Positive electrode and lithium secondary battery including same

Abstract

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 satisfies the following formula (1). In formula (1), L is the capacity (mg / cm2) of the positive electrode, P is the porosity (%) of the positive electrode, and T is the tap density (g / cc) of the positive electrode active material contained in the positive electrode active material layer. Formula (1): Y = 10 * L / (P * T2) lt; 7

Description

Technical Field

[0001] [Cross-references to related applications]

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0115742, filed on August 31, 2023, with the Korean Intellectual Property Office, the contents of which are incorporated herein by reference. [Technical Field]

[0004] This invention relates to a positive electrode and a lithium secondary battery including the same. Background Technology

[0005] With advancements in technologies such as electric vehicles and portable electronic devices, the demand for lithium-ion batteries as an energy source is rapidly increasing. In particular, the latest developments in electric vehicle technology necessitate batteries with high energy density.

[0006] To improve the energy density of lithium-ion batteries, the amount of active material in the electrode assembly can be increased to improve the utilization of the limited space inside the battery. However, if the loading of active material is increased to achieve a lithium-ion battery with high energy density, a problem arises where cracks appear in the electrode current collector in the core during the winding process of the electrode assembly. If the cracks become severe, the lithium migration path of the lithium-ion battery is interrupted, causing additional side reactions and thus degrading the long-term performance of the lithium-ion battery. Summary of the Invention

[0007] Technical issues

[0008] The present invention aims to provide a positive electrode in which no cracks occur in the core during the winding of the electrode assembly.

[0009] Technical solution

[0010] [1] The present invention provides a positive electrode for a lithium secondary battery, the positive electrode 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).

[0011] Formula (1): Y=10×L / (P×T 2 )<7

[0012] In equation (1), L is the loading of the positive electrode (mg / cm³). 2 P is the porosity (%) of the positive electrode, and T is the tap density (g / cc) of the positive electrode active material contained in the positive electrode active material layer.

[0013] [2] The present invention can provide a positive electrode for a lithium secondary battery according to [1], wherein the tap density of the positive electrode active material contained in the positive electrode active material layer is 1.8 g / cc to 2.5 g / cc.

[0014] [3] The present invention can provide a positive electrode for a lithium secondary battery according to [1] or [2], wherein the loading amount of the positive electrode active material layer is 44 mg / cm 2 to 56 mg / cm 2 .

[0015] [4] The present invention can provide a positive electrode for a lithium secondary battery according to at least one of [1] to [3], wherein the porosity of the positive electrode is 22.5% to 30.0%.

[0016] [5] The present invention can provide a positive electrode for a lithium secondary battery according to at least one of [1] to [4], wherein the positive electrode active material contained in the positive electrode active material layer is a lithium nickel-based transition metal oxide having a nickel content of 90 atomic% or more among transition metals other than lithium.

[0017] [6] The present invention can provide a positive electrode for a lithium secondary battery according to [5], wherein the positive electrode active material is a lithium nickel-based oxide represented by the following formula 2.

[0018] [Formula 2]

[0019] Li a Ni b Co c M 1 d M 2 e O2

[0020] In formula 2, M 1 is Mn, Al, or a combination thereof, M 2 is one or more selected from Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, 0.8 ≤ a ≤ 1.2, 0.9 ≤ b < 1, 0 < c < 0.1, 0 < d < 0.1, and 0 ≤ e ≤ 0.05.

[0021] [7] The present invention can provide a positive electrode for a lithium secondary battery according to at least one of [1] to [6], wherein the positive electrode active material is composed of single particles, pseudo single particles, or a combination thereof.

[0022] [8] The present invention can provide a positive electrode for a lithium secondary battery according to at least one of [1] to [7], wherein the positive electrode active material layer contains a positive electrode active material having a unimodal particle size distribution, which exhibits a single peak in the volume cumulative particle size distribution graph.

[0023] [9] The present invention can provide a positive electrode for a lithium secondary battery according to at least one of [1] to [8], wherein the average particle size D of the positive electrode active material is... 50 The thickness ranges from 3 μm to 6 μm.

[0024]

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

[0025]

[11] The present invention can provide a positive electrode for a lithium secondary battery according to

[10] , wherein the fracture point from which the brittle force is measured is at a depth greater than 21 mm from the surface of the positive electrode.

[0026]

[12] The present invention can provide a lithium secondary battery including an electrode assembly comprising a positive electrode, a negative electrode and a separator according to at least one of [1] to

[12] .

[0027]

[13] The present invention can provide a lithium secondary battery according to

[12] , wherein the electrode assembly is a jelly-roll type having a structure in which a positive electrode, a negative electrode and a separator between the positive and negative electrodes are wound in one direction.

[0028]

[14] The present invention can provide a lithium secondary battery according to

[12] or

[13] , wherein the lithium secondary battery is cylindrical.

[0029]

[15] The present invention can provide a lithium secondary battery according to at least one of

[12] to

[14] , wherein, in the electrode assembly, no cracks appear in the positive electrode with a number of turns of 3 or less.

[0030] Beneficial effects

[0031] During the winding of the positive electrode, the steps that appear at the tip of the positive electrode induce external forces on the electrode in the subsequent positive electrode pattern, leading to deformation. If the deformation becomes severe, the positive electrode may no longer be able to withstand the deformation and plastic deformation may occur. If the plastic deformation becomes even more severe, cracks will appear in the positive electrode, resulting in permanent deformation. If cracks appear in the positive electrode, side reactions with the electrolyte will occur during charging and discharging, thereby degrading lifetime characteristics and causing gas generation problems.

[0032] According to the present invention, the positive electrode adjusts the loading, porosity and tap density of the positive electrode active material contained in the positive electrode active material layer to meet a specific relationship, thereby increasing the resistance to plastic deformation, making it less prone to permanent deformation, or even if plastic deformation occurs, adjusting the degree of permanent deformation to be small, thereby suppressing permanent deformation at the beginning of the positive electrode, and solving the problems of life characteristics and gas generation in lithium secondary batteries. Detailed Implementation

[0033] The words or terms used in this specification and claims should not be construed as having the meanings defined in common dictionaries. Instead, they should be interpreted as meanings that the inventors can appropriately define to best illustrate the principles of the invention, and that are consistent with the technical concept of the invention.

[0034] In this invention, "primary particle" refers to a particle unit without grain boundaries when observed using a scanning electron microscope at magnifications of 5,000 to 20,000. "Average particle size of primary particles" refers to the arithmetic mean calculated after measuring the particle size of primary particles observed in scanning electron microscope images.

[0035] In this invention, a "secondary particle" is a particle formed by the aggregation of multiple primary particles. In this invention, to distinguish it from conventional secondary particles formed by the aggregation of tens to hundreds of primary particles, secondary particles containing 10 or fewer primary particles are referred to as pseudo-single particles.

[0036] In this invention, "average particle size D" 50 "This refers to the particle size at 50% of the volumetric cumulative particle size distribution of the positive electrode active material powder, and can be measured using laser diffraction. For example, after dispersing the positive electrode active material powder in a dispersion medium, the resulting material can be introduced into a commercially available laser diffraction particle size measurement device (e.g., MicrotracMT 3000) and irradiated with ultrasound at approximately 28 kHz with an output of 60 W to obtain a volumetric cumulative particle size distribution map, and then the particle size corresponding to 50% of the volumetric cumulative amount can be obtained."

[0037] In this specification, porosity can be calculated using the following mathematical formula A.

[0038] [Mathematical Expression A]

[0039] Porosity (%) = {1 - (electrode density / true density)} × 100

[0040] In mathematical formula A, the true density is the calculated density derived from the density and mass ratio of the component materials forming the electrode active material layer under the assumption of excluding pores, and the electrode density is the measured density of the electrode active material layer measured by sampling the electrode active material layer to a certain size.

[0041] The invention will be described in more detail below.

[0042] The positive electrode and / or lithium secondary battery according to the present invention includes at least one of the configurations described below, and may include any combination of the technically possible configurations described below.

[0043] 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).

[0044] Formula (1): Y=10×L / (P×T 2 )<7

[0045] If the positive electrode included in the lithium secondary battery has a Y value less than 7 as defined in formula (1) above, it has high resistance to plastic deformation, making it less prone to permanent deformation, or even if plastic deformation occurs, the degree of permanent deformation is small. Therefore, it is believed that the positive electrode of the present invention has small deformation caused by external force, resulting in the effect of suppressing cracks. Y can be 3 or greater and less than 7, or 3.5 or greater and less than 7.

[0046] In equation (1) above, L is the loading of the positive electrode (mg / cm³). 2 ), and the positive electrode loading refers to the weight per unit area of ​​the positive electrode active material layer coated on the positive electrode current collector.

[0047] L can be 44 mg / cm 2 Up to 56 mg / cm 2 44 mg / cm 2 Up to 55 mg / cm 2 And the optimal value is 44 mg / cm³. 2 Up to 54 mg / cm 2 The positive electrode of the present invention has a high loading capacity, enabling high capacity to be provided for lithium secondary batteries including the positive electrode. The positive electrode can be a single-sided positive electrode in which a positive active material layer is formed on one side of the positive current collector, or a double-sided positive electrode in which positive active material layers are formed on both sides of the positive current collector. Load capacity in the case of a double-sided electrode refers to the total load capacity on both sides. The positive electrode of the present invention is preferably a double-sided electrode in which the positive active material layer exists on both sides of the positive current collector.

[0048] In equation (1), P is the porosity (%) of the positive electrode, specifically the porosity of the positive electrode active material layer included in the positive electrode.

[0049] P can be from 22.5% to 40.0%, preferably from 23.0% to 30.0%, and most preferably from 23.0% to 27.0%.

[0050] In equation (1), T is the tap density (g / cc) of the positive electrode active material contained in the positive electrode active material layer.

[0051] T can be from 1.8 g / cc to 2.5 g / cc, preferably from 1.9 g / cc to 2.5 g / cc, and most preferably from 2.0 g / cc to 2.5 g / cc.

[0052] The positive electrode for lithium secondary batteries of the present invention may include a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector, and may have a brittle force of 35 gf or less, and the depth of the fracture point from the surface of the positive electrode where the brittle force is measured may be greater than 21 mm.

[0053] Brittle forces and the depth of the fracture point that measures brittle forces can be measured using, for example, a texture analysis device.

[0054] Specifically, the electrode to be measured can be stamped out and assembled into a brittle electrode fixing device, and the maximum force applied to the brittle tip can be measured while advancing the circular brittle tip from the surface of the electrode towards its depth. Furthermore, while advancing the circular brittle tip from the surface of the electrode towards its depth, the depth of advancement of the brittle tip from the surface relative to the point where electrode cracks occur and the electrode is damaged can be measured.

[0055] Brittleness refers to the property of a material that, when broken by external force, does not undergo permanent deformation, or undergoes only a very small amount of permanent deformation. Brittle force is an indicator of the rigidity of an electrode.

[0056] At the point where brittle force is measured, the force applied to the measuring tip suddenly decreases and the electrode is destroyed. The depth at which the measuring tip is embedded from the surface of the electrode is defined as the depth of the fracture point in the brittle force measurement.

[0057] The positive electrode of the present invention can be formed by means of a structure in which a layer of positive active material is formed on one or both sides of a long sheet-shaped positive electrode current collector.

[0058] The positive electrode of the present invention can be manufactured by applying a positive electrode slurry prepared by dispersing the positive electrode active material, conductive material and binder in a solvent such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, water, etc. on one or both sides of a long sheet-shaped positive electrode current collector, removing the solvent from the positive electrode slurry by a drying process, and then rolling.

[0059] As the positive electrode current collector, various positive electrode current collectors used in related technical fields can be used. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver can be used as the positive electrode current collector. The positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can also be formed on the surface of the positive electrode current collector to improve the adhesion strength of the positive electrode active material. The positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics. Most preferably, aluminum films can be used for controlling elongation, etc.

[0060] Meanwhile, as a positive electrode active material, the positive electrode active materials commonly used in related technical fields can be used.

[0061] Preferably, the positive electrode active material may include a lithium nickel-based oxide, and more specifically, may include a lithium nickel-based transition metal oxide in which the nickel content of a transition metal other than lithium is 90 atomic% or greater. Preferably, the lithium nickel-based oxide may contain Ni in amounts of 90 mol% to less than 100 mol%, 93 mol% to less than 100 mol%, or 95 mol% to less than 100 mol%. High capacity can be achieved by using a lithium nickel-based oxide with a high Ni content as described above.

[0062] More specifically, the positive electrode active material may include a lithium nickel-based oxide represented by the following formula 2.

[0063] [Equation 2]

[0064] Li a Ni b Co c M 1 d M 2 e O2

[0065] In Equation 2, M 1 It can be Mn, Al or a combination thereof, preferably Mn, or Mn and Al.

[0066] M 2 It can be one or more selected from Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 The element is not essential, but if included in appropriate amounts, it can promote grain growth during calcination or improve the stability of the crystal structure.

[0067] a represents the molar ratio of lithium in the lithium-nickel-based oxide, and can be 0.8 ≤ a ≤ 1.2, 0.85 ≤ a ≤ 1.15, or 0.9 ≤ a ≤ 1.2. If the molar ratio of lithium satisfies the above range, the crystal structure of the lithium-nickel-based oxide can be stably formed.

[0068] b represents the molar ratio of nickel among all metals other than lithium in the lithium-nickel-based oxide, and can be 0.9 ≤ b < 1, 0.93 ≤ b < 1, or 0.95 ≤ b < 1. If the molar ratio of nickel satisfies the above range, high energy density can be exhibited and high capacity can be achieved.

[0069] c represents the molar ratio of cobalt among all metals other than lithium in the lithium-nickel-based oxide, and can be 0 < c < 0.1, 0 < c < 0.07, or 0.02 ≤ c ≤ 0.07. If the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be achieved.

[0070] Above, d represents the molar ratio of the M 1 element among all metals other than lithium in the lithium-nickel-based oxide, and can be 0 < d < 0.1, 0 < d < 0.07, or 0.005 ≤ d ≤ 0.05.

[0071] If the molar ratio of the M 1 element satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0072] e represents the molar ratio of the M 2 element among all metals other than lithium in the lithium-nickel-based oxide, and can be 0 ≤ e ≤ 0.05, or 0 ≤ e ≤ 0.01.

[0073] Meanwhile, if necessary, the positive electrode active material according to the present invention may further include a coating on the surface of the lithium-nickel-based oxide particles, and the coating contains one or more coating elements selected from the following: Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. Preferably, the coating element can be Al, B, Co, or a combination thereof, and most preferably, the coating element can be B.

[0074] If there is a coating on the surface of the lithium-nickel-based oxide particles, the contact between the electrolyte and the lithium composite transition metal oxide is inhibited due to the coating, and thus, the effect of reducing the transition metal dissolution or gas generation caused by the side reaction with the electrolyte can be obtained.

[0075] Meanwhile, there are no particular restrictions on the form of the positive electrode active material, and it can be a secondary particle form in which a plurality of primary particles are aggregated, a single particle form consisting of a primary particle, or a combination thereof.

[0076] Preferably, the positive electrode active material may include a single particle consisting of one primary particle and / or a pseudo-single particle consisting of an aggregate of 10 or fewer primary particles. By using a positive electrode active material consisting of a single particle consisting of one primary particle and / or a pseudo-single particle consisting of an aggregate of 10 or fewer primary particles as the positive electrode active material, a lithium secondary battery with high capacity and excellent safety can be obtained.

[0077] Positive electrode active materials in the form of single particles consisting of a primary particle or pseudo-single particles containing 10 or fewer primary particles have higher particle strength than conventional positive electrode active materials in the form of secondary particles containing tens to hundreds of primary particles, resulting in almost no particle breakage during rolling. Furthermore, in the case of positive electrode active materials in the form of single or pseudo-single particles, due to the small number of primary particles constituting the particle, the changes caused by the volume expansion and contraction of the primary particles during charging and discharging are small, and therefore, the occurrence of internal cracks in the particles is significantly reduced.

[0078] Meanwhile, the average particle size D of the positive electrode active material of the present invention in the form of single particles and / or pseudo-single particles is... 50 The particle size can be 6 μm or smaller, 4 μm or smaller, 3 μm or smaller, or 2 μm or smaller, for example, 0.5 μm to 6 μm, preferably 1 μm to 6 μm, more preferably 3 μm to 6 μm. If the average particle size D of the positive electrode active material... 50 If the above range is met, the increase in resistance can be minimized.

[0079] Positive electrode active materials in the form of single particles and / or pseudo-single particles have the problem of lower lithium mobility than those in the form of secondary particles because the interfaces between primary particles that serve as lithium-ion diffusion paths within the particles are small, which increases resistance. The increase in resistance becomes more severe as particle size increases, and if resistance increases, capacity and output characteristics are adversely affected. Therefore, in this invention, by applying an average particle size D... 50 The positive electrode active material is a single particle or pseudo-single particle with a diameter of 5 μm or smaller, which minimizes the diffusion distance of lithium ions inside the particle, thereby suppressing the increase in resistance.

[0080] Therefore, increasing the Ni content in the cathode material to achieve high energy introduces an increase in structural instability. However, if the cathode 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, resulting in excellent safety. However, if cathode active materials with small average particle sizes in the form of single particles and / or pseudo-single particles are used, plastic deformation due to loads and external forces is likely to occur, potentially leading to cracks. Therefore, it is necessary to adjust the material to satisfy either condition 1 or condition 2.

[0081] The average particle size of the primary particles in the form of single-particle and / or pseudo-single-particle positive electrode active materials can be 5 μm or smaller, 4 μm or smaller, 3 μm or smaller, or 2 μm or smaller, for example, 0.5 μm to 5 μm, preferably 1 μm to 5 μm, and more preferably 2 μm to 5 μm. If the average particle size of the primary particles meets the above range, a positive electrode active material in the form of single-particle and / or pseudo-single-particle forms with excellent electrochemical properties can be formed. If the average particle size of the primary particles is too small, the number of agglomerates of the primary particles forming the positive electrode active material increases, thereby reducing the effect of suppressing particle breakage during rolling. If the average particle size of the primary particles is too large, the lithium diffusion path inside the primary particles becomes longer, thereby increasing the resistance and reducing the output characteristics.

[0082] In this invention, the positive electrode active material preferably has a unimodal particle size distribution, occurring in the form of single particles and / or pseudo-single particles. Conventionally, bimodal positive electrode active materials, in which large-particle positive electrode active materials with a large average particle size are mixed with small-particle positive electrode active materials with a small average particle size, have been widely used 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, if the particle size increases, the lithium migration path becomes longer, and the resistance increases significantly. Therefore, if large-diameter particles are mixed and used, there may be problems with capacity and output characteristics deterioration. Therefore, in this invention, by using a positive electrode active material with a unimodal distribution, the increase in resistance can be minimized.

[0083] The 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.

[0084] The negative electrode of the present invention can be formed in a structure in which a negative electrode active material layer is formed on one or both sides of the elongated sheet-shaped negative electrode current collector, and the negative electrode active material layer can contain a negative electrode active material containing Si, a conductive material and a binder.

[0085] Specifically, the negative electrode can be fabricated as follows: apply 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, water, etc. on one or both sides of a long sheet-shaped negative electrode current collector, and remove the solvent of the negative electrode slurry through a drying process, and then roll press.

[0086] As the negative electrode current collector, a negative electrode current collector commonly used in the relevant technical field can be used. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The thickness of the negative electrode current collector can generally be 3 μm to 500 μm, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to enhance the adhesion strength of the negative electrode active material. For example, various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics can be used.

[0087] The negative electrode active material can include a silicon-based negative electrode active material, such as Si, Si-Me alloy (where Me is one or more selected from Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), and Si-C composite material, and most preferably, a silicon-based negative electrode active material selected from SiO, SiC, and Si.

[0088] As the negative electrode active material other than the silicon-based negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium can be used. Specific examples include carbon-containing 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, etc., and any one of them or a mixture of two or more of them can be used.

[0089] Relative to the entire negative electrode active material layer, the silicon-based negative electrode active material can be included in an amount of 3% by weight or more, preferably 3% to 10% by weight, and more preferably 3% to 6% by weight.

[0090] The conductive material is used to impart conductivity to the negative electrode, and in the battery to be formed, any conductive material that does not cause chemical changes and has electronic conductivity can be used without specific limitations. 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, thermal cracking carbon black, carbon fiber, and carbon nanotube; metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and among them, a single one or a mixture of two or more of them can be used.

[0091] The conductive material may be included in an amount of typically 0.01% to 0.1% by weight, preferably 0.05% to 0.1% by weight, and more preferably 0.07% to 0.1% by weight, relative to the total weight of the negative electrode active material layer.

[0092] Binders are used to improve the adhesion between particles of the negative electrode active material and the adhesion strength between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of both or more thereof may be used.

[0093] Based on the total weight of the negative electrode active material layer, the binder may be included in an amount of 1% to 5% by weight, preferably 1% to 4% by weight, and more preferably 1% to 3% by weight.

[0094] In addition to the positive and negative electrodes, a separator between them separates the positive and negative electrodes and provides a pathway for lithium ions to move. Any of the separators commonly used in lithium-ion secondary batteries can be used without specific limitations. Specifically, the separator can be a porous polymer membrane, such as a porous polymer membrane made of polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a stacked structure of two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength.

[0095] The 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; wherein a battery can housing the electrode assembly; an electrolyte injected into the battery can; and a sealant sealing the opening of the battery can.

[0096] The external shape of the lithium secondary battery of the present invention can be cylindrical or square, and preferably, the lithium secondary battery of the present invention can be a cylindrical lithium secondary battery. The cylindrical lithium secondary battery may include: a wound electrode assembly having a structure in which a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode are wound in one direction; a battery can containing the electrode assembly; and a sealant sealing the opening end of the battery can.

[0097] The lithium secondary battery of the present invention may include a positive electrode satisfying formula (1) of the present invention, such that no cracks in the positive electrode can occur in the wound electrode assembly, and particularly no cracks can occur within the number of turns of 3 or less. The number of turns may refer to the number of windings of the electrode assembly, and the lithium secondary battery of the present invention may include an electrode assembly with a number of turns of 20 to 30.

[0098] The electrolyte used in this invention may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used to manufacture lithium secondary batteries.

[0099] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0100] Organic solvents can be used without any particular restrictions, as long as they can serve as a medium through which ions involved in the electrochemical reactions of the battery can move. Specifically, organic solvents can include: ester-based solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether-based solvents, such as dibutyl ether or tetrahydrofuran; ketone-based solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among them, carbonate solvent is preferred, and a mixture of cyclic carbonates (such as ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) that can improve the charging and discharging performance of the battery is more preferred.

[0101] Lithium salts can be used without any specific restrictions, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from one or more of the following: 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 - Lithium salts that can be used include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is recommended that the lithium salt concentration be in the range of 0.1 M to 2.0 M. If the lithium salt concentration is within this range, the electrolyte will have suitable conductivity and viscosity, exhibiting excellent electrolyte performance and efficient lithium ion movement.

[0102] In addition to electrolyte components, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. These additives may include, for example, halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted... Alzolidinediones, N,N-substituted imidazolidinyl ethers, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount from 0.1% to 10% by weight, based on the total weight of the electrolyte.

[0103] The lithium secondary battery according to the present invention can be used not only as a battery cell for power supply of small devices, but also preferably as a cell battery in a medium or large battery module comprising a plurality of battery cells.

[0104] Examples of medium or large-sized installations include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0105] The invention will be described in more detail below with reference to specific embodiments. However, these embodiments are merely illustrative of the invention and do not limit its scope. It will be apparent to those skilled in the art that various changes and modifications are possible within the scope and concept of this specification, and such modifications and variations naturally fall within the scope of the appended claims.

[0106] Example

[0107] Example 1

[0108] The particle size D has a tap density of 1.88 g / cc and an average particle size of 3.71 μm. 50 Li[Ni 0.90 Co 0.05 Mn 0.03 Al 0.02 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.8 mg / cm² on both sides. 2 And its porosity is 24.0%.

[0109] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (superC), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0110] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0111] Example 2

[0112] The particle size D has a tap density of 2.10 g / cc and an average particle size of 3.97 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.8 mg / cm² on both sides. 2 And its porosity is 24.0%.

[0113] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0114] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0115] Example 3

[0116] The particle size D has a tap density of 2.1 g / cc and an average particle size of 4.17 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 54.0 mg / cm² on both sides. 2 And its porosity is 23.8%.

[0117] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0118] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0119] Example 4

[0120] The particle size D has a tap density of 2.1 g / cc and an average particle size of 4.17 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.8 mg / cm² on both sides. 2 And its porosity is 23.8%.

[0121] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0122] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0123] Example 5

[0124] The particle size D has a tap density of 2.1 g / cc and an average particle size of 4.17 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 46.8 mg / cm² on both sides. 2 And its porosity is 23.8%.

[0125] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0126] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0127] Example 6

[0128] The particle size D has a tap density of 2.4 g / cc and an average particle size of 3.65 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 49.0 mg / cm² on both sides. 2 And its porosity is 24.1%.

[0129] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0130] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0131] Example 7

[0132] The particle size D has a tap density of 2.3 g / cc and an average particle size of 3.72 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.0 mg / cm² on both sides. 2 And its porosity is 23.8%.

[0133] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0134] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0135] Example 8

[0136] The particle size D has a tap density of 1.78 g / cc and an average particle size of 3.82 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.8 mg / cm² on both sides. 2 And its porosity is 23.1%.

[0137] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0138] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0139] Example 9

[0140] The particle size D has a tap density of 1.78 g / cc and an average particle size of 3.82 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.8 mg / cm² on both sides. 2 And its porosity is 28.8%.

[0141] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0142] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0143] Comparative Example 1

[0144] The particle size D has a tap density of 1.65 g / cc and an average particle size of 4.06 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.8 mg / cm² on both sides. 2 And its porosity is 23.8%.

[0145] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0146] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0147] Comparative Example 2

[0148] The particle size D has a tap density of 1.78 g / cc and an average particle size of 3.91 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.8 mg / cm² on both sides. 2 And its porosity is 22.8%.

[0149] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0150] A separator is inserted between the positive and negative electrodes formed as described above, and the separators / positive electrodes / separators / negative electrodes are stacked in this order and then wound to manufacture a wound electrode assembly.

[0151] Comparative Example 3

[0152] The particle size D has a tap density of 1.77 g / cc and an average particle size of 3.82 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 50.8 mg / cm² on both sides. 2 And its porosity is 21.9%.

[0153] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0154] A separator is inserted between the positive and negative electrodes formed as described above, and the separator / positive electrode / separator / negative electrode are laminated in this order, and then wound to manufacture a wound electrode assembly.

[0155] Comparative Example 4

[0156] The particle size D has a tap density of 1.88 g / cc and an average particle size of 4.17 μm. 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a 15.0 μm thick aluminum current collector, dried at 120°C, and rolled to form the positive electrode. The formed positive electrode active material layer had a loading of 58.0 mg / cm² on both sides. 2 And its porosity is 22.7%.

[0157] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:SiO = 95:5 by weight), the conductive material (super C), styrene-butadiene rubber (SBR), and 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 rolled to form the negative electrode.

[0158] A separator is inserted between the positive and negative electrodes formed as described above, and the separator / positive electrode / separator / negative electrode are laminated in this order, and then wound to manufacture a wound electrode assembly.

[0159] Experimental Example

[0160] The wound electrode assemblies of Examples 1 to 9 and Comparative Examples 1 to 4 were disassembled to check whether cracks appeared during the winding of the positive electrode. The results are shown in Table 1 below.

[0161] [Table 1]

[0162]

[0163] The electrode assemblies of Examples 1 to 9, which include positive electrodes according to the invention with a Y value of less than 7 that satisfy formula (1), did not crack during winding, but the electrode assemblies of Comparative Examples 1 to 4, which include positive electrodes with a Y value of 7 or greater, were found to have cracks during winding.

Claims

1. A positive electrode for a lithium secondary battery, the positive electrode comprising: A positive current collector; and a positive active material layer positioned on the positive current collector, wherein the positive electrode satisfies the following formula (1): Formula (1): Y = 10 × L / (P × T 2 )<7 In equation (1), L is the loading of the positive electrode (mg / cm³). 2 ), P is the porosity (%) of the positive electrode, and T is the tap density (g / cc) of the positive electrode active material contained in the positive electrode active material layer.

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

3. The positive electrode for a lithium secondary battery according to claim 1, wherein the loading of the positive electrode active material layer is 44 mg / cm³. 2 Up to 56 mg / cm 2 .

4. The positive electrode for a lithium secondary battery according to claim 1, wherein the porosity of the positive electrode is 22.5% to 30.0%.

5. The positive electrode for a lithium secondary battery according to claim 1, wherein the positive electrode active material included in the positive electrode active material layer is a lithium-nickel-based transition metal oxide with a nickel content of 90 atomic% or more in a transition metal other than lithium.

6. The positive electrode for a lithium secondary battery according to claim 5, wherein the positive electrode active material is a lithium nickel-based oxide represented by the following formula 2: Formula 2 Li a Ni b Co c M 1 d M 2 e O2 In Formula 2, M 1 is Mn, Al or a combination thereof, and M 2 is one or more selected from Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, 0.8 ≤ a ≤ 1.2, 0.9 ≤ b < 1, 0 < c < 0.1, 0 < d < 0.1, and 0 ≤ e ≤ 0.

05.

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

8. The positive electrode for a lithium secondary battery according to claim 1, wherein the positive electrode active material layer comprises a positive electrode active material having a single-peak particle size distribution, which exhibits a single peak in the volume cumulative particle size distribution diagram.

9. The positive electrode for a lithium secondary battery according to claim 8, wherein the average particle size D of the positive electrode active material is... 50 The thickness ranges from 3 μm to 6 μm.

10. The positive electrode for a lithium secondary battery according to claim 1, wherein the brittle force of the positive electrode is 35 gf or less.

11. The positive electrode for a lithium secondary battery according to claim 10, wherein the fracture point from which the brittle force is measured is at a depth greater than 21 mm from the surface of the positive electrode.

12. A lithium secondary battery, comprising an electrode assembly, the electrode assembly comprising a positive electrode, a negative electrode, and a separator as described in claim 1.

13. The lithium secondary battery of claim 12, wherein the electrode assembly is a wound type having wherein the positive electrode, the negative electrode and the separator between the positive electrode and the negative electrode are wound in one direction.

14. The lithium secondary battery according to claim 12, wherein the lithium secondary battery is cylindrical.

15. The lithium secondary battery according to claim 13, wherein, In the electrode assembly, no cracks appear in the positive electrode with a number of turns of 3 or less.

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