Negative electrode for lithium secondary battery and lithium secondary battery containing the same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery in which lithium deposition is suppressed and a lithium secondary battery including the same, the negative electrode having a form in which a carbon-based active material contained in a sliding portion of a negative electrode active layer has a high degree of alignment, and thus the negative electrode has an excellent effect of suppressing lithium deposition at an end of the negative electrode active layer during charging and discharging of the secondary battery, and thus a lithium secondary battery including the same has an advantage in that it is highly safe and can be charged and discharged for a long time under high rate conditions.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2022-0116873 dated September 16, 2022, and Korean Patent Application No. 10-2023-0062304 dated May 15, 2023, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

[0002] This invention relates to a negative electrode for a lithium secondary battery in which lithium deposition is suppressed during charging and discharging, and to a lithium secondary battery containing the same. [Background technology]

[0003] In recent years, secondary batteries have been widely applied not only to small devices such as portable electronic devices, but also to medium- and large-scale devices such as battery packs for hybrid and electric vehicles, or power storage devices.

[0004] Such a secondary battery is a power generation element capable of charging and discharging, consisting of a stacked structure of a positive electrode / separating membrane / negative electrode. Generally, the positive electrode contains lithium metal oxide as the positive electrode active material, and the negative electrode contains a carbon-based negative electrode active material such as graphite. During charging, lithium ions released from the positive electrode are absorbed into the carbon-based negative electrode active material of the negative electrode, and during discharging, lithium ions contained in the carbon-based negative electrode active material are absorbed into the lithium metal oxide of the positive electrode, resulting in a configuration in which charging and discharging are repeated.

[0005] One of the factors that influences the performance of a secondary battery is the capacity ratio of the active material contained in the positive electrode and the negative electrode, respectively. This capacity ratio can be expressed as the N / P ratio. The N / P ratio is the value obtained by dividing the total capacity of the negative electrode, which is calculated considering the capacity per unit area of ​​the negative electrode, by the total capacity of the positive electrode, which is obtained considering the capacity per unit area of ​​the positive electrode. Since this has a significant impact on the safety and capacity of the battery, it is generally adjusted to have a value of 1 or greater.

[0006] However, during the manufacturing of the positive and negative electrodes, a sliding phenomenon is induced at the edges of the electrode composite layer containing the active material, causing the thickness of the electrode composite layer to decrease outwards. This makes it difficult to maintain a constant N / P ratio between the positive and negative electrodes. In particular, when the N / P ratio falls below 1, lithium ions are not fully intercalated into the negative electrode active material during battery charging, and instead precipitate on the negative electrode surface, forming dendrites. The likelihood of these dendrites forming increases significantly when lithium secondary batteries are used for extended periods under high-rate conditions. Since these dendrites can induce internal short circuits in the battery, they can act as a factor that impairs battery safety.

[0007] To solve these problems, an attempt was made to manufacture a negative electrode by increasing the thickness of the edges where the sliding phenomenon occurs during the formation of the negative electrode composite layer. In this case, when the negative electrode composite layer is rolled, the negative electrode active material becomes denser at the edges of the negative electrode composite layer, which reduces the lithium ion mobility at the edges and thus degrades battery performance. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Korean Published Patent Publication No. 10-2015-0028457 [Patent Document 2] Korean Published Patent Publication No. 10-2016-0125720 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a negative electrode for a lithium secondary battery and a lithium secondary battery containing the same, in which lithium deposition is suppressed at the edges of the negative electrode composite layer even when the lithium secondary battery is used for a long time under high-rate conditions. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, In one embodiment, the present invention is described as follows: A negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector, comprising a carbon-based negative electrode active material, The negative electrode active layer is divided into a flat portion whose thickness is maintained constant with respect to the cross-sectional structure in the thickness direction, and a sliding portion located at the end of the flat portion and having a thickness gradient. The sliding portion provides a negative electrode for a lithium secondary battery in which the value related to the following formula 1 is 1.0 or less when analyzed by near-end X-ray absorption fine structure (NEXAFS) spectroscopy.

[0011]

number

[0012]

number

[0013]

number

[0014] In equations 1 to 3, S 60 / 0 This is the peak intensity ratio (I0) when the incident angle of X-rays is 0°. B / A The peak intensity ratio (I60) when the incident angle of X-rays to ) is 60° B / A This represents the value of ), I60 A This represents the intensity of the strongest peak among the peaks present at 286±1.0eV when the X-ray incidence angle is 60°. I60 B This represents the intensity of the strongest peak among the peaks present at 292.5±1.0eV when the incident angle of X-rays is 60°. I0 Arepresents the intensity of the peak with the highest intensity among the peaks existing at 286 ± 1.0 eV when the incident angle of X-rays is 0°, I0 B represents the intensity of the peak with the highest intensity among the peaks existing at 292.5 ± 1.0 eV when the incident angle of X-rays is 0°.

[0015] At this time, the sliding part may have a lower degree of alignment (O.I sliding ) of the carbon-based negative electrode active material according to the following formula 4 than the degree of alignment (O.I flat ) of the carbon-based negative electrode active material contained in the flat part.

[0016] [Formula 4] O.I = I 004 / I 110

[0017] In formula 4, I 004 represents the area of the peak indicating the (0, 0, 4) crystal plane during X-ray diffraction (XRD) spectroscopic analysis of the negative electrode active layer, I 110 represents the area of the peak indicating the (1, 1, 0) crystal plane during X-ray diffraction (XRD) spectroscopic analysis of the negative electrode active layer.

[0018] Specifically, the degree of alignment (O.I flat ) of the carbon-based negative electrode active material contained in the flat part may be 110% - 200% based on the degree of alignment (O.I sliding ) of the carbon-based negative electrode active material contained in the sliding part.

[0019] Also, the degree of alignment (O.I sliding ) of the carbon-based negative electrode active material contained in the sliding part may be 0.1 - 0.6.

[0020] Also, the sliding part may have a ratio (I 004 / I 002 ) of the intensity of the peak indicating the (0, 0, 4) crystal plane to the intensity of the peak indicating the (0, 0, 2) crystal plane during X-ray diffraction (XRD) spectroscopic analysis of 0.04 or more.

[0021] On the other hand, the negative electrode current collector is divided into a coated portion on which the negative electrode active layer is arranged and a plain portion on which the negative electrode active layer is not arranged, and the sliding portion may be adjacent to the plain portion on which the negative electrode tab is provided.

[0022] In this case, the sliding portion may have a width of 1 mm to 30 mm based on the cross-sectional structure in the thickness direction of the negative electrode active layer.

[0023] Furthermore, the carbon-based anode active material may contain one or more of natural graphite and artificial graphite, have spherical particulate matter, and may have a high degree of sphericity of 0.75 or higher.

[0024] Furthermore, in one embodiment of the present invention, The present invention provides a lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode according to the present invention as described above, and a separator membrane disposed between the positive electrode and the negative electrode.

[0025] In this case, the positive electrode may include a positive electrode current collector and a positive electrode active layer provided on at least one surface of the positive electrode current collector, which contains one or more positive electrode active materials from among the lithium metal oxides represented by the following chemical formulas 1 and 2.

[0026] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0027] [Chemical formula 2] LiM 2 p Mn 1-p O4

[0028] In the above chemical formulas 1 and 2, M 1It is one or more elements from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. x, y, z, w, and v are such that 1.0 ≤ x ≤ 1.30, 0.5 ≤ y < 1, and 0 respectively. <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつy+z+w+v=1であり、 M 2 It is Ni, Co, or Fe, p is 0.05 ≤ p ≤ 1.0.

[0029] Specifically, the above positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.9 Co 0.05 Mn 0.05 O2, LiLiLi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.15 Al 0.05 O 2、 LiRing 0.7 Co 0.1 Mn 0.1 Al 0.1 O2, LiLiLi 0.7 Mn 1.3 O4, LiSa 0.5 Mn 1.5 O4, LiSa 0.3 Mn 1.7 O4, LiFePO4, LiFe 0.8 Mn 0.2 PO4 and LiFe 0.5 Mn 0.5 It may contain one or more of the PO4 types.

[0030] Furthermore, the electrode assembly may be a stacked electrode assembly, a zigzag electrode assembly, or a zigzag-stacked electrode assembly. [Effects of the Invention]

[0031] The negative electrode for lithium secondary batteries according to the present invention has a degree of alignment (S) of the carbon-based active material contained in the sliding portion of the negative electrode active layer. 60 / 0 By minimizing the OI (and / or OI), it is highly effective in suppressing lithium deposition on the surface of the negative electrode active layer, specifically at the edges, during charging and discharging of secondary batteries. Therefore, lithium secondary batteries containing this material have the advantage of high safety and the ability to charge and discharge for long periods under high-rate conditions. [Brief explanation of the drawing]

[0032] [Figure 1] This is a cross-sectional view showing the cross-sectional structure of a negative electrode manufactured according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view showing the cross-sectional structure of a negative electrode manufactured according to another embodiment of the present invention. [Figure 3] This image shows the alignment of the ab-axis crystal planes of graphite when a magnetic field is applied to the negative electrode slurry during negative electrode active layer formation. (a) shows the case where no magnetic field is applied and the graphite crystal planes are not aligned, and (b) shows the case where a magnetic field is applied and the graphite crystal planes are aligned. [Figure 4] This image shows the trend of absorption peaks by type and position of each orbital depending on the incident angle of X-rays during near-end X-ray absorption fine structure (NEXAFS) spectroscopy. (a) shows the type and position of the orbitals forming the double bond in graphite, and (b) shows the positional peak morphology of each orbital when X-rays are incident. [Figure 5] This image shows the incident X-ray angle during near-end X-ray absorption fine structure (NEXAFS) spectroscopy analysis of a negative electrode manufactured according to one embodiment of the present invention. [Modes for carrying out the invention]

[0033] Since the present invention can be modified in various ways and may have a variety of embodiments, specific embodiments will be described in detail.

[0034] However, this is not intended to limit the present invention to any particular embodiment, but rather should be understood to include all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0035] In the present invention, terms such as "includes" and "have" are intended to specify the presence of features, numbers, stages, operations, components, parts, or combinations thereof as described in the specification, and do not preemptively exclude the presence or possibility of adding one or more other features, numbers, stages, operations, components, parts, or combinations thereof.

[0036] Furthermore, in this invention, when a part such as a layer, film, region, or plate is described as being "on top" of another part, this includes not only the case where it is "directly on top" of the other part, but also the case where another part is located in between. Conversely, when a part such as a layer, film, region, or plate is described as being "below" another part, this includes not only the case where it is "directly below" the other part, but also the case where another part is located in between. Also, in this application, being "on top" may include being located not only at the top but also at the bottom.

[0037] Furthermore, in the present invention, "contains as a main component" may mean that the defined component is contained in an amount of 50% by weight or more (or 50% by volume or more), 60% by weight or more (or 60% by volume or more), 70% by weight or more (or 70% by volume or more), 80% by weight or more (or 80% by volume or more), 90% by weight or more (or 90% by volume or more), or 95% by weight or more (or 95% by volume or more) of the total weight (or total volume). For example, "contains graphite as a main component as the negative electrode active material" may mean that graphite is contained in an amount of 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more of the total weight of the negative electrode active material, and in some cases it may also mean that the entire negative electrode active material consists of graphite and contains 100% by weight of graphite.

[0038] Furthermore, in the present invention, "cross-sectional structure" means the structure of a surface cut in the thickness direction of the negative electrode active layer, or the structure of a surface cut perpendicularly with respect to the surface of the negative electrode active layer. In this case, the cut surface may be the same as a surface cut perpendicular to the process direction during negative electrode active layer formation, or a surface cut in the width direction of the negative electrode slurry applied to form the negative electrode active layer. Moreover, the above cross-sectional structure is the structure of a surface cut in the thickness direction of the negative electrode active layer, and may have a structure cut in a direction progressing from one surface on which the negative electrode tab is formed to the opposite surface. That is, it may have a thickness-direction cut structure on which a negative electrode tab is provided on one side.

[0039] Furthermore, in this specification, "the carbon-based anode active material is oriented" or "the carbon-based anode active material is aligned" may mean that, as shown in Figure 3(b), a specific crystal plane (for example, the ab-axis crystal plane of graphite) that shows the two-dimensional planar structure of the carbon-based anode active material constituting the anode active material particles is arranged to have a predetermined inclination with respect to the surface of the anode current collector. This may differ from, as shown in Figure 3(a), where the particles of the carbon-based anode active material themselves are aligned in a predetermined direction only within the anode active layer, but have no directionality with respect to the anode current collector.

[0040] Furthermore, "high orientation of carbon-based anode active material" may mean that a specific crystal plane (for example, the ab-axis crystal plane of graphite) exhibiting the two-dimensional planar structure of the carbon-based anode active material contained in the anode active layer has a high frequency of having a predetermined inclination with respect to the surface of the anode current collector. In some cases, it may also mean that the above crystal planes of the carbon-based anode active material contained in the anode active layer are aligned at a high angle (for example, an angle close to perpendicular, greater than 45°, specifically 60° or more) with respect to the surface of the anode current collector.

[0041] Furthermore, "high degree of alignment of carbon-based anode active material" means that the "degree of alignment (OI)" referred to herein is large, and may mean that specific crystal planes (e.g., the ab-axis crystal plane of graphite) showing the two-dimensional planar structure of the carbon-based anode active material contained in the anode active layer are aligned at a low angle (e.g., less than 45°) with respect to the surface of the anode current collector. Conversely, "low degree of alignment of carbon-based anode active material" means that the "degree of alignment (OI)" is small, and may mean that the above-mentioned crystal planes of the carbon-based anode active material contained in the anode active layer are aligned at a high angle (e.g., an angle close to perpendicular, 45° or more, specifically 60° or more) with respect to the surface of the anode current collector.

[0042] Furthermore, in this specification, "average particle size (D 50 "50%" refers to the particle size at which the cumulative value in the particle size distribution becomes 50%, and this is also called the median diameter.

[0043] The present invention will be described in more detail below.

[0044] <Negative electrode for lithium secondary batteries> In one embodiment, the present invention is described as follows: A negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector, comprising a carbon-based negative electrode active material, The above-mentioned negative electrode active layer is divided into a flat portion in which the thickness is maintained constant based on the cross-sectional structure in the thickness direction, and a sliding portion located at the end of the flat portion and having a thickness gradient. The sliding portion described above provides a negative electrode for a lithium secondary battery in which the value related to Equation 1 below is 1.0 or less when analyzed by near-end X-ray absorption fine structure (NEXAFS) spectroscopy.

[0045]

number

[0046] The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode active layer containing a carbon-based negative electrode active material on at least one surface of the negative electrode current collector.

[0047] In this context, the negative electrode active layer refers to the layer that embodies the electrical activity of the negative electrode. The negative electrode active layer contains a carbon-based negative electrode active material as the negative electrode active material in order to embody electrical activity through a reversible oxidation-reduction reaction during the charging and discharging of the battery. Specifically, the carbon-based negative electrode active material refers to a material whose main component is carbon atoms, and such a carbon-based negative electrode active material may include graphite. The graphite may include one or more of either natural graphite or artificial graphite. For example, the carbon-based negative electrode active material may contain natural graphite or artificial graphite alone, or in some cases, a mixture of natural graphite and artificial graphite. In this case, the mixing ratio of natural graphite and artificial graphite may be 5-40:60-95 or 10-30:70-90 based on weight. By including natural graphite and artificial graphite in the above-mentioned mixing ratio, the carbon-based anode active material can achieve strong adhesion between the anode current collector and the anode active layer while also exhibiting high orientation of the carbon-based anode active material to the surface of the anode current collector.

[0048] Furthermore, the carbon-based anode active material is preferably a spherical graphite granule formed by the aggregation of multiple flake-shaped graphite particles. Examples of flake-shaped graphite include natural graphite, artificial graphite, mesophase-fired carbon (bulk mesophase) made from tar and pitch, and graphitized cokes (green coke, green coke, pitch coke, needle coke, petroleum coke, etc.). In particular, a material assembled using multiple highly crystalline natural graphite particles is preferred. Also, one graphite granule can be formed by the aggregation of 2 to 100, preferably 3 to 20, flake-shaped graphite particles.

[0049] Such carbon-based negative electrode active materials, specifically graphite, may have a spherical particle morphology. In this case, the degree of sphericity of the graphite particles can be 0.75 or higher, and may be, for example, 0.75 to 1.0, 0.75 to 0.95, 0.8 to 0.95, or 0.90 to 0.99. Here, "degree of sphericity" can mean the ratio of the shortest diameter (minor axis) to the longest diameter (major axis) among any diameter passing through the center of the particle. A degree of sphericity of 1 means that the particle morphology is spherical. The above degree of sphericity can be determined by measuring it using a particle shape analyzer, or by measuring the particle shape using a scanning electron microscope (SEM) or energy-dispersive spectrometer and then analyzing the measured results.

[0050] The present invention has the advantage of being able to achieve high electrical conductivity in the negative electrode active layer by realizing a near-spherical shape for the carbon-based negative electrode active material, thereby improving the capacity of the battery, and also being able to increase the specific surface area per unit weight of the negative electrode active material, thereby improving the adhesion between the negative electrode active layer and the current collector.

[0051] Furthermore, the above carbon-based negative electrode active material has an average particle size (D) of 0.5 μm to 10 μm. 50 ) can be shown, specifically an average particle size (D) of 2μm~7μm, 0.5μm~5μm, or 1μm~3μm. 50 ) can be shown.

[0052] For carbon-based anode active materials that are close to spherical, a smaller average particle size may be advantageous in order to maximize the degree of disorder in the expansion direction for each particle, thereby preventing particle expansion due to lithium ion charging. However, if the particle size of the carbon-based anode active material is less than 0.5 μm, a large amount of binder is required due to the increase in the number of particles per unit volume, which may result in a low degree of spheroidization and spheroidization yield. On the other hand, if the maximum particle size exceeds 10 μm, the expansion rate of the anode active material during charging and discharging of the secondary battery increases significantly, and repeated charging and discharging can reduce the interparticle bonding properties of the anode active material and the bonding properties between the anode active material particles and the current collector, which may significantly reduce the cycle performance.

[0053] Furthermore, the above-mentioned negative electrode active layer can be manufactured by applying a negative electrode slurry containing a carbon-based negative electrode active material to at least one surface of a negative electrode current collector, and then drying and rolling it, in order to realize electrical activity through a reversible oxidation-reduction reaction during the charging and discharging of the secondary battery.

[0054] Referring to Figures 1 and 2, the cross-sectional structure of the negative electrode can be described as follows: The negative electrode active layers 120 and 220 of the present invention are divided into flat portions 121 and 221 with a uniform thickness in the center, and sliding portions 122a, 122b, and 222 with a thickness gradient at the edges of the flat portions, i.e., the ends of the flat portions.

[0055] The flat portions 121 and 221 described above constitute the majority of the negative electrode active layers 120 and 220, and may have proportions of 80% or more, 85% or more, 90% or more, 93% or more, 95% or more, 97% or more, 96% to 99%, 98% to 99.5%, or 98.5% to 99.9% in the width direction based on the cross-sectional structure of the negative electrode active layers 120 and 220. As a result, the sliding portions 122a, 122b, and 222 located at the ends of the flat portions 121 and 221 and forming the negative electrode active layers 120 and 220 together with the flat portions may have proportions of 20% or less, 15% or less, 10% or less, 7% or less, 5% or less, 3% or less, 1% to 4%, 0.5% to 2%, or 0.1% to 1.5% in the width direction based on the cross-sectional structure of the negative electrode active layers. In this case, the sliding portions 122a, 122b and 222 may have a width of 1 mm to 30 mm inside the negative electrode active layer from the boundary line between the negative electrode current collectors 110 and 210, based on the cross-sectional structure of the negative electrode active layer. Specifically, they may have widths of 1 mm to 5 mm, 1 mm to 10 mm, 1 mm to 20 mm, 5 mm to 10 mm, 5 mm to 15 mm, 5 mm to 25 mm, 10 mm to 20 mm, 10 mm to 30 mm, 15 mm to 30 mm, or 20 mm to 30 mm.

[0056] Here, "width direction of the negative electrode active layer" may mean the direction perpendicular to the direction C of travel of the negative electrode current collector on the surface of the negative electrode active layer (or negative electrode slurry) during negative electrode manufacturing. It may also be the same as the direction in which the negative electrode tabs (not shown) of the manufactured negative electrodes 100 and 200 travel from one side of the negative electrode active layer to the opposite side. The present invention can increase the energy density of the negative electrode and prevent a decrease in productivity during negative electrode manufacturing by adjusting the length ratio and / or width length of the flat portions 121 and 221 and the sliding portions 122a, 122b and 222 to the above range.

[0057] On the other hand, the negative electrode current collectors 110 and 210 provided on the negative electrodes 100 and 200 are divided into a coated portion on which the negative electrode active layers 120 and 220 are arranged, and a plain portion on which the negative electrode active layers 120 and 220 are not arranged, and a negative electrode tab for electrically connecting to the negative electrode terminal may be provided on one of the plain portions.

[0058] Here, the sliding portion of the negative electrode active layer may be located along the entire edge of the flat portion, or it may be selectively located in part of it. Preferably, the sliding portions 122a and 222 are located along the edges of the negative electrode active layers 120 and 220, forming a boundary line by contacting the plain portions of the negative electrode current collectors 110 and 210, where the plain portions may be the plain portions 111a and 211a provided with the negative electrode tabs. In the region where the negative electrode tabs are located, a high current density is induced due to the uneven distribution of electrochemical reactions, and a large electrical resistance acts, so lithium deposition easily occurs on the surface of the negative electrode active layer adjacent to the negative electrode tabs. However, when the sliding portions 122a and 222a of the present invention are positioned at a boundary line (for example, a first boundary line) with the plain negative electrode portions 111a and 211a on which the negative electrode tabs are provided, the ab-axis crystal plane orientation of the carbon-based negative electrode active material contained in the sliding portions can be controlled, and the electrical resistance of the negative electrode active layer adjacent to the negative electrode tabs can be reduced, thereby preventing lithium from being deposited in a dendritic manner.

[0059] As one example, when the negative electrode 100 is manufactured via a roll-to-roll process, the sliding portions 122a and 122b may be located at the edge of the negative electrode active layer 120 as shown in Figure 1, and may be positioned at the first edge of the negative electrode active layer 120, which is in contact with the first blank portion 111a on which the negative electrode tab is provided, forming a first boundary line, and at the second edge of the negative electrode active layer 120, which is in contact with the second blank portion 111b opposite the first blank portion 111a, forming a second boundary line opposite the first boundary line. In this case, the third and fourth edges of the negative electrode active layer adjacent to the first and second edges may have cut surfaces due to slitting during negative electrode manufacturing, and as a result, there may be no sliding portions with a thickness gradient of the negative electrode active layer.

[0060] As another example, the sliding portion 222 may be located only on the edge of the negative electrode active layer 220, as shown in Figure 2, and in contact with the first blank portion 211a where the negative electrode tab is provided, forming a first boundary line. In this case, the second edge of the negative electrode active layer 120, which forms a second boundary line opposite the first boundary line, may have a cut surface (corresponding to S / F in Figure 1) due to slitting during negative electrode manufacturing, and therefore, there may be no sliding portion with a thickness gradient of the negative electrode active layer.

[0061] Furthermore, the sliding portions 122a, 122b, and 222 have a thickness gradient in which the thickness decreases as they move away from the flat portions 121 and 221 at the point where they come into contact, because a sliding phenomenon of the negative electrode slurry containing the negative electrode active material is induced at the edge of the negative electrode active layer during negative electrode manufacturing. Specifically, the negative electrode slurry used during the manufacturing of the negative electrode active layer has a form in which graphite, which is a carbon-based negative electrode active material, is mixed with a dispersion medium. In this case, water is usually used as the dispersion medium. Water is a solvent with high surface tension, and the negative electrode slurry containing it exhibits a phenomenon in which the surface area exposed to air after being applied to the negative electrode current collector is reduced due to the high surface tension of water. As a result, a sliding phenomenon is induced in the negative electrode slurry applied to the negative electrode current collector, which attempts to form a curved surface on the inside of the negative electrode slurry that has a predetermined angle with the surface of the negative electrode current collector.

[0062] However, this sliding phenomenon generally makes it difficult to maintain a constant N / P ratio between the positive and negative electrodes. In particular, when the N / P ratio falls below 1, lithium ions are not fully intercalated into the carbon-based negative electrode active material during battery charging, and instead precipitate on the negative electrode surface, forming dendrites. The likelihood of these dendrites forming increases significantly, especially when lithium secondary batteries are used for extended periods under high-rate conditions. Since these dendrites can induce internal short circuits in the battery, they can act as a factor that compromises battery safety.

[0063] However, as shown in Figure 3, the present invention can prevent lithium from being deposited in a dendritic manner on the negative electrode surface during charging and discharging by controlling the crystal plane orientation of the carbon-based negative electrode active material contained in the sliding portion. Specifically, the sliding portion may contain a carbon-based negative electrode active material in which the ab-axis crystal planes showing the two-dimensional planar structure of the carbon-based negative electrode active material are aligned nearly perpendicular to the negative electrode current collector.

[0064] Here, "the carbon-based negative electrode active material is aligned nearly perpendicular to the negative electrode current collector" can mean that the crystal planes of the carbon-based negative electrode active material constituting the spherical particles, specifically the ab-axis crystal plane representing the planar direction of graphite with a two-dimensional structure, are aligned at an inclination nearly perpendicular to the surface of the negative electrode current collector. In this case, the planar direction of the graphite (i.e., the ab-axis crystal plane direction) may have an average inclination of 60° to 120° with respect to the negative electrode current collector, preferably an average inclination of 70° to 110°, or 80° to 100°.

[0065] Furthermore, the alignment of the carbon-based negative electrode active material can be applied without particular limitations as long as it is a method commonly used in the industry. Specifically, it can be induced by applying a magnetic field to the surface of the negative electrode slurry at the top and bottom of the slurry after coating the negative electrode slurry containing the carbon-based negative electrode active material onto the surface of the negative electrode current collector. At this time, the applied magnetic field can be applied only to the sliding portion of the negative electrode slurry, but in the present invention, a method in which the magnetic field is applied to the entire surface of the negative electrode slurry, including the flat portion and the sliding portion, can be applied. The negative electrode slurry located in the sliding portion during negative electrode manufacturing will form a predetermined angle with the negative electrode current collector due to the thickness gradient. The angle of the sliding portion thus realized increases the degree of exposure of the magnetic field applied to the carbon-based negative electrode active material when a magnetic field is applied to the entire surface of the negative electrode slurry, and thus acts as a factor that causes a magnetic field with a greater strength to be applied than the magnetic field applied to the flat portion. Therefore, in this case, each carbon-based negative electrode active material contained in the sliding portion and the flat portion is aligned to have a predetermined inclination with respect to the negative electrode current collector. Furthermore, since the carbon-based negative electrode active material in the sliding portion is aligned at a high angle that is nearly perpendicular to the surface of the negative electrode current collector, the degree of alignment may be relatively lower compared to the carbon-based negative electrode active material in the flat portion. In contrast, when a magnetic field is applied only to the negative electrode slurry located in the sliding portion during negative electrode manufacturing, the carbon-based negative electrode active material contained in the sliding portion can be aligned nearly perpendicular to the negative electrode current collector, but there is a limit to the uniformity of the alignment.

[0066] Furthermore, the degree of alignment of the carbon-based anode active material can be adjusted by the strength of the applied magnetic field and the duration of exposure. For example, when a magnetic field is applied to the surface of a anode slurry containing the carbon-based anode active material for 1 to 10 seconds, the ab-axis crystal plane of the carbon-based anode active material in the anode slurry to which the magnetic field has been applied for 10 seconds may have a greater inclination with respect to the surface of the anode current collector than the carbon-based anode active material in the anode slurry to which the magnetic field has been applied for 1 second. In the present invention, the magnetic field applied to the anode slurry can be performed at an intensity of 0.5T to 2.0T and for 1 to 60 seconds, specifically at an intensity of 0.8T to 1.5T or 0.8T to 1.2T for 1 to 30 seconds or 1 to 20 seconds. Furthermore, the magnets used when applying a magnetic field to the negative electrode slurry may have a length ratio of 105% to 200% relative to the width direction of the negative electrode slurry. Specifically, they may have a length ratio of 110% to 180%, 110% to 160%, 110% to 140%, 110% to 130%, 130% to 150%, or 105% to 120% relative to the width direction length of the negative electrode slurry. By adjusting the length ratio of the magnets placed on the surface of the negative electrode slurry when applying a magnetic field to the negative electrode slurry as described above, the present invention makes it possible to apply a magnetic field more uniformly to the entire exposed surface of the sliding part.

[0067] On the other hand, the degree of alignment of the carbon-based anode active material contained in the anode active layer can be determined by molecular orientation and / or crystal structure analysis of the carbon-based anode active material.

[0068] As one example, in the sliding portion of the negative electrode active layer, the carbon-based negative electrode active material is aligned nearly perpendicularly to the negative electrode current collector, and the value related to Equation 1 below can be satisfied as 1.0 or less during near-end X-ray absorption fine structure (NEXAFS) spectroscopy.

[0069]

number

[0070] (In formula 1 above, S 60 / 0 This is the peak intensity ratio (I0) when the X-ray incident angle is 0° during near-end X-ray absorption fine structure (NEXAFS) spectroscopy. B / AThe peak intensity ratio (I60) when the incident angle of X-rays to ) is 60° B / A Represents the value of ( ).

[0071] Unlike X-ray photoelectron spectroscopy (XPS), which measures the bond energy between atoms constituting a compound, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy can only reflect the local structure near carbon atoms, including excited core electrons, and the surface structure of the measured carbon-based anode active material particles. Therefore, the present invention can measure the degree of alignment of carbon-based anode active material contained in the anode active layer by using the spectrum obtained by NEXAFS spectroscopy of the anode active layer.

[0072] Specifically, when X-rays are irradiated onto the carbon atoms (C) of a carbon-based anode active material, occupied electrons (K-shell electrons) in the inner-shell energy levels (1s orbitals) of the carbon atoms absorb X-ray energy and are excited to various unoccupied molecular orbitals. NEXAFS spectroscopy uses the absorption spectrum observed at this time. In the case of graphite, a carbon-based anode active material, these unoccupied molecular orbitals include: i) the π* orbital, which is attributed to the antibonding orbital of sp2 bonds that reflects the crystallinity of graphite (such as the basal plane and orientation); ii) the σ* orbital, which is attributed to the antibonding orbital of sp3 bonds that reflects the disorder of crystallinity (such as edge planes and non-orientation); and iii) the Rydberg orbital, which is attributed to the antibonding orbital of CH bonds and CO bonds.

[0073] Carbon-based anode active materials, such as graphite, have a crystalline structure in which carbon atoms are bonded in sp2 in a hexagonal network (see Figure 4(a)). The basal plane is the two-dimensional plane of the hexagonal network (ab-axis crystal plane), and the planes showing the ends of the hexagonal network (c-axis crystal plane) are the edge planes. At the edge planes of carbon-based anode active materials, there is a possibility of -COOH, -C=O, etc., being present at the terminal carbon atoms, so the proportion of sp3 bonds may be high. Therefore, to analyze the crystal plane orientation and / or alignment of carbon-based anode active materials, it is necessary to analyze the state of the sp2 orbitals of carbon atoms at each crystal plane of the carbon-based anode active material.

[0074] The above NEXAFS spectroscopic analysis can be performed by a total electron yield method, in which X-rays with a fixed incident angle relative to the negative electrode active layer are irradiated onto the negative electrode active layer, and the current flowing through the negative electrode active layer to complement the photoelectrons emitted from the surface of the negative electrode active layer is measured while scanning the energy of the irradiated X-rays from 280 eV to 320 eV.

[0075] In this case, since the synchrotron radiation is linearly polarized X-rays due to the application of a magnetic field E, the intensity of the observed absorption peak may differ depending on the direction of incidence of the X-rays. Specifically, referring to Figure 4(a), in the case of graphite, which is a carbon-based negative electrode active material, it has a hexagonal network structure via sp2 bonds (-C=C-) of carbon atoms. These sp2 bonds include σ orbitals located parallel to the sp2 bonds and π orbitals located perpendicular to the sp2 bonds. Here, the σ and π orbitals have a symmetrical structure with nodes at the nucleus positions of carbon atoms, respectively, with respect to the antibonding σ* and π* orbitals. Therefore, the σ* and π* orbitals have the same directionality as the σ and π orbitals.

[0076] Therefore, as shown in Figure 4(b), when the incident direction of X-rays is parallel to the sp2 bond, the intensity of the absorption peak excited from the 1s level to the π* level of carbon increases, and conversely, when it is perpendicular to the sp2 bond, the intensity of the absorption peak decreases. On the other hand, when the incident direction of X-rays is parallel to the sp2 bond, the intensity of the absorption peak excited from the 1s level to the σ* level of carbon decreases, and conversely, when it is perpendicular to the sp2 bond, the intensity of the absorption peak increases.

[0077] Due to these characteristics, if the orientation of the graphite contained in the negative electrode active layer is high, as shown in Figure 3(b), the antibonding empty-state molecular orbitals of the graphite located on the surface of the negative electrode active layer are uniformly aligned. Therefore, when the incident angle of X-rays on the negative electrode active layer is changed, the spectral shape changes significantly due to reinforcement and interference of emitted photoelectrons. In contrast, if the orientation of the graphite contained in the negative electrode active layer is low, as shown in Figure 3(a), the antibonding empty-state molecular orbitals of the graphite located on the surface of the negative electrode active layer are non-uniformly aligned, so the spectral shape hardly changes even when the incident angle of X-rays on the sample is changed.

[0078] Therefore, in order to measure the degree of orientation of the carbon-based anode active material contained in the anode active layer, the present invention performs NEXAFS spectroscopic analysis on the surface of the anode active layer and incident X-rays on the anode active layer at different incident angles (0° and 60°), and for each incident angle, the ratio of the intensity of the absorption peak (peak A = 287 ± 0.2 eV) attributed to the transition from the 1s level to the σ* level of carbon to the intensity of the absorption peak (peak B = 293 ± 0.2 eV) attributed to the transition from the 1s level to the π* level of carbon (I B / A After determining the ratio of intensity between the angles of incidence (60° and 0°), the ratio (S) 60 / 0 =I60 B / A / I0 B / A By calculating this, the orientation and / or alignment of the carbon-based anode active material contained in the anode active layer can be quantitatively measured.

[0079] In other words, the degree of orientation of the carbon-based negative electrode active material contained in the sliding portion is expressed by the absorption peak intensity (peak A = 287 ± 0.2 eV) (I60) attributed to the transition from the 1s level to the π* level of carbon, measured at an X-ray incidence angle of 60°, as shown in i) Equation 2. A Absorption peak (peak B = 293 ± 0.2 eV) intensity (I60) attributed to the transition from the 1s level to the σ* level of carbon in ) B ) ratio (I60 B / A ) is calculated, and as shown in equation 3, the absorption peak intensity (Peak A = 287 ± 0.2 eV) (I0) attributed to the transition from the 1s level to the π* level of carbon measured at an incident angle of X-rays of 0° is calculated. A Absorption peak (peak B = 293 ± 0.2 eV) intensity (I0) attributed to the transition from the 1s level to the σ* level of carbon in ) B ) proportion (I0 B / A iii) After calculating the ratios (S) shown in Equation 1, 60 / 0 =I60 B / A / I0 B / A It can be evaluated by finding the value of ).

[0080]

number

[0081]

number

[0082] In equations 2 and 3, I60 A This represents the intensity of the strongest peak among the peaks present at 286±1.0eV when the X-ray incidence angle is 60°. I60 B This represents the intensity of the strongest peak among the peaks present at 292.5±1.0eV when the incident angle of X-rays is 60°. I0 A This represents the intensity of the strongest peak among the peaks present at 286±1.0eV when the X-ray incidence angle is 0°. I0 B represents the intensity of the peak with the highest intensity among the peaks existing at 292.5 ± 1.0 eV when the incident angle of X-rays is 0°.

[0083] Here, the above formula 1 (S 60 / 0 ) can mean that the closer it is to 1, the lower the orientation of the a-b axis crystal plane of graphite, which is a carbon-based negative electrode active material, with respect to the negative electrode current collector, and the higher the degree of alignment (O.I); the closer it is to 0, the higher the orientation of the a-b axis crystal plane of graphite with respect to the negative electrode current collector, and the lower the degree of alignment (O.I). The sliding part according to the present invention can satisfy that the average value of the value (S 60 / 0 ) in formula 1 is 1.0 or less, and more specifically, it can satisfy 0.9 or less, 0.8 or less, 0.7 or less, 0.5 or less, 0.05 to 0.7, 0.05 to 0.5, 0.05 to 0.4, 0.1 to 0.7, 0.3 to 0.7, or 0.5 to 0.8.

[0084] That the sliding part of the negative electrode active layer according to the present invention satisfies formula 1 (S 60 / 0 ) being 1 or less means that the a-b axis crystal plane of the carbon-based negative electrode active material contained in the above sliding part is aligned close to perpendicular to the negative electrode current collector as shown in (b) of FIG. 3, and the negative electrode including it means that lithium precipitation can be suppressed at the end of the negative electrode active layer during charge and discharge of the secondary battery.

[0085] Also, this has a different meaning from that the particles of the carbon-based negative electrode active material satisfy formula 1 (S 60 / 0 ) being 1 or less. That the particles of the carbon-based negative electrode active material satisfy formula 1 (S[[ID=2,4]] 60 / 0 ) being 1 or less means that the a-b axis crystal plane of the molecular crystal forming the particles of the carbon-based negative electrode active material is aligned with a predetermined direction inside the particles. Therefore, including such a carbon-based negative electrode active material in the negative electrode active layer means that, unless separate treatment is performed, the a-b axis crystal plane of the carbon-based negative electrode active material tends to be non-oriented with respect to the surface of the negative electrode current collector as shown in (a) of FIG. 3, so it is differentiated from the sliding part of the negative electrode active layer according to the present invention.

[0086] As another example, in the sliding portion of the negative electrode active layer, the ab-axis crystal plane of the carbon-based negative electrode active material is aligned nearly perpendicular to the negative electrode current collector, and the degree of alignment of the carbon-based negative electrode active material (OI) is expressed in the following formula 4 during X-ray diffraction (XRD) spectroscopy analysis. sliding ) is the degree of alignment (OI) of the carbon-based negative electrode active material contained in the flat portion. flat It may be smaller than )

[0087] [Formula 4] OI=I 004 / I 110

[0088] In Equation 4, I 004 This represents the area of ​​the peak indicating the (0,0,4) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer. I 110 This represents the area of ​​the peak indicating the (1,1,0) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0089] The crystal plane orientation of the carbon-based anode active material can be determined by crystal plane analysis of the carbon-based anode active material, such as X-ray diffraction spectroscopy. The degree of alignment (OI) of the carbon-based anode active material, expressed by Equation 4 above, can serve as an indicator of the direction in which the crystal structure of the carbon-based anode active material is aligned during X-ray diffraction measurement, specifically, the degree to which the ab-axis crystal plane, which shows the two-dimensional planar structure of the carbon-based anode active material, is aligned with respect to the surface of the anode current collector. For example, when the anode active layer contains graphite as the carbon-based anode active material, the peaks for graphite during X-ray diffraction measurement of the anode active layer are 2θ = 26.5±0.2°, 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 54.7±0.2°, and 77.5±0.2°. This represents the (0,0,2), (1,0,0), (1,0,1)R, (1,0,1)H, (0,0,4), and (1,1,0) crystal planes of the graphite contained in the negative electrode active layer. Generally, in the case of graphite, graphene layers are placed on the a-axis and b-axis planes, and such graphene layers are stacked along the c-axis, resulting in a hexagonal or rhombohedral crystal structure. Here, the crystal plane peaks mentioned above are peaks that show the plane characteristics of such a crystal structure. Furthermore, the peak appearing at 2θ = 43.4 ± 0.2° may be considered to be an overlapping peak corresponding to the (1,0,1)R plane of a carbon-based material and the (1,1,1) plane of a current collector, such as Cu.

[0090] This invention allows for the measurement of graphite alignment (OI) by the area ratio of the peak at 2θ = 54.7 ± 0.2° representing the (0,0,4) plane and the peak at 2θ = 77.5 ± 0.2° representing the (1,1,0) plane, specifically, the area ratio obtained by integrating the intensities of the above peaks. Furthermore, X-ray diffraction was measured using the CuKα line as the target line, and to improve the peak intensity resolution, the target line was extracted using a monochromator. At this time, the measurement conditions were 2θ = 10° to 90°, scan speed (° / s) of 0.044 to 0.089, and step size of 0.026° / step.

[0091] In addition, the (0, 0, 4) plane that appears at 2θ = 54.7 ± 0.2° indicates the thickness-direction characteristics (c-axis direction characteristics) of the layered structure in which the two-dimensional planar structure of the graphite layer is stacked, and the (1, 1, 0) plane that appears at 2θ = 77.5 ± 0.2° indicates the planar characteristics (a-b axis direction characteristics) of the stacked graphite layers. Therefore, the smaller the (0, 0, 4) plane peak indicating the thickness-direction characteristics of the graphite layer plane, and the larger the (1, 1, 0) plane peak indicating the planar characteristics of the graphite layer, the higher the alignment of the graphite plane with respect to the surface of the negative electrode current collector at a high angle. That is, the closer the value of the above alignment degree (O.I) is to 0, the closer the angle or inclination of the graphite layer plane with respect to the surface of the negative electrode current collector is to 90°, and the larger the value, the closer the inclination with respect to the surface of the negative electrode current collector is to 0° or 180°.

[0092] In such an aspect, in the sliding portion of the negative electrode active layer according to the present invention, the a-b axis crystal plane of the carbon-based negative electrode active material is aligned close to perpendicular to the negative electrode current collector. Therefore, the alignment degree (O.I sliding ) of the carbon-based negative electrode active material contained in the sliding portion may be relatively lower than the alignment degree (O.I flat ) of the carbon-based negative electrode active material contained in the flat portion of the negative electrode active layer. Specifically, the alignment degree (O.I sliding ) of the carbon-based negative electrode active material contained in the sliding portion may be 0.1 to 0.8, more specifically 0.15 to 0.8, 0.15 to 0.6, 0.15 to 0.5, 0.2 to 0.5, 0.2 to 0.4, 0.25 to 0.45, 0.3 to 0.5, 0.3 to 0.8, 0.4 to 0.7, or 0.35 to 0.6.

[0093] By controlling the alignment degree (O.I sliding ) of the carbon-based negative electrode active material contained in the sliding portion within the above-described range, it is possible to reduce the electrode resistance while improving the lithium ion mobility at the end of the negative electrode during charge and discharge of the battery. Therefore, even if the thickness of the end of the negative electrode active layer is thinner than the thickness of the end of the positive electrode active layer, it is possible to prevent the reversal of the N / P ratio (N / P ratio).

[0094] Furthermore, the carbon-based negative electrode active material contained in the flat portion is oriented together with the carbon-based negative electrode active material contained in the sliding portion, and the ab-axis crystal plane may have a predetermined angle or inclination with respect to the surface of the negative electrode current collector, thereby the carbon-based negative electrode active material contained in the flat portion has an alignment degree (OI) according to Equation 4. flat ) can satisfy a predetermined range. Specifically, the carbon-based negative electrode active material contained in the flat portion has an alignment degree (OI flat ) is the degree of alignment (OI) of the carbon-based negative electrode active material contained in the sliding part sliding The ratio may be 110% to 200% based on ), and more specifically, it may be 115% to 180%, 120% to 160%, or 125% to 150%. In this invention, the carbon-based negative electrode active material contained in the flat portion has an alignment degree (OI flat By adjusting the above range, the ab-axis crystal planes of the carbon-based negative electrode active material contained in the flat portion are not aligned, or the degree of alignment (OI flat ) is the degree of alignment (OI) of the carbon-based negative electrode active material contained in the sliding part sliding Compared to cases where the ratio exceeds 200% based on the standard, the average lithium ion mobility of the entire negative electrode active layer is improved, so the electrical resistance of the negative electrode decreases and the energy density can be further increased. In addition, the alignment of the carbon-based negative electrode active material contained in the sliding part (OI sliding If the ratio is less than 100% based on the standard, the electrical resistance of the negative electrode active layer in contact with the plain area where the negative electrode tab is provided will relatively increase, accelerating degradation, which can be prevented.

[0095] Furthermore, the sliding portion is the ratio of the intensity of the peak representing the (0,0,4) crystal plane and the intensity of the peak representing the (0,0,2) crystal plane during X-ray diffraction (XRD) spectroscopy analysis (I 004 / I 002 ) can be controlled within a certain range. Specifically, the sliding part has the above strength ratio (I 004 / I 002The ratio of the intensity of the peaks (I) between the peaks indicating the (0,0,4) crystal plane and the peaks indicating the (0,0,2) crystal plane can be controlled to 0.04 or higher, and more specifically, it may be 0.04 to 0.09 or 0.04 to 0.07. The present invention relates to the ratio of the intensity of the peaks indicating the (0,0,4) crystal plane and the peaks indicating the (0,0,2) crystal plane among the peaks detected during X-ray diffraction (XRD) spectroscopy analysis. 004 / I 002 By controlling the above range, the increase in DC internal resistance can be suppressed, which has the advantage of improving high-rate characteristics and cycle life characteristics.

[0096] On the other hand, the negative electrode active layer according to the present invention may optionally further contain a conductive material, a binder, other additives, etc., along with the negative electrode active material.

[0097] The above conductive material may contain, but is not limited to, one or more of the following: carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, etc.

[0098] As one example, the above-mentioned negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., individually or in combination as conductive materials.

[0099] In this case, the content of the conductive material may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer, and specifically may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 0.5 to 2 parts by weight. By controlling the content of the conductive material within the above range, the present invention can prevent an increase in the resistance of the negative electrode and a decrease in charging capacity due to a low content of conductive material. Furthermore, it can prevent problems such as a decrease in charging capacity due to a decrease in the content of the negative electrode active material due to an excessive amount of conductive material, or a decrease in rapid charging characteristics due to an increase in the loading amount of the negative electrode active layer.

[0100] Furthermore, the above-mentioned binder is a component that assists in the bonding of the active material to conductive materials and to the current collector, and can be suitably applied within a range that does not degrade the electrical properties of the electrode. Specifically, it may contain one or more of the following: vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber.

[0101] The binder content may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight. By controlling the binder content in the negative electrode active layer within the above range, the present invention can prevent a decrease in the adhesive strength of the active layer due to a low binder content or a decrease in the electrical properties of the electrode due to an excessive amount of binder.

[0102] Furthermore, the negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, and calcined carbon can be used, and in the case of copper or stainless steel, those with surface treatment with carbon, nickel, titanium, silver, etc. can also be used. The average thickness of the negative electrode current collector can be suitably applied in the range of 1 μm to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0103] The negative electrode for lithium secondary batteries according to the present invention, having the above-described configuration, is excellent at suppressing lithium deposition at the edges of the negative electrode active layer during charging and discharging of the secondary battery. Therefore, lithium secondary batteries containing it have the advantage of high safety and the ability to charge and discharge for long periods of time under high-rate conditions.

[0104] <Lithium-ion secondary battery> Furthermore, in one embodiment of the present invention, An electrode assembly including a positive electrode, a negative electrode according to the present invention as described above, and a separation membrane disposed between the positive electrode and the negative electrode, and The present invention provides a lithium secondary battery containing an electrolyte composition.

[0105] Each lithium secondary battery according to the present invention comprises an electrode assembly in which a plurality of positive electrodes and a plurality of negative electrodes are arranged alternately, with a separation membrane located between them, and an electrolyte composition having a lithium salt and an electrolyte additive dissolved in a non-aqueous organic solvent. In this case, the lithium secondary battery includes the negative electrode of the present invention, in which the carbon-based negative electrode active material contained in the sliding portion of the negative electrode active layer is aligned (or oriented) so as to be perpendicular and / or nearly perpendicular with respect to the surface of the negative electrode current collector. As a result, the lithium secondary battery has the advantage of high safety because the deposition of lithium on the surface of the negative electrode active layer, especially at the edges, is prevented during charging and discharging of the battery, especially during charging and discharging under high-rate conditions.

[0106] In this case, the negative electrode has the same configuration as described above, so a detailed explanation will be omitted.

[0107] Furthermore, the positive electrode comprises a positive electrode active layer manufactured by coating, drying, and pressing a positive electrode slurry containing a positive electrode active material onto a positive electrode current collector, and the positive electrode active layer may optionally further selectively contain conductive materials, binders, and other additives.

[0108] The above-mentioned positive electrode active material is a substance that can undergo electrochemical reactions on the positive electrode current collector and may contain one or more lithium metal oxides represented by the following chemical formulas 1 and 2, which are capable of reversible intercalation and deintercalation of lithium ions.

[0109] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0110] [Chemical formula 2] LiM 2 p Mn q P r O4

[0111] In the above chemical formulas 1 and 2, M 1 It is one or more elements from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. x, y, z, w, and v are such that 1.0 ≤ x ≤ 1.30, 0.5 ≤ y < 1, and 0 respectively. <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつy+z+w+v=1であり、 M 2 It is Ni, Co, or Fe, p is 0.05 ≤ p ≤ 1.0, q is either 1-p or 2-p, r is either 0 or 1.

[0112] The lithium metal oxides represented by chemical formulas 1 and 2 above are substances containing high amounts of nickel (Ni) and manganese (Mn), respectively, and when used as positive electrode active materials, they have the advantage of being able to stably supply high capacity and / or high voltage electricity.

[0113] In this case, the lithium metal oxide represented by the above chemical formula 1 is LiNi0.8 Co 0.1 Mn 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.9 Co 0.05 Mn 0.05 O2, LiLiLi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.15 Al 0.05 O 2、 LiRing 0.7 Co 0.1 Mn 0.1 Al 0.1 The lithium metal oxide represented by the above chemical formula 2 may contain O2, etc., and LiNi 0.7 Mn 1.3 O4, LiSa 0.5 Mn 1.5 O 4、 LiRing 0.3 Mn 1.7 O 4、 LiFePO4, LiFe 0.8 Mn 0.2 PO4, LiFe 0.5 Mn 0.5 It may contain PO4 and other components, which can be used alone or in combination.

[0114] Furthermore, the above-mentioned positive electrode active material may be present in 85 parts by weight or more, based on the weight of the positive electrode active layer, specifically in the form of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0115] Furthermore, the positive electrode active layer may further contain conductive materials, binders, and other additives along with the positive electrode active material.

[0116] In this case, the conductive material is used to improve the electrical performance of the positive electrode, and may be one or more of those commonly used in the industry, specifically natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0117] Furthermore, the conductive material may be included in amounts of 0.1 to 5 parts by weight based on the weight of each positive electrode active layer, specifically in amounts of 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight.

[0118] Furthermore, the binder plays a role in binding the positive electrode active material, positive electrode additive, and conductive material together, and any binder having such a function can be used without particular limitations. Specifically, the binder may include one or more resins from among polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As one example, the binder may include polyvinylidene fluoride.

[0119] Furthermore, the above-mentioned binder may be included in an amount of 1 to 10 parts by weight based on the weight of each positive electrode active layer, specifically in an amount of 2 to 8 parts by weight, or 1 to 5 parts by weight.

[0120] The total thickness of the positive electrode active layer described above is not particularly limited, but it can be 50 μm to 300 μm, and more specifically, it can be 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0121] Furthermore, the positive electrode can be made of a material that has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can be used, and in the case of aluminum or stainless steel, materials that have been surface-treated with carbon, nickel, titanium, silver, etc. can also be used. The average thickness of the current collector can be suitably applied in the range of 3 μm to 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0122] On the other hand, the separation membrane interposed between the positive and negative electrodes of each unit cell is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the industry, but specifically, it may contain one or more polymers from among chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymer. The above separation membrane may have the form of a porous polymer substrate such as a sheet or nonwoven fabric containing the above polymer, and in some cases, it may have the form of a composite separation membrane in which organic or inorganic particles are coated with an organic binder on the above porous polymer substrate. Furthermore, the above separation membrane may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0123] On the other hand, the lithium secondary battery according to the present invention is not particularly limited, but may preferably be a secondary battery that includes a stacked type, a zigzag type, or a zigzag-stack type electrode assembly. As one example, the lithium secondary battery according to the present invention may be a pouch-type secondary battery or a prismatic secondary battery.

[0124] The negative electrode applied to the lithium secondary battery according to the present invention has a degree of alignment (OI) of the carbon-based active material contained in the sliding portion of the negative electrode active layer. sliding By minimizing the ) factor, even if the N / P ratio of the positive and negative electrodes stacked within the electrode assembly becomes less than 1, the lithium deposition on the surface of the negative electrode active layer during charging and discharging of the secondary battery, specifically at the edges, is effectively suppressed. Therefore, the above lithium secondary battery has the advantage of high safety and the ability to charge and discharge for long periods under high-rate conditions.

[0125] The present invention will be described in more detail below with reference to examples and experimental examples.

[0126] However, the following examples and experimental examples are illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0127] <Examples 1-7. Manufacturing of negative electrodes for lithium secondary batteries> Natural graphite was prepared as the negative electrode active material, carbon black as the conductive material, and carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) as binders. 95 parts by weight of natural graphite, 1 part by weight of carbon black, 1.5 parts by weight of carboxymethylcellulose (CMC), and 2.5 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to form a negative electrode slurry with a solid content of 50% to 55%, and 100 mg / cm² was applied to a copper sheet (thickness: 10 μm). 2 ~120 mg / cm³ 2 We cast them in that way.

[0128] Subsequently, a magnetic field was applied to the entire surface of the coated negative electrode slurry using magnets placed at the top and bottom of the slurry to induce the orientation of natural graphite. The applied magnetic field was at an intensity of 1.0T to 1.2T and was applied for the duration shown in Table 1 below. The magnets used to apply the magnetic field were permanent magnets with a length ratio of 110% to 120% of the width of the negative electrode slurry.

[0129] Subsequently, a copper sheet coated with a negative electrode slurry, which induced the orientation of the carbon-based negative electrode active material contained within the sliding section, was dried in a vacuum oven at 130°C, and then rolled to a density of 1.63 ± 0.2 g / cc to produce the negative electrode.

[0130] i) the degree of sphericity of the carbon-based anode active material used for the manufactured anode, and ii) the degree of alignment of the carbon-based anode active material at each position in the anode active layer (S 60 / 0 and OI sliding The following was calculated: i) The degree of sphericity of the carbon-based anode active material was obtained by using images obtained by scanning electron microscopy (SEM) to calculate the ratio of the shortest diameter (minor axis) to the longest diameter (major axis) among any diameter passing through the center of the anode active material particles. Also, ii) The degree of alignment (S) of the carbon-based anode active material at different positions in the anode active layer was calculated. 60 / 0 and OI sliding The spectra were measured by performing near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray diffraction (XRD) spectroscopy at three arbitrary points in the flat and sliding portions of the negative electrode active layer, respectively. The measurement conditions for the near-edge X-ray fluorescence spectrometer (NEXAFS) and X-ray diffraction (XRD) were as follows.

[0131] (1) Near-edge X-ray fine structure (NEXAFS) spectroscopy - Acceleration voltage slit = 1 degree, reception slit = 0.1 mm, scattering slit = 1 degree: 1.0 GeV ~ 1.5 GeV -Accumulated current: 80mA~350mA - Angle of incidence: 60° or 0°

[0132] (2)X-ray diffraction (XRD) spectroscopy -Target: Cu(Kα-ray) graphite monochromatization device - Slit: Divergence

[0133] Subsequently, the degree of alignment (S) of the natural graphite (i.e., carbon-based anode active material) was determined from each spectrum obtained using the following equations 1 to 4. 60 / 0 and OI slidingThe values ​​were calculated, and their average was determined. The results are shown in Table 1 below.

[0134]

number

[0135]

number

[0136]

number

[0137] In equations 1 to 3, S 60 / 0 This is the peak intensity ratio (I0) when the incident angle of X-rays is 0°. B / A The peak intensity ratio (I60) when the incident angle of X-rays to ) is 60° B / A This represents the value of ), I60 A This represents the intensity of the strongest peak among the peaks present at 286±1.0eV when the X-ray incidence angle is 60°. I60 B This represents the intensity of the strongest peak among the peaks present at 292.5±1.0eV when the incident angle of X-rays is 60°. I0 A This represents the intensity of the strongest peak among the peaks present at 286±1.0eV when the X-ray incidence angle is 0°. I0 B This represents the intensity of the strongest peak among the peaks present at 292.5±1.0eV when the X-ray incidence angle is 0°.

[0138] [Formula 4] OI=I 004 / I 110

[0139] In Equation 4, I 004This represents the area of ​​the peak indicating the (0,0,4) crystal plane during X-ray diffraction (XRD) spectroscopy analysis. I 110 This represents the area of ​​the peak indicating the (1,1,0) crystal plane during X-ray diffraction (XRD) spectroscopy analysis.

[0140] [Table 1]

[0141] <Comparative Examples 1-3. Manufacturing of negative electrodes for lithium secondary batteries> A negative electrode for a lithium secondary battery was manufactured using the same method as in Example 1, except that a) no magnetic field was applied to the surface of the negative electrode slurry coated on a copper sheet, or b) a magnetic field was applied only to the edge of the negative electrode slurry corresponding to the sliding portion of the negative electrode active layer.

[0142] In this case, when a magnetic field was applied only to the edge of the negative electrode slurry, the length ratio of the magnet to which the magnetic field was applied was adjusted to 100% or 110-120% of the length ratio relative to the edge of the negative electrode slurry, i.e., the width direction of the sliding part.

[0143] Furthermore, i) the degree of spheroidization of the carbon-based anode active material used in each manufactured anode, and ii) the degree of alignment (S) of the natural graphite (i.e., carbon-based anode active material) obtained by measuring near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray diffraction (XRD) spectroscopy at different positions in the anode active layer. 60 / 0 and OI sliding ), and iii) the ratio of the intensity of the peak representing the (0,0,4) plane to the intensity of the peak representing the (0,0,2) plane calculated from X-ray diffraction (XRD) (I 004 / I 002 The results are shown in Table 2 below.

[0144] [Table 2]

[0145] <Examples 8-14 and Comparative Examples 4-6. Manufacturing of Lithium Secondary Batteries> LiNi with a particle size of 5 μm is used as the positive electrode active material. 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 was prepared and mixed with polyvinylidene fluoride and N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 as a carbon-based conductive material and binder to form a slurry. This slurry was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and then rolled to produce a cathode.

[0146] A separation membrane made of polypropylene with a thickness of 18 μm was interposed between the positive electrode obtained above and the negative electrodes manufactured in the examples and comparative examples, respectively. After inserting the membrane into a case, the electrolyte composition was injected to assemble the lithium secondary battery.

[0147] The types of negative electrodes applied to each lithium secondary battery are shown in Table 3 below.

[0148] [Table 3]

[0149] <Experimental Example 1> To evaluate the safety of the lithium secondary battery according to the present invention during high-rate charge and discharge, the following experiments were conducted on each lithium secondary battery manufactured in the examples and comparative examples.

[0150] (i) Evaluation of high-rate characteristics of secondary batteries First, each manufactured lithium secondary battery underwent initial charging. Specifically, the lithium secondary batteries were initially charged at a temperature of 25°C with a charging current of 0.3C until the charging termination voltage reached 4.2V to 4.25V, and then activated by continuing to charge until the current density at the termination voltage reached 0.02C.

[0151] Each activated lithium secondary battery was fully charged at room temperature (22°C) at a rate of 0.1 C-rate. Then, the initial discharge capacity was measured while discharging the fully charged lithium secondary batteries at a rate of 0.1 C-rate. Afterward, each lithium secondary battery was fully charged again at a rate of 0.1 C-rate, and the relative discharge capacity percentage was measured relative to the initial discharge capacity at each discharge rate while discharging at 1.0 C, 2.0 C, 5.0 C, and 9.0 C-rates. The measured discharge capacity percentages are shown in Table 4.

[0152] (b) Safety evaluation of secondary batteries First, each manufactured lithium secondary battery underwent initial charging. Specifically, the lithium secondary batteries were initially charged at a temperature of 25°C with a charging current of 0.3C until the charging termination voltage reached 4.2V to 4.25V, and then activated by continuing to charge until the current density at the termination voltage reached 0.02C.

[0153] Subsequently, each activated lithium secondary battery was charged at a temperature of 25°C with a charging current of 2.0C until the charging termination voltage reached 4.2V to 4.25V, and then discharged in constant current mode until the current density at the termination voltage reached 0.02C. A total of 100 such charge-discharge cycles were performed, and each lithium secondary battery that had undergone 100 charge-discharge cycles was disassembled to check for lithium deposition on the negative electrode surface. The results are shown in Table 4.

[0154] [Table 4]

[0155] As shown in Table 4 above, the negative electrode for lithium secondary batteries according to the present invention has been found to have a high capacity retention rate during high-rate charge and discharge because the carbon-based negative electrode active material contained in the sliding portion of the negative electrode active layer is aligned nearly perpendicularly to the surface of the negative electrode current collector, thereby suppressing lithium deposition on the negative electrode surface.

[0156] These results indicate that the negative electrode for lithium secondary batteries according to the present invention is excellent at suppressing lithium deposition at the edges of the negative electrode active layer during charging and discharging of secondary batteries. Therefore, lithium secondary batteries containing it have high safety and can be charged and discharged for long periods under high-rate conditions.

[0157] While preferred embodiments of the present invention have been described above with reference to those skilled in the art or those with ordinary knowledge in the art, it will be understood that the present invention can be modified and altered in various ways without departing from the spirit and technical scope of the invention as described in the claims below.

[0158] Therefore, the technical scope of the present invention is not limited to what is described in the summary of the invention in the specification, but is defined by the claims.

Claims

1. A negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector, comprising a carbon-based negative electrode active material, The negative electrode active layer is divided into a flat portion whose thickness is maintained constant with respect to the cross-sectional structure, and a sliding portion located at the end of the flat portion and having a thickness gradient. The sliding portion, when analyzed by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, has a value of 1.0 or less according to the following formula 1. The carbon-based negative electrode active material contains graphite, A negative electrode for a lithium secondary battery, wherein the degree of alignment (O.I) of the carbon-based negative electrode active material contained in the flat portion, according to formula 4, is 110% to 200% of the degree of alignment of the carbon-based negative electrode active material contained in the sliding portion. [Math 1] [Math 2] [Math 3] In equations 1 to 3, S ６０／０ This is the peak intensity ratio (I0) when the incident angle of X-rays is 0°. Ｂ／Ａ The peak intensity ratio (I60) when the incident angle of X-rays to ) is 60° Ｂ／Ａ This represents the value of ), I60 Ａ This represents the intensity of the peak with the strongest intensity among the peaks present at 286 ± 1.0 eV when the incident angle of X-rays is 60°. I60 Ｂ This represents the intensity of the peak with the strongest intensity among the peaks present at 292.5 ± 1.0 eV when the incident angle of X-rays is 60°. I0 Ａ This represents the intensity of the peak with the strongest intensity among the peaks present at 286 ± 1.0 eV when the incident angle of X-rays is 0°. I0 Ｂ This represents the intensity of the peak with the strongest intensity among the peaks present at 292.5 ± 1.0 eV when the incident angle of X-rays is 0°. [Formula 4] O. I=I 004 / I 110 In Equation 4, I004 represents the area of ​​the peak indicating the (0,0,4) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer. I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein the degree of alignment (O.I) of the carbon-based negative electrode active material contained in the sliding portion is 0.1 to 0.

6.

3. The sliding part has a ratio (I ００４ / I ００２ ) of 0.04 or more between the intensity of the peak indicating the (0, 0, 4) crystal plane and the intensity of the peak indicating the (0, 0, 2) crystal plane during X-ray diffraction (XRD) spectroscopic analysis. The negative electrode for a lithium secondary battery according to claim 1.

4. The negative electrode current collector is divided into a coated portion where the negative electrode active layer is arranged and a plain portion where the negative electrode active layer is not arranged. The sliding portion is in contact with the plain portion of the plain portion on which the negative electrode tab is provided, as described in claim 1, for a lithium secondary battery negative electrode.

5. The sliding portion has a width of 1 mm to 30 mm based on the cross-sectional structure of the negative electrode active layer, as described in claim 1.

6. The anode for a lithium secondary battery according to claim 1, wherein the carbon-based anode active material comprises one or more of natural graphite and artificial graphite.

7. The carbon-based negative electrode active material has a spheroidization degree of 0.75 or higher, as described in claim 1, for a lithium secondary battery negative electrode.

8. A lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode according to any one of claims 1 to 7, and a separator membrane disposed between the positive electrode and the negative electrode.

9. The lithium secondary battery according to claim 8, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active layer provided on at least one surface of the positive electrode current collector and containing one or more positive electrode active materials from among lithium metal oxides represented by the following chemical formulas 1 and 2. [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ２ [Chemical formula 2] LiM ２ ｐ Mn １－ｐ O ４ In the aforementioned chemical formulas 1 and 2, M １ is one or more elements from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. x, y, z, w, and v are such that 1.0 ≤ x ≤ 1.30, 0.5 ≤ y < 1, 0 < z ≤ 0.3, 0 < w ≤ 0.3, and 0 ≤ v ≤ 0.1, and y + z + w + v = 1. M ２ is Ni, Co, or Fe, p is 0.05 ≤ p ≤ 1.

0.

10. The positive electrode active material is LiNi ０．８ Co ０．１ Mn ０．１ O ２ LiNi ０．６ Co ０．２ Mn ０．２ O ２ LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ LiNi ０．６ Co ０．２ Mn ０．１ Al ０．１ O ２ LiNi ０．６ Co ０．２ Mn ０．１５ Al ０．０５ O ２、 LiNi ０．７ Co ０．１ Mn ０．１ Al ０．１ O ２ LiNi ０．７ Mn １．３ O ４ LiNi ０．５ Mn １．５ O ４ LiNi ０．３ Mn １．７ O ４ LiFePO ４ LiFe ０．８ Mn ０．２ PO ４ , and LiFe ０．５ Mn ０．５ PO ４ A lithium secondary battery according to claim 9, comprising one or more of the following.

11. The lithium secondary battery according to claim 8, wherein the electrode assembly is a stacked electrode assembly, a zigzag electrode assembly, or a zigzag-stacked electrode assembly.

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