Conductive aid, electrode mixture layer, and nonaqueous electrolyte battery

Abstract

This conductive aid comprises carbon nanotubes and fibrous carbon. The conductive aid either contains granular carbon, or does not contain granular carbon and has a BET specific surface area of 120m2 / g or less as measured by using nitrogen gas.

Description

Conductive additives, electrode mixture layers, and non-aqueous electrolyte batteries

[0001] The present invention relates to a conductive additive, an electrode mixture layer, and a non-aqueous electrolyte battery.

[0002] Non-aqueous electrolyte batteries, with their small size, light weight, and high voltage, are widely used in electronic devices such as notebook PCs, mobile phones, smartphones, and tablet PCs. In recent years, due to environmental concerns, lithium-ion secondary batteries have become particularly popular in electric vehicles (EVs) that run solely on batteries, and hybrid electric vehicles (HEVs) that combine gasoline engines and batteries.

[0003] Carbon nanotubes (CNTs) are known as conductive additives used in the electrodes of non-aqueous electrolyte batteries. With mass production, the price of CNTs has decreased, and they are becoming widely used as conductive additives for lithium-ion secondary batteries.

[0004] Patent Document 1 discloses an electrode for a lithium-ion battery comprising an electrode active material (A) capable of intercalating and releasing lithium ions, a carbon-based conductive additive (B), and a binder (C), wherein the carbon-based conductive additive contains carbon fibers, and the carbon fibers are a mixture of two types of carbon fibers with different fiber diameter distributions (based on the number of fibers), and the carbon fiber diameter distribution in the electrode has one or more maximum values ​​at 5 to 40 nm and one or more maximum values ​​at 50 to 300 nm.

[0005] International Publication 2012 / Brochure No. 111688

[0006] Incidentally, carbon nanotubes (CNTs) have a relatively high specific surface area and are prone to reactions that decompose the electrolyte. Therefore, there is a need to minimize the amount of CNTs added.

[0007] However, due to their thinness, CNTs tend to aggregate easily. When aggregation occurs, they become less likely to participate in forming the network structure for electron conduction (conductive network) within the electrode, which may necessitate increasing the amount added.

[0008] The problem to be solved by the present invention is to provide a conductive auxiliary agent capable of reducing the addition amount of CNT in an electrode mixture layer and obtaining an electrode with reduced side reactions at high voltages, and an electrode mixture layer using the same.

[0009] Specific means for solving the above problems include the following embodiments. <1> A conductive auxiliary agent containing carbon nanotubes and fibrous carbon, the conductive auxiliary agent further containing granular carbon or not containing it, and the BET specific surface area of the conductive auxiliary agent using nitrogen gas is 120 m ２ / g or less. <2> The conductive auxiliary agent according to <1> that does not contain the granular carbon. <3> The average fiber diameter of the carbon nanotubes is 1 nm to 30 nm, the average fiber diameter of the fibrous carbon is 70 nm to 300 nm, and the average fiber length of the fibrous carbon is 1 μm to 15 μm. The conductive auxiliary agent according to <1> or <2>. <4> When the content rate of the granular carbon in the conductive auxiliary agent is w １ mass%, w １ is 50 or less. The conductive auxiliary agent according to any one of <1> to <3>. <5> When the content rate of the carbon nanotubes in the conductive auxiliary agent is w ２ mass%, w ２ is 50 or less. The conductive auxiliary agent according to any one of <1> to <4>. <6> When the content rate of the carbon nanotubes in the conductive auxiliary agent is w ２ mass%, and the content rate of the fibrous carbon is w ３ mass%, w ２ The conductive auxiliary agent according to any one of <1> to <5>, where / (w ２ + w ３ ３ ３ <0.. <7> When the content rate of the fibrous carbon in the conductive auxiliary agent is w ３ mass%, w ３ is 40 or more. The conductive auxiliary agent according to any one of <1> to <6>. <8> A dispersion liquid containing the conductive auxiliary agent according to any one of <1> to <7>. <9> A conductive layer containing the conductive auxiliary agent according to any one of <1> to <7>. <10> An electrode mixture layer containing the conductive auxiliary agent according to any one of <1> to <7>. <11> The surface area of the conductive auxiliary agent per 1 g of the electrode mixture layer is 1.14 m ２An electrode mixture layer having a value less than or equal to / (g-electrode mixture layer). <12> The electrode mixture layer according to <10> or <11>, wherein the binder in the electrode mixture layer contains a fluororesin. <13> A non-aqueous electrolyte battery comprising the electrode mixture layer according to any one of <10> to <12>.

[0010] According to the present invention, the amount of CNTs added to the electrode mixture layer can be reduced, and an electrode with reduced side reactions can be obtained.

[0011] Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and they do not limit the present invention.

[0012] In this invention, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes, provided that the purpose of that process is achieved. In this invention, numerical ranges indicated using "~" include the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in steps within this invention, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in steps. Also, in numerical ranges described within this invention, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. In this invention, each component may contain multiple types of the corresponding substance. When a composition contains multiple types of substances corresponding to a certain component, the content or amount of that component means the total content or amount of those multiple substances present in the composition, unless otherwise specified. In this invention, each component may contain multiple types of the corresponding particles. If a composition contains multiple types of particles corresponding to a certain component, the particle size of that component refers to the value for a mixture of those multiple types of particles present in the composition, unless otherwise specified. In this invention, the terms "layer" or "film" include cases where the layer or film is formed over the entire region when the region in which the layer or film exists is observed, as well as cases where it is formed only on a part of the region. In this invention, the term "stacked" indicates stacking layers, and two or more layers may be bonded together, or two or more layers may be detachable. In this invention, the term "contains" in reference to a specific component (e.g., conductive additive, dispersion, conductive layer, electrode mixture layer) means that it may contain other components besides that specific component. In this invention, a "conductive additive" is added to the electrode mixture layer to reduce the volume resistivity of the electrode mixture layer and the resistance of the electrode. In this specification, carbon black may be written as "CB" and carbon nanotube as "CNT".

[0013] <Conductive additive> The conductive additive according to one embodiment of the present invention comprises carbon nanotubes (CNTs) and fibrous carbon. The conductive additive may further contain or may not contain granular carbon. Here, the BET specific surface area of ​​the conductive additive is 150 m². ２ It is less than or equal to / g. Because the BET specific surface area is within this range, the amount of CNT added can be reduced by efficiently constructing a conductive network with CNTs and fibrous carbon, and side reactions at high voltages of the electrode are reduced. From this viewpoint, the BET specific surface area is 120 m². ２ It is preferable that it be less than or equal to 105m ２ It is more preferable that it be less than or equal to 95m ２ It is even more preferable that it be less than or equal to 90m ２ It is particularly preferable that the amount is less than or equal to / g. The BET specific surface area is the specific surface area calculated by the BET method from the adsorption isotherm measured using the nitrogen gas adsorption method. A known method can be used for the nitrogen gas adsorption method.

[0014] (Granular Carbon) The conductive additive according to one embodiment of the present invention may or may not contain granular carbon. As the granular carbon, carbon black (CB), acetylene black, Ketjen black, etc. can be used. The specific surface area of ​​the granular carbon is 100 m² from the viewpoint of suppressing side reactions of electrolyte decomposition. ２ It is preferable that the amount is less than or equal to / g.

[0015] The granular carbon in the conductive additive according to one embodiment of the present invention may be known in the art and preferably is one that is commonly used in the field of lithium-ion secondary batteries. Examples include "Denka Black®" (manufactured by Denka Co., Ltd.), "DENKA BLACK Li" (manufactured by Denka Co., Ltd.), "Super P® Li" (manufactured by Imerys Graphite & Carbon), "C-NERGY® SUPER C45" (manufactured by Imerys Graphite & Carbon), and "C-NERGY® SUPER C65" (manufactured by Imerys Graphite & Carbon). The granular carbon may be synthesized according to known methods.

[0016] lol １ w represents the content of granular carbon in the conductive additive in "mass percent". That is, it is defined by the following formula: w = granular carbon content in the conductive additive １ (Mass %) = 100 × (Mass of granular carbon in the conductive additive) / (Mass of conductive additive) ... (1)

[0017] lol １ It is preferably 50 or less, more preferably 40 or less, even more preferably 30 or less, particularly preferably 20 or less, particularly preferably 10 or less, and extremely preferably 0.

[0018] (Carbon nanotubes (CNTs)) The CNTs in the conductive additive according to one embodiment of the present invention may be those known in the art, and preferably those commonly used in the field of lithium-ion secondary batteries. Furthermore, the CNTs may be synthesized by known methods.

[0019] The average fiber diameter of the CNTs is not limited, but is preferably between 1 nm and 30 nm. This range allows the CNTs to form a conductive network that covers the active material. From this viewpoint, the average fiber diameter of the CNTs is more preferably between 1.5 nm and 20 nm, even more preferably between 2 nm and 15 nm, and particularly preferably between 3 nm and 10 nm.

[0020] The average fiber diameter of carbon nanotubes (CNTs) can be measured using a scanning electron microscope (SEM). For example, CNTs can be sprinkled onto a carbon tape on an SEM observation stage, or a thin layer of CNT dispersion on a metal foil can be dried and placed on a carbon tape. The average fiber diameter of 200 randomly selected CNTs can then be observed with an SEM and measured by averaging their diameters. Alternatively, the average fiber diameter of CNTs may be measured using a transmission electron microscope (TEM), as described later.

[0021] The average fiber length of the CNTs is not limited, but is preferably between 0.5 μm and 100 μm. This range allows the CNTs to form a conductive network. From this viewpoint, the average fiber length of the CNTs is more preferably between 1 μm and 30 μm, even more preferably between 2 μm and 10 μm, and particularly preferably between 3 μm and 8 μm.

[0022] The average fiber length of a carbon nanotube (CNT) can be determined, for example, by dispersing CNTs in a solvent to prepare a sample for scanning electron microscopy (SEM) or transmission electron microscopy (TEM) observation, observing the sample with the SEM or TEM, and averaging the lengths of 30 randomly selected CNTs whose ends can be identified.

[0023] lol ２ w represents the CNT content in the conductive additive in "mass percent". That is, it is defined by the following formula: w = CNT content in conductive additive ２ (Mass %) = 100 × (Mass of CNTs in the conductive additive) / (Mass of the conductive additive) ... (2)

[0024] If the amount of CNT added is excessive, side reactions at high voltages increase, and if it is too little, the resistance reduction effect is insufficient. From this perspective, the aforementioned w ２ It is preferably 0.1 or more and 50 or less, more preferably 1 or more and 45 or less, and even more preferably 10 or more and 40 or less.

[0025] (Fibrous Carbon) The fibrous carbon in the conductive additive according to one embodiment of the present invention is not particularly limited. Known materials or those prepared by known methods can be used. Specifically, the vapor-phase carbon fiber "VGCF-H" manufactured by Resonaq Corporation can be suitably used.

[0026] The average diameter of the fibrous carbon is preferably 70 nm to 300 nm. The diameter of the fibrous carbon, or fiber diameter, refers to the dimension of the fibrous carbon in the direction perpendicular to the longitudinal direction of the fibrous carbon. The average of this over multiple fibers is called the "average diameter of the fibrous carbon" or "average fiber diameter."

[0027] When the average diameter of the fibrous carbon is 70 nm or more, the fibrous carbon becomes less likely to aggregate and disperses easily in the electrode. This reduces the volume resistivity of the electrode mixture layer. From this viewpoint, the average diameter of the fibrous carbon is more preferably 100 nm or more, even more preferably 120 nm or more, particularly preferably 130 nm or more, and most preferably 140 nm or more.

[0028] If the average diameter of the fibrous carbon is 300 nm or less, the amount added to the electrode can be kept to a minimum. This leads to an improvement in the energy density of the battery. From this viewpoint, the average diameter of the fibrous carbon is more preferably 250 nm or less, even more preferably 200 nm or less, particularly preferably 180 nm or less, and most preferably 170 nm or less.

[0029] The average length of the fibrous carbon is preferably 1 μm to 15 μm. The length of the fibrous carbon, or fiber length, is the length from end to end. If the fibrous carbon is curved, it is the length from end to end measured along the curve. This is also called the longitudinal dimension. The average of these lengths over multiple fibers is called the "average length of the fibrous carbon" or "average fiber length."

[0030] By having an average length of 1 μm or more of fibrous carbon, an electron conduction network (also called a conductive network) can be formed in the electrode. This leads to a reduction in the volume resistivity of the electrode mixture layer. From this viewpoint, an average length of fibrous carbon of 2 μm or more is more preferable, 3 μm or more is even more preferable, and 4 μm or more is particularly preferable.

[0031] When the average length of the fibrous carbon is 15 μm or less, entanglement between the fibrous carbons is reduced, making them easier to disperse. As a result, even a small amount of additive can impart electronic conductivity to the electrode. From this viewpoint, the average length of the fibrous carbon is more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 6 μm or less.

[0032] The average fiber diameter and average fiber length can be measured by the scanning electron microscope (SEM) method described below. <Scanning electron microscope (SEM) observation of fibrous carbon> Put 40 mL of ethanol into a screw tube, add about half a microspatula of conductive additive, and perform sonication for 15 minutes. After sonication, spray the dispersion onto the non-glossy side of aluminum foil and air dry it. After air drying, cut the aluminum foil to a size that fits on the sample stage for SEM observation, and observe and photograph the fibrous carbon on the aluminum foil.

[0033] (Measurement of fiber diameter) Observe at a magnification of 20,000 times and measure the diameter (fiber diameter) of 200 randomly selected fibrous carbon fibers. The average fiber diameter is obtained by taking the arithmetic mean of these 200 fiber diameters. The diameter (fiber diameter) of fibrous carbon is the dimension in the direction perpendicular to the direction in which the fibrous carbon is growing. For each fibrous carbon fiber, measure the diameter at one random point other than both ends and take this as the diameter of that fibrous carbon fiber.

[0034] (Measurement of fiber length) The fibrous carbon on the aluminum foil is observed and photographed at a magnification that captures both ends. 200 randomly selected fibers are measured, and the average value is calculated.

[0035] The conductive additive according to one embodiment of the present invention has a specific surface area of ​​9 m² of fibrous carbon in the conductive additive. ２ / g or more 19m ２ It is preferable that the specific surface area is less than or equal to / g. By having a specific surface area within this range, side reactions can be reduced. From this viewpoint, the specific surface area is 10 m². ２ / g or more 18m ２ It is more preferable that it be less than or equal to 11m ２ / g or more 17m ２ It is even more preferable that the amount is less than or equal to / g.

[0036] The conductive additive according to one embodiment of the present invention has a CNT content in the conductive additive w ２ The mass percentage is given by the fibrous carbon content in the conductive additive, w ３ If expressed as mass%, w ２ / (w ２ +w ３It is preferable that w is 0.1 or more. This makes it possible to efficiently impart conductivity to the electrode mixture layer. From this viewpoint, ２ / (w ２ +w ３ ) is more preferably 0.15 or higher, and even more preferably 0.2 or higher.

[0037] lol ２ / (w ２ +w ３ ) is preferably 0.95 or less. This is because fibrous carbon has a low BET specific surface area and forms rigid, long-distance conductive paths, making it easier to maintain conductive paths against the contraction and expansion of the active material during charge-discharge cycles, and is thought to contribute to the improvement of long-term cycle characteristics, so it is considered better to have a certain amount or more present. From this viewpoint, w ２ / (w ２ +w ３ ) is more preferably 0.85 or less, and even more preferably 0.75 or less. ２ / (w ２ +w ３ ) is more preferably 0.65 or less, w ２ / (w ２ +w ３ It is particularly preferable that the value is 0.55 or less, and extremely preferable that it is 0.45 or less.

[0038] lol ３ w represents the content of fibrous carbon in the conductive additive in "mass%". That is, it is defined by the following formula: w = w / ３ (Mass %) = 100 × (Mass of fibrous carbon in the conductive additive) / (Mass of conductive additive) ... (3) w ３ It is preferably 40 or more, more preferably 45 or more, even more preferably 50 or more, particularly more preferably 60 or more, and extremely preferably 70 or more.

[0039] <Method for Manufacturing Conductive Additive> The method for manufacturing the conductive additive according to one embodiment of the present invention is not particularly limited. It can be prepared by mixing granular carbon, CNTs, and fibrous carbon in a dry or wet manner. It is preferable to use the CNTs in a dispersion. This is because, due to their fineness, the CNTs are aggregated in the conductive additive state, and in the dispersion state, they are thought to be somewhat loosened and dispersed. Therefore, as a method for manufacturing the conductive additive according to one embodiment of the present invention, for example, granular carbon and fibrous carbon are added to a dispersion of CNTs and stirred to obtain a dispersion in which the conductive additive is dispersed, and this is dried. However, since a slurry for electrode coating is required when preparing an electrode mixture layer, the dispersion of the conductive additive may be used as is without drying in order to prepare a slurry for electrode coating.

[0040] <Dispersion> The dispersion according to one embodiment of the present invention contains the conductive additive of the present invention as described above. The dispersion according to one embodiment of the present invention may also contain other components other than the conductive additive, such as other conductive additives, solvents, and dispersants.

[0041] Examples of solvents include water and organic solvents. Examples of organic solvents are not particularly limited, but include N-methyl-2-pyrrolidone (NMP), acetone, ethyl acetate, acetonitrile, tetrahydrofuran (THF), and dimethylformamide (DMF).

[0042] The dispersant is not particularly limited and includes polyvinylpyrrolidone (PVP), Triton X-100, sodium cholate, and the like.

[0043] The content of the conductive additive is preferably 0.1% to 30% by mass, more preferably 0.5% to 20% by mass, and even more preferably 0.5% to 10% by mass, based on the total volume of the dispersion.

[0044] The dispersant content is preferably 0.01% to 10% by mass relative to the total volume of the dispersion.

[0045] When the conductive additive according to the present invention is used in combination with other conductive additives, the content of the conductive additive according to the present invention relative to the total amount of the conductive additive according to the present invention and other conductive additives in the dispersion of the present invention may be 1% to 100% by mass, 10% to 90% by mass, or 20% to 80% by mass. The above content may be adjusted as appropriate, taking into consideration the stability of the dispersion, the resistance when used as an electrode mixture layer, etc.

[0046] <Conductive Layer> The conductive layer according to one embodiment of the present invention contains the conductive additive of the present invention as described above. The conductive layer according to one embodiment of the present invention may contain components other than the conductive additive of the present invention, for example, a binder or, if necessary, additives, other conductive additives, etc. The conductive layer is provided on a metal foil which is a current collector in a battery such as a lithium-ion secondary battery. By forming an electrode mixture layer on the conductive layer, it is possible to achieve lower resistance and improved adhesion compared to when the electrode mixture layer and the current collector are in direct contact.

[0047] The content of the conductive additive is preferably 1% to 60% by mass relative to the total mass of the conductive layer. A content of 1% by mass or more of the conductive additive provides sufficiently low resistance. From the viewpoint of low resistance, the content of the conductive additive is more preferably 10% by mass or more, and even more preferably 20% by mass or more.

[0048] By having a conductive additive content of 60% by mass or less, the detachment of the conductive additive from the conductive layer can be suppressed. From the viewpoint of suppressing the detachment of the conductive additive, the content of the conductive additive is more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0049] A conductive layer according to one embodiment of the present invention may contain a binder. The binder contained in the conductive layer is not particularly limited, and examples include binders used in batteries such as lithium-ion secondary batteries. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), butadiene styrene rubber (SBR), sodium carboxymethylcellulose (CMC-Na), polyimide, polyamide-imide, and polyacrylic acid.

[0050] The binder content is preferably 5% to 80% by mass relative to the total mass of the conductive layer. A binder content of 5% by mass or more facilitates layered molding and suppresses powder shedding. From the viewpoint of moldability and suppression of powder shedding, the binder content is more preferably 10% by mass or more, and even more preferably 20% by mass or more.

[0051] By having a binder content of 80% by mass or less, the resistance of the conductive layer can be suppressed. From the viewpoint of low resistance, the binder content is more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0052] <Electrode Mixture Layer> The electrode mixture layer according to one embodiment of the present invention contains the conductive additive described above. Other components may include an active material, a binder, and other additives, but known materials can be used for these. Methods known in the art can also be used for manufacturing the electrode mixture layer. Briefly, a slurry for electrode coating containing an active material, the conductive additive of the present invention, a binder, a solvent, and other additives as optional components can be prepared, and this slurry can be coated onto a current collector and dried to produce a current collector coated with an electrode mixture layer, i.e., an electrode (positive or negative electrode). Other additives include, for example, other conductive additives, dispersants, and thickeners.

[0053] In the electrode mixture layer according to one embodiment of the present invention, the carbon nanotube content is preferably 0.5% by mass or less. This reduces side reactions at high voltages in the electrode. From this viewpoint, the content is more preferably 0.4% by mass or less, and even more preferably 0.3% by mass or less.

[0054] In one embodiment of the present invention, the electrode mixture layer preferably contains a fluorine-based binder resin as the binder in the electrode mixture layer. This results in a dispersion state different from that of an aqueous binder, and as a result, the tendency and absolute value of the volume resistivity of the electrode mixture layer with respect to the amount added changes. In such an electrode mixture layer, low resistance can be obtained when the CNT content is high. Examples of fluorine-based binder resins include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). These fluorine-based binder resins are usually used together with organic solvents. It should be noted that it is difficult to express the dispersion state of such CNTs and fibrous carbon in terms of structure or physical properties.

[0055] In one embodiment of the present invention, the electrode mixture layer has a surface area of ​​1.14 m² of conductive additive per gram of electrode mixture layer. ２ The surface area is less than or equal to / (g-electrode mixture layer). Having the surface area within this range reduces side reactions at high voltages in the electrode. From this viewpoint, the surface area is 1.00 m². ２ It is preferable that the ratio is less than or equal to / (g-electrode mixture layer), and is 0.95 m ２ It is more preferable that the ratio is less than or equal to / (g - electrode mixture layer). The surface area of ​​the conductive additive per gram of electrode mixture layer can be calculated, for example, by taking the sum of the BET specific surface area of ​​each conductive additive in the electrode mixture layer multiplied by the content of each conductive additive in the electrode mixture layer. That is, it can be calculated by the following formula: Surface area of ​​conductive additive per gram of electrode mixture layer (m ２ ( / g - electrode mixture layer) = Σ ｉ (BET specific surface area SSA of conductive additive i) ｉ (m ２ / g) × Content c of conductive additive i in the electrode mixture layer ｉ(Mass %) / 100) ... (4) The surface area of ​​the conductive additive per gram of electrode mixture layer may be determined by measuring the specific surface area of ​​the conductive additive by the BET method and then multiplying it by the mass ratio of the conductive additive in the electrode mixture layer. A conductive additive that satisfies the above surface area condition may or may not satisfy the conditions of the conductive additive according to the above embodiment of the present invention.

[0056] <Non-aqueous electrolyte battery> A non-aqueous electrolyte battery according to one embodiment of the present invention comprises a positive electrode having a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, and a negative electrode having a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, wherein at least one of the positive electrode mixture layer and the negative electrode mixture layer contains the electrode mixture layer of the present invention.

[0057] The form of a non-aqueous electrolyte battery may be a structure in which multiple positive and negative electrodes housed in an outer casing are stacked in the thickness direction, a laminated type battery, or a wound type battery. As an example of a wound type battery, it may be a cylindrical battery in which an electrode pair and electrolyte obtained by winding a laminate in which positive and negative electrodes are stacked with a separator in between are sealed inside a cylindrical outer casing, or a cylindrical battery in which a cell obtained by winding a laminate in which positive and negative electrodes are stacked with a solid electrolyte is sealed inside a cylindrical outer casing.

[0058] A non-aqueous electrolyte battery may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a separator in between, and an electrolyte solution housed in an outer casing, or it may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a solid electrolyte in between is housed in an outer casing.

[0059] The types of non-aqueous electrolyte batteries are not particularly limited and include lithium-based batteries, sodium-based batteries, potassium-based batteries, magnesium-based batteries, aluminum-based batteries, etc. Among these, lithium-based batteries, which can achieve high voltage and high energy density, and sodium-based batteries, which can be cost-effective, are preferred. Examples of lithium-based batteries include lithium-ion secondary batteries and lithium batteries in which the negative electrode is metallic lithium (for example, lithium-sulfur batteries and lithium-air batteries are also included), and include liquid electrolyte type batteries and solid electrolyte type batteries that contain at least one of the following: electrolyte solution, polymer electrolyte, polymer gel electrolyte, inorganic solid electrolyte, etc. Furthermore, for non-aqueous electrolyte batteries other than lithium-based batteries, the positive electrode active material, negative electrode active material, electrolyte, etc. are not limited and can take various forms, similar to the lithium-based batteries mentioned above. The following describes an example of a lithium-ion secondary battery, but the present invention is not limited thereto.

[0060] The aforementioned conductive layer may be provided between the positive electrode current collector and the positive electrode mixture layer, or between the negative electrode current collector and the negative electrode mixture layer.

[0061] [Positive electrode] The non-aqueous electrolyte battery of the present invention comprises a positive electrode comprising a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector.

[0062] The material of the positive electrode current collector is not particularly limited as long as it does not oxidize and dissolve at high potential and is electrically conductive, and can be selected from aluminum, nickel, titanium, stainless steel, etc. The state of the positive electrode current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. As an example, aluminum foil is used as the positive electrode current collector.

[0063] The positive electrode mixture layer may contain the conductive additive of the present invention. For example, a positive electrode mixture layer is formed on the positive electrode current collector by coating it with a composition for forming a positive electrode mixture layer (a type of composition for forming an electrode mixture layer) which contains a positive electrode active material and the conductive additive of the present invention, and optionally carbon black, other conductive additives, a binder (for example, the binder described in the section on the electrode mixture layer), a solvent, etc., drying the coated slurry, and then pressing it.

[0064] The thickness of the positive electrode mixture layer may be 30 μm or more, 50 μm to 100 μm, or 100 μm to 300 μm, from the viewpoint of energy density and safety.

[0065] The density of the positive electrode mixture layer is 2.0 g / cm³ from the perspective of energy density. ３ It may be greater than or equal to 3.0 g / cm³. ３ It may be greater than or equal to 3.0 g / cm³. ３ ~4.5 g / cm ３ That's fine.

[0066] The basis weight of the positive electrode mixture layer is 10.0 mg / cm³, from the viewpoint of energy density and safety. ２ It may be greater than or equal to 10.0 mg / cm³. ２ ~30.0mg / cm ２ It may also be 30.0 mg / cm³. ２ ~60.0mg / cm ２ That's fine.

[0067] (Positive Electrode Active Material) The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material can be appropriately selected depending on the type of non-aqueous electrolyte battery, and examples include compounds containing at least one of lithium, sodium, potassium, magnesium, and aluminum. Examples of positive electrode active materials include nickel-containing oxides and phosphates having an olivine-type structure. When the battery is a lithium-ion secondary battery, the positive electrode active material is LiNi ｘ Mn ｙ Co ｚ Al ｗ O ２ (x, y, z, w≧0, x+y+z+w=1), LiMPO ４ (M is one or more selected from Fe, Co, Mn, and Ni), LiMn ａ Ni ｂ O ４ Examples include (a, b ≥ 0, a + b = 2). The positive electrode active material may be used alone or in combination of two or more types.

[0068] The positive electrode active material is LiNi ｘ Mn ｙ Co ｚ Al ｗO ２ (x, y, z, w ≥ 0, x + y + z + w = 1), or preferably contains LiMPO ４ (M is one or more selected from Fe, Co, Mn, and Ni).

[0069] LiNi ｘ Mn ｙ Co ｚ Al ｗ O ２ (x, y, z, w ≥ 0, x + y + z + w = 1), it is preferable that the proportion of nickel is relatively high, for example, x ≥ 0.5 or more. Li(Ni ｘ Mn ｙ Co ｚ )O ２ (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 )O ２ (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 )O ２ , Li(Ni ０．７ Mn ０．２ Co ０．１ )O ２ , Li(Ni ０．７ Mn ０．１ Co ０．２ )O ２ , Li(Ni ０．６ Mn ０．２ Co ０．２ )O ２ , Li(Ni ０．５ Mn ０．３ Co ０．２ )O ２ and Li(Ni ０．５ Mn ０．２ Co ０．３ )O ２ are mentioned.

[0070] LiMPO ４ (M is one or more selected from Fe, Co, Mn, and Ni), as the positive electrode active material represented by, for example, LiFePO ４ , LiFe ０．５ Mn０．５ PO ４ LiFe ０．３ Mn ０．７ PO ４ LiCoPO ４ and LiCo ０．５ Mn ０．５ PO ４ For example, at least a portion of the surface of the positive electrode active material may be coated with amorphous carbon.

[0071] In the positive electrode mixture layer, the content of the positive electrode active material is preferably 70% to 99% by mass, and from the viewpoint of positive electrode capacity, it is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0072] In the positive electrode mixture layer, the positive electrode active material, the conductive additive of the present invention, a binder, etc., may simply be mixed together, or the conductive additive of the present invention may be compounded onto the surface of the positive electrode active material. Examples of conductive additives other than the conductive additive of the present invention include conductive additives other than the conductive additive of the present invention.

[0073] When the positive electrode mixture layer contains the above-mentioned conductive additive, the content of the above-mentioned conductive additive in the positive electrode mixture layer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0074] In the positive electrode mixture layer, the content of the conductive additive 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] The positive electrode mixture layer may contain fibrous carbon other than the conductive additive of the present invention (other fibrous carbon). Examples of other fibrous carbon include carbon fibers, vapor-phase carbon fibers, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and carbon nanofibers.

[0076] [Negative electrode] The non-aqueous electrolyte battery comprises a negative electrode which includes a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector.

[0077] The material of the negative electrode current collector is not particularly limited as long as it is an electronically conductive material, and can be selected from copper, nickel, titanium, stainless steel, etc. The state of the negative electrode current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. As an example, copper foil is used as the negative electrode current collector.

[0078] The negative electrode mixture layer may contain the conductive additive of the present invention. For example, a negative electrode mixture layer composition (a type of electrode mixture layer forming composition) containing a negative electrode active material and the conductive additive of the present invention, and further containing other conductive additives, a binder (for example, the binder described in the section on conductive layers), a solvent, etc. as needed, is coated onto the negative electrode current collector, the coated slurry is dried, and then pressed to form a negative electrode mixture layer on the negative electrode current collector.

[0079] The thickness of the negative electrode mixture layer may be 30 μm or more, 50 μm to 100 μm, or 100 μm to 150 μm, from the viewpoint of energy density and safety.

[0080] The density of the negative electrode mixture layer is 1.3 g / cm³, from the viewpoint of energy density and safety. ３ It may be greater than or equal to 1.5 g / cm³. ３ ~2.0 g / cm ３ That's fine.

[0081] The basis weight of the negative electrode mixture layer is 5.0 mg / cm³, considering energy density and safety. ２ It may be greater than or equal to 10 mg / cm³. ２ ~20 mg / cm³ ２ That's fine.

[0082] (Negative electrode active material) The negative electrode mixture layer contains a negative electrode active material. The negative electrode active material may be a metalloid or metal that forms an alloy with lithium, such as Si, Sn, Al, or SiO ｘ (0 < x ≤ 2), soft carbon, hard carbon, graphite, silicon-carbon composite, Li ４ Ti ５ O １２ , metal Li, InO ｘ (0<x≦1.5), AlO ｘ (0<x≦1.5), AgO ｘ (0<x≦0.5), CdOｘ (0<x≦1), SbO ｘ (0<x≦1.5), BiO ｘ (0<x≦1.5), ZnO ｘ Examples include oxides such as (0 < x ≤ 1). Among these, the negative electrode active material preferably contains graphite. Furthermore, at least a portion of the surface of the negative electrode active material may be coated with amorphous carbon. The negative electrode active material may be used alone or in combination of two or more types.

[0083] In the negative electrode mixture layer, the content of the negative electrode active material is preferably 70% to 99% by mass, and from the viewpoint of negative electrode capacity, it is preferably 80% or more by mass, more preferably 90% or more by mass, and even more preferably 95% or more by mass.

[0084] In the negative electrode mixture layer, the negative electrode active material, the conductive additive of the present invention, a binder, etc., may simply be mixed together, or the conductive additive, such as the conductive additive of the present invention, may be compounded onto the surface of the negative electrode active material. Examples of conductive additives include conductive additives other than the conductive additive of the present invention (for example, other conductive additives described in the section on conductive additives).

[0085] When the negative electrode mixture layer contains the above-mentioned conductive additive, the content of the conductive additive in the negative electrode mixture layer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0086] In the negative electrode mixture layer, the content of the conductive additive 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.

[0087] (Outer packaging) The outer packaging for housing the positive and negative electrodes is not limited as long as it can accommodate the positive and negative electrodes, and optionally a separator and electrolyte, or a solid electrolyte, etc. Examples of outer packaging include commercially available battery packs, 18650 type cylindrical cells, and those packaged in aluminum foil, and the outer packaging can be freely designed and used.

[0088] (Separator) A non-aqueous electrolyte battery may be equipped with a separator between the positive electrode and the negative electrode. The separator can be freely selected from those that can be used in general non-aqueous electrolyte batteries, such as a microporous film made of polyethylene or polypropylene. SiO ２ Al ２ O ３ Separators containing particles such as these as fillers, or separators with these particles attached to the surface, can also be used.

[0089] (Electrolyte) Non-aqueous electrolyte batteries may contain an electrolyte. There are no particular restrictions on the electrolyte, and any electrolyte that can be used in a normal non-aqueous electrolyte battery can be suitably used. For example, an organic solvent in which a lithium salt is dissolved in an amount of 0.5 mol / L to 2.0 mol / L can be used.

[0090] LiPF is an example of a lithium salt. ６ LiBF ４ LiClO ４ LiAsF ６ , LiN (SO ２ F) ２ Examples include (LiFSI).

[0091] Examples of organic solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and propylene carbonate (PC). Organic solvents listed here and others may be appropriately selected and mixed. Examples of electrolyte additives include vinylene carbonate (VC), propane sultone (PS), and fluoroethylene carbonate (FEC). When additives are used, the additive content is preferably 0.01% to 20% by mass, more preferably 0.1% to 10% by mass, and even more preferably 0.5% to 5% by mass, based on 100% by mass of the organic solvent.

[0092] (Ionic Liquids) Ionic liquids may be used as electrolytes, or they may be used in combination with the aforementioned organic solvents. The ionic liquids are not particularly limited, and examples include combinations of cations such as imidazolium cations, pyrrolidinium cations, piperidinium cations, and ammonium cations with anions such as bis(trifluoromethane)sulfonimide anions.

[0093] (Solid Electrolyte) A solid electrolyte may be used as the electrolyte. When a solid electrolyte is used, a separator is not required, and a battery in which the positive electrode and negative electrode are sandwiched between solid electrolytes (for example, an all-solid-state lithium-ion secondary battery) can be formed.

[0094] Examples of solid electrolytes include polymer electrolytes and inorganic solid electrolytes. Polymer electrolytes are not particularly limited and include, for example, polymers such as polyethylene oxide (PEO), polymethyl methacrylic acid (PMMA), and polyacrylonitrile (PAN), and polymer gels impregnated with the lithium salt by adding a plasticizer (e.g., organic solvent) to the polymer. Inorganic solid electrolytes are not particularly limited, and include Li ２ S-P ２ S ５ Li ２ S-GeS ２ Li ２ S-SiS ２ -Li ３ PO ４ Sulfide-based solid electrolytes such as La ０．５１ Li ０．３４ TiO ２．９４ Li １．３ Al ０．３ Ti １．７ (PO ４ ) ３ Li ７ La ３ Zr ２ O １２ , 50Li ４ SiO ４ ・50Li ３ BO ３ Li ２．９ PO ３．３ N ０．４６ (LIPON), Li ３．６ Si０．６ P ０．４ O ４ Li １．０７ Al ０．６９ Ti １．４６ (PO ４ ) ３ Li １．５ Al ０．５ Ge １．５ (PO ４ ) ３ Examples include oxide-based solid electrolytes such as the following.

[0095] A non-aqueous electrolyte battery according to one embodiment of the present invention can be used as a power source for electronic devices such as smartphones, tablet PCs, and personal digital assistants; as a power source for electric motors such as power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and for storing electricity obtained from fuel cells, solar power generation, wind power generation, etc.

[0096] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to these examples. <Materials used> ・Fibrous carbon: Product name "VGCF-H" (manufactured by Resonac Co., Ltd., average fiber diameter 150 nm, average fiber length 4 μm, BET specific surface area 15 m²) ２ ( / g) • CNT: Average fiber diameter 10 nm, average fiber length 1.5 μm, BET specific surface area 250 m² ２ / g - Granular carbon (CB): Product name "C-NERGY SUPER C 65" (manufactured by Imerys Graphite & Carbon), BET specific surface area 65m ２ / g

[0097] <BET Specific Surface Area> The total surface area of ​​the sample in the sample cell (9 mm x 135 mm) is 2 m². ２ ~50m ２The sample was placed in the container as described above, dried at 300°C under vacuum conditions for 1 hour, and the sample weight was measured. The following measurements were then performed: • Apparatus: NOVA 4200e, manufactured by Quantachrome Instruments. • Measurement gas: Nitrogen. Liquid nitrogen density: 0.808 g / cc. Volume of 1 mole of nitrogen at standard conditions: 22.4133 L. Atomic weight of nitrogen: 14.0067. • Relative pressure settings for the measurement range: 0.1, 0.2, 0.3. • BET specific surface area calculation method: Calculated using the BET multipoint method from adsorption isotherm data at three points near relative pressures of 0.1, 0.2, and 0.3.

[0098] <Preparation of Conductive Additive Dispersion> A 10% by mass NMP solution of polyvinylidene fluoride (PVDF) was prepared in advance. 1.0 part by mass of PVDF and a CNT dispersion (5% by mass of CNT, 0.3% by mass of dispersant) were mixed in a ratio such that the solid content of CNT was 0.2 parts by mass. The mixture was stirred in a homogenizer at a rotation speed of 4500 rpm for 30 minutes. 1.0 part by mass of fibrous carbon was mixed into the stirred solution, and NMP was added to adjust the solid content concentration in the dispersion to 6.0% by mass. The prepared solution was stirred in a homogenizer at a rotation speed of 4500 rpm for 30 minutes to obtain a conductive additive dispersion. <Preparation of Electrode Mixture Layer> (Preparation of Positive Electrode) LCO (LiCoO) was used as the positive electrode active material. ２ To 97.8 parts by mass of (average particle size 15 μm), a conductive additive dispersion was added in the order of 1.2 parts by mass of conductive additive and 1.0 part by mass of PVDF, and the mixture was mixed in a kneader. Subsequently, the mixture was mixed in the kneader while adding NMP as needed to prepare a slurry with adjusted viscosity.

[0099] The slurry was coated onto a 20 μm thick aluminum foil using a roll coater and dried to obtain a positive electrode sheet.

[0100] <Measurement of Volume Resistivity of Electrode Mixture Layer> The obtained positive electrode sheet was vacuum-dried in a dry room (dew point: -45°C) at 130°C for 10 hours to prepare an electrode sample. The volume resistivity of the positive electrode sheet was measured using the RM2610 electrode resistance measurement system (manufactured by HIOKI E.E. CORPORATION). Five measurement points were randomly selected, and the average of the measured values ​​was taken as the volume resistivity of the electrode mixture layer.

[0101] <Evaluation of side reactions at high voltage: Linear sweep voltammetry; LSV> The stability of the conductive additive at high voltage was evaluated by fabricating a single electrode of the conductive additive, placing it opposite metallic lithium, and performing LSV measurement on a coin-shaped cell, integrating the amount of current flowing up to an applied voltage of 4.6 V. (Fabrication of single electrode of conductive additive) 94.0 parts by mass of NMP was mixed with 3.0 parts by mass of conductive additive and 3.0 parts by mass of PVDF in a kneader. The resulting slurry was coated onto a 20 μm thick aluminum foil using a roll coater and dried to obtain a single electrode of the conductive additive. The obtained single electrode of the conductive additive was vacuum dried at 130°C for 10 hours in a dry room where the dew point was controlled to be -45°C or lower, and then cut into a circle with a diameter of 13 mm. The weight of the cut electrode was measured, and the weight of the composite layer was calculated by subtracting the weight of the 20 μm thick aluminum foil punched out to a diameter of 13 mm. The combined layer weight was 3.0 mg.

[0102] (Fabrication of coin-type battery) The cut conductive additive electrode was introduced into a glove box filled with argon and with a dew point controlled to below -75°C. The electrolyte was mixed so that the volume ratio of EC to ethyl propionate (EC to ethyl propionate) was 30 to 70, and LiPF ６ A mixed solution was prepared by dissolving the substance to a concentration of 1 mol / L, and VC, FEC, PS, adiponitrile, and 1,2,3-cyanoethoxypropane were added to the mixed solution in weight ratios of 0.5 parts by mass, 3.0 parts by mass, 2.0 parts by mass, 3.0 parts by mass, and 2.0 parts by mass, respectively. Electrodes were placed on the lid of a 2032 type coin cell battery, and 20 microliters of the electrolyte solution were added. A separator cut to a diameter of 17.5 mm and a metallic lithium foil cut to a diameter of 15 mm were then sequentially layered on top. A cap with a gasket was then attached and crimped to produce a coin cell battery with a diameter of 20 mm and a thickness of 3.2 mm.

[0103] <Linear Sweep Voltammetry (LSV) Measurement> The coin-type battery was connected to a potentiostat (VSP-300, Biologic Co., Ltd.) in a constant temperature bath controlled at 25°C. The positive electrode (conductive additive electrode side) of the coin-type battery was connected to the working electrode terminal, and the negative electrode (metallic lithium electrode side) was connected to the counter electrode and reference electrode terminals. LSV measurement was performed from OCV to 4.6V at a sweep speed of 0.1 mV / s. The current values ​​flowing during the LSV measurement process were integrated, and the integrated value divided by the weight of the additive layer was defined as the integrated electrical charge during LSV measurement (unit: mAh / mg). The results are summarized in Table 1.

[0104] [Examples 2-4, Comparative Examples 1-6] Electrode mixture layers and single conductive additive electrodes were prepared by varying the mass ratio of fibrous carbon, granular carbon, and CNTs in the electrode mixture layer as shown in Table 1. The volume resistivity of the electrode mixture layer and the integrated electrical charge during LSV measurement were measured in the same manner as in Example 1. The results are shown in Table 1.

[0105]

[0106] As can be seen from Table 1, the conductive additive contains CNTs and fibrous carbon, wherein the conductive additive further contains or does not contain granular carbon, and the BET specific surface area of ​​the conductive additive is 120 m². ２ In electrodes using a conductive additive with a concentration of less than / g, the cumulative electrical charge during LSV measurement is suppressed. In Comparative Examples 1 and 2, which do not contain fibrous carbon, the cumulative electrical charge during LSV measurement is suppressed, while the volume resistivity of the electrode mixture layer is higher compared to Example 1, which had the same amount of CNTs added. This indicates that by using fibrous carbon in combination with CNTs, conductivity can be imparted to the electrode mixture layer with a smaller amount of CNTs added. Because CNTs have a high BET specific surface area, conductive additives with a reduced amount of CNTs have a smaller cumulative electrical charge during LSV measurement and fewer side reactions at high voltages.

[0107] The disclosure of Japanese Patent Application No. 2024-200699 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A conductive additive comprising carbon nanotubes and fibrous carbon, wherein the conductive additive further comprises or omits granular carbon, and the conductive additive has a BET specific surface area of ​​120 m² using nitrogen gas. ２ Conductive additives that are less than or equal to / g.

2. The conductive additive according to claim 1, which does not contain granular carbon.

3. The conductive additive according to claim 1, wherein the average fiber diameter of the carbon nanotubes is 1 nm to 30 nm, the average fiber diameter of the fibrous carbon is 70 nm to 300 nm, and the average fiber length of the fibrous carbon is 1 μm to 15 μm.

4. The content of granular carbon in the conductive additive is w １ If expressed as mass%, w １ The conductive additive according to claim 1, wherein the value is 50 or less.

5. The content of the carbon nanotubes in the conductive additive is w ２ If expressed as mass%, w ２ The conductive additive according to claim 1, wherein the value is 50 or less.

6. The content rate of the carbon nanotubes in the conductive auxiliary agent is w ２ mass%, and the content rate of the fibrous carbon is w ３ mass%. Then, w ２ / (w ２ + w ３ ) is 0.2 or more. The conductive auxiliary agent according to claim 1.

7. The content of the fibrous carbon in the conductive additive is w ３ If expressed as mass%, w ３ The conductive additive according to claim 1, wherein the ratio is 40 or more.

8. A dispersion containing the conductive additive according to any one of claims 1 to 7.

9. A conductive layer comprising the conductive additive according to any one of claims 1 to 7.

10. An electrode mixture layer comprising the conductive additive according to any one of claims 1 to 7.

11. The surface area of ​​the conductive additive per gram of electrode mixture layer is 1.14 m². ２ The electrode mixture layer is less than or equal to / (g-electrode mixture layer).

12. The electrode mixture layer according to claim 10, wherein the binder in the electrode mixture layer contains a fluororesin.

13. A non-aqueous electrolyte battery comprising the electrode mixture layer according to claim 10.

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