Electrode for a secondary lithium battery and secondary lithium battery comprising the same

Abstract

Electrode for lithium secondary battery and lithium secondary battery comprising the same. This disclosure relates to an electrode for a lithium secondary battery that not only effectively suppresses heat generation or ignition and thus has additional enhanced stability, but also enables the arrangement of batteries that exhibit excellent charge / discharge characteristics, and a lithium secondary battery comprising the same.The electrode for a secondary lithium battery comprises a metal current collector; and an active electrode material and a conductive material, and also comprises an active material layer formed on the metal current collector, wherein the active material layer further comprises a conductive polymer that exhibits a peak in the 1350 to 1600 cm⁻¹ band during Raman spectrum analysis, and exhibits PTC (positive temperature coefficient) characteristics, and wherein, when a cross-section of the active material layer is subjected to Raman imaging analysis, the conductive polymer is distributed in an amount of 90% by weight or more within a region that reaches 10% of the thickness of the active material layer from the surface of the metal current collector.

Description

Electrode for lithium secondary battery and lithium secondary battery including same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2022-0151839, filed November 14, 2022, the entire contents of which are incorporated herein by reference. The present invention relates to an electrode for a lithium secondary battery, which enables the provision of a battery having improved safety by effectively suppressing heat generation or ignition, and exhibiting excellent charge / discharge characteristics, and a lithium secondary battery including the same.

[0003] With the significant increase in demand for medium- and large-sized devices such as electric vehicles, hybrid electric vehicles, and mobile devices such as smartphones and tablet PCs, the demand for secondary batteries as the energy source required to power these devices is rapidly increasing. In particular, with the increasing data processing speeds and extended usage times of these mobile devices, the development of lithium secondary batteries with higher energy density and operating potential, superior long-term performance, and low self-discharge rates is actively underway.

[0004] However, as the capacity and energy density of lithium secondary batteries have increased significantly, numerous fire and explosion accidents have been reported in various mobile devices and electric vehicles containing them, caused by overcharging, exposure to high temperatures, or external impacts. Therefore, a key research topic for lithium secondary batteries has recently been improving safety by preventing these hazards.

[0005] It is known that the direct cause of fire and explosion in the lithium secondary battery is a short circuit caused by direct contact between the positive and negative electrodes inside the secondary battery due to external stimuli such as high temperature and external impact. For example, when a lithium secondary battery is overcharged or exposed to high temperature or external impact, the internal temperature of the secondary battery may rise rapidly, causing the separator to shrink, or the internal structure of the secondary battery may be destroyed due to the external impact, resulting in the positive and negative electrodes coming into contact and causing a short circuit. When such a short circuit occurs, the movement of lithium ions and electrons is concentrated through the contact area of ​​the positive and negative electrodes, which may generate an overcurrent, and this may cause heat generation, gas generation, and volume expansion inside the battery, which may pose a risk of fire or explosion in the lithium secondary battery.

[0006] Therefore, in order to improve the safety of secondary batteries by suppressing ignition and explosion during the above-described short circuit, it is necessary to increase the resistance between electrodes and block the current when high temperatures or external impacts are applied. To this end, various attempts have been made to increase the resistance when high temperatures or external impacts are applied, and thereby improve the safety of secondary batteries, by adding various functional layers or functional materials to electrodes for lithium secondary batteries.

[0007] However, in the case of electrodes with previously known functional layers added, it was difficult to sufficiently improve the safety of lithium secondary batteries, and there was still a possibility of ignition and explosion, or there were disadvantages such as the functional layer partially impeding the charge / discharge characteristics of the secondary battery.

[0008] Accordingly, the present invention provides an electrode for a lithium secondary battery that enables the provision of a battery having improved safety while effectively suppressing heat generation or ignition due to external stimuli, and exhibiting excellent charge / discharge characteristics.

[0009] In addition, the present invention provides a lithium secondary battery including the electrode and exhibiting excellent stability and charge / discharge characteristics.

[0010] The present invention comprises a metal current collector; and an electrode active material and a conductive material, and an active material layer formed on the metal current collector,

[0011] The above active material layer has a Raman spectrum analysis of 1350 to 1600 cm -1 It further includes a conductive polymer that exhibits a peak in the band and exhibits PTC (positive temperature coefficient) characteristics,

[0012] When a Raman image analysis of a cross-section of the active material layer is performed, an electrode for a lithium secondary battery is provided in which 90 wt% or more of the conductive polymer is distributed within an area from the surface of the metal current collector to 10% of the thickness of the active material layer.

[0013] The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed therebetween, wherein the electrode is included as a positive electrode.

[0014]

[0015] Hereinafter, a lithium secondary battery electrode and a lithium secondary battery including the same according to a specific embodiment of the invention will be described.

[0016] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0017] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0018] In this specification, it should be understood that terms such as “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0019] According to one embodiment of the invention, a metal current collector; and an electrode active material and a conductive material, and an active material layer formed on the metal current collector,

[0020] The above active material layer has a Raman spectrum analysis of 1350 to 1600 cm -1 It further includes a conductive polymer that exhibits a peak in the band and exhibits PTC (positive temperature coefficient) characteristics,

[0021] When a cross-section of the active material layer is analyzed by Raman image, an electrode for a lithium secondary battery is provided in which 90 wt% or more of the conductive polymer is distributed within an area from the surface of the metal current collector to 10% of the thickness of the active material layer.

[0022] The electrode of the above embodiment includes a conductive polymer that is mainly distributed in an area in contact with or close to the surface of the metal current collector, and the conductive polymer has a Raman spectrum analysis result in a region of 1350 to 1600 cm -1 , or 1500 to 1600 cm -1 It can be said that it exhibits a peak in the band and exhibits PTC (positive temperature coefficient) characteristics.

[0023] The characteristic peak appearing in the above band of the Raman spectrum can define that the conductive polymer contains a high content of aromatic rings having a conjugated π electron system among the repeating units, and for example, it can indicate that the conductive polymer has repeating units having aromatic rings containing one or more, or one or two, heteroatoms such as nitrogen or sulfur in a content of 50 mol% or more, or 70 mol% or more, or 90 to 100 mol% of the total repeating units.

[0024] The conductive polymer including an aromatic ring having the above-mentioned conjugated π electron field can exhibit conductivity when the lithium secondary battery is activated, as anions derived from the electrolyte of the secondary battery are doped onto the aromatic ring. Therefore, during the normal charging and discharging process of the secondary battery, the conductive polymer exhibits conductivity, thereby enabling the secondary battery to exhibit appropriate charge and discharge characteristics.

[0025] However, the conductive polymer may exhibit PTC characteristics in that anions derived from the electrolyte may be de-doped from the aromatic ring at a temperature above a certain level, resulting in the polymer acting as an insulator, thereby increasing resistance and blocking the flow of current.

[0026] In particular, the electrode for a lithium secondary battery of one embodiment can be configured such that the conductive polymer is mainly distributed in a region adjacent to the metal current collector, for example, in a region extending from the surface of the metal current collector to 10% (or 7%) of the thickness of the active material layer, by controlling the structure and solubility, etc. of the conductive polymer, the coating thickness and method, etc., which will be described later. Specifically, the conductive polymer may be distributed in an amount of 90 wt% or more, or 90 to 100 wt%, or 92 to 98 wt% of the total conductive polymer in the region adjacent to the metal current collector.

[0027] Additionally, in a specific example, the minimum straight-line distance from the surface of the metal current collector to the region where the conductive polymer is distributed at 90 wt% or more may be 0 to 15 μm, or 0 to 10 μm.

[0028] In this way, since a specific conductive polymer exhibiting the above PTC characteristics is concentrated and uniformly distributed within an area adjacent to a metal current collector, the electrode of one embodiment can further improve electrochemical characteristics such as safety and charge / discharge characteristics of a lithium secondary battery according to the following principle.

[0029] First, when an external stimulus such as overcharge, high temperature, or external impact is applied to a lithium secondary battery including the electrode, causing a rapid rise in the temperature inside the battery, the conductive polymer may be converted into an insulator due to the above-described de-doping of anions, etc. Therefore, the resistance inside the electrode can be significantly increased, the flow of current can be blocked, and overcurrent caused by a short circuit between electrodes can be prevented, and overheating, ignition, explosion, gas generation, etc. of the secondary battery can be suppressed. In particular, in the electrode of one embodiment, since the conductive polymer is concentratedly distributed in an area adjacent to the metal current collector, the conductive polymer converted into an insulator when the external stimulus is applied can very effectively block contact between the positive electrode active material and the electrode current collector, and as a result, the safety of the lithium secondary battery can be further improved.

[0030] Moreover, since the conductive polymer does not spread into the active material layer but is concentratedly distributed in the area adjacent to the metal current collector, the conductive polymer does not interfere with the normal charge / discharge process of the secondary battery. In particular, even if a portion of the conductive polymer is converted into an insulator due to local heat, etc., being applied within the active material layer during the normal charge / discharge process of the secondary battery, this is uniformly spread into the area adjacent to the metal current collector, so that the charge / discharge process and characteristics are not interfered with. As a result, a lithium secondary battery including the electrode of the above embodiment can exhibit improved safety and charge / discharge characteristics at an equivalent level or higher.

[0031] Meanwhile, the area where the conductive polymer is distributed and the distribution content within the area can be confirmed and measured by Raman image analysis of a cross-section of the active material layer. In a specific example, as illustrated in FIG. 1, each component included in the active material layer, for example, the electrode active material, the conductive material, and the above-described conductive polymer, exhibit different Raman spectra, and therefore, in the Raman image analysis result for the cross-section of the active material layer, each component distinguished by the Raman spectrum can be expressed with different fluorescence. From the Raman image analysis result, the area where the conductive polymer is distributed can be confirmed (for example, the red indicated area in FIG. 1), and the distribution area and ratio of the conductive polymer for various cross-sections of the active material layer can be calculated, thereby calculating the distribution content of the conductive polymer.

[0032] The conductive polymer included in the electrode of the above-described embodiment exhibits the PTC characteristics described above, and the effective operating temperature at which the conductive polymer is converted into an insulator may be 70 to 130°C, or 80 to 125°C. As the conductive polymer is converted into an insulator at the effective operating temperature, the conductive polymer can more effectively suppress ignition or explosion of the secondary battery when an external stimulus is applied without interfering with the normal charging and discharging process of the secondary battery.

[0033] The conductive polymer exhibiting the above-described effective operating temperature and distribution characteristics will be described in more detail below.

[0034] As described above, the conductive polymer may be a polymer or copolymer comprising repeating units having an aromatic ring containing one or more, or one or two, heteroatoms in an amount of 50 mol% or more, or 70 mol% or more, or 90 to 100 mol% of the total repeating units, and more specifically, may be a polythiophene-based polymer or copolymer mainly comprising repeating units containing a substituted or unsubstituted thiophene ring as the aromatic ring.

[0035] In a more specific example, the conductive polymer may 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 including a repeating unit of the following chemical formula 1:

[0036] [Chemical Formula 1]

[0037]

[0038] R in chemical formula 1 1 is a functional group of the following chemical formula 2,

[0039] [Chemical Formula 2]

[0040]

[0041] In chemical formula 2, L1 is a single bond or an alkylene group.

[0042] , L2 is an alkylene group, R3 is hydrogen or an alkyl group, n is an integer within the range of 1 to 5000, or 10 to 2000, or 50 to 1000, and the alkylene group may be an alkylene group having 2 to 5 carbon atoms, and the alkyl group may be an alkyl group having 1 to 5 carbon atoms.

[0043] Additionally, these polythiophene-based (co)polymers may have a weight average molecular weight of, for example, 5000 to 100000 g / mol, or 10000 to 80000 g / mol.

[0044] In a more specific example, the polythiophene-based (co)polymer may contain the repeating unit of the chemical formula 1 in an amount greater than 0 mol%, or 0.001 mol% or more, or 0.01 mol% or more, or 1 mol% or more, and may contain the repeating unit in an amount of 100 mol% or less, or 80 mol% or less, or 50 mol% or less, or 30 mol% or less. In this case, the polythiophene-based (co)polymer may contain the remaining amount of alkyl thiophene-based repeating units, for example, an alkyl thiophene-based repeating unit in which an alkyl group having 1 to 20 carbon atoms or 3 to 15 carbon atoms is substituted on a thiophene ring.

[0045] These polythiophene-based (co)polymers can exhibit an appropriate effective operating temperature, etc., including the above-mentioned substituted thiophene ring, and as a result, can be converted into an insulator when a certain level or higher of high temperature is applied without impairing the charge / discharge characteristics of a lithium secondary battery, thereby improving the safety of the secondary battery.

[0046] In addition, due to the above-described predetermined structure, the polythiophene-based (co)polymer exhibits relatively low affinity and solubility for organic solvents, such as N-methylpyrrolidone, which are mainly included in the slurry composition for forming the electrode active material layer, and can exhibit excellent adhesion to the metal current collector. Therefore, in the process of forming the conductive polymer of the polythiophene-based (co)polymer on the metal current collector and then applying and drying the slurry composition to form the electrode 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 the polythiophene-based (co)polymer, the conductive polymer can be intensively distributed in the area adjacent to the metal current collector, and in the Raman image analysis described above, 90 wt% or more can be distributed within an area from the surface of the metal current collector to 10% of the thickness of the active material layer. Ultimately, these polythiophene-based (co)polymers can contribute to improving the safety of secondary batteries without impairing their charge-discharge characteristics.

[0047] Meanwhile, the conductive polymer may be included 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) included in the active material layer. As a result, the electrode of one embodiment may have better safety and charge / discharge characteristics.

[0048] The conductive polymer having the repeating unit of the above-described chemical formula 1, etc., can be produced, for example, by subjecting a halogenated thiophene compound to a substitution reaction with an alkylene glycol compound to produce a monomer having a functional group of the above-described chemical formula 2, and then polymerizing this monomer alone or copolymerizing it with another monomer such as an alkyl thiophene. Specific conditions for producing such monomers and polymers are described in the manufacturing examples described below.

[0049] In addition, the conductive polymer can be formed on the metal current collector by coating and drying a liquid composition obtained by dissolving or dispersing the liquid composition in an organic solvent such as chloroform, tetrahydrofuran (THF), toluene, or xylene at a concentration of about 0.1 to 5 wt% on the metal current collector. Thereafter, a slurry composition described below is applied and dried to form an active material layer, and an electrode for a lithium secondary battery according to one embodiment can be manufactured by rolling the active material layer.

[0050] At this time, the liquid composition for forming the conductive polymer may further include, in addition to the conductive polymer, one or more additives selected from the group consisting of a carbon-based conductive material, conductive inorganic particles, a binder, and esterified saccharides.

[0051] At this time, the carbon-based conductive agent and binder may be the same components as those included in the active material layer, and by adding these components, the conductivity of the electrode of one embodiment, the adhesiveness or mechanical properties of the active material layer, etc. may be further improved. In addition, the conductive inorganic particles may be nano-sized particles, for example, alumina or zirconia particles having a particle size of 5 to 100 nm, and by adding these, the conductivity of the electrode and the secondary battery may be further improved. In addition, the esterified sugar may be a monosaccharide, oligosaccharide or polysaccharide having an acyl group. The component may generate a gas when the secondary battery is overcharged to block the conductive path between the metal current collector and the electrode active material, and by adding this component, the safety of the secondary battery may be further improved.

[0052] Meanwhile, the electrode of one embodiment further includes an active material layer formed on a metal current collector over the conductive polymer formation region described above, and the active material layer may include an electrode active material, a conductive material, and optionally a binder. In this case, since the electrode on which the conductive polymer is formed is preferably a positive electrode, the following description will be based on this example.

[0053] In the positive electrode for the lithium secondary battery, the metal current collector may generally have a thickness of 3 to 100 μm, and may be formed of any metal or alloy having excellent conductivity without causing chemical changes in the secondary battery. Examples of such metal current collectors include metal current collectors such as stainless steel, aluminum, copper, nickel, or titanium, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. In addition, the metal current collector may form fine unevenness on its surface to increase the adhesiveness of a safety protection layer, etc., and may have various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0054] In addition, in the case of the positive electrode active material included in the above-mentioned active material layer, as long as it is a material capable of reversible insertion and de-insertion of lithium ions, there is no particular limitation, and for example, it may include a lithium metal composite oxide including one or more metal elements 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.

[0055] More specifically, as the positive electrode active material, a compound represented by any one of the following chemical formulas may be used: Li a A 1-b R bD2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b R b O 4-c D c (In the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b R c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Co b R c O 2-α Z α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Co b R c O 2-α Z2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Mn b R c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Mn b R c O 2-α Z α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Lia Ni 1-b-c Mn b R c O 2-α Z2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni b E c G d O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5 and 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d GeO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5 and 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; and Li (3-f) J2(PO4)3(0 ≤ f ≤ 2).

[0056] In the above chemical formula, 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; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0057] In addition, a compound having a coating layer on the surface of the compound may be used, or a compound having the compound and a coating layer may be mixed and used. The coating layer may include a coating element compound, such as an oxide, a hydroxide, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The compounds forming the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof.

[0058] In addition, the conductive material included in the active material layer is used to provide conductivity to the electrode, and in the battery to be formed, any material that does not cause chemical change and is electronically conductive can be used. Examples of such materials include natural graphite, artificial graphite, carbon black, carbon fiber, carbon nanotubes, metal powders such as copper, nickel, aluminum, and silver, metal fibers, and the like. In addition, one or more types of conductive materials such as polyphenylene derivatives can be used in combination.

[0059] The above-mentioned conductive agent may 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 ensures that the positive electrode has excellent electrical properties while also ensuring the desirable formation of the positive electrode.

[0060] The above binder serves to adhere the particles of the positive electrode active material well to each other and also to increase the adhesion of the active material layer, and representative examples thereof include the above-described halogenated polyolefin polymer binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0061] The above binder may 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 enables the formation of a positive electrode having excellent durability without deteriorating the electrical characteristics and / or capacity characteristics of the positive electrode.

[0062] The above-described active material layer can be formed by dissolving or dispersing each component, such as the above-described positive electrode active material, conductive material, and binder, in a medium such as an organic solvent to form a slurry composition, and then applying the slurry to a metal current collector on which the above-described conductive polymer is formed, drying, and rolling the slurry composition.

[0063] At this time, examples of the organic solvent or other medium include N-methyl-2-pyrrolidone (NMP), methoxy propyl acetate, butyl acetate, glycol acid, butyl ester, butyl glycol, methylalkylpolysiloxane, alkylbenzene, propylene glycol, xylene, or monophenyl glycol, and among these, NMP or the like can be appropriately used considering the dispersibility and processability of the positive electrode active material and conductive material described above.

[0064] In this way, while forming the conductive polymer-containing region and the active material layer through separate compositions and processes, by using a polymer having low solubility and affinity for NMP or the like as the conductive polymer, for example, a polymer having a repeating unit of Chemical Formula 1, the conductive polymer can be uniformly and intensively distributed in the 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 improved safety and superior charge / discharge characteristics.

[0065] Meanwhile, the formation process and conditions of the active material layer, excluding the formation process of the conductive polymer, can follow the general anode formation process and conditions, so further description thereof will be omitted.

[0066] The active material layer formed by the above-described method may have a thickness of 5 to 200 μm, or 10 to 100 μm, and the region where the conductive polymer is distributed at 90 wt% or more may have a thickness of 0.01 to 20 μm, or 0.05 to 10 μm. This is because, in the electrode of one embodiment, the conductive polymer is uniformly and intensively distributed in an area adjacent to the surface of the metal current collector. Depending on the thickness range, when an external stimulus such as an external impact is applied, the conductive polymer may suppress direct contact between the active material layer and the metal current collector, thereby ensuring improved safety of the secondary battery. In addition, the conductive polymer distribution region may be formed too thick, thereby minimizing deterioration of the charge / discharge characteristics of the secondary battery.

[0067] Meanwhile, according to another embodiment of the invention, a lithium secondary battery is provided, which includes the electrode of the above-described embodiment as a positive electrode, together with a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0068] In the lithium secondary battery of these other embodiments, the negative electrode is manufactured by applying, 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 needed.

[0069] As the negative active material, for example, graphite having a completely formed layered crystal structure such as natural graphite, soft carbon having a low-crystalline layered crystal structure (graphene structure; a structure in which hexagonal honeycomb planes of carbon are arranged in layers), hard carbon having these structures mixed with non-crystalline parts, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, activated carbon, etc. carbon and graphite materials; LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe1-xMe'yOz (Me: Mn, Fe, Pb, Ge; Me', Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogen; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소, 규소 산화물 또는 규소계 합금; 주석계 합금; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni계 재료; 티타늄 산화물; 또는 리튬 티타늄 산화물 등을 사용할 수 있다.

[0070] In one example, the negative active material may include graphite and silicon (Si)-containing particles together, and the graphite may include at least one of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure, and the silicon (Si)-containing particles may include particles containing silicon (Si) as a main component as a metal component, and may include silicon (Si) particles, silicon oxide particles, or a mixture of the silicon (Si) particles and silicon oxide particles.

[0071] In addition, as a conductive material and binder that can be used together with the negative electrode active material, the same components as the conductive material and binder included in the positive electrode active material layer can be used.

[0072] Additionally, the negative electrode active material layer including the negative electrode active material may have a thickness of 100 µm to 200 µm, or 120 µm to 200 µm.

[0073] In addition, the negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used. In the case of copper or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used.

[0074] In addition, the negative electrode current collector, like the positive electrode current collector, can have fine irregularities formed on its surface to strengthen the bonding strength with the negative electrode active material layer, and can be formed in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc. In addition, the average thickness of the negative electrode current collector can be appropriately applied in the range of 3 to 100 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0075] In addition, the separator is interposed between the anode and the cathode, and a thin insulating film having high ion permeability and mechanical strength is used. The separator is not particularly limited as long as it is commonly used in the art, but specifically, sheets or non-woven fabrics made of chemically resistant and hydrophobic polypropylene; glass fiber; or polyethylene, etc. may be used, and in some cases, a composite separator in which inorganic particles / organic particles are coated with an organic binder polymer on a porous polymer substrate such as the sheet or non-woven fabric may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also function as the separator. In addition, the pore diameter of the separator may be 0.01 to 10 ㎛ on average, and the thickness may be 5 to 300 ㎛ on average.

[0076] The lithium secondary battery of the other embodiments described above may further include an electrolyte, which may be an electrolyte solution containing a non-aqueous organic solvent and a lithium salt, or an electrolyte membrane containing an organic or inorganic solid electrolyte, or these may be used in combination. However, the types of usable electrolytes are well known to those skilled in the art and are not particularly limited in the batteries of the other embodiments, and therefore, further description thereof will be omitted.

[0077] As described above, even if the temperature inside the battery of a lithium secondary battery including the electrode of the present invention rapidly rises due to an external stimulus such as overcharge, high temperature, or external impact, overcurrent is effectively blocked by the conductive polymer concentratedly distributed around the metal current collector, thereby minimizing ignition and explosion.

[0078] Accordingly, the lithium secondary battery can exhibit improved safety, and the deterioration of charge / discharge characteristics due to the conductive polymer can be suppressed, thereby exhibiting excellent electrochemical characteristics.

[0079] Figure 1 shows the results of Raman image analysis of the active material layer of the electrode for a lithium secondary battery manufactured in Example 1, and the drawing on the right side of Figure 1 shows the results of Raman spectrum analysis of the conductive polymer manufactured in the manufacturing example.

[0080] FIG. 2 is a diagram showing the process and result of calculating a probability density function from the Raman image analysis results of FIG. 1 and deriving the conductive polymer content in the area where the conductive polymer is distributed therefrom.

[0081] Figure 3 is a diagram showing the process and result of calculating a probability density function from the Raman image analysis results of Comparative Example 2 and deriving the conductive polymer content in the area where the conductive polymer is distributed therefrom.

[0082] Figures 4a to 4c show the results of nail penetration tests performed on five lithium secondary batteries manufactured in Example 1 (Figure 4a), Comparative Example 1 (Figure 4b), and Comparative Example 2 (Figure 4c), respectively.

[0083] Hereinafter, embodiments of the invention will be described so that those skilled in the art can easily implement the invention. However, the invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0084]

[0085] Manufacturing example: Synthesis of monomers and conductive polymers

[0086] [Chemical Formula 3]

[0087]

[0088] After the inside of a 3-way RBF (Round Bottom Flask) was made into a nitrogen environment through nitrogen flowing, 2.34 g (0.01 mol) of Copper(I) Iodide and 50.36 g (0.31 mol) of Triethylene Glycol were added. In addition, 3.68 g (0.096 mol) of Sodium Hydride 60% in mineral oil was slowly added to the RBF and stirred while maintaining the nitrogen environment. After stirring for about 1 hour, 10.0 g (0.06 mol) of 3-bromothiophene was added and refluxed at about 100°C for about 24 hours. The reaction solution was filtered through a depressurizing device, washed with 100 mL of dichloromethane solution, and then washed with NH4Cl and brine in that order. The solvent was removed through reduced pressure distillation, and the crude product was purified through 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).

[0089] 3.0 g (12.2 mmol) of the monomer compound of the above chemical formula 3 and 47.8 g (243 mmol) of 3-octylthiophene were added to a solution of 124 g (767 mmol) of iron(III) chloride in 1000 ml of methylene chloride, and the polymerization reaction was performed while stirring at about 25°C for 24 hours. The reaction solution was placed in an osmotic membrane with a molecular weight of cut-off (MWCO) of 5000, and then immersed in 1500 ml of acetonitrile to remove unreacted iron(III) chloride and monomers. The residue precipitated inside the osmotic membrane was washed with methanol and dried at about 25°C to obtain the desired conductive polymer. The weight average molecular weight (Mw) of the conductive polymer was confirmed to be about 37,000 g / mol.

[0090]

[0091] Example 1: Preparation of a cathode and a lithium secondary battery

[0092] (Manufacturing of positive electrode)

[0093] 20 g of the conductive polymer (Mw=37,000 g / mol) obtained in the above manufacturing example was dissolved in 1,980 g of chloroform solvent to obtain a composition. This composition was gravure coated and dried on an aluminum (Al) thin film, which is a positive electrode current collector, to form a conductive polymer-containing layer having a thickness of approximately 0.5 μm.

[0094] LiCoO2 as a positive electrode active material, a conductive agent (carbon black), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 60 wt%), which was then applied and dried on the conductive polymer-containing layer (provided that the weight of the conductive polymer was approximately 0.5 wt part based on 100 wt parts of the total of the positive electrode active material, conductive agent, and binder), and roll pressed to form an active material layer with a total thickness of 58 μm, thereby preparing a positive electrode.

[0095] (Manufacturing of cathode)

[0096] A negative electrode slurry (solid content: 60 wt%) was prepared by adding a negative electrode active material (graphite), a binder (SBR-CMC), and a conductive agent (carbon black) to a solvent (water) in a weight ratio of 95:3.5:1.5. The negative electrode slurry was applied to an 8 μm thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll pressed to prepare a negative electrode.

[0097] (Manufacturing of membranes)

[0098] About 8.5 wt% of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) binder was added to acetone, and the binder solution was prepared by dissolving it at a temperature of 50℃ for about 12 hours or more. Al2O3 powder was added to the binder solution so that Al2O3 / PVdF-HFP = 90 / 10 (wt% ratio), and a slurry was prepared using a ball mill method for about 12 hours or more. The slurry prepared in this way was coated on a polyolefin-based separator having a thickness of about 8 μm using a dip coating method, and the coating thickness was adjusted to about 4.5 μm to prepare a porous separator.

[0099] (Manufacturing of lithium secondary batteries)

[0100] After sequentially stacking the positive electrode, separator, and negative electrode, pressing was performed using heat and pressure of 90°C and 200kPa to manufacture an electrode assembly composed of bi-cells. The assembled electrode assembly was placed in a pouch-type battery case, and an electrolyte solution in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70 and LiPF6 was dissolved to a concentration of 1.0M was injected to manufacture a lithium secondary battery.

[0101]

[0102] Comparative Example 1

[0103] The cathode and lithium secondary battery of Comparative Example 1 were manufactured in the same manner as Example 1, except that the conductive polymer was not used (the conductive polymer-containing layer was not formed).

[0104]

[0105] Comparative Example 2

[0106] A cathode slurry (solid content: 60 wt%) was prepared by adding LiCoO2 as a cathode active material, a conductive agent (carbon black), a binder (polyvinylidene fluoride), and a conductive polymer obtained in the manufacturing example to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97:1:1.5:0.5.

[0107] This was applied and dried on a bare aluminum foil, and then roll pressed to form an active material layer with a total thickness of 58 μm, thereby manufacturing a positive electrode.

[0108]

[0109] Exam example

[0110] Raman spectrum analysis and Raman image analysis

[0111] For the positive electrodes manufactured in the examples and comparative examples, cross sections from the positive electrode surface to the current collector were secured, and the Raman spectrum and distribution of the conductive polymer were analyzed by measuring the Raman image (equipment name: DXR3xi, Thermofisher scientific, USA) of the cross sections. As shown in the right drawing of Fig. 1, the peaks in the Raman spectrum of the positive electrodes manufactured in the examples are largely divided into three types. Among them, the Raman signal (peak center) of the conductive polymer is 1350 to 1600 cm -1 (Specifically, 1350 to 1500 cm -1 ) is confirmed in the range of 1350-1500 cm, and the corresponding Raman signal is due to the vibration mode derived from the aromatic ring of the conductive polymer. Based on this, the Raman image shows 1350-1500 cm -1 The area of ​​the region was calculated to derive the red region (conductive polymer) in the left drawing of Fig. 1. Raman image analysis was performed by measuring the Raman image under the following conditions, using the thickness of the anode cross-section as the reference size for vertical mapping.

[0112] * Analysis conditions: 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

[0113] In the measured Raman image, only the image for the red area (conductive polymer) was separately plotted to calculate the content in the concentrated distribution area. For the plotted image, the value represented by each Raman image pixel was extracted using the Image J program, and then the probability density function was calculated using the extracted values ​​as in Equation 1 below.

[0114] [Formula 1]

[0115]

[0116] In Equation 1, ρ(x) represents the probability density function, and I(x) represents the value of the Raman image pixel. The average of the pixel values ​​in the thickness direction in the entire extracted Raman image area was obtained, and the values ​​were standardized and normalized using the probability density function. Normalization was performed by obtaining the integration for the entire pixel values ​​in the denominator as in the above equation, and dividing each pixel value by the corresponding integration. Finally, the normalized values ​​were profiled to confirm the ratio of the area occupied by the conductive polymer in the entire thickness.

[0117] FIG. 1 illustrates the results of Raman image analysis for the active material layer of the electrode for a lithium secondary battery manufactured in Example 1, and the right drawing of FIG. 1 illustrates the results of Raman spectrum analysis of the conductive polymer manufactured in the manufacturing example. In addition, FIG. 2 schematically illustrates the process of calculating the probability density function from the Raman image analysis results of FIG. 1 and deriving the conductive polymer content in the region where the conductive polymer is distributed therefrom. In addition, FIG. 3 schematically illustrates the process of calculating the probability density function from the results of the Raman image analysis of Comparative Example 2 in the same manner as in Example 1 and deriving the conductive polymer content in the region where the conductive polymer is distributed therefrom.

[0118] In addition, through the above process, the content (weight %) of the conductive polymer existing within an area from the surface of the positive electrode current collector to 10% of the thickness of the active material layer was calculated for each example and comparative example from the Raman image analysis results, and is shown together in Table 1 below.

[0119] High-rate discharge characteristic evaluation

[0120] The lithium secondary batteries manufactured in the examples and comparative examples were charged under constant current (0.7C) and constant voltage (4.47 V, 0.025 C cut-off) conditions, rested for 10 minutes, and then discharged until 3 V under constant current (0.1 C, 0.2 C, 0.5 C, 1.0 C, 1.5 C) conditions. That is, when 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, to evaluate the high-rate discharge capability of each battery. At this time, the high-rate discharge capability of 1.5 C is shown in Table 1 below.

[0121]

[0122] Nail penetration test

[0123] Five lithium secondary batteries each manufactured in the examples and comparative examples were prepared, and fully charged to 4.47 V (0.05 C cut off) at 100% SOC under CC / CV, 0.5 C conditions 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 speed of 100 mm / sec to measure whether or not there was ignition. The number of batteries that did not ignite among the five batteries is shown in Table 1 below, and FIGS. 4a to 4c show photographs of each battery set after the nail penetration test.

[0124] Raman image analysis 1) (Wt%)High-rate discharge characteristics (%)Nail penetration test (number of ignitions / total number)Example 198.7%91.2%5 / 5Comparative example 10%91.5%2 / 5Comparative example 250%71%4 / 5

[0125] 1) The Raman image analysis results indicate the content (weight%) of conductive polymer present within an area up to 10% of the thickness of the active material layer on the surface of the positive electrode current collector.

[0126] Referring to Table 1 above, it was confirmed that the lithium secondary battery of Example 1, despite containing a conductive polymer for improved safety, exhibited a large-rate discharge characteristic comparable to that of Comparative Example 1 and significantly improved over that of Comparative Example 2.

[0127] In addition, it was confirmed that the lithium secondary battery of Example 1 did not catch fire even under a large external impact, thereby demonstrating superior safety compared to Comparative Examples 1 and 2.

Claims

1. Metal current collector; and It includes an electrode active material and a conductive material, and includes an active material layer formed on the metal current collector, The above active material layer has a Raman spectrum analysis of 1350 to 1600 cm -1 It further includes a conductive polymer that exhibits a peak in the band and exhibits PTC (positive temperature coefficient) characteristics, An electrode for a lithium secondary battery, wherein when a cross-section of the active material layer is analyzed by Raman image, the conductive polymer is distributed at 90 wt% or more within an area from the surface of the metal current collector to 10% of the thickness of the active material layer.

2. An electrode for a lithium secondary battery, wherein the effective operating temperature of the conductive polymer exhibiting the PTC characteristics in the first paragraph is 70 to 130°C.

3. An electrode for a lithium secondary battery according to claim 1, wherein the conductive polymer comprises a repeating unit including an aromatic ring having a conjugated π electron system.

4. In the third paragraph, the conductive polymer is an electrode for a lithium secondary battery comprising a polythiophene-based polymer or copolymer.

5. In the third paragraph, the conductive polymer is an electrode for a lithium secondary battery comprising a single polymer or copolymer including a repeating unit of the following chemical formula 1: [Chemical Formula 1] R in chemical formula 1 1 is a functional group of the following chemical formula 2, [Chemical Formula 2] 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. An electrode for a lithium secondary battery in the fourth paragraph, wherein the conductive polymer has a weight average molecular weight of 5,000 to 100,000 g / mol.

7. In the first paragraph, the active material layer has a thickness of 5 to 200 μm, An electrode for a lithium secondary battery, wherein the region in which the conductive polymer is distributed at 90 wt% or more has a thickness of 0.01 to 20 μm.

8. In the first paragraph, the minimum straight-line distance from the surface of the metal current collector to the region where the conductive polymer is distributed at 90 wt% or more is 0 to 15 μm, an electrode for a lithium secondary battery.

9. An electrode for a lithium secondary battery, wherein, in the first paragraph, at least one additive selected from the group consisting of a carbon-based conductive material, a conductive inorganic particle, a binder, and an esterified saccharide is further included within a region in which the conductive polymer is distributed at 90 wt% or more.

10. An electrode for a lithium secondary battery, wherein the electrode is a positive electrode in the first paragraph.

11. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed therebetween, wherein the electrode of the first clause is included as a positive electrode.

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