ELECTRODE FOR A LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY THAT INCLUDES THIS

Abstract

The present disclosure relates to an electrode for a lithium secondary battery, which not only effectively suppresses heat generation or ignition and thus exhibits further improved stability, but also enables the provision of batteries with excellent charge / discharge characteristics, and to a lithium secondary battery comprising the same. The electrode for a lithium secondary battery comprises a metal current collector; an electrode active material; and a conductive material, and also comprises an active material layer formed on the metal current collector, the active material layer further comprising a conductive polymer exhibiting a peak in the band of 1350 to 1600 cm⁻¹. -1during a Raman spectrum analysis, it shows PTC (positive temperature coefficient) properties, and wherein, when a cross-section of the active material layer is subjected to a Raman image analysis, the conductive polymer is distributed in an amount of 90 wt.% or more within an area reaching 10% of the active material layer thickness from the surface of the metal current collector.

Description

[TECHNICAL FIELD] Cross-reference to related application(s)

[0001] This application claims priority over Korean patent application No. 10-2022-0151839, which was filed with the Korean Intellectual Property Office on November 14, 2022, and whose disclosure is hereby incorporated by reference in its entirety.

[0002] The present disclosure relates to an electrode for a lithium secondary battery which not only effectively suppresses heat generation or ignition and thus exhibits further improved stability, but also enables the provision of batteries which have excellent charge / discharge characteristics, and a lithium secondary battery which includes the same. [BACKGROUND]

[0003] As demand for medium- and large-format devices such as electric and hybrid electric vehicles and mobile devices like smartphones and tablet PCs has increased significantly, the demand for secondary batteries as the energy source needed to power such devices is rising rapidly. In particular, as data processing speeds and the operating time of mobile devices increase, lithium secondary batteries are being actively developed that offer higher energy density and operating potential, can maintain excellent characteristics over a long period, and exhibit a low self-discharge rate.

[0004] However, since the capacity and energy density of lithium secondary batteries have increased significantly, many ignition and explosion accidents have been reported, caused by overcharging, exposure to high temperatures, external influences, etc., of various mobile devices or electric vehicles containing them. Therefore, one of the main research objectives for lithium secondary batteries recently has been to improve safety by suppressing ignition and explosion.

[0005] It is known that the direct cause of ignition, explosion, and similar incidents in lithium secondary batteries is a short circuit caused by direct contact between a positive and a negative electrode inside the secondary battery due to external stimuli such as high temperatures and external influences. For example, if a lithium secondary battery is overcharged or exposed to high temperatures or external influences, the internal temperature of the secondary battery can rise rapidly, causing the separator to shrink, or the internal structure of the secondary battery can be damaged due to external influences. As a result, the positive and negative electrodes can come into contact, leading to a short circuit.If such a short circuit occurs, the movement of lithium ions and electrons can be concentrated through the contact section between the positive and negative electrodes, potentially causing overcurrent, which can lead to heat generation, gas generation within the battery, and volume expansion, thus posing a risk of ignition or explosion of the lithium secondary batteries.

[0006] Therefore, to suppress ignition and explosion during a short circuit and improve the safety of secondary batteries, it is necessary to increase the resistance between the electrodes and interrupt the current when high temperatures or external influences are applied. To this end, various attempts have been made to add different functional layers or materials to the electrodes of lithium secondary batteries to increase resistance under high temperatures, thereby improving the safety of secondary batteries.

[0007] However, in the case of electrodes to which previously known functional layers are added, there is a disadvantage that it is difficult to sufficiently improve the safety of the lithium secondary battery, and thus the possibility of ignition and explosion still exists, or the functional layer partially inhibits the charging / discharging properties of the secondary battery. [DETAILED DESCRIPTION OF THE INVENTION][Technical Problem]

[0008] Therefore, it is an objective of the present disclosure to provide an electrode for a lithium secondary battery which not only effectively suppresses heat generation or ignition and thus exhibits further improved stability, but also enables the provision of batteries which exhibit excellent charge / discharge characteristics.

[0009] Another objective of the present disclosure is to provide a lithium secondary battery that includes the electrode and thus exhibits excellent stability and charging / discharging characteristics. [Technical solution]

[0010] Provided herein is an electrode for a lithium secondary battery, comprising a metal current collector; and an electrode active material and a conductive material, comprising an active material layer formed on the metal current collector, wherein the active material layer further comprises a conductive polymer exhibiting a peak in the band from 1350 to 1600 cm⁻¹ -1 during a Raman spectrum analysis, it shows PTC (positive temperature coefficient) properties, and where, when a cross-section of the active material layer is subjected to Raman image analysis, the conductive polymer is distributed in an amount of 90 wt.% or more within an area reaching 10% of the active material layer thickness from the surface of the metal current collector.

[0011] Also provided herein is a lithium secondary battery comprising: a positive electrode, a negative electrode and a separator arranged between them, the electrode being defined as the positive electrode.

[0012] Now, an electrode for a lithium secondary battery and a lithium secondary battery, etc., comprising these according to specific embodiments of the present disclosure, are described.

[0013] Terms or words used in the present description and claims should not be interpreted as being limited to ordinary or dictionary terms, and the present disclosure should be interpreted with meanings and concepts consistent with the technical idea of ​​the present disclosure, based on the principle that the inventors can adequately define concepts of the terms in order to best describe their own invention.

[0014] The terms used herein are provided to describe the embodiments, but not to limit the inventive concept. Singular forms include plural forms unless the context clearly indicates otherwise.

[0015] It is understood that the terms “comprise”, “include”, “exhibit”, etc. are used herein to specify the presence of specified features, integers, steps, components or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components or combinations thereof.

[0016] According to one embodiment of the present disclosure, an electrode for a lithium secondary battery is provided, comprising: a metal current collector; and an electrode active material and a conductive material, and comprising an active material layer formed on the metal current collector. wherein the active material layer further comprises a conductive polymer exhibiting a peak in the band from 1350 to 1600 cm⁻¹ -1 during a Raman spectrum analysis, it shows PTC (positive temperature coefficient) properties, and where, when a cross-section of the active material layer is subjected to Raman image analysis, the conductive polymer is distributed in an amount of 90 wt.% or more within an area reaching 10% of the active material layer thickness from the surface of the metal current collector.

[0017] The electrode of one embodiment includes a conductive polymer that is mainly distributed in an area in contact with or adjacent to the surface of the metal current collector, wherein the conductive polymer has a peak in the band of 1350 to 1600 cm⁻¹ -1 or 1500 to 1600 cm -1 during a Raman spectrum analysis, it can show a PTC (positive temperature coefficient) property.

[0018] The characteristic peak that appears in the band of Raman spectra can define that the conductive polymer contains a high content of an aromatic ring with a conjugated π-electron system among the repeating units, and, for example, it can indicate that the conductive polymer has a repeating unit with an aromatic ring containing one or more or one or two heteroelements such as nitrogen or sulfur at a content of 50 mol% or more or 70 mol% or more or 90 to 100 mol% of the total repeating units.

[0019] When a lithium secondary battery is activated, a conductive polymer containing an aromatic ring with a conjugated π-electron system can exhibit conductivity by doping anions derived from the secondary battery's electrolyte onto the aromatic ring. Therefore, the conductive polymer exhibits conductivity during the normal charging / discharging process of the secondary battery, enabling the secondary battery to display appropriate charging / discharging characteristics.

[0020] However, at temperatures above a certain level, the conductive polymer can be dedoped from the aromatic ring by anions derived from the electrolyte. As a result, the conductive polymer can act as a non-conductor, increasing its resistance and exhibiting PTC properties that interrupt current flow.

[0021] In particular, the electrode for a lithium secondary battery of one embodiment adapts the properties, such as the structure and solubility of the conductive polymer, the coating thickness, and the process described later, whereby such a conductive polymer can be distributed mainly in an area adjacent to the metal current collector, for example, in an area reaching 10% (or 7%) of the active material layer thickness from the surface of the metal current collector. Specifically, the conductive polymer can be distributed in the area adjacent to the metal current collector in an amount of 90% by weight or more, or 90 to 100% by weight, or 92 to 98% by weight of the total conductive polymer.

[0022] Furthermore, in a specific embodiment, the minimum straight-line distance from the surface of the metal current collector to the area in which the conductive polymer is distributed in an amount of 90 wt.% or more can be 0 to 15 µm or 0 to 10 µm.

[0023] Since the specific conductive polymer exhibiting PTC properties is concentrated and evenly distributed in the area next to the metal current collector in this way, the electrode of one embodiment can further improve electrochemical properties such as safety and charging / discharging characteristics of a lithium secondary battery based on the following principle.

[0024] First, if an external stimulus such as overcharging, high temperature, or external influences are applied to the lithium secondary battery, including the electrode, and the temperature inside the battery rises rapidly, such a conductive polymer can be converted into a non-conductor due to the de-doping of anions or similar processes. Therefore, it is possible to significantly increase the resistance within the electrode and interrupt the current flow to prevent overcurrent due to short circuits between electrodes and to suppress heat generation, ignition, explosion, gas production, etc., in secondary batteries.In particular, in the electrode of one embodiment, since the conductive polymer is concentrated and distributed in the area next to the metal current collector, the conductive polymer, which is converted into a non-conductor upon application of an external stimulus, can very effectively interrupt contact between the electrode active material and the metal current collector, thereby further improving the safety of lithium secondary batteries.

[0025] Furthermore, since the conductive polymer does not spread into the active material layer but is concentrated and distributed in the area adjacent to the metal current collector, such a conductive polymer does not interfere with the normal charging / discharging process of the secondary battery. In particular, even if some of the conductive polymer is converted into a non-conductor due to the application of local heat within the active material layer during the normal charging / discharging process of a secondary battery, it is distributed uniformly in the area adjacent to the metal current collector and thus does not interfere with the charging / discharging process or the battery's characteristics. As a result, a lithium secondary battery, including the electrode of one embodiment, can exhibit charging / discharging characteristics at the same level or higher, while also demonstrating further improved safety.

[0026] Meanwhile, the area in which the conductive polymer is distributed and the distribution content within the corresponding area can be confirmed and measured by performing a Raman image analysis of the cross-section of the active material layer. In a specific embodiment, as described in Fig. As shown in Figure 1, the respective components contained in the active material layer, for example, the electrode active material, the conductive material, and the conductive polymer mentioned above, exhibit different Raman spectra. Therefore, in the results of the Raman image analysis of the cross-section of the active material layer, each component distinguished by its Raman spectrum can be expressed as a different fluorescence. The results of this Raman image analysis can confirm the area in which the conductive polymer is distributed (e.g., the area shown in Figure 1). Fig.1 red area shown), and the distribution content of the conductive polymer can be calculated by calculating the corresponding conductive polymer distribution area and its ratio for different cross-sections of the active material layer.

[0027] The conductive polymer contained in the electrode of the aforementioned embodiment exhibits the aforementioned PTC properties, with the effective operating temperature at which such conductive polymers are converted into a non-conductor being 70 to 130 °C or 80 to 125 °C. Since the conductive polymer is converted into a non-conductor at this effective operating temperature, it can more effectively suppress ignition or explosion of the secondary battery upon application of an external stimulus, without inhibiting the normal charging / discharging process of the secondary battery.

[0028] The conductive polymer, which exhibits the effective operating temperature and distribution properties described above, is described in more detail below.

[0029] Furthermore, the conductive polymer can be a polymer or copolymer containing a repeating unit with an aromatic ring containing one or more heteroelements or one or two heteroelements in an amount of 50 mol% or more or 70 mol% or more or 90 to 100 mol% of the total repeating units, and in particular, it can be a polythiophene-based polymer or copolymer containing mainly a repeating unit containing a substituted or unsubstituted thiophene ring as the aromatic ring.

[0030] In a more specific embodiment, the conductive polymer can be a polythiophene-based polymer or copolymer in which an alkylene oxide group is bonded to a thiophene ring in the repeating unit, for example, a homopolymer or copolymer containing a repeating unit of the following chemical formula 1: where in chemical formula 1 R1 is a functional group of the following chemical formula 2, where in chemical formula 2 L1 is a single bond or an alkylene group, L2 is an alkylene group, R3 is hydrogen or an alkyl group, and n is an integer in the range of 1 to 5000 or 10 to 2000 or 50 to 1000, wherein the alkylene group can be an alkylene group with 2 to 5 carbon atoms and the alkyl group can be an alkyl group with 1 to 5 carbon atoms.

[0031] Furthermore, such a polythiophene-based (co)polymer can have a weight-average molecular weight of, for example, 5000 to 100000 g / mol or 10000 to 80000 g / mol.

[0032] In a more specific embodiment, the polythiophene-based (co)polymer can contain the repeating unit of chemical formula 1 in an amount greater than 0 mol%, 0.001 mol% or more, 0.01 mol% or more, 1 mol% or more, and in an amount greater than 100 mol% or less, 80 mol% or less, 50 mol% or less, or 30 mol% or less. At this point, the polythiophene-based (co)polymer can include the remaining content of alkylthiophene-based repeating units, excluding, for example, an alkylthiophene-based repeating unit in which a thiophene ring is substituted with an alkyl group having 1 to 20 carbon atoms or 3 to 15 carbon atoms.

[0033] Such a polythiophene-based (co)polymer incorporates the substituted thiophene ring and can therefore exhibit a suitable effective operating temperature, among other properties. As a result, the (co)polymer not only improves the charging / discharging characteristics of the lithium secondary battery but can also be converted into a non-conductor when exposed to a high temperature above a certain level, thereby enhancing the safety of the secondary battery.

[0034] Furthermore, due to the aforementioned predetermined structure, the polythiophene-based (co)polymer exhibits relatively low affinity, solubility, and the like for organic solvents, which are mainly contained in the slurry composition used to form the active material layer, for example, solvents such as N-methylpyrrolidone, and can also show excellent adhesion to the metal current collector. Therefore, in the process of forming such a polythiophene-based (co)polymer on a metal current collector and then coating and drying the slurry composition to form an active material layer, the phenomenon of the conductive polymer dissociating and spreading over a wide area of ​​the active material layer can be minimized.Therefore, by using such a polythiophene-based (co)polymer, these conductive polymers can be concentrated and distributed in the area adjacent to the metal current collector. In the Raman image analysis mentioned above, 90 wt% or more can be distributed in an area reaching 10% of the thickness of the active material layer on the surface of the metal current collector. Ultimately, the polythiophene-based (co)polymer can contribute to improving the safety of secondary batteries without affecting their charging / discharging characteristics.

[0035] Meanwhile, the conductive polymer can be present in an amount of 0.001 to 5 parts by weight or 0.005 to 5 parts by weight, based on 100 parts by weight of the electrode active material (e.g., positive electrode active material) contained in the active material layer. This allows the electrode of one embodiment to exhibit excellent safety and charging / discharging characteristics.

[0036] The conductive polymer with the repeating unit of the aforementioned chemical formula 1, etc., can be prepared, for example, by subjecting a halogenated thiophene compound and an alkylene glycol compound to a substitution reaction to produce a monomer to which the functional group of chemical formula 2 is bonded, and then polymerizing such monomers alone or by copolymerizing them with other monomers such as alkylthiophene. Specific conditions for preparing such monomers and polymers are described in the preparation examples described later.

[0037] Furthermore, the conductive polymer can be formed on the metal current collector, for example, by coating the metal current collector with a liquid composition dissolved or dispersed in an organic solvent such as chloroform, tetrahydrofuran (THF), toluene, or xylene at a concentration of about 0.1 to 5 wt%, and then drying the collector. The slurry composition described below is then applied and dried to form an active material layer, and this active material layer can be rolled to produce an electrode for a lithium secondary battery of one embodiment.

[0038] At this stage, the liquid composition for forming the conductive polymer may further include one or more additives selected from the group consisting of a carbon-based conductive material, conductive inorganic particles, a binder and an esterified saccharide, in addition to the conductive polymer.

[0039] At this stage, the same carbon-based conductive material and binder components as those contained in the active material layer can be used, and adding these components can further improve the conductivity of the electrode in one embodiment, the adhesion, or the mechanical properties of the safety functional layer, etc. Furthermore, aluminum oxide or zirconium oxide particles with a nanoscale particle size, for example, 5 to 100 nm, can be used as the conductive inorganic particles, and adding these can further improve the conductivity of the electrode and the secondary battery. Additionally, a monosaccharide, oligosaccharide, or polysaccharide with an acyl group can be used as the esterified saccharide.This component generates gas when the secondary battery is overcharged and can play the role of blocking the conductive path between the metal current collector and the electrode active material; adding this component can further improve the safety of the secondary battery.

[0040] On the other hand, the electrode of one embodiment further comprises an active material layer formed on a metal current collector in the conductive polymer-forming region, wherein the active material layer may include an electrode active material, a conductive material, and optionally a binder. Since it is preferred that the electrode on which the conductive polymer is formed be a positive electrode, such examples are mainly described here.

[0041] In the positive electrode of a lithium secondary battery, the metal current collector can generally have a thickness of 3 to 100 µm and can be made of any metal or alloy that exhibits excellent conductivity without causing chemical changes in the secondary battery. Examples of such metal current collectors include those made of stainless steel, aluminum, copper, nickel, or titanium, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or similar materials. Furthermore, the metal current collector can have fine protrusions and depressions on its surface to improve the adhesion of safety-related functional layers, etc., and can be used in various forms such as a film, foil, sheet, mesh, porous body, foam, or non-woven structure.

[0042] Additionally, the positive electrode active material included in the active material layer is not particularly restricted, as long as it is a material capable of reversibly intercalating and deintercalating lithium ions, and examples include a lithium metal composite oxide containing at least one metal element selected from the group consisting of Co, Mn, Ni, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg and Mo.

[0043] In particular, a compound represented by one of the following formulas can be used as the positive electrode active material. Li a A 1-b R b D2(where 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05); LiE 2-b R b O 4-c D c (where 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c CobRc D a (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c CobR c O2- α Z α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c CobR c O 2-α Z2(where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c MnbR c D α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a N 1-b-c MnbR c O 2-α Z α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c MnbR c O 2α Z2(where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a NibE c GdO2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5 and 0.001 ≤ d ≤ 0.1); Li a NibCo c MndGeO2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5 and 0.001 ≤ e ≤ 0.1). Li aNiG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); LiaMnG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2Os; LiV2O5; LiTO2; LiNiVO4; and Li (3-f) J2(PO4)3(0 ≤ f ≤ 2).

[0044] In the above formulas, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, V or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0045] Furthermore, compounds with a coating layer on the surface of the aforementioned compound may be used, or a mixture of the aforementioned compound and a compound with a coating layer may be used. The coating layer may include, as the coating element compound, an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The compounds forming these coating layers may be amorphous or crystalline. The coating element included in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof.

[0046] Furthermore, the conductive material used in the active layer imparts conductivity to the electrode, and the conductive material can be used without restriction as long as it exhibits electronic conductivity without causing chemical changes in the battery being configured. Specific examples include natural graphite, synthetic graphite, carbon black, carbon fiber, carbon nanotubes, metal powders such as copper, nickel, aluminum, and silver, metal fibers, and the like. Additionally, conductive materials such as polyphenylene derivatives can be used alone or in a mixture of one or more of them.

[0047] The conductive material can be added in an amount of 1 to 50 wt.% or 2 to 20 wt.%, based on the total weight of the active material layer. This makes it possible to ensure preferential formation of the positive electrode while imparting excellent electrical properties to the positive electrode.

[0048] The binder plays a role in ensuring good adhesion between the particles of the positive electrode active material and further improving the bonding properties of the active material layer. Typical examples include the aforementioned halogenated polymer binders based on polyolefins, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polyethylene, polypropylene, styrene-butadiene rubbers, acrylated styrene-butadiene rubbers, epoxy resins, nylon, and similar materials.

[0049] The binder can be added in an amount of 1 to 50 wt% or 2 to 30 wt%, based on the total weight of the active material layer. This makes it possible to form a positive electrode with excellent durability without affecting the electrical and / or capacitance properties of the positive electrode.

[0050] The aforementioned active material layer can be formed by dissolving or dispersing each component, such as the positive electrode active material, the conductive material, and the binder, in a medium such as an organic solvent to form a slurry composition, and then coating, drying, and rolling the slurry composition onto a metal current collector on which the safety functional layer is formed.

[0051] At this time, examples of media include the organic solvent N-methyl-2-pyrrolidone (NMP), methoxypropyl acetate, butyl acetate, glycolic acid, butyl esters, butyl glycol, methylalkylpolysiloxane, alkylbenzene, propylene glycol, xylene, monophenyl glycol, or the like, among which NMP, etc., may be appropriately used, taking into account the dispersibility and processability of the aforementioned positive electrode active material and conductive material.

[0052] In this way, the conductive polymer-containing region and the active material layer are formed through separate compositions and processes, while a polymer with low solubility and affinity for the NMP, for example, a polymer with a repeating unit of chemical formula 1, is used as the conductive polymer. This allows the conductive polymer to be concentrated and uniformly distributed in a region adjacent to the surface of the metal current collector. As a result, a lithium secondary battery, including the electrode, of one embodiment can exhibit further improved safety and excellent charge / discharge characteristics.

[0053] Since the formation process and conditions of the active material layer, with the exception of the formation process of the conductive polymer, can follow the general positive electrode formation process and conditions, further description is omitted.

[0054] The active material layer formed by the aforementioned method can have a thickness of 5 to 200 µm or 10 to 100 µm, and the region in which the conductive polymer is distributed at a concentration of 90 wt.% or more can have a thickness of 0.01 to 20 µm or 0.05 to 10 µm. This is because, in one embodiment of the electrode, the conductive polymer is concentrated and uniformly distributed in the region adjacent to the surface of the metal current collector. Depending on the thickness range described above, when an external stimulus such as an external impact is applied, the conductive polymer suppresses direct contact between the active material layer and the metal current collector, thus ensuring improved safety of the secondary battery. Furthermore, it is possible to minimize the inhibition of the secondary battery's charging / discharging characteristics by creating a thicker distribution region of the conductive polymer.

[0055] Meanwhile, according to the other embodiment of the present disclosure, a lithium secondary battery is provided comprising the electrode of an embodiment as a positive electrode and simultaneously comprising a positive electrode, a negative electrode and a separator arranged between them.

[0056] In such a lithium secondary battery of the other embodiment, the negative electrode is produced by coating, drying and rolling a negative electrode active material on a negative electrode current collector and may further include a conductive material and a binder as required.

[0057] The negative electrode active material can be, for example, graphite with a fully layered crystal structure like natural graphite, soft carbon with a low-crystalline layered crystal structure (graphene structure, in which hexagonal honeycomb-shaped planes of carbon are arranged in a layer), hard carbon with a structure in which the low-crystalline structures are mixed with non-crystalline parts, carbon and graphite materials such as synthetic graphite, expanded graphite, carbon fiber, barely graphitizable carbon, carbon black, carbon nanotubes, fullerenes, activated carbon; or metal composite oxides such as LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe 1-x Me' y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of groups 1, 2, 3 in the periodic table, halogen; 0 <x≤1; 1≤y≤3; 1≤z≤8); Lithiummetall; Lithiumlegierungen; Silizium, Siliziumoxid oder Legierungen auf Siliziumbasis; Legierungen auf Zinnbasis; ein leitfähiges Polymer wie Polyacetylen; Materialien auf Li-Co-Ni-Basis; Titanoxid; oder Lithiumtitanoxid usw. beinhalten.

[0058] In one embodiment, the negative electrode active material can include both graphite and silicon(Si)-containing particles; the graphite can include at least one of natural graphite with a layered crystal structure and artificial graphite with an isotropic structure; and the silicon(Si)-containing particles are particles that contain silicon(Si) as a metal component as the main component and can include silicon(Si) particles, silicon oxide particles, or a mixture of silicon(Si) particles and silicon oxide particles.

[0059] Additionally, the conductive material and binder that can be used together with the negative electrode active material can be the same components as the conductive material and binder contained in the positive electrode active material layer.

[0060] Furthermore, the negative electrode active material layer containing the negative electrode active material can have a thickness of 100 µm to 200 µm or 120 µm to 200 µm.

[0061] Furthermore, the negative electrode current collector is not particularly restricted as long as it exhibits high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, burnt carbon, etc., can be used, and in the case of copper or stainless steel, materials surface-treated with carbon, nickel, titanium, silver, etc., can be used.

[0062] Additionally, similar to the positive electrode current collector, the negative electrode current collector can have fine protrusions and depressions formed on its surface to improve the adhesion of a negative electrode active material layer, and can be formed in various forms such as a film, foil, sheet, mesh, porous body, foam body, and non-woven structure. Furthermore, the average thickness of the negative electrode current collector can be appropriately selected in the range of 3 to 100 µm, taking into account the conductivity and the overall thickness of the negative electrode to be produced.

[0063] Furthermore, the separator is positioned between the positive and negative electrodes, and a thin insulating film with high ion permeability and mechanical strength is used. The separator is not particularly restricted as long as it is commonly used in this field.

[0064] In particular, chemically resistant and hydrophobic polypropylene, glass fiber, or polyethylene films or nonwovens, etc., can be used. In some cases, a composite separator can be used, in which inorganic / organic particles are coated onto a porous polymer substrate, such as a film or nonwoven, using an organic binder polymer. If a solid electrolyte, such as a polymer, is used as the electrolyte, the solid electrolyte can also serve as a separator. Additionally, the separator can have a mean pore diameter of 0.01–10 µm and a mean thickness of 5–300 µm.

[0065] The aforementioned lithium secondary battery may further include an electrolyte, such electrolyte being an electrolyte containing a non-aqueous organic solvent and a lithium salt, or an electrolyte membrane containing an organic or inorganic solid electrolyte, and these may be mixed and used together. However, the types of electrolytes that may be used are well known to those skilled in the art and are not particularly limited in batteries of other embodiments, and therefore a further description thereof is omitted. [Beneficial effects]

[0066] As described above, in the lithium secondary battery including the electrode of the present disclosure, even when an external stimulus such as overcharging, high temperature or external influences are applied and the temperature inside the battery rises rapidly, it is possible to effectively interrupt overcurrent through the conductive polymers that are concentrated and distributed near the metal current collector, thereby minimizing ignition and explosion.

[0067] This allows the lithium secondary battery to exhibit improved safety and suppresses the deterioration of charging / discharging characteristics due to the conductive polymer, resulting in excellent electrochemical properties. [Brief description of the drawings] Fig.Figure 1 shows the results of the Raman image analysis of the active material layer of the electrode produced in Example 1 for a lithium secondary battery, with the right-hand diagram of Fig. 1 shows the results of the Raman spectrum analysis of the conductive polymer produced in the manufacturing example; Fig. Figure 2 is a diagram illustrating the process and results of calculating a probability density function from the Raman image analysis results of Fig. 1 and of deriving the conductive polymer content in an area where the conductive polymer is distributed, from this; Fig. Figure 3 is a diagram showing the process and results of calculating a probability density function from the Raman image analysis results of Comparative Example 2 and deriving the conductive polymer content in an area where the conductive polymer is distributed; and Fig. 4a to Fig.Figure 4c shows the results of a nail penetration test for five in Example 1 ( Fig. 4a), Comparative example 1 ( Fig. 4b) or comparative example 2 ( Fig. 4c) manufactured lithium secondary batteries. Detailed description of the embodiments

[0068] Various embodiments of the present disclosure are described in detail below so that the person skilled in the art can easily implement them. However, the present disclosure can be modified in various ways and is not limited to the embodiments set forth herein. Production example: Synthesis of monomer and conductive polymer

[0069] After creating a nitrogen environment inside the 3-way round-bottomed brine (RBF) via flowing nitrogen, 2.34 g (0.01 mol) of copper(I) iodide and 50.36 g (0.31 mol) of triethylene glycol were added. 3.68 g (0.096 mol) of 60% sodium hydride in mineral oil were slowly added to the RBF, and the mixture was stirred while maintaining a nitrogen environment. After approximately 1 hour of stirring, 10.0 g (0.06 mol) of 3-bromothiophene was added, and the mixture was heated under reflux at approximately 100 °C for about 24 hours. The reaction solution was filtered through a pressure reducing device and then washed with 100 mL of dichloromethane solution, followed by washing with NH4Cl and brine in that order.The solvent was removed by distillation under reduced pressure, and the crude product was purified by column chromatography (hexane:ethyl acetate = 60:40) to obtain approximately 9.0 g (yield: 60%) of the target compound (monomer compound of chemical formula 3).

[0070] 124 g (767 mmol) of iron(III) chloride were dissolved in 1000 ml of methylene chloride, and 3.0 g (12.2 mmol) of the monomer compound of chemical formula 3 and 47.8 g (243 mmol) of 3-octylthiophene were added to the solution. The mixture was subjected to a polymerization reaction with stirring at approximately 25 °C for 24 hours. The reaction solution was placed in a reverse osmosis membrane with a molecular weight limit (MWCO) of 5000 and then immersed in 1500 ml of acetonitrile solvent to remove unreacted iron(III) chloride, monomers, and the like. The residue precipitated within the reverse osmosis membrane was washed with methanol and dried at approximately 25 °C to obtain the desired conductive polymer. The weight-mean molecular weight (Mw) of the conductive polymer was confirmed to be approximately 37,000 g / mol. Example 1: Production of a positive electrode and a lithium secondary battery (Production of a positive electrode)

[0071] 20 g of the conductive polymer obtained in the production example (Mw = 37,000 g / mol) were dissolved in 1,980 g of chloroform solvent to obtain a composition. This composition was deep-drawn and dried on an aluminum (Al) thin film, which serves as a positive electrode current collector, to form a conductive polymer-containing layer approximately 0.5 µm thick.

[0072] LiCoO2 as a positive electrode active material, a conductive material (carbon black), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.5:1:1.5 to produce a positive electrode slurry (solids content: 60 wt%). The slurry was coated onto the conductive polymer-containing layer (the weight of the conductive polymer was approximately 0.5 parts by weight, based on a total of 100 parts by weight of the positive electrode active material, the conductive material, and the binder), dried, and then roll-pressed to form an active material layer with a total thickness of 58 µm, thus producing a positive electrode. (Production of a negative electrode)

[0073] A negative electrode active material (graphite), a binder (SBR-CMC), and a conductive material (carbon black) were added to water as a solvent in a weight ratio of 95:3.5:1.5 to produce a negative electrode slurry (solids content: 60 wt%). The negative electrode slurry was coated onto a copper (Cu) thin film as a negative electrode current collector with a thickness of 8 µm, dried, and then roll-pressed to produce a negative electrode. (Manufacturing a separator)

[0074] Approximately 8.5 wt% polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) binder was added to acetone and dissolved at 50 °C for approximately 12 hours or more to prepare a binder solution. Al₂O₃ powder was added to this binder solution so that the Al₂O₃ / PVdF-HFP ratio was 90 / 10 wt%, and a slurry was prepared using a ball mill process for 12 hours or more. The slurry prepared in this manner was coated onto a polyolefin-based separator with a thickness of approximately 8 µm using a dip coating process. The coating thickness was adjusted to approximately 4.5 µm to produce a porous separator. (Manufacturing a lithium secondary battery)

[0075] The positive electrode, separator, and negative electrode were stacked sequentially and then pressed using heat and pressure of 90 °C and 200 kPa to produce an electrode assembly consisting of bicells. The assembled electrode assembly was housed in a pouch-like battery casing, and ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70. An electrolyte in which LiPF6 was dissolved to a concentration of 1.0 M was then injected, thus fabricating a lithium secondary battery. Comparative example 1

[0076] A positive electrode and a lithium secondary battery of Comparative Example 1 were manufactured in the same way as in Example 1, except that the conductive polymer was not used (the conductive polymer-containing layer was not formed). Comparative example 2

[0077] LiCoO2 as a positive electrode active material, a conductive material (carbon black), a binder (polyvinylidene fluoride) and the conductive polymer obtained in the manufacturing example were added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97:1:1.5:0.5 to produce a positive electrode slurry (solid content: 60 wt%).

[0078] This slurry was coated onto an aluminum thin film (bare Al foil) and dried, and then roll-pressed to form an active material layer with a total thickness of 58 µm and to produce a positive electrode. Test example: Raman spectrum analysis and Raman image analysis

[0079] Regarding the positive electrode produced in the examples and comparative examples, a cross-section from the positive electrode surface to the metal current collector was recorded, and a Raman image of the cross-section was measured (instrument name: DXR3xi, Thermo Fisher Scientific, USA) to analyze the Raman spectrum and the distribution of the conductive polymer. As shown in the right-hand diagram of Fig. As shown in Figure 1, the peaks on the Raman spectrum of the positive electrode prepared in the examples are broadly divided into three parts. Among them, the Raman signal (peak center) of the conductive polymer is found in the band from 1350 to 1600 cm⁻¹. -1 (especially 1350 to 1500 cm) -1 ) confirmed, with the corresponding Raman signal appearing due to vibrational modes originating from the aromatic rings of the conductive polymer. Based on this, the range of 1350-1500 cm⁻¹ was determined. -1-area calculated on the Raman image, and the red area (conductive polymer) on the left diagram of Fig. 1 was calculated. In the Raman image analysis, the thickness of the positive electrode cross-section was used as a reference for longitudinal mapping, and Raman images were measured under the following conditions.

[0080] * Analysis conditions: Excitation laser wavelength 532 nm, laser power 0.8 mW, detector exposure time (exposure time per unit analysis area) 0.15 sec, grating 1200 grooves / mm, pixel resolution 1 cm -1 , Mapping size 30 µm x 65 µm, mapping pixel size 0.6 µm x 0.6 µm

[0081] In the measured Raman image, only the image of the red region (conductive polymer) was shown separately, and the concentration in the concentrated distribution area was calculated. The value represented by each Raman image pixel for the displayed image was extracted using the Image-J program, and then the probability density function was calculated using the extracted value, as shown in Equation 1 below. ρ(x)=I(x)∫I(x)dx

[0082] In Equation 1, p(x) represents the probability density function, and I(x) represents the value of the Raman image pixel. The mean pixel values ​​in the thickness direction were obtained from the fully extracted Raman image area, and the values ​​were standardized and normalized using the probability density function. Normalization was performed by calculating the integration of all pixel values ​​in the denominator, as in the equation above, and dividing each pixel value by the corresponding integration. Finally, the normalized value was profiled to confirm the fraction of the area occupied by the conductive polymer relative to the total thickness.

[0083] Fig. Figure 1 shows the results of the Raman image analysis of the active material layer of the electrode produced in Example 1 for a lithium secondary battery, with the right-hand diagram of Fig.Figure 1 shows the results of the Raman spectrum analysis of the conductive polymer produced in the manufacturing example. It also shows Fig. 2. Schematically illustrates the process and results of calculating a probability density function from the Raman image analysis results of Fig. 1 and the derivation of the conductive polymer content in an area where the conductive polymer is distributed. Furthermore, it shows Fig. 3 schematically illustrates the process and results of calculating a probability density function in the same way as in Example 1 from the Raman image analysis results of Comparative Example 2 and of deriving the conductive polymer content in an area where the conductive polymer is distributed.

[0084] Additionally, the content (wt%) of the conductive polymer present in the area reaching 10% of the active material layer thickness from the surface of the positive electrode current collector was calculated for each example and comparison example from the Raman image analysis results above and are shown together in Table 1 below. Evaluation of high-speed discharge characteristics

[0085] The lithium secondary batteries produced in the examples and comparison examples were charged under constant current (0.7 C) and constant voltage (4.47 V, 0.025 C limit), then left to rest for 10 minutes and discharged until the voltage reached 3 V under constant current conditions (0.1 C, 0.2 C, 0.5 C, 1.0 C, 1.5 C). That is, as the number of charge / discharge cycles increased, the discharge rate was periodically changed to 0.1 C, 0.2 C, 0.5 C, 1.0 C, and 1.5 C, respectively. This allowed for the evaluation of each battery's high-speed discharge characteristics. The high-speed discharge characteristics at 1.5 C are shown in Table 1 below. Nail penetration test

[0086] Five lithium secondary batteries, as described in examples and comparison examples, were each manufactured and fully charged to 100% SOC at 4.47 V (0.05 C limit) under CC / CV conditions and 0.5 C at 25 °C, and then stored at room temperature for 24 hours. Each lithium secondary battery was placed on a flat plate, and a stainless steel nail with a diameter of 3 ± 0.2 mm and a length of 30 mm was driven into the center of the cell at a vertical angle and a penetration rate of 100 mm / s to measure the presence of ignition. Table 1 below lists the number of batteries that did not ignite among the five batteries. Fig. 4a to Fig. Figure 4c shows photos of each battery set after the preceding nail penetration test. [Table 1] Raman image analysis 1 (Wt.%) High-speed discharge characteristics (%) Nail penetration test (number of no ignitions / total number) Example 1 98.7% 91.2 % 5 / 5 Comparison example 1 0% 91.5 % 2 / 5 Comparison example 2 50 % 71 % 4 / 5 1) The Raman image analysis results represent the content (wt%) of the conductive polymer present in the area reaching 10% of the active material layer thickness from the surface of the positive electrode current collector.

[0087] Referring to Table 1, it was confirmed that even if the lithium secondary battery of Example 1 contains a conductive polymer to improve safety, it is similar to that of Comparative Example 1 and exhibits greatly improved rate discharge characteristics compared to Comparative Example 2.

[0088] Additionally, it was confirmed that the lithium secondary battery of Example 1 does not ignite despite a large external influence, thus demonstrating excellent safety compared to the comparison examples 1 and 2. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] KR 10-2022-0151839

[0001]

Claims

[1] Electrode for a lithium secondary battery, comprising: a metal pantograph; and an electrode active material and a conductive material, and comprising an active material layer formed on the metal current collector, wherein the active material layer further comprises a conductive polymer exhibiting a peak in the band from 1350 to 1600 cm⁻¹ -1 during a Raman spectrum analysis, it shows PTC (positive temperature coefficient) properties, and where, when a cross-section of the active material layer is subjected to Raman image analysis, the conductive polymer is distributed in an amount of 90 wt.% or more within an area reaching 10% of the active material layer thickness from the surface of the metal current collector. [2] Electrode for a lithium secondary battery according to claim 1, wherein the effective operating temperature of the conductive polymer exhibiting PTC properties is 70 to 130 °C. [3] Electrode for a lithium secondary battery according to claim 1, wherein the conductive polymer includes a repeating unit containing an aromatic ring with a conjugated π-electron system. [4] Electrode for a lithium secondary battery according to claim 3, wherein the conductive polymer comprises a polymer or copolymer based on polythiophene. [5] Electrode for a lithium secondary battery according to claim 3, wherein the conductive polymer comprises a homopolymer or copolymer containing a repeating unit of the following chemical formula 1: wherein in chemical formula 1 R1 is a functional group of the following chemical formula 2, wherein in chemical formula 2 L1 is a single bond or an alkylene group, L2 is an alkylene group, R3 is hydrogen or an alkyl group and n is an integer in the range of 1 to 5000. [6] Electrode for a lithium secondary battery according to claim 4, wherein the conductive polymer has a weight-average molecular weight of 5000 to 100000 g / mol. [7] Electrode for a lithium secondary battery according to claim 1, wherein the active material layer has a thickness of 5 to 200 µm and the area in which the conductive polymer is distributed in an amount of 90 wt.% or more has a thickness of 0.01 to 20 µm. [8] Electrode for a lithium secondary battery according to claim 1, wherein the minimum straight-line distance from the surface of the metal current collector to the area in which the conductive polymer is distributed in an amount of 90 wt.% or more is 0 to 15 µm. [9] Electrode for a lithium secondary battery according to claim 1, further comprising one or more additives selected from the group consisting of carbon-based conductive materials, binders and esterified saccharides, within the area in which the conductive polymer is distributed in an amount of 90 wt.% or more. [10] Electrode for a lithium secondary battery according to claim 1, wherein the electrode is a positive electrode. [11] Lithium secondary battery comprising a positive electrode, a negative electrode and a separator arranged between them, wherein the electrode according to claim 1 comprises the positive electrode.

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