 (Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, 2 parts by mass of the carbon material of the present disclosure, and 2.0 parts by mass of PVdF, and mix them in a kneader. Then, while appropriately adding NMP, mix them in a kneader to prepare a composition for forming an electrode binder layer with adjusted viscosity. The prepared composition for forming an electrode binder layer is coated on an aluminum foil with a thickness of 20 μm using a roll coater, dried, and then further vacuum dried to fabricate a test electrode provided with a positive electrode binder layer. The areal density (mass of the electrode binder layer per unit area) is 17 mg / cm 2 and the dimensions of the test electrode are 20 mm × 20 mm. Next, a test electrochemical cell is fabricated using the test electrode, a counter electrode, a reference electrode of Li metal, and an electrolyte. As the electrolyte, a solution obtained by dissolving lithium hexafluorophosphate (LiPF6) at 1 M (mol / L) in a solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) are mixed at a volume ratio of 3:7 is used.

[0028] The carbon material of the present disclosure may be a material composed only of fibrous carbon having a structure in which cylindrical carbon hexagonal net planes are laminated in the fiber thickness direction, or may be a material composed of the fibrous carbon and other carbon materials. The content of the fibrous carbon contained in the carbon material of the present disclosure may be 50% by mass to 100% by mass, may be 70% by mass to 100% by mass, or may be 90% by mass to 100% by mass with respect to the total amount of the carbon material.

[0029] The synthesis method of the carbon material of the present disclosure is not particularly limited. For example, it may be synthesized by a vapor phase method, or may be synthesized by a floating catalyst method and then heat-treated at 2000 °C or higher in an inert atmosphere. The floating catalyst method is a method of obtaining carbon fibers by introducing a raw material solution in which a catalyst source such as ferrocene and a sulfur compound are dissolved in a carbon source such as benzene, or a gasified product thereof, into a reactor heated to 1000 °C or higher using a carrier gas such as hydrogen. Generally, a hollow tube is formed starting from the catalyst metal at the initial stage of the reaction, and growth occurs in the length direction of the carbon fiber. The growth in the length direction continues until the catalytic activity is lost, for example, when the surface of the catalyst particles is covered with carbon. When the growth in the length direction ends, pyrolytic carbon is deposited on the surface of the hollow tube, and growth in the thickness direction proceeds, forming a structure in which cylindrical carbon hexagonal net planes are laminated in the fiber thickness direction. Therefore, the adjustment of the fiber diameter is possible by controlling the amount of pyrolytic carbon deposited on the carbon fiber during the reaction, that is, the reaction time, the raw material concentration in the atmosphere, and the reaction temperature. The carbon material obtained by this reaction may have low conductivity because it is covered with pyrolytic carbon with low crystallinity. Therefore, in order to increase the crystallinity of the carbon fiber, heat treatment is performed at 800 to 1500 °C in an inert gas atmosphere such as argon, and then graphitization treatment is performed at 2000 to 3000 °C. The graphitization treatment can simultaneously evaporate and remove the catalyst metal, enabling the purification of the fibrous carbon. After performing heat treatment (first firing step) at 800°C to 1500°C, preferably 900°C to 1300°C, in an inert gas atmosphere such as argon, the temperature is raised to 200°C to 500°C, preferably 1200°C to 1700°C, and a treatment (second firing step) of holding for about 30 minutes to 3 hours is preferably performed. As a result, the value of the oxidation current at 4.1 V increases, and the battery characteristics tend to improve. Further, the temperature during the graphitization treatment is preferably 2500°C to 3000°C, more preferably 2600°C to 3000°C.

[0030] In the present disclosure, the structure in which cylindrical carbon hexagonal net planes are laminated in the thickness direction refers to a structure in which structures formed by winding carbon hexagonal net planes into a cylindrical shape are laminated in the thickness direction (also referred to as a specific structure). The 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 a 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"). Then, in the TEM longitudinal image, when there are a plurality of lines along the longitudinal direction inside the carbon fiber, and in the TEM cross-sectional image, 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 carbon fiber has a specific structure. Further, in X-ray diffraction (XRD), by confirming diffraction lines similar to those of graphite particles for the planes of (002), (100), (101), (110), or (112), a structure in which carbon hexagonal net planes are laminated can be confirmed. The structure in which cylindrical carbon hexagonal net planes are laminated 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 concentric multi-tubes), 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 laminated 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.

[0031] The d of the carbon material of the present disclosure 002, the BET specific surface area and the oxygen content can be adjusted as follows. Note that the following adjustment methods are just examples, and the present disclosure is not limited thereto. d 002 For example, it can be adjusted by changing the conditions of the graphitization treatment such as the graphitization temperature, and the grinding conditions. For example, by increasing the graphitization temperature, d 002 tends to decrease. The BET specific surface area can be adjusted, for example, by changing the conditions of the graphitization treatment such as the temperature rise time and the holding time during graphitization, the conditions such as the temperature rise time and the holding time of each firing step, the conditions of various treatments such as grinding, and the synthesis reaction conditions of the powder. For example, by increasing the holding time during graphitization, the BET specific surface area tends to decrease, and by providing a second firing step or increasing the rotation speed during grinding, the BET specific surface area tends to increase. The oxygen content is, for example, correlated with the BET specific surface area, and tends to increase as the BET specific surface area increases. Therefore, the oxygen content can also be adjusted by adjusting the conditions (firing step, activation treatment, grinding conditions, etc.) of the treatment for increasing the BET specific surface area. Magnetic separation using an electromagnetic separator may or may not be performed on the carbon material of the present disclosure. It is considered that the oxygen content of the carbon material can be adjusted by performing magnetic separation using an electromagnetic separator.

[0032] The carbon material of the present disclosure may be used as a conductive aid or the like, and may also be used for the preparation of a dispersion, a composition for forming an electrode binder layer, or the like.

[0033] The carbon material of the present disclosure may be used in the form of a dispersion dispersed 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 an additive.

[0034] The carbon material of the present disclosure may also be used for the preparation of a composition for forming an electrode binder layer (composition for forming an electrode binder layer). Examples of the composition for forming the electrode mixture layer include a composition for forming a positive electrode mixture layer for forming a positive electrode mixture layer, a composition for forming a negative electrode mixture layer for forming a negative electrode mixture layer, and the like. The composition for forming the positive electrode mixture layer contains a positive electrode active material and the carbon material of the present disclosure, and may further contain carbon black, a binder, a solvent, etc. as necessary. The composition for forming the negative electrode mixture layer contains a negative electrode active material and the carbon material of the present disclosure, and may further contain a conductive auxiliary agent, a binder, a solvent, etc. as necessary.

[0035] <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 containing 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 containing a negative electrode active material 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 carbon material of the present disclosure.

[0036] 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 laminated secondary battery may be used, or a wound secondary battery may be used. As the wound secondary battery, for example, a cylindrical secondary battery in which an electrode pair and an electrolytic solution obtained by winding a laminate formed by laminating a positive electrode and a negative electrode via a separator are enclosed in a cylindrical exterior body may be used, or 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.

[0037] 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 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.

[0038] 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, aluminum-based secondary batteries, and the like. Among them, lithium-based secondary batteries capable of achieving high voltage and high energy density and sodium-based secondary batteries capable of cost reduction are preferable. Examples of the lithium-based secondary battery 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 thereof include liquid electrolyte type batteries and solid electrolyte type batteries containing at least one of electrolytes, polymer electrolytes, polymer gel electrolytes, solid electrolytes, and the like. Further, regarding secondary batteries other than lithium-based secondary batteries, similar to the aforementioned lithium-based 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-based secondary battery will be described, but the present invention is not limited thereto.

[0039] [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.

[0040] 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, and the like. The state of the positive electrode current collector is not particularly limited and can be selected from foil, perforated foil, mesh, and the like. As an example, an aluminum foil is used as the positive electrode current collector.

[0041] The positive electrode mixture layer may contain the carbon material 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 carbon material of the present disclosure, and further containing carbon black, a binder, a solvent, etc. as necessary, is applied on the positive electrode current collector, the applied slurry is dried, and then pressed to form a positive electrode mixture layer on the positive electrode current collector.

[0042] From the perspective of energy density and safety, 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.

[0043] From the perspective of energy density and safety, 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, may be 3.0 g / cm 3 ~4.0 g / cm 3 and may be.

[0044] From the perspective of energy density and safety, the areal weight of the positive electrode active material layer may be 10.0 mg / cm 2 or more, may be 10.0 mg / cm 2 ~30.0 mg / cm 2 and may be.

[0045] The average electrode area (average positive electrode area and average negative electrode area) per sheet may be 20 cm 2 ~10000 cm 2 and may be, may be 300 cm 2 ~10000 cm 2 and may be.

[0046] (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 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.

[0047] The positive electrode active material preferably contains LiNi x Mn y Co z Al w O2 (x, y, z, w ≧ 0, x + y + z + w = 1), or LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni).

[0048] LiNi x Mn y Co z Al w As O2 (x, y, z, w ≧ 0, x + y + z + w = 1), it is preferably one with a relatively high nickel ratio, for example, x ≧ 0.5 or more. Li(Ni x Mn y Co z )O2 (x ≧ 0.5, y ≦ 0.3, z ≦ 0.3, x + y + z = 1) is more preferable. As the positive electrode active material represented by Li(Ni x Mn y Co z )O2 (x ≧ 0.5, y ≦ 0.3, z ≦ 0.3, x + y + z = 1), for example, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.7 Mn 0.1 Co 0.2 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2 and Li(Ni 0.5 Mn 0.2 Co 0.3 )O2 can be mentioned.

[0049] As the positive electrode active material represented by LiMPO4 (M is one or more selected from Fe, Co, Mn, and Ni), for example, LiFePO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn0.7 PO4, LiCoPO4, and LiCo 0.5 Mn 0.5 PO4 can be mentioned.

[0050] In the positive electrode binder layer, from the viewpoint of the positive electrode capacity, 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.

[0051] In the positive electrode binder layer, from the viewpoint of ensuring the amount of other components, 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.

[0052] The positive electrode binder layer may contain the carbon material of the present disclosure. When the positive electrode binder layer contains the above carbon material, in the positive electrode binder layer, the content of the above carbon material 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.

[0053] In the positive electrode binder layer, the content of the above 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.

[0054] The positive electrode binder layer may contain fibrous carbon (other fibrous carbon) other than the carbon material of the present disclosure. 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.

[0055] (Carbon black) The positive electrode active material layer may further contain carbon black. Carbon black is used as a conductive aid for the secondary battery. 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).

[0056] The primary particle diameter of the carbon black may be 10 nm to 100 nm. Here, the primary particle refers to the portion corresponding to one bead in the bead-like structure called an aggregate. If the primary particle diameter of the carbon black is within this range, it tends to be uniformly dispersed on the surface of the active material. From the viewpoint of improving dispersibility, the primary particle diameter of the carbon black is preferably 20 nm to 80 nm, and more preferably 30 nm to 70 nm.

[0057] The primary particle diameter of the carbon black can be determined by selecting any 100 primary particles of the carbon black from the SEM photograph of the electrode and the cross-sectional SEM photograph, and calculating the arithmetic mean of the measurement results of the maximum length of the particles by image recognition software.

[0058] When the positive electrode active material layer contains carbon black, the content of the carbon black 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.

[0059] In the positive electrode active material layer, the content of the carbon black 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.

[0060] (Binder) The positive electrode active material layer may contain a binder. As the binder, a binder typically used for the positive electrode active material layer of a lithium ion secondary battery can be preferably used. Examples of the binder include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).

[0061] When the positive electrode active material layer contains a binder, the content of the binder 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 as a binder.

[0062] In the positive electrode active material layer, the content of the binder 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.

[0063] (Other components) In addition to the above, the positive electrode active material layer may contain other components such as a dispersant and an additive. For example, it may contain various dispersants for dispersing the positive electrode active material, agents for surface modification of the positive electrode active material, and the like.

[0064] [Negative electrode] The secondary battery includes a negative electrode including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0065] The material of the negative electrode current collector is not particularly limited as long as it is a material having electron conductivity, and can be selected from copper, nickel, titanium, stainless steel, and the like. The state of the negative electrode current collector is not particularly limited, and can be selected from foil, perforated foil, mesh, and the like. As an example, a copper foil is used as the negative electrode current collector.

[0066] The negative electrode active material layer may contain the carbon material of the present disclosure. For example, a composition for a negative electrode binder layer (a kind of composition for forming an electrode binder layer), which contains a negative electrode active material and the carbon material of the present disclosure on a negative electrode current collector, and further contains a conductive assistant, a binder, a solvent, etc. as required, is applied, the applied slurry is dried, and then pressed to form a negative electrode binder layer on the negative electrode current collector.

[0067] 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.

[0068] 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, may be 1.5 g / cm 3 to 2.0 g / cm 3 and may be such.

[0069] 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, may be 10 mg / cm 2 to 20 mg / cm 2 and may be such.

[0070] (Negative electrode active material) The negative electrode binder 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), etc. 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.

[0071] In the negative electrode binder layer, the content of the negative 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.

[0072] In the negative electrode binder layer, from the viewpoint of ensuring the amount of other components, 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.

[0073] The negative electrode binder layer may contain the carbon material of the present disclosure. When the negative electrode binder layer contains the above carbon material, in the negative electrode binder layer, the content of the above carbon material 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.

[0074] In the negative electrode binder layer, the content of the above 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.

[0075] (Conductive aid) The negative electrode binder layer may contain a conductive aid. Examples of the conductive aid include carbon materials such as carbon black and graphene.

[0076] (Binder) The negative electrode binder layer may contain a binder. As examples of the binder, in addition to PVdF, PTFE, etc. which can be used in the same way as in the positive electrode binder layer, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), etc. can be used.

[0077] When the negative electrode binder layer contains a binder, from the viewpoint of obtaining the function as a binder, the content of the binder 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.

[0078] In the negative electrode binder layer, the content of the binder 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.

[0079] (Other components) In addition to the above, the negative electrode binder layer may contain other components such as a dispersant and an additive. For example, it may contain various dispersants for dispersing the negative electrode active material, agents for surface modification of the negative electrode active material, and the like.

[0080] (Outer packaging material) The outer packaging material for housing the positive electrode and the negative electrode is not limited as long as it can house the positive electrode and the negative electrode, and optionally a separator and an electrolytic solution, or a solid electrolyte, etc. Examples of the outer packaging material include a commercially available battery pack, a cylindrical cell of the 18650 type, a form packed with an aluminum packaging material, etc., and the outer packaging material can be freely designed and used.

[0081] (Separator) The secondary battery may be provided with a separator between the positive electrode and the negative electrode. The separator can be freely selected from those that can be used in a general secondary battery, and examples thereof include a microporous film made of polyethylene or polypropylene. Separators in which particles such as SiO2 and Al2O3 are mixed as fillers, and separators having these particles adhered to the surface can also be used.

[0082] (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.

[0083] Examples of the lithium salt include LiPF6, LiBF4, LiClO4, LiAsF6, LiFSI, and the like.

[0084] Examples of the organic solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), etc. The organic solvent may be appropriately selected from those listed here 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.

[0085] (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.

[0086] (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.

[0087] Examples of the solid electrolyte include polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte is not particularly limited, and examples thereof include those in which the above lithium salt is impregnated in a polymer such as polyethylene oxide. The inorganic solid electrolyte is not particularly limited, and examples thereof include Li 13 Ti 1.7 Al 0.3 (PO4)3, Li2S-P2S5, etc.

[0088] 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, etc.

Example

[0089] 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.

[0090] <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, the sample weight was measured, and the measurement was carried out. Nitrogen was used as the gas for measurement.

[0091] 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 multipoint 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 linearly approximating 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 in the standard state, 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 linearly approximating 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. At this time, the density of liquid nitrogen was 0.808 g / cm3 The volume of 1 mole of nitrogen at the standard state (0 °C, 1 atm) was calculated to be 22.4133 liters, with the atomic weight of nitrogen being 14.0067.

[0092] When the relative pressure is 0.1537, the cumulative pore volume is calculated based on the BJH method assuming the pore shape is cylindrical. The sum of the average thickness t of the nitrogen multi - molecular adsorption film and the Kelvin radius r K of the cylinder is represented by the radius of the cylinder (t + r K ). Further, assuming that the t is expressed by the Halsey formula and the r K is expressed by the Kelvin formula, it is considered to be the sum of the volumes of pores with a diameter of 2 nm or less. In the present disclosure, the value obtained by doubling the radius (t + r K ) of the cylinder is used as the pore diameter, and the value obtained by rounding the numerical value in the first decimal place is adopted as the diameter.

[0093] The Halsey formula is known by the following formula (1). t = 0.354[-5 / ln(p / p0)] 1 / 3 ···(1) In formula (1), t is the average thickness (nm) of the multi - molecular adsorption film, p is the pressure, and p0 is the saturated vapor pressure. Thus, p / p0 is the relative pressure.

[0094] The Kelvin formula is known to be the following formula (2) in the case of nitrogen adsorption. r K =-0.953 / ln(p / p0)···(2) In formula (2), r K is the Kelvin radius (the distance from the central axis of the cylinder to the surface of the multi - molecular adsorption film when assuming the pore shape is cylindrical), and the unit is nm. Also, p is the pressure and p0 is the saturated vapor pressure. Thus, p / p0 is the relative pressure.

[0095] <d 002 (Powder X - ray diffraction)> Using a sample - horizontal multi - purpose X - ray diffractometer (Ultima IV, manufactured by Rigaku Corporation), the Gakushin method (the latest According to "Experimental Techniques for Carbon Materials (Analysis and Interpretation), edited by the Carbon Materials Society", using silicon powder as the internal standard, the measurement of d 002 was carried out.

[0096] <Oxygen content> The oxygen content of the carbon material was measured under the following conditions. Approximately 20 mg of the carbon material was weighed into a nickel capsule and placed in a graphite crucible of the following oxygen, nitrogen, and hydrogen analyzer. It was heated in an inert gas, and the generated CO and CO2 were quantified by infrared absorption method. (Measurement conditions) Oxygen, nitrogen, and hydrogen analyzer: EMGA-920 manufactured by Horiba, Ltd. Carrier gas: Argon

[0097] <Transmission electron microscope (TEM) observation> The carbon fibers contained in each carbon material were dispersed in ethanol, and the sample was taken with a microgrid and dried. The TEM observation of the sample was carried out. It was confirmed as follows that all the carbon fibers contained in each carbon material had a structure in which cylindrical carbon hexagonal net planes were laminated in the fiber thickness direction. First, the carbon material was observed by TEM-EDX, and an image in which the longitudinal direction of the carbon fiber could be confirmed (hereinafter also referred to as the "TEM longitudinal image") and an image in which the cross-section when the carbon fiber was cut in a direction intersecting the longitudinal direction could be confirmed (hereinafter also referred to as the "TEM cross-sectional image") were observed. Then, in the TEM longitudinal image, it was confirmed that there were a plurality of lines along the longitudinal direction inside the carbon fiber, and in the TEM cross-sectional image, a plurality of closed curves with different maximum diameters existed concentrically. Based on the above, the structure in which the cylindrical carbon hexagonal net planes in the carbon fiber were laminated in the fiber thickness direction was confirmed. Equipment name: JEM-ARM200F (manufactured by JEOL Ltd.)

[0098] <Average fiber diameter> The double-sided carbon tape was attached to the sample stage for SEM observation, and about half of the powder of the microspatula was scattered thereon. This was observed by SEM. Observation was carried out at a magnification of 20,000 times, and multiple SEM photos were taken. The number of fibrous carbons for measuring the diameter was set to 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 each fibrous carbon, the diameter at one randomly selected location other than both ends was measured and taken as the diameter of that fibrous carbon.

[0099] <Average 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 non-glossy 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 that showed both ends. The lengths along the fiber axes of 200 randomly selected fibers were measured, and the average value was obtained.

[0100] <Consolidation specific resistance, load-compression density curve> The measuring jig shown in Fig. 11 was used. The cell 4 is made of resin with a planar area of (1×4) cm 2 , a depth of 10 cm, and is equipped with a copper plate current terminal 3 for passing current through the object to be measured 5 and a voltage measurement terminal 1 in the middle. A certain amount of sample was put into the cell 4, and a force was applied to the compression rod 2 from above to compress the sample. A current of 0.1 A was passed through the sample, and the voltage between 2.0 cm of the two voltage measurement terminals 1 inserted from the bottom of the container was read at the time when the bulk density was 0.8 g / cm 3 , and the specific resistance R was calculated from the following formula. R=(E / 0.1)×D / 2 In the formula, R is the specific resistance [Ω·cm], D is the cross-sectional area of the powder in the current direction (depth×width)=10d [cm 2 .], and E is the voltage between the terminals [V]. In this example, the specific resistance when compressed to a bulk density of 0.8 g / cm 3 was taken as the consolidation specific resistance.

[0101] <Electrochemical measurement> Using the carbon materials of each example and comparative example, the following test electrochemical cell was fabricated, and electrochemical measurements were performed under the conditions shown below. (Fabrication of Test Electrochemical Cell) As the positive electrode active material, NMC811 (Li(Ni 0.8 Mn 0.1 Co 0.1 )O2)96 96 parts by mass, 2 parts by mass of the carbon material of the example or comparative example, and 2.0 parts by mass of PVdF were weighed and mixed in a kneader. Then, while appropriately adding NMP, the mixture was kneaded in a kneader to prepare a composition for forming an electrode binder layer with adjusted viscosity. The prepared composition for forming an electrode binder layer was coated on an aluminum foil with a thickness of 20 μm using a roll coater, dried, and then further vacuum dried to fabricate a test electrode having a positive electrode binder layer. The areal mass (mass of the electrode binder layer per unit area) was 17 mg / cm 2 and the dimensions of the test electrode were 20 mm × 20 mm. A test electrochemical cell was fabricated using the test electrode of the example or comparative example, a counter electrode, and a reference electrode of Li metal, and an electrolyte. As the electrolyte, a solution obtained by dissolving lithium hexafluorophosphate (LiPF6) to a concentration of 1 M (mol / L) in a solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 3:7 was used. (Conditions for Electrochemical Measurement) Using the fabricated test electrochemical cell, linear sweep voltammetry (LSV) was performed under the conditions shown below. -Measurement Conditions- Scanning range: From the natural immersion potential to +5.2 V vs. Li / Li + up to Scanning rate: 3 mV / s Measurement temperature: 45 °C

[0102] (Fabrication of Carbon Material) The carbon materials of the examples and comparative examples were fabricated as shown below.

[0103] [Example 1] Production Example 1 (Synthesis of Carbon Material: Produced Carbon Material) A reactor composed of a reaction tube with an inner diameter of 500 mm and a length of 2000 mm and a heater was prepared. A two-fluid mixing nozzle for supplying raw materials was arranged at the upper part of the reaction tube, a conveyor was arranged at the lower part of the reaction tube, and it was connected to a tank equipped with a bag filter. The combustible gas that passed through the bag filter was burned in an incinerator. Ferrocene and sulfur were dissolved in benzene to prepare a raw material solution. The composition of the raw material solution was 96.4% by mass of benzene, 3.5% by mass of ferrocene, and 0.1% by mass of sulfur. The carrier gas was hydrogen, and the prepared raw material solution was supplied under the condition of 0.59 g / NL (benzene (g / min) / hydrogen (NL / min)). The raw material solution was sprayed into the reaction tube with 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 the raw material solution and hydrogen was stopped, and nitrogen was supplied to expel the combustible gas. The carbon material produced by this operation may be referred to as the 'produced carbon material'. Production Example 2 (Firing of Carbon Material: Fired Carbon Material) The produced carbon material obtained in Production Example 1 was set in a firing furnace (inner diameter 120 mm). It was heated to 1000 °C under an argon atmosphere to remove the tar content adhering to the produced carbon material. After firing, the carbon material obtained by this operation may be referred to as the 'fired carbon material'. Production Example 3 (Graphitization of Fired Carbon Material: Graphitized Carbon Material) The fired carbon material obtained in Production Example 2 was set in a high-frequency heating furnace (inner diameter 120 mm). It was heated to 2800 °C under an argon atmosphere to graphitize the fired carbon material. The carbon material obtained by this operation may be referred to as the 'graphitized carbon material'. After the graphitization treatment, the recovered graphitized carbon material was pulverized with a jet mill type pulverizer. Also, the obtained powder was passed through a magnetic separator for magnetic separation. The carbon material was obtained as described above.

[0104] [Example 2] The operation was carried out in the same manner as in Example 1 except that the powder was not passed through the magnetic separator at the end, and a carbon material was produced.

[0105] [Example 3] 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), and the operation was carried out in the same manner as in Example 1 except that pulverization after graphitization was not performed and the powder was not passed through an electromagnetic separator at the end, and a carbon material was produced.

[0106] [Example 4] The operation was carried out in the same manner as in Example 1 except that the powder was not passed through an electromagnetic separator at the end, and a carbon material was produced.

[0107] [Comparative Example 1] In Example 1, the operation was carried out in the same manner as in Example 1 except that the graphitization process and pulverization after graphitization were not performed, and a carbon material was produced.

[0108] [Comparative Example 2] In Example 1, the operation was carried out in the same manner as in Example 1 except that the temperature during graphitization was changed from 2800 °C to 2200 °C and pulverization after graphitization was not performed, and a carbon material was produced.

[0109] [Comparative Example 3] In Example 1, the operation was carried out in the same manner as in Example 1 except that pulverization after graphitization was not performed, and a carbon material was produced.

[0110] [Comparative Example 4] The operation was carried out in the same manner as in Example 1 except that the reaction time was set to 2 hours, the firing temperature was set to 1300 °C, and pulverization after graphitization was not performed, and a carbon material was produced.

[0111] [Comparative Example 5] The operation was carried out 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), and a carbon material was produced.

[0112] For the carbon materials obtained in the examples and comparative examples, the above-described physical property values were measured and electrochemical measurements were performed. The results are shown in Tables 1 and 2. In Table 1, Volume 1 is the cumulative pore volume measured by nitrogen adsorbed by the sample up to a relative pressure of 0.00295 in the nitrogen adsorption test, and the inventors consider it to be a value reflecting 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. Volume 2 is the cumulative pore volume measured by nitrogen adsorbed by the sample up to a relative pressure of 0.1537 in the nitrogen adsorption test, and based on the BJH method and the above assumptions, it is considered to be the cumulative pore volume of pores with a diameter of 2 nm or less. φ2 is the ratio of Volume 2 to the total pore volume.

[0113]

Table 1

[0114]

Table 2

[0115] Since most of the 4.1 V oxidation current is considered to be the current due to lithium desorption from NMC811, which is the positive electrode active material, it is desirable that the value be large in terms of battery characteristics. Also, the 4.5 V oxidation current is considered to be the sum of the current due to lithium desorption from NMC811, which is the positive electrode active material, and the current due to the decomposition of the electrolytic solution. Therefore, the 4.5 V oxidation current is not simply required to be large, but it is desirable that the 4.5 V oxidation current be large in a state where the value of 4.5 V oxidation current / 4.1 V oxidation current is small (that is, a state where the influence of the decomposition of the electrolytic solution is small). As shown in Tables 1 and 2, in Examples 1 to 4, the value of the 4.1 V oxidation current was larger than that in Comparative Examples 1 to 5. Furthermore, in Examples 1 to 4, the value of 4.5 V oxidation current / 4.1 V oxidation current also tended to be equal to or less than that of the comparative examples.

Claims

1. A carbon material containing fibrous carbon having a structure in which cylindrical carbon hexagonal mesh planes are laminated in the thickness direction of the fiber, ００２ is 0.3391 nm or less, and the BET specific surface area is 10.5 m ２ / g or more 18.0m ２ / g and an oxygen content of 0.10 mass% or less.

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

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

4. The carbon material according to claim 1 , wherein the oxygen content of the carbon material is 0.08 mass % or less.

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

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

7. The carbon material according to claim 1 , wherein the oxygen content is 0.03 mass % or more.

8. 2. The carbon material according to claim 1, wherein in a nitrogen adsorption test of the carbon material, when φ1 is a ratio of a cumulative pore volume up to a relative pressure of 0.00295 to a total pore volume (cumulative pore volume up to a relative pressure of 0.99), and φ2 is a ratio of a micropore volume (cumulative pore volume up to a relative pressure of 0.1537) according to the BJH method using the Halsey equation to a total pore volume (cumulative pore volume up to a relative pressure of 0.99), φ2 / φ1 is 1.350 or more.

9. Compressed density 0.8 g / cm ３ 2. The carbon material according to claim 1, wherein the compaction resistivity at 2000 nm is greater than 0.0165 Ω·cm or less than 0.0140 Ω·cm.

10. The carbon material according to claim 1, having a BET specific surface area of ​​13.5 m 2 / g or more.

11. A conductive assistant comprising the carbon material according to any one of claims 1 to 10.

12. A dispersion comprising the carbon material according to any one of claims 1 to 10.

13. A composition for forming an electrode mixture layer, comprising the carbon material according to any one of claims 1 to 10.

14. 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 carbon material according to any one of claims 1 to 10.

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