Positive electrode for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The present disclosure relates to a positive electrode for a rechargeable lithium battery, and a rechargeable lithium battery including same, wherein the positive electrode comprises: a first positive electrode active material comprising core particles including a lithium cobalt-based oxide doped with Al, Mg, or a combination thereof, and a coating layer disposed on the surface of the core particles and including Zr, Ti, or a combination thereof; a second positive electrode active material comprising core particles including a lithium cobalt-based oxide doped with Al, Mg, or a combination thereof, and a coating layer disposed on the surface of the core particles and including Zr, Ti, or a combination thereof, the second positive electrode active material having a smaller average particle diameter (D50) than the first positive electrode active material; a first fluorine-based binder free of polar functional groups; a second fluorine-based binder containing polar functional groups; and a conductive material, with the weight ratio of the first fluorine-based binder to the second fluorine-based binder being 90:10 to 99:1.

Description

Anode for a lithium secondary battery and a lithium secondary battery comprising the same

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

[0002] Lithium secondary batteries, which boast high energy density and portability, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research is underway to utilize high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power storage devices.

[0003] To develop lithium secondary batteries suited to these applications, various cathode active materials are being explored. Among these, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are the most commonly used cathode active materials. Active research is underway to improve the energy density, cycle life, and reliability of lithium secondary batteries using lithium cobalt oxide cathode active materials capable of operating at high voltages of 4.4 V or higher.

[0004] In a positive electrode using a lithium cobalt-based oxide positive electrode active material for high voltage, the flexibility of the electrode plate is increased, thereby improving the problem of pinholes and cracks occurring at the folding portion of the electrode plate tip during winding.

[0005] In one embodiment, a first cathode active material comprising core particles containing lithium cobalt-based oxide doped with Al, Mg, or a combination thereof and a coating layer located on the surface of the core particle and containing Zr, Ti, or a combination thereof, a first cathode active material comprising core particles containing lithium cobalt-based oxide doped with Al, Mg, or a combination thereof and a coating layer located on the surface of the core particle and containing Zr, Ti, or a combination thereof, and having an average particle diameter (D) smaller than that of the first cathode active material 50) includes a second positive electrode active material, a first fluorine-based binder not containing a polar functional group, a second fluorine-based binder containing a polar functional group, and a conductive material, and a positive electrode for a lithium secondary battery is provided, wherein the weight ratio of the first fluorine-based binder and the second fluorine-based binder is 90:10 to 99:1.

[0006] In one embodiment, a lithium secondary battery is provided including the positive electrode; the negative electrode; and the electrolyte.

[0007] According to one embodiment, the anode has excellent flexibility and can effectively improve the problem of pinholes and cracks occurring at the folded portion during winding.

[0008] Figures 1 to 4 are cross-sectional views schematically showing a lithium secondary battery according to one embodiment.

[0009] Below, specific implementation examples are described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the implementation examples described herein.

[0010] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0011] “Combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0012] It should be understood that terms such as "include," "comprise," or "have" are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0013] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0014] “Layer” includes not only shapes formed on the entire surface when observed in a plan view, but also shapes formed on some surfaces.

[0015] The average particle size can be measured by methods well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with transmission electron microscope images or scanning electron microscope images. Alternatively, the average particle size can be obtained by measuring using dynamic light scattering, performing data analysis, counting the number of particles for each particle size range, and calculating from the counted number. Unless otherwise defined, the average particle size is the diameter (D) of the particles in the particle size distribution that have a cumulative volume of 50% by volume. 50 ) can mean. In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of major axis) of about 20 particles randomly in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D) of the particle having a cumulative volume of 50% by volume in the particle size distribution 50 ) may be taken as the average particle diameter.

[0016] “Or” is not interpreted as exclusive, for example, “A or B” is interpreted as including A, B, A+B, etc.

[0017] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0018] anode

[0019] In one embodiment, a positive electrode for a lithium secondary battery is provided, which includes a first positive electrode active material, a second positive electrode active material, a first fluorine-based binder not containing a polar functional group, a second fluorine-based binder containing a polar functional group, and a conductive material. The first positive electrode active material includes core particles containing a lithium cobalt-based oxide doped with Al, Mg, or a combination thereof, and a coating layer located on the surface of the core particles and containing Zr, Ti, or a combination thereof. The second positive electrode active material also includes core particles containing a lithium cobalt-based oxide doped with Al, Mg, or a combination thereof, and a coating layer located on the surface of the core particles and containing Zr, Ti, or a combination thereof, and having an average particle diameter (D) smaller than that of the first positive electrode active material. 50 ) has. Here, the weight ratio of the first fluorine-based binder and the second fluorine-based binder is characterized by being 90:10 to 99:1.

[0020] A positive electrode for a lithium secondary battery may include a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector, and the positive electrode active material layer may include the first positive electrode active material, the second positive electrode active material, a first fluorine-based binder containing a polar functional group, a second fluorine-based binder not containing a polar functional group, and a conductive material.

[0021] The above positive electrode is suitable for operation at high voltage, and can be operated at a charging voltage of, for example, 4.45 V or higher, or 4.47 V or higher, and can implement high energy density and long life characteristics. After manufacturing a battery structure by laminating the positive electrode, separator, and negative electrode, the battery structure can be wound in order to be inserted into a case such as a pouch. However, when applying a high-voltage positive electrode, if the flexibility of the electrode plate is not good, a problem occurs in which pinholes or cracks occur at the folded portion of the electrode plate during the winding process. In one embodiment, a method is proposed to improve the problem of pinholes and cracks at the folded portion by increasing the flexibility of the electrode plate.

[0022] positive electrode active material

[0023] According to one embodiment, a cathode active material is a cathode active material containing a lithium cobalt-based oxide. By mixing two types of lithium cobalt-based cathode active materials having different particle sizes, the energy density is increased, and by appropriately controlling the elements doped and coated on each of the large and small particles, the high voltage characteristics and life characteristics can be improved.

[0024] The first cathode active material can be expressed as an antipode or an antipode. The average particle diameter (D) of the first cathode active material 50 ) may be 10 ㎛ to 25 ㎛, for example, 13 ㎛ to 20 ㎛. The second positive electrode active material may be expressed as a particle or particles. The average particle diameter (D of the second positive electrode active material 50 ) may be 2 ㎛ to 6 ㎛, for example, 3 ㎛ to 5.5 ㎛. The positive electrode active material is a mixed form of a first positive electrode active material as an opposing particle and a second positive electrode active material as a small particle, and thus the composite density can be improved, and high capacity and high energy density can be realized.

[0025] In addition, when the average particle size of the first positive electrode active material is a and the particle size of the second positive electrode active material is b, a and b may satisfy 3b≤a≤4b. When a and b satisfy this relationship, the capacity characteristics and high-temperature characteristics can be improved while maximizing the composite density.

[0026] With respect to the total 100 wt% of the first positive electrode active material and the second positive electrode active material, the first positive electrode active material may be included in an amount of 60 wt% to 90 wt%, or 70 wt% to 80 wt%, and the second positive electrode active material may be included in an amount of 10 wt% to 40 wt%, or 20 wt% to 30 wt%. In this case, the positive electrode active material may implement high capacity, improve composite density, and exhibit high energy density.

[0027] The lithium cobalt-based oxide of the first positive electrode active material and the lithium cobalt-based oxide of the second positive electrode active material are each characterized by being doped with Al, Mg, or a combination thereof. For example, only Al or both Al and Mg may be doped. According to one embodiment, by doping the lithium cobalt-based oxide with Al, Mg, or a combination thereof, the formation of spinel phases such as Li2CoO4 and Co3O4 in a high voltage region is effectively suppressed, so that the crystal structure of the lithium cobalt-based oxide can be further strengthened.

[0028] The content of Al doped in the lithium cobalt-based oxide of the first positive electrode active material and the lithium cobalt-based oxide of the second positive electrode active material may be 0.2 wt% to 2 wt% with respect to 100 wt% of the total metal excluding lithium, for example, 0.2 wt% to 1.8 wt%, 0.2 wt% to 1.6 wt%, 0.2 wt% to 1.5 wt%, 0.3 wt% to 1.4 wt%, 0.4 wt% to 1.2 wt%, or 0.4 wt% to 0.9 wt%. The content of Mg doped may be 0.01 wt% to 1 wt% with respect to 100 wt% of the total metal excluding lithium, for example, 0.02 wt% to 0.9 wt%, 0.05 wt% to 0.5 wt%, or 0.1 wt% to 0.3 wt%. When the Al content and Mg content each satisfy the above range, the formation of a spinel phase in a lithium cobalt-based metal oxide at high voltage is effectively suppressed, thereby strengthening the crystal structure and improving the high voltage characteristics and life characteristics.

[0029] The sum of the Al content and the Mg content doped in the entire first positive electrode active material and the second positive electrode active material may be 0.1 wt% to 2 wt%, 0.1 wt% to 1 wt%, or 0.4 wt% to 0.8 wt%, based on the total metal excluding lithium. In addition, when both Al and Mg are doped, the ratio of the Al content to the Mg content doped in the entire first positive electrode active material and the second positive electrode active material may be 3 to 10, for example, 3 to 8, or 3 to 5. When the sum of the Al and Mg and the ratio of the Al content to the Mg content satisfy the above ranges, the crystal structure may be strengthened while implementing a high capacity, thereby improving the high-voltage characteristics.

[0030] For example, the lithium cobalt-based oxide of the first positive electrode active material may be represented by chemical formula 1, and the lithium cobalt-based oxide of the second positive electrode active material may be represented by chemical formula 2.

[0031] [Chemical Formula 1]

[0032] Li a1 Co x1 Al y1 Mg z1 M 1 w1 O 2-b1 X b1

[0033] In the above chemical formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0≤y1≤0.1, 0≤z1≤0.1, 0 <y1+z1≤0.2, 0≤w1≤0.1, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0034] [Chemical Formula 2]

[0035] Li a2 Co x2Al y2 Mg z2 M 2 w2 O 2-b2 X b2

[0036] In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0≤y2≤0.1, 0≤z2≤0.1, 0 <y2+z2≤0.2, 0≤w2≤0.1, 0.9≤x2+y2+z2+w2≤1.1, 및 0≤b2≤0.1이고, M 2 is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0037] The first positive electrode active material and the second positive electrode active material each include a coating layer located on the surface of core particles containing lithium cobalt-based oxide, and the coating layer includes Zr, Ti, or a combination thereof. The content of the coating layer component may be 0.01 wt% to 2 wt% based on 100 wt% of the total positive electrode active material, and may be, for example, 0.1 wt% to 1.5 wt%, 0.1 wt% to 1.0 wt%, or 0.1 wt% to 0.3 wt%. The coating layer may be said to include a kind of inert metal component, or "palgya* metal oxide. Such a coating layer may be used during a charge / discharge process. 4+ , can suppress the formation of a CEI (Cathode Electrolyte Interphase) layer on the surface of a lithium cobalt-based oxide due to the release of oxygen, or can reduce the thickness of the CEI layer, and can effectively suppress phase change on the surface of a lithium cobalt-based oxide. In addition, the coating layer can suppress side reactions between a lithium cobalt-based oxide and an electrolyte, thereby improving high-voltage characteristics and life characteristics.

[0038] The Zr content of the coating layer may be 0.01 wt% to 1 wt%, 0.01 wt% to 0.8 wt%, 0.01 wt% to 0.5 wt%, 0.01 wt% to 0.1 wt%, or 0.01 wt% to 0.05 wt% relative to the entire metal excluding lithium in the first positive electrode active material and the second positive electrode active material. The Ti content of the coating layer may be 0.01 wt% to 1 wt%, 0.01 wt% to 0.8 wt%, 0.01 wt% to 0.5 wt%, 0.01 wt% to 0.1 wt%, or 0.05 wt% to 0.09 wt% relative to the entire metal excluding lithium in the first positive electrode active material and the second positive electrode active material. When the contents of Zr and Ti each satisfy the above range, the phase change on the surface of the positive electrode active material is effectively suppressed, the thickness of the CEI layer is reduced, and the surface side reaction is reduced, so that the high voltage characteristics and life characteristics can be improved.

[0039] When the above coating layer contains both Zr and Ti, the ratio of the Ti content to the Zr content may be 1.5 to 5 or 1.5 to 3, in which case the thickness of the CEI layer on the surface of the positive electrode active material can be effectively reduced, thereby improving the high voltage characteristics and life characteristics.

[0040] The coating layer may be in the form of a continuous film surrounding the core particle or in the form of an island. When the coating layer contains Zr, the coating layer may specifically include zirconium oxide, zirconium hydroxide, zirconium carbonate, a lithium zirconium compound (e.g., lithium zirconium oxide), or a combination thereof. When the coating layer contains Ti, the coating layer may specifically include titanium oxide, a lithium titanium compound (e.g., lithium titanium oxide), or a combination thereof.

[0041] In the entire positive electrode active material including the first positive electrode active material and the second positive electrode active material, the average particle diameter (D 50) may be 8 ㎛ to 20 ㎛, or 10 ㎛ to 18 ㎛. At this time, the average particle diameter may be obtained by randomly measuring the size (diameter or length of major axis) of about 20 particles in a scanning electron microscope image to obtain a particle size distribution, and taking the diameter of particles having a cumulative volume of 50% by volume in the particle size distribution as the average particle diameter. In addition, the tap density of the positive electrode active material may be 2.80 g / cm 3 3.2 g / cm 3 , or 2.80 g / cm 3 3.0 g / cm 3 It can be. The BET specific surface area of ​​the above positive electrode active material is 0.17 m 2 / g to 0.3 m 2 / g, 0.18 m 2 / g to 0.25 m 2 / g, or 0.19 m 2 / g to 0.21 m 2 / g. If the positive electrode active material satisfies the above properties, high capacity, efficiency, and lifespan characteristics can be realized.

[0042] bookbinder

[0043] According to one embodiment, a positive electrode comprises the aforementioned high-voltage lithium cobalt-based positive electrode active material, and is characterized in that a weight ratio of a first fluorine-based binder not containing a polar functional group and a second fluorine-based binder containing a polar functional group is 90:10 to 99:1. The weight ratio of the first fluorine-based binder to the second fluorine-based binder may be, for example, 91:9 to 99:1, 92:8 to 99:1, 93:7 to 99:1, 94:6 to 99:1, 95:5 to 99:1, 95:5 to 98:2, or 95:5 to 97:3. Such a positive electrode may have increased flexibility, thereby reducing the occurrence rate of pinholes and cracks at a folded portion during a winding process. If the weight ratio of the first fluorine-based binder and the second fluorine-based binder is outside the above range, for example, if the second fluorine-based binder is included in an amount exceeding 10 wt% based on a total of 100 wt% of the first fluorine-based binder and the second fluorine-based binder, the flexibility of the electrode plate may decrease, resulting in pinholes and cracks occurring during the winding process.

[0044] 1st fluorine-based binder

[0045] The first fluorinated binder may be a polyvinylidene fluoride-based binder that does not contain a polar functional group. The first fluorinated binder may be a homopolymer of a vinylidene fluoride monomer, or may be a copolymer of a vinylidene fluoride monomer and at least one monomer selected from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluorovinyl, and perfluoroalkyl vinyl ether. For example, the first fluorinated binder may be polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-chlorotrifluoroethylene copolymer, or a vinylidene fluoride-hexafluoropropylene-chlorotrifluoroethylene copolymer.

[0046] When the first fluorine-based binder is a copolymer, the vinylidene fluoride monomer may be included in an amount of 60 mol% or more, for example, 80 mol% or more, based on 100 mol% of the first fluorine-based binder.

[0047] The weight average molecular weight of the first fluorine-based binder may be smaller than the weight average molecular weight of the second fluorine-based binder, for example, 300,000 g / mol to 900,000 g / mol, 400,000 g / mol to 800,000 g / mol, or 500,000 g / mol to 700,000 g / mol. When the above molecular weight range is satisfied, good dispersibility and excellent flexibility can be realized.

[0048] Second fluorine-based binder

[0049] The second fluorine-based binder contains a polar functional group, has higher physical and chemical bonding strength than the first fluorine-based binder, and can exhibit higher adhesive strength.

[0050] The polar functional group of the second fluorine-based binder may include, for example, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, or a combination thereof.

[0051] The second fluorine-based binder may include, for example, a polar functional group-containing repeating unit and a vinylidene fluoride repeating unit.

[0052] The introduction of a polar functional group-containing repeating unit into the second fluorine-based binder can be accomplished, for example, by co-polymerizing a vinylidene fluoride monomer with a monomer containing a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, or a combination thereof.

[0053] The monomer containing a carboxylic acid group can be a monocarboxylic acid and its derivatives, or a dicarboxylic acid and its derivatives. The monocarboxylic acid can be, for example, acrylic acid, methacrylic acid, crotonic acid, or a combination thereof, and the derivative of the monocarboxylic acid can be, for example, 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxy acrylic acid, β-diaminoacrylic acid, or a combination thereof. The dicarboxylic acid can be, for example, maleic acid, fumaric acid, itaconic acid, or a combination thereof, and the derivative of the dicarboxylic acid can be, for example, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, fluoroalkyl maleate, or a combination thereof.

[0054] Meanwhile, instead of a monomer containing a carboxylic acid group, an acid anhydride that generates a carboxyl group by hydrolysis may be used. The acid anhydride of a dicarboxylic acid may be, for example, maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, or a combination thereof. In addition, monoesters or diesters of α,β-ethylenically unsaturated polycarboxylic acids, such as monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate, may be used.

[0055] The monomer containing a sulfonic acid group can be, for example, vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, (meth)acrylic acid-2-sulfonate ethyl, 2-acrylamide-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, or a combination thereof.

[0056] The monomer containing a phosphate group can be, for example, 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, or a combination thereof.

[0057] Monomers containing hydroxyl groups include, for example, ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-buten-1-ol, and 5-hexene-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; general formula CH2=CR 1- COO-(C n H 2 n O) m- H(m is an integer from 2 to 9, n is an integer from 2 to 4, R 1Esters of polyalkylene glycols represented by (wherein the hydrogen or methyl group is represented by) and (meth)acrylic acid; Mono(meth)acrylic acid esters of dihydroxyesters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; Vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; Mono(meth)allyl ethers of alkylene glycols, such as (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxy butyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether; polyoxyalkylene glycol (meth)monoallyl ethers, such as diethylene glycol mono(meth)allyl ether and dipropylene glycol mono(meth)allyl ether; Mono(meta)allyl ethers of halogen and hydroxy substituents of (poly)alkylene glycols, such as glycerin mono(meta)allyl ether, (meta)allyl-2-chloro-3-hydroxypropyl ether, and (meta)allyl-2-hydroxy-3-chloropropyl ether; mono(meta)allyl ethers of polyhydric phenols, such as eugenol and isoeugenol, and halogen substituents thereof; (meta)allyl thioethers of alkylene glycols, such as (meta)allyl-2-hydroxyethylthioether and (meta)allyl-2-hydroxypropylthioether; etc.

[0058] The polar functional group-containing repeating unit may be included in an amount of 1 mol% to 10 mol% relative to 100 mol% of the second fluorine-based binder, for example, 1 mol% to 9 mol%, 1 mol% to 8 mol%, 1 mol% to 7 mol%, 1 mol% to 6 mol%, or 1 mol% to 5 mol%.

[0059] The weight average molecular weight of the second fluorinated binder may be higher than that of the first fluorinated binder, for example, 800,000 g / mol to 2,000,000 g / mol, 900,000 g / mol to 1,800,000 g / mol, or 1,000,000 g / mol to 1,500,000 g / mol. The weight average molecular weight may be a polystyrene conversion value determined by gel permeation chromatography. When the weight average molecular weight of the second fluorinated binder satisfies the above range, the binding force of the positive electrode components may be further improved.

[0060] The second fluorine-based binder may optionally further include, in addition to the polar functional group-containing repeating unit and the vinylidene fluoride repeating unit, a repeating unit derived from at least one monomer selected from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluorovinyl, and perfluoroalkyl vinyl ether.

[0061] Fluorine-free binder

[0062] According to one embodiment, the positive electrode may further include a non-fluorinated binder. In this case, the flexibility of the positive electrode may be further improved.

[0063] The non-fluorinated binder may be, for example, a nitrile-based binder, and may include, for example, a repeating unit containing a nitrile group and a repeating unit having a straight-chain alkylene structure having 2 or more carbon atoms, and optionally, may further include a repeating unit containing a polar functional group.

[0064] The monomer that derives the nitrile group-containing repeating unit may be, for example, an α,β-ethylenically unsaturated nitrile monomer, and specifically, may be acrylonitrile; α-halogenoacrylonitrile such as α-chloroacrylonitrile, α-bromoacrylonitrile; α-alkylacrylonitrile such as methacrylonitrile; etc.

[0065] A repeating unit having a straight-chain alkylene structure can be introduced, for example, by introducing a conjugated diene monomer unit and then hydrogenating it. The conjugated diene monomer may be, for example, a conjugated diene having 4 or more carbon atoms, and specifically, may be 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, etc.

[0066] The above-mentioned non-fluorinated binder may be included in an amount of 1 wt% to 10 wt% based on 100 wt% of the total of the first fluorinated binder, the second fluorinated binder, and the non-fluorinated binder, for example, 1 wt% to 8 wt%, or 2 wt% to 6 wt%. When included in the above range, the flexibility of the electrode plate can be improved while achieving excellent adhesive strength.

[0067] The total binder content may be about 0.1 wt% to 5 wt%, 0.1 wt% to 3 wt%, or 1 wt% to 2 wt% relative to 100 wt% of the positive electrode active material layer.

[0068] Challenge

[0069] Conductive materials are used to impart conductivity to electrodes. Any material that does not cause chemical changes in the battery and is electronically conductive can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0070] With respect to 100 wt% of the positive electrode active material layer, the content of the positive electrode active material may be 90 wt% to 99.8 wt%, or 95 wt% to 99 wt%, and the contents of the binder and the conductive material may be 0.1 wt% to 5 wt%, or 0.5 wt% to 2.5 wt%, respectively.

[0071] Whole house

[0072] According to one embodiment, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the lithium secondary battery, but as a specific example, it may include aluminum (Al), stainless steel (SUS), indium (In), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), germanium (Ge), lithium (Li), or a combination thereof, and as an example, it may include aluminum (Al). In this case, the shape of the current collector may be a plate-shaped body or a thin body.

[0073] In one embodiment, the thickness of the positive electrode active material layer may be, for example, 20 μm to 300 μm, 50 μm to 200 μm, or 80 μm to 150 μm.

[0074] The loading level of the anode is 5 mg / cm on a cross-sectional basis. 2 50 mg / cm 2 It can be, for example, 5 mg / cm 2 40 mg / cm 2 , 10 mg / cm 2 40 mg / cm 2 , or 10 mg / cm 2 30 mg / cm 2 This can provide an anode with excellent adhesion and flexibility while achieving high energy density.

[0075] The density of the rolled positive electrode may be 4.0 g / cc to 4.5 g / cc, for example, 4.0 g / cc to 4.4 g / cc, 4.0 g / cc to 4.3 g / cc, 4.1 g / cc to 4.3 g / cc, or 4.1 g / cc to 4.2 g / cc. When the density of the positive electrode active material layer satisfies the above range, very high energy density and high capacity can be realized. However, such a high-density positive electrode may have low flexibility, but by applying binders according to one embodiment, flexibility can be increased while also achieving high adhesive strength.

[0076] lithium secondary battery

[0077] In one embodiment, a lithium secondary battery is provided, including the positive electrode; the negative electrode; and the electrolyte. The electrolyte may be a liquid electrolyte or a solid electrolyte.

[0078] For example, in one embodiment, a lithium secondary battery may be provided that includes the aforementioned positive electrode, negative electrode, a separator positioned between the positive electrode and negative electrode, and an electrolyte. As another example, an all-solid-state secondary battery may be provided that includes the aforementioned positive electrode, negative electrode, and a solid electrolyte layer positioned between the positive electrode and negative electrode.

[0079] Below, a lithium secondary battery using an electrolyte is described as an example.

[0080] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. types according to their shapes. FIGS. 1 to 4 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, wherein FIG. 1 can be said to be a cylindrical battery, FIG. 2 a square battery, and FIGS. 3 and 4 a pouch battery. Referring to FIGS. 1 to 4, a lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and an negative electrode (20), and a case (50) in which the electrode assembly (40) is built. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as shown in FIG. 1. In addition, in FIG. 2, the lithium secondary battery (100) may include a positive lead tab (11), a positive terminal (12), a negative lead tab (21), and a negative terminal (22). As in FIGS. 3 and 4, the lithium secondary battery (100) may include electrode tabs (70), i.e., a positive tab (71) and a negative tab (72), which serve as electrical paths for inducing current formed in the electrode assembly (40) to the outside.

[0081] cathode

[0082] A negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode 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.

[0083] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0084] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0085] As the above lithium metal alloy, 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.

[0086] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (wherein 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.

[0087] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the composite may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) positioned on the surface of the secondary particles. The amorphous carbon may also be positioned between the silicon primary particles, such that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0088] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on the surface of the core.

[0089] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in a mixture with a carbon-based negative electrode active material.

[0090] For example, the negative electrode active material layer may include 90 to 99 wt% of the negative electrode active material, 0.5 to 5 wt% of the binder, and 0 to 5 wt% of the conductive material.

[0091] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0092] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0093] The above-mentioned aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0094] When using an aqueous binder as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0095] The above dry binder is a polymeric material capable of being fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0096] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0097] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0098] electrolyte

[0099] An electrolyte for a lithium secondary battery contains a non-aqueous organic solvent and a lithium salt.

[0100] The above non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0101] The above 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.

[0102] Examples of the carbonate solvent that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of the ester solvent that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0103] The above non-aqueous organic solvents can be used alone or in combination of two or more.

[0104] In addition, when using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0105] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. 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) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0106] membrane

[0107] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films comprising two or more of these. Furthermore, mixed multilayer films, such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator, may also be used.

[0108] The above separator may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0109] The above porous substrate may be a polymer film formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyarylether ketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof.

[0110] The above organic material may include a polyvinylidene fluoride-based antibody or a (meth)acrylic polymer.

[0111] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include inorganic particles selected from, but not limited to, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0112] The organic and inorganic substances may be mixed and present in one coating layer, or a coating layer including an organic substance and a coating layer including an inorganic substance may be present in a laminated form.

[0113] Hereinafter, examples and comparative examples of the present invention are described. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0114] Example 1

[0115] (1) Manufacturing of anode

[0116] Lithium cobalt oxide doped with Al and Mg and having an average particle diameter (D 50 ) with an average particle diameter (D) of approximately 20 ㎛ 50) were mixed with small particles of approximately 4 ㎛ in a weight ratio of 8:2, and then 0.1 mol% of zirconium oxide and 0.2 mol% of titanium oxide were added based on 100 mol% of the total metal excluding lithium, and heat-treated at 950°C in an air atmosphere for 15 hours to prepare a cathode active material.

[0117] The inductively coupled plasma spectroscopy (ICP) analysis results for the manufactured cathode active material confirmed that the Al content was 4710 ppm, the Mg content was 990 ppm, the Ti content was 770 ppm, and the Zr content was 320 ppm. In addition, the D of the cathode active material was analyzed using SEM images. 50 The tap density of the positive electrode active material is 15.7 ㎛, and the tap density of the positive electrode active material is 2.83 g / cm as analyzed by a density analyzer. 3 As a result of analysis using a surface area measuring device, the BET surface area of ​​the positive electrode active material was 0.19 m 2 / g was confirmed.

[0118] In NMP solvent, 98.15 wt% of the above positive electrode active material, 0.6 wt% of CNT conductive agent, 0.2 wt% of Carbon black conductive agent, and a first fluorine-based binder (carboxyl group-containing modified PVdF, M w =1,000,000 g / mol, Solvay) 0.95 wt%, second fluorine-based binder (PVdF, M w =700,000 g / mol, Solvay) 0.05 wt%, and non-fluorinated binder (hydrogenated acrylonitrile-butadiene, M w =300,000 g / mol, Nippon Zeon) was mixed with 0.05 wt% of a cathode slurry to prepare a cathode slurry, which was then applied to an aluminum foil current collector, dried, and rolled to prepare a cathode.

[0119] At this time, the loading level of the positive electrode active material layer is approximately 36.0 mg / cm 2 And the density of the final rolled anode is about 4.1 g / cc.

[0120] Manufacturing of lithium secondary batteries

[0121] A slurry for a negative electrode active material layer was prepared by mixing 97.5 wt% of graphite negative electrode active material, 1.5 wt% of carboxymethyl cellulose, and 1 wt% of styrene butadiene rubber in a water solvent. The slurry for a negative electrode active material layer was coated on a copper foil current collector, dried, and rolled to prepare a negative electrode.

[0122] A lithium secondary battery was manufactured by a conventional method using a polytetrafluoroethylene separator and an electrolyte solution containing 1M LiPF6 dissolved in a solvent containing ethylene carbonate and dimethyl carbonate mixed in a volume ratio of 3:7.

[0123] Example 2

[0124] A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the content ratio of the first fluorine-based binder and the second fluorine-based binder in the positive electrode slurry was changed to 0.9 wt% and 0.1 wt%, respectively.

[0125] Comparative Example 1

[0126] A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the content ratio of the first fluorine-based binder and the second fluorine-based binder in the positive electrode slurry was changed to 0.8 wt% and 0.2 wt%, respectively.

[0127] Evaluation Example 1: Pinhole and Crack Test

[0128] The positive electrodes manufactured in the examples and comparative examples were rolled, folded, and rolled 6 times, and the occurrence of pinholes and cracks was evaluated, and the results are shown in Tables 1 to 3. This can be said to be an evaluation to check the degree of physical damage due to the tip folding during winding. The passing criteria for this evaluation are as follows. ① The number of pinholes excluding the trimming part must be less than 5. ② The pinholes must not be clustered, and if there are 4 or more pinholes within 2 mm in the longitudinal direction, it is NG. ③ There must be no phenomenon such as breakage, and the size of the pinhole must be less than 0.5 mm.

[0129] Comparative Example 1 (First fluorine-based binder: Second fluorine-based binder = 0.8:0.2) Location Drive Side (D / S) Center Work Side (W / S) Result Fracture Fracture Fracture

[0130] Example 1 (First fluorine-based binder: Second fluorine-based binder = 0.95:0.05) Location A (D / S) EBF (Center) CGDH (W / S) Result 31200103

[0131] Example 2 (First fluorine-based binder: Second fluorine-based binder = 0.9:0.1) Location A (D / S) EBF (Center) CGDH (W / S) Result 7520134 Fracture

[0132] Referring to Tables 1 to 3 above, in the case of Comparative Example 1, both pinholes and cracks occurred at the leading edge fold, resulting in a fracture phenomenon. On the other hand, in the case of Examples 1 and 2, it can be seen that the problems of pinholes and cracks occurring at the leading edge fold were improved due to increased flexibility of the electrode plate.

[0133] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[0134] [Explanation of symbols]

[0135] 100: Lithium secondary battery 10: Cathode

[0136] 11: Positive lead tab 12: Positive terminal

[0137] 20: Negative lead tab 21: Negative lead tab

[0138] 22: Negative terminal 30: Separator

[0139] 40: Electrode assembly 50: Case

[0140] 60: Sealing member 70: Electrode tab

[0141] 71: Positive tab 72: Negative tab

Claims

1. A first positive electrode active material comprising a core particle containing a lithium cobalt-based oxide doped with Al, Mg, or a combination thereof, and a coating layer located on the surface of the core particle and containing Zr, Ti, or a combination thereof; A core particle containing a lithium cobalt-based oxide doped with Al, Mg, or a combination thereof, and a coating layer located on the surface of the core particle and containing Zr, Ti, or a combination thereof, having an average particle diameter (D) smaller than that of the first positive electrode active material. 50 ) having a second positive electrode active material, First fluorine-based binder without polar functional group, A second fluorine-based binder containing a polar functional group, and Including challenges, A positive electrode for a lithium secondary battery, wherein the weight ratio of the first fluorine-based binder and the second fluorine-based binder is 90:10 to 99:

1.

2. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the weight ratio of the first fluorine-based binder and the second fluorine-based binder is 91:9 to 99:

1.

3. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the weight ratio of the first fluorine-based binder and the second fluorine-based binder is 95:5 to 99:

1.

4. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the weight average molecular weight of the first fluorine-based binder is 300,000 g / mol to 900,000 g / mol.

5. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the polar functional group of the second fluorine-based binder includes a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, or a combination thereof.

6. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the second fluorine-based binder comprises a repeating unit containing a polar functional group and a vinylidene fluoride repeating unit.

7. In paragraph 6, A positive electrode for a lithium secondary battery, wherein the polar functional group-containing repeating unit is included in an amount of 1 mol% to 10 mol% based on 100 mol% of the second fluorine-based binder.

8. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the weight average molecular weight of the second fluorine-based binder is 800,000 g / mol to 2,000,000 g / mol.

9. In paragraph 1, The above anode further comprises a non-fluorinated binder, A positive electrode for a lithium secondary battery, wherein the non-fluorinated binder is included in an amount of 1 to 10 wt% based on a total of 100 wt% of the first fluorinated binder, the second fluorinated binder, and the non-fluorinated binder.

10. In paragraph 9, The above non-fluorine-based binder is a positive electrode for a lithium secondary battery, which is a nitrile-based binder.

11. In paragraph 1, The average particle diameter (D) of the first positive electrode active material 50 ) is 10 ㎛ to 25 ㎛, The average particle diameter (D) of the second positive electrode active material 50 ) is a positive electrode for a lithium secondary battery having a thickness of 2 ㎛ to 6 ㎛.

12. In paragraph 1, The average particle diameter (D) of the first positive electrode active material 50 ) is a, and the particle size (D) of the second positive electrode active material 50 ) is b, a positive electrode for a lithium secondary battery satisfying 3b≤a≤4b.

13. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the first positive electrode active material is included in an amount of 60 to 90 wt%, and the second positive electrode active material is included in an amount of 10 to 40 wt%, based on a total of 100 wt% of the first positive electrode active material and the second positive electrode active material.

14. In paragraph 1, The lithium cobalt oxide of the first positive electrode active material and the lithium cobalt oxide of the second positive electrode active material each contain an aluminum dopant, A positive electrode for a lithium secondary battery, wherein the content of aluminum is 0.2 wt% to 2 wt% based on 100 wt% of the total metal excluding lithium in the lithium cobalt-based oxide of the first positive electrode active material and the lithium cobalt-based oxide of the second positive electrode active material.

15. In paragraph 1, The lithium cobalt oxide of the first positive electrode active material and the lithium cobalt oxide of the second positive electrode active material each contain a Mg dopant, A positive electrode for a lithium secondary battery, wherein the content of Mg is 0.01 wt% to 1 wt% based on 100 wt% of the total metal excluding lithium in the lithium cobalt-based oxide of the first positive electrode active material and the lithium cobalt-based oxide of the second positive electrode active material.

16. In paragraph 1, The lithium cobalt oxide of the first positive electrode active material is represented by chemical formula 1, The lithium cobalt oxide of the second cathode active material is a cathode for a lithium secondary battery represented by the chemical formula 2: [Chemical Formula 1] Li a1 Co x1 Al y1 Mg z1 M 1 w1 O 2-b1 X b1 In the above chemical formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0≤y1≤0.1, 0≤z1≤0.1, 0 <y1+z1≤0.2, 0≤w1≤0.1, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is at least one element selected from the group consisting of F, P, and S. [Chemical Formula 2] Li a2 Co x2 Al y2 Mg z2 M 2 w2 O 2-b2 X b2 In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0≤y2≤0.1, 0≤z2≤0.1, 0 <y2+z2≤0.2, 0≤w2≤0.1, 0.9≤x2+y2+z2+w2≤1.1, 및 0≤b2≤0.1이고, M 2 is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

17. In paragraph 1, The above coating layer contains Zr, A positive electrode for a lithium secondary battery, wherein the Zr content of the coating layer is 0.01 wt% to 1 wt% relative to the entire metal excluding lithium in the first positive electrode active material and the second positive electrode active material.

18. In paragraph 1, The above coating layer contains Ti, A positive electrode for a lithium secondary battery, wherein the Ti content of the coating layer is 0.01 wt% to 1 wt% relative to the entire metal excluding lithium in the first positive electrode active material and the second positive electrode active material.

19. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the density of the positive electrode is 4.0 g / cc to 4.5 g / cc.

20. An anode according to any one of paragraphs 1 to 19; cathode; and A lithium secondary battery containing an electrolyte.

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