Positive electrode and lithium secondary battery containing the same

Abstract

The present invention provides a positive electrode for a lithium secondary battery that includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and satisfies the following formula (1). Equation (1): Y = 10 × L / (P × T) 2 )<7 In formula (1) above, L is the loading amount of the positive electrode (mg / cm³). 2 ) where P is the porosity of the positive electrode (%) and T is the tap density of the positive electrode active material contained in the positive electrode active material layer (g / cc).

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0115742 dated August 31, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] This invention relates to a positive electrode and a lithium secondary battery containing the same. [Background technology]

[0003] With the advancement of technologies such as electric vehicles and portable electronic devices, the demand for lithium-ion batteries as an energy source is rapidly increasing. In particular, with the recent development of electric vehicle technology, there is a growing need for batteries with high energy density.

[0004] To improve the energy density of lithium-ion batteries, increasing the amount of active material contained in the electrode assembly can enhance the utilization of the limited space inside the battery. However, increasing the amount of active material loaded to achieve high energy density in lithium-ion batteries leads to a problem where cracks occur in the electrode current collector in the core during the electrode assembly winding process. If these cracks become severe, the lithium transfer path in the lithium-ion battery is severed, triggering further side reactions and degrading the long-term performance of the lithium-ion battery. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a positive electrode that does not develop cracks in the core portion when the electrode assembly is wound up. [Means for solving the problem]

[0006] [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 located on the positive electrode current collector, satisfying the following formula (1). Formula (1): Y = 10×L / (P×T 2 )<7 In the above formula (1), L is the loading amount of the positive electrode (mg / cm 2 ), P is the porosity of the positive electrode (%), and T is the tap density (g / cc) (g / cm 3 ) of the positive electrode active material contained in the positive electrode active material layer.

[0007] [2] In the present invention, in the above [1], the tap density of the positive electrode active material contained in the positive electrode active material layer is 1.8 g / cc (g / cm 3 ) to 2.5 g / cc (g / cm 3 ), and a positive electrode for a lithium secondary battery can be provided.

[0008] [3] In the present invention, in the above [1] or [2], the loading amount of the positive electrode active material layer is 44 mg / cm 2 to 56 mg / cm 2 , and a positive electrode for a lithium secondary battery can be provided.

[0009] [4] In the present invention, in at least one of the above [1] to [3], the porosity of the positive electrode is 22.5% to 30.0%, and a positive electrode for a lithium secondary battery can be provided.

[0010] [[ID=…]] [5] In the present invention, in at least one of the above [1] to [4], the positive electrode active material contained in the positive electrode active material layer is a lithium nickel-based transition metal oxide in which the content of nickel among transition metals other than lithium is 90 atm% or more, and a positive electrode for a lithium secondary battery can be provided.

[0011] [6] In the present invention, in the above [5], the positive electrode active material is a lithium nickel-based oxide represented by the following [Chemical Formula 2], and a positive electrode for a lithium secondary battery can be provided. [Chemical Formula 2] Li a Ni b Co c M 1 d M 2 Note: There seems to be an ellipsis in the original text at line 32 which is represented as "…" in the translation for consistency with the original's format. If this is incorrect, please provide the correct content for a more accurate translation.e O2 In the above chemical formula 2, M 1 M is Mn, Al, or a combination thereof. 2 is one or more elements selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, where 0.8 ≤ a ≤ 1.2, 0.9 ≤ b < 1, 0 <c<0.1、0<d<0.1、0≦e≦0.05である。

[0012] [7] In at least one of the above [1] to [6], the present invention can provide a positive electrode for a lithium secondary battery in which the positive electrode active material consists of single particles, pseudo-single particles, or a combination thereof.

[0013] [8] In at least one of the above [1] to [7], the present invention can provide a positive electrode for a lithium secondary battery in which the positive electrode active material layer comprises a positive electrode active material having a unimodal particle size distribution that shows a single peak in a volume cumulative particle size distribution graph.

[0014] [9] In at least one of the above [1] to [8], the average particle size D of the positive electrode active material 50 This can provide a positive electrode for lithium secondary batteries with a thickness of 3 μm to 6 μm.

[0015]

[10] The present invention can provide a positive electrode for a lithium secondary battery in which, in at least one of the above [1] to [9], the brittleness force of the positive electrode is 35 gf (0.343 N) or less.

[0016]

[11] The present invention can provide a positive electrode for a lithium secondary battery in which, in

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

[0017]

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

[12] .

[0018]

[13] The present invention can provide a lithium secondary battery in which, in the present

[12] , the electrode assembly is a jelly roll type 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.

[0019]

[14] The present invention can provide a lithium secondary battery in which the lithium secondary battery is cylindrical, as described in

[12] or

[13] above.

[0020]

[15] The present invention provides a lithium secondary battery in which, in at least one of the above

[12] to

[14] , the electrode assembly does not develop a crack in the positive electrode within three turns or less. [Effects of the Invention]

[0021] During the winding of the positive electrode, a step is created at the end of the positive electrode, causing external force to be generated in the subsequent positive electrode pattern, resulting in deformation. If this deformation becomes severe, the positive electrode can no longer withstand it and undergoes plastic deformation. If this plastic deformation becomes even more severe, cracks will form in the positive electrode, leading to permanent deformation. When cracks form in the positive electrode, side reactions occur with the electrolyte during charging and discharging, resulting in a deterioration of lifespan characteristics and the generation of gases.

[0022] The positive electrode according to the present invention has high resistance to plastic deformation and prevents permanent deformation from occurring easily, or even if plastic deformation occurs, the degree of permanent deformation is reduced, thereby suppressing permanent deformation at the starting portion of the positive electrode and solving the problems of lithium secondary battery life characteristics and gas generation. This is achieved by adjusting the loading amount, the porosity of the positive electrode, and the tap density of the positive electrode active material contained in the positive electrode active material layer so that they satisfy a specific relational expression. [Modes for carrying out the invention]

[0023] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0024] In this invention, "primary particle" refers to a particle unit in which no grain boundaries are visible when observed using a scanning electron microscope at a field of view of 5,000x to 20,000x. "Average particle size of primary particles" refers to the arithmetic mean calculated after measuring the particle size of primary particles observed in a scanning electron microscope image.

[0025] In this invention, a "secondary particle" is a particle formed by the aggregation of multiple primary particles. In this invention, in order 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 pseudo-single particles.

[0026] In this invention, "average particle size D 50 This refers to the particle size at the 50% reference point 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 introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and then measured by obtaining a volume-cumulative particle size distribution graph and determining the particle size corresponding to 50% of the volume-cumulative amount.

[0027] In this specification, the porosity can be calculated using the following mathematical formula A.

[0028] [Mathematical formula A] Porosity (%)={1-(electrode density / true density)}×100

[0029] In the above mathematical formula A, true density is a calculated density obtained from the density and mass ratio of each constituent material making up the electrode active material layer, under the assumption that pores are not present, and electrode density is the measured density of the electrode active material layer measured after taking a sample of the electrode active material layer in a predetermined size.

[0030] The present invention will be described in more detail below.

[0031] The positive electrode and / or lithium secondary battery according to the present invention includes at least one of the configurations disclosed below, and may include any combination of technically possible configurations from the following.

[0032] The present invention provides a positive electrode for a lithium secondary battery that includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and satisfies the following formula (1).

[0033] Equation (1): Y = 10 × L / (P × T) 2 )<7

[0034] When the Y value defined in formula (1) above is less than 7 for the positive electrode contained in a lithium secondary battery, the resistance to plastic deformation is high, and permanent deformation does not easily occur, or even if plastic deformation occurs, the degree of permanent deformation is small. Therefore, it is considered that the positive electrode of the present invention exhibits an effect of less deformation due to external forces and suppression of cracks. The Y value can be 3 or more and less than 7, or 3.5 or more and less than 7.

[0035] In formula (1) above, L is the loading amount of the positive electrode (mg / cm³). 2 The positive electrode loading amount is the weight per unit area of ​​the positive electrode active material layer coated on the positive electrode current collector.

[0036] The aforementioned L is 44-56 mg / cm³ 2 Preferably 44-55 mg / cm³ 2 Most preferably 44-54 mg / cm³ 2The positive electrode of the present invention has a high loading capacity, and a lithium secondary battery containing 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 the positive electrode current collector, or a double-sided positive electrode in which positive electrode active material layers are formed on both sides of the positive electrode current collector. In the case of a double-sided electrode, the loading capacity refers to the total loading capacity of both sides. Preferably, the positive electrode of the present invention may be a double-sided electrode in which positive electrode active material layers are present on both sides of the positive electrode current collector.

[0037] In equation (1) above, P is the porosity (%) of the positive electrode, and specifically refers to the porosity of the positive electrode active material layer contained in the positive electrode.

[0038] The aforementioned P can be 22.5 to 40.0%, preferably 23.0 to 30.0%, and most preferably 23.0 to 27.0%.

[0039] In equation (1) above, T is the tap density (g / cc) of the positive electrode active material contained in the positive electrode active material layer.

[0040] The aforementioned T is 1.8~2.5 g / cc (g / cm³). 3 ), preferably 1.9~2.5 g / cm³ (g / cm³) 3 )c, most preferably 2.0~2.5g / cc (g / cm³) 3 ) can be.

[0041] 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 located on the positive electrode current collector, wherein the brittleness force is 35 gf (0.343 N) or less, and the depth of the fracture point where the brittleness force is measured can be more than 21 mm from the surface of the positive electrode.

[0042] The brittleness force and the depth of the fracture point at which the brittleness force is measured can be determined, for example, using texture analysis equipment.

[0043] Specifically, the electrode to be measured is punched out, and then it is clamped in a brittleness electrode fixing device. The maximum force acting on the brittleness tip can then be measured as it advances from the surface of the electrode in the direction of depth. Furthermore, as the brittleness tip advances from the surface of the electrode in the direction of depth, an electrode crack occurs, and the depth to which the brittleness tip has advanced from the surface to the point at which the electrode breaks can be measured.

[0044] Brittleness refers to the property of a material to break without permanent deformation under external force, or to undergo only a very partial permanent deformation before breaking. The brittleness force is an indicator of the stiffness of the electrode.

[0045] At the point where the brittle force is measured, the force applied to the measuring tip drops suddenly, causing the electrode to break. The depth to which the measuring tip penetrates from the electrode surface at this point is defined as the depth of the fracture point where the brittle force is measured.

[0046] The positive electrode of the present invention may have 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.

[0047] The positive electrode of the present invention can be manufactured by applying a positive electrode slurry, which is 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, or water, to one or both sides of a long sheet-shaped positive electrode current collector, removing the solvent from the positive electrode slurry in a drying process, and then rolling it.

[0048] Various positive electrode current collectors used in the art can be used as the positive electrode current collector. For example, the positive electrode current collector can be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. The positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to increase the adhesion strength of the positive electrode active material. The positive electrode current collector can be used in various forms, such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric. Most preferably, an aluminum thin film can be used, for example, in terms of adjusting the elongation.

[0049] On the other hand, as the positive electrode active material, any positive electrode active material commonly used in the relevant technical field can be used.

[0050] Preferably, the positive electrode active material may include a lithium nickel-based oxide, specifically a lithium nickel-based transition metal oxide in which the nickel content among transition metals other than lithium is 90 atm% or more. Preferably, the lithium nickel-based oxide may contain Ni in amounts 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%. As described above, when a lithium nickel-based oxide with a high Ni content is used, a high capacity can be achieved.

[0051] More specifically, the positive electrode active material may include a lithium nickel-based oxide represented by the following [Chemical Formula 2].

[0052] [Chemical formula 2] Li a Ni b Co c M 1 d M 2 e O2

[0053] In the above chemical formula 2, M 1It can be Mn, Al or a combination thereof, preferably it can be Mn or Mn and Al.

[0054] Said M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, preferably it can be one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably it can be Zr, Y or a combination thereof. The M 2 element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving crystal structure stability.

[0055] Said a represents the lithium molar ratio 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. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0056] Said 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. When the molar ratio of nickel satisfies the above range, it shows a high energy density and high capacity can be realized.

[0057] Said 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. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized. [[ID=二十一]] [[ID=二十二]]

[0058] [[ID=二十三]] [[ID=二十四]]Said d represents the molar ratio of the M [[ID=二十五]] 1 [[ID=二十六]]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. [[ID=二十七]] [[ID=二十八]]

[0059] [[ID=二十九]] M 1 When the molar ratio of the elements satisfies the aforementioned range, the structural stability of the positive electrode active material is excellent.

[0060] The aforementioned e is M, which is the total metal other than lithium in the lithium nickel oxide. 2 This indicates the molar ratio of elements and can be 0 ≤ e ≤ 0.05 or 0 ≤ e ≤ 0.01.

[0061] On the other hand, the positive electrode active material according to the present invention may further include, if necessary, a coating layer on the surface of the lithium nickel oxide particles, 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. Preferably, the coating element may be Al, B, Co, or a combination thereof, and most preferably, the coating element may be B.

[0062] When a coating layer is present on the surface of lithium nickel oxide particles, the coating layer suppresses contact between the electrolyte and the lithium composite transition metal oxide, thereby reducing the leaching of transition metals and the generation of gases due to side reactions with the electrolyte.

[0063] On the other hand, the positive electrode active material is not particularly limited in form and may be in the form of secondary particles formed by the aggregation of multiple primary particles, in the form of a single particle consisting of one primary particle, or in a form that is a combination of these.

[0064] Preferably, the positive electrode active material may include a positive electrode active material consisting of a single particle made up of one primary particle and / or a pseudo-single particle, which is an aggregate of 10 or fewer primary particles. By using a positive electrode active material consisting of a single particle made up of one primary particle and / or a pseudo-single particle, which is an aggregate of 10 or fewer primary particles, a lithium secondary battery with high capacity and excellent safety can be obtained.

[0065] Positive electrode active materials in the form of single particles or pseudo-single particles, where 10 or fewer primary particles are aggregated, have higher particle strength compared to conventional positive electrode active materials in the form of secondary particles, where tens to hundreds of primary particles are aggregated. As a result, particle cracking during rolling is almost nonexistent. Furthermore, in the case of single-particle or pseudo-single-particle positive electrode active materials, the small number of primary particles that make up the particle reduces the volume changes due to expansion and contraction of the primary particles during charging and discharging, which significantly reduces the occurrence of cracks inside the particle.

[0066] On the other hand, the positive electrode active material in single-particle and / or pseudo-single-particle form according to the present invention has an average particle size D 50 However, it can 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. Average particle size D of the positive electrode active material 50 When the above range is satisfied, the increase in resistance can be minimized.

[0067] Single-particle and / or pseudo-single-particle cathode active materials have a problem of increased resistance because they have fewer interfaces between primary particles that serve as diffusion pathways for lithium ions within the particle, resulting in lower lithium mobility compared to secondary-particle cathode active materials. This increase in resistance worsens with increasing particle size, and increased resistance negatively affects capacitance and power characteristics. Therefore, in this invention, the average particle size D 50 By applying single-particle or pseudo-single-particle cathode active materials with a diameter of 5 μm or less, the lithium ion diffusion distance within the particles is minimized, thereby suppressing the increase in resistance.

[0068] Therefore, in order to achieve high energy, increasing the Ni content in the cathode material presents the problem of increased structural instability of the cathode. However, when the cathode active material is used in single-particle and / or pseudo-single-particle form, the amount of gas generated due to particle cracking and internal cracking can be significantly reduced, thereby achieving excellent safety. However, when using cathode active material with a small average particle size in single-particle and / or pseudo-single-particle form, plastic deformation due to load and external force is likely to occur, and cracks are likely to occur, so it is necessary to adjust it to satisfy equation (1).

[0069] The positive electrode active material in single-particle and / or pseudo-single-particle form may have an average particle size of 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, and more preferably 2 μm to 5 μm. When the average particle size of the primary particles satisfies the above range, a positive electrode active material in single-particle and / or pseudo-single-particle form with excellent electrochemical properties can be formed. If the average particle size of the primary particles is too small, the number of aggregated primary particles forming the positive electrode active material increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size of the primary particles is too large, the lithium diffusion path inside the primary particles becomes longer, increasing resistance and potentially degrading the output characteristics.

[0070] In the present invention, it is preferable that the positive electrode active material in single-particle and / or pseudo-single-particle form has a unimodal particle size distribution. Conventionally, in order to improve the electrode density of the positive electrode active material layer, bimodal positive electrode active materials have been widely used, which are a mixture of large-particle positive electrode active material with a large average particle size and small-particle positive electrode active material with a small average particle size. However, in the case of positive electrode active materials in single-particle or pseudo-single-particle form, as the particle size increases, the lithium transfer path becomes longer and the resistance increases significantly. Therefore, when large-particle particles are mixed and used, problems may arise in which the capacity and output characteristics deteriorate. Accordingly, in the present invention, the increase in resistance can be minimized by using a positive electrode active material having a unimodal distribution.

[0071] The lithium secondary battery according to the present invention can include a positive electrode, a negative electrode, and an electrode assembly including the positive electrode and the negative electrode.

[0072] The negative electrode of the present invention can have a structure in which a negative electrode active material layer is formed on one or both surfaces of a long sheet-shaped negative electrode current collector, and the negative electrode active material layer can include a negative electrode active material containing Si, a conductive material, and a binder.

[0073] 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 surfaces of a long sheet-shaped negative electrode current collector, removing the solvent of the negative electrode slurry by a drying process, and then rolling.

[0074] In the negative electrode current collector, a negative electrode current collector generally used in the art can be used. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, a surface-treated product with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. can be used. The negative electrode current collector can usually have a thickness of 3 to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the binding force 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 body, etc.

[0075] The negative electrode active material can include a silicon-based negative electrode active material such as Si, a Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO y (where 0 < y < 2), a Si-C composite, etc., and most preferably, it can include a silicon-based negative electrode active material selected from the group consisting of SiO, SiC, and Si.

[0076] As a negative electrode active material other than the silicon-based negative electrode active material mentioned above, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; lithium metal thin films; and metallic substances that can be alloyed with lithium, such as Sn and Al. Any one or a mixture of two or more of these can be used.

[0077] The silicon-based anode active material can be present in an amount of 3% by weight or more, preferably 3 to 10% by weight, and more preferably 3 to 6% by weight, relative to the total anode active material layer.

[0078] The conductive material is used to impart conductivity to the negative electrode and can be used without particular limitations in a battery that does not cause chemical changes and possesses electronic conductivity. 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 black, carbon fiber, and carbon nanotubes; metal powders or metal fibers 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. One of these materials alone or a mixture of two or more can be used.

[0079] The conductive material can typically be included in an amount of 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.

[0080] The binder plays a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used.

[0081] The binder may be present in an amount of 1 to 5% by weight, preferably 1 to 4% by weight, and more preferably 1 to 3% by weight, relative to the total weight of the negative electrode active material layer.

[0082] In addition to the positive and negative electrodes, a separator interposed between the positive and negative electrodes separates the negative and positive electrodes and provides a passage for lithium ions to move. Such a separator can be used without particular limitations, as long as it is commonly used as a separator in lithium secondary batteries. Specifically, the separator can be a porous polymer film, for example, a porous polymer film made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength.

[0083] The lithium secondary battery according to the present invention may include a positive electrode, a negative electrode, an electrode assembly comprising the positive electrode and the negative electrode; a battery case in which the electrode assembly is housed; an electrolyte injected into the battery case; and a sealant that seals the open end of the battery case.

[0084] The external shape of the lithium secondary battery of the present invention can be cylindrical or rectangular using a can, 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 jelly roll type electrode assembly having a structure in which a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes are wound in one direction; a battery can in which the electrode assembly is housed; and a sealant that seals the open end of the battery can.

[0085] The lithium secondary battery of the present invention includes a positive electrode that satisfies formula (1) of the present invention, thereby preventing cracks from occurring in the positive electrode in the wound electrode assembly, and in particular, preventing cracks from occurring within three turns or less. The number of turns may refer to the number of winding cycles of the electrode assembly, and the lithium secondary battery of the present invention may include an electrode assembly having 20 to 30 turns.

[0086] Examples of electrolytes 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.

[0087] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0088] The organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, 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 and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0089] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the 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 - The lithium salt can be selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is 0.1 to 2.0 M (mol / dm³). 3 It is preferable to use within the range of ). When the lithium salt concentration falls within the above range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0090] In addition to the components of the electrolyte, 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, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride. Here, the additive may be present in an amount of 0.1 to 10% by weight relative to the total weight of the electrolyte.

[0091] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0092] Examples of the aforementioned medium- and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0093] The present invention will be described in more detail below with reference to specific examples. However, the following examples are illustrative to facilitate understanding of the present invention and do not limit its scope. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the described concept and technical idea, and it goes without saying that such variations and modifications fall within the scope of the appended claims.

[0094] Examples Example 1 Tap density is 1.88 g / cc (g / cm³). 3 ) and average particle size D 50 Li[Ni 0.90 Co 0.05 Mn 0.03Al 0.02 A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 50.8 mg / cm² on both sides. 2 The porosity was 24.0%.

[0095] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0096] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0097] Example 2 Tap density is 2.10 g / cc (g / cm³). 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 50.8 mg / cm² on both sides. 2 The porosity was 24.0%.

[0098] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0099] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0100] Example 3 Tap density is 2.1 g / cc (g / cm³) 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 54.0 mg / cm² on both sides. 2 The porosity was 23.8%.

[0101] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0102] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0103] Example 4 The tap density is 2.1 g / cc (g / cm 3 ), and the average particle size D 50 is 4.17 μm for Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 O2, carbon nanotubes, and a PVDF binder were mixed in a weight ratio of 95:2:3 in N-methylpyrrolidone to produce a positive electrode slurry. After applying the positive electrode slurry to both sides of an aluminum current collector sheet with a thickness of 15.0 μm, it was dried at 120°C and then rolled to produce a positive electrode. The loading amount of the produced positive electrode active material layer was 50.8 mg / cm 2 on a double-sided basis, and the porosity was 23.8%.

[0104] A negative electrode active material (a mixture of graphite:SiO with a weight ratio of 95:5), a conductive material (super C), styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) were mixed in a weight ratio of 98:0.1:1.4:0.9 in water to produce a negative electrode slurry. After applying the negative electrode slurry to both sides of a copper current collector sheet, it was dried at 150°C and then rolled to produce a negative electrode.

[0105] After a separator was interposed between the positive electrode and the negative electrode produced as described above and laminated in the order of separator / positive electrode / separator / negative electrode, it was wound up to produce a jelly roll type electrode assembly.

[0106] Example 5 The tap density is 2.1 g / cc (g / cm 3 ), and the average particle size D 50 is 4.17 μm for Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 46.8 mg / cm² on both sides. 2 The porosity was 23.8%.

[0107] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0108] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0109] Example 6 Tap density is 2.4 g / cc (g / cm³) 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 A positive electrode slurry was prepared by mixing O2, carbon nanotubes, and a 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 then rolled to produce a positive electrode. The loading amount of the produced positive electrode active material layer was 49.0 mg / cm² on both sides. 2 The porosity was 24.1%.

[0110] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0111] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0112] Example 7 Tap density is 2.3 g / cc (g / cm³). 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 50.0 mg / cm² on both sides. 2 The porosity was 23.8%.

[0113] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0114] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0115] Example 8 Tap density is 1.78 g / cc (g / cm³). 3 ), average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 50.8 mg / cm² on both sides. 2 The porosity was 23.1%.

[0116] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0117] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0118] Example 9 Tap density is 1.78 g / cc (g / cm³). 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 50.8 mg / cm² on both sides. 2 The porosity was 28.8%.

[0119] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0120] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0121] Comparative Example 1 Tap density is 1.65 g / cc (g / cm³). 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 50.8 mg / cm² on both sides. 2 The porosity was 23.8%.

[0122] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0123] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0124] Comparative Example 2 Tap density is 1.78 g / cc (g / cm³). 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 50.8 mg / cm² on both sides. 2 The porosity was 22.8%.

[0125] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0126] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0127] Comparative Example 3 Tap density is 1.77 g / cc (g / cm³). 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01 A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 50.8 mg / cm² on both sides. 2 The porosity was 21.9%.

[0128] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0129] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0130] Comparative Example 4 Tap density is 1.88 g / cc (g / cm³). 3 ) and average particle size D 50 Li[Ni 0.95 Co 0.03 Mn 0.01 Al 0.01A cathode slurry was prepared by mixing O2, carbon nanotubes, and a PVDF binder in a weight ratio of 95:2:3 in N-methylpyrrolidone. The cathode slurry was applied to both sides of a 15.0 μm thick aluminum current collector sheet, dried at 120°C, and then rolled to produce a cathode. The loading amount of the produced cathode active material layer was 58.0 mg / cm² on both sides. 2 The porosity was 22.7%.

[0131] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite:SiO=95:5 by weight ratio), a conductive material (super C), and styrene-butadiene rubber (SBR):carboxymethylcellulose (CMC) in water in 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 produce a negative electrode.

[0132] As described above, a separator was interposed between the positive electrode and the negative electrode, and the electrodes were stacked in the order of separator / positive electrode / separator / negative electrode. After stacking, the assembly was wound up to produce a jelly roll type electrode assembly.

[0133] Experimental example The electrode assemblies of Examples 1-9 and Comparative Examples 1-4 were disassembled to check whether cracks occurred during the winding of the positive electrode. The results are shown in Table 1 below.

[0134] [Table 1]

[0135] In Examples 1 to 9, the electrode assemblies containing the positive electrode according to the present invention, which satisfies the Y value of formula (1) of less than 7, did not develop cracks during winding. However, in Comparative Examples 1 to 4, the electrode assemblies containing the positive electrode with a Y value of 7 or more developed, it was confirmed that cracks developed 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 located on the positive electrode current collector, satisfying the following formula (1). Equation (1): Y = 10 × L / (P × T) ２ ) <7 In the above formula (1), L is the loading amount of the positive electrode (mg / cm³). ２ ) and P is the porosity (%) of the positive electrode. T is the tap density (g / cc) (g / cm³) of the positive electrode active material contained in the positive electrode active material layer. ３ )

2. The tap density of the positive electrode active material contained in the positive electrode active material layer is 1.8 g / cc (g / cm³). ３ )~2.5g / cc (g / cm ３ The positive electrode for a lithium secondary battery according to claim 1, which is the positive electrode described in claim 1.

3. The loading amount of the aforementioned positive electrode is 44 mg / cm². ２ ~56 mg / cm³ ２ The positive electrode for a lithium secondary battery according to claim 1.

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 contained 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 positive electrode active material is a lithium nickel-based oxide represented by the following [Chemical Formula 2], according to claim 5, for a lithium secondary battery. [Chemical formula 2] Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the above chemical formula 2, M １ M is Mn, Al, or a combination thereof. ２ is one or more elements selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and satisfies the following conditions: 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 consists 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 includes a positive electrode active material having a unimodal particle size distribution that shows a single peak in a volume cumulative particle size distribution graph.

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

10. The positive electrode for a lithium secondary battery according to claim 1, wherein the brittleness force of the positive electrode is 35 gf (0.343 N) or less.

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

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

13. The lithium secondary battery according to claim 12, wherein the electrode assembly is a jelly roll type 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. 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 the electrode assembly does not develop a crack in the positive electrode within three turns or less.

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