Conductive material dispersion, electrode produced using same, and lithium secondary battery

Abstract

The present invention discloses a conductive material dispersion liquid, an electrode produced using the conductive material dispersion liquid, and a secondary battery, wherein the conductive material dispersion liquid includes a carbon-based conductive material, a primary dispersant, an auxiliary dispersant, and a non-aqueous solvent, the primary dispersant includes a hydrogenated nitrile-based copolymer having a weight-average molecular weight of 5,000 to 100,000, and the auxiliary dispersant may include a compound including methyl cellulose as a main chain.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0185164, filed December 22, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a conductive material dispersion comprising a carbon-based conductive material, a primary dispersant, an auxiliary dispersant, and a non-aqueous solvent, wherein the primary dispersant comprises a hydrogenated nitrile-based copolymer having a weight-average molecular weight of 5,000 to 100,000, and the auxiliary dispersant comprises a compound having methylcellulose as a main chain, and to an electrode and a lithium secondary battery produced using the same. [Background technology]

[0003] A secondary battery is a battery that can be used repeatedly by a charging process, which is the opposite direction to discharging, in which chemical energy is converted into electrical energy. A secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator, and the positive electrode and the negative electrode are generally composed of an electrode current collector and an electrode active material layer formed on the electrode current collector. The electrode active material layer is manufactured by applying an electrode slurry composition containing an electrode active material, a conductive material, a binder, etc., onto an electrode current collector, drying the composition, and then rolling the composition.

[0004] Various materials can be used as the conductive material, but carbon black and carbon nanotubes are commonly used. If the conductive material is added in a powder state to the electrode slurry, the conductive material does not disperse uniformly, resulting in a problem of reduced conductivity of the manufactured electrode. For this reason, a method is used in which the conductive material is mixed with a dispersant and a dispersion medium to prepare a conductive material dispersion, and then the conductive material dispersion is applied to the electrode slurry. The dispersant can be PVP or hydrogenated nitrile butadiene rubber.

[0005] However, in the case of a conductive material dispersion using only PVP or hydrogenated nitrile butadiene rubber, the viscosity increases rapidly as the content of the conductive material increases, so there is a limit to increasing the content of the conductive material, and the improvement of productivity of the conductive material dispersion is limited. Specifically, if the content of the conductive material is not increased, the solid content of the positive electrode slurry cannot be increased, so the processability is reduced. In addition, during the preparation of the positive electrode active material layer, the positive electrode active material layer may be formed non-uniformly during the drying process.

[0006] To solve this problem, various methods such as jet mills and high-pressure homogenizers are used to mix the conductive material and dispersing material, thereby increasing the process time. However, these methods lead to problems such as increased process costs and time. Furthermore, in the case of a conductive material dispersion using only PVP or hydrogenated nitrile butadiene rubber, there is a limit to how much the particle size of the conductive material can be reduced even if the process conditions are changed as described above. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a conductive material dispersion liquid having improved dispersibility of a conductive material and low viscosity. Another object of the present invention is to provide an electrode and a secondary battery produced by using the conductive material dispersion liquid. [Means for solving the problem]

[0008] According to one embodiment of the present invention, there is provided a conductive material dispersion liquid comprising a carbon-based conductive material, a primary dispersant, an auxiliary dispersant, and a non-aqueous solvent, wherein the primary dispersant comprises a hydrogenated nitrile-based copolymer having a weight average molecular weight of 5,000 to 100,000, and the auxiliary dispersant comprises a compound having methylcellulose as a main chain.

[0009] According to another embodiment of the present invention, there is provided an electrode comprising an electrode active material layer formed from an electrode slurry composition, the electrode slurry composition comprising an electrode active material, the conductive material dispersion of the above embodiment, a binder, and a solvent. According to yet another embodiment of the present invention, there is provided a lithium secondary battery including a positive electrode, wherein the positive electrode may be the electrode of the above embodiment. Effect of the Invention

[0010] The conductive material dispersion according to the present invention includes a hydrogenated nitrile copolymer having a weight average molecular weight of 5,000 to 100,000 as a primary dispersant, a compound having methylcellulose as a main chain as a secondary dispersant, and a non-aqueous solvent. By using a hydrogenated nitrile copolymer having a weight average molecular weight of 5,000 to 100,000 as a primary dispersant, the hydrogenated nitrile copolymer can effectively penetrate between the carbon-based conductive materials. This allows the wetting of the carbon-based conductive material by the non-aqueous solvent to be smoothly performed, and the carbon-based conductive material can be uniformly dispersed to reduce the particle size. When the compound having methylcellulose as a main chain is used as a secondary dispersant, the dispersion state is effectively maintained, and additional dispersion of the non-aqueous solvent and the carbon-based conductive material is possible.

[0011] As a result, the dispersibility of the carbon-based conductive material in the conductive material dispersion is improved, the particle size of the conductive material can be at a low level, and the viscosity of the conductive material dispersion can be reduced. Therefore, even if the positive electrode slurry has a high solid content, the coating and drying processes of the positive electrode slurry can be performed uniformly, the cracking phenomenon of the positive electrode active material during rolling can be reduced, and gas generation in the battery at high temperatures, positive electrode resistance can be reduced, and life characteristics can be improved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The terms and words used in this specification and the claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0013] As used herein, terms such as "comprise," "comprising," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not exclude the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] In this specification, the "specific surface area" is measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan.

[0015] In this specification, D 50 and D. 90 can be defined as the particle size corresponding to 50% and 90% of the cumulative volume in the particle size distribution curve. 50 and D. 90 can be measured by using, for example, a laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0016] In this specification, "weight average molecular weight (Mw)" means a value converted to standard polystyrene measured by gel permeation chromatography (GPC). Specifically, the weight average molecular weight is a value converted from a value measured under the following conditions using GPC, and standard polystyrene from an Agilent system was used to create a calibration curve.

[0017] <Measurement conditions> Measuring instrument: Agilent GPC (Agulent 1200 series, USA) Column: PL Mixed B x 2 Column temperature: 40℃ Eluent: Tetrahydrofuran Flow rate: 1.0mL / min Concentration: ~1mg / mL (100μL injection)

[0018] In this specification, the BD weight and HBD weight for calculating the residual double bond value can be confirmed by 1H HR-MAS NMR method. As a measuring instrument, Agilent 600MHz HR-MAS NMR and Bruker 600MHz NMR can be used. Specifically, a small amount of dried hydrogenated nitrile copolymer sample can be placed in an HR-MAS rotor, and trichloroethylene (TCE) can be added to wet (swell) the sample, and then 1H HR-MAS NMR experiment can be performed (zg45, ns=32, d1=5s, room temperature condition). Alternatively, about 5 mg of dried hydrogenated nitrile copolymer sample can be dissolved in about 0.5 ml of deuterated chloroform (CDCl 3 ) and then sampling can be performed on solution NMR (1H-13C HSQC NMR, room temperature conditions). The NMR peaks can be confirmed by the above measurement method to measure the BD weight and HBD weight. The present invention will be specifically described below.

[0019] <Conductive material dispersion liquid> A conductive material dispersion liquid according to one embodiment of the present invention includes a carbon-based conductive material, a primary dispersant, an auxiliary dispersant, and a non-aqueous solvent, and the primary dispersant includes a hydrogenated nitrile-based copolymer having a weight-average molecular weight of 5,000 to 100,000, and the auxiliary dispersant may include a compound including methyl cellulose as a main chain. The conductive material dispersion may be a conductive material dispersion for forming an electrode, specifically, a conductive material dispersion for forming a positive electrode.

[0020] (1) Carbon-based conductive materials The carbon-based conductive material may include carbon nanotubes. The carbon nanotube has a graphite sheet having a cylindrical shape with a nano-sized diameter and an sp2 bond structure, and exhibits conductive or semiconductive properties depending on the angle and structure of the graphite sheet rolled up. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) depending on the number of bonds forming the wall. More specifically, the carbon nanotube may be a multi-walled carbon nanotube.

[0021] D of the carbon nanotube 50 The D of the carbon nanotube may be 2 μm to 4 μm, specifically, 2.5 μm to 3.5 μm. 90 The diameter may be 5 μm to 10 μm, specifically 6 μm to 9 μm. Satisfying the above range means that the bundled carbon nanotubes used as the raw material are effectively dispersed and present in the conductive material dispersion liquid, and therefore the resistance of the electrode and the battery is effectively improved.

[0022] The carbon nanotubes may be contained in the conductive material dispersion at 3 wt % to 8 wt %, specifically 3 wt % to 7 wt %. When the above range is satisfied, the electrode slurry can be easily transferred and charged while maintaining high productivity. In addition, since the solid content of the electrode slurry produced is not excessively low, the occurrence of binder migration during drying of the electrode can be suppressed. As a result, the electrode adhesive strength can be improved, and the packing of the electrode active material layer can be effectively performed, allowing an electrode with a low thickness to be produced. In some cases, the carbon-based conductive material may further include carbon black along with the carbon nanotubes.

[0023] (2) Dispersant The conductive material dispersion according to the present embodiment includes at least two or more dispersants. Specifically, the dispersants may include a primary dispersant and an auxiliary dispersant.

[0024] 1) Primary dispersant The primary dispersant is for improving the dispersibility of the carbon-based conductive material in the conductive material dispersion liquid, and may be a hydrogenated nitrile copolymer. The hydrogenated nitrile copolymer may be a copolymer containing an α,β-unsaturated nitrile-derived structural unit and a hydrogenated conjugated diene-derived structural unit, or a copolymer containing an α,β-unsaturated nitrile-derived structural unit, a conjugated diene-derived structural unit, and a hydrogenated conjugated diene-derived structural unit. Specifically, the hydrogenated nitrile copolymer may be a hydrogenated nitrile copolymer in which all of the conjugated diene-derived structural units are hydrogenated and no conjugated diene-derived structural units are included, or may be a partially hydrogenated nitrile copolymer in which some of the conjugated diene-derived structural units are hydrogenated and the hydrogenated conjugated diene-derived structural units are included together with the conjugated diene-derived structural units.

[0025] The hydrogenated nitrile copolymer may be a hydrogenated nitrile butadiene rubber, specifically a hydrogenated acrylonitrile-butadiene rubber, more specifically a partially hydrogenated acrylonitrile-butadiene rubber.

[0026] The method for hydrogenating the conjugated diene may be carried out by a hydrogenation reaction well known in the art, for example, a catalytic hydrogenation reaction using a catalyst system such as Rh, Ru, Pd, or Ir, and the hydrogenation rate can be adjusted by adjusting the amount of the catalyst, the reaction hydrogen pressure, the reaction time, etc.

[0027] The hydrogenated nitrile copolymer can be produced by copolymerizing an α,β-unsaturated nitrile monomer and a conjugated diene monomer, and then hydrogenating the C=C double bond in the copolymer. The polymerization reaction and hydrogenation process of the monomers may be carried out by a conventional method.

[0028] As the α,β-unsaturated nitrile monomer, for example, acrylonitrile or methacrylonitrile may be used, and one of these may be used alone or a mixture of two or more of them may be used. As the conjugated diene monomer, for example, a conjugated diene monomer having 4 to 6 carbon atoms such as 1,3-butadiene, isoprene, or 2,3-methylbutadiene may be used, and one of these may be used alone or a mixture of two or more of them may be used.

[0029] The α,β-unsaturated nitrile-derived structural unit may be contained in the hydrogenated nitrile copolymer in an amount of 20% by weight to 50% by weight, specifically 30% by weight to 40% by weight. When the above range is satisfied, the affinity between the hydrogenated nitrile copolymer and the non-aqueous solvent is at an appropriate level, so that the carbon-based conductive material can be more easily dispersed in the conductive material dispersion. This can further improve the conductivity of the manufactured electrode, reduce the battery resistance, and improve the battery life characteristics.

[0030] The hydrogenated nitrile copolymer may have a residual double bond value according to the following formula 1 of 0.3% by weight or less (0% by weight to 3% by weight), specifically 0.01% by weight to 0.3% by weight, more specifically 0.1% by weight to 0.3% by weight, for example 0.1% by weight to 0.25% by weight.

[0031] [Formula 1] Residual double bond (weight %) = BD weight / (BD weight + HBD weight) × 100

[0032] In the formula 1, the BD weight is the weight of the structural unit derived from the conjugated diene in the hydrogenated nitrile-based copolymer, and the HBD weight is the weight of the structural unit derived from the hydrogenated conjugated diene in the hydrogenated nitrile-based copolymer.

[0033] When the residual double bond value satisfies the above range, the process stability of the conductive material dispersion and the electrode slurry and the life characteristics of the battery can be improved. In addition, this effect can be further improved by using an auxiliary dispersant in combination. The residual double bond value may be 0 wt%, but is preferably 0.01 wt% or more in consideration of the cost and yield at the technical level.

[0034] According to one embodiment, the hydrogenated nitrile-based copolymer may include a unit represented by the following [Chemical Formula 1] (structural unit derived from an α,β-unsaturated nitrile) and a repeating unit represented by the following [Chemical Formula 2] (structural unit derived from a hydrogenated conjugated diene), or may include a unit represented by the following [Chemical Formula 1], a unit represented by the following [Chemical Formula 2], and a unit represented by the following [Chemical Formula 3] (structural unit derived from a conjugated diene).

[0035] [ka]

[0036] [ka]

[0037] [ka]

[0038] Meanwhile, the weight average molecular weight of the hydrogenated nitrile copolymer may be 5,000 to 100,000, specifically 20,000 to 40,000. If the weight average molecular weight of the hydrogenated nitrile copolymer is less than 5,000, the viscosity of the conductive material dispersion liquid may increase excessively, and the processability may be seriously deteriorated. If the weight average molecular weight of the hydrogenated nitrile copolymer is more than 100,000, the conductive material is not dispersed smoothly, and the conductivity of the manufactured electrode is low. That is, in the present invention, the viscosity of the conductive material dispersion liquid is at a low level, and the conductive material can be dispersed effectively.

[0039] In the conductive material dispersion, the hydrogenated nitrile copolymer may be contained in an amount of 5 to 40 parts by weight, specifically 8 to 30 parts by weight, and more specifically 10 to 20 parts by weight, based on 100 parts by weight of the carbon-based conductive material. When the above range is satisfied, the carbon-based conductive material can be smoothly dispersed in the conductive material dispersion, and the energy density of the manufactured electrode can be improved and the resistance can be reduced.

[0040] 2) Auxiliary dispersants The auxiliary dispersant is a compound containing methyl cellulose as a main chain, and serves to assist the primary dispersant in improving the dispersibility of the conductive material.

[0041] The compound containing methyl cellulose as the main chain has a bulky structure, and therefore can maintain the dispersing effect of the primary dispersant and also generate an additional dispersing effect.

[0042] The compound containing methyl cellulose as a main chain may include at least one selected from the group consisting of carboxy methyl cellulose (CMC), ethyl methyl cellulose, hydroxypropyl cellulose, and hydroxyethyl cellulose. When using the substance, the above-mentioned effects can be more effectively exhibited.

[0043] In the conductive material dispersion, the compound containing methylcellulose as a main chain may be included in an amount of 5 to 40 parts by weight, specifically 8 to 30 parts by weight, more specifically 10 to 20 parts by weight, based on 100 parts by weight of the carbon-based conductive material. When the above range is satisfied, the dispersion effect of the primary dispersant can be more effectively maintained, and the additional dispersion effect can be more effectively generated.

[0044] The weight ratio of the primary dispersant to the auxiliary dispersant may be 40:60 to 90:10, specifically 40:60 to 80:20, and more specifically 40:60 to 60:40. When the above range is satisfied, the carbon-based conductive material is effectively dispersed by the primary dispersant, while the re-agglomeration of the carbon-based conductive material can be more effectively prevented, and the additional carbon-based conductive material can be more effectively dispersed. As a result, a conductive material dispersion liquid having both a considerably low level of particle size and viscosity of the carbon-based conductive material can be obtained.

[0045] The total content of the primary dispersant and the auxiliary dispersant may be 5 parts by weight to 500 parts by weight, specifically 10 parts by weight to 100 parts by weight, and more specifically 15 parts by weight to 45 parts by weight, based on 100 parts by weight of the carbon-based conductive material. When the total content is within the above range, the carbon-based conductive material can be effectively dispersed and the proportion of active material in the electrode can be increased, thereby improving the energy density of the electrode.

[0046] (3) Nonaqueous solvent The non-aqueous solvent may be an organic solvent containing one or more heteroatoms selected from the group consisting of a nitrogen atom (N) and an oxygen atom (O) having an unshared electron pair.

[0047] Specifically, the non-aqueous solvent may be an amide-based polar organic solvent such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), or N-methylpyrrolidone (NMP); an alcohol such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; a glycol such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; or a glycerin, trimethylolpropane, pentaerythritol, or sorbitol. polyhydric alcohols 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; esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone, and any one or a mixture of two or more of these may be used. In consideration of the miscibility with the electrode slurry, N-methylpyrrolidone (NMP) is particularly preferable.

[0048] The conductive material dispersion may have a solid content of 1 wt% to 10 wt%, specifically 2 wt% to 8 wt%, more specifically 3.5 wt% to 5.5 wt%. When the above range is satisfied, the viscosity of the conductive material dispersion can be maintained at a low level, and the conductive material dispersion can be effectively dispersed. Here, the solid content may refer to the carbon-based conductive material, the primary dispersant, and the auxiliary dispersant contained in the conductive material dispersion.

[0049] The conductive material dispersion of the present invention containing the above-mentioned components can be prepared by mixing a carbon-based conductive material, a primary dispersant, an auxiliary dispersant, and a non-aqueous solvent. In this case, the mixing may be performed by a normal mixing method, specifically, by using a mixing device such as a homogenizer, a bead mill, a ball mill, a basket mill, a friction grinder, a universal stirrer, a clear mixer, a spike mill, or a TK mixer, and the mixing order of each component is not particularly limited. That is, the conductive material dispersion of the present invention may be formed by a method in which a carbon-based conductive material is added to a non-aqueous solvent, and then a primary dispersant and an auxiliary dispersant are added and mixed, or a method in which a primary dispersant and an auxiliary dispersant are first added to a non-aqueous solvent and then a carbon-based conductive material is mixed, or a method in which a primary dispersant, an auxiliary dispersant, and a carbon-based conductive material are all added to a non-aqueous solvent and then mixed.

[0050] Meanwhile, in order to enhance the dispersibility of the carbon-based conductive material during the mixing process, a cavitation dispersion process may be performed. The cavitation dispersion process is a dispersion process using shock waves generated by the bursting of vacuum bubbles generated in water when high energy is applied to the liquid, and the carbon-based conductive material can be dispersed without damaging its properties. Specifically, the cavitation dispersion process may be performed by ultrasonic waves, a jet mill, or a shear dispersion process.

[0051] 〔electrode〕 According to another embodiment of the present invention, an electrode includes an electrode active material layer formed from an electrode slurry composition including an electrode active material, a conductive material dispersion, and a binder. Specifically, the electrode includes an electrode current collector and an electrode active material layer formed on the electrode current collector, and the electrode active material layer may be formed from an electrode slurry composition including an electrode active material, a conductive material dispersion, and a binder.

[0052] In this case, the conductive material dispersion liquid is the conductive material dispersion liquid according to the present invention described above. Since the conductive material dispersion liquid is the same as that described above, detailed description will be omitted, and the remaining components will be described below.

[0053] The electrode current collector is not particularly limited as long as it is a material that does not induce chemical changes in the battery and has conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, alloys of these, those whose surfaces are surface-treated with carbon, nickel, titanium, silver, or the like, or calcined carbon may be used.

[0054] The electrode current collector may have a thickness of typically 3 μm to 500 μm, and may have fine irregularities formed on the surface of the current collector to enhance the binding force of the negative electrode active material. The electrode current collector may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, etc.

[0055] On the other hand, the electrode active material (a) contained in the electrode active material layer may be a positive electrode active material or a negative electrode active material generally used in the technical field, and the type thereof is not particularly limited.

[0056] For example, the positive electrode active material may be a lithium oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium oxide may be a lithium-manganese oxide (e.g., LiMnO 2 , LiMn 2 O), lithium-cobalt oxides (e.g., LiCoO 2etc.), lithium-nickel-based oxides (e.g., LiNiO 2 etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y1 Mn Y1 O 2 (where 0 < Y1 < 1), LiNi Z1 Mn 2-Z1 O 4 (where 0 < Z1 < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y2 Co Y2 O 2 (where 0 < Y2 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y3 Mn Y3 O 2 (where 0 < Y3 < 1), LiMn 2-Z2 Co Z2 O 4 (where 0 < Z2 < 2), etc.), lithium-nickel-cobalt-manganese-based oxides (e.g., Li(Ni P1 Co Q1 Mn R1 )O 2 (where 0 < P1 < 1, 0 < Q1 < 1, 0 < R1 < 1, P1 + Q1 + R1 = 1), or Li(Ni P2 Co Q2 Mn R2 )O 4 (where 0 < P2 < 2, 0 < Q2 < 2, 0 < R2 < 2, P2 + Q2 + R2 = 2), etc.), or lithium-nickel-cobalt-manganese-other metal (M) oxides (e.g., Li(Ni P3 Co Q3 Mn R3 M 1 S )O 2 (where M 1 is selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W, and Mo, and P3, Q3, R3, and S are atomic fractions of independent elements, where 0 < P3 < 1, 0 < Q3 < 1, 0 < R3 < 1, 0 < S < 1, and P3 + Q3 + R3 + S = 1), etc.), etc. may be mentioned, and any one or two or more of these compounds may be included.

[0057] On the other hand, examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; SiO v (0 <v<2)、SnO 2 , vanadium oxide, lithium vanadium oxide, or other metal oxide capable of doping and dedoping lithium; or a composite containing the metallic compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more of these may be used. In addition, a thin film of metallic lithium may be used as the negative electrode active material. In addition, either low-crystalline carbon or high-crystalline carbon may be used as the carbon material.

[0058] The electrode active material may be contained in an amount of 90 to 99 wt %, preferably 95 to 99 wt %, based on the total solid content in the electrode slurry composition. When the content of the electrode active material satisfies the above range, excellent energy density, electrode adhesive strength, and electrical conductivity can be achieved.

[0059] The binder is for ensuring adhesion between electrode active materials or between the electrode active material and the current collector, and may be a general binder used in the art, and is not particularly limited in type. Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and one or more of these may be used alone or in combination.

[0060] The binder may be included in an amount of 5 wt% or less, preferably 1 to 3 wt%, based on the total solid content in the electrode slurry composition. When the binder content satisfies the above range, an increase in electrode resistance can be minimized while achieving excellent electrode adhesion.

[0061] Meanwhile, the electrode slurry composition may further include a solvent as necessary for adjusting viscosity, etc. In this case, the solvent may be water, an organic solvent, or a mixture thereof. Examples of the organic solvent include amide polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, and octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; glycerin, trimethylolpropane, pentaerythritol, and 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; esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone, and the like may be used alone or in a mixture of two or more of these, but are not limited thereto.

[0062] The solvent may be included in an amount such that the solid content in the electrode slurry is 60 to 85 wt%, preferably 65 to 80 wt%. When the above range is satisfied, the electrode adhesion can be improved by suppressing binder migration, the drying temperature can be lowered to improve the coating property, and the coating speed can be increased to improve the productivity.

[0063] The electrode according to the present invention can be manufactured by applying and drying an electrode slurry composition containing the above-mentioned components to form an electrode active material layer. Specifically, the electrode active material layer can be formed by a method of applying the electrode slurry on an electrode current collector and then drying, or by a method of applying the electrode slurry on another support and then peeling it off from the support to obtain a film and laminating it on the electrode current collector. If necessary, after forming the electrode active material layer by the above-mentioned method, a rolling process may be further performed. In this case, the drying and rolling may be performed under appropriate conditions taking into account the physical properties of the electrode to be finally manufactured, and are not particularly limited.

[0064] [Lithium secondary battery] A lithium secondary battery according to another embodiment of the present invention includes a positive electrode, which may be the electrode according to the above-mentioned embodiment. Specifically, the secondary battery according to the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, in which case the positive electrode may be the electrode according to the above-mentioned embodiment.

[0065] Since the electrodes according to the present invention have been described above, a detailed description thereof will be omitted, and only the remaining components will be described below. The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator that is generally used as a separator in a secondary battery can be used without any particular limitation. Specifically, the separator may be a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fiber, polyethylene terephthalate fiber, or the like, may be used. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric substance may be used, and may be selectively used as a single layer or multilayer structure.

[0066] Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, but are not limited to these.

[0067] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt. Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0068] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high electrical conductivity can be prepared, and therefore such a mixture can be used even more preferably.

[0069] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO 3 - , N(CN) 2 - , B.F. 4 - , ClO 4 - , P.F. 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , C.F. 3 SO 3 - , C.F. 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2N - , C.F. 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH - ,(SCIENCE FICTION 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , C.F. 3 (CF 2 ) 7 SO 3 - , C.F. 3 CO 2 - , C.H. 3 CO 2 - , SCN - , and (CF 3 CF 2 SO 2 ) 2 N - One or more selected from the group consisting of may be used.

[0070] In addition to the components of the electrolyte, the electrolyte may further include one or more additives such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0071] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a semiconductor device according to an embodiment of the present invention; The specifications of the components used in the following examples and comparative examples are as follows:

[0072] (A) Primary dispersant Hydrogenated acrylonitrile-butadiene rubber (H-NBR) having the following physical properties was prepared.

[0073] [Table 1]

[0074] (B) Auxiliary dispersant An auxiliary dispersant having the following physical properties was prepared. (B1): Carboxymethyl cellulose (B2): Copolymer of polyethylene glycol and styrene (copolymer containing oxyalkylene units and styrene units, Mw: 1,250 g / mol, oxyalkylene unit content: 71.8 wt%, styrene unit content: 28.2 wt%) The content of each unit in the copolymer was measured by Nuclear Magnetic Resonance (NMR).

[0075] (C) Carbon-based conductive material (C1) BET specific surface area is 185m 2 / g bundled multi-walled carbon nanotubes (CNTs, manufacturer: LG CHEM) were used.

[0076] [Examples 1-2 and Comparative Examples 1-4] A mixture was prepared by adding the primary dispersant (A), auxiliary dispersant (B), and carbon-based conductive material (C) to N-methylpyrrolidone according to the content shown in Table 2 below, and then 30 kg of the mixture was mixed for 180 minutes using a mixer (BTM-50, disper 1000 rpm / anchor 100 rpm). The mixture was stirred for 10 minutes using a Netzsch bead mill (NETZSCH LMZ2, bead size: 0.65 mm / 2500 rpm) to obtain a conductive material dispersion.

[0077] [Table 2]

[0078] [Experimental Example 1: Particle size analysis] The particle size of each of the conductive material dispersions of the examples and comparative examples was analyzed by laser diffraction method, and the results are shown in Table 3. Specifically, after the conductive material dispersion was dispersed in a solvent, it was introduced into a laser diffraction particle size measuring device (Malvern, Mastersizer 3000) and the difference in the diffraction pattern according to the particle size when the particles passed through the laser beam was measured to calculate the particle size distribution. The particle sizes at the 50% and 90% points of the volume cumulative distribution by particle size were confirmed, and the D 50 and D. 90 was measured.

[0079] [Experimental Example 2: Viscosity analysis (immediately after production of conductive material dispersion)] The viscosity of the conductive material dispersions prepared in the above examples and comparative examples was measured at 23° C. and 12 rpm using a viscometer (Brookfield viscometer DV2T, LV). The results are shown in Table 3.

[0080] [Experimental Example 3: Confirmation of viscosity increase during long-term storage] The viscosity increase rate (%) of the conductive material dispersions produced in the examples and comparative examples was confirmed according to the following formula.

[0081] Viscosity increase rate (%) = {(viscosity of conductive material dispersion measured after storage for 4 weeks at 25°C - viscosity of conductive material dispersion immediately after production) / viscosity of conductive material dispersion immediately after production} x 100

[0082] [Table 3]

[0083] In the cases of Examples 1 and 2, it is confirmed that the particle size of the carbon nanotubes is at a low level, and it is found that the carbon nanotubes are smoothly dispersed. In addition, in the cases of Examples 1 and 2, it is found that the viscosity and viscosity increase rate of the conductive material dispersion are at a low level. In contrast, in the case of Comparative Examples 1 to 4, the particle size of the carbon nanotubes is higher than in Examples 1 and 2, and therefore it is found that relatively few carbon nanotubes are dispersed. Also, in the case of Comparative Examples 1 to 4, it is found that the viscosity of the conductive material dispersion is excessively high, and in particular in the case of Comparative Examples 1 and 3, the viscosity increase rate is also excessively high.

[0084] In addition, when comparing Comparative Example 1 and Comparative Example 4, it can be confirmed that when the weight average molecular weight of the hydrogenated nitrile copolymer used as the primary dispersant is not 5,000 to 100,000, the effect is not improved even if a compound containing methylcellulose as a main chain is used as the auxiliary dispersant. Specifically, in the case of Comparative Example 1 (primary dispersant: (A2) and auxiliary dispersant: (B1)), the D of the carbon nanotubes was significantly higher than in Comparative Example 4 (primary dispersant: (A2) and auxiliary dispersant not used). 50 Since the viscosity is still very high, the viscosity increase rate is even higher.

Claims

1. The present invention includes a carbon-based conductive material, a primary dispersant, an auxiliary dispersant, and a non-aqueous solvent, The primary dispersant comprises a hydrogenated nitrile copolymer having a weight average molecular weight of 5,000 to 100,000; The conductive material dispersion contains a compound having methyl cellulose as a main chain, as the auxiliary dispersant.

2. The conductive material dispersion according to claim 1 , wherein the hydrogenated nitrile copolymer is a hydrogenated nitrile butadiene rubber.

3. The conductive material dispersion according to claim 1, wherein the hydrogenated nitrile copolymer contains 20% by weight to 50% by weight of a structural unit derived from an α,β-unsaturated nitrile in the hydrogenated nitrile copolymer.

4. 2. The conductive material dispersion according to claim 1, wherein the hydrogenated nitrile copolymer is contained in the conductive material dispersion in an amount of 5 parts by weight to 40 parts by weight per 100 parts by weight of the carbon-based conductive material.

5. The conductive material dispersion liquid according to claim 1 , wherein the compound containing methyl cellulose as a main chain includes at least one selected from the group consisting of carboxymethyl cellulose, ethyl methyl cellulose, hydroxypropyl cellulose, and hydroxyethyl cellulose.

6. The conductive material dispersion according to claim 1, wherein the conductive material dispersion contains the compound having methyl cellulose as a main chain in an amount of 5 parts by weight to 40 parts by weight per 100 parts by weight of the carbon-based conductive material.

7. 7. The conductive material dispersion liquid according to claim 1, wherein a weight ratio of the primary dispersant to the auxiliary dispersant is from 40:60 to 90:

10.

8. 2. The conductive material dispersion according to claim 1, wherein the total content of the primary dispersant and the auxiliary dispersant is 5 parts by weight to 500 parts by weight based on 100 parts by weight of the carbon-based conductive material.

9. The conductive material dispersion according to claim 1 , wherein the carbon-based conductive material includes carbon nanotubes.

10. The conductive material dispersion liquid according to claim 9 , wherein the carbon nanotubes are multi-walled carbon nanotubes.

11. The conductive material dispersion according to claim 1 , wherein the conductive material dispersion is a conductive material dispersion for forming a positive electrode.

12. An electrode active material layer formed from an electrode slurry composition, The electrode slurry composition comprises an electrode active material, the conductive material dispersion according to claim 1 , a binder, and a solvent.

13. The electrode of claim 12 , wherein the electrode is a positive electrode.

14. Including a positive electrode, A lithium secondary battery, wherein the positive electrode is the electrode according to claim 13.

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