Positive electrode slurry composition and positive electrode prepared using the same

Abstract

This invention provides a positive electrode slurry composition comprising a positive electrode active material, a conductive material, and a binder, wherein the binder comprises: an aramid polyamide polymer containing repeating units of Formula 2; and styrene-butadiene rubber (SBR), wherein the molar fraction of the repeating units of Formula 2 is 1 to 10 mol% based on the total number of moles of all repeating units of the aramid polyamide polymer. [Formula 2]-[NH-B1-NHCO-B2-CO]- In Formula 2, B1 and B2 are each independently a divalent aliphatic organic group.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2024-0128579, filed on September 23, 2024, the disclosure of which is incorporated herein by reference.

[0002] This invention relates to a positive electrode slurry composition comprising an aramid polyamide polymer and a positive electrode prepared using the same. Background Technology

[0003] With the rapid development of industries using rechargeable batteries, such as mobile phones, laptops, and electric vehicles, extensive research and development are underway to improve rechargeable battery performance. Among these, lithium rechargeable batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Here, the electrode for a lithium-ion secondary battery typically comprises a current collector and an electrode mixture layer formed on the current collector as a functional layer. The electrode mixture layer is formed, for example, by coating a slurry-type composition, obtained by dispersing an electrode active material and a polymer-containing binder composition used as a binder in a dispersion medium, onto the current collector and then drying it.

[0005] Polyvinylidene fluoride (PVdF) binders, which exhibit excellent electrochemical properties and thermal stability, are typically used as cathode binders. However, cathode slurry compositions containing PVdF suffer from viscosity increases or gelation over time. Summary of the Invention

[0006] Technical issues

[0007] To address these problems, the present invention aims to provide a positive electrode slurry composition that remains virtually unchanged over time.

[0008] Furthermore, the present invention provides a positive electrode that has excellent electrochemical performance, thermal stability, and improved adhesion.

[0009] Technical solution

[0010] [1] The present invention provides a positive electrode slurry composition comprising an aramid polyamide polymer and styrene-butadiene rubber (SBR) as a binder. That is, the present invention provides a positive electrode slurry composition comprising a positive electrode active material, a conductive material and a binder, wherein the binder comprises: an aramid polyamide polymer comprising repeating units of chemical formula 2; and styrene-butadiene rubber (SBR), wherein the molar fraction of the repeating units of chemical formula 2 is 1 to 10 mol based on the total number of moles of all repeating units of the aramid polyamide polymer.

[0011] [Chemical Formula 2]

[0012] -[NH-B1-NHCO-B2-CO]-

[0013] In chemical formula 2, B1 and B2 are each independently a divalent aliphatic organic group.

[0014] [2] In the above [1], the present invention provides a positive electrode slurry composition, wherein the aramid polyamide polymer further comprises a repeating unit of chemical formula 1.

[0015] [Chemical Formula 1]

[0016] -[NH-A1-NHCO-A2-CO]-

[0017] In chemical formula 1, A1 and A2 are each independently a divalent organic group with an aromatic ring.

[0018] [3] In addition, the present invention provides a positive electrode comprising: a positive electrode current collector; a positive electrode active material layer comprising a positive electrode active material, a conductive material and an adhesive, wherein the adhesive comprises repeating units of the above chemical formula 1 and styrene-butadiene rubber (SBR), wherein the molar fraction of the repeating units of the above chemical formula 1 is 90 to 99 mol based on the total number of moles of all repeating units of the aramid polyamide polymer.

[0019] Beneficial effects

[0020] The aramid-based polyamide polymer binder included in the cathode slurry composition of the present invention does not cause reactions such as those with defluorinated hydrogen from lithium byproducts, and therefore does not form active material / binder / conductive material complexes. As a result, the cathode slurry composition of the present invention exhibits an effect of suppressing changes and gelation over time. Therefore, the advantage of using the cathode slurry composition of the present invention is that the slurry can be easily stirred and transferred, and its processability is improved.

[0021] Furthermore, the positive electrode prepared from the positive electrode slurry composition of the present invention exhibits improved overall characteristics due to the uniform coating of the positive electrode active material layer and the uniform physical properties of the entire electrode.

[0022] Furthermore, the cathode slurry composition of the present invention may contain a polymer comprising repeating units having aromatic rings in its structure at a level of 90 to 99 mol% and styrene-butadiene rubber (SBR) as a binder, such that the viscosity of the cathode slurry composition can be kept neither too low nor too high. That is, the present invention can provide a cathode slurry composition that does not exhibit excessively high slurry viscosity even at high solids content. Therefore, this reduces the amount of solvent evaporated during the formation of the cathode active material layer, thereby reducing the amount of heat energy used and improving the efficiency of the drying process. In addition, this results in a shorter drying time during the formation of the cathode active material layer, thereby reducing thermal wrinkles and cracks in the prepared cathode. Detailed Implementation

[0023] It should be understood that the words or terms used in this invention and the claims should not be construed as being limited to the meanings defined in commonly used dictionaries, but should be interpreted as having meanings and concepts consistent with the technical spirit of the invention, based on the principle that the inventors can appropriately define the concepts of the terms in order to best describe the invention.

[0024] It should also be understood that the terms "comprising," "including," or "having" in this invention explicitly state the presence of the stated features, numbers, steps, constituent elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, constituent elements, or combinations thereof.

[0025] Furthermore, in the description of "a to b carbon atoms" in this invention, "a" and "b" each represent the number of carbon atoms contained in a specific functional group. That is, the functional group can contain "a" to "b" carbon atoms. For example, "alkylene with 1 to 5 carbon atoms" refers to the following alkylene groups: namely, -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH3)CH-, -CH(CH3)CH2-, or -CH(CH3)CH2CH2-, etc.

[0026] Furthermore, in this specification, alkyl groups may be substituted or unsubstituted. Unless otherwise defined in the specification, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is replaced by a non-hydrogen element such as a halogen atom, a nitro group, a nitrile group, etc.

[0027] In this specification, "weight-average molecular weight" can be measured using a gel permeation chromatography (GPC) apparatus. Specifically, in this invention, measurements are performed under GPC conditions using an Agilent 1200 series column, wherein the column used can be a PL-B hybrid column manufactured by Agilent, and the solvent can be tetrahydrofuran (THF) or dimethylformamide (DMF). Note that unless otherwise specified in this specification, molecular weight can be expressed as weight-average molecular weight.

[0028] Furthermore, in this specification, "viscosity" can be measured using a commercially available viscometer. Specifically, in this invention, "viscosity" is measured using a Rheometer MCR 302 manufactured by Anton Paar, and the viscosity is measured at 25°C and a shear rate of 2.5 (1 / s).

[0029] The invention will be described in more detail below.

[0030] Positive electrode slurry composition

[0031] As a positive electrode slurry composition, the positive electrode slurry composition comprises a positive electrode active material, a conductive material, and a binder, wherein the binder comprises: an aramid polyamide polymer comprising repeating units of the following chemical formula 1; and styrene-butadiene rubber (SBR).

[0032] [Chemical Formula 1]

[0033] -[NH-A1-NHCO-A2-CO]-

[0034] In the above chemical formula 1, A1 and A2 can each be independently a divalent organic group with an aromatic ring. An aromatic ring refers to an arylene group having 6 to 12 carbon atoms. In addition, A1 and A2 can each independently contain -SO2-, -CO-, -COO-, etc. in their structure.

[0035] In the above chemical formula 1, A1 and A2 can each be a divalent organic group selected from any one of chemical formulas 1-1 to 1-5.

[0036] [Chemical Formula 1-1]

[0037] [Chemical Formula 1-2]

[0038] [Chemical Formulas 1-3]

[0039] [Chemical Formulas 1-4]

[0040] [Chemical Formulas 1-5]

[0041] In chemical formulas 1-1 to 1-5, These are bonding sites.

[0042] In the above chemical formula 1, A1 can be a divalent organic group selected from either chemical formula 1-1 or chemical formula 1-2.

[0043] In the above chemical formula 1, A2 can be any divalent organic group selected from chemical formulas 1-3 to 1-5.

[0044] Based on the total molar number of repeating units in the aramid polymer, the aramid polymer contained in the cathode slurry composition of the present invention may contain the repeating units of the above-mentioned Formula 1 in a molar fraction of 90 mol% to 99 mol%, preferably 92 mol% to 97 mol%, more preferably 93 mol% to 95 mol%. When mixed with styrene-butadiene rubber (SBR), when the content of the aromatic repeating units of Formula 1 contained in the aramid polymer meets the above range, this can maintain phase stability, inhibit gelation, and obtain a viscosity within an appropriate range.

[0045] Aramid polyamide polymers may also contain repeating units of the following chemical formula 2.

[0046] [Chemical Formula 2]

[0047] -[NH-B1-NHCO-B2-CO]-

[0048] In the above chemical formula 2, B1 and B2 can each independently be a divalent aliphatic organic group. Specifically, B1 and B2 can each independently be an alkylene group having 2 to 50 carbon atoms. B1 and B2 can each independently be -(CH2). n - where n can be in the range of 2≤n≤50, 2≤n≤20, or 2≤n≤10. As the content of aromatic repeating units in the aramid polymer increases, the viscosity of the cathode slurry composition increases significantly, making it difficult to coat the cathode active material layer onto the current collector. However, when the amount of aliphatic repeating units contained in the aramid polymer is small, the viscosity can be adjusted.

[0049] Based on the total molar number of repeating units in the aramid polyamide polymer, the aramid polyamide polymer contained in the positive electrode slurry composition of the present invention may contain the repeating units of the above-mentioned chemical formula 2 in a molar fraction of 1 mol% to 10 mol%, preferably 3 mol% to 8 mol%, more preferably 5 mol% to 7 mol%. When the content of aliphatic repeating units of chemical formula 2 contained in the aramid polyamide polymer meets the above range, the viscosity of the composition can be maintained at an appropriate level.

[0050] The weight-average molecular weight of the aramid polymer contained in the positive electrode slurry composition of the present invention can be from 200,000 g / mol to 600,000 g / mol, preferably from 250,000 g / mol to 550,000 g / mol, and more preferably from 300,000 g / mol to 500,000 g / mol. When the molecular weight meets the above range, phase separation of the slurry composition does not occur, the positive electrode active material and the like are sufficiently dispersed, and the slurry composition can be uniformly stirred. Furthermore, when the positive electrode slurry composition is used to prepare a positive electrode active material layer, it exhibits excellent adhesion to the electrode current collector.

[0051] The aramid polymer contained in the cathode slurry composition of the present invention may not contain carboxyl functional groups. If the structure of the aramid polymer is replaced by carboxyl functional groups, the slurry viscosity may increase significantly when mixed with styrene-butadiene rubber.

[0052] Since the styrene-butadiene rubber (SBR) contained in the cathode slurry composition of the present invention is an aqueous binder, solvent replacement may be necessary in order to incorporate the SBR into the cathode slurry composition. For example, the water-dispersed styrene-butadiene rubber (SBR) and the cathode slurry composition can be added to a stirring vessel with a solvent, and the mixture can be stirred at a temperature of 80°C to 95°C, a pressure of 50 Torr to 150 Torr, and a rotation speed of 200 rpm to 1000 rpm for 2 to 20 hours, thereby evaporating the water and replacing the solvent.

[0053] The average particle size of the styrene-butadiene rubber (SBR) included in the positive electrode slurry composition of the present invention can be from 150 nm to 400 nm, preferably from 200 nm to 380 nm, and more preferably from 250 nm to 350 nm. When the average particle size of the SBR meets the above range, the adhesive can be uniformly dispersed throughout the entire positive electrode active material layer even after the drying process. Furthermore, when the average particle size of the SBR meets the above range, the adhesion of the positive electrode current collector can be sufficiently high when the positive electrode active material layer is prepared from the positive electrode slurry composition.

[0054] In the repeating units of styrene-butadiene rubber (SBR) included in the positive electrode slurry composition of the present invention, the molar ratio of styrene-derived repeating units to butadiene-derived repeating units can be from 1:4 to 1:0.5, preferably from 3:1 to 1:1, and more preferably from 2.5:1 to 1.5:1. When the molar ratio of styrene-derived repeating units to butadiene-derived repeating units satisfies the above range, the adhesion to the electrode current collector can be excellent without increasing the resistance of the prepared electrode.

[0055] In the positive electrode paste composition of the present invention, the weight ratio of the aramid polyamide polymer to styrene-butadiene rubber (SBR) can be from 0.5:1 to 10:1, preferably from 1:1 to 7:1, and more preferably from 2:1 to 5:1. When the binder content ratio satisfies the above range, the positive electrode paste exhibits excellent phase stability, and when preparing the positive electrode active material layer from the positive electrode paste composition, it can provide a sufficiently high adhesion force to the positive electrode current collector.

[0056] The positive electrode paste composition of the present invention is characterized in that it does not include a fluorine-containing binder such as polyvinylidene fluoride (PVdF). As a result, the positive electrode paste composition of the present invention has environmental advantages and can have an appropriate viscosity for preparing a positive electrode with improved phase stability and excellent performance.

[0057] The viscosity of the positive electrode paste composition of the present invention at 25 °C can be from 7,500 cP to 50,000 cP, preferably from 8,000 cP to 30,000 cP, and more preferably from 8,500 cP to 20,000 cP.

[0058] Based on the total weight of the positive electrode paste composition of the present invention, the solid content can be 55% by weight or more and 80% by weight or less, 60% by weight or more and 79% by weight or less, or 65% by weight or more and 75% by weight or less. The positive electrode paste composition of the present invention maintains a low viscosity even at a high solid content, which does not impose a large load on the motor of the stirrer or the transfer pump during the preparation of the paste composition, thereby improving the processability of the positive electrode preparation process. In addition, when using the positive electrode paste composition of the present invention to prepare a positive electrode, it exhibits a uniformly coated positive electrode active material layer.

[0059] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and specifically may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium metal oxide can be: lithium manganese-based oxides (for example, LiMnO2, LiMn2O4, etc.), lithium cobalt-based oxides (for example, LiCoO2, etc.), lithium nickel-based oxides (for example, LiNiO2, etc.), lithium nickel manganese-based oxides (for example, LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium nickel cobalt-based oxides (for example, LiNi 1-Y1 Co[[ID=2】] Y1 O2 (where 0 < Y1 < 1), etc.), lithium manganese cobalt-based oxides (for example, LiCo 1- Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1Co Z1 O4 (where 0 < Z1 < 2), lithium nickel manganese cobalt oxides (e.g., Li(Ni) p Co q Mn r O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), or lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni)O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or lithium nickel cobalt transition metal (M) p2 Co q2 Mn r2 M s2 O2 (where M is selected from Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each atomic fractions of independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc., and any one of them or a mixture of two or more of them can be used.

[0060] Among these, lithium metal oxides can improve battery capacity performance and stability, including: LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxides (e.g., Li(Ni)O2). 1 / 3 Mn 1 / 3 Co 1 / 3 O2, Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 (e.g., O2), or lithium nickel cobalt aluminum oxides (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 (O2, etc.) etc., and any one of them or a mixture of two or more thereof can be used.

[0061] Among them, the positive electrode active material contained in the positive electrode paste composition of the present invention may be a lithium transition metal oxide having a composition represented by the following Chemical Formula 3. The higher the nickel content, the more lithium by-products such as LiOH and Li2CO3 are eluted from the positive electrode active material. As a result, the positive electrode paste composition is likely to change over time. However, the positive electrode paste composition of the present invention can suppress such changes by adjusting the molar fraction of aromatic repeating units in the aramid polyamide polymer binder and simultaneously containing the aramid polyamide polymer and styrene-butadiene rubber (SBR).

[0062] [Chemical Formula 3]

[0063] Li a Ni 1-x-y Co x M 1 y M 2 z O2

[0064] In Chemical Formula 3 above, M 1 may be one or more selected from Mn and Al, and preferably may be Mn or a combination of Mn and Al.

[0065] In Chemical Formula 3 above, M 2 may be any one element or two or more elements selected from Zr, Ti, Mg, Ta, Nb, W, Mo, and Cr.

[0066] a represents the molar ratio of lithium in the lithium transition metal oxide, and may be 1.0 ≤ a ≤ 1.3, 1.0 ≤ a ≤ 1.2, or 1.0 ≤ a ≤ 1.1.

[0067] 1 - x - y represents the molar ratio of nickel in the metal elements other than lithium in the lithium transition metal oxide, and may be 0.80 ≤ 1 - x - y < 1.0, 0.80 ≤ 1 - x - y ≤ 0.98, 0.80 ≤ 1 - x - y ≤ 0.95, 0.83 ≤ 1 - x - y ≤ 0.95, or 0.90 ≤ 1 - x - y ≤ 0.95. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0068] x represents the molar ratio of cobalt in the metal elements other than lithium in the lithium transition metal oxide, and may be 0 < x < 0.4, 0 < x ≤ 0.2, or 0.01 ≤ x ≤ 0.10.

[0069] y represents the molar ratio of element M 1 in the metal elements other than lithium in the lithium transition metal oxide, and may be 0 < y < 0.4, 0 < y ≤ 0.2, or 0.01 ≤ y ≤ 0.10.

[0070] z represents element M, which is a metallic element other than lithium, in lithium transition metal oxides. 2 The molar ratio can be 0≤z≤0.1 or 0≤z≤0.05.

[0071] Based on the total weight of the positive electrode active material contained in the positive electrode active material layer, the content of lithium transition metal oxide contained in the positive electrode active material layer of the present invention can be 95% to 100% by weight, preferably 98% to 100% by weight, and more preferably 99% to 100% by weight.

[0072] Conductive materials are used to impart conductivity to electrodes and can be used without any particular restrictions, provided they do not cause chemical changes in the cell to be formed and possess electronic conductivity. Specific examples include: graphite such as natural or artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode slurry composition, the content of the conductive material can be from 0.1% by weight to 15% by weight.

[0073] The adhesive of the present invention may also comprise commonly used adhesives. Specific examples include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers wherein hydrogen is substituted by Li, Na, or Ca, or various copolymers thereof, and any one or mixtures of two or more thereof may be used. Based on the total weight of the positive electrode slurry composition, the additional adhesive content may be from 0.1% by weight to 5% by weight.

[0074] The positive electrode slurry composition of the present invention can be prepared by dissolving or dispersing positive electrode active materials, conductive materials, binders, etc. in a solvent.

[0075] The solvent may be a solvent commonly used in the art and may contain dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or water, and any one or a mixture of two or more thereof may be used.

[0076] Based on the total weight of the cathode slurry composition, the amount of solvent used can be 20% or more and 45% or less, 21% or more and 40% or less, or 25% or more and 35% or less.

[0077] positive electrode

[0078] The positive electrode of the present invention comprises: a positive electrode current collector; and a positive electrode active material layer comprising a positive electrode active material, a conductive material, and a binder. Since the positive electrode active material, the conductive material, and the binder have already been described above, their detailed descriptions will be omitted, and only the remaining components will be described in detail below.

[0079] The positive electrode of the present invention can be prepared by coating the above-described positive electrode slurry composition, followed by drying and calendering. Alternatively, in another method, the positive electrode can be prepared by casting the positive electrode slurry forming composition onto a separate support, and then pressing the film layer separated from the support onto the positive electrode current collector.

[0080] The positive electrode current collector of the present invention can contain a highly conductive metal, and there are no particular limitations, as long as the positive electrode active material layer adheres easily and is non-reactive within the voltage range of the battery. As the positive electrode current collector, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., can be used. Furthermore, the thickness of the positive electrode current collector can typically be from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0081] The content of aramid polyamide polymer can be 0.1% by weight or more and 5% by weight, 0.5% by weight or more and 3.5% by weight, 0.8% by weight or more and 3.0% by weight, or 1.0% by weight or more and 2.0% by weight.

[0082] Electrochemical device

[0083] The electrochemical element according to the present invention will be described below. The electrochemical device according to the present invention includes the positive electrode described above, and the electrochemical device can specifically be a battery, a capacitor, etc., and more specifically a lithium secondary battery.

[0084] A lithium-ion secondary battery specifically comprises: a positive electrode, a negative electrode facing the positive electrode, a separator between the positive and negative electrodes, and an electrolyte. The positive electrode is the same as described above, therefore, its detailed description will be omitted. The following will only describe the remaining components in detail.

[0085] In addition, the lithium secondary battery may optionally include a battery case that houses a positive electrode, a negative electrode, and a separator, and a sealing member that seals the battery case.

[0086] In the lithium secondary battery of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0087] There is no particular limitation on the negative electrode current collector as long as it has high conductivity and does not cause adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and an aluminum-cadmium alloy can be used. The thickness of the negative electrode current collector can generally be 3 μm to 500 μm, and similar to the positive electrode current collector, fine concavities and convexities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as a film, sheet, foil, net, porous body, foam body, non-woven fabric body, etc.

[0088] The negative electrode active material layer contains both a negative electrode active material and optionally a binder and a conductive material.

[0089] Compounds capable of reversibly intercalating and deintercalating lithium can be used as the negative electrode active material. Specific examples thereof include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; (semi) metallic materials capable of forming an alloy with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; (semi) metal oxides capable of doping and dedoping lithium such as SiO x (0 < x < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composites containing (semi) metallic materials and carbonaceous materials such as Si-C composites or Sn-C composites, and any one of these or a mixture of two or more thereof can be used. In addition, a thin film of metallic lithium can be used as the negative electrode active material. As the carbon material, low-crystalline carbon and high-crystalline carbon can be used. Typical examples of low-crystalline carbon are soft carbon and hard carbon, and examples of high-crystalline carbon include irregular, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch, and high-temperature sintered carbon such as coke derived from petroleum or coal tar pitch.

[0090] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80% by weight to 99% by weight.

[0091] The adhesive is a component that facilitates the bonding between the conductive material, the active material, and the current collector. The amount of adhesive added is typically from 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer. Examples of adhesives include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0092] The conductive material is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, the amount of conductive material added can be less than 10% by weight, preferably less than 5% by weight. Any conductive material can be used without limitation, as long as it is conductive and will not cause adverse chemical changes in the battery. Examples of conductive materials that can be used include: graphite such as natural or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon 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.

[0093] The negative electrode active material layer can be prepared by coating a negative electrode current collector with a negative electrode active material layer forming composition prepared by dissolving or dispersing the negative electrode active material and optionally a binder and conductive material in a solvent, drying and then calendering, or by casting the negative electrode active material layer forming composition onto a separate support and then pressing the film layer separated from the support onto the negative electrode current collector.

[0094] On the other hand, in lithium secondary batteries, the separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used in lithium secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, separators coated with 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 be selectively used.

[0095] Examples of electrolytes used in this invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the preparation of lithium secondary batteries.

[0096] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0097] Organic solvents can be used without any particular restrictions, as long as they can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. Specific examples of organic solvents include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; and sulfolane. Carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can enhance the charge and discharge performance of the battery and linear carbonate compounds with low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) are even more preferred.

[0098] Lithium salts can be used without any particular restrictions, as long as they are compounds capable of providing lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt can be at least one selected from the following anions: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN- and (CF3CF2SO2)2N - Furthermore, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used as lithium salts. Preferably, the concentration of the lithium salt is from 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte exhibits suitable conductivity and viscosity, which enables excellent electrolyte performance and efficient lithium ion transfer.

[0099] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the components constituting the electrolyte, the electrolyte may also contain one or more additives, such as alkylene carbonate halide compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted alkyl ketones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. Based on the total weight of the electrolyte, the content of additives can be from 0.1% by weight to 5% by weight.

[0100] Lithium secondary batteries containing the positive electrode according to the present invention as described above are suitable for use in portable devices such as mobile phones, laptops and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs), because they stably exhibit excellent discharge capacity, output and lifespan characteristics.

[0101] Therefore, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit battery and a battery pack comprising the lithium secondary battery are provided.

[0102] Battery modules or battery packs can be used as a power source for at least one medium to large-sized device, including: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0103] There are no particular limitations on the shape of the lithium secondary battery of the present invention, and it can be in the form of a cylindrical can, prism, bag, or coin.

[0104] The lithium secondary battery according to the present invention can be used not only in battery cells used as power sources for small devices, but also as unit batteries in medium and large battery modules containing multiple battery cells.

[0105] Examples of medium to large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0106] Preferred Implementation

[0107] The embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0108] Example

[0109] Example 1

[0110] Prepare an aramid-based polyamide polymer containing 75 mol% of repeating units of Formula 1A, 20 mol% of repeating units of Formula 1B, and 5 mol% of repeating units of Formula 2A.

[0111] [Chemical Formula 1A]

[0112] [Chemical Formula 1B]

[0113] [Chemical Formula 2A]

[0114] -[NH-(CH2)6-NHCO-(CH2)6-CO]-

[0115] The positive electrode active material (LiNi) was mixed at a weight ratio of 96.0:2.0:1.6:0.4. 0.84 Co 0.08 Mn 0.08 O2), conductive material (carbon black), aramid polyamide polymer and styrene-butadiene rubber were mixed in N-methyl-2-pyrrolidone and stirred at 1500 rpm for 2 hours using a high-speed stirrer (Homodisper) to prepare a positive electrode slurry composition.

[0116] At this point, based on the total weight of the cathode slurry composition, the solids content of the cathode slurry composition is 70% by weight.

[0117] Example 2

[0118] Prepare an aramid-based polyamide polymer containing 75 mol% of repeating units of Formula 1A, 20 mol% of repeating units of Formula 1B, and 5 mol% of repeating units of Formula 2A.

[0119] [Chemical Formula 1A]

[0120] [Chemical Formula 1B]

[0121] [Chemical Formula 2A]

[0122] -[NH-(CH2)6-NHCO-(CH2)6-CO]-

[0123] The positive electrode active material (LiNi) was mixed at a weight ratio of 96.0:2.0:1.4:0.6. 0.84 Co 0.08 Mn 0.08 O2), conductive material (carbon black), aramid polyamide polymer and styrene-butadiene rubber were mixed in N-methyl-2-pyrrolidone and stirred at 1500 rpm for 2 hours using a high-speed stirrer (Homodisper) to prepare a positive electrode slurry composition.

[0124] At this point, based on the total weight of the cathode slurry composition, the solids content of the cathode slurry composition is 70% by weight.

[0125] Example 3

[0126] Prepare an aramid-based polyamide polymer containing 72 mol% of repeating units of Formula 1A, 20 mol% of repeating units of Formula 1B, and 8 mol% of repeating units of Formula 2A.

[0127] [Chemical Formula 1A]

[0128] [Chemical Formula 1B]

[0129] [Chemical Formula 2A]

[0130] -[NH-(CH2)6-NHCO-(CH2)6-CO]-

[0131] The positive electrode active material (LiNi) was mixed at a weight ratio of 96.0:2.0:1.6:0.4. 0.84 Co 0.08 Mn 0.08 O2), conductive material (carbon black), aramid polyamide polymer and styrene-butadiene rubber were mixed in N-methyl-2-pyrrolidone and stirred at 1500 rpm for 2 hours using a high-speed stirrer (Homodisper) to prepare a positive electrode slurry composition.

[0132] At this point, based on the total weight of the cathode slurry composition, the solids content of the cathode slurry composition is 70% by weight.

[0133] Comparative Example 1

[0134] The positive electrode active material (LiNi) was mixed at a weight ratio of 96:2:2. 0.84 Co 0.08 Mn 0.08 O2), conductive material (carbon black) and binder (polyvinylidene fluoride (PVDF)) were mixed in N-methyl-2-pyrrolidone and stirred at 1500 rpm for 2 hours using a high-speed stirrer (Homodisper) to prepare a positive electrode slurry composition.

[0135] At this point, based on the total weight of the cathode slurry composition, the solids content of the cathode slurry composition is 70% by weight.

[0136] Comparative Example 2

[0137] Prepare an aramid-based polyamide polymer containing 75 mol% of repeating units of Formula 1A, 20 mol% of repeating units of Formula 1B, and 5 mol% of repeating units of Formula 2A.

[0138] [Chemical Formula 1A]

[0139] [Chemical Formula 1B]

[0140] [Chemical Formula 2A]

[0141] -[NH-(CH2)6-NHCO-(CH2)6-CO]-

[0142] The positive electrode active material (LiNi) was mixed at a weight ratio of 96:2:2. 0.84 Co 0.08 Mn 0.08 O2), conductive material (carbon black) and aramid polyamide polymer were mixed in N-methyl-2-pyrrolidone and stirred at 1500 rpm for 2 hours using a high-speed stirrer (Homodisper) to prepare a positive electrode slurry composition.

[0143] At this point, based on the total weight of the cathode slurry composition, the solids content of the cathode slurry composition is 70% by weight.

[0144] Comparative Example 3

[0145] Prepare an aramid-based polyamide polymer containing 65 mol% of repeating units of Formula 1A, 20 mol% of repeating units of Formula 1B, and 15 mol% of repeating units of Formula 2A.

[0146] [Chemical Formula 1A]

[0147] [Chemical Formula 1B]

[0148] [Chemical Formula 2A]

[0149] -[NH-(CH2)6-NHCO-(CH2)6-CO]-

[0150] The positive electrode active material (LiNi) was mixed at a weight ratio of 96.0:2.0:1.6:0.4. 0.84 Co 0.08 Mn 0.08 O2), conductive material (carbon black), aramid polyamide polymer and styrene-butadiene rubber were mixed in N-methyl-2-pyrrolidone and stirred at 1500 rpm for 2 hours using a high-speed stirrer (Homodisper) to prepare a positive electrode slurry composition.

[0151] At this point, based on the total weight of the cathode slurry composition, the solids content of the cathode slurry composition is 70% by weight.

[0152] Comparative Example 4

[0153] Prepare an aramid-based polyamide polymer containing 80 mol% of repeating units of Formula 1A and 20 mol% of repeating units of Formula 1B.

[0154] [Chemical Formula 1A]

[0155] [Chemical Formula 1B]

[0156] The positive electrode active material (LiNi) was mixed at a weight ratio of 96.0:2.0:1.6:0.4. 0.84 Co 0.08 Mn 0.08 O2), conductive material (carbon black), aramid polyamide polymer and styrene-butadiene rubber were mixed in N-methyl-2-pyrrolidone and stirred at 1500 rpm for 2 hours using a high-speed stirrer (Homodisper) to prepare a positive electrode slurry composition.

[0157] At this point, based on the total weight of the cathode slurry composition, the solids content of the cathode slurry composition is 70% by weight.

[0158] Experimental Example 1—Viscosity Evaluation

[0159] The positive electrode slurry compositions prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were measured using a Rheometer MCR 302 manufactured by Anton Paar, and the viscosity was measured at 25°C and a shear rate of 2.5 (1 / s). Furthermore, they were each stored at 25°C, and the viscosity was measured at 25°C after 3 days and 7 days. The results are presented in Table 1 below.

[0160] [Table 1]

[0161] It was confirmed that Examples 1 to 3 maintained a stable phase even after 7 days of storage, compared to Comparative Example 1, which used a conventional polyvinylidene fluoride (PVdF) adhesive. It was confirmed that Examples 1 to 3 maintained appropriate viscosity and a stable phase, compared to Comparative Example 2, which used only aramid polymers. It was confirmed that Examples 1 to 3 maintained appropriate viscosity and a stable phase, even compared to Comparative Examples 3 and 4, where the mole fraction of repeating units of Formula 1 deviated from 90 to 99 mol% based on the total mole number of repeating units of the aramid polymer.

[0162] Experimental Example 2—Measurement of Adsorption Capacity

[0163] Five grams of each positive electrode slurry composition prepared in Examples 1 and 2 and Comparative Example 1 were centrifuged at 20,000 rpm for 30 minutes using a centrifuge (Supra R30, Hanil Scientific Inc.) to separate the solids and supernatant.

[0164] The viscosity of the supernatant was measured using a Brookfield DV-II+PRO Viscometer (Brookfield Corporation) at 25°C, 50 RH %, and 30 Hz. The results were then compared with previously obtained viscosity data based on the polyvinylidene fluoride (PVdF) content (mg / g) in N-methyl-2-pyrrolidone (NMP) to determine the supernatant concentration. The residual amount of binder in the supernatant was then calculated and subtracted from the amount of binder added to obtain the adsorbent content (mg / g) per 1g of positive electrode active material.

[0165] The results are presented in Table 2 below.

[0166] [Table 2]

[0167] Compared to Comparative Example 1, which used a conventional PVdF binder, the content of the adsorbent binder based on 1g of positive electrode active material was measured to be much smaller in Examples 1 and 2, thus the variation over time during long-term storage is expected to be small.

[0168] Experimental Example 3—Evaluation of the Adhesion Force of the Positive Electrode Active Material Layer

[0169] For the positive electrode slurry compositions prepared in Examples 1 to 3 and Comparative Examples 1 to 4, the adhesion between the positive electrode active material layer and the positive electrode current collector was compared.

[0170] Specifically, after preparing the positive electrode using the positive electrode slurry compositions prepared in Examples 1 to 3 and Comparative Examples 1 to 4, the positive electrode was cut into pieces 150 mm long and 20 mm wide, and the electrode surface was adhered along its length to a glass slide 75 mm long and 25 mm wide using double-sided adhesive tape. That is, the glass slide was adhered to the area corresponding to half of the positive electrode along its length. Evaluation samples were then prepared by rolling the double-sided adhesive tape evenly 10 times with a roller bearing a 2 kg load. The glass slide of the evaluation sample was fixed to the sample stage of a universal testing machine (UTM) (LF Plus, manufactured by LLOYD), and the half of the glass slide without the positive electrode attached was connected to the load sensor of the UTM device. While moving the load sensor to 50 mm at a speed of 100 mm / min, the load applied to the load sensor was measured. At this time, the minimum load was measured in the range of 20 mm to 40 mm within the movement range, which was taken as the electrode adhesion force (gf / 20 mm) for each sample. After a total of 5 evaluations, the average values ​​of each positive electrode are presented in Table 3.

[0171] [Table 3]

[0172] It was confirmed that, compared to the cathodes of Comparative Examples 1 and 2, the cathodes of Examples 1 and 2 of the present invention exhibited higher adhesion between the cathode active material layer and the cathode current collector. It was confirmed that, in the cathode of Comparative Example 3, the cathode active material layer prepared from the cathode slurry composition did not adhere to the cathode current collector. It was confirmed that, in Comparative Example 4, the cathode active material layer prepared from the cathode slurry composition did not adhere to the cathode current collector because of the lack of aliphatic repeating units and the extremely high cathode viscosity, resulting in poor surface coating.

Claims

1. A positive electrode slurry composition, said positive electrode slurry composition comprising a positive electrode active material, a conductive material, and a binder, The adhesive comprises: Aramid-based polyamide polymers containing repeating units of formula 2; and styrene-butadiene rubber (SBR), and Based on the total number of moles of all repeating units of the aramid polyamide polymer, the mole fraction of repeating units in Formula 2 is from 1 mol% to 10 mol%. [Chemical Formula 2] -[NH-B1-NHCO-B2-CO]- In chemical formula 2, B1 and B2 are each independently a divalent aliphatic organic group.

2. The positive electrode slurry composition according to claim 1, The aramid-based polyamide polymer further comprises repeating units of formula 1. [Chemical Formula 1] -[NH-A1-NHCO-A2-CO]- In chemical formula 1, A1 and A2 are each independently a divalent organic group with an aromatic ring.

3. The positive electrode slurry composition according to claim 2, A1 and A2 are each independently selected from chemical formulas 1-1 to 1-5. [Chemical Formula 1-1] [Chemical Formula 1-2] [Chemical Formulas 1-3] [Chemical Formulas 1-4] [Chemical Formulas 1-5] in, In chemical formulas 1-1 to 1-5, These are bonding sites.

4. The positive electrode slurry composition according to claim 1, The aramid polyamide polymer contains repeating units of Formula 1 in a weight fraction of 84% to 99.5% or less.

5. The positive electrode slurry composition according to claim 1, B1 and B2 are each independently an alkylene group having 2 to 50 carbon atoms.

6. The positive electrode slurry composition according to claim 1, The weight-average molecular weight of the aramid polyamide polymer is from 200,000 g / mol to 600,000 g / mol.

7. The positive electrode slurry composition according to claim 1, The styrene-butadiene rubber (SBR) wherein the weight-average molecular weight is 200,000 g / mol to 600,000 g / mol.

8. The positive electrode slurry composition according to claim 1, The styrene-butadiene rubber (SBR) mentioned therein has an average particle size of 150 nm to 400 nm.

9. The positive electrode slurry composition according to claim 1, In the repeating units constituting the styrene-butadiene rubber (SBR), the molar fraction of repeating units derived from styrene to repeating units derived from butadiene is 1:4 to 1:0.

5.

10. The positive electrode slurry composition according to claim 1, The weight ratio of the aramid polyamide polymer to the styrene-butadiene rubber (SBR) is 0.5:1 to 10:

1.

11. The positive electrode slurry composition according to claim 1, The solids content is 55% to 80% by weight, based on the total weight of the positive electrode slurry composition.

12. A positive electrode, said positive electrode comprising: Positive current collector; And a positive electrode active material layer comprising a positive electrode active material, a conductive material, and a binder. The adhesive comprises: an aramid polyamide polymer containing repeating units of formula 2; and styrene-butadiene rubber (SBR). Based on the total number of moles of all repeating units of the aramid polyamide polymer, the mole fraction of repeating units in Formula 2 is from 1 mol% to 10 mol%. [Chemical Formula 2] -[NH-B1-NHCO-B2-CO]- In chemical formula 2, B1 and B2 are each independently a divalent aliphatic organic group.

13. The positive electrode according to claim 12, The aramid-based polyamide polymer further comprises repeating units of formula 1. [Chemical Formula 1] -[NH-A1-NHCO-A2-CO]- In chemical formula 1, A1 and A2 are each independently a divalent organic group with an aromatic ring.

14. The positive electrode according to claim 12, The content of the aramid polyamide polymer is 0.1% to 5% by weight, based on the total weight of the positive electrode active material layer.

15. The positive electrode according to claim 12, The positive electrode active material comprises a lithium transition metal oxide represented by chemical formula 3. [Chemical Formula 3] Li a Ni 1-x-y Co x M 1 y M 2 z O2 In chemical formula 3, M 1 It is Al, Mn or a combination thereof. M 2 It is selected from one or more elements chosen from Zr, Ti, Mg, Ta, Nb, W, Mo, and Cr. Where 1.0 ≤ a ≤ 1.3, 0 <x<0.1,0<y<0.1,0≤z≤0.1,0.8≤1-x-y<1.0。

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