Composite carbonaceous conductive materials and non-aqueous electrolyte rechargeable batteries

Abstract

A composite carbonaceous conductive material is provided that exhibits good conductivity and, furthermore, not only has excellent withstand voltage characteristics under high voltage environments but also can secure long-term performance stability of the battery. The composite carbonaceous conductive material comprises carbon nanotubes and a coating film covering the surface of the carbon nanotubes, wherein the coating film contains nitrogen element (N), boron element (B), and oxygen element (O), and the weight ratio (B / N) of the average content of boron element (B) to the average content of nitrogen element (N) contained in the coating film is 0.7 or more and 1.8 or less, the average content of boron element (B) contained in the coating film is 1.0 weight% or more and 15.0 weight% or less with respect to 100 weight% of the composite carbonaceous conductive material, and the coefficient of variation ([standard deviation / average value]×100) of the average content of boron element (B) contained in the coating film is 20% or less.

Description

Technology Field

[0001] The present invention relates to a composite carbonaceous conductive material, a cathode for a secondary battery containing the same, a non-aqueous electrolyte secondary battery, and a solid-state secondary battery. Furthermore, the present invention relates to a method for manufacturing a composite carbonaceous conductive material. Background Technology

[0002] Non-aqueous electrolyte secondary batteries, including lithium-ion batteries, are widely used as power sources for devices such as smartphones and laptop computers, and recently, they are also being used in large batteries for vehicles. To increase the capacity and output of these lithium-ion secondary batteries, the voltage of the batteries is being increased. Meanwhile, the cathode of the battery mainly contains a cathode active material, but this active material lacks electron conductivity. Consequently, it is necessary to supplement the electron conductivity of the electrode by adding a carbonaceous conductive material with excellent electron conductivity to the cathode.

[0003] In high-voltage batteries, the cathode is exposed to a strong oxidizing environment when it reaches a high potential state. When the carbonaceous conductive material within the cathode is placed under a high potential environment, there is a risk that the safety and long-term performance stability of the battery may be compromised due to the degradation of the carbonaceous conductive material itself or adverse reactions between the carbonaceous conductive material and the non-aqueous electrolyte in the lithium-ion secondary battery. Therefore, further measures are required to suppress the degradation of the carbonaceous conductive material in order to ensure the safety and long-term performance stability of the battery.

[0004] As a countermeasure, a technology has been proposed to suppress the reaction between the carbonaceous conductive material and the electrolyte by installing a coating layer on the carbonaceous conductive material. Patent Document 1 discloses coating carbon black with 0.5 to 3.5 parts by weight of boron elements to improve withstand voltage characteristics. However, Patent Document 1 does not mention the long-term performance stability of the battery.

[0005] Patent Document 2 discloses forming a coating layer composed of a boric acid framework on the surface of a conductive material to reduce the degradation of the conductive material under high potential environments and to lower the rate of resistance increase associated with long-term use. However, the battery disclosed in Patent Document 2 is substantially an all-solid-state battery, and there is no mention of suppressing side reactions between the conductive material and the non-aqueous electrolyte. Prior art literature

[0006] [Patent Document 1] International Publication No. 2008 / 015779 [Patent Document 2] Japanese Patent Publication No. 2023-154562 The problem to be solved

[0007] The present invention aims to provide a composite carbonaceous conductive material that exhibits good conductivity and, furthermore, not only has excellent withstand voltage characteristics under high-voltage environments but also enables securing long-term performance stability of the battery. means of solving the problem

[0008] A composite carbonaceous conductive material according to one embodiment comprises carbon nanotubes and a coating film covering the surface of the carbon nanotubes, wherein the coating film contains a nitrogen element (N), a boron element (B), and an oxygen element (O), and the weight ratio (B / N) of the average content of the boron element (B) to the average content of the nitrogen element (N) included in the coating film is 0.7 or more and 1.8 or less, the average content of the boron element (B) included in the coating film is 1.0 weight% or more and 15.0 weight% or less with respect to 100 weight% of the composite carbonaceous conductive material, and the coefficient of variation ([standard deviation / average value]×100) of the average content of the boron element (B) included in the coating film is 20% or less.

[0009] A positive electrode for a secondary battery according to one embodiment comprises a positive electrode active material and a conductive material, wherein the conductive material is the composite carbonaceous conductive material.

[0010] A non-aqueous electrolyte secondary battery according to one embodiment comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode is a positive electrode for the secondary battery.

[0011] A solid secondary battery according to one embodiment comprises a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the positive electrode is a positive electrode for the secondary battery.

[0012] A method for manufacturing a composite carbonaceous conductive material according to one embodiment comprises: a precursor film forming process (a) in which a precursor film containing boron oxide is formed by a dry method to cover part or all of the surface of a carbon nanotube; and a coating film forming process (b) in which the boron oxide included in the precursor film is nitrated to form the precursor film into a coating film containing a boron element (B) and a nitrogen element (N), wherein in the precursor film forming process (a), a porous particle in which boric acid is supported in the pores and a carbon nanotube are introduced into a reactor. Effects of the invention

[0013] It is possible to provide a composite carbonaceous conductive material that exhibits good conductivity and, furthermore, not only has excellent withstand voltage characteristics under high voltage environments but also ensures long-term performance stability of the battery. Brief explanation of the drawing

[0014] FIG. 1 is a schematic cross-sectional diagram showing the schematic configuration of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the schematic configuration of a composite carbonaceous conductive material according to one embodiment of the present invention. Specific details for implementing the invention

[0015] Specific embodiments are described below in detail so that those skilled in the art can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. The terms used herein are used merely to describe exemplary embodiments and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0016] Here, "combinations of these" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0017] The terms "include," "equip," or "have" used herein are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] In the drawings, thicknesses have been enlarged to clearly represent various layers and regions, and the same reference numerals have been used for similar parts throughout the specification. When a part such as a layer, film, region, or plate is described as being "on" or "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between. Conversely, when a part is described as being "immediately on" another part, it means that there is no other part in between.

[0019] In addition, the term "layer" here includes not only the shape formed on the entire surface when viewed in a plan view, but also the shape formed on some surfaces.

[0020] The average particle size can be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope or a scanning electron microscope. Alternatively, the average particle size value can be obtained by measuring the particle size distribution using dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Unless otherwise defined, the average particle size (D 50 ) may refer to the diameter of a particle whose cumulative volume is 50% by volume in the particle size distribution. Additionally, unless otherwise defined, a particle size distribution is obtained using a particle size analyzer employing laser diffraction, and the diameter of the particle whose cumulative volume is 50% by volume in the said particle size distribution is defined as the average particle diameter (D 50 It may have been taken as ).

[0021] "Or" is not interpreted in an exclusive sense; for example, "A or B" is interpreted to include A, B, A+B, etc.

[0022] The term "metal" is interpreted as a concept that includes common metals, transition metals, metalloids, and semimetals.

[0023] In addition, the positive electrode for a secondary battery is also referred to simply as "positive electrode" for convenience.

[0025] Non-aqueous electrolyte secondary battery

[0026] First, according to FIG. 1, an example of a non-aqueous electrolyte secondary battery according to one embodiment will be described. Referring to FIG. 1, the non-aqueous electrolyte secondary battery (1) includes a positive electrode (10), a negative electrode (20), and a separator (30). The positive electrode (10) may include a positive current collector (11) and a positive active material layer (12). The negative electrode (20) may include a negative current collector (21) and a negative active material layer (22). The separator (30) is located between the positive electrode (10) and the negative electrode (20), and a non-aqueous electrolyte may be contained in each pore within the separator (30) and in the pores of the positive electrode (10) and the negative electrode (20). Additionally, the positive electrode (10) may be a positive electrode for a secondary battery as described later. The non-aqueous electrolyte secondary battery (1) is a lithium-ion secondary battery and may be a non-aqueous electrolyte secondary battery formed using a non-aqueous electrolyte. The shape of the non-aqueous electrolyte secondary battery (1) is not particularly limited, but may be any type such as a cylindrical shape, a prismatic shape, a laminate shape, a button shape, etc.

[0027] (anode)

[0028] Referring to FIG. 1, the anode (10) may include an anode current collector (11) and an anode active material layer (12). The anode (10) may additionally include a sulfide solid electrolyte described later. Additionally, the anode active material layer (12) may include an anode active material and a conductive material, and may further include an anode binder.

[0029] The material of the positive current collector may be, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or a combination thereof. The positive current collector may be composed of any one of these metals, or may be formed from an alloy of two or more metals. The shape of the positive current collector may be, for example, plate-shaped or thin-shaped. An undercoat layer may be formed on the positive current collector.

[0030] The positive electrode active material is, for example, a transition metal oxide or solid solution oxide containing lithium, and is not particularly limited as long as it is a material capable of electrochemically intercalating and deintercalating lithium ions. As a transition metal oxide containing lithium, for example, Li 1.0 Ni 0.88 Co 0.1 Al 0.01 Mg 0.01 It can be O2, and in addition, Li·Co-based complex oxides such as LiCoO2, LiNi x Co y Mn z It may be a Li·Ni·Co·Mn-based complex oxide such as O2, a Li·Ni-based complex oxide such as LiNiO2, or a Li·Mn-based complex oxide such as LiMn2O4. As a solid solution oxide containing lithium, for example, Li a Mn x Co y Ni z O2(1.150≤a≤1.430, 0.45≤x≤0.6, 0.10≤y≤0.15, 0.20≤z≤0.28), LiMn 1.5 Ni 0.5It may be O4, etc. In addition, the content (content ratio) of the positive active material is not particularly limited and may be an amount applicable to the positive active material layer of a non-aqueous electrolyte secondary battery. Furthermore, these compounds may be used alone or a mixture of multiple types may be used.

[0031] Examples of positive active materials include particles of various shapes such as spherical, polygonal, needle-shaped, scale-shaped, and irregular shapes, and for example, a spherical positive active material. Meanwhile, "spherical" means that the overall shape of the particle is spherical or approximately spherical. The particle diameter of the positive active material is not particularly limited and may include particles of various sizes as the positive active material. Furthermore, the average particle diameter of the positive active material may be 0.1 μm or more and 50 μm or less, and for example, may be 1 μm or more and 30 μm or less. Here, the average particle diameter of the positive active material is the median diameter (D 50 It means ) and can be measured, for example, by laser diffraction, scattering particle size distribution measuring devices, etc.

[0032] The positive active material layer may include a composite carbonaceous conductive material as a conductive material, for example, may include only the composite carbonaceous conductive material. Referring to FIG. 2, a composite carbonaceous conductive material according to one embodiment may include a carbon nanotube (12a) and a coating film (12b) covering the surface of the carbon nanotube (12a), for example, the carbon nanotube (12a) and the coating film (12b) covering the surface of the carbon nanotube (12a) may be composited and integrated. By using such a composite carbonaceous conductive material as a conductive material, the deterioration of the carbonaceous conductive material under a high-voltage environment and side reactions between the carbonaceous conductive material and the non-aqueous electrolyte can be suppressed, and as a result, a composite carbonaceous conductive material with excellent voltage resistance characteristics can be provided.

[0033] As for the carbon nanotube, it is not particularly limited as long as it can be used as a conductive material in a secondary battery, and may be a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), a multi-walled carbon nanotube (MWCNT), or a combination thereof.

[0034] The carbon nanotubes included in the composite carbonaceous conductive material may be commercially available. To further enhance conductivity, for example, the outer diameter of the carbon nanotube may be 0.4 nm or more and 50 nm or less. In addition, to better form a conductive path in the cathode active material layer, the length of the carbon nanotube may be 100 nm or more and 5 mm or less, for example, 1 μm or more and 3 mm or less. Here, the length of the carbon nanotube refers to the length of the major axis passing through the center of the carbon nanotube unit. For example, the length of the carbon nanotube can be measured based on observations made using SEM or TEM. In addition, here, the outer diameter of the carbon nanotube refers to the length of the minor axis passing through the center of the carbon nanotube unit and perpendicular to the major axis of the carbon nanotube. For example, the outer diameter of the carbon nanotube can be measured based on observations made using SEM or TEM.

[0035] The coating film contains a nitrogen element (N), a boron element (B), and an oxygen element (O). The weight ratio (B / N) of the average content of the boron element (B) to the average content of the nitrogen element (N) contained in the coating film is 0.7 or more and 1.8 or less, for example, 0.8 or more and 1.6 or less, or 0.9 or more and 1.5 or less. In addition, the oxygen element (O) contained in the coating film may be derived from boric acid that is initially added to the carbon nanotube when forming the coating film of the composite carbonaceous conductive material, as described below.

[0036] In addition to the coating film, the conductive material of the composite carbonaceous conductive material, for example, the conductive material that serves as the substrate of the composite carbonaceous conductive material (or the carbon nanotube included in the composite carbonaceous conductive material), may also contain oxygen element (O). The weight ratio ((B+N) / O ratio) of the total content of the average content of boron element (B) and the average content of nitrogen element (N) to the average content of oxygen element (O) included in the composite carbonaceous conductive material may be 0.5 or more and 6.0 or less, for example, 0.7 or more and 4.5 or less, or 1.0 or more and 2.0 or less.

[0037] Such a coating film may, for example, contain chemically stable boron nitride and may be formed by boron nitride. The coating film may be a single film covering the entire surface of the carbon nanotube (e.g., in the form of a continuous film) or a film covering a part of the surface of the carbon nanotube (e.g., in the form of an island). Additionally, when the coating film contains boron nitride, the boron nitride may exist as energetically very stable hexagonal boron nitride (h-BN). h-BN is known to have a layered structure, such as graphite and carbon nanotubes, and when the amount of boron nitride contained in the coating film is large, the coating film may have a multilayer structure due to the layered structure of this boron nitride.

[0038] The average content of boron element (B) included in the coating film is 1.0 wt% or more and 15.0 wt% or less with respect to 100 wt% of the composite carbonaceous conductive material, for example, 1.5 wt% or more and 12.0 wt%, 2.0 wt% or more and 8.0 wt% or less, or 2.5 wt% or more and 5.5 wt% or less. By having an upper limit of the average content of boron element (B) included in the coating film of 15.0 wt% or less, the increase in resistance of the coating film is suppressed, thereby providing good conductivity to the composite carbonaceous conductive material.

[0039] In addition, the total content of the average content of nitrogen element (N) and the average content of boron element (B) included in the coating film may be 2.0 wt% or more and 30.0 wt% or less with respect to 100 wt% of the composite carbonaceous conductive material, and for example, may be 5.0 wt% or more and 20.0 wt% or less.

[0040] The coefficient of variation ([standard deviation / average value]×100) of the average content of boron element (B) included in the coating film is 20% or less, and, for example, may be 15% or less, 10% or less, or 5% or less. When the coefficient of variation of the average content of boron element (B) included in the coating film is 20% or less, boron can be included more uniformly throughout the coating film, and uneven inclusion of boron within the coating film can be suppressed. As a result, the increase in resistance of the coating film is suppressed, and good conductivity can be imparted to the composite carbonaceous conductive material. In addition, since aggregation of carbonaceous conductive materials is suppressed during coating, the effect of improving the long-term performance stability of the battery can be achieved. Here, the average content and coefficient of variation of each element can be measured, for example, by X-ray photoelectron spectroscopy (XPS) using an X-ray photoelectron spectroscopy device in accordance with JIS K0152:2014. For example, the boron element (B), nitrogen element (N), and oxygen element (O) contained in the composite carbonaceous conductive material can be quantitatively analyzed, and the content of the boron element (B), nitrogen element (N), and oxygen element (O) contained in the composite carbonaceous conductive material can be measured multiple times at any part of the composite carbonaceous conductive material, and the average value of the measurement results can be taken as the average content of each element. For the boron element (B), the coefficient of variation ([standard deviation / average value]×100) can be calculated from the average value and the standard deviation.

[0041] The thickness of the coating film may be 0.3 nm or more and 2 nm or less. For example, the thickness of the coating film may be 1 / 5 or less, 1 / 8 or less, 1 / 10 or less, or 7 / 100 or less of the diameter of the carbon nanotube. For example, when the diameter of the carbon nanotube is 10 nm, the thickness of the coating film may be 2 nm or less. In addition, if the coating film is formed of an insulating material such as boron nitride, the conductivity of the positive active material layer can be sufficiently maintained because the thickness of the coating film is 1 / 5 or less of the diameter of the carbon nanotube. In addition, if the thickness of the coating film is 0.3 nm or more, it can sufficiently exert an effect of suppressing the degradation of the carbon nanotube or side reactions with other battery components such as the electrolyte. And, a thickness of 0.3 nm can be approximately the same thickness as a single layer of h-BN, which is known to have a hexagonal crystal structure similar to graphite. The thickness of the coating film can be adjusted, for example, by changing the amount of boric acid added to the carbon nanotubes when forming the coating film.

[0042] The coating film may be formed in an island shape on a part of the surface of the carbon nanotube, and, for example, the entire surface of the carbon nanotube may be uniformly covered with the coating film to the extent that the carbon nanotube and the non-aqueous electrolyte cannot come into direct contact.

[0043] The content of the composite carbonaceous conductive material included in the positive active material layer may be 0.005 wt% or more and 3.0 wt% or less from the perspective of manufacturing costs, and for example, may be 0.005 wt% or more and 2.0 wt% or less.

[0044] In addition to the aforementioned composite carbonaceous conductive material, the conductive material may further include at least one carbon material selected from the group consisting of, for example, carbon black, natural graphite, artificial graphite, fibrous carbon, and sheet carbon. Examples of carbon black include furnace black, channel black, thermal black, ketjen black, acetylene black, etc. Fibrous carbon may be, for example, carbon nanotubes, carbon nanofibers, etc., and sheet carbon may be, for example, graphene, etc.

[0045] When such carbon materials are used as conductive materials, the content of the conductive material is not particularly limited, but in order to achieve compatibility between conductivity and battery capacity, it may be 0.005 wt% or more and 5 wt% or less with respect to 100 wt% of the total positive active material layer, for example, 0.1 wt% or more and 3 wt% or less, or 0.1 wt% or more and 2 wt% or less. And, here, the content of the conductive material refers to the total content of the composite carbonaceous conductive material and the carbon material.

[0046] The positive electrode binder is not particularly limited as long as it can bind the positive electrode active material and the conductive material onto the positive electrode current collector, but for example, it may be a fluorine-containing resin such as polyvinylidene fluoride, an ethylene-containing resin such as styrene-butadiene rubber, an ethylene-propylene-diene terpolymer, an acrylonitrile-butadiene rubber, a fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, polyvinyl alcohol, carboxymethylcellulose or a carboxymethylcellulose derivative (such as a salt of carboxymethylcellulose), nitrocellulose, etc.

[0047] (cathode)

[0048] Referring to FIG. 1, the cathode (20) may include a cathode current collector (21) and a cathode active material layer (22). Additionally, the cathode active material layer (22) may further include a cathode binder.

[0049] The negative current collector may include at least one selected from the group consisting of copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), for example, it may include at least one selected from the group consisting of copper (Cu), titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), and may include copper (Cu). The negative current collector may be composed of any one of these metals, or it may be composed of an alloy or clad material of two or more metals. In addition, the surface of the negative current collector may be plated with Ni, Fe, etc. The shape of the negative current collector may be, for example, plate-shaped or thin-shaped.

[0050] The negative electrode active material is not particularly limited as long as it is a material capable of electrochemically intercalating and deintercalating lithium ions. Such negative electrode active materials include, for example, graphite active materials (synthetic graphite, natural graphite, a mixture of synthetic and natural graphite, natural graphite coated with synthetic graphite, etc.), Si-based or Sn-based active materials (for example, a mixture of graphite active material and fine particles of silicon (Si), tin (Sn), or their oxides, fine particles of silicon or tin, an alloy based on silicon or tin, etc.), metallic lithium, Li4Ti5O 12 It may be titanium oxide-based compounds, lithium nitride, etc. The above compounds may be used alone or in a mixture of multiple types. Also, the silicon oxide is SiO x It can be expressed as (0≤x≤2).

[0051] The conductive material is not particularly limited as long as it can increase the conductivity of the negative electrode, and for example, various carbon materials exemplified as conductive materials other than the composite carbonaceous conductive material that can be included in the positive active material as described above may be used. The content of the conductive material included in the negative active material layer is not particularly limited, but in order to achieve compatibility between conductivity and battery capacity, it may be 0.005 weight% or more and 5 weight% or less with respect to 100 weight% of the total negative active material layer, and for example, it may be 0.1 weight% or more and 3 weight% or less.

[0052] The cathode binder is not particularly limited as long as it can bind the cathode active material and the conductive material onto the cathode current collector. Such a cathode binder may be, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), metal salt of carboxymethylcellulose (CMC), etc. The above compounds may be used alone or in combination of two or more types.

[0053] (Separator)

[0054] The separator can be used as a separator for a lithium-ion secondary battery and is not particularly limited, but may use a porous membrane, nonwoven fabric, etc., which exhibit excellent high-rate discharge performance, either alone or in combination. The materials constituting these separators are, for example, polyolefin-based resins such as polyethylene and polypropylene, polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate, polyvinylidene difluoride, vinylidene difluoride-hexafluoropropylene copolymer, vinylidene difluoride-perfluorovinylether copolymer, vinylidene difluoride-tetrafluoroethylene copolymer, vinylidene difluoride-trifluoroethylene copolymer, vinylidene difluoride-fluoroethylene copolymer, Vinylidene difluoride-hexafluoroacetone copolymer, vinylidene difluoride-ethylene copolymer, vinylidene difluoride-propylene copolymer, vinylidene difluoride-trifluoropropylene copolymer,It may be a resin material such as a vinylidene difluoride-tetrafluoroethylene copolymer or a vinylidene difluoride-ethylene-tetrafluoroethylene copolymer. In addition, the porosity of the separator is not particularly limited and may have any porosity of a separator included in a general lithium-ion secondary battery.

[0055] The separator may further include a surface layer covering the surface of the aforementioned porous membrane or nonwoven fabric. This surface layer may include an adhesive for fixing the battery element by adhering to the electrode. Examples of adhesives may include vinylidene fluoride-hexafluoropropylene copolymer, acid-modified vinylidene fluoride polymer, styrene-(meth)acrylic acid ester copolymer, etc.

[0056] (non-aqueous electrolyte)

[0057] The non-aqueous electrolyte can be the same as the non-aqueous electrolyte used in general lithium-ion secondary batteries, and can have a composition in which an electrolyte salt is included in a non-aqueous solvent which is a solvent for the electrolyte.Non-aqueous solvents are, for example, cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate; and chain esters such as methylformate, methylacetate, methylbutyrate, ethyl propionate, and propyl propionate. It may be tetrahydrofuran or its derivatives, ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyldiglyme, ethylene glycol monopropyl ether, propylene glycol monopropyl ether, etc.; nitriles such as acetonitrile, benzonitrile, etc.; and, dioxolane or its derivatives, ethylene sulfide, sulfolane, sultone or its derivatives, etc.

[0058] The above non-aqueous solvent may be used alone or mixed with two or more types. In addition, when two or more non-aqueous solvents are mixed, the mixing ratio of each non-aqueous solvent may be the mixing ratio used in general lithium-ion secondary batteries.

[0059] Electrolytes include, for example, LiClO4, LiBF4, LiAsF6, LiPF6, and LiPF6. 6-x (C n F 2n+1 ) x [Here, 1 <x<6, n=1 또는 2], LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 Inorganic ion salts containing one of lithium (Li), sodium (Na), and potassium (K), such as NaClO4, NaI, NaSCN, NaBr, KClO4, KSCN, etc.; Or it may be an organic ionic salt such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiC(C2F5SO2)3, (CH3)4NBF4, (CH3)4NBr, (C2H5)4NClO4, (C2H5)4NI, (C3H7)4NBr, (n-C4H9)4NClO4, (n-C4H9)4NI, (C2H5)4N-maleate, (C2H5)4N-benzoate, (C2H5)4N-phtalate, lithium stearylsulfonic acid, lithium octylsulfonic acid, lithium dodecyl benzenesulfonic acid, etc.

[0060] The above electrolyte salt may be used alone or mixed with two or more types. The concentration of the electrolyte salt may be applied as a concentration used in general lithium-ion secondary batteries and is not particularly limited, but, for example, a non-aqueous electrolyte containing the above electrolyte salt at a concentration of 0.8 mol / L or more and 1.5 mol / L or less may be used.

[0061] The non-aqueous electrolyte may contain various additives. Such additives may be, for example, cathodic additives, anode additives, ester-based additives, carbonate-based additives, sulfate-based additives, phosphoric acid-based additives, boric acid-based additives, anhydrous carbonate-based additives, electrolyte-based additives, etc. Any one of these may be included in the non-aqueous electrolyte, and multiple types of additives may be included in the non-aqueous electrolyte.

[0062] Method for manufacturing a non-aqueous electrolyte secondary battery

[0063] Next, a method for manufacturing a non-aqueous electrolyte secondary battery will be described.

[0064] (Method for manufacturing a composite carbonaceous conductive material)

[0065] The method for manufacturing a composite carbonaceous conductive material according to the present embodiment includes a precursor film forming process (a) in which a precursor film containing boron oxide is formed by a dry method to cover part or all of the surface of a carbon nanotube, and a coating film forming process (b) in which the boron oxide included in the precursor film is nitrated to form the precursor film into a coating film containing boron element (B) and nitrogen element (N).

[0066] In the precursor film formation process (a), the aforementioned precursor film is formed by a dry method. As such a dry method, for example, a solution containing boron element (B) is prepared, and porous particles having pores are introduced into the solution to produce porous particles (carriers) in which a compound containing boron is supported in the pores. Subsequently, the produced porous particles and carbon nanotubes are introduced into a reactor. After that, the reactor is heated to generate vapor of boron oxide, and a precursor film in which boron oxide is attached to the surface of the carbon nanotubes can be formed.

[0067] A solution containing boron element (B) is not particularly limited, but may, for example, be a solution in which a compound containing boron is dissolved in a suitable solvent. A compound containing boron may, for example, be boric acid. In addition, the solvent that dissolves boric acid may be a solvent that is volatile by natural drying, such as water or ethanol.

[0068] Porous particles having pores are not particularly limited as long as they function as a carrier for supporting boric acid, but for example, they may be ceramic particles such as boiling stones or zeolites, silica gel particles, or activated carbon. In addition, the reactor into which the porous particles and carbon nanotubes are introduced is not particularly limited as long as it has heat resistance, and may be a fixed-bed reactor or a fluidized-bed reactor.

[0069] By heating the reactor under an inert gas atmosphere such as argon, vapor of boron oxide can be generated, and this vapor can be attached to the surface of carbon nanotubes to form a precursor film containing boron oxide. At this time, the heating temperature and heating time can be appropriately set, but the heating temperature for forming the precursor film may be 150°C or higher and lower than the heating temperature in the coating film formation process (b). For example, in order to sufficiently generate vapor of boron oxide, it may be heated at a temperature of 200°C or higher and 600°C or lower for a time of 5 minutes or more and 60 minutes or less, and heated at a temperature of 300°C or higher and 500°C or lower for a time of 15 minutes or more and 45 minutes or less.

[0070] In the aforementioned process, the precursor film formed on the surface of the carbon nanotube contains boron oxide. Accordingly, in the coating film formation process (b), the boron oxide contained in the precursor film is nitrided to form a coating film containing boron element (B) and nitrogen element (N) on the surface of the carbon nanotube. As a coating film containing boron element (B) and nitrogen element (N), a coating film containing boron nitride (BN) can be formed. The nitriding of boron oxide can be performed, for example, by heating the aforementioned precursor film containing boron oxide under an atmosphere of a gas containing nitrogen element (N), such as ammonia gas. For example, the nitriding of boron oxide can be performed by supplying a gas containing nitrogen element (N), such as ammonia gas, to a heated reactor. Through this nitriding of boron oxide, boron nitride can be attached to part or all of the surface of the carbon nanotube.

[0071] In the nitriding of boron oxide, the heating temperature and heating time can be appropriately set, but for example, the nitriding of boron oxide can be performed at a temperature of 800°C or higher and 1500°C or lower for 5 minutes or more and 90 minutes or less, and at a temperature of 1000°C or higher and 1200°C or lower for 15 minutes or more and 60 minutes or less. In addition, the nitriding of boron oxide may be performed under an inert gas atmosphere such as argon.

[0072] In the coating film formation process (b), ammonia gas is supplied and the reactor is heated to a first temperature, and then the reactor can be further heated to a second temperature higher than the first temperature without supplying ammonia gas to the heated reactor. For example, boron oxide can be nitrided by heating the reactor to the first temperature to attach boron nitride to part or all of the surface of the carbon nanotube, and then the reactor can be further heated to the second temperature. That is, two stages of heating can be performed: nitriding treatment (heating to the first temperature) and post-treatment (heating to the second temperature). When two stages of heating are performed, the porous particles used in the precursor film formation process (a) may be ceramic particles having a heat resistance temperature higher than either the first temperature or the second temperature, for example, ceramic particles having a heat resistance temperature higher than the second temperature. Here, the first temperature may be 800°C or higher and 1200°C or lower, and the second temperature may be 1000°C or higher and 1500°C or lower.

[0073] A method for manufacturing a composite carbonaceous conductive material according to one embodiment may further include a process of separating the carbon nanotubes with attached boron oxide or carbon nanotubes with attached boron nitride from the aforementioned porous particles after any one of the processes of a precursor film formation process (a), a first temperature heating process in a coating film formation process (b), and a second temperature heating process in a coating film formation process (b). This separation may be performed by a wet method or by a dry method. Accordingly, carbon nanotubes with attached boron nitride may be used alone. When the aforementioned separation process is included after the precursor film formation process (a), the heat resistance temperature of the aforementioned ceramic particles may be 600°C or lower. When the aforementioned separation process is included after the heating process by the first temperature in the coating film formation process (b), the heat resistance temperature of the aforementioned porous particles may be 1200°C or lower. In the case where the aforementioned separation process is included after the heating process by the second temperature in the coating film formation process (b), the heat resistance temperature of the aforementioned porous particles may be 1500℃ or lower.

[0074] (Method for manufacturing the anode)

[0075] The anode can be manufactured, for example, as follows. First, the composite carbonaceous conductive material and the anode active material prepared as described above are mixed with an anode binder in a desired ratio, and the resulting mixture is dispersed in a solvent for the anode slurry to prepare an anode slurry. Subsequently, the anode slurry can be applied onto an anode current collector and dried to form an anode active material layer on the anode current collector. Meanwhile, the application method is not particularly limited, but may be, for example, a knife coater method, a gravure coater method, a reverse roll coater, a slit die coater, etc. Each of the following application processes can also be performed by the same method. Subsequently, the anode can be manufactured by pressing the anode active material layer to a desired density using a press machine.

[0076] (Method for manufacturing the cathode)

[0077] The cathode can also be manufactured in the same way as the anode. First, a cathode slurry can be prepared by mixing materials constituting the cathode active material layer and dispersing the resulting mixture in a solvent for the cathode slurry. Subsequently, a cathode active material layer can be formed on the cathode current collector by applying the cathode slurry onto the cathode current collector and drying it. Additionally, the cathode can be manufactured by pressing the cathode active material layer to a desired density using a press machine.

[0078] (Method for manufacturing a non-aqueous electrolyte secondary battery)

[0079] An electrode structure can be manufactured by interposing (clamping) a separator between the positive and negative electrodes manufactured as described above. Subsequently, the electrode structure can be processed into a desired shape (e.g., cylindrical, prismatic, laminated, button-shaped, etc.) and inserted into a container of the said shape. Furthermore, by injecting a non-aqueous electrolyte into the container, the electrolyte can be impregnated into each pore within the separator or into the voids of the positive and negative electrodes. Through the above process, a lithium-ion secondary battery as a non-aqueous electrolyte secondary battery can be manufactured.

[0080] A non-aqueous electrolyte secondary battery manufactured by the above method comprises a composite carbonaceous conductive material in which a coating film containing boron nitride is formed on a carbonaceous conductive material, and in the composite carbonaceous conductive material, the average content of boron element (B) included in the coating film and the coefficient of variation of the average content of boron element are controlled. Accordingly, the carbonaceous conductive material exhibits good conductivity, and the non-aqueous electrolyte secondary battery can be charged and discharged at a voltage exceeding 4.5V. Accordingly, the voltage withstand capability of the carbonaceous conductive material under high voltage conditions can be improved, and side reactions between the carbonaceous conductive material and the non-aqueous electrolyte can be suppressed, thereby improving the long-term performance stability of the battery.

[0081] <Other embodiments>

[0082] In the above-described embodiment, the composite carbonaceous conductive material is contained in the positive electrode active material layer, but the composite carbonaceous conductive material according to the present invention may be included in the protective layer when other layers constituting the secondary battery, such as a negative electrode active material layer or a protective layer protecting the positive electrode active material layer, are further included.

[0083] In addition, in the above-described embodiment, a non-aqueous electrolyte secondary battery comprising a separator and an electrolyte was described as an example of a secondary battery, but it is not limited thereto. The composite carbonaceous conductive material according to the present invention can be used in the same way as a conductive material included in the positive electrode in a semi-solid battery having a gel-type electrolyte; a solid secondary battery having a positive electrode, a negative electrode, and a solid electrolyte layer; and an all-solid-state battery that does not contain any electrolyte. For example, in a solid secondary battery or an all-solid-state secondary battery, the solid electrolyte layer may include a sulfide solid electrolyte, and the solid secondary battery or the all-solid-state secondary battery can also be charged and discharged at a voltage exceeding 4.5V.

[0084] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but includes all forms included in the concept and claims of the present invention, and can be modified in various ways within the scope of the present invention.

[0085] Based on the above embodiments, the present invention relates to the following [1] to

[21] .

[0086] [1]

[0087] A composite carbonaceous conductive material comprising carbon nanotubes and a coating film covering the surface of the carbon nanotubes,

[0088] The above coating film contains a nitrogen element (N), a boron element (B), and an oxygen element (O), and

[0089] The weight ratio (B / N) of the average content of boron element (B) to the average content of nitrogen element (N) included in the coating film is 0.7 or more and 1.8 or less, and

[0090] The average content of boron element (B) included in the coating film is 1.0 weight% or more and 15.0 weight% or less with respect to 100 weight% of the composite carbonaceous conductive material, and

[0091] A composite carbonaceous conductive material in which the coefficient of variation ([standard deviation / average value]×100) of the average content of boron element (B) included in the coating film is 20% or less.

[0092] [2]

[0093] The composite carbonaceous conductive material described in [1], wherein the total content of the average content of nitrogen element (N) and the average content of boron element (B) included in the coating film is 2.0% by weight or more and 30.0% by weight or less with respect to 100% by weight of the composite carbonaceous conductive material.

[0094] [3]

[0095] The above coating film is a composite carbonaceous conductive material described in [1] or [2] containing boron nitride.

[0096] [4]

[0097] A composite carbonaceous conductive material described in any one of [1] to [3], wherein the weight ratio ((B+N) / O) of the average content of the boron element (B) and the average content of the nitrogen element (N) to the average content of the oxygen element (O) included in the composite carbonaceous conductive material is 0.5 or more and 6.0 or less.

[0098] [5]

[0099] A positive electrode for a secondary battery comprising a positive electrode active material and a conductive material,

[0100] A positive electrode for a secondary battery, wherein the above-mentioned conductive material is a composite carbonaceous conductive material described in any one of [1] to [4].

[0101] [6]

[0102] A positive electrode for a secondary battery described in [5], further comprising a solid sulfide electrolyte.

[0103] [7]

[0104] A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,

[0105] A non-aqueous electrolyte secondary battery in which the anode described above is the anode for a secondary battery as described in [5] or [6].

[0106] [8]

[0107] A non-aqueous electrolyte secondary battery described in [7] that can be charged and discharged at a voltage exceeding 4.5V.

[0108] [9]

[0109] A solid secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer,

[0110] A solid secondary battery in which the anode described above is the anode for a secondary battery as described in [5] or [6].

[0111]

[10]

[0112] The solid electrolyte layer described above comprises a solid secondary battery as described in [9], which is a sulfide solid electrolyte.

[0113]

[11]

[0114] A solid secondary battery as described in [9] or

[10] that can be charged and discharged at a voltage exceeding 4.5V.

[0115]

[12]

[0116] A precursor film formation process (a) for forming a precursor film containing boron oxide by a dry method to cover part or all of the surface of a carbon nanotube; and

[0117] A method for manufacturing a composite carbonaceous conductive material, comprising a coating film forming process (b) of nitriding boron oxide included in the precursor film to form the precursor film into a coating film containing boron element (B) and nitrogen element (N),

[0118] A method for manufacturing a composite carbonaceous conductive material in which, in the above precursor film formation process (a), porous particles in which boric acid is supported in the pores and carbon nanotubes are introduced into a reactor.

[0119]

[13]

[0120] The formation of the above precursor film and the formation of the above coating film are both performed under heating, and

[0121] A method for manufacturing a composite carbonaceous conductive material as described in

[12] , wherein the heating temperature in the above-mentioned precursor film forming process (a) is 150°C or higher and the heating temperature in the above-mentioned coating film forming process (b) is lower.

[0122]

[14]

[0123] The weight ratio (B / N) of the average content of boron element (B) to the average content of nitrogen element (N) included in the coating film is 0.7 or more and 1.8 or less, and

[0124] The average content of boron element (B) included in the coating film is 1.0 wt% or more and 15.0 wt% or less with respect to 100 wt% of the composite carbonaceous conductive material, and

[0125] A method for manufacturing a composite carbonaceous conductive material as described in

[12] or

[13] , wherein the coefficient of variation ([standard deviation / average value]×100) of the average content of boron element (B) contained in the coating film is 20% or less.

[0126]

[15]

[0127] A method for manufacturing a composite carbonaceous conductive material as described in any one of

[12] to

[14] , wherein in the above coating film forming process (b), ammonia gas is supplied to the heated reactor to nitrate boron oxide, thereby attaching boron nitride to part or all of the surface of the carbon nanotube.

[0128]

[16]

[0129] A method for manufacturing a composite carbonaceous conductive material as described in any one of

[12] to

[14] , wherein in the above coating film formation process (b), ammonia gas is supplied and the reactor is heated to a first temperature to nitrate boron oxide, thereby attaching boron nitride to part or all of the surface of the carbon nanotube, and then the reactor is further heated to a second temperature higher than the first temperature without supplying ammonia gas to the heated reactor.

[0130]

[17]

[0131] A method for manufacturing a composite carbonaceous conductive material as described in

[16] , wherein the porous particles are ceramic particles having a heat resistance temperature higher than any one of the heating temperature in the precursor film forming process (a), the first temperature, and the second temperature.

[0132]

[18]

[0133] A method for manufacturing a composite carbonaceous conductive material as described in any one of

[12] to

[17] , further comprising a process for separating the carbon nanotubes with attached boron oxide and the porous particles.

[0134]

[19]

[0135] A method for manufacturing a composite carbonaceous conductive material as described in any one of

[15] to

[17] , further comprising a process for separating the carbon nanotubes with the boron nitride attached thereto and the porous particles.

[0136]

[20]

[0137] A method for manufacturing a composite carbonaceous conductive material as described in any one of

[12] to

[19] , wherein the reactor is a fixed-phase reactor.

[0138]

[21]

[0139] A method for manufacturing a composite carbonaceous conductive material as described in any one of

[12] to

[19] , wherein the reactor is a fluidized bed reactor.

[0140] [Example]

[0141] Embodiments of the present invention will be described below, but the present invention is not limited to these examples without departing from the spirit thereof. Unless specifically stated otherwise, each operation is performed at room temperature, and the room temperature is within the range of 20℃±5℃.

[0142] Manufacture of Challenge Materials

[0143] (Example 1)

[0144] First, a boric acid-ethanol solution was prepared by dispersing 4.8 g of boric acid in 100 mL of ethanol. 20 g of boiling stone, vacuum-dried at 120°C for 2 hours, was added to the boric acid-ethanol solution and air-dried overnight at room temperature to produce boric acid-supported boiling stone. Then, 600 mg of multiwall carbon nanotubes (MWCNT) manufactured by Sigma-Aldrich was mixed with 5 g of boric acid-supported boiling stone, placed in a heat-resistant ceramic container, and heated to 400°C in a tubular electric furnace under an argon atmosphere and maintained for 40 minutes to produce MWCNT having a boron oxide precursor film. In addition, after removing boiling stones using a sieve, an MWCNT having a boron oxide precursor film was maintained at 1100°C for 40 minutes under an atmosphere of mixed gas in which ammonia and argon were mixed in a ratio of 1:4, and a nitriding treatment was performed to produce a boron nitride-coated MWCNT, and a composite carbonaceous conductive material (A) was produced.

[0145] (Comparative Example 1)

[0146] MWCNT prepared in Example 1, which was not coated with boron nitride, was used.

[0147] (Comparative Example 2)

[0148] A boric acid-ethanol solution was prepared by dispersing 0.48 g of boric acid in 10 mL of ethanol. 450 mg of multiwall carbon nanotubes (MWCNTs) manufactured by Sigma-Aldrich were added to the boric acid-ethanol solution and air-dried overnight at room temperature while stirring to produce boric acid-supported MWCNTs. Subsequently, the boric acid-supported MWCNTs were heated to 400°C in a tubular electric furnace under an argon atmosphere and maintained for 30 minutes to produce MWCNTs having a boron oxide precursor film. Additionally, the boron oxide-supported MWCNTs were nitrided by maintaining them at 1100°C for 40 minutes under an atmosphere of a mixed gas of ammonia and argon in a 1:4 ratio. Accordingly, a composite carbonaceous conductive material (B) was manufactured by coating MWCNT with boron nitride.

[0149] Evaluation of the Challenge Material

[0150] The following evaluations were performed on the composite carbonaceous conductive materials prepared in Example 1 and Comparative Example 2, and the MWCNT of Comparative Example 1.

[0151] (Elemental Analysis)

[0152] Using an X-ray photoelectron spectroscopy apparatus (XPS, manufactured by Thermo Fisher Scientific, ESCALAB 250Xi type), the boron element (B), nitrogen element (N), and oxygen element (O) contained in each composite carbonaceous conductive material were quantitatively analyzed in accordance with JIS K0152:2014. As a result of the quantitative analysis, it was confirmed that the coating film of each manufactured composite carbonaceous conductive material consists of the boron element (B), nitrogen element (N), and oxygen element (O). In addition, the content of the boron element (B), nitrogen element (N), and oxygen element (O) contained in the composite carbonaceous conductive material was measured, and the content of each element was measured in 10 random regions of the composite carbonaceous conductive material. The average value of the measurement results was taken as the average content of each element, and for the boron element (B), the value obtained by dividing the standard deviation by the average value was calculated as the coefficient of variation. The results are shown in Table 1. Also, in Table 1, the average content of oxygen element (O) is the average content based on the composite carbonaceous conductive material.

[0153] Oxygen element (O) is contained in carbon nanotubes as well as in the coating film, but nitrogen element (N) and boron element (B) are contained only in the coating film. Accordingly, the average content of nitrogen element (N) and boron element (B) contained in the composite carbonaceous conductive material and the average content of nitrogen element (N) and boron element (B) contained in the coating film are substantially the same. In addition, it can be confirmed by XPS that some of the constituent elements of the coating film are supported (bonded, fixed) by chemical bonding with carbon nanotubes. As an example of chemical bonding, in addition to observing a covalent bond (NC) between a nitrogen atom (N) constituting the coating film and a carbon atom (C) constituting the carbon nanotube, the existence of a bond (BOC) between a boron atom (B) and a carbon atom (C) mediated by an oxygen atom (O) can also be estimated based on the ratio of covalent bonds (BO) between a boron atom (B) and an oxygen atom (O) and a covalent bond (OC) between an oxygen atom (O) and a carbon atom (C).

[0154] (Evaluation of powder conductivity)

[0155] Using a powder resistance measurement system (manufactured by Nitto Seikou Analytic, MCP-PD51), 100 mg of the composite carbonaceous conductive material prepared in Example 1 and Comparative Example 2 and 100 mg of the MWCNT of Comparative Example 1 were each introduced into a cylindrical cylinder and pressure-molded in a hydraulic press. The volume density and volume conductivity of the pressure-molded powder were measured, and the powder conductivity (S / cm) was calculated. The results are shown in Table 1. The measurement conditions are as follows.

[0156] Load: 1.00 kN

[0157] Electrode gap: 3.0 mm

[0158] Electrode radius: 0.7 mm

[0159] Sample radius: 10.0 mm

[0160] Probe used: 4-point probe

[0161] <Evaluation of Withstand Voltage: Cyclic Voltammetry (CV) Measurement: Non-aqueous Electrolytes>

[0162] (Manufacture of anodes for CV evaluation)

[0163] The composite carbonaceous conductive material prepared in Example 1 and Comparative Example 2 and 5 mg of MWCNT from Comparative Example 1 were each dispersed in 30 mL of a 0.5 wt% aqueous solution of sodium dodecylbenzenesulfonate (SDBS). Subsequently, the obtained dispersion was suction-filtered over a membrane filter, the residue was vacuum-dried at 120°C, and the obtained solid was perforated into a circular shape (Φ: 11 mm) to prepare a free-standing film. This was used as an anode for CV evaluation.

[0164] (Manufacturing of coin cells for CV evaluation)

[0165] A polypropylene-based porous separator and a counter electrode made of lithium metal were prepared. As the electrolyte, a solution was used in which 1.3 M LiPF6 was dissolved in a solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and ethyl propionate (EP) in a volume ratio of 10 / 15 / 75. A coin cell (2032) was manufactured by perforating the anode, porous separator, and counter electrode prepared above into a size suitable for a coin cell, and the CV evaluation cells of Example 1, Comparative Example 1, and Comparative Example 2 listed in Table 1 were each manufactured.

[0166] (CV measurement)

[0167] Using a CV measuring device (VMP-3 Potentiostat manufactured by BioLogic), for the CV evaluation cells of Example 1, Comparative Example 1, and Comparative Example 2, the oxidation-reduction potential was scanned in the range of 3.0 V to 5.0 V (vs. Li) at a scan rate of 5 mV / min to measure the current value, and the oxidation current density (mA / cm²) at 5 V was measured. 2 ) was compared. The results are shown in Table 1.

[0168] Manufacturing and Evaluation of Non-Aqueous Electrolyte Secondary Batteries

[0169] [Manufacturing of the anode]

[0170] (Example 1, Comparative Example 1 and Comparative Example 2)

[0171] LiCoO2(D 50 An anode slurry was prepared by dispersing polyvinylidene fluoride (VNF), polyvinylidene fluoride, and each carbonaceous conductive material shown in Table 1 in an N-methyl-2-pyrrolidone (NMP) solvent at a solid weight ratio of 97.7:1.3:1.0. Subsequently, the coating amount (plane density) after drying was 20.00 mg / cm² on one side. 2 A slurry for the anode was applied to one side of an aluminum current collector (aluminum foil) and dried, and then rolled using a roll press to achieve a density of 4.15 g / cc for the anode active material layer to manufacture the anode.

[0172] [Manufacturing of the cathode]

[0173] (Example 1, Comparative Example 1 and Comparative Example 2)

[0174] A cathode slurry was prepared by dispersing artificial graphite, sodium carboxymethylcellulose (CMC), and a styrene-butadiene-based aqueous dispersion in an aqueous solvent at a solid-weight ratio of 97.5:1.0:1.5. Subsequently, the coating amount (plane density) after drying was 10.5 mg / cm² on one side. 2 A cathode slurry was applied to one side of a copper foil and dried, and then rolled with a roll press to achieve a density of 1.65 g / cc for the cathode active material layer to manufacture the cathode.

[0175] [Manufacturing of Non-Aqueous Electrolyte Secondary Battery Cells]

[0176] (Example 1, Comparative Example 1 and Comparative Example 2)

[0177] An electrode cell was manufactured by laminating a positive electrode and a negative electrode with a polypropylene-based porous separator interposed. Subsequently, a nickel lead tab and an aluminum lead tab were welded to the negative electrode and the positive electrode of the manufactured electrode cell, respectively, within an aluminum laminate film. Afterward, each lead tab was brought out and housed, an electrolyte was injected, and the cell was sealed under reduced pressure to manufacture a non-aqueous electrolyte secondary battery cell before initial charging. For the electrolyte, a non-aqueous electrolyte was used in which 1.3 M LiPF6 and 1 wt% vinylene carbonate (VC) were dissolved in a solvent mixed with ethylene carbonate (EC) / dimethyl carbonate (DMC) / fluoroethylene carbonate (FEC) in a volume ratio of 15 / 80 / 5.

[0178] (Cycle characteristics)

[0179] The non-aqueous electrolyte secondary battery cells prepared in Example 1, Comparative Example 1, and Comparative Example 2 were charged with a constant current to 4.5V at 0.1C of the design capacity in a constant temperature bath at 25°C, and then charged with a constant voltage to 0.05C at 4.5V. After that, discharged with a constant current to 3.0V at 0.1C. In addition, in a constant temperature bath at 25°C, one cycle of charging with a constant current at 0.2C, charging with a constant voltage at 0.05C, and discharging with a constant current at 0.2C was performed under conditions of a charge cut-off voltage of 4.5V and a discharge cut-off voltage of 3.0V, and the initial discharge capacity was measured. A life test was conducted on this non-aqueous electrolyte secondary battery cell at a temperature of 45°C for 50 cycles under conditions of a charge termination voltage of 4.5V and a discharge termination voltage of 3.0V, with constant current charging at 0.5C, constant voltage charging at 0.05CA, and constant current discharging at 0.5C. After 50 cycles, the discharge capacity was measured at constant current charging at 0.2C, constant voltage charging at 0.05C, and discharge at 0.2C. The discharge capacity after 50 cycles was divided by the initial discharge capacity to measure the capacity retention rate after 50 cycles.

[0180] (Evaluation Results)

[0181] Table 1 shows the physical properties and evaluation results of the composite carbonaceous conductive material prepared in Example 1 and Comparative Example 2 and the MWCNT of Comparative Example 1. In addition, Table 2 shows the results of the long-term performance stability of the non-aqueous electrolyte secondary battery cells prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0182] Carbonaceous conductive material Average boron (B) content (weight%) Coefficient of variation (%) of average boron (B) content Average nitrogen (N) content (weight%) Average oxygen (O) content (weight%) B / N weight ratio Total content of Boron (B) + Nitrogen (N) (weight%) (B+N) / O weight ratio Withstand voltage characteristic CV evaluation; oxidation current density (mA / cm²) 2 ) Powder conductivity (S / cm) Example 1 Composite carbonaceous conductive material (A) 4.4 4.2 3.1 4.9 1.40 7.5 1.5 1.5 24.5 Comparative Example 1 Uncoated MWCNT - - - 3.4 - - 0 1.7 31.4 Comparative Example 2 Composite carbonaceous conductive material (B) 6.6 31.7 5.3 4.3 1.24 11.9 2.8 1.5 10.8

[0184] Carbonaceous conductive material Long-term performance stability Dose retention rate (%) after 50 cycles Example 1 Composite carbonaceous conductive material (A) 94.8 Comparative Example 1 No coating MWCNT 94.0 Comparative Example 2 Composite carbonaceous conductive material (B) 33.5

[0185] Referring to Table 1, in the case of Example 1, compared to Comparative Example 1 which does not have a boron nitride coating film, the conductivity (powder conductivity) of the carbonaceous conductive material is slightly reduced, but the oxidation current can be suppressed in CV evaluation using a non-aqueous electrolyte, and the dielectric strength characteristics are excellent. In addition, when comparing Example 1 and Comparative Example 1 in Table 2, the non-aqueous electrolyte secondary battery cell prepared in Example 1 was able to secure long-term performance stability. This effect is presumed to be due to the fact that a coating film containing electrochemically very stable boron nitride is uniformly formed on the surface of the carbonaceous conductive material.

[0186] Meanwhile, in Comparative Example 2, where the coefficient of variation of the average content of boron element (B) exceeds 20% even though the average content of boron element (B) is 15.0 wt% or less, the capacity retention rate after 50 cycles was significantly reduced. Although the reason is not clear, it is presumed that aggregates of carbonaceous conductive materials were formed during the formation of the coating film, and the formation of conductive paths within the anode was insufficient.

[0187] From the above results, according to the present invention, by uniformly forming a coating film containing boron nitride while containing a certain amount of boron element (B) on the surface of carbon nanotubes which are carbonaceous conductive materials, side reactions between the carbonaceous conductive material and the electrolyte can be suppressed, and a secondary battery exhibiting good conductivity can be manufactured, and the stability of battery performance can be improved over a long period of time. Explanation of the symbols

[0188] 1: Non-aqueous electrolyte secondary battery 10: Anode 11: Positive current collector 12: Positive active material layer 12a: Carbon nanotube 12b: peritoneum 20: Cathode 21: Cathode current collector 22: Cathode active material layer 30: Separator

Claims

Claim 1 A composite carbonaceous conductive material comprising carbon nanotubes and a coating film covering the surface of the carbon nanotubes, wherein the coating film contains a nitrogen element (N), a boron element (B), and an oxygen element (O), the weight ratio (B / N) of the average content of the boron element (B) to the average content of the nitrogen element (N) contained in the coating film is 0.7 or more and 1.8 or less, the average content of the boron element (B) contained in the coating film is 1.0 weight% or more and 15.0 weight% or less with respect to 100 weight% of the composite carbonaceous conductive material, and the coefficient of variation ([standard deviation / average value]×100) of the average content of the boron element (B) contained in the coating film is 20% or less. Claim 2 A composite carbonaceous conductive material according to claim 1, wherein the total content of the average content of nitrogen element (N) and the average content of boron element (B) included in the coating film is 2.0 weight% or more and 30.0 weight% or less with respect to 100 weight% of the composite carbonaceous conductive material. Claim 3 In claim 1, the coating film is a composite carbonaceous conductive material comprising boron nitride. Claim 4 A composite carbonaceous conductive material according to claim 1, wherein the weight ratio ((B+N) / O) of the total content of the average Claim 5 A positive electrode for a secondary battery comprising a positive active material and a conductive material, wherein the conductive material is a composite carbonaceous conductive material according to any one of claims 1 to 4. Claim 6 A positive electrode for a secondary battery, further comprising a sulfide solid electrolyte in paragraph 5. Claim 7 A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode is a positive electrode for a secondary battery according to claim 5. Claim 8 In claim 7, a non-aqueous electrolyte secondary battery capable of charging and discharging at a voltage exceeding 4.5V. Claim 9 A solid secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the positive electrode is a positive electrode for a secondary battery according to claim 5. Claim 10 In claim 9, the solid electrolyte layer comprises a sulfide solid electrolyte, a solid secondary battery. Claim 11 In paragraph 10, a solid secondary battery capable of charging and discharging at a voltage exceeding 4.5V. Claim 12 A method for manufacturing a composite carbonaceous conductive material comprising: a precursor film forming process (a) for forming a precursor film containing boron oxide to cover part or all of the surface of a carbon nanotube by a dry method; and a coating film forming process (b) for nitriding the boron oxide contained in the precursor film to form the precursor film into a coating film containing a boron element (B) and a nitrogen element (N), wherein in the precursor film forming process (a), a porous particle in which boric acid is supported in the pores and a carbon nanotube are introduced into a reactor. Claim 13 A method for manufacturing a composite carbonaceous conductive material according to claim 12, wherein the formation of the precursor film and the formation of the coating film are both performed under heating, and the heating temperature in the precursor film formation process (a) is 150°C or higher and the heating temperature in the coating film formation process (b) is lower. Claim 14 A method for manufacturing a composite carbonaceous conductive material according to claim 12, wherein the weight ratio (B / N) of the average content of boron element (B) to the average content of nitrogen element (N) included in the coating film is 0.7 or more and 1.8 or less, the average content of boron element (B) included in the coating film is 1.0 weight% or more and 15.0 weight% or less with respect to 100 weight% of the composite carbonaceous conductive material, and the coefficient of variation ([standard deviation / average value]×100) of the average content of boron element (B) contained in the coating film is 20% or less. Claim 15 A method for manufacturing a composite carbonaceous conductive material according to claim 13, wherein in the coating film forming process (b), boron oxide is nitrated by supplying ammonia gas to the heated reactor to attach boron nitride to part or all of the surface of a carbon nanotube. Claim 16 A method for manufacturing a composite carbonaceous conductive material according to claim 13, wherein in the coating film forming process (b), ammonia gas is supplied and the reactor is heated to a first temperature to nitride boron oxide, thereby attaching boron nitride to part or all of the surface of the carbon nanotube, and then the reactor is further heated to a second temperature higher than the first temperature without supplying ammonia gas to the heated reactor. Claim 17 A method for manufacturing a composite carbonaceous conductive material according to claim 16, wherein the porous particles are ceramic particles having a heat resistance temperature higher than any one of the heating temperature in the precursor film forming process (a), the first temperature, and the second temperature. Claim 18 A method for manufacturing a composite carbonaceous conductive material according to claim 12, further comprising a process for separating the carbon nanotube with attached boron oxide and the porous particle. Claim 19 A method for manufacturing a composite carbonaceous conductive material, wherein, in claim 15 or 16, the process of separating the carbon nanotube with attached boron nitride and the porous particle further comprises the process of separating the porous particle. Claim 20 A method for manufacturing a composite carbonaceous conductive material, wherein, in paragraph 12, the reactor is a fixed-phase reactor. Claim 21 A method for manufacturing a composite carbonaceous conductive material, wherein, in paragraph 12, the reactor is a fluidized bed reactor.

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