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

Abstract

A negative electrode dam coating composition according to an embodiment of the present invention comprises an aqueous binder, wherein the aqueous binder comprises one or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile. The surface tension of the negative electrode dam coating composition of the embodiment of the present invention is as high as the negative electrode slurry level, thereby suppressing the appearance of rough edges on the negative electrode. In addition, the dam coating layer formed from the anode dam coating composition shortens the landslide length of the anode active material layer, thereby reducing the risk of NP ratio inversion of the lithium secondary battery.

Description

TECHNICAL FIELD

[0001] This application claims priority to Korean Patent Application No. 10-2023-0129773, filed on September 26, 2023, the disclosure of which is incorporated herein by reference.

[0002] The present application relates to a negative electrode having a short length in a negative electrode landslide area, a negative electrode dam coating composition for the negative electrode, and a lithium secondary battery including the negative electrode, which prevents or inhibits the generation of a fat edge at a negative electrode end portion. BACKGROUND

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

[0004] Secondary batteries are classified into cylindrical and prismatic batteries in which an electrode assembly is embedded in a cylindrical or prismatic metal can according to the shape of the battery case, 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 chargeable power generation device including a positive electrode / separator / negative electrode stacked structure, the electrode assembly embedded in the battery case can be a jelly-roll type electrode assembly obtained by disposing a separator between long sheet-shaped positive and negative electrodes coated with an electrode compound including an electrode active material and winding it, a stacked electrode assembly including a plurality of positive and negative electrodes punched and slotted in a predetermined size unit and stacked in order while sandwiching a separator, and a stacked / foldable electrode assembly including a stack of a double cell or a full cell in which positive and negative electrodes and a separator of a predetermined size unit are wound.

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

[0007] Figure 1 is a magnified view of one side of a cross section of a negative electrode to which an electrode slurry is coated on a current collector. Referring to Figure 1 , the negative electrode active material layer 12 to which the electrode slurry is coated is divided into a flat area 12A parallel to the plane of the negative electrode current collector 11 since its thickness is constant, and a landslide area 12S inclined with respect to the plane of the current collector 11 since the thickness of the electrode active material layer 12 gradually decreases in a direction toward the uncoated portion of the current collector 11 on which the electrode slurry is not coated.

[0008] Meanwhile, the positive electrode and the negative electrode constituting the electrode assembly face each other with a separator therebetween, the length of the landslide region of the positive electrode and the length of the landslide region of the negative electrode can be different, and the inclined shape of the landslide region can be various shapes such as an upward convex shape, a downward convex shape, a straight line shape, an S shape, and even if the inclined shape is the same, the slope can be different. As a result, depending on the facing position of the landslide region, the negative electrode landslide region can have a local NP ratio imbalance, which can cause lithium to be precipitated from the negative electrode and cause safety accidents such as short circuits.

[0009] In the theoretical positive / negative electrode facing region, the greater the ratio of the load amount of the negative electrode to the load amount of the positive electrode, the less likely it is to occur NP ratio imbalance, and thus, recently, technical attempts to increase the load amount in the negative electrode landslide region have been made. As one of these attempts, a technology is being studied in which, on the edge coated with the negative electrode slurry, a dam coating composition is stacked, the 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 the conventional dam coating composition, where the thickness of the negative electrode active material layer and the dam coating layer overlaps and becomes thicker than the thickness of the negative electrode active material layer, a hypertrophic edge phenomenon can occur. Figure 2 is a cross-sectional view of a negative electrode having a hypertrophic edge, with reference to Figure 2 , hypertrophic edges are formed at both ends in the Y-axis direction of the negative electrode active material layer 12, and a hypertrophic edge protruding upward is formed in the Z-axis direction. The presence of these hypertrophic edges on the negative electrode can cause damage to the current collector layer during the rolling process, which can cause safety problems. During the multiple stacking of the positive electrode, the negative electrode, and the separator, the hypertrophic edge can also damage other electrodes or separators.

[0011] Therefore, there is a need to develop a negative electrode technology with a short landslide length and no hypertrophic edge and a manufacturing method thereof. SUMMARY

[0012] [TECHNICAL PROBLEM]

[0013] An object of the present application is to provide a negative electrode having a short length of the negative electrode landslide region, a negative electrode dam coating composition for obtaining the negative electrode, and a lithium secondary battery including the negative electrode, in which a hypertrophic edge is prevented or inhibited from being generated at the negative electrode end portion.

[0014] [TECHNICAL SOLUTION]

[0015] According to one embodiment of the present invention, there is provided a negative electrode for a lithium secondary battery. The negative electrode includes: a negative electrode current collector; a negative electrode active material layer provided on one or both faces of the negative electrode current collector; and a dam coating layer provided on one or both faces of the negative electrode current collector, wherein the dam coating layer is in contact with an end surface of the negative electrode active material layer and contains an aqueous binder, and 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.

[0016] In an exemplary embodiment of the present disclosure, the dam coating layer further contains a cellulose-based compound and inorganic particles, and contains, based on the total weight of the dam coating layer, 0.5 to 10% by weight of the aqueous binder, 0.5 to 10% by weight of the cellulose-based compound, and 80 to 99% by weight of the inorganic particles.

[0017] In an exemplary embodiment of the present disclosure, the inorganic particles are one or two 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.

[0018] In an exemplary embodiment of the present disclosure, the aqueous binder is polyacrylamide.

[0019] In an exemplary embodiment of the present disclosure, the cellulose-based compound is at least one or two or more selected from the group consisting of carboxymethyl cellulose (CMC), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, a lithium salt of carboxymethyl cellulose (CMC-Li), and a sodium salt of carboxymethyl cellulose (CMC-Na).

[0020] In an exemplary embodiment of the present disclosure, the negative electrode active material layer is divided into a flat region and a landslide region, a surface of the flat region is parallel to a plane of the negative electrode current collector, the landslide region extends from the flat region, a surface of the landslide region is inclined with respect to the plane of the negative electrode current collector, and the landslide region is located at one end and the other end in a longitudinal direction of the negative electrode active material layer.

[0021] In an exemplary embodiment of the present disclosure, the longitudinal direction length of the landslide region is 4 mm or less.

[0022] In an exemplary embodiment of the present disclosure, the longitudinal direction length of the landslide region is 0.5 mm to 3.5 mm.

[0023] In an exemplary embodiment of the present disclosure, the thickness ratio (T2 / T1) of the maximum thickness value T2 of the dam coating layer to the average thickness T1 of the negative electrode active material layer in the flat region of the negative electrode active material layer is in the range of 0.1 to 0.4.

[0024] In an exemplary embodiment of the present disclosure, the maximum thickness of the dam coating layer is in the range of 20 μm to 40 μm, and the length thereof in the full length direction is 3 mm or less.

[0025] According to another exemplary embodiment of the present disclosure, there is provided a negative electrode dam coating composition. The negative electrode dam coating composition comprises: a solvent; and an aqueous binder, wherein the aqueous binder is one or two or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

[0026] In an exemplary embodiment of the present disclosure, the negative electrode dam coating composition further comprises a cellulose-based compound and inorganic particles, wherein based on the total weight of solids excluding the solvent, the solids include: 0.5 to 10% by weight of the aqueous binder; 0.5 to 10% by weight of the cellulose-based compound; and 80 to 99% by weight of the inorganic particles.

[0027] In an exemplary embodiment of the present disclosure, the content of the solids excluding the solvent is 15 to 35 parts by weight based on 100 parts by weight of the negative electrode dam coating composition.

[0028] In an exemplary embodiment of the present disclosure, the aqueous binder is polyacrylamide.

[0029] In an exemplary embodiment of the present disclosure, the inorganic particles are one or two 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.

[0030] In an exemplary embodiment of the present disclosure, the surface tension of the negative electrode dam coating composition is 72 mN / mm or more.

[0031] According to another exemplary embodiment of the present disclosure, there is provided a lithium secondary battery including: the above-described negative electrode; a positive electrode; a separator; and an electrolyte.

[0032] [Advantageous Effects]

[0033] According to one embodiment of the present disclosure, the surface tension of the negative electrode dam coating composition is raised 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 hypertrophied edge.

[0034] Accordingly, the dam coating shortens the landslide length of the negative active material layer, which can reduce the risk of NP ratio reversal in the lithium secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is an enlarged view of one side of a cross section of a negative electrode of the related art in which a negative slurry is coated on a current collector.

[0036] Figure 2 is a cross-sectional view of a negative electrode in which a fat edge is generated.

[0037] Figure 3 is an enlarged view of one side of a cross section of a negative electrode of the exemplary embodiment in which a negative slurry and a dam coating composition are coated.

[0038] Figure 4 is a plan view of a negative electrode sheet to show the negative electrode of the exemplary embodiment.

[0039] Figure 5 is a cross-sectional view cut along A-A' in Figure 4 .

[0040] [REFERENCE NUMERALS]

[0041] 10, 100: negative electrode

[0042] 11, 110: negative electrode current collector

[0043] 12, 120: negative active material layer

[0044] 13, 130: dam coating

[0045] NES: negative electrode sheet DETAILED DESCRIPTION

[0046] Hereinafter, the present disclosure will be described in greater detail to provide a better understanding of the present disclosure.

[0047] The terms and words used in the present specification and claims should not be interpreted in an ordinary or dictionary meaning, but should be interpreted based on the concept of the terms in accordance with the principle that the inventor can define the concept of the terms in the way he or she deems appropriate for best describing the present disclosure, in a meaning and concept consistent with the technical idea of the present disclosure.

[0048] The terms used in the present application are only used to describe certain embodiments and are not intended to limit the concept of the present invention. The singular expression includes the plural unless the context clearly dictates otherwise.

[0049] In the present application, expressions such as "comprise", "provide with" or "have" are intended to denote the presence of the described features, counts, steps, operations, components, parts or combinations thereof, and should not be understood as excluding the possibility of presence or addition of one or more other features, counts, operations, components, parts or combinations thereof.

[0050] As used herein, the term "combination thereof" literally including in the Markush form means one or more mixtures or combinations selected from the group consisting of the components described in the Markush form, and includes one or more selected from the group consisting of the components.

[0051] In the present specification, reference to "A and / or B" shall mean "A or B or both".

[0052] In the present specification, "%" means "% by weight" unless otherwise specified.

[0053] For the purposes of the present specification, the specific surface area can be measured by the Brunauer-Emmett-Teller (BET) method. For example, it can be measured by the nitrogen adsorption distribution method with the BET 6-point method using a Porosimetry analyzer (Belsorp-II mini; Bell Japan Inc.).

[0054] As used herein, the average particle diameter (D 50 ) can be defined as the particle diameter at 50% of the particle size distribution. The average particle diameter is not particularly limited, and can be measured by, for example, a laser diffraction method, scanning electron microscope (SEM) photography, or the like. The laser diffraction method is generally capable of measuring particle diameters from the sub-micron region to several millimeters, and can produce highly reproducible and highly resolvable results.

[0055] In the present specification, "Mw" means the weight average molecular weight of standard polystyrene determined by gel permeation chromatography (GPC). Specifically, Mw is a converted value of the value determined by GPC under the following conditions, calibrated using standard polystyrene from Agilent system.

[0056] <Measurement conditions>

[0057] Measurement instrument: Agilent GPC (Agilent 1200 series, USA)

[0058] Chromatography column: two PL mixed B connected

[0059] Column temperature: 40°C

[0060] Eluent: Tetrahydrofuran

[0061] Flow rate: 1.0 mL / min

[0062] Concentration: ~1 mg / mL (100 μL injection)

[0063] In the present specification, the longitudinal direction (MD) of the negative electrode sheet and the full width direction of the negative electrode are defined in the X-axis direction, the transverse direction (TD) of the negative electrode sheet and the full length direction of the negative electrode are defined in 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 in the Z-axis direction, and the X-axis direction and the Y-axis direction are referred to as the horizontal direction.

[0064] Negative electrode dam coating composition

[0065] Figure 1 is a magnified view of one side of the cross section of the negative electrode of the prior art in which the negative electrode slurry is coated on the current collector. Figure 2 is a cross-sectional view of the negative electrode having a thickened edge. Figure 3 is a magnified view of one side of the cross section of the negative electrode of the exemplary embodiment in which the negative electrode slurry and the negative dam coating composition are coated.

[0066] Referring to Figure 1 In the case where the negative dam coating composition is not coated, due to the flowability of the negative electrode slurry, the edge of the region in which the negative electrode slurry is coated spreads along the current collector 11, so that the end portion of the dried negative electrode active material layer 12 has an inclined shape with respect to the plane of the negative electrode current collector 11. The end portion of the negative electrode active material layer 12 in the negative electrode active material layer 12 having an inclined shape is referred to as a landslide region 12S, and the landslide length, i.e., the Y-axis direction length of the landslide region, reaches about 4 to 10 mm.

[0067] Meanwhile, referring to Figure 3 When the negative dam coating composition 130CD is coated on the edge of the region in which the negative electrode slurry 120SE is coated, the landslide length of the landslide region 120S of the negative electrode active material layer becomes much shorter than Figure 1 This is because the negative dam coating composition 130CD acts as a dam and inhibits the downward flow of the negative electrode slurry 120SE.

[0068] However, the negative dam coating composition 130CD is coated in a manner partially overlapping the negative electrode slurry 120S, and a portion of the negative dam coating composition 130CD located on the negative electrode slurry can diffuse into the negative electrode slurry 120S to form a thickened edge as Figure 2 illustred. The inventors of the present disclosure have found through a great deal of research that if the surface tension of the dam coating composition is controlled to the level of the negative electrode slurry, the dam coating composition will tend to remain at the interface with the negative electrode slurry, thereby inhibiting the diffusion of the dam coating composition into the negative electrode slurry.

[0069] To control the surface tension of the dam coating composition at the level of the negative electrode slurry, the dam coating composition of one embodiment includes an aqueous binder, wherein the aqueous binder can be one or two or more compounds selected from the group consisting of polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

[0070] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, or water, and one or more of these solvents can be used alone or two or more can be used in combination. Among them, water is preferred as the solvent of the negative electrode dam coating composition due to its high surface tension.

[0071] In consideration of the coatability of the negative electrode dam coating composition, the content of the solvent can be such that the negative electrode dam coating composition has a suitable viscosity.

[0072] The aqueous binder is a water-soluble polymer compound, which can increase the cohesive force of the solvent, thereby increasing the surface tension of the dam coating composition. Among the aqueous binders, polyacrylamide can be most preferred as the aqueous binder of the present disclosure, as it highly effectively increases the surface tension of the negative electrode dam coating composition.

[0073] In addition to the aqueous binder, the negative electrode dam coating composition of the present disclosure can further include a cellulose-based compound and inorganic particles.

[0074] The cellulose-based compound is a water-soluble polymer compound having a predetermined viscosity, which can increase the cohesive force of the solvent, thereby increasing the surface tension of the dam coating composition.

[0075] The cellulose-based compound can be one or two or more compounds selected from carboxymethyl cellulose (CMC), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, lithium salt of carboxymethyl cellulose (CMC-Li), sodium salt of carboxymethyl cellulose (CMC-Na), and preferably the sodium salt of carboxymethyl cellulose. As the cellulose-based compound of the present disclosure, the sodium salt of carboxymethyl cellulose can be preferred, as it highly effectively increases the surface tension of the dam coating composition.

[0076] The weight average molecular weight (Mw) of the cellulose-based compound can be 500,000 to 5,000,000, preferably 700,000 to 4,500,000, more preferably 900,000 to 4,000,000. When the weight average molecular weight of the cellulose-based compound is within the above range, it is advantageous in terms of coating performance because it imparts a suitable viscosity to the dam coating composition.

[0077] The inorganic particles are a main component for increasing the electrical insulation and thermal safety, improving the strength of the dam coating, and controlling the solid content of the negative electrode dam coating composition. The content of the inorganic particles can be appropriately adjusted in consideration of the viscosity, insulation, dispersibility, coatability, and the like of the negative electrode dam coating composition.

[0078] The inorganic particles can be one or two or more compounds selected from the group consisting of AlO(OH), AI2O3, γ-AlOOH, AI(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 the group consisting of AlO(OH), AI2O3, γ-AlOOH, and AI(OH)3. For example, the inorganic particles can be AlO(OH).

[0079] The average particle diameter (D 50 ) of the inorganic particles can be 0.1 μm to 100 μm; 0.5 μm to 80 μm; 1 μm to 50 μm; 2 μm to 30 μm; 3 μm to 20 μm; or 5 μm to 10 μm. When the size of the inorganic particles is within the above range, the negative electrode dam coating composition can be uniformly coated on the negative electrode current collector and the negative electrode slurry.

[0080] In the negative electrode dam coating composition of one embodiment, the content of solids other than the solvent can be 15 parts by weight to 35 parts by weight, more particularly 17 parts by weight to 33 parts by weight, and even more particularly 18 parts by weight 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 preferable in view of the coating properties of the negative electrode dam coating composition and the effect of reducing the runout length of the negative electrode slurry.

[0081] In the negative electrode dam coating composition of one embodiment, the solids can include, based on the total weight of the solids other than the solvent, 0.5 to 10% by weight of the water-based binder; 0.5 to 10% by weight of the cellulose-based compound; and 80 to 99% by weight of the inorganic particles.

[0082] In one embodiment, the solid can include 0.5 to 10% by weight, more particularly 1 to 10% by weight, more particularly 2 to 9% by weight of the aqueous binder. In addition, the solid can include 0.5 to 10% by weight, more particularly 1 to 8% by weight, more particularly 1.5 to 6% by weight of the cellulose-based compound. In addition, the solid can include 80 to 99% by weight, more particularly 84 to 98% by weight, more particularly 87 to 97% by weight of the inorganic particles. When the aqueous binder, the cellulose-based compound, and the inorganic particles are contained in the above content ranges, the negative electrode dam coating composition can have a surface tension comparable to that of the negative electrode slurry and good adhesion properties.

[0083] In one embodiment, the weight ratio of the aqueous binder to the cellulose-based compound can be 1:0.2 to 1:2, preferably 1:0.25 to 1:1.5, more preferably 1:0.3 to 1:1.2. If the weight ratio of the aqueous binder to the cellulose-based compound satisfies the above range, it is easier to control the surface tension of the dam coating composition.

[0084] In one embodiment, the total weight of the aqueous binder and the cellulose-based compound can be 3 to 20% by weight, preferably 4 to 18% by weight, more preferably 5 to 15% by weight, based on the total weight of the solid. When the proportion of the total weight of the aqueous binder and the cellulose-based compound satisfies the above range, the surface tension of the dam coating composition and the adhesion of the dam coating layer are excellent.

[0085] The negative electrode dam coating layer 130 can be formed by coating the negative electrode slurry on the negative electrode current collector, coating the negative electrode dam coating composition near the boundary of the negative electrode slurry and the uncoated portion, and drying it, or by co-coating the negative electrode slurry and the negative electrode dam coating composition and drying it. By simultaneously coating the negative electrode slurry and the negative electrode dam coating composition, the effect of reducing the landslide length can be further improved.

[0086] In one embodiment, the composition viscosity of the negative electrode dam coating composition, measured at 25°C at a shear rate of 2.5 / s, can be 2,000 cps to 15,000 cps, more particularly 2,000 cps to 13,000 cps, and more particularly 2,500 cps to 11,000 cps. For the negative electrode dam coating composition having a viscosity value in the above range, the thickness and width of the dam coating layer can be within an appropriate range to improve the landslide of the negative electrode active material layer.

[0087] The coating method of the negative electrode dam coating composition can include, but is not limited to, spraying, spin coating, roll coating, die coating, gravure printing, bar coating, etc., among which die coating and gravure printing methods are preferably used.

[0088] The surface tension of the negative electrode dam coating composition of one embodiment can be 72 mN / mm or more, more particularly 72.5 mN / mm to 80 mN / mm, more particularly 73 mN / mm to 80 mN / mm. The negative electrode dam coating composition having a surface tension within the above numerical range has an effect of preventing the generation of a fat edge at the negative electrode. The surface tension within the above numerical range is comparable to the surface tension of the negative electrode slurry.

[0089] The surface tension was measured using a DCA-200 (dynamic contact angle system, SEO) instrument under the following conditions:

[0090] Motor rotation speed: 15 rpm / s

[0091] Probe type: ring

[0092] Immersion depth: 4

[0093] Surface detection weight: 0.005

[0094] Stabilization time: 5

[0095] Negative electrode for lithium secondary battery

[0096] Figure 4 is a plan view of a negative electrode sheet showing a negative electrode of an exemplary embodiment, Figure 5 is a cross-sectional view taken along A-A' in Figure 4 .

[0097] Referring 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 disposed on one or both faces of the negative electrode current collector 110, and a dam coating layer 130 disposed on one or both faces of the negative electrode current collector 110, wherein the dam coating layer 130 can be configured to be in contact with the end surface of the negative electrode active material layer 120. The end is an end in the lateral direction (Y-axis direction) of the negative electrode sheet (NES) or the full-length direction (Y-axis direction) of the negative electrode 100.

[0098] Referring to Figure 3 and Figure 4 , the negative electrode active material layer 120 is formed in the center in the lateral direction (Y-axis direction) of the negative electrode sheet (NES) and serves as a base material of the negative electrode 100, and the dam coating layer 130 is formed at both edges in the lateral direction (Y-axis direction) of the negative electrode sheet (NES), respectively, and there is a non-coated portion not covered by the negative electrode active material layer 120 or the dam coating layer 130 outside the dam coating layer 130. Also, the negative electrode 100 can be manufactured by slitting and cutting along the slitting line (dotted line) shown on such a negative electrode sheet NES. Although Figure 4The negative electrode in which the dam coating layer 130 is coated on both edges of the negative electrode active material layer 120 is shown, but the present application is not limited thereto, and the dam coating layer 130 can be coated on only one edge of the negative electrode active material layer 120.

[0099] The negative electrode active material layer 120 can be formed by drying the negative electrode slurry 120SE coated on the current collector 110, and the dam coating layer 130 can be formed by drying the above-described negative electrode dam coating composition 130CD.

[0100] Reference Figure 3 and Figure 5 The negative electrode 100 of one embodiment includes a negative electrode active material layer 120 formed of a negative electrode slurry 120SE, in which the negative electrode 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 its surface is inclined with respect to the plane of the negative electrode current collector 110. Further, the landslide region 120S can be located at each of one end and the other end in the full-length direction (Y-axis direction) of the negative electrode active material layer 120, respectively.

[0101] In the negative electrode 100 of one embodiment, the dam coating layer 130 is used to prevent the negative electrode slurry from spreading along the current collector, thereby reducing the landslide length of the negative electrode active material layer 120. Further, with the reduction in the landslide length, the risk of NP ratio reversal in the landslide region can be prevented.

[0102] In one embodiment, the full-length direction length of the landslide region 120S can be 4 mm or less, preferably 0.5 to 3.5 mm, more preferably 0.5 to 3 mm. This is a reduced length compared to the landslide length of the negative electrode without the negative electrode dam coating layer shown in FIG. 1. Figure 1

[0103] The dam coating layer 130 contains an aqueous binder to control the surface tension of the negative electrode dam coating composition to the level of the negative electrode slurry, and the aqueous binder can be one or two or more compounds selected from polyacrylamide (PAM), polyvinyl alcohol, polyacrylic acid, polyethylene glycol, and polyacrylonitrile.

[0104] The aqueous binder contained in the negative electrode dam coating composition used to form the dam coating layer 130 has been described in detail above, and thus repeated description thereof will not be given here.

[0105] In one embodiment, the dam coating layer 130 can contain a cellulose-based compound and inorganic particles in addition to the aqueous binder. In the case where the dam coating layer 130 contains the cellulose-based compound and the 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, and the like have been described in detail above, and thus repeated description thereof will not be given here.​

[0106] According to one embodiment, the maximum value of the thickness of the dam coating layer 130 can be 20 to 40 μm, more specifically 22 to 40 μm, and even 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.

[0107] According to one embodiment, the length in the full length direction (Y-axis direction) of the dam coating layer 130 can be 3 mm or less, more specifically 0.5 mm to 3 mm, and more specifically 1 mm to 2.5 mm.

[0108] According to one embodiment, the thickness ratio (T2 / T1) of the maximum thickness value T2 of the dam coating layer to the average thickness T1 of the negative electrode active material layer in the flat area of the negative electrode active material layer can be 0.1 to 0.4, and more specifically, can be 0.15 to 0.3.

[0109] When the thickness and length of the dam coating layer 130 are within the above numerical ranges, it is preferable from the viewpoint of safety of the dam coating layer and the viewpoint of negative electrode capacity performance.

[0110] 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. Referring to Figure 3 When the negative electrode dam coating composition is coated, the coating thickness can have 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, and thus the thickness of the dam coating layer becomes smaller than that of the negative electrode active material layer as a series of electrode processes, such as a drying process, are experienced.

[0111] According to one embodiment, the adhesion of the dam coating layer 130 can be 60 gf / 20 mm or more, more specifically 65 gf / 20 mm to 300 gf / 20 mm, and more specifically 68 gf / 20 mm to 270 gf / 20 mm.

[0112] The adhesion was evaluated as follows: the negative electrode dam coating composition was coated on a copper foil, dried at a temperature of 80 to 90°C, cut into a length of 150 mm and a width of 20 mm, the sample was attached to a glass slide having a length of 75 mm and a width of 25 mm in the length direction using a double-sided tape such that the coated surface of the negative electrode dam coating composition faced the glass slide. The evaluation sample was then passed through a laminator to ensure uniform attachment of the double-sided tape. Then, the glass slide portion of the evaluation sample was fixed to the sample stage of a universal testing machine (UTM) (LS5, AMETEK), and the half sample without the glass slide was connected to the load cell of the UTM machine. The load applied to the load cell was measured by moving the load cell 50 mm at a speed of 100 mm / min and applying a force of 90°. The average of the measured load in the range of 20 mm to 40 mm during the travel was taken. The test was repeated 5 times, and the average was evaluated as the adhesion (gf / 20 mm) of each sample.

[0113] When the adhesion of the dam coating layer 130 is within the above numerical range, the dam coating layer does not come off during the electrode process such as a roll-pressing process, and thus is ideal.

[0114] The negative electrode current collector 110 is a metal that is highly conductive and to which the negative electrode slurry easily adheres, and any non-reactive material within the voltage range of the battery can be used, particularly: copper, stainless steel, aluminum, nickel, titanium, calcined 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. They can also have micro-irregularities on the surface to enhance the adhesion of the negative electrode active material, and can be used in various forms, including films, sheets, foils, meshes, porous materials, foams, and non-woven materials.

[0115] The negative electrode active material layer 120 can include a negative electrode active material, a binder, and a conductive material and a filler as needed.

[0116] The negative electrode active material can be any compound capable of reversibly intercalating and deintercalating lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, etc.; metal substances 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 metal oxides capable of doping and undoping lithium; or a composite including the above metal substances and carbonaceous materials, such as a Si-C composite or a Sn-C composite, any one or more of which can be used. A thin film of metallic lithium can also be used as a negative electrode active material.

[0117] 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.

[0118] The content of the negative electrode active material may be approximately 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.

[0119] 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 thereof.

[0120] 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.

[0121] The binder may be generally included in an amount of 1 to 30 wt % based on the total weight of the negative electrode active material layer.

[0122] The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and for example, 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 cracking carbon black, and the like; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as carbon fluoride, aluminum, nickel powders; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives; and the like can be used.

[0123] The content of the conductive material can generally be 1 to 30% by weight, based on the total weight of the negative electrode active material layer.

[0124] The filler, which is optionally used as a component for suppressing electrode expansion, is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery, and for example, olefin-based polymers such as polyethylene, polypropylene; fibrous materials such as glass fibers, carbon fibers, and the like can be used.

[0125] Hereinafter, a manufacturing method of the negative electrode will be described.

[0126] The manufacturing method of the negative electrode according to one embodiment can 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 roll pressing step P30.

[0127] The step P11 of preparing the negative electrode slurry can include mixing and stirring the negative electrode active material, the binder, the conductive material, and the optional dispersant or filler in a solvent.

[0128] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, or water, and these can be used alone or in a mixture of two or more. The content of the solvent can preferably ensure that the negative electrode active material has a suitable viscosity, in consideration of the coatability and processability of the negative electrode active material slurry.

[0129] The content of the solvent can provide a negative electrode slurry having a suitable viscosity and a solid content. For example, the content of the solvent 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 level of viscosity, and the negative electrode active material layer formed from the negative electrode slurry can have a thickness higher than a certain level to obtain a good energy density.

[0130] In one embodiment, the step P12 of preparing the negative dam coating composition can include mixing and stirring the aqueous binder, the cellulose-based compound, and the inorganic particles in a solvent.

[0131] The solvent, the aqueous binder, the cellulose-based compound, and the inorganic particles required when preparing the negative dam coating composition have been described in detail above, and thus repeated descriptions are omitted.

[0132] The coating process P20 of coating the negative dam coating composition and the negative slurry on the negative current collector can be performed by coating the negative dam coating composition after coating the negative slurry on the negative current collector, or can be performed by simultaneously coating the negative slurry and the negative dam coating composition on the negative current collector.

[0133] lithium secondary batteries

[0134] Next, a lithium secondary battery according to the present disclosure is described.

[0135] The lithium secondary battery of one embodiment of the present disclosure can include a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, and an electrolyte.

[0136] The lithium secondary battery according to the present disclosure can be manufactured in accordance with a conventional method known in the art. For example, it can be manufactured by placing a separator between a positive electrode and a negative electrode and adding an electrolyte.

[0137] In the lithium secondary battery, the negative electrode is as described above. For example, the negative electrode can include a negative current collector, a negative active material layer provided on one or both surfaces of the negative current collector, and a dam coating layer provided on one or both surfaces of the negative current collector, wherein the dam coating layer is in contact with an end surface of the negative active material layer and can include a cellulose-based compound.

[0138] The positive electrode can include a positive current collector and a positive active material layer formed on the positive current collector and including a positive active material.

[0139] In the positive electrode, the positive current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel subjected to surface treatment with carbon, nickel, titanium, silver, or the like can be used. In addition, the positive current collector can typically have a thickness of 3 μm to 500 μm, and can also have micro-irregularities formed on the surface of the current collector to increase adhesion of the positive 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, a nonwoven body, or the like.

[0140] The positive electrode active material is not particularly limited, and any compound known in the art capable of reversibly intercalating and deintercalating lithium can be used without limitation. Specifically, the positive electrode active material can include: a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium manganese oxide such as a compound of formula LiMnO4 (wherein x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); a vanadium oxide such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; a lithium nickel oxide represented by the formula LiNiMnO2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); a lithium manganese composite oxide represented by the formula LiMnO2 (wherein M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein M = Fe, Co, Ni, Cu, or Zn); a lithium manganese composite oxide having a spinel structure represented by LiNiMnO4; LiMn2O4 in which some of the Li atoms are substituted with an alkaline earth metal ion; a disulfide; lithium iron phosphate represented by LiFePO4; a disulfide; and Fe2(MoO4)3, etc., but is not limited thereto. 1+x Mn 2-x O4 (wherein x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); a vanadium oxide such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; a lithium nickel oxide represented by the formula LiNi 1-x M x O2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); a lithium manganese composite oxide represented by the formula LiMn 2-x M x O2 (wherein M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein M = Fe, Co, Ni, Cu, or Zn); a lithium manganese composite oxide having a spinel structure represented by LiNiMnO4; LiMn2O4 in which some of the Li atoms are substituted with an alkaline earth metal ion; a disulfide; lithium iron phosphate represented by LiFePO4; a disulfide; and Fe2(MoO4)3, etc., but is not limited thereto. x Mn 2-x O4 (wherein x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); a vanadium oxide such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; a lithium nickel oxide represented by the formula LiNi

[0141] In addition to the positive electrode active material described above, the positive electrode active material layer can further include a positive electrode conductive material and a positive electrode binder.

[0142] The positive electrode conductive material serves to impart conductivity to the electrode, and can be carbon black, graphite, carbon nanofiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material, etc. As the conductive material, 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) are currently commercially available. Among them, as the conductive material of the present disclosure, carbon nanotube, carbon nanofiber, and carbon black are preferred, and carbon nanotube is most preferred. The conductive network of carbon nanotube can alleviate the binder migration phenomenon during positive electrode slurry drying, and thus is most preferred as the positive electrode conductive material of the present disclosure.

[0143] The BET specific surface area of the carbon nanotube can be 100 m 2 / g to 1000 m 2 / g, 150 m2 / g to 800 m 2 / g, 150 m 2 / g to 500 m 2 / g, 150 m 2 / g to 300 m 2 / g or 150 m 2 / g to 200 m 2 / g.

[0144] The content of the positive electrode conductive material in the positive electrode active material layer can be 0.1 to 30% by weight, more particularly 0.1 to 10% by weight, more particularly 0.5 to 5% by weight.

[0145] The positive electrode binder can be any binder polymer commonly used 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.

[0146] The content of the positive electrode binder in the positive electrode active material layer can be 0.1 to 30% by weight, more particularly 0.1 to 10% by weight, more particularly 0.5 to 5% by weight.

[0147] The separator can be any porous material commonly used as a separator in a lithium secondary battery, such as, but not limited to, a polyolefin-based porous membrane or a nonwoven fabric. In particular, it is preferable that it has low resistance to ion migration of an electrolyte and excellent electrolyte wetting ability.

[0148] Examples of the polyolefin-based porous membrane include a membrane formed of one of polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene) and polyolefin-based polymers (e.g., polypropylene, polybutylene, and polyamylene), or a mixture thereof.

[0149] As the nonwoven fabric, in addition to the polyolefin-based nonwoven fabric, it can also include, for example, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, polyethylene naphthalate, etc., which can be alone or a mixture of these polymers. The structure of the nonwoven fabric can be a spun-bond nonwoven fabric or a melt-blown nonwoven fabric composed of long fibers.

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

[0151] Meanwhile, to improve the mechanical strength of the separator composed of the porous substrate and to suppress short circuit between the positive electrode and the negative electrode, at least one side of the porous substrate can further include a porous coating layer including inorganic particles and a binder polymer.

[0152] Meanwhile, in the lithium secondary battery, the electrolyte can include, but is not particularly limited to, an organic solvent and a lithium salt which are conventionally used in the electrolyte.

[0153] The organic solvent can be used without limitation as long as it is capable of acting as a medium in which ions participating in the electrochemical reaction of the battery are capable of moving. Specifically, the organic solvent can include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.

[0154] Among them, a carbonate-based solvent is preferred, and more preferably a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant capable of improving the charge-discharge performance of the battery and a linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) having low viscosity.

[0155] The lithium salt can be used without limitation as long as it is a compound capable of providing lithium ions for the lithium secondary battery. 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 contained in the electrolyte at a concentration of about 0.6 mol% to about 2 mol%.

[0156] In addition to the electrolyte components, for the purpose of improving the life characteristics of the battery, suppressing the decrease in the capacity of the battery, improving the discharge capacity of the battery, etc., the electrolyte can further include an additive such as pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glycol diether, triamide hexaphosphoric acid, a nitrobenzene derivative, sulfur, a quinonimine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, or aluminum trichloride. The content of the additive can be 0.1 to 5% by weight based on the total weight of the electrolyte.

[0157] The lithium secondary battery of the present disclosure can be manufactured by placing a separator between a positive electrode and a 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 layering the electrode assembly, impregnating the electrode assembly with an electrolyte, and sealing the resulting product in a battery case.

[0158] In 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 solvents 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 of the same composition as the organic solvent used in preparing the positive electrode is used as the electrolyte, the drying process of the electrode assembly can be omitted.

[0159] Unlike the above-described lithium secondary battery, the lithium secondary battery of other examples of the present disclosure can be an all-solid-state battery.

[0160] The battery case can be any one of those conventionally used in the art, the shape is not limited, and can be, for example, cylindrical, prismatic, pouch-type, or coin-type using a can, depending on the intended use of the battery.

[0161] The lithium secondary battery of the present disclosure exhibits excellent resistance characteristics, discharge capacity, power characteristics, and capacity retention rate, and thus can be used in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as energy storage systems (ESS) and hybrid electric vehicles (HEV).

[0162] The present disclosure will now be described in greater 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.

[0163] Example 1: Preparation of a negative electrode

[0164] (Preparation of a negative electrode dam coating composition)

[0165] A polyacrylamide (product name: BUH-0952R, manufacturer: Arakawa Chemical Industries) of 3 parts by weight as an aqueous binder, CMC (Daicel, 2200) of 3.3 parts by weight as a cellulose-based compound having an Mw of 1,260,000, and boehmite (AIO(OH), product name: AOH60) of 93.7 parts by weight as an inorganic particle were mixed and stirred in water, thereby preparing a negative electrode dam coating composition. The solid content was 25% by weight.

[0166] (Preparation of a negative electrode slurry)

[0167] Artificial graphite (D50 23 μm, specific surface area 1.0 m 2 A negative electrode slurry (solid content: 50 wt%) was prepared by mixing, in water, and stirring, 23 μm-sized graphite (specific surface area 1.0 m2 / g, tap density 0.9 g / cc), styrene butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickening agent, and carbon nanotubes as a conductive material in a weight ratio of 95:2:1.5:1.5.

[0168] (Preparation of the negative electrode)

[0169] A negative electrode slurry and a negative electrode dam coating composition were simultaneously coated on a copper foil (thickness 10 μm), but the negative electrode dam coating composition was coated so as to be positioned on both sides of the negative electrode slurry coated portion in the Y-axis direction, as shown in Figure 5 .

[0170] The negative electrode was then dried at a temperature of 90°C and roll-pressed to complete the preparation.

[0171] Example 2: Preparation of a negative electrode

[0172] (Preparation of the negative electrode dam coating composition)

[0173] Based on Example 1, a negative electrode dam coating composition was prepared by changing the weight ratio of the water-based binder, the cellulose-based compound, and the inorganic particles to 9:3.5:87.5.

[0174] Then, a negative electrode slurry and a negative electrode were prepared in the same manner as in Example 1.

[0175] Example 3: Preparation of a negative electrode

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

[0177] Based on Example 1, a negative electrode dam coating composition was prepared by changing the weight ratio of the water-based binder, the cellulose-based compound, and the inorganic particles to 6:3.5:90.5.

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

[0179] Example 4: Preparation of a negative electrode

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

[0181] Based on Example 1, a negative electrode dam coating composition was prepared by changing the weight ratio of the water-based binder, the cellulose-based compound, and the inorganic particles to 3:3.5:93.5.

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

[0183] Example 5: Preparation of a negative electrode

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

[0185] A negative electrode dam coating composition was prepared based on Example 1 by changing the weight ratio of the water-based binder, the cellulose-based compound, and the inorganic particles to 3:3:94.

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

[0187] Comparative Example 1: Preparation of a negative electrode

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

[0189] A negative electrode dam coating composition was prepared by mixing and stirring 4 parts by weight of CMC (Daicel, 2200) having an Mw of 1,260,000 and 96 parts by weight of boehmite (AIO(OH), product name: AOH60) in water. 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 2: Preparation of a negative electrode

[0192] (Preparation of a negative electrode dam coating composition)

[0193] A negative electrode dam coating composition 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 (AIO(OH), product name: AOH60), and 1 part by weight of styrene butadiene rubber (SBR) (BM-L302, ZEON) in water. The solid content was 25% by weight.

[0194] Then, a negative electrode slurry and a negative electrode were prepared in the same manner as in Example 1.

[0195] Comparative Example 3: Preparation of a negative electrode

[0196] A negative electrode dam coating composition (solid content 25% by weight) was prepared in the same manner as in Comparative Example 2, except that the weight ratio of CMC, boehmite, and SBR was changed to 4:93:3 in the preparation of the negative electrode dam coating composition of Comparative Example 2.

[0197] Then, a negative electrode slurry and a negative electrode were prepared in the same manner as in Example 1.

[0198] Comparative Example 4: Preparation of a negative electrode

[0199] A negative dam coating composition (solid content 25 wt%) was prepared in the same manner as Comparative Example 2, except that the weight ratio of CMC, boehmite, and SBR was changed to 4:88:8 in the preparation of the negative dam coating composition of Comparative Example 2.

[0200] Then, a negative electrode slurry and a negative electrode were prepared in the same manner as Example 1.

[0201] Comparative Example 5: Preparation of a negative electrode

[0202] A negative dam coating composition (solid content 25 wt%) was prepared in the same manner as Comparative Example 2, except that the weight ratio of CMC, boehmite, and SBR was changed to 4:88:8 in the preparation of the negative dam coating composition of Comparative Example 2.

[0203] Then, a negative electrode slurry and a negative electrode were prepared in the same manner as Example 1.

[0204] Comparative Example 6: Preparation of a negative electrode

[0205] (Preparation of a negative dam coating composition)

[0206] A negative dam coating composition was prepared by mixing and stirring 2.5 parts by weight of CMC (Daicel, 2200) having 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 wt%.

[0207] Experimental Example 1: Measurement of viscosity of a negative dam coating composition

[0208] For each of the negative dam coating compositions of Examples 1 to 5 and Comparative Examples 1 to 6, the viscosity was measured at 25°C at a shear rate of 2.5 / s using a viscometer (Brookfield) after cooling for 1 hour at a relative humidity of 1%. The viscosity measurement was performed within 2 hours after the negative dam coating composition was prepared, including the cooling time. The results are shown in Table 1.

[0209] Experimental Example 2: Evaluation of surface tension

[0210] For each of the negative dam coating compositions of Examples 1 to 5 and Comparative Examples 1 to 6, the surface tension was measured using a DCA-200 (dynamic contact angle system, SEO) instrument under the following conditions. The results are shown in Table 1.

[0211] Motor rotation speed: 15 rpm / s

[0212] Probe type: ring

[0213] Immersion depth: 4

[0214] Surface detection weight: 0.005

[0215] Stable time: 5

[0216] Experimental Example 3: Confirmation of occurrence of thickened edge

[0217] For each of the negative electrodes in Examples 1 to 5 and Comparative Examples 1 to 6, the negative electrode active material layer was visually observed to determine whether or not the thickened edge shown in FIG. 1 occurred, and the results are shown in Table 1. If the thickened edge occurred, it was marked with "O", and if the thickened edge did not occur, it was marked with "X". Figure 3

[0218] Experimental Example 4: Evaluation of adhesion

[0219] 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 a length of 150 mm and a width of 20 mm, and the sample was attached to a glass slide of 75 mm in length and 25 mm in width in the length direction using a double-sided tape so that the surface of the dam coating layer faced the glass slide. Then, the evaluation sample was passed through a laminator to uniformly attach the double-sided tape. Then, the glass slide portion of the evaluation sample was fixed to the sample stage of a universal testing machine (UTM) (LS5, AMETEK), and the half sample without the glass slide was connected to the load cell of the UTM machine. The load applied to the load cell was measured by moving the load cell 50 mm at a speed of 100 mm / min and applying a force of 90°. The average value of the measured load in the range of 20 mm to 40 mm during the travel was taken. 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.

[0220] For each of the negative electrode dam coating compositions of Examples 2 to 5 and Comparative Examples 1 to 6, the adhesion was also evaluated in the same manner as described above, and the results are shown in Table 1.

[0221] [Table 1]

[0222]

[0223] Referring to Table 1, it was found that the negative electrode dam coating compositions of each of Examples 1 to 5 had a surface tension of 72 mN / mm or more, which was sufficiently high to prevent the thickened edge. In addition, the adhesion was also 65 gf / 20 mm or more, which was expected to reduce the possibility of detachment of the dam coating layer in the roll-pressing process of the electrode.​

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 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.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein The dam coating further comprises a cellulose compound and inorganic particles, wherein Based on the total weight of the dam coating layer, the dam coating layer comprises: 0.5 wt % to 10 wt % of the aqueous binder; 0.5 wt% to 10 wt% of the cellulose-based compound; and 80 wt % to 99 wt % of the inorganic particles.

3. 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.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein The water-based adhesive is polyacrylamide.

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 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.

7. The negative electrode for a lithium secondary battery according to claim 6, wherein The total length of the landslide area is less than 4 mm.

8. The negative electrode for a lithium secondary battery according to claim 6, wherein The total length of the landslide area is 0.5 to 3.5 mm.

9. The negative electrode for a lithium secondary battery according to claim 6, 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.

10. 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.

11. A negative electrode dam coating composition comprising 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.

12. The negative electrode dam coating composition according to claim 11, further comprising a cellulose compound and inorganic particles, wherein: Based on the total weight of the solids excluding the solvent, the solids include: 0.5 wt % to 10 wt % of the aqueous binder; 0.5 wt% to 10 wt% of the cellulose-based compound; and 80 wt % to 99 wt % of the inorganic particles.

13. The negative electrode dam coating composition according to claim 11, wherein: The content of solid excluding the solvent is 15 to 35 parts by weight based on 100 parts by weight of the negative electrode dam coating composition.

14. The negative electrode dam coating composition according to claim 12, wherein: The water-based adhesive is polyacrylamide.

15. The negative electrode dam coating composition according to claim 12, 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. The negative electrode dam coating composition according to claim 11 , wherein the surface tension thereof is greater than 72 mN / mm.

17. A lithium secondary battery comprising: The negative electrode according to any one of claims 1 to 10; positive electrode; diaphragm; and electrolytes.

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