Negative electrode for lithium secondary battery, lithium secondary battery comprising same, and method for manufacturing negative electrode

Abstract

The present invention relates to a negative electrode for a lithium secondary battery. According to an exemplary embodiment, a negative electrode is provided. The negative electrode includes: a current collector; a first negative electrode active material layer; and a second negative electrode active material layer. The second negative electrode active material layer includes a plurality of recessed portions and a plurality of non-recessed portions recessed toward the first negative electrode active material layer, the recessed portions and the non-recessed portions are alternately arranged in a horizontal direction, and a surface of the second negative electrode active material layer has a pattern formed by steps.

Description

[Technical field]

[0001] This application claims priority from Korean Patent Application No. 10-2023-0085005, filed on June 30, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a negative electrode having improved cycle resistance characteristics during charge and discharge in a high-load / high-density negative electrode for meeting high energy density and high power battery specifications, a lithium secondary battery including the negative electrode, and a method for manufacturing the negative electrode. [Background Technology]

[0003] With recent technological advancements and the growing demand for mobile devices, the demand for batteries as energy sources has surged. Furthermore, with HEVs, PHEVs, and EVs attracting attention as future vehicles, research is actively underway to develop batteries that meet these diverse needs.

[0004] In particular, research on lithium secondary batteries having high energy density and excellent cycle and life characteristics is being actively conducted.

[0005] Conventional lithium secondary batteries primarily use carbon compounds as negative electrode active materials, which can reversibly intercalate and deintercalate lithium ions while maintaining their structural and electrical properties. However, with the growing demand for developing high-energy-density batteries, there is a growing interest in materials other than carbon compounds, such as silicon and tin, which are transition metals (Groups IV and V) that react chemically with lithium, or their alloys and oxides.

[0006] Silicon is particularly well-suited as a high-capacity anode material due to its theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), significantly greater than carbon-based materials. However, silicon and its alloys experience repeated significant expansion (up to 4 times) and contraction during charge and discharge, leading to anode degradation and reduced battery cycle life.

[0007] This phenomenon becomes more pronounced as the content of high-capacity negative electrode active materials increases to produce high-energy-density batteries. Therefore, the industry needs to study methods to control the volume expansion during charge and discharge to improve the structural stability of the electrode and thus improve the performance of the battery.

[0008] Furthermore, with the increasing demand for developing high-energy-density batteries, the development of high-load and high-density electrodes is being pursued. However, high-load / high-density electrodes face the problem of increased resistance due to larger pore resistance and longer lithium-ion migration paths, which slows the diffusion of lithium ions within the electrode. Therefore, efforts are still needed to improve the increased resistance associated with high-load and high-density electrodes. [Summary of the invention]

[0009] [Technical Issues]

[0010] The technical problem to be solved by the present invention is to provide a negative electrode for a lithium secondary battery that can improve the mobility of lithium ions in a high-load negative electrode while improving the degradation of structural stability due to volume expansion.

[0011] [Technical solution]

[0012] According to one embodiment, the present invention provides a negative electrode for a lithium secondary battery, comprising:

[0013] current collector;

[0014] a first negative electrode active material layer formed on one or both surfaces of the current collector and containing a first negative electrode active material that is a carbon-based compound as a negative electrode active material; and

[0015] a second negative electrode active material layer formed on the first negative electrode active material layer and comprising a second negative electrode active material different from the carbon-based compound as a negative electrode active material, wherein:

[0016] The second negative electrode active material layer includes a plurality of concave portions and a plurality of non-concave portions that are recessed toward the first negative electrode active material layer, wherein the concave portions and the non-concave portions are alternately arranged in a horizontal direction.

[0017] The recess is filled with a conductive layer comprising a conductive material, wherein:

[0018] The thickness of the conductive layer filled in the recessed portion is smaller than that of the non-recessed portion, and the surface of the second negative electrode active material layer has a pattern formed by steps between the conductive layer and the non-recessed portion.

[0019] In one embodiment, the conductive layer further comprises a negative electrode active material.

[0020] In one embodiment, the conductive layer has the same composition as the second negative active material layer.

[0021] In one embodiment, the conductive material included in the conductive layer includes a greater weight % of the conductive material than that included in the second negative active material layer.

[0022] In one embodiment, the conductive layer includes: 70 to 94 parts by weight of a negative electrode active material; 5 to 20 parts by weight of a conductive material; and 1 to 10 parts by weight of a binder.

[0023] In one embodiment, the conductive layer does not include a negative electrode active material, and includes: 80 to 100 parts by weight of a conductive material, and 20 parts by weight or less of a binder.

[0024] According to another embodiment of the present invention, the present invention provides a negative electrode for a lithium secondary battery, comprising: a current collector; a first negative electrode active material layer formed on one or both surfaces of the current collector and containing a first negative electrode active material as a carbonaceous compound as the negative electrode active material; and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second negative electrode active material different from the carbonaceous compound as the negative electrode active material, wherein the second negative electrode active material layer contains a plurality of concave portions and a plurality of non-concave portions recessed toward the first negative electrode active material layer, wherein the concave portions and the non-concave portions are alternately arranged in the horizontal direction, and wherein the surface of the second negative electrode active material layer has a pattern formed by steps between the non-concave portions and the concave portions.

[0025] In one embodiment, the horizontal width of each non-concave portion is from 50 μm to 1500 μm.

[0026] In one embodiment, the horizontal width of each concave portion is from 10 μm to 800 μm and is less than or equal to the horizontal width of the non-concave portion.

[0027] In one embodiment, the length of the step is from 5 μm to 60 μm.

[0028] In one embodiment, the negative electrode active material contained in the first negative electrode active material layer is composed of a carbonaceous first negative electrode active material.

[0029] In one embodiment, the carbonaceous first negative electrode active material is a graphite-based negative electrode active material.

[0030] In one embodiment, the second negative electrode active material is a mixture of one or more selected from the group consisting of Si, SiO x (0 < x < 2), Si-C composite, and Si metal alloy.

[0031] In one embodiment, the average value of the total loading amount of the first negative electrode active material layer and the second negative electrode active material layer is 4 mAh / cm 2 or more.

[0032] According to another embodiment of the present invention, the present invention provides a lithium secondary battery comprising the above negative electrode.

[0033] According to another embodiment of the present invention, the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, which includes: mixing and stirring a carbon-based first negative electrode active material, a conductive material and a binder in a solvent to prepare a first negative electrode slurry; mixing and stirring a second negative electrode active material different from the carbon-based first negative electrode active material, a conductive material and a binder in a solvent to prepare a second negative electrode slurry; preparing a conductive layer slurry; a first coating process of coating the first negative electrode slurry on a collector; a second coating process of coating the second negative electrode slurry and the conductive layer slurry on the first negative electrode slurry; and drying the first negative electrode slurry, the second negative electrode slurry and the conductive layer slurry, wherein the second coating process is performed in a manner such that the second negative electrode slurry and the conductive layer slurry are alternately arranged in a horizontal direction.

[0034] In one embodiment, the solid content of the second negative electrode slurry is greater than the solid content of the conductive layer slurry.

[0035] In one embodiment, the second coating process includes coating the second negative electrode slurry and the conductive layer slurry using a nozzle printer.

[0036] In one embodiment, the conductive layer slurry further includes a negative electrode active material.

[0037] In one embodiment, the conductive layer slurry and the second negative electrode slurry have the same composition.

[0038] In one embodiment, the weight percent of the conductive material contained in the solids of the conductive layer slurry is greater than the weight percent of the conductive material contained in the solids of the second negative electrode slurry.

[0039] In one embodiment, the conductive layer slurry does not contain a negative electrode active material, and contains 80 to 100 parts by weight of a conductive material and 20 parts by weight or less of a binder in solid matter.

[0040] According to another embodiment of the present invention, the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, comprising: mixing and stirring a carbon-based first negative electrode active material, a conductive material, and a binder in a solvent to prepare a first negative electrode slurry; mixing and stirring a second negative electrode active material different from the carbon-based first negative electrode active material, a conductive material, and a binder in a solvent to prepare a second negative electrode slurry; coating the first negative electrode slurry and the second negative electrode slurry on a collector so that the second negative electrode slurry is stacked on the first negative electrode slurry; drying the first negative electrode slurry and the second negative electrode slurry; and etching the second negative electrode active material layer formed by drying the second negative electrode slurry at a predetermined spacing and width to form a pattern in which concave portions recessed toward the collector and non-concave portions are alternately arranged in a horizontal direction.

[0041] In one embodiment, the patterning process includes etching using a laser.

[0042] [Beneficial Effects]

[0043] In one embodiment of the present invention, the negative electrode includes a first negative electrode active material which is a carbon compound with excellent structural stability in the lower layer and a second negative electrode active material with excellent capacity and input / output characteristics in the upper layer, which can alleviate the problem of expansion of the negative electrode active material layer in the thickness direction with repeated cycles, and can improve the resistance and input / output characteristics even when the negative electrode is highly loaded.

[0044] The negative electrode of one embodiment of the present invention has an increased reaction area on the surface of the negative electrode due to the step-like pattern formed on the surface of the second negative electrode active material layer, thereby suppressing the increase in resistance caused by the high load of the negative electrode, and the step-like space on the surface of the second negative electrode active material layer has a buffering effect on the volume change of the negative electrode active material layer, and therefore has excellent structural stability. [Brief Description of the Drawings]

[0045] Figure 1 FIG1 is a top view of a negative electrode according to one embodiment of the present invention.

[0046] Figure 2 is a vertical cross-sectional view of a negative electrode according to one embodiment of the present invention.

[0047] Figure 3 is a vertical cross-sectional view of a negative electrode according to another embodiment of the present invention.

[0048] Figure 4 is a vertical cross-sectional view of a negative electrode according to still another embodiment of the present invention.

[0049] Figure 5 1 is a flowchart illustrating a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention.

[0050] Figure 6 1 is a flowchart illustrating a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention.

[0051] Figure 7 1 is a diagram illustrating a secondary coating process in a method for manufacturing a negative electrode according to one embodiment of the present invention. [Specific implementation method]

[0052] Hereinafter, the present invention will be described in more detail to help understanding of the present invention.

[0053] The terms or words used in this specification and claims should not be interpreted as limited to their ordinary meanings or dictionary meanings, but should be interpreted based on the principle that the inventor can appropriately define the concept of the term in order to best explain his invention. Therefore, they should be understood in a sense and meaning consistent with the technical concept of the present invention.

[0054] The terms used in this specification are only used to describe exemplary embodiments and are not intended to limit the present invention. Unless the context clearly indicates otherwise, a singular expression includes a plural expression.

[0055] In this specification, terms such as "include", "comprises" or "has" specify the presence of stated features, numbers, steps, components or their combinations, but do not preclude the presence or addition of one or more other features, numbers, steps, components or their combinations.

[0056] The term "combination thereof" contained in a Markush statement refers to a mixture or combination of one or more selected from the group consisting of the listed elements in the Markush statement and refers to including one or more selected from the group consisting of the listed elements.

[0057] In this specification, "A and / or B" means "A or B or both".

[0058] In this specification, unless otherwise specifically stated, "%" means % by weight.

[0059] The specific surface area herein can be measured by the BET (Brunauer-Emmett-Teller) method, for example, by a porosimetry analyzer (Bell Japan Inc., Belsorp-II mini) using a nitrogen adsorption and desorption method using a BET 6-point method.

[0060] In this specification, the average particle size (D 50 ) can be defined as the particle size at the 50% point in the particle size distribution. The average particle size is not particularly limited but can be measured using methods such as laser diffraction or scanning electron microscopy (SEM) imaging. Laser diffraction methods can generally measure particle sizes from submicron to several millimeters, providing results with high reproducibility and resolution.

[0061] In this specification, the full width of the negative electrode is defined as the X-axis direction, the full length of the negative electrode is defined as the Y-axis direction, and the direction perpendicular to the plane formed by the combination of the X-axis and Y-axis directions is defined as the Z-axis direction. The X-axis and Y-axis directions are referred to as the horizontal direction.

[0062] Negative electrode for lithium secondary battery

[0063] [First embodiment]

[0064] Figure 1 is a top view of a negative electrode according to one embodiment of the present invention, Figure 2 is a vertical cross-sectional view of a negative electrode according to one embodiment of the present invention.

[0065] Referring to these figures, a negative electrode 10 for a lithium secondary battery (hereinafter referred to as "negative electrode") according to a first embodiment includes: a first negative electrode active material layer 11 formed on one or both surfaces of a current collector 13; and a second negative electrode active material layer 12 formed on the first negative electrode active material layer 11, wherein the second negative electrode active material layer 12 includes a plurality of recessed portions 12a and a plurality of non-recessed portions 12b recessed toward the first negative electrode active material layer 11, wherein the recessed portions 12a and the non-recessed portions 12b are alternately arranged in a horizontal direction, and the recessed portions 12a are filled with a conductive layer 14 containing a conductive material, wherein the thickness of the conductive layer 14 filled in the recessed portions 12a is less than the thickness of the non-recessed portions 12b, and the surface of the second negative electrode active material layer 12 has a pattern formed by steps between the conductive layer 14 and the non-recessed portions 12b.

[0066] Figure 2 The embodiment shown here has first negative electrode active material layer 11 and second negative electrode active material layer 12 sequentially formed on one surface of current collector 13. However, the present invention is not limited to this configuration, and first negative electrode active material layer 11 and second negative electrode active material layer 12 may be sequentially formed on both surfaces of current collector 13.

[0067] The first negative electrode active material layer 11 contains a carbon-based first negative electrode active material, which provides excellent structural stability despite its slightly smaller capacity. The second negative electrode active material layer 12 contains a second negative electrode active material that is different from the carbon compound. The second negative electrode active material is selected because it has a higher capacity and excellent input / output characteristics compared to the carbon-based first negative electrode active material. For example, in order to enhance the fast charging performance of the battery, the upper layer of the negative electrode may contain a second negative electrode active material such as a transition metal or its oxide represented by a silicon-based material that is conducive to the diffusion of lithium ions, and in order to compensate for the inherent structural instability of these active materials, the first negative electrode active material layer contains a carbon-based first negative electrode active material. This structure alleviates the problem of expansion of the negative electrode active material layer in the thickness direction during repeated cycles, and can improve the input / output characteristics even when the negative electrode is highly loaded.

[0068] The concave portion 12a may be recessed toward the first negative electrode active material layer 11 to a depth corresponding to the thickness of the non-concave portion 12b. Figure 2As shown, the interior of the recessed portion 12a of the second negative electrode active material layer 12 may not contain the second negative electrode active material, thereby exposing the first negative electrode active material layer 11. The conductive layer 14 fills the recessed portion 12a, resulting in a structure in which multiple columns of non-recessed portions 12b and multiple columns of conductive layer 14 are alternately arranged on the first negative electrode active material layer 11.

[0069] Multiple non-recessed portions 12b are spaced apart by a predetermined distance. Recessed portions 12a are located between the separated non-recessed portions 12b. These recessed portions 12a are filled with a conductive layer 14. The thickness of the conductive layer 14 is smaller than that of the non-recessed portions 12b. The step created by the thickness difference between the non-recessed portions 12b and the conductive layer 14 acts to buffer the volume changes of the negative electrode active material layers 11 and 12 during repeated charge and discharge cycles. This buffering effect helps prevent the negative electrode active material from peeling off during charge and discharge, thereby improving battery performance.

[0070] When a step pattern is formed between the non-recessed portion 12b and the conductive layer 14, the surface area of ​​the second negative electrode active material layer is larger than when such a step pattern is absent. This increased surface area can enhance lithium ion pathways, reduce negative electrode resistance, and improve input / output characteristics.

[0071] In the exemplary embodiment, the second negative active material layer 12 and the conductive layer 14 are provided on the first negative active material layer 11, covering the surface of the first negative active material layer 11. As a result, the second negative active material layer having excellent input / output characteristics is located on the negative electrode surface, providing the advantage of rapid charging.

[0072] The number of columns of the non-recessed portion 12b and the recessed portion 12a can be appropriately selected according to the size of the negative electrode after punching, and there is no particular limitation. Specifically, these columns can be configured to be at least 100 columns, more specifically 200 to 9000 columns, and even more specifically 200 to 8000 columns. Here, the negative electrode after punching refers to a negative electrode that is grooved and cut into a predetermined full width and full length suitable for assembly into a secondary battery (see Figure 1 ).

[0073] The horizontal width (X-axis or Y-axis direction) of each of the plurality of non-concave portions 12 b may be 50 μm to 1500 μm, more specifically 150 μm to 1250 μm, and even more specifically 200 μm to 1000 μm.

[0074] The horizontal width (X-axis or Y-axis direction) of each of the plurality of recesses 12a may be less than or equal to the horizontal width of the non-recessed portion 12b, specifically 10 to 800 μm, more specifically 10 to 600 μm, and even more specifically 20 to 400 μm.

[0075] When the horizontal widths of the non-concave portion 12 b and the concave portion 12 a are within these ranges, the effects of improving input / output characteristics and resistance are optimized, and life characteristics and capacity characteristics can be further improved.

[0076] The length of the step, i.e., the difference in thickness between the non-recessed portion 12b and the conductive layer 14, can be 5 μm to 60 μm, preferably 7.5 μm to 40 μm, and more preferably 10 μm to 30 μm. A negative electrode having a step within this range can exhibit excellent resistance improvement due to the step, while also improving the energy density of the battery. Here, the step refers to the length in the thickness direction (Z direction).

[0077] The recesses 12a may be formed at regular intervals or at irregular (random) intervals. In addition, the recesses 12a may be formed in a uniform shape or in an irregular shape.

[0078] In one embodiment of the present invention, the negative electrode is a high-load negative electrode, and the average combined loading of the first negative electrode active material layer and the second negative electrode active material layer is 4 mAh / cm 2 More specifically, 4 mAh / cm 2 Up to 8 mAh / cm 2 .

[0079] In one embodiment of the present invention, the conductive layer 14 may not include negative electrode active materials.

[0080] When the conductive layer 14 does not contain negative electrode active material, lithium ions can move quickly through the conductive layer 14, which can be more conducive to improving resistance and input / output characteristics. However, since there is no negative electrode active material in the conductive layer 14 to absorb lithium, there is a risk of lithium precipitation. In this case, it is preferred to design the horizontal width (X-axis or Y-axis direction) of the conductive layer to be smaller than the horizontal width of the recess 12a. Specifically, the horizontal width of the conductive layer 14 can be 10μm to 400μm, preferably 10μm to 300μm, and more preferably 20μm to 200μm.

[0081] When the conductive layer 14 does not contain a negative electrode active material, the conductive layer 14 may contain 80 to 100 parts by weight of a conductive material and up to 20 parts by weight of a binder. The conductive material and the binder are not particularly limited and may be known materials for negative electrodes for lithium secondary batteries. Specific examples of the conductive material include carbon black, graphite, carbon fiber, carbon nanotubes, metal powders, conductive metal oxides, and organic conductive materials, among which carbon nanotubes, carbon nanofibers, and carbon black are preferred as the conductive material for the conductive layer.

[0082] In another embodiment of the present invention, the conductive layer 14 may further include a negative electrode active material.

[0083] When the conductive layer 14 contains a negative electrode active material, the conductive layer contributes to the negative electrode's capacity performance and is more advantageous in terms of high electrode loading. In addition, the presence of the negative electrode active material in the conductive layer 14 allows lithium to be absorbed, thereby reducing the risk of lithium precipitation.

[0084] In one embodiment, the negative electrode active material included in the conductive layer 14 may be the same compound as the second negative electrode active material included in the non-recessed portion 12 b , and may further include a carbon-based first negative electrode active material.

[0085] In an exemplary embodiment, the conductive layer 14 may have the same composition as the second negative electrode active material layer. The term "same composition" means that the negative electrode active material, conductive material, and binder constituting the conductive layer 14 are identical compounds and have the same weight ratio as the negative electrode active material, conductive material, and binder constituting the second negative electrode active material layer. When the conductive layer 14 and the second negative electrode active material layer 12 have the same composition, the negative electrode manufacturing method can be simplified.

[0086] When the conductive layer 14 includes a negative electrode active material, in one embodiment, the weight percent of the conductive material included in the conductive layer 14 may be greater than the weight percent of the conductive material included in the second negative electrode active material layer 12. In this case, the excellent electrical conductivity of the conductive layer 14 can alleviate the structural destruction of the conductive network caused by the volume change of the negative electrode active material layer.

[0087] In one embodiment, the conductive layer 14 may include 70 to 94 parts by weight of the negative electrode active material, 5 to 20 parts by weight of the conductive material, and 1 to 10 parts by weight of the binder, relative to 100 parts by weight of the conductive layer. In a preferred embodiment, the conductive layer 14 may include 80 to 93 parts by weight of the negative electrode active material, 5.5 to 15 parts by weight of the conductive material, and 2 to 9 parts by weight of the binder. More preferably, it may include 82 to 92 parts by weight of the negative electrode active material, 6 to 10 parts by weight of the conductive material, and 2.5 to 8 parts by weight of the binder.

[0088] To control the electrical conductivity of conductive layer 14 to be greater than that of second negative electrode active material layer 12, the content of the conductive material in the conductive layer can be increased as described above. Alternatively, a conductive material having a higher electrical conductivity than that of the conductive material contained in second negative electrode active material layer 12b can be selected as the conductive material for conductive layer 14.

[0089] The current collector 13 can be made of a metal with high conductivity that facilitates the adhesion of the electrode active material slurry. It can be any material as long as it is non-reactive within the battery's voltage range. Specifically, copper, stainless steel, aluminum, nickel, titanium, calcined carbon; stainless steel surface-treated with carbon, nickel, titanium, or silver; aluminum-cadmium alloys; non-conductive polymers surface-treated with a conductive material; or conductive polymers can be used. Furthermore, the surface may have fine irregularities to enhance the binding force of the negative electrode active material. The current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, or non-woven fabrics.

[0090] The first negative electrode active material layer 11 may include a carbon-based first negative electrode active material as the negative electrode active material. The carbon-based first negative electrode active material is structurally more stable than the second negative electrode active material included in the second negative electrode active material layer described below. Because it exhibits minimal volume change during repeated charge and discharge cycles, it is preferably used as the negative electrode active material in the lower layer.

[0091] Specifically, both low-crystalline carbon and high-crystalline carbon can be used as carbon-based first negative electrode active materials. Representative low-crystalline carbons include soft carbon and hard carbon. High-crystalline carbons that can be used include natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesocarbon microbeads, mesophase pitch, and coke derived from petroleum or coal tar pitch. Particularly preferred are graphite-based negative electrode active materials, such as natural graphite or artificial graphite, which maintain structural and electrical properties while allowing reversible intercalation and deintercalation of lithium ions.

[0092] Typically, to address the problem of insufficient adhesion between the negative electrode active material and the negative electrode current collector, a binder is added or the negative electrode is further rolled. However, increasing the binder content or the degree of rolling can reduce the porosity of the negative electrode active material layer. This reduced porosity makes it difficult for lithium ions to diffuse from the surface of the negative electrode active material layer to the interior, thereby increasing the resistance of the negative electrode and causing a decrease in secondary battery performance.

[0093] By including natural graphite or a spherical graphite-based negative electrode active material with excellent adhesion in the first negative electrode active material layer located between the second negative electrode active material layer and the collector, the adhesion between the negative electrode active material and the collector can be improved without increasing the binder content or the degree of rolling of the negative electrode.

[0094] In one embodiment of the present invention, in order to improve adhesion while maintaining output characteristics within an appropriate range, the first negative electrode active material layer may be composed of natural graphite and / or artificial graphite as a negative electrode active material. In order to maximize adhesion, the carbon-based first negative electrode active material may specifically be composed of natural graphite.

[0095] In one embodiment of the present invention, the average particle size (D 50 ) can be 1 μm to 30 μm, specifically 5 μm to 25 μm, and more specifically 7 μm to 23 μm.

[0096] When the graphite-based active material contained in the first negative electrode active material layer has an average particle size within this range, appropriate electrode density can be achieved while allowing the first negative electrode active material layer to be appropriately formed on the current collector.

[0097] In one embodiment of the present invention, the specific surface area of ​​natural graphite can be 1.5m 2 / g to 8m 2 / g, specifically 2.1m 2 / g to 4.5m 2 / g, more specifically 2.5m 2 / g to 4m 2 When the natural graphite has a specific surface area within this range, it can provide adhesion to the negative electrode while preventing an excessive increase in initial irreversible capacity during charge and discharge due to the specific surface area.

[0098] In addition, the tap density of natural graphite can be 0.9 g / cc to 1.3 g / cc, specifically 0.92 g / cc to 1.2 g / cc, and more specifically 0.95 g / cc to 1.15 g / cc. When the natural graphite has a tap density within this range, the first negative electrode active material can have sufficient adhesion to the negative electrode and achieve excellent energy density.

[0099] In one embodiment of the present invention, the specific surface area of ​​artificial graphite can be 0.4m 2 / g to 5.0m 2 / g, specifically 0.5m 2 / g to 4.0m 2 / g, more specifically 0.6m 2 / g to 3.0m 2 When the artificial graphite has a specific surface area within this range, an increase in the initial irreversible capacity during charge and discharge can be prevented.

[0100] Furthermore, the tap density of the artificial graphite may be 0.7 g / cc to 1.1 g / cc, specifically 0.75 g / cc to 1.05 g / cc, and more specifically 0.8 g / cc to 1.0 g / cc. When the artificial graphite has a tap density within this range, the first negative active material may achieve excellent energy density.

[0101] In one embodiment of the present invention, the sphericity of the graphite-based negative electrode active material included in the first negative electrode active material layer may be 0.8 or more, preferably 0.85 to 1, and more preferably 0.9 to 1.

[0102] The higher the sphericity of the graphite-based negative electrode active material, the better the binder can adhere to the surface of the negative electrode active material. This prevents agglomeration or aggregation, thereby achieving smooth dispersion and improving the overall adhesion of the first negative electrode active material layer.

[0103] The sphericity can be a value obtained by dividing the circumference of a circle having the same area as the projected image when the graphite-based negative electrode active material is projected by the perimeter of the projected image, and can be expressed by the following mathematical formula 1. The sphericity can be measured using a particle shape analyzer (e.g., Sysmex FPIA-3000 from Malvern Instruments).

[0104] [Mathematical formula 1]

[0105] Sphericity = (circumference of a circle with the same area as the projected image of the graphite-based active material) / (circumference of the projected image)

[0106] In one embodiment of the present invention, for the sake of structural stability and capacity retention of the negative electrode, it is preferred that the negative electrode active material contained in the first negative electrode active material layer 11 only consists of the above-mentioned carbon-based first negative electrode active material.

[0107] In one embodiment of the present invention, the first negative electrode active material layer 11 may have a thickness of 200 μm or less, specifically, 20 μm to 150 μm, and more specifically, 30 μm to 100 μm.

[0108] When the first negative electrode active material layer has a thickness within the specified range, it can be appropriately formed on the negative electrode collector and provide appropriate adhesion between the collector and the second negative electrode active material layer.

[0109] Carbon-based first negative electrode active materials maintain the structure and electrical properties of negative electrode active materials, allowing reversible insertion and deinsertion of lithium ions. However, their low capacity limits their use in high-energy-density batteries. The present invention addresses this issue by including a second negative electrode active material, different from the carbon-based first negative electrode active material, in the second negative electrode active material layer.

[0110] In one embodiment of the present invention, the second negative electrode active material may be at least one active material particle selected from the group consisting of transition metals, transition metal oxides, transition metal alloys, oxides of transition metal alloys, and transition metal-containing composites. The transition metal may be any one of Group 14 and Group 15 transition metals. Specifically, the transition metal may be a silicon-based material, a tin-based material, or a germanium-based material. The transition metals contained in the transition metal oxides, transition metal alloys, oxides of transition metal alloys, and transition metal-containing composites may be the above-mentioned transition metals.

[0111] For example, when the transition metal is a silicon-based material, the second negative electrode active material may be selected from the group consisting of Si, SiO x (0 < x < 2), Si-C composites, and Si metal alloys, or a mixture of one or more of these materials. Specifically, it may be silicon oxide particles (SiO x , 0 < x < 2), where the silicon oxide particles (SiO x , 0 < x < 2) may be a composite of crystalline SiO2 and amorphous Si.

[0112] The metal in the Si metal alloy may be an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, excluding Si. Specific examples of the metal include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0113] The average particle size (D 50 ) of the silicon-based particles may be from 1 μm to 30 μm, specifically from 3 μm to 20 μm, and more specifically from 4 μm to 10 μm. If the average particle size (D 50 ) of the silicon-based particles is too small, the side reactions with the electrolyte may increase, resulting in a decrease in the cycling performance. On the contrary, if the average particle size (D 50 ) is too large, the significant volume expansion during the charge-discharge process may cause the particles to crack, also leading to a decrease in the cycling performance. Therefore, when the silicon-based particles meet the above size range, the side reactions with the electrolyte and the volume expansion of the silicon-based particles can be maintained at an optimal level, thereby providing excellent cycling performance for the battery containing these particles.

[0114] In one embodiment of the present invention, in addition to the second negative electrode active material, the second negative electrode active material layer may further include a carbon-based first negative electrode active material. The carbon-based first negative electrode active material included in the second negative electrode active material layer may be one or both selected from natural graphite and artificial graphite.

[0115] In one embodiment of the present invention, the second negative electrode active material layer 11 may have a thickness of 200 μm or less, specifically, 20 μm to 150 μm, and more specifically, 30 μm to 100 μm.

[0116] The first negative electrode active material layer and the second negative electrode active material layer may each optionally contain a binder, a conductive material, a filler, and other additives in addition to the negative electrode active material.

[0117] The binder facilitates the bonding of the active material and the conductive material and their bonding to the current collector, and is not particularly limited. Examples of binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers.

[0118] The content of the binder may generally be 1 to 30 wt % based on the total weight of the first negative electrode active material layer or the second negative electrode active material layer.

[0119] The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. Examples include conductive materials such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate whiskers; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

[0120] The content of the conductive material may generally be 1 to 30 wt % based on the total weight of the first negative electrode active material layer or the second negative electrode active material layer.

[0121] Fillers are optionally used as a component to suppress electrode expansion and are not particularly limited as long as they are fibrous materials that do not cause chemical changes in the battery. Examples include fibrous materials such as olefin polymers such as polyethylene and polypropylene; glass fibers; and carbon fibers.

[0122] [Second embodiment]

[0123] Figure 3is a vertical cross-sectional view of a negative electrode according to another embodiment of the present invention, Figure 4 is a vertical cross-sectional view of a negative electrode according to still another embodiment of the present invention.

[0124] Referring to these drawings, the negative electrode 10 according to the second embodiment includes: a first negative electrode active material layer 11 formed on a collector 13; and a second negative electrode active material layer 12 formed on the first negative electrode active material layer 11, wherein the second negative electrode active material layer 12 includes a plurality of recessed portions 12a and a plurality of non-recessed portions 12b recessed toward the first negative electrode active material layer 11, wherein the recessed portions 12a and the non-recessed portions 12b are alternately arranged in a horizontal direction, and wherein the surface of the second negative electrode active material layer has a pattern formed by steps between the non-recessed portions and the recessed portions.

[0125] The second negative electrode active material layer 12 includes a plurality of recessed portions 12a and a plurality of non-recessed portions 12b arranged alternately with steps, thereby forming a stepped pattern across the entire surface of the second negative electrode active material layer 12. As a result, the reactive specific surface area of ​​the negative electrode surface of the present invention is increased compared to a flat negative electrode. This suppresses the increase in resistance associated with high negative electrode loads. Furthermore, the stepped spaces on the surface of the second negative electrode active material layer 12 act as a buffer against volume changes in the negative electrode active material layers 11 and 12, resulting in excellent structural stability.

[0126] Specifically, in the negative electrode 10 of the second embodiment, since the interior of the recessed portion 12 a is vacant, stress caused by volume expansion of the non-recessed portion 12 b can be more effectively alleviated.

[0127] The first negative electrode active material layer 11 includes a carbon-based first negative electrode active material, which, despite having a slightly lower capacity, provides excellent structural stability. The second negative electrode active material layer 12 may include a second negative electrode active material having a high capacity and excellent input / output characteristics. The details of the first and second negative electrode active materials have been previously described, and therefore, a repetitive description thereof will be omitted.

[0128] In the exemplary embodiment, the second negative active material layer 12 is provided on the first negative active material layer 11, covering the surface of the first negative active material layer 11. As a result, the second negative active material layer having excellent input / output characteristics is located on the negative electrode surface, providing a negative electrode that is advantageous for rapid charging.

[0129] The cross-sectional shape of the recess 12a may also be as follows Figure 3 The inverted triangle shown, or Figure 4 However, the present invention is not limited to these shapes.

[0130] The recesses 12a may be formed at regular intervals or irregular (random) intervals. In addition, the recesses 12a may have a uniform shape or a non-uniform shape.

[0131] The horizontal width (Y-axis direction) of the non-concave portion 12 b may be 50 to 1500 μm, more specifically 150 to 1250 μm, and even more specifically 200 to 1000 μm.

[0132] The horizontal width (Y-axis direction) of the recess 12a may be 10 to 800 μm, more specifically 10 to 600 μm, and even more specifically 20 to 400 μm, within a range less than or equal to the horizontal width of the non-recessed portion 12b.

[0133] The number of rows of non-recessed portions 12b and recessed portions 12a can be appropriately selected according to the size of the electrode after punching and is not particularly limited. Specifically, it can be configured to be 100 or more rows, more specifically 200 to 9000 rows, and even more specifically 200 to 8000 rows.

[0134] The plurality of rows of non-recessed portions 12b are spaced apart at predetermined intervals, and the recessed portions 12a are located between the spaced non-recessed portions. Unlike the first embodiment, the interior of the recessed portions 12a in this embodiment is not filled.

[0135] The length of the step, i.e., the difference in thickness between the non-recessed portion 12b and the recessed portion 12a, can be from 5 μm to the thickness of the non-recessed portion 12b. Specifically, it can be from 5 μm to 60 μm, preferably from 7.5 μm to 40 μm, and more preferably from 10 μm to 30 μm. Here, the step can be defined as the difference between the maximum thickness of the non-recessed portion 12b and the minimum thickness of the recessed portion 12a. A negative electrode having a step within this range can achieve an excellent resistance improvement effect due to the step, while also improving the energy density of the battery.

[0136] Figure 3 and 4 While an embodiment in which the second negative electrode active material layer is exposed in recess 12a is shown, the present invention does not exclude embodiments in which both the first and second negative electrode active material layers are exposed. However, because the first negative electrode active material layer has a slower lithium ion diffusion rate than the second negative electrode active material layer, it is preferred that the first negative electrode active material layer not be exposed or that the exposed surface area be extremely small.

[0137] The negative electrode of the second embodiment of the present invention is a high-load negative electrode, and the average total loading of the first and second negative electrode active material layers can be 4 mAh / cm 2 More specifically, 4 mAh / cm 2 Up to 8 mAh / cm 2 .

[0138] Regarding the negative electrode of the second embodiment, details of the current collector, the first negative electrode active material layer, and the second negative electrode active material layer are the same as those of the negative electrode of the first embodiment, and thus duplicate contents are omitted.

[0139] lithium secondary batteries

[0140] Next, the lithium secondary battery of the present invention will be described.

[0141] A lithium secondary battery according to one embodiment of the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0142] The lithium secondary battery of the present invention can be manufactured by conventional methods known in the art. For example, it can be manufactured by placing a separator between a positive electrode and a negative electrode and introducing an electrolyte.

[0143] In a lithium secondary battery, the negative electrode is as described above. For example, the negative electrode may include: a first negative electrode active material layer formed on one or both surfaces of the current collector and containing a first negative electrode active material that is a carbon compound as the negative electrode active material; and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second negative electrode active material different from the carbon compound as the negative electrode active material, wherein the second negative electrode active material layer includes a plurality of recessed portions and a plurality of non-recessed portions that are recessed toward the first negative electrode active material layer, wherein the recessed portions and the non-recessed portions are alternately arranged in a horizontal direction, the recessed portions are filled with a conductive layer containing a conductive material, wherein the thickness of the conductive layer filled in the recessed portions is less than the thickness of the non-recessed portions, and the surface of the second negative electrode active material layer has a pattern formed by steps between the conductive layer and the non-recessed portions.

[0144] In addition, the negative electrode may be a negative electrode including the following components: a first negative electrode active material layer, which is formed on one or both surfaces of the collector and contains a first negative electrode active material which is a carbon compound as a negative electrode active material; and a second negative electrode active material layer, which is formed on the first negative electrode active material layer and contains a second negative electrode active material different from the carbon compound as a negative electrode active material, wherein the second negative electrode active material layer includes a plurality of recessed portions and a plurality of non-recessed portions which are recessed toward the first negative electrode active material layer, wherein the recessed portions and the non-recessed portions are alternately arranged in a horizontal direction, and wherein the surface of the second negative electrode active material layer has a pattern formed by steps between the non-recessed portions and the recessed portions.

[0145] The first negative active material layer 11 includes a carbon-based first negative active material that provides excellent structural stability despite having a slightly smaller capacity. The second negative active material layer 12 may include a second negative active material having a high capacity and excellent input / output characteristics.

[0146] The positive electrode may include a positive electrode current collector and a positive electrode active material layer including a positive electrode active material formed on the positive electrode current collector.

[0147] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. Examples include stainless steel, aluminum, nickel, titanium, calcined carbon, or surface-treated materials such as aluminum or stainless steel treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector is generally 3 to 500 μm, and may have fine concavoconvexities on its surface to enhance the adhesion of the positive electrode active material. It can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, or non-woven fabrics.

[0148] The positive electrode active material is not particularly limited and may include any compound known in the art that can reversibly intercalate and deintercalate lithium. Specifically, the positive electrode active material may include: a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a compound of the formula Li 1+x Mn 2-x Lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O; LiNi 1-x M x Nickel-type lithium nickel oxide represented by O2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); formula LiMn 2-x M x Lithium manganese composite oxide represented by Li2Mn3MO8 (wherein M=Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x Lithium manganese composite oxide with a spinel structure represented by O4; LiMn2O4 in which a portion of Li is replaced by alkaline earth metal ions; disulfide compounds; lithium iron phosphate represented by LiFePO4; disulfide compounds; Fe2(MoO4)3, etc., but not limited thereto.

[0149] However, since improving energy density is very important for the battery to which the present invention is applied, the positive electrode active material may be a lithium transition metal oxide having a high nickel (Ni) content represented by the following Chemical Formula 1.

[0150] Li 1+x Ni a Co b Mn c M1-(a+b+c) O 2-y A y (1)

[0151] In the above formula:

[0152] M is at least one selected from the group consisting of Cu, Ti, Mg, Al, Pt and Zr,

[0153] A is a halogen that replaces oxygen,

[0154] 0≤x≤0.5, 0.8≤a≤1, 0≤b≤0.2, 0≤c≤0.2, 0.9≤a+b+c≤1, 0≤y≤0.001.

[0155] More specifically, in the above Chemical Formula 1, a may be in the range of 0.88≤a<1.

[0156] In addition, the lithium transition metal oxide represented by Chemical Formula 1 may be mixed with other active materials.

[0157] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the above-mentioned positive electrode active material.

[0158] Positive electrode conductive material is used to give electrode conductivity, and can include carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide or organic conductive material. Commercially available conductive materials include acetylene black series (for example, the product of Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (for example, the product of Armak Company), Vulcan XC-72 (for example, the product of Cabot Company) and Super P (for example, the product of MMM). Among them, carbon nanotube, carbon nanofiber and carbon black are the preferred conductive materials of the present invention, and carbon nanotube is most preferably. The conductive network of carbon nanotube can alleviate the binder migration in the positive electrode slurry drying process, so that carbon nanotube becomes the most ideal conductive material of the positive electrode of the present invention.

[0159] The BET specific surface area of ​​carbon nanotubes can be 100 m 2 / g to 1000m 2 / g, specifically 150m 2 / g to 800m 2 / g, 150m 2 / g to 500m 2 / g, 150m 2 / g to 300m 2 / g or 150m 2 / g to 200m 2 / g.

[0160] In the positive electrode active material layer, the content of the positive electrode active material may be 0.1 wt % to 30 wt %, specifically 0.1 wt % to 10 wt %, and more specifically 0.5 wt % to 5 wt %.

[0161] The positive electrode binder can be any commonly used binder polymer without limitation. Examples include various binder polymers such as polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like.

[0162] In the positive electrode active material layer, the positive electrode binder may be included in an amount of 0.1 wt % to 30 wt %, specifically 0.1 wt % to 10 wt %, and more specifically 0.5 wt % to 5 wt %.

[0163] The separator may be any porous substrate commonly used as a separator in lithium secondary batteries. Examples include, but are not limited to, polyolefin-based porous films or nonwoven fabrics. It is particularly preferred that the separator exhibit low resistance to ion migration and have excellent electrolyte wettability.

[0164] Examples of the polyolefin-based porous membrane include membranes formed from polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polybutene, and polypentene, alone or in combination.

[0165] In addition to polyolefin nonwovens, nonwovens can also include nonwovens made from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, either alone or in combination. Nonwovens can be made from spunbond or meltblown fibers made from long fibers.

[0166] The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm. The pore size and porosity of the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

[0167] Meanwhile, in order to improve the mechanical strength of the separator made of the porous substrate and prevent a short circuit between the positive electrode and the negative electrode, a porous coating layer containing inorganic particles and a binder polymer may be further included on at least one surface of the porous substrate.

[0168] Meanwhile, in the lithium secondary battery, the electrolyte may contain an organic solvent and a lithium salt, which are generally used in the electrolyte without particular limitation.

[0169] Any organic solvent can be used without limitation, as long as it is a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, examples of organic solvents include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0170] Among them, carbonate solvents are preferred. More specifically, a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, and a linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) with low viscosity is more preferred.

[0171] Lithium salts can be used without limitation as long as they are any compounds capable of providing lithium ions for lithium secondary batteries. Specifically, the lithium salts may include: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2. Preferably, the concentration of the lithium salt contained in the electrolyte is about 0.6 mol% to 2 mol%.

[0172] In addition to the above-mentioned electrolyte components, the electrolyte may also include one or more additives to improve the life characteristics of the battery, prevent battery capacity degradation, and increase discharge capacity. Examples of such additives include pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glycol ethers, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum chloride. The content of these additives may be 0.1 to 5 weight % based on the total weight of the electrolyte.

[0173] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly with a separator provided between the positive electrode and the negative electrode, placing the electrode assembly into a cylindrical or prismatic battery case, and then injecting the electrolyte. Alternatively, the electrode assemblies can be stacked, impregnated with electrolyte, and then the resulting product can be placed in a battery case and sealed to complete the manufacturing process.

[0174] In the manufacturing process of the lithium secondary battery of the present invention, the electrode assembly can be dried to remove one or more organic solvents used in the positive electrode preparation process. These solvents can be selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate. If the electrolyte used contains the same composition as the organic solvent used in the positive electrode preparation, the drying process of the electrode assembly can be omitted.

[0175] Unlike the above-described lithium secondary battery, a lithium secondary battery according to another embodiment of the present invention may be an all-solid-state battery.

[0176] The battery case may be any battery case conventionally used in the art and may not be limited in shape according to the intended use of the battery, and may be, for example, cylindrical using a can, prismatic, pouch, or coin-shaped.

[0177] The lithium secondary battery of the present invention exhibits excellent resistance characteristics, discharge capacity, output characteristics and capacity retention, making it useful in portable devices such as mobile phones, notebook computers, digital cameras, energy storage systems (ESS) and electric vehicles such as hybrid electric vehicles (HEV).

[0178] Method for manufacturing negative electrode for lithium secondary battery

[0179] Next, a method for producing the negative electrode for a lithium secondary battery of the present invention will be described.

[0180] Figure 5 1 is a flowchart illustrating a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention.

[0181] Reference Figure 5 , a method for manufacturing a negative electrode in one embodiment includes: preparing a first negative electrode slurry P11; preparing a second negative electrode slurry P12; preparing a conductive layer slurry P13; a first coating process of coating the first negative electrode slurry P14; a second coating process of coating the second negative electrode slurry and the conductive layer slurry P15; and drying the first negative electrode slurry, the second negative electrode slurry and the conductive layer slurry P16.

[0182] This negative electrode manufacturing method is used to manufacture the negative electrode of the first embodiment described above. It is characterized by a secondary coating process in which the second negative electrode slurry and the conductive layer slurry are applied in a horizontally alternating pattern. Specifically, the second negative electrode slurry is applied in multiple columns at a predetermined pitch, and the conductive layer slurry is applied in multiple columns at a predetermined pitch, but the second negative electrode slurry and the conductive layer slurry are alternately applied.

[0183] The second negative electrode slurry applied in multiple columns is dried to form the non-recessed portions 12b of the second negative electrode active material layer, and the conductive layer slurry applied in multiple columns is dried to form the conductive layer 14. The conductive layer 14 fills a portion of the recessed portions 12a, which are the spacing regions between the separated non-recessed portions and the adjacent non-recessed portions.

[0184] This negative electrode manufacturing method is different from the method of forming a pattern on the surface of the negative electrode active material layer by laser etching described below, and has the advantage of not damaging any of the negative electrode active material layer, thereby reducing manufacturing costs.

[0185] Process P11 for preparing the first negative electrode slurry may include mixing and stirring a carbon-based first negative electrode active material, a conductive material, and a binder in a solvent. Compared to the second negative electrode active material, the carbon-based first negative electrode active material has superior structural stability, making it less likely to be deintercalated from the current collector. Therefore, it is preferably used as the active material in the first negative electrode slurry to form a first negative electrode active material layer closer to the current collector.

[0186] The carbon-based first negative electrode active material, the conductive material, and the binder contained in the first negative electrode slurry have been described in detail above, and thus repeated descriptions are omitted.

[0187] The process P12 of preparing the second negative electrode slurry may include mixing and stirring the second negative electrode active material, the conductive material, and the binder in a solvent.

[0188] Carbon-based first negative electrode active materials can maintain the structure and electrical properties of negative electrode active materials, allowing reversible insertion and extraction of lithium ions. However, due to their low capacity, they are limited in the manufacture of high-energy-density batteries. Therefore, by including a second negative electrode active material of a different type from the carbon-based first negative electrode active material in the second negative electrode slurry to form a second negative electrode active material layer, a negative electrode suitable for high-energy-density batteries can be manufactured.

[0189] The second negative electrode active material, the conductive material, and the binder contained in the second negative electrode slurry have been described in detail above, and thus repeated descriptions are omitted.

[0190] The process P13 of preparing the conductive layer slurry includes mixing and stirring the electrode materials in a solvent.

[0191] As previously mentioned, the conductive layer may or may not contain negative electrode active materials. In one embodiment, the conductive layer slurry may contain negative electrode active materials, while in another embodiment, it may not contain negative electrode active materials.

[0192] In an embodiment in which the conductive layer slurry includes a negative electrode active material, the conductive layer slurry may include the same compound as the second negative electrode active material included in the second negative electrode slurry, and may further include a carbon-based first negative electrode active material.

[0193] In an embodiment where the conductive layer slurry includes a negative electrode active material, the conductive layer slurry and the second negative electrode slurry may have the same composition. Having the same composition means that the negative electrode active material, conductive material, and binder constituting the conductive layer 14 and the negative electrode active material, conductive material, and binder constituting the second negative electrode active material layer are each the same compound and have the same weight ratio.

[0194] In embodiments where the conductive layer slurry includes a negative electrode active material, the weight percent of the conductive material in the solids of the conductive layer slurry may be greater than the weight percent of the conductive material in the solids of the second negative electrode slurry.

[0195] The conductive layer may not contain negative active material to maximize the buffering effect on the volume change of the second negative active material layer. In this embodiment, the conductive layer slurry may contain 80 to 100 parts by weight of conductive material and 20 parts by weight or less of binder in solid matter.

[0196] The conductive material and the adhesive have been described in detail above, and thus repeated description will be omitted.

[0197] The solvent used to prepare the first negative electrode slurry, the second negative electrode slurry, and the conductive layer slurry can be any solvent commonly used in the art. Examples include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One or more of these solvents, or a mixture of two or more thereof, can be used.

[0198] At the same time, in order to form a step between the non-recessed portion of the second negative electrode active material layer formed by the second negative electrode slurry and the conductive layer formed by the conductive layer slurry, the solid content of the second negative electrode slurry can be higher than the solid content of the conductive layer slurry. Therefore, the thickness of the second negative electrode active material layer formed by the dried second negative electrode slurry can be greater than the thickness of the conductive layer formed by the conductive layer slurry. In other words, the level of the step between the non-recessed portion and the conductive layer can be controlled by adjusting the solid content of each of the second negative electrode slurry and the conductive layer slurry.

[0199] The first coating process P14 includes coating the first negative electrode slurry onto the current collector 13. The coating method of the first negative electrode slurry is not limited, and any coating method commonly used in the art can be used. For example, a slot die coater can be used to coat the first negative electrode slurry.

[0200] The second coating process P15 includes coating the second negative electrode slurry and the conductive layer slurry onto the first negative electrode slurry. The second coating process P15 may be performed without drying the first negative electrode slurry after the first coating process P14, or after drying the first negative electrode slurry after the first coating process P14.

[0201] In the second coating process P15, the second negative electrode slurry may be coated in a plurality of columns at predetermined intervals and predetermined widths in the cross direction (CD). The coating width of the second negative electrode slurry in one column may be 50 to 1500 μm, more specifically 150 to 1250 μm, and even more specifically 200 to 1000 μm.

[0202] In the second coating process P15, the conductive layer slurry may be applied in a plurality of columns at predetermined intervals along the cross direction (CD) to have a predetermined width. The coating width of the conductive layer slurry of one column may be within the coating width range of the second negative electrode slurry, and may be 10 μm to 800 μm, more specifically 10 μm to 600 μm, and more specifically 20 μm to 400 μm. On the other hand, if the second negative electrode slurry does not contain a negative electrode active material, the coating width of the conductive layer slurry may be smaller. Specifically, the coating width of the conductive layer slurry may be 10 μm to 400 μm, preferably 10 μm to 300 μm, and even more preferably 20 μm to 200 μm.

[0203] In one embodiment, the coating width of the conductive layer slurry is consistent with the coating interval of the second negative electrode slurry, so that the first negative electrode slurry or the first negative electrode mixture layer is almost covered by the second negative electrode slurry and the conductive layer slurry, which is preferable in terms of the capacity and input / output characteristics of the negative electrode.

[0204] In one embodiment of the present invention, the second coating process P15 may use a nozzle printer to alternately coat the second negative electrode slurry and the conductive layer slurry.

[0205] Figure 7 The second coating process is shown. Figure 7 As shown, a nozzle printer is used as a coating device to simultaneously coat the second negative electrode slurry and the conductive layer slurry.

[0206] Reference Figure 7 The nozzle printer can continuously dispense the second negative electrode slurry 21 and the conductive layer slurry 22 in lines of predetermined width. Since the nozzle printer can easily control the coating width according to the coating speed, it is preferably used as a coating device for applying the second negative electrode slurry and the conductive layer slurry in an alternating pattern. The nozzle printer can include two or more nozzles, and the second negative electrode slurry 21 and the conductive layer slurry 22 can be discharged from multiple nozzles (first nozzle, second nozzle). The second negative electrode slurry 21 is dried to form the non-concave portion 12b of the second negative electrode active material layer, and the conductive layer slurry 22 is dried to form the conductive layer 14.

[0207] In an exemplary embodiment, the ratio of the total loading amount of the second negative electrode slurry and the conductive layer slurry to the loading amount of the first negative electrode slurry may be 3:1 to 1:3, specifically 2:1 to 1:2, more specifically 6:4 to 4:6. When the loading amount ratio is within this range, the negative electrode exhibits excellent structural stability and rate characteristics.

[0208] The drying process P16 is a process for drying and removing the solvent in the first negative electrode slurry, the second negative electrode slurry and the conductive layer slurry. The drying process can be performed after the first and second coating processes, or the first negative electrode slurry, the second negative electrode slurry and the conductive layer slurry can be dried at one time, or can be performed after the first coating process and after the second coating process respectively.

[0209] Figure 6 This is a flowchart showing another embodiment of the negative electrode manufacturing method of the present invention.

[0210] Reference Figure 6 According to another embodiment of the present invention, a method for manufacturing a negative electrode includes: preparing a first negative electrode slurry P21; preparing a second negative electrode slurry P22; coating the first negative electrode slurry and the second negative electrode slurry P23; drying the first negative electrode slurry and the second negative electrode slurry P24; and etching the second negative electrode active material layer to form a pattern in which concave portions and non-concave portions are alternately arranged P25.

[0211] The first negative electrode slurry preparation process P21 and the second negative electrode slurry preparation process P22 are the same as those described in the previous embodiment, and thus repeated descriptions are omitted.

[0212] The process P23 of applying the first and second negative electrode slurries includes applying the slurries to the current collector. The second negative electrode slurry can be applied after the first negative electrode slurry, or the two slurries can be applied simultaneously using a device such as a double slot die configured to discharge the two slurries simultaneously.

[0213] In an exemplary embodiment, the loading ratio of the first negative electrode slurry to the second negative electrode slurry may be 3: 1 to 1: 3, specifically 2: 1 to 1: 2, more specifically 6: 4 to 4: 6. When the loading ratio is within this range, the negative electrode exhibits excellent structural stability and rate characteristics.

[0214] The drying process P24 includes drying the first negative electrode slurry and the second negative electrode slurry. The first negative electrode slurry can be applied and dried first, and then the second negative electrode slurry can be applied and dried. Alternatively, the first and second negative electrode slurries can be applied simultaneously and then dried together.

[0215] The drying process P24 can be performed using conventional methods known in the art.

[0216] The patterning process P25 includes forming a pattern in which recesses and non-recesses alternate on the surface of the second negative electrode active material layer. This is achieved by irradiating the dried second negative electrode active material layer with a laser to form recesses that are recessed toward the first negative electrode active material layer.

[0217] The area irradiated with the laser detaches from the second negative electrode active material layer, forming recesses 12a that are recessed toward the first negative electrode active material layer, as Figure 3 and 4 shown.

[0218] Details regarding the width-direction lengths of the non-recesses 12b and the recesses have been described above, so repeated description is omitted.

[0219] Hereinafter, the present invention will be described in more detail with reference to embodiments. However, these embodiments are provided only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0220] Example 1: Preparation of negative electrode

[0221] (Preparation of the first negative electrode paste)

[0222] The first negative electrode paste (solid content: 50% by weight) is prepared by mixing and stirring natural graphite (D 50 15 μm) with a sphericity of 0.9 as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, carboxymethyl cellulose (CMC) as the thickener, and carbon nanotubes as the conductive material in a weight ratio of 94:3:1.5:1.5 in water.

[0223] (Preparation of the second negative electrode paste)

[0224] Prepare a negative electrode active material composed of 10% by weight of natural graphite (D 50 16 μm, specific surface area 3.0 m 2 / g, tapped density 1.1 g / cc), 85% by weight of artificial graphite (D 50 23 μm, specific surface area 1.0 m 2 / g, tapped density 0.9 g / cc), and 5% by weight of silicon oxide particles (SiO 50 ) with an average particle diameter (D x , 0 < x < 2). Mix and stir this negative electrode active material, styrene-butadiene rubber (SBR) as the binder, carboxymethyl cellulose (CMC) as the thickener, and carbon nanotubes as the conductive material in a weight ratio of 95:2:1.5:1.5 in water to prepare the second negative electrode paste (solid content: 50% by weight).

[0225] (Preparation of negative electrode)

[0226] A dual-slot die coater was used to simultaneously coat the first and second negative electrode slurries onto a 20μm thick copper current collector. The first negative electrode slurry was applied to the copper current collector, followed by the second negative electrode slurry. The loading ratio of the first negative electrode slurry to the second negative electrode slurry was 1:1. The coating was then dried at 80-90°C and rolled.

[0227] On the second negative electrode active material layer formed by drying the rolled second negative electrode slurry, laser etching was performed at 200 μm intervals with a width of 30 μm to form recessed portions that were recessed inward toward the first negative electrode active material layer. The resulting negative electrode had a total thickness of 110 μm, and the step between the recessed portion and the non-recessed portion was 31 μm.

[0228] Example 2: Preparation of negative electrode

[0229] (Preparation of First and Second Negative Electrode Slurries)

[0230] The first and second negative electrode slurries were prepared in the same manner as described in Example 1.

[0231] (Preparation of Conductive Layer Paste)

[0232] A slurry having the same composition as that of the second negative electrode slurry was prepared, except that the solid content was changed to 40 wt %.

[0233] (Preparation of negative electrode)

[0234] The first negative electrode slurry is coated on a copper current collector with a thickness of 20 μm using a single slot die coater and dried to form a first negative electrode active material layer. The second negative electrode slurry and the conductive layer slurry are simultaneously coated on the first negative electrode active material layer using a nozzle printer. The second negative electrode slurry and the conductive layer slurry are alternately arranged along the width direction (CD) of the current collector, with the horizontal width of the second negative electrode slurry in one column being 200 μm and the horizontal width of the conductive layer slurry in one column being 20 μm. Here, the ratio of the loading amount of the first negative electrode slurry to the second negative electrode slurry and the conductive layer slurry is set to 1:1. The coating is then dried and calendered at a temperature of 80-90°C to prepare the negative electrode.

[0235] In the manufactured negative electrode, the total thickness of the negative electrode active material layer was 110 μm, and the step between the non-concave portion formed by the dried second negative electrode slurry and the conductive layer formed by the dried conductive layer slurry was 31 μm.

[0236] Comparative Example: Preparation of Negative Electrode

[0237] (Preparation of First and Second Negative Electrode Slurries)

[0238] The first and second negative electrode slurries were prepared in the same manner as described in Example 1.

[0239] A double-slot die coater was used to simultaneously coat the first and second negative electrode slurries onto a 20μm-thick copper current collector. The first negative electrode slurry was applied to the copper current collector, and the second negative electrode slurry was applied onto the first negative electrode slurry. The loading ratio of the first negative electrode slurry to the second negative electrode slurry was 1:1. The coatings were then dried at 80-90°C and rolled to produce a negative electrode with a total negative electrode active material layer thickness of 110μm.

[0240] Experimental Example 1: Cycle Capacity Retention Evaluation

[0241] (Half-cell preparation)

[0242] Lithium (Li) metal foil was used as the positive electrode. Each negative electrode prepared in Examples 1 and 2 and the comparative example was used as the negative electrode. A polyethylene separator (thickness 20 μm) was placed between the positive electrode and each negative electrode to assemble the electrode assembly. These electrode assemblies were inserted into a pouch battery box and injected with an electrolyte to prepare a half-cell. The electrolyte used was a solution of 1M LiPF6 dissolved in an organic solvent consisting of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70.

[0243] (Capacity retention rate evaluation)

[0244] Each half-cell prepared using the negative electrodes of Examples 1 and 2 and Comparative Example was subjected to 500 charge and discharge cycles at 25° C. under the following conditions. The capacity retention was calculated using the following formula, and the results are shown in Table 1.

[0245] Charging: 0.7C CC / CV, 4.2V, 0.05C cutoff

[0246] Discharge: 0.5C, CC, 2.5V cut-off

[0247] The capacity retention rate was calculated as follows, and the results are shown in Table 1.

[0248] Capacity retention (%) = (discharge capacity after 500 cycles) / (discharge capacity after 1 cycle) × 100

[0249] Experimental Example 2: Constant Current Charging Capacity Ratio Measurement

[0250] Half-cells were prepared in the same manner as described in Experimental Example 1. Each half-cell prepared using the negative electrodes from Examples 1 and 2 and the Comparative Example was charged at a constant current (CC) rate of 0.5C until the voltage reached 4.2V, at which point charging was terminated and the CC charge capacity was measured. Subsequently, constant voltage (CV) charging was performed until the current dropped to 0.02C, and the CC-CV charge capacity was measured. The CC charge capacity ratio was calculated using the following formula. A higher CC charge capacity ratio indicates better resistance characteristics and rate characteristics (charging speed).

[0251] Constant current charge capacity ratio (%) = (CC charge capacity / CC-CV charge capacity) × 100

[0252] The charge rate was then changed to 1.0C and 2.0C, and the same process was repeated to calculate the constant current charge capacity ratio. The results are shown in Table 1.

[0253]

Table 1

[0254]

[0255] Referring to Table 1, the half-cells containing the negative electrodes of Examples 1 and 2 exhibited superior capacity retention and constant current charge capacity ratio compared to the half-cell containing the negative electrode of the comparative example.

[0256] Experimental Example 3: Resistance Characteristics Evaluation

[0257] (Preparation of positive electrode)

[0258] By using LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, carbon black as a conductive material, and PVDF as a binder were mixed and stirred in an N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 97:1.5:1.5 to prepare a positive electrode slurry.

[0259] The positive electrode slurry was coated on an aluminum current collector with a thickness of 20 μm, and then dried and rolled at 130° C. to prepare a positive electrode.

[0260] (Preparation of full battery)

[0261] An electrode assembly was prepared by inserting a polyethylene separator (20 μm thick) between the negative electrode and the positive electrode of each of Examples 1 and 2 and the Comparative Example. The electrode assembly was inserted into a pouch-type battery case, and an electrolyte was added to prepare a full cell. The electrolyte was 1 M LiPF6 dissolved in an organic solvent consisting of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70.

[0262] (DCIR measurement)

[0263] When each full cell was charged to SOC 50% at room temperature and discharged at 2.5C for 10 seconds, the voltage drop was recorded and the resistance (mOhm) of each coin-type full cell was measured using R=V / I. The results are shown in Table 2.

[0264] Charging: 0.5C CC / CV, 4.2V, 0.05C cut-off

[0265] Discharge: 0.5C CC, 2.5V cut-off

[0266] Experimental Example 4: Fast Charging Performance Evaluation

[0267] Each full cell was charged at a temperature of 25° C. at a constant current of 0.33 C to 4.2 V, charged at a constant voltage of 4.2 V to a current value of 0.05 C, and discharged at a constant current of 0.33 C to 2.5 V after a rest period of 10 minutes.

[0268] Then, the battery was charged as described above and discharged at a constant current of 2 C to 2.5 V to evaluate the discharge rate characteristics. The results are shown in Table 2.

[0269]

Table 2

[0270]

[0271] Referring to Table 2, in the case of the negative electrodes of Examples 1 and 2, since the second negative electrode active material layer has a patterned negative electrode surface with alternating concave portions and non-concave portions, the full batteries prepared using the negative electrodes of Examples 1 and 2 have excellent resistance characteristics and rate characteristics compared with the full batteries prepared using the negative electrodes of the comparative example.

[0272] The present invention has been described in detail with reference to the accompanying drawings and embodiments. However, the structures described in the drawings or embodiments are merely exemplary embodiments of the present invention and do not represent the entire technical concept of the present invention. Therefore, it should be understood that various equivalents and modifications thereof may be made at the time of filing this application.

[0273] [reference numerals]

[0274] 10: Negative electrode

[0275] 11: First negative electrode active material layer

[0276] 12: Second negative electrode active material layer

[0277] 12a: concave part

[0278] 12b: Non-recessed portion

[0279] 13: Current collector

Claims

1. A negative electrode for a lithium secondary battery, comprising: current collector; a first negative electrode active material layer formed on one or both surfaces of the current collector and containing a first negative electrode active material that is a carbon-based compound as a negative electrode active material; and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second negative electrode active material different from the carbon-based compound as a negative electrode active material, The second negative electrode active material layer comprises a plurality of concave portions and a plurality of non-concave portions that are recessed toward the first negative electrode active material layer, wherein the concave portions and the non-concave portions are alternately arranged in a horizontal direction. wherein the recess is filled with a conductive layer containing a conductive material, The thickness of the conductive layer filled in the concave portion is smaller than that of the non-concave portion, and the surface of the second negative electrode active material layer has a pattern formed by steps between the conductive layer and the non-concave portion.

2. The negative electrode for a lithium secondary battery according to claim 1, in, The conductive layer also contains a negative electrode active material.

3. The negative electrode for a lithium secondary battery according to claim 2, in, The conductive layer has the same composition as the second negative electrode active material layer.

4. The negative electrode for a lithium secondary battery according to claim 2, in, The weight % of the conductive material included in the conductive layer is greater than the weight % of the conductive material included in the second negative active material layer.

5. The negative electrode for a lithium secondary battery according to claim 4, in, The conductive layer comprises: 70 to 94 parts by weight of a negative electrode active material; 5 to 20 parts by weight of a conductive material; and 1 to 10 parts by weight of a binder.

6. The negative electrode for a lithium secondary battery according to claim 1, in, The conductive layer does not contain a negative electrode active material and comprises: 80 to 100 parts by weight of a conductive material, and 20 parts by weight or less of adhesive.

7. A negative electrode for a lithium secondary battery, comprising: current collector; a first negative electrode active material layer formed on one or both surfaces of the current collector and containing a first negative electrode active material that is a carbon-based compound as a negative electrode active material; and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second negative electrode active material different from the carbon-based compound as a negative electrode active material, The second negative electrode active material layer comprises a plurality of concave portions and a plurality of non-concave portions that are recessed toward the first negative electrode active material layer, wherein the concave portions and the non-concave portions are alternately arranged in a horizontal direction. The surface of the second negative electrode active material layer has a pattern formed by steps between the non-concave portion and the concave portion.

8. The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, in, The horizontal width of each non-concave portion is 50 μm to 1500 μm.

9. The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, in, The horizontal width of each concave portion is 10 μm to 800 μm and is smaller than or equal to the horizontal width of the non-concave portion.

10. The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, in, The length of the step is 5 μm to 60 μm.

11. The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, in, The negative electrode active material contained in the first negative electrode active material layer is composed of a carbon-based first negative electrode active material.

12. The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, in, The carbon-based first negative electrode active material is a graphite-based negative electrode active material.

13. The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, in, The second negative electrode active material is a mixture of one or more selected from the group consisting of Si, SiO x (0 < x < 2), Si-C composite, and Si metal alloy.

14. The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, in, The average total loading of the first negative electrode active material layer and the second negative electrode active material layer is 4 mAh / cm 2 above. 15 . A lithium secondary battery comprising the negative electrode according to claim 1 .

16. A method for manufacturing a negative electrode for a lithium secondary battery, the method comprising: Mixing and stirring a carbon-based first negative electrode active material, a conductive material, and a binder in a solvent to prepare a first negative electrode slurry; Mixing and stirring a second negative electrode active material different from the carbon-based first negative electrode active material, a conductive material, and a binder in a solvent to prepare a second negative electrode slurry; preparing a conductive layer slurry; a first coating process of coating a first negative electrode slurry on a current collector; a second coating process of coating a second negative electrode slurry and a conductive layer slurry on the first negative electrode slurry; as well as The first negative electrode slurry, the second negative electrode slurry and the conductive layer slurry are dried, wherein: The second coating process is performed in such a manner that the second negative electrode slurry and the conductive layer slurry are alternately arranged in a horizontal direction.

17. The method for producing a negative electrode for a lithium secondary battery according to claim 16, in, The solid content of the second negative electrode slurry is greater than the solid content of the conductive layer slurry.

18. The method for producing a negative electrode for a lithium secondary battery according to claim 16, in, The second coating process includes coating the second negative electrode slurry and the conductive layer slurry using a nozzle printer.

19. The method for producing a negative electrode for a lithium secondary battery according to claim 16, in, The conductive layer slurry further includes a negative electrode active material.

20. The method for producing a negative electrode for a lithium secondary battery according to claim 19, in, The conductive layer slurry has the same composition as the second negative electrode slurry.

21. The method for producing a negative electrode for a lithium secondary battery according to claim 19, in, The weight percent of the conductive material contained in the solid content of the conductive layer slurry is greater than the weight percent of the conductive material contained in the solid content of the second negative electrode slurry.

22. The method for producing a negative electrode for a lithium secondary battery according to claim 16, in, The conductive layer slurry does not contain a negative electrode active material, and contains, in solids: 80 to 100 parts by weight of a conductive material, and 20 parts by weight or less of adhesive.

23. A method for manufacturing a negative electrode for a lithium secondary battery, the method comprising: Mixing and stirring a carbon-based first negative electrode active material, a conductive material, and a binder in a solvent to prepare a first negative electrode slurry; Mixing and stirring a second negative electrode active material different from the carbon-based first negative electrode active material, a conductive material, and a binder in a solvent to prepare a second negative electrode slurry; applying the first negative electrode slurry and the second negative electrode slurry on the current collector so that the second negative electrode slurry is stacked on the first negative electrode slurry; drying the first negative electrode slurry and the second negative electrode slurry; and The second negative electrode active material layer formed by drying the second negative electrode slurry is etched at predetermined intervals and widths to form a pattern in which concave portions concave toward the current collector and non-concave portions are alternately arranged in a horizontal direction.

24. The method for producing a negative electrode for a lithium secondary battery according to claim 23, in, During the patterning process, etching is performed using a laser.

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