Anode, anode dam coating composition, and lithium secondary battery

Abstract

The coating composition for a negative electrode dam according to one embodiment of the present invention is in surface contact with the edge of the negative electrode active material layer, and includes a carbon-based material, a cellulose-based compound, a rubber-based binder, and inorganic particles. The composition for coating a negative electrode dam has excellent surface tension and adhesive strength, and thus suppresses the occurrence of fat edges on the negative electrode. The dam coating layer formed from the composition for coating a negative electrode dam has the effect of reducing the sliding length of the negative electrode active material layer.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0129809, filed on September 26, 2023.

[0002] The present invention relates to a negative electrode in which the length of the negative electrode sliding region is short but the occurrence of fat edges at the negative electrode end is prevented or suppressed, a negative electrode dam coating composition therefor, and a lithium secondary battery including the negative electrode. [Background technology]

[0003] As technological development and demand for mobile devices, automobiles, energy storage devices, and other industrial fields increase, the demand for batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and discharge voltage, have been the subject of much research and are now commercially available and widely used.

[0004] Depending on the shape of the battery case, secondary batteries are classified into cylindrical batteries and prismatic batteries, in which the electrode assembly is housed in a cylindrical or prismatic metal can, and pouch batteries, in which the electrode assembly is housed in a pouch-shaped case made of an aluminum laminate sheet.

[0005] The electrode assembly housed in the battery case is a chargeable and dischargeable power generating element having a laminated structure of a positive electrode / separator / negative electrode. Examples of such an electrode assembly include a jelly-roll type electrode assembly in which a long sheet-like positive electrode and negative electrode coated with an electrode mixture containing an electrode active material are wound up with a separator interposed between them; a stack type electrode assembly in which a number of positive electrodes and negative electrodes perforated and notched in predetermined sizes are sequentially stacked with a separator interposed between them; and a stack / folding type electrode assembly in which a bi-cell or full cell in which a predetermined number of positive electrodes, negative electrodes, and separators are stacked with a separator interposed between them is wound up.

[0006] The positive and negative electrodes that make up the electrode assembly are manufactured by applying electrode slurry, which is prepared in a mixing process, to an electrode current collector in a predetermined pattern and thickness through a slot die, followed by drying. However, since the electrode slurry is a fluid, after the electrode slurry application process, the electrode slurry may flow down due to its fluidity, which is called sliding.

[0007] 1 is an enlarged view of one side of a cross section of a negative electrode in which electrode slurry is coated on a current collector. Referring to FIG. 1, negative electrode active material layer 12 coated with the electrode slurry is divided into flattened region 12A, which has a uniform thickness and is parallel to the plane of negative electrode current collector 11, and sliding region 12S, in which the thickness of electrode active material layer 12 gradually decreases in the direction toward the uncoated portion where electrode slurry is not coated, and is inclined relative to the plane of current collector 11.

[0008] The positive and negative electrodes that make up the electrode assembly face each other with a separator interposed therebetween, and the lengths of the positive and negative electrode sliding regions may differ. The inclined shapes of the sliding regions may also vary, such as convex upward, convex downward, linear, or S-shaped. Even if the inclined shape is the same, the gradient may vary. As a result, depending on the opposing position, the negative electrode sliding region may have a localized imbalance in the NP ratio. This imbalance in the NP ratio can cause lithium to precipitate from the negative electrode, leading to accidents such as a short circuit.

[0009] In theory, the greater the ratio of negative electrode loading to positive electrode loading at the facing portion of the positive / negative electrodes, the less likely the NP ratio imbalance is. Therefore, recent technological attempts have been made to increase the loading in the negative electrode sliding region. One such attempt involves applying a dam coating composition to the edge where the negative electrode slurry is applied, thereby preventing the dam coating composition from running off and minimizing the sliding length of the negative electrode active material layer.

[0010] However, conventional dam coating compositions suffer from a problem known as a "fat edge," 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. Figure 2 is a cross-sectional view of a negative electrode with a fat edge. Referring to Figure 2, the fat edge protrudes upward along the Z-axis direction from both ends of the negative electrode active material layer 12 in the Y-axis direction. The presence of such a fat edge in a negative electrode can damage the current collector layer during the rolling process, which can pose a safety hazard. Furthermore, the fat edge can also damage other electrodes and separators during the process of stacking multiple positive and negative electrodes and separators.

[0011] Therefore, there is a need to develop a technique for manufacturing an anode that has a short sliding length but does not produce a fat edge. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention provides a negative electrode in which the length of the negative electrode sliding region is short but the occurrence of fat edges at the negative electrode end is prevented or suppressed, a negative electrode dam coating composition therefor, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0013] According to one embodiment of the present invention, there is provided a negative electrode for a lithium secondary battery, the negative electrode for the lithium secondary battery including a negative electrode current collector, a negative electrode active material layer disposed on one or both sides of the negative electrode current collector, and a dam coating layer disposed on one or both sides of the negative electrode current collector, the dam coating layer being in surface contact with an end of the negative electrode active material layer and including a carbon-based material, a cellulose-based compound, a rubber-based binder, and inorganic particles.

[0014] In one embodiment, based on the total weight of the dam coating layer, the carbon-based material may be included in an amount of 3 wt % to 25 wt %, the cellulose-based compound in an amount of 0.5 wt % to 5 wt %, the rubber-based binder in an amount of 3 wt % to 25 wt %, and the inorganic particles in an amount of 45 wt % to 93.5 wt %.

[0015] In one embodiment, the carbon-based material may be one or more selected from carbon black, graphite, carbon nanotubes, and carbon nanofibers.

[0016] In one embodiment, the inorganic particles may be one or more selected from the group consisting of AlO(OH), Al2O3, γ-AlOOH, Al(OH)3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, YO3, SrTiO3, BaTiO3, and Mg(OH)2.

[0017] In one embodiment, the cellulose-based compound may be one or more selected from the group consisting of carboxyl methyl 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).

[0018] In one embodiment, the weight average molecular weight of the cellulose-based compound may be in the range of 800,000 to 2,000,000.

[0019] In one embodiment, the rubber binder can be styrene-butadiene rubber (SBR).

[0020] In one embodiment, the negative electrode active material layer may be divided into a planarized region, the surface of which is parallel to the plane of the negative electrode current collector, and a sliding region, the sliding region extending from the planarized region and having the surface inclined toward the plane of the negative electrode current collector, and the sliding region may be located at one end and the other end of the negative electrode active material layer in the overall length direction.

[0021] In one embodiment, the sliding region may have a total length of 4 mm or less.

[0022] In one embodiment, the overall length of the sliding region may be in the range of 0.5 mm to 3.5 mm.

[0023] In 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 planarized region of the negative electrode active material layer may be within a range of 0.1 to 0.4.

[0024] In one embodiment, the dam coating layer may have a maximum thickness within a range of 20 μm to 40 μm, and a length in the overall direction of the layer of 3 mm or less.

[0025] In one embodiment, the adhesion strength of the dam coating layer may be 90 gf / 20 mm or greater.

[0026] According to another embodiment of the present invention, there is provided a composition for coating a negative electrode dam, which may include a solvent, a carbon-based material, a cellulose-based compound, a rubber-based binder, and inorganic particles.

[0027] In one embodiment of the coating composition for a negative electrode dam, the solid content excluding the solvent may include 3 wt % to 25 wt % of the carbon-based material, 0.5 wt % to 5 wt % of the cellulose-based compound, 3 wt % to 25 wt % of the rubber-based binder, and 45 wt % to 93.5 wt % of the inorganic particles, based on the total weight of the solid content.

[0028] In one embodiment, the carbon-based material and the rubber-based binder may be included in a weight ratio of 4:6 to 6:4.

[0029] In one embodiment, the content of the solid content excluding the solvent may be 16 to 36 parts by weight based on 100 parts by weight of the composition for coating a negative electrode dam.

[0030] In one embodiment, the carbon-based material may be one selected from carbon black, graphite, carbon nanotubes, and carbon nanofibers.

[0031] The negative electrode dam coating composition according to one embodiment may have a surface tension of 70 mN / mm or more.

[0032] According to another embodiment of the present invention, there is provided a lithium secondary battery comprising the above-mentioned negative electrode, a positive electrode, a separator, and an electrolyte. [Effects of the Invention]

[0033] According to one embodiment of the present invention, the surface tension of the negative electrode dam coating composition increases to the level of the negative electrode slurry, and the negative electrode dam coating composition tends to maintain the interface without being mixed into the negative electrode slurry, thereby preventing the formation of fat edges.

[0034] As a result, the sliding length of the negative electrode active material layer is shortened by the dam coating layer, and the risk of NP ratio reversal in the lithium secondary battery can be reduced. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is an enlarged view of one side of a cross section of a negative electrode in which a negative electrode slurry is applied to a current collector according to a conventional technique. [Figure 2] FIG. 1 is a cross-sectional view of a negative electrode in which a fat edge has occurred. [Figure 3]4 is an enlarged view of one side of a cross section of a negative electrode to which a negative electrode slurry and a dam coating composition are applied according to an exemplary embodiment; [Figure 4] FIG. 2 is a top view of a negative electrode sheet for illustrating a negative electrode according to an exemplary embodiment. [Figure 5] FIG. 5 is a cross-sectional view taken along line AA' in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will now be described in more detail to aid in its understanding.

[0037] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his / her own invention.

[0038] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0039] In this specification, terms such as "comprise," "comprise," or "have" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and may be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0040] As used herein, the term "combinations thereof" in Markush expressions means a mixture or combination of one or more components selected from the group of components described in the Markush expressions, and means including one or more components selected from the group of components described above.

[0041] In this specification, the phrase "A and / or B" means "A or B, or both."

[0042] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0043] The specific surface area herein can be measured by the Brunauer-Emmett-Teller (BET) method, for example, by the BET 6-point method using a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) and a nitrogen gas adsorption / flow method.

[0044] In this specification, the average particle size (D 50 ) can be defined as the particle size at 50% of the particle size distribution. The average particle size is not particularly limited, but can be measured, for example, using the laser diffraction method or scanning electron microscope (SEM) photographs. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0045] In this specification, "weight average molecular weight (Mw)" refers to a value measured by gel permeation chromatography (GPC) and converted to a standard polystyrene. Specifically, the weight average molecular weight is a value measured by GPC under the following conditions and converted, and a calibration curve was prepared using standard polystyrene from an Agilent system.

[0046] <Measurement conditions> Measuring instrument: Agilent GPC (Agilent 1200 series, USA) Column: PL Mixed B 2 columns connected Column temperature: 40℃ Eluent: tetrahydrofuran Flow rate: 1.0mL / min Concentration: ~1mg / mL (100μL injection)

[0047] In this specification, the longitudinal direction MD of the negative electrode sheet and the overall width direction of the negative electrode are defined as the X-axis direction, the transverse direction TD of the negative electrode sheet and the overall length direction of the negative electrode are defined as the Y-axis direction, the direction perpendicular to the plane formed by the combination of the X-axis direction and the Y-axis direction are defined as the Z-axis direction, and the X-axis direction and the Y-axis direction are referred to as the horizontal direction.

[0048] <Coating composition for negative electrode dam>

[0049] Figure 1 is an enlarged view of one side of a cross section of a negative electrode in which a negative electrode slurry is coated on a current collector according to a conventional technique. Figure 2 is a cross section of a negative electrode in which a fat edge has occurred. Figure 3 is an enlarged view of one side of a cross section of a negative electrode in which a negative electrode slurry and a negative electrode dam coating composition are coated according to an exemplary embodiment.

[0050] 1, when the negative electrode dam coating composition is not applied, the edge of the portion 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 dried negative electrode active material layer 12 has an inclined shape with respect to the plane of the negative electrode current collector 11. The inclined end of the negative electrode active material layer 12 is called a sliding region 12S, and the sliding length, which is the length of the sliding region in the Y-axis direction, reaches approximately 4 mm to 10 mm.

[0051] Meanwhile, 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 and prevents the negative electrode slurry 120SE from flowing down, so that the sliding length of the sliding region 120S of the negative electrode active material layer becomes much shorter compared to FIG. 1.

[0052] However, when the anode dam coating composition 130CD is applied so as to partially overlap the anode slurry 120S, a portion of the dam coating composition 130CD located on the anode slurry may diffuse into the anode slurry 120S, forming a fat edge as shown in Figure 2. After many years of research, the inventors of the present invention discovered that when the surface tension of the dam coating composition is controlled to the level of the anode slurry, the dam coating composition tends to maintain an interface with the anode slurry, thereby preventing the dam coating composition from diffusing into the anode slurry, leading to the present invention.

[0053] In order to control the surface tension of the dam coating composition to the same level as the negative electrode slurry, an embodiment of the negative electrode dam coating composition may include a carbon-based material, a cellulose-based compound, a rubber-based binder, and inorganic particles. The carbon-based material increases the surface tension of the negative electrode dam coating composition, and the rubber-based binder provides adhesion to the dam coating layer, allowing the dam coating layer to adhere to the current collector. In addition, the rubber-based binder improves the flexibility of the dam coating layer, preventing detachment of the dam coating layer when subjected to external physical forces, ultimately improving the stability of the dam coating layer.

[0054] The solvent may be a solvent commonly used in the art, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. Among these, water is preferred as the solvent for the negative electrode dam coating composition because of its high surface tension.

[0055] The solvent may be included in an amount that allows the composition for coating a negative electrode dam to have an appropriate viscosity in consideration of the coating properties of the composition for coating a negative electrode dam.

[0056] The carbon-based material may be one or a mixture of two or more selected from the group consisting of graphite such as artificial graphite and natural graphite; carbon black such as acetylene black, ketjen black, furnace black, channel black, lamp black, and thermal black; carbon fiber, carbon nanotube, and carbon nanofiber.

[0057] The cellulose-based compound is a water-soluble polymer compound having a predetermined viscosity, and can increase the cohesive force of the solvent, thereby allowing the anode dam coating composition to have an appropriate viscosity and increasing the surface tension.

[0058] Specifically, the cellulose-based compound may be one or more compounds selected from the group consisting of carboxyl methyl 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).

[0059] The cellulose compound may have a weight-average molecular weight (Mw) of 800,000 to 2,000,000, preferably 900,000 to 1,800,000, and more preferably 1,000,000 to 1,500,000. When the weight-average molecular weight of the cellulose compound is within the above range, it imparts an appropriate viscosity to the dam coating composition, which is preferable in terms of coating performance.

[0060] The rubber binder may be one or a mixture of two or more selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, and fluororubber, and is preferably styrene-butadiene rubber (SBR). Styrene-butadiene rubber is preferred as the rubber binder of the present invention because of its excellent wet adhesion and flexibility.

[0061] The styrene-butadiene rubber may contain repeating units derived from styrene monomers and repeating units derived from butadiene monomers in a weight ratio of 70:30 to 30:70. The total weight of the repeating units derived from styrene monomers and repeating units derived from butadiene monomers may be 30% by weight to 100% by weight or 30% by weight to 70% by weight based on the total weight of the styrene-butadiene rubber.

[0062] Examples of the styrene monomer include styrene, α-methylstyrene, p-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 1-vinylnaphthalene, 4-cyclohexylstyrene, 4-(p-methylphenyl)styrene, 1-vinyl-5-hexylnaphthalene, derivatives thereof, and mixtures thereof. Examples of the butadiene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, derivatives thereof, and mixtures thereof.

[0063] If necessary, the styrene-butadiene rubber may further contain a repeating unit derived from a monomer having a crosslinkable group, in an amount of 12 parts by weight or less based on the total weight of the styrene-butadiene rubber, in order to reduce the absorption rate of the electrolyte.

[0064] The inorganic particles have the effect of improving electrical insulation and thermal stability and improving the strength of the dam coating layer. The content of the inorganic particles may be appropriately adjusted in consideration of the viscosity, insulation properties, dispersibility, coatability, etc. of the negative electrode dam coating composition.

[0065] The inorganic particles may be one or more compounds selected from the group consisting of AlO(OH), Al2O3, γ-AlOOH, Al(OH)3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, YO3, 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 particles may be AlO(OH).

[0066] The average particle size (D 50 ) may 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.

[0067] In one embodiment of the composition for coating a negative electrode dam, the content of the solids excluding the solvent may be in the range of 16 to 36 parts by weight, specifically 18 to 34 parts by weight, and more specifically 20 to 32 parts by weight, relative to 100 parts by weight of the composition for coating a negative electrode dam. When the content of the solids in the composition for coating a negative electrode dam satisfies the above range, it is preferable in terms of the coating performance of the composition for coating a negative electrode dam and the effect of reducing the sliding length of the negative electrode slurry.

[0068] In one embodiment of the coating composition for anode dam, the solid content excluding the solvent may include 3 wt % to 25 wt % of the carbon-based material, 0.5 wt % to 5 wt % of the cellulose-based compound, 3 wt % to 25 wt % of the rubber-based binder, and 45 wt % to 93.5 wt % of the inorganic particles, based on the total weight of the solid content.

[0069] In one embodiment, the solid content may include the carbon-based material in an amount of 3 wt% to 25 wt%, specifically 6 wt% to 23 wt%, and more specifically 10 wt% to 17 wt%. The solid content may include the cellulose-based compound in an amount of 0.5 wt% to 5 wt%, specifically 1 wt% to 4.5 wt%, and more specifically 2 wt% to 4 wt%. The solid content may include the rubber-based binder in an amount of 3 wt% to 25 wt%, specifically 6 wt% to 23 wt%, and more specifically 10 wt% to 17 wt%. The solid content may include the inorganic particles in an amount of 45 wt% to 93.5 wt%, specifically 50 wt% to 83 wt%, and more specifically 60 wt% to 77 wt%. When the carbon-based material, cellulose-based compound, rubber-based binder, and inorganic particles are contained in the above content ranges, the coating composition for anode dam may have a surface tension and excellent adhesive performance similar to that of a slurry for anodes, and may have an appropriate viscosity.

[0070] According to a preferred embodiment, the weight ratio of the carbon-based material to the rubber-based binder may be 4:6 to 6:4, and more preferably 45:55 to 55:45.

[0071] By including the carbon-based material and the rubber-based binder in the above content ranges, it is possible to prevent a decrease in surface tension due to the addition of the rubber-based binder and improve the flexibility of the dam coating layer.

[0072] The negative electrode dam coating layer 130 may be formed by applying the negative electrode slurry to the negative electrode current collector, and then applying the negative electrode dam coating composition around the boundary between the negative electrode slurry and an uncoated portion, and then drying them, or by simultaneously coating the negative electrode slurry and the negative electrode dam coating composition and drying them.

[0073] In one embodiment, the viscosity of the negative electrode dam coating composition, measured at 25° C. and a shear rate of 2.5 s, may be 2,000 cps to 15,000 cps, specifically 2,500 cps to 12,000 cps, and more specifically 3,000 cps to 10,000 cps. A negative electrode dam coating composition having a viscosity value within the above range may have a thickness and width within an appropriate range for improving the sliding of the negative electrode active material layer.

[0074] The method for coating the negative electrode dam coating composition may include, but is not limited to, spray coating, spin coating, roll coating, die coating, gravure printing, bar coating, etc., and preferably, die coating and gravure printing may be used.

[0075] The surface tension of the negative electrode dam coating composition according to one embodiment may be 70 mN / mm or more, specifically 71 mN / mm or more, and more specifically in the range of 72 mN / mm to 80 mN / mm. A negative electrode dam coating composition having a surface tension within this range is effective in preventing the occurrence of fat edges on the negative electrode. The surface tension within this range is at the same level as the surface tension of a negative electrode slurry.

[0076] The surface tension is a value measured using a DCA-200 (Dynamic Contact Angle System, SEO) device under the following conditions.

[0077] Motor speed: 15 rpm / s Probe type: Ring Immersion depth: 4 Surface Detect weight: 0.005 Stabilization time:5

[0078] <Anode for lithium secondary batteries>

[0079] FIG. 4 is a top view of a negative electrode sheet for explaining a negative electrode according to an exemplary embodiment, and FIG. 5 is a cross-sectional view taken along line AA' in FIG.

[0080] Referring to these drawings, an anode 100 according to an exemplary embodiment includes an anode current collector 110, an anode active material layer 120 disposed on one or both sides of the anode current collector 110, and a dam coating layer 130 disposed on one or both sides of the anode current collector 110, and the dam coating layer 130 may be structured to be in surface contact with an end of the anode active material layer 120. The end is an end based on the lateral direction (Y-axis direction) of the anode sheet NES or the overall length direction (Y-axis direction) of the anode 100.

[0081] 3 and 4, a negative electrode active material layer 120 is formed in the center of a negative electrode sheet NES, which serves as the base material of the negative electrode 100, in the horizontal direction (Y-axis direction), and a dam coating layer 130 is formed on both side edges of the negative electrode sheet NES in the horizontal direction. Outside the dam coating layer 130, there is a plain area that is not covered by the negative electrode active material layer 120 or the dam coating layer 130. The negative electrode 100 can be manufactured by notching and cutting along the notch lines (dotted lines) shown on the negative electrode sheet NES. While FIG. 4 shows a negative electrode in which the dam coating layer 130 is applied to both side edges of the negative electrode active material layer 120, the present invention is not limited thereto, and the dam coating layer 130 may be applied to only one side edge of the negative electrode active material layer 120.

[0082] The negative electrode active material layer 120 may be formed by drying the negative electrode slurry 120SE coated on the current collector 110, and the dam coating layer 130 may be formed by drying the negative electrode dam coating composition 130CD.

[0083] 3 and 5, an anode 100 according to an embodiment includes an anode active material layer 120 formed from an anode slurry 120SE, and the anode active material layer 120 is divided into a planarized region 12A whose surface is parallel to the plane of the anode current collector 110 and a sliding region 120S extending from the planarized region 12A and having a surface inclined toward the plane of the anode current collector 110. The sliding region 120S may be located at one end and the other end of the anode active material layer 120 in the overall length direction (Y-axis direction).

[0084] In the anode 100 according to one embodiment, the dam coating layer 130 prevents the anode slurry from spreading along the current collector and reduces the sliding length of the anode active material layer 120. The reduced sliding length can prevent the N / P ratio from reversing in the sliding region.

[0085] In one embodiment, the overall length of the sliding region 120S may be 4 mm or less, preferably 0.5 mm to 3.5 mm, and more preferably 0.5 mm to 3 mm, which is a reduced length compared to the sliding length of the negative electrode without the negative electrode dam coating layer shown in FIG.

[0086] The dam coating layer 130 may contain a carbon-based material, a cellulose-based compound, a rubber-based binder, and inorganic particles to control the surface tension of the negative electrode dam coating composition to the same level as the negative electrode slurry. The carbon-based material increases the surface tension of the negative electrode dam coating composition, and the rubber-based binder imparts flexibility to the dam coating layer, preventing it from peeling off when subjected to external physical forces, ultimately improving the stability of the dam coating layer.

[0087] The carbonaceous material, cellulose compound, rubber binder and inorganic particles have been described in detail above, so a duplicated description will be omitted.

[0088] According to one embodiment, the maximum thickness of the dam coating layer 130 may be in the range of 20 μm to 40 μm, specifically 22 μm to 40 μm, and more specifically 25 μm 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.

[0089] According to an embodiment, the length of the dam coating layer 130 in the overall length direction (Y-axis direction) may be 3 mm or less, specifically 0.5 mm to 3 mm, and more specifically 1 mm to 2.5 mm.

[0090] 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 planarized region of the negative electrode active material layer may be in the range of 0.1 to 0.4, specifically 0.15 to 0.3.

[0091] When the thickness and length of the dam coating layer 130 are within the above ranges, it is preferable in terms of safety due to the dam coating layer and capacity development of the negative electrode.

[0092] Because the negative electrode dam coating composition must act as a dam to prevent the negative electrode slurry from spreading, it is preferable that the coating thickness of the negative electrode dam coating composition be at least a certain level. Referring to FIG. 3, the coating thickness of the negative electrode dam coating composition may be the same as the coating thickness of the negative electrode slurry at the moment of coating. Even if the coating thickness of the negative electrode dam coating composition is the same as the coating thickness of the negative electrode slurry, the solid content of the negative electrode dam coating composition is much lower than the solid content of the negative electrode slurry. Therefore, after a series of electrode processes, such as a drying process, the thickness of the dam coating layer will be smaller than the thickness of the negative electrode active material layer.

[0093] According to one embodiment, the adhesive strength of the dam coating layer 130 may be 90 gf / 20 mm or more, specifically, in the range of 95 gf / 20 mm to 200 gf / 20 mm, and more specifically, in the range of 100 gf / 20 mm to 150 gf / 20 mm.

[0094] The adhesive strength was measured by applying a negative electrode dam coating composition to copper foil, drying it at 80°C to 90°C, and then cutting it into a length of 150 mm and a width of 20 mm. The coated surface of the negative electrode dam coating composition was placed facing a 75 mm long and 25 mm wide glass slide, and the specimen was attached longitudinally to the glass slide using double-sided tape. The specimen was then passed through a laminator to ensure uniform adhesion of the double-sided tape, producing an evaluation specimen. Next, the glass slide portion of the evaluation specimen was fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the half of the specimen not attached to the glass slide was connected to the load cell of the UTM device. The load cell was moved 50 mm at a speed of 100 mm / min, applying a 90° force, and the load applied to the load cell was measured. The average load measured over a 20 mm to 40 mm section of the travel section was calculated. This is repeated a total of five times, and the average value is evaluated as the adhesive strength (gf / 20 mm) of each sample.

[0095] When the adhesive strength of the dam coating layer 130 is within the above range, the dam coating layer is preferably not detached during electrode processes such as rolling.

[0096] The negative electrode current collector 110 may be made of any metal that is highly conductive, easily adheres to the negative electrode slurry, and is non-reactive within the battery voltage range, such as 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. Furthermore, the surface may be formed with fine irregularities to enhance the bonding strength of the negative electrode active material, and the negative electrode current collector 110 may be made in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0097] The negative electrode active material layer 120 may include a negative electrode active material, a binder, and optionally a conductive material and a filler.

[0098] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof 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 alloys, Sn alloys, and Al alloys; and SiO. β Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material.

[0099] The carbonaceous material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and calcined carbons such as petroleum or coal tar pitch-derived cokes. Graphite-based negative electrode active materials, such as natural graphite and artificial graphite, are preferred because they are capable of reversible lithium ion insertion and extraction while maintaining structural and electrical properties.

[0100] The negative electrode active material may be contained in a range of about 80 wt % to 99.5 wt % or 88 wt % to 99 wt % based on the total weight of the negative electrode active material layer, but the content is not limited to the above.

[0101] The binder is not particularly limited as long as it is a component that helps bind the negative electrode active material to the conductive material and the like and to the current collector. Examples of the binder 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.

[0102] When the solvent for the negative electrode slurry is an aqueous solvent such as water, the binder is preferably an aqueous binder. Specific examples of the aqueous binder include styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetyl cellulose. In a specific example, the water-based binder may be one or more selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber. For example, the water-based binder may be styrene-butadiene rubber.

[0103] The binder may be contained in an amount of 1 wt % to 30 wt % based on the total weight of the negative electrode active material layer.

[0104] The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. 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, or thermal black; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or 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 can be used.

[0105] The conductive material may be contained in an amount of 1 wt % to 30 wt % based on the total weight of the negative electrode active material layer.

[0106] The filler is a component that suppresses expansion of the electrode and is used selectively. There are no particular limitations on the filler as long as it is a fibrous material that does not induce chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene; glass fiber, carbon fiber, and other fibrous materials can be used.

[0107] The method for producing the negative electrode will be described below.

[0108] A method for manufacturing a negative electrode according to one embodiment may include a step of preparing a negative electrode slurry (P11), a step of preparing a negative electrode dam coating composition (P12), a coating step of applying the negative electrode dam coating composition and the negative electrode slurry onto a negative electrode current collector (P20), and a drying and rolling step (P30).

[0109] The step (P11) of preparing the negative electrode slurry may include mixing and stirring a negative electrode active material, a binder, a conductive material, and optionally a dispersant or a filler, in a solvent.

[0110] The solvent may be a solvent commonly used in the art, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. It may be preferable that the solvent be included in an amount that allows the negative electrode active material slurry to have an appropriate viscosity, taking into account the coating and processability of the negative electrode active material slurry.

[0111] The solvent may be included in an amount that allows the negative electrode slurry to have an appropriate viscosity and solid content. For example, the solvent may be included in an amount that allows the negative electrode slurry to have a solid content of 40 wt% to 75 wt%, specifically 50 wt% to 70 wt%, 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 certain level of thickness or more, thereby ensuring excellent energy density.

[0112] In one embodiment, the step (P12) of preparing a composition for coating a negative electrode dam may include mixing and stirring the carbon-based material, the cellulose-based compound, the rubber-based binder, and the inorganic particles in a solvent.

[0113] In the coating step (P20) of applying the anode dam coating composition and the anode slurry onto the anode current collector, the anode dam coating composition may be applied after applying the anode slurry onto the anode current collector, or the anode slurry and the anode dam coating composition may be applied simultaneously onto the anode current collector.

[0114] <Lithium secondary battery>

[0115] Next, the lithium secondary battery according to the present invention will be described.

[0116] A lithium secondary battery according to an 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.

[0117] The lithium secondary battery of the present invention can be manufactured by a conventional method known in the art, for example, by disposing a separator between a positive electrode and a negative electrode and injecting an electrolyte therein.

[0118] In the lithium secondary battery, the negative electrode may be as described above. For example, the negative electrode may include a negative electrode current collector, a negative electrode active material layer disposed on one or both sides of the negative electrode current collector, and a dam coating layer disposed on one or both sides of the negative electrode current collector, the dam coating layer being in surface contact with an end of the negative electrode active material layer and including the carbon-based material, the cellulose-based compound, the rubber-based binder, and the inorganic particles.

[0119] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0120] In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0121] The positive electrode active material is not particularly limited, and any compound known in the art that allows reversible intercalation and deintercalation of lithium may be used without limitation. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O; and the chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3) 2-x M x Lithium manganese composite oxides represented by Li2Mn3MO8 (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 Examples of lithium manganese composite oxides include, but are not limited to, lithium manganese oxides with a spinel structure represented by O4; LiMn2O4 in which part of the Li in the chemical formula is replaced with an alkaline earth metal ion; disulfide compounds; lithium iron phosphate compounds represented by LiFePO4; disulfide compounds; and Fe2(MoO4)3.

[0122] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0123] The positive electrode conductive material is used to impart conductivity to the electrode and may be carbon black, graphite, carbon fiber, carbon nanotubes, metal powder, conductive metal oxides, organic conductive materials, etc. Currently available conductive materials include acetylene black (e.g., products of Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC (products of Armak Company), Vulcan XC-72 (products of Cabot Company), and Super P (products of MMM). Among these, carbon nanotubes, carbon nanofibers, and carbon black are preferred as conductive materials in the present invention, with carbon nanotubes being most preferred. The conductive network of carbon nanotubes can mitigate binder lift-off during the drying process of the positive electrode slurry, making them the most preferred conductive material in the positive electrode of the present invention.

[0124] The BET specific surface area of ​​the carbon nanotubes is 100m 2 / g~1000m 2 / g, 150m 2 / g~800m 2 / g, 150m 2 / g~500m 2 / g, 150m 2 / g~300m 2 / g, or 150m 2 / g~200m 2 / g.

[0125] The positive electrode conductive material may be contained in the positive electrode active material layer in an amount of 0.1% by weight to 30% by weight, specifically 0.1% by weight to 10% by weight, and more specifically 0.5% by weight to 5% by weight.

[0126] The positive electrode binder may be any commonly used binder polymer without limitation, such as polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene butadiene rubber (SBR), carboxyl methyl cellulose (CMC), and various other binder polymers.

[0127] The positive electrode binder may be contained in the positive electrode active material layer in an amount of 0.1% by weight to 30% by weight, specifically 0.1% by weight to 10% by weight, and more specifically 0.5% by weight to 5% by weight.

[0128] The separator may be any porous substrate commonly used as a separator in lithium secondary batteries, such as, but not limited to, a polyolefin-based porous membrane or nonwoven fabric, and is particularly preferably one that has low resistance to ion migration of the electrolyte and excellent electrolyte humidifying ability.

[0129] Examples of the polyolefin-based porous membrane include membranes formed from polyolefin-based polymers such as polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or in combination.

[0130] In addition to polyolefin-based nonwoven fabrics, examples of the nonwoven fabric include nonwoven fabrics made from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylene naphthalene, either alone or in combination. The nonwoven fabric may be a spunbonded or meltblown nonwoven fabric made from long fibers.

[0131] The thickness of the porous substrate is not particularly limited, but may be 5 μm to 50 μm. The pore size and pore density of the porous substrate are also not particularly limited, but may be 0.01 μm to 50 μm and 10% to 95%, respectively.

[0132] Meanwhile, in order to improve the mechanical strength of the separator formed from the porous substrate and to prevent short circuits between the positive electrode and the negative electrode, a porous coating layer including inorganic particles and a binder polymer may be further included on at least one surface of the porous substrate.

[0133] Meanwhile, in the lithium secondary battery, the electrolyte may contain an organic solvent and a lithium salt that are commonly used in electrolytes, and is not particularly limited.

[0134] The organic solvent is not particularly limited as long as it can function as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent that can be used include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0135] Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0136] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, or LiB(C, O) . The lithium salt is preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%.

[0137] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine 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 battery's life characteristics, suppressing battery capacity reduction, improving the battery's discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0138] The lithium secondary battery of the present invention may be fabricated by forming an electrode assembly by disposing a separator between a positive electrode and a negative electrode, and then inserting the electrode assembly into a cylindrical or prismatic battery case and then injecting an electrolyte thereinto, or by stacking the electrode assemblies, impregnating them with an electrolyte, and then inserting the resulting assembly into a battery case and sealing it.

[0139] When manufacturing the lithium secondary battery of the present invention, the electrode assembly can 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. When an electrolyte having the same components as the organic solvent used in manufacturing the positive electrode is used, the step of drying the electrode assembly can be omitted.

[0140] Unlike the above-described lithium secondary batteries, the lithium secondary battery according to another embodiment of the present invention may be an all-solid-state battery.

[0141] The battery case may be one commonly used in the art, and may have any shape depending on the intended use of the battery, such as a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0142] 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 the fields of portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles such as energy storage systems (ESS) and hybrid electric vehicles (HEV).

[0143] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0144] Example 1: Preparation of negative electrode

[0145] (Production of a coating composition for negative electrode dams) A coating composition for anode dams was prepared by mixing and stirring 13 parts by weight of carbon black as a carbon-based material, 3 parts by weight of CMC (Daicel, 2200) with Mw of 1,260,000 as a cellulose-based compound, 13 parts by weight of styrene-butadiene rubber SBR as a rubber-based binder, and 71 parts by weight of boehmite (AlO(OH) product name: AOH60) as inorganic particles in water. The solid content was 26 wt%.

[0146] (Production of negative electrode slurry) The negative electrode active material is artificial graphite (D 50 23μm, specific surface area 1.0m 2 / g, tap density 0.9 g / cc), styrene butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and carbon nanotubes as a conductive material were mixed with water in a weight ratio of 95:2:1.5:1.5 and stirred to prepare a slurry for the negative electrode (solid content: 50 wt%).

[0147] (Manufacturing of negative electrodes) The negative electrode slurry and the negative electrode dam coating composition were simultaneously coated onto a copper foil (thickness: 10 μm), and the negative electrode dam coating composition was applied so as to be positioned on both side edges in the Y-axis direction of the negative electrode slurry application area, as shown in FIG. 5.

[0148] Thereafter, the mixture was dried at a temperature of 90°C and rolled to complete the manufacture of the negative electrode.

[0149] Example 2: Preparation of negative electrode

[0150] (Production of a coating composition for negative electrode dams) In Example 1, the weight ratio of carbon black, cellulose compound, rubber binder, and inorganic particles was changed to 15:3:15:67 to prepare a coating composition for a negative electrode dam.

[0151] Thereafter, a negative electrode slurry and a negative electrode were produced in the same manner as in Example 1.

[0152] Example 3: Preparation of negative electrode

[0153] (Production of a coating composition for negative electrode dams) In Example 1, the weight ratio of carbon black, cellulose compound, rubber binder, and inorganic particles was changed to 11:2:11:76 to prepare a coating composition for a negative electrode dam.

[0154] Thereafter, a negative electrode slurry and a negative electrode were produced in the same manner as in Example 1.

[0155] Comparative Example 1: Production of negative electrode

[0156] (Production of a coating composition for negative electrode dams) A composition for coating anode dams was prepared by mixing 4 parts by weight of CMC (Daicel, 2200) with a molecular weight of 1,260,000 and 96 parts by weight of boehmite (AlO(OH) product name: AOH60) with water and stirring. The solid content was 25 wt%.

[0157] Thereafter, a negative electrode slurry and a negative electrode were produced in the same manner as in Example 1.

[0158] Comparative Example 2: Production of negative electrode

[0159] (Production of a coating composition for negative electrode dams) A composition for coating an anode dam was prepared by mixing 4 parts by weight of CMC (Daicel, 2200) with a molecular weight 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) with water and stirring. The solid content was 25 wt%.

[0160] Thereafter, a negative electrode slurry and a negative electrode were produced in the same manner as in Example 1.

[0161] Comparative Example 3: Production of negative electrode

[0162] A composition for coating an anode dam (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 when preparing the composition for coating an anode dam in Comparative Example 2. Then, a slurry for an anode and an anode were prepared in the same manner as in Example 1.

[0163] Comparative Example 4: Production of negative electrode

[0164] A composition for coating an anode dam (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 when preparing the composition for coating an anode dam in Comparative Example 2. Then, a slurry for an anode and an anode were prepared in the same manner as in Example 1.

[0165] Comparative Example 5: Production of negative electrode

[0166] A composition for coating an anode dam (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 when preparing the composition for coating an anode dam in Comparative Example 2. Then, a slurry for an anode and an anode were prepared in the same manner as in Example 1.

[0167] Comparative Example 6: Production of negative electrode

[0168] (Production of a coating composition for negative electrode dams) A coating composition for anode dams was prepared by mixing 2.5 parts by weight of CMC (Daicel, 2200) with a molecular weight of 1,260,000 and 97.5 parts by weight of SBR (styrene butadiene rubber) (BM-L302, Zeon) with water and stirring, resulting in a solid content of 24 wt%.

[0169] Experimental Example 1: Viscosity measurement of anode dam coating composition

[0170] For each of the negative electrode dam coating compositions in Examples 1 to 3 and Comparative Examples 1 to 6, the viscosity was measured at 25°C and a shear rate of 2.5 / s using a Brookfield viscometer after cooling for 1 hour under a relative humidity condition of 1%. The viscosity measurement was carried out within 2 hours after preparation of the negative electrode dam coating composition, including the cooling time. The results are shown in Table 1.

[0171] Experimental example 2: Surface tension evaluation

[0172] The surface tension of each of the negative electrode dam coating compositions of Examples 1 to 3 and Comparative Examples 1 to 6 was measured under the following conditions using a DCA-200 (Dynamic Contact Angle System, SEO Co.) device, and the results are shown in Table 1.

[0173] Motor speed: 15 rpm / s Probe type: Ring Immersion depth: 4 Surface Detect weight: 0.005 Stabilization time:5

[0174] Experimental example 3: Checking for the occurrence of fat edges

[0175] For each of the negative electrodes of Examples 1 to 3 and Comparative Examples 1 to 6, the negative electrode active material layer was visually inspected to determine whether or not a fat edge as shown in Fig. 2 had occurred, and the results are shown in Table 1. If a fat edge had occurred, it was marked with "O", and if no fat edge had occurred, it was marked with "X".

[0176] Experimental Example 4: Adhesion strength evaluation

[0177] To evaluate the adhesive strength of the dam coating layer formed by the negative electrode dam coating composition, the negative electrode dam coating composition of Example 1 was applied to the copper foil of Example 1 and dried at 80-90°C. The specimen was then cut to a length of 150 mm and a width of 20 mm. The surface of the dam coating layer was placed facing a 75-mm-long, 25-mm-wide glass slide, and the specimen was attached longitudinally to the glass slide using double-sided tape. The specimen was then passed through a laminator to ensure uniform adhesion of the double-sided tape, producing an evaluation specimen. The glass slide portion of the evaluation specimen was then fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the half of the specimen not attached to the glass slide was connected to the load cell of the UTM device. The load cell was moved 50 mm at a speed of 100 mm / min, applying a 90° force, and the load applied to the load cell was measured. The average load measured over a 20-40 mm section of the travel section was calculated. This was repeated five times, and the average value was evaluated as the adhesive strength (gf / 20 mm) of each sample. The results are shown in Table 1.

[0178] The adhesive strength of each of the coating compositions for the negative electrode dam of Examples 2 and 3 and Comparative Examples 1 to 6 was evaluated in the same manner as above, and the results are shown in Table 1.

[0179] [Table 1]

[0180] Referring to Table 1, it was confirmed that the negative electrode dam coating compositions of Examples 1 to 3 each had a high surface tension of 72 mN / mm or more, preventing the occurrence of fat edges. In addition, the adhesive strength was high at 90 gf / 20 mm or more, which is expected to reduce the possibility of the dam coating layer peeling off during the electrode rolling process. [Explanation of symbols]

[0181] 10, 100: Negative electrode 11, 110: Negative electrode current collector 12, 120: Negative electrode active material layer 13, 130: Dam coating layer NES: Negative electrode sheet

Claims

1. 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; The dam coating layer is in surface contact with an end of the negative electrode active material layer, and includes a carbon-based material, a cellulose-based compound, a rubber-based binder, and inorganic particles.

2. Based on the total weight of the dam coating layer, the carbon-based material is 3% to 25% by weight, 0.5% to 5% by weight of a cellulose-based compound, 3% to 25% by weight of a rubber binder; and 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the inorganic particles are contained in an amount of 45% by weight to 93.5% by weight.

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

4. The inorganic particles include AlO(OH), Al ２ O ３ , γ-AlOOH, Al(OH) ３ , SiO ２ , TiO ２ , SnO ２ , CeO ２ , MgO, NiO, CaO, ZnO, ZrO ２ , Y ２ O ３ , SrTiO ３ , BaTiO ３ and Mg(OH) ２ 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode is one or more selected from the group consisting of:

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the cellulose-based compound is one or more selected from the group consisting of carboxymethyl cellulose (CMC), cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, a lithium salt of carboxymethyl cellulose (CMC-Li), and a sodium salt of carboxymethyl cellulose (CMC-Na).

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

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

8. the negative electrode active material layer is divided into a planarized region, the surface of which is parallel to the plane of the negative electrode current collector, and a sliding region, the planarized region extending from the planarized region and having a surface inclined toward the plane of the negative electrode current collector; 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the sliding region is located at one end and the other end of the negative electrode active material layer in the overall length direction.

9. 9. The negative electrode for a lithium secondary battery according to claim 8, wherein the length of the sliding region in the overall length direction is 4 mm or less.

10. 9. The negative electrode for a lithium secondary battery according to claim 8, wherein the length of the sliding region in the overall length direction is within a range of 0.5 mm to 3.5 mm.

11. 9. The negative electrode for a lithium secondary battery according to claim 8, wherein a thickness ratio (T2 / T1) of a maximum thickness value T2 of the dam coating layer to an average thickness T1 of the negative electrode active material layer in the planarized region in the negative electrode active material layer is within a range of 0.1 to 0.

4.

12. The dam coating layer is The maximum thickness is within the range of 20 μm to 40 μm, 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the length in the overall direction is 3 mm or less.

13. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the adhesive strength of the dam coating layer is 90 gf / 20 mm or more.

14. A composition for coating an anode dam, comprising a solvent, a carbon-based material, a cellulose-based compound, a rubber-based binder, and inorganic particles.

15. The solid content excluding the solvent is based on the total weight of the solid content. 3% by weight to 25% by weight of the carbon-based material, 0.5% by weight to 5% by weight of a cellulose-based compound, 3% to 25% by weight of a rubber binder, and The coating composition for a negative electrode dam according to claim 14, comprising 45% by weight to 93.5% by weight of the inorganic particles.

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

4.

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

18. The composition for coating a negative electrode dam according to claim 13, wherein the carbon-based material is one selected from the group consisting of carbon black, graphite, carbon nanotubes, and carbon nanofibers.

19. The composition for coating a negative electrode dam according to claim 13, having a surface tension of 70 mN / mm or more.

20. The negative electrode according to any one of claims 1 to 13, positive electrode, Separation membranes, and A lithium secondary battery, including an electrolyte.

Images