Anode, composition for anode dam coating, and lithium secondary battery

Abstract

A composition for anode dam coating according to an embodiment of the present invention comprises an aqueous binder, the aqueous binder comprising one or more types of compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile. A composition for anode dam coating according to an embodiment of the present invention suppresses the occurrence of pet-edge on an anode since the surface tension of the composition is as high as the level of a slurry for an anode. Additionally, a dam coating layer formed from the composition for anode dam coating shortens the sliding length of an anode active material layer, thereby reducing the NP-ratio reversal risk of a lithium secondary battery.

Description

Composition for cathode and cathode dam coating and lithium secondary battery

[0001] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2023-0129773, filed on September 26, 2023.

[0002] The present invention relates to a negative electrode having a short negative electrode sliding region and preventing or suppressing the occurrence of a fat edge at the negative electrode end, a composition for negative electrode dam coating therefor, and a lithium secondary battery including the negative electrode.

[0003] As technological development and demand for industrial fields such as mobile devices, automobiles, and energy storage devices increase, the demand for batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries with high energy density and discharge voltage have been studied extensively and are now commercialized and widely used.

[0004] Secondary batteries are classified into cylindrical and prismatic batteries, in which the electrode assembly is built into a cylindrical or prismatic metal can, and pouch-type batteries, in which the electrode assembly is built into a pouch-type case made of aluminum laminate sheet, depending on the shape of the battery case.

[0005] In addition, the electrode assembly built into the battery case is a power plant capable of charging and discharging, which is composed of a stacked structure of anode / separator / cathode, and includes a jelly-roll type electrode assembly in which a long sheet-shaped cathode and cathode on which an electrode mixture including an electrode active material is applied are wound with a separator interposed between them, a stack type (laminated type) electrode assembly in which a plurality of cathodes and anodes punched and notched in units of a predetermined size are sequentially stacked with a separator interposed between them, and a stack / folding type electrode assembly in which bi-cells or full cells are wound with a structure in which anodes and cathodes in predetermined units are stacked with a separator interposed between them.

[0006] The positive and negative electrodes that make up the electrode assembly are manufactured by applying the electrode slurry manufactured in the mixing process to the electrode current collector through a slot die in a set pattern and at a constant thickness, and then drying. However, since the electrode slurry is a fluid, after the electrode slurry application process, the electrode slurry flows down due to its fluidity, and this phenomenon is called sliding.

[0007] Fig. 1 is an enlarged view of one side of a cross-section of a negative electrode on which an electrode slurry has been applied. Referring to Fig. 1, the negative electrode active material layer (12) on which the negative electrode slurry has been applied is divided into a flattening region (12A) having a constant thickness and being parallel to the plane of the negative electrode current collector (11), and a sliding region (12S) in which the thickness of the electrode active material layer (12) gradually decreases along the direction toward the uncoated region on which the electrode slurry has not been applied and is inclined to the plane of the current collector (11).

[0008] Meanwhile, the positive and negative electrodes constituting the electrode assembly face each other with a separator interposed between them, and the length of the sliding region of the positive electrode and the length of the sliding region of the negative electrode may be different, and the inclined shape of the sliding region may also appear in various forms such as an upward convex shape, a downward convex shape, a straight shape, an S shape, etc., and even if the inclined shape is the same, the inclination may appear differently. Accordingly, there is a risk that the negative electrode sliding region may have a part that locally has an imbalance in the NP Ratio depending on the facing position, and the imbalance in the NP Ratio may cause lithium to precipitate from the negative electrode, which may cause a safety accident such as a short circuit.

[0009] Since the possibility of an imbalance in the NP Ratio theoretically tends to be lower when the ratio of the anode loading to the cathode loading at the anode / cathode facing area is greater, recent technological attempts have been made to increase the loading in the anode sliding region. One such attempt involves overlapping a dam coating composition on the edge where the anode slurry is applied, thereby minimizing the sliding length of the anode active material layer by suppressing the anode slurry from flowing down.

[0010] However, the conventional dam coating composition has a problem in that a fat-edge phenomenon occurs, in which the thickness of the overlapping portion of the negative electrode active material layer and the dam coating layer becomes thicker than the thickness of the negative electrode active material layer. Fig. 2 is a cross-sectional view of a negative electrode in which a fat-edge occurs. Referring to Fig. 2, a fat-edge protruding upward along the Z-axis direction is formed at both ends of the negative electrode active material layer (12) in the Y-axis direction. If such a fat-edge exists in the negative electrode, damage may occur to the current collector layer during the rolling process, which may cause a safety issue. In addition, the fat-edge may damage other electrodes or separators during the process of stacking multiple positive / negative electrodes and separators.

[0011] Therefore, there is a need for technological development for a cathode with a short sliding length and no pet-edge formation, and a method for manufacturing the same.

[0012] The purpose of the present invention is to provide a negative electrode having a short negative sliding region and preventing or suppressing the occurrence of a fat edge at the negative electrode end, a composition for negative electrode dam coating therefor, and a lithium secondary battery including the negative electrode.

[0013] According to one embodiment of the present invention, an anode for a lithium secondary battery is provided. The anode includes: an anode current collector; an anode active material layer disposed on one surface or both surfaces of the anode current collector; and a dam coating layer disposed on one surface or both surfaces of the anode current collector, wherein the dam coating layer contacts an end of the anode active material layer and includes an aqueous binder, and the aqueous binder is characterized in that it is one or two or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

[0014] In one embodiment of the present invention, the dam coating layer further comprises a cellulose-based compound and inorganic particles, and comprises, based on the total weight of the dam coating layer, 0.5 to 10 wt% of the aqueous binder; 0.5 to 10 wt% of the cellulose-based compound; and 80 to 99 wt% of the inorganic particles.

[0015] In one embodiment of the present invention, the inorganic particles are AlO(OH), Al2O3, γ-AlOOH, Al(OH) 3, One or more selected from the group consisting of SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3 and Mg(OH)2.

[0016] In one embodiment of the present invention, the aqueous binder is polyacrylamide.

[0017] In one embodiment of the present invention, the cellulose-based compound is one or more compounds selected from the group consisting of carboxyl methyl cellulose (CMC), cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, lithium salt of carboxymethyl cellulose (CMC-Li), and sodium salt of carboxymethyl cellulose (CMC-Na).

[0018] In one embodiment of the present invention, the negative electrode active material layer is divided into a flattening region whose surface is parallel to the plane of the negative electrode current collector and a sliding region extending from the flattening region but whose surface is inclined to the plane of the negative electrode current collector, and the sliding region is structured to be located at one end and the other end of the negative electrode active material layer based on the electric field direction.

[0019] In one embodiment of the present invention, the length in the longitudinal direction of the sliding area is 4 mm or less.

[0020] In one embodiment of the present invention, the length of the sliding region in the longitudinal direction is in the range of 0.5 to 3.5 mm.

[0021] In one embodiment of the present invention, the thickness ratio (T2 / T1) of the maximum thickness value T2 of the dam coating layer to the average thickness value T1 of the negative active material layer in the flattened region in the negative active material layer is in the range of 0.1 to 0.4.

[0022] In one embodiment of the present invention, the dam coating layer has a maximum thickness within a range of 20 to 40 μm and a length in the longitudinal direction of the dam coating layer of 3 mm or less.

[0023] According to another embodiment of the present invention, a composition for cathode dam coating is provided. The composition for cathode dam coating comprises a solvent; and an aqueous binder, wherein the aqueous binder is one or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

[0024] In one embodiment of the present invention, the composition for cathode dam coating further comprises a cellulose-based compound and inorganic particles, and the solid content excluding the solvent comprises, based on the total weight of the solid content, 0.5 to 10 wt% of the aqueous binder; 0.5 to 10 wt% of the cellulose-based compound; and 80 to 99 wt% of the inorganic particles.

[0025] In one embodiment of the present invention, the content of the solid content excluding the solvent is 15 to 35 parts by weight per 100 parts by weight of the composition for cathode dam coating.

[0026] In one embodiment of the present invention, the aqueous binder is polyacrylamide.

[0027] In one embodiment of the present invention, the inorganic particles are AlO(OH), Al2O3, γ-AlOOH, Al(OH) 3, One or more selected from the group consisting of SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3 and Mg(OH)2.

[0028] In one embodiment of the present invention, the composition for cathode dam coating has a surface tension of 72 mN / mm or more.

[0029] According to another embodiment of the present invention, a lithium secondary battery is provided, including the negative electrode; the positive electrode; the separator; and the electrolyte.

[0030] According to one embodiment of the present invention, the surface tension of the composition for cathode dam coating is raised to the level of the cathode slurry, so that the composition for cathode dam coating has a tendency to maintain the interface without being mixed into the cathode slurry, thereby preventing the occurrence of a pet-edge.

[0031] Accordingly, the sliding length of the negative electrode active material layer is shortened by the dam coating layer, which can reduce the risk of NP-ratio reversal in a lithium secondary battery.

[0032] Figure 1 is an enlarged view of one side of a cross-section of a cathode on which a cathode slurry is applied on a current collector according to a conventional technique.

[0033] Figure 2 is a cross-sectional view of a cathode where a pet-edge has occurred.

[0034] FIG. 3 is an enlarged view of one side of a cross-section of a cathode to which a slurry for a cathode and a composition for a dam coating have been applied according to exemplary embodiments.

[0035] FIG. 4 is a top view of a cathode sheet for explaining a cathode according to exemplary embodiments.

[0036] Figure 5 is a cross-sectional view taken along line A-A' of Figure 4.

[0037] [Explanation of symbols]

[0038] 10, 100: cathode

[0039] 11, 110: Negative current collector

[0040] 12, 120: Negative active material layer

[0041] 13, 130: Dam coating layer

[0042] NES: Negative Sheet

[0043] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0044] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0045] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0046] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0047] In this specification, the term “combination(s) thereof” included in the surface of the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Makushi format, and means including one or more selected from the group consisting of the above components.

[0048] In this specification, the description of “A and / or B” means “A or B or both.”

[0049] In this specification, “%” means weight percent unless explicitly indicated otherwise.

[0050] In this specification, the specific surface area can be measured using the BET (Brunauer-Emmett-Teller; BET) method. For example, it can be measured using the BET 6-point method by nitrogen gas adsorption flow using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

[0051] In this specification, the average particle diameter (D 50 ) can be defined as the particle diameter at 50% of the particle diameter distribution. The average particle diameter is not particularly limited, but can be measured using, for example, a laser diffraction method or a scanning electron microscope (SEM) photograph. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0052] In this specification, "weight average molecular weight (Mw)" refers to a conversion value for standard polystyrene measured by gel permeation chromatography (GPC). Specifically, the weight average molecular weight is a value converted from a value measured under the following conditions using GPC, and standard polystyrene of the Agilent system was used to prepare a calibration curve.

[0053] <Measurement conditions>

[0054] Measuring instrument: Agilent GPC (Agulent 1200 series, USA)

[0055] Column: PL Mixed B 2 connections

[0056] Column temperature: 40 ℃

[0057] Eluent: Tetrohydrofuran

[0058] Flow rate: 1.0 mL / min

[0059] Concentration: ~ 1 mg / mL (100 μL injection)

[0060] 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, and the direction perpendicular to the plane obtained 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.

[0061]

[0062] Composition for cathode dam coating

[0063] Figure 1 is an enlarged view of one side of a cross-section of a negative electrode on which a negative electrode slurry has been applied on a current collector according to a conventional technique. Figure 2 is a cross-section of a negative electrode in which a PET edge has been formed. Figure 3 is an enlarged view of one side of a cross-section of a negative electrode on which a negative electrode slurry and a negative electrode dam coating composition have been applied according to exemplary embodiments.

[0064] Referring to Fig. 1, when the composition for negative electrode dam coating is not applied, the edge of the area where the negative electrode slurry is applied spreads along the current collector (11) due to the fluidity of the negative electrode slurry, and the end of the negative electrode active material layer (12) dried in this way has an inclined shape with respect to the plane of the negative electrode current collector (11). The end of the negative electrode active material layer (12) having an inclined shape in the negative electrode active material layer (12) is called a sliding region (12S), and the sliding length, which is the length in the Y-axis direction of the sliding region, reaches about 4 to 10 mm.

[0065] On the other hand, referring to FIG. 3, when the negative electrode dam coating composition (130CD) is applied to the edge of the area where the negative electrode slurry (120SE) is applied, the dam coating composition (130CD) acts as a dam to prevent the negative electrode slurry (120SE) from flowing down, so the sliding length of the sliding region (120S) of the negative electrode active material layer becomes much shorter compared to FIG. 1.

[0066] However, the cathode dam coating composition (130CD) is applied so as to partially overlap with the cathode slurry (120S), and a portion of the dam coating composition (130CD) positioned on the cathode slurry can diffuse into the cathode slurry (120S) to form a PET-edge as illustrated in FIG. 2. As a result of extensive research, the inventors of the present invention have discovered that when the surface tension of the dam coating composition is controlled to the level of the cathode slurry, the dam coating composition tends to maintain an interface with the cathode slurry, thereby suppressing the dam coating composition from diffusing into the cathode slurry, leading to the present invention.

[0067] In order to control the surface tension of the dam coating composition to the level of the cathode slurry, the dam coating composition according to one embodiment includes an aqueous binder, wherein the aqueous binder may be one or two or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

[0068] The solvent may be a solvent commonly used in the art, and may include dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone, or a mixture of two or more may be used. Among these, water is preferable as a solvent for the cathode dam coating composition because it has a high surface tension.

[0069] The above solvent may be included in an amount that allows the cathode dam coating composition to have an appropriate viscosity, taking into account the coating properties of the cathode dam coating composition, etc.

[0070] The above-mentioned aqueous binder is a water-soluble polymer compound that can increase the cohesive force of the solvent and thereby increase the surface tension of the dam coating composition. Among the above-mentioned aqueous binders, polyacrylamide is particularly preferred as the aqueous binder of the present invention because it has a significant effect of increasing the surface tension of the cathode dam coating composition.

[0071] The composition for a cathode dam coating of the present invention may additionally include a cellulose-based compound and inorganic particles in addition to the aqueous binder.

[0072] The above cellulose compound is a water-soluble polymer compound having a predetermined viscosity, which can increase the cohesive force of the solvent and increase the surface tension by making the composition for cathode dam coating have an appropriate viscosity.

[0073] The above cellulose compound may be one or two or more compounds selected from the group consisting of carboxymethylcellulose (CMC; carboxyl methyl cellulose), cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, lithium salt of carboxymethylcellulose (CMC-Li), and sodium salt of carboxymethylcellulose (CMC-Na).

[0074] The above cellulose-based compound may have a weight average molecular weight (Mw) within the range of 500,000 to 5,000,000, preferably 700,000 to 4,500,000, and more specifically 900,000 to 4,000,000. When the weight average molecular weight of the cellulose-based compound is within the above range, it provides an appropriate viscosity to the dam coating composition, which is preferable in terms of coating performance.

[0075] The above-mentioned inorganic particles are the main component that enhances electrical insulation and thermal stability, improves the strength of the dam coating layer, and controls the solid content of the cathode dam coating composition. The content of the above-mentioned inorganic particles can be appropriately adjusted in consideration of the viscosity, insulation, dispersibility, coatability, etc. of the cathode dam coating composition.

[0076] The above inorganic particles are AlO(OH), Al2O3, γ-AlOOH, Al(OH) 3, It may be one or two or more compounds selected from the group consisting of SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3 and Mg(OH)2, and may be one or more compounds selected from the group consisting of AlO(OH), Al2O3, γ-AlOOH and Al(OH)3. For example, the inorganic particle may be AlO(OH).

[0077] The average particle diameter of the above inorganic particles (D 50 ) may be 0.1 ㎛ to 100 ㎛, 0.5 ㎛ to 80 ㎛, 1 ㎛ to 50 ㎛; 2 ㎛ to 30 ㎛; 3 ㎛ to 20 ㎛ or 5 ㎛ to 10 ㎛. When the size of the inorganic particles is within the above range, the composition for negative electrode dam coating can be uniformly coated on the negative electrode current collector and the negative electrode slurry.

[0078] In a composition for cathode dam coating according to one embodiment, the content of the solids excluding the solvent may be in the range of 15 to 35 parts by weight, specifically 17 to 33 parts by weight, and more specifically 18 to 32 parts by weight, based on 100 parts by weight of the composition for cathode dam coating. When the content of the solids in the composition for cathode dam coating satisfies the above numerical range, it is preferable in terms of the coating performance of the composition for cathode dam coating and the effect of reducing the sliding length of the cathode slurry.

[0079] In a composition for cathode dam coating according to one embodiment, the solid content excluding the solvent may include, based on the total weight of the solid content, 0.5 to 10 wt% of the aqueous binder; 0.5 to 10 wt% of the cellulose-based compound; and 80 to 99 wt% of the inorganic particles.

[0080] In one embodiment, the solid content may include 0.5 to 10 wt%, specifically 1 to 10 wt%, and more specifically 2 to 9 wt% of the aqueous binder. In addition, the solid content may include 0.5 to 10 wt%, specifically 1 to 8 wt%, and more specifically 1.5 to 6 wt% of the cellulose-based compound. In addition, the solid content may include 80 to 99 wt%, specifically 84 to 98 wt%, and more specifically 87 to 97 wt% of the inorganic particles. When the aqueous binder, the cellulose-based compound, and the inorganic particles are included in the above content ranges, the composition for cathode dam coating may have a surface tension similar to that of a cathode slurry and excellent adhesive performance.

[0081] In one embodiment, the weight ratio of the aqueous binder and the cellulose-based compound may be in the range of 1:0.2 to 1:2, preferably 1:0.25 to 1:1.5, and more preferably 1:0.3 to 1:1.2. When the weight ratio of the aqueous binder and the cellulose-based compound satisfies the above range, surface tension control of the composition for dam coating is easier.

[0082] In one embodiment, the total weight of the aqueous binder and the cellulose-based compound may be 3 to 20 wt%, preferably 4 to 18 wt%, and more preferably 5 to 15 wt%, based on the total weight of the solid content. When the total weight ratio of the aqueous binder and the cellulose-based compound satisfies the above range, the surface tension of the dam coating composition and the adhesive strength of the dam coating layer are excellent.

[0083] The negative electrode dam coating layer (130) may be formed by applying the negative electrode slurry to the negative electrode current collector, applying the negative electrode dam coating composition around the boundary between the negative electrode slurry and the non-coated portion, and drying them, or by simultaneously coating the negative electrode slurry and the negative electrode dam coating composition and drying them. When the negative electrode slurry and the negative electrode dam coating composition are simultaneously coated, the effect of reducing the sliding length can be further improved.

[0084] In one embodiment, the composition for a negative electrode dam coating may have a viscosity of the composition measured at a shear rate of 2.5 / s at 25°C of from 2,000 cps to 15,000 cps, specifically from 2,000 cps to 13,000 cps, and more specifically from 2,500 cps to 11,000 cps. The composition for a negative electrode dam coating having a viscosity value within the above range may have a thickness and width length appropriately ranged to improve sliding of the dam coating layer with respect to the negative electrode active material layer.

[0085] Methods for coating the composition for cathode dam coating include, but are not limited to, spray coating, spin coating, roll coating, die coating, gravure printing, bar coating, etc., but are preferably used die coating and gravure printing methods.

[0086] According to one embodiment, a composition for cathode dam coating may have a surface tension of 72 mN / mm or more, more specifically, 72.5 mN / mm to 80 mN / mm, and even more specifically, 73 mN / mm to 80 mN / mm. A composition for cathode dam coating having a surface tension within the above numerical range is effective in preventing the occurrence of a pet-edge on the cathode. The surface tension within the above numerical range is similar to the surface tension of a slurry for cathode.

[0087] The above surface tension is a measurement value measured using the DCA-200 (Dynamic Contact Angle System, SEO) equipment under the following conditions.

[0088] Motor speed: 15 rpm / s

[0089] Probe type: Ring

[0090] Immersion depth: 4

[0091] Surface Detect weight: 0.005

[0092] Stabilization time: 5

[0093]

[0094] Cathode for lithium secondary batteries

[0095] FIG. 4 is a top view of a cathode sheet for explaining a cathode according to exemplary embodiments, and FIG. 5 is a cross-sectional view taken along line A-A' of FIG. 4.

[0096] Referring to these drawings, the negative electrode (100) according to exemplary embodiments includes a negative electrode current collector (110); a negative electrode active material layer (120) disposed on one or both surfaces of the negative electrode current collector (110); and a dam coating layer (130) disposed on one or both surfaces of the negative electrode current collector (110). The dam coating layer (130) may have a structure that contacts an end of the negative electrode active material layer (120). The end is an end based on the transverse direction (Y-axis direction) of the negative electrode sheet (NES) or the electric field direction (Y-axis direction) of the negative electrode (100).

[0097] Referring to FIGS. 3 and 4, a negative electrode active material layer (120) is formed in the center of the negative electrode sheet (NES), which is the base material of the negative electrode (100), in the transverse direction (Y-axis direction), and a dam coating layer (130) is formed on each of the edges on both sides of the negative electrode sheet (NES), and an uncoated portion not covered by the negative electrode active material layer (120) or the dam coating layer (130) exists on the outside of the dam coating layer (130). In addition, the negative electrode (100) can be manufactured by notching and cutting along the indicated notching line (dotted line) in the negative electrode sheet (NES). In FIG. 4, the negative electrode is illustrated in which the dam coating layer (130) is applied to both edge portions of the negative electrode active material layer (120), but the present invention is not limited thereto, and the dam coating layer (130) may be applied only to one edge portion of the negative electrode active material layer (120).

[0098] The above negative electrode active material layer (120) can be formed by drying the negative electrode slurry (120SE) applied on the current collector (110), and the above dam coating layer (130) can be formed by drying the above-described negative electrode dam coating composition (130CD).

[0099] Referring to FIGS. 3 and 5, a negative electrode (100) according to one embodiment includes a negative electrode active material layer (120) formed from a negative electrode slurry (120SE), and the negative electrode active material layer (120) may be divided into a planarization region (120A) whose surface is parallel to the plane of the negative electrode current collector (110) and a sliding region (120S) extending from the planarization region (120A) but whose surface is inclined with respect to the plane of the negative electrode current collector (110). In addition, the sliding region (120S) may be located at one end and the other end of the negative electrode active material layer (120) with respect to the electric field direction (Y-axis direction), respectively.

[0100] In one embodiment, the negative electrode (100) has a dam coating layer (130) that prevents the negative electrode slurry from spreading along the current collector, thereby reducing the sliding length of the negative electrode active material layer (120). As the sliding length is reduced, the risk of NP / Ratio reversal in the sliding region can be prevented.

[0101] In one embodiment, the longitudinal length of the sliding region (120S) may be within a range of 4 mm or less, preferably 0.5 to 3.5 mm, and more preferably 0.5 to 3 mm. This is a reduced length compared to the sliding length of the cathode without the cathode dam coating layer illustrated in FIG. 1.

[0102] The above dam coating layer (130) includes the aqueous binder to control the surface tension of the composition for the negative electrode dam coating to the level of the slurry for the negative electrode, and the aqueous binder may be one or two or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

[0103] The aqueous binder included in the cathode dam coating composition for forming the above dam coating layer (130) has been described in detail above, so a duplicate description will be omitted.

[0104] In one embodiment, the dam coating layer (130) may further include, in addition to the aqueous binder, a cellulose-based compound and inorganic particles. When the dam coating layer (130) includes the cellulose-based compound and inorganic particles, the weight ratio of the aqueous binder, the cellulose-based compound and the inorganic particles, the specific type of the cellulose-based compound, the specific type of the inorganic particles, etc. have been described in detail above, and therefore, redundant descriptions will be omitted.

[0105] According to one embodiment, the dam coating layer (130) may have a maximum thickness in the range of 20 to 40 μm, specifically 22 to 40 μm, and more specifically 25 to 35 μm. The thickness refers to the distance in the Z-axis direction from the plane of the negative electrode current collector to the surface of the dam coating layer (130).

[0106] According to one embodiment, the length of the dam coating layer (130) in the longitudinal direction (Y-axis direction) may be 3 mm or less, specifically 0.5 to 3 mm, and more specifically 1 to 2.5 mm.

[0107] According to one embodiment, a thickness ratio (T2 / T1) of the maximum thickness value T2 of the dam coating layer to the average thickness value T1 of the negative active material layer of the flattened region in the negative active material layer may be in the range of 0.1 to 0.4, specifically, 0.15 to 0.3.

[0108] When the thickness and length of the dam coating layer (130) are within the above numerical range, it is preferable in terms of safety due to the dam coating layer and capacity expression of the cathode.

[0109] Since the composition for negative electrode dam coating must act as a dam to prevent the negative electrode slurry from spreading out, it is preferable that the coating thickness of the composition for negative electrode dam coating be at least a certain level. Referring to Fig. 3, at the moment of coating the composition for negative electrode dam coating, the coating thickness may be similar to the coating thickness of the negative electrode slurry. Even if the coating thickness of the composition for negative electrode dam coating is similar to the coating thickness of the negative electrode slurry, the solid content of the composition for negative electrode dam coating is much smaller than the solid content of the negative electrode slurry, and thus, through 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.

[0110] According to one embodiment, the adhesive strength of the dam coating layer (130) may be 60 gf / 20mm or more, specifically 65 to 300 gf / 20mm, and more specifically 68 to 270 gf / 20mm.

[0111] The adhesive strength is as follows: a composition for cathode dam coating is applied on a copper foil, dried at a temperature of 80 to 90°C, and then cut to a length of 150 mm and a width of 20 mm. The coated surface of the composition for cathode dam coating is placed against a slide glass having a length of 75 mm and a width of 25 mm, and the specimen is attached to the slide glass in the length direction using double-sided tape. Thereafter, the specimen for evaluation is manufactured by passing it through a laminator so that the double-sided tape is evenly attached. Next, the slide glass portion of the specimen for evaluation is fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the half of the specimen to which the slide glass is not attached is connected to the load cell of the UTM equipment. The load cell is moved by 50 mm at a speed of 100 mm / min, applying a force at 90°, and measuring the load applied to the load cell. At this time, the average value of the load measured in sections of 20 mm to 40 mm during the driving section is obtained. This is repeated a total of 5 times, and the average value is evaluated as the adhesive strength (gf / 20mm) of each sample.

[0112] When the adhesive strength of the dam coating layer (130) is within the above numerical range, it is preferable because the dam coating layer is not detached during an electrode process such as a rolling process.

[0113] The negative electrode current collector (110) is a metal having high conductivity and to which the negative electrode slurry can easily adhere, and any metal that is non-reactive within the voltage range of the battery can be used. Specifically, copper, stainless steel, aluminum, nickel, titanium, sintered carbon; stainless steel surface-treated with carbon, nickel, titanium or silver; aluminum-cadmium alloy; non-conductive polymer surface-treated with a conductive material; or conductive polymer can be used. In addition, fine unevenness can be formed on the surface to strengthen the bonding strength of the negative electrode active material, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0114] The above negative electrode active material layer (120) may include a negative electrode active material, a binder, and, if necessary, a conductive material and a filler.

[0115] The above negative active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and one or a mixture of two or more of these may be used. A metallic lithium thin film may also be used as the negative electrode active material.

[0116] The above carbonaceous material may specifically be both low-crystalline carbon and high-crystalline carbon. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and examples of high-crystalline carbon include calcined carbon such as natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes. Specifically, graphite-based negative electrode active materials such as natural graphite or artificial graphite are more preferable because they can reversibly insert and de-insert lithium ions while maintaining structural and electrical properties.

[0117] The above negative active material may be included in an amount of about 80 wt% to 99.5 wt% or 88 wt% to 99 wt% relative to the total weight of the negative active material layer, but the content is not limited thereto.

[0118] The above binder is not particularly limited as long as it is a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and examples thereof include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers.

[0119] When the solvent of the cathode slurry is an aqueous solvent such as water, the above binder is preferably an aqueous binder. In a specific example, the aqueous binder may be at least one selected from the group consisting of styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluoroelastomer, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, 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 may be at least one selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber. For example, the aqueous binder may be styrene-butadiene rubber.

[0120] The above binder may typically be included in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer.

[0121] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, and the like; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0122] The above-mentioned conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer.

[0123] The above filler is optionally used as a component that suppresses expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does 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.

[0124] Below, the method for manufacturing the cathode is described.

[0125] A method for manufacturing a cathode according to one embodiment may include a step of manufacturing a slurry for a cathode (P11), a step of manufacturing a composition for a cathode dam coating (P12), a coating step of applying the composition for a cathode dam coating and the slurry for a cathode onto a cathode current collector (P20), and a drying and rolling step (P30).

[0126] The step (P11) of preparing the above-mentioned negative electrode slurry may include a process of mixing and stirring a negative electrode active material, a binder, a conductive material, and optionally a dispersant or filler in a solvent.

[0127] The solvent may be a solvent generally used in the relevant technical field, and may include dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or a mixture of two or more thereof. It may be preferable to include the solvent in an amount that provides an appropriate viscosity in consideration of the applicability and processability of the negative electrode active material slurry.

[0128] The solvent may be included in an amount such that the negative electrode slurry has an appropriate viscosity and solids content. For example, the solvent may be included in an amount such that the solids content in the negative electrode slurry is 40 wt% to 75 wt%, specifically 50 wt% to 70 wt%, and more specifically 55 wt% to 70 wt%. In addition, the negative electrode slurry may have a viscosity that allows coating, and the negative electrode active material layer formed from the negative electrode slurry may have a thickness of a certain level or more, thereby ensuring excellent energy density.

[0129] The step (P12) of preparing a composition for cathode dam coating may, in one embodiment, include a process of mixing and stirring the aqueous binder, cellulose-based compound, and inorganic particles in a solvent.

[0130] The solvent, aqueous binder, cellulose compound, and inorganic particles required for manufacturing the above-mentioned cathode dam coating composition have been described in detail above, so a duplicate description will be omitted.

[0131] The coating step (P20) of applying the negative electrode dam coating composition and the negative electrode slurry onto the negative electrode current collector may be performed by applying the negative electrode slurry onto the negative electrode current collector and then applying the negative electrode dam coating composition, or by simultaneously applying the negative electrode slurry and the negative electrode dam coating composition onto the negative electrode current collector.

[0132]

[0133] lithium secondary battery

[0134] Next, a lithium secondary battery according to the present invention will be described.

[0135] A lithium secondary battery according to one embodiment of the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0136] The lithium secondary battery of the present invention can be manufactured using conventional methods known in the art. For example, it can be manufactured by inserting a separator between the positive and negative electrodes and injecting an electrolyte.

[0137] In the lithium secondary battery, the negative electrode is as described above. For example, the negative electrode 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 layer disposed on one or both surfaces of the negative electrode current collector, wherein the dam coating layer contacts an end of the negative electrode active material layer and may include a cellulosic compound.

[0138] The above 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 the positive electrode active material.

[0139] In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0140] The positive electrode active material is not particularly limited, and compounds known in the art that are capable of reversible intercalation and deintercalation of lithium can be used without limitation. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-xLithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); LiV3O8, LiV3O4, V2O5, Cu2V2O Vanadium oxide, chemical 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 and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxides expressed as O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x It may include, but is not limited to, lithium manganese composite oxides having a spinel structure represented by O4; LiMn2O4 in which a portion of Li in the chemical formula is replaced by an alkaline earth metal ion; disulfide compounds; lithium iron phosphate represented by LiFePO4; disulfide compounds; Fe2(MoO4)3, etc.

[0141] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0142] The above-mentioned positive electrode conductive material is used to provide conductivity to the electrode, and carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material, etc. can be used. Products currently sold as conductive materials include acetylene black series (products of Chevron Chemical Company or Gulf Oil Company, etc.), Ketjen Black EC series (product of Armak Company), Vulcan XC-72 (product of Cabot Company), and Super P (product of MMM). Among these, carbon nanotubes, carbon nanofibers, and carbon black are preferable as the conductive material of the present invention, and carbon nanotubes are most preferable. The conductive network of carbon nanotubes is most preferable as a conductive material included in the positive electrode of the present invention because it can alleviate the phenomenon of binder lifting during the drying process of the positive electrode slurry.

[0143] The BET specific surface area of ​​the above carbon nanotube may be 100 m2 / g to 1000 m2 / g, 150 m2 / g to 800 m2 / g, 150 m2 / g to 500 m2 / g, 150 m2 / g to 300 m2 / g, or 150 m2 / g to 200 m2 / g.

[0144] The above-mentioned positive electrode conductive material may be included in the positive electrode active material layer in an amount of 0.1 to 30 wt%, specifically 0.1 to 10 wt%, and more specifically 0.5 to 5 wt%.

[0145] The above-mentioned positive electrode binder may be any binder polymer that is commonly used without limitation. For example, various types of binder polymers such as polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene butadiene rubber (SBR), and carboxyl methyl cellulose (CMC) may be used.

[0146] The above positive electrode binder may be included in the positive electrode active material layer in an amount of 0.1 to 30 wt%, specifically 0.1 to 10 wt%, and more specifically 0.5 to 5 wt%.

[0147] The above separator can be any porous substrate typically used as a separator in lithium secondary batteries. Examples include, but are not limited to, a polyolefin-based porous membrane or non-woven fabric. In particular, one having low resistance to electrolyte ion movement and excellent electrolyte moisture retention capacity is preferred.

[0148] Examples of the above polyolefin porous membrane include a membrane formed from a single or mixed polymer of polyolefin polymers such as polyethylene, polypropylene, polybutylene, polypentene, etc., such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene.

[0149] The above nonwoven fabric may include, in addition to polyolefin-based nonwoven fabrics, nonwoven fabrics formed from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, either singly or in combination. The structure of the nonwoven fabric may be a spunbond nonwoven fabric composed of long fibers or a meltblown nonwoven fabric.

[0150] The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm, and the pore size and pore content present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

[0151] Meanwhile, in order to improve the mechanical strength of the separator composed of the porous substrate and to suppress short circuits between the anode and cathode, a porous coating layer including inorganic particles and a binder polymer may be further included on at least one side of the porous substrate.

[0152] Meanwhile, in the lithium secondary battery, the electrolyte may include an organic solvent and lithium salt commonly used in electrolytes, and is not particularly limited.

[0153] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC) can be used.

[0154] Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0155] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the lithium salt be included in the electrolyte at a concentration of approximately 0.6 mol% to 2 mol%.

[0156] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, 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 trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0157] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly by placing a separator between the positive and negative electrodes, placing the electrode assembly in a cylindrical or square battery case, and then injecting an electrolyte. Alternatively, the electrode assembly can be manufactured by stacking the electrode assembly, impregnating it with an electrolyte, and placing the resulting product in a battery case and sealing it.

[0158] When manufacturing the lithium secondary battery of the present invention, the electrode assembly may be dried to remove one or more organic solvents selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate used in manufacturing the positive electrode. If an electrolyte having the same composition as the organic solvent used in manufacturing the positive electrode is used as the electrolyte, the process of drying the electrode assembly may be omitted.

[0159] Unlike the lithium secondary battery described above, a lithium secondary battery according to another embodiment of the present invention may be an all-solid-state battery.

[0160] The above battery case can be adopted as one commonly used in the field, and there is no limitation on the external shape according to the use of the battery. For example, it can be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0161] The lithium secondary battery according to the present invention stably exhibits excellent resistance characteristics, discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in electric vehicles such as energy storage systems (ESS) and hybrid electric vehicles (HEVs).

[0162]

[0163] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0164]

[0165] Example 1: Preparation of the cathode

[0166] (Preparation of a composition for cathode dam coating)

[0167] A composition for cathode dam coating was prepared by mixing and stirring in water 3 parts by weight of polyacrylamide (product name: BUH-0952R, manufacturer: Arakawa Chemical Industries) as an aqueous binder, 3.3 parts by weight of CMC (Daicel, 2200) with an Mw of 1,260,000 as a cellulose compound, and 93.7 parts by weight of boehmite (AlO(OH) product name: AOH60) as an inorganic particle. The solid content at this time was 25 wt%.

[0168] (Manufacture of slurry for cathode)

[0169] Artificial graphite (D) with a sphericity of 0.85 as a negative active material 50 A slurry for the negative electrode was prepared by mixing and stirring styrene butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and carbon nanotubes as a conductive agent in water at a weight ratio of 95:2:1.5:1.5 (solid content: 50 wt%).

[0170] (Manufacturing of cathode)

[0171] On copper foil (thickness 10㎛), the above-mentioned cathode slurry and the above-mentioned cathode dam coating composition were simultaneously coated, and the cathode dam coating composition was applied so as to be positioned on both sides of the Y-axis direction of the cathode slurry application portion, as shown in Fig. 5.

[0172] Afterwards, the cathode was manufactured by drying and rolling at a temperature of 90℃.

[0173]

[0174] Example 2: Preparation of the cathode

[0175] (Preparation of a composition for cathode dam coating)

[0176] In Example 1 above, a composition for cathode dam coating was prepared by changing the weight ratio of the aqueous binder, cellulose compound, and inorganic particles to 9:3.5:87.5.

[0177] Thereafter, a slurry for the negative electrode and a negative electrode were prepared using the same method as in Example 1.

[0178]

[0179] Example 3: Preparation of the cathode

[0180] (Preparation of a composition for cathode dam coating)

[0181] In Example 1 above, a composition for cathode dam coating was prepared by changing the weight ratio of the aqueous binder, cellulose compound, and inorganic particles to 6:3.5:90.5.

[0182] Thereafter, a slurry for the negative electrode and a negative electrode were prepared using the same method as in Example 1.

[0183]

[0184] Example 4: Preparation of the cathode

[0185] (Preparation of a composition for cathode dam coating)

[0186] In Example 1 above, the weight ratio of the aqueous binder, cellulose-based compound, and inorganic particles was changed to 3:3.5:93.5 to prepare a composition for cathode dam coating.

[0187] Thereafter, a slurry for the negative electrode and a negative electrode were prepared using the same method as in Example 1.

[0188]

[0189] Example 5: Preparation of the cathode

[0190] (Preparation of a composition for cathode dam coating)

[0191] In Example 1 above, a composition for cathode dam coating was prepared by changing the weight ratio of the aqueous binder, cellulose compound, and inorganic particles to 3:3:94.

[0192] Thereafter, a slurry for the negative electrode and a negative electrode were prepared using the same method as in Example 1.

[0193]

[0194] Comparative Example 1: Manufacturing of a cathode

[0195] (Preparation of a composition for cathode dam coating)

[0196] A composition for cathode dam coating was prepared by mixing and stirring 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) in water. At this time, the solid content was 25 wt%.

[0197] Thereafter, a slurry for the negative electrode and a negative electrode were prepared using the same method as in Example 1.

[0198]

[0199] Comparative Example 2: Manufacturing of a cathode

[0200] (Preparation of a composition for cathode dam coating)

[0201] A composition for cathode dam coating was prepared by mixing and stirring 4 parts by weight of CMC (Daicel, 2200) having an Mw of 1,260,000, 95 parts by weight of boehmite (AlO(OH) product name: AOH60), and 1 part by weight of SBR (styrene butadiene rubber) (BM-L302, ZEON) in water. At this time, the solid content was 25 wt%.

[0202] Thereafter, a slurry for the negative electrode and a negative electrode were prepared using the same method as in Example 1.

[0203]

[0204] Comparative Example 3: Manufacturing of a cathode

[0205] In Comparative Example 2, a composition for cathode dam coating (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. Thereafter, a slurry for cathode and a cathode were prepared in the same manner as in Example 1.

[0206]

[0207] Comparative Example 4: Manufacturing of a cathode

[0208] In Comparative Example 2, when preparing the composition for a cathode dam coating, a composition for a cathode dam coating (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. Thereafter, a slurry for a cathode and a cathode were prepared in the same manner as in Example 1.

[0209]

[0210] Comparative Example 5: Manufacturing of a cathode

[0211] In Comparative Example 2, when preparing the composition for a cathode dam coating, a composition for a cathode dam coating (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. Thereafter, a slurry for a cathode and a cathode were prepared in the same manner as in Example 1.

[0212]

[0213] Comparative Example 6: Manufacturing of a cathode

[0214] (Preparation of a composition for cathode dam coating)

[0215] A composition for cathode dam coating was prepared by mixing and stirring 2.5 parts by weight of CMC (Daicel, 2200) with an Mw of 1,260,000 and 97.5 parts by weight of SBR (styrene butadiene rubber) (BM-L302, ZEON) in water. At this time, the solid content was 24 wt%.

[0216]

[0217] Experimental Example 1: Viscosity Measurement of a Composition for Cathode Dam Coating

[0218] For each of the cathode dam coating compositions of Examples 1 to 5 and Comparative Examples 1 to 6, the compositions were cooled for 1 hour under conditions of 1% relative humidity, and then the viscosity was measured at 25°C and a shear rate of 2.5 / s using a viscometer (Brookfield). The viscosity measurement was performed within 2 hours, including the cooling time, after the preparation of the cathode dam coating compositions. The results are shown in Table 1.

[0219]

[0220] Experimental Example 2: Surface Tension Evaluation

[0221] For each cathode dam coating composition of Examples 1 to 5 and Comparative Examples 1 to 6, the surface tension was measured under the following conditions using a DCA-200 (Dynamic Contact Angle System, SEO). The results are shown in Table 1.

[0222] Motor speed: 15 rpm / s

[0223] Probe type: Ring

[0224] Immersion depth: 4

[0225] Surface Detect weight: 0.005

[0226] Stabilization time: 5

[0227]

[0228] Experimental Example 3: Checking for Pet-Edge Occurrence

[0229] For each negative electrode of Examples 1 to 5 and Comparative Examples 1 to 6, whether a PET-edge as shown in FIG. 3 occurred in the negative electrode active material layer was visually observed, and the results are shown in Table 1. If a PET-edge occurred, it was marked as 'O', and if a PET-edge did not occur, it was marked as 'X'.

[0230]

[0231] Experimental Example 4: Adhesion Evaluation

[0232] The composition for cathode dam coating of Example 1 is applied on copper foil, dried at a temperature of 80 to 90°C, and then cut to a length of 150 mm and a width of 20 mm. The surface of the dam coating layer is placed against a slide glass having a length of 75 mm and a width of 25 mm, and the specimen is attached to the slide glass in the longitudinal direction using double-sided tape. Thereafter, the specimen is passed through a laminator so that the double-sided tape is evenly attached, thereby producing an evaluation specimen. Next, the slide glass portion of the evaluation sample is fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the half of the sample to which the slide glass is not attached is connected to the load cell of the UTM equipment. The load cell is moved by applying a force at a speed of 100 mm / min at an angle of 90° to 50 mm, and the load applied to the load cell is measured. At this time, the average value of the load measured in a section of 20 mm to 40 mm during the traveling section is obtained. This was repeated a total of 5 times, and the average value was evaluated as the adhesive strength (gf / 20mm) of each sample. The results are shown in Table 1.

[0233] The adhesive strength of each cathode dam coating composition of Examples 2 to 5 and Comparative Examples 1 to 6 was evaluated in the same manner as above, and the results are shown in Table 1.

[0234] Viscosity (cps) Surface tension (mN / mm) Fat-edge occurrence Adhesion (gf / 20mm) Example 13,48773.8X75.0 Example 21001778.1X260 Example 3816376.7X155 Example 4592174.5X103 Example 5293072.4X69 Comparative example 1486174.1X48.9 Comparative example 2554971.1X53.0 Comparative example 3538765.1X56.0 Comparative example 4570762.2X161.0 Comparative example 5569761.3X283.4 Comparative example 6320052.96O350 or more

[0235] Referring to Table 1 above, it was confirmed that the cathode dam coating compositions of Examples 1 to 5 each had a surface tension of 72 mN / mm or higher, thereby preventing the occurrence of pet-edges. In addition, the adhesive strength was also high at 65 gf / 20 mm or higher, so it is expected that the possibility of the dam coating layer being detached during the electrode rolling process will be low.

Claims

1. Negative current collector; A negative electrode active material layer disposed on one or both sides of the negative electrode current collector; and A dam coating layer is disposed on one or both sides of the negative electrode current collector, The above dam coating layer is applied to the end of the negative electrode active material layer and includes an aqueous binder, The above aqueous binder is a negative electrode for a lithium secondary battery, which is one or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

2. In claim 1, The above dam coating layer is, Further comprising cellulose compounds and inorganic particles, Based on the total weight of the above dam coating layer, 0.5 to 10 wt% of the above aqueous binder; 0.5 to 10 wt% of the above cellulose compound; and A negative electrode for a lithium secondary battery comprising 80 to 99 wt% of the above inorganic particles.

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

4. In claim 1, The above aqueous binder is a negative electrode for a lithium secondary battery made of polyacrylamide.

5. In claim 1, A negative electrode for a lithium secondary battery, characterized in that the cellulose compound is one or more compounds selected from the group consisting of carboxymethyl cellulose (CMC; carboxyl methyl cellulose), cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, lithium salt of carboxymethyl cellulose (CMC-Li), and sodium salt of carboxymethyl cellulose (CMC-Na).

6. In claim 1, The negative electrode active material layer is divided into a flattening region whose surface is parallel to the plane of the negative electrode current collector and a sliding region extending from the flattening region but whose surface is inclined to the plane of the negative electrode current collector. The above sliding region is a negative electrode for a lithium secondary battery having a structure located at one end and the other end of the negative electrode active material layer based on the electric field direction.

7. In claim 6, A negative electrode for a lithium secondary battery, wherein the length of the sliding region in the electrical direction is 4 mm or less.

8. In claim 6, A negative electrode for a lithium secondary battery, wherein the length of the sliding region in the electrical direction is in the range of 0.5 to 3.5 mm.

9. In claim 6, A negative electrode for a lithium secondary battery, characterized in that the thickness ratio (T2 / T1) of the maximum thickness value T2 of the dam coating layer to the average thickness value T1 of the negative active material layer in the flattened region in the negative active material layer is within the range of 0.1 to 0.

4.

10. In claim 1, The above dam coating layer is, The maximum thickness is in the range of 20 to 40㎛, A negative electrode for a lithium secondary battery having a length in the direction of the electric field of 3 mm or less.

11. As a composition for cathode dam coating, a solvent; and an aqueous binder, A composition for cathode dam coating, wherein the above aqueous binder is one or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

12. In claim 11, Further comprising cellulose compounds and inorganic particles, The solid content excluding the above solvent is Based on the total weight of the above solids, 0.5 to 10 wt% of the above aqueous binder; 0.5 to 10 wt% of the above cellulose compound; and A composition for cathode dam coating comprising 80 to 99 wt% of the above inorganic particles.

13. In claim 11, A composition for cathode dam coating, wherein the content of solids excluding the solvent is 15 to 35 parts by weight per 100 parts by weight of the composition for cathode dam coating.

14. In claim 12, The above aqueous binder is a composition for cathode dam coating which is polyacrylamide.

15. In claim 12, The above inorganic particles are AlO(OH), Al2O3, γ-AlOOH, Al(OH) 3, A composition for cathode dam coating, characterized in that it comprises one or more kinds selected from the group consisting of SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3 and Mg(OH)2.

16. In claim 11, A composition for cathode dam coating having a surface tension of 72 mN / mm or more.

17. A cathode according to any one of claims 1 to 10; anode; membrane; and A lithium secondary battery containing an electrolyte.

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