Electrode for secondary battery and secondary battery including same

Abstract

The present invention relates to an electrode for a secondary battery and a secondary battery including the same. An electrode for a secondary battery according to one embodiment includes: a coated portion in which an electrode active material layer is provided on a current collector; and an uncoated portion in which the electrode active material layer is not provided on the current collector; and an insulating coating layer disposed on at least a portion of the uncoated portion and including an electrode insulating polymer, in which the electrode insulating polymer has a coefficient of thermal expansion of 66 [mu] m / m DEG C to 127 [mu] m / m DEG C.

Description

Technical Field

[0001] This invention relates to an electrode for a secondary battery and a secondary battery including the electrode. Background Technology

[0002] In recent years, with the increasing use of portable electronic devices such as mobile phones and laptops, and with the research and development of electric vehicles and hybrid electric vehicles that can replace fossil fuel vehicles such as gasoline and diesel vehicles, there is a need for smaller, lighter, and more durable secondary batteries. In particular, research on high-energy-density secondary batteries is being actively conducted to achieve the goals of miniaturization and weight reduction.

[0003] To achieve high energy density, high-density electrodes are necessary. However, manufacturing high-density electrodes requires a high-pressure calendering process, which can introduce various quality defects such as ripples, wrinkles, fractures, and peeling. The main cause of these defects is the difference in properties of the materials used in the electrode, such as the current collector and the active material, particularly the difference in their thermal properties.

[0004] Furthermore, in abnormal situations where the positive and negative current collectors of a secondary battery are in direct contact, a short circuit may occur. When a short circuit occurs, the likelihood of fire is high, potentially posing a fatal hazard. To prevent this, an insulating coating is being applied to the uncoated portions of the electrodes on the current collectors where no active material is applied, to mitigate the risks associated with short circuits.

[0005] However, when the thermal properties of the insulating coating are not considered, more serious quality defects as described above may occur at the interfaces of the current collector, the active material layer, and the coating.

[0006] Therefore, there is a need to develop an electrode for secondary batteries that can achieve both safety and high energy density, while also improving various defects that may occur in the secondary battery manufacturing process. Summary of the Invention

[0007] (a) Technical problems to be solved According to one aspect of the present invention, an electrode for secondary batteries can be provided that exhibits high energy density while improving various defects that may occur in the electrode manufacturing process.

[0008] According to another aspect of the invention, a secondary battery with improved safety can be provided.

[0009] The electrode for secondary batteries of this invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar and wind power generation. Furthermore, the electrode for secondary batteries of this invention can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0010] (II) Technical Solution The electrode for a secondary battery according to the present invention includes: a coated portion on which an electrode active material layer is disposed and an uncoated portion on which no electrode active material layer is disposed; and an insulating coating disposed on at least a portion of the uncoated portion, wherein the insulating coating comprises an electrode insulating polymer, wherein the coefficient of thermal expansion of the electrode insulating polymer is from 66 μm / m℃ to 127 μm / m℃.

[0011] According to one embodiment, the coefficient of thermal expansion of the electrode insulating polymer can be from 72 μm / m℃ to 80 μm / m℃.

[0012] The electrode insulating polymer according to one embodiment may include at least one selected from polyamide-based polymers, polyamide-imide-based polymers, fluorinated vinyl polymers, butadiene-based rubbers, and copolymers thereof.

[0013] According to one embodiment, the electrode insulating polymer may include a polyamide-based polymer and a fluorinated vinyl polymer, wherein the weight ratio of the polyamide-based polymer to the fluorinated vinyl polymer may be from 1:8.5 to 1:9.5.

[0014] The electrode insulating polymer according to one embodiment may include a copolymer comprising: an amide-imide first repeating unit; and at least one second repeating unit selected from butadiene repeating units, nitrile repeating units, and styrene repeating units.

[0015] According to one embodiment, the first repeating unit may contain an aromatic ring.

[0016] According to one embodiment, the first repeating unit may contain a benzene ring.

[0017] According to one embodiment, the second repeating unit may be at least one selected from butadiene-based repeating units, acrylonitrile-butadiene-based repeating units, and hydrogenated acrylonitrile-butadiene-based repeating units.

[0018] According to one embodiment, the molar ratio of the first repeating unit to the second repeating unit may be 60 to 80: 40 to 20.

[0019] According to one embodiment, the copolymer may be at least one selected from random copolymers, alternating copolymers, block copolymers and graft copolymers.

[0020] According to one embodiment, an insulating coating may be applied to at least a portion of the coated portion and at least a portion of the uncoated portion.

[0021] According to one embodiment, the insulating coating disposed on at least a portion of the uncoated portion and the insulating coating disposed on at least a portion of the coated portion may be continuous.

[0022] According to one embodiment, the electrode can be a positive electrode, and the current collector can include at least one metal selected from stainless steel, nickel, titanium, aluminum, and alloys thereof.

[0023] According to one embodiment, the elongation of the uncoated portion with an insulating coating can be from 25% to 43%.

[0024] The secondary battery according to the present invention includes electrodes according to one embodiment.

[0025] (III) Beneficial Effects According to one embodiment of the present invention, the manufacturability of high energy density electrodes for secondary batteries can be improved, thereby improving the defect rate of electrodes for secondary batteries.

[0026] According to another embodiment of the present invention, the energy efficiency and safety of secondary batteries can be improved.

[0027] Preferred Implementation The embodiments described in this specification can be varied in various other forms, and therefore the technology according to a particular embodiment is not limited to the embodiments described below. Furthermore, throughout the specification, unless otherwise specifically stated to the contrary, "comprising," "including," "having," "containing," or "having" a constituent element means that it may also include other constituent elements, not exclude other constituent elements, and does not exclude elements, materials, or processes not further listed.

[0028] The numerical ranges used in this specification include lower and upper limits, all values ​​within that range, increments logically derived from the form and width of the defined range, all values ​​defined therein, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. As an example, when the content of a component is defined as 10% to 80% or 20% to 50%, it should be interpreted that numerical ranges of 10% to 50% or 50% to 80% are also described in this specification. In this specification, unless otherwise specifically defined, values ​​outside the defined numerical range that may occur due to experimental error or rounding are also included within the defined numerical range.

[0029] Hereinafter, unless otherwise specifically defined, “about” may be considered as a value within 30%, 25%, 20%, 15%, 10% or 5% of the explicitly stated value.

[0030] As used in this specification, the term "secondary battery" can refer to a lithium secondary battery that generates electrical energy through oxidation and reduction reactions during the insertion and extraction of lithium ions in the positive and negative electrodes.

[0031] The present invention will now be described in detail. However, this is merely an exemplary description, and the present invention is not limited to the specific embodiments described herein.

[0032] <Electrode Insulating Polymer> According to a specific embodiment of the present invention, the electrode insulating polymer can refer to an electrode insulating polymer coated on at least a portion of the uncoated portion of the electrode, such that a short circuit will not occur even when the two electrodes of the secondary battery are in contact. The lower limit of the coefficient of thermal expansion of the electrode insulating polymer according to one embodiment can be 66 μm / m℃ or higher, 70 μm / m℃ or higher, 72 μm / m℃ or higher, or 74 μm / m℃ or higher, and the upper limit of the coefficient of thermal expansion of the electrode insulating polymer can be 127 μm / m℃ or lower, 120 μm / m℃ or lower, 110 μm / m℃ or lower, 100 μm / m℃ or lower, 90 μm / m℃ or lower, 80 μm / m℃ or lower, or 78 μm / m℃ or lower. Specifically, the coefficient of thermal expansion of the electrode insulating polymer can be from 66 μm / m℃ to 127 μm / m℃ or from 72 μm / m℃ to 80 μm / m℃.

[0033] The electrode insulating polymer according to one embodiment may include at least one selected from polyamide-based polymers, polyamide-imide-based polymers, fluorinated vinyl polymers, butadiene-based rubbers, and copolymers thereof.

[0034] According to one embodiment, a polyamide-based polymer can refer to a polymer containing repeating units with amide groups, and the polyamide-based polymer can be polyamide or polycaprolactam.

[0035] According to one embodiment, the polyamide-imide polymer can refer to a polymer containing repeating units containing amide and imide groups, and the polyamide-imide polymer can be a bis(4-aminophenyl)methane-triphenyltrihydride copolymer, a 4,4'-diaminodiphenyl sulfone-triphenyltrihydride copolymer, a bisphenol A-diamine-triphenyltrihydride copolymer, or a p-phenylenediamine-triphenyltrihydride copolymer.

[0036] According to one embodiment, the fluorinated vinyl polymer can be polyvinylidene fluoride or polytetrafluoroethylene.

[0037] According to one embodiment, the butadiene-based rubber may be butadiene rubber (BR), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (H-NBR), or styrene butadiene rubber (SBR).

[0038] The electrode insulating polymer according to one embodiment may include: two or more selected from polyamide-based polymers, polyamide-imide-based polymers, fluorinated vinyl polymers or butadiene-based rubbers (specifically, a mixture of two or more polymers); or copolymers of polyamide-based polymers, polyamide-imide-based polymers, fluorinated vinyl polymers or butadiene-based rubbers.

[0039] According to one embodiment, the electrode insulating polymer may include a polyamide-based polymer and a fluorinated vinyl polymer. Specifically, the weight ratio of the polyamide-based polymer to the fluorinated vinyl polymer may be from 1:8.5 to 1:9.5, more specifically from 1:8.8 to 1:9.2, and even more specifically from 1:8.8 to 1:9.0. When the weight ratio of the polyamide-based polymer to the fluorinated vinyl polymer is not within the above range, if the content of the polyamide-based polymer is too low, it will swell excessively when immersed in the electrolyte during the assembly process, resulting in difficulty in ensuring adhesion to the substrate. If the content of the polyamide-based polymer is too high, it will be difficult to effectively distribute the stress applied in calendering processes, which may lead to reduced performance, such as breakage.

[0040] Furthermore, the electrode insulating polymer according to one embodiment can be a copolymer comprising: an amide-imide first repeating unit; and at least one second repeating unit selected from butadiene repeating units, nitrile repeating units, and styrene repeating units.

[0041] As used in this specification, the term "repeating unit" refers to monomers used to form a polymer that are linked together through addition polymerization or condensation polymerization, such that the structure of the monomers is repeated in the polymer. As an example, polybutadiene, as a butadiene rubber, is a polymer having repeating units derived from butadiene, meaning that butadiene monomers are linked together through addition polymerization, such that the structure of the butadiene monomers is repeated in the polybutadiene polymer.

[0042] According to one embodiment, the first repeating unit may comprise an aromatic ring, specifically, it may comprise at least one selected from substituted or unsubstituted C6 to C20 aromatic rings, substituted or unsubstituted C6 to C10 aromatic rings, substituted or unsubstituted C6 to C20 heteroaromatic rings, and substituted or unsubstituted C6 to C10 heteroaromatic rings, specifically, it may comprise substituted or unsubstituted benzene or substituted or unsubstituted naphthalene.

[0043] As an example, the amide-imide repeating unit, serving as the first repeating unit, can be prepared from a monomeric composition comprising a diamine compound and a carboxylic acid compound, or a diamine compound and an isocyanate compound. Specifically, the first repeating unit can be prepared by subjecting a diamine compound and a carboxylic acid compound, or a diamine compound and an isocyanate compound, to a polymer condensation reaction, so that the repeating unit structure, linking the amide and imide structures, repeats in the electrode insulating polymer. The specific structure of the amide-imide repeating unit can vary depending on the monomers used in the reaction.

[0044] According to one embodiment, the second repeating unit may be at least one selected from butadiene-based repeating units, acrylonitrile-butadiene-based repeating units, and hydrogenated acrylonitrile-butadiene-based repeating units.

[0045] As an example, the hydrogenated acrylonitrile-butadiene repeating unit, serving as the second repeating unit, can be prepared from a monomeric composition comprising an acrylonitrile compound and a butadiene compound. Specifically, the second repeating unit can be prepared by polymer addition polymerization of the acrylonitrile compound and the butadiene compound, so that the repeating unit structure, linking the hydrogenated acrylonitrile structure and the butadiene structure, repeats in the electrode insulating polymer. The specific structure of the hydrogenated acrylonitrile-butadiene repeating unit can vary depending on the monomers used in the reaction.

[0046] In one embodiment, the molar ratio of the first repeating unit to the second repeating unit can be 60 to 80:40 to 20, more specifically 70 to 75:30 to 25. When the copolymer has the molar ratio of repeating units as described above, the coefficient of thermal expansion of the electrode insulating polymer can meet the numerical range described above.

[0047] According to one embodiment, the copolymer may be at least one selected from random copolymers, alternating copolymers, block copolymers and graft copolymers, and more specifically, a graft copolymer.

[0048] In the existing field of secondary batteries, polyamide-imide can be used as an electrode insulating polymer to prevent short circuits when the positive / negative electrode contacts are in contact, by applying it to the uncoated portion of the positive or negative electrode. However, existing electrode insulating polymers containing only polyamide-imide have the following problems: during the drying process of the electrode manufacturing process for secondary batteries, quality defects such as warping of the uncoated portion may occur due to the relaxation of residual stress; during the calendering and winding of the electrode, there is a problem that the coated and uncoated portions of the current collector are prone to breakage; and when immersed in electrolyte, there is a possibility of serious process defects such as peeling of the insulating coating. These problems may be more severe, especially in high-density electrodes used to achieve high energy density, and the aforementioned process problems may limit the electrode density.

[0049] On the other hand, the electrode insulating polymer according to the present invention includes at least one selected from polyamide-based polymers, polyamide-imide-based polymers, fluorinated vinyl polymers, butadiene-based rubbers and copolymers thereof, and the coefficient of thermal expansion of the electrode insulating polymer meets a specific range, thereby having the advantage of improving process problems, etc.

[0050] <Electrodes for Secondary Batteries> An electrode for a secondary battery according to a specific embodiment of the present invention may include: a coated portion on which an electrode active material layer is disposed, and an uncoated portion on which no electrode active material layer is disposed; and an insulating coating disposed on at least a portion of the uncoated portion, the insulating coating comprising an electrode insulating polymer. An electrode for a secondary battery according to one embodiment may refer to a positive electrode. The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the current collector, and may include a coated portion on which the positive electrode active material layer is disposed on at least one side of the current collector and an uncoated portion on which no positive electrode active material layer is disposed, and may include an insulating coating disposed on at least a portion of the uncoated portion, the insulating coating being formed by coating with the electrode insulating polymer as described above.

[0051] In one embodiment, the positive current collector may include at least one metal selected from stainless steel, nickel, titanium, aluminum, or alloys thereof. Specifically, the metal may be aluminum, which may be untreated aluminum or aluminum surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive current collector is not limited thereto, but may, for example, be from 10 μm to 50 μm.

[0052] Furthermore, as described above, the lower limit of the coefficient of thermal expansion of the electrode insulating polymer according to a specific embodiment of the present invention can be 66 μm / m℃ or higher, 70 μm / m℃ or higher, 72 μm / m℃ or higher, or 74 μm / m℃ or higher, and the upper limit of the coefficient of thermal expansion of the electrode insulating polymer can be 127 μm / m℃ or lower, 120 μm / m℃ or lower, 110 μm / m℃ or lower, 100 μm / m℃ or lower, 90 μm / m℃ or lower, 80 μm / m℃ or lower, or 78 μm / m℃ or lower. Specifically, the coefficient of thermal expansion of the electrode insulating polymer can be from 66 μm / m℃ to 127 μm / m℃ or from 72 μm / m℃ to 80 μm / m℃. By having a coefficient of thermal expansion within the numerical range described above, when introduced as an electrode insulating coating into the current collector, compared with the case of introducing existing electrode insulating polymers, the process defects or safety defects described above, mainly caused by the difference in elongation and stress relaxation behavior between the current collector and the coated and uncoated portions, can be improved.

[0053] In one embodiment, the coating portion may refer to the area of ​​the current collector in which an electrode active material layer is disposed on at least one side of the current collector.

[0054] According to one embodiment, an insulating coating may be applied to at least a portion of the coated portion and at least a portion of the uncoated portion. Furthermore, the insulating coating applied to at least a portion of the uncoated portion and the insulating coating applied to at least a portion of the coated portion may be continuous.

[0055] The positive electrode active material layer may contain a positive electrode active material. The positive electrode active material may contain compounds that enable reversible insertion and extraction of lithium ions.

[0056] According to an exemplary embodiment, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0057] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may comprise a layered structure or a crystal structure represented by the following chemical formula 1.

[0058] [Chemical Formula 1] Lix Ni a M b O 2+z In chemical formula 1, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0059] The chemical structure represented by Formula 1 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 1 is provided to represent the bonding relationships of the main active elements, and it should be understood that Formula 1 includes the introduction and substitution of additional elements.

[0060] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure and form bonds; this should be understood to also include the chemical structures represented by Formula 1.

[0061] The auxiliary element may include at least one of, for example, 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 auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0062] For example, the positive electrode active material or the lithium-nickel metal oxide may contain a layered structure or a crystal structure represented by the following chemical formula 1-1.

[0063] [Chemical Formula 1-1] Li x Ni a M1 b1 M2 b2 O 2+z In chemical formula 1-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 1-1, the following conditions may be met: 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, -0.5≤z≤0.1.

[0064] The positive electrode active material may further include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, one or more combinations of the elements described above can be used as coating elements or doping elements.

[0065] The coating element or dopant element may exist on the surface of the lithium-nickel metal oxide particles, or may penetrate through the surface of the lithium-nickel metal oxide particles and be contained in the bonding structure represented by chemical formula 1 or chemical formula 1-1.

[0066] The positive electrode active material may contain nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0067] Ni can be provided as a transition metal related to the power and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (High-Ni) composition for the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0068] However, with increasing Ni content, the long-term storage stability and lifetime stability of the cathode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, while lifetime stability and capacity retention characteristics can be improved by including Mn.

[0069] The Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content can 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.

[0070] In some embodiments, the positive electrode active material may further comprise lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0071] In some embodiments, the positive electrode active material may include, for example, a manganese-rich (Mn-rich) active material having a chemical structure or crystal structure represented by Formula 2, a lithium-rich layered oxide (LLO) / over-lithiated oxide (OLO) active material, or a cobalt-less active material.

[0072] [Chemical Formula 2] p[Li2MnO3]·(1 - p)[Li q JO2] In Chemical Formula 2, 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.

[0073] In one embodiment, the positive electrode may further include a binder and a conductive material.

[0074] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride - co - hexafluoropropylene) copolymer, polyacrylonitrile, polymethylmethacrylate, butadiene rubber, etc. In one embodiment, a PVDF - based binder may be used as the positive electrode binder.

[0075] The conductive material may be added to enhance the conductivity of the positive electrode active material layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon - based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor - grown carbon fiber (VGCF), carbon fiber, etc. and / or metal - based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc., but is not limited thereto.

[0076] In one embodiment, the uncoated portion may refer to the region of the entire current collector surface where no electrode active material layer is provided on either surface of the current collector. Alternatively, the uncoated portion may refer to the region of the entire current collector excluding the coated portion.

[0077] In one embodiment, the elongation rate of the uncoated portion provided with the insulating coating may be 25% to 43%, more specifically 30% to 38%.

[0078] In some embodiments, the electrode insulating polymer contained in the insulating coating may be the electrode insulating polymer having a thermal expansion coefficient according to a specific embodiment of the present invention, and the current collector may include aluminum.

[0079] The elongation can refer to the maximum elongation measured by taking an uncoated portion of the electrode for a secondary battery according to a specific embodiment of the present invention, which is provided with the insulating coating, and performing a tensile test on the uncoated portion using, for example, a universal testing machine.

[0080] In some embodiments, by coating the uncoated portion with an electrode insulating polymer having the coefficient of thermal expansion as described above, the uncoated portion can exhibit elongation within the range described above.

[0081] Since the uncoated portion has an elongation rate within the aforementioned range, compared to the case where an insulating coating is formed by introducing an existing electrode insulating polymer into the uncoated portion, the process defects or safety defects mentioned above, which are mainly caused by the difference in elongation rate and stress relaxation behavior between the current collector and the coated and uncoated portions, can be improved.

[0082] As described above, the electrode for a secondary battery according to one embodiment can be a positive electrode, but is not necessarily limited to this. In an exemplary embodiment, the electrode for a secondary battery can refer to a negative electrode, or both a positive and a negative electrode.

[0083] When the electrode for a secondary battery according to one embodiment refers to a negative electrode, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the current collector, and may include a coated portion on the current collector where the electrode active material layer is disposed and an uncoated portion on the current collector where the electrode active material layer is not disposed, and may include an insulating coating disposed on at least a portion of the uncoated portion, the insulating coating being disposed by coating an electrode insulating polymer as described above.

[0084] Secondary batteries One specific embodiment of the present invention provides a secondary battery comprising electrodes, a separator between the electrodes, an electrolyte, and other additives. The secondary battery may include at least one of the electrodes described above, according to one specific embodiment of the present invention, as either a positive or negative electrode.

[0085] The secondary battery can be made in forms such as pouch, prism, cylinder, coin, etc.

[0086] The secondary battery according to a specific embodiment of the present invention can be applied to various fields such as laptops, mobile phones, electric vehicles, and hybrid electric vehicles. Detailed Implementation

[0087] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and do not limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and its technical concept, which is obvious to those skilled in the art, and such variations and modifications naturally fall within the scope of the claims.

[0088] Experimental Example (Example 1) On an aluminum foil current collector, a slurry for forming a positive electrode active material layer, having the composition shown in Table 1 below, is applied using a slit extrusion coating method to form uncoated portions of 15 mm horizontally on both sides of the current collector in the width direction, thereby forming a positive electrode active material layer. The width direction can refer to a direction perpendicular to the current collector's travel direction, or it can refer to a direction perpendicular to the boundary line between the uncoated portion and the coated portion.

[0089] An insulating coating forming composition is applied to the uncoated portion of the positive electrode active material layer and a portion of the positive electrode active material layer in contact with the uncoated portion, thereby forming an insulating coating with a width of approximately 5 mm. The insulating coating forming composition comprises a graft copolymer of polyamide-imide (PAI) as an electrode insulating polymer and hydrogenated nitrile butadiene rubber (H-NBR) (PAI:H-NBR repeating unit molar ratio = 75:25, copolymerization temperature 130°C), specifically, the polyamide-imide (PAI) is a bis(4-aminophenyl)methane-triphenyltriglyceridyl anhydride copolymer. Subsequently, drying is performed at 120°C to produce a positive electrode with a positive electrode active material layer and an insulating coating formed on the current collector.

[0090] [Table 1] (Example 2) The positive electrode was manufactured using the same method as in Example 1, except that a polyvinylidene fluoride (PVDF) polymer and a polyamide (PA) polymer were mixed in a weight ratio of 9:1 as the electrode insulating polymer.

[0091] (Example 3) The positive electrode was manufactured using the same method as in Example 1, except that the copolymer was polymerized at a high temperature above 130°C.

[0092] (Comparative Example 1) The positive electrode was manufactured using the same method as in Example 1, except that a PVDF polymer was used as the electrode insulating polymer.

[0093] (Comparative Example 2) The positive electrode was manufactured using the same method as in Example 1, except that a polyamide-imide (PAI) polymer was used as the electrode insulating polymer.

[0094] (Comparative Example 3) The positive electrode was manufactured using the same method as in Example 1, except that a polyacrylonitrile (PAN) polymer was used as the electrode insulating polymer.

[0095] <Evaluation Example> Evaluation Example 1: Evaluation of the coefficient of thermal expansion and elongation of current collector of electrode insulating polymer The coefficients of thermal expansion of each polymer used as electrode insulating polymers in Examples 1 to 3 and Comparative Examples 1 to 3, and the elongation of the current collectors with insulating coatings formed by coating the polymers were evaluated, and the results are recorded in Table 2 below. The coefficients of thermal expansion were measured using a thermomechanical analysis (TMA Q400, TA Instruments) apparatus, with a temperature increase of 5°C / min within a temperature range of 25°C to 200°C. The strain was measured, and the coefficient of thermal expansion was calculated from the slope of the resulting dimension change-temperature curve. The elongation was measured using a universal testing machine (UTM 3400, Instron), with a gauge length of 50 mm and a tensile speed of 20 mm / min, and the maximum elongation was measured.

[0096] [Table 2] Evaluation Example 2: Processability Evaluation of Electrodes for Secondary Batteries The positive electrodes with a positive active material layer and an insulating coating prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 were calendered using a roll press to produce a positive electrode with a diameter of 800 μm. At this time, the travel speed of the roll press was 20 m / min.

[0097] During the calendering process of the positive electrode, the number of times the electrode broke was confirmed to evaluate the calendering processability, and the results are recorded in Table 3 below. During the calendering process of the positive electrodes prepared by Examples 1 to 3 and Comparative Examples 1 to 3, except for cases where breakage occurred due to reasons unrelated to the polymer, such as operator error, cases with 8 or more breakages were evaluated as X, cases with 5 or more breakages but less than 8 breakages were evaluated as △, and cases with less than 5 breakages were evaluated as O.

[0098] Furthermore, after notching the positive electrodes prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 to the predetermined dimensions, the cutting processability was evaluated by checking whether wrinkles or tears occurred, and the results are recorded in Table 3 below. A state with no special circumstances where the shape is similar to that of a conventional secondary battery electrode without electrode insulating polymer coating on the uncoated portion is evaluated as O. In contrast, a state where wrinkles occur is evaluated as △, and a state where tears occur is evaluated as X.

[0099] Furthermore, the positive electrodes manufactured through Examples 1 to 3 and Comparative Examples 1 to 3 were cut to predetermined dimensions and vacuum-dried at 120°C and 5 Torr for 12 hours. The degree of camber at the uncoated end of the electrode relative to the ground was evaluated and recorded in Table 3 below. The degree of camber was measured using a ruler, and the average value of the values ​​measured at the top, middle, and bottom of the electrode along its length direction was calculated as the average warpage value. The length direction can refer to the direction parallel to the travel direction of the positive electrode during slurry coating and calendering, or it can refer to the direction parallel to the boundary line between the uncoated and coated portions.

[0100] Furthermore, the positive electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were immersed in the electrolyte for 24 hours. The swelling ratio and whether surface peeling occurred were confirmed to evaluate the electrolyte resistance, and the results are recorded in Table 3 below. Whether surface peeling occurred was evaluated based on whether the insulating coating peeled off during immersion in the electrolyte. The swelling ratio was evaluated by measuring the thickness of the insulating coating before and after immersion in the electrolyte and calculating it according to the following formula.

[0101] [Relational Formula] Swelling rate (%) = ((thickness of the insulating coating after immersion in electrolyte) - (thickness of the insulating coating before immersion in electrolyte)) / (thickness of the insulating coating before immersion in electrolyte) [Table 3] Referring to Table 3, it can be confirmed that in Examples 1 to 3, where the electrode insulating polymer having a coefficient of thermal expansion range according to a specific embodiment of the present invention was coated, the number of fractures during an 800m journey was less than 5. In Comparative Examples 1 and 3, where the electrode insulating polymer did not meet the above conditions was coated, the number of fractures was 8 or more, or in Comparative Example 2, the number of fractures was 5 or more but less than 8. Therefore, it can be confirmed that the calendering processability of Examples 1 to 3 having a coefficient of thermal expansion range according to a specific embodiment of the present invention is improved compared to Comparative Examples 1 to 3.

[0102] While not bound by any particular theory, it can be understood that, in the cases of Examples 1 to 3, by using an electrode insulating polymer having a coefficient of thermal expansion range according to a specific embodiment of the present invention, even with an insulating coating, the difference in elongation between the commonly used aluminum current collector and the coated and uncoated portions can be mitigated, thus preventing breakage during travel.

[0103] Furthermore, as shown in Table 3, in Examples 1 to 3, where the electrode insulating polymer was coated with an electrode insulating polymer having a coefficient of thermal expansion range according to a specific embodiment of the present invention, no special circumstances were observed during the cutting process. However, in Comparative Example 1, where the electrode insulating polymer was coated with an electrode insulating polymer that did not meet the above conditions, tearing occurred during the cutting process. In Comparative Examples 2 and 3, although no tearing occurred, wrinkling was observed. Therefore, it can be confirmed that the cutting processability of Examples 1 to 3 was improved compared to the comparative examples. It can be understood that this difference is also attributed to whether or not the above-mentioned elongation difference exists or the magnitude of the above-mentioned elongation difference.

[0104] Furthermore, as shown in Table 3, it can be confirmed that in Examples 1 to 3, where an electrode insulating polymer with a coefficient of thermal expansion range according to a specific embodiment of the present invention is coated, warping hardly occurs even after vacuum drying. However, in Comparative Examples 1 to 3, where an electrode insulating polymer that does not meet the above conditions is coated, warping occurs to a greater extent.

[0105] This can be understood as being due to the fact that, in the cases of Examples 1 to 3, the elongation difference described above was mitigated and / or the stress relaxation behavior was improved. On the other hand, it can be understood that, unlike Example 1, in Comparative Examples 1 to 3, due to the unsuitable thermal properties of the electrode insulating polymer, the relaxation of residual stress, especially during the drying process, led to significant warping.

[0106] Furthermore, as shown in Table 3, it can be confirmed that in Examples 1 to 3, which were coated with an electrode insulating polymer having a coefficient of thermal expansion range according to a specific embodiment of the present invention, the swelling rate after immersion in the electrolyte was only at the 7% level, and no surface peeling caused by immersion in the electrolyte was observed. In contrast, Comparative Example 1, which did not meet the above conditions, exhibited a high swelling rate of 19%, and therefore surface peeling occurred. Thus, it can be confirmed that, in the case of Example 1, even when the electrode insulating polymer is coated on the uncoated portion of the electrode as described above, the processability of the manufacturing process can be significantly improved, while simultaneously achieving electrolyte resistance equal to or better than that of conventional electrode insulating polymers.

[0107] The swelling ratio refers to the degree to which the structure of the insulating coating applied to the uncoated portion becomes loose when immersed in an electrolyte solution. A higher swelling ratio indicates a more frequent penetration of electrolyte molecules into the coating. Therefore, although not bound by a specific theory, a higher swelling ratio may increase the likelihood of coating peeling when immersed in an electrolyte solution. Furthermore, peeling within the battery cell, as described above, could significantly reduce battery capacity and potentially lead to serious safety issues. In the case of Example 1, as described above, excellent electrolyte resistance can be confirmed, thereby avoiding the possibility of unnecessary capacity reduction or safety degradation.

[0108] Therefore, it can be confirmed that by applying an insulating coating of an electrode insulating polymer according to a specific embodiment of the present invention, safety can be fundamentally improved (preventing short circuits, etc.), and at the same time, this application can improve processability or other defects.

[0109] The above description is merely an example of applying the principles of this invention, and other configurations may be further included without departing from the scope of this invention.

Claims

1. An electrode for a secondary battery, comprising: A coated portion on the current collector having an electrode active material layer and an uncoated portion on the current collector without an electrode active material layer; as well as An insulating coating is disposed on at least a portion of the uncoated portion, and the insulating coating comprises an electrode insulating polymer. The coefficient of thermal expansion of the electrode insulating polymer is between 66 μm / m℃ and 127 μm / m℃.

2. The electrode for a secondary battery according to claim 1, wherein, The coefficient of thermal expansion of the electrode insulating polymer is 72 μm / m℃ to 80 μm / m℃.

3. The electrode for a secondary battery according to claim 1, wherein, The electrode insulating polymer includes at least one selected from polyamide-based polymers, polyamide-imide-based polymers, fluorinated vinyl polymers, butadiene-based rubbers, and copolymers thereof.

4. The electrode for a secondary battery according to claim 3, wherein, The electrode insulating polymer comprises a polyamide-based polymer and a fluorinated vinyl polymer, wherein the weight ratio of the polyamide-based polymer to the fluorinated vinyl polymer is from 1:8.5 to 1:9.

5.

5. The electrode for a secondary battery according to claim 1, wherein, The electrode insulating polymer includes copolymers. The copolymer comprises: an amide-imide first repeating unit; and at least one second repeating unit selected from butadiene repeating units, nitrile repeating units, and styrene repeating units.

6. The electrode for a secondary battery according to claim 5, wherein, The first repeating unit contains an aromatic ring.

7. The electrode for a secondary battery according to claim 5, wherein, The first repeating unit contains a benzene ring.

8. The electrode for a secondary battery according to claim 5, wherein, The second repeating unit is selected from at least one of butadiene repeating units, acrylonitrile-butadiene repeating units, and hydrogenated acrylonitrile-butadiene repeating units.

9. The electrode for a secondary battery according to claim 5, wherein, The molar ratio of the first repeating unit to the second repeating unit is 60 to 80: 40 to 20.

10. The electrode for a secondary battery according to claim 5, wherein, The copolymer is selected from at least one of random copolymers, alternating copolymers, block copolymers and graft copolymers.

11. The electrode for a secondary battery according to claim 1, wherein, The insulating coating is disposed on at least a portion of the coated portion and at least a portion of the uncoated portion.

12. The electrode for a secondary battery according to claim 11, wherein, The insulating coating disposed on at least a portion of the uncoated portion is continuous with the insulating coating disposed on at least a portion of the coated portion.

13. The electrode for a secondary battery according to claim 1, wherein, The electrode is a positive electrode, and the current collector includes at least one metal selected from stainless steel, nickel, titanium, aluminum, and their alloys.

14. The electrode for a secondary battery according to claim 1, wherein, The elongation of the uncoated portion having the insulating coating is 25% to 43%.

15. A secondary battery comprising an electrode for a secondary battery according to any one of claims 1 to 14.

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