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

Abstract

To provide a lithium secondary battery that can inhibit occurrence of ignition so as to improve the safety.SOLUTION: According to an embodiment, an electrode for a secondary battery includes: an electrode current collector; and an electrode mixture layer and an insulating layer on at least one surface of the electrode current collector. The insulating layer contains a copolymer, and the copolymer includes a repeating unit having an imide group and a rubber-based repeating unit.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Recently, many studies have been conducted on electric vehicles (EVs) that can replace 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 having a high discharge voltage and output stability are mainly used.

[0003] In the driving process of the above lithium secondary battery, there is a possibility of occurrence of safety problems 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 if the short circuit state continues, it may induce a fire inside the secondary battery.

[0004] Therefore, there is a demand for the development of a technology capable of suppressing the occurrence of problems such as short circuits inside the secondary battery and fires caused thereby.

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to one aspect of the present disclosure, it is possible to suppress the occurrence of low voltage defects due to a short circuit between electrodes in a lithium secondary battery.

[0006] According to another aspect of the present disclosure, it is possible to suppress the occurrence of ignition in a lithium secondary battery.

[0007] According to another aspect of the present disclosure, it is possible to suppress the occurrence of breakage in an electrode during the manufacturing process of an electrode for a lithium secondary battery.

[0008] According to another aspect of the present disclosure, the manufacturability of the electrode for a lithium secondary battery can be improved.

Means for Solving the Problems

[0009] The electrode for a lithium secondary battery according to an embodiment of the present disclosure includes an electrode current collector, an electrode binder layer and an insulating layer on at least one surface of the electrode current collector, the insulating layer includes a copolymer, and the copolymer includes a repeating unit having an imide group and a rubber-based repeating unit.

[0010] In some embodiments, the imide group can be represented by the following Chemical Formula 1.

[0011] [Chemical Formula 1]

Chem.

[0012] In some embodiments, the repeating unit having the imide group can further include an amide group.

[0013] In some embodiments, the amide group can be represented by the following Chemical Formula 2.

[0014] [Chemical Formula 2]

Chem.

[0015] In some embodiments, the repeating unit having the imide group can include a repeating unit that constitutes polyamideimide (PAI). In some embodiments, the rubber-based repeating unit can include at least one of a styrene-butadiene rubber (SBR)-based repeating unit, a butadiene rubber (BR)-based repeating unit, a hydrogenated nitrile butadiene rubber (HNBR)-based repeating unit, a nitrile butadiene rubber (NBR)-based repeating unit, an acrylic rubber-based repeating unit, a butyl rubber-based repeating unit, and a fluororubber-based repeating unit.

[0016] In some embodiments, the copolymer can include a graft copolymer in which a second block containing a rubber-based repeating unit is grafted onto a first block containing a repeating unit having an imide group.

[0017] In some embodiments, the first block can include a repeating unit having an imide group and an amide group, and the second block can include a hydrogenated nitrile butadiene rubber (HNBR)-based repeating unit.

[0018] In some embodiments, the first block in the graft copolymer can be included at 50 to 95% by weight based on the weight of the entire graft copolymer.

[0019] In some embodiments, the second block in the graft copolymer can be included at 5 to 50% by weight based on the weight of the entire graft copolymer.

[0020] In some embodiments, the insulating layer can further include a ceramic material.

[0021] In some embodiments, the electrode current collector can include a plain portion on which no electrode binder layer is disposed.

[0022] In some embodiments, the insulating layer can cover a part of the plain portion and a part of the electrode binder layer.

[0023] In one implementation example, the insulating layer can be disposed on the non-patterned portion.

[0024] The method for manufacturing an electrode for a lithium secondary battery according to one implementation example of the present disclosure includes a step of forming an electrode active material layer and an insulating layer on at least one surface of an electrode current collector. The insulating layer contains a copolymer, and the copolymer contains a repeating unit having an imide group and a rubber-based repeating unit.

[0025] A lithium secondary battery according to one implementation example of the present disclosure includes an electrode for a lithium secondary battery according to any one of the above-described implementation examples.

Advantages of the Invention

[0026] According to one implementation example of the present disclosure, it is possible to suppress the occurrence of low-voltage defects in a lithium secondary battery.

[0027] According to another implementation example of the present disclosure, it is possible to suppress the occurrence of ignition in a lithium secondary battery and improve safety.

[0028] According to another implementation example of the present disclosure, it is possible to prevent the occurrence of quality defects when manufacturing an electrode for a lithium secondary battery.

[0029] According to another implementation example of the present disclosure, it is possible to improve the yield of the manufacturing process of an electrode for a lithium secondary battery.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0031] Hereinafter, the technology disclosed in this specification and its implementation examples will be described in detail with reference to the accompanying drawings. However, the embodiments of the above technology can be deformed into various different forms, and its scope is not limited to the implementation examples described below. In addition, the technology disclosed in this specification can be applied not only limited to the configuration of the implementation examples described below, but also can be configured by selectively combining all or part of each implementation example so that various deformations are possible.

[0032] As described above, there is a demand for the development of a technology capable of suppressing the occurrence of a short circuit inside the lithium secondary battery. According to one implementation example, an insulating layer can be coated on the plain part of the electrode current collector where the electrode binder layer is not disposed to prevent a short circuit between the electrodes. Exemplarily, when an insulating layer is coated on the plain part of the positive electrode current collector, even if the plain part comes into contact with the negative electrode, the occurrence of a short circuit can be prevented.

[0033] On the other hand, when an insulating layer is coated on the plain part of the electrode current collector, depending on the difference in the properties of each substance contained in the electrode binder layer, the electrode current collector, and the insulating layer, there may be a difference in the elongation rate during electrode rolling. As a result, a foil curl phenomenon may occur in which the plain part warps at the interface between the electrode binder layer and the plain part of the electrode current collector. When the above foil curl phenomenon occurs, various quality defects may occur in the subsequent manufacturing process of the secondary battery.

[0034] Exemplarily, during the electrode rolling or notching process, stress may accumulate at the interface between the plain part and the insulating layer, and a phenomenon may occur in which the electrode breaks or the interface peels off. During the welding process, there may be a problem that wrinkles are formed in the electrode tab part. When the insulating layer contains both a ceramic material and a polymer binder, such a phenomenon may become more severe due to the difference between the ceramic composition and the polymer composition.

[0035] According to an embodiment of the present disclosure, the above-described problems can be alleviated. Hereinafter, embodiments of the present disclosure will be specifically described with reference to FIGS. 1 to 3.

[0036] FIG. 1 is a cross-sectional view conceptually showing an electrode for a secondary battery according to one embodiment, FIG. 2 is a cross-sectional view conceptually showing an electrode for a secondary battery according to another embodiment, and FIG. 3 is a plan view conceptually showing a form of the electrode for a secondary battery shown in FIG. 1 as viewed from above.

[0037] Electrode for lithium secondary battery An electrode 100 for a lithium secondary battery according to one embodiment includes an electrode current collector 10, an electrode binder layer 20 on at least one surface of the electrode current collector, and an insulating layer 30. The insulating layer 30 includes a copolymer, and the copolymer includes a repeating unit having an imide group and a rubber-based repeating unit.

[0038] By including a copolymer containing a repeating unit having an imide group and a rubber-based repeating unit, the insulating layer 30 is excellent in insulating properties and heat resistance, excellent in peeling resistance in an electrolytic solution, improved in softness, and can have an improved elongation rate. Thereby, it is possible to prevent a quality decrease due to a breakage phenomenon of the electrode or the like during a subsequent manufacturing process of the secondary battery.

[0039] The repeating unit having an imide group contains an imide group, and the copolymer and the insulating layer 30 containing the same can be imparted with insulating properties. In the present specification, the imide group may be a functional group composed of two acyl groups bonded to nitrogen. Exemplarily, the imide group can be represented by the following Chemical Formula 1.

[0040] [Chemical Formula 1]

Chemical formula

[0041] In some embodiments, the repeating unit having the imide group may further have an amide group. In the present 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.

[0042] [Chemical Formula 2] [Chem.] In Chemical Formula 2 above, R, R' and R'' are each independently hydrogen or an organic group.

[0043] In some embodiments, the repeating unit having the imide group may include a repeating unit that constitutes polyamideimide (PAI) (hereinafter, a repeating unit derived from polyamideimide). By including a repeating unit containing an imide group and an amide group in the insulating layer 30, the peel resistance in the electrolytic solution is further improved, the elongation rate is increased, and peeling of the interface during the electrode rolling / notching process can be suppressed.

[0044] In addition to the repeating unit having the 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, and flexibility can be imparted to the copolymer containing the same. When the copolymer contained in the insulating layer 30 includes a rubber-based repeating unit, the elongation rate of the insulating layer 30 can be further improved.

[0045] The above rubber-based repeating unit is not particularly limited. Exemplarily, the above rubber-based repeating unit can include at least one of a styrene-butadiene rubber (SBR)-based repeating unit, a butadiene rubber (BR)-based repeating unit, a hydrogenated nitrile butadiene rubber (HNBR)-based repeating unit, a nitrile butadiene 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 above rubber-based repeating unit may be a hydrogenated nitrile butadiene rubber (HNBR)-based repeating unit.

[0046] In some embodiments, the above copolymer may be a block copolymer or a graft copolymer including a first block and a second block. Specifically, the above copolymer may be a graft copolymer in which the second block is grafted to the first block.

[0047] In some embodiments, the above first block can include a repeating unit having the above imide group, and the above second block can include the above rubber-based repeating unit. Specifically, the above copolymer can include a graft copolymer in which a second block including a rubber-based repeating unit is grafted to a first block including a repeating unit having an imide group.

[0048] In some embodiments, the above first block can be composed of repeating units constituting polyamideimide, and the above second block can be composed of rubber-based repeating units.

[0049] In some embodiments, the above first block can include a repeating unit having an imide group and an amide group, and the above second block can include a hydrogenated nitrile butadiene rubber (HNBR)-based repeating unit.

[0050] In some embodiments, the copolymer may include a graft copolymer in which a polymer composed of repeating units having imide groups is grafted with a polymer composed of rubber-based repeating units. Exemplarily, the graft copolymer may include polyamideimide (PAI) grafted with hydrogenated nitrile butadiene rubber (HNBR).

[0051] In some embodiments, the first block in the graft copolymer may be included in an amount of 50 to 95% by weight based on the weight of the total graft copolymer. Exemplarily, in the graft copolymer, the first block may be included in an amount of 55 to 90% by weight, 60 to 85% by weight, 65 to 75% by weight, 70 to 85% by weight, or 80 to 90% by weight based on the weight of the total graft copolymer. Specifically, the first block in the graft copolymer may be included in an amount of 70% by weight or more, or 80% by weight or more, and may also be included in an amount of 90% by weight or less, or 85% by weight or less based on the weight of the total graft copolymer.

[0052] When the graft ratio of the first block is excessively low, swelling of the insulating layer 30 is likely to occur, and peeling of the insulating layer in the electrolytic solution may occur. On the contrary, when the graft ratio of the first block is excessively high, the softness improvement rate of the insulating layer 30 may be insufficient.

[0053] In some embodiments, the second block in the graft copolymer may be included in an amount of 5 to 50% by weight based on the weight of the total graft copolymer. Exemplarily, in the graft copolymer, the second block may be included in an amount of 10 to 45% by weight, 15 to 40% by weight, 25 to 35% by weight, 15 to 30% by weight, or 10 to 20% by weight based on the weight of the total graft copolymer. Specifically, the second block in the graft copolymer may be included in an amount of 10% by weight or more, or 15% by weight or more, and may also be included in an amount of 30% by weight or less, or 20% by weight or less based on the weight of the total graft copolymer.

[0054] If the graft ratio of the second block is excessively low, the softness improvement rate of the insulating layer 30 may be insufficient. On the other hand, if the graft ratio of the second block is excessively high, although the softness of the insulating layer 30 is excellent, swelling is likely to occur, and peeling of the insulating layer may occur in the electrolytic solution.

[0055] In some embodiments, the weight ratio of the first block and the second block in the graft copolymer 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.

[0056] In some embodiments, the insulating layer 30 may further contain a ceramic material. The insulating ceramic material is not particularly limited as long as it can prevent short circuit between electrodes. Exemplarily, the ceramic material may include at least one selected from the group consisting of alumina (Al2O3), boehmite (AlO(OH)), silicon oxide (SiOx; 0 < x ≦ 2), alumina hydrate (AI2O3·nH2O), aluminum nitride (AlN), silicon carbide (SiC), and magnesium oxide (MgO).

[0057] In some 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.

[0058] The components of the electrode current collector 10 are not particularly limited. Exemplarily, the electrode current collector 10 may be a plate or foil made 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 alloys thereof. 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 to 50 μm.

[0059] When the secondary battery electrode 100 is a negative electrode, in some embodiments, the electrode current collector 10 may be a copper foil (Cu-foil). When the secondary battery electrode 100 is a positive electrode, in some embodiments, the electrode current collector 10 may be an aluminum foil (Al-foil).

[0060] The electrode current collector 10 may include a plain portion on which the electrode binder layer 20 is not disposed. According to one embodiment, the insulating layer 30 may cover a part of the plain portion and a part of the electrode binder layer 20. Specifically, the insulating layer 30 on the plain portion and the insulating layer 30 on the electrode binder layer 20 may be continuously connected to each other. More specifically, the insulating layer 30 may be disposed so as to cover a part of the electrode binder layer 20 from a part of the plain portion (see FIGS. 1 and 3). In this case, exposure of the electrode current collector 10 can be prevented. In the secondary battery electrode 100, the region where the insulating layer 30 covers a part of the electrode binder layer may be the overlapping region A. According to another embodiment, the insulating layer 30 may be disposed on the plain portion (see FIG. 2).

[0061] The electrode binder layer 20 may include an electrode active material. When the lithium secondary battery electrode is a negative electrode, the electrode binder layer 20 may be a negative electrode binder layer containing a negative electrode active material. When the lithium secondary battery electrode is a positive electrode, the electrode binder layer 20 may be a positive electrode binder layer containing a positive electrode active material.

[0062] The negative electrode active material is not particularly limited. Exemplarily, the negative electrode active material may be one or more selected from the group consisting of carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon-containing substances, and tin-containing substances.

[0063] The crystalline carbon may, by way of example, be a graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized mesocarbon microbeads (MCMB), graphitized mesophase pitch-based carbon fiber (MPCF), or the like.

[0064] The amorphous carbon may, by way of example, be hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), or mesophase pitch-based carbon fiber (MPCF).

[0065] The elements contained in the lithium alloy may, by way of example, be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0066] The silicon-containing substance is not particularly limited as long as it contains silicon, and may be an active material capable of alloying with lithium (Li). By way of example, the silicon-containing substance may be one or more selected from the group consisting of silicon (Si), silicon oxide (SiOx; 0 < x < 2), metal-doped silicon oxide (SiOx; 0 < x < 2), carbon-coated silicon oxide (SiOx; 0 < x < 2), silicon-carbon composite (Si-C), and silicon alloy.

[0067] The positive electrode active material is not particularly limited. By way of example, the positive electrode active material can include a lithium-nickel metal oxide. The lithium-nickel metal oxide can further contain at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0068] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide can include a layered structure or a crystal structure represented by the following Chemical Formula 3.

[0069] [Chemical Formula 3] Li x Ni a M b O 2+z

[0070] In the above Chemical Formula 3, 0.9 ≦ x ≦ 1.2, 0.6 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.4, and -0.5 ≦ z ≦ 0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0071] The chemical structure represented by the above Chemical Formula 3 shows 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 includes Co and / or Mn, and Co and / or Mn may be provided as the main active element of the positive electrode active material together with Ni. The above Chemical Formula 3 is provided to represent the bonding relationship of the main active element, and should be understood as a formula including the introduction and substitution of additional elements.

[0072] In some embodiments, in addition to the above main active element, the positive electrode active material or an auxiliary element for enhancing the chemical stability of the above layered structure / crystal structure may further be included. The above auxiliary element can be mixed together in the above layered structure / crystal structure to form a bond, and in this case as well, it should be understood as being included within the range of the chemical structure represented by Chemical Formula 3.

[0073] The above auxiliary element can include, for example, 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, or Zr. The above auxiliary element can also act as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn, such as Al.

[0074] Exemplarily, the above positive electrode active material or the above lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following Chemical Formula 3-1.

[0075] [Chemical Formula 3-1] Li x Ni a M1 b1 M2 b2 O 2+z

[0076] In Chemical Formula 3-1, M1 can contain Co, Mn, and / or Al. M2 can contain the above-mentioned auxiliary elements. In Chemical Formula 3-1, 0.9 ≦ x ≦ 1.2, 0.6 ≦ a ≦ 0.99, 0.01 ≦ b1 + b2 ≦ 0.4, and -0.5 ≦ z ≦ 0.1 may be satisfied.

[0077] The above positive electrode active material can further contain a coating element or a doping element. For example, an element substantially the same as or similar to the above-mentioned auxiliary element can be used as the coating element or the doping element. Exemplarily, among the above-mentioned elements, they can be used alone or in combination of two or more as the coating element or the doping element.

[0078] The above coating element or doping element can be present on the surface of the lithium-nickel metal oxide particles or can be included in the bonding structure represented by the above Chemical Formula 3 or Chemical Formula 3-1 through the surface of the lithium-nickel metal oxide particles.

[0079] The above positive electrode active material can contain a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content can be used.

[0080] The content of Ni in the above NCM-based lithium oxide (for example, the molar fraction of nickel among 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.

[0081] In some embodiments, the positive electrode active material may 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-based (LFP) active material (e.g., LiFePO4).

[0082] In some embodiments, the positive electrode active material may include an Mn-rich-based active material, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide)-based active material, or a Co-less-based active material having a chemical structure or crystal structure represented by Chemical Formula 4.

[0083] [Chemical Formula 4] p[Li2MnO3]·(1-p)[Li q JO2]

[0084] In Chemical Formula 4, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J can include at least one element among Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0085] The electrode binder layer 20 may further include a binder. The binder is not particularly limited. Exemplarily, the positive electrode binder layer can include, as the binder, one or more of polyvinylidene fluoride, styrene-butadiene rubber (SBR), polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate.

[0086] Also, the negative electrode binder layer can include any one selected from rubber-based binders such as styrene-butadiene rubber (SBR), fluorine-based rubber, ethylene-propylene rubber, butadiene rubber, isoprene rubber, and silane-based rubber; cellulose-based binders such as carboxymethyl cellulose (CMC), hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof; and combinations thereof.

[0087] The above electrode binder layer 20 can further contain a conductive material. The conductive material is not particularly limited. Exemplarily, the conductive material can include one or more of graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, carbon nanotube (CNT); metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0088] The electrode 100 for a lithium secondary battery according to the above embodiment can be manufactured by the manufacturing method described below.

[0089] Manufacturing Method of Electrode for Lithium Secondary Battery The manufacturing method of the electrode 100 for a lithium secondary battery according to one embodiment includes a step of forming an electrode binder layer 20 and an insulating layer 30 on at least one surface of the electrode current collector 10. The insulating layer 30 contains a copolymer, and the copolymer contains a copolymer having a repeating unit with an imide group and a rubber-based repeating unit. Since the detailed description of the electrode current collector 10, the electrode binder layer 20, the insulating layer 30, etc. overlaps with the above-described content, the description is omitted.

[0090] In some embodiments, the electrode binder layer 20 can be formed on at least one surface of the electrode current collector 10 by applying 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 to 200°C. The coating method of the electrode slurry is not particularly limited. Exemplarily, the electrode slurry may be applied to the surface of the electrode current collector 10 by any method such as slot die coating, bar coating, casting, or spraying.

[0091] In some embodiments, the electrode slurry may further contain a solvent. The solvent is not particularly limited. Exemplarily, as the solvent, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, water, etc. can be used. According to one embodiment, the solvent may be N-methyl-2-pyrrolidone (NMP). The amount of the solvent used is such that when considering the coating thickness of the slurry, production yield, etc., it can dissolve or disperse the components and has a viscosity that can exhibit excellent thickness uniformity when coated on the current collector, and is not particularly limited as long as it can achieve this.

[0092] In some embodiments, the insulating layer 30 can be formed on at least one surface of the electrode current collector 10 by applying a composition for insulating coating on at least one surface of the electrode current collector 10 and drying the composition at 60 to 200 °C. The coating method of the composition for insulating coating is not particularly limited. Exemplarily, it may be coated on the surface of the electrode current collector 10 by methods such as slot die coating, bar coating, casting, or spraying of the composition for insulating coating.

[0093] The formation order of the electrode mixture layer 20 and the insulating layer 30 is not particularly limited. That is, within the range where there is no significant difference in the characteristics of the finally formed electrode mixture layer 20 and insulating layer 30, the coating order of the electrode slurry and the composition for insulating coating is not particularly limited.

[0094] According to one embodiment, after simultaneously coating the electrode slurry and the composition for insulating coating on at least one surface of the electrode current collector 10, they can be dried to form both the electrode mixture layer 20 and the insulating layer 30.

[0095] According to another implementation example, first, after applying the above electrode slurry on at least one surface of the electrode current collector 10, a composition for insulating coating is applied (that is, the electrode slurry and the composition for insulating coating are sequentially applied), and these are dried simultaneously to form both the electrode mixture layer 20 and the insulating layer 30.

[0096] According to another implementation example, first, after applying the above electrode slurry on at least one surface of the electrode current collector 10, it is dried to first form the electrode mixture layer 20, and then, a composition for insulating coating is applied and dried to sequentially form the electrode mixture layer 20 and the insulating layer 30.

[0097] The composition for insulating coating can include a copolymer containing a repeating unit having an imide group and a rubber-based repeating unit. When a mixture obtained by blending a polymer composed of the repeating unit having an imide group and a polymer composed of the rubber-based repeating unit is applied as the composition for insulating coating, since the compatibility of the two polymers is not good, phase separation may occur, and it may become impossible to manufacture the insulating layer 30. Therefore, when the composition for insulating coating 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.

[0098] Since the detailed description of the above repeating unit having an imide group, rubber-based repeating unit, copolymer, etc. overlaps with the above-described content, the description is omitted.

[0099] The composition for insulating coating can further include a solvent. The type of the solvent is not particularly limited. Exemplarily, as the solvent, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, water, etc. can be used. According to one embodiment, the solvent may be N-methyl-2-pyrrolidone (NMP).

[0100] In some embodiments, the content of the copolymer contained in the insulating coating composition may be 5 wt% to 50 wt% based on the total insulating coating composition. Exemplarily, the content of the copolymer contained in the insulating coating composition may be 10 to 40 wt%, 15 to 35 wt%, 10 to 30 wt%, or 15 to 25 wt% based on the total insulating coating composition. Specifically, the content of the copolymer contained in the insulating coating composition may be 10 wt% to 20 wt% based on the total insulating coating composition.

[0101] In some embodiments, the content of the solvent contained in the insulating coating composition may be 50 wt% to 95 wt% based on the total insulating coating composition. Exemplarily, the content of the solvent contained in the insulating coating composition may be 60 to 90 wt%, 65 to 85 wt%, 70 to 90 wt%, or 75 to 85 wt% based on the total insulating coating composition. Specifically, the content of the solvent contained in the insulating coating composition may be 80 wt% to 90 wt% based on the total insulating coating composition.

[0102] When the contents of the copolymer and the solvent contained in the insulating coating composition are as described above, the coating processability can be improved while the copolymer contained in the insulating coating composition is well dispersed.

[0103] In some embodiments, the insulating layer 30 may be formed in a structure disposed on the plain portion of the electrode current collector 10 (see FIG. 2), or may be formed in a structure disposed so as to cover a part of the electrode mixture layer from a part of the plain portion (see FIGS. 1 and 3).

[0104] Lithium secondary battery A lithium secondary battery according to one embodiment includes the secondary battery electrode 100 according to any one of the above embodiments. Specifically, the lithium secondary battery may include a unit cell including the lithium secondary battery electrode 100 according to any one of the above-described embodiments as a negative electrode or a positive electrode.

[0105] In some embodiments, the unit cell can further include a separator membrane between the positive electrode and the negative electrode. The separator membrane is not particularly limited. Exemplarily, the separator membrane can include a porous polymer film made of a polyolefin polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. Also, the separator membrane can include a non-woven fabric formed from high melting point glass fibers, polyethylene terephthalate fibers, etc.

[0106] In some embodiments, the lithium secondary battery can be manufactured by housing the above-described unit cell in a pouch which is a battery case and then injecting an electrolytic solution.

[0107] The electrolytic solution can include an organic solvent and a lithium salt. The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move and is not particularly limited. Exemplarily, the electrolytic solution can be used alone or as a mixture of two or more of carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents. When used as a mixture of two or more, the mixing ratio can be appropriately adjusted according to the intended battery performance.

[0108] The lithium salt can be dissolved in the organic solvent and act as a source of lithium ions in the battery, enabling the basic operation of the lithium secondary battery and promoting the movement 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 concentrations suitable for the purpose. The electrolytic solution may further include a known solvent and a known additive as necessary to improve charge-discharge characteristics, flame retardancy characteristics, etc.

[0109] In one implementation example, the unit cell may include a solid electrolyte and not include a separator between the positive electrode and the negative electrode. 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.

[0110] Examples 1. Manufacturing of Electrodes 1) Composition for Insulating Coating (1) Examples 1 to 4 Solutions in which polyamideimide (PAI) grafted with hydrogenated nitrile butadiene rubber (HNBR) and a solvent (NMP) were mixed at a weight ratio of 15:85 were used as the compositions for insulating coating in Examples 1 to 4. At this time, the graft ratio of hydrogenated nitrile butadiene rubber (HNBR) to the polyamideimide (PAI) was adjusted to be different as shown in Table 1 below according to the examples.

[0111] (2) Comparative Example 1 A solution in which polyamideimide (PAI) and a solvent (NMP) were mixed at a weight ratio of 15:85 was used as the composition for insulating coating in Comparative Example 1.

[0112] (3) Comparative Example 2 A solution in which hydrogenated nitrile butadiene rubber (HNBR) and a solvent (NMP) were mixed at a weight ratio of 20:80 was used as the composition for insulating coating in Comparative Example 2.

[0113] (4) Comparative Example 3 A solution in which polyamideimide (PAI), hydrogenated nitrile butadiene rubber (HNBR), and a solvent (NMP) were mixed 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 butadiene rubber (HNBR) and polyamideimide (PAI) was adjusted to a weight ratio of 15:85.

[0114] 2) Manufacturing of Insulating Layer Test Pieces After applying the insulating coating compositions of Examples 1 to 4 and Comparative Examples 1 to 3 on a polyethylene terephthalate (PET) film with a thickness of 125 μm, they were thoroughly dried in a hot air oven at 120 °C for 6 hours to produce 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 test piece.

[0115] 3) Production of the positive electrode On one side of an aluminum foil (Al-foil) serving as a positive electrode current collector, a slurry containing an NCM-based positive electrode active material (Li[Ni 0.8 Co 0.1 Mn 0.1 O2) was applied at a loading level of 20 mg / cm 2 . After applying the insulating coating compositions produced in the above Examples and Comparative Examples so as to cover a part of the binder layer from a part of the non-coated portion, it was passed through a hot air drying oven at 60 °C to 200 °C for drying, and a positive electrode including a positive electrode mixture layer and an insulating layer in the structure shown in FIG. 1 was produced on one side of the positive electrode current collector.

[0116] 2. Evaluation of the electrode 1) Swelling of the insulating layer An electrolytic solution in which a 1.5 M LiPF6 electrolyte was added to a solvent in which ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) were mixed at a volume ratio of 2:7:1 was prepared. The insulating layer test piece produced as described above was impregnated with the above electrolytic solution at 25 °C for 24 hours, and the mass of the insulating layer test piece before and after impregnation was measured respectively. The results of measuring the swelling degree of the insulating layer in % according to the following formula 1 are shown in Table 1 below.

[0117] [Formula 1] Swelling ratio (%) = (W2 - W1) / W1 × 100

[0118] In the above formula 1, W1 is the mass of the insulating layer test piece before impregnation with the electrolytic solution, and W2 is the mass of the insulating layer test piece after impregnation with the electrolytic solution and dried at room temperature for 6 hours.

[0119] 2) Elongation ratio The insulating layer test pieces manufactured as described above were cut into a size of 100 mm × 10 mm, and test pieces for measuring the elongation rate were prepared. The above test pieces were put into a UTM tensile testing machine, pulled up and down at a speed of 50 mm / s, and the length of elongation until the above test pieces broke was measured. The results of calculating the elongation rate in % are shown in Table 1 below.

[0120] 3) Defects in the manufacturing process (1) Presence or absence of peeling during electrolyte impregnation An electrolyte in which 1.5 M LiPF6 electrolyte was added to a solvent obtained by mixing ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) in a volume ratio of 2:7:1 was prepared. After impregnating the electrodes manufactured as described above in the above electrolyte at 60 °C for 120 minutes, the results of evaluation where ○ indicates the case of complete peeling, △ indicates the case of partial peeling, and X indicates the case of no peeling are shown in Table 1 below.

[0121] (2) Presence or absence of peeling of the plain part during notching When notching the electrodes manufactured as described above to form the plain part of the positive current collector into a positive tab, the results of evaluation where ○ indicates the case where a phenomenon of peeling of the interface between the plain part and the insulating layer occurs, △ indicates the case where the interface is partially peeled or damaged, and X indicates the case where no peeling phenomenon of the interface occurs are shown in Table 1 below.

[0122] (3) Rollability The results of evaluation by converting the number of breakages per 1000 m in the process of rolling the electrodes manufactured as described above at a density of 3.6 g / cc are shown in Table 1 below.

[0123]

Table 1

[0124] Referring to Table 1 above, in Comparative Example 1, the elongation rate of the insulating layer is relatively low, and a phenomenon occurs where the interface between the plain part and the insulating layer peels off during notching of the electrode. It can be confirmed that the number of breakages during rolling of the electrode is relatively large and the rolling processability is poor. Without being bound by a specific theory, this is judged to be due to the insulating layer containing only polyamideimide (PAI) which lacks softness.

[0125] Also, in Comparative Examples 2 and 3, when the insulating layer is impregnated with the electrolytic solution, it is shown that the insulating layer partially dissolves, and it can be confirmed that it is not suitable for use in lithium secondary batteries. Without being bound by a specific theory, this is judged to be due to the property that hydrogenated nitrile butadiene rubber (HNBR) contained in the insulating layer dissolves in the electrolytic solution.

[0126] In contrast, in Examples 1 to 4 where the insulating layer contains polyamideimide grafted with hydrogenated nitrile butadiene rubber (PAI-HNBR), it can be confirmed that they have excellent performance compared to Comparative Examples 1 to 3 from the viewpoints of the swelling / elongation rate of the insulating layer and defective matters in the manufacturing process. In particular, in Examples 1 and 3 where the insulating layer contains PAI-HNBR with a graft ratio of polyamideimide (PAI) and hydrogenated nitrile butadiene rubber (HNBR) of 70:30 to 85:15, it can be confirmed that the swelling of the insulating layer is less than that in Example 4 and the rolling processability is superior to that in Example 2.

[0127] Therefore, when the insulating layer contains a copolymer containing repeating units having imide groups and rubber-based repeating units at a specific ratio, it is judged that the performance such as the insulating property, heat resistance, peel resistance, and stretchability of the insulating layer can be improved, and the issue of quality degradation can be effectively prevented in the subsequent manufacturing process of the secondary battery.

Explanation of Symbols

[0128] 10: Current collector of electrode 20: Electrode mixture layer 30: Insulating layer 100: Electrode for lithium secondary battery A: Overlapping region

Claims

1. An electrode current collector, an electrode mixture layer and an insulating layer on at least one surface of the electrode current collector, The insulating layer contains a copolymer, The copolymer contains a repeating unit having an imide group and a rubber-based repeating unit, and is an electrode for a lithium secondary battery.

2. The imide group is represented by the following Chemical Formula 1, and the electrode for a lithium secondary battery according to Claim 1. 【Chemical Formula 1】 【Chemical 1】 In the above Chemical Formula 1, R １ , R ２ and R ３ are each independently hydrogen or an organic group.

3. The repeating unit having an imide group further contains an amide group, and the electrode for a lithium secondary battery according to Claim 1.

4. The amide group is represented by the following Chemical Formula 2, and the electrode for a lithium secondary battery according to Claim 3. 【Chemical Formula 2】 【Chemical 2】 In Chemical Formula 2, R, R' and R'' are each independently hydrogen or an organic group.

5. The repeating unit having an imide group contains a repeating unit constituting polyamideimide (PAI), and the electrode for a lithium secondary battery according to Claim 1.

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

7. The copolymer contains a graft copolymer in which a second block containing a rubber-based repeating unit is grafted onto a first block containing a repeating unit having an imide group, and the electrode for a lithium secondary battery according to Claim 1.

8. The first block contains a repeating unit having an imide group and an amide group, The second block contains a hydrogenated nitrile butadiene rubber (HNBR)-based repeating unit, and the electrode for a lithium secondary battery according to Claim 7.

9. In the graft copolymer, the first block is contained in an amount of 50 to 95% by weight based on the weight of the entire graft copolymer, and the electrode for a lithium secondary battery according to Claim 7.

10. In the graft copolymer, the second block is contained in an amount of 5 to 50% by weight based on the weight of the entire graft copolymer, and the electrode for a lithium secondary battery according to Claim 7.

11. The insulating layer further contains a ceramic material, and the electrode for a lithium secondary battery according to Claim 1.

12. The electrode current collector includes a plain portion on which no electrode binder layer is disposed. The insulating layer covers a part of the plain portion and a part of the electrode binder layer. The electrode for a lithium secondary battery according to claim 1. **Claim 13** The electrode current collector includes a plain portion on which no electrode binder layer is disposed. The insulating layer is disposed on the plain portion. The electrode for a lithium secondary battery according to claim 1. **Claim 14** Forming an electrode binder layer and an insulating layer on at least one surface of an electrode current collector. The insulating layer includes a copolymer. The copolymer includes a repeating unit having an imide group and a rubber-based repeating unit. A method for manufacturing an electrode for a lithium secondary battery. **Claim 15** A lithium secondary battery including the electrode for a lithium secondary battery according to any one of claims 1 to 13.

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