Multi-walled carbon nanotube powder, conductive material dispersion solution containing same, and lithium secondary battery

Abstract

The present invention relates to a multi-walled carbon nanotube powder, a conductive agent dispersion comprising the carbon nanotube powder, and a lithium secondary battery comprising the carbon nanotube powder, in which the particle size distribution (PSD) measured by a particle size analyzer in a dry powder state, the particle size distribution (PSD) of the conductive agent dispersion is greater than the particle size distribution (PSD) of the conductive agent dispersion. The multiwalled carbon nanotube powder has an average particle diameter (D50) at 50% cumulative volume of 10 [mu] m to 20 [mu] m, an average particle diameter (D90) at 90% cumulative volume of 20 [mu] m to 40 [mu] m, a maximum particle diameter (Dmaximum) of 45 [mu] m to 70 [mu] m, and an oxygen atom content of 1.0 at% to 3.0 at% as measured by XPS analysis, in which the viscosity of the dispersion can be reduced by controlling the particle size characteristics in the powder state, and the viscosity of the dispersion can be reduced by controlling the particle size characteristics in the powder state. According to the present invention, excellent dispersibility can be exhibited in an actual electrode, and uniform dispersion in an electrode can improve resistance characteristics and life characteristics of a lithium secondary battery.

Description

Technical Field

[0001] This invention relates to multi-walled carbon nanotube powder with excellent particle size characteristics, conductive agent dispersions containing the same, and lithium secondary batteries containing multi-walled carbon nanotube powder. Background Technology

[0002] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy sources has increased, and as part of this trend, generating and storing electricity using electrochemical reactions is one of the most active research areas.

[0003] Currently, a typical example of an electrochemical device utilizing electrochemical energy is the secondary battery, and its application areas are increasingly expanding. In recent years, with technological advancements and the increasing demand for portable devices (such as laptops, mobile phones, and cameras), the demand for secondary batteries as an energy source has increased significantly. Among these secondary batteries, lithium secondary batteries with high energy density (i.e., high capacity) have received considerable research and have been commercialized and widely used.

[0004] To fabricate batteries with high energy density, it is crucial to use positive electrode active materials with high capacity characteristics. However, the materials contained in the positive electrode can also be a significant factor. Research is underway to maximize the ratio of active materials while minimizing the amounts of conductive agents and binders. However, due to the problem that the increase in battery unit price is significantly greater than the performance improvement when the amount of active material used increases, it is not easily applicable to large-scale practical production.

[0005] Therefore, recent research trends focus on improving price competitiveness while meeting certain or higher energy density requirements.

[0006] Carbon nanotubes (CNTs) are widely used as conductive agents, largely because their superior conductivity and length properties compared to carbon black facilitate the formation of conductive networks. Among carbon nanotubes, single-walled carbon nanotubes (SWCNTs) are particularly advantageous for forming conductive networks; however, their high cost and difficulty in dispersion make them a significant disadvantage in terms of price competitiveness, despite their excellent performance.

[0007] Therefore, the present invention aims to provide a conductive agent that is superior in performance and also competitively priced. Summary of the Invention

[0008] Technical issues

[0009] One aspect of the invention provides a multi-walled carbon nanotube powder that, due to its excellent dispersibility in a dispersion by containing an appropriate amount of oxygen functional groups and having a particle size distribution characterized by a relatively small particle size (where the size and ratio of large particles are small), can have its viscosity controlled to a low level and thus can be uniformly distributed in an electrode due to its excellent dispersibility also in an electrode slurry.

[0010] Another aspect of the invention provides a lithium secondary battery that has improved lifespan and excellent output due to low resistance achieved by using multi-walled carbon nanotubes that are uniformly distributed in the electrodes due to their excellent dispersibility.

[0011] Technical solution

[0012] [1] According to one embodiment, multi-walled carbon nanotube powder is provided, wherein the average particle size (D) at 50% cumulative volume is measured in the particle size distribution (PSD) by a particle size analyzer in the dry powder state. 50 The average particle size (D) at 90% cumulative volume, ranging from 10 μm to 20 μm. 90 The particle size ranges from 20 μm to 40 μm, with a maximum particle size (D). 最大 The atomic size ranges from 45 μm to 70 μm, and the oxygen atom content measured by XPS analysis ranges from 1.0 atomic% to 3.0 atomic%.

[0013] [2] The multi-walled carbon nanotube powder of [1] above, wherein the average particle size (D) at 50% cumulative volume. 50 It can be in the range of 13μm to 19μm.

[0014] [3] The multi-walled carbon nanotube powders of [1] and / or [2] above, wherein the average particle size (D) at 90% of the cumulative volume. 90 It can be in the range of 28 μm to 40 μm.

[0015] [4] Multi-walled carbon nanotube powder of at least one of [1] to [3] above, wherein the maximum particle size (D) 最大 It can be in the range of 54 μm to 70 μm.

[0016] [5] Multi-walled carbon nanotube powder of at least one of [1] to [4] above, wherein the oxygen atom content measured by XPS analysis is in the range of 1.5 atomic% to 2.5 atomic%.

[0017] [6] Multi-walled carbon nanotube powder of at least one of [1] to [5] above, wherein the BET specific surface area can be 150 m² 2 / g to 300 m 2 Within the range of / g.

[0018] [7] According to another embodiment, a conductive agent dispersion is provided, comprising the above-described multi-walled carbon nanotube powder, a dispersant and an organic solvent.

[0019] [8] The conductive agent dispersion of [7] above, wherein 100 parts by weight of the conductive agent dispersion may contain 5 to 60 parts by weight of multi-walled carbon nanotubes and 5 to 60 parts by weight of dispersant.

[0020] [9] The conductive agent dispersions of [7] and / or [8] above, wherein the dispersant may include at least one of the following: polyacrylate, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyvinyl alcohol, polyacrylamide, polyethylene oxide, carboxymethyl cellulose (CMC) and diisopropylamine (DIPA).

[0021]

[10] According to another embodiment, a lithium secondary battery is provided, comprising: a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, the positive electrode comprising a positive current collector and a layer of positive electrode material mixture, the negative electrode comprising a negative current collector and a layer of negative electrode material mixture, wherein at least one of the positive electrode material mixture layer and the negative electrode material mixture layer comprises the aforementioned multi-walled carbon nanotube powder.

[0022]

[11] The lithium secondary battery of

[10] above, wherein the positive electrode material mixture layer may include a positive electrode active material, and the positive electrode active material may include at least one selected from lithium nickel-based oxides and lithium metal phosphate-based compounds.

[0023]

[12] The lithium secondary battery described above

[11] has a positive electrode active material that is a single particle type, and the degree of single particle formation (D) is high. 50 / D 平均 The value ranges from 1 to 10, and the single particle formation degree (D) is... 50 / D 平均 ) is the volumetric cumulative average particle size (D 50 ) and the average particle size of the nodules (D 平均 The ratio of ).

[0024]

[13] The lithium secondary batteries of

[11] and / or

[12] above, wherein the lithium nickel-based oxide may have a composition represented by Formula 1, and the lithium metal phosphate-based compound may have a composition represented by Formula 2.

[0025] [Formula 1]

[0026] Li 1+x Ni a Co b M 1 c M 2d O 2-e X e

[0027] In Formula 1, M 1 includes at least one selected from Mn and Al, M 2 includes at least one selected from W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, X includes at least one selected from N, P, S, F, and Cl, and 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 < b ≤ 0.35, 0 < c ≤ 0.35, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.05, and

[0028] [Formula 2]

[0029] Li 1+x [Fe 1-y M y PO4

[0030] In Formula 2, M includes at least one selected from Mn, Co, Ni, Al, Mg, and Ti, and -0.5 ≤ x ≤ 0.5 and 0 ≤ y < 1.

[0031]

[14] The lithium secondary battery of at least one of

[10] to

[13] above, wherein the negative electrode material mixture layer may include a negative electrode active material, and the negative electrode active material may include at least one selected from a silicon-based active material, a carbon-based active material, and a silicon-carbon composite active material.

[0032] Advantageous Effects

[0033] Due to the excellent dispersibility in the dispersion of the multi-walled carbon nanotubes according to the present invention, which is characterized by having a large number of oxygen functional groups and a particle size distribution with a relatively small particle size (where the size and ratio of large particles are small), the viscosity of the dispersion can be controlled to a low level, and thus it can be uniformly distributed in the electrode due to its excellent dispersibility in the electrode paste.

[0034] Furthermore, it can be expected that the lithium secondary battery according to the present invention has a low resistance due to the use of multi-walled carbon nanotubes uniformly distributed in the electrode due to their excellent dispersibility, and has the effects of improved lifespan and excellent output. Detailed Embodiments

[0035] It will be understood that the words or terms used in the specification and claims should not be construed as having the meanings defined in a common dictionary. It will be further understood that the words or terms should be construed as having meanings consistent with their meanings in the context of the relevant field and technical concept of the present invention, in order that the inventor can appropriately define the words or terms to best illustrate the invention.

[0036] It will be further understood that the terms “comprising,” “including,” or “having” in this specification mean the presence of the stated features, number, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more additional features, number, steps, elements, or combinations thereof.

[0037] In this specification, "specific surface area" is measured by the BET method, wherein, specifically, the specific surface area can be calculated by the amount of nitrogen adsorbed using BELSORP-mino II from BEL Japan at liquid nitrogen temperature (77 K).

[0038] In this invention, the term "single-particle type" refers to a particle consisting of 30 or fewer nodules, wherein the concept of a single-particle type particle includes a single particle consisting of one nodule and a pseudo-single particle as a complex of 2 to 30 nodules.

[0039] "Nodules" are sub-particle units that make up single particles and pseudo-single particles. Nodules can be single crystals without crystal boundaries, or polycrystalline structures in which no crystal boundaries are visible when observed with a scanning electron microscope at 5,000 to 20,000x magnification.

[0040] In this invention, "secondary particle" refers to a particle formed by the aggregation of dozens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of 50 or more primary particles.

[0041] The term "particle" as used in this invention may include any or all of the following: single particle, pseudo-single particle, primary particle, nodule, and secondary particle.

[0042] The "average particle size (D) of nodules" in this invention 平均 The average particle size is obtained after taking pictures of approximately 30 particles, each containing one or more nodules, using a scanning electron microscope (SEM) to photograph the positive electrode active material particles.

[0043] D in this instruction manual 50 D 90 and D 最大 These can be defined as the particle size at 50% and 90% of the cumulative volume, and the maximum particle size, respectively, in the particle size distribution curve of the particles (powder or dispersion). D 50 D 90 and D 最大 For example, this can be measured using laser diffraction. Laser diffraction can typically measure particle sizes ranging from submicrometers to several millimeters, and can obtain highly reproducible and high-resolution results.

[0044] The present invention will be described in detail below.

[0045] The multi-walled carbon nanotube powder, multi-walled carbon nanotube dispersion and lithium secondary battery according to the present invention include at least one of the configurations described below, and may include any combination of technically feasible configurations among the following configurations.

[0046] Multi-walled carbon nanotube powder

[0047] According to one embodiment of the present invention, the multi-walled carbon nanotube powder is characterized in that, in the particle size distribution (PSD) measured by a particle size analyzer in the dry powder state, the average particle size (D) at 50% of the cumulative volume is... 50 Within the range of 10 μm to 20 μm, the average particle size at 90% of the cumulative volume (D) 90 Within the range of 20 μm to 40 μm, the maximum particle size (D) 最大 The oxygen atom content measured by XPS analysis was in the range of 1.0 atomic% to 3.0 atomic% within the range of 45 μm to 70 μm.

[0048] According to one embodiment of the invention, the average particle size and maximum particle size at 50% and 90% cumulative volume are not measured in the state of multi-walled carbon nanotubes dispersed in an organic solvent, but in the state of dry powder under air conditions. Although these values ​​are different from those measured in the dispersed state, it can be understood that these values ​​are substantially the same as the shape and size of the particles present and distributed in the active material layer of the electrode.

[0049] That is, typically, particle size distribution is used to determine the degree of dispersion in the dispersed state after the conductive agent is dispersed in an organic solvent with a dispersant, using a particle size analyzer. In a specific measured particle size distribution, the presence of many large-diameter particles is considered poor dispersion, while the presence of too many small-diameter particles is considered over-dispersion. However, since multi-walled carbon nanotubes according to an embodiment of the present invention are characterized by measuring the particle size distribution in the powder state using a particle size analyzer and simultaneously specifying the amount of oxygen functional groups, their dispersion in the dispersion or electrode easily facilitates control of the dispersion viscosity, and is therefore intended to limit the characteristic that multi-walled carbon nanotubes can be uniformly distributed in the electrode.

[0050] In the particle size distribution in the dry powder state, the average particle size (D) at 50% cumulative volume of the multi-walled carbon nanotubes according to an embodiment of the present invention is... 50 The average particle size (D) at 90% of the cumulative volume is 10 μm to 20 μm. 90 The particle size ranges from 20 μm to 40 μm, and the maximum particle size (D) is... 最大 The thickness ranges from 45 μm to 70 μm.

[0051] Average particle size (D) at 50% cumulative volume 50 The particle size is in the range of 10 μm to 20 μm, preferably 12 μm or larger, 13 μm or larger, or 14 μm or larger, and may also be 19.5 μm or smaller, 19 μm or smaller, or 18.5 μm or smaller. Furthermore, the average particle size (D) at 90% of the accumulated volume... 90 Within the range of 20 μm to 40 μm, it is preferably 23 μm or larger, 25 μm or larger, 28 μm or larger, 29 μm or larger, 30 μm or larger, 31 μm or larger, or 32 μm or larger, and may also be 39.5 μm or smaller, 39 μm or smaller, 38.5 μm or smaller, or 38 μm or smaller. Furthermore, the maximum particle size (D...) 最大 In the range of 45 μm to 70 μm, it is preferably 48 μm or larger, 50 μm or larger, 52 μm or larger, 54 μm or larger, 56 μm or larger, or 58 μm or larger, and may also be 69 μm or smaller, 68 μm or smaller, 67 μm or smaller, or 66 μm or smaller.

[0052] The above particle size distribution is where D is located. 90 Relatively small and D 最大 Suppressed to the minimum value while D 50 Maintaining a particle size distribution above a certain size, where the dispersion can be excellent while keeping the viscosity of the dispersion at a low level, allows for uniform distribution in the electrode. Furthermore, since the particle size distribution is essentially the same as that of multi-walled carbon nanotubes in the active material layer after the electrode slurry is applied to the current collector and dried, the formation of conductive paths can also be predicted.

[0053] Specifically, in D 50 Less than 10 μm, D 90 Less than 20 μm or D 最大 When the electrode length is less than 45 μm, the difficulty in forming conductive paths within the electrode due to the deterioration of its length characteristics may be a factor contributing to increased resistance. However, in the case of D... 50 Greater than 20 μm, D 90 Greater than 40 μm or D 最大 For particles larger than 70 μm, although the length characteristics can be evaluated as relatively excellent, there is a problem of deterioration in the number characteristics. That is, many particles are in an aggregated state, which may reduce the total number and the specific surface area. Therefore, the electrode performance may be degraded because the minimum amount of particles required to form a conductive path in the electrode is not reached.

[0054] Furthermore, the multi-walled carbon nanotubes according to embodiments of the present invention are characterized in that the oxygen atom content, as measured by XPS analysis, is in the range of 1.0 atomic% to 3.0 atomic%.

[0055] The oxygen atom content is the content of oxygen atoms derived from oxygen functional groups, which can be attributed to CO bonds or C=O bonds present in the carbon nanotubes. Oxygen functional groups can be generated by grinding or disintegration processes when multi-walled carbon nanotubes are unbundled from large micron-sized bundles, and can be incorporated into nodes or cut surfaces present in the multi-walled carbon nanotubes. Oxygen functional groups can contribute to more efficient dispersion during the dispersion process of multi-walled carbon nanotubes. Therefore, since the particle size characteristics of the carbon nanotube powder with excellent dispersibility can be maintained in the electrode even if the dispersion and electrode are prepared through several dispersion processes, the conductivity of the electrode can be improved more precisely, and the predictability and reproducibility of excellent conductivity can be significantly improved. Preferably, the oxygen atom content can be 1.2 atomic% or more, 1.5 atomic% or more, or 1.7 atomic% or more, and can also be 2.8 atomic% or less, 2.5 atomic% or less, or 2.3 atomic% or less.

[0056] The oxygen atom content can ultimately be varied depending on the degree to which oxygen-containing functional groups are included. When oxygen-containing functional groups are included at the content described above, the excellent dispersibility of carbon nanotubes, as determined by the powder, can be achieved when they are in the electrode. This further improves the dispersibility of multi-walled carbon nanotubes, offering the advantage of achieving electrodes with excellent conductivity with high reproducibility and predictability. However, when the oxygen atom content is less than 1.0 atomic%, there is no effect on improving dispersibility, and even if the particle size distribution is the same as described above, the effect on improving the dispersion viscosity may not be significant. Furthermore, when the oxygen atom content is greater than 3.0 atomic%, reaggregation begins after dispersion, potentially leading to an increase in viscosity even if the proportion of large-diameter particles in the powder state is low, due to the increased proportion of large-diameter particles in the dispersion.

[0057] The BET specific surface area of ​​the multi-walled carbon nanotube powder according to an embodiment of the present invention can be 150 m². 2 / g to 300 m 2 / g. While conductive agents with large specific surface areas, such as single-walled carbon nanotubes, are commonly used because even small amounts are beneficial for ensuring conductivity, they are difficult to disperse and are expensive, making their use in large-scale production likely only in rare cases. However, the advantage of this invention is that even with a lower specific surface area, performance levels comparable to those of conductive agents with large specific surface areas can be achieved by defining particle size characteristics that ensure excellent dispersibility, while also maintaining excellent price competitiveness.

[0058] The specific surface area can preferably be 160 m² 2 / g or greater, 170 m 2 / g or greater, 175 m 2 / g or larger, or 180m 2 / g or greater, and can also be 290 m 2 / g or less, 280 m 2 / g or less, 270 m 2 / g or less, 265 m 2 / g or less, or 260 m 2 / g or less. For multi-walled carbon nanotubes with a specific surface area in this range, there is an advantage that can ensure the electrical conductivity achieved by the above-mentioned particle size distribution and oxygen atom content, while maximizing price competitiveness.

[0059] According to one embodiment of the invention, multi-walled carbon nanotubes can be included in an amount of 0.5 to 10 parts by weight, and more specifically, in an amount of 0.7 to 7.0 parts by weight, more preferably 0.7 to 5.0 parts by weight, based on 100 parts by weight of the conductive agent dispersion. When the above ranges are met, the transfer and addition of the electrode slurry are easy, while high productivity is maintained. Furthermore, since the solid content of the prepared electrode slurry is not too low, binder migration during electrode drying can be suppressed. Therefore, electrode adhesion can be improved, and since the filling of the electrode active material layer can be effectively achieved, electrodes with small thicknesses can be prepared.

[0060] Conductive agent dispersion

[0061] The conductive agent dispersion according to one embodiment of the present invention is characterized in that it comprises the above-described multi-walled carbon nanotube powder, dispersant, and organic solvent. Since the multi-walled carbon nanotube powder is the same as described above, its description will be omitted.

[0062] dispersant

[0063] The conductive agent dispersion according to embodiments of the present invention comprises a dispersant, wherein the dispersant may include at least one selected from: polyacrylate, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyvinyl alcohol, polyacrylamide, polyethylene oxide, hydrogenated nitrile copolymers, cellulose compounds, and diisopropylamine (DIPA). In this document, the hydrogenated nitrile copolymer may be hydrogenated acrylonitrile-butadiene rubber, and the cellulose compound may be carboxymethyl cellulose (CMC) or hydroxyethyl cellulose (HEC).

[0064] Furthermore, based on 100 parts by weight of the conductive agent dispersion, the dispersant in the conductive agent dispersion may be included in an amount of 0.5 parts by weight to 20 parts by weight, particularly 0.7 parts by weight to 10 parts by weight, and more particularly 0.9 parts by weight to 8.0 parts by weight. When the above ranges are met, the carbon-based conductive agent can be smoothly dispersed in the conductive agent dispersion, which can improve the energy density of the prepared electrode and reduce the resistance.

[0065] organic solvents

[0066] According to one embodiment of the invention, the conductive agent dispersion comprises an organic solvent, and the organic solvent may be an organic solvent containing one or two or more heteroatoms selected from nitrogen (N) and oxygen (O) atoms having lone pairs of electrons.

[0067] Specifically, the organic solvents may include amide-based polar organic solvents, such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols, such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; and diols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, and 1,3-propanediol. 5-Pentanediol or hexanediol; polyols, such as glycerol, trimethylolpropane, pentaerythritol, or sorbitol; glycol ethers, such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones, such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; and esters, such as ethyl acetate, γ-butyrolactone, and ε-propiolactone, and mixtures of any one or more of these may be used. N-methylpyrrolidone (NMP) is particularly preferred for its compatibility with electrode pastes.

[0068] other

[0069] According to one embodiment of the invention, the solid content of the conductive agent dispersion can be in the range of 1 wt% to 10 wt%, particularly 2 wt% to 8 wt%, and more particularly 3.5 wt% to 5.5 wt%. When the above ranges are met, the dispersion of the conductive agent dispersion can be effectively achieved, while the viscosity of the conductive agent dispersion can be maintained at a low level. Hereinafter, solid content can refer to the multi-walled carbon nanotubes and dispersant contained in the conductive agent dispersion.

[0070] The conductive agent dispersion of the present invention comprising the above-mentioned components can be prepared by mixing multi-walled carbon nanotubes, a dispersant, and an organic solvent. In this case, the mixing can be performed using conventional mixing methods, specifically mixing apparatus such as homogenizers, bead mills, ball mills, basket mills, grinders, general-purpose stirrers, transparent mixers, nail crushers, or TK mixers, and the mixing order of the components is not particularly limited. That is, the conductive agent dispersion according to the present invention can be prepared by a method in which the dispersant is added and mixed after the multi-walled carbon nanotubes are added to the organic solvent, by a method in which the multi-walled carbon nanotubes are mixed after the dispersant is first added to the organic solvent, and by a method in which the multi-walled carbon nanotubes and the dispersant are added together to the organic solvent and then mixed.

[0071] To improve the dispersibility of multi-walled carbon nanotubes (MWCNTs) during the above mixing process, cavitation dispersion can also be performed. Cavitation dispersion utilizes the shock waves generated by the collapse of vacuum bubbles formed in water when high energy is applied to the liquid. This method can disperse MWCNTs without damaging their properties. Specifically, cavitation dispersion can be performed using ultrasonication, jet milling, or shear dispersion.

[0072] Lithium secondary batteries

[0073] A lithium secondary battery according to another embodiment of the present invention is characterized in that it comprises: a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the positive electrode comprising a positive electrode current collector and a positive electrode material mixture layer, the negative electrode comprising a negative electrode current collector and a negative electrode material mixture layer, wherein at least one of the positive electrode material mixture layer and the negative electrode material mixture layer comprises the aforementioned multi-walled carbon nanotube powder.

[0074] Since the multi-walled carbon nanotube powder is the same as described above, only the remaining components will be described below.

[0075] positive electrode

[0076] According to one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode material mixture layer formed on the positive electrode current collector and comprising a positive electrode active material, wherein the positive electrode material mixture layer may comprise a positive electrode active material, and the positive electrode active material may comprise at least one selected from lithium nickel-based oxides and lithium metal phosphate-based compounds.

[0077] The positive electrode active material can be a single particle type, and the degree of single particle formation (D) 50 / D 平均 The number of particles can be 1 to 10. Since the particle strength of the single-particle positive electrode active material is higher than that of conventional positive electrode active materials that are secondary particles aggregated from tens to hundreds of primary particles, particle cracking during rolling is reduced. Furthermore, regarding the single-particle positive electrode active material according to the invention, since the number of sub-components (i.e., nodules) constituting the particle is small, the changes caused by the volume expansion and contraction of the primary particles during charging and discharging are small, and therefore the occurrence of cracks in the particles is significantly reduced.

[0078] A smaller degree of single-particle formation can mean that there are fewer nodules constituting the particles. Therefore, the degree of single-particle formation can preferably be in the range of 1 to 8, 1 to 7, 1 to 6, or 1 to 5, and when the above ranges are met, both life characteristics and energy density can be expected to be improved because the degree of particle cracking can be reduced and the rolling density can be improved.

[0079] According to one embodiment of the present invention, the volume-cumulative average particle size (D) of the positive electrode active material 50 It can be in the range of 1.0 μm to 10.0 μm.

[0080] The average particle size at 50% of the cumulative volume of the positive electrode active material can be from 1.0 μm to 10.0 μm, preferably 1.1 μm or larger, 1.5 μm or larger, 2.0 μm or larger, 2.5 μm or larger, 3.0 μm or larger, or 3.5 μm or larger, and 9.0 μm or smaller, 8.0 μm or smaller, 7.5 μm or smaller, 7.0 μm or smaller, 6.5 μm or smaller, 6.0 μm or smaller, 5.5 μm or smaller, or 5.0 μm or smaller. The cumulative average particle size D of the positive electrode active material... 50 When the above range is met, it has the advantage of increasing the roll density without damaging the active material particles.

[0081] According to one embodiment of the present invention, the single-particle positive electrode active material may include 30 or fewer nodules, wherein the average particle size (D) of the nodules is... 平均)(It) can be within the range of 0.2 μm to 3.0 μm. The average particle size of the nodules can preferably be 0.3 μm or greater, 0.5 μm or greater, 0.7 μm or greater, or 1.0 μm or greater, and can be 2.8 μm or smaller, 2.5 μm or smaller, or 2.0 μm or smaller. And when the above ranges are satisfied, since the range of single-particle formation degree can be satisfied, corresponding effects can be expected.

[0082] The positive electrode active material according to the present invention can include at least one selected from lithium nickel-based oxides and lithium metal phosphate-based compounds. For example, the lithium nickel-based oxide can have a composition represented by the following formula 1.

[0083] [Formula 1]

[0084] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e

[0085] In formula 1, M 1 [[ID=2 and]] includes at least one selected from Mn and Al, M 2 includes at least one selected from W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, X includes at least one selected from N, P, S, F, and Cl, and 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 < b ≤ 0.35, 0 < c ≤ 0.35, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.05.

[0086] In formula 1, M 1 is Mn, Al, or a combination thereof, and can preferably be Mn or a combination of Mn and Al, M 2 is at least one selected from Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, can preferably be at least one selected from Zr, Y, Mg, and Ti, and can more preferably be Zr, Y, or a combination thereof. The element M 2 is not necessarily included, but when it is included in an appropriate amount, it can play a role in promoting grain growth during sintering or improving the crystal structure stability. In addition, X is an anion substituted at the oxygen site, and X can include N, P, S, F, or Cl.

[0087] 1 + x represents the molar ratio of lithium in the lithium nickel-based oxide, where x can satisfy 0 ≤ x ≤ 0.1, 0 ≤ x ≤ 0.08, 0 ≤ x ≤ 0.05, 0 ≤ x ≤ 0.03, or 0 ≤ x ≤ 0.02.

[0088] a represents the molar ratio of nickel in the lithium-nickel-based oxide among all metals other than lithium, where a can satisfy 0.50 ≤ a < 1.00, 0.60 ≤ a ≤ 0.99, 0.70 ≤ a ≤ 0.99 or 0.75 ≤ a ≤ 0.99, 0.80 ≤ a ≤ 0.99, 0.82 ≤ a ≤ 0.99, 0.84 ≤ a ≤ 0.99 or 0.86 ≤ a ≤ 0.99.

[0089] b represents the molar ratio of cobalt in the lithium-nickel-based oxide among all metals other than lithium, where b can satisfy 0 < b ≤ 0.35, 0.01 ≤ b ≤ 0.34, 0.01 ≤ b ≤ 0.30, 0.01 ≤ b ≤ 0.25, 0.01 ≤ b ≤ 0.20 or 0.01 ≤ b ≤ 0.15.

[0090] c represents the molar ratio of element M in the lithium-nickel-based oxide among all metals other than lithium 1 where c can satisfy 0 < c ≤ 0.35, 0.01 ≤ c ≤ 0.34, 0.01 ≤ c ≤ 0.30, 0.01 ≤ c ≤ 0.25, 0.01 ≤ c ≤ 0.20 or 0.01 ≤ c ≤ 0.15.

[0091] d represents the molar ratio of element M in the lithium-nickel-based oxide among all metals other than lithium 2 where d can satisfy 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.02 or 0 ≤ d ≤ 0.01.

[0092] e represents the molar ratio of element X in all non-metals other than oxygen in the lithium-nickel-based oxide, where e can satisfy 0 ≤ e ≤ 0.05, 0 ≤ e ≤ 0.02 or 0 ≤ e ≤ 0.01.

[0093] The lithium-nickel-based oxide may further include a coating on the surface of the particles, and the coating contains at least one coating element selected from the following: Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

[0094] When there is a coating on the surface of the lithium-nickel-based oxide particles, the contact between the electrolyte and the lithium-nickel-based oxide is inhibited by the coating, and thus the effect of reducing gas generation or transition metal dissolution caused by side reactions with the electrolyte can be obtained.

[0095] Preferably, the coating may contain Co as a coating element. When a coating containing Co is formed on the surface of the lithium-nickel-based oxide particles in the form of single particles and / or pseudo single particles, the effect of improving the output and the effect of suppressing side reactions with the electrolyte can be obtained.

[0096] Furthermore, compounds based on lithium metal phosphates can have a composition represented by Formula 2 below.

[0097] [Equation 2]

[0098] Li 1+x [Fe 1-y M y ]PO4

[0099] In Equation 2, M includes at least one selected from Mn, Co, Ni, Al, Mg and Ti, and -0.5≤x≤0.5 and 0≤y<1.

[0100] Compounds based on lithium metal phosphates can be doped with M. In this case, the diffusion of lithium ions increases due to changes in the lattice structure and spacing within the olivine crystal structure, which is a crystalline structure, and thus the electrochemical characteristics of the battery containing the positive electrode active material can be improved.

[0101] x can be in the range of -0.5 to 0.5, preferably -0.3 or greater, -0.1 or greater, or 0 or greater, and can be 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0102] y can be 0 or greater, less than 1, and can be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, 0.20 or less, 0.10 or less, or 0.05 or less.

[0103] Compounds based on lithium metal phosphates can be, for example, LiFePO4.

[0104] The lithium metal phosphate-based compound according to the present invention can be in the form of a single particle consisting of only one primary particle, or in the form of irregular secondary particles consisting of 2 to 50 primary particles. Furthermore, the lithium metal phosphate-based compound can contain an olivine structure, and specifically can consist only of an olivine structure. The coating according to the present invention can be formed not only on the secondary particles but also on the primary particles. That is, the coating according to the present invention can be uniformly present on the surface of the primary particles present in the secondary particles.

[0105] The coating may include a carbon coating with a graphite structure, and the coating thickness may be from 0.5 nm to 5 nm. With a coating thickness within this range, there is an advantage in improving conductivity without hindering the entry and exit of lithium ions. Specifically, the coating thickness may be 0.5 nm or greater, 1.0 nm or greater, 1.5 nm or greater, 2.0 nm or greater, 2.5 nm or greater, or 3.0 nm or greater, and may be 5.0 nm or less.

[0106] The coating can be uniformly applied to the surface of a lithium metal phosphate-based compound. That is, the coating can be in the form of a thin film. The coating can improve the ionic conductivity and electrical conductivity of batteries containing positive electrode active materials during charging and discharging. In addition to carbon, the coating can also contain trace amounts of impurities such as nitrogen, oxygen, and hydrogen.

[0107] Based on the total weight of the lithium metal phosphate-based compound, the coating can be included in an amount of 0.5% to 3% by weight, thereby improving conductivity without hindering the entry and exit of lithium ions.

[0108] Based on the total weight of the cathode material mixture layer, the cathode active material can be included in an amount of 90% to 99% by weight, more specifically, 93% or more, 95% or more, 96% or more, or 97% or more, and 98.5% or less, or 98% or less, and when the cathode active material is included in the amount within the above range, excellent capacity characteristics can be obtained.

[0109] Furthermore, according to one embodiment of the invention, the positive electrode may also include a binder. The binder improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of binders may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-copolymer-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen is replaced by Li, Na, or Ca, or various copolymers thereof, and mixtures of any one or more thereof may be used. Based on the total weight of the cathode material mixture layer, the binder may be included in an amount from 0.1 wt% to 10 wt%, preferably 0.3 wt% or more, 0.5 wt% or more, 0.7 wt% or more, or 1.0 wt% or more, and 9.0 wt% or less, 8.5 wt% or less, 8.0 wt% or less, 7.5 wt% or less, 7.0 wt% or less, or 6.5 wt% or less.

[0110] The positive electrode current collector can include a highly conductive metal, and there are no particular limitations, as long as it is not reactive within the battery's voltage range and the positive electrode material mixture layer can easily adhere to it. Examples of positive electrode current collectors include stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and minute irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. The positive electrode current collector can be used in a variety of shapes, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0111] The positive electrode can be prepared according to typical methods for preparing a positive electrode, except that the above-mentioned positive electrode active material powder is used. Specifically, a positive electrode current collector is coated with a positive electrode slurry composition, and then the positive electrode can be prepared by drying and rolling the coated positive electrode current collector. The positive electrode slurry composition is prepared by dissolving or dispersing the above-mentioned positive electrode active material powder, along with optional binders, conductive agents, and dispersants (if desired), in a solvent.

[0112] The solvent can be any solvent commonly used in the art, including dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and mixtures of any one or more of these can be used. The amount of solvent used may be sufficient if it can dissolve or disperse the positive electrode active material, conductive agent, binder, and dispersant, taking into account the coating thickness and manufacturing yield of the slurry, and allows for a viscosity that provides excellent thickness uniformity during subsequent coating for positive electrode preparation.

[0113] In addition, as another method, the positive electrode can be prepared by casting the positive electrode slurry composition onto a separate support, and then laminating the film separated from the support onto the positive electrode current collector.

[0114] negative electrode

[0115] In a lithium secondary battery according to an embodiment of the present invention, the negative electrode includes a negative electrode current collector and a layer of negative electrode material mixture disposed on the negative electrode current collector.

[0116] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and will not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel with surface treatment of one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used.

[0117] The thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and is preferably 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. Minor irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in a variety of shapes, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0118] Compounds capable of reversibly inserting and deintercalating lithium can be used as anode active materials. For example, anode active materials may include: carbon materials such as artificial graphite, natural graphite, crystalline graphite (Kish graphite), pyrolytic carbon, mesophase carbon microspheres, mesophase pitch, coke derived from petroleum or coal tar pitch, carbon fibers based on mesophase pitch, graphitized carbon fibers, amorphous carbon, soft carbon, or hard carbon; (semi-)metallic materials that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and (semi-)metal oxide materials that can be doped or undoped with lithium, such as SiO₂. bwhere \(0 < b\leq2\), \(SnO_2\), vanadium oxides, and lithium vanadium oxides; heterogeneous composite materials, such as Si-C composite materials or Sn-C composite materials; or thin films of metallic lithium, and any one of them or a mixture of two or more of them can be used.

[0119] Preferably, the negative electrode active material may include at least one selected from silicon-based active materials, carbon-based active materials, and silicon-carbon composite active materials. Among them, more preferably, the carbon-based active material may include at least one selected from artificial graphite, natural graphite, soft carbon, and hard carbon, and the silicon-based active material may include pure Si particles and / or SiO b where \(0 < b\leq2\), and the silicon-carbon composite active material may include Si-C composite materials. In addition, a mixed active material in which two or more of the above materials are mixed can be used as the negative electrode active material.

[0120] Based on the total weight of the negative electrode material mixture layer, the negative electrode active material may be included in an amount of 60% to 99% by weight, preferably in an amount of 70% or more, 80% or more, 85% or more, or 90% or more by weight, and may also be included in an amount of 98% or less, 97% or less, or 95% or less by weight.

[0121] Preferably, the negative electrode active material may include at least one selected from silicon-based active materials, carbon-based active materials, and silicon-carbon composite active materials.

[0122] Based on the total solid content in the negative electrode slurry, the negative electrode active material may be included in an amount of 70% to 99% by weight, may be included in an amount of 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more by weight, and may also be included in an amount of 99.0% or less, 98.5% or less, 98.0% or less, or 97.5% or less by weight. When the amount of the negative electrode active material satisfies the above range, excellent energy density, electrode adhesion, and conductivity can be achieved.

[0123] The binder is a component that facilitates the bonding between the conductive agent, the active material, and the current collector. Based on the total weight of the negative electrode material mixture layer, the binder can typically be added in amounts from 0.1% to 10% by weight, and can be included in amounts of 0.2% or more, 0.3% or more, or 0.5% or more by weight, and can also be included in amounts of 8% or less, or 5% or less by weight. Examples of binders may include at least one selected from: styrene-butadiene copolymers, acrylate styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylonitrile-butadiene-styrene copolymers, acrylic rubbers, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymers, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymers, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resins, acrylic resins, phenolic resins, epoxy resins, and polyvinyl alcohol. The adhesive may include at least one selected from the following: styrene-butadiene copolymer, acrylate styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose. Preferably, carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, or mixtures thereof are preferred.

[0124] A conductive agent is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode material mixture layer, the conductive agent can be added in amounts of 10% by weight or less, preferably 5% by weight or less, 3% by weight or less, 2% by weight or less, or 1% by weight or less, and can be included in amounts of 0.01% by weight or more, 0.05% by weight or more, 0.08% by weight or more, 0.1% by weight or more, or 0.3% by weight or more. There are no particular limitations on the conductive agent, as long as it is conductive and does not cause chemical changes in the battery. For example, conductive materials such as: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lampblack, and thermal cracking black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0125] The negative electrode material mixture layer can be prepared by coating a negative electrode current collector with a negative electrode slurry composition and drying the coated negative electrode current collector. The negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material, along with optional binders and conductive agents, in a solvent. Alternatively, the negative electrode material mixture layer can be prepared by casting the negative electrode slurry composition onto a separate support and then bonding the film layer separated from the support onto the negative electrode current collector.

[0126] Others: separators and electrolytes, etc.

[0127] The separator separates the negative electrode from the positive electrode and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is typically used in secondary batteries. Specifically, as a separator, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or laminated structures having two or more layers thereof. Additionally, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0128] The electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or melt inorganic electrolytes that can be used to prepare lithium secondary batteries, but the present invention is not limited thereto.

[0129] Specifically, electrolytes may contain non-aqueous organic solvents and metal salts.

[0130] As non-aqueous organic solvents, for example, aprotic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0131] In particular, cyclic carbonates are preferred in organic solvents based on carbonates because ethylene carbonate and propylene carbonate, as cyclic carbonates, are highly viscous organic solvents that effectively dissociate lithium salts due to their high dielectric constants. Furthermore, cyclic carbonates are even more preferred because an electrolyte with high conductivity can be prepared by mixing the above cyclic carbonates with low-viscosity, low-dielectric-constant linear carbonates (such as dimethyl carbonate and diethyl carbonate) in an appropriate ratio.

[0132] Lithium salts can be used as metal salts, and lithium salts are materials that are readily soluble in non-aqueous organic solvents. For example, at least one of the following can be used as the anion of the lithium salt: F... - Cl - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - .

[0133] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also contain at least one additive, such as compounds based on alkylene carbonates (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether (n-glyme), triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted compounds. Zolpidemone, N,N-substituted imidazolidinyl ether, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0134] Example

[0135] In the following description, embodiments of the invention will be described in detail in a manner that enables those skilled in the art to readily implement it. However, the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0136] 1. Multi-walled carbon nanotube powder

[0137] Examples 1a to 4a and Comparative Examples 1a to 11a

[0138] Multi-walled carbon nanotube powders with particle size characteristics listed in Table 1 were prepared.

[0139] Regarding the particle size characteristics of the powder, the particle size distribution is calculated by measuring the difference in diffraction pattern caused by particle size when the powder is introduced into a laser diffraction particle size measuring instrument (Malvern, Mastersizer 3000) and the particles pass through the laser beam. 50 D 90 and maximum particle size D 最大 The particle size is measured by determining the particle size at the 50% and 90% points obtained according to the cumulative volume distribution based on particle size, as well as at the point with the largest particle size.

[0140] Regarding the oxygen atom content, the O 1s spectrum was obtained using X-ray photoelectron spectroscopy (XPS) (Nexsa ESCA system, ThermoFisher Scientific (ESCA-02)) under the conditions of Al-Kα light source (1486.6 eV), accelerating voltage of 1 kV / 300 W, energy resolution of approximately 1.0 eV, minimum analytical region of 400 μm, and sputtering rate of 0.13 nm / min. The intensity values ​​of each peak are listed in Table 1 below.

[0141] [Table 1]

[0142]

[0143] 2. Conductive agent dispersion

[0144] Examples 1b to 4b and Comparative Examples 1b to 11b

[0145] 1.25 kg of multi-walled carbon nanotube powder from each of Examples 1a to 4a and Comparative Examples 1a to 11a, 0.375 kg of HNBR as a dispersant, and 36.17 kg of N-methylpyrrolidone were mixed and then mixed for 180 minutes using a mixer (BTM-50, dispersant 1000 rpm / anchor 100 rpm). The mixture was stirred for 180 minutes using a NETZSCH bead mill (NETZSCH LMZ2, bead size: 0.65 mm / 2500 rpm) to obtain conductive agent dispersions corresponding to each of Examples 1b to 4b and Comparative Examples 1b to 11b.

[0146] Experimental Example 1: Particle Size Analysis of Conductive Agent Dispersion

[0147] Regarding the particle size characteristics of the conductive agent dispersions, the particle size of each of the conductive agent dispersions in the Examples and Comparative Examples was analyzed by laser diffraction and is presented in Table 2. Specifically, after the conductive agent dispersion was dispersed in a solvent, the particle size distribution was calculated by measuring the difference in diffraction pattern caused by particle size when the solution was introduced into a laser diffraction particle size measuring instrument (Malvern, Mastersizer 3000) and the particles passed through the laser beam. 50 and D 90 The measurement is performed by determining the particle size at the 50% and 90% points obtained based on the cumulative volume distribution of the particle size.

[0148] Experimental Example 2: Viscosity Analysis

[0149] The viscosity of the conductive agent dispersions prepared by the examples and comparative examples was measured using a Brookfield viscometer (DV2T, LV) at 25°C and 12 rpm, and is presented in Table 2.

[0150] [Table 2]

[0151]

[0152] Referring to Table 2, unlike the particle size characteristics of multi-walled carbon nanotube powder, the particle size characteristics of the pre-dispersion are not significantly different. However, for the embodiments that meet the particle size characteristics of the powder of the present invention, since the initial viscosity is significantly lower than that of the comparative example, it can be determined that it is very advantageous in the dispersion process and slurry preparation process.

[0153] 3. Lithium secondary batteries

[0154] Examples 1c to 4c and Comparative Examples 1c to 11c

[0155] Using LiNi 0.6 Co 0.1 Mn0.3 Single-particle type lithium nickel oxide particles of O2 were used as positive electrode active materials, and positive electrodes were prepared using multi-walled carbon nanotube dispersions of Examples 1b to 4b and Comparative Examples 1b to 11b.

[0156] Regarding the positive electrode, a lithium-nickel based oxide, each of the multi-walled carbon nanotube dispersions used as conductive agents in the examples and comparative examples, and a PVDF binder were mixed in a weight ratio of 97.0:1.2:1.8, and N-methylpyrrolidone solvent was added to bring the solids content to 72%. The mixture was then homogenized at 2,500 rpm for 1 hour to prepare a positive electrode slurry. Subsequently, the positive electrode was prepared by coating one surface of an aluminum current collector with the slurry, drying it at 130°C, and then rolling the coated aluminum current collector twice using a roll-to-roll press at a pressure of 2,000 kgf / cm.

[0157] Using average particle size D 50 Silicon particles with a diameter of 5 μm were used as the negative electrode active material. The negative electrode was prepared by comprising a negative electrode material mixture layer, which included negative electrode active material in a weight ratio of 80:10:10, CMC as a negative electrode binder, and carbon nanotubes as a negative electrode conductive agent. The loading capacity of the negative electrode material mixture layer was 10 mAh / cm³. 2 And a thickness of 75 μm.

[0158] The positive electrode, negative electrode, and porous polyethylene separator were assembled using a winding method, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), lithium hexafluorophosphate (LiPF6 1 mol)) was injected into the assembled battery to prepare lithium secondary batteries of each of Examples 1c to 7c and Comparative Examples 1c to 10c.

[0159] The lithium secondary battery is charged to 4.2 V at a C-rate of 0.1 C and then discharged to 2.5 V for the formation process.

[0160] Experiment Example 3: Battery Performance Evaluation 1 (Resistance Characteristics)

[0161] After charging and discharging the lithium secondary battery, when the lithium secondary battery was fully charged again and then discharged, a 2.5 C pulse current was applied for a certain period of time according to the change in state of charge (SOC) to measure the surface resistance (resistance for 0.1 seconds), charge transfer resistance (resistance from 0.1 seconds to 30 seconds), and diffusion resistance (resistance for 30 seconds), and the results are presented in Table 3. In addition, for ease of comparison, the exponent of each resistance value based on Comparative Example 1 (the percentage of the resistance value relative to Comparative Example 1) was calculated.

[0162] Experiment Example 4: Battery Performance Evaluation 2 (Lifetime Characteristics)

[0163] The lithium secondary batteries prepared in Experimental Example 3 were charged to 4.25 V at 0.2 C in constant current-constant voltage (CCCV) mode (termination current 1 / 20 C). Then, the lithium secondary batteries were charged to 4.25 V at a constant current of 0.33 C at 45°C and discharged to 2.5 V at a constant current of 0.33 C, which was defined as one cycle. This cycle was performed for 200 charge-discharge cycles, and the charge / discharge capacity was measured. The capacity retention rate was calculated as follows.

[0164] Capacity retention (%) = (Discharge capacity after 200 cycles / Discharge capacity after 1 cycle) × 100

[0165] [Table 3]

[0166]

[0167] Referring to Table 3, regarding the lithium secondary batteries of Examples 1c to 4c, it can be determined that the measured resistance values ​​are about 10% lower than those of Comparative Example 1c, but the measured resistance values ​​of the comparative examples are similar to those of Comparative Example 1c. It can also be determined that capacity degradation occurs faster in the comparative examples, as the lifetime characteristics also show a difference of about 7% to 8% between the examples and the comparative examples. Since such a large difference is shown at 200 cycles, it can be expected that the difference may increase exponentially after a long period of time (e.g., about 500 cycles). The dispersibility and viscosity characteristics of the pre-dispersion can be improved by controlling the particle size characteristics of the multi-walled carbon nanotube powder, and thus it is determined that the battery characteristics can be improved.

Claims

1. A multi-walled carbon nanotube powder, In the particle size distribution (PSD) measured by a particle size analyzer in dry powder condition, the average particle size (D) at 50% cumulative volume is... 50 The thickness ranges from 10 μm to 20 μm. Average particle size (D) at 90% cumulative volume 90 The thickness ranges from 20 μm to 40 μm. Maximum particle size (D) 最大 The range is from 45 μm to 70 μm, and The oxygen atom content measured by XPS analysis ranged from 1.0 atomic% to 3.0 atoms.

2. The multi-walled carbon nanotube powder according to claim 1, wherein the average particle size (D) at 50% of the cumulative volume is... 50 The range is from 13 μm to 19 μm.

3. The multi-walled carbon nanotube powder according to claim 1, wherein the average particle size (D) at 90% of the cumulative volume... 90 The range is from 28 μm to 40 μm.

4. The multi-walled carbon nanotube powder according to claim 1, wherein the maximum particle size (D) 最大 (In the range of 54 μm to 70 μm) 5. The multi-walled carbon nanotube powder according to claim 1, wherein the oxygen atom content, as measured by XPS analysis, is in the range of 1.5 atomic% to 2.5 atomic%.

6. The multi-walled carbon nanotube powder according to claim 1, wherein the BET specific surface area is 150 m². 2 / g to 300 m 2 Within the range of / g.

7. A conductive agent dispersion comprising the multi-walled carbon nanotube powder according to claim 1, a dispersant, and an organic solvent.

8. The conductive agent dispersion according to claim 7, wherein 100 parts by weight of the conductive agent dispersion comprises 0.5 to 10 parts by weight of multi-walled carbon nanotubes and 0.5 to 20 parts by weight of the dispersant.

9. The conductive agent dispersion according to claim 7, wherein the dispersant comprises at least one selected from: polyacrylate, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyvinyl alcohol, polyacrylamide, polyethylene oxide, carboxymethyl cellulose (CMC), and diisopropylamine (DIPA).

10. A lithium secondary battery, comprising: The device comprises a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and a layer of positive electrode material mixture, and the negative electrode includes a negative electrode current collector and a layer of negative electrode material mixture. At least one of the positive electrode material mixture layer and the negative electrode material mixture layer comprises the multi-walled carbon nanotube powder according to claim 1.

11. The lithium secondary battery of claim 10, wherein the positive electrode material mixture layer comprises a positive electrode active material, and The positive electrode active material includes at least one selected from lithium nickel-based oxides and lithium metal phosphate-based compounds.

12. The lithium secondary battery according to claim 11, wherein the positive electrode active material is a single-particle type, and Single particle formation degree (D 50 / D 平均 The degree of single particle formation (D) is 1 to 10. 50 / D 平均 ) is the volumetric cumulative average particle size (D 50 ) and the average particle size of the nodules (D 平均 The ratio of ).

13. The lithium secondary battery of claim 11, wherein the lithium nickel-based oxide has a composition represented by Formula 1, and The lithium metal phosphate-based compound has a composition represented by Formula 2: [Formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e Among them, in Formula 1, M 1 includes at least one selected from Mn and Al, M 2 includes at least one selected from W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, X includes at least one selected from N, P, S, F, and Cl, and 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 < b ≤ 0.35, 0 < c ≤ 0.35, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.05, and [Equation 2] Li 1+x [Fe 1-y M y ]PO4 In Equation 2, M includes at least one selected from Mn, Co, Ni, Al, Mg and Ti, and -0.5≤x≤0.5 and 0≤y<1.

14. The lithium secondary battery of claim 10, wherein the negative electrode material mixture layer comprises a negative electrode active material, and The negative electrode active material includes at least one selected from silicon-based active materials, carbon-based active materials, and silicon-carbon composite active materials.

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