Electrode and method for manufacturing the same

Abstract

The present invention discloses an electrode, a method for manufacturing the same, and a lithium secondary battery comprising the same. The electrode comprises: a current collector; and an electrode active material layer arranged on at least one surface of the current collector, wherein the electrode active material layer comprises a lower region facing the current collector and an upper region facing the lower region and extending to the surface of the electrode active material layer, the lower region comprises a first active material and a first non-rubber adhesive and does not contain a rubber adhesive, the upper region comprises a second active material, a second non-rubber adhesive and a rubber adhesive, the rubber adhesive is hydrogenated nitrile rubber (H-NBR), the first non-rubber adhesive and the second non-rubber adhesive each comprise a polyvinylidene fluoride (PVDF)-based polymer, and the weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper region is 1:0.03 to 1:0.07.

Description

Technical Field

[0001] The present invention relates to an electrode with enhanced flexibility and a method for manufacturing the same.

[0002] This application claims priority to Korean Patent Application No. 10-2021-0032998 filed in Korea on March 12, 2021, the disclosure of which is incorporated herein by reference. Background Art

[0003] As the technology development and demand for mobile devices increase, the demand for secondary batteries that are rechargeable, miniaturized and provide high capacity is increasing. In addition, among such secondary batteries, lithium secondary batteries with high energy density and operating voltage have been commercialized and widely used.

[0004] The lithium secondary battery has a structure including an electrode assembly and a lithium salt electrolyte injected into the electrode assembly, wherein the electrode assembly has a positive electrode and a negative electrode each including an active material coated on an electrode current collector, and a porous separator disposed between the two electrodes. The electrode is obtained by applying a slurry including an active material, a binder and a conductive material dispersed in a solvent to the current collector, followed by drying and pressing.

[0005] Generally, a secondary battery comprises a positive electrode, a negative electrode, an electrolyte and a separator. Electrodes such as a positive electrode or a negative electrode are obtained by forming an electrode active material layer comprising an electrode active material on at least one surface of a current collector. Here, in order to ensure the performance of the electrode active material, attempts have been made to apply active materials with small particle sizes, for example, particle sizes of hundreds of nanometers to several micrometers, when preparing the active material.

[0006] However, in the case of an electrode active material having a particle size that is too small, there is a problem of low adhesion to a current collector (e.g., metal foil). In order to solve this problem, a method of coating an electrode active material on a current collector coated with a thin coating layer containing a binder and a conductive material, or a method of manufacturing an electrode with a low weight due to the difficulty in providing an electrode with a high weight per unit area has been proposed.

[0007] In addition, recently, due to rapid technological development and user demands in the digital industry, new products that are different from existing products, such as wearable devices, have been launched.

[0008] Such wearable devices include various types of products, such as glasses, watches / bracelets, shoes / shoe insoles, rings, belts, armbands, necklaces, earmuffs, clothes or badges, etc., depending on the part of the body where they are worn. Batteries suitable for such wearable devices are required to be flexible so that they will not deform after repeated bending. In particular, electrodes applied to such batteries are required to have excellent flexibility. In order to improve the flexibility of such electrodes, attempts have been made to add soft materials as binders for forming electrode active material layers. However, in this case, there are the following problems: the solid content of the slurry for forming the electrode active material layer is reduced, resulting in a decrease in coating productivity, or an undesirable large amount of soft material is added, resulting in an increase in electrode thickness, thereby resulting in a decrease in energy density. Summary of the invention

[0009] Technical issues

[0010] The present invention is designed to solve the problems of the related art, and thus the present invention aims to provide an electrode showing improved adhesion between a current collector and an electrode active material layer and having enhanced flexibility, and a method for manufacturing the same.

[0011] The present invention also aims to provide a lithium secondary battery comprising the electrode.

[0012] Technical Solution

[0013] In one aspect of the present invention, there is provided an electrode according to any one of the following embodiments.

[0014] According to a first embodiment, there is provided an electrode comprising:

[0015] a current collector; and

[0016] an electrode active material layer disposed on at least one surface of the current collector,

[0017] The electrode active material layer includes a lower region facing the current collector and an upper region facing the lower region and extending to the surface of the electrode active material layer.

[0018] The lower region comprises a first active material and a first non-rubber binder and is free of a rubber binder,

[0019] The upper region comprises a second active material, a second non-rubber binder and a rubber binder,

[0020] The rubber adhesive is hydrogenated nitrile rubber (H-NBR),

[0021] The first non-rubber adhesive and the second non-rubber adhesive each comprise a polyvinylidene fluoride (PVDF) based polymer, and

[0022] The weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer region is 1:0.03 to 1:0.07.

[0023] According to a second embodiment, there is provided an electrode as defined in the first embodiment, wherein a weight ratio of the lower layer region to the upper layer region is 1:1 to 1:5.

[0024] According to a third embodiment, there is provided the electrode as defined in the first or second embodiment, which is a positive electrode, wherein the first active material and the second active material each contain a lithium iron phosphate (LFP) compound.

[0025] According to a fourth embodiment, there is provided the electrode as defined in the third embodiment, wherein the average particle size (D50) of the lithium iron phosphate (LFP) compound is 0.8 μm to 2.5 μm.

[0026] According to a fifth embodiment, an electrode as defined in any one of the first to fourth embodiments is provided, wherein the polyvinylidene fluoride (PVDF)-based polymer includes polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-trichloroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, or two or more thereof.

[0027] According to a sixth embodiment, there is provided an electrode as defined in any one of the first to fifth embodiments, wherein a weight ratio of the second non-rubber binder to the rubber binder in the upper layer region is 1:0.04 to 1:0.06.

[0028] According to a seventh embodiment, there is provided a method for manufacturing an electrode as defined in the first embodiment, comprising the following steps:

[0029] preparing a slurry for a lower layer comprising a first active material, a first non-rubber binder, and a first dispersion medium and containing no rubber binder, and a slurry for an upper layer comprising a second active material, a second non-rubber binder, a rubber binder, and a second dispersion medium;

[0030] coating the lower layer slurry on one surface of an electrode current collector, and coating the upper layer slurry on the lower layer slurry simultaneously or at predetermined time intervals; and

[0031] drying the coated lower layer slurry and upper layer slurry simultaneously to form an active material layer,

[0032] Wherein, the rubber adhesive is hydrogenated nitrile rubber (H-NBR), the first non-rubber adhesive and the second non-rubber adhesive each contain a polyvinylidene fluoride (PVDF)-based polymer, and the weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer slurry is 1:0.03 to 1:0.07.

[0033] According to an eighth embodiment, there is provided a method for manufacturing an electrode as defined in the first embodiment, comprising the following steps:

[0034] coating a slurry for a lower layer including a first active material, a first non-rubber binder, and a first dispersion medium and not containing a rubber binder on one surface of an electrode current collector, and then drying to form a lower active material layer; and

[0035] applying an upper layer slurry comprising a second active material, a second non-rubber binder, a rubber binder, and a second dispersion medium on the upper surface of the lower active material layer, and then drying to form an upper active material layer,

[0036] Wherein, the rubber adhesive is hydrogenated nitrile rubber (H-NBR), the first non-rubber adhesive and the second non-rubber adhesive each contain a polyvinylidene fluoride (PVDF)-based polymer, and the weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer slurry is 1:0.03 to 1:0.07.

[0037] According to a ninth embodiment, there is provided a method for manufacturing an electrode as defined in the seventh or eighth embodiment, wherein the electrode is a positive electrode, and the first active material and the second active material each contain a lithium iron phosphate (LFP) compound.

[0038] According to a tenth embodiment, there is provided the method for manufacturing an electrode as defined in the ninth embodiment, wherein an average particle size (D50) of the lithium iron phosphate (LFP) compound is 0.8 μm to 2.5 μm.

[0039] According to an eleventh embodiment, there is provided a lithium secondary battery including the electrode as defined in any one of the first to sixth embodiments as at least one of a positive electrode and a negative electrode.

[0040] Beneficial Effects

[0041] According to one embodiment of the present invention, use and electrolyte wettability high to be able to fully swell and have pliability hydrogenated nitrile rubber as the adhesive of electrode active material layer.In this way, can enhance the flexibility of electrode and make up for the shortcomings that the active material layer and the adhesive force of current collector caused by the content increase of hydrogenated nitrile rubber reduce.In other words, according to one embodiment of the present invention, electrode has double-layer structure, and wherein hydrogenated nitrile rubber is only introduced into the upper layer region of double-layer structure as additional adhesive.Therefore, reduce the amount of hydrogenated nitrile rubber used in electrode, therefore can improve the flexibility of electrode, keep the adhesive force between electrode layer and current collector simultaneously. DETAILED DESCRIPTION

[0042] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Before the description, it should be understood that the terms used in the specification and the appended claims should not be interpreted as limited to the general and dictionary meanings, but are interpreted based on the meanings and concepts corresponding to the technical aspects of the present invention based on the principle of allowing the inventor to appropriately define the terms for the best interpretation.

[0043] In one aspect of the present invention, there is provided an electrode comprising:

[0044] a current collector; and

[0045] an electrode active material layer disposed on at least one surface of the current collector,

[0046] The electrode active material layer includes a lower region facing the current collector and an upper region facing the lower region and extending to the surface of the electrode active material layer.

[0047] The lower region comprises a first active material and a first non-rubber binder and is free of a rubber binder,

[0048] The upper region comprises a second active material, a second non-rubber binder and a rubber binder,

[0049] The rubber adhesive is hydrogenated nitrile rubber (H-NBR),

[0050] The first non-rubber adhesive and the second non-rubber adhesive each comprise a polyvinylidene fluoride (PVDF) based polymer, and

[0051] The weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer region is 1:0.03 to 1:0.07.

[0052] The electrode can be either positive or negative.

[0053] When the electrode is the positive electrode, each of the first active material and the second active material may include any active material particles selected from the group consisting of LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi 1-x-y-z Co x M1 y M2 z O2 (wherein M1 and M2 each independently represent any one selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, x, y, and z each independently represent the atomic ratio of the elements forming the oxide, and 0 ≤ x < 0.5, 0 ≤ y < 0.5, 0 ≤ z < 0.5 and 0 < x + y + z ≤ 1), or a mixture of at least two of them.

[0054] According to an embodiment of the present invention, the electrode may be a positive electrode, and each of the first active material and the second active material may include a lithium iron phosphate (LFP) compound.

[0055] The average particle size (D50) of the lithium iron phosphate (LFP) compound may be 0.8 μm to 2.5 μm, 0.8 μm to 1.2 μm, or 1.8 μm to 2.5 μm.

[0056] Here, the term "average particle size, D50" refers to the particle size at the 50% point in the cumulative particle number distribution depending on the particle size. The particle size D50 can be determined using the laser diffraction method. Specifically, the powder to be analyzed is dispersed in a dispersion medium and introduced into a commercially available laser diffraction particle size analyzer (such as Microtrac S3500), and then the difference in the diffraction pattern depending on the particle size is determined when the particles pass through the laser beam, and then the particle size distribution is calculated. Then, the particle size at the 50% point of the cumulative distribution of the particle number depending on the particle size is calculated to determine D50.

[0057] According to an embodiment of the present invention, the electrode may be a negative electrode, and each of the first active material and the second active material may independently include a carbonaceous material, a silicon-based material (such as silicon oxide represented by SiO x (0 < x < 2)), Si, metal composite oxides such as Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Sn x Me 1-x Me’ y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2 or Group 3 elements in the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni type materials; titanium oxides or lithium titanium oxides, etc.)

[0058] The carbonaceous material may be at least one selected from the group consisting of natural graphite, artificial graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon.

[0059] In the electrode of the present invention, when the first active material contained in the lower layer region and the second active material contained in the upper layer region are different from each other in terms of average particle size and shape, there may be an intermixing region where different kinds of active materials are mixed at the portion where the lower layer region and the upper layer region are in contact. This is because when the lower layer containing the first active material and the upper layer containing the second active material are simultaneously coated with a slurry or continuously coated at a very short time interval and then simultaneously dried to form an electrode active material layer, a certain intermixing zone is generated at the interface where the lower layer slurry and the upper layer slurry are in contact before drying, and then, while drying the lower layer slurry and the upper layer slurry subsequently, the intermixing zone is formed in the layer shape of the intermixing region.

[0060] According to an embodiment of the present invention, the first active material in the lower layer region of the active material layer and the second active material in the upper layer region of the active material layer may be the same or different in terms of physical properties such as average particle size and tapped density.

[0061] According to an embodiment of the present invention, the weight ratio of the first active material in the lower layer region of the active material layer to the second active material in the upper layer region of the active material layer may be 1:1 to 1:5, or 1:2 to 1:3. When the above weight ratio is satisfied, a larger amount of hydrogenated nitrile rubber (H-NBR) can be incorporated into the upper layer region, and thus the electrode can have improved flexibility. In other words, if the total thickness of the electrode is the same, compared with 1:1, the larger the upper layer weight ratio, the more rubber can be incorporated.

[0062] According to an embodiment of the present invention, the thickness ratio of the upper layer region to the lower layer region may be 1:1 to 5:1, or 2:1 to 3:1.

[0063] According to one embodiment of the present invention, the total thickness of the electrode active material layer is not particularly limited. For example, the total thickness of the electrode active material layer may be 40 μm to 200 μm. In addition, in the active material layer, the thickness of the lower region may be 20 μm to 98 μm, or 7 μm to 35 μm, and the thickness of the upper region may be 102 μm to 180 μm, or 33 μm to 165 μm.

[0064] Here, when the thickness ratio of the upper layer region to the lower layer region satisfies the above range, a larger amount of hydrogenated nitrile rubber (H-NBR) can be incorporated into the upper layer region, so the electrode can have improved flexibility. Such a thickness ratio can be calculated based on a weight ratio.

[0065] In the active material layer of the electrode of the present invention, the weight ratio of the lower layer region to the upper layer region (or the ratio of the loading amount per unit area) may be 1:1 to 1:5, or 1:2 to 1:3.

[0066] Here, when the weight ratio of the lower layer region to the upper layer region satisfies the above range, a larger amount of hydrogenated nitrile rubber (H-NBR) may be incorporated into the upper layer region, and thus the electrode may have improved flexibility.

[0067] In the upper layer region, the weight ratio of the second non-rubber adhesive to the rubber adhesive is 1:0.03 to 1:0.07. According to one embodiment of the present invention, the weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer region may be 1:0.04 to 1:0.06.

[0068] When the weight ratio of the second non-rubber binder to the rubber binder in the upper layer region is less than 1:0.03, that is, when the content ratio of the rubber binder is further reduced, the effect of improving the flexibility of the electrode cannot be obtained. When the weight ratio of the second non-rubber binder to the rubber binder in the upper layer region is greater than 1:0.07, that is, when the content of the rubber binder is further increased, due to the high viscosity of the slurry, the slurry cannot be uniformly coated on the current collector, and thus the electrode itself cannot be manufactured.

[0069] The weight ratio of non-rubber binder to rubber binder in the finished battery can be determined by spectroscopic methods. For example, the electrodes can be analyzed by IR and the detected intensity of one binder can be compared to the detected intensity of another binder.

[0070] The rubber adhesive is hydrogenated nitrile rubber (H-NBR). The hydrogenated nitrile rubber includes a repeating unit having an α,β-unsaturated nitrile-derived structure and a repeating unit having a hydrogenated conjugated diene-derived structure.

[0071] Specifically, the hydrogenated nitrile rubber can be prepared by copolymerizing an α,β-unsaturated nitrile and a conjugated diene, optionally with another copolymerizable comonomer, and hydrogenating the C═C double bonds in the resulting copolymer. The polymerization and hydrogenation processes can be carried out in a conventional manner.

[0072] Specific examples of the α,β-unsaturated nitrile include acrylonitrile or methacrylonitrile, and any one of them may be used alone, or a mixture of two or more thereof may be used.

[0073] Specific examples of the conjugated diene include C4-C6 conjugated dienes such as 1,3-butadiene, isoprene, or 2,3-methylbutadiene, and any one of them may be used alone, or a mixture of two or more thereof may be used.

[0074] Specific examples of copolymerizable comonomers that can be optionally used include, but are not limited to, aromatic vinyl monomers (such as styrene, α-methylstyrene, vinylpyridine or fluoroethyl vinyl ether, etc.), α,β-unsaturated carboxylic acids (such as acrylic acid, methacrylic acid, maleic acid or fumaric acid, etc.), esters or amides of α,β-unsaturated carboxylic acids (such as methyl (meth)acrylate, ethyl (meth)acrylate, n-dodecyl (meth)acrylate, methoxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate or polyethylene glycol (meth)acrylate, etc.), and anhydrides of α,β-unsaturated dicarboxylic acids (such as maleic anhydride, itaconic anhydride or citraconic anhydride, etc.).

[0075] In the hydrogenated nitrile rubber obtained by the above method, the weight ratio of repeating units having an α,β-unsaturated nitrile-derived structure, repeating units having a conjugated diene-derived structure, repeating units having a hydrogenated conjugated diene-derived structure and repeating units having an optionally used copolymerizable comonomer-derived structure can vary within a wide range, provided that the sum of the above repeating units is 100 weight %.

[0076] The hydrogenated nitrile rubber may include a repeating unit having an α,β-unsaturated nitrile-derived structure in an amount of about 20 to about 50% by weight, for example about 20 to about 30% by weight, based on the total weight of the hydrogenated nitrile rubber.

[0077] The content of the repeating unit having an α,β-unsaturated nitrile derivative structure in the hydrogenated nitrile rubber is the weight ratio of the repeating unit having an α,β-unsaturated nitrile derivative structure relative to the total weight of the hydrogenated nitrile rubber, and may be an average value of values ​​determined by measuring nitrogen generation by the mill furnace method defined in JIS K6364 and converting its bound content from the molecular weight of acrylonitrile.

[0078] The hydrogenated nitrile rubber may include a repeating unit having a hydrogenated conjugated diene-derived structure in an amount of 20 to 70 wt %, specifically 20 to 50 wt %, more specifically 30 to 50 wt %, based on the total weight of the hydrogenated nitrile rubber. When the content of the repeating unit having a hydrogenated conjugated diene-derived structure satisfies the above range, the active material may have improved dispersibility by increasing miscibility with the dispersion medium.

[0079] The weight average molecular weight of hydrogenated nitrile rubber can be 10,000 to 700,000 g / mol, specifically 10,000 to 200,000 g / mol. In addition, the polydispersity index (PDI) (Mw / Mx ratio, wherein Mw is the weight average molecular weight and Mn is the number average molecular weight) of hydrogenated nitrile rubber can be 2.0 to 6.0, specifically 2.0 to 4.0.

[0080] According to the present invention, the weight average molecular weight and the number average molecular weight are each a molecular weight analyzed by gel permeation chromatography (GPC) using polystyrene as a standard.

[0081] The weight percentage (wt %) of the first non-rubber adhesive in the lower layer region may be equal to or greater than the total weight percentage (wt %) of the second non-rubber adhesive and the rubber adhesive in the upper layer region.

[0082] Specifically, the weight percentage (wt %) of the first non-rubber adhesive in the lower layer region may be 1 to 3 times or 1.5 to 2 times the total weight percentage (wt %) of the second non-rubber adhesive and the rubber adhesive in the upper layer region.

[0083] Here, when the weight percentage of the first binder in the lower layer region and the weight percentage of the second binder in the upper layer region satisfy the above ranges, adhesion between the active material layer and the current collector may be improved.

[0084] According to one embodiment of the present invention, the proportion (weight %) of the first non-rubber binder in the lower layer of the electrode active material layer may be 2 to 4 weight %, or 2.5 to 3.5 weight %, and the total weight percentage (weight %) of the second non-rubber binder and the rubber binder in the upper layer of the electrode active material layer may be 0.5 to 2 weight %, or 1.2 to 1.8 weight %.

[0085] According to one embodiment of the present invention, the total weight percentage (wt %) of the first non-rubber binder, the second non-rubber binder and the rubber binder may be 1 to 4 wt %, or 2.5 to 3.5 wt %, based on the total weight of the electrode active material layer.

[0086] According to one embodiment of the present invention, the electrode current collector used as the substrate for forming the active material layer is not particularly limited as long as it has conductivity and does not cause any chemical changes in the corresponding battery. For example, copper, stainless steel, aluminum, nickel, titanium, roasted carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0087] Although the thickness of the current collector is not particularly limited, its currently used thickness may be 3 to 500 μm.

[0088] The first non-rubber adhesive and the second non-rubber adhesive each include a polyvinylidene fluoride (PVDF) based polymer.

[0089] The polyvinylidene fluoride (PVDF)-based polymer may include polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-trichloroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, or two or more thereof.

[0090] The first non-rubber adhesive and the second non-rubber adhesive contained in the lower layer region and the upper layer region may each independently include one or more of the above-mentioned polyvinylidene fluoride (PVDF)-based polymers.

[0091] In addition to the polyvinylidene fluoride (PVDF)-based polymer, the first non-rubber adhesive and the second non-rubber adhesive can each independently further contain a polymer such as polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene or polyacrylic acid, etc.

[0092] In addition, a portion of the first non-rubber binder and the second non-rubber binder can be used as a thickener capable of increasing the viscosity of the active material layer slurry to improve the dispersibility of the active material. For example, carboxymethyl cellulose (CMC), carboxyethyl cellulose or polyvinyl pyrrolidone can be used as a thickener.

[0093] Optionally, at least one of the lower region and the upper region may further contain a conductive material. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the corresponding battery. Specific examples of the conductive material include: carbon black, such as acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; carbon nanotubes; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum or nickel powders; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0094] In another aspect of the present invention, there is provided a method for manufacturing the electrode as described above, comprising the following steps:

[0095] preparing a slurry for a lower layer comprising a first active material, a first non-rubber binder, and a first dispersion medium and containing no rubber binder, and a slurry for an upper layer comprising a second active material, a second non-rubber binder, a rubber binder, and a second dispersion medium;

[0096] coating the lower layer slurry on one surface of an electrode current collector, and coating the upper layer slurry on the lower layer slurry simultaneously or at predetermined time intervals; and

[0097] The coated lower layer slurry and upper layer slurry are simultaneously dried to form an active material layer,

[0098] The rubber adhesive is hydrogenated nitrile rubber (H-NBR), the first non-rubber adhesive and the second non-rubber adhesive each contain a polyvinylidene fluoride (PVDF)-based polymer, and the weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer slurry is 1:0.03 to 1:0.07.

[0099] The first active material, the second active material, the first non-rubber binder, the second non-rubber binder, and the rubber binder contained in the lower layer slurry and the upper layer slurry are the same as those described above.

[0100] The first dispersion medium and the second dispersion medium may each independently include N-methylpyrrolidone, acetone, water, or the like.

[0101] Here, the lower layer region of the electrode active material layer of the present invention is formed by the coated lower layer slurry, and the upper layer region of the electrode active material layer of the present invention is formed by the coated upper layer slurry.

[0102] In the active material layer of the electrode of the present invention, the thickness of the lower region and the upper region may not be completely the same as the thickness of the coated lower layer slurry and the coated upper layer slurry. However, after the drying process or the optional pressing process, the thickness ratio of the lower region to the upper region of the active material layer in the finished electrode of the present invention may be the same as the thickness ratio of the coated lower layer slurry to the coated upper layer slurry.

[0103] According to one embodiment of the present invention, by using a device such as a double slot die, the lower layer slurry may be applied, and the upper layer slurry may be applied on the lower layer slurry simultaneously or at a predetermined interval.

[0104] The step of simultaneously drying the coated lower layer slurry and upper layer slurry to form an active material layer may be performed by using an oven including a plurality of zones while controlling temperature and air flow conditions.

[0105] Next, the applied first slurry and second slurry were simultaneously dried using a drying device equipped with a hot air dryer and an infrared (IR) heater to form an active material layer.

[0106] According to one embodiment of the present invention, a drying device may include: a drying chamber through which an electrode sheet having a current collector and an electrode active material slurry coated on the current collector passes; a process stage, which is arranged on the lower surface of the electrode sheet to move the electrode sheet in a longitudinal and transverse direction within the drying chamber; a hot air blower, which is configured to supply hot air to the electrode sheet to apply convection heat thereto; and an infrared (IR) dryer, which is configured to apply radiant heat to the electrode sheet.

[0107] In the step of forming the active material layer, the method may further include a step of pressing the active material layer after the drying step. Here, the roll pressing may be performed at a temperature of 15 to 30° C. under a pressure of 1 to 20 MPa.

[0108] In another aspect of the present invention, there is provided a method for manufacturing the electrode as described above, comprising the following steps:

[0109] coating a slurry for a lower layer including a first active material, a first non-rubber binder, and a first dispersion medium and not containing a rubber binder on one surface of an electrode current collector, and then drying to form a lower active material layer; and

[0110] applying an upper layer slurry comprising a second active material, a second non-rubber binder, a rubber binder, and a second dispersion medium on the upper surface of the lower active material layer, and then drying to form an upper active material layer,

[0111] The rubber adhesive is hydrogenated nitrile rubber (H-NBR), the first non-rubber adhesive and the second non-rubber adhesive each contain a polyvinylidene fluoride (PVDF)-based polymer, and the weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer slurry is 1:0.03 to 1:0.07.

[0112] Unlike the method comprising coating the lower layer slurry and the upper layer slurry simultaneously or at a predetermined time interval and simultaneously drying the coated lower layer slurry and the upper layer slurry, the above method comprises coating and drying the lower layer slurry to form a lower active material layer, and then coating and drying the upper layer slurry on the lower active material layer. Then, a pressing step may be performed.

[0113] Here, reference will be made to the above description regarding the coating, drying and pressing steps.

[0114] According to the present invention, the thickness ratio of the coated lower layer slurry to the coated upper layer slurry may be 1:1 to 1:5, or 1:2 to 1:3.

[0115] Here, the thickness of the coated lower layer slurry and the thickness of the coated upper layer slurry can be controlled using a double slot die.

[0116] According to one embodiment of the present invention, the thickness of the coated lower layer slurry may be 20 to 98 μm, or 7 to 35 μm, and the thickness of the coated upper layer slurry may be 102 to 180 μm, or 33 to 165 μm.

[0117] Here, when the thickness ratio of the coated lower layer slurry to the coated upper layer slurry satisfies the above range, a larger amount of hydrogenated nitrile rubber (H-NBR) may be incorporated into the upper layer region, and thus the electrode may have improved flexibility.

[0118] According to the present invention, a weight ratio of the solid content of the coated lower layer slurry to the solid content of the coated upper layer slurry may be 1:1 to 1:5, or 1:2 to 1:3.

[0119] Here, when the weight ratio of the solid content of the coated lower layer slurry to the solid content of the coated upper layer slurry satisfies the above range, a larger amount of hydrogenated nitrile rubber (H-NBR) may be incorporated into the upper layer region, and thus the electrode may have improved flexibility.

[0120] The weight percentage (wt%) of the first binder polymer in the solid content of the lower layer slurry may be equal to or greater than the weight percentage (wt%) of the second binder polymer in the solid content of the upper layer slurry. According to one embodiment of the present invention, the weight percentage (wt%) of the first binder polymer in the solid content of the lower layer slurry may be 1-3 times, or 1.5-2 times, the weight percentage (wt%) of the second binder polymer in the solid content of the upper layer slurry.

[0121] Here, when the ratio of the weight percentage (wt %) of the first binder in the coated lower layer slurry to the weight percentage (wt %) of the second binder in the coated upper layer slurry satisfies the above range, a larger amount of hydrogenated nitrile rubber (H-NBR) can be incorporated into the upper layer region, so that the electrode can have improved flexibility.

[0122] The weight percentage (wt%) of the first binder polymer in the solid content of the lower layer slurry may be 2 to 4 wt%, or 1.5 to 3.5 wt%, and the weight percentage (wt%) of the second binder polymer in the solid content of the upper layer slurry may be 0.5 to 2 wt%, or 1.2 to 1.8 wt%.

[0123] The total content (wt %) of the first binder polymer and the second binder polymer in the total solid content of the slurry for the lower layer and the slurry for the upper layer may be 1 to 4 wt %, or 2.5 to 3.5 wt %.

[0124] In another aspect of the present invention, a lithium secondary battery is provided, which includes the above-mentioned electrode as at least one of a positive electrode and a negative electrode.

[0125] When the lithium secondary battery of one embodiment of the present invention includes the above-mentioned electrode as only one of the positive electrode and the negative electrode, the other electrode, ie, the positive electrode or the negative electrode, may be obtained by using a conventional electrode material such as an active material or a binder, etc.

[0126] In addition, a lithium secondary battery can be obtained by injecting a lithium salt-containing electrolyte into an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the two electrodes.

[0127] Here, the separator can be a conventional porous polymer film conventionally used as a separator. For example, the porous polymer film can be a porous polymer film made of a polyolefin polymer (such as an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene / hexene copolymer or an ethylene / methacrylate copolymer). Such porous polymer films can be used alone or in a laminated form. In addition, an insulating film with high ion permeability and mechanical strength can be used. The separator can include a safety reinforced separator (SRS), which includes a ceramic material coated on the separator surface with a small thickness. In addition, a conventional porous nonwoven web can be used, such as a nonwoven web made of high melting point glass fiber or polyethylene terephthalate fiber, but the scope of the present invention is not limited thereto.

[0128] The electrolyte includes a lithium salt as an electrolyte salt and an organic solvent for dissolving the lithium salt.

[0129] Any lithium salt conventionally used for electrolytes for secondary batteries can be used without particular limitation. For example, the anion of the lithium salt can be selected from F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N -CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - Any of the groups consisting of.

[0130] The organic solvent contained in the electrolyte may be any organic solvent conventionally used without particular limitation. Typical examples of the organic solvent include at least one selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, cyclopentane, γ-butyrolactone, propylene sulfite and tetrahydrofuran.

[0131] Particularly, in carbonate organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonate are organic solvents with high viscosity and high dielectric constant, and therefore can be preferably used, because they can easily dissociate the lithium salt in the electrolyte. When such cyclic carbonate is used after being mixed with the linear carbonate (for example, dimethyl carbonate or diethyl carbonate) with low viscosity and low dielectric constant in an appropriate ratio, it is possible to more preferably prepare an electrolyte with higher conductivity.

[0132] Alternatively, the electrolyte used according to the present invention may further contain additives contained in conventional electrolytes, such as an overcharge preventing agent and the like.

[0133] The lithium secondary battery of one embodiment of the present invention can be obtained by placing a separator between a positive electrode and a negative electrode to form an electrode assembly, introducing the electrode assembly into a bag, a cylindrical battery case or a prismatic battery case, and then injecting an electrolyte therein. In one variant, the lithium secondary battery can be obtained by stacking the electrode assemblies, impregnating the stack with an electrolyte, and introducing the resulting product into a battery case, which is then sealed.

[0134] According to one embodiment of the present invention, the lithium secondary battery may be a stacked, wound, stacked and folded, or cable type battery.

[0135] The lithium secondary battery of the present invention can be used as a battery cell used as a power source for small devices, and can be preferably used as a unit cell of a medium or large battery module containing multiple battery cells. Specific examples of such medium or large devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, or power storage systems. In particular, the lithium secondary battery can be used for batteries for hybrid electric vehicles requiring high output and new renewable energy storage batteries.

[0136] Hereinafter, embodiments will be described more fully so that the present invention can be easily understood. However, the following embodiments can be embodied in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein. On the contrary, these exemplary embodiments are provided so that the present invention will be thorough and complete, and the scope of the present invention will be fully communicated to those skilled in the art.

[0137] Example 1: Fabrication of electrodes and lithium secondary batteries

[0138] <Manufacturing of positive electrode>

[0139] Lithium iron phosphate oxide (average particle size D50: 2 μm) composed of LiFePO4 as the first active material, carbon black as the conductive material, and polyvinylidene fluoride (PVDF) as the first non-rubber binder are added to N-methylpyrrolidone (NMP) as the first dispersion medium in a weight ratio of 94:3:3 and dispersed therein to prepare a slurry for the lower layer.

[0140] Lithium iron phosphate oxide (D50: 1 μm) composed of LiFePO4 as a second active material, carbon black as a conductive material, polyvinylidene fluoride (PVDF) as a second non-rubber binder, and hydrogenated nitrile rubber (H-NBR) as a rubber binder were added to N-methylpyrrolidone (NMP) as a second dispersion medium at a weight ratio of 94:3:3:0.09 to prepare an upper layer slurry. In other words, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer slurry was 1:0.03.

[0141] Using a double slot die, the lower layer slurry was coated on one surface of an aluminum (Al) foil (thickness: 10 μm) as a positive electrode current collector, and the upper layer slurry was coated on the lower layer slurry. Here, the loading amounts of the lower layer slurry and the upper layer slurry were 300 mg / cm 2 and 300mg / cm 2 .

[0142] Then, the coated first slurry and the coated second slurry were simultaneously dried using a drying system equipped with a hot air blower and an IR heater to form an active material layer.

[0143] Specifically, the drying chamber of the drying system has ten drying zones from the first drying zone to the tenth drying zone, in which the slurry-coated current collector is first introduced into the drying system. From the first drying zone to the third drying zone, 8 hot air dryers are provided and an IR heater is provided between two adjacent hot air dryers, so that a total of 8 IR heaters are provided. In addition, from the fourth drying zone to the sixth drying zone, the hot air flow of the hot air dryer is controlled so that it can flow from the top to the bottom. In addition, from the seventh drying zone to the tenth drying zone, the hot air dryer in which the hot air flow flows from the top to the bottom and the hot air dryer in which the hot air flow flows from the bottom to the top are alternately arranged.

[0144] In the drying system, a process rack is set on the lower surface of the slurry-coated current collector (electrode sheet) to transport the slurry-coated current collector, wherein the slurry-coated current collector is transported at a rate of 50 m / min. The air supply fan for forming the supply air flow from the outside of the drying system is operated at a rate of 1000 rpm, and the exhaust fan for forming the exhaust air flow from the inside of the drying chamber is operated at a rate of 1000 rpm. The temperature of the hot air dryer in each drying zone is as follows: 140°C in the first drying zone, 130°C in the second drying zone, 120°C in the third to eighth drying zones, 90°C in the ninth drying zone, and 50°C in the tenth drying zone.

[0145] Since the IR heaters installed in the first to third drying zones emit near infrared rays having a wavelength of 0.7 μm, and the irradiation length of the IR heaters is 30 cm per heater (the length from the lamp irradiating the near infrared rays of the IR heaters is 30 cm), 24 IR heaters are arranged at constant intervals throughout the three drying zones (24 IR heaters are arranged in the three drying zones, 8 IR heaters in each drying zone). Here, only 3 IR heaters are used among the total 24 IR heaters while maintaining a constant interval. In other words, the IR heaters operate at an efficiency of 12.5% ​​based on the efficiency obtained when all IR heaters are used.

[0146] The upper and lower active material layers thus formed were pressed by roller pressing to obtain a layer having a loading amount per unit area of ​​16 mg / cm after drying. 2 The positive electrode has an upper / lower double-layer structure of active material layers.

[0147] Here, the thickness of the lower layer was 55 μm, the thickness of the upper layer was 55 μm, and the weight ratio of the lower layer region to the upper layer region was 1: 1. The weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer region was 1:0.03.

[0148] <Manufacturing of negative electrode>

[0149] First, 30.0 parts by weight of natural graphite with an average sphericity of 0.95 as a negative electrode active material, 63.8 parts by weight of artificial graphite with an average sphericity of 0.9, 1 part by weight of carbon black as a conductive material, 3.7 parts by weight of styrene-butadiene rubber (SBR) as a binder, and 1.5 parts by weight of carboxymethyl cellulose (CMC) as a binder which also acts as a thickener are mixed with water as a dispersion medium to prepare a slurry with a solid content of 46% by weight.

[0150] The slurry was coated on one surface of a copper (Cu) foil (thickness: 10 μm) as a negative electrode current collector, and dried and pressed under the same conditions as the positive electrode to obtain a negative electrode. Here, the loading amount was 11 mg / cm based on the dry weight of the negative electrode active material layer. 2 , and the thickness of the negative electrode is 80 μm.

[0151] <Manufacturing of lithium secondary batteries>

[0152] The nonaqueous electrolyte was prepared by dissolving LiPF 6 in an organic solvent including ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) mixed in a volume ratio of 3:3:4 to a concentration of 1.0 M.

[0153] A porous polypropylene separator was interposed between the positive electrode and the negative electrode obtained as described above, and an electrolyte was injected therein to obtain a lithium secondary battery.

[0154] Example 2: Production of positive electrode and lithium secondary battery

[0155] The positive electrode was obtained in the same manner as in Example 1, except that lithium iron phosphate oxide (average particle size D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as the conductive material, polyvinylidene fluoride (PVDF) as the second non-rubber binder, and hydrogenated nitrile rubber (H-NBR) as the rubber binder were added to N-methylpyrrolidone (NMP) as the second dispersion medium in a weight ratio of 94:3:3:0.15 to prepare an upper layer slurry. Here, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer region of the positive electrode was 1:0.05.

[0156] A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode obtained as described above was used.

[0157] Example 3: Production of positive electrode and lithium secondary battery

[0158] The positive electrode was obtained in the same manner as in Example 1, except that a lithium iron phosphate oxide (average particle size D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as the conductive material, polyvinylidene fluoride (PVDF) as the second non-rubber binder, and hydrogenated nitrile rubber (H-NBR) as the rubber binder were added to N-methylpyrrolidone (NMP) as the second dispersion medium in a weight ratio of 94:3:3:0.21 to prepare an upper layer slurry. Here, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer region of the positive electrode was 1:0.07.

[0159] A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode obtained as described above was used.

[0160] Comparative Example 1: Production of positive electrode and lithium secondary battery

[0161] The positive electrode was obtained in the same manner as in Example 1, except that lithium iron phosphate oxide (average particle size D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as the conductive material, and polyvinylidene fluoride (PVDF) as the second non-rubber binder were added to N-methylpyrrolidone (NMP) as the second dispersion medium in a weight ratio of 94:3:3 to prepare an upper layer slurry. Here, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer region of the positive electrode was 1:0.

[0162] A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode obtained as described above was used.

[0163] Comparative Example 2: Production of positive electrode and lithium secondary battery

[0164] The positive electrode was obtained in the same manner as in Example 1, except that a lithium iron phosphate oxide (average particle size D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as the conductive material, polyvinylidene fluoride (PVDF) as the second non-rubber binder, and hydrogenated nitrile rubber (H-NBR) as the rubber binder were added to N-methylpyrrolidone (NMP) as the second dispersion medium in a weight ratio of 94:3:3:0.03 to prepare an upper layer slurry. Here, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer region of the positive electrode was 1:0.01.

[0165] A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode obtained as described above was used.

[0166] Comparative Example 3: Production of positive electrode and lithium secondary battery

[0167] An attempt was made to obtain a positive electrode in the same manner as in Example 1, except that a lithium iron phosphate oxide (average particle size D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as a conductive material, polyvinylidene fluoride (PVDF) as a second non-rubber binder, and hydrogenated nitrile rubber (H-NBR) as a rubber binder were added to N-methylpyrrolidone (NMP) as a second dispersion medium in a weight ratio of 94:3:3:0.3 to prepare a slurry for the upper layer. However, the viscosity of the slurry was too high, making it difficult to evenly apply the slurry to the current collector. Therefore, a positive electrode could not be obtained.

[0168] Here, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer region of the positive electrode was 1:0.1.

[0169] Comparative Example 4: Production of positive electrode and lithium secondary battery

[0170] Lithium iron phosphate oxide (average particle size D50: 2 μm) composed of LiFePO4 as the first active material, carbon black as the conductive material, polyvinylidene fluoride (PVDF) as the first non-rubber binder, and hydrogenated nitrile rubber as the rubber binder were added to N-methylpyrrolidone (NMP) as the first dispersion medium at a weight ratio of 94:3:3:0.15 and dispersed therein to prepare a slurry for the lower layer. In other words, the weight ratio of the first non-rubber binder to the rubber binder in the slurry for the lower layer was 1:0.05.

[0171] Lithium iron phosphate oxide (D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as the conductive material, polyvinylidene fluoride (PVDF) as the second non-rubber binder, and hydrogenated nitrile rubber (H-NBR) as the rubber binder were added to N-methylpyrrolidone (NMP) as the second dispersion medium at a weight ratio of 94:3:3:0.15 to prepare the upper layer slurry. In other words, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer slurry was 1:0.05.

[0172] A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode was manufactured using the slurry for the lower layer and the slurry for the upper layer prepared as described above.

[0173] Comparative Example 5: Production of positive electrode and lithium secondary battery

[0174] Lithium iron phosphate oxide (average particle size D50: 2 μm) composed of LiFePO4 as the first active material, carbon black as the conductive material, polyvinylidene fluoride (PVDF) as the first non-rubber binder, and hydrogenated nitrile rubber as the rubber binder were added to N-methylpyrrolidone (NMP) as the first dispersion medium at a weight ratio of 94:3:3:0.15 and dispersed therein to prepare a slurry for the lower layer. In other words, the weight ratio of the first non-rubber binder to the rubber binder in the slurry for the lower layer was 1:0.05.

[0175] Lithium iron phosphate oxide (D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as the conductive material, and polyvinylidene fluoride (PVDF) as the second non-rubber binder were added to N-methylpyrrolidone (NMP) as the second dispersion medium at a weight ratio of 94:3:3 to prepare the upper layer slurry. In other words, no hydrogenated nitrile rubber was added to the upper layer slurry.

[0176] A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode was manufactured using the slurry for the lower layer and the slurry for the upper layer prepared as described above.

[0177] Example 4: Production of positive electrode and lithium secondary battery

[0178] The positive electrode was obtained in the same manner as in Example 1, except that lithium iron phosphate oxide (D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as the conductive material, polyvinylidene fluoride (PVDF) as the second non-rubber binder, and hydrogenated nitrile rubber (H-NBR) as the rubber binder were added to N-methylpyrrolidone (NMP) as the second dispersion medium at a weight ratio of 94:3:3:0.15 to prepare the upper layer slurry, and the thickness of the lower layer region was 37 μm, the thickness of the upper layer region was 73 μm, and the weight ratio of the lower layer region to the upper layer region was 1:2. Here, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer slurry of the positive electrode was 1:0.05.

[0179] A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode obtained as described above was used.

[0180] Example 5: Production of positive electrode and lithium secondary battery

[0181] The positive electrode was obtained in the same manner as in Example 1, except that lithium iron phosphate oxide (D50: 1 μm) composed of LiFePO4 as the second active material, carbon black as the conductive material, polyvinylidene fluoride (PVDF) as the second non-rubber binder, and hydrogenated nitrile rubber (H-NBR) as the rubber binder were added to N-methylpyrrolidone (NMP) as the second dispersion medium at a weight ratio of 94:3:3:0.15 to prepare the upper layer slurry, and the thickness of the lower layer region was 18 μm, the thickness of the upper layer region was 92 μm, and the weight ratio of the lower layer region to the upper layer region was 1:5. Here, the weight ratio of the second non-rubber binder to the rubber binder in the upper layer slurry of the positive electrode was 1:0.05.

[0182] A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode obtained as described above was used.

[0183] Electrode bending test

[0184] Each of the positive electrodes of Examples 1 to 5 and Comparative Examples 1 to 3 was cut into a size of 5 cm in width×10 cm in length to prepare a sample.

[0185] The prepared sample was used to surround a rod to determine whether cracks were generated on the active material layer of the positive electrode. The test was conducted while changing the rod diameter. The diameter of the rod in which cracks were generated on the active material layer is shown in Table 1 below. Here, cracks can be found by observing fine splitting phenomena in the active material layer.

[0186] The smaller the diameter of the rods generating cracks in the active material layer, the higher the flexibility of the electrode.

[0187] [Table 1]

[0188]

[0189] Referring to Table 1, in the case of Examples 1 to 5 of the present invention satisfying a weight ratio of the second non-rubber binder to the rubber binder in the upper layer region of 1:0.03 to 1:0.07, the diameter of the rods generating cracks in the active material layer was smaller, indicating that the electrode showed significantly improved flexibility.

[0190] Electrode adhesion test

[0191] Each of the positive electrodes of Example 2 and Comparative Examples 4 and 5 was cut into a size of 20 mm in width×200 mm in length to prepare a sample.

[0192] The sample was fixed on a glass slide so that the active material layer of the sample could contact the glass slide, and the force required to peel the current collector from the active material layer was measured while peeling the current collector at a rate of 100 mm / min using a UTM instrument (available from TA). The results are shown in Table 2 below. Here, the peeling force was measured at an angle of 90° between the glass slide and the electrode.

[0193] [Table 2]

[0194] Electrode adhesion (gf / 20mm) Example 2 50 Comparative Example 4 16 Comparative Example 5 18

[0195] Referring to Table 2, the electrode of Example 2, which includes a rubber binder according to one embodiment of the present invention so that the weight ratio of the second non-rubber binder to the rubber binder in the upper layer region may satisfy 1:0.03 to 1:0.07 and does not include a rubber binder in the lower layer region, shows significantly improved electrode adhesion. In particular, it can be seen that Comparative Examples 4 and 5, which include a rubber binder in the lower layer region, show significantly low electrode adhesion.

Claims

1. An electrode, comprising: current collector; as well as an electrode active material layer disposed on at least one surface of the current collector, The electrode active material layer includes a lower region facing the current collector and an upper region facing the lower region and extending to the surface of the electrode active material layer. The lower region comprises a first active material and a first non-rubber binder and is free of a rubber binder, The upper region comprises a second active material, a second non-rubber binder and a rubber binder, The rubber adhesive is hydrogenated nitrile rubber (H-NBR), The first non-rubber adhesive and the second non-rubber adhesive each comprise a polyvinylidene fluoride (PVDF) based polymer, and The weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer region is 1:0.03 to 1:0.

07.

2. The electrode according to claim 1, wherein The weight ratio of the lower layer region to the upper layer region is 1:1 to 1:

5.

3. The electrode according to claim 1, which is a positive electrode, wherein The first active material and the second active material each include a lithium iron phosphate (LFP) compound.

4. The electrode according to claim 3, wherein The average particle size D50 of the lithium iron phosphate (LFP) compound is 0.8 μm to 2.5 μm.

5. The electrode according to claim 1, wherein The polyvinylidene fluoride (PVDF)-based polymer includes polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-trichloroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, or two or more thereof.

6. The electrode according to claim 1, wherein The weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer region is 1:0.04 to 1:0.

06.

7. A method for manufacturing the electrode according to claim 1, comprising the following steps: preparing a slurry for a lower layer comprising a first active material, a first non-rubber binder, and a first dispersion medium and containing no rubber binder, and a slurry for an upper layer comprising a second active material, a second non-rubber binder, a rubber binder, and a second dispersion medium; coating the lower layer slurry on one surface of an electrode current collector, and coating the upper layer slurry on the lower layer slurry simultaneously or at predetermined time intervals; and drying the coated lower layer slurry and upper layer slurry simultaneously to form an active material layer, wherein the rubber adhesive is hydrogenated nitrile rubber (H-NBR), the first non-rubber adhesive and the second non-rubber adhesive each contain a polyvinylidene fluoride (PVDF)-based polymer, and the weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer slurry is 1:0.03 to 1:0.

07.

8. A method for manufacturing the electrode according to claim 1, comprising the following steps: coating a slurry for a lower layer including a first active material, a first non-rubber binder, and a first dispersion medium and not containing a rubber binder on one surface of an electrode current collector, and then drying to form a lower active material layer; as well as applying an upper layer slurry comprising a second active material, a second non-rubber binder, a rubber binder, and a second dispersion medium on the upper surface of the lower active material layer, and then drying to form an upper active material layer, wherein the rubber adhesive is hydrogenated nitrile rubber (H-NBR), the first non-rubber adhesive and the second non-rubber adhesive each contain a polyvinylidene fluoride (PVDF)-based polymer, and the weight ratio of the second non-rubber adhesive to the rubber adhesive in the upper layer slurry is 1:0.03 to 1:0.

07.

9. The method for manufacturing an electrode according to claim 7 or 8, wherein: The electrode is a positive electrode, and the first active material and the second active material each include a lithium iron phosphate (LFP) compound.

10. The method for manufacturing an electrode according to claim 9, wherein: The average particle size D50 of the lithium iron phosphate (LFP) compound is 0.8 μm to 2.5 μm. 11 . A lithium secondary battery comprising the electrode according to claim 1 as at least one of a positive electrode and a negative electrode.

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