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

Abstract

The negative electrode dam coating composition according to one embodiment of the present invention is in contact with an end surface of a 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 adhesiveness, thereby suppressing the formation of a thick edge of a negative electrode, and the dam coating layer formed from the negative electrode dam coating composition reduces the landslide length of a negative electrode active material layer.

Description

Technical Field

[0001] This application claims the benefit of priority from 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. The negative electrode prevents or suppresses the generation of a thickened edge at the negative electrode terminal. Background Art

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

[0004] According to the shape of the battery case, secondary batteries are classified into cylindrical and prismatic batteries (in which an electrode assembly is embedded in a cylindrical or prismatic metal can) and pouch-type batteries (in which an electrode assembly is embedded in a pouch-type case made of an aluminum laminate sheet).

[0005] In addition, as a rechargeable power generation device including a positive electrode / separator / negative electrode stacking structure, the electrode assembly embedded in the battery shell can be: a core-wound electrode assembly, which is obtained by arranging a separator between a long sheet of positive electrode and a negative electrode coated with an electrode compound containing an electrode active material and winding them; a stacked electrode assembly, which includes a plurality of positive electrodes and negative electrodes punched and slotted in predetermined size units and stacked in sequence with a separator sandwiched therebetween; a stacked / foldable electrode assembly, which includes a stack of dual cells or full cells wound with positive and negative electrodes of predetermined size units and a separator.

[0006] The positive and negative electrodes that make up the electrode assembly are manufactured by applying the electrode slurry prepared in a mixing process to the electrode current collector in a predetermined pattern and at a certain thickness through a slit die, and then drying it. However, since the electrode slurry is fluid, after the electrode slurry coating process, the electrode slurry flows downward due to its fluidity, resulting in a phenomenon called sliding.

[0007] Figure 1 This is an enlarged view of one side of the cross section of the negative electrode with the electrode slurry coated on the current collector. Figure 1 The negative electrode active material layer 12 coated with the electrode slurry is divided into a flat area 12A and a landslide area 12S. The flat area 12A is parallel to the plane of the negative electrode collector 11 due to its constant thickness, and the landslide area 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 toward the non-coated part of the current collector 11 where the electrode slurry is not coated.

[0008] At the same time, the positive electrode and the negative electrode constituting the electrode assembly face each other with a separator between them. The length of the landslide zone of the positive electrode and the length of the landslide zone of the negative electrode can be different, and the slope shape of the landslide zone can be various shapes, such as upward convex shape, downward convex shape, straight shape, S-shaped shape, and even if the slope shape is the same, the slope can be different. As a result, depending on the facing position of the landslide zone, the negative electrode landslide zone may have a local NP ratio imbalance, which may cause lithium to precipitate from the negative electrode and lead to safety accidents such as short circuits.

[0009] In the theoretical positive / negative electrode facing region, the greater the ratio of the negative electrode loading to the positive electrode loading, the less likely an imbalance in the NP ratio will occur. Consequently, recent attempts have been made to increase the negative electrode loading in the landslide region. One such attempt is researching a technique in which a dam coating composition is applied to the edge of the negative electrode slurry coating. This dam coating composition inhibits the downward flow of the negative electrode slurry, thereby minimizing the landslide length of the negative electrode active material layer.

[0010] However, in a conventional dam coating composition, a hypertrophy edge phenomenon may occur where the thicknesses of the negative electrode active material layer and the dam coating layer overlap to become thicker than the thickness of the negative electrode active material layer. Figure 2 This is a cross-sectional view of a negative electrode with a thickened edge, see Figure 2 The negative electrode active material layer 12 has thickened edges at both ends in the Y-axis direction and a thickened edge protruding upward in the Z-axis direction. The presence of these thickened edges on the negative electrode may cause damage to the current collector layer during rolling, which may cause safety issues. During the multi-stack process of positive electrodes, negative electrodes, and separators, the thickened edges may also damage other electrodes or separators.

[0011] Therefore, it is necessary to develop a negative electrode technology and a manufacturing method thereof with a short landslide length and no thick edge. Summary of the Invention

[0012] [Technical Issues]

[0013] An object of the present invention is to provide a negative electrode having a short negative electrode landslide region, a negative electrode dam coating composition for obtaining the negative electrode, and a lithium secondary battery including the negative electrode, wherein generation of a hypertrophic edge at a negative electrode terminal end is prevented or suppressed.

[0014] [Technical solution]

[0015] According to one embodiment of the present 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 surfaces of the negative electrode current collector; and a dam coating disposed on one or both surfaces of the negative electrode current collector, wherein the dam coating contacts an end surface of the negative electrode active material layer and comprises a carbon-based material, a cellulose compound, a rubber binder, and inorganic particles.

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

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

[0018] In an exemplary embodiment of the present 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 exemplary embodiments, the cellulose-based 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 exemplary embodiments, the cellulose-based compound may have a weight average molecular weight of 800,000 to 2,000,000.

[0021] In exemplary embodiments, 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 area and a landslide area, the surface of the flat area is parallel to the plane of the negative electrode current collector, the landslide area extends from the flat area, and the surface of the landslide area is inclined relative to the plane of the negative electrode current collector, wherein the landslide area can be located at one end and the other end of the entire length direction of the negative electrode active material layer.

[0023] In an exemplary embodiment, the entire length of the landslide area may be 4 mm or less.

[0024] In an exemplary embodiment, the landslide area may have a length in the entire length direction of 0.5 mm to 3.5 mm.

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

[0026] In exemplary embodiments, the maximum thickness of the dam coating layer may be in the range of 20 μm to 40 μm, and the length thereof in the entire length direction may be 3 mm or less.

[0027] In exemplary embodiments, the adhesion of the dam coating layer may be 90 gf / 20 mm or more.

[0028] According to another exemplary embodiment of the present disclosure, a negative electrode dam coating composition is provided, which may include a solvent, a carbon-based material, a cellulose compound, a rubber binder, and inorganic particles.

[0029] In the negative electrode dam coating composition of the exemplary embodiment, the solid may include, based on the total weight of the solid excluding the solvent: 3 wt % to 25 wt % of a carbon-based material; 0.5 wt % to 5 wt % of a cellulose-based compound; 3 wt % to 25 wt % of a rubber-based binder; and 45 wt % to 93.5 wt % of inorganic particles.

[0030] In exemplary embodiments, the carbon-based material and the rubber-based binder may be included in a weight ratio of 4:6 to 6:4.

[0031] In exemplary embodiments, the content of solids excluding the solvent may be 16 to 36 parts by weight based on 100 parts by weight of the negative electrode dam coating composition.

[0032] In exemplary embodiments, the carbon-based material may be one selected from the group consisting of carbon black, graphite, carbon nanotubes, and carbon nanofibers.

[0033] The surface tension of the negative electrode dam coating composition according to the exemplary embodiment may be 70 mN / mm or more.

[0034] According to yet another exemplary embodiment of the present disclosure, there is provided a lithium secondary battery including: the negative electrode; a 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, so that the negative electrode dam coating composition has a tendency to remain at the interface without being incorporated into the negative electrode slurry, thereby preventing the occurrence of a hypertrophic edge.

[0037] Therefore, the dam coating layer shortens the landslide length of the negative electrode active material layer, which can reduce the risk of NP ratio inversion in lithium secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is an enlarged view of one side of a cross section of a negative electrode in the prior art in which a negative electrode slurry is coated on a current collector.

[0039] Figure 2 This is a cross-sectional view of a negative electrode with a hypertrophic edge.

[0040] Figure 3 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 is a top view of a negative electrode sheet to illustrate the negative electrode according to an exemplary embodiment.

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

[0043] [Explanation of Reference Numerals]

[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 plate DETAILED DESCRIPTION

[0049] Hereinafter, the present disclosure will be described in more detail to provide a better understanding of the present disclosure.

[0050] The terms and words used in this specification and claims should not be interpreted with their ordinary or dictionary meanings, but should be interpreted with meanings and concepts consistent with the technical ideas of the present disclosure based on the principle that the inventor can define the concepts of the terms in a manner that he believes is appropriate to best describe the present disclosure.

[0051] The terms used in this application are only used to describe certain embodiments and are not intended to limit the concepts of the present invention. Unless the context clearly indicates otherwise, a singular expression includes a plural expression.

[0052] In the present application, expressions such as "including", "provided with" or "having" are intended to indicate the existence of the described features, counts, steps, operations, components, parts or their combinations, and should not be understood as excluding the possibility of the existence or addition of one or more other features, counts, operations, components, parts or their combinations.

[0053] As used herein, the literal term "combination thereof" included in the Markush form expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush form expression, and includes one or more selected from the group consisting of these components.

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

[0055] In this specification, "%" means weight % unless otherwise specified.

[0056] For the purpose of this specification, the specific surface area can be measured by the Brunauer-Emmett-Teller (BET) method. For example, it can be measured by a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) using a nitrogen adsorption distribution method and a BET 6-point method.

[0057] As used herein, the average particle size (D 50 ) can be defined as the particle size at the 50th percentile of the particle size distribution. The average particle size is not particularly limited and can be measured, for example, by laser diffraction, scanning electron microscopy (SEM) photography, etc. Laser diffraction methods are generally capable of measuring particle diameters from the submicron region to several millimeters and can produce highly reproducible and highly resolvable results.

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

[0059] <Measurement conditions>

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

[0061] Column: Two PL Mix B connected

[0062] Column temperature: 40°C

[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 sheet and the full width direction of the negative electrode are defined as the X-axis direction, the transverse direction (TD) of the negative electrode sheet and the full length direction of the negative electrode are defined as the Y-axis direction, the direction perpendicular to the plane formed by the combination of the X-axis direction and the Y-axis direction is defined as the Z-axis direction, and the X-axis direction and the Y-axis direction are referred to as horizontal directions.

[0067] Negative electrode dam coating composition

[0068] Figure 1 This is an enlarged view of one side of a cross section of a negative electrode in the prior art in which a negative electrode slurry is coated on a current collector. Figure 2 is a cross-sectional view of a negative electrode with a thickened edge. Figure 3 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 the 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 end of the negative electrode active material layer 12 with an inclined shape is called a landslide area 12S, and the landslide length, that is, the length of the landslide area in the Y-axis direction, is about 4 to 10 mm.

[0070] At the same time, refer to Figure 3 When the negative electrode dam coating composition 130CD is applied to the edge of the region coated with the negative electrode slurry 120SE, the landslide length of the landslide region 120S of the negative electrode active material layer becomes longer than Figure 1 This is much shorter because the negative electrode dam coating composition 130CD acts as a dam and inhibits the negative electrode slurry 120SE from flowing downward.

[0071] However, the negative electrode dam coating composition 130CD is coated in a manner partially overlapping the negative electrode slurry 120S, and a portion of the negative electrode dam coating composition 130CD located on the negative electrode slurry may diffuse into the negative electrode slurry 120S to form a negative electrode slurry. Figure 2 The inventors of the present disclosure have found 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 dam coating composition from diffusing 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 a carbon-based material, a cellulose compound, a rubber-based binder, and inorganic particles. The carbon-based material increases the surface tension of the negative electrode dam coating composition, while the rubber-based binder imparts adhesion to the dam coating, allowing it to adhere to the current collector and further enhancing its flexibility, thereby preventing it from detaching when subjected to physical force, ultimately improving its stability.

[0073] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these solvents may be used alone or in combination. Water is preferably used as the 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 content of the solvent may allow the negative electrode dam coating composition to have a suitable viscosity.

[0075] The carbon-based material can be one or a mixture of two or more 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 black, etc.; carbon fiber, carbon nanotube and carbon nanofiber.

[0076] The cellulose-based compound is a water-soluble polymer compound having a predetermined viscosity, which can increase the cohesive force of the solvent and make the negative electrode dam coating composition have a suitable viscosity, thereby increasing the surface tension.

[0077] The cellulose compound is 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 may be 800,000 to 2,000,000, preferably 900,000 to 1,800,000, more preferably 1,000,000 to 1,500,000. When the weight average molecular weight of the cellulose compound is within the above range, it imparts appropriate viscosity to the dam coating composition, which is desirable 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 the present disclosure.

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

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

[0082] If necessary, the styrene-butadiene rubber may further include a monomeric repeating unit having a crosslinking group. The monomeric repeating unit having a crosslinking group may be included in an amount of 12 parts by weight or less based on the total weight of the styrene-butadiene rubber to reduce electrolyte absorption.

[0083] The inorganic particles have the effect of increasing electrical insulation and thermal safety and improving the strength of the dam coating. The content of the inorganic particles can be appropriately adjusted considering the viscosity, insulation, dispersibility, coatability, etc. of the negative electrode dam coating composition.

[0084] The inorganic particles may 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, the inorganic particles may be AlO(OH).

[0085] The average particle size of the inorganic particles (D 50) 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 the negative electrode dam coating composition of one embodiment, the content of solids excluding the solvent may be 16 to 36 parts by weight, more specifically 18 to 34 parts by weight, and even more specifically 20 to 32 parts by weight, based on 100 parts by weight of the negative electrode dam coating composition. When the solid content in the negative electrode dam coating composition satisfies the above numerical range, it is preferred from the perspective of the coating performance of the negative electrode dam coating composition and the effect of reducing the landslide length of the negative electrode slurry.

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

[0088] In one embodiment, the solid may include 3 to 25 weight %, more particularly 6 to 23 weight %, more particularly 10 to 17 weight % of carbon-based materials. In addition, the solid may include 0.5 to 5 weight %, more particularly 1 to 4.5 weight %, more particularly 2 to 4 weight % of cellulose compounds. In addition, the solid may include 3 to 25 weight %, more particularly 6 to 23 weight %, more particularly 10 to 17 weight % of rubber-based binders. In addition, the solid may include 45 to 93.5 weight %, more particularly 50 to 83 weight %, more particularly 60 to 77 weight % of inorganic particles. When the carbon-based material, cellulose compound, rubber-based binder 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 the carbon-based material to the rubber-based adhesive may be 4:6 to 6:4, more preferably 45:55 to 55:45.

[0090] Since the carbon-based material and the rubber-based binder are included within this content range, it is possible to prevent surface tension degradation due to the introduction of the rubber-based binder while improving the flexibility of the dam coating layer.

[0091] The negative dam coating layer 130 may be formed by coating a negative electrode slurry on a current collector, coating a negative electrode dam coating composition near a boundary between the negative electrode slurry and an uncoated portion, and drying it, or by simultaneously coating the negative electrode slurry and the negative electrode dam coating composition and drying them.

[0092] In one embodiment, the negative electrode dam coating composition may have a viscosity of 2,000 cps to 15,000 cps, more specifically 2,500 cps to 12,000 cps, and even more specifically 3,000 cps to 10,000 cps, as measured at a shear rate of 2.5 s at 25° C. For negative electrode dam coating compositions having a viscosity value within the above range, the thickness and width of the dam coating layer may be within an appropriate range to improve the landslide of the negative electrode active material layer.

[0093] The coating method of the negative electrode dam coating composition may include, but is not limited to, spray coating, spin coating, roller coating, die coating, gravure printing, rod coating, etc., among which die coating and gravure printing are preferably used.

[0094] The surface tension of the negative electrode dam coating composition of one embodiment can be at least 70 mN / mm, more specifically at least 71 mN / mm, and even more specifically between 72 mN / mm and 80 mN / mm. A negative electrode dam coating composition having a surface tension within this numerical range is effective in preventing the formation of a thickened edge on the negative electrode. The surface tension within this numerical 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] Immersion depth: 4

[0099] Surface detection weight: 0.005

[0100] Stabilization time: 5

[0101] Negative electrode for lithium secondary battery

[0102] Figure 4 is a top view of a negative electrode sheet, showing a negative electrode according to an exemplary embodiment, Figure 5 It is along Figure 4 Cross-sectional view of the A-A' cut.

[0103] With reference to these drawings, the negative electrode 100 of the exemplary embodiment includes: a negative electrode current collector 110; a negative electrode active material layer 120 provided on one or both surfaces of the negative electrode current collector 110; and a dam coating layer 130 provided on one or both surfaces of the negative electrode current collector 110, wherein the dam coating layer 130 may be configured to contact an end surface of the negative electrode active material layer 120. The end portion is an end portion in the lateral direction (Y-axis direction) of the negative electrode sheet (NES) or in the entire length direction (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 horizontal direction (Y-axis direction) and serves as the base material of the negative electrode 100, while the dam coating layer 130 is formed on both edges of the negative electrode sheet (NES) in the horizontal direction (Y-axis direction), and there is a non-coated portion outside the dam coating layer 130 that is not covered by the negative electrode active material layer 120 or the dam coating layer 130. Moreover, the negative electrode 100 can be manufactured by notching and cutting along the notching line (dashed line) shown on such a negative electrode sheet NES. Although Figure 4 The negative electrode is shown in which the dam coating layer 130 is coated on both edges of the negative active material layer 120 , but is not limited thereto, and the dam coating layer 130 may be coated on only one edge of the negative active material layer 120 .

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

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

[0107] In the negative electrode 100 of one embodiment, 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. As the landslide length is reduced, the risk of NP ratio reversal in the landslide area can be prevented.

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

[0109] The dam coating layer 130 may include a carbon-based material, a cellulose compound, a rubber-based binder, and inorganic particles to control the surface tension of the negative electrode dam coating composition to the level of the negative electrode slurry. The carbon-based material increases the surface tension of the negative electrode dam coating composition, while the rubber-based binder imparts flexibility to the dam coating layer, preventing it from detaching when subjected to physical force, ultimately improving its stability.

[0110] The 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 layer 130 may be 20 to 40 μm, more specifically 22 to 40 μm, even more specifically 25 to 35 μm. The thickness refers to the Z-axis distance from the plane of the current collector to the surface of the dam coating layer 130 .

[0112] According to one embodiment, the length of the dam coating layer 130 in the entire length direction (Y-axis direction) may be 3 mm or less, more specifically 0.5 mm to 3 mm, and even more specifically 1 mm to 2.5 mm.

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

[0114] When the thickness and length of the dam coating layer 130 are within the above numerical ranges, it is preferable from the viewpoint of the safety of the dam coating layer and the viewpoint of the negative electrode capacity performance.

[0115] Since the negative electrode dam coating composition must act as a dam to prevent the negative electrode slurry from spreading, the coating thickness of the negative electrode dam coating composition is preferably at least a certain level. Figure 3 When the negative electrode dam coating composition is applied, 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 the electrode undergoes a series of electrode processes, such as a drying process, the thickness of the dam coating layer becomes smaller than the thickness of the negative electrode active material layer.

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

[0117] Adhesion is evaluated as follows: the negative electrode dam coating composition is coated on the copper foil, dried at a temperature of 80 to 90°C, cut into 150 mm long and 20 mm wide, and the sample is attached to a 75 mm long and 25 mm wide slide in the length direction using double-sided tape, so that the coated surface of the negative electrode dam coating composition faces the slide. The evaluation sample is then passed through a laminator to ensure uniform attachment of the double-sided tape. The slide portion of the evaluation sample is then fixed to the sample stage of a universal testing machine (UTM) (LS5, AMETEK), and the half of the sample without the slide is connected to the load cell of the UTM machine. The load applied to the load cell is measured by moving the load cell 50 mm at a speed of 100 mm / min and applying a 90° force. The average value of the measured loads in the range of 20 mm to 40 mm is taken during the stroke. The test is repeated 5 times, and the average value is evaluated as the adhesion (gf / 20 mm) of each sample.

[0118] When the adhesiveness of the dam coating layer 130 is within the above numerical range, the dam coating layer is not separated during an electrode process such as a roll pressing process, which is ideal.

[0119] The negative electrode current collector 110 is a highly conductive metal to which the negative electrode slurry easily adheres. Any non-reactive material within the battery voltage range can be used, 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. These current collectors may also have microscopic irregularities on their surfaces to enhance adhesion of the negative electrode active material and may be used in a variety of forms, including films, sheets, foils, meshes, porous materials, foams, and non-woven materials.

[0120] The negative active material layer 120 may include a negative active material, a binder, and, as needed, a conductive material and a filler.

[0121] The negative electrode active material can be any compound that can reversibly intercalate and deintercalate lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, amorphous carbon, etc.; metal substances that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiO β(0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and metal oxides capable of being doped and dedoped with lithium; or composites comprising the above metal substances and carbonaceous materials, such as Si-C composites or Sn-C composites, any one or more of which can be used. Metallic lithium thin films can also be used as negative electrode active materials.

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

[0123] The negative electrode active material may be present in an amount of about 80 wt % to 99.5 wt % or 88 wt % to 99 wt % based on the total weight of the negative electrode active material layer, but the content is not limited thereto.

[0124] There is no particular limitation on the binder, as long as it is a component that helps to bond the negative electrode active material to the conductive material and the conductive material to the current collector, for example: polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorinated rubber, and various copolymers.

[0125] In the case where the solvent of the negative electrode slurry is an aqueous solvent such as water, the binder is preferably an aqueous binder. In a specific example, the aqueous binder can be 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, polyvinyl pyrrolidone, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose and diacetyl cellulose. In a specific example, the aqueous binder can be selected from styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber and acrylonitrile-butadiene-styrene rubber One or more. For example, the aqueous binder can be styrene-butadiene rubber.

[0126] The content of the binder may generally be 1 to 30 wt % based on the total weight of the negative electrode active material layer.

[0127] There is no particular limitation on the conductive material as long as it has conductivity and does not cause chemical changes in the battery. For example, the following can be used: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc.; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbons, aluminum, nickel powder; conductive whiskers, such as zinc oxide, potassium titanate; conductive metal oxides, such as titanium oxide; conductive materials such as polyphenylene derivatives; and the like.

[0128] The conductive material may be generally contained in an amount of 1 to 30% by weight based on the total weight of the negative electrode active material layer.

[0129] Fillers are optionally used as components to inhibit electrode expansion. There are no special restrictions on fillers as long as they are fibrous materials that do not cause chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber can be used.

[0130] Hereinafter, a method for manufacturing the negative electrode will be described.

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

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

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

[0134] The solvent content can provide a negative electrode slurry having a suitable viscosity and solid content. For example, the solvent content can be such that the solid content in the negative electrode slurry is 40% to 75% by weight, more particularly 50% to 70% by weight, and more particularly 55% to 70% by weight. In addition, 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 greater than a certain level to achieve good energy density.

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

[0136] The coating step P20 of coating the negative electrode dam coating composition and the negative electrode slurry on the negative electrode current collector may be performed by coating the negative electrode dam coating composition after coating the negative electrode slurry on the negative electrode current collector, or by coating the negative electrode slurry and the negative electrode dam coating composition on the negative electrode current collector simultaneously.

[0137] lithium secondary batteries

[0138] Next, the lithium secondary battery of the present disclosure will be described.

[0139] A lithium secondary battery according to one embodiment of the present disclosure may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0140] The lithium secondary battery of the present disclosure can be prepared according to conventional methods known in the art. For example, it can be prepared by placing a separator between a positive electrode and a negative electrode 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 surfaces of the negative electrode current collector; and a dam coating disposed on one or both surfaces of the negative electrode current collector, wherein the dam coating contacts the end surface of the negative electrode active material layer and may include a carbon-based material, a cellulose compound, a rubber-based binder, and inorganic particles.

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

[0143] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can generally have a thickness of 3 μm to 500 μm, and may also have microscopic irregularities formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a non-woven body.

[0144] The positive electrode active material is not particularly limited, and any compound known in the art that can reversibly intercalate and deintercalate lithium can be used without limitation. 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 O4 (wherein, x is 0 to 0.33), LiMnO3, LiMn2O3 and LiMnO2 compounds; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5 and Cu2V2O7; 1-x M x Ni-type lithium nickel oxide represented by O2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); 2-x M x Lithium manganese composite oxide represented by LiNiO2 (wherein M=Co, Ni, Fe, Cr, Zn or Ta, x=0.01 to 0.1) or Li2Mn3MO8 (wherein, M=Fe, Co, Ni, Cu or Zn); x Mn 2-x O4 represents a lithium manganese composite oxide having a spinel structure; LiMn2O4 in which some Li atoms are replaced by alkaline earth metal ions; disulfide; lithium iron phosphate represented by LiFePO4; disulfide; and Fe2(MoO4)3, etc., but are not limited thereto.

[0145] The positive electrode active material layer may further include a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material described above.

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

[0147] The BET specific surface area of ​​carbon nanotubes can be 100 m 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 may be 0.1 wt % to 30 wt %, more specifically 0.1 wt % to 10 wt %, and more specifically 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 may be 0.1 wt % to 30 wt %, more specifically 0.1 wt % to 10 wt %, and more specifically 0.5 wt % to 5 wt %.

[0151] The separator may be any porous material commonly used as a separator in lithium secondary batteries, such as, but not limited to, a polyolefin porous film or a nonwoven fabric. In particular, it is preferred that the separator has low resistance to ion migration of the electrolyte and excellent electrolyte wettability.

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

[0153] Nonwoven fabrics include, in addition to polyolefin nonwoven fabrics, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalate, and the like, either alone or as a mixture. Nonwoven fabrics can be made of spunbond or meltblown fibers composed of long fibers.

[0154] The thickness of the porous substrate is not particularly limited and may be 5 to 50 μm. The pore size and porosity in the porous substrate are also not particularly limited and may be 0.01 to 50 μm and 10 to 95%, respectively.

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

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

[0157] The organic solvent can be used without limitation, as long as it can serve as a medium in which ions participating in the electrochemical reaction of the battery can move. Specifically, the organic solvent 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 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), propylene carbonate (PC), etc.

[0158] Among them, carbonate solvents are preferred, and more preferably a mixture of a cyclic carbonate (such as 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 (such as ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate).

[0159] Lithium salts can be used without limitation as long as they are compounds capable of providing lithium ions for lithium secondary batteries. Specifically, the lithium salt 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 included in the electrolyte at a concentration of about 0.6 mol% to about 2 mol%.

[0160] In addition to the electrolyte components, the electrolyte may further include additives such as pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum chloride for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, and increasing the discharge capacity of the battery. The content of the additives may be 0.1 to 5 weight % based on the total weight of the electrolyte.

[0161] The lithium secondary battery of the present disclosure can be manufactured by placing a separator between the positive electrode and the negative electrode 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 the electrode assemblies, impregnating the electrode assemblies with an electrolyte, and sealing the resulting product in a battery case.

[0162] When manufacturing the lithium secondary battery of the present disclosure, the electrode assembly can be dried to remove one or more organic solvents used in manufacturing the positive electrode, the solvent being 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 above-described lithium secondary batteries, lithium secondary batteries according to other examples of the present disclosure may be all-solid-state batteries.

[0164] The battery case may be any one conventionally used in the art, and the shape is not limited according to the intended use of the battery, and may be, for example, cylindrical, prismatic, pouch-type, or coin-type using a can.

[0165] The lithium secondary battery of the present disclosure exhibits excellent resistance characteristics, discharge capacity, power characteristics, and capacity retention, and thus can be used in portable devices such as mobile phones, notebook computers, and digital cameras, as well as electric vehicles such as energy storage systems (ESS) and hybrid electric vehicles (HEV).

[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 the scope of the present disclosure.

[0167] Example 1: Preparation of negative electrode

[0168] (Preparation of 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 an Mw of 1,260,000 as a cellulose-based compound, 13 parts by weight of styrene butadiene rubber (SBR) as a rubber-based binder, and 71 parts by weight of boehmite (AlO(OH), product name: AOH60) as inorganic particles in water. The solid content was 26% by weight.

[0170] (Preparation of negative electrode slurry)

[0171] Artificial graphite (D 50 23μm, specific surface area 1.0m2 / g, tap density 0.9 g / cc), styrene butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and carbon nanotubes as a conductive material were 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 wt %).

[0172] (Preparation of negative electrode)

[0173] On a copper foil (thickness 10 μm), the negative electrode slurry and the negative electrode dam coating composition were simultaneously coated, but the negative electrode dam coating composition was coated so as to be located at both edges of the negative electrode slurry coating portion in the Y-axis direction, as shown in FIG. Figure 5 shown.

[0174] The negative electrode was then dried at 90°C and roll-pressed to complete the preparation.

[0175] Example 2: Preparation of negative electrode

[0176] (Preparation of 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-based compound, rubber-based binder, and inorganic particles to 15:3:15:67.

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

[0179] Example 3: Preparation of negative electrode

[0180] (Preparation of 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-based compound, rubber-based binder, and inorganic particles to 11:2:11:76.

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

[0183] Comparative Example 1: Preparation of negative electrode

[0184] (Preparation of Negative Electrode Dam Coating Composition)

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

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

[0187] Comparative Example 2: Preparation of negative electrode

[0188] (Preparation of Negative Electrode Dam Coating Composition)

[0189] 4 parts by weight of CMC (Daicel 2200) with an 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) were mixed and stirred in water to prepare a negative electrode dam coating composition. The solid content was 25% by weight.

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

[0191] Comparative Example 3: Preparation of negative electrode

[0192] A negative electrode dam coating composition (solid content 25 wt %) 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.

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

[0194] Comparative Example 4: Preparation of negative electrode

[0195] A negative electrode dam coating composition (solid content 25 wt %) 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.

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

[0197] Comparative Example 5: Preparation of negative electrode

[0198] A negative electrode dam coating composition (solid content 25 wt %) 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.

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

[0200] Comparative Example 6: Preparation of negative electrode

[0201] (Preparation of 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 solid content was 24% by weight.

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

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

[0205] Experimental Example 2: Evaluation of surface tension

[0206] For each of 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.

[0207] Motor speed: 15 rpm / s

[0208] Probe Type: Ring

[0209] Immersion depth: 4

[0210] Surface detection weight: 0.005

[0211] Stabilization time: 5

[0212] Experimental Example 3: Confirming the appearance of hypertrophic margins

[0213] For each of the negative electrodes in Examples 1 to 3 and Comparative Examples 1 to 6, the negative electrode active material layer was visually observed to determine whether Figure 3 The hypertrophic margin shown in FIG was used, and the results are shown in Table 1. If a hypertrophic margin was present, it was marked with an "O," and if no hypertrophic margin was present, it was marked with an "X."

[0214] Experimental Example 4: Evaluation of Adhesion

[0215] The negative electrode dam coating composition of Example 1 was coated on a copper foil, dried at a temperature of 80 to 90°C, cut into 150 mm long and 20 mm wide, and the sample was attached to a 75 mm long and 25 mm wide glass slide in the length direction using double-sided tape so that the surface of the dam coating faced the glass slide. The evaluation sample was then passed through a laminator to evenly adhere the double-sided tape. The glass 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 glass slide was connected to the weighing sensor of the UTM machine. The load applied to the weighing sensor was measured by moving the weighing sensor 50 mm at a speed of 100 mm / min and applying a 90° force. The average value of the measured loads in the range of 20 mm to 40 mm was taken during the stroke. The test was repeated 5 times, and the average value was evaluated as the adhesion force (gf / 20 mm) of each sample. The results are shown in Table 1.

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

[0217] [Table 1]

[0218] Viscosity (cps) Surface tension (mN / mm) Whether hypertrophic margins appear Adhesion (gf / 20mm) 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, the negative electrode dam coating compositions of Examples 1 to 3 each exhibited a surface tension of 72 mN / mm or greater, which prevented the formation of a thickened edge. Furthermore, the adhesiveness was also greater than or equal to 90 gf / 20 mm, which is expected to reduce the likelihood 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 negative electrode active material layer disposed on one or both sides of the negative electrode current collector; and a dam coating provided on one or both sides of the negative electrode current collector, The dam coating layer contacts the end surface of the negative electrode active material layer and contains a carbon-based material, a cellulose compound, a rubber-based binder, and inorganic particles.

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

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

4. The negative electrode for a lithium secondary battery according to claim 1, wherein The inorganic particles are 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.

5. The negative electrode for a lithium secondary battery according to 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 according to claim 1, wherein The weight average molecular weight of the cellulose compound is 800,000 to 2,000,000.

7. The negative electrode for a lithium secondary battery according to claim 1, wherein The rubber-based adhesive is styrene butadiene rubber (SBR).

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

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

10. The negative electrode for a lithium secondary battery according to 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 according to claim 8, wherein A thickness ratio (T2 / T1) of a maximum thickness value T2 of the dam coating layer to an average thickness value 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 according to claim 1, wherein The maximum thickness of the dam coating layer is in the range of 20 μm to 40 μm, and the total length thereof is 3 mm or less.

13. The negative electrode for a lithium secondary battery according to claim 1, wherein The dam coating has an adhesiveness of 90 gf / 20 mm or more.

14. A negative electrode dam coating composition comprising: a solvent, a carbon-based material, a cellulose compound, a rubber binder and inorganic particles.

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

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

4.

17. The negative electrode dam coating composition according to claim 15, wherein: The content of solid excluding the solvent is 16 to 36 parts by weight based on 100 parts by weight of the negative electrode dam coating composition.

18. The negative electrode dam coating composition according to claim 13, wherein: The carbon-based material is one selected from carbon black, graphite, carbon nanotubes and carbon nanofibers. The negative electrode dam coating composition according to claim 12 , wherein the surface tension thereof is greater than 70 mN / mm.

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

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