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

Abstract

To provide a negative electrode for a lithium secondary battery that contains a carbon-based negative electrode active material such as natural graphite, has little volume change during charge and discharge, and exhibits high charge and discharge rates and high energy density, and a method for manufacturing the same.SOLUTION: 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 on a negative electrode current collector, and the negative electrode active layer is divided into a center region, an edge region, and a sliding region. The degree of alignment (O.I) of each carbon-based negative electrode active material contained in the center region, the edge region, and the sliding region satisfies Equation 1 and Equation 2. This results in little volume change during charge and discharge, and the negative electrode exhibits high-rate charge and discharge performance and high energy density.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0182981, filed December 23, 2022, and Korean Patent Application No. 10-2023-0017346, filed February 9, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

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

[0003] BACKGROUND ART In recent years, secondary batteries have been widely used not only in small devices such as portable electronic devices but also in medium to large devices such as battery packs for hybrid cars and electric cars or power storage devices.

[0004] Such secondary batteries are chargeable and dischargeable power generating elements having a laminated structure of a positive electrode / separator / negative electrode. In general, 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 absorbed into the carbon-based negative electrode active material of the negative electrode, and during discharging, the lithium ions contained in the carbon-based negative electrode active material are absorbed into the lithium metal oxide of the positive electrode, thereby allowing for repeated charging and discharging.

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

[0006] Artificial graphite has a higher discharge efficiency than natural graphite, and has less swelling during charging and discharging, giving it excellent lifespan. However, compared to natural graphite, it has a lower reversible capacity and its particles are hard, making it difficult to roll during electrode manufacturing, resulting in little morphological change and poor orientation. In particular, it requires a graphitization heat treatment at 3,000°C, which makes it expensive to manufacture.

[0007] On the other hand, natural graphite is widely used as an anode active material because it is less expensive than artificial graphite, has a high reversible capacity, and exhibits similar electrochemical properties. However, natural graphite has a plate-like shape, which has a large surface area and exposed edges. When electrolytes penetrate or decompose, the edges can peel off or break, causing significant irreversible reactions, increasing the expansion rate and reducing long-term life.

[0008] In addition to these carbon-based anode materials, lithium metal has been considered as an anode active material, and while it has a very high energy density and can realize high capacity, it has safety issues due to dendrite growth during repeated charge and discharge, and a short cycle life.

[0009] Other negative electrode active materials, such as silicon, tin, and their alloys, are known to be capable of reversibly absorbing and releasing large amounts of lithium through compound formation reactions with lithium, and much research has been conducted in this area in recent years. For example, silicon has a theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is significantly higher than graphite-based materials, making it a promising high-capacity negative electrode material. However, these negative electrode active materials suffer from significant volumetric changes during charge and discharge, resulting in poor high-rate discharge performance.

[0010] Therefore, there is a need for improved anode active material performance to achieve a low expansion coefficient, a predetermined capacity, and high output and life characteristics. In this regard, anode active materials in which a crystalline carbon-based compound such as graphite is coated with an amorphous carbon layer may be considered. However, while this approach improves energy density, the proportion of amorphous carbon-based compound in the anode active material is low, which is insufficient to achieve high output characteristics. Furthermore, if a uniform coating layer is not formed, electrical conductivity is poor, preventing the desired level of life characteristics from being achieved.

[0011] Therefore, various attempts have been made to develop a negative electrode active material that has improved high-rate charge / discharge characteristics, low expansion capability, and excellent life characteristics. There is a strong need for a technology that can fundamentally solve these problems and simultaneously realize high-rate charge / discharge characteristics and high energy density of a negative electrode active material. Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a negative electrode for a lithium secondary battery that contains a carbon-based negative electrode active material such as natural graphite, has little volume change during charge and discharge, and exhibits high charge and discharge rates and high energy density, and a method for producing the same. [Means for solving the problem]

[0013] To solve the above problem, In one embodiment, the present invention comprises: 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 The negative electrode active layer is divided into a central region including a center portion in a width direction thereof, a sliding region located at an edge of the negative electrode active layer and having a thickness gradient, and an edge region located between the central region and the sliding region, Provided is a negative electrode for a lithium secondary battery that satisfies the following formulas 1 and 2:

[0014] [Formula 1] 1.6≦[OI edge ] / [OI center ]≦2.5

[0015] [Formula 2] 2.6≦[OI sliding ] / [OI center ]≦3.5

[0016] (In Equation 1 and Equation 2, OI edge represents the alignment degree (OI) in the edge region, OI center represents the degree of alignment (OI) in the central region, OI sliding represents the degree of alignment (OI) in the sliding region, The degree of alignment (OI) is the area (I 004 ) and the area of ​​the peak representing the (1,1,0) crystal plane (I 110 ) ratio (I 004 / I 110 )

[0017] At this time, the central region of the negative electrode active layer has an alignment degree (OI center ) can be 0.7 to 1.5.

[0018] In addition, the central region of the negative electrode active layer may occupy 90% or more of the entire length of the negative electrode active layer in the width direction, and the sliding region of the negative electrode active layer may occupy 3% or less of the entire length of the negative electrode active layer in the width direction.

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

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

[0021] (In Equation 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] 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 exposed surface with an inclination angle of 70° or more with respect to the negative electrode current collector.

[0023] Meanwhile, the carbon-based negative electrode active material may include at least one of natural graphite and artificial graphite.

[0024] Furthermore, in one embodiment, the present invention provides 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; and drying the negative electrode slurry to which the magnetic field is applied to form a negative electrode active layer; The negative electrode active layer is divided into a central region including a center portion in a width direction of the negative electrode active layer, a sliding region located at an 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 active layer satisfies the following formulas 1 and 2:

[0025] [Formula 1] 1.6≦[OI edge ] / [OI center ]≦2.5

[0026] [Formula 2] 2.6≦[OI sliding ] / [OI center ]≦3.5

[0027] (In Equation 1 and Equation 2, OI edge represents the alignment degree (OI) in the edge region, OI center represents the degree of alignment (OI) in the central region, OI sliding represents the degree of alignment (OI) in the sliding region, The degree of alignment (OI) is the area (I 004 ) and the area of ​​the peak representing the (1,1,0) crystal plane (I 110 ) ratio (I 004 / I 110 )

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

[0029] In addition, the step of applying the magnetic field is performed by magnet portions introduced above and below the applied negative electrode slurry, and the magnet portions may have a length that is 105% to 200% of the width direction length of the negative electrode slurry.

[0030] The step of forming the negative electrode active layer may include the steps of drying the negative electrode slurry and rolling the dried negative electrode slurry.

[0031] In this case, the edge region of the negative electrode active layer may have a thickness ratio of 90% to less than 105% of the average thickness of the central region of the negative electrode active layer before rolling. [Effects of the Invention]

[0032] The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode active layer on a negative electrode current collector, the negative electrode active layer being divided into a center region, an edge region, and a sliding region, and the degrees of alignment (OI) of the carbon-based negative electrode active materials contained in the center region, the edge region, and the sliding region satisfy Equation 1 and Equation 2, thereby exhibiting small volume change during charge and discharge, high rate charge and discharge, and high energy density. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 2 is a conceptual diagram showing a cross-sectional structure of a negative electrode according to the present invention. [Figure 2] FIG. 2 is a conceptual diagram showing a cross-sectional structure of a negative electrode according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] Because the present invention is susceptible to various modifications and can have various embodiments, specific embodiments are described in detail in the detailed description.

[0035] However, this is not intended to limit the invention to any particular embodiment, but rather to be understood as including all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0036] In the present invention, terms such as "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and may be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0037] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0038] Furthermore, in this specification, "comprising as a main component" may mean containing 50 wt% or more (or 50 vol% or more), 60 wt% or more (or 60 vol% or more), 70 wt% or more (or 70 vol% or more), 80 wt% or more (or 80 vol% or more), 90 wt% or more (or 90 vol% or more), or 95 wt% or more (or 95 vol% or more) of the defined component relative to the total weight (or total volume). For example, "comprising graphite as a main component as a negative electrode active material" may mean containing 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more of graphite relative to the total weight of the negative electrode active material. In some cases, it may mean that the entire negative electrode active material is composed of graphite, with graphite accounting for 100 wt%.

[0039] Furthermore, in this specification, the terms "the carbon-based negative electrode active material is oriented" or "the carbon-based negative electrode active material is aligned" mean that the crystal planes of the carbon-based negative electrode active material constituting the negative electrode active material particles are distributed to have a predetermined direction based on the surface of the negative electrode current collector, which may differ from the case where the carbon-based negative electrode active material particles themselves are aligned to have a specific direction within the negative electrode active layer.

[0040] Furthermore, "high orientation of the carbon-based negative electrode active material" may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned with a high frequency based on 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 based on the surface of the negative electrode current collector.

[0041] Furthermore, "high degree of alignment of the carbon-based negative electrode active material" refers to a carbon-based negative electrode active material having a high "degree of alignment (OI)" 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 relative to the surface of the negative electrode current collector. Conversely, "low degree of alignment of the carbon-based negative electrode active material" refers to a carbon-based negative electrode active material having a low "degree of alignment (OI)" 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 relative to the surface of the negative electrode current collector.

[0042] The present invention will now be described in more detail.

[0043] <Anode for lithium secondary batteries>

[0044] In one embodiment, the present invention comprises: 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 The negative electrode active layer is divided into a central region including a center portion in a width direction thereof, a sliding region located at an edge of the negative electrode active layer and having a thickness gradient, and an edge region located between the central region and the sliding region, Provided is a negative electrode for a lithium secondary battery that satisfies the following formulas 1 and 2:

[0045] [Formula 1] 1.6≦[OI edge ] / [OI center ]≦2.5

[0046] [Formula 2] 2.6≦[OI sliding ] / [OI center ]≦3.5

[0047] (In Equation 1 and Equation 2, OI edge represents the alignment degree (OI) in the edge region, OI center represents the degree of alignment (OI) in the central region, OI sliding represents the degree of alignment (OI) in the sliding region, The degree of alignment (OI) is the area (I 004 ) and the area of ​​the peak representing the (1,1,0) crystal plane (I 110 ) ratio (I 004 / I 110 )

[0048] 1 and 2 are cross-sectional views showing the structures of negative electrodes 100 and 200 according to the present invention, each having a negative electrode active layer provided on one surface of a negative electrode current collector.

[0049] The negative electrodes 100 and 200 for lithium secondary batteries according to the present invention include negative electrode active layers 120 and 220 containing a carbon-based negative electrode active material on at least one surface of negative electrode current collectors 110 and 210. The negative electrode active layers 120 and 220 are layers that realize the electrical activity of the negative electrode and are prepared by coating at least one surface of the negative electrode current collectors 110 and 210 with a negative electrode slurry containing a negative electrode active material that realizes an electrochemical oxidation-reduction reaction during charge and discharge of the battery, followed by drying and rolling.

[0050] The negative electrode active layers 120 and 220 are divided into a center 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 center region 121 and 221 that includes a center portion in the width direction and accounts for 90% or more of the overall length in the width direction. The center region 121 and 221 constitutes the majority of the negative electrode active layers 120 and 220 and may account for 93% or more, 95% or more, 97% or more, or 96% to 99% of the overall 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 refer to a direction perpendicular to the running direction of the negative electrode current collector during negative electrode fabrication, and in some cases, may be the same as the direction from one side on which the negative electrode tab is formed to the opposite side of the manufactured negative electrode. In the present invention, by adjusting the length ratios of the central regions 121 and 221 of the negative electrode active layers 120 and 220 within the above range, the output and energy density of the negative electrode lithium secondary battery can be further increased.

[0051] Furthermore, edge regions 122 and 222 are located outside the central regions 121 and 221, and sliding regions 123 and 223 are located outside the edge regions 122 and 222.

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

[0053] The sliding regions 123 and 223 are located at the edges of the negative electrode active layers 120 and 220 and have a thickness gradient, and may occupy 3% or less of the overall width of the negative electrode active layers 120 and 220. Specifically, the sliding regions 123 and 223 may have a shape in which the thickness decreases outward in regions adjacent to the edge regions 122 and 222. Taking into account the energy density of the negative electrode, the sliding regions 123 and 223 may occupy 2% or less, 1% or less, 0.5% or less, 0.01% to 1%, or 0.01% to 0.5% of the overall width of the negative electrode active layers 120 and 220. Here, the length ratio is the ratio of the overall width of the negative electrode active layers 120 and 220. When the sliding regions 123 and 223 are provided on both sides of the central region 121 as shown in FIG. 1, the length ratio of each sliding region may be halved.

[0054] Furthermore, the sliding regions 123 and 223 have a thickness gradient in which the thickness decreases toward the outside, so that the exposed surfaces of the sliding regions 123 and 223 may have a predetermined inclination angle relative to the negative electrode current collectors 110 and 210. For example, the exposed surfaces of the sliding regions 123 and 223 may have an inclination angle of 70° or more relative to the negative electrode current collectors 110 and 210, specifically, an inclination angle of 75° or more, 80° or more, 85° or more, 70° to 85°, 75° to 80°, or 70° to 75°. By adjusting the inclination angle of the exposed surfaces of the sliding regions 123 and 223 relative to the negative electrode current collectors 110 and 210 within the above range, the present invention can prevent the N / P ratio from being reversed at the end of the electrode assembly assembled with the positive electrode and further improve the adhesion strength with the separator at the end of the negative electrode.

[0055] The edge regions 122 and 222 may also serve as buffer regions located between the central regions 121 and 221 and the sliding regions 123 and 223, and may occupy the remaining length excluding the length ratios of the central regions 121 and 221 and the sliding regions 123 and 223. For example, the edge regions 122 and 222 may occupy less than 7%, less than 5%, less than 4%, less than 2.5%, 0.09% to 3%, or 0.5% to 1% of the overall 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 may be reduced to half of the length ratio.

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

[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 Equation 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] Equation 3 above shows the correlation between the average thickness of each region, and indicates that the average thickness of each region of the negative electrode active layers 120 and 220 according to the present invention tends to decrease as the position changes from the center to the periphery of the negative electrode active layers 120 and 220. Here, the "average thickness" may be measured using a confocal microscope, and the measurement method may vary depending on the region. Specifically, in the case of the center region and edge region, it may refer to the average value calculated from the thickness measurements at three or more arbitrary points. In the case of the sliding region, it may be the thickness measured at a point where the length of the sliding region is half the width 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, the average loading amount per unit area of ​​each region of the negative electrode active layers 120 and 220 may decrease as the position changes from the center to the periphery of the negative electrode active layers 120 and 220. Here, the average loading amount per unit area of ​​each region is not limited as long as it is the average loading amount for the same area.

[0063] The negative electrode active layers 120 and 220 of the present invention can further improve the high-rate charge / discharge characteristics and energy density of a battery including them by ensuring that the average loading amount and / or average thickness per unit area of ​​each region has the above-mentioned tendency.

[0064] Specifically, the carbon-based negative electrode active material CA contained in the negative electrode active layers 120 and 220 may have a crystal plane oriented at a predetermined angle relative to the surfaces of the negative electrode current collectors 110 and 210. The degree and / or direction of orientation of the negative electrode active material may affect the movement of electrons and lithium ions, and may also affect the physical and chemical behavior of the carbon-based negative electrode active material, such as volume expansion and contraction. The crystal plane orientation of the carbon-based negative electrode active material may be achieved by applying a magnetic field to a negative electrode slurry containing the carbon-based negative electrode active material during negative electrode fabrication, and the degree and / or direction of orientation may depend on the state and conditions of the negative electrode slurry that forms the negative electrode active layers 120 and 220. Therefore, the present invention may be characterized by controlling the orientation of the carbon-based negative electrode active material in each region constituting the negative electrode active layers 120 and 220 such that the angle of the crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layers decreases as the loading amount and / or thickness of the negative electrode active layers 120 and 220 decreases.

[0065] For example, the negative electrode active layers 120 and 220 according to the present invention may be oriented such that the average loading amount and / or average thickness per unit area decreases in the order of the center region, the edge region, and the sliding region, thereby lowering 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. In this case, the orientation of the carbon-based negative electrode active material (e.g., graphite) may be determined by crystal plane analysis of the carbon-based negative electrode active material CA contained in the negative electrode active layers.

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

[0067] [Formula 1] 1.6≦[OI edge ] / [OI center ]≦2.5

[0068] [Formula 2] 2.6≦[OI sliding ] / [OI center ]≦3.5

[0069] (In Equation 1 and Equation 2, OI edge represents the alignment degree (OI) in the edge region, OI center represents the degree of alignment (OI) in the central region, OI sliding represents the degree of alignment (OI) in the sliding region, The degree of alignment (OI) is the area (I 004 ) and the area of ​​the peak representing the (1,1,0) crystal plane (I 110 ) ratio (I 004 / I 110 )

[0070] The degree of alignment (OI) of the carbon-based negative electrode active material CA can be an index of the degree to which the crystalline structure of the spherical carbon-based negative electrode active material is oriented in a certain direction, specifically, relative to the surface of the negative electrode current collector, as measured by X-ray diffraction (XRD). More specifically, the negative electrode active layer exhibits peaks of 2θ=26.5±0.2°, 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 54.7±0.2°, and 77.5±0.2°, which are the peaks for the carbon-based negative electrode active material graphite, as measured by X-ray diffraction, and these peaks 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. In addition, the peak appearing at 2θ=43.4±0.2° is thought to be an overlap of the peaks corresponding to the (1,0,1)R plane of the carbon-based negative electrode active material CA and the (1,1,1) plane of the current collector, for example, copper (Cu).

[0071] The degree of alignment (OI) of the carbon-based negative electrode active material CA can be measured by the area ratio of the peak at 2θ = 54.7 ± 0.2°, which indicates the (0,0,4) plane, to the peak at 2θ = 77.5 ± 0.2°, which indicates the (1,1,0) plane, specifically, the area ratio obtained by integrating the intensities of the above peaks. Here, the peak at 2θ = 54.7 ± 0.2° is a peak indicating the (0,0,4) plane, which is one of the crystal planes of graphite and is tilted relative to the negative electrode current collector. Therefore, the closer the OI value is to 0, the closer the tilt relative to the surface of the negative electrode current collector is to 90°, and the larger the OI value is, the closer the tilt relative 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, the carbon-based negative electrode active material CA is aligned at a high angle relative to the negative electrode current collector, for example, 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, and therefore the degree of alignment (OI) of the carbon-based negative electrode active material CA may be lower than when the carbon-based negative electrode active material CA is aligned at a lower angle.

[0072] Considering this, Equation 1 can be expressed as the degree of alignment (OI) of the carbon-based negative electrode active material contained in the central region. center ) in the edge region of the carbon-based negative electrode active material. edge ), which means that the carbon-based negative electrode active material in the center region is aligned at a higher angle relative to the negative electrode current collector surface than the carbon-based negative electrode active material in the edge regions. In the negative electrode active layers 120 and 220 of the present invention, the carbon-based negative electrode active material in the center region is aligned at a higher angle relative to the negative electrode current collector surface than the carbon-based negative electrode active material in the edge regions, and the above formula 1 is set to 1.6 to 2.5 (i.e., 1.6≦[OI edge ] / [OI center ]≦2.5), specifically, 1.7 to 2.0 (i.e., 1.7≦[OI edge ] / [OI center ]≦2.0), 1.8~2.2 (i.e., 1.8≦[OI edge ] / [OI center ]≦2.2), 2.1~2.4 (i.e., 2.1≦[OI edge ] / [OI center]≦2.4, or 1.7 to 2.3 (i.e., 1.7≦[OI edge ] / [OI center ]≦2.3).

[0073] In addition, Equation 2 is the degree of alignment (OI) of the carbon-based negative electrode active material contained in the central region. center ) is the degree of alignment (OI) of the carbon-based negative electrode active material contained in the sliding region. sliding ), which means that the carbon-based negative electrode active material in the central region is aligned at a higher angle relative to the negative electrode current collector surface than the carbon-based negative electrode active material in the sliding region. In the negative electrode active layers 120 and 220 of the present invention, the carbon-based negative electrode active material in the central region is aligned at a higher angle relative to the negative electrode current collector surface than the carbon-based negative electrode active material in the sliding region, and the above formula 2 is 2.6 to 3.5 (2.6≦[OI sliding ] / [OI center ]≦3.5), specifically, 2.6 to 2.9 (2.6≦[OI sliding ] / [OI center ]≦2.9), 3.0~3.5(3.0≦[OI sliding ] / [OI center ]≦3.5), 2.8~3.3(2.8≦[OI sliding ] / [OI center ]≦3.3), 3.1~3.3(3.1≦[OI sliding ] / [OI center ]≦3.3), or 2.6~2.8(2.6≦[OI sliding ] / [OI center ]≦2.8).

[0074] In each region of the negative electrode active layers 120 and 220, the degree of alignment (OI) of the carbon-based negative electrode active material CA may satisfy a predetermined range so as to satisfy the conditions of Equations 1 and 2 above, thereby maintaining a low average degree of alignment of the carbon-based negative electrode active material CA contained throughout the negative electrode active layers 120 and 220.

[0075] Specifically, in the negative electrode active layers 120 and 220, the central regions 121 and 221 have a low degree of alignment (OI) of the carbon-based negative electrode active material CA contained in these regions.center ) may 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 degree of alignment (OI) of the central regions 121 and 221 may be center ) may have a deviation of 5% or less from the average alignment degree of the negative electrode active layers 120 and 220.

[0076] By controlling the degree of alignment (OI) of the carbon-based negative electrode active material CA contained in the center regions 121 and 221, the edge regions 122 and 222, and the sliding regions 123 and 223 of the negative electrode active layers 120 and 220, respectively, as described above, the present invention has the advantage that 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 electrons and / or lithium ions can easily move into the negative electrode active layers 120 and 220, thereby reducing electrode resistance and improving the high-rate charge and discharge characteristics of the battery.

[0077] Meanwhile, the average thickness of the negative electrode active layers 120 and 220 may 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 may 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 within the above range, the present invention can easily control the orientation tendency of the carbon-based negative electrode active material CA contained in each region according to the thickness change tendency, thereby improving the high-rate charge / discharge characteristics and energy density of batteries including the negative electrodes 100 and 200.

[0078] Furthermore, the negative electrode active layers 120 and 220 may have a structure in which two individual layers are stacked depending on the battery model or product application to which the negative electrode of the present invention is applied, but are not limited thereto. In this case, the negative electrode of the present invention may have a structure in which a first negative electrode active layer (not shown) is provided on the negative electrode current collectors 110 and 210, and a second negative electrode active layer (not shown) is provided on the first negative electrode active layer. In this case, the first negative electrode active layer and the second negative electrode active layer contain a carbon-based negative electrode active material CA, and the carbon-based negative electrode active material CA contained in each layer may be the same or different.

[0079] In addition, the negative electrode active layers 120 and 220 include a carbon-based negative electrode active material CA as a negative electrode active material to realize electrical activity through a reversible oxidation-reduction reaction during charging and discharging of the battery.

[0080] The carbon-based negative electrode active material CA refers to a material primarily composed of carbon atoms, and may include graphite. The graphite may include at least one 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 CA is preferably a spherical graphite granule formed by the aggregation of multiple flake graphite particles. Examples of flake graphite include natural graphite, artificial graphite, mesophase calcined carbon (bulk mesophase) made from tar or pitch, and graphitized cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.). A graphite granule assembled from multiple pieces of highly crystalline natural graphite is particularly preferred. Each graphite granule may be formed by the aggregation of 2 to 100, preferably 3 to 20, flake graphite particles.

[0082] The carbon-based negative electrode active material CA has an average particle size (D 50), and specifically, the average particle size (D 50 ) can be shown.

[0083] The average particle size of natural graphite is preferably as small as possible to maximize the degree of disorder in the direction of expansion of each particle, preventing particle expansion during charging with lithium ions. 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, excessive expansion occurs, which reduces the adhesion between particles and the current collector with repeated charge and discharge, resulting in a significant decrease in cycle performance.

[0084] In addition, the negative electrode active layer according to the present invention may further include, in addition to the carbon-based negative electrode active material CA as the main component, a conductive material, a binder, other additives, and the like, as needed.

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

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

[0087] The content of the conductive material may be 0.1 to 10 parts by weight, specifically 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, based on 100 parts by weight of the total negative electrode active layer. By controlling the content of the conductive material within the above range, the present invention can prevent a decrease in charge capacity due to an increase in negative electrode resistance caused by a low content of conductive material, and can prevent problems such as a decrease in charge capacity due to a decrease in the content of negative electrode active material caused by an excessive amount of conductive material, or a decrease in fast charge characteristics due to an increase in the loading amount of the negative electrode active layer.

[0088] The binder is a component that aids in bonding between the negative electrode active material and the conductive material, etc., and between the negative electrode active material and the current collector, and may be suitably used within a range that does not degrade the electrical properties of the electrode. Specifically, the binder may include at least one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, 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 fluororubber.

[0089] The content of the binder may be 0.1 to 10 parts by weight, 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, based on 100 parts by weight of the total negative electrode active layer. By controlling the content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent a decrease in adhesive strength of the active layer due to a low content of binder or a decrease in electrical properties of the electrode due to an excessive amount of binder.

[0090] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery, and may be made of, for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. In the case of copper or stainless steel, it may also be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector is preferably 1 μm to 500 μm, taking into account the conductivity and total thickness of the negative electrode to be manufactured.

[0091] <Lithium secondary battery>

[0092] In one embodiment, the present invention further comprises: There is provided a lithium secondary battery including an electrode assembly including a positive electrode, the above-described negative electrode of the present invention, and a separator disposed between the positive electrode and the negative electrode.

[0093] The lithium secondary battery according to the present invention includes an electrode assembly having a plurality of positive electrodes, a separator, and a negative electrode sequentially disposed thereon, 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 active layer laminated on a negative electrode current collector, the negative electrode active layer being divided into a center region, an edge region, and a sliding region, and the degrees of alignment (OI) of the carbon-based negative electrode active materials contained in the center region, the edge region, and the sliding region satisfy Equations 1 and 2. This allows the lithium secondary battery to exhibit excellent battery life, high-rate charge / discharge characteristics, and high energy density due to minimal volume change of the negative electrode during charge / discharge.

[0094] In this case, the negative electrode has the same configuration as that described above, and therefore a detailed description thereof will be omitted.

[0095] The positive electrode includes a positive electrode active layer prepared by applying a slurry containing a positive electrode active material onto a positive electrode current collector, followed by drying and pressing, and may optionally further include a conductive material, a binder, other additives, and the like, as needed.

[0096] The positive electrode active material is a material capable of undergoing an electrochemical reaction on a positive electrode current collector, and may include one or more lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2, which are capable of reversibly intercalating and deintercalating 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 1.0≦x≦1.30, 0.5≦y<1, 0 <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつ、y+z+w+v=1であり、 M 2 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 Chemical Formula 1 and Chemical Formula 2 above are materials containing high amounts of nickel (Ni) and manganese (Mn), respectively, and when used as a positive electrode active material, have the advantage of being able to stably supply electricity at a high capacity and / or high voltage compared to conventionally used positive electrode active materials such as iron phosphate oxide (LiFeO4).

[0101] In this case, the lithium metal oxide represented by the above chemical formula 1 is 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., and the lithium metal oxide represented by the above chemical formula 2 is 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., which may be used alone or in combination.

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

[0103] The positive electrode active layer may further include a conductive material, a binder, and other additives in addition to the positive electrode active material.

[0104] In this case, the conductive material is used to improve the electrical performance of the positive electrode, and may be a conductive material commonly used in the art. Specifically, the conductive material may include at least one 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] The conductive material may be contained in an amount of 0.1 to 5 parts by weight based on the weight of each positive electrode active layer, specifically 0.1 to 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.

[0106] The binder functions to bind the positive electrode active material, the positive electrode additive, and the conductive material together, and any material having this function may be used without particular limitation. 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, polymethylmethacrylate, and copolymers thereof. As one example, the binder may include polyvinylidene fluoride.

[0107] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 1 to 5 parts by weight, based on the weight of each positive electrode active layer.

[0108] The total thickness of the positive electrode active layer is not particularly limited, but may be specifically 50 μm to 300 μm, more specifically 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] The positive electrode may use a current collector having high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used. In the case of aluminum or stainless steel, it may also be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the current collector may be preferably 3 μm to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0110] Meanwhile, the separator interposed between the positive and negative electrodes of each unit cell is an insulating thin film with high ion permeability and mechanical strength. It may be made of any material commonly used in the art, including at least one polymer selected from the group consisting of chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymer. The separator may be in the form of a porous polymer substrate, such as a sheet or nonwoven fabric containing the polymer. In some cases, the separator may be in the form of a composite separator, in which organic or inorganic particles are coated on the porous polymer substrate with an organic binder. The separator may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0111] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery having a stack type, a zigzag type, or a zigzag-stack type electrode assembly. For example, the lithium secondary battery according to the present invention may be a pouch type secondary battery or a prismatic type secondary battery.

[0112] <Method of manufacturing the negative electrode>

[0113] In one embodiment, the present invention further comprises: 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; and drying the negative electrode slurry to which the magnetic field is applied to form a negative electrode active layer; The negative electrode active layer is divided into a central region including a center portion in a width direction of the negative electrode active layer, a sliding region located at an 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 active layer satisfies the following formulas 1 and 2:

[0114] [Formula 1] 1.6≦[OI edge ] / [OI center ]≦2.5

[0115] [Formula 2] 2.6≦[OI sliding ] / [OI center ]≦3.5

[0116] (In Equation 1 and Equation 2, OI edge represents the alignment degree (OI) in the edge region, OI center represents the degree of alignment (OI) in the central region, OI sliding represents the degree of alignment (OI) in the sliding region, The degree of alignment (OI) is the area (I 004 ) and the area of ​​the peak representing the (1,1,0) crystal plane (I 110 ) ratio (I 004 / I 110 )

[0117] In a method for manufacturing a negative electrode according to the present invention, a negative electrode slurry containing a carbon-based negative electrode active material is applied to a negative electrode current collector, and a magnetic field is applied to the surface of the applied negative electrode slurry to align the carbon-based negative electrode active material in the negative electrode slurry at a predetermined angle relative to the surface of the negative electrode current collector. Thereafter, the negative electrode slurry, in which the degree of alignment of the carbon-based negative electrode active material is reduced, is dried to form a negative electrode active layer, thereby manufacturing a negative electrode.

[0118] The step of applying the negative electrode slurry involves discharging a negative electrode slurry containing a carbon-based negative electrode active material onto the surface of a moving negative electrode current collector. While any method commonly used in the art can be used without limitation, a die coating method is preferred. The die coating method can be performed using a slot die equipped with a shim for controlling the discharging conditions of the negative electrode slurry. In this case, the loading amount and coating thickness of the negative electrode slurry applied to the negative electrode current collector can be easily controlled by controlling the shape of the shim.

[0119] The step of applying a magnetic field to the negative electrode slurry may be a step of orienting a crystal plane of the carbon-based negative electrode active material contained in the negative electrode slurry at a predetermined angle relative to the negative electrode current collector. To this end, the step of applying a magnetic field may be performed by magnets disposed above and below the negative electrode current collector, on whose surface the negative electrode slurry is applied and moved.

[0120] Here, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode slurry can be adjusted by the strength of the applied magnetic field and the time of exposure to the magnetic field, and thus, the step of applying the magnetic field can be performed under predetermined magnetic field strength and time conditions.

[0121] Specifically, the step of applying the magnetic field may involve applying a magnetic field of 2,000 G (Gauss) to 6,000 G (Gauss), and more specifically, applying a magnetic field with an intensity of 2,500 G to 5,500 G, 3,000 G to 5,500 G, 3,500 G to 5,500 G, 4,000 G to 5,500 G, 3,500 G to 4,500 G, or 4,500 G to 5,000 G.

[0122] Furthermore, the step of applying the magnetic field may be carried out for 5 to 60 seconds, 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.

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

[0124] Furthermore, the step of applying the magnetic field is performed by magnets introduced above and below the applied negative electrode slurry, as described above, and the size of the magnets may 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 across the entire surface of the negative electrode slurry. For example, the magnets may have a length ratio of 105% to 200% based on the width of the negative electrode slurry, and specifically, may have a length ratio of 110% to 180%, 110% to 160%, 110% to 140%, 110% to 130%, 130% to 150%, or 105% to 120% based on the width of the negative electrode slurry.

[0125] In the present invention, by controlling the magnetic field strength, application time, and / or size of the magnet unit in the step of applying a magnetic field as described above, the regional orientation of the carbon-based negative electrode active material contained in the negative electrode slurry can be controlled to satisfy Equation 1 and Equation 2.

[0126] The step of forming the negative electrode active layer may include the steps of drying the negative electrode slurry and rolling the dried negative electrode slurry.

[0127] At this time, the step of drying the negative electrode slurry may be performed in any manner that can maintain the orientation of the carbon-based negative electrode active material contained in the negative electrode active layer.

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

[0129] 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, etc. In this case, the rolling may be performed at a temperature higher than room temperature.

[0130] Specifically, the rolling can be carried out at a temperature of 50°C to 100°C, more specifically at a temperature of 60°C to 100°C, 75°C to 100°C, 85°C to 100°C, 50°C to 90°C, 60°C to 80°C, or 65°C to 90°C. Specifically, the rolling may be performed at a rolling speed of 2 m / s to 7 m / s, more specifically, at a rolling speed 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. The rolling can be carried out under a pressure of 50 MPa to 200 MPa, specifically 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 changes in the alignment of the carbon-based negative electrode active material contained in the negative electrode active layer formed by rolling the dried negative electrode slurry under the above-mentioned temperature, speed, and / or pressure conditions.

[0132] Furthermore, the average thickness of the edge regions may be equal to or thinner than the average thickness of the central region before rolling, thereby allowing the amount of negative electrode slurry loading in the edge regions to be equal to or smaller than the amount of negative electrode slurry loading in the central region. Specifically, the edge regions of the negative electrode active layer may have a thickness ratio of 90% or more and less than 105% of the average thickness of the central region of the negative electrode active layer before rolling. More specifically, the thickness of the edge regions may be 95% to 100%, 98% to 102%, or 97% to 100% of the average thickness of the central region before rolling.

[0133] The present invention will be described in more detail below with reference to examples and experimental examples.

[0134] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0135] <Examples 1 to 3 and Comparative Examples 1 to 3. Production of negative electrodes for lithium secondary batteries>

[0136] A negative electrode for a lithium secondary battery was manufactured according to 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 produced using the prepared carbon-based negative electrode active materials.

[0138] Specifically, a graphite mixture consisting of natural graphite and artificial graphite mixed in a weight ratio of 1-3:7-9 was prepared as the negative electrode active material, carbon black was used as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were used as binders. 95 parts by weight of the graphite mixture, 1 part by weight of carbon black, 1.5 parts by weight of CMC, and 2.5 parts by weight of SBR were mixed with water to a solid content of 50% to produce a negative electrode slurry.

[0139] After the negative electrode slurry was prepared, it was cast onto a copper sheet (thickness: 10 μm) being transferred roll-to-roll (transfer speed: 5 m / min) using a die coater. The negative electrode slurry was cast to an average thickness of 190 μm along the transfer direction of the copper sheet, and the shape of the shim installed 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] Next, permanent magnets with a length ratio of 110% to 120% of the width of the negative electrode slurry were placed on top of the applied negative electrode slurry and below the negative electrode current collector, and a magnetic field of 4,700±100 G was applied for 15 seconds. The magnetically-applied negative electrode slurry was then dried with hot air to form a negative electrode active layer. The formed negative electrode active layer was rolled at 50±1°C, a pressure of 100MPa to 150MPa, and a transfer speed of 3m / s to produce a lithium secondary battery negative electrode with the cross-sectional structure shown in Figure 1.

[0141] For each negative electrode, a central region having a length ratio of 98.5% of the width of the negative electrode active layer was defined as a central region, and regions on both sides of the central region with a total length ratio of 1.0% (each with a length ratio of 0.5%) were defined as edge regions. Regions on the outer sides of the edge regions with a length ratio of 0.5% (each with a length ratio of 0.25%) were defined as sliding regions.

[0142] The average thickness of each of the set regions was then measured, and the results are shown in Table 1. The confocal thickness of each of the central region and edge region of the negative electrode active layer was measured three times, and the average thickness was calculated by averaging the measurements. The average thickness of the sliding region of the negative electrode active layer was defined as the thickness at the point where the length of the sliding region was half the width of the negative electrode active layer.

[0143] In addition, 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) were as follows:

[0144] - Target: Cu (Kα line) 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 representing the (0,0,4) crystal plane and the (1,1,0) crystal plane were calculated, and the ratio of these areas (I 004 / I 110 ) was calculated to calculate the degree of alignment (OI) of the mixed graphite in each region. The calculated values ​​are shown in Table 1 below.

[0146] [Table 1]

[0147] <Comparative Examples 4 and 5. Production of negative electrodes for lithium secondary batteries>

[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 magnetic field was applied using a permanent magnet having a length ratio of 95% to 100% based on the width of the negative electrode slurry.

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

[0150] [Table 2]

[0151] <Examples 4 to 6 and Comparative Examples 6 to 10. Production of Lithium Secondary Batteries>

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

[0153] The obtained positive electrode and the negative electrode prepared in each of Examples 1 to 3 and Comparative Examples 1 to 5 were inserted into a case with a separator made of 18 μm polypropylene, and then an electrolyte composition was injected to assemble a lithium secondary battery.

[0154] The type of negative electrode used in each lithium secondary battery is 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 experiment was carried out.

[0158] a) Evaluation of thickness expansion characteristics of negative electrode

[0159] The lithium secondary batteries manufactured in Examples 4 to 6 and Comparative Examples 6 to 10 were charged and discharged 30 times at a 0.5C rate (C-rate), and then recharged to a fully charged state (SOC 100%) and disassembled. The negative electrodes were recovered from the disassembled batteries, washed with DEC (diethyl carbonate), and dried. The thickness expansion rate of the negative electrodes after charge and discharge was analyzed. The results are shown in Table 4.

[0160] b) Evaluation of high-efficiency charging performance

[0161] The lithium secondary batteries manufactured in Examples 4 to 6 and Comparative Examples 6 to 10 were charged to an SOC of 80% by applying a current of 3.0 C-rate, and the voltage change and dV / dQ were measured as a function of the SOC. If a voltage plateau was present in the measured voltage change or the graph showing dV / dQ was bimodal, it was determined that lithium had been deposited on the negative electrode surface. The SOC value at which lithium was determined to have been deposited was defined as the maximum SOC at which the secondary battery could be rapidly charged, and this was measured. The results are shown in Table 4 below.

[0162] c) Evaluation of high rate discharge performance

[0163] The lithium secondary batteries manufactured in Examples 4 to 6 and Comparative Examples 6 to 10 were fully charged (SOC 100%) at a 0.5 C rate (C-rate), and the fully charged lithium secondary batteries were discharged to 1.5 V at a 0.1 C rate (C-rate) to measure their capacities. Each lithium secondary battery was then fully charged (SOC 100%) at a 0.5 C rate (C-rate) and discharged to 1.5 V at a 2.0 C rate (C-rate), repeating this charge-discharge cycle 100 times. The capacity retention after 100 discharges at a 2.0 C rate (C-rate) was calculated based on the capacity at the 0.1 C rate (C-rate), and the results are shown in Table 4 below. A percentage of the calculated initial charge capacity of 85% or greater was marked with "Good," a percentage of 80% or less of the initial charge capacity was marked with "Poor," and a percentage of the initial charge capacity of more than 80% but less than 85% was marked with "Average."

[0164] [Table 4]

[0165] As shown in Table 4 above, the negative electrode for a lithium secondary battery according to the present invention has little expansion in thickness during charging and discharging, and is therefore excellent in output performance.

[0166] Specifically, the lithium secondary batteries manufactured in the Examples showed a low thickness expansion rate of 25% or less after charge and discharge of the negative electrode, and lithium plating occurred more slowly than the secondary batteries manufactured in the Comparative Examples during high-rate charging at 3.0 C-rate, resulting in a high SOC of 40% or more at which lithium precipitates. Furthermore, the lithium secondary batteries were shown to have a capacity retention rate of 85% or more after 100 discharges at a high rate of 2.0 C-rate.

[0167] This means that the negative electrode of the embodiment has a configuration in which the degree of alignment (OI) of each carbon-based negative electrode active material contained in the center region, edge region, and sliding region of the negative electrode active layer satisfies Equation 1 and Equation 2, thereby further reducing the volume change of the negative electrode during charge and discharge of the secondary battery, further improving the accessibility of lithium ions in the negative electrode active layer, and improving high-rate characteristics.

[0168] These results show that the negative electrode for a lithium secondary battery according to the present invention undergoes little volume change during charge and discharge, has excellent high-rate charge and discharge performance, and exhibits a high energy density.

[0169] Although the present invention has been described above with reference to preferred embodiments, it will be understood that a person skilled in the art or having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

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

[0171] 100 and 200: Negative electrode for lithium secondary battery according to the present invention 110 and 210: negative electrode current collector 120 and 220: negative electrode active layer 121 and 221: central region of the negative electrode active layer 122 and 222: Edge regions of the negative electrode active layer 123 and 223: Sliding region of the negative electrode active layer CA: Carbon-based negative electrode active material ↑: Crystal plane alignment direction of 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, The negative electrode active layer is the negative electrode active layer is divided into a central region including a center portion in a width direction thereof, a sliding region located at an 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: [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 Equation 1 and Equation 2, O.I. ｅｄｇｅ represents the degree of alignment (O.I) in the edge region, O.I. ｃｅｎｔｅｒ represents the degree of alignment (O.I) in the central region, O.I. ｓｌｉｄｉｎｇ represents the degree of alignment (O.I) in the sliding region, The degree of alignment (O.I) is the area (I) of the peak representing the (0,0,4) crystal plane in XRD measurement of the negative electrode active layer. ００４ ) and the area of ​​the peak representing the (1,1,0) crystal plane (I １１０ ) ratio (I ００４ / I １１０ ) represents

2. The central region of the negative electrode active layer has an alignment degree (O.I. ｃｅｎｔｅｒ 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the value of (A) is 0.7 to 1.

5.

3. the central region of the negative electrode active layer occupies 90% or more of the entire length in the width direction of the negative electrode active layer, The negative electrode for a lithium secondary battery according to claim 1 , wherein the sliding region of the negative electrode active layer has a proportion of 3% or less of the entire length in a width direction of the negative electrode active layer.

4. The negative electrode for a lithium secondary battery according to any one of claims 1 to 3, wherein the negative electrode active layer satisfies the following formula 3: [Formula 3] R ｓｌｉｄｉｎｇ <R ｅｄｇｅ ≦R ｃｅｎｔｅｒ In Equation 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.

5. 2. 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.

6. The negative electrode for a lithium secondary battery according to claim 1 , wherein the carbon-based negative electrode active material comprises at least one of natural graphite and artificial graphite.

7. 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; and drying the negative electrode slurry to which the magnetic field is applied to form a negative electrode active layer; The negative electrode active layer is divided into a central region including a center portion in a width direction of the negative electrode active layer, a sliding region located at an 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 active layer 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 Equation 1 and Equation 2, O.I. ｅｄｇｅ represents the degree of alignment (O.I) in the edge region, O.I. ｃｅｎｔｅｒ represents the degree of alignment (O.I) in the central region, O.I. ｓｌｉｄｉｎｇ represents the degree of alignment (O.I) in the sliding region, The degree of alignment (O.I) is the area (I) of the peak representing the (0,0,4) crystal plane in XRD measurement of the negative electrode active layer. ００４ ) and the area of ​​the peak representing the (1,1,0) crystal plane (I １１０ ) ratio (I ００４ / I １１０ ) represents

8. 8. The method for producing a negative electrode for a lithium secondary battery according to claim 7, wherein a magnetic field of 2,000 G to 6,000 G is applied in the step of applying a magnetic field.

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

10. the step of applying a magnetic field is performed by magnets introduced above and below the applied negative electrode slurry; and 10. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 7, wherein the magnet portion has a length that is 105% to 200% of the width direction length of the negative electrode slurry.

11. The step of forming the negative electrode active layer includes: drying the negative electrode slurry; and rolling the dried negative electrode slurry.

12. 12. The method of claim 11, wherein the edge region of the negative electrode active layer has a thickness ratio of 90% to 105% of the average thickness of the central region of the negative electrode active layer before rolling.

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