Positive electrode and lithium secondary battery comprising 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 on the positive electrode current collector, in which the positive electrode current collector includes a coated portion in which the positive electrode active material layer is formed on at least one surface thereof and an uncoated portion in which the positive electrode active material layer is not formed on the positive electrode current collector, and satisfies the following mathematical formula (1): P > = [(a1 / a2) * b] / 0.05 c, p is the rolling density (g / cc) of the positive electrode, a1 is D50 ([mu] m) of positive electrode active material particles contained in the positive electrode active material layer, a2 is Dmax ([mu] m) of positive electrode active material particles contained in the positive electrode active material layer, b is the elongation (%) of the positive electrode current collector at 25 DEG C, and c is the thickness ([mu] m) of the positive electrode current collector.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10 - 2022 - 0179921, filed on December 20, 2022, the disclosure of which is incorporated herein by reference in its entirety. Technical field

[0003] The present invention relates to a positive electrode and a lithium secondary battery including the positive electrode. Background art

[0004] With the development of technologies such as electric vehicles and portable electronic devices, the demand for lithium secondary batteries as an energy source has increased rapidly.

[0005] Lithium secondary batteries can be classified into cylindrical, prismatic, and pouch - type batteries according to the battery case type. Among them, a cylindrical battery has a form in which an electrode assembly is accommodated in a cylindrical battery can, and then the top of the battery can is covered with a cover plate for sealing. The electrode assembly is formed by sequentially stacking a sheet - shaped positive electrode, a separator, and a negative electrode, and then winding them in one direction. The positive electrode and the negative electrode are respectively provided with a strip - shaped positive electrode tab and a negative electrode tab, and the positive electrode tab and the negative electrode tab are connected to electrode terminals to be electrically connected to an external power source. For reference, the positive electrode terminal is the cover plate, and the negative electrode terminal is the battery can. However, in the case of a conventional cylindrical battery having such a structure, there is a problem that current is concentrated on the strip - shaped electrode tab, resulting in a large resistance, a lot of heat generation, and poor current collection efficiency.

[0006] In this case, by adopting a structure that does not form a separate electrode tab and uses the uncoated portions of the positive electrode and the negative electrode as electrode tabs (for example, a tab - less structure), the problem of current concentration around the electrode tab can be solved.

[0007] However, in the case of an electrode having a coated portion and an uncoated portion, there are the following problems: during the calendering process, due to the different elongation rates of the coated portion and the uncoated portion, the electrode expands, resulting in a warping phenomenon in which the electrode bends toward the uncoated portion.

[0008] If the warping phenomenon becomes serious, when winding the electrode assembly, the tip of the electrode bends, generating a snake - like defect, which causes the electrode assembly to not be laminated at the correct position. If the electrode assembly is not laminated at the correct position, internal short - circuits may occur because the uncoated portion of the positive electrode contacts the active material of the negative electrode, the uncoated portion of the negative electrode contacts the active material of the positive electrode, and the uncoated portion of the positive electrode contacts the uncoated portion of the negative electrode.

[0009] In addition, depending on the size of the positive electrode active material particles contained in the positive electrode active material layer of the coating portion, particle depression phenomena occur differently in the positive electrode current collector, resulting in the problem of open circuit (current collector damage phenomenon) in the positive electrode current collector.

[0010] It is difficult to solve the open circuit problem caused by the positive electrode active material simply by adjusting the thickness and elongation rate of the current collector.

[0011] Therefore, a technique is needed to suppress the warping phenomenon to solve the open circuit that occurs during the manufacturing process and prevent the occurrence of open circuit even during the charge and discharge process. Summary of the Invention

[0012] Technical Problem

[0013] The present invention is to solve the two problems of warping phenomenon and open circuit phenomenon in the positive electrode including the coating portion and the uncoated portion, and seeks to solve the above problems by adjusting the calendering 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.

[0014] Technical Solution

[0015] The present invention provides a positive electrode for a lithium secondary battery, which includes: 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 coating portion having a positive electrode active material layer formed on at least one surface thereof and an uncoated portion on which no positive electrode active material layer is formed, and satisfies the following mathematical formula (1):

[0016] Mathematical formula (1): P≥[(a1 / a2)×b] / 0.05c

[0017] Wherein, P is the calendering density (g / cc) of the positive electrode, a1 is the D 50 (μm) of the positive electrode active material particles contained in the positive electrode active material layer, a2 is the D max (μm) of the positive electrode active material particles contained in the positive electrode active material layer, 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.

[0018] In addition, the present invention provides a lithium secondary battery, which includes: an electrode assembly in which a positive electrode for a lithium secondary battery, a negative electrode, and a separator inserted between the positive electrode and the negative electrode are wound in one direction; an electrolyte; and a battery can for accommodating the electrode assembly and the electrolyte.

[0019] Advantageous Effects

[0020] In a positive electrode having a coated portion and an uncoated portion, during the calendering process, due to the different elongation rates of the coated portion and the uncoated portion, electrode swelling occurs. When the positive electrode with electrode swelling is straightened for manufacturing an electrode assembly, the positive electrode bends toward the uncoated portion, and the degree of bending increases at the positive electrode end (tip) to form warping. If the warping phenomenon becomes severe, an open circuit may occur during the manufacturing process, and cracking may increase during long-term driving, thereby deteriorating the life characteristics.

[0021] In addition, depending on the size of the positive electrode active material particles contained in the positive electrode active material layer of the coated portion, particle depression phenomena differently occur in the positive electrode current collector, leading to an open circuit in the positive electrode current collector.

[0022] The present invention can provide a positive electrode with suppressed warping phenomenon by adjusting the calendering 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 effect of suppressing the warping phenomenon, and thus does not cause an open circuit problem during the manufacturing process and even during the charge and discharge process.

[0023] In addition, the lithium secondary battery containing the positive electrode has fewer defects caused by an open circuit and has excellent durability. Detailed Description

[0024] Hereinafter, the present invention will be described in more detail.

[0025] The terms or words used in the present application specification and claims should not be construed as limited to their conventional meanings or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical spirit of the present invention based on the principle that the inventor can appropriately define the terms to best explain his invention.

[0026] In the present specification, a "primary particle" refers to a particle unit that does not have grain boundaries in appearance when observed with a scanning electron microscope at a magnification of 5,000 to 20,000 times. The "average particle size of primary particles" refers to the arithmetic average calculated by measuring the particle size of the primary particles observed in the scanning electron microscope image.

[0027] In the present invention, a "secondary particle" refers to a particle formed by the aggregation of multiple primary particles. In the present invention, a secondary particle formed by the aggregation of 10 or fewer primary particles is called a quasi-single particle to distinguish it from the conventional secondary particles formed by the aggregation of dozens to hundreds of primary particles.

[0028] 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, which can be measured by the laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves at a frequency of about 28 kHz and an output power of 60 W. Thereafter, the measurement can be performed by obtaining a volume cumulative particle size distribution diagram and then obtaining the particle size corresponding to 50% of the volume cumulative amount.

[0029] 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, which can be measured by the laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves at a frequency of about 28 kHz and an output power of 60 W. Thereafter, the measurement can be performed by obtaining a volume cumulative particle size distribution diagram and then obtaining the maximum particle size.

[0030] 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, wherein the current collector includes a coated portion having an electrode active material layer formed on at least one surface thereof and an uncoated portion where no electrode active material layer is formed on the current collector, and satisfies the following mathematical formula (1):

[0031] Mathematical formula (1): P≥[(a1 / a2)×b] / 0.05c

[0032] When the calendering density of the positive electrode, the particle size distribution of the particles contained in the active material layer, and the thickness and elongation rate of the current collector satisfy the relationship of a specific mathematical formula (1), the current collector can have a specification sufficient to solve the open circuit problem caused by the active material particles getting stuck in the current collector, thereby solving the open circuit problem after electrode manufacturing. Therefore, the open circuit problem does not occur even after multiple charge and discharge operations, and the cracking of the active material can be suppressed during long-term driving.

[0033] When the calendering density of the positive electrode, the particle size distribution of the particles contained in the active material layer, and the thickness and elongation rate of the current collector satisfy the relationship of a specific mathematical formula (1), the warping phenomenon can be suppressed, thereby solving the open circuit problem occurring during the manufacturing process.

[0034] Specifically, the wider the particle size distribution of the positive electrode active material, i.e., the difference between D max and D 50 is larger, the higher the packing density of the positive electrode active material layer. Thus, when achieving the same electrode calendering density, the physical damage to the positive electrode current collector can be reduced, thereby reducing the occurrence of cracking of the positive electrode during the calendering process.

[0035] However, when the particle size distribution becomes wider, the proportion of the active material with a large particle size increases. As a result, due to the particle depression phenomenon of the active material, the open circuit of the current collector may increase. To improve this problem, it is necessary to increase the thickness of the positive current collector. However, when the thickness of the current collector increases, the space occupied by the active material layer inside the battery can decreases. When the active material layer decreases, there is a problem that the energy density of the lithium secondary battery decreases. On the contrary, when the thickness of the positive current collector decreases, it is necessary to reduce the calendering density to prevent cracking in the positive current collector. Therefore, as the absolute space inside the can decreases, the volume of the active material layer ultimately decreases, thereby reducing the energy density of the lithium secondary battery.

[0036] On the other hand, as the elongation rate of the positive current collector increases, the difference in the elongation level between the coated portion and the uncoated portion also increases, resulting in a problem of increased electrode swelling. If the elongation rate of the positive current collector is reduced to improve this problem, there is a problem of cracking in the current collector due to the volume expansion of the electrode that occurs during the charge and discharge process. This problem tends to be exacerbated when the particle size distribution becomes wider and when the proportion of the active material with a large particle size increases.

[0037] Therefore, the thickness and elongation rate of the positive current collector should be adjusted considering the particle size distribution of the positive active material and the calendering density of the positive electrode. The present inventors have found that the relationship between these variables should satisfy the mathematical formula (1).

[0038] In the above mathematical formula (1), P is the calendering density (g / cc) of the positive electrode. The calendering density of the positive electrode can be calculated using the loading amount of the positive electrode and the thickness of the positive active material layer as shown in the following mathematical formula: Calendering density (g / cm 3 ) = Loading amount of positive electrode (g / cm 2 ) / Thickness of positive active material layer (cm). P can 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.

[0039] In the above mathematical formula (1), a1 is the D 50 (μm) of the positive active material particles contained in the positive active material layer. a1 can 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.

[0040] In the above mathematical formula (1), a2 is the D max (μm) of the positive active material particles contained in the positive active material layer. a2 can be 10 μm to 30 μm, preferably 10.5 μm to 28.0 μm, and most preferably 11 μm to 26 μm.

[0041] In the above mathematical formula (1), b is the elongation rate (%) of the positive current collector at 25°C. The elongation rate of the current collector can be measured using an Instron 5543 device at a speed of 20 mm / min.

[0042] b can be 1.0% to 5.5%, preferably 1.3% to 5.0%, and most preferably 1.5% to 4.5%.

[0043] In the above mathematical formula (1), c is the thickness (μm) of the positive current collector. c can be 10 μm to 20 μm, preferably 11 μm to 18 μm, and most preferably 12 μm to 17 μm.

[0044] The positive electrode for a lithium secondary battery of the present invention includes: a positive current collector; and a positive electrode active material layer located on the positive current collector, wherein the positive current collector includes a coated portion having a positive electrode active material layer formed on at least one of its surfaces and an uncoated portion where no positive electrode active material layer is formed on the positive current collector.

[0045] The positive electrode can have a structure in which a positive electrode active material layer is formed on one or both surfaces of a long sheet-shaped positive current collector, wherein the positive electrode active material layer can include a positive electrode active material, a conductive material, and a binder.

[0046] Specifically, the positive electrode can be prepared by coating a positive electrode slurry on one or both surfaces of a long sheet-shaped positive current collector, removing the solvent of the positive electrode slurry through a drying process, and then calendering it, wherein the positive electrode slurry 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, water, etc. At the same time, a positive electrode including an uncoated portion can be prepared by not coating the positive electrode slurry on a partial area (for example, one end of the positive current collector) of the positive current collector when coating the positive electrode slurry.

[0047] As the positive current collector, various positive current collectors used in the art can be used. For example, the positive current collector can be stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel treated with carbon, nickel, titanium, silver, etc. on its surface. The positive current collector can have fine irregularities formed on its surface to improve the adhesion of the positive electrode active material. For example, the positive current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric, etc. Most preferably, an aluminum thin film can be used in terms of controlling the elongation rate, etc.

[0048] At the same time, as the positive electrode active material, any positive electrode active material commonly used in the art can be used.

[0049] Preferably, the positive electrode active material may include lithium nickel-based oxides. Specifically, it may include lithium nickel-based oxides containing 80 mol% or more of Ni based on the total number of moles of transition metals. Preferably, the content of Ni in the lithium nickel-based oxide may be 80 mol% or more and less than 100 mol%, or 82 mol% or more and less than 100 mol%, or 83 mol% or more and less than 100 mol%. When using the lithium nickel-based oxide with a high Ni content as described above, high capacity can be achieved.

[0050] More specifically, the positive electrode active material may include a lithium nickel-based oxide represented by Chemical Formula 2 below:

[0051] [Chemical Formula 2]

[0052] Li a Ni b Co c M 1 d M 2 e O 2

[0053] In Chemical Formula 2, M 1 may be Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

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

[0055] a represents the molar ratio of lithium in the lithium nickel-based oxide and may be 0.8 ≤ a ≤ 1.2, 0.85 ≤ a ≤ 1.15, or 0.9 ≤ a ≤ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be formed stably.

[0056] b represents the molar ratio of Ni among all metals other than 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 Ni satisfies the above range, high energy density can be exhibited, thereby achieving high capacity.

[0057] c represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based oxide, and can 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.

[0058] d represents M in all metals other than lithium in the lithium nickel-based oxide 1 The molar ratio of the element, and can be 0 < d < 0.15, 0 < d < 0.14, or 0.01 ≤ d ≤ 0.12. When the molar ratio of M 1 The element satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0059] e represents M in all metals other than lithium in the lithium nickel-based oxide 2 The molar ratio of the element, and can be 0 ≤ e ≤ 0.1, or 0 ≤ e ≤ 0.05.

[0060] Meanwhile, if necessary, the positive electrode active material of the present invention may further include a coating 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 on the surface of the lithium nickel-based oxide particles. Preferably, the coating element can be Al, B, Co, or a combination thereof, and most preferably B.

[0061] When a coating exists on the surface of the lithium nickel-based oxide particles, the contact between the electrolyte and the lithium composite transition metal oxide can be inhibited through the coating, thereby having the effect of reducing the transition metal dissolution or gas generation caused by the side reaction with the electrolyte.

[0062] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80 to 99% by weight, preferably 85 to 99% by weight, and more preferably 90 to 99% by weight.

[0063] Meanwhile, the positive electrode active material of the present invention can have a unimodal particle size distribution or a bimodal particle size distribution. By using the positive electrode active material with a unimodal distribution, the increase in resistance can be minimized. If a bimodal positive electrode active material is used by mixing large particle size positive electrode active materials with a large average particle size and small particle size positive electrode active materials with a small average particle size, the electrode density can be improved.

[0064] The positive electrode active material has no particular limitation in terms of its form, and can be in the form of secondary particles aggregated by a plurality of primary particles, a single particle form formed by one primary particle, or a combined form thereof.

[0065] Preferably, the positive electrode active material may include a single particle formed of one primary particle and / or a positive electrode active material composed of quasi-single particles that are aggregates of 10 or fewer primary particles. By using a positive electrode active material composed of a single particle formed of one primary particle and / or quasi-single particles that are aggregates of 10 or fewer primary particles as the positive electrode active material, a large cylindrical battery having excellent safety while achieving high capacity can be obtained.

[0066] Conventionally, as a positive electrode active material for a lithium secondary battery, spherical secondary particles formed by aggregating dozens to hundreds of primary particles have generally been used. However, in the case of a positive electrode active material in the form of secondary particles formed by aggregating a large number of primary particles, there are problems such as particle breakage where primary particles are likely to fall off during the rolling process when manufacturing the positive electrode, and cracking occurring inside the particles during charge and discharge. When particle breakage of the positive electrode active material or cracking inside the particles occurs, the contact area with the electrolyte increases, resulting in an increase in gas generation due to side reactions with the electrolyte. If the gas generation inside the cylindrical battery increases, the pressure inside the battery rises, leading to a risk of battery explosion. In particular, when the volume of the cylindrical battery increases, the amount of the active material inside the battery increases with the increase in volume, so the amount of gas generated increases significantly, thereby increasing the risk of battery fire and / or explosion.

[0067] In contrast, in the case of a positive electrode active material in the form of a single particle formed of one primary particle or quasi-single particles formed by aggregating 10 or fewer primary particles, since the particle strength is higher compared to the conventional secondary particle type positive electrode active material formed by aggregating dozens to hundreds of primary particles, it is difficult for particle breakage to occur during the rolling process. In addition, in the case of a positive electrode active material in the form of a single particle or quasi-single particles, the number of primary particles constituting the particle is small, so the changes due to volume expansion and contraction of the primary particles during charge and discharge are small, and thus the occurrence of cracking inside the particles is also significantly reduced.

[0068] Therefore, when using a positive electrode active material formed of single particles or quasi-single particles, the amount of gas generated due to particle breakage or internal cracking can be significantly reduced, so that excellent safety can be achieved even in a large cylindrical battery.

[0069] Meanwhile, based on the weight of all the positive electrode active materials contained in the positive electrode active material layer, the content of the positive electrode active material formed of single particles and / or quasi-single particles is preferably 95% by weight to 100% by weight, more preferably 98% by weight to 100% by weight, still more preferably 99% by weight to 100% by weight, and even more preferably 100% by weight. When the content of the single particles and / or quasi-single particles satisfies the above range, sufficient safety can be obtained when applied to a large cylindrical battery.

[0070] Next, a conductive material is used to impart conductivity to the electrode. It can be any material without particular limitation as long as it has conductivity and does not cause chemical changes in the formed battery. Specific examples thereof may include: graphite, such as natural graphite or artificial graphite; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon fiber, and carbon nanotube; metal powders or fibers, such as copper, nickel, aluminum, silver, etc.; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives. Any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material is usually 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0071] The binder is used to improve the binding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene rubber (EPDM rubber), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof. Any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the content of the binder is usually 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0072] Meanwhile, if necessary, an insulating layer covering a part of the positive electrode active material layer and a part of the uncoated portion may be further formed on the positive electrode of the present invention. The insulating layer can be formed along a direction parallel to the winding direction of the electrode assembly.

[0073] The lithium secondary battery of the present invention may include: an electrode assembly obtained by winding the above - mentioned positive electrode, negative electrode, and a separator inserted between the positive electrode and the negative electrode in one direction; an electrolyte; and a battery can for accommodating the electrode assembly and the electrolyte.

[0074] Specifically, the positive electrode and the negative electrode may have a structure in which an active material layer is formed on a long - sheet - like current collector, and may include an uncoated portion where the active material layer is not formed on a part of the current collector.

[0075] When using the positive electrode and the negative electrode including the uncoated portion as described above, a battery with a structure without an electrode tab can be realized, in which no separate electrode tab is provided, and at least a part of the uncoated portions of the positive electrode and the negative electrode define the electrode tab.

[0076] 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. The negative electrode active material layer may contain a negative electrode active material, a conductive material, and a binder.

[0077] Specifically, the negative electrode can be prepared by coating a negative electrode slurry on one or both surfaces of a long sheet-like negative electrode current collector, removing the solvent of the negative electrode slurry through a drying process, and then calendering it. The negative electrode slurry is prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc. At the same time, a negative electrode including an uncoated portion can be prepared by not coating the negative electrode slurry on a partial area (for example, one end of the negative electrode current collector) when coating the negative electrode slurry.

[0078] As the negative electrode active material, a compound capable of reversibly inserting and extracting lithium can be used. Specific examples of the negative electrode active material may include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, etc.; silicon-based materials such as Si, Si-Me alloy (where Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO y (where 0 < y < 2) and Si-C composite materials; lithium metal thin films; metal materials capable of alloying with lithium such as Sn and Al; any one or a mixture of two or more of them can be used.

[0079] Preferably, the negative electrode of the present invention may contain a silicon-based negative electrode active material. The silicon-based negative electrode active material can be Si, Si-Me alloy (where Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO y (0 < y < 2), Si-C composite material or a combination thereof, and preferably can be SiO y (0 < y < 2). Since the silicon-based negative electrode active material has a high theoretical capacity, the capacity characteristics can be improved when the silicon-based negative electrode active material is included.

[0080] At the same time, the silicon-based negative electrode active material can be doped with M b metal, where M b metal can be a Group 1 metal element or a Group 2 metal element, specifically Li, Mg, etc. Specifically, the silicon negative electrode active material can be Si, SiO b doped with M y metal, (where 0 < y < 2), Si-C composite material, etc. In the case of the metal-doped silicon-based negative electrode active material, due to the doped element, the capacity of the active material is reduced, but it has high efficiency, and thus high energy density can be achieved.

[0081] In addition, the silicon-based negative electrode active material may further include a carbon coating on the particle surface. At this time, based on the total weight of the silicon-based negative electrode active material, the carbon coating amount may be 20% by weight or less, preferably 1 to 20% by weight.

[0082] In addition, if necessary, the negative electrode may further include a carbon-based negative electrode active material as the negative electrode active material. 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.

[0083] Meanwhile, 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 weight 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, more preferably 1:99 to 10:90.

[0084] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be 80 to 99% by weight, preferably 85 to 99% by weight, more preferably 90 to 99% by weight.

[0085] The negative electrode current collector may be any negative electrode current collector commonly used in the art. For example, it may be copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with carbon, nickel, titanium or silver, or an aluminum-cadmium alloy, etc. The thickness of the negative electrode current collector may generally be 3 to 500 μm, and, like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam or non-woven fabric, etc.

[0086] The conductive material is used to impart conductivity to the negative electrode and may be any material without particular limitation as long as it has conductivity and does not cause chemical changes in the formed battery. Specific examples thereof may include: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon fiber and carbon nanotube; metal powders or fibers, such as copper, nickel, aluminum, silver, etc.; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives. Any one or a mixture of two or more thereof may be used. Based on the total weight of the negative electrode active material layer, the content of the conductive material may generally be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0087] The binder is used to improve the binding between the negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof may include: polyvinylidene fluoride (PVDF), polyvinylidene 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 or various copolymers thereof, and any one or a mixture of two or more thereof can be used. Based on the total weight of the negative electrode active material layer, the content of the binder is usually 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0088] The separator is used to separate the negative electrode from the positive electrode and provide a channel for the movement of lithium ions. Any separator can be used without particular limitation as long as it is commonly used as a separator in lithium secondary batteries. Specifically, as the separator, a porous polymer membrane can be used, for example, a porous polymer membrane made of 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 can be used. Additionally, a conventional porous non - woven fabric can also be used, for example, a non - woven fabric made of high - melting - point glass fiber or polyethylene terephthalate fiber, etc. Moreover, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can also be used.

[0089] Meanwhile, the uncoated portions of the positive electrode and the negative electrode can be processed into the form of a plurality of independently bendable segmented pieces, and at least a part of the plurality of segmented pieces can be bent toward the winding center of the electrode assembly.

[0090] The segmented pieces can be formed by processing the current collectors of the positive electrode and the negative electrode through metal foil cutting processes such as laser slitting, ultrasonic cutting, punching, etc.

[0091] When the uncoated portions of the positive electrode and the negative electrode are processed in the form of a plurality of segmented pieces, the stress applied to the uncoated portions during bending is reduced, thereby preventing deformation or damage of the uncoated portions and improving the welding characteristics with the current - collecting plate.

[0092] The current collector plate and the uncoated portion are generally joined by welding. To improve the welding characteristics, it is necessary to bend the uncoated portion as flat as possible by applying strong pressure to the welding area of the uncoated portion. However, during this bending process, the shape of the uncoated portion may be deformed due to irregular twisting, and the deformed part may contact the electrodes of the opposite polarity, causing an internal short circuit, or resulting in fine cracks in the uncoated portion. However, if the uncoated portions of the positive and negative electrodes are processed in the form of a plurality of independently bendable segmented pieces, the stress applied to the uncoated portion during the bending process can be reduced, thereby minimizing the deformation and damage of the uncoated portion.

[0093] In addition, when the uncoated portion is processed in the form of the above-mentioned segmented pieces, overlapping occurs between the plurality of segmented pieces during the bending process, thereby increasing the welding strength with the current collector plate, and when using the latest technologies such as laser welding, laser penetration into the electrode assembly can be prevented from ablating the separator or the active material. Preferably, at least a part of the plurality of bent segmented pieces can be overlapped on the upper and lower ends of the electrode assembly, and the current collector plate can be joined to the plurality of bent segmented pieces.

[0094] The lithium secondary battery of the present invention can be a cylindrical lithium secondary battery. The cylindrical lithium secondary battery can be a large cylindrical battery having a form factor ratio (defined as the diameter of the cylindrical battery divided by its height, i.e., the ratio of the diameter (Ф) to the height (H)) of 0.4 or more. Here, the form factor refers to the value representing the diameter and height of the cylindrical battery.

[0095] The cylindrical battery of the present invention can be, 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), a 4695 cell (diameter 46 mm, height 95 mm, form factor ratio 0.484). In the numerical value representing the form factor, the first two digits represent the diameter of the cell, and the next two or three digits represent the height of the cell.

[0096] Compared with the prior art, the cylindrical lithium secondary battery of the present invention can significantly reduce the gas generation amount, so excellent safety can be achieved even in a large cylindrical battery having a form factor ratio of 0.4 or more.

[0097] Meanwhile, the cylindrical battery of the present invention is a battery with a structure without electrode tabs, i.e., a tabless structure. The cylindrical lithium secondary battery of the present invention may have a structure in which at least a part of the uncoated portion of the positive electrode defines the electrode tab, that is, a tabless structure. In addition, the cylindrical lithium secondary battery of the present invention may have a structure in which at least a part of the uncoated portion of the negative electrode defines the electrode tab, that is, a tabless structure. Specifically, the uncoated portion may be formed at one end of the current collector and extend along the winding direction, and a battery with a tabless structure can be realized by bonding a current collecting plate to each of the uncoated portions of the positive electrode and the negative electrode and connecting the current collecting plate to the electrode terminal.

[0098] For example, a battery with a tabless structure can be manufactured by the following method. First, a separator, a positive electrode, a separator, and a negative electrode are stacked in sequence such that the uncoated portions of the positive electrode and the negative electrode are in opposite directions, and then wound in one direction to form a jelly roll type electrode assembly. Then, the uncoated portions of the positive electrode and the negative electrode are bent in the direction of the winding center; the current collecting plates are welded and bonded to the uncoated portions of the positive electrode and the negative electrode respectively; and then the current collecting plates are connected to the electrode terminals, thereby manufacturing a battery with a tabless structure. At the same time, the current collecting plate has a larger cross-sectional area compared with a strip-shaped electrode tab, and the resistance is inversely proportional to the cross-sectional area of the channel through which the current flows. Therefore, when the secondary battery is formed with the above structure, the internal resistance of the battery cell can be significantly reduced. In addition, when the cylindrical lithium secondary battery is formed with the above tabless structure, compared with a conventional battery with electrode tabs, the current concentration is smaller, so the heat generation inside the battery can be effectively reduced, and thus the thermal safety of the battery can be improved.

[0099] The battery can is electrically connected to the uncoated portion of the negative electrode and serves as the negative terminal, which contacts an external power source to transmit the current applied from the external power source to the negative electrode.

[0100] The electrolyte used in the cylindrical lithium secondary battery of the present invention may include a lithium salt, an organic solvent, and an additive.

[0101] The lithium salt is used as an electrolyte salt in the lithium secondary battery and serves as a medium for transporting ions. Generally, the lithium salt may contain, for example, Li + as a cation, and selected from F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , B 10 Cl 10 -, AlCl 4 - , AlO 2 - , PF 6 - , CF 3 SO 3 - , CH 3 CO 2 - , CF 3 CO 2 - , AsF 6 - , SbF 6 - , CH 3 SO 3 - , (CF 3 CF 2 SO 2 ) 2 N - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , BF 2 C 2 O 4 - , BC 4 O 8 - , PF 4 C 2 O 4 - , PF 2 C 4 O 8 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , C4 F 9 SO 3 - 、CF 3 CF 2 SO 3 - 、CF 3 CF 2 (CF 3 ) 2 CO - 、(CF 3 SO 2 ) 2 CH - 、CF 3 (CF 2 ) 7 SO 3 - and SCN - as at least one anion in the group consisting of.

[0102] Specifically, the lithium salt may include those selected from the group consisting of LiCl, LiBr, LiI, LiBF 4 , LiClO 4 , LiB 10 Cl 10 , LiAlCl 4 , LiAlO 2 , LiPF 6 , LiCF 3 SO 3 , LiCH 3 CO 2 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiCH 3 SO 3 , LiN(SO 2 F) 2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO 2 CF 2 CF 3 ) 2 (lithium bis(perfluoroethylsulfonyl)imide; LiBETI) and LiN(SO 2 CF 3 ) 2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI), and any one or a mixture of two or more thereof. In addition, any lithium salt commonly used in the electrolyte of a lithium secondary battery may be used without limitation.

[0103] The concentration of the lithium salt contained in the electrolyte can be from 1.0 M to 1.5 M, preferably from 1.1 M to 1.3 M, to achieve the best electrolyte impregnation for a large-capacity cylindrical lithium secondary battery. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics when the lithium secondary battery is stored at high temperature is sufficient, and the viscosity of the non-aqueous electrolyte can be appropriate, thereby improving the electrolyte impregnation.

[0104] 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.

[0105] Specifically, the organic solvent may include cyclic carbonate organic solvents, linear carbonate organic solvents, and their mixed organic solvents.

[0106] The cyclic carbonate organic solvent is a high-viscosity organic solvent with a high dielectric constant, so it can easily dissociate the lithium salt in the electrolyte. As specific examples, it may 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 particularly may include ethylene carbonate.

[0107] Based on the total volume of the organic solvent, the content of cyclic carbonate, such as ethylene carbonate, can be from 15 vol% to 30 vol%, preferably from 15 vol% to 25 vol%, and most preferably from 15 vol% to 20 vol%. When the content of ethylene carbonate is within the above range, an optimized electrolyte can be provided in terms of viscosity and performance.

[0108] In addition, the linear carbonate organic solvent is an organic solvent with low viscosity and low dielectric constant. As a representative example, it may include 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 ethyl methyl carbonate (EMC).

[0109] Based on the total volume of the organic solvent, the content of linear carbonate, such as ethyl methyl carbonate, can be from 15 vol% to 30 vol%, preferably from 15 vol% to 25 vol%, and most preferably from 15 vol% to 20 vol%. When the content of ethyl methyl carbonate is within the above range, an optimized electrolyte can be provided in terms of viscosity and performance.

[0110] Preferably, the organic solvents contained in the electrolyte of the present invention include ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and based on the total volume of the organic solvents, the content of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is 25% by volume or less. At this time, since the impregnation property of the electrolyte becomes appropriate, when the injection fraction range of the present invention is applied, the best performance can be provided.

[0111] In addition, in order to manufacture an electrolyte having high ionic conductivity, in addition to at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents, 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.

[0112] Specific examples of such linear ester organic solvents may 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.

[0113] In addition, the cyclic ester organic solvents may include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0114] Meanwhile, if necessary, the organic solvent can be used by adding organic solvents commonly used in non-aqueous electrolytes without limitation. For example, it may further include at least one organic solvent selected from ether organic solvents, glycol ether solvents, and nitrile organic solvents.

[0115] 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 of them, but is not limited thereto.

[0116] The glycol ether solvent is a solvent having a higher dielectric constant and a lower surface tension than linear carbonate organic solvents and a lower reactivity with metals, and may include at least one selected from the group consisting of dimethoxyethane (glycol ether, DME), diethoxyethane, diethylene glycol ether, triethylene glycol ether, and tetraethylene glycol dimethyl ether (TEGDME), but is not limited thereto.

[0117] The nitrile solvent may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, octanenitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0118] The non-aqueous electrolyte of the present invention may contain an electrolyte additive to prevent the non-aqueous electrolyte from decomposing in a high-power environment and causing negative electrode breakdown, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, prevention of overcharging, and the effect of suppressing battery swelling at high temperatures, etc.

[0119] As a representative example, the electrolyte additive may include at least one SEI film-forming additive selected from the group consisting of cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate / salt compounds, phosphate / salt compounds, borate / salt compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0120] The cyclic carbonate compound may be vinylene carbonate (VC) or ethylene vinyl carbonate.

[0121] The halogenated carbonate compound may be fluoroethylene carbonate (FEC).

[0122] The sultone compound may be at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethyl sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0123] The sulfate / salt compound may be ethylene sulfite (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0124] The phosphate / salt compound may be at least one compound selected from the group consisting of lithium difluorobis(oxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(2,2,2-trifluoroethyl) phosphite compounds.

[0125] The borate / salt compound may be tetraphenylborate, lithium difluoro(oxalato)borate (LiODFB), and lithium bis(oxalato)borate (LiB(C 2 O 4 ) 2 , LiBOB).

[0126] The nitrile compound may be at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanenitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0127] The benzene compounds may include fluorobenzene, the amine compounds may include triethanolamine or ethylenediamine, and the silane compounds may include tetraethenylsilane.

[0128] The lithium salt compounds are different from the lithium salts contained in the non-aqueous electrolyte and may include lithium difluorophosphate (LiDFP), LiPO 2 F 2 or LiBF 4 。

[0129] Meanwhile, the other electrolyte additives may be used as a mixture of two or more, and based on the total weight of the non-aqueous electrolyte, their content may be 0.01% by weight to 30% by weight, specifically 0.1% by weight to 25% by weight, preferably 1% by weight to 20% by weight. When the content of the above other electrolyte additives satisfies the above range, the effects of improving ionic conductivity and cycle characteristics are more excellent.

[0130] Hereinafter, the present invention will be described in more detail by way of specific examples.

[0131] Example

[0132] Example 1

[0133] By mixing the positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2 、carbon nanotubes and PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone, a positive electrode paste was prepared. Among them, the positive electrode active material has a bimodal particle size distribution, D 50 is 8.3 μm, D max is 18.0 μm, and is in the form of secondary particles. The positive electrode paste was coated on one surface of an aluminum current collector sheet with a thickness of 15.0 μm and an elongation rate of 2.3% at 25 °C, dried at 120 °C, and calendered to prepare a positive electrode. The calendered density P of the prepared positive electrode is 3.41 g / cc.

[0134] The negative electrode active material (a mixture of graphite:SiO = 95:5 weight ratio), a conductive material (super C), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 96:2:1.5:0.5 in water to prepare a negative electrode paste. The negative electrode paste was coated on one surface of a copper current collector sheet, dried at 150 °C, and calendered to prepare a negative electrode.

[0135] Insert the separator between the above-prepared positive electrode and negative electrode, stack them in the order of separator / positive electrode / separator / negative electrode, and then wind them to prepare a jelly-roll type electrode assembly. Insert the electrode assembly prepared as described above into a cylindrical battery can, and then inject an electrolyte to prepare a 4680 battery cell.

[0136] Example 2

[0137] By mixing the positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2 , carbon nanotubes and PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone to prepare a positive electrode slurry. The positive electrode active material has a single-peak particle size distribution, D 50 is 4.3 μm, D max is 13.7 μm, and is in the form of single particles. Coat the positive electrode slurry on one surface of an aluminum current collector sheet with a thickness of 10.0 μm and an elongation rate of 3.4% at 25°C, dry it at 120°C, and calender it to prepare a positive electrode. The calendered density P of the prepared positive electrode is 3.63 g / cc.

[0138] Except for using the above positive electrode, a 4680 battery cell is manufactured in the same manner as in Example 1.

[0139] Example 3

[0140] By mixing the positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2 , carbon nanotubes and PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone to prepare a positive electrode slurry. The positive electrode active material has a bimodal particle size distribution, D 50 is 12.4 μm, D max is 27.0 μm, and is in the form of secondary particles. Coat the positive electrode slurry on one surface of an aluminum current collector sheet with a thickness of 12.0 μm and an elongation rate of 4.1% at 25°C, dry it at 120°C, and calender it to prepare a positive electrode. The calendered density P of the prepared positive electrode is 3.28 g / cc.

[0141] Except for using the above positive electrode, a 4680 battery cell is manufactured in the same manner as in Example 1.

[0142] Example 4

[0143] By mixing the positive electrode active material Li[Ni 0.9 Co0.06 Mn 0.03 Al 0.01 O 2 , carbon nanotubes, and a PVDF binder are mixed in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6 to prepare a positive electrode paste. Among them, the positive electrode active material has a bimodal particle size distribution, D 50 is 5.5 μm, D max is 15.0 μm, and it is in the form of secondary particles. The positive electrode paste is coated on one surface of an aluminum current collector sheet with a thickness of 15.0 μm and an elongation rate of 4.6% at 25°C, dried at 120°C, and calendered to prepare a positive electrode. The calendered density P of the obtained positive electrode is 3.59 g / cc.

[0144] Except for using the said positive electrode, a 4680 battery cell is manufactured in the same manner as in Example 1.

[0145] Example 5

[0146] By mixing the positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2 , carbon nanotubes, and a PVDF binder are mixed in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6 to prepare a positive electrode paste. Among them, the positive electrode active material has a bimodal particle size distribution, D 50 is 9.1 μm, D max is 24.0 μm, and it is in the form of secondary particles. The positive electrode paste is coated on one surface of an aluminum current collector sheet with a thickness of 12.0 μm and an elongation rate of 4.7% at 25°C, dried at 120°C, and calendered to prepare a positive electrode. The calendered density P of the obtained positive electrode is 3.38 g / cc.

[0147] Except for using the said positive electrode, a 4680 battery cell is manufactured in the same manner as in Example 1.

[0148] Comparative Example 1

[0149] By mixing the positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2 , carbon nanotubes, and a PVDF binder are mixed in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6 to prepare a positive electrode paste. Among them, the positive electrode active material has a bimodal particle size distribution, D 50 is 8.4 μm, D maxIt is 20.0 μm and in the form of secondary particles. This positive electrode paste is coated on one surface of an aluminum current collector sheet with a thickness of 10.0 μm and an elongation at 25 °C of 4.5%, dried at 120 °C, and rolled to prepare a positive electrode. The rolling density P of the obtained positive electrode is 3.58 g / cc.

[0150] Except for using the said positive electrode, a 4680 battery cell is manufactured in the same manner as in Example 1.

[0151] Comparative Example 2

[0152] By mixing a positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2 、carbon nanotubes and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone to prepare a positive electrode paste, wherein the positive electrode active material has a unimodal particle size distribution, D 50 is 4.5 μm, D max is 11.1 μm, and is in the form of single particles. This positive electrode paste is coated on one surface of an aluminum current collector sheet with a thickness of 12.0 μm and an elongation at 25 °C of 5.5%, dried at 120 °C, and rolled to prepare a positive electrode. The rolling density P of the obtained positive electrode is 3.63 g / cc.

[0153] Except for using the said positive electrode, a 4680 battery cell is manufactured in the same manner as in Example 1.

[0154] Comparative Example 3

[0155] By mixing a positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2 、carbon nanotubes and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone to prepare a positive electrode paste, wherein the positive electrode active material has a bimodal particle size distribution, D 50 is 12.9 μm, D max is 23.0 μm, and is in the form of secondary particles. This positive electrode paste is coated on one surface of an aluminum current collector sheet with a thickness of 12.0 μm and an elongation at 25 °C of 3.8%, dried at 120 °C, and rolled to prepare a positive electrode. The rolling density P of the obtained positive electrode is 3.48 g / cc.

[0156] Except for using the said positive electrode, a 4680 battery cell is manufactured in the same manner as in Example 1.

[0157] Comparative Example 4

[0158] By mixing the positive electrode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2 , carbon nanotubes, and PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone to prepare a positive electrode paste. Among them, the positive electrode active material has a bimodal particle size distribution, D 50 is 10.4 μm, D max is 21.0 μm, and it is in the form of secondary particles. The positive electrode paste is coated on one surface of an aluminum current collector sheet with a thickness of 10.0 μm and an elongation rate of 3.6% at 25°C, dried at 120°C, and calendered to prepare a positive electrode. The calendered density P of the prepared positive electrode is 3.53 g / cc.

[0159] Except for using the said positive electrode, the 4680 battery cells are manufactured in the same manner as in Example 1.

[0160] Experimental Example 1

[0161] For the 4680 battery cells of Examples 1 to 5 and Comparative Examples 1 to 4, it is confirmed whether an open circuit occurs during the battery cell assembly process.

[0162] [Table 1]

[0163]

[0164] Experimental Example 2

[0165] For the 4680 battery cells of Examples 1 to 5 and Comparative Examples 1 to 4, it is confirmed whether an open circuit occurs during the charge and discharge process.

[0166] Specifically, for each of the 4680 battery cells of Examples 1 to 5 and Comparative Examples 1 and 2, 300 charge and discharge cycles are carried out, and then it is confirmed whether an open circuit occurs. Among them, one cycle consists of constant current and constant voltage charging at 1C to 4.25V at 25°C and constant current discharging at 1C to 2.5V. The results are shown in Table 2 below.

[0167] [Table 2]

[0168] Whether open circuit occurs Example 1 X Example 2 X Example 3 X Example 4 X Example 5 X Comparative Example 1 O Comparative Example 2 X Comparative Example 3 O Comparative Example 4 O

[0169] As shown in Tables 1 and 2, in the case of the 4680 battery cells of Examples 1 to 5 where the value of the calendering density P is greater than or equal to the value of [(a1 / a2)×b] / 0.05c, no open circuit occurred during the assembly process or the charge-discharge process. However, in the case of the 4680 battery cells of Comparative Examples 1 to 4 where the value of the calendering density P is less than the value of [(a1 / a2)×b] / 0.05c, an open circuit occurred during the assembly process or the charge-discharge process.

Claims

1. A positive electrode for a lithium secondary battery, comprising: a positive electrode current collector; and a positive electrode active material layer disposed 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 which no positive electrode active material layer is formed, and satisfies the following mathematical formula (1): Mathematical formula (1): P≥[(a1 / a2)×b] / 0.05c where: P is the calendering density of the positive electrode, in g / cc, a1 is the D of the positive active material particles contained in the positive active material layer 50 , with the unit of μm a2 is the D of the positive active material particles included in the positive active material layer max , with the unit of μm b is the elongation rate of the positive electrode current collector at 25 °C in %, c is the thickness of the positive electrode current collector, in μm.

2. The positive electrode for a lithium secondary battery according to claim 1, wherein, P is from 3.2 g / cc to 3.8 g / cc.

3. The positive electrode for a lithium secondary battery according to claim 1, wherein, a1 is from 3.5 μm to 13.5 μm.

4. The positive electrode for a lithium secondary battery according to claim 1, wherein, a2 is from 10 μm to 30 μm.

5. The positive electrode for a lithium secondary battery according to claim 1, wherein, b is from 10 μm to 20 μm.

6. The positive electrode for a lithium secondary battery according to claim 1, wherein, c is from 1.0% to 5.5%.

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

8. 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 Among them, M 1 is Mn, Al or a combination thereof, and M 2 is at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, and 0.8 ≤ a ≤ 1.2, 0.8 ≤ b < 1, 0 < c < 0.2, 0 < d < 0.2, 0 ≤ e ≤ 0.

1.

9. The positive electrode according to claim 1, wherein, the positive electrode active material has a bimodal particle size distribution.

10. The positive electrode according to claim 1, wherein, the positive electrode active material has a unimodal particle size distribution.

11. A lithium secondary battery, comprising: an electrode assembly obtained by winding the positive electrode for a lithium secondary battery according to claim 1, a negative electrode, and a separator inserted between the positive electrode and the negative electrode in one direction; an electrolyte; and a battery can for accommodating the electrode assembly and the electrolyte.

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 form factor ratio of the cylindrical lithium secondary battery is 0.4 or more.

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

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