Method for preparing negative electrode paste for lithium-ion batteries

Abstract

The proposed invention relates to the electrotechnical industry, more particularly to lithium-ion batteries, and even more particularly to lithium-ion batteries with silicon-containing anodes. The invention provides a method for preparing an anode paste, an anode paste, a method for preparing an anode for a lithium-ion battery, an anode for a lithium-ion battery, and a lithium-ion battery with a high initial specific capacity and many charge-discharge cycles while retaining at least 80% of the initial capacity. This technical result is achievable as a result of the presence of an anode material of bundles of single-walled and / or double-walled carbon nanotubes having lengths less than 5 μm, along with bundles of single-walled / double-walled carbon nanotubes having diameters greater than 500 nm and lengths greater than 10 μm.

Description

[Technical Field]

[0001] The present invention relates to the electrical industry, particularly to lithium-ion batteries, and more particularly to lithium-ion batteries equipped with a silicon-containing anode and to the anode of a lithium-ion battery. [Background technology]

[0002] When used in lithium-ion batteries, silicon-containing anodes offer several advantages. The most significant of these is their high specific capacity, theoretically reaching 4200 mAh / g. However, the lifespan of such materials—that is, the number of charge-discharge cycles that maintain their capacity compared to carbon-based anodes—is generally lower. This is because, during battery charging, the Li22Si5 phase (density 0.96 g / cm³)... 3 Silicon forms a weight fraction of 48% by weight, with a density of 2.33 g / cm³. 3 This is related to the fact that the interaction between silicon and lithium increases the volume of the active component particles by 400% (5 times). After multiple charge-discharge cycles, voids form between the silicon particles that make up the negative electrode composite material, and these voids bond together to form cracks. After several cycles, the negative electrode loses its integrity, which causes insulation in parts of the negative electrode and leads to a decrease in battery capacity. Eventually, the negative electrode is completely destroyed. This is a major challenge that limits the widespread application of silicon and silicon-containing negative electrodes in lithium-ion batteries.

[0003] For the efficiency of a silicon-containing anode to be guaranteed over a sufficiently large number of charge-discharge cycles of a lithium-ion battery, both the integrity of the silicon-containing anode and the high conductivity of the material must be provided. Manufacturing a silicon-containing anode that has a high specific capacity, such as a 500 mAh / g anode material, and can maintain that capacity over a sufficiently large number of charge-discharge cycles, such as retaining more than 80% of the initial capacity over more than 500 cycles, is a challenging technical problem, but the present invention provides a solution to this problem.

[0004] As used herein, the term "negative electrode material" refers to a composite material of a negative electrode without a current collector. As used herein, the term "negative electrode active material" refers to a combination of materials in the negative electrode that chemically react with lithium during the battery charging process, such as graphite, silicon, or silicon oxide (SiO).

[0005] To ensure reliable operation through multiple charge-discharge cycles without loss of battery capacity, several patents and research publications propose the use of silicon-carbon composites with relatively low volume change during the lithiumization process in the charging stage as the anode active material. However, this approach does not solve these problems because it has inherent limitations related to the primary dependence of the specific capacity of the anode material on the relative volume change during lithiumization. Therefore, relatively low volume change means a low specific capacity of the battery.

[0006] Another proposed solution involves pre-forming a porous structure in the silicon-containing anode material so that the formed lithium silicate fills the pores. This prevents the aggregation of composite aggregates over tens of charge-discharge cycles.

[0007] Accordingly, the disclosures [Patent Document 1] and [Patent Document 2] provide Si / C nanocomposites into pores in which crystalline or amorphous carbon particles are embedded, derived from porous silicon particles. Disclosure [Patent Document 1] also provides a method for producing such a composite, comprising mixing an alkali metal or alkaline earth metal with a silicon oxide nanocomposite containing crystalline or amorphous carbon; a method for heat-treating such a composite to reduce silicon oxide; and a method for heat-treating the thus obtained composite in an acid to remove alkali metal oxide or alkaline earth metal oxide. The negative electrode material of the cited disclosure has an initial charge capacity of 847-855 mAh / g and retains 73-78% of the initial capacity after 50 cycles.

[0008] The proposed solutions have two main drawbacks: (1) the complex method for obtaining the anode material, followed by its coating onto the anode current collector, requires an essential modification of existing processes for lithium-ion battery manufacturing; and (2) the insufficient increase in the useful life of the anode material, which remains short compared to graphite anode materials, due to the recrystallization of silicon in the Si / C composite and the gradual breakdown of the formed porous structure.

[0009] Another solution for obtaining a negative electrode active material with a long useful life is to introduce fibrous carbon particles into the silicon-containing negative electrode material not only as a conductive additive but also as a reinforcing additive. It is known that reinforcement of composite materials can be obtained by introducing additives that have inherently high strength due to the preferred use of elongated particles such as fibers. Furthermore, the larger the ratio of length to thickness, the lower the volume fraction of the additive that produces the reinforcing effect becomes. Disclosure [Patent Document 3] provides a negative electrode active material comprising a porous composite material “silicon oxide-carbon material” containing porous silicon oxide and “linear” carbon material laminated on and / or within the pores of the porous silicon oxide. The linear material is carbon nanofibers, carbon nanotubes, or a mixture thereof, and the average pore diameter of the porous silicon oxide is in the range of 10 nm to 1000 nm when measured from the surface of the porous silicon oxide, the average diameter of the linear material is in the range of 5 nm to 200 nm, and its average length is in the range of 100 nm to 5 μm. By preparing a negative electrode slurry (for example, together with conductive components such as acetylene black and a binder such as PVDF), and then using this composite material as the active material for manufacturing the negative electrode of a lithium-ion battery, a lithium-ion battery is produced in which the number of charge-discharge cycles increases and the composite material aggregates (particles) are maintained without fracture. Furthermore, this composite material retains its conductivity even after internal cracks have occurred. The achieved specific capacity is 1568 mAh / g, and 95% of the capacity of this material is retained after 49 cycles.

[0010] The drawbacks of the solution provided in the disclosure [Patent Document 3] include weak mechanical bonding and insufficient conductivity between aggregates (particles) of the composite material. This requires the introduction of a considerable amount of conductive components and binders into the anode slurry in addition to the porous composite material "silicon oxide-carbon material" (in the embodiments of this disclosure, the content is 20% by weight) in order to obtain the required parameters of the anode material. The introduction of a considerable amount of inert material into the lithiation chemical process reduces the specific capacity of the anode. A second major drawback of the solution provided in the disclosure [Patent Document 3] is that obtaining such a composite material, the "silicon oxide-carbon material," is a technically challenging process. This composite material requires coating silicon oxide with a metal catalyst, for example using chemical vapor deposition, and further involves a technically challenging and energy-consuming process of forming linear carbon material on the thus deposited metal catalyst.

[0011] The negative electrode active material disclosed in [Patent Document 3] is the closest to the negative electrode slurry and negative electrode material provided in the present invention, and [Patent Document 3] is used as a prototype for the negative electrode slurry and negative electrode material of the present invention.

[0012] The closest solution to the present invention regarding a method for producing a negative electrode slurry and a method for manufacturing a negative electrode is Disclosure [Patent Document 4]. This involves pulverizing a non-carbon material and hollow carbon nanofibers in an organic solvent to obtain a mixture, drying this mixture, producing a negative electrode active material containing secondary particles of aggregated primary nanoparticles including hollow carbon fibers bonded to the non-carbon material, mixing the negative electrode active material with a polymer binder having an electron-donating group and a solvent to produce a composition of the negative electrode active material, coating this composition of the negative electrode active material onto a current collector, drying the coated composition of the negative electrode active material, and forming a negative electrode. The average particle size of the non-carbon material ranges from about 10 nm to about 50 nm, the secondary particles have a maximum particle size of about 50 μm, and the hollow carbon nanofibers are single-walled nanotubes, multi-walled nanotubes, circular nanotubes, or a combination thereof. Examples 1 and Figure 8 of the cited invention show that the negative electrode produced by such a method has an initial capacity of 850 mAh / g and decreases to 710 mAh / g (83% of the initial capacity) during 20 charge-discharge cycles. Examples 2 and Figure 10 of the cited invention show that the negative electrode produced by such a method has an initial capacity of 1130 mAh / g and decreases to 800 mAh / g (70% of the initial capacity) during 20 charge-discharge cycles.

[0013] Therefore, the produced material has the same drawbacks as the material of Disclosure [Patent Document 3]. That is, the nanocarbon nanofibers are contained in the primary nanoparticles, thereby affecting the strength and integrity of the primary nanoparticles and in some cases the secondary particles having a size less than 50 μm. However, the bonding between secondary particles within the negative electrode material is weak, and the negative electrode material during the charge-discharge cycle is broken along the boundaries of the secondary particles. This reduces the number of effective charge-discharge cycles in which the negative electrode retains more than 80% of its initial capacity. Disclosure [Patent Document 4] is adopted as a prototype regarding the method for producing the negative electrode slurry of the present invention and the method for manufacturing the negative electrode of the present invention.

Prior Art Documents

Patent Documents

[0014] [Patent Document 1] U.S. Patent No. 8,263,265 [Patent Document 2] U.S. Patent No. 8,617,746 [Patent Document 3] European Patent No. 2,755,263 [Patent Document 4] U.S. Patent No. 8,697,286 [Summary of the Invention] [Problems to be Solved by the Invention]

[0015] The present invention provides a method for producing a negative electrode slurry, a negative electrode slurry, a method for producing a negative electrode for a lithium ion battery, a negative electrode for a lithium ion battery, and a lithium ion battery having a long cycle with a high initial specific capacity and a large number of charge-discharge cycles in which the battery retains at least 80% of its initial capacity. The technical result of the provided disclosure is that the initial specific capacity of the negative electrode is more than 500 mAh / g, and the negative electrode and the lithium ion battery retain more than  80% of the initial capacity for at least 500 charge-discharge cycles at a charge current and a discharge current of at least 1 C. A further important technical result of the provided disclosure is the simplicity of the process and the industrial applicability of the method provided in standard techniques for manufacturing lithium ion batteries. [Means for Solving the Problems]

[0016] To achieve such technical results, the negative electrode material for lithium-ion batteries is required to contain a silicon-containing active material, for example, a silicon and / or silicon oxide (SiOx) phase at a high concentration of more than 50% by weight. To achieve such technical results, it is further required that the secondary aggregates or domains of silicon and / or silicon oxide (SiOx) nanoparticles in the negative electrode material maintain their integrity over a very large number of charge-discharge cycles. To achieve such technical results, it is further required that there be strong mechanical and electrical bonds between the secondary aggregates or domains of silicon and / or silicon oxide (SiOx) nanoparticles in the negative electrode material, enabling the negative electrode to maintain integrity and conductivity over a very large number of charge-discharge cycles.

[0017] The achievement of such technical results is made possible by the presence of both bundles of single-walled and / or double-walled carbon nanotubes (SWCNTs and / or DWCNTs) having a length of less than 5 μm, and bundles of single-walled and / or double-walled carbon nanotubes having a length of more than 10 μm, in the anode material. The thin and short bundles of single-walled and / or double-walled carbon nanotubes having a length of less than 5 μm ensure the integrity of the secondary aggregates of silicon and / or silicon oxide (SiOx) nanoparticles is reliably maintained during lithiation and delithiation during charge-discharge cycles, and electrical contact with these particles is provided. The long bundles of single-walled and / or double-walled carbon nanotubes having a length of more than 10 μm ensure the integrity of the entire anode material, reliably maintain the mechanical bonding between the silicon and / or silicon oxide (SiOx) nanoparticle secondary aggregates during lithiation and delithiation during charge-discharge cycles, and provide conductivity throughout the entire anode layer. The generation of networks from bundles of carbon nanotubes containing both elements having lengths less than the characteristic dimensions of secondary aggregates (less than 5 μm) and elements having lengths greater than the characteristic dimensions of secondary aggregates (greater than 10 μm) is not possible by prior art methods, including the method disclosed [U.S. Patent No. 8,697,286]. For a substantial proportion of the bundles of carbon nanotubes to have lengths less than 5 μm, it is sufficient that the mode of the length distribution of the number of carbon nanotube bundles is less than 5 μm.

[0018] The achievement of the required technical results is ensured when the anode slurry is prepared using a carbon nanotube suspension containing both a substantial number of single-walled and / or double-walled carbon nanotube bundles having lengths less than the characteristic dimensions of the secondary aggregates of the active material, and a substantial number of single-walled and / or double-walled carbon nanotube bundles having lengths substantially exceeding the characteristic dimensions of the secondary aggregates of the active material, and when the active material and such suspension are mixed using a method in which the shear force is insufficient to break the carbon nanotubes and their bundles. Many such methods are known to include, but are not limited to, overhead stirrers with impellers of various shapes, drum mixers, planetary mixers, etc. The size distribution of single-walled and / or double-walled carbon nanotube bundles specific to the suspension used is maintained within the anode slurry and further within the anode.

[0019] The size distribution of suspended particles (such as bundles of carbon nanotubes) is generally determined by dynamic light scattering (DLS). Dynamic light scattering is based on the well-known Stokes-Einstein relationship (1):

[0020]

number

[0021] Therefore, for cylindrical particles (nanotubes and bundles thereof) having length L and diameter d, taking into account the average for all possible orientations, equation (2):

[0022]

number

[0023] [N.Nair, W.Kim, RDBraatz, MSStrano, “Dynamics of Surfactant-Suspended Single-Walled Carbon Nanotubes in a Centrifugal Field” Langmuir, 2008, Vol.24, pp.1790-1795, doi:10.1021 / la702516u] Or, if the particles are considered as horizontally elongated ellipses, then equation (3):

[0024]

number

[0025] The diffusion coefficient (Ddiff) of suspended particles, related to the effective hydrodynamic diameter (Dh), can be determined by [J. Gigault, I. Le Hecho, S. Dubascoux, M. Potin-Gautier, G. Lespes Single-walled carbon nanotube length determination by asymmetrical-flow field-flow fractionation hyphenated to multi-angle laser-light scattering. J. Chromatogr. A, 2010, Vol. 1217, pp. 7891-7897]. Both models (2) and (3) yield very similar values ​​with respect to the shape factor, although the length of the bundle exceeds this factor. Considering that for the vast majority of nanotube bundles in suspension, the length-to-diameter ratio certainly exists in the range of 100 to 10000, the shape factor lies in a narrow range of 5 to 10. For this reason, the length L of the carbon nanotube bundle can be estimated by inequality (4) to be up to twice the value of the effective hydrodynamic diameter.

[0026]

number

[0027] Therefore, in order to generate a network of carbon nanotube bundles containing both elements with lengths less than the characteristic dimensions of secondary aggregates (less than 5 μm) and elements with lengths substantially exceeding the characteristic dimensions of secondary aggregates (greater than 10 μm), it is necessary to prepare a negative electrode slurry using a suspension of carbon nanotubes having a mode of hydrodynamic diameter distribution of carbon nanotube bundles less than 500 nm. In this case, more than 5% by weight of all carbon nanotubes in the suspension (C) are bundled single-walled or double-walled carbon nanotubes with bundle lengths greater than 10 μm. Mixing the silicon-containing active ingredient with such a suspension does not break the bundles of single-walled or double-walled carbon nanotubes, nor does it change their lengths. For this reason, in the negative electrode material prepared from such a suspension, the length distribution of carbon nanotube bundles is characterized by a mode of less than 5 μm, and more than 5% by weight of all carbon nanotubes in the negative electrode material are bundled single-walled or double-walled carbon nanotubes with bundle lengths greater than 10 μm.

[0028] Preferably, the hydrodynamic diameter distribution of the number of carbon nanotube aggregates (bundles) in the suspension is bimodal, having low modes less than 500 nm and high modes greater than 2 μm. However, technical results can also be achieved with a unimodal distribution, but the range of aggregate sizes becomes wider.

[0029] Single-walled and double-walled carbon nanotubes are known to be able to aggregate and form bundles, with the nanotubes bonded to each other by van der Waals forces (π-π interactions). Multi-walled carbon nanotubes do not form such bundles and tend to form coiled aggregates, which do not provide the advantages necessary for guaranteeing the integrity of the anode material. The longer the bundle, the greater the number of nanotubes. Dispersion of single-walled or double-walled carbon nanotubes in a suspension of water or an organic solvent causes bundle breakdown and a reduction in bundle size. The larger the amount of energy applied (mechanical shear or ultrasonic treatment), the smaller the size of the carbon nanotube bundle. When a considerable amount of carbon nanotubes, for example more than 5% by weight, is present in a bundle with a length of more than 10 μm, the challenge of obtaining a suspension of single-walled or double-walled carbon nanotubes having a mode of hydrodynamic diameter distribution of carbon nanotube aggregates (bundles) smaller than 500 nm can be solved in various ways. One possible method is to prepare two or more suspensions containing bundles of monolayer and / or bilayer carbon nanotubes with different degrees of dispersion, and then mix them. Methods for preparing such suspensions are outside the scope of this disclosure.

[0030] This invention relates to a silicon phase or silicon oxide (SiO x A silicon phase (where x is a positive number less than or equal to 2) or a silicon phase in which the total atomic ratio of oxygen:silicon content in the negative electrode material is greater than 0 and less than 1.8, and silicon oxide (SiO2) x It is a combination with the phase of ), containing a high concentration of active ingredients ranging from over 50% by weight to less than 99.9% by weight, and

[0031] (1) Silicon phase or silicon oxide (SiO xA step of introducing a composition (C) comprising a phase of ) (wherein x is a positive number less than or equal to 2) or a combination of such phases, wherein the total atomic ratio of oxygen:silicon content in the combination of phases is greater than 0 and less than 1.8, into a liquid phase suspension (S) containing 0.01% to 5% by weight of carbon nanotubes, wherein of all carbon nanotubes in the suspension (S), 5% by weight of the carbon nanotubes are bundled single-walled and / or double-walled carbon nanotubes having a bundle length greater than 10 μm, and the mode of the hydrodynamic diameter distribution of the number of bundles of carbon nanotubes in the suspension (S) is less than 500 nm.

[0032] (2) A method for producing a negative electrode slurry containing more than 0.1% to less than 20% by weight of carbon nanotubes and including a dry residue, is provided, characterized by comprising a series of steps including (2) mixing a mixture of composition (C) in a suspension (S) until a uniform slurry is obtained.

[0033] In certain embodiments of this method, to ensure optimal rheological or adhesive properties of the slurry for subsequent coating onto the current collector, the graphite and / or binder additive and / or dispersant and / or solvent are silicon and silicon oxide (SiO2). x Composition (C), which includes a combination of phases, may be introduced simultaneously with the introduction of the suspension (S) containing carbon nanotubes. In other applications, graphite and / or binder additives and / or dispersants and / or solvents may be introduced in a separate step or in multiple process steps, rather than simultaneously with the introduction of composition (C) into the suspension (S). In most cases, the order in which the binder additives and / or dispersants and / or solvents are introduced does not affect the technical results achieved.

[0034] Composition (C) is an active component of the negative electrode material contained in the negative electrode slurry, which reacts with lithium during charging. It is also silicon or silicon oxide (SiO2). x Silicon and silicon oxide (SiO₂) (wherein x is a positive number less than or equal to 2) in which the total atomic ratio of oxygen:silicon content in the phase or negative electrode material is greater than 0 and less than 1.8x ) is a combination of phases. The phase of silicon oxide (SiO x ) means both stoichiometric silicon oxide (SiO2) and non-stoichiometric silicon oxide. In the active component, particles and domains with a uniform chemical composition and an interfering crystal structure are often aggregated into bound aggregates referred to as "secondary aggregates" or "secondary particles" in the reference literature. Preferably, in order to achieve the best technical results, the size of the domain having an interfering crystal structure, also referred to as the size of the coherent-scattering domain (CSD) of the phases of silicon and silicon oxide, is less than 10 nm. However, it should be noted that the technical results can also be achieved when the composition (C) contains a good crystallization phase such as a CSR dimension exceeding 100 nm, and further can be achieved even when mechanically pulverized single-crystal silicon is used. More preferably, with respect to processability and occupational safety (for example, for the purpose of avoiding the formation of fine dust), the size of the aggregates in which the particles and domains of silicon and silicon oxide are bundled is distributed with a diameter having a median value (D50) exceeding 5 μm. However, the main technical results such as an increase in the specific capacity and the number of charge-discharge cycles can also be achieved when the median value (D50) of the distribution of the secondary aggregates by diameter is low, for example, 1 μm to 3 μm.

[0035] Preferably, the active component of the negative electrode material also contains carbon covering the surface of the aggregates of silicon and / or silicon oxide. The ratio of C:Si in the composition (C) is greater than 0.01 and less than 0.1. This composition can be produced by various methods known in the art, including but not limited to CVD deposition of carbon on the surface of pre-pulverized silicon and / or silicon oxide. However, the main technical results can also be achieved when using a composition (C) that does not contain carbon. The coating of the surface of the aggregates of silicon and / or silicon oxide with a carbon material occurs during the process of preparing the negative electrode slurry. That is, when the composition (C) and the suspension (S) are mixed, short bundles of single-layer and / or bilayer carbon nanotubes having a bundle length less than 5 μm cover the surface of the aggregates of silicon and / or silicon oxide.

[0036] The carbon nanotubes in the suspension must include single-walled carbon nanotubes and / or double-walled carbon nanotubes. The carbon nanotubes in the suspension may also include nanotubes with more than two graphene layers in their walls (i.e., multi-walled carbon nanotubes and / or two- or three-walled carbon nanotubes, as well as other forms of carbon nanofibers). To achieve the technical results of the present invention, it is essential that the weight fraction of bundled single-walled or double-walled carbon nanotubes with a bundle length greater than 10 μm is at least 5% of all carbon nanotubes in the suspension. To achieve the technical results of the present invention, it is also essential that the mode of the hydrodynamic diameter distribution of the number of bundles of carbon nanotubes in the suspension (S) is less than 500 nm. Preferably, the single-walled and double-walled carbon nanotubes have a low number of structural defects. The defect rate or integrity of the structure of the single-walled and double-walled carbon nanotubes can be quantified by the ratio of the G-band to the D-band of the Raman spectrum. Preferably, the G / D band ratio of the Raman spectrum at a wavelength of 532 nm is greater than 5. Most preferably, the G / D band ratio of the Raman spectrum at a wavelength of 532 nm is greater than 50.

[0037] In certain embodiments of this method, the best technical results are achieved when the surface of the carbon nanotubes in the composite material contains functional groups containing elements having a higher Pauling electronegativity than carbon, including, but not limited to, hydroxyl, carboxyl, chlorine-containing functional groups (-Cl, -O-Cl), and fluorine-containing functional groups. The presence of such groups ensures good adhesion of the carbon nanotubes to particles of the active ingredient. Functional groups can be generated on the surface of carbon nanotubes by various methods known in the art. For example, carboxyl functional groups can be generated on the surface of carbon nanotubes by heat treatment in a nitric acid solution. Chlorine-containing functional groups, on the other hand, can be generated by one of the methods described in the disclosure [Russian Patent Application Publication No. 2717516, MCD TECH, March 23, 2020, IPC:C01B32 / 174,B82B3 / 00,B82B1 / 00], but are not limited to the examples provided. Methods for functionalizing carbon nanotubes are outside the scope of this invention.

[0038] In certain embodiments of the method, the best technical results are achieved when the suspension (S) contains more than 0.01% by weight and less than 5% by weight of carbon nanotubes in water. The suspension may also contain, but is not limited to, a dispersant or a surfactant used to prepare the suspension, including, but not limited to, Na-carboxymethylcellulose.

[0039] In other embodiments of this method, the best technical results are achieved when the suspension (S) contains more than 0.01% to less than 5% by weight of carbon nanotubes in a polar organic solvent having a bipolar moment greater than 1.5D. From the standpoint of compatibility with existing manufacturing processes for lithium-ion batteries, the most preferred polar organic solvent for suspending carbon nanotubes is n-methylpyrrolidone (NMP). However, the main technical results can also be achieved when using a carbon nanotube suspension in another polar organic solvent, including but not limited to dimethylacetamide or dimethyl sulfoxide. The suspension in the polar organic solvent may further contain a dispersant or a surfactant used for suspension preparation, including but not limited to polyvinylpyrrolidone or polyvinylidene fluoride.

[0040] This invention relates to a silicon phase or silicon oxide (SiO x A silicon phase (where x is a positive number less than or equal to 2) or a silicon phase in which the total atomic ratio of oxygen:silicon content in the negative electrode material is greater than 0 and less than 1.8, and silicon oxide (SiO2) x The present invention also provides a negative electrode slurry containing a dry residue, which includes more than 0.1% to more than 20% carbon nanotubes, characterized in that it is a combination of the phase of ), contains more than 50% to less than 99.9% by weight of an active ingredient, and of all carbon nanotubes in the negative electrode slurry, more than 5% by weight of carbon nanotubes have a bundle length of more than 10 μm, and the mode of the length distribution of the number of carbon nanotube bundles in the negative electrode slurry is less than 5 μm, and is a bundled single-layer and / or double-layer carbon nanotube.

[0041] In some applications, the negative electrode slurry preferably further comprises one or more binding polymer substances selected from the group including polyvinylidene fluoride, carboxymethylcellulose or its Li or Na salt, polyacrylic acid or its Li or Na salt, styrene-butadiene rubber or its latex, fluoroelastomer or its latex. The negative electrode slurry may further comprise one or more dispersants selected from the group including carboxymethylcellulose or its Li or Na salt, polyacrylic acid or its Li or Na salt, or polyvinylpyrrolidone.

[0042] To achieve the best technical results, in some applications, the negative electrode slurry may further preferably contain carbon black, graphite, and one or more conductive additives that differ in composition and structure from the carbon nanotubes, including but not limited to metals from groups 8 to 11 of the periodic table (including, but not limited to, iron, nickel, copper, and silver). The metals from groups 8 to 11 of the periodic table may also be introduced into the negative electrode slurry as impurities present in the carbon suspension by the method of fabricating the nanotubes.

[0043] The present invention relates to (1) a silicon phase or silicon oxide (SiO xThe present invention also provides a method for producing a negative electrode for a lithium-ion battery, comprising the steps of: (2) mixing a mixture of the composition (C) in the suspension (S) until a uniform slurry is obtained; (3) coating the obtained slurry onto a current collector; (4) drying the coated slurry to form a negative electrode; and (5) compressing the negative electrode to a required density. The method also provides a series of steps including: (6) introducing a composition (C) comprising a phase of ) (wherein x is a positive number less than or equal to 2), or a combination of such phases, wherein the total atomic ratio of oxygen:silicon content in the combination of phases is greater than 0 to less than 1.8, into a liquid suspension (S) containing 0.01% to 5% by weight of carbon nanotubes, wherein more than 5% by weight of all carbon nanotubes in the suspension (S) are bundled single-layer and / or double-layer carbon nanotubes having a bundle length of more than 10 μm, and the mode of the hydrodynamic diameter distribution of the number of bundles of carbon nanotubes in the suspension (S) is less than 500 nm; (6) mixing the mixture of the composition (C) in the suspension (S) until a uniform slurry is obtained; (7) coating the obtained slurry onto a current collector; (8) drying the coated slurry to form a negative electrode; and (9) compressing the negative electrode to a required density.

[0044] The present invention also provides a method for producing a negative electrode for a lithium-ion battery, comprising a series of steps: (1) coating a current collector with the negative electrode slurry described above; (2) drying the coated slurry to form a negative electrode; and (3) compressing the negative electrode to a required density.

[0045] The present invention also provides a negative electrode for a lithium-ion battery, characterized in that it is manufactured according to any of the methods described above.

[0046] This invention relates to a silicon phase or silicon oxide (SiO x、 In the formula, x is a positive number less than or equal to 2. The silicon phase or negative electrode material has a total atomic ratio of oxygen:silicon content greater than 0 and less than 1.8, and silicon oxide (SiO2 xThe present invention also provides a negative electrode for a lithium-ion battery, which includes a negative electrode material containing 0.1% to 20% by weight of carbon nanotubes, characterized in that it contains a high concentration of active ingredients, more than 50% by weight to less than 99.9% by weight, in combination with the phase of ), and more than 5% by weight of carbon nanotubes in the negative electrode material have a bundle length of more than 10 μm, and the mode of the length distribution of the number of carbon nanotube bundles in the negative electrode is less than 5 μm, and is a bundled single-layer and / or double-layer carbon nanotube.

[0047] This invention relates to a silicon phase or silicon oxide (SiO x A silicon phase (where x is a positive number less than or equal to 2) or a silicon phase in which the total atomic ratio of oxygen:silicon content in the negative electrode material is greater than 0 and less than 1.8, and silicon oxide (SiO2) x The present invention also provides a lithium-ion battery containing a negative electrode material comprising 0.1% to 20% by weight of carbon nanotubes, characterized in that it contains a high concentration of active ingredients in combination with the phase of ), and more than 5% by weight of carbon nanotubes in the negative electrode of the lithium-ion battery have a bundle length of more than 10 μm, and the mode of the length distribution of the number of carbon nanotube bundles in the negative electrode of the lithium-ion battery is less than 5 μm, and is a bundled single-layer and / or double-layer carbon nanotube.

[0048] The present invention is illustrated by the accompanying drawings and examples, which are provided for illustrative purposes only and are not intended to limit the possible uses of the invention. For convenience, information on the provided examples is also provided in the table.

[0049] [Table 1]

[0050] (continuation) JPEG0007855520000006.jpg162151 [Brief explanation of the drawing]

[0051] [Figure 1] The X-ray diffraction pattern of composition (C) used in Example 1 is shown. [Figure 2] Micrographs of the suspensions (S) used in Examples 1, 3, and 8 are shown. [Figure 3] Micrographs of the suspensions (S) used in Examples 1, 3, and 8, after the long bundles of nanotubes have been precipitated by centrifugation, are shown. [Figure 4] The DLS data for the hydrodynamic diameter distribution of the number of particles (nanotubes and their bundles) in the suspension (S) used in Examples 1, 3, and 8 (circular), in the suspension (S) used in Example 2 (square), and in the suspension (S) used in Example 9 (triangular) are shown. [Figure 5] This shows the dependence of the specific capacity of the negative electrode in Example 1 on the number of charge-discharge cycles (charging current: 2A / g, discharging current: 1A / g). [Figure 6] The capacity of the lithium-ion battery in Example 1 is shown, relative to the number of charge-discharge cycles (charging current and discharging current: 46mA), with reference to its initial capacity. [Figure 7] A micrograph of the suspension (S) used in Example 2 is shown. [Figure 8] This image shows a micrograph of the suspension (S) used in Example 2, after the long bundles of nanotubes have been precipitated by centrifugation. [Figure 9] This shows the specific capacitance of the negative electrode in Example 2 relative to the number of charge-discharge cycles (charging current: 2A / g, discharging current: 1A / g). [Figure 10] The electron microscope image (TEM) of the dried residue of the suspension used in Example 4 is shown. [Figure 11] The energy dispersion spectrum (EDS) of the dried residue of the suspension used in Example 6 is shown. [Figure 12] A micrograph of the suspension (S) used in Example 7 is shown. [Figure 13]This shows the specific capacitance of the negative electrode in Example 7 relative to the number of charge-discharge cycles (charging current: 2A / g, discharging current: 1A / g). [Figure 14] The capacity of the lithium-ion battery in Example 7 is shown, relative to the number of charge-discharge cycles (charging current and discharging current: 37.5 mA), with reference to its initial capacity. [Figure 15] This shows the specific capacitance of the negative electrode in Example 8 relative to the number of charge-discharge cycles (charging current: 2A / g, discharging current: 1A / g). [Modes for carrying out the invention] [Examples]

[0052] This is a preferred embodiment of the present invention. [Examples]

[0053] A negative electrode slurry was prepared using powder of composition (C), which contains a silicon phase covered with an amorphous carbon layer and a silicon oxide phase. Particle size distribution analysis of composition (C) yielded a median powder particle size of 6.2 μm. Figure 1 shows the X-ray diffraction pattern of this composition. These data indicate that the composition consists of a Si phase with a coherent scattering domain size of 5.0 nm (powder diffraction file 27-1402) and an amorphous SiO2 phase with a coherent scattering domain size of 1.5 nm. x The presence of the phase (the broadest value in the 20-23° region is cristobalite, the diffraction line with the highest intensity for the structure of SiO2) may be suggested. Data on the change in sample weight of composition (C) during temperature-programmed oxidation by oxygen flow while increasing temperature demonstrate that amorphous carbon accounts for 2.6 wt% of the composition (weight loss at 700°C), while oxygen deficiency relative to stoichiometric SiO2 accounts for 14 wt% of the initial weight of composition (C) (weight increase in the range of 200-1400°C). Therefore, the total atomic ratio of oxygen:silicon content in this phase combination is 1.55. The weight ratio of C:Si in composition (C) is 0.048.

[0054] Diameters of 1.2-2.1 nm and average diameter of 1.6 nm (using TEM of the dried residue of the suspension, and further using the absorption band S in the optical absorption spectrum of the suspension) 1-1 A negative electrode slurry was prepared using an aqueous suspension (S) of single-walled carbon nanotubes (SWCNT) Tuball® having a diameter determined from its position. Raman spectroscopy at a wavelength of 532 nm determined the position at 1580 cm⁻¹. -1 A prominent G-band characteristic of single-walled carbon nanotubes is observed, as well as at 1330 cm⁻¹. -1 A prominent D-band characteristic of other allotropic changes in carbon and defects in single-walled carbon nanotubes was observed. The intensity ratio of the G / D band was 75. The SWCNT concentration in the suspension was 0.4% by weight. This suspension also contained 0.6% by weight of Na-carboxymethylcellulose (CMC) as a dispersant.

[0055] The proportion of carbon nanotubes contained in bundles longer than 10 μm was determined by comparing the optical density at 500 nm of the suspension (S) and the suspension after precipitation by centrifugation at 8000 g for 1 hour to remove long bundles. A micrograph of the suspension placed between glass panes is shown in Figure 2. The micrograph clearly shows long bundles of carbon nanotubes with a maximum thickness of 2 μm and a length of 10-50 μm. To determine the optical density, the suspension was diluted with water to a concentration of 0.001 wt% SWCNTs (400-fold dilution). Before precipitation, the suspension was diluted with water to a concentration of 0.01 wt% SWCNTs (40-fold dilution). A micrograph of the suspension after precipitation by centrifugation is shown in Figure 3. The micrograph shows the absence of long bundles of carbon nanotubes. At an optical path length of 10 mm, the optical density of the 400-fold diluted suspension (SWCNTs) is 0.56. This corresponds to an SWCNT concentration of 0.38 wt% in the suspension (S). The optical density of the suspension (S) obtained by diluting it 40-fold, precipitating it, and then diluting it further 10-fold is 0.45. This corresponds to a SWCNT concentration of 0.31 wt% in the suspension (S). Therefore, the proportion of carbon nanotubes in long bundles of carbon nanotubes having a length greater than 10 μm is 19 wt% of the total amount of carbon nanotubes in the suspension.

[0056] The size distribution of carbon nanotube bundles was determined by subjecting a suspension (S) diluted to a SWCNT concentration of 0.001 wt% to dynamic light scattering (DLS). Figure 4 shows the hydrodynamic diameter distribution of the number of particles (nanotubes and their bundles) in the suspension (S), obtained by DLS using a Malvern Zetasizer ZS instrument, as a curve marked with circular markers. Based on the data in Figure 4, the size distribution of nanotube bundles is bimodal, with hydrodynamic diameters in the ranges of 100–700 nm and 4–6 μm. The second mode of the distribution corresponds to nanotube bundles with lengths greater than 10 μm. The weight fraction of these nanotube bundles was determined to be approximately 19 wt%, as explained above. The first maximum mode definitely corresponds to bundles with lengths less than 7 μm (less than 10 × 700 nm). This maximum is explained by a log-normal distribution of the hydrodynamic diameter of the number of bundles, with a mode at Dhm = 400 nm. According to inequality (4), this is 2 μm <L m This means <4μm.

[0057] 75g of suspension (S) 150cm 3 The mixture was placed in a beaker, followed by the addition of 9 g of composition (C). The mixture was then mixed for 2 hours using an overhead stirrer equipped with a disc impeller at an impeller rotation speed of 2000 rpm. Subsequently, 1.25 g of 20% by weight butadiene styrene latex was added, and the mixture was further mixed for another 15 minutes under the same conditions to obtain a homogeneous anode slurry. The dried residue of the obtained anode slurry contained 90% by weight of the active ingredient, 3% by weight of carbon nanotubes, 4.5% by weight of CMC, and 2.5% by weight of butadiene styrene rubber. In the obtained slurry, 19% by weight of carbon nanotubes were bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes were distributed in a bimodal pattern depending on their length, with a higher intensity mode at a length of 4 μm.

[0058] To fabricate the negative electrode, the obtained negative electrode slurry was coated onto copper foil using a doctor blade, dried at 40°C for 1 hour, and compacted using a calender with a force of 5 tons, resulting in a density of 1.2 g / cm³ of negative electrode material. 3 The load of the active material on the negative electrode was set to 2.2 mg / cm³. 2 It is 17.5 cm from the foil containing the negative electrode material. 2 The negative electrode was cut and nickel leads were welded to it. No carbon nanotubes were introduced into the negative electrode except for those introduced into the negative electrode slurry. Therefore, 19% by weight of carbon nanotubes in the negative electrode are bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes are distributed in a bimodal pattern depending on their length, with a more intense distribution mode at bundle lengths less than 4 μm.

[0059] To determine the negative electrode characteristics, a cell was assembled containing a Li positive electrode, a Li reference electrode, and an electrolyte using 1 M LiPF6 in a solvent mixture of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate in a volume ratio of 1:1:1 with 5 v / v% vinyl carbonate added. The initial specific capacity of the negative electrode material at a charging current of 2 A / g is 1296 mAh / g. Figure 5 shows the specific capacity against the number of charge-discharge cycles (charging current: 2 A / g, discharge current: 1 A / g). The negative electrode maintains its specific capacity (1318 mAh / g) during the first 50 cycles. After 500 cycles, the specific capacity of the negative electrode is 1050 mAh / g, which is more than 80% of the initial specific capacity.

[0060] The fabricated negative electrode, and 16 mg / cm³ 2A lithium-ion battery was assembled from a positive electrode containing nickel-manganese-cobalt oxide (NCM), an active material with an atomic ratio of Ni:Co:Mn of 6:2:2 under load. A 10 μm lithium foil was placed as the negative electrode to increase the Coulomb efficiency in the initial cycle. A 25 μm thick polypropylene separator was used. A 1 M LiPF6 solution was used as the electrolyte in a solvent mixture with a volume ratio of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate = 1:1:1, with 5 v / v% vinyl carbonate added. At a discharge current of 0.1 C, the initial capacity of this battery was 46.5 mAh. The dependence of the capacity on the number of charge-discharge cycles (charge current: 46 mA, discharge current: 46 mA) is shown in Figure 6. The battery did not lose its capacity (99.6%) during the first 50 cycles. After 500 cycles, the battery capacity was 39 mAh. This means it is more than 83.5% of the initial capacity. [Examples]

[0061] A negative electrode slurry was prepared using the powder of composition (C) in the same manner as in Example 1. Using the dispersant BYK-LP N24710, a negative electrode slurry was prepared using a suspension (S) of single-walled carbon nanotubes (SWCNTs) Tuball® in n-methylpyrrolidone. The SWCNT diameter was distributed in the range of 1.2 to 2.1 nm with an average diameter of 1.49 nm (TEM was used for the dried residue of the suspension, and the absorption band S in the optical absorption spectrum of the suspension was also examined). 1-1 (The diameter was determined from the position.) Raman spectroscopy at a wavelength of 532 nm determined that 1580 cm⁻¹ -1 A prominent G-band characteristic of single-walled carbon nanotubes is observed, as well as at 1330 cm⁻¹. -1 A prominent D-band characteristic of other allotropic changes in carbon and defects in single-walled carbon nanotubes was observed. The intensity ratio of the G / D band was 64. The concentration of SWCNTs in the suspension was 0.4 wt%. The concentration of the dispersant BYK-LP N24710 was 0.8 wt%.

[0062] The proportion of carbon nanotubes contained in bundles longer than 10 μm was determined by comparing the optical density at 500 nm of the suspension (S) and the suspension after precipitation by centrifugation at 8000 g for 1 hour to remove long bundles. A micrograph of the suspension placed between glass is shown in Figure 7. The micrograph clearly shows long bundles of carbon nanotubes with a maximum thickness of 2 μm and a length of 10-50 μm. To determine the optical density, the suspension was diluted with n-methylpyrrolidone to a SWCNT concentration of 0.001 wt% (400-fold dilution). Before precipitation, the suspension was diluted with n-methylpyrrolidone to a SWCNT concentration of 0.01 wt% (40-fold dilution). A micrograph of the suspension after precipitation by centrifugation is shown in Figure 8. The micrograph shows the absence of long bundles of carbon nanotubes. The optical density of the 400-fold diluted suspension (SWCNT) in a 10 mm thick cuvette is 0.56. This corresponds to the SWCNT concentration of a 0.38 wt% suspension (S). The optical density of the suspension (S) after being diluted 40-fold, precipitated, and then further diluted 10-fold is 0.30. This corresponds to the SWCNT concentration of a 0.21 wt% suspension (S). Therefore, the proportion of carbon nanotubes in long bundles of carbon nanotubes with a length greater than 10 μm is approximately 54 wt% of the total amount of carbon nanotubes in the suspension.

[0063] The size distribution of carbon nanotube bundles was determined by subjecting a 400-fold diluted suspension (S) to dynamic light scattering (DLS). Figure 4 shows the hydrodynamic diameter distribution of particles (nanotubes and their bundles) in the suspension (S), obtained by DLS using a Malvern Zetasizer ZS instrument, as indicated by a curve marked with square markers. Based on the data in Figure 4, the size distribution of nanotube bundles is bimodal, with hydrodynamic diameters in the ranges of 100-700 nm and 4-8 μm. The second mode of the distribution corresponds to nanotube bundles with lengths greater than 10 μm. The weight fraction of these nanotube bundles was determined to be approximately 54 wt%, as described above. The first mode definitely corresponds to bundles with lengths less than 8 μm (less than 10 × 800 nm). This maximum value is D hm This is explained by a log-normal distribution of the number of hydrodynamic diameters of the bundles, with a mode at =370 nm. According to inequality (4), this is 2.25 μm <L m This means <3.7μm.

[0064] 400 g of NMP suspension (S) was placed in an 800 mL glass beaker, 47.7 g of composition (C) was added, and the mixture was stirred for 30 minutes at an impeller rotation speed of 2000 rpm using an overhead stirrer equipped with a disc impeller. For a further 2 hours, 0.53 g of polyvinylidene fluoride was added while stirring under the same conditions to obtain a homogeneous anode slurry. The dried residue of the obtained anode slurry contained 90 wt% active ingredient, 3 wt% carbon nanotubes, 6 wt% dispersant BYK-LP N24710, and 1 wt% polyvinylidene fluoride. In the obtained slurry, 60 wt% of carbon nanotubes were bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes were distributed in a bimodal pattern depending on their length, with stronger modes occurring at lengths less than 3.7 μm.

[0065] To fabricate the negative electrode, the obtained negative electrode slurry was coated onto copper foil using a doctor blade, dried at 110°C for 1 hour, and compacted using a calender with a force of 5 tons, resulting in a density of 1.3 g / cm³ of negative electrode material. 3 The load of the active material on the negative electrode was set to 2.4 mg / cm³. 2 It is 17.5 cm from the foil containing the negative electrode material. 2 The negative electrode was cut and nickel leads were welded to it. No carbon nanotubes were introduced into the negative electrode except for those introduced into the negative electrode slurry. Therefore, 54 wt% of the carbon nanotubes in the negative electrode are bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes are distributed in a bimodal pattern depending on their length, with a more intense distribution mode at bundle lengths less than 3.7 μm.

[0066] To determine the negative electrode characteristics, a cell was assembled containing a Li positive electrode, a Li reference electrode, and an electrolyte using a 1M LiPF6 solution in a solvent mixture with a volume ratio of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate = 1:1:1, with 5v / v% vinyl carbonate added. The initial specific capacity of the negative electrode material at a charging current of 2A / g is 1079mAh / g. Figure 9 shows the specific capacity as a percentage of the number of charge-discharge cycles (charging current: 2A / g, discharge current: 1A / g). The negative electrode maintains its specific capacity (1116mAh / g) during the first 50 cycles. After 500 cycles, the specific capacity of the negative electrode is 868mAh / g, which is more than 80% of the initial specific capacity. [Examples]

[0067] A negative electrode slurry was prepared in the same manner as in Example 1. However, as composition (C), dispersed silicon powder with a CSR dimension of 60 nm and a median weight distribution of powder particle size of 2.5 μm was used, and this composition (C) was introduced into the suspension along with a solvent, water, and a Na-carboxymethylcellulose dispersant. Before introduction into the suspension (S), composition (C) was moistened with a Na-carboxymethylcellulose solution to prevent fine silicon dust from entering the air at the work site. Based on data regarding the change in sample weight of composition (C) during the process of temperature-programmed oxidation by oxygen flow while increasing the temperature, the silicon powder used is partially oxidized and contains X-ray amorphous silicon oxide. The oxygen deficiency relative to the stoichiometric SiO2 is 10.4% by weight of the initial weight of composition (C) (weight increase in the temperature range of 200-1400°C). Therefore, the total atomic ratio of oxygen:silicon content in this phase combination is 0.09.

[0068] 2.0 g of powder (C), pre-moistened with 10 g of a 0.1 wt% sodium-carboxymethylcellulose aqueous solution, was introduced into 30 g of suspension (S) and mixed until a uniform slurry was obtained. The dried residue of the resulting negative electrode slurry contained 86.3 wt% active ingredient, 8.3 wt% sodium-carboxymethylcellulose, and 5.3 wt% carbon nanotubes. In the resulting slurry, 19 wt% of carbon nanotubes were bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes were distributed in a bimodal pattern depending on the bundle length, with a more intense mode at a hydrodynamic diameter of 400 nm.

[0069] A negative electrode was fabricated from the obtained negative electrode slurry, similar to Example 1. The initial specific capacity of the negative electrode material with a charging current of 2 A / g was 1160 mAh / g. After 50 charge-discharge cycles (charging current: 2 A / g, discharge current: 1 A / g), the specific capacity of the negative electrode was 1115 mAh / g. After 500 cycles, the specific capacity of the negative electrode was 970 mAh / g. This is equivalent to more than 83% of the initial specific capacity. 19 wt% of the carbon nanotubes in the negative electrode are bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes are distributed in a bimodal pattern depending on their length, with a more intense distribution mode at bundle lengths less than 4 μm.

[0070] A lithium-ion battery was manufactured using the fabricated negative electrode, similar to Example 1. At a discharge current of 0.1C, the initial capacity of this battery was 44.8mAh. During the first 50 charge-discharge cycles (charge current: 45mA, discharge current: 45mA), the battery did not lose any capacity (99.0%). After 500 cycles, the battery capacity was 37mAh, which is more than 82.5% of the initial capacity. [Examples]

[0071] A negative electrode slurry was prepared in the same manner as in Example 1. However, as the suspension (S), an aqueous suspension of a mixture of single-walled and double-walled carbon nanotubes having diameters of 1.2 to 2.8 nm and an average diameter of 1.8 nm (the diameter was determined from the band position of the breathing mode in the Raman spectrum using TEM of the dried residue of the suspension) was used. After the step of introducing composition (C) into the suspension (S), styrene-butadiene rubber latex was added to the mixture, and the resulting mixture was mixed to obtain a homogeneous slurry. The intensity ratio of the G / D bands in the Raman spectrum is 34. The presence of double-walled carbon nanotubes bundled together with single-walled carbon nanotubes is confirmed by the electron microscope image shown in Figure 10. The concentration of carbon nanotubes in the aqueous suspension (S) is 0.05% by weight. This suspension also contains 0.1% by weight of Li-carboxymethylcellulose (Li-CMC) as a dispersant.

[0072] In long bundles of carbon nanotubes exceeding 10 μm in length, the proportion of carbon nanotubes is 12 wt% of the total amount of carbon nanotubes in the suspension. Based on DLS data, the nanotube bundles exhibit a bimodal distribution with hydrodynamic diameter modes at 360 nm and approximately 6 μm (the second peak is very weak).

[0073] 2.0 g of composition (C) and 0.3 g of 20% by weight butadiene styrene rubber latex were simultaneously added to 30 g of suspension (S) and mixed until a uniform slurry was obtained. The dried residue of the resulting negative electrode slurry contained 94.9% by weight of the active ingredient, 2.9% of carbon nanotube styrene butadiene rubber, 1.47% of Li-carboxymethylcellulose, and 0.73% by weight of carbon nanotubes. In the resulting slurry, 12% by weight of carbon nanotubes were bundled single-walled and double-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled and double-walled carbon nanotubes were distributed in a bimodal pattern depending on the bundle length, with a higher intensity mode at a length of 3.6 μm.

[0074] A negative electrode was fabricated from the obtained negative electrode slurry, similar to Example 1. The initial specific capacity of the negative electrode material at a charging current of 2 A / g was 1481 mAh / g. After 50 charge-discharge cycles (charging current: 2 A / g, discharge current: 1 A / g), the specific capacity of the negative electrode was 1284 mAh / g. After 500 cycles, the specific capacity of the negative electrode was 1193 mAh / g. This is less than 80% of the initial specific capacity. The 12 wt% carbon nanotubes in the negative electrode are bundled single-walled and double-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled and double-walled carbon nanotubes are distributed in a bimodal pattern depending on the bundle length, with a more intense distribution mode at a length of 3.6 μm. [Examples]

[0075] A negative electrode slurry was prepared in the same manner as in Example 2. However, a suspension of a mixture of single-walled and multi-walled carbon nanotubes in n-methylpyrrolidone (NMP) was used as the suspension (S). Simultaneously with the introduction of composition (C) into the suspension (S), an NMP solution of the Li salt of polyacrylic acid was added, and the resulting mixture was mixed to obtain a homogeneous slurry. The concentration of single-walled carbon nanotubes in the suspension (S) was 0.4% by weight, and the concentration of multi-walled carbon nanotubes was 3.0% by weight. The average diameter of the single-walled carbon nanotubes was 1.6 nm, and the average diameter of the multi-walled carbon nanotubes was 10 nm (TEM was used on the dried residue of the suspension, and for single-walled carbon nanotubes, the diameter was also determined from the position of the radial breathing mode (RBM) in the Raman spectrum). The intensity ratio of the G / D bands in the Raman spectrum of the dried residue of the suspension was 7. The suspension also contained 1.0% by weight of polyvinylpyrrolidone (PVP) as a dispersant.

[0076] The proportion of single-walled carbon nanotubes in long bundles of carbon nanotubes with a length greater than 10 μm, determined by comparing the optical density at 500 nm between the suspension (S) and the suspension after sedimentation to remove long bundles by centrifugation, is 6 wt% of the total amount of carbon nanotubes in the suspension. Based on DLS data, the particles in the suspension have a broad, asymmetric, unimodal distribution in the mode at a hydrodynamic diameter of 300 nm.

[0077] 7.0 g of composition (C) and 10.0 g of an NMP solution of 3 wt% polyacrylic acid Li salt (Li-PA) were simultaneously added to 30 g of suspension (S), and the mixture was mixed to obtain a homogeneous slurry. The dried residue of the obtained anode slurry contained 80.8 wt% of the active ingredient and 12.1 wt% of carbon nanotubes. In the obtained slurry, 6 wt% of the carbon nanotubes were bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The carbon nanotube bundles in the anode slurry were distributed by length, with some having bundle lengths of less than 3 μm.

[0078] A negative electrode was fabricated from the obtained negative electrode slurry, similar to Example 2. The initial specific capacity of the negative electrode material at a charging current of 2 A / g was 963 mAh / g. After 50 charge-discharge cycles (charging current: 2 A / g, discharge current: 1 A / g), the specific capacity of the negative electrode was 928 mAh / g. After 500 cycles, the specific capacity of the negative electrode was 795 mAh / g. This is less than 82% of the initial specific capacity. The 6 wt% carbon nanotubes in the negative electrode are bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The carbon nanotube bundles in the negative electrode are distributed by length, with modes having bundle lengths less than 3 μm. [Examples]

[0079] A negative electrode slurry was prepared in the same manner as in Example 2. However, a dimethylacetamide (DMAA) suspension of single-walled carbon nanotubes having surfaces containing chlorine-containing and oxygen-containing functional groups was used as the suspension (S). After introducing composition (C) into the suspension (S), the dispersant polyvinylpyrrolidone was added to the resulting mixture, and the resulting mixture was then mixed to obtain a homogeneous slurry. The suspension contains 0.6 wt% single-walled carbon nanotubes in n-methylpyrrolidone. Elemental analysis by energy dispersive spectroscopy (EDS) revealed that the dried residue of the suspension contains 97.1 wt% carbon, 2.2 wt% oxygen, 0.27 wt% iron, and 0.47 wt% chlorine. The EDS spectra of the modified material are shown in Figure 11. Therefore, the surfaces of the carbon nanotubes in the suspension (S) contain more than 0.47 wt% chlorine-containing functional groups and more than 2.2 wt% oxygen-containing functional groups.

[0080] According to Raman spectroscopy results at a wavelength of 532 nm, the integrated intensity ratio of the G mode to the D mode is 97. The single-walled carbon nanotubes have an average diameter of 1.6 nm and are distributed in a diameter range of 1.2 to 2.8 nm (the diameter was determined using TEM of the dried residue of the suspension, and further determined from the band position of the breathing mode in the Raman spectrum).

[0081] The proportion of carbon nanotubes in long bundles of carbon nanotubes with a length greater than 10 μm, determined by comparing the optical density at 500 nm between the suspension (S) and the suspension after sedimentation to remove long bundles by centrifugation, is 28 wt% of the total amount of carbon nanotubes in the suspension. Based on DLS data, the carbon nanotube bundles are distributed in a bimodal pattern based on their hydrodynamic diameter, with a 420 nm mode (higher intensity mode) and a 6.5 μm mode (lower intensity mode).

[0082] 2.0 g of composition (C) was added to 30 g of suspension (S) and mixed, and then 1.5 g of a DMAA solution of 5% by weight of polyvinylpyrrolidone was added to the mixture and mixed until a homogeneous slurry was obtained. The dried residue of the resulting anode slurry contained 88.4% by weight of the active ingredient, 3.4% by weight of polyvinylpyrrolidone, and 8.2% by weight of single-walled carbon nanotubes. In the resulting slurry, 28% by weight of carbon nanotubes were bundled single-walled carbon nanotubes with bundle lengths greater than 10 μm. The bundles of single-walled carbon nanotubes in the anode slurry were distributed in a bimodal pattern depending on their length, with a higher intensity mode at lengths less than 4.2 μm.

[0083] A negative electrode was fabricated from the obtained negative electrode slurry, similar to Example 2. The initial specific capacity of the negative electrode material at a charging current of 2 A / g was 1122 mAh / g. After 50 charge-discharge cycles (charging current: 2 A / g, discharge current: 1 A / g), the specific capacity of the negative electrode was 1081 mAh / g. After 500 cycles, the specific capacity of the negative electrode was 931 mAh / g. This is less than 83% of the initial specific capacity. In the obtained slurry, 28 wt% of carbon nanotubes were bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes in the negative electrode were distributed in a bimodal pattern depending on their length, with stronger modes at lengths less than 4.2 μm. [Examples]

[0084] A negative electrode slurry was prepared in the same manner as in Example 2. However, a suspension of n-methylpyrrolidone containing 0.25 wt% fluorine-modified single-walled carbon nanotubes was used as suspension (S). After mixing (S) with composition (C), polyvinylidene fluoride (PVDF) powder was added to the mixture. The single-walled carbon nanotubes in the suspension were modified with fluorine. Based on TEM data, the carbon nanotubes in the suspension are single-walled with an average diameter of 1.5 nm. This corresponds to the absorption band S in the optical absorption spectrum. 1-1 This is also confirmed by positional data. Based on X-ray photoemission spectroscopy (XPS) data, the weight fraction of fluorine in the carbon nanotube is 14%, the weight fraction of oxygen is 7%, and the remainder is carbon. The G / D ratio of the Raman spectrum at a wavelength of 532 nm is 2.4. A very low G / D value also indicates that the surface of the SWCNT containing fluorine-containing functional groups is highly functionalized.

[0085] A micrograph of the suspension (S) is provided in Figure 12. The proportion of carbon nanotubes in long bundles of carbon nanotubes with a length greater than 10 μm, determined by comparing the optical density at a wavelength of 500 nm between the suspension (S) and the suspension after sedimentation to remove long bundles by centrifugation, is 9 wt% of the total amount of carbon nanotubes in the suspension. Based on DLS data, the carbon nanotube bundles are distributed in a bimodal pattern based on their hydrodynamic diameter at 370 nm (higher intensity mode) and 4.8 μm (lower intensity mode).

[0086] 30g of suspension (S) to 100cm 3The mixture was placed in a beaker, followed by the addition of 2.375 g of composition (C). The mixture was then mixed for 0.5 hours using an overhead stirrer equipped with a disc impeller at an impeller rotation speed of 2000 rpm. Subsequently, 50 mg of polyvinylidene fluoride powder was added, and the mixture was further mixed under the same conditions for a total of 2 hours until a uniform slurry was obtained. The dried residue of the resulting negative electrode slurry contained 95% by weight of the active ingredient, 3% by weight of carbon nanotubes, and 2% by weight of polyvinylidene fluoride. In the resulting slurry, 9% by weight of carbon nanotubes were bundled single-walled carbon nanotubes with bundle lengths greater than 10 μm. The bundles of single-walled carbon nanotubes were distributed in a bimodal pattern depending on the bundle length, with weaker modes at bundle lengths less than 3.7 μm.

[0087] A negative electrode was prepared from the obtained negative electrode slurry, similar to Example 2. The active material load on the negative electrode was 2.4 mg / cm³. 2 It is 17.5 cm from the foil containing the negative electrode material. 2 The negative electrode was cut and nickel leads were welded to it. No carbon nanotubes were introduced to the negative electrode except for those introduced into the negative electrode slurry. Therefore, 9% by weight of carbon nanotubes in the obtained slurry are bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes are distributed in a bimodal pattern depending on the bundle length, with weaker modes at bundle lengths less than 3.7 μm.

[0088] To determine the negative electrode characteristics, a cell was assembled containing a Li positive electrode, a Li reference electrode, and an electrolyte using a 1M LiPF6 solution in a solvent mixture with a volume ratio of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate = 1:1:1, with 5v / v% fluoroethylene carbonate added. The initial specific capacity of the negative electrode material at a charging current of 2A / g is 1257mAh / g. Figure 13 shows the specific capacity against the number of charge-discharge cycles (charging current: 2A / g, discharge current: 1A / g). During the first 50 cycles, the specific capacity of the negative electrode increased from 1257mAh / g to 1302mAh / g. After 500 cycles, the specific capacity of the negative electrode is 1117mAh / g, which is less than 88% of the initial specific capacity.

[0089] 14 mg / cm³ 2 A lithium-ion battery was assembled from the obtained negative electrode and a positive electrode having lithium ferrous phosphate (LFP, LiFePO4) as the active materials for the load. A 10 μm lithium foil was placed on the negative electrode to increase the Coulomb efficiency in the initial cycle. A 25 μm thick polypropylene separator was used. A 1 M LiPF6 solution was used as the electrolyte in a solvent mixture with a volume ratio of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate = 1:1:1, with 5 v / v% fluoroethylene carbonate added. At a discharge current of 0.1 C, the initial capacity of this battery was 37.5 mAh. The capacity, referenced to the initial capacity as a percentage of the number of charge-discharge cycles (charge current and discharge current: 37.5 mA), is shown in Figure 14. During the first 200 cycles, the battery increased its capacity somewhat. After 500 cycles, the battery capacity is 37.5 mAh, which is 100% of the initial capacity. [Examples]

[0090] A negative electrode slurry was prepared in the same manner as in Example 1. However, after adding composition (C) to the suspension (S) and mixing, graphite was added and mixed. Styrene butadiene latex was further added and then mixed until a homogeneous slurry was obtained.

[0091] 225g of suspension (S) to 400cm 3The mixture was placed in a beaker, then 13.5 g of composition (C) was added, and the mixture was stirred for 0.5 hours using an overhead stirrer equipped with a disc impeller at an impeller rotation speed of 2000 rpm. Subsequently, 3 m 2 13.5 g of graphite having a BET ratio surface of 1 / g was added and mixed for 2 hours, followed by the addition of 3.5 g of 20 wt% styrene-butadiene latex, and the mixture was further mixed for 2 hours under the same conditions until a homogeneous slurry was obtained. The dried residue of the resulting negative electrode slurry contained 50.1 wt% composition (C), 3 wt% carbon nanotubes, 40 wt% graphite, 4.5 wt% carboxymethylcellulose, and 2.3 wt% styrene-butadiene rubber. In the resulting slurry, 19 wt% of carbon nanotubes were bundled single-walled carbon nanotubes with bundle lengths greater than 10 μm. The bundles of single-walled carbon nanotubes were bimodally distributed by length, with higher intensity modes at lengths less than 4 μm.

[0092] To fabricate the negative electrode, the obtained negative electrode slurry was coated onto copper foil using a doctor blade, dried at 50°C for 1 hour, and compacted using a calender with a force of 7 tons, resulting in a density of 1.4 g / cm³ of negative electrode material. 3 The load of active material on the negative electrode was set to 3.2 mg / cm³. 2 It is 17.5 cm from the foil containing the negative electrode material. 2 The negative electrode was cut and nickel leads were welded to it. No carbon nanotubes were introduced into the negative electrode except for those introduced into the negative electrode slurry. Therefore, 19% by weight of carbon nanotubes in the negative electrode are bundled single-walled carbon nanotubes with bundle lengths exceeding 10 μm. The bundles of single-walled carbon nanotubes in the negative electrode are distributed in a bimodal pattern depending on their length, with stronger modes occurring at lengths less than 4 μm.

[0093] To determine the negative electrode characteristics, a cell was assembled containing a Li positive electrode, a Li reference electrode, and an electrolyte using a 1M LiPF6 solution in a solvent mixture with a volume ratio of propylene carbonate:ethylmethyl carbonate:dimethyl carbonate = 1:1:1, with 3v / v% vinyl carbonate added. The initial specific capacity of the negative electrode material at a charging current of 2A / g is 634mAh / g. Figure 15 shows the specific capacity against the number of charge-discharge cycles (charging current: 2A / g, discharge current: 1A / g). During the first 300 cycles, the specific capacity of this negative electrode increased to a maximum of 670-690mAh / g. After 500 cycles, the specific capacity of the negative electrode is 581mAh / g, which is less than 91% of the initial specific capacity. [Examples]

[0094] (Comparative example) A negative electrode slurry was prepared in the same manner as in Example 1. However, an aqueous suspension (S) of single-walled carbon nanotubes (SWCNT) Tuball® that contained almost no long bundles of single-walled carbon nanotubes with a length greater than 10 μm was used. Optical microscopy data showed that no significant amount of such bundles were present and did not show any fibrous particles visible under an optical microscope. Similarly, DLS data did not show any particles with a hydrodynamic diameter greater than 800 nm. This means that, based on the DLS data, a bimodal particle distribution with modes in the hydrodynamic diameter range of approximately 90 nm to 380 nm was observed in the suspension, with the lower intensity modes possibly corresponding to individual carbon nanotubes and very thin bundles. On the other hand, the second mode corresponds to bundles of carbon nanotubes with a length of less than 6 μm. Among the length distribution of carbon nanotube bundles, the larger modes were less than 3.8 μm. The DLS curve of the suspension (S) is provided in Figure 1, with the curve marked with a triangle.

[0095] The proportion of carbon nanotubes contained in bundles longer than 10 μm was determined by comparing the optical density at 500 nm of the suspension (S) and the suspension after precipitation by centrifugation to remove long bundles, as in Example 1. The optical density of the 400-fold diluted suspension (SWCNT) at an optical path length of 10 mm is 0.58. This corresponds to an SWCNT concentration of 0.39 wt% in the suspension (S). The optical density of the 400-fold diluted suspension (S) subjected to precipitation is 0.56. This corresponds to an SWCNT concentration of 0.38 wt% in the suspension (S). Therefore, the proportion of carbon nanotubes in long bundles of carbon nanotubes longer than 10 μm is less than 3 wt% of the total amount of carbon nanotubes in the suspension.

[0096] The G / D band intensity ratio of the dried residue of this suspension (S) is 87. As in Example 1, the SWCNT concentration in the suspension is 0.4% by weight. This suspension also contains 0.6% by weight of Na-carboxymethylcellulose (CMC) as a dispersant.

[0097] As in Example 1, the dried residue of the obtained negative electrode slurry contains 90% by weight of the active ingredient, 3% by weight of carbon nanotubes, 4.5% by weight of Na-CMC, and 2.5% by weight of butadiene styrene rubber.

[0098] The procedure for manufacturing the negative electrode and assembling the cell for this test was the same as in Example 1. The initial specific capacity of the negative electrode material at a charging current of 2 A / g was 1241 mAh / g. This is very close to the negative electrode capacity obtained in Example 1. However, after 50 cycles (charging current: 2 A / g, discharge current: 1 A / g), the specific capacity of the negative electrode decreased to 1056 mAh / g. After 500 cycles, the specific capacity of the negative electrode was 712 mAh / g. This is less than 58% of the initial specific capacity. Therefore, the absence of long bundles of carbon nanotubes in the suspension (S) negatively affects the number of cycles the negative electrode can continue to operate for until it loses 20% of its initial capacity. The presence of bundles of carbon nanotubes longer than 10 μM in the suspension (S) is necessary to achieve the claimed technical results. [Industrial applicability]

[0099] The present invention can be used in the electrical technology industry, more specifically in lithium-ion batteries, the manufacture of lithium-ion batteries equipped with a silicon-containing anode, and the manufacture of anodes for lithium-ion batteries. List of References

[0100] List of cited references Patent Documents

[0101] Patent Document 1: U.S. Patent No. 8,263,265

[0102] Patent Document 2: U.S. Patent No. 8,617,746

[0103] Patent Document 3: Specification of European Patent No. 2755263

[0104] Patent Document 4: U.S. Patent No. 8,697,286

[0105] Patent Document 5: Specification of Russian Patent Application Publication No. 2717516 Non-patent literature

[0106] Non-Patent Document 1: N. Nair, W. Kim, R. D. Braatz, M. S. Strano, “Dynamics of Surfactant-Suspended single-walled Carbon Nanotubes in a Centrifugal Field” Langmuir, 2008, Vol. 24, pp. 1790-1795, doi:10.1021 / la702516u

[0107] Non-Patent Document 2: J. Gigault, I. Le He´cho, S. Dubascoux, M. Potin-Gautier, G. Lespes Single-walled carbon nanotube length determination by asymmetrical-flow field-flow fractionation hyphenated to multi-angle laser-light scattering. J. Chromatogr. A, 2010, Vol. 1217, pp. 7891-7897

Claims

1. A method for preparing a negative electrode slurry for lithium-ion batteries, wherein the drying material for the negative electrode slurry is a silicon phase or silicon oxide (SiO ｘ A phase of silicon (wherein x is a positive number less than or equal to 2), or a silicon phase in which the total atomic ratio of oxygen:silicon content in the negative electrode material is greater than 0 and less than 1.8, and silicon oxide (SiO ｘ The combination with the phase of ) contains an active ingredient in an amount of more than 50% to less than 99.9% by weight, and also contains carbon nanotubes in an amount of more than 0.1% to less than 20% by weight, and the method is (1) The silicon phase or the silicon oxide (SiO ｘ A step of introducing a composition (C) comprising a phase (wherein x is a positive number less than or equal to 2) or a combination of such phases, wherein the total atomic ratio of oxygen:silicon in the combination of phases is greater than 0 to less than 1.8, into a liquid phase suspension (S) containing 0.01% to 5% by weight of carbon nanotubes, wherein more than 5% by weight of all carbon nanotubes in the suspension (S) are bundled single-layer and / or double-layer carbon nanotubes having a bundle length of more than 10 μm, and the mode of the hydrodynamic diameter distribution of the number of bundles of carbon nanotubes in the suspension (S) is less than 500 nm, and (2) A method comprising a series of steps, such as mixing the mixture of composition (C) in the suspension (S) until a uniform slurry is obtained.

2. The method according to claim 1, wherein the hydrodynamic diameter distribution of the number of carbon nanotube bundles in the suspension (S) is bimodal.

3. Silicon and silicon oxide (SiO ｘ The method according to claim 1, wherein the composition (C) containing the aforementioned combination of phases is introduced into the suspension (S) containing carbon nanotubes, and at the same time, graphite and / or binder additives and / or dispersants and / or solvents are introduced.

4. The method according to claim 1, further comprising one or more steps of introducing graphite and / or binder additives and / or dispersants and / or solvents into the suspension (S) containing carbon nanotubes, or into the mixture of the composition (C) in the suspension (S).

5. The method according to claim 1, wherein the silicon and silicon oxide phases in the composition (C) are aggregated into bound aggregates having a diameter with a median distribution of more than 5 μm.

6. The method according to claim 1, wherein the size of the X-ray coherent scattering domains relating to the silicon and silicon oxide phases is less than 10 nm.

7. The method according to claim 1, wherein the surface of the silicon and silicon oxide aggregates is covered with a carbon layer, and the mass ratio of C:Si in the composition (C) is greater than 0.01 and less than 0.

1.

8. The method according to claim 1, wherein the carbon nanotubes in the suspension (S) are characterized by having a G / D band intensity ratio greater than 5 in the Raman spectrum at a wavelength of 532 nm.

9. The method according to claim 8, wherein the carbon nanotubes in the suspension (S) are characterized by having a G / D band intensity ratio of more than 50 in the Raman spectrum at a wavelength of 532 nm.

10. The method according to claim 1, wherein the carbon nanotube in the composite material contains more than 0.1% by weight of a functional group on its surface that includes an element having a higher Pauling electronegativity than carbon.

11. The method according to claim 10, wherein the carbon nanotubes in the suspension (S) contain more than 0.1% by weight of a functional group on their surface, the functional group comprising at least one of the following elements: oxygen, fluorine, or chlorine.

12. The method according to claim 11, wherein the carbon nanotubes in the suspension (S) contain more than 0.1% by weight of carboxyl groups on their surface.

13. The method according to claim 1, wherein the suspension (S) containing 0.01 to 5% by weight of carbon nanotubes is an aqueous suspension or a suspension of a polar organic solvent having a bipolar moment greater than 1.5D.

14. The method according to claim 13, wherein the suspension (S) containing 0.01 to 5% by weight of carbon nanotubes is a suspension of n-methylpyrrolidone.

15. A negative electrode slurry for a lithium-ion battery, (1) An active component comprising a silicon phase or a silicon oxide phase (SiO x, where x is a positive number of 2 or less), or a combination of such phases, wherein the total atomic ratio of oxygen:silicon content in the combination of phases is greater than 0 and less than 1.8, (2) Carbon nanotubes, Of all the carbon nanotubes in the negative electrode slurry, more than 5% by weight of carbon nanotubes have a bundle length of more than 10 μm and are bundled single-layer and / or double-layer carbon nanotubes. The mode of the bundle length distribution of the number of carbon nanotube bundles in the negative electrode slurry is less than 5 μm. The dried material of the negative electrode slurry contains more than 50% by weight and less than 99.9% by weight of the active component. The total atomic ratio of oxygen to silicon content in the dry material of the negative electrode slurry is greater than 0 and less than 1.

8. A negative electrode slurry wherein the dried material of the negative electrode slurry contains 0.1% to less than 20% by weight of carbon nanotubes.

16. The negative electrode slurry according to claim 15, wherein the slurry comprises one or more binding polymer substances selected from polyvinylidene fluoride, styrene butadiene rubber, its latex, carboxymethylcellulose, its sodium salt, its Li salt, polyacrylic acid, its sodium salt, its Li salt, fluoroelastomers and their latex, and / or one or more dispersants selected from carboxymethylcellulose, its sodium salt, its Li salt, polyacrylic acid, its sodium salt, its Li salt, and polyvinylpyrrolidone.

17. The negative electrode slurry according to claim 15, wherein the slurry differs in composition and structure from carbon nanotubes and comprises more than 0.1% by weight of one or more conductive additives selected from carbon black, graphite, and metals of groups 8 to 11 of the periodic table.

18. A method for manufacturing a negative electrode for a lithium-ion battery, (1) A step of introducing a composition (C) containing an active ingredient, which includes a silicon phase or a silicon oxide phase (SiO₂x, where x is a positive number of 2 or less), or a combination of such phases, wherein the total atomic ratio of oxygen to silicon in the combination of phases is greater than 0 to less than 1.8, into a liquid phase suspension (S) containing 0.01% to 5% by weight of carbon nanotubes, wherein more than 5% by weight of all carbon nanotubes in the suspension (S) are bundled single-layer and / or double-layer carbon nanotubes having a bundle length of more than 10 μm, and the mode of the hydrodynamic diameter distribution of the number of bundles of carbon nanotubes in the suspension (S) is less than 500 nm. (2) A step of mixing the mixture of composition (C) in the suspension (S) until a uniform negative electrode slurry is obtained, After step (2), the dried material of the uniform negative electrode slurry contains 50% to less than 99.9% by weight of the active ingredient. The total atomic ratio of oxygen to silicon content in the dry material of the homogeneous negative electrode slurry is greater than 0 and less than 1.

8. The drying material of the homogeneous negative electrode slurry contains more than 0.1% by weight and less than 20% by weight of carbon nanotubes, in the process, (3) A step of coating the homogeneous negative electrode slurry onto the current collector of the lithium-ion battery, (4) A method comprising the steps of drying the coated uniform negative electrode slurry to form the negative electrode of the lithium-ion battery, and (5) compressing the negative electrode.

19. A negative electrode for a lithium-ion battery, (1) Current collector and (2) An active component comprising a silicon phase or a silicon oxide phase (SiO x, where x is a positive number of 2 or less), or a combination of such phases, wherein the total atomic ratio of oxygen:silicon content in the combination of phases is greater than 0 and less than 1.8, (3) Carbon nanotubes, Of all the carbon nanotubes in the negative electrode, more than 5% by weight of the carbon nanotubes have a bundle length of more than 10 μm and are bundled single-layer and / or double-layer carbon nanotubes. The mode of the bundle length distribution of the number of carbon nanotube bundles in the negative electrode is less than 5 μm. The active component constitutes more than 50% by weight and less than 99.9% by weight of the negative electrode, excluding the current collector. The total atomic ratio of oxygen to silicon content in the negative electrode is greater than 0 and less than 1.

8. A negative electrode in which the carbon nanotubes constitute 0.1% to less than 20% by weight of the negative electrode, excluding the current collector.

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