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

Abstract

The present disclosure relates to a negative electrode for a lithium secondary battery and a manufacturing method thereof. The negative electrode has a pattern structure in which first regions having a predetermined deviation in L * values of a CIE LAB color difference meter and second regions are alternately disposed on a surface of a negative electrode active layer, whereby the negative electrode current collector has excellent adhesion with the negative electrode active layer. In addition, the negative electrode has the advantage of not only improved swelling phenomenon during charging but also excellent rapid charging performance.

Description

Technical Field

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0097451, filed on July 23, 2024, the entire contents of which are incorporated herein by reference. Background Technology

[0003] In recent years, lithium-ion batteries have been widely used not only in small devices, such as portable electronic devices, but also in medium and large devices, such as battery packs for hybrid or electric vehicles, and in energy storage devices. In particular, with the recent increase in attention to environmental issues, the demand base for high-capacity batteries is expanding due to the growing market for devices using high-capacity batteries, such as electric vehicles and hybrid electric vehicles, which can replace vehicles using fossil fuels, such as gasoline and diesel vehicles, which are one of the main causes of air pollution.

[0004] Typically, lithium-ion batteries are rechargeable and dischargeable power generation devices with a stacked structure of positive / separator / negative electrodes. When a lithium-ion battery is charged, a lithium deintercalation reaction is induced (where lithium contained in the positive electrode active material is oxidized and released at the positive electrode inside the battery), and a lithium insertion reaction occurs (where lithium is reduced and enters the negative electrode active material at the negative electrode). Because the deintercalation reaction in the positive electrode active material is faster than the insertion reaction in the negative electrode active material, the performance (such as speed) of a lithium-ion battery during charging and discharging is primarily determined by the negative electrode.

[0005] Materials including graphite are widely used as negative electrode active materials. Graphite-containing materials exhibit an average lithium discharge potential of approximately 0.2 V (based on Li / Li⁺) and a relatively flat discharge potential. For this reason, when graphite is used as the negative electrode active material, the secondary battery has the advantage of high and constant voltage.

[0006] Amorphous or crystalline carbon is used as the negative electrode active material in anode applications. Crystalline carbon is primarily used due to its high capacity. This crystalline carbon includes graphite-based carbon, such as natural graphite and synthetic graphite.

[0007] Graphite-based carbon exhibits different properties depending on its type. For example, natural graphite is inexpensive and exhibits excellent adhesion to current collectors, but it is relatively inferior to synthetic graphite in terms of high-rate charge / discharge performance or lifetime characteristics. On the other hand, synthetic graphite has weak adhesion to current collectors due to surface defects or low functional group content. Furthermore, when propylene carbonate (PC) is used in the electrolyte for the purpose of improving low-temperature performance, synthetic graphite presents the following problem: propylene carbonate causes exfoliation of the layers that make up the graphite interlayer structure.

[0008] Therefore, hybrid graphite has been explored as a negative electrode active material for lithium-ion batteries, appropriately combining the advantages of both natural and artificial graphite. However, hybrid graphite has the following limitations: due to its low adhesion to the current collector, it exhibits poor lifetime characteristics and shock resistance. Furthermore, when increasing the content of the negative electrode active material for high-capacity electrode design, the expansion caused by lithium insertion into the graphite during lithium-ion battery charging not only reduces energy density but also degrades lifetime characteristics.

[0009] Therefore, there is a great need for a negative electrode technology that has excellent lifespan characteristics due to its high adhesion to the current collector and improved expansion during lithium secondary battery charging, while also having a fast charging speed.

[0010] [Existing Technical Documents]

[0011] Korean Patent Publication No. 10-2018-0028797

[0012] Korean Patent Grant Announcement No. 10-2022-0057715 Summary of the Invention

[0013] Technical issues

[0014] The purpose of this disclosure is to provide a negative electrode and a method for manufacturing the negative electrode, which has excellent lifetime characteristics (due to excellent adhesion to the current collector), fast charging speed, and improves the swelling phenomenon during the charging of lithium secondary batteries.

[0015] Technical solution

[0016] This disclosure provides a negative electrode, comprising:

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

[0018] The surface of the negative electrode active layer includes the following forms: (based on L according to CIE LAB colorimeter)* Based on this, ΔL, expressed by Equation 1, is 0.45 or greater. * The first and second regions are alternately set once or multiple times;

[0019] [Formula 1]

[0020] ΔL * =|L1 * -L2 * |

[0021] In Equation 1,

[0022] L1 * L represents the average value of the first region. * Value, and

[0023] L2 * L represents the average value of the second region. * value.

[0024] At this point, the average L1 of the first region * The value can range from 35 to 48, and the average L2 in the second region is... * The value can be in the range of 36 to 50.

[0025] The first and second regions formed on the surface of the negative electrode active layer can be formed with any one or more patterns selected from stripe patterns, concentric circle patterns, checkerboard patterns and dot patterns.

[0026] Furthermore, the negative electrode can have a rectangular shape and a structure in which a negative electrode contact is formed on the first side of the rectangular shape. Between the first side and the third side facing the first side, the surface of the negative electrode active layer can include the following form: the first region and the second region are alternately arranged once or multiple times.

[0027] Alternatively, the negative electrode may have a rectangular shape and may have a structure in which a negative electrode contact is formed on a first side of the rectangular shape, and between the second and fourth sides adjacent to the first side, the surface of the negative electrode active layer may include the following form: the first region and the second region are alternately arranged once or multiple times.

[0028] The ratio (D1:D2) of the average width of the first region (D1) to the average width of the second region (D2) can be in the range of 0.4:1 to 1:1.

[0029] Carbon-based anode active materials may include one or more of the following: natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase sintered carbon made from pitch or tar as raw materials, and graphitized coke.

[0030] The negative electrode active layer may contain materials selected from Si, SiC, and SiO. q One or more silicon-based anode active materials (where 0.5≤q≤2.5).

[0031] Furthermore, the interfacial resistance between the negative electrode current collector and the negative electrode active layer can be as low as 0.1 mΩ·m. 2 Up to 8.0 mΩ·m 2 Within the range.

[0032] The tortuosity of the negative electrode active layer can range from 2.0% to 8.0%.

[0033] Furthermore, this disclosure provides a method for manufacturing a negative electrode, comprising the following steps:

[0034] A negative electrode slurry containing a carbon-based negative electrode active material is applied to at least one side of the negative electrode current collector (S1);

[0035] A magnetic field (S2) is applied to the applied negative electrode slurry; and

[0036] The negative electrode slurry, to which a magnetic field has been applied, is dried to form a negative electrode active layer (S3);

[0037] In the step of applying the magnetic field (S2),

[0038] A magnetic field with an average value in the range of 1,000 G to 9,000 G is applied to region A of the negative electrode slurry corresponding to the first region of the aforementioned negative electrode active layer; and

[0039] No magnetic field is applied to region B of the negative electrode slurry corresponding to the second region, or a magnetic field of 5,000 G or less is applied.

[0040] In the step of applying the magnetic field (S2), the magnetic field strength applied to region B of the negative electrode slurry can be 0.1% to 0.9% of the magnetic field strength applied to region A.

[0041] Furthermore, in the step of applying the magnetic field (S2), the magnetic field can be applied by applying the magnetic field from the lower part of the negative pole.

[0042] Beneficial effects

[0043] The negative electrode for a lithium secondary battery according to this disclosure has a patterned structure in which a first region and a second region are alternately disposed on the surface of the negative electrode active layer, wherein the first region and the second region have an L-type colorimeter of a CIE LAB colorimeter. * The predetermined deviation is eliminated, resulting in excellent adhesion between the negative electrode current collector and the negative electrode active layer. Furthermore, the negative electrode not only improves expansion during charging but also exhibits excellent fast-charging performance. Attached Figure Description

[0044] Figure 1 This is a top view showing the surface of the negative electrode according to this disclosure;

[0045] Figure 2 This is a cross-sectional view showing the cross-sectional structure of the negative electrode 10 for a lithium secondary battery according to the present disclosure in the thickness direction (z direction).

[0046] Figure 3 It is a photograph of the surface of the negative electrode manufactured according to this disclosure.

[0047] Figure 4 This is a cross-sectional view of the negative electrode, schematically showing the ab-axis crystal plane state of the carbon-based negative electrode active material depending on whether the carbon-based negative electrode active material is aligned and / or oriented.

[0048] Figure 5 This is a cross-sectional view showing the cross-sectional structure of the negative electrode 10 for a lithium secondary battery according to the present disclosure in the thickness direction (z direction). Detailed Implementation

[0049] This disclosure may have various modifications and implementations, and specific implementations will be described in detail below.

[0050] As used herein, the terms “comprise,” “include,” and “have” indicate the presence of a feature, number, step, action, component, or element, or a combination thereof, as described in the specification. It should be understood that the presence or addition of one or more other features, numbers, steps, actions, components, elements, or combinations thereof is not excluded in advance.

[0051] Furthermore, in this specification, "average particle size (D)" 50The average particle size refers to the particle size at which the cumulative value in the particle size distribution reaches 50%, and is also known as the median diameter. The average particle size can be measured by methods conventionally used in the art. For example, the average particle size can be determined using a particle size analyzer or an analyzer that utilizes laser diffraction scattering particle size distribution measurement methods, but is not limited to these methods.

[0052] In this specification, the "thickness direction of the negative electrode active layer" can be the same as the direction perpendicular to the plane formed by the combination of the width direction and the longitudinal direction of the negative electrode active layer, and can be defined as follows: Figure 1 The "z-axis direction" in the text.

[0053] Furthermore, in this specification, "color coordinates according to the CIE LAB colorimeter" refers to coordinates in the CIE color space, which are color values ​​defined by the CIE (International Commission on Illumination). Any position in the CIE color space can be determined by L... * a * and b * It is represented by three coordinate values.

[0054] Here, L * The value represents brightness, where L * =0 represents black, L * =100 represents white. Additionally, a * The value indicates whether the color with the corresponding color coordinates leans towards pure magenta or pure green, and b * The value indicates whether a color with the corresponding color coordinates leans towards pure yellow or pure blue. Specifically, based on the CIE LAB colorimeter, a color with an average luminance coordinate of 60 or less (L... * The color of a color can be defined as black, and the black can include achromatic colors such as gray and black.

[0055] This disclosure will now be described in more detail.

[0056] Anode for lithium secondary batteries

[0057] In one embodiment, this disclosure provides a negative electrode, comprising:

[0058] A negative electrode current collector; and a negative electrode active layer disposed on at least one side of the negative electrode current collector and comprising a carbon-based negative electrode active material;

[0059] The surface of the negative electrode active layer includes the following forms: (based on L according to CIE LAB colorimeter) * Based on this, ΔL, expressed by Equation 1, is 0.45 or greater. * The first and second regions are alternately set once or multiple times;

[0060] [Formula 1]

[0061] ΔL * =|L1 * -L2 * |

[0062] According to this disclosure, the negative electrode refers to a negative electrode used in lithium secondary batteries. The negative electrode includes a negative electrode active layer comprising a carbon-based negative electrode active material on at least one side of the negative electrode current collector. The negative electrode active layer has the following form: a first region and a second region are alternately disposed on the surface once or multiple times. The first region and the second region can form an L-shape according to a CIE LAB colorimeter. * The pattern with predetermined deviation.

[0063] The negative electrode has a structure in which L * The first and second regions with predetermined deviations are alternately set once or multiple times, thereby exhibiting excellent adhesion between the negative electrode current collector and the negative electrode active layer due to improved interface characteristics. Furthermore, the negative electrode has the following advantages: it not only improves the expansion phenomenon during lithium secondary battery charging, but also increases the fast charging speed by reducing the tortuosity of the negative electrode active layer, and significantly improves the expansion phenomenon caused by lithium-ion intercalation.

[0064] For example, the interfacial resistance between the negative electrode current collector and the negative electrode active layer can be reduced to 0.1 mΩ·m due to the improved interfacial properties. 2 Up to 8.0 mΩ·m 2 Within a certain range. Specifically, the interfacial resistance between the negative electrode current collector and the negative electrode active layer can be within the following range: 0.1 mΩ·m 2 Up to 7.5 mΩ·m 2 ; 0.1 mΩ·m 2 Up to 7.0 mΩ·m 2 ; 0.1 mΩ·m 2 Up to 6.5 mΩ·m 2 ; 0.1 mΩ·m 2 Up to 6.0 mΩ·m 2 ; 0.1 mΩ·m 2 Up to 5.5 mΩ·m 2 ; 0.1 mΩ·m 2 Up to 5.0 mΩ·m 2 ; 0.1 mΩ·m2 Up to 4.5 mΩ·m 2 ; 0.5 mΩ·m 2 Up to 7.5 mΩ·m 2 ; 0.5 mΩ·m 2 Up to 5.0 mΩ·m 2 ; 0.5 mΩ·m 2 Up to 4.5 mΩ·m 2 ; 4.0 mΩ·m 2 Up to 8.0 mΩ·m 2 3.0 mΩ·m 2 Up to 5.5 mΩ·m 2 2.7 mΩ·m 2 Up to 5.1 mΩ·m 2 ; 1.0 mΩ·m 2 Up to 4.35 mΩ·m 2 1.5 mΩ·m 2 Up to 4.35 mΩ·m 2 2.0 mΩ·m 2 Up to 4.35 mΩ·m 2 2.5 mΩ·m 2 Up to 4.35 mΩ·m 2 2.8 mΩ·m 2 Up to 4.35 mΩ·m 2 3.0 mΩ·m 2 Up to 4.35 mΩ·m 2 3.1 mΩ·m 2 Up to 4.3 mΩ·m 2 3.4 mΩ·m 2 Up to 4.1 mΩ·m 2 3.6 mΩ·m 2 Up to 4.35 mΩ·m 2 3.1 mΩ·m 2 Up to 4.1 mΩ·m 2 ; or 3.6 mΩ·m 2 Up to 4.0 mΩ·m 2 Interfacial resistance can represent the average value of the resistance induced between the negative electrode current collector and the negative electrode active layer. This disclosure can prevent or further improve the reduction of interfacial adhesion between the negative electrode active layer and the negative electrode current collector by ensuring that the interfacial resistance between them is within the aforementioned range.

[0065] Furthermore, the tortuosity of the negative electrode active layer can range from 2.0% to 8.0%. Specifically, the tortuosity of the negative electrode active layer can be within the following ranges: 3.0% 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 tortuosity of the negative electrode active layer is a parameter that indirectly indicates the path length provided by the pores contained within the negative electrode active layer, allowing electrolytes and the like to move from the surface of the negative electrode active layer to the negative electrode current collector. A lower tortuosity means a shorter path length. This disclosure improves the rate at which lithium ions insert into the carbon-based negative electrode active material during lithium-ion battery charging by adjusting the tortuosity of the negative electrode active layer to the aforementioned range. Therefore, this disclosure provides a negative electrode with excellent fast-charging performance.

[0066] Furthermore, the negative electrode can satisfy the following equation 1:

[0067] [Formula 1]

[0068] 0.01 m 2 ≤ MP R / R pore ≤ 0.20 m 2

[0069] In Equation 1,

[0070] MP R This represents the interfacial resistance between the negative electrode active layer and the negative electrode current collector (unit: mΩ·cm). 2 ),as well as

[0071] R pore This represents the pore resistance (unit: Ω) in the negative electrode active layer.

[0072] Specifically, the negative electrode can satisfy Equation 1 within the following range: 0.01 m 2 up to 0.19 m 2 (that is, 0.01 m) 2 ≤ MP R / R pore ≤0.19 m 2 ); 0.05 m 2 up to 0.19 m 2 (i.e., 0.05 m) 2 ≤ MP R / R pore ≤0.19 m 2 ); 0.09 m2 up to 0.19m 2 (i.e., 0.09 m) 2 ≤ MP R / R pore ≤0.19 m 2 ); 0.1 m 2 up to 0.19 m 2 (i.e., 0.1 m) 2 ≤ MP R / R pore ≤0.19m 2 ); 0.12 m 2 up to 0.19 m 2 (i.e., 0.12 m) 2 ≤ MP R / R pore ≤0.19 m 2 ); 0.13 m 2 up to 0.19 m 2 (i.e., 0.13 m) 2 ≤ MP R / R pore ≤0.19 m 2 ); 0.14 m 2 up to 0.19 m 2 (i.e., 0.14 m) 2 ≤ MP R / R pore ≤0.19 m 2 ); 0.09 m 2 up to 0.18 m 2 (i.e., 0.09 m) 2 ≤ MP R / R pore ≤0.18 m 2 ); 0.11 m 2 up to 0.18 m 2 (that is, 0.11 m) 2 ≤ MP R / R pore ≤0.18 m 2 ); 0.13 m 2 up to 0.175 m 2 (i.e., 0.13 m) 2 ≤ MP R / R pore ≤0.175 m 2 ); 0.15 m 2 up to 0.175 m 2 (i.e., 0.15 m) 2 ≤ MP R / Rpore ≤0.175 m 2 ); 0.15 m 2 up to 0.17 m 2 (i.e., 0.15 m) 2 ≤ MP R / R pore ≤0.17m 2 ); 0.14 m 2 Up to 0.16 m 2 (i.e., 0.14 m) 2 ≤ MP R / R pore ≤0.16 m 2 ); 0.05 m 2 Up to 0.15 m 2 (i.e., 0.05 m) 2 ≤ MP R / R pore ≤0.15 m 2 ); 0.1 m 2 up to 0.14 m 2 (i.e., 0.1 m) 2 ≤ MP R / R pore ≤0.14 m 2 ); 0.05 m 2 up to 0.10 m 2 (i.e., 0.05 m) 2 ≤ MP R / R pore ≤0.10 m 2 ); or 0.13 m 2 Up to 0.16 m 2 (i.e., 0.13 m) 2 ≤ MP R / R pore ≤0.16 m 2 ).

[0073] Equation 1 is a parameter indicating the overall expansion characteristics of the negative electrode active layer, where the interfacial resistance between the negative electrode active layer and the negative electrode current collector, as well as the pore resistance contained in the negative electrode active layer, are organically combined. An increase in the pore resistance of the negative electrode active layer implies an increase in the degrees of freedom of the ab-axis crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer. This affects the interfacial characteristics between the negative electrode active layer and the negative electrode current collector. Therefore, the negative electrode of this disclosure can effectively suppress the expansion phenomenon of the negative electrode during charging by adjusting Equation 1 to the above-mentioned range, while simultaneously increasing the adhesion between the negative electrode active layer and the negative electrode current collector.

[0074] Figure 1This is a top view showing the surface of the negative electrode 10 for a lithium secondary battery according to the present disclosure, and Figure 2 This is a cross-sectional view showing the cross-sectional structure of the negative electrode 10 for a lithium secondary battery according to the present disclosure in the thickness direction (z direction).

[0075] Reference Figure 1 and Figure 2 The various components of the negative electrode 10 for a lithium secondary battery according to this disclosure are described in detail.

[0076] The negative electrode 10 includes a negative electrode active layer 12 containing a carbon-based negative electrode active material on at least one side of the negative electrode current collector 11. The negative electrode active layer 12 is a layer that realizes the electroactivity of the negative electrode and is manufactured by applying a negative electrode slurry containing a negative electrode active material to at least one side of the negative electrode current collector 11, then drying and rolling the negative electrode slurry, wherein the negative electrode active material performs an electrochemical redox reaction during battery charging and discharging.

[0077] Figure 2 The diagram shows a negative electrode 10 when the negative electrode active layer 12 is formed on one surface of the negative electrode current collector 11, but it is not limited thereto; the negative electrode active layer 12 may be formed on both surfaces of the negative electrode current collector 11.

[0078] Furthermore, the negative electrode active layer 12 includes a carbon-based negative electrode active material as a main component, which is 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, based on 100 parts by weight of the entire negative electrode active layer, the carbon-based negative electrode active material may be included in an amount of 80 parts by weight to 99.8 parts by weight, and more specifically, it 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.

[0079] Carbon-based anode active materials refer to materials with carbon atoms as the main component, and such carbon-based anode active materials can include graphite-based compounds. For example, carbon-based anode active materials can include natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase sintered carbon (bulk mesophase, liquid crystal pitch-based carbon fiber, etc.) made from tar or pitch as raw materials, graphitized coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, coal coke, etc.), and so on.

[0080] Carbon-based anode active materials can take the form of an assembly in which multiple particles are assembled. In this case, a graphite assembly can be formed by aggregating 2 to 100, preferably 3 to 20, graphite particles.

[0081] Furthermore, carbon-based anode active materials can meet the average particle size requirement within a predetermined range. Specifically, carbon-based anode active materials can exhibit an average particle size (Dsize) ranging from 0.5 μm to 20 μm. 50 For example, carbon-based anode active materials can exhibit an average particle size (D) within the following range. 50 ): 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.

[0082] Smaller particle sizes of carbon-based anode active materials are advantageous to maximize the degree of disorder in the expansion direction of each particle, thereby preventing particle expansion due to lithium-ion charging. However, when the particle size of the carbon-based anode active material is less than 0.5 μm, a large amount of binder may be required due to the increased number of particles per unit volume. On the other hand, when the maximum particle size exceeds 20 μm, expansion becomes severe, and with repeated charging and discharging, the bonding performance between particles and between particles and the current collector deteriorates, potentially leading to a significant reduction in cycle characteristics.

[0083] The negative electrode active layer 12 includes a carbon-based negative electrode active material, which may have a structure in which the alignment and / or orientation of the carbon-based negative electrode active material in each region is controlled.

[0084] Specifically, the surface of the negative electrode active layer 12 includes a first region and a second region, and the first and second regions may have a form in which they are alternately arranged once or multiple times. This form can be confirmed when the negative electrode active layer 12 is visually observed. 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 that the first region 12a and the second region 12b are alternately arranged once or multiple 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 of the first region 12a and the second region 12b can be controlled differently. Therefore, when the surface of the negative electrode active layer 12 including the carbon-based negative electrode active material is visually observed, it appears black, and as... Figure 3 As shown, the predetermined brightness difference between the first region 12a and the second region 12b can be confirmed.

[0085] Carbon-based anode active materials (especially graphite) exist in particulate form, in which crystal planes exhibiting a two-dimensional planar structure composed of carbon atoms (i.e., the ab-axis crystal planes of graphite) are stacked along the c-axis direction. If the ab-axis crystal planes of graphite are not individually aligned and / or oriented during the formation of the anode active layer comprising these graphites, the contained graphite will be in a state such that... Figure 4 The state shown in (a) is characterized by misalignment and / or unorientation of the ab-axis crystal plane. In this case, the negative electrode active layer is visually identified as black when the surface is observed, which is the characteristic color of graphite, and because of the high reflectivity of light incident on the surface, L is... * The value displayed is large, exceeding 46.

[0086] However, the negative electrode of this disclosure includes graphite as a carbon-based negative electrode active material in the negative electrode active layer 12, and as... Figure 4 As shown in (b), for each region of the negative electrode active layer 12, the ab-axis crystal plane of graphite can be aligned and / or oriented at a predetermined angle relative to the negative electrode current collector 11. In this case, the larger the angle of alignment and / or orientation of the graphite ab-axis crystal plane relative to the negative electrode current collector 11 (e.g., closer to 90°), the greater the increase in 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 is used to reduce the L of the negative electrode active layer 12 according to the CIE LAB colorimeter. * .

[0087] Therefore, the negative electrode active layer of the negative electrode according to the present disclosure may have the following structure: the graphite contained in the first region 12a and the second region 12b is aligned and / or oriented, but the degree is different for each region, resulting in a deviation in the absorption rate of incident light in each region of the negative electrode active layer 12.

[0088] Specifically, in the negative electrode active layer 12 according to this disclosure, the degree of alignment and / or orientation of the ab-axis crystal plane of the graphite contained in the first region 12a with respect to the negative electrode current collector 11 can be greater than the degree of alignment and / or orientation of the ab-axis crystal plane of the graphite contained in the second region 12b with respect to the negative electrode current collector 11. Therefore, the average L of the first region 12a according to the CIE LAB colorimeter... * The value can be less than the average L value of the second region 12b according to the CIE LAB colorimeter. * value.

[0089] For example, when measuring each area using a CIE LAB colorimeter, the first area 12a and the second area 12b may have a predetermined L value indicating black. * Values, and can have predetermined L values ​​between regions. * Deviation (ΔL)* ).

[0090] Specifically, the average L1 of the first region 12a * Value and the average L2 of the second region 12b * The values ​​can each range from 35 to 48, and the average L1 * The value can be less than the average L2. * More specifically, when the color coordinates are measured according to a CIE LAB colorimeter, the first region 12a can be represented by an average L1 within the following range. * Values: 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. Additionally, when color coordinates are measured according to a CIE LAB colorimeter, the second region 12b can be represented by an average L1 within the following range. * Values: 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, and the L2 * The value can be greater than the average L1 of the first region. * value.

[0091] Additionally, L in region 12a * Value (L1) * ) and L of the second region 12b * Value (L2) * It may have a deviation of 0.45 or more (ΔL) * Specifically, the first region 12a and the second region 12b may have L within the following range. * Deviation (ΔL) * ): 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; or 0.6 to 2. In this case, the first region 12a may have a lower L than the second region 12b. * The value is lower, and therefore has a lower brightness, and thus the black of the first region 12a can appear darker than the black of the second region 12b.

[0092] This disclosure can adjust the average L between the first region 12a and the second region of the negative electrode active layer 12. * Value and L * Deviation (ΔL) * This further improves the adhesion between the negative electrode active layer 12 and the negative electrode current collector 11 within the aforementioned range, and effectively suppresses expansion during the charging process of the lithium secondary battery, while simultaneously increasing the charging speed. Specifically, when the average L of the first region 12a and the second region 12b... *When the upper limit of the above range is exceeded, not only is the charging rate of the lithium secondary battery significantly lower during charging, but the negative electrode may also expand rapidly. Furthermore, when the average L of the first region 12a and the second region 12b... * When the value is less than the lower limit of the above range, the adhesion between the negative electrode active layer 12 and the negative electrode current collector 11 may deteriorate.

[0093] Additionally, when the average L of the first region 12a * Compared with the average L of the second region 12b * The deviation between (ΔL) * When the upper limit of the above range is exceeded, the effect of increasing the charging speed during lithium secondary battery charging may not be significant. Furthermore, when the average L between the first region 12a and the second region 12b... * Deviation (ΔL) * When the value is less than the lower limit of the above range, there is a limitation on the deterioration of the interface properties between the negative electrode active layer 12 and the negative electrode current collector 11, thereby reducing the electrical performance and lifespan characteristics.

[0094] As described above, the negative electrode active layer 12 according to this disclosure may have the following technical features: it includes a carbon-based negative electrode active material, in which the ab axis crystal plane is aligned and / or oriented to form a predetermined angle with the negative electrode current collector 11, but the degree of alignment is controlled differently for each region.

[0095] When the ab-axis crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is aligned and / or oriented at an angle close to 90° with reference to the surface of the negative electrode current collector, the following limitation exists: due to the significant reduction in the contact area between the negative electrode active material contained in the negative electrode active layer and the negative electrode current collector, the adhesion between the negative electrode active layer and the negative electrode current collector is low. However, this disclosure can significantly improve the adhesion 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 relative to the surface of the negative electrode current collector 11 in each region constituting the negative electrode active layer 12, while improving the charging speed of the lithium secondary battery and the expansion phenomenon during charging.

[0096] Furthermore, the negative electrode active layer 12 can be affected by the average L1 of the first region 12a. * Value and the average L2 of the second region 12b * A pattern is formed on the surface due to a predetermined deviation between values. The first region 12a and the second region 12b are distinguishable due to L... *The degree to which the boundaries between regions are visually observable can be distinguished, and these boundaries can be repeated and / or regularly patterned. In this case, the pattern formed on the surface of the negative electrode active layer 12 can include any one or more patterns selected from stripe patterns, concentric circle patterns, checkerboard patterns, and dot patterns. This patterned structure of the negative electrode active layer has the advantage of enabling a more intuitive distinction between the first and second regions.

[0097] In addition, such as Figure 1 As shown, the negative electrode can have a rectangular shape, and when viewed from the surface, the negative electrode active layer has a first side to a fourth side connected in sequence, and can have a structure in which the negative electrode tab 13 is pulled out and formed on the first side.

[0098] At this time, the first region 12a and the second region 12b on the surface of the negative electrode active layer can have the following form: the first region 12a and the second region 12b are alternately disposed between the first side and the third side facing the first side once or multiple times; or, the first region 12a and the second region 12b on the surface of the negative electrode active layer can have the following form: the first region 12a and the second region 12b are alternately disposed between the second side and the fourth side adjacent to the first side once or multiple times.

[0099] For example, the first region 12a and the second region 12b on the surface of the negative electrode active layer can have the following form: the first region 12a and the second region 12b are alternately disposed between the first side and the third side once or multiple times. In this case, the first region 12a and the second region 12b have an average L * Deviation (ΔL) * They may tend to increase as they get closer to the negative electrode contact 13.

[0100] In conventional negative electrode active layers, during the charging and discharging processes of lithium secondary batteries, the region adjacent to the negative electrode contact exhibits a high redox reaction rate compared to other regions due to the smooth movement of electrons and lithium ions. This phenomenon causes degradation in the region adjacent to the negative electrode contact, resulting in a decrease in capacity in that region, and thus the following problem exists: inducing lithium plating at the end of the negative electrode active layer adjacent to the negative electrode contact. However, this disclosure can improve the situation by making the L in the first region 12a and the second region 12b constituting the negative electrode active layer 12... * To mitigate this problem, the deviation increases as the electrode gets closer to the negative electrode contact 13.

[0101] Specifically, as mentioned above, low L *The value indicates that the ab-axis crystal plane of the carbon-based negative electrode active material is aligned and / or oriented at a high angle relative to the negative electrode current collector. This can improve the diffusion performance of lithium ions during the charging of the lithium secondary battery. Therefore, as the lithium secondary battery is charged and discharged, the degradation of the region of the negative electrode active layer adjacent to the negative electrode contact can be improved, thereby achieving the effect of suppressing lithium plating. At this time, the average L in the first region 12a is... * Compared with the average L of the second region 12b * The deviation between (ΔL) * The increasing trend can show an increase of about 0.1 to 0.5.

[0102] Meanwhile, the first region 12a and the second region 12b can have a predetermined length ratio relative to the entire length of the negative electrode active layer 12 in the width direction (i.e., the y-axis direction). Since the first region 12a and the second region 12b are aligned and / or oriented to different degrees on the ab-axis crystal plane of the carbon-based negative electrode active material, their length ratio may affect the performance of the negative electrode active layer. Therefore, in this disclosure, the length ratio of the first region 12a and the second region in the width direction (y-axis direction) of the negative electrode active layer can be adjusted to meet a predetermined range.

[0103] Specifically, the ratio (D1:D2) of the average width of the first region to 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 of the first region to the average width (D1) of the second region can satisfy the following ranges: 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.

[0104] For example, such as Figure 5 As shown in (a), the length ratio of the first region 12a and the second region 12b in the width direction (i.e., the y-axis direction) of the negative electrode active layer 12 can be the same (i.e., W1 = W2, D1:D2 = 1:1). In this case, by effectively reducing the interfacial resistance between the negative electrode active layer 12 and the negative electrode current collector 11 while suppressing the expansion phenomenon during the charging of the lithium secondary battery, the life characteristics of the negative electrode can be significantly improved.

[0105] In addition, such as Figure 5As shown in (b), in the width direction (i.e., the y-axis direction) of the negative electrode active layer 12, the length ratio of the first region 12a can be greater than the length ratio of the second region 12b (i.e., W1>W2, D1∶D2=1∶0.40 to 0.99). In this case, the negative electrode active layer 12 has the advantage of significantly improving the charging speed during lithium secondary battery charging while maintaining strong adhesion to the negative electrode current collector.

[0106] Meanwhile, depending on the needs, the anode active layer may selectively include silicon-based anode active materials, conductive materials, adhesives, other additives, etc., together with the carbon-based anode active material as the main component.

[0107] Silicon-based anode active materials are materials containing silicon (Si) as the main component and capable of improving the charge / discharge capacity of the anode. Examples of such silicon-based anode active materials include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), and silicon dioxide (SiO2), which can be included individually or in combination in the anode active layer. When silicon oxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as a silicon-based anode active material and contained in the anode active layer, they can be represented as silicon oxide (SiO2). q (where 0.8≤q≤2.5).

[0108] Silicon-based anode active materials can be doped with Li, Mg, Al, Ca, Ti, etc., or alloyed with Li, Mg, Al, Ca, Ti, etc. Furthermore, when silicon-based anode active materials contain oxygen (O), surface treatments such as carbon coatings can be applied to suppress volume expansion during charging and simultaneously improve the conductivity of the anode active material.

[0109] Based on the total weight of the negative electrode active layer, silicon-based negative electrode active material can be included in an amount ranging from 0.1 wt% to 40 wt%. Specifically, based on the total weight of the negative electrode active layer, silicon-based negative electrode active material can be included in amounts ranging from 0.5 wt% to 20 wt%, 1 wt% to 9 wt%, 5 wt% to 15 wt%, 3 wt% to 7 wt%, 11 wt% to 19 wt%, 13 wt% to 17 wt%, 15 wt% to 20 wt%, 10 wt% to 30 wt%, 20 wt% to 40 wt%, 25 wt% to 35 wt%, 15 wt% to 25 wt%, or 9 wt% to 22 wt%. By adjusting the content ratio of silicon-based negative electrode active material to the above ranges, this disclosure can increase the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charging / discharging of the secondary battery. In addition, since the structural stability of the negative electrode active layer can be improved by minimizing the volume change of the negative electrode active layer during the charging / discharging of the secondary battery, the lifespan of the secondary battery can be increased.

[0110] Conductive materials may include one or more of carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, etc., but are not limited to these.

[0111] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. as conductive materials, either alone or in combination.

[0112] Based on 100 parts by weight of the negative electrode active layer, the content of conductive material can be from 0.1 parts by weight to 10 parts by weight. Specifically, the conductive material can be from 0.1 parts by weight to 8 parts by weight, 0.1 parts by weight to 5 parts by weight, 0.1 parts by weight to 3 parts by weight, 2 parts by weight to 6 parts by weight, or 0.5 parts by weight to 2 parts by weight. By controlling the content of conductive material within the above range, this disclosure can prevent the negative electrode resistance from increasing due to a low content of conductive material, thereby causing a decrease in charging capacity. In addition, this disclosure can prevent the problem of a decrease in charging capacity caused by an excessive content of conductive material exceeding the above range, or the problem of increased resistance caused by an increased loading of the negative electrode active layer.

[0113] Furthermore, the adhesive is a component that facilitates the bonding of the negative electrode active material, conductive material, etc., and the bonding with the current collector, and can be applied appropriately within a range that does not impair the electrical properties of the negative electrode. For example, the adhesive may include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber, or any one or more of these.

[0114] Based on 100 parts by weight of the negative electrode active layer, the binder content can be from 0.1 parts by weight to 10 parts by weight. Specifically, the binder can be from 0.1 parts by weight to 8 parts by weight, 0.1 parts by weight to 5 parts by weight, 0.1 parts by weight to 3 parts by weight, or 2 parts by weight to 6 parts by weight. By controlling the binder content in the negative electrode active layer to the above range, this disclosure can prevent reduced adhesion of the active layer due to low binder content or reduced electrical performance of the negative electrode due to excessive binder.

[0115] Furthermore, there are no particular restrictions on the negative electrode current collector, as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector can be made of copper, stainless steel, nickel, titanium, sintered carbon, etc. When the negative electrode current collector is made of copper or stainless steel, it can also be surface-treated with carbon, nickel, titanium, silver, etc. Considering the conductivity and total thickness of the negative electrode to be manufactured, the average thickness of the negative electrode current collector can be appropriately applied in the range of 1 μm to 500 μm.

[0116] The negative electrode for lithium secondary batteries according to this disclosure exhibits excellent adhesion between the negative electrode current collector and the negative electrode active layer due to the above-described configuration. Furthermore, the negative electrode offers the advantages of not only reducing expansion during charging but also providing excellent fast-charging performance.

[0117] Lithium secondary batteries

[0118] Furthermore, this disclosure provides a lithium secondary battery, comprising:

[0119] An electrode assembly includes a positive electrode, a negative electrode as described above, and a partition disposed between the positive and negative electrodes.

[0120] The lithium secondary battery according to this disclosure includes 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, including the negative electrode of this disclosure, not only minimizes the increase in resistance due to high load / high density by improving lithium-ion diffusion capability, but also achieves the advantages of high output characteristics while possessing excellent lifespan and safety.

[0121] Since the negative electrode has the same configuration as described above, its detailed description is omitted.

[0122] Furthermore, the positive electrode includes a positive electrode active layer containing positive electrode active material on the positive electrode current collector. Optionally, the positive electrode active layer may further include conductive materials, binders, other additives, etc., as needed.

[0123] The positive electrode active material is a material capable of inducing an electrochemical reaction on the positive electrode current collector, and may include one or more lithium metal oxides represented by the following chemical formulas 1 and 2, which are capable of reversibly inserting and deintercalating lithium ions:

[0124] [Chemical Formula 1]

[0125] Li1[Ni m Co n Mn w M 1 v O2

[0126] [Chemical Formula 2]

[0127] LiM 2 p Mn q P r O4

[0128] In the above chemical formulas 1 and 2,

[0129] Where M 1 It is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo;

[0130] l, m, n, w, and v are respectively: 1.0≤l≤1.30, 0.5≤m<1, 0<n≤0.3, 0<w≤0.3, 0≤v≤0.1, where m+n+w+v=1;

[0131] Where M 2 Is it Ni, Co, or Fe?

[0132] Where p is 0.05 ≤ p ≤ 1.0,

[0133] Where q is 2-p, and

[0134] Where r is 0 or 1.

[0135] The lithium metal oxides represented by the above chemical formulas 1 and 2 are materials containing high contents of nickel (Ni) and manganese (Mn), respectively. When used as positive electrode active materials, they have the advantage of being able to stably supply high capacity and / or high voltage electrical energy compared with conventional positive electrode active materials such as lithium iron phosphate (LiFeO4).

[0136] At this point, the lithium metal oxide represented by chemical formula 1 may include LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co0.1 Mn 0.1 Al 0.1 O2, etc., while the lithium metal oxide represented by chemical formula 2 may include LiNi. 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4, LiNi 0.3 Mn 1.7 O4, etc., and these can be used alone or in combination.

[0137] Furthermore, based on 100 parts by weight of the entire positive electrode active layer, the positive electrode active material may be included in an amount of 85 parts by weight or more. Specifically, based on 100 parts by weight of the entire positive electrode active layer, 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.

[0138] The conductive material is used to improve the electrical properties of the positive electrode and can be a conductive material conventionally used in the art. Specifically, the conductive material may include one or more of the following: natural graphite, artificial graphite, carbon black, acetylene black, Denca black, Ketjen black, Super-P, channel black, furnace black, lamp black, pyrolytic black, graphene, and carbon nanotubes.

[0139] Furthermore, based on 100 parts by weight of each positive electrode active layer, conductive material may be included in an amount of 0.1 parts by weight to 5 parts by weight. Specifically, based on 100 parts by weight of the positive electrode active layer, conductive material may be included in an amount of 0.1 parts by weight to 4 parts by weight, 2 parts by weight to 4 parts by weight, 1.5 parts by weight to 5 parts by weight, 1 part by weight to 3 parts by weight, 0.1 parts by weight to 2 parts by weight, or 0.1 parts by weight to 1 part by weight.

[0140] The adhesive serves to bond the positive electrode active material, positive electrode additive, and conductive material together, and can be used without particular restriction, as long as it has this function. Specifically, the adhesive may include one or more resins selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. For example, the adhesive may include polyvinylidene fluoride.

[0141] Furthermore, based on 100 parts by weight of the positive electrode active layer, the binder may be included in an amount of 1 to 10 parts by weight. Specifically, based on 100 parts by weight of the positive electrode active layer, the binder may be included in an amount of 2 to 8 parts by weight, or 1 to 5 parts by weight.

[0142] There is no particular limitation on the total thickness of the positive electrode active layer, but it can specifically be from 50 μm to 300 μm, and more specifically in the range of 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.

[0143] As the positive electrode current collector, materials with high conductivity that do not cause chemical changes in the battery can be used. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, etc., can be used, and in the case of aluminum or stainless steel, materials with surface treatments such as carbon, nickel, titanium, silver, etc., can also be used. In addition, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the current collector can be appropriately applied in the range of 3 μm to 500 μm.

[0144] The separator is an insulating film with high ion permeability and mechanical strength, and there are no particular limitations, as long as it is conventionally used in the art. Specifically, separators comprising one or more polymers selected from chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymers can be used. The separator can be in the form of a porous polymer substrate, such as a sheet or nonwoven fabric comprising the aforementioned polymers. In some cases, it can also be in the form of a composite separator, wherein organic or inorganic particles are coated onto the porous polymer substrate by an organic adhesive. Furthermore, the separator can have an average pore size of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0145] Furthermore, the lithium secondary battery according to this disclosure is not particularly limited, but can be a secondary battery that includes stacked, zigzag, or zig-stacked electrode assemblies. For example, the lithium secondary battery according to this disclosure can be a pouch-type secondary battery or a prismatic secondary battery.

[0146] In terms of energy density, pouch-type and / or prismatic-type secondary batteries have the advantage of high utilization because the cell units of the secondary battery can be packed in a high density within a limited space.

[0147] Method for manufacturing negative electrodes for lithium secondary batteries

[0148] Furthermore, this disclosure provides a method for manufacturing the negative electrode for a lithium secondary battery according to this disclosure.

[0149] Specifically, the method for manufacturing a negative electrode for a lithium secondary battery according to the present disclosure includes: applying a negative electrode slurry containing a carbon-based negative electrode active material to at least one side of a negative electrode current collector (S1), applying a magnetic field to the coated negative electrode slurry (S2), and drying the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer (S3).

[0150] At this point, step (S1) refers to the process of discharging the negative electrode slurry containing the carbon-based negative electrode active material and coating it onto at least one side of the moving negative electrode current collector.

[0151] This step (S1) can be applied without particular limitation, as long as it is a method conventionally used in the art, but mold coating is preferred. Mold coating can be performed using a slit mold having a shim for controlling the discharge of the negative electrode slurry. By controlling the shape, position, etc., of the shim, the slit mold can easily control the loading amount of negative electrode slurry applied to the negative electrode current collector, the coating thickness, etc.

[0152] The negative electrode slurry comprises a carbon-based negative electrode active material as its main component, and may further include conductive materials and binders. Since each component contained in the negative electrode slurry is the same as the negative electrode active layer described above for a lithium secondary battery, its detailed description will be omitted.

[0153] In addition, the negative electrode slurry can have a predetermined viscosity at room temperature.

[0154] "Viscosity" refers to the magnitude of physical and / or chemical interactions (such as friction and resistance) between each component (e.g., carbon-based anode active material, additives, etc.) within the anode slurry. Even with the same molar number and / or weight of components, these interactions increase with increasing component concentration. A limitation of high-viscosity anode slurries is that the orientation of the carbon-based anode active material decreases when a magnetic field is applied, making it difficult to achieve a high degree of tilt relative to the anode current collector. Therefore, the viscosity can be adjusted at room temperature to facilitate the alignment and / or orientation of the ab-axis crystal plane of the carbon-based anode active material relative to the anode current collector.

[0155] Specifically, the negative electrode slurry can have a viscosity of less than 10,000 cps at room temperature (22±3℃). Specifically, at room temperature (22±3℃), the viscosity of the negative electrode slurry can be in the following ranges: 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.

[0156] Next, step (S2) refers to the process of aligning and / or orienting the ab-axis crystal planes of the carbon-based anode active material contained in the anode slurry by applying a magnetic field to the anode slurry.

[0157] At this point, the degree of alignment and / or orientation of the ab-axis crystal planes of the carbon-based anode active material contained in the anode slurry can vary depending on the applied magnetic field strength. Therefore, in order to achieve the first and second regions of the anode active layer (where the degree of alignment and / or orientation of the ab-axis crystal planes of the carbon-based anode active material relative to the anode current collector is different), the magnetic field conditions applied to the regions in the anode slurry corresponding to the first and second regions can be adjusted differently.

[0158] Specifically, in this step (S2), region A, corresponding to the first region of the negative electrode active layer, and region B, corresponding to the second region of the negative electrode active layer, can be set on the surface of the negative electrode slurry applied to the negative electrode current collector. Then, a magnetic field can be applied to the designated region A of the negative electrode slurry, while no magnetic field is applied to region B, or a weaker magnetic field can be applied to region B than to region A.

[0159] Here, the magnetic field applied to region A of the negative electrode slurry can have a strength of 1,000 G to 9,000 G (Gauss) in order to enhance the effect of aligning and / or orienting the ab-axis crystal planes of the carbon-based negative electrode active material. Specifically, the magnetic field applied to region A of the negative electrode slurry can be applied in the following ranges of strength: 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 7,500 G; 5,500 G to 6,500 G; 1,000 G to 7,000 G; 2,000 G to 6,000 G; 1,500 G to 5,000 G; 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.

[0160] Furthermore, when a magnetic field is applied to region B of the negative electrode slurry, the magnetic field applied to region B of the negative electrode slurry can be applied at an intensity of 5,000 G or less, 4,500 G or less, or within the following ranges: 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.

[0161] At this time, a magnetic field can be applied to region B of the negative electrode slurry with an intensity of 0.1% to 0.9% of the magnetic field strength applied to region A. Specifically, the magnetic field applied to region B of the negative electrode slurry can be applied with an intensity 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 region A.

[0162] This disclosure achieves effective L-axis measurement according to a CIE LAB colorimeter in the first and second regions of the negative electrode active layer by adjusting the magnetic field strength applied to regions A and B of the negative electrode slurry as described above. * deviation.

[0163] Simultaneously, this step (S2) can be performed by installing a magnet along the path of the negative electrode slurry applied to the negative electrode current collector, thereby applying a magnetic field to the negative electrode slurry. In this case, the magnet can be positioned at the lower part (i.e., the lower portion of the negative electrode current collector) of the negative electrode slurry applied to it. When the magnet is positioned at both the upper and lower parts of the negative electrode slurry, the ab-axis crystal plane of the carbon-based negative electrode active material contained in the negative electrode slurry can be aligned and / or oriented at an angle close to 90° relative to the negative electrode current 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 deviations in the alignment and / or orientation of the carbon-based negative electrode active material, even if the magnetic field strength in each region is adjusted differently. Therefore, preferably, the magnet for applying the magnetic field is positioned on the path of the negative electrode slurry and is positioned at the lower part of the negative electrode slurry.

[0164] In addition, when a magnetic field is applied to region A of the negative electrode slurry but not to region B, i) a magnet can be placed only at the point corresponding to region A of the negative electrode slurry, or ii) a magnet can be placed in the width direction of the negative electrode slurry (the same direction as the width direction (y-axis direction) of the negative electrode active layer), but the magnetic field can be blocked by introducing a magnetic field shielding member or the like at the point corresponding to region B.

[0165] Furthermore, when a magnetic field is applied to both region A and region B of the negative electrode slurry, i) a unit magnet can be set in each region and the magnetic field strength of the unit magnet can be adjusted, or ii) a magnet can be set in the width direction of the negative electrode slurry (the same direction as the width direction (y-axis direction) of the negative electrode active layer), but the magnetic field strength applied to each region can be adjusted by adjusting the thickness, length, shape, etc. of the magnet.

[0166] Next, step (S3) refers to the process of forming the negative electrode active layer by drying the negative electrode slurry to which a magnetic field has been applied.

[0167] Drying can be applied without particular limitations, as long as it is a method conventionally applicable in the art. For example, drying can be performed by applying heat to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like.

[0168] Furthermore, the method for manufacturing the negative electrode according to this disclosure may further include a process of rolling the negative electrode active layer formed by drying. Rolling refers to the process of increasing the density of the entire negative electrode active layer by applying pressure to the surface of the formed negative electrode active layer using a rolling mill or the like. For this purpose, rolling can be performed at a temperature above room temperature under predetermined pressure and speed conditions.

[0169] Specifically, rolling can be performed at temperatures ranging from 20°C to 100°C. More specifically, rolling can be performed at temperatures ranging from: 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.

[0170] Furthermore, rolling can be performed at rolling speeds ranging from 2 m / s to 7 m / s. More specifically, rolling can be performed at rolling speeds within the following ranges: 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.

[0171] Furthermore, rolling can be performed under pressure conditions ranging from 50 MPa to 200 MPa, and specifically, rolling can be performed under pressure conditions ranging from 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.

[0172] This disclosure maximizes the energy density of the formed negative electrode active layer while minimizing damage to the negative electrode active layer by rolling under the above-mentioned temperature, speed and / or pressure conditions.

[0173] The present disclosure will now be described in more detail through examples and comparative examples.

[0174] However, the following embodiments and comparative examples are only for illustrating this disclosure, and the content of this disclosure is not limited to the following embodiments and comparative examples.

[0175] Examples 1 to 5 and Comparative Examples 1 to 3: Manufacturing of negative electrodes for lithium secondary batteries

[0176] Preparation of natural graphite (average particle size (D) 50 (Approximately 11 μm to 13 μm) and artificial graphite (average particle size (D) 50(Approximately 15 μm to 16 μm) was used as the first carbon-based negative electrode active material and the second carbon-based negative electrode active material. Simultaneously, styrene-butadiene rubber (SBR) was prepared as an adhesive, carboxymethyl cellulose (CMC) was prepared as a thickener, and carbon black (Super-P) was prepared as a conductive material.

[0177] Then, as shown in Table 1 below, ① a carbon-based negative electrode active material was prepared, and a negative electrode slurry was prepared by mixing 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 with water, so that the solid content was 50%. At this time, the viscosity of the prepared negative electrode slurry at room temperature (22±3℃) was 5,000±100 (cps).

[0178] Using a die coating machine, the prepared negative electrode slurry is applied onto a copper foil (thickness: 6 μm) that is transferred by roller to roller (transfer speed: 6 m / min) (S1). Then, a magnetic field is applied to the applied negative electrode slurry using a magnet for 2 to 9 seconds (S2).

[0179] On the surface of the negative electrode paste applied to the copper foil, a magnet is installed between the first side where the negative electrode contact is located and the third side facing the first side, such that six regions A and four regions B are alternately arranged. At this time, the following table shows the adjustment of ② the position of the magnet used to apply the magnetic field, ③ the length ratio of region A to region B relative to the overall length of the negative electrode paste, and ④ the magnetic field strength applied to region A and region B of the negative electrode paste.

[0180] A negative electrode active layer is formed on a negative electrode current collector by drying the negative electrode slurry with hot air under a magnetic field. The formed negative electrode active layer is then rolled at 50±1°C, a pressure of 100 MPa to 150 MPa, and a conveying speed of 3 m / s to manufacture a negative electrode for lithium secondary batteries (average thickness of the negative electrode active layer: approximately 90±5 μm).

[0181] Table 1

[0182]

[0183] Examples 6 to 10 and Comparative Examples 4 to 6: Manufacturing of lithium secondary batteries

[0184] Preparation of LiNi with a particle size of 5 μm 0.7 Co 0.1 Mn 0.1 Al 0.1O2 is used as the positive electrode active material. The positive electrode is formed by mixing N-methylpyrrolidone (NMP) with a carbon-based conductive agent and polyvinylidene fluoride as a binder in a weight ratio of 94:3:3 to form a slurry, which is then coated onto aluminum foil, dried in a vacuum oven at 120°C, and then rolled to manufacture the positive electrode.

[0185] A 1Ah-class lithium secondary battery was assembled by inserting a separator made of 18 μm thick polypropylene between the obtained positive electrode and the negative electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 3, respectively, inserting them into a casing, and then injecting an electrolyte composition.

[0186] At this point, the types of negative electrodes applied to each lithium secondary battery are shown in Table 2 below.

[0187] Table 2

[0188]

[0189] Experimental Example

[0190] The following experiments were conducted to evaluate the physical properties and performance of the negative electrode manufactured according to this disclosure.

[0191] 1) Measure color coordinates using a CIE LAB colorimeter

[0192] For the negative electrodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 3, a first region and a second region in the width direction were identified based on a cross-section in the thickness direction of the negative electrode active layer, and color coordinates were measured at three arbitrary points within each region using a CIE LAB colorimeter. At this time, a non-contact CIE LAB colorimeter was used to measure the color coordinates, and the value representing luminance (L) at the three measured points was calculated. * The average value is used to obtain L for each region. * and the deviation between regions (ΔL) * The results are shown in Table 3 below.

[0193] 2) Interfacial resistance (MPa) between the negative electrode active layer and the negative electrode current collector R Measurement of )

[0194] For the negative electrodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 3, the interfacial resistance between the negative electrode active layer and the negative electrode current collector was measured. The interfacial resistance was measured using an XF057 electrode resistance measuring instrument from Hiokki at 22±2°C and 50±5% relative humidity, at a measuring current of 100μA or 1 mA, and a measuring voltage of 1V or 10V.

[0195] 3) The tortuosity and pore resistance (R) of the negative electrode active layer pore )Measurement

[0196] Symmetrical coin cell cells were prepared, wherein the working electrode and the counter electrode were made using the same negative electrode as those prepared in Examples 1 to 5 and Comparative Examples 1 to 3. An electrolyte in which 1.0 M of lithium salt LiPF6 was mixed with an organic solvent (EC:EMC = 1:4 vol%) was used.

[0197] Then, impedance spectroscopy analysis (frequency range from 500 kHz to 100 MHz) was performed on the fabricated symmetrical electrodes. After representing the results of the impedance spectroscopy measurements as Nyquist curves, tortuosity and pore resistance (Ro) were calculated through data analysis. pore ).

[0198] In addition, its ratio (MP) R / R pore The interfacial resistance (MPa) between the previously measured negative electrode active layer and the negative electrode current collector was determined by... R ) and pore resistance (R pore The results were calculated and are shown in Table 3 below.

[0199] Table 3

[0200]

[0201] As shown in Table 3 above, it can be seen that the negative electrode according to this disclosure has excellent interfacial characteristics between the negative electrode active layer and the negative electrode current collector, and has excellent tortuosity and pore resistance in the negative electrode active layer.

[0202] Specifically, it has been confirmed that by controlling the magnetic field applied to regions A and B of the negative electrode slurry at the bottom of the moving negative electrode slurry, the negative electrode manufactured in the embodiment achieves a first region and a second region L, which are distinguished along the width direction based on the cross-section in the thickness direction of the negative electrode active layer. * Deviation, thus forming a pattern on the surface. Furthermore, it has been confirmed that the negative electrode manufactured in the embodiment, as it gets closer to the negative electrode tab, the L between the first and second regions... * The deviation is showing an increasing trend.

[0203] Furthermore, it was found that the negative electrode manufactured in the embodiments had a strength of 4.4 Ωm·cm. 2 Or a lower interfacial resistance between the negative electrode active layer and the negative electrode current collector, indicating a high contact area at the interface between the negative electrode active layer and the negative electrode current collector.

[0204] Furthermore, it was found that the negative electrode manufactured in the embodiments not only has a low tortuosity of 5% or less in the negative electrode active layer, but also a low pore resistance (R0) of less than 3.1 Ω. pore ).

[0205] These results show that the negative electrode manufactured according to this disclosure has a patterned structure, wherein a first region and a second region are alternately arranged along the width direction based on a cross-section in the thickness direction of the negative electrode active layer, and the first region and the second region have an L-shape according to a CIE LAB colorimeter. * The predetermined deviation ensures excellent adhesion between the negative electrode current collector and the negative electrode active layer. Furthermore, the negative electrode not only mitigates expansion during charging but also exhibits excellent fast-charging performance.

[0206] Although this disclosure has been described with reference to preferred embodiments thereof, those skilled in the art will understand that various modifications and variations may be made therein without departing from the scope of this disclosure as defined by the appended claims.

[0207] Therefore, the scope of this disclosure should not be limited by the specific description in the specification, but should be determined by the appended claims.

Claims

1. A negative electrode, comprising: Negative electrode current collector; and a negative electrode active layer disposed on at least one side of the negative electrode current collector, the negative electrode active layer comprising a carbon-based negative electrode active material. The surface of the negative electrode active layer comprises the following form: L according to the CIE LAB colorimeter * Based on this, ΔL, expressed by Equation 1, is 0.45 or greater. * The first and second regions are alternately set once or multiple times; [Formula 1] ΔL * =|L1 * -L2 * | In Equation 1, L1 * L represents the average value of the first region. * Value, and L2 * L represents the average value of the second region. * value.

2. The negative electrode according to claim 1, wherein, The average L1 of the first region * The value is in the range of 35 to 48. And the average L2 of the second region * The value is in the range of 36 to 50.

3. The negative electrode according to claim 1, wherein, The first and second regions formed on the surface of the negative electrode active layer form any one or more patterns selected from stripe patterns, concentric circle patterns, checkerboard patterns, and dot patterns.

4. The negative electrode according to claim 1, The negative electrode has a rectangular shape and a structure in which a negative electrode contact is formed on the first side of the rectangular shape. Between the first side and the third side facing the first side, the surface of the negative electrode active layer includes the following form: the first region and the second region are alternately disposed once or multiple times.

5. The negative electrode according to claim 1, wherein, The negative electrode has a rectangular shape and a structure in which a negative electrode contact is formed on the first side of the rectangular shape. Between the second and fourth sides adjacent to the first side, the surface of the negative electrode active layer includes the following form: the first region and the second region are alternately disposed once or multiple times.

6. The negative electrode according to claim 1, wherein, The ratio (D1:D2) of the average width of the first region to the average width of the second region is in the range of 0.4:1 to 1:

1.

7. The negative electrode according to claim 1, wherein, The carbon-based anode active material comprises one or more of the following: natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase sintered carbon made from tar or pitch as raw materials, and graphitized coke.

8. The negative electrode according to claim 1, wherein, The negative electrode active layer contains materials selected from Si, SiC, and SiO. q One or more silicon-based anode active materials (where 0.5≤q≤2.5).

9. The negative electrode according to claim 1, wherein, The interfacial resistance between the negative electrode current collector and the negative electrode active layer is 0.1 mΩ·m. 2 Up to 8.0 mΩ·m 2 Within the range.

10. The negative electrode according to claim 1, wherein, The tortuosity of the negative electrode active layer is in the range of 2.0% to 8.0%.

11. A method for manufacturing a negative electrode, comprising the following steps: A negative electrode slurry containing a carbon-based negative electrode active material is applied to at least one side of the negative electrode current collector; Apply a magnetic field to the applied negative electrode slurry; and The negative electrode slurry, to which a magnetic field has been applied, is dried to form a negative electrode active layer; In the step of applying the magnetic field, A magnetic field with an average range of 1,000 G to 9,000 G is applied to region A of the negative electrode slurry corresponding to the first region; and No magnetic field is applied to region B of the negative electrode slurry corresponding to the second region, or a magnetic field of 5,000 G or less is applied.

12. The method for manufacturing a negative electrode according to claim 11, wherein, In the step of applying the magnetic field, When a magnetic field is applied to region B of the negative electrode slurry The magnetic field strength applied to region B of the negative electrode slurry is in the range of 0.1% to 0.9% of the magnetic field strength applied to region A of the negative electrode slurry.

13. The method for manufacturing a negative electrode according to claim 11, wherein, In the step of applying the magnetic field, The magnetic field is applied by a method of applying a magnetic field from the lower part of the negative electrode.

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