Positive electrode and lithium secondary battery containing the 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 located on the positive electrode current collector, wherein the positive electrode current collector includes a coated portion having a positive electrode active material layer formed on at least one surface thereof; and an uncoated portion on the positive electrode current collector where no positive electrode active material layer is formed, and the positive electrode current collector satisfies the following formula (1): [Mathematical formula 1] Formula (1): P≧[(a1 / a2)×b] / 0.05c In the formula (1), P is the rolling density (g / cc) of the positive electrode, and a1 is the D of the positive electrode active material particles contained in the positive electrode active material layer. 50 (μm), and a2 is the D of the positive electrode active material particles contained in the positive electrode active material layer. max (μm), b is the elongation rate (%) of the positive electrode current collector at 25° C., and c is the thickness (μm) of the positive electrode current collector.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0179921, filed on December 20, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode and a lithium secondary battery including the same. [Background technology]

[0003] With the advancement of technologies for electric vehicles, portable electronic devices, and the like, the demand for lithium secondary batteries as energy sources is rapidly increasing.

[0004] Lithium secondary batteries are classified into cylindrical, prismatic, and pouch-type batteries depending on the shape of the battery case. Among these, cylindrical batteries are constructed by housing an electrode assembly (made by sequentially stacking a sheet-shaped positive electrode, a separator, and a negative electrode and winding them in one direction) in a cylindrical battery can, and then sealing the battery can with a cap plate. The positive and negative electrodes are provided with strip-shaped positive and negative electrode tabs, respectively, which are connected to electrode terminals for electrical connection to an external power source. The positive electrode terminal is the cap plate, and the negative electrode terminal is the battery can. However, conventional cylindrical batteries with this structure suffer from problems such as high resistance, excessive heat generation, and poor current collection efficiency due to current concentration in the strip-shaped electrode tabs.

[0005] In this case, the problem of current concentration around the electrode tabs can be solved by applying a structure in which the uncoated portions of the positive and negative electrodes serve as electrode tabs (e.g., a tab-less structure) without forming separate electrode tabs.

[0006] However, electrodes having coated and uncoated portions have a problem in that electrode swelling occurs due to the difference in the amount of elongation between the coated and uncoated portions during the rolling process, resulting in a camber phenomenon in which the electrode bends toward the uncoated portion.

[0007] If the camber phenomenon becomes severe, the tip of the electrode bends when the electrode assembly is wound up, causing poor meandering, which results in the electrode assembly not being laminated in the correct position. If the electrode assembly is not laminated in the correct position, an internal short circuit may occur due to reasons such as the positive electrode uncoated portion contacting the negative electrode active material, the negative electrode uncoated portion contacting the positive electrode active material, or the positive electrode uncoated portion contacting the negative electrode uncoated portion.

[0008] In addition, the particle dimpling phenomenon that occurs in the positive electrode current collector varies depending on the size of the positive electrode active material particles contained in the positive electrode active material layer in the ground portion, which can cause the positive electrode current collector to break (the current collector is cut).

[0009] The problem of disconnection caused by the positive electrode active material is difficult to solve by simply adjusting the thickness and elongation rate of the current collector.

[0010] Therefore, there is a need for technology that can suppress the camber phenomenon and solve the problem of wire breakage that occurs during the manufacturing process, while also preventing wire breakage during charging and discharging. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention aims to solve both the problems of camber and disconnection in positive electrodes including coated and uncoated regions by adjusting the rolling density of the positive electrode, the particle size of the positive electrode active material, the thickness of the positive electrode current collector, and the elongation rate of the positive electrode current collector so that specific relationship formulas are satisfied. [Means for solving the problem]

[0012] 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, wherein the positive electrode current collector includes a coated portion having a positive electrode active material layer formed on at least one surface thereof; and an uncoated portion on the positive electrode current collector where no positive electrode active material layer is formed, and the positive electrode current collector satisfies the following formula (1):

[0013] [Mathematical formula 1] Formula (1): P≧[(a1 / a2)×b] / 0.05c

[0014] In the formula (1), P is the rolling density (g / cc) of the positive electrode, and a1 is the D of the positive electrode active material particles contained in the positive electrode active material layer. 50 (μm), and a2 is the D of the positive electrode active material particles contained in the positive electrode active material layer. max (μm), b is the elongation rate (%) of the positive electrode current collector at 25° C., and c is the thickness (μm) of the positive electrode current collector.

[0015] The present invention also provides a lithium secondary battery, including an electrode assembly 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; an electrolyte; and a battery can in which the electrode assembly and the electrolyte are housed. [Effects of the Invention]

[0016] In a positive electrode with a coated and uncoated portion, electrode swelling occurs during the rolling process due to the difference in elongation rate between the coated and uncoated portions. When a positive electrode with electrode swelling is stretched in a straight line to manufacture an electrode assembly, the positive electrode bends toward the uncoated portion, and the degree of bending increases at the end (tip) of the positive electrode, forming camber. If the camber phenomenon becomes severe, breakage may occur during the manufacturing process, and cracks may occur frequently during long-term operation, resulting in reduced lifespan characteristics.

[0017] Furthermore, the particle dimpling phenomenon occurring in the positive electrode current collector varies depending on the size of the positive electrode active material particles contained in the positive electrode active material layer of the ground portion, which can cause disconnection of the positive electrode current collector.

[0018] The present invention provides a positive electrode in which camber is suppressed by adjusting the rolling density of the positive electrode, the particle size of the positive electrode active material, the thickness of the positive electrode current collector, and the elongation rate of the positive electrode current collector to satisfy a specific relationship. Therefore, the positive electrode for a lithium secondary battery of the present invention has the advantage that camber is suppressed during the manufacturing process, so that the problem of disconnection does not occur, and the problem of disconnection does not occur during charge and discharge.

[0019] Furthermore, lithium secondary batteries containing the same have the advantage of being less susceptible to defects due to disconnection and having excellent durability. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described in more detail below.

[0021] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his or her invention.

[0022] In the present invention, the term "primary particle" refers to a particle unit that does not appear to have grain boundaries when observed under a scanning electron microscope at a magnification of 5,000 to 20,000 times. The term "average particle size of primary particles" refers to the arithmetic mean value calculated after measuring the particle sizes of primary particles observed from a scanning electron microscope image.

[0023] In the present invention, "secondary particles" are particles formed by agglomeration of multiple primary particles. In order to distinguish them from conventional secondary particles formed by agglomeration of tens to hundreds of primary particles, secondary particles formed by agglomeration of 10 or less primary particles are referred to as "similar particles."

[0024] In the present invention, "D 50" refers to the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder, and can be measured using a laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W. A volume cumulative particle size distribution graph is then obtained, and the particle size corresponding to 50% of the volume cumulative amount is then determined.

[0025] In the present invention, "D max " refers to the maximum particle size in the volume cumulative particle size distribution of the positive electrode active material powder, and can be measured using a laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W. A volume cumulative particle size distribution graph is then obtained, and the maximum particle size can be measured.

[0026] The positive electrode for a lithium secondary battery of the present invention includes a current collector and an electrode active material layer located on the current collector, the current collector including a coated portion having an electrode active material layer formed on at least one surface thereof, and an uncoated portion on the current collector where no electrode active material layer is formed, and is characterized in that the following formula (1) is satisfied:

[0027] [Mathematical formula 1] Formula (1): P≧[(a1 / a2)×b] / 0.05c

[0028] When the rolling density of the positive electrode, the particle size distribution of the particles contained in the active material layer, the thickness of the current collector, and the elongation ratio satisfy the relationship expressed by a specific formula (1), the current collector has specifications sufficient to eliminate the problem of wire breakage caused by the active material particles being driven into the current collector, thereby solving the problem of wire breakage after electrode manufacture. Therefore, the problem of wire breakage does not occur even after multiple charge / discharge cycles, and cracks in the active material during long-term operation can also be suppressed.

[0029] When the rolling density of the positive electrode satisfies the relationship of a specific formula (1) with the particle size distribution of the particles contained in the active material layer, the thickness of the current collector, and the elongation ratio, the camber phenomenon can be suppressed, thereby solving the problem of wire breakage that occurs during the manufacturing process.

[0030] Specifically, the wider the particle size distribution of the positive electrode active material, i.e., D max and D 50 The larger the difference between these two, the higher the packing density of the positive electrode active material layer. Therefore, while achieving the same rolling density of the electrode, physical damage to the positive electrode current collector is reduced, and the occurrence of cracks in the positive electrode during rolling can be reduced.

[0031] However, as the particle size distribution widens, the proportion of large-particle active material increases, increasing the likelihood of current collector breakage due to dimpling of active material particles. To address this issue, the thickness of the positive electrode current collector must be increased, but increasing the thickness of the current collector reduces the space occupied by the active material layer inside the battery can. This reduction in the active material layer results in a decrease in the energy density of the lithium secondary battery. In contrast, reducing the thickness of the positive electrode current collector requires a reduction in rolling density to prevent cracks from occurring in the positive electrode current collector. This reduces the absolute space inside the can, thereby reducing the final volume of the active material layer and potentially reducing the energy density of the lithium secondary battery.

[0032] On the other hand, as the elongation ratio of the positive electrode current collector increases, the difference in elongation level between the coated and uncoated regions increases, resulting in an increase in electrode swelling. If the elongation ratio of the positive electrode current collector is reduced to alleviate this problem, cracks may occur in the current collector due to volumetric expansion of the electrode during charge and discharge. This problem tends to become more severe when the particle size distribution is broadened or the proportion of active material with large particle sizes increases.

[0033] Therefore, the thickness and elongation ratio of the positive electrode current collector must be adjusted in consideration of the particle size distribution of the positive electrode active material and the rolling density of the positive electrode, and the inventors have found that the relationship between these variables must satisfy the above formula (1).

[0034] In the formula (1), P is the rolling density (g / cc) of the positive electrode. 3 ) = Positive electrode loading (g / cm 2 It can be calculated using the loading amount of the positive electrode and the thickness of the positive electrode active material layer, as in the formula: P / thickness (cm) of the positive electrode active material layer. The P may be 3.2 g / cc to 3.8 g / cc, preferably 3.3 g / cc to 3.6 g / cc, and most preferably 3.4 g / cc to 3.5 g / cc.

[0035] In the formula (1), a1 is the D of the positive electrode active material particles contained in the positive electrode active material layer. 50 (μm) The a1 may be 3.5 μm to 13.5 μm, preferably 3.6 μm to 13.0 μm, and most preferably 3.7 μm to 12.5 μm.

[0036] In the formula (1), a2 is the D of the positive electrode active material particles contained in the positive electrode active material layer. max (μm) The a2 may be 10 μm to 30 μm, preferably 10.5 μm to 28.0 μm, and most preferably 11 μm to 26 μm.

[0037] In the formula (1), b is the elongation ratio (%) of the positive electrode current collector at 25° C. The elongation ratio of the current collector can be measured using an Instron 5543 device at a standard speed of 20 mm / min.

[0038] The b may be 1.0% to 5.5%, preferably 1.3% to 5.0%, and most preferably 1.5% to 4.5%.

[0039] In the formula (1), c is the thickness (μm) of the positive electrode current collector, and may be 10 μm to 20 μm, preferably 11 μm to 18 μm, and most preferably 12 μm to 17 μm.

[0040] The positive electrode for a lithium secondary battery of the present invention includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector. The positive electrode current collector includes a coated portion having a positive electrode active material layer formed on at least one surface thereof, and an uncoated portion on the positive electrode current collector where no positive electrode active material layer is formed.

[0041] The positive electrode 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, and the positive electrode active material layer may include a positive electrode active material, a conductive material, and a binder.

[0042] Specifically, the positive electrode may be manufactured by coating one or both sides of a long sheet-shaped positive electrode current collector with a positive electrode slurry prepared by dispersing a positive electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and then drying the coated positive electrode current collector to remove the solvent. Alternatively, a positive electrode including a non-coated portion may be manufactured by not coating a portion of the positive electrode current collector, for example, one end of the positive electrode current collector, with the positive electrode slurry.

[0043] The positive electrode current collector may be any of various positive electrode current collectors used in the art. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Forming fine irregularities on the surface of the positive electrode current collector can also enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric. Most preferably, an aluminum thin film can be used in terms of adjusting the elongation ratio.

[0044] On the other hand, as the positive electrode active material, a positive electrode active material generally used in the technical field can be used.

[0045] Preferably, the positive electrode active material may contain a lithium nickel-based oxide, specifically, a lithium nickel-based oxide containing 80 mol% or more of Ni relative to the total number of moles of transition metals. Preferably, the lithium nickel-based oxide may contain 80 mol% or more but less than 100 mol%, 82 mol% or more but less than 100 mol%, or 83 mol% or more but less than 100 mol% of Ni. As described above, when a lithium nickel-based oxide with a high Ni content is used, a high capacity can be achieved.

[0046] More specifically, the positive electrode active material may contain a lithium nickel-based oxide represented by the following [Chemical Formula 2].

[0047] [Chemical formula 2] Li a Ni b Co c M 1 d M 2 e O2

[0048] In the above Chemical Formula 2, M 1It may be Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

[0049] Said M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. The M 2 element is not necessarily included, but when included in an appropriate amount, it plays a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0050] Said a represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 0.8 ≦ a ≦ 1.2, 0.85 ≦ a ≦ 1.15, or 0.9 ≦ a ≦ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide is stably formed.

[0051] Said b represents the molar ratio of nickel in all metals excluding lithium in the lithium nickel-based oxide, and may be 0.85 ≦ b < 1, 0.86 ≦ b < 1, or 0.88 ≦ b < 1. When the molar ratio of nickel satisfies the above range, it exhibits a high energy density and can achieve a high capacity.

[0052] Said c represents the molar ratio of cobalt in all metals excluding lithium in the lithium nickel-based oxide, and may be 0 < c < 0.15, 0 < c < 0.14, or 0.01 ≦ c ≦ 0.12. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be achieved.

[0053] Said d represents the molar ratio of the M 1 element in all metals excluding lithium in the lithium nickel-based oxide, and may be 0 < d < 0.15, 0 < d < 0.14, or 0.01 ≦ d ≦ 0.12. The M 1When the molar ratio of the elements satisfies the above range, the positive electrode active material has excellent structural stability.

[0054] The e is M in all metals other than lithium in the lithium nickel-based oxide. 2 It indicates the molar ratio of elements, and may be 0≦e≦0.1 or 0≦e≦0.05.

[0055] Meanwhile, 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-based oxide particles, the coating layer containing 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.

[0056] When a coating layer is present on the surface of the lithium nickel-based oxide particles, the coating layer suppresses contact between the electrolyte and the lithium composite transition metal oxide, thereby achieving the effect of reducing elution of the transition metal and generation of gas due to side reactions with the electrolyte.

[0057] The positive electrode active material may be contained in an amount of 80 to 99 wt %, preferably 85 to 99 wt %, and more preferably 90 to 99 wt %, based on the total weight of the positive electrode active material layer.

[0058] Meanwhile, the positive electrode active material according to the present invention may have a unimodal particle size distribution or a bimodal particle size distribution. By using a positive electrode active material having a unimodal distribution, an increase in resistance can be minimized. When a bimodal positive electrode active material is used, which is a mixture of a large particle size positive electrode active material having a large average particle size and a small particle size positive electrode active material having a small average particle size, the electrode density is improved.

[0059] The form of the positive electrode active material is not particularly limited, and may be in the form of secondary particles formed by aggregation of a plurality of primary particles, in the form of a single particle formed by one primary particle, or in the form of a combination thereof.

[0060] Preferably, the positive electrode active material may include a positive electrode active material consisting of a single particle formed from one primary particle and / or similar single particles that are an aggregate of 10 or less primary particles. By using a positive electrode active material consisting of a single particle formed from one primary particle and / or similar single particles that are an aggregate of 10 or less primary particles as the positive electrode active material, a large cylindrical battery that achieves high capacity and is excellent in safety can be obtained.

[0061] Conventionally, positive electrode active materials for lithium secondary batteries have typically been spherical secondary particles formed by agglomeration of tens to hundreds of primary particles. However, such positive electrode active materials in the form of secondary particles formed by agglomeration of many primary particles are prone to particle fracture, in which the primary particles separate during the rolling process during positive electrode production, leading to problems such as internal cracks during charge and discharge. Particle fracture or internal cracks in the positive electrode active material increase the contact area with the electrolyte, resulting in increased gas generation due to side reactions with the electrolyte. Increased gas generation within a cylindrical battery increases the internal pressure of the battery, potentially leading to a battery explosion. In particular, increasing the volume of a cylindrical battery increases the amount of active material within the battery, significantly increasing the amount of gas generation, further increasing the risk of battery fire and / or explosion.

[0062] In contrast, positive electrode active materials in the form of single particles consisting of one primary particle or similar single particles consisting of an aggregation of 10 or fewer primary particles have higher particle strength than conventional positive electrode active materials in the form of secondary particles in which tens to hundreds of primary particles are aggregated, and therefore hardly suffer particle breakage during rolling. Furthermore, in the case of positive electrode active materials in the form of single particles or similar single particles, because the number of primary particles constituting the particle is small, changes due to expansion and contraction of the volume of the primary particles during charge and discharge are small, and therefore the occurrence of cracks inside the particles is also significantly reduced.

[0063] Therefore, when a positive electrode active material consisting of single particles and / or similar single particles is used, the amount of gas generated due to particle destruction and internal cracking can be significantly reduced, thereby achieving excellent safety even in large cylindrical batteries.

[0064] On the other hand, the positive electrode active material consisting of the single particles and / or similar single particles is preferably contained in an amount of 95% by weight to 100% by weight, preferably 98% by weight to 100% by weight, more preferably 99% by weight to 100% by weight, and even more preferably 100% by weight, based on the total weight of the positive electrode active material contained in the positive electrode active material layer. When the content of the single particles and / or similar single particles satisfies the above range, sufficient safety can be obtained when applied to large cylindrical batteries.

[0065] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it does not undergo chemical changes in the resulting battery and has 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 fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may typically be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0066] The binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), 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, and various copolymers thereof. These binders may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0067] Meanwhile, an insulating layer may be further formed on the positive electrode according to the present invention, if necessary, to cover a portion of the positive electrode active material layer and a portion of the uncoated portion, and the insulating layer may be formed in a direction parallel to the winding direction of the electrode assembly.

[0068] The lithium secondary battery according to the present invention may include an electrode assembly in which the above-described positive electrode, negative electrode, and separator interposed between the positive electrode and negative electrode are wound in one direction; an electrolyte; and a battery can in which the electrode assembly and the electrolyte are housed.

[0069] Specifically, the positive electrode and the negative electrode have a structure in which an active material layer is formed on a long sheet-shaped current collector, and a part of the current collector may include a plain portion where no active material layer is formed.

[0070] By using positive and negative electrodes including uncoated portions as described above, it is possible to realize a battery with a tabless structure in which at least a part of the uncoated portions of the positive and negative electrodes defines the electrode tabs, without providing a separate electrode tab.

[0071] The negative electrode may have a structure in which a negative electrode active material layer is formed on one or both surfaces of a long sheet-like negative electrode current collector, and the negative electrode active material layer may contain a negative electrode active material, a conductive material, and a binder.

[0072] 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-like negative electrode current collector, removing the solvent of the negative electrode slurry by a drying process, and then rolling. On the other hand, when applying the negative electrode slurry, a negative electrode including a plain part can be manufactured by a method of not applying the negative electrode slurry to a part of the region of the negative electrode current collector, for example, one end of the negative electrode current collector.

[0073] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; silicon-based materials such as Si, 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), SiOy (where 0 < y < 2), and Si-C composite; lithium metal thin film; and metal materials capable of alloying with lithium such as Sn and Al. Among them, any one or a mixture of two or more of them may be used.

[0074] Preferably, the negative electrode according to the present invention may contain a silicon-based negative electrode active material. The silicon-based negative electrode active material may be Si, 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), SiOy (where 0 < y < 2), Si-C composite, or a combination thereof, and preferably, it may be SiOy (where 0 < y < 2). Since the silicon-based negative electrode active material has a high theoretical capacity, when the silicon-based negative electrode active material is included, the capacity characteristics can be improved.

[0075] On the other hand, the silicon-based negative electrode active material may be doped with M b metal, where the M b metal may be a Group 1 metal element or a Group 2 metal element, and specifically, it may be Li, Mg, etc. Specifically, the silicon negative electrode active material may be Si, SiOy (where 0 < y < 2), Si-C composite, etc. doped with M b metal. In the case of a metal-doped silicon-based negative electrode active material, although the capacity of the active material slightly decreases due to the doping element, since it has high efficiency, a high energy density can be realized.

[0076] Further, the silicon-based negative electrode active material may further include a carbon coating layer on the surface of the particles. Here, the amount of the carbon coating may be 20% by weight or less, preferably 1 to 20% by weight, based on the total weight of the silicon-based negative electrode active material.

[0077] Further, the negative electrode may further include a carbon-based negative electrode active material as a negative electrode active material, if necessary. The carbon-based negative electrode active material may be, for example, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc., but is not limited thereto.

[0078] On the other hand, when a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material is used as the negative electrode active material, the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material may be 1:99 to 20:80, preferably 1:99 to 15:85, and more preferably 1:99 to 10:90, by weight.

[0079] The negative electrode active material may be contained in an amount of 80 to 99 wt %, preferably 85 to 99 wt %, and more preferably 90 to 99 wt %, based on the total weight of the negative electrode active material layer.

[0080] The negative electrode current collector may be a negative electrode current collector commonly used in the art, such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector may typically have a thickness of 3 to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be provided with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0081] The conductive material is used to impart conductivity to the negative electrode. Any conductive material can be used without particular limitations, as long as it does not undergo chemical changes in the resulting battery and has 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 fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may typically be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0082] The binder functions to improve adhesion between negative electrode active material particles and 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, 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, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0083] The separator separates the negative electrode and the positive electrode to provide a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used. Specifically, the separator may be a porous polymer film, such as a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate 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, may be used. Furthermore, a separator coated with a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength.

[0084] Meanwhile, the uncoated portions of the positive and negative electrodes may be processed into the form of a plurality of segmented pieces that can be bent independently, and at least some of the segmented pieces may be bent toward the winding center of the electrode assembly.

[0085] The segment pieces may be formed by processing the positive and negative electrode current collectors through a metal foil cutting process such as laser notching, ultrasonic cutting, or punching.

[0086] When the uncoated portions of the positive and negative electrodes are processed into the form of multiple segments, the stress applied to the uncoated portions during bending can be reduced, preventing deformation or damage to the uncoated portions and improving the welding characteristics with the current collecting plate.

[0087] The current collecting plate and the plain portion are typically joined by welding. To improve the welding characteristics, strong pressure must be applied to the welded area of ​​the plain portion to bend it as flat as possible. However, during this bending process, the shape of the plain portion may become irregularly distorted and deformed, and the deformed portion may come into contact with the electrode of the opposite polarity, causing an internal short circuit or inducing microcracks in the plain portion. However, if the plain portions of the positive and negative electrodes are processed into multiple segments that can be bent independently, stress applied to the plain portion during bending can be alleviated, minimizing deformation and damage to the plain portion.

[0088] Furthermore, when the uncoated portion is processed into segmented pieces as described above, the segmented pieces overlap each other during folding, thereby increasing the welding strength with the current collecting plate, and when using cutting-edge technology such as laser welding, this can prevent the laser from penetrating into the electrode assembly and ablating the separator or active material. It is preferable that at least a portion of the folded segmented pieces overlap on the upper and lower ends of the electrode assembly, and that the current collecting plate be bonded to the overlapped segmented pieces.

[0089] The lithium secondary battery according to the present invention may be a cylindrical lithium secondary battery. The cylindrical lithium secondary battery may be a large cylindrical battery having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of a cylindrical battery divided by the diameter of the cylindrical battery) of 0.4 or more. Here, the form factor refers to values ​​indicating the diameter and height of a cylindrical battery.

[0090] Cylindrical batteries according to the present invention may have, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 4875 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), a 4680 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575), or a 4695 cell (diameter 46 mm, height 95 mm, form factor ratio 0.484). In the form factor numbers, the first two digits indicate the cell diameter, and the next two or three digits indicate the cell height.

[0091] The cylindrical lithium secondary battery of the present invention significantly reduces the amount of gas generated compared to conventional batteries, thereby achieving excellent safety even in large cylindrical batteries with a form factor ratio of 0.4 or more.

[0092] Meanwhile, the cylindrical battery according to the present invention is a battery with a tabless structure that does not include an electrode tab. The cylindrical lithium secondary battery according to the present invention may have a structure in which at least a portion of the uncoated area of ​​the positive electrode defines an electrode tab, i.e., a tabless structure. The cylindrical lithium secondary battery according to the present invention may also have a structure in which at least a portion of the uncoated area of ​​the negative electrode defines an electrode tab, i.e., a tabless structure. Specifically, the uncoated area may be formed elongated along the winding direction at an end of one side of the current collector, and a current collecting plate may be bonded to each of the positive electrode uncoated area and the negative electrode uncoated area, and the current collecting plate may be connected to an electrode terminal, thereby realizing a tabless battery.

[0093] For example, a tabless battery can be manufactured using the following method. First, a separator, a positive electrode, a separator, and a negative electrode are sequentially stacked so that the uncoated portions of the positive and negative electrodes face each other, and then the stack is wound in one direction to form a jelly-roll electrode assembly. The uncoated portions of the positive and negative electrodes are then folded toward the center of the winding. Current collecting plates are then welded to the uncoated portions of the positive and negative electrodes, respectively, and the current collecting plates are connected to electrode terminals to form a tabless battery. Meanwhile, the current collecting plates have a larger cross-sectional area than strip-type electrode tabs, and their resistance is inversely proportional to the cross-sectional area of ​​the path through which current flows. Therefore, when a secondary battery is constructed in this manner, cell resistance can be significantly reduced. Furthermore, when a cylindrical lithium secondary battery is constructed in this manner, current concentration is reduced compared to conventional batteries with electrode tabs, which effectively reduces heat generation within the battery, thereby improving the thermal stability of the battery.

[0094] The battery can is electrically connected to the uncoated portion of the negative electrode and functions as a negative electrode terminal that contacts an external power source and transmits current applied from the external power source to the negative electrode.

[0095] The electrolyte used in the cylindrical lithium secondary battery of the present invention may contain a lithium salt, an organic solvent, and an additive.

[0096] The lithium salt is used as an electrolyte salt in a lithium secondary battery and is used as a medium for transferring ions. Generally, the lithium salt contains, for example, Li as a cation. + and the anion is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 -, AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - At least one selected from the group consisting of:

[0097] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10, LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI), or a mixture of two or more selected from the group consisting of: LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries can be used without limitation.

[0098] In order to achieve optimal electrolyte impregnation for large-capacity cylindrical lithium secondary batteries, the lithium salt may be contained in the electrolyte at a concentration of 1.0 M to 1.5 M, preferably 1.1 M to 1.3 M. When the concentration of the lithium salt satisfies the above range, the cycle characteristics of the lithium secondary battery are sufficiently improved during high-temperature storage, and the viscosity of the nonaqueous electrolyte is appropriate, thereby improving electrolyte impregnation.

[0099] The organic solvent may include at least one organic solvent selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0100] Specifically, the organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixed organic solvent thereof.

[0101] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and therefore easily dissociates the lithium salt in the electrolyte. Specific examples of the cyclic carbonate organic solvent include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among these, ethylene carbonate may be included.

[0102] The cyclic carbonate, for example, ethylene carbonate, may be contained in an amount of 15 to 30% by volume, preferably 15 to 25% by volume, and most preferably 15 to 20% by volume, based on the total volume of the organic solvent. When the amount of ethylene carbonate is within the above range, an electrolyte optimized in terms of viscosity and performance can be provided.

[0103] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and a representative example thereof may be at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate. Specifically, the linear carbonate organic solvent may include ethyl methyl carbonate (EMC).

[0104] The linear carbonate, for example, ethyl methyl carbonate, may be contained in an amount of 15 to 30% by volume, preferably 15 to 25% by volume, and most preferably 15 to 20% by volume, based on the total volume of the organic solvent. When the amount of ethyl methyl carbonate is in the above range, an electrolyte optimized in terms of viscosity and performance can be provided.

[0105] The organic solvent contained in the electrolyte of the present invention preferably contains ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and the content of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is preferably 25% by volume or less relative to the total volume of the organic solvent, which provides an appropriate level of electrolyte impregnation and provides optimal performance when the range of the infusion fraction of the present invention is applied.

[0106] In addition, in order to produce an electrolyte having high ionic conductivity, the organic solvent may further include at least one ester organic solvent selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents in addition to at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents.

[0107] Specific examples of such linear ester-based organic solvents include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0108] The cyclic ester organic solvent may be at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0109] Meanwhile, the organic solvent may further include any organic solvent commonly used in non-aqueous electrolytes, as needed, without limitation, for example, at least one of an ether-based organic solvent, a glyme-based organic solvent, and a nitrile-based organic solvent.

[0110] The ether solvent may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more thereof, but is not limited thereto.

[0111] The glyme-based solvent has a higher dielectric constant and lower surface tension than linear carbonate-based organic solvents and is less reactive with metals, and may include, but is not limited to, at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME).

[0112] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0113] In addition, the non-aqueous electrolyte of the present invention may contain an electrolyte additive to prevent the breakdown of the negative electrode due to decomposition of the non-aqueous electrolyte in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0114] Representative examples of such electrolyte additives may include at least one additive for forming an SEI film selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

[0115] Examples of the cyclic carbonate compounds include vinylene carbonate (VC) and vinylethylene carbonate.

[0116] The halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0117] The sultone compound includes at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0118] Examples of the sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0119] The phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalate)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(2,2,2-trifluoroethyl)phosphite.

[0120] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0121] Examples of the nitrile compound include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0122] The benzene-based compound includes fluorobenzene, the amine-based compound includes triethanolamine and ethylenediamine, and the silane-based compound includes tetravinylsilane.

[0123] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include lithium difluorophosphate (LiDFP), LiPO2F2, and LiBF4.

[0124] On the other hand, the other electrolyte additives may be used in combination of two or more kinds, and may be contained in an amount of 0.01 to 30 wt %, specifically 0.1 to 25 wt %, and preferably 1 to 20 wt %, based on the total weight of the non-aqueous electrolyte. When the content of the other electrolyte additives satisfies the above range, the effects of improving ionic conductivity and cycle characteristics are even more excellent.

[0125] The present invention will be described in more detail below with reference to specific examples.

[0126] [Example] Example 1 D 50is 8.3 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 A positive electrode slurry was prepared by mixing 02, carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 15.0 μm thick aluminum current collector sheet with an elongation of 2.3% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.41 g / cc.

[0127] Anode active material (a mixture of graphite and SiO2 in a weight ratio of 95:5), conductive material (Super C), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 96:2:1.5:0.5 to prepare anode slurry. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to prepare anodes.

[0128] A separator was interposed between the cathode and anode prepared as described above, and the layers were stacked in the order of separator / cathode / separator / anode, and then wound up to prepare a jelly roll-type electrode assembly. The electrode assembly prepared as described above was inserted into a cylindrical battery can, and then an electrolyte was injected to prepare a 4680 cell.

[0129] Example 2 D 50 is 4.3 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01A positive electrode slurry was prepared by mixing 02, carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 10.0 μm thick aluminum current collector sheet with an elongation of 3.4% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.63 g / cc.

[0130] A 4680 cell was produced in the same manner as in Example 1, except that the above positive electrode was used.

[0131] Example 3 D 50 is 12.4 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 A positive electrode slurry was prepared by mixing 02, carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 12.0 μm thick aluminum current collector sheet with an elongation of 4.1% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.28 g / cc.

[0132] A 4680 cell was produced in the same manner as in Example 1, except that the above positive electrode was used.

[0133] Example 4 D 50 is 5.5 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01A positive electrode slurry was prepared by mixing 02, carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 15.0 μm-thick aluminum current collector sheet with an elongation of 4.6% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.59 g / cc.

[0134] A 4680 cell was produced in the same manner as in Example 1, except that the above positive electrode was used.

[0135] Example 5 D 50 is 9.1 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 A positive electrode slurry was prepared by mixing 02, carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 12.0 μm thick aluminum current collector sheet with an elongation of 4.7% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.38 g / cc.

[0136] A 4680 cell was produced in the same manner as in Example 1, except that the above positive electrode was used.

[0137] Comparative Example 1 D 50 is 8.4 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01A positive electrode slurry was prepared by mixing 02, carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 10.0 μm thick aluminum current collector sheet with an elongation of 4.5% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.58 g / cc.

[0138] A 4680 cell was produced in the same manner as in Example 1, except that the above positive electrode was used.

[0139] Comparative Example 2 D 50 is 4.5 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 A positive electrode slurry was prepared by mixing 02, carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 12.0 μm thick aluminum current collector sheet with an elongation of 5.5% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.63 g / cc.

[0140] A 4680 cell was produced in the same manner as in Example 1, except that the above positive electrode was used.

[0141] Comparative Example 3 D 50 is 12.9 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01A positive electrode slurry was prepared by mixing O2, carbon nanotubes, and PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 12.0 μm thick aluminum current collector sheet with an elongation of 3.8% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.48 g / cc.

[0142] A 4680 cell was produced in the same manner as in Example 1, except that the above positive electrode was used.

[0143] Comparative Example 4 D 50 is 10.4 μm, and D max The positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 A positive electrode slurry was prepared by mixing 02, carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of a 10.0 μm-thick aluminum current collector sheet with an elongation of 3.6% at 25°C, dried at 120°C, and rolled to prepare a positive electrode. The rolled density P of the prepared positive electrode was 3.53 g / cc.

[0144] A 4680 cell was produced in the same manner as in Example 1, except that the above positive electrode was used.

[0145] Experimental Example 1 The 4680 cells of Examples 1 to 5 and Comparative Examples 1 to 4 were checked for the occurrence of wire breakage during the cell assembly process.

[0146] [Table 1]

[0147] Experimental Example 2 The 4680 cells of Examples 1 to 5 and Comparative Examples 1 to 4 were checked for the occurrence of disconnection during charging and discharging.

[0148] Specifically, each of the 4680 cells of Examples 1 to 5 and Comparative Examples 1 to 4 was charged to 4.25 V at 25° C. with a constant current and voltage of 1 C and discharged to 2.5 V with a constant current of 1 C, and then subjected to 300 charge-discharge cycles, after which the occurrence of disconnection was confirmed. The results are shown in Table 2 below.

[0149] [Table 2]

[0150] As shown in Tables 1 and 2, the 4680 cells of Examples 1 to 5, in which the rolling density P was greater than or equal to the value of [(a1 / a2) × b] / 0.05c, did not experience disconnections during the assembly process or during charge / discharge, whereas the 4680 cells of Comparative Examples 1 to 4, in which the rolling density P was less than the value of [(a1 / a2) × b] / 0.05c, experienced disconnections during the assembly process or during charge / discharge.

Claims

1. a positive electrode current collector; and a positive electrode active material layer located on the positive electrode current collector, the positive electrode current collector includes a coated portion having the positive electrode active material layer formed on at least one surface thereof, and an uncoated portion on the positive electrode current collector where the positive electrode active material layer is not formed, A positive electrode for a lithium secondary battery, which satisfies the following formula (1): [Mathematical formula 1] Formula (1): P≧[(a1 / a2)×b] / 0.05c In the formula (1), P is the rolling density of the positive electrode (g / cc), a1 is the D of the positive electrode active material particles contained in the positive electrode active material layer ５０ (μm), a2 is the D of the positive electrode active material particles contained in the positive electrode active material layer ｍａｘ (μm), b is the elongation rate (%) of the positive electrode current collector at 25°C, c is the thickness (μm) of the positive electrode current collector.

2. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the P is 3.2 g / cc or more and 3.8 g / cc or less.

3. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein a1 is 3.5 μm or more and 13.5 μm or less.

4. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein a2 is 10 μm or more and 30 μm or less.

5. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein c is 10 μm or more and 20 μm or less.

6. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein b is 1.0% or more and 5.5% or less.

7. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the positive electrode current collector is an aluminum thin film.

8. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the positive electrode active material is a lithium nickel-based oxide represented by the following [Chemical Formula 2]: [Chemical formula 2] Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the above formula 2, M １ is Mn, Al, or a combination thereof, and M ２ is one or more elements selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and 0.8≦a≦1.2, 0.8≦b<1, 0<c<0.2, 0<d<0.2, 0≦e≦0.

1.

9. 10. The cathode of claim 1, wherein the cathode active material has a bimodal particle size distribution.

10. 10. The cathode of claim 1, wherein the cathode active material has a unimodal particle size distribution.

11. A lithium secondary battery comprising: an electrode assembly in which the positive electrode for a lithium secondary battery according to any one of claims 1 to 10, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are wound in one direction; an electrolyte; and a battery can in which the electrode assembly and the electrolyte are housed.

12. The lithium secondary battery according to claim 11, wherein the lithium secondary battery is cylindrical.

13. The lithium secondary battery according to claim 12 , wherein the cylindrical lithium secondary battery has a form factor ratio of 0.4 or more.

14. The lithium secondary battery according to claim 11 , wherein at least a portion of the uncoated portion of the positive electrode has a structure that defines an electrode tab.

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