Conductivity aid, conductivity aid dispersion, negative electrode mixture slurry, negative electrode mixture layer, negative electrode, and lithium ion battery

Abstract

A conductivity aid according to the present invention includes single-walled carbon nanotubes and fibrous carbon, the percentage of the entire conductivity aid that is the fibrous carbon being at least 70 mass%, and the percentage of the entire conductivity aid that is the single-walled carbon nanotubes being at least 3.0 mass%.

Description

Conductive additive, conductive additive dispersion, negative electrode mixture slurry, negative electrode mixture layer, negative electrode, and lithium ion battery

[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.

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

[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 to contain carbon nanotubes together with a larger amount of active material, thereby enabling the production of an electrode for a lithium-ion battery with improved battery performance.

[0004] Patent No. 6857443

[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. From this perspective, a method using single-walled carbon nanotubes (hereinafter also referred to as SWCNTs) as a conductive additive is commonly known. However, increasing the amount of SWCNTs added is currently undesirable because it increases the viscosity of the electrode mixture used for electrode coating. 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 performance and further increase the 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.

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

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

[0009] <7> A negative electrode mixture slurry containing the conductive additive according to any one of <1> to <5>, a dispersant, a solvent, and a negative electrode active material. <8> The negative electrode active material contains a Si-based active material, and the Si-based active material contains Si, SiO ｘ <9> The negative electrode mixture slurry according to <7>, containing at least one selected from the group consisting of an Si-based active material (where x is greater than 0 and 1.5 or less), and an Si—C composite. ５０ The average length L of the fibrous carbon ５０ The ratio (L ５０ / D ５０ ) is less than 2. <10> The negative electrode mixture slurry according to <8>, wherein the negative electrode active material further contains graphite. <11> The negative electrode mixture slurry according to any one of <8> to <10>, 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 any one of <8> to <11>, wherein the oxygen content of the Si-based active material is 0.1% by mass to 70% by mass.

[0010] <13> A negative electrode mixture layer containing the conductive additive according to any one of <1> to <5> and a negative electrode active material, wherein the ratio of the single-walled carbon nanotubes to the entire negative electrode mixture layer is more than 0.01% by mass and less than 0.1% by mass. <14> The negative electrode active material contains a Si-based active material, and the Si-based active material is a material containing Si, SiO ｘ (x is greater than 0 and not greater than 1.5), and a Si—C composite. ５０ Average length L of fibrous carbon ５０ The ratio (L ５０ / D ５０) is less than 2. <16> The negative electrode mixture layer according to <11>, wherein the silicon content is 3% by mass to 50% by mass. <17> The negative electrode mixture layer according to any one of <13> to <16>, 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 between themselves. (2) The single-walled carbon nanotubes cross the fiber axes of at least some of the fibrous carbons a plurality of times. (3) At least some of the single-walled carbon nanotubes contact the negative electrode active material and the fibrous carbon so as to bridge the negative electrode active material between themselves.

[0011] <18> A negative electrode having a current collector and the negative electrode mixture layer according to any one of <13> to <17> provided on the current collector. <19> A lithium ion battery having the negative electrode according to <18> and a positive electrode.

[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.

[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 numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present 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 corresponding substances. 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, each component may contain multiple types of particles. 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 two or more multi-layered graphene sheet layers in addition to nanotubes having a single graphene sheet layer, with a proportion of nanotubes being within 10%. In the present disclosure, "fibrous carbon" refers to carbon fibers having multiple graphene sheet layers and having 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 = 0.339 nm, each typical value).

[0016] <Conductive Aid> The conductive aid of the present disclosure contains single-walled carbon nanotubes and fibrous carbon, and the proportion of fibrous carbon in the entire conductive aid is 70 mass% or more, and the proportion of single-walled carbon nanotubes in the entire conductive aid is 3.0 mass% or more. A conductive aid 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 from the current collector when a negative electrode mixture layer and a lithium ion battery are fabricated. 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 SWCNT are used together, most of the SWCNT is entangled in the CB portion, making it almost impossible for the SWCNT to bridge the CB portions, and thus making it impossible to effectively form a conductive path.

[0018] In contrast, when fibrous carbon and SWCNT are used in combination, the SWCNTs are prevented from being excessively unevenly distributed on the fibrous carbon due to the low specific surface area of ​​the fibrous carbon, and the SWCNTs can bridge the gap between the fibrous carbons, effectively forming a conductive path. In particular, since the proportion of fibrous carbon in the entire conductive additive is 70 mass% or more, the SWCNT content is at most 30 mass%, and the amount of SWCNT used is kept low. This is achieved by combining fibrous carbon with SWCNT. Furthermore, since the proportion of SWCNT in the entire conductive additive is 3.0 mass% or more, the SWCNTs can sufficiently 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, in the negative electrode mixture layer, which is thought to improve the peel strength from the current collector.The effective formation of conductive paths and the improved peel strength from the current collector are thought to also improve the cycle characteristics of lithium-ion batteries.

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

[0020] From the viewpoint of bridging between fibrous carbon fibers 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 a 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] Due to their thinness, SWCNTs typically form bundles called "bundles" due to the strong van der Waals forces acting between the individual fibers. The average diameter of the bundles varies depending on the dispersant, dispersion solvent, dispersion process, etc. used when preparing the negative electrode mixture layer, but is preferably 90 nm or less. Since thinner and longer fibers can be imparted with smaller amounts of additives, a relatively small bundle diameter is advantageous from the standpoint of electrode conductivity. From this perspective, the average bundle diameter is more preferably 50 nm or less, and even more preferably 40 nm or less. Furthermore, from the standpoint 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 the bundles 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 a portion 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 the SWCNT bundles is determined by first identifying the SWCNT bundles whose both ends are visible using a TEM, then increasing the magnification and tracing the length of each bundle. This procedure is performed for 30 bundles, and the average value is calculated. If measurement is possible using an SEM, this may also be used.

[0026] From the viewpoint of effectively forming a conductive path, the proportion of SWCNT 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-shaped carbon] In the conductive additive of the present disclosure, the proportion of fibrous carbon in the entire conductive additive is 70% by mass or more, preferably 87% by mass or more, more preferably 90% by mass or more, and even more preferably 93% by 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 the fibrous carbon in a solvent, scooping up the fibrous carbon with a microgrid to prepare a sample for observation, observing the sample with a transmission electron microscope (TEM), measuring the diameter of 30 pieces in a portion excluding the regions near both ends in the length direction, and calculating the average value.

[0033] The average length of the fibrous carbon is preferably 1 μm or more. Such an average length can reduce the resistance of the battery. 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. Such an average length further reduces entanglement, thereby reducing the resistance of the battery. From this viewpoint, the average length of the fibrous carbon is more preferably 15 μm or less, even more 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 identifying fibrous carbon whose both ends are visible by TEM, and then increasing the magnification to measure the length while tracing each fibrous carbon. This operation is performed for 30 pieces, and the average value is calculated. When measurement is possible using SEM, it may be performed using SEM.

[0035] The average length of the fibrous carbon (L５０ ) 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 that is in contact with the fibrous carbon but is not in contact with the fibrous carbon in one bundle increases, so that a conductive path that spans 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 ​​the fibrous carbon is 2 m ２ / g to 100m ２ / g, and 5m ２ / g~80m ２ / g, more preferably 10m ２ / g~60m ２ / g. 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, a conductive path is 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 more than the lower limit, the number of SWCNTs per unit mass increases, and therefore 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) planes 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 crystal 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 can be calculated using the Gakushin method from the diffraction peak corresponding to the carbon 002 plane that appears at a diffraction angle 2θ of approximately 24° to 27° in a diffraction profile obtained by irradiating a sample with X-rays (CuKα rays) and measuring the diffraction rays with a goniometer.

[0041] The fibrous carbon has a Raman scattering spectrum of 1341 cm －１ ~1349cm －１ The peak height of the band (I ｄ ) and 1570 cm －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] Raman spectroscopy 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: Wavelength of argon laser beam: 532 nm Wavenumber resolution: 2.56 cm －１ Measurement range: 1180 cm －１ ~1730cm －１ Peak Processing: Background Removal The "peak height" mentioned above is the height from the baseline after background removal to the peak apex.

[0043] [Other Conductive Fillers] The conductive additive of the present disclosure may contain conductive fillers other than SWCNT and fibrous carbon. Examples of other conductive fillers that may be used in combination include general multi-walled carbon nanotubes (MWCNT) and graphene. MWCNT refers to carbon fibers having 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 the other conductive additive. The proportion of CB in the entire conductive additive is preferably 10% by mass or less. Because CB tends to trap SWCNT, a content of 10% by mass or less allows SWCNT 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] The conductive additive dispersion of the present disclosure contains the conductive additive of the present disclosure, a dispersant, and a solvent. The conductive additive dispersion of the present disclosure uses the conductive additive of the present disclosure, and therefore can suppress an increase in viscosity when preparing a negative 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.

[0045] 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 assistant 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 additive 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. The organic solvent is not particularly limited, and examples include 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 assistant dispersion is applied to the negative electrode mixture slurry, it is preferable to use the same solvent in the conductive assistant as that used in the negative electrode mixture slurry.

[0049] The content of the solvent in the conductive additive dispersion can be adjusted appropriately depending on the application, and is, for example, preferably 75.0% by mass to 99.9% by mass, more preferably 87.0% by mass to 98.9% by mass, and even more preferably 91.0% by mass to 97.5% by 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 SWCNT and fibrous carbon are adjusted so as to obtain the conductive additive dispersion of the present disclosure. The order of mixing is not particularly limited, but it is preferable to mix the SWCNT, dispersant, and solvent first, and then add the fibrous carbon. Mixing in this order makes it easier for each component to disperse, thereby reducing agglomerates.

[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 produced, the peel strength to the current collector and cycle characteristics can be improved. Details of the conductive additive, 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. For example, it is 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% by mass to 0.5% by mass, more preferably 0.1% by mass to 0.3% by mass, and even more preferably 0.15% by mass to 0.25% by mass, relative to the total amount of solids.

[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 may be used in combination. Examples of thickeners include CMC. One thickener may be used alone, or two or more may be used in combination. CMC is also cited as an example of a dispersant, and may be included for dispersing purposes or for thickening purposes. The total content of the binder and thickener in the negative electrode mixture slurry is preferably 20% by mass or less, 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. Si-based active materials have the advantage of high specific capacity, but their volume changes significantly during charging and discharging, 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 commonly known material can be used, and it is preferable to contain 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, negative electrode active materials are lithiated and delithiated during charge and discharge. Therefore, Si-based active materials also include 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 embodiment), those in which silicon is impregnated into the pores of porous carbon (second embodiment), and those in which the surface of silicon or silicon oxide is coated with carbon (third embodiment). 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 change due to lithium absorption, and tends to result in 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 average particle diameter D of the Si-based active material is preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 4 μm or more. 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 a particle diameter distribution measured by a laser diffraction / scattering method. The volume-average particle diameter of the negative electrode material can be measured, for example, by a laser diffraction particle size distribution analyzer (e.g., SALD-3100J manufactured by 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. In addition, if the fibrous carbon is too long, it is difficult to increase the density of the electrode. For these reasons, it is preferable that the ratio is less than 2. In addition to the Si-based active material, even when other negative electrode active materials such as graphite are used in combination as the negative electrode active material, maintaining the conductive path for the Si-based active material, which has a large volume change accompanying charge and discharge, is effective in improving the cycle characteristics, so the ratio (L 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 When the length of the fibrous carbon is within the above range, the length of the fibrous carbon is sufficient relative to the size of the Si-based active material, and therefore a conductive path can be efficiently formed even if the Si-based active material is present nearby, which tends to result in good cycle characteristics.

[0066] As the negative electrode active material, in addition to the Si-based active material, other negative electrode active materials generally used in the field of lithium ion batteries may be used in combination. Examples of other negative electrode active materials include graphite, hard carbon, alloy-based negative electrodes, Li ４ Ti ５ O １２ Examples of the other negative electrode active materials include lithiated toric oxide (LTO), composites of alloy-based negative electrodes and other materials, etc. The other negative electrode active materials may be used alone or in combination of two or more. It is preferable to use a Si-based active material in combination with graphite as the negative electrode active material. While Si-based active materials have large expansion and contraction rates during lithiation and delithiation, the use of carbon in combination reduces the volume change. Furthermore, 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 appropriately adjusted depending on the type of Si-based active material, the type of active material used in combination, the application, etc., and is, for example, 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. For example, it is 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 amount of solids.

[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 constituent 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 SWCNT and fibrous carbon are adjusted to obtain the composition of 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 SWCNT and fibrous carbon to form a dispersion and obtain 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 viewpoint, 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 SWCNT 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 SWCNT 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 or the like in a solvent or the like and then observing the resultant negative electrode mixture layer using a TEM, and checking whether or not a layered fiber structure is present. Another method involves decomposing the surface region of the electrode or the negative electrode mixture layer using a solvent or the like, extracting the SWCNTs using an appropriate separation and aggregation procedure such as centrifugation, and 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 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 or the like with a solvent or the like to decompose the negative electrode mixture layer, dispersing the resultant, observing the dispersion with a TEM, and then determining the average length D of the Si-based active material contained in the negative electrode mixture layer using the above-mentioned method. If measurement is possible with an SEM, it may also be performed with an SEM. 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 or EDS mapping images are also used as necessary.

[0076] In addition, the negative electrode can be processed into a thin-film sample by FIB (Focused Ion Beam) processing, and the diameters of the SWCNTs, their bundles, and fibrous carbon can be measured by observing this with a TEM. Thirty such samples are measured and averaged to determine the average diameter of each. When SWCNT bundles and fibrous carbon can be clearly distinguished from each other based on the appearance, thickness, etc., of the fibers, the electrode surface and electrode cross section can be observed with an SEM, and multiple diameters of each can be measured and averaged to determine the average diameter of each.

[0077] In the negative electrode mixture layer, the SWCNTs (including those in bundles) and the 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 between themselves; (2) The SWCNTs cross the fiber axes of at least some of the fibrous carbons multiple times; and (3) At least some of the SWCNTs contact the negative electrode active material and the fibrous carbon so as to bridge the negative electrode active material between themselves. When the negative electrode mixture layer is observed with an SEM at a magnification of 30,000 to 50,000 times, and 100 visual fields are shifted horizontally or vertically by 100 μm from a certain measurement visual field, it is more preferable that the above states (1), (2), and (3) are each observed in 10 or more visual fields, and even more preferably in 20 or more visual fields.

[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 an acid, dissolving the residue in an alkali to prepare a solution, and quantifying the silicon 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, thereby obtaining a conductive additive dispersion, and then add the remaining components. By doing so, the above states (1), (2), and (3) can be more easily obtained.

[0083] <Negative electrode> The negative electrode of the present disclosure includes a current collector and a 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 ~1.9 g / cm ３ It is preferable that the density is 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 according to 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. The lithium-ion battery may be provided with components known in the art, such as an electrolyte and a separator. Materials, compositions, and the like known in the art may be applied to the positive electrode, electrolyte, separator, and the like. A method known in the art may be used to manufacture the lithium-ion battery.

[0088] The capacity retention rate at the 33rd cycle relative to the capacity at the 1st 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 is measured according to the method described in the Examples.

[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] (Measurement of the average diameter of SWCNT bundles, MWCNT, and fibrous carbon) The negative electrode was cut into a size of 10 mm x 10 mm and processed by FIB into a thin section sample of 10 μm x 10 μm x 0.05 μm ("Helios 5UX," manufactured by Thermo Fisher Scientific). This was placed on a sample stage and observed with a TEM. This confirmed the presence of SWCNT bundles and fibrous carbon in the electrode. After observing a certain field of view at a magnification at which the diameter of the SWCNT bundles or the diameter of the fibrous carbon could be observed, an image was taken with the field shifted 100 nm to the right. This was repeated, and then an image was taken with the field shifted 100 nm downward at an appropriate point, followed by another image with the field shifted 100 nm to the left. This procedure was repeated until 30 fibers were captured for each of the SWCNT bundles and fibrous carbon. The diameters of the SWCNT bundles and the carbon fibers were measured at the midpoint of their length using TEM photographs and a ruler. The diameters of 30 fibers were averaged to determine the average diameters of the SWCNTs and the carbon fibers, respectively.

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

[0092] Example 1 Preparation of Mixed Negative Electrode Active Material Carbon-coated SiO 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 were determined in advance by coin cell tests, and the SiO ｘThe value of the SiO 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. 96.47 parts by mass of the mixed negative electrode active material was prepared.

[0093] [Preparation of Conductive Aid Dispersion] A 2.5 mass% aqueous solution of carboxymethyl cellulose (CMC) was prepared in advance, and 1.5 parts by mass of CMC solid content 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 a conductive additive (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 solution 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 (Awatori Rentaro 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. －１ The viscosity was measured 1 minute after the start of measurement and the results are shown in Table 1.

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

[0097] [Peel Test] The obtained negative electrode was cut into a 3 cm x 10 cm strip. A 2.5 cm x 5 cm double-sided tape (model number G9000, manufactured by Dexerials Corporation) was attached to a stainless steel plate, and the strip-shaped negative electrode was attached so that the negative electrode mixture layer was in contact with the double-sided tape and the negative electrode mixture layer 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 number STA-1150, manufactured by A&D Co., Ltd.). 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) from the measurement section 30 mm to 60 mm was calculated, and the peel strength was calculated in units of mN / mm by dividing by the peel width of 2.5 cm. The results are shown in Table 1.

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

[0099] [Fabrication of Coin Cells] The obtained negative electrode was punched out to a diameter of 13 mm and pressure-molded using a uniaxial press to obtain a coin cell with an electrode density of 1.6 g / cm. ３The electrode was adjusted to a value of 0.75 mm. In a glove box under a dry argon atmosphere (dew point: -86°C), a coin cell was assembled using the punched 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, a charge-discharge test was performed using the lithium foil as the counter electrode and the sample electrode as the positive electrode. Generally, lithium foil is used as the counter electrode for negative electrode evaluation half cells. The electrolyte solution was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2 with 1 mass% vinylene carbonate (VC) and 10 mass% fluoroethylene carbonate (FEC), and the electrolyte LiPF ６ was dissolved to a concentration of 1 mol / L.

[0100] [Charge-Discharge Cycle Test] A charge-discharge cycle test was conducted using the prepared coin cells. Charging was first performed in a constant current (CC) mode equivalent to 0.05 C until the cell voltage reached 0.005 V, and then in a constant voltage (CV) mode until the current decayed to 0.01 C. Subsequent discharging 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, "a current equivalent to 0.05 C" refers to the magnitude of the current required to 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 a constant current (CC) mode equivalent to 0.2 C until the cell voltage reached 0.005 V, and then in a constant voltage (CV) mode until the current attenuated 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] When the discharge capacity at the first cycle was designated as Q1 and the discharge capacity at the 33rd cycle 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 the 33rd cycle (%) = 100 × (Q33) / (Q1)

[0103] Examples 2 to 9, Comparative Examples 1 to 7 Anode mixture slurries, anode mixture layers, and coin cells were obtained in the same manner as in Example 1, except that the physical properties or amounts of the anode active material, SWCNT, MWCNT, CB, fibrous carbon, CMC, and SBR were changed as shown in Table 1. Various physical properties and battery characteristics were evaluated. The CB used was C-NERGY SUPER C 45 (manufactured by 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 the SBR content in the negative electrode mixture layer were each 1.5 mass %. The results are shown in Table 1.

[0104]

[0105] Comparative Example 1, in which only SWCNT was added as the conductive additive, exhibited excellent cycle characteristics, but the slurry viscosity was high. Comparative Examples 2 and 4, in which SWCNT and CB were used in combination as the conductive additive and no fibrous carbon was added, exhibited poor peel strength. In particular, Comparative Example 4, in which CB accounted for most of the conductive additive, also exhibited poor cycle characteristics. Comparative Example 3 exhibited poor cycle characteristics because the proportion of SWCNT relative to the total conductive additive was 2.0% by mass and the SWCNT content in the negative electrode mixture layer was 0.01% by mass, which was too low. Comparative Examples 5, 6, and 7 used MWCNT instead of SWCNT, varying the amount added, but exhibited poor peel strength and cycle characteristics. It was found that SWCNT was a good choice for combining with fibrous carbon.

[0106] The disclosure of Japanese Patent Application No. 2024-030695 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A conductive additive comprising single-walled carbon nanotubes and fibrous carbon, wherein the proportion of fibrous carbon in the entire conductive additive is 70% by mass or more, and the proportion of single-walled carbon nanotubes in the entire conductive additive is 3.0% by mass or more.

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 average diameter of the bundles of single-walled carbon nanotubes is 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 additive 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. A negative electrode mixture slurry containing the conductive additive according to any one of claims 1 to 5, 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. Average particle size 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, wherein the proportion of the single-walled carbon nanotubes in the entire negative electrode mixture layer is more than 0.01% by mass and less than 0.1% by mass.

14. The negative electrode active material includes a Si-based active material, and the Si-based active material is a mixture of 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. Average particle size 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 between themselves; (2) The single-walled carbon nanotubes cross the fiber axes of at least some of the fibrous carbon multiple times; and (3) At least some of the single-walled carbon nanotubes contact the negative electrode active material and the fibrous carbon so as to bridge the negative electrode active material between themselves.

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.

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