Electrode assembly and lithium secondary battery including the same

Abstract

The present invention relates to an electrode assembly for a cylindrical lithium secondary battery 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, in which: the positive electrode comprises a positive electrode current collector and a positive electrode active material layer; the negative electrode comprises a non-coating part and a coating part, the non-coating part is not provided with a negative electrode active material layer arranged on the negative electrode current collector, and the coating part is provided with a negative electrode active material layer arranged on the negative electrode current collector; the coating part comprises a first region in which the thickness of the negative electrode active material layer is constant and a second region in which the thickness of the negative electrode active material layer is reduced; equation (1): t > = a (b + 2c) is satisfied.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims the priority benefit of Korean Patent Application No. 10 - 2022 - 0181141, filed on December 21, 2022, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to an electrode assembly and a lithium secondary battery including the electrode assembly. Background Art

[0005] 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.

[0006] According to the battery case type, lithium secondary batteries can be classified into cylindrical, prismatic, and pouch - type batteries. Among them, a cylindrical battery has the following form: an electrode assembly is accommodated in a cylindrical battery can, and then the top of the battery can is sealed by covering it with a cap plate. The electrode assembly is manufactured 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 strip - shaped positive - electrode tabs and negative - electrode tabs, 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 cap 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 in that current concentrates on the strip - shaped electrode tabs, resulting in a large resistance, generating a large amount of heat, and having a low current - collecting efficiency.

[0007] In this case, by applying a structure in which non - coated portions of the positive electrode and the negative electrode are used as electrode tabs without forming separate electrode tabs (for example, a tab - less structure), the problem of current concentration around the electrode tabs can be solved.

[0008] However, in the case where the electrode has a coated portion and a non - coated portion, there is a sliding region where the loading amount decreases in the middle of moving from the coated portion to the non - coated portion. Generally, since the size of the negative electrode is designed to be larger than that of the positive electrode, there is a region where the sliding region of the negative electrode and the active - material layer of the positive electrode face each other, and in this region, the NP ratio (negative - electrode capacity / positive - electrode capacity) is low. In this region, if the NP ratio (negative - electrode capacity / positive - electrode capacity) is less than 100%, stability problems such as lithium deposition may occur during the operation of the secondary battery.

[0009] To solve the above problems, if the NP ratio is adjusted to be greater than 100% even in the region where the sliding region of the negative electrode and the active material layer of the positive electrode face each other, the NP ratio at the center of the negative electrode must be designed to be even larger. In such a design, the thickness of the negative electrode increases because the negative electrode loading amount should be increased. However, when increasing the thickness of the negative electrode while keeping the outer diameter specification of the lithium secondary battery can constant, the length of the input electrode decreases, which instead reduces the cell capacity.

[0010] Therefore, a technique for obtaining the maximum cell capacity in an electrode assembly including a negative electrode having a coated portion and an uncoated portion is needed. Summary of the Invention

[0011] Technical Problem

[0012] The present invention attempts to provide a lithium secondary battery that has the maximum capacity by minimizing the capacity loss caused by the reduced length of the electrode input into the electrode assembly and additionally using the region where the sliding region of the negative electrode and the active material layer of the positive electrode face each other.

[0013] Technical Solution

[0014] To solve the above problems, according to the present invention, the thickness of the negative electrode active material layer in the negative electrode including a coated portion and an uncoated portion, the length of the positive electrode active material layer in the first region where the thickness facing the negative electrode active material layer is constant, the length of the positive electrode active material layer in the second region (sliding region) where the thickness facing the negative electrode active material layer decreases, and the slope of the starting portion of the sliding region are adjusted to satisfy a specific relationship.

[0015] Specifically, an electrode assembly for a cylindrical lithium secondary battery is provided, 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. Among them, the positive electrode includes a positive electrode current collector and a positive electrode active material layer. Among them, the negative electrode includes an uncoated portion where no negative electrode active material layer is formed on the negative electrode current collector and a coated portion where a negative electrode active material layer is formed on the negative electrode current collector. Among them, the coated portion includes a first region where the thickness of the negative electrode active material layer is constant and a second region where the thickness of the negative electrode active material layer decreases. And the electrode assembly satisfies the following equation (1):

[0016] Equation (1): t≥a(b + 2c)

[0017] Wherein, t is the thickness (mm) of the negative electrode active material layer in the first region, b is the length (mm) where the first region faces the positive electrode active material layer, c is the length (mm) where the second region faces the positive electrode active material layer, and a is the value represented by the following equation (2):

[0018] Equation (2): a = 0.1t / △x

[0019] Wherein, △x is the longitudinal distance (mm) between the boundary point between the first region and the second region and the point where the thickness of the negative electrode active material layer in the second region is 0.9t.

[0020] In addition, a lithium secondary battery is also provided, including: the above electrode assembly; an electrolyte; and a battery can for accommodating the electrode assembly and the electrolyte.

[0021] Beneficial effects

[0022] The negative electrode formed with the coated portion and the non-coated portion has a sliding region. The sliding region is a region where the loading amount of the negative electrode active material decreases, that is, a region where the thickness of the negative electrode active material layer decreases. When this region is designed to face the positive electrode, the sliding region also helps to increase the capacity of the secondary battery, so that an increase in the total battery capacity can be expected.

[0023] However, since the loading amount of the negative electrode in the sliding region is reduced, the N / P ratio (negative electrode capacity / positive electrode capacity) may be less than 100%, and when the N / P ratio is less than 100%, stability problems during the operation of the secondary battery, such as lithium deposition, may occur. To solve the stability problem, by increasing the thickness of the negative electrode to increase the N / P ratio at the center of the negative electrode, the N / P ratio in the sliding region can be not less than 100%. However, if the thickness of the negative electrode increases when the external specifications of the lithium secondary battery are constant, the length of the input electrode assembly decreases, so that the total battery capacity will instead decrease.

[0024] As in the present invention, when the thickness of the negative electrode active material layer in the negative electrode, the length of the positive electrode active material layer in the first region where the thickness of the positive electrode active material layer facing the negative electrode active material layer is constant, the length of the positive electrode active material layer in the second region (sliding region) where the thickness of the negative electrode active material layer facing the negative electrode active material layer decreases, and the slope of the starting portion of the sliding region are adjusted to satisfy a specific relationship, it has the effect of minimizing the capacity loss caused by the decrease in the length of the electrode input into the electrode assembly, while additionally using the sliding region of the negative electrode and the region where the active material layer of the positive electrode faces each other.

[0025] Specifically, when the length of the positive electrode is increased to increase the capacity of the lithium secondary battery, the negative electrode facing the longer positive electrode (especially the sliding region of the negative electrode) must also have an increased loading amount to prevent the reversal of the NP ratio. As the sliding region of the negative electrode and the positive electrode face each other more, there are problems such as short circuits caused by the reversal of the NP ratio between the positive electrode and the negative electrode. To solve these problems, when the loading amount of the negative electrode increases, the thickness of the negative electrode thus increases. In the case of a cylindrical or prismatic battery, since the size of the battery can is limited, the input length P of the negative electrode decreases as the thickness of the negative electrode increases. For example, the input length of the negative electrode is atFigure 2 It is represented as P in the figure and represents the length in the negative electrode winding direction.

[0026] Due to the risk of NP reversal, it is difficult to design the positive electrode facing the negative electrode to have a larger area than the negative electrode. Therefore, the input length of the positive electrode also decreases as the input length of the negative electrode decreases. In summary, when the input length of the positive electrode decreases, the total capacity of the lithium secondary battery decreases.

[0027] The present invention minimizes the decrease in the input length of the positive electrode while maximizing the use of the sliding area of the negative electrode, thereby achieving the highest capacity of the lithium secondary battery while showing the effect of solving the stability problem caused by the NP ratio reversal.

[0028] In addition, the lithium secondary battery including the above has fewer defects due to disconnection and has excellent durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural view of an electrode assembly according to an embodiment of the present invention. Figure 1 It is a side view of the electrode assembly.

[0030] Figure 2 It is Figure 1 a plan view of the negative electrode 30 of

[0031] Figure 3 It is Figure 1 an example of an enlarged view of region A of

[0032] Figure 4 It is Figure 1 an example of an enlarged view of region A of DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] Hereinafter, the present invention will be described in more detail.

[0034] The terms or words used in the specification and claims of the present application should not be construed as limited to their ordinary 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 describe his invention.

[0035] The present invention relates to an electrode assembly for a lithium secondary battery, 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. Among them, the positive electrode includes a positive electrode current collector and a positive electrode active material layer. Among them, the negative electrode includes an uncoated portion where no negative electrode active material layer is formed on the negative electrode current collector and a coated portion where a negative electrode active material layer is formed on the negative electrode current collector. Among them, the coated portion includes a first region where the thickness of the negative electrode active material layer is constant and a second region where the thickness of the negative electrode active material layer decreases, and the electrode assembly satisfies the following equation (1):

[0036] Equation (1): t ≥ a(b + 2c)

[0037] Wherein, t is the thickness (mm) of the negative electrode active material layer in the first region, b is the length (mm) of the first region facing the positive electrode active material layer, c is the length (mm) of the second region facing the positive electrode active material layer, and a is the value represented by the following Equation (2):

[0038] Equation (2): a = 0.1t / Δx

[0039] Wherein, Δx is the longitudinal distance (mm) between the boundary point between the first region and the second region and the point where the thickness of the negative electrode active material layer in the second region is 0.9t. The a in the above Equation (2) refers to the average slope of the sliding region (the region until the thickness of the negative electrode becomes 0.1).

[0040] When the thickness of the negative electrode active material layer, the length of the positive electrode active material layer in the first region where the thickness of the positive electrode active material layer facing the negative electrode active material layer is constant, the length of the positive electrode active material layer in the second region (sliding region) where the thickness of the positive electrode active material layer facing the negative electrode active material layer decreases, and the slope of the starting part of the sliding region satisfy the specific relationship of Equation (1), it is possible to provide a lithium secondary battery with the maximum capacity by minimizing the capacity loss caused by the decrease in the length of the input electrode, and at the same time additionally using the sliding region of the negative electrode and the region where the active material layers of the positive electrode face each other.

[0041] In the above Equation (1), t is the thickness at the center of the negative electrode active material layer or the average thickness of the negative electrode active material layer in the first region where the thickness of the negative electrode active material layer is constant. Since the actual thickness of the negative electrode may not be completely constant, the region with a constant thickness may have a thickness error within 0.05t.

[0042] t can be 0.100 mm to 0.180 mm, preferably 0.120 mm to 0.160 mm, and most preferably 0.135 mm to 0.150 mm.

[0043] When the length of the negative electrode active material layer is x, x can be 60 mm to 95 mm, preferably 65 mm to 90 mm, and most preferably 69 mm to 86 mm.

[0044] In the above Equation (1), a is the value represented by the following Equation (2), and is the average slope of the part where the thickness of the negative electrode active material layer starts to decrease at the longitudinal end of the negative electrode current collector. That is, a refers to the average slope of the starting part of the sliding region (the second region). The slope of the starting part of the sliding region can decrease constantly as shown in Figure 3 shown, or can be as shown in Figure 4decreases irregularly as shown.

[0045] Equation (2): a = 0.1t / Δx

[0046] In Equation (2), a can be from 0.0001 to 0.01, preferably from 0.0005 to 0.008, and most preferably from 0.001 to 0.002.

[0047] In Equation (2), Δx is the distance (mm) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer is constant and the second region where the thickness of the negative electrode active material layer decreases, and the point where the thickness of the negative electrode active material layer in the second region is 0.9t. Δx can be from 1.5 mm to 20 mm, preferably from 10 mm to 15 mm, and most preferably from 12 mm to 13.5 mm.

[0048] In Equation (1), b is the length (mm) of the positive electrode active material layer facing the first region (where the thickness of the negative electrode active material layer is constant). b can be from 60 mm to 69 mm, preferably from 64 mm to 66 mm, and most preferably from 64.5 mm to 65.5 mm.

[0049] In Equation (1) above, c is the length (mm) of the positive electrode active material layer facing the second region (where the thickness of the negative electrode active material layer decreases), that is, the length where the sliding region of the negative electrode and the positive electrode active material layer face each other. c can be from 0.1 mm to 5 mm, preferably from 0.5 mm to 4.5 mm, and most preferably from 1 mm to 4 mm.

[0050] In Equation (1) above, c / b can be 0.22 or less, preferably from 0.01 to 0.20, and most preferably from 0.02 to 0.10.

[0051] The negative electrode included in the electrode assembly of the present invention includes: a negative electrode current collector; and a negative electrode active material layer located on the negative electrode current collector, wherein the negative electrode current collector includes a coated portion and an uncoated portion, the coated portion has a negative electrode active material layer formed on at least one surface of the negative electrode current collector, and the uncoated portion does not have a negative electrode active material layer formed on the negative electrode current collector.

[0052] The negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder. Specifically, the negative electrode may be prepared by applying a negative electrode slurry to one or both surfaces of a long sheet of negative electrode current collector, removing the solvent of the negative electrode slurry by a drying process, and then rolling it, wherein the negative electrode slurry is prepared by dispersing the negative electrode active material, the conductive material, and the binder in a solvent such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, water, etc. At the same time, the negative electrode including the non-coating portion may be prepared by not applying the negative electrode slurry to a certain area of ​​the negative electrode current collector (e.g., one end of the negative electrode current collector) when applying the negative electrode slurry.

[0053] As the negative electrode active material, a compound capable of reversibly inserting and deinserting 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; silicon-based materials such as Si, Si-Me alloy (wherein Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti and Ni), SiO y (where 0 <y<2)和Si-C复合材料;锂金属薄膜;能够与锂合金化的金属材料,诸如Sn和Al;可以使用它们中的任何一种或两种以上的混合物。

[0054] Preferably, the negative electrode according to the present invention may include a silicon-based negative electrode active material. The silicon-based negative electrode active material may be Si, a Si-Me alloy (wherein Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti and Ni), SiO y (Here 0 <y<2)、Si-C复合材料或其组合,并且优选可以是SiO y (Here 0 <y<2)。由于硅基负极活性材料具有较高的理论容量,因此当包括硅基负极活性材料时可以改善容量特性。

[0055] At the same time, silicon-based negative electrode active materials can be doped with M b Metal, M b The metal may be a first group metal element or a second group metal element, specifically Li, Mg, etc. Specifically, the silicon negative electrode active material may be doped with M b Metallic Si, SiO y (where 0 <y<2)、Si-C复合材料等。在金属掺杂的硅基负极活性材料的情况下,活性材料容量由于掺杂元素而稍微降低,但是具有高效率,因此可以实现高能量密度。

[0056] In addition, the silicon-based negative electrode active material may further include a carbon coating layer on the particle surface. In this case, based on the total weight of the silicon-based negative electrode active material, the carbon coating amount may be 20 wt% or less, preferably 1 wt% to 20 wt%.

[0057] 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.

[0058] 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 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. Most preferably, the negative electrode active material is formed of a mixture of graphite and SiO, wherein, based on the total weight of the negative electrode active material, the content of SiO is preferably 1 wt% to 5 wt%.

[0059] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be 80 wt% to 99 wt%, preferably 85 wt% to 99 wt%, more preferably 90 wt% to 99 wt%.

[0060] Meanwhile, the negative electrode current collector may be any negative electrode current collector commonly used in the art, and may be, for example, copper; stainless steel; aluminum; nickel; titanium; sintered carbon; copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.; aluminum cadmium alloy, etc., but most preferably a copper thin film.

[0061] The negative electrode current collector generally may have a thickness of 3 μm to 500 μm, and like the positive electrode current collector, may have fine irregularities formed on the surface of the current collector to increase the adhesion of the negative electrode active material. For example, the negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0062] The conductive material is used to impart conductivity to the negative electrode and can be any material without particular limitation as long as it has conductivity without causing chemical changes in the battery to be configured. 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 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, and any one or a mixture of two or more of these materials can be used. Based on the total weight of the negative electrode active material layer, the content of the conductive material is usually 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%.

[0063] 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), 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, or various copolymers thereof, and any one or a mixture of two or more of them can be used. Based on the total weight of the negative electrode active material layer, the content of the binder is usually 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%.

[0064] The positive electrode of the present invention includes a positive electrode current collector and a positive electrode active material layer. The positive electrode of the present invention can be prepared by applying a positive electrode slurry to one or two surfaces of a long sheet-shaped positive electrode current collector, removing the solvent of the positive electrode slurry by a drying process, and then rolling 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 applying the positive electrode slurry to a certain area (for example, one end of the positive electrode current collector) when applying the positive electrode slurry.

[0065] As the positive electrode current collector, various positive electrode current collectors used in the art can be used. For example, the positive electrode current collector can be stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel having a surface treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector can have fine irregularities formed on its surface to increase the adhesion of the positive electrode active material. For example, various forms of positive electrode current collectors can be used, such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc. Most preferably, a thin aluminum film can be used in terms of elongation rate control.

[0066] Meanwhile, as the positive electrode active material, any positive electrode active material commonly used in the art can be used.

[0067] Preferably, the positive electrode active material can include lithium nickel-based oxides, specifically lithium nickel-based oxides containing 80 mol% or more of Ni based on the total number of moles of transition metals. Preferably, the Ni content of the lithium nickel-based oxide can be 80 mol% or more and less than 100 mol%, 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.

[0068] More specifically, the positive electrode active material can include a lithium nickel-based oxide represented by the following Chemical Formula 3:

[0069] [Chemical Formula 3]

[0070] Li x Ni y Co z M 1 d M 2 e O 2

[0071] In Chemical Formula 3, M 1 can be Mn, Al, or a combination thereof, and preferably Mn or a combination of Mn and Al.

[0072] M 2 can 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, and more preferably Zr, Y, or a combination thereof. The M 2 element is not necessarily included, but when an appropriate amount of M 2 is included, M 2 can promote grain growth or improve crystal structure stability during firing.

[0073] x represents the molar ratio of lithium in the lithium nickel-based oxide, and can be 0.8 ≤ x ≤ 1.2, 0.85 ≤ x ≤ 1.15 or 0.9 ≤ x ≤ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0074] y represents the molar ratio of nickel among all metals except lithium in the lithium nickel-based oxide, and can be 0.85 ≤ y < 1, 0.86 ≤ y < 1 or 0.88 ≤ y < 1. When the molar ratio of nickel satisfies the above range, high energy density can be exhibited, thereby achieving high capacity.

[0075] z represents the molar ratio of cobalt among all metals except lithium in the lithium nickel-based oxide, and can be 0 < z < 0.15, 0 < z < 0.14 or 0.01 ≤ z ≤ 0.12. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be achieved.

[0076] d represents the molar ratio of the M 1 element among all metals except lithium in the lithium nickel-based oxide, and can be 0 < d < 0.15, 0 < d < 0.14 or 0.01 ≤ d ≤ 0.12. When the molar ratio of the M 1 element satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0077] e represents the molar ratio of the M 2 element among all metals except lithium in the lithium nickel-based oxide, and can be 0 ≤ e ≤ 0.1 or 0 ≤ e ≤ 0.05.

[0078] Meanwhile, if necessary, the positive electrode active material according to the present invention may further include a coating layer on the surface of the lithium nickel-based oxide particles, and the coating layer contains 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 B.

[0079] When the coating layer is present on the surface of the lithium nickel-based oxide particles, the coating layer can inhibit the contact between the electrolyte and the lithium composite transition metal oxide, thereby having the effect of reducing the elution of transition metals or generating gas due to side reactions with the electrolyte.

[0080] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80 wt% to 99 wt%, preferably 85 wt% to 99 wt%, more preferably 90 wt% to 99 wt%.

[0081] 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 by mixing 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 can be increased.

[0082] The positive electrode active material is not particularly limited in terms of its form, and may be in the form of secondary particles in which a plurality of primary particles are aggregated, in the form of single particles formed of one primary particle, or in a combined form thereof.

[0083] Preferably, the positive electrode active material may include a positive electrode active material composed of single particles, the single particles being formed of one primary particle and / or quasi-single particles that are aggregates of 10 or fewer primary particles. By using a positive electrode active material composed of single particles 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.

[0084] Conventionally, spherical secondary particles in which dozens to hundreds of primary particles are aggregated are generally used as the positive electrode active material of a lithium secondary battery. However, in the case of a positive electrode active material in the form of secondary particles in which a large number of primary particles are aggregated, particle breakage (primary particle detachment) may occur during the rolling process in the manufacture of the positive electrode, and cracks may occur inside the particles during charge and discharge. When particle breakage of the positive electrode active material or cracks inside the particles occur, the contact area with the electrolyte increases, resulting in an increase in gas generated due to side reactions with the electrolyte. If the gas generation inside the cylindrical battery increases, the pressure inside the battery increases, leading to a risk of battery explosion. In particular, when the volume of the cylindrical battery increases, the amount of active material inside the battery increases as the volume increases, so the amount of gas generated increases significantly, increasing the risk of battery ignition and / or explosion.

[0085] In contrast, in the case of a positive electrode active material in the form of single particles formed of one primary particle and / or quasi-single particles in which 10 or fewer primary particles are aggregated, particle breakage hardly occurs during rolling because the particle strength is higher compared to the conventional secondary particle type positive electrode active material in which dozens to hundreds of primary particles are aggregated. In addition, in the case of a positive electrode active material in the form of single particles or quasi-single particles, the number of primary particles constituting the particles is small. Therefore, during charge and discharge, there is almost no change in the primary particles due to the volume expansion and contraction of the primary particles, and thus the occurrence of cracks inside the particles is also significantly reduced.

[0086] 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 and internal cracks can be significantly reduced, thereby achieving excellent safety even in large cylindrical batteries.

[0087] Meanwhile, based on the total weight of the positive electrode active material included 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 wt% to 100 wt%, more preferably 98 wt% to 100 wt%, still more preferably 99 wt% to 100 wt%, and even more preferably 100 wt%. When the content of single particles and / or quasi-single particles satisfies the above range, sufficient safety can be obtained when applied to large cylindrical batteries.

[0088] Next, the conductive material is used to impart conductivity to the electrode, and it can be any material without particular limitation as long as it has conductivity without causing chemical changes in the battery to be configured. 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 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, and any one or a mixture of two or more of these materials can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material is usually 1 wt% to 30 wt%, preferably 1% to 20%, more preferably 1 wt% to 10 wt%.

[0089] The binder is used to improve the binding between 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), 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, or various copolymers thereof, and any one or a mixture of two or more of them can be used. Based on the total weight of the positive electrode active material layer, the content of the binder is usually 1 wt% to 30 wt%, preferably 1 wt% to 20%, more preferably 1 wt% to 10 wt%.

[0090] The separator is used to isolate the negative electrode and the positive electrode and provide a moving channel for 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, the following structures can be used as the separator: a porous polymer membrane, such as a porous polymer membrane made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer; or a laminated structure having two or more layers. In addition, conventional porous non-woven fabrics, such as non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., can also be used. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can also be used.

[0091] Meanwhile, the positive electrode and the negative electrode can have uncoated portions and coated portions. The uncoated portions can be processed into the form of a plurality of independently bendable segmental members, and at least a part of the plurality of segmental members can be bent toward the winding center of the electrode assembly.

[0092] The current collectors of the positive electrode and the negative electrode can be processed by metal foil cutting processes such as laser slitting, ultrasonic cutting, stamping, etc. to form the segmental members.

[0093] When the uncoated portions are processed into the form of a plurality of segmental members, the stress applied to the uncoated portions during bending is reduced to prevent the uncoated portions from deforming or being damaged, and the welding characteristics with the current collecting plate are improved.

[0094] The current collecting plate and the uncoated portions are usually joined by welding, and the uncoated portions must be bent as flat as possible by applying strong pressure to the welding areas of the uncoated portions to improve the welding characteristics. However, in this bending process, the shape of the uncoated portions may be deformed due to irregular distortion, and the deformed portions may contact the electrodes of the opposite polarity, resulting in an internal short circuit or causing fine cracks in the uncoated portions. However, if the uncoated portions are processed into the form of a plurality of independently bendable segmental members, the stress applied to the uncoated portions during bending can be reduced, thereby minimizing the deformation and damage of the uncoated portions.

[0095] In addition, when the uncoated portions are processed into the form of segmented members as described above, overlapping occurs between the plurality of segmented members during bending, whereby the welding strength with the current collecting plate can be increased, and when using the latest technologies such as laser welding, it is possible to prevent the laser from penetrating the electrode assembly and ablating the separator or the active material. Preferably, at least some of the plurality of bent segmental members can overlap at the upper and lower ends of the electrode assembly, and the current collecting plate can be coupled to the plurality of bent segmental members.

[0096] 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 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 values representing the diameter and height of the cylindrical battery.

[0097] The cylindrical battery according to the present invention may be, for example, a 46110 cell (diameter of 46 mm, height of 110 mm, form factor ratio of 0.418), a 4875 cell (diameter of 48 mm, height of 75 mm, form factor ratio of 0.640), a 48110 cell (diameter of 48 mm, height of 110 mm, form factor ratio of 0.436), a 4880 cell (diameter of 48 mm, height of 80 mm, form factor ratio of 0.600), a 4680 cell (diameter of 46 mm, height of 80 mm, form factor ratio of 0.575), a 4695 cell (diameter of 46 mm, height of 95 mm, form factor ratio of 0.484). In the numerical values 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.

[0098] Compared with the prior art, the cylindrical lithium secondary battery according to the present invention can significantly reduce the amount of gas generated, and thus excellent safety can be achieved even in a large cylindrical battery having a form factor ratio of 0.4 or more.

[0099] Meanwhile, the cylindrical battery according to the present invention is a battery having a jointless structure that does not include an electrode joint. The cylindrical lithium secondary battery of the present invention may have a structure in which at least a part of the non-coated portion of the negative electrode defines the electrode joint, i.e., a jointless structure. In addition, the cylindrical lithium secondary battery of the present invention may have a structure in which at least a part of the non-coated portion of the negative electrode defines the electrode joint, i.e., a jointless structure. Specifically, the non-coated portion may be formed at one side end of the current collector extending along the winding direction, and a battery having a jointless structure may be achieved by connecting a current collecting plate to each of the positive electrode non-coated portion and the negative electrode non-coated portion and connecting the current collecting plate to the electrode terminal.

[0100] For example, a battery with a jointless 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 non-coated portions of the positive electrode and the negative electrode are in opposite directions, and then wound in one direction to manufacture a wound core type electrode assembly. Then, the non-coated portions of the positive electrode and the negative electrode are bent in the direction of the winding center; a current collector plate is welded and bonded to each of the non-coated portions of the positive electrode and the negative electrode; and then the current collector plate is connected to an electrode terminal, thereby manufacturing a battery with a jointless structure. At the same time, compared with a strip-shaped electrode joint, the current collector plate has a larger cross-sectional area, 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 core can be greatly reduced. In addition, when a cylindrical lithium secondary battery is formed with a jointless structure as described above, compared with a conventional battery having an electrode joint, the degree of current concentration is lower, so that heat generation inside the battery can be effectively reduced, and thus the thermal safety of the battery can be improved.

[0101] The battery can be electrically connected to the non-coated portion of the electrode and used as an electrode terminal that contacts an external power source to transfer the current applied from the external power source to the electrode.

[0102] The electrolyte used in the cylindrical lithium secondary battery of the present invention may include a lithium salt, an organic solvent, and an additive.

[0103] The lithium salt is used as an electrolyte salt in the lithium secondary battery and as a medium for transferring 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 - , AsF6 - , SbF 6 -

[0104] , 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 -

[0105] , 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 -

[0106] , C 4 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 - is used as an anion in the group consisting of

[0107] 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(perfluoroethanesulfonyl)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 electrolytes for lithium secondary batteries may be used without limitation.

[0108] The concentration of the lithium salt contained in the electrolyte may be 1.0 M to 1.5 M, preferably 1.1 M to 1.3 M, in order to achieve the best electrolyte impregnation in 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 is sufficient when the lithium secondary battery is stored at a high temperature, and the viscosity of the non-aqueous electrolyte can be appropriate, thereby improving electrolyte impregnation.

[0109] The organic solvent may include at least one organic solvent selected from the group consisting of cyclic carbonate-based organic solvents, linear carbonate-based organic solvents, linear ester-based organic solvents, and cyclic ester-based organic solvents.

[0110] Specifically, the organic solvent may include cyclic carbonate organic solvents, linear carbonate organic solvents, or a mixed organic solvent thereof.

[0111] The cyclic carbonate-based organic solvent is a high-viscosity organic solvent with a high dielectric constant, and thus can easily dissociate the lithium salt in the electrolyte. As a specific example thereof, 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 vinyl carbonate. In particular, it may include ethylene carbonate.

[0112] In addition, the linear carbonate-based organic solvent is an organic solvent with low viscosity and low dielectric constant, and as a representative example thereof, 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, it may include ethyl methyl carbonate (EMC).

[0113] In addition, in order to prepare an electrolyte with high ionic conductivity, in addition to at least one carbonate-based organic solvent selected from the group consisting of cyclic carbonate-based organic solvents and linear carbonate-based organic solvents, the organic solvent may further include at least one ester-based organic solvent selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents.

[0114] Specific examples of such linear ester-based 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.

[0115] In addition, the cyclic ester-based organic solvent may include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0116] Meanwhile, the organic solvent can be used by adding, as needed, but not limited to, organic solvents commonly used in non-aqueous electrolytes. For example, it may further include at least one organic solvent selected from ether-based organic solvents, glycol dimethyl ether-based solvents, and nitrile-based organic solvents.

[0117] The ether-based 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), 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more thereof, but is not limited thereto.

[0118] Compared with the linear carbonate-based organic solvent, the glycol dimethyl ether-based solvent is a solvent having a higher dielectric constant, a lower surface tension, and a lower reactivity with metals, and may include at least one selected from the group consisting of dimethoxyethane (amido dimethyl ether, DME), diethoxyethane, diglyme, triglyme, and tetraethylene glycol dimethyl ether (TEGDME), but is not limited thereto.

[0119] The nitrile-based 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.

[0120] The non-aqueous electrolyte of the present invention may include an electrolyte additive to prevent the non-aqueous electrolyte from decomposing in a high-power environment, resulting in negative electrode collapse, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery swelling at high temperatures, etc.

[0121] As a representative example, the electrolyte additive may include at least one additive selected from the group consisting of the following substances for forming a SEI film: cyclic carbonate-based compounds; halogen-substituted carbonate-based compounds; sultone-based compounds; sulfate-based compounds; phosphate-based compounds; borate-based compounds; nitrile-based compounds; phenyl-based compounds; amine-based compounds; silyl-based compounds; and lithium salt-based compounds.

[0122] The cyclic carbonate-based compound may be vinylene carbonate (VC) or ethylene vinylene carbonate.

[0123] The halogen-substituted carbonate-based compound may be fluoroethylene carbonate (FEC).

[0124] The sultone-based compound may be at least one compound selected from 1,3-propane sultone (PS), 1,4-butane sultone, ethylene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0125] The sulfate-based compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0126] The phosphate-based compound may be at least one compound selected from the group consisting of lithium difluoro(oxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(2,2,2-trifluoroethyl)phosphite.

[0127] The borate-based compound may be tetraphenylborate, lithium difluorooxalate (LiODFB), and lithium bis(oxalato)borate (LiBOB). 2 O 4 ) 2 , LiBOB).

[0128] The nitrile-based compound may be 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.

[0129] The phenyl compound may include fluorobenzene, the amine compound may include triethanolamine or ethylenediamine, and the silyl compound may include tetraethenylsilane.

[0130] The lithium salt-based compound is different from the lithium salt included in the non-aqueous electrolyte and may include lithium difluorophosphate (LiDFP), LiPO 2 F 2 or LiBF 4 .

[0131] Hereinafter, the present invention will be described in more detail by way of specific examples.

[0132] Example

[0133] Example 1

[0134] A negative electrode active material (a mixture of graphite:SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode paste. The negative electrode paste was applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode was 0.1605 mm, and the length (x) of the negative electrode was 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer was constant and the second region where the thickness of the negative electrode active material layer decreased and the point where the thickness of the negative electrode active material layer in the second region was 0.9t was measured to be 13.2 mm, and a was measured to be 0.00122.

[0135] The positive electrode paste is prepared by mixing nickel cobalt manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode paste is applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare the positive electrode.

[0136] A separator is inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region with a constant thickness of the negative electrode active material layer is 65 mm, and the length (c) of the positive electrode active material layer facing the second region with a decreasing thickness of the negative electrode active material layer is 1 mm. In the prepared electrode assembly, a(b + 2c) is calculated to be 0.0821.

[0137] The electrode assembly prepared as described above is inserted into a cylindrical battery can, and then an electrolyte is injected to prepare a 4680 cell.

[0138] Example 2

[0139] A negative electrode paste is prepared by mixing a negative electrode active material (a mixture of graphite:SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a weight ratio of 98:0.05:1.1:0.85 in water. The negative electrode paste is applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare the negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode is 0.1592 mm, and the length (x) of the negative electrode is 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region with a constant thickness of the negative electrode active material layer and the second region with a decreasing thickness of the negative electrode active material layer and the point where the thickness of the negative electrode active material layer in the second region is 0.9t is measured to be 13.0 mm, and a is measured to be 0.00122.

[0140] The positive electrode paste is prepared by mixing nickel cobalt manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode paste is applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare the positive electrode.

[0141] Insert a separator between the positive electrode and the negative electrode, stack them in the order of separator / positive electrode / separator / negative electrode, and then wind them to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region with a constant thickness of the negative electrode active material layer is 65 mm, and the length (c) of the positive electrode active material layer facing the second region with a decreasing thickness of the negative electrode active material layer is 2 mm. In the prepared electrode assembly, a(b + 2c) is calculated to be 0.0845.

[0142] Insert the electrode assembly prepared as described above into a cylindrical battery can, and then inject an electrolyte to prepare a 4680 battery cell.

[0143] Example 3

[0144] Mix a negative electrode active material (a mixture of graphite:SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. Apply the negative electrode slurry to one surface of a copper current collector sheet, dry it at 150 °C, and roll it to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode is 0.1580 mm, and the length (x) of the negative electrode is 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region with a constant thickness of the negative electrode active material layer and the second region with a decreasing thickness of the negative electrode active material layer and the point where the thickness of the negative electrode active material layer in the second region is 0.9t is measured to be 13.0 mm, and a is measured to be 0.00122.

[0145] Prepare a positive electrode slurry by mixing nickel-cobalt-manganese-based lithium oxide (NCM) as a positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. Apply the positive electrode slurry to one surface of an aluminum current collector sheet, dry it at 120 °C, and roll it to prepare a positive electrode.

[0146] Insert a separator between the positive electrode and the negative electrode, stack them in the order of separator / positive electrode / separator / negative electrode, and then wind them to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region with a constant thickness of the negative electrode active material layer is 65 mm, and the length (c) of the positive electrode active material layer facing the second region with a decreasing thickness of the negative electrode active material layer is 3 mm. In the prepared electrode assembly, a(b + 2c) is calculated to be 0.0870.

[0147] Insert the electrode assembly prepared as described above into a cylindrical battery can, and then inject an electrolyte to prepare a 4680 battery cell.

[0148] Example 4

[0149] The negative electrode active material (a mixture of graphite:SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode was 0.1595 mm, and the length (x) of the negative electrode was 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer was constant and the second region where the thickness of the negative electrode active material layer decreased and the point where the thickness of the negative electrode active material layer in the second region was 0.9t was measured to be 12.2 mm, and a was measured to be 0.00131.

[0150] The positive electrode slurry was prepared by mixing nickel-cobalt-manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry was applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0151] A separator was inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer was constant was 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreased was 1 mm. In the prepared electrode assembly, a(b + 2c) was calculated to be 0.0881.

[0152] 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.

[0153] Example 5

[0154] The negative electrode active material (a mixture of graphite and SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode was 0.1582 mm, and the length (x) of the negative electrode was 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer was constant and the second region where the thickness of the negative electrode active material layer decreased and the point where the thickness of the negative electrode active material layer in the second region was 0.9t was measured to be 12.1 mm, and a was measured to be 0.00131.

[0155] The positive electrode slurry was prepared by mixing nickel cobalt manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry was applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0156] A separator was inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer was constant was 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreased was 2 mm. In the prepared electrode assembly, a(b + 2c) was calculated to be 0.0907.

[0157] The electrode assembly prepared as described above was inserted into a cylindrical battery can, and then an electrolyte was injected to prepare a 4680 battery cell.

[0158] Example 6

[0159] The negative electrode active material (a mixture of graphite and SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode was 0.1569 mm, and the length (x) of the negative electrode was 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer was constant and the second region where the thickness of the negative electrode active material layer decreased and the point where the thickness of the negative electrode active material layer in the second region was 0.9t was measured to be 12.0 mm, and a was measured to be 0.00131.

[0160] The positive electrode slurry was prepared by mixing nickel cobalt manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry was applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0161] A separator was inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer was constant was 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreased was 3 mm. In the prepared electrode assembly, a(b + 2c) was calculated to be 0.0933.

[0162] 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.

[0163] Comparative Example 1

[0164] The negative electrode active material (a mixture of graphite:SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry is applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode is 0.1605 mm, and the length (x) of the negative electrode is 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer is constant and the second region where the thickness of the negative electrode active material layer decreases and the point where the thickness of the negative electrode active material layer in the second region is 0.9t is measured to be 2.7 mm, and a is measured to be 0.00590.

[0165] The positive electrode slurry is prepared by mixing nickel cobalt manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry is applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0166] A separator is inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer is constant is 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreases is 1 mm. In the prepared electrode assembly, a(b + 2c) is calculated to be 0.3954.

[0167] The electrode assembly prepared as described above is inserted into a cylindrical battery can, and then an electrolyte is injected to prepare a 4680 cell.

[0168] Comparative Example 2

[0169] The negative electrode active material (a mixture of graphite and SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry is applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode is 0.1546 mm, and the length (x) of the negative electrode is 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer is constant and the second region where the thickness of the negative electrode active material layer decreases and the point where the thickness of the negative electrode active material layer in the second region is 0.9t is measured to be 2.6 mm, and a is measured to be 0.00590.

[0170] The positive electrode slurry is prepared by mixing nickel-cobalt-manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry is applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0171] A separator is inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer is constant is 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreases is 2 mm. In the prepared electrode assembly, a(b + 2c) is calculated to be 0.4072.

[0172] The electrode assembly prepared as described above is inserted into a cylindrical battery can, and then an electrolyte is injected to prepare a 4680 battery cell.

[0173] Comparative Example 3

[0174] The negative electrode active material (a mixture of graphite:SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode was 0.1487 mm, and the length (x) of the negative electrode was 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer was constant and the second region where the thickness of the negative electrode active material layer decreased and the point where the thickness of the negative electrode active material layer in the second region was 0.9t was measured to be 2.5 mm, and a was measured to be 0.00590.

[0175] The positive electrode slurry was prepared by mixing nickel cobalt manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry was applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0176] A separator was inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer was constant was 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreased was 3 mm. In the prepared electrode assembly, a(b + 2c) was calculated to be 0.4191.

[0177] 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.

[0178] Comparative Example 4

[0179] The negative electrode active material (a mixture of graphite and SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry is applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode is 0.1595 mm, and the length (x) of the negative electrode is 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer is constant and the second region where the thickness of the negative electrode active material layer decreases and the point where the thickness of the negative electrode active material layer in the second region is 0.9t is measured to be 2.0 mm, and a is measured to be 0.00803.

[0180] A positive electrode slurry is prepared by mixing nickel-cobalt-manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry is applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0181] A separator is inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer is constant is 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreases is 1 mm. In the prepared electrode assembly, a(b + 2c) is calculated to be 0.5380.

[0182] The electrode assembly prepared as described above is inserted into a cylindrical battery can, and then an electrolyte is injected to prepare a 4680 cell.

[0183] Comparative Example 5

[0184] The negative electrode active material (a mixture of graphite:SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry is applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode is 0.1515 mm, and the length (x) of the negative electrode is 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer is constant and the second region where the thickness of the negative electrode active material layer decreases and the point where the thickness of the negative electrode active material layer in the second region is 0.9t is measured to be 1.9 mm, and a is measured to be 0.00803.

[0185] The positive electrode slurry is prepared by mixing nickel-cobalt-manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry is applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0186] A separator is inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer is constant is 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreases is 2 mm. In the prepared electrode assembly, a(b + 2c) is calculated to be 0.5540.

[0187] The electrode assembly prepared as described above is inserted into a cylindrical battery can, and then an electrolyte is injected to prepare a 4680 battery cell.

[0188] Comparative Example 6

[0189] The negative electrode active material (a mixture of graphite:SiO with a weight ratio of 96.5:3.5), a conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed in water at a weight ratio of 98:0.05:1.1:0.85 to prepare a negative electrode slurry. The negative electrode slurry is applied to one surface of a copper current collector sheet, dried at 150 °C, and rolled to prepare a negative electrode. The thickness (t) of the negative electrode active material layer in the prepared negative electrode is 0.1435 mm, and the length (x) of the negative electrode is 70 mm. In addition, the distance (Δx) in the longitudinal direction between the boundary point between the first region where the thickness of the negative electrode active material layer is constant and the second region where the thickness of the negative electrode active material layer decreases and the point where the thickness of the negative electrode active material layer in the second region is 0.9t is measured to be 1.8 mm, and a is measured to be 0.00803.

[0190] The positive electrode slurry is prepared by mixing nickel cobalt manganese-based lithium oxide (NCM) as the positive electrode active material, carbon nanotubes, and a PVDF binder in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6. The positive electrode slurry is applied to one surface of an aluminum current collector sheet, dried at 120 °C, and rolled to prepare a positive electrode.

[0191] A separator is inserted between the positive electrode and the negative electrode, stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to prepare an electrode assembly. Here, the length (b) of the positive electrode active material layer facing the first region where the thickness of the negative electrode active material layer is constant is 65 mm, and the length (c) of the positive electrode active material layer facing the second region where the thickness of the negative electrode active material layer decreases is 3 mm. In the prepared electrode assembly, a(b + 2c) is calculated to be 0.5701.

[0192] The electrode assembly prepared as described above is inserted into a cylindrical battery can, and then an electrolyte is injected to prepare a 4680 cell.

[0193] Experimental Example

[0194] For the 4680 cells of Examples 1 to 6 and Comparative Examples 1 to 6, the initial capacity is measured. The initial capacity is measured by charging under CC / CV conditions with a cut-off at 1 / 3C, 4.2V, and 1 / 100C, and discharging under CC conditions with a cut-off at 19.1W and 2.5V.

[0195] [Table 1]

[0196] t a(b + 2c) Initial Capacity (mAh) Example 1 0.1605 0.0821 96818 Example 2 0.1592 0.0845 97137 Example 3 0.1580 0.0870 97033 Example 4 0.1595 0.0881 96798 Example 5 0.1582 0.0907 97103 Example 6 0.1569 0.0933 96992 Comparative Example 1 0.1605 0.3954 96605 Comparative Example 2 0.1546 0.4072 96512 Comparative Example 3 0.1487 0.4191 95987 Comparative Example 4 0.1595 0.5380 96643 Comparative Example 5 0.1515 0.5540 96578 Comparative Example 6 0.1435 0.5701 95850

[0197] As shown in Table 1, it can be seen that Examples 1 to 6 (where the value of the thickness (t) of the negative electrode active material layer is greater than the value of a(b + 2c)) exhibit a high initial capacity due to a small cell capacity loss, while the 4680 cells of Comparative Examples 1 to 6 (where the value of the thickness (t) of the negative electrode active material layer is less than the value of a(b + 2c)) have a low initial capacity.

[0198] [Description of Reference Numerals]

[0199] 10: Positive electrode

[0200] 11: Positive electrode current collector

[0201] 12: Positive electrode active material layer

[0202] 20: Separator

[0203] 30: Negative electrode

[0204] 31: Negative electrode active material layer

[0205] 32: Negative electrode current collector

Claims

1. 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. Wherein, The positive electrode includes a positive electrode current collector and a positive electrode active material layer. Wherein, the negative electrode includes an uncoated portion where no negative electrode active material layer is formed on the negative electrode current collector and a coated portion where a negative electrode active material layer is formed on the negative electrode current collector. Wherein, the coated portion includes a first region where the thickness of the negative electrode active material layer is constant and a second region where the thickness of the negative electrode active material layer decreases, and Wherein, the electrode assembly satisfies the following equation (1): Equation (1): t≥a(b + 2c) Wherein, t is the thickness (mm) of the negative electrode active material layer in the first region, b is the length (mm) where the first region faces the positive electrode active material layer, c is the length (mm) where the second region faces the positive electrode active material layer, and a is a value represented by the following equation (2): Equation (2): a = 0.1t / △x Wherein, △x is the longitudinal distance (mm) between the boundary point between the first region and the second region and the point where the thickness of the negative electrode active material layer in the second region is 0.9t.

2. The electrode assembly according to claim 1, Wherein, a is from 0.0001 to 0.

01.

3. The electrode assembly according to claim 1, Wherein, b is from 60 mm to 69 mm.

4. The electrode assembly according to claim 1, Wherein, c is from 0.1 mm to 5 mm.

5. The electrode assembly according to claim 1, Wherein, The length (x) of the negative electrode active material layer is from 60 mm to 95 mm.

6. The electrode assembly according to claim 1, Wherein, t is from 0.100 mm to 0.180 mm.

7. The electrode assembly according to claim 1, Wherein, c / b in Equation (1) is 0.22 or less.

8. The electrode assembly according to claim 1, Wherein, The negative electrode current collector is a thin copper film.

9. The electrode assembly according to claim 1, Wherein, The negative electrode active material included in the negative electrode active material layer is formed of a mixture of graphite and SiO.

10. The electrode assembly according to claim 9, Wherein, Based on the total weight of the negative electrode active material, the content of SiO is from 1 wt% to 5 wt%.

11. A lithium secondary battery, the lithium secondary battery Comprises: The electrode assembly according to claim 1; an electrolyte; and a battery can 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 lithium secondary battery has a form factor ratio of 0.4 or greater.

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 negative electrode defines an electrode terminal.

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