Conductive auxiliary agent, conductive auxiliary agent dispersion liquid, negative electrode mixture slurry, negative electrode mixture layer, negative electrode, and lithium ion battery

Abstract

To provide a conductive auxiliary agent, a conductive auxiliary agent dispersion liquid, a negative electrode mixture slurry, a negative electrode mixture layer, a negative electrode, and a lithium ion battery, in which the increase in viscosity at preparation of an electrode mixture slurry is suppressed and whose peeling strength against a current collector and cycle characteristic can be improved when the negative electrode mixture layer and the lithium ion battery are manufactured.SOLUTION: A conductive auxiliary agent includes single-layer carbon nanotube and fibrous carbon. The ratio of the fibrous carbon in the entire conductive auxiliary agent is 70 mass% or more. The ratio of the single-layer carbon nanotube in the entire conductive auxiliary agent is 3.0 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a conductive additive, a conductive additive dispersion, a negative electrode mixture slurry, a negative electrode mixture layer, a negative electrode, and a lithium ion battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, especially lithium-ion batteries, are widely used in electronic devices such as smartphones, laptop PCs, portable game devices, and portable power tools, taking advantage of their small size, light weight, and high voltage characteristics. In recent years, against the backdrop of environmental concerns, lithium-ion secondary batteries have also become popular in electric vehicles (EVs) that run solely on batteries and hybrid electric vehicles (HEVs) that combine a gasoline engine with a battery.

[0003] For example, Patent Document 1 proposes a material composition for a conductive layer on a battery electrode, which contains a conductive additive including a three-dimensional network structure of a carbonaceous material containing carbon nanotubes having a first small diameter and carbon nanotubes having a second large diameter larger than the first small diameter, an electrode material, a dispersant, and a polymer binder in a specific mass ratio. It explains that the material composition described in Patent Document 1 allows the addition of a small amount of conductive filler and a small amount of binder, thereby allowing the carbon nanotubes to be contained together with a larger amount of active material, thereby enabling the production of a lithium-ion battery electrode with improved battery performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6857443 Summary of the Invention [Problem to be solved by the invention]

[0005] In lithium-ion batteries, Si-based active materials used as negative electrode active materials undergo large volume changes during charge and discharge, making it difficult to improve cycle performance. To fully utilize Si-based active materials, it is desirable to form conductive paths between the active materials. To this end, a commonly known method is to use single-walled carbon nanotubes (SWCNTs) as a conductive additive. However, the current situation is that it is undesirable to increase the amount of additive because the viscosity of the electrode mixture used for coating the electrode increases. Furthermore, even when using negative electrode active materials other than Si-based active materials, it is desirable to form conductive paths between the active materials to improve cycle characteristics and further increase peel strength from the current collector.

[0006] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a conductive additive, a conductive additive dispersion, a negative electrode mixture slurry, a negative electrode mixture layer, a negative electrode, and a lithium ion battery that can suppress an increase in viscosity when an electrode mixture slurry is prepared, and that can improve the peel strength to a current collector and the cycle characteristics when a negative electrode mixture layer and a lithium ion battery are fabricated. [Means for solving the problem]

[0007] The present disclosure includes the following aspects. <1> A conductive additive containing single-walled carbon nanotubes and fibrous carbon, The proportion of fibrous carbon in the entire conductive additive is 70 mass% or more, The conductive additive contains single-walled carbon nanotubes in an amount of 3.0 mass % or more of the entire conductive additive. <2> The fibrous carbon has an average diameter of 80 nm or more. <1> The conductive additive described in <3> The average diameter of the bundle of single-walled carbon nanotubes is 90 nm or less; <1> or <2> The conductive additive described in <4> The average length (L 50 ) to the average length (L b ) ratio (Lb / L 50 ) is 0.3 or more, <1> The conductive additive described in <5> further comprising carbon black, <1> ~ <3> The conductive additive according to any one of the above.

[0008] <6> <1> ~ <5> 10. A conductive additive dispersion comprising the conductive additive according to any one of 1 to 9, a dispersant, and a solvent.

[0009] <7> <1> ~ <5> 10. A negative electrode mixture slurry comprising the conductive additive according to any one of 1 to 9, a dispersant, a solvent, and a negative electrode active material. <8> The negative electrode active material includes a Si-based active material, and the Si-based active material is Si, SiO x (x is greater than 0 and less than 1.5), and Si-C composites, <7> The negative electrode mixture slurry according to claim 1. <9> The average particle diameter D of the Si-based active material 50 The average length L of the fibrous carbon 50 The ratio (L 50 / D 50 ) is less than 2, <8> The negative electrode mixture slurry according to claim 1. <10> The negative electrode active material further contains graphite. <8> The negative electrode mixture slurry according to claim 1. <11> The silicon content of the Si-based active material is 20% by mass to 80% by mass. <8> ~ <10> 10. The negative electrode mixture slurry according to claim 9, wherein the negative electrode mixture slurry is a mixture of a first electrode and a second electrode. <12> The oxygen content of the Si-based active material is 0.1% by mass to 70% by mass. <8> ~ <11> 10. The negative electrode mixture slurry according to claim 9, wherein the negative electrode mixture slurry is a mixture of a first electrode and a second electrode.

[0010] <13> <1> ~ <5> a negative electrode mixture layer containing the conductive additive according to any one of the above items and a negative electrode active material, The negative electrode mixture layer has a proportion of the single-walled carbon nanotubes that is more than 0.01% by mass and less than 0.1% by mass of the entire negative electrode mixture layer. <14> The negative electrode active material contains a Si-based active material, and the Si-based active material is Si, SiO x(x is greater than 0 and less than 1.5), and Si-C composites, <13> The negative electrode mixture layer according to claim 1. <15> Average particle size D of Si-based active material 50 Average length L of fibrous carbon 50 The ratio (L 50 / D 50 ) is less than 2, <14> The negative electrode mixture layer according to claim 1. <16> The silicon content is 3% by mass to 50% by mass. <11> The negative electrode mixture layer according to claim 1. <17> The single-walled carbon nanotubes and the fibrous carbon are arranged so as to satisfy the following (1) to (3): <13> ~ <16> 10. The negative electrode mixture layer according to claim 9, wherein the negative electrode mixture layer is a layer of a material selected from the group consisting of fluororesin, ... (1) At least some of the single-walled carbon nanotubes contact the surface of the negative electrode active material so as to bridge the negative electrode active material. (2) The single-walled carbon nanotubes cross the fiber axis of at least a part of the fibrous carbon a plurality of times. (3) At least some of the single-walled carbon nanotubes are in contact with the negative electrode active material and the fibrous carbon so as to bridge both of them.

[0011] <18> a current collector and a <13> ~ <17> and the negative electrode mixture layer according to any one of the above items. <19> <18> A lithium ion battery comprising the negative electrode according to claim 1 and a positive electrode. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to provide a conductive additive, a conductive additive dispersion, a negative electrode mixture slurry, a negative electrode mixture layer, a negative electrode, and a lithium ion battery that can suppress an increase in viscosity when preparing an electrode mixture slurry, and that can improve the peel strength to a current collector and the cycle characteristics when a negative electrode mixture layer and a lithium ion battery are fabricated. DETAILED DESCRIPTION OF THE INVENTION

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

[0014] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0015] In the present disclosure, "single-walled carbon nanotubes" (SWCNTs) refer to nanotubes having a single graphene sheet layer, or nanotubes having a single graphene sheet layer and including nanotubes having two or more graphene sheet layers in an amount of up to 10%. In the present disclosure, "fibrous carbon" refers to a carbon fiber having multiple graphene sheet layers and an average diameter of 80 nm or more. For example, "VGCF-H" (BET specific surface area = 15 m) manufactured by Resonac Co., Ltd. 2 / g, d 002 This includes so-called "vapor grown carbon fibers" such as those with a pore size of 0.25 nm or 0.339 nm, respectively.

[0016] <Conductive additive> The conductive additive of the present disclosure contains single-walled carbon nanotubes and fibrous carbon, and the proportion of fibrous carbon in the entire conductive additive is 70 mass% or more, and the proportion of single-walled carbon nanotubes in the entire conductive additive is 3.0 mass% or more. A conductive additive having such a configuration can suppress an increase in viscosity when preparing an electrode mixture slurry, and can improve the peel strength and cycle characteristics of a negative electrode mixture layer and a lithium-ion battery when produced. The reason for this is unclear, but is presumed to be as follows.

[0017] Fibrous carbon has multiple graphene sheet layers and an average diameter of 80 nm or more, making it more rigid and linear than typical multi-walled carbon nanotubes. Because of this shape, fibrous carbon has a smaller specific surface area than carbon black (hereinafter also referred to as CB), which is commonly used as a conductive additive. Therefore, when CB and SWCNTs are used together, most of the SWCNTs are entangled in the CB, making it almost impossible for the SWCNTs to bridge the CB segments, and thus preventing the formation of an effective conductive path.

[0018] In contrast, when fibrous carbon and SWCNTs are used together, the low specific surface area of ​​the fibrous carbon prevents the SWCNTs from being distributed too unevenly on the fibrous carbon, allowing the SWCNTs to bridge the gap between the fibrous carbons, effectively forming a conductive path. In particular, because the proportion of fibrous carbon in the entire conductive additive is 70% by mass or more, the SWCNT content is at most 30% by mass, and the amount of SWCNTs used is kept low. This is achieved by combining fibrous carbon with SWCNTs. Furthermore, because the proportion of SWCNTs in the entire conductive additive is 3.0% by mass or more, the SWCNTs can adequately bridge the gap between the fibrous carbons. Furthermore, because the SWCNTs are not distributed unevenly in the fibrous carbon, they are entangled with other components, such as the binder, within the negative electrode mixture layer, presumably improving the peel strength to the current collector.The effective formation of conductive paths and improved peel strength to the current collector are presumably also contributing to improved cycle performance of lithium-ion batteries.

[0019] [Single-walled carbon nanotubes (SWCNT)] The diameter of the SWCNTs is not particularly limited, and the average diameter is usually 3.0 nm or less, and preferably 0.4 nm or more. The average diameter of SWCNTs is determined by dispersing them in a solvent, scooping them up with a microgrid to prepare a sample for observation, observing this with a transmission electron microscope (TEM), measuring the diameter of 30 SWCNTs in a region excluding the regions near both ends in the longitudinal direction, and calculating the average value.

[0020] From the viewpoint of bridging between fibrous carbons by SWCNTs, the longer the SWCNTs, the better, and the average length of the SWCNTs is preferably 1.1 μm or more, more preferably 4.0 μm or more, and even more preferably 6.0 μm or more. Furthermore, from the viewpoint of suppressing the generation of ball-like aggregates and forming effective conductive paths, the average length of the SWCNTs is preferably 21 μm or less, more preferably 16 μm or less, and even more preferably 11 μm or less.

[0021] The average length of SWCNTs is determined by first identifying SWCNTs whose both ends are visible using TEM, then increasing the magnification and tracing the length of each SWCNT. This procedure is performed on 30 SWCNTs, and the average length is calculated.

[0022] Because SWCNTs are so thin, strong van der Waals forces act between the individual fibers, forming bundles called "bundles." The average diameter of the bundles varies depending on the dispersant, dispersion solvent, and dispersion process used when preparing the negative electrode mixture layer, but it is preferable that it be 90 nm or less. Since thinner and longer bundles can be made conductive with smaller amounts added, a relatively small bundle diameter is advantageous from the viewpoint of electrode conductivity. From this viewpoint, the average bundle diameter is preferably 50 nm or less, and more preferably 40 nm or less. Furthermore, from the viewpoint of suppressing re-aggregation, the average bundle diameter is preferably 1 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more.

[0023] The average diameter of the bundles was determined by dispersing them in a solvent, then scooping up the bundles with a microgrid to prepare a sample for observation, observing this with a transmission electron microscope (TEM), and measuring the diameters of 30 bundles in areas excluding the regions near both ends in the longitudinal direction, and calculating the average value.

[0024] The length of the SWCNT bundle is preferably 1 μm to 20 μm, more preferably 3 μm to 17 μm, and even more preferably 5 μm to 15 μm.

[0025] The average length of SWCNT bundles is determined by first identifying SWCNT bundles whose both ends are visible using TEM, then increasing the magnification and measuring the length of each bundle one by one. This procedure is performed for 30 bundles, and the average value is calculated. Measurements can also be performed using SEM if this is possible.

[0026] From the viewpoint of effectively forming a conductive path, the proportion of SWCNTs in the entire conductive additive is 3.0 mass % or more, preferably 4.0 mass % or more, and more preferably 5.0 mass % or more.

[0027] From the viewpoint of keeping the viscosity of the slurry low when forming the negative electrode mixture layer, the proportion of SWCNTs in the entire conductive additive is preferably 13 mass% or less, more preferably 12 mass% or less, even more preferably 10 mass% or less, and most preferably 8 mass% or less.

[0028] [Fiber carbon] In the conductive additive of the present disclosure, the proportion of fibrous carbon in the entire conductive additive is 70 mass% or more, preferably 87 mass% or more, more preferably 90 mass% or more, and even more preferably 93 mass% or more.

[0029] The proportion of fibrous carbon in the entire conductive additive is preferably 97 mass% or less. Such a proportion can increase the density of the electrode. From this perspective, the proportion of fibrous carbon in the entire conductive additive is more preferably 96 mass% or less, and even more preferably 95 mass% or less.

[0030] The average diameter of the fibrous carbon is preferably 80 nm or more. When the fibrous carbon has such a thickness, the fibers have rigidity, and the fibrous carbon is twisted between the active materials to generate voids, which contributes to the penetration and retention of the electrolyte, and therefore tends to further reduce the resistance of the battery. From this viewpoint, the average diameter of the fibrous carbon is more preferably 100 nm or more, and even more preferably 120 nm or more.

[0031] The average diameter of the fibrous carbon is preferably 400 nm or less. Such a diameter can increase the density of the electrode. From this viewpoint, the average diameter of the fibrous carbon is more preferably 300 nm or less, and further preferably 250 nm or less.

[0032] The average diameter of the fibrous carbon is determined by dispersing it in a solvent, scooping up the fibrous carbon with a microgrid to prepare a sample for observation, observing this with a transmission electron microscope (TEM), measuring the diameter of 30 pieces in a region excluding the regions near both ends in the longitudinal direction, and calculating the average value.

[0033] The average length of the fibrous carbon is preferably 1 μm or more. With such an average length, the resistance of the battery can be reduced. From this viewpoint, the average length of the fibrous carbon is more preferably 2 μm or more, and further preferably 3 μm or more.

[0034] The average length of the fibrous carbon is preferably 20 μm or less. With such an average length, entanglement is further reduced, and the battery resistance can be reduced. From this viewpoint, the average length of the fibrous carbon is more preferably 15 μm or less, further preferably 10 μm or less, particularly preferably 7 μm or less, and extremely preferably 5 μm or less. The average length of the fibrous carbon is determined by first identifying the fibrous carbon whose both ends are visible by TEM, then increasing the magnification and measuring the length of each fibrous carbon fiber. This procedure is carried out for 30 fibers, and the average value is calculated. If measurement is possible using SEM, this may also be used.

[0035] The average length of the fibrous carbon (L 50 ) versus the average length of the SWCNT bundle (L b ) ratio (L b / L 50 ) is preferably 0.3 or more, more preferably 0.8 or more, and even more preferably 1 or more. With such a length ratio, the SWCNTs can bridge between the fibrous carbons, effectively forming a conductive path, and as a result, when a negative electrode mixture layer and a lithium ion battery are produced, the peel strength from the current collector and the cycle characteristics tend to be further improved.

[0036] Also, the ratio (L b / L 50 ) is preferably 10 or less, more preferably 5 or less, even more preferably 3 or less, and most preferably 2 or less. With such a length ratio, the area in one bundle that is in contact with the fibrous carbon but is not in contact with the fibrous carbon increases, so that a conductive path spanning from one fibrous carbon to another is effectively formed, and as a result, when a negative electrode mixture layer and a lithium ion battery are produced, the peel strength to the current collector and the cycle characteristics tend to be further improved.

[0037] The fibrous carbon is preferably hollow. The BET specific surface area of ​​fibrous carbon is 2m 2 / g~100m 2 / g, and 5m 2 / g~80m 2 / g, more preferably 10m 2 / g~60m 2 / g is even more preferable. When the BET specific surface area is equal to or less than the upper limit, the SWCNTs are prevented from being entangled with the fibrous carbon and being unevenly distributed, conductive paths are effectively formed, and the peel strength to the current collector and cycle characteristics tend to be further improved. When the BET specific surface area is equal to or greater than the lower limit, the number of SWCNTs per unit mass increases, and sufficient conductivity tends to be imparted to the electrode.

[0038] The BET specific surface area of ​​the fibrous carbon can be determined by the BET method from an adsorption isotherm obtained by nitrogen adsorption measurement at 77K.

[0039] The fibrous carbon has an average interplanar spacing d of (002) by X-ray diffraction. 002 The average interplanar spacing d is preferably 0.345 nm or less, and more preferably 0.336 to 0.340 nm. 002 When the average interplanar spacing d is 0.345 nm or less, the graphite crystals are sufficiently developed, and when a lithium ion secondary battery is fabricated, both the initial efficiency and the energy density tend to be excellent. 002 The theoretical value of graphite crystals is 0.3354 nm, and the closer the value is to this, the greater the energy density tends to be.

[0040] Average spacing d 002 The diffraction peak corresponding to the carbon 002 plane, which appears at a diffraction angle 2θ of 24° to 27°, can be calculated using the JSPS method by irradiating a sample with X-rays (CuKα rays) and measuring the diffraction rays with a goniometer to obtain a diffraction profile.

[0041] Fibrous carbon has a Raman scattering spectrum of 1341 cm -1 ~1349cm -1The peak height of the band (I d ) and 1570cm -1 ~1578cm -1 The peak height of the band (I g ) ratio (I d / I g ) is preferably 0.1 to 2.0, and more preferably 0.1 to 0.5.

[0042] The Raman spectroscopy measurement is performed using a laser Raman spectrophotometer (for example, model number NRS-1000, JASCO Corporation) by irradiating an argon laser beam onto a sample plate on which the sample is placed so that it is flat. The measurement conditions are as follows: Argon laser light wavelength: 532 nm Wavenumber resolution: 2.56cm -1 Measurement range: 1180cm -1 ~1730cm -1 Peak Processing: Background Removal The "peak height" is the height from the background-subtracted baseline to the peak apex.

[0043] [Other conductive fillers] The conductive additive of the present disclosure may contain other conductive fillers in addition to SWCNTs and fibrous carbon. Examples of other conductive fillers that may be used in combination include general multi-walled carbon nanotubes (MWCNTs) and graphene. MWCNTs are carbon fibers with multiple graphene sheet layers and an average diameter of less than 80 nm. The other conductive fillers may be used alone or in combination of two or more. Among these, carbon black (CB) such as acetylene black and ketjen black is preferred as another conductive additive. The proportion of CB in the entire conductive additive is preferably 10% by mass or less. Because CB tends to trap SWCNTs, setting the content to 10% by mass or less allows SWCNTs to form conductive paths relatively effectively, and also contributes to improving the conductivity of the active material surface through CB, which tends to further improve cycle characteristics. From this perspective, the proportion of CB in the entire conductive additive is more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0044] <Conductive additive dispersion> The conductive additive dispersion of the present disclosure includes the conductive additive of the present disclosure, a dispersant, and a solvent. Because the conductive additive dispersion of the present disclosure uses the conductive additive of the present disclosure, an increase in viscosity during preparation of a negative electrode mixture slurry is suppressed, and when a negative electrode mixture layer and a lithium ion battery are fabricated, peel strength from the current collector and cycle characteristics can be improved.

[0045] The details of the conductive additive are as described above. The content of the conductive additive in the conductive additive dispersion can be adjusted appropriately depending on the application, and is, for example, preferably 0.1% by mass to 20% by mass, more preferably 1% by mass to 10% by mass, and even more preferably 2% by mass to 7% by mass.

[0046] The dispersant is not particularly limited as long as it has the function of improving the dispersibility of the conductive additive in the solvent, and examples thereof include polymer compounds such as carboxymethyl cellulose (CMC) and polyvinylpyrrolidone (PVP), and surfactants such as Triton X-100 and sodium cholate. One type of dispersant may be used alone, or two or more types may be used in combination. The content of the dispersant is preferably 0.01% by mass to 20% by mass with respect to the total amount of the conductive assistant dispersion.

[0047] The content of the dispersant in the conductive assistant dispersion can be adjusted appropriately depending on the application, and is, for example, preferably 0.01% by mass to 5% by mass, more preferably 0.1% by mass to 3% by mass, and even more preferably 0.5% by mass to 2% by mass.

[0048] Examples of the solvent include water and organic solvents. Examples of the organic solvent include, but are not limited to, N-methyl-2-pyrrolidone (NMP), acetone, ethyl acetate, acetonitrile, tetrahydrofuran (THF), and dimethylformamide (DMF). The solvent may be used alone or in combination of two or more. When the conductive additive dispersion is used in the negative electrode mixture slurry, it is preferable to use the same solvent for the conductive additive as for the negative electrode mixture slurry.

[0049] The content of the solvent in the conductive assistant dispersion can be adjusted appropriately depending on the application, and is, for example, preferably 75.0 mass % to 99.9 mass %, more preferably 87.0 mass % to 98.9 mass %, and even more preferably 91.0 mass % to 97.5 mass %.

[0050] The method for producing the conductive additive dispersion is not particularly limited, and methods generally known to those skilled in the art can be used. For example, the conductive additive dispersion can be prepared by weighing the constituent components, adding a solvent, and mixing them. In the method for producing the conductive additive dispersion, the proportions of SWCNTs and fibrous carbon are adjusted so as to obtain the conductive additive dispersion of the present disclosure. Although there are no particular restrictions on the order of mixing, it is preferable to mix the SWCNTs, dispersant, and solvent first, and then add the fibrous carbon. Mixing in this order makes it easier for each component to disperse, reducing the amount of agglomerated particles.

[0051] <Negative electrode mixture slurry> The negative electrode mixture slurry of the present disclosure includes the conductive additive of the present disclosure, a dispersant, a solvent, and a negative electrode active material. Because the negative electrode mixture slurry of the present disclosure uses the conductive additive of the present disclosure, when a negative electrode mixture layer and a lithium ion battery are fabricated, the peel strength from the current collector and cycle characteristics can be improved. The details of the conductive aid, dispersant, and solvent are as described above.

[0052] The content of the conductive auxiliary agent in the negative electrode mixture slurry can be adjusted appropriately depending on the application, and is, for example, preferably 0.1 mass % to 1 mass %, more preferably 0.2 mass % to 0.8 mass %, and even more preferably 0.3 mass % to 0.6 mass %, relative to the total solid content.

[0053] The content of the dispersant in the negative electrode mixture slurry can be adjusted appropriately depending on the application. For example, it is preferably 0.01 mass % to 0.5 mass %, more preferably 0.1 mass % to 0.3 mass %, and even more preferably 0.15 mass % to 0.25 mass %, relative to the total solid content.

[0054] The content of the solvent in the negative electrode mixture slurry can be adjusted appropriately depending on the desired viscosity, and is, for example, preferably 50% by mass to 90% by mass, more preferably 60% by mass to 80% by mass, and even more preferably 65% ​​by mass to 75% by mass.

[0055] The negative electrode mixture slurry may further contain a binder, a thickener, etc., to the extent that performance is not impaired. Materials used in electrode mixtures for lithium-ion batteries can be appropriately selected and used as the binder. Examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), polyvinyl acetate (PVAc), polyacrylate (PAA), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC). One binder may be used alone, or two or more binders may be used in combination. Examples of thickeners include CMC. One thickener may be used alone, or two or more thickeners may be used in combination. CMC is also listed as an example of a dispersant, and may be included for its dispersing effect or its thickening effect. The total content of the binder and thickener in the negative electrode mixture slurry is preferably 20% by mass or less, and more preferably 15% by mass or less.

[0056] The negative electrode active material is not particularly limited, but preferably contains a Si-based active material. Although the Si-based active material has the advantage of a high specific capacity, it undergoes large volume changes during charge and discharge, making it difficult to improve cycle characteristics. However, by using the conductive additive of the present disclosure, it is possible to improve cycle characteristics. As the Si-based active material, a generally known material can be used, and it is preferable that the active material contains at least one selected from the group consisting of silicon, silicon oxide, and a composite of silicon and another material, and Si, SiO x (x is greater than 0 and not greater than 1.5), and Si—C composites. As will be apparent to those skilled in the art, in lithium-ion batteries, the negative electrode active material is lithiated and delithiated during charge and discharge, and therefore, the Si-based active material also includes those with lithiated compositions up to their theoretical specific capacity.

[0057] Examples of Si-C composites include those having a structure in which silicon particles are dispersed in a carbon matrix (first form), those in which silicon is impregnated into the pores of porous carbon (second form), and those in which carbon is coated on the surface of silicon or silicon oxide (third form). In the Si-C composite of the first embodiment, the silicon particles preferably have a volume average particle size of nanometers, ranging from several tens to several hundreds of nanometers. In the Si-C composite of the third embodiment, the silicon or silicon oxide preferably has a particle size on the order of nanometers to micrometers.

[0058] The silicon content of the Si-based active material is preferably 20% by mass or more. This value tends to result in a negative electrode with a large capacity. From this perspective, the silicon content of the Si-based active material is more preferably 30% by mass or more, and even more preferably 40% by mass or more.

[0059] The silicon content of the Si-based active material is preferably 80% by mass or less. This value allows the Si-based active material to suppress excessive volume changes due to lithium absorption, tending to provide a lithium-ion battery with excellent cycle characteristics. From this perspective, the silicon content of the Si-based active material is more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less.

[0060] The oxygen content of the Si-based active material is preferably 70% by mass or less. This value tends to increase the specific capacity and improve the initial coulombic efficiency. From this perspective, the oxygen content of the Si-based active material is more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0061] The oxygen content of the Si-based active material is preferably 0.1% by mass or more. This value tends to reduce the volume change associated with lithiation and delithiation of the active material, resulting in a lithium-ion battery with excellent cycle characteristics. From this perspective, the oxygen content of the Si-based active material is more preferably 5% by mass or more, and even more preferably 10% by mass or more.

[0062] Average particle size D of Si-based active material 50 From the viewpoint of reducing side reactions, the particle size is preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 4 μm or more. In addition, the average particle size D of the Si-based active material 50 From the viewpoint of reducing the resistance of the electrode, the thickness is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less.

[0063] Average particle size D of Si-based active material 50 is the particle diameter (50% D) at 50% cumulative volume when a cumulative volume distribution curve is drawn from the smallest diameter side in the particle size distribution measured by laser diffraction / scattering. The volume-average particle diameter of the negative electrode material can be measured, for example, by using a laser diffraction particle size analyzer (e.g., SALD-3100J from Shimadzu Corporation) in a state where the negative electrode material is dispersed in purified water containing a surfactant.

[0064] When a Si-based active material is included as the negative electrode active material, the average particle size D of the Si-based active material 50 Average length L of fibrous carbon 50 The ratio (L 50 / D 50 ) is preferably less than 2, more preferably 1.5 or less, and even more preferably 1.3 or less. 50 / D 50 ) is within the above range, it can follow the volume change accompanying charge and discharge of the Si-based active material, the conductive path is maintained, and the cycle characteristics tend to be further improved. Also, if the fibrous carbon is too long, it is difficult to increase the density of the electrode. For these reasons, it is preferable that it is less than 2. Even when other negative electrode active materials such as graphite are used in addition to the Si-based active material as the negative electrode active material, maintaining a conductive path for the Si-based active material, which has a large volume change during charging and discharging, is effective in improving cycle characteristics. 50 / D 50 ) is preferably in the above range.

[0065] Also, the ratio (L 50 / D 50 ) is preferably 0.6 or more, more preferably 0.8 or more, and even more preferably 1.0 or more. 50 / D 50 ) is within the above range, the fibrous carbon has a sufficient length relative to the size of the Si-based active material, so that even if the Si-based active material is present nearby, a conductive path can be efficiently formed, and therefore, the cycle characteristics tend to be good.

[0066] As the negative electrode active material, in addition to the Si-based active material, other general negative electrode active materials used in the field of lithium ion batteries may be used in combination. Other negative electrode active materials include graphite, hard carbon, alloy-based negative electrodes, and Li4Ti5O 12 (LTO), a composite of an alloy-based negative electrode and another material, etc. The other negative electrode active materials may be used alone or in combination of two or more. As the negative electrode active material, it is preferable to use a combination of a Si-based active material and graphite. While the Si-based active material has a large expansion and contraction rate during lithiation and delithiation, the use of carbon in combination reduces the volume change. In addition, since graphite itself can act as a conductive path, the addition of graphite tends to further improve the cycle characteristics of the battery.

[0067] The proportion of the Si-based active material in the entire negative electrode active material is not particularly limited and can be adjusted appropriately depending on the type of Si-based active material, the type of active material used in combination, the intended use, etc. For example, it is preferably 1% by mass to 50% by mass, more preferably 2% by mass to 25% by mass, and even more preferably 3% by mass to 15% by mass.

[0068] The content of the negative electrode active material in the negative electrode mixture slurry can be adjusted appropriately depending on the application, and is, for example, preferably 75% by mass to 99.9% by mass, more preferably 80% by mass to 98% by mass, and even more preferably 90% by mass to 97% by mass, relative to the total solid content.

[0069] The viscosity of the negative electrode mixture slurry is preferably adjusted appropriately depending on the application, etc., and is, for example, preferably 100 mPa·s to 1700 mPa·s, more preferably 500 mPa·s to 1600 mPa·s, and even more preferably 900 mPa·s to 1500 mPa·s.

[0070] The method for producing the negative electrode mixture slurry is not particularly limited, and methods generally known to those skilled in the art can be used. For example, the components can be weighed, a solvent added, and mixed to prepare the negative electrode mixture slurry. In the method for producing the negative electrode mixture slurry, the proportions of SWCNTs and fibrous carbon are adjusted to obtain the negative electrode mixture slurry of the present disclosure. The order of mixing is not particularly limited, but it is preferable to first add a solvent to the SWCNTs and fibrous carbon to form a dispersion, thereby obtaining a conductive additive dispersion, and then add the remaining components. The method for producing the conductive additive dispersion is as described above.

[0071] <Negative electrode mixture layer> The negative electrode mixture layer of the present disclosure is a negative electrode mixture layer containing the conductive additive of the present disclosure and a negative electrode active material, and the proportion of single-walled carbon nanotubes in the entire negative electrode mixture layer is more than 0.01 mass% and less than 0.1 mass%.

[0072] If the proportion of SWCNTs in the entire negative electrode mixture layer is less than 0.1 mass%, the cost of manufacturing the negative electrode can be reduced and the peel strength from the current collector can be increased. From this perspective, the proportion of SWCNTs in the entire negative electrode mixture layer is preferably 0.07 mass% or less, and more preferably 0.04 mass% or less.

[0073] When the proportion of SWCNTs in the entire negative electrode mixture layer is 0.01% by mass or more, sufficient conductivity can be imparted to the negative electrode, and cycle characteristics tend to be further improved. From this viewpoint, the amount of SWCNTs added is preferably 0.02% by mass or more, more preferably 0.04% by mass or more, and even more preferably 0.05% by mass or more.

[0074] The details of the conductive additive and the negative electrode active material are as described above. Whether or not the SWCNTs contained in the negative electrode mixture layer of the electrode form bundles can be determined by observing the SWCNT portion near the surface of the negative electrode mixture layer arranged on the surface of the electrode using a TEM, or by dissolving the negative electrode mixture layer by dissolving the binder, etc., of the negative electrode mixture layer using a solvent, etc., and then observing the result using a TEM to determine whether or not the SWCNTs form bundles. Another method involves decomposing the surface region of the electrode or the negative electrode mixture layer using a solvent, etc., and extracting the SWCNTs using appropriate separation and aggregation procedures such as centrifugation, and then subjecting the SWCNTs to Raman spectroscopy to determine whether or not the SWCNTs form bundles based on the presence or absence of a radial breathing mode (RBM) in the resulting Raman spectrum.

[0075] The average length of the SWCNTs, the average length of the SWCNT bundles, and the average length of the fibrous carbon contained in the negative electrode mixture layer are determined by dissolving the binder, etc., with a solvent, etc. to decompose the negative electrode mixture layer, dispersing it, observing it with a TEM, and then determining the average length using the method described above. If measurement is possible with an SEM, it may also be performed with an SEM. Average particle size D of the Si-based active material contained in the negative electrode mixture layer 50 The negative electrode mixture layer is decomposed by dissolving the binder etc. with a solvent etc., and the dispersion treatment is observed with an SEM. An image of the Si-based active material is extracted from the SEM image, and the circle equivalent diameter of the Si-based active material is calculated. This circle is defined as the projected area of ​​a sphere, and D is calculated from the sphere volume. 50 The calculation is performed using 30 or more extracted images. The shape of the SEM image is used to distinguish the Si-based active material, but secondary electron images and EDS mapping images are also used as necessary.

[0076] In addition, the diameters of SWCNTs, their bundles, and fibrous carbon can be measured by processing the anode into thin flake samples using FIB (Focused Ion Beam) and observing them with a TEM. By measuring 30 samples and averaging the results, the average diameter of each can be calculated. When SWCNT bundles and fibrous carbon can be clearly distinguished from each other based on the appearance, such as the stiffness of the fibers, and their thickness, the electrode surface and cross section can be observed using an SEM, and the diameters of each can be measured multiple times and averaged to determine the average diameter of each.

[0077] In the negative electrode mixture layer, the SWCNTs (including those in the form of bundles) and fibrous carbon are preferably arranged as follows. (1) At least some of the SWCNTs contact the surface of the negative electrode active material so as to bridge the negative electrode active material. (2) SWCNTs cross the fiber axis of at least some of the carbon fibers multiple times. (3) At least some of the SWCNTs are in contact with the negative electrode active material and the fibrous carbon so as to bridge them. When the negative electrode mixture layer is observed with an SEM at a magnification of 30,000 times to 50,000 times, and 100 fields of view are observed by shifting the fields of view horizontally or vertically by 100 μm from a certain measurement field of view, it is more preferable that the above states (1), (2), and (3) are observed in 10 or more fields of view, and even more preferable that they are observed in 20 or more fields of view.

[0078] The silicon content in the negative electrode mixture layer is preferably 3% by mass or more. With such a value, the negative electrode tends to have a large capacity. From this viewpoint, the silicon content in the negative electrode mixture layer is more preferably 5% by mass or more, and further preferably 10% by mass or more.

[0079] The silicon content in the negative electrode mixture layer is preferably 50% by mass or less. With such a value, the battery tends to have excellent cycle characteristics. From this viewpoint, the silicon content in the negative electrode mixture layer is more preferably 40% by mass or less, further preferably 30% by mass or less, and particularly preferably 20% by mass or less.

[0080] The silicon content in the negative electrode mixture layer can be determined, for example, by decomposing the negative electrode mixture layer with acid, dissolving the residue in an alkali to prepare a solution, and quantifying the content by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0081] The method for producing the negative electrode mixture layer is not particularly limited, and any method generally known to those skilled in the art can be used, such as a method of applying a negative electrode mixture slurry onto a current collector and drying it.

[0082] The method for producing the negative electrode mixture slurry is as described above. In the method for producing the negative electrode mixture slurry, the order of mixing the components is not particularly limited, but it is preferable to first add a solvent to the SWCNTs and fibrous carbon to form a dispersion, obtain a conductive additive dispersion, and then add the remaining components. By doing so, the above states (1), (2), and (3) can be easily obtained.

[0083] <Negative electrode> The negative electrode of the present disclosure includes a current collector and the negative electrode mixture layer of the present disclosure provided on the current collector. The current collector is not particularly limited, and a material that has electronic conductivity and generally does not form an alloy with lithium is selected. Examples of the current collector include metal foils such as copper foil and nickel foil, and mesh-shaped copper and nickel.

[0084] The negative electrode obtained by forming a negative electrode mixture layer on a current collector using the above-described method for producing a negative electrode mixture layer is pressed by a roll press, a uniaxial press, or the like to adjust the electrode density to a desired value.

[0085] From the viewpoint of increasing the energy density of the battery and allowing the electrolyte to penetrate the electrodes well, the electrode density is set to 1.1 g / cm 3 ~1.9g / cm 3 and preferably 1.2 g / cm 3 ~1.8g / cm 3 More preferably, it is 1.3 g / cm 3 ~1.7g / cm 3 It is more preferable that:

[0086] The peel strength of the negative electrode is preferably 6.3 mN / mm or more, more preferably 6.5 mN / mm or more, and even more preferably 6.7 mN / mm or more. The peel strength is measured in accordance with the method described in the examples.

[0087] <Lithium-ion battery> The lithium ion battery of the present disclosure includes the negative electrode of the present disclosure and a positive electrode, and may include components known in the art, such as an electrolyte and a separator. For the positive electrode, electrolyte, separator, etc., materials, compositions, etc. known in the art can be applied. The lithium ion battery can be manufactured by any method known in the art.

[0088] The capacity retention rate at the 33rd cycle relative to the capacity at the first cycle (capacity retention rate at the 33rd cycle) is preferably 93% or more, more preferably 94% or more, and even more preferably 95% or more. The capacity retention rate at the 33rd cycle was measured in accordance with the method described in the Examples. [Example]

[0089] The contents of the present disclosure will be specifically explained below using examples, but the present invention is not limited to these examples.

[0090] (Measuring the average diameter of SWCNT bundles, MWCNTs, and fibrous carbon) The negative electrode was cut into a size of 10 mm x 10 mm and processed by FIB into a thin sample of 10 μm x 10 μm x 0.05 μm (Helios5UX, Thermo Fisher Scientific). This was placed on a sample stage and observed by TEM. This confirmed whether SWCNTs formed bundles in the electrode and whether fibrous carbon was present. After observing a certain field of view at a magnification that allowed the diameter of the SWCNT bundle or the diameter of the fibrous carbon to be observed, an image was taken with the field shifted 100 nm to the right, and this was repeated. After this, at an appropriate point, an image was taken with the field shifted 100 nm downward, and then another image was taken with the field shifted 100 nm to the left. This procedure was repeated until 30 fibers each were photographed for the SWCNT bundle and the fibrous carbon. The diameter of the SWCNT bundle and the carbon fiber was measured at the midpoint of the fiber length using a TEM photograph and a ruler. The diameters of 30 fibers were averaged to determine the average diameter of the SWCNT and the carbon fiber, respectively.

[0091] (Average length of SWCNT bundles, MWCNTs and fibrous carbon) A small amount of the conductive additive dispersion liquid prepared below was taken and diluted 10 times with water while stirring to prepare a diluted solution. The diluted solution was dropped onto a substrate for electron microscope observation, dried to remove moisture, and then observed with an SEM. 30 lengths were measured for each sample, and the average value was calculated. It has been confirmed that the average lengths of the SWCNT bundles, MWCNTs, and fibrous carbon in the negative electrode active material layer are similar to the average lengths of the SWCNT bundles, MWCNTs, and fibrous carbon collected from the conductive additive dispersion and measured.

[0092] Example 1 [Preparation of Mixed Negative Electrode Active Material] Carbon-coated SiO as the negative electrode active material x (x=1, average particle size 5μm, silicon content: 66.1% by mass, oxygen content: 30.6% by mass, carbon content: 3.3% by mass) and graphite (average particle size 20μm, specific surface area 3m 2 The specific capacities of these capacitors were determined in advance by coin cell tests, and the SiO x The capacity of graphite was 1600mAh / g, and that of graphite was 360mAh / g. x The mixture was mixed in a mass ratio of 11.3:88.7, and a mixed negative electrode active material having a specific capacity of 500 mAh / g was prepared, and 96.47 parts by mass of the mixed negative electrode active material was prepared.

[0093] [Preparation of Conductive Aid Dispersion] A 2.5% by mass aqueous solution of carboxymethyl cellulose (CMC) was prepared in advance, and 1.5 parts by mass of CMC solids and 0.03 parts by mass of SWCNT1 (average fiber diameter: 2 nm, average fiber length: 8 μm, average bundle diameter: 30 nm, average bundle length: 10 μm) were mixed and stirred for 30 minutes using a homogenizer at a rotation speed of 4500 rpm. After stirring, fibrous carbon (product name "VGCF-H", manufactured by Resonac Corporation, average diameter: 150 nm, average fiber length: 6 μm, BET specific surface area: 15 m) was added to the solution. 2 / g, average spacing d 002 0.5 parts by mass of PEG-400 (0.339 nm) was mixed, and purified water was added to adjust the solid content concentration in the dispersion to 2.0% by mass. The prepared liquid was stirred with a homogenizer at a rotation speed of 4500 rpm for 30 minutes to obtain a conductive additive dispersion.

[0094] [Preparation of negative electrode mixture slurry] The conductive additive dispersion was added to 96.47 parts by mass of the mixed negative electrode active material so that the solid content was 2.03 parts by mass, and the mixture was kneaded using a rotation-revolution mixer (Thinky Mixer ARE-310, manufactured by Thinky Corporation). Next, a 40% by mass aqueous dispersion of styrene butadiene rubber (SBR) was added to this solution so that the solid content was 1.5 parts by mass, and the mixture was mixed using the rotation-revolution mixer to prepare a negative electrode mixture slurry.

[0095] A cone plate (model number: CP25-2) was attached to a rheometer (model number: MCR301, manufactured by Anton Paar) as a measuring jig, and the viscosity of the negative electrode mixture slurry was measured at 25 °C. The shear rate was set to 60 s -1 The viscosity was measured 1 minute after the start of measurement and the results are shown in Table 1.

[0096] [Preparation of negative electrode] The negative electrode mixture slurry was applied to a copper foil having a thickness of 20 μm using a doctor blade (gap: 150 μm), and the resultant was dried in a hot air dryer at 70°C for 10 hours, and then further dried under reduced pressure at 110°C for 10 hours to obtain a negative electrode.

[0097] [Peel test] The resulting negative electrode was cut into a 3 cm x 10 cm strip. A 2.5 cm x 5 cm double-sided tape (model G9000, manufactured by Dexerials Corporation) was attached to a stainless steel plate, and the negative electrode strip was attached so that the negative electrode mixture layer was in contact with the double-sided tape and covered the entire tape. The copper foil side of the negative electrode was then attached to the sample stage of a universal testing machine (model STA-1150, manufactured by A&D Corporation). The stainless steel plate was pulled at a rate of 100 mm / min so that the peel angle was 180 degrees, and the magnitude of the force was measured. The integrated average strength (mN) over the measurement section from 30 mm to 60 mm was calculated, and then divided by the peel width of 2.5 cm to calculate the peel strength in mN / mm. The results are shown in Table 1.

[0098] When the negative electrode mixture layer was observed with an SEM in 100 visual fields using the above method, the above states (1), (2) and (3) were observed in 10 or more visual fields.

[0099] [Coin cell fabrication] The obtained negative electrode was punched out to a diameter of 13 mm and pressure-molded using a uniaxial press to obtain an electrode density of 1.6 g / cm. 3 The electrode was adjusted to the following. In a glove box under a dry argon atmosphere (dew point: -86°C), a coin cell was assembled using the punched-out negative electrode as the sample electrode, a 0.75 mm thick lithium foil punched to 16 mmφ as the counter electrode, and a single-layer polyolefin microporous membrane as the separator. In this cell, charge / discharge tests were performed using the lithium foil counter electrode as the negative electrode and the above sample electrode as the positive electrode. Generally, lithium foil is used as the counter electrode for negative electrode evaluation half cells. The electrolyte solution used was a solution prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2, adding 1 mass % vinylene carbonate (VC) and 10 mass % fluoroethylene carbonate (FEC), and further dissolving the electrolyte LiPF6 to a concentration of 1 mol / L.

[0100] [Charge-discharge cycle test] A charge-discharge cycle test was performed using the coin cell. Charging was first performed in constant current (CC) mode equivalent to 0.05 C until the cell voltage reached 0.005 V, and then in constant voltage (CV) mode until the current decayed to 0.01 C. The subsequent discharge was performed at a constant current equivalent to 0.05 C until the cell voltage reached 1.5 V. Three charge-discharge cycles were performed using the above protocol. Here, "current equivalent to 0.05 C" refers to the magnitude of the current that will discharge the capacity of the coin cell calculated from the amount of active material charged and the theoretical specific capacity over 20 hours.

[0101] Next, charging was first performed in constant current (CC) mode equivalent to 0.2 C until the cell voltage reached 0.005 V, and then in constant voltage (CV) mode until the current decayed to 0.05 C, followed by discharging at a constant current equivalent to 0.2 C until the cell voltage reached 1.5 V. 30 charge / discharge cycles were performed using the above protocol, for a total of 33 charge / discharge cycle tests.

[0102] The discharge capacity at the first cycle was defined as Q1, and the discharge capacity at the 33rd cycle was defined as Q33. The "capacity retention rate at the 33rd cycle" was calculated using the following formula and used as an index of cycle characteristics. The results are shown in Table 1. Capacity retention rate at 33rd cycle (%) = 100 × (Q33) / (Q1)

[0103] (Examples 2 to 9, Comparative Examples 1 to 7) A negative electrode mixture slurry, a negative electrode mixture layer, and a coin cell were obtained in the same manner as in Example 1, except that the physical properties or the amounts added of the negative electrode active material, SWCNT, MWCNT, CB, fibrous carbon, CMC, and SBR were changed as shown in Table 1, and various physical properties and battery characteristics were evaluated. The CB used was C-NERGY SUPER C 45 (product name: Imerys Graphite & Carbon). SWCNTs different from SWCNT1 were SWCNT2, which had an average fiber diameter of 2 nm, an average fiber length of 5 μm, an average bundle length of 7 μm, and an average bundle diameter of 30 nm, and SWCNT3, which had an average fiber diameter of 2 nm, an average fiber length of 3 μm, an average bundle length of 5 μm, and an average bundle diameter of 30 nm. In addition, in all of the Examples and Comparative Examples, the CMC content and SBR content in the negative electrode mixture layer were each 1.5 mass %. The results are shown in Table 1.

[0104] [Table 1]

[0105] It can be seen that Comparative Example 1, in which only SWCNT was added as the conductive additive, had excellent cycle characteristics but high slurry viscosity. It can be seen that comparative examples 2 and 4, which use a combination of SWCNT and CB as the conductive additive and do not contain fibrous carbon, have poor peel strength. In particular, comparative example 4, in which CB accounts for most of the conductive additive, also has poor cycle characteristics. In Comparative Example 3, the proportion of SWCNTs in the entire conductive additive was 2.0 mass %, and the content of SWCNTs in the negative electrode mixture layer was 0.01 mass %, which is too small an amount of SWCNTs, resulting in poor cycle characteristics. In Comparative Examples 5, 6 and 7, MWCNT was used instead of SWCNT and the amount added was varied, but the peel strength and cycle characteristics were low. It is clear that SWCNT is a good material to combine with fibrous carbon.

Claims

1. A conductive additive containing single-walled carbon nanotubes and fibrous carbon, The proportion of fibrous carbon in the entire conductive additive is 70 mass% or more, The conductive additive contains single-walled carbon nanotubes in an amount of 3.0 mass % or more of the entire conductive additive.

2. The conductive additive according to claim 1 , wherein the fibrous carbon has an average diameter of 80 nm or more.

3. The conductive additive according to claim 1 , wherein the bundles of single-walled carbon nanotubes have an average diameter of 90 nm or less.

4. The average length (L ５０ ) to the average length (L ｂ ) ratio (L ｂ / L ５０ 2. The conductive additive according to claim 1, wherein the value of (a) is 0.3 or more.

5. The conductive aid according to claim 1 , further comprising carbon black.

6. A conductive additive dispersion comprising the conductive additive according to any one of claims 1 to 5, a dispersant, and a solvent.

7. 6. A negative electrode mixture slurry comprising the conductive additive according to claim 1, a dispersant, a solvent, and a negative electrode active material.

8. The negative electrode active material includes a Si-based active material, and the Si-based active material is Si, SiO ｘ 8. The negative electrode mixture slurry according to claim 7, comprising at least one selected from the group consisting of: (x is greater than 0 and not greater than 1.5); and Si—C composites.

9. The average particle diameter D of the Si-based active material ５０ The average length L of the fibrous carbon ５０ The ratio (L ５０ / D ５０ 9. The negative electrode mixture slurry according to claim 8, wherein the ratio of the number of ions to the number of carbon atoms is less than 2.

10. The negative electrode mixture slurry according to claim 8 , wherein the negative electrode active material further comprises graphite.

11. The negative electrode mixture slurry according to claim 8, wherein the silicon content of the Si-based active material is 20% by mass to 80% by mass.

12. The negative electrode mixture slurry according to claim 8, wherein the oxygen content of the Si-based active material is 0.1% by mass to 70% by mass.

13. A negative electrode mixture layer containing the conductive additive according to any one of claims 1 to 5 and a negative electrode active material, The negative electrode mixture layer has a ratio of the single-walled carbon nanotubes that is more than 0.01% by mass and less than 0.1% by mass of the entire negative electrode mixture layer.

14. The negative electrode active material includes a Si-based active material, and the Si-based active material is Si, SiO ｘ 14. The negative electrode mixture layer according to claim 13, comprising at least one selected from the group consisting of: (x is greater than 0 and 1.5 or less); and a Si—C composite.

15. The average particle diameter D of the Si-based active material ５０ Average length L of fibrous carbon ５０ The ratio (L ５０ / D ５０ 15. The negative electrode mixture layer according to claim 14, wherein ) is less than 2.

16. The negative electrode mixture layer according to claim 14, wherein the silicon content is 3% by mass to 50% by mass.

17. The negative electrode mixture layer according to claim 13, wherein the single-walled carbon nanotubes and the fibrous carbon are arranged so as to satisfy the following (1) to (3): (1) At least some of the single-walled carbon nanotubes contact the surface of the negative electrode active material so as to bridge the negative electrode active material. (2) The single-walled carbon nanotubes cross the fiber axis of at least a part of the fibrous carbon a plurality of times. (3) At least some of the single-walled carbon nanotubes are in contact with the negative electrode active material and the fibrous carbon so as to bridge both of them.

18. A negative electrode comprising: a current collector; and the negative electrode mixture layer according to claim 13 provided on the current collector.

19. A lithium ion battery comprising the negative electrode of claim 18 and a positive electrode.

Images