Cathode and lithium secondary battery comprising same

Abstract

The present invention provides a lithium secondary battery cathode which comprises a cathode current collector and a cathode active material layer positioned on the cathode current collector, and which satisfies relation (1). Relation (1): Y = 10 × L / (P×T2) < 7, In relation (1), L is the loading amount (mg / cm2) of the cathode, P is the porosity (%) of the cathode, and T is the tap density (g / cc) of the cathode active material included in the cathode active material layer.

Description

Anode and lithium secondary battery containing the same [Cross-reference with related applications] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0115742, filed August 31, 2023, the entire contents of which are incorporated herein by reference. [Technical Field] The present invention relates to a positive electrode and a lithium secondary battery including the same. With technological advancements in electric vehicles, portable electronic devices, and other sectors, the demand for lithium secondary batteries as an energy source is rapidly increasing. With technological advancements in electric vehicles, portable electronic devices, and other sectors, the demand for lithium secondary batteries as an energy source is rapidly increasing. Among these, recent advancements in electric vehicle technology have led to a demand for batteries with high energy density. To improve the energy density of lithium secondary batteries, increasing the amount of active material contained in the electrode assembly can improve the utilization of the limited space within the battery. However, increasing the active material loading to achieve high energy density in lithium secondary batteries poses the problem of cracks occurring in the electrode current collector at the core during the winding process of the electrode assembly. If these cracks become severe, the lithium movement path in the lithium secondary battery is interrupted, causing additional side reactions and deteriorating the long-term performance of the lithium secondary battery. The present invention seeks to provide an anode in which cracks do not occur in the core portion when the electrode assembly is wound. [1] The present invention provides a positive electrode for a lithium secondary battery, comprising: a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector; and satisfying the following formula (1). Equation (1): Y = 10 × L / (P×T 2 ) < 7 In the above equation (1), L is the loading amount of the anode (mg / cm 2), P is the porosity (%) of the positive electrode, and T is the tap density (g / cc) of the positive electrode active material included in the positive electrode active material layer. [2] The present invention can provide a positive electrode for a lithium secondary battery in which the tap density of the positive electrode active material included in the positive electrode active material layer in the above [1] is 1.8 g / cc to 2.5 g / cc. [3] The present invention, in the above [1] or [2], the loading amount of the positive electrode active material layer is 44 mg / cm 2 56 mg / cm 2 A cathode for a lithium secondary battery can be provided. [4] The present invention can provide a positive electrode for a lithium secondary battery, wherein the positive electrode has a porosity of 22.5% to 30.0% in at least one of the above [1] to [3]. [5] The present invention can provide a positive electrode for a lithium secondary battery, wherein, in at least one of the above [1] to [4], the positive electrode active material included in the positive electrode active material layer is a lithium nickel-based transition metal oxide having a nickel content of 90 atm% or more among transition metals other than lithium. [6] The present invention can provide a positive electrode for a lithium secondary battery, wherein, in the above [5], the positive electrode active material is a lithium nickel-based oxide represented by the following [chemical formula 2]. [Chemical Formula 2] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 2, M 1 is Mn, Al or a combination thereof, and M 2 is at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, and 0.8≤a≤1.2, 0.9≤b<1, 0 <c<0.1, 0<d<0.1, 0≤e≤0.05이다. [7] The present invention can provide a positive electrode for a lithium secondary battery, wherein in at least one of the above [1] to [6], the positive electrode active material is composed of single particles, pseudo-single particles, or a combination thereof. [8] The present invention can provide a positive electrode for a lithium secondary battery, wherein in at least one of the above [1] to [7], the positive electrode active material layer includes a positive electrode active material having a unimodal particle size distribution showing a single peak in a volume cumulative particle size distribution graph. [9] The present invention, in at least one of the above [1] to [8], the average particle diameter D of the positive electrode active material 50 It can provide a positive electrode for a lithium secondary battery having a diameter of 3㎛ to 6㎛.

[0010] The present invention can provide a positive electrode for a lithium secondary battery, wherein the brittleness force of the positive electrode is 35 gf or less, in at least one of the above [1] to [9].

[0011] The present invention can provide a positive electrode for a lithium secondary battery, wherein the depth of the fracture point at which the brittle force is measured is more than 21 mm from the positive electrode surface in the above

[0010] .

[0012] The present invention can provide a lithium secondary battery including an electrode assembly including at least one of the positive electrode, negative electrode, and separator among the above [1] to

[0012] .

[0013] The present invention can provide a lithium secondary battery having a jelly-roll type structure in which, in the above

[0012] , the electrode assembly has a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, which are wound in one direction.

[0014] The present invention can provide a cylindrical lithium secondary battery in the above

[0012] or

[0013] .

[0015] The present invention can provide a lithium secondary battery in which, in at least one of the above

[0012] to

[0014] , the electrode assembly does not cause cracks in the positive electrode within three turns. When winding the positive electrode, a step at the positive electrode tip generates external force on the subsequent positive electrode pattern, causing deformation. If this deformation becomes severe, the positive electrode can no longer withstand it and undergoes plastic deformation. If this plastic deformation worsens further, cracks develop in the positive electrode, resulting in permanent deformation. Cracks in the positive electrode can cause side reactions with the electrolyte during charge / discharge, deteriorating life characteristics and causing gas generation. The positive electrode according to the present invention has a high resistance to plastic deformation by adjusting the loading amount, the porosity of the positive electrode, and the tap density of the positive electrode active material included in the positive electrode active material layer to satisfy a specific relationship, so that permanent deformation does not easily occur, or even if plastic deformation occurs, the degree of permanent deformation is adjusted to be small, thereby suppressing permanent deformation at the beginning of the positive electrode, thereby solving the life characteristics and gas generation problem of a lithium secondary battery. Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner. In the present invention, "primary particle" refers to a particle unit that has no apparent grain boundary when observed under a magnification of 5,000 to 20,000 times using a scanning electron microscope. "Average particle diameter of primary particles" refers to the arithmetic mean value calculated after measuring the particle diameters of primary particles observed in a scanning electron microscope image. In the present invention, a "secondary particle" is a particle formed by the aggregation of multiple primary particles. In the present invention, to distinguish it from conventional secondary particles formed by the aggregation of tens to hundreds of primary particles, secondary particles formed by the aggregation of 10 or fewer primary particles are referred to as "quasi-single particles." In the present invention, "average particle diameter D 50 "It refers to the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder, and can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume cumulative amount. In this specification, the porosity can be calculated using the following mathematical formula A. [Mathematical Formula A] Porosity (%) = {1-(electrode density / true density)} × 100 In the above mathematical formula A, the true density is a calculated density derived from the density and mass ratio of each component material forming the electrode active material layer under the assumption that no pores are included, and the electrode density is a measured density of the electrode active material layer measured by sampling the electrode active material layer to a certain size. Hereinafter, the present invention will be described in more detail. The cathode and / or lithium secondary battery according to the present invention comprises at least one of the configurations disclosed below, and may comprise any combination between the technically possible configurations among the configurations below. The present invention provides a positive electrode for a lithium secondary battery, comprising: a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector; and satisfying the following formula (1). Equation (1): Y = 10 × L / (P×T 2 ) < 7 For the positive electrode included in the lithium secondary battery, when the Y value defined as in the above formula (1) is less than 7, the resistance to plastic deformation is high, so that permanent deformation does not easily occur, or even if plastic deformation occurs, the degree of permanent deformation is small. Therefore, it is thought that the positive electrode of the present invention has the effect of suppressing cracks because it is less deformed by external force. The above Y may be 3 or more and less than 7, or 3.5 or more and less than 7. In the above equation (1), L is the loading amount of the anode (mg / cm 2 ), and the loading amount of the positive electrode means the weight per unit area of ​​the positive electrode active material layer coated on the positive electrode current collector. The above L is 44 to 56 mg / cm 2 , preferably 44 to 55 mg / cm 2 , most preferably 44 to 54 mg / cm 2 It can be. The positive electrode of the present invention has a high loading amount, so that a lithium secondary battery including the positive electrode can be provided with a high capacity. The positive electrode may be a single-sided positive electrode in which a positive electrode active material layer is formed on one side of a positive electrode current collector, or may be a double-sided positive electrode in which a positive electrode active material layer is formed on both sides of a positive electrode current collector. The loading amount refers to the total loading amount of both sides in the case of a double-sided electrode. The positive electrode of the present invention may preferably be a double-sided electrode in which a positive electrode active material layer is present on both sides of a positive electrode current collector. In the above equation (1), P represents the porosity (%) of the positive electrode, and specifically, it refers to the porosity of the positive electrode active material layer included in the positive electrode. The above P may be 22.5 to 40.0%, preferably 23.0 to 30.0%, and most preferably 23.0 to 27.0%. In the above equation (1), T is the tap density (g / cc) of the positive electrode active material included in the positive electrode active material layer. The above T may be 1.8 to 2.5 g / cc, preferably 1.9 to 2.5 g / cc, and most preferably 2.0 to 2.5 g / cc. The positive electrode for a lithium secondary battery of the present invention comprises a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector; and has a brittleness force of 35 gf or less, and a depth of a fracture point at which the brittleness force is measured may be greater than 21 mm from the positive electrode surface. The brittleness force and the depth of the fracture point at which the brittleness force is measured can be measured, for example, using Texture Analysis equipment. Specifically, after the electrode to be measured is struck and fitted into a brittleness electrode fixing device, the maximum force applied to the round brittleness tip can be measured as the round brittleness tip advances from the electrode surface toward the electrode depth. In addition, the depth to which the round brittleness tip has advanced from the surface to the electrode depth can be measured with respect to the point at which an electrode crack occurs and the electrode is destroyed as the round brittleness tip advances from the electrode surface toward the electrode depth. Brittleness refers to the property of a material to be destroyed without permanent deformation or with only a very small degree of permanent deformation due to external force, and the brittleness force is an indicator of the rigidity of the electrode. At the point where the brittle force is measured, the force applied to the measuring tip suddenly drops and the electrode is destroyed. The depth to which the measuring tip penetrates from the electrode surface at this time is defined as the depth of the fracture point where the brittle force is measured. The positive electrode of the present invention can be formed in a structure in which a positive electrode active material layer is formed on one or both sides of a long sheet-shaped positive electrode current collector. The positive electrode of the present invention can be manufactured by applying a positive electrode slurry prepared by dispersing a positive electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc., to one or both sides of a long sheet-shaped positive electrode current collector, removing the solvent of the positive electrode slurry through a drying process, and then rolling. As the positive electrode current collector, various positive electrode current collectors used in the relevant technical field can be used. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, or non-woven fabric. Most preferably, an aluminum thin film may be used in terms of elongation control, etc. Meanwhile, as the positive electrode active material, positive electrode active materials generally used in the relevant technical field can be used. Preferably, the positive electrode active material may include a lithium nickel-based oxide, and specifically, may include a lithium nickel-based transition metal oxide having a nickel content of 90 atm% or more among transition metals excluding lithium. Preferably, the lithium nickel-based oxide may include Ni in an amount of 90 mol% or more and less than 100 mol%, 93 mol% or more and less than 100 mol%, or 95 mol% or more and less than 100 mol%. When a lithium nickel-based oxide having a high Ni content as described above is used, a high capacity can be realized. More specifically, the positive electrode active material may include a lithium nickel-based oxide represented by the following [chemical formula 2]. [Chemical Formula 2] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 2, M 1 It may be Mn, Al or a combination thereof, preferably Mn or Mn and Al. Above M 2 is at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, preferably at least one selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y or a combination thereof. M 2 Although elements are not essential, when included in appropriate amounts, they can promote grain growth during firing or play a role in improving crystal structure stability. The above a represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 0.8≤a≤1.2, 0.85≤a≤1.15, or 0.9≤a≤1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed. The above b represents the molar ratio of nickel among all metals excluding lithium in the lithium nickel-based oxide, and may be 0.9≤b<1, 0.93≤b<1, or 0.95≤b<1. When the molar ratio of nickel satisfies the above range, a high energy density is exhibited, enabling high capacity implementation. The above c represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel oxide, and is 0. <c<0.1, 0<c<0.07, 또는 0.02≤c≤0.07일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다. The above d is M of all metals excluding lithium in lithium nickel oxide. 1 It represents the molar ratio of elements, 0 <d<0.1, 0<d<0.07, 또는 0.005≤d≤0.05일 수 있다. M 1 When the molar ratio of the elements satisfies the above range, the structural stability of the positive electrode active material is excellent. The above e is M of all metals except lithium in lithium nickel oxide. 2 It represents the molar ratio of elements, and can be 0≤e≤0.05 or 0≤e≤0.01. Meanwhile, the cathode active material according to the present invention may further include, if necessary, a coating layer comprising one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si and S on the surface of the lithium nickel-based oxide particles. Preferably, the coating element may be Al, B, Co or a combination thereof, and most preferably, the coating element may be B. When a coating layer exists on the surface of lithium nickel-based oxide particles, the contact between the electrolyte and the lithium composite transition metal oxide is suppressed by the coating layer, thereby reducing the elution of transition metal or gas generation due to side reactions with the electrolyte. Meanwhile, the form of the positive electrode active material is not particularly limited, and may be in the form of a secondary particle in which a plurality of primary particles are aggregated, a single particle formed of a single primary particle, or a combination thereof. Preferably, the positive electrode active material may include a positive electrode active material composed of a single particle consisting of one primary particle and / or a quasi-single particle which is an aggregate of 10 or fewer primary particles. By using a positive electrode active material composed of a single particle consisting of one primary particle and / or a quasi-single particle which is an aggregate of 10 or fewer primary particles, a lithium secondary battery having high capacity and excellent safety can be obtained. The positive electrode active material in the form of a single particle or a pseudo-single particle in which 10 or fewer primary particles are aggregated has higher particle strength than the existing secondary particle type positive electrode active material in which tens to hundreds of primary particles are aggregated, so that the particles are hardly broken during rolling. In addition, in the case of the positive electrode active material in the form of a single particle or a pseudo-single particle, since the number of primary particles constituting the particle is small, the change due to volume expansion and contraction of the primary particles during charge and discharge is small, and accordingly, the occurrence of cracks inside the particle is also significantly reduced. Meanwhile, the cathode active material in the form of single particles and / or pseudo-single particles according to the present invention has an average particle diameter D 50 The average particle size of the positive electrode active material may be 6 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less, for example, 0.5 μm to 6 μm, preferably 1 μm to 6 μm, and more preferably 3 μm to 6 μm. The average particle size D of the positive electrode active material 50 When this above range is satisfied, the increase in resistance can be minimized. Single particle and / or pseudo-single particle type cathode active materials have a problem in that lithium mobility is lower than that of secondary particle type cathode active materials because the interface between primary particles, which serves as a diffusion path for lithium ions within the particles, is small, which increases resistance. This increase in resistance becomes more severe as the particle size increases, and an increase in resistance adversely affects capacity and output characteristics. Therefore, in the present invention, the average particle diameter D 50By applying a single particle or pseudo-single particle positive electrode active material of 5㎛ or less, the diffusion distance of lithium ions within the particle can be minimized, thereby suppressing the increase in resistance. Therefore, there is a problem that the structural instability of the positive electrode increases as the Ni content in the positive electrode material increases in order to implement high energy, but when the positive electrode active material is used in the form of single particles and / or pseudo-single particles, the amount of gas generated due to particle breakage and internal cracks can be significantly reduced, and excellent safety can be implemented. However, when a positive electrode active material with a small average particle size in the form of single particles and / or pseudo-single particles is used, plastic deformation due to load and external force is easily caused, so it is necessary to adjust so that Condition 1 or Condition 2 is satisfied. The above-mentioned single particle and / or pseudo-single particle type positive electrode active material may have an average particle diameter of silver primary particles of 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less, for example, 0.5 μm to 5 μm, preferably 1 μm to 5 μm, more preferably 2 μm to 5 μm. When the average particle diameter of the primary particles satisfies the above range, a single particle and / or pseudo-single particle type positive electrode active material having excellent electrochemical properties can be formed. If the average particle diameter of the primary particles is too small, the number of agglomerates of the primary particles forming the positive electrode active material increases, which reduces the effect of suppressing particle breakage during rolling, and if the average particle diameter of the primary particles is too large, the lithium diffusion path within the primary particles becomes long, which may increase the resistance and deteriorate the output characteristics. In the present invention, it is preferable that the positive electrode active material in the form of single particles and / or pseudo-single particles have a unimodal particle size distribution. Conventionally, bimodal positive electrode active materials have been widely used, in which a large-particle positive electrode active material with a large average particle size and a small-particle positive electrode active material with a small average particle size are mixed to improve the electrode density of the positive electrode active material layer. However, in the case of positive electrode active materials in the form of single particles or pseudo-single particles, when the particle size increases, the lithium migration path becomes longer, which significantly increases the resistance. Therefore, when large-particle particles are mixed and used, a problem of reduced capacity and output characteristics may occur. Therefore, in the present invention, by using a positive electrode active material with a unimodal distribution, the increase in resistance can be minimized. A lithium secondary battery according to the present invention may include a positive electrode, a negative electrode, and an electrode assembly including the positive electrode and the negative electrode. The negative electrode of the present invention may have a structure in which a negative electrode active material layer is formed on one or both sides of a long sheet-shaped negative electrode collector, and the negative electrode active material layer may include a negative electrode active material including Si, a conductive material, and a binder. Specifically, the negative electrode can be manufactured by applying a negative electrode slurry prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water on one or both sides of a long sheet-shaped negative electrode collector, removing the solvent of the negative electrode slurry through a drying process, and then rolling. As the negative electrode current collector, negative electrode collectors generally used in the relevant technical field can be used, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. The above negative active material is Si, Si-Me alloy (wherein, Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (wherein, 0 <y<2), Si-C 복합체 등과 같은 실리콘계 음극 활물질을 포함할 수 있고, 가장 바람직하게는 SiO, SiC 및 Si로 이루어지는 군으로부터 선택되는 실리콘계 음극 활물질을 포함할 수 있다. As a negative electrode active material other than the silicon-based negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; lithium metal thin films; metal materials capable of alloying with lithium, such as Sn and Al; and the like. One or a mixture of two or more of these may be used. The above silicon-based negative electrode active material may be included in an amount of 3 wt% or more, preferably 3 to 10 wt%, and more preferably 3 to 6 wt%, relative to the entire negative electrode active material layer. The above conductive material is used to provide conductivity to the negative electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The above-mentioned conductive material may be typically included in an amount of 0.01 to 0.1 wt%, preferably 0.05 to 0.1 wt%, and more preferably 0.07 to 0.1 wt%, based on the total weight of the negative electrode active material layer. The above binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used. The above binder may be included in an amount of 1 to 5 wt%, preferably 1 to 4 wt%, and more preferably 1 to 3 wt%, based on the total weight of the negative electrode active material layer. In addition to the positive and negative electrodes described above, a separator interposed between the positive and negative electrodes separates the positive and negative electrodes and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries may be used without particular limitations. Specifically, the separator may be a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength. A lithium secondary battery according to the present invention may include a positive electrode, a negative electrode, an electrode assembly including the positive electrode and the negative electrode; a battery can in which the electrode assembly is accommodated; an electrolyte poured into the battery can; and a sealing body sealing an open end of the battery can. The external shape of the lithium secondary battery of the present invention may be a cylindrical or square shape using a can, and preferably, the lithium secondary battery of the present invention may be a cylindrical lithium secondary battery. The cylindrical lithium secondary battery may include a jelly-roll type electrode assembly having a structure in which a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are wound in one direction; a battery can in which the electrode assembly is accommodated; and a sealing body that seals an open end of the battery can. The lithium secondary battery of the present invention may not cause cracks in the positive electrode in the wound electrode assembly by including a positive electrode satisfying the above formula (1) of the present invention, and in particular, may not cause cracks in less than 3 turns. The turns may refer to the number of winding wheels of the electrode assembly, and the lithium secondary battery of the present invention may include an electrode assembly having a number of turns of 20 to 30. Examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may include an organic solvent and a lithium salt. As the organic solvent, any solvent that can serve as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); Alcohol solvents such as ethyl alcohol, isopropyl alcohol, etc.; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc. can be used. Among these, carbonate solvents are preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable. The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - At least one selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. It is recommended that the concentration of the lithium salt be within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 10 wt% based on the total weight of the electrolyte. The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells. Examples of the above medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. Hereinafter, the present invention will be described in more detail through specific examples. However, the following examples are merely illustrative and serve to aid understanding of the present invention and do not limit its scope. It will be apparent to those skilled in the art that various modifications and variations are possible within the scope and technical spirit of this disclosure, and such modifications and variations are naturally within the scope of the appended claims. Example Example 1 Tap density is 1.88 g / cc and average particle size is D 50 This 3.71㎛ Li[Ni 0.90 Co 0.05 Mn 0.03 Al 0.02 ]O 2,A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.8 mg / cm on both sides. 2 , and the porosity was 24.0%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Example 2 Tap density is 2.10 g / cc and average particle size D 50 This 3.97㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.8 mg / cm on both sides. 2 , and the porosity was 24.0%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Example 3 Tap density is 2.1 g / cc and average particle size D 50 This 4.17㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 54.0 mg / cm2 on both sides. 2 , and the porosity was 23.8%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Example 4 Tap density is 2.1 g / cc and average particle size D 50 This 4.17㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.8 mg / cm on both sides. 2 , and the porosity was 23.8%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Example 5 Tap density is 2.1 g / cc and average particle size D 50 This 4.17㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2,A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 46.8 mg / cm on both sides. 2 , and the porosity was 23.8%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Practical example 6 Tap density is 2.4 g / cc and average particle size D 50 This 3.65㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 49.0 mg / cm on both sides. 2 , and the porosity was 24.1%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Example 7 Tap density is 2.3 g / cc and average particle size D 50 This 3.72㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.0 mg / cm on both sides. 2 , and the porosity was 23.8%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Example 8 Tap density 1.78 g / cc, average particle size D 50 This 3.82㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.8 mg / cm on both sides. 2 , and the porosity was 23.1%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Example 9 Tap density is 1.78 g / cc, and average particle size D 50 This 3.82㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.8 mg / cm on both sides.2 , and the porosity was 28.8%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Comparative Example 1 Tap density is 1.65 g / cc and average particle size D 50 This 4.06㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.8 mg / cm on both sides. 2 , and the porosity was 23.8%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Comparative Example 2 Tap density is 1.78 g / cc and average particle size D 50 This 3.91㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.8 mg / cm on both sides. 2 , and the porosity was 22.8%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Comparative Example 3 Tap density is 1.77 g / cc and average particle size D 50 This 3.82㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2,A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 50.8 mg / cm on both sides. 2 And the porosity was 21.9%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Comparative Example 4 Tap density is 1.88 g / cc and average particle size D 50 This 4.17㎛ Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 ]O 2, A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode. The loading amount of the prepared positive electrode active material layer was 58.0 mg / cm on both sides. 2 , and the porosity was 22.7%. A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 95:5 weight ratio mixture), a conductive agent (super C), and styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.4:0.9. The negative electrode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. A separator was interposed between the positive and negative electrodes manufactured as described above, and the electrodes were laminated in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a jelly-roll type electrode assembly. Experimental example The electrode assemblies of Examples 1 to 9 and Comparative Examples 1 to 4 were disassembled to check whether cracks occurred during the winding of the positive electrode. The results are shown in Table 1 below. Y-crack occurrenceExample 16.00XExample 24.80XExample 35.14XExample 44.84XExample 54.46XExample 63.53XExample 73.97XExample 86.94XExample 95.57XComparative Example 17.84OComparative Example 27.03OComparative Example 37.40OComparative Example 47.23O The electrode assemblies of Examples 1 to 9 including the positive electrode according to the present invention satisfying the Y value of Equation (1) of less than 7 did not exhibit cracks during winding, but it was confirmed that the electrode assemblies of Comparative Examples 1 to 4 including the positive electrode having the Y value of 7 or more exhibited cracks during winding.

Claims

1. A positive electrode for a lithium secondary battery, comprising: a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector; and satisfying the following formula (1). Equation (1): Y = 10 × L / (P×T 2 ) < 7 In the above equation (1), L is the loading amount of the anode (mg / cm 2 ) and, P is the porosity (%) of the anode, T is the tap density (g / cc) of the positive electrode active material included in the positive electrode active material layer.

2. In claim 1, A positive electrode for a lithium secondary battery, wherein the tap density of the positive electrode active material included in the positive electrode active material layer is 1.8 g / cc to 2.5 g / cc.

3. In claim 1, The loading amount of the above positive electrode active material layer is 44 mg / cm 2 56 mg / cm 2 Anode for lithium secondary batteries.

4. In claim 1, A positive electrode for a lithium secondary battery having a porosity of 22.5% to 30.0%.

5. In claim 1, A positive electrode for a lithium secondary battery, wherein the positive electrode active material included in the positive electrode active material layer is a lithium nickel-based transition metal oxide having a nickel content of 90 atm% or more among transition metals excluding lithium.

6. In claim 5, A positive electrode for a lithium secondary battery, wherein the positive electrode active material is a lithium nickel-based oxide represented by the following [chemical formula 2]. [Chemical Formula 2] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 2, M 1 is Mn, Al or a combination thereof, and M 2 is at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, and 0.8≤a≤1.2, 0.9≤b<1, 0 <c<0.1, 0<d<0.1, 0≤e≤0.05임.

7. In claim 1, A positive electrode for a lithium secondary battery, wherein the positive electrode active material is composed of single particles, pseudo-single particles, or a combination thereof.

8. In claim 1, A positive electrode for a lithium secondary battery, wherein the positive electrode active material layer includes a positive electrode active material having a unimodal particle size distribution showing a single peak in a volume cumulative particle size distribution graph.

9. In claim 8, Average particle diameter D of the above positive electrode active material 50 A cathode for a lithium secondary battery having a diameter of 3㎛ to 6㎛.

10. In claim 1, A positive electrode for a lithium secondary battery having a brittleness force of 35 gf or less.

11. In claim 10, A positive electrode for a lithium secondary battery, wherein the depth of the fracture point at which the above brittle force is measured is more than 21 mm from the positive electrode surface.

12. A lithium secondary battery comprising an electrode assembly including the positive electrode, negative electrode and separator of claim 1.

13. In claim 12, The above electrode assembly is a jelly-roll type lithium secondary battery having a structure in which a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are wound in one direction.

14. In claim 12, The above lithium secondary battery is a cylindrical lithium secondary battery.

15. In claim 13, The above electrode assembly is a lithium secondary battery in which cracks in the positive electrode do not occur within three turns.