Negative electrode for lithium secondary battery and method for manufacturing the same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a method for manufacturing the same. The negative electrode according to the present invention includes a negative electrode active layer on a negative electrode current collector, the negative electrode active layer being divided into a central region, an edge region, and a sliding region, and the degree of alignment (OI) of each carbon-based negative electrode active material contained in the central region, the edge region, and the sliding region satisfies formula 1 and formula 2, so that lithium deposition at the edge of the negative electrode active layer can be suppressed. In addition, a secondary battery including the same has an advantage of excellent quick charging performance.

Description

[Technical Field]

[0001] This invention relates to a negative electrode for lithium secondary batteries and a method for manufacturing the same.

[0002] This application claims priority rights under Korean Patent Application No. 10-2022-0183016 dated December 23, 2022, and Korean Patent Application No. 10-2023-0017427 dated February 9, 2023, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference. [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 active material such as graphite. During charging, lithium ions released from the positive electrode are absorbed into the carbon-based active material of the negative electrode, and during discharging, lithium ions contained in the carbon-based active material are absorbed into the lithium metal oxide of the positive electrode, resulting in repeated charging and discharging.

[0005] On the other hand, one of the factors that affects the performance of a secondary battery is the capacity ratio of the active material contained in the positive electrode and the negative electrode, respectively. The above capacity ratio can be expressed as the N / P ratio, which is the value obtained by dividing the total capacity of the negative electrode, calculated by considering the capacity per unit area and / or weight of the negative electrode, by the total capacity of the positive electrode, obtained by considering the capacity per unit area and / or weight of the positive electrode. Since this ratio 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 process of lithium secondary batteries, if the positive electrode active layer separates from the negative electrode active layer when the positive and negative electrodes are stacked, a reversal phenomenon occurs where the N / P ratio becomes less than 1. When the N / P ratio is less than 1, lithium ions cannot be 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, 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 impairs battery safety.

[0007] To address these issues, attempts have been made to increase the amount of negative electrode active material loaded at the active layer edge of conventional negative electrodes. However, in this case, as the amount of negative electrode active material loaded increases, the distance lithium ions travel within the negative electrode increases, which can degrade rapid charging characteristics and other factors, potentially reducing the commercial viability of the battery.

[0008] Therefore, in order to suppress lithium deposition at the edges of the negative electrode active layer, there is a high need for technology that can maintain or improve rapid charging characteristics above a certain level, even when the amount of negative electrode active material loaded at the edges of the negative electrode active layer increases. [Overview of the project] [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 method for manufacturing the same, which have a high loading amount of negative electrode active material at the edge of the negative electrode active layer and excellent fast charging performance in order to suppress lithium deposition at the edge of the negative electrode active layer. [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 and containing a carbon-based negative electrode active material, The negative electrode active layer is, divided into a central region including a central part in the width direction of the negative electrode active layer, a sliding region located at the edge of the negative electrode active layer and having a thickness gradient, and an edge region located between the central region and the sliding region, Provided is a negative electrode for a lithium secondary battery that satisfies the following formulas (1) and (2):

[0011] [Formula (1)] 2.7 ≦ [O.I edge / [O.I center ≦ 4.8

[0012] [Formula (2)] 1.5 ≦ [O.I sliding / [O.I center ≦ 2.6

[0013] (In Formulas (1) and (2), O.I edge represents the degree of alignment (O.I) in the edge region, O.I center represents the degree of alignment (O.I) in the central region, O.I sliding represents the degree of alignment (O.I) in the sliding region, The degree of alignment (O.I) is the ratio (I 004 ) of the area (I 110 ) of the peak indicating the (0, 0, 4) crystal plane to the area (I 004 / I 110 ) of the peak indicating the (1, 1, 0) crystal plane during XRD measurement with respect to the negative electrode active layer)

[0014] At this time, the central region of the negative electrode active layer may have a degree of alignment (O.I center ) of 0.7 to 1.5.

[0015] Furthermore, the central region of the negative electrode active layer may account for 90% or more of the total length in the width direction of the negative electrode active layer, while the sliding region of the negative electrode active layer may account for 3% or less of the total length in the width direction of the negative electrode active layer.

[0016] Furthermore, the central region of the negative electrode active layer may have an average thickness of 100 μm to 300 μm, and the sliding region of the negative electrode active layer may have an inclination angle of 70° or more with respect to the negative electrode current collector.

[0017] On the other hand, the carbon-based active material may contain one or more of the following: natural graphite and artificial graphite.

[0018] Furthermore, in one embodiment of the present invention, The steps include: applying a negative electrode slurry containing a carbon-based active material onto the negative electrode current collector; The steps include applying a magnetic field to the coated negative electrode slurry, The process includes the step of drying a negative electrode slurry to which a magnetic field has been applied to form a negative electrode active layer, The negative electrode active layer described above is divided into a central region including the center in the width direction of the negative electrode active layer, a sliding region located at the edge of the negative electrode active layer and having a thickness gradient, and an edge region located between the central region and the sliding region, and provides a method for manufacturing a negative electrode for a lithium secondary battery that satisfies the following formulas 1 and 2:

[0019] [Formula 1] 2.7 ≤ [OI edge ] / [OI center ]≦4.8

[0020] [Formula 2] 1.5≦[OI sliding ] / [OI center ]≦2.6

[0021] (In equations 1 and 2, OI edge This represents the degree of alignment (OI) in the edge region, OI center This represents the degree of alignment (OI) in the central region, OIsliding This represents the degree of alignment (OI) in the sliding region. The above alignment degree (OI) is the area of ​​the peak showing the (0,0,4) crystal plane during XRD measurement relative to the negative electrode active layer (I 004 ) and the area of ​​the peak showing the (1,1,0) crystal plane (I 110 ) proportion (I 004 / I 110 ) represents)

[0022] Here, in the step of applying the negative electrode slurry, the applied negative electrode slurry may satisfy the following equation 3:

[0023] [Formula 3] R sliding <R center <R edge

[0024] (In equation 3, R sliding This represents the average thickness of the sliding area. R edge This represents the average thickness of the edge region. R center (This represents the average thickness of the central region.)

[0025] Furthermore, the step of applying the magnetic field described above may involve applying a magnetic field of 2,000G to 6,000G, and the application time may be 5 seconds to 60 seconds.

[0026] Furthermore, the step of applying the magnetic field is performed by magnets introduced to the upper and lower parts of the coated negative electrode slurry, and the magnets may have a length of 105% to 200% of the widthwise length of the negative electrode slurry.

[0027] Furthermore, the step of forming the negative electrode active layer may include the step of drying the negative electrode slurry and the step of rolling the dried negative electrode slurry.

[0028] In this case, the edge region of the negative electrode active layer may have a thickness ratio of 105% to 130% based on the average thickness of the central region of the negative electrode active layer before rolling. [Effects of the Invention]

[0029] The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode active layer divided into a central region, an edge region, and a sliding region on a negative electrode current collector, and the degree of alignment (OI) of each carbon-based negative electrode active material contained in the central region, edge region, and sliding region satisfies Equations 1 and 2, thereby suppressing lithium deposition at the edges of the negative electrode active layer, and a secondary battery containing it has the advantage of excellent fast charging performance. [Brief explanation of the drawing]

[0030] [Figure 1] This is an image showing the cross-sectional structure of the negative electrode according to the present invention. [Figure 2] This is an image showing the cross-sectional structure of the negative electrode according to the present invention. [Figure 3] This image shows the cross-sectional structure of the anode active layer that is not rolled after drying during the anode manufacturing process according to the present invention. [Modes for carrying out the invention]

[0031] Since the present invention can be modified in various ways and may have a variety of embodiments, specific embodiments will be described in detail.

[0032] 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.

[0033] In the present invention, terms such as "includes" and "have" are intended to specify the presence of features, numbers, steps, 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, steps, operations, components, parts, or combinations thereof.

[0034] 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.

[0035] Furthermore, in the present invention, "contains as a main component" may mean that the defined component is contained in an amount of 50% or more by weight (or 50% by volume), 60% or more by weight (or 60% by volume), 70% or more by weight (or 70% by volume), 80% or more by weight (or 80% by volume), 90% or more by weight (or 90% by volume), or 95% or more by weight (or 95% by volume) 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% or more by weight, 60% or more by weight, 70% or more by weight, 80% or more by weight, 90% or more by weight, or 95% or more by weight 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.

[0036] Furthermore, in this specification, "carbon-based anode active material is oriented" or "carbon-based anode active material is aligned" means that the crystal planes of the carbon-based anode active material constituting the anode active material particles are distributed such that they have a predetermined orientation with respect to the surface of the anode current collector. This may differ from the arrangement of the carbon-based anode active material particles themselves so that they have a specific orientation within the anode active layer.

[0037] Furthermore, "high orientation of carbon-based anode active material" can mean that the carbon-based anode active material contained in the anode active layer is aligned at a high frequency with respect to the surface of the anode current collector, and in some cases, it can mean that the carbon-based anode active material contained in the anode active layer is aligned at a high angle with respect to the surface of the anode current collector.

[0038] Furthermore, "high degree of alignment of carbon-based anode active material" means that the "degree of alignment (OI)" referred to herein is large, and that the carbon-based anode active material contained in the anode active layer is aligned at a low angle 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 that the carbon-based anode active material contained in the anode active layer is aligned at a high angle with respect to the surface of the anode current collector.

[0039] The present invention will be described in more detail below.

[0040] <Negative electrode for lithium secondary batteries>

[0041] In one embodiment, the present invention is described as follows: The negative electrode current collector and the negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a carbon-based negative electrode active material are included. The above negative electrode active layer is The negative electrode active layer is divided into a central region including the center in the width direction, a sliding region located at the edge of the negative electrode active layer and having a thickness gradient, and an edge region located between the central region and the sliding region. The following negative electrode for a lithium secondary battery is provided, satisfying equations 1 and 2 below:

[0042] [Formula 1] 2.7 ≤ [OI edge ] / [OI center ]≦4.8

[0043] [Formula 2] 1.5≦[OI sliding ] / [OI center ]≦2.6

[0044] (In equations 1 and 2, OI edge This represents the degree of alignment (OI) in the edge region, OI center This represents the degree of alignment (OI) in the central region, OIsliding This represents the degree of alignment (OI) in the sliding region. The above alignment degree (OI) is the area of ​​the peak showing the (0,0,4) crystal plane during XRD measurement relative to the negative electrode active layer (I 004 ) and the area of ​​the peak showing the (1,1,0) crystal plane (I 110 ) proportion (I 004 / I 110 ) represents)

[0045] Figures 1 and 2 are cross-sectional views showing the structures of negative electrodes 100 and 200, in which a negative electrode active layer is provided on one surface of the negative electrode current collector according to the present invention.

[0046] The negative electrodes 100 and 200 for lithium secondary batteries according to the present invention include negative electrode active layers 120 and 220 containing a carbon-based negative electrode active material on at least one surface of the negative electrode current collectors 110 and 210. The negative electrode active layers 120 and 220 are layers that embody the electrical activity of the negative electrode. The negative electrode active layers 120 and 220 are manufactured by coating at least one surface of the negative electrode current collectors 110 and 210 with a negative electrode slurry containing a negative electrode active material that embodies an electrochemical oxidation-reduction reaction during battery charging and discharging, and then drying and rolling it.

[0047] In this case, the negative electrode active layers 120 and 220 are divided into a central region, an edge region, and a sliding region in the width direction of the negative electrodes 100 and 200. Specifically, the negative electrode active layers 120 and 220 include a central region 121 and 221 that includes a central region in the width direction and has a proportion of 90% or more of the total length with respect to the width direction. The central regions 121 and 221 constitute the majority of the negative electrode active layers 120 and 220 and may have a proportion of 93% or more, 95% or more, 97% or more, or 96% to 99% of the total length in the width direction of the negative electrode active layers 120 and 220. Here, "the width direction of the negative electrode active layers 120 and 220" may mean the direction perpendicular to the direction in which the negative electrode current collector travels during negative electrode manufacturing. In some cases, "the width direction of the negative electrode active layers 120 and 220" may be the same as the direction in which the negative electrode tab is formed on one side of the manufactured negative electrode and proceeds to the opposite side. The present invention can further increase the energy density of the negative electrode by adjusting the length ratio of the central regions 121 and 221 in the negative electrode active layers 120 and 220 to the above range.

[0048] Furthermore, edge regions 122 and 222 are located outside the central regions 121 and 221, and sliding regions 123 and 223 are located outside the edge regions 122 and 222.

[0049] In this case, the edge region and sliding region may be arranged sequentially and continuously on both sides of the central region 121, as shown in Figure 1. In some cases, the edge region and sliding region may be arranged sequentially and continuously only on one side of the central region 221, as shown in Figure 2, after punching (or notching) the electrode sheet during the manufacturing process of the negative electrode.

[0050] The sliding regions 123 and 223 described above refer to regions located at the edges of the negative electrode active layers 120 and 220 and having a thickness gradient. The sliding regions 123 and 223 may have a proportion of 3% or less of the total length in the width direction of the negative electrode active layers 120 and 220. Specifically, the sliding regions 123 and 223 may have a form in which the thickness decreases outward in the region adjacent to the edge regions 122 and 222, and considering the energy density of the negative electrode, they may have a proportion of 2% or less, 1% or less, 0.5% or less, 0.01% to 1%, or 0.01% to 0.5% of the total length in the width direction of the negative electrode active layers 120 and 220. In this case, the above length ratio is the ratio of the total length provided with respect to the width direction of the negative electrode active layers 120 and 220, and when sliding regions 123 and 223 are provided on both sides of the central region 121 as shown in Figure 1, the length ratio of each sliding region can be halved to 1 / 2 of the above length ratio.

[0051] Furthermore, the sliding regions 123 and 223 have a thickness gradient in which the thickness decreases as it extends outward, so that the exposed surfaces can have a predetermined inclination angle with respect to the negative electrode current collectors 110 and 210. For example, the sliding regions 123 and 223 can have an inclination angle of 70° or more with respect to the negative electrode current collectors 110 and 210. Specifically, the sliding regions 123 and 223 can have an inclination angle of 75° or more, 80° or more, 85° or more, 70-85°, 75-80°, and 70-75° with respect to the negative electrode current collectors 110 and 210. The present invention can prevent the N / P ratio from being reversed at the end of the electrode assembly assembled with the positive electrode by adjusting the inclination angle of the exposed surfaces of the sliding regions 123 and 223 with respect to the negative electrode current collectors 110 and 210 within the above range, and can further improve the adhesion force with the separation film at the negative electrode end.

[0052] Furthermore, the edge regions 122 and 222 have a higher loading amount of negative electrode active material than the central regions 121 and 221, thereby suppressing the N / P ratio from becoming less than 1 when the stacking position of the positive electrode active layer deviates from the negative electrode active layer inside the secondary battery, and thus preventing lithium from precipitation at the edges of the negative electrode active layers 120 and 220.

[0053] In this case, the edge regions 122 and 222 can occupy the remaining length after subtracting the length ratio of the central regions 121 and 221 and the sliding regions 123 and 223. For example, the edge regions 122 and 222 may have a width of less than 7%, less than 5%, less than 4%, less than 2.5%, 0.09% to 3%, or 0.5% to 1% of the total length of the negative electrode active layers 120 and 220. Similar to the sliding regions 123 and 223, when the edge regions 122 and 222 are provided on both sides of the central region 121, the length ratio of each edge region may be halved to half of the length ratio.

[0054] Furthermore, the negative electrodes 100 and 200 according to the present invention have excellent fast charging performance. As described above, the negative electrodes 100 and 200 can prevent lithium deposition at the edges of the negative electrode active layers 120 and 220 due to a reversal of the N / P ratio between the negative and positive electrodes by controlling the loading amount per unit area of ​​the carbon-based negative electrode active material in the edge regions 122 and 222 to be higher than the loading amount per unit area of ​​the carbon-based negative electrode active material in the central regions 121 and 221. However, in this case, the edge regions 122 and 222, where the loading amount of the carbon-based negative electrode active material is high, have a relatively increased structural tortuosity of the negative electrode active layer compared to the remaining regions, which increases the migration distance of lithium ions and decreases the diffusion rate, so lithium deposition may occur on the negative electrode surface during fast charging. Therefore, the anodes 100 and 200 of the present invention solve this problem by orienting the carbon-based anode active material contained in the anode active layers 120 and 220 such that the angle of the crystal planes it has with respect to the surface of the anode current collectors 110 and 210 is reduced, and by having the carbon-based anode active material oriented in each region of the anode active layers 120 and 220 have a predetermined tendency. In this case, the orientation and / or alignment of the carbon-based anode active material (e.g., graphite) can be determined by crystal plane analysis of the carbon-based anode active material (CA) contained in the anode active layer.

[0055] As one example, the negative electrode active layers 120 and 220 described above may satisfy the following equations 1 and 2:

[0056] [Formula 1] 2.7 ≤ [OI edge ] / [OI center ]≦4.8

[0057] [Formula 2] 1.5≦[OI sliding ] / [OI center ]≦2.6

[0058] (In equations 1 and 2, OI edge This represents the degree of alignment (OI) in the edge region, OI center This represents the degree of alignment (OI) in the central region, OI sliding This represents the degree of alignment (OI) in the sliding region. The above alignment degree (OI) is the area of ​​the peak showing the (0,0,4) crystal plane during XRD measurement relative to the negative electrode active layer (I 004 ) and the area of ​​the peak showing the (1,1,0) crystal plane (I 110 ) proportion (I 004 / I 110 ) represents)

[0059] The degree of alignment (OI) of the carbon-based anode active material (CA) can serve as an indicator of the degree to which the crystal structure of the spherical carbon-based anode active material is oriented in a certain direction, specifically relative to the surface of the anode current collector, as measured by X-ray diffraction (XRD). More specifically, the anode active layer shows peaks of 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° relative to graphite, which is the carbon-based anode active material, as measured by X-ray diffraction. These represent the (0,0,2) plane, (1,0,0) plane, (1,0,1)R plane, (1,0,1)H plane, (0,0,4) plane, and (1,1,0) plane. Furthermore, the peak appearing at 2θ = 43.4 ± 0.2° could be considered to be an overlapping peak between the (1,0,1)R surface of the carbon-based negative electrode active material (CA) and the (1,1,1) surface of the current collector, such as copper (Cu).

[0060] Of these, the degree of alignment (OI) of the carbon-based negative electrode active material (CA) can be measured by the area ratio of the peak at 2θ = 54.7 ± 0.2°, which represents the (0,0,4) plane, and the peak at 2θ = 77.5 ± 0.2°, which represents the (1,1,0) plane. Specifically, the area ratio obtained by integrating the intensity of the above peaks can be used to measure the degree of alignment (OI) of the carbon-based negative electrode active material (CA). Here, the peak at 2θ = 54.7 ± 0.2° represents the (0,0,4) plane among the crystal planes of graphite that have an inclination with respect to the negative electrode current collector. Therefore, the closer the degree of alignment (OI) is to 0, the closer the inclination 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°. In other words, in the negative electrode active layer according to the present invention, the carbon-based negative electrode active material (CA) is aligned at a high angle with respect to the negative electrode current collector, for example, at an angle of 60° or more, 70° or more, 70° to 90°, 80° to 90°, 65° to 85°, or 70° to 85° with respect to the negative electrode current collector. Therefore, the degree of alignment (OI) of the carbon-based negative electrode active material (CA) may be lower compared to when the carbon-based negative electrode active material (CA) is aligned at a low angle.

[0061] When this is taken into consideration, Equation 1 gives the degree of alignment of the carbon-based negative electrode active material contained in the central region (OI center ) is the degree of alignment (OI) of carbon-based negative electrode active material contained in the edge region edge This indicates that the value is smaller than 2.7 ≤ [OI]. This means that the carbon-based anode active material in the central region is aligned at a higher angle to the anode current collector surface than the carbon-based anode active material in the edge region. The anode active layers 120 and 220 of the present invention are such that the carbon-based anode active material in the central region is aligned at a higher angle to the anode current collector surface than the carbon-based anode active material in the edge region, and the above equation 1 has a value of 2.7 to 4.8 (i.e., 2.7 ≤ [OI]. edge ] / [OI center This can be satisfied by ]≦4.8), specifically 2.7~4.8 (i.e., 2.7≦[OI edge ] / [OI center ]≦4.8), 2.9~4.5 (i.e., 2.9≦[OI edge ] / [OI center ]≦4.5), 3.0~4.5 (i.e., 3.0≦[OI edge ] / [OIcenter ]≦4.5), 2.9~3.8 (i.e., 2.9≦[OI edge ] / [OI center ]≦3.8), 3.8~4.6 (i.e., 3.8≦[OI edge ] / [OI center ]≦4.6), or 3.1~4.2 (i.e., 3.1≦[OI edge ] / [OI center This can be satisfied if ]≦4.2).

[0062] Furthermore, Equation 2 shows the degree of alignment of the carbon-based negative electrode active material contained in the central region (OI center ) is the degree of alignment (OI) of the carbon-based negative electrode active material contained in the sliding region. sliding This indicates that the value is smaller than ). This means that the carbon-based anode active material in the central region is aligned at a higher angle with respect to the anode current collector surface than the carbon-based anode active material in the sliding region. The anode active layers 120 and 220 of the present invention are such that the carbon-based anode active material in the central region is aligned at a higher angle with respect to the anode current collector surface than the carbon-based anode active material in the sliding region, and the above equation 2 is 1.5 to 2.6 (1.5 ≤ [OI sliding ] / [OI center The condition ]≦2.6) can be satisfied, specifically 1.8~2.6(1.8≦[OI sliding ] / [OI center ]≦2.6), 1.7~2.3(1.7≦[OI sliding ] / [OI center ]≦2.3), 2.2~2.5(2.2≦[OI sliding ] / [OI center ]≦2.5), 1.9~2.2(1.9≦[OI sliding ] / [OI center ]≦2.2), or 2.0~2.5(2.0≦[OI sliding ] / [OI center This can be satisfied if ]≦2.5).

[0063] Each region of the negative electrode active layers 120 and 220 can satisfy the conditions of formulas 1 and 2 above, so that the alignment (OI) of the carbon-based negative electrode active material (CA) can be within a predetermined range. This makes it possible to maintain a low average alignment of the carbon-based negative electrode active material (CA) contained throughout the negative electrode active layers 120 and 220. Specifically, in the central regions 121 and 221 of the negative electrode active layers 120 and 220, the alignment (OI) of the carbon-based negative electrode active material (CA) contained in these regions center ) can be 0.7 to 1.5, more specifically 0.7 to 1.3, 0.7 to 1.0, 0.9 to 1.2, or 0.8 to 1.1. In this case, the alignment degree (OI) of the above central regions 121 and 221 center The negative electrode active layers 120 and 220 may have a deviation of 5% or less from the average alignment degree.

[0064] Furthermore, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the edge regions 122 and 222. edge ) is the degree of alignment (OI) of the carbon-based negative electrode active material contained in the central regions 121 and 221. center It can be greater than ). This is because the edge regions 122 and 222 have a relatively larger loading amount of carbon-based anode active material compared to the central regions 121 and 221, and as a result, the carbon-based anode active material contained in the edge regions 122 and 222 becomes denser during the rolling process after orientation of the carbon-based anode active material, resulting in a greater degree of alignment (OI edge ) is the degree of alignment (OI) of the carbon-based negative electrode active material contained in the central region. center ) may be relatively slightly higher.

[0065] The present invention makes it possible to secure ion migration channels that allow lithium ions to move shorter distances within each region by adjusting the degree of alignment (OI) of the carbon-based negative electrode active material (CA) contained in the central regions 121 and 221, edge regions 122 and 222, and sliding regions 123 and 223 of the negative electrode active layers 120 and 220, respectively, as described above. As a result, the negative electrode according to the present invention can prevent an increase in resistance due to the long migration distance of lithium ions during fast charging, thereby preventing a decrease in charging performance and preventing the deposition of lithium on the negative electrode surface.

[0066] On the other hand, the average thickness of the negative electrode active layers 120 and 220 can be 100 μm to 300 μm, specifically 100 μm to 250 μm, or 130 μm to 190 μm, and the average thickness can be the same as the average thickness of the central regions 121 and 221. By adjusting the average thickness of the negative electrode active layers 120 and 220 to the above range, the orientation of the carbon-based negative electrode active material (CA) contained in each region can be easily controlled, thereby improving the fast charging characteristics of the battery including the negative electrodes 100 and 200.

[0067] Furthermore, the negative electrode active layers 120 and 220 may, but are not limited to, have a structure in which two separate layers are stacked, depending on the battery model and product application to which the negative electrode of the present invention is applied. In this case, the negative electrode according to the present invention may have a structure in which a first negative electrode active layer (not shown) is provided on the negative electrode current collectors 110 and 210, and a second negative electrode active layer (not shown) is provided on the first negative electrode active layer. In this case, the first negative electrode active layer and the second negative electrode active layer contain a carbon-based negative electrode active material (CA), and the carbon-based negative electrode active material (CA) contained in each layer may be the same or different.

[0068] Furthermore, the negative electrode active layers 120 and 220 contain a carbon-based negative electrode active material (CA) as a negative electrode active material in order to realize electrical activity through a reversible oxidation-reduction reaction during charging and discharging of the battery.

[0069] The carbon-based anode active material (CA) mentioned above refers to a material whose main component is carbon atoms, and such a carbon-based anode active material (CA) may include graphite. The graphite may include one or more of natural graphite and artificial graphite. Preferably, it may include natural graphite or a mixture of natural graphite and artificial graphite.

[0070] The carbon-based anode active material (CA) described above 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 (such as green coke, pitch coke, needle coke, and petroleum coke). In particular, a material assembled using multiple highly crystalline natural graphite particles is preferred. Furthermore, a single graphite granule can be formed by the aggregation of 2 to 100, preferably 3 to 20, flake-shaped graphite particles.

[0071] Furthermore, the above carbon-based negative electrode active material (CA) has an average particle size (D) of 0.5 μm to 20 μm. 50 ) can be shown, specifically the average particle size (D) of 0.5μm~15μm, 0.5μm~10μm, 5μm~20μm, 10μm~20μm, 12μm~18μm, 2μm~7μm, 0.5μm~5μm, or 1μm~3μm. 50 ) can be shown.

[0072] The average particle size of natural graphite can be optimized by reducing its size to maximize the degree of disorder in the expansion direction of each particle, thereby preventing particle expansion due to lithium-ion charging. However, when the particle size of natural graphite is less than 0.5 μm, a large amount of binder may be required due to the increased number of particles per unit volume. On the other hand, when the maximum particle size exceeds 20 μm, expansion becomes more severe, and repeated charging and discharging can reduce inter-particle bonding and bonding between particles and current collectors, potentially significantly degrading cycle performance.

[0073] Furthermore, the negative electrode active layer according to the present invention may selectively further contain, as needed, conductive materials, binders, other additives, etc., along with the main component, carbon-based negative electrode active material (CA).

[0074] 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.

[0075] 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.

[0076] 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. Specifically, the content of the conductive material may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 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, the present invention 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.

[0077] Furthermore, the above-mentioned binder is a component that assists in the bonding of the negative electrode 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, the above-mentioned binder 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, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0078] 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.

[0079] 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.

[0080] <Lithium-ion secondary battery>

[0081] Also, in one embodiment, the present invention provides a lithium secondary battery including an electrode assembly including a positive electrode, the negative electrode of the present invention described above, and a separator disposed between the positive electrode and the negative electrode.

[0082] The lithium secondary battery according to the present invention includes, respectively, an electrode assembly in which a plurality of positive electrodes, a separator, and a negative electrode are sequentially arranged, and an electrolyte composition in which a lithium salt and an electrolyte additive are dissolved in a non-aqueous organic solvent. At this time, the lithium secondary battery has a structure in which a negative electrode active layer is laminated on a negative electrode current collector, and the negative electrode active layer is divided into a central region, an edge region, and a sliding region, and the degree of alignment (O.I) of each carbon-based negative electrode active material contained in the central region, the edge region, and the sliding region satisfies Formula 1 and Formula 2. Thus, the lithium secondary battery has an advantage of excellent high-rate charging characteristics without lithium precipitation occurring at the end of the negative electrode active layer during charge and discharge.

[0083] At this time, since the negative electrode has the same configuration as the above-described configuration, a detailed description thereof is omitted.

[0084] Also, the positive electrode may include a positive electrode active layer manufactured by applying, drying, and rolling a slurry containing a positive electrode active material on a positive electrode current collector. Here, the positive electrode active layer may further selectively include a conductive material, a binder, and other additives in addition to the positive electrode active material, if necessary.

[0085] The positive electrode active material is a material that can electrochemically react on a positive electrode current collector, and may include one or more of lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2 that enable reversible intercalation and deintercalation of lithium ions:

[0086] [Chemical Formula 1] Li x [Ni y Co z Mn w M 1 v O2

[0087] [Chemical Formula 2] LiM 2 p Mn q P r O4

[0088] In the above Chemical Formula 1 and Chemical Formula 2, M 1 is one or more elements selected 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 respectively 1.0 ≦ x ≦ 1.30, 0.5 ≦ y < 1, 0 < z ≦ 0.3, 0 < w ≦ 0.3, 0 ≦ v ≦ 0.1, and y + z + w + v = 1, M 2 is Ni, Co or Fe, p is 0.05 ≦ p ≦ 1.0, q is 1 - p or 2 - p, r is 0 or 1.

[0089] The lithium metal oxides represented by the above Chemical Formula 1 and Chemical Formula 2 are substances each containing nickel (Ni) and manganese (Mn) in high contents, and when used as a positive electrode active material, they have the advantage of being able to stably supply electricity with high capacity and / or high voltage as compared with positive electrode active materials such as conventionally commonly used iron phosphate oxide (LiFeO4).

[0090] At this time, examples of the lithium metal oxide represented by the above Chemical Formula 1 include LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn<00001​​​​​​​​​​​​​​​​Co 0.2 Mn 0.15 Al 0.05 O2, LiLiLi 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 O4, LiFePO4, LiFe 0.7 Mn 0.3 It may contain PO4 and other elements, which can be used alone or in combination.

[0091] 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.

[0092] Furthermore, the positive electrode active layer may further contain conductive materials, binders, and other additives along with the positive electrode active material.

[0093] In this case, the conductive material is used to improve the electrical performance of the positive electrode, and any conductive material commonly used in the industry may be applied. Specifically, the conductive material may include one or more of the following: 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.

[0094] 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.

[0095] Furthermore, the binder plays a role in binding the positive electrode active material, positive electrode additive, and conductive material to each other, 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.

[0096] 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.

[0097] The total thickness of the positive electrode active layer described above is not particularly limited, but it may be 50 μm to 300 μm, and more specifically, it may 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.

[0098] 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.

[0099] 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.

[0100] On the other hand, the lithium secondary battery according to the present invention is not particularly limited, but may 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.

[0101] <Method for manufacturing a negative electrode>

[0102] Furthermore, in one embodiment of the present invention, The steps include: applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector; The steps include applying a magnetic field to the coated negative electrode slurry, The process includes the step of drying a negative electrode slurry to which a magnetic field has been applied to form a negative electrode active layer, The negative electrode active layer described above is divided into a central region including the center in the width direction of the negative electrode active layer, a sliding region located at the edge of the negative electrode active layer and having a thickness gradient, and an edge region located between the central region and the sliding region, and provides a method for manufacturing a negative electrode for a lithium secondary battery that satisfies the following formulas 1 and 2:

[0103] [Formula 1] 2.7 ≤ [OI edge ] / [OI center ]≦4.8

[0104] [Formula 2] 1.5≦[OI sliding ] / [OI center ]≦2.6

[0105] (In equations 1 and 2, OI edge This represents the degree of alignment (OI) in the edge region, OI center This represents the degree of alignment (OI) in the central region, OI sliding This represents the degree of alignment (OI) in the sliding region. The above alignment degree (OI) is the area of ​​the peak showing the (0,0,4) crystal plane during XRD measurement relative to the negative electrode active layer (I 004 ) and the area of ​​the peak showing the (1,1,0) crystal plane (I 110 ) proportion (I 004 / I 110 ) represents)

[0106] The present invention provides a method for manufacturing a negative electrode, which involves coating a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector, and applying a magnetic field to the surface of the coated negative electrode slurry to align the carbon-based negative electrode active material in the slurry to a predetermined angle with respect to the surface of the negative electrode current collector. Subsequently, the negative electrode slurry, in which the degree of alignment of the carbon-based negative electrode active material has decreased, is dried to form a negative electrode active layer, thereby manufacturing the negative electrode.

[0107] Here, the step of applying the negative electrode slurry is a step of discharging a negative electrode slurry containing a carbon-based negative electrode active material onto the surface of a moving negative electrode current collector and coating it, and can be applied without particular limitation as long as it is a method commonly used in the industry. Preferably, the step of applying the negative electrode slurry can be performed by a die coating method. The die coating method can be performed via a slot die equipped with a shim for controlling the discharging conditions of the negative electrode slurry. In this case, by controlling the shape of the shim, the loading amount of the negative electrode slurry applied to the negative electrode current collector, the coating thickness, etc., can be easily controlled.

[0108] Furthermore, the step of applying the negative electrode slurry may be performed in such a way as to satisfy the following formula 3 in order to prevent lithium from precipitation at the edges of the negative electrode active layer during charging and discharging of the secondary battery:

[0109] [Formula 3] R sliding <R center <R edge

[0110] (In equation 3, R sliding This represents the average thickness of the negative electrode slurry in the sliding region. R edge This represents the average thickness of the negative electrode slurry in the edge region. R center (This represents the average thickness of the negative electrode slurry in the central region.)

[0111] Equation 3 above shows the correlation between the average thicknesses of the negative electrode slurry applied to each region. As shown in Figure 3, the negative electrode slurry applied according to the present invention may have a greater average thickness in the edge region 122 than in the central region 121, and a tendency for the average thickness to decrease significantly in the sliding region 123 according to the thickness gradient. Here, "average thickness" can be measured using a confocal microscope, and the method may differ for each region. Specifically, in the case of the central region and the edge region, it may mean the average value calculated from the thickness measured at three or more arbitrary points. In the case of the sliding region, it may be the thickness measured at the point where the length of the sliding region is 1 / 2 of the widthwise length of the applied negative electrode slurry.

[0112] For example, the central regions 121 and 221 of the negative electrode slurry may have an average thickness of 180 ± 3 μm, the edge regions 122 and 222 may have an average thickness of 210 ± 3 μm, and the sliding regions 123 and 223 may have an average thickness of 120 ± 3 μm.

[0113] The present invention makes it possible to easily control the loading amount of carbon-based anode active material in each region, even if the average thickness of each region becomes uniform after rolling, by controlling the average thickness of each region of the anode slurry applied on the anode current collector as described above. Specifically, even if the average thickness of the central regions 121 and 221 and the edge regions 122 and 222 of the anode active layer are the same or similar after rolling, the loading amount per unit area of ​​the edge regions 122 and 222 may be greater than the loading amount per unit area of ​​the central regions 121 and 221.

[0114] On the other hand, the step of applying a magnetic field to the negative electrode slurry may be a step of orienting the carbon-based negative electrode active material contained in the negative electrode slurry so that its crystal plane has a predetermined angle with respect to the negative electrode current collector. For this purpose, the step of applying a magnetic field may be performed by applying a magnetic field using magnets positioned above and below the negative electrode current collector, which is moved with the negative electrode slurry coated on its surface.

[0115] In this case, the degree of alignment (OI) of the carbon-based anode active material contained in the anode slurry can be adjusted by the strength of the applied magnetic field and the time of exposure to the magnetic field. Thus, the step of applying the magnetic field can be performed under predetermined magnetic field strength and time conditions.

[0116] Specifically, the step of applying the above magnetic field may involve applying a magnetic field of 2,000 G (Gauss) to 6,000 G (Gauss). More specifically, the step of applying the above magnetic field may involve applying a magnetic field with an intensity of 2,500 G to 5,500 G, 3,000 G to 5,500 G, 3,500 G to 5,500 G, 4,000 G to 5,500 G, 3,500 G to 4,500 G, or 4,500 G to 5,000 G.

[0117] Furthermore, the step of applying the magnetic field described above may be performed for 5 to 60 seconds, specifically for 10 to 60 seconds, 10 to 30 seconds, 30 to 60 seconds, 40 to 50 seconds, 15 to 35 seconds, or 10 to 50 seconds.

[0118] As one example, in the step of applying the magnetic field described above, a magnetic field of 4,700 ± 100 G can be applied to the negative electrode slurry for 12 to 33 seconds.

[0119] Furthermore, the step of applying the magnetic field is performed by magnets introduced to the upper and lower parts of the coated negative electrode slurry, as described above, and the size of the magnets can be adjusted to be larger than the size of the negative electrode slurry so that the magnetic field applied to the negative electrode slurry can be applied uniformly to the entire surface of the negative electrode slurry. For example, the magnets may have a length ratio of 105% to 200% of the widthwise length of the negative electrode slurry, and 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% of the widthwise length of the negative electrode slurry.

[0120] The present invention allows for the regional orientation of the carbon-based anode active material contained in the anode slurry to satisfy Equations 1 and 2 by controlling the magnetic field strength, application time, and / or the size of the magnetic part as described above in the step of applying a magnetic field.

[0121] Furthermore, the step of forming the negative electrode active layer may include a step of drying the negative electrode slurry and a step of rolling the dried negative electrode slurry.

[0122] In this case, the step of drying the negative electrode slurry can be applied without particular limitation as long as it is a method that can maintain the orientation of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0123] For example, the drying step described above can be performed by applying thermal energy to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like to dry the negative electrode slurry.

[0124] Furthermore, the step of rolling the dried anode slurry involves increasing the density of the anode active layer by applying pressure to the dried anode slurry using a roll press or the like. In this case, the rolling may be carried out at a temperature higher than room temperature.

[0125] Specifically, the rolling described above may be carried out at temperatures of 50°C to 100°C, more specifically at temperatures of 60°C to 100°C, 75°C to 100°C, 85°C to 100°C, 50°C to 90°C, 60°C to 80°C, or 65°C to 90°C. Specifically, the above rolling may be carried out at rolling speeds of 2 m / s to 7 m / s, and more specifically at rolling speeds of 2 m / s to 6.5 m / s, 2 m / s to 6 m / s, 2 m / s to 5.5 m / s, 2 m / s to 5 m / s, 2 m / s to 4.5 m / s, 2 m / s to 4 m / s, 2.5 m / s to 4 m / s, 2.5 m / s to 3.5 m / s, 3.5 m / s to 5 m / s, 5 m / s to 7 m / s, 5.5 m / s to 6.5 m / s, or 6 m / s to 7 m / s. Furthermore, the above rolling may be carried out under pressure conditions of 50 MPa to 200 MPa, specifically under pressure conditions of 50 MPa to 150 MPa, 50 MPa to 100 MPa, 100 MPa to 200 MPa, 150 MPa to 200 MPa, or 80 MPa to 140 MPa.

[0126] The present invention makes it possible to increase the energy density of the anode while minimizing changes in the alignment of the carbon-based anode active material contained in the anode active layer formed by rolling a dried anode slurry under the above temperature, speed, and / or pressure conditions.

[0127] The present invention will be described in more detail below with reference to examples and experimental examples.

[0128] 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.

[0129] <Examples 1-2 and Comparative Examples 1-2. Manufacturing of negative electrodes for lithium secondary batteries>

[0130] The negative electrode for the lithium secondary battery was manufactured according to the conditions shown in Table 1 below.

[0131] First, natural graphite (average particle size: 10±1 μm) and artificial graphite (average particle size: 8±1 μm) were prepared as carbon-based anode active materials, and anode slurry was manufactured using the prepared carbon-based anode active materials.

[0132] Specifically, a mixed graphite, prepared by mixing natural graphite and artificial graphite in a weight ratio of 1-3:7-9, was used as the negative electrode active material. Carbon black was used as the conductive material, and carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) were used as binders. Subsequently, 95 parts by weight of the mixed 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 produce a negative electrode slurry with a solid content of 50%.

[0133] Once the negative electrode slurry was prepared, it was cast onto a copper sheet (thickness: 10 μm) being transported roll-to-roll (transport speed: 5 m / min) using a die coater. At this time, the negative electrode slurry was cast so that the average thickness was 190 μm along the transport direction of the copper sheet, and the shape of the shim provided in the die coater was changed so that the average thickness of each region of the negative electrode active layer before rolling was adjusted as shown in Table 1.

[0134] At this time, the cross-sectional structure of the applied negative electrode slurry is as shown in Figure 3, and each negative electrode slurry had a central region in the middle with a length ratio of 98.5% based on the width of the negative electrode slurry. Subsequently, regions with a total length ratio of 1.0% on both sides of the central region were set as edge regions (each with a length ratio of 0.5%), and regions with a length ratio of 0.5% outside the edge regions were set as sliding regions (each with a length ratio of 0.25%).

[0135] In measuring the average thickness of each defined region, the average thickness of the central and edge regions of the negative electrode slurry was obtained by measuring the confocal thickness for each region three times and calculating the average value. For the sliding region of the negative electrode slurry, the average thickness was defined as the thickness at the point where the length of the sliding region was half of the width of the negative electrode slurry.

[0136] After measuring the average thickness of each region of the negative electrode slurry, permanent magnets having a length ratio of 110-120% of the width of the negative electrode slurry were placed on the top of the coated negative electrode slurry and below the negative electrode current collector. A magnetic field of 4,700±100G was applied for 15 seconds, and then the negative electrode slurry with the applied magnetic field was dried with hot air to form a negative electrode active layer. The formed negative electrode active layer was rolled at 50±1℃ at a pressure of 100-150MPa and a transfer speed of 3m / s to manufacture a negative electrode for lithium secondary batteries.

[0137] Furthermore, X-ray diffraction (XRD) spectroscopy was performed on each region of the negative electrode active layer for each manufactured negative electrode, and the spectra were measured. The X-ray diffraction (XRD) measurement conditions were as follows:

[0138] -Target: Cu (Kα) graphite monochromatization device - Slit: Divergent slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree -Measurement area: (1,1,0) plane: 76.5 degrees < 2θ < 78.5 degrees / (0,0,4) plane: 53.5 degrees < 2θ < 56.0 degrees

[0139] From the spectrum measured under the above conditions, determine the area of ​​the peak representing the (0,0,4) crystal plane and the area of ​​the peak representing the (1,1,0) crystal plane, and the ratio of these areas (I 004 / I 110 The degree of alignment (OI) of the mixed graphite in each region was calculated by performing the calculation. The calculated values ​​are shown in Table 1 below.

[0140] [Table 1]

[0141] <Comparative Examples 3 and 4. Manufacturing of negative electrodes for lithium secondary batteries>

[0142] A negative electrode for a lithium secondary battery was manufactured in the same manner as in Example 1, except that a magnetic field was not applied after casting the negative electrode slurry, or a magnetic field was applied using a permanent magnet having a length ratio of 95-100% of the width of the negative electrode slurry.

[0143] (1) the average thickness of each region of the coated anode slurry during anode manufacturing and (2) the degree of alignment (OI) of the carbon-based anode active material contained in each region after rolling were measured using the same method as in Example 1, and the measured results are shown in Table 2 below.

[0144] [Table 2]

[0145] <Examples 3-4 and Comparative Examples 5-8. Manufacturing of Lithium Secondary Batteries>

[0146] 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.

[0147] A separation membrane made of polypropylene with a thickness of 18 μm was placed between the positive electrode obtained above and the negative electrodes manufactured in Examples 1-2 and Comparative Examples 1-4, respectively, and the case was inserted. After that, the electrolyte composition was injected to assemble the lithium secondary battery.

[0148] The types of negative electrodes applied to each lithium secondary battery are shown in Table 3 below.

[0149] [Table 3]

[0150] <Example of experiment>

[0151] The following experiment was conducted to evaluate the performance of the negative electrode according to the present invention.

[0152] i) Evaluation of the presence or absence of lithium deposition

[0153] The lithium secondary batteries manufactured in Examples 3-4 and Comparative Examples 5-8 were charged to 80% SOC by applying a 1.5C-rate current, and the voltage change and dV / dQ were measured according to the SOC. Lithium deposition was determined to have occurred on the negative electrode surface if a voltage plateau was present in the measured voltage change, or if the graph showing dV / dQ was bimodal. The results are shown in Table 4 below.

[0154] (b) Evaluation of fast charging performance The lithium secondary batteries manufactured in Examples 3-4 and Comparative Examples 5-8 were subjected to a charge-discharge process of 300 cycles, in which they were discharged at 0.5C and then charged at a charging rate of 1.7C. After each cycle, the charge capacity and charge rate were measured. The measured charge capacity and its ratio to the initial charge capacity were calculated, and the results are shown in Table 4 below. A "○" indicates that the calculated ratio to the initial charge capacity was 80% or more, a "×" indicates that the ratio was 50% or less, and a "△" indicates that the ratio was between 50% and less than 80%.

[0155] [Table 4]

[0156] As shown in Table 4 above, the negative electrode for lithium secondary batteries according to the present invention not only suppresses lithium deposition but also exhibits excellent rapid charging performance. Specifically, it was confirmed that the negative electrode manufactured in the example did not deposit lithium on the negative electrode surface during charging and discharging, and that the charging capacity during rapid charging was maintained at 80% or more.

[0157] This means that the negative electrode of the example contains a high loading amount of carbon-based negative electrode active material in the edge region of the negative electrode active layer, which is excellent in suppressing lithium deposition during battery charging, and the degree of alignment (OI) of each carbon-based negative electrode active material contained in the central region, edge region, and sliding region of the negative electrode active layer satisfies Equations 1 and 2, thereby improving the rapid charging performance of the battery.

[0158] These results show that the negative electrode for lithium secondary batteries according to the present invention suppresses lithium deposition at the edges of the negative electrode active layer, and secondary batteries containing it exhibit excellent rapid charging performance.

[0159] 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.

[0160] 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. [Explanation of symbols]

[0161] 100, 200: Negative electrode for lithium secondary battery according to the present invention 110, 210: Negative electrode current collector 120, 220: Negative electrode active layer 121, 221: Central region of the negative electrode active layer 122, 222: Edge region of the negative electrode active layer 123, 223: Sliding region of the negative electrode active layer CA: Carbon-based negative electrode active material ↑: Crystal plane alignment direction of carbon-based anode active material

Claims

1. The negative electrode current collector and the negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a carbon-based negative electrode active material are included. The aforementioned negative electrode active layer is The negative electrode active layer is divided into a central region including the center in the width direction, a sliding region located at the edge of the negative electrode active layer having a thickness gradient that decreases outward, and an edge region located between the central region and the sliding region. The central region of the negative electrode active layer has a proportion of 90% or more of the total length in the width direction of the negative electrode active layer. The sliding region of the negative electrode active layer has a proportion of 3% or less of the total length in the width direction of the negative electrode active layer. The loading amount per unit area of ​​the carbon-based anode active material in the edge region is higher than the loading amount per unit area of ​​the carbon-based anode active material in the central region. The following equations 1 and 2 are satisfied, [Formula 1] 2.7≦[O.I] ｅｄｇｅ ] / [O.I ｃｅｎｔｅｒ ]≦4.8 [Formula 2] 1.5≦[O.I] ｓｌｉｄｉｎｇ ] / [O.I ｃｅｎｔｅｒ ]≦2.6 In equations 1 and 2, O.I ｅｄｇｅ This represents the degree of alignment (O.I) in the edge region, O.I ｃｅｎｔｅｒ This represents the degree of alignment (O.I) in the central region, O.I ｓｌｉｄｉｎｇ This represents the degree of alignment (O.I) in the sliding region. The degree of alignment (O.I) is the ratio of the area (I ００４ ) of the peak indicating the (0, 0, 4) crystal plane to the area (I １１０ ) of the peak indicating the (1, 1, 0) crystal plane during XRD measurement with respect to the negative electrode active layer, and is represented by (I ００４ / I １１０ ). The central region of the negative electrode active layer has an alignment degree (O.I center) of 0.7 to 1.

5. The negative electrode for a lithium secondary battery has a central region of the negative electrode active layer having an average thickness of 100 μm to 300 μm.

2. The carbon-based negative electrode active material comprises one or more natural graphite and artificial graphite, as described in claim 1, for a lithium secondary battery.

3. The steps include: applying a negative electrode slurry containing a carbon-based active material onto the negative electrode current collector; The steps include applying a magnetic field to the coated negative electrode slurry, The process includes the step of drying a negative electrode slurry to which a magnetic field has been applied to form a negative electrode active layer, The negative electrode active layer is divided into a central region including the center in the width direction of the negative electrode active layer, a sliding region located at the edge of the negative electrode active layer having a thickness gradient that decreases outward, and an edge region located between the central region and the sliding region, satisfying the following equations 1 and 2. The central region of the negative electrode active layer has a proportion of 90% or more of the total length in the width direction of the negative electrode active layer. The sliding region of the negative electrode active layer has a proportion of 3% or less of the total length in the width direction of the negative electrode active layer. In the step of applying the negative electrode slurry, the applied negative electrode slurry satisfies the following formula 3, [Formula 1] 2.7≦[O.I] ｅｄｇｅ ] / [O.I ｃｅｎｔｅｒ ]≦4.8 [Formula 2] 1.5≦[O.I] ｓｌｉｄｉｎｇ ] / [O.I ｃｅｎｔｅｒ ]≦2.6 In equations 1 and 2, O.I ｅｄｇｅ This represents the degree of alignment (O.I) in the edge region, O.I ｃｅｎｔｅｒ This represents the degree of alignment (O.I) in the central region, O.I ｓｌｉｄｉｎｇ This represents the degree of alignment (O.I) in the sliding region. The aforementioned alignment degree (O.I) is the area of ​​the peak showing the (0,0,4) crystal plane during XRD measurement with respect to the negative electrode active layer (I ００４ ) and the area of ​​the peak showing the (1,1,0) crystal plane (I １１０ ) proportion (I ００４ / I １１０ ) represents, [Formula 3] R ｓlｉｄｉｎg <R ｃｅｎｔｅｒ <R ｅｄｇｅ In Equation 3, R ｓlｉｄｉｎg This represents the average thickness of the sliding area. R ｅｄｇｅ This represents the average thickness of the edge region. R ｃｅｎｔｅｒ This represents the average thickness of the central region. The central region of the negative electrode active layer has an alignment degree (O.I center) of 0.7 to 1.

5. A method for manufacturing a negative electrode for a lithium secondary battery, wherein the central region of the negative electrode active layer has an average thickness of 100 μm to 300 μm.

4. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 3, wherein the step of applying the magnetic field is to apply a magnetic field of 2,000 G to 6,000 G.

5. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 3, wherein the step of applying the magnetic field is performed for 5 to 60 seconds.

6. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 3, wherein the step of applying the magnetic field is performed by magnets introduced to the upper and lower parts of the coated negative electrode slurry, and the magnets have a length of 105% to 200% with respect to the widthwise length of the negative electrode slurry.

7. The step of forming the negative electrode active layer is, The steps include drying the negative electrode slurry, A method for manufacturing a negative electrode for a lithium secondary battery according to any one of claims 3 to 6, comprising the step of rolling a dried negative electrode slurry.

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