Positive electrode and lithium secondary battery containing the same

Abstract

To provide a positive electrode with excellent resistance characteristics and superior mechanical strength. [Solution] The positive electrode mixture layer comprises a binder containing a positive electrode active material and hydrogenated carboxylated nitrile butadiene rubber, comprising 20% ​​to 40% by weight of a first structural unit derived from acrylonitrile represented by a specific formula, based on 100% by weight of the rubber; 30% to 78% by weight of a second structural unit containing a hydrogenated butadiene-derived structural unit represented by a specific formula and a butadiene-derived structural unit represented by a specific formula; 2% to 10% by weight of a third structural unit represented by a specific formula; and 0% to 20% by weight of a fourth structural unit represented by a specific formula, wherein the hydrogenated butadiene-derived structural unit represented by the specific formula is present in an amount of 90% or more and less than 100% by weight relative to 100% by weight of the second structural unit, and the butadiene-derived structural unit represented by the specific formula is present in an amount of more than 0% and 10% or less relative to 100% by weight of the second structural unit.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode and a lithium secondary battery including the same.

Background Art

[0002] Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. As a result, research and development for improving the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of insertion (intercalation) and desorption (deintercalation) of lithium ions, and an electrolyte, and produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed at the positive electrode and the negative electrode.

[0004] The lithium secondary battery can be recharged again after discharge and continuously used, and shows a difference in performance depending on the charge and discharge state. Therefore, efforts are being made to improve the charging method to improve the performance of the lithium secondary battery.

[0005] The positive electrode for a lithium secondary battery includes a positive electrode current collector and a positive electrode mixture layer formed thereon. The positive electrode mixture layer essentially contains a positive electrode active material and selectively further contains a positive electrode binder and / or a conductive material.

[0006] As the positive electrode binder, a polyvinylidene fluoride-based binder is widely used, but this also acts as a resistor.

[0007] Therefore, in order to increase the adhesion of the positive electrode and lower the resistance while increasing the life of the lithium secondary battery, it is necessary to use a polyvinylidene fluoride-based positive electrode binder to a minimum or completely replace it with another binder.

Prior Art Documents

[0008] [Patent Document 1] Chinese Patent Application Publication No. 117769773 Specification [Overview of the project] [Problems that the invention aims to solve]

[0009] One embodiment provides a positive electrode that has excellent resistance characteristics while also having excellent mechanical strength. Another embodiment provides a lithium secondary battery with excellent lifespan characteristics by including the positive electrode. [Means for solving the problem]

[0010] One embodiment includes a positive electrode current collector and a positive electrode mixture layer located on the positive electrode current collector. The positive electrode mixture layer comprises a binder containing a positive electrode active material and hydrogenated carboxylated nitrile butadiene rubber. The hydrogenated carboxylated nitrile butadiene rubber contains, per 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, 20% to 40% by weight of a first structural unit derived from acrylonitrile represented by the following chemical formula 1; 30% to 78% by weight of a second structural unit including a hydrogenated butadiene-derived structural unit represented by the following chemical formula 2A and a butadiene-derived structural unit represented by the following chemical formula 2B; 2% to 10% by weight of a third structural unit represented by the following chemical formula 3; and 0% to 20% by weight of a fourth structural unit represented by the following chemical formula 4. The present invention provides a positive electrode in which, with respect to 100% by weight of the second structural unit, the structural unit derived from hydrogenated butadiene represented by chemical formula 2A is contained in an amount of 90% by weight or more and less than 100% by weight, and the structural unit derived from butadiene represented by chemical formula 2B is contained in an amount of more than 0% by weight and 10% by weight or less, with respect to 100% by weight of the second structural unit.

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[0016] In the aforementioned chemical formula 3, R 1 These include hydrogen, substituted or unsubstituted C1-C20 alkyl groups, ester groups (-COOR, where R is a substituted or unsubstituted C1-C20 alkyl group), cyano groups (-CN), pyrrolidonyl groups (-C3H5NHCO), carboxyl groups (-COOH), and caprolactamyl groups (-NCOC5H 10 These are morpholinyl (-NC4H8O), a hydroxyl group (-OH), an amino group (-NH2), a vinyl group (-CH=CH2), an epoxy group (-COCH2), or a thiol group (-SH).

[0017] Other embodiments include a positive electrode active material, a binder containing hydrogenated carboxylated nitrile butadiene rubber, and a solvent. The hydrogenated carboxylated nitrile butadiene rubber contains, per 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, 20% to 40% by weight of a first structural unit derived from acrylonitrile represented by the following chemical formula 1; 30% to 78% by weight of a second structural unit including a hydrogenated butadiene-derived structural unit represented by the following chemical formula 2A and a butadiene-derived structural unit represented by the following chemical formula 2B; 2% to 10% by weight of a third structural unit represented by the following chemical formula 3; and 0% to 20% by weight of a fourth structural unit represented by the following chemical formula 4. With respect to 100% by weight of the second structural unit, the structural unit derived from hydrogenated butadiene represented by chemical formula 2A is contained in an amount of 90% by weight or more and less than 100% by weight. The present invention provides a positive electrode composition in which, with respect to 100% by weight of the second structural unit, the structural unit derived from butadiene represented by chemical formula 2B is contained in an amount greater than 0% by weight and less than or equal to 10% by weight.

[0018] The definitions for each chemical formula are the same as those described above.

[0019] Another embodiment provides a lithium secondary battery comprising the positive electrode, a negative electrode containing a negative electrode active material, and an electrolyte. [Effects of the Invention]

[0020] One embodiment of the positive electrode has the advantage of having excellent resistance characteristics while also having excellent mechanical strength, and a lithium secondary battery containing this electrode has the advantage of having excellent lifespan characteristics. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 3] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 4] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Modes for carrying out the invention]

[0022] Embodiments of the present invention will be described in detail below. However, these are presented as examples only and do not limit the present invention, which is defined solely by the scope of the claims.

[0023] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0024] Here, "these combinations" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0025] Here, terms such as “include,” “equip,” or “possess” are intended to specify the presence of an implemented feature, figure, stage, component, or combination thereof, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, figures, stages, components, or combinations thereof.

[0026] In the drawings, thicknesses are shown enlarged to clearly represent various layers and regions, and similar parts are denoted by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on top" of another part, this includes not only when it is "directly above" another part, but also when there is another part in between. Conversely, when a part is said to be "directly above" another part, it means that there is no other part in between.

[0027] Furthermore, in this context, "layer" includes not only the shapes formed on the entire surface when observed in a plan view, but also the shapes formed on some of the surfaces.

[0028] In this specification, unless otherwise specified, singular nouns may also include plural nouns. Similarly, unless otherwise specified, "A or B" may mean "containing A, containing B, or containing both A and B."

[0029] The term "metal" is interpreted as a concept that includes general metals, transition metals, and metalloids.

[0030] In this specification, unless otherwise defined, particle size may refer to average particle size. Furthermore, particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. Average particle size (D50) can be measured by methods widely known to those skilled in the art, such as using a particle size analyzer, or by using a transmission electron microscope or scanning electron microscope. Alternatively, it can be measured using a dynamic light-scattering device, followed by data analysis to count the number of particles for each particle size range, and then calculating the average particle size (D50) value. Alternatively, it can be measured using the laser diffraction method. More specifically, when measuring using the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac's MT3000), and after irradiating with ultrasound at approximately 28 kHz at an output of 60 W, the average particle size (D50) based on the 50% standard of the particle size distribution in the analyzer can be calculated.

[0031] In this specification, unless otherwise specified, “alkyl group” means a C1-C20 alkyl group, “alkenyl group” means a C2-C20 alkenyl group, “cycloalkenyl group” means a C3-C20 cycloalkenyl group, “heterocycloalkenyl group” means a C3-C20 heterocycloalkenyl group, “aryl group” means a C6-C20 aryl group, “arylalkyl group” means a C6-C20 arylalkyl group, “alkylene group” means a C1-C20 alkylene group, “arylene group” means a C6-C20 arylene group, “alkylarylene group” means a C6-C20 alkylarylene group, “heteroarylene group” means a C3-C20 heteroarylene group, and “alkoxylene group” means a C1-C20 alkoxylene group.

[0032] In this specification, unless otherwise specified, “substitution” means that at least one hydrogen atom is replaced by a halogen atom (F, Cl, Br, I), a hydroxyl group, a C1-C20 alkoxy group, a nitro group, a cyano group, an amine group, an imino group, an azide group, an amidino group, a hydrazino group, a hydrazono group, a carbonyl group, a carbamyl group, a thiol group, an ester group, an ether group, a carboxyl group or its salt, a sulfonic acid group or its salt, a phosphoric acid or its salt, a C1- This means that the substituent is substituted with a C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C3-C20 cycloalkyl group, a C3-C20 cycloalkenyl group, a C3-C20 cycloalkynyl group, a C2-C20 heterocycloalkyl group, a C2-C20 heterocycloalkenyl group, a C2-C20 heterocycloalkynyl group, a C3-C20 heteroaryl group, or a combination thereof.

[0033] Furthermore, unless otherwise specified herein, "hetero" means that the chemical formula contains at least one heteroatom of at least one of N, O, S, and P.

[0034] In this specification, unless otherwise specified, “combination” means mixing or copolymerization.

[0035] In the chemical formulas herein, unless otherwise defined, the absence of a chemical bond at a position where one would normally be depicted means that a hydrogen atom is bonded to that position.

[0036] In this specification, the weight-average molecular weight (Mw) may be a value measured using gel permeation chromatography (GPC).

[0037] Generally, high-nickel cathode active materials are used to realize high-capacity batteries, but high-nickel cathode active materials have the problem of having a large amount of residual lithium (LiOH, Li2CO3, or free Li, etc.) on the surface of the active material.

[0038] The residual lithium reacts with the polyvinylidene fluoride-based positive electrode binder, causing modification of the binder in the positive electrode composition. This leads to a rapid increase in viscosity and gelation of the positive electrode composition (slurry), making it difficult to coat the current collector with the slurry. Furthermore, when manufacturing electrode plates with a positive electrode composition containing the modified binder, there is a problem of excessively increased resistance of the electrode plates.

[0039] positive electrode One embodiment provides a positive electrode for a lithium secondary battery, comprising a positive electrode current collector and a positive electrode mixture layer located on the positive electrode current collector, wherein the positive electrode mixture layer comprises a positive electrode active material and a binder containing hydrogenated carboxylated nitrile butadiene rubber.

[0040] The binder containing the hydrogenated carboxylated nitrile butadiene rubber can suppress gelation of the cathode composition while achieving an adhesive strength equivalent to or better than that of a polyvinylidene fluoride-based cathode binder.

[0041] Furthermore, the positive electrode containing the hydrogenated carboxylated nitrile butadiene rubber as a binder has the advantage of showing less change in electrode plate resistance during prolonged storage and having far superior mechanical properties such as electrode plate flexibility compared to the positive electrode containing the polyvinylidene fluoride-based binder.

[0042] The following describes a positive electrode according to one embodiment in more detail.

[0043] binder In one embodiment, the positive electrode mixture layer includes a binder containing hydrogenated carboxylated nitrile butadiene rubber (H-XNBR).

[0044] In one embodiment, the hydrogenated carboxylated nitrile butadiene rubber comprises a first structural unit derived from acrylonitrile represented by the following chemical formula 1; a second structural unit including a hydrogenated butadiene-derived structural unit represented by the following chemical formula 2A and a butadiene-derived structural unit represented by the following chemical formula 2B; a third structural unit represented by the following chemical formula 3; and a fourth structural unit represented by the following chemical formula 4.

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[0050] In the aforementioned chemical formula 3, R 1 These include hydrogen, substituted or unsubstituted C1-C20 alkyl groups, ester groups (-COOR, where R is a substituted or unsubstituted C1-C20 alkyl group), cyano groups (-CN), pyrrolidonyl groups (-C3H5NHCO), carboxyl groups (-COOH), and caprolactamyl groups (-NCOC5H 10 These are morpholinyl (-NC4H8O), a hydroxyl group (-OH), an amino group (-NH2), a vinyl group (-CH=CH2), an epoxy group (-COCH2), or a thiol group (-SH).

[0051] As an example, the first structural unit may be present in an amount of 20% to 40% by weight relative to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, or for example, 25% to 40% by weight, 30% to 40% by weight, or 30% to 35% by weight. If the amount of the first structural unit is less than 20% by weight relative to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, the electrolyte resistance may decrease, and if it is more than 40% by weight, mechanical properties such as the flexibility of the positive electrode may decrease.

[0052] As an example, the second structural unit may be present in an amount of 30% to 78% by weight relative to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, or for example, in amounts of 30% to 70% by weight, 40% to 70% by weight, 50% to 70% by weight, or 50% to 60% by weight. When the second structural unit is present in the above numerical range relative to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, conductive materials such as CNTs (carbon nanotubes) can be well dispersed in the electrode plate.

[0053] As an example, the third structural unit may be present in an amount of 2% to 10% by weight relative to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, or for example, 3% to 10% by weight, 4% to 10% by weight, or 4% to 8% by weight. If the third structural unit is present in an amount of less than 2% by weight relative to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, the adhesive strength of the binder may decrease, and if it is present in an amount of more than 10% by weight, the adhesive strength of the binder may increase excessively, leading to a problem of reduced flexibility of the electrode plate.

[0054] As an example, the fourth structural unit may be present in an amount of 0% to 20% by weight relative to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, or, for example, in an amount of 1% to 15% by weight, 5% to 20% by weight, 5% to 15% by weight, or 5% to 10% by weight. If the fourth structural unit is not present relative to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, the flexibility of the electrode plate may decrease, and the dispersibility of conductive materials such as CNTs within the electrode plate may decrease. If it is present in an amount exceeding 20% ​​by weight, the adhesive strength of the binder may decrease.

[0055] In one embodiment, the amount of structural units derived from hydrogenated butadiene represented by chemical formula 2A is 90% or more and less than 100% by weight relative to 100% by weight of the second structural units, and the amount of structural units derived from butadiene represented by chemical formula 2B is greater than 0% and less than or equal to 10% by weight relative to 100% by weight of the second structural units.

[0056] If the second structural unit does not contain the butadiene-derived structural unit represented by chemical formula 2B (0% by weight), π-π bonding between the conductive material (CNT) and butadiene may be difficult, reducing the dispersibility of CNTs within the electrode plate. If it contains more than 10% by weight, the solubility of the binder in the solvent (e.g., NMP) in the positive electrode composition may decrease, reducing the wettability of the CNTs.

[0057] The binder containing the hydrogenated carboxylated nitrile butadiene rubber may be present in amounts of 0.1% to 5% by weight, 0.3% to 3% by weight, 0.5% to 2% by weight, or 0.55% to 1.1% by weight, based on the total amount of the positive electrode mixture layer.

[0058] The binder containing the hydrogenated carboxylated nitrile butadiene rubber may have a weight-average molecular weight (Mw) measured by the GPC method of 50,000 g / mol to 500,000 g / mol, or for example, 100,000 g / mol to 500,000 g / mol, 200,000 g / mol to 500,000 g / mol, or 200,000 g / mol to 400,000 g / mol.

[0059] As an example, the positive electrode mixture layer may selectively further contain other binders.

[0060] For example, the other binder may include polyvinylidene fluoride, its derivatives, copolymers containing the same, or combinations thereof, or it may include acrylic binders, its derivatives, copolymers containing the same, or combinations thereof. For example, the other binder may include polyvinylidene fluoride (PVdF), PVDF-HFP (Hexafluoropropylene) copolymer, PVDF-TrFE (Trifluoroethylene) copolymer, PVDF-CTFE (Chlorotrifluoroethylene) copolymer, poly(meth)acrylic acid, poly(meth)acrylate, polymethyl(meth)acrylate, polyacrylonitrile, acrylonitrile-styrene-butadiene copolymer, or combinations thereof.

[0061] It is preferable to completely replace the other binders with the binder containing the hydrogenated carboxylated nitrile butadiene rubber, but the other binders may be mixed and used in order to ensure adhesive strength, compatibility, etc.

[0062] The aforementioned other binders may have a weight-average molecular weight (Mw) measured by the GPC method ranging from 500,000 g / mol to 5,000,000 g / mol, 500,000 g / mol to 3,000,000 g / mol, or 500,000 g / mol to 1,500,000 g / mol.

[0063] The aforementioned other binders may be present in amounts of more than 0% by weight to 3% by weight or less, more than 0% by weight to 2% by weight or less, more than 0% by weight to 1% by weight or less, or more than 0% by weight to 0.1% by weight or less, based on the total amount of the positive electrode mixture layer.

[0064] positive electrode active material As the positive electrode active material, a compound capable of reversible insertion and desorption of lithium (lithium insertion compound) can be used. Specifically, one or more of composite oxides of metals selected from cobalt, manganese, nickel, aluminum, and combinations thereof and lithium can be used.

[0065] The composite oxide may be a lithium transition metal composite oxide. Specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0066] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Mn 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni b Co c L 1 d G e O2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0 ≦ e ≦ 0.1); Li a NiG bO2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4 (0.90 ≤ a ≤ 1.8).

[0067] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 This is Mn, Al, or a combination of these.

[0068] In one embodiment, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium is 80 mol% or more, 85 mol% or more, 88 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. High-nickel positive electrode active materials can achieve high capacity and are applicable to high-capacity, high-density lithium secondary batteries.

[0069] High-nickel cathode active materials have a high residual lithium content on the surface of the cathode active material particles. This residual lithium reacts with PVdF, which is commonly used as a cathode binder, to induce gelation of the cathode slurry. This can increase the slurry viscosity during electrode plate fabrication, leading to deviations in the loading level during the coating process and potentially resulting in coating defects.

[0070] A binder according to one embodiment does not react with residual lithium on the surface of the high-nickel positive electrode active material and can prevent gelation of the positive electrode slurry. This makes it possible to maintain the viscosity of the positive electrode composition at an appropriate level, improve processability, lower the resistance of the positive electrode, and improve physical properties such as the bending strength of the positive electrode.

[0071] As an example, the positive electrode active material may include a lithium nickel-based composite oxide, and for example, it may include a compound represented by the following chemical formula 5.

[0072] [Chemical formula 5] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the above chemical formula 5, 0.9≦a1≦1.8, 0.3≦x1≦1, 0≦y1≦0.7, 0≦z1≦0.7, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1, M 1 and M 2 X is a distinct element, each independently selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, while X is a distinct element, each independently selected from the group consisting of F, P, and S.

[0073] In the aforementioned chemical formula 5, either 0.6≦x1≦1, 0≦y1≦0.4, and 0≦z1≦0.4, or 0.8≦x1≦1, 0≦y1≦0.2, and 0≦z1≦0.2, or 0.9≦x1<1, 0 <y1≦0.1、および0≦z1≦0.1であってもよい。

[0074] The positive electrode active material may, as a specific example, include a lithium nickel-cobalt composite oxide represented by the following chemical formula 6.

[0075] [Chemical formula 6] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2 In the above chemical formula 6, 0.9 ≤ a² ≤ 1.8, 0.3 ≤ x² < 1, 0 <y2≦0.7、0≦z2≦0.7、0.9≦x2+y2+z2≦1.1、および0≦b2≦0.1であり、M 3 X is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0076] In the aforementioned chemical formula 6, for example, 0.7 ≤ x² < 1, 0 <y2≦0.3、0≦z2≦0.3であるか、0.8≦x2<1、0<y2≦0.2、0≦z2≦0.2であるか、0.9≦x2<1、0<y2≦0.1、0≦z2≦0.1であってもよい。

[0077] The positive electrode active material may, as a more specific example, include a lithium nickel-cobalt-manganese composite oxide, a lithium nickel-cobalt-aluminum composite oxide, or a lithium nickel-cobalt-aluminum-manganese composite oxide represented by the following chemical formula 7.

[0078] [Chemical formula 7] Li a3 Ni x3 Co y3M 3 z3 M 4 w3 O 2-b3 X b3 In the above chemical formula 7, 0.9≦a3≦1.8, 0.3≦x3≦0.98, 0.01≦y3≦0.69, 0.01≦z3≦0.69, 0≦w3≦0.69, 0.9≦x3+y3+z3+w3≦1.1, and 0≦b3≦0.1, M 4 is Al, Mn, or a combination thereof, M 5 X is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0079] The positive electrode active material may be in the form of secondary particles formed by the aggregation of multiple primary particles, or in the form of single particles, or it may contain both secondary particles and single particles.

[0080] The average particle size (D) of the positive electrode active material 50 The particle size may be 1 μm to 25 μm, for example, 1 μm to 20 μm or 3 μm to 18 μm. The positive electrode active material has an average particle size (D 50 ) are large particles of 10 μm to 25 μm, or average particle size (D 50 The average particle size (D) may be small particles of 1 μm to 8 μm, or it may contain both large and small particles. 50 The particle size may be obtained by selecting approximately 20 particles from a scanning electron microscope image of the positive electrode active material, measuring their particle size (diameter, major axis, or major axis length), obtaining a particle size distribution, and then taking the size of the particle with a cumulative volume of 50% in the particle size distribution as the average particle size.

[0081] The content of the positive electrode active material may be 90% to 99.5% by weight relative to 100% by weight of the positive electrode mixture layer.

[0082] conductive material As an example, the positive electrode mixture layer may further contain a conductive material.

[0083] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0084] The conductive material may be present in an amount of 0.1% to 5% by weight, 0.5% to 3% by weight, or 1% to 2% by weight, of the total amount of the positive electrode mixture layer.

[0085] As an example, the binder may be present in an amount of 0.1% to 2% by weight relative to 100% by weight of the combined positive electrode active material, the binder containing hydrogenated carboxylated nitrile butadiene rubber, and the conductive material.

[0086] As an example, the positive electrode active material may be present in an amount of 97% to 99.8% by weight relative to 100% by weight of the combined positive electrode active material, the binder containing hydrogenated carboxylated nitrile butadiene rubber, and the conductive material.

[0087] As an example, the conductive material may be present in an amount of 0.1% to 1% by weight relative to 100% by weight of the combined positive electrode active material, the binder containing hydrogenated carboxylated nitrile butadiene rubber, and the conductive material.

[0088] When the above numerical range is satisfied, a positive electrode can be realized that effectively suppresses gelation of the positive electrode composition while exhibiting excellent mechanical properties of the electrode plate.

[0089] Crosslinking agent As an example, the positive electrode mixture layer may further contain a crosslinking agent in addition to the binder in order to ensure that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector.

[0090] Specifically, the crosslinking agent may be a carbodiimide compound-based crosslinking agent.

[0091] More specifically, the crosslinking agent may be represented by the following chemical formula 12:

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[0093] In the aforementioned chemical formula 12, R 4 and R 5 Each of these is independently a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group comprising one or more elements selected from the group consisting of N, O, S, and P; L 1 and L 2 Each of these is independently a substituted or unsubstituted C1-C20 alkylene group, a substituted or unsubstituted C3-C20 cycloalkylene group, a substituted or unsubstituted C6-C20 arylene group, or a substituted or unsubstituted C2-C20 heteroarylene group containing one or more selected from the group consisting of N, O, S, and P; n is an integer between 1 and 20.

[0094] As an example, the crosslinking agent may include one or more compounds selected from the following Group 1.

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[0098] The crosslinking agent may be present in an amount of more than 0% to 3% by weight, more than 0% to 3% by weight, more than 0% to 2% by weight, more than 0% to 1% by weight, or more than 0% to 0.1% by weight, based on the total amount of the positive electrode mixture layer.

[0099] Al can be used as the positive electrode current collector, but is not limited to it.

[0100] Cathode composition One embodiment discloses a positive electrode composition comprising a positive electrode active material, a binder containing hydrogenated carboxylated nitrile butadiene rubber, and a solvent. The positive electrode composition may exist in the form of a positive electrode slurry.

[0101] The positive electrode active material and the binder containing the hydrogenated carboxylated nitrile butadiene rubber are all identical to those described above.

[0102] As an example, the hydrogenated carboxylated nitrile butadiene rubber contains, per 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, 20% to 40% by weight of a first structural unit derived from acrylonitrile represented by the following chemical formula 1; 30% to 78% by weight of a second structural unit including a hydrogenated butadiene-derived structural unit represented by the following chemical formula 2A and a butadiene-derived structural unit represented by the following chemical formula 2B; 2% to 10% by weight of a third structural unit represented by the following chemical formula 3; and 0% to 20% by weight of a fourth structural unit represented by the following chemical formula 4.

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[0108] In the aforementioned chemical formula 3, R 1 These include hydrogen, substituted or unsubstituted C1-C20 alkyl groups, ester groups (-COOR, where R is a substituted or unsubstituted C1-C20 alkyl group), cyano groups (-CN), pyrrolidonyl groups (-C3H5NHCO), carboxyl groups (-COOH), and caprolactamyl groups (-NCOC5H 10 These are morpholinyl (-NC4H8O), a hydroxyl group (-OH), an amino group (-NH2), a vinyl group (-CH=CH2), an epoxy group (-COCH2), or a thiol group (-SH).

[0109] With respect to 100% by weight of the second structural unit, the amount of structural unit derived from hydrogenated butadiene represented by chemical formula 2A is 90% or more but less than 100% by weight, and with respect to 100% by weight of the second structural unit, the amount of structural unit derived from butadiene represented by chemical formula 2B is more than 0% but 10% or less by weight.

[0110] The binder containing the hydrogenated carboxylated nitrile butadiene rubber may have a weight-average molecular weight (Mw) measured by the GPC method of 50,000 g / mol to 500,000 g / mol, or for example, 100,000 g / mol to 500,000 g / mol, 200,000 g / mol to 500,000 g / mol, or 200,000 g / mol to 400,000 g / mol.

[0111] As an example, the solvent included in the positive electrode composition can be any solvent that does not cause side reactions with the positive electrode active material and binder, and as an example, it may include N-methyl-2-pyrrolidone (NMP).

[0112] As an example, the positive electrode composition may further selectively contain other binders.

[0113] For example, the other binder may include polyvinylidene fluoride, its derivatives, copolymers containing the same, or combinations thereof, or it may include acrylic binders, its derivatives, copolymers containing the same, or combinations thereof. For example, the other binder may include polyvinylidene fluoride (PVdF), PVDF-HFP (Hexafluoropropylene) copolymer, PVDF-TrFE (Trifluoroethylene) copolymer, PVDF-CTFE (Chlorotrifluoroethylene) copolymer, poly(meth)acrylic acid, poly(meth)acrylate, polymethyl(meth)acrylate, polyacrylonitrile, acrylonitrile-styrene-butadiene copolymer, or combinations thereof.

[0114] The aforementioned other binders may have a weight-average molecular weight (Mw) measured by the GPC method ranging from 500,000 g / mol to 5,000,000 g / mol, 500,000 g / mol to 3,000,000 g / mol, or 500,000 g / mol to 1,500,000 g / mol.

[0115] As an example, the positive electrode composition may further contain a conductive material.

[0116] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes in the battery can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0117] As an example, the binder may be present in an amount of 0.1% to 2% by weight relative to 100% by weight of the combined positive electrode active material, the binder containing hydrogenated carboxylated nitrile butadiene rubber, and the conductive material.

[0118] As an example, the positive electrode active material may be present in an amount of 97% to 99.8% by weight relative to 100% by weight of the combined positive electrode active material, the binder containing hydrogenated carboxylated nitrile butadiene rubber, and the conductive material.

[0119] As an example, the conductive material may be present in an amount of 0.1% to 1% by weight relative to 100% by weight of the combined positive electrode active material, the binder containing hydrogenated carboxylated nitrile butadiene rubber, and the conductive material.

[0120] When the above numerical range is satisfied, a positive electrode can be realized that effectively suppresses gelation of the positive electrode composition while exhibiting excellent mechanical properties of the electrode plate.

[0121] As an example, the positive electrode composition may further contain a crosslinking agent, the same as described above.

[0122] As an example, the positive electrode composition may further include a lithium-containing compound present on the surface of the positive electrode active material, the lithium-containing compound may include LiOH, Li2CO3, free Li, or a combination thereof.

[0123] In the positive electrode composition, the LiOH may be present in an amount of 0.002% by weight or more, 0.01% by weight or more, or 0.1% by weight or more, or 1.0% by weight or less, 0.6% by weight or less, or 0.58% by weight or less, based on 100% by weight of the positive electrode active material.

[0124] With respect to 100% by weight of the positive electrode active material, the Li2CO3 may be present in an amount of 0.004% by weight or more, 0.01% by weight or more, or 0.1% by weight or more, or in an amount of 0.4% by weight or less, or 0.36% by weight or less.

[0125] With respect to 100% by weight of the positive electrode active material, the free Li may be present in an amount of 0.002% by weight or more, 0.01% by weight or more, or 0.07% by weight or more, or 0.3% by weight or less, or 0.24% by weight or less.

[0126] The content of the lithium-containing compound in the positive electrode active material may vary depending on the type of positive electrode active material, and for example, the numerical range may be the content of the lithium-containing compound when using a high-nickel positive electrode active material.

[0127] When the positive electrode active material described above is a high-nickel (High-Ni) positive electrode active material in which the nickel content is 80 mol% or more relative to 100 mol% of the metal excluding lithium in a lithium transition metal composite oxide, a large amount of the lithium-containing compound (hereinafter also referred to as residual lithium) may be present on the surface of the positive electrode active material. Such lithium-containing compounds can adversely affect the electrochemical properties, thermal safety, and life characteristics of the battery, and methods such as cleaning the surface of the positive electrode active material are used to remove or reduce the lithium-containing compounds.

[0128] For example, when the lithium-containing compound is mixed with a polyvinylidene fluoride binder such as PVdF, there is a problem in that the viscosity of the positive electrode composition increases rapidly and gels.

[0129] A positive electrode composition according to one embodiment includes a binder containing the hydrogenated carboxylated nitrile butadiene rubber, and such a binder can effectively prevent a rapid increase in the viscosity of the positive electrode composition even when mixed with a high-nickel positive electrode active material.

[0130] Lithium-ion battery Another embodiment provides a lithium secondary battery comprising the positive electrode, a negative electrode containing a negative electrode active material, and an electrolyte, wherein the lithium secondary battery can have improved battery life characteristics and the like by including the positive electrode described above.

[0131] The electrolyte may be a liquid electrolyte solution or a solid electrolyte.

[0132] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment, with Figure 1 being cylindrical, Figure 2 being prismatic, and Figures 3 and 4 being pouch-type batteries. Referring to Figures 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 can include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium secondary battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, and a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0133] A lithium secondary battery according to one embodiment of the present invention is applicable to automobiles, mobile phones, and / or various forms of electrical devices, and the present invention is not limited thereto.

[0134] The following will provide a detailed explanation of the elements that make up the lithium secondary battery, in addition to the positive electrode mentioned above.

[0135] negative electrode active material The negative electrode active material includes a material into which lithium ions can be reversibly inserted / de-inserted, lithium metal, an alloy of lithium metal, a material that can be doped and de-doped with lithium, or a transition metal oxide.

[0136] As the substance capable of reversibly inserting / desorbing the lithium ions, a carbon-based negative electrode active material can be included, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0137] For the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0138] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0139] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0140] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0141] The Si-based or Sn-based anode active material can be used in combination with a carbon-based anode active material.

[0142] negative electrode A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0143] For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0144] The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0145] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0146] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylicated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0147] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound capable of imparting viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0148] The dry binder is a fibrous polymeric substance, which may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0149] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes in the battery can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0150] As the negative electrode current collector, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be selected.

[0151] electrolyte The electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0152] The aforementioned non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0153] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0154] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of ester-based solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. Suitable ether solvents include dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Suitable ketone solvents include cyclohexanone. Suitable alcohol solvents include ethyl alcohol and isopropyl alcohol. Suitable aprotic solvents include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0155] The aforementioned non-aqueous organic solvents can be used alone or in combination of two or more.

[0156] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and these can be mixed in a volume ratio of 1:1 to 1:9.

[0157] The lithium salt dissolves in an organic solvent and acts as a source of lithium ions in the battery, enabling the operation of a basic lithium secondary battery and playing a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), lithium bis(oxalato)borate (LiBOB), and can include one or more selected therefrom.

[0158] Separator Depending on the type of lithium secondary battery, a separator can also be present between the positive electrode and the negative electrode. Such separators can use polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these, and of course, mixed multilayer films such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, and a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0159] The separator can include a porous substrate and a coating layer located on one or both sides of the porous substrate and containing an organic substance, an inorganic substance, or a combination thereof.

[0160] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon®, and polytetrafluoroethylene, or from copolymers or mixtures of two or more of these polymers.

[0161] The aforementioned organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0162] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0163] The organic and inorganic materials can exist mixed in a single coating layer, or in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are stacked.

[0164] Examples and comparative examples of the present invention are described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0165] (Examples) Example 1 (1) Manufacturing of binders A hydrogenated carboxylated nitrile butadiene rubber binder (hereinafter sometimes referred to as H-XNBR) is manufactured, containing 33% by weight of a first structural unit represented by the following chemical formula 1, 57% by weight of a second structural unit including the compound represented by the following chemical formula 2A and the compound represented by the following chemical formula 2B, 5% by weight of a third structural unit represented by the following chemical formula 3, and 5% by weight of a fourth structural unit represented by the following chemical formula 4 (wherein R1 in the above chemical formula 3 is a methyl group (-CH3)).

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[0171] At this time, the compound represented by chemical formula 2A is present in an amount of 95% by weight and the compound represented by chemical formula 2B is present in an amount of 5% by weight, relative to 100% by weight of the second structural unit.

[0172] The weight-average molecular weight of the H-XNBR produced in Example 1 is 300,000 g / mol.

[0173] (2) Manufacturing of the positive electrode A positive electrode slurry (positive electrode composition) was prepared by dispersing the positive electrode active material, conductive material, and binder in N-methyl-2-pyrrolidone according to the composition shown in Table 1 below.

[0174] At this time, the amount of lithium-containing compounds present on the surface of the positive electrode active material was measured by HCl titration and is shown in Table 1 below.

[0175] Specifically, 10 g of positive electrode active material is placed in 100 ml of distilled water and stirred at a speed of 300 rpm for 30 minutes. After stirring is complete, the positive electrode active material is allowed to settle, and then 40 ml of the supernatant is filtered under reduced pressure and added to 100 ml of distilled water, and then titrated with 1N HCl.

[0176] Lithium-containing compounds, which are unreacted residual lithium on the surface of the positive electrode active material, exist in forms such as Li2CO3, LiOH, and free Li, therefore CO3 2- , OH - Ions and other elements of HCl + The reaction is carried out through titration. The amount of HCl solution added was calculated to determine the amount of unreacted residual lithium.

[0177] The positive electrode slurry was coated onto a 12 μm thick aluminum foil, then dried and rolled to produce a positive electrode containing a positive electrode mixture layer.

[0178] Examples 2-4 and Comparative Examples 1-2 The positive electrode composition and positive electrode were manufactured in the same manner as in Example 1, except that the contents of the positive electrode active material, conductive material, and binder were adjusted as shown in Table 1 below.

[0179] Examples 5-6 and Comparative Example 3 The manufacturing process was the same as in Example 1, except that the type of positive electrode active material was changed to LiCoO2 (LCO), and the content of the positive electrode active material, conductive material, and binder was adjusted as shown in Table 1 below to produce the positive electrode composition and positive electrode.

[0180] [Table 1]

[0181] The substances used in Table 1 are as follows:

[0182] (A) Positive electrode active material NCA:LiNi 0.94 Co 0.045 Al 0.015 O2 LCO: LiCoO2 (B) Conductive material CNT: Carbon nanotube (C) Binder PVdF: Polyvinylidene fluoride H-XNBR: Hydrogenated carboxylated nitrile butadiene rubber binder

[0183] (Example of evaluation) Evaluation Example 1: Viscosity (cP) evaluation of positive electrode slurry The viscosity of the positive electrode slurries produced in Examples 1-6 and Comparative Examples 1-3 was evaluated.

[0184] Specifically, viscosity was measured at different shear rates using an Anton Paar rheometer, and the viscosity values ​​at a shear rate of 10 (1 / s) are shown in Table 2 below.

[0185] Specifically, the "initial viscosity," "viscosity after 3 days of stirring," and "viscosity after 7 days of stirring" of the positive electrode slurry were measured. Furthermore, the "viscosity change after 7 days of stirring" was calculated by subtracting the viscosity after 7 days of stirring from the initial viscosity of the positive electrode composition, and this is shown in Table 2 below.

[0186] In Table 2, "Unmeasurable" means that the slurry has solidified and is no longer fluid.

[0187] Evaluation Example 2: Resistance Evaluation of Cathode Slurry Powder The positive electrode slurries produced in Examples 1-6 and Comparative Examples 1-3 were solidified into powder and then measured using a 4-pin resistance meter. A constant current was passed through the two end pins of the 4-pin resistance meter, and the voltage was measured at the two middle pins to determine the resistance. Then, the initial resistance value was calculated, taking into account the thickness of the positive electrode and the slurry powder, and is shown in Table 2 below.

[0188] Next, the resistance value after 7 days was calculated and is shown in Table 2 below.

[0189] Next, the resistance value after 7 days minus the initial resistance was divided by the initial resistance, and the result was multiplied by 100 to obtain the "resistance change rate (%)", which is shown in Table 2 below.

[0190] Evaluation Example 3: Evaluation of the bending strength of the positive electrode The bending strength of the positive electrodes manufactured in Examples 1-6 and Comparative Examples 1-3 was evaluated using a three-point bending tester, and the results are shown in Table 2 below.

[0191] [Table 2]

[0192] Referring to Table 2, in the positive electrode compositions (slurries) of Examples 1 to 4, the high-nickel positive electrode active material NCA has a large amount of lithium-containing compound, which is residual lithium. When H-XNBR is applied as a binder to such NCA, it can be confirmed that gelation is suppressed and the viscosity change after the slurry is left standing is small. As a result, it can be confirmed that the resistance change rate of the positive electrode slurry powder is also very small.

[0193] In contrast, in the positive electrode slurries of Comparative Examples 1 and 2, the PVdF binder reacts with residual lithium on the NCA surface, causing the slurry to solidify. As a result, the viscosity change after the slurry is left standing is significantly larger than in the examples, and the resistance change rate of the positive electrode slurry powder is also significantly larger than in the examples.

[0194] Furthermore, in Examples 5, 6, and Comparative Example 3, LCO with a very low amount of residual lithium is used as the positive electrode active material. Because there is almost no residual lithium, it can be confirmed that the viscosity change after the slurry has been left to stand is at a similarly low level in both cases where H-XNBR is used as a binder (Examples 5 and 6) and where PVdF is used (Comparative Example 3). In addition, it can be confirmed that the resistance change rate is also at a similarly low level in Examples 5, 6, and Comparative Example 3.

[0195] Referring to Table 2, it can be confirmed that Comparative Examples 1 and 2 have significantly higher positive electrode bending strength compared to Examples 1-4, and significantly lower positive electrode flexibility. Furthermore, it can be confirmed that Comparative Example 3 has significantly higher positive electrode bending strength than Examples 5 and 6, and significantly lower positive electrode flexibility. This confirms that the flexibility of the H-XNBR material itself is superior to that of PVdF.

[0196] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, and this also falls within the scope of the present invention. [Explanation of symbols]

[0197] 100: Lithium secondary battery, 10: Positive electrode 11: Positive lead tab, 12: Positive terminal 20: Negative electrode, 21: Negative electrode lead tab 22: Negative terminal, 30: Separator 40: Electrode assembly, 50: Case 60: Sealing member, 70: Electrode tab 71: Positive tab, 72: Negative tab

Claims

1. A positive electrode comprising a positive electrode current collector and a positive electrode mixture layer located on the positive electrode current collector, The positive electrode mixture layer comprises a binder containing a positive electrode active material and hydrogenated carboxylated nitrile butadiene rubber. The hydrogenated carboxylated nitrile butadiene rubber is, in proportion to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, 20% to 40% by weight of the first structural unit derived from acrylonitrile, represented by the following chemical formula 1; 30% to 78% by weight of a second structural unit containing a structural unit derived from hydrogenated butadiene represented by the following chemical formula 2A and a structural unit derived from butadiene represented by the following chemical formula 2B; Third structural unit represented by the following chemical formula 3: 2% to 10% by weight; and 0% to 20% by weight of the fourth structural unit represented by the following chemical formula 4 Includes, The positive electrode contains, with respect to 100% by weight of the second structural unit, 90% or more and less than 100% by weight of the structural unit derived from hydrogenated butadiene represented by chemical formula 2A, and with respect to 100% by weight of the second structural unit, more than 0% by weight and 10% by weight or less of the structural unit derived from butadiene represented by chemical formula 2B, 【Chemistry 1】 【Chemistry 2】 【Transformation 3】 【Chemistry 4】 【Transformation 5】 In the aforementioned chemical formula 3, R 1 is hydrogen, a substituted or unsubstituted C1-C20 alkyl group, an ester group (—COOR, where R is a substituted or unsubstituted C1-C20 alkyl group), a cyano group (—CN), a pyrrolidonyl group (—C 3 H 5 NHCO), a carboxy group (—COOH), a caprolactamyl group (—NCOC 5 H 10 ), a morpholinyl (—NC 4 H 8 O), a hydroxy group (—OH), an amino group (—NH 2 ), a vinyl group (—CH═CH 2 ), an epoxy group (—COCH 2 [[ID=ZO]]), or a thiol group (—SH).

2. The positive electrode according to claim 1, wherein the weight-average molecular weight (Mw) of the binder containing the hydrogenated carboxylated nitrile butadiene rubber is 50,000 g / mol to 500,000 g / mol.

3. The positive electrode according to claim 1, wherein the positive electrode mixture layer contains 0.1% to 5% by weight of a binder containing the hydrogenated carboxylated nitrile butadiene rubber, relative to 100% by weight.

4. The positive electrode according to claim 1, wherein the positive electrode active material comprises a compound represented by the following chemical formula 5: [Chemical formula 5] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the aforementioned chemical formula 5, 0.9 ≤ a1 ≤ 1.8, 0.3 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.7, 0 ≤ z1 ≤ 0.7, 0.9 ≤ x1 + y1 + z1 ≤ 1.1, and 0 ≤ b1 ≤ 0.

1. M 1 and M 2 These are all distinct elements, each independently selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr. X is one or more elements selected from the group consisting of F, P, and S.

5. The positive electrode according to claim 1, wherein the positive electrode active material contains a lithium nickel-based composite oxide, wherein nickel is present in an amount of 80 mol% or more relative to the total metal excluding lithium.

6. The positive electrode according to claim 1, wherein the positive electrode active material is present in an amount of 90% to 99.5% by weight relative to 100% by weight of the positive electrode mixture layer.

7. The positive electrode according to claim 1, wherein the positive electrode mixture layer further comprises a conductive material.

8. The positive electrode according to claim 7, wherein the conductive material is contained in an amount of 0.1% to 5% by weight relative to 100% by weight of the positive electrode mixture layer.

9. The positive electrode according to claim 7, wherein, with respect to 100% by weight of the combined positive electrode active material, binder, and conductive material, the positive electrode active material is present in an amount of 97% to 99.8% by weight, the binder in an amount of 0.1% to 2% by weight, and the conductive material in an amount of 0.1% to 1% by weight.

10. The positive electrode active material comprises a binder containing hydrogenated carboxylated nitrile butadiene rubber, and a solvent. The hydrogenated carboxylated nitrile butadiene rubber is, in proportion to 100% by weight of the hydrogenated carboxylated nitrile butadiene rubber, 20% to 40% by weight of the first structural unit derived from acrylonitrile, represented by the following chemical formula 1; 30% to 78% by weight of a second structural unit containing a structural unit derived from hydrogenated butadiene represented by the following chemical formula 2A and a structural unit derived from butadiene represented by the following chemical formula 2B; Third structural unit represented by the following chemical formula 3: 2% to 10% by weight; and 0% to 20% by weight of the fourth structural unit represented by the following chemical formula 4 Includes, With respect to 100% by weight of the second structural unit, the structural unit derived from hydrogenated butadiene represented by chemical formula 2A is contained in an amount of 90% by weight or more and less than 100% by weight. A positive electrode composition containing, with respect to 100% by weight of the second structural unit, the structural unit derived from butadiene represented by chemical formula 2B, which is greater than 0% and less than or equal to 10% by weight: 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】 In the aforementioned chemical formula 3, R 1 These include hydrogen, substituted or unsubstituted C1-C20 alkyl groups, ester groups (-COOR, where R is a substituted or unsubstituted C1-C20 alkyl group), cyano groups (-CN), and pyrrolidonyl groups (-C). 3 H 5 NHCO), carboxyl group (-COOH), caprolactamyl group (-NCOC) 5 H 10 ), morpholinil (-NC 4 H 8 O), hydroxyl group (-OH), amino group (-NH) 2 ), vinyl group (-CH=CH 2 ), epoxy group (-COCH 2 ), or a thiol group (-SH).

11. The positive electrode composition according to claim 10, wherein the weight-average molecular weight (Mw) of the binder containing the hydrogenated carboxylated nitrile butadiene rubber is 50,000 g / mol to 500,000 g / mol.

12. The positive electrode composition according to claim 10, wherein the positive electrode active material comprises a compound represented by the following chemical formula 5: [Chemical formula 5] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the aforementioned chemical formula 5, 0.9 ≤ a1 ≤ 1.8, 0.3 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.7, 0 ≤ z1 ≤ 0.7, 0.9 ≤ x1 + y1 + z1 ≤ 1.1, and 0 ≤ b1 ≤ 0.

1. M 1 and M 2 These are all distinct elements, each independently selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr. X is one or more elements selected from the group consisting of F, P, and S.

13. The positive electrode composition according to claim 10, wherein the positive electrode active material comprises a lithium nickel-based composite oxide containing 80 mol% or more nickel with respect to the total metal excluding lithium.

14. The positive electrode composition according to claim 10, further comprising a conductive material.

15. The positive electrode composition according to claim 14, wherein, with respect to 100% by weight of the combined positive electrode active material, binder, and conductive material, the positive electrode active material is present in an amount of 97% to 99.8% by weight, the binder in an amount of 0.1% to 2% by weight, and the conductive material in an amount of 0.1% to 1% by weight.

16. The positive electrode composition further comprises a lithium-containing compound present on the surface of the positive electrode active material, The lithium-containing compound is LiOH, Li 2 CO 3 The positive electrode composition according to claim 10, comprising free Li, or a combination thereof.

17. With respect to 100% by weight of the positive electrode active material, the amount of LiOH is 0.002% to 0.6% by weight, and the Li 2 CO 3 The positive electrode composition according to claim 16, wherein the amount of is 0.004% to 0.4% by weight, and the free Li is 0.002% to 0.3% by weight.

18. A positive electrode according to any one of claims 1 to 9, A negative electrode containing a negative electrode active material, Electrolytes and Lithium-ion batteries, including lithium-ion batteries.

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