Negative electrode, negative electrode dam coating composition, and lithium secondary battery

Abstract

The negative electrode dam coating composition of one embodiment of the present application is in contact with the end surface of the negative electrode active material layer, and contains a carbon-based material, a cellulose-based compound, a rubber-based binder, and inorganic particles. The negative electrode dam coating composition exhibits excellent surface tension and adhesion, thereby suppressing the formation of a negative electrode thickened edge, and the dam coating layer formed by the negative electrode dam coating composition reduces the landslide length of the negative electrode active material layer.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2023-0129809, filed on September 26, 2023, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a negative electrode with a short negative electrode landslide area, a negative electrode dam coating composition for the negative electrode, and a lithium secondary battery comprising the negative electrode, wherein the negative electrode prevents or inhibits the formation of thickened edges at the negative electrode end. Background Technology

[0003] With the increasing development and demand for technologies in mobile devices, automobiles, and energy storage, the demand for batteries as an energy source is rapidly increasing, and among these secondary batteries, lithium secondary batteries with high energy density and high discharge voltage have been extensively researched, commercialized, and used.

[0004] Based on the shape of the battery casing, secondary batteries are classified into cylindrical and prismatic batteries (where the electrode assembly is embedded in a cylindrical or prismatic metal can) and pouch batteries (where the electrode assembly is embedded in a pouch-shaped casing made of aluminum laminate).

[0005] Furthermore, as a rechargeable power generation device including a positive electrode / separator / negative electrode stacked structure, the electrode assembly embedded in the battery casing can be: a wound electrode assembly, which is obtained by placing a separator between an elongated sheet-shaped positive electrode and a negative electrode coated with an electrode compound containing an electrode active material and then winding it; a stacked electrode assembly, which includes a plurality of positive electrodes and negative electrodes punched and slotted in predetermined size units and stacked sequentially with a separator sandwiched between them; and a stacked / foldable electrode assembly, which includes a stack of dual-cell or full-cell cells with a positive electrode and a negative electrode and a separator wound in predetermined size units.

[0006] The positive and negative electrodes constituting the electrode assembly are manufactured by applying an electrode slurry, prepared during the mixing process, in a predetermined pattern and thickness, onto an electrode current collector through a slit mold, and then drying it. However, since the electrode slurry is a fluid, after the coating process, due to its fluidity, the electrode slurry flows downwards, resulting in a phenomenon known as sliding.

[0007] Figure 1 This is an enlarged view of one side of the cross-section of the negative electrode, on which the electrode paste is coated on the current collector. (Refer to...) Figure 1 The negative electrode active material layer 12 coated with electrode paste is divided into a flat region 12A and a slope region 12S. The flat region 12A is parallel to the plane of the negative electrode current collector 11 because its thickness is constant. The slope region 12S is inclined relative to the plane of the current collector 11 because the thickness of the electrode active material layer 12 gradually decreases along the direction towards the uncoated part of the uncoated electrode paste on the current collector 11.

[0008] Meanwhile, the positive and negative electrodes constituting the electrode assembly face each other across a separator between them. The lengths of the slip zone in the positive electrode and the slip zone in the negative electrode can differ, and the inclination shape of the slip zone can be various, such as convex, convex, straight, or S-shaped. Even if the inclination shape is the same, the slope can be different. As a result, depending on the facing position of the slip zone, the negative electrode slip zone may have a local NP ratio imbalance, which may lead to lithium deposition from the negative electrode and cause safety accidents such as short circuits.

[0009] In the theoretical positive / negative electrode face region, the higher the ratio of the negative electrode loading to the positive electrode loading, the lower the probability of NP ratio imbalance. Therefore, recent attempts have been made to increase the loading in the negative electrode slippage zone. As one of these attempts, a technique is being investigated in which a dam coating composition is stacked on the edge of the negative electrode slurry. The dam coating composition inhibits the downward flow of the negative electrode slurry, thereby minimizing the slippage length of the negative electrode active material layer.

[0010] However, in conventional dam coating compositions, a thickened edge phenomenon occurs where the thickness of the negative electrode active material layer and the dam coating overlaps and becomes thicker than the thickness of the negative electrode active material layer. Figure 2 This is a cross-sectional view of a negative electrode with thick edges, see reference. Figure 2 Thick edges are formed at both ends of the negative electrode active material layer 12 in the Y-axis direction, and thick edges protruding upwards in the Z-axis direction. The presence of these thick edges on the negative electrode may cause damage to the current collector layer during the rolling process, which may cause safety issues. During the multiple stacking of the positive electrode, negative electrode, and separator, the thick edges may also damage other electrodes or separators.

[0011] Therefore, there is a need to develop a negative electrode technology and manufacturing method for landslides with short lengths and no thick edges. Summary of the Invention

[0012] [Technical Issues]

[0013] One object of the present invention is to provide a negative electrode with a short negative electrode landslide area, a negative electrode dam coating composition for obtaining the negative electrode, and a lithium secondary battery including the negative electrode, wherein the formation of thick edges at the negative electrode end is prevented or suppressed.

[0014] [Technical Solution]

[0015] According to one embodiment of this disclosure, a negative electrode for a lithium secondary battery is provided. The negative electrode for a lithium secondary battery includes: a negative electrode current collector; a negative electrode active material layer disposed on one or both sides of the negative electrode current collector; and a dam coating disposed on one or both sides of the negative electrode current collector, wherein the dam coating is in contact with the end surface of the negative electrode active material layer and comprises a carbon-based material, a cellulose compound, a rubber-based adhesive, and inorganic particles.

[0016] In an exemplary embodiment, based on the total weight of the dam coating, the content of the carbon-based material can be from 3% to 25% by weight; the content of the cellulose compound can be from 0.5% to 5% by weight; the content of the rubber-based adhesive can be from 3% to 25% by weight; and the content of the inorganic particles can be from 45% to 93.5% by weight.

[0017] In an exemplary embodiment, the carbon-based material may be at least one or more selected from carbon black, graphite, carbon nanotubes and carbon nanofibers.

[0018] In an exemplary embodiment of this disclosure, the inorganic particles may be one or more selected from the group consisting of AlO(OH), Al2O3, γ-AlOOH, Al(OH)3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3 and Mg(OH)2.

[0019] In an exemplary embodiment, the cellulose compound may be at least one or more compounds selected from carboxymethyl cellulose (CMC), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, lithium salt of carboxymethyl cellulose (CMC-Li), and sodium salt of carboxymethyl cellulose (CMC-Na).

[0020] In an exemplary embodiment, the weight-average molecular weight of the cellulose compound may be from 800,000 to 2,000,000.

[0021] In an exemplary embodiment, the rubber-based adhesive may be styrene-butadiene rubber (SBR).

[0022] In an exemplary embodiment, the negative electrode active material layer is divided into a flat region and a slope region. The surface of the flat region is parallel to the plane of the negative electrode current collector, and the slope region extends from the flat region. The surface of the slope region is inclined relative to the plane of the negative electrode current collector. The slope region may be located at one end and the other end along the entire length of the negative electrode active material layer.

[0023] In an exemplary embodiment, the total length of the landslide area can be less than 4 mm.

[0024] In an exemplary embodiment, the total length of the landslide area can be from 0.5 mm to 3.5 mm.

[0025] In an exemplary embodiment, the thickness ratio (T2 / T1) of the maximum thickness T2 of the dam coating to the average thickness T1 of the negative electrode active material layer in the flat region of the negative electrode active material layer can be in the range of 0.1 to 0.4.

[0026] In an exemplary embodiment, the maximum thickness of the dam coating can be in the range of 20 μm to 40 μm, and its length in the entire length direction can be less than 3 mm.

[0027] In an exemplary embodiment, the adhesion of the dam coating can be above 90gf / 20mm.

[0028] According to another exemplary embodiment of this disclosure, a negative electrode dam coating composition is provided. The negative electrode dam coating composition may comprise: a solvent, a carbon-based material, a cellulose compound, a rubber-based adhesive, and inorganic particles.

[0029] In the negative electrode dam coating composition of the exemplary embodiment, the solids may comprise, based on the total weight of solids excluding solvents: 3% to 25% by weight of carbon-based material; 0.5% to 5% by weight of cellulose-based compound; 3% to 25% by weight of rubber-based adhesive; and 45% to 93.5% by weight of inorganic particles.

[0030] In an exemplary embodiment, the carbon-based material and the rubber-based adhesive may be contained in a weight ratio of 4:6 to 6:4.

[0031] In an exemplary embodiment, based on 100 parts by weight of the negative electrode dam coating composition, the content of solids other than solvent can be 16 to 36 parts by weight.

[0032] In an exemplary embodiment, the carbon-based material may be selected from carbon black, graphite, carbon nanotubes, and carbon nanofibers.

[0033] The surface tension of the negative electrode dam coating composition in the exemplary embodiment can be above 70 mN / mm.

[0034] According to another exemplary embodiment of this disclosure, a lithium secondary battery is provided, comprising: the negative electrode; the positive electrode; a separator and an electrolyte.

[0035] [Beneficial Effects]

[0036] According to one embodiment of the present disclosure, the surface tension of the negative electrode dam coating composition is increased to the level of the negative electrode slurry, such that the negative electrode dam coating composition tends to remain at the interface without being incorporated into the negative electrode slurry, thereby preventing the formation of thick edges.

[0037] Therefore, the dam coating shortens the slippage length of the negative electrode active material layer, which can reduce the risk of NP ratio reversal in lithium secondary batteries. Attached Figure Description

[0038] Figure 1 This is an enlarged view of one side of the cross-section of a negative electrode with negative electrode slurry coated on a current collector, according to existing technology.

[0039] Figure 2 It is a cross-sectional view of the negative electrode that has produced a thick edge.

[0040] Figure 3 This is an enlarged view of one side of a cross-section of a negative electrode coated with a negative electrode slurry and a dam coating composition according to an exemplary embodiment.

[0041] Figure 4 This is a top view of the negative electrode to illustrate the negative electrode of an exemplary embodiment.

[0042] Figure 5 It is along Figure 4 The cross-sectional view of the A-A' cut.

[0043] [Explanation of reference numerals in the attached figures]

[0044] 10, 100: Negative electrode

[0045] 11, 110: Negative electrode current collector

[0046] 12, 120: Negative electrode active material layer

[0047] 13, 130: Dam coating

[0048] NES: Negative electrode sheet Detailed Implementation

[0049] This disclosure will be described in more detail below to provide a better understanding of it.

[0050] The terms and words used in this specification and claims should not be interpreted in their ordinary or dictionary sense, but rather should be interpreted based on the principle that the inventors can define the concepts of the terms in a manner they deem best suited to describe this disclosure, in a meaning and concept consistent with the technical idea of ​​this disclosure.

[0051] The terminology used in this application is for describing certain embodiments only and is not intended to limit the concept of the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0052] In this application, expressions such as “comprising,” “equipped with,” or “having” are intended to indicate the presence of the described features, counts, steps, operations, components, parts, or combinations thereof, and should not be construed as excluding the possibility of the presence or addition of one or more other features, counts, operations, components, parts, or combinations thereof.

[0053] As used herein, the literal term “combination of” in a Markush formal expression means one or more mixtures or combinations of the groups consisting of the components described in the Markush formal expression, and includes one or more of the groups consisting of these components.

[0054] In this specification, references to "A and / or B" shall mean "A or B or both".

[0055] In this specification, unless otherwise stated, “%” refers to weight%.

[0056] For the purposes of this specification, specific surface area can be measured using the Brunauer-Emmett-Teller (BET) method. For example, it can be determined using the BET 6-point method via nitrogen adsorption distribution using a porosimetry analyzer (Bell Japan Inc., Belserp-IImini).

[0057] As used in this article, the average particle size (D) 50 The average particle size can be defined as the particle size at 50% of the particle size distribution. There is no particular limitation on the average particle size; it can be determined, for example, by laser diffraction, scanning electron microscopy (SEM), etc. Laser diffraction methods are typically capable of measuring particle diameters from the submicron region to several millimeters, and can produce highly reproducible and highly resolveable results.

[0058] In this specification, "Mw" refers to the weight-average molecular weight of standard polystyrene as determined by gel permeation chromatography (GPC). Specifically, Mw is a converted value of the GPC determination under the following conditions, calibrated using standard polystyrene from Agilent Systems.

[0059] <Measurement Conditions>

[0060] Measuring instrument: Agilent GPC (Agulent 1200 series, USA)

[0061] Chromatographic column: two connected PL mixed B

[0062] Column temperature: 40℃

[0063] Eluent: Tetrahydrofuran

[0064] Flow rate: 1.0 mL / min

[0065] Concentration: ~1 mg / mL (100 μL injection)

[0066] In this specification, the longitudinal direction (MD) of the negative electrode and the full width direction of the negative electrode are defined in the X-axis direction, the transverse direction (TD) of the negative electrode and the full length direction of the negative electrode are defined in 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 in the Z-axis direction. The X-axis and Y-axis directions are referred to as the horizontal direction.

[0067] Negative electrode dam coating composition

[0068] Figure 1 This is an enlarged view of one side of the cross-section of a negative electrode with negative electrode slurry coated on a current collector, according to existing technology. Figure 2 It is a cross-sectional view of a negative electrode with thick edges. Figure 3 This is an enlarged view of one side of a cross-section of a negative electrode coated with a negative electrode slurry and a negative electrode dam coating composition according to an exemplary embodiment.

[0069] Reference Figure 1 In the absence of a negative electrode dam coating composition, due to the fluidity of the negative electrode slurry, the edge of the area coated with the negative electrode slurry spreads along the current collector 11, so that the end of the dried negative electrode active material layer 12 is inclined relative to the plane of the negative electrode current collector 11. The inclined end of the negative electrode active material layer 12 is referred to as the landslide zone 12S, and the landslide length, that is, the Y-axis length of the landslide zone, reaches about 4 to 10 mm.

[0070] At the same time, refer to Figure 3 When the negative electrode dam coating composition 130CD is coated onto the edge of the area coated with negative electrode slurry 120SE, the landslide length of the landslide zone 120S of the negative electrode active material layer becomes greater than that of the negative electrode active material layer. Figure 1 It is much shorter because the negative electrode dam coating composition 130CD acts as a dam and inhibits the downward flow of the negative electrode slurry 120SE.

[0071] However, the negative electrode dam coating composition 130CD is coated in a manner that partially overlaps with the negative electrode slurry 120S, and a portion of the negative electrode dam coating composition 130CD located on the negative electrode slurry can diffuse into the negative electrode slurry 120S to form a dam coating composition 130CD located on the negative electrode slurry. Figure 2 The thickened edge is shown. The inventors of this disclosure have discovered through extensive research that if the surface tension of the dam coating composition is controlled to the level of the negative electrode slurry, the dam coating composition will tend to remain at the interface with the negative electrode slurry, thereby inhibiting the diffusion of the dam coating composition into the negative electrode slurry.

[0072] To control the surface tension of the dam coating composition to the level of the negative electrode slurry, one embodiment of the negative electrode dam coating composition may include carbon-based materials, cellulose compounds, rubber-based binders, and inorganic particles. The carbon-based materials have the effect of increasing the surface tension of the negative electrode dam coating composition, while the rubber-based binders impart adhesion to the dam coating, enabling it to adhere to the current collector and further improving the flexibility of the dam coating. This prevents the dam coating from detaching under applied physical forces, ultimately improving the stability of the dam coating.

[0073] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these solvents can be used alone or in mixtures of two or more. Water is preferred as a solvent for the negative electrode dam coating composition due to its high surface tension.

[0074] Considering the coatability of the negative electrode dam coating composition, the solvent content can be adjusted to give the negative electrode dam coating composition a suitable viscosity.

[0075] Carbon-based materials can be one or more mixtures selected from the group consisting of: graphite, such as artificial graphite, natural graphite, etc.; carbon black, such as acetylene black, Ketjen black, furnace black, channel black, lamp black, thermal cracking carbon black, etc.; carbon fibers, carbon nanotubes and carbon nanofibers.

[0076] Cellulose compounds are water-soluble polymer compounds with a predetermined viscosity that can increase the cohesive force of the solvent and give the negative electrode dam coating composition a suitable viscosity, thereby increasing the surface tension.

[0077] Cellulose compounds, particularly one or more compounds selected from carboxymethyl cellulose (CMC), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, lithium salt of carboxymethyl cellulose (CMC-Li), and sodium salt of carboxymethyl cellulose (CMC-Na).

[0078] The weight-average molecular weight (Mw) of the cellulose compound can be from 800,000 to 2,000,000, preferably from 900,000 to 1,800,000, and more preferably from 1,000,000 to 1,500,000. When the weight-average molecular weight of the cellulose compound is within the above range, it imparts a suitable viscosity to the dam coating composition, which is ideal in terms of coating performance.

[0079] The rubber adhesive may be one or a mixture of two or more selected from styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, and fluororubber, preferably styrene-butadiene rubber (SBR). Styrene-butadiene rubber has excellent wet adhesion and good flexibility, and is therefore preferred as the rubber adhesive of this disclosure.

[0080] Styrene-butadiene rubber may comprise repeating units derived from styrene monomers and repeating units derived from butadiene monomers in a weight ratio of 70:30 to 30:70. Furthermore, based on the total weight of the styrene-butadiene rubber, the total weight of the repeating units derived from styrene monomers and the repeating units derived from butadiene monomers may be 30 to 100% by weight or 30 to 70% by weight.

[0081] Examples of styrene monomers include styrene, α-methylstyrene, p-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 1-vinylnaphthalene, 4-cyclohexylstyrene, 4-(p-methylphenyl)styrene, 1-vinyl-5-hexylnaphthalene, their derivatives and mixtures thereof, and examples of butadiene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, their derivatives and mixtures thereof.

[0082] If necessary, the styrene-butadiene rubber may further comprise monomer repeating units with crosslinking groups. Based on the total weight of the styrene-butadiene rubber, monomer-derived repeating units with crosslinking groups may be included in an amount of up to 12 parts by weight to reduce electrolyte absorption.

[0083] Inorganic particles can increase electrical insulation and thermal safety, as well as improve the strength of the dam coating. The content of inorganic particles can be appropriately adjusted by taking into account the viscosity, insulation, dispersibility, and coatability of the negative electrode dam coating composition.

[0084] Inorganic particles can be one or more compounds selected from AlO(OH), Al2O3, γ-AlOOH, Al(OH)3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, and Mg(OH)2, or one or more compounds selected from AlO(OH), Al2O3, γ-AlOOH, and Al(OH)3. For example, inorganic particles can be AlO(OH).

[0085] The average particle size (D) of inorganic particles 50The size of the inorganic particles can be 0.1 μm to 100 μm; 0.5 μm to 80 μm; 1 μm to 50 μm; 2 μm to 30 μm; 3 μm to 20 μm; or 5 μm to 10 μm. When the size of the inorganic particles is within the above range, the negative electrode dam coating composition can be uniformly coated on the current collector and the negative electrode slurry.

[0086] In one embodiment of the negative electrode dam coating composition, based on 100 parts by weight of the negative electrode dam coating composition, the content of solids other than solvent can be from 16 parts by weight to 36 parts by weight, more particularly from 18 parts by weight to 34 parts by weight, and even more particularly from 20 parts by weight to 32 parts by weight. When the solid content in the negative electrode dam coating composition meets the above-mentioned numerical range, it is preferred from the viewpoint of the coating performance of the negative electrode dam coating composition and the effect of reducing the slippage length of the negative electrode slurry.

[0087] In one embodiment of the negative electrode dam coating composition, the solids may comprise 3 to 25% by weight of carbon-based material, 0.5 to 5% by weight of cellulose compound, 3 to 25% by weight of rubber-based binder, and 45 to 93.5% by weight of inorganic particles, based on the total weight of solids excluding solvent.

[0088] In one embodiment, the solids may include 3 to 25 wt%, more particularly 6 to 23 wt%, and more particularly 10 to 17 wt% of carbon-based materials. Additionally, the solids may include 0.5 to 5 wt%, more particularly 1 to 4.5 wt%, and more particularly 2 to 4 wt% of cellulose compounds. Furthermore, the solids may include 3 to 25 wt%, more particularly 6 to 23 wt%, and more particularly 10 to 17 wt% of rubber-based adhesives. Furthermore, the solids may include 45 to 93.5 wt%, more particularly 50 to 83 wt%, and more particularly 60 to 77 wt% of inorganic particles. When the carbon-based materials, cellulose compounds, rubber-based adhesives, and inorganic particles are included within the above-mentioned content ranges, the negative electrode dam coating composition can have a surface tension similar to that of the negative electrode slurry and good adhesion properties, and can have a suitable viscosity.

[0089] According to a preferred embodiment, the weight ratio of carbon-based material to rubber-based adhesive can be 4:6 to 6:4, more preferably 45:55 to 55:45.

[0090] By including carbon-based materials and rubber-based adhesives within this content range, surface tension degradation caused by the introduction of rubber-based adhesives can be prevented, while improving the flexibility of the dam coating.

[0091] The negative electrode dam coating 130 can be formed by coating the negative electrode slurry onto the current collector, coating the negative electrode dam coating composition near the boundary between the negative electrode slurry and the uncoated portion, and then drying it, or by simultaneously coating the negative electrode slurry and the negative electrode dam coating composition and then drying it.

[0092] In one embodiment, the viscosity of the negative electrode dam coating composition, measured at 25°C and a shear rate of 2.5 / s, can be from 2,000 cps to 15,000 cps, more particularly from 2,500 cps to 12,000 cps, and even more particularly from 3,000 cps to 10,000 cps. For negative electrode dam coating compositions with viscosity values ​​within the above ranges, the thickness and width of the dam coating can be within appropriate ranges to improve the slippage of the negative electrode active material layer.

[0093] The coating method for the negative electrode dam coating composition may include, but is not limited to, spraying, spin coating, roller coating, die coating, gravure printing, bar coating, etc., with die coating and gravure printing being preferred.

[0094] The surface tension of the negative electrode dam coating composition in one embodiment can be at least 70 mN / mm, more particularly at least 71 mN / mm, and even more particularly from 72 mN / mm to 80 mN / mm. The negative electrode dam coating composition with a surface tension within the above-mentioned range has the effect of preventing the formation of thickened edges on the negative electrode. The surface tension within the above-mentioned range is comparable to the surface tension of the negative electrode slurry.

[0095] Surface tension was measured using a DCA-200 (Dynamic Contact Angle System, SEO) instrument under the following conditions:

[0096] Motor speed: 15 rpm / s

[0097] Probe type: Ring

[0098] Submersion depth: 4

[0099] Surface inspection weight: 0.005

[0100] Stabilization time: 5

[0101] Negative electrode for lithium secondary batteries

[0102] Figure 4 This is a top view of the negative electrode, showing the negative electrode of an exemplary embodiment. Figure 5 It is along Figure 4 The cross-sectional view of the A-A' cut.

[0103] Referring to these figures, the negative electrode 100 of an exemplary embodiment includes: a negative electrode current collector 110; a negative electrode active material layer 120 disposed on one or both sides of the negative electrode current collector 110; and a dam coating 130 disposed on one or both sides of the negative electrode current collector 110, wherein the dam coating 130 may be configured to contact an end surface of the negative electrode active material layer 120. The end is an end in the transverse direction (Y-axis direction) of the negative electrode sheet (NES) or along the entire length (Y-axis direction) of the negative electrode 100.

[0104] Reference Figure 3 and Figure 4 The negative electrode active material layer 120 is formed in the center of the negative electrode sheet (NES) in the transverse (Y-axis direction) and serves as the substrate of the negative electrode 100. Dam coatings 130 are formed at the two edges of the negative electrode sheet (NES) in the transverse (Y-axis direction). Uncoated portions not covered by the negative electrode active material layer 120 or the dam coating 130 exist on the outer side of the dam coatings 130. Furthermore, the negative electrode 100 can be fabricated by slotting and cutting along the groove lines (dashed lines) shown on the negative electrode sheet NES. Although Figure 4 A negative electrode with a dam coating 130 coated on both edges of the negative electrode active material layer 120 is shown, but it is not limited thereto; the dam coating 130 may be coated on only one edge of the negative electrode active material layer 120.

[0105] The negative electrode active material layer 120 can be formed by drying the negative electrode slurry 120SE coated on the current collector 110, and the dam coating 130 can be formed by drying the negative electrode dam coating composition 130CD.

[0106] refer to Figure 3 and Figure 5 In one embodiment, the negative electrode 100 includes a negative electrode active material layer 120 formed of a negative electrode slurry 120SE. The negative electrode active material layer 120 can be divided into a flat region 120A and a slope region 120S. The surface of the flat region 120A is parallel to the plane of the negative electrode current collector 110, and the slope region 120S extends from the flat region 120A, but its surface is inclined relative to the plane of the negative electrode current collector 110. Furthermore, the slope region 120S can be located at one end and the other end along the entire length (Y-axis direction) of the negative electrode active material layer 120.

[0107] In one embodiment of the negative electrode 100, the dam coating 130 is used to prevent the negative electrode slurry from diffusing along the current collector, thereby reducing the landslide length of the negative electrode active material layer 120. Furthermore, as the landslide length decreases, the risk of NP ratio reversal in the landslide area can be prevented.

[0108] In one embodiment, the total length of the landslide zone 120S can be less than 4 mm, preferably 0.5 to 3.5 mm, and more preferably 0.5 to 3 mm. Figure 1 Compared to the landslide length shown without the negative electrode dam coating, this is a reduced length.

[0109] The dam coating 130 may include carbon-based materials, cellulose compounds, rubber-based adhesives, and inorganic particles to control the surface tension of the negative electrode dam coating composition at the level of the negative electrode slurry. The carbon-based materials have the effect of increasing the surface tension of the negative electrode dam coating composition, while the rubber-based adhesives impart flexibility to the dam coating, thereby preventing the dam coating from detaching when physical forces are applied, ultimately improving the stability of the dam coating.

[0110] Carbon-based materials, cellulose compounds, rubber adhesives, and inorganic particles have been described in detail above and will not be repeated here.

[0111] According to one embodiment, the maximum thickness of the dam coating 130 can be 20 to 40 μm, more specifically 22 to 40 μm, or even more specifically 25 to 35 μm. This thickness refers to the distance along the Z-axis from the plane of the current collector to the surface of the dam coating 130.

[0112] According to one embodiment, the length of the dam coating 130 along its entire length (Y-axis direction) can be less than 3 mm, more specifically from 0.5 mm to 3 mm, and more specifically from 1 mm to 2.5 mm.

[0113] According to one embodiment, the thickness ratio (T2 / T1) of the maximum thickness T2 of the dam coating to the average thickness T1 of the negative electrode active material layer in the flat region of the negative electrode active material layer can be from 0.1 to 0.4, and more specifically, from 0.15 to 0.3.

[0114] When the thickness and length of the dam coating 130 are within the above-mentioned range, it is preferred from the viewpoint of the safety of the dam coating and the performance of the negative electrode capacity.

[0115] Since the negative electrode dam coating composition must act as a dam to prevent the diffusion of the negative electrode slurry, the coating thickness of the negative electrode dam coating composition is preferably at least a certain level. (Refer to...) Figure 3 When coating the negative electrode dam coating composition, the coating thickness can be at a level similar to that of the negative electrode slurry. Even if the coating thickness of the negative electrode dam coating composition is at a level similar to that of the negative electrode slurry, the solid content of the negative electrode dam coating composition is much smaller than that of the negative electrode slurry. Therefore, as a series of electrode processes, such as drying processes, are performed, the thickness of the dam coating becomes less than the thickness of the negative electrode active material layer.

[0116] According to one embodiment, the adhesion of the dam coating 130 can be above 90gf / 20mm, more specifically from 95gf / 20mm to 200gf / 20mm, and more specifically from 100gf / 20mm to 150gf / 20mm.

[0117] Adhesion was evaluated as follows: A negative electrode dam coating composition was coated onto copper foil, dried at 80-90°C, and cut into 150 mm long and 20 mm wide pieces. The samples were then attached longitudinally to a 75 mm long and 25 mm wide glass slide using double-sided tape, with the coated side of the negative electrode dam coating composition facing the slide. The evaluation samples were then passed through a laminator to ensure uniform adhesion of the double-sided tape. The slide portion of the evaluation sample was then fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the half of the sample without the slide was connected to the UTM's load cell. The load applied to the load cell was measured by moving it 50 mm at 100 mm / min and applying a 90° force. The average value of the measured loads within the range of 20 mm to 40 mm during the stroke was taken. The test was repeated 5 times, and the average value was evaluated as the adhesion (gf / 20 mm) for each sample.

[0118] When the adhesion of the dam coating 130 is within the above-mentioned value range, the dam coating will not detach in electrode processes such as rolling processes, and is therefore ideal.

[0119] The negative electrode current collector 110 is a highly conductive metal to which the negative electrode slurry readily adheres. Any non-reactive material within the battery voltage range can be used, particularly: 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 conductive materials; or conductive polymers. They can also have microscopic irregularities on their surface to enhance the adhesion of the negative electrode active material and can be used in various forms, including films, sheets, foils, meshes, porous materials, foams, and nonwoven materials.

[0120] The negative electrode active material layer 120 may include a negative electrode active material, an adhesive, and conductive materials and fillers as needed.

[0121] The negative electrode active material can be any compound capable of reversibly inserting and deintercalating lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic materials capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂. β(0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and metal oxides capable of doping and dedoping lithium; or composites of the above-mentioned metallic substances and carbonaceous materials, such as Si-C composites or Sn-C composites, may be used, any one or more of these. Lithium metal thin films can also be used as negative electrode active materials.

[0122] In particular, both low-crystallinity carbon and high-crystallinity carbon can be used as carbonaceous materials. Examples of low-crystallinity carbon include soft carbon and hard carbon, while examples of high-crystallinity carbon include natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and coke derived from petroleum or coal tar pitch. More specifically, graphite-based anode active materials, such as natural or artificial graphite, are preferred because they allow reversible insertion and extraction of lithium ions while maintaining structural and electrical properties.

[0123] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be from about 80% to 99.5% by weight or from 88% to 99% by weight, but the content is not limited to the above contents.

[0124] There are no particular restrictions on the adhesive, as long as it is an ingredient that helps to bond the negative electrode active material to the conductive material and the conductive material to the current collector. Examples include: polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorinated rubber, and various copolymers.

[0125] When the solvent for the negative electrode slurry is an aqueous solvent such as water, the adhesive is preferably an aqueous adhesive. In specific examples, the aqueous adhesive may be one or more selected from styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetylcellulose. In specific examples, the aqueous adhesive may be one or more selected from styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber. For example, the aqueous adhesive may be styrene-butadiene rubber.

[0126] Based on the total weight of the negative electrode active material layer, the binder content can typically be between 1 and 30% by weight.

[0127] There are no particular restrictions on conductive materials, as long as they are conductive and will not cause chemical changes in the battery. Examples of materials that can be used include: graphite, such as natural or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, etc.; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbons, aluminum, and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; conductive materials such as polyphenylene derivatives; and so on.

[0128] Based on the total weight of the negative electrode active material layer, the content of conductive material can typically be between 1 and 30% by weight.

[0129] Fillers are optional components used to suppress electrode expansion. There are no particular limitations on fillers, as long as they are fibrous materials that do not cause chemical changes in the battery. Examples of suitable fillers include: olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.

[0130] The manufacturing method of the negative electrode will be explained below.

[0131] One embodiment of the negative electrode manufacturing method may include: step P11 of preparing a negative electrode slurry, step P12 of preparing a negative electrode dam coating composition, coating step P20 of coating the negative electrode dam coating composition and the negative electrode slurry onto a negative electrode current collector, and drying and rolling step P30.

[0132] Step P11 in preparing the negative electrode slurry may include mixing and stirring the negative electrode active material, binder, conductive material and optional dispersant or filler in a solvent.

[0133] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and these can be used alone or in mixtures of two or more. Considering the coatability and processability of the negative electrode active material slurry, the solvent content is preferably chosen to ensure that the negative electrode active material has a suitable viscosity.

[0134] The solvent content can provide a negative electrode slurry with suitable viscosity and solids content. For example, the solvent content can result in a solids content of 40% to 75% by weight, more particularly 50% to 70% by weight, and even more particularly 55% to 70% by weight in the negative electrode slurry. Furthermore, the negative electrode slurry can have a coatable viscosity, and the negative electrode active material layer formed from the negative electrode slurry can have a thickness exceeding a certain level to obtain good energy density.

[0135] In one embodiment, step P12 of preparing the negative electrode dam coating composition may include: mixing and stirring carbon-based materials, cellulose compounds, rubber-based binders, and inorganic particles in a solvent.

[0136] The coating process P20, which involves coating the negative electrode dam coating composition and the negative electrode slurry onto the negative electrode current collector, can be performed by coating the negative electrode dam coating composition after coating the negative electrode slurry onto the negative electrode current collector, or by simultaneously coating the negative electrode slurry and the negative electrode dam coating composition onto the negative electrode current collector.

[0137] Lithium secondary batteries

[0138] Next, the lithium secondary battery disclosed herein will be described.

[0139] One embodiment of the lithium secondary battery disclosed herein may include a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte.

[0140] The lithium secondary battery disclosed herein can be prepared according to conventional methods known in the art. For example, it can be prepared by placing a separator between the positive and negative electrodes and adding an electrolyte.

[0141] In a lithium secondary battery, the negative electrode is as described above. For example, the negative electrode may include: a negative electrode current collector; a negative electrode active material layer disposed on one or both sides of the negative electrode current collector; and a dam coating disposed on one or both sides of the negative electrode current collector, wherein the dam coating is in contact with the end surface of the negative electrode active material layer, and may include carbon-based materials, cellulose compounds, rubber-based adhesives, and inorganic particles.

[0142] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including positive electrode active material.

[0143] In the positive electrode, the current collector is not particularly limited, as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments using carbon, nickel, titanium, silver, etc., can be used. Furthermore, the positive electrode current collector can typically have a thickness from 3 μm to 500 μm, and can also have microscopic irregularities formed on its surface to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0144] There are no particular limitations on the positive electrode active material, and any compound known in the art capable of reversibly inserting and deintercalating lithium can be used without restriction. Specifically, the positive electrode active material may include: layered compounds, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; lithium manganese oxide, such as Li... 1+x Mn 2-x Compounds of O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides, such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and compounds of the formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); LiMn 2-x M x Lithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); and LiNi x Mn 2-x O4 represents lithium manganese composite oxides with a spinel structure; LiMn2O4 in which some Li atoms are replaced by alkaline earth metal ions; disulfides; lithium iron phosphate represented by LiFePO4; disulfides; and Fe2(MoO4)3, etc., but not limited to these.

[0145] In addition to the aforementioned positive electrode active material, the positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder.

[0146] The positive electrode conductive material is used to impart conductivity to the electrode and can be carbon black, graphite, carbon fiber, carbon nanotubes, metal powder, conductive metal oxide, organic conductive materials, etc. Currently commercially available conductive materials include acetylene black series (e.g., Chevron Chemical or Gulf Oil), Ketjen Black EC series (Armak), Vulcan XC-72 (Cabot), and Super P (MMM). Among these, carbon nanotubes, carbon nanofibers, and carbon black are preferred as the conductive materials disclosed in this invention, with carbon nanotubes being the most preferred. The conductive network of carbon nanotubes can mitigate binder migration during the drying process of the positive electrode slurry, therefore, it is the most preferred positive electrode conductive material disclosed in this invention.

[0147] The BET specific surface area of ​​carbon nanotubes can be 100 m². 2 / g to 1000m 2 / g, 150m2 / 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.

[0148] The content of the positive electrode conductive material in the positive electrode active material layer can be from 0.1 wt% to 30 wt%, more particularly from 0.1 wt% to 10 wt%, and more particularly from 0.5 wt% to 5 wt%.

[0149] The positive electrode binder can be any commonly used binder polymer without limitation. For example, polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and many other types of binder polymers can be used.

[0150] The content of the positive electrode binder in the positive electrode active material layer can be from 0.1% to 30% by weight, more particularly from 0.1% to 10% by weight, and more particularly from 0.5% to 5% by weight.

[0151] The separator can be any porous material commonly used in lithium secondary batteries, such as, but not limited to, polyolefin porous membranes or nonwoven fabrics. In particular, it is preferred to have low resistance to ion migration of the electrolyte and excellent electrolyte wetting ability.

[0152] Examples of polyolefin porous membranes include membranes formed from one or a mixture of polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene) and polyolefin polymers (e.g., polypropylene, polybutene, and polypentene).

[0153] As for nonwoven fabrics, in addition to polyolefin nonwoven fabrics, they can also include, for example, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyethylene naphthalate, etc., which can be alone or a mixture of these polymers. The structure of nonwoven fabrics can be spunbond nonwoven fabric or meltblown nonwoven fabric composed of long fibers.

[0154] There are no particular limitations on the thickness of the porous substrate, which can be 5 to 50 μm. There are also no particular limitations on the pore size and porosity present in the porous substrate, which can be 0.01 to 50 μm and 10 to 95%, respectively.

[0155] Meanwhile, in order to improve the mechanical strength of the membrane made of porous substrate and suppress short circuits between the positive and negative electrodes, at least one side of the porous substrate may also include a porous coating containing inorganic particles and binder polymer.

[0156] Meanwhile, in lithium secondary batteries, the electrolyte may include, but is not particularly limited to, organic solvents and lithium salts commonly used in electrolytes.

[0157] Organic solvents can be used without restriction, as long as they can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. Specifically, organic solvents can include ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.

[0158] Preferably, a carbonate solvent is used; more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is used.

[0159] Lithium salts can be used without restriction, as long as they are compounds capable of providing lithium ions for lithium secondary batteries. Specifically, lithium salts can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. Preferably, the lithium salt is contained in the electrolyte at a concentration of about 0.6 mol% to about 2 mol%.

[0160] In addition to the electrolyte component, to improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, the electrolyte may also include additives such as pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol diether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. Based on the total weight of the electrolyte, the content of additives can be from 0.1% to 5% by weight.

[0161] The lithium secondary battery disclosed herein can be manufactured by placing a separator between the positive and negative electrodes to form an electrode assembly, placing the electrode assembly in a cylindrical or prismatic battery case, and then injecting an electrolyte. Alternatively, the lithium secondary battery can be manufactured by stacking electrode assemblies, impregnating the electrode assemblies with an electrolyte, and sealing the resulting product in a battery case.

[0162] In manufacturing the lithium secondary battery of this disclosure, the electrode assembly can be dried to remove one or more organic solvents used in manufacturing the positive electrode. The solvents are selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate. If an electrolyte with the same composition as the organic solvent used to prepare the positive electrode is used as the electrolyte, the drying process of the electrode assembly can be omitted.

[0163] Unlike the lithium secondary batteries described above, the lithium secondary batteries in other examples of this disclosure can be all-solid-state batteries.

[0164] The battery casing can be any type conventionally used in the art, and its shape is not limited depending on the intended use of the battery, and can be, for example, cylindrical, prismatic, pouch-shaped, or coin-shaped using a can.

[0165] The lithium secondary battery disclosed herein exhibits excellent resistance characteristics, discharge capacity, power characteristics, and capacity retention, and therefore can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as in electric vehicles such as energy storage systems (ESS) and hybrid electric vehicles (HEVs).

[0166] The present disclosure will now be described in more detail by way of examples. However, the following examples are intended to illustrate the present disclosure and are not intended to limit its scope.

[0167] Example 1: Preparation of the negative electrode

[0168] (Preparation of the negative electrode dam coating composition)

[0169] A negative electrode dam coating composition was prepared by mixing and stirring 13 parts by weight of carbon black as a carbon-based material, 3 parts by weight of CMC (Daicel, 2200) with a Mw of 1,260,000 as a cellulose compound, 13 parts by weight of styrene-butadiene rubber (SBR) as a rubber binder, and 71 parts by weight of boehmite (AlO(OH), product name: AOH60) as inorganic particles. The solid content was 26% by weight.

[0170] (Preparation of negative electrode slurry)

[0171] Artificial graphite (D) with a sphericity of 0.85 will be used as the negative electrode active material. 50 23μm, specific surface area 1.0m²2 Styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and carbon nanotubes as a conductive material are mixed in water at a weight ratio of 95:2:1.5:1.5 and stirred to prepare a negative electrode slurry (solid content: 50% by weight).

[0172] (Preparation of the negative electrode)

[0173] On a copper foil (10 μm thick), a negative electrode slurry and a negative electrode dam coating composition are simultaneously coated, but the negative electrode dam coating composition is coated so that it is located at the two edges of the negative electrode slurry coating portion in the Y-axis direction, as shown. Figure 5 As shown.

[0174] The negative electrode is then dried and rolled at 90°C to complete the preparation.

[0175] Example 2: Preparation of the negative electrode

[0176] (Preparation of the negative electrode dam coating composition)

[0177] Based on Example 1, a negative electrode dam coating composition was prepared by changing the weight ratio of carbon black, cellulose compounds, rubber adhesives and inorganic particles to 15:3:15:67.

[0178] Then, the negative electrode slurry and negative electrode were prepared in the same manner as in Example 1.

[0179] Example 3: Preparation of the negative electrode

[0180] (Preparation of the negative electrode dam coating composition)

[0181] Based on Example 1, a negative electrode dam coating composition was prepared by changing the weight ratio of carbon black, cellulose compounds, rubber adhesives and inorganic particles to 11:2:11:76.

[0182] Then, the negative electrode slurry and negative electrode were prepared in the same manner as in Example 1.

[0183] Comparative Example 1: Preparation of the negative electrode

[0184] (Preparation of the negative electrode dam coating composition)

[0185] A negative electrode dam coating composition was prepared by mixing and stirring 4 parts by weight of CMC (Daicel, 2200) with a Mw of 1,260,000 and 96 parts by weight of boehmite (AlO(OH), product name: AOH60) in water. The solid content was 25% by weight.

[0186] Then, the negative electrode slurry and negative electrode were prepared in the same manner as in Example 1.

[0187] Comparative Example 2: Preparation of the Negative Electrode

[0188] (Preparation of the negative electrode dam coating composition)

[0189] A negative electrode dam coating composition was prepared by mixing and stirring 4 parts by weight of CMC (Daicel, 2200) with a Mw of 1,260,000, 95 parts by weight of boehmite (AlO(OH), product name: AOH60), and 1 part by weight of styrene-butadiene rubber (SBR) (BM-L302, ZEON) in water. The solids content was 25% by weight.

[0190] Then, the negative electrode slurry and negative electrode were prepared in the same manner as in Example 1.

[0191] Comparative Example 3: Preparation of the Negative Electrode

[0192] The negative electrode dam coating composition (25% by weight of solids) was prepared in the same manner as in Comparative Example 2, except that the weight ratio of CMC, boehmite and SBR was changed to 4:93:3 in the preparation of the negative electrode dam coating composition of Comparative Example 2.

[0193] Then, the negative electrode slurry and negative electrode were prepared in the same manner as in Example 1.

[0194] Comparative Example 4: Preparation of the Negative Electrode

[0195] The negative electrode dam coating composition (25% by weight of solids) was prepared in the same manner as in Comparative Example 2, except that the weight ratio of CMC, boehmite and SBR was changed to 4:88:8 in the preparation of the negative electrode dam coating composition of Comparative Example 2.

[0196] Then, the negative electrode slurry and negative electrode were prepared in the same manner as in Example 1.

[0197] Comparative Example 5: Preparation of the Negative Electrode

[0198] The negative electrode dam coating composition (25% by weight solids) was prepared in the same manner as in Comparative Example 2, except that the weight ratio of CMC, boehmite and SBR was changed to 4:83:13 in the preparation of the negative electrode dam coating composition in Comparative Example 2.

[0199] Then, the negative electrode slurry and negative electrode were prepared in the same manner as in Example 1.

[0200] Comparative Example 6: Preparation of the Negative Electrode

[0201] (Preparation of the negative electrode dam coating composition)

[0202] A negative electrode dam coating composition was prepared by mixing and stirring 2.5 parts by weight of CMC (Daicel, 2200) with a Mw of 1,260,000 and 97.5 parts by weight of SBR (styrene-butadiene rubber) (BM-L302, ZEON) in water. The solids content was 24% by weight.

[0203] Experimental Example 1: Determination of the viscosity of the negative electrode dam coating composition

[0204] For the negative electrode dam coating compositions of Examples 1 to 3 and Comparative Examples 1 to 6, the viscosity was measured using a Brookfield viscometer at 25°C and a shear rate of 2.5 / s after cooling for 1 hour at 1% relative humidity. Viscosity measurements were performed within 2 hours after the preparation of the negative electrode dam coating compositions, including the cooling time. The results are shown in Table 1.

[0205] Experiment Example 2: Evaluating Surface Tension

[0206] For the negative electrode dam coating compositions of Examples 1 to 3 and Comparative Examples 1 to 6, the surface tension was measured using a DCA-200 (Dynamic Contact Angle System, SEO) instrument under the following conditions. The results are shown in Table 1.

[0207] Motor speed: 15 rpm / s

[0208] Probe type: Ring

[0209] Submersion depth: 4

[0210] Surface inspection weight: 0.005

[0211] Stabilization time: 5

[0212] Experiment Example 3: Confirming the presence of thickened borders

[0213] For each negative electrode in Examples 1 to 3 and Comparative Examples 1 to 6, the active material layer of the negative electrode was visually observed to determine whether any defects were observed. Figure 3 The thick edges shown are illustrated in Table 1. A thick edge is marked with "O" if it appears, and marked with "X" if it does not appear.

[0214] Experiment Example 4: Evaluation of Adhesion

[0215] The negative electrode dam coating composition of Example 1 was coated onto copper foil, dried at 80 to 90°C, and cut into 150 mm long and 20 mm wide pieces. The samples were then attached longitudinally to a 75 mm long and 25 mm wide glass slide using double-sided tape, with the dam coating surface facing the slide. The evaluation samples were then passed through a laminator to ensure uniform tape adhesion. The slide portion of the evaluation sample was then fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the half of the sample without the slide was connected to the UTM's load cell. The load applied to the load cell was measured by moving it 50 mm at 100 mm / min and applying a 90° force. The average value of the measured loads within the range of 20 mm to 40 mm during the stroke was taken. The test was repeated 5 times, and the average value was evaluated as the adhesion force (gf / 20 mm) for each sample. The results are shown in Table 1.

[0216] For each negative electrode dam coating composition of Examples 2 to 3 and Comparative Examples 1 to 6, the adhesion was evaluated in the same manner as described above, and the results are shown in Table 1.

[0217] [Table 1]

[0218] Example 1 9,110 76.55 X 110.9 Example 2 10,275 78.37 X 138.8 Example 3 1,582 72.55 X 102 Comparative Example 1 4,861 74.1 X 48.9 Comparative Example 2 5,549 71.1 O 53.0 Comparative Example 3 5,387 65.1 O 56.0 Comparative Example 4 5,707 62.2 O 161.0 Comparative Example 5 5,697 61.3 O 283.4 Comparative Example 6 3,200 52.96 O 350 and above

[0219] Referring to Table 1, it was found that the negative electrode dam coating compositions of Examples 1 to 3 each have a surface tension of 72 mN / mm or higher, which prevents the formation of thick edges. In addition, the adhesion is also greater than or equal to 90 gf / 20 mm, which is expected to reduce the possibility of dam coating detachment during the electrode rolling process.

Claims

1. A negative electrode for a lithium secondary battery, comprising: Negative electrode current collector; A layer of negative electrode active material disposed on one or both sides of the negative electrode current collector; and A dam coating is applied to one or both sides of the negative electrode current collector. The dam coating is in contact with the end surface of the negative electrode active material layer and comprises carbon-based materials, cellulose compounds, rubber-based adhesives, and inorganic particles. The carbon-based material content is between 3% and 25% by weight, based on the total weight of the dam coating.

2. The negative electrode for a lithium secondary battery as described in claim 1, wherein, Based on the total weight of the dam coating The content of the carbon-based material is from 6% to 23% by weight. The content of the cellulose compound is from 0.5% to 5% by weight. The content of the rubber adhesive is from 3% to 25% by weight. The content of the inorganic particles is from 45% to 93.5% by weight.

3. The negative electrode for a lithium secondary battery as described in claim 1, wherein, The carbon-based material is selected from at least one or more of carbon black, graphite, carbon nanotubes, and carbon nanofibers.

4. The negative electrode for a lithium secondary battery as described in claim 1, wherein, The inorganic particles are selected from one or more of the group consisting of AlO(OH), Al2O3, γ-AlOOH, Al(OH)3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3 and Mg(OH)2.

5. The negative electrode for a lithium secondary battery as described in claim 1, wherein, The cellulose compound is at least one or more compounds selected from the group consisting of carboxymethyl cellulose (CMC), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, lithium salt of carboxymethyl cellulose (CMC-Li), and sodium salt of carboxymethyl cellulose (CMC-Na).

6. The negative electrode for a lithium secondary battery as described in claim 2, wherein, The weight-average molecular weight of the cellulose compounds is between 800,000 and 2,000,000.

7. The negative electrode for a lithium secondary battery as described in claim 2, wherein, The rubber adhesive is styrene-butadiene rubber (SBR).

8. The negative electrode for a lithium secondary battery as described in claim 1, wherein, The negative electrode active material layer is divided into a flat region and a slope region. The surface of the flat region is parallel to the plane of the negative electrode current collector, and the slope region extends from the flat region, with its surface inclined relative to the plane of the negative electrode current collector. The landslide area is located at one end and the other end along the entire length of the negative electrode active material layer.

9. The negative electrode for a lithium secondary battery as described in claim 8, wherein, The total length of the landslide area is less than 4 mm.

10. The negative electrode for a lithium secondary battery as described in claim 8, wherein, The total length of the landslide area is 0.5 to 3.5 mm.

11. The negative electrode for a lithium secondary battery as described in claim 8, wherein, The thickness ratio T2 / T1 of the maximum thickness T2 of the dam coating and the average thickness T1 of the negative electrode active material layer in the flat region of the negative electrode active material layer is in the range of 0.1 to 0.

4.

12. The negative electrode for a lithium secondary battery as described in claim 1, wherein, The maximum thickness of the dam coating is in the range of 20 μm to 40 μm, and its overall length is less than 3 mm.

13. The negative electrode for a lithium secondary battery as described in claim 1, wherein, The adhesion of the dam coating is above 90 gf / 20 mm.

14. A negative electrode dam coating composition for coating the edge of a region coated with a negative electrode slurry, the negative electrode dam coating composition comprising: a solvent, a carbon-based material, a cellulose compound, a rubber-based binder, and inorganic particles; in, Based on the total weight of the solids excluding the solvent, the solids comprise 3% to 25% by weight of the carbon-based material.

15. The negative electrode dam coating composition of claim 14, wherein, Based on the total weight of the solids excluding the solvent, the solids comprise: 6% to 23% by weight of the carbon-based material; 0.5% to 5% by weight of the aforementioned cellulosic compound; 3% to 25% by weight of the rubber-based adhesive; and The inorganic particles comprise 45% to 93.5% by weight.

16. The negative electrode dam coating composition of claim 15, wherein, The carbon-based material and the rubber-based adhesive are contained in a weight ratio of 4:6 to 6:

4.

17. The negative electrode dam coating composition of claim 15, wherein, Based on 100 parts by weight of the negative electrode dam coating composition, the content of solids other than solvent is 16 to 36 parts by weight.

18. The negative electrode dam coating composition of claim 14, wherein, The carbon-based material is selected from carbon black, graphite, carbon nanotubes, and carbon nanofibers.

19. The negative electrode dam coating composition as described in claim 14, wherein the surface tension is 72 mN / mm or higher.

20. A lithium secondary battery, comprising: The negative electrode according to any one of claims 1 to 13; positive electrode; Diaphragm; and Electrolytes.

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