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

Abstract

The conductive aid contains single-walled carbon nanotubes and fibrous carbon, the proportion of the fibrous carbon in the entire conductive aid is 70% or more by mass, and the proportion of the single-walled carbon nanotubes in the entire conductive aid described above is 3.0% or more by mass.

Description

Technical Field

[0001] This disclosure relates to conductive additives, conductive additive dispersions, negative electrode slurries, negative electrode slurries, negative electrode layers, negative electrodes, and lithium-ion batteries. 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 consoles, and portable power tools due to their advantages of small size, light weight, and high voltage. In recent years, against the backdrop of environmental issues, lithium-ion secondary batteries are also becoming increasingly popular in electric vehicles (EVs) that run solely on batteries and hybrid electric vehicles (HEVs) that combine gasoline engines and batteries.

[0003] For example, in Patent Document 1, a material composition for a conductive layer on a battery electrode is proposed, comprising a conductive additive, an electrode material, a dispersant, and a polymeric binder in a specific mass ratio. The conductive additive comprises a three-dimensional network structure of a carbonaceous material, which includes carbon nanotubes having a first minimum diameter and carbon nanotubes having a second maximum diameter larger than the first minimum diameter. Regarding the material composition described in Patent Document 1, it is explained that by adding a small amount of conductive filler and a small amount of binder, it is possible to include more active material while containing carbon nanotubes, thus enabling the fabrication of electrodes for lithium-ion batteries with improved battery performance.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6857443 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In lithium-ion batteries, Si-based active materials used as negative electrode active materials undergo significant volume changes during charge and discharge, making it difficult to improve cycle performance. From the perspective of efficiently utilizing Si-based active materials, it is desirable to form conductive pathways between active materials. From this perspective, methods using single-walled carbon nanotubes (hereinafter also referred to as SWCNTs) as conductive additives are generally known.

[0009] However, since this would increase the viscosity of the electrode mixture used for electrode coating, it is currently not desirable to increase the amount added.

[0010] In addition, when using negative electrode active materials other than Si-based active materials, it is also desirable to form conductive pathways between active materials to improve cycle characteristics and thereby increase the stripping strength relative to the current collector.

[0011] This disclosure was made in view of the above circumstances, and its object is to provide a conductive additive, a conductive additive dispersion, a negative electrode additive slurry, a negative electrode additive layer, a negative electrode, and a lithium-ion battery that can suppress the increase in viscosity during the preparation of electrode additive slurry and improve the peel strength and cycle characteristics relative to the current collector during the fabrication of negative electrode additive layer and lithium-ion battery.

[0012] Methods for solving problems

[0013] This disclosure includes the following methods.

[0014] <1> A conductive additive comprising single-walled carbon nanotubes and fibrous carbon,

[0015] The proportion of fibrous carbon in the above-mentioned conductive additives is more than 70% by mass.

[0016] The proportion of single-walled carbon nanotubes in the total conductive additives is more than 3.0% by mass.

[0017] <2> According to the conductive additive described in <1>, the average diameter of the fibrous carbon is 80 nm or more.

[0018] <3> According to the conductive additive described in <1> or <2>, the average diameter of the single-walled carbon nanotube bundle is less than 90 nm.

[0019] <4> According to the conductive additive described in <1>, the average length (L) of the single-walled carbon nanotube bundles mentioned above. b ) relative to the average length of the aforementioned fibrous carbon (L 50 The ratio of (L) b / L 50 The value is above 0.3.

[0020] <5> The conductive additive described in any of <1> to <3> also includes carbon black.

[0021] <6> A conductive additive dispersion comprising the conductive additive, dispersant and solvent described in any one of <1> to <5>.

[0022] <7> A negative electrode slurry containing any one of the conductive additives, dispersants, solvents and negative electrode active substances described in <1> to <5>.

[0023] <8> According to the negative electrode slurry described in <7>, the aforementioned negative electrode active material includes a Si-based active material, which comprises materials selected from Si and SiO2. x (x represents more than 0 and less than 1.5) and at least one of the Si-C complexes.

[0024] <9> According to the negative electrode slurry described in <8>, wherein the average length L of the aforementioned fibrous carbon is 50 Compared to the average particle size D of the above-mentioned Si-based active materials 50 The ratio (L) 50 / D 50 () Less than 2.

[0025] <10> According to the negative electrode slurry described in <8>, the aforementioned negative electrode active material also includes graphite.

[0026] <11> According to any one of <8> to <10>, the negative electrode slurry contains 20% to 80% by mass of silicon in the above-mentioned Si-based active material.

[0027] <12> According to any one of <8> to <11>, the negative electrode slurry contains an oxygen content of 0.1% to 70% by mass of the above-mentioned Si-based active material.

[0028] <13> A negative electrode mixture layer, comprising a conductive additive and a negative electrode active material as described in any one of <1> to <5>.

[0029] The proportion of the aforementioned single-walled carbon nanotubes in the overall negative electrode mixture layer exceeds 0.01% by mass and is less than 0.1% by mass.

[0030] <14> According to the negative electrode mixture layer described in <13>, the negative electrode active material includes a Si-based active material, and the Si-based active material includes materials selected from Si and SiO. x (x represents more than 0 and less than 1.5) and at least one of the Si-C complexes.

[0031] <15> According to the negative electrode mixture layer described in <14>, the average length L of the fibrous carbon is 50 The average particle size D of Si-based active materials 50 The ratio (L) 50 / D 50 () Less than 2.

[0032] <16> According to the negative electrode compound layer described in <11>, the silicon content is 3% to 50% by mass.

[0033] <17> According to any one of <13> to <16>, the negative electrode compound layer, wherein the above-mentioned single-walled carbon nanotubes and the above-mentioned fibrous carbon are configured in a manner that satisfies the following (1) to (3).

[0034] (1) At least a portion of the single-walled carbon nanotubes are in contact with the surface of the negative electrode active material in a manner that bridges the negative electrode active material with each other.

[0035] (2) The single-walled carbon nanotubes mentioned above traverse at least a portion of the fiber axis of the fibrous carbon multiple times.

[0036] (3) At least a portion of the above-mentioned single-walled carbon nanotubes are in contact with both the above-mentioned negative electrode active material and the above-mentioned fibrous carbon in a manner that bridges the above-mentioned negative electrode active material and the above-mentioned fibrous carbon.

[0037] <18> A negative electrode having a current collector and a negative electrode mixture layer described in any one of <13> to <17> disposed on the current collector.

[0038] <19> A lithium-ion battery having a positive electrode and a negative electrode as described in <18>.

[0039] Invention Effects

[0040] According to this disclosure, conductive additives, conductive additive dispersions, negative electrode additive slurries, negative electrode additive layers, negative electrodes, and lithium-ion batteries can be provided to suppress viscosity increase during the preparation of electrode additive slurries and to improve peel strength and cycle characteristics relative to current collectors during the fabrication of negative electrode additive layers and lithium-ion batteries. Detailed Implementation

[0041] The embodiments of this disclosure will now be described in detail. However, this disclosure is not limited to the embodiments described below. In the embodiments described below, the constituent elements (including element steps, etc.) are not essential unless specifically stated otherwise. The same applies to numerical values ​​and their ranges, which are not limiting to this disclosure.

[0042] In this disclosure, the range of values ​​represented by “~” includes the minimum and maximum values ​​recorded before and after “~”, respectively.

[0043] In the numerical ranges described in this disclosure in stages, the upper or lower limit value described in one numerical range may be replaced by the upper or lower limit value of other numerical ranges described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of the numerical range may be replaced by the values ​​shown in the embodiments.

[0044] In this disclosure, each component may also contain multiple corresponding substances. When multiple substances equivalent to each component are present in the composition, the content or percentage of each component, unless otherwise specified, refers to the total content or percentage of the multiple substances present in the composition.

[0045] This disclosure may also include multiple particles equivalent to each component. When multiple particles equivalent to each component are present in the composition, the particle size of each component, unless otherwise specified, refers to the value of a mixture of the multiple particles present in the composition.

[0046] In this disclosure, "single-walled carbon nanotube" (SWCNT) refers to a nanotube having a single layer of graphene sheets, or to a nanotube having, in addition to having a single layer of graphene sheets, up to 10% of which contains multiple layers of graphene sheets (two or more).

[0047] In this disclosure, "fibrous carbon" refers to carbon fibers having multiple layers of graphene sheets and an average diameter of 80 nm or more. Examples include "VGCF-H" (BET specific surface area = 15 m²) manufactured by Resonac Co., Ltd. 2 / g,d 002 =0.339nm, which are representative values) and so-called "vapor phase carbon fibers".

[0048] <Conductive additives>

[0049] The conductive additive disclosed herein comprises single-walled carbon nanotubes and fibrous carbon, with the fibrous carbon accounting for more than 70% by mass and the single-walled carbon nanotubes accounting for more than 3.0% by mass. This conductive additive composition can suppress the increase in viscosity during the preparation of electrode slurry and improve the peel strength and cycle characteristics relative to the current collector when fabricating the negative electrode slurry layer and lithium-ion batteries. The rationale is not yet clear, but is speculated as follows.

[0050] The graphene sheets of fibrous carbon are multilayered with an average diameter of over 80 nm, making them more rigid and linear compared to typical multi-walled carbon nanotubes. Due to this shape, the fibrous carbon has a smaller specific surface area compared to 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 wrapped around the CB portions, making it almost impossible to bridge the CB portions with SWCNTs, thus failing to effectively form conductive pathways.

[0051] In contrast, when fibrous carbon and SWCNTs are used in combination, the uneven distribution of SWCNTs within the fibrous carbon due to its low specific surface area can be suppressed. SWCNTs can effectively bridge the gaps between fibrous carbon particles, forming conductive pathways. Specifically, since the proportion of fibrous carbon in the overall conductive additive is 70% by mass or more, the maximum SWCNT content is 30% by mass, thus keeping the amount of SWCNT used low. This is achieved by combining fibrous carbon and SWCNTs. Furthermore, since the proportion of SWCNTs in the overall conductive additive is 3.0% by mass or more, sufficient bridging between fibrous carbon particles can be achieved using SWCNTs.

[0052] Furthermore, it is speculated that because SWCNTs are not excessively unevenly distributed within fibrous carbon, they are also entangled with binders and other components within the negative electrode binder layer, resulting in increased peel strength relative to the current collector. It is further speculated that the effective formation of conductive pathways and the increased peel strength relative to the current collector contribute to improved cycle characteristics of the lithium-ion battery.

[0053] [Single-walled carbon nanotubes (SWCNTs)]

[0054] There is no particular limitation on the diameter of SWCNTs, but the average diameter is usually less than 3.0 nm. The average diameter of SWCNTs is preferably greater than 0.4 nm.

[0055] The average diameter of SWCNTs was determined as follows: After dispersing SWCNTs in a solvent, SWCNTs were collected using a micromesh to prepare an observation sample. The sample was then observed using a transmission electron microscope (TEM). For 30 SWCNTs, the diameter of the portion along the length direction excluding the areas near the two ends was measured, and the average value was calculated to determine the average diameter of the SWCNTs.

[0056] From the viewpoint of utilizing SWCNTs to bridge fibrous carbon, the longer the SWCNT, the better. The average length of the SWCNT is preferably 1.1 μm or more, more preferably 4.0 μm or more, and even more preferably 6.0 μm or more.

[0057] Furthermore, from the viewpoint of suppressing the formation of filamentous aggregates and forming an effective conductive path, the average length of SWCNTs is preferably 21 μm or less, more preferably 16 μm or less, and even more preferably 11 μm or less.

[0058] To determine the average length of SWCNTs, after identifying SWCNTs visible at both ends using TEM, the magnification was increased, and the length of each SWCNT was measured while tracking it individually. This process was performed on 30 SWCNTs, and the average value was calculated to determine the average length of the SWCNTs.

[0059] SWCNTs typically exhibit strong van der Waals forces between individual fibers due to their fineness, forming bundles known as "tubes". The average diameter of these tubes varies depending on the dispersant, dispersion solvent, and dispersion process used in fabricating the negative electrode binder layer, and is preferably below 90 nm.

[0060] The finer and longer the tube bundle, the more conductivity can be imparted with a small amount of additive. Therefore, from the viewpoint of electrode conductivity, a sufficiently small tube bundle diameter is advantageous. From this viewpoint, the average diameter of the tube bundle is more preferably 50 nm or less, and even more preferably 40 nm or less. Furthermore, from the viewpoint of suppressing re-condensation, the average diameter of the tube bundle is preferably 1 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more.

[0061] The average diameter of the tube bundle was determined as follows: After dispersing the tube bundle in a solvent, the tube bundle was retrieved using a micromesh to prepare an observation sample. The sample was then observed using a transmission electron microscope (TEM). For 30 tube bundles, the diameter of the portion along the length direction, excluding the area near the two ends, was measured, and the average value was calculated.

[0062] The length of the SWCNT tube bundle is preferably 1 μm to 20 μm, more preferably 3 μm to 17 μm, and even more preferably 5 μm to 15 μm.

[0063] To determine the average length of the SWCNT bundles, after identifying the SWCNT bundles visible from both ends using TEM, the magnification was increased, and the lengths were measured while tracking each bundle individually. This process was performed on 30 bundles, and the average length of the SWCNT bundles was calculated. If SEM is available, it can also be used for measurement.

[0064] From the viewpoint of effectively forming conductive pathways, the proportion of SWCNT in the total conductive additive is 3.0% by mass or more, preferably 4.0% by mass or more, and more preferably 5.0% by mass or more.

[0065] From the viewpoint of suppressing the viscosity of the slurry when forming the negative electrode additive layer, the proportion of SWCNT in the total conductive additive is preferably 13% by mass or less, more preferably 12% by mass or less, further preferably 10% by mass or less, and most preferably 8% by mass or less.

[0066] [Fibrous carbon]

[0067] In the conductive additive disclosed herein, the proportion of fibrous carbon in the total 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.

[0068] The proportion of fibrous carbon in the total conductive additive is preferably 97% by mass or less. This proportion increases the electrode density. From this viewpoint, the proportion of fibrous carbon in the total conductive additive is more preferably 96% by mass or less, and even more preferably 95% by mass or less.

[0069] The average diameter of the fibrous carbon is preferably 80 nm or more. If the fibrous carbon is of such a fineness, the fibers are rigid, and the voids created by embedding the fibrous carbon between the active materials facilitate the penetration and retention of the electrolyte, thus tending to further reduce the battery resistance. From this perspective, the average diameter of the fibrous carbon is more preferably 100 nm or more, and even more preferably 120 nm or more.

[0070] The average diameter of the fibrous carbon is preferably 400 nm or less. This thickness allows for an increase in electrode density. From this perspective, the average diameter of the fibrous carbon is more preferably 300 nm or less, and even more preferably 250 nm or less.

[0071] The average diameter of the fibrous carbon was determined as follows: After dispersing the fibrous carbon in a solvent, the fibrous carbon was collected with a micromesh to prepare an observation sample. The sample was observed using a transmission electron microscope (TEM). For 30 fibrous carbons, the diameter of the portion along the length direction excluding the area near the two ends was measured, and the average value was calculated to determine the average diameter of the fibrous carbon.

[0072] The average length of the fibrous carbon is preferably 1 μm or more. This average length reduces the resistance of the battery. From this perspective, the average length of the fibrous carbon is more preferably 2 μm or more, and even more preferably 3 μm or more.

[0073] The average length of the fibrous carbon is preferably 20 μm or less. By using such an average length, the winding length is further reduced, thereby reducing the resistance of the battery. From this point of view, the average length of the fibrous carbon is more preferably 15 μm or less, more preferably 10 μm or less, particularly preferably 7 μm or less, and extremely preferably 5 μm or less.

[0074] To determine the average length of the fibrous carbon, after identifying fibrous carbon visible at both ends using TEM, the magnification is increased, and the length is measured while tracing each individual fibrous carbon. This process is repeated for 30 fibrous carbons, and the average length is calculated by taking the average value. If SEM is available, it can also be used for measurement.

[0075] The average length of the tube bundle of SWCNT (L) b ) relative to the average length of fibrous carbon (L 50 The ratio of (L) b / L 50The length ratio is preferably 0.3 or more, more preferably 0.8 or more, and even more preferably 1 or more. With such a length ratio, conductive pathways can be effectively formed between fibrous carbons by using SWCNTs to bridge them. As a result, when manufacturing the negative electrode binder layer and lithium-ion batteries, there is a tendency to further improve the peel strength and cycle characteristics relative to the current collector.

[0076] In addition, compared to (L) b / L 50 The length ratio is preferably 10 or less, more preferably 5 or less, further preferably 3 or less, and most preferably 2 or less. By having such a length ratio, the area in the bundle of tubes that is in contact with fibrous carbon but not with fibrous carbon increases, thus effectively forming a conductive path from fibrous carbon to fibrous carbon. As a result, when manufacturing the negative electrode binder layer and lithium-ion battery, there is a tendency to further improve the peel strength and cycle characteristics relative to the current collector.

[0077] The fibrous carbon is preferably hollow.

[0078] The preferred BET specific surface area of ​​fibrous carbon is 2m². 2 / g~100m 2 / g, more preferably 5m 2 / g~80m 2 / g, more preferably 10m 2 / g~60m 2 / g. When the BET specific surface area is below the upper limit mentioned above, it is possible to suppress the uneven existence of SWCNTs wrapped around fibrous carbon, effectively forming conductive pathways, and there is a tendency to further improve the peel strength and cycling characteristics relative to the current collector. When the BET specific surface area is above the lower limit mentioned above, the number of wires per unit mass increases, and therefore, there is a tendency to impart sufficient conductivity to the electrode.

[0079] The BET specific surface area of ​​fibrous carbon can be determined using the BET method from the adsorption isotherm obtained by measuring nitrogen adsorption at 77 K.

[0080] The average surface spacing d of the (002) plane of fibrous carbon based on X-ray diffraction 002 Preferably, it is 0.345 nm or less, more preferably 0.336 to 0.340 nm. The average surface spacing d 002 When the graphite crystal size is below 0.345 nm, it grows sufficiently, exhibiting excellent initial efficiency and energy density in the fabrication of lithium-ion secondary batteries. It should be noted that the average surface spacing d... 002 The value of 0.3354nm is the theoretical value for graphite crystals, and there is a trend that the closer the value is to this value, the greater the energy density.

[0081] Average surface spacing d 002 The following calculation can be performed: Irradiate the sample with X-rays (CuKα rays), and calculate the diffraction pattern obtained by measuring the diffraction lines using a goniometer, based on the diffraction peaks that appear near the diffraction angle 2θ = 24° to 27° corresponding to the carbon 002 plane using the vibration method.

[0082] Raman scattering spectrum of fibrous carbon at 1341 cm⁻¹ -1 ~1349cm -1 The peak height of the band (I) d ) and 1570cm -1 ~1578cm -1 The peak height of the band (I) g The ratio of (I) d / I g The preferred value is 0.1 to 2.0, and more preferably 0.1 to 0.5.

[0083] For Raman spectroscopy determination, a laser Raman spectrophotometer (e.g., model NRS-1000, Nippon Spectrophotometer Co., Ltd.) is used to irradiate an argon laser onto a sample plate positioned to ensure the sample is flat. The determination conditions are as follows.

[0084] The wavelength of the argon laser is 532nm.

[0085] Wavenumber resolution: 2.56cm -1

[0086] Measurement range: 1180cm -1 ~1730cm -1

[0087] Peak processing: removing background

[0088] It should be noted that the "peak height" mentioned above is the height from the baseline (excluding the background) to the peak.

[0089] [Other conductive fillers]

[0090] The conductive additives disclosed herein may include other conductive fillers besides SWCNTs and fibrous carbon. Examples of other conductive fillers used in combination include common multi-walled carbon nanotubes (MWCNTs) and graphene. MWCNTs are carbon fibers with multiple graphene sheets, referring to carbon fibers with an average diameter of less than 80 nm. Other conductive fillers may be used individually or in combination of two or more.

[0091] Among these, carbon black (CB) such as acetylene black and Ketjen black are preferred as other conductive additives. The proportion of CB in the total conductive additive is preferably 10% by mass or less. CB tends to capture SWCNTs; therefore, by keeping its content at 10% by mass or less, SWCNTs can more effectively form conductive pathways, and it also contributes to the increased conductivity of the active material surface brought about by CB, tending to further improve cycle performance. From this perspective, the proportion of CB in the total conductive additive is more preferably 5% by mass or less, and more preferably 3% by mass or less.

[0092] <Conductive Additive Dispersion>

[0093] The conductive additive dispersion disclosed herein comprises the conductive additive, dispersant, and solvent of this disclosure. Because the conductive additive dispersion of this disclosure uses the conductive additive of this disclosure, it can suppress the increase in viscosity during the preparation of the negative electrode slurry, and improve the peel strength and cycle characteristics relative to the current collector when fabricating the negative electrode layer and lithium-ion battery.

[0094] Details of the conductive additives are as described above.

[0095] The content of conductive additives in the conductive additive dispersion can be adjusted appropriately according to the application, for example, preferably 0.1% to 20% by mass, more preferably 1% to 10% by mass, and even more preferably 2% to 7% by mass.

[0096] As a dispersant, any substance that improves the dispersibility of conductive additives in a solvent is acceptable; there are no particular limitations. Examples include high molecular weight compounds such as carboxymethyl cellulose (CMC) and polyvinylpyrrolidone (PVP), as well as surfactants such as Triton X-100 and sodium cholate. A single dispersant can be used, or two or more can be used in combination.

[0097] The content of the dispersant relative to the total amount of the conductive additive dispersion is preferably 0.01% to 20% by mass.

[0098] The content of dispersant in the conductive additive dispersion can be adjusted appropriately according to the application, for example, preferably 0.01% to 5% by mass, more preferably 0.1% to 3% by mass, and even more preferably 0.5% to 2% by mass.

[0099] Examples of solvents include water and organic solvents. There are no particular limitations on organic solvents; examples include N-methyl-2-pyrrolidone (NMP), acetone, ethyl acetate, acetonitrile, tetrahydrofuran (THF), and dimethylformamide (DMF). A single solvent or a combination of two or more solvents can be used. When applying the conductive additive dispersion to a negative electrode slurry, it is preferable to use the same solvent in the conductive additive as in the negative electrode slurry.

[0100] The solvent content in the conductive additive dispersion can be adjusted appropriately according to the application, for example, preferably 75.0% to 99.9% by mass, more preferably 87.0% to 98.9% by mass, and even more preferably 91.0% to 97.5% by mass.

[0101] The method for manufacturing the conductive additive dispersion is not particularly limited, and methods commonly known to those skilled in the art can be used. For example, the constituent components can be weighed and mixed with a solvent to prepare the conductive additive dispersion. It should be noted that in the method for manufacturing the conductive additive dispersion, the ratio of SWCNT and fibrous carbon is adjusted to achieve the composition of the conductive additive dispersion disclosed herein.

[0102] There is no particular order to the mixing, but it is preferable to mix the SWCNT, dispersant, and solvent first, and then add the fibrous carbon. Mixing in this order allows for easy dispersion of each component, thus reducing agglomerates.

[0103] <Negative Electrode Mixture Slurry>

[0104] The negative electrode slurry disclosed herein comprises the conductive additives, dispersants, solvents, and negative electrode active materials disclosed herein. Because the negative electrode slurry of this disclosure uses the conductive additives disclosed herein, it can improve the peel strength and cycle characteristics relative to the current collector when fabricating the negative electrode layer and lithium-ion battery.

[0105] Details of the conductive additives, dispersants, and solvents are as described above.

[0106] The content of conductive additives in the negative electrode slurry can be adjusted appropriately according to the application. For example, it is preferably 0.1% to 1% by mass relative to the total amount of solid components, more preferably 0.2% to 0.8% by mass, and even more preferably 0.3% to 0.6% by mass.

[0107] The content of dispersant in the negative electrode mixture slurry can be adjusted appropriately according to the application. For example, it is preferably 0.01% to 0.5% by mass relative to the total amount of solid components, more preferably 0.1% to 0.3% by mass, and even more preferably 0.15% to 0.25% by mass.

[0108] The solvent content in the negative electrode slurry can be adjusted appropriately according to the desired viscosity, for example, preferably 50% to 90% by mass, more preferably 60% to 80% by mass, and even more preferably 65% ​​to 75% by mass.

[0109] The negative electrode slurry may further contain binders, thickeners, etc., within a range that does not impair performance. As binders, materials used in the electrode slurries of lithium-ion batteries can be appropriately selected. 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. CMC may be used as a thickener. One thickener may be used alone, or two or more may be used in combination. It should be noted that CMC is also cited as an example of a dispersant, and may be included for both dispersion and thickening purposes.

[0110] The total content of binder and thickener in the negative electrode slurry is preferably 20% by mass or less, and more preferably 15% by mass or less.

[0111] There are no particular limitations on the negative electrode active material, but it is preferred to contain Si-based active materials. Si-based active materials have the advantage of high specific capacity, but their large volume change during charge and discharge makes it difficult to improve cycle characteristics. However, if the conductive additive of this disclosure is used, the cycle characteristics can be improved.

[0112] As a Si-based active material, commonly known Si-based active materials can be used, preferably including at least one selected from silicon, silicon oxide, and composites of silicon and other materials, more preferably including one selected from Si and SiO. x (x represents greater than 0 and less than 1.5) and at least one of the Si-C complexes.

[0113] It should be noted that, as will be obvious to those skilled in the art, in lithium-ion batteries, the negative electrode active material undergoes lithiation or delithiation through charging and discharging. Therefore, Si-based active materials also include those that have undergone lithiation within their theoretical specific capacity range.

[0114] Examples of Si-C composites include composites with a structure in which silicon particles are dispersed in a carbon matrix (first type), composites in which silicon is impregnated in the pores of porous carbon (second type), and composites in which carbon is coated on the surface of silicon or silicon oxide (third type).

[0115] In the first type of Si-C composite, the silicon particles are preferably nanoscale with a volume average particle size of tens to hundreds of nm. In the third type of Si-C composite, the silicon or silicon oxide preferably has a particle size in the nanometer to micrometer range.

[0116] The silicon content of the Si-based active material is preferably 20% by mass or more. With such a value, it is possible to obtain a negative electrode with a large capacity. From this viewpoint, 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.

[0117] The silicon content of the Si-based active material is preferably 80% by mass or less. With such a value, the Si-based active material can suppress excessive volume changes caused by lithium uptake, and there is a tendency to obtain lithium-ion batteries with excellent cycle characteristics. From this point of view, 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.

[0118] The oxygen content of the Si-based active material is preferably 70% by mass or less. This value tends to increase specific capacity and improve 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.

[0119] The oxygen content of the Si-based active material is preferably 0.1% by mass or more. With such a value, the volume change associated with lithiation and delithiation of the active material is reduced, leading to a tendency to obtain lithium-ion batteries 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.

[0120] From the perspective of reducing side reactions, the average particle size D of Si-based active materials... 50 Preferably, it is 2μm or more, more preferably 3μm or more, and even more preferably 4μm or more.

[0121] Furthermore, from the perspective of reducing electrode resistance, the average particle size D of Si-based active materials... 50 Preferably, it is 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less.

[0122] The average particle size D of Si-based active materials 50This refers to the particle size (50%D) at which the cumulative volume distribution reaches 50% when the particle size is plotted from the small particle size side in the particle size distribution determined by laser diffraction and scattering. The volume average particle size of the negative electrode material can be measured, for example, by using a laser diffraction particle size distribution measuring device (e.g., Shimadzu Corporation's SALD-3100J) while the negative electrode material is dispersed in purified water containing a surfactant.

[0123] When Si-based active materials are used as the negative electrode active material, the average length L of the fibrous carbon is... 50 The average particle size D of Si-based active materials 50 The ratio (L) 50 / D 50 Preferably less than 2, more preferably 1.5 or less, and even more preferably 1.3 or less. If the ratio (L) is less than 2, more preferably 1.5 or less, and even more preferably 1.3 or less. 50 / D 50 If the value is within the aforementioned range, the volume change accompanying charge and discharge of the Si-based active material can be tracked, the conductive path can be maintained, and there is a tendency for further improvement in cycle performance. Furthermore, if the fibrous carbon is too long, it is difficult to increase the electrode density. For this reason, a value less than 2 is preferred.

[0124] It should be noted that even when other negative electrode active materials such as graphite are used in addition to Si-based active materials, maintaining the conductive path is still effective in improving cycle performance for Si-based active materials with large volume changes during charge and discharge. Therefore, a ratio (L) is preferred. 50 / D 50 () refers to the above range.

[0125] In addition, compared to (L) 50 / D 50 The ratio is preferably 0.6 or higher, more preferably 0.8 or higher, and even more preferably 1.0 or higher. If the ratio (L) is higher than that of L, the ratio is lower than that of L. 50 / D 50 If the range is as described above, then the fibrous carbon has sufficient length relative to the size of the Si-based active material, so even if the Si-based active material is present nearby, it can effectively form a conductive path, thus tending to improve the cycling characteristics.

[0126] In addition to Si-based active materials, other commonly used negative electrode active materials in the field of lithium-ion batteries can also be used as negative electrode active materials.

[0127] Other examples of anode active materials include graphite, hard carbon, alloy-based anodes, and Li4Ti5O. 12 (LTO), alloy-based anodes, and composites with other materials. Other anode active materials can be used alone or in combination of two or more.

[0128] As the negative electrode active material, a combination of Si-based active materials and graphite is preferred. Si-based active materials exhibit large expansion and contraction rates during lithiation and delithiation, so the volume change is mitigated by combining them with carbon. Furthermore, graphite itself can function as a conductive pathway; therefore, there is a trend towards further improving the battery's cycle characteristics by adding graphite.

[0129] The proportion of Si-based active material in the overall negative electrode active material is not particularly limited, and can be appropriately adjusted according to the type of Si-based active material, the type of active material used, and the purpose. For example, it is preferably 1% to 50% by mass, more preferably 2% to 25% by mass, and even more preferably 3% to 15% by mass.

[0130] The content of negative electrode active material in the negative electrode mixture slurry can be adjusted appropriately according to the application. For example, it is preferably 75% to 99.9% by mass relative to the total amount of solid components, more preferably 80% to 98% by mass, and even more preferably 90% to 97% by mass.

[0131] The viscosity of the negative electrode slurry is preferably adjusted appropriately according to the application, 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.

[0132] The method for manufacturing the negative electrode slurry is not particularly limited, and methods commonly known to those skilled in the art can be used. For example, the constituent components can be weighed and mixed with a solvent to prepare the negative electrode slurry. It should be noted that in the method for manufacturing the negative electrode slurry, the ratio of SWCNT and fibrous carbon is adjusted to achieve the composition of the negative electrode slurry disclosed herein.

[0133] The mixing order is not particularly limited, but it is preferable to first add solvent to SWCNT and fibrous carbon for dispersion and liquefaction to obtain a conductive additive dispersion, and then add the remaining components. The method for manufacturing the conductive additive dispersion is as described above.

[0134] <Negative Electrode Mixture Layer>

[0135] The negative electrode mixture layer disclosed herein contains the conductive additive and negative electrode active material disclosed herein, and the proportion of single-walled carbon nanotubes in the entire negative electrode mixture layer is greater than 0.01% by mass and less than 0.1% by mass.

[0136] If the proportion of SWCNTs in the overall negative electrode flux layer is less than 0.1% by mass, the cost of negative electrode manufacturing can be suppressed, and the peel strength relative to the current collector can be improved. From this point of view, the proportion of SWCNTs in the overall negative electrode flux layer is preferably 0.07% by mass or less, and more preferably 0.04% by mass or less.

[0137] If the proportion of SWCNTs in the overall negative electrode additive layer is 0.01% by mass or more, sufficient conductivity can be imparted to the negative electrode, and there is a tendency to further improve cycle characteristics. From this point of view, 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.

[0138] Details of the conductive additives and negative electrode active materials are as described above.

[0139] It should be noted that whether the SWCNTs contained in the negative electrode binder layer of the electrode form tube bundles can be determined in the following ways: In the negative electrode binder layer disposed on the surface of the electrode, the SWCNT portion near the surface of the negative electrode binder layer is observed using TEM; or the binder or other components of the negative electrode binder layer are dissolved using a solvent, and the negative electrode binder layer is decomposed and observed using TEM. The presence or absence of a fibrous layered structure indicates whether this is the case. Alternatively, the surface area of ​​the electrode or the negative electrode binder layer is decomposed using a solvent, and the SWCNTs are removed through appropriate separation and agglomeration operations such as centrifugation. These are then subjected to Raman spectroscopy, and the presence or absence of radial breathing patterns (RBMs) in the obtained Raman spectra indicates whether SWCNTs have formed tube bundles.

[0140] Furthermore, the average length of SWCNTs, the average length of SWCNT bundles, and the average length of fibrous carbon contained in the negative electrode mixture layer were determined as follows: the negative electrode mixture layer was decomposed by dissolving the binder with a solvent, etc., and dispersed. The resulting material was observed using TEM, and the values ​​were determined using the above method. If SEM measurement is available, it can also be performed.

[0141] Regarding the average particle size D of the Si-based active material contained in the negative electrode mixture layer 50 The negative electrode binder layer was decomposed by dissolving the binder with solvents, and then dispersed. The resulting material was observed using SEM, and the image of the Si-based active material was extracted from the SEM image. The equivalent circle diameter of the Si-based active material was calculated. This circle was defined as the projected area of ​​a sphere, and D was calculated based on the volume of the sphere. 50 It should be noted that more than 30 extracted images are used for calculations. The shape of the SEM image is used to identify Si-based active substances, but secondary electron images and EDS mapping images are used as needed.

[0142] In addition, the negative electrode was processed into a thin sheet using FIB (Focused Ion Beam) and observed by TEM, which allowed for the determination of the diameter of SWCNTs, their bundles, and fibrous carbon. Measurements were taken from 30 samples, and the average diameter was calculated.

[0143] When the tubular and fibrous carbon in SWCNTs are clearly distinguishable based on their appearance, such as fiber stiffness and thickness, the electrode surface and cross-section can be observed by SEM, and their diameters can be measured multiple times and averaged to obtain their average diameter.

[0144] In the negative electrode mixture layer, SWCNTs (including the case of forming bundles) and fibrous carbon are preferably configured as follows.

[0145] (1) At least a portion of the SWCNTs are in contact with the surface of the negative electrode active material in a manner that bridges the negative electrode active material with each other.

[0146] (2) SWCNT crosses at least part of the fiber axis of fibrous carbon multiple times.

[0147] (3) At least a portion of the SWCNTs are in contact with both the negative electrode active material and the fibrous carbon in a manner that bridges the negative electrode active material and the fibrous carbon.

[0148] For the negative electrode compound layer, using SEM at a magnification of 30,000 to 50,000 times, 100 fields of view are observed starting from a certain field of view and shifted 100 μm laterally or longitudinally each time. At this time, it is more preferable that the states of (1), (2) or (3) above are observed in more than 10 fields of view, and it is even more preferable that they are observed in more than 20 fields of view.

[0149] The silicon content in the negative electrode flux layer is preferably 3% by mass or more. With such a value, there is a tendency for the negative electrode to have a large capacity. From this point of view, the silicon content in the negative electrode flux layer is more preferably 5% by mass or more, and even more preferably 10% by mass or more.

[0150] The silicon content in the negative electrode additive layer is preferably 50% by mass or less. With such a value, the battery tends to have excellent cycle characteristics. From this point of view, the silicon content in the negative electrode additive layer is more preferably 40% by mass or less, further preferably 30% by mass or less, and particularly preferably 20% by mass or less.

[0151] 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 alkali to form a solution, and then quantifying it by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0152] There is no particular limitation on the manufacturing method of the negative electrode mixture layer; methods commonly known to those skilled in the art can be used. For example, a method of applying a negative electrode mixture slurry onto the current collector and then drying it can be employed.

[0153] The method for manufacturing the negative electrode slurry is as described above.

[0154] It should be noted that in the manufacturing method of the negative electrode slurry, there is no particular limitation on the order of mixing the components. It is preferable to first add solvent to SWCNT and fibrous carbon for dispersion and liquefaction to obtain a conductive additive dispersion, and then add the remaining components. Thus, the states (1), (2), and (3) above can be easily obtained.

[0155] <Negative electrode>

[0156] The negative electrode of this disclosure has a current collector and a negative electrode mixture layer of this disclosure disposed on the current collector.

[0157] There are no particular limitations on the current collector; materials with electronic conductivity that do not typically form alloys with lithium can be selected. Examples of current collectors include metal foils such as copper foil and nickel foil, as well as mesh-like copper and nickel foils.

[0158] The negative electrode obtained by forming a negative electrode mixture layer on the current collector using the above-mentioned manufacturing method is pressed by a roller press, a single-axis press, etc., and adjusted to the desired electrode density.

[0159] From the viewpoint of increasing the energy density of the battery and ensuring good electrolyte penetration into the electrodes, the electrode density is preferably 1.1 g / cm³. 3 ~1.9g / cm 3 More preferably 1.2 g / cm³ 3 ~1.8g / cm 3 Further preferred value is 1.3 g / cm³. 3 ~1.7g / cm 3 .

[0160] 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.

[0161] The method for determining peel strength is based on the method described in the examples.

[0162] <Lithium-ion batteries>

[0163] The lithium-ion battery disclosed herein has a negative electrode and a positive electrode. The lithium-ion battery can incorporate components known in the art, such as an electrolyte and a separator.

[0164] For the positive electrode, electrolyte, and separator, materials and compositions known in this field can be used.

[0165] The manufacturing methods for lithium-ion batteries can employ methods known in the field.

[0166] The capacity retention rate of the 33rd cycle relative to the capacity of the 1st cycle (capacity retention rate of the 33rd cycle) is preferably 93% or more, more preferably 94% or more, and even more preferably 95% or more.

[0167] The method for determining the capacity retention rate in the 33rd cycle is based on the method described in the examples.

[0168] Example

[0169] The present disclosure is described in detail below through embodiments, but the present invention is not limited to these embodiments.

[0170] (Determination of the average diameter of SWCNT tubular bundles, MWCNTs, and fibrous carbon)

[0171] The negative electrode was cut into 10mm × 10mm pieces and processed by FIB into thin sheet samples of 10μm × 10μm × 0.05μm (“Helios5UX”, manufactured by Thermo Fisher Scientific). These samples were then placed on a sample stage for TEM observation. This confirmed whether SWCNTs formed tube bundles within the electrode and the presence of fibrous carbon.

[0172] After observing a field of view using magnification equal to the diameter of the SWCNT tube bundles or the diameter of the fibrous carbon, take a picture with the field of view shifted 100 nm to the right. Repeat this operation. Then, at an appropriate position, take a picture with the field of view shifted 100 nm downwards, followed by a picture with the field of view shifted 100 nm to the left. Repeat this operation, photographing the SWCNT tube bundles and fibrous carbon repeatedly, until 30 fibers are captured in each.

[0173] For the tubular and fibrous carbon of SWCNTs, the diameter at the midpoint along the length of the fiber was determined using TEM images and a ruler. The average diameter of 30 fibers was then calculated to determine the average diameter of both SWCNTs and fibrous carbon.

[0174] (Average length of SWCNT tubular bundles, MWCNTs, and fibrous carbon)

[0175] A small amount of the prepared conductive additive dispersion was taken, and water was added while stirring to prepare a 10-fold dilution. The dilution was dropped onto a substrate for electron microscopy observation, dried to remove moisture, and then observed using SEM. The lengths of 30 samples were measured, and the average value was calculated.

[0176] It should be noted that the average lengths of the SWCNT bundles, MWCNTs, and fibrous carbon in the negative electrode active material layer were confirmed to be equivalent to those measured from the conductive additive dispersion.

[0177] (Example 1)

[0178] [Preparation of mixed negative electrode active materials]

[0179] As the negative electrode active material, carbon-coated SiO2 is prepared. 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 3m²). 2 / g). Their specific capacity was determined in advance through experiments based on coin cells, SiO x The capacity is 1600 mAh / g for graphite and 360 mAh / g for SiO₂. x A mixed negative electrode active material with a specific capacity of 500 mAh / g was prepared by mixing graphite in a mass ratio of 11.3:88.7, and 96.47 parts by mass were prepared.

[0180] [Preparation of conductive additive dispersion]

[0181] A 2.5% (w / w) aqueous solution of carboxymethyl cellulose (CMC) was prepared beforehand. The CMC solids were mixed with SWCNT1 (average fiber diameter 2 nm, average fiber length 8 μm, average bundle diameter 30 nm, average bundle length 10 μm) at a ratio of 1.5 parts by weight to 0.03 parts by weight. The mixture was stirred for 30 minutes at 4500 rpm using a homogenizer. Fibrous carbon (product name "VGCF-H", manufactured by Resonac Co., Ltd., average diameter: 150 nm, average fiber length: 6 μm, BET specific surface area: 15 m²) was then mixed into the stirred solution. 2 / g, average surface spacing d 002 0.5 parts by weight of a conductive additive (0.339 nm) were added with purified water to prepare a dispersion with a solid content of 2.0% by weight. The prepared solution was then homogenized at 4500 rpm for 30 minutes to obtain the conductive additive dispersion.

[0182] [Preparation of negative electrode slurry]

[0183] The conductive additive dispersion was added to the above-mentioned mixed negative electrode active material in a manner that yielded 2.03 parts by weight of solids, relative to 96.47 parts by weight of the mixed negative electrode active material. The mixture was then kneaded using a rotation-revolution mixer (Defoaming Rentarō ARE-310, manufactured by THINKY Co., Ltd.). Next, a 40% by weight aqueous dispersion of styrene-butadiene rubber (SBR) was added to the solution to bring the solids content to 1.5 parts by weight. This mixture was then kneaded using a rotation-revolution mixer to prepare the negative electrode slurry.

[0184] A cone plate (model: CP25-2) was mounted on a rheometer (model: MCR301, manufactured by Anton Paar) as a measuring fixture to measure the viscosity of the negative electrode mixture slurry at 25°C. The shear rate was set to 60 s. -1 The viscosity results after 1 minute of measurement are shown in Table 1.

[0185] [Making the negative electrode]

[0186] The negative electrode slurry was coated onto a 20 μm thick copper foil using a scraper (gap: 150 μm). The resulting material was dried at 70 °C for 10 hours using a hot air dryer, and then further dried under reduced pressure at 110 °C for 10 hours to obtain the negative electrode.

[0187] [Peeling test]

[0188] The obtained negative electrode was cut into strips measuring 3cm x 10cm. A 2.5cm x 5cm double-sided adhesive tape (model G9000, manufactured by Dexerials Co., Ltd.) was adhered to a stainless steel plate, with the negative electrode adhesive layer in contact with the tape and covering the entire tape. Then, the copper foil side of the negative electrode was attached to the test stage of a universal testing machine (model: STA-1150, manufactured by A&D Co., Ltd.).

[0189] A stainless steel sheet was stretched at a speed of 100 mm / min with a peel angle of 180 degrees, and the magnitude of the force was measured. The integral average strength (mN) over the test range of 30 mm to 60 mm was calculated, and then divided by the peel width of 2.5 cm to obtain the peel strength in mN / mm. The results are shown in Table 1.

[0190] For the negative electrode mixture layer, when using the above method to observe 100 fields of view with SEM, the states of (1), (2) or (3) above were observed in more than 10 fields of view respectively.

[0191] [Making of a button battery cell]

[0192] The obtained negative electrode was punched to a diameter of 13 mm and then pressurized using a uniaxial press to adjust the electrode density to 1.6 g / cm³.3 In a glove box under a dry argon atmosphere (dew point: -86°C), a punched negative electrode was used as the sample electrode, and a 0.75 mm thick lithium foil was punched into a 16 mm diameter piece and used as the counter electrode. A microporous membrane of monolayer polyolefin was used as the separator to assemble a button cell. In this cell, the lithium foil, serving as the counter electrode, was used as the negative electrode, and the aforementioned negative electrode, serving as the sample electrode, was used as the positive electrode for charge-discharge testing. Typically, lithium foil is used as the counter electrode for the half-cell used for negative electrode evaluation.

[0193] As an electrolyte, it is a liquid prepared by mixing 1% by mass of vinylene carbonate (VC) and 10% by mass of fluoroethylene carbonate (FEC) in a solvent in a volume ratio of 3:5:2 to dissolve the electrolyte LiPF6 to a concentration of 1 mol / L.

[0194] [Charge-discharge cycle test]

[0195] Charge-discharge cycle tests were conducted using the fabricated coin cell cells. Charging was first performed in constant current (CC) mode (equivalent to 0.05C) until the cell voltage reached 0.005V, then in constant voltage (CV) mode until the current decayed to 0.01C. Discharging was then performed with a constant current (equivalent to 0.05C) until the cell voltage reached 1.5V. Three charge-discharge cycles were performed according to this scheme.

[0196] Here, "equivalent to 0.05C current" refers to the current required to discharge a button cell at its capacity calculated from the mass of active material and theoretical specific capacity over 20 hours.

[0197] Next, the battery was first charged in constant current (CC) mode (equivalent to 0.2C) until the cell voltage reached 0.005V, then charged in constant voltage (CV) mode until the current decreased to 0.05C. Discharge was then carried out at a constant current (equivalent to 0.2C) until the cell voltage reached 1.5V. This process was repeated for 30 charge-discharge cycles, for a total of 33 charge-discharge cycle tests.

[0198] With the discharge capacity of the first cycle set as Q1 and the discharge capacity of the 33rd cycle set as Q33, the "capacity retention rate of the 33rd cycle" is calculated using the following formula and used as an indicator of cycle characteristics. The results are shown in Table 1.

[0199] Capacity maintenance rate (%) after 33 cycles = 100 × (Q33) / (Q1)

[0200] (Examples 2-9, Comparative Examples 1-7)

[0201] Except for changing the properties or addition amounts of the negative electrode active material, SWCNT, MWCNT, CB, fibrous carbon, CMC, and SBR as shown in Table 1, the same procedure as in Example 1 was followed to obtain the negative electrode slurry, negative electrode layer, and button cell, and various properties and battery characteristics were evaluated.

[0202] It should be noted that, as a CB, the product name used is C-NERGY SUPER C 45, manufactured by Imerys Graphite & Carbon.

[0203] As different from SWCNT1, SWCNT2 and SWCNT3 are used, which have 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.

[0204] In addition, in all embodiments and comparative examples, the content of CMC and SBR in the negative electrode mixture layer was set to 1.5% by mass.

[0205] The results are shown in Table 1.

[0206] Table 1

[0207]

[0208] It can be seen that in Comparative Example 1, which only added SWCNT as a conductive additive, the cycling characteristics were excellent, but the slurry viscosity was high.

[0209] It can be seen that in Comparative Examples 2 and 4, which use both SWCNT and CB as conductive additives and do not contain fibrous carbon, the peel strength is poor. It can be seen that, especially in Comparative Example 4, CB accounts for the majority of the conductive additives, and the cycling characteristics are also poor.

[0210] In Comparative Example 3, it can be seen that the proportion of SWCNT relative to the overall conductive additive is 2.0% by mass, and the content of SWCNT in the negative electrode additive layer is 0.01% by mass. The amount of SWCNT is too small, so the cycle characteristics are poor.

[0211] In Comparative Examples 5, 6, and 7, MWCNT was used instead of SWCNT, changing the amount added, but the peel strength and cycling characteristics were lower. This indicates that SWCNT is a better material for combination with fibrous carbon.

[0212] The entire disclosure of Japanese Patent Application No. 2024-030695 is incorporated herein by reference. All documents, patent applications, and technical standards described herein are incorporated herein by reference as if each document, patent application, and technical standard were specifically and separately described therein and incorporated by reference.

Claims

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

2. The conductive additive according to claim 1, wherein, The average diameter of the fibrous carbon is above 80 nm.

3. The conductive additive according to claim 1, wherein, The average diameter of the single-walled carbon nanotube bundles is less than 90 nm.

4. The conductive additive according to claim 1, wherein, The average length L of the single-walled carbon nanotube bundle b Relative to the average length L of the fibrous carbon 50 The ratio is L b / L 50 It is above 0.

3.

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

6. A conductive additive dispersion comprising the conductive additive, dispersant, and solvent as described in any one of claims 1 to 5.

7. A negative electrode slurry, comprising the conductive additive, dispersant, solvent and negative electrode active substance as described in any one of claims 1 to 5.

8. The negative electrode mixture slurry according to claim 7, wherein, The negative electrode active material includes a Si-based active material, which comprises materials selected from Si and SiO. x At least one of the Si-C complexes, where x represents more than 0 and less than 1.

5.

9. The negative electrode mixture slurry according to claim 8, wherein, The average length L of the fibrous carbon 50 Relative to the average particle size D of the Si-based active material 50 The ratio is L 50 / D 50 Less than 2.

10. The negative electrode mixture slurry according to claim 8, wherein, The negative electrode active material also includes graphite.

11. The negative electrode mixture slurry according to claim 8, wherein, The silicon content of the Si-based active material is 20% 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% to 70% by mass.

13. A negative electrode mixture layer comprising the conductive additive and the negative electrode active material as described in any one of claims 1 to 5. The single-walled carbon nanotubes account for more than 0.01% by mass and less than 0.1% by mass in the overall negative electrode mixture layer.

14. The negative electrode mixture layer according to claim 13, wherein, The negative electrode active material comprises a Si-based active material, which includes materials selected from Si and SiO. x At least one of the Si-C complexes, where x represents more than 0 and less than 1.

5.

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

16. The negative electrode mixture layer according to claim 14, wherein, The silicon content is 3% 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 configured in a manner that satisfies the following (1) to (3), (1) At least a portion of the single-walled carbon nanotubes are in contact with the surface of the negative electrode active material in a manner that bridges the negative electrode active material with each other; (2) The single-walled carbon nanotubes traverse at least a portion of the fiber axis of the fibrous carbon multiple times; (3) At least a portion of the single-walled carbon nanotubes are in contact with both the negative electrode active material and the fibrous carbon in a manner that bridges them.

18. A negative electrode having a current collector and a negative electrode mixture layer of claim 13 disposed on the current collector.

19. A lithium-ion battery comprising a positive electrode and a negative electrode as described in claim 18.

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