Cylindrical lithium secondary battery

Abstract

The present invention provides a cylindrical lithium secondary battery including an electrode assembly in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction, a battery can in which the electrode assembly is housed, an electrolyte injected into the battery can, and a seal for sealing an open end of the battery can, wherein the positive electrode plate and the negative electrode plate each include a plain portion on which no active material layer is formed, and at least a portion of the plain portion of the positive electrode plate or the plain portion of the negative electrode plate defines an electrode tab, and the cylindrical lithium secondary battery has a form factor ratio of 0. The present invention relates to a cylindrical lithium secondary battery, wherein the electrolyte contains a lithium salt, an organic solvent, and an additive, and the additive contains a compound represented by Chemical Formula 1, a cyclic carbonate compound, and 1,3-propane sultone, the compound represented by Chemical Formula 1 being contained in an amount of 0.5 wt% to 5.0 wt% based on the total content of the electrolyte, and the compound represented by Chemical Formula 1, the cyclic carbonate compound, and 1,3-propane sultone being contained in a weight ratio of 1:0.5:0.2 to 1:20:10.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0182368 filed December 22, 2022 and Korean Patent Application No. 10-2023-0187677 filed December 20, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a cylindrical lithium secondary battery. [Background technology]

[0003] BACKGROUND ART With technological advances in electric vehicles, portable electronic devices, and the like, the demand for lithium secondary batteries as energy sources is rapidly increasing.

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

[0005] Meanwhile, with the recent development of electric vehicle technology, the demand for high-capacity batteries has increased, necessitating the development of large-volume cylindrical batteries. Conventionally, the small cylindrical batteries commonly used, i.e., cylindrical batteries with 1865 or 2170 form factors, have small capacities, so resistance and heat generation do not seriously affect battery performance.

[0006] However, applying the specifications of conventional small cylindrical batteries to large cylindrical batteries without modification can result in serious battery safety issues. Specifically, as the battery size increases, the amount of heat and gas generated inside the battery also increases. This heat and gas can increase the temperature and pressure inside the battery, potentially leading to battery fire or explosion. To prevent this, the heat and gas inside the battery must be properly discharged to the outside. To achieve this, the cross-sectional area of ​​the battery, which serves as a path for dissipating heat to the outside of the battery, must increase in line with the increase in volume. However, because the increase in cross-sectional area typically does not match the increase in volume, the amount of heat generated inside the battery increases as the battery size increases, resulting in increased risk of explosion and reduced output. Furthermore, when fast charging at high voltages, a large amount of heat is generated around the electrode tabs in a short period of time, potentially leading to battery fire.

[0007] Therefore, there is a need to develop a cylindrical battery that can maintain high safety even at high power output. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems, and has an object to provide a cylindrical lithium secondary battery that can maintain high safety even at high power output by improving electrolyte impregnation by applying an electrolyte of a specific composition and controlling the amount of gas generated inside the battery. [Means for solving the problem]

[0009] According to one embodiment, the present invention provides a cylindrical lithium secondary battery including an electrode assembly in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction, a battery can in which the electrode assembly is housed, an electrolyte injected into the battery can, and a seal for sealing an open end of the battery can, wherein the positive electrode plate and the negative electrode plate each include a plain portion on which no active material layer is formed, and at least a portion of the plain portion of the positive electrode plate or the plain portion of the negative electrode plate defines an electrode tab, and the cylindrical lithium secondary battery has a form factor ratio of The electrode assembly has a core diameter of 5 mm to 8 mm, the electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive, and the additive includes a compound represented by Chemical Formula 1 below, a cyclic carbonate compound, and 1,3-propane sultone, the compound represented by Chemical Formula 1 below being included in an amount of 0.5 wt % to 5.0 wt % based on the total content of the electrolyte, and the compound represented by Chemical Formula 1 below, the cyclic carbonate compound, and 1,3-propane sultone are included in a weight ratio of 1:0.5:0.2 to 1:20:10.

[0010] [Chemical formula 1] [ka]

[0011] In the above Chemical Formula 1, n is an integer from 3 to 10.

[0012] According to another embodiment, the present invention provides a battery pack including the cylindrical lithium secondary battery according to the present invention. [Effects of the Invention]

[0013] The cylindrical lithium secondary battery having a form factor ratio within a specific range according to the present invention uses an electrolyte containing specific additives at specific content ratios, thereby controlling the amount of gas generated inside the battery and adjusting the internal pressure of the cell. This maximizes the impregnation of the electrolyte into the electrode assembly, thereby ensuring high thermal stability even at high output. [Brief explanation of the drawings]

[0014] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical concept of the present invention, and therefore the present invention should not be interpreted as being limited only to the matters depicted in such drawings.

[0015] [Figure 1] 4 is a diagram showing a stacked state of an electrode assembly according to the present invention before being wound up; FIG. [Figure 2] 2 is a cross-sectional view showing a structure of an electrode plate of an electrode assembly according to an embodiment of the present invention; [Figure 3] 1 is a cross-sectional view showing the structure of a cylindrical battery with a tabless structure according to one embodiment of the present invention. [Figure 4] FIG. 10 is a cross-sectional view showing the structure of a cylindrical battery with a tabless structure according to another embodiment of the present invention. [Figure 5] 1A and 1B are diagrams illustrating a structure of an electrode assembly according to an embodiment of the present invention; [Figure 6] 1 is a diagram illustrating a battery pack according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in more detail below.

[0017] 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, in accordance with the principle that an inventor can appropriately define the concept of a term in order to best describe his or her invention.

[0018] In the present invention, "primary particles" refers to particle units that do not appear to have grain boundaries when observed under a scanning electron microscope at a magnification of 5,000 to 20,000 times. "Average particle size of primary particles" refers to the arithmetic mean value calculated after measuring the particle sizes of primary particles observed under a scanning electron microscope image.

[0019] In the present invention, "secondary particles" are particles formed by agglomeration of a plurality of primary particles. In order to distinguish them from conventional secondary particles formed by agglomeration of tens to hundreds of primary particles, secondary particles formed by agglomeration of 10 or less primary particles are referred to as pseudo-single particles.

[0020] In the present invention, the "average particle size D 50 " refers to the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder, and can be measured using the laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W. After obtaining a volume cumulative particle size distribution graph, the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0021] In the present invention, the phrase "consist essentially of A" indicates that the component A is contained as the main component, and means that the component A is contained in an amount of, for example, 95% by weight to 100% by weight, preferably 98% by weight to 100% by weight, and more preferably 99% by weight to 100% by weight.

[0022] In conventional large cylindrical lithium secondary batteries, the impregnation of electrolyte varies depending on the degree of gas generation inside the cell and the internal pressure of the cell. In particular, when an electrode assembly having a core diameter (diameter) of 5 mm to 8 mm is applied to a large cylindrical battery, it is difficult to control the impregnation of electrolyte, and safety cannot be sufficiently ensured. In contrast, the cylindrical lithium secondary battery of the present invention uses an electrolyte of a specific composition to adjust the amount of gas generation inside the cell and control the internal pressure of the cell, thereby improving the impregnation of electrolyte into the electrode assembly, thereby achieving the effect of improving the thermal stability of the battery.

[0023] The configuration of the cylindrical lithium secondary battery of the present invention will be specifically described below.

[0024] electrode assembly The electrode assembly has a structure in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction.

[0025] FIG. 1 shows the laminated structure of the electrode assembly according to the present invention before being wound up, and FIG. 2 shows the cross-sectional structure of an electrode plate (positive electrode plate or negative electrode plate) according to the present invention.

[0026] Referring to FIGS. 1 and 2, the electrode assembly A of the present invention may be manufactured by winding a stack formed by sequentially stacking a separator 12, a positive electrode plate 10, a separator 12, and a negative electrode plate 11 at least once in one direction X.

[0027] In this case, the positive electrode plate 10 and the negative electrode plate 11 each have a structure in which an active material layer 21 is formed on a long sheet-shaped current collector 20, and may include a plain portion 22 in which the active material layer 21 is not formed in a portion of the current collector 20.

[0028] By using the positive electrode plate 10 and the negative electrode plate 11 including the uncoated portion 22 as described above, a battery with a tabless structure can be realized in which separate electrode tabs are not provided, and at least a portion of the uncoated portion of the positive electrode plate 10 and the negative electrode plate 11 defines the electrode tabs.

[0029] Specifically, the uncoated portion 22 may be formed long along the winding direction X at one end of the current collector 20, and a current collecting plate may be bonded to each of the uncoated portions of the positive electrode plate and the negative electrode plate, and the current collecting plate may be connected to an electrode terminal, thereby realizing a battery with a tab-less structure.

[0030] For example, a tabless battery can be manufactured by the following method. First, a separator, a positive electrode plate, a separator, and a negative electrode plate are sequentially stacked so that the uncoated portions 22 of the positive electrode plate 10 and the negative electrode plate 11 are positioned opposite each other, and then the stack is wound in one direction to manufacture an electrode assembly. The uncoated portions 22 of the positive electrode plate and the negative electrode plate are then bent toward the winding center C, and current collecting plates are welded to the uncoated portions of the positive electrode plate and the negative electrode plate, respectively. The current collecting plates are then connected to electrode terminals to manufacture a tabless battery. Meanwhile, the current collecting plates have a larger cross-sectional area than strip-type electrode tabs, and since their resistance is inversely proportional to the cross-sectional area of ​​the path through which current flows, forming a secondary battery with this structure can significantly reduce cell resistance.

[0031] In addition, the uncoated portions of the positive and negative electrode plates may be processed into a plurality of segments that can be bent independently, and at least some of the plurality of segments may be bent toward the winding center C of the electrode assembly.

[0032] The segments can be formed by processing the current collectors of the positive and negative plates using a metal foil cutting process such as laser notching, ultrasonic cutting, punching, and the like.

[0033] When the uncoated portions of the positive and negative electrode plates are processed into multiple segments, the stress applied to the uncoated portions during bending can be reduced, preventing deformation or damage to the uncoated portions and improving the welding characteristics with the current collecting plate.

[0034] The current collecting plate and the uncoated portion are typically joined by welding. To improve the welding characteristics, strong pressure must be applied to the welded area of ​​the uncoated portion to bend the uncoated portion as flat as possible. However, this bending process can cause the shape of the uncoated portion to become irregularly distorted and deformed. This can lead to contact with the electrode of the opposite polarity, causing an internal short circuit or microcracks in the uncoated portion. However, if the uncoated portions of the positive and negative electrode plates are processed into multiple segments that can be bent independently, stress applied to the uncoated portion during bending can be alleviated, minimizing deformation and damage to the uncoated portion.

[0035] Furthermore, when the uncoated portion is processed into segments as described above, overlaps occur between the segments during folding, which increases the strength of the weld with the current collecting plate and prevents problems such as laser penetration into the electrode assembly and damage to the separator or active material when using cutting-edge technologies such as laser welding. Preferably, at least some of the folded segments may overlap on the upper and lower ends of the electrode assembly, and current collecting plates may be bonded to the overlapping segments.

[0036] Meanwhile, the electrode assembly according to the present invention may be formed in a structure in which an insulating layer 24 is further formed on the positive electrode plate 10, as shown in Fig. 5. Specifically, the insulating layer 24 may be formed to cover a portion of the positive electrode active material layer and a portion of the uncoated portion in a direction parallel to the winding direction of the electrode assembly.

[0037] In a battery with a tabless structure that uses the uncoated portion 22c of the positive electrode plate 10 and the uncoated portion 22a of the negative electrode plate 11 as electrode tabs, the electrode assembly is formed so that the positive electrode plate 10 protrudes above the separator 12 and the negative electrode plate 11 protrudes below the separator 12. The protruding positive electrode plate 10 and / or negative electrode plate 11 are then folded and combined with a current collecting plate. However, when the positive electrode plate 10 or negative electrode plate 11 is folded as described above, the current collector of the positive electrode plate 10 or negative electrode plate 11 passes over the separator and is positioned adjacent to the electrode of the opposite polarity, which can lead to electrical contact between the positive electrode plate and the negative electrode plate, potentially causing an internal short circuit. However, when an insulating layer 24 is formed that covers a portion of the positive electrode active material layer and the uncoated portion, as shown in FIG. 5, the insulating layer 24 can prevent electrical contact between the positive electrode plate 10 and the negative electrode plate 11, thereby preventing a short circuit within the battery.

[0038] Preferably, the insulating layer 24 is provided on at least one surface of the current collector of the positive electrode plate 10, and more preferably, on both surfaces of the positive electrode plate 10.

[0039] Furthermore, the insulating layer 24 may be formed in a region of the positive electrode plate 10 that may face the active material layer 21a of the negative electrode plate 11. For example, the insulating layer 24 may extend to the end of the uncoated portion 22c of the positive electrode plate 10, on the surface that faces the negative electrode plate 11 after being folded. However, on the surface opposite the surface that faces the negative electrode plate 11 after being folded, the insulating layer 24 is preferably formed only on a portion of the uncoated portion 22c, for example, up to the bending point of the uncoated portion 22c. This is because if the insulating layer 24 were formed over the entire uncoated portion on the surface opposite the surface that faces the negative electrode plate 11, electrical contact with the current collecting plate would be impossible and the electrode tab would not function.

[0040] Meanwhile, the insulating layer 24 may be any material or component that can be attached to the positive electrode plate while maintaining insulating properties. For example, the insulating layer may be an insulating coating layer or insulating tape, and the insulating coating layer may contain an organic binder and inorganic particles. In this case, the organic binder may be, for example, styrene-butadiene rubber (SBR), and the inorganic particles may be, but are not limited to, alumina oxide.

[0041] Meanwhile, the diameter of the core portion of the electrode assembly of the present invention may be 5 mm or more, specifically 5 mm to 8 mm. When the diameter of the core portion of the electrode assembly satisfies this range, the defect rate during the winding process for manufacturing the electrode assembly can be reduced, and sufficient space for injecting the electrolyte can be secured inside the cylindrical secondary battery. On the other hand, when the diameter of the core portion of the electrode assembly is less than 5 mm, gas generated by the electrolyte during charge and discharge increases the internal pressure of the cell, which may cause issues such as venting. Conversely, when the diameter of the core portion of the electrode assembly is more than 8 mm, the energy density per cell volume decreases, and wettability with the electrolyte decreases, which may lead to deterioration of cell performance. In particular, for large cylindrical batteries with a form factor of 0.4 or more, maintaining an appropriate level of internal pressure is necessary to improve the wettability of the electrolyte to the electrode assembly and maximize cell performance. Therefore, in the present invention, by using an electrode assembly having a core diameter (diameter) of 5 mm or more, specifically 5 mm to 8 mm, together with an electrolyte having a specific additive composition, the amount of gas generated inside the cell can be adjusted, thereby maintaining the internal pressure of the cell at an appropriate level, thereby improving the impregnation of the electrolyte into the electrode assembly.

[0042] Meanwhile, the overall diameter of the electrode assembly can have a normal diameter that corresponds to a large cylindrical battery with a form factor of 0.4 or greater.

[0043] Next, each component of the electrode assembly of the present invention will be described in more detail.

[0044] (1) Positive electrode plate The positive electrode plate may have a structure in which a positive electrode active material layer is formed on one or both sides of a long sheet-shaped positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material, a conductive material, and a binder.

[0045] Specifically, the positive electrode plate may be manufactured by coating one or both sides of a long sheet-shaped positive electrode current collector with a positive electrode slurry prepared by dispersing a positive electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and then rolling the coated positive electrode current collector after removing the solvent from the positive electrode slurry through a drying process. Meanwhile, a positive electrode plate including a non-coated portion may be manufactured by not coating a portion of the positive electrode current collector, for example, one end of the positive electrode current collector, with the positive electrode slurry during coating.

[0046] 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. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0047] In addition, the positive electrode plate of the present invention may use a positive electrode active material having a Ni content of 80 mol% or more among transition metals other than lithium to achieve high capacity. Specifically, the positive electrode active material may use a positive electrode active material having a Ni content of 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% among metal elements other than lithium, and preferably includes a lithium nickel-based oxide represented by the following [Chemical Formula 2]:

[0048] [Chemical formula 2] Li a Ni b Co c M 1 d M 2 e O2

[0049] In the above formula 2, M 1 may be Mn, Al or a combination thereof, preferably Mn or Mn and Al.

[0050] Said M 2 is at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, preferably at least one selected from the group consisting of Zr, Y, Mg and Ti, more preferably Zr, Y or a combination thereof. 2 Although the elements are not essential, when contained in an appropriate amount, they can play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0051] The a represents the molar ratio of lithium in the lithium nickel-based oxide and may be 0.8≦a≦1.2, or 0.85≦a≦1.15, and more specifically, 0.9≦a≦1.2. When the lithium molar ratio satisfies this range, the crystalline structure of the lithium nickel-based oxide can be stably formed.

[0052] Said b represents the molar ratio of nickel among all the metals excluding lithium in the lithium nickel-based oxide, and it may be 0.85 ≦ b < 1, or may be 0.86 ≦ b < 1, specifically, it may be 0.88 ≦ b < 1. When the molar ratio of nickel satisfies the above range, it shows a high energy density and it is possible to achieve a high capacity.

[0053] Said c represents the molar ratio of cobalt among all the metals excluding lithium in the lithium nickel-based oxide, and it may be 0 < c < 0.15, or may be 0 < c < 0.14, specifically, it may be 0.01 ≦ c ≦ 0.12. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0054] Said d represents the molar ratio of M 1 element among all the metals excluding lithium in the lithium nickel-based oxide, and it may be 0 < d < 0.15, or may be 0 < d < 0.14, specifically, it may be 0.01 ≦ d ≦ 0. 1 When the molar ratio of the M

[0055] Said e represents the molar ratio of M 2 element among all the metals excluding lithium in the lithium nickel-based oxide, and it may be 0 ≦ e ≦ 0.1, or may be 0 ≦ e ≦ 0.05.

[0056] On the other hand, the positive electrode active material according to the present invention may further include, if necessary, a coating layer containing one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S on the surface of the lithium nickel-based oxide particles. Preferably, the coating element may be Al, B, Co, or a combination thereof, and most preferably, the coating element may be B.

[0057] 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 gas generation due to side reactions with the electrolyte.

[0058] 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.

[0059] On the other hand, the form of the positive electrode active material is not particularly limited, and may be a secondary particle form in which a plurality of primary particles are aggregated, a single particle form consisting of one primary particle, or a combination of these forms.

[0060] The secondary particles are advantageous in forming voids in the electrode and improving the wettability of the electrolyte. When the secondary particles and the single particles are used in combination, the secondary particles and the single particles can be mixed in a ratio of 80:20, specifically 50:50.

[0061] Preferably, the positive electrode active material can include a positive electrode active material consisting of a single particle formed from one primary particle and / or a pseudo-single particle which is an aggregate of 10 or less primary particles, or a combination thereof. By using a positive electrode active material consisting of a single particle formed from one primary particle and / or a pseudo-single particle which is an aggregate of 10 or less primary particles as the positive electrode active material, a large cylindrical battery that achieves high capacity and excellent safety can be obtained.

[0062] 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 cracking, in which primary particles are detached during the rolling process during positive electrode manufacturing, and have the problem of internal cracks occurring during charge and discharge. When particle cracking or internal cracks occur in 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 within a cylindrical battery increases the internal pressure of the battery, posing a risk of battery explosion. In particular, when the volume of a cylindrical battery is increased, the amount of active material within the battery increases with the increase in volume, which significantly increases the amount of gas generation, further increasing the risk of battery fire and / or explosion.

[0063] In contrast, positive electrode active materials in the form of single particles consisting of one primary particle or pseudo-single particles in which 10 or fewer primary particles are aggregated have higher particle strength than existing positive electrode active materials in the form of secondary particles in which tens to hundreds of primary particles are aggregated, and therefore hardly ever experience particle cracking during rolling. Furthermore, in the case of positive electrode active materials in the form of single particles or pseudo-single particles, the number of primary particles that make up the particle is small, so there is little change due to volume expansion and contraction of the primary particles during charge and discharge, and therefore the occurrence of cracks inside the particles is significantly reduced.

[0064] Therefore, when a positive electrode active material consisting of single particles and / or pseudo-single particles is used, the amount of gas generated due to particle cracking and internal cracking can be significantly reduced, thereby achieving excellent safety even in large cylindrical batteries.

[0065] The positive electrode active material composed of the single particles and / or pseudo-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 weight of the total positive electrode active material contained in the positive electrode active material layer. When the content of the single particles and / or pseudo-single particles satisfies the above range, sufficient safety can be obtained when applied to large cylindrical batteries.

[0066] On the other hand, the positive electrode active material in the form of single particles and / or pseudo-single particles according to the present invention has an average particle diameter D 50 The average particle size D of the positive electrode active material may be 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less, for example, 0.5 μm to 5 μm, preferably 1 μm to 5 μm, and more preferably 2 μm to 5 μm. 50 When satisfies the above range, the increase in resistance can be minimized.

[0067] A positive electrode active material in the form of a single particle and / or quasi-single particle has fewer interfaces between primary particles, which serve as diffusion paths for lithium ions within the particle, and therefore has a problem of lower lithium mobility than a positive electrode active material in the form of a secondary particle, resulting in increased resistance. This increase in resistance becomes more severe as the particle size increases, and the increased resistance adversely affects capacity and output characteristics. Therefore, in the present invention, the average particle size D 50 By using a single particle or pseudo-single particle positive electrode active material with a particle size of 5 μm or less, the diffusion distance of lithium ions inside the particle is minimized, thereby suppressing an increase in resistance.

[0068] The positive electrode active material in the form of single particles and / or pseudo-single particles may have an average primary particle size of 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less, for example, 0.5 μm to 5 μm, preferably 1 μm to 5 μm, and more preferably 2 μm to 5 μm. When the average primary particle size satisfies the above range, a positive electrode active material in the form of single particles and / or pseudo-single particles with excellent electrochemical properties can be formed. If the average primary particle size is too small, the number of agglomerates of the primary particles forming the positive electrode active material increases, reducing the effect of suppressing particle cracking during rolling. If the average primary particle size is too large, the lithium diffusion path within the primary particles may become longer, increasing resistance and potentially reducing output characteristics.

[0069] Meanwhile, in the present invention, the positive electrode active material in the form of a single particle and / or a quasi-single particle preferably has a unimodal particle size distribution. To improve the electrode density of the positive electrode active material layer, bimodal positive electrode active materials, which combine a large-particle positive electrode active material with a small-particle positive electrode active material, have been widely used. However, in the case of a positive electrode active material in the form of a single particle or a quasi-single particle, increasing particle size significantly increases the lithium migration path, resulting in a significant increase in resistance. Therefore, when large-particle particles are mixed, problems such as reduced capacity and output characteristics may occur. Therefore, in the present invention, a positive electrode active material with a unimodal particle distribution is used to minimize the increase in resistance.

[0070] The conductive material is used to impart conductivity to the electrode and can be any material that exhibits electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite powders such as natural graphite and artificial graphite; carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer 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 can be used alone or in combination. The conductive material is typically 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.

[0071] The binder serves to improve adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples of the binder include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders. These binders may be used alone or in combination. The binder may be contained 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 positive electrode active material layer.

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

[0073] (2) Negative electrode plate The negative electrode plate may have a structure in which a negative electrode active material layer is formed on one or both sides of a long sheet-shaped negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder.

[0074] Specifically, the negative electrode plate may be manufactured by coating one or both sides of a long sheet-shaped negative electrode current collector with a negative electrode slurry prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and then rolling the coated negative electrode current collector after removing the solvent from the negative electrode slurry by a drying process. Meanwhile, a negative electrode plate including a non-coated portion may be manufactured by not coating a portion of the negative electrode current collector, for example, one end of the negative electrode current collector, with the negative electrode slurry during coating.

[0075] The negative electrode active material may include a negative electrode active material capable of reversible intercalation and deintercalation of lithium.

[0076] Preferably, the negative electrode active material can include 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 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.

[0077] On the other hand, the silicon-based negative electrode active material may be doped with M b metal, and at this time, the M b metal may be a Group 1 metal element or a Group 2 metal element, and specifically, may be Li, Mg, etc. Specifically, the silicon negative electrode active material may be Si, SiOy (where 0 < y < 2), Si-C composite, etc. doped with M b metal. In the case of a metal-doped silicon-based negative electrode active material, although the capacity of the active material decreases somewhat due to the doping element, since it has high efficiency, a high energy density can be realized.

[0078] Further, the silicon-based negative electrode active material can further include a carbon coating layer on the particle surface. At this time, 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.

[0079] Also, the negative electrode active material can further include a carbon-based 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.

[0080] 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 to the carbon-based negative electrode active material may be 1:99 to 20:80, preferably 1:99 to 15:85, and more preferably 1:99 to 10:90, by weight.

[0081] The negative electrode active material may be contained in an amount of 80 to 99 wt %, preferably 85 to 99 wt %, and more preferably 90 to 99 wt %, based on the total weight of the negative electrode active material layer.

[0082] Meanwhile, the negative electrode current collector may be a negative electrode current collector commonly used in the art, such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy. The negative electrode current collector may typically have a thickness of 3 to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0083] 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 has electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotubes; metal powder or metal fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material is typically 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.

[0084] The binder serves to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples of the binder include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders, among which one or more may be used alone or in combination. The binder may be contained 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.

[0085] (3) Separator The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitation. Specifically, the separator may be a porous polymer film, such as a porous polymer film made of a polyolefin-based 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. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may also be used.

[0086] Cylindrical lithium secondary battery Next, the cylindrical lithium secondary battery according to the present invention will be described.

[0087] The cylindrical battery according to the present invention may include an electrode assembly in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction; a battery can in which the electrode assembly is housed; an electrolyte injected into the battery can; and a seal that seals an open end of the battery can.

[0088] Preferably, the cylindrical lithium secondary battery according to the present invention may be a large cylindrical battery having a form factor ratio (defined as the ratio of the diameter (T) to the height (H) of a cylindrical battery, i.e., the value obtained by dividing the diameter by the height 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.

[0089] Cylindrical batteries according to the present invention may be, for example, 46110 cells (diameter 46 mm, height 110 mm, form factor ratio 0.418), 48110 cells (diameter 48 mm, height 110 mm, form factor ratio 0.44), 4880 cells (diameter 48 mm, height 80 mm, form factor ratio 0.600), 4680 cells (diameter 46 mm, height 80 mm, form factor ratio 0.58), or 4695 cells (diameter 46 mm, height 95 mm, form factor ratio 0.48). In the form factor number, the first two digits indicate the diameter of the cell, and the following two or three digits indicate the height of the cell.

[0090] The cylindrical lithium secondary battery according to the present invention significantly reduces the amount of gas generated compared to conventional batteries, and as a result, even cylindrical batteries with a form factor ratio of 0.4 to 0.6 can achieve excellent safety.

[0091] Meanwhile, the cylindrical battery according to the present invention may preferably be a battery of tab-less structure that does not include electrode tabs, but is not limited thereto.

[0092] The tabless-structured battery may have a structure in which, for example, each of the positive and negative electrode plates includes an uncoated portion where no active material layer is formed, the uncoated portion of the positive electrode plate and the uncoated portion of the negative electrode plate are located at the upper and lower ends of the electrode assembly, respectively, current collecting plates are bonded to the uncoated portions of the positive and negative electrode plates, and the current collecting plates are connected to electrode terminals.

[0093] Fig. 3 shows a cross-sectional view of a cylindrical battery with a tabless structure according to one embodiment of the present invention. Hereinafter, a cylindrical battery according to one embodiment of the present invention will be described with reference to Fig. 3. However, Fig. 3 merely shows one embodiment of the present invention, and the structure of the cylindrical battery of the present invention is not limited to the scope disclosed in Fig. 3.

[0094] A cylindrical battery 140 according to one embodiment of the present invention includes the above-described electrode assembly 141, a battery can 142 in which the electrode assembly 141 is housed, and a seal 143 that seals the open end of the battery can 142.

[0095] In this case, the positive and negative electrode plates of the electrode assembly may each include an uncoated portion where no active material layer is formed, and may be stacked and wound such that the positive and negative electrode uncoated portions are located at the upper and lower ends of the electrode assembly, respectively. Since the electrode assembly has been described above, only the remaining components excluding the electrode assembly will be described below.

[0096] The battery can 142 is a cylindrical container with an opening at the top and is made of a conductive metal material such as aluminum or steel. The battery can accommodates the electrode assembly 141 in the inner space through the opening at the top, along with an electrolyte (not shown).

[0097] On the other hand, the cylindrical battery 140 of the present invention preferably does not include a current interruption device (CUD).

[0098] (A) Electrolyte The electrolyte used in the cylindrical lithium secondary battery of the present invention includes (i) a lithium salt, (ii) a non-aqueous organic solvent, and (iii) an additive, and the additive (iii) may include a compound represented by the following Chemical Formula 1, a cyclic carbonate compound, and 1,3-propane sultone.

[0099] [Chemical formula 1] [ka]

[0100] In the above Chemical Formula 1, n is an integer from 3 to 10.

[0101] (i) Lithium salt 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. + Contains F as an anion - , 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:

[0102] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl10 , 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 thereof. In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries may be used without limitation.

[0103] The lithium salt may be contained in the electrolyte at a concentration of 1.3 M or less, specifically, 1.2 M to 1.3 M. When the concentration of the lithium salt satisfies this range, the impregnation of the electrolyte into an electrode assembly having a core diameter of 5 mm or more can be improved.

[0104] (ii) Non-aqueous organic solvent The non-aqueous organic solvent may include at least one selected from the group consisting of a cyclic carbonate-based compound, a linear carbonate-based compound, a linear ester-based compound, and a cyclic ester-based compound.

[0105] Specifically, the non-aqueous organic solvent may include a cyclic carbonate compound, a linear carbonate compound, or a mixture thereof.

[0106] The cyclic carbonate-based compound has a high viscosity and a high dielectric constant, and can easily dissociate a lithium salt in the electrolyte. Specific examples of the cyclic carbonate-based compound 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 them, ethylene carbonate can be included.

[0107] The cyclic carbonate compound may be contained in the organic solvent in an amount of 15 to 30% by volume, preferably 15 to 25% by volume, and most preferably 15 to 20% by volume. When the cyclic carbonate compound is contained in the above range, a uniform SEI layer can be formed on the negative electrode plate, thereby improving thermal stability.

[0108] The linear carbonate compound is a compound having low viscosity and low dielectric constant, and representative examples thereof 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, and specifically, ethyl methyl carbonate (EMC).

[0109] In addition, the non-aqueous organic solvent may further include at least one ester-based compound selected from the group consisting of linear ester-based compounds and cyclic ester-based compounds in order to prepare an electrolyte having high ionic conductivity.

[0110] Specific examples of such linear ester compounds include at least one compound selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0111] The cyclic ester compound may be at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0112] (iii) Additives The electrolyte of the present invention may contain, as additives, a compound represented by the following Chemical Formula 1, a cyclic carbonate compound, and 1,3-propane sultone.

[0113] [Chemical formula 1] [ka]

[0114] In the above Chemical Formula 1, n is an integer from 3 to 10.

[0115] Specifically, in the above Chemical Formula 1, n may be an integer of 3 to 7.

[0116] When the integer n is within the above range, the thermal properties of the compound itself can be improved, thereby increasing the stability of the resulting coating. If n is less than 3 in Formula 1, the molecular size becomes smaller and the fluorine content decreases, resulting in a lower boiling point, reduced flame retardancy, increased vulnerability to electrochemical decomposition, and reduced high-temperature durability. This can lead to gas generation and deterioration of swelling properties during high-temperature storage. Furthermore, if n is greater than 8 in Formula 1, the excessive fluorine content can increase the viscosity and non-polarity of the material and reduce its solubility in the electrolyte, potentially resulting in deterioration of battery performance.

[0117] Preferably, the compound represented by Chemical Formula 1 may include at least one of compounds represented by the following Chemical Formulas 1-1 and 1-2.

[0118] [Chemical formula 1-1] [ka]

[0119] [Chemical formula 1-2] [ka]

[0120] The compound represented by Chemical Formula 1 can form a robust SEI film containing fluorine on the surface of the negative electrode by electrochemically reacting with the double bond (C=C) functional group contained in the molecular structure during electrochemical decomposition. In particular, the compound represented by Chemical Formula 1 contains a fluorine-substituted alkyl group, which has excellent flame retardancy and non-flammability, contained in the molecular structure. This allows the compound to form a passivation film on the surface of the positive electrode that ensures excellent oxidation resistance and also acts as a radical scavenger due to the fluorine. Therefore, side reactions between the electrode and electrolyte during charge / discharge operation are controlled, providing a lithium secondary battery with improved life characteristics at both room temperature and low temperature.

[0121] In particular, in the case of the compound of Formula 1, the double bond of the acrylate undergoes reductive decomposition to generate radicals, which can promote the decomposition reaction of the additives, cyclic carbonate and / or 1,3-propane sultone, described below, thereby forming a stronger SEI film.

[0122] Meanwhile, in the compound represented by Chemical Formula 1 of the present invention, the acrylate functional group and the terminal fluorine-substituted alkyl group are linked via an ethylene group (-CH2-CH2-). Therefore, compared to a compound such as 2,2,3,3,4,4,4-heptafluorobutyl acrylate, in which the acrylate functional group and the terminal fluorine-substituted alkyl group are linked via a methylene group (-CH2-), the flexibility of the compound is relatively high due to the increase in the molecular chain of the linking group, and a coating with improved durability can be formed on the surface of the negative electrode.

[0123] Furthermore, the compound of the present invention represented by Chemical Formula 1 contains two oxygen atoms in its molecular structure, and due to its structural feature of having an acrylate functional group and a terminal fluorine-substituted alkyl group linked (bonded) via an ethylene group (—CH—CH—), it forms a low-resistance, robust SEI on the electrode surface before side reactions occur, suppressing an increase in interfacial resistance and preventing exposure of the electrode surface, thereby suppressing side reactions between the electrode and the electrolyte. As a result, it effectively prevents the leaching of transition metals from the positive electrode due to film breakdown and improves high-temperature stability, thereby realizing a cylindrical lithium secondary battery that has excellent high-temperature storage and high-temperature cycle characteristics and reduced battery swelling. However, compounds containing three or more oxygen atoms in their molecular structure have the disadvantage of limited effectiveness due to reduced oxidation stability.

[0124] The compound represented by Chemical Formula 1 may be included in an amount of 0.5 wt % to 5.0 wt %, more specifically 0.5 wt % to 3.0 wt %, based on the total content of the electrolyte.

[0125] When the content of the compound represented by Chemical Formula 1 satisfies the above range, a stable coating can be formed, effectively suppressing the elution of transition metals from the positive electrode at high temperatures, thereby achieving excellent high-temperature durability. That is, when the content of the compound represented by Chemical Formula 1 is less than 0.5 wt %, the coating formation effect is minimal, and the SEI film deteriorates even during high-temperature storage, which may lead to an increase in resistance and a decrease in capacity after high-temperature storage. Furthermore, when the content of the compound represented by Chemical Formula 1 exceeds 5.0 wt %, an excessively thick coating is formed during initial charge, which may increase resistance and lead to a decrease in the initial capacity and output characteristics of the secondary battery.

[0126] In addition, the electrolyte of the present invention may further include a cyclic carbonate compound as an electrolyte additive in addition to the compound represented by Chemical Formula 1. That is, by using the compound represented by Chemical Formula 1 and the cyclic carbonate compound together as an electrolyte additive, when a coating is formed by the reduction reaction of the cyclic carbonate compound, the decomposition of the cyclic carbonate compound is promoted by the radical chemical reaction generated by the compound represented by Chemical Formula 1, thereby forming a more stable coating. The synergistic effect of these two compounds allows the formation of a more robust coating, thereby effectively improving the high-temperature durability and capacity retention rate of large cylindrical secondary batteries.

[0127] The cyclic carbonate compound may include vinylene carbonate, vinylethylene carbonate, or a mixture thereof. When the cyclic carbonate compound includes a mixture of vinylene carbonate and vinylethylene carbonate, the vinylene carbonate and vinylene carbonate may be contained in a weight ratio of 1:1 to 10:0.

[0128] The electrolyte of the present invention may also contain 1,3-propane sultone as an additive to enhance the coating on the electrode surface.

[0129] The 1,3-propane sultone can form a strong coating on the surface of not only the negative electrode but also the positive electrode. Such a coating has excellent durability, can suppress further side reactions between the electrode and the electrolyte, and can suppress an increase in resistance due to the side reactions.

[0130] Meanwhile, the electrolyte of the present invention may contain the compound of Formula 1, the cyclic carbonate compound, and 1,3-propane sultone in a weight ratio of 1:0.5:0.2 to 1:20:10, specifically, in a weight ratio of 1:0.5:0.2 to 1:10:8, and preferably in a weight ratio of 1:0.5:0.2 to 1:8:5.

[0131] When the content ratio of the additive satisfies the above range, a stronger SEI film and passivation film can be formed on the electrode surface, and at the same time, an appropriate level of gas can be generated, thereby controlling the internal pressure of a large cylindrical cell to be maintained within a specific range. As a result, the impregnation of the electrolyte can be maximized, and a cylindrical lithium secondary battery that can maintain high safety even at high output can be provided.

[0132] Meanwhile, the non-aqueous electrolyte of the present invention may further contain other additives to prevent the non-aqueous electrolyte from decomposing and causing anode collapse in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery expansion at high temperatures.

[0133] Representative examples of such other additives include at least one additive for forming an SEI film selected from the group consisting of halogen-substituted carbonate-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.

[0134] The halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0135] Examples of the sulfate-based compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0136] The phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalate)phosphate, lithium difluorophosphate, tetramethyltrimethylsilylphosphate, trimethylsilylphosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0137] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bis(oxalate)borate (LiB(C2O4)2, LiBOB).

[0138] The nitrile compound may be at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0139] The benzene-based compound may be fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0140] 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.

[0141] Meanwhile, the other additives may be used in a mixture of two or more types, and may be included in an amount of less than 10 wt %, specifically 0.01 wt % to 8.0 wt %, and preferably 0.05 wt % to 5.0 wt %, based on the total weight of the electrolyte. When the content of the other additives satisfies the above range, it is possible to suppress the induction of side reactions due to unreacted additives, and it is possible to further improve the effects of improving the low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery.

[0142] (B) Battery can Meanwhile, in FIG. 3, the battery can 142 is electrically connected to the uncoated portion 146b of the negative electrode plate and functions as a negative electrode terminal that contacts an external power source and transfers current applied from the external power source to the negative electrode plate.

[0143] If necessary, a beading portion 147 and a crimping portion 148 may be provided at the upper end of the battery can 142. The beading portion 147 may be formed by pressing around the outer periphery of the battery can 142 to a distance D1. The beading portion 147 prevents the electrode assembly 141 housed inside the battery can 142 from slipping out through the upper opening of the battery can 142 and may function as a support on which the seal 143 is placed.

[0144] The crimping portion 148 may be formed on the upper portion of the beading portion 147, and has an extended and bent shape to surround the outer circumferential surface of the cap plate 143a disposed on the beading portion 147 and a part of the upper surface of the cap plate 143a.

[0145] Next, the seal 143 seals the open end of the battery can 142 and includes a cap plate 143a, a first gasket 143b having insulating properties and providing airtightness between the cap plate 143a and the battery can 142, and may further include a connection plate 143c electrically and mechanically coupled to the cap plate 143a, if necessary. The cap plate 143a may be crimped onto a beading portion 147 formed on the battery can 142 and fixed by a crimping portion 148.

[0146] The cap plate 143a is a component made of a conductive metal material and covers the upper opening of the battery can 142. The cap plate 143a is electrically connected to the positive electrode plate of the electrode assembly 141 and is electrically insulated from the battery can 142 via a first gasket 143b. Therefore, the cap plate 143a can function as a positive electrode terminal of the cylindrical secondary battery. The cap plate 143a may have a protrusion 143d protruding upward from a center C thereof, and the protrusion 143d may come into contact with an external power source so that current can be applied from the external power source.

[0147] A first gasket 143b may be interposed between the cap plate 143a and the crimping portion 148 to ensure airtightness of the battery can 142 and to provide electrical insulation between the battery can 142 and the cap plate 143a.

[0148] Meanwhile, the cylindrical battery 140 according to the present invention may further include current collecting plates 144 and 145, if necessary. The current collecting plates are bonded to the uncoated portion 146a of the positive electrode plate and the uncoated portion 146b of the negative electrode plate, and are connected to the electrode terminals (i.e., the positive electrode terminal and the negative electrode terminal).

[0149] Specifically, the cylindrical battery 140 according to the present invention may include a first current collecting plate 144 coupled to the upper part of the electrode assembly 141 and a second current collecting plate 145 coupled to the lower part of the electrode assembly 141.

[0150] A first current collecting plate 144 and / or a second current collecting plate 145 may further be included.

[0151] The first current collecting plate 144 is coupled to the upper part of the electrode assembly 141. The first current collecting plate 144 is made of a conductive metal material such as aluminum, copper, or nickel, and is electrically connected to the uncoated portion 146a of the positive electrode plate. A lead 149 may be coupled to the first current collecting plate 144. The lead 149 may extend upwardly of the electrode assembly 141 and be coupled to the connecting plate 143c, or may be directly coupled to the lower surface of the cap plate 143a. The lead 149 may be coupled to other components by welding. Preferably, the first current collecting plate 144 may be integrally formed with the lead 149. In this case, the lead 149 may have a long plate shape extending outward from the center of the first current collecting plate 144.

[0152] Meanwhile, the first current collecting plate 144 is coupled to the end of the uncoated portion 146a of the positive electrode plate, and the coupling may be performed by, for example, laser welding, resistance welding, ultrasonic welding, soldering, or the like.

[0153] The second current collecting plate 145 is coupled to the lower part of the electrode assembly 141. The second current collecting plate 145 is made of a conductive metal material such as aluminum, copper, or nickel, and is electrically connected to the uncoated portion 146b of the negative electrode plate. One side of the second current collecting plate 145 may be coupled to the uncoated portion 146b of the negative electrode plate, and the opposite side may be coupled to the inner bottom surface of the battery can 142. In this case, the coupling may be performed by a method such as laser welding, resistance welding, ultrasonic welding, or soldering.

[0154] Meanwhile, the cylindrical battery 140 according to the present invention may further include an insulator 146, if necessary. The insulator 146 may be disposed to cover the upper surface of the first current collecting plate 144. By covering the first current collecting plate 144 with the insulator 146, direct contact between the first current collecting plate 144 and the inner peripheral surface of the battery can 142 can be prevented.

[0155] The insulator 146 has lead holes 151 through which the leads 149 extending upward from the first current collecting plate 144 are drawn out. The leads 149 are drawn out upward through the lead holes 151 and coupled to the lower surface of the connecting plate 143c or the lower surface of the cap plate 143a.

[0156] The insulator 146 may be made of a polymer resin material having insulating properties, such as polyethylene, polypropylene, polyimide, or polybutylene terephthalate.

[0157] Meanwhile, the cylindrical battery 140 according to the present invention may further include a vent 152 formed on the bottom surface of the battery can 142, if necessary. The vent 152 corresponds to a region of the bottom surface of the battery can 142 that is thinner than the surrounding region. Because the vent 152 is thinner, it is structurally weaker than the surrounding region. Therefore, when the pressure inside the cylindrical battery 140 increases above a certain level, the vent 152 ruptures, releasing gas inside the battery can 152 to the outside, thereby preventing the battery from exploding.

[0158] Fig. 4 shows a cross-sectional view of a cylindrical battery with a tabless structure according to another embodiment of the present invention. Hereinafter, a cylindrical battery according to another embodiment of the present invention will be described with reference to Fig. 4. However, Fig. 4 merely shows one embodiment of the present invention, and the structure of the cylindrical battery according to the present invention is not limited to the scope disclosed in Fig. 4.

[0159] Referring to FIG. 4, a cylindrical battery 170 according to another embodiment of the present invention differs from the cylindrical battery 140 shown in FIG. 3 in the structure of the battery can and the sealing body, but the configuration of the electrode assembly and electrolyte is substantially the same.

[0160] Specifically, the cylindrical battery 170 includes a battery can 171 through which a rivet terminal 172 is installed. The rivet terminal 172 is installed on a partially closed surface (top surface in the drawing) at one end of the battery can 171. The rivet terminal 172 is riveted into a through-hole (first opening at a first end) of the battery can 171 with an insulating second gasket 173 interposed therebetween. The rivet terminal 172 is exposed to the outside in the direction opposite to the direction of gravity.

[0161] The rivet terminal 172 includes a terminal exposing portion 172a and a terminal inserting portion 172b. The terminal exposing portion 172a is exposed to the outside of the closed surface of the battery can 171. The terminal exposing portion 172a may be located approximately at the center of the partially closed surface of the battery can 171. The maximum diameter of the terminal exposing portion 172a may be larger than the maximum diameter of the through-hole formed in the battery can 171. The terminal inserting portion 172b may penetrate approximately the center of the closed surface of the battery can 171 to be electrically connected to the uncoated portion 146a of the positive electrode plate. The terminal inserting portion 172b may be rivet-connected to the inner surface of the battery can 171. That is, an end of the terminal inserting portion 172b may be curved toward the inner surface of the battery can 171. The maximum diameter of the end of the terminal inserting portion 172b may be larger than the maximum diameter of the through-hole of the battery can 171.

[0162] The lower end surface of the terminal insertion portion 172b may be welded to the first current collecting plate 144 connected to the uncoated portion 146a of the positive electrode plate. An insulating cap 174 made of an insulating material may be interposed between the first current collecting plate 144 and the inner surface of the battery can 171. The insulating cap 174 covers the upper portion of the first current collecting plate 144 and the upper end portion of the electrode assembly 141. This prevents the uncoated portion B3 on the outer periphery of the electrode assembly 141 from coming into contact with the inner surface of the battery can 171 having the opposite polarity, causing a short circuit. The terminal insertion portion 172b of the rivet terminal 172 may penetrate the insulating cap 174 and be welded to the first current collecting plate 144.

[0163] The second gasket 173 is interposed between the battery can 171 and the rivet terminal 172 to prevent electrical contact between the battery can 171 and the rivet terminal 172, which have opposite polarities. This allows the upper surface of the battery can 171, which has a substantially flat shape, to function as the positive electrode terminal of the cylindrical battery 170.

[0164] The second gasket 173 includes a gasket exposing portion 173a and a gasket inserting portion 173b. The gasket exposing portion 173a is interposed between the terminal exposing portion 172a of the rivet terminal 172 and the battery can 171. The gasket inserting portion 173b is interposed between the terminal inserting portion 172b of the rivet terminal 172 and the battery can 171. The gasket inserting portion 173b may deform during riveting of the terminal inserting portion 172b, thereby adhering closely to the inner surface of the battery can 171. The second gasket 173 may be made of, for example, an insulating polymer resin.

[0165] The gasket exposing portion 173a of the second gasket 173 may extend to cover the outer peripheral surface of the terminal exposing portion 172a of the rivet terminal 172. When the second gasket 173 covers the outer peripheral surface of the rivet terminal 172, it is possible to prevent a short circuit from occurring during the process of connecting an electrical connecting component, such as a bus bar, to the upper surface of the battery can 171 and / or the rivet terminal 172. Although not shown in the drawings, the gasket exposing portion 173a may extend to cover not only the outer peripheral surface of the terminal exposing portion 172a but also a portion of the upper surface.

[0166] When the second gasket 173 is made of a polymer resin, the second gasket 173 may be joined to the battery can 171 and the rivet terminal 172 by heat sealing. In this case, the airtightness at the joining interface between the second gasket 173 and the rivet terminal 172 and the joining interface between the second gasket 173 and the battery can 171 may be strengthened. Meanwhile, when the gasket exposing portion 173a of the second gasket 173 extends to the upper surface of the terminal exposing portion 172a, the rivet terminal 172 may be joined integrally with the second gasket 173 by insert injection.

[0167] The remaining area 175 of the top surface of the battery can 171 excluding the area occupied by the rivet terminal 172 and the second gasket 173 corresponds to a negative terminal having a polarity opposite to that of the rivet terminal 172 .

[0168] The second current collecting plate 176 is coupled to the lower part of the electrode assembly 141. The second current collecting plate 176 is made of a conductive metal material such as aluminum, steel, copper, or nickel, and is electrically connected to the uncoated portion 146b of the negative electrode plate.

[0169] Preferably, the second current collecting plate 176 is electrically connected to the battery can 171. To this end, the second current collecting plate 176 may be fixed such that at least a portion of its end portion is interposed between the inner surface of the battery can 171 and the first gasket 178b. In one example, at least a portion of the end portion of the second current collecting plate 176 may be fixed to the beading portion 180 by welding while being supported on a lower end surface of the beading portion 180 formed at the lower end of the battery can 171. In a modified example, at least a portion of the end portion of the second current collecting plate 176 may be directly welded to the inner wall surface of the battery can 171.

[0170] The second current collecting plate 176 may have a plurality of projections (not shown) formed radially on the surface facing the non-coating portion 146b. When the projections are formed, the second current collecting plate 176 can be pressed into the non-coating portion 146b.

[0171] Preferably, the ends of the second current collecting plate 176 and the plain portion 146b may be joined by welding, for example, laser welding.

[0172] The seal 178 that seals the lower open end of the battery can 171 includes a cap plate 178a and a first gasket 178b. The first gasket 178b electrically isolates the cap plate 178a from the battery can 171. A crimping portion 181 secures the edge of the cap plate 178a and the first gasket 178b together. The cap plate 178a is provided with a vent portion 179. The configuration of the vent portion 179 is substantially the same as in the above-described embodiment.

[0173] Preferably, the cap plate 178a is made of a conductive metal material. However, the cap plate 178a does not exhibit electrical polarity because the first gasket 178b is interposed between the cap plate 178a and the battery can 171. The seal 178 seals the open end of the lower part of the battery can 171 and functions to discharge gas when the internal pressure of the battery cell 170 increases above a critical value.

[0174] Preferably, the rivet terminal 172 electrically connected to the uncoated portion 146a of the positive electrode plate is used as the positive electrode terminal. Furthermore, a portion 175 of the upper surface of the battery can 171, excluding the rivet terminal 172, electrically connected to the uncoated portion 146b of the negative electrode plate via the second current collecting plate 176 is used as the negative electrode terminal. When two electrode terminals are located at the top of the cylindrical battery, electrical connection components such as bus bars can be disposed on only one side of the cylindrical battery 170. This simplifies the battery pack structure and improves energy density. Furthermore, the portion 175 used as the negative electrode terminal has a substantially flat shape, ensuring a sufficient contact area for connecting electrical connection components such as bus bars. This allows the cylindrical battery 170 to reduce resistance at the contact points of the electrical connection components to a desirable level.

[0175] When a cylindrical lithium secondary battery is formed in a tabless structure as described above, current concentration is reduced compared to conventional batteries with electrode tabs, which effectively reduces heat generation inside the battery, thereby improving the thermal safety of the battery.

[0176] The cylindrical lithium secondary battery of the present invention as described above can be used to manufacture a battery pack. Figure 6 shows a schematic configuration of a battery pack according to an embodiment of the present invention. Referring to Figure 6, a battery pack 3 according to an embodiment of the present invention includes an assembly of electrically connected cylindrical secondary batteries 1 and a pack housing 2 that accommodates the assembly. The cylindrical secondary batteries 1 are the battery cells according to the above-described embodiment. For ease of illustration, components such as bus bars, cooling units, and external terminals for electrically connecting the cylindrical secondary batteries 1 are omitted from the drawings.

[0177] The battery pack 3 can be mounted in a vehicle. The vehicle may be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle may include a four-wheeled vehicle or a two-wheeled vehicle.

[0178] The present invention will be described in more detail below with reference to specific examples.

[0179] Example 1 (Electrolyte production) LiPF was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3 M, and then 0.5 wt % of the compound represented by Formula 1-2, 2.0 wt % of vinylene carbonate (VC), 1.0 wt % of 1,3-propane sultone (PS), and other additives such as 0.2 wt % of adiponitrile (AD), 0.2 wt % of succinonitrile, and 0.3 wt % of lithium difluorophosphate (hereinafter referred to as "LiDFP") were added to prepare an electrolyte (see Table 1 below).

[0180] (Secondary battery manufacturing) Average particle size D 50 The positive electrode active material (Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 ]O2), carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 97.8:0.6:1.6 to prepare a positive electrode slurry. 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 plate.

[0181] Anode active materials (graphite and SiO2 in a weight ratio of 95:5), conductive material (Super C), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 96:2:1.5:0.5 to prepare anode slurry. The anode slurry was applied to one side of a copper current collector sheet, dried at 150°C, and rolled to prepare anode plates.

[0182] The positive and negative electrode plates prepared as described above were stacked in the order of separator / positive electrode / separator / negative electrode, with a separator interposed between them, and then wound up to prepare an electrode assembly (core diameter: 7 mm). The electrode assembly prepared as described above was inserted into a cylindrical battery can, and the electrolyte was injected to prepare a 4680 cell (form factor ratio: 0.58).

[0183] Example 2. (Electrolyte production) LiPF6 was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3M. Then, 1.0 wt% of the compound represented by Formula 1-2, 2.0 wt% of vinylene carbonate (VC), 1.0 wt% of 1,3-propane sultone (PS), and other additives such as 0.2 wt% of adiponitrile (AD), 0.2 wt% of succinonitrile, and 0.3 wt% of LiDFP were added to prepare an electrolyte (see Table 1 below).

[0184] (Secondary battery manufacturing) A 4680 cell (form factor ratio: 0.58) was fabricated in the same manner as in Example 1, except that the prepared electrolyte was injected.

[0185] Example 3 LiPF6 was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3M, and then 3.0 wt% of the compound represented by Formula 1-2, 3.0 wt% of vinylene carbonate (VC), 1.0 wt% of 1,3-propane sultone (PS), and other additives such as 0.2 wt% adiponitrile (AD), 0.2 wt% succinonitrile, and 0.3 wt% LiDFP were added to prepare an electrolyte (see Table 1 below).

[0186] (Secondary battery manufacturing) A 4680 cell (form factor ratio: 0.58) was fabricated in the same manner as in Example 1, except that the prepared electrolyte was injected.

[0187] Example 4. LiPF6 was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3M, and then 3.0 wt% of the compound represented by Formula 1-2, 4.5 wt% of vinylene carbonate (VC), 3.0 wt% of 1,3-propane sultone (PS), and other additives such as 0.2 wt% adiponitrile (AD), 0.2 wt% succinonitrile, and 0.3 wt% LiDFP were added to prepare an electrolyte (see Table 1 below).

[0188] (Secondary battery manufacturing) A 4680 cell (form factor ratio: 0.58) was fabricated in the same manner as in Example 1, except that the prepared electrolyte was injected.

[0189] Comparative Example 1 LiPF6 was dissolved in a non-aqueous organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3M, and then 2.0 wt% vinylene carbonate (VC), 1.0 wt% 1,3-propane sultone (PS), and other additives such as 0.2 wt% adiponitrile (AD), 0.2 wt% succinonitrile, and 0.3 wt% LiDFP were added to prepare an electrolyte (see Table 1 below).

[0190] (Secondary battery manufacturing) A 4680 cell (form factor ratio: 0.58) was fabricated in the same manner as in Example 1, except that the prepared electrolyte was injected.

[0191] Comparative Example 2 LiPF6 was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3M, and then 0.1 wt% of the compound represented by Formula 1-2, 2.0 wt% of vinylene carbonate (VC), 1.0 wt% of 1,3-propane sultone (PS), and other additives such as 0.2 wt% adiponitrile (AD), 0.2 wt% succinonitrile, and 0.3 wt% LiDFP were added to prepare an electrolyte (see Table 1 below).

[0192] (Secondary battery manufacturing) A 4680 cell (form factor ratio: 0.58) was fabricated in the same manner as in Example 1, except that the prepared electrolyte was injected.

[0193] Comparative Example 3. LiPF6 was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3M, and then 1.0 wt% of the compound represented by Formula 1-2, 2.0 wt% of vinylene carbonate (VC), 0.1 wt% of 1,3-propane sultone (PS), and other additives such as 0.2 wt% adiponitrile (AD), 0.2 wt% succinonitrile, and 0.3 wt% LiDFP were added to prepare an electrolyte (see Table 1 below).

[0194] (Secondary battery manufacturing) A 4680 cell (form factor ratio: 0.58) was fabricated in the same manner as in Example 1, except that the prepared electrolyte was injected.

[0195] Comparative Example 4. LiPF6 was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3M, and then 0.3 wt% of the compound represented by Formula 1-2, 2.0 wt% of vinylene carbonate (VC), 4.5 wt% of 1,3-propane sultone (PS), and other additives such as 0.2 wt% adiponitrile (AD), 0.2 wt% succinonitrile, and 0.3 wt% LiDFP were added to prepare an electrolyte (see Table 1 below).

[0196] (Secondary battery manufacturing) A 4680 cell (form factor ratio: 0.58) was fabricated in the same manner as in Example 1, except that the prepared electrolyte was injected.

[0197] Comparative Example 5. LiPF6 was dissolved in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75 to a concentration of 1.3M. Then, 5.5 wt% of the compound represented by Formula 1-2, 2.0 wt% of vinylene carbonate (VC), 1.0 wt% of 1,3-propane sultone (PS), and other additives such as 0.2 wt% adiponitrile (AD), 0.2 wt% succinonitrile, and 0.3 wt% LiDFP were added to prepare an electrolyte (see Table 1 below).

[0198] (Secondary battery manufacturing) A 4680 cell (form factor ratio: 0.58) was fabricated in the same manner as in Example 1, except that the prepared electrolyte was injected.

[0199] Comparative Example 6. (Secondary battery manufacturing) The electrode assembly (core diameter: 7 mm) prepared in Example 1 was inserted into a cylindrical battery can, and the electrolyte prepared in Example 1 was injected to prepare a 21700 cell (form factor ratio: 0.03).

[0200] [Table 1]

[0201] [Experimental Example] Experimental example 1. Evaluation of gas generation rate Each cell prepared in Example 1 and Comparative Example 1 was activated by charging at room temperature with a constant current and constant voltage at a C-rate of 0.33 C up to 4.0 V, and then discharging at a C-rate of 0.2 C down to 2.5 V. Gases inside the cells were then collected and the amount of gas generated was measured by GC-MS analysis (BGA-10).

[0202] The amount of gas generated in Comparative Example 1 was set to 100%, and the volume change rate in Example 1 was calculated as a relative value to Comparative Example 1, and the values ​​are shown in Table 2 below.

[0203] [Table 2]

[0204] From Table 2, it can be seen that in the case of the cell of Example 1, the total content of additives was higher than that of Comparative Example 1, but the amount of gas generated inside the cell was reduced.

[0205] Experimental Example 2: Evaluation of initial capacitance and initial resistance (1) Evaluation of initial discharge energy (Wh) Each of the cells prepared in Examples 1 to 4 and Comparative Examples 2, 4, and 5 was fully charged at room temperature at a C-rate of 0.33 C up to 4.0 V under constant current and constant voltage conditions, and then discharged at a C-rate of 0.2 C down to 2.5 V, and the discharge energy was measured. The results are shown in Table 3 below.

[0206] (2) Evaluation of initial DC resistance Each of the cells prepared in Examples 1 to 4 and Comparative Examples 2, 4, and 5 was charged at room temperature at a constant current and constant voltage at a C-rate of 0.33 C to an SOC of 50%, and then discharged at a C-rate of 0.5 C to an SOC of 50% for 10 seconds. The initial DC resistance was calculated using the voltage difference, and the results are shown in Table 3 below.

[0207] [Table 3]

[0208] As shown in Table 3, it can be seen that the cells of Examples 1 to 4 had improved initial discharge energy and mostly reduced initial resistance compared to the cells of Comparative Examples 2, 4, and 5.

[0209] Based on these results, it can be confirmed that when the three additives are contained in a specific composition ratio, the internal pressure of the cell is reduced by controlling gas generation, thereby improving the electrolyte impregnation and reducing the initial resistance.

[0210] Experimental Example 3: Discharge capacity by C-rate Each of the cells prepared in Examples 1 to 4 and Comparative Examples 1 to 5 was charged at room temperature at a constant current and constant voltage up to 4.2 V at a C-rate of 0.33 C, and then discharged to 2.5 V at a C-rate of 1 C and a C-rate of 2 C, respectively. The discharge capacity retention rate was calculated, and the results are shown in Table 4 below.

[0211] [Table 4]

[0212] As shown in Table 4, it can be seen that the discharge capacity retention rates of the cells of Examples 1 to 4 were all improved compared to the cells of Comparative Examples 1 to 5.

[0213] Experimental Example 4: Evaluation of high-temperature cycle capacity retention rate Each of the cells prepared in Examples 1 to 3 and Comparative Examples 2 to 6 was charged at room temperature (25°C) at a constant current and constant voltage up to 4.2 V at a C-rate of 0.33 C, and then discharged at a C-rate of 0.2 C to 2.5 V, and the initial capacity was measured. Next, the cells were charged at a high temperature (40°C) at a constant current and constant voltage up to 4.2 V at a C-rate of 0.33 C, and then discharged at a C-rate of 0.2 C to 2.5 V, and 100 charge-discharge cycles were performed. The capacity retention rate after 100 cycles at 40°C relative to the initial capacity after the first cycle was measured, and the results are shown in Table 5 below.

[0214] [Table 5]

[0215] As shown in Table 5, in the cells of Examples 1 to 3, the high temperature cycle capacity retention rates were all improved compared to the cells of Comparative Examples 2 to 6.

[0216] In particular, in the case of the cell of Comparative Example 6, which has a different form factor, when an electrolyte solution with the same additive composition is applied, it is difficult to adjust the internal cell pressure, and the impregnation of the electrolyte is reduced, resulting in a significant decrease in the high-temperature cycle capacity retention rate compared to the cells of Examples 1 to 3.

[0217] Experimental Example 5. Evaluation of thermal stability The ignition temperature of each of the cells produced in Examples 1 to 3 and Comparative Examples 1 to 6 was measured while raising the temperature at a rate of 2°C per minute. The ignition temperature of Comparative Example 1 was set to "0," and the ignition temperature values ​​of the cells of Examples 1 to 3 and Comparative Examples 2 to 6 were calculated as relative values ​​to the cell of Comparative Example 1, and the results are shown in Table 6 below.

[0218] [Table 6]

[0219] As shown in Table 6, in the case of the cells of Examples 1 to 3, the impregnation of the electrolyte was improved, resulting in improved stability, and ignition was induced at a higher temperature than in the cells of Comparative Examples 1 to 6. [Explanation of symbols]

[0220] 10: Positive electrode plate 11: Negative electrode plate 12: Separator 20: Current collector 21, 21a: Active material layer 22, 22a, 22c, 146b: Plain part 24: Insulating layer 140, 170: Cylindrical battery 141: Electrode assembly 142, 171: Battery can 143, 178: Sealing body 144: First current collecting plate 145, 176: Second current collecting plate 146a: Uncoated part of positive electrode plate 146b: Uncoated portion of negative electrode plate 146: Insulator 152: Venting section 172: Rivet terminal 173: Second gasket 173a: Exposed gasket 173b: Gasket insert 147, 180: Beading section 148: Crimping section 149: Lead 172a: Exposed terminal part 172b: Terminal insertion part 174: Insulation cap 178b: First gasket 180: Beading section

Claims

1. A cylindrical lithium secondary battery comprising: an electrode assembly in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction; a battery can in which the electrode assembly is housed; an electrolyte injected into the battery can; and a seal that seals an open end of the battery can, the positive electrode plate and the negative electrode plate each include an uncoated portion on which an active material layer is not formed, and at least a portion of the uncoated portion of the positive electrode plate or the uncoated portion of the negative electrode plate defines an electrode tab; The cylindrical lithium secondary battery has a form factor ratio of 0.4 or more, The diameter of the core portion of the electrode assembly is 5 mm to 8 mm, the electrolyte comprises a lithium salt, a non-aqueous organic solvent, and an additive; The additive includes a compound represented by the following Chemical Formula 1, a cyclic carbonate compound, and 1,3-propane sultone: The compound represented by the following Chemical Formula 1 is contained in an amount of 0.5 wt % to 5.0 wt % based on the total content of the electrolyte, A cylindrical lithium secondary battery, comprising a compound represented by the following Chemical Formula 1, a cyclic carbonate compound, and 1,3-propane sultone in a weight ratio of 1:0.5:0.2 to 1:20:10: [Chemical formula 1] 【Chemistry 1】 In the above Chemical Formula 1, n is an integer from 3 to 10.

2. 2. The cylindrical lithium secondary battery according to claim 1, wherein the positive electrode plate contains a positive electrode active material in which the content of Ni among metal elements other than lithium is 80 mol % or more.

3. 3. The cylindrical lithium secondary battery according to claim 2, wherein the positive electrode active material is a lithium nickel-based oxide represented by the following Chemical Formula 2: [Chemical formula 2] Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the above Chemical Formula 2, M １ is Mn, Al or a combination thereof, M ２ is one or more elements selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and 0.8≦a≦1.2, 0.85≦b<1, 0<c<0.15, 0<d<0.15, and 0≦e≦0.

1.

4. 2. The cylindrical lithium secondary battery according to claim 1, wherein the positive electrode plate contains a positive electrode active material consisting of a single particle, a pseudo-single particle, or a combination thereof.

5. The cylindrical lithium secondary battery according to claim 1 , wherein the negative electrode plate comprises a silicon-based negative electrode active material and a carbon-based negative electrode active material.

6. 6. The cylindrical lithium secondary battery of claim 5, wherein the silicon-based negative electrode active material and the carbon-based negative electrode active material are contained in a weight ratio of 1:99 to 20:

80.

7. 2. The cylindrical lithium secondary battery according to claim 1, wherein the cylindrical lithium secondary battery has a form factor ratio of 0.4 to 0.

6.

8. 2. The cylindrical lithium secondary battery according to claim 1, wherein the cylindrical lithium secondary battery is a 46110 cell, a 48110 cell, a 4880 cell, a 4680 cell, or a 4695 cell.

9. 2. The cylindrical lithium secondary battery according to claim 1, wherein the concentration of the lithium salt is 1.2M to 1.3M.

10. 2. The cylindrical lithium secondary battery according to claim 1, wherein n is an integer of 3 to 7 in Chemical Formula 1.

11. 10. The cylindrical lithium secondary battery of claim 1, wherein the compound represented by Chemical Formula 1 is contained in an amount of 0.5 wt % to 3.0 wt % based on the total content of the electrolyte.

12. 2. The cylindrical lithium secondary battery according to claim 1, wherein the cyclic carbonate compound comprises vinylene carbonate, vinylethylene carbonate, or a mixture thereof.

13. 2. The cylindrical lithium secondary battery of claim 1, wherein the compound represented by Chemical Formula 1, the cyclic carbonate compound, and the 1,3-propane sultone are contained in a weight ratio of 1:0.5:0.2 to 1:10:

8.

14. the uncoated portions of the positive electrode plate and the negative electrode plate are formed on one edge of the positive electrode plate and one edge of the negative electrode plate, respectively, along a winding direction of the electrode assembly; a current collecting plate is coupled to each of the uncoated portions of the positive electrode plate and the negative electrode plate, 2. The cylindrical lithium secondary battery according to claim 1, wherein the current collecting plate is connected to an electrode terminal.

15. The uncoated portion of the positive electrode plate and the uncoated portion of the negative electrode plate are processed into a plurality of segments that can be bent independently, The cylindrical lithium secondary battery according to claim 14 , wherein at least some of the plurality of segments are bent toward the winding center of the electrode assembly.

16. At least some of the folded segments overlap the upper and lower ends of the electrode assembly, 16. The cylindrical lithium secondary battery according to claim 15, wherein the current collecting plates are bonded onto the overlapping segments.

17. 15. The cylindrical lithium secondary battery of claim 14, further comprising an insulating layer formed on the positive electrode plate in a direction parallel to the winding direction, the insulating layer covering a portion of the positive electrode active material layer and a portion of the uncoated portion.

18. A battery pack comprising the cylindrical lithium secondary battery according to any one of claims 1 to 17.

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