Electrode for secondary battery, method for manufacturing same, and lithium secondary battery including same

Abstract

An electrode for a secondary battery according to one embodiment of the present invention comprises an electrode current collector, an electrode mixture layer on at least one surface of the electrode current collector, and an insulating layer, in which the insulating layer contains a copolymer containing a repeating unit having an imide group and a rubber-based repeating unit. According to one embodiment of the present invention, it is possible to improve safety by suppressing the occurrence of fire in a lithium secondary battery.

Description

Technical Field

[0001] The present invention relates to an electrode for a secondary battery, a method for manufacturing the electrode, and a lithium secondary battery including the electrode. Background Art

[0002] In recent years, extensive research has been conducted on electric vehicles (EVs) as an alternative to vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. As a power source for such electric vehicles (EVs), lithium secondary batteries with high discharge voltage and power stability are mainly used.

[0003] During the driving process of the lithium secondary battery, safety problems may occur due to a short circuit inside the secondary battery. Such a short circuit phenomenon may occur due to direct contact between the electrodes of the secondary battery, and when the short circuit state continues, a fire inside the secondary battery may be caused.

[0004] Therefore, there is a need to develop a technology that can suppress the occurrence of problems such as short circuits inside the secondary battery and fires caused thereby. Summary of the Invention

[0005] (I) Technical Problems to be Solved

[0006] According to one aspect of the present invention, low voltage defects occurring due to short circuits between electrodes in a lithium secondary battery can be suppressed.

[0007] According to another aspect of the present invention, the occurrence of fires in a lithium secondary battery can be suppressed.

[0008] According to another aspect of the present invention, breakage of electrodes during the manufacturing process of an electrode for a lithium secondary battery can be suppressed.

[0009] According to another aspect of the present invention, the manufacturability of an electrode for a lithium secondary battery can be improved.

[0010] (II) Technical Solutions

[0011] An electrode for a lithium secondary battery according to a specific embodiment of the present invention includes an electrode current collector, an electrode mixture layer on at least one surface of the electrode current collector, and an insulating layer, wherein the insulating layer contains a copolymer, and the copolymer contains a repeating unit having an imide group and a rubber-based repeating unit.

[0012] In some specific embodiments, the imide group may be represented by the following Chemical Formula 1.

[0013] [Chemical Formula 1]

[0014]

[0015] In the Chemical Formula 1, R 1 , R 2 and R 3 are each independently hydrogen or an organic group.

[0016] In some specific embodiments, the repeating unit having an imide group may further contain an amide group.

[0017] In some specific embodiments, the amide group may be represented by the following Chemical Formula 2.

[0018] [Chemical Formula 2]

[0019]

[0020] In the Chemical Formula 2, R, R' and R'' are each independently hydrogen or an organic group.

[0021] In some specific embodiments, the repeating unit having an imide group may contain a repeating unit constituting polyamideimide (PAI). In some specific embodiments, the rubber-based repeating unit may contain at least one of a styrene-butadiene rubber (SBR)-based repeating unit, a butadiene rubber (BR)-based repeating unit, a hydrogenated nitrile rubber (HNBR)-based repeating unit, a nitrile rubber (NBR)-based repeating unit, an acrylic rubber-based repeating unit, a butyl rubber-based repeating unit, and a fluororubber-based repeating unit.

[0022] In some specific embodiments, the copolymer may contain a graft copolymer, and a second block containing a rubber-based repeating unit in the graft copolymer is grafted onto a first block containing a repeating unit having an imide group.

[0023] In some specific embodiments, the first block may contain a repeating unit having an imide group and an amide group, and the second block may contain a hydrogenated nitrile rubber (HNBR)-based repeating unit.

[0024] In some specific embodiments, in the graft copolymer, based on the total weight of the graft copolymer, the content of the first block may be 50-95% by weight.

[0025] In some specific embodiments, in the graft copolymer, based on the total weight of the graft copolymer, the content of the second block may be 5-50% by weight.

[0026] In some specific embodiments, the insulating layer may further contain a ceramic material.

[0027] In some specific embodiments, the electrode current collector may include an uncoated portion on the electrode current collector where no electrode mixture layer is provided.

[0028] In some specific embodiments, the insulating layer may cover a part of the uncoated portion and a part of the electrode mixture layer.

[0029] In some specific embodiments, the insulating layer may be provided on the uncoated portion.

[0030] A method for manufacturing an electrode for a lithium secondary battery according to a specific embodiment of the present invention includes the steps of forming an electrode mixture layer and an insulating layer on at least one surface of an electrode current collector, wherein the insulating layer contains a copolymer, and the copolymer contains a repeating unit having an imide group and a rubber-based repeating unit.

[0031] A lithium secondary battery according to a specific embodiment of the present invention includes an electrode for a lithium secondary battery according to any one of the above specific embodiments.

[0032] (III) Beneficial effects

[0033] According to a specific embodiment of the present invention, the occurrence of low-voltage defects in a lithium secondary battery can be suppressed.

[0034] According to another specific embodiment of the present invention, the occurrence of fire in a lithium secondary battery can be suppressed, thereby improving safety.

[0035] According to another specific embodiment of the present invention, quality defects can be prevented from occurring when manufacturing an electrode for a lithium secondary battery.

[0036] According to another specific embodiment of the present invention, the yield of the manufacturing process of an electrode for a lithium secondary battery can be improved. Description of the drawings

[0037] Figure 1 is a schematic cross-sectional view showing an electrode for a secondary battery according to a specific embodiment.

[0038] Figure 2 is a schematic cross-sectional view showing an electrode for a secondary battery according to another specific embodiment.

[0039] Figure 3 is schematically shown as viewed from above Figure 1 the morphology of the electrode for a secondary battery shown in a plan view.

[0040] Description of reference numerals

[0041] 10: Electrode current collector

[0042] 20: Electrode mixture layer

[0043] 30: Insulating layer

[0044] 100: Electrode for lithium secondary battery

[0045] A: Overlapping region Detailed implementation manners

[0046] Hereinafter, with reference to the accompanying drawings, the technologies disclosed in this specification and their specific implementation manners will be described in detail. However, the implementation manners of the above technologies can be modified into various other schemes, and their scope is not limited to the specific implementation manners described below. In addition, the technologies disclosed in this specification can be applied not only limited to the configurations of the specific implementation manners described below, but also various modifications can be achieved by selectively combining all or part of the specific implementation manners.

[0047] As described above, it is necessary to develop a technology capable of suppressing internal short circuits occurring in the lithium secondary battery. According to a specific implementation manner, by coating an insulating layer on the uncoated portion of the electrode current collector where the electrode mixture layer is not provided, short circuits between electrodes can be prevented. Exemplarily, when an insulating layer is coated on the uncoated portion of the positive electrode current collector, even if the uncoated portion comes into contact with the negative electrode, short circuits can be prevented from occurring.

[0048] In addition, when an insulating layer is coated on the uncoated portion of the electrode current collector, due to the differences in the characteristics of the substances contained in the electrode mixture layer, the electrode current collector, and the insulating layer, differences in elongation may occur during electrode rolling. Therefore, a foil curl phenomenon in which the uncoated portion bends may occur at the interface between the electrode mixture layer and the uncoated portion of the electrode current collector. When the foil curl phenomenon occurs, various quality defects may occur in the subsequent manufacturing process of the secondary battery.

[0049] Exemplarily, in the rolling or notching process of the electrode, stress accumulates at the interface between the uncoated portion and the insulating layer, so that the electrode may break or the interface may tear, and problems such as the formation of wrinkles in the tab portion may occur in the welding process. When the insulating layer contains both a ceramic material and a polymer binder, these phenomena may be further aggravated due to the differences in the compositions of the ceramic and the polymer.

[0050] According to a specific implementation manner of the present invention, the above problems can be alleviated. Hereinafter, with reference to Figures 1 to 3 , the specific implementation manners of the present invention will be specifically described.

[0051] Figure 1 is a cross-sectional view schematically showing an electrode for a secondary battery according to a specific implementation manner.

[0052] Figure 2It is a cross-sectional view schematically showing an electrode for a secondary battery according to another specific embodiment.

[0053] Figure 3 It is schematically shown when viewed from above Figure 1 A plan view of the form of the electrode for a secondary battery shown.

[0054] Electrode for a lithium secondary battery

[0055] The electrode 100 for a lithium secondary battery according to one specific embodiment includes an electrode current collector 10, an electrode mixture layer 20 on at least one surface of the electrode current collector, and an insulating layer 30. Among them, the insulating layer 30 contains a copolymer, and the copolymer contains a repeating unit having an imide group and a rubber-based repeating unit.

[0056] The insulating layer 30 contains a copolymer, and the copolymer contains a repeating unit having an imide group and a rubber-based repeating unit. Therefore, it has excellent insulating properties and heat resistance, and has excellent peeling resistance in the electrolyte, and has improved softness, so that it can have an increased elongation rate. Therefore, it is possible to prevent a decrease in quality due to electrode breakage phenomena or the like in subsequent manufacturing processes of secondary batteries.

[0057] The repeating unit having an imide group may contain an imide group, and can impart insulation to the copolymer and the insulating layer 30 containing the repeating unit having an imide group. In this specification, the imide group may be a functional group composed of two acyl groups bonded to nitrogen. Exemplarily, the imide group may be represented by the following Chemical Formula 1.

[0058] [Chemical Formula 1]

[0059]

[0060] In the Chemical Formula 1, R 1 , R 2 and R 3 are each independently hydrogen or an organic group.

[0061] In some specific embodiments, the repeating unit having an imide group may further have an amide group. In this specification, the amide group may be a functional group composed of a carbonyl group bonded to nitrogen. Exemplarily, the amide group may be a functional group represented by the following Chemical Formula 2.

[0062] [Chemical Formula 2]

[0063]

[0064] In Chemical Formula 2, R, R', and R'' are each independently hydrogen or an organic group.

[0065] In some specific embodiments, the repeating unit having an imide group may include a repeating unit constituting polyamideimide (PAI) (hereinafter, a repeating unit derived from polyamideimide). The insulating layer 30 includes a repeating unit containing an imide group and an amide group, so that the peel resistance in the electrolyte can be further improved, and the elongation at break can be increased, thereby suppressing tearing at the interface in the calendering / cutting process of the electrode.

[0066] In addition to the repeating unit having an imide group described above, the copolymer further includes a rubber-based repeating unit. The rubber-based repeating unit includes a rubber-based repeating unit having flexibility, so that the copolymer containing the rubber-based repeating unit can be given flexibility. When the copolymer contained in the insulating layer 30 includes a rubber-based repeating unit, the elongation at break of the insulating layer 30 can be further improved.

[0067] The rubber-based repeating unit is not particularly limited. Exemplarily, the rubber-based repeating unit may include at least one of a styrene-butadiene rubber (SBR)-based repeating unit, a butadiene rubber (BR)-based repeating unit, a hydrogenated nitrile rubber (HNBR)-based repeating unit, a nitrile rubber (NBR)-based repeating unit, an acrylic rubber-based repeating unit, a butyl rubber-based repeating unit, and a fluororubber-based repeating unit. Specifically, the rubber-based repeating unit may be a hydrogenated nitrile rubber (HNBR)-based repeating unit.

[0068] In some specific embodiments, the copolymer may be a block copolymer or a graft copolymer including a first block and a second block. Specifically, the copolymer may be a graft copolymer in which the second block is grafted onto the first block.

[0069] In some specific embodiments, the first block may include the repeating unit having an imide group described above, and the second block may include the rubber-based repeating unit described above. Specifically, the copolymer may include a graft copolymer in which the second block containing the rubber-based repeating unit is grafted onto the first block containing the repeating unit having an imide group.

[0070] In some specific embodiments, the first block may be composed of a repeating unit constituting polyamideimide, and the second block may be composed of a rubber-based repeating unit.

[0071] In some specific embodiments, the first block may include a repeating unit having an imide group and an amide group, and the second block may include a hydrogenated nitrile rubber (HNBR)-based repeating unit.

[0072] In some specific embodiments, the copolymer may comprise a graft copolymer, in which a polymer composed of rubber-based repeating units is grafted onto a polymer composed of repeating units having imide groups. Exemplarily, the graft copolymer may comprise polyamideimide (PAI) grafted with hydrogenated nitrile rubber (HNBR).

[0073] In some specific embodiments, in the graft copolymer, based on the total weight of the graft copolymer, the content of the first block may be 50-95% by weight. Exemplarily, in the graft copolymer, based on the total weight of the graft copolymer, the content of the first block may be 55-90% by weight, 60-85% by weight, 65-75% by weight, 70-85% by weight or 80-90% by weight. Specifically, in the graft copolymer, based on the total weight of the graft copolymer, the content of the first block may be 70% by weight or more or 80% by weight or more, and may be 90% by weight or less or 85% by weight or less.

[0074] When the grafting ratio of the first block is too low, swelling of the insulating layer 30 is likely to occur, which may cause the insulating layer to peel off in the electrolyte. On the other hand, when the grafting ratio of the first block is too high, the improvement rate of the flexibility of the insulating layer 30 may be insufficient.

[0075] In some specific embodiments, in the graft copolymer, based on the total weight of the graft copolymer, the content of the second block may be 5-50% by weight. Exemplarily, in the graft copolymer, based on the total weight of the graft copolymer, the content of the second block may be 10-45% by weight, 15-40% by weight, 25-35% by weight, 15-30% by weight or 10-20% by weight. Specifically, in the graft copolymer, based on the total weight of the graft copolymer, the content of the second block may be 10% by weight or more or 15% by weight or more, and may be 30% by weight or less or 20% by weight or less.

[0076] When the grafting ratio of the second block is too low, the improvement rate of the flexibility of the insulating layer 30 may be insufficient. On the other hand, when the grafting ratio of the second block is too high, the flexibility of the insulating layer 30 is excellent, but swelling is likely to occur, which may cause the insulating layer to peel off in the electrolyte.

[0077] In some specific embodiments, in the graft copolymer, the weight ratio of the first block to the second block may be 50:50 to 95:5, 55:45 to 90:10, 60:40 to 85:15, 65:35 to 75:25, 70:30 to 85:15 or 80:20 to 90:10.

[0078] In some specific embodiments, the insulating layer 30 may further comprise a ceramic material. The insulating ceramic material is not particularly limited, as long as it is a material that can prevent short circuits between the electrodes. Exemplarily, the ceramic material may comprise at least one selected from alumina (Al2O3), boehmite (AlO(OH)), silicon oxide (SiO X ; 0 < x ≤ 2), aluminum hydrate (Al2O3·nH2O), aluminum nitride (AlN), silicon carbide (SiC), and magnesium oxide (MgO).

[0079] In some specific embodiments, the thickness of the insulating layer 30 may be 3 μm to 50 μm. Exemplarily, the thickness of the insulating layer 30 may be 10 μm.

[0080] The composition of the electrode current collector 10 is not particularly limited. Exemplarily, the electrode current collector 10 may be a plate or foil formed of one or more of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), and their alloys. The thickness of the electrode current collector 10 is not particularly limited. Exemplarily, the thickness of the electrode current collector 10 may be 0.1 μm to 50 μm.

[0081] When the lithium secondary battery electrode 100 is a negative electrode, in some specific embodiments, the electrode current collector 10 may be a copper foil (Cu-foil). When the lithium secondary battery electrode 100 is a positive electrode, in some specific embodiments, the electrode current collector 10 may be an aluminum foil (Al-foil).

[0082] The electrode current collector 10 may include an uncoated portion on the electrode current collector where the electrode mixture layer 20 is not provided. According to a specific embodiment, the insulating layer 30 may cover a part of the uncoated portion and a part of the electrode mixture layer 20. Specifically, the insulating layer 30 on the uncoated portion and the insulating layer 30 on the electrode mixture layer 20 may be continuously connected to each other. More specifically, the insulating layer 30 may be provided to cover a part of the uncoated portion to a part of the electrode mixture layer 20 (see Figure 1 and Figure 3 ). In this case, exposure of the electrode current collector 10 can be prevented. In the lithium secondary battery electrode 100, the region where the insulating layer 30 covers a part of the electrode mixture layer may be the overlapping region A. According to another specific embodiment, the insulating layer 30 may be provided on the uncoated portion (see Figure 2 ).

[0083] The electrode mixture layer 20 may include an electrode active material. When the electrode for the lithium secondary battery is an anode, the electrode mixture layer 20 may be an anode mixture layer including an anode active material. When the electrode for the lithium secondary battery is a cathode, the electrode mixture layer 20 may be a cathode mixture layer including a cathode active material.

[0084] The anode active material is not particularly limited. Exemplarily, the anode active material may be one or more selected from the following: carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers; lithium metal; lithium alloys; silicon-containing substances and tin-containing substances.

[0085] Exemplarily, the crystalline carbon may be graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized mesocarbon microbead (MCMB), graphitized mesophase pitch-based carbon fiber (MPCF).

[0086] Exemplarily, the amorphous carbon may be hard carbon, soft carbon, coke, mesocarbon microbead (MCMB) or mesophase pitch-based carbon fiber (MPCF).

[0087] Exemplarily, the elements included in the lithium alloy may be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium.

[0088] The silicon-containing substance is not particularly limited as long as it contains silicon, and may be an active substance that can be alloyed with lithium (Li). Exemplarily, the silicon-containing substance may be one or more selected from silicon (Si), silicon oxide (SiO X ; 0 < x < 2), metal-doped silicon oxide (SiO X ; 0 < x < 2), carbon-coated silicon oxide (SiO X ; 0 < x < 2), silicon-carbon composite (Si-C) and silicon alloy.

[0089] The cathode active material is not particularly limited. Exemplarily, the cathode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn) and aluminum (Al).

[0090] In some specific embodiments, the cathode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 3.

[0091] [Chemical Formula 3]

[0092] Li x Ni aM b O 2+z

[0093] In the formula 3, it can be 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.4, -0.5 ≤ z ≤ 0.1. As described above, M can include Co, Mn, and / or Al.

[0094] The chemical structure represented by the formula 3 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material, and does not exclude other additional elements. Exemplarily, M can include Co and / or Mn, and Co and / or Mn can be provided together with Ni as the main active element of the positive electrode active material. The formula 3 is provided to represent the bonding relationship of the main active element, and it should be understood that the formula 3 is a formula including the introduction and substitution of additional elements.

[0095] In some specific embodiments, in addition to the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure can be further included. The auxiliary element can be mixed into the layered structure / crystal structure together to form a bond, and it should be understood that this situation is also included within the chemical structure range represented by the formula 3.

[0096] Exemplarily, the auxiliary element can include at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element can act as an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Co or Mn, such as Al.

[0097] Exemplarily, the positive electrode active material or the lithium-nickel metal oxide can include a layered structure or crystal structure represented by the following formula 3-1.

[0098] [Formula 3-1]

[0099] Li x Ni a M1 b1 M2 b2 O 2+z

[0100] In the formula 3-1, M1 can include Co, Mn, and / or Al. M2 can include the above-mentioned auxiliary elements. In the formula 3-1, it can be 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b1 + b2 ≤ 0.4, -0.5 ≤ z ≤ 0.1.

[0101] The positive electrode active material may further include a coating element or a doping element. For example, an element that is substantially the same as or similar to the above-mentioned auxiliary element may be used as the coating element or the doping element. Exemplarily, one or a combination of two or more of the above elements may be used as the coating element or the doping element.

[0102] The coating element or the doping element may be present on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal oxide particles and be included in the bonding structure represented by Chemical Formula 3 or Chemical Formula 3-1.

[0103] The positive electrode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0104] The content of Ni in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0105] In some specific embodiments, the positive electrode active material may further include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0106] In some specific embodiments, the positive electrode active material may include a manganese-rich (Mn-rich)-based active material, a lithium-rich layered oxide (LLO) / over-lithiated oxide (OLO)-based active material, a cobalt-less (Co-less)-based active material, etc., having a chemical structure or crystal structure represented by Chemical Formula 4.

[0107] [Chemical Formula 4]

[0108] p[Li2MnO3]·(1-p)[Li q JO2]

[0109] In Chemical Formula 4, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0110] The electrode mixture layer 20 may further include a binder. The binder is not particularly limited. Exemplarily, the positive electrode mixture layer may include one or more of styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc. as the binder.

[0111] In addition, the negative electrode mixture layer may include any one of the following as the binder: rubber-based binders such as styrene-butadiene rubber (SBR), fluorine-based rubber, ethylene-propylene rubber, butadiene rubber, isoprene rubber, silane rubber, etc.; cellulose-based binders such as carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof; and combinations thereof.

[0112] The electrode mixture layer 20 may further include a conductive material. The conductive material is not particularly limited. Exemplarily, the conductive material may include one or more of the following: graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon fiber, carbon nanotube (CNT), etc.; metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide, potassium titanate, etc.; conductive metal oxides such as titanium oxide, etc.; or conductive polymers such as polyphenylene derivatives, etc.

[0113] The lithium secondary battery electrode 100 according to the above specific embodiments can be manufactured by the manufacturing method described below.

[0114] Manufacturing method of lithium secondary battery electrode

[0115] The manufacturing method of the lithium secondary battery electrode 100 according to a specific embodiment includes the step of forming an electrode mixture layer 20 and an insulating layer 30 on at least one surface of the electrode current collector 10, wherein the insulating layer 30 includes a copolymer, and the copolymer includes a copolymer including a repeating unit having an imide group and a rubber-based repeating unit. The detailed description of the electrode current collector 10, the electrode mixture layer 20, the insulating layer 30, etc. is repeated with the above content, and thus the description is omitted.

[0116] In some specific embodiments, the electrode mixture layer 20 can be formed on at least one surface of the electrode current collector 10 by a process of coating a slurry containing an electrode active material on at least one surface of the electrode current collector 10 and drying the electrode slurry at 60 - 200 °C. The coating method of the electrode slurry is not particularly limited. Exemplarily, the electrode slurry can be coated onto the surface of the electrode current collector 10 by methods such as slot die coating, bar coating, casting, or spraying.

[0117] In some specific embodiments, the electrode slurry may further contain a solvent. The solvent is not particularly limited. Exemplarily, the solvent can be dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, water, etc. According to one embodiment, the solvent can be N-methyl-2-pyrrolidone (NMP). Regarding the amount of the solvent used, considering the coating thickness of the slurry, manufacturing yield, etc., as long as it can dissolve or disperse the components and has a viscosity such that it can exhibit excellent thickness uniformity when coated onto the current collector, the amount of the solvent used is not particularly limited.

[0118] In some specific embodiments, the insulating layer 30 can be formed on at least one surface of the electrode current collector 10 by a process of coating a composition for an insulating coating on at least one surface of the electrode current collector 10 and drying the composition at 60 - 200 °C. The coating method of the composition for the insulating coating is not particularly limited. Exemplarily, the composition for the insulating coating can be coated onto the surface of the electrode current collector 10 by methods such as slot die coating, bar coating, casting, or spraying.

[0119] The formation order of the electrode mixture layer 20 and the insulating layer 30 is not particularly limited. That is, within the range where the characteristics of the finally formed electrode mixture layer 20 and insulating layer 30 do not show significant differences, the coating order of the electrode slurry and the composition for the insulating coating is not particularly limited.

[0120] According to one specific embodiment, the electrode slurry and the composition for the insulating coating can be simultaneously coated on at least one surface of the electrode current collector 10 and then dried to simultaneously form the electrode mixture layer 20 and the insulating layer 30.

[0121] According to another specific embodiment, the electrode slurry can be first coated on at least one surface of the electrode current collector 10, and then the composition for the insulating coating is coated (i.e., the electrode slurry and the composition for the insulating coating are coated in sequence), and they are simultaneously dried to simultaneously form the electrode mixture layer 20 and the insulating layer 30.

[0122] According to another specific embodiment, the electrode paste may be first coated on at least one surface of the electrode current collector 10 and then dried to first form the electrode mixture layer 20, and then the insulating coating composition is coated and dried to sequentially form the electrode mixture layer 20 and the insulating layer 30.

[0123] The insulating coating composition may include a copolymer including a repeating unit having an imide group and a rubber-based repeating unit. When a mixture of a polymer composed of the repeating unit having an imide group and a polymer composed of the rubber-based repeating unit is used as the insulating coating composition, phase separation may occur due to poor compatibility between the two polymers, and the insulating layer 30 may not be manufactured. Therefore, when the insulating coating composition includes a copolymer containing a repeating unit having an imide group and a rubber-based repeating unit, the insulating layer 30 can be stably manufactured.

[0124] The detailed description of the repeating unit having an imide group, the rubber-based repeating unit, the copolymer, etc. is repeated with the above content, and thus the description is omitted.

[0125] The insulating coating composition may further include a solvent. The type of the solvent is not particularly limited. Exemplarily, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, water, etc. may be used as the solvent. According to one embodiment, the solvent may be N-methyl-2-pyrrolidone (NMP).

[0126] In some specific embodiments, based on the entire insulating coating composition, the content of the copolymer included in the insulating coating composition may be 5 wt% to 50 wt%. Exemplarily, based on the entire insulating coating composition, the content of the copolymer included in the insulating coating composition may be 10-40 wt%, 15-35 wt%, 10-30 wt% or 15-25 wt%. Specifically, based on the entire insulating coating composition, the content of the copolymer included in the insulating coating composition may be 10 wt% to 20 wt%.

[0127] In some specific embodiments, based on the entire insulating coating composition, the content of the solvent included in the insulating coating composition may be 50 wt% to 95 wt%. Exemplarily, based on the entire insulating coating composition, the content of the solvent included in the insulating coating composition may be 60-90 wt%, 65-85 wt%, 70-90 wt% or 75-85 wt%. Specifically, based on the entire insulating coating composition, the content of the solvent included in the insulating coating composition may be 80 wt% to 90 wt%.

[0128] When the contents of the copolymer and the solvent contained in the composition for the insulating coating are as described above, the copolymer contained in the composition for the insulating coating can be excellently dispersed, and at the same time, the coating processability can be improved.

[0129] In some specific embodiments, the insulating layer 30 may be formed in a structure provided on the uncoated portion of the electrode current collector 10 (refer to Figure 2 ), and may also be formed in a structure provided to cover a part of the uncoated portion to a part of the electrode mixture layer (refer to Figure 1 and Figure 3 ).

[0130] Lithium secondary battery

[0131] The lithium secondary battery according to a specific embodiment includes the electrode 100 for a lithium secondary battery according to any one of the above specific embodiments. Specifically, the lithium secondary battery may include a unit cell, and the unit cell includes the electrode 100 for a lithium secondary battery according to any one of the above specific embodiments as a negative electrode or a positive electrode.

[0132] In some specific embodiments, the unit cell may further include a separator between the positive electrode and the negative electrode. The separator is not particularly limited. Exemplarily, the separator may include a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. In addition, the separator may also include a non-woven fabric formed of glass fibers with a high melting point, polyethylene terephthalate fibers, etc.

[0133] In some specific embodiments, the lithium secondary battery can be manufactured by accommodating the above unit cell in a soft package as a battery case and then injecting an electrolyte.

[0134] The electrolyte may contain an organic solvent and a lithium salt. The organic solvent serves as a medium through which ions participating in the electrochemical reaction of the battery can move, and is not particularly limited. Exemplarily, the following solvents may be used alone or two or more of the following solvents may be used in combination: carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, or aprotic solvents. When two or more solvents are used in combination, the mixing ratio can be appropriately adjusted according to the desired battery performance.

[0135] The lithium salt can be a substance that is dissolved in an organic solvent and serves as a source of lithium ions in the battery, enables the basic operation of the lithium secondary battery, and promotes the migration of lithium ions between the positive electrode and the negative electrode. The lithium salt is not particularly limited, and known substances can be used at a concentration suitable for the purpose. The electrolyte may further contain a known solvent as needed to improve charge-discharge characteristics, flame retardant characteristics, etc., and may contain a known additive.

[0136] In some specific embodiments, the unit cell may not include a separator between the positive electrode and the negative electrode, but may include a solid electrolyte. The solid electrolyte is not particularly limited. Exemplarily, the solid electrolyte may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a polymer-based solid electrolyte.

[0137] Examples

[0138] 1. Fabrication of Electrodes

[0139] 1) Composition for Insulating Coating

[0140] (1) Examples 1 to 4

[0141] A solution prepared by mixing polyamideimide (PAI) grafted with hydrogenated nitrile rubber (HNBR) and a solvent (NMP) at a weight ratio of 15:85 was used as the composition for insulating coating in Examples 1 to 4. At this time, as shown in Table 1 below, the grafting ratio of hydrogenated nitrile rubber (HNBR) relative to the polyamideimide (PAI) was adjusted differently for each example.

[0142] (2) Comparative Example 1

[0143] A solution prepared by mixing polyamideimide (PAI) and a solvent (NMP) at a weight ratio of 15:85 was used as the composition for insulating coating in Comparative Example 1.

[0144] (3) Comparative Example 2

[0145] A solution prepared by mixing hydrogenated nitrile rubber (HNBR) and a solvent (NMP) at a weight ratio of 20:80 was used as the composition for insulating coating in Comparative Example 2.

[0146] (4) Comparative Example 3

[0147] A solution prepared by mixing polyamideimide (PAI), hydrogenated nitrile rubber (HNBR), and a solvent (NMP) at a weight ratio of 12.75:2.25:85 was used as the composition for insulating coating in Comparative Example 3. At this time, the weight ratio of hydrogenated nitrile rubber (HNBR) to polyamideimide (PAI) was adjusted to a weight ratio of 15:85.

[0148] 2) Manufacture of Insulating Layer Specimens

[0149] The insulating coating compositions of Examples 1 to 4 and Comparative Examples 1 to 3 were coated on a polyethylene terephthalate (PET) film with a thickness of 125 μm, and then thoroughly dried in a hot air oven at 120 °C for 6 hours to manufacture an insulating layer with a thickness of 20 μm. The dried insulating layer was peeled off from the PET film and used as an insulating layer specimen.

[0150] 3) Manufacture of Positive Electrodes

[0151] A slurry containing an NCM-based positive electrode active material (Li[Ni 0.8 Co 0.1 Mn 0.1 O2) was coated on one side of an aluminum foil serving as a positive electrode current collector at a loading amount of 20 mg / cm 2 , and the insulating coating composition prepared in the above Examples and Comparative Examples was coated so as to cover a part of the uncoated portion to a part of the mixture layer, and then dried in a hot air drying furnace at 60 °C to 200 °C, thereby manufacturing a positive electrode, on one side of the positive electrode current collector of which there was a positive electrode mixture layer and an insulating layer having the structure shown as Figure 1 .

[0152] 2. Evaluation of Electrodes

[0153] 1) Swelling of Insulating Layer

[0154] An electrolytic solution was prepared, which was an electrolytic solution obtained by adding 1.5 M of LiPF6 electrolyte to a solvent prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 2:7:1. The insulating layer specimen prepared as described above was immersed in the electrolytic solution at 25 °C for 24 hours, and the mass of the insulating layer specimen before and after immersion was measured respectively. The swelling degree of the insulating layer was measured in percentage (%) according to the following formula 1, and the measurement results are shown in Table 1 below.

[0155] [Formula 1]

[0156] Swelling ratio (%) = (W2 - W1) / W1 × 100

[0157] In the above formula 1, W1 is the mass of the insulating layer specimen before immersion in the electrolytic solution, and W2 is the mass of the insulating layer specimen after immersion and dried at room temperature for 6 hours.

[0158] 2) Elongation at Break

[0159] Cut the prepared insulating layer specimen into a size of 100 mm × 10 mm to prepare a specimen for measuring the elongation rate. Place the specimen in a UTM tensile force testing machine and pull it up and down at a speed of 50 mm / second. Measure the elongation length until the specimen breaks and calculate the elongation rate as a percentage (%). The results are shown in Table 1 below.

[0160] 3) Defects in the manufacturing process

[0161] (1) Whether it peels off when immersed in the electrolyte

[0162] Prepare an electrolyte, which is an electrolyte obtained by adding 1.5 M of LiPF6 electrolyte to a solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) mixed in a volume ratio of 2:7:1. After immersing the prepared electrode in the electrolyte at 60 °C for 120 minutes, evaluate the case of complete peeling as ○, the case of partial peeling as △, and the case of no peeling as Ⅹ. The evaluation results are shown in Table 1 below.

[0163] (2) Whether the uncoated part tears during cutting

[0164] When cutting the prepared electrode to form the uncoated part of the positive current collector into a positive electrode tab, evaluate the case where tearing occurs at the interface between the uncoated part and the insulating layer as ○, the case where partial tearing or damage occurs at the interface as △, and the case where no tearing occurs at the interface as Ⅹ. The evaluation results are shown in Table 1 below.

[0165] (3) Rollability

[0166] Convert and evaluate the number of breaks per 1000 m during the process of rolling the prepared electrode to a density of 3.6 g / cubic centimeter (cc). The evaluation results are shown in Table 1 below.

[0167] [Table 1]

[0168]

[0169] PAI-HNBR: Polyamideimide (PAI) grafted with hydrogenated nitrile rubber (HNBR); the ratio in parentheses is the grafting ratio (weight ratio) of hydrogenated nitrile rubber (HNBR) relative to polyamideimide (PAI).

[0170] PAI + HNBR: Hybrid hydrogenated nitrile rubber (HNBR) and polyamideimide (PAI); the ratio in parentheses is the mixing ratio (by weight) of polyamideimide (PAI) and hydrogenated nitrile rubber (HNBR).

[0171] Referring to Table 1, it can be confirmed that the elongation rate of the insulating layer in Comparative Example 1 is relatively low, and when the electrode is cut, tearing occurs at the interface between the uncoated portion and the insulating layer, and when the electrode is calendered, the number of breaks is relatively large, resulting in poor calendering processability. Although not bound by a specific theory, it is judged that this is because the insulating layer only contains polyamideimide (PAI) alone, which lacks flexibility.

[0172] In addition, in Comparative Example 2 and Comparative Example 3, when the insulating layer is immersed in the electrolyte, partial dissolution of the insulating layer occurs, so it can be confirmed that it is not suitable for use in lithium secondary batteries. Although not bound by a specific theory, it is judged that this is because the hydrogenated nitrile rubber (HNBR) contained in the insulating layer has the property of dissolving in the electrolyte.

[0173] On the other hand, in the case of Examples 1 to 4 where the insulating layer contains polyamideimide grafted with hydrogenated nitrile rubber (PAI-HNBR), it can be confirmed that the insulating layer has more excellent performance than Comparative Examples 1 to 3 in terms of the expansion ratio / elongation rate of the insulating layer and manufacturing process defect matters. In particular, in the case of Examples 1 and 3 where the insulating layer contains PAI-HNBR with a grafting ratio of polyamideimide (PAI) and hydrogenated nitrile rubber (HNBR) of 70:30 to 85:15, it can be confirmed that the expansion ratio of the insulating layer is less than that of Example 4, and the calendering processability is more excellent than that of Example 2.

[0174] Therefore, when the insulating layer contains a copolymer containing repeating units having an imide group and rubber-based repeating units in a specific ratio, it is judged that the insulating properties, heat resistance, peel resistance, elongation, etc. of the insulating layer can be improved, and the problem of quality degradation in the subsequent secondary battery manufacturing process can be effectively prevented.

Claims

1. An electrode for a lithium secondary battery, comprising an electrode current collector, an electrode mixture layer on at least one side of the electrode current collector, and an insulating layer, in, The insulating layer comprises a copolymer, The copolymer includes repeating units having an imide group and repeating units based on rubber.

2. The lithium secondary battery electrode according to claim 1, wherein The imide group is represented by the following Chemical Formula 1, [Chemical formula 1] In the chemical formula 1, R 1 , R 2 and R 3 Each is independently hydrogen or an organic group.

3. The lithium secondary battery electrode according to claim 1, wherein The repeating unit having an imide group further comprises an amide group.

4. The lithium secondary battery electrode according to claim 3, wherein The amide group is represented by the following chemical formula 2, [Chemical formula 2] In the chemical formula 2, R, R' and R" are each independently hydrogen or an organic group.

5. The lithium secondary battery electrode according to claim 1, wherein The repeating unit having an imide group includes a repeating unit constituting polyamideimide (PAI).

6. The lithium secondary battery electrode according to claim 1, wherein The rubber-based repeating unit includes at least one of a styrene-butadiene rubber (SBR)-based repeating unit, a butadiene rubber (BR)-based repeating unit, a hydrogenated nitrile rubber (HNBR)-based repeating unit, a nitrile rubber (NBR)-based repeating unit, an acrylic rubber-based repeating unit, a butyl rubber-based repeating unit, and a fluororubber-based repeating unit.

7. The lithium secondary battery electrode according to claim 1, wherein The copolymer includes a graft copolymer in which a second block including a rubber-based repeating unit is grafted onto a first block including a repeating unit having an imide group.

8. The lithium secondary battery electrode according to claim 7, wherein The first block includes repeating units having an imide group and an amide group, and the second block includes repeating units based on hydrogenated nitrile rubber (HNBR).

9. The electrode for lithium secondary battery according to claim 7, wherein In the graft copolymer, the content of the first block is 50-95 wt % based on the total weight of the graft copolymer.

10. The lithium secondary battery electrode according to claim 7, wherein In the graft copolymer, the content of the second block is 5-50 wt % based on the total weight of the graft copolymer.

11. The lithium secondary battery electrode according to claim 1, wherein The insulating layer further comprises a ceramic material.

12. The lithium secondary battery electrode according to claim 1, wherein The electrode current collector includes an uncoated portion on which the electrode mixture layer is not provided, and the insulating layer covers a portion of the uncoated portion and a portion of the electrode mixture layer.

13. The lithium secondary battery electrode according to claim 1, wherein The electrode current collector includes an uncoated portion on which the electrode mixture layer is not disposed, and the insulating layer is disposed on the uncoated portion.

14. A method for producing an electrode for a lithium secondary battery, comprising the steps of forming an electrode mixture layer and an insulating layer on at least one side of an electrode current collector, in, The insulating layer comprises a copolymer, The copolymer includes repeating units having an imide group and repeating units based on rubber. 15 . A lithium secondary battery comprising the lithium secondary battery electrode according to claim 1 .

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