Anode for lithium secondary battery and manufacturing method therefor

Abstract

The present invention relates to an anode for a lithium secondary battery and a manufacturing method therefor. The anode has a pattern structure in which a first region and a second region that have a predetermined deviation in L* of CIE LAB colorimeter are alternately disposed on a surface of an anode active layer, thereby having excellent adhesion between an anode current collector and the anode active layer. In addition, the anode has the advantages of not only improving a swelling phenomenon during charging, but also having excellent rapid charging performance.

Description

Anode for lithium secondary battery and method for manufacturing the same

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a method for manufacturing the same.

[0002] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0097451, dated July 23, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Lithium secondary batteries are increasingly being used not only in small devices like portable electronic devices, but also in medium- to large-sized devices like battery packs for hybrid and electric vehicles and power storage systems. In particular, growing concern over environmental issues has led to a growing demand for high-capacity batteries in devices like electric vehicles and hybrid electric vehicles, which can replace fossil fuel-powered vehicles like gasoline and diesel, a major source of air pollution.

[0005] Typically, lithium secondary batteries are rechargeable power generation devices comprised of a stacked structure of a cathode / separator / cathode. When charging a lithium secondary battery, a lithium desorption reaction occurs at the cathode, where lithium contained in the cathode active material is oxidized and released. A lithium insertion reaction also occurs at the anode, where lithium is reduced and inserted into the cathode active material. Because the desorption reaction in the cathode active material is faster than the insertion reaction in the anode active material, the charge / discharge performance of a lithium secondary battery, including its speed, is primarily determined by the anode.

[0006] Graphite-containing materials are widely used as the negative electrode active material for the above-mentioned negative electrode. The average potential when graphite-containing materials release lithium is approximately 0.2 V (based on Li / Li+), and the discharge potential exhibits a relatively flat pattern. Therefore, when graphite is used as the negative electrode active material, secondary batteries have the advantage of high and consistent voltage.

[0007] Amorphous or crystalline carbon is used as the cathode active material. Of these, crystalline carbon is primarily used due to its high capacity. Examples of this type of crystalline carbon include graphite-based carbons such as natural graphite and artificial graphite.

[0008] The above graphite-based carbon has different properties depending on its type. For example, natural graphite is inexpensive and exhibits excellent adhesion to a current collector, but is relatively inferior to artificial graphite in terms of high-rate charge / discharge performance and life characteristics. On the other hand, the artificial graphite has a low content of surface defects and functional groups, so its adhesion to a current collector is weak. In addition, when propylene carbonate (PC) is used in the electrolyte for the purpose of improving low-temperature performance, the artificial graphite has a problem in that the propylene carbonate exfoliates each layer forming the interlayer structure of the graphite.

[0009] Accordingly, there have been attempts to apply mixed graphite, which appropriately combines natural graphite and artificial graphite to take advantage of each other's strengths, as an anode active material for lithium secondary batteries. However, the mixed graphite has limitations in that it exhibits poor characteristics such as lifespan characteristics and impact stability due to low adhesion to the current collector. In addition, when the content of the anode active material is increased to design a high-capacity electrode, swelling occurs due to lithium insertion into the graphite during charging of the lithium secondary battery, which not only reduces the energy density but also deteriorates the lifespan characteristics.

[0010] Therefore, there is a high need for a cathode technology that has excellent lifespan characteristics due to high adhesion to the entire body, and has a fast charging speed as the swelling phenomenon during charging of lithium secondary batteries is improved.

[0011]

[0012] [Prior Art Literature]

[0013] Republic of Korea Patent Publication No. 10-2018-0028797

[0014] Republic of Korea Patent Publication No. 10-2022-0057715

[0015]

[0016] The purpose of the present invention is to provide an anode having excellent adhesion to a current collector, excellent life characteristics, improved swelling phenomenon during charging of a lithium secondary battery, and a fast charging speed, and a method for manufacturing the same.

[0017]

[0018] The present invention,

[0019] A negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector and including a carbon-based negative electrode active material;

[0020] The surface of the above cathode active layer provides a cathode including a first region and a second region having △L* of 0.45 or more, expressed by Equation 1 based on L* according to the CIE LAB colorimeter, and alternately arranged at least once:

[0021] [Formula 1]

[0022] △L*= ┃L1*-L2*┃

[0023] In the above equation 1,

[0024] L1* means the average L* value of the first region above,

[0025] L2* refers to the average L* value of the second region.

[0026] At this time, the L1* value of the first region may be in the range of 35 to 48, and the average L2* value of the second region may be in the range of 36 to 50.

[0027] The first region and the second region formed on the surface of the above-described negative active layer can form at least one pattern among a stripe pattern, a concentric circle pattern, a check pattern, and a dot pattern.

[0028] In addition, the cathode may have a rectangular shape, and may have a structure in which a cathode tab is formed on a first side of the rectangular shape, and a third side facing the first side may include a form in which a first region and a second region are alternately arranged one or more times on the surface of the cathode active layer.

[0029] Alternatively, the cathode may have a rectangular shape, and may have a structure in which a cathode tab is formed on a first side of the rectangular shape, and a second side and a fourth side adjacent to the first side may include a form in which a first region and a second region are alternately arranged one or more times on the surface of the cathode active layer.

[0030] The ratio (D1:D2) of the average width (D1) of the first region and the average width (D2) of the second region may be in the range of 0.4:1 to 1:1.

[0031] The above carbon-based negative electrode active material may include at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0032] The above cathode active layer is made of Si, SiC and SiO. q (However, 0.5≤q≤2.5) may include at least one silicon-based negative electrode active material.

[0033] Additionally, the interface resistance between the negative electrode current collector and the negative electrode active layer may be in the range of 0.1 mΩ·㎡ to 8.0 mΩ·㎡.

[0034] The tortuosity of the above cathode active layer may be in the range of 2.0% to 8.0%.

[0035]

[0036] Furthermore, the present invention,

[0037] A step (S1) of applying a negative electrode slurry containing a carbon-based negative electrode active material to at least one surface of a negative electrode current collector;

[0038] A step (S2) of applying a magnetic field to the applied cathode slurry, and

[0039] A step (S3) of drying a cathode slurry to which a magnetic field is applied to form a cathode active layer;

[0040] In the step (S2) of applying the above magnetic field,

[0041] A magnetic field having an average range of 1,000 G to 9,000 G is applied to the A region of the cathode slurry corresponding to the first region of the cathode active layer described above,

[0042] A method for manufacturing a cathode is provided in which no magnetic field is applied to the B region of the cathode slurry corresponding to the second region, or a magnetic field of 5,000 G or less is applied.

[0043] In the step (S2) of applying the magnetic field, the strength of the magnetic field applied to the B region of the cathode slurry may be applied at 0.1% to 0.9% of the strength of the magnetic field applied to the A region.

[0044] In addition, in the step (S2) of applying the magnetic field, the magnetic field can be applied in a bottom application manner by applying it from below the cathode.

[0045]

[0046] The negative electrode for a lithium secondary battery according to the present invention has a pattern structure in which first and second regions having a predetermined deviation in L* of the CIE LAB colorimeter are alternately arranged on the surface of the negative electrode active layer, thereby providing excellent adhesion between the negative electrode current collector and the negative electrode active layer. In addition, the negative electrode has the advantage of not only improving swelling during charging but also exhibiting excellent rapid charging performance.

[0047]

[0048] Figure 1 is a top view showing the surface of a cathode according to the present invention.

[0049] Figure 2 is a cross-sectional view showing the cross-sectional structure in the thickness direction (z direction) of a negative electrode (10) for a lithium secondary battery according to the present invention.

[0050] Figure 3 is a photographic image of the surface of a cathode manufactured according to the present invention.

[0051] Figure 4 is a cross-sectional view of a cathode schematically showing the ab-axis crystal plane state of a carbon-based cathode active material depending on whether the carbon-based cathode active material is aligned and / or oriented.

[0052] Figure 5 is a cross-sectional view showing the cross-sectional structure in the thickness direction (z direction) of a negative electrode (10) for a lithium secondary battery according to the present invention.

[0053]

[0054] The present invention can be modified in various ways and has many embodiments, and specific embodiments will be described in detail in the detailed description.

[0055] In the present invention, it should be understood that terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0056] Also, in this specification, "average particle diameter (D 50 )" means the particle diameter at which the integrated value is 50% in the particle diameter distribution of the particles, and is also called the median diameter. The above average particle diameter can be measured by a method commonly applied in the art. For example, the above average particle diameter can be measured using a particle size analyzer or an analysis device using a laser diffraction scattering particle size distribution measurement method, but is not limited thereto.

[0057] In this specification, the “thickness direction of the negative electrode active layer” may be the same as the direction perpendicular to the plane resulting from the combination of the width direction and the length direction of the negative electrode active layer, which may be defined as the “z-axis direction” in FIG. 1.

[0058] Furthermore, in this specification, "color coordinates according to the CIE LAB colorimetric system" means coordinates in the CIE color space, which is a color value specified by the CIE (Commission International de l'Eclairage), and any arbitrary position in the CIE color space can be expressed by three coordinate values: L*, a*, and b*.

[0059] Here, the L* value represents brightness, and if L*=0, it represents black, and if L*=100, it represents white. In addition, the a* value represents whether the color with the corresponding color coordinates is biased toward pure magenta or pure green, and the b* value represents whether the color with the corresponding color coordinates is biased toward pure yellow or pure blue. Specifically, a color with an average color coordinate (L*) for brightness of 60 or less based on the CIE LAB colorimeter can be defined as black, and the black may include achromatic colors such as gray and black.

[0060]

[0061] Hereinafter, the present invention will be described in more detail.

[0062]

[0063] Cathode for lithium secondary batteries

[0064] In one embodiment of the present invention,

[0065] A negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector and including a carbon-based negative electrode active material;

[0066] The surface of the above-described cathode active layer provides a cathode including a first region and a second region having △L* of 0.45 or more, based on L* according to the CIE LAB colorimeter, as represented by the following formula 1, and arranged alternately at least once.

[0067]

[0068] The negative electrode according to the present invention refers to a negative electrode for a lithium secondary battery. The negative electrode includes a negative electrode active layer including a carbon-based negative electrode active material on at least one surface of a negative electrode current collector. The negative electrode active layer has a form in which a first region and a second region are alternately arranged at least once on the surface. The first region and the second region can form a pattern by having a predetermined deviation in L* according to the CIE LAB colorimeter.

[0069] The above-described negative electrode has a structure in which first and second regions having a predetermined L* deviation are alternately arranged at least once, thereby improving the interfacial characteristics between the negative electrode current collector and the negative electrode active layer, and exhibiting excellent adhesive strength. In addition, the above-described negative electrode has the advantage of lowering the tortuosity of the negative electrode active layer, thereby not only increasing the charging speed when charging a lithium secondary battery, but also significantly improving the swelling phenomenon caused by the insertion of lithium ions.

[0070] For example, the interfacial characteristics of the negative electrode current collector and the negative electrode active layer of the negative electrode may be improved so that the interfacial resistance may be in the range of 0.1 mΩ·m2 to 8.0 mΩ·m2. Specifically, the interfacial resistance of the negative electrode current collector and the negative electrode active layer may be 0.1 mΩ·m2 to 7.5 mΩ·m2; 0.1 mΩ·m2 to 7.0 mΩ·m2; 0.1 mΩ·m2 to 6.5 mΩ·m2; 0.1 mΩ·m2 to 6.0 mΩ·m2; 0.1 mΩ·m2 to 5.5 mΩ·m2; 0.1 mΩ·m2 to 5.0 mΩ·m2; 0.1 mΩ·m2 to 4.5 mΩ·m2; 0.5 mΩ·m2 to 7.5 mΩ·m2; 0.5 mΩ·m2 to 5.0 mΩ·m2; 0.5 mΩ·m2 to 4.5 mΩ·m2; 4.0 mΩ·m2 to 8.0 mΩ·m2; 3.0 mΩ·m2 to 5.5 mΩ·m2; 2.7 mΩ·m2 to 5.1 mΩ·m2; 1.0 mΩ·m2 to 4.35 mΩ·m2; 1.5 mΩ·m2 to 4.35 mΩ·m2; 2.0 mΩ·m2 to 4.35 mΩ·m2; 2.5 mΩ·m2 to 4.35 mΩ·m2; 2.8 mΩ·m2 to 4.35 mΩ·m2; 3.0 mΩ·m2 to 4.35 mΩ·m2; 3.1 mΩ·m2 to 4.3 mΩ·m2; 3.4 mΩ·m2 to 4.1 mΩ·m2; 3.6 mΩ·m2 to 4.35 mΩ·m2; 3.1 mΩ·m2 to 4.1 mΩ·m2; Or it may be in the range of 3.6 mΩ·㎡ to 4.0 mΩ·㎡. The above interfacial resistance may mean an average value of the resistance induced between the negative electrode current collector and the negative electrode active layer. The present invention can prevent or further improve the interfacial adhesive strength between the negative electrode active layer and the negative electrode current collector by satisfying the interfacial resistance of the negative electrode active layer and the negative electrode current collector within the above-described range.

[0071] Additionally, the negative electrode active layer of the negative electrode may have a tortuosity in a range of 2.0% to 8.0%. Specifically, the tortuosity of the negative electrode active layer may be in a range of 3.0% to 8.0%; 4.0% to 8.0%; 5.0% to 8.0%; 4.0% to 8.0%; 5.0% to 8.0%; 3.0% to 7.0%; 4.0% to 7.0%; 4.0% to 6.5%; 5.0% to 6.5%; 4.0% to 6.0%; 3.5% to 6.0%; 4.0% to 5.0%; 4.0% to 4.9%; 4.0% to 4.5%; 4.2% to 4.8%; or 4.1% to 4.4%. The curvature of the negative electrode active layer is a parameter that indirectly indicates the length of the path provided by the pores contained within the negative electrode active layer so that the electrolyte, etc. can move from the negative electrode active layer surface to the negative electrode current collector. The lower the curvature ratio, the shorter the path length. The present invention can increase the speed at which lithium ions are inserted into the carbon-based negative electrode active material during charging of a lithium secondary battery by controlling the curvature of the negative electrode active layer within the above-described range. Therefore, the present invention can provide an negative electrode with excellent rapid charging performance.

[0072] In addition, the cathode can satisfy the following equation 1:

[0073] [Formula 1] 0.01 ㎡ ≤ MP R / R pore ≤ 0.20 ㎡

[0074] In the above equation 1,

[0075] MP R represents the interfacial resistance (unit: mΩ·㎠) of the negative electrode active layer and the negative electrode current collector,

[0076] R pore represents the pore resistance (unit: Ω) within the cathode active layer.

[0077] Specifically, the cathode has a surface area of ​​0.01 ㎡ to 0.19 ㎡ (i.e., 0.01 ㎡ ≤ MP) according to the above formula 1. R / Rpore ≤ 0.19 ㎡); 0.05 ㎡ to 0.19 ㎡ (i.e., 0.05 ㎡ ≤ MP R / R pore ≤ 0.19 ㎡); 0.09 ㎡ to 0.19 ㎡ (i.e., 0.09 ㎡ ≤ MP R / R pore ≤ 0.19 ㎡); 0.1 ㎡ to 0.19 ㎡ (i.e., 0.1 ㎡ ≤ MP R / R pore ≤ 0.19 ㎡); 0.12 ㎡ to 0.19 ㎡ (i.e., 0.12 ㎡ ≤ MP R / R pore ≤ 0.19 ㎡); 0.13 ㎡ to 0.19 ㎡ (i.e., 0.13 ㎡ ≤ MP R / R pore ≤ 0.19 ㎡); 0.14 ㎡ to 0.19 ㎡ (i.e., 0.14 ㎡ ≤ MP R / R pore ≤ 0.19 ㎡); 0.09 ㎡ to 0.18 ㎡ (i.e., 0.09 ㎡ ≤ MP R / R pore ≤ 0.18 ㎡); 0.11 ㎡ to 0.18 ㎡ (i.e., 0.11 ㎡ ≤ MP R / R pore ≤ 0.18 ㎡); 0.13 ㎡ to 0.175 ㎡ (i.e., 0.13 ㎡ ≤ MP R / R pore ≤ 0.175 ㎡); 0.15 ㎡ to 0.175 ㎡ (i.e., 0.15 ㎡ ≤ MP R / R pore ≤ 0.175 ㎡); 0.15 ㎡ to 0.17 ㎡ (i.e., 0.15 ㎡ ≤ MP R / R pore ≤ 0.17 ㎡); 0.14 ㎡ to 0.16 ㎡ (i.e., 0.14 ㎡ ≤ MP R / R pore ≤ 0.16 ㎡); 0.05 ㎡ to 0.15 ㎡ (i.e., 0.05 ㎡ ≤ MP R / R pore ≤ 0.15 ㎡); 0.1 ㎡ to 0.14 ㎡ (i.e., 0.1 ㎡ ≤ MP R / Rpore ≤ 0.14 ㎡); 0.05 ㎡ to 0.10 ㎡ (i.e., 0.05 ㎡ ≤ MP R / R pore ≤ 0.10 ㎡); or 0.13 ㎡ to 0.16 ㎡ (i.e., 0.13 ㎡ ≤ MP R / R pore It can be satisfied with a range of ≤ 0.16 ㎡.

[0078] The above equation 1 is a parameter representing the swelling characteristics of the negative electrode active layer as a whole in which the interfacial resistance of the negative electrode active layer and the negative electrode current collector and the pore resistance contained within the negative electrode active layer are organically combined. As the pore resistance of the negative electrode active layer increases, it means that the degree of freedom of the ab-axis crystal plane of the carbon-based negative electrode active material contained within the negative electrode active layer increases. This affects the interfacial characteristics of the negative electrode active layer and the negative electrode current collector. Accordingly, the negative electrode of the present invention can effectively suppress the swelling phenomenon of the negative electrode during charging while increasing the adhesive strength of the negative electrode active layer and the negative electrode current collector by controlling equation 1 within the above-described range.

[0079]

[0080] FIG. 1 is a top view showing the surface of a negative electrode (10) for a lithium secondary battery according to the present invention, and FIG. 2 is a cross-sectional view showing the cross-sectional structure in the thickness direction (z direction) of a negative electrode (10) for a lithium secondary battery according to the present invention.

[0081] Referring to the above drawings 1 and 2, the negative electrode (10) for a lithium secondary battery according to the present invention will be described in detail for each component.

[0082] The above-described negative electrode (10) includes a negative electrode active layer (12) containing a carbon-based negative electrode active material on at least one surface of a negative electrode current collector (11). The negative electrode active layer (12) is a layer that implements electrical activity of the negative electrode, and is manufactured by applying a negative electrode slurry containing a negative electrode active material that implements an electrochemical redox reaction during charge / discharge of a battery to at least one surface of the negative electrode current collector (11), and then drying and rolling the same.

[0083] In Fig. 2, the negative electrode (10) is shown in the case where the negative electrode active layer (12) is formed on one side of the negative electrode current collector (11), but the present invention is not limited thereto and the negative electrode active layer (12) may be formed on both sides of the negative electrode current collector (11).

[0084] In addition, the negative electrode active layer (12) includes a carbon-based negative electrode active material as a main component as a negative electrode active material exhibiting electrochemical activity. Here, the negative electrode active material may include a carbon-based negative electrode active material as a main component. Specifically, the carbon-based negative electrode active material may be included in an amount of 80 parts by weight to 99.8 parts by weight based on the total 100 parts by weight of the negative electrode active layer, and specifically, may be included in an amount of 95 parts by weight or more, 98 parts by weight or more, 84 parts by weight to 99.8 parts by weight, 90 parts by weight to 99.8 parts by weight, 94 parts by weight to 99.8 parts by weight, 88 parts by weight to 96 parts by weight, or 92 parts by weight to 97.5 parts by weight.

[0085] The above carbon-based negative electrode active material refers to a material whose main component is carbon atoms, and such carbon-based negative electrode active material may include a graphite compound. For example, the above carbon-based negative electrode active material may include, in addition to natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, and carbon microbeads, mesophase calcined carbon (bulk mesophase, liquid crystal pitch-based carbon fiber, etc.) made from tar or pitch, or graphitized coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, coal coke, etc.).

[0086] The above carbon-based negative electrode active material may have the form of an assembly in which multiple particles are assembled. In this case, one graphite assembly may be formed by assembling 2 to 100 graphite particles, preferably 3 to 20 particles.

[0087] In addition, the carbon-based negative electrode active material may have an average particle diameter satisfying a predetermined range. Specifically, the carbon-based negative electrode active material may have an average particle diameter (D) in the range of 0.5 μm to 20 μm. 50 ) can be represented. For example, the carbon-based negative electrode active material may have an average particle diameter (D) in the range 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 expressed.

[0088] The average particle size of the carbon-based negative electrode active material may be advantageously made smaller to maximize the degree of disorder in the direction of expansion of each particle so as to prevent expansion of the particles due to lithium ion charging. However, when the particle size of the carbon-based negative electrode active material is less than 0.5 ㎛, 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 size exceeds 20 ㎛, expansion becomes severe, and as charge and discharge are repeated, the adhesion between particles and the adhesion between the particles and the current collector deteriorates, which may significantly reduce the cycle characteristics.

[0089] The negative electrode active layer (12) including the above carbon-based negative electrode active material may have a structure in which the alignment and / or orientation of the carbon-based negative electrode active material is controlled by region.

[0090] Specifically, the surface of the negative electrode active layer (12) may include a first region and a second region, and the first region and the second region may have a form in which the first region and the second region are alternately arranged one or more times. This form can be confirmed when observing the negative electrode active layer (12) with the naked eye, and in some cases, when analyzing a cross-section in the thickness direction (i.e., the z direction) of the negative electrode active layer, it can be confirmed from a form in which the first region (12a) and the second region (12b) are alternately arranged one or more times in the width direction of the cross-section. Here, the alignment and / or orientation of the carbon-based negative electrode active material included in each region of the first region (12a) and the second region (12b) may be controlled differently. Accordingly, when the surface of the negative electrode active layer (12) is observed with the naked eye, it appears black because it contains a carbon-based negative electrode active material, and a difference in brightness between the first region (12a) and the second region (12b) can be confirmed as shown in FIG. 3.

[0091] Carbonaceous anode active materials, specifically graphite, have a particle form in which crystal planes (i.e., the ab-axis crystal planes of graphite) representing a two-dimensional planar structure composed of carbon atoms are stacked in the c-axis direction. If a separate treatment to align and / or orient the ab-axis crystal planes of graphite is not performed during the formation of the anode active layer, the anode active layer will contain graphite in a state in which the ab-axis crystal planes are not aligned and / or oriented, as shown in (a) of Fig. 4. In this case, the anode active layer is confirmed to be black, the color unique to graphite, when observed on the surface with the naked eye, and since the reflectivity of light incident on the surface is high, the L* according to the CIE LAB chromaticity system exhibits a large value exceeding 46.

[0092] However, the negative electrode of the present invention may include graphite as a carbon-based negative electrode active material in the negative electrode active layer (12), and may have a configuration in which the ab-axis crystal plane of the graphite is aligned and / or oriented at a predetermined angle with respect to the negative electrode current collector (11) in each region of the negative electrode active layer (12), as shown in (b) of FIG. 4. In this case, the larger the angle at which the ab-axis crystal plane of the graphite is aligned and / or oriented with respect to the negative electrode current collector (11) (for example, the closer it is to 90°), the higher the absorption rate of light incident on the surface of the negative electrode active layer (12). This increase in the absorption rate of incident light serves to lower the L* of the negative electrode active layer (12) according to the CIE LAB chromaticity.

[0093] Accordingly, the cathode active layer of the cathode according to the present invention may have a structure in which the graphite included in the first region (12a) and the second region (12b) is aligned and / or oriented, but the degree thereof is different for each region, thereby inducing a difference in the absorption rate of incident light for each region of the cathode active layer (12).

[0094] Specifically, in the negative electrode active layer (12) according to the present invention, the degree to which the graphite included in the first region (12a) has its ab-axis crystal plane aligned and / or oriented with respect to the negative electrode current collector (11) may be greater than that of the graphite included in the second region (12b). Accordingly, the first region (12a) may have an average L* value according to the CIE LAB chromaticity system that is lower than the average L* according to the CIE LAB chromaticity system of the second region (12b).

[0095] As an example, the first region (12a) and the second region (12b) may have a predetermined L* value indicating black when measured by a CIE LAB colorimeter for each region, and may have a predetermined L* deviation (△L*) between the regions.

[0096] Specifically, the average L1* value of the first region (12a) and the average L2* value of the second region (12b) may each be in the range of 35 to 48, and the average L1* value may be smaller than the average L2* value. More specifically, the first region (12a) may exhibit an average L1* value in the range of 37 to 48; 40 to 48; 42 to 47; 44 to 47; 44 to 46; 42 to 45; 45 to 48; or 43 to 47.5 when measuring color coordinates according to the CIE LAB chromaticity system. In addition, the second region (12b) may exhibit an average L1* value in the range of 36 to 48; 40 to 48; 42 to 47; 44 to 47; 44 to 46; 42 to 45; 45 to 48; or 43 to 47.5, which may be greater than the average L1* value of the first region.

[0097] In addition, the L* value (L1*) of the first region (12a) and the L* value (L2*) of the second region (12b) may have a deviation (△L*) of 0.45 or more. Specifically, the first region (12a) and the second region (12b) may have an L* deviation (△L*) in the range of 0.3 to 4; 0.3 to 3; 0.3 to 2; 0.5 to 2; 0.5 to 1.8; 0.5 to 1.4; 0.6 to 1.4; 0.7 to 1.3; 1 to 1.5; 0.6 to 2. In this case, the first region (12a) may have a lower L* value than the second region (12b) and thus have lower brightness, and accordingly, the black of the first region (12a) may appear darker than the black of the second region (12b).

[0098] The present invention can further improve the adhesive strength between the negative electrode active layer (12) and the negative electrode current collector (11) by controlling the average L* and L* deviation (△L*) of the first region (12a) and the second region of the negative electrode active layer (12) within the above-described range, and can effectively suppress the swelling phenomenon while increasing the charging speed when charging a lithium secondary battery. Specifically, when the average L* of the first region (12a) and the second region (12b) exceeds the upper limit of the above-described range, not only is the charging speed significantly low when charging a lithium secondary battery, but swelling of the negative electrode may also occur rapidly. In addition, when the average L* of the first region (12a) and the second region (12b) is less than the lower limit of the above-described range, the adhesive strength between the negative electrode active layer (12) and the negative electrode current collector (11) may decrease.

[0099] In addition, if the deviation (△L*) between the average L* of the first region (12a) and the average L* of the second region (12b) exceeds the upper limit of the above-described range, the effect of increasing the charging speed when charging the lithium secondary battery may be minimal. In addition, if the deviation (△L*) between the average L* of the first region (12a) and the second region (12b) is less than the lower limit of the above-described range, there is a limitation that the interfacial properties between the negative electrode active layer (12) and the negative electrode current collector (11) deteriorate, resulting in lower electrical performance and life characteristics.

[0100] In this way, the negative electrode active layer (12) according to the present invention may include a carbon-based negative electrode active material whose ab-axis crystal plane is aligned and / or oriented at a predetermined angle with respect to the negative electrode current collector (11), and may be characterized by a technical feature in which the degree is controlled differently for each region.

[0101] When the ab-axis crystal plane of the carbon-based negative electrode active material included in the negative electrode active layer is aligned and / or oriented at an angle close to 90° with respect to the surface of the negative electrode current collector, the contact area between the negative electrode active material included in the negative electrode active layer and the negative electrode current collector is significantly reduced, so there is a limitation in that the adhesive strength between the negative electrode active layer and the negative electrode current collector is low. However, the present invention can improve the charging speed and swelling phenomenon during charging of a lithium secondary battery while at the same time significantly increasing the adhesive strength between the negative electrode active layer (12) and the negative electrode current collector (11) by differently controlling the alignment and / or orientation of the carbon-based negative electrode active material with respect to the surface of the negative electrode current collector (11) for each region constituting the negative electrode active layer (12).

[0102] Furthermore, the negative active layer (12) can form a pattern on the surface by having a predetermined deviation between the average L1* value of the first region (12a) and the average L2* value of the second region (12b). The first region (12a) and the second region (12b) can be distinguished by the L* difference to the extent that the boundary between the regions can be observed with the naked eye, and the boundary between the regions can be implemented repeatedly and / or regularly to form a pattern. At this time, the pattern formed on the surface of the negative active layer (12) can include at least one pattern of a stripe pattern, a concentric circle pattern, a check pattern, and a dot pattern. This pattern structure of the negative active layer has the advantage of being able to more intuitively distinguish the first region and the second region.

[0103] In addition, as shown in Fig. 1, the cathode may have a rectangular shape in which the cathode active layer is sequentially connected to the first side to the fourth side when observed from the surface, and may have a structure formed in which a cathode tab (13) is drawn out from the first side.

[0104] At this time, the first region (12a) and the second region (12b) of the surface of the negative electrode active layer may have a form in which they are alternately arranged one or more times between the first side and the third side facing it, or the first region (12a) and the second region (12b) of the surface of the negative electrode active layer may have a form in which they are alternately arranged one or more times between the second side and the fourth side adjacent to the first side.

[0105] For example, the first region (12a) and the second region (12b) of the surface of the negative electrode active layer may have a form in which they are alternately arranged one or more times between the first side and the third side. In this case, the deviation (△L*) between the L* of the first region (12a) and the average L* of the second region (12b) may tend to increase as it approaches the negative electrode tab (13).

[0106] In a conventional negative electrode active layer, the region adjacent to the negative electrode tab exhibits a higher redox reaction rate than other regions due to smooth movement of electrons and lithium ions during charging and discharging of a lithium secondary battery. This phenomenon promotes degradation of the region adjacent to the negative electrode tab, resulting in a decrease in capacity of the region, and thus, there is a problem in that lithium plating is induced at the end of the negative electrode active layer adjacent to the negative electrode tab. However, the present invention can improve this by making the L* deviation between the first region (12a) and the second region (12b) constituting the negative electrode active layer (12) increase as it approaches the negative electrode tab (13).

[0107] Specifically, as described above, a low L* means that the ab-axis crystal plane of the carbon-based negative electrode active material is aligned and / or oriented at a high angle with respect to the negative electrode current collector. This can improve the diffusion performance of lithium ions during charging of a lithium secondary battery. Accordingly, since the degradation of the negative electrode active layer region adjacent to the negative electrode tab, which is induced as the charging and discharging of the lithium secondary battery progresses, can be improved, the effect of suppressing lithium plating can be implemented. At this time, the tendency of the deviation (△L*) between the average L* of the first region (12a) and the average L* of the second region (12b) to increase can exhibit an increase of about 0.1 to 0.5.

[0108] Meanwhile, the first region (12a) and the second region (12b) may have a predetermined length ratio with respect to the entire length in the width direction (i.e., y-axis direction) of the negative electrode active layer (12). Since the first region (12a) and the second region (12b) align and / or orient the ab-axis crystal planes of the carbon-based negative electrode active material but to different degrees, their length ratios may affect the performance of the negative electrode active layer. Accordingly, in the present invention, the length ratios of the first region (12a) and the second region in the width direction (y-axis direction) of the negative electrode active layer may be adjusted to satisfy a predetermined range.

[0109] Specifically, the ratio (D1:D2) of the average width (D1) of the first region and the average width (D2) of the second region can satisfy a range of 0.4:1 to 1:1. More specifically, the ratio (D1:D2) of the average width (D1) of the first region and the average width (D2) of the second region can satisfy a range of 0.6:1 to 1:1, 0.8:1 to 1:1, 0.9:1 to 1:1, 0.6:1 to 0.8:1, 0.7:1 to 0.9:1, or 0.6:1 to 0.75:1.

[0110] For example, the first region (12a) and the second region (12b) may have the same length ratio in the width direction (i.e., y-axis direction) of the negative electrode active layer (12), as shown in (a) of FIG. 5 (i.e., W1=W2, D1:D2=1:1). In this case, the negative electrode active layer (12) can effectively lower the interfacial resistance with the negative electrode current collector (11) while suppressing the swelling phenomenon during charging of the lithium secondary battery, thereby significantly improving the life characteristics of the negative electrode.

[0111] In addition, as shown in (b) of FIG. 5, the length ratio of the first region (12a) in the width direction (i.e., y-axis direction) of the negative electrode active layer (12) may be longer than that of the second region (12b) (i.e., W1>W2, D1:D2=1:0.40~0.99). In this case, the negative electrode active layer (12) has the advantage of being able to significantly increase the charging speed when charging a lithium secondary battery and at the same time, maintaining firm adhesion with the negative electrode current collector.

[0112] Meanwhile, the above-described negative electrode active layer may optionally further include a silicon-based negative electrode active material, a conductive material, a binder, other additives, etc., as needed, in addition to the carbon-based negative electrode active material as the main component.

[0113] The above silicon-based negative electrode active material is a material containing silicon (Si) as a main component, and can increase the charge / discharge capacity of the negative electrode. Examples of such silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), silicon dioxide (SiO2), etc., and these may be included alone or in combination in the negative electrode active layer. When silicon monoxide (SiO2) and silicon dioxide (SiO2) are uniformly mixed or composited and included in the negative electrode active layer as the silicon-based negative electrode active materials, they are silicon oxide (SiO q , but can be expressed as 0.8≤q≤2.5).

[0114] The above silicon-based negative electrode active material may be doped with Li, Mg, Al, Ca, Ti, etc. or may form an alloy. In addition, if the silicon-based negative electrode active material contains oxygen element (O), the surface may be treated with a carbon coating layer or the like for the purpose of suppressing volume expansion during charging and improving the electrical conductivity of the negative electrode active material.

[0115] The silicon-based negative electrode active material may be included in an amount of 0.1 to 40 wt% based on the total weight of the negative electrode active layer. Specifically, the silicon-based negative electrode active material may be included in an amount of 0.5 to 20 wt%, 1 to 9 wt%, 5 to 15 wt%, 3 to 7 wt%, 11 to 19 wt%, 13 to 17 wt%, 15 to 20 wt%, 10 to 30 wt%, 20 to 40 wt%, 25 to 35 wt%, 15 to 25 wt%, or 9 to 22 wt% based on the total weight of the negative electrode active layer. The present invention can reduce lithium consumption and irreversible capacity loss during initial charge and discharge of a secondary battery by controlling the content ratio of the silicon-based negative electrode active material within the above range, while improving the charge capacity per unit mass. In addition, the structural stability of the negative electrode active layer can be improved by minimizing the change in volume of the negative electrode active layer during charging and discharging of the secondary battery, thereby increasing the lifespan of the secondary battery.

[0116] The above-mentioned challenge material may include one or more of carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0117] For example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0118] The content of the conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of the negative electrode active layer. Specifically, the conductive material may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight. The present invention can prevent the resistance of the negative electrode from increasing due to a low content of the conductive material and thus reducing the charging capacity by controlling the content of the conductive material within the above range, thereby preventing the problem of the charging capacity from decreasing due to a low content of the conductive material or the problem of the electrical resistance from increasing due to an increase in the loading amount of the negative electrode active layer.

[0119] In addition, the above binder is a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and can be appropriately applied within a range that does not deteriorate the electrical properties of the negative electrode. For example, the binder may include at least one of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluoroelastomer.

[0120] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of the negative electrode active layer. Specifically, the binder may be 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. The present invention can prevent the adhesive strength of the active layer from being lowered due to a low content of binder or the electrical properties of the negative electrode from being lowered due to an excessive amount of binder by controlling the content of the binder contained in the negative electrode active layer within the above range.

[0121] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be made of copper, stainless steel, nickel, titanium, calcined carbon, etc. If the negative electrode current collector is made of copper or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector may be appropriately applied from 1 ㎛ to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0122]

[0123] The anode for a lithium secondary battery according to the present invention has the above-described configuration, thereby exhibiting excellent adhesion between the anode current collector and the anode active layer. Furthermore, the anode not only exhibits improved swelling during charging, but also exhibits excellent rapid charging performance.

[0124]

[0125] lithium secondary battery

[0126] In addition, the present invention,

[0127] A lithium secondary battery is provided, comprising an electrode assembly including a positive electrode, a negative electrode of the present invention described above, and a separator disposed between the positive electrode and the negative electrode.

[0128]

[0129] A lithium secondary battery according to the present invention comprises an electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately arranged and a separator is positioned between them. The lithium secondary battery, equipped with the negative electrode of the present invention described above, not only improves lithium ion diffusion capacity and minimizes increases in electrical resistance due to high loading / high density, but also has the advantages of excellent life characteristics and safety while implementing high output characteristics.

[0130] At this time, since the cathode has the same configuration as the configuration described above, a detailed description is omitted.

[0131] In addition, the positive electrode includes a positive electrode active layer including a positive electrode active material on a positive electrode current collector. The positive electrode active layer may optionally further include a conductive material, a binder, other additives, etc., as needed.

[0132] The above cathode active material is a material capable of causing an electrochemical reaction on the cathode current collector, and may include at least one lithium metal oxide represented by the following chemical formulas 1 and 2, which is capable of reversibly intercalating and deintercalating lithium ions:

[0133] [Chemical Formula 1]

[0134] Li l [Ni m Co n Mn w M 1 v ]O2

[0135] [Chemical Formula 2]

[0136] LiM 2 p Mn q P r O4

[0137] In the above chemical formulas 1 and 2,

[0138] M 1is at least one element among 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,

[0139] l, m, n, w and v are 1.0≤l≤1.30, 0.5≤m<1, 0, respectively. <n≤0.3, 0<w≤0.3, 0≤v≤0.1이되, m+n+w+v=1이고,

[0140] M 2 is Ni, Co or Fe,

[0141] p is 0.05≤p≤1.0,

[0142] q is 2-p,

[0143] r is either 0 or 1.

[0144]

[0145] The lithium metal oxides represented by the above chemical formulas 1 and 2 are substances containing high contents of nickel (Ni) and manganese (Mn), respectively, and when used as a cathode active material, they have the advantage of being able to stably supply electricity at a high capacity and / or high voltage compared to cathode active materials such as iron phosphate (LiFeO4) that are conventionally used.

[0146] At this time, the lithium metal oxide represented by the 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 Al0.1 It may include 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 It may include O4, etc., and these may be used alone or in combination.

[0147] In addition, the positive electrode active material may be included in an amount of 85 parts by weight or more based on 100 parts by weight of the entire positive electrode active layer. Specifically, the positive electrode active material may be included in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more based on 100 parts by weight of the entire positive electrode active layer.

[0148] The conductive material is used to improve the electrical performance of the anode, and can be applied as commonly used in the art. Specifically, the conductive material can include one or more 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.

[0149] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the positive electrode active layer. Specifically, the conductive material may be included in an amount of 0.1 to 4 parts by weight; 2 to 4 parts by weight; 1.5 to 5 parts by weight; 1 to 3 parts by weight; 0.1 to 2 parts by weight; or 0.1 to 1 part by weight based on 100 parts by weight of each positive electrode active layer.

[0150] The above binder serves to bind the positive electrode active material, positive electrode additive, and conductive material to each other, and any binder having this function may be used without particular limitation. Specifically, the binder may include at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

[0151] Additionally, the binder may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the positive electrode active layer. Specifically, the binder may be included in an amount of 2 to 8 parts by weight based on 100 parts by weight of the positive electrode active layer; or in an amount of 1 to 5 parts by weight based on 100 parts by weight of the positive electrode active layer.

[0152] The total thickness of the above-mentioned positive electrode active layer is not particularly limited, but may be specifically 50 µm to 300 µm, and 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.

[0153] The positive electrode can be a positive electrode current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used. In the case of aluminum or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the current collector can be appropriately applied in the range of 3 µm to 500 µm, taking into account the conductivity and total thickness of the positive electrode being manufactured.

[0154] The above-mentioned separator 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, the separator may be one comprising at least one polymer selected from the group consisting of chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymers. The separator may have a porous polymer substrate form, such as a sheet or non-woven fabric comprising the above-mentioned polymer. In some cases, the separator may have a composite separator form in which organic or inorganic particles are coated on the porous polymer substrate using an organic binder. In addition, 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.

[0155] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery in a form that may include a stacked, zigzag, or zigzag-stacked electrode assembly. For example, the lithium secondary battery according to the present invention may be a pouch-type secondary battery or a square-shaped secondary battery.

[0156] Pouch-type secondary batteries and / or square secondary batteries have the advantage of high utilization in terms of energy density because the unit cells of the secondary batteries can be packed at a high density in a limited space.

[0157]

[0158] Method for manufacturing a negative electrode for a lithium secondary battery

[0159] Furthermore, the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery according to the present invention described above.

[0160]

[0161] Specifically, the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention includes a step (S1) of applying a negative electrode slurry containing a carbon-based negative electrode active material to at least one surface of a negative electrode current collector, a step (S2) of applying a magnetic field to the applied negative electrode slurry, and a step (S3) of drying the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer.

[0162] At this time, the above step (S1) refers to a process of coating at least one surface of a moving negative electrode current collector by discharging a negative electrode slurry containing a carbon-based negative electrode active material.

[0163] This step (S1) can be applied without any particular limitation as long as it is a method commonly applied in the art, but preferably, a die coating method can be used. The die coating method can be performed using a slot die equipped with a shim for controlling the discharge conditions of the negative electrode slurry. The slot die can easily control the loading amount, coating thickness, etc. of the negative electrode slurry applied on the negative electrode current collector by controlling the shape, position, etc. of the shim.

[0164] The above-mentioned negative electrode slurry contains a carbon-based negative electrode active material as a main component and may further contain a conductive material and a binder. Since each component contained in the above-mentioned negative electrode slurry is the same as the negative electrode active layer of the negative electrode for a lithium secondary battery, a detailed description thereof will be omitted.

[0165] Additionally, the cathode slurry may have a predetermined viscosity at room temperature.

[0166] "Viscosity" refers to the magnitude of physical and / or chemical interactions, such as friction and resistance, between each raw material (e.g., carbon-based negative electrode active material, additives, etc.) present in the negative electrode slurry. This interaction increases as the concentration of the raw material increases, even if the mole number and / or weight of the raw material is the same. When a magnetic field is applied to a negative electrode slurry with high viscosity, the orientation of the carbon-based negative electrode active material contained therein decreases, making it difficult to implement a high inclination with respect to the negative electrode current collector. Therefore, the viscosity at room temperature can be controlled so that the ab-axis crystal plane of the carbon-based negative electrode active material is easily aligned and / or oriented with respect to the negative electrode current collector.

[0167] Specifically, the cathode slurry may have a viscosity of less than 10,000 cps at room temperature (22±3°C). Specifically, the viscosity of the cathode slurry may be in a range of 1,000 cps to 9,000 cps; 3,000 cps to 8,000 cps; 3,000 cps to 7,000 cps; 5,000 cps to 7,000 cps; 4,000 cps to 6,500 cps; 5,000 cps to 6,500 cps; 3,000 cps to 5,500 cps; 5,500 cps to 6,500 cps; or 4,000 cps to 6,500 cps at room temperature (22±3°C).

[0168] Next, the above step (S2) means a process of applying a magnetic field to the negative electrode slurry to align and / or orient the ab-axis crystal plane of the carbon-based negative electrode active material included in the negative electrode slurry.

[0169] At this time, the degree to which the ab-axis crystal planes of the carbon-based anode active material included in the anode slurry are aligned and / or oriented may vary depending on the strength of the applied magnetic field. Therefore, in order to implement the first region and the second region of the anode active layer in which the ab-axis crystal planes of the carbon-based anode active material are aligned and / or oriented with respect to the anode current collector to different degrees, the magnetic field conditions applied to the regions of the anode slurry corresponding to the first region and the second region may be differently controlled.

[0170] Specifically, the present step (S2) can be performed by setting an A region corresponding to a first region of the negative electrode active layer and a B region corresponding to a second region of the negative electrode active layer on the surface of the negative electrode slurry applied to the negative electrode current collector. Thereafter, a magnetic field can be applied to the A region of the set negative electrode slurry, and a magnetic field can be applied to the B region of the negative electrode slurry without applying a magnetic field or by applying a magnetic field weaker than the magnetic field applied to the A region.

[0171] Here, the magnetic field applied to the A region of the negative electrode slurry may have a strength of 1,000 G to 9,000 G (Gauss) to enhance the effect of aligning and / or orienting the ab-axis crystal plane of the carbon-based negative electrode active material. Specifically, the magnetic field applied to the A region of the negative electrode slurry is 1,000 G to 8,000 G; 2,000 G to 8,000 G; 3,000 G to 8,000 G; 5,000 G to 9,000 G; 5,000 G to 7,5000 G; 5,500 G to 6,5000 G; 1,000 G to 7,000 G; 2,000 G to 6,000 G; 1,500 G to 5,000 G; The magnetic field can be applied with a strength in the range of 1,500 G to 4,500 G; 4,000 G to 8,000 G; 4,500 G to 7,000 G; 3,000 G to 6,500 G; or 3,500 G to 6,500 G.

[0172] In addition, when a magnetic field is applied to the B region of the cathode slurry, the magnetic field applied to the B region of the cathode slurry may be applied with a strength in the range of 5,000 G or less, 4,500 G or less, 500 G to 5,000 G, 1,000 G to 4,500 G, 1,500 G to 4,500 G, 1,500 G to 3,000 G, 3,000 G to 5,000 G, 2,000 G to 4,000 G, or 3,600 G to 4,300 G.

[0173] At this time, the B region of the cathode slurry may be applied with a magnetic field of 0.1% to 0.9% of the magnetic field strength applied to the A region. Specifically, the magnetic field applied to the B region of the cathode slurry may be applied with a strength in the range of 0.1% to 0.7%; 0.1% to 0.5%; 0.1% to 0.3%; 0.5% to 0.9%; 0.7% to 0.9%; 0.3% to 0.5%; or 0.4% to 0.6% of the magnetic field strength applied to the A region.

[0174] The present invention can implement an L* deviation according to the CIE Lab chromaticity system effective for the first region and the second region of the cathode active layer by controlling the strength of the magnetic field applied to the A region and the B region of the cathode slurry as described above.

[0175] Meanwhile, the present step (S2) can be performed by installing a magnet in the path along which the negative electrode slurry applied on the negative electrode collector moves and applying a magnetic field to the negative electrode slurry. At this time, the magnet can be placed below the negative electrode slurry applied on the negative electrode collector (i.e., below the negative electrode collector). When the magnet is placed both above and below the negative electrode slurry, the ab-axis crystal plane of the carbon-based negative electrode active material included in the negative electrode slurry can be aligned and / or oriented at an angle close to 90° with respect to the negative electrode collector. However, in this case, since the magnetic field is uniformly applied to the entire surface of the negative electrode slurry, it is difficult to induce a deviation in the alignment and / or orientation of the carbon-based negative electrode active material in each region even if the strength of the magnetic field is adjusted differently in each region. Therefore, it is preferable that the magnet for applying the magnetic field be positioned in the path along which the negative electrode slurry moves, but placed below the negative electrode slurry.

[0176] In addition, when a magnetic field is applied to the A region of the cathode slurry and no magnetic field is applied to the B region, i) a magnet may be placed only at a point corresponding to the A region of the cathode slurry, or ii) one magnet may be placed in the width direction of the cathode slurry (in the same direction as the width direction of the cathode active layer (y-axis direction)), but a magnetic field shielding member or the like may be introduced at a point corresponding to the B region to block the magnetic field.

[0177] Furthermore, when applying a magnetic field to both the A region and the B region of the cathode slurry, i) a unit magnet is placed in each region and the magnetic field strength of the unit magnet is controlled, or ii) one magnet is placed in the width direction of the cathode slurry (in the same direction as the width direction of the cathode active layer (y-axis direction)) and the thickness, length, shape, etc. of the magnet are controlled so that the strength of the magnetic field implemented in each region can be controlled.

[0178] Next, the above step (S3) refers to a process of forming a cathode active layer by drying the cathode slurry to which a magnetic field is applied.

[0179] The above drying can be applied without particular limitations as long as it is a method that can be commonly applied in the art. For example, the above drying can be performed by applying heat energy to the cathode slurry using a hot air dryer, a vacuum oven, or the like, thereby drying the cathode slurry.

[0180] Meanwhile, the method for manufacturing a cathode according to the present invention may further include a step of rolling the cathode active layer formed by drying. The rolling refers to a process of increasing the density of the entire cathode active layer by applying pressure to the surface of the formed cathode active layer using a roll press or the like. To this end, the rolling may be performed under predetermined pressure and speed conditions at a temperature higher than room temperature.

[0181] Specifically, the rolling may be performed at a temperature in the range of 20°C to 100°C. More specifically, the rolling may be performed at a temperature in the range of 20°C to 80°C; 20°C to 60°C; 20°C to 40°C; 20°C to 30°C; 30°C to 100°C; 40°C to 100°C; 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.

[0182] Additionally, the rolling can be performed at a rolling speed in the range of 2 m / s to 7 m / s. More specifically, the rolling can be performed at a rolling speed in the range 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.

[0183] In addition, the rolling can be performed under pressure conditions in the range of 50 MPa to 200 MPa, and specifically, can be performed under pressure conditions in the range 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.

[0184] The present invention can maximize the energy density of the negative electrode active layer while minimizing damage to the negative electrode active layer formed by performing rolling under the above-mentioned temperature, speed and / or pressure conditions.

[0185]

[0186] Hereinafter, the present invention will be described in more detail through examples and comparative examples.

[0187] However, the following examples and comparative examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and comparative examples.

[0188]

[0189] Examples 1 to 5 and Comparative Examples 1 to 3. Preparation of negative electrode for lithium secondary battery

[0190] Natural graphite (average particle diameter (D 50 ): about 11~13㎛) and artificial graphite (average particle diameter (D 50 ): approximately 15~16㎛) were prepared as the first carbon-based negative electrode active material and the second carbon-based negative electrode active material. In addition, styrene butadiene rubber (SBR) was prepared as a binder, carboxymethyl cellulose (CMC) was prepared as a thickener, and carbon black (Super-P) was prepared as a conductive material.

[0191] Then, as shown in Table 1 below, ① a carbon-based negative electrode active material was prepared, and 97 wt% of the carbon-based negative electrode active material, 1.05 wt% of carboxymethyl cellulose (CMC), 1.45 wt% of styrene butadiene rubber (SBR), and 0.5 wt% of carbon black were mixed with water to obtain a solid content of 50% to prepare a negative electrode slurry. At this time, the viscosity of the prepared negative electrode slurry at room temperature (22±3℃) was 5,000±100 cps.

[0192] The prepared cathode slurry was applied (S1) onto a copper foil (thickness: 6 μm) being transported roll-to-roll (transport speed: 6 m / min) using a die coater. Thereafter, a magnetic field was applied to the applied cathode slurry using a magnet for 2 to 9 seconds (S2).

[0193] Magnets were installed so that six A regions and four B regions were alternately arranged between the first side where the negative tabs were to be formed and the third side facing it on the surface of the negative electrode slurry applied to the copper foil. At this time, ② the position of the magnets for applying a magnetic field; ③ the length ratio of the A regions and the B regions with respect to the entire length of the negative electrode slurry; and ④ the strength of the magnetic field applied to the A regions and the B regions of the negative electrode slurry were controlled as shown in Table 1 below.

[0194] A negative electrode slurry to which a magnetic field was applied was dried with hot air to form a negative electrode active layer on a negative electrode current collector. The formed negative electrode active layer was rolled at 50±1°C under a pressure of 100 to 150 MPa and a conveying speed of 3 m / s to manufacture a negative electrode for a lithium secondary battery (average thickness of the negative electrode active layer: approximately 90±5 μm).

[0195] ① Weight ratio in carbon-based negative electrode active material ② Position of reference magnet in negative electrode slurry ③ Length ratio ④ Magnetic field strength Natural graphite Artificial graphite A area B area A area B area Comparative example 150 Weight % 50 Weight % Not installed 10% 10% 0G 0G Comparative example 250 Weight % 50 Weight % Top and bottom 10% 10% 4,000G 2,000G Comparative example 350 Weight % 50 Weight % Bottom 10% 10% 4,000G 4,000G Example 1100 Weight % 0 Weight % Bottom 10% 10% 4,000G 2,000G Example 250 Weight % 50 Weight % Bottom 10% 10% 4,000G 2,000G Example 350 Weight % 50 Weight % Bottom 13% 5.5% 4,000G 2,000G Example 450 Weight % 50 Weight % Bottom 10% 10% 4,000G 0G Example 550 Weight % 50 Weight % Bottom 10% 10% 6,000G 2,000G

[0196]

[0197] Examples 6 to 10 and Comparative Examples 4 to 6. Manufacturing of lithium secondary batteries

[0198] LiNi with a particle size of 5㎛ as a cathode active material 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 was prepared, and polyvinylidene fluoride as a carbon-based conductive agent and binder and N-methyl pyrrolidone (NMP) were mixed in a weight ratio of 94:3:3 to form a slurry, which was cast on an aluminum sheet, dried in a vacuum oven at 120°C, and then rolled to manufacture a cathode.

[0199] A separator made of 18 μm polypropylene was interposed between the positive electrode obtained above and the negative electrode manufactured in Examples 1 to 5 and Comparative Examples 1 to 3, respectively, and inserted into a case, and then an electrolyte composition was injected to assemble a 1 Ah-class lithium secondary battery.

[0200] At this time, the types of negative electrodes applied to each lithium secondary battery are shown in Table 2 below.

[0201] Type of applied cathode Example 6 The cathode manufactured in Example 1 Example 7 The cathode manufactured in Example 2 Example 8 The cathode manufactured in Example 3 Example 9 The cathode manufactured in Example 4 Example 10 The cathode manufactured in Example 5 Comparative Example 4 The cathode manufactured in Comparative Example 1 Comparative Example 5 The cathode manufactured in Comparative Example 2 Comparative Example 6 The cathode manufactured in Comparative Example 3

[0202]

[0203] Experimental example.

[0204] In order to evaluate the properties and performance of the cathode manufactured according to the present invention, the following experiments were conducted.

[0205]

[0206] 1) Color coordinate measurement according to the CIE LAB colorimeter

[0207] For the cathodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 3, a first region and a second region were identified in the width direction based on the cross-section in the thickness direction of the cathode active layer, and the color coordinates for three arbitrary points in each region were measured according to a CIE LAB colorimeter. At this time, the color coordinates were measured using a non-contact CIE LAB colorimeter, and the average value for L* indicating brightness among the values ​​of the three measured points was calculated to obtain the L* of each region and the deviation between the regions (△L*). The results are shown in Table 3 below.

[0208]

[0209] 2) Interfacial resistance (MP) between the negative active layer and the negative current collector R ) measurement

[0210] The interfacial resistance between the negative electrode active layer and the negative electrode current collector was measured for the negative electrodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 3. The interfacial resistance was measured using an XF057 electrode resistance measuring device from Hioki Co., Ltd. at 22±2°C and a relative humidity of 50±5%, with a measurement current of 100 uA or 1 mA; and a measurement voltage of 1 V or 10 V.

[0211]

[0212] 3) Curvature and pore resistance (R) of the cathode active layer pore ) measurement

[0213] A symmetric coin cell was fabricated using the negative electrodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 3, with the same working electrode and counter electrode applied. At this time, the electrolyte used was a mixture of 1.0 M LiPF6 lithium salt in an organic solvent (EC:EMC = 1:4 Vol%).

[0214] After that, impedance spectroscopy (frequency range from 500 KHz to 100 mHz) was performed on the fabricated symmetric electrode. The results measured through the impedance spectroscopy were expressed as a Nyquist plot, and then the tortuosity and pore resistance (R) were analyzed through data interpretation. pore ) was calculated.

[0215] In addition, the interfacial resistance value (MP) between the previously measured negative electrode active layer and negative electrode current collector R ) and pore resistance (R pore ) from their ratio (MP R / R pore ) was produced. The results are shown in Table 3 below.

[0216] L*△L*Interface resistance[Ωm·㎠]Curvature[%]Pore resistance[Ω]MP R / R pore [㎡] Area 1 Area 2 Comparative Example 149.549.90.42.7255.703.270.0833 Comparative Example 241.141.20.14.4054.092.240.1966 Exemplary Example 145.045.60.62.8674.243.080.0930 Exemplary Example 244.845.30.53.8334.252.450.1564 Exemplary Example 344.845.30.54.0114.192.380.1685 Exemplary Example 444.245.00.84.0024.412.590.1545 Exemplary Example 544.144.90.83.9754.292.300.1728

[0217]

[0218] As shown in Table 3 above, it can be seen that the negative electrode according to the present invention has excellent interfacial properties between the negative electrode active layer and the negative electrode current collector, and excellent bending rate and pore resistance within the negative electrode active layer.

[0219] Specifically, it was confirmed that the negative electrode manufactured in the examples formed a pattern on the surface by controlling the magnetic field applied to the A and B regions at the bottom of the moving negative electrode slurry, thereby implementing the L* deviation of the first and second regions, which are distinguished in the width direction based on the cross-section in the thickness direction of the negative electrode active layer. In addition, it was confirmed that the negative electrode manufactured in the examples had a tendency for the L* deviation of the first and second regions to be larger as they approached the negative electrode tab.

[0220] In addition, the negative electrode manufactured in the example had a low interface resistance of 4.4 Ωm·㎠ or less between the negative electrode active layer and the negative electrode current collector, indicating that the area of ​​contact between the negative electrode active layer and the negative electrode current collector at the interface was high.

[0221] Furthermore, the cathode manufactured in the example not only has a low curvature of the cathode active layer of 5.0% or less, but also has a low pore resistance (R pore ) was found to be low, below 3.1 Ω.

[0222]

[0223] From these results, the negative electrode manufactured according to the present invention has a pattern structure in which first and second regions having a predetermined deviation in L* of the CIE Lab chromaticity scale in the width direction relative to the thickness direction cross-section of the negative electrode active layer are alternately arranged, thereby exhibiting excellent adhesion between the negative electrode current collector and the negative electrode active layer. In addition, the negative electrode has the advantage of not only improving the swelling phenomenon during charging but also excellent rapid charging performance.

[0224]

[0225] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that the present invention can be variously modified and changed within a scope that does not depart from the technical features of the present invention described in the claims to be described later.

[0226] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the patent claims.

Claims

1. A negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector and including a carbon-based negative electrode active material, The surface of the above cathode active layer is a cathode including a first region and a second region having △L* of 0.45 or more, represented by the following formula 1 based on L* according to the CIE LAB colorimeter, and arranged alternately at least once: [Formula 1] △L*= ┃L1*-L2*┃ In the above equation 1, L1* means the average L* value of the first region above, L2* refers to the average L* value of the second region.

2. In paragraph 1, The average L1* value of the first region is in the range of 35 to 48, The average L2* value of the second region is in the range of 36 to 50.

3. In paragraph 1, A cathode in which the first region and the second region formed on the surface of the above cathode active layer form at least one pattern among a stripe pattern, a concentric circle pattern, a check pattern, and a dot pattern.

4. In paragraph 1, The above cathode has a rectangular shape, and has a structure in which a cathode tab is formed on the first side of the rectangular shape. A cathode including a form in which a first region and a second region are alternately arranged at least once on the surface of a cathode active layer between the first region and the third region facing the first region.

5. In paragraph 1, The above cathode has a rectangular shape, and has a structure in which a cathode tab is formed on the first side of the rectangular shape. A cathode including a form in which a first region and a second region are alternately arranged at least once on the surface of a cathode active layer between the first region and the adjacent second region and the fourth region.

6. In paragraph 1, A cathode having a ratio (D1:D2) of the average width (D1) of the first region and the average width (D2) of the second region in the range of 0.4:1 to 1:

1.

7. In paragraph 1, The above carbon-based negative electrode active material is a negative electrode including at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

8. In paragraph 1, The above cathode active layer is made of Si, SiC and SiO. q (However, 0.5≤q≤2.5) A negative electrode containing at least one silicon-based negative electrode active material.

9. In paragraph 1, A cathode having an interface resistance between the cathode current collector and the cathode active layer in the range of 0.1 mΩ·㎡ to 8.0 mΩ·㎡.

10. In paragraph 1, The above cathode active layer is a cathode having a tortuosity in the range of 2.0% to 8.0%.

11. A step of applying a negative electrode slurry containing a carbon-based negative electrode active material to at least one surface of a negative electrode current collector; A step of applying a magnetic field to the applied cathode slurry, and A step of drying a cathode slurry to which a magnetic field is applied to form a cathode active layer; In the step of applying the above magnetic field, A magnetic field of an average range of 1,000 G to 9,000 G is applied to the negative slurry A region corresponding to the first region, A method for manufacturing a cathode in which no magnetic field is applied to the cathode slurry B region corresponding to the second region, or a magnetic field of 5,000 G or less is applied.

12. In paragraph 11, In the step of applying the above magnetic field, When a magnetic field is applied to the above cathode slurry B region, A method for manufacturing a cathode, wherein the strength of the magnetic field applied to the cathode slurry B region is in the range of 0.1% to 0.9% of the strength of the magnetic field applied to the cathode slurry A region.

13. In paragraph 11, In the step of applying the above magnetic field, A method for manufacturing a cathode, characterized in that the magnetic field is applied from below the cathode in a bottom application manner.

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