Negative electrode and secondary battery including the same

Abstract

The present invention provides a negative electrode comprising: a negative electrode current collector; a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material; and a coating layer including an N-type organic active material; the negative electrode active material layer includes an inclined portion defined on at least one side thereof and a flat portion defined excluding the inclined portion, the inclined portion having a slope toward a surface of the negative electrode current collector, and the coating layer is disposed on at least a portion of the inclined portion.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0046986 dated April 15, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference. The present invention relates to a negative electrode and a secondary battery including the same. [Background technology]

[0002] In recent years, the development of the information society has led to the development of personal IT devices and networks, and as a result, society as a whole has become more dependent on electrical energy, which has created a demand for the development of battery technology to efficiently store and utilize electrical energy.

[0003] In particular, with the growing interest in solving environmental problems and realizing a sustainable recycling-based society, extensive research has been conducted on electricity storage devices such as lithium-ion batteries and electric double-layer capacitors. Among these, lithium secondary batteries have been in the spotlight as a battery system with the highest theoretical energy density among battery technologies.

[0004] The lithium secondary battery generally includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. In addition, the positive electrode and the negative electrode may have an active material layer including a positive electrode active material or a negative electrode active material formed on a current collector.

[0005] Among these, the negative electrode active material layer is generally prepared by adding the negative electrode active material and the like to a solvent for forming a negative electrode slurry, and then coating the negative electrode slurry on a negative electrode current collector, drying and rolling. In this case, the negative electrode active material layer may have a slope at the end due to the fluid characteristics of the negative electrode slurry, which causes a decrease in the adhesive strength between the negative electrode and the separator, and the sloped end cannot sufficiently accept lithium from the facing positive electrode, resulting in lithium precipitation. In addition, the sloped end of the negative electrode causes a polarization phenomenon of the electrolyte, which increases the resistance and causes an overvoltage, which causes problems such as the elution of transition metals in the positive electrode active material and the acceleration of side reactions in the electrolyte, resulting in a decrease in cell performance.

[0006] Korean Patent Publication No. 10-2021-0114376 discloses an electrode for a lithium battery, a lithium battery including the same, and a method for manufacturing the lithium battery, but fails to provide an alternative to the above problems. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-2021-0114376 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide an anode that can effectively improve cell performance, specifically, the charge / discharge efficiency and life performance of a cell, by forming a coating layer including an N-type organic active material on a slope of the anode to improve adhesion between the anode and a separator, suppress the formation of overvoltage on the slope of the anode, and prevent lithium precipitation.

[0009] Another object of the present invention is to provide a secondary battery including the above-mentioned negative electrode. [Means for solving the problem]

[0010] The present invention provides a negative electrode comprising: a negative electrode current collector; a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material; and a coating layer including an N-type organic active material; the negative electrode active material layer includes an inclined portion defined on at least one side thereof and a flat portion defined excluding the inclined portion, the inclined portion having a slope toward a surface of the negative electrode current collector, and the coating layer is disposed on at least a portion of the inclined portion.

[0011] The present invention also provides a lithium secondary battery, including: the negative electrode; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte. Effect of the Invention

[0012] The negative electrode according to the present invention includes a negative electrode active material layer including an inclined portion inclined toward a surface of a negative electrode current collector, and a coating layer disposed on at least a part of the inclined portion, the coating layer including an N-type organic active material. The N-type organic active material can provide radicals due to its structural characteristics, and the presence of such radicals can enable lithium ions to be inserted and removed through oxidation and reduction reactions. The coating layer prevents overvoltage caused by polarization of the electrolyte concentration due to the inclination of the negative electrode inclined portion, and suppresses problems such as an increase in resistance due to electrolyte side reactions and lithium precipitation caused by insufficient acceptance of lithium from the positive electrode facing the negative electrode inclined portion, thereby improving the charge / discharge efficiency and life characteristics of the negative electrode and a lithium secondary battery including the same. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic side view for specifically illustrating the negative electrode of the present invention. [Diagram 2] FIG. 2 is a schematic plan view for specifically illustrating the negative electrode of the present invention. [Diagram 3]1 is a graph of the thickness profile using a rotary caliper for the negative electrodes of Example 1 and Comparative Example 1. [Figure 4] 1 is a graph showing the results of measuring the cycle capacity retention rates of secondary batteries of Examples 1 to 3 and Comparative Example 1. BEST MODE FOR CARRYING OUT THEINVENTION

[0014] The terms and words used in this specification and the claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concept of a term in order to best describe his or her invention.

[0015] Furthermore, in this specification, terms such as "including," "comprising," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0016] The average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to about several mm, and can provide results with high reproducibility and high resolution.

[0017] Hereinafter, the present invention will be described in detail with reference to the drawings. Specifically, Fig. 1 is a schematic side view for explaining the anode of the present invention. Also, Fig. 2 is a schematic plan view for explaining the anode of the present invention. In the description of the present invention, if it is determined that a detailed description of related known configurations or functions may obscure the gist of the present invention, the detailed description may be omitted.

[0018] negative electrode The present invention provides a negative electrode 10. Specifically, the negative electrode 10 may be a negative electrode for a lithium secondary battery.

[0019] The negative electrode 10 according to the present invention includes a negative electrode current collector 100; a negative electrode active material layer 200 disposed on at least one surface of the negative electrode current collector 100 and including a negative electrode active material; and coating layers 300a, 300b including an N-type organic active material. The negative electrode active material layer 200 includes inclined portions 210a, 210b defined on at least one side thereof, and a flat portion 220 defined excluding the inclined portions 210a, 210b, the inclined portions 210a, 210b have an inclination toward a surface of the negative electrode current collector 100, and the coating layers 300a, 300b are disposed on at least a portion of the inclined portions 210a, 210b.

[0020] In general, the negative electrode active material layer included in the negative electrode is generally prepared by applying a negative electrode slurry prepared by adding a negative electrode active material to a solvent for forming a negative electrode slurry to a negative electrode current collector, drying and rolling the negative electrode slurry. At this time, since the negative electrode slurry has fluid properties, the formed negative electrode active material layer has an inclined portion or end portion that forms a slope toward the surface of the negative electrode current collector. Since the negative electrode active material layer is not sufficiently loaded on the inclined portion having such an inclination, lithium ions transferred from the facing positive electrode cannot be sufficiently inserted, resulting in a problem of lithium being precipitated to the outside. In addition, the inclined end portion of the negative electrode causes a polarization phenomenon of the electrolyte, which increases the resistance and causes a problem of overvoltage formation, which causes problems such as the elution of transition metals in the positive electrode active material and the acceleration of electrolyte side reactions, resulting in a problem of a decrease in cell performance.

[0021] In order to solve these problems, the negative electrode according to the present invention includes a negative electrode active material layer including an inclined portion inclined toward the surface of the negative electrode current collector, and a coating layer disposed on at least a part of the inclined portion, the coating layer including an N-type organic active material. The N-type organic active material can provide radicals due to its structural characteristics, and the presence of such radicals can enable lithium ions to be inserted and removed by oxidation and reduction reactions. The coating layer prevents overvoltage caused by the polarization of the electrolyte concentration due to the inclination of the negative electrode inclined portion, and suppresses the problems of increased resistance due to electrolyte side reactions and lithium precipitation caused by insufficient acceptance of lithium from the positive electrode facing the negative electrode inclined portion, thereby improving the charge / discharge efficiency and life characteristics of the negative electrode and the lithium secondary battery including the same.

[0022] The negative electrode current collector 100 is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery. Specifically, the negative electrode current collector 100 may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and may specifically include copper.

[0023] The negative electrode current collector 100 can typically have a thickness of 3 μm to 500 μm. The negative electrode current collector 100 may have fine irregularities on its surface to strengthen the binding force of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, etc.

[0024] The negative electrode active material layer 200 is disposed on at least one surface of the negative electrode current collector 100. Specifically, the negative electrode active material layer 200 may be disposed on one surface or both surfaces of the negative electrode current collector 100.

[0025] The negative electrode active material layer may include inclined portions 210a, 210b defined on at least one side, and a flat portion 220 defined excluding the inclined portions 210a, 210b. In this specification, the inclined portions 210a, 210b and the flat portion 220 may be abstractly defined to identify positions where coating layers 300a, 300b, which will be described later, are formed, as shown in Fig. 1. For example, the inclined portions 210a, 210b and the flat portion 220 may have the same composition or may be manufactured using the same negative electrode slurry.

[0026] In this specification, "at least one side of the negative electrode active material layer" may mean at least one side in the width direction (e.g., the direction of arrow W in Figs. 1 and 2) of the negative electrode active material layer. In this case, the "width direction" may mean a direction perpendicular to the coating direction of the negative electrode active material layer. The "width direction" may be understood as a concept opposite to the "length direction (e.g., the direction of arrow L in Fig. 2)" which is the coating direction of the negative electrode active material layer.

[0027] The inclined portion may be defined on at least one side of the negative electrode active material layer. Specifically, the inclined portion may be defined on one side or both sides of the negative electrode active material layer. In FIG. 1 and FIG. 2, the inclined portions 210a and 210b are shown as being defined on both sides of the negative electrode active material layer, but the present invention is not limited thereto, and the negative electrode active material layer may be defined into one inclined portion and the other flat portion. As shown in FIG. 1, the inclined portions 210a and 210b may have a slope toward the surface of the negative electrode current collector 100. Specifically, the inclined portions 210a and 210b may have a continuous slope toward the surface of the negative electrode current collector 100. The slope of the inclined portions 210a and 210b may be formed, for example, by the fluid properties of the negative electrode slurry when the negative electrode slurry is applied to manufacture the negative electrode active material layer. The inclination of such an inclined portion may cause insufficient insertion of lithium ions migrated from the opposing positive electrode, resulting in problems of reduced charge / discharge efficiency and reduced life characteristics. However, the presence of coating layers 300a and 300b described below prevents such problems, and can achieve the effect of improving the capacity, charge / discharge efficiency, and life characteristics of the negative electrode.

[0028] The inclination angle and width of the inclined portions 210a and 210b may be determined according to, for example, the viscosity of the negative electrode slurry, the application conditions, the drying conditions, etc. for manufacturing the negative electrode active material layer, and are not particularly limited.

[0029] The flat portion 220 may be a region defined by excluding the inclined portions 210a and 210b of the negative electrode active material layer. Specifically, the flat portion 220 may have no substantial inclination or may have a substantially flat surface. The flat portion 220 is merely a concept for distinguishing it from the inclined portions 210a and 210b having an inclination toward the surface of the negative electrode current collector 100, and does not have a completely uniform thickness or height as a whole.

[0030] The negative electrode active material layer 200 may include a negative electrode active material. The negative electrode active material is a material capable of inserting / desorbing lithium, and may include at least one selected from the group consisting of a carbon-based active material and a (semi)metal-based active material.

[0031] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon.

[0032] The (semi)metal-based active material is at least one (semi)metal selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn and lithium; The material may include at least one selected from the group consisting of: a complex of at least one (semi)metal and carbon selected from the group consisting of Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; and an oxide of at least one (semi)metal selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn.

[0033] More specifically, the (semi)metallic active material is SiO x (0≦x<2) and a silicon-carbon composite. The silicon-based active material has excellent capacity, so that the effect of improving the capacity of the negative electrode can be more effectively realized.

[0034] The negative electrode active material layer may include the negative electrode active material in an amount of 60 wt % or more, specifically, 60 wt % to 99 wt %.

[0035] The negative electrode active material layer 200 may include at least one selected from a negative electrode binder, a negative electrode conductive material, and a thickener in addition to the negative electrode active material.

[0036] The negative electrode binder is used to improve the adhesive strength between the negative electrode active material layer and the negative electrode current collector to improve the performance of the battery, and may include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0037] The negative electrode binder may be included in the negative electrode active material layer in an amount of 0.5% by weight to 20% by weight.

[0038] The negative electrode conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and examples of the negative electrode conductive material that can be used include graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0039] The negative electrode conductive material may be contained in the negative electrode active material layer in an amount of 0.5% by weight to 20% by weight. As the thickener, any thickener that has been used in the prior art lithium secondary batteries may be used, and an example thereof is carboxymethyl cellulose (CMC).

[0040] The height or thickness of the negative electrode active material layer based on the surface of the negative electrode current collector may be from 10 μm to 300 μm, preferably from 50 μm to 150 μm.

[0041] The coating layers 300a and 300b may be disposed on at least a portion of the inclined portions 210a and 210b. Specifically, the coating layers 300a and 300b may be disposed on the inclined portions 210a and 210b along the inclined surfaces of the inclined portions 210a and 210b.

[0042] The coating layers 300a and 300b include a negative-type organic active material.

[0043] In this specification, an organic active material may be defined as an organic compound capable of reversible oxidation and reduction reactions. In this case, the electrochemical activity of the organic active material may contribute to the transport of electrons and the stabilization of charges, and a bond, functional group, or conjugated structure having electroactivity may reversibly form a bond with a lithium cation or an anion of the lithium salt contained in the electrolyte. Meanwhile, organic active materials may be classified into N-type organic active materials capable of donating electrons, P-type organic active materials capable of accepting electrons, and B-type organic active materials capable of donating or accepting electrons, depending on their role in oxidation and reduction reactions.

[0044] In this case, the N-type organic active material may form radicals due to elements, functional groups, and / or resonance structures in the compound structure, and convert such radicals into lithium ions (Li + The N-type organic active material can provide radicals to lithium ions (Li + ) to undergo oxidation and reduction reactions, and thus, the lithium ions and the N-type organic active material can form a reversible bond structure. Thus, the coating layer including the N-type organic active material may be capable of inserting and extracting lithium ions through oxidation and reduction reactions.

[0045] The coating layers 300a, 300b are disposed on at least a portion of the inclined portions 210a, 210b of the negative electrode active material layer 200 and contain an N-type organic active material, so that they can easily receive lithium ions from the positive electrode facing the inclined portions 210a, 210b. As a result, the negative electrode according to the present invention can suppress the problem of lithium precipitation that may occur in the absence of a coating layer, the consumption of electrolyte caused by the space between the inclined portions 210a, 210b and the positive electrode facing them, the increase in resistance, and the formation of overvoltage, and can remarkably improve the charge / discharge efficiency and life performance of the negative electrode.

[0046] The coating layers 300a, 300b may be disposed on at least a portion of the inclined portions 210a, 210b of the negative electrode active material layer 200, and more specifically, may be disposed to cover the entire inclined portions 210a, 210b of the negative electrode active material layer 200. Alternatively, the coating layers 300a, 300b may be disposed to cover the entire inclined portions 210a, 210b of the negative electrode active material layer 200 and at least a portion of the uncoated portions 110a, 110b of the negative electrode current collector 100.

[0047] In the present invention, the maximum height (H2) of the coating layers 300a, 300b based on the surface of the negative electrode current collector 100 may be equal to or less than the maximum height (H1) of the negative electrode active material layer. Specifically, the maximum height (H2) of the coating layers based on the surface of the negative electrode current collector may be equal to the maximum height (H1) of the negative electrode active material layer. That is, the maximum distance between the coating layers 300a, 300b formed or disposed on the inclined portions 210a, 210b and the surface of the negative electrode current collector 100 may not exceed the maximum distance between the negative electrode active material layer 200 and the surface of the negative electrode current collector 100. As a result, the overall flatness of the negative electrode may be realized, and the structural stability of the negative electrode may be improved, and lithium may be smoothly inserted and removed between the inclined portions 210a, 210b and the positive electrode facing them.

[0048] At least a portion of the coating layers 300a and 300b may have a flat surface having the same height as the maximum height (H1) of the negative active material layer based on the surface of the negative current collector 100.

[0049] In the present specification, the N-type organic active material may be an organic compound capable of donating a radical to a lithium ion, or a metal salt of the organic compound.

[0050] Specifically, the N-type organic active material may include at least one selected from the group consisting of carbonyl compounds, imine compounds, nitrile compounds, organic sulfur compounds, and azo compounds, and may specifically include a carbonyl compound. The N-type organic active material may be a metal salt of the aforementioned compound, more specifically, a lithium salt of the aforementioned compound. A functional group such as a carbonyl group, an imine group, a nitrile group, sulfur, or an azo group contained in the material; or a conjugated structure connected to the functional group; may provide a radical to the lithium ion, so that the insertion and desorption of the lithium ion through the coating layer may be smoothly performed.

[0051] Specifically, the N-type organic active material may be p-benzoquinone, anthraquinone, dilithium terephthalate, tetralithium salt of 2,5-dihydroxy terephthalate, 7,7,8,8-tetracyanoquinodimethane (TCNQ), phenylazo benzoic acid lithium salt (PBALS), 1,4,5,8-naphthalenetetracarboxylic dianhydride, or the like. The compound may include at least one selected from the group consisting of poly(1,6-dihydropyrazino[2,3g]quinoxaline-2,3,8-triyl-7-(2H)-ylidene-7,8-dimethylidene) (PQL) and poly[chalcogenoviologen-alt-triphenylamine] (the chalcogen element may be tellurium).

[0052] The N-type organic active material may be included in the coating layers 300a and 300b in an amount of 15 wt % to 95 wt %, specifically, 40 wt % to 70 wt %, and more specifically, 50 wt % to 65 wt %, and when included in the above range, it is preferable in that it can sufficiently secure sites for oxidation and reduction reactions with lithium ions and prevent a decrease in electronic conductivity due to an excessive content of the N-type organic active material.

[0053] The coating layers 300a and 300b may further include a binder in addition to the N-type organic active material. The binder may be used to improve adhesion between the coating layer and the negative electrode active material layer or the negative electrode current collector.

[0054] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, and may further include various copolymers thereof.

[0055] The binder may be included in the coating layers 300a and 300b in an amount of 1% by weight to 10% by weight, specifically, 3% by weight to 10% by weight.

[0056] The coating layers 300a and 300b may further include a conductive material to improve conductivity.

[0057] The conductive material is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and examples of the conductive material that can be used include graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0058] The conductive material may be included in the coating layer in an amount of 3% to 80% by weight, specifically, 25% to 55% by weight, and more specifically, 30% to 45% by weight.

[0059] When the coating layer further includes a conductive material, the ratio of the weight of the N-type organic active material to the weight of the conductive material may be 0.5 to 3.5, specifically 0.7 to 2.8, more specifically 1.1 to 2.2. When the ratio is within the above range, it is preferable in that it is possible to realize a coating layer having improved conductivity while sufficiently securing sites for oxidation and reduction reactions with lithium ions.

[0060] Meanwhile, when the coating layer includes a binder and / or a conductive material together with the N-type organic active material, the coating layer may include the binder and / or the conductive material in a weight percentage corresponding to the remaining weight percentage of the N-type organic active material relative to the weight of the coating layer (100 wt% - weight percentage relative to the weight of the coating layer of the N-type organic active material).

[0061] In the present invention, the negative electrode current collector may include uncoated portions 110a, 110b. The uncoated portions 110a, 110b may refer to portions of the negative electrode current collector on which a negative electrode active material layer is not disposed. As shown in Figs. 1 and 2, the coating layers 300a, 300b may be disposed on at least a portion of the surface of the uncoated portions 110a, 110b. Also, the negative electrode active material layer and the coating layer may not be disposed on the surface of the uncoated portions 110a, 110b.

[0062] Specifically, as shown in FIGS. 1 and 2, the negative electrode current collector may include uncoated portions 110a, 110b located on at least one side where the negative electrode active material layer 200 is not disposed, the inclined portions 210a, 210b may be adjacent to the uncoated portions 110a, 110b, and the flat portion 220 may be spaced apart from the uncoated portions 110a, 110b.

[0063] In this specification, "at least one side of the negative electrode current collector" may mean at least one side in the width direction (e.g., the direction of arrow W in FIG. 2) of the negative electrode current collector. In this case, the "width direction" may mean a direction perpendicular to the coating direction of the negative electrode active material layer. The "width direction" may be understood as the opposite concept to the "length direction (e.g., the direction of arrow L in FIG. 2)" which is the coating direction of the negative electrode active material layer.

[0064] The uncoated portion may be located on at least one side of the negative electrode current collector. Specifically, the uncoated portion may be partitioned on one side of the negative electrode current collector or may be located on both sides. In Figs. 1 and 2, the uncoated portions 110a and 110b are shown to be located on both sides of the negative electrode current collector, but are not limited thereto and may be located on only one side of the negative electrode current collector.

[0065] The present invention also provides a method for producing the above-mentioned negative electrode. Specifically, the method for manufacturing a negative electrode of the present invention may include the steps of: applying a negative electrode slurry, including a negative electrode active material and a solvent for forming a negative electrode slurry, onto a negative electrode current collector; and forming a coating layer on a sloped portion of the applied negative electrode slurry.

[0066] The negative electrode slurry may further include at least one selected from a binder and a conductive material, in addition to the negative electrode active material.

[0067] The negative electrode slurry-forming solvent may include at least one selected from the group consisting of N-methylpyrrolidone (NMP), distilled water, ethanol, methanol, and isopropyl alcohol, and preferably distilled water.

[0068] The coating layer may be formed simultaneously with the application of the negative electrode slurry or after the application of the negative electrode slurry.

[0069] When the coating layer is formed after the application of the negative electrode slurry, the coating layer may be formed after the application of the negative electrode slurry and before drying, or after the application of the negative electrode slurry and drying.

[0070] The coating layer may be formed by preparing a coating layer composition by adding the N-type organic active material or the N-type organic active material and the binder to a solvent, and applying the coating layer composition to a sloped portion of the applied negative electrode slurry and drying the coating layer composition.

[0071] The solvent used in the coating layer composition may include, but is not limited to, water, N-methylpyrrolidone (NMP), etc.

[0072] The method of applying the coating layer composition is not particularly limited, and may be spray coating, slot die coating, gravure coating, curtain coating, etc. Meanwhile, the coating layer composition may be formed by a method in which a film is prepared in advance and then the film is transferred to an inclined portion of the applied negative electrode slurry.

[0073] secondary battery The present invention also provides a secondary battery including the above-mentioned negative electrode. The secondary battery may be a lithium secondary battery.

[0074] Specifically, the secondary battery includes the negative electrode; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

[0075] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0076] 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, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used.

[0077] The positive electrode current collector may generally have a thickness of 3 μm to 500 μm. The positive electrode active material layer is formed on the positive electrode current collector and contains a positive electrode active material.

[0078] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2)O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.) can be mentioned, and one or more of these compounds may be included. Among these, in terms of being able to enhance the capacity characteristics and stability of the battery, the lithium composite metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (for example, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (for example, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.).

[0079] The positive electrode active material may be contained at 80% to 99% by weight based on the total weight of the positive electrode active material layer.

[0080] In addition to the above-described positive electrode active material, the positive electrode active material layer may further selectively contain at least one additive selected from the group consisting of a binder and a conductive material.

[0081] The binder is a component that aids in binding between the active material and the conductive material and between the current collector, and is generally added in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0082] The conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and examples of the conductive material include graphite; carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and other carbon-based materials; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black series (products of Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC series (products of Armak Company), Vulcan XC-72 (products of Cabot Company), and Super P (products of Timcal).

[0083] The conductive material may be included in an amount of 1 wt % to 30 wt % based on the total weight of the positive electrode active material layer.

[0084] The positive electrode active material layer may be manufactured by preparing a positive electrode slurry by adding a positive electrode active material and, optionally, an additive including a binder and / or a conductive material to a solvent, and then coating, rolling, and drying the positive electrode slurry on the positive electrode current collector.

[0085] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desired viscosity when the positive electrode active material, and optionally a binder and a conductive material, are included. For example, the solvent may be included so that the concentration of solids including the positive electrode active material, and optionally a binder and a conductive material, is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0086] In the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide a path for lithium ions to move. Any separator that is generally used in lithium secondary batteries may be used without any particular limitations. In particular, a separator that has low resistance to ion movement of the electrolyte and has excellent humidification ability of the electrolyte solution is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting point glass fiber, a polyethylene terephthalate fiber, or the like, may be used. In addition, a coated separator containing a ceramic component or a polymeric material may be used to ensure heat resistance or mechanical strength, and may be selectively used in a single layer or multilayer structure.

[0087] In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0088] The organic solvent may be any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent that may be used include ester-based solvents such as methyl acetate, ethyl acetate, gamma-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; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched, or cyclic hydrocarbon group that may contain a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of enhancing the charge / discharge performance of a battery and a low-viscosity chain carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) is more preferred. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte solution can be excellent.

[0089] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within a range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0090] As described above, the secondary battery according to the present invention is useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs), and can be particularly preferably used as a constituent battery of a medium- to large-sized battery module. Thus, the present invention also provides a medium- to large-sized battery module including the above-described secondary battery as a unit cell.

[0091] Such a medium- to large-sized battery module can be preferably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices.

[0092] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0093] Examples and Comparative Examples Example 1: Preparation of negative electrode A negative electrode slurry was prepared by mixing artificial graphite as a negative electrode active material, acetylene black as a conductive material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a solvent (water) in a weight ratio of 95.35:0.50:3.00:1.15, which was then applied to both sides of a copper current collector (thickness: 8 μm), dried, and rolled to form a negative electrode active material layer. The negative electrode active material layer had a sloped portion at the end due to the fluid properties of the negative electrode slurry.

[0094] Thereafter, a coating layer was formed on the inclined portion of the negative active material layer by preparing a coating layer composition by adding p-benzoquinone as an N-type organic active material, acetylene black as a conductive material, and PVdF as a binder in a weight ratio of 60:35:5 to NMP as a solvent, and then coating the coating layer composition on the inclined portion of the negative active material layer and drying the coating layer composition.

[0095] The cross-sectional coating height (thickness) of the negative active material layer based on the surface of the negative current collector was 62 μm. In addition, the coating layer was formed so as not to exceed the height of the negative active material layer based on the surface of the negative current collector.

[0096] Example 2: Preparation of the negative electrode A negative electrode was prepared in the same manner as in Example 1, except that a coating layer composition was used in which p-benzoquinone was used as an N-type organic active material, acetylene black was used as a conductive material, and PVdF was used as a binder in a weight ratio of 40:55:5 added to NMP.

[0097] Example 3: Preparation of negative electrode A negative electrode was prepared in the same manner as in Example 1, except that a coating layer composition was used, which was prepared by adding p-benzoquinone as an N-type organic active material, acetylene black as a conductive material, and PVdF as a binder to NMP in a weight ratio of 70:25:5.

[0098] Comparative Example 1: Production of negative electrode A negative electrode was prepared in the same manner as in Example 1, except that no coating layer was formed on the inclined portion of the negative electrode active material layer.

[0099] Example 1: Evaluation of thickness profile using rotary calipers The thickness profiles of the negative electrodes prepared in Example 1 and Comparative Example 1 were evaluated using a rotary caliper. Specifically, the thickness profile of the negative electrode was evaluated by measuring the thickness in a contact manner by placing the negative electrode between the rollers of the rotary caliper in the transverse direction of the negative electrode. The results are shown in FIG.

[0100] As shown in FIG. 3, in the case of the negative electrode of Example 1, an additional coating was observed at the end of the negative electrode when compared with the negative electrode of Comparative Example 1, and it was confirmed that a coating layer was formed on the inclined portion of the negative electrode active material layer through this.

[0101] Experimental example 2: Evaluation of life performance <Secondary battery manufacturing> A positive electrode slurry was prepared by adding LiCoO2 as a positive electrode active material, acetylene black as a conductive material, and PVdF as a binder to NMP, a solvent, in a weight ratio of 96.5:1.5:2.0 in N-methylpyrrolidone solvent, and the positive electrode slurry was applied to an aluminum current collector (thickness: 10 μm), dried and rolled to form a positive electrode active material layer (thickness: 105 μm), which was used as a positive electrode.

[0102] An electrode assembly including the negative electrode according to Example 1, a positive electrode facing the negative electrode, and a separator interposed between the positive electrode and the negative electrode was prepared, and the assembly was then housed in a battery case, and the electrolyte was injected and sealed to prepare a secondary battery.

[0103] The electrolyte used at this time was an organic solvent in which ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate were mixed in a weight ratio of 20:10:25:45, to which LiPF6 was added at a molar concentration of 1.2 M.

[0104] Secondary batteries of Examples 2, 3 and Comparative Example 1 were manufactured in the same manner as in Example 1, except that the negative electrodes of Examples 2, 3 and Comparative Example 1 were used, respectively.

[0105] <Evaluation of cycle capacity retention rate> The secondary batteries of the examples and comparative examples prepared above were charged and discharged for 500 cycles at 25° C. under the following conditions to evaluate the capacity retention rate. A graph of the capacity retention rate according to cycles is shown in FIG. 4, and the capacity retention rate at 500 cycles is shown in Table 1 below. *Charging and discharging conditions Charging: CC / CV mode; 2.0C; 4.48V, 0.025C cut-off Discharge: CC mode; 1.0C; 3.0V cut-off

[0106] [Table 1]

[0107] As shown in Table 1, the negative electrodes and secondary batteries of Examples 1 to 3 in which a coating layer containing an N-type organic active material was formed on the inclined portion of the negative electrode active material layer had significantly superior life performance compared to the negative electrode and secondary battery of Comparative Example 1 in which a coating layer containing an N-type organic active material was not formed. [Explanation of symbols]

[0108] 10 negative electrode 100 Negative electrode current collector 110a, 110b Plain area 200 Negative electrode active material layer 210a, 210b Slope section 220 Flat area 300a, 300b coating layers H1: Maximum height of the negative electrode active material layer based on the surface of the negative electrode current collector H2 Maximum height of the coating layer based on the surface of the negative electrode current collector W Width direction L Length direction

Claims

1. Negative electrode current collector; a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material; and a coating layer comprising an N-type organic active material; the negative electrode active material layer includes an inclined portion defined on at least one side thereof and a flat portion defined excluding the inclined portion, the inclined portion has an inclination toward a surface of the negative electrode current collector, The coating layer is disposed on at least a portion of the inclined portion.

2. The negative electrode according to claim 1 , wherein a maximum height of the coating layer is equal to or less than a maximum height of the negative electrode active material layer based on a surface of the negative electrode current collector.

3. The negative electrode according to claim 1 , wherein the inclined portions are defined on both sides in a width direction of the negative electrode active material layer.

4. 2. The negative electrode according to claim 1, wherein the N-type organic active material comprises at least one selected from the group consisting of a carbonyl-based compound, an imine-based compound, a nitrile-based compound, an organic sulfur-based compound, and an azo-based compound.

5. The N-type organic active material is p-benzoquinone, anthraquinone, dilithium terephthalate, tetralithium salt of 2,5-dihydroxyterephthalate, 7,7,8,8-tetracyanoquinodimethane, lithium salt of phenylazobenzoic acid, 1,4,5,8-naphthalenetetracarboxylic dianhydride, polydopamine, phenazine, and poly(1,6-dihydropyrazino[2,3g]quinoxaline-2,3,8-triyl-7-(2H)-ylidene-7,8-diamine).

2. The negative electrode according to claim 1, comprising at least one selected from the group consisting of poly(1,6-dihydropyrazino[2,3g]quinoxaline-2,3,8-triyl-7-(2H)-ylidene-7,8-dimethylidene) and poly[chalcogenoviologen-alt-triphenylamine].

6. The negative electrode according to claim 1 , wherein the negative electrode active material comprises at least one selected from a carbon-based active material and a (semi)metal-based active material.

7. The negative electrode according to claim 6 , wherein the carbon-based active material comprises at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon.

8. The (semi)metallic active material is at least one (semi)metal selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn, and lithium; 7. The negative electrode according to claim 6, comprising at least one selected from the group consisting of: a composite of at least one (semi)metal and carbon selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; and an oxide of at least one (semi)metal selected from the group consisting of Li, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn.

9. The (semi)metallic active material is SiO ｘ 7. The negative electrode of claim 6, comprising at least one silicon-based active material selected from (0≦x<2) and silicon-carbon composites.

10. The negative electrode according to claim 1 , wherein the coating layer comprises 15% to 95% by weight of the N-type organic active material.

11. The negative electrode of claim 1 , wherein the coating layer further comprises a binder.

12. The negative electrode of claim 1 , wherein the coating layer further comprises a conductive material.

13. 13. The anode of claim 12, wherein a ratio of a weight of the N-type organic active material to a weight of the conductive material is from 0.5 to 3.

5.

14. the negative electrode current collector includes a blank portion located on at least one side thereof where the negative electrode active material layer is not disposed, The negative electrode according to claim 1 , wherein the inclined portion is adjacent to the uncoated portion, and the flat portion is spaced apart from the uncoated portion.

15. The negative electrode of claim 1 ; a positive electrode facing the negative electrode; A separator interposed between the negative electrode and the positive electrode; and an electrolyte.

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