Lithium secondary battery

Abstract

To provide a lithium secondary battery capable of realizing excellent thermal stability even when the volume of a can type battery is increased by applying single particles or pseudo-single particles as a positive electrode active material.SOLUTION: The present invention relates to a 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 accommodated, and a sealing body for sealing an open end of the battery can, wherein the positive electrode plate includes a positive electrode active material including single particles, quasi-single particles, or a combination thereof, and Dmin of the positive electrode active material is 1.0 μm or more.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0136711 filed on October 14, 2021, and Korean Patent Application No. 10-2022-0121172 filed on September 23, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, and more specifically to a lithium secondary battery that can achieve excellent thermal stability even when its volume is increased by applying a single-particle and / or quasi-single-particle positive electrode active material. [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 divided into can-type batteries (such as cylindrical or prismatic ones) and pouch-type batteries, depending on the material of the battery case. A can-type battery is constructed by stacking a sheet-like positive electrode plate, a separator, and a negative electrode plate in order inside a battery can and then winding them in one direction to form a jelly-roll electrode assembly, which is then sealed by covering the top of the battery can with a cap plate. The positive electrode plate and the negative electrode plate are provided with strip-shaped positive and negative electrode tabs, respectively, which are connected to electrode terminals and electrically connected to an external power source. For reference, the positive electrode terminal is the cap plate, and the negative electrode terminal is the battery can. However, conventional can-type batteries with this structure suffer from problems such as high resistance, excessive heat generation, and poor current collection efficiency due to current concentration in the strip-shaped electrode tabs.

[0005] Meanwhile, with the recent advancement of electric vehicle technology, the demand for high-capacity batteries has increased, necessitating the development of large-volume can-type batteries. Conventionally, commonly used small can-type batteries, such as small cylindrical batteries with 1865 or 2170 form factors, have low capacities, so resistance and heat generation do not seriously affect battery performance. However, if the specifications of conventional small can-type batteries are directly applied to large can-type batteries, serious problems may arise in terms of battery safety.

[0006] As the size of a battery increases, the amount of heat and gas generated inside the battery also increases, which can increase the temperature and pressure inside the battery, potentially causing the battery to catch fire or explode. 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 discharging heat to the outside of the battery, must increase in line with the increase in volume. However, because the increase in cross-sectional area is typically less than the increase in volume, the amount of heat generated inside the battery increases as the battery size increases, which can lead to problems such as an increased risk of explosion and reduced output. Furthermore, when fast charging at high voltage, a large amount of heat is generated around the electrode tabs in a short period of time, which can cause the battery to catch fire.

[0007] Therefore, in order to achieve high capacity, there is a demand for the development of a can-type battery that has a large volume and is highly safe. 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 aims to provide a lithium secondary battery that can achieve excellent thermal stability even when the volume of a can-type battery is increased by using a single particle or a pseudo-single particle as a positive electrode active material. [Means for solving the problem]

[0009] According to one embodiment, the present invention provides a 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, and a sealing body that seals an open end of the battery can, wherein the positive electrode plate includes a positive electrode active material including a single particle, a pseudo-single particle, or a combination thereof, and the D of the positive electrode active material is min The present invention provides a cylindrical lithium secondary battery having a particle size of 1.0 μm or more.

[0010] In addition, the positive electrode active material may include a lithium nickel-based oxide containing 80 mol% or more of Ni relative to the total number of moles of transition metals, for example, a lithium nickel-based oxide represented by the following [Chemical Formula 1]. [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2

[0011] In the above Chemical Formula 1, M 1 is Mn, Al or a combination thereof, and M 2 are Zr, W, Ti, Mg, Ca, Sr, and Ba, and 0.8≦a≦1.2, 0.83≦b<1, 0 <c<0.17、0<d<0.17、0≦e≦0.1である。

[0012] Meanwhile, the negative electrode plate may include a silicon-based negative electrode active material.

[0013] The negative electrode plate may include a silicon-based negative electrode active material and a carbon-based negative electrode active material, and the silicon-based negative electrode active material and the carbon-based negative electrode active material may be included in a weight ratio of 1:99 to 20:80.

[0014] Meanwhile, the secondary battery may be a cylindrical battery with a form factor ratio of 0.4 or more, for example, a 46110 cell, a 4875 cell, a 48110 cell, a 4880 cell, or a 4680 cell, where the form factor ratio is the diameter of the cylindrical battery divided by its height.

[0015] In addition, the secondary battery according to the present invention may be a battery in which the positive electrode plate and the negative electrode plate each include an uncoated portion on which no active material layer is formed, and at least a portion of the uncoated portion of the positive electrode plate or the negative electrode plate defines an electrode tab.

[0016] The positive electrode plate uncoated portion and the negative electrode plate uncoated portion may be located along one edge of the positive electrode plate and the negative electrode plate, respectively, that is parallel to the winding direction of the electrode assembly. A current collecting plate may be coupled to each of the positive electrode plate uncoated portion and the negative electrode plate uncoated portion, and the current collecting plate may be connected to an electrode terminal.

[0017] Meanwhile, the positive electrode uncoated portion and the negative electrode uncoated portion may be processed into a plurality of segmented pieces that can be bent independently, at least some of the segmented pieces defining the electrode tabs and bent toward the winding center C of the electrode assembly. Also, at least some of the folded segmented pieces may overlap each other on the upper and lower ends of the electrode assembly, and the current collecting plates may be coupled to the overlapping segmented pieces.

[0018] Meanwhile, an insulating layer may be further formed on the positive electrode plate in a direction parallel to the winding direction, covering a portion of the positive electrode active material layer and a portion of the uncoated portion.

[0019] According to another embodiment, the present invention provides a battery pack including the lithium secondary battery according to the present invention, and a vehicle including the battery pack. [Effects of the Invention]

[0020] The lithium secondary battery according to the present invention uses a positive electrode active material consisting of a single particle and / or a pseudo-single particle as a positive electrode active material, which can minimize gas generation due to particle cracking during electrode manufacturing and internal cracking during charge and discharge, thereby achieving excellent safety even in large batteries with increased volume.

[0021] The lithium secondary battery according to the present invention is also min By using a positive electrode active material having a particle size of 1.0 μm or more, the thermal stability of the battery can be further improved. Research by the present inventors has shown that even when single particles and / or pseudo-single particles are used as the positive electrode active material, the effects of suppressing particle cracking and improving thermal stability after rolling vary depending on the particle size of the positive electrode active material. In particular, when particles with a particle size of less than 1.0 μm are contained in the positive electrode active material, the linear pressure increases during the rolling process, causing increased particle cracking and reduced thermal stability, making it impossible to ensure sufficient thermal stability when applied to large cylindrical batteries. Therefore, in the present invention, a minimum particle size (D min By using a cathode active material with a particle size controlled to 1.0 μm or more, the thermal stability improvement effect can be maximized.

[0022] The lithium secondary battery according to the present invention is also 50 , D max By applying a positive electrode active material with an appropriately controlled particle size distribution (PSD), the increase in resistance due to the application of single particles can be minimized, thereby achieving excellent capacity and output characteristics.

[0023] Furthermore, the lithium secondary battery according to the present invention may contain a silicon-based negative electrode active material having a large capacity as the negative electrode active material, and in this case, a higher energy density may be achieved.

[0024] Furthermore, the lithium secondary battery according to the present invention may have a structure in which the uncoated portions of the positive and negative electrode plates function as electrode tabs, e.g., a tabless structure. Conventional batteries are configured to connect electrode plates and electrode leads via electrode tabs. However, in this case, a large amount of current concentrates on the electrode tabs during charging, generating a lot of heat around the electrode tabs. This phenomenon is particularly severe during fast charging, which can lead to battery fire or explosion. In contrast, the lithium secondary battery according to the present invention may be configured to form uncoated portions, where no active material layer is formed, at the ends of the positive and negative electrode plates, and connect the uncoated portions to electrode terminals by welding them to current collecting plates with a large cross-sectional area. A battery with this structure has less current concentration than a conventional battery with electrode tabs, effectively reducing internal heat generation and thereby improving the thermal stability of the battery. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a diagram showing a stacked state of an electrode assembly according to the present invention before being wound up; [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 battery having a tablets structure according to one embodiment of the present invention. [Figure 4] FIG. 10 is a cross-sectional view showing the structure of a tablets structure battery according to another embodiment of the present invention. [Figure 5] 1A and 1B are views 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; [Figure 7] 1 is a diagram illustrating a vehicle including a battery pack according to the present invention; [Figure 8] 1 is a SEM photograph of the positive electrode active material used in Example 1. [Figure 9] 1 is a SEM photograph of the positive electrode active material used in Example 2. [Figure 10] 1 is a SEM photograph of the positive electrode active material used in Comparative Example 2. [Figure 11] 1 is a graph showing the results of a hot box test of 4680 cells manufactured according to Sample 1 of Example 1 and Comparative Example 1. [Figure 12] 1 is a graph showing the results of a hot box test of Samples 2 and 3 of Example 1, Samples 1 and 2 of Example 2, and 4680 cells of Comparative Example 2. [Figure 13] 1 is a cross-sectional SEM photograph of a positive electrode plate manufactured in Example 1. [Figure 14] 1 is a cross-sectional SEM photograph of a positive electrode plate manufactured in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described in more detail below.

[0027] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0028] In the present invention, "primary particles" refers to particle units that do not appear to have grain boundaries when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope or an electron backscatter diffraction (EBSD) pattern analyzer. "Average particle size of primary particles" refers to the arithmetic mean value calculated after measuring the particle sizes of primary particles observed using a scanning electron microscope or an EBSD image.

[0029] 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 called pseudo-single particles.

[0030] In the present invention, "D min "," "D 50 " and "D max " is the particle size value of the volume cumulative distribution of the positive electrode active material measured using the laser diffraction method. Specifically, D min is the minimum particle size indicated by the volume cumulative distribution, and D 50 is the particle diameter when the cumulative volume is 50%, and D max is the maximum particle size indicated by the volume cumulative distribution. The particle size value of the volume cumulative distribution can be measured, for example, by dispersing the positive electrode active material in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, and then obtaining a volume cumulative particle size distribution graph.

[0031] As a result of extensive research into the development of a large-scale battery that achieves high capacity and is also excellent in safety, the inventors discovered that the safety of large-scale batteries can be significantly improved by using a positive electrode active material that is a single particle consisting of one primary particle and / or a pseudo-single particle that is an aggregate of 10 or fewer primary particles, and thus completed the present invention.

[0032] Specifically, the lithium secondary battery according to the present invention includes 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, and a seal that seals an open end of the battery can.

[0033] The configuration of the lithium secondary battery of the present invention will be specifically described below.

[0034] 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, and may be, for example, a jelly roll type electrode assembly.

[0035] FIG. 1 shows the laminated structure of an electrode assembly according to the present invention before being wound, and FIG. 2 shows the cross-sectional structure of an electrode plate (positive electrode plate or negative electrode plate) according to the present invention.

[0036] Referring to FIGS. 1 and 2, the electrode assembly of the present invention can be manufactured by stacking a separator 12, a positive electrode plate 10, a separator 12, and a negative electrode plate 11, in this order, at least once, and winding the stack in one direction X.

[0037] Here, the positive electrode plate 10 and the negative electrode plate 11 have a structure in which an active material layer 21 is formed on a 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.

[0038] By using the positive electrode plate 10 and the negative electrode plate 11 including the uncoated portion 22 as described above, it is possible to realize a battery with a tabless structure in which at least a part of the uncoated portion of the positive electrode plate 10 and the negative electrode plate 11 defines the electrode tab without providing a separate electrode tab.

[0039] Specifically, the uncoated portion 22 may be formed long along the winding direction X at an end of one side 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.

[0040] 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 stacked in this order so that the uncoated portions 22 of the positive electrode plate 10 and the negative electrode plate 11 are positioned in opposite directions, 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 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.

[0041] On the other hand, the uncoated portions of the positive electrode plate and the negative electrode plate may be processed into a plurality of segmented pieces that can be bent independently, and at least some of the segmented pieces may be bent toward the winding center C of the electrode assembly.

[0042] The segment pieces can be formed by processing the current collectors of the positive and negative electrode plates using a metal foil cutting process such as laser notching, ultrasonic cutting, or punching.

[0043] When the uncoated portions of the positive and negative electrode plates are processed into multiple segmented pieces, 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.

[0044] The current collecting plate and the plain area are typically joined by welding. To improve the welding characteristics, strong pressure must be applied to the welded area of ​​the plain area to bend it as flat as possible. However, this bending process can cause the plain area to become irregularly distorted and deformed, which can come into contact with the electrode of the opposite polarity, causing an internal short circuit or microcracks in the plain area. However, if the plain areas of the positive and negative electrodes are processed into multiple segments that can be bent independently, the stress applied to the plain area during bending can be alleviated, minimizing deformation and damage to the plain area.

[0045] Furthermore, when the uncoated portion is processed into segmented pieces as described above, overlaps occur between the segments during folding, which increases the strength of the weld with the current collecting plate and prevents the laser from penetrating into the electrode assembly and melting the separator or active material when using cutting-edge technology such as laser welding. Preferably, at least some of the folded segments may overlap at the upper and lower ends of the electrode assembly, and current collecting plates may be bonded to the overlapping segments.

[0046] 5, 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. 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.

[0047] 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 through the separator and is positioned adjacent to the electrode of the opposite polarity, which can cause electrical contact between the positive electrode plate 10 and the negative electrode plate 11 and lead to 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.

[0048] Preferably, the insulating layer 24 is provided on at least one side of the current collector of the positive electrode plate 10, and more preferably, on both sides of the positive electrode plate 10.

[0049] 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 up to a portion of the uncoated portion 22c, for example, up to the front of the folding 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.

[0050] 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 include an organic binder and inorganic particles. Here, the organic binder may be, for example, styrene-butadiene rubber (SBR), and the inorganic particles may be, but are not limited to, alumina oxide.

[0051] Next, each component of the electrode assembly of the present invention will be described in more detail.

[0052] (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 and, optionally, a conductive material and / or a binder.

[0053] 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 / or 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.

[0054] 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.

[0055] In the present invention, the positive electrode plate contains a positive electrode active material consisting of a single particle made of one primary particle and / or a quasi-single particle that is an aggregate of 10 or less primary particles.

[0056] 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, where primary particles break off during the rolling process during positive electrode manufacturing, and internal cracks occur during charge and discharge. When particle cracking or internal cracking occurs in the positive electrode active material, the contact area with the electrolyte increases, resulting in increased gas generation due to side reactions with the electrolyte. Increased gas generation within the battery increases the internal pressure of the battery, potentially leading to battery explosion. In particular, when the volume of a cylindrical battery is increased, the amount of active material inside the battery increases with the volume increase, which significantly increases the amount of gas generation, increasing the risk of battery fire and / or explosion.

[0057] 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 crack during rolling. Furthermore, in the case of positive electrode active materials in the form of single particles or pseudo-single particles, because the number of primary particles that make up the particle is small, there is little change due to volume expansion and contraction of the primary particles during charge and discharge, and as a result, the occurrence of cracks inside the particles is significantly reduced.

[0058] Therefore, when a positive electrode active material consisting of single particles and / or quasi-single particles is used as in the present invention, the amount of gas generated due to particle cracking and internal cracking can be significantly reduced, thereby achieving excellent safety even in large batteries.

[0059] The monoparticles and / or quasi-monoparticles are preferably contained in an amount of 95% to 100% by weight, preferably 98% to 100% by weight, more preferably 99% to 100% by weight, and even more preferably 100% by weight, based on the total weight of the positive electrode active material contained in the positive electrode plate. When the content of the monoparticles and / or quasi-monoparticles satisfies this range, sufficient safety can be achieved when applied to large-scale batteries. If the amount of secondary particle-form positive electrode active material exceeds 5% by weight of the total positive electrode active material, side reactions with the electrolyte due to the generation of impurities from the secondary particles during electrode fabrication and charge / discharge may increase, reducing the gas generation suppression effect. This may result in a reduced stability improvement effect when applied to large-scale batteries.

[0060] On the other hand, the positive electrode active material containing the monoparticles and / or quasi-monoparticles according to the present invention is D min The D of the positive electrode active material can be 1.0 μm or more, 1.1 μm or more, 1.15 μm or more, 1.2 μm or more, 1.25 μm or more, 1.3 μm or more, or 1.5 μm or more. minIf the particle size is less than 1.0 μm, the voltage increases during the rolling process of the positive electrode plate, which makes it easy for particle cracks to occur, and the thermal stability decreases, making it impossible to ensure sufficient thermal stability when applied to large cylindrical batteries.

[0061] On the other hand, considering the resistance and output characteristics, the D min can be 3 μm or less, 2.5 μm or less, or 2 μm or less. min If r is too large, the diffusion distance of lithium ions within the particles increases, which can reduce the resistance and output characteristics.

[0062] For example, D of the positive electrode active material min can be 1.0 μm to 3 μm, 1.0 μm to 2.5 μm, or 1.3 μm to 2.0 μm.

[0063] On the other hand, the positive electrode active material is D 50 The diameter can be 5 μm or less, 4 μm or less, or 3 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. Positive electrode active materials in the form of single particles and / or quasi-single particles have fewer interfaces between primary particles that serve as diffusion paths for lithium ions within the particles, resulting in poorer lithium mobility than positive electrode active materials in the form of secondary particles, which causes an increase in resistance. This increase in resistance becomes more severe as the particle diameter increases, and the increased resistance adversely affects the capacity and output characteristics. Therefore, the D of the positive electrode active material 50 By adjusting the diameter to 5 μm or less, the diffusion distance of lithium ions inside the positive electrode active material particles can be minimized, thereby suppressing an increase in resistance.

[0064] The positive electrode active material is D max The D of the positive electrode active material can be 12 μm to 17 μm, preferably 12 μm to 16 μm, and more preferably 12 μm to 15 μm. max When the D of the positive electrode active material satisfies the above range, better resistance characteristics and capacitance characteristics are exhibited. maxIf D is too large, aggregation between individual particles occurs, and the lithium migration path inside the aggregated particles becomes longer, which reduces lithium mobility and increases resistance. max If the value is too small, excessive crushing will occur, and excessive crushing will cause D min The grain size can be as small as less than 1 μm, which can cause grain cracking during rolling and reduce thermal stability.

[0065] Meanwhile, the positive electrode active material may have a particle size distribution (PSD) represented by the following formula (1) of 3 or less, preferably 2 to 3, and more preferably 2.3 to 3.

[0066] Equation (1): Particle size distribution (PSD) = (D max -D min ) / D 50

[0067] When the positive electrode active material has the above particle size distribution, the electrode density of the positive electrode can be appropriately maintained, and particle cracking and an increase in resistance can be effectively suppressed.

[0068] Meanwhile, the positive electrode active material 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 this range, a single-particle and / or quasi-single-particle positive electrode active material 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 becomes longer, increasing resistance and potentially reducing output characteristics.

[0069] In the present invention, the positive electrode active material preferably has a unimodal particle size distribution. Conventionally, 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 to improve the electrode density of the positive electrode active material layer. However, in the case of single-particle or quasi-single-particle positive electrode active materials, increasing particle size significantly increases the lithium migration path, resulting in a significant increase in resistance. Therefore, when large-particle particles are mixed, the capacity and output characteristics may be reduced. Therefore, in the present invention, a positive electrode active material with a unimodal distribution is used to minimize the increase in resistance.

[0070] Meanwhile, the positive electrode active material may include a lithium nickel-based oxide, specifically, a lithium nickel-based oxide containing 80 mol% or more of Ni relative to the total moles of transition metals. Preferably, the lithium nickel-based oxide may contain Ni in an amount 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%. As described above, when a lithium nickel-based oxide with a high Ni content is used, high capacity can be achieved.

[0071] More specifically, the positive electrode active material may include a lithium nickel-based oxide represented by the following [Chemical Formula 1].

[0072] [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2

[0073] In the above Chemical Formula 1, M 1 can be Mn, Al or a combination thereof, preferably Mn or Mn and Al.

[0074] Said M 2is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably can be one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably can be Zr, Y, or a combination thereof. M 2 The element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving crystal structure stability.

[0075] The said a represents the lithium molar ratio in the lithium nickel-based oxide, and can be 0.8 ≦ a ≦ 1.2, 0.85 ≦ a ≦ 1.15, or 0.9 ≦ a ≦ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0076] The said b represents the nickel molar ratio among all the metals other than lithium in the lithium nickel-based oxide, and can be 0.8 ≦ b < 1, 0.82 ≦ b < 1, 0.83 ≦ b < 1, 0.85 ≦ b < 1, 0.88 ≦ b < 1, or 0.90 ≦ b < 1. When the nickel molar ratio satisfies the above range, it shows a high energy density and enables the realization of a high capacity.

[0077] The said c represents the cobalt molar ratio among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < c < 0.2, 0 < c < 0.18, 0.01 ≦ c ≦ 0.17, 0.01 ≦ c ≦ 0.15, 0.01 ≦ c ≦ 0.12, or 0.01 ≦ c ≦ 0.10. When the cobalt molar ratio satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0078] The said d represents the molar ratio of the M 1 element among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < d < 0.2, 0 < d < 0.18, 0.01 ≦ d ≦ 0.17, 0.01 ≦ d ≦ 0.15, 0.01 ≦ d ≦ 0.12, or 0.01 ≦ d ≦ 0.10. M 1 When the molar ratio of the element satisfies the above range, the structure stability of the positive electrode active material is excellent.

[0079] The e is M among all metals other than lithium in the lithium nickel-based oxide. 2 It denotes the molar ratio of the elements and can be 0≦e≦0.1, or 0≦e≦0.05.

[0080] Meanwhile, the positive electrode active material according to the present invention may further include, if necessary, a coating layer on the surface of the lithium nickel-based oxide particles, the coating layer including one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. Preferably, the coating element may be Al, B, Co, or a combination thereof.

[0081] When a coating layer is present on the surface of the lithium nickel-based oxide particles, the coating layer suppresses contact between the electrolyte and the lithium composite transition metal oxide, thereby achieving the effect of reducing elution of the transition metal and generation of gas due to side reactions with the electrolyte.

[0082] The positive electrode active material can be contained in an amount of 80 to 99% by weight, preferably 85 to 99% by weight, and more preferably 90 to 99% by weight, based on the total weight of the positive electrode active material layer.

[0083] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations, as long as it does not cause chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials 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.

[0084] The binder functions to improve adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0085] On one hand, an insulating layer covering a part of the positive electrode active material layer and a part of the non-coated portion can be further formed on the positive electrode plate according to the need. The insulating layer can be formed along a direction parallel to the winding direction of the electrode assembly.

[0086] (2) Negative electrode plate The negative electrode plate can have a structure in which a negative electrode active material layer is formed on one or both sides of a long sheet-like negative electrode current collector. The negative electrode active material layer can contain a negative electrode active material, a conductive material, and a binder.

[0087] Specifically, the negative electrode plate can be manufactured by applying a negative electrode slurry produced 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 on one or both sides of a sheet-like negative electrode current collector, removing the solvent of the negative electrode slurry by a drying process, and then rolling it. On the other hand, when applying the negative electrode slurry, a negative electrode plate including a non-coated portion can be manufactured by a method of not applying the negative electrode slurry to a partial region of the negative electrode current collector, for example, one end portion of the negative electrode current collector.

[0088] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; silicon-based materials such as Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), and Si-C composite; lithium metal thin film; metal materials capable of alloying with lithium such as Sn and Al; etc. Any one or a mixture of two or more of these can be used.

[0089] Preferably, the negative electrode plate according to the present invention can contain a silicon-based negative electrode active material. The silicon-based negative electrode active material can 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 can 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.

[0090] On the other hand, the silicon-based negative electrode active material can be doped with M b metal, where the M b metal can be a Group 1 metal element or a Group 2 metal element, and specifically can be Li, Mg, etc. Specifically, the silicon negative electrode active material can be Si, SiOy (where 0 < y < 2), Si-C composite, etc. doped with M b metal. In the case of the 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.

[0091] Further, the silicon-based negative electrode active material can further include a carbon coating layer on the surface of the particles. Here, the amount of the carbon coating can be 20% by weight or less, preferably 1 - 20% by weight, based on the total weight of the silicon-based negative electrode active material.

[0092] Also, the negative electrode plate can further contain a carbon-based negative electrode active material as a negative electrode active material as needed. The carbon-based negative electrode active material can be, for example, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc., but is not limited thereto.

[0093] On the other hand, when a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material is used as the negative electrode active material, the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material may be 1:99 to 20:80, preferably 1:99 to 15:85, and more preferably 1:99 to 10:90, by weight.

[0094] The negative electrode active material can be contained in an amount of 80 to 99% by weight, preferably 85 to 99% by weight, and more preferably 90 to 99% by weight, based on the total weight of the negative electrode active material layer.

[0095] 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.

[0096] The conductive material is used to impart conductivity to the negative electrode. Any conductive material can be used without particular limitations, as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powder or 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.

[0097] The binder functions to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0098] (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 limitations. 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 polymeric material may also be used.

[0099] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described.

[0100] The lithium secondary battery according to the present invention may include an electrode assembly having 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, a battery can in which the electrode assembly is housed, and a seal that seals an open end of the battery can.

[0101] Preferably, the lithium secondary battery according to the present invention is a cylindrical battery, and more preferably a large cylindrical battery having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of a cylindrical battery divided by the diameter of the cylindrical battery) of 0.4 or more. Here, the form factor refers to values ​​indicating the diameter and height of a cylindrical battery.

[0102] Cylindrical batteries according to the present invention can be, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 4875 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), or a 4680 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575). In the form factor number, the first two digits indicate the cell diameter, and the next two or three digits indicate the cell height.

[0103] The lithium secondary battery according to the present invention significantly reduces the amount of gas generation compared to conventional batteries by using a positive electrode active material in the form of a single particle and / or a pseudo-single particle, thereby achieving excellent safety even in large cylindrical batteries with a form factor ratio of 0.4 or more.

[0104] Meanwhile, the lithium secondary battery according to the present invention may preferably be a battery having a tab-less structure that does not include electrode tabs, but is not limited thereto.

[0105] The tabless-structured battery may have a structure in which, for example, the positive electrode plate and the negative electrode plate each include an uncoated portion where no active material layer is formed, the uncoated positive electrode plate portion and the uncoated negative electrode plate portion are located at the upper and lower ends of the electrode assembly, respectively, current collecting plates are bonded to the uncoated positive electrode plate portion and the uncoated negative electrode plate portion, and the current collecting plates are connected to electrode terminals.

[0106] Fig. 3 shows a cross-sectional view of a battery with a tabless structure according to one embodiment of the present invention. Hereinafter, a lithium secondary battery according to one embodiment of the present invention will be described with reference to Fig. 3. However, Fig. 3 shows one embodiment of the present invention, and the structure of the lithium secondary battery of the present invention is not limited to the scope disclosed in Fig. 3.

[0107] A lithium secondary battery 140 according to an embodiment of the present invention includes a jelly-roll type 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.

[0108] Here, the positive and negative electrode plates of the electrode assembly may each include an uncoated portion where an active material layer is not 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 other than the electrode assembly will be described below.

[0109] The battery can 142 is a 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 the electrolyte.

[0110] The electrolyte used in the present invention is not particularly limited to any particular type, and may be any of various electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes.

[0111] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0112] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0113] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, and LiB(C, O) . The lithium salt concentration is preferably within a range of 0.1 to 5.0 M, and more preferably 0.1 to 3.0 M. When the lithium salt concentration is within this range, the electrolyte exhibits appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0114] In addition to the electrolyte components, the electrolyte may further contain additives for purposes such as improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. Examples of additives include, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, which may be used alone or in combination. The additives may be present in an amount of 0.1 to 10 wt %, preferably 0.1 to 5 wt %, based on the total weight of the electrolyte.

[0115] 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 transmits current applied from the external power source to the negative electrode plate.

[0116] If necessary, a beading portion 147 and a crimping portion 148 may be provided on the upper end of the battery can 142. The beading portion 147 may be formed by pressing the periphery of the outer periphery of the battery can 142 up to a distance D1. The beading portion 147 prevents the electrode assembly 141 housed inside the battery can 142 from being removed through the upper opening of the battery can 142 and may function as a support on which the sealing body 143 is placed.

[0117] The crimping portion 148 may be formed on the beading portion 147 and has an extended and bent shape to enclose 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.

[0118] Next, the sealing body 143 is for sealing 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.

[0119] 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 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.

[0120] 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 electrically insulate the battery can 142 from the cap plate 143a.

[0121] Meanwhile, the lithium secondary 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).

[0122] Specifically, the lithium secondary battery 140 according to the present invention may include a first current collecting plate 144 coupled to an upper portion of the electrode assembly 141 and a second current collecting plate 145 coupled to a lower portion of the electrode assembly 141.

[0123] A first current collecting plate 144 and / or a second current collecting plate 145 may further be included.

[0124] The first current collecting plate 144 is attached 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 connected to the first current collecting plate 144. The lead 149 may extend upwardly of the electrode assembly 141 and be attached to the connecting plate 143c, or may be directly attached to the lower surface of the cap plate 143a. The connection of the lead 149 to other components may be performed 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.

[0125] Meanwhile, the first current collecting plate 144 is connected to the end of the uncoated portion 146a of the positive electrode plate, and the connection may be performed by, for example, laser welding, resistance welding, ultrasonic welding, soldering, or the like.

[0126] 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. Here, the coupling may be performed by a method such as laser welding, resistance welding, ultrasonic welding, or soldering.

[0127] Meanwhile, the battery 140 according to the present invention may further include an insulating member (insulator) 146, if necessary. The insulating member 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 insulating member 146, direct contact between the first current collecting plate 144 and the inner peripheral surface of the battery can 142 can be prevented.

[0128] The insulating member 146 has a lead hole 151 through which the lead 149 extending upward from the first current collecting plate 144 is drawn out. The lead 149 is drawn out upward through the lead hole 151 and coupled to the lower surface of the connecting plate 143c or the lower surface of the cap plate 143a.

[0129] The insulating member 146 may be made of an insulating polymer resin, such as polyethylene, polypropylene, polyimide, or polybutylene terephthalate.

[0130] Meanwhile, the 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 more fragile than the surrounding region. Therefore, when the pressure inside the battery 140 increases above a predetermined level, the vent 152 ruptures, releasing the gas inside the battery can 142 to the outside, thereby preventing the battery from exploding.

[0131] Fig. 4 shows a cross-sectional view of a battery having a tabless structure according to another embodiment of the present invention. Hereinafter, a battery according to another embodiment of the present invention will be described with reference to Fig. 4. However, Fig. 4 shows one embodiment of the present invention, and the structure of the battery according to the present invention is not limited to the scope disclosed in Fig. 4.

[0132] Referring to FIG. 4, a battery 170 according to another embodiment of the present invention has a different structure of the battery can and the sealed body compared to the battery 140 shown in FIG. 3, but the configuration of the electrode assembly and electrolyte is substantially the same.

[0133] Specifically, a battery 170 according to another embodiment includes a battery can 171 having a rivet terminal 172 penetrating therethrough. 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.

[0134] 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 partially 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-coupled to the inner surface of the battery can 171. That is, an end of the terminal inserting portion 172b may be bent 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.

[0135] 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 edge portion of the electrode assembly 141. This prevents the uncoated portion 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.

[0136] 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 rivet terminal 172, which has a substantially flat shape, to function as the positive terminal of the battery 170.

[0137] 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 is deformed when the terminal inserting portion 172b is riveted, and can be tightly attached to the inner surface of the battery can 171. The second gasket 173 may be made of, for example, an insulating polymer resin.

[0138] 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.

[0139] When the second gasket 173 is made of a polymer resin, the second gasket 173 can be joined to the battery can 171 and the rivet terminal 172 by heat sealing. In this case, it is possible to strengthen the airtightness at the joining interface between the second gasket 173 and the rivet terminal 172 and at the joining interface between the second gasket 173 and the battery can 171. On the other hand, when the gasket exposed portion 173a of the second gasket 173 has a shape that extends to the upper surface of the terminal exposed portion 172a, the rivet terminal 172 can be joined integrally with the second gasket 173 by insert injection.

[0140] The remaining area 175 of the top surface of the battery can 171 other than 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 .

[0141] 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.

[0142] 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 with at least a portion of its edge interposed between the inner surface of the battery can 171 and the first gasket 178b. In one example, at least a portion of the edge of the second current collecting plate 176 may be supported on a lower end surface of a beading portion 180 formed at the lower end of the battery can 171 and fixed to the beading portion 180 by welding. In a modified example, at least a portion of the edge of the second current collecting plate 176 may be directly welded to the inner wall surface of the battery can 171.

[0143] The second current collecting plate 176 may have a plurality of projections (not shown) formed radially on the surface facing the uncoated portion 146b. When the projections and recesses are formed, the second current collecting plate 176 may be pressed to press the projections and recesses into the uncoated portion 146b.

[0144] Preferably, the end of the second current collecting plate 176 and the uncoated portion 146b can be joined by welding, for example, laser welding.

[0145] The sealing body 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.

[0146] Preferably, the cap plate 178a is made of a conductive metal material. However, the cap plate 178a does not have 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 release gas when the internal pressure of the battery cell 170 exceeds a critical value.

[0147] Preferably, the rivet terminal 172 electrically connected to the uncoated portion 146a of the positive electrode plate is used as a positive electrode terminal. Furthermore, a portion 175 of the upper surface of the battery can 171, other than 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 a negative electrode terminal. When two electrode terminals are located on the upper portion of the battery, electrical connecting components such as bus bars can be disposed on only one side of the 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 when connecting electrical connecting components such as bus bars. This allows the battery 170 to reduce resistance at the contact points of the electrical connecting components to a desirable level.

[0148] When a 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 stability of the battery.

[0149] The lithium secondary battery of the present invention as described above can be used to manufacture a battery pack. Figure 6 schematically illustrates the 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 secondary batteries 1 and a pack housing 2 that accommodates the assembly. Here, the secondary batteries 1 are the battery cells according to the above-described embodiment. For ease of illustration, components such as bus bars for electrically connecting the secondary batteries 1, a cooling unit, and external terminals are omitted from the drawing.

[0150] The battery pack 3 can be mounted on a vehicle. The vehicle can be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle can be a four-wheeled vehicle or a two-wheeled vehicle.

[0151] FIG. 7 is a diagram illustrating a vehicle including the battery pack 3 of FIG.

[0152] Referring to FIG. 7, an automobile 5 according to an embodiment of the present invention includes a battery pack 3 according to an embodiment of the present invention, and operates by receiving power from the battery pack 3.

[0153] The present invention will now be described in more detail with reference to specific examples.

[0154] [Example 1] It has a unimodal particle size distribution, D min = 1.78 μm, D 50 = 4.23 μm, D max = 13.1 μm, and the positive electrode active material (composition: Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 ]O2) was prepared. FIG. 8 shows an SEM photograph of the positive electrode active material used in Example 1.

[0155] Positive electrode active material: carbon nanotubes: 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.

[0156] Anode active material (graphite:SiO = 95:5 by weight mixture): conductive material (Super C): styrene-butadiene rubber (SBR): 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.

[0157] A separator was interposed between the positive and negative electrode plates, and the plates were stacked in the order of separator / positive electrode plate / separator / negative electrode plate and wound up to prepare a jelly roll type electrode assembly. The electrode assembly prepared as described above was inserted into a battery can, and an electrolyte was injected to prepare a 4680 cell.

[0158] [Example 2] The positive electrode active material has a unimodal particle size distribution and D min = 1.38 μm, D 50 = 4.69 μm, D max = 18.5 μm, and the positive electrode active material (composition: Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 ]O2) was used, a 4680 cell was fabricated in the same manner as in Example 1. FIG. 9 shows an SEM photograph of the positive electrode active material used in Example 2.

[0159] [Comparative Example 1] As a positive electrode active material, large particle size average particle size D 50 is 9 μm, and the small particle average particle size D 50 The positive electrode active material (composition: Li[Ni 0.9 Co 0.05 Mn 0.04 Al 0.01 ]O2) was used, the same method as in Example 1 was used to prepare a 4680 cell.

[0160] Comparative Example 2 The positive electrode active material has a unimodal particle size distribution and D min =0.892μm, D 50 = 3.02 μm, D max = 11 μm, and the positive electrode active material is a mixture of single particles and pseudo-single particles (composition: Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 ]O2) was used, the same method as in Example 1 was used to prepare a 4680 cell.

[0161] FIG. 10 shows an SEM photograph of the positive electrode active material used in Comparative Example 2.

[0162] [Experimental Example 1] A hot box test was carried out on the 4680 cells manufactured in Examples 1 and 2 and Comparative Examples 1 and 2.

[0163] Specifically, each of the 4680 cells prepared in Example 1 and Comparative Example 1 was placed in a hot box chamber at room temperature, heated to 130°C at a rate of 5°C / min, and maintained at that temperature for 30 minutes, after which the temperature change of the battery was measured. A case in which no thermal runaway or ignition occurred during the test was marked as Pass, and a case in which thermal runaway and / or ignition occurred was marked as Fail. To ensure test accuracy, the test was performed more than twice on the cells of Examples 1 and 2.

[0164] The measurement results are shown in Table 1 below and in Figures 11 and 12. Figure 11 is a graph showing the hot box test results of the 4680 cells manufactured according to Sample 1 of Example 1 and Comparative Example 1, and Figure 12 is a graph showing the hot box test results of the 4680 cells manufactured according to Samples 2 and 3 of Example 1, Samples 1 and 2 of Example 2, and Comparative Example 2.

[0165] [Table 1]

[0166] Referring to Table 1, Figs. 11 and 12, D min In the case of the cylindrical battery of Example 1, which uses a positive electrode active material in the form of a single particle / quasi-single particle having a particle size of 1.0 μm or more, the voltage and temperature of the battery are stably maintained up to 65 minutes. minIt can be seen that the lithium secondary battery of Comparative Example 2, which used a positive electrode active material in the form of a single particle / quasi-single particle having a particle size of less than 1.0 μm, experienced a rapid rise in the temperature of the battery.

[0167] [Experimental Example 2] After rolling the positive electrode plates prepared in Example 1 and Comparative Example 1, the positive electrode plates were cut using an ion milling device and the cross sections were photographed using an SEM to check the degree of cracking of the positive electrode active material particles. Fig. 13 shows an SEM photograph of a cross section of the positive electrode plate prepared in Example 1, and Fig. 14 shows an SEM photograph of a cross section of the positive electrode plate prepared in Comparative Example 1.

[0168] 13 and 14, the positive electrode plate of Example 1 had almost no cracks in the particles of the positive electrode active material even after rolling, whereas the positive electrode plate of Comparative Example 2, which used secondary particles, had many cracks in the particles of the positive electrode active material after rolling. [Explanation of symbols]

[0169] 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 batteries 141 Electrode assembly 142, 171 Battery can 143, 178 Sealed body 144 First current collecting plate 145, 176 Second current collecting plate 146 Insulators 152 Venting section 172 Rivet terminal 173 Second gasket 147 Beading section 148 Crimping section 149 leads

Claims

1. A 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; and a sealing body that seals an open end of the battery can, The positive electrode plate includes a positive electrode active material including a single particle, a pseudo-single particle, or a combination thereof, and the D of the positive electrode active material ｍｉｎ A lithium secondary battery having a particle size of 1.0 μm or more.

2. The positive electrode active material is D ５０ 2. The lithium secondary battery according to claim 1, wherein the thickness of the surface roughness layer is 5 μm or less.

3. The positive electrode active material is D ｍａｘ 2. The lithium secondary battery according to claim 1, wherein the average particle diameter is 12 μm to 17 μm.

4. 2. The lithium secondary battery according to claim 1, wherein the positive electrode active material has a particle size distribution (PSD) represented by the following formula (1) of 3 or less: Equation (1): Particle size distribution (PSD) = (D ｍａｘ -D ｍｉｎ ) / D ５０

5. The lithium secondary battery according to claim 1 , wherein the positive electrode active material has a unimodal particle size distribution that exhibits a single peak in a volume cumulative particle size distribution graph.

6. 2. The lithium secondary battery according to claim 1, wherein the single particles, pseudo-single particles, or a combination thereof are contained in an amount of 95% by weight to 100% by weight based on the total weight of the positive electrode active material contained in the positive electrode plate.

7. 2. The lithium secondary battery according to claim 1, wherein the positive electrode active material contains a lithium nickel-based oxide containing 80 mol % or more of Ni relative to the total number of moles of transition metals.

8. The lithium secondary battery according to claim 1 , wherein the positive electrode active material comprises a lithium nickel-based oxide represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the above formula 1, M １ is Mn, Al or a combination thereof, and M ２ are Zr, W, Ti, Mg, Ca, Sr, and Ba, and 0.8≦a≦1.2, 0.83≦b<1, 0<c<0.17, 0<d<0.17, and 0≦e≦0.

1.

9. 2. The lithium secondary battery according to claim 1, wherein the positive electrode active material has a primary particle size of 0.5 μm to 5 μm.

10. The lithium secondary battery according to claim 1 , wherein the negative electrode plate contains a silicon-based negative electrode active material.

11. The 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.

12. The lithium secondary battery according to claim 11, 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.

13. 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is a cylindrical battery having a form factor ratio of 0.4 or more, the form factor being a value obtained by dividing the diameter of the cylindrical battery by its height.

14. 14. The lithium secondary battery according to claim 13, wherein the lithium secondary battery is a 46110 cell, a 4875 cell, a 48110 cell, a 4880 cell, or a 4680 cell.

15. the positive electrode plate and the negative electrode plate each include a plain portion on which no active material layer is formed, 2. The lithium secondary battery according to claim 1, wherein at least a portion of the uncoated portion of the positive electrode plate or the negative electrode plate defines an electrode tab.

16. the positive electrode plate uncoated portion and the negative electrode plate uncoated portion are formed at one end of one side of the positive electrode plate and the negative electrode plate, respectively, along a winding direction of the electrode assembly, a current collecting plate is coupled to each of the positive electrode uncoated portion and the negative electrode uncoated portion, The lithium secondary battery according to claim 15 , wherein the current collecting plate is connected to an electrode terminal.

17. The positive electrode uncoated portion and the negative electrode uncoated portion are processed into a plurality of segmented pieces that can be bent independently, The lithium secondary battery according to claim 16 , wherein at least some of the plurality of segment pieces are bent toward the winding center of the electrode assembly.

18. At least some of the folded segments overlap each other on the upper and lower ends of the electrode assembly, 18. The lithium secondary battery according to claim 17, wherein the current collecting plates are bonded onto the overlapping segments.

19. The lithium secondary battery of claim 15, 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.

20. A battery pack comprising the lithium secondary battery according to any one of claims 1 to 19.

21. 21. A motor vehicle comprising the battery pack of claim 20.

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