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 manufacturing method thereof. The negative electrode includes a negative active layer divided into a central region, an edge region, and a sliding region on a negative electrode current collector, wherein the alignment index (O.I) of each carbon-based negative active material contained in the central region, the edge region, and the sliding region satisfies Formula 1 and Formula 2, and thus has the advantage of exhibiting high-rate charge / discharge performance and high energy density with a small volume change during charge / discharge.

Description

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0182981, filed on December 23, 2022, and Korean Patent Application No. 10-2023-0017346, filed on February 9, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the negative electrode for lithium secondary batteries and its manufacturing method. Background Technology

[0003] Recently, rechargeable batteries have been widely used not only in small devices such as portable electronic devices, but also in medium and large devices such as battery packs or energy storage devices in hybrid or electric vehicles.

[0004] This type of secondary battery is a power generation device capable of being charged and discharged, consisting of a stacked structure of positive electrode / separator / negative electrode. It typically has a configuration in which the positive electrode includes lithium metal oxide as the positive electrode active material, and the negative electrode includes a carbon-based negative electrode active material such as graphite, such that lithium ions emitted from the positive electrode are adsorbed into the carbon-based negative electrode active material of the negative electrode during charging, and lithium ions included in the carbon-based negative electrode active material are adsorbed into the lithium metal oxide of the positive electrode during discharging, and the charging and discharging are repeated.

[0005] In addition, amorphous carbon or crystalline carbon are used as active materials for negative electrodes, and among them, crystalline carbon is mainly used due to its high capacity. These crystalline carbons include natural graphite and artificial graphite.

[0006] Synthetic graphite exhibits higher charge-discharge efficiency and less expansion during charge-discharge, resulting in better lifetime characteristics compared to natural graphite. However, it also suffers from lower reversible capacity, harder particles, difficulty in rolling during electrode fabrication, and poor orientation due to low shape change. In particular, it requires a 3000°C graphitization heat treatment, leading to high manufacturing costs.

[0007] In addition, natural graphite has been used as a negative electrode active material because it is cheaper than synthetic graphite, has high reversible capacity, and exhibits similar electrochemical performance. However, because natural graphite has a plate-like shape, it has a large surface area and exposed edges. Therefore, when electrolyte permeation or decomposition reactions occur, the edges may be delaminated or damaged, leading to large irreversible reactions and increased expansion rates, resulting in a decrease in long-term lifetime characteristics.

[0008] Besides these carbon-based anode materials, lithium metal, which has been considered an anode active material, has very high energy density and can achieve high capacity, but it has safety issues and short cycle life due to dendrite growth (dendrites) during repeated charge and discharge.

[0009] Silicon, tin, or their alloys, have become the subject of much research in recent years as another type of anode active material, as they have been recognized to reversibly adsorb and release large amounts of lithium through recombination reactions with lithium. For example, silicon has a theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is very large compared to graphite-based materials, and therefore shows promise as a high-capacity anode material. However, the aforementioned anode active materials suffer from drawbacks such as very large volume changes during charge and discharge and poor high-rate discharge characteristics.

[0010] Therefore, it is necessary to improve the performance of anode active materials to exhibit low expansion rate, predetermined capacity, high output characteristics, and lifetime characteristics. In this regard, anode active materials comprising crystalline carbon-based compounds such as graphite coated with amorphous carbon are initially considered. However, while this increases the energy density, the proportion of amorphous carbon-based compounds included in the carbon-based anode active material is low, which is insufficient to achieve high output characteristics, and the desired level of lifetime characteristics cannot be obtained due to poor conductivity in the absence of a uniform coating.

[0011] Therefore, various attempts have been made to develop anode active materials with excellent lifetime characteristics by improving high-rate charge-discharge characteristics and low expansion capacity. There is a great need for a technology that can fundamentally solve these problems while simultaneously achieving high-rate charge-discharge characteristics and high energy density in anode active materials. Summary of the Invention

[0012] Technical issues

[0013] The present invention aims to provide a negative electrode for lithium secondary batteries, including carbon-based anode active materials such as natural graphite, which exhibit small volume changes during charge and discharge, while also exhibiting high charge and discharge rates and high energy density, and a method thereof.

[0014] Technical solution

[0015] To solve the above problems,

[0016] In one embodiment, the present invention provides a negative electrode for a lithium secondary battery, comprising:

[0017] A negative electrode current collector; and a negative electrode active layer, the negative electrode active layer being disposed on at least one side of the negative electrode current collector and comprising a carbon-based negative electrode active material.

[0018] Among them, the negative electrode active layer,

[0019] The negative electrode active layer is divided in the width direction into a central region including a central portion, 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.

[0020] Furthermore, the negative electrode for the lithium secondary battery satisfies the following equations 1 and 2:

[0021] [Formula 1]

[0022] 1.6≤[OI edge ] / [OI center ≤2.5

[0023] [Equation 2]

[0024] 2.6≤[OI sliding ] / [OI center ≤3.5

[0025] In Equations 1 and 2,

[0026] OI edge Indicates the alignment (OI) in the edge region.

[0027] OI center Indicates the alignment (OI) at the central region, and

[0028] OI sliding Indicates the alignment (OI) in the sliding region.

[0029] Furthermore, the alignment (OI) indicates the area (I0) of the peak representing the [0,0,4] crystal plane in the XRD measurement of the negative electrode active layer. 004 ) and the area of ​​the peak representing the [1,1,0] crystal plane (I 110 The ratio of (I) 004 / I 110 ).

[0030] In this case, the central region of the negative electrode active layer can have an alignment accuracy (OI) of 0.7 to 1.5. center ).

[0031] Furthermore, the ratio of the central region of the negative electrode active layer to the total length of the negative electrode active layer in the width direction can be more than 90%, and the ratio of the sliding region of the negative electrode active layer to the total length of the negative electrode active layer in the width direction can be less than 3%.

[0032] Furthermore, the negative electrode active layer can satisfy the following equation 3:

[0033] [Formula 3]

[0034] R sling <R edge ≤R center

[0035] (In Equation 3,

[0036] R sling Indicates the average thickness of the sliding region.

[0037] R edge Indicates the average thickness of the edge region, and

[0038] R center (Indicates the average thickness of the central region).

[0039] In addition, the average thickness of the central region of the negative electrode active layer can be from 100 μm to 300 μm, and the sliding region of the negative electrode active layer can have an inclination angle of more than 70° relative to the exposed surface of the current collector.

[0040] In addition, the carbon-based negative electrode active material may include one or more of natural graphite and artificial graphite.

[0041] In one embodiment, the present invention also provides a method for manufacturing a negative electrode for a lithium secondary battery, comprising:

[0042] A negative electrode slurry, including a carbon-based negative electrode active material, is applied to the negative electrode current collector;

[0043] Apply a magnetic field to the applied negative electrode slurry; and

[0044] The negative electrode slurry, to which a magnetic field has been applied, is dried to form a negative electrode active layer;

[0045] The negative electrode active layer is divided into a central region comprising a central portion 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 the negative electrode for the lithium secondary battery satisfies the following equations 1 and 2:

[0046] [Formula 1]

[0047] 1.6≤[OI edge ] / [OI center ≤2.5

[0048] [Equation 2]

[0049] 2.6≤[OIsliding ] / [OI center ≤3.5

[0050] (in Equations 1 and 2,

[0051] OI edge Indicates the alignment (OI) in the edge region.

[0052] OI center Indicates the alignment (OI) at the central region, and

[0053] OI sliding Indicates the alignment (OI) in the sliding region.

[0054] Furthermore, the alignment (OI) indicates the area (I0) of the peak representing the [0,0,4] crystal plane in the XRD measurement of the negative electrode active layer. 004 ) and the area of ​​the peak representing the [1,1,0] crystal plane (I 110 The ratio of (I) 004 / I 110 )).

[0055] Here, the step of applying the magnetic field involves applying a magnetic field of 2000G to 6000G, and the duration of applying the magnetic field can be from 5 seconds to 60 seconds.

[0056] Furthermore, the step of applying a magnetic field can be performed by introducing magnetic portions into the upper and lower portions of the applied negative electrode slurry, wherein the magnetic portions can have a length of 105% to 200% based on the length of the negative electrode slurry in the width direction.

[0057] In addition, the step of forming the negative electrode active layer may include drying the negative electrode slurry; and rolling the dried negative electrode slurry.

[0058] In this case, based on the average thickness of the central region of the negative electrode active layer before rolling, the edge region of the negative electrode active layer can have a thickness ratio of more than 90% and less than 105%.

[0059] Beneficial effects

[0060] The negative electrode for lithium secondary batteries according to the present invention comprises a negative electrode active layer divided into a central region, an edge region and a sliding region on a current collector, and has the advantages of exhibiting high-rate charge and discharge and high energy density with small volume change during charge and discharge by satisfying the alignment (OI) of each carbon-based negative electrode active material contained in the central region, the edge region and the sliding region. Attached Figure Description

[0061] Figure 1 and Figure 2 This is an image illustrating the cross-sectional structure of the negative electrode according to the present invention. Detailed Implementation

[0062] This invention can have various modifications and various implementations, and therefore its specific implementations will be described in detail below.

[0063] However, it should be understood that the present invention is not limited to the specific embodiments, but includes all modifications, equivalents or alternatives within the spirit and technical scope of the present invention.

[0064] The terms “comprising,” “including,” and “having” as used herein mean the presence of a feature, quantity, step, action, component, or element or combination thereof described in the specification, and it should be understood that the possibility of the presence or addition of one or more other features, quantities, steps, actions, components, elements, or combinations thereof is not excluded in advance.

[0065] Furthermore, in this invention, when a portion of a layer, film, region, plate, etc., is disposed "on" another portion, this includes not only the case where one portion is disposed "directly" on the other portion, but also the case where another portion is inserted between them. Conversely, when a portion of a layer, film, region, plate, etc., is disposed "below" another portion, this includes not only the case where one portion is disposed "directly" below the other portion, but also the case where another portion is inserted between them. Additionally, in this application, "on" can include not only the case where it is disposed on the upper portion, but also the case where it is disposed on the lower portion.

[0066] Additionally, as used herein, "comprising as a major component" can mean comprising at least 50 wt% (or at least 50 vol%), at least 60 wt% (or at least 60 vol%), at least 70 wt% (or at least 70 vol%), at least 80 wt% (or at least 80 vol%), at least 90 wt% (or at least 90 vol%), or at least 95 wt% (or at least 95 vol%) of the defined component by total weight (or total volume). For example, "comprising graphite as a major component as a negative electrode active material" can mean that the total weight of the negative electrode active material comprises at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, or at least 95 wt% graphite, and in some cases can mean that the entire negative electrode active material is graphite (including at least 100 wt% graphite).

[0067] Additionally, as used herein, “the carbon-based anode active material is oriented” or “the carbon-based anode active material is aligned” means that the crystal plane distribution of the carbon-based anode active material, including the anode active material particles, is a predetermined orientation relative to the surface of the anode current collector, which may differ from the carbon-based anode active material particles themselves being arranged in a specific orientation within the anode active layer.

[0068] In addition, "high orientation of carbon-based anode active material" can refer to the high frequency alignment of the carbon-based anode active material contained in the anode active layer with the surface of the anode current collector, and in some cases, the large angle alignment of the carbon-based anode active material contained in the anode active layer with the surface of the anode current collector.

[0069] Furthermore, "high alignment of carbon-based anode active materials" can refer to a large value for the "alignment degree (OI)" as used herein, resulting in the carbon-based anode active materials contained in the anode active layer being aligned at a low angle relative to the surface of the anode current collector. Conversely, "low alignment of carbon-based anode active materials" can refer to a small value for the "alignment degree (OI)," indicating that the carbon-based anode active materials contained in the anode active layer are aligned at a large angle relative to the surface of the anode current collector.

[0070] The invention will be described in more detail below.

[0071] Negative electrode for lithium secondary batteries

[0072] In one embodiment, the present invention provides a negative electrode for a lithium secondary battery, comprising:

[0073] A current collector includes a negative electrode; and a negative electrode active layer disposed on at least one side of the negative electrode current collector and comprising a carbon-based negative electrode active material.

[0074] Among them, the negative electrode active layer

[0075] The negative electrode active layer is divided in the width direction into a central region including a central portion, 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.

[0076] The negative electrode for the lithium secondary battery satisfies the following equations 1 and 2:

[0077] [Formula 1]

[0078] 1.6≤[OI edge ] / [OI center ≤2.5

[0079] [Equation 2]

[0080] 2.6≤[OI sliding ] / [OIcenter ≤3.5

[0081] (in Equations 1 and 2,

[0082] OI edge Indicates the alignment (OI) in the edge region.

[0083] OI center Indicates the alignment (OI) in the central region, and

[0084] OI sliding Indicates the alignment (OI) within the sliding region.

[0085] Furthermore, alignment (OI) indicates the area (I0) of the peak representing the [0,0,4] crystal plane in the XRD measurements of the negative electrode active layer. 004 ) and the area of ​​the peak representing the [1,1,0] crystal plane (I 110 The ratio of (I) 004 / I 110 )).

[0086] Figure 1 and Figure 2 This is a cross-sectional view illustrating the structure of negative electrodes 100 and 200 according to the present invention, having a negative electrode active layer arranged on one side of the negative electrode current collector.

[0087] The negative electrodes 100 and 200 for lithium secondary batteries according to the present invention include negative electrode active layers 120 and 220 comprising a carbon-based negative electrode active material on at least one side of negative electrode current collectors 110 and 210. The negative electrode active layers 120 and 220 are layers embodying the electroactive properties of the negative electrode and are prepared by applying a negative electrode slurry comprising a negative electrode active material embodying an electrochemical redox reaction to at least one surface of the negative electrode current collectors 110 and 210 during battery charge and discharge, followed by drying and rolling.

[0088] In this configuration, 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 in the width direction, and the central regions 121 and 221 account for at least 90% of the total length in the width direction. The central regions 121 and 221 comprise the majority of the negative electrode active layers 120 and 220 and may account for more than 93%, more than 95%, more than 97%, or 96% to 99% of the total length in the width direction of the negative electrode active layers 120 and 220. As used herein, the term "width direction of the negative electrode active layers 120 and 220" may refer to a direction perpendicular to the direction in which the current collector is driven during the manufacture of the negative electrode, and in some cases may be the same as the direction in which the negative electrode connector is driven from one side of the manufactured negative electrode to its opposite side. The present invention can further increase the power output and energy density of the lithium secondary battery anode 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.

[0089] Furthermore, edge regions 122 and 222 are located outside of central regions 121 and 221, and sliding regions 123 and 223 are located outside of edge regions 122 and 222.

[0090] At this time, as Figure 1 As shown, the edge regions and sliding regions can be sequentially and continuously arranged on both sides of the central region 121, or, in some cases, due to the fact that the electrode sheet is punched (or slotted) during the negative electrode manufacturing process, they can be arranged as follows: Figure 2 The arrangement is shown in sequence and continuously on only one side of the central region 221.

[0091] Furthermore, sliding regions 123 and 223 can be regions with a thickness gradient located at the edges of negative electrode active layers 120 and 220, and the ratio of their total length in the width direction to the negative electrode active layers 120 and 220 can be less than 3%. Specifically, sliding regions 123 and 223 can have a shape in which the thickness decreases outward in the region adjacent to edge regions 122 and 222, and considering the energy density of the negative electrode, the ratio of their total length in the width direction to the negative electrode active layers 120 and 220 can be less than 2%, less than 1%, less than 0.5%, 0.01% to 1%, or 0.01% to 0.5%. In this case, the above length ratio is based on the total length ratio of the negative electrode active layers 120 and 220 arranged in the width direction, and when sliding regions 123 and 223 are arranged as follows... Figure 1 When arranged on both sides of the central region 121 as shown, the length ratio of each sliding region can be reduced to half of the aforementioned ratio.

[0092] Furthermore, the sliding regions 123 and 223 may have a thickness gradient that decreases in thickness as they advance outward, allowing the exposed surfaces to have a predetermined tilt angle relative to the negative electrode current collectors 110 and 210. For example, the sliding regions 123 and 223 may have a tilt angle of 70° or more relative to the negative electrode current collectors 110 and 210, resulting in exposed surfaces having tilt angles of 75° or more, 80° or more, 85° or more, 70° to 85°, 75° to 80°, and 70° to 75°. This invention prevents the N / P ratio from reversing at the ends of the electrode assembly assembled with the positive electrode by adjusting the tilt angle of the negative electrode current collectors 110 and 210 with the exposed surfaces having the sliding regions 123 and 223 to the aforementioned ranges, and further improves adhesion to the separator at the negative electrode end.

[0093] Furthermore, edge regions 122 and 222 can serve as buffer regions located between central regions 121 and 221 and sliding regions 123 and 223, and can occupy the remaining length besides the ratio of the lengths of the central regions 121 and 221 and the sliding regions 123 and 223. For example, edge regions 122 and 222 can have 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 in the width direction of the negative electrode active layers 120 and 220. Edge regions 122 and 222, like sliding regions 123 and 223, can be arranged on either side of the central region 121, such that the length ratio of each edge region can be reduced to half of the aforementioned length ratio.

[0094] Edge regions 122 and 222 can be located between central regions 121 and 221 with constant high load and / or thickness and sliding regions 123 and 223 with variable low load and / or thickness, thereby having a constant high or low load and / or thickness configuration.

[0095] In one embodiment, the negative electrode active layers 120 and 220 can satisfy the following equation 3:

[0096] [Formula 3]

[0097] R sling <R edge ≤R center

[0098] (In Equation 3,

[0099] R sling Indicates the average thickness of the sliding area.

[0100] R edge Indicates the average thickness of the edge region, and

[0101] R center(Indicates the average thickness of the central region).

[0102] Equation 3 illustrates the correlation between the average thicknesses of each region, meaning that each region of the negative electrode active layers 120 and 220 according to the invention tends to have a decreasing average thickness as the position changes from the center to the periphery of the negative electrode active layers 120 and 220. Here, a confocal microscope can be used to measure the "average thickness," and the method of measurement can be different for each region. Specifically, for the central and edge regions, it can mean measuring the thickness at three or more random points and calculating the average value based on the measurements. In the case of the sliding region, it can mean measuring the thickness at a point where the length of the sliding region is half the length of the negative electrode active layers 120 and 220 in the width direction.

[0103] For example, the central regions 121 and 221 of the negative electrode active layers 120 and 220 may have an average thickness of 140±3 μm, the edge regions 122 and 222 may have an average thickness of 139±3 μm, and the sliding regions 123 and 223 may have an average thickness of 75±3 μm.

[0104] In another embodiment, the negative electrode active layers 120 and 220 can be configured such that the average load per unit area in each region decreases as the position of the negative electrode active layers 120 and 220 changes from the center to the periphery. Here, the average load per unit area in each region is not limited to area, as long as it is the average load in the same region.

[0105] By giving the negative electrode active layers 120 and 220 of the present invention an average load per unit area and / or an average thickness per region as described above, the high-rate charge-discharge characteristics and energy density of the battery comprising them can be further improved.

[0106] Specifically, the carbon-based anode active material (CA) included in the anode active layers 120 and 220 can have crystal planes oriented at predetermined angles relative to the surfaces of the anode current collectors 110 and 210, such that the movement of electrons or lithium ions can be altered according to the degree of orientation and / or orientation direction of the anode active material, and the physicochemical movement of the carbon-based anode active material, such as volume expansion or contraction, can also be altered. In this case, the crystal plane orientation of the carbon-based anode active material can be achieved by applying a magnetic field to the anode slurry containing the carbon-based anode active material during the manufacture of the anode, and the degree of orientation and / or orientation direction can be determined according to the state or conditions of the anode slurry to form the anode active layers 120 and 220. Therefore, the present invention is characterized by the ability to control the orientation of the carbon-based anode active material in each region including the anode active layers 120 and 220, such that as the loading and / or thickness of the anode active layer decreases, the angle of the crystal plane of the carbon-based anode active material included in the anode active layer decreases.

[0107] For example, the negative electrode active layers 120 and 220 according to the invention can be oriented such that the average loading and / or average thickness per unit area decreases in the order of central region, edge region, and sliding region, such that the crystal plane angle of the carbon-based negative electrode active material contained in the negative electrode active layers 120 and 220 relative to the surfaces of the negative electrode current collectors 110 and 210 is reduced. In this case, the orientation of the carbon-based negative electrode active material (e.g., graphite) can be determined by crystal plane analysis of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0108] In one embodiment, the negative electrode active layers 120 and 220 can satisfy the following equations 1 and 2:

[0109] [Formula 1]

[0110] 1.6≤[OI edge ] / [OI center ≤2.5

[0111] [Equation 2]

[0112] 2.6≤[OI sliding ] / [OI center ≤3.5

[0113] (in Equations 1 and 2,

[0114] OI edge Indicates the alignment (OI) in the edge region.

[0115] OI center Indicates the alignment (OI) in the central region, and

[0116] OI slidingIndicates the alignment (OI) within the sliding region.

[0117] Alignment (OI) indicates the area (I0) of the peak representing the [0,0,4] crystal plane in XRD measurements of the negative electrode active layer. 004 ) and the area of ​​the peak representing the [1,1,0] crystal plane (I 110 The ratio of (I) 004 / I 110 )).

[0118] The orientation degree (OI) of carbon-based anode active materials (CA) can be an indicator of the orientation degree of the crystal structure of a spherical carbon-based anode active material relative to the surface of the anode current collector in a specific direction during X-ray diffraction (XRD) measurements. More specifically, the anode active layer has a crystal structure oriented in an orientation manner during X-ray diffraction measurements, wherein the graphite (carbon-based anode active material) has peaks at 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°, respectively, representing 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° can be considered as an overlap of the peaks corresponding to the [1,0,1]R plane of carbon-based anode active materials (CA) and the [1,1,1] plane of current collectors such as copper (Cu).

[0119] The alignment (OI) of the carbon-based anode active material (CA) can be measured by the ratio of the area of ​​the peak at 2θ = 54.7 ± 0.2° representing the [0,0,4] plane to the area of ​​the peak at 2θ = 77.5 ± 0.2° representing the [1,1,0] plane. Specifically, it is measured by the ratio of the areas obtained by integrating the intensity of the aforementioned peaks. Here, since the peak at 2θ = 54.7 ± 0.2° is the peak of the [0,0,4] plane representing the graphite crystal plane with tilt relative to the anode current collector, the orientation (OI) can mean that when the value is close to 0, the tilt relative to the surface of the anode current collector is close to 90°, and when the value is large, the tilt relative to the surface of the anode current collector is close to 0° or 180°. In other words, according to the invention, the negative electrode active layer is aligned such that the carbon-based negative electrode active material (CA) has a large angle relative to the negative electrode current collector, such as an angle of 60° or more, 70° or more, 70° to 90°, 80° to 90°, 65° to 85° or 70° to 85° relative to the negative electrode current collector, so that the alignment degree (OI) of the carbon-based negative electrode active material (CA) can be lower compared to the case where the carbon-based negative electrode active material (CA) is aligned at a small angle.

[0120] With this in mind, Equation 1 indicates the degree of orientation (OI) of the carbon-based anode active material contained in the edge region. edge Compared to the central region, the alignment (OI) of the carbon-based anode active material is higher. center The smaller value of ) means that the carbon-based negative electrode active material in the central region is aligned at a larger angle relative to the surface of the negative electrode current collector compared to the carbon-based negative electrode active material in the edge region. The negative electrode active layers 120 and 220 of the present invention ensure that the carbon-based negative electrode active material in the central region is aligned at a larger angle relative to the surface of the negative electrode current collector compared to the carbon-based negative electrode active material in the edge region, such that Equation 1 can satisfy a ratio of 1.6 to 2.5 (in other words, 1.6 ≤ [OI]). edge ] / [OI center ]≤2.5), and more specifically, 1.7 to 2.0 (i.e., 1.7≤[OI edge ] / [OI center ]≤2.0), 1.8 to 2.2 (i.e., 1.8≤[OI edge ] / [OI center ]≤2.2), 2.1 to 2.4 (in other words, 2.1≤[OI edge ] / [OI center [ ]≤2.4), or 1.7 to 2.3 (in other words, 1.7≤[ OI ≤ 2.4) edge ] / [OI center ]≤2.3).

[0121] Furthermore, Equation 2 indicates the alignment (OI) with the carbon-based anode active material contained in the sliding region. sliding Compared to the central region, the alignment (OI) of the carbon-based anode active material is higher. center The smaller value means that the carbon-based negative electrode active material in the central region is aligned at a larger angle relative to the surface of the negative electrode current collector compared to the carbon-based negative electrode active material in the sliding region. Because the carbon-based negative electrode active material in the central region is aligned at a larger angle relative to the surface of the negative electrode current collector compared to the carbon-based negative electrode active material in the sliding region, the negative electrode active layers 120 and 220 of the present invention can achieve an angle of 2.6 to 3.5 (2.6 ≤ [OI]). sliding ] / [OI center The ratio of 2.6 to 2.9 (2.6 ≤ [OI] ≤ 3.5) satisfies Equation 2 above, and more specifically, 2.6 to 2.9 (2.6 ≤ [OI] ≤ 3.5) sliding ] / [OI center]≤2.9), 3.0 to 3.5(3.0≤[O.Isliding] / [O.Icenter]≤3.5), 2.8 to 3.3(2.8≤[O.Isliding] / [O.Icenter]≤3. 3), 3.1 to 3.3 (3.1≤[O.Isliding] / [O.Icenter]≤3.3), or 2.6 to 2.8 (2.6≤[O.Isliding] / [O.Icenter]≤2.8).

[0122] Each region of the negative electrode active layers 120 and 220 can have an alignment (OI) of the carbon-based negative electrode active material (CA) that satisfies the conditions of Equations 1 and 2 above, such that the average alignment of the carbon-based negative electrode active material (CA) contained in the entire negative electrode active layer (120 and 220) can be kept low.

[0123] Specifically, the alignment (OI) of the carbon-based anode active material (CA) contained in the central regions 121 and 221 of the anode active layers 120 and 220 center The alignment value 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 (OI) of the central regions 121 and 221... center It can have a deviation of less than 5% from the average alignment of the negative electrode active layers 120 and 220.

[0124] As described above, by adjusting the 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, the present invention advantageously results in smaller volume changes of the negative electrode active layers 120 and 220 during charge and discharge on the current collector, easier movement of electrons and / or lithium ions within the negative electrode active layers 120 and 220, and lower electrode resistance, thereby improving the high-rate charge and discharge characteristics of the battery.

[0125] Furthermore, the average thickness of the negative electrode active layers 120 and 220 can be from 100 μm to 300 μm, more specifically, from 100 μm to 250 μm, or from 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 present invention can easily control the orientation trend of the carbon-based negative electrode active material contained in each region according to the thickness variation trend, thereby improving the high-rate charge-discharge characteristics and energy density of the battery including negative electrodes 100 and 200.

[0126] Furthermore, depending on the battery model or product application to which the negative electrode according to the invention is applied, the negative electrode active layers 120 and 220 may have a structure of two separate layers stacked, but are not limited thereto. In this case, the negative electrode according to the invention may have a structure in which a first negative electrode active layer (not shown) is disposed on current collectors 110 and 210, and a second negative electrode active layer (not shown) is disposed on the first negative electrode active layer. In this case, the first and second negative electrode active layers contain carbon-based negative electrode active material (CA), but the carbon-based negative electrode active material (CA) contained in each layer may be the same or different.

[0127] In addition, the negative electrode active layers 120 and 220 include a carbon-based negative electrode active material (CA) as the negative electrode active material to achieve electroactivity through a reversible redox reaction during the charge and discharge of the battery.

[0128] Carbon-based anode active material (CA) refers to a material having carbon atoms as its main component, and such carbon-based anode active material (CA) may include graphite. Graphite may include one or more of natural graphite and artificial graphite, but preferably includes natural graphite, or may include a mixture of natural graphite and artificial graphite.

[0129] Preferably, the carbon-based negative electrode active material (CA) is a spherical graphite composition formed by the aggregation of multiple flake graphite particles. The flake graphite includes natural graphite, artificial graphite, tar- and pitch-based mesophase calcined carbon (massive mesophase), graphitized coke (raw coke, pitch coke, needle coke, petroleum coke, etc.), and preferably uses multiple highly crystalline natural graphite particles for assembly. Furthermore, a graphite assembly can be formed by assembling 2 to 100, preferably 3 to 20, flake graphite particles.

[0130] Furthermore, carbon-based anode active materials (CA) can exhibit an average particle size (D50) of 0.5 μm to 20 μm, and more specifically, can exhibit an average particle size (D50) of 0.5 μm to 15 μm, 0.5 μm to 10 μm, 5 μm to 20 μm, 10 μm to 20 μm, 12 μm to 18 μm, 2 μm to 7 μm, 0.5 μm to 5 μm, or 1 μm to 3 μm.

[0131] The smaller average particle size of natural graphite can help maximize the disorder of each particle in the expansion direction, preventing the particles from expanding 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 severe, and with repeated charge and discharge cycles, the bonding performance between particles and between particles and the current collector may decrease, and the cycle performance may be significantly reduced.

[0132] In addition, the negative electrode active layer according to the present invention may optionally include conductive materials, binders, other additives, etc., as needed, in addition to the carbon-based negative electrode active material (CA) as the main component.

[0133] Conductive materials may include, but are not limited to, one or more of the following: carbon black, acetylene black, ketene black, carbon nanotubes, and carbon fibers.

[0134] As an example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., as conductive materials, either alone or in combination.

[0135] In this case, the content of conductive material can be 0.1 to 10 parts by weight out of 100 parts by weight of the total negative electrode active layer, and more specifically, it can 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 conductive material within the range described above, the present invention can prevent the problem of reduced charging capacity due to increased resistance of the negative electrode caused by low conductive material content, the problem of reduced charging capacity due to reduced content of negative electrode active material caused by excessive conductive material, or the problem of reduced fast charging characteristics due to increased loading of the negative electrode active layer.

[0136] In addition, binders can be suitably used as components that help to connect negative electrode active materials and conductive materials to the current collector (without reducing the electrical performance of the electrode), specifically, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile and polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR) and fluorinated rubber, including one or more selected from the group consisting of them.

[0137] Based on a total of 100 parts by weight of the negative electrode active layer, the binder content can be 0.1 to 10 parts by weight, more 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. This invention enables the binder content in the negative electrode active layer to be controlled within the above ranges, thereby preventing the adhesion of the active layer from deteriorating due to a low binder content, or preventing the electrical performance of the electrode from decreasing due to an excessive binder.

[0138] Furthermore, the negative electrode current collector is not particularly limited, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, calcined carbon, etc., can be used. In the case of copper or stainless steel, copper or stainless steel with surface treatments such as carbon, nickel, titanium, silver, etc., can also be used. In addition, considering the conductivity and total thickness of the manufactured negative electrode, negative electrode current collectors with an average thickness of 1 μm to 500 μm can be appropriately used.

[0139] Lithium secondary batteries

[0140] In one embodiment, the present invention also provides:

[0141] A lithium secondary battery, comprising: an electrode assembly including a positive electrode, a negative electrode as described above, and a separator disposed between the positive electrode and the negative electrode.

[0142] The lithium secondary battery according to the present invention comprises: an electrode assembly having a plurality of positive electrodes, a separator, and a negative electrode arranged sequentially; and an electrolyte composition having a lithium salt and an electrolyte additive dissolved in a non-aqueous organic solvent. The lithium secondary battery includes a negative electrode having a structure in which a negative electrode active layer is stacked on a current collector, the negative electrode active layer being divided into a central region, an edge region, and a sliding region, wherein the alignment (OI) of each carbon-based negative electrode active material contained in the central region, the edge region, and the sliding region satisfies Formulas 1 and 2. Therefore, the lithium secondary battery has the advantage of small negative electrode volume change during charge and discharge, thus exhibiting excellent battery life, high-rate charge-discharge characteristics, and high energy density.

[0143] In this case, the negative electrode has the same configuration as described above, and therefore a detailed description is omitted.

[0144] In addition, the positive electrode includes a layer of positive electrode active material prepared by applying, drying and pressing a slurry comprising positive electrode active material onto a current collector. The positive electrode active material layer may optionally further include conductive materials, binders, other additives, etc., as needed.

[0145] Positive electrode active materials are materials capable of electrochemical reactions on positive electrode current collectors, and may include one or more lithium metal oxides represented by the following chemical formulas 1 and 2 that are capable of reversibly inserting and deintercalating lithium ions:

[0146] [Chemical Formula 1]

[0147] Li x [Ni y Co z Mn w M 1 v O2

[0148] [Chemical Formula 2]

[0149] LiM 2 p Mn q P r O4

[0150] In the above chemical formulas 1 and 2,

[0151] M 1 It is at least one element selected from the group consisting of 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.

[0152] 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, and 0 ≤ v ≤ 0.1, where y + z + w + v = 1.

[0153] M 2 It is Ni, Co, or Fe; and

[0154] p is 0.05 ≤ p ≤ 1.0, and

[0155] q is 1-p or 2-p, and

[0156] r is 0 or 1.

[0157] The lithium metal oxides represented by the above chemical formulas 1 and 2 are materials containing high amounts of nickel (Ni) and manganese (Mn), respectively. When used as positive electrode active materials, they have the advantage of being able to stably supply high capacity and / or high voltage electricity compared with conventionally used positive electrode active materials such as lithium iron phosphate (LiFeO4).

[0158] In this case, the lithium metal oxide represented by Formula 1 may include LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi0.7 Co 0.1 Mn 0.1 Al 0.1 O2, etc., and lithium metal oxides represented by chemical formula 2 may include LiNi. 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4, LiNi 0.3 Mn 1.7 O4, LiFePO4, LiFe q Mn 1-q PO4, etc., and these can be used alone or in combination.

[0159] In addition, the positive electrode active material can account for more than 85 parts by weight of the positive electrode active material layer, and more specifically, it can account for more than 90 parts by weight, more than 93 parts by weight, or more than 95 parts by weight.

[0160] In addition, the positive electrode active material layer may also include conductive materials, binders, other additives, and the positive electrode active material itself.

[0161] In this context, conductive materials can be used to improve the electrical properties of the positive electrode, and conductive materials conventionally used in the art can be applied, but may specifically include at least one type selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super P, channel black, furnace black, lamp black, summer black, graphene, and carbon nanotubes.

[0162] In addition, the conductive material may account for 0.1 to 5 parts by weight of each positive electrode active layer, more specifically, 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.

[0163] Furthermore, the binder is used to bond the positive electrode active material, positive electrode additive, and conductive material together, and can be used without limitation, as long as it has this function. Specifically, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. In one embodiment, the binder may include polyvinylidene fluoride.

[0164] In addition, the binder may comprise 1 to 10 parts by weight, more specifically 2 to 8 parts by weight, or 1 to 5 parts by weight of each positive electrode active layer.

[0165] There is no particular limitation on the total thickness of the positive electrode active layer, but it can be 50μm to 300μm, more specifically 100μm to 200μm, 80μm to 150μm, 120μm to 170μm, 150μm to 300μm, 200μm to 300μm, or 150μm to 190μm.

[0166] Furthermore, a positive electrode current collector with high conductivity that does not cause chemical changes in the battery can be used as the positive electrode. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., can be used. In the case of aluminum or stainless steel, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., can also be used. Additionally, considering the conductivity and overall thickness of the positive electrode to be manufactured, the average thickness of the aforementioned current collector can be appropriately applied from 3 μm to 500 μm.

[0167] Furthermore, the separator inserted between the positive and negative electrodes of each cell is an insulating film with high ion permeability and mechanical strength, and is not particularly limited to those conventionally used in the art; however, polymers including one or more chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymers can be used. The separator can be in the form of a porous polymer substrate such as a sheet or nonwoven fabric comprising the aforementioned polymers, and in some cases, it can also be in the form of a composite separator in which organic or inorganic particles are coated on a porous polymer substrate with an organic binder. Furthermore, the separator can have an average pore size of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0168] Furthermore, the lithium secondary battery according to the present invention can be a secondary battery of any shape, including but not limited to stacked, serrated, or serrated stacked electrode assemblies. As an embodiment, the lithium secondary battery according to the present invention can be a pouch-type secondary battery or a square secondary battery.

[0169] Method for manufacturing the negative electrode

[0170] In one embodiment, the present invention also provides a method for manufacturing a negative electrode for a lithium-ion battery, comprising:

[0171] A negative electrode slurry, including a carbon-based negative electrode active material, is applied to the negative electrode current collector;

[0172] A magnetic field is applied to the applied negative electrode slurry; and

[0173] The negative electrode slurry subjected to a magnetic field is dried to form the negative electrode active layer.

[0174] The negative electrode active layer is divided into a central region including a central portion 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 the negative electrode for the lithium secondary battery satisfies the following equations 1 and 2:

[0175] [Formula 1]

[0176] 1.6≤[OI edge ] / [OI center ≤2.5

[0177] [Equation 2]

[0178] 2.6≤[OI sliding ] / [OI center ≤3.5

[0179] (in Equations 1 and 2,

[0180] OI edge Indicates the alignment (OI) in the edge region.

[0181] OI center Indicates the alignment (OI) in the central region, and

[0182] OI sliding Indicates the alignment (OI) within the sliding region.

[0183] Alignment (OI) indicates the area (I0) of the peak representing the [0,0,4] crystal plane in XRD measurements of the negative electrode active layer. 004 ) and the area of ​​the peak representing the [1,1,0] crystal plane (I 110 The ratio of (I) 004 / I 110 )).

[0184] The method for manufacturing a negative electrode according to the present invention may include applying a negative electrode slurry comprising a carbon-based negative electrode active material onto a current collector, and aligning the carbon-based negative electrode active material in the negative electrode slurry to a predetermined angle relative to the surface of the current collector by applying a magnetic field to the surface of the applied negative electrode slurry. Subsequently, the negative electrode may be manufactured by drying the negative electrode slurry in which the alignment of the carbon-based negative electrode active material is reduced to form a negative electrode active layer.

[0185] Here, the negative electrode slurry is applied by coating the surface of the moving current collector with a negative electrode slurry containing carbon-based negative electrode active material. This can be done in any manner conventionally used in the art, without particular limitation, but die coating is preferred. Die coating can be performed using a slit die with a shim for controlling the discharge conditions of the negative electrode slurry. In this case, the loading amount and thickness of the negative electrode slurry applied to the current collector can be easily controlled by controlling the shape of the shim, etc.

[0186] Furthermore, applying a magnetic field to the negative electrode slurry can be achieved by aligning the crystal planes of the carbon-based negative electrode active material contained in the negative electrode slurry to a predetermined angle relative to the current collector. For this purpose, the magnetic field can be applied by magnetic portions disposed on the upper and lower portions of the negative electrode current collector (which moves by applying the negative electrode slurry to its surface).

[0187] In this case, the alignment (OI) of the carbon-based anode active material contained in the anode slurry can be adjusted by the applied magnetic field strength or the exposure time to the magnetic field, and therefore, the application of the magnetic field can be performed under predetermined magnetic field strength and time conditions.

[0188] Specifically, the applied magnetic field can be a magnetic field of 2000G (Gauss) to 6000G (Gauss), and more specifically, the magnetic field can be applied with an intensity of 2500G to 5500G, 3000G to 5500G, 3500G to 5500G, 4000G to 5500G, 3500G to 4500G, or 4500G to 5000G.

[0189] In addition, the application of a magnetic field can be performed for a period of 5 to 60 seconds, more specifically, 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.

[0190] In one embodiment, applying the magnetic field may include applying a magnetic field of 4700±100G to the negative electrode slurry for 12 to 33 seconds.

[0191] Furthermore, as described above, the application of a magnetic field can be performed by introducing magnetic portions into the upper and lower portions of the applied negative electrode paste. However, the size of the magnetic portions can be adjusted to be larger than the size of the negative electrode paste, so that the magnetic field applied to the negative electrode paste can be uniformly applied to the entire surface of the negative electrode paste. For example, based on the width-to-length ratio of the negative electrode paste, the magnetic portions can have a length ratio of 105% to 200%, and more specifically, based on the width-to-length ratio of the negative electrode paste, they can have a length ratio of 110% to 180%, 110% to 160%, 110% to 140%, 110% to 130%, 130% to 150%, or 105% to 120%.

[0192] The present invention can control the regional orientation of the carbon-based anode active material contained in the anode slurry to satisfy Formulas 1 and 2 by controlling the magnetic field strength, application time and / or magnet portion size as described above in the step of applying the magnetic field.

[0193] In addition, forming the negative electrode active layer may include: drying the negative electrode slurry; and rolling the dried negative electrode slurry.

[0194] In this case, drying of the negative electrode slurry can be applied in any manner that maintains the orientation of the carbon-based negative electrode active material contained within the negative electrode active layer, without particular limitation.

[0195] For example, drying can be performed by applying heat to the negative electrode slurry using a hot air dryer, a vacuum oven, or similar equipment.

[0196] Furthermore, rolling the dried negative electrode slurry increases the density of the negative electrode active layer by applying pressure to the dried negative electrode slurry using a roller press or similar device. In this case, rolling can be performed at temperatures above room temperature.

[0197] Specifically, rolling can be performed at temperatures of 50% to 100%, 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. More specifically, rolling can be performed at rolling speeds of 2 m / s to 7 m / s, and even more specifically, rolling can be performed 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. In addition, rolling can be performed under pressure conditions of 50 MPa to 200 MPa, more 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.

[0198] The present invention enables the rolling of dried negative electrode slurry under the above-mentioned temperature, speed and / or pressure conditions, thereby increasing the energy density of the negative electrode while minimizing the variation in the alignment of the carbon-based negative electrode active material contained in the formed negative electrode active layer.

[0199] Furthermore, the average thickness of the edge region can be equal to or less than the average thickness of the central region before rolling, and therefore, the negative electrode slurry loading in the edge region can be equal to or less than the negative electrode slurry loading in the central region. Specifically, based on the average thickness of the central region of the negative electrode active layer before rolling, the edge region of the negative electrode active layer can have a thickness ratio greater than 90% and less than 105%. More specifically, based on the average thickness of the central region before rolling, the edge region can be 95% to 100%, 98% to 102%, or 97% to 100%.

[0200] Invention Model

[0201] The invention will be described in more detail below through examples and experimental cases.

[0202] However, the following embodiments and experimental examples are merely illustrative of the present invention, and the present invention is not limited to the following embodiments and experimental examples.

[0203] Examples 1 to 3 and Comparative Examples 1 to 3. Preparation of negative electrode for lithium secondary batteries.

[0204] The negative electrode for lithium secondary batteries is prepared by reflecting the conditions shown in Table 1 below.

[0205] First, natural graphite (average particle size: 10±1μm) and artificial graphite (average particle size: 8±1μm) were prepared as carbon-based anode active materials, and the prepared carbon-based anode active materials were used to prepare anode slurry.

[0206] Specifically, the negative electrode active material is prepared by mixing natural graphite and artificial graphite in a weight ratio of 1 to 3:7 to 9, with carbon black as a conductive material and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binders. Then, a negative electrode slurry is prepared by mixing 95 parts by weight of the mixed graphite, 1 part by weight of carbon black, 1.5 parts by weight of carboxymethyl cellulose (CMC), and 2.5 parts by weight of styrene-butadiene rubber (SBR) with water to prepare a 50% solids content.

[0207] Once the negative electrode slurry is prepared, it is cast onto a copper sheet (thickness: 10 μm) using a die-casting machine with roller-to-roll transfer (transfer speed: 5 m / min). The casting process aims to achieve an average thickness of 190 μm along the transfer direction of the copper sheet. The average thickness of each region of the rolled negative electrode active layer is controlled by varying the shape of the shims in the die-casting machine, as shown in Table 1.

[0208] Then, based on the length in the width direction of the applied negative electrode slurry, permanent magnets with a length ratio of 110% to 120% are positioned in the upper portion of the applied negative electrode slurry and the lower portion of the current collector, and a magnetic field of 4700±100G is applied for 15 seconds. The negative electrode slurry with the applied magnetic field is then thermally dried to form a negative electrode active layer. The formed negative electrode active layer is rolled at 50±1℃, a pressure of 100MPa to 150MPa, and a conveying speed of 3m / s to prepare a material with the following properties: Figure 1 The cross-sectional structure shown is used for the negative electrode of a lithium secondary battery.

[0209] For each prepared negative electrode active layer, a region at the center with a length ratio of 98.5% based on the width direction of the negative electrode active layer is designated as the central region, and regions on either side of the central region with a total length ratio of 1.0% (each with a length ratio of 0.5%) are designated as edge regions. Then, regions outside the edge regions with a length ratio of 0.5% (each with a length ratio of 0.25%) are designated as sliding regions.

[0210] Then, the average thickness of each set region was measured, and the results are shown in Table 1 below. In this case, the average thickness of the central and edge regions of the negative electrode active layer was obtained by measuring the confocal thickness of each region three times and calculating its average value; and the sliding region of the negative electrode active layer was defined as the average thickness of the point where the length of the sliding region in the width direction is 1 / 2 of the length of the negative electrode active layer.

[0211] In addition, X-ray diffraction (XRD) spectroscopy was performed on each region of the negative electrode active layer to measure the spectrum. The X-ray diffraction (XRD) measurement conditions are as follows:

[0212] - Target material: Cu (Kα line) graphite monochromator

[0213] - Slits: Diverging slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree

[0214] - Measurement area: [1,1,0] plane: 76.5 degrees < 2θ < 78.5 degrees / [0,0,4] plane: 53.5 degrees < 2θ < 56.0 degrees.

[0215] Based on the spectra measured under the above conditions, calculate the corresponding areas of the peaks representing the [0,0,4] crystal plane and the peaks representing the [1,1,0] crystal plane, and calculate the ratio of these areas (I0). 004 / I 110 The alignment index (OI) of the mixed graphite by region was obtained. The calculated values ​​are shown in Table 1 below.

[0216] [Table 1]

[0217]

[0218]

[0219] Comparative Examples 4 and 5. Preparation of the negative electrode for lithium secondary batteries.

[0220] The negative electrode for lithium secondary batteries is prepared by the same method as in Example 2, except that no magnetic field is applied after the negative electrode slurry is cast, or a magnetic field is applied using a permanent magnet with a length ratio of 95% to 100% based on the width direction of the negative electrode slurry.

[0221] The fabricated negative electrode was measured using the same method as in Example 2, with the average thickness of each region of the negative electrode active layer and the alignment (OI) of the carbon-based negative electrode active material measured. The measurement results are shown in Table 2 below.

[0222] [Table 2]

[0223]

[0224] Examples 4 to 6 and Comparative Examples 6 to 10. Manufacturing of lithium secondary batteries.

[0225] By preparing LiNi with a particle size of 5 μm 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 is used as the positive electrode active material. It is mixed with polyvinylidene fluoride, which is used as a carbon-based conductive agent and binder, in N-methylpyrrolidone (NMP) at a weight ratio of 94:3:3 to form a slurry. The slurry is then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and rolled to prepare the positive electrode.

[0226] A separator comprising 18 μm polypropylene was inserted between the positive and negative electrodes prepared in Examples 1 to 3, Comparative Examples 1 to 3, and Comparative Example 5, respectively, and the lithium secondary battery was assembled by inserting it into a housing and then injecting an electrolyte composition.

[0227] At this point, the type of negative electrode applied to each lithium secondary battery is indicated in Table 3 below.

[0228] [Table 3]

[0229] Type of applying negative electrode Example 4 The negative electrode prepared in Example 1 Example 5 The negative electrode prepared in Example 2 Example 6 The negative electrode prepared in Example 3 Comparative Example 6 The negative electrode prepared in Comparative Example 1 Comparative Example 7 The negative electrode prepared in Comparative Example 2 Comparative Example 8 The negative electrode prepared in Comparative Example 3 Comparative Example 9 The negative electrode prepared in Comparative Example 4 Comparative Example 10 The negative electrode prepared in Comparative Example 5

[0230] Experimental example.

[0231] The following experiments were performed to evaluate the performance of the negative electrode according to the present invention.

[0232] a) Evaluation of the thickness expansion characteristics of the negative electrode

[0233] The lithium secondary batteries prepared in Examples 4 to 6 and Comparative Examples 6 to 10 were subjected to 30 charge-discharge cycles at a rate of 0.5C, and then recharged to disassemble the batteries at a fully charged state (SOC 100%). After collecting the negative electrode from the disassembled batteries, it was washed with diethyl carbonate (DEC) and dried to analyze the thickness expansion rate of the negative electrode after charge and discharge. The results are shown in Table 4.

[0234] b) Evaluation of high-speed charging performance

[0235] The lithium secondary batteries prepared in Examples 4 to 6 and Comparative Examples 6 to 10 were charged to 80% SOC by applying a current at a rate of 3.0C, and the voltage change and dV / dQ were measured according to the SOC. If a voltage plateau was present in the measured voltage change, or if the plotted dV / dQ was bimodal, lithium was identified as deposited from the negative electrode surface. Furthermore, the corresponding SOC value at which lithium was identified as deposited was defined as the maximum SOC value at which the secondary battery could be rapidly charged, and this was measured. The results are shown in Table 4 below.

[0236] c) Evaluation of high-rate discharge performance

[0237] For the lithium secondary batteries prepared in Examples 4 to 6 and Comparative Examples 6 to 10, the capacity was measured when the lithium secondary batteries were buffered to a 0.5C rate (SOC 100%) and the buffered lithium secondary batteries were discharged to 1.5V at a 0.1C rate. Then, each lithium secondary battery was buffered again at a 0.5C rate (SOC 100%) and discharged to 1.5V at a 2.0C rate. The charge-discharge process was repeated 100 times, and the capacity at a 0.1C rate discharge was calculated based on the capacity at a 2.0C rate. The capacity retention rate after 100 discharges was also calculated, and the results are shown in Table 4 below. If the calculated percentage of the initial charge capacity is greater than 85%, it is marked as "○"; if the percentage of the initial charge capacity is less than 80%, it is marked as "X"; and if the percentage of the initial charge capacity is greater than 80% but less than 85%, it is marked as "△".

[0238] [Table 4]

[0239]

[0240] As shown in Table 4 above, it can be seen that the negative electrode for lithium secondary batteries according to the present invention has small negative electrode thickness expansion during charging and discharging and has excellent output performance.

[0241] Specifically, it was found that the lithium secondary battery manufactured in the examples had a low thickness expansion rate of less than 25% for the negative electrode after charge and discharge, and that when charged at a high rate of 3.0C, lithium plating occurred later than in the secondary battery manufactured in the comparative example, and the state of charge (SOC) of lithium deposition was higher than 40%. Furthermore, it was found that the above-mentioned lithium secondary battery had a capacity retention rate of over 85% after 100 discharge cycles at a high rate of 2.0C.

[0242] This means that the negative electrode of the embodiment has a configuration in which the alignment order (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 further reducing the volume change of the negative electrode during the charge and discharge of the secondary battery and further improving the accessibility of lithium ions in the negative electrode active layer, thereby improving high-rate characteristics.

[0243] These results show that the negative electrode for lithium secondary batteries according to the present invention exhibits small volume change, excellent high-rate charge-discharge performance, and high energy density during charge and discharge.

[0244] As described above, the present invention has been described in more detail through embodiments. However, since the configurations described in the embodiments herein are merely one embodiment of the invention and do not represent the overall technical concept of the invention, it should be understood that the invention covers various equivalents, modifications, and substitutions at the time of filing this application.

[0245] Therefore, the technical scope of this invention is not limited to what is described in the detailed description of the specification, but should be determined by the patent claims.

[0246] [Explanation of reference numerals in the attached figures]

[0247] 100 and 200: Negative electrodes for lithium secondary batteries according to the present invention

[0248] 110 and 210: Negative electrode current collector

[0249] 120 and 220: Negative electrode active layer

[0250] 121 and 221: Central region of the negative electrode active layer

[0251] 122 and 222: Edge regions of the negative electrode active layer

[0252] 123 and 223: Sliding regions of the negative electrode active layer

[0253] CA: Carbon-based anode active material

[0254] ↑: Alignment direction of the crystal facets of the carbon-based anode active material

Claims

1. A negative electrode for a lithium secondary battery, the negative electrode for the lithium secondary battery comprising: Negative electrode current collector; and a negative electrode active layer, said negative electrode active layer being disposed on at least one side of the negative electrode current collector and comprising a carbon-based negative electrode active material. The negative electrode active layer is divided in the width direction of the negative electrode active layer into a central region including a central portion, 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. Wherein, the central region accounts for more than 90% of the total length of the negative electrode active layer in the width direction, the sliding region accounts for less than 3% of the total length of the negative electrode active layer in the width direction, and the edge region accounts for the ratio of the total length of the negative electrode active layer in the width direction after deducting the ratios of the central region and the sliding region. The load per unit area of ​​the carbon-based negative electrode active material contained in the negative electrode active layer decreases in the following order: central region, edge region, and sliding region. The central region has an alignment accuracy (OI) of 0.7 to 1.

5. center And satisfy the following equations 1 and 2: [Formula 1] 1.6≤[OI edge ] / [OI center ]≤2.5 [Equation 2] 2.6≤[OI sliding ] / [OI center ]≤3.5 In Equations 1 and 2, OI edge Indicates the alignment (OI) in the edge region. OI center Indicates the alignment (OI) at the central region, and OI sliding Indicates the alignment (OI) in the sliding region. Furthermore, the alignment (OI) indicates the area (I0) of the peak representing the [0,0,4] crystal plane in the XRD measurement of the negative electrode active layer. 004 ) and the area of ​​the peak representing the [1,1,0] crystal plane (I 110 The ratio of (I) 004 / I 110 ), The carbon-based anode active material includes one or more of natural graphite and artificial graphite.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein, The negative electrode active layer satisfies the following equation 3: [Formula 3] R sling <R edge ≤R center In Equation 3, R sling Indicates the average thickness of the sliding region. R edge Indicates the average thickness of the edge region, and R center Indicates the average thickness of the central region.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein, The average thickness of the central region of the negative electrode active layer is 100 μm to 300 μm.

4. A method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, the method comprising the following steps: A negative electrode slurry, including a carbon-based negative electrode active material, is applied to the negative electrode current collector; Apply a magnetic field to the applied negative electrode slurry; and The negative electrode slurry, to which a magnetic field has been applied, is dried to form a negative electrode active layer; The negative electrode active layer is divided into a central region comprising a central portion 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 the negative electrode for the lithium secondary battery satisfies the following equations 1 and 2: [Formula 1] 1.6≤[OI edge ] / [OI center ]≤2.5 [Equation 2] 2.6≤[OI sliding ] / [OI center ]≤3.5 In Equations 1 and 2, OI edge Indicates the alignment (OI) in the edge region. OI center Indicates the alignment (OI) at the central region, and OI sliding Indicates the alignment (OI) in the sliding region. Furthermore, the alignment (OI) indicates the area (I0) of the peak representing the [0,0,4] crystal plane in the XRD measurement of the negative electrode active layer. 004 ) and the area of ​​the peak representing the [1,1,0] crystal plane (I 110 The ratio of (I) 004 / I 110 ).

5. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 4, wherein, The procedure for applying a magnetic field involves applying a magnetic field of 2000G to 6000G.

6. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 4, wherein, The magnetic field is applied for a period of 5 to 60 seconds.

7. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 4, wherein, The step of applying a magnetic field is performed by introducing magnetic portions into the upper and lower portions of the applied negative electrode slurry, wherein the magnetic portions have a length of 105% to 200% based on the length of the negative electrode slurry in the width direction.

8. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 4, wherein, The steps for forming the negative electrode active layer include: drying the negative electrode slurry; and rolling the dried negative electrode slurry.

9. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 8, wherein, Based on the average thickness of the central region of the negative electrode active layer before rolling, the edge region of the negative electrode active layer has a thickness ratio of more than 90% and less than 105%.

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