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 includes a negative electrode active layer divided into a central region, an edge region, and a sliding region on a negative electrode current collector. By satisfying the alignment degree (O.I) of each carbon-based negative electrode active material contained in the central region, the edge region, and the sliding region with Formula 1 and Formula 2, there is an advantage that the volume change during charge and discharge is small, and high-rate charge and discharge performance and high energy density are exhibited.

Description

Technical Field

[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, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference in their entirety.

[0002] The present invention relates to a negative electrode for a lithium secondary battery and a method for manufacturing the same.

Background Art

[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-sized devices such as battery packs or power storage devices for hybrid vehicles and electric vehicles.

[0004] Such a secondary battery is a power generation element capable of charging and discharging, having a laminated structure of a positive electrode / separator / negative electrode. Generally, the positive electrode contains a lithium metal oxide as a positive electrode active material, and the negative electrode contains a carbon-based negative electrode active material such as graphite. During charging, lithium ions released from the positive electrode are occluded inside the carbon-based negative electrode active material of the negative electrode, and during discharging, lithium ions contained inside the carbon-based negative electrode active material are occluded in the lithium metal oxide of the positive electrode, and charging and discharging are repeated.

[0005] On the other hand, as the negative electrode active material used for the negative electrode, amorphous carbon or crystalline carbon is used, and among them, crystalline carbon is mainly used because of its high capacity. Examples of such crystalline carbon include natural graphite and artificial graphite.

[0006] Artificial graphite has higher discharge efficiency than natural graphite during charging, less swelling during charging and discharging, and excellent life characteristics. However, compared with natural graphite, it has a problem of lower reversible capacity, hard particles, difficulty in rolling during electrode manufacturing, less morphological change, and poor orientation. In particular, graphitization heat treatment at 3000 °C is required, resulting in high manufacturing costs.

[0007] On the one hand, in the case of natural graphite, it has a lower price than artificial graphite while having a high reversible capacity and showing similar electrochemical properties, so it is widely used as a negative electrode active material. However, since natural graphite has a plate-like shape, it has a large surface area, and the edge portions are exposed, resulting in electrolyte penetration and decomposition reactions, and the edge portions may be peeled off or destroyed, leading to a large irreversible reaction and an increase in the expansion rate, which may cause a decline in long-term life characteristics.

[0008] In addition to such carbon-based negative electrode materials, lithium metal, which has been considered as a negative electrode active material, has a very high energy density and can achieve high capacity, but has problems such as safety issues due to dendritic growth during repeated charge and discharge and a short cycle life.

[0009] As another negative electrode active material, it is known that silicon, tin, or their alloys can reversibly adsorb and release a large amount of lithium through a compound formation reaction with lithium, and many studies on this have been carried out in recent years. For example, silicon has a theoretical maximum capacity of about 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is very large compared to graphite-based materials, so it is promising as a high-capacity negative electrode material. However, the above negative electrode active materials have the disadvantages of a very large volume change during charge and discharge and low high-rate discharge characteristics.

[0010] Therefore, in fact, it is necessary to improve the performance of the negative electrode active material to exhibit a low expansion rate, a predetermined capacity, high output characteristics, and long life characteristics. In this regard, first, a negative electrode active material in which an amorphous carbon layer is coated on a crystalline carbon-based compound such as graphite can be considered. However, in this case, although the energy density is improved, the proportion of the amorphous carbon-based compound contained in the negative electrode active material is low, which is insufficient to achieve high output characteristics, and if a uniform coating layer is not formed, the electrical conductivity is not good, and the desired level of life characteristics cannot be obtained.

[0011] Therefore, various attempts have been made to improve the high-rate charge / discharge characteristics and low expansion ability and to obtain a negative electrode active material having excellent life characteristics. In fact, there is a high need for a technology that can simultaneously realize the high-rate charge / discharge characteristics and high energy density of the negative electrode active material while fundamentally solving such problems.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] An object of the present invention is to provide a negative electrode for a lithium secondary battery and a method for manufacturing the same, which include a carbon-based negative electrode active material such as natural graphite, have little volume change during charge and discharge, and exhibit high-rate charge / discharge and high energy density.

MEANS FOR SOLVING THE PROBLEMS

[0013] To solve the above problems, In one embodiment, the present invention includes 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 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. A negative electrode for a lithium secondary battery that satisfies the following formulas (1) and (2) is provided:

[0014] [Formula (1)] 1.6 ≦ [O.I edge / [O.I center ≦ 2.5

[0015] [Formula (2)] 2.6 ≦ [O.I sliding / [O.I center ≦ 3.5

[0016] (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 above degree of alignment (O.I) is the ratio (I 004 ) of the area of the peak indicating the (0, 0, 4) crystal plane to the area of the peak indicating the (1, 1, 0) crystal plane in the XRD measurement for the negative electrode active layer (I 110 ) (represented by I 004 / I 110 ).

[0017] 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.

[0018] Also, the central region of the negative electrode active layer may have a ratio of 90% or more of the total length in the width direction of the negative electrode active layer, and the sliding region of the negative electrode active layer may have a ratio of 3% or less of the total length in the width direction of the negative electrode active layer.

[0019] Also, the negative electrode active layer may satisfy the following formula 3:

[0020] [Formula 3] R sliding <R edge ≦R center

[0021] (In formula 3, R sliding represents the average thickness of the sliding region, R edge represents the average thickness of the edge region, R center represents the average thickness of the central region).

[0022] Also, 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 exposure surface with an inclination angle of 70° or more with respect to the negative electrode current collector.

[0023] On the one hand, the carbon-based negative electrode active material may contain one or more of natural graphite and artificial graphite.

[0024] Furthermore, in one embodiment of the present invention, a step of applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector; a step of applying a magnetic field to the applied negative electrode slurry; a step of drying the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer, and includes: 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 provides a method for manufacturing a negative electrode for a lithium secondary battery that satisfies the following Formula 1 and Formula 2:

[0025] [Formula 1] 1.6 ≦ [O.I edge / [O.I center ≦ 2.5

[0026] [Formula 2] 2.6 ≦ [O.I sliding / [O.I center ≦ 3.5

[0027] (In Formula 1 and Formula 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) represents the ratio (I 004 ) of the area (I 110 ) of the peak indicating the (0, 0, 4) crystal plane to the area (I 004 ) of the peak indicating the (1, 1, 0) crystal plane during XRD measurement with respect to the negative electrode active layer (I 110 / I

[0028] Here, in the step of applying the magnetic field, a magnetic field of 2,000 G to 6,000 G can be applied, and the application time can be 5 seconds to 60 seconds.

[0029] Also, the step of applying the magnetic field is performed by magnet parts introduced at the upper and lower parts of the applied negative electrode slurry, and the magnet parts can have a length of 105% to 200% based on the length in the width direction of the negative electrode slurry.

[0030] Also, 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.

[0031] At this time, the edge region of the negative electrode active layer may have a thickness ratio of 90% or more and less than 105% based on the average thickness of the central region of the negative electrode active layer before rolling.

Advantages of the Invention

[0032] 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 alignment degree (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, so that there is an advantage of less volume change during charge and discharge and showing high-rate charge and discharge and high energy density.

Brief Description of the Drawings

[0033]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0034] The present invention can be subjected to various modifications and can have various embodiments, so specific embodiments will be described in detail in the detailed description.

[0035] However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0036] In the present invention, terms such as "comprising" and "having" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and are not intended to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0037] Also, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only the case where it is directly on the other part but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only the case where it is directly under the other part but also the case where there is another part in between. Also, in this application, being "disposed on" can include not only the upper part but also the case of being disposed on the lower part.

[0038] Also, in this specification, "comprising as a main component" can mean containing a component defined with respect to the total weight (or total volume) of 50% by weight or more (or 50% by volume or more), 60% by weight or more (or 60% by volume or more), 70% by weight or more (or 70% by volume or more), 80% by weight or more (or 80% by volume or more), 90% by weight or more (or 90% by volume or more), or 95% by weight or more (or 95% by volume or more). For example, "comprising graphite as a main component as the negative electrode active material" can mean containing graphite in an amount of 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more with respect to the total weight of the negative electrode active material, and in some cases, it can also mean that the entire negative electrode active material consists of graphite and contains 100% by weight of graphite.

[0039] In addition, in this specification, "the carbon-based negative electrode active material is oriented" or "the carbon-based negative electrode active material is aligned" means that the crystal planes of the carbon-based negative electrode active material constituting the negative electrode active material particles are distributed so as to have a predetermined direction with respect to the surface of the negative electrode current collector, which may be different from the case where the particles of the carbon-based negative electrode active material are arranged so as to have a specific direction inside the negative electrode active layer.

[0040] Further, "the carbon-based negative electrode active material has a high degree of orientation" may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned with a high frequency with respect to the surface of the negative electrode current collector, and in some cases, may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high angle with respect to the surface of the negative electrode current collector.

[0041] In addition, "the carbon-based negative electrode active material has a high degree of alignment" means that the "degree of alignment (O.I)" mentioned in this specification has a large value, and may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a low angle with respect to the surface of the negative electrode current collector. Conversely, "the carbon-based negative electrode active material has a low degree of alignment" means that the "degree of alignment (O.I)" has a small value, and may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high angle with respect to the surface of the negative electrode current collector.

[0042] Hereinafter, the present invention will be described in more detail.

[0043] <Negative electrode for lithium secondary battery>

[0044] In one embodiment, the present invention includes 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 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. provides a negative electrode for a lithium secondary battery that satisfies the following formulas (1) and (2):

[0045] [Formula 1] 1.6 ≦ [O.I edge / [O.I center ≦ 2.5

[0046] [Formula 2] 2.6 ≦ [O.I sliding / [O.I center ≦ 3.5

[0047] (In Formula 1 and Formula 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 above 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 of the negative electrode active layer)

[0048] 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 a negative electrode current collector according to the present invention.

[0049] The negative electrodes 100 and 200 for a lithium secondary battery 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 negative electrode current collectors 110 and 210. The above negative electrode active layers 120 and 220 are layers that embody the electrical activity of the negative electrode, and are manufactured by applying a negative electrode slurry containing a negative electrode active material that embodies an electrochemical oxidation-reduction reaction during charge and discharge of the battery to at least one surface of the negative electrode current collectors 110 and 210, and then drying and rolling it.

[0050] At this time, 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 portion in the width direction and include central regions 121 and 221 having a ratio of 90% or more of the total length based on the width direction. The central regions 121 and 221 are regions that constitute most of the negative electrode active layers 120 and 220, and may have a ratio 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 a direction perpendicular to the running direction of the negative electrode current collector during the manufacture of the negative electrode, and in some cases, may be the same as the direction from one surface on which the negative electrode tab is formed to the opposite surface in the manufactured negative electrode. By adjusting the length ratio of the central regions 121 and 221 in the negative electrode active layers 120 and 220 within the above range, the present invention can further increase the output and energy density of the lithium secondary battery of the negative electrode.

[0051] In addition, 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.

[0052] At this time, as shown in FIG. 1, the edge region and the sliding region may be sequentially and continuously arranged on both sides of the central region 121. In some cases, punching (or notching) of the electrode sheet is performed during the manufacturing process of the negative electrode, and as shown in FIG. 2, they may be sequentially and continuously arranged only on one side of the central region 221.

[0053] Further, the sliding regions 123 and 223 are located at the edges of the negative electrode active layers 120 and 220, and are regions having a thickness gradient, and may have a ratio 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 regions adjacent to the edge regions 122 and 222, and in consideration of the energy density of the negative electrode, the ratio may be 2% or less, 1% or less, 0.5% or less, 0.01% - 1%, or 0.01% - 0.5% of the total length in the width direction of the negative electrode active layers 120 and 220. At this time, the above length ratio is the ratio of the total length provided based on the width direction of the negative electrode active layers 120 and 220. As shown in FIG. 1, when the sliding regions 123 and 223 are provided on both sides of the central region 121, the length ratio of each sliding region may be halved to 1 / 2 of the above ratio.

[0054] Further, since the sliding regions 123 and 223 have a thickness gradient in which the thickness becomes thinner as going outward, the exposed surfaces may have a predetermined inclination angle with respect to the negative electrode current collectors 110 and 210. For example, the sliding regions 123 and 223 may have an inclination angle of 70° or more with respect to the negative electrode current collectors 110 and 210, specifically 75° or more, 80° or more, 85° or more, 70° - 85°, 75° - 80°, 70° - 75°. The present invention can prevent the N / P ratio (N / P ratio) from reversing 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 adhesive force with the separator at the negative electrode end.

[0055] Further, the edge regions 122 and 222 can serve as buffer regions located between the central regions 121 and 221 and the sliding regions 123 and 223, and can occupy the remaining length excluding the length ratios of the above-described central regions 121 and 221 and the sliding regions 123 and 223. For example, the edge regions 122 and 222 may have a ratio of less than 7%, less than 5%, less than 4%, less than 2.5%, 0.09% - 3%, or 0.5 - 1% of the total length in the width direction of the negative electrode active layers 120 and 220. When the edge regions 122 and 222 are provided on both sides of the central region 121, similar to the sliding regions 123 and 223, the length ratio of each edge region can be halved to 1 / 2 of the above length ratio.

[0056] The edge regions 122 and 222 are located between the central regions 121 and 221 with a constant and relatively high loading amount and / or thickness, and the sliding regions 123 and 223 with a variably low loading amount and / or thickness, and may have a configuration with a constant and relatively high or low loading amount and / or thickness.

[0057] As an example, the negative electrode active layers 120 and 220 may satisfy the following formula 3:

[0058] [Formula 3] R sliding <R edge ≦R center

[0059] (In formula 3, R sliding represents the average thickness of the sliding region, R edge represents the average thickness of the edge region, R center represents the average thickness of the central region.)

[0060] The above formula (3) shows the correlation between the average thicknesses of the respective regions. Each region of the negative electrode active layers 120 and 220 according to the present invention means that the average thickness has a tendency to decrease as the position changes from the center of the negative electrode active layers 120 and 220 to the outside. Here, the "average thickness" can be measured using a confocal microscope, and the measurement method can be different for each region. Specifically, in the case of the central region and the edge region, it can mean the average value calculated from the measured values of the thicknesses at any three or more points. In the case of the sliding region, it can be the measurement of the thickness at the point where the length of the sliding region becomes 1 / 2 based on the length in the width direction of the negative electrode active layers 120 and 220.

[0061] 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.

[0062] As another example, in the negative electrode active layers 120 and 220, the average loading amount per unit area of each region may decrease as the position changes from the center of the negative electrode active layers 120 and 220 to the outside. Here, the average loading amount per unit area of each region is not limited as long as it is the average loading amount in the same area.

[0063] By making the average loading amount per unit area and / or the average thickness of each region of the negative electrode active layers 120 and 220 of the present invention have the above-described tendency, the high-rate charge and discharge characteristics and the energy density of the battery including the same can be further improved.

[0064] Specifically, the carbon-based negative electrode active material C-A contained in the negative electrode active layers 120 and 220 can have a crystal plane oriented at a predetermined angle with respect to the surfaces of the negative electrode current collectors 110 and 210. However, the movement of electrons and lithium ions can change depending on the degree of orientation and / or the orientation direction of the negative electrode active material, and the physical and chemical movements of the carbon-based negative electrode active material such as volume expansion and contraction can also change. At this time, the crystal plane orientation of the carbon-based negative electrode active material can be realized by applying a magnetic field to the negative electrode slurry containing the carbon-based negative electrode active material during the production of the negative electrode, and the degree of orientation and / or the orientation direction can depend on the state and conditions of the negative electrode slurry forming the negative electrode active layers 120 and 220. Therefore, the present invention can be characterized in that when the loading amount and / or the thickness of the negative electrode active layers 120 and 220 decrease, the orientation of the carbon-based negative electrode active material in each region constituting the negative electrode active layers 120 and 220 is controlled so that the angle of the crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer becomes lower.

[0065] For example, the negative electrode active layers 120 and 220 according to the present invention can be oriented so that the average loading amount and / or the average thickness per unit area decrease in the order of the central region, the edge region, and the sliding region, so that the crystal plane angle of the carbon-based negative electrode active material contained in the negative electrode active layers 120 and 220 with respect to the surfaces of the negative electrode current collectors 110 and 210 becomes lower. At this time, the orientation of the carbon-based negative electrode active material (for example, graphite) can be determined by crystal plane analysis of the carbon-based negative electrode active material C-A contained in the negative electrode active layer.

[0066] As an example, the negative electrode active layers 120 and 220 can satisfy the following formulas 1 and 2:

[0067] [Formula 1] 1.6 ≦ [O.I edge / [O.I center ≦ 2.5

[0068] [Formula 2] 2.6 ≦ [O.I sliding / [O.I center ≦ 3.5

[0069] (In Formula 1 and Formula 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 above 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 for the negative electrode active layer)

[0070] The degree of alignment (O.I) of the carbon-based negative electrode active material C-A can be an index indicating the degree to which the crystal structure of the spherical carbon-based negative electrode active material during X-ray diffraction (XRD) measurement is oriented in a certain direction, specifically, with respect to the surface of the negative electrode current collector. More specifically, the negative electrode active layer shows 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° for graphite, which is the carbon-based negative electrode active material during XRD measurement, and 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. Also, the peak appearing at 2θ = 43.4 ± 0.2° may be considered to be due to the overlap of the peak corresponding to the (1, 0, 1)R plane of the carbon-based negative electrode active material C-A and the (1, 1, 1) plane of the current collector, such as copper (Cu).

[0071] Among these, the alignment degree (O.I) of the carbon-based negative electrode active material C-A can be measured by the area ratio of the peak at 2θ = 54.7 ± 0.2° indicating the (0,0,4) plane and the peak at 2θ = 77.5 ± 0.2° indicating the (1,1,0) plane, specifically, the ratio of the areas obtained by integrating the intensities of the above peaks. Here, since the peak at 2θ = 54.7 ± 0.2° is a peak indicating the (0,0,4) plane having an inclination with respect to the negative electrode current collector among the crystal planes of graphite, the above alignment degree (O.I) means that the closer the value 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°. That is, in the negative electrode active layer according to the present invention, since the carbon-based negative electrode active material C-A 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, the alignment degree (O.I) of the carbon-based negative electrode active material C-A may be lower compared to the case where the carbon-based negative electrode active material C-A is aligned at a low angle.

[0072] When considering this, Equation 1 shows that the alignment degree (O.I center ) of the carbon-based negative electrode active material contained in the central region is smaller than the alignment degree (O.I edge ) of the carbon-based negative electrode active material contained in the edge region, which means that the carbon-based negative electrode active material in the central region is aligned at a higher angle with respect to the surface of the negative electrode current collector than the carbon-based negative electrode active material in the edge region. The negative electrode active layers 120 and 220 of the present invention are such that the carbon-based negative electrode active material in the central region is aligned at a higher angle with respect to the surface of the negative electrode current collector than the carbon-based negative electrode active material in the edge region, and Equation 1 can be satisfied at 1.6 to 2.5 (that is, 1.6 ≦ [O.I edge / [O.I center ≦ 2.5), specifically 1.7 to 2.0 (that is, 1.7 ≦ [O.I edge / [O.I center ≦ 2.0), 1.8 to 2.2 (that is, 1.8 ≦ [O.I edge / [O.I center ≦ 2.2), 2.1 to 2.4 (that is, 2.1 ≦ [O.I edge / [O.I center≤2.4, or 1.7 to 2.3 (i.e., 1.7 ≤ [O.I edge / [O.I center ≤ 2.3) can be satisfied.

[0073] Also, in Formula 2, the degree of alignment (O.I center ) of the carbon-based negative electrode active material contained in the central region is smaller than the degree of alignment (O.I sliding ) of the carbon-based negative electrode active material contained in the sliding region, which means that the carbon-based negative electrode active material in the central region is aligned at a higher angle with respect to the surface of the negative electrode current collector than the carbon-based negative electrode active material in the sliding region. The negative electrode active layers 120 and 220 of the present invention are such that the carbon-based negative electrode active material in the central region is aligned at a higher angle with respect to the surface of the negative electrode current collector than the carbon-based negative electrode active material in the sliding region, and the above Formula 2 can be satisfied at 2.6 to 3.5 (2.6 ≤ [O.I sliding / [O.I center ≤ 3.5), specifically 2.6 to 2.9 (2.6 ≤ [O.I sliding / [O.I center ≤ 2.9), 3.0 to 3.5 (3.0 ≤ [O.I sliding / [O.I center ≤ 3.5), 2.8 to 3.3 (2.8 ≤ [O.I sliding / [O.I center ≤ 3.3), 3.1 to 3.3 (3.1 ≤ [O.I sliding / [O.I center ≤ 3.3), or 2.6 to 2.8 (2.6 ≤ [O.I sliding / [O.I center ≤ 2.8) can be satisfied.

[0074] Each region of the negative electrode active layers 120 and 220 can satisfy a predetermined range of the degree of alignment (O.I) of the carbon-based negative electrode active material C-A so as to satisfy the conditions of the above Formula 1 and Formula 2, whereby the average degree of alignment of the carbon-based negative electrode active material C-A contained in the entire negative electrode active layers 120 and 220 can be maintained low.

[0075] Specifically, among the negative electrode active layers 120 and 220, the central regions 121 and 221 have the degree of alignment (O.I of the carbon-based negative electrode active material C-A contained in this regioncenter ) 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. At this time, the alignment degree (O.I center ) of the central regions 121 and 221 can have a deviation of 5% or less from the average alignment degree of the negative electrode active layers 120 and 220.

[0076] According to the present invention, by adjusting the alignment degree (O.I) of the carbon-based negative electrode active material C-A 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 as described above, the volume change of the negative electrode active layers 120 and 220 during charge and discharge on the negative electrode current collector is small, and the movement of electrons and / or lithium ions into the negative electrode active layers 120 and 220 is easy. As a result, since the electrode resistance is low, there is an advantage that the high-rate charge and discharge characteristics of the battery can be improved.

[0077] 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, 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. According to the present invention, by adjusting the average thickness of the negative electrode active layers 120 and 220 to the above range, the orientation tendency of the carbon-based negative electrode active material C-A contained in each region can be easily controlled according to the thickness change tendency, and thereby, the high-rate charge and discharge characteristics and energy density of the battery including the negative electrodes 100 and 200 can be improved.

[0078] Further, the negative electrode active layers 120 and 220 may have a structure in which two individual layers are stacked according to the battery model and product application to which the negative electrode of the present invention is applied, but are not limited thereto. 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. At this time, the first negative electrode active layer and the second negative electrode active layer contain the carbon-based negative electrode active material C-A, and the carbon-based negative electrode active material C-A contained in each layer may be the same or different.

[0079] Further, the negative electrode active layers 120 and 220 contain the carbon-based negative electrode active material C-A as a negative electrode active material in order to exhibit electrical activity by a reversible oxidation-reduction reaction during charging and discharging of the battery.

[0080] The carbon-based negative electrode active material C-A means a material mainly composed of carbon atoms, and such a carbon-based negative electrode active material C-A may include graphite. The graphite may include any one or more of natural graphite and artificial graphite, and preferably includes natural graphite or a mixture of natural graphite and artificial graphite.

[0081] The carbon-based negative electrode active material C-A is preferably a spherical graphite granulated material formed by aggregating a plurality of flaky graphites. Examples of the flaky graphite include, in addition to natural graphite and artificial graphite, mesophase-fired carbon (bulk mesophase) made from tar pitch, cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.) graphitized, and the like. In particular, those assembled using a plurality of highly crystalline natural graphites are preferred. Further, one graphite granulated material may be formed by aggregating 2 to 100, preferably 3 to 20, flaky graphites.

[0082] Further, the carbon-based negative electrode active material C-A has an average particle size (D) of 0.5 μm to 20 μm 50) can be shown, specifically, an average particle diameter (D 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 50 ) can be shown.

[0083] The average particle diameter of natural graphite can be more advantageous as the particle diameter is made smaller in order to maximize the degree of disorder in the expansion direction for each particle so as to prevent the expansion of particles due to the charging of lithium ions. However, when the particle diameter of natural graphite is less than 0.5 μm, a large amount of binder may be required due to an increase in the number of particles per unit volume. On the other hand, when the maximum particle diameter exceeds 20 μm, the expansion becomes intense, and as charge and discharge are repeated, the inter-particle binding property and the binding property between the particles and the current collector decrease, and the cycle characteristics may be significantly reduced.

[0084] In addition, the negative electrode active layer according to the present invention may further selectively contain a conductive material, a binder, other additives, etc. as necessary together with the carbon-based negative electrode active material C-A which is the main component.

[0085] The above conductive material may contain one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0086] As an example, the above negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as the conductive material.

[0087] At this time, the content of the conductive material can be 0.1 part by weight to 10 parts by weight with respect to 100 parts by weight of the entire negative electrode active layer, specifically, 0.1 part by weight to 8 parts by weight, 0.1 part by weight to 5 parts by weight, 0.1 part by weight to 3 parts by weight, 2 parts by weight to 6 parts by weight, or 0.5 part by weight to 2 parts by weight. By controlling the content of the conductive material within the above range, the present invention can prevent the resistance of the negative electrode from increasing and the charge capacity from decreasing due to a low content of the conductive material, and can prevent problems such as a decrease in the charge capacity due to a decrease in the content of the negative electrode active material caused by an excessive amount of the conductive material, or a decrease in the rapid charging characteristics due to an increase in the loading amount of the negative electrode active layer.

[0088] In addition, the binder is a component that helps the binding between the negative electrode active material and the conductive material and the binding to the current collector, and can be preferably applied within a range that does not lower the electrical physical properties of the electrode. Specifically, vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene - propylene - diene monomer, sulfonated ethylene - propylene - diene monomer, styrene - butadiene rubber (SBR), and fluororubber, and may contain any one or more selected from the group consisting of them.

[0089] The content of the binder can be 0.1 part by weight to 10 parts by weight with respect to 100 parts by weight of the entire negative electrode active layer, specifically, 0.1 part by weight to 8 parts by weight, 0.1 part by weight to 5 parts by weight, 0.1 part by weight to 3 parts by weight, or 2 parts by weight to 6 parts by weight. By controlling the content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent the adhesive force of the active layer from decreasing due to a low content of the binder or the electrical physical properties of the electrode from decreasing due to an excessive amount of the binder.

[0090] Further, 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, fired carbon, etc. can be used. In the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used. Further, the average thickness of the negative electrode current collector can be preferably applied in the range of 1 μm to 500 μm in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0091] <Lithium secondary battery>

[0092] Further, in one embodiment of the present invention, There is provided 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.

[0093] 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 that the volume change of the negative electrode during charge and discharge is small, so that the battery life is excellent, and high-rate charge and discharge characteristics and high energy density are exhibited.

[0094] At this time, since the negative electrode has the same configuration as the above-described configuration, a specific description thereof is omitted.

[0095] Further, the positive electrode includes a positive electrode active layer manufactured by applying, drying, and pressing a slurry containing a positive electrode active material on a positive electrode current collector, and may further selectively include a conductive material, a binder, other additives, etc. as necessary.

[0096] The above-mentioned positive electrode active material is a substance that can electrochemically react on the positive electrode current collector, and may contain one or more of the lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2 that can reversibly intercalate and deintercalate lithium ions:

[0097] [Chemical Formula 1] Li x [Ni y Co z Mn w M 1 v O2

[0098] [Chemical Formula 2] LiM 2 p Mn q P r O4

[0099] In the above Chemical Formula 1 and Chemical Formula 2, M 1 is one or more elements 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, 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.

[0100] The lithium metal oxides represented by the above Chemical Formula 1 and Chemical Formula 2 are substances containing high contents of nickel (Ni) and manganese (Mn), respectively. 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 iron phosphate oxide (LiFeO4) that are conventionally and commonly used.

[0101] 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 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, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2, etc. may be included. The lithium metal oxide represented by the above 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. may be included, and these may be used alone or in combination.

[0102] Further, the above positive electrode active material may be contained in an amount of 85 parts by weight or more based on the weight of the positive electrode active layer, and specifically, may be contained in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0103] Further, the above positive electrode active layer may further contain a conductive material, a binder, other additives, etc. together with the positive electrode active material.

[0104] At this time, the above conductive material is used to improve the electrical performance of the positive electrode, and those commonly used in the industry can be applied. Specifically, it may include one or more 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.

[0105] Also, the above conductive material may be included in an amount of 0.1 part by weight to 5 parts by weight based on the weight of each positive electrode active layer. Specifically, it may be included in an amount of 0.1 part by weight to 4 parts by weight, 2 parts by weight to 4 parts by weight, 1.5 parts by weight to 5 parts by weight, 1 part by weight to 3 parts by weight, 0.1 part by weight to 2 parts by weight, or 0.1 part by weight to 1 part by weight.

[0106] Also, the above binder serves to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any material having such a function can be used without particular limitation. Specifically, the above 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. As an example, the above binder may include polyvinylidene fluoride.

[0107] Also, the above binder may be included in an amount of 1 part by weight to 10 parts by weight based on the weight of each positive electrode active layer. Specifically, it may be included in an amount of 2 parts by weight to 8 parts by weight, or 1 part by weight to 5 parts by weight.

[0108] The total thickness of the above positive electrode active layer is not particularly limited, but specifically, it can be 50 μm to 300 μm, more specifically, it can be 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0109] In addition, for the above positive electrode, as the positive electrode current collector, one having high conductivity without inducing chemical changes in the battery can be used. For example, stainless steel, aluminum, nickel, titanium, fired carbon, etc. can be used, and in the case of aluminum or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used. Further, the average thickness of the above current collector can be suitably applied in the range of 3 μm to 500 μm in consideration of the conductivity and total thickness of the manufactured positive electrode.

[0110] On the other hand, the separator interposed between the positive electrode and the negative electrode 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 art. Specifically, one containing one or more polymers among chemical-resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymer can be used. The above separator can have a porous polymer base material form such as a sheet or non-woven fabric containing the above-described polymer, and in some cases, it may have a form of a composite separator in which organic or inorganic particles are coated on the above porous polymer base material with an organic binder. Further, the average diameter of the pores of the above separator can be 0.01 μm to 10 μm, and the average thickness can be 5 μm to 300 μm.

[0111] On the other hand, the lithium secondary battery according to the present invention is not particularly limited, but can be a secondary battery in a form that can include a stack type, a zigzag type, or a zigzag-stack type electrode assembly. As one example, the lithium secondary battery according to the present invention can be a pouch type secondary battery or a prismatic secondary battery.

[0112] <Method for manufacturing negative electrode>

[0113] Further, in one embodiment of the present invention, applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; drying the negative electrode slurry to which the magnetic field is applied to form a negative electrode active layer, wherein 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 provides a method for manufacturing a negative electrode for a lithium secondary battery that satisfies the following formulas (1) and (2):

[0114] [Formula (1)] 1.6 ≤ [O.I edge / [O.I center ≤ 2.5

[0115] [Formula (2)] 2.6 ≤ [O.I sliding / [O.I center ≤ 3.5

[0116] (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, and the degree of alignment (O.I) represents the ratio (I 004 ) of the area (I 110 ) of the peak indicating the (0, 0, 4) crystal plane to the area (I 004 ) of the peak indicating the (1, 1, 0) crystal plane in the XRD measurement of the negative electrode active layer (I 110 / I

[0117] The method for manufacturing a negative electrode according to the present invention can align the carbon-based negative electrode active material in the negative electrode slurry at a predetermined angle with respect to the surface of the negative electrode current collector by applying a magnetic field to the surface of the applied negative electrode slurry after applying the negative electrode slurry containing the carbon-based negative electrode active material on the negative electrode current collector. Thereafter, the negative electrode can be manufactured by continuously drying the negative electrode slurry with a low degree of alignment of the carbon-based negative electrode active material to form a negative electrode active layer.

[0118] Here, the step of applying the negative electrode slurry is a step of discharging and coating the negative electrode slurry containing the carbon-based negative electrode active material on the surface of the moving negative electrode current collector, and it can be applied without particular limitation as long as it is a method commonly applied in the art. Preferably, the die coating method can be used. The die coating method can be performed through a slot die provided with a shim for controlling the discharge conditions of the negative electrode slurry. In this case, by controlling the shape of the shim, etc., the loading amount, coating thickness, etc. of the negative electrode slurry applied on the negative electrode current collector can be easily controlled.

[0119] Also, the step of applying a magnetic field to the negative electrode slurry can be a step of orienting the crystal plane of the carbon-based negative electrode active material contained in the negative electrode slurry to have a predetermined angle with respect to the negative electrode current collector. For this purpose, the step of applying the magnetic field can apply a magnetic field by magnet portions arranged above and below the negative electrode current collector on which the negative electrode slurry is applied and moved on the surface.

[0120] At this time, the degree of alignment (O.I) of the carbon-based negative electrode active material contained in the negative electrode slurry can be adjusted by the intensity of the applied magnetic field, the time exposed to the magnetic field, etc. Thus, the step of applying the magnetic field can be performed under predetermined magnetic field intensity and time conditions.

[0121] Specifically, in the step of applying the magnetic field, a magnetic field of 2,000 G (gauss) to 6,000 G (gauss) can be applied. Specifically, a magnetic field can be applied at intensities 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.

[0122] Also, the step of applying the magnetic field can be performed for 5 seconds to 60 seconds. Specifically, it can be performed for 10 seconds to 60 seconds, 10 seconds to 30 seconds, 30 seconds to 60 seconds, 40 seconds to 50 seconds, 15 seconds to 35 seconds, or 10 seconds to 50 seconds.

[0123] As an example, in the step of applying the magnetic field, a magnetic field of 4,700 ± 100 G can be applied to the negative electrode slurry for 12 seconds to 33 seconds.

[0124] Furthermore, as described above, the step of applying the magnetic field is performed by the magnet parts introduced at the upper and lower parts of the applied negative electrode slurry, and the size of the magnet parts 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 uniformly applied to the entire surface of the negative electrode slurry. For example, the magnet part can have a length ratio of 105% to 200% based on the length in the width direction of the negative electrode slurry. Specifically, it 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% based on the length in the width direction of the negative electrode slurry.

[0125] The present invention can control the orientation by region of the carbon-based negative electrode active material contained in the negative electrode slurry so as to satisfy Formula 1 and Formula 2 by controlling the intensity, application time, and / or the size of the magnet part in the step of applying the magnetic field as described above.

[0126] Also, 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.

[0127] At this time, the step of drying the negative electrode slurry can be applied without particular limitation as long as it can maintain the orientation of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0128] For example, the step of drying can dry the negative electrode slurry by applying thermal energy to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like.

[0129] Further, the step of rolling the dried negative electrode slurry is a step of increasing the density of the negative electrode active layer by applying pressure to the dried negative electrode slurry using a roll press or the like. At this time, the rolling can be performed under temperature conditions higher than room temperature.

[0130] Specifically, the rolling can be performed at a temperature of 50°C to 100°C, more specifically 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 rolling can be performed at a rolling speed of 2 m / s to 7 m / s, more specifically 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. Further, the rolling can be performed under a pressure condition of 50 MPa to 200 MPa, specifically under a pressure condition 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.

[0131] The present invention can increase the energy density of the negative electrode while minimizing the change in the alignment degree of the carbon-based negative electrode active material contained in the negative electrode active layer formed by performing the rolling of the dried negative electrode slurry under the above temperature, speed, and / or pressure conditions.

[0132] Further, the average thickness of the edge region can be equal to or thinner than the average thickness of the central region before rolling. As a result, the amount of negative electrode slurry loading in the edge region can be equal to or less than the amount of negative electrode slurry loading in the central region. Specifically, the edge region of the negative electrode active layer can have a thickness ratio of 90% or more and less than 105% based on the average thickness of the central region of the negative electrode active layer before rolling. More specifically, the edge region can be 95% - 100%, 98% - 102%, or 97% - 100% based on the average thickness of the central region before rolling.

[0133] Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples.

[0134] 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.

[0135] <Manufacture of Negative Electrodes for Lithium Secondary Batteries in Examples 1 - 3 and Comparative Examples 1 - 3>

[0136] Negative electrodes for lithium secondary batteries were manufactured in accordance with the conditions shown in Table 1 below.

[0137] First, natural graphite (average particle size: 10 ± 1 μm) and artificial graphite (average particle size: 8 ± 1 μm) were prepared as carbon - based negative electrode active materials, and negative electrode slurries were manufactured using the prepared carbon - based negative electrode active materials.

[0138] Specifically, mixed graphite obtained by mixing natural graphite and artificial graphite at a weight ratio of 1 - 3:7 - 9 was prepared as the negative electrode active material, carbon black was prepared as the conductive material, and carboxymethyl cellulose (CMC) and styrene - butadiene rubber (SBR) were prepared as the binder. Then, 95 parts by weight of 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) were mixed with water so that the solid content was 50% to manufacture a negative electrode slurry.

[0139] Once the negative electrode slurry was prepared, it was cast onto a copper thin sheet (thickness: 10 μm) being roll-to-roll transferred (transfer speed: 5 m / min) using a die coater. At this time, the negative electrode slurry was cast so that the average thickness became 190 μm along the transfer direction of the copper thin sheet, and the form of the shim provided in the die coater was changed so that the average thickness of each region of the negative electrode active layer after rolling was adjusted as shown in Table 1.

[0140] Thereafter, permanent magnets having a length ratio of 110% to 120% based on the length in the width direction of the negative electrode slurry were arranged above the applied negative electrode slurry and below the negative electrode current collector, and after applying a magnetic field of 4,700 ± 100 G for 15 seconds, the negative electrode slurry to which the magnetic field was applied was dried with hot air to form a negative electrode active layer. The formed negative electrode active layer was rolled at 50 ± 1 °C under a pressure of 100 MPa to 150 MPa and a transfer speed of 3 m / s to manufacture a negative electrode for a lithium secondary battery having a cross-sectional structure as shown in FIG. 1.

[0141] For the negative electrode active layer of each manufactured negative electrode, a region having a length ratio of 98.5% based on the length in the width direction of the negative electrode active layer was set as the central region in the center, and regions arranged on both sides of the central region at a total length ratio of 1.0% (each 0.5% length ratio) were set as the edge regions. Thereafter, regions arranged at a length ratio of 0.5% outside the edge regions (each 0.25% length ratio) were set as the sliding regions.

[0142] Thereafter, the average thickness of each set region was measured, and the results are shown in Table 1 below. At this time, for the central region and the edge region of the negative electrode active layer, the average thickness was obtained by measuring the confocal thickness for each region three times and calculating the average value, and for the sliding region of the negative electrode active layer, the thickness at the point where the length of the sliding region became 1 / 2 based on the length in the width direction of the negative electrode active layer was defined as the average thickness.

[0143] Also, X-ray diffraction spectroscopy (XRD) was performed on each region of the negative electrode active layer to measure the spectrum. At this time, the measurement conditions for X-ray diffraction (XRD) are as follows:

[0144] - Target: Cu(Kα ray) graphite monochromator - Slit: Divergence 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

[0145] From the spectrum measured under the above conditions, the areas of the peaks indicating the (0,0,4) crystal plane and the (1,1,0) crystal plane were determined, and the ratio (I 004 / I 110 ) was calculated to calculate the alignment degree (O.I) of the region-specific mixed graphite. The calculated values are shown in Table 1 below.

[0146]

Table 1

[0147] <Comparative Example 4 and Comparative Example 5. Production of negative electrode for lithium secondary battery>

[0148] A negative electrode for a lithium secondary battery was manufactured in the same manner as in Example 2, except that a magnetic field was not applied after casting the negative electrode slurry, or a permanent magnet having a length ratio of 95% to 100% based on the length in the width direction of the negative electrode slurry was used to apply a magnetic field.

[0149] The manufactured negative electrode was measured for the average thickness and the alignment degree (O.I) of the carbon-based negative electrode active material for each region of the negative electrode active layer in the same manner as in Example 2, and the measured results were as shown in Table 2 below.

[0150]

Table 2

[0151] <Examples 4 to 6 and Comparative Examples 6 to 10. Production of lithium secondary battery>

[0152] As the positive electrode active material, LiNi with a particle size of 5 μm 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 was prepared, mixed with a carbon-based conductive material and polyvinylidene fluoride as a binder in a weight ratio of 94:3:3 in N-methylpyrrolidone (NMP) to form a slurry, cast on an aluminum thin plate, dried in a vacuum oven at 120 °C, and then rolled to produce a positive electrode.

[0153] After inserting a separator made of 18-μm polypropylene between the obtained positive electrode and the negative electrodes respectively manufactured in Examples 1 to 3 and Comparative Examples 1 to 5 and inserting them into a case, an electrolyte composition was injected to assemble a lithium secondary battery.

[0154] At this time, the types of negative electrodes applied to each lithium secondary battery are shown in Table 3 below.

[0155]

Table 3

[0156] <Experimental Example>

[0157] In order to evaluate the performance of the negative electrode according to the present invention, the following experiments were conducted.

[0158] i) Evaluation of the thickness expansion characteristics of the negative electrode

[0159] After charging and discharging the lithium secondary batteries manufactured in Examples 4 to 6 and Comparative Examples 6 to 10 30 times at a 0.5C rate (C-rate), the battery in a fully charged state (SOC100%) after recharging was disassembled. After recovering the negative electrode from the disassembled battery, it was washed with DEC (diethyl carbonate) and then dried to analyze the thickness expansion rate of the negative electrode after charge and discharge. The results are shown in Table 4.

[0160] ii) Evaluation of high-rate charging performance

[0161] For the lithium secondary batteries manufactured in Examples 4 to 6 and Comparative Examples 6 to 10, a current at a rate of 3.0 C (C-rate) was applied, and while charging up to the point of SOC 80%, the voltage change according to SOC and dV / dQ were measured. When there was a voltage plateau in the measured voltage change or the aspect of the graph showing dV / dQ was bimodal, it was determined that lithium was deposited from the negative electrode surface. Also, the SOC value determined to have lithium deposited was defined as the maximum SOC value at which rapid charging of the secondary battery was possible, and it was measured. The results are shown in Table 4 below.

[0162] (c) Evaluation of high-rate discharge performance

[0163] For the lithium secondary batteries manufactured in Examples 4 to 6 and Comparative Examples 6 to 10, they were fully charged (SOC 100%) at a rate of 0.5 C (C-rate), and the capacity when the fully charged lithium secondary batteries were discharged to 1.5 V at a rate of 0.1 C (C-rate) was measured. Then, each lithium secondary battery was fully charged again at a rate of 0.5 C (C-rate), and the charge-discharge process of discharging to 1.5 V at a rate of 2.0 C (C-rate) was repeated 100 times. After that, based on the capacity during discharge at a rate of 0.1 C (C-rate), the capacity retention rate after 100 discharges at a rate of 2.0 C (C-rate) was calculated, and the results are shown in Table 4 below. At this time, when the ratio to the calculated initial charge capacity was 85% or more, it was indicated as "〇", when the ratio to the initial charge capacity was 80% or less, it was indicated as "×", and when the ratio to the initial charge capacity was more than 80% and less than 85%, it was indicated as "△".

[0164] [Table 4]

[0165] As shown in Table 4 above, it can be seen that the negative electrode for a lithium secondary battery according to the present invention has little thickness expansion of the negative electrode during charge and discharge and is excellent in output performance.

[0166] Specifically, the lithium secondary battery manufactured in the example has a low thickness expansion rate of 25% or less after charge and discharge of the negative electrode, and lithium plating occurs later than that of the secondary battery manufactured in the comparative example during high-rate charging at a rate of 3.0 C (C-rate), and it was confirmed that the state of charge (SOC) at which lithium precipitates has a high value of 40% or more. Further, it was shown that the above lithium secondary battery has a capacity retention rate of 85% or more during 100 discharges at a high rate of 2.0 C (C-rate).

[0167] This is because the negative electrode of the example has a structure in which the alignment degree (O.I) 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 Formula 1 and Formula 2, so that the volume change of the negative electrode during charge and discharge of the secondary battery can be further reduced, the accessibility of lithium ions in the negative electrode active layer is further improved, and the high-rate characteristics are improved.

[0168] From these results, it can be seen that the negative electrode for a lithium secondary battery according to the present invention has little volume change during charge and discharge, excellent high-rate charge and discharge performance, and exhibits a high energy density.

[0169] The above has been described with reference to the preferred embodiments of the present invention. However, those skilled in the art or those having ordinary knowledge in the technical field can understand that the present invention can be variously modified and changed without departing from the spirit and technical scope of the present invention described in the claims to be described later.

[0170] Therefore, the technical scope of the present invention is not limited to the content described in the summary of the invention in the specification, but is defined by the claims.

Description of Reference Numerals

[0171] 100 and 200: Negative electrodes for lithium secondary batteries according to the present invention 110 and 210: Negative electrode current collectors 120 and 220: Negative electrode active layers 121 and 221: Central region of the negative electrode active layer 122 and 222: Edge region of the negative electrode active layer 123 and 223: Sliding region of the negative electrode active layer C-A: Carbon-based negative electrode active material ↑: Crystal plane alignment direction of the carbon-based negative electrode active material

Claims

1. A negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a carbon-based negative electrode active material, wherein: 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; the central region has a ratio of 90% or more of the total length in the width direction of the negative electrode active layer, the sliding region has a ratio of 3% or less of the total length in the width direction of the negative electrode active layer, and the edge region has a remaining ratio excluding the length ratios of the central region and the sliding region in the total length in the width direction of the negative electrode active layer; the loading amount per unit area of the carbon-based negative electrode active material contained in the negative electrode active layer decreases in the order of the central region, the edge region, and the sliding region; the central region has an alignment degree (O.I center) of 0.7 to 1.5; a negative electrode for a lithium secondary battery satisfying the following formulas (1) and (2): [Formula (1)] 1.6 ≤ [O.I ｅｄｇｅ / [O.I ｃｅｎｔｅｒ ≤ 2.5 [Formula (2)] 2.6 ≤ [O.I ｓｌｉｄｉｎｇ / [O.I ｃｅｎｔｅｒ ≤ 3.5 In Formulas (1) and (2), O.I ｅｄｇｅ represents the degree of alignment (O.I) in the edge region, O.I ｃｅｎｔｅｒ represents the alignment degree (O.I) in the central region, O.I ｓｌｉｄｉｎｇ represents the alignment degree (O.I) in the sliding region, The degree of alignment (O.I) is the ratio of the area (I ００４ ), which is the peak area of the (0, 0, 4) crystal plane during XRD measurement for the negative electrode active layer, to the area (I １１０ ), which is the peak area of the (1, 1, 0) crystal plane (I ００４ / I １１０ ).

2. The negative electrode for a lithium secondary battery according to Claim 1, wherein the negative electrode active layer satisfies the following formula (3): [Formula (3)] R ｓｌｉｄｉｎｇ <R ｅｄｇｅ ≦R ｃｅｎｔｅｒ In Formula (3), R ｓｌｉｄｉｎｇ represents the average thickness of the sliding region, R ｅｄｇｅ represents the average thickness of the edge region, R ｃｅｎｔｅｒ represents the average thickness of the central region.

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

4. The negative electrode for a lithium secondary battery according to Claim 1, wherein the carbon-based negative electrode active material contains one or more of natural graphite and artificial graphite.

5. A method for manufacturing a negative electrode for a lithium secondary battery, comprising the steps of: applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; drying the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer, wherein 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 satisfies the following formulas (1) and (2): [Formula (1)] 1.6 ≤ [O.I ｅｄｇｅ / [O.I ｃｅｎｔｅｒ ≤ 2.5 [Formula (2)] 2.6 ≤ [O.I ｓｌｉｄｉｎｇ / [O.I ｃｅｎｔｅｒ ≤ 3.5 In Formulas (1) and (2), O.I ｅｄｇｅ represents the alignment degree (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 alignment degree (O.I) in the sliding region, The degree of alignment (O.I) is the area (I ００４ of the peak indicating the (0, 0, 4) crystal plane during XRD measurement with respect to the negative electrode active layer) and the area (I １１０ of the peak indicating the (1, 1, 0) crystal plane), and represents the ratio (I ００４ / I １１０ ).

6. The method for manufacturing a negative electrode for a lithium secondary battery according to Claim 5, wherein in the step of applying the magnetic field, a magnetic field of 2,000 G to 6,000 G is applied.

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

8. The step of applying the magnetic field is performed by magnet parts introduced to the upper and lower portions of the applied negative electrode slurry, and the magnet parts have a length of 105% to 200% based on the length in the width direction of the negative electrode slurry. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 5.

9. The step of forming the negative electrode active layer includes a step of drying the negative electrode slurry and a step of rolling the dried negative electrode slurry. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 5.

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

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