Electrode assembly and lithium secondary battery containing 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 priority under Korean Patent Application No. 10-2022-0181141, filed on 21 December 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

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

[0003] As technologies such as electric vehicles and portable electronic devices advance, the demand for lithium-ion batteries as an energy source is rapidly increasing.

[0004] Lithium-ion batteries are classified into cylindrical, prismatic, and pouch-type batteries depending on the shape of the battery case. Of these, cylindrical batteries consist of an electrode assembly, manufactured by sequentially stacking sheet-shaped positive electrode, separator membrane, and negative electrode in a cylindrical battery case and then winding it in one direction, which is then housed inside the battery case and sealed by covering the top with a cap plate. The positive and negative electrodes are provided with strip-shaped positive and negative electrode tabs, respectively, and these tabs are connected to electrode terminals to electrically connect to an external power source. The positive electrode terminal is the cap plate, and the negative electrode terminal is the battery case. However, in the case of conventional cylindrical batteries with such a structure, current is concentrated in the strip-shaped electrode tabs, resulting in high resistance, excessive heat generation, and poor current collection efficiency.

[0005] In that case, the problem of current concentration around the electrode tabs can be solved by applying a structure in which the plain areas of the positive and negative electrodes serve as electrode tabs without forming separate electrode tabs (for example, a tabless structure).

[0006] However, for an electrode having a land portion and a non-land portion, there is a sliding region where the loading amount decreases in the middle connecting the land portion to the non-land 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 faces the positive electrode active material layer, and in that region, the N / P ratio (negative electrode capacity / positive electrode capacity) becomes low. When the N / P ratio (negative electrode capacity / positive electrode capacity) in that region is less than 100%, problems of stability such as lithium precipitation may occur during the operation of the secondary battery.

[0007] In order to solve the above problems, when adjusting so that the N / P ratio is 100% or more even in the region where the sliding region of the negative electrode faces the positive electrode active material layer, the N / P ratio at the center of the negative electrode has to be designed much larger. When designed in such a way, since the negative electrode loading amount has to be increased, the thickness of the negative electrode increases. However, the outer diameter specification of the can of the lithium secondary battery is constant, and when the thickness of the negative electrode increases, the length of the electrode to be inserted decreases, and conversely, the cell capacity may decrease.

[0008] Therefore, there is a need for a technique to maximize the cell capacity in an electrode assembly including a negative electrode having a land portion and a non-land portion.

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to obtain a lithium secondary battery having the maximum capacity by minimizing the capacity loss caused by the decrease in the length of the electrode inserted into the electrode assembly while further using the region where the sliding region of the negative electrode faces the positive electrode active material layer.

Means for Solving the Problems

[0010] In the negative electrode including a land portion and a non-land portion, by adjusting the thickness of the negative electrode active material layer, the length where the first region with a constant thickness of the negative electrode active material layer 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 inclination at the start of the sliding region so as to satisfy a specific relational expression, an attempt is made to solve the above problems.

[0011] Specifically, 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, the negative electrode includes a non-land portion where no negative electrode active material layer is formed on the negative electrode current collector, and a land portion where a negative electrode active material layer is formed on the negative electrode current collector, the land 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 provides an electrode assembly for a cylindrical lithium secondary battery that 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) 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 formula (2).

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

[0015] The △x is the length direction 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 becomes 0.9t.

[0016] Also provided is a lithium secondary battery including the electrode assembly, an electrolyte, and a battery can in which the electrode assembly and the electrolyte are housed.

Effects of the Invention

[0017] A sliding region exists in the negative electrode where a textured area and a textured area are formed. This 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 contributes to the capacity of the secondary battery, and an increase in the total cell capacity can be expected.

[0018] However, since the amount of negative electrode loading 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 falls below 100%, stability problems such as lithium deposition during operation of the secondary battery are likely to occur. To solve the stability problem, the N / P ratio can be increased in the center of the negative electrode by increasing the thickness of the negative electrode, thereby preventing the N / P ratio from falling below 100% in the sliding region. However, if the external dimensions of the lithium secondary battery remain constant, increasing the thickness of the negative electrode reduces the length of the electrode assembly that is inserted, which may actually decrease 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 of the area where the first region with a constant negative electrode active material layer faces the positive electrode active material layer, the length of the area where the second region (sliding region) with a decreasing negative electrode active material layer faces the positive electrode active material layer, and the inclination of the starting part of the sliding region are adjusted to satisfy a specific relationship, it is possible to minimize the capacitance loss caused by the reduction in the length of the electrode inserted into the electrode assembly, even while further utilizing the area where the sliding region of the negative electrode and the positive electrode active material layer face each other.

[0020] Specifically, when increasing the length of the positive electrode to increase the capacity of a lithium secondary battery, the loading amount of the negative electrode, particularly the negative electrode sliding region, which faces the lengthened positive electrode, must also be increased to prevent reversal of the N / P ratio. The more the negative electrode sliding region faces the positive electrode, the more problems such as short circuits caused by the reversal of the N / P ratio between the positive and negative electrodes occur. Increasing the loading amount of the negative electrode to solve this problem results in an increase in the thickness of the negative electrode. In the case of cylindrical and prismatic batteries, the size of the battery can is limited, so increasing the thickness of the negative electrode reduces the negative electrode insertion length (P). For example, the negative electrode insertion length is shown as P in Figure 2, and it represents the length in the direction in which the negative electrode is wound.

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

[0022] This invention has the effect of solving the stability problem caused by the reversal of the N / P ratio, while allowing lithium secondary batteries to exhibit the highest capacity, by maximizing the use of the negative electrode sliding region and minimizing the reduction in the insertion length of the positive electrode.

[0023] Furthermore, lithium-ion rechargeable batteries containing this technology have the advantage of being less prone to failure due to wire breakage and possessing superior durability. [Brief explanation of the drawing]

[0024] [Figure 1] This is a side view of an electrode assembly illustrating the structure of an electrode assembly according to one embodiment of the present invention. [Figure 2] Figure 1 is a plan view of the negative electrode 30. [Figure 3] This is an enlarged view of an example of area A in Figure 1. [Figure 4] This is an enlarged view of an example of area A in Figure 1. [Modes for carrying out the invention]

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

[0026] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical concept of the present invention, in accordance with the principle that inventors can appropriately define the concepts of terms in order to best describe their invention.

[0027] The present invention relates to an electrode assembly for a lithium secondary battery, comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, 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 blank portion on the negative electrode current collector where no negative electrode active material layer is formed, and a textured portion on the negative electrode current collector where a negative electrode active material layer is formed, wherein the textured 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 satisfies the following formula (1).

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

[0029] The above t is the thickness (mm) of the negative electrode active material layer in the first region, b is the length (mm) between the first region and the positive electrode active material layer facing each other, c is the length (mm) between the second region and the positive electrode active material layer facing each other, and a is the value expressed by the following formula (2).

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

[0031] The triangle △x is the longitudinal distance (mm) 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. In equation (2), a represents the average slope of the sliding region up to the region where the thickness of the negative electrode becomes 0.1.

[0032] If the thickness of the negative electrode active material layer satisfies the relationship between the length of the first region where the thickness of the negative electrode active material layer is constant and the positive electrode active material layer, the length of the second region (sliding region) where the thickness of the negative electrode active material layer decreases and the positive electrode active material layer, and the slope of the starting part of the sliding region, then a lithium secondary battery with maximum capacity can be provided by minimizing the capacity loss caused by the reduction in the length of the inserted electrode, while still utilizing the region where the sliding region of the negative electrode and the positive electrode active material layer face each other.

[0033] In equation (1) above, 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 of the negative electrode active material layer is constant. Since the actual negative electrode cannot have a perfectly constant thickness, the region with a constant thickness may have a thickness error of up to 0.05t.

[0034] The aforementioned 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] If the length of the negative electrode active material layer is x, then x may be 60 mm to 95 mm, preferably 65 mm to 90 mm, and most preferably 69 mm to 86 mm.

[0036] In equation (1) above, a is a value expressed by equation (2) below, and is the average slope of the portion where the thickness of the negative electrode active material layer begins to decrease at the longitudinal end of the negative electrode current collector. That is, a means the average slope of the beginning of the sliding region (second region). The slope at the beginning of the sliding region may decrease at a constant rate, as illustrated in Figure 3, or it may not decrease at a constant rate, as illustrated in Figure 4.

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

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

[0039] In equation (2) above, △x is the longitudinal distance (mm) 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. △x may be 1.5mm to 20mm, preferably 10mm to 15mm, and most preferably 12mm to 13.5mm.

[0040] In formula (1) above, b is the facing length (mm) between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer. b 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 formula (1) above, c is the facing length (mm) between the second region where the thickness of the negative electrode active material layer decreases and the positive electrode active material layer, that is, 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 formula (1) above, 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 located on the negative electrode current collector, wherein the negative electrode current collector includes a surface area on which the negative electrode active material layer is formed on at least one surface, and a surface area on which 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 is formed 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 through a drying process, and then rolling it. On the other hand, when applying the negative electrode slurry, a negative electrode without a coating can be manufactured by not applying the negative electrode slurry 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 one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), and Si-C composite; a thin film of lithium metal; 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 one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), Si-C composite, or a combination thereof, and preferably, it may be SiOy (where 0 < y < 2). Since the silicon-based negative electrode active material has a high theoretical capacity, when the silicon-based negative electrode active material is included, the capacity characteristics can be improved.

[0047] On the one hand, the silicon-based negative electrode active material is M b 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 somewhat 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 a 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 to 20:80, preferably 1:99 to 15:85, more preferably 1:99 to 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] On the other hand, as the negative electrode current collector, a negative electrode current collector commonly used in the art can be used. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy may be used, but most preferably a thin copper film is used.

[0053] The negative electrode current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

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

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

[0056] The 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 manufactured by applying a positive electrode slurry, which is prepared by dispersing a positive electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, to one or both sides of a long sheet-shaped positive electrode current collector, removing the solvent from the positive electrode slurry in a drying step, and then rolling it. On the other hand, when applying the positive electrode slurry, a positive electrode including a plain area can be manufactured by not applying the positive electrode slurry to a part of the positive electrode current collector, for example, one end of the positive electrode current collector.

[0057] As the positive electrode current collector, various positive electrode current collectors used in the relevant technical field can be employed. For example, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. By forming fine irregularities on the surface of the positive electrode current collector, the adhesive force of the positive electrode active material can also be enhanced. The positive electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc. Most preferably, an aluminum thin film can be used in terms of adjusting the elongation rate, etc.

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

[0059] Preferably, the positive electrode active material may contain a lithium nickel-based oxide, and specifically, it may contain a lithium nickel-based oxide containing 80 mol% or more of Ni with respect to the total molar number of transition metals. Preferably, the lithium nickel-based oxide may contain Ni in an amount of 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%. As described above, when a lithium nickel-based oxide with a high Ni content is used, a high capacity can be realized.

[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 Chemical 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 promotes grain growth during firing or plays a role in 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. The M 1When the molar ratio of the elements satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0068] The aforementioned e is M in all metals excluding lithium in lithium nickel oxides. 2 This represents the molar ratio of elements, and may be 0 ≤ e ≤ 0.1 or 0 ≤ e ≤ 0.05.

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

[0070] When a coating layer is present on the surface of lithium nickel oxide particles, the coating layer suppresses contact between the electrolyte and the lithium composite transition metal oxide, thereby reducing the leaching of transition metals and the generation of gases due to side reactions with the electrolyte.

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

[0072] On the other hand, the positive electrode active material according to the 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, the increase in resistance can be minimized. When a bimodal positive electrode active material is used, which is a mixture of a large-particle positive electrode active material with a large average particle size and a small-particle positive electrode active material with a small average particle size, the electrode density is improved.

[0073] The positive electrode active material is not particularly limited in form and may be in the form of secondary particles formed by the aggregation of multiple primary particles, in the form of a single particle consisting of one primary particle, or in a form in which these are combined.

[0074] Preferably, the positive electrode active material may include a positive electrode active material consisting of a single particle made up of one primary particle and / or a similar single particle which is an aggregate of 10 or fewer primary particles. By using a positive electrode active material consisting of a single particle made up of one primary particle and / or a similar single particle which is an aggregate of 10 or fewer primary particles as the positive electrode active material, a large cylindrical battery with high capacity and excellent safety can be obtained.

[0075] Traditionally, lithium secondary batteries commonly used spherical secondary particles, which are aggregates of tens to hundreds of primary particles, as the positive electrode active material. However, with positive electrode active materials in the form of secondary particles aggregated from many primary particles, particle fracture, where primary particles separate during the rolling process in manufacturing the positive electrode, is prone to occur, and cracks can develop inside the particles during the charge and discharge process. When particle fracture or cracks occur inside the particles of the positive electrode active material, the contact area with the electrolyte increases, leading to increased gas generation due to side reactions with the electrolyte. Increased gas generation inside a cylindrical battery increases the pressure inside the battery, posing a risk of explosion. In particular, increasing the volume of a cylindrical battery increases the amount of active material inside the battery, which in turn significantly increases the amount of gas generated, further increasing the risk of battery ignition 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 formed by the aggregation of 10 or fewer primary particles have higher particle strength compared to conventional positive electrode active materials in the form of secondary particles, where tens to hundreds of primary particles are aggregated, resulting in almost no particle fracture during rolling. Furthermore, in the case of positive electrode active materials in the form of single particles or similar single particles, the number of primary particles constituting the particle is small, so there is less change due to the expansion and contraction of the volume of the primary particles during charging and discharging, which significantly reduces the occurrence of cracks inside the particles.

[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 breakage and internal crack formation 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 single particles and / or similar single particles is preferably included in an amount of 95% to 100% by weight, preferably 98% to 100% by weight, more preferably 99% to 100% by weight, and even more preferably 100% by weight, relative to the total weight of the positive electrode active material contained in the positive electrode active material layer. When the content of single particles and / or similar single particles satisfies the above range, sufficient safety can be obtained when applied to large cylindrical batteries.

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

[0080] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used. The binder may be present in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0081] The separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any membrane that is commonly used as a separator in lithium secondary batteries can be used without particular limitations. Specifically, the separation membrane may be a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separation membrane containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength.

[0082] On the other hand, the positive electrode and the negative electrode may have a plain portion and a textured portion. The plain portion may be processed into a plurality of independently bendable segmented pieces, and at least a portion of the plurality of segmented pieces may be bent toward the winding center of the electrode assembly.

[0083] The segmented pieces may be formed by processing the current collectors of the positive and negative electrodes using metal foil cutting processes such as laser notching, ultrasonic cutting, or punching.

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

[0085] The current collector plate and the blank section are generally joined by welding. However, to improve welding characteristics, strong pressure must be applied to the welding area of ​​the blank section to bend it as flat as possible. However, during such bending processes, the shape of the blank section may become irregularly distorted and deformed, and the deformed parts may come into contact with electrodes of opposite polarity, causing an internal short circuit, or inducing micro-cracks in the blank section. However, if the blank section is processed into the form of multiple independently bendable segmented pieces, the stress applied to the blank section during bending is reduced, minimizing deformation and damage to the blank section.

[0086] Furthermore, if the plain portion is processed into the form of segmented pieces as described above, multiple segmented pieces will overlap when bent, thereby increasing the welding strength with the current collector plate. When using advanced technologies such as laser welding, it is possible to prevent the problem of the laser penetrating into the inside of the electrode assembly and ablating the separation film or active material. Preferably, at least a portion of the bent multiple segmented pieces will overlap on the upper and lower ends of the electrode assembly, and the current collector plate will be bonded to the overlapping multiple 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 diameter (Φ) to height (H) of the cylindrical battery, i.e., the value obtained by dividing the diameter of the cylindrical battery by its height) of 0.4 or more. Here, the form factor refers to the values ​​indicating the diameter and height of the cylindrical battery.

[0088] The cylindrical battery according to the embodiment of the present invention may be, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 4875 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), a 4680 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575), or a 4695 cell (diameter 46 mm, height 95 mm, form factor ratio 0.484). In the numerical value indicating the form factor, the first two digits indicate the diameter of the cell, and the next two or three digits indicate the height of the cell.

[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 higher.

[0090] On the other hand, the cylindrical battery according to the embodiment of the present invention is a tabless battery that does not include electrode tabs. The cylindrical lithium secondary battery according to the embodiment of the present invention may have a structure in which at least a part of the blank portion of the negative electrode defines an electrode tab, i.e., a tabless structure. Furthermore, the cylindrical lithium secondary battery according to the embodiment of the present invention may have a structure in which at least a part of the blank portion of the negative electrode defines an electrode tab, i.e., a tabless structure. Specifically, the blank portion may be formed to be long along the winding direction at the end of one side of the current collector, and a current collector plate can be attached to the respective blank portions of the positive electrode and the negative electrode, and the current collector plate can be connected to the electrode terminals to realize a tabless battery.

[0091] For example, a tabless battery can be manufactured by the following method. First, a separator membrane, a positive electrode, a separator membrane, and a negative electrode are sequentially stacked so that the blank portions of the positive and negative electrodes are positioned in opposite directions, and then wound in one direction to manufacture a jelly roll type electrode assembly. Subsequently, the blank portions of the positive and negative electrodes are bent towards the center of the winding, and then current collector plates are welded to the blank portions of the positive and negative electrodes, respectively, and the current collector plates are connected to the electrode terminals to manufacture a tabless battery. On the other hand, the current collector plate has a larger cross-sectional area than a strip-type electrode tab, and resistance is inversely proportional to the cross-sectional area of ​​the current passage, so if a secondary battery is made with the above structure, the cell resistance can be significantly reduced. Furthermore, if a cylindrical lithium secondary battery is made with the tabless structure as described above, there is less current concentration compared to a conventional battery with electrode tabs, so heat generation inside the battery can be effectively reduced, thereby improving the thermal stability of the battery.

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

[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 additives.

[0094] The lithium salt is used as an electrolyte salt in lithium secondary batteries and is used as a medium for transferring ions. Typically, lithium salts include, for example, Li as a cation. + It includes, and as an anion, 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 of the following can be selected from the group consisting of these.

[0095] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 It may also contain a single substance or a mixture of two or more substances 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 as electrolytes in lithium secondary batteries can be used without limitation.

[0096] The lithium salt may be included in the electrolyte at a concentration of 1.0 M to 1.5 M, preferably 1.1 M to 1.3 M, in order to achieve optimal electrolyte impregnation for large-capacity cylindrical lithium secondary batteries. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of the lithium secondary battery is sufficient, and the viscosity of the non-aqueous electrolyte is appropriate, thus improving the 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 mixture thereof.

[0099] The aforementioned cyclic carbonate-based organic solvent is a highly viscous organic solvent with a high dielectric constant, which facilitates the dissociation of lithium salts in electrolytes. Specific examples of such organic solvents include at least one 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 also be included.

[0100] Furthermore, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant. Typical examples 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).

[0101] Furthermore, in order to produce an electrolyte having high ionic conductivity, the organic solvent may further contain 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] Furthermore, the cyclic ester organic solvents include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0104] On the other hand, the organic solvent may further contain any organic solvent commonly used with non-aqueous electrolytes, as needed. For example, it may further contain at least one or more organic solvents from among ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0105] 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), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more of these, but is not limited to these.

[0106] The aforementioned glyme-based solvent is a solvent that has a higher dielectric constant and lower surface tension than linear carbonate-based organic solvents, and has low reactivity with metals. It 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, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited to these.

[0108] Furthermore, the non-aqueous electrolyte according to the embodiment of the present invention may contain electrolyte additives to prevent the non-aqueous electrolyte from decomposing and causing the anode to collapse 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 swelling at high temperatures.

[0109] Such electrolyte additives may include, as a typical example, at least one SEI film-forming additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

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

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

[0112] Examples of the sultone compounds include at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone.

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

[0114] Examples of the phosphate compound include 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 compounds include tetraphenyl borate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate borate (LiB(C2O4)2, LiBOB).

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

[0117] Examples of the benzene-based compound include fluorobenzene, examples of the amine-based compound include triethanolamine and ethylenediamine, and examples of the silane-based compound include tetravinylsilane.

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

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

[0120] <Examples> [Example 1] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1605 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 13.2 mm, and a was measured to be 0.00122.

[0121] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0122] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 1 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.0821.

[0123] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0124] [Example 2] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1592 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 13.0 mm, and a was measured to be 0.00122.

[0125] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0126] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 2 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.0845.

[0127] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0128] [Example 3] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, and then dried at 150°C and rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1580 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 13.0 mm, and a was measured to be 0.00122.

[0129] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0130] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 3 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.0870.

[0131] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0132] [Example 4] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1595 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 12.2 mm, and a was measured to be 0.00131.

[0133] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0134] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 1 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.0881.

[0135] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0136] [Example 5] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, and then dried at 150°C and rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1582 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 12.1 mm, and a was measured to be 0.00131.

[0137] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0138] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 2 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.0907.

[0139] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0140] [Example 6] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1569 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 12.0 mm, and a was measured to be 0.00131.

[0141] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0142] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 3 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.0933.

[0143] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0144] [Comparative Example 1] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, and then dried at 150°C and rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1605 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 2.7 mm, and a was measured to be 0.00590.

[0145] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0146] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 1 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.3954.

[0147] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0148] [Comparative Example 2] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1546 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 2.6 mm, and a was measured to be 0.00590.

[0149] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0150] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 2 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.4072.

[0151] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0152] [Comparative Example 3] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1487 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 2.5 mm, and a was measured to be 0.00590.

[0153] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0154] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 3 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.4191.

[0155] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0156] [Comparative Example 4] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1595 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 2.0 mm, and a was measured to be 0.00803.

[0157] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0158] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 1 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.5380.

[0159] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0160] [Comparative Example 5] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, and then dried at 150°C and rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1515 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 1.9 mm, and a was measured to be 0.00803.

[0161] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0162] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 2 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.5540.

[0163] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

[0164] [Comparative Example 6] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite: SiO = 96.5:3.5 by weight ratio), a conductive material (carbon nanotube), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 98:0.05:1.1:0.85. The negative electrode slurry was applied to one surface of a copper current collector sheet, and then dried at 150°C and rolled to produce a negative electrode. In the produced negative electrode, the thickness t of the negative electrode active material layer was 0.1435 mm, and the length x of the negative electrode was 70 mm. Furthermore, the longitudinal distance △x 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, was measured to be 1.8 mm, and a was measured to be 0.00803.

[0165] A positive electrode slurry was prepared by mixing nickel-cobalt-manganese lithium oxide (NCM), carbon nanotubes, and a PVDF binder in N-methylpyrrolidone in 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 then rolled to produce the positive electrode.

[0166] An electrode assembly was manufactured by interposing a separation membrane between the positive electrode and the negative electrode, stacking them in the order of separation membrane / positive electrode / separation membrane / negative electrode, and then winding them up. Here, the face-to-face length b between the first region, where the thickness of the negative electrode active material layer is constant, and the positive electrode active material layer was 65 mm, and the face-to-face length c between the second region, where the thickness of the negative electrode active material layer decreases, and the positive electrode active material layer was 3 mm. In the manufactured electrode assembly, a(b+2c) was calculated to be 0.5701.

[0167] The electrode assemblies manufactured as described above were inserted into a cylindrical battery case, and then the electrolyte was injected to produce 4680 cells.

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

[0169] [Table 1]

[0170] As shown in Table 1 above, 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), have low cell capacity loss and therefore high initial capacity, while Comparative Examples 1 to 6, with their 4680 cells, where the value of the thickness t of the negative electrode active material layer is less than the value of a(b+2c), have 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 separation membrane 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 plain portion on the negative electrode current collector where no negative electrode active material layer is formed, and a portion where a negative electrode active material layer is formed on the negative electrode current collector. The aforementioned land area includes 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 decreases. An electrode assembly that satisfies the following equation (1). [Mathematical formula 1] Formula (1): t≧a(b+2c) The above t is the thickness (mm) of the negative electrode active material layer in the first region, b is the length (mm) between the first region and the positive electrode active material layer facing each other, and c is the length (mm) between the second region and the positive electrode active material layer facing each other. a is a value expressed by the following formula (2): [Mathematical formula 2] Formula (2): a=0.1t / △x The triangle △x is the longitudinal distance (mm) 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.

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

01.

3. The electrode assembly according to claim 1 or 2, wherein b is 60 mm to 69 mm.

4. The electrode assembly according to claim 1 or 2, wherein c is 0.1 mm to 5 mm.

5. The electrode assembly according to claim 1 or 2, wherein the length x of the negative electrode active material layer is 60 mm to 95 mm.

6. The electrode assembly according to claim 1 or 2, wherein t is 0.100 mm to 0.180 mm.

7. The electrode assembly according to claim 1 or 2, wherein in formula (1), c / b 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 or 2, wherein the negative electrode active material contained in the negative electrode active material layer consists of a mixture of graphite and SiO.

10. The electrode assembly according to claim 9, wherein SiO is contained in 1 to 5% by weight relative to the total weight of the negative electrode active material.

11. A lithium secondary battery comprising an electrode assembly according to claim 1 or 2, an electrolyte, and a battery case in which the electrode assembly and the electrolyte are housed.

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

13. The lithium secondary battery according to claim 12, wherein the 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 plain portion of the negative electrode has a structure that defines an electrode tab.

Images