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, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer, and the negative electrode includes a plain portion where the negative electrode active material layer is not formed on the negative electrode current collector, and a ground portion where the negative electrode active material layer is formed on the negative electrode current collector, and the ground 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 for a cylindrical lithium secondary battery satisfies the following formula (1): [Mathematical formula 1] Formula (1): t≧a(b+2c)

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0181141, filed on December 21, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

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

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

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

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

[0006] However, electrodes with both coated and uncoated regions have a sliding region between the coated and uncoated regions where the loading capacity decreases. Because the size of the negative electrode is generally larger than that of the positive electrode, there is a region where the sliding region of the negative electrode faces the positive electrode active material layer, resulting in a low N / P ratio (negative electrode capacity / positive electrode capacity). If the N / P ratio (negative electrode capacity / positive electrode capacity) in this region is less than 100%, stability issues such as lithium precipitation can occur during operation of the secondary battery.

[0007] To solve this problem, if the N / P ratio is adjusted to be 100% or higher even in the area where the anode sliding region and the cathode active material layer face each other, the N / P ratio at the center of the anode must be designed to be much larger. This design requires an increased anode loading, which increases the thickness of the anode. However, if the outer diameter of the lithium secondary battery can is constant and the anode thickness increases, the inserted electrode length decreases, which can actually reduce cell capacity.

[0008] Therefore, there is a need for a technique for maximizing cell capacity in an electrode assembly that includes a negative electrode having a coated portion and an uncoated portion. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to obtain a lithium secondary battery having maximum capacity by minimizing capacity loss caused by a reduction in the length of an electrode inserted into an electrode assembly while further utilizing the area where the sliding region of the negative electrode and the positive electrode active material layer face each other. [Means for solving the problem]

[0010] The present invention aims to solve the above problem by adjusting the thickness of the negative electrode active material layer, the length of the area where the first region where the thickness of the negative electrode active material layer is constant faces the positive electrode active material layer, the length of the area where the second region (sliding region) where the thickness of the negative electrode active material layer decreases faces the positive electrode active material layer, and the slope of the start of the sliding region in a negative electrode including a coated portion and an uncoated portion so that they satisfy specific relational expressions.

[0011] Specifically, the present invention provides 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, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer, and the negative electrode includes a plain portion where the negative electrode active material layer is not formed on the negative electrode current collector, and a ground portion where the negative electrode active material layer is formed on the negative electrode current collector, and the ground 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 for a cylindrical lithium secondary battery satisfies the following formula (1):

[0012] [Mathematical formula 1] Formula (1): t≧a(b+2c)

[0013] The t is the thickness (mm) of the negative electrode active material layer in the first region, b is the length (mm) of the face between the first region and the positive electrode active material layer, c is the length (mm) of the face between the second region and the positive electrode active material layer, and a is a value represented by the following formula (2):

[0014] [Mathematical formula 2] Formula (2): a=0.1t / △x

[0015] The Δx is the distance (mm) in the longitudinal direction between the boundary point between the first region and the second region and the point in the second region where the thickness of the negative electrode active material layer becomes 0.9t.

[0016] The present invention also provides a lithium secondary battery including the electrode assembly, an electrolyte, and a battery can containing the electrode assembly and the electrolyte. [Effects of the Invention]

[0017] A negative electrode having a coated portion and an uncoated portion has a sliding region. The sliding region is a region where the loading amount of the negative electrode active material is reduced, i.e., the thickness of the negative electrode active material layer is reduced. When the sliding region is designed to face the positive electrode, the sliding region also contributes to the capacity of the secondary battery, which can result in an increase in the total cell capacity.

[0018] However, because the negative electrode loading amount decreases in the sliding region, the N / P ratio (negative electrode capacity / positive electrode capacity) becomes less than 100%, and when the N / P ratio is less than 100%, stability issues such as lithium precipitation can occur during operation of the secondary battery. To resolve this stability issue, the thickness of the negative electrode can be increased to increase the N / P ratio at the center of the negative electrode, preventing the N / P ratio from becoming less than 100% in the sliding region. However, for a given external specification of a lithium secondary battery, increasing the thickness of the negative electrode reduces the length of the inserted electrode assembly, which can actually reduce the total cell capacity.

[0019] As in the embodiment of the present invention, when the thickness of the negative electrode active material layer, the length where the first region where the negative electrode active material layer has a constant thickness faces the positive electrode active material layer, the length where the second region (sliding region) where the thickness of the negative electrode active material layer decreases faces the positive electrode active material layer, and the slope of the start of the sliding region are adjusted to satisfy specific relationships, it is possible to minimize capacity loss caused by a reduction in the length of the electrode inserted into the electrode assembly while still using the region where the sliding region of the negative electrode faces the positive electrode active material layer.

[0020] Specifically, if the length of the positive electrode is increased to increase the capacity of a lithium secondary battery, the negative electrode facing the increased length of the positive electrode, particularly the negative electrode sliding area, must also be increased in loading to prevent N / P ratio reversal. The greater the area of ​​contact between the negative electrode sliding area and the positive electrode, the greater the risk of problems such as short circuits caused by N / P ratio reversal between the positive and negative electrodes. Increasing the negative electrode loading to address this issue results in an increase in the thickness of the negative electrode. In the case of cylindrical or prismatic batteries, the battery can size is limited, so increasing the thickness of the negative electrode reduces the insertion length (P) of the negative electrode. For example, the insertion length of the negative electrode is shown as P in Figure 2 and refers to the length in the direction in which the negative electrode is wound.

[0021] Because it is difficult to design the positive electrode facing the negative electrode to have a larger area than the negative electrode due to the risk of N / P reversal, the negative electrode insertion length decreases, which in turn decreases the positive electrode insertion length. Consequently, the total capacity of a lithium secondary battery decreases as the positive electrode insertion length decreases.

[0022] The present invention has the effect of maximizing the negative electrode sliding area while minimizing the reduction in the positive electrode insertion length, thereby enabling the lithium secondary battery to exhibit the highest capacity while resolving stability issues caused by N / P ratio inversion.

[0023] Furthermore, lithium secondary batteries containing the same have the advantage of being less susceptible to defects due to disconnection and having excellent durability. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a side view of an electrode assembly illustrating the structure of the electrode assembly according to one embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the negative electrode 30 of FIG. [Figure 3] FIG. 2 is an enlarged view of an example of region A in FIG. [Figure 4] FIG. 2 is an enlarged view of an example of region A in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be described in more detail below.

[0026] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his or her invention.

[0027] The present invention provides 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, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer, and the negative electrode includes a plain portion where the negative electrode active material layer is not formed on the negative electrode current collector, and a ground portion where the negative electrode active material layer is formed on the negative electrode current collector, and the ground 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 is characterized by satisfying the following formula (1):

[0028] [Mathematical formula 1] Formula (1): t≧a(b+2c)

[0029] The t is the thickness (mm) of the negative electrode active material layer in the first region, b is the length (mm) of the face between the first region and the positive electrode active material layer, c is the length (mm) of the face between the second region and the positive electrode active material layer, and a is a value represented by the following formula (2):

[0030] [Mathematical formula 2] Formula (2): a=0.1t / △x

[0031] The Δx is the distance (mm) in the longitudinal direction between the boundary point between the first and second regions and the point in the second region where the thickness of the negative electrode active material layer becomes 0.9t. The a in the formula (2) represents the average slope of the sliding region up to the region where the thickness of the negative electrode becomes 0.1t.

[0032] When the thickness of the negative electrode active material layer satisfies the relationship of specific formula (1) among the length where the first region where the thickness of the negative electrode active material layer is constant faces the positive electrode active material layer, the length where the second region (sliding region) where the thickness of the negative electrode active material layer decreases faces the positive electrode active material layer, and the slope of the start portion of the sliding region, a lithium secondary battery with maximum capacity can be provided by minimizing capacity loss caused by a decrease in the length of the inserted electrode while still using the region where the sliding region of the negative electrode faces the positive electrode active material layer.

[0033] In Equation (1), t is the thickness of the negative electrode active material layer 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 is constant. Since an actual negative electrode does not have a perfectly constant thickness, the region where the thickness is constant may have a thickness error of 0.05t or less.

[0034] The value of t may 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.

[0035] When the length of the negative electrode active material layer is x, x may be 60 mm to 95 mm, preferably 65 mm to 90 mm, and most preferably 69 mm to 86 mm.

[0036] In the formula (1), a is a value expressed by the following formula (2), and is the average slope of the portion 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 means the average slope of the start of the sliding region (second region). The start of the sliding region may decrease at a constant slope as shown in the example of FIG. 3, or may not decrease at a constant slope as shown in the example of FIG. 4.

[0037] [Mathematical formula 2] Formula (2): a=0.1t / △x

[0038] In the formula (2), a may be 0.0001 to 0.01, preferably 0.0005 to 0.008, and most preferably 0.001 to 0.002.

[0039] In the formula (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 in the second region where the thickness of the negative electrode active material layer becomes 0.9t. Δx may be 1.5 mm to 20 mm, preferably 10 mm to 15 mm, and most preferably 12 mm to 13.5 mm.

[0040] In the formula (1), b is the facing length (mm) between the first region where the negative electrode active material layer has a constant thickness and the positive electrode active material layer, and may be 60 mm to 69 mm, preferably 64 mm to 66 mm, and most preferably 64.5 mm to 65.5 mm.

[0041] In the formula (1), c is the facing length (mm) between the second region where the thickness of the negative electrode active material layer is reduced and the positive electrode active material layer, i.e., the facing length between the negative electrode sliding region and the positive electrode active material layer. The c may be 0.1 mm to 5 mm, preferably 0.5 mm to 4.5 mm, and most preferably 1 mm to 4 mm.

[0042] In the formula (1), c / b may be 0.22 or less, preferably 0.01 to 0.20, and most preferably 0.02 to 0.10.

[0043] The negative electrode included in the electrode assembly according to an embodiment of the present invention includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode current collector includes a coated portion having the negative electrode active material layer formed on at least one surface thereof, and an uncoated portion on the negative electrode current collector where the negative electrode active material layer is not formed.

[0044] The negative electrode active material layer may contain a negative electrode active material, a conductive material, and a binder. Specifically, the negative electrode can be produced by applying a negative electrode slurry, which 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, or water, onto one or both surfaces of a long sheet-like negative electrode current collector, removing the solvent of the negative electrode slurry by a drying process, and then rolling. On the other hand, when applying the negative electrode slurry, a negative electrode including a plain portion can be produced by a method in which the negative electrode slurry is not applied to a partial region of the negative electrode current collector, for example, one end of the negative electrode current collector.

[0045] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; silicon-based materials such as Si, Si-Me alloy (where Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), and Si-C composite; lithium metal thin film; and metal materials capable of alloying with lithium such as Sn and Al. Among them, any one or a mixture of two or more of them may be used.

[0046] Preferably, the negative electrode according to an embodiment of the present invention may contain a silicon-based negative electrode active material. The silicon-based negative electrode active material may be Si, Si-Me alloy (where Me is at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), Si-C composite, or a combination thereof, and preferably, it may be SiOy (where 0 < y < 2). Since the silicon-based negative electrode active material has a high theoretical capacity, when the silicon-based negative electrode active material is included, the capacity characteristics can be improved.

[0047] On the one hand, the silicon-based negative electrode active material is M , ,

[0051] , ,

[0052] It may be doped with a metal. Here, the M b The metal may be a Group 1 metal element or a Group 2 metal element. Specifically, it may be Li, Mg, etc. Specifically, the silicon negative electrode active material is M b It may be Si doped with a metal, SiOy (where 0 < y < 2), a Si-C composite, etc. In the case of a metal-doped silicon-based negative electrode active material, the capacity of the active material decreases slightly due to the doping element, but since it has high efficiency, a high energy density can be realized.

[0048] In addition, the silicon-based negative electrode active material may further include a carbon coating layer on the surface of the particles. Here, the amount of the carbon coating may be 20% by weight or less, preferably 1 - 20% by weight, based on the total weight of the silicon-based negative electrode active material.

[0049] In addition, the negative electrode may further include a carbon-based negative electrode active material as the negative electrode active material as needed. 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.

[0050] On the other hand, when a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material is used as the negative electrode active material, the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material may be 1:99 - 20:80, preferably 1:99 - 15:85, more preferably 1:99 - 10:90 in weight ratio. Most preferably, the negative electrode active material is composed of a mixture of graphite and SiO, and SiO may be contained at 1 - 5% by weight based on the total weight of the negative electrode active material.

[0051] The negative electrode active material may be contained at 80 - 99% by weight, preferably 85 - 99% by weight, more preferably 90 - 99% by weight based on the total weight of the negative electrode active material layer.

[0052] Meanwhile, as the negative electrode current collector, a negative electrode current collector generally used in the technical field can be used. For example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used, but a copper thin film is most preferred.

[0053] The negative electrode current collector may have a thickness of typically 3 to 500 μm, and like the positive electrode current collector, the surface of the current collector may be provided with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, or a nonwoven fabric.

[0054] The conductive material is used to impart conductivity to the negative electrode. Any conductive material can be used without particular limitations, as long as it does not undergo chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may typically be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0055] The binder functions to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0056] A positive electrode according to an embodiment of the present invention includes a positive electrode current collector and a positive electrode active material layer. The positive electrode according to an embodiment of the present invention can be fabricated by coating one or both sides of a long sheet-shaped positive electrode current collector with a positive electrode slurry prepared by dispersing a positive electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and then drying the coated positive electrode slurry to remove the solvent. The coated positive electrode can also be fabricated by not coating a portion of the positive electrode current collector, for example, one end of the positive electrode current collector, with the positive electrode slurry.

[0057] The positive electrode current collector may be any of various positive electrode current collectors used in the art. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Forming fine irregularities on the surface of the positive electrode current collector can also enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric. Most preferably, an aluminum thin film can be used in terms of adjusting the elongation ratio.

[0058] On the other hand, as the positive electrode active material, a positive electrode active material generally used in the technical field can be used.

[0059] Preferably, the positive electrode active material may contain a lithium nickel-based oxide, specifically, a lithium nickel-based oxide containing 80 mol% or more of Ni relative to the total number of moles of transition metals. Preferably, the lithium nickel-based oxide may contain 80 mol% or more but less than 100 mol%, 82 mol% or more but less than 100 mol%, or 83 mol% or more but less than 100 mol% of Ni. As described above, when a lithium nickel-based oxide with a high Ni content is used, a high capacity can be achieved.

[0060] More specifically, the positive electrode active material may contain a lithium nickel-based oxide represented by the following [Chemical Formula 3].

[0061] [Chemical formula 3] Li x Ni y Co z M 1 d M 2 e O2

[0062] In the above formula 3, M 1It may be Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

[0063] Said M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. The M 2 element is not necessarily included, but when included in an appropriate amount, it plays a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0064] Said x represents the molar ratio of lithium in the lithium nickel-based oxide, and may 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 is stably formed.

[0065] Said y represents the molar ratio of nickel in all metals excluding lithium in the lithium nickel-based oxide, and may be 0.85 ≦ y < 1, 0.86 ≦ y < 1, or 0.88 ≦ y < 1. When the molar ratio of nickel satisfies the above range, it exhibits a high energy density and can achieve a high capacity.

[0066] Said z represents the molar ratio of cobalt in all metals excluding lithium in the lithium nickel-based oxide, and may 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.

[0067] Said d represents the molar ratio of the M 1 element in all metals excluding lithium in the lithium nickel-based oxide, and may be 0 < d < 0.15, 0 < d < 0.14, or 0.01 ≦ d ≦ 0.12.M 1When the molar ratio of the elements satisfies the above range, the positive electrode active material has excellent structural stability.

[0068] The e is M in all metals other than lithium in the lithium nickel-based oxide. 2 It indicates the molar ratio of elements, and may be 0≦e≦0.1 or 0≦e≦0.05.

[0069] Meanwhile, the cathode active material according to an embodiment of the present invention may further include, if necessary, a coating layer on the surface of the lithium nickel-based oxide particles, the coating layer including one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. Preferably, the coating element may be Al, B, Co, or a combination thereof, and most preferably, the coating element may be B.

[0070] When a coating layer is present on the surface of the lithium nickel-based oxide particles, the coating layer suppresses contact between the electrolyte and the lithium composite transition metal oxide, thereby achieving the effect of reducing elution of the transition metal and generation of gas due to side reactions with the electrolyte.

[0071] The positive electrode active material may be contained in an amount of 80 to 99 wt %, preferably 85 to 99 wt %, and more preferably 90 to 99 wt %, based on the total weight of the positive electrode active material layer.

[0072] Meanwhile, the positive electrode active material according to an embodiment of the present invention may have a unimodal particle size distribution or a bimodal particle size distribution. By using a positive electrode active material having a unimodal distribution, an increase in resistance can be minimized. When a bimodal positive electrode active material is used, which is a mixture of a large particle size positive electrode active material having a large average particle size and a small particle size positive electrode active material having a small average particle size, the electrode density is improved.

[0073] The form of the positive electrode active material is not particularly limited, and may be in the form of secondary particles formed by aggregation of a plurality of primary particles, in the form of a single particle formed by one primary particle, or in the form of a combination thereof.

[0074] Preferably, the positive electrode active material may include a positive electrode active material consisting of a single particle formed from one primary particle and / or similar single particles that are an aggregate of 10 or less primary particles. By using a positive electrode active material consisting of a single particle formed from one primary particle and / or similar single particles that are an aggregate of 10 or less primary particles as the positive electrode active material, a large cylindrical battery that achieves high capacity and is excellent in safety can be obtained.

[0075] Conventionally, positive electrode active materials for lithium secondary batteries have typically been spherical secondary particles formed by agglomeration of tens to hundreds of primary particles. However, such positive electrode active materials in the form of secondary particles formed by agglomeration of many primary particles are prone to particle fracture, in which the primary particles separate during the rolling process during positive electrode production, leading to problems such as internal cracks during charge and discharge. Particle fracture or internal cracks in the positive electrode active material increase the contact area with the electrolyte, resulting in increased gas generation due to side reactions with the electrolyte. Increased gas generation within a cylindrical battery increases the internal pressure of the battery, potentially leading to a battery explosion. In particular, increasing the volume of a cylindrical battery increases the amount of active material within the battery, significantly increasing the amount of gas generation, further increasing the risk of battery fire and / or explosion.

[0076] In contrast, positive electrode active materials in the form of single particles consisting of one primary particle or similar single particles consisting of an aggregation of 10 or fewer primary particles have higher particle strength than conventional positive electrode active materials in the form of secondary particles in which tens to hundreds of primary particles are aggregated, and therefore hardly suffer particle breakage during rolling. Furthermore, in the case of positive electrode active materials in the form of single particles or similar single particles, because the number of primary particles constituting the particle is small, changes due to expansion and contraction of the volume of the primary particles during charge and discharge are small, and therefore the occurrence of cracks inside the particles is also significantly reduced.

[0077] Therefore, when a positive electrode active material consisting of single particles and / or similar single particles is used, the amount of gas generated due to particle destruction and internal cracking can be significantly reduced, thereby achieving excellent safety even in large cylindrical batteries.

[0078] On the other hand, the positive electrode active material consisting of the single particles and / or similar single particles is preferably contained in an amount of 95% by weight to 100% by weight, preferably 98% by weight to 100% by weight, more preferably 99% by weight to 100% by weight, and even more preferably 100% by weight, based on the total weight of the positive electrode active material contained in the positive electrode active material layer. When the content of the single particles and / or similar single particles satisfies the above range, sufficient safety can be obtained when applied to large cylindrical batteries.

[0079] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it does not undergo chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may typically be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0080] The binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0081] The separator separates the negative electrode and the positive electrode to provide a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used. Specifically, the separator may be a porous polymer film, such as a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a separator coated with a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength.

[0082] The positive electrode and the negative electrode may have an uncoated portion and a coated portion. The uncoated portion may be formed into a plurality of segments that can be bent independently, and at least some of the segments may be bent toward the winding center of the electrode assembly.

[0083] The segment pieces may be formed by processing the positive and negative current collectors through a metal foil cutting process such as laser notching, ultrasonic cutting, or punching.

[0084] When the plain portion is processed into multiple segmented pieces, the stress applied to the plain portion during bending can be reduced, preventing deformation or damage to the plain portion and improving the welding characteristics with the current collecting plate.

[0085] The current collecting plate and the plain portion are typically joined by welding. To improve welding characteristics, strong pressure must be applied to the welded area of ​​the plain portion to bend it as flat as possible. However, during this bending process, the shape of the plain portion may become irregularly distorted and deformed, and the deformed portion may come into contact with the electrode of the opposite polarity, causing an internal short circuit or inducing microcracks in the plain portion. However, if the plain portion is processed into multiple segments that can be bent independently, the stress applied to the plain portion during bending is alleviated, minimizing deformation and damage to the plain portion.

[0086] Furthermore, when the non-coating portion is processed into segmented pieces as described above, the segmented pieces overlap each other during folding, thereby increasing the welding strength with the current collecting plate, and when using cutting-edge technology such as laser welding, this can prevent the laser from penetrating into the electrode assembly and ablating the separator or active material. It is preferable that at least a portion of the folded segmented pieces overlap at the upper and lower ends of the electrode assembly, and that the current collecting plate be bonded to the overlapped segmented pieces.

[0087] The lithium secondary battery according to the embodiment of the present invention may be a cylindrical lithium secondary battery. The cylindrical lithium secondary battery may be a large cylindrical battery having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of a cylindrical battery divided by the diameter of the cylindrical battery) of 0.4 or more. Here, the form factor refers to values ​​indicating the diameter and height of a cylindrical battery.

[0088] Cylindrical batteries according to embodiments of the present invention may have, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 4875 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), a 4680 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575), or a 4695 cell (diameter 46 mm, height 95 mm, form factor ratio 0.484). In the form factor numbers, the first two digits indicate the cell diameter, and the next two or three digits indicate the cell height.

[0089] The cylindrical lithium secondary battery according to the embodiment of the present invention significantly reduces the amount of gas generated compared to conventional batteries, thereby achieving excellent safety even in large cylindrical batteries with a form factor ratio of 0.4 or more.

[0090] Meanwhile, cylindrical batteries according to embodiments of the present invention are batteries with a tabless structure that does not include an electrode tab. Cylindrical lithium secondary batteries according to embodiments of the present invention may have a tabless structure in which at least a portion of the uncoated region of the negative electrode defines an electrode tab. Cylindrical lithium secondary batteries according to embodiments of the present invention may also have a tabless structure in which at least a portion of the uncoated region of the negative electrode defines an electrode tab. Specifically, the uncoated region may be formed elongated along the winding direction at an end of one side of the current collector. A current collecting plate may be bonded to each of the positive and negative uncoated regions, and the current collecting plate may be connected to an electrode terminal, thereby realizing a tabless battery.

[0091] For example, a tabless battery can be manufactured using the following method. First, a separator, a positive electrode, a separator, and a negative electrode are sequentially stacked so that the uncoated portions of the positive and negative electrodes face each other, and then the stack is wound in one direction to form a jelly-roll electrode assembly. The uncoated portions of the positive and negative electrodes are then folded toward the center of the winding. Current collecting plates are then welded to the uncoated portions of the positive and negative electrodes, respectively, and the current collecting plates are connected to electrode terminals to form a tabless battery. Meanwhile, the current collecting plates have a larger cross-sectional area than strip-type electrode tabs, and their resistance is inversely proportional to the cross-sectional area of ​​the path through which current flows. Therefore, when a secondary battery is constructed in this manner, cell resistance can be significantly reduced. Furthermore, when a cylindrical lithium secondary battery is constructed in this manner, current concentration is reduced compared to conventional batteries with electrode tabs, which effectively reduces heat generation within the battery, thereby improving the thermal stability of the battery.

[0092] The battery can is electrically connected to the uncoated portion of the electrode and functions as an electrode terminal that contacts an external power source and transmits current applied from the external power source to the electrode.

[0093] The electrolyte used in the cylindrical lithium secondary battery according to the embodiment of the present invention may include a lithium salt, an organic solvent, and an additive.

[0094] The lithium salt is used as an electrolyte salt in a lithium secondary battery and is used as a medium for transferring ions. Generally, the lithium salt contains, for example, Li as a cation. + and the anion is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - At least one selected from the group consisting of:

[0095] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI), or a mixture of two or more selected from the group consisting of: LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries can be used without limitation.

[0096] In order to achieve optimal electrolyte impregnation for large-capacity cylindrical lithium secondary batteries, the lithium salt may be contained in the electrolyte at a concentration of 1.0 M to 1.5 M, preferably 1.1 M to 1.3 M. When the concentration of the lithium salt satisfies the above range, the cycle characteristics of the lithium secondary battery are sufficiently improved during high-temperature storage, and the viscosity of the nonaqueous electrolyte is appropriate, thereby improving electrolyte impregnation.

[0097] 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.

[0098] Specifically, the organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixed organic solvent thereof.

[0099] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and therefore easily dissociates the lithium salt in the electrolyte. Specific examples of the cyclic carbonate organic solvent include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among these, ethylene carbonate may be included.

[0100] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and a representative example thereof may be at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate. Specifically, the linear carbonate organic solvent may include ethyl methyl carbonate (EMC).

[0101] In addition, in order to produce an electrolyte having high ionic conductivity, the organic solvent may further include at least one ester organic solvent selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents in addition to at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents.

[0102] Specific examples of such linear ester-based organic solvents include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0103] The cyclic ester organic solvent may be at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0104] Meanwhile, the organic solvent may further include any organic solvent commonly used in non-aqueous electrolytes, as needed, without limitation, for example, at least one of an ether-based organic solvent, a glyme-based organic solvent, and a nitrile-based organic solvent.

[0105] The ether solvent may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more thereof, but is not limited thereto.

[0106] The glyme-based solvent has a higher dielectric constant and lower surface tension than linear carbonate-based organic solvents and is less reactive with metals, and may include, but is not limited to, at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME).

[0107] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0108] In addition, the non-aqueous electrolyte according to an embodiment of the present invention may contain an electrolyte additive to prevent the breakdown of the negative electrode due to decomposition of the non-aqueous electrolyte in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0109] Representative examples of such electrolyte additives may include at least one additive for forming an SEI film selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

[0110] Examples of the cyclic carbonate compounds include vinylene carbonate (VC) and vinylethylene carbonate.

[0111] The halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0112] The sultone compound includes at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0113] Examples of the sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0114] The phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalate)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(2,2,2-trifluoroethyl)phosphite.

[0115] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0116] Examples of the nitrile compound include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0117] The benzene-based compound includes fluorobenzene, the amine-based compound includes triethanolamine and ethylenediamine, and the silane-based compound includes tetravinylsilane.

[0118] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include lithium difluorophosphate (LiDFP), LiPO2F2, and LiBF4.

[0119] The present invention will be described in more detail below with reference to specific examples. [Example]

[0120] <Example> [Example 1] Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1605 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness reaches 0.9t was measured as 13.2 mm, and a was measured as 0.00122.

[0121] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0122] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to prepare an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 1 mm. The calculated value of a(b + 2c) for the prepared electrode assembly was 0.0821.

[0123] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0124] [Example 2] Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1592 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness reaches 0.9t was measured as 13.0 mm, and a was measured as 0.00122.

[0125] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0126] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 2 mm. The calculated value of a(b + 2c) for the fabricated electrode assembly was 0.0845.

[0127] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0128] [Example 3] Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1580 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness becomes 0.9t was measured as 13.0 mm, and a was measured as 0.00122.

[0129] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0130] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 3 mm. The calculated value of a(b + 2c) for the fabricated electrode assembly was 0.0870.

[0131] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0132] [Example 4] Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1595 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness reaches 0.9t was measured as 12.2 mm, and a was measured as 0.00131.

[0133] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0134] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 1 mm. For the fabricated electrode assembly, a(b + 2c) was calculated to be 0.0881.

[0135] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0136] [Example 5] Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1582 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness reaches 0.9t was measured as 12.1 mm, and a was measured as 0.00131.

[0137] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0138] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 2 mm. The calculated value of a(b + 2c) for the fabricated electrode assembly was 0.0907.

[0139] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0140] [Example 6] Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1569 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness becomes 0.9t was measured as 12.0 mm, and a was measured as 0.00131.

[0141] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0142] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 3 mm. The calculated value of a(b + 2c) for the fabricated electrode assembly was 0.0933.

[0143] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0144] [Comparative Example 1] Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1605 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness becomes 0.9t was measured as 2.7 mm, and a was measured as 0.00590.

[0145] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0146] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 1 mm. For the fabricated electrode assembly, a(b + 2c) was calculated to be 0.3954.

[0147] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0148] Comparative Example 2 Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1546 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness reaches 0.9t was measured as 2.6 mm, and a was measured as 0.00590.

[0149] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0150] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 2 mm. The calculated value of a(b + 2c) for the fabricated electrode assembly was 0.4072.

[0151] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0152] Comparative Example 3 Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1487 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness reaches 0.9t was measured as 2.5 mm, and a was measured as 0.00590.

[0153] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0154] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 3 mm. The calculated value of a(b + 2c) for the fabricated electrode assembly was 0.4191.

[0155] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0156] Comparative Example 4 Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1595 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness becomes 0.9t was measured as 2.0 mm, and a was measured as 0.00803.

[0157] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0158] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 1 mm. For the fabricated electrode assembly, a(b + 2c) was calculated to be 0.5380.

[0159] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0160] Comparative Example 5 Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1515 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness becomes 0.9t was measured as 1.9 mm, and a was measured as 0.00803.

[0161] A positive electrode slurry was prepared by mixing a positive electrode active material (nickel-cobalt-manganese-based lithium oxide (NCM), carbon nanotubes, and a PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one side of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a positive electrode.

[0162] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 2 mm. For the fabricated electrode assembly, a(b + 2c) was calculated to be 0.5540.

[0163] The electrode assembly prepared as above was inserted into a cylindrical battery can, and then an electrolyte was poured into it to prepare a 4680 cell.

[0164] Comparative Example 6 Anode slurry was prepared by mixing anode active material (a mixture of graphite and SiO2 in a weight ratio of 96.5:3.5), conductive material (carbon nanotubes), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to fabricate an anode. The anode had a thickness (t) of 0.1435 mm and a length (x) of 70 mm. The longitudinal distance (Δx) between the boundary between the first region (where the anode active material layer has a constant thickness) and the second region (where the anode active material layer thickness decreases) and the point in the second region where the anode active material layer thickness reaches 0.9t was measured as 1.8 mm, and a was measured as 0.00803.

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

[0166] A separator was interposed between the positive and negative electrodes, and the electrodes were stacked in the order separator / positive electrode / separator / negative electrode, followed by winding to fabricate an electrode assembly. The facing length b between the first region where the negative electrode active material layer had a constant thickness and the positive electrode active material layer was 65 mm, and the facing length c between the second region where the negative electrode active material layer had a reduced thickness and the positive electrode active material layer was 3 mm. The calculated value of a(b + 2c) for the fabricated electrode assembly was 0.5701.

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

[0168] <Experimental Example> The initial capacity of the 4680 cells was measured in Examples 1 to 6 and Comparative Examples 1 to 6. The initial capacity was measured by charging under CC / CV conditions at 1 / 3 C, 4.2 V, and 1 / 100 C cut-off, and discharging under CC conditions at 19.1 W and 2.5 V cut-off.

[0169] [Table 1]

[0170] As shown in Table 1, Examples 1 to 6, in which the thickness t of the negative electrode active material layer is greater than the value a(b+2c), have a small loss of cell capacity and therefore a high initial capacity, whereas the 4680 cells of Comparative Examples 1 to 6, in which the thickness t of the negative electrode active material layer is smaller than the value a(b+2c), have a low initial capacity. [Explanation of symbols]

[0171] 10 positive electrode 11 Positive electrode current collector 12 Cathode active material layer 20 Separation membrane 30 negative electrode 31 Negative electrode active material layer 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, the positive electrode includes a positive electrode current collector and a positive electrode active material layer, the negative electrode includes a non-coated portion on a negative electrode current collector where no negative electrode active material layer is formed, and a coated portion on a negative electrode current collector where a negative electrode active material layer is formed, the landed 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; An electrode assembly that satisfies the following formula (1): [Mathematical formula 1] Formula (1): t≧a(b+2c) the t is the thickness (mm) of the negative electrode active material layer in the first region, the b is the length (mm) of the first region facing the positive electrode active material layer, and the c is the length (mm) of the second region facing the positive electrode active material layer; a is a value represented by the following formula (2), [Mathematical formula 2] Formula (2): a=0.1t / △x The Δx is the distance (mm) in the longitudinal direction between the boundary point between the first region and the second region and the point in the second region where the thickness of the negative electrode active material layer becomes 0.9t.

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

01.

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

4. 3. The electrode assembly according to claim 1, wherein c is 0.1 mm to 5 mm.

5. 3. The electrode assembly according to claim 1, wherein the length x of the negative electrode active material layer is 60 mm to 95 mm.

6. 3. The electrode assembly according to claim 1, wherein t is 0.100 mm to 0.180 mm.

7. 3. The electrode assembly according to claim 1, wherein in the formula (1), c / b is 0.22 or less.

8. The electrode assembly of claim 1 , wherein the negative electrode current collector is a copper thin film.

9. 3. The electrode assembly of claim 1, wherein the negative electrode active material contained in the negative electrode active material layer is a mixture of graphite and SiO.

10. 10. The electrode assembly of claim 9, wherein the negative electrode active material contains 1 to 5 wt % of SiO based on the total weight of the negative electrode active material.

11. A lithium secondary battery comprising the electrode assembly according to claim 1 or 2, an electrolyte, and a battery can containing 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 more.

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

Images